1.9 Constant Current or Constant Voltage
1.9.4 Power Source Controls
machines having a tapped reactor, a moveable shunt or diverter, or a moveable coil. Elec-trical types of controls, such as magnetic amplifiers or saturable reactors, are also utilized and the most modern types, containing silicon controlled rectifiers, give precise electronic control.
1.9.4.1 A detailed discussion of the many types of welding power sources on the market today is much too lengthy a subject for this course, although additional information on the type of power sources for the various welding processes will be covered in Lesson II.
1.9.4.2 Excellent literature is available from power source manufacturers, however, and should be consulted for further reference.
Lesson 1 The Basics of Arc
Welding
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low Alloy
Steels
Go To
Lesson 5 Welding Filler Metals
for Stainless Steels
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Glossary
Lesson 7 Flux Cored Arc Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld Metal Costs
Lesson 10
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LESSON I, GLOSSARY
APPENDIX A
LESSON I - GLOSSARY OF TERMS
AISI — American Iron and Steel Institute
Allotropic — A material in which the atoms are capable of transforming into two or more crystalline structures at different temperatures.
Alternating — An electrical current which alternately travels in either direction in a Current conductor. In 60 cycles per second (60 Hz) AC, the frequency
used in the U.S.A., the current direction reverses 120 times every second.
Ampere — Unit of electrical rate of flow. Amperage is commonly referred to as the “current” in an electrical circuit.
ASME — American Society of Mechanical Engineers
ASTM — American Society for Testing and Materials
Atom — The smallest particle of an element that posses all of the characteristics of that element. It consists of protons, neutrons, and electrons.
Carbon Steel — (Sometimes referred to as mild steel.) An alloy of iron and carbon.
Carbon content is usually below 0.3%.
Conductor — A material which has a relatively large number of loosely bonded electrons which may move freely when voltage (electrical pressure) is applied. Metals are good conductors.
Constant Current — (As applied to welding machines.) A welding power source which will produce a relatively small change in amperage despite changes in voltage caused by a varying arc length. Used mostly for welding with coated electrodes.
Lesson 1 The Basics of Arc
Welding
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low Alloy
Steels
Go To
Lesson 5 Welding Filler Metals
for Stainless Steels
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Glossary
Lesson 7 Flux Cored Arc Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld Metal Costs
Lesson 10 Reliability of Welding
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LESSON I, GLOSSARY
Constant Voltage — (As applied to welding machines.) A welding power source which will produce a relatively small change in voltage when the amperage is changed substantially. Used mostly for welding with solid or flux cored electrodes.
Direct Current — An electrical current which flows in only one direction in a conductor. Direction of current is dependent upon the electrical connections to the battery or other DC power source. Terminals on all DC devices are usually marked (+) or (-). Reversing the leads will reverse the direction of current flow.
Electron — Negatively charged particles that revolve around the positively charged nucleus in an atom.
Ferrous — Containing iron. Example: carbon steel, low alloy steels, stainless steel.
Hertz — Hertz (Hz) is the symbol which has replaced the term “cycles per second.” Today, rather than saying 60 cycles per second or simply 60 cycles, we say 60 Hertz or 60 Hz.
High Alloy Steels — Steels containing in excess of 10% alloy content. Stainless steel is considered a high alloy because it contains in excess of 10%
chromium.
Induced Current or
Induction — The phenomena of causing an electrical current to flow through a conductor when that conductor is subjected to a varying magnetic field.
Ingot — Casting of steel (weighing up to 200 tons) formed at mill from melt of ore, scrap limestone, coke, etc.
Insulator — A material which has a tight electron bond, that is, relatively few electrons which will move when voltage (electrical pressure) is applied. Wood, glass, ceramics and most plastics are good insulators.
Lesson 1 The Basics of Arc
Welding
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low Alloy
Steels
Go To
Lesson 5 Welding Filler Metals
for Stainless Steels
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Glossary
Lesson 7 Flux Cored Arc Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld Metal Costs
Lesson 10
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LESSON I, GLOSSARY
Kilowatt — 1,000 watts
Low Alloy Steels — Steels containing small amounts of alloying elements (usually 1½%
to 5% total alloy content) which drastically improves their properties.
Non-Ferrous — Containing no iron. Example: Aluminum, copper, copper alloys.
Ohm — Unit of electrical resistance to current flow.
Phase
Transformation — The changes in the crystalline structure of metals caused by temperature and time.
Proton — Positively charged particles which are part of the nucleus of atoms.
Rectifier — An electrical device used to change alternating current to direct current.
SAE — Society of Automotive Engineers
Transformer — An electrical device used to raise or lower the voltage and inversely change the amperage.
