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WeldingCurrent Chapter Table of ContentsLesson 2Common ElectriArc
WeldingProcessesLesson 3Covered Electrodesfor WeldingMild
SteelsBASICWELDING FILLER METALTECHNOLOGYGo To TestPrintLesson 2 -
Common Electric Arc Welding
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123.11.2009 10:24Lesson 4Covered Electrodesfor Welding LowAlloy
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Welding Processeshttp://www.esabna.con/EuWeb/AWTC/Lesson2_11.ht1
din 123.11.2009 10:24Lesson 5Welding Filler Metalsfor Stainless
SteelsLesson 6Carbon & Low AlloySteel Filler Metals
-GMAW,GTAW,SAWLESSON IICOMMON ELECTRIC ARCWELDING PROCESSESTurn
PagesLesson 2 - Common Electric Arc Welding
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123.11.2009 10:241 din 123.11.2009 10:24Lesson 7Flux Cored
ArcElectrodes CarbonLow Alloy SteelsLesson
8HardsurfacingElectrodesLesson 9Estimating &Comparing WeldMetal
Costs ESAB ESABWelding&Cutting Products
SearchChapter(FasterDownload)Search Document (Slower
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123.11.2009 10:24Lesson 1The Basics of ArcWeldingTABLE OF
CONTENTSLESSON IICOMMON ELECTRIC ARC WELDING PROCESSESCurrent
Chapter Table of ContentsLesson 2Common ElectricArc
WeldingProcessesGo To TestLesson 3Section Nr.Section
TitlePageCovered Electrodesfor WeldingPrintMild
Steels2.1INTRODUCTION
..............................................................................1Lesson
2 - Common Electric Arc Welding
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Common Electric Arc Welding
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123.11.2009 10:241 din 123.11.2009 10:24Turn
PagesGlossarySearchChapter(FasterDownload)SearchDocument(SlowerDownload)2.2SHIELDED
METAL ARC WELDING
...............................................1Lesson 4Covered
Electrodesfor Welding LowAlloy SteelsLesson 5Welding Filler
Metalsfor Stainless SteelsLesson 6Carbon & Low AlloySteel
Filler Metals -GMAW,GTAW,SAWLesson 7Flux Cored ArcElectrodes
CarbonLow Alloy SteelsLesson 8HardsurfacingElectrodesLesson
9Estimating &Comparing WeldMetal Costs2.2.1Equipment &
Operation
.....................................................................22.2.2Welding
Power Sources
....................................................................22.2.3Electrode
Holder................................................................................42.2.4Ground
Clamp
...................................................................................42.2.5Welding
Cables
.................................................................................42.2.6Coated
Electrodes
............................................................................42.3GAS-TUNGSTEN
ARC WELDING
..................................................52.3.1Equipment
& Operation
.....................................................................62.3.2Power
Sources
..................................................................................72.3.3Torches..............................................................................................102.3.4Shielding
Gases
................................................................................112.3.5Electrodes
.........................................................................................122.3.6Summary
...........................................................................................132.4GAS
METAL ARC WELDING
..........................................................132.4.1Current
Density
..................................................................................142.4.2Metal
Transfer Modes
........................................................................152.4.3Equipment
and Operation
..................................................................172.4.4Power
Source....................................................................................182.4.5Wire
Feeder
......................................................................................192.4.6Welding
Gun......................................................................................202.4.7Shielding
Gases
................................................................................212.4.7.1Short
Circuiting Transfer
....................................................222.4.7.2Spray
Arc Transfer
............................................................23Lesson
2 - Common Electric Arc Welding
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123.11.2009 10:241 din 123.11.2009 10:24Lesson 10Reliability of
WeldingFiller Metals COPYRIGHT 2000 THE ESAB GROUP, INCLesson 2 -
Common Electric Arc Welding
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123.11.2009 10:24Lesson 1The Basics of ArcWeldingTABLE OF
CONTENTSLESSON II- Con't.Lesson 2Common ElectricArc
WeldingProcessesSection Nr.Section TitlePageLesson 32.4.7.3Pulse
SprayTransfer........................................................23Covered
Electrodesfor
Welding2.4.8Electrodes........................................................................................23Mild
Steels2.5FLUX CORED ARC
WELDING......................................................242.5.1Sell-ShieldedProcess......................................................................24Lesson
42.5.2GasShieldedProcess......................................................................25Covered
Electrodesfor Welding
Low2.5.3CurrentDensity.................................................................................26Alloy
Steels2.5.4Equipment........................................................................................262.5.5PowerSource...................................................................................262.5.6WireFeeder.....................................................................................26Lesson
