Applying Shielded Metal Arc Welding

Applying Shielded Metal Arc Welding
Interest Approach
Applying Shielded Metal
Arc Welding
(SMAW) Techniques
Here is a broken machinery part.
How might the broken piece be
repaired?
Should we repair the part or replace
it?
If the part is to be repaired, what
skills will be necessary to complete
the job?
Student Learning Objectives
Student Learning Objectives
1. Explain the fundamentals and
developments of shielded metal arc
welding.
2. Describe how to select shielded
metal arc welding equipment and
supplies.
3. Explain how to prepare metal for
welding.
4. Describe the procedures and
techniques for shielded metal arc
welding.
5. Identify the safety practices that
should be observed when working
with shielded metal arc welding.
Terms
Alternating current
Amperage
Arc length
Arc welding
Conductor
Crater
Direct current
Duty cycle
Electricity
Electrode
Electrons
Fillet weld
Groove weld
Terms
Padding
Polarity
Resistance
Shielded metal
arc welding
Surface welds
Voltage
Weaving
Weld root
Welder
Welding
Weldor
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What are the
fundamentals and
developments of shielded
metal arc welding?
Welding
Welding is the melting, flowing
together, and freezing of metals
under controlled conditions.
1. Arc welding uses electricity to heat
and melt the metal.
2. A Weldor is the person doing the
welding.
3. A Welder is the machine doing the
welding.
There are basic fundamentals
of welding that must be
understood.
Welding
4. Shielded metal arc welding is
welding where fusion is produced
by heating with an arc between a
consumable stick electrode and the
work piece.
Welding
5. An electrode is a bare metal rod
which is usually coated with
chemical compounds called flux.
The flux coatings burn in the
intense heat and form a blanket of
smoke and gas that shields the
weld puddle from the air.
2
Electrical Terms
A basic understanding of
electrical terms is necessary
to fully understand shielded
metal arc welding.
1. Electricity is the flow of tiny
particles called electrons through a
conductor.
2. Electrons are negatively charged
particles.
3. A conductor allows the flow of
electrons.
Electrical Terms
Electrical Terms
4. Voltage is a measure of electrical
pressure.
5. Most welders operate on a 220
volt source.
A welder changes or transforms the
220 volt pressure to a much lower
pressure at the electrode, usually
between 15 and 25 volts.
Electrical Terms
8. Resistance is the opposition to
the flow of current in a circuit.
Resistance is what causes the electric
energy to be transformed into heat.
6. Amperage is a measure of
electrical current flowing through a
circuit and is an indication of the heat
being produced.
The amount of current available is
determined by the amperage setting on
the welder.
7. Polarity is the direction the current
is flowing.
Electrical Terms
9. When electricity is conducted
through a conductor, the movement
of the electric energy heats the
conductor due to the resistance of
the conductor to the flow of electric
current through it.
3
Electrical Terms
Electrical Terms
10. The greater the flow of current
through a conductor, the greater the
resistance to it, and the greater the
heat generated (the higher the
amperage setting, the greater the
heat produced).
11. When electrical current
alternates or reverses the direction
of electron flow it is called
alternating current (AC).
Electrical Terms
Electrical Terms
12. The arc is extinguished every
half-cycle as the current passes
through zero, usually at the rate of
120 times per second.
13. Electron flow in one direction is
called direct current (DC) which is
either straight polarity (DCSP) or
reverse polarity (DCRP)
When the electrons flow from the
electrode to the work piece it is straight
polarity.
When the electrons flow from workpiece
to the electrode it is reverse polarity.
History of Welding
The art of welding is an ancient one
but the science of shielded metal
arc welding is relatively new.
1. 1801—English scientist discovered
that an electric current would form an
arc when forced across a gap.
2. 1881—A French inventor used the
carbon arc.
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History of Welding
3. 1887—A Russian improved on
the carbon arc and patented the
process.
4. 1887—Another Russian
discovered that a bare metal rod
would melt off by the heat of the arc
and act as a filler metal in a weld.
History of Welding
5. 1889—An American
experimented with the metallic arc
and received a patent.
A bare electrode was difficult to use
and resulted in a weld which was
porous, brittle, and not as strong as
the base metal.
History of Welding
History of Welding
6. 1910—A Swede found that welds
were stronger and easier to make
when a chemical coating was put
on the metal electrode.
7. 1927—Mass production method
developed to apply the flux to the
bare metal rod.
