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TC 9-237
OPERATOR'S CIRCULAR
WELDING THEORY AND APPLICATION
REPORTING ERRORS AND RECOMMENDING
IMPROVEMENTS
MAY 1993
HEADQUARTERS, DEPARTMENT OF THE ARMY
DISTRIBUTION RESTRICTION: Approved for public release; distribution
is unlimited.
TC 9-237
CHAPTER 1
INTRODUCTION
Section I. GENERAL
1-1.
SCOPE
This training circular is published for use by personnel concerned with welding and
other metal joining operations in the manufacture and maintenance of materiel.
1-2.
a.
DESCRIPTION
This circular contains information as outlined below:
(1) Introduction
(2) Safety precautions in welding operations
(3) Print reading and welding symbols
(4) Joint design and preparation of metals
(5) Welding and cutting equipment
(6) Welding techniques
(7) Metals identification
(8) Electrodes and filler metals
(9) Maintenance welding operations for military equipment
(10) Arc welding and cutting processes
(11) Oxygen fuel gas welding processes
(12) Special applications
(13) Destructive and nondestructive testing
b. Appendix A contains a list of current references, including supply and tech–
nical manuals and other available publications relating to welding and cutting
operations.
c. Appendix B contains procedure guides for welding.
d. Appendix C contains a troubleshooting chart.
e. Appendix D contains tables listing materials used for brazing.. welding.
-,
soldering, arc cutting, and metallizing.
f. Appendix E contains miscellaneous data as to temperature ranges, melting
points, and other information not contained in the narrative portion of this manual.
Section II. THEORY
1-3. GENERAL
Welding is any metal joining process wherein coalescence is produced by heating the
metal to suitable temperatures , with or without the application of pressure and
with or without the use of filler metals. Basic welding processes are described
and illustrated in this manual. Brazing and soldering, procedures similar to weld–
ing, are also covered.
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1-4.
METALS
a. Metals are divided into two classes, ferrous and nonferrous. Ferrous metals
are those in the iron class and are magnetic in nature. These metals consist of
iron, steel,and alloys related to them. Nonferrous metals are those that contain
either no ferrous metals or very small amounts. These are generally divided into
the aluminum, copper, magnesium, lead, and similar groups.
b. Information contained in this circular covers theory and application of
welding for all types of metals including recently developed alloys.
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CHAPTER 2
SAFETY PRECAUTIONS IN WELDING
OPERATIONS
Section I. GENERAL SAFETY PRECAUTIONS
2-1. GENERAL
a. To prevent injury to personnel, extreme caution should be exercised when using any
types of welding equipment. Injury can result from fire, explosions, electric shock, or
harmful agents. Both the general and specific safety precautions listed below must be
strictly observed by workers who weld or cut metals.
b. Do not permit unauthorized persons to use welding or cutting equipment.
c. Do not weld in a building with wooden floors, unless the floors are protected from hot
metal by means of fire resistant fabric, sand, or other fireproof material. Be sure that hot
sparks or hot metal will not fall on the operator or on any welding equipment
components.
d. Remove all flammable material, such as cotton, oil, gasoline, etc., from the vicinity of
welding.
e. Before welding or cutting, warm those in close proximity who are not protected to
wear proper clothing or goggles.
f. Remove any assembled parts from the component being welded that may become
warped or otherwise damaged by the welding process.
g. Do not leave hot rejected electrode stubs, steel scrap, or tools on the floor or around the
welding equipment. Accidents and/or fires may occur.
h. Keep a suitable fire extinguisher nearby at all times. Ensure the fire extinguisher is in
operable condition.
i. Mark all hot metal after welding operations are completed. Soapstone is commonly
used for this purpose.
2-2. PERSONAL PROTECTIVE EQUIPMENT
a. General. The electric arc is a very powerful source of light, including visible,
ultraviolet, and infrared. Protective clothing and equipment must be worn during all
welding operations. During all oxyacetylene welding and cutting processes, operators
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must use safety goggles to protect the eyes from heat, glare, and flying fragments of hot
metals. During all electric welding processes, operators must use safety goggles and a
hand shield or helmet equipped with a suitable filter glass to protect against the intense
ultraviolet and infrared rays. When others are in the vicinity of the electric welding
processes, the area must be screened so the arc cannot be seen either directly or by
reflection from glass or metal.
b. Helmets and Shields.
(1) Welding arcs are intensely brilliant lights. They contain a proportion of
ultraviolet light which may cause eye damage. For this reason, the arc should
never be viewed with the naked eye within a distance of 50.0 ft (15.2 m). The
brilliance and exact spectrum, and therefore the danger of the light, depends on
the welding process, the metals in the arc, the arc atmosphere, the length of the
arc, and the welding current. Operators, fitters, and those working nearby need
protection against arc radiation. The intensity of the light from the arc increases
with increasing current and arc voltage. Arc radiation, like all light radiation,
decreases with the square of the distance. Those processes that produce smoke
surrounding the arc have a less bright arc since the smoke acts as a filter. The
spectrum of the welding arc is similar to that of the sun. Exposure of the skin and
eyes to the arc is the same as exposure to the sun.
(2) Being closest, the welder needs a helmet to protect his eyes and face from
harmful light and particles of hot metal. The welding helmet (fig. 2-1) is generally
constructed of a pressed fiber insulating material. It has an adjustable headband
that makes it usable by persons with different head sizes. To minimize reflection
and glare produced by the intense light, the helmet is dull black in color. It fits
over the head and can be swung upward when not welding. The chief advantage
of the helmet is that it leaves both hands free, making it possible to hold the work
and weld at the same time.
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(3) The hand-held shield (fig. 2-1) provides the same protection as the helmet, but
is held in position by the handle. This type of shield is frequently used by an
observer or a person who welds for a short period of time.
(4) The protective welding helmet has lens holders used to insert the cover glass
and the filter glass or plate. Standard size for the filter plate is 2 x 4-1/4 in. (50 x
108 mm). In some helmets lens holders open or flip upwards. Lenses are designed
to prevent flash burns and eye damage by absorption of the infrared and
ultraviolet rays produced by the arc. The filter glasses or plates come in various
optical densities to filter out various light intensities, depending on the welding
process, type of base metal, and the welding current. The color of the lens, usually
green, blue, or brown, is an added protection against the intensity of white light or
glare. Colored lenses make it possible to clearly see the metal and weld. Table 2-1
lists the proper filter shades to be used. A magnifier lens placed behind the filter
glass is sometimes used to provide clear vision.
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A cover plate should be placed outside the filter glass to protect it from weld
spatter. The filter glass must be tempered so that is will not break if hit by flying
weld spatter. Filter glasses must be marked showing the manufacturer, the shade
number, and the letter “H” indicating it has been treated for impact resistance.
NOTE
Colored glass must be manufactured in accordance with specifications
detailed in the “National Safety Code for the Protection of Hands and Eyes
of Industrial Workers”, issued by the National Bureau of Standards,
Washington DC, and OSHA Standards, Subpart Q, “Welding, Cutting, and
Brazing”, paragraph 1910.252, and American National Standards Institute
Standard (ANSI) Z87.1-1968, “American National Standard Practice for
Occupational and Educational Eye and Face Protection”.
(5) Gas metal-arc (MIG) welding requires darker filter lenses than shielded metalarc (stick) welding. The intensity of the ultraviolet radiation emitted during gas
metal-arc welding ranges from 5 to 30 times brighter than welding with covered
electrodes.
(6) Do not weld with cracked or defective shields because penetrating rays from
the arc may cause serious burns. Be sure that the colored glass plates are the
proper shade for arc welding. Protect the colored glass plate from molten metal
spatter by using a cover glass. Replace the cover glass when damaged or spotted
by molten metal spatter.
(7) Face shields (fig. 2-2) must also be worn where required to protect eyes.
Welders must wear safety glasses and chippers and grinders often use face shields
in addition to safety glasses.
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(8) In some welding operations, the use of mask-type respirators is required.
Helmets with the "bubble" front design can be adapted for use with respirators.
c. Safety Goggles. During all electric welding processes, operators must wear safety
goggles (fig. 2-3) to protect their eyes from weld spatter which occasionally gets inside
the helmet. These clear goggles also protect the eyes from slag particles when chipping
and hot sparks when grinding. Contact lenses should not be worn when welding or
working around welders. Tinted safety glasses with side shields are recommended,
especially when welders are chipping or grinding. Those working around welders should
also wear tinted safety glasses with side shields.
d. Protective Clothing.
(1) Personnel exposed to the hazards created by welding, cutting, or brazing
operations shall be protected by personal protective equipment in accordance with
OSHA standards, Subpart I, Personal Protective Equipment, paragraph 1910.132.
The appropriate protective clothing (fig. 2-4) required for any welding operation
will vary with the size, nature, and location of the work to be performed. Welders
should wear work or shop clothes without openings or gaps to prevent arc rays
from contacting the skin. Those working close to arc welding should also wear
protective clothing. Clothing should always be kept dry, including gloves.
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(2) Woolen clothing should be worn instead of cotton since wool is not easily
burned or damaged by weld spatter and helps to protect the welder from changes
in temperature. Cotton clothing, if used, should be chemically treated to reduce its
combustibility. All other clothing, such as jumpers or overalls, should be
reasonably free from oil or grease.
(3) Flameproof aprons or jackets made of leather, fire resistant material, or other
suitable material should be worn for protection against spatter of molten metal,
radiated heat, and sparks. Capes or shoulder covers made of leather or other
suitable materials should be worn during overhead welding or cutting operations.
Leather skull caps may be worn under helmets to prevent head burns.
(4) Sparks may lodge in rolled-up sleeves, pockets of clothing, or cuffs of overalls
and trousers. Therefore, sleeves and collars should be kept buttoned and pockets
should be eliminated from the front of overalls and aprons. Trousers and overalls
should not be turned up on the outside. For heavy work, fire-resistant leggings,
high boots, or other equivalent means should be used. In production work, a sheet
metal screen in front of the worker’s legs can provide further protection against
sparks and molten metal in cutting operations.
(5) Flameproof gauntlet gloves, preferably of leather, should be worn to protect
the hands and arms from rays of the arc, molten metal spatter, sparks, and hot
metal. Leather gloves should be of sufficient thickness so that they will not shrivel
from the heat, burn through, or wear out quickly. Leather gloves should not be
used to pick up hot items, since this causes the leather to become stiff and crack.
Do not allow oil or grease to cane in contact with the gloves as this will reduce
their flame resistance and cause them to be readily ignited or charred.
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e. Protective Equipment.
(1) Where there is exposure to sharp or heavy falling objects or a hazard of
bumping in confined spaces, hard hats or head protectors must be used.
(2) For welding and cutting overhead or in confined spaces, steel-toed boots and
ear protection must also be used.
(3) When welding in any area, the operation should be adequately screened to
protect nearby workers or passers-by from the glare of welding. The screens
should be arranged so that no serious restriction of ventilation exists. The screens
should be mounted so that they are about 2.0 ft above the floor unless the work is
performed at such a low level that the screen must be extended closer to the floor
to protect adjacent workers. The height of the screen is normally 6.0 ft (1.8 m) but
may be higher depending upon the situation. Screen and surrounding areas must
be painted with special paints which absorb ultraviolet radiation yet do not create
high contrast between the bright and dark areas. Light pastel colors of a zinc or
titanium dioxide base paint are recommended. Black paint should not be used.
2-3. FIRE HAZARDS
a. Fire prevention and protection is the responsibility of welders, cutters, and supervisors.
Approximately six percent of the fires in industrial plants are caused by cutting and
welding which has been done primarily with portable equipment or in areas not
specifically designated for such work. The elaboration of basic precautions to be taken
for fire prevention during welding or cutting is found in the Standard for Fire Prevention
in Use of Cutting and Welding Processes, National Fire Protection Association Standard
51B, 1962. Some of the basic precautions for fire prevention in welding or cutting work
are given below.
b. During the welding and cutting operations, sparks and molten spatter are formal which
sometimes fly considerable distances. Sparks have also fallen through cracks, pipe holes,
or other small openings in floors and partitions, starting fires in other areas which
temporarily may go unnoticed. For these reasons, welding or cutting should not be done
near flammable materials unless every precaution is taken to prevent ignition.
c. Hot pieces of base metal may come in contact with combustible materials and start
fires. Fires and explosions have also been caused when heat is transmitted through walls
of containers to flammable atmospheres or to combustibles within containers. Anything
that is combustible or flammable is susceptible to ignition by cutting and welding.
d. When welding or cutting parts of vehicles, the oil pan, gasoline tank, and other parts of
the vehicle are considered fire hazards and must be removed or effectively shielded from
sparks, slag, and molten metal.
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e. Whenever possible, flammable materials attached to or near equipment requiring
welding, brazing, or cutting will be removed. If removal is not practical, a suitable shield
of heat resistant material should be used to protect the flammable material. Fire
extinguishing equipment, for any type of fire that may be encountered, must be present.
2-4. HEALTH PROTECTION AND VENTILATION
a. General.
(1) All welding and thermal cutting operations carried on in confined spaces must
be adequately ventilated to prevent the accumulation of toxic materials,
combustible gases, or possible oxygen deficiency. Monitoring instruments should
be used to detect harmful atmospheres. Where it is impossible to provide adequate
ventilation, air-supplied respirators or hose masks approved for this purpose must
be used. In these situations, lookouts must be used on the outside of the confined
space to ensure the safety of those working within. Requirements in this section
have been established for arc and gas welding and cutting. These requirements
will govern the amount of contamination to which welders may be exposed:
(a) Dimensions of the area in which the welding process takes place (with
special regard to height of ceiling).
(b) Number of welders in the room.
(c) Possible development of hazardous fumes, gases, or dust according to
the metals involved.
(d) Location of welder's breathing zone with respect to rising plume of
fumes.
(2) In specific cases, there are other factors involved in which respirator
protective devices (ventilation) should be provided to meet the equivalent
requirements of this section. They include:
(a) Atmospheric conditions.
(b) Generated heat.
(c) Presence of volatile solvents.
(3) In all cases, the required health protection, ventilation standards, and standard
operating procedures for new as well as old welding operations should be
coordinated and cleaned through the safety inspector and the industrial hygienist
having responsibility for the safety and health aspects of the work area.
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b. Screened Areas. When welding must be performed in a space entirely screened on all
sides, the screens shall be arranged so that no serious restriction of ventilation exists. It is
desirable to have the screens mounted so that they are about 2.0 ft (0.6 m) above the
floor, unless the work is performed at such a low level that the screen must be extended
closer to the floor to protect workers from the glare of welding. See paragraph 2-2 e (3).
c. Concentration of Toxic Substances. Local exhaust or general ventilating systems shall
be provided and arranged to keep the amount of toxic frees, gas, or dusts below the
acceptable concentrations as set by the American National Standard Institute Standard
7.37; the latest Threshold Limit Values (TLV) of the American Conference of
Governmental Industrial Hygienists; or the exposure limits as established by Public Law
91-596, Occupational Safety and Health Act of 1970. Compliance shall be determined by
sampling of the atmosphere. Samples collected shall reflect the exposure of the persons
involved. When a helmet is worn, the samples shall be collected under the helmet.
NOTE
Where welding operations are incidental to general operations, it is
considered good practice to apply local exhaust ventilation to prevent
contamination of the general work area.
d. Respiratory Protective Equipment. Individual respiratory protective equipment will be
well retained. Only respiratory protective equipment approved by the US Bureau of
Mines, National Institute of Occupational Safety and Health, or other governmentapproved testing agency shall be utilized. Guidance for selection, care, and maintenance
of respiratory protective equipment is given in Practices for Respiratory Protection,
American National Standard Institute Standard 788.2 and TB MED 223. Respiratory
protective equipment will not be transferred from one individual to another without being
disinfected.
e. Precautionary Labels. A number of potentially hazardous materials are used in flux
coatings, coverings, and filler metals. These materials, when used in welding and cutting
operations, will become hazardous to the welder as they are released into the atmosphere.
These include, but are not limited to, the following materials: fluorine compounds, zinc,
lead, beryllium, cadmium, and mercury. See paragraph 2-4 i through 2-4 n. The suppliers
of welding materials shall determine the hazard, if any, associated with the use of their
materials in welding, cutting, etc.
(1) All filler metals and fusible granular materials shall carry the following notice,
as a minimum, on tags, boxes, or other containers:
CAUTION
Welding may produce fumes and gases hazardous to health. Avoid
breathing these fumes and gases. Use adequate ventilation. See American
National Standards Institute Standard Z49.1-1973, Safety in Welding and
Cutting published by the American Welding Society.
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(2) Brazing (welding) filler metals containing cadmium in significant amounts
shall carry the following notice on tags, boxes, or other containers:
WARNING
CONTAINS CADMIUM - POISONOUS FUMES MAY BE FORMED ON HEATING
Do not breathe fumes. Use only with adequate ventilation, such as fume
collectors, exhaust ventilators, or air-supplied respirators. See American
National Standards Institute Standard Z49.1-1973. If chest pain, cough, or
fever develops after use, call physician immediately.
(3) Brazing and gas welding fluxes containing fluorine compounds shall have a
cautionary wording. One such wording recommended by the American Welding
Society for brazing and gas welding fluxes reads as follows:
CAUTION
CONTAINS FLUORIDES
This flux, when heated, gives off fumes that may irritate eyes, nose, and
throat.
Avoid fumes--use only in well-ventilated spaces.
Avoid contact of flux with eyes or skin.
Do not take internally.
f. Ventilation for General Welding and Cutting.
(1) General. Mechanical ventilation shall be provided when welding or cutting is
done on metals not covered in subparagraphs i through p of this section, and
under the following conditions:
(a) In a space of less than 10,000 cu ft (284 cu m) per welder.
(b) In a roan having a ceiling height of less than 16 ft (5 m).
(c) In confined spaces or where the welding space contains partitions,
balconies, or other structural barriers to the extent that they significantly
obstruct cross ventilation.
(2) Minimum rate. Ventilation shall be at the minimum rate of 200 cu ft per
minute (57 cu m) per welder, except where local exhaust heeds, as in paragraph 24 g below, or airline respirators approved by the US Bureau of Mines, National
Institute of Occupational Safety and Health, or other government-approved testing
agency, are used. When welding with rods larger than 3/16 in. (0.48 cm) in
diameter, the ventilation shall be higher as shown in the following:
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Rod diameter
(inches)
Required ventilation
(cfm)
1/4 (0.64 cm)
3500
3/8 (0.95 cm)
4500
Natural ventilation is considered sufficient for welding or cutting operations
where the conditions listed above are not present. Figure 2-5 is an illustration of a
welding booth equipped with mechanical ventilation sufficient for one welder.
g. Local Exhaust Ventilation. Mechanical local exhaust ventilation may be obtained by
either of the following means:
(1) Hoods. Freely movable hoods or ducts are intended to be placed by the welder
as near as practicable to the work being welded. These will provide a rate of
airflow sufficient to maintain a velocity the direction of the hood of 100 in linear
feet per minute in the zone of welding. The ventilation rates required to
accomplish this control velocity using a 3-in. wide flanged suction opening are
listed in table 2-2.
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(2) Fixed enclosure. A fixed enclosure with a top and two or more sides which
surrounds the welding or cutting operations will have a rate of airflow sufficient
to maintain a velocity away from the welder of not less than 100 linear ft per
minute. Downdraft ventilation tables require 150 cu ft per minute per square foot
of surface area. This rate of exhausted air shall be uniform across the face of the
grille. A low volume, high-density fume exhaust device attached to the welding
gun collects the fumes as close as possible to the point of origin or at the arc. This
method of fume exhaust has become quite popular for the semiautomatic
processes, particularly the flux-cored arc welding process. Smoke exhaust
systems incorporated in semiautomatic guns provide the most economical exhaust
system since they exhaust much less air they eliminate the need for massive air
makeup units to provide heated or cooled air to replace the air exhausted. Local
ventilation should have a rate of air flow sufficient to maintain a velocity away
from the welder of not less than 100 ft (30 m) per minute. Air velocity is
measurable using a velometer or air flow inter. These two systems can be
extremely difficult to use when welding other than small weldments. The down
draft welding work tables are popular in Europe but are used to a limited degree
North America. In all cases when local ventilation is used, the exhaust air should
be filtered.
h. Ventilation in Confined Spaces.
(1) Air replacement. Ventilation is a perquisite to work in confined spaces. All
welding and cutting operations in confined spaces shall be adequately ventilated
to prevent the accumulation of toxic materials -or possible oxygen deficiency.
This applies not only to the welder but also to helpers and other personnel in the
immediate vicinity.
(2) Airline respirators. In circumstances where it is impossible to provide
adequate ventilation in a confined area, airline respirators or hose masks,
approved by the US Bureau of Mines, National Institute of Occupational Safety
and Health, or other government-approved testing agency, will be used for this
purpose. The air should meet the standards established by Public Law 91-596,
Occupational Safety and Health Act of 1970.
(3) Self-contained units. In areas immediately hazardous to life, hose masks with
blowers or self-contained breathing equipment shall be used. The breathing
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equipment shall be approved by the US Bureau of Mines or National Institute of
Occupational Safety and Health, or other government-approved testing agency.
(4) Outside helper. Where welding operations are carried on in confined spaces
and where welders and helpers are provided with hose masks, hose masks with
blowers, or self-contained breathing equipment, a worker shall be stationed on the
outside of such confined spaces to ensure the safety of those working within.
(5) Oxygen for ventilation. Oxygen must never be used for ventilation.
i. Fluorine Compounds.
(1) General. In confined spaces, welding or cutting involving fluxes, coverings, or
other materials which fluorine compounds shall be done in accordance with
paragraph 2-4 h, ventilation in confined spaces. A fluorine compound is one that
contains fluorine as an element in chemical combination, not as a free gas.
(2) Maximum allowable concentration. The need for local exhaust ventilation or
airline respirators for welding or cutting in other than confined spaces will depend
upon the individual circumstances. However, experience has shown that such
protection is desirable for fixed-location production welding and for all
production welding on stainless steels. When air samples taken at the welding
location indicate that the fluorides liberated are below the maximum allowable
concentration, such protection is not necessary.
j. Zinc.
(1) Confined spaces. In confined spaces, welding or cutting involving zincbearing filler metals or metals coated with zinc-bearing materials shall be done in
accordance with paragraph 2-4 h, ventilation in confined spaces.
(2) Indoors. Indoors, welding or cutting involving zinc-bearing metals or filler
metals coated with zinc-bearing materials shall be done in accordance with
paragraph 2-4 g.
k. Lead.
(1) Confined spaces. In confined spaces, welding involving lead-base metals
(erroneously called lead-burning) shall be done in accordance with paragraph 2-4
h.
(2) Indoors. Indoors, welding involving lead-base metals shall be done in
accordance with paragraph 2-4 g, local exhaust ventilation.
(3) Local ventilation. In confined spaces or indoors, welding or cutting involving
metals containing lead or metals coated with lead-bearing materials, including
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paint, shall be done using local exhaust ventilation or airline respirators.
Outdoors, such operations shall be done using respirator protective equipment
approved by the US Bureau of Mines, National Institute of Occupational Safety
and Health, or other government-approved testing agency. In all cases, workers in
the immediate vicinity of the cutting or welding operation shall be protected as
necessary by local exhaust ventilation or airline respirators.
l. Beryllium. Welding or cutting indoors, outdoors, or in confined spaces involving
beryllium-bearing material or filler metals will be done using local exhaust ventilation
and airline respirators. This must be performed without exception unless atmospheric
tests under the most adverse conditions have established that the workers’ exposure is
within the acceptable concentrations of the latest Threshold Limit Values (TLV) of the
American Conference of Governmental Industrial Hygienists, or the exposure limits
established by Public Law 91-596, Occupational Safety and Health Act of 1970. In all
cases, workers in the immediate vicinity of the welding or cutting operations shall be
protected as necessary by local exhaust ventilation or airline respirators.
m. Cadmium.
(1) General. Welding or cutting indoors or in confined spaces involving cadmiumbearing or cadmium-coated base metals will be done using local exhaust
ventilation or airline respirators. Outdoors, such operations shall be done using
respiratory protective equipment such as fume respirators, approved by the US
Bureau of Mines, National Institute of Occupational Safety and Health, or other
government-approved testing agency, for such purposes.
(2) Confined space. Welding (brazing) involving cadmium-bearing filler metals
shall be done using ventilation as prescribed in paragraphs 2-4 g, local exhaust
ventilation, and 2-4 h, ventilation in confined spaces, if the work is to be done in a
confined space.
NOTE
Cadmium-free rods are available and can be used in most instances with
satisfactory results.
n. Mercury. Welding or cutting indoors or in a confined space involving metals coated
with mercury-bearing materials, including paint, shall be done using local exhaust
ventilation or airline respirators. Outdoors, such operations will be done using respiratory
protective equipment approved by the National Institute of Occupational Safety and
Health, US Bureau of Mines, or other government-approved testing agency.
o. Cleaning Compounds.
(1) Manufacturer’s instructions. In the use of cleaning materials, because of their
toxicity of flammability, appropriate precautions listed in the manufacturer’s
instructions will be followed.
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(2) Degreasing. Degreasing or other cleaning operations involving chlorinated
hydrocarbons will be located so that no vapors from these operations will reach or
be drawn into the area surrounding any welding operation. In addition,
trichloroethylene and perchloroethylene should be kept out of atmospheres
penetrated by the ultraviolet radiation of gas-shielded welding operations.
p. Cutting of Stainless Steels. Oxygen cutting, using either a chemical flux or iron
powder, or gas-shielded arc cutting of stainless steel will be done using mechanical
ventilation adequate to remove the fumes generated.
q. First-Aid Equipment. First-aid equipment will be available at all times. On every shift
of welding operations, there will be personnel present who are trained to render first-aid.
All injuries will be reported as soon as possible for medical attention. First-aid will be
rendered until medical attention can be provided.
2-5. WELDING IN CONFINED SPACES
a. A confined space is intended to mean a relatively small or restricted space such as a
tank, boiler, pressure vessel, or small compartment of a ship or tank.
b. When welding or cutting is being performed in any confined space, the gas cylinders
and welding machines shall be left on the outside. Before operations are started, heavy
portable equipment mounted on wheels shall be securely blocked to prevent accidental
movement.
c. Where a welder must enter a confined space through a manhole or other all opening,
means will be provided for quickly removing him in case of emergency. When safety
belts and life lines are used for this purpose, they will be attached to the welder’s body so
that he cannot be jammed in a small exit opening. An attendant with a preplanned rescue
procedure will be stationed outside to observe the welder at all times and be capable of
putting rescue operations into effect.
d. When arc welding is suspended for any substantial period of time, such as during lunch
or overnight, all electrodes will be removed from the holders with the holders carefully
located so that accidental contact cannot occur. The welding machines will be
disconnected from the power source.
e. In order to eliminate the possibility of gas escaping through leaks or improperly closed
valves when gas welding or cutting, the gas and oxygen supply valves will be closed, the
regulators released, the gas and oxygen lines bled, and the valves on the torch shut off
when the equipment will not be used for a substantial period of time. Where practical, the
torch and hose will also be removed from the confined space.
f. After welding operations are completed, the welder will mark the hot metal or provide
some other means of warning other workers.
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Section II. SAFETY PRECAUTIONS IN OXYFUEL WELDING
2-6. GENERAL
a. In addition to the information listed in section I of this chapter, the following safety
precautions must be observed.
b. Do not experiment with torches or regulators in any way. Do not use oxygen regulators
with acetylene cylinders. Do not use any lubricants on regulators or tanks.
c. Always use the proper tip or nozzle, and always operate it at the proper pressure for the
particular work involved. This information should be taken from work sheets or tables
supplied with the equipment.
d. When not in use, make sure the torch is not burning. Also, release the regulators, bleed
the hoses, and tightly close the valves. Do not hang the torch with its hose on the
regulator or cylinder valves.
e. Do not light a torch with a match or hot metal, or in a confined space. The explosive
mixture of acetylene and oxygen might cause personal injury or property damage when
ignited. Use friction lighters or stationary pilot flames.
f. When working in confined spaces, provide adequate ventilation for the dissipation of
explosive gases that may be generated. For ventilation standards, refer to paragraph 2-4,
Health Protection and Ventilation.
g. Keep a clear space between the cylinder and the work so the cylinder valves can be
reached easily and quickly.
h. Use cylinders in the order received. Store full and empty cylinders separately and mark
the empty ones with “MT”.
i. Compressed gas cylinders owned by commercial companies will not be painted
regulation Army olive drab.
j. Never use cylinders for rollers, supports, or any purpose other than that for which they
are intended.
k. Always wear protective clothing suitable for welding or flame cutting.
l. Keep work area clean and free from hazardous materials. When flame cutting, sparks
can travel 30 to 40 ft (9 to 12 m). Do not allow flare cut sparks to hit hoses, regulators, or
cylinders.
m. Use oxygen and acetylene or other fuel gases with the appropriate torches and only for
the purpose intended.
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n. Treat regulators with respect. Do not turn valve handle using force.
o. Always use the following sequence and technique for lighting a torch:
(1) Open acetylene cylinder valve.
(2) Open acetylene torch valve 1/4 turn.
(3) Screw in acetylene regulator adjusting valve handle to working pressure.
(4) Turn off the acetylene torch valve (this will purge the acetylene line).
(5) Slowly open oxygen cylinder valve all the way.
(6) Open oxygen torch valve 1/4 turn.
(7) Screw in oxygen regulator screw to working pressure.
(8) Turn off oxygen torch valve (this will purge the oxygen line).
(9) Open acetylene torch valve 1/4 turn and light with lighter.
NOTE
Use only friction type lighter or specially provided lighting device.
(10) Open oxygen torch valve 1/4 turn.
(11) Adjust to neutral flame.
p. Always use the following sequence and technique for shutting off a torch:
(1) Close acetylene torch valve first, then the oxygen valve.
(2) Close acetylene cylinder valve, then oxygen cylinder valve.
(3) Open torch acetylene and oxygen valves to release pressure in the regulator
and hose.
(4) Back off regulator adjusting valve handle until no spring tension is left.
(5) Close torch valves.
q. Use mechanical exhaust at the point of welding when welding or cutting lead,
cadmium, chromium, manganese, brass, bronze, zinc, or galvanized steel.
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r. Do not weld or flame cut on containers that have held combustibles without taking
special precautions.
s. Do not weld or flame cut into sealed container or compartment without providing vents
and taking special precautions.
t. Do not weld or cut in a confined space without taking special precautions.
2-7. ACETYLENE CYLINDERS
CAUTION
If acetylene cylinders have been stored or transported horizontally (on
their sides), stand cylinders vertically (upright) for 45 minutes prior to
(before) use.
a. Always refer to acetylene by its full name and not by the word “gas” alone. Acetylene
is very different from city or furnace gas. Acetylene is a compound of carbon and
hydrogen, produced by the reaction of water and calcium carbide.
b. Acetylene cylinders must be handled with care to avoid damage to the valves or the
safety fuse plug. The cylinders must be stored upright in a well ventilated, well protected,
dry location at least 20 ft from highly combustible materials such as oil, paint, or
excelsior. Valve protection caps must always be in place, hand tight, except when
cylinders are in use. Do not store the cylinders near radiators, furnaces, or in any are with
above normal temperatures. In tropical climates, care must be taken not to store acetylene
in areas where the temperature is in excess of 137°F (58°C). Heat will increase the
pressure, which may cause the safety fuse plug in the cylinder to blow out. Storage areas
should be located away from elevators, gangways, or other places where there is danger
of cylinders being knocked over or damaged by falling objects.
c. A suitable truck, chain, or strap must be used to prevent cylinders from falling or being
knocked over while in use. Cylinders should be kept at a safe distance from the welding
operation so there will be little possibility of sparks, hot slag, or flames reaching them.
They should be kept away from radiators, piping systems, layout tables, etc., which may
be used for grounding electrical circuits. Nonsparking tools should be used when
changing fittings on cylinders of flammable gases.
d. Never use acetylene without reducing the pressure with a suitable pressure reducing
regulator. Never use acetylene at pressures in excess of 15 psi.
e. Before attaching the pressure regulators, open each acetylene cylinder valve for an
instant to blow dirt out of the nozzles. Wipe off the connection seat with a clean cloth. Do
not stand in front of valves when opening them.
f. Outlet valves which have become clogged with ice should be thawed with warm water.
Do not use scalding water or an open flame.
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g. Be sure the regulator tension screw is released before opening the cylinder valve.
Always open the valve slowly to avoid strain on the regulator gage which records the
cylinder pressure. Do not open the valve more than one and one-half turns. Usually, onehalf turn is sufficient. Always use the special T-wrench provided for the acetylene
cylinder valve. Leave this wrench on the stem of the valve tile the cylinder is in use so
the acetylene can be quickly turned off in an emergency.
h. Acetylene is a highly combustible fuel gas and great care should be taken to keep
sparks, flames, and heat away from the cylinders. Never open an acetylene cylinder valve
near other welding or cutting work.
i. Never test for an acetylene leak with an open flame. Test all joints with soapy water.
Should a leak occur around the valve stem of the cylinder, close the valve and tighten the
packing nut. Cylinders leaking around the safety fuse plug should be taken outdoors,
away from all fires and sparks, and the valve opened slightly to permit the contents to
escape.
j. If an acetylene cylinder should catch fire, it can usually be extinguished with a wet
blanket. A burlap bag wet with calcium chloride solution is effective for such an
emergency. If these fail, spray a stream of water on the cylinder to keep it cool.
k. Never interchange acetylene regulators, hose, or other apparatus with similar
equipment intended for oxygen.
l. Always turn the acetylene cylinder so the valve outlet will point away from the oxygen
cylinder.
m. When returning empty cylinders, see that the valves are closed to prevent escape of
residual acetylene or acetone solvent. Screw on protecting caps.
n. Make sure that all gas apparatus shows UL or FM approval, is installed properly, and
is in good working condition.
o. Handle all compressed gas with extreme care. Keep cylinder caps on when not in use.
p. Make sure that all compressed gas cylinders are secured to the wall or other structural
supports. Keep acetylene cylinders in the vertical condition.
q. Store compressed gas cylinders in a safe place with good ventilation. Acetylene
cylinders and oxygen cylinders should be kept apart.
r. Never use acetylene at a pressure in excess of 15 psi (103.4 kPa). Higher pressure can
cause an explosion.
s. Acetylene is nontoxic; however, it is an anesthetic and if present in great enough
concentrations, is an asphyxiant and can produce suffocation.
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2-8. OXYGEN CYLINDERS
a. Always refer to oxygen by its full name and not by the word “air” alone.
b. Oxygen should never be used for “air” in any way.
WARNING
Oil or grease in the presence of oxygen will ignite violently, especially in
an enclosed pressurized area.
c. Oxygen cylinders shall not be stored near highly combustible material, especially oil
and grease; near reserve stocks of carbide and acetylene or other fuel gas cylinders, or
any other substance likely to cause or accelerate fire; or in an acetylene generator
compartment.
d. Oxygen cylinders stored in outside generator houses shall be separated from the
generator or carbide storage rooms by a noncombustible partition having a fire resistance
rating of at least 1 hour. The partition shall be without openings and shall be gastight.
e. Oxygen cylinders in storage shall be separated from fuel gas cylinders or combustible
materials (especially oil or grease) by a minimum distance of 20.0 ft (6.1 m) or by a
noncombustible barrier at least 5.0 ft (1.5 m) high and having a fire-resistance rating of at
least one-half hour.
f. Where a liquid oxygen system is to be used to supply gaseous oxygen for welding or
cutting and a bulk storage system is used, it shall comply with the provisions of the
Standard for Bulk Oxygen Systems at Consumer Sites, NFPA No. 566-1965, National
Fire Protection Association.
g. When oxygen cylinders are in use or being roved, care must be taken to avoid
dropping, knocking over, or striking the cylinders with heavy objects. Do not handle
oxygen cylinders roughly.
h. All oxygen cylinders with leaky valves or safety fuse plugs and discs should be set
aside and marked for the attention of the supplier. Do not tamper with or attempt to repair
oxygen cylinder valves. Do not use a hammer or wrench to open the valves.
i. Before attaching the pressure regulators, open each oxygen cylinder valve for an instant
to blow out dirt and foreign matter from the nozzle. Wipe off the connection seat with a
clean cloth. Do not stand in front of the valve when opening it.
WARNING
Do not substitute oxygen for compressed air in pneumatic tools. Do not
use oxygen to blow out pipe lines, test radiators, purge tanks or containers,
or to “dust” clothing or work.
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j. Open the oxygen cylinder valve slowly to prevent damage to regulator high pressure
gage mechanism. Be sure that the regulator tension screw is released the before opening
the valve. When not in use, the cylinder valve should be closed and the protecting caps
screwed on to prevent damage to the valve.
k. When the oxygen cylinder is in use, open the valve to the full limit to prevent leakage
around the valve stem.
l. Always use regulators on oxygen cylinders to reduce the cylinder pressure to a low
working pressure. High cylinder pressure will burst the hose.
m. Never interchange oxygen regulators, hoses, or other apparatus with similar
equipment intended for other gases.
2-9. MAPP GAS CYLINDERS
a. MAPP gas is a mixture of stabilized methylacetylene and propadiene.
b. Store liquid MAPP gas around 70°F (21°C) and under 94 psig pressure.
c. Repair any leaks immediately. MAPP gas vaporizes when the valve is opened and is
difficult to detect visually. However, MAPP gas has an obnoxious odor detectable at 100
parts per million, a concentration 1/340th of its lower explosive limit in air. If repaired
when detected, leaks pose little or no danger. However, if leaks are ignored, at very high
concentrations (5000 parts per million and above) MAPP gas has an anesthetic effect.
d. Proper clothing must be worn to prevent injury to personnel. Once released into the
open air, liquid MAPP gas boils at -36 to -4°F (-54 to -20°C). This causes frost-like burns
when the gas contacts the skin.
e. MAPP gas toxicity is rated very slight, but high concentrations (5000 part per million)
may have an anesthetic affect.
f. MAPP gas has some advantages in safety which should be considered when choosing a
process fuel gas, including the following:
(1) MAPP gas cylinders will not detonate when dented, dropped, or incinerated.
(2) MAPP gas can be used safely at the full cylinder pressure of 94 psig.
(3) Liquefied fuel is insensitive to shock.
(4) Explosive limits of MAPP gas are low compared to acetylene.
(5) Leaks can be detected easily by the strong smell of MAPP gas.
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(6) MAPP cylinders are easy to handle due to their light weight.
2-10. FUEL GAS CYLINDERS
a. Although the most familiar fuel gas used for cutting and welding is acetylene, propane,
natural gas, and propylene are also used. Store these fuel gas cylinders in a specified,
well-ventilated area or outdoors, and in a vertical condition.
b. Any cylinders must have their caps on, and cylinders, either filled or empty, should
have the valve closed.
c. Care must be taken to protect the valve from damage or deterioration. The major
hazard of compressed gas is the possibility of sudden release of the gas by removal or
breaking off of the valve. Escaping gas which is under high pressure will cause the
cylinder to act as a rocket, smashing into people and property. Escaping fuel gas can also
be a fire or explosion hazard.
d. In a fire situation there are special precautions that should be taken for acetylene
cylinders. All acetylene cylinders are equipped with one or more safety relief devices
filled with a low melting point metal. This fusible metal melts at about the killing point of
water (212°F or 100°C). If fire occurs on or near an acetylene cylinder the fuse plug will
melt. The escaping acetylene may be ignited and will burn with a roaring sound.
Immediately evacuate all people from the area. It is difficult to put out such a fire. The
best action is to put water on the cylinder to keep it cool and to keep all other acetylene
cylinders in the area cool. Attempt to remove the burning cylinder from close proximity
to other acetylene cylinders, from flammable or hazardous materials, or from combustible
buildings. It is best to allow the gas to burn rather than to allow acetylene to escape, mix
with air, and possibly explode.
e. If the fire on a cylinder is a small flame around the hose connection, the valve stem, or
the fuse plug, try to put it out as quickly as possible. A wet glove, wet heavy cloth, or
mud slapped on the flame will frequently extinguish it. Thoroughly wetting the gloves
and clothing will help protect the person approaching the cylinder. Avoid getting in line
with the fuse plug which might melt at any time.
f. Oxygen cylinders should be stored separately from fuel gas cylinders and separately
from combustible materials. Store cylinders in cool, well-ventilated areas. The
temperature of the cylinder should never be allowed to exceed 130°F (54°C).
g. When cylinders are empty they should be marked empty and the valves must be closed
to prohibit contamination from entering.
h. When the gas cylinders are in use a regulator is attached and the cylinder should be
secured to prevent falling by means of chains or clamps.
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i. Cylinders for portable apparatuses should be securely mounted in specially designed
cylinder trucks.
j. Cylinders should be handled with respect. They should not be dropped or struck. They
should never be used as rollers. Hammers or wrenches should not be used to open
cylinder valves that are fitted with hand wheels. They should never be moved by
electromagnetic cranes. They should never be in an electric circuit so that the welding
current could pass through them. An arc strike on a cylinder will damage the cylinder
causing possible fracture, requiring the cylinder to be condemned and discarded from
service.
2-11. HOSES
a. Do not allow hoses to come in contact with oil or grease. These will penetrate and
deteriorate the rubber and constitute a hazard with oxygen.
b. Always protect hoses from being walked on or run over. Avoid kinks and tangles. Do
not leave hoses where anyone can trip over them. This could result in personal injury,
damaged connections, or cylinders being knocked over. Do not work with hoses over the
shoulder, around the legs, or tied to the waist.
c. Protect hoses from hot slag, flying sparks, and open flames.
d. Never force hose connections that do not fit. Do not use white lead, oil, grease, or other
pipe fitting compounds for connections on hose, torch, or other equipment. Never crimp
hose to shut off gases.
e. Examine all hoses periodically for leaks by immersing them in water while under
pressure. Do not use matches to check for leaks in acetylene hose. Repair leaks by cutting
hose and inserting a brass splice. Do not use tape for mending. Replace hoses if
necessary.
f. Make sure that hoses are securely attached to torches and regulators before using.
g. Do not use new or stored hose lengths without first blowing them out with compressed
air to eliminate talc or accumulated foreign matter which might otherwise enter and clog
the torch parts.
h. Only approved gas hoses for flame cutting or welding should be used with oxyfuel gas
equipment. Single lines, double vulcanized, or double multiple stranded lines are
available.
i. The size of hose should be matched to the connectors, regulators, and torches.
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j. In the United States, the color green is used for oxygen, red for acetylene or fuel gas,
and black for inert gas or compressed air. The international standard calls for blue for
oxygen and orange for fuel gas.
k. Connections on hoses are right-handed for inert gases and oxygen, and left-handed for
fuel gases.
l. The nuts on fuel gas hoses are identified by a groove machined in the center of the nuts.
m. Hoses should be periodically inspected for burns, worn places, or leaks at the
connections. They must be kept in good repair and should be no longer than necessary.
Section III. SAFETY IN ARC WELDING AND CUTTING
2-12. ELECTRIC CIRCUITS
a. A shock hazard is associated with all electrical equipment, including extension lights,
electric hand tools, and all types of electrically powered machinery. Ordinary household
voltage (115 V) is higher than the output voltage of a conventional arc welding machine.
b. Although the ac and dc open circuit voltages are low compared to voltages used for
lighting circuits and motor driven shop tools, these voltages can cause severe shock,
particularly in hot weather when the welder is sweating. Consequently, the precautions
listed below should always be observed.
(1) Check the welding equipment to make certain that electrode connections and
insulation on holders and cables are in good condition.
(2) Keep hands and body insulated from both the work and the metal electrode
holder. Avoid standing on wet floors or coming in contact with grounded
surfaces.
(3) Perform all welding operations within the rated capacity of the welding cables.
Excessive heating will impair the insulation and damage the cable leads.
WARNING
Welding machine, Model 301, AC/DC, Heliarc with inert gas attachment,
NSN 3431-00-235-4728, may cause electrical shock if not properly
grounded. If one is being used, contact Castolin Institute, 4462 York St.
Denver, Colorado 80216.
c. Inspect the cables periodically for looseness at the joints, defects due to wear, or other
damage. Defective or loose cables are a fire hazard. Defective electrode holders should
be replaced and connections to the holder should be tightened.
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d. Welding generators should be located or shielded so that dust, water, or other foreign
matter will not enter the electrical windings or the bearings.
e. Disconnect switches should be used with all power sources so that they can be
disconnected from the main lines for maintenance.
2-13. WELDING MACHINES
a. When electric generators powered by internal combustion engines are used inside
buildings or in confined areas, the engine exhaust must be conducted to the outside
atmosphere.
b. Check the welding equipment to make sure the electrode connections and the
insulation on holders and cables are in good condition. All checking should be done with
the machine off or unplugged. All serious trouble should be investigated by a trained
electrician.
c. Motor-generator welding machines feature complete separation of the primary power
and the welding circuit since the generator is mechanically connected to the electric rotor.
A rotor-generator type arc welding machine must have a power ground on the machine.
Metal frames and cases of motor generators must be grounded since the high voltage
from the main line does come into the case. Stray current may cause a severe shock to the
operator if he should contact the machine and a good ground.
d. In transformer and rectifier type welding machines, the metal frame and cases must be
grounded to the earth. The work terminal of the welding machine should not be grounded
to the earth.
e. Phases of a three-phase power line must be accurately identified when paralleling
transformer welding machines to ensure that the machines are on the same phase and in
phase with one another. To check, connect the work leads together and measure the
voltage between the electrode holders of the two machines. This voltage should be
practically zero. If it is double the normal open circuit voltage, it means that either the
primary or secondary connections are reversed. If the voltage is approximately 1-1/2
times the normal open circuit voltage it means that the machines are connected to
different phases of the three phase power line. Corrections must be made before welding
begins.
f. When large weldments, like ships, buildings, or structural parts are involved, it is
normal to have the work terminal of many welding machines connected to it. It is
important that the machines be connected to the proper phase and have the same polarity.
Check by measuring the voltage between the electrode holders of the different machines
as mentioned above. The situation can also occur with respect to direct current power
sources when they are connected to a common weldment. If one machine is connected for
straight polarity and one for reverse polarity, the voltage between the electrode holders
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will be double the normal open circuit voltage. Precautions should be taken to see that all
machines are of the same polarity when connected to a common weldment.
g. Do not operate the polarity switch while the machine is operating under welding
current load. Consequent arcing at the switch will damage the contact surfaces and the
flash may burn the person operating the switch.
h. Do not operate the rotary switch for current settings while the machine is operating
under welding current load. Severe burning of the switch contact surfaces will result.
Operate the rotary switch while the machine is idling.
i. Disconnect the welding machines from the power supply when they are left unattended.
j. The welding electrode holders must be connected to machines with flexible cables for
welding application. Use only insulated electrode holders and cables. There can be no
splices in the electrode cable within 10 feet (3 meters) of the electrode holder. Splices, if
used in work or electrode leads, must be insulated. Wear dry protective covering on
hands and body.
k. Partially used electrodes should be removed from the holders when not in use. A place
will be provided to hang up or lay down the holder where it will not come in contact with
persons or conducting objects.
l. The work clamp must be securely attached to the work before the start of the welding
operation.
m. Locate welding machines where they have adequate ventilation and ventilation ports
are not obstructed.
2-14. PROTECTIVE SCREENS
a. When welding is done near other personnel, screens should be used to protect their
eyes from the arc or reflected glare. See paragraph 2-2 e for screen design and method of
use.
b. In addition to using portable screens to protect other personnel, screens should be used,
when necessary, to prevent drafts of air from interfering with the stability of the arc.
c. Arc welding operations give off an intense light. Snap-on light-proof screens should be
used to cover the windows of the welding truck to avoid detection when welding at night.
2-15. PLASMA ARC CUTTING AND WELDING
a. Plasma arc welding is a process in which coalescence is produced by heating with a
constricted arc between an electrode and the work piece (transfer arc) or the electrode and
the constricting nozzle (nontransfer arc). Shielding is obtained from the hot ionized gas
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issuing from the orifice which may be supplemented by an auxiliary source of shielding
gas. Shielding gas may be an inert gas or a mixture of gases; pressure may or may not be
used, and filler metal may or may not be supplied. Plasma welding is similar in many
ways to the tungsten arc process. Therefore, the safety considerations for plasma arc
welding are the same as for gas tungsten arc welding.
b. Adequate ventilation is required during the plasma arc welding process due to the
brightness of the plasma arc, which causes air to break down into ozone.
c. The bright arc rays also cause fumes from the hydrochlorinated cleaning materials or
decreasing agents to break down and form phosgene gas. Cleaning operations using these
materials should be shielded from the arc rays of the plasma arc.
d. When welding with transferred arc current up to 5A, safety glasses with side shields or
other types of eye protection with a No. 6 filter lens are recommended. Although face
protection is not normally required for this current range, its use depends on personal
preference. When welding with transferred arc currents between 5 and 15A, a full plastic
face shield is recommended in addition to eye protection with a No. 6 filter lens. At
current levels over 15A, a standard welder's helmet with proper shade of filter plate for
the current being used is required.
e. When a pilot arc is operated continuously, normal precautions should be used for
protection against arc flash and heat burns. Suitable clothing must be worn to protect
exposed skin from arc radiation.
f. Welding power should be turned off before electrodes are adjusted or replaced.
g. Adequate eye protection should be used when observation of a high frequency
discharge is required to center the electrode.
h. Accessory equipment, such as wire feeders, arc voltage heads, and oscillators should
be properly grounded. If not grounded, insulation breakdown might cause these units to
become electrically “hot” with respect to ground.
i. Adequate ventilation should be used, particularly when welding metals with high
copper, lead, zinc, or beryllium contents.
2-16. AIR CARBON ARC CUTTING AND WELDING
a. Air carbon arc cutting is an arc cutting process in which metals to be cut are melted by
the heat of a carbon arc and the molten metal is removed by a blast of air. The process is
widely used for back gouging, preparing joints, and removing defective metal.
b. A high velocity air jet traveling parallel to the carbon electrode strikes the molten
metal puddle just behind the arc and blows the molten metal out of the immediate area.
Figure 2-6 shows the operation of the process.
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TC 9-237
c. The air carbon arc cutting process is used to cut metal and to gouge out defective
metal, to remove old or inferior welds, for root gouging of full penetration welds, and to
prepare grooves for welding. Air carbon arc cutting is used when slightly ragged edges
are not objectionable. The area of the cut is small, and since the metal is melted and
removed quickly, the surrounding area does not reach high temperatures. This reduces the
tendency towards distortion and cracking. The air carbon arc can be used for cutting or
gouging most of the common metals.
d. The process is not recommended for weld preparation for stainless steel, titanium,
zirconium, and other similar metals without subsequent cleaning. This cleaning, usually
by grinding, must remove all of the surface carbonized material adjacent to the cut. The
process can be used to cut these materials for scrap for remelting.
e. The circuit diagram for air carbon arc cutting or gouging is shown by figure 2-7.
Normally, conventional welding machines with constant current are used. Constant
voltage can be used with this process.
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f. When using a constant voltage (CV) power source precautions must be taken to operate
it within its rated output of current and duty cycle.
g. Alternating current power sources having conventional drooping characteristics can
also be used for special applications. AC type carbon electrodes must be used.
h. Special heavy duty high current machines have been made specifically for the air
carbon arc process. This is because of extremely high currents used for the large size
carbon electrodes.
i. The air pressure must range from 80 to 100 psi (550 to 690 kPa). The volume of
compressed air required ranges from as low as 5.0 cu ft/min. (2.5 liter/rein.) up to 50 cu
ft/min. (24 liter/min.) for the largest-size carbon electrodes.
j. The air blast of air carbon arc welding will cause the molten metal to travel a very long
distance. Metal deflection plates should be placed in front of the gouging operation, and
all combustible materials should be moved away from the work area. At high-current
levels, the mass of molten metal removed is quite large and will become a fire hazard if
not properly contained.
k. A high noise level is associated with air carbon arc welding. At high currents with high
air pressure a very loud noise occurs. Ear protection, ear muffs or ear plugs must be worn
by the arc cutter.
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Section IV. SAFETY PRECAUTIONS FOR GAS SHIELDED ARC
WELDING
2-17. POTENTIAL HAZARDS
When any of the welding processes are used, the shielded from the air in order to obtain a
high molten puddle of metal should be quality weld deposit. In shielded metal arc
welding, shielding from the air is accomplished by gases produced by the disintegration
of the coating in the arc. With gas shielded arc welding, shielding from the air is
accomplished by surrounding the arc area with a localized gaseous atmosphere
throughout the welding operation at the molten puddle area.
Gas shielded arc welding processes have certain dangers associated with them. These
hazards, which are either peculiar to or increased by gas shielded arc welding, include arc
gases, radiant energy, radioactivity from throated tungsten electrodes, and metal fumes.
2-18. PROTECTIVE MEASURES
a. Gases.
(1) Ozone. Ozone concentration increases with the type of electrodes used,
amperage, extension of arc tine, and increased argon flow. If welding is carried
out in confined spaces and poorly ventilated areas, the ozone concentration may
increase to harmful levels. The exposure level to ozone is reduced through good
welding practices and properly designed ventilation systems, such as those
described in paragraph 2-4.
(2) Nitrogen Oxides. Natural ventilation may be sufficient to reduce the hazard of
exposure to nitrogen oxides during welding operations, provided all three
ventilation criteria given in paragraph 2-4 are satisfied. Nitrogen oxide
concentrations will be very high when performing gas tungsten-arc cutting of
stainless steel using a 90 percent nitrogen-10 percent argon mixture. Also, high
concentrations have been found during experimental use of nitrogen as a shield
gas. Good industrial hygiene practices dictate that mechanical ventilation, as
defined in paragraph 2-4, be used during welding or cutting of metals.
(3) Carbon Dioxide and Carbon Monoxide. Carbon dioxide is disassociated by the
heat of the arc to form carbon monoxide. The hazard from inhalation of these
gases will be minimal if ventilation requirements found in paragraph 2-4 are
satisfied.
WARNING
The vapors from some chlorinated solvents (e.g., carbon tetrachloride,
trichloroethylene, and perchloroethylene) break down under the ultraviolet radiation of an electric arc and forma toxic gas. Avoid welding
where such vapors are present. Furthermore, these solvents vaporize easily
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and prolonged inhalation of the vapor can be hazardous. These organic
vapors should be removed from the work area before welding is begun.
Ventilation, as prescribed in paragraph 2-4, shall be provided for control
of fumes and vapors in the work area.
(4) Vapors of Chlorinated Solvents. Ultraviolet radiation from the welding or
cutting arc can decompose the vapors of chlorinated hydrocarbons, such as
perchloroethylene, carbon tetrachloride, and trichloroethylene, to form highly
toxic substances. Eye, nose, and throat irritation can result when the welder is
exposed to these substances. Sources of the vapors can be wiping rags, vapor
degreasers, or open containers of the solvent. Since this decomposition can occur
even at a considerable distance from the arc, the source of the chlorinated solvents
should be located so that no solvent vapor will reach the welding or cutting area.
b. Radiant Energy. Electric arcs, as well as gas flames, produce ultraviolet and infrared
rays which have a harmful effect on the eyes and skin upon continued or repeated
exposure. The usual effect of ultraviolet is to “sunburn” the surface of the eye, which is
painful and disabling but generally temporary. Ultraviolet radiation may also produce the
same effects on the skin as a severe sunburn. The production of ultraviolet radiation
doubles when gas-shielded arc welding is performed. Infrared radiation has the effect of
heating the tissue with which it comes in contact. Therefore, if the heat is not sufficient to
cause an ordinary thermal burn, the exposure is minimal. Leather and Wool clothing is
preferable to cotton clothing during gas-shielded arc welding. Cotton clothing
disintegrates in one day to two weeks, presumably because of the high ultraviolet
radiation from arc welding and cutting.
c. Radioactivity from Thoriated Tungsten Electrodes. Gas tungsten-arc welding using
these electrodes may be employed with no significant hazard to the welder or other room
occupants. Generally, special ventilation or protective equipment other than that specified
in paragraph 2-4 is not needed for protection from exposure hazards associated with
welding with thoriated tungsten electrodes.
d. Metal Fumes. The physiological response from exposure to metal fumes varies
depending upon the metal being welded. Ventilation and personal protective equipment
requirements as prescribed in paragraph 2-4 shall be employed to prevent hazardous
exposure.
Section V. SAFETY PRECAUTIONS FOR WELDING AND CUTTING
CONTAINERS THAT HAVE HELD COMBUSTIBLES
2-19. EXPLOSION HAZARDS
a. Severe explosions and fires can result from heating, welding, and cutting containers
which are not free of combustible solids, liquids, vapors, dusts, and gases. Containers of
this kind can be made safe by following one of the methods described in paragraphs 2-22
through 2-26. Cleaning the container is necessary in all cases before welding or cutting.
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WARNING
Do not assume that a container that has held combustibles is clean and
safe until proven so by proper tests. Do not weld in places where dust or
other combustible particles are suspended in air or where explosive vapors
are present. Removal of flammable material from vessels and/or
containers may be done either by steaming out or boiling.
b. Flammable and explosive substances may be present in a container because it
previously held one of the following substances:
(1) Gasoline, light oil, or other volatile liquid that releases potentially hazardous
vapors at atmospheric pressure.
(2) An acid that reacts with metals to produce hydrogen.
(3) A nonvolatile oil or a solid that will not release hazardous vapors at ordinary
temperatures, but will release such vapors when exposed to heat.
(4) A combustible solid; i. e., finely divided particles which may be present in the
form of an explosive dust cloud.
c. Any container of hollow body such as a can, tank, hollow compartment in a welding,
or a hollow area on a casting, should be given special attention prior to welding. Even
though it may contain only air, heat from welding the metal can raise the temperature of
the enclosed air or gas to a dangerously high pressure, causing the container to explode.
Hollow areas can also contain oxygen-enriched air or fuel gases, which can be hazardous
when heated exposed to an arc or flame. Cleaning the container is necessary in all cases
before cutting or welding.
2-20. USING THE EXPLOSIMETER
a. The explosimeter is an instrument which can quickly measure an atmosphere for
concentrations of flammable gases and vapors.
b. It is important to keep in mind that the explosimeter measures only flammable gases
and vapors. For example, an atmosphere that is indicated non-hazardous from the
standpoint of fire and explosion may be toxic if inhaled by workmen for some time.
c. Model 2A Explosimeter is a general purpose combustible gas indicator. It will not test
for mixtures of hydrogen, acetylene, or other combustibles in which the oxygen content
exceeds that of normal air (oxygen-enriched atmospheres). Model 3 Explosimeter is
similar except that it is equipped with heavy duty flashback arresters which are capable of
confining within the combustion chambers explosions of mixtures of hydrogen or
acetylene and oxygen in excess of its normal content in air. Model 4 is designed for
testing oxygen-acetylene mixtures and is calibrated for acetylene.
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d. Testing Atmospheres Contaminated with Leaded Gasoline. When an atmosphere
contaminated with lead gasoline is tested with a Model 2A Explosimeter, the lead
produces a solid product of combustion which, upon repeated exposure, may develop a
coating upon the detector filament resulting in a loss of sensitivity. To reduce this
possibility, an inhibitor-filter should be inserted in place of the normal cotton filter in the
instrument. This device chemically reacts with the tetraethyl lead vapors to produce a
more volatile lead compound. One inhibitor-filter will provide protection for an
instrument of eight hours of continuous testing.
CAUTION
Silanes, silicones, silicates, and other compounds containing silicon in the
test atmosphere may seriously impair the response of the instrument.
Some of these materials rapidly “poison” the detector filament so that it
will not function properly. When such materials are even suspected to be
in the atmosphere being tested, the instrument must be checked frequently
(at least after 5 tests). Part no. 454380 calibration test kit is available to
conduct this test. If the instrument reads low on the test gas, immediately
replace the filament and the inlet filter.
e. Operation Instructions. The MSA Explosimeter is set in its proper operating condition
by the adjustment of a single control. This control is a rheostat regulating the current to
the Explosimeter measuring circuit. The rheostat knob is held in the “OFF” position by a
locking bar. This bar must be lifted before the knob can be turned from “OFF” position.
To test for combustible gases or vapors in an atmosphere, operate the Model 2A
Explosimeter as follows:
(1) Lift the left end of the rheostat knob “ON-OFF” bar and turn the rheostat knob
one quarter turn clockwise. This operation closes the battery circuit. Because of
unequal heating or circuit elements, there will be an initial deflection of the meter
pointer. The meter pointer may move rapidly upscale and then return to point
below “ZERO”, or drop directly helm “ZERO”.
(2) Flush fresh air through the instrument. The circuit of the instrument must be
balanced with air free of combustible gases or vapors surrounding the detector
filament. Five squeezes of the aspirator bulb are sufficient to flush the combustion
chamber. If a sampling line is used, an additional two squeezes will be required
for each 10 ft (3m) of line.
(3) Adjust rheostat knob until meter pointer rests at “ZERO”. Clockwise rotation
of the rheostat knob causes the meter pointer to move up scale. A clockwise
rotation sufficient to move the meter pointer considerably above “ZERO” should
be avoided as this subjects the detector filament to an excessive current and may
shorten its life.
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(4) Place end of sampling line at, or transport the Model 2A Explosimeter to, the
point where the sample is to be taken.
(5) Readjust meter pointer to "ZERO" if necessary by turning rheostat knob.
(6) Aspirate sample through instrument until highest reading is obtained.
Approximately five squeezes of the bulb are sufficient to give maximum
deflection. If a sampling line is used, add two squeezes for each 10 ft (3 m) of
line. This reading indicates the concentration of combustible gases or vapors in
the sample.
The graduations on the scale of the indicating inter are in percent of the lower
explosive limit. Thus, a deflection of the meter pointer between zero and 100
percent shins how closely the atmosphere being tested approaches the minimum
concentration required for the explosion. When a test is made with the instrument
and the inter pointer is deflected to the extreme right side of the scale and remains
there, the atmosphere under test is explosive.
If the meter pointer moves rapidly across the scale, and on continued aspiration
quickly returns to a position within the scale range or below “ZERO”, it is an
indication that the concentration of flammable gases or vapors may be above the
upper explosive limit. To verify this, immediately aspirate fresh air through the
sampling line or directly into the instrument. Then, if the meter pointer moves
first to the right and then to the left of the scale, it is an indication that the
concentration of flammable gas or vapor in the sample is above the upper
explosive limit.
When it is necessary to estimate or compare concentrations of combustible gases
above the lower explosive limit a dilution tube may be employed. See paragraph
2-20 f (1).
The meter scale is red above 60 to indicate that gas concentrations within that
range are very nearly explosive. Such gas-air mixtures are considered unsafe.
(7) To turn instrument off: Rotate rheostat knob counterclockwise until arrow on
knob points to “OFF”. The locking bar will drop into position in its slot indicating
that the rheostat is in the “OFF” position.
NOTE
When possible, the bridge circuit balance should be checked before each
test. If this is not practical, the balance adjustment should be made at 3minute internals during the first ten minutes of testing and every 10
minutes thereafter.
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f. Special Sampling Applications
(1) Dilution tube. For those tests in which concentrations of combustible gases in
excess of liner explosive limit concentrations (100 percent on instrument inter)
are to be compared, such as in testing bar holes in the ground adjacent to a leak in
a buried gas pipe, or in following the purging of a closed vessel that has contained
f flammable gases or vapors, a special air-dilution tube must be used. Such
dilution tubes are available in 10:1 and 20:1 ratios of air to sample, enabling rich
concentrations of gas to be compared.
In all tests made with the dilution tube attached to the instrument, it is necessary
that the instrument be operated in fresh air and the gaseous sample delivered to
the instrument through the sampling line in order to permit a comparison of a
series of samples beyond the normal range of the instrument to determine which
sample contains the highest concentration of combustible gases. The tube also
makes it possible to follow the progress of purging operation when an atmosphere
of combustibles is being replaced with inert gases.
(2) Pressure testing bar holes. In sane instances when bar holes are drilled to
locate pipe line leaks, a group of holes all containing pure gas may be found. This
condition usually occurs near a large leak. It is expected that the gas pressure will
be greatest in the bar hole nearest the leak. The instrument may be used to locate
the position of the leak by utilizing this bar hole pressure. Observe the time
required for this pressure to force gas through the instrument sampling line. A
probe tube equipped with a plug for sealing off the bar hole into which it is
inserted is required. To remove the flow regulating orifice from the instrument,
aspirate fresh air through the Explosimeter and unscrew the aspirator bulb
coupling. Adjust the rheostat until the meter pointer rests on “ZERO”.
The probe tube is now inserted in the bar hole and sealed off with the plug.
Observe the time at which this is done. Pressure developed in the bar hole will
force gas through the sampling line to the instrument, indicated by an upward
deflection of the meter pointer as the gas reaches the detector chamber.
Determine the time required for the gas to pass through the probe line. The bar
hole showing the shortest time will have the greatest pressure.
When the upward deflection of the meter pointer starts, turn off the instrument,
replace the aspirator bulb and flush out the probe line for the next test.
2-21. PREPARING THE CONTAINER FOR CLEANING
CAUTION
Do not use chlorinated hydrocarbons, such as trichloroethylene or carbon
tetrachloride, when cleaning. These materials may be decomposed by heat
or radiation from welding or cutting to form phosgene. Aluminum and
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aluminum alloys should not be cleaned with caustic soda or cleaners
having a pH above 10, as they may react chemically. Other nonferrous
metals and alloys should be tested for reactivity prior to cleaning.
NOTE
No container should be considered clean or safe until proven so by tests.
Cleaning the container is necessary in all cases before welding or cutting.
a. Disconnect or remove from the vicinity of the container all sources of ignition before
starting cleaning.
b. Personnel cleaning the container must be protected against harmful exposure. Cleaning
should be done by personnel familiar with the characteristics of the contents.
c. If practical, move the container into the open. When indoors, make sure the room is
well ventilated so that flammable vapors may be carried away.
d. Empty and drain the container thoroughly, including all internal piping, traps, and
standpipes. Removal of scale and sediment may be facilitated by scraping, hammering
with a nonferrous mallet, or using a nonferrous chain as a scrubber. Do not use any tools
which may spark and cause flammable vapors to ignite. Dispose of the residue before
starting to weld or cut.
e. Identify the material for which the container was used and determine its flammability
and toxicity characteristics. If the substance previously held by the container is not
known, assure that the substance is flammable, toxic, and insoluble in water.
f. Cleaning a container that has held combustibles is necessary in all cases before any
welding or cutting is done. This cleaning may be supplemental by filling the container
with water or an inert gas both before and during such work.
g. Treat each compartment in a container in the same manner, regardless of which
compartment is be welded or cut.
2-22. METHODS OF PRECLEANING CONTAINERS WHICH HAVE HELD
FLAMMABLE LIQUIDS
a. General. It is very important for the safety of personnel to completely clean all tanks
and containers which have held volatile or flammable liquids. Safety precautions cannot
be over-emphasized because of the dangers involved when these items are not thoroughly
purged prior to the application of heat, especially open flame.
b. Accepted Methods of Cleaning. Various methods of cleaning containers which have
held flammable liquids are listed in this section. However, the automotive exhaust and
steam cleaning methods are considered by military personnel to be the safest and easiest
methods of purging these containers.
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2-23. AUTOMOTIVE EXHAUST METHOD OF CLEANING
WARNING
Head and eye protection, rubber gloves, boots, and aprons must be worn
when handling steam, hot water, and caustic solutions. When handling dry
caustic soda or soda ash, wear approved respiratory protective equipment,
long sleeves, and gloves. Fire resistant hand pads or gloves must be worn
when handling hot drums.
The automotive exhaust method of cleaning should be conducted only in
well-ventilated areas to ensure levels of toxic exhaust gases are kept below
hazardous levels.
CAUTION
Aluminum and aluminum alloys should not be cleaned with caustic soda
or cleaners having a pH above 10, as they may react chemically. Other
nonferrous metals and alloys should be investigated for reactivity prior to
cleaning.
a. Completely drain the container of all fluid.
b. Fill the container at least 25 percent full with a solution of hot soda or detergent (1 lb
per gal of water (0.12 kg per 1)) and rinse it sufficiently to ensure that the inside surface
is thoroughly finished.
c. Drain the solution and rinse the container again with clean water.
d. Open all inlets and outlets of the container.
e. Using a flexible tube or hose, direct a stream of exhaust gases into the container. Make
sure there are sufficient openings to allow the gases to flow through the container.
f. Allow the gases to circulate through the container for 30 minutes.
g. Disconnect the tube from the container and use compressed air (minimum of 50 psi
(345 kPa)) to blow out all gases.
h. Close the container openings. After 15 minutes, reopen the container and test with a
combustible gas indicator. If the vapor concentration is in excess of 14 percent of the
lower limit of flammability, repeat cleaning procedure.
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2-24. STEAM METHOD OF CLEANING
WARNING
Head and eye protection, rubber gloves, boots, and aprons must be worn
when handling steam, hot water, and caustic solutions. When handling dry
caustic soda or soda ash, wear approved respiratory protective equipment,
long sleeves, and gloves. Fire resistant hand pads or gloves must be worn
when handling hot drums.
The automotive exhaust method of cleaning should be conducted only in
well-ventilated areas to ensure levels of toxic exhaust gases are kept below
hazardous levels.
CAUTION
Aluminum and aluminum alloys should not be cleaned with caustic soda
or cleaners having a pH above 10, as they may react chemically. Other
nonferrous metals and alloys should be investigated for reactivity prior to
cleaning.
a. Completely drain the container of all fluid.
b. Fill the container at least 25 percent full with a solution of hot soda, detergent, or soda
ash (1 lb per gal of water (0.12 kg per 1)) and agitate it sufficiently to ensure that the
inside surfaces are thoroughly flushed.
NOTE
Do not use soda ash solution on aluminum.
c. Drain the solution thoroughly.
d. Close all openings in the container except the drain and filling connection or vent. Use
damp wood flour or similar material for sealing cracks or other damaged sections.
e. Use steam under low pressure and a hose of at least 3/4-in. (19.05 mm) diameter.
Control the steam pressure by a valve ahead of the hose. If a metal nozzle is used at the
outlet end, it should be made of nonsparking material and should be electrically
connected to the container. The container, in turn, should be grounded to prevent an
accumulation of static electricity.
f. The procedure for the steam method of cleaning is as follows:
(1) Blow steam into the container, preferably through the drain, for a period of
time to be governed by the condition or nature of the flammable substance
previously held by the container. When a container has only one opening, position
it so the condensate will drain from the same opening the steam inserted into.
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TC 9-237
(When steam or hot water is used to clean a container, wear suitable clothing,
such as boots, hood, etc., to protect against burns.)
(2) Continue steaming until the container is free from odor and the metal parts are
hot enough to permit steam vapors to flow freely out of the container vent or
similar opening. Do not set a definite time limit for steaming containers since
rain, extreme cold or other weather conditions may condense the steam as fast as
it is introduced. It may take several hours to heat the container to such a
temperature that steam will flow freely from the outlet of the container.
(3) Thoroughly flush the inside of the container with hot, preferably boiling,
water.
(4) Drain the container.
(5) Inspect the inside of the container to see if it is clean. To do this, use a mirror
to reflect light into the container. If inspection shows that it is not clean, repeat
steps (1) through (4) above and inspect again. (Use a nonmetal electric lantern or
flashlight which is suitable for inspection of locations where flammable vapors
are present.)
(6) Close the container openings. In 15 minutes, reopen the container and test
with a combustible gas indicator. If the vapor concentration is in excess of 14
percent of the lower limit of flammability, repeat the cleaning procedure.
2-25. WATER METHOD OF CLEANING
a. Water-soluble substances can be removed by repeatedly filling and draining the
container with water. Water-soluble acids, acetone, and alcohol can be removed in this
manner. Diluted acid frequently reacts with metal to produce hydrogen; care must be
taken to ensure that all traces of the acid are removed.
b. When the original container substance is not readily water-soluble, it must be treated
by the steam method or hot chemical solution method.
2-26. HOT CHEMICAL SOLUTION METHOD OF CLEANING
WARNING
Wear head and eye protection, rubber gloves, boots, and aprons when
handling steam, hot water, and caustic solutions. When handling dry
caustic soda or soda ash, wear approved respiratory protective equipment,
long sleeves, and gloves. Wear fire resistant hand pads or gloves to handle
hot drums.
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TC 9-237
CAUTION
Aluminum and aluminum alloys should not be cleaned with caustic soda
or cleaners having a pH above 10, as they may react chemically. Other
nonferrous metals and alloys should be investigated for reactivity prior to
cleaning.
a. The chemicals generally used in this method are trisodium phosphate (strong washing
powder) or a commercial caustic cleaning compound dissolved in water to a
concentration of 2 to 4 oz (57 to 113 g) of chemical per gallon of water.
b. The procedure for the hot chemical solution method of cleaning is as follows:
(1) Close all container openings except the drain and filling connection or vent.
Use damp wood flour or similar material for sealing cracks or other damaged
sections.
(2) Fill the container to overflowing with water, preferably letting the water in
through the drains. If there is no drain, flush the container by inserting the hose
through the filling connection or vent. Lead the hose to the bottom of the
container to get agitation from the bottom upward. This causes any remaining
liquid, scum, or sludge to be carried upward and out of the container.
(3) Drain the container thoroughly.
(4) Completely dissolve the amount of chemical required in a small amount of hot
or boiling water and pour this solution into the container. Then fill the container
with water.
(5) Make a steam connection to the container either through the drain connection
or by a pipe entering through the filling connection or vent. Lead the steam to the
bottom of the container. Admit steam into the chemical solution and maintain the
solution at a temperature of 170 to 180°F (77 to 82°C). At intervals during the
steaming, add enough water to permit overflying of any volatile liquid, scum, or
sludge that may have collected at the top. Continue steaming to the point where
no appreciable amount of volatile liquid, scum, or sludge appears at the top of the
container.
(6) Drain the container.
(7) Inspect the inside of the container as described in paragraph 2-24 f (5). If it is
not clean, repeat steps (4) thru (6) above and inspect again.
(8) Close the container openings. In 15 minutes, test the gas concentration in the
container as described in paragraph 2-24 f (6).
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c. If steaming facilities for heating the chemical solution are not available, a less effective
method is the use of a cold water solution with the amount of cleaning compound
increased to about 6 oz (170 g) per gal of water. It will help if the solution is agitated by
rolling the container or by blowing air through the solution by means of an air line
inserted near the bottom of the container.
d. Another method used to clean the container is to fill it 25 percent full with cleaning
solution and clean thoroughly, then introduce low pressure steam into the container,
allowing it to vent through openings. Continue to flow steam through the container for
several hours.
2-27. MARKING OF SAFE CONTAINERS
After cleaning and testing to ensure that a container is safe for welding and cutting,
stencil or tag it. The stencil or tag must include a phrase, such as “safe for welding and
cutting,” the signature of the person so certifying, and the date.
2-28. FILLING TREATMENT
It is desirable to fill the container with water during welding or cutting as a supplement to
any of the cleaning methods (see fig. 2-8). Where this added precaution is taken, place
the container so that it can be kept find to within a few inches of the point where the work
is to be done. Make sure the space above the water level is vented so the heated air can
escape from the container.
2-29. PREPARING THE CLEAN CONTAINER FOR WELDING OR CUTTING-INERT GAS TREATMENT
a. General. Inert gas may be used as a supplement to any of the cleaning methods and as
an alternative to the water filling treatment. If sufficient inert gas is mixed with
flammable gases and vapors, the mixture will come non-flammable. A continuous flow of
steam may also be used. The steam will reduce the air concentration and make the air
flammable gas mixture too lean to burn. Permissible inert gases include carbon dioxide
and nitrogen.
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b. Carbon Dioxide and Nitrogen.
(1) When carbon dioxide is used, a minimum concentration of 50 percent is
required, except when the flammable vapor is principally hydrogen, carbon
monoxide, or acetylene. In these cases, a minimum concentration of 80 percent
carbon dioxide is required. Carbon dioxide is heavier than air, and during welding
or cutting operations will tend to remain in containers having a top opening.
(2) When nitrogen is used, the concentrations should be at least 10 percent greater
than those specified for carbon dioxide.
(3) Do not use carbon monoxide.
c. Procedure. The procedure for inert gas, carbon dioxide, or nitrogen treatment is as
follows:
(1) Close all openings in the container except the filling connection and vent. Use
damp wood flour or similar material for sealing cracks or other damaged sections.
(2) Position the container so that the spot to be welded or cut is on top. Then fill it
with as much water as possible.
(3) Calculate the volume of the space above the water level and add enough inert
gas to meet the minimum concentration for nonflammability. This will usually
require a greater volume of gas than the calculated minimum, since the inert gas
may tend to flow out of the vent after displacing only part of the previously
contained gases or vapors.
(4) Introduce the inert gas, carbon dioxide, or nitrogen from the cylinder through
the container drain at about 5 psi (34.5 kPa). If the drain connection cannot be
used, introduce the inert gas through the filling opening or vent. Extend the hose
to the bottom of the container or to the water level so that the flammable gases are
forced out of the container.
(5) If using solid carbon dioxide, crush and distribute it evenly over the greatest
possible area to obtain a rapid formation of gas.
d. Precautions When Using Carbon Dioxide. Avoid bodily contact with solid carbon
dioxide, which may produce “burns”. Avoid breathing large amounts of carbon dioxide
since it may act as a respiratory stimulant, and, in sufficient quantities, can act as an
asphyxiant.
e. Inert Gas Concentration. Determine whether enough inert gas is present using a
combustible gas indicator instrument. The inert gas concentration must be maintained
during the entire welding or cutting operation. Take steps to maintain a high inert gas
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concentration during the entire welding or cutting operation by one of the following
methods:
(1) If gas is supplied from cylinders, continue to pass the gas into the container.
(2) If carbon dioxide is used in solid form, add small amounts of crushed solid
carbon dioxide at intervals to generate more carbon dioxide gas.
Section VI. SAFETY PRECAUTIONS FOR WELDING AND CUTTING
POLYURETHANE FOAM FILLED ASSEMBLIES
2-30. HAZARDS OF WELDING POLYURETHANE FOAM FILLED
ASSEMBLIES
WARNING
Welding polyurethane foam-filled parts can produce toxic gases. Welding
should not be attempted on parts filled with polyurethane foam. If repair
by welding is necessary, the foam must be removed from the heat-affected
area, including the residue, prior to welding.
a. General. Welding polyurethane foam filled parts is a hazardous procedure. The hazard
to the worker is due to the toxic gases generated by the thermal breakdown of the
polyurethane foam. The gases that evolve from the burning foam depend on the amount
of oxygen available. Combustion products of polyurethane foam in a clean, hot fire with
adequate oxygen available are carbon dioxide, water vapor, and varying amounts of
nitrogen oxides, carbon monoxide, and traces of hydrogen cyanide. Thermal
decomposition of polyurethanes associated with restricted amounts of oxygen as in the
case of many welding operations results in different gases being produced. There are
increased amounts of carbon monoxide, various aldehydes, isocyanates and cyanides, and
small amounts of phosgene, all of which have varying degrees of toxicity.
b. Safety Precautions.
(1) It is strongly recommended that welding on polyurethane foam filled parts not
be performed. If repair is necessary, the foam must be removed from the heat
affected zone. In addition, all residue must be cleaned from the metal prior to
welding.
(2) Several assemblies of the M113 and M113A1 family of vehicles should not be
welded prior to removal of polyurethane foam and thorough cleaning.
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CHAPTER 3
PRINT READING AND WELDING SYMBOLS
Section I.
PRINT READING
3-1. GENERAL
a. Drawings. Drawing or sketching is a universal language used to convey all
necessary information to the individual who will fabricate or assemble an object.
Prints are also used to illustrate how various equipment is operated, maintained,
repaired, or lubricated. The original drawings for prints are made either by directly drawing or tracing a drawing on a translucent tracing paper or cloth using
waterproof (India) ink or a special pencil. The original drawing is referred to as
a tracing or master copy.
b. Reproduction Methods. Various methods of reproduction have been developed
which will produce prints of different colors from the master copy.
(1) One of the first processes devised to reproduce a tracing produced white
lines on a blue background, hence the term “blueprints”.
(2) A patented paper identified as "BW" paper produces prints with black
lines on a white background.
(3) The ammonia process, or “Ozalids” , produces prints with either black,
blue, or maroon lines on a white background.
(4)
Vandyke paper produces a white line on a dark brown background .
(5) Other reproduction methods are the mmeograph machine, ditto machine, and
photostatic process.
3-2.
PARTS OF A DRAWING
a. Title Block. The title block contains the drawing number and all the
information required to identify the part or assembly represented. Approved military prints will include the name and address of the Government Agency or organization preparing the drawing, the scale, the drafting record, authentication, and the
date.
b. Revision Block. Each drawing has a revision block which is usually located in the upper right corner. All changes to the drawing are noted in this block.
Changes are dated and identified by a number or letter. If a revision block is not
used, a revised drawing may be shown by the addition of a letter to the original
number.
c. Drawing Number. All drawings are identified by a drawing number. If a
print has more than one sheet and each sheet has the same number, this information
is included in the number block, indicating the sheet number and the number of
sheets in the series.
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3-2.
PARTS OF A DRAWING (cent)
d. Reference Numbers and Dash Numbers. Reference numbers that appear in the
title block refer to other print numbers. When more than one detail is shown on a
drawing, dashes and numbers are frequently used. If two parts are to be shown in
one detail drawing, both prints will have the same drawing nunber plus a dash and
an individual number such as 7873102-1 and 7873102-2.
e. Scale. The scale of the print is indicated in one of the spaces within
the title block. It indicates the size of the drawing as compared with the actual
size of the part. Never measure a drawing--use dimensions. The print may have
been reduced in size from the original drawing.
f . Bill of Material. A special block or box on the drawing may contain a
list of necessary stock to make an assembly. It also indicates the type of stock,
size, and specific amount required.
3-3.
CONSTRUCTION LINES
a. Full Lines (A, fig. 3-1).
lines of an object.
Full lines represent the visible edges or out-
b. Hidden Lines (A, fig. 3-1). Hidden lines are made of short dashes which
represent hidden edges of an object.
c. Center Lines (B, fig. 3-1). Center lines are made with alternating short
and long dashes. A line through the center of an object is called a center line.
d. Cutting Plane Lines (B, fig. 3-1). Cutting plane lines are dashed lines,
generally of the same width as the full lines , extending through the area being
cut . Short solid wing lines at each end of the cutting line project at 90 degrees
to that line and end in arrowheads which point in the direction of viewing. Capital letters or numerals are placed just beyond the points of the arrows to designate the section.
e. Dimension Lines (A, fig. 3-1). Dimension lines are fine full lines ending
in arrowheads . They are used to indicate the measured distance between two points.
f . Extension Lines (A, fig. 3-1). Extension lines are fine lines from the
outside edges or intermedi‘ate points of a drawn object. They indicate the limits
of dimension lines.
g. Break Lines (C, fig. 3-1). Break lines are used to show a break in a drawing and are used when it is desired to increase the scale of a drawing of uniform
cross section while showing the true size by dimension lines. There are two kinds
of break lines: short break and long break. Short break lines are usually heavy,
wavy, semiparallel lines cutting off the object outline across a uniform section.
Long break lines are long dash parallel lines with each long dash in the line connected to the next by a “2” or sharp wave line.
3-2
TC 9-237
Section II. WELD AND WELDING SYMBOLS
3-4. GENERAL
Welding cannot take its proper place as an engineering tool unless means are provided for conveying the information from the designer to the workmen. Welding symbols
provide the means of placing complete welding information on drawings. The scheme
for symbolic representation of welds on engineering drawings used in this manual is
consistent with the “third angle” method of projection. This is the method predomninantly used in the United States.
3-3
TC 9-237
3-4. GENERAL (cont)
The joint is the basis of reference for welding symbols. The reference line of the
welding symbol (fig. 3-2) is used to designate the type of weld to be made, its
location, dimensions, extent, contour, and other supplementary information. Any
welded joint indicated by a symbol will always have an arrow side and an other
side. Accordingly, the terms arrow side, other side, and both sides are used herein to locate the weld with respect to the joint.
The tail of the symbol is used for designating the welding and cutting processes as
well as the welding specifications, procedures, or the supplementary information to
be used in making the weld. If a welder knows the size and type of weld, he has
only part of the information necessary for making the weld. The process, identification of filler metal that is to be used, whether or not peening or root chipping
is required, and other pertinent data must be related to the welder. The notation
to be placed in the tail of the symbol indicating these data is to be establish
by each user. If notations are not used, the tail of the symbol may be omitted.
3-4
TC 9-237
3-5.
ELMENTS OF A WELDING SYMBOL
A distinction is made between the terms “weld symbol” and “welding symbol”. The
weld symbol (fig. 3-3) indicates the desired type of weld. The welding symbol
(fig. 3-2) is a method of representing the weld symbol on drawings. The assembled
“welding symbol” consists of the following eight elements, or any of these elements
as necessary: reference line, arrow, basic weld symbols, dimensions and other
data, supplementary symbols, finish symbols, tail, and specification, process, or
other reference. The locations of welding symbol elements with respect to each
other are shown in figure 3-2.
3-6.
BASIC WELD SYMBOLS
a. General. Weld symbols are used to indicate the welding processes used in
metal joining operations, whether the weld is localized or “all around”, whether it
is a shop or field weld, and the contour of welds. These basic weld symbols are
summrized below and illustrate in figure 3-3.
b. Arc and Gas Weld Symbols.
c.
Resistance Weld Symbols.
See figure 3-3.
See figure 3-3.
d. Brazing, Forge, Thermit, Induction, and Flow Weld Symbols.
(1) These welds are indicated by using a process or specification reference
in the tail of the welding symbol as shown in figure 3-4.
(2) When the use of a definite process is required (fig. 3-5) , the process
may be indicated by one or more of the letter designations shown in tables 3-1 and
3-2.
3-5
TC 9-237
(3) When no specification, process, or other reference is used with a welding
symbol, the tail may be omitted (fig. 3-6).
3-6
TC 9-237
3-7
TC 9-237
3-6.
BASIC WELD SYMBOLS (cont)
e. Other Common Weld Symbols. Figures 3-7 and 3-8 illustrate the weld-allaround and field weld symbol, and resistance spot and resistance seam welds.
f. Supplermntary Symbols. These symbols are used in many welding processes in
congestion with welding symbols and are used as shown in figure 3-3, p 3-5.
3-7.
LOCATION SIGNIFICANCE OF ARROW
a. Fillet, Groove, Flange, Flash, and Upset welding symbols. For these symbols, the arrow connects the welding symbol reference line to one side of the joint
and this side shall be considered the arrow side of the joint (fig. 3-9). The side
opposite the arrow side is considered the other side of the joint (fig. 3-10).
3-8
TC 9-237
b. Plug, Slot, Arc Spot, Arc Seam, Resistance Spot, Resistance Seam, and Projection Welding Symbols. For these symbols, the arrow connects the welding symbol
reference line to the outer surface of one member of the joint at the center line
of the desired weld. The member to which the arrow- points is considered the arrow
side member. The other member of the joint shall be considered the other side
member (fig. 3-11).
c. Near Side. When a joint is depicted by a single line on the drawing and
the arrow of a welding symbol is directed to this line, the arrow side of the joint
is considered as the near side of the joint, in accordance with the usual conventions of drafting (fig. 3-12 and 3-13).
d. Near Member. When a joint is depictd as an area parallel to the plane of
projection in a drawing and the arrow of a welding symbol is directed to that area,
the arrow side member of the joint is considered as the near member of the joint,
in accordance with the usual conventions of drafting (fig. 3-11).
3-9
TC 9-237
3-8.
LOCATION OF THE WELD WITH RESPECT TO JOINT
a. Arrow Side. Welds on the arrow side of the joint are shown by placing the
weld symbol on the side of the reference line toward the reader (fig. 3-14).
b. Other Side. Welds on the other side of the joint are shown by placing the
weld symbol on the side of the reference line away from the reader (fig. 3-15).
c. Both Sides. Welds on both sides of the joint are shown by placinq weld
symbols on both sides of the reference line, toward and away from the reader
(fig. 3-16).
d. No Side Significance. Resistance spot, resistance seam, flash, and upset
weld symbols have no arrow side or other side significance in themselves. although
.
supplementary symbols used in conjunction with these symbols may have such significance. For example, the flush contour symbol (fig. 3-3) is used in conjunction
with the spot and seam symbols (fig. 3-17) to show that the exposed surface of one
member of the joint is to be flush. Resistance spot, resistance seam, flash, and
upset weld symbols shall be centered on the reference line (fig. 3-17).
3-10
TC 9-237
3-9.
REFERENCES AND GENERAL NOTES
a. Symbols With References. When a specification, process, or other reference is used with a welding symbol, the reference is placed in the tail fig. 3-4,
p 3-5).
b. S ymbols Without References.
process, or other references when:
Symbols may be used without specification,
(1) A note similar to the following appears on the drawing: “Unless otherwise designated, all welds are to be made in accordance with specification no....”
(2) The welding procedure to be used is described elsewhere, such as in shop
instructions and process sheets.
c. General Notes. General notes similar to the follwing may be placed on a
drawing to provide detailed information pertaining to the predominan t welds. This
information need not be repeated on the symbols:
(1)
size.”
“Unless otherwise indicated, all fillet welds are 5/16 in. (0.80 cm)
(2) “Unless otherwise indicated, root openings for all groove welds are 3/16
in. (0.48 cm).”
d. Process Indication. When use of a definite process is required, the process
may be indicated by the letter designations listed in tables 3-1 and 3-2
(fig. 3-5, p 3-6).
e. Symbol Without a Tail. When no specification, process, or other reference
is used with a welding symbol, the tail may be omitted (fig. 3-6, p 3–6).
3-10.
WELD-ALL-AROUND AND FIELD WELD SYMBOLS
a. Welds extending completely around a joint are indicated by mans of the
weld-all-around symbol (fig. 3-7, p 3-8). Welds that are completely around a joint
which includes more than one type of weld, indicated by a combination weld symbol,
are also depicted by the weld–all-around symbol. Welds completely around a joint
in which the metal intersections at the points of welding are in more than one
plane are also indicated by the weld-all-around symbol.
b. Field welds are welds not made in a shop or at the place of initial construction and are indicated by means of the field weld symbol (fig. 3–7, p 3–8).
3-11
TC9-237
3-11.
EXTENT OF WELDING DENOTED BY SYMBOLS
a. Abrupt Changes. Symbols apply between abrupt changes in the direction of
the welding or to the extent of hatching of dimension lines, except when the weldall-around symbol (fig. 3-3, p 3-5) is used.
b. Hidden Joints. Welding on hidden joints may be
is the same as that of the visible joint. The drawing
hidden members. If the welding on the hidden joint is
visible joint, specific information for the welding of
3-12.
covered when the welding.
indicates the presence of
different from that of the
both must be given.
LOCATION OF WELD SYMBOLS
a. Weld symbols, except resistance spot and resistance seam, must be shown only
on the welding symbol reference line and not on the lines of the drawing.
b. Resistance spot and resistance seam weld symbols may be placed directly at
the locations of the desired welds (fig. 3-8, p 3-8) .
3-13.
USE OF INCH, DEGREE, AND POUND MARKS
NOTE
Inch marks are used for indicating the diameter of arc spot, resistance
spot, and circular projection welds, and the width of arc seam and resistance seam welds when such welds are specified by decimal dimensions.
In general, inch, degree, and pound marks may or may not be used on welding symbols, as desired.
3-14.
CONSTRUCTION OF SYMBOLS
Fillet, bevel and J-groove, flare bevel groove, and corner flange symbols
shall be shown with the perpendicular leg always to the left (fig. 3–18 ) .
b. In a bevel or J-groove weld symbol, the arrow shall point with a definite
break toward the member which is to be chamfered (fig. 3-19) . In cases where the
member to be chamfered is obvious, the break in the arrow may be omitted.
3-12
TC 9-237
c. Information on welding symbols shall be placed to read from left to right
along the reference line in accordance with the usual conventions of drafting
(fig. 3-20) .
having more than one weld, a symbol shall be shown for each weld
e. The letters CP in the tail of the arrow indicate a complete penetration weld
regardless of the type of weld or joint preparation (fig. 3-22).
3-13
TC 9-237
3-14.
CONSTRUCTION OF SYMBOLS (cont)
f. When the basic weld symbols are inadequate to indicate the desired weld, the
weld shall be shown by a cross section, detail, or other data with a reference on
the welding symbol according to location specifications given i n p a r a 3 - 7
(fig. 3-23).
g. Two or more reference lines may be used to indicate a sequence of operations. The first operation must be shown on the reference line nearest the arrow.
Subsequent operations must be shown sequentially on other reference lines
(fig. 3-24). Additional reference lines may also be used to show data supplementary to welding symbol information included on the reference line nearest the arrow.
Test information may be shown on a second or third line away from the arrow
(fig. 3-25). When required, the weld-all-around symbol must be placed at the junction of the arrow line and reference line for each operation to which it applies
(fig. 3-26). The field weld symbol may also be used in this manner.
3-14
TC 9-237
3-15.
FILLET WELDS
Dimensions of fillet welds must be shown on the same side of the reference
line as the weld symbol (A, fig. 3-27).
b. When fillet welds are indicated on both sides of a joint and no general note
governing the dimensions of the welds appears on the drawing, the dimensions are
indicated as follows:
(1) When both welds have the same dimensions, one or both may be dimensioned
(B or C, fig. 3-27).
(2) When the welds differ in dimensions, both must be dimensioned (D, fig.
3-27).
When fillet welds are indicated on both sides of a joint and a general note
governing the dimensions of the welds appears on the drawing, neither weld need be
dimensioned. However, if the dimensions of one or both welds differ from the dimensions given in the general note, both welds must be dimensioned (C or D, fig. 3-27).
3-16.
SIZE OF FILLET WELDS
The size of a fillet weld must be shown to the left of the weld symbol (A,
fig. 3-27).
b. The size of a fillet weld with unequal legs must be shown in parentheses to
the left of the weld symbol. Weld orientation is not shown by the symbol and must
be shown on the drawing when necessary (E, fig. 3-27).
c. Unless otherwise indicated, the deposited fillet weld size must not be less
than the size shown on the drawing.
d. When penetration for a given root opening is specified, the inspection method for determining penetration depth must be included in the applicable specification.
3-17.
LENGTH OF FILLET WELDS
a. The length of a fillet weld, when indicated on the welding symbol, must be
shown to the right of the weld symbol (A through D, fig. 3-27).
3-15
TC 9-237
3-17.
LENGTH OF FILLET WELDS (cont)
b. When fillet welding extends for the full distance between abrupt changes in
the direction of the welding, no length dimension need be shown on the welding
symbol.
c. Specific lengths of fillet welding may be indicated by symbols in conjunction with dimension lines (fig. 3-28).
3-18.
EXTENT OF FILLET WELDING
a. Use one type of hatching (with or without definite lines) to show the extent
of fillet welding graphically.
b. Fillet welding extending beyond abrupt changes in the direction of the welding must be indicated by additional arrows pointing to each section of the joint to
be welded (fig. 3-29) except when the weld-all-around symbol is used.
3-16
TC 9-237
3-19.
DIMENSIONING OF INTERMITTENT FILLET WELDING
a. The pitch (center-to-center spacing) of intermittent fillet welding shall be
shown as the distance between centers of increments on one side of the joint.
b. The pitch of intermittent fillet welding shall be shown to the right of the
length dimension (A, fig 3-27, p 3-15).
c. Dimensions of chain intermittent fillet welding must be shown on both sides
of the reference line. Chain intermittent fillet welds shall be opposite each
other (fig. 3-30).
d. Dimensions of staggered intermittent fillet welding must be shown on both
sides of the reference line as shown in figure 3-31.
Unless otherwise specified, staggered intermittent fillet welds on both sides shall
be symmetrically spaced as in figure 3-32.
3-17
TC 9-237
3-20.
TERMINATION OF INTERMITTENT FILLET WELDING
a.. When intermittent fillet welding is used by itself, the symbol indicates
that increments are located at the ends of the dimensioned length.
b. When intermittent fillet welding is used between continuous fillet welding,
the symbol indicates that spaces equal to the pitch minus the length of one increment shall be left at the ends of the dimensioned length.
c. Separate symbols must be used for intermittent and continuous fillet welding
when the two are combined along one side of the joint (fig. 3-28, p 3-16).
3-21.
SURFACE CONTOUR OF FILLET WELDS
a. Fillet welds that are to be welded approximately flat, convex, or concave
faced without recourse to any method of finishing must be shown by adding the flush,
convex, or concave contour symbol to the weld symbol, in accordance with the location specifications given in paragraph 3-7 (A, fig. 3-33).
b. Fillet welds that are to be made flat faced by mechanical means must be
shown by adding both the flush contour symbol and the user’s standard finish symbol
to the weld symbol, in accordance with location specifications given in paragraph
3-7 (B, fig. 3-33).
c. Fillet welds that are to be mechanically finished to a convex contour shall
be shown by adding both the convex contour symbol and the user’s standard finish
symbol to the weld symbol, in accordance with location specifications given in
paragraph 3-7 (C, fig. 3-33).
d. Fillet welds that are to be mechanically finished to a concave contour must
be shown by adding both the concave contour symbol and the user’s standard finish
symbol to the weld symbol in accordance with location specification given in paragraph 3-7.
e. In cases where the angle between fusion faces is such that the identification of the type of weld and the proper weld symbol is in question, the detail of
the desired joint and weld configuration must be shown on the drawing.
3-18
TC 9-237
NOTE
Finish symbols used here indicate the method of finishing (“c” = chipping, “G” = grinding, “H” = hammering, "M" = machining), not the degree
of finish.
3-22.
PLUG AND SLOT WELDING SYMBOLS
a. General. Neither the plug weld symbol nor the slot weld symbol may be
used to designate fillet welds in holes.
b. Arrow Side and Other Side Indication of Plug and Slot Welds. Holes or
slots in the arrow side member of a joint for plug or slot welding must be indicated by placing the weld symbol on the side of the reference line toward the reader
(A, fig. 3-11, p 3-9) . Holes or slots in the other side member of a joint shall be
indicated by placing the weld symbol on the side of the reference line away from
the reader (B, fig. 3-11, p 3-9).
c. Plug Weld Dimensions. Dimensions of plug welds must be shown on the same
side of the reference line as the weld symbol. The size of a weld must be shown to
the left of the weld symbol. Included angle of countersink of plug welds must be
the user’s standard unless otherwise indicated. Included angle of countersink,
when not the user’s standard, must be shown either above or below the weld symbol
(A and C, fig. 3-34). The pitch (center-to-center spacing) of plug welds shall be
shown to the right of the weld symbol.
d. Depth of Filling of Plug and Slot Welds. Depth of filling of plug and
slot welds shall be completed unless otherwise indicated. When the depth of filling
is less than complete, the depth of filling shall be shown in inches inside the
weld symbol (B, fig. 3-34).
3-19
TC 9-237
3-22.
PLUG AND SLOT WELDING SYMBOLS (cont)
e. Surface Contour of Plug Welds and Slot Welds. Plug welds that are to be
welded approximately flush without recourse to any method of finishing must be
shown by adding the finish contour symbol to the weld symbol (fig. 3-35). Plug
welds that are to be welded flush by mechanical means must be shown by adding both
the flush contour symbol and the user’s standard finish symbol to the weld symbol
(fig. 3-36).
f . Slot Weld Dimensions. Dimensions of slot welds must be shown on the same
side of the reference line as the the symbol (fig. 3-37).
g. Details of Slot Welds. Length, width, spacing, included angle of countersink, orientation , and location of slot welds cannot be shown on the welding symbols. This data must be shown on the drawing or by a detail with a reference to it
on the welding symbol, in accordance with location specifications given in paragraph 3-7 (D, fig. 3-34, p 3-19).
3-23.
ARC SPOT AND ARC SEAM WELDs
a. General. The spot weld symbol, in accordance with its location in relation to the reference line, may or may not have arrow side or other side significance. Dimensions must be shown on the same side of the reference line as the
symbol or on either side when the symbol is located astride the reference line and
has no arrow side or other side significance. The process reference is indicated
in the tail of the welding symbol. Then projection welding is to be used, the spot
weld symbol shall be used with the projection welding process reference in the tail
of the welding symbol. The spot weld symbol must be centered above or below the,
reference line.
3-20
TC 9-237
b.
Size of Arc Spot and Arc Seam Welds.
(1) These welds may be dimensioned by either size or strength.
(2) The size of arc spot welds must be designated as
weld. Arc seam weld size shall be designated as the width
will be expressed in fractions or in decimals in hundredths
shown, with or without inch marks, to the left of the weld
the diameter of the
of the weld. Dimensions
of an inch and shall be
symbol (A, fig. 3-38).
(3) The strength of arc spot welds must be designated as the minimum acceptable shear strength in pounds or newtons per spot. In arc seam welds, strength is
designated in pounds per linear inch. Strength is shown to the left of the weld
symbol (B, fig. 3-38).
c.
Spacing of Arc Spot and Arc Seam Welds.
(1) The pitch (center-to-center spacing) of arc spot welds and, when indicated, the length of arc seam welds, must be shown to the right of the weld symbol (C,
fig. 3-38).
(2) When spot welding or arc seam welding extends for the full distance between abrupt changes in the direction of welding, no length dimension need be shown
on the welding symbol.
d.
Extent and Number of Arc Spot Welds and Arc Seam Welds.
(1) When arc spot welding extends less than the distance between abrupt changes in the direction of welding or less than the full length of the joint, the extent must be dimensioned (fig. 3-39).
3-21
TC 9-237
3-23.
ARC SPOT AND ARC SEAM WELDS (cont)
(2) When a definite number of arc spot welds is desired in a certain joint,
the number must be shown in parentheses either above or below the weld symbol
(fig. 3-40) .
(3) A group of spot welds may be located on a drawing by intersecting center
lines. The arrows point to at least one of the centerlines passing through each
weld location.
e. Flush Arc Spot and Arc Seam Welded Joints. When the exposed surface of
one member of an arc spot or arc seam welded joint is to be flush, that surface
must be indicated by adding the flush contour symbol (fig. 3-41) in the same manner
as that for fillet welds (para 3-21).
f. Details of Arc Seam Welds. Spacing, extent, orientation, and location of
arc seam welds cannot be shown on the welding symbols. This data must be shown on
the drawing.
3-24.
a.
GROOVE WELDS
General.
(1) Dimensions of groove welds must be shown on the same side of the reference line as the weld symbol (fig. 3-42).
3-22
TC 9-237
(2) When no general note governing the dimensions of double groove welds appears, dimensions shall be shown as follows:
(a) When both welds have the same dimensions, one or both may be dimensioned (fig. 3-43).
(b)
3-44).
When the welds differ in dimensions, both shall be dimensioned (fig.
(3) When a general note governing the dimensions of groove welds appears, the
dimensions of double groove welds shall be indicated as follows:
(a) If the dimensions of both welds are as indicated in the note, neither
symbol need be dimensioned.
(b) When the dimensions of one or both welds differ from the dimensions
given in the general note, both welds shall be dimensioned (fig. 3-44).
b.
Size of Groove Welds.
(1) The size of groove welds shall be shown to the left of the weld symbol
(fig. 3-44).
(2) Specifications for groove welds with no specified root penetration are
shown as follows:
(a) The size of single groove and symmetrical double groove welds which
extend completely through the member or members being joined need not be shown on
the welding symbol (A and B, fig. 3-45).
3-23
TC 9-237
3-24.
GROOVE WELDS (cont)
(b) The size of groove welds which extend only partly through the member
members being joined must be shown on the welding symbol (A and B, fig. 3-46).
(3) The size of groove welds with specified root penetration, except square
groove welds, must be indicated by showing the depth of chamfering and the root
penetration separated by a plus mark and placed to the left of the weld symbol.
The depth of chamfering and the root penetration must read in that order from left
to right along the reference line (A and B, fig. 3-47). The size of square groove
welds must be indicated by showing only the root penetration.
(4) The size of flare groove welds is considered to extend only to the tangent points as indicated by dimension lines (fig. 3-48).
3-24
TC 9-237
c.
Groove Dimensions
(1) Root opening, groove angle, groove radii, and root faces of the U and J
groove welds are the user’s standard unless otherwise indicated.
(2) When the user’s standard is not used, the weld symbols are as follows:
(a) Root opening is shown inside the weld symbol (fig. 3-49) .
(b) Groove angle of groove welds is shown outside the weld symbol
(fig. 3-42, p 3-22).