5Welding Filler
Metals2.5.7WeldingGuns...................................................................................26for
Stainless
Steels2.5.8ShieldingGases...............................................................................272.6SUBMERGED
ARC WELDING
......................................................27Lesson
62.6.1Submerged
ArcFlux.........................................................................28Carbon
& Low
Alloy2.6.2TheWeldingGun..............................................................................28Steel
Filler Metals
-GMAW,GTAW,SAW2.6.3PowerSources.................................................................................282.6.4Equipment........................................................................................282.6.5Electrodes........................................................................................29Lesson
7Flux Cored
Arc2.6.6Summary..........................................................................................29Electrodes
CarbonLow Alloy Steels2.7ELECTROSLAG AND ELECTROGAS WELDING
.........................302.7.1ElectroslagWelding..........................................................................302.7.2Flux..................................................................................................30Lesson
8Hardsurfacing2.7.3Process............................................................................................30Electrodes2.7.4Equipment........................................................................................312.7.5Summary.........................................................................................31Lesson
9Appendix A- GLOSSARY OF TERMS
................................................................32Estimating
&Comparing WeldMetal CostsLesson 10Reliability of WeldingFiller
MetalsCurrent Chapter Table of ContentsGo To TestPrintGlossaryTurn
PagesSearchChapter (Faster Download)SearchDocument (Slower
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123.11.2009 10:24Go To TestTurn PagesLesson 1The Basics of
ArcWeldingLESSON IICurrent Chapter Table of ContentsLesson 2Common
ElectricArc WeldingProcessesLesson 3Covered Electrodesfor
WeldingMild SteelsLesson 4Covered Electrodesfor Welding LowAlloy
SteelsLesson 5Welding Filler Metalsfor Stainless SteelsLesson
6Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAWLesson
7Flux Cored ArcElectrodes CarbonLow Alloy SteelsLesson 8
Hardsurfacin ElectrodesLesson 9Estimating &Comparing WeldMetal
CostsLesson 10Reliability of WeldinFiller
MetalsPrintGlossarySearchChapter(FasterDownload)SearchDocument(SlowerDownload)COMMON
ELECTRIC ARC WELDING PROCESSES2.1 INTRODUCTIONAfter much ex
perimentation by others in the ear(y 1800's, an Eng(ishman named
Wi(de obtained the first e(ectric we(ding patent in 1865. He
successfu((y joined two sma(( pieces of iron by passing an e(ectric
current through both pieces producing a fusion we(d. Approximate(y
twenty years (ater, Bernado, a Russian, was granted a patent for an
e(ectric arc we(ding process in which he maintained an arc between
a carbon e(ectrode and the pieces to be joined, fusing the meta(s
together as the arc was manua((y passed o'er the joint to be
we(ded.2.1.0.1During the 1890's, arc we(ding was accom p(ished with
bare meta( e(ectrodes thatwere consumed in the mo(ten pudd(e and
became part of the we(d meta(. The we(ds were of poor qua(ity due
to the nitrogen and oxygen in the atmosphere forming harmfu( oxides
and nitrides in the we(d meta(. Ear(y in the Twentieth Century, the
im portance of shie(ding the arc from the atmosphere was rea(ized.
Co2ering the e(ectrode with a materia( that decomposed in the heat
of the arc to form a gaseous shie(d appeared to be the best method
to accom p(ish this end. As a resu(t, 2arious methods of co2ering
e(ectrodes, such as wrapping and dipping, were tried. These efforts
cu(minated in the extruded coated e(ectrode in the mid- 1920's,
great(y im pro2ing the qua(ity of the we(d meta( and pro2iding what
many consider the most significant ad2ance in e(ectric arc
we(ding.2.1.0.2Since we(ding with coated e(ectrodes is a rather
s(ow procedure, more rapidwe(ding processes were de2e(oped. This
(esson wi(( co'er the more common(y used e(ectric arc we(ding
processes in use today.2.2SHIELDED METAL ARC WELDINGShielded Metal
Arc Welding*, a(so known as manua( meta( arc we(ding, stick
we(ding, or e(ectric arc we(ding, is the most wide(y used of the
2arious arc we(ding processes. We(ding is performed with the heat
of an e(ectric arc that is maintained between the end of a coated
meta( e(ectrode and the work piece (See Figure 1). The heat
produced by the arc me(ts the base meta(, the e(ectrode core rod,
and the coating. As the mo(ten meta( drop(ets are transferred
across the arc and into the mo(ten we(d pudd(e, they are shie(ded
from the atmosphere by the gases produced from the decom position
of the f(ux coating. The mo(ten s(ag f(oats to the top of the we(d
pudd(e where it protects the we(d meta( from the atmosphere during
so(idification.Lesson 2 - Common Electric Arc Welding
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123.11.2009 10:24Lesson 1The Basics of ArcWeldingLesson 2Common
ElectricArc WeldingProcessesLesson 3Covered Electrodesfor
WeldingMild SteelsLesson 4Covered Electrodesfor Welding LowAlloy
SteelsLesson 5Welding Filler Metalsfor Stainless SteelsLesson
6Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAWLesson
7Flux Cored ArcElectrodes CarbonLow Alloy SteelsLesson
8HardsurfacingElectrodesLesson 9Estimating &Comparing WeldMetal
CostsLesson 10Reliability of WeldingFiller Metals Other functions
of the coating are to provide arc stabi(ity and contro( bead shape.