Volt — Unit of electromotive force, or electrical pressure which causes current to flow in an electrical circuit.
Watt — A unit of electrical power. Watts = Volts x Amperes Lesson 1
The Basics of Arc Welding
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low Alloy
Steels
Go To
Lesson 5 Welding Filler Metals
for Stainless Steels
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Glossary
Lesson 7 Flux Cored Arc Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld Metal Costs
Lesson 10 Reliability of Welding
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BASIC WELDING FILLER METAL TECHNOLOGY
A Correspondence Course
LESSON II COMMON ELECTRIC ARC WELDING PROCESSES
ESAB ESAB Welding &
Cutting Products
Lesson 1 The Basics of Arc
Welding
Current Chapter Table Contents
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low Alloy
Steels
Go To
Lesson 5 Welding Filler Metals
for Stainless Steels
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Glossary
Lesson 7 Flux Cored Arc Electrodes Carbon
Low Alloy Steels
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Lesson 8 Hardsurfacing
Electrodes
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Lesson 9 Estimating &
Comparing Weld Metal Costs
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Lesson 10
TABLE OF CONTENTS LESSON II
COMMON ELECTRIC ARC WELDING PROCESSES
2.1 INTRODUCTION ... 1
2.2 SHIELDED METAL ARC WELDING ... 1 2.2.1 Equipment & Operation ... 2 2.2.2 Welding Power Sources ... 2 2.2.3 Electrode Holder... 4 2.2.4 Ground Clamp ... 4 2.2.5 Welding Cables ... 4 2.2.6 Coated Electrodes ... 4
2.3 GAS-TUNGSTEN ARC WELDING ... 5 2.3.1 Equipment & Operation ... 6 2.3.2 Power Sources ... 7 2.3.3 Torches... 10 2.3.4 Shielding Gases ... 11 2.3.5 Electrodes ... 12 2.3.6 Summary ... 13 2.4 GAS METAL ARC WELDING ... 13 2.4.1 Current Density ... 14 2.4.2 Metal Transfer Modes ... 15 2.4.3 Equipment and Operation ... 17 2.4.4 Power Source... 18 2.4.5 Wire Feeder ... 19 2.4.6 Welding Gun ... 20 2.4.7 Shielding Gases ... 21 2.4.7.1 Short Circuiting Transfer ... 22 2.4.7.2 Spray Arc Transfer ... 23
Section Nr. Section Title Page
Lesson 1 The Basics of Arc
Welding
Current Chapter Table Contents
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low Alloy
Steels
Go To
Lesson 5 Welding Filler Metals
for Stainless Steels
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Glossary
Lesson 7 Flux Cored Arc Electrodes Carbon
Low Alloy Steels
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Lesson 8 Hardsurfacing
Electrodes
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Lesson 9 Estimating &
Comparing Weld Metal Costs
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Lesson 10 Reliability of Welding
2.4.7.3 Pulse Spray Transfer ... 23 2.4.8 Electrodes ... 23 2.5 FLUX CORED ARC WELDING ... 24 2.5.1 Self-Shielded Process ... 24 2.5.2 Gas Shielded Process... 25 2.5.3 Current Density ... 26 2.5.4 Equipment ... 26 2.5.5 Power Source... 26 2.5.6 Wire Feeder ... 26 2.5.7 Welding Guns ... 26 2.5.8 Shielding Gases ... 27 2.6 SUBMERGED ARC WELDING ... 27 2.6.1 Submerged Arc Flux ... 28 2.6.2 The Welding Gun ... 28 2.6.3 Power Sources ... 28 2.6.4 Equipment ... 28 2.6.5 Electrodes ... 29 2.6.6 Summary ... 29 2.7 ELECTROSLAG AND ELECTROGAS WELDING ... 30 2.7.1 Electroslag Welding... 30 2.7.2 Flux ... 30 2.7.3 Process ... 30 2.7.4 Equipment... 31 2.7.5 Summary ... 31 Appendix A - GLOSSARY OF TERMS ... 32
TABLE OF CONTENTS LESSON II - Con't.
Section Nr. Section Title Page
Lesson 1 The Basics of Arc
Welding
Current Chapter Table Contents
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low Alloy
Steels
Go To
Lesson 5 Welding Filler Metals
for Stainless Steels
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Glossary
Lesson 7 Flux Cored Arc Electrodes Carbon
Low Alloy Steels
Search Chapter
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Lesson 8 Hardsurfacing
Electrodes
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Lesson 9 Estimating &
Comparing Weld Metal Costs
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Lesson 10
LESSON II
COMMON ELECTRIC ARC WELDING PROCESSES
2.1 INTRODUCTION
After much experimentation by others in the early 1800's, an Englishman named Wilde obtained the first electric welding patent in 1865. He successfully joined two small pieces of iron by passing an electric current through both pieces producing a fusion weld. Approximately twenty years later, Bernado, a Russian, was granted a patent for an electric arc welding process in which he maintained an arc between a carbon electrode and the pieces to be joined, fusing the metals together as the arc was manually passed over the joint to be welded.
