able electrode is the filler metal. The weld area is protectedby a shielding gas. This process is used in production, inwelding shops, and in automobile body repair shops. It iscapable of making excellent welds almost continuously.The welding skills required for this process are not as greatas those required for some manual welding processes. Inshop terms, this process is also known as metal inert gas orMIG welding. Refer to Heading 4.3 for a basic descriptionof the GMAW process.

Flux cored arc welding (FCAW) is similar in mostrespects to the gas metal arc welding (GMAW) process.The difference is in the electrode wire used. FCAW uses ahollow-core electrode that contains flux and alloyingmaterials. The flux core provides a gaseous shield aroundthe arc. FCAW may also use a shielding gas providedthrough the gun, similar to the GMAW process. Refer toHeading 4.4 for a basic description of the FCAW process.

The equipment and supplies used for each processwill be explained in this chapter. Chapter 8 will cover gastungsten arc welding techniques and principles, whileChapter 9 will cover gas metal arc welding and flux coredarc welding principles and techniques. Studying thesechapters, coupled with actual welding practice, will buildthe skills and techniques you need to master these weld-ing processes.

7.1 The Gas Tungsten Arc Welding StationThe typical gas tungsten arc welding (GTAW) outfit

will contain the following equipment and supplies:• An ac or a dc or an ac/dc arc welding power

source.• Shielding gas cylinders or facilities to handle liq-

uid gases.• A shielding gas regulator.• A gas flowmeter.• Shielding gas hoses and fittings.• Electrode lead, workpiece lead, and hoses.• A welding torch (electrode holder).• Tungsten electrodes.

165

Learning Objectives

After studying this chapter, you will be able to:� Identify and describe the function of each com-

ponent of a GTAW, GMAW, and FCAW station.� Name the various types of shielding gases used

in GTAW, describe their characteristics, and eval-uate their effectiveness.

� Name the various types of shielding gases usedin GMAW, describe their characteristics, andevaluate their effectiveness.

� Identify and specify the type of electrode used forGTAW, referring to the tables provided in thebook and using the AWS electrode classificationsystem.

� Identify and specify the various electrode wiresused for GMAW and FCAW, using the tables pro-vided in the book and the AWS electrode classifi-cation system.

Gas tungsten arc welding (GTAW) is a weldingprocess in which an arc is struck between a nonconsum-able tungsten electrode and the metal workpiece. Theweld area is shielded by inert (chemically inactive) gas toprevent contamination. Filler metal may or may not beadded to the weld. It is possible to join most weldable met-als with GTAW. This process is excellent for welding rootpasses in heavy metal sections. GTAW is also known, inshop terms, as tungsten inert gas or TIG welding. Heading4.2 describes the basics of GTAW.

Gas metal arc welding (GMAW) is a welding processin which an arc is struck between a consumable metal elec-trode and the metal workpiece. The consumable electrodewire is fed to the welding gun from a large spool that mayhold several hundred feet (meters) of wire. The consum-

Chapter 7GTAW and GMAWEquipment and Supplies

• Welding rods.• Optional accessories.

� A water cooling system with hoses forheavy duty welding operations.

� Foot or finger operated rheostat.� Arc timers.

Figure 7-1 shows a schematic drawing of a gas tung-sten arc welding outfit. The booth and exhaust system arenot shown in this illustration. Refer also to Figure 4-2.

7.2 Arc Welding Power Sources for GTAWWelding power sources for gas tungsten arc welding

(GTAW) can be alternating current (ac), direct current (dc),or both alternating and direct current (ac/dc) in onemachine. The most popular arc welding power source isthe transformer-rectifier type. This machine produces bothac and dc current. Other arc welding power sourcesinclude the transformer and generator. The transformertype produces only ac; generator-type machines produceac, dc, or both types of current.

Gas tungsten arc welding power sources must supplya constant current. In constant current machines, the volt-ampere curve is either drooping or a true constant current.A drooping volt-ampere curve has a steep slope. The

amperage will change slightly as the voltage changes. Thisallows a welder to vary the amperage by changing the arclength. Newer power supply designs have nearly a verti-cal line on the volt-ampere curve. This is a true constantcurrent power source, because the amperage is constanteven though the voltage changes. This is made possible byusing electronics to control the power supply. These elec-tronically controlled power sources are more efficient,more responsive, and more repeatable. They also producean excellent pulsed welding current.

Figure 7-2 shows volt-ampere curves for droopingand constant current welding power sources. Two droop-ing curves are shown in this illustration. Curve 1 is for an80V open circuit voltage set for a 150A maximum weldingcurrent. A 5V change in the closed circuit (welding) volt-age from 20V to 25V, represents a 25% change in voltagewith only a 5% change in the current. Curve 2 represents acurve for an 80V open circuit voltage set for 50A maximumwelding current. A 25% change in voltage (from 20V to25V) will only change the amperage about 2A, or 4%. Theamperage is therefore considered to be relatively constantwith large changes in voltage.

Figure 7-2 also shows two curves (3 and 4), for anelectronically controlled constant current power source.The same voltage change from 20V to 25V producesalmost zero change in amperage.

166 Modern Welding

Filler metal

Basemetal

Footpedalfine

control(optional)

Inertgas

supply

Flowmeterand

regulator

Workpiece lead

Power source

Electrodelead

Watercooler

Torch

Gas

Figure 7-1. A diagram of a complete gas tungsten arc welding station.

This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.

The power source for GTAW may be an ac or a dcwelding machine. Most often, the machine will produceboth ac and dc constant currents. Figures 7-3 and 7-4 showGTAW power sources.

A direct current power source may be equipped witha device that produces a high-frequency voltage and feedsit into the welding circuit. High-frequency voltage, whenused in a dc circuit, is used only for starting the arc. Oncethe dc welding arc is stabilized, the superimposed high-frequency starting voltage is automatically stopped. High-frequency voltage is produced by an oscillator or a similar

device. Several thousand volts are produced at a frequen-cy of several million cycles per second or megahertz. Thecurrent in this high-frequency circuit is only a fraction ofan ampere.

When ac welding, the current and voltage reversedirections many times each second. The electrode is posi-tive, then the voltage switches so the electrode is negative.This repeats continuously when ac welding.

An ac power source must have a way to keep the cur-rent flowing while the current switches from electrode-negative to electrode-positive. Without a method to keep

Chapter 7 GTAW and GMAW Equipment and Supplies 167

50 75 100 125 150250

0

10

20

30

40

50

60

70

80

8A

31

2

4

2A

Volts

Amperage

Figure 7-2. The volt-ampere curves for a drooper type and constant current power source. Curves 1 and 2 are droopercurves which show a 2A and an 8A change with a change of 5V. Curves 3 and 4 are true constant current curves. Theyshow a nearly constant amperage with voltage changes.

the current flowing, there would be no arc during the elec-trode positive part of the cycle. When no current flows, thearc is said to be rectified. This is not good for the weldingmachine or the weld.

To reduce or eliminate such rectification, the follow-ing methods are suggested:

• Use a welding machine with a higher open cir-cuit voltage of about 100V (rms). Weldingmachines for manual GTAW have a maximumopen circuit voltage of 80V.

• Discharge capacitors at the start of the electrodepositive half of each cycle.

• Put a high-frequency voltage supply, which pro-duces several thousand volts, in series with themain transformer.

• Use a power source that produces a square-waveoutput.

Almost all GTAW machines currently produced usehigh-frequency or have a square-wave output.

The construction, operation, and control of ac, dc andinverter power sources are covered in Headings 5.1, 5.2,and 5.2.2. Review this basic information for a more com-plete understanding of welding power sources.

7.3 Balanced and Unbalanced AC WavesEach alternating current cycle, when plotted against

time on a graph, has a shape like a wave, as shown inFigure 7-5C. This wave shape is called a sinusoidal wave.Normally, alternating current has equal current flowingduring both halves of each wave, or cycle. However, whensinusoidal alternating current is used for welding, the cur-rent is less during the half of the ac cycle when the elec-trode is positive. This may be explained as follows:

During one half of an ac cycle, the electrode is nega-tive and the workpiece is positive. After going through thezero current point, the cycle reverses. The electrode thenbecomes positive and the workpiece negative.

Electrons flow from negative to positive. During theelectrode-negative half of the cycle, the hotter electrodegives off electrons readily. Since the electrode tip has asmall surface, the electrons are concentrated and flow eas-ily toward the large surface of the workpiece.

When the workpiece is negative, the electrons mustflow from a large surface to a small point (the electrode).The electrons on the surface are not concentrated at anyone point. Electrons, therefore, cannot easily travel fromthe surface to the electrode. This resistance of electron flowfrom a surface to a point is called rectification.Rectification may be so severe that the entire flow of cur-rent in the electrode-positive half of the cycle is stopped, asshown in Figure 7-5A.

The question may be asked by the welder: “Whathappens to the current during the electrode-positive halfcycle?” No current flows during the electrode-positive halfcycle. This lack of current flow makes the ac arc veryunstable. Such rectification of the current is undesirable forboth the welding operation and the welding power source.

168 Modern Welding

Figure 7-3. An ac/dc, single-phase power source for GTAW(Hobart Brothers Co.)

Figure 7-4. The face of a CC/CV and AC/DC weldingpower source. (Miller Electric Mfg. Co.)

To overcome this lack of flow during one half of thealternating current cycle, a high-frequency voltage is gen-erated and fed into the welding circuit. Several thousandvolts, with only a fraction of an ampere, are created. Thishigh voltage has a frequency of several megahertz (millioncycles per second).

A high-frequency unit is normally built into the gastungsten arc welding machine. It consists of a step-uptransformer, capacitors, a control rheostat, a set of sparkgap points, and a coil to couple the high-frequency unit tothe welding circuit.

High-frequency voltage flows continually in thewelding circuit. This high-frequency voltage keeps theshielding gas in the arc area in an ionized state. When thegas is ionized, the arc is maintained during the half of thecycle when the electrode is positive. While the arc is main-tained, some current will flow across to the electrode.However, because the work surface does not emit (giveoff) electrons easily, less current flows during this half ofthe ac cycle, or wave, as shown in, in Figure 7-5B. Thewave shown is an unbalanced wave.

A completely balanced wave is shown in Figure 7-5C. In older machines, a balanced current output wavewas achieved by using a large number of capacitors inseries or a battery in the welding circuit. Newer GTAWpower sources use electronics to create and maintain a bal-anced wave.

Most new GTAW power sources produce a square-wave current output. A square-wave power supply canchange the current from electrode-positive to electrode-negative very quickly. See Figure 7-6. This provides a highvoltage as the current crosses zero and allows the arc to

restart easily. The arc will reinitiate or restart even withoutthe use of high-frequency or another arc stabilizingmethod.

Because the output current and voltage are controlledelectronically, the amount of direct current electrode posi-tive and direct current electrode negative can be adjusted.This allows the welder to adjust the amount of cleaningand the amount of penetration. See Figure 8-15, whichshows how the amount of current in the electrode-positiveand electrode-negative portion of the weld cycle can beadjusted to get a balanced wave, one with more penetra-tion or one with more cleaning.

Balanced current is not necessary for most manualwelding. It becomes more necessary for automatic weld-ing as the duty cycles increase, often to near 100%. Theadvantages of a balanced current output wave are:

• Better oxide cleaning is provided because morecurrent flows during the electrode-positive halfcycle.

• A more stable arc.• Reliable restarting of the arc during the elec-

trode-positive half cycle.• The output rating of the welding transformer

does not need to be reduced because of outputimbalance.

The advantages of the unbalanced wave, Figure 7-5B(or a square wave with greater electrode-negative currentflow), are:

• Higher currents can be used with a given elec-trode, since the electrode-positive cycle has lesscurrent flowing than with a balanced wave.

• The power source is less expensive than for abalanced wave machine.

• Better penetration is possible with an unbal-anced wave because penetration takes place dur-ing the electrode-negative half cycle.

The advantages of a square-wave power source thatallows the ac balance to be adjusted are:

• The square wave provides high voltage and cur-rents while the electrode switches polarities. Thiseliminates rectification.

Chapter 7 GTAW and GMAW Equipment and Supplies 169

Onecycle

Time

A

B

C

Time

O

O

O

Time

Electrodenegative

Electrodepositive

Electrodenegative

Electrodepositive

Cur

rent

Cur

rent

Cur

rent

Electrodenegative

Electrodepositive

Figure 7-5. Alternating current plotted against time. A—Completely rectified ac wave with no current flow during electrode positive. B—Unbalanced wave. C—Balanced wave.

