Shielded Metal Arc Welding

Shielded Metal Arc Welding
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Topic 6.
Welding Process Training Series
Shielded Metal Arc Welding
SAFETY
Standard for Fire Prevention During Welding, Cutting, and Other Hot
Work, NFPA Standard 51B, from National Fire Protection Association,
Quincy, MA 02269 (Phone: 1-800-344-3555, website: www.nfpa.org.)
OSHA, Occupational Safety and Health Standards for General Industry, Title 29, Code of Federal Regulations (CFR), Part 1910, Subpart
Q, and Part 1926, Subpart J, from U.S. Government Printing Office, Superintendent of Documents, P.O. Box 371954, Pittsburgh,
PA 15250-7954 (Phone: 1-866-512-1800) (There are 10 OSHA Regional Offices—phone for Region 5, Chicago, is 312-353-2220,
website: www.osha.gov).
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As in all occupations, safety is paramount. Because there are
numerous safety codes and regulations in place, we recommend
that you always read all labels and the Owner’s Manual carefully
before installing, operating, or servicing the unit. Read the safety
information at the beginning of the manual and in each section.
Also read and follow all applicable safety standards, especially
ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes.
Safe Practice For Occupational And Educational Eye And Face Protection, ANSI Standard Z87.1, from American National Standards Institute, 25 West 43rd Street, New York, NY 10036 (Phone: 212-642-4900,
website: www.ansi.org).
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Arc
Welding
and Cutting
the
Safe Way!
Safety in Welding, Cutting, and Allied Processes, CSA Standard
W117.2, from Canadian Standards Association, Standards Sales, 5060
Spectrum Way, Suite 100, Ontario, Canada L4W 5NS (Phone: 800-4636727, website: www.csa-international.org).
ANSI Z49.1:, Safety in Welding, Cutting, and Allied Processes is
available as a free download from the American Welding Society
at: http://www.aws.org
Towing a Trailer − Being Equipped for Safety, Publication from U.S. Department of Transportation, National Highway Traffic Safety Administration, 400 Seventh Street, SW, Washington, D.C. 20590
U.S. Consumer Product Safety Commission (CPSC), 4330 East
West Highway, Bethesda, MD 20814 (Phone: 301-504-7923,
website: www.cpsc.gov).
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Here is a list of additional safety standards and where to get
them.
Booklet, TLVs, Threshold Limit Values, from American Conference of Governmental Industrial Hygienists (ACGIH), 1330 Kemper Meadow Drive, Cincinnati, OH 45240 (Phone: 513−742−3355,
website: www.acgih.org).
Safe Practices for the Preparation of Containers and Piping for Welding and Cutting, American Welding Society Standard AWS F4.1, from
Global Engineering Documents (Phone: 1-877-413-5184, website:
www.global.ihs.com).
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National Electrical Code, NFPA Standard 70, from National Fire Protection Association, Quincy, MA 02269 (Phone: 1-800-344-3555, website:
www.nfpa.org and www. sparky.org).
Applications Manual for the Revised NIOSH Lifting Equation, The
National Institute for Occupational Safety and Health (NIOSH), 1600
Clifton Rd, Atlanta, GA 30333 (Phone: 1-800-232-4636, website:
www.cdc.gov/NIOSH).
Safe Handling of Compressed Gases in Cylinders, CGA Pamphlet P-1,
from Compressed Gas Association, 4221 Walney Road, 5th Floor,
Chantilly, VA 20151 (Phone: 703-788-2700, website:www.cganet.com).
Prepared by the Miller Electric Mfg. Co. Training Department.
©2014 Miller Electric Mfg. Co.
The contents of this publication may not be reproduced without permission of Miller Electric Mfg. Co. , Appleton Wisconsin, U.S.A.
WARNING
This document contains general information about the topics discussed herein. This document is not an application manual and does not contain a
complete statement of all factors pertaining to those topics.
The installation, operation, and maintenance of arc welding equipment and the employment of procedures described in this document should be conducted only by qualified persons in accordance with applicable codes, safe practices, and manufacturer’s instructions.
Always be certain that work areas are clean and safe and that proper ventilation is used. Misuse of equipment and failure to observe applicable codes and
safe practices can result in serious personal injury and property damage.