More information on coating functions wi(( be covered in subsequent
(essons.Current Chapter Table of ContentsGo To
TestPrintGlossaryTurn PagesMOLTEN POOLLESSON IICOATINGCORE
RODSHIELDING GASESSOLIDIFIEDSLAG* Shielded Metal Arc Welding (SMAW)
is the terminologyapproved by the American Welding Society.WELD
METALWORK PIECE2.2.1Equipment & Operation - OneSHIELDED METAL
ARC WELDINGFIGURE 1AC OR DC POWER SOURCEELECTRODECABLEELECTRODE
HOLDERELECTRODEGROUNDCABLEWORKreason for the wide acceptance of the
SMAW process is the simp(icity of the necessary equipment. The
equipment consists of the fo((owing items. (See Figure 2)1.We(ding
power sourceE(ectrode ho(derGround c(ampWe(ding cab(es and
connectorsAccessory equipment (chippingSHIELDED METAL ARC WELDING
CIRCUIT FIGURE 2hammer, wire
brush)SearchChapter(FasterDownload)SearchDocument(SlowerDownload)2.2.2Welding
Power Sources - Shie(ded meta( arc we(ding may uti(ize
eithera(ternating current (AC) or direct current (DC), but in
either case, the power source se(ected must be of the constant
current type. This type of power source wi(( de(iver a re(ative(y
constant amperage or we(ding current regard(ess of arc (ength
variations by the operator (See Lesson I, Section 1.9). The
amperage determines the amount of heat at the arc and since it wi((
remain re(ative(y constant, the we(d beads produced wi(( be uniform
in size and shape.2.2.2.1Whether to use an AC, DC, or ACIDC power
source depends on the type of we(dingto be done and the e(ectrodes
used. The fo((owing factors shou(d be considered:1.Electrode
Selection - Using a DC power source a((ows the use of a greater
range of e(ectrode types. Whi(e m ost of the e(ectrodes are
designed to be used on AC or DC, some wi(( work proper(y on(y on
DC.Metal Thickness - DC power sources may be used for we(ding both
heavy sections and (ight gauge work. Sheet meta( is m ore easi(y
we(ded with DC because it is easier to strike and maintain the DC
arc at (ow currents.2.Protective equipment (he(met, g(oves,
etc.)Lesson 2 - Common Electric Arc Welding
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123.11.2009 10:24Lesson 1The Basics of ArcWeldingLesson 2Common
ElectricArc WeldingProcessesLesson 3Covered Electrodesfor
WeldingMild SteelsLesson 4Covered Electrodesfor Welding LowAlloy
SteelsLesson 5Welding Filler Metalsfor Stainless SteelsLesson
6Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAWLesson
7Flux Cored ArcElectrodes CarbonLow Alloy SteelsLesson
8HardsurfacingElectrodesLesson 9Estimating &Comparing WeldMetal
Costs LESSON IICurrent Chapter Table of ContentsGo To
TestPrint3.Distance from Work - If the distance from the work to
the power source is great,AC is the best choice since the voltage
drop through the cables is lower than with DC. Even though welding
cables are m ade of copper or aluminum (both good conductors), the
resistance in the cables becomes greater as the cable length
increases. In other words, a voltage reading taken between the
electrode and the work will be somewhat lower than a reading taken
at the output terminals of the power source. This is known as
voltage drop.Welding Position (See Appendix A - Glossary of Terms)
- Because DC may beoperated at lower welding currents, it is more
suitable for overhead and vertical welding than AC. AC can
successfully be used for out-of-position work if proper electrodes
are selected.Glossa5.Arc Blow- When welding with DC, m agnetic
fields are set up throughout theweldment. In weldments that
havevarying thickness and protrusions, this m agnetic field can
affect the arc by m aking it stray or fluctuate in direction. This
condition is especially troublesome when welding in corners. AC
seldom causes this problem because of the rapidly reversing m
agnetic field produced.Turn Pages2.2.2.2Combination power sources
that produce both AC and DC are av ailable andprovide the
versatility necessary to select the proper welding current for the
application.2.2.2.3When using a DC power source, the question of
whether to use electrode negativeor positive polarity arises. Some
electrodes operate on both DC straight and reverse polarity, and
others on DC negative or DC positive polarity only. Direct current
flows in one direction in an electrical circuit and the direction
of current flow and the composition of the electrode coating will
have a definite effect on the welding arc and weld bead. Figure 3
shows the connections and effects of straight and reverse
polarity.SearchChapter(FasterDownload)SearchDocument(SlowerDownload)2.2.2.4Electrode
negative (-) produces welds with shallow penetration; however,
theelectrode melt-off rate is high. The weld bead is rather wide
and shallow as shown at 'A' in Figure 3. ElectrodeWORK PIECEWORK
PIECEDCPOWER SOURCEI-IGI-ER BURN-OFF RATE, LESS
PENETRATIONELECTRODEADEEP PENETRATION, LOW BURN-OFF
RATEELECTRODEBDCPOWER SOURCEpositive (+) produces welds with deep
penetration and a narrower weld bead as shown at 'B' in Figure
3.Lesson 2 - Common Electric Arc Welding
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123.11.2009 10:241 din 123.11.2009 10:24STRAIGI-T POLARITYREVERSE
POLARITYLesson 10FIGURE 3Reliability of WeldingFiller Metals
COPYRIGI-T 1998 TI-E ESAB GROUP, INC.Lesson 2 - Common Electric Arc
Welding Processeshttp://www.esabna.con/EuWeb/AWTC/Lesson2_11.ht1
din 123.11.2009 10:24Lesson 1The Basics of ArcWeldingLesson 2Common
ElectricArc WeldingProcessesLesson 3Covered Electrodefor
WeldingMild SteelsLesson 4Covered Electrodefor Welding LowAlloy
SteelsLesson 5Welding Filler Metalfor Stainless SteelsLesson
6Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAWLesson
7Flux Cored ArcElectrodes CarbonLow Alloy SteelsLesson
8HardsurfacingElectrodesLesson 9Estimating &Comparing WeldMetal
CostsLesson 10Reliability of WeldingFiller Metals LESSON IICurrent
Chapter Table of Contents2.2.2.5While polarity affects the
penetration and burn-off rate, the electrode coating alsohas a
strong influence on arc characteristics. Perform ance of indi.idual
electrodes will be discussed in succeeding lessons.Go To
TestPrint2.2.3Electrode Holder-The electrode holder connects to the
welding cable and conducts the welding current to the electrode.