Sinusoidal wave: Voltage and currentgradually increase from zero

Square wave: Voltage and current go from positive to negative instantly

Figure 7-6. Comparing voltage and current in a sinusoidalac wave and a square wave. The square wave goes from apositive value to a negative value instantly. The voltage andcurrent allow the arc to reinitiate (restart). The traditional acwave has voltage and current near zero for some period oftime.

• The welding power source can be adjusted toobtain a balanced wave and obtain the advan-tages of the balanced current wave listed above.

• Power source can be adjusted for greater pene-tration and still have the electrode-positive halfcycle be present (not rectified).

• Power source can be adjusted for greater clean-ing than can be obtained with a balanced wave.

7.4 Shielding Gases Used with GTAWInert gases are gases that will not react with metals or

other gases. Inert gases are used to create a protective bub-ble around the arc, molten metals, and the tungsten elec-trode while welding is being done. Argon, helium, argon-helium, and argon-hydrogen mixtures are used as the inertgases when doing gas tungsten arc welding. Because thisprocess uses a tungsten electrode and inert gases, it isknown in the shop as TIG. TIG is an older term that standsfor “tungsten inert gas.” The correct name for the process,however, is gas tungsten arc welding. The abbreviation isGTAW.

Argon (Ar) has an atomic weight of 40 and a densityof 1.78 gm/l. It is, therefore, a relatively heavy gas. Argonis usually furnished in heavy steel cylinders similar in con-struction to those used for oxygen. The usual cylinder sizeis 330 ft3 (9.34 m3). Argon as used for welding is a mini-mum 99.995% pure. It is capable of being shipped in theliquid form at –300ºF (–184ºC). Liquid argon can beshipped more cheaply than gaseous argon. However,equipment must be purchased by the user to vaporize theargon for use in welding.

Argon is used more often than helium for the follow-ing reasons:

• It provides easier arc starting.• It provides a smoother, quieter arc action.• It requires a lower arc voltage for a given arc

length and current. This allows for better controlof the weld pool.

• It has reduced penetration. • It has a lower overall cost and is more readily

available.• It provides a greater metal cleaning action on

aluminum and magnesium when used withalternating current.

• It is heavier than helium, and requires a lowerflow rate for good shielding.

• Because it is heavier than helium, it provides forbetter cross-draft shielding.

• Because it requires lower arc voltages to main-tain the arc, argon has great advantages for usewith thin metal and in out-of-position welding.

Helium (He) is the lightest inert gas. It has an atomicweight of 4 and a density of 0.178 gm/l. Argon thereforeis ten times heavier than helium. Helium used for weld-ing is a minimum 99.95% pure. It is normally shipped andused as a gas. The cylinders are similar to those used foroxygen. Helium is usually used in cylinders of the 330 ft3

(9.34 m3) size. Because helium is so light, it requires about

two to three times more helium than argon to shield agiven weld area.

The chief advantage of helium over argon is that heli-um can be used with greater arc voltages. Helium alsoyields a much higher available heat on the metal than ispossible with argon. Helium is therefore used to weldthick sections of metal or metals with a high heat conduc-tivity, such as copper or aluminum. Helium also producesgreater weld penetration.

To produce the same available heat at the metal, high-er currents must be used with argon than with helium.Studies have shown that undercutting will occur at thesame current levels with either gas. Helium, therefore, willproduce better weld results at higher speeds withoutundercutting than will argon.

Both helium and argon provide good cleaning actionwith direct current electrode positive (DCEP). However,since DCEN produces greater heat and penetration, DCENis the polarity normally used for GTAW. With ac, which isused on aluminum and magnesium, argon provides a bet-ter cleaning action. Argon also provides better arc stabilitywith ac than helium.

Argon and helium can be mixed to obtain desiredresults. Mixtures provide a combination of the results fromeach gas. Good arc starting and a stable arc can be com-bined with increased penetration and increased weldingspeeds.

Argon-hydrogen mixtures are used to produce higherwelding speeds. The welding speed possible is in directproportion to the amount of hydrogen added to argon gas.The addition of hydrogen to argon permits the mixture tocarry higher arc voltages. Too much hydrogen will causeporosity (gas pockets) in the weld metal. Porosity weakensa weld. Mixtures of 65% argon and 35% hydrogen havebeen used on stainless steel with a 0.010" to 0.020" (approx-imately 0.250mm to 0.500mm) root opening. The mostcommon argon-hydrogen ratio is 85% argon and 15%hydrogen. Argon-hydrogen mixtures are used with stain-less steels, nickel-copper, and nickel-based alloys.Hydrogen produces negative welding effects with mostother metals.

Argon, helium, or argon-helium mixtures can be usedfor most GTAW welding jobs. Manual welding on thinmetals is done best with argon because of the low arc volt-ages and welding currents required. Whenever there is across draft, it is advisable to construct a wind break. Thiswill reduce the possibility of the shielding gas being blownaway from the weld area.

7.4.1 Shielding Gas CylindersThe gases described in the previous heading can be

obtained in cylinders of various sizes. These cylinders aresimilar to the oxygen cylinders described in Chapter 12.They are manufactured to Interstate CommerceCommission (ICC) specifications.

Some gases are stored in cylinders as a gas. Somegases may also be stored as liquids in thermos-like tanks,similar to the Dewar flask shown in Figure 12-3. The quan-tity of gas in the cylinder is determined by:

170 Modern Welding

• The high pressure gauge or volume scale, ifstored as a gas.

• The weight, if stored as a liquid.Shielding gases, with the exception of hydrogen, are

not flammable. Inert gases will not burn, nor will they sup-port combustion. The gases in cylinders are stored underhigh pressure. The high pressures in the full cylindersmake it necessary to handle the cylinders with care. Referto Chapter 1 and to Heading 13.5.2 for more informationon handling cylinders.

The cap should be securely threaded over the cylin-der valve whenever the cylinders are being moved, orwhen they are in storage. The cylinder should be fas-tened to a wall or very stable object when in use.Cylinders should be placed where it is virtually impos-sible to accidentally damage them with an arc or cuttingtorch. Gas cylinders should always be stored and used inan upright position.

7.4.2 Inert Gas RegulatorsShielding gas regulators are designed to perform in

the same way as the oxygen, acetylene, and hydrogen reg-ulators described in Chapter 12. Review that material foradditional understanding.

Inert gas regulators have either a gauge or a pressureindicator to show the cylinder pressure. Some of themhave only a flowmeter gauge on the gas delivery side.Figure 7-7 shows a regulator with a high-pressure gaugeon the inlet side. On the outlet side, a gauge indicates thevolume of gas flowing. This regulator has a constant out-let pressure to the flowmeter of approximately 50 psig(344.7 kPa).

Figure 7-8 shows a regulator and flowmeter. The fit-ting used to connect the regulator to the cylinder varieswith the kind of gas. These regulators will deliver gasflows up to 60 ft3/hr. (28.3 L/min). The flowmeter

scales are accurate only if the gas entering them is atapproximately 50 psig (345 kPa). If higher inlet pressuresare used, the gas flow rate will be higher than the actualreading; the reverse is true if the inlet pressure is lowerthan 50 psig (345 kPa). It is therefore important to use accu-rately adjusted regulators. Figure 7-9 illustrates a two-stage regulator for argon gas. The gauge is a high-pressuregauge and is used to indicate the pressure in the cylinder.

A regulator is attached to an inert shielding gas cylin-der. Start the threads by hand. Be careful not to cross thethreads. Once the threads become snug, use a proper fit-ting wrench to finish tightening the nut on the regulator.Do not overtighten, just firmly secure the nut.

7.4.3 Flowmeters and Gas MixersThe amount of gas around the arc can best be mea-

sured by the volume of gas coming out of the nozzle,rather than the pressure of the gas. Therefore the shieldinggas system is usually equipped with a flowmeter that iscalibrated in cubic feet per hour (ft3/hr. or cfh) or in litersper minute (L/min).

In one type of flowmeter, a tapered plastic or glasstube contains a loosely fitted ball. As the gas flows up thetube, it passes around and lifts the ball. The more gas that moves up the tube, the higher the ball is lifted.

Chapter 7 GTAW and GMAW Equipment and Supplies 171

Flowgauge

Cylinderpressuregauge

Gas flowadjusting

knob

Figure 7-7. A gas regulator with a flowmeter gauge insteadof a low-pressure gauge. The flowmeter gauge may be usedwith CO2 or argon. It is calibrated in cubic feet per hour.(CONCOA)

Gas flowadjusting knob

Cylinderpressuregauge

Flowmeter

Figure 7-8. A gas regulator and flowmeter. The low pres-sure to the flowmeter is preset. The flowmeter has two cali-brations. One is for argon and the other for CO2.(CONCOA)

Figure 7-10 shows a cross section of a tapered-tubeflowmeter. For an accurate reading, it is important that thistype instrument be mounted in a vertical position. Anyslant will cause an inaccurate reading.

The tube and return gas housing are either clear plas-tic or glass. Some have a metal protecting cover. The jointsbetween plastic tubes and the flowmeter body must begas-tight. The scale on the inner tube is usually calibratedfrom 0 ft3/hr. (or cfh) to 60 ft3/hr. (0 L/min to 28.3 L/min).The flowmeter scale is usually read by aligning the top ofthe ball with the ft3/hr. or L/min reading desired. A dif-ferent flowmeter or a different scale must be used for eachgas. The reason for a different flowmeter or scale is thateach shielding gas has a different density or weight.Because the weight of the gas is different, the height towhich the ball will be lifted is different for helium, argon,and carbon dioxide, even if all have the same flow rate.

Universal-type flowmeters that have a square outertube are available. Each side of the square is calibrated fora different shielding gas. See Figure 7-9.

Gas volume is related to pressure if the orifices andgas passages remain constant in size and shape. Therefore,a gas pressure gauge can be used as a volume gauge whenthe scale is calibrated as shown in Figure 7-7.

Most flowmeters have a needle valve to turn the gasflow on and off and to control the volume of the gas flow.Because this valve controls the volume, and because thepressure to the valve is constant, the valve orifice and theneedle must be accurate and in good condition at all times.

Any abuse of the needle and/or seat will result in erraticvolume feeds. Also, if the needle threads or packingaround the needle have been damaged, the needle will notstay in adjustment. It is necessary that this valve be han-dled carefully. It should not be forced. Fingertip handlingonly is recommended.

It is sometimes necessary to use mixtures of inertgases in GTAW or GMAW. Most common mixtures areavailable from local gas distributors in cylinders. For somejobs and in some companies, individual gases are mixed.Such mixing must be done with great accuracy. Gases aremixed by percentages of volume. Each gas to be mixed isfed to a separate flowmeter, where the desired volume ofeach gas is set. These gases are then mixed by volume in a

172 Modern Welding

High-pressuregauge

Flowmeterreads in

ft3/hr. (cfh)

First stage Second stageFlowmeter

adjustment knob

Figure 7-9. A two-stage regulator with a flowmeter. The gasis fed to the flowmeter at 50 psig (345 kPa). This flowmeterhas four separate calibrated gauges to accurately show theflow of argon, helium, carbon dioxide, or nitrogen. (ESABWelding and Cutting Products).

Body

Gasket

Gasflow

Regulatoradapter

O-ring

O-ring

O-ring

Flowmeter dome

Floatball

Wing nut

Tube and ball assembly

Inletfitting

Argon,helium,CO2, oroxygen

Hose nipple nut

Hose nipple

Controlvalve

assembly

Figure 7-10. A cross section of a floating ball-type flowmeter.

special mixing chamber and fed to the welding torchthrough a final flowmeter.

7.5 Electrode Leads and Hoses Used for GTAWA water-cooled gas tungsten arc welding (GTAW)

torch generally has two hoses and one combination hoseand electrode lead connected to it. These hoses may bemade of rubber or plastic materials. One hose carries theshielding gas to the torch. The second is a combinationwater hose and electrode lead. The electrode lead is awoven metal tube with excellent current carrying capabil-ities. This electrode lead is surrounded by a rubber or plas-tic tube. Welding current travels through the woven metaltube while water travels through the rubber or plastictube. The third hose carries the water from the torch to thewater drain. In a closed water system, the water isreturned to the water cooling device and recirculated,Figure 7-11.

Figure 7-12 shows the hoses and fittings used in a typ-ical water-cooled GTAW torch. Figure 7-13 shows a similartorch completely assembled for use.

Light-duty GTAW torches are gas-cooled. Thesetorches have only one hose connected to them. This hose isa combination electrode lead and shielding gas hose. Theelectrode lead may be a flexible cable or a woven tube. The

shielding gas flows through a rubber or plastic tube whichsurrounds the electrode lead. Figure 7-14 shows anextremely light-duty GTAW torch which is gas-cooled.Figure 7-15 and 7-16 illustrate light-duty gas-cooledGTAW torches.