2.1.0.1 During the 1890's, arc welding was accomplished with bare metal electrodes that were consumed in the molten puddle and became part of the weld metal. The welds were of poor quality due to the nitrogen and oxygen in the atmosphere forming harmful oxides and nitrides in the weld metal. Early in the Twentieth Century, the importance of shielding the arc from the atmosphere was realized. Covering the electrode with a material that decomposed in the heat of the arc to form a gaseous shield appeared to be the best method to accomplish this end. As a result, various methods of covering electrodes, such as wrapping and dipping, were tried. These efforts culminated in the extruded coated electrode in the mid-1920's, greatly improving the quality of the weld metal and providing what many consider the most significant advance in electric arc welding.
2.1.0.2 Since welding with coated electrodes is a rather slow procedure, more rapid welding processes were developed. This lesson will cover the more commonly used electric arc welding processes in use today.
2.2 SHIELDED METAL ARC WELDING
Shielded Metal Arc Welding*, also known as manual metal arc welding, stick welding, or electric arc welding, is the most widely used of the various arc welding processes. Welding is performed with the heat of an electric arc that is maintained between the end of a coated metal electrode and the work piece (See Figure 1). The heat produced by the arc melts the base metal, the electrode core rod, and the coating. As the molten metal droplets are transferred across the arc and into the molten weld puddle, they are shielded from the atmosphere by the gases produced from the decomposition of the flux coating. The molten slag floats to the top of the weld puddle where it protects the weld metal from the atmosphere during solidification.
Lesson 1 The Basics of Arc
Welding
Current Chapter Table Contents
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low Alloy
Steels
Go To
Lesson 5 Welding Filler Metals
for Stainless Steels
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Glossary
Lesson 7 Flux Cored Arc Electrodes Carbon
Low Alloy Steels
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Lesson 8 Hardsurfacing
Electrodes
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Lesson 9 Estimating &
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Lesson 10 Reliability of Welding
LESSON II
Other functions of the coating are to provide arc stability and control bead shape. More information on coating functions will be covered in subsequent lessons.
* Shielded Metal Arc Welding (SMAW) is the terminology approved by the American Welding Society.
2.2.1 Equipment & Operation - One reason for the wide acceptance of the SMAW process is the simplicity of the necessary equipment.
The equipment consists of the following items. (See Figure 2)
1. Welding power source 2. Electrode holder 3. Ground clamp
4. Welding cables and connectors 5. Accessory equipment (chipping
hammer, wire brush)
6. Protective equipment (helmet, gloves, etc.)
2.2.2 Welding Power Sources - Shielded metal arc welding may utilize either alternating current (AC) or direct current (DC), but in either case, the power source selected must be of the constant current type. This type of power source will deliver a relatively constant amperage or welding current regardless of arc length variations by the operator (See Lesson I, Section 1.9). The amperage determines the amount of heat at the arc and since it will remain relatively constant, the weld beads produced will be uniform in size and shape.
2.2.2.1 Whether to use an AC, DC, or AC/DC power source depends on the type of welding to be done and the electrodes used. The following factors should be considered:
1. Electrode Selection - Using a DC power source allows the use of a greater range of electrode types. While most of the electrodes are designed to be used on AC or DC, some will work properly only on DC.
2. Metal Thickness - DC power sources may be used for welding both heavy sections and light gauge work. Sheet metal is more easily welded with DC because it is easier to strike and maintain the DC arc at low currents.
FIGURE 1
SHIELDED METAL ARC WELDING
AC OR DC
SHIELDED METAL ARC WELDING CIRCUIT FIGURE 2
Lesson 1 The Basics of Arc
Welding for Welding Low Alloy
Steels
Go To
Lesson 5 Welding Filler Metals
for Stainless Steels
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Glossary
Lesson 7 Flux Cored Arc Electrodes Carbon
Low Alloy Steels
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LESSON II
3. Distance from Work - If the distance from the work to the power source is great, AC is the best choice since the voltage drop through the cables is lower than with DC. Even though welding cables are made of copper or aluminum (both good conductors), the resistance in the cables becomes greater as the cable length increases. In other words, a voltage reading taken between the electrode and the work will be somewhat lower than a reading taken at the output terminals of the power source. This is known as voltage drop.
4. Welding Position (See Appendix A - Glossary of Terms) - Because DC may be operated at lower welding currents, it is more suitable for overhead and vertical welding than AC. AC can successfully be used for out-of-position work if proper electrodes are selected.