The coating was called flux because it
cleaned the metal and aided in mixing
the filler metal with the vase metal,
however it was difficult to apply.
How are equipment and
supplies selected for use with
shielded metal arc welding?
There are several different
types of equipment and
supplies to choose from.
5
Welding machines are
classified in several
different ways.
1. One common way is by the
type of output current
produced by the welder, AC,
DC, or AC/DC.
2. Another way to classify
welders is by their service.
2. Another way to classify
welders is by their service.
Limited input welders provide
satisfactory operation and are fairly
inexpensive to operate.
Their cost is about a dollar per ampere
of output.
Limited service welders are used
where lower cost is desired, because
the operation is quite intermittent.
Industrial welders have a high duty
cycle, but their price is much higher.
3. Power source is another
way welders are classified.
3. Power source is another
way welders are classified.
An electric motor driven welder is selfcontained and requires three-phase
power.
An internal combustion engine drives
a generator that produces the power
for the welder to run.
Electric power runs the motor which
turns a generator to produce DC
welding current.
Line voltage welders run on the power
supplied by the power company.
6
4. Duty cycle
Buying a Welder
Duty cycle is the percentage of a 10
minute period that a welder can
operate at a given current setting
and is another way to classify
welders.
When buying a new welder,
consider only one made by a wellknown manufacturer and distributed
by a reliable dealer.
A welder with a 60 per-cent duty cycle
can be operated safely for six minutes
of a ten minute cycle repeated
indefinitely.
Check the nameplate to see if the
welder is National Electrical
Manufactures Association (NEMA)
rated and approved and listed by
Underwriters Laboratories (UL).
Buying a Welder
Compare prices of welders, equal
capacity, and the kinds of
accessories available.
Read the guarantee carefully and
ask questions.
1. Two cables, No. 2 gauge,
are required.
There are several other pieces
of equipment and supplies
necessary in order to operate
the shield metal arc welder.
2. The electrode holder grips the
electrode during welding and
should be completely insulated,
have a spring-grip release, and
jaws that hold rods in 60, 90, 120,
and 180 degree positions in
relation to the handle.
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3. The ground clamp is fastened
to the work or to the welding table.
5. A wire brush is used to clean
dirt, rust, and slag from metal.
4. The chipping hammer, with a
straight peen, and straight cone
with a spiral wire-grip, is
necessary to remove slag from the
weld bead.
6. Pliers are needed for handling
hot metal. Welding gloves will be
ruined by touching hot metal
because moisture will be drawnout and the leather will harden
and shrink.
7. Safety glasses or goggles are
required to protect the
operator’s eyes when chipping
hot slag, and grinding or
cleaning metal for joint
preparation.
8. Full gauntlet leather gloves
should always be worn.
11. Use only filter lenses that
are clearly labeled with standard
shade numbers and be sure
they meet the specifications of
the welding you are performing.
A No. 10 lens meets
applications up to 200 amps.
9. Upper body protection is
necessary to protect against rays,
heat, spatter, and slag while
welding.
10. A head shield is necessary for
protection from the rays of the
electric arc, and the heat and
spatter of the molten metal.
12. Electrodes convey electric
current from the welding
machine into a hot arc between
its tip and the metal being
welded.
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13. Electrodes are covered with
flux. The flux provides four
important functions.
13. Electrodes are covered with
flux. The flux provides four
important functions.
a. Flux protects the molten metal from
the atmosphere.
b. The flux-covering burns in the intense
heat of the arc, forming a blanket or
shield of gas around the bead. Air
contains oxygen and nitrogen which
would combine with the metal to cause
it to be brittle and weak.
c. Flux mixes with the weld metal, floating the
impurities to the top in the form of slag. Slag
covers the bead to protect it from the air and
slow the rate of solidification and cooling.
d. Flux stabilizes the arc. After the arc is
started, current flows across the gap between
the end of the electrode and the work.
14. Current does not jump the
gap but is conducted by a
mass of ionized gas.
15. Gas is produced when
chemical substances are
vaporized by the heat of the
arc.
17. Every electrode has been assigned
a specific symbol, such as E7014.
a. The “E” indicates the electrode is
used for electric welding.
b. The first two digits of a four digit
number indicate tensile strength in
thousands of pounds per square
inch.
i. An E7014 electrode produces a weld
with 70,000 psi of tensile strength.
16. There are two
classifications of electrodes.