Chapter 7 GTAW and GMAW Equipment and Supplies 173

Figure 7-11. A water circulating and cooling unit used withclosed-circuit water-cooled systems. The coolant containeris available in larger sizes, as well. This unit can be usedwith GTAW, GMAW, PAW, resistance, and electroslag welding. (Tweco-Arcair, a Thermadyne Company)

Ceramic cups1/4″ dia.

5/16″ dia.

Collets.040″1/16″3/32″1/8″

Flexibletorch body

Body hex, adaptors

Innerhandle

Water-out andpower gland

Water nut

5/16″ circle clamp

Outer handle

12 1/2′ hose assemblyincludes: power, water,gas supply hoses and

hose gland parts

Torch body connection parts3/16″ circle clamps

Water-in and gas glands

Water-in and gas glandnuts only

5/16″hose glands

Gas nut Gas nutGascoupling

Water nut Water-in coupling

Water nut

1/4″circle clamps

5/16″circle clamps

Water nut

Welding machine connectionsPower lug and

water-out coupling

3/16″hose glands

3/16″hose glands

Water Shielding Gas Electricity

Figure 7-12. Exploded view of a gas tungsten arc welding torch and hose assembly. This torch has a flexible body that canbe bent to suit the job. (Falstrom Co.)

7.6 GTAW TorchesGas tungsten arc welding torches come in many dif-

ferent designs, sizes, amperages, and shapes. Torchesdesigned for lower amperages and light-duty use arecooled by the shielding gas flowing through the torch.Figures 7-14, 7-15, and 7-16 show examples of gas-cooledtorches. Current capacity for the largest shielding gas-cooled torches is about 200A. Smaller gas-cooled torchescarry significantly less current.

Torches used for higher amperages and those that are used to do a lot of welding at lower amperages arewater-cooled. Most torches used in production and mosttorches used for continuous automatic welding are water-cooled. Figures 7-13 and 7-17 show water-cooled torches.Figure 7-18 shows a cross section of a water-cooled torch.Figure 7-19 shows how the different parts of a water-cooled GTAW torch are assembled. These parts are also

174 Modern Welding

Water/powercable

Waterout hose

Torch

Shielding gas

Figure 7-13. A water-cooled GTAW torch. The inlet waterhose also carries the welding current to the electrode.

Water fittings

Gas fittings

Figure 7-14. A pen-sized gas tungsten arc welding torch.This torch is used when welding small parts. Note that it iswater cooled.

Cap

Collet

Collet body

Gasfitting

Electricalterminal

Tungstenelectrode

Nozzle

Figure 7-15. A gas-cooled, gas tungsten arc welding torch.A short cap and electrode permit use of this torch in difficult-to-reach places.

Figure 7-16. A gas-cooled gas tungsten torch. Note that theshielding gas and the electrode lead are separate.

Figure 7-17. Three GTAW torches. The two torches to theleft are water-cooled; the torch at the right is gas-cooled.Note the difference in length from the nozzle to the cap.(CK Worldwide, Inc.)

Chapter 7 GTAW and GMAW Equipment and Supplies 175

shown in Figure 7-20. Figure 7-15 shows some of the torchparts as they would be assembled.

There are two basic torch designs. These are:• Torches designed for general access. These torch-

es usually use a long electrode and have a longcap. They also use standard collets, collet bodies,and nozzles. See Figure 7-17.

• Torches designed for work in areas where spaceis limited. These torches are called stubby orstubs. They use a very short electrode and have avery short cap. These also use stubby collets,stubby collet bodies, and stubby nozzles. SeeFigures 7-16 and 7-17.

There are variations of the general access design.These variations allow a welder to select different parts ofthe torch for a specific job.

7.6.1 Collets, Collet Bodies, and Gas LensesTungsten electrodes are held in a collet. The function

of the collet is to firmly hold the electrode and make anelectrical connection to it. Collets are made with variousinside diameters. A collet must be selected to match thediameter of electrode that is being used. Figure 7-21 showsa typical collet.

Figure 7-18. A cross section of a water-cooled gas tungsten arc welding torch designed for automatic welding. This torch isdesigned with a current capacity of up to 500A. (Weldma Co.)

Water in

Electrical leadand water out

Nozzle

Tungsten electrode

Collet

176 Modern Welding

Nozzles

ElectrodeInsulators

Gas lens collet

End capsColletbodies

Torch body

Stubbyend caps

Collets

Figure 7-19. The various parts in a typical water-cooled GTAW torch, and how they fit together. (American Torch Tip Co.)

Figure 7-20. Note the different sizes of nozzles, collets, and collet bodies available for a typical water-cooled GTAW torch.(American Torch Tip Co.)

Shortback cap Long

back cap

Torch bodyInsertback

insulator

Gas hose

Powercable

Water hose

Handle-textured

Power cableadapter

Collets

Collet body

Nozzles

Collet body/gas lens

Large dia. gaslens adapter

Gas lensinsulator

Cup gasket

Stubby gasket

Handle-smooth

A collet is installed into the top of a torch assembly, asshown in Figure 7-22. To make a collet tighten around theelectrode, the cap is tightened. Tightening the cap forcesthe collet against the collet body, squeezing the collet. Theinside diameter of the collet reduces in size, firmly grip-ping the electrode.

The collet body locates the collet and transfers theelectrical current to the collet. The collet in turn transfersthe electrical current to the electrode. The collet body isthreaded into the end of the torch. Examples of collet bod-ies are shown in Figures 7-19 and 7-20. Collet bodies areusually made for a single size of collet. When the electrodediameter is changed, both the collet and the collet bodyneed to be changed.

A collet body with a gas lens can be very useful to awelder. The purpose of a gas lens is to make the shieldinggas exit the nozzle more as a column than as a turbulentstream of gas that begins to spread out after exiting. See Figures 7-20 and 7-23. The column of gas allows theelectrode to stick out farther for visibility and for betteraccess to the weld area.

A gas lens is a series of stainless steel wire meshscreens. The collet body with gas lens is installed in thetorch in place of a standard collet body. See Figures 7-19

and 7-20. A different gas lens is required for each differentelectrode diameter. Different nozzles are also requiredbecause the gas lens has a larger diameter than a standardcollet body.

Chapter 7 GTAW and GMAW Equipment and Supplies 177

Figure 7-21. Two copper GTAW collets.

Figure 7-22. A copper electrode collet being installed in aGTAW torch. The electrode and electrode cap are installednext.

Collet

Torch

Ceramicnozzle

Figure 7-23. The torch at the right has a gas lens installed.The gas flow from the conventional GTAW nozzle at theleft is turbulent and dissipates more rapidly. (CK Worldwide, Inc.)

7.6.2 NozzlesGas nozzles are used to direct the shielding gas over

the tungsten electrode and to cover the weld area withshielding gas. Nozzles must be able to withstand very hightemperatures because they are very close to the arc.Different designs are available to meet the requirements ofdifferent welding jobs.

Nozzles are made from different materials. Most com-monly, nozzles are made from a ceramic material. Othermaterials used include metal-jacketed ceramics, metal, andfused quartz.

One end of a gas nozzle must attach to the end of thetorch. Different designs are necessary to properly attach todifferent manufacturers’ torches. The nozzle may bethreaded onto the torch or held by friction.

The exit end of the GTAW nozzle is more standard.The exit diameter is identified with a number. The numberis the exit diameter measured in 1/16″ (1.6mm) incre-ments. A number 6 nozzle thus has a diameter of 3/8″(9.6mm):

6 x 1/16″ = 6/16″ or 3/8″ (6 x 1.6mm = 9.6mm)

A number 8 nozzle diameter is 1/2″ (12.8mm):8 x 1/16″ = 8/16″ or 1/2″ (8 x 1.6mm = 12.8mm)

Nozzle exit diameters must be the correct size for thejob. If they are too small, they will not allow the shieldinggas to cover the weld area. They cannot be too large, or thevelocity of the gas coming out will be too slow and willeasily be blown away. A high velocity and a small diameter is also not good, because air may be caught up inthe turbulence and contaminate the weld area. Selectingthe correct size nozzle is important.

Factors, such as accessibility of the weld area, mayaffect selection of the nozzle. Different nozzle styles can beseen in Figures 7-19 and 7-20 and other figures in thischapter. See Figure 7-24 for suggested nozzle size for agiven electrode diameter.

7.7 Tungsten ElectrodesThe electrodes used in gas tungsten arc welding may

be one of the following types:• Pure tungsten.• Tungsten with 1% or 2% thoria (thorium

oxide).• Tungsten with 0.15% to 0.40% zirconia (zirconi-

um oxide).• Tungsten with 2% ceria (cerium oxide).• Tungsten with 1% lanthana (lanthanum oxide).The chemical composition of tungsten electrodes,

from the AWS A5.12 specification, is shown in Figure 7-25. Letters and numbers used in tungsten electrode classifications are interpreted as follows:

178 Modern Welding

E – electrode

W – tungsten

P – pure

Ce – ceria

La – lanthana

Th – thoria

Zr – zirconia

Suggestedin. mm nozzle size (in.)

.010 .25 1/4

.020 .50 1/4

.040 1.00 3/8

1/6 1.6 3/8

3/32 2.4 1/2

1/8 3.2 1/2

5/32 4.0 1/2

3/16 4.8 5/8

1/4 6.4 5/8

Electrode diameter

Electrodes are referred to as follows:Pure tungsten EWPThoriated tungsten EWThZirconiated tungsten EWZrCeriated tungsten EWCeLanthanum tungsten EWLa

Tungsten electrodes not covered in the preceding list aredesignated EWG.

Pure tungsten electrodes are the least expensive.However, they carry less current than alloyed electrodes.Pure tungsten electrodes are usually used only with acwelding. Pure tungsten electrodes may split or breakdown and cause inclusions (tungsten) in the weld if usedwith excessive current.

Electrodes with thoria added carry more current thanpure tungsten or zirconia electrodes. It is easier to strike anarc and maintain a stable arc with thoria electrodes. Theseelectrodes have a greater resistance to contamination of theweld. Electrodes with thoria added are usually used onlywith direct current.

Zirconia added to tungsten electrodes gives the elec-trode qualities which fall somewhere between pure tung-sten and tungsten with thoria added. Tungsten electrodeswith zirconia are the best electrode to use when ac weldingaluminum or magnesium. They do not cause inclusions aspure tungsten electrodes can. For this reason, tungstenelectrodes with zirconia are used for high quality applications.

Electrodes with ceria or lanthana are very similar toelectrodes with thoria. They can be used with ac or dc.They allow for a stable arc; arc starting is easy.

Since these electrodes are identical in appearance, anapproved color code is used to identify the type of elec-trode. The color is a painted band near one end of the elec-trode or a color painted on the end of the electrode. TheAWS color codes are listed in Figure 7-26.

Figure 7-24. A table of suggested nozzle sizes for use withvarious electrode diameters.

Chapter 7 GTAW and GMAW Equipment and Supplies 179

Tungsten electrode diameters are available in diame-ters of 0.010″, 0.020″, 0.040″, 1/16″, 3/32″, 1/8″, 5/32″,3/16″, and 1/4″ (0.25, 0.51, 1.02, 1.59, 2.38, 3.18, 3.97, 4.76,and 6.35mm). Electrodes come in lengths of 3″, 6″, 7″, 12″,18″, or 24″ (76, 152, 178, 305, 457, or 610mm). The surfaceof a tungsten electrode, when purchased is either groundor chemically cleaned.

7.7.1 Care of Tungsten ElectrodesA tungsten electrode must be straight. If it is bent or

off-center in the nozzle, the arc may wander to one sideand produce uneven penetration. Contamination of theweld may also occur. Make sure the electrode is straightand is prepared correctly.

Sometimes the electrode comes in contact with themolten weld pool. This contaminates the tungsten elec-trode. The end of such an electrode must be removed toform a new clean end. A pair of pliers may be used tobreak off the dirty end of the electrode. Another method isto use a grinding wheel to notch the electrode just behindthe contamination and then break the electrode using pliers or a special fixture. See Figure 7-27B. This method ofnotching the electrode is shown in Figure 7-27A.

Tungsten electrodes must be clean and must havegood electrical contact with the collet. The tungsten shouldbe adjusted to extend about 1/8″ (1.6mm) beyond the endof the nozzle.

AWSclassification

Tungstenmin. percent

(by difference)Ceria(CeO)

Lanthana(LaO)

Thoria(ThO)

Zirconia(ZrO)

Total otherelements oroxides, max.