The insulated handle is used to guide the electrode o'er the weld
joint and feed the electrode o'er the weld joint and feed the
electrode into the weld puddle as it is consumed. Electrode holders
are a. ailable in different sizes and are rated on their current
carrying capacity.2.2.4Ground Clamp - The ground clamp is used to
connect the ground cable to the workpiece. It m ay be connected
directly to the work or to the table or fixture upon which the work
isGlossarypositioned.Being a part of the welding circuit, the
ground clamp must be capable of carryingthe welding current without
o.erheating due to electrical resistance.Turn Page2.2.5Welding
Cables - The electrode cable and the ground cable are important
parts ofthe welding circuit. They must be .ery flexible and ha.e a
tough heat-resistant insulation. Connections at the electrode
holder, the ground clamp, and at the power source lugs must be
soldered or well crimped to assure low electrical resistance. The
cross-sectional area of the cable must be sufficient size to carry
the welding current with a minimum of oltage drop. Increasing the
cable length necessitates increasing the cable diameter to lessen
resistance and voltage drop. The table in Figure 4 lists the
suggested Mmerican Wire Gauge (MWG) cable size to be used for
.arious welding currents and cable
lengths.SearchChapter(FasterDownload)SearchDocument(SlowerDownload)WeldingTotal
Cable Length (Ground Lead Plus Electrode Lead)VoltageSer.iceUpto50
ft.Upto 100 ft.Upto250 ft.Upto500
ft.DropRangeCableVoltageCableVoltageCableVoltageCableVoltageFigured(Mmperes)SizeDropSizeDropSizeDropSizeDropMt20to
180#31.8#22.9#15.7#09.1180 Mmps30 to 250#21.8#12.5#05.0#09.9200
Mmps60 to 375#01.7#03.0#005.9#0009.3300 Mmps80 to
500#001.8#0002.5#00005.0#00009.9400
Mmps100to600#002.0#00002.5.........500MmpsVoltage drops indicated
do not include any drop caused by poor connection, electrode
holder, or work metal FIGURE 42.2.6Coated Electrodes - Various
types of coated electrodes are used in shieldedmetal arc
welding.Electrodes used for welding mild or carbon steels are quite
different thanthose used for welding the low alloys and stainless
steels.Details on the specific types will becovered in subsequent
lessons.Lesson 2 - Common Electric Arc Welding
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123.11.2009 10:24Go To TestTurn PagesLesson 1The Basics of
ArcWelding2.3 GAS TUNGSTEN ARC WELDINGLESSON IICurrentChapterTable
ofContentsLesson 2Common ElectricArc WeldingProcessesLesson
3Covered Electrodesfor WeldingMild SteelsLesson 4Covered
Electrodesfor Welding LowAlloy SteelsLesson 5Welding Filler
Metalsfor Stainless SteelsLesson 6Carbon & Low AlloySteel
Filler Metals -GMAW,GTAW,SAWLesson 7Flux Cored ArcElectrodes
CarbonLow Alloy SteelsLesson 8HardsurfacingElectrodesLesson
9Estimating &Comparing WeldMetal CostsLesson 10Reliability of
WeldingFiller
MetalsPrintGlossarySearchChapter(FasterDownload)SearchDocument(SlowerDownload)Gas
Tungsten Arc Welding* is a welding process performed using the heat
of an arc established between a nonconsumable tungsten electrode
and the work piece. See Figure 5. The electrode, the arc, and the
area surrounding the molten weld puddle are protected from the
atmosphere by an inert gas shield. The electrode is not consumed in
the weld puddle as in shielded metal arc welding. If a filler metal
isTRAVEL DIRECTIONnecessary, it is added to the leadingthe molten
puddle as shown inTORCH2.3.0.1Gas tungsten arc weldingproduces
exceptionally clean welds no slag is produced, the chance
inclusions in the weld metal isTUNGSTEN ELECTRODEARCSHIELDING
GASNOZZLEand the finished weld requires virtually no cleaning.
Argonand Helium, the primaryshielding gases em ployed,INERT GAS
SHIELDare inert gases. Inert gasesFILLER @ETALWORK PIECEGAS
TUNGSTEN ARC WELDINGIGURE 5do not chemically combine with other
elements and therefore, are used to excludethe reactive gases, such
as oxygen and nitrogen, from forming com pounds that could be
detrimental to the weld metal.2.3.0.2Gas tungsten arc welding may
be used for welding almost all metals - mild steel,low alloys,
stainless steel, copper and copper alloys, aluminum and aluminum
alloys, nickel and nickel alloys, magnesium and magnesium alloys,
titanium, and others. This process is most extensively used for
welding aluminum and stainless steel alloys where weld integrity is
of the utmost im portance. Another use is for the root pass
(initial pass) in pipe welding, which requires a weld of the
highest quality. Full penetration without an excessively high
inside bead is im portant in the root pass, and due to the ease of
current control of this process, it lends itself to control of
back-bead size. For high quality welds, it is usually necessary to
provide an inert shielding gas inside the pipe to prevent oxidation
of the inside weld bead.* Gas Tungsten Arc Welding (GTAW) is the
current terminology approved by the American Welding Society,
formerly known as "TIG" (Tungsten Inert Gas) welding.Lesson 2 -
Common Electric Arc Welding
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123.11.2009 10:24Go To TestTurn PagesCurrent Chapter Table of
ContentsPrintGlossaryLesson 1The Basics of ArcWeldingLesson 2Common
ElectricArc WeldingProcessesLesson 3Covered Electrodesfor
WeldingMild SteelsLesson 4Covered Electrodesfor Welding LowAlloy
SteelsLesson 5Welding Filler Metalsfor Stainless SteelsLesson
6Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAW LESSON
II2.3.0.3Gas tungsten arc welding lends itself to both manual and
automatic operation. Inmanual operation, the welder holds the torch
in one hand and directs the arc into the weld joint. The filler
metal is fed manually into the leading edge of the puddle. In
automatic applications, the torch may be automatically mo' ed o' er
a stationary work piece or the torch may be stationary with the
work mo' ed or rotated in relation to the torch. Filler metal, if
required, is also fed automatically.2.3.1EQUIPMENT AND OPERATION -
Gas tungsten arc welding may be accomplishedwith relati' ely simple
equipment, or it may require some highly sophisticated components.