The American Welding Society
(AWS) and the American
Society for Testing Materials
(ASTM) have set up standard
numerical classifications for
most electrodes.
ii.. An E6011 electrode produces a weld
with 60,000 psi of tensile strength.
c. If the number has five digits, the first
three digits indicate tensile strength.
d. The next to last digit indicates welding
position for which the electrode is
recommended.
e. The last digit indicates the operating
characteristics of the electrode.
9
18. The National Electrical
Manufacturers Association
(NEMA) has adopted color
marking for some classes.
One of the most important and
most often neglected parts of
the welding job is preparation
of the metal for welding.
B. Preparing the correct type of
joint for each kind of metal is
crucial to securing strong
welded structures.
How is metal prepared for
welding?
A. The metal must be free of
dirt, grease, rust, paint, or other
impurities which may combine
with a molten weld bead and
cause it to be weakened.
Metal should be cleaned by
grinding, brushing, filing, or
cutting before welding.
1. The basic types of joints are
the butt, lap, tee, corner, and
edge. These joints may be
applied to the different types of
welds: fillet, groove, plug, slot,
and surface.
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2. A tee weld is a type of fillet
weld. The fillet weld has two
surfaces at right angles, and
the bead is triangular in shape.
4. The plug and slot welds are
used to join pieces that
overlap. The welds are placed
in plug or slot holes. These
types of welds commonly take
the place of rivets in welded
structures.
3. The groove weld is a weld
made in a groove between the
two pieces of metal to be
joined.
5. Surface welds are beads
deposited on a metal surface
for the purpose of building up
the base metal.
6. The square butt joint is used on
metal sections no thicker than 3 /16
inch. This joint is strong in tension
loads but not good for repeated
loads and impact forces.
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7. The single V butt joint is often used
on plate steel 3 /8 inch to ¾ inch in
thickness. This joint is strong in loads
with tension forces but weak in loads
that bend at the weld root. The weld
root is the bottom of the weld groove
opposite the weld face.
8. The single-bevel butt joint is used
on metals from 1/8 inch to ½ inch in
thickness and the bevel is 45
degrees.
10. The lap joint is a type of fillet
weld. Its strength depends on the
size of weld bead.
9. The double V butt joint is
excellent for all load conditions and
is often used on metal sections over
¾ inch in thickness.
11. The single lap joint is one of the
stronger weld joints. It is used on
metal up to ½ inch in thickness.
12. The double lap joint is almost as
strong as the base metal.
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13. The T-joint is a fillet weld and
can be used on metals up to ½ inch
in thickness. It can withstand strong
longitudinal shear forces. The Tjoint can be square, beveled, or
double beveled.
14. Corner Joints
14. Corner Joint
The corner joints can be flush, halfopen, or full-open
c. The full-open corner joint is used
for the metals that will carry heavy
loads and can withstand large
fatigue and impact loads and can
be welded on both sides.
a. The flush corner joint is primarily
used on sheet metal.
b. The half-open joint can be used
on metals heavier than sheet metal
and for joints that will not have large
fatigue or impact loads. This joint can
be welded from one side.
15. Edge joints are
used for metals less
than ¼ inch in
thickness and can
only sustain light
load applications.
What are the procedures and
techniques for shielded metal
arc welding?
13
Good welds can be attributed
to correct selection and
manipulation of the electrode
and welding current.
A. The following skills must be
performed in unison to
achieve a weld of acceptable
quality.
1. The proper amperage
1. The proper amperage
The proper amperage setting for
any welding job is necessary to get
good penetration with minimum
spatter. Correct amperage can be
identified somewhat by sound.
a. When the amperage is correct,
a sharp crackling sound can be
heard.
b. A humming sound will indicate
too low an amperage setting and
the deposited electrode will pile up,
leaving a narrow, high bead that
has poor penetration and little
strength.
1. The proper amperage
c. A popping sound will indicate too
high an amperage setting and the
bead will be flat with excessive
spatter. The electrode will become
red hot, and the metal along the
edge of the bead will be undercut.
2. Correct amp setting
depends on the thickness of
the base metal and the
diameter of the electrode.
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3. Arc Length
Electrode Angle
Learning to maintain the correct arc
length for the electrode you are
using is necessary in order to be
successful.
The correct angle of the electrode
will depend on the type of weld that
is to be completed.
Hold the electrode at a 90 degree
angle to the work as viewed from
the end of the two plates being
joined, and 5 to 15 degrees in the
direction of travel.