Shielded Metal Arc Welding
Welding Process and Filler Metals
Training Series:
Welcome to the Welding Process and Filler Metals Training
Series. This training series was developed for the purpose of
providing a basic set of educational materials that can be used
individually or in a classroom setting.
The topics covered in the series are:
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Power Source ������������������������������������������������������������1
Selecting The Type Of Current
• Topic 2. Welding Safety
• Topic 3. Basic Electricity For Welding
• Topic 4. Welding Power Source Design
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• Topic 6. Shielded Metal Arc Welding
• Topic 7. Gas Tungsten Arc Welding
• Topic 8. Gas Metal Arc Welding
• Topic 9. Flux Cored Arc Welding
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• Topic 11. Troubleshooting Welding Processes
• Topic 12.Submerged Arc Welding
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• Topic A. Introduction To Metals
• Topic B. Tubular Wires
• Topic C. Low Alloy Steel
• Topic D. Stainless Steel
• Topic E. Aluminum
• Topic F. Hard Surfacing
Please note, this series was not developed to teach the skill of
welding or cutting, but rather to provide a foundation of general
knowledge about the various processes and related topics.
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Dig����������������������������������������������������������������������������5
Arc-Drive™����������������������������������������������������������������7
Hot Start™ ����������������������������������������������������������������7
Adaptive Hot Start™����������������������������������������������������8
Welding Accessories
Remote Controls
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• Topic 5. Engine Driven Power Sources
Arc Blow
Setting Current
Arc Control, Arc Force, Dig, and Hot Start
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• Topic 1. Introduction To Welding
Filler Metals
Definition And General Description
Principles of Operation
SMAW Equipment
Direct Current������������������������������������������������������������2
Alternating Current������������������������������������������������������3
Welding Processes
• Topic 10. Metal Cutting
Table of Contents
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Electrode Holder ��������������������������������������������������������8
Chipping Hammers and Wire Brushes����������������������������9
Definition of an Electrode��������������������������������������������9
Purpose of Electrode Coatings��������������������������������������9
AWS Classification System For Mild Steel SMAW
Electrodes10
Electrode Selection11
Basic Considerations
Storage and Reconditioning of
Electrodes12
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Essentials of Good Welding Technique
Welding Joint Types
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Edge Joints�������������������������������������������������������������� 16
Lap Joints���������������������������������������������������������������� 17
Corner Joints������������������������������������������������������������ 17
T-Joints ������������������������������������������������������������������ 18
Weld Types and Positions 18
Fillet Welds�������������������������������������������������������������� 18
Groove Welds���������������������������������������������������������� 18
Weld Positions �������������������������������������������������������� 18
Welding Symbols
Terms and Definitions
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Definition And General Description
Welding Power Source
Shielded Metal Arc Welding (SMAW) is defined by the American
Welding Society (AWS) as an arc welding process with an arc
between a covered electrode and the weld pool. The process
uses a disposable electrode with a flux coating. As the weld is
made the flux burns off to provide shielding for the weld while
the electrode provides the filler metal.
Work Cable
Work Clamp
Electrode Cable
Shielded Metal Arc Welding, also called Stick Welding, is one of
the most widely used processes, particularly for short welds in
production, maintenance and repair work, and for field construction. The process has many advantages:
• The filler metal, and the means of protecting it and the
weld metal from harmful oxidation during welding, are
provided by the covered electrode.
• The process is less sensitive to wind and draft than gas
shielded arc welding
processes.
• It can be used in areas of
limited access.
• The process is suitable
for most of the commonly
used metals and alloys.
As illustrated in Figure 2, the arc is generated between the base
metal and the core wire that makes up the electrode. This electric arc produces enough heat, about 9000O F (5000O C), to melt
both the base metal and electrode forming a weld pool. Small
droplets of the core wire melt and transfer to the weld pool providing additional metal to the weld pool. As the electrode covering is heated and melted, it produces gasses that protect the
molten puddle from atmospheric contamination. The electrode
covering also contains elements that help to stabilize the welding arc, clean the base metal, and provide a protective slag coating that helps form the weld bead as well as protect it from the
atmosphere.
Electrode Covering
Core Wire
Shielding Atmosphere
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Principles of Operation
Figure 1 – SMAW System
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• Auxiliary gas shielding or granular flux is not required.