Choice of equipment depends upon the type of metal being joined,
the position of the weld being made, and the quality of the weld
metal necessary for the application. The basic equipment consists
of the following:1.The power sourceElectrode holder
(torch)Shielding gasTungsten electrodeWater supply when
necessaryGround cable7.Protecti'e equipmentFigure 6 shows a basic
gas tungsten arc welding schematic.Lesson 2 - Common Electric Arc
Welding Processeshttp://www.esabna.con/EuWeb/AWTC/Lesson2_11.ht1
din 123.11.2009 10:24Lesson 7Flux Cored ArcElectrodes CarbonLow
Alloy SteelsLesson 8 Hardsurfacing ElectrodesLesson 9Estimating
&Comparing WeldMetal CostsSHIELDING GAS SUPPLYGAS TUNGSTEN ARC
WELDING CONNECTION SCHEMATICREGULATOR FLOW METERGAS HOSE (WATER
COOLED ONLY)GAS COOLED ONLYTORCH*COMPOSITE CABLEWELDING CABLEWATER
COOLERWORK*COMPOSITE CABLE GAS COOLED TORCH. CURRENT IN &
GASIN.WATER COOLED TORCH. CURRENT IN & WATER OUTPOWER
SOURCEWATER TO TORCHWATER FROM TORCHGROUND CABLESearchChapter
(Faster Download)SearchDocument (Slower Download)Lesson 2 - Common
Electric Arc Welding
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123.11.2009 10:24FIGURE 6Lesson 2 - Common Electric Arc Welding
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Common Electric Arc Welding
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123.11.2009 10:241 din 123.11.2009 10:24Lesson 10Reliability of
WeldingFiller MetalsLesson 2 - Common Electric Arc Welding
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123.11.2009 10:24Current Chapter Table of ContentsLesson 1The
Basics of ArcWeldingLesson 2Common ElectricArc
WeldingProcessesLesson 3Covered Electrodesfor WeldingMild
SteelsLesson 4Covered Electrodesfor Welding LowAlloy SteelsLESSON
IIGo To TestPrint2.3.2Power Sources - Both AC and DC power sources
are used in gas tungsten arcwe(ding. They are the constant current
type with a drooping vo(t-ampere curve. This type of power source
produces very s(ight changes in the arc current when the arc (ength
(vo(tage) is varied. Refer to Lesson I, Section
1.9.Glossary2.3.2.1The choice between an AC or DC we(der depends on
the type and thickness of themeta( to be we(ded. Distinct
differences exist between AC and DC arc characteristics, and if DC
is chosen, the po(arity a(so becomes an important factor. The
effects of po(arity in GTAW are direct(y opposite the effects of
po(arity in SMAW as described in paragraphs 2.2.2.3 through
2.2.2.5. In SMAW, the distribution of heat between the e(ectrode
and work, which determines the penetration and we(d bead width, is
contro((ed main(y by the ingredients in the f(ux coating on the
e(ectrode. In GTAW where no f(ux coating exists, heat distribution
between the e(ectrode and the work is contro((ed so(e(y by the
po(arity. The choice of the proper we(ding current wi(( be better
understood by ana(yzing each type separate(y. The chart in Figure 7
(ists current recommendations.Lesson 2 - Common Electric Arc
Welding Processeshttp://www.esabna.con/EuWeb/AWTC/Lesson2_11.ht1
din 123.11.2009 10:24Lesson 5Welding Filler Metalsfor Stainless
SteelsLesson 6Carbon & Low AlloySteel Filler Metals
-GMAW,GTAW,SAWLesson 7Flux Cored ArcElectrodes CarbonLow Alloy
SteelsLesson 8HardsurfacingElectrodesTurn
PagesSearchChapter(FasterDownload)SearchDocument(SlowerDownload)WELDING
CURRENTSHIELDING GASMaterial&ACThicknessDCENDCEPHigh
Freq.ArgonHeliumAr/HeA(uminumUnder
1/82112Over1/8'2&31132MagnesiumUnder1/16"2112Over 1/1611Carbon
Stee( Under 1/811Over1/8'1123Stain(ess Stee(Under 1/8112Over
1/8'112CopperUnder 1/811Over 1/811Nicke( A((oysUnder 1/81132Over
1/8'121TitaniumUnder 1/8112Over 1/8'21Lesson 2 - Common Electric
Arc Welding
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123.11.2009 10:24Lesson 9Estimating &Comparing WeldMetal
Costs1.Preferred Choice - Manua( We(dingPreferred Choice -
Automatic We(ding 3. Second Choice - Automatic
We(dingCURRENT/SHIELDING GAS SELECTION, TUNGSTEN GAS ARC
WELDINGFIGURE 7Lesson 10Reliability of WeldingFiller Metals
COPYRIGHT 1998 THE ESAB GROUP, INC.Lesson 2 - Common Electric Arc
Welding Processeshttp://www.esabna.con/EuWeb/AWTC/Lesson2_11.ht1
din 123.11.2009 10:24Electrode PolarityPenetrationO,ide
CleaningI-eatConcentrationDirect
CurrentDeepPenetrationNoneAtStraight PolarityNarrowWorkElectrode
NegativeBeadMedium PenetrationGoodCycleAlternating CurrentMedium
WidthCleans O,ideAlternates BetweenBeadon Each I-alfElectrode and
WorkDirect Current Reverse PolarityShallow PenetrationWide
BeadMa,imumAtElectrodeElectrode PositiveLESSON II2.3.2.2Direct
current electrode negative (DCEN) is produced when the electrode
isconnected to the negative terminal of the power source. Since the
electrons flow from the electrode to the plate, appro,imately 70%
of the heat of the arc is concentrated at the work, and
appro,imately 30% at the electrode end. This allows the use of
smaller tungsten electrodes that produce a relatively narrow
concentrated arc. The weld shape has deep penetration and is quite
narrow. See Figure 8. Direct current electrode negative is suitable
for welding most metals. Magnesium and aluminum have a refractory
o,ide coating on the surface that must be physically removed
immediately prior to welding if DCSP is to be used.2.3.2.3Direct
current electrode positive (DCEP) is produced when the electrode
isconnected to the positive terminal of the welding power source.
