Training Handbook For Welderspart 3.docx
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Training Handbook For Welderspart 3.docx
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TrainingHandbookForWelderspart3
Manualmetalarcwelding(111)
Systemdescription
Theheatsourceisanarcwhichburnsbetweenanelectrodecovering(fillermetal)andtheworkpiece.Thearcmeltsthebasicmaterial(attemperaturesofmorethan5000°C).Atthesametime,thecorerod(oftennon-alloyedsteel)andthecoveringoftheelectrodemeltintodroplets.Thecoveringiscomprisedofmineralmaterialsand/orcellulose.Itisdesignedtoimproveconductivityofthearcgap,toprotecttheliquidweldpoolagainstcontactwithairviaaformationofgasesandslagandtoincorporatetherequiredalloyingelementsintotheweldpool.Therespectivetypeofcoveringmaterialalsoinfluencestheweldingbehaviour,withregardtothetypeofweldcurrent,dropsize,weldpoolviscosity,weldingpositionandremovabilityofslag.Theelectrodecoveringisselectedinaccordancewiththerespectiveweldingassignment.
Electrodecorerod
Electrodecovering
Shieldinggasfromtheelectrodecovering
Liquidslag
CompactslagDroptransfer
CompactweldmetalArc
Weldpool
Workpiece
Applicationarea:
Non-alloyedandalloyedsteels,sheetplates,profilesandtubes,workpiecethicknessupwardsof1.5mminallpositions,eveninbuildingsiteconditions(intheopenair).Inmetalconstruction,steelconstruction,pipelineconstruction,containerconstructionandmachineconstruction.
Typicalweldingdata
Weldingcurrent:
60Ato360A
Typeofcurrent:
Directcurrent(+/-pole)oralternatingcurrentwithdippingcharacteristiccurve
Electrodes:
Diameter:
2.0–2.5–3.2–4.0–5.0-6.0mm
Length:
250–450mm
Depositionrate:
0.5to5.5kg/h(upto100%ED)
Assemblyofaweldingsystemformanualmetalarcwelding
Electrodeholder
Currentadjuster
Electrode
Connectingsocket
Plug
Arc
-Mains
Weldingcurrentcable
Weldingcurrentreturncable
–Weldingcurrentsource
Workpiece
Workpiececlamp
Weldingcurrentsource:
Thereisanextensivevariationofcurrentsourcesformanualmetalarcwelding.
–Step-regulatedtransformer
–Scatteringkerneltransformer
–Transductor
–Step-regulatedrectifier
–Rectifierwithscatteringkerneltransformer
–Withpre-magnetisation(transductor)
–Thyristorisedrectifier
–Analoguecurrentsource
–Secondary-switchedsources
–Primary-switchedsources(inverter)
–Withelectricmotor
–Withcombustionmotor(weldingset)
Olderweldingequipmentisstillusedtodayduetoitsrobustness.Thisincludesweldingconverters,weldingtransformersandweldingrectifiers.
Weldingconverters/weldinginvertersarebecomingevermorepopularduetotheirsmallerdimensions,portabilityofequipmentandexcellentefficiency.
Layoutofacurrentweldingsource,usingaweldingtransformerasanexample
Assemblies:
(1)Mainssupply250
(2)On/Offswitch
(3)Transformer(single-phase)
Assignment:
∙Conversionofhighmainsvoltageintolower
weldingvoltage
∙Conversionoflowmainsvoltageintohigh
weldingcurrent
(4)Adjustmentoftheweldingcurrentwithadjusting
crankandscale
(5)Connectionsocketandweldingcurrentcable
(6)Connectionsocketandweldingreturncable
Theweldingtransformersuppliesalternatingcurrent.
Disadvantages:
∙Notsuitablefortheweldingofbasicelectrodes
∙Only48voltno-loadvoltagepermittedwhenweldinginconditionsofincreasedelectrical
hazard;Thiscouldresultinanimpairmentofweldingproperties,suchasignitionofthearc
Advantages:
∙Nobloweffect
∙Simpleandrobustdesign
∙Veryreasonablypriced.