Arc length is the distance from the tip
of the bare end of the electrode to the
base metal.
Arc length is equal to the diameter of
the bare end of the electrode.
5. Speed of Travel
Correct speed of travel affects the
amount of electrode deposited and
the uniformity of the bead.
It should produce a bead that is 1.5
to 2 times the diameter of the bare
end of the electrode.
B. Welding Procedures (Cont.)
2. Make a final check to see that
flammable materials are out of the
way and that unnecessary tools are
not lying around.
3. Be sure the machine is turned
off.
4. Set the machine to the desired
amperage.
B. Following proper procedures
when preparing to weld and
striking the arc will develop
confidence in your abilities.
1. Prepare the work area so that
everything is ready and convenient
before you start.
B. Welding Procedures (Cont.)
5. Insert the bare end of the
electrode in the electrode holder
and hold the end of the electrode
about 1 inch above the metal at the
point where the weld is to be
started.
6. Turn the welder on.
15
B. Welding Procedures (Cont.)
7. Lower the helmet over your eyes,
bring the electrode in contact with the
work and withdraw it slightly.
Current jumps this small gap creating the
electric arc.
The moment the arc is struck the
concentration of intense heat, estimated
between 6,000 and 9,000 degrees F, melts
the base metal and the end of the electrode
forming a molten metal pool called a crater.
B. Welding Procedures (Cont.)
b. A tapping movement is where the
electrode is quickly tapped on the
surface of the metal to prevent it from
sticking to the base metal.
B. Welding Procedures (Cont.)
8. There are two methods used in
starting the arc.
A striking movement is similar to striking
a match.
B. Welding Procedures (Cont.)
c. If the electrode is not instantly
pulled away it will fuse with the base
metal and stick.
d. If the electrode is pulled too far
away, the arc will be extinguished.
B. Welding Procedures (Cont.)
9. Raise the tip of the electrode to
about 3 /16 inch above the base
metal. This forms a long arc which is
held for a three count in order to
preheat the base metal.
10. Lower the electrode to the correct
arc length.
16
C. To make a wider bead or
when doing out-of-position
welding, use a motion of
weaving or oscillating
movements.
1. Weaving is running a bead
with a sideways or oscillating
motion. It is used when
covering a wide area with
weld metal or to maintain a
large molten weld crater.
2. Padding is the process of
building up several layers of weld
deposit by running over-lapping
passes. Padding is used to
rebuild worn pieces by building up
the piece to an oversized
condition and grinding or
machining to the correct size.
3. These movements usually
require more time and the beads
are shorter per inch of electrode
used.
17
D. There are four positions used
when welding:
Flat
D. There are four positions used
when welding:
Vertical
The flat position produces welds
that are stronger than in any other
position.
D. There are four positions used
when welding:
Horizontal
E. Controlling distortion,
warping, and cracking is a
major concern when welding
due to forces that cause their
shape or position to change.
D. There are four positions used
when welding:
Overhead
1. During the welding process, the
arc heats the area being welded,
causing it to become larger, or
expand.
As heat is removed, the surrounding
metal and air cause a cooling effect
upon the heated area.
This results in the metal becoming
smaller or contracting.
There is no way to avoid the laws of
expansion and contraction
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2. There are several methods that can
be used to help control distortion.
Use a tack weld, where a short
bead is placed at the edge of the
end that you are welding to. The
length of the tack weld should be
twice the thickness of the base
metal. Avoid over-welding by using
as little weld metal as possible for
the necessary strength.
Control Distortion (Cont.)
b. Practice intermittent welding,
where short beads are run, skipping
spaces between them. Run short
passes and allow them to cool
before running the next pass.
Control Distortion (Cont.)
Control Distortion (Cont.)
c. Use the back step method, in
which each short pass is started
ahead and run back into the
previous weld.
d. Balance the contraction of one
bead by the contraction of another.
What are the safety practices
that should be observed when
doing shielded metal arc
welding?
e. Carefully hammer or peen a weld
deposit to stretch the weld and make up
for contraction due to cooling.
f. Clamp material in a jig or to other rigid
support during welding and cooling.
g. Preheat the materials being welded.
Preheating makes welding easier and
lessens the possibility of cracks.
The following are suggested
practices and tips that will help
to eliminate shop accidents
when arc welding.
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Safety Procedures
A. Wear a welding helmet.
B. Wear leather or special fabric
gloves at all times when arc welding
to protect from hot electrodes,
particles of spatter and slag, or the
metal being welded.