(c) Groove radii and root faces of U and J groove welds are shown by a
cross section, detail, or other data, with a reference to it on the welding symbol,
in accordance with location specifications given in paragraph 3-7 (fig. 3-22,
p 3-13).
d. Back and Backing Welds. Bead-type back and backing welds of single~oove
welds shall be shown by means of the back or backing weld symbol (fig. 3-50).
e. Surface Contour of Groove Welds. The contour symbols for groove welds (F,
fig. 3-51) are indicated in the same manner as that for fillet welds (para 3-21).
3-25
TC 9-237
3-24.
GROOVE WELDS (cont )
(1) Groove welds that are to be welded approximately flush without recourse
to any method of finishing shall be shown by adding the flush contour symbol to the
weld symbol, in accordance with the location specifications given in paragraph 3-7
(fig. 3-52).
(2) Groove welds that are to be made flush by mechanical means shall be shown
by adding the the flush contour symbol and the user’s standard finish symbol to
the weld symbol, in accordance with the location specifications given in paragraph
3-7 (fig. 3-53).
(3) Groove welds that are to be mechanically finished to a convex contour
shall be shown by adding both the convex contour symbol and the user’s standard
finish symbol to the weld symbol, in accordance with the location specifications
given in para 3-7 (fig. 3-54).
3-25.
a.
BACK OR BACKING WELDS
General.
(1) The back or backing weld symbol (fig. 3-50, p 3-25) must be used to indicate bead-type back or backing welds of single-groove welds.
(2) Back or backing welds of single-groove welds must be shown by placing a
back or backing weld symbol on the side of the reference line opposite the groove
weld symbol (fig. 3-50, p 3-25).
(3) Dimensions of back or backing welds should not be shown on the welding
symbol . If it is desired to specify these dimensions, they must be shown on the
drawing .
3-26
TC 9-237
b. Surface Contour of Back or Backing Welds. The contour symbols (fig. 3-55)
for back or backing welds are indicated in the same manner as that for fillet welds
(para 3-21).
3-26.
a.
MELT-THRU WELDS
General.
(1) The melt-thru symbol shall be used where at least 100 percent joint penetration of the weld through the material is required in welds made from one side
only (fig. 3-56).
(2) Melt-thru welds shall be shown by placing the melt-thru weld symbol on
the side of the reference line opposite the groove weld, flange, tee, or corner
weld symbol (fig. 3-56).
(3) Dimensions of melt-thru welds should rot be shown on the welding symbol.
I f i t is desired to specify these dimensions, they must be shown on the drawing.
b. Surface Contour of Melt-thru Welds. The contour symnbols for melt-thru
welds are indicated in the same manner as that for fillet welds (fig. 3-57).
3-27
TC 9–237
3-27.
a.
SURFACING WELDS
General.
(1) The surfacing weld symbol shall be used to indicate surfaces built up by
welding (fig. 3-58), whether built up by single- or multiple-pass surfacing welds.
(2) The surfacing weld symbol does not indicate the welding of a joint and
thus has no arrow or other side significance. This symbol shall be drawn on the
side of the reference line toward the reader and the arrow shall point clearly to
the surface on which the weld is to be deposited.
b. Size of Built-up Surfaces. The size (height) of a surface built up by
welding shall be indicated by showing the minimum height of the weld deposit to the
left of the weld symbol. The dimensions shall always be on the same side of the
reference line as the weld symbol (fig. 3-58). When no specific height of weld
deposit is desired, no size dimension need be shown on the welding symbol.
c. Extent, Location, and Orientation of Surfaces Built up by Welding. When
the entire area of a plane or curved surface is to be built up by welding, no dimension, other than size, need be shown on the welding symbol. If only a portion of
the area of a plane or curved surface is to be built up by welding, the extent,
location, and orientation of the area to be built up shall be indicated on the
drawing.
3-28.
a.
FLANGE WELDS
General.
(1) The following welding symbols are used for light gage metal joints involving the flaring or flanging of the edges to be joined (fig. 3-59). These symbols
have no arrow or other side significance.
(2) Edge flange welds shall be shown by the edge flange weld symbol (A,
fig. 3-59).
(3) Corner flange welds shall be shown by the corner flange weld symbol (B,
fig. 3-59). In cases where the corner flange joint is not detailed, a break in the
arrow is required to show which member is flanged (fig. 3-59).
b.
Dimensions of Flange Welds.
(1) Dimensions of flange welds are shown on the same side of the reference
line as the weld symbol.
3-28
TC 9-237
(2) The radius and the height above the point of tangency must be indicated
by showing the radius and height, separated by a plus mark, and placed to the left
of the weld symbol. The radius and height must read in that order from left to
right along the reference line (C, fig. 3-59).
(3) The size (thickness) of flange welds must be shown by a dimension placed
outward of the flange dimensions (C, fig. 3-59).
(4) Root opening of flange welds are not shown on the welding symbol. If
specification of this dimension is desired, it must be shown on the drawing.
c. Multiple-Joint Flange Welds. For flange welds in which one or more pieces
are inserted between the two outer pieces, the same symbol shall be used as for the
two outer pieces, regardless of the number of pieces inserted.
3-29
TC 9-237
3-29.
RESISTANCE SPOT WELDS
a. General. Resistance spot weld symbols (fig. 3-3, p 3-5) have no arrow or
other side significance in themselves, although supplementary symbols used in conjunction with them may have such significance. Resistance spot weld symbols shall
be centered on the reference line. Dimensions may be shown on either side of the
reference line.
b. Size of Resistance Spot Welds.
either size or strength as follows:
Resistance spot welds are dimensioned by
(1) The size of resistance spot welds is designated as the diameter of the
weld expressed in fractions or in decimals in hundredths of an inch and must be
shown, with or without inch marks, to the left of the weld symbol (fig. 3-60).
(2) The strength of resistance spot welds is designated as the minimum acceptable shear strength in pounds per spot and must be shown to the left of the weld
symbol (fig. 3-61).
c.
Spacing of Resistance Spot Welds.
(1) The pitch of resistance spot welds shall be shown to the right of the
weld symbol (fig. 3-62).
(2) When the symbols are shown directly on the drawing, the spacing is shown
by using dimension lines.
3-30
TC 9-2 37
(3) When resistance spot welding extends less than the distance between
abrupt changes in the direction of the welding or less than the full length of the
joint, the extent must be dimensioned (fig. 3-63).
d. Number of Resistance Spot Welds. When a definite number of welds is desired in a certain joint, the number must be shown in parentheses either above or
below the weld symbol (fig. 3-64).
e. Flush Resistance Spot Welding Joints. When the exposed surface of one member of a resistance spot welded joint is to be flush, that surface shall be indicated by adding the flush contour symbol (fig. 3-3, p 3-5) to the weld symbol, (fig.
3-65) in accordance with location specifications given in paragraph 3-7.
3-30.
a.
RESISTANCE SEAM WELDS
General.
(1) Resistance seam weld symbols have no arrow or other side significance in
themselves, although supplementary symbols used in injunction with them may have
such significance. Resistance seam weld symbols must be centered on the reference
line.
(2) Dimensions of resistance seam welds may be shown on either side of the
reference line.
3-31
TC 9-237
3-30.
RESISTANCE SEAM WELDS (cont )
b. Size of Resistance Seam Welds. Resistance seam welds must be dimensioned
by either size or strength as follows:
(1) The size of resistance seam welds must be designated as the width of the
weld expressed in fractions or in decimals in hundredths of an inch and shall be
shown, with or without inch marks, to the left of the weld symbol (fig. 3-66).
(2) The strength of resistance seam welds must be designated as the minimum
acceptable shear strength in pounds per linear inch and must be shown to the left
of the weld symbol (fig. 3-67).
c. Length of Resistance Seam Welds.
(1) The length of a resistance seam weld, when indicated on the welding symbol, must be shown to the right of the welding symbol (fig. 3-68).
(2) When resistance seam welding extends for the full distance between abrupt
changes in the direction of the welding, no length dimension need be shown on the
welding symbol.
(3) When resistance seam welding extends less than the distance between
abrupt changes in the direction of the welding or less than the full length of the
joint, the extent must be dimensioned (fig. 3-69).
3-32
TC 9-237
d. Pitch of Resistance Seam Welds. The pitch of intermittent resistance seam
welding shall be designated as the distance between centers of the weld increments
and must be shown to the right of the length dimension (fig. 3-70).
e. Termination of Intermittent Resistance Seam Welding. When intermittent
resistance seam welding is used by itself, the symbol indicates that increments are
located at the ends of the dimensioned length. When used between continuous resistance seam welding, the symbol indicates that spaces equal to the pitch minus the
length of one increment are left at the ends of the dimensional length. Separate
symbols must be used for intermittent and continuous resistance seam welding when
the two are combined.
f . Flush Projection Welded Joints. When the exposed surface of one member of a
projection welded joint is to be made flush, that surface shall be indicated by
adding the flush contour symbol (fig. 3-3, p 3-5) to the weld symbol, observing the
usual location significance (fig. 3-79).
3-33
TC 9–237
3-31.
PROJECTION WELDS
a.
General.
(1) When using projection welding, the spot weld symbol must be used with the
projection welding process reference in the tail of the welding symbol. The spot
weld symbol must be centered on the reference line.
(2) Embossments on the arrow side member of a joint for projection welding
shall be indicated by placing the weld symbol on the side of the reference line
toward the reader (fig. 3-72).
(3) Embossment on the other side member of a joint
for projection weldingshall be indicated by placing the weld symbol on the side of the reference line
away from the reader (fig. 3-73).
(4)
means .
Proportions of projections must be shown by a detail or other suitable
(5) Dimensions of projection welds must be shown on the same side of the
reference line as the weld symbol.
b.
Size of Projection Welds.
(1) Projection welds must be dimensioned by strength. Circular projection
welds may be dimensioned by size.
3-34
TC 9-237
(2) The size of circular projection welds shall be designated as the diameter
of the weld expressed in fractions or in decimals in hundredths of an inch and
shall be shown, with or without inch marks, to the left of the weld symbol ( fig.
3-74) .
(3) The strength of projection welds shall be designated as the minimum acceptable shear strength in pounds per weld and shall be shown to the left of the
weld symbol (fig. 3-75).
c. Spacing of Projection Welds. The pitch of projection welds shall be shown
to the right of the weld symbol (fig. 3-76).
d. Number of Projection Welds. When a definite number of projection welds is
desired in a certain joint, the number shall be shown in parentheses (F, fig. 3-77).
3-35
TC 9-237
3-31.
PROJECTION WELDS (cont)
e. Extent of Projection Welding. When the projection welding extends less
than the distance between abrupt changes in the direction of the welding or less
than the full length of the joint, the extent shall be dimensioned (fig. 3-78).
f . Flush Resistance Seam Welded Joints. When the exposed surface of one member
of a resistance seam welded joint is to be flush, that surface shall be indicated
by adding the flush contour symbol (fig. 3-3, p 3-5) to the weld symbol, observing
the usual location significance (fig. 3-71).
3-32.
FLASH OR UPSET WELDS
a. General. Flash or upset weld symbols have no arrow side or other side
significance in themselves, although supplementary symbols used in conjunction with
then may have such significance. The weld symnbols for flash or upset welding must
be centered on the reference line. Dimensions need not be shown on the welding
symbol .
b. Surface Contour of Flash or Upset Welds. The contour symbols (fig. 3-3,
p 3-5) for flash or upset welds (fig. 3-80) are indicated in the same manner as
that for fillet welds (paragraph 3-21).
3-36
TC 9-237
CHAPTER 4
JOINT DESIGN AND PREPARATION OF METALS
4-1.
JOINT TYPES
Welds are made at the junction of the various pieces that make up the weldment.
The junctions of parts, or joints, are defined as the location where two or more
nembers are to be joined. Parts being joined to produce the weldment may be in the
form of rolled plate, sheet, shapes, pipes, castings, forgings, or billets. The
five basic types of welding joints are listed below.
- - -
a. B, Butt Joint.
plane.
A joint between two members lying approximately in the same
b. C, Corner Joint. A joint between two members located approximately at right
angles to each other in the form of an angle.
c. E, Edge Joint.
parallel members.
d.
L, Lap Joint.
A joint between the edges of two or more parallel or mainly
A joint between two overlapping members.
e. T, Tee Joint. A joint between two members located approximately at right
angles to each other i n the form of a T.
4-1
TC 9-237
4-2.
WELD JOINTS
In order to produce weldments , it is necessary to combine the joint types with weld
types to produce weld joints for joining the separate members. Each weld type
cannot always be combined with each joint type to make a weld joint. Table 4-1
shows the welds applicable to the basic joints.
4-3.
WELD JOINT DESIGN AND PREPARATION
a. Purpose. Weld joints are designed to transfer the stresses between the
members of the joint and throughout the weldment. Forces and loads are introduced
at different points and are transmitted to different areas throughout the weldment. The type of loading and service of the weldment have a great bearing on the
joint design required.
4-2
TC
9-237
b. Categories. All weld joints can be classified into two basic categories:
full penetration joints and partial penetration joints.
(1) A full penetration joint has weld metal throughout the entire cross section of the weld joint.
(2) A partial penetration joint has an unfused area and the weld does not
completely penetrate the joint. The rating of the joint is based on the percentage
of weld metal depth to the total joint; i.e., a 50 percent partial penetration
joint would have weld metal halfway through the joint.
NOTE
When joints are sub jetted to dynamic loading, reversing loads, and
impact leads, the weld joint must be very efficient. This is more
important if the weldment is sub jetted to cold-temperature service.
Such services require full-penetration welds. Designs that increase
stresses by the use of partial-penetration joints are not acceptable
for this type of service.
c. Strength. The strength of weld joints depends not only on the size of the
weld, but also on the strength of the weld metal.
(1) Mild and low alloy steels are generally stronger than the materials being
joined.
(2) When welding high-alloy or heat-treated materials, special precautions
must be taken to ensure the welding heat does not cancel the heat treatment of the
base metal, causing it to revert to its lower strength adjacent to the weld.
d. D e s i g n . The weld joint must be designed so that its cross-sectional area is
the minimum possible. The cross-sectional area is a measurement of the amount or
weight of weld metal that must be used to make the joint. Joints may be prepared
by shearing, thermal cutting, or machining.
(1) Carbon and loW alloy joint design and preparation. These weld joints are
prepared either by flame cutting or mechanically by machining or grinding, depending on the joint details. Before welding, the joint surfaces must be cleared of
all foreign materials such as paint, dirt, scale, or must. Suitable solvents or
light grinding can be used for cleaning. The joint surface should not be nicked or
gouged since nicks and gouges may interfere with the welding operation. Specific
information on welding carbon and low alloy metals may be found in chapter 7, paragraph 7-10.
CAUTION
Aluminum and aluminum alloys should not be cleaned with caustic soda or
strong cleaner with a pH above 10. The aluminum or aluminum alloy will
react chemically with these types of cleaners. Other nonferrous metals
and alloys should be investigated prior to using these cleaners to
determine their reactivity.
4-3
TC 9-237
4-3.
WELD JOINT DESIGN AND PREPARATION (cent)
(2) Aluminum and aluminum alloy joint design and preparation. Weld joint
designs often unintentionally require welds that cannot be made. Check your design
to avoid these and similar errors. Before welding, the joint surfaces must be
cleared of all foreign materials such as paint, dirt, scale, or oxide; solvent
cleaning, light grinding, or etching can be used. The joint surfaces should not be
nicked or gouged since nicks and gouges may interfere with welding operations.
Specific information regarding welding aluminum and aluminum alloy metals may be
found in chapter 7, paragraph 7-17.
(3) Stainless steel alloy joint design and preparation. These weld joints
are prepared either by plasma arc cutting or by machining or grinding, depending on
the alloy. Before welding, the joint surfaces must be cleaned of all foreign material, such as paint, dirt, scale, or oxides. Cleaning may be done with suitable
solvents (e.g., acetone or alcohol) or light grinding. Care should be taken to
avoid nicking or gouging the joint surface since such flaws can interfere with the
welding operation. Specific information regarding welding stainless steel alloy
metals may he found in chapter 7, paragraph 7-14.
4-4.
WELD ACCESSIBILITY
The weld joint must be accessible to the welder using the process that is employed . Weld joints are often designed for welds that cannot be made. Figure 4-2
illustrates several types of inaccessible welds.
4-4
TC 9-237
CHAPTER 5
WELDING AND CUTTING EQUIPMENT
Section I.
OXYACETYLENE WELDING EQUIPMENT
5-1. GENERAL
The equipment used for oxyacetylene welding consists of a source of oxygen and a
source of acetylene from a portable or stationary outfit, along with a cutting
attachment or a separate cutting torch. Other equipment requirements include suitable goggles for eye protection, gloves to protect the hands, a method to light the
torch, and wrenches to operate the various connections on the cylinders, regulators, and torches.
5-2.
STATIONARY WELDING EQUIPMENT
Stationay welding equipment is installed where welding operations are conducted in
a fixed location. Oxygen and acetylene are provided in the welding area as outlined below.
a. Oxygen. Oxygen is obtained from a number of Cylinders manifolded and
equipped with a master regulator. The regulator and manifold control the pressure
and the flow together (fig. 5-1). The oxygen is supplied to the welding stations
through a pipe line equipped with station outlets (fig. 5-2, p 5-2).
5-1
TC 9-237
5-2.
STATIONARY WELDING EQUIPMENT (cont)
b. Acetylene. Acetylene is obtained either from acetylene cylinders set up as
shown in figure 5-3, or an acetylene generator ( fig. 5-4). The acetylene is supplied to the welding stations through a pipe line equipped with station outlets as
shown in figure 5-2.
5-2
TC 9-237
5-3
TC 9-237
5-3.
PORTABLE WELDING EQUIPMENT
The portable oxyacetylene welding outfit consists of an oxygen cylinder and an
acetylene cylinder with attached valves, regulators, gauges, and hoses (fig. 5-5).
This equipment may be temporarily secured on the floor or mounted on an all welded
steel truck. The trucks are equipped with a platform to support two large size
cylinders. The cylinders are secured by chains attached to the truck frame. A
metal toolbox, welded to the frame, provides storage space for torch tips, gloves,
fluxes, goggles, and necessary wrenches.
5-4.
ACETYLENE GENERATOR
NOTE
Acetylene generator equipment is not a standard item of issue and is
included in this manual for information only.
a. Acetylene is a fuel gas composed of carbon and hydrogen. (C 7H 2), generated by
the action of calcium carbide, a gray stonelike substance, and water in a generating unit. Acetylene is colorless, but has a distinctive odor that can be easily
detected.
b. Mixtures of acetylene and air, containing from 2 to 80 percent acetylene by
volume , will explode when ignited. However, with suitable welding equipment and
5-4
TC 9-237
proper precautions, acetylene can be safely burned with oxygen for heating, welding, and cutting putposes.
Acetylene, when burned with oxygen, produces0 an oxyacetylene
flame with
0
inner; cone tip
temperatures
of
approximately
6300
F
(3482
C),
for
an oxidizing
0
0
0
0
flame; 5850 F (3232 C) for a neutral flame; and 5700 F (3149 C) for a
carburizing flame.
d. The generator shown in figure 5–4 is a commonly used commercial type. A
single rated 300-lb generator uses 300 lb of calcium carbide and 300 gal. of water.
This amount of material will generate 4.5 cu ft of acetylene per pound; the output
for this load is appr oximately 300 cu ft per hour for 4.5 hours. A double rated
generator uses 300 lb of finer sized calcium carbide fed through a special hopper
and will deliver 600 cu ft of acetylene per hour for 2.5 hours.
CAUTION
Since considerable heat is given off during the reaction, precautions
must be taken to prevent excessive pressures in the generator which
might cause fires or explosions.
e. In the operation of the generator, the calcium carbide is added to the water
through a hopper mechanism at a rate which will maintain a working pressure of
approximately 15 psi (103.4 kPa). A pressure regulator is a built-in part of this
equipment. A sludge, consisting of hydrated or slaked lime, settles in the bottom
of the generator and is removed-by means of a sludge outlet.
5-5. ACETYLENE CYLINDERS
Acetylene, stored in a free state under pressure greater than 15 psi
(103.4 kPa), can break down from heat or shock, and possibly explode.
Under pressure of 29.4 psi (203 kPa), acetylene becomes selfexplosive, and a slight shock can cause it to explode spontaneously.
CAUTION
Although acetylene is nontoxic, it is an anesthetic, and if present in
a sufficiently high concentration, is an asphyxiant in that it replac–
es oxygen and can produce suffocation.
a. Acetylene is a colorless, flammable gas composed of carbon and hydrogen,
manufactured by the reaction of water and calcium carbide. It is slightly lighter
than air. Acetylene burns in the air with an intensely hot, yellow, luminous,
smoky flare.
b. Although acetylene is stable under low pressure, if compressed to 15 psi
(103.4 kPa), it becomes unstable. Heat or shock can cause acetylene under pressure
to explode. Avoid exposing filled cylinders to heat, furnaces, radiators, open
fires, or sparks (from a torch). Avoid striking the cylinder against other objects
and creating sparks. To avoid shock when transporting cylinders, do not drag,
roll, or slide them on their sides. Acetylene can be compressed into cylinders
when dissolved in acetone at pressures up to 250 psi (1724 kPa) .
c. For welding purposes, acetylene is contained in three common cylinders with
capacities of 1, 60, 100, and 300 cu ft. Acetylene must not be drawn off in vol–
umes greater than 1/7 of the cylinder’s rated capacity.
5-5
TC 9-237
5-5.
ACETYLENE CYLINDERS (cont)
d. In order to decrease the size of the open spaces in the cylinder, acetylene
cylinders (fig. 5-6) are filled with porous materials such as balsa wood, charcoal,
corn pith, or portland cement. Acetone, a colorless, flammable liquid, is added to
the cylinder until about 40 percent of the porous material is saturated. The porous material acts as a large sponge which absorbs the acetone, which then absorbs
the acetylene. In this process, the volume of acetone increases as it absorbs the
acetylene, while acetylene, being a gas, decreases in volume.
CAUTION
Do not fill acetylene cylinders at a rate greater than 1/7 of their
rated capacity, or about 275 cu ft per hour. To prevent drawing off
of acetone and consequent impairment of weld quality and damage to the
welding equipment, do not draw acetylene from a cylinder at continuous
rates in volumes greater than 1/7 of the rated capacity of the cylinder, or 32.1 cu ft per hour. When more than 32.1 cu ft per hour are
required, the cylinder manifold system must be used.
e. Acetylene cylinders are equipped with safety plugs (fig. 5-6 ) which have a
small hole through the0 center.0 This hole is filled with a metal alloy which melts
at approximately 212 F (100 C), or releases at 500 psi (3448 kPa). When a cylinder is overheated, the plug will melt and permit the acetylene to escape before
dangerous pressures can be developed. The plug hole is too small to premit a flame
to burn back into the cylinder if escaping acetylene is ignited.
5-6
TC 9–237
f . The brass acetylene cylinder valves have squared stainless steel valve
stems. These stems can be fitted with a cylinder wrench and opened or closed when
the cylinder is in use. The outlet of the valve is threaded for connection to an
acetylene pressure regulator by means of a union nut. The regulator inlet connection gland fits against the face of the threaded cylinder connection, and the union
nut draws the two surfaces together. Whenever the threads on the valve connections
are damaged to a degree that will prevent proper assembly to the regulator, the
cylinder should be marked and set aside for return to the manufacturer.
WARNING
Acetylene which may accumulate in a storage room or in a confined
space is a fire arid explosion hazard. All acetylene cylinders should
be checked, using a soap solution, for leakage at the valves and safety fuse plugs.
g. A protective metal cap (fig. 5-6) screws onto the valve to prevent damage
during shipment or storage.
h. Acetylene, when used with oxygen, produces the highest flame temperature of
any of the fuel gases. It also has the most concentrated flame, but produces less
gross heat of combustion than the liquid petroleum gases and the synthetic gases.
5-6.
OXYGEN AND ITS PRODUCTION
a. General. Oxygen is a colorless, tasteless, odorless gas that is slightly
heavier than air. It is nonflammable but will support combustion with other elements . In its free state, oxygen is one of the most common elements. The atmosphere is made up of approximately 21 parts of oxygen and 78 parts of nitrogen, the
remainder being rare gases. Rusting of- ferrous metals, discoloration of copper,
and the corrosion of aluminum are all due to the action of atmospheric oxygen,
known as oxidation.
b. Production of Oxygen. Oxygen is obtained commercially either by the liquid
air process or by the electrolytic process.
(1) In the liquid air process, air is compressed and cooled to a point where
the gases become liquid. As the temperature of the liquid air rises, nitrogen in a
gaseous form is given off first, since its boiling point is lower than that of
liquid oxygen. These gases, having been separated, are then further purified and
compressed into cylinders for use. The liquid air process is by far the most wide–
ly used to produce oxygen.
(2) In the electrolytic process, water is broken down into hydrogen and oxy–
gen by the passage of an electric current. The oxygen collects at the positive
terminal and the hydrogen at the negative terminal. Each gas is collected and
compressed into cylinders for use.
5-7
TC 9-237
5-7.
OXYGEN CYLINDER
CAUTION
Always refer to oxygen as oxygen, never as air. Combustibles should be
kept away from oxygen, including the cylinder, valves, regulators, and
other hose apparatus. Oxygen cylinders and apparatus should not be
handled with oily hands or oily gloves. Pure oxygen will support and
accelerate combustion of almost any material, and is especially dangerous in the presence of oil and grease. Oil and grease in the presence of
oxygen may spontaneously ignite and burn violently or explode. Oxygen
should never be used in any air tools or for any of the purposes for
which compressed air is normally used.
A typical oxygen cylinder is shown in figure 5-7. It is made of steel and has a
capacity
of0 220 cu ft at a pressure of 2000 psi (13,790 kPa) and a temperature of
0
70 F (21 C ) . Attached equipment provided by the oxygen supplier consists of an
outlet valve, a removable metal cap for the protection of the valve, and a low
melting point safety fuse plug and disk. The cylinder is fabricated from a single
plate of high grade steel so that it will have no seams and is heat treated to
achieve maximum strength. Because of their high pressure, oxygen cylinders undergo
extensive testing prior to their release for work, and must be periodically tested
thereafter.
5-8.
OXYGEN AND ACETYLENE REGULATORS
a. General. The gases compressed in oxygen and acetylene cylinders are held at
pressures too high for oxyacetylene welding. Regulators - reduce pressure and control the flow of gases from the cylinders. The pressure in an oxygen cylinder can
5-8
TC 9-237
be as high as 2200 psi (15,169 kPa), which must be reduced to a working pressure of
1 to 25 psi (6.90 to 172.38 kPa). The pressure of acetylene in an acetylene cylinder can be as high as 250 psi (1724 kPa) and must be reduced to a working pressure
of from 1 to 12 psi (6.90 to 82.74 kPa). A gas pressure regulator will automatically deliver a constant volume of gas to the torch at the adjusted working pressure.
NOTE
The regulators for oxygen, acetylene, and liquid petroleum fuel gases
are of different construction. They must be used only for the gas for
which they were designed.
Most regulators in use are either the single stage or the two stage type. Check
valves must be installed between the torch hoses and the regulator to prevent flashback through the regulator.
b. Single Stage Oxygen Regulator. The single stage oxygen regulator reduces
the cylinder pressure of a gas to a working pressure in one step. The single stage
oxygen regulator mechanism (fig. 5-8) has a nozzle through which the high pressure
gas passes, a valve seat to close off the nozzle, and balancing springs. Some
types have a relief valve and an inlet filter to exclude dust and dirt. Pressure
gauges are provided to show the pressure in the cylinder or pipe line and the working pressure.
5-9
TC 9–237
5-8.
OXYGEN AND ACETYLENE REGULATORS (cont)
NOTE
In operation, the working pressure falls as the cylinder pressure
falls, which occurs gradually as gas is withdrawn. For this reason,
the working pressure must be adjusted at intervals during welding
operations when using a single stage oxygen regulator.
The oxygen regulator controls and reduces the oxygen pressure from any standard
commercial oxygen cylinder containing pressures up to 3000 psi. The high pressure
gauge, which is on the inlet side of the regulator, is graduated from 0 to 3000
p s i . The low or working pressure gauge, which is on the outlet side of the regulator, is graduated from O to 500 psi.
c.
Operation of Single Stage Oxygen Regulator.
(1) The regulator consists of a flexible diaphragm, which controls a needle
valve between the high pressure zone and the working zone, a compression spring,
and an adjusting screw, which compensates for the pressure of the gas against the
diaphragm. The needle valve is on the side of the diaphragm exposed to high gas
pressure while the compression spring and adjusting screw are on the opposite side
in a zone vented to the atomsphere.
(2) The oxygen enters the regulator through the high pressure inlet connection and passes through a glass wool filter, which removes dust and dirt. The
seat, which closes off the nozzle, is not raised until the adjusting screw is
turned in. Pressure is applied to the adjusting spring by turning the adjusting
screw, which bears down on the rubber diaphragm. The diaphragm presses downward on
the stirrup and overcomes the pressure on the compensating spring. When the stirrup is forced downward, the passage through the nozzle is open. Oxygen is then
allowed to flow into the low pressure chamber of the regulator. The oxygen then
passes through the regulator outlet and the hose to the torch. A certain set pressure must be maintained in the low pressure chamber of the regulator so that oxygen
will continue to be forced through the orifices of the torch, even if the torch
needle valve is open. This pressure is indicated on the working pressure gage of
the regulator, and depends on the position of the regulator adjusting screw. Pressure is increased by turning the adjusting screw to the right and decreased by
turning this screw to the left.
(3) Regulators used at stations to which gases are piped from an oxygen manifold, acetylene manifold, or acetylene generator have only one low pressure gage
because the pipe line pressures are usually set at 15 psi (103.4 kPa) for acetylene
and approximately 200 psi (1379 kPa) for oxygen. The two stage oxygen regulator
(fig. 5–9) is similar in operation to the one stage regulator, but reduces pressure
in two steps. On the high pressure side, the pressure is reduced from cylinder
pressure to intermediate pressure. On the low pressure side the pressure is reduced from intermediate pressure to work pressure. Because of the two stage pressure control, the working pressure is held constant, and pressure adjustment during
welding operations is not required.
5-10
TC 9-237
e.
Acetylene Regulator.
CAUTION
Acetylene should never be used at pressures exceeding 15 psi (103.4
kPa).
This regulator controls the acetylene pressure from any standard commercial cylinder containing pressures up to 500 psi (3447.5 kPa). The acetylene regulator design is generally the same as that of the oxygen regulator, but will not withstand
such high pressures. The high pressure gage, on the inlet side of the regulator,
is graduated from O to 500 psi (3447.5 kPa). The low pressure gage, on the outlet
side of the regulator, is graduated from O to 30 psi (207 kPa). Acetylene should
not be used at pressures exceeding 15 psi (103.4 kPa).
5-9.
OXYACETYLENE WELDING TORCH
a. General. The oxyacetylene welding torch is used to mix oxygen and acetylene
in definite proportions. It also controls the volume of these gases burning at the
welding tip, which produces the required type of flame. The torch consists of a
handle or body which contains the hose connections for the oxygen and the fuel
gas. The torch also has two needle valves, one for adjusting the flew of oxygen
and one for acetylene, and a mixing head. In addition, there are two tubes, one
for oxygen, the other for acetylene; inlet nipples for the attachment of hoses; a
tip; and a handle. The tubes and handle are of seamless hard brass, copper-nickel
alloy, stainless steel. For a description and the different sized tips, see paragraph 5-10.
b. Types of Torches. There are two general types of welding torches; the low
pressure or injector type, and the equal pressure type.
5-11
TC 9-237
5-9.
OXYACETYLENE WELDING TORCH (cont)
(1) In the low pressure or injector type (fig. 5-10), the acetylene pressure
is less than 1 psi (6.895 kPa). A jet of high pressure oxygen is used to produce a
suction effect to draw in the required amount of acetylene. Any change in oxygen
flow will produce relative change in acetylene flow so that the proportion of the
two gases remains constant. This is accomplishd by designing the mixer in the
torch to operate on the injector principle. The welding tips may or may not have
separate injectors designed integrally with each tip.
(2) The equal pressure torch (fig. 5-11) is designed to operate with equal
pressures for the oxygen and acetylene. The pressure ranges from 1 to 15 psi
(6.895 to 103.4 kPa). This torch has certain advantages over the lo W pressure
type. It can be more readily adjusted, and since equal pressures are used for each
gas, the torch is less susceptible to flashbacks.
5-12
TC 9-237
5-10.
WELDING TIPS AND MIXERS
a. The welding tips (fig. 5-10 and 5-11) are made of hard drawn electrolytic
copper or 95 percent copper and 5 percent tellurium. They are made in various
styles and types, some having a one-piece tip either with a single orifice or a
number of orifices. The diameters of the tip orifices differ in order to control
the quantity of heat and the type of flame. These tip sizes are designated by
numbers which are arranged according to the individual manufacturer’s system.
Generally, the smaller the number, the smaller the tip orifice.
b. Mixers (fig. 5-10 and 5-11) are frequently provided in tip tier assemblies
which assure the correct flow of mixed gases for each size tip. In this tip mixer
assembly, the mixer is assembled with the tip for which it has been drilled and
then screwed onto the torch head. The universal type mixer is a separate unit
which can be used with tips of various sizes.
5-11. HOSE
a. The hoses used to make the connection betwen the regulators and the torch
are made especially for this purpose.
(1) Hoses are built to withstand high internal pressures.
(2) They are strong, nonporous, light, and flexible to permit easy manipulation of the torch.
(3) The rubber used in the manufacture of hose is chemically treated to remove free sulfur to avoid possible spontaneous combustion.
(4) The hose is not impaired by prolonged exposure to light.
CAUTION
Hose should never be used for one gas if it was previously used for
another .
b.
Hose identification and composition.
(1) In North America, the oxygen hose is green and the acetylene hose is
red. In Europe, blue is used for oxygen and orange for acetylene. Black is sometimes also used for oxygen.
(2) The hose is a rubber tube with braided or wrapped cotton or rayon reinforcements and a rubber covering. For heavy duty welding and cutting operations,
requiring 1/4- to l/2-in. internal diameter hose, three to five plies of braided or
wrapped reinforcements are used. One ply is used in the 1/8- to 3/16-in. hose for
light torches.
c . Hoses are provided with connections at each end so that they may be connected to their respective regulator outlet and torch inlet connections. To prevent a
dangerous interchange of acetylene and oxygen hoses, all threaded fittings used for
the acetylene hook up are left hand, and all threaded fittings for the oxygen hook
up are right hand. Notches are also placed on acetylene fittings to prevent a
mixup .
5-13
TC 9-237
5-11.
HOSE (cont)
d. Welding and cutting hoses are obtainable as a single hose for each gas or
with the hoses bonded together along their length under a common outer rubber jacke t . The latter type prevents the hose from kinking or becoming tangled during the
welding operation.
5-12. SETTING UP THE EQUIPMENT
WARNING
Always have suitable fire extinguishing equipment at hand when doing
any welding.
When setting up welding and cutting equipment, it is important that all operations
be performed systematically in order to avoid mistakes and possible trouble. The
setting up procedures given in a through d below will assure safety to the operator
and the apparatus.
a. Cylinders.
WARNING
Do not stand facing cylinder valve outlets of oxygen, acetulene, or
other compressed gases when opening them.
(1) Place the oxygen and the acetylene cylinders on a level floor (if they
are not mounted on a truck), and tie them firmly to a work bench, post, wall, or
other secure anchorage to prevent their being knocked or pulled over.
(2) Remove the valve protecting caps.
(3) “Crack” both cylinder valves by opening first the acetylene and then the
oxygen valve slightly for an instant to blow out any dirt or foreign matter that
may have accumulated during shipment or storage.
(4) Close the valves and wipe the connection seats with a clean cloth.
b.
Pressure Regulators.
(1) Check the regulator fittings for dirt and obstructions. Also check
threads of cylinders and regulators for imperfections.
(2) Connect the acetylene regulator to the acetylene regulator and the oxygen
regulator to the oxygen cylinder. Use either a regulator wrench or a close fitting
wrench and tighten the connecting nuts sufficiently to prevent leakage.
(3) Check hose for burns, nicks, and bad fittings.
(4) Connect the red hose to the acetylene regulator and the green hose to the
oxygen regulator. Screw the connecting nuts tightly to insure leakproof seating.
Note that the acetylene hose connection has left hand threads.
5-14
TC 9-237
WARNING
If it is necessary to blow out the acetylene hose, do it in a well
ventilated place which is free of sparks, flame, or other sources of
ignition.
(5) Release the regulator screws to avoid damage to the regulators and gages. Open the cylinder valves slowly. Read the high pressure gages to check the
cylinder gas pressure. Blow out the oxygen hose by turning the regulator screw in
and then release the regulator screw. Flashback suppressors must be attached to
the torch whenever possible.
c. Torch. Connect the red acetylene hose to the torch needle valve which is
stamped “AC or flashback suppressor”. Connect the green oxygen hose to the torch
needle valve which is stamped “OX or flashback suppressor”. Test all hose connec–
tions for leaks at the regulators and torch valves by turning both regulators’
screws in with the torch needle valves closed. Use a soap and water solution to
test for leaks at all connections. Tighten or replace connections where leaks are
found . Release the regulator screws after testing and drain both hose lines by
opening the torch needle valves. Slip the tip nut over the tip, and press the tip
into the mixing head. Tighten by hand and adjust the tip to the proper angle.
Secure this adjustment by tightening with the tip nut wrench.
WARNING
Purge both acetylene and oxygen lines (hoses) prior to igniting
torch. Failure to do this can cause serious injury to personnel and
damage to the equipment.
d. Adjustment of Working Pressure. Adjust the acetylene working pressure by
opening the acetylene needle valve on the torch and turnin g the regulator screw to
the right. Then adjust the acetylene regulator to the required pressure for the
tip size to be used (tables 5-1 and 5-2). Close the needle valve. Adjust the oxygen working pressure in the same manner.
5-15
TC 9-237
5-12.
SETTING UP THE WELDING EQUIPMENT (cont)
5-13.
SHUTTING DOWN WELDING APPARATUS
a. Shut off the gases. Close the acetylene valve first, then the oxygen valve
on the torch. Then close the acetylene and oxygen cylinder valves.
b.
Drain the regulators and hoses by the following procedures:
(1) Open the torch acetylene valve until the gas stops flowing and the gauges
read zero, then close the valve.
(2) Open the torch oxygen valve to drain the oxygen regulator and hose. When
gas stops flowing and the gauges read zero, close the valve.
(3) When the above operations are performed properly, both high and low pressure gauges on the acetylene and oxygen regulators will register zero.
c. Release the tension on both regulator screws by turning the screws to the
left until they rotate freely.
d. Coil the hoses without kinking them and suspend them on a suitable holder or
hanger. Avoid upsetting the cylinders to which they are attached.
5-14.
REGULATOR MALFUNCTIONS AND CORRECTIONS
a. Leakage of gas between the regulator seat and the nozzle is the principal
problem encounter with regulators. It is indicated by a gradual increase in
pressure on the working pressure gauge when the adjusting screw is fully released
or is in position after adjustment. This defect, called “creeping regulator”, is
caused by bad valve seats or by foreign matter lodged between the seat and the
nozzle.
5-16
TC 9-237
WARNING
Regulators with leakage of gas between the regulator seat and the
nozzle must be replaced immediately to avoid damage to other parts of
the regulator or injury to personnel. With acetylene regulators, this
leakage is particularity dangerous because acetylene at high pressure
in the hose is an explosion hazard.
b.
The leakage of gas, as described. above, can be corrected as outlined below:
(1) Remove and replace the seat if it is worn , cracked, or otherwise damaged.
(2) If the malfunction is caused by fouling with dirt or other foreign matter, clean the seat and nozzle thoroughly and blow out any dust or dirt in the
valve chamber.
c. The procedure for removing valve seats and nozzles will vary with the make
or design.
d. Broken or buckled gage tubes and distorted or buckled diaphragms are usually
caused by backfire at the torch, leaks across the regulator seats, or by failure to
release the regulator adjusting screw fully before opening the cylinder valves.
e. Defective bourdon tubes in the gages are indicated by improper action of the
gages or by escaping gas from the gage case. Gages with defective bourdon tubes
should be removed and replaced with new gages. Satisfactory repairs cannot be made
without special equipment.
f . Buckled or distorted diaphragms cannot be adjusted properly and should be
replaced with new ones. Rubber diaphragms can be replaced easily by removing the
spring case with a vise or wrench. Metal diaphragms are sometimes soldered to the
valve case and their replacement is a factory or special repair shop job. Such
repairs should not be attempted by anyone unfamiliar with the work.
5-15.
TORCH MALFUNCTIONS AND CORRECTIONS
WARNING
Defects in oxyacetylene welding torches which are sources of gas leaks
must be corrected immediately, as they may result in flashbacks or
backfires, with resultant injury to the operator and/or damage to the
welding apparatus.
a . General. Improved functioning of welding torches is usually due to one or
more of the following causes: leaking valves, leaks in the mixing head seat, scored
or out-of-round welding tip orifices, clogged tubes or tips, and damaged inlet
connection threads. Corrective measures for these common torch defects are described below.
b.
Leaking Valves.
(1) Bent or worn valve stems should be replaced and damaged seats should be
refaced.
5-17
TC 9-237
(2) Loose packing may be corrected by tightening the packing nut or by installing new packing and then tightening the packing nut.
CAUTION
This work should be done by the manufacturer because special reamers
are required for trueing these seats.
c. Leaks in the Mixing Heads. These are indicated by popping out of the flame
and by emission of sparks from the tips accompanied by a squealing noise. Leaks in
the mixing head will cause improper mixing of the oxygen and acetylene causing
flashbacks. A flashback causes the torch head and handle to suddenly become very
hot . Repair by reaming out and trueing the mixing head seat.
d. Scored or Out-of-Round Tip Orifices.
to be irregular and must be replaced.
e.
Tips in this condition cause the flame
Clogged Tubes and Tips.
(1) Carbon deposits caused by flashbacks or backfire, or the presence of
foreign matter that has entered the tubes through the hoses will clog tubes. If
the tubes or tips are clogged, greater working pressures will be needed to produce
the flame required. The flame produced will be distorted.
(2) The torch should be disassembled so that the tip, mixing head, valves,
and hose can be cleaned and cleaned out with compressed air at a pressure of 20 to 30
psi (137.9 to 206.85 kPa).
(3) The tip and mixing head should be cleaned either with a cleaning drill or
with soft copper or brass wire , and then blown out with compressed air. The cleaning drills should be approximately one drill size smaller than the tip orifice to
avoid enlarging the orifice during cleaning.
WARNING
Damages inlet connection threads may cause fires by ignition of the
leaking gas, resulting in injury to the welding operator and/or damage
to the equipment.
f . Damaged Inlet Connection Threads. Leaks due to damaged inlet connection
threads can be detected by opening the cylinder valves and keeping the needle
valves closed. Such leaks will cause the regulator pressure to drop. Also, if the
threads are damaged, the hose connection at the torch inlet will be difficult or
impossible to tighten. To correct this defect, the threads should be recut and the
hose connections thoroughly cleaned.
5-18
TC 9-237
Section II.
5-16.
OXYACETYLENE CUTTING EQUIPMENT
CUTTING TORCH AND OTHER CUTTING EQUIPMENT
a. The cutting torch (fig. 5-12), like the welding torch, has a tube for oxygen
and one for acetylene. In addition, there is a tube for high pressure oxygen,
along with a cutting tip or nozzle. The tip (fig. 5-13) is provided with a center
hole through which a jet of pure oxygen passes. Mixed oxygen and acetylene pass
through holes surrounding the center holes for the preheating flames. The number
of orifices for oxyacetlylene flames ranges from 2 to 6, depending on the purpose
for which the tip is used. The cutting torch is controlled by a trigger or lever
operated valve. The cutting torch is furnished with interchangeable tips for cutting steel from less than 1/4 in. (6.4 mm) to more than 12.0 in. (304.8 mm) in
thickness.
5-19
TC 9–237
5-16.
CUTTING TORCH AND OTHER CUTTING EQUIPMENT (cont)
b. A cutting attachment fitted to a welding torch in place of the welding tip
is shown in figure 5-14.
c. In order to make uniformly clean cuts on steel plate, motor driven cutting
machines are used to support and guide the cutting torch. Straight line cutting or
beveling is acccomplished by guiding the machine along a straight line on steel
tracks. Arcs and circles are cut by guiding the machine with a radius rod pivoted
about a central point. Typical cutting machines in operation are shown in figures
5-15 and 5-16.
5-20
TC 9-237
d. There is a wide variety of cutting tip styles and sizes available to suit
various types of work. The thickness of the material to be cut generally governs
the selection of the tip. The cutting oxygen pressure, cutting speed, and preheating intensity should be controlled to produce narrow, parallel sided kerfs. Cuts
that are improperly made will produce ragged, irregular edges with adhering slag at
the bottom of the plates. Table 5-3 identifies cutting tip numbers, gas pressures,
and hand-cutting speeds used for cutting mild steel up to 12 in. (304.8 mm) thick.
5-21
TC 9-237
5-17.
OPERATION OF CUTTING EQUIPMENT
Attach the required cutting tip to the torch and adjust the oxygen and acetylene pressures in accordance with table 5-3.
NOTE
The oxygen and acetylene gas pressure settings listed are only approximate. In actual use, pressures should be set to effect the best metal
cut .
b.
Adjust the preheating flame to neutral.
c. Hold the torch so that the cutting oxygen lever or trigger can be operated
with one hand. Use the other hand to steady and maintain the position of the torch
head to the work. Keep the flame at a 90 degree angle to work in the direction of
travel. The inner cones of the preheating flames should be about 1/16 in. (1.6 mm)
above the end of the line to be cut. Hold this position until the spot has been
raised to a bright red heat, and then slowly open the cutting oxygen valve.
d. If the cut has been started properly, a shower of sparks will fall from the
opposite side of the work. Move the torch at a speed which will allow the cut to
continue penetrating the work. A good cut will be clean and narrow.
e. When cutting billets, round bars, or heavy sections, time and gas are saved
if a burr is raised with a chisel at the point where the cut is to start. This
small portion will heat quickly and cutting will start immediately. A welding rod
can be used to start a cut on heavy sections. When used, it is called a starting
rod.
Section III.
ARC WELDING EQUIPMENT AND ACCESSORIES
5-18. GENERAL
In electric welding processes , an arc is produced between an electrode and the work
piece (base metal). The arc is formed by passing a current between the electrode
and the workpiece across the gap. The current melts the base metal and the electrode (if the electrode is a consumable type), creating a molten pool. On solidifying, the weld is formal. An alternate method employs a nonconsumable electrode,
such as a tungsten rod. In this case, the weld is formed by melting and solidifying the base metal at the joint. In some instances, additional metal is required,
and is added to the molten pool from a filler rod.
Electrical equipment required for arc welding depends on the source from which the
electric power is obtained. If the power is obtained from public utility lines,
one or more of the following devices are required: transformers (of which there
are several types), rectifiers, motor generators, and control equipment. If public
utility power is not available, portable generators driven by gasoline or diesel
engines are used.
5-22
TC 9-237
5-19.
DIRECT CURRENT ARC WELDING MACHINES
a. The direct current welding machine has a heavy duty direct current generator
5-17). The generators are made in six standardized ratings for general purposes as described below:
(1) The machines rated 150 and 200 amperes, 30 volts, are used for light
shielded metal-arc welding and for gas metal-arc welding. They are also used for
general purpose job shop work.
(2) The machines rated 200, 300, and 400 amperes, 40 volts, used for
general welding purposes by machine or manual application.
(3) Machines rated 600 amperes, 40 volts, are used for submerged arc welding
and for carbon-arc welding.
b. The electric motors must commonly used to drive the welding generators are
220/440 volts, 3 phase, 60 cycle. The gasoline and diesel engines should have a
rated horsepower in excess of the rated output of the generator. This will allow
for the rated overload capacity of the generator and for the power required to
operate the accessories of the engine. The simple equarion HP = 1.25P/746 can be
used; HP is the engine horsepower and P is the generator rating in watts. For
exapmle, a 20 horsepower engine would be used to drive a welding generator with a
rated 12 kilowatt output.
5-23
TC 9-237
5-19.
DIRECT CURRENT ARC WELDING MACHINES (cont)
c. In most direct current welding machines, the generator is of the variable
voltage type, and is arranged so that the voltage is automatically adjusted to the
demands of the arc. However, the voltage may be set manually with a rheostat.
d. The welding current amperage is also manually adjustable, and is set by
means of a selector switch or series of plug receptacles. In either case, the
desired amperage is obtained by tapping into the generator field coils. When both
voltage and amperage of the welding machine are adjustable, the machine is known as
dual control type. Welding machines are also manufactured in which current controls are maintained by movement of the brush assembly.
e. A direct current welding machine is described in TM 5-3431-221-15, and is
illustrated in figure 5-18.
f. A maintenance schedule should be set up to keep the welding machine in good
operating condition. The machine should be thoroughly inspected every 3 months and
blown free of dust with clean, dry, compressed air. At least once each year, the
contacts of the motor starter switches and the rheostat should be cleaned and replaced if necessary. Brushes should be inspected frequently to see if they are
making proper contact on the commutator, and that they move freely in the brush
holders. Clean and true the commutator with sandpaper or a commutator stone if it
is burned or roughened. Check the bearings twice a year. Remove all the old
grease and replace it with new grease.
5-24
TC 9-237
g. Direct current rectifier type welding machines have been designed with copper oxide, silicon, or selenium dry plates. These machines usually consist of a
transform to reduce the power line voltage to the required 220/440 volts, 3
phase, 60 cycle input current; a reactor for adjustment of the current; and a rectifier to change the alternating current to direct current. Sometimes another reactor is used to reduce ripple in the output current.
5-20.
ALTERNATING CURRENT ARC WELDING MACHINES
a. Most of the alternating current arc welding machines in use are of the single operator, static transformer type (fig. 5-19). For manual operation in industrial applications, machines having 200, 300, and 400 amphere ratings are the sizes
in general use. Machines with 150 ampere ratings are sometimes used in light industrial, garage and job shop welding.
b. The transformers are generally equipped with arc stabilizing capacitors.
Current control is provided in several ways. One such method is by means of an
adjustable reactor in the output circuit of the transformer. In other types, internal reactions of the transformer are adjustable. A handwheel, usually installed on
the front or the top of the machine, makes continuous adjustment of the output
current, without steps, possible.
c. The screws and bearings on machines with screw type adjustments should be
lubricated every 3 months. The same lubrication schedule applies to chain drives.
Contacts, switches, relays, and plug and jack connections should be inspected every
3 months and cleaned or replaced as required. The primary input current at no load
should be measured and checked once a year to ensure the power factor connecting
capacitors are working, and that input current is as specified on the nameplate or
in the manufacturer’s instruction book.
5-25
TC 9-237
5-21.
GAS TUNGSTEN-ARC WELDING (GTAW) EQUIPMENT (TIG)
a. General. In tungsten inert gas (TIG) welding, (also known as GTAW), an arc
is struck between a virtually nonconsumable tungsten electrode and the workpiece.
The heat of the arc causes the edges of the work to melt and flow together. Filler
rod is often required to fill the joint. During the welding operation, the weld
area is shielded from the atmosphere by a blanket of inert argon gas. A steady
stream of argon passes through the torch, which pushes the air away from the welding area and prevents oxidation of the electrode, weld puddle, and heat affected
zone.
b.
Equipment.
(1) The basic equipment requirements for manual TIG welding are shown in
figure 5-20. Equipment consists of the welding torch plus additional apparatus to
supply electrical power, shielding gas, and a water inlet and outlet. Also, personal protective equipment should be worn to protect the operator from the arc rays
during welding operations.
NOTE
Different types of TIG welding equipment are available through normal
supply channels. Water-cooled torches and air-cooled torches are both
available. Each type carries different amperage ratings. Consult the
appropriate manual covering the type torch used.
(2) Argon is supplied in steel cylinders containing approximately 330 cu ft
at a pressure to 2000 psi (13,790 kPa). A single or two stage regulator may be
used to control the gas flow. A specially designed regulator containing a
flowmeter, as shown in figure 5-21, may be used. The flowmeter provides better
adjustment via flow control than the single or two stage regulator and is calibrated in cubic feet per hour (cfh). The correct flow of argon to the torch is set by
turning the adjusting screw on the regulator. The rate of flow depends on the kind
and thickness of the metal to be welded.
5-26
TC 9-237
(3) Blanketing of the weld area is provided by a steady flow of argon gas
directed through the welding torch (fig. 5-22). Since argon is slightly more than
1-1/3 times as heavy as air, it pushes the lighter air molecules aside, effectively
preventing oxidation of the welding electrode, the molten weld puddle, and the heat
affected zone adjacent to the weld bead.
5-27
TC 9-237
5-21.
GAS TUNGSTEN-ARC WELDING (GTAW) EQUIPMENT (TIG) (cent)
(4) The tremendous heat of the arc and the high current often used usually
necessitate water cooling of the torch and power cable ( fig. 5-22). The cooling
water must be clean; otherwise, restricted or blocked passages may cause excessive
overheating and damage to the equipment. It is advisable to use a suitable water
strainer or filter at the water supply source. If a self-contained unit is used,
such as the one used in the field (surge tank) where the cooling water is recirculated through a pump, antifreeze is required if the unit is to be used outdoors
during the winter months or freezing weather. Some TIG welding torches require
less than 55 psi (379 kPa) water pressure and will require a water regulator of
some type. Check the operating manual for this information.
c.
Nomenclature of Torch (fig. 5-22).
(1) Cap. Prevents the escape of gas from the top of the torch and locks the
electrode in place.
(2) C o l l e t . Made of copper; the electrode fits inside and when the cap is
tightened, it squeezes against the electrode and leeks it in place.
(3) Gas orifice nut.
Allows the gas to escape.
(4) Gas nozzle. Directs the flew of shielding gas onto the weld puddle. Two
types of nozzles are used; the one for light duty welding is made of a ceramic
material, and the one for heavy duty welding is a copper water-cooled nozzle.
(5) Hoses. Three plastic hoses, connected inside the torch handle, carry
water, gas, and the electrode power cable.
5-22.
GAS METAL-ARC WELDING (GMAW) EQUIPMENT
a. General. GMAW is most commonly referred to as “MIG” welding, and the following text will use “MIG” or “MIG welding” when referring to GMAW. MIG welding is a
process in which a consumable, bare wire electrode is fed into a weld at a controlled rate of speed, while a blanket of inert argon gas shields the weld zone
from atmospheric contamination. In addition to the three basic types of metal
transfer which characterize the GMAW process, there are several variations
of significance.
(1) Pulsed spray welding. Pulsed spray welding is a variation of the MIG
welding process that is capable of all–position welding at higher energy levels
than short circuiting arc welding. The power source provides two current levels; a
steady “background” level, which is too low to produce spray transfer; and a
“pulsed peak” current, which is superimposed upon the background current at a regulated interval. The pulse peak is well above the transition current, and usually
one drop is transferred during each pulse. The combination of the two levels of
current produces a steady arc with axial spray transfer at effective welding currents below those required for conventional spray arc welding. Because the heat
input is lower, this variation in operation is capable of welding thinner sections
than are practical with the conventional spray transfer.
(2) Arc spot welding. Gas metal arc spot welding is a method of joining
similar to resistance spot welding and riveting. A variation of continuous gas
5-28
TC 9-237
metal arc welding, the process fuses two pieces of sheet metal together by penetrating entirely through one piece into the other. No joint preparation is required
other than cleaning of the overlap areas. The welding gun remains stationary while
a spot weld is being made. Mild steel, stainless steel, and aluminum are commonly
joined by this method.
(3) Electrog as welding. The electrogas (EG) variation of the MIG welding
process is a fully automatic, high deposition rate method for the welding of butt,
corner, and T-joints in the vertical position. The eletrogas variation essentially combines the mechanical features of electroslag welding (ESW) with the MIG welding process. Water-coded copper shoes span the gap between the pieces being welded to form a cavity for the molten metal. A carriage is mounted on a vertical
column; this combination provides both vertical and horizontal movement. Welding
head, controls, and electrode spools are mounted on the carriage. Both the carriage and the copper shoes move vertically upwards as welding progresses. The
welding head may also be oscillated to provide uniform distribution of heat and
filler metal. This method is capable of welding metal sections of from 1/2 in. (13
mm) to more than 2 in. (5.08 an) in thickness in a single pass. Deposition rates
of 35 to 46 lb (16 to 21 kg) per hour per electrode can be achieved.
b. MIG Equipment.
NOTE
Different types of MIG welding equipment are available through normal
supply channels. Manuals for each type must be consulted prior to
welding operations.
(1) The MIG welding unit is designed for manual welding with small diameter
wire electrodes, using a Spool-on-gun torch. The unit consists of a torch (fig.
5-23), a voltage control box, and a welding contractor (fig. 5-24). The torch
handle contains a complete motor and gear reduction unit that pulls the welding
wire electrode from a 4 in. (102 mm) diameter spool containing 1 lb (0.5 kg) of
wire electrode mounted in the rear of the torch.
5-29
TC 9-237
(2) Three basic sizes of wire electrode maybe used: 3/32 in. (2.38 mm),
3/64 in. (1.19 mm), and 1/16 in. (1.59 mm). Many types of metal may be welded
provided the welding wire electrode is of the same composition as the base metal.
(3) The unit is designed for use with an ac-dc conventional, constant-current
welding power supply. Gasoline engine-driven arc welding machines issued to field
units may be used as both a power source and a welding source.
c.
Nomenclature of Torch.
(1) Contact tube (fig. 5-23). This tube is made of copper and has a hole in
the center of the tube that is from 0.01 to 0.02 in. (0.25 to 0.51 mm) larger than
the size of the wire electrode being used. The contact tube and the inlet and
outlet guide bushings must be charged when the size of the wire electrode is
changed . The contact tube transfers power from the electrode cable to the welding
wire electrode. An insulated lock screw is provided which secures the contact tube
in the torch.
(2) Nozzle and holder (fig. 5-23). The nozzle is made of copper to dissipate
heat and is chrome-plated to reflect the heat. The holder is made of stainless
steel and is connected to an insulating material which prevents an arc from being
drawn between the nozzle and the ground in case the gun canes in contact with the
work.
(3) Inlet and outlet gu ide bushings (fig. 5-23). The bushings are made of
nylon for long wear. They must be changed to suit the wire electrode size when the
electrode wire is changed.
(4) Pressure roll assembly (fig. 5-23). This is a smooth roller, under
spring tension, which pushes the wire electrode against the feed roll and allows
the wire to be pulled from the spool. A thumbscrew applies tension as required.
(5) Motor (fig. 5-23). When the inch button is depressed, the current for
running the motor comes from the 110 V ac-dc source, and the rotor pulls the wire
electrode from the spool before starting the welding operation. When the trigger
is depressed, the actual welding operation starts and the motor pulls the electrode
from the spool at the required rate of feed. The current for this rotor is supplied by the welding generator.
(6) Spool enclosure assembly (fig. 5-23). This assembly is made of plastic
which prevents arc spatter from j amming the wire electrode on the spool. A small
window allows the operator to visually check the amount of wire electrode remaining
on the spool.
NOTE
If for any reason the wire electrode stops feeding, a burn-back will
result. With the trigger depressed, the welding contactor is closed,
thereby allowing the welding current to flow through the contact tube.
AS long as the wire electrode advances through the tube, an arc will be
drawn at the end of the wire electrode. Should the wire electrode stop
feeding while the trigger is still being depressed, the arc will then
form at the end of the contact tube, causing it to melt off. This is
called burn-back.
5-31
TC 9-237
5-21.
GAS TUNGSTEN-ARC WELDING (GTAW) EQUIPMENT (TIG) (cent)
(7) Welding contactor (fig. 5-24). The positive cable from the dc welding
generator is connected to a cable coming out of the welding contactor, and the
ground cable is connected to the workpiece. The electrode cable and the welding
contactor cable are connected between the welding contactor and voltage control box
as shown.
(8) Argon gas hose (fig. 5-24). This hose is connected from the voltage
control box to the argon gas regulator on the argon cylinder.
(9) Electrode cable (fig. 5-24). The electrode cable enters through the
welding current relay and connects into the argon supply line. Both then go out of
the voltage control box and into the torch in one line.
(10 ) Voltage pickup cable (fig. 5-24). This cable must be attached to the
ground cable at the workpiece. This supplies the current to the motor during welding when the trigger is depressed.
(11 ) Torch switch and grounding cables ( fig. 5-24). The torch switch cable is
connected into the voltage control box, and the torch grounding cable is connected
to the case of the voltage control box.
5-23.
OPERATING THE MIG
a.
Starting to Weld.
(1) Press the inch button and allow enough wire electrode to emerge from the
nozzle until 1/2 in. (13 mm) protrudes beyond the end of the nozzle. With the main
line switch “ON” and the argon gas and power sources adjusted properly, the operator may begin to weld.
(2) When welding in the open air, a protective shield must be installed to
prevent the argon gas from being blown away from the weld zone and allowing the
weld to become contaminate.
(3) Press the torch trigger. This sends current down the torch switch cable
and through the contactor cable, closing the contactor.
(4) When the contactor closes, the welding circuit from the generator to the
welding torch is completed.
(5) At the same time the contactor closes, the argon gas solenoid valve
opens, allowing a flow of argon gas to pass out of the nozzle to shield the weld
zone.
(6) Lower the welding helmet and touch the end of the wire electrode to the
workpiece. The gun is held at a 90 degree angle to the work but pointed at a 10
degree angle toward the line of travel.
CAUTION
To prevent overloading the torch motor when stopping the arc, release
the trigger; never snap the arc out by raising the torch without first
releasing the trigger.
5-32
TC 9-237
(7) Welding will continue as long as the arc is maintained and the trigger is
depressed.
b.
Setting the Wire Electrode Feed.
(1) A dial on the front of the voltage control box, labeled WELDING CONTROL,
is used to regulate the speed of the wire electrode feed.
(2) To increase the speed of the wire electrode being fed from the spool.
turn the dial counterclockwise. This decreases the amount of resistance across the
arc and allows the motor to turn faster. Turning the dial clockwise will increase
the amount of resistance, thereby decreasing the speed of the wire electrode being
fed from the spool.
(3) At the instant that the wire electrode touches the work, between 50 and
100 volts dc is generated. This voltage is picked up by the voltage pickup cable
and shunted back through the voltage control box into a resistor. There it is
reduced to the correct voltage (24 V dc) and sent to the torch motor.
c.
Fuses.
(1) Two 10-ampere fuses, located at the front of the voltage control box,
protect and control the electrical circuit within the voltage control box.
(2) A l-ampere fuse, located on the front of the voltage control box, protects and controls the torch motor.
d.
Installing the Wire Electrode.
(1) Open the spool enclosure cover assembly, brake, and pressure roll assembly (fig. 5-23) .
(2) Unroll and straighten 6 in. (152 mm) of wire electrode from the top of
the spool.
(3) Feed this straightened end of the wire electrode into the inlet and outlet bushings; then place spool onto the mounting shaft.
(4) Close the Pressure roller and secure it in place. Press the inch button.
feeding
the wire electrode until there is 1/2 in. (13 mm) protruding beyond the end
.
to the nozzle.
e.
Setting the Argon Gas Pressure.
(1) Flip the argon switch on the front of the voltage control panel to the
MANUAL position.
tor.
(2) Turn on the argon gas cylinder valve and set the pressure on the regula-
(3) When the proper pressure is set on the regulator, flip the argon switch
to the AUTOMATIC POSITION.
5-33
TC 9-237
5-23.
OPERATING THE MIG TORCH (cont)
(4) When in the MANUAL position, the argon gas continues to flow. When in
the AUTOMATIC position, the argon gas flows only when the torch trigger is depressed, and stops flowing when the torch trigger is released.
f. Generator Polarity. The generator is set on reverse polarity. When set on
straight polarity, the torch motor will run in reverse, withdrawing the wire electrode and causing a severe burn-back.
g. Reclaiming Burned-Back Contact Tubes. When the contact tubes are new, they
are 5-3/8 in. (137 mm) long. When burn-backs occur, a maximum of 3/8 in. (9.5 mm)
may be filed off. File a flat spot on top of the guide tube, place a drill pilot
on the contact tube, then drill out the contact tube. For a 3/64 in. (1.2 mm)
contact tube, use a No. 46 or 47 drill bit.
h.
Preventive Maintenance.
(1) Keep all weld spatter cleaned out of the inside of the torch. Welding in
the vertical or overhead positions will cause spatter to fall down inside the torch
nozzle holder and restrict the passage of the argon gas. Keep all hose connections
tight.
(2) To replace the feed roll, remove the nameplate on top of the torch, the
flathead screw and retainer from the feed roll mounting shaft, and the contact ring
and feed roll. Place a new feed roll on the feed roll mounting shaft, making certain that the pins protruding from the shaft engage the slots in the feed roll.
Reassemble the contact ring and nameplate.
5-24.
OTHER WELDING EQUIPMENT
a. Cables. Two welding cables of sufficient current carrying capacity with
heavy, tough, resilient rubber jackets are required. One of the cables should be
composed of fine copper strands to permit as much flexibility as the size of the
cable will allow. One end of the less flexible cable is attached to the ground lug
or positive side of the direct current welding machine; the other end to the work
table or other suitable ground. One end of the flexible cable is attached to the
electrode holder and the other end to the negative side of a direct current welding
machine for straight polarity. Most machines are equipped with a polarity switch
which is used to change the polarity without interchanging the welding cables at
the terminals of the machine. For those machines not equipped with polarity switches, for reverse polarity, the cables are reversed at the machine.
b. Electrode Holders. An electrode holder is an insulated clamping device for
holding the electrode during the welding operation. The design of the holder depends on the welding process for which it is used, as explained below.
(1) Metal-arc electrode holder. This is an insulated clamp in which a metal
electrode can be held at any desired angle. The jaws can be opened by means of a
lever held in place by a spring (fig. 5-25).
5-34
TC 9-237
(2) Atomic hydrogen torch. This electrode holder or torch consists of two
tubes in an insulated handle, through which both hydrogen gas and electric current
flow. The hydrogen is supplied to a tube in the rear of the handle from which it
is led into the two current carrying tubes by means of a manifold. One of the two
electrode holders is movable, and the gap between this and the other holder is
adjusted by means of a trigger on the handle fig. 5-26).
(3) Carbon-arc electrode holder. This holder is manufactured in three specific types. One type holds two electrodes and is similar in design to the atomic
hydrogen torch, but has no gas tubes; a second type is a single electrode holder
equipped with a heat shield; the third type is for high amperage welding and is
watercooled.
c.
Accessories.
(1) Chipping hammer and wire brush. A chipping hammer is required to loosen
scale, oxides and slag. A wire brush is used to clean each weld bead before further welding. Figure 5-27 shows a chipping hammer with an attachable wire brush.
5-35
TC 9-237
5-24.
OTHER WELDING EQUIPMENT (cont)
(2) Welding table. A welding table should be of all-steel construction. A
container for electrodes with an insulated hook to hold the electrode holder when
not in use should be provided. A typical design for a welding table is shown in
figure 5-28.
(3) Clamps and backup bars. Workpieces for welding should be clamped in
position with C-clamps or other clamp brackets. Blocks, strips, or bars of copper
or cast iron should be available for use as backup bars in welding light sheet
aluminum and in making certain types of joints. Carbon blocks, fire clay, or other
fire-resistant material should also be available. These materials are used to form
molds which hold molten metal within given limits when building up sections. A
mixture of water, glass, and fire clay or carbon powder can be used for making
molds .
d. Goggles. Goggles with green lenses shaped to cover the eye orbit should be
available to provide glare protection for personnel in and around the vicinity of
welding and cutting operations (other than the welder).
NOTE
These goggles should not be used in actual welding operations.
5-36
TC 9-237
5-25. ELECTRODES AND THEIR USE
a. General. When molten metal is exposed to air, it absorbs oxygen and nitrogen, and becomes brittle or is otherwise adversely affected. A slag cover is needed to protect molten or solidifying weld metal from the atmosphere. This cover can
be obtained from the electrode coating, which protects the metal from damage, stabilizes the arc, and improves the weld in the ways described below.
b. Types of Electrodes. The metal-arc electrodes may be grouped and classified
as bare electrodes, light coated electrodes, and shielding arc or heavy coated
electrodes. The type used depends on the specific properties required in the weld
deposited. These include corrosion resistance, ductility, high tensile strength,
the type of base metal to be welded; the position of the weld (i.e., flat, horizontal, vertical, or overhead); and the type of current and polarity required.
c. Classification of Electrodes. The American Welding Society’s classification
number series has been adopted by the welding industry. The electrode identification system for steel arc welding is set up as follows:
(1) E indicates electrode for arc welding.
(2) The first two (or three) digits indicate tensile strength (the resistance
of the material to forces trying to pull it apart) in thousands of pounds per
square inch of the deposited metal.
(3) The third (or fourth) digit indicates the position of the weld. 0 indicates the classification is not used; 1 is for all positions; 2 is for flat and
horizontal positions only; 3 is for flat position only.
(4) The fourth (or fifth) digit indicates the type of electrode coating and
the type of power supply used; alternating or direct current, straight or reverse
polarity.
(5) The types of coating, welding current, and polarity position designated
by the fourth (or fifth) identifying digit of the electrode classification are as
listed in table 5-4.
(6) The number E601O indicates an arc welding electrode with a minimum stress
relieved tensile strength of 60,000 psi; is used in all positions; and reverse
polarity direct current is required.
5-37
TC 9-237
5-25.
ELECTRODES AND THEIR USE (cont)
(3) The eletrode identification system for stainless steel arc welding is
set up as follows:
(a) E indicates electrode for arc welding.
(b) The first three digits indicated the American Iron and Steel Institute
type of stainless steel.
(c) The last two digits indicate the current and position used.
(d) The number E-308-16 by this system indicates stainless steel type 308;
used in all positions; with alternating or reverse polarity direct current.
d. Bare Electrodes. Bare electrodes are made of wire compositions required for
specific applications. These electrodes have no coatings other than those required
in wire drawing. These wire drawing coatings have some slight stabilizing effect
on the arc but are otherwise of no consequence. Bare electrodes are used for welding manganese steel and other purposes where a coated electrode is not required or
is undesirable. A diagram of the transfer of metal across the arc of a bare electrode is shown in figure 5-29.
e. Light Coated Electrodes.
(1) Light coated electrodes have a definite composition. A light coating has
been applied on the surface by washing, dipping, brushing, spraying, tumbling, or
wiping to improve the stability and characteristics of the arc stream. They are
listed under the E45 series in the electrode identification system.
(2) The coating generally serves the following functions:
phorus.
(a) It dissolves or reduces impurities such as oxides, sulfur, and phos-
(b) It changes the surface tension of the molten metal so that the globules
of metal leaving the end of the electrode are smaller and more frequent, making the
flow of molten metal more uniform.
(c) It increases the arc stability by introducing materials readily ionized
(i.e., changed into small particles with an electric charge) into the arc stream.
5-38
TC 9-237
(3) Some of the light coatings may produce a slag, but it is quite thin and
does not act in the same manner as the shielded arc electrode type slag. The arc
action obtained with light coated electrodes is shown in figure 5-30.
f. Shielded Arc or Heavy Coated Electrodes. Shielded arc or heavy coated electrodes have a definite composition on which a coating has been applied by dipping
or extrusion. The electrodes are manufactured in three general types: those with
cellulose coatings; those with mineral coatings; and those with coatings of combinations of mineral and cellulose. The cellulose coatings are composed of soluble
cotton or other forms of cellulose with small amounts of potassium, sodium, or
titanium, and in some cases added minerals. The mineral coatings consist of sodium
silicate, metallic oxides, clay, and other inorganic substances or combinations
thereof. Cellulose coated electrodes protect the molten metal with a gaseous zone
around the arc as well as slag deposit over the weld zone. The mineral coated
electrode forms a slag deposit only. The shielded arc or heavy coated electrodes
are used for welding steels, cast iron, and hard surfacing. The arc action obtained with the shielded arc or heavy coated electrode is shown in figure 5-31.
5-39
TC 9-237
5-25.
g.
ELECTRODES AND THEIR USE (cont)
Functions of Shielded Arc or Heavy Coated Electrodes.
(1) These electrodes produce a reducing gas shield around the arc which prevents atmospheric oxygen or nitrogen from contaminating the weld metal. The oxygen
would readily combine with the molten metal, removing alloying elements and causing
porosity. The nitrogen would cause brittleness, low ductility, and in some cases,
low strength and poor resistance to corrosion.
(2) The electrodes reduce impurities such as oxides, sulfur, and phosphorus
so that these impurities will not impair the weld deposit.
(3) They provide substances to the arc which increase its stability and eliminate wide fluctuations in the voltage so that the arc can be maintained without
excessive spattering.
(4) By reducing the attractive force between the molten metal and the end of
the electrode, or by reducing the surface tension of the molten metal, the vaporized and melted coating causes the molten metal at the end of the electrode to
break up into fine, small particles.
(5) The coatings contain silicates which will form a slag over the molten
weld and base metal. Since the slag solidifies at a relatively slow rate, it holds
the heat and allows the underlying metal to cool and slowly solidify. This slow
solidification of the metal eliminates the entrapment of gases within the weld and
permits solid impurities to float to the surface. Slow cooling also has an annealing effect on the weld deposit.
(6) The physical characteristics of the weld deposit are modified by incorporating alloying materials in the electrode coating. The fluxing action of the slag
will also produce weld metal of better quality and permit welding at higher speeds.
(7) The coating insulates the sides of the electrode so that the arc is concentrated into a confined area. This facilitates welding in a deep U or V groove.
(8) The coating produces a cup, cone, or sheath (fig. 5-31) at the tip of the
electrode which acts as a shield, concentrates and directs the arc, reduces heat
losses and increases the temperature at the end of the electrode.
h. Storing Electrodes. Electrodes must be kept dry. Moisture destroys the
desirable characteristics of the coating and may cause excessive spattering and
lead to the formation of cracks in the welded area. Electrodes exposed to damp air
for more than two or three hours 0 should be
dried by heating in a suitable oven
0
(fig. 5-32) for two hours at 500 F (260 C ) . After they have dried, they should
be stored in a moisture proof container. Bending the electrode can cause the coating to break loose from the core wire. Electrodes should not be used if the core
wire is exposed.
5-40
TC 9-237
i.
Tungsten Electrodes.
(1) Nonconsumable electrodes for gas tungsten-arc (TIG) welding are of three
types : pure tungsten, tungsten containing 1 or 2 percent thorium, and tungsten
containing 0.3 to 0.5 percent zirconium.
(2) Tungsten electrodes can be identified as to type by painted end marks as
follows.
(a) Green -- pure tungsten.
(b) Yellow -- 1 percent thorium.
(c) Red -- 2 percent thorium.
(d) Brown -- 0.3 to 0.5 percent zirconium.
(3) Pure tungsten (99. 5 percent tungsten) electrodes are generally used on
less critical welding operations than the tungstens which are alloyed. This type
of electrode has a relatively low current-carrying capacity and a low resistance to
contamination.
(4) Thoriated tungsten electrodes (1 or 2 percent thorium) are superior to
pure tungsten electrodes because of their higher electron output, better arc-starting and arc stability, high current-carrying capacity, longer life, and greater
resistance to contamination.
(5) Tungsten electrodes containing 0.3 to 0.5 percent zirconium generally
fall between pure tungsten electrodes and thoriated tungsten electrodes in terms of
performance. There is, however, some indication of better performance in certain
types of welding using ac power.
(6) Finer arc control can be obtained if the tungsten alloyed electrode is
ground to a point (fig. 5-33). When electrodes are not grounded, they must be
operated at maximum current density to obtain reasonable ar C stability. Tungsten
electrode points are difficult to maintain if standard direct current equipment is
used as a power source and touch-starting of the arc is standard practice. Maintenance of electrode shape and the reduction of tungsten inclusions in the weld can
best be accomplished by superimposing a high-frequency current on the regular welding current. Tungsten electrodes alloyed with thorium and zirconium retain their
shape longer when touch-starting is used.
5-41
TC 9-237
5-25.
ELECTRODES AND THEIR USE (cont)
(7) The electrode extension beyond the gas cup is determined by the type of
joint being welded. For example, an extension beyond the gas cup of 1/8 in.
(3.2 mm) might be used for butt joints in light gage material, while an extension
of approximately 1/4 to 1/2 in. (6.4 to 12.7 mm) might be necessary on some fillet
welds. The tungsten electrode of torch should be inclined slightly and the filler
metal added carefully to avoid contact with the tungsten. This will prevent contamination of the electrode. If contamination does occur, the electrode must be removed, reground, and replaced in the torch.
j . Direct Current Welding. In direct current welding, the welding current
circuit may be hooked up as either straight polarity (dcsp) or reverse polarity
(dcrp). The polarity recommended for use with a specific type of electrode is
established by the manufacturer.
(1) For dcsp, the welding machine connections are electrode negative and
workpiece positive (fig. 5-34); electron flow is from electrode to workpiece. For
dcrp, the welding machine connections are electrode positive and workpiece negative; electron flow is from workpiece to electrode.
5-42
TC 9-237
(2) For both current polarities, the greatest part of the heating effect occurs at the positive side of the arc. The workpiece is dcsp and the electrode is
dcrp. Thus, for any given welding current, dcrp requires a larger diameter electrode than does dcsp. For example, a l/16-in. (1.6-mm) diameter pure tungsten
electrode can handle 125 amperes of welding current under straight polarity conditions. If the polarity were reversed, however, this amount of current would melt
off the electrode and contaminate the weld metal. Hence, a 1/4-in. (6.4-mm) diameter pure tungsten electrode is required to handle 125 amperes dcrp satisfactorily
and safely. However, when heavy coated electrodes are used, the composition of the
coating and the gases it produces may alter the heat conditions. This will produce
greater heat on the negative side of the arc. One type of coating may provide the
most desirable heat balance with straight polarity, while another type of coating
on the same electrode may provide a more desirable heat balance with reverse polarity .
(3) The different heating effects influence not only the welding action, but
also the shape of the weld obtained. DCSP welding will produce a wide, relatively
shallow weld (fig. 5-35). DCRP welding, because of the larger electrode diameter
and lower currents generally employed, gives a narrow, deep weld.
(4) One other effect of dcrp welding is the so-called plate cleaning effect.
This surface cleaning action is caused either by the electrons leaving the plate or
by the impact of the gas ions striking the plate, which tends to break up the surface oxides, and dirt usually present.
(5) In general, straight polarity is used with all mild steel, bare, or light
coated electrodes. Reverse polarity is used in the welding of non-ferrous metals
such as aluminum, bronze, monel, and nickel. Reverse polarity is also used with
sane types of electrodes for making vertical and overhead welds.
(6) The proper polarity for a given electrode can be recognized by the sharp,
cracking sound of the arc. The wrong polarity will cause the arc to emit a hissing
sound, and the welding bead will be difficult to control.
5-43
TC 9-237
5-25.
ELECTRODES AND THEIR USE (cont)
k. Alternating Current Welding.
(1) Alternating current welding, theoretically, is a combination of dcsp and
dcrp welding. This can be best explained by showing the three current waves visually. As shown in figure 5-36, half of each complete alternating current (ac) cycle
is dcsp, the other half is dcrp.
(2) Moisture, oxides, scale, etc., on the surface of the plate tend, partial–
ly or completely, to prevent the flow of current in the reverse polarity direction. This is called rectification. For example, in no current at all flowed in
the reverse polarity direction, the current wave would be similar to figure 5-37.
Figure 5-37.
Rectified ac wave.
(3) To prevent rectification from occurring, it is common practice to introduce into the welding current an additional high-voltage, high-frequency, low-power
current. This high-frequency current jumps the gap between the electrode and the
workpiece and pierces the oxide film, thereby forming a path for the welding current to follow. Superimposing this high-voltage, high-frequency current on the
welding current gives the following advantages:
(a)
The arc may be started without touching the electrode to the workpiece.
(b)
Better arc stability is obtained.
(c) A longer arc is possible.
hardfacing operations.
(d)
This is particularly useful in surfacing and
Welding electrodes have longer life.
(e) The use of wider current range for a specific diameter electrode is
possible.
5-44
TC 9-237
(4) A typical weld contour produced with high-frequency stabilized ac is
shown in figure 5-38, together with both dcsp and dcrp welds for comparison.
1.
Direct Current Arc Welding Electrodes.
(1) The manufacturer’s recommendations should be followed when a specific
type of electrode is being used. In general, direct current shielded arc electrodes are designed either for reverse polarity (electrode positive) or for
straight polarity (electrode negative), or both. Many, but not all, of the direct
current electrodes can be used with alternating current. Direct current is preferred for many types of covered, nonferrous, bare and alloy steel electrodes.
Recommendations from the manufacturer also include the type of base metal for which
given electrodes are suited, corrections for poor fit-ups, and other specific conditions.
(2) In most cases, straight polarity electrodes will provide less penetration
than reverse polarity electrodes, and for this reason will permit greater welding
speed. Good penetration can be obtained from either with proper welding conditions and arc manipulation.
m.
Alternating Current Arc Welding Electrodes.
(1) Coated electrodes which can be used with either direct or alternating
current are available. Alternating current is more desirable while welding in restricted areas or when using the high currents required for thick sections because
it reduces arc blow. Arc blow causes blowholes, slag inclusions, and lack of fusion in the weld.
(2) Alternating current is used in atomic hydrogen welding and in those carbon arc processes that require the use of two carbon electrodes. It permits a
uniform rate of welding and electrode consumption. In carbon-arc processes where
one carbon electrode is used, direct current straight poarity is recommended,
because the electrode will be consumed at a lower rate.
n.
Electode Defects and Their Effects.
(1) If certain elements or oxides are present in electrode coatings, the arc
stability will be affected. In bare electrodes, the composition and uniformity of
the wire is an important factor in the control of arc stability. Thin or heavy
coatings on the electrodes will riot completely remove the effects of defective wire.
(2) Aluminum or aluminum oxide (even when present in quantities not exceeding
0.01 percent), silicon, silicon dioxide, and iron sulphate cause the arc to be
unstable. Iron oxide, manganese oxide, calcium oxide, and iron sulphate tend to
stabilize the arc.
5-45
TC 9-237
5-25.
ELECTRODES AND THEIR USE (cont)
(3) When phosphorus or sulfur are present in the electrode in excess of 0.04
percent, they will impair the weld metal because they are transferred from the electrode to the molten metal with very little loss. Phosphorus causes grain growth,
brittleness, and “cold shortness” (i.e., brittle when below red heat) in the weld.
These defects increase in magnitude as the carbon content of the steel increases.
Sulfur acts as a slag, breaks up the soundness of the weld metal, and causes “hot
shortness” (i.e., brittle when above red heat). Sulfur is particularly harmful to
bare, low-carbon steel electrodes with a low manganese content. Manganese promotes
the formation of sound welds.
(4) If the heat treatment, given the wire core of an electrode, is not uniform, the electrode will produce welds inferior to those produced with an electrode
of the same composition that has been properly heat treated.
Section IV.
5-26.
RESISTANCE WELDING EQUIPMENT
RESISTANCE WELDING
a. General. Resistance welding is a group of welding processes in which the
joining of metals is produced by the heat obtained from resistance of the work to
the electric current, in a circuit of which the work is a part, and by the application of pressure. The three factors involved in making a resistance weld are the
amount of current that passes through the work, the pressure that the electrodes
transfer to the work, and the time the current flows through the work. Heat is
generated by the passage of electrical current through a resistance current, with
the maximum heat being generated at the surfaces being joined. Pressure is required throughout the welding cycle to assure a continuous electrical circuit
through the work. The amount of current employed and the time period are related
to the heat input required to overcome heat losses and raise the temperature of the
metal to the welding temperature. The selection of resistance welding equipment is
usually determined by the joint design, construction materials, quality requirments, production schedules, and economic considerations. Standard resistance
welding machines are capable of welding a variety of alloys and component sizes.
There are seven major resistance welding processes: resistance projection welding,
resistance spot welding, resistance flash welding, resistance upset welding, resistance seam welding, resistance percussion welding, and resistance high frequency
welding.
b. Principal Elements of Resistance Welding Machines.
machine has three principal elements:
A resistance welding
(1) An electrical circuit with a welding transformer and a current regulator,
and a secondary circuit, including the electrodes which conduct the welding current
to the work.
(2) A mechanical system consisting of a machine frame and associated mechanisms to hold the work and apply the welding force.
(3) The control equipment (timing devices) to initiate the time and duration
of the current flow. This equipment may also control the current magnitude, as
well as the sequence and the time of other parts of the welding cycle.
5-46
TC 9-237
c. Electrical Operation. Resistance welds are made with either semiautomatic
or mechanized machines. With the semiautomatic machine, the welding operator positions the work between the electrodes and pushes a switch to initiate the weld; the
weld programmer completes the sequence. In a mechanized setup, parts are automatically fed into a machine, then welded and ejected without welding operator assistance. Resistance welding machines are classified according to their electrical
operation into two basic groups: direct energy and stored energy. Machines in
both groups may be designed to operate on either single-phase or three-phase power.
d.
Spot Welding.
(1) There are several types of spot welding machines, including rocker arm,
press, portable, and multiple type. A typical spot welding machine, with its essential operating elements for manual operation, is shown in figure 5-39. In these
machines, the electrode jaws are extended in such a manner as to permit a weld to
be made at a considerable distance f ran the edqe of the base metal sheet. The electrodes are composed of a copper alloy and are assembled in a manner by which considerable force or squeeze may be applied to the metal during the welding process.
r
5-47
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5-26.
RESISTANCE WELDING (cont)
(a) Rocker arm type. These machines consist essentially of a cylindrical
arm or extension of an arm which transmits the electrode force and in most cases,
the welding current. They are readily adaptable for spot welding of most weldable
metals. The travel path of the upper electrode is in an arc about the fulcrum of
the upper arm. The electrodes must be positioned so that both are in the plane of
the horn axes. Because of the radial motion of the upper electrode, these machines
are not recommended for projection welding.
(b) Press type. In this type of machine, the moveable welding head travels
in a straight line in guide bearings or ways. Press type machines are classified
according to their use and method of force application. They may be designed for
spot welding, projection welding, or both. Force may be applied by air or hydraulic cylinders, or manually with small bench units.
(c) Portable type. A typical portable spot welding machine consists of
four basic units: a portable welding gun or tool; a welding transformer and, in
some cases, a rectifier; an electrical contactor and sequence timer; and a cable
and hose unit to carry power and cooling water between the transformer and welding
gun. A typical portable welding gun consists of a frame, an air or hydraulic actuating cylinder, hand grips, and an initiating switch. The design of the gun is
tailored to the needs of the assembly to be welded.
(d) Multiple spot welding type. These are special-purpse machines designed to weld a specific assembly. They utilize a number of transformers. Force
is applied directly to the electrode through a holder by an air or hydraulic cylin–
der. For most applications, the lower electrode is made of a piece of solid copper
alloy with one or more electrode alloy inserts that contact the part to be welded.
Equalizing guns are often used where standard electrodes are needed on both sides
of the weld to obtain good heat balance, or where variations in parts will not permit consistent contact with a large, solid, lower electrode. The same basic welding gun is used for the designs, but it is mounted on a special “C” frame similar
to that for a portable spot welding gun. The entire assembly can move as electrode
force is applied to the weld location.
(2) When spot welding aluminum , conventional spot welding machines used to
weld sheet metal may be used. However, the best results are obtained only if certain refinements are incorporated into these machines. These features include the
following:
(a) Ability to handle high current for short welding times.
(b) Precise electronic control of current and length of time it is applied.
(c) Rapid follow up of the electrode force by employing anti-friction bearings and lightweight, low-inertia heads.
(d) High structural rigidity of the welding machine arms, holders, and
platens in order to minimize deflection under the high electrode forces used for
aluminum, and to reduce magnetic deflections, a variable or dual force cycle to
permit forging the weld nugget.
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TC 9-237
(e) Slope control to permit a gradual buildup and tapering off of the welding current.
(f) Postheat current to allow slower cooling of the weld.
ing .
(g) Good cooling of the Class I electrodes to prevent tip pickup or stickRefrigerated cooling is often helpful.
e. Projection Welding. The projection welding dies or electrodes have flat
surfaces with larger contacting areas than spot welding electrodes. The effectiveness of this type of welding depends on the uniformity of the projections or embossments on the base metal with which the electrodes are in contact (fig. 5-40). The
press type resistance welding machine is normally used for projection welding.
Flat nose or special electrodes are used.
f . Seam Welding. A seam welding machine is similar in principle to a spot
welding machine , except that wheel-shaped electrodes are used rather than the electrode tips used in spot welding. Several types of machines are used for seam welding, the type used depending on the sevice requirements. In some machines, the
work is held in a fixed position and a wheel type electrode is passed over it.
Portable seam welding machines use this principle. In the traveling fixture type
seam welding machine, the electrode is stationary and the work is moved. Seam
welding machine controls must provide an on-ff sequencing of weld current and a
control of wheel rotation. The components of a standard seam welding machine include a main frame that houses the welding transformer and tap switch; a welding
head consisting of an air cylinder, a ram, and an upper electrode mounting and
drive mechanism; the lower electrode mounting and drive mechanism, if used; the
secondary circuit connections; electronic controls and contactor; and wheel electrodes.
g. Upset and Flash Welding. Flash and upset welding machines are similar in
construct ion. The major difference is the motion of the movable platen during
welding and the mechanisms used to impart the motion. Flash weld-fig is generally
preferred for joining components of equal cross section end-to-end. Upset welding
is normally used to weld wire, rod, or bar of small cross section and to join the
seam continuously in pipe or tubing. Flash welding machines are generally of much
larger capacity than upset welding machines. However, both of these processes can
be performed on the same type of machine. The metals that are to be joined serve
as electrodes.
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5-26.
RESISTANCE WELDING (Cont)
(1) A standard flash welding machine consists of a main frame, stationary
platen, movable platen , clamping mechanisms and fixtures, a transformer, a tap
switch, electrical controls, and a flashing and upsetting mechanism. Electrodes
that hold the parts and conduct the welding current to them are mounted on the
platens.
(2) Upset welding machines consist of a main frame that houses a transform
and tap switch, electrodes to hold the parts and conduct the welding current, and
means to upset the joint. A primary contactor is used to control the welding current.
h. Percussion Welding. This process uses heat from an arc produced by a rapid
discharge of electrical energy to join metals. Pressure is applied progressively
during or immediately following the electrical discharge. The process is similar
to flash and upset welding. Two types of welding machines are used in percussion
welding: magnetic and capacitor discharge. A unit generally consists of a modified press-type resistance welding machine with specially designed transform,
controls, and tooling.
i . High Frequency Welding. This process joins metals with the heat generated
from the resistance of the work pieces to a high frequency alternating current in
the 10,000 to 500,000 hertz range, and the rapid application of an upsetting force
after heating is completed. The process is entirely automatic and utilizes equipment designed specifically for this process.
Section V.
5-27.
THERMIT WELDING EQUIPMENT
THERMIT WELDING (TW)
a. General. . Thermit material is a mechanical mixture of metallic aluminum and
processed iron oxide. Molten steel is produced by the thermit reaction in a
magnesite-lined crucible. At the bottom of the crucible, a magnesite stone is
burned, into which a magnesite stone thimble is fitted. This thimble provides a
passage through which the molten steel is discharged into the mold. The hole
through the thimble is plugged with a tapping pin, which is covered with a fireresistant washer and refractory sand. The crucible is charged by placing the correct quantity of thoroughly mixed thermit material in it. In preparing the joint
for thermit welding, the parts to be welded must be cleaned, alined, and held firmly in place. If necessary, metal is removed from the joint to permit a free flow
of the thermit metal into the joint. A wax pattern is then made around the joint
in the size and shape of the intended weld. A mold made of refractory sand is
built around the wax pattern and joint to hold the molten metal after it is
poured. The sand mold is then heated to melt out the wax and dry the mold. The
mold should be properly vented to permit the escape of gases and to allow the proper distribution of the thermit metal at the joint. A thermit welding crucible and
mold is shown in figure 5-41.
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Section VI.
FORGE WELDING TOOLS AND EQUIPMENT
5-28. FORGES
Forge welding is a form of hot pressure welding which joins metals by heating them
in an air forge or other furnace, and then applying pressure. The forge, which may
be either portable or stationary, is the most important component of forge welding.
equipment. The two types used in hand forge welding are described below.
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5-28.
FORGES (cont)
a. Portable Forge. The essential parts of a forge are a hearth, a tuyere, a
water tank, and a blower. One type of portable forge is shown in figure 5-42. The
tuyere is a valve mechanism designed to direct an air blast into the fire. It is
made of cast iron and consists of a fire pot, base with air inlet, blast valve, and
ash gate. The air blast passes through the base and is admitted to the fire
through the valve. The valve can be set in three different positions to regulate
the size and direction of the blast according to the fire required. The valve
handle is also used to free the valve from ashes. A portable forge may have a
handcrank blower, as shown in figure 5-42, or it may be equipped with an electric
blower. The blower produces air blast pressure of about 2 oz per sq in. A hood is
provided on the forge for carrying away smoke and fumes.
b. Stationary Forge. The stationary forge is similar to the portable forge
except that it is usually larger with larger air and exhaust connections. The
forge may have an individual blower or there may be a large capacity blower for a
group of forges. The air blast valve usually has three slots at the top, the positions of which can be controlled by turning the valve. The opening of these slots
can be varied to regulate the volume of the blast and the size of the fire. The
stationary forges, like portable forges, are available in both updraft and
downdraft types. In the updraft type, the smoke and gases pass up through the hood
and chimney by natural draft or are drawn off by an exhaust fan. In the downdraft
type, the smoke and fumes are drawn down under an adjustable hood and carried
through a duct by an exhaust fan that is entirely separate from the blower. The
downdraft forge permits better air circulation and shop ventilation, because the
removal of furies and smoke is positive.
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5-29.
a.
FORGING TOOLS
Anvil.
(1) The anvil (fig. 5-43) is usually made of two forgings or steel castings
welded together at the waist. The table or cutting block is soft so that cutters
and chisels caning in contact with it will not be dulled. The face is made of
hardened, tempered tool steel which is welded to the top of the anvil. It cannot
be easily damaged by hammering.
(2) The edges of an anvil are rounded for about 4.00 in. (102 mm) back from
the table to provide edges where stock can be bent without danger of cutting it.
All other edges are sharp and will cut stock when it is hammered against them. The
hardy hole is square and is designed to hold the hardy, bottom, swages, fullers,
and other special tools. The pritchel hole is round and permits slugs of metal to
pass through when holes are punched in the stock. The anvil is usually mounted on
a heavy block of wood, although steel pedestals or bolsters are sometimes used.
The height of the anvil should be adjusted so that the operator’s knuckles will
just touch its face when he stands erect with his arms hanging naturally.
(3) Anvils are designated by weight (i.e., No. 150 weighs 150 lb), and range
in size from No. 100 to No. 300.
b. Other Tools. In addition to the anvil, other tools such as hammers , sledges, tongs, fullers, flatters, chisels, swage blocks, punches, and a vise are used
in forging operations.
5-53/ (5-54 blank)
TC 9-237
CHAPTER 6
WELDING TECHNIQUES
Section I.
DESCRIPTION
6-1. GENERAL
The purpose of this chapter is to
processes. Welding processes may
methods and materials may be used
methods of welding used in modern
6-1.
outline the various techniques used in welding
be broken down into many categories. Various
to accomplish good welding practices. Common
metal fabrication and repair are shown in figure
6-1
TC 9-237
6-2.
ARC WELDING
The term arc welding applies to a large and varied group of processes that use an
electric arc as the source of heat to melt and join metals. In arc welding processes, the joining of metals, or weld, is produced by the extreme heat of an electric
arc drawn between an electrode and the workpiece, or between two electrodes. The
formation of a joint between metals being arc welded may or may not require the use
of pressure or filler metal. The arc is struck between the workpiece and an electrode that is mechanically or manually moved along the joint, or that remains stationary while the workpiece is roved underneath it. The electrode will be either a
consumable wire rod or a nonconsumable carbon or tungsten rod which carries the
current and sustains the electric arc between its tip and the workpiece. When a
nonconsumable electrode is used, a separate rod or wire can supply filler material,
if needed. A consumable electrode is specially prepared so that it not only conducts the current and sustains the arc, but also melts and supplies filler metal to
the joint, and may produce a slag covering as well.
a. Metal Electrodes. In bare metal-arc welding, the arc is drawn between a
bare or lightly coated consumable electrode and the workpiece. Filler metal is
obtained from the electrode, and neither shielding nor pressure is used. This type
of welding electrode is rarely used, however, because of its low strength, brittleness, and difficulty in controlling the arc.
(1) Stud welding. The stud welding process produces a joining of metals by
heating them with an arc drawn between a metal stud, or similar part, and the
workpiece. The molten surfaces to be joined, when properly heated, are forced
together under pressure. No shielding gas is used. The most common materials
welded with the arc stud weld process are low carbon steel, stainless steel, and
aluminum. Figure 6-2 shows a typical equipment setup for arc stud welding.
(2) Gas shielded stud welding. This process, a variation of stud welding, is
basically the same as that used for stud welding, except that an inert gas or flux,
such as argon or helium, is used for shielding. Shielding gases and fluxes are
6-2
TC 9-237
used when welding nonferrous metals such as aluminum and magnesium. Figure 6-3
shows a typical setup for gas shielded arc stud welding.
(3) Submerged arc welding. This process joins metals by heating them with an
arc maintained between a bare metal electrode and the workpiece. The arc is shielded by a blanket of granular fusible material and the workpiece. Pressure is not
used and filler metal is obtained from the electrode or from a supplementary welding rod. Submerged arc welding is distinguished from other arc welding processes
by the granular material that covers the welding area. This granular material is
called a flux, although it performs several other important functions. It is responsible for the high deposition rates and weld quality that characterize the
submerged arc welding process in joining and surfacing applications. Basically, in
submerged arc welding, the end of a continuous bare wire electrode is inserted into
a mound of flux that covers the area or joint to be welded. An arc is initiated,
causing the base metal, electrode, and flux in the immediate vicinity to melt. The
electrode is advanced in the direction of welding and mechanically fed into the
arc, while flux is steadily added. The melted base metal and filler metal flow
together to form a molten pool in the joint. At the same time, the melted flux
floats to the surface to form a protective slag cover. Figure 6-4 shows the submerged arc welding process.
6-3
TC 9-237
6-2.
ARC WELDING (cont )
(4) Gas tungsten-arc welding (TIG welding or GTAW). The arc is drawn between
a nonconsumable tungsten eletrode and the workpiece. Shielding is obtained from
an inert gas or gas mixture. Pressure and/or filler metal may or may not be used.
The arc fuses the metal being welded as well as filler metal, if used. The shield
gas protects the electrode and weld pool and provides the required arc characterist i c s . A variety of tungsten electrodes are used with the process. The electrode
is normally ground to a point or truncated cone configuration to minimize arc wandering. The operation of typical gas shielded arc welding machines may be found in
TM 5-3431-211-15 and TM 5-3431-313-15. Figure 6-5 shows the relative position of
the torch, arc, tungsten electrode, gas shield, and the welding rod (wire) as it is
being fed into the arc and weld pool.
(5) Gas metal-arc Welding (MIG welding or GMAW). In this process, coalescence is produced by heating metals with an arc between a continuous filler metal
(consumable) electrode and the workpiece. The arc, electrode tip and molten weld
metal are shielded from the atmosphere by a gas. Shielding is obtained entirely
from an externally supplied inert gas, gas mixture, or a mixture o f a g a s a n d a
flux. The electrode wire for MIG welding is continuously fed into the arc and
deposited as weld metal. Electrodes used for MIG welding are quite small in diameter compared to those used in other types of welding. Wire diameters 0.05 to 0.06
in. (0.13 to 0.15 cm) are average. Because of the small sizes of the electrode and
high currents used in MIG welding, the melting rates of the electrodes are very
high. Electrodes must always be provided as long, continuous strands of tempered
wire that can be fed continuously through the welding equipment. Since the small
electrodes have a high surface-to-volume ratio, they should be clean and free of
contaminants which may cause weld defects such as porosity and cracking. Figure
6-6 shows the gas metal arc welding process. All commercially important metals
such as carbon steel, stainless steel, aluminum, and copper can be welded with this
process in all positions by choosing the appropriate shielding gas, electrode, and
welding conditions.
6-4
TC 9-237
(6) Shielded metal-arc welding. The arc is drawn between a covered consumable metal electrode and workpiece. The electrode covering is a source of arc
stabilizers, gases to exclude air, metals to alloy the weld, and slags to support
and protect the weld. Shielding is obtained from the decomposition of the electrode covering. Pressure is not used and filler metal is obtained from the electrode. Shielded metal arc welding electrodes are available to weld carbon and low
alloy steels; stainless steels; cast iron; aluminum, copper, and nickel, and their
alloys. Figure 6-7 describes the shielded metal arc welding process.
(7) Atomic hydrogen welding. The arc is maintained between two metal electrodes in an atmosphere of hydrogen. Shielding is obtained from the hydrogen.
Pressure and/or filler metal may or may not be used. Although the process has
limited industrial use today, atomic hydrogen welding is used to weld hard-to-weld
metals, such as chrome, nickel, molybdenum steels, Inconel, Monel, and stainless
steel. Its main application is tool and die repair welding and for the manufacture
of steel alloy chain.
6-5
TC 9-237
6-2.
ARC WELDING (cont)
(8) Arc spot welding. An arc spot weld is a spot weld made by an arc welding
process. A weld is made in one spot by drawing the arc between the electrode and
workpiece. The weld is made without preparing a hole in either member. Filler
metal, shielding gas, or flux may or may not be used. Gas tungsten arc welding and
gas metal arc welding are the processes most commonly used to make arc spot welds.
However, flux-cored arc welding and shielded metal arc welding using covered electrodes can be used for making arc spot welds.
(9) Arc seam welding. A continuous weld is made along faying surfaces by
drawing the arc between an electrode and workpiece. Filler metal, shielding gas,
or flux may or may not be used.
b.
Carbon Electrode.
(1) Carbon-arc welding. In this process, the arc is drawn between an electrode and the workpiece. No shielding is USA. Pressure and/or filler metal may
or may not he used. Two types of electrodes are used for carbon arc welding: pure
qraphite and baked carbon. The pure graphite electrode does not erode away
as
quickly as the carbon electrode, but iS more expensive and more fragile.
(2) Twin carbon-arc welding. In this variation on carbon-arc welding, the
arc is drawn between two carbon electrodes. When the two carbon electrodes are
brought together, the arc is struck and established between them. The angle of the
electrodes provides an arc that forms in front of the apex angle and fans out as a
soft source of concentrated heat or arc flame, softer than a single carbon arc.
Shielding and pressure are not used. Filler metal may or may not be used. The
twin carbon-arc welding process can also be used for brazing.
(3) Gas-carbon arc welding. This process is also a variation of carbon arc
welding, except shielding by inert gas or gas mixture is used. The arc is drawn
between a carbon electrode and the workpiece. Shielding is obtained from an inert
gas or gas mixture. Pressure and/or filler metal may or may not be used.
(4) Shielded carbon-arc welding. In this carbon-arc variation, the arc is
drawn between a carbon electrode and the workpiece. Shielding is obtained from the
combustion of a solid material fed into the arc, or from a blanket of flux on the
arc, or both. Pressure and/or filler metal may or may not be used.
6-3.
GAS WELDING
Gas welding processes are a group of welding processes in which a weld is made by
heating with a gas flame or flares. Pressure and/or filler metal may or may not be
used. Also referred to as oxyfuel gas welding, the term gas welding is used to
describe any welding process that uses a fuel gas combined with oxygen, or in rare
cases, with air, to produce a flame having sufficient energy to melt the base meta l . The fuel gas and oxygen are mixed in the proper proportions in a chamber,
which is generally a part of the welding tip assembly. The torch is designed to
give the welder complete control of the welding flare, allowing the welder to regulate the melting of the base metal and the filler metal. The molten metal from the
plate edges and the filler metal intermix in a common molten pool and join upon
cooling to form one continuous piece. Manual welding methods are generally used.