Percent

Not Specified

EWPEWCe-2EWLa-1EWTh-1EWTh-2EWZr-1EWG

99.597.398.398.397.399.194.5

–1.8 - 2.2

––––

––

0.9 - 1.2–––

–––

0.8 - 1.21.7 - 2.2

–

–––––

0.15 - 0.40

0.50.50.50.50.50.5

Figure 7-25. The chemical composition of the AWS classifications for tungsten electrodes. (AWS A5.12)

AWSclassification Defined Color

EWP Pure tungsten GreenEWCe-2 2% Ceria OrangeEWLa-1 1% Lanthana BlackEWTh-1 1% Thoria YellowEWTh-2 2% Thoria RedEWZr-1 0.15-0.40% Zirconia BrownEWG Other Gray

Figure 7-26. The AWS color code for various types of tung-sten electrodes. (AWS A5.12)

It is extremely important that shielding gas alwaysprotect the electrode and the weld area. Shielding gas hoseconnections must be tight to prevent air or moisture frommixing with the shielding gas, then coming in contact withthe electrode. Such contamination of the shielding gaswould be harmful to the weld and to the electrode.

Preparing the electrode end for welding is veryimportant. Refer to Heading 8.3.5 on selecting and prepar-ing a tungsten electrode for welding.

7.8 Filler Metals Used with GTAW

Gas tungsten arc welding is used to weld almost allweldable metals. The choice of filler metals, therefore, isvery large.

Figure 7-28 lists the American Welding Society (AWS)filler metal, electrode and gas specification booklets for usewith GTAW, GMAW, and FCAW. Each “A5” specificationbooklet contains a list of filler metal specifications andtheir suggested uses, and current settings in addition totheir chemical compositions. Filler metal is available invarious diameters. The filler metal can be purchased cut tolength, usually 24″ (610mm) or 36″ (915mm), or as a con-tinuous coil. Continuous coils of filler wire are used insemiautomatic, mechanized, or automatic welding opera-tions. GTAW with continuous coil filler metal requires awire feeder and a method to guide the filler metal to theweld pool. Figure 7-29 shows equipment used to feedGTAW wire.

7.9 The Gas Metal Arc Welding Station

Gas metal arc welding (GMAW) uses the equipmentlisted below to make a weld. This equipment is used tofeed a continuous wire electrode to the weld. As the elec-trode melts, it also melts the base metal to form a weld.

The typical GMAW outfit contains the followingequipment and supplies:

• A constant voltage dc arc welding power source.

• An electrode wire feed mechanism.• Shielding gas cylinders. See Heading 7.4.1.• A gas regulator. See Heading 7.4.2.• A shielding gas flowmeter. See Heading 7.4.3.• Shielding gas, coolant hoses and fittings, and the

electrode and workpiece leads.• A GMAW welding gun.

180 Modern Welding

A

B

C

Figure 7-27. Three steps are required to prepare a tungstenelectrode for welding. A—Notching the electrode prior tobreaking. B—Breaking the electrode in special fixture. C—Grinding the electrode in a special grinder. (Intercon Enterprises, Inc.)

Figure 7-28. AWS filler metal, electrode, and gas specifica-tions. The material covered in the listed A5 specificationnumbers are for GTAW, GMAW, and PAW unless other-wise indicated.

Wireguide tube

Wire feedspeed control

Figure 7-29. Two models of GTAW power sources with anautomatic wire drive to provide filler metal to the weldpool during the welding process. Note the wire guide tube.(CK Worldwide, Inc.)

• Electrode wire.• Optional equipment.

� A coolant system. See Figure 7-11.� Remote controls.

AWSspecification

numberGeneral Content of Booklet

A5.7 Copper Alloys

A5.9 Stainless Steel

A5.10 Aluminum Alloys

A5.12 Tungsten Electrodes

A5.14 Nickel Alloys

A5.15 Cast Iron (FCAW)

A5.16 Titanium Alloys

A5.18 Carbon Steel

A5.19 Magnesium Alloys

A5.20 Carbon Steel (FCAW)

A5.21 Surfacing Alloys

A5.22 Stainless Steel (FCAW)

A5.24 Zirconium Alloys

A5.28 Low-Alloy Steel

A5.29 Low-Alloy Steel Electrodes (FCAW)

A5.30 Consumable Inserts

A5.32 Shielding Gases

Chapter 7 GTAW and GMAW Equipment and Supplies 181Chapter 7 GTAW and GMAW Equipment and Supplies 181

Workpiece

Auto torch

Wire feeder

Control system

Powersupply

Shieldinggas

Regulatorwith flowmeter

Wire feed drive motor

Wire reelMetal electrode

Manuallyheld gun

Figure 7-30. A diagram of a combination manual and automatic gas metal arc welding outfit.

Figure 7-30 is a schematic drawing of a GMAW outfit.A complete station would include the arc welding booth, aventilation system, and a welding bench. Refer also toFigure 4-13.

7.10 Arc Welding Power Sources for GMAW

Gas metal arc welding (GMAW) uses a weldingpower source and a wire feeder that feeds the electrodewire through the welding gun to the weld. Welding powersources used for GMAW produce a constant voltage. Thefollowing types of power sources are used when gas metalarc welding:

• Transformer-rectifier type. See Figure 7-31.• Inverter type. See Figure 7-32.• Engine-driven generator type. See Figure 7-33.The preferred power sources are the transformer-rec-

tifier and inverter type machines. They provide betterresponse and control over the welding process then anengine-driven generator machine. When welding whereno source of electrical power is available, however, anengine-driven generator type machine must be used. SeeChapter 5 for information on the construction, operation,and control of these machines.

Direct current electrode positive (DCEP), also calledreverse polarity (DCRP), is used when GMAW. WhenGMAW, constant voltage is required. A constant voltagepower source will maintain a constant arc voltage, which

Figure 7-31. A transformer-rectifier type constant voltage(cv) power source for GMAW. (Hobart Brothers Co.)

should decrease. However, the machine will deliver morecurrent to burn off the electrode faster and maintain the arclength determined by the set voltage. Also if the weldinggun is moved further from the work, the machine willdeliver less current, so the electrode will burn off moreslowly. By burning off the wire at a slower rate, the arclength and voltage remain constant. The arc welding

means it will maintain a constant arc length. To change thearc length, the set voltage must be changed. The output ofa constant voltage power source has a very flat volt-ampere curve, as shown in Figure 7-34.

Constant voltage power sources have the ability toself adjust to maintain a constant arc length. When thewelding gun is moved closer to the work, the arc length

182 Modern Welding

5

50 100 150 200 250 300

10

15

20

25

30

35

40

AB

C

Figure 7-34. Characteristic volt-ampere curve for a constant voltage arc welding machine. A 100-ampere change (from 200Ato 300A) results from a voltage change of 3V from 22V to 19V.

Figure 7-32. An inverter type power source for GMAW.(Hobart Brothers Co.)

Vol

tage

Amperage

Engine

Workpiecelead terminal

CV terminal

CC terminal

Figure 7-33. An engine-driven generator type powersource. (Miller Electric Mfg. Co.)

transfer. This prevents excessive current when the shortcircuit occurs. If too-steep a slope is used with short cir-cuiting transfer, the molten metal drop will not separatefrom the electrode and the arc will not restart.

7.11 Wire Feeders Used with GMAW The wire electrode used in gas metal arc welding

comes in large coils (spools) or drums. These wire coils ordrums contain hundreds or even thousands of feet(meters) of wire.

Small coils of wire are mounted on free-turning axlesnear the wire feed mechanism. If the larger drums of wireare used, the drum is placed near the wire feeder. The wireis smoothly drawn from either the coil or drum.

Wire feeders consist of a coil-mounting device, a set ofdrive wheels for the wire, and an adjustable, constant-speed motor to turn the wire drive wheels. Figure 7-36shows a wire feeder with the drive wheels outside the wirefeed control unit. Both drive wheels have gear teeth on theoutside circumference. The driven wheel moves the sec-ond wheel by means of the gear teeth. One of the wheels isdriven by the adjustable dc type constant-speed motor.The tension on the wire passing between these wheels isadjusted by moving the wheels closer together or fartherapart. This is done by turning a tensioning device.

Sometimes, wire feeders are contained inside theGMAW machine. Figure 7-31 shows such a machine.Other welding outfits have the wire drive unit separatefrom the welding machine. See Figure 7-37.

A switch on the wire drive control panel is used torotate the drive motor slowly. Occasionally, it is necessaryto change wire reels, replace parts, or clear a problem in

Wirefeeder

Remote controlconnection

Wirefeeder

Wire feedspeedcontrol

Wire jog orinch control

Gas purgecontrol

machine amperage is changed proportionately when thewire feed speed is changed.

Figure 7-34 shows how large a current change willoccur when the voltage changes only slightly. A weldersets a welding machine and wire feeder to weld at 22V and200A (Point B on Figure 7-34). If the gun is moved closer tothe work, the voltage will attempt to decrease to 19V. Toprevent this change in voltage, the machine will increasethe current automatically to 300A . See Point C in Figure 7-34. This increase in current will quickly burn off the elec-trode wire and actually maintain the voltage at 22V. If thegun is moved away from the work and the voltageattempts to increase to 25V, the current will decrease. Theelectrode will burn off at a slower rate. This will allow thearc length and the voltage to remain very close to their setvalue of 22V.

The slope of the volt-ampere curve is important.Some welding machines allow the slope to be changed;others machines have only one preset slope. Electronicallycontrolled machines have different slopes preset for com-mon types of metal and methods of transfer. The slope ofa machine is very important when using short circuitingtransfer. Short circuiting transfer and other transfer meth-ods are discussed in Headings 9.1.1 through 9.1.4

Figure 7-35 shows various slopes for GMAW powersources. Nonferrous metals and large-diameter flux coredelectrode wires use a slope of 1.5V to 2V per 100A . A medi-um slope of 2V to 3V per 100A is used for GMAW with car-bon dioxide (CO2) gas and small-diameter flux cored elec-trode wires, as shown in Figure 7-35B. A steeper slope,Figure 7-35C, has a slope of 3V to 4V per 100A. This steep-er slope is recommended for short circuiting arc transfer.

A slope of 1.5V to 2V per 100A is used with large-diameter electrode wires to allow a large current change toburn off the large-diameter electrode wire. A steeper slopeof 3V to 4V per 100A is used when using short circuiting

Chapter 7 GTAW and GMAW Equipment and Supplies 183

Setvoltage

Vol

tage

-1

-2

-3

-4

Amperage10 20 30 40 50 60 70 80 90 100

A

B

C

Figure 7-35. Volt-ampere curves for various weldingmachine slope settings. Curve A—1.5V to 2V per 100A forGMAW of nonferrous metals. Curve B—2V to 3V per 100Afor GMAW with CO2. Curve C—3V to 4V per 100A forGMAW short circuiting arc transfer.

Figure 7-36. A wire feeder and controller. Note the controlsand the fact that two wire feeders may be used individuallyor together. (Miller Electric Mfg. Co.)

the wire drive unit. To reinstall the electrode wire throughthe cable liner and contact tube, the wire must be movedslowly ahead. The wire is moved slowly so that it does notbend or kink within the electrode cable. The switch on thewire drive control panel is called an inch switch or a jogswitch. See the switch in Figure 7-36.

The shielding gas hose may have air in it before itsfirst use after a long shutdown period. To clear or purgethe hose and gun, the shielding gas is turned on for a shortperiod prior to welding. A purge switch may be providedfor this purpose on the wire feed control box.

7.12 GMAW Shielding GasesThe shielding gases used with gas metal arc welding

(GMAW) may be inert, reactive, or mixtures of both typesof gases. Inert gases used are argon (Ar) and helium (He).These gases, being inert, will not react with other chemicalelements. Reactive gases will react with other chemicalelements. Used properly, reactive gases will not causedefects in welds.

The reactive gases used in GMAW are carbon dioxide(CO2) and oxygen (O2). Hydrogen (H) and nitrogen (N2)are also used, but only in highly specialized applications.Their use results in better control of penetration.Hydrogen and nitrogen will cause embrittlement andporosity in the welds on most metals.

Mixtures of argon and helium; argon and oxygen;argon and carbon dioxide; and helium, argon, and carbondioxide are used. The gas or gas mixture used will bedetermined by the metal being welded and the type of arctransfer method desired. See Headings 9.1.1 through 9.1.4for an explanation of metal transfer methods.

184 Modern Welding

Constant voltagepower source

GMAWgun

Cableconnection

Separatewire drive unit

Figure 7-37. A constant voltage (cv) power source with aseparate wire feeder are being used to GMAW a small steelwheel. (Lincoln Electric Co.)