In this condition, the electrons flow from the work to the
electrode tip, concentrating appro,imately 70% of the heat of the
arc at the electrode and 30% at the work. This higher heat at the
electrode necessitates using larger diameter tungsten to prevent it
from melting and contaminating the weld metal. Since the electrode
diameter is larger and the heat is less concentrated at the work,
the resultant weld bead is relatively wide and shallow. See Figure
8."GAS IONSELECTRONFLOW!!""!EFFECTS OF CURRENT TYPE - GAS TUNGSTEN
ARC WELDINGFIGURE2.3.2.4Aluminum and magnesium are two metals that
have a heavy o,ide coating that actsas an insulator and must be
removed before successful welding can take place. Welding with
electrode positive provides a good o,ide cleaning action in the
arc. If we were to study the physics of the welding arc, we find
that the electric current causes the shielding gas atoms to lose
some of their electrons. Since electrons are negatively charged,
these gas atoms now are unbalanced and have an e,cessive positive
charge. As we learned in Lesson I, unlike charges attract. These
positively charged atoms (or positive ions as they are known
inshapeType20fFlipH0fFlipV0posrelh2posrelv2shapePath4fFillOK0fFilled0lineWidth12065fArrowheadsOK1fBehindDocument0dxWrapDistLeft0dxWrapDistTop0dxWrapDistRight0dxWrapDistBottom0lineColor8355711Lesson
1The Basics of ArcWeldingLesson 2Common ElectricArc
WeldingProcessesLesson 3Covered Electrodesfor WeldingMild
SteelsLesson 4Covered Electrodesfor Welding LowAlloy SteelsLesson
5Welding Filler Metalsfor Stainless SteelsLesson 6Carbon & Low
AlloySteel Filler Metals -GMAW,GTAW,SAWLesson 7Flux Cored
ArcElectrodes CarbonLow Alloy SteelsLesson
8HardsurfacingElectrodesLesson 9Estimating &Comparing WeldMetal
CostsLesson 10Reliability of WeldingFiller Metals Current Chapter
Table of ContentsGo To TestPrintGlossaryTurn
PagesSearchChapter(FasterDownload)SearchDocument(SlowerDownload)Lesson
2 - Common Electric Arc Welding
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Common Electric Arc Welding
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123.11.2009 10:241 din 123.11.2009 10:24 COPYRIGI-T 1998 TI-E ESAB
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123.11.2009 10:251 din 123.11.2009 10:25Go To TestTurn PagesCurrent
Chapter Table of
ContentsPrintGlossarySearchChapter(FasterDownload)Search Document
(Slower Download)Lesson 1The Basics of ArcWeldingLesson 2Common
ElectricArc WeldingProcessesLesson 3Cove red Electrodesfor
WeldingMild SteelsLesson 4Cove red Electrodesfor Welding LowAlloy
SteelsLesson 5Welding Filler Metalsfor Stainless SteelsLesson
6Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAWLesson
7Flux Cored ArcElectrodes CarbonLow Alloy SteelsLesson
8HardsurfacingElectrodesLesson 9Estimating & Comparing WelMetal
CostsLesson 10Reliability of WeldingFiller Metals LESSON IIchemical
terminology) are attracted to the negative pole, in this case the
work, at high velocity. Upon striking the work surface, they
dislodge the oxide coating permitting good electrical conductivity
for the maintenance of the arc, and elimi nate the impurities in
the weld metal that could be caused by these oxides.2.3.2.5Direct
current electrode positive is rarely used in gas-tungsten arc
welding. Despitethe excellent oxide cleaning action, the lower heat
input in the weld area makes it a slow process, and in metals
having higher thermal conductivity, the heat is rapidly conducted
away from the weld zone. When used, DCEP is restricted to welding
thin sections (under 118') of magnesium and alumi
num.2.3.2.6Alternating current is actually a combination of DCEN
and DCEP and is widelyused for welding alumi num. In a sense, the
adva ntages of both DC processes are combined, and the weld bead
produced is a compromise of the two. Remember that when welding
with 60 Hz current, the electron flow from the electrode tip to the
work reverses direction 120 times every second. Thereby, the
intense heat alternates from electrode to work piece, allowing the
use of an intermediate size electrode. The weld bead is a
compromise having medium penetration and bead width. The gas ions
blast the oxides from the surface of alumi num and magnesium during
the positive half cycle. Figure 8 illustrates the effects of the
different types of current used in gas-tungsten arc
welding.2.3.2.7DC constant current power sources - Constant current
power sources, used forshielded metal arc welding, may also be used
for gas-tungsten arc welding. In applications where weld integrity
is not of utmost importance, these power sources will suffice. With
machines of this type, the arc must be initiated by touching the
tungsten electrode to the work and quickly withdrawi ng it to
maintain the proper arc length. This starting method contami nates
the electrode and blunts the point which has been grounded on the
