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Selecting and Using Arc

Welding EquipmentAg Mechanics

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Arc Welding IntroductionHeat for arc welding obtained by usingelectricity

Electric current flows from a transformer connected to lines from a power plantAnother source is electric motors or gas

engines driving special generators

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Arc Welding IntroductionArc welder : machine that produces currentfor welding

Arc : discharge of electricity through an air spaceW elder (weldor) : person who welds

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P rocess and P rinciplesSM AW : shielded metal arc welding

C alled arc welding or stick welding

Utilizes flux-coated metal welding rods calledelectrodesShi elded : refers to gaseous cloud formed aroundweld by burning flux

Gases help metal electrode burn evenly as it mixes withbase metalFlux removes impurities from base metal and preventsoxidationS lag : flux and impurities that float to top of weld and form

a layer

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Advantages of Arc WeldingElectricity is relatively inexpensive as a sourceof heat for welding

Electric welders suitable for farm welding arerelatively inexpensiveWelders are available that work on ordinary

230-volt household or farmstead wiringEngine-driven portable welders are available

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Advantages continuedArc welding is fast and reliableAgricultural students and workers can becomegood arc weldors quicklyAn arc weldor can be used for heating,brazing, and hardsurfacing as well as welding

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T emperatureArc has temperature of about 9000 oFExact temperature varies with :

L ength of arcSize of electrodeAmperage setting

T ypically range from 20 to 225 amps

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D uty C ycleDu ty cycle : percentage of time a welder can operatewithout overheating

Number of minutes out of 60 a welder can operate at fullcapacity

20% duty cycle ± should weld only 12 minutes out of every hour

Welders available with duty cycles from 20 to 100%Based on midrange setting

Shorter if used at higher settingsL onger if used at lower settings

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Electricity for WeldingBasic terms

Ampere (amp) : measure of rate of flow of current

in conductor C ond u ctor : any material that permits current tomove through itV olt or voltage : measure of electrical pressureW att or wattage : measure of energy available or work that can be done

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Electricity for WeldingWest Virginia FormulaW = V x AW = wattsV = voltsA = amperes

W

V A

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Electricity continuedWelding machines put out high amperage andrelatively low voltage

L ow voltage allows welder to be relatively safemachine while putting out so much energy

Requires 60 volts to push current through

human bodyL ow to moderate settings put out less than 60 voltsST ILL N EE D TO BE C AU T IO US

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Alternating C urrentT ransformers : convert high voltage and lowamperage to low voltage and high amperage

Welders that are transformers receive currentdirectly from utility power linesC alled alternating current welders

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Alternating C urrent continuedAlternat ing c u rrent (A C ): current thatreverses its direction of flow 60 times per

secondAlso called 60-cycle current

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D irect currentG enerator : machine that produces directcurrent, driven by an electric motor or gas or

diesel engineD irect c u rrent ( D C ): current that flows in onedirection only in accordance with how the

welder is setStraight or reverse polarity

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P olarityP olar i ty: refers to direction of flow of electricity in welding

C ertain electrodes and certain jobs work better with current flowing a certain wayS tra ig h t polar ity: work is positive pole andelectrode is negative poleR everse polar ity: work is negative pole andelectrode is positive pole

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Welding EquipmentC ablesElectrode holdersGround clampsWelding table and boothEquipment for cleaning welds

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C ablesC ables ± welders need large electrical cables

C arry current from welder to electrode, across

arc, and back to welder C AREFU L: P rotect cables from forceful impactand contact with sharp objects that may damagetheir coverings

C overings insulate conductors and prevent dangerousshocks and electrical shorts

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Electrode HoldersE lectrode h older : spring loaded device withinsulated handles used to grip a welding

electrodeC able to holder has copper or aluminum core

C ore is clamped or soldered to metal part of electrodeholder Insulated sleeve slides over connection to protectoperator from electric shock All other parts are insulated except jaws

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Ground C lampG ro u nd clamp : Spring-loaded clamp attachedto an electrical cable

N ot insulatedN ot a shock hazardC arries current between welding table or project

and to the welder

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Welding T able and BoothBooth and metal table are convenient andefficient

P roper table permits operator to stand or sitcomfortablyBooth must have curtains to protect other workers from blinding light flashesN eed exhaust equipment to remove fumesEntire area must be fire-resistant and free of flammable materials

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Equipment for C leaning WeldsT ongs or pliers : useful for handling hot metalHand wire brushes and chipping hammers : used for removing slag