6-6
TC 9-237
Acetylene was originally used as the fuel gas in oxyfuel gas welding, but other
gases, such as MAPP gas, have also been used. The flames must provide high localized energy to produce and sustain a molten pool. The flames can also supply a
protective reducing atmosphere over the molten metal pool which is maintained during welding. Hydrocarbon fuel gases such as propane, butane, and natural gas are
not suitable for welding ferrous materials because the heat output of the primary
flame is too low for concentrated heat transfer, or the flame atmosphere is too
oxidizing. Gas welding processes are outlined below.
a. Pressure Gas Welding. In this process, a weld is made simultaneously over
the entire area of abutting surfaces with gas flames obtained from the combustion
of a fuel gas with oxygen and the application of pressure. No filler metal is
used . Acetylene is normally used as a fuel gas in pressure gas welding. Pressure
gas welding has limited uses because of its low flame temperature, but is extensively used for welding lead.
b. Oxy-Hydrogen Welding. In this process, heat is obtained from the combustion
of hydrogen with oxygen. No pressure is used, and filler metal
may or may not be
used. Hydrogen has a maximum flame temperature of 4820 0F (2660 0C), but has limitd use in oxyfuel gas welding because of its colorless flare, which makes adjustment of the hydrogen-oxygen ratio difficult. This process is used primarily for
welding low melting point metals such as lead, light gage sections, and small parts.
c. Air-Acetylene Welding. In this process, heat is obtained from the combustion of acetylene with air. No pressure is used, and filler metal may or may not
be used. This process is used extensively for soldering and brazing of copper pipe.
d. Oxy-Acetylene Welding. In this process, heat is obtained from the combustion of acetylene with oxygen. Pressure and/or filler metal may or may not be
used . This process produces the hottest flame and is currently the most widely
used fuel for gas welding.
e. Gas Welding with MAPP Gas. Standard acetylene gages, torches, and welding
tips usually work well with MAPP gas. A neutral MAPP gas flame has a primary cone
about 1 1/2 to 2 times as long as the primary acetylene flare. A MAPP gas
carburizing flare will look similar to a carburizing acetylene flare, and the MAPP
gas oxidizing flame will look like the short, intense blue flare of the neutral
acetylene flame. The neutral MAPP gas flame is a very deep blue.
6-4.
BRAZING
Brazing is a group of welding processes in which materials are joined by heating to
a suitable
temperature
and by using a filler metal with a melting point above
0
0
840 F (449 C), but helm that of the base metal. The filler metal is distributed
to the closely fitted surfaces of the joint by capillary action. The various brazing processes are described below.
6-7
TC 9-237
6-4.
BRAZING (cont)
a. Torch Brazing (TB). Torch brazing is performed by heating the parts to be
brazed with an oxyfuel gas torch or torches. Depending upon the temperature and
the amount of heat required, the fuel gas may be burned with air, compressed air,
or oxygen. Brazing filler metal may be preplaced at the joint or fed from handheld filler metal. Cleaning and fluxing are necessary. Automated TB machines use
preplaced fluxes and preplaced filler metal in paste, wire, or shim form. For
manual torch brazing, the torch may be equipped with a single tip, either single or
multiple flame.
b. Twin Carbon-Arc Brazing. In this process, an arc is maintained between two
carbon electrodes to produce the heat necessary for welding.
c. Furnace Brazing. In this process, a furnace produces the heat necessary for
welding. In furnace brazing, the flame does not contact the workpiece. Furnace
brazing is used extensively where the parts to be brazed can be assembled with the
filler metal preplaced near or in the joint. Figure 6-8 illustrates a furnace
brazing operation.
d. Induction Brazing. In this process, the workpiece acts as a short circuit
in the flow of an induced high frequency electrical current. The heat is obtained
from the resistance of the workpiece to the current. Once heated in this manner,
brazing can begin. Three common sources of high frequency electric current used
for induction brazing are the motor-generator, resonant spark gap, and vacuum tube
oscillator. For induction brazing, the parts are placed in or near a water-cooled
coil carrying alternating current. Careful design of the joint and the coil are
required to assure the surfaces of all members of the joint reach the brazing temperature at the same time. Typical coil designs are shown in figure 6-9.
6-8
TC 9-237
e. Dip Brazing. There are two methods of dip brazing: chemcial bath and molten metal bath. In chemical bath dip brazing, the brazing f i l l e r m e t a l i s
preplaced and the assembly is immersed in a bath of molten salt, as shown in figure
6-10. The salt bath furnishes the heat necessary for brazing and usually provides
the necessary protection from oxidation. The salt bath is contained in a metal or
other suitable pot and heated. In molten metal bath dip brazing, the parts are
immersed in a bath of molten brazing filler metal contained in a suitable pot. A
cover of flux should be maintained over the molten bath to protect it from oxidation. Dip brazing is mainly used for joining small parts such as wires or narrow
strips of metal. The ends of wires or parts must be held firmly together when
removed from the bath until the brazing filler metal solidifies.
f . Resistance Brazing. The heat necessary for resistance brazing is obtained
from the resis tance to the flow of an electric current through the electrodes and
the joint to be brazed. The parts of the joint are a part of the electrical current. Brazing is done by the use of a low-voltage, high-current transformer. The
conductors or electrodes for this process are made of carbon, molybdenum, tungsten,
or steel. The parts to be brazed are held between two electrodes and the proper
pressure and current are applied. Pressure should be maintained until the joint
has solidified.
6-9
TC 9-237
6-4.
BRAZING (cont)
g. Block Brazing. In this process, heat is obtained from heated blocks applied
to the t o b e j o i n e d .
h. Flow Brazing. In flow brazing, heat is obtained from molten, nonferrous
f i l l e r metal poured over the joint until the brazing temperature is obtained.
i . Infrared Brazing (IRB). Infared brazing uses a high intensity quartz lamp
as a heat source. The process is suited to the brazing of very thin materials and
is normally not used on sheets thicker than 0.50 in. (1.27 cm). Assembies to be
brazed are supported in a position which enables radiant energy to be focused on
can be placed in an evacuated or controlled
the joint. The assembly and the lamps
atmosphere. Figure 6-11 illustrates t h e equipment used for infrared brazing.
j . Diffusion Brazing (DFB). Unlike all of the previous brazing processes,
diffusion brazing is not defined by its heat source, but by the mechanism involved. A joint is formed by holding the brazement at a suitable temperature for a
sufficient time to allow mutual diffusion of the base and filler metals. The joint
produced has a composition considerably different than either the filler metal or
base metal, and no filler metal should be discernible in the finished microstructure. The DFB process produces stronger joints than the normal brazed joint.
Also, the DFB joint remelts at temperatures approaching that of the base metal.
The typical thickness of the base metals that are diffusion brazed range from very
thin foil up to 1 to 2 in. (2.5 to 5.1 cm). Much heavier parts can also be
brazed since thickness has very little bearing on the process. Many parts that are
difficult to braze by other processes can be diffusion brazed. Both butt and lap
joints having superior mechanical properties can be produced, and the parts are
usually fixtured mechanically or tack welded together. Although DFB requires a
relatively long period of time (30 minutes to as long as 24 hours) to complete, it
can produce many parts at the same time at a reasonable cost. Furnances are most
frequently used for this method of processing.
6-10
TC 9-237
k.
Special Processes.
(1) Blanket brazing is another process used for brazing. A blanket is resistance heated, and most of the heat is transferred to the parts by conduction and
radiation. Radiation is responsible for the majority of the heat transfer.
(2) Exothemic brazing is another special process, by which the heat required
to melt and flow a commercial filler metal is generated by a solid state exothermic
chemical reaction. An exothermic chemical reaction is any reaction between two or
more reactants in which heat is given off due to the free energy of the system.
Exothermic brazing uses simple tooling and equipment. The process uses the reaction heat in bringing adjoining or nearby metal interfaces to a temperature where
preplaced brazing filler metal will melt and wet the metal interface surfaces. The
brazing filler metal can be a commercially available one having suitable melting
and flow temperatures. The only limitations may be the thickness of the metal that
must be heated through and the effects of this heat, or any previous heat treatment, on the metal properties.
6-5. RESISTANCE WELDING
Resistance welding consists of a group of processes in which the heat for welding
is generated by the resistance to the electrical current flow through the parts
being joined, using pressure. It is commonly used to weld two overlapping sheets
or plates which may have different thicknesses. A pair of electrodes conducts
electrical current through the sheets, forming a weld. The various resistance
processes are outlined below.
a. Resistance Spot Welding. In resistance spot welding, the size and shape of
the individually formed welds are limited primarily by the size and contour of the
electrodes. The welding current is concentrated at the point of joining using
cylindrical electrodes with spherical tips. The electrodes apply pressure.
b. Resistance Seam Welding. This weld is a series of overlapping spot welds
made progressively along a joint by rotating the circular electrodes. Such welds
are leaktight. A variation of this process is the roll spot weld, in which the
spot spacing is increased so that the spots do not-overlap and the weld is not
leaktight. In both processes, the electrodes apply pressure.
c. Projection Welding. These welds are localized at points predetermined by
the design of the parts to be welded. The localization is usually accomplished by
projections, embossments, or intersections. The electrodes apply pressure.
d. Flash Welding. In this process, heat is created at the joint by its resistance to the flow of the electric current, and the metal is heated above its melting point. Heat is also created by arcs at the interface. A force applied immediately following heating produces an expulsion of metal and the formation of a
flash. The weld is made simultaneously over the entire area of abutting surfaces
by the application of pressure after the heating is substantially completed.
6-11
TC 9-237
6-5.
RESISTANCE WELDING (cont)
e. Upset Welding. In this process, the weld is made either simultaneously over
the entire area of two abutting surfaces, or progressively along a joint. Heat for
welding is obtained from the resistance to the flow of electric current through the
metal at the joint. Force is applied to upset the joint and start a weld when the
metal reaches welding temperature. In some cases, force is applied before heating
starts to bring the faying surfaces in contact. Pressure is maintained throughout
the heating period.
f . Percussion Welding. This weld is made simultaneously over the entire area
of abutting surfaces by the heat obtained from an arc. The arc is produced by a
rapid discharge of electrical energy. It is extinguished by pressure applied percussively during the discharge.
g. High–Frequency Welding. High frequency welding includes those processes in
which the joining of metals is produced by the heat generated from the electrical
resistance of the workpiece to the flow of high-frequency current, with or without
the application of an upsetting force. The two processes that utilize high-frequency current to produce the heat for welding are high-frequency resistance welding
and high-frequency induction welding, sometimes called induction resistance welding. Almost all high-frequency welding techniques apply sane force to bring the
heated metals into close contact. During the application or force, an upset or
bulging of metal occurs in the weld area.
6-6.
THERMIT WELDING
a. Thermit welding (TW) is a process which joins metals by heating them with
superheated liquid metal from a chemical reaction between a metal oxide and aluminum or other reducing agent, with or without the application of pressure. F i l l e r
metal is obtained from the liquid metal.
b. The heat for welding is obtained from an exothermic reaction or chemical
change between iron oxide and aluminum. This reaction is shown by the following
formula:
0
0
The temperature resulting from this reaction is approximately 4500 F (2482 C).
c. The superheated steel is contained in a crucible located immediately above
the weld joint. The exothermic reaction is relatively slow and requires 20 to 30
seconds, regardless of the amount of chemicals involved. The parts to be welded
are alined with a gap between them. The superheated steel runs into a mold which
is built around the parts to be welded. Since it is almost twice as hot as the
melting temperature of the base metal, melting occurs at the edges of the joint and
alloys with the molten steel from the crucible. Normal heat losses cause the mass
of molten metal to solidify, coalescence occurs, and the weld is completed. If the
parts to be welded are large, preheating withtin the mold cavity may be necessary to
bring the pats to welding temperature and to dry out the mold. If the parts are
small, preheating is often eliminated. The thermit welding process is applied only
in the automatic mode. Once the reaction is started, it continues until completion.
6-12
TC 9-237
d. Themit welding utilizes gravity, which causes the molten metal to fill the
cavity between the parts being welded. It is very similar to the foundry practice
of pouring a casting. The difference is the extremely high temperature of the
molten metal. The making of a thermit weld is shown in figure 6-12. When the
filler metal has cooled, all unwanted excess metal may be removed by oxygen cutting, machining, or grinding. The surface of the completed weld is usually sufficiently smooth and contoured so that it does not require additional metal finishing. Information on thermit welding equipment may be found on p 5-50.
L
e. The amount of thermit is calculated to provide sufficient metal to produce
the weld. The amount of steel produced by the- reaction is approximately one-half
the original quantity of thermit material by weight and one-third by volume.
f . The deposited weld metal is homgenous and quality is relatively high.
Distortion is minimized since the weld is accomplished in one pass and since cooling is uniform across the entire weld cross section. There is normally shrinkage
across the joint, but little or no angular distortion.
g. Welds can be made with the parts to be joined in almost any position as long
as the cavity has vertical sides. If the cross-sectional area or thicknesses of
the parts to be joined are quite large, the primary problem is to provide sufficient thermit metal to fill the cavity.
h. Thermit welds can also be used for welding nonferrous materials. The most
popular uses of nonferrous thermit welding are the joining of copper and aluminum
conductors for the electrical industry. In these cases, the exothermic reaction is
a reduction of copper oxide by aluminum, which produces molten superheated copper.
The high-temperature molten copper flows into the mold, melts the ends of the parts
to be welded, and, as the metal cools, a solid homgenous weld results. In welding
copper and aluminum cables, the molds are made of graphite and can be used over and
over. When welding nonferrous materials, the parts to be joined must be extremely
clean. A flux is normally applied toc the joint prior to welding. Special kits are
available that provide the molds for different sizes of cable and the premixed
thermit material. This material also includes enough of the igniting material so
that the exothermic reaction is started by means of a special lighter.
6-13
TC 9-237
Section II.
NOMENCLATURE OF THE WELD
6-7. GENERAL
Common terms used to describe the various facets of the weld are explained in paragraphs 6-8 and 6-9 and are illustrated in figure 6-13.
6-14
TC 9-237
6-8.
SECTIONS OF A WELD
a. Fusion Zone (Filler Penetration). The fusion zone is the area of base metal
melted as determined in the cross section of a weld.
b. Leg of a Fillet Weld. The leg of a fillet weld is the distance from the
root of the joint to the toe of the fillet weld. There are two legs in a fillet
weld.
c. Root of the Weld. This is the point at which the bottom of the weld intersects the base metal surface, as shown in the cross section of a weld.
d.
Size of the Weld.
( 1 ) Equal leg-length fillet welds. The size of the weld is designated by the
leg-length of the largest isosceles right triangle that can be inscribed within the
fillet weld cross section.
(2) Unequal leg-length fillet welds. The size of the weld is designated by
the leg-length of the largest right triangle that can be inscribed within the fillet weld cross section.
of chamfering plus the
(3) Groove weld. The size of the weld is the depth
.
root penetration when specified.
e.
Throat of a Fillet Weld.
(1) Theoretical throat. This is the perpendicular distance between the root
of the-weld and the hypotenuse of the largest right triangle that can be inscribed
within tie fillet weld cross section.
(2) Actual throat. This is the distance from the root of a fillet weld to
the center of its face.
f . Face of the Weld. This is the exposed surface of the weld, made by an arc
or gas welding process, on the side from which the welding was done.
g. Toe of the Weld.
base metal.
This is the junction between the face of the weld and the
h. Reinforcement of the Weld. This is the weld metal on the face of a groove
weld in excess of the metal necessary for the specified weld size.
6-15
TC 9-237
6-9.
MULTIPASS WELDS
a. The nomenclature of the weld, the zones affected by the welding heat when a
butt weld is made by more than one pass or layer, and the nomenclature applying to
the grooves used in butt welding are shown in figure 6-14. Figure 6-15 is based on
weld type and position.
b. The primary heat zone is the area fused or affected by heat in the first
pass or application of weld metal. The secondary heat zone is the area affected in
the second pass and overlaps the primary heat zone. The portion of base metal that
hardens or changes its properties as a result of the welding heat in the primary
zone is partly annealed or softened by the welding heat in the secondary zone. The
weld metal in the first layer is also refined in structure by the welding heat of
the second layer. The two heating conditions are important in determin ing the
order or sequence in depositing weld metal in a particular joint design.
6-16
TC 9-237
6-17
.
TC 9-237
Section III.
TYPES OF WELDS AND WELDED JOINTS
6-10. GENERAL
a. Welding is a materials joining process used in making welds. A weld is a
localized coalescence of metals or nonmetals produced either by heating the materials to a suitable temperate with or without the application of pressure, or by
the application of pressure alone, with or without the use of filler metal. C o a l e s cence is a growing together or a growing into one body, and is used in all of the
welding process definitions. A weldment is an assembly of component parts joined
by welding, which can be made of many or few metal parts. A weldment may contain
metals of different compositions, and the pieces may be in the form of rolled
shapes, sheet, plate, pipe, forgings, or castings. To produce a usable structure
or weldnent, there must be weld joints between the various pieces that make the
weldment. The joint is the junction of members or the edges of members which are
to be joined or have been joined. Filler metal is the material to be added in
making a welded, brazed, or soldered joint. Base metal is the material to be welded, soldered, or cut.
b. The properties of a welded joint depend partly on the correct preparation of
the edges being welded. All mill scale, rust, oxides, and other impurities must be
removed from the joint edges or surfaces to prevent their inclusion in the weld
metal. The edges should be prepared to permit fusion without excessive melting.
Care must be taken to keep heat loss due to radiation into the base metal from the
weld to a minimum. A properly prepared joint will keep both expansion on heating
and contraction on coaling to a minimum.
c. Preparation of the metal for welding depends upon the form, thickness, and
kind of metal, the load the weld will be required to support, and the available
means for preparing the edges to be joined.
d. There are five basic types of joints for bringing two members together for
welding. These joint types or designs are also used by other skilled trades. The
five basic types of joints are described below and shown in figure 6-16.
(1) B, Butt joint - parts in approximately the same plane.
(2) C, Corner joint - parts at approximately right angles and at the edge of
both parts.
(3) E, Edge joint - a n e d g e o f t w o o r m o r e p a r a l l e l p a r t s .
(4) L, Lap joint - between overlapping parts.
part.
6-20
(5) T, T joint - parts at approximately right angles, not at the edge of one
TC 9-237
6-11.
BUTT JOINT
a. This type of joint is used to join the edges of two plates or surfaces located in approximately the same plane. Plane square butt joints in light sections are
shown in figure 6-17. Grooved butt joints for heavy sections with several types of
edge preparation are shown in figure 6-18. These edges can be prepared by flame
cutting, shearing, flame grooving, machining, chipping, or carbon arc air cutting
or gouging. The edge surfaces in each case must be free of oxides, scales, dirt,
grease, or other foreign matter.
6-21
TC 9-237
6-11.
BUTT JOINT (cont)
b. The square butt joints shown in figure 6-16 are used for butt welding light
sheet metal. Plate thicknesses 3/8 to 1/2 in. (0.95 to 1.27 an) can be welded
using the single V or single U joints as shown in views A and C, figure 6-18,
p. 6-21. The edges of heavier sections (1/2 to 2 in. (1.27 to 5.08 an)) are prepared as shown in view B, figure 6-18, p 6-21. Thicknesses of 3/4 in. (1.91 cm)
and up are prepared as shown in view D, figure 6-18, p 6-21. The edges of heavier
sections should be prepared as shown in views B and D, figure 6-18, p 6-21. The
single U groove (view C, fig. 6-18, p 6-21) is more satisfactory and requires less
filler metal than the single V groove when welding heavy sections and when welding
in deep grooves. The double V groove joint requires approximately one-half the
amount of filler metal used to produce the single V groove joint for the same plate
thickness. In general, butt joints prepared from both sides permit easier welding,
produce less distortion, and insure better weld metal qualities in heavy sections
than joints prepared from one side only.
6-12.
CORNER JOINT
a. The common corner joints are classified as flush or closed, half open, and
full open.
b. This type of joint is used to join two members located at approximately
right angles to each other in the form of an L. The fillet weld corner joint (view
A, fig. 6-19) is used in the construction of boxes, box frames, tanks, and similar
fabrications.
c. The closed corner joint (view B, fig. 6-19) is used on light sheet metal,
usually 20 gage or less, and on lighter sheets when high strength is not required
at the joint. In making the joint by oxyacetylene welding, the overlapping edge is
melted dawn, and little or no filler metal is added. In arc welding, only a very
light bead is required to make the joint. When the closed joint is used for heavy
sections, the lapped plate is V beveled or U grooved to permit penetration to the
root of the j o i n t .
d. Half open comer joints are suitable for material 12 gage and heavier. This
joint is used when welding can only be performed on one side and when loads will
not be severe.
e. The open corner joint (view C, fig. 6-19) is used on heavier sheets and
plates. The two edges are melted down and filler metal is added to fill up the
corner. This type of joint is the strongest of the corner joints.
f . Corner joints on heavy plates are welded from both sides as shown in view D,
figure 6-19. The joint is first welded from the outside, then reinforced from the
back side with a seal bead.
6-22
TC 9-237
6-13.
EDGE JOINT
This type of joint is used to join two or more parallel or nearly parallel
members. It is not very strong and is used to join edges of sheet metal, reinforcing plates in flanges of I beams, edges of angles, mufflers, tanks for liquids,
housing, etc. Two parallel plates are joined together as shown in view A, figure 6-20.
On heavy plates, sufficient filler metal is added to fuse or melt each plate
edge completely and to reinforce the joint.
b. Light sheets are welded as shown in view B, figure 6-20. No preparation is
necessary other than to clean the edges and tack weld them in position. The edges
are fused together so no filler metal is required. The heavy plate joint as shown
in view C, figure 6-20, requires that the edges be beveled in order to secure good
penetration and fusion of the side walls. Filler metal is used in this joint.
6-14.
LAP JOINT
This type of joint is used to join two overlapping members. A single lap joint
where welding must be done from one side is shown in view A, figure 6-21. The
double lap joint is welded on both sides and develops the full strength of the
welded members (view B, fig. 6-21). An offset lap joint (view C, fig. 6-21) is
used where two overlapping plates must be joined and welded in the same plane.
This type of joint is stronger than the single lap type, but is more difficult to
prepare.
6-23
TC 9-237
6-15.
TEE JOINT
a. Tee joints are used to weld two plates or sections with surfaces located
approximately 90 degrees to each other at the joint, but the surface of one plate
or section is not in the same plane as the end of the other surface. A plain tee
joint welded from both sides is shown in view B, figure 6-22. The included angle
of bevel in the preparation of tee joints is approximately half that required for
butt joints.
b . Other edge preparations used in tee joints are shown in figure 6-23. A
plain tee joint, which requires no preparation other than cleaning the end of the
vertical plate and the surface of the horizontal plate, is shown in view A, figure
6-23. The single beveled joint (view B, fig. 6-23) is used in plates and sections
Up to 1/2 in. (1.27 cm) thick. The double beveled joint (view C, fig. 6-23) is
used on heavy plates that can be welded from both sides. The single J joint (view)
D, fig. 6-23) is used for welding plates 1 in. thick or heavier where welding is
done from one side. The double J joint (view E, fig. 6-23) is used for welding
very heavy plates from both sides.
6-24
TC 9-237
c. Care must be taken to insure penetration into the root of the weld. This
penetration is promoted by root openings between the ends of the vertical members
and the horizontal surfaces.
6-16.
TYPES OF WELDS
a. General. It is important to distinguish between the joint and the weld.
Each must be described to completely describe the weld joint. There are many different types of welds, which are best described by their shape when shown in cross
section. The most popular weld is the fillet weld, named after its cross-sectional
shape. Fillet welds are shown by figure 6-24. The second nest popular is the
groove weld. There are seven basic types of groove welds, which are shown in figure 6-25. Other types of welds include flange welds, plug welds, slot welds, seam
welds, surfacing welds, and backing welds. Joints are combined with welds to make
weld joints. Examples are shown in figure 6-26, p 6-26. The type of weld used
will determine the manner in which the seam, joint, or surface is prepared.
6-25
TC 9-237
6-16.
TYPES OF WELDS (cont)
b. Groove Weld. These are beads deposited in a groove between two members to
be joined. See figure 6-27 for the standard types of groove welds.
6-26
TC 9-237
6-27
TC 9-237
6-16.
TYPES OF WELDS (cont)
c. Surfacing weld (fig. 6-28). These are welds composed of one or more strings
or weave beads deposited on an unbroken surface to obtain desired properties or
dimensions. This type of weld is used to build up surfaces or replace metal on
worn surfaces. It is also used with square butt joints.
d. Plug Weld (fig. 6-28). Plug welds are circular welds made through one member of a lap or tee joint joining that member to the other. The weld may or may
not be made through a hole in the first member; if a hole is used, the walls may or
may not be parallel and the hole may be partially or completely filled with weld
metal. Such welds are often used in place of rivets.
NOTE
A fillet welded hole or a spot weld does not conform to this definition.
e. Slot Weld (fig. 6-28). This is a weld made in an elongated hole in one
member of a lap or tee joint joining that member to the surface of the other member
that is exposed through the hole. This hole may be open at one end and may be
partially or completely filled with weld metal.
NOTE
A fillet welded slot does not conform to this definition.
f . Fillet Weld (top, fig. 6-28). This is a weld of approximately triangular
cross section joining two surfaces at approximately right angles to each other, as
in a lap or tee joint.
6-28
TC
g.
Flash Weld (fig. 6-29).
9-237
A weld made by flash welding (p 6-11).
h. Seam Weld (fig. 6-29). A weld made by arc seam or resistance seam welding
(p 6-11). Where the welding process is not specified, this term infers resistance
seam welding.
i. Spot Weld (fig. 6-29). A weld made by arc spot or resistance spot welding
(p 6-11). Where the welding process is not specified, this term infers a resistance spot weld.
j.
Upset Weld (fig. 6-29).
A weld made by upset welding (para 6-12).
6-29
TC 9-237
Section IV.
WELDING POSITIONS
6-17. GENERAL
Welding is often done on structures in the position in which they are found. Techniques have been developed to allow welding in any position. Sane welding processes have all-position capabilities, while others may be used in only one or two
positions. All welding can be classified according to the position of the
workpiece or the position of the welded joint on the plates or sections being welded. There are four basic welding positions, which are illustrated in figures 6-30
and 6-31. Pipe welding positions are shown in figure 6-32. Fillet, groove, and
surface welds may be made in all of the following positions.
6-30
TC 9-237
6-18.
FLAT POSITION WELDING
In this position, the welding is performed from the upper side of the joint, and
the face of the weld is approximately horizontal. Flat welding is the preferred
term; however, the same position is sometimes called downhand. (See view A, figure
6-30 and view A, figure 6-31 for examples of flat position welding for fillet and
groove welds).
6-31
TC 9-237
6-19.
HORIZONTAL POSITION WELDING
NOTE
The axis of a weld is a line through the length of the weld, perpendicu–
lar to the cross section at its center of gravity.
a. Fillet Weld. In this position, welding is performed on the upper side
of an approximately horizontal surface and against an approximately vertical
surface. View B, figure 6-31, p 6-30 illustrates a horizontal fillet weld.
b. Groove Weld. In this position, the axis of the weld lies in an approximately horizontal plane and the face of the weld lies in an approximately
vertical plane. View B, figure 6-30, p 6-30 illustrates a horizontal groove
weld.
c . Horizontal Fixed Weld. In this pipe welding position, the axis of the
pipe is approximately horizontal, and the pipe is not rotated during welding.
Pipe welding positions are shown in figure 6-32, p 6-31.
d. Horizontal Rolled Weld. In this pipe welding position, welding is
performed in the flat position by rotating the pipe. Pipe welding positions
are shown in figure 6-32, p 6-31.
6-20.
VERTICAL POSITION WELDING
a. In this position, the axis of the weld is approximately vertical.
Vertical welding positions are shown in view C, figures 6-30 and 6-31, p 6-30.
b. In vertical position pipe welding, the axis of the pipe is vertical,
and the welding is performed in the horizontal position. The pipe may or may
not be rotated. Pipe welding positions are shown in figure 6-32, p 6-31.
6-21.
OVERHEAD POSITION WELDING
In this welding position, the welding is performed from the underside of a
joint. Overhead position welds are illustrated in view D, figures 6-30 and
6-31, p 6-30.
6-22.
POSITIONS FOR PIPE WELDING
Pipe welds are made under many different requirements and in different welding
situations. The welding position is dictated by the job. In general, the
position is fixed, but in sane cases can be rolled for flat-position work.
Positions and procedures for welding pipe are outlined below.
(1) Align the joint and tack weld or hold in position with steel bridge
clamps with the pipe mounted on suitable rollers (fig. 6-33). Start welding at
point C, figure 6-33, progressing upward to point B. When point B is reached,
rotate the pipe clockwise until the stopping point of the weld is at point C and
again weld upward to point B. When the pipe is being rotated, the torch should be
held between points B and C and the pipe rotated past it.
6-32
TC 9-237
(2) The position of the torch at point A (fig. 6-33) is similar to that for a
vertical weld. As point B is approached, the weld assumes a nearly flat position
and the angles of application of the torch and rod are altered slightly to compensate for this change.
(3) The weld should be stopped just before the root of the starting point so
that a small opening remains. The starting point is then reheated, so that the
area surrounding the junction point is at a uniform temperature. This will insure
a complete fusion of the advancing weld with the starting point.
(4) If the side wall of the pipe is more than 1/4 in. (0.64 cm) in thickness,
a multipass weld should be made.
b.
Horizontal Pipe Fixed Position Weld.
(1) After tack welding, the pipe is set up so that the tack welds are oriented approximately as shown in figure 6-34. After welding has been started, the pipe
must not be moved in any direction.
6-33
TC 9-237
6-22.
POSITIONS FOR PIPE WELDING (cont)
(2) When welding in the horizontal fixed position, the pipe is welded in four
steps as described below.
Step 1. Starting at the bottom or 6 o'clock position, weld upward to the
3 o’clock position.
tion.
Step 2.
Starting back at the bottom, weld upward to the 9 o'clock posi-
Step 3.
Starting back at the 3 o’clock position,
weld to the top.
Step 4. Starting back at the 9 o’clock position, weld upward to the top.
overlapping the bead.
(3) When welding downward, the weld is made in two stages. Start at the top
(fig. 6-35) and work down one side (1, fig. 6-35) to the bottom, then return to the
top and work down the other side (2, fig. 6-35) to join with the previous weld at
the bottom. The welding downward method is particularly effective with arc welding, since the higher temperature of the electric arc makes possible the use of
greater welding speeds. With arc welding, the speed is approximately
three times
that of the upward welding method.
(4) Welding by the backhand method is used for joints in lo W carbon or loW
alloy steel piping that can be rolled or are in horizontal position. One pass is
used for wall thicknesses not exceeding 3/8 in. (0.95 cm), two passes for wall
thicknesses 3/8 to 5/8 in. (0.95 to 1.59 cm), three passes for wall thicknesses 5/8
to 7/8 in. (1.59 to 2.22 cm), and four passes for wall thicknesses 7/8 to 1-1/8 in.
(2.22 to 2.87 cm).
c. Vertical Pipe Fixed Position Weld. Pipe in this position, wherein the joint
is horizontal, is most frequently welded by the backhand method (fig. 6-36). The
weld is started at the tack and carried continuously around the pipe.
6-34
TC 9-237
d. Multipass Arc Welding.
(l) Root beads. If a lineup clamp is used, the root bead (view A, fig. 6-37)
is started at the bottom of the groove while the clamp is in position. W h e n n o
backing ring is used, care should be taken to build up a slight bead on the inside
of the pipe. If a backing ring is used, the root bead should be carefully fused to
i t . As much root bead as the bars of the lineup clamp will permit should be applied before the clamp is removed. Complete the bead after the clamp is removed.
(2) Filler beads. Care should be taken that the filler beads (view B, fig. 6-37)
are fused into the root bead, in order to remove any undercut causal by the
deposition of the root bead. One or more filler beads around the pipe usually will
be required.
(3) Finish beads. The finish beads (view C, fig. 6-37 ) are applied over the
filler beads to complete the joint. Usually, this is a weave bead about 5/8 in.
(1. 59 cm) wide and approximately 1/16 in. (O. 16 cm) above the outside surface of
the pipe when complete. The finished weld is shown in view D, figure 6-37.
6-35
TC 9-237
6-22.
POSITIONS FOR PIPE WELDING (cont)
e.. Aluminum pipe welding. For aluminum pipe, special joint details have been
developed and are normally associated with combination-type procedures. A backing
ring is not used in most cases. The rectangular backing ring is rarely used when
fluids are transmitted through the piping system. It may be used for structural
applications in which pipe and tubular members are used to transmit loads rather
than materials.
6-23.
FOREHAND WELDING
a. Work angle is the angle that the electrode, or centerline of the welding
gun, makes with the referenced plane or surface of the base metal in a plane perpendicular to the axis of a weld. Figure 6-38 shows the work angle for a fillet weld
and a groove weld. For pipe welding, the work angle is the angle that the electrode, or centerline of the welding gun, makes with the referenced plane or surface
of the pipe in a plane extending from the center of the pipe through the puddle.
Travel angle is the angle that the electrode, or centerline of the welding gun,
makes with a reference line perpendicular to the axis of the weld in the plane of
the weld axis. Figure 6-39 illustrates the travel angle for fillet and groove
welds. For pipe welding, the travel angle is the angle that the electrode, or
centerline of the welding gun, makes with a reference line extending from the center of the pipe through the arc in the plane of the weld axis. The travel angle is
further described as a drag angle or a push angle. Figure 6–39 shows both drag
angles and push angles. The push angle, which points forward in the direction of
travel, is also known as forehand welding.
6-36
TC 9-237
b. In forehand welding, the welding rod precedes the torch. The torch is held
at an approximately 30 degree angle from vertical, in the direction of welding as
shown in figure 6-40. The flame is pointed in the direction of welding and directed between the rod and the molten puddle. This position permits uniform preheating
of the plate edges immediately ahead of the molten puddle. By moving the torch and
the rod in opposite semicircular paths, the heat can be carefully balanced to melt
the end of the rod and the side walls of the plate into a uniformly distributed
molten puddle. The rod is dipped into the leading edge of the puddle so that
enough filler metal is melted to produce an even weld joint. The heat reflected
backwards from the rod keeps the metal molten. The metal is distributed evenly to
both edges being welded by the motion of the tip and rod.
c. This method is satisfactory for welding sheets and light plates in all positions. Some difficulties are encountered in welding heavier plates for the reasons
given below:
(1) In forehand welding, the edges of the plate must be beveled to provide a
wide V with a 90 degree included angle. This edge preparation is necessary to
insure satisfactory melting of the plate edges, good penetration, and fusion of the
weld metal to the base metal.
(2) Because of this wide V, a relatively large molten puddle is required. It
is difficult to obtain a good joint when the puddle is too large.
6-24.
BACKHAND WELDING
a. Backhand welding, also known as drag angle, is illustrated i n f i g u r e 6 - 4 1 .
The drag angle points backward from the direction of travel.
6-37
TC 9-237
6-24.
BACKHAND WELDING (cont)
b. In this method, the torch precedes the welding rod, as shown in figure
6-41, p 37. The torch is held at an angle approximately 30 degrees from the vertical, away from the direction of welding, with the flame directed at the molten
puddle. The welding rod is between the flame and the molten puddle. This position
requires less transverse motion than is used in forehand welding.
c. Backhand welding is used principally for welding heavy sections because it
permits the use of narrower V‘s at the joint. A 60 degree included angle of bevel.
is sufficient for a good weld. In general, there is less puddling, and less welding rod is used with this method than with the forehand method.
Section V.
EXPANSION AND CONTRACTION IN WELDING OPERATIONS
6-25. GENERAL
a. Most of the welding processes involve heat. High-temperature heat is responsible for much of the welding warpages and stresses that occur. When metal is
heated, it expands in all directions. When metal cools, it contracts in all directions. Some distortions caused by weld shrinkage are shown in figure 6-42.
b. There is a direct relationship between the anmount of temperature change and
change in dimension. This is based on the coefficient of thermal expansion. Thermal expansion is a measure of the linear increase in unit length based on the
change in temperature of the material. The coefficient of expansion is different
for the various metals. Aluminum has one of the highest coefficient of expansion
ratios, and changes in dimension almost twice as much as steel for the same temperature change.
c.
same
ed is
parts
6-38
A metal expands or contracts by the same amount when heated or cooled the
temperature if it is not restrained. If the expansion of the part being weldrestrained, buckling or warping may occur. If contraction is restrained, the
may be cracked or distorted because of the shrinkage stresses.
TC 9-237
d. when welding, the metals that are heated and cooled are not unrestrained
since they are a part of a larger piece of metal which is not heated to the same
temperature. Parts not heated or not heated as much tend to restrain that portion
of the same piece of metal that is heated to a higher temperature. This non-uniform heating always occurs in welding. The restraint caused by the part being
non-uniformly heated is the principal cause for the thermal distortion and warpages
that occur in welding.
e. Residual stresses that occur when metal is subjected to non-uniform temperature change are called thermal stresses. These stresses in weldments have two
major effects: they produce distortion, and may cause premature failure in
weldments.
6-26.
CONTROLLING CONTRACTION IN SHEET METAL
a. The welding procedure should be devised so that contraction stresses will be
held to a minimum order to keep the desired shape and strength of the welded
part. Some of the methods used for controlling contraction are described below.
b. The backstep method as shown in view A, figure 6-43, may be used. With the
backstep method, each small weld increment has its own shrinkage pattern, which
then becomes insignificant to the total pattern of the entire weldment.
6-39
TC 9-237
6-26.
CONTROLLING CONTRACTION IN SHEET METAL (cont)
c . In welding long seams, the contraction of the metal deposited at the joint
will cause the edges being welded to draw together and possibly overlap. This
action should be offset by wedging the edges apart as shown in view B, figure
6-43, p 6-39. The wedge should be moved forward as the weld progresses. The spacing of the wedge depends on the type of metal and its thickness. Spacing for metals more than 1/8 in. (3.2 mm) thick is approximately as follows:
d. Sheet metal under 1/16 in. (0. 16 cm) thick may be welded by flanging the
edges as shown in figure 6-20, p 6-23, and tacking at internals along the seam
before welding. A weld can be produced in this manner without the addition of
filler metal.
e. Buckling and warping can be prevented by the use of quench plates as shown
in figure 6-44. The quench plates are heavy pieces of metal clamped parallel to
the seam being welded with sufficient space between to permit the welding operation. These quench plates absorb the heat of welding, thereby decreasing the
stresses due to expansion and contraction.
f . Jigs and fixtures may be used to hold members in place for welding. These
are usually heavy sections in the vicinity of the seam (fig. 6-45). The heavy
sections cool the plate beyond the area of the weld.
6-40
TC 9-237
In pipe welding, spacing as illustrated in figure 6-43, p 6-39, is not p r a c t i c a l . Proper alignment of pipe can be best obtained by tack welding to hold t h e
pieces in place. The pipes should be separated by a gap of 1/8 to 1/4 in. (0.32 to)
0.64 cm), depending on the size of the pipe being welded.
g.
6-27.
CONTROLLING CONTRACTION AND EXPANSION IN CASTINGS
a. Prior to welding gray iron castings, expansion and contraction are provided
for by preheating. Before welding, small castings can be preheated by means of a
torch to a very dull red heat, visible in a darkened room. After welding, a reheating and controlled slow cooling or annealing will relieve internal stresses and
assure a proper gray iron structure.
b. For larger castings, temporary charcoal-fired furnaces built of fire brick
and covered with fire resistant material are often used. Only local preheating of
parts adjacent to the weld is usually necessary (fig. 6-46). Such local preheating
can be done with a gasoline, kerosene, or welding torch.
6-41
TC 9-237
6-27.
CONTROLLING CONTRACTION AND EXPANSION IN CASTINGS (cont)
c. Before welding a crack that extends from the edge of a casting, it is advisable to drill a small hole 1/2 to 1 in. (1.27 to 2.54 cm) beyond the visible end of
the crack. If the applied heat causes the crack to run, it will only extend t o t h e
drill hole.
d. If a crack does not extend to the end of a casting, it is advisable to drill
a small hole 1/2 to 1 in. (1.27 to 2.54 cm) beyond each end of the visible crack.
e. The above procedures apply to gray iron castings, as well as bronze welded
castings, except that less preheat is required for bronze welded castings.
6-28.
WELDING DISTORTION AND WARPAGE
a. General. The high temperature heat involved in most welding processes is
largely responsible for the distortion, warpage, and stresses that occur. When
heated, metal expands in all directions and when it cools, it contracts in all
directions. As described in paragraph 6-25, there is a direct relationship between
the amount of temperature change and the change in dimension of the metal. A metal
expands or contracts by the same amount when heated or cooled the same temperature,
if it is not restrained. However, in welding, the metals that are heated and
cooled are not unrestrained, because they are a part of a larger piece of metal
which is not heated to the same temperature. This non-uniform heating and partial
restraint is the main cause of thermal distortion and warpage that occur in welding. Figure 6-47 shows the effects of expansion on a cube of metal. When the cube
of metal is exposed to a temperature increase, it will expand in the x, y, and z
directions. When it cools, if unrestricted, it will contract by the same amount as
it expanded.
b. A weld is usually made progressively, which causes the solidified portions
of the weld to resist the shrinkage of later portions of the weld bead. The portions welded first are forced in tension down the length of the weld bead (longitudinal to the weld) as shown in figure 6-48. In the case of a butt weld, little
motion of the weld is permitted in the direction across the material face (transverse direction) because of the weld joint preparation or stiffening effect of
underlying passes. In these welds, as shown in figure 6-48, there will also be
transverse residual stresses. For fillet welds, as shown in figure 6-49, the
shrinkage stresses are rigid down the length of the weld and across its face.
6-42
TC 9-237
c. At the point of solidification, the molten metal has little or no strength.
A S it cools, it squires strength. It is also in its expanded form because of its
high temperature. The weld metal is now fused to the base metal, and they work
together. As the metal continues to cool, it acquires higher strength and is now
contracting in three directions. The arc depositing molten metal is a moving
source of heat and the cooling differential is also a moving factor, but tends to
follow the travel of the arc. With the temperature still declining and each small
increment of heated metal tending to contract, contracting stresses will occur, and
there will be movement in the metal adjacent to the weld. The unheated metal tends
to resist the cooling dimension changes of the previously molten metal. Temperature differential has an effect on this.
d. The temperate differential is determined by thermal conductivity. The
higher the thermal conductivity of the metal, the less effect differential heating
will have. For example, the thermal conductivity of copper is the highest, aluminum is half that amount, and steel about one-fifth that of copper. Heat would move
more quickly through a copper bar than through a steel bar, and the temperature
differential would not be so great. This physical property must be consiered when
welding, along with the fact that arc temperatures are very similar but the metal
melting points are somewhat different.
e. Another factor is the travel speed of the heat source or arc. If the travel
speed is relatively fast, the effect of the heat of the arc will cause expansion of
the edges of the plates, and they will bow outward and open up the joint. This is
the same as running a bead on the edge of the plate. In either case, it is a momentary situation which continues to change as the weld progresses. By adjusting the
current and travel speed, the exact speed can be determined for a specific joint
design so that the root will neither open up nor close together.
TC 9-237
6-28.
WELDING DISTORTION AND WARPAGE (cont)
f. Residual stresses in weldments produce distortion and may be the cause of
premature failure in weldments. Distortion is caused when the heated weld region
contracts non-uniformly, causing shrinkage in one part of the weld to exert eccentric forces on the weld cross section. The weldment strains elastically in response to these stresses, and this non-uniform strain is seen in macroscopic distortion. The distortion may appear in butt joints as both longitudinal and transverse
shrinkage or contraction and as angular change (rotation) when the face of the weld
shrinks more than the root. The angular change produces transverse bending in the
plates along the weld length. These effects are shown in figure 6-50.
g. Distortion in fillet welds is similar to that in butt welds. Transverse and
longitudinal shrinkage as well as angular distortion result from the unbalanced
nature of the stresses in these welds (fig. 6-51). Since fillet welds are often
used in combination with other welds in a weldment, the distortion may be complex.
h. Residual stresses and distortion affect materials by contributing to buckling, curling, and fracturing at low applied stress levels. When residual stresses
and their accompanying distortion are present, buckling may occur at liner compressive loads than would be predicted otherwise. In tension, residual stresses may
lead to high local stresses in weld regions of low toughness and may result in
running brittle cracks which can spread to low overall stress areas. Residual
stresses may also contribute to fatigue or corrosion failures.
i . Control of distortion can be achieved by several methods. Commonly used
methods include those which control the geometry of the weld joint, either before
or during welding. These methods include prepositioning the workplaces before
welding so that weld distortion leaves them in the desired final geometry, or restraining the workplaces so they cannot move and distort during welding. Designing
6-44
TC 9-237
the joint so that weld deposits are balanced on each side of the center line is
another useful technique. Welding process selection and weld sequence also influence distortion and residual stress. Some distorted weldments can be straightened
mechanically after welding, and thermal or flame straightening can also be applied.
j . Residual stresses may be eliminated by both thermal and mechanical means.
During thermal stress relief, the weldment is heated to a temperature at which the
yield point of the metal is low enough for plastic flow to occur and allow relaxation of stress. The mechanical properties of the weldment may also change, but not
always toward a more uniform distribution across the joint. For example, the brittle fracture resistance of many steel weld-rents is improved by thermal stress relief not only because the residual stresses in the weld are reduced, but also because hard weld heat-affected zones are tempered and made tougher by this procedure. Mechanical stress relief treatments will also reduce residual stresses, but
will not change the microstructure or hardness of the weld or heat-affected zone.
Peening, proof stressing, and other techniques are applied to weldments to acccomplish these ends.
k. The welder must consider not only reducing the effects of residual stresses
and distortion, but also the reduction of cracks, porosity, and other discontinuities; material degradation due to thermal effects during welding; the extent of
nondestructive testing; and fabrication cost. A process or procedure which produces less distortion may also produce more porosity and cracking in the weld zone.
Warping and distortion can be minimized by several methods. General methods include:
(1) Reducing residual stresses and distortion prior to welding by selecting
proper processes and procedures.
(2) Developing better means for stress relieving and removing distortion.
(3) Changing the structural design and the material so that the effects of
residual stresses and distortion can be minimized.
The following factors should be taken into consideration when welding in order to
reduce welding warpage:
(1) The location of the neutral axis and its relationship in both directions.
(2) The location of welds, size of welds, and distance from the neutral axis
in both directions.
(3) The time factor for welding and cooling rates when making the various
welds.
(4) The opportunity for balancing welding around the neutral axis.
(5) Repetitive identical structure and varying the welding techniques based
on measurable warpage.
(6) The use or procedures and sequences to minimize weldment distortion.
6-45
TC 9-237
6-28.
WELDING DISTORTION AND WARPAGE (cont)
When welding large structures and weldments, it is important to establish a procedure to minimize warpage. The order of joining plates in a deck or on a tank will
affect stresses and distortion. As a general rule, transverse welds should be made
before longitudinal welds. Figure 6-52 shows the order in which the joints should
be welded.
Warpage can be minimized in smaller structures by different techniques, which include the following:
(1) The use of restraining fixtures , strong backs, or many tack welds.
(2) The use of heat sinks or the fast cooling of welds.
(3) The predistortion or prehending of parts prior to welding.
(4) Balancing welds about the weldment neutral axis or using wandering sequences or backstep welding.
(5) The use of intermittent welding to reduce the volume of weld metal.
(6) The use of proper joint design selection and minimum size.
(7) As a last resort, use preheat or peening.
6-46
TC 9-237
Section VI.
6-29.
WELDING PROBLEMS AND SOLUTIONS
STRESSES AND CRACKING
a. In this section, welding stresses and their effect on weld cracking is explained. Factors related to weldment failure include weld stresses, cracking, weld
distortion, lamellar tearing, brittle fracture, fatigue cracking, weld design, and
weld defects.
b. When weld metal is added to the metal being welded, it is essentially cast
metal. Upon cooling, the weld metal shrinks to a greater extent than the base
metal in contact with the weld, and because it is firmly fused, exerts a drawing
action. This drawing action produces stresses in and about the weld which may
cause warping, buckling, residual stresses, or other defects.
c. Stress relieving is a process for lowering residual stresses or decreasing
their intensity. Where parts being welded are fixed too firmly to permit movement,
or are not heated uniformly during the welding operation, stresses develop by the
shrinking of the weld metal at the joint. Parts that cannot move to allow expansion and contraction must be heated uniformly during the welding operation. Stress
must be relieved after the weld is completed. These precautions are important in
welding aluminum, cast iron, high carbon steel, and other brittle metals, or metals
with low strength at temperatures immediately below the malting point. Ductile
materials such as bronze, brass, copper, and mild steel yield or stretch while in
the plastic or soft conditions, and are less liable to crack. However, they may
have undesirable stresses which tend to weaken the finished weld.
d. When stresses applied to a joint exceed the yield strength, the joint will
yield in a plastic fashion so that stresses will be reduced to the yield point.
This is normal in simple structures with stresses occurring in one direction on
parts made of ductile materials. Shrinkage stresses due to normal heating and
cooling do occur in all three dimensions. In a thin, flat plate, there will be
tension stresses at right angles. As the plate becomes thicker, or in extremely
thick materials, the stresses occur in three directions.
e. When simple stresses are imposed on thin, brittle materials, the material
will fail in tension in a brittle manner and the fracture will exhibit little or no
p l i a b i l i t y . In such cases, there is no yield point for the material, since the
yield strength and the ultimate strength are nearly the same. The failures that
occur without plastic deformation are known as brittle failures. When two or more
stresses occur in a ductile material, and particularly when stresses occur in three
directions in a thick material, brittle fracture may occur.
f . Residual stresses also occur in castings, forgings, and hot rolled shapes.
In forgings and castings, residual stresses occur as a result of the differential
cooling that occurs. The outer portion of the part cools first, and the thicker
and inner portion cools considerably faster. As the parts cool, they contract and
pick up strength so that the portions that cool earlier go into a compressive load,
and the portions that cool later go into a tensile stress mode. In complicated
parts, the stresses may cause warpage.
6-47
TC 9-237
6-29.
STRESSES AND CRACKING (cont)
g. Residual stresses are not always detrimental. They may have no effect or
may have a beneficial effect on the service life of parts. Normally, the outer
fibers of a part are subject to tensile loading and thus, with residual compression
loading, there is a tendency to neutralize stress in the outer fibers of the part.
An example of the use of residual stress is in the shrink fit of parts. A typical
example is the cooling of sleeve bearings to insert them into machined holes, and
allow them to expand to their normal dimension to retain then in the proper location. Sleeve bearings are used for heavy, S low machinery, and are subject to compressive residual loading, keeping them within the hole. Large roller bearings are
usually assembled to shafts by heating to expand them slightly so they will fit on
the shaft, then allowing them to cool, to produce a tight assembly.
h. Residual stresses occur in all arc welds. The most common method of measuring stress is to produce weld specimens and then machine away specific amounts of
metal, which are resisting the tensile stress in and adjacent to the weld. The
movement that occurs is then measured. Another method is the use of grid marks or
data points on the surface of weldments that can be measured in multiple directions. Cuts are made to reduce or release residual stresses from certain parts of
the weld joint, and the measurements are taken again. The amount of the movement
relates to the magnitude of the stresses. A third method utilizes extremely small
strain gauges. The weldment is gradually and mechanically cut from adjoining portions to determine the change in internal stresses. With these methods, it is
possible to establish patterns and actually determine amounts of stress within
parts that were caused by the thermal effects of welds.
i . Figure 6-53 shows residual stresses in an edge weld. The metal close to the
weld tends to expand in all directions when heated by the welding arc. This metal
is restrained by adjacent cold metal and is slightly upset, or its thickness slightly increased, during this heating period. When the weld metal starts to cool, the
upset area attempts to contract, but is again restrained by cooler metal. This
results in the heated zone becoming stressed in tension. When the weld has cooled
to room temperature, the weld metal and the adjacent base metal are under tensile
stresses close to the yield strength. Therefore, there is a portion that is compressive, and beyond this, another tensile stress area. The two edges are in tensile residual stress with the center in compressive residual stress, as illustrated.
6-48
TC 9-237
j . The residual stresses in a butt weld joint made of relatively thin plate are
more difficult to analyze. This is because the stresses occur in the longitudinal
direction of the weld and perpendicular to the axis of the weld. The residual
stresses within the weld are tensile in the longitudinal direction of the weld and
the magnitude is at the yield strength of the metal. The base metal adjacent to
the weld is also at yield stress, parallel to the weld and along most of the length
of the weld. When moving away from the weld into the base metal, the residual
stresses quickly fall to zero, and in order to maintain balance, change to compression. This is shown in figure 6-54. The residual stresses in the weld at right
angles to the axis of the weld are tensile at the center of the plate and compressive at the ends. For thicker materials when the welds are made with multipasses,
the relationship is different because of the many passes of the heat source. Except for single-pass, simple joint designs, the compressive and tensile residual
stresses can only be estimated.
k. As each weld is made, it will contract as it solidifies and gain strength as
the metal cools. As it contracts, it tends to pull, and this creates tensile
stresses at and adjacent to the weld. Further from the weld or bead, the metal
must remain in equilibrium, and therefore compressive stresses occur. In heavier
weldments when restraint is involved, movement is not possible, and residual stresses are of a higher magnitude. In a multipass single-groove weld, the first weld or
root pass originally creates a tensile stress. The second, third, and fourth passes contract and cause a compressive load in the root pass. As passes are made
until the weld is finished, the top passes will be in tensile load, the center of
the plate in compression, and the root pass will have tensile residual stress.
1.
Residual stresses can be decreased in several ways, as described below:
(1) If the weld is stressed by a load beyond its yield, strength plastic
deformation will occur and the stresses will be more uniform, but are still located
at the yield petit of the metal. This will not eliminate residual stresses, but
will create a more uniform stress pattern. Another way to reduce high or peak
residual stresses is by means of loading or stretching the weld by heating adjacent
areas, causing them to expand. The heat reduces the yield strength of the weld
metal and the expansion will tend to reduce peak residual stresses within the
weld. This method also makes the stress pattern at the weld area more uniform.
6-49
TC 9-237
6-29.
STRESSES AND CRACKING (cont)
(2) High residual stresses can be reduced by stress relief heat treatment.
With heat treatment, the weldment is uniformly heated to an elevated temperature,
at which the yield strength of the metal is greatly reduced. The weldment is then
allowed to cool slowly and uniformly so that the temperature differential between
parts is minor. The cooling will be uniform and a uniform low stress pattern will
develop within the weldment.
(3) High-temperature preheating can also reduce residual stress, since the
entire weldment is at a relatively high temperature, and will cool more or less
uniformly from that temperature and so reduce peak residual stresses.
m. Residual stresses also contribute to weld cracking. Weld cracking sometimes
occurs during the manufacture of the weldment or shortly after the weldment is
completed. Cracking occurs due to many reasons and may occur years after the weldment is completed. Cracks are the most serious defects that occur in welds or weld
joints in weldments. Cracks are not permitted in most weldments, particularly
those subject to low-temperature service, impact loading, reversing stresses, or
when the failure of the weldment will endanger life.
n. Weld cracking that occurs during or
weldment can be classified as hot cracking
may crack in the weld metal or in the base
ly in the heat-affected zone. Welds crack
ing :
shortly after the
or cold cracking.
metal adjacent to
for many reasons,
fabrication of the
In addition, welds
the weld metal, usualincluding the follow-
(1) Insufficient weld metal cross section to sustain the loads involved.
(2) Insufficient ductility of weld metal to yield under stresses involved.
(3) Under-bead cracking due to hydrogen pickup in a hardenable type of base
material.
o. Restraint and residual stresses are the main causes of weld cracking during
the fabrication of a weldment. Weld restraint can come from several factors,
including the stiffness or rigidity of the weldment itself. Weld metal shrinks as
it cools, and if the parts being welded cannot move with respect to one another and
the weld metal has insufficient ductility, a crack will result. Movement of welds
may impose high loads on other welds and cause them to crack during fabrication. A
more ductile filler material should be used, or the weld should be made with sufficient cross-sectional area so that as it cools, it will have enough strength to
withstand cracking tendencies. Typical weld cracks occur in the root pass when the
parts are unable to move.
p. Rapid cooling of the weld deposit is also responsible for weld cracking. If
the base metal being joined is cold and the weld is small, it will cool quickly.
6-50
TC 9-237
Shrinkage will also occur quickly, and cracking can occur. If the parts being
joined are preheated even slightly, the cooling rate will be lower and cracking can
be eliminated.
q. Alloy or carbon content of base material can also affect cracking. When a
weld is made with higher-carbon or higher-alloy base material, a certain amount of
the base material is melted and mixed with the electrode to produce the weld meta l . The resulting weld metal has higher carbon and alloy content. It may have
higher strength, but it has less ductility. As it shrinks, it may not have enough
ductility to cause plastic deformation, and cracking may occur.
r . Hydrogen pickup in the weld metal and in the heat-affected zone can also
cause cracking. When using cellulose-covered electrodes or when hydrogen is
present because of damp gas, damp flux, or hydrocarbon surface materials, the hydrogen in the arc atmosphere will be absorbed in the molten weld metal and in adjoining high-temperature base metal. As the metal cools, it will reject the hydrogen,
and if there is enough restraint, cracking can occur. This type of cracking can be
reduced by increasing preheat, reducing restraint, and eliminating hydrogen from
the arc atmosphere.
s. When cracking is in the heat-affected zone or if cracking is delayed, the
cause is usually hydrogen pickup in the weld metal and the heat-affected zone of
the base metal. The presence of higher-carbon materials or high alloy in the base
metal can also be a cause. When welding high-alloy or high-carbon steels, the
buttering technique can be used to prevent cracking. This involves surf acing the
weld face of the joint with a weld metal that is much lower in carbon or alloy
content than the base metal. The weld is then made between the deposited surfacing
material and avoids the carbon and alloy pickup in the weld metal, so a more ductile weld deposit is made. Total joint strength must still be great enough to meet
design requirements. Underbead cracking can be reduced by the use of low-hydrogen
processes and filler metals. The use of preheat reduces the rate of cooling, which
tends to decrease the possibility of cracking.
t.
Stress Relieving Methods.
(1) Stress0 relieving in steel
welds may be accomplished by preheating between
0
800 and 1450 F (427 and 788 C), depending on the material, and then slowly
cooling. Cooling under some conditions may take 10 to 12 hours. Small pieces,
such as butt welded high speed tool tips, may be annealed by putting them in a box
of fire resistant material and cooling for 24 hours. In stress relieving mild
steel, heating the completed weld for 1 hour per 1.00 in. (2.54 cm) of thickness is
common practice. On this basis, steel 1/4 in. (0.64 cm) thick should be preheated
for 15 minutes at the stress relieving temperature.
(2) Peening is another method of relieving stress on a finished weld, usually
with compressed air and a roughing or peening tool. However, excessive peening may
cause brittleness or hardening of the finished weld and may actually cause cracking.
6-51
TC 9-237
6-29.
STRESSES AND CRACKING (cont)
(3) Preheating facilitates welding in many cases. It prevents cracking in
the heat affected zone, particularly on the first passes of the weld metal. If
proper preheating times and temperatures are used, the cooling rate is slowed sufficiently to prevent the formation of hard martensite, which causes cracking. Table 6-1
lists preheating temperatures of specific metals.
*The preheating temperatures for alloy steels are governed by the carbon as well as
the alloy content of the steel.
(4) The need for preheating steels and other metals is increased under the
following conditions:
(a) When the temperature of the part or the surrounding atmosphere is at or
below freezing.
(b) When the diameter of the welding rod is small in comparison to the
thickness of the metal being joined.
(c) When the welding speed is high.
(d) When the shape and design of the parts being welded are complicated.
(e) When there is a great difference in mass of the parts being welded.
6-52
TC 9-237
content.
(f) When welding steels with a high carbon, low
manganese, or other alloy
(g) When the steel being welded tends to harden when cooled in air from the
welding temperature.
u. The following general procedures can be used to relieve stress and to reduce
cracking:
(1)
Use ductile weld metal.
(2)
Avoid extremely high restraint or residual stresses.
(3)
Revise welding procedures to reduce restraint.
(4)
Utilize low-alloy and low-carbon materials.
(5)
Reduce the cooling rate by use of preheat.
(6)
Utilize low-hydrogen welding processes and filler metals.
(7) When welds are too small for the service intended, they will probably
crack. The welder should ensure that the size of the welds are not smaller than
the minimum weld size designated for different thicknesses of steel sections.
6-30.
IN-SERVICE CRACKING
Weldments must be designed and built to perform adequately in service. The risk of
failure of a weldment is relatively small, but failure can occur in structures such
as bridges, pressure vessels , storage tanks, ships, and penstocks. Welding has
sometimes been blamed for the failure of large engineering structures, but it
should be noted that failures have occurred in riveted and bolted structures and in
castings, forgings, hot rolled plate and shapes, as well as other types of construction. Failures of these types of structures occurred before welding was widely
used and still occur in unwelded structures today. However, it is still important
to make weldments and welded structures as safe against premature failure of any
type as possible. There are four specific types of failures, including brittle
fracture, fatigue fracture, lamellar tearing, and stress corrosion cracking.
a. Brittle Fracture.
ductile and brittle.
Fracture can be classified into two general categories,
(1) Ductile fracture occurs by deformation of the crystals and slip relative to each other. There is a definite stretching or yielding and a reduction of
cross-sectional area at the fracture (fig. 6-55) .
6-53
TC 9-237
6-30.
IN-SERVICE CRACKING (cont)
(2) Brittle fracture occurs by cleavage across individual crystals. The
fracture exposes the granular structure, and there is little or no stretching or
yielding. There is no reduction of area at the fracture (fig. 6-56).
(3) It is possible that a broken surface will display both ductile and brittle fracture over different areas of the surface. This means that the fracture
which propagated across the section changed its mode of fracture.
(4) There are four factors that should be reviewed when analyzing a fractured
surface. They are growth marking, fracture mode, fracture surface texture and
appearance, and amount of yielding or plastic deformation at the fracture surface.
(5) Growth markings are one way to identify the type of failure. Fatigue
failures are characterized by a fine texture surface with distinct markings produced by erratic growth of the crack as it progresses. The chevron or herringbone
pattern occurs with brittle or impact failures. The apex of the chevron appearing
on the fractured surface always points toward the origin of the fracture and is an
indicator of the direction of crack propagation.
(6) Fracture mode is the second factor. Ductile fractures have a shear mode
of crystalline failure. The surface texture is silky or fibrous in appearance.
Ductile fractures often appear to have failed in shear as evidenced by all parts of
the fracture surface as sinning an angle of approximately 45 degrees with respect to
the axis of the load stress.
(7) The third factor is fracture surface and texture. Brittle or cleavage
fractures have either a granular or a crystalline appearance. Brittle fractures
usually have a point of origin. The chevron pattern will help locate this point.
(8) An indication of the amount of plastic deformation is the necking down of
the surface. There is little or no deformation for a brittle fracture , and usually
a considerable necked down area in the case of a ductile fracture.
(9) One characteristic of brittle fracture is that the steel breaks quickly
and without warning. The fractures increase at very high speeds, and the steels
fracture at stresses below the normal yield strength for steel. Mild steels, which
show a normal degree of ductility when tested in tension as a normal test bar, may
fail in a brittle manner. In fact, mild steel may exhibit good toughness characteristics at roan temperature. Brittle fracture is therefore more similar to the
fracture of glass than fracture of normal ductile materials. A combination of
conditions must be present at the same time for brittle fracture to occur. Some of
6-54
TC 9-237
these factors can be eliminated and thus reduce the possibility of brittle fracture. The following conditions must be present for brittle fracture to occur: lo W
temperature, a notch or defect, a relatively high rate of loading, and triaxial
stresses normally due to thickness of residual stresses. The microstructure of the
metal also has an effect.
(10) Temperature is an important factor which must be considered in conjunction with microstructure of the material and the presence of a notch. Impact testing of steels using a standard notched bar specimen at different temperatures shows
a transition from a ductile type failure to a brittle type failure based on a lowered temperature, which is known as the transition temperature.
(11) The notch that can result from faulty workmanship or from improper design
produces an extremely high stress concentration which prohibits yielding. A crack
will not carry stress across it, and the load is transmitted to the end of the
crack. It is concentrated at this point and little or no yielding will occur.
Metal adjacent to the end of the crack which does not carry load will not undergo a
reduction of area since it is not stressed. It is, in effect, a restraint which
helps set up triaxial stresses at the base of the notch or the end of the crack.
Stress levels much higher than normal occur at this point and contribute to starting the fracture.
(12) The rate of loading is the time versus strain rate. The high rate of
strain, which is a result of impact or shock loading, does not allow sufficient
time for the normal slip process to occur. The material under load behaves elastically, allowing a stress level beyond the normal yield point. When the rate of
loading, from impact or shock stresses, occurs near a notch in heavy thick material, the material at the base of the notch is subjected very suddenly to very high
stresses. The effect of this is often complete and rapid failure of a structure
and is what makes brittle fracture so dangerous.
(13) Triaxial stresses are more likely to occur in thicker material than in
thin material. The z direction acts as a restraint at the base of the notch, and
for thicker material, the degree of restraint in the through direction is higher.
This is why brittle fracture is more likely to occur in thick plates or complex
sections than in thinner materials. Thicker plates also usually have less mechanical working in their manufacture than thinner plates and are more susceptible to
lower ductility in the z axis. The microstructure and chemistry of the material in
the center of thicker plates have poorer properties than the thinner material,
which receives more mechanical working.
(14) The microstructure of the material is of major importance to the fracture
behavior and transition temperature range. Microstructure of a steel depends on
the chemical composition and production processes used in manufacturing it. A
steel in the as-rolled condition will have a higher transition temperature or liner
toughness than the same steel in a normalized condition. Normalizing, or heating
to the proper temperature and cooling slowly, produces a grain refinement which
provides for higher toughness. Unfortunately, fabrication operations on steel,
such as hot and cold forming, punching, and flame cutting, affect the original
microstructure. This raises the transition temperature of the steel.
6-55
TC 9-237
6-30.
IN-SERVICE CRACKING (cont)
(15) Welding tends to accentuate S ome of the undesirable characteristics that
contribute to brittle fracture. The thermal treatment resulting from welding tends
to reduce the toughness of the steel or to raise its transition temperature in the
heat–affected zone. The monolithic structure of a weldment means that more energy
is locked up and there is the possibility of residual stresses which may be at
yield point levels. The monolithic structure also causes stresses and strains to
be transmitted throughout the entire weldment, and defects in weld joints can be
the nucleus for the notch or crack that will initiate fracture.
(16) Brittle fractures can be reduced in weldments by selecting steels that
have sufficient toughness at the service temperatures. The transition temperature
should be below the service temperature to which the weldment will be subjected.
Heat treatment, normalizing, or any method of reducing locked-up stresses will
reduce the triaxial yield strength stresses within the weldment. Design notches
must be eliminated and notches resulting from poor workmanship must not occur.
Internal cracks within the welds and unfused root areas must be eliminated.
b. Fatigue Failure. Structures sometimes fail at nominal stresses considerably below the tensile strength of the materials involved. The materials involved
were ductile in the normal tensile tests, but the failures generally exhibited
little or no ductility. Most of these failures development after the structure had
been subjected to a large number of cycles of loading. This type of failure is
called a fatigue failure.
(1) Fatigue failure is the formation and development of a crack by repeated
or fluctuating loading. when sudden failure occurs, it is because the crack has
increased enough to reduce the load-carrying capacity of the part. Fatigue cracks
may exist in some weldments, but they will not fail until the load-carrying area is
sufficiently reduced. Repeated loading causes progressive enlargement of the fatigue cracks through the material. The rate at which the fatigue crack increases
depends upon the type and intensity of stress as well as other factors involving
the design, the rate of loading, and type of material.
(2) The fracture surface of a fatigue failure is generally smooth and frequently shins concentric rings or areas spreading from the point where the crack
initiated. These rings show the propagation of the crack, which might be related
to periods of high stress followed by periods of inactivity. The fracture surface
also tends to become rougher as the rate of propagation of the crack increases.
Figure 6-57 shows the characteristic fatigue failure surface.
6-56
TC 9-237
(3) Many structures are designed to a permissible static stress based on the
yield point of the material in use and the safety factor that has been selected.
This is based on statically loaded structures, the stress of which remains relatively constant. Many structures, however, are subject to other than static loads in
service. These changes may range from simple cyclic fluctuations to completely
random variations. In this type of loading, the structure must be designed for
dynamic loading and considered with respect to fatigue stresses.
(4) The varying loads involved with fatigue stresses can be categorized in
different manners. These can be alternating cycles from tension to compression, or
pulsating loads with pulses from zero load to a maximum tensile load, or from a
zero load to a compressive load, or loads can be high and rise higher, either tensile or compressive. In addition to the loadings, it is important to consider the
number of times the weldment is subjected to the cyclic loading. For practical
purposes, loading is considers in millions of cycles. Fatigue is a cumulative
process and its effect is in no way healed during periods of inactivity. Testing
machines are available for loading metal specimens to millions of cycles. The
results are plotted on stress vs. cycle curves, which show the relationship between
the stress range and the number of cycles for the particular stress used. Fatigue
test specimens are machined and polished, and the results obtained on such a specimen may not correlate with actual service life of a weldment. It is therefore
important to determine those factors which adversely affect the fatigue life of a
weldment.
(5) The possibility of a fatigue failure depends on four factors: the material used, the number of loading cycles, the stress level and nature of stress variations, and total design and design details. The last factor is controllable in the
design and manufacture of the weldment. Weld joints can be designed for uniform
stress distribution utilizing a full-penetration weld, but in other cases, joints
may not have full penetration because of an unfused root. This prohibits uniform
stress distribution. Even with a full-penetration weld, if the reinforcement is
excessive, a portion of the stress will flow through the reinforced area and will
not be uniformly distributed. Welds designed for full penetration might not have
complete penetration because of workmanship factors such as cracks, slag inclusions, and incomplete penetration, and therefore contain a stress concentration.
One reason fatigue failures in welded structures occur is because the welded design
can introduce more severe stress concentrations than other types of design. The
weld defects mentioned previously, including excessive reinforcement, undercut, or
negative reinforcement, will contribute to the stress concentration factor. A weld
also forms an integral part of the structure , and when parts are attached by welding, they may produce sudden changes of section which contribute to stress concentrations under normal types of loading. Anything that can be done to smooth out
the stress flow in the weldment will reduce stress concentrations and make the
weldment less subject to fatigue failure. Total design with this in mind and careful workmanship will help to eliminate this type of problem.
6-57
TC 9-237
6-30.
IN-SERVICE CRACKING (cont )
c. Lamellar Tearing. Lamellar tearing is a cracking which occurs beneath
welds, and is found in rolled steel plate weldments. The tearing always lies within the base metal, usually outside the heat-affected zone and generally parallel to
the weld fusion boundary. This type of cracking has been found in corner joints
where the shrinkage across the weld tended to open up in a manner similar to lamination of plate steel. In these cases, the lamination type crack is removed and
replaced with weld metal. Before the advent of ultrasonic testing, this type of
failure was probably occuring and was not found. It is only when welds subjected
the base metal to tensile loads in the z , or through, direction of the rolled steel
that the problem is encountered. For many years, the lower strength of rolled
steel in the through direction was recognized and the structural code prohibited
z-directional tensile loads on steel spacer plates. Figure 6-58 shows how lamellar
tearing will come to the surface of the metal. Figure 6-59, shining a tee joint,
is a more common type of lamellar tearing, which is much more difficult to find.
In this case, the crack does not cane to the surface and is under the weld. This
type of crack can only be found with ultrasonic testing or if failure occurs, the
section can actually come out and separate from the main piece of metal.
(1) Three conditions must occur to cause lamellar tearing. These are strains
in the through direction of the plate caused by weld metal shrinkage in the joint
and increased by residual stresses and by loading; stress through the joint across
the plate thickness or in the z direction due to weld orientation in which the
fusion line beneath the weld is roughly parallel to the lamellar separation; and
poor ductility of the material in the z, or through, direction.
(2) Lamellar tearing can occur during flame-cutting operations and also in
cold-shearing operations. It is primarily the low strength of the material in the
z, or through, direction that contributes to the problem. A stress placed in the z
6-58
TC 9-237
direction triggers the tearing. The thermal heating and stresses resulting from
weld shrinkage create the fracture. Lamellar tearing is not associated with the
under-bead hydrogen cracking problem. It can occur soon after the weld has been
made, but on occasion will occur at a period months later. Also, the tears are
under the heat-affected zone, and are more apt to occur in thicker materials and in
higher-strength materials.
(3) Only a very small percentage of steel plates are susceptible to lamellar
tearing. There are only certain plates where the concentration of inclusions are
coupled with the unfavorable shape and type that present the risk of tearing.
These conditions rarely occur with the other two factors mentioned previously. In
general, three situations must occur in combination: structural restraint, joint
design, and the condition of the steel.
(4) Joint details can be changed to avoid the possibility of lamellar tearing. In tee joints, double-fillet weld joints are less susceptible than fullpenetration welds. Balanced welds on both sides of the joint present less risk of
lamelalar tearing than large single-sided welds. corner joints are common in box
columns. Lamellar tearing at the corner joints is readily detected on the exposed
edge of the plate. Lamellar tearing can be overcome in corner joints by placing
the bevel for the joint on the edge of the plate that would exhibit the tearing
rather than on the other plate. This is shown by figure 6-60. Butt joints rarely
are a problem with respect to lamellar tearing since the shrinkage of the weld does
not set up a tensile stress in the thickness direction of the plates.
(5) Arc welding processes having higher heat input are less likely to create
lamellar tearing. This may be because of the fewer number of applications of heat
and the lesser number of shrinkage cycles involved in making a weld. Deposited
filler metal with lower yield strength and high ductility also reduces the possibility of lamellar tearing. Preheat and stress relief heat treatment are not specifically advantageous with respect to lamellar tearing. The buttering technique of
laying one or more layers of low strength, high-ductility weld metal deposit on the
surface of the plate stressed in the z direction will reduce the possibility of
lamellar tearing. This is an extreme solution and should only be used as a last
resort. By observing the design factors mentioned above, the lamellar tearing problem is reduced.
d. Stress Corrosion Cracking. Stress corrosion cracking and delayed cracking
due to hydrogen embrittlement can both occur when the weldment is subjected to the
type of environment that accentuates this problem.
6-59
TC 9-237
6-30.
IN-SERVICE CRACKING (cont)
(1) Delayed cracking is caused by hydrogen absorbed in the base metal or weld
metal at high temperatures. Liquid or molten steel will absorb large quantities of
hydrogen. As the metal solidifies, it cannot retain all of the hydrogen and is
forced out of solution. The hydrogen coming out of the solution sets up high
stresses, and if enough hydrogen is present, it will cause cracking in the weld or
the heat-affected zone. These cracks develop over a period of time after the weld
is completed. The concentration of hydrogen and the stresses resulting from it
when coupled with residual stresses promote cracking. Cracking will be accelerated
if the weldment is subjected to thermal stresses due to repeated heating and cooling.
(2) Stress corrosion cracking in steels is sometimes called caustic
embrittlement. This type of cracking takes place when hot concentrated caustic
solutions are in contact with steel that is stressed in tension to a relatively
high level. The high level of tension stresses can be created by loading or by
high residual stresses. Stress corrosion cracking will occur if the concentration
of the caustic solution in contact with the steel is sufficiently high and if the
stress level in the weldment is sufficiently high. This situation can be reduced
by reducing the stress level and the concentration of the caustic solution. Various inhibitors can be added to the solution to reduce the concentration. Close
inspection must be maintained on highly stressed areas.
(3) Graphitization is another type of cracking, caused by long service life
exposed to thermal cycling or repeated heating and cooling. This may cause a breakdown of carbides in the steel into small areas of graphite and iron. This formation of graphite in the edge of the heat-affected area exposed to the thermal cycling causes cracking. It will often occur in carbon steels deoxidized with aluminum. The addition of molybdenum to the steel tends to restrict graphitization, and
for this reason, carbon molybdenum steels are normally used in high-temperature
power plant service. These steels must be welded with filler metals of the same
composition.
6-31.
ARC BLOW
a. General. Arc blew is the deflection of an electric arc from its normal
path due to magnetic forces. It is mainly encountered with dc welding of magnetic
materials, such as steel, iron, and nickel, but can also be encountered when welding nonmagnetic materials. It will usually adversely affect appearance of the
weld, cause excessive spatter, and can also impair the quality of the weld. It is
often encountered when using the shielded metal arc welding process with covered
electrodes. It is also a factor in semiautomatic and fully automatic arc welding
processes. Direct current, flowing through the electrode and the base metal, sets
up magnetic fields around the electrode, which deflect the arc from its intended
path. The welding arc is usually deflected forward or backward of the direction of
travel; however, it may be deflected from one side to the other. Back blow is
encountered when welding toward the ground near the end of a joint or into a corner. Forward blow is encountered when welding away from the ground at the start of
a joint. Arc blow can become so severe that it is impossible to make a satisfactory weld. Figure 6-61 shows the effect of ground location on magnetic arc blow.
6-60
TC 9-237
b. When an electric current passes through an electrical conductor, it produces
a magnetic flux in circles around the conductor in planes perpendicular to the conductor and with their centers in the conductor. The right-hand rule is used to
determine the direction of the magnetic flux. It states that when the thumb of the
right hand points in the direction in which the current flows (conventional flow)
in the conductor, the fingers point in the direction of the flux. The direction of
the magnetic flux produces polarity in the magnetic field, the same as the north
and south poles of a permanent magnet. This magnetic field is the same as that
produced by an electromagnet. The rules of magnetism, which state that like poles
repel and opposite poles attract, apply in this situation. Welding current is much
higher than the electrical current normally encountered. Likewise, the magnetic
fields are also much stronger.
c. The welding arc is an electrical conductor and the magnetic flux is set up
surrounding it in accordance with the right-hand rule. The magnetic field in the
vicinity of the welding arc is the field produced by the welding current which
passes through it from the electrode and to the base metal or work. This is a
self-induced circular magnetic field which surrounds the arc and exerts a force on
it from all sides according to the electrical-magnetic rule. As long as the magnetic field is symmetrical, there is no unbalanced magnetic force and no arc deflection. Under these conditions, the arc is parallel or in line with the centerline
of the electrode and takes the shortest path to the base plate. If the symmetry of
this magnetic field is disturbed, the forces on the arc are no longer equal and the
arc is deflected by the strongest force.
d. The electrical-magnetic relationship is used in welding applications for
magnetically moving, or oscillating, the welding arc. The gas tungsten arc is
deflected by means of magnetic flux. It can be oscillated by transverse magnetic
fields or be made to deflect in the direction of travel. Moving the flux field
surrounding the arc and introducing an external-like polarity field roves the arc
magnetically. Oscillation is obtained by reversing the external transverse field
to cause it to attract the field surrounding the arc. As the self-induced field
around the arc is attracted and repelled, it tends to move the arc column, which
tries to maintain symmetry within its own self-induced magnetic field. Magnetic
oscillation of the gas tungsten welding arc is used to widen the deposition. Arcs
can also be made to rotate around the periphery of abutting pipes by means of rotating magnetic fields. Longer arcs are moved more easily than short arcs. The
amount of magnetic flux to create the movement must be of the same order as the
flux field surrounding the arc column. Whenever the symmetry of the field is disturbed by some other magnetic force, it will tend to move the self-induced field
surrounding the arc and thus deflect the arc itself.
6-61
TC 9-237
6-31.
ARC BLOW (cont)
e. Except under the most simple conditions, the self-induced magnetic field is
not symmetrical throughout the entire electric circuit and changes direction at the
arc. There is always an unbalance of the magnetic field around the arc because the
arc is roving and the current flow pattern through the base material is not constant. The magnetic flux will pass through a magnetic material such as steel much
easier than it will pass through air, and the magnetic flux path will tend to stay
within the steel and be more concentrated and stronger than in air. Welding current passes through the electrode lead, the electrode holder to the welding electrode, then through the arc into the base metal. At this point the current changes
direction to pass to the work lead connection, then through the work lead back to
the welding machine. This is shown by figure 6-62. At the point the arc is in
contact with the work, the change of direction is relatively abrupt, and the fact
that the lines of force are perpendicular to the path of the welding current creates a magnetic unbalance. The lines of force are concentrated together on the
inside of the angle of the current path through the electrode and the work, and are
spread out on the outside angle of this path. Consequently, the magnetic field is
much stronger on the side of the arc toward the work lead connection than on the
other side, which produces a force on the stronger side and deflects the arc to the
l e f t . This is toward the weaker force and is opposite the direction of the current
path. The direction of this force is the same regardless of the direction of the
current. If the welding current is reversed, the magnetic field is also reversed,
but the direction of the magnetic force acting on the arc is always in the same
direction, away from the path of the current through the work.
6-62
TC 9-237
f . The second factor that keeps the magnetic field from being symmetrical is
the fact that the arc is moving and depositing weld metal. As a weld is made joining two plates, the arc moves from one end of the joint to the other and the magnetic field in the plates will constantly change. Since the work lead is immediately
under the arc and moving with the arc, the magnetic path in the work will not be
concentric about the point of the arc, because the lines of force take the easiest
path rather than the shortest path. Near the start end of the joint the lines of
force are crowded together and will tend to stay within the steel. Toward the
finish end of the joint, the lines of force will be separated since there is more
area. This is shown by figure 6-63. In addition, where the weld has been made the
lines of force go through steel. Where the weld is not made, the lines of force
must cross the air gap or root opening. The magnetic field is more intense on the
short end and the unbalance produces a force which deflects the arc to the right or
toward the long end.
g. When welding with direct current, the total force tending to cause the arc
to deflect is a combination of these two forces. These forces may add or subtract
from each other, and at times may meet at right angles. The polarity or direction
of flow of the current does not affect the direction of these forces nor the resultant force. By analyzing the path of the welding current through the electrode and
into the base metal to the work lead, and analyzing the magnetic field within the
base metal, it is possible to determine the resultant forces and predict the resulting arc deflection or arc blow.
h. Forward blow exists for a short time at the start of a weld, then diminishes. This is because the flux soon finds an easy path through the weld metal. Once
the magnetic flux behind the arc is concentrated in the plate and the weld, the arc
is influenced mainly by the flux in front of it as this flux crosses the root opening. At this point, back blow may be encountered. Back blow can occur right up to
the end of the joint. As the weld approaches the end, the flux ahead of the arc
becomes more crowded, increasing the back blow. Back blow can become extremely
severe right at the very end of the joint.
6-63
TC 9-237
6-31.
ARC BLOW (cont)
i . The use of alternating current for welding greatly reduces the magnitude of
deflection or arc blow; however, ac welding does not completely eliminate arc
blow. Reduction of arc blow is reduced because the alternating current sets up
other currents that tend to either neutralize the magnetic field or greatly reduce
its strength. Alternating current varies between maximum value of one polarity and
the maximum value of the opposite polarity. The magnetic field surrounding the
alternating current conductor does the same thing. The alternating magnetic field
is a roving field which induces current in any conductor through which it passes,
according to the induction principle. Currents are induced in nearby conductors in
a direction opposite that of the inducing current. These induced currents are
called eddy currents. They produce a magnetic field of their own which tends to
neutralize the magnetic field of the arc current. These currents are alternating
currents of the same frequency as the arc current and are in the part of the work
nearest the arc. They always flow from the opposite direction as shown by figure
6-64. When alternating current is used for welding, eddy currents are induced in
the workpiece, which produce magnetic fields and reduce the intensity of the field
acting on the arc. Alternating current cannot be used for all welding applications
and for this reason changing from direct current to alternating current may not
always be possible to eliminate or reduce arc blow.
j. Summary of Factors Causing Arc Blow.
(1) Arc blow is caused by magnetic forces. The induced magnetic forces are
not symmetrical about the magnetic field surrounding the path of the welding current. The location of magnetic material with respect to the arc creates a magnetic
force on the arc which acts toward the easiest magnetic path and is independent of
electrode polarity. The location of the easiest magnetic path changes constantly
as welding progresses; therefore, the intensity and the direction of the force
changes.
(2) Welding current will take the easiest path but not always the most direct
path through the work to the work lead connection. The resultant magnetic force is
opposite in direction to the current from the arc to the work lead connection, and
is independent of welding current polarity.
(3) Arc blow is not as severe with alternating current because the induction
principle creates current flow within the base metal which creates magnetic fields
that tend to neutralize the magnetic field affecting the arc.
6-64
TC 9-237
(4) The greatest magnetic force on the arc is caused by the difference in
resistance of the magnetic path in the base metal around the arc. The location of
the work lead connection is of secondary importance, but may have an effect on
reducing the total magnetic force on the arc. It is best to have the work lead
connection at the starting point of the weld. This is particularly true in
electroslag welding where the work lead should be connected to the starting sump.
On occasion, the work lead can be changed to the opposite end of the joint. In
sane cases, leads can be connected to both ends.
k. Minimizing Arc Blow.
(1) The magnetic forces acting on the arc can be modified by changing the
magnetic path across the joint. This can be accomplished by runoff tabs, starting
plates, large tack welds, and backing strips, as well as the welding sequence.
(2) An external magnetic field produced by an electromagnet may be effective. This can be accomplished by wrapping several turns of welding lead around
the workpiece.
(3) Arc blow is usually more pronounced at the start of the weld seam. In
this case, a magnetic shunt or runoff tab will reduce the blow.
(4) Use as short an arc as possible so that there is less of an arc for the
magnetic forces to control.
(5). The welding fixture can be a source of arc blow; therefore, an analysis
with respect to fixturing is important. The hold-down clamps and backing bars must
fit closely and tightly to the work. In general, copper or nonferrous metals
should be used. Magnetic structure of the fixture can affeet the magnetic forces
controlling the arc.
(6) Place ground connections as far as possible from the joints to be welded.
(7) If back blow is the problem, place the ground connection at the start of
welding, and weld toward a heavy tack weld.
(8) I f forward blow causes trouble, place the ground connection at the end of
the joint t o be welded.
(9)
Position the electrode so that the arc force counteracts the arc blow.
(10) Reduce the welding current.
(11) Use the backstep sequence of welding.
(12) Change to ac, which may require a change in electrode classification.
(13) Wrap the ground cable around the workpiece in a direction such that the
magnetic field it sets up will counteract the magnetic field causing the arc blow.
(14) Another major problem can result from magnetic fields already in the base
metal, particularly when the base metal has been handled by magnet lifting cranes.
Residual magnetism in heavy thick plates handled by magnets can be of such magnitude that it is almost impossible to make a weld. Attempt to demagnetize the
parts, wrap the part with welding leads to help overcome their effect, or stress
relieve or anneal the parts.
6-65
TC 9-237
6-32.
WELD FAILURE ANALYSIS
a. General. Only rarely are there failures of welded structures, but failures of large engineered structures do occur occasionally. Catastrophic failures
of major structures are usually reported whenever they occur. The results of investigations of these failures are usually reported and these reports often provide
information that is helpful in avoiding future similar problems. In the same manner, there are occasional failures of noncritical welds and weldments that should
also be investigated. Once the reason is determined it can then be avoided. An
objective study must be made of any failure of parts or structures to determine the
cause of the failure. This is done by investigating the service life, the conditions that led up to the failure, and the actual mode of the failure. An objective
study of failure should utilize every bit of information available, investigate all
factors that could remotely be considered , and evaluate all this information to
find the reason for the failure. Failure investigation often uncovers facts that
lead to changes in design, manufacturing, or operating practice, that will eliminate similar failures in the future. Failures of insignificant parts can also lead
to advances in knowledge and should be done objectively, as with a large structure. Each failure and subsequent investigation will lead to changes that will
assure a more reliable product in the future.
b. The following four areas of interest should be investigated to determine the
cause of weld failure and the interplay of factors involved:
(1) Initial observation. The detailed study by visual inspection of the
actual component that failed should be made at the failure site as quickly as possi–
ble. Photographs should be taken, preferably in color, of all parts, structures,
failure surfaces, fracture texture appearance, final location of component debris,
and all other factors. Witnesses to the failure should all be interviewed and all
information determined from them should be recorded.
(2) Background data. Investigators should gather all information concerning specifications, drawings, component design, fabrication methods, welding procedures, weld schedules, repairs in and during manufacturing and in service, maintenance, and service use. Efforts should be made to obtain facts pertinent to all
possible failure modes. Particular attention should be given to environmental
details, including operating temperatures, normal service loads, overloads, cyclic
loading, and abuse.
(3) Laboratory studies. Investigators should make tests to verify that the
material in the failed parts actually possesses the specified composition, mechanical properties, and dimensions. Studies should also be made microscopically in
those situations in which it would lead to additional information. Each failed
part should be thoroughly investigated to determine what bits of information can be
added to the total picture. Fracture surfaces can be extremely important. Original drawings should be obtained and marked showing failure locations, along with
design stress data originally used in designing the product. Any other defects in
the structure that are apparent, even though they might not have contributed to the
failure, should also be noted and investigated.
(4) Failure assumptions. The investigator should list not only all positive facts and evidence that may have contributed to the failure, but also all
negative responses that may be learned about the failure. It is sometimes important to know what specific things did not happen or what evidence did not appear to
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help determine what happened. The data should be tabulated and the actual failure
should be synthesized to include all available evidence.
c. Failure cause can usually be classified in one of the following three classifications:
(1) Failure due to faulty design or misapplication of material.
(2) Failure due to improper processing or improper workmanship.
(3) Failure due to deterioration during service.
d.
The following is a summary of the above three situations:
(1) Failure due to faulty design or misapplication of the material involves
failure due to inadequate stress analysis, or a mistake in design such as incorrect
calculations on the basis of static loading instead of dynamic or fatigue loading.
Ductile failure can be caused by a load too great for the section area or the
strength of the material. Brittle fracture may occur from stress risers inherent
in the design, or the wrong material may have been specified for producing the part.
(2) Failures can be caused by faulty processing or poor workmanship that may
be related to the design of the weld joint, or the weld joint design can be proper
but the quality of the weld is substandard. The poor quality weld might include
such defects as undercut, lack of fusion, or cracks. Failures can be attributed to
poor fabrication practice such as the elimination of a root opening, which will
contribute to incomplete penetration. There is also the possibility that the incorrect filler metal was used for welding the part that failed.
(3) Failure due to deterioration during service can cause overload, which may
be difficult to determine. Normal wear and abuse to the equipment may have resulted in reducing sections to the degree that they no longer can support the load.
Corrosion due to environmental conditions and accentuated by stress concentrations
will contribute to failure. In addition, there may be other types of situations
such as poor maintenance, poor repair techniques involved with maintenance, and
accidental conditions beyond the user’s control. The product might be exposed to
an environment for which it was not designed.
e. Conclusion. Examination of catastrophic and major failures has led the
welding industry to appreciate the following facts:
(1) Weldments are monolithic in character.
(2) Anything welded onto a structure will carry part of the load whether
intended or not.
(3) Abrupt changes in section, either because of adding a deckhouse or removing a portion of the deck for a hatch opening, create stress concentration. Under
normal loading, if the steel at the point of stress concentration is notch sensitive at the service temperature, failure can result.
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6-33.
OTHER WELDING PROBLEMS
a. There are two other welding problems that require some explanation and solutions. These are welding over painted surfaces and painting of welds.
CAUTION
Cutting painted surfaces with arc or flame processes should be done
with caution. Demolition of old structural steel work that had been
painted many times with flame-cutting or arc-cutting techniques can
create health problems. Cutting through many layers of lead paint
will cause an abnormally high lead concentration in the immediate area
and will require special precautions such as extra ventilation or
personnel protection.
b. Welding over paint is discouraged. In every code or specification, it is
specifically stated that welding should be done on clean metal. In some industries, however, welds are made over paint, and in others flame cutting is done on
painted base metal.
(1) In the shipbuilding industry and in several other industries, steel when
it is received from tie steel mill, is shot blasted, given a coating of prime
paint, and then stored outdoors. Painting is done to preserve the steel during
storage, and to identify it. In sane shipyards a different color paint is used for
different classes of steel. When this practice is used, every effort should be
made to obtain a prime paint that is compatible with welding.
(2) There are at least three factors involved with the success of the weld
when welding over painted surfaces: the compatibility of the paint with welding;
the dryness of the paint; and the paint film thickness.
(3) Paint compatibility varies according to the composition of the paint.
Certain paints contain large amounts of aluminum or titanium dioxide, which are
usually compatible with welding. Other paints may contain zinc, lead, vinyls, and
other hydrocarbons, and are not compatible with welding. The paint manufacturer or
supplier should be consulted. Anything that contributes to deoxidizing the weld
such as aluminum, silicon, or titanium will generally be compatible. Anything that
is a harmful ingredient such as lead, zinc, and hydrocarbons will be detrimental.
The fillet break test can be used to determin e compatibility. The surfaces should
be painted with the paint under consideration. The normal paint film thickness
should be used, and the paint must be dry.
(4) The fillet break test should be run using the proposed welding procedure
over the painted surface. It should be broken and the weld examined. If the weld
breaks at the interface of the plate with the paint it is obvious that the paint is
not compatible with the weld.
(5) The dryness of the paint should be considered. Many paints employ an oil
base which is a hydrocarbon. These paints dry slowly, since it takes a considerable length of time for the hydrocarbons to evaporate. If welding is done before
the paint is dry, hydrogen will be in the arc atmosphere and can contribute to
underbead cracking. The paint will also cause porosity if there is sufficient oil
present. Water based paints should also be dry prior to welding.
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(6) The thickness of the paint film is another important factor. Some paints
may be compatible if the thickness of the film is a maximum of 3 to 4 mm. If the
paint film thicknesses are double that amount, such as occurs at an overlap area,
there is the passability of weld porosity. Paint films that are to be welded over
should be of the minimum thickness possible.
(7) Tests should be run with the dry maximum film thickness to be used with
the various types of paints to determine which paint has the least harmful effects
on the weld deposit.
c. Painting over welds is also a problem. The success of any paint film depends on its adherence to the base metal and the weld, which is influenced by surface deposits left on the weld and adjacent to it. The metallurgical factors of
the weld bead and the smoothness of the weld are of minor importance with regard to
the success of the paint. Paint failure occurs when the weld and the immediate
area are not properly cleaned prior to painting. Deterioration of the paint over
the weld also seems to be dependent upon the amount of spatter present. Spatter on
or adjacent to the weld leads to rusting of the base material under the paint. It
seems that the paint does not completely adhere to spatter and some spatter does
fall off in time, leaving bare metal spots in the paint coating.
CAUTION
Aluminum and aluminum alloys should not be cleaned with caustic soda
or cleaners having a pH above 10, as they may react chemically. Other
nonferrous metals should be investigated for reactivity prior to cleaning .
(1) The success of the paint job can be insured by observing both preweld and
postweld treatment. Preweld treatment found most effective is to use antispatter
compounds, as well as cleaning the weld area, before welding. The antispatter
compound extends the paint life because of the reduction of spatter. The antispatter compound must be compatible with the paint to be used.
(2) Postweld treatment for insuring paint film success consists of mechanical
and chemical cleaning. Mechanical cleaning methods can consist of hand chipping
and wire brushing, power wire brushing, or sand or grit blasting. Sand or grit
blasting is the most effective mechanical cleaning method. If the weldment is
furnace stress relieved and then grit blasted, it is prepared for painting. When
sand or grit blasting cannot be used, power wire brushing is the next most effective method. In addition to mechanical cleaning, chemical bath washing is also
recommended. Slag coverings on weld depsits must be thoroughly removed from the
surface of the weld and from the adjacent base metal. Different types of coatings
create more or less problems in their removal and also with respect to paint adherence. Weld slag of many electrodes is alkaline in nature and for this reason must
be neutralized to avoid chemical reactions with the paint, which will cause the
paint to loosen and deteriorate. For this reason, the weld should be scrubbed with
water, which will usually remove the residual coating slag and smoke film from the
weld. If a small amount of phosphoric acid up to a 5% solution is used, it will be
more effective in neutralizing and removing the slag. It must be followed by a
water rinse. If water only is used, it is advisable to add small amounts of phosphate or chromate inhibitors to the water to avoid rusting, which might otherwise
occur.
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6-33.
OTHER WELDING PROBLEMS (cont)
(3) It has been found that the method of applying paint is not an important
factor in determining the life of the paint over welds. The type of paint employed
must be suitable for coating metals and for the service intended.
(4) Successful paint jobs over welds can be obtained by observing the following: minimize weld spatter using a compatible anti-spatter compound; mechanically
clean the weld and adjacent area; and wash the weld area with a neutralizing bath
and rinse.
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CHAPTER 7
METALS IDENTIFICATION
Section I.
CHARACTERISTICS
7-1. GENERAL
Most of the metals and alloys used in Army materiel can be welded by one or more of
the processes described in this manual. This section describes the characteristics
of metals and their alloys, with particular reference to their significance in
welding operations.
7-2.
a.
PROPERTIES OF METALS
Definitions.
All metals fall within two categories, ferrous or nonferrous.
(1) Ferrous metals are metals that contain iron. Ferrous metals appear in
the form of cast iron, carbon steel, and tool steel. The various alloys of-iron,
after undergoing cetain processes, are pig iron, gray cast iron, white iron, white
cast iron, malleable cast iron, wrought iron, alloy steel, and carbon steel. All
these types of iron are mixtures of iron and carbon, manganese, sulfur, silicon,
and phosphorous. Other elements are also present, but in amounts that do not appreciably affect the characteristics of the metal.
(2) Nonferrous metals are those which do not contain iron. Aluminum, copper, magnesium, and titanium alloys are among those metals which belong to this
group .
b. Physical Proper t i e s . Many of the physical properties of metals determine if
and how they can be welded and how they will perform in service. Physical properties of various metals are shown in table 7-1, p 7-2.
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(1) Color.
Color relates to the quality of light reflected from the metal.
(2) Mass or density. Mass or density relates to mass with respect to volume. Commonly known as specific gravity, this property is the ratio of the mass of
a given volume of the metal
to0 the mass of the same volume of water at a specified
0
temperature, usually 39 F (4 C ) . For example, the ratio of weight of one cubic
foot of water to one cubic foot of cast iron is the specific gravity of cast iron.
This property is measured by grams per cubic millimeter or centimeter in the metric
system.
(3) Melting point. The melting point of a metal is important with regard
to welding. A metal’s fusibility is related to its melting point, the temperature
at which the metal changes from a solid to a molten state. Pure substances have a
sharp melting point and pass from a solid state to a liquid without a change in
temperature. During this process, however, there is an absorption of heat during
melting and a liberation of heat during freezing. The absorption or release of
thermal energy when a substance changes state is called its latent heat. Mercury
is the only common metal that is in its molten state at normal room temperature.
Metals having loW melting temperatures can be welded with lower temperature heat
sources. The soldering and brazing processes utilize low-temperature metals to
join metals having higher melting temperatures.
(4) Boiling point. Boiling point is also an important factor in welding.
The boiling point is the temperature at which the metal changes from the liquid
state to the vapor state. Some metals, when exposed to the heat of an arc, will
vaporize.
(5) Conductivity.
Thermal and electrical conductivity relate to the metal’s ability to conduct or transfer heat and electricity. Thermal conductivity,
the ability of a metal to transmit heat throughout its mass, is of vital importance
in welding, since one metal may transmit heat from the welding area much more quickly than another. The thermal conductivity of a metal indicates the need for preheating and the size of heat source required. Thermal conductivity is usually
related to copper. Copper has the highest thermal conductivity of the common metals, exceeded only by silver. Aluminum has approximately half the thermal conductivity of copper, and steels have abut one-tenth the conductivity of copper.
Thermal conductivity is measured in calories per square centimeter per second per
degree Celsius. Electrical conductivity is the capacity of metal to conduct an
electric current. A measure of electrical conductivity is provided by the ability
of a metal to conduct the passage of electrical current. Its opposite is resistivity, which is measured
in micro-ohms per cubic centimeter at a standardize tempera0
ture, usually 20 C . Electrical conductivity is usually considered as a percentage
and is related to copper or silver. Temperature bears an important part in this
property. As temperature of a metal increases, its conductivity decreases. This
property is particularly important to resistance welding and to electrical circuits.
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TC 9-237
7-2.
PROPERTIES OF METALS (cont)
(6) Coefficient of linear thermal expansion. With few exceptions, solids
expand when they are heated and contract when they are cooled. The coefficient of
linear thermal expansion is a measure of the linear increase per unit length based
on the change in temperature of the metal. Expansion is the increase on the dimension of a metal caused by heat. The expansion of a metal in a longitudinal direction is known as the linear expansion. The coefficient of linear expansion is
expressed as the linear expansion per unit length for one degree of temperature increase. When metals increase in size, they increase not only in length but also in
breadth and thickness. This is called volumetric expansion. The coefficient of
linear and volumetric expansion varies over a wide range for different metals.
Aluminum has the greatest coefficient of expansion, expanding almost twice as much
as steel for the same temperature change. This is important for welding with respect to warpage, wapage control and fixturing, and for welding together dissimilar metals.
(7) Corrosion resistance. Corrosion resistance is the resistance to eating
or wearing away by air, moisture, or other agents.
c. Mechanical Properties. The mechanical properties of metals determine the
range of usefulness of the metal and establish the service that can be expected.
Mechanical properties are also used to help specify and identify the metals. They
are important in welding because the weld must provide the same mechanical properties as the base metals being joined. The adequacy of a weld depends on whether or
not it provides properties equal to or exceeding those of the metals being joined.
The most common mechanical properties considered are strength, hardness, ductility,
and impact resistance. Mechanical properties of various metals are shown in table
7-2.
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(1) Tensile strength. Tensile strength is defined as the maximum load in
tension a material will withstand before fracturing, or the ability of a material
to resist being pulled apart by opposing forces. Also known as ultimate strength,
it is the maximum strength developed in a metal in a tension test. (The tension
test is a method for det erming the behavior of a metal under an actual stretch
loading. This test provides the elastic limit , elongation, yield point, yield
strength, tensile strength, and the reduction in area.) The tensile strength is
the value most commonly given for the strength of a material and is given in pounds
per square inch (psi) (kiloPascals (kPa)). The tensile strength is the number of
pounds of force required to pull apart a bar of material 1.0 in. (25.4 mm) wide and
1.00 in. (25.4 mm) thick (fig. 7-1).
(2) Shear strength. Shear strength is the ability of a material to resist
being fractured by opposing forces acting of a straight line but not in the same
plane, or the ability of a metal to resist being fractured by opposing forces not
acting in a straight line (fig. 7-2).
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7-2.
PROPERTIES OF METALS (cont)
(3) Fatigue strength. Fatigue strength is the maximum load a material can
withstand without failure during a large number of reversals of load. For example,
a rotating shaft which supports a weight has tensile forces on the top portion of
the shaft and compressive forces on the bottom. As the shaft is rotated, there is
a repeated cyclic change in tensile and compressive strength. Fatigue strength
values are used in the design of aircraft wings and other structures subject to
rapidly fluctuating loads. Fatigue strength is influenced by microstructure, surface condition, corrosive environment, and cold work.
(4) Compressive strength. Compressive strength is the maximum load in
compression a material will withstand before a predetermined amount of deformation,
or the ability of a material to withstand pressures acting in a given plane
(fig. 7-3). The compressive strength of both cast iron and concrete are greater
than their tensile strength. For most materials, the reverse is true.
(5) E l a s t i c i t y . Elasticity is the ability of metal to return to its original size, shape, and dimensions after being deformed, stretched, or pulled out of
shape. The elastic limit is the point at which permanent damage starts. The yield
point is the point at which definite damage occurs with little or no increase in
load. The yield strength is the number of pounnds per square inch (kiloPascals) it
takes to produce damage or deformation to the yield point.
(6) Modulus of elasticity. The modulus of elasticity is the ratio of the
internal stress to the strain produced.
(7) D u c t i l i t y . The ductility of a metal is that property which allows it
to be stretched or otherwise changed in shape without breaking, and to retain the
changed shape after the load has been ramoved. It is the ability of a material,
such as copper, to be drawn or stretched permanently without fracture. The ductility of a metal can be determined by the tensile test by determin ing the percentage
of elongation. The lack of ductility is brittleness or the lack of showing any
permanent damage before the metal cracks or breaks (such as with cast iron).
(8) P l a s t i c i t y .
sively without rupture.
Plasticity is the ability of a metal to be deformed extenPlasticity is similar to ductility.
(9) Malleability. Malleability is another form of plasticity, and is the
ability of a material to deform permanently under compression without rupture. It
is this property which allows the hammering and rolling of metals into thin
sheets. Gold, silver, tin, and lead are examples of metals exhibiting high malleab i l i t y . Gold has exceptional malleability and can be rolled into sheets thin
enough to transmit light.
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(10) Reduction of area. This is a measure of ductility and is obtained
from the tensile test by measuring the original cross-sectional area of a specimen
to a cross-sectional area after failure.
(11) Brittleness. Brittleness is the property opposite of plasticity or
ductility. A brittle metal is one than cannot be visibly deformed permanently, or
one that lacks plasticity.
