Shielded Metal Arc Welding

Safe practices when Arc Welding

Don’t stand in waterDon’t stand in water Discard frayed cords and wiresDiscard frayed cords and wires Keep flammable liquids away from heatKeep flammable liquids away from heat

Don’t look at the arc with out a number 10 Don’t look at the arc with out a number 10 lens.lens.

Dress Code

Wear properly fitted clothes.Wear properly fitted clothes. When welding, sleeves should be buttoned and When welding, sleeves should be buttoned and

gloves should be worn.gloves should be worn. Wear boots or high top; Tightly laced shoes.Wear boots or high top; Tightly laced shoes. Do not wear loose clothing, shirt tails, and Do not wear loose clothing, shirt tails, and

unbuttoned sleeves around power equipment.unbuttoned sleeves around power equipment. Do not wear clothes that you do not want to get Do not wear clothes that you do not want to get

dirty. dirty.

The Arc

When electrons jump through the airWhen electrons jump through the air

When the pressure overcomes resistance When the pressure overcomes resistance

V=A X RV=A X R

Parts of the Arc

Arc streamArc stream Vaporized metalVaporized metal

Appears yellowAppears yellow Liquid metalLiquid metal

Appears greenAppears green Arc flameArc flame

Natural gases surrounding arc streamNatural gases surrounding arc streamPale redPale red

Arc Control

LengthLength

AngleAngle

Reverse Polarity(DCEP)

Electrode positiveElectrode positive

Better penetrated welds Better penetrated welds

Straight Polarity (DCEN) Electrode NegativeElectrode Negative

Used when a high rate of filler metal is Used when a high rate of filler metal is required.required.

EXX2X Electrodes EXX2X Electrodes

Alternating Current

Stops and starts Stops and starts Must have enough voltage restart arcMust have enough voltage restart arc

Good penetration Good penetration

Less expensive Less expensive

Classification of Steel Electrodes

Electrode designated by “E” followed by a Electrode designated by “E” followed by a 4- or 5- digit number4- or 5- digit number

First two or three digits - minimum tensile First two or three digits - minimum tensile strength as-welded deposited weld metal strength as-welded deposited weld metal expressed in thousands of pounds per expressed in thousands of pounds per square inch (1000psi)square inch (1000psi) E-60xx - 60,000psi TSE-60xx - 60,000psi TS E-120xx - 120,000 psi TSE-120xx - 120,000 psi TS

Classification of Steel Electrodes

Third or fourth digit refers to the welding Third or fourth digit refers to the welding position.position. E-xx1x - all positionsE-xx1x - all positions E-xx2x - flat and horizontal fillet E-xx2x - flat and horizontal fillet

positionspositions E-xx3x - flat position onlyE-xx3x - flat position only

Classification cont.

The fourth or fifth and last digit indicates the type The fourth or fifth and last digit indicates the type of welding current and the type of flux coveringof welding current and the type of flux covering E-xx10 - DC reverse polarity (electrode E-xx10 - DC reverse polarity (electrode

positive) only (cellulose sodium).positive) only (cellulose sodium). E-xx11 - AC or DC reverse polarity (cellulose E-xx11 - AC or DC reverse polarity (cellulose

potassium ) Fast freeze, cuttingpotassium ) Fast freeze, cutting E-xx13 - AC or DC straight polarity (titania E-xx13 - AC or DC straight polarity (titania

potassium) potassium)

Factors of Electrode Selection

Type of metal to be weldedType of metal to be welded Thickness of metalThickness of metal Position of weldPosition of weld Type of power (DC or AC)Type of power (DC or AC) Cleanliness of metalCleanliness of metal Weld bead appearance desiredWeld bead appearance desired

Flux

Improves the performance in handling, storage Improves the performance in handling, storage and operation of the electrodeand operation of the electrode

Floats out impuritiesFloats out impurities Directs arc stream (stabilizer)Directs arc stream (stabilizer) InsulatorInsulator Prevents oxidation (slag or gas)Prevents oxidation (slag or gas) Holds in heatHolds in heat Iron-powder improves striking ability and Iron-powder improves striking ability and

increases metal deposition rateincreases metal deposition rate

Striking the Arc

Pecking Pecking Touching electrode to Touching electrode to

the base metal and the base metal and moving away to proper moving away to proper arc distance. Moving arc distance. Moving electrode in a vertical electrode in a vertical motion. motion.

Can start precisely Can start precisely where the weld is to where the weld is to be.be.

ScratchingScratching Moving electrode Moving electrode

across base metal across base metal then moving then moving electrode away to electrode away to the proper arc the proper arc distance.distance.

Dose not work Dose not work good in tight placesgood in tight places

Common Striking Problems

Sticking Sticking Lift electrode and Lift electrode and

metalmetal Break electrode Break electrode

from metalfrom metal Remove electrode Remove electrode

from clamp from clamp

Arc is extinguishedArc is extinguished The electrode is The electrode is

moved to far away moved to far away from the base metal from the base metal after the arc is after the arc is struck.struck.

Arc Length

Longer arc Longer arc Increases Increases

Resistance Resistance Increases Voltage Increases Voltage Decreases Current Decreases Current Decreases filler Decreases filler

consumptionconsumption

Shorter arcShorter arc Decreases Decreases

Resistance Resistance Decreases Voltage Decreases Voltage Increases CurrentIncreases Current Increases filler Increases filler

consumption consumption

Arc Length

Should be no more then ¼ inch Should be no more then ¼ inch

The sound of the arc should sound like eggs The sound of the arc should sound like eggs fryingfrying

Bead Width

Stringer beadStringer bead Only motion is in the Only motion is in the

direction of travel direction of travel About 3 times the About 3 times the

width of the electrodewidth of the electrode With 1/8 inch electrode With 1/8 inch electrode

should be 3/8 inchshould be 3/8 inch

Weaving beadWeaving bead Motion side to side Motion side to side

as well as forwardas well as forward About 6 times the About 6 times the

width of the width of the electrode electrode

With 1/8 inch With 1/8 inch electrode should be electrode should be 3/4 inch3/4 inch

Stringer Bead

Weaving Bead

Electrode Angle

Should be 15Should be 15° to 20° tipped forward in the ° to 20° tipped forward in the direction of travel direction of travel

Stringer bead should be at 90° from the Stringer bead should be at 90° from the base metalbase metal

Travel Speed

Bead widthBead width

Bullet-nose-shaped ripplesBullet-nose-shaped ripples

Restarting

Strike ark 3/8 inch in front of previous weld Strike ark 3/8 inch in front of previous weld

Move back to craterMove back to crater

Move forward to finish weldMove forward to finish weld

Restarting