Pure argon (Ar) and helium (He) are excellent gasesfor protecting the arc, metal electrode, and weld metalfrom contamination. They are not, however, as suitable forsome GMAW processes as mixtures of gases. Gas mixturesseem to create arc stability, reduce spatter, and improve thebead contour.

Reactive gases like carbon dioxide, oxygen, and nitro-gen are not practical to use alone as shielding gases.Carbon dioxide is the exception. It is inexpensive andworks well on carbon and low-alloy steels. Carbon dioxidegenerally costs about one-tenth as much as pure argon gas.

7.12.1 Argon and Helium Gases Used in GMAWArgon and helium are the gases generally used with

nonferrous metals, as seen in Figure 7-38. Helium con-ducts heat better in the arc than argon. Helium is usedwhen high heat input is required in a welding application.Helium gas, therefore, is chosen for use on thick metals. Itis also used on metals, like copper and aluminum, whichconduct heat away from the weld area rapidly. Whenwelding thin metal and metals that conduct heat poorly,argon is a good choice. Argon is often used for out-of-posi-tion welding because of its lower heat conductivity.Because argon is ten times heavier than helium, it shieldsbetter. Less gas is required to provide a good shield. Argoncosts less than helium, and because less argon is requiredto obtain good shielding, the cost of using argon as ashielding gas is a lot less than using helium.

The weld bead contour and penetration are alsoaffected by the gas used. Welds made with argon general-ly have deeper penetration. They also have a tendency toundercut at the edges. Welds made with helium generallyhave wider and thicker beads. Figure 7-39 shows the shapeof welds made with various gases and gas mixtures.

Argon used with the gas metal arc spray transferprocess tends to produce deeper penetration through thecenterline of the bead. True spray transfer occurs onlywhen an argon or very high percentage argon shieldinggas is used. For spray transfer in steel, the amount of argonmust be at least 90%. The GMAW globular and short cir-cuiting arc metal transfer methods produce wider beadswith shallower penetration.

7.12.2 Gas Mixtures Used in GMAWWelds made with pure argon have deep penetration.

On carbon and low-alloy steels, the filler metal tends todraw in from the toe of the weld (weld edge) when argonis used as the shielding gas. This can cause undercutting.To overcome this tendency of the filler metal not to flowout to the edges of the weld, a gas mixture is used. Forsteels, oxygen (O2) or carbon dioxide (CO2) is added toargon. This addition of O2 or CO2 to argon tends to causebetter metal transfer and flow. It also reduces metal spatterand stabilizes the arc.

As little as 0.5% oxygen will cause noticeableimprovement. Additions of 1% to 5% oxygen or 3% to 10%carbon dioxide are usually used. Figure 7-38 shows somegas mixtures and their applications.

Adding oxygen or carbon dioxide to argon or heliumcauses the shielding gas to become slightly oxidizing. Thismay cause porosity in some ferrous metals. To offset thisoxidizing tendency, a deoxidizer is added to the electrodewire.

7.12.3 Carbon Dioxide Gas

Carbon dioxide is used only on carbon steel and low-alloy steels. Carbon dioxide (CO2) reduces to carbonmonoxide (CO) and oxygen (O2) in the arc. However, thesegases return to CO2 as they cool.

Carbon dioxide is not an inert gas. It will react withthe base metal and oxidize the base metal. When usingCO2, an electrode with alloys to eliminate this oxidationmust be chosen.

Carbon dioxide is 50% heavier than air and its abilityto shield the arc is quite good. Moisture-free carbon dioxidemust be used, or the hydrogen generated while weldingwill cause weld porosity and brittleness.

Carbon dioxide has a rather high electrical resistanceand it, therefore, has a rather critical arc length. Even smallchanges in the arc length will produce spattering and a“wild arc.” A very short and constant arc length must be

Chapter 7 GTAW and GMAW Equipment and Supplies 185

Shielding gasor mixture

Chemicalbehavior Metals and applications

Argon Inert Virtually all metals except steels.Helium Inert Aluminum, magnesium, and copper alloys for greater heat input and to minimize porosity.Ar + He (20-80% Inert Aluminum, magnesium, and copper alloys for greater heat input and to minimize porosity to 50-50%) (better arc action than 100% helium).Nitrogen Greater heat input on copper (Europe).Ar + 25-30% N2 Greater heat input on copper (Europe); better arc action than 100% nitrogen.Ar + 1-2% O2 Slightly oxidizing Stainless and alloy steels; some deoxidized copper alloys.Ar + 3-5% O2 Oxidizing Carbon and some low-alloy steels.CO2 Oxidizing Carbon and some low-alloy steels.Ar + 20-50% CO2 Oxidizing Various steels, chiefly short circuiting arc.Ar + 10% CO2 + Oxidizing Various steels (Europe). 5% O2CO2 + 20% O2 Oxidizing Various steels (Japan).90% He + 7.5% Ar Slightly oxidizing Stainless steels for good corrosion resistance, short circuiting arc. + 2.5% CO260-70% He + Oxidizing Low-alloy steels for toughness, short circuiting arc. 25-35% Ar + 4-5% CO2

Figure 7-38. Shielding gases used with various metals. (American Welding Society)

Argon Argon-Helium Helium CO2

Figure 7-39. The shape and depth of penetration of beads obtained with various shielding gases used when GMAW.

maintained. Carbon dioxide is furnished in liquid form in50 lb. (23kg) cylinders. These cylinders are approximately9″ (229mm) in diameter and 51″ (1.30m) high and weigh105 lb. (48kg), when empty. Each pound (0.45kg) of liquidwill furnish 8.7 ft3 (0.25m3) of gas, which is equal to 435 ft3

(12.3m3) per cylinder. It must change from a liquid to a gasas it is being used. This change from liquid to gaseous CO2is dependent on the room temperature. When the deliveryline from the liquid tank is opened, carbon dioxide gas“boils” or bubbles out of the liquid. The expansion of thegas as it leaves the liquid and passes through the regulatorcauses the CO2 gas to cool. If moisture is present, it maycondense and freeze in the regulator, blocking the gas pas-sage. Excessive moisture may also be indicated by erraticflowmeter operation. It is recommended that CO2 with a–20°F (–29°C) or lower dew point be used.

One cylinder can furnish only about 35 ft3/hr.(16.5L/min) when the cylinder is in a 70°F (21°C) room.Sometimes, two or more cylinders must be connected inparallel to furnish enough gas for welding. The pressure inthe cylinder when liquid is present is about 835 psig at70°F (5760 kPa at 21°C).

Carbon dioxide is also available in the gaseous formin cylinders. These cylinders are similar to the oxygencylinders described in Chapter 12.

7.13 The GMAW Welding GunA typical gas-cooled gas metal arc welding gun and

its electrode lead and gas hose are shown in Figure 7-40.The gas hose, the electrode lead, and the electrode wirecarrier, called a liner, are all built into one large cable. Thegun has a fully insulated handle, a trigger switch, a currentcontact tube, and a nozzle. The trigger switch turns on the

current and wire feeder and starts the shielding gas flow-ing. Figure 7-41 shows the main parts of a gas-cooledGMAW gun.

Gas metal arc welding guns are usually gas-cooled.Gas flowing through the gun and air on the outside of thewelding gun keep the gun from overheating. Carbondioxide GMAW guns may be used for intermittent dutyup to 600A. Figure 7-42 shows a gas-cooled GMAW gun.Gas metal arc welding using a gas-cooled gun with argonor helium must be done at much lower currents than arepossible with carbon dioxide.

GMAW guns are water-cooled when used with argonor helium above 300A or for continuous duty. Torches usedwith CO2 above 600A, or for continuous duty, are alsowater-cooled. Figure 7-43 shows a water-cooled GMAW

186 Modern Welding

Hanginghook

Trigger

Nozzle

Electrodewire carrier

Shieldinggas

Combinationcable

Figure 7-40. A gas-cooled GMAW gun. Note how the elec-trode wire travels through the center of the combinationcable. (Bernard Welding Equipment Co.)

Hollow, flexible,current-carryingelectrode lead

Control switchwire

Combinationcable

Torchhandle

On-offswitch

Shieldinggas

Electrodewire

Nozzle

Currentcontact

tube

Trigger

Figure 7-41. A cross-sectional drawing of an air-cooled GMAW gun. The shielding gas, electrode wire, and control switchwire are carried in a combination cable. The electrode wire runs through the cable liner and contact tube.

gun. In addition to an electrical lead and a shielding gashose, a water-cooled gun must have a hose to carry waterto the gun. The water returns to the water cooler throughthe combination power cable and water tube.

Gas metal arc welding guns that have self-containedwire drive units are available. See Figures 7-44 and 7-45.These guns have an electric motor to drive the electrodewire and a small coil of wire enclosed in the gun.

Another type of gun that is used is called a pull-typewelding gun. When welding long distances from the wirefeeder or when welding using aluminum wire (especially

smaller diameter aluminum wire), a pull-type weldinggun is used. See Figure 7-45.

A pull-type gun has a motor in it, which pulls theelectrode wire. Attempting to feed aluminum wire bypushing it through the cable to the gun will cause it to kinkor bend. Aluminum electrode wire is not rigid enough tobe pushed. Kinking can also happen when feeding steel orstainless steel electrode wire a long distance, because thereis a lot of friction on the wire. To prevent kinking the wire,a pull gun is used. The pull-type gun pulls the wire whilethe regular wire drive unit pushes the wire. This is a push-pull set-up. Figure 7-46 shows a push-pull system thatincludes a power source with a wire feeder and a pull-typewelding gun. Welding can be done 50′ (16m) from the wirefeeder using this push-pull method.

Welding guns used for automatic GMAW often havea straight body and nozzle. They do not have a handle.They are firmly attached to a carriage, robot, or othermechanism for welding, as shown in Figure 7-47. Sinceautomatic welding is done almost continuously, the gun is

Chapter 7 GTAW and GMAW Equipment and Supplies 187

Nozzle

Remote controlconnector

Gas/power cable

Figure 7-42. A gas-cooled GMAW gun. The flow of shield-ing gas acts to cool this type of gun.

Figure 7-43. A water-cooled GMAW gun. The gas andpower cable are combined. The gun has a flexible tubebetween the handle and nozzle. It can be bent to any convenient angle by the welder.

Flexible tube

Nozzle

Figure 7-44. A self-contained wire feeder and GMAW gun.A small spool of wire, drive motor, and drive wheels arecontained within this type of gun to smoothly feed thewire. (Miller Electric Mfg. Co.)

Figure 7-45. A pull type GMAW gun. The drive motor is inthe handle, and the drive rolls are just above the motor.(Thermadyne Industries, Inc.)

almost always water-cooled. Gas-cooled guns are usedwhen welding with lower amperages that will not causethem to overheat. Electrode wire and shielding gas is fedthrough the gun body to the arc area in the same manneras shown in Figure 7-41.

A new GMAW system has been developed for use inemergency or quick repairs. The system is highly portableand relatively light in weight. The power source is two 12volt long-life batteries to provide 24 volt power. The weld-ing gun contains the wire drive rolls, wire speed controls,and an on-board computer. See Figure 7-48.

7.13.1 Contact Tubes, Nozzles, and LinersSome of the parts of the welding gun need to be

changed or replaced on occasion. These include the contacttube, nozzle, and liner.

The contact tube is the part that transfers the electri-cal current from the welding gun to the electrode wire.Contact tubes, also referred to as contact tips, are madefrom copper or copper alloys. The contact tube must havea hole diameter 0.005″ to 0.010″ (0.13mm to 0.25mm) larg-er than the diameter of the electrode wire being used. Thisis necessary to make good contact and yet allow easymovement of the wire. Each contact tube is usuallystamped with the electrode diameter for which it isdesigned. Figure 7-49 shows different contact tubes, nozzles, and adaptors and how they are assembled.

The electrode wire continuously rubs against the con-tact tube, causing wear that enlarges the hole. As the holeincreases in size, it makes less solid contact with the elec-trode wire and allows the electrode and arc to wander.This will cause problems when welding. The contact tubemust be replaced when it gets worn.

Nozzles used for GMAW direct the shielding gas tothe weld area. Nozzles are exposed to very high tempera-tures for long periods of time. Nozzles are usually madefrom copper or copper alloy. The exterior may be brightchrome-plated to reflect the heat and keep the nozzle cooler. The nozzle is insulated from the torch. Usually, theyhave an insulator permanently installed on the inside.

Nozzle designs vary. One end must fit onto the weld-ing gun being used. Nozzles are attached to the welding

gun using two different methods. One is by threading thenozzle onto the gun. The second way is to use an adaptorand slide-on nozzle. Both types are shown in Figure 7-49.