(12) Toughness. Toughness is a combination of high strength and medium
ductility. It is the ability of a material or metal to resist fracture, plus the
ability to resist failure after the damage has begun. A tough metal, such as cold
chisel, is one that can withstand considerable stress, slowly or suddenly applied,
and which will deform before failure. Toughness is the ability of a material to
resist the start of permanent distortion plus the ability to resist shock or absorb
energy.
(13) Machinability and weldability. The property of machinability and
weldability is the ease or difficulty with which a material can be machined or
welded.
(14) Abrasion resistance.
by friction.
Abrasion resistance is the resistance to wearing
(15) I mpact resistance. Resistance of a metal to impacts is evaluated in
terms of impact strength. A metal may possess satisfactory ductility under static
loads, but may fail under dynamic loads or impact. The impact strength of a metal
is determined by measuring the energy absorbed in the fracture.
(16) Hardness. Hardness is the ability of a metal to resist penetration
and wear by another metal or material. It takes a combination of hardness and
toughness to withstand heavy pounding. The hardness of a metal limits the ease
with which it can be machined, since toughness decreases as hardness increases.
Table 7–3, p 7-8, illustrates hardness of various metals.
(a) Brinell hardness test. In this test, a hardened steel ball is
pressed slowly by a known force against the surface of the metal to be tested. The
diameter of the dent in the surface is then measured, and the Brinell hardness
number (bhn) is det ermined by from standard tables (table 7-3, p 7-8).
(b) Rockwell hardness test. This test is based upon the difference
between the depth to which a test point is driven into a metal by a light load and
the depth to which it is driven in by a heavy load. The light load is first applied and then, without moving the piece, the heavy load is applied. The hardness
number is automatically indicated on a dial. The letter designations on the Rockwell scale, such as B and C, indicate the type of penetrator used and the amount of
heavy load (table 7-3, p 7-8). The same light load is always used.
(c) Scleroscope hardness test. This test measures hardness by letting
a diamond-tipped hammer fall by its own weight from a fixed height and rebound from
the surface; the rebound is measured on a scale. It is used on smooth surfaces
where dents are not desired.
7-7
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TC 9-237
7-3.
CATEGORIES OF METALS (cont)
a. General. It is necessary to know the composition of the metal being welded
in order to produce a successful weld. Welders and metal workers must be able to
identify various metal products so that proper work methods may be applied. For
Army equipment, drawings (MWOs) should be available. They must be examined in
order to determine the metal to be used and its heat treatment, if required. After
S ome practice, the welder will learn that certain parts of machines or equipment
are always cast iron, other parts are usually forgings, and so on.
b. Tests. There are seven tests that can be performed in the shop to identify
metals. Six o f t h e d i f f e r e n t t e s t s a r e summarized in table 7-4, p 7-10. These
should be supplemented by tables 7-1 and 7-2 (p 7-2 and 7-4) which present physical
and mechanical properties of metal, and table 7-3, which presents hardness data.
These tests are as follows:
7-9
TC 9-237
(1) A ppearance test. The appearance test includes such things as color and
appearance of machined as well as unmachined surfaces. Form and shape give definite clues as to the identity of the metal. The shape can be descriptive; for
example, shape includes such things as cast engine blocks, automobile bumpers,
reinforcing rods, I beams or angle irons, pipes, and pipe fittings. Form should be
considered and may show how the part was rode, such as a casting with its obvious
surface appearance and parting mold lines, or hot rolled wrought material, extruded
or cold rolled with a smooth surface. For example, pipe can be cast, in which case
it would be cast iron, or wrought, which would normally be steel. Color provides a
very strong clue in metal identification. It can distinguish many metals such as
copper, brass, aluminum, magnesium, and the precious metals. If metals are oxidized, the oxidation can be scraped off to determine the color of the unoxidized
metal. This helps to identify lead, magnesium, and even copper. The oxidation on
steel, or rust, is usually a clue that can be used to separate plain carbon steels
from the corrosion-resisting steels.
(2) Fracture test. Some metal can be quickly identified by looking at the
surface of the broken part or by studying the chips produced with a hammer and
chisel. The surface will show the color of the base metal without oxidation. This
will be true of copper, lead, and magnesium. In other cases, the coarseness or
roughness of the broken surface is an indication of its structure. The ease of
breaking the part is also an indication of its ductility of lack of ductility. If
the piece bends easily without breaking, it is one of the more ductile metals. If
it breaks easily with little or no bending, it is one of the brittle metals.
(3) Spark test. The spark test is a method of classifying steels and iron
according to their composition by observing the sparks formed when the metal is
held against a high speed grinding wheel. This test does not replace chemical
analysis, but is a very convenient and fast method of sorting mixed steels whose
spark characteristics are known. When held lightly against a grinding wheel, the
different kinds of iron and steel produce sparks that vary in length, shape, and
color. The grinding wheel should be run to give a surface speed of at least 5000
ft (1525 m) per minute to get a good spark stream. Grinding wheels should be hard
enough to wear for a reasonable length of time, yet soft enough to keep a free-cutting edge. Spark testing should be done in subdued light, since the color of the
spark is important. In all cases, it is best to use standard samples of metal for
the purpose of comparing their sparks with that of the test sample.
(a) Spark testing is not of much use on nonferrous metals such as coppers, aluminums, and nickel-base alloys, since they do not exhibit spark streams of
any significance. However, this is one way to separate ferrous and nonferrous
metals.
7-11
TC 9-237
7-3.
CATEGORIES OF METALS (cont)
(b) The spark resulting from the test should be directed downward and
studied. The color, shape, length, and activity of the sparks relate to characteristics of the material being tested. The spark stream has specific items which C ar.
be identified. The straight lines are called carrier lines. They are usually
solid and continuous. At the end of the carrier line, they may divide into three
short lines, or forks. If the spark stream divides into more lines at the end, it
is called a sprig. Sprigs also occur at different places along the carrier line.
These are called either star or fan bursts. In some cases, the carrier line will
enlarge slightly for a very short length, continue, and perhaps enlarge again for a
short length. When these heavier portions occur at the end of the carrier line,
they are called spear points or buds. High sulfur creates these thicker spots in
carrier lines and the spearheads. Cast irons have extremely short streams, whereas
low–carbon steels and most alloy steels have relatively long streams. Steels usually have white to yellow color sparks, while cast irons are reddish to straw yellow. A 0.15 percent carbon steel shins sparks in long streaks with some tendency
to burst with a sparkler effect; a carbon tool steel exhibits pronounced bursting;
and a steel with 1.00 percent cabon shows brilliant and minute explosions or sparklers. As the carbon content increases, the intensity of bursting increases.
(c) One big advantage of this test is that it can be applied to metal in,
all stages, bar stock in racks, machined forgings or finished parts. The spark
test is best conducted by holding the steel stationary and touching a high speed
portable grinder to the specimen with sufficient pressure to throw a horizontal
spark stream about 12.00 in. (30.48 cm) long and at right angles to the line of
vision. Wheel pressure against the work is important r because increasing pressure
will raise the temperature of the spark stream and give the appearance of higher
carbon content. The sparks near and around the wheel, the middle of the spark
stream, and the reaction of incandescent particles at the end of the spark stream
should be observed. Sparks produced by various metals are shown in figure 7-4.
7-12
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7-3.
CATEGORIES OF METALS (cont)
CAUTION
The torch test should be used with discretion, as it may damage the
part being tested. Additionally, magnesium may ignite when heated in
the open atmosphere.
(4) Torch test. With the oxyacetylene torch, the welder can identify various metals by studying how fast the metal melts and how the puddle of molten metal
and slag looks, as well as color changes during heating. When a sharp corner of a
white metal part is heated, the rate of melting can be an indication of its identity. If the material is aluminum, it will not melt until sufficient heat has been
used because its high conductivity. If the part is zinc, the sharp corner will
melt quickly, since zinc is not a good conductor. In the case of copper, if the
sharp comer melts, it is normally deoxidized copper. If it does not melt until
much heat has been applied, it is electrolytic copper. Copper alloys, if composed
of lead, will boil. To distinguish aluminum from magnesium, apply the torch to
filings. Magnesium will burn with a sparkling white flame. Steel will show characteristic colors before melting.
(5) Magnetic test. The magnetic test can be quickly performed using a
small pocket magnet. With experience, it is possible to judge a strongly magnetic
material from a slightly magnetic material. The nonmagnetic materials are easily
recognized. Strongly magnetic materials include the carbon and low-alloy steels,
iron alloys, pure nickel, and martensitic stainless steels. A slightly magnetic
reaction is obtained from Monel and high-nickel alloys and the stainless steel of
the 18 chrome 8 nickel type when cold worked, such as in a seamless tube. Nonmagnetic materials include copper-base alloys, aluminum-base alloys, zinc-base alloys,
annealed 18 chrome 8 nickel stainless, the magnesium, and the precious metals.
(6) Chisel test. The chip test or chisel test may also be used to identify
metals. The only tools required are a banner and a cold chisel. Use the cold
chisel to hammer on the edge or corner of the material being examined. The ease of
producing a chip is an indication of the hardness of the metal. If the chip is
continuous, it is indicative of a ductile metal, whereas if chips break apart, it
indicates a brittle material. On such materials as aluminum, mild steel and malleable iron, the chips are continuous. They are easily chipped and the chips do not
tend to break apart. The chips for gray cast iron are so brittle that they become
small, broken fragments. On high-carbon steel, the chips are hard to obtain because of the hardness of the material, but can be continuous.
(7) Hardness test. Refer to table 7-3, p 7-8, for hardness values of the
various metals, and to p 7-7 for information on the three hardness tests that are
commonly used. A less precise hardness test is the file test. A summary of the
reaction to filing, the approximate Brinell hardness, and the possible type of
steel is shown in table 7-6. A sharp mill file must be used. It is assumed that
the part is steel and the file test will help identify the type of steel.
7-14
TC 9-237
(8). Chemical test. There are numerous chemical test than can be made in
the shop to identify some material. Monel can be distinguished form Inconel by
one drop of nitric acid applied to the surface. It will turn blue-green on Monel,
but will show no reaction on Inconel. A few drops of a 45 percent phosphoric acid
will bubble on low-chomium stainless steels. Magnesium can be distinguished from
aluminum using silver nitrate, which will leave a black deposit on magnesium, but
not on aluminum. These tests can become complicated, and for this reason are not
detailed further here.
c. Color Code for Marking Steel Bars. The Bureau of Standards of the United
States Department of Commerce has a color code for making steel bars. The color
markings provided in the code may be applied by painting the ends of bars. Solid
colors usually mean carbon steel, while twin colors designate alloy and free-cutting steel.
d. Ferrous Metal. The basic substance used to make both steel and cast iron
(gray and malleable) is iron. It is used in the form of pig iron. Iron is produced form iron ore that occurs chiefly in nature as an oxide, the two most important oxides being hematite and magetite. Iron ore is reduced to pig iron in a
blast furnace, and the impurtities are removed in the form of slag (fig. 7-5, p
7-16). Raw materials charged into the furnace include iron ore, coke, and limestone. The pig iron produced is udes to manufacture steel or cast iron.
Plain carbon steel consists of iron and carbon. Carbon is the hardening element.
Tougher alloy steel contains other elements such as chromium, nickel, and molybdenum. Cast iron is nothing more than basic carbon steel with more carbon added,
along with silicon. The carbon content range for steel is 0.03 to 1.7 percent, and
4.5 percent for cast iron.
7-15
TC 9-237
7-3.
CATEGORIES OF METALS (cont)
Steel is produced in a variety of melting furnaces, such as open-hearth, Bessemer
converter, crucible, electric-arc, and induction. Most carbon steel is made in
open-hearth furnaces, while alloy steel is melted in electric-arc and induction
furnaces. Raw materials charged into the furnace include mixtures of iron ore, pig
iron, limestone, and scrap. After melting has been completed, the steel is tapped
from the furnace into a ladle and then poured into ingots or patterned molds. The
ingots are used to make large rectangular bars, which are reduced further by rolling operations. The molds are used for castings of any design.
7-16
TC 9-237
Cast iron is produced by melting a charge of pig iron, limestone, and coke in a
cupola furnace. It is then poured into sand or alloy steel molds. When making
gray cast iron castings, the molten metal in the mold is allowed to become solid
and cool to room temperature in open air. Malleable cast iron, on the other hand,
is made from white cast iron, which is similar in content to gray cast iron except
that malleable iron contains less carbon and silicon. White cast iron
is annealed
O
F
(815
to
for more
than
150
hours
at
temperatures
ranging
from
1500
to
1700
0
927 C). The result is a product called malleable cast iron. The desirable properties of cast iron are less than those of carbon steel because of the difference in
chemical makeup and structure. The carbon present in hardened steel is in solid
solution, while cast iron contains free carbon known as graphite. In gray cast
iron, the graphite is in flake form, while in malleable cast iron the graphite is
in nodular (rounded) form. This also accounts for the higher mechanical properties
of malleable cast iron as compared with gray cast iron.
Iron ore is smelted with coke and limestone in a blast furnace to remove the oxygen
(the process of reduction) and earth foreign matter from it. Limestone is used to
combined with the earth matter to form a liquid slag. Coke is used to supply the
carbon needed for the reduction and carburization of the ore. The iron ore, limestone, and coke are charged into the top of the furnace. Rapid combustion with a
blast of preheated air into the smelter causes a chemical reaction, during which
the oxygen is removed from the iron. The iron melts, and the molten slag consisting of limestone flux and ash from the coke, together with compounds formed by
reaction of the flux with substances present in the ore, floats on the heavier iron
liquid. Each material is then drawn off separately (fig. 7-6, p 7-18).
All forms of cast iron, steel, and wrought iron consist of a mixture of iron, carbon, and other elements in small amounts. Whether the metal is cast iron or steel
depends entirely upon the amount of carbon in it. Table 7-7 shows this principle.
Cast iron differs from steel mainly because its excess of carbon (more than 1.7
percent) is distributed throughout as flakes of graphite, causing most of the remaining carbon to separate. These particles of graphite form the paths through
which failures occur, and are the reason why cast iron is brittle. By carefully
controlling the silicon content and the rate of cooling, it is possible to cause
any definite amount of the carbon to separate as graphite or to remain combined.
Thus, white, gray, and malleable cast iron are all produced from a similar base.
7-17
TC 9-237
(1) Wrought iron.
(a) General. Wrought iron is almost pure iron. It is made from pig
iron in a puddling Furnace and has a carbon content of less than 0.08 percent.
Carbon and other elements present in pig iron are taken out, leaving almost pure
iron. In the process of manufacture, some slag is mixed with iron to form a fibrous structure in which long stringers of slag, running lengthwise, are mixed with
long threads of iron. Because of the presence of slag, wrought iron resists corrosion and oxidation, which cause rusting .
(b) Uses. Wrought iron is used for porch railings, fencing, farm
implements, nails, barbed wire, chains, modern household furniture, and decorations.
(c) Capabilities.
plated, and is easily formed.
strength.
(d) Limitations.
Wrought iron can be gas and arc welded, machined,
Wrought iron has loW hardness and low fatigue
(e) Properties. Wrought iron has Brinell hardness number of 105; 0
tensile strength of 35,000 psi; specific gravity of 7.7; melting point of 2750 F
0
(151O C); and is ductile and corrosion resistant.
(f) Appearance test.
that of rolled, low-carbon steel.
The appearance of wrought iron is the same as
(g) Fracture test. Wrought iron has a fibrous structure due to
threads of slag. As a result, it can be split in the direction in which the fibers
run. The metal is soft and easily cut with a chisel, and is quite ductile. When
nicked and bent, it acts like rolled steel. However, the break is very jagged due
to its fibrous structure. Wrought iron cannot be hardened.
(h) S p a rk test. When wrought iron is ground, straw-colored sparks
form near the grinding wheel, and change to white, forked sparklers near the end of
the stream.
(i) Torch test. Wrought iron melts quietly without sparking. It has
a peculiar slag coating with white lines that are oily or greasy in appearance.
(2) Cast iron (gray, white, and malleable).
(a) General. Cast iron is a manmade alloy of iron, carbon, and silicon. A portion of the carbon exists as free carbon or graphite. Total carbon
content is between 1.7 and 4.5 percent.
(b) Uses. Cast iron is used for water pipes, machine tool castings,
transmission housing, engine blocks, pistons, stove castings, etc.
(c) Capabi l i t i e s . Cast iron may be brazed or bronze welded, gas and
arc welded, hardened, or machined.
(d) Limitations.
cannot be worked cold.
Cast iron must be preheated prior to welding. It
7-19
TC 9-237
7-3.
CATEGORIES OF METALS (cont)
(e) Properties. Cast iron has a Brinell hardness number of 150 to 220
(no alloys) and 300 to 600 (alloyed); tensile strength of 25,000 to 50,000 psi
(172,375 to 344,750 kPa) (no alloys) and 50,000 to 100,OOO psi (344,750 to 689,500
kPa) (alloyed); specific gravity of 7.6; high compressive strength that is four
times its tensile strength; high rigidity; good wear resistance; and fair corrosion
resistance.
(f) Gray cast iron. If the molten pig iron is permitted to cool slowly, the chemical compund of iron and carbon breaks up to a certain extent. Much
of the carbon separates as tiny flakes of graphite scattered throughout the metal.
This graphite-like carbon, as distinguish from combined carbon, causes the gray
appearance of the fracture, which characterizes ordinary gray cast iron. Since
graphite is an excellent lubricant , and the metal is shot throughout with tiny,
flaky cleavages, gray cast iron is easy to machine but cannot withstand a heavy
shock. Gray cast iron consists of 90 to 94 percent metallic iron with a mixture of
carbon, manganese, phosphorus, sulfur, and silicon. Special high-strength grades
of this metal also contain 0.75 to 1.50 percent nickel and 0.25 to 0.50 percent
chromium or 0.25 to 1.25 percent molybdenum. Commercial gray iron has 2.50 to 4.50
percent carbon. About 1 percent of the carbon is combined with the iron, while
about 2.75 percent remains in the free or graphitic state. In making gray cast
iron, the silicon content is usually increased, since this allows the formation of
graphitic carbon. The combined carbon (iron carbide), which is a small percentage
of the total carbon present in cast iron, is known as cementite. In general, the
more free carbon (graphitic carbn) present in cast iron, the lower the combined
carbon content and the softer the iron.
1. Appe arance test. The unmachined surface of gray cast iron
castings is a very dull gray in color and may be somewhat roughened by the sand
mold used in casting the part. Cast iron castings are rarely machined all over.
Unmachined castings may be ground in places to remove rough edges.
2. Fracture test. Nick a corner all around with a chisel or
hacksaw and strike the corner with a sharp blow of the hammer. The dark gray color
of the broken surface is caused by fine black specks of carbon present in the form
of graphite. Cast iron breaks short when fractured. Small, brittle chips made
with a chisel break off as soon as they are formed.
3. S park test. A small volume of dull-red sparks that follow a
straight line close to the wheel are given off when this metal is spark tested.
These break up into many fine, repeated spurts that change to a straw color.
4. Torch test. The torch test results in a puddle of molten
metal that is quiet and has a jelly like consistency. When the torch flame is
raised, the depression in the surface of the molts-puddle disappears instantly. A
heavy, tough film forms on the surface as it melts. The molten puddle takes time
to harden and gives off no sparks.
(g) White cast iron. When gray cast iron is heated to the molten
state, the carbon completely dissolves in the iron, probably combining chemically
with it. If this molten metal is cooled quickly, the two elements remain in the
combined state, and white cast iron is formed. The carbon in this type of iron
7-20
TC 9-237
measures above 2.5 to 4.5 percent by weight, and is referred to as combined carbon. White cast iron is very hard and brittle, often impossible to machine, and
has a silvery white fracture.
cast iron is made by heating white
(h) Malleable cast
iron. Malleable
0
0
cast iron froman 1400 to 1700 F (760 and 927 C) for abut 150 hours in boxes containing hematite ore or iron scale. This heating causes a part of the combined
carbon to change into the free or uncombined state. This free carbon separates in
a different way from carbon in gray cast iron and is called temper carbon. It
exists in the form of small, rounded particles of carbon which give malleable iron
castings the ability to bend before breaking and to withstand shock better than
gray cast iron. The castings have properties more like those of pure iron: high
strength, ductility, toughness, and ability to resist shock. Malleable cast iron
can be welded and brazed. Any welded part should be annealed after welding.
1. Appearance test. The surface of malleable cast iron is very
much like gray cast iron, but is generally free from sand. It is dull gray and
somewhat lighter in color than gray cast iron.
2. Fracture test. When malleable cast iron is fractured, the
central portion of the broken surface is dark gray with a bright, steel-like band
at the edges. The appearance of the fracture may best be described as a picture
frame. When of good quality, malleable cast iron is much tougher than other cast
iron and does not break short when nicked.
3 . S p a rk test. When malleable cast iron is ground, the outer,
bright layer gives off bright sparks like steel. As the interior is reached, the
sparks quickly change to a dull-red color near the wheel. These sparks from the
interior section are very much like those of cast iron; however, they are somewhat
longer and are present in large volume.
4. Torch test. Molten malleable cast iron boils under the torch
flame. After the-flame has been withdrawn, the surface will be full of blowholes.
When fractured, the melted parts are very hard and brittle, having the appearance
of white cast iron (they have been changed to white or chilled iron by melting and
fairly rapid cooling). The outside, bright, steel-like band gives off sparks, but
the center does not.
(3) S t e e l .
(a) General. A form of iron, steel contains less carbon than cast
iron, but considerably more than wrought iron. The carbon content is from 0.03 to
1.7 percent. Basic carbon steels are alloyed with other elements, such as chromium
and nickel, to increase certain physical properties of the metal.
(b) Uses. Steel is used to make nails, rivets, gears, structural
steel, roles, desks, hoods, fenders, chisels, hammers, etc.
(c) Capab ilities. Steel can be machined, welded, and forged, all to
varying degrees, depending on the type of steel.
(d) Limitations.
Highly alloyed steel is difficult to produce.
7-21
TC 9-237
7-3.
CATEGORIES OF METALS (cont)
(e) P r o p e rt i e s . Steel has tensile strength of 45,000 psi (310,275
kPa) for low-carbon steel, 80,000 psi (551,600 kPa) for medium-carbon steel, 99,000
psi (692,605 kPa) for high-carbon steel, 0and 150,000
psi (1,034,250 kPa) for al0
loyed steel; and a melting point of 2800 F (1538 C).
(f) Low-carbon steel (carbon content up to 0.30 percent. This steel
is soft and ductile, and can be rolled, punched, sheared, and worked when either
hot or cold. It is easily machined and can readily be welded by all methods. It
does not harden to any great amount; however, it can easily be case hardened.
1. Appearance test. The appearance of the steel depends upon the
method of preparation rather than upon composition. Cast steel has a relatively
rough, dark-gray surface, except where it has been machined. Rolled steel has fine
surface lines running in one direction. Forged steel is usually recognizable by
its shape, hammer marks, or fins.
2. Fracture test. When low-carbon steel is fractured, the color
is bright crystalline gray. It is tough to chip or nick. Low carbon steel,
wrought iron, and steel castings cannot be hardened.
3. Spark test. The steel gives off sparks in long yellow-orange
streaks, brighter than cast iron, that show some tendency to burst into white,
forked sparklers.
4. Torch test.
ens almost instantly.
The steel gives off sparks when melted, and hard-
(g) Medium-carbon steel (carbon content ranging from 0.30 to 0.50
percent). This steel may be heat-treated after fabrication. It is used for general machining and forging of parts that require surface hardness and strength. It
is made in bar form in the cold-rolled or the normalized and annealed condition.
During welding, the weld zone will become hardened if cooled rapidly and must be
stress-relieved after welding.
(h) High-carbon steel (carbon content ranging from 0.50 to 0.90 percent ) . This steel is used for the manufacture of drills, taps, dies, springs, and
other machine tools and hand tools that are heat treated after fabrication to develop the hard structure necessary to withstand high shear stress and wear. It is
manufactured in bar, sheet, and wire forms, and in the annealed or normalized condition in order to be suitable for machining before heat treatment. This steel is
difficult to weld because of the hardening effect of heat at the welded joint.
1. Appe arance test. The unfinished surface of high-carbon steel
is dark gray and similar to other steel. It is more expensive, and is usually
worked to produce a smooth surface finish.
2. Fracture test. High-carbon steel usually produces a very
fine-grained fracture, whiter than low-carbon steel. Tool steel is harder and more
brittle than plate steel or other low-carbon material. High-carbon steel can be
hardened by heating to a good red and quenching in water.
7-22
TC 9-237
3. Spark test.
bright yellow-orange sparks.
High-carbon steel gives off a large volume of
4. Torch test. Molten high-carbon steel is brighter than lowcarbon steel, and the melting surface has a porous appearance. It sparks
more
freely than low-carbon (mild) steels, and the sparks are whiter.
(i) High carbon tool steel. Tool steel (carbon content ranging from
0.90 to 1.55 percent) is used in the manufacture of chisels, shear blades, cutters,
large taps, wood-turning tools, blacksmith’s tools, razors, and similar parts where
high hardness is required to maintain a sharp cutting edge. It is difficult to
weld due to the high carbon content. A spark test shows a moderately large volume
of white sparks having many fine, repeating bursts.
(4) Cast steel.
(a) General. Welding is difficult on steel castings containing over
0.30 percent carbon and 0.20 percent silicon. Alloy steel castings containing nickel, molybdenum, or both of these metals , are easily welded if the carbon content is
low. Those containing chromium or vanadium are more difficult to weld. Since
manganese steel is nearly always used in the form of castings, it is also considered with cast steel. Its high resistance to wear is its most valuable property.
(b) Appearance test. The surface of cast steel is brighter than cast
or malleable iron and sometimes contains small, bubble-like depressions.
(c) Fracture test.
crystalline gray. This steel is
are tougher than malleable iron,
nese steel, however, is so tough
machined.
The color of a
tough and does
and chips made
that is cannot
fracture in cast steel is bright
not break short. Steel castings
with a chisel curl up more. Mangabe cut with a chisel nor can it be
(d) Spark test. The sparks created from cast steel are much brighter
than those from cast iron. Manganese steel gives off marks that explode, throwing
off brilliant sparklers at right angles to the original-path of the spark:
(e) Torch test.
When melted, cast steel sparks and hardens quickly.
(5) Steel forgings.
(a) General. Steel forgings may be of carbon or alloy steels. Alloy
steel forgings are harder and more brittle than low carbon steels.
(b) Appearance test. The surface of steel forgings is smooth. Where
the surface of drop forgings has not been finished, there will be evidence of the
fin that results from the metal squeezing out between the two forging dies. This
fin is removed by the trimming dies, but enough of the sheared surface remains for
identification. All forgings are covered with reddish brown or black scale, unless
they have been purposely cleaned.
7-23
TC 9-237
7-3.
CATEGORIES OF METALS (cont)
(c) Fracture test. The color of a fracture in a steel forging varies
from bright crystalline to silky gray. Chips are tough; and when a sample is
nicked, it is harder to break than cast steel and has a finer grain. Forgings may
be of low- or high-carbon steel or of alloy steel. Tool steel is harder and more
brittle than plate steel or other low-carbon material. The fracture is usually
whiter and finer grained. Tool steel can be hardened by heating to a good red and
then quenching in water. Low-carbon steel, wrought iron, and steel castings cannot
be usefully hardened.
(d) S p a rk test. The sparks given off are long, yellow-orange streamers and are typical steel sparks. Sparks from high-carbon steel (machinery and
tool steel) are much brighter than those from low-carbon steel.
(e) Torch test. Steel forgings spark when melted, and the sparks
increase in number and brightness as the carbon content becomes greater.
(6) Alloy steel.
(a) General. Alloy steel is frequently recognizable by its use.
There are many varieties of alloy steel used in the manufacture of Army equipment.
They have greater strength and durability than carbon steel, and a given strength
is secured with less material weight. Manganese steel is a special alloy steel
that is always used in the cast condition (see cast steel, p 7-23).
Nickel, Chromiumr vanadium, tungsten, molybdenum, and silicon are the most common
elements used in alloy steel.
1. Chromium is used as an alloying element in carbon steels to
increase hardenability, corrosion resistance, and shock resistance. It imparts
high strength with little loss in ductility.
2. Nickel increases the toughness, strength, and ductility of
steels, and lowers the hardening temperatures so than an oil quench, rather than a
water quench, is used for hardening.
3. Manganese is used in steel to produce greater toughness, wear
resistance, easier hot rolling, and forging. An increase in manganese content
decreases the weldability of steel.
4. Molybdenum increases hardenability, which is the depth of
hardening possible through heat treatment. The impact fatigue property of the
steel is improved with up to 0.60 percent molybdenum. Above 0.60 percent molybdenum, the impact fatigue property is impaired. Wear resistance is improved with
molybdenum content above 0.75 percent. Molybdenum is sometimes combined with chromium, tungsten, or vanadium to obtain desired properties.
5. Titanium and columbium (niobium) are used as additional alloying agents in low-carbon content, corrosion resistant steels. They support resistance to intergranular corrosion after the metal is subjected to high temperatures
for a prolonged time period.
7-24
TC 9-237
6. Turgsten, as an alloying element in tool steel, produces a
fine, dense grain-when used in small quantities. When used in larger quantities,
from 17 to 20 percent, and in combination with other alloys, it produces a steel
that retains its hardness at high temperatures.
7. Vanadium is used to help control grain size. It tends to
increase hardenability and causes marked secondary hardness, yet resists tempering. It is also added to steel during manufacture to remove oxygen.
—8. Silicon is added to steel to obtain greater hardenability and
corrosion resistance, and is often used with manganese to obtain a strong, tough
steel. High speed tool steels are usually special alloy compositions designed for
cutttig tools. The carbon content ranges from 0.70 to 0.80 percent. They are
difficult to weld except by the furnace induction method.
9. High yield strength, low alloy structural steels (often referred to as constructional alloy steels) are special low carbon steels containing
specific small amounts of alloying elements. These steels are quenched and tempered to obtain a yield strength of 90,000 to 100,000 psi (620,550 to 689,500 kPa)
and a tensile strength of 100,000 to 140,000 psi (689,500 to 965,300 kPa), depending upon size and shape. Structural members fabricated of these high strength
steels may have smaller cross sectional areas than common structural steels, and
still have equal strength. In addition, these steels are more corrosion and abrasion resistant. In a spark test, this alloy appears very similar to the low carbon
steels.
NOTE
This type of steel is much tougher than low carbon steels, and shearing machines must have twice the capacity required for low carbon
steels.
(b) Apperance test.
Alloy steel appear the same as drop-forged
steel.
(c) Fracture test. Alloy steel is usually very close grained; at
times the fracture appears velvety.
(d) Spark test. Alloy steel produces characteristic sparks both in
color and shape. some of the more common alloys used in steel and their effects on
the spark stream are as follows:
1. Chromium. Steels containing 1 to 2 percent chromium have no
outstanding features in the spark test. Chromium in large amounts shortens the
spark stream length to one-half that of the same steel without chromium, but does
not appreciably affect the stream’s brightness. Other elements shorten the stream
to the same extent and also make it duller. An 18 percent chromium, 8 percent
nickel stainless steel produces a spark similar to that of wrought iron, but only
half as long. Steel containing 14 percent chromium and no nickel produces a shorter version of the low-carbon spark. An 18 percent chromium, 2 percent carbon steel
(chromium die steel) produces a spark similar to that of carbon tool steel, but
one-third as long.
7-25
TC 9-237
7-3.
CATEGORIES OF METALS (cont)
2. N i c k e l . The nickel spark has a short, sharply defined dash of
brilliant light just before the fork. In the amounts found in S.A.E. steels, nickel can be recognized only when the carbon content is so low that the bursts are not
too noticeable.
3. High chromium-nickel alloy (stainless) steels. The sparks
given off during a spark test are straw colored near the grinding wheel and white
near the end of the streak. There is a medium volume of streaks having a moderate
number of forked bursts.
4. Manganese. Steel containing this element produces a spark
similar to a carbon steel spark. A moderate increase in manganese increases the
volume of the spark stream and the force of the bursts. Steel containing more than
the normal amount of manganese will spark in a manner similar to high-carbon steel
with low manganese content.
5. Molybdenum. Steel containing this element produces a characteristic spark with a detached arrowhead similar to that of wrought iron. It can
be seen even in fairly strong carbon bursts. Molybdenum alloy steel contains nickel, chromium, or both.
6. Molybdenum with other elements. When molybdenum and other
elements are substituted for S ome of the tungsten in high-speed steel, the spark
stream turns orange. Although other elements give off a red spark, there is enough
difference in their color to tell them from a tungsten spark.
7. Tungsten . Tungsten will inpart a dull red color to the spark
stream near the wheel. It also shortens the spark stream, decreases the size, or
completely eliminates the carbon burst. Steel containing 10 percent tungsten causes short, curved, orange spear points at the end of the carrier lines. Still lower
tungsten content causes small white bursts to appear at the end of the spear
p i n t . Carrier lines may be anything from dull red to orange in color, depending
on the other elements present, if the tungsten content is not too high.
8. Vanadium. Alloy steels containing vanadium produce sparks
with a detached arrowhead at the end of the carrier line similar to those arising
from molybdenum steels. The spark test is not positive for vanadium steels.
9. High speed tool steels. A spark test in these steels will
impart a few long; forked sparks which are red near the wheel, and straw-colored
near the end of the spark stream.
(7) Special steel. Plate steel is used in the manufacture of built-up
welded structures such as gun carriages. In using nickel plate steel, it has been
found that commericial grades of low-alloy structural steel of not over 0.25 percent
carbon, and several containing no nickel at all, are better suited to welding than
those with a maximum carbon content of 0.30 percent. Armorplate, a low carbon alloyed steel, is an example of this kind of plate. Such plate is normally used in
the “as rolled” condition. Electric arc welding with a covered electrode may require preheating of the metal, followed by a proper stress-relieving heat treatment
(post heating), to produce a structure in which the welded joint has properties
equal to those of the plate metal.
7-26
TC 9-237
e.
Nonferrous metal.
(1) Aluminum (Al).
(a) General. Aluminum is a lightweight, soft, low strength metal
which can easily be cast, forged, machined, formed, and welded. It is suitable
only in low temperature applications, except when alloyed with specific elements.
Commercial aluminum alloys are classified into two groups, wrought alloys and cast
alloys. The wrought alloy group includes those alloys which are designed for mill
products whose final physical forms are obtained by working the metal mechanically . The casting alloy group includes those alloys whose final shapes are obtained
by allowing the molten metal to solidify in a mold.
(b) Uses. Aluminum is used as a deoxidizer and alloying agent in the
manufacture of steel. Castings, pistons, torque converter pump housings, aircraft
structures, kitchen utensils, railways cars, and transmission lines are made of
aluminum.
welded.
(c) Capabilities.
Aluminum can be cast, forged, machined, formed, and
(d) Limitations. Direct metal contact of aluminum with copper and
copper alloys should be avoided. Aluminum should be used in low-temperature appli.cations.
(e) Properties. Pure aluminum has a Brinell hardness number of 17 to
27; tensile strength of 6000 to 16,000 0 psi (41,370
to 110,320 kPa); specific gravi0
ty of 2.7; and a melting point of 1220 F (660 C ) . Aluminum alloys have a Brinell
hardness number of 100 to 130, and tensile strength of 30,000 to 75,000 psi
(206,850 to 517,125 kPa). Generally, aluminum and aluminum alloys have excellent
heat conductivity; high electrical conductivity (60 percent that of copper, volume
for volume; high strength/weight ratio at room temperature; and unfairly corrosion resistant.
(f) Appearance test. Aluminum is light gray to silver in color, very
bright when polished, dull when oxidized, and light in weight. Rolled and sheet
aluminum materials are usually pure metal. Castings are alloys of aluminum with
other metals, usually zinc, copper, silicon, and sometimes iron and magnesium.
Wrought aluminum alloys may contain chromium, silicon, magnesium, or manganese.
Aluminum strongly resembles magnesium in appearance. Aluminum is distinguished
from magnesium by the application of a drop of silver nitrate solution on each
surface. The silver nitrate will not react with the aluminum, but leaves a black
deposit of silver on the magnesium.
(g) Fracture test. A fracture in rolled aluminum sections shows a
smooth, bright structure. A fracture in an aluminum casting shins a bright crystalline structure.
(h) S p a rk test.
No sparks are given off from aluminum.
(i) Torch test. Aluminum does not turn red before melting. It holds
its shape until almost molten, then collapses (hot shorts) suddenly. A heavy film
of white oxide forms instantly on the molten surface.
7-27
TC 9-237
7-3.
CATEGORIES OF METALS (cont)
(2) Chromium (Cr).
(a) General. Chromium is an alloying agent used in steel, cast iron,
and nonferrous alloys of nickel, copper, aluminum, and cobalt. It is hard, brittle, corrosion resistant, can be welded, machined, forged, and is widely used in
electroplating. Chromium is not resistant to hydrochloric acid and cannot be used
in its pure state because of its difficulty to work.
(b) Uses. Chromium is one of the most widely used alloys. It is used
as an alloying agent-in steel and cast iron (0.25 to 0.35 percent) and in
nonferrou s alloys of nickel, copper, aluminum, and cobalt. It is also used in
electroplating for appearance and wear, in powder metallurgy, and to make mirrors
and stainless steel.
forged.
(c) Ca pabilities. Chromium alloys can be welded, machined, and
Chromium is never used in its pure state.
(d) Limitations. Chromium is not resistant to hydrochloric acid, and
cannot be used in the pure state because of its brittleness and difficulty to work.
(e) Properties
(pure).
Chromium has a specific gravity of 7.19; a
0
0
melting point of 3300 F (1816 C); Brinell hardness number of 110 to 170; is resistant to acids other than hydrochloric; and is wear, heat, and corrosion resistant.
(3) Cobalt (Co).
(a) General. Cobalt is a hard, white metal similar to nickel in appearance, but has a slightly bluish cast.
(b) Uses. Cobalt is mainly used as an alloying element in permanent
and soft magnetic materials, high-speed tool bits and cutters, high-temperature,
creep-resisting alloys, and cemented carbide tools, bits, and cutters. It is also
used in making insoluble paint pigmnts and blue ceramic glazes. In the metallic
form, cobalt does not have many-uses. However, when combined with other elements,
it is used for hard-facing materials.
drawn.
ters.
(c) C a p a b i l i t i e s . Cobalt can be welded, machined (limited), and cold(d) Limitations. Cobalt must be machined with cemented carbide cutWelding high carbon cobalt steel often causes cracking.
(e) Pro perties. Pure cobalt has a tensile strength of 34,000 psi
hardness
number of 125; specific gravity of 8.9; and a melt(234,430 kPa); Brinell
0
0
ing point of 2720 F (1493 C). Cobalt alloy (Stellite 21) has a tensile strength
of 101,000 psi (696,395 kPa) and is heat and corrosion resistant.
(4) C o pper (Cu).
(a) General. Copper is a reddish metal, is very ductile and malleable, and has high electrical and heat conductivity. It is used as a major element
in hundreds of alloys. Commercially pure copper is not suitable for welding.
7-28
TC 9-237
Though it is very soft, it is very difficult to machine due to its high ductility.
Beryllium copper contains from 1.50 to 2.75 percent beryllium. It is ductile when
soft, but loses ductility and gains tensile strength when hardened. Nickel copper
contains either 10, 20, or 30 percent nickel. Nickel alloys have moderately high
to high tensile strength, which increases with the nickel content. They are moderately hard, quite tough, and ductile. They are V ery resistant to the erosive and
corrosive effects of high velocity sea water, stress corrosion, and corrosion fatigue. Nickel is added to copper zinc alloys (brasses) to lighten their color; the
resultant alloys are called nickel silver. These alloys are of two general types,
one type containing 65 percent or more copper and nickel combined, the other containing 55 to 60 percent copper and nickel combined. The first type can be cold
worked by such operations as deep drawing, stamping, and spinning. The second type
is much harder end is not processed by any of the cold working methods. Gas welding is the preferred process for joining copper and copper alloys.
(b) Uses. The principal use of commericially pure copper is in the
electrical industry where it is made into wire or other such conductors. It is
also used in the manufacture of nonferrous alloys such as brass, bronze, and Monel
metal. Typical copper products are sheet roofing, cartridge cases, bushings, wire,
bearings, and statues.
(c) Capababilities. Copper can be forged, cast, and cold worked. I t
can also be welded, but its machinability is only fair. Copper alloys can be welded.
(d) Limitations. Electrolytic tough pitch copper cannot be welded
satisfactorily. Pure copper is not suitable for welding and is difficult to machine due to its ductility.
(e) Properties. Pure copper is nonmagnetic; has a Brinell hardness
number of 60 to 110; a tensile strength of 32,000 to 60,000
psi 0 (220,640 to 413,700
0
kPa); specific gravity of 8.9; melting point of 1980 F (1082 C); and is corrosion
resistant. Copper alloys have a tensile strength of 50,000 to 90,000 psi (344,750
to 620,550 kPa) and a Brinell hardness number of 100 to 185.
(f) Appearance test. Copper is red in color when polished, and oxidizes to various shades of green.
(g) Fracture test. Copper presents a smooth surface when fractured,
which is free from crystalline appearance.
(h) Spark test.
Copper gives off no sparks.
(i) Torch test. Because copper conducts heat rapidly, a larger flame
is required to produce fusion of copper than is needed for the same size piece of
steel. Copper melts suddenly and solidifies instantly. Copper alloy, containing
small amounts of other metals, melts more easily and solidifies more slowly than
pure copper.
7-29
TC 9-237
7-3.
CATEGORIES OF METALS (cont)
(j) Brass and bronze. Brass, an alloy of copper and zinc (60 to 68
percent copper and 32 to 40 percent zinc) , has a lo W melting point and high heat
conductivity. There are several types of brass, such as naval, red, admiralty,
yellow, and commercial. All differ in copper and zinc content; may be alloyed with
other elements such as lead, tin, manganese, or iron; have good machinability; and
can be welded. Bronze is an alloy of copper and tin and may contain lead, zinc,
nickel, manganese, or phosphorus. It has high strength, is rust or corrosion resistant, has good machinability, and can be welded.
1 . Appearance test. The color of polished brass and bronze varies with the composition from red, almost like copper, to yellow brass. They oxidize to various shades of green, brown, or yellow.
. 2. Fracture test. The surface of fractured brass or bronze ranges from smooth to crystalline, depending upon composition and method of preparation; i.e., cast, rolled, or forged.
3.
Spark test.
Brass and bronze give off no sparks.
4. Torch test. Brass contains zinc, which gives off white fumeS
when it is melted. Bronze contains tin. Even a slight amount of tin makes the
alloy flow very freely, like water. Due to the small amount of zinc or tin that is
usually present, bronze may fume slightly, but never as much as brass.
(k) Aluminum bronze.
1. Appearance test.
darker yellow than brass.
2.
Fracture test.
When polished, aluminum bronze appears a
Aluminum bronze presents a smooth surface when
fractured.
3.
Spark test. Aluminum bronze gives off no sparks.
4. Torch test. Welding aluminum bronze is very difficult. The
surface is quickly covered with a heavy stun that tends to mix with the metal and
is difficult to remove.
(5) Lead (Pb).
CAUTION
Lead dust and fumes are poisonous. Exercise extreme care when welding
lead, and use personal protective equipment as described in chapter 2.
(a) General. Lead is a heavy, soft, malleable metal with low melting
point, lo W tensile strength, and low creep strength. It is resistant to corrosion
from ordering atmosphere, moisture, and water, and is effective against many acids. Lead is well suited for cold working and casting. The low melting point of
lead makes the correct welding rod selection very important.
(b) Uses. Lead is used mainly in the manufacture of electrical equipment such as lead-coated power and telephone cables, and storage batteries. I t i s
7-30
TC 9-237
also used in building construction in both pipe and sheet form, and in solder.
Zinc alloys are used in the manufacture of lead weights, bearings, gaskets, seals,
bullets, and shot. Many types of chemical compounds are produced from lead; among
these are lead carbonate (paint pigment) and tetraethyl lead (antiknock gasoline).
Lead is also used for X-ray protection (radiation shields). Lead has more fields
of application than any other metal.
(c) Capab i l i t i e s . Lead can be cast, cold worked, welded, and machined . It is corrosion, atmosphere, moisture, and water resistant, and is resistant to many acids.
(d) Limitations.
and fumes are very poisonous.
Lead has low strength with heavy weight. Lead dust
(e) Properties. Pure lead has tensile strength of 2500 to 3000 psi0
(17,237.5 to 20,685 kPa); specific gravity of 11.3; and a melting point of 620 F
(327 C). Alloy lead B32-467 has tensile strength of 5800 psi (39,991 kPa). Generally, lead has low electrical conductivity; is self-lubricating; is malleable; and
is corrosion resistant.
(6) Magnesium (Mg).
(a) General. Magnesium is an extremely light metal, is white in color, has a loW melting point, excellent machinability, and is weldable. Welding by
either the arc or gas process requires the use of a gaseous shield. Magnesium is
moderately resistant to atmospheric exposure, many chemicals such as alkalies,
chromic and hydrofluoric acids, hydrocarbons, and most alcohols, phenols, esters,
and oils. It is nonmagnetic. Galvanic corrosion is an important factor in any
assembly with magnesium.
(b) Uses. Magnesium is used as a deoxidizer for brass, bronze, nickel, and silver. Because of its light weight, it is used in many weight-saving
applications, particularly in the aircraft industry. It is also used in the manufacture and use of fireworks for railroad flares and signals, and for military
purposes. Magnesium castings are used for engine housings, blowers, hose pieces,
landing wheels, and certain parts of the fuselage of aircraft. Magnesium alloy
materials are used in sewing machines, typewriters, and textile machines.
(c) Capabi l i t i e s .
Magnesium can be forged, cast, welded, and machined.
Magnesium in fine chip form will ignite at loW tem(d) Limitations.
0
peratures (800 to 1200 F (427 to 649 °C)). The flame can be mothered with suitable materials such as carbon dioxide (C02), foam, and sand.
(e) Properties. Pure magnesium has tensile strength of 12,000 psi
(82,740 kPa) (cast) and tensile strength of 37,000 psi (255,115 kPa) (rolled);
Brinell hardness number 0 of 30 (cast)
and 50 (rolled); specific gravity of 1.7; and
0
a melting point of 1202 F (650 C). Magnesium alloy has Brinell hardness number
of 72 (hard) and 50 (forged); and tensile strength of 42,000 psi (289,590 kPa)
(hard) and 32,000 psi (220,640 kPa) (forged).
7-31
TC 9-237
7-3.
CATEGORIES OF MATERIALS (cont)
(f) Appearance test. Magnesium resembles aluminum in appearance. The
polished surface is silver-white, but quickly oxidizes to a grayish film. Like
aluminum, it is highly corrosion resistant and has a good strength-to-weight ratio,
but is lighter in weight than aluminum. It has a very low kindling point and is
not very weldable, except when it is alloyed with manganese and aluminum. Magnesium is distinguished from aluminum by the use of a silver nitrate solution. The
solution does not react with aluminum, but leaves a black deposit of silver on
magnesium. Magnesium is produced in large quantities from sea water. It has excellent machinability, but special care must be used when machining because of its loW
kindling point.
structure.
(g) Fracture test.
Magnesium has a rough surface with a fine grain
(h) S p a rk test. No sparks are given off.
CAUTION
Magnesium may ignite and burn when heated in the open atmosphere.
(i) Torch test. Magnesium oxidizes rapidly when heated in open air,
producing an oxide film which is insoluble in the liquid metal. A fire may result
when magnesium is heated in the open atmosphere. As a safety precaution, magnesium
should be melted in an atmosphere of inert gas.
(7) Manganese (Mn).
(a) General. Pure manganese has a relatively high tensile strength,
but is very brittle. Manganese is used as an alloying agent in steel to deoxidize
and desulfurize the metal. In metals other than steel, percentages of 1 to 15
percent manganese will increase the toughness and the hardenability of the metal
involved.
(b) Uses. Manganese is used mainly as an alloying agent in making
steel to increase tensile strength. It is also added during the steel-making
process to remove sulfur as a slag. Austenitic manganese steels are used for railroad track work, power shovel buckets, and rock crushers. Medium-carbon manganese
steels are used to make car axles and gears.
(c) Capab i l i t i e s .
Manganese can be welded, machined, and cold-worked.
(d) Limitations. Austenitic manganese steels are best machined with
cemented carbide, cobalt, and high-speed steel cutters.
(e) Properties. Pure manganese has tensile strength of 72,000 psi
(496,440 kPa) (quenched) Brinell hardness number of 330; specific gravity of 7.43:
0
0
a melting point of 2270 F (1243 C); and is brittle. Manganese alloy has a tensile strength of 110,000 psi (758,450 kPa). Generally, manganese is highly
polishable and brittle.
7-32
TC 9-237
(8) Molybdenum (Mo).
(a) General. Pure molybdenum has a high tensile strength and is very
resistant to heat. It is principally used as an alloying agent in steel to increase strength, hardenability, and resistance to heat.
(b) Uses. Molybdenum is used mainly as an alloy. Heating elements,
switches, contacts, thermocouplers, welding electrodes, and cathode ray tubes are
made of molybdenum.
(c) Capabilities.
Molybdenum can be swaged, rolled, drawn, or ma-
chined.
(d) Limitations. Molybdenum can only be welded by atomic hydrogen
arc, or butt welded by resistance heating in vacuum. It is attacked by nitric
acid, hot sulfuric acid, and hot hydrochloric acid.
(e) Properties. Pure molybdenum has a tensile strength of 100,000 psi
(689,500 kPa) (sheet) and 30,000 Psi (206,850 kPa) (wire); Brinell
hardness
number
0
0
of 160 to 185; specific gravity of 10.2; meting point of 4800 F (2649 C); retains hardness and strength at high temperatures; and is corrosion resistant.
(9) Nickel (Ni).
(a) General. Nickel is a hard, malleable, ductile metal. As an alloy, it will increase ductility, has no effect on grain size, lowers the critical
point for heat treatment, aids fatigue strength, and increases impact values in low
temperature operations. Both nickel and nickel alloys are machinable and are readily welded by gas and arc methods.
(b) Uses. Nickel is used in making alloys of both ferrous and
nonferrous metal. Chemical and food processing equipment, electrical resistance
heating elements, ornamental trim, and parts that must withstand elevated temperatures are all produced from nickel-containing metal. Alloyed with chromium, it is
used in the making of stainless steel.
(c) C a p a b i l i t i e s . Nickel alloys are readily welded by either the gas
or arc methods. Nickel alloys can be machined, forged, cast, and easily formed.
(d) Limitations.
ture or corrosive gases.
Nickel oxidizes very slowly in the presence of mois-
(e) Properties. Pure nickel has tensile strength of 46,000 psi
(317,170 kPa);0 Brinell 0hardness number 220; specific gravity of 8.9; and melting
point of 2650 F (1454 C). Nickel alloys have Brinell hardness number of 140 to
230. Monel-forged nickel has tensile strength of 100,000 psi (689,500 kPa), and
high strength and toughness at high temperatures.
(f) A p p earance. Pure nickel has a grayish white color.
(g) Fracture.
The fracture surface of nickel is smooth and fine
grained.
7-33
TC 9-237
7-3.
CATEGORIES OF METALS (cont)
(h) Spark test. In a spark test, nickel produces a very small amount
of short, orange streaks which are generally wavy.
(i) Monel metal. Monel metal is a nickel alloy of silver-white color
containing about 67.00 percent nickel, 29.00 to 80.00 percent copper, 1.40 percent
iron, 1.00 percent manganese, 0.10 percent silicon, and 0.15 percent carbon. In
appearance, it resembles untarnished nickel. After use, or after contact with
chemical solutions, the silver-white color takes on a yellow tinge, and some of the
luster is lost. It has a very high resistance to corrosion and can be welded.
(10) Tin (Sn).
(a) General. Tin is a very soft, malleable, somewhat ductile, corrosion resistant metal having low tensile strength and high crystalline structure.
It is used in coating metals to prevent corrosion.
(b) Uses. The major application of tin is in coating steel. It
serves as the best container for preserving perishable focal. Tin, in the form of
foil, is often used in wrapping food products. A second major use of tin is as an
alloying element. Tin is alloyed with copper to produce tin brass and bronze, with
lead to produce solder , and with antimony and lead to form babbitt.
Tin can be die cast, cold worked (extruded), ma-
(c) Ca pabilities.
chined, and soldered.
(d) Limitations.
Tin is not weldable.
(e) Properties. Pure tin has tensile strength
of 0 2800 psi (19,306
O
kPa); specific gravity of 7.29; meltinq point of 450 F (232 C); and is corrosion
resistant. Babbitt alloy tin has tensile strength of 10,000 psi’ (68,950 kPa) and
Brinell hardness number of 30.
(f) Appearance. Tin is silvery white in color.
(g) Fracture test.
fairly smooth.
torch.
The fracture surface of tin is silvery white and
(h) S p a rk test.
Tin gives off no sparks in a spark test.
(i) Torch
Tin melts at 450 F (232 C), and will boil under the
test.
0
0
(11) Titanium (Ti).
(a) General. Titanium is a very soft, silvery white, medium-strength
metal having very good corrosion resistance. It has a high strength to weight
ratio, and its tensile strength increases as the temperature decreases. Titanium
h a s l o w0
impact
and creep strengths, as well as seizing tendencies, at temperatures
0
above 80 F (427 C).
7-34
TC 9-237
(b) Uses. Titanium is a metal of the tin group which occurs naturally
as titanium oxide or in other oxide forms. The free element is separated by heating the oxide with aluminum or by the electrolysis of the solution in calcium chloride. Its most important compound is titanium dioxide, which is used widely in
welding electrode coatings. It is used as a stabilizer in stainless steel so that
carbon will not be separated during the welding operation. It is also used as an
additive in alloying aluminum, copper, magnesium, steel, and nickel; making powder
for fireworks; and in the manufacture of turbine blades, aircraft firewalls, engine
nacelles, frame assemblies, ammunition tracks, and mortar base plates.
(c) Capabilities. Titanium can be machined at loW speeds and fast
feeds; formal; spot- and seam-welded, and fusion welded using inert gas.
(d) Limitations. Titanium has0 loW impact
strength, and low creep
0
strength at high temperatures (above 800 F (427 C)). It can only be cast into
simple shapes, and it cannot be welded by any gas welding process because of its
high attraction for oxygen. Oxidation causes this metal to become quite brittle.
The inert gas welding process is re commended to reduce contamination of the weld
metal.
(e) P roperties. Pure titanium has a tensile strength of 100,000 psi;
0
Brinell hardness number of 200; specific gravity of 4.5; melting point of 3300 F
0
(1851 C); and good corrosion resistance. Alloy titanium has a Brinell hardness
number of 340; tensile strength of 150,000 psi; and a high strength/weight ratio
O
0
(twice that of aluminum alloy at 400 F (204 C)).
(f) A p p earance test. Titanium is a soft, shiny, silvery-white metal
burns in air and is the only element that burns in nitrogen. Titanium alloys look
like steel, and can be distinguished from steel by a copper sulfate solution. The
solution will not react with titanium, but will leave a coating of copper on steel.
(g) Spark test.
of medium length.
The sparks given off are large, brilliant white, and
(12) Turgsten (W).
(a) General. Tungsten is a hard, heavy, nonmagnetic metal which will
0
0
melt at approximately 6150 F (3400 C).
(b) Uses. Tungsten is used in making light bulb filaments, phonograph
needles, and as an alloying agent in production of high-speed steel, armorplate,
and projectiles. It is also used as an alloying agent in nonconsumable welding
electrodes, armor plate, die and tool steels, and hard metal carbide cutting tools.
(c) Capab ilities. Tungsten can be cold and hot drawn.
(d) Limitations. Tungsten is hard to machine, requires high temperatures for melting, and is produced by powered metallurgy (sintering process).
0
(e) Properties. Tungsten has a melting point of 6170 ± 35 F (3410 ±–
0
19 C); is ductile; has tensile strength of 105,OOO psi (723,975 kPa); a specific
gravity of 19.32; thermal conductivity of 0.397; a Brinell hardness number of 38;
and is a dull white color.
7-35
TC 9-237
7-3.
CATEGORIES 0F METALS (cont)
(f) A ppearance.
Tungsten is steel gray in color.
(g) S p a rk test. Tungsten produces a very small volume of short,
straight, orange streaks in a spark test.
(13) Zinc (Zn).
(a) General. Zinc is a medium low strength metal having a very low
melting point. I to is easy 0 to machine, but coarse grain zinc should be heated to
approximately 180 F (82 C) to avoid cleavage of crystals. Zinc can be soldered
or welded if it is properly cleaned and the heat input closely controlled.
(b) Uses.
1. Galvanizing metal is the largest use of zinc and is done by
dipping the part in molten zinc or by electroplating it. Examples of items made in
this way are galvanized pipe, tubing, sheet metal, wire, nails, and bolts. Zinc is
also used as an alloying element in producing alloys such as brass and bronze.
Those alloys that are made up primarily of zinc itself.
2 . Typical parts made with zinc alloy are die castings, toys,
ornaments, building equipment, carburetor and fuel pump bodies, instrument panels,
wet and dry batteries, fuse plugs, pipe organ pipes, munitions, cooking utensils,
and flux. Other forms of zinc include zinc oxide and zinc sulfide, widely used in
paint and rubber, and zinc dust, which is used in the manufacture of explosives and
chemical agents.
Zinc can be cast, cold worked (extruded), machined,
(c) Capabi l i t i e s .
and welded.
with steam.
(d) Limitations.
DO
not use zinc die castings in continuous contact
(e) Properties. Zinc has a tensile strength of 12,000 psi (82,740
kPa) (cast) and 27,0000 psi (186,165
kPa) (rolled); a specific gravity of 7.1; a O
0
melting
point of 790 F (421 C); is corrosion resistant; and is brittle at 220 F
0
(104 C) .
(f) A p p earance. Both zinc and zinc alloys are blue-white in color
when polished, and oxidize to gray.
(g) Fracture test.
(h) S p a rk test.
Zinc fractures appear somewhat granular.
Zinc and zinc alloys give off no sparks in a spark
test.
(i) Zinc die castings.
7-36
TC 9-237
1. A ppearance test. Die castings are usually alloys of zinc,
aluminum, magnesium, lead, and tin. They are light in weight, generally silvery
white in color (like aluminum), and sometimes of intricate design. A die-cast
surface is much smoother than that of a casting made in sand, and is almost as
smooth as a machined surface. Sometimes, die castings darkened by use may be mistaken for malleable iron when judged simply by looks, but the die casting is lighter in weight and softer.
2. Fracture test.
has a slight granular structure.
3.
Spark test.
The surface of a zinc die casting is white and
Zinc die castings give off no sparks.
4. Torch test. Zinc die castings can be recognized by their low
melting temperatures. The metal boils when heated with the oxyacetylene flame. A
die casting, after thorough cleaning, can be welded with a carburizing flare using
tin or aluminum solders as filler metal. If necessary, the die-cast part can be
used as a pattern to make a new brass casting.
(14) White metal die castings.
(a) G e n e r a l . These are usually made with alloys of aluminum, lead,
magnesium, or tin. Except for those made of lead and tin, they are generally light
in weight and white in color.
(b) Appearance.
castings made in sand.
torch.
The surface is much smoother than that produced by
(c)
Fracture test. Fractured surface is white and somewhat granular.
(d)
Spark test.
No sparks given off in a spark test.
(e)
Torch test.
Melting points are low, and the metal boils under the
Section II.
STANDARD METAL DESIGNATIONS
7-4. GENERAL
The numerical index system for the classification of metals and their alloys has
been generally adopted by industry for use on drawings and specifications. In this
system, the class to which the metal belongs, the predominant alloying agent, and
the average carbon content percentage are given.
7-5.
STANDARD DESIGNATION SYSTEM FOR STEEL
a.
Numbers are used to designate different chemical compositions. A fourdigit number series designates carbon and alloying steels according to the types
and classes shown in table 7-8, p 7-38. This system has been expanded, and in some
cases five digits are used to designate certain alloy steels.
b.
cates
alloy
tured
Two letters are often used as a prefix to the numerals. The letter C indibasic open hearth carbon steels, and E indicates electric furnace carbon and
steels.
The letter H is sometimes used as a suffix to denote steels manufacto meet hardenability limits.
7-37
TC 9-237
7-5.
STANDARD DESIGNATION SYSTEM FOR STEEL (cont)
c. The first two digits indicate the major alloying metals in a steel, such as
manganese, nickel-chromium, and chrome-molybdenum.
d. The last digits indicate the approximate middle of the carbon content range
in percent. For example, 0.21 indicates a range of 0.18 to 0.23 percent carbon.
In a few cases, the system deviates from this rule, and some carbon ranges relate
to the ranges of manganese, sulfur, phosphorous, chromium, and other elements.
e. The system designates the major elements of a steel and the approximate
carbon range of the steel. It also indicates the manufacturing process used to
produce the steel. The complete designation system is shown in table 7-9, p 7-40.
7-38
TC 9-237
f . The number 2340 by this system indicates a nickel steel with approximately 3
percent nickel and 0.40 percent carbon. The number 4340 indicates a nickel-chromemolybdenum metal with 0.40 percent carbon.
S.A.E. Steel Specifications
The following numerical system for identifying carbon and alloy steels of various
specifications has been adopted by the Society of Automotive Engineers.
COMPARISION
A.I.S.I. --S.A.E. Steel Specifications
The ever-growing variety of chemical compositions and quality requirements of steel
specifications have resulted in several thousand different combinations of chemical
elements being specified to meet individual demands of purchasers of steel products.
The S.A.E. developed a system of nomenclature for identification of various chemical compositions which symbolize certain standards as to machining, heat treating,
and carburizing performance. The American Iron and Steel Institute has now gone
further in this regard with a new standardization setup with similar nomenclature,
but with restricted carbon ranges and combinations of other elements which have
been accepted as standard by all manufacturers of bar steel in the steel industry.
The Society of Automotive Engineers have, as a result, revised most of their specifications to coincide with those set up by the American Iron and Steel Institute.
7-39
TC 9-237
7-5.
STANDARD DESIGNATION SYSTEM FOR STEEL (Cont)
7-6.
STANDARD DESIGNATION SYSTEM FOR ALUMINUM AND ALUMINUM ALLOYS
a. Currently, there is no standard designation system for aluminum castings.
Wrought aluminum and aluminum alloys have a standard four-digit numbering system.
b. The first digit represents the major alloying element.
c. The second digit identifies alloy modifications (a zero means the original
alloy).
d. The last two digits seine only to identify different aluminum alloys which
are in common commercial use, except in the 1XXX class. In the 1XXX class, the
last two digits indicate the aluminum content above 99 percent, in hundredths of
one percent.
e . In number 1017, the 1 indicates a minimum aluminum composition of 99 percent; the O indicates it is the original composition; and the 17 indicates the
hundredths of one percent of aluminum above the 99 percent minimum composition. In
this example, the aluminum content is 99.17 percent.
f . In number 3217, the 3 indicates a manganese aluminum alloy; the 2 indicates
the second modification of this particular alloy; and the 17 indicates a commonly
u s e d commercial alloy.
g. The various classes of aluminum and aluminum alloys are identified by numbers as shown in table 7-10.
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7-7.
STANDARD DESIGNATION SYSTEM FOR MAGNESIUM AND MAGNESIUM ALLOYS
a. Wrought magnesium and magnesium alloys are identified by a combination of
letters and numbers. The letters identify which alloying elements were used in the
magnesium alloy (table 7-11). Numbers, which may follow the letters, designate
the percentage of the elements in the magnesium alloy. There may be an additional
letter following the percentage designators which indicates the alloy modifications. For example, the letter A means 1; B means 2; and C means 3.
b. In the identification number AZ93C, the A indicates aluminum; the Z indicates zinc; the 9 indicates there is 9 percent aluminum in the alloy; the 3 indicates there is 3 percent zinc in the alloy; and the C indicates the third modification to the alloy. The first digit, 9 in this example, always indicates the percentage of the first letter, A in this example. The second digit gives the percentage of the second letter (table 7-12, p 7-42).
c. Temper designations may be added to the basic magnesium designation, the two
being separated by a dash. The temper designations are the same as those used for
aluminum (see Heat Treatment of Steel, p 12-72).
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7-8. STANDARD DESIGNATION SYSTEM FOR COPPER AND COPPER ALLOYS
a. There are over 300 different wrought copper and copper alloys commercially
available. The Copper Development Association, Inc., has established an alloy
designation system that is widely accepted in North America. It is not a specification system but rather a method of identifying and grouping different coppers and
copper alloys. This system has been updated so that it now fits the unified numbering system (UNS). It provides one unified numbering ring system which includes all of
the commercially available metals and alloys. The UNS designation consists of the
prefix letter C followed by a space, three digits, another space, and, finally, two
zeros.
b. The information shown by table 7-13 is a grouping of these copper alloys by
common names which normally include the constituent alloys. Welding information
for those alloy groupings is provided. There may be those alloys within a grouping
that may have a composition sufficiently different to create welding problems.
These are the exception, however, and the data presented will provide starting
point guidelines. There are two categories, wrought materials and cast materials.
The welding information is the same whether the material is cast or rolled.
7-42
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7-43
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7-8.
7-44
STANDARD DESIGNATION SYSTEM FOR COPPER AND COPPER ALLOYS (cent)
TC 9-237
7-9.
STANDARD DESIGNATION SYSTEM FOR TITANIUM
There is no recognized standard designation system for titanium and titanium alloys. However, these compositions are generally designated by using the chemical
symbol for titanium, Ti, followed by the percentage number(s) and the chemical symbols(s) of the alloying element(s). For example, Ti-5 A1-2.5 Sn would indicate
that 5 percent aluminum and 2-1/2 percent tin alloying elements are present in the
titanium metal.
Section III.
7-10.
GENERAL DESCRIPTION AND WELDABILITY OF FERROUS METALS
LOW CARBON STEELS
a. General. The loW carbon (mild) steels include those with a carbon content
of up to 0.30 percent (fig. 7-7). In most low carbon steels, carbon ranges from
0.10 to 0.25 percent, manganese from 0.25 to 0.50 percent, phosphorous O.40 percent
maximum, and sulfur 0.50 percent maximum. Steels in this range are most widely
used for industrial fabrication and construction. These low carbon steels do not
harden appreciably when welded, and therefore do not require preheating or
postheating except in special cases, such as when heavy sections are to be welded.
In general, no difficulties are encountered when welding low carbon steels. Properly made low carbon steel welds will equal or exceed the base metal in strength.
Low carbon steels are soft, ductile, can be rolled, punched, sheared, and worked
when either hot or cold. They can be machined and are readily welded. Cast steel
has a rough, dark gray surface except where machined. Rolled steel has fine surface lines running in one direction. Forged steel is usually recognizable by its
shape, hammer marks, or fins. The fracture color is bright crystalline gray, and
the spark test yields sparks with long, yellow-orange streaks that have a tendency
to burst into white, forked sparklers. Steel gives off sparks when melted and
solidifies almost instantly. Low carbon steels can be easily welded with any of
the arc, gas, and resistance welding processes.
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7-10.
LOW CARBON STEELS (cont)
b. Copper coated loW carbon rods should be used for welding low carbon steel.
The rod sizes for various plate thicknesses are as follows:
Plate thickness
1/16 to 1/8 in. (1.6 to 3.2 mm)
1/8 to 3/8 in. (3.2 to 9.5 mm)
3/8 to 1/2 in. (9.5 to 12.7 mm)
1/2 in. (12.7 mm) and heavier
Rod diameter
1/16 in. (1.6 mm)
1/8 in. (3.2 mm)
3/16 in. (4.8 mm)
1/4 in. (6.4 mm)
NOTE
Rods from 5/16 to 3/8 in. (7.9 to 9.5 mm) are available for heavy
welding. However, heavy welds can be made with the 3/16 or 1/4 in.
(4.8 or 6.4 mm) rods by properly controlling the puddle and melting
rate of the rod.
c. The joints may be prepared by flame cutting or machining. The type of preparation (fig. 7-8) is determined by the plate thickness and the welding position.
d. The flame should be adjusted to neutral. Either the forehand or backhand
welding method may be used (p 6-36), depending on the thickness of the plates being
welded .
e. The molten metal should not be overheated, because this will cause the metal
to boil and spark excessively. The resultant grain structure of the weld metal
will be large, the strength lowered, and the weld badly scarred.
7-46
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f.
ing.
g.
The low carbon steels do not harden in the fusion zone as a result of weldMetal-Arc Welding.
(1) When metal-arc welding low carbon steels, the bare, thin coated or heavy
coated shielded arc types of electrodes may be used. These electrodes are of lo W
carbon type (0.10 to 0.14 percent).
(2) Low carbon sheet or plate materials that have been exposed to low temperatures should be preheated slightly to room temperature before welding.
(3) In welding sheet metal up to 1/8 in. (3.2 mm) in thickness, the plain
square butt joint type of edge preparation may be used. When long seams are to be
welded in these materials, the edges should be spaced to allow for shrinkage, because the deposited metal tends to pull the plates together. This shrinkage is
less severe in arc welding than in gas welding, and spacing of approximately 1/8
in. (3.2 mm) will be sufficient.
(4) The backstep, or skip, welding technique should be used for short seams
that are fixed in place. This will prevent warpage or distortion, and will minimize residual stresses.
(5) Heavy plates should be beveled to provide an included angle of up to 60
degrees, depending on the thickness. The parts should be tack welded in place at
short intervals along the seam. The first, or root, bead should be made with an
electrode small enough in diameter to obtain good penetration and fusion at the
base of the joint. A 1/8 or 5/32 in. (3.2 or 4.0 mm) electrode is suitable for
this purpose. The first bead should be thoroughly cleaned by chipping and wire
brushing before additional layers of weld metal are deposited. Additional passes
of the filler metal should be made with a 5/32 or 3/16 in. (4.0 or 4.8 mm) electrode. The passes should be made with a weaving motion for flat, horizontal, or
vertical positions. When overhead welding, the best results are obtained by using
string beads throughout the weld.
(6) When welding heavy sections that have been beveled from both sides, the
weave beads should be deposited alternately on one side and then the other. This
will reduce the amount of distortion in the welded structure. Each bead should be
cleaned thoroughly to remove all scale, oxides, and slag before additional metal is
deposited. The motion of the electrode should be controlled so as to make the bead
uniform in thickness and to prevent undercutttig and overlap at the edges of the
weld. All slag and oxides must be removed from the surface of the completed weld
to prevent rusting.
h. Carbon-Arc Welding. Low carbon sheet and plate up to 3/4 in. (19.0 mm) in
thickness can be welded using the carbon-arc welding process. The arc is struck
against the plate edges, which are prepared in a manner similar to that required
for metal-arc welding. A flux should be used on the joint and filler metal should
be added as in oxyacetylene welding. A gaseous shield should be provided around
the molten base. Filler metal, by means of a flux coated welding rod, should also
be provided. Welding must be done without overheating the molten metal. Failure
to observe these precautions can cause the weld metal to absorb an excessive amount
of carbon from the electrode and oxygen and nitrogen from the air, and cause brittleness in the welded joint.
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7-11.
MEDIUM CARBON STEELS
a. General. Medium carbon steels are non-alloy steels which contain from 0.30
to 0.55 percent carbon. These steels may be heat treated after fabrication and
used for general machining and forging of parts which require surface hardness and
strength. They are manufactured in bar form and in the cold rolled or the normalized and annealed condition.
When heat 0 treated steels are welded, they should be
0
preheated from 300 to 500 F (149 to 260 C), depending on the carbon content (O.25
to 0.45 percent) and the thickness of the steel. The preheating temperature may be
checked by applying a stick of 50-50 solder (melting point 450 F (232 C)) to the
plate at the joint , and noting when the solder begins to melt. During welding, the
weld zone will become hardened if cooled rapidly, and must be stress relieved after
welding. Medium carbon steels may be welded with any of the arc, gas, and resistance welding processes.
b. With higher carbon and manganese content, the low-hydrogen type electrodes
should be used, particularly in thicker sections. Electrodes of the low-carbon,
heavy coated, straight or reverse polarity type, similar to those used for metalarc welding of low carbon steels, are satisfactory for welding medium carbon steels.
c. Small parts should be annealed to induce softness before welding. The parts
should be preheated at the joint and welded with a filler rod that produces heat
treatable welds. After welding, the entire piece should be heat treated to restore
its original properties.
d. Either a loW carbon or high strength rod can be used for welding medium
carbon steels. The welding flame should be adjusted to slightly carburizing, and
the puddle of metal kept as small as possible to make a sound joint. Welding with
a carburizing flame causes the metal to heat quickly, because heat is given off
when steel absorbs carbon. This permits welding at higher speeds.
e. Care should be taken to slowly cool the parts after welding to prevent cracking of the weld. The entire welded part should be stress relieved by heating to
0
0
between 1100 and 1250 F (593 and 677 C) for one hour per inch (25.4 mm) of thickness, and then slowly cooling. Cooling can be accomplished by covering the parts
with fire resistant material or sand.
0
f. Medium
carbon steels can be brazed by using a preheat of 200 to 400 F (93
0
to 204 C), a good bronze rod, and a brazing flux. However, these steels are better welded by the metal-arc process with mild steel shielded arc electrodes.
g.
When welding mild steels, keep the following general techniques in mind:
(1) The plates should be prepared for welding in a manner similar to that
used for welding low carbon steels. When welding with low carbon steel electrodes,
the welding heat should be carefully controlled to avoid overheating the weld metal
and excessive penetration into the side walls of the joint. This control is accomplished by directing the electrode more toward the previously deposited filler
metal adjacent to the side walls than toward the side walls directly. By using
this procedure, the weld metal is caused to wash up against the side of the joint
and fuse with it without deep or excessive penetration.
7-48
TC 9-237
(2) High welding heats will cause large areas of the base metal in the fusion
zone adjacent to the welds to become hard and brittle. The area of these hard
zones in the base metal can be kept to a minimum by making the weld with a series
of small string or weave beads, which will limit the heat input. Each bead or
layer of weld metal will refine the grain in the weld immediately beneath it, and
will anneal and lessen the hardness produced in the base metal by the previous bead.
(3) When possible, the finished joint should be heat treated after welding.
Stress relieving is normally used when joining mild steel, and high carbon alloys
should be annealed.
(4) In welding medium carbon steels with stainless steel electrodes, the
metal should be deposited in string beads in order to prevent cracking of the weld
metal in the fusion zone. When depositing weld metal in the upper layers of welds
made on heavy sections, the weaving motion of the electrode should not exceed three
electrode diameters.
(5) Each successive bead of weld should be chipped, brushed, and cleaned
prior to the laying of another bead.
7-12.
HIGH CARBON STEELS
a. General. High carbon steels include those with a carbon content exceeding
O.55 percent. The unfinished surface of high carbon steels is dark gray and similar to other steels. High carbon steels usually produce a very fine grained fracture, whiter than low carbon steels. Tool steel is harder and more brittle than
plate steel or other low carbon material. High carbon steel can be hardened by
heating to a good red and quenching in water. Low carbon steel, wrought iron, and
steel castings cannot be hardened. Molten high carbon steel is brighter than low
carbon steel, and the melting surface has a cellular appearance. It sparks more
freely than lo W carbon (mild) steel, and the sparks are whiter. These steels are
used to manufacture tools which are heat treated after fabrication to develop the
hard structure necessary to withstand high shear stress and wear. They are manufactured in bar, sheet, and wire forms, and in the annealed or normalized and annealed
condition in order to be suitable for machining before heat treatment. The high
carbon steels are difficult to weld because of the hardening effect of heat at the
welded joint. Because of the high carbon content and the heat treatment usually
given to these steels, their basic properties are impaired by arc welding.
b. The welding heat changes the properties of high carbon steel in the vicinity
of the weld. To restore the original properties, heat treatment is necessary.
O
0
c. High carbon steels should be preheated from 500 to 800 F (260 to 427 C )
before welding. The preheating temperature can be checked with a pine stick, which
will char at these temperatures.
d. Since high carbon steels melt at lower temperatures than low and medium
carbon steels, care should be taken not to overheat the weld or base metal. Overheating is indicated by excessive sparking of the molten metal. Welding should be
completed as soon as possible and the amount of sparking should be used as a check
on the welding heat. The flame should be adjusted to carburizing. This type of
flame tends to produce sound welds.
7-49
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7-12.
HIGH CARBON STEELS (cont)
e. Either a medium or high carbon welding rod should be used to make the weld.
After welding, the
entire piece 0should be stress relieved by heating to between
O
1200 and 1450 F (649 and 788 C) for one hour per inch (25.4 mm) of thickness, and
then slowly cooling. If the parts can easily be softened before welding, a high
carbon welding rod should be used to make the joint. The entire piece should then
be heat treated to restore the original properties of the base metal.
f . In some cases, minor repairs to these steels can be made by brazing. This
process does not require temperatures as high as those used for welding, so the
properties of the base metal are not seriously affected. Brazing should only be
used in special cases, because the strength of the joint is not as high as the
original base metal.
g. Either mild or stainless steel electrodes can be used with high carbon
steels.
h. Metal-arc welding in high carbon steels requires critical control of the
weld heat. The following techniques should be kept in mind:
(1) The welding heat should be adjusted to provide good fusion at the side
walls and root of the joint without excessive penetration. Control of the welding
heat can be accomplished by depositing the weld metal in small string beads. Excessive puddling of the metal should be avoided, because this can cause carbon to be
picked up from the base metal, which in turn will make the weld metal hard and
b r i t t l e . Fusion between the filler metal and the side walls should be confined to
a narrow zone. Use the surface fusion procedure prescribed for medium carbon
steels (para 7-11, p 7-48).
(2) The same procedure for edge preparation, cleaning of the welds, and sequence of welding beads as prescribed for low and medium carbon steels also applies
to high carbon steels.
(3) Small, high carbon steel partS are sometimes repaired by building up worn
surfaces. When this is done, the piece should be annealed or softened by heating
to a red heat and cooling slowly. The piece should then be welded or built up with
medium carbon or high strength electrodes, and heat treated after welding to restore its original properties.
7-13.
TOOL STEELS
a. G e n e r a l . Steels used for making tools, punches, and dies are perhaps the
hardest, strongest, and toughest steels used in industry. In general, tool steels
are medium to high carbon steels with specific elements included in different
amounts to provide special characteristics. A spark test shows a moderately large
volume of white sparks having many fine, repeating bursts.
b. Carbon is provided in tool steel to help harden the steel for cutting and
wear resistance. Other elements are added to provide greater toughness or
strength. In S ome cases, elements are added to retain the size and shape of the
tool during its heat treat hardening operation, or to make the hardening operation
safer and to provide red hardness so that the tool retains its hardness and
7-50
TC 9-237
strength when it becomes extremely hot. Iron is the predominant element in the
composition of tool steels. Other elements added include chromium, cobalt, manganese, molybdenum, nickel, tungsten, and vanadium. The tool or die steels are designed for special purpose that are dependent upon composition. Certain tool
steels are made for producing die blocks; some are made for producing molds, others
for hot working, and others for high-speed cutting application.
c. Another way to classify tool steels is according to the type of quench required to harden the steel. The most severe quench after heating is the water
quench (water-hardening steels). A less severe quench is the oil quench, obtained
by cooling the tool steel in oil baths (oil-hardening steels). The least drastic
quench is cooling in air (air-hardening steels).
d . Tool steels and dies can also be classified according to the work that is to
be done by the tool. This is based on class numbers.
(1) Class I steels are used to make tools that work by a shearing or cutting
actions, such as cutoff dies, shearing dies, blanking dies, and trimming dies.
(2) Class II steels are used to make tools that produce the desired shape of
the part by causing the material being worked, either hot or cold, to flow under
tension. This includes drawing dies, forming dies, reducing dies, forging dies,
plastic molds, and die cast molding dies.
(3) Class III steels are used to make teds that act upon the material being
worked by partially or wholly reforming it without changing the actual dimensions.
This includes bending dies, folding dies, and twisting dies.
(4) Class IV steels are used to make dies that work under heavy pressure and
that produce a flow of metal or other material caressing it into the desired
form. This includes crimping dies, embossing dies, heading dies, extrusion dies,
and staking dies.
e.
Steels in the
1.55 percent. They
ness produced in the
either mild steel or
tool steels group have a carbon content ranging from 0.83 to
are rarely welded by arc welding because of the excessive hardfusion zone of the base metal. If arc welding must be done,
stainless steel electrodes can be used.
0
0
f . Uniformly high preheating temperatures (up to 1000 F (583 C)) must be used
when welding tool steels.
g.
In general, the same precautions should be taken as those required for welding high carbon steels (para 6-12, p 6-22). The welding flare should be adjusted
to carburizing to prevent the burning out of carbon in the weld metal. The welding
should be done as quickly as possible, taking care not to overheat the molten meta l . After welding, the steel should be heat treated to restore its original properties.
h. Drill rods can be used as filler rods because their high carbon content
compares closely with that of tool steels.
i . A flux suitable for welding cast iron should be used in small quantities to
protect the puddle of high carbon steel and to remove oxides in the weld metal.
7-51
TC 9-237
7-13.
TOOL STEEL (cont)
j. Welding Technique. When welding tool steels, the following techniques
should be kept in mind:
(1) If the parts to be welded are small, they should be annealed or softened
before welding. The edges should then be preheated up to 1000 0F (538 0C), depending on the carbon content and thickness of the plate. Welding should be done with
either a mild steel or high strength electrode.
(2) High carbon electrodes should not be used for welding tool steels. The
carbon picked up from the base metal by the filler metal will cause the weld to
become glass hard, whereas the mild steel weld metal can absorb additional carbon
without becoming excessively hard. The welded part should then be heat treated to
restore its original properties.
(3) When welding with stainless steel electrodes, the edge of the plate
should be preheated to prevent the formation of hard zones in the base metal. The
weld metal should be deposited in small string beads to keep the heat input to a
minimum. In general, the application procedure is the same as that required for
medium and high carbon steels.
k. There are four types of die steels that are weld repairable. These are
water-hardening dies, oil-hardening dies, air-hardening dies, and hot work tools.
High-speed tools can also be repaired.
7-14.
HIGH HARDNESS ALLOY STEELS
a. General. A large number and variety of alloy steels have been developed to
obtain high strength, high hardness, corrosion resistance, and other -special propert i e s . Most of these steels depend on a special heat treatment process in ordered to
develop the desired characteristic in the finished state. Alloy steels have greater strength and durability than other carbon steels, and a given strength is secured with less material weight.
b.
High hardness alloy steels include the following:
(1) Chromium alloy steels. Chromium is used as an alloying element in carbon
steels to increase hardenability, corrosion resistance, and shock resistance, and
gives high strength with little loss in ductility. Chromium in large amounts shortens the spark stream to one half that of the same steel without chromium, but does
not affect the stream’s brightness.
(2) Nickel
tility of steels,
er than a water
ly defined dash
alloy steels. Nickel increases the toughness, strength, and ducand liners the hardening temperature so that an oil quench, r a t h quench, is used for hardening. The nickel spark has a short, sharpof brilliant light just before the fork.
(3) High chromium -nickel alloy (stainless) steels. These high alloy steels
cover a wide range of compositions. Their stainless, corrosion, and heat resistant
properties vary with the alloy content, and are due to the formation of a very thin
oxide film which forms on the surface of the metal. Sparks are straw colored near
7-52
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the grinding wheel, and white near the end of the streak. There is a medium volume
of streaks which have a moderate number of forked bursts.
(4) Manganese alloy steels. Manganese is used in steel to produce greater
toughness, wear resistance, easier hot rolling, and forging. An increase in manganese content decreases the weldability of steel. Steels containing manganese produce a spark similar to a carbon spark. A moderate increase in manganese increases
the volume of the spark stream and the intensity of the bursts. A steel containing
more than a normal amount of manganese will produce a spark similar to a high carbon steel with a lower manganese content.
(5) Molybdenum alloy steels. Molybdenum increases hardenability, which is
the depth of hardening possible through heat treatment. The impact fatigue property of the steel is improved with up to 0.60 percent molybdenum. Above 0.60 percent
molybdenum, the impact fatigue proper is impaired. Wear resistance is improved
with molybdemnn content above about 0.75 percent. Molybdenum is sometimes cabined
with chromium, tungsten, or vanadium to obtain desired properties. Steels containing this element produce a charcteristic spark with a detached arrowhead similar
to that of wrought iron, which can be seen even in fairly strong carbon bursts.
Molybdenum alloy steels contain either nickel and/or chromium.
(6) Titanium and columbium (niobium) alloy steels. These elements are used
as additional alloying agents in low carbon content, corrosion resistant steels.
They support resistance to intergranular corrosion after the metal is subjected to
high temperatures for a prolonged period of time.
(7) Tungsten alloy steels. Tungsten, as an alloying element in tool steel,
tends to produce a fine, dense grain when used in relatively small quantities.
when used in larger quantities, from 17 to 20 percent, and in combination with
other alloys, tungsten produces a steel that retains its hardness at high temperatures. This element is usually used in combination with chromium or other alloying
agents. In a spark test, tungsten will show a dull red color in the spark stream
near the wheel. It also shortens the spark stream and decreases the size of or
completely eliminates the carbon burst. A tungsten steel containing about 10 percent tungsten causes short, curved, orange spear points at the end of the carrier
lines. Still lower tungsten content causes small, white bursts to appear at the
end of the spear petit. Carrier lines may be from dull red to orange, depending on
the other elements present, providing the tunsten content is not too high.
(8) Vanadium alloy steels. Vanadium is used to help control grain size. It
tends to increase hardenability and causes marked secondary hardness, yet resists
tempering. It is added to steel during manufacture to remove oxygen. Alloy steels
containing vanadium produce sparks with detached arrowheads at the end of the carrier line similar to those produced by molybdenum steels.
(9) Silicon alloy s t e e l s . Silicon is added to steel to obtain greater
hardenability and corrosion resistance. It is often used with manganese to obtain
a strong, tough steel.
(l0) High speed tool steels. These steels are usually special alloy composiitions designed for cutting tools. The carbon content ranges from 0.70 to 0.80
percent. They are difficult to weld, except by the furnace induction method. A
spark test will show a few long, forked spades which are red near the wheel, and
straw colored near the end of the spark stream.
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7-14.
HIGH HARDNESS ALLOY STEELS (cont)
c. Many of these steels can be welded with a heavy coated electrode of the
shielded arc type, whose composition is similar to that of the base metal. Low
carbon electrodes can also be used with some steels. Stainless steel electrodes
are effective where preheating is not feasible or desirable. Heat treated steels
should be preheated, if possible, in order to minimize the formation of hard zones,
or layers, in the base metal adjacent to the weld. The molten metal should not be
overheated, and the welding heat should be controlled by depositing the metal in
narrow string beads. In many cases, the procedures for welding medium carbon
steels (para 7-11, p 7-48) and high carbon steels (para 7-12, p 7-49) can be used
in the welding of alloy steels.
7-15.
HIGH YIELD STRENGTH, LOW ALLOY STRUCTURAL STEELS
a. General. High yield strength, low alloy structural steels (constructional
alloy steels) are special steels that are tempered to obtain extreme toughness and
durability. The special alloys and general makeup of these steels require special
treatment to obtain satisfactory weldments. These steels are special, low-carbon
steels containing specific, small amounts of alloying elements. They are quenched
and tempered to obtain a yield strength of 90,000 to 100,000 psi (620,550 to
689,500 kPa) and a tensile strength of 100,000 to 140,000 psi (689,500 to 965,300
kPa), depending upon size and shape. Structural members fabricated from these high
strength steels may have smaller cross-sectional areas than common structural
steels and still have equal strength. These steels are also more corrosion and
abrasion resistant than other steels. In a spark test, these alloys produce a
spark very similar to low carbon steels.
b. Welding Technique. Reliable welding of high yield strength, low alloy structural steels can be performed by using the following guidelines:
CAUTION
To prevent underbead cracking, only low hydrogen electrodes should be
used when welding high yield strength, low alloy structural steels.
(1) Correct electrodes. Hydrogen is the number one enemy of sound welds in
alloy steels; therefore, use only low hydrogen (MIL-E-18038 or MIL-E-22200/1) electrodes to prevent underbead cracking. Underbead cracking is caused by hydrogen
picked up in the electrode coating, released into the arc, and absorbed by the
molten metal.
(2) Moisture control of electrodes. If the electrodes are in an airtight
container, place them, immediately upon opening the container, in a ventilated
0
O
holding oven set at 250 to 300 F (121 to 149 C) . In the event that the electrodes are not in an airtight Ocontainer,
put them in a ventilated baking oven and
O
bake for 1-1/4 hours at 800 F (427 C). Baked electrodes should, while still
warm, be placed in the holding oven until used. Electrodes must be kept dry to
e liminate absorption of hydrogen. Testing for moisture should be in accordance
with MIL-E-22200.
7-54
TC 9-237
NOTE
Moisture stabilizer NSN 3439-00-400-0090 is an ideal holding oven for
field use (MIL-M-45558).
c. Low Hydrogen Electrode Selection. Electrodes are identified by classification numbers which are always marked on the electrode containers. For low hydrogen
coatings, the last two nunbers of the classification should be 15, 16, or 18.
Electrodes of 5/32 and 1/8 in. (4.0 and 3.2 mm) in diameter are the most commonly
used, since they are more adaptable to all types of welding of this type steel.
Table 7-14 lists electrodes used to weld high yield strength, low alloy structural
steels. Table 7-15 is a list of electrodes currently established in the Army supply system
1
The E indicates electrode; the first two or three digits indicate tensile
strength; the last two digits indicate covering. The numbers 15, 16, and 18 all
indicate2 a loW hydrogen covering.
Low hydrogen electrodes E80 and E90 are recommended for fillet welds, since
they are more ductile than the higher strength electrodes, which are desirable for
butt welds.
d. Selecting Wire-Flux and Wire-Gas Combinations. Wire electrodes for submerged arc and gas-shielded arc welding are not classified according to strength.
Welding wire and wire-flux combinations used for steels to be stress relieved
should contain no more than 0.05 recent vanadium. Weld metal with more than 0.05
percent vanadium may brittle if stress relieved. When using either the
submerged arc or gas metal-arc welding processes to weld high yield strength, lo W
alloy structural steels to lower strength steels the wire-flux and wire-gas combination should be the same as that recommended for the lower strength steels.
7-55
TC 9-237
7-15.
HIGH YIELD STRENGTH, LOW ALLOY STRUCTURAL STEELS (cont)
e. P r e h0 e a t i n g0 . For welding plates under 1.0 in. (25.4 mm) thick, preheating
above 50 F (10 C) is not required except to remove surface moisture from the base
metal. Table 7-16 contains suggested preheating temperatures.
Table 7-16.
Suggested Preheat Temperatures
1
Preheated temperatures above the minimum shown may be necessary for highly
restrained
welds.
However, preheat or interpass temperatures should never exceed
0
0
400 F0 (204 C) for thicknesses up to and including 1-1/2 in. (38.1 mm) or 450 0F
(2322 C) for thicknesses over 1-1/2 in. (38.1 mm).
Electrode E11018 is normal for this type steel. However, E12015, 16 or 18 may
be necessary for thin sections, depending on design stress. Lower strength low
hydrogen electrodes E1OOXX may also be used.
3
Example: A-632 wire (Airco) and argon with 1 percent oxygen.
4
Example: Oxweld 100 wire (Linde) and 709-5 flux.
5
Example: L61 wire (Lincoln) and A0905 X 10 flux.
f.
Welding Heat.
(1) General. It is important to avoid excessive heat concentration in order
to allow the weld area to cool quickly. Either the heat input nomograph or the
heat input calculator can be used to det ermine the heat input into the weld.
(2) Heat input nomograph. To use the heat input nomograph (fig. 7-9), find
the volts value in column 1 and draw a line to the amps value in column 3. Fran
the point where this line intersects Colunm 2, draw another line to the in./min
value in column 5. Read the heat units at the point where this second line intersects column 4. The heat units represent thousands of joules per inch. For example, at 20 volts and 300 amps, the line intersects column 2 at the value 6. At 12
in./min, the heat input is determined as 30 heat units, or 30,000 joules/in.
7-56
TC 9-237
(3) Heat input calculator. The heat input calculator can be made by copying
the pattern printed on the inside of the back cover of this manual onto plastic,
l i g h t cardboard, or other suitable material and cutting out the pieces. If no
suitable material is available, the calculator may be assembled by cutting the pattern out of the back cover. After the two pieces are cut out, a hole is punched in
the center of each. They are then assembled using a paper fastener, or some similar device, which will allow the pieces to rotate. To determinewelding heat input
using the calculator, rotate until the value on the volts scale is aligned directly
opposite the value on the speed (in./min) scale. The value on the amps scale will
then be aligned directly opposite the calculated value for heat units. As with the
nomograph, heat units represent thousands of joules per inch.
7-57
TC 9-237
HIGH YIELD STRENGTH, LOW ALLOY STRUCTURAL STEELS (cont)
(4) Maximum heat input. Check the heat input value obtained from the
nomograph or calculator against the suggested maximums in tables 7-17 and 7-18. If
the calculated value is too high, adjust the amperes, travel speed, or preheat
temperature until the calculated heat input is within the proper range. (The tables are applicable only to single-arc, shielded metal-arc, submerged arc, gas
tungsten-arc, flux-cored arc, and gas metal-arc processes. They are not applicable
to multiple-arc or electroslag welding, or other high heat input vertical-welding
processes, since welds made by these in the “T-1” steels should be heat treated by
quenching and tempering.) For welding conditions exceeding the range of the
nomograph or calculator, the heat input can be calulated using the following formula:
7-15.
1 .
Maximum heat
inputs0 are based on a minimum Charpy V-notch impact value of 10
O
ft-lb at -50 F (-46 C) in the heat-affected zone.
0
at O F
7-58
heat inputs are based on a minimum Charpy V-notch impact value of 10 ft-lb
0
(-18 C) in the heat-affected zone.
TC 9-237
g. Welding Process. Reliable welding of high yield strength, low alloy structural steel can be per formal by choosing an electrode with low hydrogen content or
selecting the proper wire-flux or wire gas combination when using the submerged arc
or gas metal arc processes. Use a straight stringer bead whenever possible. Avoid
using the weave pattern; however, if needed, it must be restricted to a partial
weave pattern. Best results are obtained by a slight circular motion of the electrode with the weave area never exceeding two elect-rode diameters. Never use a
full weave pattern. The partial weave pattern should not exceed twice the diameter
of the electrode. Skip weld as practical. Peening of the weld is sometimes recommended to relieve stresses while cooling larger pieces. Fillet welds should be
smooth and correctly contoured. Avoid toe cracks and undercutting. Electrodes
used for fillet welds should be of lower strength than those used for butt welding. Air-hammer peening of fillet welds can help to prevent cracks, especially if
the welds are to be stress relieved. A soft steel wire pedestal can help to absorb
shrinkage forces. Butter welding in the toe area before actual fillet welding
strengths the area where a toe crack may start. A bead is laid in the toe area,
then ground off prior to the actual fillet welding. This butter weld bead must be
located so that the toe of the fillet will be laid directly over it during actual
fillet welding. Because of the additional mateial involved in fillet welding, the
cooling rate is increased and heat inputs may be extended about 25 percent.
7-16.
CAST IRON
a. General. A cast iron is an alloy of iron, carbon, and silicon, in which the
amount of carbon is usually more than 1.7 percent and less than 4.5 percent.
(1) The most widely used type of cast iron is known as gray iron. Gray iron
has a variety of compositions, but is usually such that it is primarily perlite
with many graphite flakes dispersed throughout.
(2) There are also alloy cast irons which contain small amounts of chromium,
nickel, molybdenum, copper, or other elements added to provide specific properties.
(3) Another alloy iron is austenitic cast iron, which is modified by additions of nickel and other elements to reduce the transformation temperature so that
the structure is austenitic at room or normal temperatures. Austenitic cast irons
have a high degree of corrosion resistance.
(4) In white cast iron , almost all the carbon is in the combined form. This
provides a cast iron with higher hardness, which is used for abrasion resistance.
(5) Malleable cast iron is made by giving white cast iron a special annealing
heat treatment to change the structure of the carbon in the iron. The structure is
changed to perlitic or ferritic, which increases its ductility.
(6) Nodular iron and ductile cast iron are made by the addition of magnesium
or aluminum which will either tie up the carbon in a combined state or will give
the free carbon a spherical or nodular shape, rather than the normal flake shape in
gray cast iron. This structure provides a greater degree of ductility or malleability of the casting.
7-59
TC 9-237
7-16.
CAST IRON (cont)
(7) Cast irons are widely used in agricultural equipment; on machine tools as
bases, brackets, and covers; for pipe fittings and cast iron pipe; and for automobile engine blocks, heads, manifolds, and water preps. Cast iron is rarely used in
structural work except for compression members. It is widely used in construction
machinery for counterweights and in other applications for which weight is required.
b. Gray cast iron has low ductility and therefore will not expand or stretch to
any considerable extent before breaking or cracking. Because of this characteristic, preheating is necessary when cast iron is welded by the oxyacetylene welding
process. It can, however, be welded with the metal-arc process without preheating
if the welding heat is carefully controlled. This can be accomplished by welding
only short lengths of the joint at a time and allowing these sections to cool. By
this procedure, the heat of welding is confined to a small area, and the danger of
cracking the casting is eliminated. Large castings with complicated sections, such
as motor blocks, can be welded without dismantling or preheating. Special electrodes designed for this purpose are usually desirable. Ductile cast irons, such
as malleable iron, ductile iron, and nodular iron, can be successfully welded. For
best results, these types of cast irons should be welded in the annealed condition.
c. Welding is used to salvage new iron castings, to repair castings that have
failed in service, and to join castings to each other or to steel parts in manufacturing operations. Table 7-19 shows the welding processes that can be used for
welding cast, malleable, and nodular irons. The selection of the welding process
and the welding filler metals depends on the type of weld properties desired and
the service life that is expected. For example, when using the shielded metal arc
welding process, different types of filler metal can be used. The filler metal
will have an effect on the color match of the weld compared to the base material.
The color match can be a determining factor, specifically in the salvage or repair
of castings, where a difference of color would not be acceptable.
7-60
TC 9-237
NOTE 1 See AWS Specification for Welding Rods and Covered Electrode for Welding Cast Iron.
2 Would be considered a brass weld.
3 Heat source any for brazing also carbon arc, twin carbon arc, gas tungsten
arc, or plasma arc.
d. No matter which of the welding processes is selected, certain preparatory
steps should be made. It is important to determine the exact type of cast iron to
be welded, whether it is gray cast iron or a malleable or ductile type. If exact
information is not known, it is best to assume that it is gray cast iron with little or no ductility. In general, it is not recommended to weld repair gray iron
castings that are subject to heating and cooling in normal service, especially
when
O
0
heating and cooling vary over a range of temperatures exceeding 400 F (204 C).
Unless cast iron is used as the filler material, the weld metal and base metal may
have different coefficients of expansion and contraction. This will contribute to
internal stresses which cannot be withstood by gray cast iron. Repair of these
types of castings can be made, but the reliability-and service life on such repairs
cannot be predicted with accuracy.
e.
Preparation for Welding.
(1) In preparing the casting for welding, it is necessary to remove all surface materials to completely clean the casting in the area of the weld. This means
removing paint, grease, oil, and other foreign material from the weld zone. I t i s
desirable to heat the weld area for a short time to remove entrapped gas from the
weld zone of the base metal. The skin or high silicon surface should also be removed adjacent to the weld area on both the face and root side. The edges of a
joint should be chipped out or ground to form a 60° angle or bevel. Where grooves
are involved, a V groove from a 60-90° included angle should be used. The V should
extend approximately 1/8 in. (3.2 mm) from the bottom of the crack. A small hole
should be drilled at each end of the crack to keep it from spreading. Complete
penetration welds should always be used, since a crack or defect not completely
removed may quickly reappear under service conditions.
7-61
TC 9-237
7-16.
CAST IRON (cont)
(2) Preheating is desirable for welding cast irons with any of the welding
processes. It can be reduced when using extremely ductile filler metal. Preheating will reduce the thermal gradient between the weld and the remainder of the cast
iron. Preheat temperatures should be related to the welding process, the filler
metal type, the mass, and the complexity of the casting. Preheating can be done by
any of the normal methods. Torch heating is normally used for relatively small
castings weighing 30.0 lb (13.6 kg) or less. Larger parts may be furnace preheated, and in some cases, temporary furnaces are built around the part rather than
taking the part to a furnace. In this way, the parts can be maintained at a high
interpass temperature in the temporary furnace during welding. Preheating should
be general, since it helps to improve the ductility of the material and will spread
shrinkage stresses over a large area to avoid critical stresses at any one point.
Preheating tends to help soften the area adjacent to the weld; it assists in
degassing the casting, and this in turn reduces the possibility of porosity of the
deposited weld metal; and it increases welding speed.
(3) Slow cooling or post
affected zone in the cast iron
slow as possible. This can be
als to keep the air or breezes
heating improves the machinability of the heatadjacent to the weld. The post cooling should be as
done by covering the casting with insulating materifrom it.
f. Welding Technique.
(1) Electrodes.
(a) Cast iron can be welded with a coated steel electrode, but this method
should be used as an emergency measure only. When using a steel electrode, the
contraction of the steel weld metal, the carbon picked up from the cast iron by the
weld metal, and the hardness of the weld metal caused by rapid cooling must be
considered. Steel shrinks more than cast iron when ceded from a molten to a solid
state. When a steel electrode is used, this uneven shrinkage will cause strains at
the joint after welding. When a large quantity of filler metal is applied to the
joint, the cast iron may crack just back of the line of fusion unless preventive
steps are taken. To overcome these difficulties, the prepared joint should be
welded by depositing the weld metal in short string beads, 0.75 to 1.0 in. long
(19.0 to 25.4 mm). These are made intermittently and, in some cases, by the
backstep and skip procedure. To avoid hard spots, the arc should be struck in the
V, and not on the surface of the base metal. Each short length of weld metal applied to the joint should be lightly peened while hot with a small ball peen hammer, and allowed to cool before additional weld metal is applied. The peening
action forges the metal and relieves the cooling strains.
(b) The electrodes used should be 1/8 in. (3.2 mm) in diameter to prevent
excessive welding heat. Welding should be done with reverse polarity. Weaving of
the electrode should be held to a minimum. Each weld metal deposit should be thoroughly cleaned before additional metal is added.
(c) Cast iron electrodes must be used where subsequent machining of the
welded joint is required. Stainless steel electrodes are used when machining of
the weld is not required. The procedure for making welds with these electrodes is
the same as that outlined for welding with mild steel electrodes. Stainless steel
electrodes provide excellent fusion between the filler and base metals. Great care
7-62
TC 9-237
must be taken to avoid cracking in the weld, because stainless steel expands and
contracts approximately 50 percent more than mild steel in equal changes of temperature.
(2) Arc Welding.
(a) The shielded metal arc welding process can be utilized for welding cast
iron. There are four types of filler metals that may be used: cast iron covered
electrodes; covered copper base alloy electrodes; covered nickel base alloy electrodes; and mild steel covered electrodes. There are reasons for using each of the
different specific types of electrodes, which include the machinability of the
deposit, the color match of the deposit, the strength of the deposit, and the ductility of the final weld.
(b) When arc
welding with 0 the cast iron electrodes (ECI), preheat to beO
tween 250 and 800 F (121 and 425 C), depending on the size and complexity of the
casting and the need to machine the deposit and adjacent areas. The higher degree
of heating, the easier it will be to machine the weld deposit. In general, it is
best to use small-size electrodes and a relatively 1ow current setting. A medium
arc length should be used, and, if at all possible, welding should be done in the
flat position. Wandering or skip welding procedure should be used, and peening
will help reduce stresses and will minimize distortion. Slow cooling after welding
is recommended. These electrodes provide an excellment color match cm gray iron.
The strength of the weld will equal the strength of the base metal. There are two
types of copper-base electrodes: the copper tin alloy and the copper aluminum
types. The copper zinc alloys cannot be used for arc welding electrodes because of
the low boiling temperature of zinc. Zinc will volatilize in a r c a n d w i l l
cause weld metal porosity.
0
(c) When
the copper base electrodes are used, a preheat of 250 to 400 F
0
(121 to 204 C) is recommended. Small electrodes and low current should be used.
The arc should be directed against the deposited metal or puddle to avoid penetration and mixing the base metal with the weld metal. Slow cooling is recommended
after welding. The copper-base electrodes do not provide a good color match.
(d) There are three types of nickel electrodes used for welding0 cast iron.