Electrode Holder
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• The equipment is relatively simple, inexpensive, and
portable.
Electrode
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Shielded Metal Arc Welding occurs when a constant current,high
amperage, low voltage welding power supply generates an electric arc between an electrode and the workpiece. Using a welding
power supply that generates a constant current high amperage
low voltage welding arc. Figure 1 shows the basic components
needed for the welding process:
• Constant current welding power source
Weld Pool
Penetration Depth
Solidified Weld Metal
Base Metal
Figure 2 – SMAW Arc
SMAW Equipment
• Work clamp
Power Source
• Covered welding electrodes
Metal and Slag Droplets
Solidified Slag
• Welding and work cables (electrode and work leads)
• Electrode holder
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Arc
There are two types of welding power sources used for the
electric arc welding processes: constant current and constant
voltage. The Shielded Metal Arc Welding process requires a
constant current welding power source. This type of welding
power source requires the operator to set welding amperage.
The source may be any of the types: transformer, transformer
-rectifier, inverter, or engine-driven.
Shielded Metal Arc Welding
Figure 4 – An AC/DC
Transformer-Rectifier
Welding Power Source
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Figure 5 – An AC/DC
Transformer-Rectifier
Engine-Driven Welding
Power Source
Physical size can be another issue when selecting a welding
power source. Inverter power
sources offer exceptional arc characteristics in all processes
and are considerably smaller in size than conventional power
sources. Inverter power sources are also more electrically efficient than conventional welding power sources.
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AC power sources are generally
used to eliminate arc blow. Arc
blow occurs with direct current
because of magnetic fields set
up by a steady current flow in
one direction. Arc blow is most
severe when welding in tight fillet corners or box sections. The
arc will wander from its intended
path and molten metal droplets
are expelled as spatter. Arc blow
can cause welding defects in the
form of undercut and unfilled
weld craters, plus excessive
spatter. Arc blow is most severe
when using large electrodes at
high amperages.
The duty cycle of the welding
power source is another consideration. Analyzing the amperage
needs and selecting a power
source which will provide the
required output within the duty
cycle rating is important. A welding power source can be overloaded for a short period of time,
but continuous overloading will
cause damage to the unit.
The primary power available must be considered when selecting
a welding power source. Primary power is normally available
at 208 volts, 230 volts, 460 volts, or 575 volts. Some welding
power sources may operate from only one primary voltage while
others can be connected for several primary voltages. AC and
AC/DC power sources require single-phase power while DC
power sources normally require three-phase primary power. In
rural and residential areas, single-phase power is common and
three-phase power would require special wiring. Most industrial
locations have three-phase power available since it is required
by many electric motors and other electrical equipment.
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With the many types of power
sources available, some criteria are necessary in selecting
the right one for the job. One
consideration is current type AC or DC. The light duty power
sources found in many small
repair shops, on the farm, and
around the home, are usually AC
machines. They are inexpensive
to purchase, very simple to operate, and can usually be operated
Figure 3 – An Inverter
from residential type electrical
Welding Power Source
service. They provide the necessary power for use with electrodes designed for alternating
current.
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Direct current machines are selected when the application calls
for an electrode that operates from direct current. DC is normally preferred for out-of-position work and for use with stainless
steel or non-ferrous electrodes. DC is usually preferred for pressure vessels, pipelines, and other critical weldments because of
the arc characteristics it provides with the low alloy electrodes
frequently used for these applications. Direct current welding
power sources offer extra versatility because of polarity selection. Nearly all electrodes can be used with direct current.
Engine-driven power sources are used on construction sites,
mines, cross country pipelines and in remote areas where mobility is a factor and welding utility power is not readily available.
Air and liquid-cooled engines are available in gasoline or diesel
versions for this type of power source.
Regardless of the type of input voltage, whether they are AC or
DC, static equipment or engine-driven, a welding power source
has one function: to provide electrical energy at the arc. Amperage demands for welding may vary from a few amperes to over
1000 amperes. Welding power sources are available in many
sizes and types to fill the needs of the application.
In some shops it is desirable to have available both AC and DC
power sources. Transformer rectifier-type welding power sources can provide both AC and DC power. The operator can easily select alternating current or direct current from this type of
power source.
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