5. Arc Blow - When welding with DC, magnetic fields are set up throughout the weldment. In weldments that have varying thickness and protrusions, this magnetic field can affect the arc by making it stray or fluctuate in direction. This condition is especially troublesome when welding in corners. AC seldom causes this problem because of the rapidly reversing magnetic field produced.
2.2.2.2 Combination power sources that produce both AC and DC are available and provide the versatility necessary to select the proper welding current for the application.
2.2.2.3 When using a DC power source, the question of whether to use electrode negative or positive polarity arises. Some electrodes operate on both DC straight and reverse polarity, and others on DC negative or DC positive polarity only. Direct current flows in one direction in an electrical circuit and the direction of current flow and the composition of the electrode coating will have a definite effect on the welding arc and weld bead. Figure 3 shows the connections and effects of straight and reverse polarity.
2.2.2.4 Electrode negative (-) produces welds with shallow penetration; however, the electrode melt-off rate is high. The weld bead is rather wide and shallow as shown at"A"in Figure 3. Electrode
positive (+)
produces welds with deep penetration and a narrower weld bead as shown at
"B"in Figure 3.
FIGURE 3
HIGHER BURN-OFF RATE, LESS PENETRATION
DEEP PENETRATION, LOW BURN-OFF RATE
WORK PIECE
B
STRAIGHT POLARITY REVERSE POLARITY
WORK PIECE
The Basics of Arc Welding for Welding Low Alloy
Steels
Lesson 5 Welding Filler Metals
for Stainless Steels
Glossary
Lesson 6 Carbon & Low Alloy
Steel Filler Metals -GMAW,GTAW,SAW
Flux Cored Arc Electrodes Carbon
Low Alloy Steels
Turn Reliability of Welding
LESSON II
2.2.2.5 While polarity affects the penetration and burn-off rate, the electrode coating also has a strong influence on arc characteristics. Performance of individual electrodes will be discussed in succeeding lessons.
2.2.3 Electrode Holder- The electrode holder connects to the welding cable and con-ducts the welding current to the electrode. The insulated handle is used to guide the electrode over the weld joint and feed the electrode over the weld joint and feed the electrode into the weld puddle as it is consumed. Electrode holders are available in different sizes and are rated on their current carrying capacity.
2.2.4 Ground Clamp- The ground clamp is used to connect the ground cable to the work piece. It may be connected directly to the work or to the table or fixture upon which the work is positioned. Being a part of the welding circuit, the ground clamp must be capable of carrying the welding current without overheating due to electrical resistance.
2.2.5 Welding Cables- The electrode cable and the ground cable are important parts of the welding circuit. They must be very flexible and have a tough heat-resistant insulation.
Connections at the electrode holder, the ground clamp, and at the power source lugs must be soldered or well crimped to assure low electrical resistance. The cross-sectional area of the cable must be sufficient size to carry the welding current with a minimum of voltage drop.
Increasing the cable length necessitates increasing the cable diameter to lessen resistance and voltage drop. The table in Figure 4 lists the suggested American Wire Gauge (AWG) cable size to be used for various welding currents and cable lengths.
Total Cable Length (Ground Lead Plus Electrode Lead) Up to 50 ft. Up to 100 ft. Up to 250 ft. Up to 500 ft.
Cable Voltage Cable Voltage Cable Voltage Cable Voltage
Size Drop Size Drop Size Drop Size Drop
20 to 180 #3 1.8 #2 2.9 #1 5.7 #0 9.1 180 Amps
30 to 250 #2 1.8 #1 2.5 #0 5.0 #0 9.9 200 Amps
60 to 375 #0 1.7 #0 3.0 #00 5.9 #000 9.3 300 Amps
80 to 500 #00 1.8 #000 2.5 #0000 5.0 #0000 9.9 400 Amps
100 to 600 #00 2.0 #0000 2.5 ... ... ... 500 Amps
Voltage drops indicated do not include any drop caused by poor connection, electrode holder, or work metal Welding
Service Range (Amperes)
Voltage Drop Figured
At
FIGURE 4
2.2.6 Coated Electrodes- Various types of coated electrodes are used in shielded metal arc welding. Electrodes used for welding mild or carbon steels are quite different than those used for welding the low alloys and stainless steels. Details on the specific types will be covered in subsequent lessons.
Current Chapter Table Contents Lesson 1
The Basics of Arc Welding
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Go To
Lesson 4 Covered Electrodes for Welding Low Alloy
Steels
Lesson 5 Welding Filler Metals
for Stainless Steels
Glossary
Lesson 6 Carbon & Low Alloy
Steel Filler Metals
Steel Filler Metals