C. Wear high-top shoes to protect
your feet and ankles from burns
caused by weld spatter.
Safety Procedures
G. Never weld when your body is
exposed, as when not wearing a
shirt, or wearing a short sleeved
shirt or shorts.
H. If leather clothing is not
available, wear woolen clothing
rather than cotton. Wool does not
ignite as readily and provides better
protection from heat.
Safety Procedures
D. Do not wear clothing with turned
up cuffs.
E. Keep your collar and pockets
buttoned.
F. Do not wear ragged, oily or
greasy clothing.
Safety Procedures
I. Inspect welding cables for broken
insulation and frayed conductors.
K. Check electrode holder and
ground clamps for positive
connections before beginning to
weld. Loose connections and
grounds may prove dangerous.
Safety Procedures
Safety Procedures
L. Provide a dry wooden platform to
stand on or wear rubber soled
shoes where there are damp floors.
M. Clear all combustible materials
away from the welding area before
beginning to weld.
N. Flying sparks from the spatter
may ignite combustible material
several feet from the welding
operation. Clear the welding area of
rags, straw, paper, shavings, and
other combustible items before
starting to weld.
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Safety Procedures
Safety Procedures
O. Keep matches, lighters, papers,
and cellophane wrappers out of
pockets as these items ignite
quickly and/or may explode.
P. Turn on an exhaust system before
beginning to weld. Welding fumes soon
spread to all parts of the shop and may
be injurious when inhaled. Take special
measures to avoid noxious fumes that
occur when welding or cutting metals
containing zinc. Inhaling zinc fumes will
cause you to feel ill for several hours
after welding.
Safety Procedures
Safety Procedures
Q. Do not strike an arc before covering
face and eyes with the protective shield
or helmet. The ultraviolet light rays
given off by the arc are the same as
those transmitted by sunlight, except
that they are more intense and
concentrated. Exposure to these rays
will cause a severe burn. Eye irritation
and burn will result if your eyes are not
shielded.
R. Protect other workers by using a
welding screen to enclose your
area. Warn persons standing
nearby, by saying “cover”, to cover
their eyes when your are ready to
strike an arc.
Safety Procedures
Safety Procedures
S. Never look directly at the arc
without protecting your eyes. The
rays can penetrate though closed
eyelids if you are welding at close
range. Do not wear contact lenses
while welding or around a welder.
T. Do not weld barrels, tanks or
other containers which may have
held combustible material. These
operations are best performed by
professional welders.
U. Do not chip slag from a weld
unless your eyes and those of
others near you are protected by
safety glasses.
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Safety Procedures
Safety Procedures
V. Be alert for fires at all times.
Because the operator’s helmet is
lowered, and clothing may catch fire
without being noticed. Depend on
your senses of touch, smell, and
hearing to indicate that something is
wrong.
W. In case of a clothing fire, strip off
the article if possible. Do not run, as
running fans the flames. Wrap
yourself in a fire blanket, or
improvise with a coat or a piece of
canvas. If there is nothing at hand
to wrap in, drop to the floor and roll
slowly.
Safety Procedures
Safety Procedures
X. Handle all hot metal with tongs or
pliers to prevent burning your hands
or gloves. Place all hot metal where
no one will come in contact with it.
Develop the habit of feeling all
metal cautiously before picking it
up. Do not leave hot metals where
anyone may pick them up or step
on them.
Y. Guard against saturation of
clothing by perspiration or moisture.
This increases the shock hazard.
Z. Disconnect the welder when
repairing or adjusting it.
AA. Always unplug the welder and
put all equipment away when you
have finished for the day.
Safety Procedures
Safety Procedures
BB. In case of eye or skin burns,
get first-aid treatment. Report all
burns and injuries immediately to
the instructor.
CC. Protect fuel tanks and fuel lines
with wet sheet asbestos when
welding near motors or power units.
DD. Clean accumulations of dry
trash, husks, lint, and chaff off of
farm machinery before welding.
EE. The paint on machinery also
may start to burn from the heat of
welding.
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Review/Summary
1. Explain the fundamentals and
developments of shielded metal arc
welding.
2. Describe how to select shielded
metal arc welding equipment and
supplies.
3. Explain how to prepare metal for
welding.
Review/Summary
4. Describe the procedures and
techniques for shielded metal arc
welding.
5. Identify the safety practices that
should be observed when working
with shielded metal arc welding.
23
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