0
These electrodes can be used without preheat; however, heating to 100 F (38 C) is
recommended. These electrodes can be used in all positions; however, the flat
position is recommended. The welding slag should be removed between passes. The
nickel and nickel iron deposits are extremely ductile and will not become brittle
with the carbon pickup. The hardness of the heat-affected zone can be minimized by
reducing penetration into the cast iron base metal. The technique mentioned above,
playing the arc on the puddle rather than on the base metal, will help minimize
dilution. Slow cooling and, if necessary, postheating will improve machinability
of the heat-affected zone. The nickel-base electrodes do not provide a close color
match.
(e) Copper nickel type electrodes cane in two grades. Either of these
electrodes can be used in the sames manner as the nickel or nickel iron electrode
with about the same technique and results. The deposits of these electrodes do not
provide a color match.
7-63
TC 9-237
7-16.
CAST IRON (cont)
(f) Mild steel electrodes are not recommended for welding cast iron if the
deposit is to be machined. The mild steel deposit will pick up sufficient carbon
to make a high-carbon deposit, which is impossible to machine. Additionally, the
mild steel deposit will have a reduced level of ductility as a result of increased
carbon content. This type of electrode should be used only for small repairs and
should not be used when machining is required. Minimum preheat is possible for
small repair jobs. Small electrodes at low current are recommended to minimize
dilution and to avoid the concentration of shrinkage stresses. Short welds using a
wandering sequence should be used, and the weld should be peened as quickly as
possible after welding. The mild steel electrode deposit provides a fair color
match.
(3) Carbon-arc welding of cast iron. Iron castings may be welded with a
carbon arc, a cast iron rod, and a cast iron welding flux. The joint should be
preheated by moving the carbon electrodes along the surface. This prevents toorapid cooling after welding. The molten puddle of metal can be worked with the
carbon electrode so as to move any slag or oxides that are formed to the surface.
Welds made with the carbon arc cool more slowly and are not as hard as those made
with the metal arc and a cast iron electrode. The welds are machinable.
(4) Oxyfuel gas welding. The oxyfuel gas process is often used for welding
cast iron. Most of the fuel gases can be used. The flame should be neutral to
slightly reducing. Flux should be used. Two types of filler metals are available: the cast iron rods and the copper zinc rods. Welds made with the proper
cast iron electrode will be as strong as the base metal. Good color match is provided by all of these welding reds. The optimum welding procedure should be used
with regard to joint preparation, preheat, and post heat. The copper zinc rods
produce braze welds. There are two classifications: a managanese bronze and a
low-fuming bronze. The deposited bronze has relatively high ductility but will not
provide a color match.
(5) Brazing and braze welding.
(a) Brazing is used for joining cast iron to cast iron and steels. In
these cases, the joint design must be selected for brazing so that capillary attraction causes the filler metal to flow between closely fitting parts. The torch
method is normally used. In addition, the carbon arc, the twin carbon arc, the gas
tungsten arc, and the plasma arc can all be used as sources of heat. Two brazing
filler metal alloys are normally used; both are copper zinc alloys. Braze welding
can also be used to join cast iron. In braze welding, the filler metal is not
drawn into the joint by capillary attraction. This is sometimes called bronze
welding. The filler material having a liquidous above 850 0F (454 0C) should be
used. Braze welding will not provide a color match.
(b) Braze welding can also be acccmpolished by the shielded metal arc and
the gas metal arc welding processes. High temperature preheating is not usually
required for braze welding unless the part is extremely heavy or complex in geometry. The bronze weld metal deposit has extremely high ductility, which compensates
for the lack of ductility of the cast iron. The heat of the arc is sufficient to
bring the surface of the cast iron up to a temperature at which the copper base
filler metal alloy will make a bond to the cast iron. Since there is little or no
intermixing of the materials, the zone adjacent to the weld in the base metal is
7-64
TC 9-237
not appreciably hardened. The weld
and0 adjacent area are machinable after the weld
0
is completed. In general, a 200 F (93 C) preheat is sufficient for most applicat i o n . The cooling rate is not extremely critical and a stress relief heat treatment is not usually required. This type of welding is commonly used for repair
welding of automotive parts, agricultural implement parts, and even automotive
engine blocks and heads. It can only be used when the absence of color match is
not objectionable.
(6) Gas metal arc welding. The gas metal arc welding process can be used for
making welds between malleable iron and carbon steels. Several types of electrode
wires can be used, including:
(a) Mild steel using 75% argon + 25% CO2 for shielding.
(b) Nickel copper using 100% argon for shielding.
(c) Silicon bronze using 50% argon + 50% helium for shielding.
In all cases, small diameter electrode wire should be used at low current. With
the mild steel electrode wire, the Argon-CO 2 shielding gas mixture issued to minimize penetration. In the case of the nickel base filler metal and the Copper base
filler metal, the deposited filler metal is extremely ductile. The mild steel
provides a fair color match. A higher preheat is usually required to reduce residual stresses and cracking tendencies.
(7) Flux-cored arc welding. This process has recently been used for welding
cast irons. The more successful application has been using a nickel base fluxcored wire. This electrode wire is normally operated with CO 2 shielding gas, but
when lower mechanical properties are not objectionable, it can be operated without
external shielding gas. The minimum preheat temperatures can be used. The technique should minimize penetration into the cast iron base metal. Postheating is
normally not required. A color match is not obtained.
(8) Studding. Cracks in large castings are somtimes repaired by studding
(fig. 7-10). In this process, the fracture is removed by grinding a V groove.
Holes are drilled and tapped at an angle on each side of the groove, and studs are
screwed into these holes for a distance equal to the diameter of the studs, with
the upper ends projecting approximately 1/4 in. (6.4 mm) above the cast iron surface. The studs should be seal welded in place by one or two beads around each
stud, and then tied together by weld metal beads. Welds should be made in short
lengths, and each length peened while hot to prevent high stresses or cracking upon
cooling. Each bead should be allowed to cool and be thoroughly cleaned before
additional metal is deposited. If the studding method cannot be applied, the edges
of the joint should be chipped out or machined with a round-nosed tool to form a U
groove into which the weld metal should be deposited.
(9) Other welding processes can be used for cast iron. Thermit welding has
been used for repairing certain types of cast iron machine tool parts. Soldering
can be used for joining cast iron, and is sometimes used for repairing small defects in small castings . Flash welding can also be used for welding cast iron.
7-65
TC 9-237
Section IV.
GENERAL DESCRIPTION AND WELDABILITY OF NONFERROUS METALS
7-17. ALUMINUM WELDING
a. General. Aluminum is a lightweight, soft, low strength metal which can
easily be cast, forged, machined, formed and welded. Unless alloyed with specific
elements, it is suitable only in low temperature applications. Aluminum is light
gray to silver in color, very bright when polished, and dull when oxidized. A
fracture in aluminum sections shins a smooth, bright structure. Aluminum gives off
no sparks in a spark test, and does not show red prior to melting. A heavy film of
white oxide forms instantly on the molten surface. Its combination of light weight
and high strength make aluminum the second most popular metal that is welded.
Aluminum and aluminum alloys can be satisfactorily welded by metal-arc, carbon-arc,
and other arc welding processes. The principal advantage of using arc welding
processes is that a highly concentrated heating zone is obtained with the arc. For
this reason, excessive expansion and distortion of the metal are prevented.
b. A l l o y s . Many alloys of aluminum have been developed. It is important to
know which alloy is to be welded. A system of four-digit numbers has been developed by the Aluminum Association, Inc., to designate the various wrought aluminum
alloy types. This system of alloy groups, shown by table 7-20, is as follows:
(1) lXXX series. These are aluminums of 99 percent or higher purity which
are used primarily in the electrical and chemical industries.
(2) 2XXX series. Copper is the principal alloy in this group, which provides
extremely high strength when properly heat treated. These alloys do not produce as
good corrosion resistance and are often clad with pure aluminum or special-alloy
aluminum. These alloys are used in the aircraft industry.
(3) 3XXX series. Manganese is the major alloying element in this group,
which is non-heat-treatable. Manganese content is limited to about 1.5 percent.
These alloys have moderate strength and are easily worked.
(4) 4XXX series. Silicon is the major alloying element in this group. It
can be added in sufficient quantities to substantially reduce the melting point and
is used for brazing alloys and welding electrodes. Most of the alloys in this
group are non-heat-treatable.
(5) 5XXX series. Magnesium is the major alloying element of this group,
which are alloys of medium strength. They possess good welding characteristics and
good resistance to corrosion, but the amount of cold work should be limited.
(6). 6XXX series. Alloys in this group contain silicon and magnesium, which
make them heat treatable. These alloys possess medium strength and good corrosion
resistance.
(7) 7XXX series. Zinc is the major alloying element in this group. Magnesium is also included in most of these alloys. Together, they form a heat-treatable
alloy of very high strength, which is used for aircraft frames.
7-66
TC 9-237
c. Welding Aluminum Alloys. Aluminum posesses a number of properties that
make welding it different than the welding of steels. These are: aluminum oxide
surface coating; high thermal conductivity; high thermal expansion coefficient; low
melting temperature; and the absence of color change as temperature approaches the
melting point. The normal metallurgical factors that apply to other metals apply
to aluminum as well.
(1) Aluminum is an active metal which reacts with oxygen in the air to produce a hard, thin film of aluminum oxide
on the surface. The melting point of
aluminum oxide is approximately 3600 0F0 (1982 00C) which is almost three times the
melting point of pure aluminum (1220 F (660 C)). In addition, this aluminum
oxide film absorbs moisture from the air, particularly as it becomes thicker.
Moisture is a source of hydrogen, which causes porosity in aluminum welds. Hydrogen may also come from oil, paint, and dirt in the weld area. It also comes from
the oxide and foreign materials on the electrode or filler wire, as well as from
the base metal. Hydrogen will enter the weld pool and is soluble in molten aluminum. As the aluminum solidifies, it will retain much less hydrogen. The hydrogen
is rejected during solidification. With a rapid cooling rate, free hydrogen is
retained within the weld and will cause porosity. Porosity will decrease weld
strength and ductility, depending on the amount.
CAUTION
Aluminum and aluminum alloys should not be cleaned with caustic soda
or cleaners with a pH above 10 , as they may react chemically.
(a) The aluminum oxide film must be removed prior to welding. If it is not
completely removed, small particles of unmelted oxide will be trapped in the weld
pool and will cause a reduction in ductility, lack of fusion, and possibly weld
cracking.
(b) The aluminum oxide can be removed by mechanical, chemical, or electrical means. Mechanical removal involves scrapting with a sharp tool, sandpaper, wire
brush (stainless steel), filing, or any other mechanical method. Chemical removal
can be done in two ways. One is by use of cleaning solutions, either the etching
types or the nonetching types. The nonetching types should be used only when starting with relatively clean parts, and are used in conjunction with other solvent
cleaners. For better cleaning, the etching type solutions are recommended, but
must be used with care. When dipping is employed, hot and cold rinsing is highly
recommended. The etching type solutions are alkaline solutions. The time in the
solution must be controlled so that too much etching does not occur.
7-67
TC 9-237
7-17.
ALUMINUM WELDING (cont)
(c) Chemical cleaning includes the use of welding fluxes. Fluxes are used
for gas welding, brazing, and soldering. The coating on covered aluminum electrodes also maintains fluxes for cleaning the base metal. Whenever etch cleaning or
flux cleaning is used, the flux and alkaline etching materials must be completely
removed from the weld area to avoid future corrosion.
(d) The electrical oxide removal system uses cathodic bombardment.
Cathodic bombardment occurs during the half cycle of alternating current gas tungsten arc welding when the electrode is positive (reverse polarity). This is an
electrical phenomenon that actually blasts away the oxide coating to produce a
clean surface. This is one of the reasons why AC gas tungsten arc welding is so
popular for welding aluminum.
(e) Since aluminum is so active chemically, the oxide film will immediately
start to reform. The time of buildup is not extremely fast, but welds should be
made after aluminum is cleaned within at least 8 hours for quality welding. If a
longer time period occurs, the quality of the weld will decrease.
(2) Aluminum has a high thermal conductivity and low melting temperature. It
conducts heat three to five times as fast as steel, depending on the specific alloy. More heat must be put into the aluminum, even though the melting temperature
of aluminum is less than half that of steel. Because of the high thermal conductivity, preheat is often used for welding thicker sections. If the temperature is too
high or the time period is too long, weld joint strength in both heat-treated and
work-hardend
alloys may be diminished. The preheat for aluminum should not exceed
0
0
400 F (204 C), and the parts should not be held at that temperature longer than
necessary. Because of the high heat conductivity, procedures should utilize higher
speed welding processes using high heat input. Both the gas tungsten arc and the
gas metal arc processes supply this requirement. The high heat conductivity of
aluminum can be helpful, since the weld will solidify very quickly if heat is conducted away from the weld extremely fast. Along with surface tension, this helps
hold the weld metal in position and makes all-position welding with gas tungsten
arc and gas metal arc welding practical.
(3) The thermal expansion of aluminum is twice that of steel. In addition,
aluminum welds decrease about 6 percent in volume when solidifying from the molten
s t a t e . This change in dimension may cause distortion and cracking.
(4) The final reason aluminum is different from steels when welding is that
it does not exhibit color as it approaches its melting temperature until it is
raised above the melting point, at which time it will glow a dull red. When soldering or brazing aluminum with a torch, flux is used. The flux will melt as the
temperature of the base metal approaches the temperature required. The flux dries
out first, and melts as the base metal reaches the correct working temperature.
When torch welding with oxyacetylene or oxyhydrogen, the surface of the base metal
will melt first and assume a characteristic wet and shiny appearance. (This aids
in knowing when welding temperatures are reached.) When welding with gas tungsten
arc or gas metal arc , color is not as important, because the weld is completed
before the adjoining area melts.
7-68
TC 9-237
d. Metal-Arc Welding of Aluminum.
(1) Plate welding. Because of the difficulty of controlling the arc, butt
and fillet welds are difficult to produce in plates less than 1/8 in. (3.2 mm)
thick. when welding plate heavier than 1/8 in. (3.2 mm), a joint prepared with a
20 degree bevel will have strength equal to a weld made by the oxyacetylene process. This weld may be porous and unsuitable for liquid- or gas-tight joints.
Metal-arc welding is, however, particularly suitable for heavy material and is used
on plates up to 2-1/2 in. (63.5 mm) thick.
(2) Current and polarity settings. The current and polarity settings will
vary with each manufacturer's type of electrodes. The polarity to be used should
be determined by trial on the joints to be made.
(3) Plate edge preparation. In general, the design of welded joints for
aluminum is quite consistent with that for steel joints. However, because of the
higher fluidity of aluminum under the welding arc, some important general principles should be kept in mind. With the lighter gauges of aluminum sheet, less
groove spacing is advantageous when weld dilution is not a factor. The controlling
factor is joint preparation. A specially designed V groove that is applicable to
aluminum is shown in A, figure 7-11. This type of joint is excellent where welding
can be done from one side only and where a smooth, penetrating bead is desired.
The effectiveness of this particular design depends upon surface tension, and
should be applied on all material over 1/8 in. (3.2 mm) thick. The bottom of the
special V groove must be wide enough to contain the root pass completely. This
requires adding a relatively large amount of filler alloy to fill the groove.
Excellent control of the penetration and sound root pass welds are obtained. This
edge preparation can be employed for welding in all positions. It eliminates difficulties due to burn-through or over-penetration in the overheat and horizontal
welding positions. It is applicable to all weldable base alloys and all filler
alloys.
7-69
TC 9-237
7-17.
e.
ALUMINUM WELDING (cont)
Gas Metal-Arc (MIG) Welding (GMAW).
(1) General. This fast, adaptable process is used with direct current reverse polarity and an inert gas to weld heavier thicknesses of aluminum alloys, in
any position, from 1/16 in. (1.6 mm) to several inches thick. TM 5-3431-211-15
describes the operation of a typical MIG welding set.
(2) Shielding gas. Precautions should be taken to ensure the gas shield is
extremely efficient. Welding grade argon, helium, or a mixture of these gases is
used for aluminum welding. Argon produces a smother and more stable arc than
helium. At a specific current and arc length, helium provides deeper penetration
and a hotter arc than argon. Arc voltage is higher with helium, and a given change
in arc length results in a greater change in arc voltage. The bead profile and
penetration pattern of aluminum welds made with argon and helium differ. With
argon, the bead profile is narrower and more convex than helium. The penetration
pattern shows a deep central section. Helium results in a flatter, wider bead, and
has a broader under-bead penetration pattern. A mixture of approximately 75 percent helium and 25 percent argon provides the advantages of both shielding gases
with none of the undesirable characteristics of either. Penetration pattern and
bead contour show the characteristics of both gases. Arc stability is comparable
to argon. The angle of the gun or torch is more critical when welding aluminum
with inert shielding gas. A 30° leading travel angle is recommen ded . The electrode wire tip should be oversize for aluminum. Table 7-21 provides welding procedure schedules for gas metal-arc welding of aluminum.
(3) Welding technique . The electrode wire must be clean. The arc is struck
with the electrode wire protruding about 1/2 in. (12.7 mm) from the cup. A frequently used technique is to strike the arc approximately 1.0 in. (25.4 mm) ahead
of the beginning of the weld and then quickly bring the arc to the weld starting
point, reverse the direction of travel, and proceed with normal welding. Alternaatively, the arc may
be struck outside the weld groove on a starting tab. When
finishing or terminatingweld, a similar practice may be followed by reversing
the direction of welding, and simultaneously increasing the speed of welding to
taper the width Of the molten pool prior to breaking the arc. This helps to avert
craters and crater cracking. Runoff tabs are commonly used. Having established
the arc, the welder moves the electrode along the joint while maintaining a 70 to
85 degree forehand angle relative to the work. A string bead technique is normally
preferred. Care should be taken that the forehand angle is not changed or increased as the end of the weld is approached. Arc travel speed controls the bead
size. When welding aluminum with this process, it is must important that high travel speeds be maintained. When welding uniform thicknesses, the electrode to work
angle should be equal on both sides of the weld. When welding in the horizontal
position, best results are obtained by pointing the gun slightly upward. When
welding thick plates to thin plates, it is helpful to direct the arc toward the
heavier section. A slight backhand angle is sometimes helpful when welding thin
sections to thick sections. The root pass of a joint usually requires a short arc
to provide the desired penetration. Slightly longer arcs and higher arc voltages
may be used on subsequent passes.
7-70
TC 9-237
7-17.
ALUMINUM WELDING (cont)
The wire feeding equipment for aluminum welding must be in good adjustment for
efficient wire feeding. Use nylon type liners in cable assemblies. Proper drive
rolls must be selected for the aluminum wire and for the size of the electrode
wire. It is more difficult to push extremely small diameter aluminum wires through
long gun cable assemblies than steel wires. For this reason, the spool gun or the
newly developed guns which contain a linear feed motor are used for the small diameter electrode wires. Water-cooled guns are required except for low-currentw e l d i n g .
Both the constant current (CC) power source with matching voltage sensing wire
feeder and the constant voltage (CV) power source with constant speed wire feeder
are used for welding aluminum. In addition, the constant speed wire feeder is
somtimes used with the constant current power source. In general, the CV system
is preferred when welding on thin material and using all diameter electrode
wire. It provides better arc starting and regulation. The CC system is preferred
when welding thick material using linger electrode wires. The weld quality seems
better with this system. The constant current power source with a moderate drop of
15 to 20 volts per 100 amperes and a constant speed wire feeder provide the most
stable power input to the weld and the highest weld quality.
(4) Joint design. Edges may be prepare for welding by sawing, machining,
rotary planing, routing or arc cutting. Acceptable joint designs are shown in
figure 7-12.
f . Gas Tungsten-Arc (TIG) Welding (GTAW).
(1) The gas tungsten arc welding process is used for welding the thinner
sections of aluminum and aluminum alloys. There are several precautions that
should be mentioned with respect to using this process.
(a) Alternating current is recommended for general-purpose work since it
provides the half-cycle of cleaning action. Table 7-22, p 7-74, provides welding
procedure schedules for using the process on different thicknesses to produce different welds. AC welding, usually with high frequency, is widely used with manual
and automatic applications. Procedures should be followed closely and special
attention given to the type of tungsten electrode , size of welding nozzle, gas
type, and gas flow rates. When manual welding, the arc length should be kept short
and equal to the diameter of the electrode. The tungsten electrode should not
protrude too far beyond the end of the nozzle. The tungsten electrode should be
kept clean. If it does accidentally touch the molten metal, it must be redressed.
(b) Welding power sources designed for the gas tungsten arc welding process
should be used. The newer equipment provides for programing, pre- and post-flow
of shielding gas, and pulsing.
(c) For automatic or machine welding, direct current electrode negative
(straight polarity) can be used. Cleaning must be extremely efficient, since there
is no cathodic bombardment to assist. When dc electrode negative is used, extremely deep penetration and high speeds can be obtained. Table 7-23, p 7-75 lists
welding procedure schedules for dc electrode negative welding.
(d) The shielding gases are argon, helium, or a mixture of the two. Argon
is used at a lower flow rate. Helium increases penetration, but a higher flow rate
7-72
TC 9-237
is required. When filler wire is used, it must be clean. Oxide not removed from
the filler wire may include moisture that will produce polarity in the weld deposit.
7-73
TC 9-237
7-17.
ALUMINUM WELDING (cont)
(2) Alternating current.
(a) Characteristics of process. The welding of aluminum by the gas tungsten-arc welding process using alternating current produces an oxide cleaning action. Argon shielding gas is used. Better results are obtained when welding aluminum with alternating current by using equipment designed to produce a balanced wave
or equal current in both directions. Unbalance will result in loss of power and a
reduction in the cleaning action of the arc. Characteristics of a stable arc are
the absence of snapping or cracking, smooth arc starting, and attraction of added
filler metal to the weld puddle rather than a tendency to repulsion. A stable arc
results in fewer tungsten inclusions.
(b) Welding technique. For manual welding of aluminum with ac, the electrode holder is held in one hand and filler rod, if used, in the other. An initial
arc is struck on a starting block to heat the electrode. The arc is then broken
and reignited in the joint. This technique reduces the tendency for tungsten inclusions at the start of the weld. The arc is held at the starting point until the
metal liquifies and a weld pool is established. The establishment and maintenance
of a suitable weld pool is important, and welding must not proceed ahead of the
puddle. If filler metal is required, it may be added to the front or leading edge
of the pool but to one side of the center line. Both hands are moved in unison
with a slight backward and forward motion along the joint. The tungsten electrode
should not touch the filler rod. The hot end of the filler rod should not be withdrawn from the argon shield. A short arc length must be maintained to obtain sufficient penetration and avoid undercutting, excessive width of the weld bead, and
consequent loss of penetration control and weld contour. One rule is to use an arc
length approximately equal to the diameter of the tungsten electrode. When the arc
is broken, shrinkage cracks may occur in the weld crater, resulting in a defective
weld. This defect can be prevented by gradually lengthening the arc while adding
filler metal to the crater. Then, quickly break and restrike the arc several times
while adding additional filler metal to the crater, or use a foot control to reduce
the current at the end of the weld. Tacking before welding is helpful in controlling distortion. Tack welds should be of ample size and strength and should be
chipped out or tapered at the ends before welding over.
(c) Joint design. The joint designs shown in figure 7-11, p 7-69 are applicable to the gas tungsten-arc welding process with minor exceptions. Inexperienced
welders who cannot maintain a very short arc may require a wider edge preparation,
included angle, or joint spacing. Joints may be fused with this process without
the addition of filler metal if the base metal alloy also makes a satisfactory
filler alloy. Edge and corner welds are rapidly made without addition of filler
metal and have a good appearance, but a very close fit is essential.
(3) Direct current straight polarity.
(a) Charcteristics of process. This process, using helium and thoriated
tungsten electrodes is advantageous for many automatic welding operations, especially in the welding of heavy sections. Since there is less tendency to heat the
electrode, smiler electrodes can be used for a given welding current. This will
contribute to keeping the weld bead narrow. The use of direct current straight
polarity (dcsp) provides a greater heat input than can be obtained with ac current. Greater heat is developed in the weld pool, which is consequently deeper and
narrower.
7-76
TC 9-237
(b) Welding techniques. A high frequency current should be used to initiate the arc. Touch starting will contaminate the tungsten electrode. It is not
necessary to form a puddle as in ac welding, since melting occurs the instant the
arc is struck. Care should be taken to strike the arc within the weld area to
prevent undesirable marking of the material. Standard techniques such as runoff
tabs and foot operated heat controls are used. These are helpful in preventing or
filling craters, for adjusting the current as the work heats, and to adjust for a
change in section thickness. In dcsp welding, the torch is moved steadily forward. The filler wire is fed evenly into the leading edge of the weld puddle, or
laid on the joint and melted as the arc roves forward. In all cases, the crater
should be filled to a point above the weld bead to eliminate crater cracks. The
fillet size can be controlled by varying filler wire size. DCSP is adaptable to
repair work. Preheat is not required even for heavy sections, and the heat affected zone will be smaller with less distortion.
(c) Joint designs. The joint designs shown in figure 7-11, p 7-69, are
applicable to the automatic gas tungsten-arc dcsp welding process with minor exceptions. For manual dcsp, the concentrated heat of the arc gives excellent root
fusion. Root face can be thicker, grooves narrower, and build up can be easily
controlled by varying filler wire size and travel speed.
g.
Square Wave Alternating Current Weldinq (TIG).
(1) General. Square wave gas tungsten-arc welding with alternating current
differs frozen conventional balanced wave gas tungsten-arc welding in the type of
wave from used. With a square wave, the time of current flow in either direction
is adjustable from 20 to 1. In square wave gas tungsten-arc welding, there are the
advantages of surface cleaning produced by positive ionic bombardment during the
reversed polarity cycle, along with greater weld depth to width ratio produced by
the straight polarity cycle. Sufficient aluminum surface c leaning action has been
obtained with a setting of approximately 10 percent dcrp. Penetration equal to
regular dcsp welding can be obtained with 90 percent dcsp current.
(2) Welding technique. It is necessary to have either superimposed high
frequency or high open circuit voltage, because the arc is extinguished every half
cycle as the current decays toward zero, and must be restarted each tire. Precision shaped thoriated tungsten electrodes should be used with this process. Argon,
helium, or a combination of the two should be used as shielding gas, depending on
the application to be used.
(3) Joint design. Square wave alternating current welding offers substantial
savings over conventional alternating current balanced wave gas tungsten arc welding in weld joint preparation. Smaller V grooves, U grooves, and a thicker root
face can be used. A greater depth to width weld ratio is conducive to less weldment distortion, along with favorable welding residual stress distribution and less
use of filler wire. With S ome slight modification, the same joint designs can be
used as in dcsp gas tungsten-arc welding (fig. 7-11, p 7-69).
h. Shielded Metal-Arc Welding. In the shielded metal-arc welding process, a
heavy dipped or extruded flux coated electrode is used with dcrp. The electrodes
are covered similarly to conventional steel electrodes. The flux coating provides
a gaseous shield around the arc and molten aluminum puddle, and chemically combines
and removes the aluminum oxide, forming a slag. when welding aluminum, the process
is rather limited due to arc spatter, erratic arc control, limitations on thin
material, and the corrosive action of the flux if it is not removed properly.
7-77
TC 9-237
7-17.
ALUMINUM WELDING (cont)
i . Shielded Carbon-Arc Welding. The shielded carbon-arc welding process can be
used in joining aluminum. It requires flux and produces welds of the same appearance, soundness, and structure as those produced by either oxyacetylene or
oxyhydrogen welding. Shielded carbon-arc welding is done both manually and automatically. A carbon arc is used as a source of heat while filler metal is supplied
from a separate filler rod. Flux must be removed after welding; otherwise severe
corrosion will result. Manual shielded carbon-arc welding is usually limited to a
thickness of less than 3/8 in. (9.5 mm), accomplished by the same method used for
manual carbon arc welding of other material. Joint preparation is similar to that
used for gas welding. A flux covered rod is used.
j . Atomic Hydrogen Welding. This welding process consists of maintaining an
arc between two tungsten electrodes in an atmosphere of hydrogen gas. The process
can be either manual or automatic with procedures and techniques closely related to
those used in oxyacetylene welding. Since the hydrogen shield surrounding the base
metal excludes oxygen, smaller amounts of flux are required to combine or remove
aluminum oxide. Visibility is increased, there are fewer flux inclusions, and a
very sound metal is deposited.
k.
Stud Welding.
(1) Aluminum stud welding may be accomplished with conventional arc stud
welding equipment, using either the capacitor discharge or drawn arc capacitor
discharge techniques. The conventional arc stud welding process may be used to
weld aluminum studs 3/16 to 3/4 in. (4.7 to 19.0 mm) diameter. The aluminum stud
welding gun is modified slightly by the addition of a special adapter for the control of the high purity shielding gases used during the welding cycle. An added
accessory control for controlling the plunging of the stud at the completion of the
weld cycle adds materially to the quality of weld and reduces spatter loss. Reverse polarity is used, with the electrode gun positive and the workpiece negative. A small cylindrical or cone shaped projection on the end of the aluminum
stud initiates the arc and helps establish the longer arc length required for aluminum welding.
(2) The unshielded capacitor discharge or drawn arc capacitor discharge stud
welding processes are used with aluminum studs 1/16 to 1/4 in. (1.6 to 6.4 mm)
diameter. Capacitor discharge welding uses a low voltage electrostatic storage
system, in which the weld energy is stored at a low voltage in capacitors with high
capacitance as a power source. In the capacitor discharge stud welding process, a
small tip or projection on the end of the stud is used for arc initiation. The
drawn arc capacitor discharge stud welding process uses a stud with a pointed or
slightly rounded end. It does not require a serrated tip or projection on the end
of the stud for arc initiation. In both cases, the weld cycle is similar to the
conventional stud welding process. However, use of the projection on the base of
the stud provides the most consistent welding. The short arcing time of the capacitor discharge process limits the melting so that shallow penetration of the
workpiece results. The minimum aluminum work thickness considered practical is
0.032 in. (0.800 mm).
1. Electron Beam Welding. Electron beam welding is a fusion joining process in
which the workpiece is bombarded with a dense stream of high velocity electrons,
7-78
TC 9-237
and virtually all of the kinetic energy of the electrons is transformed into heat
upon impact. Electron beam welding usually takes place in an evacuated chamber.
The chamber size is the limiting factor on the weldment size. Conventional arc and
gas heating melt little more than the surface. Further penetration comes solely by
conduction of heat in all directions from this molten surface spot. The fusion
zone widens as it depends. The electron beam is capable of such intense local
heating that it almost instantly vaporizes a hole through the entire joint thickness. The walls of this hole are molten, and as the hole is moved along the joint,
more metal on the advancing side of the hole is melted. This flaws around the bore
of the hole and solidifies along the rear side of the hole to make the weld. The
intensity of the beam can be diminished to give a partial penetration with the same
narrow configuration. Electron beam welding is generally applicable to edge, butt,
fillet, melt-thru lap, and spot welds. Filler metal is rarely used except for
surfacing.
m.
Resistance Welding.
(1) General. The resistance welding processes (spot, seam, and flash welding) are important in fabricating aluminum alloys. These processes are especially
useful in joining the high strength heat treatable alloys, which are difficult to
join by fusion welding, but can be joined by the resistance welding process with
practically no loss in strength. The natural oxide coating on aluminum has a rather high and erratic electrical resistance. To obtain spot or seam welds of the
highest strength and consistency, it is usually necessary to reduce this oxide
coating prior to welding.
(2) Spot welding. Welds of uniformly high strength and good appearance depend upon a consistently low surface resistance between the workplaces. For most
applications , some cleaning operations are necessary before spot or seam welding
aluminum. Surface preparation for welding generally consists of removal of grease,
oil, dirt, or identification markings, and reduction and improvement of consistency
of the oxide film on the aluminum surface. Satisfactory performance of spot welds
in service depends to a great extent upon joint design. Spot welds should always
be designed to carry shear loads. However, when tension or combined loadings may
be expected, special tests should be conducted to determine the actual strength of
the joint under service loading. The strength of spot welds in direct tension may
vary from 20 to 90 percent of the shear strength.
(3) Seam welding. Seam welding of aluminum and its alloys is very similar to
spot welding, except that the electrodes are replaced by wheels. The spots made by
a seam welding machine can be overlapped to form a gas or liquid tight joint. By
adjusting the timing, the seam welding machine can produce uniformly spaced spot
welds equal in quality to those produced on a regular spot welding machine, and at
a faster rate. This procedure is called roll spot or intermittent seam welding.
(4) Flash welding. All aluminum alloys may be joined by the flash welding
process. This process is particularly adapted to making butt or miter joints between two parts of similar cross section. It has been adapted to joining aluminum
to copper in the form of bars and tubing. The joints so produced fail outside of
the weld area when tension loads are applied.
7-79
TC 9-237
7-17.
ALUMINUM WELDING (cont)
n. Gas welding. Gas welding has been done on aluminum using both oxyacetylene
and oxyhydrogen flames. In either case, an absolutely neutral flame is required.
Flux is used as well as a filler rod. The process also is not too popular because
of low heat input and the need to remove flux.
o. Electroslag welding. Electroslag welding is used for joining pure aluminum,
but is not successful for welding the aluminum alloys. Submerged arc welding has
been used in some countries where inert gas is not available.
p. Other processes. Most of the solid state welding processes, including friction welding, ultrasonic welding, and cold welding are used for aluminums. Aluminum can also be joined by soldering and brazing. Brazing can be accomplished by
most brazing methods. A high silicon alloy filler material is used.
7-18.
BRASS AND BRONZE WELDING
a. General. Brass and bronze are alloys of copper. Brass has zinc, and bronze
has tin as the major alloying elements. However, some bronze metals contain more
zinc than tin, and some contain zinc and no tin at all. High brasses contain from
20 to 45 percent zinc. Tensile strength, hardness , and ductility increase as the
percentage of zinc increases. These metals are suitable for both hot and cold
working.
b. Metal-Arc Welding. Brasses and bronzes can be successfully welded by the
metal-arc process. The electrode used should be of the shielded arc type with
straight polarity (electrode positive). Brasses can be welded with phosphor
bronze, aluminum bronze, or silicon bronze electrodes, depending on the base metal
composition and the service required. Backing plates of matching metal or copper
should be used. High welding current should not be used for welding copper-zinc
alloys (brasses), otherwise the zinc content will be volatilized. All welding
should be done in the flat position. If possible, the weld metal should be deposited with a weave approximately three times the width of the electrode.
c. Carbon-Arc Welding. This method can be used to weld brasses and bronzes
with filler reds of approximately the same composition as the base metal. In this
process, welding is accomplished in much the same way the bronze is bonded to
s t e e l . The metal in the carbon arc is superheated, and this very hot metal is
alloyed to the base metal in the joint.
d. Oxyacetylene Welding. The loW brasses are readily jointed by oxyacetylene
welding. This process is particularly suited for piping because it can be done in
all welding positions. Silicon copper welding rods or one of the brass welding
rods may be used. For oxyacetylene welding of the high brasses, low-fuming welding
rods are used. These low-fuming rods have composition similar to many of the high
brasses. A flux is required, and the torch flame should be adjusted to a slightly
oxidizing flame to assist in controlling fuming. Preheating and an auxiliary heat
source may also be necessary. The welding procedures for copper are also suitable
for the brasses.
e. Gas Metal Arc Welding. Gas metal arc welding is recommended for joining
large phosphor bronze fabrications and thick sections. Direct current, electrode
7-80
TC 9-237
positive, and argon shielding are normally used. The molten weld pool should be
kept small and the travel speed rather high. Stringer beads should be used. Hot
peening of each layer will reduce welding stresses and the likelihood of cracking.
f . Gas Tungsten Arc Welding. Gas tungsten arc welding is used primarily for
repair of castings and joining of phosphor bronze sheet. As with gas metal arc
welding, hot peening of each layer of weld metal is beneficial. Either stabilized
ac or direct current, electrode negative can be used with
helium or argon shielding . The metal should be preheated to the 350 to 400 0F (177 to 204 0C) range, and
the travel speed should be as fast as practical.
g. Shielded Metal Arc Welding. Phosphor bronze covered electrodes are available for joining bronzes of similar compositions. These electrodes are designed
for use with direct current, electrode positive. Filler metal should be deposited
as stringer
beads
for best weld joint mechanical properties. Postweld annealing at
0
0
900 F (482 C) is not always necessary, but is desirable for maximum ductility,
particularly if the weld metal is to be cold worked. Moisture, both on the work
and in the 0 electrode coverings,
must be strictly avoided. Baking the electrodes at
0
250 to 300 F (121 to 149 C) before use may be necessary to reduce moisture in the
covering to an acceptable level.
7-19.
COPPER WELDING
a. General. Copper and copper-base alloys have specific properties which make
them widely used. Their high electrical conductivity makes them widely used in the
electrical industries, and corrosion resistance of certain alloys makes them very
useful in the process industries. Copper alloys are also widely used for friction
or bearing applications. Copper can be welded satisfactorily with either bare or
coated electrodes. The oxygen free copper can be welded with more uniform results
than the oxygen bearing copper, which tends to become brittle when welded. Due to
the high thermal conductivity of copper, the welding currents are higher than those
required for steel, and preheating of the base metal is necessary. Copper shares
some of the characteristics of aluminum, but is weldable. Attention should be
given to its properties that make the welding of copper and copper alloys different
from the welding of carbon steels. Copper alloys possess properties that require
special attention when welding. These are:
(1)
High thermal conductivity.
(2)
High thermal expansion coefficient.
(3)
Relatively low melting point.
(4)
Hot short or brittle at elevated temperatures.
(5)
Very fluid molten metal.
(6)
High electrical conductivity.
(7)
Strength due to cold working.
7-81
TC 9-237
7-19.
COPPER WELDING (cont)
Copper has the highest thermal conductivity of all commercial metals, and the comments made concerning thermal conductivity of aluminum apply to copper, to an even
greater degree.
Copper has a relatively high coefficient of thermal expansion, approximately 50
percent higher than carbon steel, but lower than aluminum.
The melting point of the different
copper
alloys varies over a relatively wide
0
0
r a n g e r but is at least 1000 F (538 C) lower than carbon steel. Some of the copper alloys are hot short. This means that they become brittle at high temperatures, because some of the alloying elements form oxides and other compounds at the
grain boundaries, embrittling the material.
Copper does not exhibit heat colors like steel, and when it melts it is relatively
fluid. This is essentially the result of the high preheat normally used for heavier sections. Copper has the highest electrical conductivity of any of the commercial metals. This is a definite problem in the resistance welding processes.
All of the copper alloys derive their strength from cold working. The heat of
welding will anneal the copper in the heat–affected area adjacent to the weld, and
reduce the strength provided by cold working. This must be considered when welding
high-strength joints.
There are three basic groups of copper designations. The first is the oxygen-free
type which has a copper analysis of 99.95 percent or higher. The second subgroup
are the tough pitch coppers which have a copper composition of 99.88 percent or
higher and some high copper alloys which have 96.00 percent or more copper.
The oxygen-free high-conductivity copper contains no oxygen and is not subject to
grain boundary migration. Adequate gas coverage should he used to avoid oxygen of
the air caning into contact with the molten metal. Welds should be made as quickly
as possible, since too much heat or slow welding can contribute to oxidation. The
deoxidized coppers are preferred because of their freedom from embrittlement by
hydrogen. Hydrogen enbrittlement occurs when copper oxide is exposed to a reducing
gas at high temperature. The hydrogen reduces the copper oxide to copper and water
vapor. The entrapped high temperature water vapor or steam can create sufficient
pressure to cause cracking. In common
with all copper
welding, preheat should be
O
0
used and can run from 250 to 1000 F (121 to 538 C), depending on the mass involved .
The tough pitch electrolytic copper is difficult to weld because of the presence of
copper oxide within the material. During welding, the copper oxide will migrate to
the grain boundaries at high temperatures, which reduces ductility and tensile
strength. The gas-shielded processes are recommended since the welding area is
more localized and the copper oxide is less able to migrate in appreciable quantities.
The third copper subgroup is the high-copper alloys which may contain deoxidizers
such as phosphorus. The copper silicon filler wires are used with this material.
The preheat temperatures needed to make the weld quickly apply to all three grades.
7-82
TC 9-237
c.
Gas Metal-Arc (MIG) Welding (GMAW).
(1) The gas metal
als. It is faster, has a
tortion. It can produce
rent, electrode positive.
below:
arc welding process is used for welding thicker materihigher deposition rate, and usually results in less dishigh-quality welds in all positions. It uses direct curThe CV type power source is recommended.
(2) Metal-arc welding of copper differs from steel welding as indicated
(a) Greater root openings are required.
(b) Tight joints should be avoided in light sections.
(c) Larger groove angles are required, particularly in heavy sections,
in order to avoid excessive undercutting, slag inclusions, and porosity. More
frequent tack welds should be used.
(d) Higher preheat
and
interpass temperatures are required
0
0
0
(427 C) for copper, 700 F (371 C) for beryllium copper).
thickness.
0
800 F
(e) Higher currents are required for a given size electrode or plate
(3) Most copper and copper alloy coated electrodes are designed for use
with reverse (electrode positive) polarity. Electrodes for use with alternating
currents are available.
(4) Peening is used to reduce stresses. in the joints. Flat-nosed tools are
used for this purpose. Numerous moderate blows should be used, because vigorous
blows could cause crystallization or other defects in the joint.
d.
Gas Tungsten-Arc (TIG) Welding (GTAW).
CAUTION
Never use a flux containing fluoride when welding copper or copper
alloys.
(1) Copper can be successfully welded by the gas tungsten-arc welding process. The weldability of each copper alloy group by this process depends upon the
alloying elements used. For this reason, no one set of welding conditions will
cover all groups.
(2) Direct current straight polarity is generally used for welding most
copper alloys. However, high frequency alternating current or direct current reverse polarity is used for beryllium copper or copper alloy sheets less than 0.05
in. (0.13 cm) thick.
(3) For some copper alloys, a flux is recommended. However, a flux containing fluoride should never be used since the arc will vaporize the fluoride and
irritate the lungs of the operator.
7-83
TC 9-237
7-19.
e.
COPPER WELDING (cont)
Carbon-Arc Welding.
(1) This process for copper welding is most satisfactory for oxygen-free
copper, although it can be used for welding oxygen-bearing copper up to 3/8 in.
(9.5 mm) in thickness. The root opening for thinner material should be 3/16 in.
(4.8 mm), and 3/8 in. (9.5 mm) for heavier material. The electrode should be graphite type carbon, sharpened to a long tapered point at least equal to the size of
the welding rod. Phosphor bronze welding rods are used most frequently in this
process.
(2) The arc should be sharp and directed entirely on the weld metal, even
at the start. If possible, all carbon-arc welding should be done in the flat welding position or on a moderate slope.
7-20.
MAGNESIUM WELDING
a. General. Magnesium is a white, very lightweight, machinable, corrosion
resistant, high strength metal. It can be alloyed with small quantities of other
metals, such as aluminum, manganese, zinc and zirconium, to obtain desired propert i e s . It can be welded by most of the welding processes used in the metal working
trades. Because this metal oxidizes rapidly when heated to its melting point in
air, a protective inert gas shield must be provided in arc welding to prevent destructive oxidation.
b. Magnesium possesses properties that make welding it different from the welding of steels. Many of these are the same as for aluminum. These are:
(1) Magnesium oxide surface coating which increases with an increase in
temperature.
(2) High thermal conductivity.
(3) Relatively high thermal expansion coefficient.
(4) Relatively loW melting temperature.
(5) The absence of color change as temperature approaches the melting point.
The normal metallurgical factors that apply to other metals apply to magnesium as
well.
c. The welds produced between similar alloys will develop the full strength of
the base metals; however, the strength of the heat-affected zone may be reduced
slightly. In all magnesium alloys, the solidification range increases and the
melting point and the thermal expansion decrease as the alloy content increases.
Aluminum added as an alloy up to 10 percent improves weldability, since it tends to
refine the weld grain structure. Zinc of more than 1 percent increases hot shortness, which can result in weld cracking. The high zinc alloys are not recommended
for arc welding because of their cracking tendencies. Magnesium, containing small
amounts of thorium, possesses excellent welding qualities and freedom from cracki n g Weldments of these alloys do not require stress relieving. Certain magnesium
7-84
TC 9-237
alloys are subject to stress corrosion. Weldments subjected to corrosive attack
over a Period of time may crack adjacent to welds if the residual stresses are not
removed. Stress relieving is required for weldments intended for this type of
service.
d . Cleaning. An oil coating or chrome pickle finish is usually provided on
magnesium alloys for surface protection during shipment and storage. T h i s o i l ,
along with other foreign matter and metallic oxides, must be removed from the surface prior to welding. Chemical cleaning is preferred, because it is faster and
more uniform in its action. Mechanical cleaning can be utilized if chemical cleani n g f a c i l i t i e s a r e n o t a v a i l a b l e . A final bright chrome pickle finish is recommended for parts that are to be arc welded. The various methods for cleaning magnesium
are described below.
WARNING
The vapors from some chlorinated solvents (e.g., carbon tetrachloride,
trichloroethylene, and perchloroethylene) break down under the ultraviolet radiation of an electric arc and form a toxic gas. Avoid welding
where such vapors are present. These solvents vaporize easily, and
prolonged inhalation of the vapor can be hazardous. These organic
vapors should be removed from the work area before welding begins.
Dry cleaning solvent and mineral spirits paint thinner are highly flammable. Do not clean parts near an open flame or in a smoking area.
Dry cleaning solvent and mineral spirits paint thinner evaporate quickly and have a defatting effect on the skin. When used without protective gloves, these chemicals may cause irritation or cracking of the
skin. Cleaning operations should be performed only in well ventilated
areas.
(1) Grease should be removed by the vapor degreasing system in which
trichloroethylene is utilized or with a hot alkaline cleaning compound. Grease may
also be removed by dipping small parts in dry cleaning solvent or mineral spirits
paint thinner.
(2) Mechanical cleaning can be done satisfactorily with 160 and 240 grit
aluminum oxide abrasive cloth, stainless steel wool, or by wire brushing.
WARNING
Precleaning and postcleaning acids used in magnesium welding and brazing are highly toxic and corrosive. Goggles, rubber gloves, and rubber
aprons should be worn when handling the acids and solutions. D O n o t
inhale
fumes and mists. When spilled on the body or clothing, wash
.
immediately with large quantities of cold water, and seek medical attent i o n . Never pour water into acid when preparing solution: instead,
pour acid into water. Always mix acid and water slowly. Cleaning
operations should be performed only in well ventilated areas.
7-85
TC 9-237
7-20.
MAGNESIUM WELDING (cont)
(3) Immediately after the grease, oil, and other foreign materials have
been removed from the surface, the metal should be dipped for 3 minutes in a hot
solution with the following composition:
Chromic acid (Cr03) -- 24 oz (680 g)
Sodium nitiate (NaNO3) -- 4 oz (113 g)
Calcium or magnesium fluoride -- 1/8 oz (3.5 g)
Water --------------------------- to make 1 gal. (3.8 1)
0
0
The bath should be operated at 70 F (21 C). The work should be removed from the
solution, thoroughly rinsed with hot water, and air dried. The welding rod should
also be cleaned to obtain the best results.
e. Joint Preparation. Edges that are to be welded must be smooth and free of
loose pieces and cavities that might contain contaminating agents, such as oil or
oxides. Joint preparations for arc welding various gauges of magnesium are shown
in figure 7-13.
f.
Safety Precautions.
CAUTION
Magnesium can ignite and burn when heated in the open atmosphere.
(1) Goggles, gloves, and other equipment designed to protect the eyes and
skin of the welder must be worn.
(2) The possibility of fire caused by welding magnesium metal is very remote. The temperature of initial fusion must be reached before solid magnesium
metal ignites. Sustained burning occurs only if this temperature is maintained.
Finely divided magnesium particles such as grinding dust, filings, shavings, borings, and chips present a fire hazard. They ignite readily if proper precautions
are not taken. Magnesium scrap of this type is not common to welding operations.
If a magnesium fire does start, it can be extinguished with dry sand, dry powdered
soapstone, or dry cast iron chips. The preferred extinguishing agents for magnesium fires are graphite base powders.
g.
Gas Tungsten-Arc (TIG) Welding (GTAW) of Magnesium.
(1) Because of its rapid oxidation when magnesium is heated to its melting
point, an inert gas (argon or helium) is used to shield metal during arc welding.
This process requires no flux and permits high welding speeds, with sound welds of
high strength.
7-86
TC 9-237
7-87
TC 9-237
7-20.
MAGNESIUM WELDING (cont)
(2) Direct current machines of the constant current type operating on
straight polarity (electrode positive) and alternating current machines are used
with a high frequency current superimposed on the welding current. Both alternating and direct current machines are used for thin gauge material. However, because
of better penetrating power, alternating current machines are used on material over
3/16 in. (4.8 mm) thick. Helium is considered more practical than argon for use
with direct current reverse polarity. However, three times as much helium by volme as argon is required for a given amount of welding. Argon is used with alternating current.
(3) The tungsten electrodes are held in a water cooled torch equipped with
required electrical cables and an inlet and nozzle for the inert gas.
(4) The two magnesium alloys, in the form of sheet, plate, and extrusion,
that are most commonly used for applications involving welding are ASTM-1A (Fed
Spec QQ-M-54), which is alloyed with manganese, and ASTM-AZ31A (Fed SPec QQ-44),
which is alloyed with aluminum, manganese, and zinc.
(5) In general, less preparation is required for welding with alternating
current than welding with direct current because of the greater penetration obtained. Sheets up to 1/4 in. (6. 4 mm) thickness may be welded from one side with a
square butt joint. Sheets over 1/4 in. (6. 4 mm) thickness should be welded from
both sides whenever the nature of the structure permits, as sounder welds may be
obtained with less warpages. For a double V joint, the included angle should extend from both sides to leave a minimum 1/16 in. (1.6 mm) root face in the center
of the sheets. When welding a double V joint, the back of the first bead should be
chipped out using a chipping hammer fitted with a cape chisel. Remove oxide film,
dirt, and incompletely fused areas before the second bead is added. In this manner, maximum soundness is obtained.
(6) The gas should start flowing a fraction of a second before the arc is
struck. The arc is struck by brushing the electrode over the surface. With alternating current, the arc should be started and stopped by means of a remote control
switch. The average arc length should be about 1/8 in. (3.2 mm) when using helium
and 1/16 in. (1.6 mm) when using argon. Current data and rod diameter are shown in
table 7-24.
(7) When welding with alternating current, maximum penetration is obtained
when the end of the electrode is held flush with or slightly below the surface of
the work. The torch should be held nearly perpendicular to the surface of the
work, and the welding rod added from a position as neatly parallel with the work as
possible (fig. 7-14). The torch should have a slightly leading travel angle.
7-88
TC 9-237
1
Dimensions
are given in inches.
2
Currents shown are for all alloys except alloy Ml, which requires 5 to 10
amperes more current for materials up to 0.05 in. (1.27 mm) thick and 15 to 30
amperes more current for thicker materials. Currents given are for welding speeds
of 12
in. (304.8 mm) per minute.
3
Sheets thicker than 0.15 in. (3.81 mm) should be welded in more than one pass.
A current of about 60 amperes is used on the first pass and the currents given in
the table are used for subsequent passes.
7-89
TC 9-237
7-20.
MAGNESIUM WELDING (cont)
(8) Welding should progress in a straight line at a uniform speed. There
should be no rotary or weaving motion of the rod or torch, except for larger corner
joints or fillet welds. The welding rod can be fed either continuously or intermittently. Care should be taken to avoid withdrawing the heated end from the protective gaseous atmosphere during the welding operation. The cold wire filler metal
should be brought in as near to horizontal as possible (on flat work). The filler
wire is added to the leading edge of the weld puddle. Runoff tabs are recommended
for welding any except the thinner metals. Forehand welding, in which the welding
rod precedes the torch in the direction of welding, is preferred. If stops are
necessary, the weld should be started about 1/2 in. (12.7 mm) back from the end of
the weld when welding is resumed.
(9) Because of the high coefficient of thermal expansion and conductivity,
control of distortion in the welding of magnesium requires jigging, small beads,
and a properly selected welding sequence to help minimize distortion. Magnesium
parts can beO straightened by
holding them in position with clamps and heating to
0
300 to 400 F (149 to 204 C). If this heating is done by local torch application,
care must be taken not to overheat the metal and destroy its properties.
(10) If cracking is encountered during the welding of certain magnesium
alloys, starting and stopping plates may be used to overcome this difficult.
These plates consist of scrap pieces of magnesium stock butted against opposite
ends of the joint to be welded as shown in A, figure 7-15. The weld is started on
one of the abutting plates, continued across the junction along the joint to be
welded, and stopped on the opposite abutting plate. If a V groove is used, the
abutting plates should also be grooved. An alternate method is to start the weld
in the middle of the joint and weld to each edge (B, fig. 7-15). Cracking may also
0
be miniimized
by preheating the plate and holding the jig to 200 to 400 F (93 to
0
204 C) by increasing the speed of the weld.
7-90
TC 9-237
(11) Filler reds must be of the same composition as the alloy being joined
when arc welding. One exception is when welding AZ31B. In this case, grade C rod
(MIL-R-6944), which produces a stronger weld metal, is used to reduce cracking.
(12) Residual stress should be relieved through heat treatment. Stress
relief is essential so that lockup stresses will not cause stress corrosion cracking . The recommended stress relieving treatment for arc welding magnesium sheet is
shown in table 7-25.
(13) The only cleaning required after arc welding of magnesium alloys is
wire brushing to remove the slight oxide deposit on the surface. Brushing may
leave traces of iron, which may cause galvanic corrosion. If necessary, clean as
smoke can be removed by immersing the parts for 1/2 to 2
in b above. Arc welding
0
0
minutes at 180 to 212 F (82 to 100 C), in a solution composed of 16 oz (453 g)
tetrasodium pyrophosphate (Na4P 2O 2), 16 oz (453 g) sodium metaborate (NaB02), and
enough water to make 1 gallon (3.8 1).
(14) Welding procedure schedules for GTAW of magnesium (TIG welding) are
shown in table 7-26, p 7-92.
h. Gas Metal-Arc (MIG) Welding of Magnesium (GMAW). The gas metal arc welding
process is used for the medium to thicker sections. It is considerably faster than
gas tungsten arc welding. Special high-speed gear ratios are usually required in
the wire feeders since the magnesium electrode wire has an extremely high meltoff
r a t e . The normal wire feeder and power supply used for aluminum welding is suitable for welding magnesium. Different types of arc transfer can be obtained when
welding magnesium. This is primarily a matter of current level or current density
and voltage setting. The short-circuiting transfer and the spray transfer are
recommended. Argon is usually used for gas metal arc welding of magnesium; however, argon-helium mixtures can be used. In general, the spray transfer should be
used on material 3/16 in. (4.8 mm) and thicker and the short-circuiting arc used
for thinner metals. Welding procedure schedules for GMAW of magnesium (MIG welding) are shown in table 7-27, p 7-93.
i . Other Welding Processes. Magnesium can be welded using the resistance welding processes, including spot welding, seam welding, and flash welding. Magnesium
can also be joined by brazing. Most of the different brazing techniques can be
used. In all cases, brazing flux is required and the flux residue must be completely removed from the finish part. Soldering is not as effective, since the strength
of the joint is relatively low. Magnesium can also be stud welded, gas welded, and
plasma-arc welded.
7-91
TC 9-237
7-21.
a.
TITANIUM WELDING
General.
(1) Titanium is a
corrosion resistance. It
strength increases as the
strengths. It has seizing
soft, silvery white, medium strength metal with very good
has a high strength to weight ratio, and its tensile
temperature decreases. Titanium has low
impact
and creep
0
0
tendencies at temperatures above 800 F (427 C).
(2) Titanium has a high affinity for oxygen and other gases at elevated
temperatures, and for this reason, cannot be welded with any process that utilizes
fluxes, or where heated metal is exposed to the atmosphere. Minor amounts of impurities cause titanium to become brittle.
(3) Titanium has the characteristic known as the ductile-brittle transition. This refers to a temperature at which the metal breaks in a brittle manner,
rather than in a ductile fashion. The recrystallization of the metal during welding
can raise the transition temperature. Contamination during the high temperate
period and impurities can raise the transition temperature period and impurities
can raise the transition temperature so that the material is brittle at room temperatures. If contamination occurs so that transition temperature is raised sufficiently, it will make the welding worthless. Gas contamination can occur at temper- 0
atures 0 below the melting
point
of the metal. These temperatures range from 700 F
0
0
(371 C) up to 1000 F (538 C).
(4) At room temperature, titanium has an impervious oxide coating that resists further reaction with air. The oxide coating melts at temperatures considerably higher than the melting point of the base metal and creates problems. The
oxidized coating may enter molten weld metal and create discontinuities which greatly reduce the strength and ductility of the weld.
(5) The procedures for welding titanium and titanium alloys are similar to
other metals. Some processes, such as oxyacetylene or arc welding processes using
active gases, cannot be used due to the high chemical activity of titanium and its
sensitivity to embrittlement by contamination. Processes that are satisfactory for
welding titanium and titanium alloys include gas shielded metal-arc welding, gas
tungsten arc welding, and spot, seam, flash, and pressure welding. Special procedures must be employed when using the gas shielded welding processes. These special procedures include the use of large gas nozzles and trailing shields to shield
the face of the weld from air. Backing bars that provide inert gas to shield the
back of the welds from air 0are also 0 used. Not only the molten weld metal, but the
material heated above 1000 F (538 C) by the weld must be adequately shielded in
order to prevent embrittlement. All of these processes provide for shielding of
the molten weld metal and heat affected zones. Prior to welding, titanium and its
alloys must be free of all scale and other material that might cause weld contamination.
7-94
TC 9-237
b.
Surface Prepar ation.
WARNING
The nitric acid used to preclean titanium for inert gas shield arc
welding is highly toxic and corrosive. Goggles, rubber gloves, and
rubber aprons must be worn when handling acid solutions. Do
not inhale gases and mists. When spilled on the body or clothing, wash
immediately with large quantities of cold water, and seek medical
help. Never pour water into acid when preparing the solution; instead,
pour acid into water. Always mix acid and water slowly. Perform cleaning operations only in well ventilated places.
The caustic chemicals (including hydrode) used to
preclean titanium for inert gas shielded arc welding are highly toxic and corro—
sive. Goggles, rubber gloves, and rubber aprons must be worn when
handling these chemicals. Do not inhale gases or mists. When spilled
on the body or clothing, wash immediately with large quantities of cold
water and seek medical help. Special care should be taken at all times
to prevent any water from coming in contact with the molten bath or any
other large amount of sodium hydride, as this will cause the fomation
of highly explosive hydrogen gas.
(1) Surface cleaning is important in preparing titanium and its alloys for
welding. Proper surface cleaning prior to welding reduces contamination of the
weld due to surface scale or other foreign materials. Small amounts of contamination can render titanium completely brittle.
(2) Several cleaning procedures are used, depending on the surface condition of the base and filler metals. Surface conditions most often encountered are
as follows:
(a) Scale free (as received from the mill).
(b) Light scale0 (after hot
forming or annealing at intermediate temper0
ature; ie., less than 1300 F (704 C).
(c) Heavy scale (after hot forming, annealing, or forging at high
temperature).
(3) Metals that are scale free can be cleaned by simple decreasing.
(4) Metals with light oxide scale should be cleaned by acid pickling. In
order to minimize hydrogen pickup, pickling solutions for this operation should
have a nitric acid concentration greater than 20 percent. Metals to be welded
O
should 0 be pickled for 1 to 20 minutes at a bath temperature from 80 to 160 F (27
to 71 C ) . After pickling, the parts are rinsed in hot water.
(5) Metals with a heavy scale should be cleaned with sand, grit, or
vaporblasting, molten sodium hydride salt baths, or molten caustic baths. Sand,
grit, or vaporblasting is preferred where applicable. Hydrogen pickup may occur
with molten bath treatments, but it can be minimized by controlling the bath temper0
ature and pickling
time. Bath temperature should be held at about 750 to 850 F
0
(399 to 454 C). Parts should not be pickled any longer than necessary to remove
scale. After heavy scale is removed, the metal should be pickled as described in
(4) above.
7-95
TC 9-237
7-21.
TITANIUM WELDING (cont)
(6) Surfaces of metals that have undergone oxyacetylene flame cutting operations have a very heavy scale, and may contain microscopic cracks due to excessive
contamination of the metallurgical characteristics of the alloys. The best cleaning method for flame cut surfaces is to remove the contaminated layer and any
cracks by machining operations. Certain alloys can be stress relieved immediately
after cutting to prevent the propagation of these cracks. This stress relief is
usually made in conjunction with the cutting operation.
c.
MIG or TIG Welding of titanium.
(1) General. Both the MIG and TIG welding processes are used to weld titanium and titanium alloys. They are satisfactory for manual and automatic installations. With these processes, contamination of the molten weld metals and adjacent
heated zones is minimized by shielding the arc and the root of the weld with inert
gases (see (2)(b)) or special backing bars (see (2)(c)). In some cases, inert gas
filler welding chambers (see (3)) are used to provide the required shielding. When
using the TIG welding process, a thoriated tungsten electrode should be used. The
electrode size should be the smallest diameter that will carry the welding current. The electrode should be ground to a point. The electrode may extend 1-1/2
times its diameter beyond the end of the nozzle. Welding is done with direct current, electrode negative (straight polarity). Welding procedure for TIG welding
titanium are shown in table 7-28. Selection of the filler metal will depend upon
the titanium alloys being joined. When welding pure titanium, a pure titanium wire
should be used. When welding a titanium alloy, the next lowest strength alloy
should be used as a filler wire. Due to the dilution which will take place dining
welding, the weld deposit will pick up the required strength. The same considerations are true when MIG welding titaniun.
(2) Shielding.
(a) General. Very good shielding conditions ue necessary to produce
arc welded joints with maximum ductility and toughness. To obtain these conditions, the amount of air or other active gases which contact the molten weld metals
and. adjacent heated zones must be very low. Argon is normally used with the gasshielded process. For thicker metal, use helium or a mixture of argon and helium.
Welding grade shielding gases are generally free from contamination; however, tests
can be made before welding. A simple test is to make a bead on a piece of clean
scrap titanium, and notice its color. The bead should be shiny. Any discoloration
of the surface indicates a contamination. Extra gas shielding provides protection
for the heated solid metal next to the weld metal. This shielding is provided by
special trailing gas nozzles, or by chill bars laid immediately next to the weld.
Backup gas shielding should be provided to protect the underside of the weld
joint. Protection of the back side of the joint can also be provided by placing
chill bars in intimate contact with the backing strips. If the contact is close
enough, backup shielding gas is not required. For critical applications, use an
inert gas welding chamber. These can be flexible, rigid, or vacuum-purge chambers.
7-96
TC 9-237
7-21.
TITANIUM WELDING (cont)
(b) Inert gases. Both helium and argon are used as the shielding
gases. With helium as the shielding gas high welding speeds and better penetration
are obtained than with argon, but the arc is more stable in argon. For open air
welding operations, most welders prefer argon as the shielding gas because its
density is greater than that of air. Mixtures of argon and helium are also used.
With mixtures,
‘
the arc characteristics of both helium and argon are obtained. The
mixtures usually vary in composition from about 20 to 80 percent argon. They are
often used with the consumable electrode process. To provide adequate shielding
for the face and root sides of welds, special precautions often are taken. The
precautions include the use of screens and baffles (see (c) 3), trailing shields
(see (c) 7), and special backing fixtures (see (c) 1 0 ) in open air welding, and the
use of inert gas filler welding chambers.
(c) Open air welding.
1. In open air welding operations, the methods used to shield the
face of the weld vary with joint design, welding conditions, and the thickness of
the materials being joined. The most critical area in regard to the shielding is
the molten weld puddle. Impurities diffuse into the molten metal very rapidly and
remain in solution. The gas flowing through a standard welding torch is sufficient
to shield the molten zone. Because of the loW thermal conductivity of titanium,
however, the molten puddle tends to be larger than most metals. For this reason
and because of shielding conditions required in welding titanium, larger nozzles
are used on the welding torch, with proportionally higher gas flows that are required for other metals. Chill bars often are used to limit the size of the puddle.
2. The primary sources of contamination in the molten weld puddle
are turbulence in-the gas flow, oxidation of hot filler reds, insufficient gas
flow, small nozzles on the welding torch, and impure shielding gases. The latter
three sources are easily controlled.
3. If turbulence occurs in the gas flowing from the torch, air
will be inspired and contamination will result. Turbulence is generally caused by
excessive amounts of gas flowing through the torch, long arc lengths, air currents
blowing across the weld, and joint design. Contamination from this source can be
minimized by adjusting gas flows and arc lengths, and by placing baffles alongside
the welds. Baffles protect the weld from drafts and tend to retard the flow of
shielding gas from the joint area. Chill bars or the clamping toes of the welding
jig can serve as baffles (fig. 7-16). Baffles are especially important for making
corner type welds. Additional precautions can be taken to protect the operation
from drafts and turbulence. This can be achieved by erecting a canvas (or other
suitable material) screen around the work area.
4. In manual welding operations with the tungsten-arc process,
oxidation of the hot filler metal is a very important source of contamination. To
control it, the hot end of the filler wire must be kept within the gas shield of
the welding torch. Welding operators must be trained to keep the filler wire
shielded when welding titanium and its alloys. Even with proper manipulation,
however, contamination from this source probably cannot be eliminated completely.
7-98
TC 9-237
5 . Weld contamination which occurs in the molten
especially hazardous. The impurities go into solution, and do not
tion. Although discolored welds may have been improperly shielded
weld discoloration is usually caused by contamination which occurs
has solidified.
weld puddle is
cause discolorawhile molten,
after the weld
6. Most of the auxiliary equipment used on torches to weld titanium is designed to improve shielding conditions for the welds as they solidify and
heat input 0 is low and the weld cools to temperatures
cool. However, if the welding
O
below about 1200 to 1300 F (649 to 704 C) while shielded, auxiliary shielding
equipment is not required. If the weld is at an excessively high temperature after
it is no longer shielded by the welding torch, auxiliary shielding must be supplied.
7. Trailing shields often are used to supply auxiliary shielding . These shields extend behind the welding torch and vary considerably in size,
shaper and design. They are incorporated into special cups which are used on the
welding torch, or may consist only of tubes or hoses attached to the torch or manipulated by hand to direct a stream of inert gas on the welds. Figure 7-17 shows a
drawing of one type of trailing shield currently in use. Important features of
this shield are that the porous diffusion plate allows an even flow of gas over the
shielded area. This will prevent turbulence in the gas stream The shield fits on
the torch so that a continuous gas stream between the torch and shield is obtained.
7-99
TC 9-237
7-21.
TITANIUM WELDING (cont)
for welds
be placed
instances,
Also, chill
8. Baffles are also beneficial in improving shielding conditions
by retarding the flow of shielding gas from the joint area. Baffles may
alongside the weld, over the top, or at the ends of the weld. In some
they may actually form a chamber around the arc and molten weld puddle.
bars may be used to increase weld cooling rates and may make auxiliary
9 . Very little difficulty has been encountered in shielding the
face of welds in automatic welding operations. However, considerable difficulty
has been encountered in manual operations.
1 0 . In open air welding operations, means must be provided for
shielding the root or back of the welds. Backing fixtures are often used for this
purpose. In one type, an auxiliary supply of inert gas is provided to shield the
back of the weld. In the other, a solid or grooved backing bar fits tightly
against the back of the weld and provides the required shilding. Fixtures which
provide an inert gas shield are preferred, especiallly in manual welding operations
with low welding speeds. Figure 7-18 shows backing fixtures used in butt welding
heavy plate and thin sheet, respectively. Similar types of fixtures are used for
other joint designs. However, the design of the fixtures varies with the design of
the joints. For fillet welds on tee joints, shielding should be supplied for two
sides of the weld in addition to shielding the face of the weld.
7-100
TC 9-237
1 1 . For some applications, it may be easier to enclose the back of
the weld, as in a tank, and supply inert gas for shielding purposes. This method
is necessary in welding tanks, tubes, or other enclosed structures where access to
the back of the weld is not possible. In some weldments, it may be necessary to
machine holes or grooves in the structures in order to provide shielding gas for
the back or root of the welds.
WARNING
When using weld backup tape, the weld must be allowed to cool for several minutes before attempting to remove the tape from the workpiece.
12. Use of backing fixtures such as shown in figure 7-18 can be
eliminated in many cases by the use of weld backup tape. This tape consists of a
center strip of heat resistant fiberglass adhered to a wider strip of aluminum
foil, along with a strip of adhesive on each side of the center strip that is used
to hold tape to the underside of the tack welded joint. During the welding, the
fiberglass portion of the tape is in direct contact with the molten metal, preventing excessive penetration. Contamination or oxidation of the underside of the weld
is prevented by the airtight seal created by the aluminum foil strip. The tape can
be used on butt or corner joints (fig. 7-19) or, because of its flexibility, on
curved or irregularly shaped surfaces. The surf ace to which the tape is applied
must be clean and dry. Best results are obtained by using a root gap wide enough
to allow full penetration.
7-101
TC 9-237
7-21.
TITANIUM WELDING (cont)
13. Bend or notch toughness tests are the best methods for evaluating shielding conditions, but visual inspection of the weld surface, which is not
an infallible method, is the only nondestructive means for evaluating weld quality
at the present time. With this method, the presence of a heavy gray scale with a
nonmetallic luster on the weld bead indicates that the weld has been contaminate
badly and has low ductility. Also, the weld surface may be shiny but have different colors, ranging from grayish blue to violet to brown. This type of discoloration may be found on severely contaminated welds or may be due only to surface
contamination, while the weld itself may be satisfactory. However, the quality of
the weld cannot be determined without a destructive test. With good shielding
procedures, weld surfaces are shiny and show no discoloration.
(3) Welding chambers.
(a) For some applications, inert gas filled welding chambers are
used. The advantage of using such chambers is that good shielding may be obtained
for the root and face of the weld without the use of special fixtures. Also, the
surface appearance of such welds is a fairly reliable measure of shielding conditions. The use of chambers is especially advantageous when complex joints are
being welded. However, chambers are not required for many applications, and their
use may be limited.
(b) Welding chambers vary in size and shape, depending on their use
and the size of assemblies to be welded. The inert atmospheres maybe obtained by
evacuating the chamber and filling it with helium or argon, purging the chamber
with inert gas, or collapsing the chamber to expel air and refilling it with an
inert gas. Plastic bags have been used in this latter manner. when the atmospheres are obtained by purging or collapsing the chambers, inert gas usually is
supplied through the welding torch to insure complete protection of the welds.
(4) Joint designs.
Joint designs for titanium are similar to those used
for other metals. For welding a thin sheet, the tungsten-arc process generally is
used. With this process, butt welds may be made with or without filler rod, depending on the thickness of the joint and fitup. Special shearing procedures somtimes
are used so that the root opening does not exceed 8 percent of the sheet thickness. If fitup is this good, filler rod is not required. If fitup is not this
good, filler metal is added to obtain full thickness joints. In welding thicker
sheets (greater than 0.09 in. (2.3 mm) ), both the tungsten-arc and consumable electrode processes are used with a root opening. For welding titanium plates, bars,
or forgings, both the tungsten-arc and consumable electrode processes also are used
with single and double V joints. In all cases, good weld penetration may be obtained with excessive drop through. However, penetration and dropthrough are controlled more easily by the use of proper backing fixtures.
NOTE
Because of the low thermal conductivity of titanium, weld beads tend to
be wider than normal. However, the width of the beads is generally controlled by using short arc lengths, or by placing chill bars or the
clamping toes of the jig close to the sides of the joints.
7-102
TC 9-237
(5) Welding variables.
(a) Welding speed and current for titanium alloys depend on the process used, shielding gas, thickness of the material being welded, design of the
backing fixtures, along with the spacing of chill bars or clamping bars in the
welding jig. Welding speeds vary from about 3.0 to 40.0 in. (76.2 to 1016.0 mm)
per minute. The highest welding speeds are obtained with the consumable electrode
process. In most cases, direct current is used with straight polarity for the
tungsten-arc process. Reverse polarity is used for the consumable electrode process.
(b) Arc wander has proven troublesome in some automatic welding operations. With arc wander, the arc from the tungsten or consumable electrode moves
from one side of the weld joint to the other side. A straight, uniform weld bead
will not be produced. Arc wander is believed to be caused by magnetic disturbances, bends in the filler wire, coatings on the filler wire, or a combination of
these. Special metal shields and wire straighteners have been used to overcome arc
wander, but have not been completely satisfactory. Also, constant voltage welding
machines have been used in an attempt to overcome this problem. These machines
also have not been completely satisfactory.
(c) In setting up arc welding operations for titanium, the welding
conditions should be evaluated on the basis of weld joint properties and appearance. Radiographs will show if porosity or cracking is present in the weld joint.
A simple bend test or notch toughness test will show whether or not the shielding
conditions are adequate. A visual examination of the weld will show if the weld
penetration and contour are satisfactory. After adequate procedures are established, careful controls are desirable to ensure that the shielding conditions are
not changed.
(6) Weld defects.
(a) General. Defects in arc welded joints in titanium alloys consist
mainly of porosity (see (b)) and cold cracks (see (c)). Weld penetration can be
controlled by adjusting welding conditions.
(b) P o r o s i t y . Weld porosity is a major problem in arc welding titanium alloys. Although acceptable limits for porosity in arc welded joints have not
been establish, porosity has been observed in tungsten-arc welds in practically
all of the alloys which appear suitable for welding operations. It does not extend
to the surface of the weld, but has been detected in radiographs. It usually occurs close to the fusion line of the welds. Weld porosity may be reduced by agitating the molten weld puddle and adjusting welding speeds. Also, remelting the weld
will eliminate some of the porosity present after the first pass. However, the
latter method of reducing weld porosity tends to increase weld contamination.
7-103
TC 9-237
7-21.
TITANIUM WELDING (cont)
(c)
Cracks.
1. With adequate shielding procedures and suitable alloys, cracks
should not be a problem. However, cracks have been troublesome in welding some
alloys. Weld cracks are attributed to a number of causes. In commercially pure
titanium, weld metal cracks are believed to be caused by excessive oxygen or nitrogen contamination. These cracks are usually observed in weld craters. In some of
the alpha-beta alloys, transverse cracks in the weld metal and heat affected zones
are believed to be due to the low ductility of the weld zones. However, cracks in
these alloys also may be due to contamination. Cracks also have been observed in
alpha-beta welds made under restraint and with high external stresses. These
cracks are sometimes attributed to the hydrogen content of the alloys.
NOTE
If weld cracking is due to contamination, it may be controlled by improving shielding conditions. However, repair welding on excessively
contaminated welds is not practical in many cases.
2. Cracks which are caused by the loW ductility of welds in
alpha-beta alloys–can be prevented by heat treating or stress relieving the weldment in a furnance immediately after welding. Oxyacetylene torches also have been
used for this purpose. However, care must be taken so that the weldment is not
overheated or excessively contaminated by the torch heating operation.
3. Cracks due to hydrogen may be prevented by vacuum annealing
treatments prior to welding.
(7) Availability of welding filler wire. Most of the titanium alloys which
are being used in arc welding applications are available as wire for use as welding
filler metal. These alloys are listed below:
(a) Commercially pure titanium — commercially available as wire.
ties.
ties.
(b) Ti-5Al-2-l/2Sn alloy -- available as wire in experimental quanti(c) Ti-1-l/2Al-3Mn alloy -- available as wire in experimental quanti
(d) Ti-6Al-4V alloy -- available as wire in experimental quantities.
(e) There has not been a great deal of need for the other alloys as
welding filler wires. However, if such a need occurs, most of these alloys also
could be reduced to wire. In fact, the Ti-8Mn alloy has been furnished as welding
wire to met some requests.
d. Pressure Welding. Solid phase or pressure welding has been used to join
titanium and titanium alloys. In these Processes, the surfaces to be jointed are
not melted. They are
held-together 0 under pressure and heated to elevated tempera
0
tures (900 to 2000 F (482 to 1093 C)). One methd of heating used in pressure
welding is the oxyacetylene flame. With suitable pressure and upset, good welds
7-104
TC 9-237
are obtainable in the high strength alpha-beta titanium alloys. The contaminated
area on the surface of the weld is displaced from the joint area by the upset,
which occurs during welding. This contaminated surface is machined off after welding. Another method of heating is by heated dies. Strong lap joints are obtained
with this method in commercially pure titanium and a high strength alpha-beta alloy. By heating in this manner, welds may be made in very short periods of time,
and inert gas shielding may be supplied to the joint. With all of the heating
methods, less than 2 minutes is required to complete the welding operation. With
solid phase or pressure welding processes, it is possible to produce ductile welds
in the high strength alpha-beta alloys by using temperatures which do not cause
embrittlement in these alloys.
7-22.
NICKEL AND MONTEL WELDING
a. General. Nickel is a hard, malleable, ductile metal. Nickel and its alloys
are commonly used when corrosion resistance is required. Nickel and nickel alloys
such as Monel can, in general, be welded by metal-arc and gas welding methods.
Some nickel alloys are more difficult to weld due to different compositions. The
operator should make trial welds with reverse polarity at several current values
and select the one best suited for the work. Generally, the oxyacetylene welding
methods are preferred for smiler plates. However, small plates can be welded by
the metal-arc and carbon-arc processes, and large plates are most satisfactorily
joined, especially if the plate is nickel clad steel.
When welding, the nickel alloys can be treated much in the same manner as
austenitic stainless steels with a few exceptions. These exceptions are:
acquire
a surface or coating which melts at a
(1) The nickel alloys will
0
0
temperature approximately 1000 F (538 C) above the melting point of the base
metal.
(2) The nickel alloys are susceptible to embrittlement at welding temperatures by lead, sulfur, phosphorus, and some low-temperature metals and alloys.
(3) Weld penetration is less than expected with other metals.
When compensation is made for these three factors, the welding procedures used for
the nickel alloys can he the same as those used for stainless steel. This is because the melting point, the coefficient of thermal expansion, and the thermal
conductivity are similar to austenitic stainless steel.
It is necessary that each of these precautions be considered. The surface oxide
should be completely removed from the joint area by grinding, abrasive blasting,
machining, or by chemical means. When chemical etches are used, they must be completely removed by rinsing prior to welding. The oxide which melts at temperatures
above the melting point of the base metal may enter the weld as a foreign material,
or impurity, and will greatly reduce the strength and ductility of the weld. The
problem of embrittlement at welding temperatures also means that the weld surface
must be absolutely clean. paints, crayon markings, grease, oil, machining lubricants, and cutting oils may all contain the ingredients which will cause
embrittlement. They must be completely removed for the weld area to avoid
embrittlement. It is necessary to increase the opening of groove angles and to
provide adequate root openings when full-penetration welds are used. The bevel or
groove angles should be increased to approximately 40 percent over those used for
carbon steel.
7-105
TC 9-237
7-22.
NICKEL AND MONEL WELDING (cont)
b. Joint Design. Butt joints are preferred but corner and lap joints can be
effectively welded. Beveling is not required on plates 1/16 to 1/8 in. (1.6 to 3.2
mm) thick. With thicker materials, a bevel angle of 35 to 37-1/2 degrees should be
made. When welding lap joints, the weld should be made entirely with nickel electrodes if water or air tightness is required.
c.
Welding Techniques.
(1) Clean all surfaces to be welded either mechanically by machine, sandblasting, grinding, or with abrasive cloth; or chemically by pickling.
(2) Plates having U or V joints should be assembled, and if nickel clad
steel, should be tacked on the steel side to prevent warping and distortion. After
it is determined that the joint is even and flat, complete the weld on the steel
side. Chip out and clean the nickel side and weld. If the base metal on both
sides is nickel, clean out the groove on the unwelded side prior to beginning the
weld on that side.
(3) If desired, the nickel side maybe completed first. However, the steel
side must be tacked and thoroughly cleaned and beveled (or gouged) down to the root
of the nickel weld prior to welding.
(4) Lap and corner joints are successfully welded by depositing a bead of
nickel metal into the root and then weaving successive beads over the root weld.
(5) The arc drawn for nickel or nickel alloy welding should be slightly
shorter than that used in normal metal-arc welding. A 1/16 to 1/8 in. (1.6 to 3.2
mm) arc is a necessity.
(6) Any position weld can be accomplished that can be satisfactorily welded
by normal metal-arc welding of steel.
d.
alloys.
Welding Methods.
(1) Almost all the welding processes can be used for welding the nickel
In addition, they can be joined by brazing and soldering.
(2) Welding nickel alloys. The most popular processes for welding nickel
alloys are the shielded metal arc welding process,the gas tungsten arc welding
process, and the gas metal arc welding process. Process selection depends on the
normal factors. When shielded metal arc welding is used the procedures are essentially the same as those used for stainless steel welding.
The welding procedure schedule for using gas tungsten arc welding (TIG) is shown by
table 7-29. The Welding procedure schedule for gas metal arc welding (MIG) is
shown by table 7-30, p 7-108. The procedure information set forth on these tables
will provide starting points for developing the welding procedures.
(3) NO postweld heat treatment is required to maintain or restore corrosion
resistance of the nickel alloys. Heat treatment is required for precipitating
hardening alloys. Stress relief may be required to meet certain specifications to
avoid stress corrosion cracking in applications involving hydrofluoric acid vapors
or caustic solutions.
7-106
TC 9-237
CHAPTER 8
ELECTRODES AND FILLER METALS
Section I. TYPES OF ELECTRODES
8-1. COVERED ELECTRODES
a. General. When molten metal is exposed to air, it absorbs oxygen and nitrogen, and
becomes brittle or is otherwise adversely affected. A slag cover is needed to protect
molten or solidifying weld metal from the atmosphere. This cover can be obtained from
the electrode coating. The composition of the electrode coating determines its usability,
as well as the composition of the deposited weld metal and the electrode specification.
The formulation of electrode coatings is based on well-established principles of
metallurgy, chemistry, and physics. The coating protects the metal from damage,
stabilizes the arc, and improves the weld in other ways, which include:
(1) Smooth weld metal surface with even edges.
(2) Minimum spatter adjacent to the weld.
(3) A stable welding arc.
(4) Penetration control.
(5) A strong, tough coating.
(6) Easier slag removal.
(7) Improved deposition rate.
The metal-arc electrodes may be grouped and classified as bare or thinly coated
electrodes, and shielded arc or heavy coated electrodes. The covered electrode is the most
popular type of filler metal used in arc welding. The composition of the electrode
covering determines the usability of the electrode, the composition of the deposited weld
metal, and the specification of the electrode. The type of electrode used depends on the
specific properties required in the weld deposited. These include corrosion resistance,
ductility, high tensile strength, the type of base metal to be welded, the position of the
weld (flat, horizontal, vertical, or overhead); and the type of current and polarity required.
b. Types of Electrodes. The coatings of electrodes for welding mild and low alloy steels
may have from 6 to 12 ingredients, which include cellulose to provide a gaseous shield
with a reducing agent in which the gas shield surrounding the arc is produced by the
8-1
TC 9-237
disintegration of cellulose; metal carbonates to adjust the basicity of the slag and to
provide a reducing atmosphere; titanium dioxide to help form a highly fluid, but quickfreezing slag and to provide ionization for the arc; ferromanganese and ferrosilicon to
help deoxidize the molten weld metal and to supplement the manganese content and
silicon content of the deposited weld metal; clays and gums to provide elasticity for
extruding the plastic coating material and to help provide strength to the coating; calcium
fluoride to provide shielding gas to protect the arc, adjust the basicity of the slag, and
provide fluidity and solubility of the metal oxides; mineral silicates to provide slag and
give strength to the electrode covering; alloying metals including nickel, molybdenum,
and chromium to provide alloy content to the deposited weld metal; iron or manganese
oxide to adjust the fluidity and properties of the slag and to help stabilize the arc; and iron
powder to increase the productivity by providing extra metal to be deposited in the weld.
The principal types of electrode coatings for mild steel and are described below.
(1) Cellulose-sodium (EXX10). Electrodes of this type cellulosic material in the
form of wood flour or reprocessed low alloy electrodes have up to 30 percent
paper. The gas shield contains carbon dioxide and hydrogen, which are reducing
agents. These gases tend to produce a digging arc that provides deep penetration.
The weld deposit is somewhat rough, and the spatter is at a higher level than other
electrodes. It does provide extremely good mechanical properties, particularly
after aging. This is one of the earliest types of electrodes developed, and is widely
used for cross country pipe lines using the downhill welding technique. It is
normally used with direct current with the electrode positive (reverse polarity).
(2) Cellulose-potassium (EXX11). This electrode is very similar to the cellulosesodium electrode, except more potassium is used than sodium. This provides
ionization of the arc and makes the electrode suitable for welding with alternating
current. The arc action, the penetration, and the weld results are very similar. In
both E6010 and E6011 electrodes, small amounts of iron powder may be added.
This assists in arc stabilization and will slightly increase the deposition rate.
(3) Rutile-sodium (EXX12). When rutile or titanium dioxide content is relatively
high with respect to the other components, the electrode will be especially
appealing to the welder. Electrodes with this coating have a quiet arc, an easily
controlled slag, and a low level of spatter. The weld deposit will have a smooth
surface and the penetration will be less than with the cellulose electrode. The weld
metal properties will be slightly lower than the cellulosic types. This type of
electrode provides a fairly high rate of deposition. It has a relatively low arc
voltage, and can be used with alternating current or with direct current with
electrode negative (straight polarity).
(4) Rutile-potassium (EXX13). This electrode coating is very similar to the rutilesodium type, except that potassium is used to provide for arc ionization. This
makes it more suitable for welding with alternating current. It can also be used
8-2
TC 9-237
with direct current with either polarity. It produces a very quiet, smooth running
arc.
(5) Rutile-iron powder (EXXX4). This coating is very similar to the rutile
coatings mentioned above, except that iron powder is added. If iron content is 25
to 40 percent, the electrode is EXX14. If iron content is 50 percent or more, the
electrode is EXX24. With the lower percentage of iron powder, the electrode can
be used in all positions. With the higher percentage of iron paler, it can only be
used in the flat position or for making horizontal fillet welds. In both cases, the
deposition rate is increased, based on the amount of iron powder in the coating.
(6) Low hydrogen-sodium (EXXX5). Coatings that contain a high proportion of
calcium carbonate or calcium fluoride are called low hydrogen, lime ferritic, or
basic type electrodes. In this class of coating, cellulose, clays, asbestos, and other
minerals that contain combined water are not used. This is to ensure the lowest
possible hydrogen content in the arc atmosphere. These electrode coatings are
baked at a higher temperature. The low hydrogen electrode family has superior
weld metal properties. They provide the highest ductility of any of the deposits.
These electrodes have a medium arc with medium or moderate penetration. They
have a medium speed of deposition, but require special welding techniques for
best results. Low hydrogen electrodes must be stored under controlled conditions.
This type is normally used with direct current with electrode positive (reverse
polarity).
(7) Low hydrogen-potassium (EXXX6). This type of coating is similar to the low
hydrogen-sodium, except for the substitution of potassium for sodium to provide
arc ionization. This electrode is used with alternating current and can be used with
direct current, electrode positive (reverse polarity). The arc action is smother, but
the penetration of the two electrodes is similar.
(8) Low hydrogen-potassium (EXXX6). The coatings in this class of electrodes
are similar to the low-hydrogen type mentioned above. However, iron powder is
added to the electrode, and if the content is higher than 35 to 40 percent, the
electrode is classified as an EXX18.
(9) Low hydrogen-iron powder (EXX28). This electrode is similar to the EXX18,
but has 50 percent or more iron powder in the coating. It is usable only when
welding in the flat position or for making horizontal fillet welds. The deposition
rate is higher than EXX18. Low hydrogen coatings are used for all of the higheralloy electrodes. By additions of specific metals in the coatings, these electrodes
become the alloy types where suffix letters are used to indicate weld metal
compositions. Electrodes for welding stainless steel are also the low-hydrogen
type.
(10) Iron oxide-sodium (EXX20). Coatings with high iron oxide content produce
a weld deposit with a large amount of slag. This can be difficult to control. This
8-3
TC 9-237
coating type produces high-speed deposition, and provides medium penetration
with low spatter level. The resulting weld has a very smooth finish. The electrode
is usable only with flat position welding and for making horizontal fillet welds.
The electrode can be used with alternating current or direct current with either
polarity.
(11) Iron-oxide-iron power (EXX27). This type of electrode is very similar to the
iron oxide-sodium type, except it contains 50 percent or more iron power. The
increased amount of iron power greatly increases the deposition rate. It may be
used with alternating direct current of either polarity.
(12) There are many types of coatings other than those mentioned here, most of
which are usually combinations of these types but for special applications such as
hard surfacing, cast iron welding, and for nonferrous metals.
c. Classification and Storage of Electrodes. Refer to paragraph 5-25 for classification and
storage of electrodes.
d. Deposition Rates. The different types of electrodes have different deposition rates due
to the composition of the coating. The electrodes containing iron power in the coating
have the highest deposition rates. In the United States, the percentage of iron power in a
coating is in the 10 to 50 percent range. This is based on the amount of iron power in the
coating versus the coating weight. This is shown in the formula:
These percentages are related to the requirements of the American Welding Society
(AWS) specifications. The European method of specifying iron power is based on the
weight of deposited weld metal versus the weight of the bare core wire consumed. This is
shown as follows:
Thus, if the weight of the deposit were double the weight of the core wire, it would
indicate a 200 percent deposition efficiency, even though the amount of the iron power in
the coating represented only half of the total deposit. The 30 percent iron power formula
used in the United States would produce a 100 to 110 percent deposition efficiency using
the European formula. The 50 percent iron power electrode figured on United States
standards would produce an efficiency of approximately 150 percent using the European
formula.
8-4
TC 9-237
e. Light Coated Electrodes.
(1) Light coated electrodes have a definite composition. A light coating has been
applied on the surface by washing, dipping, brushing, spraying, tumbling, or
wiping. The coatings improve the characteristics of the arc stream. They are listed
under the E45 series in the electrode identification system, refer to paragraph 525.
(2) The coating generally serves the functions described below:
(a) It dissolves or reduces impurities such as oxides, sulfur, and
phosphorus.
(b) It changes the surface tension of the molten metal so that the globules
of metal leaving the end of the electrode are smaller and more frequent.
This helps make flow of molten metal more uniform.
(c) It increases the arc stability by introducing materials readily ionized
(i.e., changed into small particles with an electric charge) into the arc
stream.
(3) Some of the light coatings may produce a slag. The slag is quite thin and does
not act in the same manner as the shielded arc electrode type slag.
f. Shielded Arc or Heavy Coated Electrodes. Shielded arc or heavy coated electrodes
have a definite composition on which a coating has been applied by dipping or extrusion.
The electrodes are manufactured in three general types: those with cellulose coatings;
those with mineral coatings; and those whose coatings are combinations of mineral and
cellulose. The cellulose coatings are composed of soluble cotton or other forms of
cellulose with small amounts of potassium, sodium, or titanium, and in some cases added
minerals. The mineral coatings consist of sodium silicate, metallic oxides clay, and other
inorganic substances or combinations thereof. Cellulose coated electrodes protect the
molten metal with a gaseous zone around the arc as well as the weld zone. The mineral
coated electrode forms a slag deposit. The shielded arc or heavy coated electrodes are
used for welding steels, cast iron, and hard surfacing.
g. Functions of Shielded Arc or Heavy Coated Electrodes.
(1) These electrodes produce a reducing gas shield around the arc. This prevents
atmospheric oxygen or nitrogen from contaminating the weld metal. The oxygen
readily combines with the molten metal, removing alloying elements and causing
porosity. Nitrogen causes brittleness, low ductility, and in Some cases low
strength and poor resistance to corrosion.
(2) They reduce impurities such as oxides, sulfur, and phosphorus so that these
impurities will not impair the weld deposit.
8-5
TC 9-237
(3) They provide substances to the arc which increase its stability. This eliminates
wide fluctuations in the voltage so that the arc can be maintained without
excessive spattering.
(4) By reducing the attractive force between the molten metal and the end of the
electrodes, or by reducing the surface tension of the molten metal, the vaporized
and melted coating causes the molten metal at the end of the electrode to break up
into fine, small particles.
(5) The coatings contain silicates which will form a slag over the molten weld and
base metal. Since the slag solidifies at a relatively slow rate, it holds the heat and
allows the underlying metal to cool and solidify slowly. This slow solidification
of the metal eliminates the entrapment of gases within the weld and permits solid
impurities to float to the surface. Slow cooling also has an annealing effect on the
weld deposit.
(6) The physical characteristics of the weld deposit are modified by incorporating
alloying materials in the electrode coating. The fluxing action of the slag will also
produce weld metal of better quality and permit welding at higher speeds.
h. Direct Current Arc Welding Electrodes.
(1) The manufacturer's recommendations should be followed when a specific type
of electrode is being used. In general, direct current shielded arc electrodes are
designed either for reverse polarity (electrode positive) or for straight polarity
(electrode negative), or both. Many, but not all, of the direct current electrodes
can be used with alternating current. Direct current is preferred for many types of
covered nonferrous, bare and alloy steel electrodes. Recommendations from the
manufacturer also include the type of base metal for which given electrodes are
suitable, corrections for poor fit-ups, and other specific conditions.
(2) In most cases, reverse polarity electrodes will provide more penetration than
straight polarity electrodes. Good penetration can be obtained from either type
with proper welding conditions and arc manipulation.
i. Alternating Current Arc Welding Electrodes.
(1) Coated electrodes which can be used with either direct or alternating current
are available. Alternating current is more desirable while welding in restricted
areas or when using the high currents required for thick sections because it
reduces arc blow. Arc blow causes blowholes, slag inclusions, and lack of fusion
in the weld.
(2) Alternating current is used in atomic hydrogen welding and in those carbon
arc processes that require the use of two carbon electrodes. It permits a uniform
rate of welding and electrode consumption ion. In carbon-arc processes where one
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carbon electrode is used, direct current straight polarity is recommended, because
the electrode will be consumed at a lower rate.
j. Electrode Defects and Their Effect.
(1) If certain elements or oxides are present in electrode coatings, the arc stability
will be affected. In bare electrodes, the composition and uniformity of the wire is
an important factor in the control of arc stability. Thin or heavy coatings on the
electrodes will not completely remove the effects of defective wire.
(2) Aluminum or aluminum oxide (even when present in quantities not exceeding
0.01 percent), silicon, silicon dioxide, and iron sulfate cause the arc to be
unstable. Iron oxide, manganese oxide, calcium oxide, and iron sulfide tend to
stabilize the arc.
(3) When phosphorus or sulfur are present in the electrode in excess of 0.04
percent, they will impair the weld metal. They are transferred from the electrode
to the molten metal with very little loss. Phosphorus causes grain growth,
brittleness, and "cold shortness" (i.e., brittle when below red heat) in the weld.
These defects increase in magnitude as the carbon content of the steel increases.
Sulfur acts as a slag, breaks up the soundness of the weld metal, and causes "hot
shortness" (i.e., brittle when above red heat). Sulfur is particularly harmful to bare
low carbon steel electrodes with a low manganese content. Manganese promotes
the formation of sound welds.
(4) If the heat treatment given the wire core of an electrode is not uniform, the
electrode will produce welds inferior to those produced with an electrode of the
same composition that has been properly heat treated.
8-2. SOLID ELECTRODE WIRES
a. General. Bare or solid wire electrodes are made of wire compositions required for
specific applications, and have no coatings other than those required in wire drawing.
These wire drawing coatings have a slight stabilizing effect on the arc, but are otherwise
of no consequence. Bare electrodes are used for welding manganese steels and for other
purposes where a covered electrode is not required or is undesirable. A sketch of the
transfer of metal across the arc of a bare electrode is shown in figure 8-1.
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b. Solid steel electrode wires may not be bare. Many have a very thin copper coating on
the wire. The copper coating improves the current pickup between contact tip and the
electrode, aids drawing, and helps prevent rusting of the wire when it is exposed to the
atmosphere. Solid electrode wires are also made of various stainless steels, aluminum
alloys, nickel alloys, magnesium alloys, titanium alloys, copper alloys, and other metals.
c. When the wire is cut and straightened, it is called a welding rod, which is a form of
filler metal used for welding or brazing and does not conduct the electrical current. If the
wire is used in the electrical circuit, it is called a welding electrode, and is defined as a
component of the welding circuit through which current is conducted. A bare electrode is
normally a wire; however, it can take other forms.
d. Several different systems are used to identify the classification of a particular electrode
or welding rod. In all cases a prefix letter is used.
(1) Prefix R. Indicates a welding rod.
(2) Prefix E. Indicates a welding electrode.
(3) Prefix RB. Indicates use as either a welding rod or for brazing filler metal.
(4) Prefix ER. Indicates wither an electrode or welding rod.
e. The system for identifying bare carbon steel electrodes and rods for gas shielded arc
welding is as follows:
(1) ER indicates an electrode or welding rod.
(2) 70 indicates the required minimum as-welded tensile strength in thousands of
pounds per square inch (psi).
(3) S indicates solid electrode or rod.
(4) C indicates composite metal cored or stranded electrode or rod.
(5) 1 suffix number indicates a particular analysis and usability factor.
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Table 8-1. Mild Steel Electrode Wire Composition for Submerged Arc Welding
f. Submerged Arc Electrodes. The system for identifying solid bare carbon steel for
submerged arc is as follows:
(1) The prefix letter E is used to indicate an electrode. This is followed by a letter
which indicates the level of manganese, i.e., L for low, M for medium, and H for
high manganese. This is followed by a number which is the average amount of
carbon in points or hundredths of a percent. The composition of some of these
wires is almost identical with some of the wires in the gas metal arc welding
specification.
(2) The electrode wires used for submerged arc welding are given in American
Welding Society specification, "Bare Mild Steel Electrodes and Fluxes for
Submerged Arc Welding." This specification provides both the wire composition
and the weld deposit chemistry based on the flux used. The specification does
give composition of the electrode wires. This information is given in table 8-1.
When these electrodes are used with specific submerged arc fluxes and welded
with proper procedures, the deposited weld metal will meet mechanical properties
required by the specification.
(3) In the case of the filler reds used for oxyfuel gas welding, the prefix letter is R,
followed by a G indicating that the rod is used expressly for gas welding. These
letters are followed by two digits which will be 45, 60, or 65. These designate the
approximate tensile strength in 1000 psi (6895 kPa).
(4) In the case of nonferrous filler metals, the prefix E, R, or RB is used, followed
by the chemical symbol of the principal metals in the wire. The initials for one or
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two elements will follow. If there is more than one alloy containing the same
elements, a suffix letter or number may be added.
(5) The American Welding Society's specifications are most widely used for
specifying bare welding rod and electrode wires. There are also military
specifications such as the MIL-E or -R types and federal specifications, normally
the QQ-R type and AMS specifications. The particular specification involved
should be used for specifying filler metals.
g. The most important aspect of solid electrode wires and rods in their composition,
which is given by the specification. The specifications provide the limits of composition
for the different wires and mechanical property requirements.
h. Occasionally, on copper-plated solid wires, the copper may flake off in the feed roll
mechanism and create problems. It may plug liners, or contact tips. A light copper
coating is desirable. The electrode wire surface should be reasonably free of dirt and
drawing compounds. This can be checked by using a white cleaning tissue and pulling a
length of wire through it. Too much dirt will clog the liners, reduce current pickup in the
tip, and may create erratic welding operation.
i. Temper or strength of the wire can be checked in a testing machine. Wire of a higher
strength will feed through guns and cables better. The minimum tensile strength
recommended by the specification is 140,000 psi (965,300 kPa).
j. The continuous electrode wire is available in many different packages. They range
from extremely small spools that are used on spool guns, through medium-size spools for
fine-wire gas metal arc welding. Coils of electrode wire are available which can be
placed on reels that are a part of the welding equipment. There are also extremely large
reels weighing many hundreds of pounds. The electrode wire is also available in drums or
payoff packs where the wire is laid in the round container and pulled from the container
by an automatic wire feeder.
8-3. FLUX-CORED OR TUBULAR ELECTRODES
a. General. The flux-cored arc welding process is made possible by the design of the
electrode. This inside-outside electrode consists of a metal sheath surrounding a core of
fluxing and alloying compounds. The compounds contained in the electrode perform
essentially the same functions as the coating on a covered electrode, i.e., deoxidizers, slag
formers, arc stabilizers, alloying elements, and may provide shielding gas. There are three
reasons why cored wires are developed to supplement solid electrode wires of the same
or similar analysis.
(1) There is an economic advantage. Solid wires are drawn from steel billets of
the specified analyses. These billets are not readily available and are expensive. A
single billet might also provide more solid electrode wire than needed. In the case
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of cored wires, the special alloying elements are introduced in the core material to
provide the proper deposit analysis.
(2) Tubular wire production method provides versatility of composition and is not
limited to the analysis of available steel billets.
(3) Tubular electrode wires are easier for the welder to use than solid wires of the
same deposit analysis, especially for welding pipe in the fixed position.
b. Flux-Cored Electrode Design. The sheath or steel portion of the flux-cored wire
comprises 75 to 90 percent of the weight of the electrode, and the core material represents
10 to 25 percent of the weight of the electrode.
For a covered electrode, the steel represents 75 percent of the weight and the flux 25
percent. This is shown in more detail below:
Flux Cored Electrode Wire
Covered Electrode
(E70T-1)
(E7016)
By area
By weight
Flux
25%
steel
75%
Flux
15%
steel
85%
By area
By weight
Flux
55%
steel
45%
Flux
24%
steel
76%
More flux is used on covered electrodes than in a flux-cored wire to do the same job. This
is because the covered electrode coating contains binders to keep the coating intact and
also contains agents to allow the coating to be extruded.
c. Self-Shielding Flux-Cored Electrodes. The self-shielding type flux-cored electrode
wires include additional gas forming elements in the core. These are necessary to prohibit
the oxygen and nitrogen of the air from contacting the metal transferring across the arc
and the molten weld puddle. Self-shielding electrodes also include extra deoxidizing and
denigrating elements to compensate for oxygen and nitrogen which may contact the
molten metal. Self-shielding electrodes are usually more voltage-sensitive and require
electrical stickout for smooth operation. The properties of the weld metal deposited by
the self-shielding wires are sometimes inferior to those produced by the externally
shielded electrode wires because of the extra amount of deoxidizers included. It is
possible for these elements to build up in multipass welds, lower the ductility, and reduce
the impact values of the deposit. Some codes prohibit the use of self-shielding wires on
steels with yield strength exceeding 42,000 psi (289,590 kPa). Other codes prohibit the
self-shielding wires from being used on dynamically loaded structures.
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d. Metal Transfer. Metal transfer from consumable electrodes across an arc has been
classified into three general modes. These are spray transfer, globular transfer, and short
circuiting transfer. The metal transfer of flux-cored electrodes resembles a fine globular
transfer. On cored electrodes in a carbon dioxide shielding atmosphere, the molten
droplets build up around the outer sheath of the electrode. The core material appears to
transfer independently to the surface of the weld puddle. At low currents, the droplets
tend to be larger than when the current density is increased. Transfer is more frequent
with smaller drops when the current is increased. The larger droplets at the lower currents
cause a certain amount of splashing action when they enter the weld puddle. This action
decreases with the smaller droplet size. This explains why there is less visible spatter, the
arc appears smoother to the welder, and the deposition efficiency is higher when the
electrode is used at high current rather than at the low end of its current range.
e. Mild Steel Electrodes. Carbon steel electrodes are classified by the American Welding
Society specification, "Carbon Steel Electrodes for Flux-cored-Arc Welding". This
specification includes electrodes having no appreciable alloy content for welding mild
and low alloy steels. The system for identifying flux-cored electrodes follows the same
pattern as electrodes for gas metal arc welding, but is specific for tubular electrodes. For
example, in E70T-1, the E indicates an electrode; 70 indicates the required minimum aswelded tensile strength in thousands of pounds per square inch (psi); T indicates tubular,
fabricated, or flux-cored electrode; and 1 indicates the chemistry of the deposited weld
metal, gas type, and usability factor.
f. Classification of Flux-Cored Electrodes.
(1) E60T-7 electrode classification. Electrodes of this classification are used
without externally applied gas shielding and may be used for single-and multiplepass applications in the flat and horizontal positions. Due to low penetration and
to other properties, the weld deposits have a low sensitivity to cracking.
(2) E60T-8 electrode classifications. Electrodes of this classification are used
without externally applied gas shielding and may be used for single-and multiplepass applications in the flat and horizontal positions. Due to low penetration and
to other properties, the weld deposits have a low sensitivity to cracking.
(3) E70T-1 electrode classification. Electrodes of this classification are designed
to be used with carbon dioxide shielding gas for single-and multiple-pass welding
in the flat position and for horizontal fillets. A quiet arc, high-deposition rate, low
spatter loss, flat-to-slightly convex bead configuration, and easily controlled and
removed slag are characteristics of this class.