The exit end of the nozzle also varies. It needs to belarge enough to allow a continuous flow of shielding gasto cover the weld area. It should not have spatter inside,

188 Modern Welding

Figure 7-46. A push-pull wire drive system. The weldinggun pulls the wire while the wire drive at the power sourcepushes the wire. This system is generally used with softwire like aluminum. (Miller Electric Mfg. Co.)

Wire spooland drive wheels

Gun oscillationcontrols

Gun speedcontrols

GMAW gun

I-beam

Figure 7-47. A GMAW gun mounted on a rigid beam inorder to make linear (straight line) welds on a structural “I”beam. This GMAW system has an oscillator which movesthe gun from side to side along the weld line. (MillerElectric Mfg. Co.)

Figure 7-48. A battery powered GMAW unit. Two 12 voltbatteries provide a 24 volt power supply. The gun containsthe wire drive and speed controls. (Broco, Inc.)

Deoxidizers are added to most electrode wires. This isdone to reduce the porosity in the finished weld. Duringthe welding process, the deoxidizer added to the wire willreact with any oxygen, nitrogen, or hydrogen. The deoxi-dizers reduce the possibility of these gases producingporosity, which would lower the mechanical strength ofthe weld.

The American Welding Society chemical compositionspecifications for carbon steel filler metal used withGMAW are shown in Figure 7-51. Figure 7-52 lists the AWSfiller wire specifications for GMAW low-alloy steels.

The numbers and letters used in the AWS classifica-tions in Figures 7-51 and 7-52 have the following meanings:

Example: ER70S-2E – electrode

R – rod

70 – tensile strength in ksi (1000 psi)

S – solid rod

2 – variations in chemical compositions

Examples of dash numbers:

B2 – chrome-molybdenum steel

B3L – chrome-molybdenum steel with alower carbon content

Ni (1-3) – Nickel steel

D2 – manganese-molybdenum steel

since this will affect the flow of the shielding gas. The exitdiameter is selected based on the application and jointaccess. Nozzle exit diameters are measured in 1/16″(1.6mm) increments. An example is a number 6 nozzlewhich has a 3/8″ (6 × 1/16″) or 9.5mm (6 × 1.6mm) exitdiameter.

A liner is installed in the cable that carries the elec-trode from the wire feeder to the welding gun. The elec-trode wire is constantly moving through this cable andwould wear out the cable. To protect the cable, a liner isinstalled. For most applications, a coiled steel wire liner isused. This coiled steel liner is sometimes called a conduit.When using aluminum electrode wire, a nylon liner isused. Figure 7-50 shows a coiled steel liner.

7.14 GMAW ElectrodesBare metal electrodes used for gas metal arc welding

are small in diameter. Diameters range from 0.020″ to0.125″ (0.51mm to 3.18mm). The most common diametersare 0.030″, 0.035″, and 0.045″ (0.76mm, 0.89mm, and1.14mm). Electrode wire is sold in spools of several hun-dred feet or meters, or in drums containing up to severalthousand feet or meters of wire coiled inside.

A variety of wire compositions are available for use asGMAW electrodes. Figure 7-28 lists the AWS specificationsfor electrodes.

Chapter 7 GTAW and GMAW Equipment and Supplies 189

Threadednozzle

Slide-onself-insulating

nozzles

Threadednozzle

Contact tubes Collet body Collet

Adaptor

Contact tubesTube

adaptors

Nozzle adaptor,used with slide-on

nozzles

Figure 7-49. Parts for a gas-cooled GMAW gun. (American Torch Tip Co.)

7.15 Smoke Extracting SystemsThe GMAW process can generate some smoke. Flux

cored arc welding (FCAW) often produces quite a bit ofsmoke. FCAW is discussed in the next few headings.When welding with carbon dioxide (CO2), there is somecarbon monoxide (CO) created. Some ozone is also creat-ed. Both of these gases are toxic. It is especially importantto prevent breathing these gases or any metal or metaloxide fumes.

Removal of these gases from the weld area can bedone by means of a GMAW torch equipped with a fumeextractor. Fume extractors may be built into the gun, asshown in Figure 7-53. Gas fumes, contaminated air, and airnear the weld are drawn away by the torch, filtered, andreleased to the atmosphere. Figure 7-54 shows a fumeextractor in use.

Another method to remove fumes is to use a large airremoval system, as shown in Figure 7-55. This pickuphood can be located near the welding area to remove thecontaminated air. This type of exhaust system can be usedwith any welding process or other process in the weldingshop, such as grinding.

An inexpensive option to move fumes away from thewelder is to use a portable fan. This does not eliminate thefumes, only moves them. The fan cannot blow too muchair or it will blow the shielding gas away from the weldand cause contamination of the weld.

Sometimes, welding must be done in a closed or con-fined area, or on metals that are hazardous. In such cases,it is necessary for the welder to wear a purified air breath-ing apparatus to supply fresh, clean air. Refer to Heading1.3.2. Figure 7-56 shows a welder wearing a purified airbreathing apparatus.

Whenever it is necessary to use a purified air breath-ing apparatus, always make sure the system is operatingproperly before entering a closed, confined, or contami-nated area and before doing any welding.

7.16 Flux Cored Arc Welding (FCAW)The flux cored arc welding (FCAW) process is used to

weld ferrous metals. Ferrous metals are those with iron asthe main element. Flux cored arc welding is very similar togas metal arc welding. The difference is in the metal elec-trode that is used. Flux cored electrode wire is hollow ortubular. Fluxing ingredients are contained within the tubu-lar electrode. The shielding of the weld from atmosphericcontamination is accomplished by two methods. The self-shielded FCAW method uses the gases formed when thefluxing agents within the hollow electrode vaporize in theheat of the arc. See Figure 7-57. A second method is calledgas-shielded FCAW. In this method, a shielding gas, suchas argon or carbon dioxide, is used in addition to thevaporizing flux in the electrode core. See Figure 7-58. Referto Heading 4.4 for an additional description of FCAW.

Flux cored arc welding combines the benefits ofshielded metal arc welding (SMAW), submerged arc weld-ing (SAW), and gas metal arc welding (GMAW). Theseinclude:

• The use of fluxing agents to dissolve and removeoxides and undesirable substances.

• A thin slag layer to shield the hot weld bead.• The ability to weld continuously for long

periods.• The metallurgical effects which can be controlled

by using various fluxing and alloying elements.Flux cored arc welding is generally done semiauto-

matically. The welding gun is held and manipulated by thewelder when doing semiautomatic welding. Flux coredarc welding may be used on fully automatic machineswith excellent results.

Self-shielded FCAW gives better results than gas-shielded FCAW when cross winds are present. The shield-ing gas for gas-shielded FCAW may be disturbed orremoved by a cross wind. This would result in poor welds.

190 Modern Welding

Wire guideat wire

drive end

Coiled wireliner

Liner

A

BFigure 7-50. A cable liner is used to carry the electrodethrough the combination cable to the welding gun. A—Thewire guide used in the wire drive. B—The liner within thewelding gun.

Chapter 7 GTAW and GMAW Equipment and Supplies 191

AWSclassification

Chemical Composition, Weight Percent

C Mn Si P S Nia Cra Moa Va Cub Ti Zr Al

ER70S-2 0.07 0.025 0.035

ER70S-3

ER70S-4

ER70S-5

ER70S-6

ER70S-7

ER70S-G

0.06to

0.15

0.90to

1.40

0.90to

1.40

1.00to

1.50

0.90to

1.40

1.40to

1.85

1.50to

2.00

0.40to

0.70

0.05to

0.15

0.02to

0.12

0.05to

0.15

0.50to

0.90

0.45to

0.70

0.65to

0.85

0.30to

0.60

0.80to

1.15

0.50to

0.80

0.07to

0.15

0.07to

0.19

0.07to

0.15

0.07to

0.15

No chemical requirementsc

0.50

a. These elements may be present but are not intentionally added.b. The maximum weight percent of copper in the rod or electrode due to any coating plus the

residual copper content in the steel shall be 0.50.c. For this classification, there are no chemical requirements for the elements listed, with the

exception that there shall be no intentional addition of Ni, Cr, Mo, or V.

Figure 7-51. Chemical composition specifications for carbon steel filler metal used with GMAW. For exact limitations andmore information, see AWS specification A5.18.

AWSclassification

Manga-nese

Phos-phorus

Chrom-ium

Molyb-denum

Vana-dium

Tita-nium

Zirco-nium

Alumi-num

Chemical Composition

Carbon Silicon Sulfur Nickel

ER80S-B2 0.07-0.12 0.40-0.70 0.40-0.70 0.025 0.35 0.500.025 0.20 1.20-1.50 0.40-0.65 — — — —

ER80S-B2L 0.05 0.40-0.70 0.40-0.70 0.025 0.35 0.500.025 0.20 1.20-1.50 0.40-0.65 — — — —

ER90S-B3 0.07-0.12 0.40-0.70 0.40-0.70 0.025 0.35 0.500.025 0.20 2.30-2.70 0.90-1.20 — — — —

ER90S-B3L 0.05 0.40-0.70 0.40-0.70 0.025 0.35 0.500.025 0.20 2.30-2.70 0.90-1.20 — — — —

ER100S-1 0.08 1.25-1.80 0.20-0.50 0.010 0.25 0.500.010 1.40-2.10 0.30 0.25-0.55 0.05 0.10 0.10 0.10

ER100S-2 0.12 1.25-1.80 0.20-0.60 0.010 0.35-0.65 0.500.010 0.80-1.25 0.30 0.20-0.55 0.05 0.10 0.10 0.10

ER110S-1 0.09 1.40-1.80 0.20-0.55 0.010 0.25 0.500.010 1.90-2.60 0.50 0.25-0.55 0.04 0.10 0.10 0.10

ER120S-1

ERXXS-G Subject to agreement between supplier and purchaser.b0.10 1.40-1.80 0.25-0.60 0.010 0.25 0.500.010 2.00-2.80 0.60 0.30-0.65 0.03 0.10 0.10 0.10

ER80S-Ni1 0.12 1.25 0.40-0.80 0.025 0.35 0.500.025 0.80-1.10 0.15 0.35 0.05 — — —

ER80S-Ni2 0.12 1.25 0.40-0.80 0.025 0.35 0.500.025 2.00-2.75 — — — — — —

ER80S-Ni3 0.12 1.25 0.40-0.80 0.025 0.35 0.500.025 3.00-3.75 — — — — — —

ER80S-D2 0.07-0.12 1.60-2.10 0.50-0.80 0.025 0.50 0.500.025 0.15 — 0.40-0.60 — — — —

a. The maximum weight percent of copper in the rod or electrode due to any coating plus the residual copper content in the steel shall comply with the stated value.b. In order to meet the requirements of the G classification, the electrode must have as a minimum either 0.50 percent nickel, 0.30 percent chromium, or 0.20 percent molybdenum.

Total otherelementsCoppera

Other low-alloy steel electrodes and rods

Manganese-molybdenum steel electrodes and rods

Nickel steel electrodes and rods

Chromium-molybdenum steel electrodes and rods

Figure 7-52. The chemical composition specifications for low-alloy steel filler metals used with GMAW. For exact limitationsand more information, see AWS specification A5.28.

• A shielding gas flowmeter. See Heading 7.4.3.• Shielding gas and coolant hoses and fittings. See

Heading 7.5. Shielding gas is used only for gas-shielded FCAW.

• Electrode lead and workpiece lead.

The self-shielded FCAW process also is preferred for welding in hard-to-reach or hard-to-see places. Since thereis no shielding gas, there is no nozzle so visibility isimproved. The electrode extension may be greater.Moving the arc out and away from the electrode contacttube permits the welder to see the joint more easily.

7.17 The Flux Cored Arc Welding Station

The equipment required in a flux cored arc weldingstation is similar in most respects to the equipment used ingas metal arc welding. The equipment required for FCAWis as follows:

• A constant voltage dc arc welding power source.See Heading 7.10.

• An electrode wire feed mechanism. See Heading7.11.

• Shielding gas cylinders. See Heading 7.12.• A gas regulator. See Heading 7.4.2.

192 Modern Welding

Smoke extractorholes

Figure 7-53. Smoke extractors. A—This GMAW gun has abuilt-in smoke extractor. B—A portable smoke collectorand filter. (Thermadyne Industries, Inc.)

Smokepickupfilter

Figure 7-54. A smoke pickup and filter set up on top of aGMAW power source. The pickup hose is attached to theGMAW gun. (Kemper Purification Systems, Inc.)

Smokeextractorand filter

Pickuphood

Figure 7-55. A smoke extractor is attached to a pickuphood by a flexible tube and positioned over the weld area.The smoke is removed from the weld area and filtered.(Kemper Purification Systems, Inc.)