electrode end. These conditions can cause weld metal inclusions and
poor arc direction. Using a power source designed for gas tungsten
arc welding with a high frequency stabilizer will elimi nate this
problem. The electrode need not be touched to the work for arc
initiation. Instead, the high frequency voltage, at very low
current, is superimposed onto the welding current. When the
electrode is brought to within approximately 118 inch of the base
metal, the high frequency ionizes the gas path, making it
conductive and a welding arc is established. The high frequency is
automatically turned off immediately after arc initiation when
using direct current.2.3.2.8AC Constant Current Power Source -
Designed for gas tungsten arc welding,always incorporates high
frequency, and it is turned on throughout the weld cycle to
maintain a stable arc. When welding with AC, the current passes
through 0 twice in every cycle and theLesson 2 - Common Electric
Arc Welding
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123.11.2009 10:25Lesson 1The Basics of ArcWeldingLesson 2Common
ElectricArc WeldingProcessesLesson 3Covered Electrodesfor
WeldingMild SteelsLesson 4Covered Electrodesfor Welding LowAlloy
SteelsLesson 5Welding Filler Metalsfor Stainless SteelsLesson
6Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAWLesson
7Flux Cored ArcElectrodes CarbonLow Alloy SteelsLesson
8HardsurfacingElectrodesLesson 9Estimating &Comparing WeldMetal
CostsLesson 10Reliability of WeldingFiller Metals LESSON IICurrent
Chapter Table of ContentsGo To TestPrintarc must be reestablished
each time it does so. The oxide coating on metals, such as aluminum
and magnesium, can act much like a rectifier as discussed in Lesson
I. The positi,e half-cycle will be eliminated if the arc does not
reignite, causing an unstable condition. Continuous high frequency
maintains an ionized path for the welding arc, and assures arc
re-ignition each time the current changes direction. AC is
extensi,e ly used for welding aluminum and magnesium.2.3.2.9AC/DC
Constant Current Power Sources - Designed for gas tungsten
arcGlossarywelding, are a,ailable, and can be used for welding
practically all metals. The gas tungsten arc welding process is
usually chosen because of the high quality welds it can produce.
The metals that are commonly welded th this process, such as
stainless steel, aluminum and some of the more exotic metals, cost
many times the price of mi ld steel; and therefore, the power
sources designed for this process ha,e many desirable features to
insure high quality welds. Among these are:1.Remote current
control, which allows the operator to control welding amperage ith
a hand control on the torch, or a foot control at the welding
station.Turn Pages2.Automatic soft-start, which presents a high
current surge when the arc is initiated..Shielding gas and cooling
water solenoid valves, which automatically controlflow before,
during and for an adjustable length of time after the weld is comp
leted.SearchChapter(FasterDownload)SearchDocument(SlowerDownload)4.Spot-weld
timers, which automatically control all elements during
eachspot-weld cycle.Other options and accessories are also
a,ailable.2.3.2.10Power sources for automatic welding with complete
programmable output are alsoa,ailable. Such units are used
extensi,e ly for the automatic welding of pipe in position. The
welding current is automatically ,aried as the torch tra,e ls
around the pipe. Some units pro,ide a pulsed welding current where
the amperage is automatically ,aried between a low and high se,eral
times per second. This produces welds th good penetration and
impro,ed weld bead shape.2.3.3Torches - The torch is actually an
electrode holder that supplies welding current tothe tungsten
electrode, and an inert gas shield to the arc zone. The electrode
is held in a collet-like clamping de,ice that allows adjustment so
that the proper length of electrode protrudes beyond the shielding
gas cup. Manual torches are designed to accept electrodes of
3Lesson 2 - Common Electric Arc Welding
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Common Electric Arc Welding
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123.11.2009 10:251 din 123.11.2009 10:25 COPYRIGHT 1998 THE ESAB
GROUP, INCLesson 2 - Common Electric Arc Welding
Processeshttp://www.esabna.con/EuWeb/AWTC/Lesson2_26.ht1 din
123.11.2009 10:25Lesson 1The Basics of ArcWeldingLesson 2Common
ElectricArc WeldingProcessesLesson 3Covered Electrodesfor
WeldingMild SteelsLesson 4Covered Electrodesfor Welding LowAlloy
SteelsLesson 5Welding Filler Metalsfor Stainless SteelsLesson
6Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAWLesson
7Flux Cored ArcElectrodes CarbonLow Alloy SteelsLesson
8HardsurfacingElectrodesLesson 9Estimating &Comparing WeldMetal
CostsLesson 10Reliability of WeldingFiller Metals LESSON IICurrent
Chapter Table of ContentsGo To TestPrintinch or 7 inch lengths.