(4) E70T-2 electrode classification. Electrodes of this classification are used with
carbon dioxide shielding gas and are designed primarily for single-pass welding
in the flat position and for horizontal fillets. However, multiple-pass welds can be
made when the weld beads are heavy and an appreciable amount of mixture of the
base and filler metals occurs.
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(5) E70T-3 electrode classification. Electrodes of this classification are used
without externally applied gas shielding and are intended primarily for depositing
single-pass, high-speed welds in the flat and horizontal positions on light plate
and gauge thickness base metals. They should not be used on heavy sections or
for multiple-pass applications.
(6) E70T-4 electrode classification. Electrodes of this classification are used
without externally applied gas shielding and may be used for single-and multiplepass applications in the flat and horizontal positions. Due to low penetration, and
to other properties, the weld deposits have a low sensitivity to cracking.
(7) E70T-5 electrode classification. This classification covers electrodes primarily
designed for flat fillet or groove welds with or without externally applied
shielding gas. Welds made using-carbon dioxide shielding gas have better quality
than those made with no shielding gas. These electrodes have a globular transfer,
low penetration, slightly convex bead configuration, and a thin, easily removed
slag.
(8) E70T-6 electrode classification. Electrodes of this classification are similar to
those of the E70T-5 classification, but are designed for use without an externally
applied shielding gas.
(9) E70T-G electrode classification. This classification includes those composite
electrodes that are not included in the preceding classes. They may be used with
or without gas shielding and may be used for multiple-pass work or may be
limited to single-pass applications. The E70T-G electrodes are not required to
meet chemical, radiographic, bend test, or impact requirements; however, they are
required to meet tension test requirements. Welding current type is not specified.
g. The flux-cored electrode wires are considered to be low hydrogen, since the materials
used in the core do not contain hydrogen. However, some of these materials are
hydroscopic and thus tend to absorb moisture when exposed to a high-humidity
atmosphere. Electrode wires are packaged in special containers to prevent this. These
electrode wires must be stored in a dry room.
h. Stainless Steel Tubular Wires. Flux-cored tubular electrode wires are available which
deposit stainless steel weld metal corresponding to the A.I.S.I. compositions. These
electrodes are covered by the A.W.S specification, "Flux-Cored Corrosion Resisting
Chromium and Chromium-Nickel Steel Electrodes." These electrodes are identified by
the prefix E followed by the standard A.I.S.I. code number. This is followed by the letter
T indicating a tubular electrode. Following this and a dash are four-possible suffixes as
follows:
(1) -1 indicates the use of C02 (carbon dioxide) gas for shielding and DCEP.
(2) -2 indicates the use of argon plus 2 percent oxygen for shielding and DCEP.
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(3) -3 indicates no external gas shielding and DCEP.
(4) -G indicates that gas shielding and polarity are not specified.
Tubular or flux-cored electrode wires are also used for surfacing and submerged arc
welding applications.
i. Deposition Rates and Weld Quality. The deposition rates for flux-cored electrodes are
shown in figure 8-2. These curves show deposition rates when welding with mild and
low-alloy steel using direct current electrode positive. Two type of of covered electrodes
are shown for comparison. Deposition rates of the smaller size flux-cored wires exceed
that of the covered electrodes. The metal utilization of the flux-cored electrode is higher.
Flux-cored electrodes have a much broader current range than covered electrodes, which
increases the flexibility of the process. The quality of the deposited weld metal produced
by the flux-cored arc welding process depends primarily on the flux-cored electrode wire
that is used. It can be expected that the deposited weld metal will match or exceed the
properties shown for the electrode used. This assures the proper matching of base metal,
flux-cored electrode type and shielding gas. Quality depends on the efficiency of the gas
shielding envelope, on the joint detail, on the cleanliness of the joint, and on the skill of
the welder. The quality level of of weld metal deposited by the self-shielding type
electrode wires is usually lower than that produced by electrodes that utilize external gas
shielding.
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Section II. OTHER FILLER METALS
8-4. GENERAL
There are other filler metals and special items normally used in making welds. These
include the nonconsumable electrodes (tungsten and carbon), and other materials,
including backing tapes, backing devices, flux additives, solders, and brazing alloys.
Another type of material consumed in making a weld are the consumable rings used for
root pass welding of pipe. There are also ferrules used for stud welding and the guide
tubes in the consumable guide electroslag welding method. Other filler materials are
solders and brazing alloys.
8-5. NONCONSUMABLE ELECTRODES
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a. Types of Nonconsumable Electrodes. There are two types of nonconsumable
electrodes. The carbon electrode is a non-filler metal electrode used in arc welding or
cutting, consisting of a carbon graphite rod which may or may not be coated with copper
or other coatings. The second nonconsumable electrode is the tungsten electrode, defined
as a non-filler metal electrode used in arc welding or cutting, made principally of
tungsten.
b. Carbon Electrodes. The American Welding Society does not provide specification for
carbon electrodes but there is a military specification, no. MIL-E-17777C, entitled,
"Electrodes Cutting and Welding Carbon-Graphite Uncoated and Copper Coated". This
specification provides a classification system based on three grades: plain, uncoated, and
copper coated. It provides diameter information, length information, and requirements for
size tolerances, quality assurance, sampling, and various tests. Applications include
carbon arc welding, twin carbon arc welding, carbon cutting, and air carbon arc cutting
and gouging.
c. Tungsten Electrodes.
(1) Nonconsumable electrodes for gas types: pure tungsten, tungsten containing
tungsten arc (TIG) welding are of four 1.0 percent thorium, tungsten containing
2.0 percent thorium, and tungsten containing 0.3 to 0.5 percent zirconium. They
are also used for plasma-arc and atomic hydrogen arc welding.
(2) Tungsten electrodes can be identified by painted end marks:
(a) Green - pure tungsten.
(b) Yellow - 1.0 percent thorium.
(c) Red - 2.0 percent thorium.
(d) Brown - 0.3 to 0.5 percent zirconium.
(3) Pure tungsten (99. 5 percent tungsten) electrodes are generally used on less
critical welding operations than the tungstens which are alloyed. This type of
electrode has a relatively low current carrying capacity and a low resistance to
contamination.
(4) Thoriated tungsten electrodes (1.0 or 2.0 percent thorium) are superior to pure
tungsten electrodes because of their higher electron output, better arc starting and
arc stability, high current-carrying capacity, longer life, and greater resistance to
contamination.
(5) Tungsten electrodes containing 0.3 to 0.5 percent zirconium generally fall
between pure tungsten electrodes and thoriated tungsten electrodes in terms of
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performance. There is, however, some indication of better performance in certain
types of welding using ac power.
(6) Finer arc control can be obtained if the tungsten alloyed electrode is ground to
a point (fig. 8-3). When electrodes are not grounded, they must be operated at
maximum current density to obtain reasonable arc stability. Tungsten electrode
points are difficult to maintain if standard direct current equipment is used as a
power source and touch--starting arc is standard practice. Maintenance of
electrode shape and the reduction of tungsten inclusions in the weld can best be
ground by superimposing a high-frequency current on the regular welding current.
Tungsten electrodes alloyed with thorium retain their shape longer when touchstarting is used. Unless high frequency alternating current is available, touchstarting must be used with thorium electrodes.
(7) The electrode extension beyond the gas cup is determined by the type of joint
being welded. For example, an extension beyond the gas cup of 1/8 in. (0.32 cm)
might be used for butt joints in light gauge material, while an extension of
approximately 1/4 to 1/2 in. (0.64 to 1.27 cm) might be necessary on some fillet
welds. The tungsten electrode or torch should be inclined slightly and the filler
metal added carefully to avoid contact with the tungsten to prevent contamination
of the electrode. If contamination does occur, the electrode must be removed,
reground, and replaced in the torch.
d. Backing Materials. Backing materials are being used more frequently for welding.
Special tapes exist, some of which include small amounts of flux, which can be used for
backing the roots of joints. There are also different composite backing materials, for oneside welding. Consumable rings are used for making butt welds in pipe and tubing. These
are rings made of metal that are tack welded in the root of the weld joint and are fused
into the joint by the gas tungsten arc. There are three basic types of rings called
consumable inert rings which are available in different analyses of metal based on normal
specifications.
8-6. SUBMERGED ARC FLUX ADDITIVES
Specially processed metal powder is sometimes added to the flux used for the submerged
arc welding process. Additives are provided to increase productivity or enrich the alloy
composition of the deposited weld metal. In both cases, the additives are of a proprietary
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nature and are described by their manufacturers, indicating the benefit derived by using
the particular additive. Since there are no specifications covering these types of materials,
the manufacturer's information must be used.
8-7. SOLDERING
a. General. Soldering is the process of using fusible alloys for joining metals. The kind of
solder used depends on the metals being joined. Hard solders are called spelter, and hard
soldering is called silver solder brazing. This process gives greater strength and will
withstand more heat than soft solder. Soft soldering is used for joining most common
metals with an alloy that melts at a temperature below that of the base metal, and always
below 800°F (427°C). In many respects, this is similar to brazing, in that the base is not
melted, but merely tinned on the surface by the solder filler metal. For its strength, the
soldered joint depends on the penetration of the solder into the pores of the base metal
and. the formation of a base metal-alloy solder.
b. Solders of the tin-lead alloy system constitute the largest portion of all solders in use.
They are used for joining most metals and have good corrosion resistance to most
materials. Most cleaning and soldering processes may be used with the tin-lead solders.
Other solders are: tin-antimony; tin-antimony-lead; tin-silver; tin-lead-silver; tin-zinc;
cadmium-silver; cadmium-zinc; zinc-aluminum; bismuth (fusible) solder; and indium
solders. These are described below. Fluxes of all types can also be used; the choice
depends on the base metal to be joined.
(1) Tin-antinmony solder. The 95 percent tin-5 percent antimony solder provides
a narrow melting range at a temperature higher than the tin-lead eutectic. the
solder is used many plumbing, refrigeration, and air conditioning applications
because of its good creep strength.
(2) Tin-antimony-lead solders. Antimony may be added to a tin-lead solder as a
substitute for some of the tin. The addition of antimony up to 6 percent of the tin
content increases the mechanical properties of the solder with only slight
impairment to the soldering characteristics. All standard methods of cleaning,
fluxing, and heating may be used.
(3) Tin-silver and tin-lead-silver solders. The 96 percent tin-4 percent silver solder
is free of lead and is often used to join stainless steel for food handling equipment.
It has good shape and creep strengths, and excellent flow characteristics. The 62
percent tin-38 percent lead-2 percent silver solder is used when soldering silvercoated surfaces for electronic applications. The silver addition retards the
dissolution of the silver coating during the soldering operation. The addition of
silver also increases creep strength. The high lead solders containing tin and silver
provide higher temperature solders or many applications. They exhibit good
tensile, shear, and creep strengths and are recommended for cryogenic
applications. Because of their high melting range, only inorganic fluxes are
recommended for use with these solders.
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(4) Tin-zinc solders. A large number of tin-zinc solders have come into use for
joining aluminum. Galvanic corrosion of soldered joints in aluminum is
minimized if the metals in the joint are close to each other in the electrochemical
series. Alloys containing 70 to 80 percent tin with the balance zinc are
recommended for soldering aluminum. The addition of 1 to 2 percent aluminum,
or an increase of the zinc content to as high as 40 percent, improves corrosion
resistance. However, the liquidus temperature rises correspondingly, and these
solders are therefore more difficult to apply. The 91/9 and 60/40 tin-zinc solders
may be used for high temperature applications (above 300°F (149°C)), while the
80/20 and the 70/30 tin-zinc solders are generally used to coat parts before
soldering.
CAUTION
Cadmium fumes can be health hazards. Improper use of solders containing
cadmium can be hazardous to personnel.
(5) Cadmium-silver solder. The 95 percent cadmium-5 percent silver solder is in
applications where service temperatures will be higher than permissible with
lower melting solders. At room temperature, butt joints in copper can be made to
produce tensile strengths of 170 MPa (25,000 psi). At 425°F (218°C), a tensile
strength of 18 MPa (2600 psi) can be obtained. Joining aluminum to itself or to
other metals is possible with this solder. Improper use of solders containing
cadmium may lead to health hazards. Therefore, care should be taken in their
application, particularly with respect to fume inhalation.
(6) Cadmium-zinc solders. These solders are also useful for soldering aluminum.
The cadmium-zinc solders develop joints with intermediate strength and corrosion
resistance when used with the proper flux. The 40 percent cadmium-60 percent
zinc solder has found considerable use in the soldering of aluminum lamp bases.
Improper use of this solder may lead to health hazards, particularly with respect to
fume inhalation.
(7) Zinc-aluminum solder. This solder is specifically for use on aluminum. It
develops joints with high strength and good corrosion resistance. The solidus
temperature is high, which limits its use to applications where soldering
temperature is in excess of 700°F (371°C) can be tolerated. A major application is
in dip soldering the return bends of aluminum air conditioner coils. Ultrasonic
solder pots are employed without the use of flux. In manual operations, the heated
aluminum surface is rubbed with the solder stick to promote wetting without a
flux.
(8) Fusible alloys. Bismuth-containing solders, the fusible alloys, are useful for
soldering operations where soldering temperatures helm 361°F (183°C) are
required. The low melting temperature solders have applications in cases such as
soldering heat treated surfaces where higher soldering temperatures would result
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in the softening of the part; soldering joints where adjacent material is very
sensitive to temperature and would deteriorate at higher soldering temperatures;
step soldering operations where a low soldering temperature is necessary to avoid
destroying a nearby joint that has been made with a higher melting temperature
solder; and on temperature-sensing devices, such as fire sprinkler systems, where
the device is activated when the fusible alloy melts at relatively low temperature.
Many of these solders, particularly those containing a high percentage of bismuth,
are very difficult to use successfully in high-speed soldering operations. Particular
attention must be paid to the cleanliness of metal surfaces. Strong, corrosive
fluxes must be used to make satisfactory joints on uncoated surfaces of metals,
such as copper or steel. If the surface can be plated for soldering with such metals
as tin or tin-lead, noncorrosive rosin fluxes may be satisfactory; however, they are
not effective below 350°F (177°C).
(9) Indium solders. These solders possess certain properties which make them
valuable for some special applications. Their usefulness for any particular
application should be checked with the supplier. A 50 percent indium-50 percent
tin alloy adheres to glass readily and may be used for glass-to-metal and glass-toglass soldering. The low vapor pressure of this alloy makes it useful for seals in
vacuum systems. Iridium solders do not require special techniques during use. All
of the soldering methods, fluxes, and techniques used with the tin-lead solders are
applicable to iridium solders.
8-8. BRAZING ALLOYS
a. General.
(1) Brazing is similar to the soldering processes in that a filler rod with a melting
point lower than that of the base metal, but stove 800°F (427°C) is used. A
groove, fillet, plug, or slot weld is made and the filler metal is distributed by
capillary attraction. In brazing, a nonferrous filler rod, strip, or wire is used for
repairing or joining cast iron, malleable iron, wrought iron, steel, copper, nickel,
and high melting point brasses and bronzes. Some of these brasses and bronzes,
however, melt at a temperature so near to that of the filler rod that fusion welding
rather than brazing is required.
(2) Besides a welding torch with a proper tip size, a filler metal of the required
composition and a proper flux are important to the success of any brazing
operation.
(3) The choice of the filler metal depends on the types of metals to be joined.
Copper-silicon (silicon-bronze) rods are used for brazing copper and copper
alloys. Copper-tin (phosphor-bronze) rods are used for brazing similar copper
alloys and for brazing steel and cast iron. Other compositions are used for brazing
specific metals.
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(4) Fluxes are used to prevent oxidation of the filler metal and the base metal
surface, and to promote the free flowing of the filler metal. They should be
chemically active and fluid at the brazing temperature. After the joint members
have been fitted and thoroughly cleaned, an even coating of flux should be
brushed over the adjacent surfaces of the joint, taking care that no spots are left
uncovered. The proper flux is a good temperate indicator for torch brazing
because the joint should be heated until the flux remains fluid when the torch
flame is momentarily removed.
b. Characteristics. For satisfactory use in brazing applications, brazing filler metals must
possess the following properties:
(1) The ability to form brazed joints possessing suitable mechanical and physical
properties for the intended service application.
(2) A melting point or melting range compatible with the base metals being joined
and sufficient fluidity at brazing temperature to flow and distribute into properly
prepared joints by capillary action.
(3) A composition of sufficient homogeneity and stability to minimize separation
of constituents (liquation) under the brazing conditions encountered.
(4) The ability to wet the surfaces of the base metals being joined and form a
strong, sound bond.
(5) Depending on the requirements, ability to produce or avoid base metal-filler
metal interactions.
c. Filler Metal Selection. The following factors should be considered when selecting a
brazing filler metal:
(1) Compatibility with base metal and joint design.
(2) Service requirements for the brazed assembly. Compositions should be
selected to suit operating requirements, such as service temperature (high or
cryogenic), thermal cycling, life expectancy, stress loading, corrosive conditions,
radiation stability, and vacuum operation.
(3) Brazing temperature required. Low brazing temperatures are usually preferred
to economize on heat energy; minimize heat effects on base metal (annealing,
grain growth, warpage, etc.); minimize base metal-filler metal interaction; and
increase the life of fixtures and other teals. High brazing temperatures are
preferred in order to take advantage of a higher melting, but more economical,
brazing filler metal; to combine annealing, stress relief, or heat treatment of the
base metal with brazing; to permit subsequent processing at elevated
temperatures; to promote base metal-filler metal interactions to increase the joint
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remelt temperature; or to promote removal of certain refractory oxides by vacuum
or an atmosphere.
(4) Method of heating. Filler metals with narrow melting ranges (less than 50°F
(28°C) between solidus and liquidus) can be used with any heating method, and
the brazing filler metal may be preplaced in the joint area in the form of rings,
washers, formed wires, shims, powder, or paste. Such alloys may also be
manually or automatically face fed into the joint after the base metal is heated.
Filler metals that tend to liquate should be used with heating methods that bring
the joint to brazing temperature quickly, or allow the introduction of the brazing
filler metal after the base metal reaches the brazing temperature.
d. Aluminum-Silicon Filler Metals. This group is used for joining aluminum and
aluminum alloys. They are suited for furnace and dip brazing, while some types are also
suited for torch brazing using lap joints rather than butt joints. Flux should be used in all
cases and removed after brazing, except when vacuum brazing. Use brazing sheet or
tubing that consists of a core of aluminum alloy and a coating of lower melting filler
metal to supply aluminum filler metal. The coatings are aluminum-silicon alloys and may
be applied to one or both sides of sheet. Brazing sheet or tubing is frequently used as one
member of an assembly with the mating piece made of an unclad brazeable alloy. The
coating on the brazing sheet or tubing melts at brazing temperature and flows by capillary
attraction and gravity to fill the joints.
e. Magnesium Filler Metals. Because of its higher melting range, one magnesium filler
metal (BMg-1) is used for joining AZ10A, KIA, and MIA magnesium alloys, while the
other alloy (BMg-2a), with a lower melting range, is used for the AZ31B and ZE10A
compositions. Both filler metals are suited for torch, dip, or furnace brazing processes.
Heating must be closely controlled with both filler metals to prevent melting of the base
metal.
f. Copper and Copper-Zinc Filler Metals. These brazing filler metals are used for joining
various ferrous metals and nonferrous metals. They are commonly used for lap and butt
joints with various brazing processes. However, the corrosion resistance of the copperzinc alloy filler metals is generally inadequate for joining copper, silicon bronze, coppernickel alloys, or stainless steel.
(1) The essentially pure copper brazing filler metals are used for joining ferrous
metals, nickel base, and copper-nickel alloys. They are very free flowing and are
often used in furnace brazing with a combusted gas, hydrogen, or dissociated
ammonia atmosphere without flux. However, with metals that have components
with difficult-to-reduce oxides (chromium, manganese, silicon, titanium,
vanadium, and aluminum), a higher quality atmosphere or mineral flux may be
required. copper filler metals are available in wrought and powder forms.
(2) Copper-zinc alloy filler metals are used on most common base metals. A
mineral flux is commonly used with the filler metals.
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(3) Copper-zinc filler metals are used on steel, copper, copper alloys, nickel and
nickel base alloys, and stainless steel where corrosion resistance is not a
requirement. They are used with the torch, furnace, and induction brazing
processes. Fluxing is required, and a borax-boric acid flux is commonly used.
g. Copper-Phosphorus Filler Metals. These filler metals are primarily used for joining
copper and copper alloys and have some limited use for joining silver, tungsten, and
molybdenum. They should not be used on ferrous or nickel base alloys, or on coppernickel alloys with more than 10 percent nickel. These filler metals are suited for all
brazing processes and have self fluxing properties when used on copper. However, flux is
recommended with all other metals, including copper alloys.
h. Silver Filler Metals.
(1) These filler metals are used for joining most ferrous and nonferrous metals,
except aluminum and magnesium, with all methods of heating. They may be prep
laced in the joint or fed into the joint area after heating. Fluxes are generally
required, but fluxless brazing with filler metals free of cadmium and zinc can be
done on most metals in an inert or reducing atmosphere (such as dry hydrogen,
dry argon, vacuum, and combusted fuel gas).
CAUTION
Do not overheat filler metals containing cadmium. Cadmium oxide fumes
are hazardous.
(2) The addition of cadmium to the silver-copper-zinc alloy system lowers the
melting and flew temperatures of the filler metal. Cadmium also increases the
fluidity and wetting action of the filler metal on a variety of base metals.
Cadmium bearing filler metals should be used with caution. If they are improperly
used and subjected to overheating, cadmium oxide frees can be generated.
Cadmium oxide fumes are a health hazard, and excessive inhalation of these
fumes must be avoided.
(3) Of the elements that are commonly used to lower the melting and flow
temperatures of copper-silver alloys, zinc is by far the most helpful wetting agent
when joining alloys based on iron, cobalt, or nickel. Alone or in combination with
cadmium or tin, zinc produces alloys that wet the iron group metals but do not
alloy with them to any appreciable depth.
(4) Tin has a low vapor pressure at normal brazing temperatures. It is used in
silver brazing filler metals in place of zinc or cadmium when volatile constituents
are objectionable, such as when brazing is done without flux in atmosphere or
vacuum furnaces, or when the brazed assemblies will be used in high vacuum at
elevated temperatures. Tin additions to silver-copper alloys produce filler metals
with wide melting ranges. Alloys containing zinc wet ferrous metals more
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effectively than those containing tin, and where zinc is tolerable, it is preferred to
tin.
(5) Stellites, cemented carbides, and other molybdenum and tungsten rich
refractory alloys are difficult to wet with the alloys previously mentioned.
Manganese, nickel, and infrequently, cobalt, are often added as wetting agents in
brazing filler metals for joining these materials. An important characteristic of
silver brazing filler metals containing small additions of nickel is improved
resistance to corrosion under certain conditions. They are particularly
recommended where joints in stainless steel are to be exposed to salt water
corrosion.
(6) When stainless steels and other alloys that form refractory oxides are to be
brazed in reducing or inert atmospheres without flux, silver brazing filler metals
containing lithium as the wetting agent are quite effective. Lithium is capable of
reducing the adherent oxides on the base metal. The resultant lithium oxide is
readily displaced by the brazing alloy. Lithium bearing alloys are advantageously
used in very pure dry hydrogen or inert atmospheres.
i. Gold Filler Metals. These filler metals are used for joining parts in electron tube
assemblies where volatile components are undesirable; and the brazing of iron, nickel,
and cobalt base metals where resistance to oxidation or corrosion is required. Because of
their low rate of interaction with the base metal, they are commonly used on thin
sections, usually with induction, furnace, or resistance heating in a reducing atmosphere
or in vacuum without flux. For certain applications, a borax-boric acid flux may be used.
j. Nickel Filler Metals.
(l) These brazing filler metals are generally used for their corrosion resistance and
heat resistant properties up to 1800°F (982°C) continuous service, and 2200°F
(1204°C) short time service, depending on the specific filler metals and operating
environment. They are generally used on 300 and 400 series stainless steels and
nickel and cobalt base alloys. Other base metals such as carbon steel, low alloy
steels, and copper are also brazed when specific properties are desired. The filler
metals also exhibit satisfactory room temperature and cryogenic temperature
properties down to the liquid point of helium. The filler metals are normally
applied as powders, pastes, or in the form of sheet or rod with plastic binders.
(2) The phosphorus containing filler metals exhibit the lowest ductility because of
the presence of nickel phosphides. The boron containing filler metals should not
be used for brazing thin sections because of their erosive action. The quantity of
filler metal and time at brazing temperatures should be controlled because of the
high solubility of some base metals in these filler metals.
k. Cobalt Filler Metal. This filler metal is generally used for its high temperature
properties and its compatibility with cobalt base metals. For optimum results, brazing
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TC 9-237
should be performed in a high quality atmosphere. Special high temperature fluxes are
available.
1. Filler Metals for Refractory Metals.
(1) Brazing is an attractive means for fabricating many assemblies of refractory
metals, in particular those involving thin sections. The use of brazing to join these
materials is somewhat restricted by the lack of filler metals specifically designed
for brazing them. Although several references to brazing are present, the reported
filler metals that are suitable for applications involving both high temperature and
high corrosion are very limited.
(2) Low melting filler metals, such as silver-copper-zinc, copper-phosphorus, and
copper, are used to join tungsten for electrical contact applications. These filler
metals are limited in their applications, however, because they cannot operate at
very high temperatures. The use of higher melting metals, such as tantalum and
columbium, is warranted in those cases. Nickel base and precious-metal base
filler metals may be used for joining tungsten.
(3) A wide variety of brazing filler metals may be used to join molybdenum. The
brazing temperature range is the same as that for tungsten. Each filler metal
should be evaluated for its particular applicability. The service temperature
requirement in many cases dictates the brazing filler metal selection. However,
consideration must -be given to the effect of brazing temperature on the base
metal properties, specifically recrystallization. When brazing above the
recrystallization temperature, time should be kept as short as possible. When high
temperature service is not required, copper and silver base filler metals may be
used. For electronic parts and other nonstructural applications requiring higher
temperatures, gold-copper, gold-nickel, and copper-nickel filler metals can be
used. Higher melting metals and alloys may be used as brazing filler metals at still
higher temperatures.
(4) Copper-gold alloys containing less than 40 percent gold can also be used as
filler metals, but gold content between 46 and 90 percent tends to form age
hardening compounds which are brittle. Although silver base filler metals have
been used to join tantalum and columbium, they are not recommended because of
a tendency to embrittle the base metals.
m. Filler metal specifications and welding processes are shown in table 8-2.
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8-26
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8-27
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CHAPTER 9
MAINTENANCE WELDING OPERATIONS
FOR MILITARY EQUIPMENT
9-1. SCOPE
a. This chapter contains information necessary to determine the size of the
welding job and proper welding procedures for military items.
b. Appendix A
equipment used by
ing procedures as
contains references
military personnel
contains references to formal DA publications covering additional
military item and other equipment not covered by standard weldset forth in other chapters of this manual. Appendix A also
to formal DA publications covering additional equipment used by
which are not included in this chapter.
c. Welding techniques for equipment containing high yield strength, low alloy
structural steels (such as TI) used for bulldozer blades, armor, and heavy structural work are covered in chapter 12, section VII of this circular.
9-2.
SIZING UP THE JOB
a. General. All of the materials used in the manufacture of military materiel, as well as the assembled equipment are thoroughly tested before the material
is issued to the using services in the field. Therefore, most of the damage to and
failures of the equipment are due to accidents, overloading, or unusual shocks for
which the equipment was not designed to withstand. It is in this class of repair
work that field service welding is utilized most frequently.
b. De termination
of Weldability. Before repairing any damaged materiel, it
must be determined whether or not the materiel can be satisfactorily welded. This
determination is based upon the factors listed below.
(1) Determine the nature and extent of the damage and the amount of straightening and fitting of the metal that will be required.
(2) Determine the possibility of restoring the structure to usable condition
without the use of welding.
(3) Determine the type of metal used in the damaged part, whether it was heat
treated, and if so, what heat treatment was used.
(4) Determine if the welding heat will distort the shape or in any manner
impair the physical properties of the part to be repaired.
(5) Determine if heat treating or other equipment or materials will be required in order to make the repair by welding.
9-1
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9-2.
c.
SIZING UP THE JOB (cont)
Repairing Heat Treated Parts.
(1) In emergency cases, some heat treated parts can be repaired in the heat
treated condition by welding with stainless steel electrodes containing 25 percent
chromium and 20 percent nickel, or an 18 percent chromium-8 nickel electrode containing manganese or molybdenum. These electrodes will produce a satisfactory
weld, although a narrow zone in the base metal in the vicinity of the weld will be
affected by the heat of welding.
(2) Minor defects on the surface of heat treated parts may be repaired by
either hard surfacing or brazing, depending on their application in service. In
any of these repairs, the heat treated part will lose some of its strength, hardness, or toughness, even though the weld metal deposited has good properties.
(3) The preferred metal of repairing heat treated steels, when practicable,
requires the annealing of the broken part and welding with a high strength rod.
This method produces a welded joint that can be heat treated. The entire part
should be heat treated after welding to obtain the properties originally found in
the welded parts. This method should not be attempted unless proper heat treating
equipment is available.
9-3.
IDENTIFYING THE METAL
Welding repairs should not be made until the type of metal used for the components
or sections to be repaired has been determined. This information can be obtained
by previous experience with similar materiel, by test procedures as described in
chapter 7, or from assembly drawings of the components. These drawings should be
carried by maintenance companies in the field and should show the type of material
and the heat treatment of the parts.
9-4.
DETERMINING THE WELDABLE PARK
a. Welding operations on ordnance materiel are restricted largely to those
parts whose essential physical properties are not impaired by the welding heat.
b. Successful welded repairs cannot be made on machined parts that carry a
dynamic load . This applies particularly to high alloy steels that are heat treated
for hardness or toughness, or both.
c. Gears, shafts, antifriction bearings, springs, connecting rods, piston rods,
pistons, valves, and cam are considered to be unsuitable for field welding because
welding heat alters or destroys the heat treatment of these parts.
9-5.
SELECTING THE PROPER WELDING PROCDURES
The use of welding equipment and the application of welding processes to different
metals is covered in other chapters of this manual. A thorough working knowledge
of these processes and metals is necessary before a welding procedure for any given
job can be selected. When it has been decided by competent authority that the
repair can be made by welding, the factors outlined below must be considered.
9-2
TC 9-237
a. The proper type and size of electrode, together with the current and polarity setting, must be det ermined if an arc welding process is used. If a gas welding process is used, the proper type of welding rod, correct gas pressure, tip
size, flux, and flame adjustment must be determined.
b. In preparing the edges of plates or parts to be welded, the proper cleaning
and beveling of the parts to be joined must be considered. The need for backing
strips, quench plates, tack welding, and preheating must be determined.
c. Reducing warping and internal stresses requires the use of the proper sequence for welding, control and proper distribution of the welding heat, spacing of
the parts to permit some movment, control of the size and location of the deposited weld metal beads, and proper cooling procedure.
d. Military materiel is designed for lightness and the safety factors are, of
necessity, lo W in some cases. This necessitates sane reinforcement at the joint to
compensate for the strength lost in the welded part due to the welding heat. A
reinforcement must be designed that will provide the required strength without
producing high local rigidity or excessive weight.
9-6.
PRELIMINARY PRECAUTIONS
Before beginning any welding or cutting operations on the equipment, the safety
precautions listed below must be considered.
a.
Remove all ammunition from, on, or about the vehicle or materiel.
b. Drain the fuel tank and close the fuel and oil tank shut off valves. If
welding or cutting is to be done on the tanks, prepare them for welding in accordance with the instructions in chapter 2, section V.
c.
Have a fire extinguisher nearby.
d.
Keep heat away from optical elements.
e. Be familiar with and observe the safety precautions prescribed in chapter 2
of this circular.
9-3 (9-4 blank)
TC 9-237
CHAPTER 10
ARC WELDING AND CUTTING PROCESS
Section I. GENERAL
10-1.
DEFINITION OF ARC WELDING
a. Definition. In the arc welding process, the weld is produced by the extreme
heat of an electric arc drawn between an electrode and the workpiece, or in some
cases, between two electrodes. Welds are made with or without the application of
pressure and with or without filler metals. Arc welding processes may be divided
into two classes based on the type of electrode used: metal electrodes and carbon
electrodes. Detailed descriptions of the various processes may be found in chapter
6, paragraph 6-2.
(1) Metal electrodes. Arc welding processes that fall into this category
include bare metal-arc welding, stud welding, gas shielded stud welding, submerged
arc welding, gas tungsten arc welding, gas metal-arc welding, shielded metal-arc
welding, atomic hydrogen welding, arc spot welding, and arc seam welding.
(2) Carbon electrodes. Arc welding processes that fall into this category
include carbon-arc welding, twin carbon-arc welding, gas carbon-arc welding, and
shielded carbon-arc welding.
b.
Weld Metal Deposition.
(1) General. In metal-arc welding, a number of separate forces are responsible for the transfer of molten filler metal and molten slag to the base metal.
These forces are described in (2) through (7) helm.
(2) Vaporization and condensation. A small part of the metal passing through
the arc, especially the metal in the intense heat at the end of the electrode, is
vaporized. some of this vaporized metal escapes as spatter, but most of it is
condensed in the weld crater, which is at a much lower temperature. This occurs
with all types of electrodes and in all welding positions.
(3) Gravity. Gravity affects the transfer of metal in flat position welding . In other positions, small electrodes must be used to avoid excessive loss of
weld metal, as the surface tension is unable to retain a large amount of molten
metal in the weld crater.
(4) Pinch effect. The high current passing through the molten metal at the
tip of the electrode sets up a radial compressive magnetic force that tends to
pinch the molten globule and detach it from the electrode.
(5) Surface tension. This force holds filler metal and the slag globules in
contact with the molten base or weld metal in the crater. It has little to do with
the transfer of metal across the arc, but is an important factor in retaining the
molten weld metal in place and in the shaping of weld contours.
10-1
TC 9-237
10-1.
DEFINITION OF ARC WELDING (cont)
(6) Gas stream from electrode coatings. Gases are produced by the burning
and volatilization of the electrode covering and are expanded by the heat of the
boiling electrode tip. The velocity and movement of this gas stream give the small
particles in the arc a movement away from the electrode tip and into the molten
crater on the work.
(7) Carbon monoxide evolution from electrode. According to this theory of
metal movement in the welding arc, carbon monoxide is evolved within the molten
metal at the electrode tip, causing miniature explosions which expel molten metal
away from the electrode and toward the work. This theory is substantiated by the
fact that bare wire electrodes made of high purity iron or “killed steel” (i.e.,
steel that has been almost completely deoxidized in casting) cannot he used successfully in the overhead position. The metal transfer from electrode to the work, the
spatter, and the crater formation are, in this theory, caused by the decarburizing
action in molten steel.
c . Arc Crater. Arc craters are formal by the pressure of expanding gases from
the electrode tip (arc blast), forcing the liquid metal towards the edges of the
crater. The higher temperature of the center , as compared with that of the sides
of the crater, causes the edges to cool first. Metal is thus drawn from the center
to the edges, forming a low spot.
10-2.
WELDING WITH CONSTANT CURRENT
The power source is the heart of all arc welding process. Two basic types of power
sources are expressed by their voltage-ampere output characteristics. The constant
current machine is considered in this paragraph. The other power source, the constant voltage machine, is discussed in paragraph 10-3. The static output characteristic curve produced by both sources is shown in figure 10-1. The characteristic
curve of a welding machine is obtained by measuring and plotting the output voltage
and the output current while statically loading the machine.
a. The conventional machine is known as the constant current (CC) machine, or
the variable voltage type. The CC machine has the characteristic drooping volt-ampere curve, (fig. 10-1), and has been used for many years for the shielded metal
arc welding process. A constant-current arc-welding machine is one which has means
for adjusting the arc current. It also has a static volt-ampere curve that tends
to produce a relatively constant output current. The arc voltage, at a given welding current, is responsive to the rate at which a consumable electrode is fed into
the arc. When a nonconsumable electrode is used, the arc voltage is responsive to
the electrode-to-work distance. A constant-current arc-welding machine is usually
used with welding processes which use manually held eletrodes, continuously fed
consumable electrodes, or nonconsumable electrodes. If the arc length varies because of external influences, and slight changes in the arc voltage result, the
welding current remains constant.
b. The conventional or constant current (CC) type power source may have direct
current or alternating current output. It is used for the shielded metal-arc welding process, carbon arc welding and gouging, gas tungsten arc welding, and plasma
arc welding. It is used for stud welding and can be used for the continuous wire
processes when relatively large electrode wires are used.
10-2
TC 9-237
c. There are two control systems for constant current welding machines: the
single-control machine and the dual-control machine.
(1) The single-control machine has one adjustment which changes the current
output from minimum to maximum, which is usually greater than the rated output of
the machine. The characteristic volt-ampere curve is shown by figure 10-2. The
shaded area is the normal arc voltage range. By adjusting the current control, a
large number of output curves can be obtained. The dotted lines show intermediate
adjustments of the machine. With tap or plug-in machines, the number of covers
will correspond to the number of taps or plug-in combinations available. Most
transformer and transformer-rectifier machines are single-control welding machines.
Figure 10-2.
Curve for single control welding machine.
10-3
TC 9-237
10-2.
WELDING WITH CONSTANT CURRENT (cont)
(2) Dual control machines have both current and voltage controls. They have
two adjustments , one for coarse-current control and the other for fine-current
control, which also acts as an open-circuit voltage adjustment. Generator welding
machines usually have dual controls. They offer the welder the most flexibility
for different welding requirements. These machines inherently have slope control.
The slope of the characteristic curve can be changed from a shallow to a steep
slope according to welding requirements. Figure 10-3 shows some of the different
curves that can be obtained. Other tunes are obtained with intermediate open-circuit voltage settings. The slope is changed by changing the open-circuit voltage
with the fine—current control adjustment bob. The coarse adjustment sets the
current output of the machine in steps from the minimum to the maximum current.
The fine —current control will change the open-circuit voltage from approximately 55
volts to 85 volts. However, when welding, this adjustment does not change arc
voltage. Arc voltage is controlled by the welder by changing the length of the
welding arc. The open-circuit voltage affects the ability to stike an arc. If
the open-circuit voltage is much below 60 volts, it is difficult to strike an arc.
10-4
TC 9-237
(a) The different slopes possible with a dual-control machine have an important effect on the welding characteristic of the arc. The arc length can vary,
depending on the welding technique. A short arc has lower voltage and the long arc
has higher voltage. With a short arc (lower voltage), the power source produces
more current, and with a longer arc (higher voltage), the power source provides
less welding current. This is illustrated by figure 10-4, which shows three curves
of arcs and two characteristic curves of a dual-control welding machine. The three
arc curves are for a long arc, a normal arc, and the lower curve is for a short
arc. The intersection of a curve of an arc and a characteristic curve of a welding
machine is known as an operating point. The operating point changes continuously
during welding. While welding, and without changing the control on the machine,
the welder can lengthen or shorten the arc and change the arc voltage from 35 to 25
volts. With the same machine setting, the short arc (lower voltage) is a high-current arc. Conversely, the long arc (high voltage) is a lower current arc. This
allows the welder to control the size of the molten puddle while welding. When the
welder purposely and briefly lengthens the arc, the current is reduced, the arc
spreads out, and the puddle freezes quicker. The amount of molten metal is reduced, which provides the control needed for out-of-position work. This type of
control is built into conventional constant current type of machine, single- or
dual-control, ac or dc.
(b) With the dual-control machine, the welder can adjust the machine for
more or less change of current for a given change of arc voltage. Both curves in
figure 10-4 are obtained on a dud-control machine by adjusting the fine control
knob. The top curve shows an 80-volt open-circuit voltage and the bottom curve
shins a 60-volt open-circuit voltage. With either adjustment, the voltage and
current relationship will stay on the same curve or line. Consider first the 80volt open-circuit curve which produces the steeper slope. When the arc is long
10-5
TC 9-237
10-2.
WELDING WITH CONSTANT CURRENT (cont)
with 35 volts and is shortened to 25 volts, the current increases. This is done
without touching the machine control. The welder manipulates the arc. With the
flatter, 60-volt open-circuit curve, when the arc is shortened from 35 volts to 25
volts, the welding current will increase almost twice as much as it did when following the 80-volt open-circuit curve. The flatter slope curve provides a digging arc
where an equal change in arc voltage produces a greater change in arc current. The
steeper slope curve has less current change for the same change in arc length and
provides a softer arc. There are many characteristic curves between the 80 and 60
open circuit voltage curves, and each allows a different current change for the
same arc voltage change. This is the advantage of a dual-control welding machine
over a single-control type, since the slope of the curve through the arc voltage
range is adjustable only on a dual-control machine. The dual-control generator
welding machine is the most flexible of all types of welding power sources, since
it allows the welder to change to a higher-current arc for deep penetration or to a
lower-current, less penetrating arc by changing the arc length. This ability to
control the current in the arc over a fairly wide range is extremely useful for
making pipe welds.
d. The rectifier welding machine, technically known as the transformer-rectifier, produces direct current for welding. These machines are essentially single-control machines and have a static volt ampere output characteristic curve similar to
that shown by figure 10-4, p 10-5. These machines, though not as flexible as the
dual-control motor generator, can be used for all types of shielded metal arc welding where direct current is required. The slope of the volt-ampere curve through
the welding range is generally midway between the maximum and minimum of a dual-control machine.
e. Alternating current for welding is usually produced by a transformer type
welding machine, although engine-driven alternating current generator welding machines are available for portable use. The static volt ampere characteristic curve
of an alternating current power source the same as that shown by figure 10-4, p
10-5. some transformer welding power sources have fine and coarse adjustment
knobs, but these are not dual control machines unless the open-circuit voltage is
changed appreciably. The difference between alternating and direct current welding
is that the voltage and current pass through zero 100 or 120 times per second,
according to line frequency or at each current reversal. Reactance designed into
the machine causes a phase shift between the voltage and current so that they both
do not go through zero at the same instant. When the current goes through zero,
the arc is ex inguished,
t
but because of the phase difference, there is voltage
present which helps to re-establish the arc quickly. The degree of ionization in
the arc stream affects the voltage required to re-establish the arc and the overall
stability of the arc. Arc stabilizers (ionizers) are included in the coatings of
electrodes designed for ac welding to provide a stable arc.
f . The constant—current type welding machine can be used for some automatic
welding processes. The wire feeder and control must duplicate the motions of the
welder to start and maintain an arc. This requires a complex system with feedback
from the arc voltage to compensate for changes in the arc length. The constant-current power supplies are rarely used for very small electrode wire welding processes.
g. Arc welding machines have been developed with true constant—current volt-ampere static characteristics, within the arc voltage range, as shown by figure
10-5. A welder using this type of machine has little or no control over welding
10-6
TC 9-237
current by shortening or lengthening the arc, since the welding current remains the
same whether the arc is short or long. This is a great advantage for gas tungsten
current by shortening or lengthening the arc, since the welding current remains the
same whether the arc is short or long. This is a great advantage for gas tungsten
arc welding, since the working arc length of the tungsten arc is limited. In
shield metal-arc welding, to obtain weld puddle control, it is necessary to be
able to change the current level while welding. This is done by the machine, which
can be programmed to change from a high current (HC) to a low current (LC) on a
repetitive basis, known as pulsed welding. In pulsed current welding there are two
current levels, the high current and low current, sometimes called background curBy programming a control circuit, the output of the machine continuously
switches from the high to the low current as shown by figure 10-6, p 10-8. The
level of both high and low current is adjustable. In addition, the length of time
for the high and low current pulses is adjustable. This gives the welder the necessary control over the arc and weld puddle. Pulsed current welding is useful for
shielded metal-arc welding of pipe when using certain types of electrodes. Pulsed
arc is very useful when welding with the gas tungsten arc welding process.
10-7
TC 9-237
10-2.
WELDING WITH CONSTANT CURRENT (cont)
10-3.
WELDING WITH CONSTANT VOLTAGE
The second type of power source is the constant voltage (CV) machine or the constant potential (CP) machine. It has a relatively flat volt-ampere characteristic
curve.
The static output characteristic tune produced by both the CV and CC machine is shown by figure 10-1, p 10-3. The characteristic curve of a welding machine is obtained by measuring and plotting the output voltage and the output current while statically loading the machine. The constant voltage (CV) characteristic curve is essentially flat but with a slight droop. The curve may be adjusted
up and down to change the voltage; however, it will never rise to as high an opencircuit voltage as a constant current (CC) machine. This is one reason that the
constant voltage (CV) machine is not used for manual shielded metal arc welding
with covered electrodes. It is only used for continuous electrode wire welding.
The circuit consists of a pure resistance load which is varied from the minimum or
no load to the maximum or short circuit. The constant current (CC) curve shows
that the machine produces maximum output voltage with no load, and as the load
increases, the output voltage decreases. The no-load or open-circuit voltage is
usually about 80 volts.
b. The CV electrical system is the basis of operation of the entire commercial
electric power system. The electric power delivered to homes and available at
every receptacle has a constant voltage. The same voltage is maintained continuously at each outlet whether a small light bulb, with a very low wattage rating, or a
heavy-duty electric heater with a high wattage rating, is connected. The current
that flows through each of these circuits will be different based on the resistance
of the particular item or appliance in accordance with Ohm’s law. For example, the
small light bulb will draw less than 0.01 amperes of current while the electric
heater may draw over 10 amperes. The voltage throughout the system remain s con–
stant, but the current flowing through each appliance depends on its resistance or
electrical load. The same principle is utilized by the CV welding system.
10-8
TC 9-237
c. When a higher current is used when welding, the electrode is melted off more
rapidly. With lo W current, the electrode melts off slower. This relationship between melt-off rate and welding current applies to all of the arc welding processes
that use a continuously fed electrode. This is a physical relationship that depends upon the size of the electrode, the metal composition, the atmosphere that
surrounds the arc, and welding current. Figure 10-7 shows the melt-off rate curves
for different sizes of steel electrode wires in a C0 2 atmosphere. Note that these
curves are nearly linear, at least in the upper portion of the curve. Similar
curves are available for all sizes of electrode wires of different compositions and
in different shielding atmospheres. This relationship is definite and fixed, but
some variations can occur. This relationship is the basis of the simplified control for wire feeding using constant voltage. Instead of regulating the electrode
wire feed rate to maintain the constant arc length, as is done when using a constant current power source, the electrode wire is fed into the arc at a fixed
speed. The power source is designed to provide the necessary current to melt off
the electrode wire at this same rate. This concept prompted the development of the
constant voltage welding power source.
d. The volt-ampere characteristics of the constant voltage power source shown
by figure 10-8, p 10-10, was designed to produce substantially the same voltage at
no load and at rated or full load. It has characteristics similar to a standard
commercial electric power generator. If the load in the circuit changes, the power
source automaticaly adjusts its current output to satisfy this requirement, and
maintains essentially the same voltage across the output terminals. This ensures a
self-regulating voltage power source.
10-9
TC 9-237
10-3.
WELDING WITH CONSTANT VOLTAGE (cont)
e. Resistances or voltage drops occur in the welding arc and in the welding
cables and connecters, in the welding gun, and in the electrode length beyond the
current pickup tip. These voltage drops add up to the output voltage of the welding machine, and represent the electrical resistance load on the welding power
source. When the resistance of any component in the external circuit changes, the
voltage balance will be achieved by changing the welding current in the system.
The greatest voltage drop occurs across the welding arc. The other voltage drops
in the welding cables and connections are relatively small and constant. The voltage drop across the welding arc is directly dependent upon the arc length. A small
change in arc volts results in a relatively large change in welding current. Figure 10-9 shins that if the arc length shortens slightly, the welding current increases by approximately 100 amperes. This change in arc length greatly increases
the melt-off rate and quickly brings the arc length back to normal.
10-10
TC 9-237
f . The constant voltage power source is continually changing its current output
in order to maintain the voltage drop in the external portion of the welding circuit. Changes in wire feed speed which might occur when the welder moves the gun
toward or away from the work are compensated for by changing the current and the
melt-off rate briefly until equilibrium is re-established. The same corrective
action occurs if the wire feeder has a temporary reduction in speed. The CV power
source and fixed wire feed speed system is self-regulating. Movemment of the cable
assembly often changes the drag or feed rate of the electrode wire. The CV welding
power source provides the proper current so that the malt-off is equal to the wire
feed rate. The arc length is controlled by setting the voltage on the power
source. The welding current is controlled by adjusting the wire feed speed.
g. The characteristics of the welding power source must be designed to provide
a stable arc when gas metal arc welding with different electrode sizes and metals
and in different atmospheres. Most constant voltage power sources have taps or a
means of adjusting the slope of the volt-ampere curve. A curve having a slope of
1-1/2 to 2 volts per hundred amperes is best for gas metal arc welding with
nonferrous electrodes in inert gas, for submerged arc welding, and for flux-cored
arc welding with larger-diameter electrode wires. A curve having a medium slope of
2 to 3 volts per hundred amperes is preferred for CO2 gas shielded metal arc welding and for small flux-cored electrode wires. A steeper slope of 3 to 4 volts per
hundred amperes is reccomended for short circuiting arc transfer. These three
slopes are shown in figure 10-10. The flatter the curve, the more the current
changes for an equal change in arc voltage.
h. The dynamic characteristics of the power source must be carefully engineered. Refer again to figure 10-9. If the voltage changes abruptly with a short
circuit, the current will tend to increase quickly to a very high value. This is
an advantage in starting the arc but will create unwanted spatter if not controlled. It is controlled by adding reactance or inductance in the circuit. This
changes the time factor or response time and provides for a stable arc. In most
machines, a different amount of inductance is included in the circuit for the different slopes.
10-11
TC 9-237
10-3.
WELDING WITH CONSTANT VOLTAGE (cont)
i. The constant voltage welding power system has its greatest advantage when
the current density of the electrode wire is high. The current density (amperes/sq
in.) relationship for different electrode wire sizes and different currents is
shown by figure 10-11. There is a vast difference between the current density
employed for gas metal arc welding with a fine electrode wire compared with conventional shielded metal arc welding with a covered electrode.
j . Direct current electrode positive (DCEP) is used for gas metal arc welding.
When dc electrode negative (DCEN) is used, the arc is erratic and produces an inferior weld. Direct current electrode negative (DCEN) can be used for submerged arc
welding and flux-cored arc welding.
k. Constant voltage welding with alternating current is normally not used. It
can be used for submerged arc welding and for electroslag welding.
l . The constant voltage power system should not be used for shielded metal-arc
welding. It may overload and damage the power source by drawing too much current
too long. It can be used for carbon arc cutting and gouging with small electrodes
and the arc welding processes.
10-12
TC 9-237
10-4.
DC STRAIGHT AND REVERSE POLARITY WELDING
a. General. The electrical arc welding circuit is the same as any electrical
circuit. In the simplest electrical circuits, there are three factors: current,
or the flow of electricity; pressure, or the force required to cause the current to
flow; and resistance, or the force required to regulate the flow of current.
(1) Current is a rate of flew and is measured by the amount of electricity
that flows through a wire in one second. The term ampere denotes the amount of
current per second that flows in a circuit. The letter I is used to designate
current amperes.
(2) Pressure is the force that causes a current to flow. The measure of
electrical pressure is the volt. The voltage between two points in an electrical
circuit is called the difference in potential. This force or potential is called
electromotive force or EMF. The difference of potential or voltage causes current
to flow in an electrical circuit. The letter E is used to designate voltage or EMF.
(3) Resistance is the restriction to current flow in an electrical circuit.
Every component in the circuit, including the conductor, has some resistance to
current flow. Current flows easier through some conductors than others; that is,
the resistance of some conductors is less than others. Resistance depends on the
material, the cross-sectional area, and the temperature of the conductor. The unit
of electrical resistance is the ohm. It is designated by the letter R.
b. Electrical circuits. A simple electrical circuit is shown by figure 10-12.
This circuit includes two meters for electrical measurement: a voltmeter, and an
ammeter. It also shows a symbol for a battery. The longer line of the symbol
represents the positive terminal. Outside of a device that sets up the EMF, such
as a generator or a battery, the current flows from the negative (-) to the positive (+). The arrow shows the direction of current flow. The ammeter is a low
resistance meter shown by the round circle and arrow adjacent to the letter I. The
pressure or voltage across the battery can be measured by a voltmeter. The
voltmeter is a high resistance meter shown by the round circle and arrow adjacent
to the letter E. The resistance in the circuit is shown by a zigzag symbol. The
resistance of a resistor can be measured by an ohmmeter. An ohmmeter must never be
used to measure
resistance in a circuit when current is flowing.
..
10-13
TC 9-237
10-4. DC STRAIGHT AND REVERSE POLARITY WELDING (cont)
c. Arc Welding Circuit. A few changes to the circuit shown by figure 10-12, p
10-13, can be made to represent an arc welding circuit. Replace the battery with a
welding generator, since they are both a source of EMF (or voltage), and replace
the resistor with a welding arc which is also a resistance to current flow. The
arc welding circuit is shown by figure 10-13. The current will flow from the negative terminal through the resistance of the arc to the positive terminal.
d. Reverse and Straight Polarity. In the early days of arc welding, when welding was done with bare metal electrodes on steel, it was normal to connect the
positive side of the generator to the work and the negative side to the electrode.
This provided 65 to 75 percent of the heat to the work side of the circuit to increase penetration. When welding with the electrode negative, the polarity of the
welding current was termed straight. When conditions such as welding cast iron or
nonferrous metals made it advisable to minimize the heat in the base metal, the
work was made negative and the electrode positive , and the welding current polarity
was said to be reverse. In order to change the polarity of the welding current, it
was necessary to remove the cables from the machine terminals and replace them in
the reverse position. The early coated electrodes for welding steel gave best
results with the electrode positive or reverse polarity; however, bare electrodes
were still used. It was necessary to change polarity frequently when using both
bare and covered electrodes. Welding machines were equipped with switches that
changed the polarity of the terminals and with dual reading meters. The welder
could quickly change the polarity of the welding current. In marking welding machines and polarity switches, these old terms were used and indicated the polarity
as straight when the electrode was negative, and reverse when the electrode was
positive. Thus, electrode negative (DCEN) is the same as straight polarity (dcsp),
and electrode positive (DCEP) is the same as reverse polarity (dcrp).
e. The ammeter used in a welding circuit is a millivoltmeter calibrated in
amperes connected across a high current shunt in the welding circuit. The shunt is
a calibrated, very low resistance conductor. The voltmeter shown in figure 10-12
will measure the welding machine output and the voltage across the arc, which are
essentially the same. Before the arc is struck or if the arc is broken, the
voltmeter will read the voltage across the machine with no current flowing in the
c i r c u i t . This is known as the open circuit voltage, and is higher than the arc
voltage or voltage across the machine when current is flowing.
f. Another unit in an electrical circuit is the unit of power. The rate of
producing or using energy is called power, and is measured in watts. Power in a
circuit is the product of the current in amperes multiplied by the pressure in
volts. Power is measured by a wattmeter, which is a combination of an ammmeter and
a voltmeter.
10-14
TC 9-237
g. In addition to power, it is necessary to know the amount of work involved.
Electrical work or energy is the product of power multiplied by time, and is expressed as watt seconds, joules, or kilowatt hours.
10-5.
WELDING ARCS
a. General. The arc is used as a concentrated source of high temperature heat
that can be moved and manipulated to melt the base metal and filler metal to produce welds.
b. Types of Welding Arcs. There are two basic types of welding arcs.
the nonconsumable electrode and the other uses the consumable electrode.
One uses
(1) The nonconsumable electrode does not melt in the ar C and filler metal is
not carried across the arc stream. The welding processes that use the nonconsumable electrode arc are carbon arc welding, gas tungsten arc welding, and plasma
arc welding.
(2) The consumable electrode melts in the arc and is carried across the arc
in a stream to become the deposited filler metal. The welding processes that use
the consumable electrode arC are shielded metal arc welding, gas metal arc welding,
flux-cored arc welding, and submerged arc welding.
c.
Function of the Welding Arc.
(1) The main function of the arc is to procduce heat. At the same time, it
produces a bright light, noise, and, in a special case, bombardment that removes
surface films from the base metal.
(2) A welding arc is a sustained electrical discharge through a high conducting plasma. It produces sufficient thermal energy which is useful for joining
metals by fusion. The welding arc is a steady-state condition maintained at the
gap between an electrode and workpiece that can carry current ranging from as lo W
as 5 amperes to as high as 2000 amperes and a voltage as low as 10 volts to the
highest voltages used on large plasma units. The welding arc is somewhat different
from other electrical arcs since it has a point-to-plane geometric configuration,
the point being the arcing end of the electrode and the plane being the arcing area
of the workpiece. Whether the electrode is positive or negative, the arc is restricted at the electrode and spreads out toward the workpiece.
(3) The length of the arc is proportional to the voltage across the ar C . If
the arc length is increased beyond a certain point, the arc will suddenly go out.
This means that there is a certain current necessary to sustain an arc of different
lengths. If a higher current is u S e d , a longer arc can be maintained.
(4) The arc column is normally round in cross section and is made up of an
inner core of plasma and an outer flame. The plasma carries most of the current.
The plasma of a high—current arc can reach a temperature of 5000 to 50,000
0
Kelvin. The outer flame of the arc is much cooler and tends to keep the plasma
in the center. The temperature and the diameter of the central plasma depend on
the amount of current passing through the arc, the shielding atmosphere, and the
electrode size and type.
10-15
TC 9-237
10-5.
WELDING ARCS (cont )
(5) The curve of an arc, shown by figure 10-14, takes on a nonlinear form
which in one area has a negative slope. The arc voltage increases slightly as the
current increases. This is true except for the very low—current arc which has a
higher arc voltage. This is because the low—current plasma has a fairly small
cross-sectional area, and as the current increases the cross section of the plasma
increases and the resistance is reduced. The conductivity of the arc increases at
a greater rate than simple proportionality to current.
(6) The arc is maintained when electrons are emitted or evaporated from the
surface of the negative pole (cathode) and flow across a region of hot electrically
charged gas to the positive pole (anode), where they are absorbed Cathode and.
anode are electrical terms for the negative and positive poles.
(7) Arc action can best be explained by considering the dc tungsten electrode
arc in an inert gas atmosphere as shown by figure 10-15. On the left, the tungsten
arc is connected for direct current electrode negative (DCEN). When the arc is
started, the electrode becomes hot and emits electrons. The emitted electrons are
attracted to the positive pole, travel through the arc gap, and raise the temperature of the argon shielding gas atoms by colliding with them. The collisions of
electrons with atoms and molecules produce thermal ionization of some of the atoms
of the shielding gas. The positively charged gaseous atoms are attracted to the
negative electrode where their kinetic (motion) energy is converted to heat. This
heat keeps the tungsten electrode hot enough for electron emission. Emission of
electrons from the surface of the tungsten cathode is known as thermionic emiss ion. Positive ions also cross the arc. They travel from the positive pole, or
the work, to the negative pole, or the electrode. Positive ions are much heavier
than the electrons, but help carry the current flow of the relatively low voltage
welding arc. The largest portion of the current flow, approximately 99 percent, is
via electron flew rather than through the flow of positive ions. The continuous
feeding of electrons into the welding circuit from the power source accounts for
the continuing balance between electrons and ions in the arc. The electrons colliding with the work create the intense localized heat which provides melting and deep
penetration of the base metals.
10-16
TC 9-237
(8) In the dc tungsten to base metal arc in an inert gas atmosphere, the
maximum heat occurs at the positive pole (anode). When the electrode is positive
(anode ) and the work is negative (cathode), as shown by figure 10-15, the electrons
flow from the work to the electrode where they create intense heat. The electrode
tends to overheat. A larger electrode with more heat-absorbing capacity is used
for DCEP (dcsp) than for DCEN (dcrp) for the same welding current. In addition,
since less heat is generated at the work, the penetration is not so great. One
result of DCEP welding is the cleaning effect on the base metal adjacent to the arc
area. This appears as an etched surface and is known as catholic etching. It
results from positive ion bombardment. This positive ion bombardment also occurs
during the reverse polarity half-cycle when using alternating current for welding.
(9) Constriction occurs in a plasma arc torch by making the arc pass through
a small hole in a water-cooled copper nozzle. It is a characteristic of the arc
that the more it is cooled the hotter it gets; however, it requires a higher voltage. By flowing additional gas through the small hole, the arc is further constricted and a high velocity, high temperature gas jet or plasma emerges. This
plasma is used for welding, cutting, and metal spraying.
10-17
TC 9-237
10-5. WELDING ARCS (cont)
(10) The arc length or gap between the electrode and the work can be divided
into three regions: a central region, a region adjacent to the electrode, and a
region adjacent to the work. At the end regions, the cooling effect of the electrode and the work causes a rapid drop in potential. These two regions are known
as the anode and cathode drop, according to the direction of current flow. The
length of the central region or arc column represents 99 percent of the arc length
and is linear with respect to arc voltage. Figure 10-16 shows the distribution of
heat in the arc, which varies in these three regions. In the central region, a
circular magnetic field surrounds the arc. This field, produced by the current
flow, tends to constrict the plasma and is known as the magnetic pinch effect. The
constriction causes high pressures in the arc plasma and extremely high velocit i e s . This, in turn, produces a plasma jet. The speed of the plasma jet approaches sonic speed.
(11 ) The cathode drop is the electrical connection between the arc column and
the negative pole (cathode). There is a relatively large temperature and potential
drop at this point. The electrons are emitted by the cathode and given to the arc
column at this point. The stability of an arc depends on the smoothness of the
flow of electrons at this point. Tungsten and carbon provide thermic emissions,
since both are good emitters of electrons. They have high melting temperatures,
are practically nonconsumable, and are therefore used for welding electrodes.
Since tungsten has the highest melting point of any metal, it is preferred.
(12) The anode drop occurs at the other end of the arc and is the electrical
connection between the positive pole (anode) and the arc column. The temperature
changes from that of the arc column to that of the anode, which is considerably
lower. The reduction in temperature occurs because there are fewer ions in this
region. The heat liberated at the anode and at the cathode is greater than that
from the arc column.
d. Carbon Arc. In the carbon arc, a stable dc arc is obtained when the carbon
is negative. In this condition, about 1/3 of the heat occurs at the negative pole
(cathode), or the electrode, and about 2/3 of the heat occurs at the positive pole
(anode), or the workpiece.
10-18
TC 9-237
e. Consumable Electrode Arc. In the consumable electrode welding arc, the
electrode is melted and molten metal is carried across the arc. A uniform arc
length is maintained between the electrode and the base metal by feeding the electrode into the arc as fast as it melts. The arc atmosphere has a great effect on
the polarity of maximum heat. In shielded metal arc welding, the arc atmosphere
depends on the composition of the coating on the electrode. Usually the maximum
heat occurs at the negative ple (cathode). When straight polarity welding with an
E6012 electrode, the electrode is the negative pole (DCEN) and the melt-off rate is
high. Penetration is minimum. When reverse polarity welding with an E6010 electrode (DCEP), the maximum heat still occurs at the negative pole (cathode), but
this is now the base metal, which provides deep penetration. This is shown by figure 10-17. With a bare steel electrode on steel, the polarity of maximum heat is
the positive pole (anode). Bare electrodes are operated on straight polarity
(DCEN) so that maximum heat is at the base metal (anode) to ensure enough penetration. When coated electrodes are operated on ac, the same amount of heat is produced on each polarity of the arc.
f.
Consumable Electrode Arc.
(1) The forces that cause metal to transfer across the arc are similar for
all the consumable electrode arc welding processes. The type of metal transfer
dictates the usefulness of the welding
- process. It affects the welding position
that can be used, the depth of weld penetration, the stability of the welding pool,
the surface contour of the weld, and the amount of spatter loss. The metal being
transferred ranges from small droplets, smaller than the diameter of the electrode,
to droplets larger in diameter than the electrode. The type of transfer depends on
the current density, the polarity of the electrode, the arc atmosphere, the electrode size, and the electrode composition.
(2) Several forces affect the transfer of liquid metal across an arc. These
are surface tension, the plasma jet, gravity in flat position welding, and electromagnetic force.
10-19
TC 9-237
10-5.
WELDING ARCS (cont)
(a) Surface tension of a liquid causes the surface of the liquid to contract to the smallest .possible area. This tension tends to hold the liquid drops
on the end of a melting electrode without regard to welding position. This force
works against the transfer of metal across the arc and helps keep molten metal in
the weld pool when welding in the overhead position.
(b) The welding arc is constricted at the electrode and spreads or flares
out at the workpiece. The current density and the arc temperature are the highest
where the arc is most constricted, at the end of the electrode. An arc operating
in a gaseous atmosphere contains a plasma jet which flows along the center of the
arc column between the electrode and the base metal. Molten metal drops in the
process of detachment from the end of the electrode, or in flight, are accelerated
towards the work piece by the plasma jet.
(c) Earth gravity detaches the liquid drop when the electrode is pointed
downward and is a restraining force when the electrode is pointing upward. Gravity
has a noticeable effect only at low currents. The difference between the mass of
the molten metal droplet and the mass of the workpiece has a gravitational effect
which tends to pull the droplet to the workpiece. An arc between two electrodes
will not deposit metal on either.
(d) Electromagnetic force also helps transfer metal across the arc. When
the welding current flows through the electrode, a magnetic field is set up around
i t . The electromagnetic force acts on the liquid metal drop when it is about to
detach from the electrode. As the metal melts, the cross-sectional area of the
electrode changes at the molten tip. The electromagnetic force depends upon whether the cross section is increasing or decreasing. There are two ways in which the
electromagnetic force acts to detach a drop at the tip of the electrode. When a
drop is larger in diameter than the electrode and the electrode is positive (DCEP),
the magnetic force tends to detach the drop. When there is a constriction or necking down which occurs when the drop is about to detach, the magnetic force acts
away from the point of constriction in both directions. The drop that has started
to separate will be given a push which increases the rate of separation. Figure
10-18 illustrates these two points. Magnetic force also sets up a pressure within
the liquid drop. The maximum pressure is radial to the axis of the electrode and
at high currents causes the drop to lengthen. It gives the drop stiffness and
causes it to project in line with the electrode regardless of the welding position.
10-20
TC 9-237
10-6.
AC WELDING
a. General. Alternating current is an electrical current which flows back and
forth at regular intervals in a circuit. When the current rises from zero to a
maximum, returns to zero, increases to a maximum in the opposite direction, and
finally returns to zero again, it is said to have completed one cycle.
(1) A cycle is divided into 360 degrees. Figure 10-19 is a graphical representation of a cycle and is called a sine wave. It is generated by one revolution
of a single loop coil armature in a two-pole alternating current generator. The
maximum value in one direction is reached at the 90° position, and in the other
direction at the 270° p o s i t i o n .
(2) The number of times this cycle is repeated in one second is called the
frequency, measured in hertz.
b. Alternating current for arc welding normally has the same frequency as the
line current. The voltage and current in the ac welding arc follow the sine wave
and return to zero twice each cycle. The frequency is so fast that the arc appears
continuous and steady. The sine wave is the simplest form of alternating current.
c. Alternating current and voltage are measured with ac meters. An
voltmeter measures the value of both the positive and negative parts of
wave. It reads the effective, or root-mean-square (RMS) voltage. The
direct current value of an alternating current or voltage is the product
multiplied by the maximum value.
ac
the sine
effective
of 0.707
d. An alternating current has no unit of its own, but is measured in terms of
direct current, the ampere. The ampere is defined as a steady rate of flow, but an
alternating current is not a steady current. An alternating current is said to be
equivalent to a direct current when it produces the same average heating effect
under exactly similar conditions. This is used since the heating effect of a negative current is the same as that of a positive current. Therefore, an ac ammeter
will measure a value, called the effective value, of an alternating current which
is shown in amperes. All ac meters, unless otherwise marked, read effective values
of current and voltage.
10-21
TC 9-237
10-6.
AC WELDING (cont)
e. Electrical power for arc welding is obtained in two different ways. It is
either generated at the point of use or converted from available power from the
utility line. There are two variations of electrical power conversion.
(1) In the first variation, a transformer converts the relatively high voltages from the utility line to a liner voltage for ac welding.
(2) The second variation is similar in that it includes the transformer to
lower the voltage, but it is followed by a rectifier which changes alternating
current to direct current for dc welding.
f . With an alternating flew of current, the arc is extinguished during each
half-cycle as the current reduces to zero , requiring reignition as the voltage
rises again. After reignition, it passes, with increasing current, through the
usual falling volts-amperes characteristic. As the current decreases again, the
arc potential is lower because the temperature and degree of ionization of the arc
path correspond to the heated condition of the plasma, anode, and cathode during
the time of increasing current.
g. The greater the arc length, the less the arc gas will be heated by the hot
electrode terminals, and a higher reignition potential will be required. Depending
upon the thermal inertia of the hot electrode terminals and plasma, the cathode
emitter may cool enough during the fall of the current to zero to stop the arc
completely. When the electrode and welding work have different thermal inertia
ability to emit electrons, the current will flow by different amounts during each
half-cycle. This causes rectification to a lesser or greater degree. Complete
rectification has been experienced in arcs with a hot tungsten electrode and a cold
copper opposing terminal. Partial rectification of one half-cycle is common when
using the TIG welding process with ac power.
10-7.
MULTILAYER WELDING
a. Multiple layer welding is used when maximum ductility of a steel weld is
desired or several layers are required in welding thick metal. Multiple layer
welding is accomplished by depositing filler metal in successive passes along the
joint until it is filled (fig. 10-20). Since the area covered with each pass is
small, the weld puddle is reduced in size. This procedure enables the welder to
obtain complete joint penetration without excessive penetration and overheating
while the first few passes are being deposited. The smaller puddle is more easily
controlled, and the welder can avoid oxides, slag inclusions, and incomplete fusion
with the base metal.
10-22
TC 9-237
b. The multilayer method allows the welder to concentrate on getting good penetration at the root of the V in the first pass or layer. The final layer is easily
controlled to obtain a good smooth surface.
This method permits the metal deposited in a given layer to be partly or
wholly refined by the succeeding layers, and therefore improved in ductility. The
lower layer of weld metal, after cooling, is reheated by the upper layer and then
cooled again. In effect, the weld area is being heat treated. In work where this
added
quality is desired in the top layer of the welded joint, an excess of weld
.
metal is deposited on the finshed weld and then machined off. The purpose of this
last layer is simply to provide welding heat to refine layer of weld metal.
Section II.
10-8.
ARC PROCESSES
SHIELDED METAL-ARC WELDING (SMAW)
a. General. This is the most widely used method for general welding applications. It is also refereed to as metallic arc, manual metal-arc, or stick-electrode welding. It is an arc welding process in which the joining of metals is
produced by heat from an electric arc that is maintained between the tip of a covered electrode and the base metal surface of the joint being welded.
10-23
TC 9-237
10-8.
SHIELDED METAL-ARC WELDING (SMAW) (cont)
b. Advantages. The SMAW process can be used for welding most structural and
alloy steels. These include low-carbon or mild steels; low-alloy, heat-treatable
steels; and high-alloy steels such as stainless steels. SMAW is used for joining
common nickel alloys and can be used for copper and aluminum alloys. This welding
process can be used in all positions --flat, vertical, horizontal, or overhead-and requires only the simplest equipment. Thus, SMAW lends itself very well to
field work (fig. 10-21).
c. Disadvantages. Slag removal, unused electrode stubs, and spatter add to the
cost of SMAW. Unused electrode stubs and spatter account for about 44 percent of
the consumed electrodes. Another cost is the entrapment of slag in the form of
inclusions, which may have to be removed.
d.
Processes.
(1) The core of the covered electrode consists of either a solid metal rod of
drawn or cast material, or one fabricated by encasing metal powders in a metallic
sheath. The core rod conducts the electric current to the arc and provides filler
metal for the joint. The electrode covering shields the molten metal from the
atmosphere as it is transferred across the arc and improves the smoothness or stability of the arc.
(2) Arc shielding is obtained from gases which form as a result of the decomposition of certain ingredients in the covering. The shielding ingredients vary
according to the type of electrode. The shielding and other ingredients in the
covering and core wire control the mechanical properties, chemical composition, and
metallurgical structure of the weld metal, as well as arc characteristics of the
electrode.
(3) Shielded metal arc welding employs the heat of the arc to melt the base
metal and the tip of a consumable covered electrode. The electrode and the work
are part of an electric circuit known as the welding circuit, as shown in figure
10-22. This circuit begins with the electric power source and includes the welding
cables, an electrode holder, a ground clamp, the work, and an arc welding electrode. One of the two cables from the power source is attached to the work. The
other is attached to the electrode holder.
10-24
TC 9-237
(4) Welding begins when an electric arc is struck between the tip of the
electrode and the work. The intense heat of the arc melts the tip of the electrode
and the surface of the work beneath the arc. Tiny globules of molten metal rapidly
form on the tip of the electrode, then transfer through the arc stream into the
molten weld pool. In this manner, filler metal is deposited as the electrode is
progressively consumed. The arc is moved over the work at an appropriate arc
length and travel speed, melting and fusing a portion of the base metal and adding
filler metal as the arc progresses. Since the arc is one of the hottest of the
commercial sources of heat (temperatures above 9000 °F (5000 °C) have been measured
at its center), melting takes place almost instantaneously as the arc contacts the
metal. If welds are made in either the flat or the horizontal position, metal
transfer is induced by the force of gravity, gas expansion, electric and electromagnetic forces, and surface tension. For welds in other positions, gravity works
against the other forces.
(a) Gravity. Gravity is the principal force which accounts for the transfer of filler metal in flat position welding. In other positions, the surface
tension is unable to retain much molten metal and slag in the crater. Therefore,
smaller electrodes must be used to avoid excessive loss of weld metal and slag.
See figure 10-23.
(b) Gas expansion. Gases are produced by the burning and volatilization of
the electrode coating, and are expanded by the heat of the boiling electrode tip.
The coating extending beyond the metal tip of the electrode controls the direction
of the rapid gas expansion and directs the molten metal globule into the weld metal
pool fomed in the base metal.
10-25
TC 9-237
10-8. SHIELDED METAL-ARC WELDING (SMAW) (cont)
(c) Electromagnetic forces. The electrode tip is an electrical conductor,
as is the moliten metal globule at the tip. Therefore, the globule is affected by
magnetic forces acting at 90 degrees to the direction of the current flow. These
forces produce a pinching effect on the metal globules and speed up the separation
of the molten metal from the end of the electrode. This is particularly helpful in
transferring metal in horizontal, vertical, and overhead position welding.
(d) Electrical forces. The force produced by the voltage across the arc
pulls the small, pinched-off globule of metal, regardless of the position of welding . This force is especially helpful when using direct-current, straight-polarity, mineral-coated electrodes, which do not produce large volumes of gas.
(e) Surface tension. The force which keeps the filler metal and slag globules in contact with molten base or weld metal in the crater is known as surface
tension. It helps to retain the molten metal in horizontal, vertical, and overhead
welding, and to determine the shape of weld countours.
e. Equipment. The equipment needed for shielded metal-arc welding is much less
complex than that needed for other arc welding processes. Manual welding equipment
includes a power source (transformer, dc generator, or dc rectifier),
electrode holder, cables, connectors, chipping hammer, wire brush, and electrodes.
f. Welding Parameters.
(1) Welding voltage, current, and travel speed are very important to the
quality of the deposited SMAW bead. Figures 10-24 thru 10-30 show the travel speed
limits for the electrodes listed in table 10-1, p 10-30. Table 10-1 shows voltage
limits for some SMAW electrodes.
10-26
TC 9-237
10-8.
SHIELDED METAL-ARC WELDING (SMAW) (cont)
(2) The process requires sufficient electric current to melt both the electrode and a proper amount of base metal, and an appropriate gap between the tip of
the electrode and base metal or molten weld pool. These requirements are necessary
for coalescence. The sizes and types of electrodes for shielded metal arc welding
define the arc voltage requirements (within the overall range of 16 to 40 V) and
the amperage requirements (within the overall range of 20 to 550 A). The current
may be either alternating or direct, but the power source must be able to control
the current level in order to respond to the complex variables of the welding process itself.
g. Covered
Electrodes. In addition to establishing the arc and supplying filler metal for the weld deposit, the electrode introduces other materials into or
around the arc. Depending upon the type of electrode being used, the covering
performs one or more of the following functions:
(1) Provides a gas to shield the arc and prevent excessive atmospheric contamination of the molten filler metal as it travels across t h e a r c .
(2) Provides scavengers, deoxidizers, and fluxing agents to cleanse the weld
and prevent excessive grain growth in the weld metal.
(3) Establishes the electrical characteristics of the electrode.
(4) Provides a slag blanket to protect the hot weld metal from the air and
enhance the mechanical properties, bead shape, and surface cleanliness of the weld
metal.
(5) Provides a means of adding alloying elements to change the mechanical
properties of the weld metal.
Functions 1 and 4 prevent the pick-up of oxygen and nitrogen from the air by the
molten filler metal in the arc stream and by the weld metal as it solidifies and
cools.
10-30
TC 9-237
The covering on shielded metal arc electrodes is applied by either the extrusion or
the dipping process. Extrusion is much more widely used. The dipping process is
used primarily for cast and some fabricated core rods. In either case, the covering contains most of the shielding, scavenging, and deoxidizing materials. Most
SMAW electrodes have a solid metal core. Some are made with a fabricated or composite core consisting of metal powders encased in a metallic sheath. In this latter
case, the purpose of some or even all of the metal powders is to produce an alloy
weld deposit.
In addition to improving the mechanical properties of the weld metal, the covering
on the electrode can be designed for welding with alternating current. With ac,
the welding arc goes out and is reestablished each time the current reverses its
direction. For good arc stability, it is necessary to have a gas in the arc stream
that will remain ionized during each reversal of the current. This ionized gas
makes possible the reignition of the arc. Gases that readily ionize are available
from a variety of compunds, including those that contain potassium. It is the
incorporation of these compounds in the electrode covering that enables the electrode to operate on ac.
To increase the deposition rate, the coverings of some carbon and low alloy steel
electrodes contain iron powder. The iron powder is another source of metal avail–
able for deposition, in addition to that obtained from the core of the electrode.
The presence of iron powder in the covering also makes more efficient use of the
arc energy. Metal powders other than iron are frequently used to alter the mechanical properties of the weld metal.
The thick coverings on electrodes with relatively large amounts of iron powder
increase the depth of the crucible at the tip of the electrode. This deep crucible
helps contain the heat of the arc and maintains a constant arc length by using the
“drag” technique. When iron or other metal powders are added in relatively large
amounts, the deposition rate and welding speed usually increase. Iron powder electrodes with thick coverings reduce the level of skill needed to weld. The tip of
the electrode can be dragged along the surface of the work while maintaining a
welding arc. For this reason, heavy iron powder electrodes frequently are called
“drag electrodes.” Deposition rates are high; but because slag solidification is
slow, these electrodes are not suitable for out-of-position use.
h. Electrode Classification System. The SMAW electrode classification cede
contains an E and three numbers, followed by a dash and either “15” or “16” (EXXX15) . The E designates that the material is an electrode and the three digits indicate composition. Sometimes there are letters following the three digits; these
letters indicate a modification of the standard composition. The “15” or “16”
specifies the type of current with which these electrodes may be used. Both desig–
nations indicate that the electrode is usable in all positions: flat, horizontal,
vertical and overhead.
(1) The “15” indicates that the covering of this electrode is a lime type,
which contains a large proportion of calcium or alkaline earth materials. These
electrodes are usable with dc reverse-polarity only.
(2) The designation “16” indicates electrodes that have a lime- or titaniatype covering with a large proportion of titanium-bearing minerals. The coverings
of these electrodes also contain readily ionizing elements, such as potassium, to
stabilize the arc for ac welding.
10-31
TC 9-237
10-8.
SHIELDED METAL-ARC WELDING (SMAW) (cont)
i . Chemical Requirements. The AWS divides SMAW electrodes into two groups:
mild steel and low-alloy steel. The E60XX and E70XX electrodes are in the mild
steel specification. The chemical requirements for E70XX electrodes are listed in
AWS A5.1 and allow for wide variations of composition of the deposited weld metal.
There are no specified chemical requirements for the E60XX electrodes. The lowalloy specification contains electrode classifications E70XX through E120XX. These
codes have a suffix indicating the chemical requirements of the class of electrodes
(e.g., E7010-Al or E8018-Cl). The composition of low-alloy E70XX electrodes is
controlled much more closely than that of mild steel E70XX electrodes. Low-alloy
electrodes of the low-hydrogen classification (EXX15, EXX16, EXX18) require special
handling to keep the coatings from picking up water. Manufacturers’ recommendations abut storage and rebaking must be followed for these electrodes. AWS A5.5
provides a specific listing of chemical requirements.
Weld Metal Mechanical Properties. The AWS requires the deposited weld metal
to have a minimum tensile strength of 60,000 to 100,000 psi (413,700 to 689,500
kPa), with minimum elongations of 20 to 35 percent.
k.
Arc Shielding.
(1) The arc shielding action, illustrated in figure 10-31, is essentially the
same for the different types of electrodes, but the specific method of shielding
and the volume of slag produced vary from type to type. The bulk of the covering
materials in some electrodes is converted to gas by the heat of the arc, and only a
small amount of slag is produced. This type of electrode depends largely upon a
gaseous shield to prevent atmospheric contamination. Weld metal from such electrodes can be identified by the incomplete or light layer of slag which covers the
bead.
(2) For electrodes at the other extreme, the bulk of the covering is converted to slag by the arc heat, and only a small volume of shielding gas is produced.
The tiny globules of metal transferred across the arc are entirely coated with a
thin film of molten slag. This slag floats to the weld puddle surface because it
is lighter than the metal. It solidifies after the weld metal has solidified.
Welds made with these electrodes are identified by the heavy slag deposits that
completely cover the weld beads. Between these extremes is a wide variety of elec–
trode types, each with a different combination of gas and slag shielding.
10-32
TC 9-237
(3) The variations in the amount of slag and gas shielding also influence the
welding characteristics of the different types of covered electrodes. Electrodes
that have a heavy slag carry high amperage and have high deposition rates. These
electrodes are ideal for making large beads in the flat position. Electrodes that
develop a gaseous arc shield and have a light layer of slag carry lower amperage
and have lower deposition rates. These electrodes produce a smaller weld pool and
are better suited for making welds in the vertical and overhead positions. Because
of the differences in their welding characteristics, one type of covered electrode
will usually be best suited for a given application.
10-9.
GAS TUNGSTEN ARC (TIG) WELDING (GTAW)
a. General. Gas tungsten arc welding (TIG welding or GTAW) is a process in
which the joining of metals is produced by heating therewith an arc between a tungsten (nonconsumable) electrode and the work. A shielding gas is used, normally
argon. TIG welding is normally done with a pure tungsten or tungsten alloy rod,
but multiple electrodes are sometimes used. The heated weld zone, molten metal,
and tungsten electrode are shielded from the atmosphere by a covering of inert gas
fed through the electrode holder. Filler metal may or may not be added. A weld is
made by applying the arc so that the touching workpiece and filler metal are melted
and joined as the weld metal solidifies. This process is similar to other arc
welding processes in that the heat is generated by an arc between a nonconsumable
electrode and the workpiece, but the equipment and electrode type distinguish TIG
from other arc welding processes. See figure 10-32.
10-33
TC 9-237
10-9.
GAS TUNGSTEN ARC (TIG) WELDING (GTAW) (cont)
b. Equipment. The basic features of the equipment used in TIG welding are
shown in figure 10-33. The major components required for TIG welding are:
(1) the welding machine, or power source
(2) the welding electrode holder and the tungsten electrode
(3) the shielding gas supply and controls
(4) Several optional
accessories are available, which include a foot rheostat
.
to control the current while welding, water circulating systems to cool the electrode holders, and arc timers.
NOTE
There are ac and dc power units with built-in high frequency generators
designed specifically for TIG welding. These automatically control gas
and water flow when welding begins and ends. If the electrode holder
(torch) is water-cooled, a supply of cooling water is necessary. Electrode holders are made so that electrodes and gas nozzles can readily be
changed . Mechanized TIG welding equipment may include devices for checking and adjusting the welding torch level, equipment for work handling,
provisions for initiating the arc and controlling gas and water flow,
and filler metal feed mechanisms.
c. Advantages. Gas tungsten arc welding is the most popular method for welding aluminum stainless steels, and nickel-base alloys. It produces top quality
welds in almost all metals and alloys used by industry. The process provides more
precise control of the weld than any other arc welding process, because the arc
10-34
TC 9-237
heat and filler metal are independently controlled. Visibility is excellent because no smoke or fumes are produced during welding, and there is no slag or spatter that must be cleaned between passes or on a completed weld. TIG welding also
has reduced distortion in the weld joint because of the concentrated heat source.
The gas tungsten arc welding process is very good for joining thin base metals
because of excellent control of heat input. As in oxyacetylene welding, the heat
source and the addition of filler metal can be separately controlled. Because the
electrode is nonconsumable, the process can be used to weld by fusion alone without
the addition of filler metal. It can be used on almost all metals, but it is gener–
ally not used for the very low melting metals such as solders, or lead, tin, or
zinc alloys. It is especially useful for joining aluminum and magnesium which
form refractory oxides, and also for the reactive metals like titanium and zirconium, which dissolve oxygen and nitrogen and become embrittled if exposed to air
while melting. In very critical service applications or for very expensive metals
or parts, the materials should be carefully cleaned of surface dirt, grease, and oxides before welding.
d. Disadvantages. TIG welding is expensive because the arc travel speed and
weld metal deposition rates are lower than with some other methods. Some limita–
tions of the gas tungsten arc process are:
(1) The process is slower than consumable electrode arc welding processes.
(2) Transfer of molten tungsten from the electrode to the weld causes contamination. The resulting tungsten inclusion is hard and brittle.
(3) Exposure of the hot filler rod to air using improper welding techniques
causes weld metal contamination.
(4) Inert gases for shielding and tungsten electrode costs add to the total
cost of welding compared to other processes. Argon and helium used for shielding
the arc are relatively expensive.
(S) Equipment costs are greater than that for other processes, such as shielded metal arc welding, which require less precise controls.
For these reasons, the gas tungsten arc welding process is generally not commercially competitive with other processes for welding the heavier gauges of metal if they
can be readily welded by the shielded metal arc, submerged arc, or gas metal arc
welding processes with adequate quality.
e.
Process Principles.
(1) Before welding begins, all oil, grease, paint, rust, dirt, and other
contaminants must be removed from the welded areas. This may
be accomplished by
mechanical means or by the use of vapor or liquid cleaners.
(2) Striking the arc maybe done by any of the following methods :
it.
(a) Touching the electrode to the work momentarily and quickly withdrawing
(b) Using an apparatus that will cause a spark to jump from the electrode
to the work.
10-35
TC 9-237
10-9.
GAS TUNGSTEN ARC (TIG) WELDING (GTAW) (cont)
(c) Using an apparatus that initiates and maintains a small pilot arc,
providing an ionized path for the main arc.
(3) High frequency arc stabilizers are required when alternating current is
used. They provide the type of arc starting described in (2)(b) above. High frequency arc initiation occurs when a high frequency, high voltage signal is superimposed on the welding circuit. High voltage (low current) ionizes the shielding gas
between the electrode and the workpiece, which makes the gas conductive and initiates the arc. Inert gases are not conductive until ionized. For dc welding, the
high frequency voltage is cut off after arc initiation. However, with ac welding,
it usually remains on during welding, especially when welding aluminum.
(4) When welding manually, once the arc is started, the torch is held at a
travel angle of about 15 degrees. For mechanized welding, the electrode holder is
positioned vertically to the surface.
(5) To start manual welding, the arC is moved in a small circle until a pool
of molten metal forms. The establishment and maintenance of a suitable weld pool
is important and welding must not proceed ahead of the puddle. Once adequate fusion is obtained, a weld is made by gradually moving the electrode along the parts
to be welded to melt the adjoining surfaces. Solidification of the molten metal
follows progression of the arc along the joint, and completes the welding cycle.
(6) The welding rod and torch must be moved progressively and smoothly so the
weld pool, hot welding rod end, and hot solidified weld are not exposed to air that
will contaminate the weld metal area or heat-affected zone. A large shielding gas
cover will prevent exposure to air. Shielding gas is normally argon.
(7) The welding rod is held at an angle of about 15 degrees to the work surface and slowly fed into the molten pool. During welding, the hot end of the welding rod must not be removed from the inert gas shield. A second method is to press
the welding rod against the work, in line with the weld, and melt the rod along
with the joint edges. This method is used often in multiple pass welding of Vgroove joints. A third method, used frequently in weld surfacing and in making
large welds, is to feed filler metal continuously into the molten weld pool by
oscillating the welding rod and arc from side to side. The welding rod moves in
one direction while the arc moves in the opposite direction, but the welding rod is
at all times near the arc and feeding into the molten pool. When filler metal is
required in automatic welding, the welding rod (wire) is fed mechanically through a
guide into the molten weld pool.
(8) The selection of welding position is determined by the mobility of the
weldment, the availability of tooling and fixtures, and the welding cost. The
minimum time, and there fore cost, for producing a weld is usually achieved in the
flat position. Maximum joint wet-ration and deposition rate are obtained in this
position, because a large volume of molten metal can be supported. Also, an acceptably shaped reinforcement is easily obtained in this position.
(9) Good penetration can be achieved in the vertical-up position, but the
rate of welding is slower because of the effect of gravity on the molten weld meta l . Penetration in vertical-dam welding is poor. The molten weld metal droopS,
10-36
TC 9-237
and lack of fusion occurs unless high welding speeds are used to deposit thin layers of weld metal. The welding torch is usually pointed forward at an angle of
about 75 degrees from the weld surface in the vertical-up and flat positions. Too
great an angle causes aspiration of air into the shielding gas and consequent oxidation of the molten weld metal.
(10) Joints that may be welded by this process include all the standard types,
such as square-groove and V-groove joints, T-joints, and lap joints. As a rule, it
is not necessary to bevel the edges of base metal that is 1/8 in. (3.2 mm) or less
in thickness. Thicker base metal is usually beveled and filler metal is always
added.
(11) The gas tungsten arc welding process can be used for continuous welds,
intermittent welds, or for spot welds. It can be done manually or automatically by
machine.
(12) The major operating variables summarized briefly are:
(a) Welding current, voltage, and power source characteristics.
(b) Electrode composition, current carrying capacity, and shape.
(c) Shielding gas--welding grade argon, helium, or mixtures of both.
(d) Filler metals that are generally similar to the metal being- joined
and suitable for the intended service.
(13) Welding is stopped by shutting off the current with foot-or-hand-controlled switches that permit the welder to start, adjust. and stop the welding
current. They also allow the welder to control the welding current to obtain good
fusion and penetration. Welding may also be stopped by withdrawing the electrode
from the current quickly, but this can disturb the gas shielding and expose the
tungsten and weld pool to oxidation.
f . Filler Metals. The base metal thickness and joint design determine whether
or not filler metal needs to be added to the joints. When filler metal is added
during manual welding, it is applied by manually feeding the welding rod into the
pool of molten metal ahead of the arc, but to one side of the center line. The
technique for manual TIG welding is shown in figure 10-34.
l0-37
TC 9-237
10-10.
PLASMA ARC WELDING (PAW)
a. General. Plasma arc welding (PAW) is a process in which coalescence, or the
joining of metals, is produced by heating with a constricted arc between an electrode and the workpiece (transfer arc) or the electrode and the constricting nozzle
(nontransfer arc). Shielding is obtained from the hot ionized gas issuing from the
orifice, which may be supplemented by an auxiliary source of shielding gas. Shielding gas may be an inert gas or a mixture of gases. Pressure may or may not be
used, and filler metal may or may not be supplied. The PAW process is shown in
figure 10-35.
b. Equipment.
(1) Power source. A constant current drooping characteristic power source
supplying the dc welding current is recommended; however, ac/dc type power source
can be used. It should have an open circuit voltage of 80 volts and have a duty
cycle of 60 percent. It is desirable for the power source to have a built-in
contactor and provisions for remote control current adjustment. For welding very
thin metals, it should have a minimum amperage of 2 amps. A maximum of 300 is
adequate for most plasma welding applications.
(2) Welding torch. The welding torch for plasma arc welding is similar in
appearance to a gas tungsten arc torch, but more complex.
(a) All plasma torches are water cooled, even the lowest—curr ent range
torch. This is because the arc is contained inside a chamber in the torch where it
generates considerable heat. If water flow is interrupted briefly, the nozzle may
melt. A cross section of a plasma arc torch head is shown by figure 10-36. During the nontransferred period, the arc will be struck between the nozzle or tip
with the orifice and the tungsten electrode. Manual plasma arc torches are made in
various sizes starting with 100 amps through 300 amperes. Automatic torches for
machine operation are also available.
10-38
TC 9-237
(b) The torch utilizes the 2 percent thoriated tungsten electrode similar
to that used for gas tungsten welding. Since the tungsten electrode is located
inside the torch, it is almost impossible to contaminate it with base metal.
(3) Control console. A control console is required for plasma arc welding.
The plasma arc torches are designed to connect to the control console rather than
the power source. The console includes a power source for the pilot arc, delay
timing systems for transferring from the pilot arc to the transferred arc, and
water and gas valves and separate flow meters for the plasma gas and the shielding
gas. The console is usually connected to the power source and may operate the
contactor. It will also contain a high-frequency arc starting unit, a nontransferred pilot arc power supply, torch protection circuit, and an ammeter. The highfrequency generator is used to initiate the pilot arc. Torch protective devices
include water and plasma gas pressure switches which interlock with the contactor.
(4) Wire feeder. A wire feeder may be used for machine or automatic welding
and must be the constant speed type. The wire feeder must have a speed adjustment
covering the range of from 10 in. per minute (254 mm per minute) to 125 in. per
minute (3.18 m per minute) feed speed.
c.
Advantages and Major Uses.
(1) Advantages of plasma arc welding when compared togas tungsten arc welding stem from the fact that PAW has a higher energy concentration. Its higher
temperature, constricted cross-sectional area, and the velocity of the plasma jet
create a higher heat content. The other advantage is based on the stiff columnar
type of arc or form of the plasma, which doesn’t flare like the gas tungsten arc.
These two factors provide the following advantages:
(a) The torch-to-work distance from the plasma arc is less critical than
for gas tungsten arc welding. This is important for manual operation, since it
gives the welder more freedom to observe and control the weld.
TC 9-237
10-10.
PLASMA ARC WELDING (PAW) (cont)
(b) High temperature and high heat concentration of the plasma allow for
the keyhole effect, which provides complete penetration single pass welding of many
joints. In this operation, the heat affected zone and the form of the weld are
more desirable. The heat-affected zone is smaller than with the gas tungsten arc,
and the weld tends to have more parallel sides, which reduces angular distortion.
(c) The higher heat concentration and the plasma jet allow for higher travel speeds. The plasma arc is more stable and is not as easily deflected to the
closest point of base metal. Greater variation in joint alignment is possible with
plasma arc welding. This is important when making root pass welds on pipe and
other one-side weld joints. Plasma welding has deeper penetration capabilities and
produces a narrower weld. This means that the depth-to-width ratio is more advantageous.
(2) Uses.
(a) Some of the major uses of plasma arc are its application for the manufacture of tubing. Higher production rates based on faster travel speeds result
from plasma over gas tungsten arc welding. Tubing made of stainless steel, titanium, and other metals is being produced with the plasma process at higher production
rates than previously with gas tungsten arc welding.
(b) Most applications of plasma arc welding are in the low—current range.
from 100 amperes or less. The plasma can be operated at extremely low currents to
allow the welding of foil thickness material.
(c) Plasma arc welding is also used for making small welds on weldments for
i n s t r u m e n t manufacturing and other small components made of thin metal. It is used
for making butt joints of wall tubing.
This process is also used to do work similar to electron beam welding,
but with a much lower equiment cost.
(3) Plasma arc welding is nornally applied as a manual welding process, but
is also used in automatic and machine applications. Manual application is the most
popular. Semiautomatic methods of application are not useful. The normal methods
of applying plasma arc welding are manual (MA), machine (ME), and automatic (AU).
(4) The plasma arc welding process is an all-position welding process.
Table 10-2 shows the welding position capabilities.
10-40
TC 9-237
(5) The plasma
ly available metals.
cess for welding some
that the gas tungsten
arc welding process is able to join practicallv all commercialIt may not be the best selection or the most economical prometals. The plasma arc welding process will join all metals
arc process will weld. This is illustrated in table 10-3.
(6) Regarding thickness ranges welded by the plasma process, the keyhole mode
of operation can be used only where the plasma jet can penetrate the joint. In
this mode, it can be used for welding material from 1/16 in. (1.6 mm through 1/4
in. (12.0 mm). Thickness ranges vary with different metals. The melt-in mode is
used to weld material as thin as 0.002 in. (0.050 mm) up through 1/8 in. (3.2 mm).
Using multipass techniques, unlimited thicknesses of metal can be welded. Note
that filler rod is used for making welds in thicker material. Refer to table 10-4
for base metal thickness ranges.
10-41
TC 9-237
d. Limitations of the Process. The major limitations of the process have to
do more with the equipment and apparatus. The torch is more delicate and complex
than a gas tungsten arc torch. Even the lowest rated torches must be water
cooled. The tip of the tungsten and the alignment of the orifice in the nozzle is
extremely important and must be maintained within very close limits. The current
level of the torch cannot be exceeded without damaging the tip. The water-cooling
passages in the torch are relatively small and for this reason water filters and
deionized water are recommended for the lower current or smaller torches. The
control console adds another piece of equipment to the system. This extra equipment makes the system more expensive and may require a higher level of maintenance.
e.
Principles of Operation.
(1) The plasma arc welding process is normally compared
arc process. If an electric arc between a tungsten electrode
stricted in a cross-sectional area, its temperature increases
the same amount of current. This constricted arc is called a
state of matter.
to the gas tungsten
and the work is conbecause it carries
plasma, or the fourth
(2) Two modes of operation are the non-transferred arc and the transferred
arc.
(a) In the non-transferred mode, the current flow is from the electrode
inside the torch to the nozzle containing the orifice and back to the power supply. It is used for plasma spraying or generating heat in nonmetals.
(b) In transferred arc mode, the current is transferred from the tungsten
electrode inside the welding torch through the orifice to the workpiece and back to
the power supply.
(c) The difference between these two modes of operation is shown by figure
10-37. The transferred arc mode is used for welding metals. The gas tungsten arc
process is shown for comparison.
10-43
TC 9-237
10-10.
PLASMA ARC WELDING (PAW) (cont)
(3) The plasma is generated by constricting the electric arc passing through
the orifice of the nozzle. Hot ionized gases are also forced through this opening. The plasma has a stiff columnar form and is parallel sided so that it does
not flare out in the same manner as the gas tungsten arc. This high temperature
arc, when directed toward the work, will melt the base metal surface and the filler
metal that is added to make the weld. In this way, the plasma acts as an extremely
high temperature heat source to form a molten weld puddle. This is similar to the
gas tungsten arc. The higher-temperature plasma, however, causes this to happen
faster, and is known as the melt-in mode of operation.
Figure 10-36, p 10-39,
shows a cross-sectional view of the plasma arc torch head.
(4) The high temperature of the plasma or constricted arc and the high velocity plasma jet provide an increased heat transfer rate over gas tungsten arc welding
when using the same current. This results in faster welding speeds and deeper weld
penetration. This method of operation is used for welding extremely thin material.
and for welding multipass groove and welds and fillet welds.
(5) Another method of welding with plasma is the keyhole method of welding.
The plasma jet penetrates through the workpiece and forms a hole, or keyhole.
Surface tension forces the molten base metal to flow around the keyhole to form the
weld. The keyhole method can be used only for joints where the plasma can pass
through the joint. It is used for base metals 1/16 to 1/2 in. (1.6 to 12.0 mm) in
thickness. It is affected by the base metal composition and the welding gases.
The keyhole method provides for full penetration single pass welding which may be
applied either manually or automatically in all positions.
(6) Joint design.
(a) Joint design is based on the metal thicknesses and determined by the
two methods of operation. For the keyhole method, the joint design is restricted
to full-penetration types. The preferred joint design is the square groove, with
no minimum root opening. For root pass work, particularly on heavy wall pipe, the
U groove design is used. The root face should be 1/8 in. (3.2 mm) to allow for
full keyhole penetration.
(b) For the melt-in method of operation for welding thin gauge, 0.020 in.
(0.500 mm) to 0.100 in. (2.500 mm) metals, the square groove weld should be utilized. For welding foil thickness, 0.005 in. (0.130 mm) to 0.020 in. (0.0500 mm),
the edge flange joint should be used. The flanges are melted to provide filler
metal for making the weld.
(c) When using the melt-in mode of operation for thick materials, the same
general joint detail as used for shielded metal arc welding and gas tungsten arc
welding can be employed. It can be used for fillets, flange welds, all types of
groove welds, etc., and for lap joints using arc spot welds and arc seam welds.
Figure 10-38 shows various joint designs that can be welded by the plasma arc process.
(7) Welding circuit and current. The welding circuit for plasma arc welding
is more complex than for gas tungsten arc welding. An extra component is required
as the control circuit to aid in starting and stopping the plasma arc. The same
power source is used. There are two gas systems, one to supply the plasma gas and
the second for the shielding gas. The welding circuit for plasma arc welding is
shown by figure 10-39. Direct current of a constant current (CC) type is used.
Alternating current is used for only a few applications.
10-44
TC 9-237
10-10. PLASMA ARC WELDING (PAW) (cont)
(8) Tips for Using the Process.
(a) The tungsten electrode must be precisely centered and located with
respect to the orifice in the nozzle. The pilot arc current must be kept sufficiently low, just high enough to maintain a stable pilot arc. When welding extreme–
ly thin materials in the foil range, the pilot arc may be all that is necessary.
(b) When filler metal is used, it is added in the same manner as gas tungsten arc welding. However, with the torch–to-work distance a little greater there
is more freedom for adding filler metal. Equipment must be properly adjusting so
that the shielding gas and plasma gas are in the right proportions. Proper gases
must also be used.
fect.
e.
(c) Heat input is imprtant. Plasma gas flow also has an important efThese factors are shown by figure 10-40.
Filler Metal and Other Equipment.
(1) Filler metal is normally used except when welding the thinnest metals.
Composition of the filler metal should match the base metal. The filler metal rod
size depends on the base metal thickness and welding current. The filler metal is
usually added to the puddle manually, but can be added automatically.
(2) Plasma and shielding gas. An inert gas, either argon, helium, or a mixture, is used for shielding the arc area from the atmosphere. Argon is more common
because it is heavier and provides better shielding at lower flow rates. For flat
and vertical welding, a shielding gas flow of 15 to 30 cu ft per hour (7 to 14
liters per minute) is sufficient. Overhead position welding requires a slightly
higher flow rate. Argon is used for plasma gas at the flew rate of 1 cu ft per
hour (0.5 liters per minute) up to 5 cu ft per hour (2.4 liters per minute) for
welding, depending on torch size and application. Active gases are not reccommended
for plasma gas. In addition, cooling water is required.
f.
Quality, Deposition Rates, and Variables.
(1) The quality of the plasma arc welds is extremely high and usually higher
than gas tungsten arc welds because there is little or no possibility of tungsten
inclusions in the weld. Deposition rates for plasma arc welding are somewhat higher than for gas tungsten arc welding and are shown by the curve in figure 10-41.
Weld schedules for the plasma arc process are shown by the data in table 10-5.
(2) The process variables for plasma arc welding are shown by figure 10-41.
Most of the variables shown for plasma arc are similar to the other arc welding
processes. There are two exceptions: the plasma gas flow and the orifice diameter
in the nozzle. The major variables exert considerable control in the process. The
minor variables are generally fixed at optimum conditions for the given application. All variables should appear in the welding procedure. Variables such as the
angle and setback of the electrode and electrode type are considered fixed for the
application. The plasma arc process does respond differently to these variables
than does the gas tungsten arc process. The standoff, or torch-to-work distance,
is less sensitive with plasma but the torch angle when welding parts of unequal
thicknesses is more important than with gas tungsten arc.
10-46
TC 9-237
g.
Variations of the Process.
(1) The welding current may be pulsed to gain the same advantages pulsing
provides for gas tungsten arc welding. A high current pulse is used for maximum
penetration but is not on full time to allow for metal solidification. This gives
a more easily controlled puddle for out-of-position work. Pulsing can be accomplished by the same apparatus as is used for gas tungsten arc welding.