A

B

• A FCAW welding gun. See GMAW gun,Heading 7.13.

• Flux cored metal electrode wire.• Optional equipment:

� A coolant system. See Figure 7-11.� Remote controls.

• A booth, table, and a ventilation system.The differences occur in the wire drive and shielding

gas equipment.Shielding gas is used with the gas-shielded FCAW

process. Therefore, shielding gas cylinders, regulators,flowmeters, gauges, and hoses are required. When self-shielded FCAW wire electrodes are used, none of theshielding gas equipment listed above is necessary. Alsowhen self-shielded FCAW is done, there is no need for agas nozzle. See Figures 7-57 and 7-59.

The gun for FCAW may be gas-cooled or water-cooled. Gas-cooled guns are generally used up to 200A.Water-cooled guns are used when using currents of morethan 200A. Water cooling is also used on guns which oper-ate on a 100% duty cycle.

Chapter 7 GTAW and GMAW Equipment and Supplies 193

Bead

Electricalcontact tube

Tubularelectrode

wire

Slag Powdered metal,deoxidizers, andfluxing agents

Arc andmetal

transfer

Gas shieldformed from fluxcore materials

Weldpool

Directionof travel

Figure 7-57. Flux cored arc welding. A—This sketch showsa self-shielded flux cored arc weld in progress. B—AnFCAW torch. Note that no nozzle is required when usingthe self-shielded process. (Thermadyne Industries, Inc.)

Fume filter andcleaned air pump

to helmet

Figure 7-56. This welder is wearing a powered air purifieraround the waist. The purifier pumps cleaned air to thehood and helmet combination. (Racal Health and Safety, Inc.)

End cap(not a nozzle)

Weldpool

Directionof travel

Arc andmetal

transfer

Fluxing agents,metal powders,and deoxidizers

Shieldinggas

Current-carryingcontact tubeTubular

flux-filled

electrode

Nozzle

Slag

Figure 7-58. A gas-shielded flux cored arc weld in progressis shown in this sketch.

A

B

Flux cored arc welding electrodes are tubular andeasily flattened. The wire drive wheels used for FCAWare usually knurled to firmly grip, but not crush, thetubular electrodes. The adjustment of these drive wheelsmust be carefully done to permit the wire to be driven,but not flattened.

7.18 Flux Cored Arc Welding Electrode Wire

The tubular, flux cored filler wire used in flux coredarc welding is made as follows:

1. Flat strip steel is formed by rolls into a “U” shape.2. The U-shaped area is then filled with a carefully pre-

pared granular flux and/or alloying material.3. After filling, the metal is closed and rolled into a

round shape. This closing and rolling compresses theflux material.

4. The tubular wire is then passed through drawing(forming) dies. This further compresses the granularflux and forms a perfectly round form of an exactdiameter.

5. In a continuous operation, the completed flux coredwire is then wrapped on spools or into coil drums.Flux cored wire has the advantage of varying the core

ingredients to match any weld requirements. Such weld-ing requirements may include:

• Adding deoxidizers, such as silicon, manganese,or aluminum, to reduce weld porosity.

• Adding denitrifiers, such as aluminum, toreduce nitrogen by forming stable nitrides.

• Providing mechanical, metallurgical, and corro-sion-resistant properties to the weld metal byadding alloying elements.

• Forming gases to shield the weld area from theoxygen and nitrogen in the atmosphere.

• Creating a slag covering over the weld bead toshield it while it cools.

• Stabilizing the arc by providing for better ioniza-tion of the arc.

• Trapping the impurities in the molten weldmetal and floating them to the top of the weld toform slag.

Figure 7-60 gives the chemical composition for fluxcored arc welding electrode wire used on carbon steels.These electrodes may be used for self-shielded or gas-shielded FCAW. Dash numbers are used at the end of thecarbon steel electrode classifications. They are used toindicate electrode polarity, the shielding gas used, or the

194 Modern Welding

Chemical Composition, Percenta

AWSclassification

Phos-phorus Vanadium Chromium

Molyb-denum Manganese

Alumi-numbSiliconCarbon Sulfur Nickel

EXXT-1EXXT-4EXXT-5EXXT-6EXXT-7EXXT-8EXXT-11EXXT-G

EXXT-GSEXXT-2EXXT-3EXXT-10

— 0.04 0.03 0.08 0.09 0.50 0.20 0.30 1.75 1.8

No chemical requirements

a. Values are maximums. Composition limits are intended to insure a plain carbon steel deposit.b. For self-shielded electrodes only.

Figure 7-60. The chemical composition of various carbon steel electrodes for flux cored arc welding. Note that aluminum isused as a denitrifier only for self-shielded electrodes. See Figure 7-61 for the meanings of the dash numbers. (AmericanWelding Society, A5.20.)

Figure 7-59. A GMAW or FCAW wire feeder. A FCAW gunis attached. Note that no nozzle is required when a shield-ing gas is not used. (Miller Electric Mfg. Co.)

number of weld passes recommended. See Figure 7-61 forthe meaning of these dash numbers.

The number and letter classifications for mild steelFCAW electrodes are explained as follows:

Example: EXXT-1E – electrode

XX – The first numbers in a two-digit numberspecify minimum tensile strength of thedeposited weld metal in thousands of poundsper square inch (ksi). The second digit representsthe position in which the electrode is to be used.A 0 is for flat and horizontal fillet welds. A 1 is forall-position welding.

T – indicates a flux cored electrode

1 to 11 – a grouping of chemical composition,method of shielding, or its suitability to makesingle or multiple pass welds.

Example: E70T-3This is a tubular electrode with 70 ksi (483MPa) ten-

sile strength in the deposited weld metal to be used for flator horizontal fillet welds. The dash three (-3) in this casemeans it is self-shielded and intended for single-passwelds. For a complete description of these FCAW elec-trodes, refer to the AWS 5.15, 5.20, 5.22, 5.29 electrode spec-ification manuals.

Chemical compositions and AWS classification numbers for low-alloy FCAW electrodes are shown inFigure 7-62.

The meaning of electrode numbers and letters used inFigure 7-62 are shown below:

Example: E80T1-B2HE – electrode

80 – 80 ksi (80,000 psi or 552MPa) tensilestrength

T – tubular flux cored electrode1 – intended usageB – major alloying ingredients as follows:

A – carbon-molybdenum

B – chromium-molybdenum

Ni – nickel

D – manganese-molybdenum

K – all other low-alloy electrodes

2 – Chemical composition group. Seebrackets on Figure 7-60.H – comparative carbon content

H – higher carbonL – lower carbon

Figure 7-63 lists the chemical composition of thedeposited weld metal when using chromium and chromi-um-nickel flux cored electrodes.

The electrode classification numbers are explainedbelow:

Example: E308T-X and E308LT-X

E – electrode

308 – the stainless steel classification

T – tubular flux cored electrode

LT – low carbon, tubular electrode

X – numbers from 1 to 3 plus the letter “G”

1 – used with carbon dioxide (CO2)

2 – used with argon plus 2% oxygen

3 – self-shielded. No external shielding gasused.

G – not specified. Used only for specialcompositions.

Example: E316T-3This describes a tubular (T) stainless steel (316) elec-

trode (E) used without any external shielding gas (-3).For complete specifications and information on flux

cored arc welding electrodes, refer to one of the followingAWS electrode specifications:

A5.20, Specifications for Carbon Steel Electrodes for FluxCored Arc Welding.

A5.22, Specifications for Flux Cored Corrosion-ResistingChromium and Chromium-Nickel Steel Electrodes.

A5.29, Specifications for Low-Alloy Steel Flux Cored ArcWelding Electrodes.

7.19 Accessory DevicesWhen water-cooled guns are used, it is important that

water flow be maintained. If the water flow stops or slows,the torch or gun and the electrode lead may quickly over-heat and be damaged. To protect the equipment, a safetyswitch is sometimes placed in the water circuit. If the

Chapter 7 GTAW and GMAW Equipment and Supplies 195

AWS classification

Externalshieldingmedium

Currentand

polarityEXXT-1 (Multiple-pass)EXXT-2 (Single-pass)EXXT-3 (Single-pass)EXXT-4 (Multiple-pass)EXXT-5 (Multiple-pass)EXXT-6 (Multiple-pass)EXXT-7 (Multiple-pass)EXXT-8 (Multiple-pass)EXXT-10 (Single-pass)EXXT-11 (Multiple-pass)EXXT-G (Multiple-pass)EXXT-GS (Single-pass)

dc, electrode positivedc, electrode positivedc, electrode positivedc, electrode positivedc, electrode positivedc, electrode positivedc, electrode negativedc, electrode negativedc, electrode negativedc, electrode negative

aa

CO2

CO2

NoneNoneCO2

NoneNoneNoneNoneNone

aa

a. As agreed upon between supplier and user.

Figure 7-61. The meanings and uses of the dash numbersat the end of carbon steel FCAW electrode designations.The letter “G” is used when a manufacturer and purchaserdevelop a special electrode.

Figure 7-62. The chemical composition and AWS classification numbers for low-alloy FCAW electrodes. Numbers and let-ters are explained in Heading 7.18.

196 Modern Welding

Chemical Composition, Percent

AWSclassification

C Mn P S Si Ni Cr Mo V Ala Cu

E70T5-A1E80T1-A1E81T1-A1

0.12 1.25 0.03 0.03 —0.80 — — 0.40/0.65 — —

E81T1-B1 0.12 1.25 0.03 0.03 0.80 — 0.40/0.65 0.40/0.65 — — —E80T5-B2L 0.05 1.25 0.03 0.03 0.80 — 1.00/1.50 0.40/0.65 — — —E80T1-B2E81T1-B2 0.12 1.25 0.03 0.03 0.80 — 1.00/1.50 0.40/0.65 — — —E80T5-B2E80T1-B2H 0.10/0.15 1.25 0.03 0.03 0.80 — 1.00/1.50 0.40/0.65 — — —E90T1-B3L 0.05 1.25 0.03 0.03 0.80 — 2.00/2.50 0.90/1.20 — — —E90T1-B3E91T1-B3 0.12 1.25 0.03 0.03 0.80 — 2.00/2.50 0.90/1.20 — — —

E71T8-Ni1E80T1-Ni1 0.12 1.50 0.03 0.03 0.80 0.80/1.10 0.15 0.35 0.05 1.8 —E81T1-Ni1E80T5-Ni1E71T8-Ni2E80T1-Ni2E81T1-Ni2 0.12 1.50 0.03 0.03 0.80 1.75/2.75 — — — 1.8 —E80T5-Ni2E90T1-Ni2E91T1-Ni2E80T5-Ni3E90T5-Ni3 0.12 1.50 0.03 0.03 0.80 2.75/3.75 — — — — —

E91T1-D1 0.12 1.25/2.00 0.03 0.03 0.80 — — 0.25/0.55 — — —E90T5-D2E100T5-D2 0.15 1.65/2.25 0.03 0.03 0.80 — — 0.25/0.55 — — —E90T1-D3 0.12 1.00/1.75 0.03 0.03 0.80 — — 0.40/0.65 — — —

E80T5-K1 0.15 0.80/1.40 0.03 0.03 0.80 0.80/1.10 0.15 0.20/0.65 0.05 — —E70T4-K2E71T8-K2E80T1-K2E90T1-K2 0.15 0.50/1.75 0.03 0.03 0.80 1.00/2.00 0.15 0.35 0.05 1.8 —E91T1-K2E80T5-K2E90T5-K2E100T1-K3E110T1-K3E100T5-K3 0.15 0.75/2.25 0.03 0.03 0.80 1.25/2.60 0.15 0.25/0.65 0.05 — —E110T5-K3E110T5-K4E111T1-K4 0.15 1.20/2.25 0.03 0.03 0.80 1.75/2.60 0.20/0.60 0.30/0.65 0.05 — —E120T5-K4E120T1-K5 0.10/0.25 0.60/1.60 0.03 0.03 0.80 0.75/2.00 0.20/0.70 0.15/0.55 0.05 — —E61T8-K6E71T8-K6 0.15 0.50/1.50 0.03 0.03 0.80 0.40/1.10 0.15 0.15 0.05 1.8 —E101T1-K7 0.15 1.00/1.75 0.03 0.03 0.80 2.00/2.75 — — — — —EXXXTX-G — 1.00 min* 0.03 0.03 0.80 0.50 min* 0.30 min* 0.20 min* 0.10 1.8 —

min* min*E80T1-W 0.12 0.50/1.30 0.03 0.03 0.35/0.80 0.40/0.80 0.45/0.70 — — — 0.30/0.75

a. For self-shielded electrodes only.* All values are maximum except where min (minimum) is indicated.