Torches may be either air or water-cooled. The air-cooled types
actually are cooled to a degree by the shielding gas that is fed to
the torch head through a composite cable. The gas actually
surrounds the copper welding cable, affording some degree of
cooling. Water-cooled torches are usually used for applications
where the welding current exceeds 200 amperes. The water inlet hose
is connected to the torch head. Circulating around the torch head,
the water leaves the torch via the current-in hose and cable
assembly. Cooling the welding cable in this manner allows the use
of a smaller diameter cable that is more flexible and lighter in
weight.2.3.3.1The gas nozzles are made of ceramic materials and are
available in various sizesand shapes. In some heavy duty, high
current applications, metal water-cooled nozzles are used.Turn
PagesGlossary2.3.3.2A switch on the torch is used to energize the
electrode with welding current and startthe shielding gas flow.
High frequency current and water flow are also initiated by this
switch if the power source is so equipped. In many installations,
these functions are initiated by a foot control that also is
capable of controlling the welding current. This method gives the
operator full control of the arc. The usual welding method is to
start the arc at a low current, gradually increase the current
until a molten pool is achieved, and welding begins. At the end of
the weld, current is slowly decreases and the arc extinguished,
preventing the crater that forms at the end of the weld when the
arc is broken abruptly.2.3.4Shielding Gases - Argon and helium are
the major shielding gases used in gastungsten arc welding. In some
applications, mixtures of the two gases prove advantageous. To a
lesser extent, hydrogen is mixed with argon or helium for special
applications.SearchChapter(FasterDownload)SearchDocument(SlowerDownload)2.3.4.1Argon
and helium are colorless, odorless, tasteless and nontoxic gases.
Both areinert gases, which means that they do not readily combine
with other elements. They will not burn nor support combustion.
Commercial grades used for welding are 99.99% pure. Argon is .38%
heavier than air and about 10 times heavier than helium. Both gases
ionize when present in an electric arc. This means that the gas
atoms lose some of their electrons that have a negative charge.
These unbalanced gas atoms, properly called positive ions, now have
a positive charge and are attracted to the negative pole in the
arc. When the arc is positive and the work is negative, these
positive ions impinge upon the work and remove surface oxides or
scale in the weld area.2.3.4.2Argon is most commonly used of the
shielding gases. Excellent arc starting andease of use make it most
desirable for manual welding. Argon produces a better cleaning
action when welding aluminum and magnesium with alternating
current. The arc produced isLesson 2 - Common Electric Arc Welding
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Common Electric Arc Welding
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123.11.2009 10:251 din 123.11.2009 10:25 COPYRIGHT 1998 THE ESAB
GROUP, INCLesson 2 - Common Electric Arc Welding
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123.11.2009 10:25Go To TestTurn PagesCurrent Chapter Table of
ContentsPrintGlossarySearchChapter(FasterDownload)SearchDocument(SlowerDownload)Lesson
1The Basics of ArcWeldingLesson 2Common ElectricArc
WeldingProcessesLesson 3Covered Electrodesfor WeldingMild
SteelsLesson 4Covered Electrodesfor Welding LowAlloy SteelsLesson
5Welding Filler Metalsfor Stainless SteelsLesson 6Carbon & Low
AlloySteel Filler Metals -GMAW,GTAW,SAWLesson 7Flux Cored
ArcElectrodes CarbonLow Alloy SteelsLesson
8HardsurfacingElectrodesLesson 9Estimating &Comparing WeldMetal
CostsLesson 10Reliability of WeldingFiller Metals LESSON
IIrelatively narrow. Argon is m ore suitable for welding thinner
material. At equal amperage, helium produces a higher arc voltage
than argon. Since welding heat is the product of volts times
amperes, helium produces m ore available heat at the arc. This
makes it m ore suitable for welding heavy sections of metal that
have high heat conductivity, or for automatic welding operations
where higher welding speeds are required.2.3.4.3Argon-helium gas
mixtures are used in applications where higher heat input and
thedesirable characteristics of argon are required. Argon, being a
relatively heavy gas, blankets the weld area at lower flow rates.
Argon is preferred for many applications because it costs less than
helium.2.3.4.4Helium, being approximately 10 times lighter than
argon, requires flow rates of 23 times that of argon to
satisfactorily shield the arc.2.3.5Electrodes - Electrodes for gas
tungsten arc welding are available in diametersfrom .010' to 114'
in diameter and standard lengths range from 3' to 24'. The m ost
comm only used sizes, however, are the .040', 1116', 3132', and
118' diameters.2.3.5.1The shape of the tip of the electrode is an
imp ortant factor in gas tungsten arcwelding. When welding with
DCEN, the tip must be ground to a point. The included angle at
which the tip is ground varies with the application, the electrode
diameter, and the welding current. Narrowjoints require a
relatively small included angle. When welding very thin material at
low currents, a needlelike point ground onto the smallest available
electrode may be necessary to stabilize the arc. Properly ground
electrodes will assure easy arc starting, good arc stability, and
proper bead width.2.3.5.2When welding with AC, grinding the
electrode tip is not necessary. When properwelding current is used,
the electrode will form a hemispherical end. If the proper welding
current is exceeded, the end will become bulbous in shape and
possibly melt off to contaminate the weld metal.2.3.5.3 The
American Welding Society has published Specification AWS A5.12-80
for tungsten arc welding electrodes that classifies the electrodes
on the basis of their chemical comp osition, size and finish.
Briefly, the types specified are listed below