(2) Programmed welding can also be employed for plasma arc welding in the
same manner as it is used for gas tungsten arc welding. The same power source with
programming abilities is used and offers advantages for certain types of work. The
complexity of the programming depends on the needs of the specific application. In
addition to programming the welding current, it is often necessary to program the
plasma gas flow. This is particularly important when closing a keyhole which is
required to make the root pass of a weld joining two pieces of pipe.
(3) The method of feeding the filler wire with plasma is essentially the same
as for gas tungsten arc welding. The “hot wire” concept can be used. This means
that low-voltage current is applied to the filler wire to preheat it prior to going
into the weld puddle.
10-47
TC 9-237
10-11. CARBON ARC WELDING (CAW)
a. G e n e r a l . Carbon arc welding is a process in which the joining of metals
is produced by heating with an arc between a carbon electrode and the work. No
shielding is used. Pressure and/or filler metal may or may not be used.
b. Equipment.
(1) Electrodes. Carbon electrodes range in size from 1/8 to 7/8 in. (3.2
to 22.2 mm) in diameter. Baked carbon electrodes last longer than graphite electrodes. Figure 10-42 shows typical air-cooled carbon electrode holders. Watercooled holders are available for use with the larger size electrodes, or adapters
can be fitted to regular holders to permit accommodation of the larger electrodes.
(2) Machines. Direct current welding machines of either the rotating or
rectifier type are power sources for the carbon arc welding process.
(3) Welding circuit and welding current.
(a) The welding circuit for carbon arc welding is the same as for shielded
metal arc welding. The difference in the apparatus is a special type of electrode
holder used only for holding carbon electrodes. This type of holder is used because the carbon electrodes become extremely hot in use, and the conventional electrode holder will not efficiently hold and transmit current to the carbon electrode. The power source is the conventional or constant current type with drooping
volt-amp characteristics. Normally, a 60 percent duty cycle power source is utilized. The power source should have a voltage rating of 50 volts, since this voltage is used when welding copper with the carbon arc.
(b) Single electrode carbon arc welding is always used with direct current
electrode negative (DCEN), or straight polarity. In the carbon steel arc, the
positive pole (anode) is the pole of maximum heat. If the electrode were positive,
the carbon electrode would erode very rapidly because of the higher heat, and would
cause black carbon smoke and excess carbon, which could be absorbed by the weld
metal. Alternating current is not recommended for single-electrcde carbon arc
welding. The electrode should be adjusted often to compensate for the erosion of
carbon. From 3.0 to 5.0 in. (76.2 to 127.0 mm) of the carbon electrode should
protrude through the holder towards the arc.
10-48
TC 9-237
c.
Advantages and Major Uses.
(1) The single electrode carbon arc welding process is no longer widely
used . It is used for welding copper, since it can be used at high currents to
develop the high heat usually required. It is also used for making bronze repairs
on cast iron parts. When welding thinner materials, the process is used for making
autogenous welds, or welds without added filler metal. Carbon arc welding is also
used for joining galvanized steel. In this case, the bronze filler rod is added by
placing it between the arc and the base metal.
(2) The carbon arc welding process has been used almost entirely by the manual method of applying. It is an all-position welding process. Carbon arc welding
is primarily used as a heat source to generate the weld puddle which can be carried
in any position. Table 10-6 shows the normal method of applying carbon-arc welding. Table 10-7 shows the welding position capabilities.
d. Weldable Metals. Since the carbon arc is used primarily as a heat source
to generate a welding puddle, it can be used on metals that are not affected by
carbon pickup or by the carbon monoxide or carbon dioxide arc atmosphere. It can
be used for welding steels and nonferrous metals, and for surfacing.
10-49
TC 9-237
10-11.
CARBON ARC WELDING (CAW) (cont)
(1) S t e e l s . The main use of carbon arc welding of steel is making edge
welds without the addition of filler metal. This is done mainly in thin gauge
sheet metal work, such as tanks, where the edges of the work are fitted closely
together and fused using an appropriate flux. Galvanized steel can be braze welded
with the carbon arc. A bronze welding rod is used. The arc is directed on the rod
so that the galvanizing is not burned off the steel sheet. The arc should be started on the welding rod or a starting block Low current, a short arc length, and.
rapid travel speed should be used. The welding rod should melt and wet the galvanized steel.
(2) Cast iron. Iron castings may be welded with the carbon arc and a cast
iron welding rod. The casting should be preheated to about 1200 °F (649 °C)
and slowly cooled if a machinable weld is desired.
(3) Copper. Straight polarity should always be used for carbon arc welding
of copper. Reverse polarity will produce carbon deposits on the work that inhibit
fusion. The work should be preheated in the range of 300 to 1200 °F (149 to 649
°C) depending upon the thickness of the parts. If this is impractical, the arc
should be used to locally preheat the weld area. The high thermal conductivity of
copper causes heat to be conducted away from the point of welding so rapidly that
it is difficult to maintain welding heat without preheating. A root opening of 1/8
in. (3.2 mm) is recommended. Best results are obtained at high travel speeds with
the arc length directed on the welding rod. A long arc length should be used to
permit carbon from the electrode to combine with oxygen to form carbon dioxide,
which will provide some shielding of weld metal.
e.
Principles of Operation.
(1) Carbon arc welding, as shown in figure 10-43, uses a single electrode
with the arc between it and the base metal. It is the oldest arc process, and is
not popular today.
(2) In carbon arc welding, the arc heat between the carbon electrode and the
work melts the base metal and, when required, also melts the filler rod. As the
molten metal solidifies, a weld is produced. The nonconsumable graphite electrode
erodes rapidly and, in disintegrating, produces a shielding atmosphere of carbon
monoxide and carbon dioxide gas. These gases partially displace air from the arc
10-50
TC 9-237
atmosphere and prohibit the oxygen and nitrogen from coming in contact with molten
metal. Filler metal, when used, is of the same composition as the base metal.
Bronze filler metal can be used for brazing and braze welding.
(3) The workpieces must be free from grease, oil, scale, paint, and other
foreign matter. The two pieces should be clamped tightly together with no root
opening. They may be tack welded together.
(4) Carbon electrodes 1/8 to 5/16 in. (3.2 to 7.9 mm) in diameter may be
used, depending upon the current required for welding. The end of the electrode
should be prepared with a long taper to a point. The diameter of the point should
be about half that of the electrode. For steel, the electrode should protrude
about 4.0 to 5.0 in. (101.6 to 127.0 mm) from the electrode holder.
(5) A carbon arc may be struck by bringing the tip of the electrode into
contact with the work and immediately withdrawing it to the correct length for
welding. In general, an arc length between 1/4 and 3/8 in. (6.4 and 9.5 mm) is
best. If the arc length is too short, there is likely to be excessive carburization of the molten metal resulting in a brittle weld.
(6) When the arc is broken for any reason, it should not be restarted directly upon the hot weld metal. This could cause a hard spot in the weld at the point
of contact. The arc should be started on cold metal to one side of the joint, and
then quickly returned to the point where welding is to be resumed.
(7) When the joint requires filler metal, the welding rod is fed into the
molten weld pool with one hand while the arc is manipulated with the other. The
arc is directed on the surface of the work and gradually moved along the joint,
constantly maintaining a molten pool into which the welding rod is added in the
same manner as in gas tungsten arc welding. Progress along the weld joint and the
addition of a welding rod must be tired to provide the size and shape of weld bead
desired. Welding vertically or overhead with the carbon arc is difficult because
carbon arc welding is essentially a puddling process. The weld joint should be
backed up, especially in the case of thin sheets, to support the molten weld pools
and prevent excessive melt-thru.
(8) For outside corner welds in 14 to 18 gauge steel sheet, the carbon arc
can be used to weld the two sheets together without a filler metal. Such welds are
usually smother and more economical to make than shielded metal arc welds made
under similar conditions.
f . Welding schedules. The welding schedule for carbon arc welding galvanized
iron using silicon bronze filler metal is given in table 10-8. A short arc should
be used to avoid damaging the galvanizing. The arc must be directed on the filler
wire which will melt and flow on to the joint. For welding copper, use a high arc
voltage and follow the schedule given in table 10-9. Table 10-10 shows the welding
current to be used for each size of the two types of carbon electrodes.
10-51
TC 9-237
g.
Variations of the Process.
(1) There are two important variations of carbon arc welding. One is twin
carbon arc welding. The other is carbon arc cutting and gouging.
(2) Twin carbon arc welding is an arc welding process in which the joining of
metals is produced, using a special electrode holder, by heating with an electric
arc maintained between two carbon electrodes. Filler metal may or may not he
used. The process can also be used for brazing.
(a) The twin carbon electrode holder is designed so that one electrode is
movable and can be touched against the other to initiate the arc. The carbon electrodes are held in the holder by means of set screws and are adjusted so they protrude equally from the clamping jaws. When the two carbon electrodes are brought
together, the arc is struck and established between them. The angle of the electrodes provides an arc that forms in front of the apex angle and fans out as a soft
source of concentrated heat or arc flame. It is softer than that of the single
carbon arc. The temperature of this arc flame is between 8000 and 9000 °F (4427
and 4982 °C).
(b) Alternating current is used for the twin carbon welding arc. With
alternating current, the electrodes will burn off or disintegrate at equal rates.
Direct current power can be used, but when it is, the electrode connected to the
positive terminal should be one size larger than the electrode connected to the
negative terminal to ensure even disintegration of the carbon electrodes. The arc
gap or spacing between the two electrodes most be adjusted more or less continuously to provide the fan shape arc.
10-53
TC 9-237
CARBON ARC WELDING (CAW) (cont)
(c) The twin carbon arc can be used for many applications in addition to
welding, brazing, and soldering. It can be used as a heat source to bend or form
metal. The welding current settings or schedules for different size of electrodes
is shown in table 10-11.
10-11.
The twin carbon electrode method is relatively slow and does not have much use as
an industrial welding process.
(3) Carbon arc cutting is an arc cutting process in which metals are severed
by melting them with the heat of an arc between a carbon electrode and the base
metal. The process depends upon the heat input of the carbon arc to melt the meta l . Gravity causes the molten metal to fall away to produce the cut. The process
is relatively slow, results in a ragged cut, and is used only when other cutting
equipment is not available.
10-12.
a.
GAS METAL-ARC WELDING (GMAW OR MIG WELDING)
General.
(1) Gas metal arc welding ( GMAW or MIG welding) is an electric arc welding
process which joins metals by heating them with an arc established beween a continuous filler metal (consumable) electrode and the work. Shielding of the arc and
molten weld pool is obtained entirely from an externally supplied gas or gas mixture, as shown in figure 10-44. The process is sometimes referred to as MIG or CO 2
welding. Recent developments in the process include operation at low current densities and pulsed direct current, application to a broader range of materials, and
the use of reactive gases, particularly CO2, or gas mixtures.
This latter development has led to the formal acceptance of the term gas metal arc welding (GMAW) for
the process because both inert and reactive gases are used. The term MIG welding
is still more commonly used.
(2) MIG welding is operated in semiautomatic, machine, and automatic modes.
It is utilized particularly in high production welding operations. All commercially important metals such as carbon steel, stainless steel, aluminum, and copper can
be welded with this process in all positions by choosing the appropriate shielding
gas, electrode, and welding conditions.
10-54
TC 9-237
b. Equipment.
(1) Gas metal arc welding equipment consists of a welding gun, a power supply, a shielding gas supply, and a wire-drive system which pulls the wire electrode
from a spool and pushes it through a welding gun. A source of cooling water may be
required for the welding gun. In passing through the gun, the wire becomes energized by contact with a copper contact tube, which transfers current from a power
source to the arc. While simple in principle, a system of accurate controls is
employed to initiate and terminate the shielding gas and cooling water, operate the
welding contactor, and control electrode feed speed as required. The basic features of MIG welding equipment are shown in figure 10-45. The MIG process is used
for semiautomatic, machine, and automatic welding. Semiautomatic MIG welding is
often referred to as manual welding.
10-55
TC 9-237
10-12.
GAS METAL-ARC WELDING (GMAW OR MIG WELDING) (cont)
(2) Two types of power sources are used for MIG welding: constant current
and constant voltage.
Constant current power supp ly . With this type, the welding current is
(a)
established by the appropriate setting on the power supply. Arc length (voltage)
is ax-trolled by the automatic adjustment of the electrode feed rate. This type of
welding is best suited to large diameter electrodes and machine or automatic welding, where very rapid change of electrode feed rate is not required. Most constant
current power sources have a drooping volt-ampere output characteristic. However,
true constant current machines are available. Constant current power sources are
not normally selected for MIG welding because of the control needed for electrode
feed speed. The systems are not self-regulating.
(b) Constant voltage power supply. The arc voltage is established by setting the output voltage on the power supply. The power source will supply the
necessary amperage to melt the welding electrode at the rate required to maintain
the present voltage or relative arc length. The speed of the electrode drive is
used to control the average welding current. This characteristic is generally
preferred for the welding of all metals. The use of this type of power supply in
conjunction with a constant wire electrode feed results in a self–correcting arc
length system.
(3) Motor generator or dc rectifier power sources of either type may be
used. With a pulsed direct current power supply, the power source pulses the dc
output from a loW background value to a high peak value. Because the average power
is lower, pulsed welding current can be used to weld thinner sections than those
that are practical with steady dc spray transfer.
(4) Welding guns. Welding guns for MIG welding are available for manual
manipulation (semiautomatic welding) and for machine or automatic welding. Because
the electrode is fed continuously, a welding gun must have a sliding electrical
contact to transmit the welding current to the electrode. The gun must also have a
gas passage and a nozzle to direct the shielding gas around the arc and the molten
weld pool. Cooling is required to remove the heat generated within the gun and
radiated from the welding arc and the molten weld metal. Shielding gas, internal
circulating water, or both, are used for cooling. An electrical switch is needed
to start and stop the welding current, the electrode feed system, and shielding gas
f low.
(a) Semiautomatic guns. Semiautomatic, hand-held guns are usually similar
to a pistol in shape. Sometimes they are shaped similar to an oxyacetylene torch,
with electrode wire fed through the barrel or handle. In some versions of the
pistol design, where the most cooling is necessary, water is directed through passages in the gun to cool both the contact tube and the metal shielding gas nozzle.
The curved gun uses a curved current-carrying body at the front end, through which
the shielding gas is brought to the nozzle. This type of gun is designed for small
diameter wires and is flexible and maneuverable. It is suited for welding in
tight, hard to reach corners and other confined places. Guns are equipped with
metal nozzles of various internal diameters to ensure adequate gas shielding. The
orifice usually varies from approximately 3/8 to 7/8 in. (10 to 22 mm), depending
upon welding requirements. The nozzles are usually threaded to make replacement
10-56
TC 9-237
easier. The conventional pistol type holder is also used for arc spot welding
applications where filler metal is required. The heavy nozzle of the holder is
slotted to exhaust the gases away from the spot. The pistol grip handle pen-nits
easy manual loading of the holder against the work. The welding control is designed to reguate the flow of cooling water and the supply of shielding gas. It
is also designed to prevent the wire freezing freezing to the weld by timing the weld
over a preset interval. A typical semiautomatic gas-cooled gun is shown in figure
10-46.
(b) Air cooled guns. Air-cooled guns are available for applications where
water is not readily obtainable as a cooling medium. These guns are available for
service up to 600 amperes, intermittent duty, with carbon dioxide shielding gas.
However, they are usually limited to 200 amperes with argon or heliun shielding.
The holder is generally pistol-like and its operation is similar to the watercooled type. Three general types of air-cooled guns are available.
1. A gun that has the electrode wire fed to it through a flexible conduit from a remote wire feeding mechanism. The conduit is generally in the 12 ft
(3.7 m) length range due to the wire feeding limitations of a push-type system.
Steel wires of 7/20 to 15/16 in. (8.9 to 23.8 mm) diameter and aluminum wires of
3/64 to 1/8 in. (1.19 to 3.18 mm) diameter can be fed with this arrangement.
2. A gun that has a self-contained wire feed mechanism and electrode
wire supply. The wire supply is generally in the form of a 4 in. (102 mm) diamter, 1 to 2-1/2 lb (0.45 to 1.1 kg) spool. This type of gun employs a pull-type
wire feed system, and it is not limited by a 12 ft (3.7 m) flexible conduit. Wire
diameters of 3/10 to 15/32 in. (7.6 to 11.9 mm) are normally used with this type of
gun.
3. A pull-type gun that has the electrode wire fed to it through a flexible conduit from a remote spool. This incorporates a self-contained wire feeding
mechanism. It can also be used in a push-pull type feeding system. The system
permits the use of flexible conduits in lengths up to 50 ft (15 m) or more from the
remote wire feeder. Aluminum and steel electrodes with diameters of 3/10 to 5/8
in. (7.6 to 15.9 mm) can be used with these types of feed mechanisms.
10-57
TC 9-237
10-12.
GAS METAL-ARC WELDING (GMAW OR MTG WELDING) (cont)
(c) Water-cooled guns for manual MIG welding similar to gas-cooled types
with the addition of water cooling ducts. The ducts circulate water around the
contact tube and the gas nozzle. Water cooling permits the gun to operate continuously at rated capacity and at lower temperatures. Water-coded guns are used for
applications requiring 200 to 750 amperes. The water in and out lines to the gun
add weight and reduce maneuverability of the gun for welding.
(d) The selection of air- or water-cooled guns is based on the type of
shielding gas, welding current range, materials, weld joint design, and existing
shop practice. Air-cooled guns are heavier than water-cooled guns of the same
welding current capacity. However, air-cooled guns are easier to manipulate to
weld out-of-position and in confined areas.
c.
Advantages.
(1) The major advantage of gas metal-arc welding is thathigh quality welds
can be produced much faster than with SMAW or TIG welding.
(2) Since a flux is not used, there is no chance for the entrapment of slag
in the weld metal.
(3) The gas shield protects the arc so that there is very little loss of
alloying elements as the metal transfers across the arc. Only minor weld spatter
is produced, and it is easily removed.
(4) This process is versatile and can be used with a wide variety of metals
and alloys, including aluminum, copper, magnesium, nickel, and many of their alloys, as well as iron and most of its alloys. The process can be operated in several ways, including semi- and fully automatic. MIG welding is widely used by many
industries for welding a broad variety of materials, parts, and structures.
d.
Disadvantages.
(1) The major disadvantage of this process is that it cannot be used in the
vertical or overhead welding positions due to the high heat input and the fluidity
of the weld puddle.
(2) The equipment is complex compared to equipment used for the shielded
metal–arc welding process.
e.
Process Principles.
(1) Arc power and polarity.
The vast majority of MIG welding applications require the use of di(a)
rect current reverse polarity (electrode positive). This type of electrical connection yields a stable arc, smooth metal transfer, relatively low spatter loss, and
good weld bead characteristics for the entire range of welding currents used.
Direct current straight polarity (electrode negative) is seldom used, since the arc
can become unstable and erratic even though the electrode melting rate is higher
10-58
TC 9-237
than that achieved with dcrp (electrode positive). When emloyed, dcsp (electrode
negative) is used in conjunction with a “buried” arc or short circuiting metal
transfer. Penetration is lower with straight polarity than with reverse polarity
direct current.
(b)
Alternating current has found no commercial acceptance with the MIG
welding process for two reasons: the arc is extinguished during each half cycle as
the current reduces to zero, and it may not reignite if the cathode cools sufficiently; and rectification of the reverse polarity cycle promotes the erratic arc
operation.
(2) Metal transfer.
(a) Filler metal can be transferred from the electrode to the work in two
ways: when the electrode contacts the molten weld pool, thereby establishing a
short circuit, which is known as short circuiting transfer (short circuiting arc
welding); and when discrete drops are moved across the arc gap under the influence
of gravity or electromagnetic forces. Drop transfer can be either globular or
spray type.
(b) Shape, size, direction of drops (axial or nonaxial), and type of transfer are determined by a number of factors. The factors having the most influence
are:
1. Magnitude and type of welding current.
2 . Current density.
3.
Electrode composition.
4 . E l e c t r o d e extension.
5.
Shielding gas.
6.
Power supply characteristics.
(c) Axially directed transfer refers to the movement of drops along a line
that is a continuation of the longitudinal axis of the electrode. Nonaxially directed transfer refers to movement in any other direction.
(3) Short circuiting transfer.
(a) Short circuiting arc welding uses the lowest range of welding currents
and electrode diameters associated with MIG welding. This type of transfer produces a small, fast-freezing weld pool that is generally suited for the joining of
thin sections, out-of-position welding, and filling of large root openings. When
weld heat input is extremely lo W , plate distortion is small. Metal is transferred
from the electrode to the work only during a period when the electrode is in contact with the weld pool. There is no metal transfer across the arc gap.
10-59
TC 9-237
10-12.
GAS METAL-ARC WELDING (GMAW OR MIG WELDING) (cont)
(b) The electrode contacts the molten weld pool at a steady rate in a range
of 20 to over 200 times each second. As the wire touches the weld metal, the current increases. It would continue to increase if an arc did not form. The rate of
current increase must be high enough to maintain a molten electrode tip until filler metal is transferred. It should not occur so fast that it causes spatter by
disintegration of the transferring drop of filler metal. The rate of current increase is controlled by adjustment of the inductance in the power source. The
value of inductance required depends on both the electrical resistance of the welding circuit and the temperature range of electrode melting. The open circuit voltage of the power source must be low enough so that an arc cannot continue under the
existing welding conditions. A portion of the energy for arc maintenance is provided by the inductive storage of energy during the period of short circuiting.
(c) AS metal transfer only occurs during short circuiting, shielding gas
has very little effect on this type of transfer. Spatter can occur. It is usually
caused either by gas evolution or electromagnetic forces on the molten tip of the
electrode.
(4) Globular transfer.
(a) With a positive electrode (dcrp), globular transfer takes place when
the current density is relatively low, regardless of the type of shielding gas.
However, carbon dioxide (CO 2 ) shielding yields this type of transfer at all usable
welding currents. Globular transfer is characterized by a drop size of greater
diameter than that of the electrode.
(b) Globular, axially directed transfer can be achieved in a substantially
inert gas shield without spatter. The arc length must be long enough to assure
detachment of the drop before it contacts the molten metal. However, the resulting
weld is likely to be unacceptable because of lack of fusion, insufficient penetration, and excessive reinforcement.
(c) Carbon dioxide shielding always yields nonaxially directed globular
transfer. This is due to an electromagnetic repulsive force acting upon the bottom
of the molten drops. Flow of electric current through the electrode generates
several forces that act on the molten tip. The most important of these are pinch
force and anode react ion force. The magnitude of the pinch force is a direct function of welding current and wire diameter, and is usually responsible for drop
detachment. With CO 2 shielding, the wire electrode is melted by the arc heat conducted through the molten drop. The electrode tip is not enveloped by the arc
plasma. The molten drop grows until it detaches by short circuiting or gravity.
(5) Spray transfer.
(a) In a gas shield of at least 80 percent argon or helium, filler metal
transfer changes from globular to spray type as welding current increases for a
given size electrode. For all metals, the change takes place at a current value
called the globular-to-spray transition current.
10-60
TC 9-237
(b) Spray type transfer has a typical fine arc column and pointed wire tip
associated with it. Molten filler metal transfers across the arc as fine dropl e t s . The droplet diameter is equal to or less than the electrode diameter. The
metal spray is axially directed. The reduction in droplet size is also accompanied
by an increase in the rate of droplet detachment, as illustrated in figure 10-47.
Metal transfer rate may range from less than 100 to several hundred droplets per
second as the electrode feed rate increases from approximately 100 to 800 in./min
(42 to 339 mm/s).
(6) Free flight transfer.
(a) In free-flight transfer, the liquid drops that form at the tip of the
consumable electrode are detached and travel freely across the space between the
electrode and work piece before plunging into the weld pool. When the transfer is
gravitational, the drops are detached by gravity alone and fall slowly through the
arc column. In the projected type of transfer, other forces give the drop an initial acceleration and project it independently of gravity toward the weld pool.
During repelled transfer, forces act on the liquid drop and give it an initial
velocity directly away from the weld pool. The gravitational and projected ties
of free-flight metal transfer may occur in the gas metal-arc welding of steel,
nickel alloys, or aluminum alloys using a direct current, electrode-positive (reverse polarity) arc and properly selected types of shielding gases.
10-61
TC 9-237
10-12.
GAS METAL-ARC WELDING (GMAW OR MIG WELDING) (cont)
(b) At low currents, wires of these alloys melt slowly. A large spherical
drop forms at the tip and is detached when the force due to gravity exceeds that of
surface tension. As the current increases, the electromagnetic force becomes significant and the total. separating force increases. The rate at which drops are
formed and detached also increases. At a certain current, a change occurs in the
character of the arc and metal transfer. The arc column, previously bell-shaped or
spherical and having relatively low brightness, becomes narrower and more conical
and has a bright central core. The droplets that form at the wire tip become elongated due to magnetic pressure and are detached at a much higher rate. When carbon
dioxide is used as the shielding gas, the type of metal transfer is much different. At low and medium reversed-polarity currents, the drop appears to be repelled
from the work electrode and is eventually detached while moving away from the workpiece and weld pool. This causes an excessive amount of spatter. At higher currents, the transfer is less irregular because other forces, primarily electrical,
overcame the repelling forces. Direct current reversed-polarity is recommended for
the MIG welding process. Straight polarity and alternating current can be used,
but require precautions such as a special coating on the electrode wire or special
shield gas mixtures.
(c) The filler wire passes through a copper contact tube in the gun, where
it picks up the welding current. Some manual welding guns contain the wire-driving
mechanism within the gun itself. Other guns require that the wire-feeding mechanism be located at the spool of wire, which is some distance from the gun. In this
case, the wire is driven through a flexible conduit to the welding gun. Another
manual gun design combines feed mechanisms within the gun and at the wire supply
i t s e l f . Argon is the shielding gas used most often. Small amounts of oxygen (2 to
5 percent) frequently are added to the shielding gas when steel is welded. This
stabilizes the arc and promotes a better wetting action, producing a more uniform
weld bead and reducing undercut. Carbon dioxide is also used as a shielding gas
because it is cheaper than argon and argon-oxygen mixtures. Electrodes designed to
be used with carbon dioxide shielding gas require extra deoxidizers in their formulation because in the heat of the arc, the carbon dioxide dissociates to carbon
monoxide and oxygen, which can cause oxidation of the weld metal.
(7) Welding parameters. Figures 10-48 through 10-54 show the relationship
between the voltage and the current levels , and the type of transfer across the
arcs.
10-62
TC 9-237
10-12. GAS METAL-ARC WELDING (GMAW OR MIG WELDING) (cont)
f. Welding Procedures.
(1) The welding procedures for MIG welding are similar to those for other arc
welding processes. Adequate fixturing and clamping of the work are required with
adequate accessibility for the welding gun. Fixturing must hold the work rigid to
minimize distortion from welding. It should be designed for easy loading and unloading. Good connection of the work lead (ground) to the workpiece or fixturing
is required. Location of the connectio is important, particularly when welding
ferromagnetic materials such as steel. The best direction of welding is away from
the work lead connection. The position of the electrode with respect to the weld
joint is important in order to obtain the desired joint penetration, fusion, and
weld bead geometry. Electrode positions for automatic MIG welding are similar to
those used with submerged arc welding.
(2) When complete joint penetration is required, somemethod of weld backing
will help to control it. A backing strip, backing weld, or copper backing bar can
be used. Backing strips and backing welds usually are left in place. Copper backing bars are removable.
(3) The assembly of the welding equipnent should be done according to the
manufacturer’s directions. All gas and water connections should be tight; there
should be no leaks. Aspiration of water or air into the shielding gas will result
in erractic arc operation and contamination of the weld. Porosity may also occur.
10-66
TC 9-237
(4) The gun nozzle size and the shielding gas flow rate should be set according to the recommended welding procedure for the material and joint design to be
welded. Joint designs that require long nozzle-to-work distances will need higher
gas flow rates than those used with normal nozzle-to-work distances. The gas nozzle should be of adequate size to provide good gas coverage of the weld area. When
welding is done in confined areas or in the root of thick weld joints, small size
nozzles are used.
(5) The gun contact tube and electrode feed drive rolls are selected for the
particular electrode composition and diameter , as specified by the equipment manufacturer. The contact tube will wear with usage, and must be replaced periodically
if good electrical contact with electrode is to be maintained and heating of the
gun is to be minimized.
(6) Electrode extension is set by the distance between the tip of the contact
tube and the gas nozzle opening. The extension used is related to the type of MIG
welding, short circuiting or spray type transfer. It is important to keep the
electrode extension (nozzle-to-work distance) as uniform as-possible during welding . Therefore, depending on the application, the contact tube may be inside,
flush with, or extending beyond the gas nozzle.
(7) The electrode feed rate and welding voltage are set to the recommended
values for the electrode size and material. With a constant voltage power source,
the welding current will be establish by the electrode feed rate. A trial bead
weld should be made to establish proper voltage (arc length) and feed rate values.
Other variables, such as slope control, inductance, or both, should be adjusted to
give good arc starting and smooth arc operation with minimum spatter. The optimum
settings will depend on the equipment design and controls, electrode material and
size, shielding gas, weld joint design, base metal composition and thickness, welding position , and welding speed.
10-67
TC 9-237
10-13.
a.
FLUX-CORED ARC WELDING FCAW)
General.
(1) Flux-cored, tubular electrode welding has evolved from the MIG welding
process to improve arc action, metal transfer, weld metal properties, and weld
appearance. It is an arc welding process in which the heat for welding is provided
by an arc between a continuously fed tubular electrode wire and the workpiece.
Shielding is obtained by a flux contained within the tubular electrode wire or by
the flux and an externally supplied shielding gas. A diagram of the process is
shown in figure 10-55.
(2) Flux-cored arc welding is similar to gas metal arc welding in many ways.
The flux-cored wire used for this process gives it different characteristics.
Flux-cored arc welding is widely used for welding ferrous metals and is particularly good for applications in which high deposition rates are needed. At high welding currents, the arc is smooth and more manageable when compared in using large
diameter gas metal arc, welding electrodes with carbon dioxide. The arc and weld
pool are clearly visible to the welder. A slag coating is left on the surface of
the weld bead, which must be removed. Since the filler metal transfers across the
arc, some spatter is created and some smoke produced.
b.
Equipment.
(1) The equipment used for flux-cored arc welding is similar to that used for
gas metal arc welding. The basic arc welding equipment consists of a power source,
controls, wire feeder, welding gun, and welding cables. A major difference between
the gas shielded electrodes and the self -shielded electrodes is that the gas shielded wires also require a gas shielding system. This may also have an effect on the
type of welding gun used. Fume extractors are often used with this process. For
machines and automatic welding, several items, such as seam followers and motion
devices, are added to the basic equipment. Figure 10-56 shows a diagram of the
equipment used for semiautomatic flux-cored arc welding.
10-68
TC 9-237
(2) The power source, or welding machine, provides the electric power of the
proper voltage and amperage to maintain a welding arc. Most power sources operate
on 230 or 460 volt input power, but machines that operate on 200 or 575 volt input
are also available. Power sources may operate on either single phase or threephase input with a frequency of 50 to 60 hertz. Most power sources used for fluxcored arc welding have a duty cycle of 100 percent, which indicates they can be
used to weld contiuously. Some machines used for this process have duty cycles of
60 percent, which means that they can be used to weld 6 of every 10 minutes. The
power sources generally recommended for flux-cored arc welding are direct current
constant voltage type. Both rotating (generator) and static (single or threephase transformer-rectifiers) are used. The same power sources used with gas metal
arc welding are used with flux-cored arc welding. Flux-cored arc welding generally
uses higher welding currents than gas metal arc welding, which sometimes requires a
larger power source. It is important to use a power source that is capable of
producing the maximum current level required for an application.
(3) Flux-cored arc welding uses direct current. Direct current can be either
reverse or straight polarity. Flux-cored electrode wires are designed to operate
on either DCEP or DCEN. The wires designed for use with an external gas shielding
system are generally designed for use with DCEP. Some self-shielding flux-cored
ties are used with DCEP while others are developed for use with DCEN. Electrode
positive current gives better penetration into the weld joint. Electrode negative
current gives lighter penetration and is used for welding thinner metal or metals
where there is poor fit-up. The weld created by DCEN is wider and shallower than
the weld produced by DCEP.
(4) The generator welding machines used for this process can be powered by an
electric rotor for shop use, or by an internal combustion engine for field applications. The gasoline or diesel engine-driven welding machines have either liquidor air-cooled engines. Motor-driven generators produce a very stable arc, but are
noisier, more expensive, consume more power, and require more maintenance than
transformer-rectifier machines.
10-69
TC 9-237
10-13.
FLUX-CORED ARC WELDING (FCAW) (cont)
(5) A wire feed motor provides power for driving the electrode through the
cable and gun to the work. There are several different wire feeding systems available. System selection depends upon the application. Most of the wire feed systems used for flux-cored arc welding are the constant speed type, which are used
with constant voltage power sources. With a variable speed wire feeder, a voltage
sensing circuit is used to maintain the desired arc length by varying the wire feed
speed. Variations in the arc length increase or decrease the wire feed speed. A
wire feeder consists of an electrical rotor connected to a gear box containing
drive rolls. The gear box and wire feed motor shown in figure
10-57 have form feed
.
rolls in the gear box.
(6) Both air-cooled and water-cooled guns are used for flux-cored arc welding . Air-cooled guns are cooled primarily by the surrounding air, but a shielding
gas, when used, provides additional cooling effects. A water-cooled gun has ducts
to permit water to circulate around the contact tube and nozzle. Water-cooled guns
permit more efficient cooling of the gun. Water-cooled guns are recommended for
use with welding currents greater than 600 amperes , and are preferred for many
applications using 500 amperes. Welding guns are rated at the maximum current
capacity for continuous operation. Air-cooled guns are preferred for most applications less than 500 amperes, although water-cooled guns may also be used. Aircooled guns are lighter and easier to manipulate.
(7) Shielding gas equipment and electrodes.
(a) Shielding gas equipment used for gas shielded flux-cored wires consists
of a gas supply hose, a gas regulator, control valves, and supply hose to the welding gun.
(b) The
age tanks with
tion to this is
both liquid and
10-70
shielding gases are supplied in liquid form when they are in storvaporizers, or in a gas form in high pressure cylinders. An excepcarbon dioxide. When put in high pressure cylinders, it exists in
gas forms.
TC 9-237
(c) The primary purpose of the shielding gas is to protect the arc and weld
puddle from contaminating effects of the atmosphere. The nitrogen and oxygen of
the atmosphere, if allowed to come in contact with the molten weld metal, cause
porosity and brittleness. In flux-cored arc welding, shielding is accomplished by
the decomposition of the electrode core or by a combination of this and surrounding
the arc with a shielding gas supplied from an external source. A shielding gas
displaces air in the arc area. Welding is accomplished under a blanket of shielding gas. Inert and active gases may both be used for flux-cored arc welding.
Active gases such as carbon dioxide, argon-oxygen mixture, and argon-carbon dioxide
mixtures are used for almost all applications. Carbon dioxide is the most common.
The choice of the proper shielding gas for a specific application is based on the
type of metal to be welded, arc characteristics and metal transfer, availability,
cost of the gas, mechanical property requirements, and penetration and weld bead
shape. The various shielding gases are summarized below.
1. Carbon dioxide. Carbon dioxide is manufactured from fuel gases which
are given off by the burning of natural gas, fuel oil, or coke. It is also obtained as a by-product of calcining operation in lime kilns, from the manufacturing
of ammonia and from the fermentation of alcohol, which is almost 100 percent
pure. Carbon dioxide is made available to the user in either cylinder or bulk
containers. The cylinder is more common. With the bulk system, carbon dioxide is
usually drawn off as a liquid and heated to the gas state before going to the weld-ing torch. The bulk system is normally only used when supplying a large number of
welding stations. In the cylinder, the carbon dioxide is in both a liquid and a
vapor form with the liquid carbon dioxide occupying approximately two thirds of the
space in the cylinder. By weight, this is approximately 90 percent of the content
of the cylinder. Above the liquid, it exists as a vapor gas. As carbon dioxide is
drawn from the cylinder, it is replaced with carbon dioxide that vaporizes from the
liquid in the cylinder and therefore the overall pressure will be indicated by the
pressure gauge. When the pressure in the cylinder has dropped to 200 psi (1379
kPa), the cylinder should be replaced with a new cylinder. A positive pressure
should always be left in the cylinder in order to prevent moisture and other contaminants from backing up into the cylinder. The normal discharge rate of the CO2
cylinder is about 10 to 50 cu ft per hr (4.7 to 24 liters per min). However, a
maximum discharge rate of 25 cu ft per hr (12 liters per min is recommended when
welding using a single cylinder. As the vapor pressure drops from the cylinder
pressure to discharge pressure through the CO 2 regulator, it absorbs a great deal
of heat. If flow rates are set too high, this absorption of heat can lead to freezing of the regulator and flowmeter which interrupts the shielding gas flow. When
flow rate higher than 25 cu ft per hr (12 liters per rein) is required, normal practice is to manifold two CO 2 cylinders in parallel or to place a heater between the
cylinder and gas regulator, pressure regulator, and flowmeter. Excessive flow
rates can also result in drawing liquid from the cylinder. Carbon dioxide is the
most widely used shielding gas for flux-cored arc welding. Most active gases cannot be used for shielding, but carbon dioxide provides several advantages for use
in welding steel. These are deep penetration and low cost. Carbon dioxide promotes a globular transfer. The carbon dioxide shielding gas breaks down into components such as carbon monoxide and oxygen. Because carbon dioxide is an oxidizing
gas, deoxidizing elements are added to the core of the electrode wire to remove
oxygen. The oxides formed by the deoxidizing elements float to the surface of the
weld and become part of the slag covering. Some of the carbon dioxide gas will
break down to carbon and oxygen. If the carbon content of the weld pool is below
10-71
TC 9-237
10-13.
FLUX-CORED ARC WELDING (FCAW) (cont)
about 0.05 percent, carbon dioxide shielding will tend to increase the carbon content of the weld metal. Carbon, which can reduce the corrosion resistance of some
stainless steels, is a problem for critical corrosion application. Extra carbon
can also reduce the toughness and ductility of some low alloy steels. If the carbon content in the weld metal is greater than about 0.10 percent, carbon dioxide
shielding will tend to reduce the carbon content. This loss of carbon can be attributed to the formation of carbon monoxide, which can be trapped in the weld as
porosity deoxidizing elements in the flux core reducing the effects of carbon monoxide formation.
2. Argon-carbon dioxide mixtures. Argon and carbon dioxide are sometimes mixed for use with flux-cored arc welding. A high percentage of argon gas in
the mixture tends to promote a higher deposition efficiency due to the creation of
less spatter. The most commonly used gas mixture
“
in flux-cored arc welding is a 75
percent argon-25 percent carbon dioxide mixture. The gas mixture produces a fine
globular metal transfer that approaches a spray. It also reduces the amount of
oxidation that occurs, compared to pure carbon dioxide. The weld deposited in an
argon-carbon dioxide shield generally has higher tensile and yield strengths.
Argon-carbon dioxide mixtures are often used for out-of-position welding, achieving
better arc characteristics. These mixtures are often used on loW alloy steels and
stainless steels. Electrodes that are designed for use with CO 2 may cause an excessive buildup of manganese, silicon, and other deoxidizing elements if they are used
with shielding gas mixtures containing a high percentage of argon. This will have
an effect on the mechanical properties of the weld.
3. Argon-oxygen mixtures. Argon-oxygen mixtures containing 1 or 2 percent oxygen are used for some applications. Argon-oxygen mixtures tend to promote
a spray transfer which reduces the amount of spatter produced. A major application
of these mixtures is the welding of stainless steel where carbon dioxide can cause
corrosion problems.
(d) The electrodes used for flux-cored arc welding provide the filler metal
to the weld puddle and shielding for the arc. Shielding is required for sane electrode types. The purpose of the shielding gas is to provide protection from the
atmosphere to the arc and molten weld puddle. The chemical composition of the
electrode wire and flux core, in combination with the shielding gas, will determine
the weld metal composition and mechanical properties of the weld. The electrodes
for flux-cored arc welding consist of a metal shield surrounding a core of fluxing
and/or alloying compounds as shown in figure 10-58. The cores of carbon steel and
low alloy electrodes contain primarily fluxing compounds. Some of the low alloy
steel electrode cares contain high amounts of alloying compounds with a low flux
content. Most low alloy steel electrodes require gas shielding. The sheath comprises approximately 75 to 90 percent of the weight of the electrode. Self-shielded electrodes contain more fluxing compounds than gas shielded electrodes. The
compounds contained in the electrode perform basically the same functions as the
coating of a covered electrode used in shielded metal arc welding. These functions
are:
1. To form a slag coating that floats on the surface of the weld metal
and protects it during solidification.
10-72
TC 9-237
2. To provide deoxidizers and scavengers which help purify and produce
solid weld-metal.
3. To provide arc stabilizers which produce a smooth welding arc and
keep spatter to a minimum.
4. To add alloying elements to the weld metal which will increase the
strength and improve other properties in the weld metal.
5. To provide shielding gas. Gas shielded wires require an external
supply of shielding gas to supplement that produced by the core of the electrode.
(e) The classification system used for tubular wire electrodes was devised
by the American Welding Society. Carbon and low alloy steels are classified on the
basis of the following items:
1.
Mechanical properties of the weld metal.
2 . Welding position.
3.
Chemical composition of the weld metal.
4.
Type of welding current.
5.
Whether or not a CO2 shielding gas is used.
An example of a carbon steel electrode classification is E70T-4 where:
1.
The “E” indicates an electrode.
2. The second digit or “7“ indicates the minimum tensile strength in
units of 10,000 psi (69 MPa). Table 10-12, p 10-74, shows the mechanical property
requirements for the various carbon steel electrodes.
3.
The third digit or “0” indicates the welding positions. A “0” indicates flat and horizontal positions and a “1” indicates all positions.
10-73
TC 9-237
10-13.
FLUX-CORED ARC WELDING (FCAW) (cont)
4.
The “T” stands for a tubular or flux cored wire classification.
5. The suffix “4” gives the performance and usability capabilities as
shown in table 10-13. When a “G” classification is used, no specific performance
and usability requirements are indicated. This classification is intended for
electrodes not covered by another classification. The chemical composition requirements of the deposited weld metal for carbon steel electrodes are shown in table
10-14. Single pass electrodes do not have chemical composition requirements because checking the chemistry of undiluted weld metal does not give the true results
of normal single pass weld chemistry.
10-74
TC 9-237
10-13.
FLUX-CORED ARC WELDING (FCAW) (cont)
The classification of low alloy steel electrodes is similar to the classification
of carbon steel electrodes. An example of a low alloy steel classification is
E81T1-NI2 where:
1 . The “E” indicates electrode.
2. The second digit or “8” indicates the minimum tensile in strength in
units of 10,000 psi (69 MPa). In this case it is 80,000 psi (552 MPa). The mechanical property requirements for low alloy steel electrodes are shown in table 1015. Impact strength requirements are shown in table 10-16.
3. The third digit or “1” indicates the welding position capabilities of
the electrode. A “1” indicates all positions and an “0” flat and horizontal position only.
4. The “T” indicates a tubular or flux-cored electrode used in flux
cored arc welding.
5. The fifth digit or “l” describes the usability and performance characteristics of the electrode. These digits are the same as used in carbon steel
electrode classification but only EXXT1-X, EXXT4-X, EXXT5-X and EXXT8-X are used
with low alloy steel flux-cored electrode classifications.
6. The suffix or “Ni2” tells the chemical compsition of the deposited
weld metal as shown in table 10-17, p 10-78.
10-76
TC 9-237
The classification system for stainless steel electrodes is based on the chemical
composition of the weld metal and the type of shielding to be employed during welding. An example of a stainless steel electrode classification is E308T–1 where:
1. The “E” indicates the electrode.
2. The digits between the “E” and the “T” indicates the chemical composition of the weld as shown in table 10-18, p 10-80.
3. The “T” designates a tubular or flux cored electrode wire.
4 . The suffix of “1” indicates the type of shielding to be used as shown
in table 10-19, p 10-81.
10-79
TC 9-237
(8) Welding Cables.
(a) The welding cables and connectors are used to connect the power source
to the welding gun and to the work. These cables are normally made of copper. The
cable consists of hundreds of wires that are enclosed in an insulated casing of
natural or synthetic rubber. The cable that connects the power source to the welding gun is called the electrode lead. In semiautomatic welding, this cable is
often part of the cable assembly, which also includes the shielding gas hose and
the conduit that the electrode wire is fed through. For machine or automatic welding, the electrode lead is normally separate. The cable that connects the work to
the power source is called the work lead. The work leads are usually connected to
the work by pinchers, clamps, or a bolt.
10-81
TC 9-237
10-13.
FLUX-CORED ARC WELDING (FCAW) (cont)
(b) The size of the welding cables used depends on the output capacity of
the welding machine, the duty cycle of the machine, and the distance between the
welding machine and the work. Cable sizes range from the smallest AWG No 8 to AWG
No 4/0 with amperage ratings of 75 amperes on up. Table 10-20 shows recommended
cable sizes for use with different welding currents and cable lengths. A cable
that is too small may become too hot during welding.
c. Advantages. The major advantages of flux-cored welding are reduced cost and
higher deposition rates than either SMAW or solid wire GMAW. The cost is less for
flux-cored electrodes because the alloying agents are in the flux, not in the steel
filler wire as they are with solid electrodes. Flux-cored welding is ideal where
bead appearance is important and no machining of the weld is required. Flux-cored
welding without carbon dioxide shielding can be used for most mild steel construction applications. The resulting welds have higher strength but less ductility
than those for which carbon dioxide shielding is used. There is less porosity and
greater penetration of the weld with carbon dioxide shielding. The flux-cored
process has increased tolerances for scale and dirt. There is less weld spatter
than with solid-wire MIG welding. It has a high deposition rate, and faster travel
speeds are often used. Using small diameter electrode wires, welding can be done
in all positions. Some flux-cored wires do not need an external supply of shielding gas, which simplifies the equipment. The electrode wire is fed continuously
so there is very little time spent on changing electrodes. A higher percentage of
the filler metal is deposited when compared to shield metal arc welding. Finally,
better penetration is obtained than from shielded metal arc welding.
d. Disadvantages. Most low-alloy or mild-steel electrodes of the flux-cored
type are more sensitive to changes in welding conditions than are SMAW electrodes.
This sensitivity, called voltage tolerance, can be decreased if a shielding gas is
used, or if the slag-forming components of the core material are increased. A
constant-potential power source and constant-speed electrode feeder are needed to
maintain a constant arc voltage.
10-82
TC 9-237
e. Process Principles. The flux-cored welding wire, or electrode, is a hollow
tube filled with a mixture of deoxidizers, fluxing agents, metal powders, and
ferro-alloys. The closure seam, which appears as a fine line, is the only visible
difference between flux-cored wires and solid cold-drawn wire. Flux-cored electrode welding can be done in two ways: carbon dioxide gas can be used with. the
flux to provide additional shielding, or the flux core alone can provide all the
shielding gas and slagging materials. The carbon dioxide gas shield produces a
deeply penetrating arc and usually provides better weld than is possible without an
external gas shield. Although flux-cored arc welding may be applied semiautomati–
tally, by machine, or automatically, the process is usually applied semiautomatically. In semiautomatic welding, the wire feeder feeds the electrode wire and the
power source maintains the arc length. The welder manipulates the welding gun and
adjusts the welding parameters. Flux-cored arc welding is also used in machine
welding where, in addition to feeding the wire and maintaining the arc length, the
machinery also provides the joint travel. The welding operator continuously moni–
tors the welding and makes adjustments in the welding parameters. Automatic welding is used in high production applications.
10-14. SUBMERGED ARC WELDING (SAW)
a. General. Submerged arc welding is a process in which the joining of metals
is produced by heating with an arc or arcs between a bare metal electrode or elec–
trodes and the work. The arc is shielded by a blanket of granular fusible material
on the work. Pressure is not used. Filler metal is obtained from the electrode or
from a supplementary welding rod.
b. Equipment.
(1) The equipment components required for submerged arc welding are shown by
figure 10-59. Equipment consists of a welding machine or power source, the wire
feeder and control system, the welding torch for automatic welding or the welding
gun and cable assembly for semiautomatic welding, the flux hopper and feeding mechanism, usually a flux recovery system, and a travel mechanism for automatic welding.
10-83
TC 9-237
10-14.
SUBMERGED ARC WELDING (SAW) (cont)
(2) The power source for submerged arc welding must be rated for a 100 percent duty cycle, since the submerged arc welding operations are continuous and the
length of time for making a weld may exceed 10 minutes. If a 60 percent duty cycle
power source is used, it must be derated according to the duty cycle curve for 100
percent operation.
(3) When constant current is used, either ac or dc, the voltage sensing electrode wire feeder system must be used. When constant voltage is used, the simpler
fixed speed wire feeder system is used. The CV system is only used with direct
current.
(4) Both generator and transformer-rectifier power sources are used, but the
rectifier machines are more popular. Welding machines for submerged arc welding
range in size from 300 amperes to 1500 amperes. They may be connected in parallel
to provide extra power for high —current applications. Direct current power is used
for semiautomatic applications, but alternating current power is used primarily
with the machine or the automatic method. Multiple electrode systems require specialized types of circuits, especially when ac is employed.
(5) For semiautomatic application, a welding gun and cable assembly are used
to carry the electrode and current and to provide the flux at the arc. A small
flux hopper is attached to the end of the cable assembly. The electrode wire is
fed through the bottom of this flux hopper through a current pickup tip to the
arc. The flux is fed from the hopper to the welding area by mans of gravity. The
amount of flux fed depends on how high the gun is held above the work. The hopper
gun may include a start switch to initiate the weld or it may utilize a “hot” electrode so that when the electrode is touched to the work, feeding. will begin automatically.
(6) For automatic welding, the torch is attached to the wire feed motor and
includes current pickup tips for transmitting the welding current to the electrode
wire. The flux hopper is normally attached to the torch, and may have magnetically
operated valves which can be opened or closed by the control system.
(7) Other pieces of equipment sometimes used may include a travel carriage,
which can be a simple tractor or a complex moving specialized fixture. A flux
recovery unit is normally provided to collect the unused submerged arc flux and
return it to the supply hopper.
(8) Submerged arc welding system can become quite complex by incorporating
additional devices such as seam followers, weavers, and work rovers.
c.
Advantages and Major Uses.
(1) The major advantages of the submerged arc welding process are:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
10-84
high quality of the weld metal.
extremely high deposition rate and speed.
smooth, uniform finished weld with no spatter.
little or no smoke.
no arc flash, thus minimal need for protective clothing.
high utilization of electrode wire.
easy automation for high-operator factor.
normally, no involvement of manipulative skills.
TC 9-237
(2) The submerged arc process is widely used in heavy steel plate fabrication
work. This includes the welding of structural shapes, the longitudinal seam of
larger diameter pipe, the manufacture of machine components for all types of heavy
industry, and the manufacture of vessels and tanks for pressure and storage use.
It is widely used in the shipbuilding industry for splicing and fabricating subassemblies, and by many other industries where steels are used in medium to heavy
thicknesses. It is also used for surfacing and buildup work, maintenance, and
repair.
d.
Limitations of the Process.
(1) A major limitation of submerged arc welding is its limitation of welding
positions. The other limitation is that it is primarily used only to weld mild and
low-alloy high-strength steels.
(2) The high-heat input, slow-cooling cycle can be a problem when welding
quenched and tempered steels. The heat input limitation of the steel in question
must be strictly-adhered to when using submerged arc welding. This may require the
making of multipass welds where a single pass weld would be acceptable in mild
steel. In some cases, the economic advantages may be reduced to the point where
flux-cored arc welding or some other process should be considered.
(3) In semiautomatic submerged arc welding, the inability to see the arc and
puddle can be a disadvantage in reaching the root of a groove weld and properly
filling or sizing.
e. Principles of Operation.
(1) The submerged arc welding process is shown by figure 10-60. It utilizes
the heat of an arc between a continuously fed electrode and the work. The heat of
the arc melts the surface of the base metal and the end of the electrode. The
metal melted off the electrode is transferred through the arc to the workpiece,
where it becomes the deposited weld metal. Shielding is obtained from a blanket of
granular flux , which is laid directly over the weld area. The flux close to the
arc melts and intermixes with the molten weld metal, helping to purify and fortify
i t . The flux forms a glass-like slag that is lighter in weight than the deposited
weld metal and floats on the surface as a protective cover. The weld is submerged
under this layer of flux and slag, hence the name submerged arc welding. The flux
and slag normally cover the arc so that it is not visible. The unmelted portion of
the flux can be reused. The electrode is fed into the arc automatically from a
c o i l . The arc is maintained automatically. Travel can be manual or by machine.
The arc is initiated by a fuse type start or by a reversing or retrack system.
10-85
TC 9-237
10-14. SUBMERGED
ARC
WELDING (SAW) (cont)
(2) Normal method of application and position capabilities. The most popular
method of application is the machine method, where the operator monitors the welding operation. Second in popularity is the automatic method, where welding is a
pushbutton operation. The process can be applied semiautomatically; however, this
method of application is not too popular. The process cannot be applied manually
because it is impossible for a welder to control an arc that is not visible. The
submerged arc welding process is a limited-position welding process. The welding
positions are limited because the large pool of molten metal and the slag are very
fluid and will tend to run out of the joint. Welding can be done in the flat position and in the horizontal fillet position with ease. Under special controlled
procedures, it is possible to weld in the horizontal position, sometimes called 3
o' clock welding. This requires special devices to hold the flux up so that the
molten slag and weld metal cannot run away. The process cannot be used in the
vertical or overhead position.
(3) Metals weldable and thickness range. Submerged arc welding is used to
weld low- and medium-carbon steels, low-alloy high-strength steels, quenched and
tempered steels, and many stainless steels. Experimentally, it has been used to
weld certain copper alloys, nickel alloys, and even uranium. This information is
summarized in table 10-21.
Metal thicknesses from 1/16 to 1/2 in. (1.6 to 12.7 mm) can be welded with no edge
preparation. With edge preparation, welds can be made with a single pass on material from 1/4 to 1 in. (6.4 to 25.4 mm). When multipass technique is used, the maximum thickness is practically unlimited. This information is summarized in table
10-22. Horizontal fillet welds can be made up to 3/8 in. (9.5 mm) in a single pass
and in the flat position, fillet welds can be made up to 1 in. (25 mm) size.
10-86
TC 9-237
(4) Joint design. Although the submerged arc welding process can utilize the
same joint design details as the shielded metal arc welding process, different
joint details are suggested for maximum utilization and efficiency of submerged arc
welding . For groove welds, the square groove design can be used up to 5/8 in. (16
mm) thickness. Beyond this thickness, bevels are required. Open roots are used
but backing bars are necessary since the molten metal will run through the joint.
When welding thicker metal, if a sufficiently large root face is used, the backing
bar may be eliminate. However, to assure full penetration when welding from one
side, backing bars are recommended. Where both sides are accessible, a backing
weld can be made which will fuse into the original weld to provide full penetration. Recommended submerged arc joint designs are shown by figure 10-61, p 10-88.
(5) Welding circuit and current.
(a) The welding circuit employed for single electrode submerged arc welding
is shown by figure 10-59, p 10-83. This requires a wire feeder system and a power
supply.
(b) The submerged arc welding process uses either direct or alternating
current for welding power. Direct current is used for most applications which use
a single arc. Both direct current electrode positive (DCEP) and electrode negative
(DCEN) are used.
(c) The constant voltage type of direct current power is more popular for
submerged arc we welding with 1/8 in. (3.2 mm) and smaller diameter electrode negative
(d) The constant current power system is normally used for welding with
5/3 2 in. (4 mm) and larger-diameter electrode wires. The control circuit for CC
power is more complex since it attempts to duplicate the actions of the welder to
retain a specific arc length. The wire feed system must sense the voltage across
the arc and feed the electrode wire into the arc to maintain this voltage. As
conditions change, the wire feed must slow down or speed up to maintain the prefixed voltage across the arc. This adds complexity to the control system. The
system cannot react instantaneously. Arc starting is mare complicated with the
constant current system since it requires the use of a reversing system to strike
the arc, retract, and then maintain the preset arc voltage.
10-87
TC 9-237
(e) For ac welding, the constant current power is always used. when multiple electrode wire systems are used with both ac and dc arcs, the constant current
power system is utilized. The constant voltage system, however, can be applied
when two wires are fed into the arc supplied by a single power source. Welding
current for submerged arc welding can vary from as low as 50 amperes to as high as
2000 amperes. Most submerged arc welding is done in the range of 200 to 1200 amperes.
10-89
TC 9-237
10-14. SUBMERGED ARC WELDING (cont)
(6) Deposition rates and weld quality.
(a) The deposition rates of the submerged arc welding process are higher
than any other arc welding process. Deposition rates for single electrodes are
shown by figure 10-62. There are at least four related factors that control the
deposition rate of submerged arc welding: polarity, long stickout, additives in
the flux, and additional electrodes. The deposition rate is the highest for direct
current electrode negative (DCEN). The deposition rate for alternating current is
between DCEP and DCEN. The polarity of maximum heat is the negative pole.
(b) The deposition rate with any welding current can be increased by extending the “stickout.” This is the distance from the point where current is introduced into the electrode to the arc. When using “long stickout” the amount of
penetration is reduced. The deposition rates can be increased by metal additives
in the submerged arc flux. Additional electrodes can be used to increase the overall deposition rate.
(c) The quality of the weld metal deposited by the submerged arc welding
process is high. The weld metal strength and ductility exceeds that of the mild
steel or low-alloy base material when the correct combination of electrode wire and
submerged arc flux is used. When submerged arc welds are made by machine or automatically, the human factor inherent to the manual welding processes is eliminated.
The weld will be more uniform and free from inconsistencies. In general, the weld
bead size per pass is much greater with submerged arc welding than with any of the
other arc welding processes. The heat input is higher and cooling rates are slower. For this reason, gases are allowed more time to escape. Additionally, since
the submerged arc slag is lower in density than the weld metal, it will float out
to the top of the weld. Uniformity and consistency are advantages of this process
when applied automatically.
10-90
TC 9-237
(d) Several problems may occur when using the semiautomatic application
method. The electrode wire may be curved when it leaves the nozzle of the welding
gun. This curvature can cause the arc to be struck in a location not expected by
the welder. When welding in fairly deep grooves, the curvature may cause the arc
to be against one side of the weld joint rather than at the root. This will cause
incomplete root fusion. Flux will be trapped at the root of the weld. Another
problem with semiautomatic welding is that of completely filling the weld groove or
maintaining exact size, since the weld is hidden and cannot be observed while it is
being made. This requires making an extra pass. In some cases, too much weld is
deposited. Variations in root opening affect the travel speed. If travel speed is
uniform, the weld may be under- or overfilled in different areas. High operator
skill will overcome this problem.
(e) There is another quality problem associated with extremely large
single-pass weld deposits. When these large welds solidify, the impurities in the
melted base metal and in the weld metal all collect at the last point to freeze,
which is the centerline of the weld. If there is sufficient restraint and enough
impurities are collected at this point, centerline cracking may occur. This can
happen
when making large single-pass flat fillet welds if the base metal plates
are
0
0
4 5 from flat. A simple solution is to avoid placing the parts at a true 45
angle. It should be varied approximately 10 so that the root of the joint is not
in line with the centerline of the fillet weld. Another solution is to make multiple passes rather than attempting to make a large weld in a single pass.
(f) Another quality problem has to do with the hardness of the deposited
weld metal . Excessively hard weld deposits contribute to cracking of the weld
during fabrication or during service. A maximum hardness level of 225 Brinell is
recommended. The reason for the hard weld in carbon and low-alloy steels is too
rapid cooling, inadequate postweld treatment, or excessive alloy pickup in the weld
metal. Excessive alloy pickup is due to selecting an electrode that has too much
alloy, selecting a flux that introduces too much alloy into the weld, or the use of
excessively high welding voltages.
(g) In automatic and machine welding, defects may occur at the start or at
the end of the weld. The best solution is to use runout tabs so that S tartS a n d
stops will be on the tabs rather than on the product.
(7) Weld schedules. The submerged arc welding process applied by machine or
fully automatically should be done in accordance with welding procedure schedules.
Table 10-23, p 10-93, and figure 10-63, p 10-92, show the recommended welding schedules for submerged arc welding using a single electrode on mild and low-alloy
steels. The table can be used for welding other ferrous materials, but was developed for mild steel. All of the welds made by this procedure should pass qualification, tests, assuming that the correct electrode and flux have been selected. If
the schedules are varied more than 10 percent, qualification tests should be performed to determine the weld quality.
10-91
TC 9-237
(8) Welding variables.
(a) The welding variables for submerged arc welding are similar to the
other arc welding processes, with several exceptions.
(b) In submerged arc welding, the electrode type and the flux type are
usually based on the mechanical properties required by the weld. The electrode and
flux combination selection is based on table 10-24, p 10-103, to match the metal
being welded. The electrode size is related to the weld joint size and the current
recommended for the particular joint. This must also be considered in determining
the number of passes or beads for a particular joint. Welds for the same joint
dimension can be made in many or few passes, depending on the weld metal metallurgy
desired. Multiple passes usually deposit higher-quality weld metal. Polarity is
established initially and is based on whether maximum penetration or maximum deposi–
tion rate is required.
(c) The major variables that affect the weld involve heat input and include
the welding current, arc voltage, and travel speed. Welding current is the most
important. For single-pass welds, the current should be sufficient for the desired
penetration without burn-through. The higher the current, the deeper the penetration. In multi-pass work, the current should be suitable to produce the size of
the weld expected in each pass. The welding current should be selected based on
the electrode size. The higher the welding current, the greater the melt-off rate
(deposition rate).
(d) The arc voltage is varied within narrower limits than welding current.
It has an influence on the bead width and shape. Higher voltages will cause the
bead to be wider and flatter. Extremely high arc voltage should be avoided, since
it can cause cracking. This is because an abnormal amount of flux is melted and
excess deoxidizers may be transferred to the weld deposit, lowering its ductility.
Higher arc voltage also increases the amount of flux consumed. The low arc voltage
produces a stiffer arc that improves penetration, particularly in the bottom of
deep grooves. If the voltage is too low, a very narrow bead will result. It will
have a high crown and the slag will be difficult to remove.
(e) Travel speed influences both bead width and penetration. Faster travel
speeds produce narrower beads that have less penetration. This can be an advantage
for sheet metal welding where small beads and minimum penetration are required. If
speeds are too fast, however, there is a tendency for undercut and porosity, since
the weld freezes quicker. If the travel speed is too slow, the electrode stays in
the weld puddle too long. This creates poor bead shape and may cause excessive
spatter and flash through the layer of flux.
10-95
TC 9-237
10-14.
SUBMERGED ARC WELDING (cont)
(f) The secondary variables include the angle of the electrode to the work,
the angle of the work itself, the thickness of the flux layer, and the distance
between the current pickup tip and the arc. This latter factor, called electrode
“stickout,“ has a considerable effect on the weld. Normally, the distance between
the contact tip and the work is 1 to 1-1/2 in. (25 to 38 mm). If the stickout is
increased beyond this amount, it will cause preheating of the electrode wire, which
will greatly increase the deposition rate. As stickout increases, the penetration
into the base metal decreases. This factor must be given serious consideration
because in some situations the penetration is required. The relationship between
stickout and deposition rate is shown by figure 10-64.
(g) The depth of the flux layer must also be considered. If it is too
thin, there will be too much arcing through the flux or arc flash. This also may
cause porosity. If the flux depth is too heavy, the weld may be narrow and
humped. Too many small particles in the flux can cause surface pitting since the
gases generated in the weld may not be allowed to escape. These are sometimes
called peck marks on the bead surface.
10-96
TC 9-237
(9) Tips for using the process.
(a) One of the major applications for submerged arc welding is on circular
welds where the parts are rotated under a fixed head. These welds can be made on
the inside or outside diameter. Submerged arc welding produces a large molten weld.
puddle and molten slag which tends to run. This dictates that on outside diameters, the electrode should be positioned ahead of the extreme top, or 12 o'clock
position, so that the weld metal will begin to solidify before it starts the
downside slope. This becomes more of a problem as the diameter of the part being
welded gets smaller. Improper electrode position will increase the possibility of
slag entrapment or a poor weld surface. The angle of the electrode should also be
changed and pointed in the direction of travel of the rotating part. When the
welding is done on the inside circumference, the electrode should be angled so that
it is ahead of bottom center, or the 6 o'clock position. Figure 10-65 illustrates
these two conditions.
(b) Sometimes the work being welded is sloped downhill or uphill to provide
different types of weld bead contours. If the work is sloped downhill, the bead
will have less penetration and will be wider. If the weld is sloped uphill, the
bead will have deeper penetration and will be narrower. This is based on all other
factors remaining the same. This information is shown by figure 10-66.
10-97
TC 9-237
10-14.
SUBMERGED ARC WELDING (cont)
(c) The weld will be different depending on the angle of the electrode with
respect to the work when the work is level. This is the travel angle, which can be
a drag or push angle. It has a definite effect on the bead contour and weld metal
penetration. Figure 10-67 shows the relationship.
(d) One side welding with complete root penetration can be obtained with
submerged arc welding. When the weld joint is designed with a tight root opening
and a fairly large root face, high current and electrode positive should be used.
If the joint is designed with a root opening and a minimum root face, it is necessary to use a backing bar, since there is nothing to support the molten weld meta l . The molten flux is very fluid and will run through narrow openings. If this
happens, the weld metal will follow and the weld will burn through the joint.
Backing bars are needed whenever there is a root opening and a minimum root face.
(e) Copper backing bars are useful when welding thin steel. Without backing bars, the weld would tend to melt through and the weld metal would fall away
from the joint. The backing bar holds the weld metal in place until it solidif i e s . The copper backing bars may be water cooled to avoid the possibility of
melting and copper pickup in the weld metal. For thicker materials, the backing
may be submerged arc flux or other specialized type flux.
(10) Variations of the process.
(a) There are a large number of variations to the process that give submerged arc welding additional capabilities. Some of the more popular variations
are:
1. Two-wire systems — same power source.
10-98
2.
Two-wire systems — separate power source.
3.
Three-wire systems — separate power source.
4.
Strip electrode for surfacing.
5.
Iron powder additions to the flux.
6.
Long stickout welding.
7.
Electrically “cold” filler wire.
TC 9-237
(b) The multi-wire systems offer advantages since deposition rates and travel speeds can be improved by using more electrodes. Figure 10-68 shows the two
methods of utilizing two electrodes, one with a single-power source and one with
two power sources. When a single-power source is used, the same drive rolls are
used for feeding both electrodes into the weld. When two power sources are used,
individual wire feeders must be used to provide electrical insulation between the
two electrodes. With two electrodes and separate power, it is possible to utilize
different polarities on the two electrodes or to utilize alternating current on one
and direct current on the other. The electrodes can be placed side by side. This
is called transverse electrode position. They can also be placed one in front of
the other in the tandem electrode position.
(c) The two-wire tandem electrode position with individual power sources is
used where extreme penetration is required. The leading electrode is positive with
the trailing electrode negative. The first electrode creates a digging action and
the second electrode fills the weld joint. When two dc arcs are in close proximity, there is a tendency for arc interference between them. In some cases, the
second electrode is connected to alternating current to avoid the interaction of
the arc.
10-99
TC 9-237
10-14.
SUBMERGED ARC WELDING (SAW) (cont)
(d) The three-wire tandem system normally uses ac power on all three electrodes connected to three-phase power systems. These systems are used for making
high-speed longitudinal seams for large-diameter pipe and for fabricated beams.
Extremely high currents can be used with correspondingly high travel speeds and
deposition rates.
(e) The strip welding system is used to overlay mild and alloy steels usually with stainless steel. A wide bead is produced that has a uniform and minimum
penetration. This process variation is shown by figure 10-69. It is used for
overlaying the inside of vessels to provide the corrosion resistance of stainless
steel while utilizing the strength and economy of the low-alloy steels for the wall
thickness. A strip electrode feeder is required and special flux is normally
used . When the width of the strip is over 2 in. (51 mm), a magnetic arc oscillating device is used to provide for even burnoff of the strip and uniform penetration.
(f) Another way of increasing the deposition rate of submerged arc welding
is to add iron base ingredients to the joint under the flux. The iron in this
material will melt in the heat of the arc and will become part of the deposited
weld metal. This increases deposition rates without decreasing weld metal propert i e s . Metal additives can also be used for special surfacing applications. This
variation can be used with single-wire or multi-wire installations. Figure 10-70
shins the increased deposition rates attainable.
10-100
TC 9-237
(g) Another variation is the use of an electrically “cold” filler wire fed
into the arc area. The “cold” filler rod can be solid or flux-cored to add special
alloys to the weld metal. By regulating the addition of the proper material, the
properties of the deposited weld metal can be improved. It is possible to utilize
a flux-cored wire for the electrode, or for one of the multiple electrodes to introduce special alloys into the weld metal deposit. Each of these variations requires
special engineering to ensure that the proper material is added to provide the
desired deposit properties.
(11) Typical applications. The submerged arc welding process is widely used
in the manufacture of most heavy steel products. These include pressure vessels,
boilers, tanks, nuclear reactors, chemical vessels, etc. Another use is in the
fabrication of trusses and beams. It is used for welding flanges to the web. The
heavy equipment industry is a major user of submerged arc welding.
f.
Materials Used.
(1) Two materials are used in submerged arc welding: the welding flux and
the consumable electrode wire.
(2) Submerged arc welding flux shields the arc and the molten weld metal from
the harmful effects of atmospheric oxygen and nitrogen. The flux contains
deoxidizers and scavengers which help to remove impurities from the molten weld
metal. Flux also provides a means of introducing alloys into the weld metal. As
this molten flux cools to a glassy slag, it forms a covering which protects the
surface of the weld. The unmelted portion of the flux does not change its form and
its properties are not affected, so it can be recovered and reused. The flux that
does melt and forms the slag covering must be removed from the weld bead. This is
easily done after the weld has cooled. In many cases, the slag will actually peel
without requiring special effort for removal. In groove welds, the solidified slag
may have to be removed by a chipping hammer.
10-101
TC 9-237
10-14.
SURMERGED ARC WELDING (cont)
(3) Fluxes are designed for specific applications and for specific types of
weld deposits. Submerged arc fluxes come in different particle sizes. Many fluxes
are not marked for size of particles because the size is designed and produced for
the intended application.
(4) There is no specification for submerged arc fluxes in use in North America. A method of classifying fluxes, however, is by means of the deposited weld
metal produced by various combinations of electrodes and proprietary submerged arc
fluxes. This is covered by the American Welding Society Standard. Bare carbon
steel electrodes and fluxes for submerged arc welding. In this way, fluxes can be
designated to be used with different electrodes to provide the deposited weld metal
analysis that is desired. Table 10-24 shows the flux wire combination and the
mechanical properties of the deposited weld metal.
Section III. RELATED PROCESSES
10-15.
PLASMA ARC CUTTING (PAC)
a. General. The plasma arc cutting process cuts metal by melting a section of
metal with a constricted arc. A high velocity jet flow of hot ionized gas melts
the metal and then removes the molten material to form a kerf. The basic arrangement for a plasma arc cutting torch, similar to the plasma arc welding torch, is
shown in figure 10-71. Three variations of the process exist: low current plasma
cutting, high current plasma cutting, and cutting with water added. Low current
arc cutting, which produces high-quality cuts of thin materials, uses a maximum of
100 amperes and a much smaller torch than the high current version. Modifications
of processes and equipment have been developed to permit use of oxygen in the orifice gas to allow efficient cutting of steel. All plasma torches constrict the
arc by passing it through an orifice as it travels away from the electrode toward
the workpiece. As the orifice gas passes through the arc, it is heated rapidly to
a high temperature, expands and accelerates as it passes through the constricting
orifice. The intensity and velocity of the arc plasma gas are determined by such
variables as the type of orifice gas and its entrance pressure, constricting orifice shape and diameter, and the plasma energy density on the work.
10-102
TC 9-237
10-15.
PLASMA ARC CUTTING (PAC) (cont)
b. Equipment. Plasma arc cutting requires a torch, a control unit, a power
supply, one or more cutting gases, and a supply of clean cooling water. Equipment
is available for both manual and mechanized PAC.
(1) Cutting torch. A cutting torch consists of an electrode holder which
centers the electrode tip with respect to the orifice in the constricting nozzle.
The electrode and nozzle are water cooled to prolong their lives. Plasma gas is
injected into the torch around the electrode and exits through the nozzle orifice.
Nozzles with various orifice diameters are available for each type of torch. Orifice diameter depends on the cutting current; larger diameters are required at
higher currents. Nozzle design depends on the type of PAC and the metal being
cut. Both single and multiple port nozzles may be used for PAC. Multiple port
nozzles have auxiliary gas ports arranged in a circle around the main orifice. All
of the arc plasma passes through the main orifice with a high gas flew rate per
unit area. These nozzles produce better quality cuts than single port nozzles at
equivalent travel speeds. However, cut quality decreases with increasing travel
speed. Torch designs for introducing shielding gas or water around the plasma
flame are available. PAC torches are similar in appearance to gas tungsten arc
welding electrode holders, both manual and machine types. Mechanized PAC torches
are mounted on shape cutting machines similar to mechanized oxyfuel gas shape cutting equipment. Cutting may be controlled by photoelectric tracing, numerical
control, or computer.
(2) Controls. Control consoles for PAC may contain solenoid valves to turn
gases and cooling water on and off. They usually have flowmeters for the various
types of cutting gases used and a water flow switch to stop the operation if cooling water flow falls below a safe limit. Controls for high-power automatic PAC may
also contain programnin g features for upslope and downslope of current and orifice
gas flow.
(3) Power sources. Power sources for PAC are specially
open-circuit voltages in the range of 120 to 400 V. A power
the basis of the design of PAC torch to be used, the type and
metal, and the cutting speed range. Their volt-ampere output
be the typical drooping type.
designed units with
source is selected on
thickness of the work
characteristic must
(a) Heavy cutting requires high open-circuit voltage (400 V) for capability
of piercing material as thick as 2 in. (51 mm). Low current, manual cutting equipment uses lower open-circuit voltages (120 to 200 V). Some power sources have the
connections necessary to change the open-circuit voltage as required for specific
applications.
(b) The output current requirements range from about 70 to 1000 A depending
on the material, its thickness, and cutting speed. The unit may also contain the
pilot arc and high frequency power source circuitry.
(4) Gas selection.
(a) Cutting gas selection depends on the material being cut and the cut
surface quality requirements. Most nonferrous metals are cut by using nitrogen,
nitrogen-hydrogen mixtures, or argon-hydrogen mixtures. Titanium and zirconium are
10-104
‘TC 9-237
(b) Carbon steels are cut by using compressed air (80 percent N2, 20 percent 0 2 ) or nitrogen for plasma gas. Nitrogen is used with the water injection
method of PAC. Some systems use nitrogen for the plasma forming gas with oxygen
injected into the plasma downstream of the electrode. This arrangement prolongs
the life of the electrode by not exposing it to oxygen.
(c) For some nonferrous cutting with the dual flow system, nitrogen is used
for the plasma gas with carbon dioxide (C0 2 ) for shielding. For better quality
cuts, argon-hydrogen plasma gas and nitrogen shielding are used.
c.
Principles of Operation.
(1) The basic plasma arc cutting circuitry is shown in figure 10-72. The
process operates on direct current, straight polarity (dcsp), electrode negative,
with a constricted transferred arc. In the transferred arc mode, an arc is struck
between the electrode in the torch and the workpiece. The arc is initiated by a
pilot arc between the electrode and the constricting nozzle. The nozzle is connect–
ed to ground (positive) through a current limiting resistor and a pilot arc relay
contact. The pilot arc is initiated by a high frequency generator connected to the
electrode and nozzle. The welding power supply then maintains this low current arc
inside the torch. Ionized orifice gas from the pilot arc is blown through the
constricting nozzle orifice. This forms a low resistance path to ignite the main
arc between the electrode and the workpiece. When the main arc ignites, the pilot
arc relay may be opened automatically to avoid unnecessary heating of the constricting nozzle.
10-105
TC 9-237
10-15.
PLASMA ARC CUTTING (PAC) (cont)
cut with pure argon because of their susceptibility to embrittlement by reactive
gases.
(2) Because the plasma constricting nozzle is exposed to the high plasma
flare temperatures (estimated at 18,032 to 25,232 °F (10,000 to 14,000° C)), the
nozzle must be made of water-cooled copper. In addition, the torch should be designed to produce a boundary layer of gas between the plasma and the nozzle.
(3) Several process variations are used to improve the PAC quality for particular applications. They are generally applicable to materials in the 1/8 to 1-1/2
in. (3 to 38 mm) thickness range. Auxiliary shielding, in the form of gas or water, is used to improve cutting quality.
(a) Dual flow plasma cutting. Dual flow plasma cutting provides a secondary gas blanket around the arc plasma, as shown in figure 10-73. The usual orifice gas is nitrogen. The shielding gas is selected for the material to be cut.
For mild steel, it may be carbon dioxide (CO 2 ) or air; for stainless steals, CO 2 ;
and an argon-hydrogen mixture for aluminum. For mild steel, sutting speeds are
slightly faster than with conventional PAC, but the cut quality is not satisfactory
for many applications.
(b) Water shield plasma cutting. This technique is similar to dual flow
plasma cutting. Water is used in place of the auxiliary shielding gas. Cut appearance and nozzle life are improved by the use of water in place of gas for auxiliary
shielding. Cut squareness and cutting speed are not significantly improved over
conventional PAC.
10-106
TC 9-237
(c) Water injection plasma cutting. This modification of the PAC process
uses a symmetrical impinging water jet near the constricting nozzle orifice to
further constrict the plasma flame. The arrangement is shown in figure 10-74. The
water jet also shields the plasma from mixing with the surrounding atmosphere. The
end of the nozzle can be made of ceramic, which helps to prevent double arcing.
The water constricted plasma produces a narrow, sharply defined cut at speeds above
those of conventional PAC. Because most of the water leaves the nozzle as a liquid
spray, it cools the kerf edge, producing a sharp corner. The kerf is clean. When
the orifice gas and water are injected in tangent, the plasma gas swirls as it
emerges from the nozzle and water jet. This can produce a high quality perpendicular face on one side of the kerf. The other side of the kerf is beveled. In shape
cutting applications, the direction of travel must be selected to produce a perpendicular cut on the part and the bevel cut on the scrap.
(4) For high current cutting, the torch is mounted on a mechanical carriage.
Automatic shape cutting can be done with the same equipment used for oxygen cutting, if sufficiently high travel speed is attainable. A water spray is used surrounding the plasma to reduce smoke and noise. Work tables containing water which
is in contact with the underside of the metal being cut will also reduce noise and
smoke.
(5) The plasma arc cutting torch can be used in all positions. It can also
be used for piercing holes and for gouging. The cutting torch is of special design
for cutting and is not used for welding.
(6) The metals usually cut with this process are the aluminums and stainless
steels. The process can also be used for cutting carbon steels, copper alloys, and
nickel alloys.
(7) Special controls are required to adjust both plasma and secondary gas
flow. Torch-cooling water is required and is monitored by pressure or flow switches for torch protection. The cooling system should be self-contained, which includes a circulating pump and a heat exchanger.
10-107
TC 9-237
10-15.
PLASMA ARC CUTTING (PAC) (cont)
(8) Plasma cutting torches will fit torch holders in automatic flame cutting
machines.
(9) The amount of gases and tines generated requires the use of local exhaust
for proper ventilation. Cutting should be done over a water reservoir so that the
particles removed from the cut will fall in the water. This will help reduce the
amount of fumes released into the air.
d. Applications. Plasma arc cutting can be used to cut any metal. Most applications are for carbon steel, aluminum, and stainless steel. It can be used for
stack cutting, plate beveling, shape cutting, and piercing.
WARNING
Ear protection must be worn when working with high-powered equipment.
(1) The noise level generated by the high-powered
able. The cutter must wear ear protection. The normal
protect the cutter from the arc must also be worn. This
ing, gloves, and helmet. The helmet should be equipped
glass lens.
equipment is uncomfortprotective clothing to
involves protective clothwith a shade no. 9 filter
(2) There are many applications for low-current plasma arc cutting, including
the cutting of stainless and aluminum for production and maintenance. Plasma cutting can also be used for stack cutting and it is more efficient than stack cutting
with the oxyacetylene torch. Low current plasma gouging can also be used for upgrading castings.
10-16.
AIR CARBON ARC CUTTING (AAC)
a. General. Air carbon arc cutting is an arc cutting process in which metals
to be cut are melted by the heat of a carbon arc. The molten metal is removed by a
blast of air. This is a method for cutting or removing metal by melting it with an
electric arc and then blowing away the molten metal with a high velocity jet of
compressed air. The air jet is external to the consumable carbon-graphite electrode. It strikes the molten metal immediately behind the arc. Air carbon arc
cutting and metal removal differ from plasma arc cutting in that they employ an
open (unconstricted) arc, which is independent of the gas jet. The air carbon arc
process is shown in figure 10-75.
10-108
b.
Equipment.
(1) The circuit diagram for air carbon arc cutting or gouging is shown by
figure 10-76.
Normally, conventional welding machines with constant current are
used. Constant voltage can be used with this process. When using a CV power
source, precautions must be taken to operate it within its rated output of current
and duty cycle. Alternating current power sources having conventional drooping
characteristics can also be used for special applications. AC type carbon electrodes must be used.
(2) Equipment required is shown by the block diagram. Special heavy duty
high current machines have been made specifically for the air carbon arc process.
This is because of extremely high currents used for the large size carbon elec–
trodes.
(3) The electrode holder is designed for the air carbon arc process. The
holder includes a small circular grip head which contains the air jets to direct
compressed air along the electrode. It also has a groove for gripping the electrode. This head can be rotated to allow different angles of electrode with respect to the holder. A heavy electrical lead and an air supply hose are connected
10-109
TC 9-237
10-16.
AIR CARBON ARC CUTTING (AAC) (cont)
to the holder through a terminal block. A valve is included in th holder for
turning the compressed air on and off. Holders are available in several sizes
depending on the duty cycle of the work performed, the welding current, and size of
carbon electrode used. For extra heavy duty work, water-cooled holders are used.
(4) The air pressure is not critical but should range from 80 to 100 psi (552
to 690 kPa). The volume of compressed air required ranges from as low as 5 cu ft
per min (2.5 liter per min) up to 50 cu ft per min (24 liter per min) for the largest-size carbon electrodes. A one-horsepower compressor will supply sufficient air
for smaller-size electrodes. It will require up to a ten-horsepower compressor
when using the largest-size electrodes.
(5) The carbon graphite electrodes are made of a mixture of carbon and graphite plus a binder which is baked to produce a homogeneous structure. Electrodes
come in several types.
(a) The plain uncoated electrode is less expensive, carries less current,
and starts easier.
(b) The copper-coated electrode provides better electrical conductivity
between it and the holder. The copper-coated electrode is better for maintaining
the original diameter during operation. It lasts longer and carries higher current. Copper-coated electrodes are of two types, the dc type and the ac type. The
composition ratio of the carbon and graphite is slightly different for these two
types. The dc type is more common. The ac type contains special elements to stabilize the arc. It is used for direct current electrode negative when cutting cast
irons. For normal use, the electrode is operated with the electrode positive.
Electrodes range in diameter from 5/32 to 1 in. (4.0 to 25.4 mm). Electrodes are
normally 12 in. (300 mm) long; however, 6 in. (150 mm) electrodes are available
Copper-coated electrodes with tapered socket joints are available.
operation, and allow continuous operation. Table 10-25 shows the electrode types
and the arc current range for different sizes.
10-110
TC 9-237
c.
Advantages and Major Uses.
(1) The air carbon arc cutting process is used to cut metal, to gouge out
defective metal, to remove old or inferior welds, for root gouging of full penetration welds, and to prepare grooves for welding. Air carbon arc cutting is used
when slightly ragged edges are not objectionable. The area of the cut is small
and, since the metal is melted and removed quickly, the surrounding area does not
reach high temperatures. This reduces the tendency towards distortion and cracking.
(2) The air carbon arc cutting and gouging process is normally manually operated. The apparatus can be mounted on a travel carriage. This is considered machine cutting or gouging. Special applications have been made where cylindrical
work has been placed on a lathe-like device and rotated under the air carbon arc
torch. This is machine or automatic cutting, depending on operator involvement.
(3) The air carbon arc cutting process can be used in all positions. It can
also be used for gouging in all positions. Use in the overhead position requires a
high degree of skill.
(4) The air carbon arc process can be used for cutting or gouging most of the
common metals. Metals include: aluminums, copper, iron, magnesium, and carbon and
stainless steels.
(5) The process
titanium, zirconium,
cleaning, usually by
adjacent to the cut.
remelting.
d.
is not recommended for weld preparation for stainless steel,
and other similar metals without subsequent cleaning. This
grinding, must remove all of the surface carbonized material
The process can be used to cut these materials for scrap for
Process Principles.
(1) The procedure schedule for making grooves in steel is shown in table
10-26, p 10-112.
(2) To make a cut or a gouging operation, the cutter strikes an arc and almost immediately starts the air flow. The electrode is -pointed in the direction of
travel with a push angle approximately 45° with the axis of the groove. The speed
of travel, the electrode angle, and the electrode size and current determine the
groove depth. Electrode diameter determines the groove width.
(3) The normal safety precautions similar to carbon arc welding and shielded
metal arc welding apply to air carbon arc cutting and gouging. However, two other
precautions must be observed. First, the air blast will cause the molten metal to
travel a very long distance. Metal deflection plates should be placed in front of
the gouging operation. All combustible materials should be moved away from the
work area. At high-current levels, the mass of molten metal removed is quite large
and will become a fire hazard if not properly contained.
(4) The second factor is the high noise level. At high currents with high
air pressure a very loud noise occurs. Ear protection , ear muffs or ear plugs
should be worn by the arc cutter.
10-111
TC 9-237
10-16.
AIR CARBON ARC CUTTING (AAC) (cont)
(5) The process is widely used for back gouging, preparing joints, and removing defective weld metal.
TC 9-237
10-17.
RESISTANCE WELDING
a. General. Resistance welding is a group of welding processes in which coalescence is produced by the heat obtained from resistance of the work to electric
current in a circuit of which the work is a part and by the application of pressure. There are at least seven important resistance-welding processes. These are
flash welding, high frequency resistance welding, percussion welding, projection
welding, resistance seam welding, resistance spot welding, and upset welding.
b.
Principles of the Process.
(1) The resistance welding processes differ from all those previously mentioned. Filler metal is rarely used and fluxes are not employed. Three factors
involved in making a resistance weld are the amount of current that passes through
the work, the pressure that the electrodes transfer to the work, and the time the
current flows through the work. Heat is generated by the passage of electrical
current through a resistance circuit. The force applied before, during, and after
the current flow forces the heated parts together so that coalescence will occur.
Pressure is required throughout the entire welding cycle to assure a continuous
electrical circuit through the work.
(2) This concept of resistance welding is most easily understood by relating
it to resistance spot welding. Resistance spot welding, the most popular, is shown
by figure 10-77. High current at a low voltage flows through the circuit and is in
accordance with Ohm’s law,
I = E or R = E
R
I
(a) I is the current in amperes, E is the voltage in volts, and R is the
resistance of the material in ohms. The total energy is expressed by the formula:
Energy equals I x E x T in which T is the time in seconds during which current
flows in the circuit.
10-113
TC 9-237
10-17.
RESISTANCE WELDING (cont)
2
(b) Combining these two equations gives H (heat energy) = 1 x R x T. For
practical reasons a factor which relates to heat losses should be included; therefore, the actual resistance welding formula is
H(heat energy) = I2 x R x T x K
(c) In this formula, I = current squared in amperes, R is the resistance of
the work in ohms, T is the time of current flow in seconds, and K represents the
heat losses through radiation and conduction.
(3) Welding heat is proportional to the square of the welding current. If
the current is doubled, the heat generated is quadrupled. Welding heat is proportional to the total time of current flow, thus, if current is doubled, the time can
be reduced considerably. The welding heat generated is directly proportional to
the resistance and is related to the material being welded and the pressure applied. The heat losses should be held to a minimum. It is an advantage to shorten
welding tire. Mechanical pressure which forces the parts together helps refine the
grain structure of the weld.
(4) Heat is also generated at the contact between the welding electrodes and
the work. This amount of heat generated is lower since the resistance between high
conductivity electrode material and the normally employed mild steel is less than
that between two pieces of mild steel. In most applications, the electrodes are
water cooled to minimize the heat generated between the electrode and the work.
(5) Resistance welds are made very quickly; however, each process has its own
time cycle.
(6) Resistance welding operations are automatic. The pressure is applied by
mechanical, hydraulic, or pneumatic systems. Motion, when it is involved, is applied mechanically. Current control is completely automatic once the welding operator initiates the weld. Resistance welding equipment utilizes programmers for
controlling current, time cycles, pressure, and movement. Welding programs for
resistance welding can become quite complex. In view of this, quality welds do not
depend on welding operator skill but more on the proper set up and adjustment of
the equipment and adherence to weld schedules.
(7) Resistance welding is used primarily in the mass production industries
where long production runs and consistent conditions can be maintained. Welding is
performed with operators who normally load and unload the welding machine and operate the switch for initiating the weld operation. The automotive industry is the
major user of the resistance welding processes, followed by the appliance industry. Resistance welding is used by many industries manufacturing a variety of
products made of thinner guage metals. Resistance welding is also used in the
steel industry for manufacturing pipe, tubing and smaller structural sections.
Resistance welding has the advantage of producing a high volume of work at high
speeds and does not require filler materials. Resistance welds are reproducible
and high-quality welds are normal.
(8) The position of making resistance welds is not a factor, particularly in
the welding of thinner material.
10-114
TC 9-237
c.
Weldable Metals.
(1) Metals that are weldable, the thicknesses that can be welded, and joint
design are related to specific resistance welding processes. Most of the common
metals can be welded by many of the resistance welding processes (see table 1027) . Difficulties may be encountered when welding certain metals in thicker sections. Some metals require heat treatment after welding for satisfactory mechanical properties.
(2) Weld ability is controlled by three factors:
tivity, and melting temperature.
resistivity,
thermal
conduc-
(3) Metals with a high resistance to current flow and with a low thermal
conductivity and a relatively low melting temperature would be easily weldable.
Ferrous metals all fall into this category. Metals that have a lower resistivity
but a higher thermal conductivity will be slightly more difficult to weld. This
includes the light metals, aluminum and magnesium. The precious metals comprise
the third group. These are difficult to weld because of very high thermal conduct i v i t y . The fourth group is the refractory metals, which have extremely high melting points and are more difficult to weld.
(4) These three properties can be combined into a formula which will provide
an indication of the ease of welding a metal. This formula is:
In this formula, W equals weldability, R is resistivity, and F is the melting temperature of the metal in degrees C, and Kt is the relative thermal conductivity
with copper equal to 1.00. If weldability (W) is below 0.25, it is a poor rating.
10-115
TC 9-237
10-17.
RESISTANCE WELDING (cont)
If W is between 0.25 and 0.75, weldability becomes fair. Between 0.75 and 2.0,
weldability is good. Above 2.0 weldability is excellent. In this formula, mild
steel would have a weldability rating of over 10. Aluminum has a weldability factor of from 1 to 2 depending on the alloy and these are considered having a good
weldability rating. Copper and certain brasses have a low weldability factor and
are known to be very difficult to weld.
10-18.
a.
FLASH WELDING (FW)
General.
(1) Flash welding is a resistance welding process which produces coalescence
simultaneously over the entire area of abutting surfaces by the heat obtained from
resistance to electric current between the two surfaces, and by the application of
pressure after heating is substantially completed. Flashing and upsetting are
accompanied by expulsion of metal from the joint. This is shown by figure 10-78.
During the welding operation, there is an intense flashing arc and heating of the
metal on the surfaces abutting each other. After a predetermined time, the two
pieces are forced together and joining occurs at the interface. Current flow is
possible because of the light contact between the two parts being flash welded.
Heat is generated by the flashing and is localized in the area between the two
parts. The surfaces are brought to the melting point and expelled through the
abutting area. As soon as this material is flashed away, another small arc is
formed which continues until the entire abutting surfaces are at the melting temperrature. Pressure is then applied. The arcs are extinguished and upsetting occurs.
10-116
TC 9-237
(2) Flash welding can be used on most metals. No special preparation is
required except that heavy scale, rust, and grease must be removed. The joints
must be cut square to provide an even flash across the entire surface. The material to be welded is clamped in the jaws of the flash welding machine with a high
clamping pressure. The upset pressure for steel exceeds 10,000 psi (68, 950 kPa).
For high-strength materials, these pressures may be doubled. For tubing or hollow
members, the pressures are reduced. As the weld area is more compact, upset pressures are increased. If insufficient upset pressure is used, a porous low strength
weld will result. Excess upset pressure will result in expelling too much weld
metal and upsetting cold metal. The weld may not be uniform across the entire
cross section, and fatigue and impact strength will be reduced. The speed of upset, or the time between the end of flashing period and the end of the upset period,
should be extremely short to minimize oxidation of the molten surfaces. In the
flash welding operation, a certain amount of material is flashed or burned away.
The distance between the jaws after welding compared to the distance before welding
is known as the burnoff. It can be from 1/8 in. (3.2 mm) for thin material up to
several inches for heavy material. Welding currents are high and are related to
the following: 50 kva per square in. cross section at 8 seconds. It is desirable
to use the lowest flashing voltage at a desired flashing speed. The lowest voltage
is normally 2 to 5 volts per square in. of cross section of the weld.
(3) The upsetting force is usually accomplished by means of mechanical cam
action. The design of the cam is related to the size of the parts being welded.
Flash welding is completely automatic and is an excellent process for mass-produced
parts. It requires a machine of large capacity designed specifically for the parts
to be welded. Flash welds produce a fin around the periphery of the weld which is
normally removed.
10-19.
a.
FRICTION WELDING (FRW)
General.
(1) Friction welding is a solid state welding process which produces coalescence of materials by the heat obtained from mechanically-induced sliding motion
between rubbing surfaces. The work parts are held together under pressure. This
process usually involves the rotating of one part against another to generate frictional heat at the junction. When a suitable high temperature has keen reached,
rotational notion ceases. Additional pressure is applied and coalescence occurs.
(2) There are two variations of the friction welding process. They are described below.
(a) In the original process, one part is held stationary and the other part
is rotated by a motor which maintains an essentially constant rotational speed.
The two parts are brought in contact under pressure for a specified period of time
with a specific pressure. Rotating power is disengaged from the rotating piece and
the pressure is increased. When the rotating piece stops, the weld is completed.
This process can be accurately controlled when speed, pressure, and time are closely regulated.
10-117
TC 9-237
10-19.
FRICTION WELDING (FRW) (cont)
(b) The other variation is inertia welding. A flywheel is revolved by a
motor until a preset speed is reached. It, in turn, rotates one of the pieces to
be welded. The motor is disengaged from the flywheel and the other part to be
welded is brought in contact under pressure with the rotating piece. During the
predetermined time during which the rotational speed of the part is reduced, the
flywheel is brought to an immediate stop. Additional pressure is provided to complete the weld.
(c) Both methods utilize frictional heat and produce welds of similar quality. Slightly better control is claimed with the original process. The two methods
are similar, offer the same welding advantages, and are shown by figure 10-79.
10-118
TC 9-237
b.
Advantages.
(1) Friction welding can produce high quality welds in a short cycle time.
(2) No filler metal is required and flux is not used.
(3) The process is capable of welding most of the common metals. It can also
be used to join many combinations of dissimilar metals. Friction welding requires
relatively expensive apparatus similar to a machine tool.
c.
Process Principles.
(1) There are three important factors involved in making a friction weld:
(a) The rotational speed which is related to the material to be welded and
the diameter of the weld at the interface.
(b) The pressure between the two parts to be welded. Pressure changes
during the weld sequence. At the start, pressure is very low, but is increased to
create the frictional heat. When the rotation is stopped, pressure is rapidly
increased so forging takes place immediately before or after rotation is stopped.
(c) The welding time is related to the shape and the type of metal and the
surface area. It is normally a matter of a few seconds. The actual operation of
the machine is automatic. It is controlled by a sequence controller, which can be
set according to the weld schedule established for the parts to be joined.
(2) Nomally for friction welding, one of the parts to be welded is round in
cross section. This is not an absolute necessity. Visual inspection of weld quality can be based on the flash, which occurs around the outside perimeter of the
weld. This flash will usually extend beyond the outside diameter of the parts and
will curl around back toward the part but will have the joint extending beyond the
outside diameter of the part.
(a) If the flash sticks out relatively straight from the joint, it indicates that the welding time was too short, the pressure was too low, or the speed
was too high. These joints may crack.
(b) If the flash curls too far back on the outside diameter, it indicates
that the the was too long and the pressure was too high.
(c) Between these extremes is the correct flash shape.
ly remved after welding.
The flash is normal-
10-119
TC 9-237
10-20. ELECTRON BEAM WELDING
a.
General.
(1) Electron beam welding (EBW) is a welding process which produces coalescence of metals with heat from a concentrated beam of high velocity electrons striking the surfaces to be joined. Heat is generated in the workpiece as it is bomarded by a dense stream of high-velocity electrons. Virtually all of the kinetic
energy, or the energy of motion, of the electrons is transformed into heat upon
impact .
(2) Two basic designs of this process are: the low-voltage electron beam
system, which uses accelerating voltages in 30,000-volt (30 kv) to 60,000-volt (60
kv) range, and the high voltage system with accelerating voltages in the
100,000-volt (100 kv) range. The higher voltage system emits more X-rays than the
lower voltage system. In an X-ray tube, the beam of electrons is focused on a target of either tungsten or molybdenum which gives off X-rays. The target becomes
extremely hot and must be water cooled. In welding, the target is the base metal
which absorbs the heat to bring it to the molten stage. In electron beam welding,
X-rays may be produced if the electrical potential is sufficiently high. In both
systems, the electron gun and the workpiece are housed in a vacuum chamber. Figure
10-80 shows the principles of the electron beam welding process
b.
Equipment.
(1) There are three basic components in an electron beam welding machine.
These are the electron beam gun, the power supply with controls, and a vacuum work
chamber with work-handling equipment.
10-120
TC 9-237
(2) The electron beam gun emits electrons, accelerates the beam of electrons,
and focuses it on the workpiece. The electron beam gun is similar to that used in
a television picture tube. The electrons are emitted by a heated cathode or filament and accelerated by an anode which is a positively-charged plate with a hole
through which the electron beam passes. Magnetic focusing coils located beyond the
anode focus and deflect the electron beam.
(3) In the electron beam welding machine, the electron beam is focused on the
workpiece at the point of welding. The power supply furnishes both the filament
current and the accelerating voltage. Both can be changed to provide different
power input to the weld.
(4) The vacuum work chamber must be an absolutely airtight container. It is
evacuated by means of mechanical pumps and diffusion pumps to reduce the pressure
to a high vacuum. Work-handling equipnent is required to move the workpiece under
the electron beam and to manipulate it as required to make the weld. The travel
mechanisms must be designed for vacuum installations since normal greases, lubricants, and certain insulating varnishes in electric rotors may volatilize in a
vacuum. Heretically sealed motors and sealed gearboxes must be used. In some
cases, the rotor and gearboxes are located outside the vacuum chamber with shafts
operating through sealed bearings.
c. Advantages. One of the major advantages of electron beam welding is its
tremendous penetration. This occurs when the highly accelerated electron hits the
base metal. It will penetrate slightly below the surface and at that point release
the bulk of its kinetic energy which turns to heat energy. The addition of the
heat brings about a substantial temperature increase at the point of impact. The
succession of electrons striking the same place causes melting and then evaporation
of the base metal. This creates metal vapors but the electron beam travels through
the vapor much easier than solid metal. This causes the beam to penetrate deeper
into the base metal. The width of the penetration pattern is extremely narrow.
The depth-to-width can exceed a ratio of 20 to 1. As the power density is in–
creased, penetration is increased. Since the electron beam has tremendous penetrating characteristics, with the lower heat input, the heat affected zone is much
smaller than that of any arc welding process. In addition, because of the almost
parallel sides of the weld nugget, distortion is very greatly minimized. The cooling rate is much higher and for many metals this is advantageous; however, for high
carbon steel this is a disadvantage and cracking may occur.
d.
Process Principles.
(1) Recent advances in equipment allow the work chamber to operate at a medium vacuum or pressure. In this system, the vacuum in the work chamber is not as
high. It is sometimes called a “soft” vacuum This vacuum range allowed the same
contamination that would be obtained in atmosphere of 99.995 percent argon. Mechanical pumps can produce vacuums to the medium pressure level.
(2) Electron beam welding was initially done in a vacuum because the electron
beam is easily deflected by air. The electrons in the beam collide with the molecules of the air and lose velocity and direction so that welding can not be performed .
10-121
TC 9-237
10-20.
ELECTRON BEAM WELDING (cont)
(3) In a high vacuum system, the electron beam can be located as far as 30.0
in. (762.0 mm) away from the workpiece. In the medium vacuum, the working distance
is reduced to 12.0 in. (304.8 mm). The thickness that can be welded in a high
vacuum is up to 6.0 in. (152.4 mm) thick while in the medium vacuum the thickness
that can be welded is reduced to 2.0 in. (50.8 mm). This is based on the same
electron gun and power in both cases. With the medium vacuum, pump down time is
reduced. The vacuum can be obtained by using mechanical pumps only. In the medium
vacuum mode, the electron gun is in its own separate chamber separate from the
work chamber by a small orifice through which the electron beam travels. A diffusion vacuum pump is run continuously, connected to the chamber containing the electron gun, so that it will operate efficiently.
(4) The most recent development is the nonvacuum electron beam welding system. In this system, the work area is maintained at atmospheric pressure during
welding. The electron beam gun is housed in a high vacuum chamber. There are
several intermediate chambers between the gun and the atmospheric work area. Each
of these intermediate stages is reduced in pressure by means of vacuum pumps. The
electron beam passes from one chamber to another through a small orifice large
enough for the electron beam but too small for a large volume of air. By means of
these differential pressure chambers, a high vacuum is maintained in the electron
beam gun chamber. The nonvacuum system can thus be used for the largest weldments,
however the workpiece must be positional with 1-1/2 in. (38 mm) of the beam exit
nozzle. The maximum thickness that can be welded currently is approximately 2 in.
(51 mm). The nonvacuum system utilizes the high-voltage power supply.
(5) The heat input of electron beam welding is controlled by four variables:
(a)
Number of electrons per second hitting the workpiece or beam current.
(b)
Electron speed at the moment of impact, the accelerating potential.
(c)
Diameter of the beam at or within the workpiece, the beam spot size.
(d)
Speed of travel or the welding speed.
(6) The first two variables in (5), beam current and accelerating potential,
are used in establishing welding parameters. The third factor, the beam spot size,
is related to the focus of the beam, and the fourth factor is also part of the
procedure. The electron beam current ranges from 250 to 1000 milliamperes, the
beam currents can be as low as 25 milliamperes. The accelerating voltage is within
the two ranges mentioned previously. Travel speeds can be extremely high and relate to the thickness of the base metal. The other parameter that must be controlled is the gun-to-work distance.
(7) The beam spot size can be varied by the location of the fecal point with
respect to the surface of the part. Penetration can be increased by placing the
fecal point below the surface of the base metal. As it is increased in depth below
the surface, deeper penetration will result. When the beam is focused at the surface, there will be more reinforcement on the surface. When the beam is focused
above the surface, there will be excessive reinforcement and the width of the weld
will be greater.
10-122
TC 9-237
(8) Penetration is also dependent on the beam current. As beam current is
increased, penetration is increased. The other variable, travel speed, also affects penetration. As travel speed is increased, penetration is reduced.
(9) The heat input produced by electron beam welds is relatively small compared to the arc welding processes. The power in an electron beam weld compared
with a gas metal arc weld would be in the same relative amount. The gas metal arc
weld would require higher power to produce the same depth of penetration. The
energy in joules per inch for the electron beam weld may be only 1/10 as great as
the gas metal arc weld. The electron beam weld is equivalent to the SMAW weld with
less power because of the penetration obtainable by electron
beam welding. The
2
power density is in the range of 100 to 10,000 kw/in .