All other low-alloy steel electrodes

Manganese-molybdenum steel electrodes

Nickel steel electrodes

Chromium-molybdenum steel electrodes

Carbon-molybdenum steel electrodes

E90T5-B3E100T1-B3E90T1-B3H 0.10/0.15 1.25 0.03 0.03 0.80 — 2.00/2.50 0.90/1.20 — — —

Chapter 7 GTAW and GMAW Equipment and Supplies 197

Figure 7-63. The chemical composition of the deposited weld metal for flux cored chromium and chromium-nickel steelelectrodes. (American Welding Society, A5.22)

AWSclassification C Cr Ni Mo Cb + Ta Mn Si P S Fe Cu

E307T-X 0.13 18.0-20.5 9.0-10.5 0.5-1.5 — 3.3-4.75 1.0 0.04 0.03 Rem 0.5E308T-X 0.08 18.0-21.0 9.0-11.0 0.5 — 0.5-2.5E308LT-X a 18.0-21.0 9.0-11.0 0.5 —E308MoT-X 0.08 18.0-21.0 9.0-12.0 2.0-3.0 —E308MoLT-X a 18.0-21.0 9.0-12.0 2.0-3.0

E309T-X 0.10 22.0-25.0 12.0-14.0 0.5 —E309CbLT-X a 22.0-25.0 12.0-14.0 0.70-1.00E309LT-X a 22.0-25.0 12.0-14.0 —E310T-X 0.20 25.0-28.0 20.0-22.5 — 1.0-2.5 0.03E312T-X 0.15 28.0-32.0 8.0-10.5 — 0.5-2.5 0.04

E316T-X 0.08 17.0-20.0 11.0-14.0 2.0-3.0 —

E316LT-X a 17.0-20.0 11.0-14.0 2.0-3.0 —

E317LT-X a 18.0-21.0 12.0-14.0 3.0-4.0 —

E347T-X 0.08 18.0-21.0 9.0-11.0 0.5 8 x C min

to 1.0 maxE409T-X 0.10 10.5-13.0 0.60 0.5 — 0.8E410T-X 0.12 11.0-13.5 0.60 0.5 — 1.2E410NiMoT-X 0.06 11.0-12.5 4.0-5.0 0.40-0.70 — 1.0E410NiTiT-X a 11.0-12.0 3.6-4.5 0.05 — 0.70 0.60 0.03E430T-X 0.10 15.0-18.0 0.60 0.5 — 1.2 1.0 0.04

E502T-X 0.10 4.0-6.0 0.40 0.45-0.65 — 1.2

E505T-X 0.10 8.0-10.5 0.40 0.85-1.20 — 1.2

E307T-3 0.13 19.5-22.0 9.0-10.5 0.5-1.5 — 3.3-4.75

E308T-3 0.08 19.5-22.0 9.0-11.0 0.5 — 0.5-2.5

E308LT-3 0.03 19.5-22.0 9.0-11.0 0.5 —

E308MoT-3 0.08 18.0-21.0 9.0-12.0 2.0-3.0 —

E308MoLT-3 0.03 18.0-21.0 9.0-12.0 2.0-3.0 —

E309T-3 0.10 23.0-25.5 12.0-14.0 0.5 —

E309LT-3 0.03 23.0-25.5 12.0-14.0 —

E309CbLT-3 0.03 23.0-25.5 12.0-14.0 0.70-1.00

E310T-3 0.20 25.0-28.0 20.0-22.5 — 1.0-2.5 0.03

E312T-3 0.15 28.0-32.0 8.0-10.5 — 0.5-2.5 0.04

E316T-3 0.08 18.0-20.5 11.0-14.0 2.0-3.0 —

E316LT-3 0.03 18.0-20.5 11.0-14.0 2.0-3.0 —

E317LT-3 0.03 18.5-21.0 13.0-15.0 3.0-4.0 —

E347T-3 0.08 19.0-21.5 9.0-11.0 0.5 8 x C minto 1.0 max

E409T-3 0.10 10.5-13.0 0.60 0.5 — 0.80E410T-3 0.12 11.0-13.5 0.60 0.5 — 1.0E410NiMoT-3 0.06 11.0-12.5 4.0-5.0 0.40-0.70 — 1.0

E410NiTiT-3 0.04 11.0-12.0 2.6-4.5 0.5 — 0.70 0.50 0.03E430T-3 0.10 15.0-18.0 0.60 0.5 — 1.0 1.0 0.04

EXXXT-G As agreed upon between supplier and purchaser.

a. The carbon content shall be 0.04% maximum when the suffix “X” is “1”; it shall be 0.03% when the suffix “X” is “2”.

Several types of remote controls and their uses aredescribed in Heading 5.9.

7.20 Filter Lenses for Use When Gas-Shielded Arc Welding

Because of the clearer atmosphere around the arc,the operator must use arc welding lenses with a darkershade to reduce eye fatigue and possible eye damage.Most helmets for gas arc welding use a clear cover lensand a filter lens. Sometimes a clear cover lens is used onthe inside of the helmet, as well. It is very important thatall these lenses be clean. Figure 7-67 shows a helmet witha lens that automatically darkens when an arc is struck.Figure 7-68 shows the effect of such an automatic-darkening lens. Figure 7-69 lists recommended shade numbers for gas tungsten, gas metal, and flux cored arcwelding.

7.21 Protective ClothingFire-resistant clothing and accessories of leather are

recommended. Wool also is satisfactory. Cotton does notprovide sufficient protection and deteriorates rapidlyunder infrared and ultraviolet rays. However, flame-resistant cotton clothing is made and is often used whilearc welding. Always wear dark clothing to reduce reflec-tion of light behind the helmet. The clothing should bewithout cuffs or open pockets, since these can collectsparks.

Leather or leather-palm gloves should be worn. SeeChapters 1 and 11 for additional information on clothingrecommended for arc welding.

water flow decreases below a set limit, a switch opens andshuts off the electrical power source. Figure 7-64 shows aflow safety device.

Some systems use a (thermal) heat fuse to protect thewater-cooled welding gun. If the water flow stops ordecreases to a dangerous minimum, the fuse link willoverheat and open to interrupt the electrical current flow.See Figure 7-65.

Most arc welding machines are equipped with aremote control circuit switch and external plug. Theremote control is used to vary the voltage or amperagewithin a rough setting range. The welder at the job site canadjust the arc welding machine at a distance with this con-trol. Figure 7-66 shows one type of remote control device.

Figure 7-66. A remote current adjuster. (Miller Electric Mfg. Co.)

198 Modern Welding

Figure 7-64. Water flow safety control. If the water flowdecreases below a set limit, the current is shut off until theflow of water resumes. (Hayes Fluid Controls)

Thermal fuse

Insulator cover

Figure 7-65. Fuse and hose assembly with insulator coverremoved. If the thermal fuse overheats, it will shut off thecurrent flow to the torch. (ESAB Welding and Cutting Products)

Chapter 7 GTAW and GMAW Equipment and Supplies 199

Figure 7-67. An electronic quick change lens is installed inthis arc welding helmet. The welder can see the weld jointclearly until the arc is struck. When the arc is struck, thelens darkens in about 0.00004 second. (Jackson Products, Inc.)

7.22 Safety ReviewWhen using gas tungsten, gas metal,or flux cored arc

welding equipment, follow all the safety precautions nor-mally used with arc welding equipment as follows.

• Electrical connection leads should be in goodcondition and tight. They should be protectedfrom accidental damage from shop traffic.

• When arc welding, it is necessary to preventfumes and contaminated air from reaching thewelder’s face. Adequate ventilation and filtra-tion equipment must be used. In some weldingconditions, it is necessary to use purified airbreathing apparatus.

• Proper clothing should be worn to prevent burnsfrom hot metal and ultraviolet and infrared rays.

• Flammable materials should not be carried in thepockets of clothing. Pockets should be closedand cuffs rolled down to prevent hot metal fromgoing into them.

• A welding helmet with the proper number filter-ing lens for the type of welding being done mustbe used.

• Shielding curtains should be placed around alljobs so that workers in the area are protectedfrom arc flashes.

Figure 7-68. The action of an electronic quick-change lensis shown in this pair of photos. A—View before arc isstruck. B—View after arc is struck. (Hornell Speedglas, Inc.)

200 Modern Welding

Figure 7-69. A guide to the correct welding lens shade for various welding processes and applications. (ANSI/AWS Z49.1)

Guide for Shade Numbers

Operation

Plate thicknessin. mm

Electrode size1/32 in. (mm) Arc current (A)

Minimumprotective

shade

Suggested*shade no.(comfort)

Shielded metal arc welding

Less than 3 (2.5)3-5 (2.5-4)5-8 (4-6.4)

More than 8 (6.4)

(Light)(Heavy)

Less than 6060-160160-250250-550

Less than 6060-160160-250250-500

78

1011

—101214

7101010

—111214

Gas metal arc welding and flux cored arc welding

Less than 5050-150

88

1012

Gas tungsten arc welding

150-500Less than 500

500-1000

101011

141214

Air carbonArc cutting

Under 1/81/8 to 1/2Over 1/2

Under 3.23.2 to 12.7Over 12.7

4 or 55 or 66 or 8

Gas welding Light Medium Heavy

Under 11 to 6Over 6

Under 2525 to 150Over 150

3 or 44 or 55 or 6

Oxygen cutting Light Medium Heavy

Less than 2020-100100-400400-800

68

1011

6 to 8101214

Plasma arc welding

Less than 300300-400400-800

(Light)**(Medium)**(Heavy)**

89

10

91214

Plasma arc cutting

Torch brazing — — 3 or 4

Torch soldering — — 2

Carbon arc welding — — 14

*As a rule of thumb, start with a shade that is too dark to see the weld zone. Then go to a lighter shade which gives sufficient view of the weld zone without going below the minimum. In oxyfuel gas welding or cutting where the torch produces a high yellow light, it is desirable to use a filter lens that absorbs the yellow or sodium line in the visible light of the (spectrum) operation.

**These values apply where the actual arc is clearly seen. Experience has shown that lighter filters may be used when the arc is hidden by the workpiece.

Chapter 7 GTAW and GMAW Equipment and Supplies 201

Test Your KnowledgeWrite your answers on a separate sheet of paper. Do

not write in this book.1. Name the welding processes covered in this chapter

which may use a shielding gas to shield the weldarea.

2. What type welding current may be used with GTAW?3. A GTAW electrode is held in the torch by a _____ .4. GTAW welding power sources are constant _____

machines.5. What is the advantage of using a constant voltage

power source?6. Why is a high-frequency voltage used continually in

an ac circuit that is being used for GTAW?7. List five reasons why argon is more frequently used

for GTAW than helium.8. When GTAW, which shielding gas is best for use in

cross drafts? Gives the best cleaning action? Providesthe greatest heat conductivity?

9. A regulator controls and measures _____ . A flowme-ter measures and controls the _____ of gas flow.

10. The maximum amperage used on a gas-cooledGTAW torch is generally _____ amperes.

11. What determines the nozzle diameter when selectinga nozzle for GTAW or GMAW?

12. What is the advantage of using thoriated tungstenelectrodes?

13. The color coding of a 2% thoriated tungsten electrodeis _____ .

14. The arc welding power source used for GMAW andFCAW produces a constant _____ .

15. GMAW power sources have a sloping voltage curve.How much slope should the curve have for use withcarbon dioxide (CO2) gas?

16. Increasing the rate of speed on the wire feed inGMAW or FCAW increases the _____ in the circuit.

17. The shielding gas mixture suggested in Figure 13-37for welding low-alloy steel with the short circuitGMAW process is _____% –_____% He,_____% –_____% Ar, and_____% –_____% CO2.

18. Which gas produces the deepest penetration whenused in GMAW?

19. To produce better metal transfer through the arc,reduce spatter, and stabilize the arc, _____ and _____are added to argon or helium.

20. Describe the following GMAW electrode completely:ER90S-B3L

21. What two methods are used in FCAW to shield theweld from atmospheric contamination?

22. When feeding a FCAW electrode through the wirefeed mechanism, care must be taken not to _____ theflux cored wire.

23. List five ways that FCAW wires are altered to meetthe requirements of a weld.

24. Describe the following FCAW electrode completely:E80T-2.

25. What number filter lens is recommended whenGTAW steel with 80A? When GMAW steel, using220A?

202 Modern Welding

Manual GTAW requires greater skill than other manual welding processes, but is capable of producing very high qualitywelds. Careful addition of filler metal at the proper time is critical. (Miller Electric Mfg. Co.)