(10) The weld joint details for electron beam welding must be selected with
care. In high vacuum chamber welding, special techniques must be used to properly
align the electron beam with the joint. Welds are extremely narrow. Preparation
for welding must be extremely accurate. The width of a weld in 1/2 in. (12.7 mm)
thick stainless steel would only be 0.04 in. (1.00 mm). Small misalignment would
cause the electron beam to completely miss the weld joint. Special optical systems
are used which allow the operator to align the work with the electron beam. The
electron beam is not visible in the vacuum. Welding joint details normally used
with gas tungsten arc welding can be used with electron beam welding. The depth to
width ratio allows for special lap type joints. Where joint fitup is not precise,
ordinary lap joints are used and the weld is an arc seam type of weld. Normally,
filler metal is not used in electron beam welding; however, when welding mild steel
highly deoxidized filler metal is sometimes used. This helps deoxidize the molten
metal and produce dense welds.
(11 ) In the case of the medium vacuum system, much larger work chambers can be
used. Newer systems are available where the chamber is sealed around the part to
be welded. In this case, it has to be designed specifically for the job at hand.
The latest uses a sliding seal and a movable electron beam gun. In other versions
of the medium vacuum system, parts can be brought into and taken out of the vacuum
work chamber by means of interlocks so that the process can be made more or less
continuous. The automotive industry is using this system for welding gear clusters
and other small assemblies of completely machined parts. This can be done since
the distortion is minimal.
(12) The non-vacuum system is finding acceptance for other applications. One
of the most productive applications is the welding of automotive catalytic converters around the entire periphery of the converter.
(13) The electron beam process is becoming increasingly popular where the cost
of equipment can be justified over the production of many parts. It is also used
to a very great degree in the automatic energy industry for remote welding and for
welding the refractory metals. Electron beam welding is not a cure-all; there are
still the possibilities of defects of welds in this process as with any other. The
major problem is the welding of plain carbon steel which tends to become porous
when welded in a vacuum. The melting of the metal releases gases originally in the
metal and results in a porous weld. If deoxidizers cannot be used, the process is
not suitable.
10-123
TC 9-237
10-20. ELECTRON BEAM WELDING (cont)
e.
Weldable Metals.
Almost all metals can be welded with the electron beam welding process. The metals
that are most often welded are the super alloys, the refractory metals, the reactive metals, and the stainless steels. Many combinations of dissimilar metals can
also be welded.
10-21.
a.
LASER BEAM WELDING (LBW)
General.
(1) Laser beam welding (LBW) is a welding process which produces coalescence
of materials with the heat obtained from the application of a concentrate coherent
light beam impinging upon the surfaces to be joined.
(2) The focused laser beam has the highest energy concentration of any known
source of energy. The laser beam is a source of electromagnetic energy or light
that can be pro jetted without diverging and can be concentrated to a precise spot.
The beam is coherent and of a single frequency.
(3) Gases can emit coherent radiation when contained in an optical resonant
cavity. Gas lasers can be operated continuously but originally only at low levels
of power. Later developments allowed the gases in the laser to be cooled so that
it could be operated continuously at higher power outputs. The gas lasers are
pumped by high radio frequency generators which raise the gas atoms to sufficiently
high energy level to cause lasing. Currently, 2000-watt carbon dioxide laser systems are in use. Higher powered systems are also being used for experimental and
developmental work. A 6-kw laser is being used for automotive welding applications
and a 10-kw laser has been built for research purposes. There are other types of
lasers; however, the continuous carbon dioxide laser now available with 100 watts
to 10 kw of power seems the most promising for metalworking applications.
(4) The coherent light emitted by the laser can be focused and reflected in
the same way as a light beam. The focused spot size is controlled by a choice of
lenses and the distance from it to the base metal. The spot can be made as small
as 0.003 in. (O. 076 mm) to large areas 10 times as big. A sharply focused spot is
used for welding and for cutting. The large spot is used for heat treating.
(S) The laser offers a source of concentrated energy for welding; however,
there are only a few lasers in actual production use today. The high-powered laser
is extremely expensive. Laser welding technology is still in its infancy so there
will be improvements and the cost of equipment will be reduced. Recent use of
fiber optic techniques to carry the laser beam to the point of welding may greatly
expand the use of lasers in metal-working.
b.
Welding with Lasers.
(1) The laser can be compared to solar light beam for welding. It can be
used in air. The laser beam can be focused and directed by special optical lenses
and mirrors. It can operate at considerable distance from the workpiece.
10-124
TC 9-237
(2) When using the laser beam for welding, the electromagnetic radiation
impinges on the surface of the base metal with such a concentration of energy that
the temperature of the surface is melted vapor and melts the metal below. One of
the original questions concerning the use of the laser was the possibility of reflectivity of the metal so that the beam would be reflected rather than heat the
base metal. It was found, however, that once the metal is raised to its melting
temperature, the surface conditions have little or no effect.
(3) The distance from the optical cavity to the base metal has little effect
on the laser. The laser beam is coherent and it diverges very little. It can be
focused to the proper spot size at the work with the same amount of energy available, whether it is close or far away.
(4) With laser welding, the molten meta1 takes on a radial configuration
similar to convectional arc welding. However, when the power density rises above a
certain threshold level, keyholing occurs, as with plasma arc welding. Keyholing
provides for extremely deep penetration. This provides for a high depth-to-width
ratio. Keyholing also minimizes the problem of beam reflection from the shiny
molten metal surface since the keyhole behaves like a black body and absorbs the
majority of the energy. In some applications, inert gas is used to shield the
molten metal from the atmosphere. The metal vapor that occurs may cause a break–
down of the shielding gas and creates a plasma in the region of high-beam intensity
just above the metal surface. The plasma absorbs energy from the laser beam and
can actually block the beam and reduce melting. Use of an inert gas jet directed
along the metal surface eliminates the plasma buildup and shields the surface from
the atmosphere.
(5) The welding characteristics of the laser and of the electron beam are
similar. The concentration of energy 6y both beams is similar with the laser having a power density in the order of 10 watts per square centimeter. The power
density of the electron 4 beam is only slightly greater. This is compared to a current density of only 10 watts per square centimeter for arc welding.
(6) Laser beam welding has a tremendous temperature differential between the
molten metal and the base metal immediately adjacent to the weld. Heating and
cooling rates are much higher in laser beam welding than in arc welding, and the
heat-affected zones are much smaller. Rapid cooling rates can create problems such
as cracking in high carbon steels.
(7) Experimental work with the laser beam welding process indicates that the
normal factors control the weld. Maximum penetration occurs when the beam is focused slightly below the surface. Penetration is less when the beam is focused on
the surface or deep within the surface. As power is increased the depth of penetration is increased.
c. Weldable Metals. The laser beam has been used to weld carbon steels, high
strength 1ow alloy steels, aluminum, stainless steel, and titanium. Laser welds
made in these materials are similar in quality to welds made in the same materials
by electron beam process. Experimental work using filler metal is being used to
weld metals that tend to show porosity when welded with either EB or LB welding.
Materials 1/2 in. (12.7 mm) thick are being welded at a speed of 10.0 in. (254.0
mm) per minute.
10-125(10-126 blank)
TC 9-237
CHAPTER 11
OXYGEN FUEL GAS WELDING PROCEDURES
Section I. WELDING PROCESSES AND TECHNIQUES
11-1.
a.
GENERAL GAS WELDING PROCDURES
General.
(1) Oxyfuel gas welding (OEW) is a group of welding processes which join
metals by heating with a fuel gas flame or flares with or without the application
of pressure and with or without the use of filler metal. OFW includes any welding
operation that makes use of a fuel gas combined with oxygen as a heating medium.
The process involves the melting of the base metal and a filler metal, if used, by
means of the flame produced at the tip of a welding torch. Fuel gas and oxygen are
mixed in the proper proportions in a mixing chamber which may be part of the welding tip assembly. Molten metal from the plate edges and filler metal, if used,
intermix in a common molten pool. Upon cooling, they coalesce to form a continuous
piece.
(2) There are three major processes within this group: oxycetylene welding,
oxyhydrogen welding, and pressure gas welding. There is one process of minor industrial significance, known as air acetylene welding, in which heat is obtained from
the combustion of acetylene with air. Welding with methylacetone-propadiene gas
(MAPP gas) is also an oxyfuel procedure.
b.
Advantages.
(1) One advantage of this welding process is the control a welder can exercise over the rate of heat input, the temperature of the weld zone, and the oxidizing or reducing potential of the welding atmosphere.
(2) Weld bead size and shape and weld puddle viscosity are also controlled in
the welding process because the filler metal is added independently of the welding
heat source.
(3) OFW is ideally suited to the welding of thin sheet, tubes, and small
diameter pipe. It is also used for repair welding. Thick section welds, except
for repair work, are not economical.
c.
Equipment .
(1) The equipment used in OFW is low in cost , usually portable, and versatile
enough to be used for a variety of related operations, such as bending and straightening, preheating, postheating, surface, braze welding, and torch brazing. With
relatively simple changes in equipment, manual and mechanized oxygen cutting operations can be performed. Metals normally welded with the oxyfuel process include
steels, especially low alloy steels , and most nonferrous metals. The process is
generally not used for welding refractory or reactive metals.
11-1
TC 9-237
11-1. GENERAL GAS WELDING PROCEDURES (cont)
d.
Gases.
(1) Commercial fuel gases have one common property: they all require oxygen
to support combustion. To be suitable for welding operations, a fuel gas, when
burned with oxygen, must have the following:
(a) High flare temperature.
(b) High rate of flame propagation.
(c) Adequate heat content.
(d)
Minimum chemical reaction of the flame with base and filler metals.
(2) Among the commercially available fuel gases, acetylene most closely meets
all these requirements. Other gases, fuel such as MAPP gas, propylene, propane,
natural gas, and proprietary gases based on these, have sufficiently high flame
temperatures but exhibit low flame propagation rates. These gas flames are excessively oxidizing at oxygen-to-fuel gas ratios high enough to produce usable heat
transfer rates. Flame holding devices, such as counterbores on the tips, are necessary for stable operation and good heat transfer, even at the higher ratios. These
gases, however, are used for oxygen cutting. They are also used for torch brazing,
soldering, and many other operations where the demands upon the flame characteristics and heat transfer rates are not the same as those for welding.
e. Base Metal Preparation.
(1) Dirt, oil, and oxides can cause incomplete fusion, slag inclusions, and
porosity in the weld. Contaminants must be removed along the joint and sides of
the base metal.
(2) The root opening for a given thickness of metal should permit the gap to
be bridged without difficulty, yet it should be large enough to permit full penetration. Specifications for root openings should be followed exactly.
(3) The thickness of the base mteal at the joint determines the type of edge
preparation for welding. Thin sheet metal is easily melted completelv by the
flame. Thus, edges with square faces can be butted-together and welded. This type
of joint is limited to material under 3/16 in. (4.8 mm) in thickness. For
thicknesses of 3/16 to ¼ in. (4.8 to 6.4 mm), a slight root opening or groove is
necessary for complete penetration, but filler metal must be added to compensate
for the opening.
(4) Joint edges ¼ in. (6.4 mm) and thicker should be beveled. Beveled
edges at the joint provide a groove for better penetration and fusion at the
sides. The angle of bevel for oxyacetylene welding varies from 35 to 45 degrees,
which is equivalent to a variation in the included angle of the joint from 70 to 90
degrees, depending upon the application. A root face 1/16 in. (1.6 mm) wide is
normal, but feather edges are sometimes used. Plate thicknesses ¾ in. (19 mm)
11-2
TC 9-237
and above are double beveled when welding can be done from both sides. The root
face can vary from O to 1/8 in. (O to 3.2 mm). Beveling both sides reduces the
amount of filler metal required by approximately one-half. Gas consumption per
unit length of weld is also reduced.
(5) A square groove edge preparation is the easiest to obtain. This edge can
be machined, chipped, ground, or oxygen cut. The thin oxide coating on oxygen-cut
surface does not have to be removed, because it is not detrimental to the welding
operation or to the quality of the joint. A bevel angle can be oxygen cut.
f.
Multiple Layer Welding.
(1) Multiple layer welding is used when maximum ductility of a steel weld in
the as-welded or stress-relieved condition is desired, or when several layers are
required in welding thick metal. Multiple layer welding is done by depositing
filler metal in successive passes along the joint until it is filled. Since the
area covered with each pass is small, the weld puddle is reduced in size. This
procedure enables the welder to obtain complete joint penetration without excessive
penetration and overheating while the first few passes are being deposited. The
smaller puddle is more easily controlled. The welder can avoid oxides, slag inclusions, and incomplete fusion with the base metal.
(2)
ductility
unless an
bring the
g.
Grain refinement in the underlying passes as they are reheated increases
in the deposited steel. The final layer will not have this refinement
extra pass is added and removed or the torch is passed over the joint to
last deposit up to normalizing temperature.
Weld Quality.
(1) The appearance of a weld does not necessarily indicate its quality.
Visual examination of the underside of a weld will determine whether there is complete penetration or whether there are excessive globules of metal. Inadequate
joint penetration may be due to insufficient beveling of the edges, too wide a root
face, too great a welding speed, or poor torch and welding rod manipulation.
(2) Oversized and undersized welds can be observed readily. Weld gauges are
available to determine whether a weld has excessive or insufficient reinforcement.
Undercut or overlap at the sides of the welds can usually be detected by visual
inspection.
(3) Although other discontinuities, such as incomplete fusion, porosity, and
cracking may or may not be apparent, excessive grain growth or the presence of hard
spots cannot be determined visually. Incomplete fusion may be caused by insufficient heating of the base metal, too rapid travel, or gas or dirt inclusions.
Porosity is a result of entrapped gases, usually carbon monoxide, which may be
avoided by more careful flame manipulation and adequate fluxing where needed. Hard
spots and cracking are a result of metallurgical characteristics of the weldment.
11-3
TC 9-237
11-1.
h.
GENERAL GAS WELDING PROCEDURES (cont)
Welding With Other Fuel Gases.
(1) Principles of operation.
(a) Hydrocarbon gases, such as propane, butane, city gas, and natural gas,
are not suitable for welding ferrous materials due to their oxidizing characterist i c s . In some instances, many nonferrous and ferrous metals can be braze welded
with care taken in the adjustment of flare and the use of flux. It is important to
use tips designed for the fuel gas being employed. These gases are extensively
used for brazing and soldering operations, utilizing both mechanized and manual
methods .
(b) These fuel gases have relatively low flame propagation rates, with the
exception of some manufactured city gases containing considerable amounts of hydrogen. When standard welding tips are used, the maximum flame velocity is so 1ow
that it interferes seriously with heat transfer from the flame to the work. The
highest flame temperatures of the gases are obtained at high oxygen-to-fuel gas
ratios. These ratios produce highly oxidizing flames, which prevent the satisfacto–
ry welding of most metals.
(c) Tips should be used having flame-holding devices, such as skirts, counterbores, and holder flames, to permit higher gas velocities before they leave the
tip. This makes it possible to use these fuel gases for many heating applications
with excellent heat transfer efficiency.
(d) Air contains approximately 80 percent nitrogen by volume. This does
not support combustion. Fuel gases burned with air, therefore, produce lower flame
temperatures than those burned with oxygen. The total heat content is also lower.
The air-fuel gas flame is suitable only for welding light sections of lead and for
light brazing and soldering operations.
(2) Equipment.
(a) Standard oxyacetylene equipment, with the exception of torch tips and
regulators, can be used to distribute and bum these gases. Special regulators may
be obtained, and heating and cutting tips are available. City gas and natural gas
are supplied by pipelines; propane and butane are stored in cylinders or delivered
in liquid form to storage tanks on the user’s property.
(b) The torches for use with air-fuel gas generally are designed to aspirate the proper quantity of air from the atmosphere to provide combustion. The
fuel gas flows through the torch at a supply pressure of 2 to 40 psig and serves to
aspirate the air. For light work, fuel gas usually is supplied from a small cylinder that is easily transportable.
(c) The plumbing, refrigeration, and electrical trades use propane in small
cylinders for many heating and soldering applications. The propane flows through
the torch at a supply pressure from 3 to 60 psig and serves to aspirate the air.
The torches are used for soldering electrical connections, the joints in copper
pipelines, and light brazing jobs.
11-4
TC 9-237
(3)
Applications.
Air-fuel gas is used for welding lead up to approximately ¼ in. (6.4 mm)
in thickness. The greatest field of application in the plumbing and electrical
industry. The process is used extensively for soldering copper tubing.
11-2.
WORKING PRESSURES FOR WELDING OPERATIONS
The required working pressure increases as the tip orifice increases. The relation
between the tip number and the diameter of the orifice may vary with different
manufacturers. However, the smaller number always indicates the smaller diameter.
For the approximate relation between the tip number and the required oxygen and
acetylene pressures, see tables 11-1 and 11-2.
N O T E
Oxygen pressures are approximately the same as acetylene pressures in
the balanced pressure type torch. Pressures for specific types of
mixing heads and tips are specified by the manufacturer.
11-5
TC 9-237
11-3.
a.
FLAME ADJUSTMENT AND FLAME TYPES
General.
(1) The oxyfuel gas welding torch mixes the combustible and combustionsupporting gases. It provides the means for applying the flame at the desired location. A range of tip sizes is provided for obtaining the required volume or size
of welding flame which may vary from a short, small diameter needle flame to a
flare 3/16 in. (4.8 mm) or more in diameter and 2 in. (51 mm) or more in length.
(2) The inner cone or vivid blue flare of the burning mixture of gases issuing from the tip is called the working flare. The closer the end of the inner cone
is to the surface of the metal being heated or welded, the more effective is the
heat transfer from flame to metal. The flame can be made soft or harsh by varying
the gas flow. Too lo W a gas flow for a given tip size will result in a soft, ineffective flame sensitive to backfiring. Too high a gas flow will result in a harsh,
high velocity flame that is hard to handle and will blow the molten metal from the
puddle.
(3) The chemical action of the flame on a molten pool of metal can be altered
by changing the ratio of the volume of oxygen to acetylene issuing from the tip.
Most oxyacetylene welding is done with a neutral flame having approximately a 1:1
gas ratio. An oxidizing action can be obtained by increasing the oxygen flow, and
a reducing action will result from increasing the acetylene flow. Both adjustments
are valuable aids in welding.
b.
Flare Adjustment.
(1) Torches should be lighted with a friction lighter or a pilot flame. The
instructions of the equipment manufacturer should be observed when adjusting operating pressures at the gas regulators and torch valves before the gases issuing from
the tip are ignited.
(2) The neutral flame is obtained most easily by adjustment from an excessacetylene flame, which is recognized by the feather extension of the inner cone.
The feather will diminish as the flow of acetylene is decreased or the flow of
oxygen is increased. The flame is neutral just at the point of disappearance of
the “feather” extension of the inner cone. This flame is actually reducing in
nature but is neither carburizing or oxidizing.
(3) A practical method of determining the amount of excess acetylene in a
reducing flame is to compare the length of the feather with the length of the inner
cone, measuring both from the torch tip. A 2X excess-acetylene flame has an acetylene feather that is twice the length of the inner cone. Starting with a neutral
flame adjustment, the welder can produce the desired acetylene feather by increasing the acetylene flow (or by decreasing the oxygen flow). This flame also has a
carburizing effect on steel.
(4) The oxidizing flame adjustment is sometimes given as the amount by which
the length of a neutral inner cone should be reduced, for example, one tenth.
Starting with the neutral flare, the welder can increase the oxygen or decrease the
See
acetylene until the length of the inner cone is decreased the desired amount.
figure 11-1.
11-6
TC 9-237
c.
Lighting the Torch.
(1) To start the welding torch, hold it so as to direct the flame away from
the operator, gas cylinders, hose, or any flammable material. Open the acetylene
torch valve ¼-turn and ignite the gas by striking the sparklighter in front of
the tip.
(2) Since the oxygen torch valve is closed, the acetylene is burned by the
oxygen in the air. There is not sufficient oxygen to provide complete combustion,
so the flame is smoky and produces a soot of fine unburned carbon. Continue to
open the acetylene valve slowly until the flame burns clean. The acetylene flame
is long, bushy, and has a yellowish color. This pure acetylene flame is unsuitable
for welding.
(3) Slowly open the oxygen valve. The flame changes to a bluish-white and
forms a bright inner cone surrounded by an outer flame. The inner cone develops
the high temperature required for welding.
(4) The temperature of the oxyacetylene flame is not uniform throughout its
length and the combustion is also different in different parts of the flame. It is
so high (up to 6000°F (3316°C)) that products of complete combustion (carbon
dioxide and water) are decomposed into their elments. The temperature is the
highest just beyond the end of the inner cone and decreases gradually toward the
end of the flame. Acetylene burning in the inner cone with oxygen supplied by the
torch forms carbon monoxide and hydrogen. As these gases cool from the high temperatures of the inner cone, they burn completely with the oxygen supplied by the
surrounding air and form the lower temperature sheath f1ame. The carbon monoxide
burns to form carbon dioxide and hydrogen burns to form water vapor. Since the
inner cone contains only carbon monoxide and hydrogen, which are reducing in character (i.e., able to combine with and remove oxygen), oxidation of the metal will not
occur within this zone. The chemical reaction for a one-to-one ratio of acetylene
and oxygen plus air is as follows:
C 2 H 2 + 02 = 2 C O + H 2 + H e a t
11-7
TC 9-237
11-3.
FLAME ADJUSTMENT AND FLAME TYPES (cont)
This is the primary reaction: however, both carbon monoxide and hydrogen are combustible and will react with oxygen from the air:
2C0 + H2 + 1.502 = 2C02 + H20 + Heat
This is the secondary reaction which produces carbon dioxide, heat, and water.
d.
Types of Flames.
(1) General. There are three basic flame types: neutral (balanced), excess
acetlyene (carburizing), and excess oxygen (oxidizing). They are shown in figure
11-2.
11-8
TC 9-237
(a) The neutral flame has a one-to-one ratio of acetylene and oxygen. It
obtains additional oxygen from the air and provides complete combustion. I t i s
generally preferred for welding. The neutral flame has a clear, well-defined, or
luminous cone indicating that combustion is complete.
(b) The carburizing flame has excess acetylene,
the inner cone has a feathery edge extending beyond it.
called the acetylene feather. If the acetylene feather
inner cone it is known as a 2X flame, which is a way of
excess acetylene. The carburizing flame may add carbon
indicated in the flame when
This white feather is
is twice as long as the
expressing the amount of
to the weld metal.
(c) The oxidizing flame, which has an excess of oxygen, has a shorter envelope and a small pointed white cone. The reduction in length of the inner core is
a measure of excess oxygen. This flame tends to oxidize the weld metal and is used
only for welding specific metals.
(2) Neutral flame.
(a) The welding flame should be adjusted to neutral before either the
carburizing or oxidizing flame mixture is set. There are two clearly defined zones
in the neutral flame. The inner zone consists of a luminous cone that is bluishwhite. Surrounding this is a light blue flame envelope or sheath. This neutral
flame is obtained by starting with an excess acetylene flame in which there is a
“feather” extension of the inner cone. When the flow of acetylene is decreased or
the flow of oxygen increased the feather will tend to disappear. The neutral flame
begins when the feather disappears.
(b) The neutral or balanced flame is obtained when the mixed torch gas
consists of approximately one volume of oxygen and one volume of acetylene. I t i s
obtained by gradually opening the oxygen valve to shorten the acetylene flame until
a clearly defined inner cone is visible. For a strictly neutral flame, no whitish
streamers should be present at the end of the cone. In some cases, it is desirable
to leave a slight acetylene streamer or “feather” 1/16 to 1/8 in. (1.6 to 3.2 mm)
long at the end of the cone to ensure that the flame is not oxidizing. This flame
adjustment is used for most welding operations and for preheating during cutting
operations. When welding steel with this flare, the molten metal puddle is quiet
and clear. The metal flows easily without boiling, foaming, or sparking.
(c) In the neutral flame, the temperature at the inner cone tip is approximately 5850°F (3232°C), while at the end of the outer sheath or envelope the
temperature drops to approximately 2300°F (1260°C). This variation within the
flame permits some temperature control when making a weld. The position of the
flame to the molten puddle can be changed, and the heat controlled in this manner.
(3) Reducing or carburizing flame.
(a) The reducing or carburizing flame is obtained when slightly less than
one volume of oxygen is mixed with one volume of acetylene. This flame is obtained
by first adjusting to neutral and then slowly opening the acetylene valve until an
acetylene streamer or “feather” is at the end of the inner cone. The length of
this excess streamer indicates the degree of flame carburization. For most welding
operations, this streamer should be no more than half the length of the inner cone.
11-9
TC 9-237
11-3.
FLAME ADJUSTMENT AND FLAME TYPES (cont)
(b) The reducing or carburizing flame can always be recognized by the presence of three distinct flame zones. There is a clearly defined bluish-white inner
cone, white intermediate cone indicating the amount of excess acetylene, and a
light blue outer flare envelope. This type of flare burns with a coarse rushing
sound. It has a temperature of approximately 5700°F (3149°C) at the inner cone
tips.
(c) When a strongly carburizing flame is used for welding, the metal boils
and is not clear. The steel, which is absorbing carbon from the flame, gives off
heat. This causes the metal to boil. When cold, the weld has the properties of
high carbon steel, being brittle and subject to cracking.
(d) A slight feather flame of acetylene is sometimes used for back-hand
welding. A carburizing flame is advantageous for welding high carbon steel and
hard facing such nonferrous alloys as nickel and Monel. When used in silver solder
and soft solder operations, only the intermediate and outer flame cones are used.
They impart a low temperature soaking heat to the parts being soldered.
(4) Oxidizing flame.
(a) The oxidizing flame is produced when slightly more than one volume of
oxygen is mixed with one volume of acetylene. To obtain this type of flame, the
torch should first be adjusted to a neutral flame. The flow of oxygen is then
increased until the inner cone is shortened to about one-tenth of its original
length. When the flame is properly adjusted, the inner cone is pointed and slightly purple. An oxidizing flame can also be recognized by its distinct hissing
sound. The temperature of this flame is approximately 6300°F (3482°C) at the
inner cone tip.
(b) When applied to steel, an oxidizing flame causes the molten metal to
foam and give off sparks. This indicates that the excess oxygen is combining with
the steel and burning it. An oxidizing flame should not be used for welding steel
because the deposited metal will be porous, oxidized, and brittle. This flame will
ruin most metals and should be avoided, except as noted in (c) below.
iron.
( C ) A slightly oxidizing flame is used in torch brazing of steel and cast
A stronger oxidizing flame is used in the welding of brass or bronze.
(d) In most cases, the amount of excess oxygen used in this flame must be
determin ed by observing the action of the flame on the molten metal.
(5) MAPP gas flames.
(a) The heat transfer properties of primary and secondary flames differ for
different fuel gases. MAPP gas has a high heat release in the primary flame, and a
high heat release in the secondary. Propylene is intermediate between propane and
MAPP gas. Heating values of fuel gases are shown in table 11-3.
11-10
TC 9-237
(b) The coupling distance between the work and the flame is not nearly as
critical with MAPP gas as it is with other fuels.
(c) Adjusting a MAPP gas flame. Flame adjustment is the most important
factor for successful welding or brazing with MAPP gas. As with any other fuel
gas, there are three basic MAPP gas flames: carburizing, neutral, and oxidizing
(fig. 11-3).
1. A carburizing flame looks much the same with MAPP gas or acetylene.
It has a yellow feather on the end of the primary cone. Carburizing flames are
obtained with MAPP gas when oxyfuel ratios are around 2.2:1 or lower. Slightly
carburizing or “reducing” flames are used to weld or braze easily oxidized alloys
such as aluminum.
2. As oxygen is increased, or the fuel is turned down, the carburizing
feather pulls off and disappears. When the feather disappears, the oxyfuel ratio
is about 2.3:1. The inner flame is a very deep blue. This is the neutral MAPP gas
flame for welding, shown in figure 11-3. The flame remains neutral up to about
2.5:1 oxygen-to-fuel ratio.
11-11
TC 9-237
11-3.
FLAME ADJUSTMENT AND FLAME TYPES (cont)
—3. Increasing the oxygen flame produces a lighter blue flame, a longer
inner cone, and a louder burning sound.
This is an oxidizing MAPP gas flare. An
operator experience with acetylene will immediately adjust the MAPP gas flame to
look like the short, intense blue flame typical of the neutral acetylene flame
setting. What will be produced, however, is a typical oxidizing MAPP gas flame.
With certain exceptions such as welding or brazing copper and copper alloys, an
oxidizing flame is the worst possible flame setting, whatever the fuel gas used.
The neutral flame is the principle setting for welding or brazing steel. A neutral
MAPP gas flame has a primary flame cone abut 1-½ to 2 times as long as the primary acetylene flame cone.
11-4.
OXYFUEL WELDING RODS
a . The welding rod, which is melted into the welded joint, plays an important
part in the quality of the finished weld. Good welding rods are designed to permit
free flowing metal which will unite readily with the base metal to produce sound,
clean welds of the correct composition.
b. Welding rods are made for various types of carbon steel, aluminum, bronze,
stainless steel, and other metals for hard surfacing.
11-5.
a.
OXYFUEL WELDING FLUXES
General.
(1) Oxides of all ordinary commercial metals and alloys (except steel) have
higher melting points than the metals themselves. They are usually pasty when the
metal is quite fluid and at the proper welding temperature. An efficient flux will
combine with oxides to form a fusible slag. The slag will have a melting point
lower than the metal so it will flow away from the immediate field of action. It
combines with base metal oxides and removes them. It also maintains cleanliness of
the base metal at the welding area and helps remove oxide film on the surface of
the metal. The welding area should be cleaned by any method. The flux also serves
as a protection for the molten metal against atmospheric oxidation.
(2) The chemical characteristics and melting points of the oxides of different metals vary greatly. There is no one flux that is satisfactory for all metals,
and there is no national standard for gas welding fluxes. They are categorized
according to the basic ingredient in the flux or base metal for which they are to
be used.
(3) Fluxes are usually in powder form. These fluxes are often applied by
sticking the hot filler metal rod in the flux. Sufficient flux will adhere to the
rod to provide proper fluxing action as the filler rod is melted in the flame.
(4) Other types of fluxes are of a paste consistency which are usually painted on the filler rod or on the work to be welded.
(5) Welding rods with a covering of flux are also available. Fluxes are
available from welding supply companies and should be used in accordance with the
directions accompanying them.
11-12
TC 9-237
b. The melting point of a flux must be lower than that of either the metal or
the oxides formed, so that it will be liquid. The ideal flux has exactly the right
fluidity when the welding temperature has been reached. The flux will protect the
molten metal from atmospheric oxidation. Such a flux will remain close to the weld
area instead of flowing all over the base metal for some distance from the weld.
c. Fluxes differ in their composition according to the metals with which they
are to be used. In cast iron welding, a slag forms on the surface of the puddle.
The flux serves to break this up. Equal parts of a carbonate of soda and bicarbonate of soda make a good compound for this purpose. Nonferrous metals usually require a flux. Copper also requires a filler rod containing enough phosphorous to
produce a metal free from oxides. Borax which has been melted and powdered is
often used as a flux with copper alloys. A good flux is required with aluminum,
because there is a tendency for the heavy slag formed to mix with the melted aluminum and weaken the weld. For sheet aluminum welding, it is customary to dissolve
the flux in water and apply it to the rod. After welding aluminum, all traces of
the flux should be removed.
11-6.
FOREHAND WELDING
a. In this method, the welding rod precedes the torch. The torch is held at
approximately a 45 degree angle from the vertical in the direction of welding, as
shown in figure 11-4. The flame is pointed in the direction of welding and directed between the rod and the molten puddle. This position permits uniform preheating
of the plate edges immediately ahead of the molten puddle. By moving the torch and
the rod in opposite semicircular paths, the heat can be carefully balanced to melt
the end of the rod and the side walls of the plate into a uniformly distributed
molten puddle. The rod is dipped into the leading edge of the puddle so that
enough filler metal is melted to produce an even weld joint. The heat which is
reflected backwards from the rod keeps the metal molten. The metal is distributed
evenly to both edges being welded by the motion of the tip.
11-13
TC 9–237
11-6.
FOREHAND WELDING (cont)
b. In general, the forehand method is recommended for welding material up
to 1/8 in. (3.2 mm) thick, because it provides better control of the small
weld puddle, resulting in a smoother weld at both top and bottom. The puddle
of molten metal is small and easily controlled. A great deal of pipe welding
is done using the forehand technique, even in 3/8 in. (9.5 mm) wall thicknesses. In contrast, some difficulties in welding heavier plates using the
forehand metod are:
(1) The edges of the plate must be beveled to provide a wide V with a
90 degree included angle. This edge preparation is necessary to ensure satis–
factory melting of the plate edges, good penetration, and fusion of the weld
metal to the base metal.
(2) Because of this wide V, a relatively large molten puddle is required. It is difficult to obtain a good joint when the puddle is too large.
11-7.
BACKHAND WELDING
a. In this method, the torch precedes the welding rod, as shown in figure
11-5. The torch is held at approximately a 45 degree angle from the vertical
away from the direction of welding, with the flame directed at the molten
puddle. The welding rod is between the flame and the molten puddle. This
position requires less transverse motion than is used in forehand welding.
b. Increased speeds and better control of the puddle are possible with backhand
technique when metal 1/8 in. (3.2 mm) and thicker is welded, based on the study of
speeds normally achieved with this technique and on greater ease of obtaining fusion at the weld root. Backhand welding may be used with a slightly reducing flame
(slight acetylene feather) when desirable to melt a minimum amount of steel in
making a joint. The increased carbon content obtained from this flame lowers the
11-14
TC 9-237
melting point of a thin layer of steel and increases welding speed. This technique
increases speed of making pipe joints where the wall thickness is ¼ to 5/16 in.
(6.4 to 7.9 mm) and groove angle is less than normal. Backhand welding is sometimes used in surfacing operations.
11-8.
a.
FILLET WELDING
General.
(1) The fillet weld is the most popular of all types of welds because there
is normally no preparation required. In some cases, the fillet weld is the least
expensive, even though it might require more filler metal than a groove weld since
the preparation cost would be less. It can be used for the lap joint, the tee
joint, and the corner joint without preparation. Since these are extremely popular, the fillet has wide usage. On corner joints, the double fillet can actually
produce a full-penetration weld joint. The use of the fillet for making all five
of the basic joints is shown by figure 11-6. Fillet welds are also used in conjunction with groove welds, particularly for corner and tee joints.
11-15
TC 9-237
11-8.
FILLET WELDING (cont)
(2) The fillet weld is expected to have equal length legs and thus the face
of the fillet is on a 45 degree angle. This is not always so, since a fillet may
be designed to have a longer base than height, in which case it is specified by the
two leg lengths. On the 45 degree or normal type of fillet, the strength of the
fillet is based on the shortest or throat dimension which is 0.707 x the leg
length. For fillets having unequal legs, the throat length must be calculated and
is the shortest distance between the root of the fillet and the theoretical face of
the fillet. In calculating the strength of fillet welds, the reinforcement is
ignored. The root penetration is also ignored unless a deep penetratingq process is
used . If semi- or fully-automatic application is used, the extra penetration can
be considered. See figure 11-7 for details about the weld.
(3) Under these circumstances, the size of the fillet can be reduced, yet
equal strength will result. Such reductions can be utilized only when strict welding procedures are enforced. The strength of the fillet weld is determined by its
failure area, which relates to the throat dimension. Doubling the size or leg
length of a fillet will double its strength, since it doubles the throat dimension
and area. However, doubling the fillet size will increase its cross-sectional area
and weight four times. This illustrated in figure 11-8, which shows the relationship to throat-versus-cross-sectional area, or weight, of a fillet weld. For example, a 3/8 in. (9.5 mm) fillet is twice as strong as a 3/16 in. (4.8 mm) fillet;
however, the 3/8 in. (9.5 mm) fillet requires four times as much weld metal.
11-16
TC 9-237
(4) In design work, the fillet size is sometimes governed by the thickness of
the metals joined. In some situations, the minimum size of the fillet must be
based on practical reasons rather than the theoretical need of the design. Intermittent fillets are sometimes used when the size is minimum, based on code, or for
practical reasons, rather than because of strength requirements. Many intermittent
welds are based on a pitch and length so that the weld metal is reduced in half.
Large intermittent fillets are not recommended because of the volume-throat dimension relationship mentioned previously. For example, a 3/8 in. (9.5 mm) fillet 6
in. (152.4 mm) long on a 12 in. (304.8 mm) pitch (center to center of intermittent
welds) could be reduced to a continuous 3/16 in. (4.8 mm) fillet, and the strength
would be the same, but the amount of weld metal would be only half as much.
(5) Single fillet welds are extremely vulnerable to cracking if the root of
the weld is subjected to tension loading. This applies to tee joints, corner
joints, and lap joints. The simple remedy for such joints is to make double fillets, which prohibit the tensile load from being applied to the root of the fill e t . This is shown by figure 11-6, page 11-15. Notice the F (force) arrowhead.
b. A different welding technique is required for fillet welding than for butt
joints because of the position of the parts to be welded. When welding is done in
the horizontal position, there is a tendency for the top plate to melt before the
bottom plate because of heat rising. This can be avoided, however, by pointing the
flame more at the bottom plate than at the edge of the upper plate. Both plates
must reach the welding temperature at the same time.
c. In making the weld, a modified form of backhand technique should be used.
The welding rod should be kept in the puddle between the completed portion of the
weld and the flame. The flame should be pointed ahead slightly in the direction in
which the weld is being made and directed at the lower plate. To start welding,
the flame should be concentrated on the lower plate until the metal is quite red.
Then the flame should be directed so as to bring both plates to the welding temperature at the same time. It is important that the flame not be pointed directly at
the inner corner of the fillet. This will cause excessive amount of heat to build
up and make the puddle difficult to control.
d. It is essential in this form of welding that fusion be obtained at the inside corner or root of the joint.
11-9.
HORIZONTAL POSITION WELDING
a. Welding cannot always be done in the most desirable position. It must be
done in the position in which the part will be used. Often that may be on the
ceiling, in the corner, or on the floor. Proper description and definition is
necessary since welding procedures must indicate the welding position to be performed, and welding process selection is necessary since some have all-position
capabilities whereas others may be used in only one or two positions. The American
Welding Society has defined the four basic welding positions as shown in figure
11-9, p 11-8.
11-17
TC 9-237
11-9. HORZONITAL POSITION WELDING (cont)
b. In horizontal welding, the weld axis is approximately horizontal, but the
weld type dictates the complete definition. For a fillet weld, welding is performed on the upper side of an approximately horizontal surface and against an
approximately vertical surface. For a groove weld, the face of the weld lies in an
approximately vertical plane.
c. Butt welding in the horizontal position is a little more difficult to master
than flat position. This is due to the tendency of molten metal to flow to the
lower side of the joint. The heat from the torch rises to the upper side of the
joint. The combination of these opposing factors makes it difficult to apply a
uniform deposit to this joint.
11-18
TC 9-237
d. Align the plates and tack weld at both ends (fig. 11-10). The torch should
move with a slight oscillation up and down to distribute the heat equally to both
sides of the joint, thereby holding the molten metal in a plastic state. This
prevents excessive flow of the metal to the lower side of the joint, and permits
faster solidification of the weld metal. A joint in horizontal position will require considerably more practice than the previous techniques. It is, however,
important that the technique be mastered before passing on to other types of weld
positions.
11-10.
a.
joint.
b.
FLAT POSITION WELDING
General. This type of welding is performed from the upper side of the
The face of the weld is approximately horizontal.
Bead Welds.
(1) In order to make satisfactory bead welds on a plate surface, the flare
motion, tip angle, and position of the welding flame above the molten puddle should
be carefully maintained. The welding torch should be adjusted to give the proper
type of flame for the particular metal being welded.
11-19
TC 9-237
11-10.
FLAT POSITION WELDING (cont)
(2) Narrow bead welds are made by raising and lowering the welding flare
with a slight circular motion while progressing forward. The tip should form an
angle of approximately 45 degrees with the plate surface. The flame will be pointed in the welding direction (figs. 11-11 and 11-12).
11-20
TC 9-237
(3) TO increase the depth of fusion, either increase the angle between the
tip and the plate surface , or decrease the welding speed. The size of the puddle
should not be too large because this will cause the flame to burn through the
plate. A properly made bead weld, without filler rod, will be slightly below the
upper surface of the plate. A bead weld with filler rod shows a buildup on the
surface.
(4) A small puddle should be formed on the surface when making a bead weld
with a welding rod (fig. 11-12). The welding rod is inserted into the puddle and
the base plate and rod are melted together. The torch should be moved slightly
from side to side to obtain good fusion. The size of the bead can be controlled by
varying the speed of welding and the amount of metal deposited from the welding rod.
c.
Butt Welds.
(1)
Several types of joints are used to make butt welds in the flat position.
(2) Tack welds should be used to keep the plates aligned. The lighter sheets
should be spaced to allow for weld metal contraction and thus prevent warpage.
(3) The following guide should be used for selecting the number of passes
(fig. 11-8, p 11-16) in butt welding steel plates:
(4) The position of the welding rod and torch tip in making a flat position
butt joint is shown in figure 11-13. The motion of the flame should be controlled
so as to melt the side walls of the plates and enough of the welding rod to produce
a puddle of the desired size. By oscillating the torch tip, a molten puddle of a
given size can be carried along the joint. This will ensure both complete penetration and sufficient filler metal to provide some reinforcement at the weld.
(5) Care should be taken not to overheat the molten puddle. This will result
in burning the metal, porosity, and loW strength in the completed weld.
11-21
TC 9-237
11-11.
VERTICAL POSITION WELDING
a. General. In vertical position welding, the axis of the weld is approximately vertical.
b. When welding is done on a vertical surface, the molten metal has a tendency
to run downward and pile up. A weld that is not carefully made will result in a
joint with excessive reinforcement at the lower end and some undercutting on the
surface of the plates.
c. The flew of metal can be controlled by pointing the flame upward at a 45
degree angle to the plate, and holding the rod between the flame and the molten
puddle (fig. 11-14). The manipulation of the torch and the filler rod keeps
the
.
metal from sagging or falling and ensures good penetration and fusion at the
joint. Both the torch and the welding rod should be oscillated to deposit a uniform bead. The welding rod should be held slightly above the center line of the
joint, and the welding flame should sweep the molten metal across the joint to
distribute it evenly.
d. Butt joints welded in the vertical position should be prepared for welding
in the same manner as that required for welding in the flat position.
11-12.
a.
OVERHEAD POSITION WELDING
General.
Overhead welding is performed from the underside of a joint.
b. Bead welds. In overhead welding, the metal deposited tends to drop or sag
on the plate, causing the bead to have a high crown. To overcome this difficulty,
the molten puddle should be kept small, and enough filler metal should be added to
obtain good fusion with some reinforcement at the bead. If the puddle becomes too
large, the flame should be removed for an instant to permit the weld metal to
freeze. When welding light sheets, the puddle size can be controlled by applying
the heat equally to the base metal and filler rod.
11-22
TC 9-237
c. Butt Joints. The torch and welding rod position for welding overhead butt
joints is shown in figure 11-15. The flame should be directed so as to melt both
edges of the joint. Sufficient filler metal should be added to maintain an adequate puddle with enough reinforcement. The welding flame should support the molten metal and distribute it along the joint. Only a small puddle is required, so a
small welding rod should be used. Care should be taken to control the heat to
avoid burning through the plates. This is particularly important when welding is
done from one side only.
Section I I .
WELDING AND BRAZING FERROUS METALS
11-13. GENERAL
a.
Welding Sheet Metal.
(1) For welding purposes, the term “sheet metal” is restricted to thicknesses
of metals up to and including 1/8 in. (3.2 mm).
(2) Welds in sheet metal up to 1/16 in. (1.6 mm) thick can be made satisfactorily by flanging the edges at the joint. The flanges must be at least equal to the
thickness of the metal. The edges should be aligned with the flanges and then tack
welded every 5 or 6 in. (127.0 to 152.4 mm). Heavy angles or bars should be
clamped on each side of the joint to prevent distortion or buckling. The raised
edges are equally melted by the welding flare. This produces a weld nearly flush
with the sheet metal surface. By controlling the welding speed and the flame motion, good fusion to the underside of the sheet can he obtained without burning
through. A plain square butt joint can also be made on sheet metal up to 1/16 in.
(1.6 mm) thick by using a rust-resisting, copper-coated lo W carbon filler rod 1/16
in. (1.6 mm) in diameter. The method of aligning the joint and tacking the edges
is the same as that used for welding flanged edge joints.
(3) Where it is necessary to make an inside edge or corner weld, there is
danger of burning through the sheet unless special care is taken to control the
welding heat. Such welds can be made satisfactorily in sheet metal up to 1/16 in.
(1.6 mm) thick by following the procedures below:
(a) Heat the end of a 1/8 in. (3.2 mm) low carbon welding rod until approximately ½ in. (12.7 mm) of the rod is molten.
(b) Hold the rod so that the molten end is above the joint to be welded.
11-23
TC 9-237
11-13. GENERAL (cont)
(c) By sweeping the flame across the molten end of the rod, the metal can
be removed and deposited on the seam. The quantity of molten weld metal is relatively large as compared with the light gauge sheet. Its heat is sufficient to
preheat the sheet metal. By passing the flame quickly back and forth, the filler
metal is distributed along the joint. The additional heat supplied by the flame
will produce complete fusion. This method of welding can be used for making difficult repairs on automobile bodies, metal containers, and similar applications.
Consideration should be given to expansion and contraction of sheet metal before
welding is stated.
(4) For sheet metal 1/16 to 1/8 in. (1.6 to 3.2 mm) thick, a butt joint, with
a space of approximately 1/8 in. (3.2 mm) between the edges, should be prepared. A
1/8 in. (3.2 mm) diameter copper-coated low carbon filler rod should be used.
Sheet metal welding with a filler rod on butt joints should be done by the forehand
method of welding.
b.
(1) General. The term “steel” may be applied to many ferrous metals which
differ greatly in both chemical and physical properties. In general, they may be
divided into plain carbon and alloy groups. By following the proper procedures,
most steels can be successfully welded. However, parts fabricated by welding generally contain less than 0.30 percent carbon. Heat increases the carbon combining
power of steel. Care must be taken during all welding processes to avoid carbon
pickup.
(2) Welding process. Steel heated with an oxyacetylene flame becomes fluid
between 2450 and 2750°F (1343 and 1510°C), depending on its composition. It passes through a soft range between the solid and liquid states. This soft range enables the operator to control the weld. To produce a weld with good fusion, the
welding rod should be placed in the molten puddle. The rod and base metal should
be melted together so that they will solidify to form a solid joint. Care should
be taken to avoid heating a large portion of the joint. This will dissipate the
heat and may cause some of the weld metal to adhere to but not fuse with the sides
of the welded joint. The flare should be directed against the sides and bottom of
the welded joint. This will allow penetration of the lower section of the joint.
Weld metal should be added in sufficient quantities to fill the joint without leaving any undercut or overlap. Do not overheat. Overheating will burn the weld
metal and weaken the finished joint.
(3)
Impurities.
(a) Oxygen, carbon, and nitrogen impurities produce defective weld metal because they tend to increase porosity, blowholes, oxides, and slag inclusions.
(b) When oxygen combines with steel to form iron oxides at high temperatures, care should be taken to ensure that all the oxides formed are removed by
proper manipulation of the rod and torch flame. An oxidizing flame causes the
steel to foam and give off sparks. The oxides formed are distributed through the
metal and cause a brittle, porous weld. Oxides that form on the surface of the
finished weld can be removed by wire brushing after cooling.
11-24
TC 9-237
(c) A carburizing flame adds carbon to the molten steel and causes boiling
of the metal. Steel welds made with strongly carburizing flames are hard and brittle.
(d) Nitrogen from the atmosphere will combine with molten steel to form
nitrides of iron. These will impair its strength and ductility if included in
sufficient quantities.
(e) By controlling the melting rate of the base metal and welding rod, the
size of the puddle, the speed of welding,
-- and the flame adjustment, the inclusion
of impurities from the above sources may be held to a minimum.
c.
Welding Steel Plates.
(1) In plates up to 3/16 in. (4.8 mm) in thickness, joints are prepared with
a space between the edges equal to the plate thickness. This allows the flame and
welding rod to penetrate to the root of the joint. Proper allowance should be made
for expansion and contraction in order to eliminate warping of the plates or cracking of the weld.
(2) The edges of heavy section steel plates (more than 3/16 in. (4.8 mm)
thick) should be beveled to obtain full penetration of the weld metal and good
fusion at the joint. Use the forehand method of welding.
(3) Plates ½ to ¾ in. (12.7 to 19.l mm) thick should be prepared for a U
type joint in all cases. The root face is provided at the base of the joint to
cushion the first bead or layer of weld metal. The backhand method is generally
used in welding these plates.
NOTE
Welding of plates ½ to ¾ in. (12.7 to 19.1 mm) thick is not recommended for oxyacetylene welding.
(4) The edges of plates ¾ in. (19.1 mm) or thicker are usually prepared by
using the double V or double U type joint when welding can be done from both sides
of the plate. A single V or single U joint is used for all plate thicknesses when
welding is done from one side of the plate.
d.
General Principles in Welding Steel.
(1) A well balanced neutral flame is used for welding most steels. To be
sure that the flame is not oxidizing, it is sometimes used with a slight acetylene
feather. A very slight excess of acetylene may be used for welding alloys with a
high carbon, chromium, or nickel content. However, increased welding speeds are
possible by using a slightly reducing flame. Avoid excessive gas pressure because
it gives a harsh flame. This often results in cold shuts or laps, and makes molten
metal control difficult.
(2) The tip size and volume of flame used should be sufficient to reduce the
metal to a fully molten state and to produce complete joint penetration. Care
should be taken to avoid the formation of molten metal drip heads from the bottom
of the joint. The flame should bring the joint edges to the fusion point ahead of
the puddle as the weld progresses.
(3) The pool of the molten metal should progress evenly down the seam as the
weld is being made.
11-25
TC 9-237
11-13. GENERAL (cont)
(4) The inner cone tip of the flame should not be permitted to come in contact with the welding rod, molten puddle, or base metal. The flame should be manipulated so that the molten metal is protected from the atmosphere by the envelope or
outer flame.
(5) The end of the welding rod should be melted by placing it in the puddle
under the protection of the enveloping flame. The rod should not be melted above
the puddle and allowed to drip into it.
11-14.
a.
BRAZING
General.
(1) Brazing is a group of welding processes which produces coalescence of
materials by heating to a suitable temperature and using a filler metal having a
liquidus above 840° F (449°C) and below the solidus of the base metals. The filler metal is distributed between the closely fitted surfaces of the joint by capillary attraction. Brazing is distinguished from soldering in that soldering employs
a filler metal having a liquidus below 840°F (449°C).
(2) When brazing with silver alloy filler metals (silver soldering), the
alloys have liquidus temperatures above 840°F (449°C).
(3) Brazing must meet each of three criteria:
(a) The parts must be joined without melting the base metals.
(b) The filler metal must have a liquidus temperature above 840°F (449°C).
(c) The filler metal must wet the base metal surfaces and be drawn onto or
held in the joint by capillary attraction.
(4) Brazing is not the same as braze welding, which uses a brazing filler
metal that is melted and deposited in fillets and grooves exactly at the points it
is to be used. The brazing filler metal also is distributed by capillary action.
Limited base metal fusion may occur in braze welding.
(5) To achieve a good joint using any of the various brazing processes, the
parts must be properly cleaned and protected by either flux or the atmosphere during heating to prevent excessive oxidation. The parts must provide a capillary for
the filler metal when properly aligned, and a heating process must be selected that
will provide proper brazing temperatures and heat distribution.
b.
Principles.
(1) Capillary flow is the most important physical principle which ensures
good brazements providing both adjoining surfaces molten filler metal. The joint
must also be properly spaced to permit efficient capillary action and resulting
coalescence. More specifically, capillarity is a result of surface tension between
base metal(s), filler metal, flux or atmosphere, and the contact angle between base
and filler metals. In actual practice, brazing filler metal flow characteristics
11-26
TC 9-237
are also influenced by considerations involving fluidity, viscosity, vapor pressure, gravity, and by the effects of any metallurgical reactions between the filler
and base metals.
(2) The brazed joint, in general, is one of a relatively large area and very
small thickness. In the simplest application of the process, the surfaces to be
joined are cleaned to remove contaminants and oxide. Next, they are coated with
flux or a material capable of dissolving solid metal oxides present and preventing
new oxidation. The joint area is then heated until the flux melts and cleans the
base metals, which are protected against further oxidation by the liquid flux layer.
(3) Brazing filler metal is then melted at some point on the surface of the
joint area. Capillary attraction is much higher between the base and filler metals
than that between the base metal and flux. Therefore, the flux is removed by the
filler metal. The joint, upon cooling to room temperature, will be filled with
solid filler metal. The solid flux will be found on the joint surface.
(4) High fluidity is a desirable characteristic of brazing filler metal because capillary attraction may be insufficient to cause a viscous filler metal to
run into tight fitting joints.
(5) Brazing is sometimes done with an active gas, such as hydrogen, or in an
inert gas or vacuum. Atmosphere brazing eliminates the necessity for post cleaning
and ensures absence of corrosive mineral flux residue. Carbon steels, stainless
steels, and super alloy components are widely processed in atmospheres of reacted
gases, dry hydrogen, dissociated ammonia, argon, and vacuum. Large vacuum furnaces
are used to braze zirconium, titanium, stainless steels, and the refractory meta l s . With good processing procedures, aluminum alloys can also be vacuum furnace
brazed with excellent results.
(6) Brazing is a process preferred for making high strength metallurgical
bonds and preserving needed base metal properties because it is economical.
c.
Processes.
(1) Generally, brazing processes are specified according to heating methods
(sources) of industrial significance. Whatever the process used, the filler metal
has a melting point above 840°F (450°C) but below the base metal and distributed
in the joint by capillary attraction. The brazing processes are:
(a)
Torch brazing.
(b)
Furnace brazing.
(c)
Induction brazing.
(d)
Resistance brazing.
(e)
Dip brazing.
(f)
Infrared brazing.
11-27
TC 9-237
11-14.
BRAZING (cont)
(2) Torch brazing.
(a) Torch brazing is performed by heating with a gas torch with a proper
tip size, filler metal of required composition, and appropriate
flux. This depends
- - on the temperature and heat amount required. The fuel gas (acetylene, propane,
city gas, etc.) may be burned with air, compressed air, or oxygen.
(b) Brazing filler metal may be preplaced at the joint in the forms of
rings, washers, strips, slugs, or powder, or it may be fed from hand-held filler
metal in wire or rod form. In any case, proper cleaning and fluxing are essential.
(c) For manual torch brazing, the torch may be equipped with a single tip,
either single or multiple flame. Manual torch brazing is particularly useful on
assemblies involving sections of unequal mass. Welding machine operations can be
set up where the production rate allows, using one or several torches equipped with
single or multiple flame tips. The machine may be designed to move either the work
or torches, or both. For premixed city gas–air flames, a refractory type burner is
used.
(3) Furnance brazing.
(a) Furance brazing is used extensively where the parts to be brazed can be
assembled with the brazing filler metal in form of wire, foil, filings, slugs,
powder, paste, or tape is preplaced near or in the joint. This process is particularly applicable for high production brazing. Fluxing is employed except when an
atmosphere is specifically introduced in the furnace to perform the same function.
Most of the high production brazing is done in a reducing gas atomosphere, such as
hydrogen and combusted gases that are either exothermic (formed with heat evolution) or endothermic (formed with heat absorption). Pure inert gases, such as
argon or helium, are used to obtain special atmospheric properties.
(b) A large volume of furnace brazing is performed in a vacuum, which prevents oxidation and often eliminates the need for flux. Vacuum brazing is widely
used in the aerospace and nuclear fields, where reactive metals are joined or where
entrapped fluxes would be intolerable. If the vacuum is maintained by continuous
pumping, it will remove volatile constituents liberated during brazing. There are
several base metals and filler metals that should not be brazed in a vacuum because
low boiling point or high vapor pressure constituents may be lost. The types of
furnaces generally used are either batch or contiguous. These furnaces are usually
heated by electrical resistance elements, gas or oil, and should have automatic
time and temperature controls. Cooling is sometimes accomplished by cooling chambers, which either are placed over the hot retort or are an integral part of the
furnace design. Forced atmosphere injection is another method of cooling. Parts
may be placed in the furnance singly, in batches, or on a continuous conveyor.
(c) Vacuum is a relatively economical method of providing an accurately
controlled brazing atmosphere. Vacuum provides the surface cleanliness needed for
good wetting and flow of filler metals without the use of fluxes. Base metals
containing chromium and silicon can be easily vacuum brazed where a very pure, low
dew point atmosphere gas would otherwise be required.
11-28
TC 9-237
(4) Induction brazing.
(a) In this process, the heat necessary to braze metals is obtained from a
high frequency electric current consisting of a motor-generator, resonant spark
gap, and vacuum tube oscillator. It is induced or produced without magnetic or
electric contact in the parts (metals). The parts are placed in or near a watercooled coil carrying alternating current. They do not form any part of the electrical circuit. The brazing filler metal normally is preplaced.
(b) Careful design of the joint and the coil setup are necessary to assure
that the surfaces of all members of the joint reach the brazing temperature at the
same time. Flux is employed except when an atmosphere is specifically introduced
to perform the same function.
(c) The equipment consists of tongs or clamps with the electrodes attached
at the end of each arm. The tongs should preferably be water-cooled to avoid overheating. The arms are current carrying conductors attached by leads to a transformer. Direct current may be used but is comparatively expensive. Resistance welding
machines are also used. The electrodes may be carbon, graphite, refractory metals,
or copper alloys according to the required conductivity.
(5) Resistance brazing. The heat necessary for resistance brazing is obtained from the resistance to the flow of an electric current through the electrodes and the joint to be brazed. The parts comprising the joint form a part of
the electric circuit. The brazing filler metal, in some convenient form, is
preplaced or face fed. Fluxing is done with due attention to the conductivity of
the fluxes. (Most fluxes are insulators when dry.) Flux is employed except when
an atmosphere is specifically introduced to perform the same function. The parts
to be brazed are held between two electrodes, and proper pressure and current are
applied. The pressure should be maintained until the joint has solidified. In
some cases, both electrodes may be located on the same side of the joint with a
suitable backing to maintain the required pressure.
(6) Dip brazing.
(a) There are two methods of dip brazing: chemical bath dip brazing and
molten metal bath dip brazing.
(b) In chemical bath dip brazing, the brazing filler metal, in suitable
form, is preplaced and the assembly is immersed in a bath of molten s a l t . The salt
bath furnishes the heat necessary for brazing and usually provides the necessary
protection from oxidation; if not, a suitable flux should be used. The salt bath
is contained in a metal or other suitable pot, also called the furnace, which is
heated from the outside through the wall of the pot, by means of electrical resistance units placed in the bath, or by the I²R loss in the bath itself.
(c) In molten metal bath dip brazing, the parts are immersed in a bath of
molten brazing filler metal contained in a suitable pot. The parts must be cleaned
and fluxed if necessary. A cover of flux should be maintained over the molten bath
to protect it from oxidation. This method is largely confined to brazing small
11-29
TC 9-237
11-14.
BRAZING (cont)
parts, such as wires or narrow strips of metal. The ends of the wires or parts
must be held firmly together when they are removed from the bath until the brazing
filler metal has fully solidified.
(7) Infrared brazing.
(a) Infrared heat is radiant heat obtained below the red rays in the spectrum. While with every “black” source there is sane visible light, the principal
heating is done by the invisible radiation. Heat sources (lamps) capable of delivering up to 5000 watts of radiant energy are commercially available. The lamps do
not necessarily need to follow the contour of the part to be heated even though the
heat input varies inversely as the square of the distance from the source. Reflectors are used to concentrate the heat.
(b) Assemblies to be brazed are supported in a position that enables the
energy to impinge on the part. In some applications, only the assembly itself is
enclosed. There are, however, applications where the assembly and the lamps are
placed in a bell jar or retort that can be evacuated, or in which an inert gas
atmosphere can be maintained. The assembly is then heated to a controlled temperature, as indicated by thermocouples. The part is moved to the cooling platens
after brazing.
(8) Special processes.
(a) Blanket brazing is another of the processes used for brazing. A blanket is resistance heated, and most of the heat is transferred to the parts by two
methods, conduction and radiation, the latter being responsible for the majority of
the heat transfer.
(b) Exothermic brazing is another special process by which the heat required to melt and flow a commercial filler metal is generated by a solid state
exothermic chemical reaction. An exothermic chemical reaction is defined as any
reaction between two or more reactants in which heat is given off due to the free
energy of the system. Nature has provided us with countless numbers of these reactions; however, only the solid state or nearly solid state metal-metal oxide reactions are suitable for use in exothermic brazing units. Exothermic brazing utilizes simplified tooling and equipment. The process employs the reaction heat in
bringing adjoining or nearby metal interfaces to a temperature where preplaced
brazing filler metal will melt and wet the metal interface surfaces. The brazing
filler metal can be a commercially available one having suitable melting and flow
temperatures. The only limitations may be the thickness of the metal that must be
heated through and the effects of this heat, or any previous heat treatment, on the
metal properties.
d.
Selection of Base Metal.
(1) In addition to the normal mechanical requirements of the base metal in
the brazement, the effect of the brazing cycle on the base metal and the final
joint strength must be considered. Cold-work strengthened base metals will be
annealed when the brazing process temperature and time are in the annealing range
of the base metal being processed. “Hot-cold worked” heat resistant base metals
11-30
TC 9-237
can also be brazed; however, only the annealed physical properties will be available in the brazement. The brazing cycle will usually anneal the cold worked base
metal unless the brazing temperature is very low and the time at heat is very
short. It is not practical to cold work the base metal after the brazing operation.
(2) When a brazement must have strength above the annealed properties of the
base metal after the brazing operation, a heat treatable base metal should be selected. The base metal can be an oil quench type, an air quench type that can be
brazed and hardened in the same or separate operation, or a precipitation hardening
type in which the brazing cycle and solution treatment cycle may be combined.
Hardened parts may be brazed with a low temperature filler metal using short times
at temperature to maintain the mechanical properties.
(3) The strength of the base metal has an effect on the strength of the
brazed joint. Some base metals are also easier to braze than others, particularly
by specific brazing processes. For example, a nickel base metal containing high
titanium or aluminum additions will present special problems in furnace brazing.
Nickel plating is sometimes used as a barrier coating to prevent the oxidation of
the titanium or aluminum, and it presents a readily wettable surface to the brazing
filler metal.
e . Brazing Filler Metals. For satisfactory use in brazing applications, brazing filler metals must possess the following properties:
(1) The ability to form brazed joints possessing suitable mechanical and
physical properties for the intended service application.
(2) A melting point or melting range compatible with the base metals being
joined and sufficient fluidity at brazing temperature to flow and distribute into
properly prepared joints by capillary action.
(3) A composition of sufficient homogeneity and stability to minimize separation of constituents (liquation) under the brazing conditions to be encountered.
(4) The ability to wet the surfaces of the base metals being joined and form
a strong, sound bond.
(5) Depending on the requirements, ability to produce or avoid base metalfiller metal interactions.
11-15.
BRAZING GRAY CAST IRON
a. Gray cast iron can be brazed with very little or no preheating. For this
reason, broken castings that would otherwise need to be dismantled and preheated
can be brazed in place. A nonferrous filler metal such as naval brass (60 percent
copper, 39.25 percent zinc, 0.75 percent tin) is satisfactory for this purpose.
This melting point of the nonferrous filler metal is several hundred degrees lower
than the cast iron; consequently the work can be accomplished with a lower heat
input, the deposition of metal is greater and the brazing can be accomplished faste r . Because of the lower heat required for brazing, the thermal stresses developed
are less severe and stress relief heat treatment is usually not required.
11-31
TC 9-237
b. The preparation of large castings for brazing is much like that required for
welding with cast iron rods. The joint to be brazed must be clean and the part
must be sufficiently warm to prevent chilling of filler metal before sufficient
penetration and bonding are obtained. When possible, the joint should be brazed
from both sides to ensure uniform strength throughout the weld. In heavy sections,
the edges should be beveled to form a 60 to 90 degree V.
11-16.
BRAZING MALLEABLE IRON
Malleable iron castings are usually repaired by brazing because the heat required
for fusion welding will destroy the properties of malleable iron. Because of the
special heat treatment required to develop malleability, it is impossible to completely restore these properties by simply annealing. Where special heat treatment
can be performed, welding with a cast iron filler rod and remalleabilizing are
feasible.
Section III.
11-17.
RELATED PROCESSES
SILVER BRAZING (SOLDERING)
a. Silver brazing, frequently called “silver soldering,” is a low temperature
brazing process with rods having melting points ranging from 1145 to 1650°F (618
to 899°C). This is considerably lower than that of the copper alloy brazing filler metals. The strength of a joint made by this process is dependent on a thin
film of silver brazing filler metal. Silver brazing joints are shown in figure
11-16.
11-32
TC 9-237
b. Silver brazing filler metals are composed of silver with varying percentages
of copper, nickel, tin, and zinc. They are used for joining all ferrous and nonferrous metals except aluminum, magnesium, and other metals which have too low a
melting point.
WARNING
.
Cadmium oxide fumes formed by heating and melting of silver brazing
alloys are highly toxic. To prevent injury to personnel, personal
protective equipment must be worn and adequate ventilation provided.
c. It is essential that the joints be free of oxides, scale, grease, dirt, or
other foreign matter. Surfaces other than cadmium plating can be easily cleaned
mechanically by wire brushing or an abrasive cloth; chemically by acid pickling or
other means. Extreme care must be used to grind all cadmium surfaces to the base
metals since cadmium oxide fumes formed by heating and melting of silver brazing
alloys are highly toxic.
d. Flux is generally required. The melting point of the flux must be lower
than the melting point of the silver brazing filler metal. This will keep the base
metal clean and properly flux the molten metal. A satisfactory flux should be
applied by means of a brush to the parts to be joined and also to the silver brazing filler metal rod.
e. When silver brazing by the oxyacetylene process, a strongly reducing flame
is desirable. The outer envelope of the f1ame, not the inner cone, should be applied to the work. The cone of the flame is too hot for this purpose. Joint clearances should be between 0.002 and 0.005 in. (0.051 to 0.127 mm) for best filler
metal distribution. A thin film of filler metal in a joint is stronger and more
effective, and a fillet build up around the joint will increase its strength.
f . The base metal should be heated until the flux starts to melt along the line
of the joint. The filler metal is not subjected to the flame, but is applied to
the heated area of the base metal just long enough to flow the filler metal completely into the joint. If one of the parts to be joined is heavier than the other, the heavier part should receive the most heat. Also, parts having high heat
conductivity should receive more heat.
11-18. OXYFUEL CUTTING
a.
General.
(1) If iron or steel is heated to its kindling temperature (not less than
1600°F (871°C)), and is then brought into contact with oxygen, it burns or oxidizes very rapidly. The reaction of oxygen with the iron or steel forms iron oxide
( F e3 O 4 ) and gives off considerable heat. This heat is sufficient to melt the oxide
and some of the base metal; consequently, more of the metal is exposed to the oxygen stream. This reaction of oxygen and iron is used in the oxyacetylene cutting
process. A stream of oxygen is firmly fixed onto the metal surface after it has
been heated to the kindling temperature. The hot metal reacts with oxygen, generating more heat and melting. The molten metal and oxide are swept away by the rapidly moving stream of oxygen. The oxidation reaction continues and furnishes heat
11-33
TC 9-237
11-18.
OXYFUEL CUTTING (cont)
for melting another layer of metal. The cut progresses in this manner. The principle of the cutting process is shown in figure 11-17.
(2) Theoretically, the heat created by the burning iron would be sufficient
to heat adjacent iron red hot, so that once started the cut could be continued
indefinitely with oxygen only, as is done with the oxygen lance. In practice,
however, excessive heat absorption at the surface caused by dirt, scale, or other
substances, make it necessary to keep the preheating flames of the torch burning
throughout the operation.
b.
Cutting Steel and Cast Iron.
(1) General. Plain carbon steels with a carbon content not exceeding 0.25
percent can be cut without special precautions other than those required to obtain
cuts of good quality. Certain steel alloys develop high resistance to the action
of the cutting oxygen, making it difficult and sometimes impossible to propagate
the cut without the use of special techniques. These techniques are described
briefly in (2) and (3) which follow:
11-34
TC 9-237
(2) High carbon steels. The action of the cutting torch on these metals is
similar to a flame hardening procedure, in that the metal adjacent to the cutting
area is hardened by being heated above its critical temperature by the torch and
quenched by the adjacent mass of cold metal. This condition can be minimized or
overcome by preheating the part from 500 to 600°F (260 to 316°C) before the cut
i s made.
(3) Waster plate on alloy steel. The cutting action on an alloy steel that
i s difficult to cut can be improved by clamping a mild steel “waster plate” tightly
t o the upper surface and cutting through both thicknesses. This waster plate methcd will cause a noticeable improvement in the cutting action, because the molten
steel dilutes or reduces the alloying content of the base metal.
(4) Chromium and stainless steels. These and other alloy steels that previously could only be cut by a melting action can now be cut by rapid oxidation
through the introduction of iron powder or a special nonmetallic powdered flux into
the cutting oxygen stream. This iron powder oxidizes quickly and liberates a large
quantity of heat. This high heat melts the refractory oxides which normally protect the alloy steel from the action of oxygen. These molten oxides are flushed
from the cutting face by the oxygen blast. Cutting oxygen is enabled to continue
its reaction with the iron powder and cut its way through the steel plates. The
nonmetallic flux, introduced into the cutting oxygen stream, combines chemically
with the refractory oxides and produces a slag of a lower melting point, which is
washed or eroded out of the cut, exposing the steel to the action of the cutting
oxygen.
(5) Cast iron. Cast iron melts at a temperature lower than its oxides.
Therefore, in the cutting operation, the iron tends to melt rather than oxidize.
For this reason, the oxygen jet is used to wash out and erode the molten metal when
cast iron is being cut. To make this action effective, the cast iron must be preheated to a high temperature. Much heat must be liberated deep in the cut. This
is done by adjusting the preheating flames so that there is an excess of acetylene. The length of the acetylene streamer and the procedure for advancing the cut
are shown in figure 11-18. The use of a mild iron flux to maintain a high temperature in the deeper recesses of the cut, as shown in figure 11-18, is also effective.
11-35
TC 9-237
11-18.
c.
OXYFUEL CUTTING (cont)
Cutting with MAPP gas.
(1) Quality cuts with MAPP gas require a proper balance between preheat flame
adjustment, oxygen pressure, coupling distance, torch angle, travel speed, plate
quality, and tip size. Oxyfuel ratios to control flame condition are given in
table 11-4.
11-36
TC 9-237
(2) MAPP gas is similar to acetylene and other fuel gases in that it can be
made to produce carburizing, neutral or oxidizing flames (table 11-4). The neutral
flame is the adjust most likely to be used for flame cutting. After lighting
the torch, slowly increase the preheat oxygen until the initial yellow flame becomes blue, with some yellow feathers remaining on the end of the preheat cones.
This is a slightly carburizing flame. A slight twist of the oxygen valve will
cause the feathers to disappear. The preheat cones will be dark blue in color and
will be sharply defined. This is a neutral flame adjustment and will remain so,
even with a small additional amount of preheat oxygen. Another slight twist of the
oxygen valve will cause the flame to suddenly change color from a dark blue to a
lighter blue color. An increase in sound also will be noted, and the preheat cones
will become longer. This is an oxidizing flame. Oxidizing flames are easier to
look at because of their lower radiance.
(3) MAPP gas preheat flame cones are at least one and one-half times longer
than acetylene preheat cones when produced by the same basic style of tip.
(4) The situation is reversed for natural gas burners, or for torches with a
two-piece tip. MAPP gas flame cones are much shorter than the preheat flame on a
natural gas two-piece tip.
(5) Neutral flame adjustments are used most cutting. Carburizing and
oxidizing flames also are used in special applications. For exanple, carburizing
flame adjustments are used in stack cutting, or where a very square top edge is
desired. The “slightly carburizing” flare is used to stack cut light material
because slag formation is minimized. If a strongly oxidizing flame is used, enough
slag may be produced in the kerf to weld the plates together. Slag-welded plates
often cannot be separated after the cut is completed.
(6) A “moderately oxidizing” flame is used for fast starts when cutting or
piercing. It produces a slightly hotter flame temperature, and higher burning
velocity than a neutral flame. An oxidizing flame commonly is used with a “highlow” device. The large “high” oxidizing flame is used to obtain a fast start. As
soon as the cut has started, the operator drops to the “low” position and continues
the cut with a neutral flame.
11-37
TC 9-237
11-18.
OXYFUEL CUTTING (cont)
(7) “Very oxidizing” flames should not be used for fast starting. An overly
oxidizing flame will actually increase starting time. The extra oxygen flow does
not contribute to combustion, but only cools the flame and oxidizes the steel surface.
(8) The oxygen pressure at the torch , not at some remotely located regulator,
should be used. Put a low volume, soft flame on the tip. Then turn on the cutting
oxygen and vary the pressure to find the best looking stinger (visible oxygen cutting stream).
(a) LoW pressures give very short stingers, 20 to 30 in. (50.8 to 76.2 cm)
long. Low-pressure stingers will break up at the end. As pressure is increased,
the stinger will suddenly become coherent and long. This is the correct cutting
oxygen pressure for the given tip. The long stinger will remain over a fairly wide
pressure range. But as oxygen pressures are increased, the stinger returns to the
short, broken form it had under low pressure.
(b) If too high an oxygen pressure is used, concavity often will show on
the cut surface. Too high an oxygen pressure also can cause notching of the cut
surface. The high velocity oxygen stream blows the metal and slag out of the kerf
so fast that the cut is continuously being started. If too low a pressure is used,
the operation cannot run at an adequate speed. Excessive drag and slag formation
results, and a wide kerf often is produced at the bottom of the cut.
(9) Cutting oxygen, as well as travel speed, also affects the tendency of
slag to stick to the bottom of a cut. This tendency increases as the amount of
metallic iron in the slag increases. Two factors cause high iron content in slag:
too high a cutting oxygen pressure results in an oxygen velocity through the kerf
high enough to blow out molten iron before the metal gets oxidized; and too high a
cutting speed results in insufficient time to thoroughly oxidize the molten iron,
with the same result as high oxygen pressure.
(10) The coupling distance is the distance between the end of the flame cones
and the workpiece. Flame lengths vary with different fuels, and different flame
adjusts. Therefore, the distance between the end of the preheat cones and the
workpiece is the preferred measure (fig. 11-19). When cutting ordinary plate
thicknesses up to 2 to 3 in. (5.08 to 7.62 cm) with MAPP gas, keep the end of the
preheat cones abut 1/16 to 1/8 in. (0.16 to 0.32 cm) off the surface of the work.
When piercing, or for very fast starts, let the preheat cones impinge on the surface. This will give faster preheating. As plate thicknesses increase above 6 in.
(15.24 cm), increase the coupling distance to get more heating from the secondary
flame cone. The secondary MAPP gas flame will preheat the thick plate far ahead of
the cut. When material 12 in. (30.48 cm) thick or more is cut, use a coupling
distance of ¾ to 1¼ in. (1.91 to 3.18 cm) long.
11-38
TC 9-237
(11) Torch angle
(a) Torch, or lead angle, is the acute angle between the axis of the torch
and the workpiece surface when the torch is pointed in the direction of the cut
(fig. 11-20). When cutting light-gauge steel (up to ¼ in. (0.64 cm) thick) a 40
to 50 degree torch angle allows much faster cutting speeds than if the torch were
mounted perpendicular to the plate. On plate up to ½ in. (1.27 cm) thick, travel
speed can be increased with a torch lead angle, but the angle is larger, about 60
to 70 degrees. Little benefit is obtained from cutting plate over ½ in. (1.27
cm) thick with an acute lead-angle. Plate over this thickness should be cut with
the torch perpendicular to the workpiece surface.
11-39
TC 9-237
11-18.
OXYFUEL CUTTING (cont)
(b) An angled torch cuts faster on thinner-gauge material. The intersection of the kerf and the surface presents a knife edge which is easily ignited.
Once the plate is burning, the cut is readily carried through to the other side of
the work. When cutting heavy plate, the torch should be perpendicular to the
workpiece surface and parallel to the starting edge of the work. This avoids problems of non-drop cuts, incomplete cutting on the opposite side of the thicker
plate, gouging cuts in the center of the kerf and similar problems.
(12) There is a best cutting speed for each job. On plate up to about 2 in.
(5.08 cm) thick, a high quality cut will be obtained when there is a steady “purring” sound from the torch and the spark stream under the plate has a 15 degree lead
angle. This is the angle made by the sparks coming out of the bottom of the cut in
the same direction as the torch is traveling. If the sparks go straight down, or
even backwards, it means travel speed is too high.
(13) Cut quality.
(a) Variations in cut quality can result from different workpiece surface
conditions or plate compositions. For example, rusty or oily plates require more
preheat, or slower travel speeds than clean plates. Most variations from the ideal
condition of a clean, flat, low-carbon steel plate tend to slow down the cuttting
action.
(b) One method to use for very rusty plate is to set as big a preheat flame
as possible on the torch, then run the flame back and forth over the line to be
cut. The extra preheat passes do several things. They spall off much of the scale
that would otherwise interfere with the cuttting action; and the passes put extra
preheat into the plate which usually is beneficial in obtaining improved cut quality and speed.
(c) When working with high strength low alloy plates such as ASTM A-242
steel, or full alloy plates such as ASTM A-514, cut a little bit slower. Also use
a low oxygen pressure because these steels are more sensitive to notching than
ordinary carbon steels.
(d) Clad carbon-alloy, carbon-stainless, or low-carbon-high-carbon plates
require a lower oxygen pressure, and perhaps a lower travel speed than straight
low-carbon steel. Ensure the low carbon-steel side is on the same side as the
torch. The alloyed or higher carbon cladding will not burn as readily as the carbon steel. By putting the cladding on the bottom, and the carbon steel on the top,
a cutting action similar to powder cutting results. The low-carbon steel on top
burns readily and forms slag. As the iron-bearing slag passes through the highcarbon or high-alloy cladding, it dilutes the cladding material. The torch, in essence, still burns a lower carbon steel. If the clad or high-carbon steel is on
the top surface, the torch is required to cut a material that is not readily
oxidizable, and forms refractory slags that can stop the cutting action.
11-40
TC 9-237
(14) Tip size and style.
(a) Any steel section has a corresponding tip size that gives the most
economical operation for a particular fuel. Any fuel will burn in any tip, of
course. But the fuel will not burn efficiently, and may even overheat and melt the
tip, or cause problems in the cut. For example, MAPP gas will not operate at peak
efficiency in most acetylene tips because the preheat orifices are not large
enough for MAPP. If MAPP gas is used with a natural-gas tip, there will be a tendency to overheat the tip. The tips also will be susceptible to flash back. A
natural-gas tip can be used with MAPP gas, in an emergency, by removing the skirt.
Similarly, an acetylene tip can be used if inefficient burning can be tolerated for
a short run.
(b) The reasons for engineering different tips for different fuel gases are
complex. But the object is to engineer the tip to match the burning velocity, port
velocity, and other relationships for each type of gas and orifice size, and to
obtain the optimum flame shape and heat transfer properties for each type of fuel.
Correct cutting tips cost so little that the cost of conversion is minute compared
with the cost savings resulting from efficient fuel use, improved cut quality, and
increased travel speed.
Section IV.
11-19.
a.
WELDING, BRAZING, AND SOLDERING NONFERROUS METALS
ALUMINUM WELDING
General.
(1) General. Aluminum is readily joined by welding, brazing, and soldering.
In many instances, aluminum is joined with the conventional equipment and techniques used with other metals. However, specialized equipment or techniques may
sometimes be required. The alloy, joint configuration, strength required, appearance, and cost are factors dictating the choice of process. Each process has certain advantages and limitations.
(2) Characteristics of aluminum. Aluminum is light in weight and retains
good ductility at subzero temperatures. It also has high resistance to corrosion,
good electrical and thermal conductivity, and high reflectivity to both heat and
light. Pure aluminum melts at 1220°F (660°C), whereas aluminum alloys have an
approximate melting range from 900 to 1220°F (482 to 660°C). There is no color
change in aluminum when heated to the welding or brazing range.
(3) Aluminum forms. Pure aluminum can be alloyed with many other metals to
produce a wide range of physical and mechanical properties. The means by which the
alloying elements strengthen alminum is used as a basis to classify alloys into
two categories: nonheat treatable and heat treatable. Wrought alloys in the form
of sheet and plate, tubing, extruded and rolled shapes, and forgings have similar
joining characteristics regardless of the form. Aluminum alloys are also produced
as castings in the form of sand, permanent mold, or die castings. Substantially
the same welding, brazing, or soldering practices are used on both cast and wrought
11-41
TC 9-237
11-19.
ALUMINUM WELDING (cont)
metal.
quired.
dered.
castings
Die castings have not been widely used where welded construction is reHowever, they have been adhesively bonded and to a limited extent solRecent developments in vacuum die casting have improved the quality of the
to the point where they may be satisfactorily welded for some applications.
(4) Surface preparation. Since aluminum has a great affinity for oxygen, a
film of oxide is always present on its surface. This film must be removed prior to
any attempt to weld, braze, or solder the material. It also must be prevented from
forming during the joining procedure. In preparation of aluminum for welding,
brazing, or soldering, scrape this film off with a sharp tool, wire brush, sand
paper, or similar means. The use of inert gases or a generous application of flux
prevents the forming of oxides during the joining process.
b.
Gas Welding.
(1) General. The gas welding processes most commonly used on aluminum and
aluminum alloys are oxyacetylene and oxyhydrogen. Hydrogen may be burned with
oxygen using the same tips as used with acetylene. However, the temperature is
lower and larger tip sizes are necessary (table 11-5). Oxyhydrogen welding permits
a wider range of gas pressures than acetylene without losing the desired slightly
reducing flame. Aluminum from 1/32 to 1 in. (0.8 to 25.4 mm) thick may be gas
welded. Heavier material is seldom gas welded, as heat dissipation is so rapid
that it is difficult to apply sufficient heat with a torch. When compared with arc
welding, the weld metal freezing rate of gas welding is very slow. The heat input
in gas welding is not as concentrated as in other welding processes and unless
precautions are taken greater distortion may result. Minimum distortion is obtained with edge or corner welds.
11-42
TC 9-237
(2) Edge preparation. Sheet or plate edges must be properly prepared to
obtain gas welds of maximum strength. They are usually prepared the same as similar thicknesses of steel. However, on material up to 1/16 in. (1.6 mm) thick, the
edges can be formed to a 90 degree flange. The flanges prevent excessive warping
and buckling. They serve as filler metal during welding. Welding without filler
rod is normally limited to the pure aluminum alloys since weld cracking can occur
in the higher strength alloys. In gas welding thickness over 3/16 in. (4.8 mm),
the edges should be beveled to secure complete penetration. The included angle of
bevel may be 60 to 120 degrees. Preheating of the parts is recommended for all
castings and plate ¼ in. (6.4 mm) thick or over. This will avoid severe thermal
stresses and insure good penetration and satisfactory welding speeds. Common practice is to preheat to a temperature of 700°F (371°C). Thin material should be
warmed with the welding torch prior to welding. Even this slight preheat helps to
prevent cracks. Heat treated alloys should not be preheated above 800°F (427°C),
unless they are to be postweld heat treated. Preheating above 800°F (427°C) will
cause a “hot-short” and the metal strength will deteriorate rapidly.
(3) Preheat temperature checking technique. When pyrolytic equipment (temperature gauges) is not available, the following tests can be made to determine the
proper preheat temperatures:
(a) Char test. Using a pine stick, rub the end of the stick on the metal
being preheated. At the proper temperatures, the stick will char. The darker the
char, the higher the temperature.
(b) C a r p e n t e r ' s c h a l k . Mark the metal with ordinary blue carpenter's
chalk. The blue line will turn white at the proper preheat temperature.
(c) Hammer test. Tap the metal lightly with a hand hammer. The metal
loses its ring at the proper preheat temperature.
(d) Carburizing test. Carburize the surface of the metal, sooting the
entire surface. As the heat from the torch is applied, the soot disappears. At
the point of soot disappearance, the metal surface is slightly above 300°F
(149°C). Care should be used not to coat the fluxed area with soot. Soot can be
absorbed into the weld, causing porosity.
(4) Welding flame. A neutral or slightly reducing flame is recommended f o r
welding aluminum. Oxidizing flames will cause the formation of aluminum oxide,
resulting in poor fusion and a defective weld.
(5) Welding fluxes.
(a) Aluminum welding flux is designed to remove the aluminum oxide film and
exclude oxygen from the vicinity of the puddle.
(b) The fluxes used in gas welding are usually in powder form and are mixed
with water to form a thin paste.
11-43
TC 9-237
11-19.
ALUMINUM WELDING (cont)
(c) The flux should be applied to the seam by brushing, sprinkling, spraying, or other suitable methods. The welding rod should also be coated. The flux
wil1 melt below the welding temperature of the metal and form a protective coating
on the surface of the puddle. This coating breaks up the oxides, prevents oxidation, and permits slow cooling of the weld.
WARNING
The acid solutions used to remove aluminum welding and brazing fluxes
after welding or brazing are toxic and highly corrosive. Goggles,
rubber gloves, and rubber aprons must be worn when handling the acids
and solutions. Do not inhale fumes. When spilled on the body or clothing, wash immediately with large quantities of cold water. Seek medical attention. Never pour water into acid when preparing solutions;
instead, pour acid into water. Always mix acid and water slowly.
These operations should only be performed in well ventilated areas.
(d) The aluminum welding fluxes contain chlorides and flourides. In the
presence of moisture, these will attack the base metal. Therefore, all flux remaining on the joints after welding must be completely removed. If the weld is readily
accessible, it can be cleaned with boiling water and a fine brush. Parts having
joints located so that cleaning with a brush and hot water is not practical may be
cleansed by an acid dip and a cold or hot water rinse. Use 10 percent sulfuric
acid cold water solution for 30 minutes or a 5 percent sulfuric acid hot water
(150°F (66°C)) solution for 5 to 10 minutes for this purpose.
(6) Welding technique. After the material to be welded has been properly
prepared, fluxed, and preheated, the flame is passed in small circles over the
starting point until the flux melts. The filler rod should be scraped over toe
surface at three or four second intervals, permitting the filler rod to come clear
of the flame each time. The scraping action will reveal when welding can be started without overheating the aluminum. The base metal must be melted before the
filler rod is applied. Forehand welding is generally considered best for welding
on aluminum, since the flame will preheat the area to be welded. In welding thin
aluminum, there is little need for torch movement other than progressing forward.
On material 3/16 in. (4.8 mm) thick and over, the torch should be given a uniform
lateral motion. This will distribute the weld metal over the entire width of the
weld. A slight back and forth motion will assist the flux in the removal of oxide. The filler rod should be dipped into the weld puddle periodically, and with–
drawn from the puddle with a forward motion. This method of withdrawal closes the
puddle, prevents porosity, and assists the flux in removing the oxide film.
11-20.
ALUMINUM BRAZING
a. General. Many aluminum alloys can be brazed. Aluminum brazing alloys are
used to provide an all-aluminum structure with excellent corrosion resistance and
good strength and appearance. The melting point of the brazing filler metal is
relatively close to that of the material being joined. However, the base metal
should not be melted; as a result, close temperate control is necessary. The
brazing temperature required for aluminum assemblies is determined by the melting
points of the base metal and the brazing filler metal.
11-44
TC 9-237
b. Commercial Filler Metals. Commerical brazing filler metals for aluminum
alloys are aluminum base. These filler metals are available as wire or shim
stock. A convenient method of preplacing filler metal is by using a brazing sheet
(an aluminum alloy base metal coated on one or both sides). Heat treatable or core
alloys composed mainly of manganese or magnesium are also used. A third method of
applying brazing filler metal is to use a paste mixture of flux and filler metal
powder. Common aluminum brazing metals contain silicon as the melting point depressant with or without additions of zinc, copper, and magnesium.
c . Brazing Flux. Flux is required in all aluminum brazing operations. Aluminum brazing fluxes consist of various combinations of fluorides and chlorides and
are supplied as a dry powder. For torch and furnace brazing, the flux is mixed
with water to make paste. This paste is brushed, sprayed, dipped, or flowed onto
the entire area of the joint and brazing filler metal. Torch and furnace brazing
fluxes are quite active, may severely attack thin aluminum, and must be used with
care. In dip brazing, the bath consists of molten flux. Less active fluxes can be
used in this application and thin components can be safely brazed.
d. Brazed Joint Design. Brazed joints should be of lap, flange, lock seam, or
tee type. Butt or scarf joints are not generally recommended. Tee joints allow
for excellent capillary flow and the formation of reinforcing fillets on both sides
of the joint. For maximum efficiency lap joints should have an overlap of at least
twice the thickness of the thinnest joint member. An overlap greater than ¼ in.
(6.4 mm) may lead to voids or flux inclusions. In this case, the use of straight
grooves or knurls in the direction of brazing filler metal flow is beneficial.
Closed assemblies should allow easy escape of gases, and in dip brazing easy entry
as well as drainage of flux. Good design for long laps requires that brazing filler metal flows in one direction only for maximum joint soundness. The joint design
must also permit complete postbraze flux removal.
e. Brazing Fixtures. Whenever possible, parts should be designed to be selfjigging. When using fixtures, differential expansion can occur between the assembly and the fixture to distort the parts. Stainless steel or Inconel springs are
often used with fixtures to accommodate differences in expansion. Fixture material
can be mild steel or stainless steel. However, for repetitive furnace brazing
operations and for dip brazing to avoid flux bath contamination, fixtures of nickel, Inconel, or aluminum coated steel are preferred.
f . Precleanig. Precleaning is essential for the production of strong,
leaktight, brazed joints. Vapor or solvent cleaning will usually be adequate for
the nonheat treatable alloys. For heat treatable alloys, however, chemical cleaning or manual cleaning with a wire brush or sandpaper is necessary to remove the
thicker oxide film.
g. Furnace Brazing. Furnace brazing is performed in gas, oil, or electrically
heated furnaces. Temperature regulation within 5°F (2.8°C) is necessary to secure consistent results. Continuous circulation of the furnace atmosphere is desirable, since it reduces brazing time and results in more uniform heating. Products
of combustion in the furnace can be detrimental to brazing and ultimate serviceability of brazed assemblies in the heat treatable alloys.
11-45
TC 9-237
11-20.
ALUMINUM BRAZING (cont)
h. Torch Brazing. Torch brazing differs from furnace brazing in that heat is
localized. Heat is applied to the part until the flux and brazing filler metal
melt and wet the surfaces of the base metal. The process resembles gas welding
except that the brazing filler metal is more fluid and flows by capillary action.
Torch brazing is often used for the attachment of fittings to previously weld or
furnace brazed assemblies, joining of return bends, and similiar applications.
i . Dip Brazing. In dip brazing operations, a large amount of molten flux is
held in a ceramic pot at the dip brazing temperature. Dip brazing pots are heated
internally by direct resistance heating. Low voltage, high current transformers
supply alternating current to pure nickel, nickel alloy, or carbon electrodes immersed in the bath. Such pots are generally lined with high alumina content fire
brick and a refractory mortar.
WARNING
The acid solutions used to remove aluminum welding and brazing fluxes
after welding or brazing are toxic and highly corrosive. Goggles,
rubber gloves, and rubber aprons must be worn when handling the acids
and solutions. Do not inhale fumes. When spilled on the body or clothing, wash immediately with large quantities of cold water. Seek medical attention.
Never pour water into acid when preparing solutions: instead, pour acid
into water. Always mix acid and water slowly. These operations should
only be performed in well ventilated areas.
j. P o s t b r a z i n g C l e a n i n g . It is always necessary to clean the brazed assemblies, since brazing fluxes accelerate corrosion if left on the parts. The most
satisfactory way of removing the major portion of the flux is to immerse the hot
parts in boiling water as soon as possible after the brazing alloy has solidified.
The steam formed removes a major amount of residual flux. If distortion from
quenching is a problem, the part should be allowed to cool in air before being
immersed in boiling water. The remaining flux may be removed by a dip in concentrated nitric acid for 5 to 15 minutes. The acid is removed with a water rinse,
preferably in boiling water in order to accelerate drying. An alternate cleaning
method is to dip the parts for 5 to 10 minutes in a 10 percent nitric plus 0.25
percent hydrofluoric acid solution at room temperature. This treatment is also
followed by a hot water rinse. For brazed assemblies consisting of sections thinner than 0.010 in. (0.254 mm), and parts where maximum resistance to corrosion is
important. A common treatment is to immerse in hot water followed by a dip in a
solution of 10 percent nitric acid and 10 percent sodium dichromate for 5 to 10
minutes. This is followed by a hot water rinse. When the parts emerge from the
hot water rinse they are immediately dried by forced hot air to prevent staining.
11-21.
SOLDERING
a. General. Soldering is a group of processes that join metals by heating them
to a suitable temperature. A filler metal that melts at a temperature above 840°F
(449°C) and below that of the metals to be joined is used. The filler metal is
distributed between the closely fitted surfaces of the joint by capillary attraction. Soldering uses fusible alloys to join metals. The kind of solder used depends on the metals to be joined. Hard solders are called spelter and hard soldering is called silver solder brazing. This process gives greater strength and will
stand more heat than soft solder.
11-46
TC 9-237
b. Soft Soldering. This process is used for joining most common metals with an
alloy that melts at a temperature below that of the base metal. In many respects,
this operation is similar to brazing in that the base is not melted, but is merely
tinned on the surface by the solder filler metal. For its strength the soldered
joint depends on the penetration of the solder into the pores of the base metal
surface, along with the consequent formation of a base metal-solder alloy, together
with the mechanical bond between the parts. Soft solders are used for airtight or
watertight joints which are not exposed to high temperatures.
c. Joint Preparation. The parts to be soldered should be free of all oxide,
scale, oil, and dirt to ensure sound joints. Cleaning may be performed by immersing in caustic or acid solutions, filing, scraping, or sandblasting.
d. Flux. All soldering operations require a flux in order to obtain a complete
bond and full strength at the joints. Fluxes clean the joint area, prevent oxidations, and increase the wetting power of the solder by decreasing its surface tension. The following types of soft soldering fluxes are in common use: rosin, or
rosin and glycerine. These are used on clean joints to prevent the formation of
oxides during the soldering operations. Zinc chloride and ammonium chloride may be
used on tarnished surfaces to permit good tinning. A solution of zinc cut in hydrochloric (muriacic) acid is commonly used by tin workers as a flux.
e. Application. Soft solder joints may be made by using gas flames, wiping,
sweating the joints, or by dipping in solder baths. Dipping is particularly applicable to the repair of radiator cores. Electrical connections and sheet metal are
soldered with a soldering iron or gun. Wiping is a method used for joining lead
pipe and also the lead jacket of underground and other lead-covered cables. Sweated joints may be made by applying a mixture of solder powder and paste flux to the
joints. Then heat the part until this solder mixture liquifies and flows into the
joints, or tin mating surfaces of members to be joined, and apply heat to complete
the joint.
11-22.
ALUMINUM SOLDERING
a. General. Aluminum and aluminum base alloys can be soldered by techniques
which are similar to those used for other metals. Abrasion and reaction soldering
are more commonly used with aluminum than with other metals. However, aluminum
requires special fluxes. Rosin fluxes are not satisfactory.
b. Solderability of Aluminum Alloys. The most readily soldered aluminum alloys
contain no more than 1 percent magnesium or 5 percent silicon. Alloys containing
greater amounts of these constituents have poor flux wetting characteristics. High
copper and zinc-containing alloys have poor soldering characteristics because of
rapid solder penetration and loss of base metal properties.
c. Joint Design. The joint designs used for soldering aluminum assemblies are
similar to those used with other metals. The most commonly used designs are forms
of simple lap and T-type joints. Joint clearance varies with the specific soldering method, base alloy composition, solder composition, joint design, and flux
11-47
TC 9-237
11-22. ALUMINUM SOLDERING (cont)
composition employed. However, as a guide, joint clearance ranging from 0.005 to
0.020 in. (0.13 to 0.51 mm) is required when chemical fluxes are used. A 0.002 to
0.010 in. (0.05 to 0.25 mm) spacing is used when a reaction type flux is used.
d. Preparation for Soldering. Grease, dirt, and other foreign material must be
removed from the surface of aluminum before soldering. In most cases, only solvent
degreasing is required. However, if the surface is heavily oxidized, wire-brushing
or chemical cleaning may be required.
CAUTION
Caustic soda or cleaners with a pH above 10 should not be used on aluminum or aluminum alloys, as they may react chemically.
e. Soldering techniques. The higher melting point solders normally used to
join aluminum assemblies plus the excellent thermal conductivity of aluminum dictate that a large capacity heat source must be used to bring the joint area to
proper soldering temperature. Uniform, well controlled heating should be provided. Tinning of the aluminum surface can best be accomplished by covering the material with a molten puddle of solder and then scrubbing the surface with a non-heat
absorbing item such as a glass fiber brush, serrated wooden stick or fiber block.
Wire brush or other metallic substances are not recommended.
They tend to leave
metallic deposits, absorb heat, and quickly freeze the solder.
f . Solders. The commercial solders for aluminum can be classified into three
general groups according to their melting pints:
(1) Lay temperature solders. The melting point of these solders is between
300 and 500°F (149 and 260°C). Solders in this group contain tin, lead, zinc,
and/or cadmium and produce joints with the least corrosion resistance.
(2) Intermediate temperature solders. These solders melt between 500 and 700
°F (260 and 371°C). Solders in this group contain tin or cadmium in various combinations with zinc, plus small amounts of aluminum, copper, nickel or silver, and
lead.
(3) High temperature solders. These solders melt between 700 and 800°F (371
and 427°C). These zinc base solders contain 3 to 10 percent aluminum and small
amounts of other metals such as copper, silver, nickel; and iron to modify their
melting and wetting characteristics. The high zinc solders have the highest
strength of the aluminum solders, and form the most corrosion-resistant soldered
assemblies.
11-23.
COPPER WELDING
welding is
a. Copper has a high thermal conductivity. The heat required f o r
approximately twice that required for steel of similar thickness. Too offset this
heat loss, a tip one or two sizes larger than that required for steel is recommended. When welding large sections of heavy thicknesses, supplementary heating is
advisable. This process produces a weld that is less porous.
b. Copper may be welded with a slightly oxidizing flame because the molten
metal is protected by the oxide which is formed by the flame. If a flux is used to
protect the molten metal, the flame should be neutral.
11-48
TC 9-237
c. Oxygen-free copper (deoxidized copper red) should be used rather than oxygenbearing copper for gas welded assemblies. The rod should be of the same composition as the base metal.
d. In welding copper sheets, the heat is conducted away from the welding zone
so rapidly that it is difficult to bring the temperature up to the fusion point.
It is often necessary to raise the temperature level of the sheet in an area 6.0 to
12.0 in. (152.4 to 304.8 mm) away from the weld. The weld should be started at
some point away from the end of the joint and welded back to the end with filler
metal being added. After returning to the starting point, the weld should be started and made in the opposite direction to the other end of the seam. During the
operation, the torch should be held at approximately a 60 degree angle to the base
metal.
e. It is advisable to back up the seam on the underside with carbon blocks or
thin sheet metal to prevent uneven penetration. These materials should be channeled or undercut to permit complete fusion to the base of the joint. The metal on
each side of the weld should be covered to prevent radiation of heat into the atmosp h e r e . This would allow the molten metal in the weld to solidify and cool slowly.
f . The welding speed should be uniform. The end of the filler rod should be
kept in the molten puddle. During the entire welding operation, the molten metal
most be protected by the outer flame envelope. If the metal fails to flow freely
during the operation, the rod should be raised and the base metal heated to a red
heat along the seam. The weld should be started again and continued until the seam
weld is completed.
g. When welding thin sheets, the forehand welding method is preferred. The
backhand method is preferred for thicknesses of ¼ in. (6.4 mm) or more. For
sheets up to 1/8 in. (3.2 mm) thick a plain butt joint with squared edges is preferred. For thicknesses greater than 1/8 in. (3.2 mm) the edges should be beveled
for an included angle of 60 to 90 degrees. This will ensure penetration with
spreading fusion over a wide area.
11-24.
COPPER BRAZING
a. Both oxygen-bearing and oxygen-free copper can be brazed to produce a joint
with satisfactory properties. The full strength of an annealed copper brazed joint
will be developed with a lap joint.
b. The flame used should be slightly carburizing. All of the silver brazing
alloys can be used with the proper fluxes. With the copper-phosphorous or copperphosphorous-silver alloys, a brazed joint can be made without a flux, although the
use of flux will result in a joint of better appearance.
c. Butt, lap, and scarf joints are used in brazing operations, whether the
joint members are flat, round, tubular, or of irregular cross sections. Clearances
to permit the penetration of the filler metal, except in large diameter pipe
joints, should not be more than 0.002 to 0.003 in. (0.051 to 0.076 mm). The clearances of large diameter pipe joinings may be 0.008 to 0.100 in. (0.203 to 2.540
mm) . The joint may be made with inserts of the filler metal or the filler metal
may be fed in from the outside after the joint has been brought up to the proper
temperature. The scarf joint is used in joining bandsaws and for joints where the
double thickness of the lap is not desired.
11-49
TC 9-237
11-25.
BRASS AND BRONZE WELDING
a. General. The welding of brasses and bronzes differs from brazing. This
welding process requires the melting of both base metal edges and the welding rod,
whereas in brazing only the filler rod is melted.
b. Low Brasses (Copper 80 to 95 Percent, Zinc 5 to 20 Percent). Brasses of
this type can be welded readily in all positions by the oxyacetylene process.
Welding rods of the same composition as the base metal are not available. For this
reason, 1.5 percent silicon rods are recommended as filler metal. Their
weldability differs from copper in that the welding point is progressively reduced
as zinc is added. Fluxes are required. Preheating and supplementary heating may
also be necessary.
c. High Brasses (Copper 55 to 80 Percent, Zinc 20 to 45 Percent). These brasses can be readily welded in all positions by the oxyacetylene process. Welding
rods of substantially the same composition are available. The welding technique is
the same as that required for copper welding, including supplementary heating.
Fluxes are required.
d. Aluminum Bronze. The aluminum bronzes are seldom welded by the oxyacetylene
process because of the difficulty in handling the aluminum oxide with the fluxes
designed for the brasses. Sane success has been reported by using welding rods of
the same content as the base metal and a bronze welding flux, to which has been
added a small amount of aluminum welding flux to control the aluminum oxide.
e. Copper-Beryllium Alloys. The welding of these alloys by the oxyacetylene
process is very difficult because of the formation of beryllium oxide.
f. C o p p er-Nickel Alloys. From a welding standpoint, these alloys are similar
to Monel, and oxyacetylene welding can be used successfully. The flame used should
be slightly reducing. The rod must be of the same composition as the base metal.
A sufficient deoxidizer (manganese or silicon) is needed to protect the metal during welding. Flux designed specifically for Monel and these alloys must be used to
prevent the formation of nickel oxide and to avoid porosity. Limited melting of
the base metal is desirable to facilitate rapid solidification of the molten meta l . Once started, the weld should be completed without stopping. The rod should
be kept within the protective envelope of the flame.
g. Nickel Silver. Oxyacetylene welding is the preferred method for joining
alloys of this type. The filler metal is a high zinc bronze which contains more
than 10 percent nickel. A suitable flux must be used to dissolve the nickel oxide
and avoid porosity.
11-50
TC 9-237
h. Phosphor Bronze. Oxyacetylene welding is not commonly used for welding the
copper-tin alloys. The heating and slow cooling causes contraction, with consequent cracking and porosity in this hot-short material. However, if the oxyacetylene process must be used the welding rod should be grade E (1.0 to 1.5 percent tin) with a good flux of the type used in braze welding. A neutral flame is
preferred unless there is an appreciable amount of lead present. In this case an
oxidizing flame will be helpful in producing a sound weld. A narrow heat zone will
promote quick solidification and a sound weld.
NOTE
Hot-short is defined as a marked loss in strength at high temperatures
below the melting point.
i . Silicon Bronze. Copper-silicon alloys are successfully welded by the
oxyacetylene process. The filler metal should be of the same composition as the
base metal. A flux with a high boric acid content should be used. A weld pool as
small as possible should be maintained to facilitate rapid solidification. This
will keep the grain size small and avoid contraction strains during the hot-short
temperature range. A slightly oxidizing flare will keep the molten metal clean in
oxyacetylene welding of these alloys. This flame is helpful when welding in the
vertical or overhead positions.
11-26.
MAGNESIUM WELDING
a. General.
work. A broken
such a repair is
welding has been
does not require
Gas welding of magnesium is usually used only in emergency repair
or cracked part can be restored and placed back into use. However,
only temporary until a replacement part can be obtained. Gas
almost completely phased out by gas-shielded arc welding, which
th