Thecontrolforadjustmentoftheweldingcurrentisconfiguredverysimplyandisavailableintwo
differentvariants:
1.viascatteringkerneladjustmentusingthecrank(seediagram)
2.viacoiltappingonthetransformerbywayofon-loadtapchanger
U1=Mainsvoltage
U2=Weldingvoltage
Assemblyofaprimary-switchedtransistorcurrentsource(principle)
Thecurrentsourceusedpredominantlytodayformanualmetalarcwelding
Mainssupply:
Alternatingcurrent230V
Three-phasecurrent3x400v
High-frequencytransformer
(withsmallerdimensions)
First,thefrequencyofthealternatingcurrentisincreasedbywayofaconverter(inverter)usingtransistorsascontrolelementsfrom50Hztobetween10000Hzand20000Hz.Onlythendothe
transformerandrectifierfollow.
Thisdesignsavesconsiderablyonweight,whileatthesametimeincreasingefficiency.Thus,aninvertercurrentsourceforaweldingcurrentofupto320Aweighsonlyapprox.30kg.
Advantages:
∙Suitableforweldingwithallelectrodes
∙Reducedweight,compactdesign
∙Notsensitivetofluctuationsinmainspower
Disadvantage:
∙Bloweffect
Electrodeholder
Torealiseanyweldingprocedure,itisessentialthattheweldingcurrentsourceandworkpiececonstituteaclosedcircuitwithinthesystem.
Thisisresultedononehandfromthecurrentsourcetotheelectrodeholder,andthentotheelectrodeitselfviatheweldingcurrentcable.Theelectrodeholdermustbefully-insulatedasaprotectionagainstelectricalcurrent.
Fully-insulatedelectrodeholder
Handlever
Insulatingjaws
Spring
Handhold
Workpiececonnection
Ontheotherhand,theweldingcurrentmustflowfromtheworkpiece,backtothecurrentsourceagainviatheweldingreturncable.Thecircuitisclosedbythearc.
Thefollowingshouldbeobservedifoptimumconditionsarealsotobeobtainedonthereturncableside:
-Applyaworkpiececlamp(e.g.screwclamp,magneticclamp)inimmediateproximity
totheweldingpoint
-Ensuresecureclampingofthelines
-Ensurethatthecontactsurfacesarecleanandsmooth
-Donotuseanyaccessoriessuchasrods,tubes,waterlinesorsteelgirdersinthe
hall'sstructureasaweldingreturncable
ScrewclampMagneticclamp
Arcformanualmetalarcwelding
Theelectricarcisashortairgaporgasgap(betweentipofelectrodeandworkpiece),throughwhichelectricalcurrentflows.Asairandgasesarepoorconductors,thearcmustbeignited.Ignitionisresultedassoonastheelectrodestrikestheworkpieceforafractionofasecond.
Propertiesofthearc:
Thearc
oIsagaseous,electricalconductor
oCanbeinfluencedbymagnetism(bloweffect)
oEmitsradiationininfrared,visibleandultravioletranges
oExertspressureontotheweldpool
Formanualmetalarcwelding,weldingcanberealisedwithalternatingcurrent,aswellaswithdirectcurrent.Therespectivetypeofcurrentwillaffectbehaviourofthearc,weldsuitabilityforelectrodesandthedistributionofenergy.
DirectcurrentarcAlternatingcurrentarc
MinusPlus
polepole
PlusMinusu
1
polepole
2
Uz
1Arcextinguishingpoint
Δt
2Arcignitionpoint
Δt
Oneperiod
Arcdowntime
UzIgnitionvoltage
Loadcharacteristiccurveformanualmetalarcwelding
Weldingequipmentformanualmetalarcweldingrequirescurrentsourceswithdippingcharacteristiccurve
Typeofcurrent:
Directcurrentoralternatingcurrent
WeldingvoltageUSinV1
U0Arc
Dipping(static)characteristiccurveToolong
Arccharacteristiccurve
2
Arc
Correct
3
I0Arc
Tooshort
WeldingcurrentISinA
Withafixedcharacteristiccurve(switchposition,scale),theweldingcurrentandtheweldingvoltagechangesalongtheloadcharacteristiccurve,resultingachangeinthearclength.Weldingwithalongarcyieldsalowcurrentandahighvoltage
(1).
Weldingwithashortarcyieldsahighcurrentandalowvoltage
(2).
Theno-loadvoltage(U0)isthevoltagebetweentheconnectingclamps.Theshort-circuitcurrent(I0)isthecurrentapplieduponsettingtheelectrodedownontotheworkpiece.
Theworkingpoint(1,2,3)istheintersectionpointofarccharacteristiccurvewiththestaticcharacteristiccurve.
Ignitionprocess
LoweringContactRaising
(Short-circuit)
I=0I=Max.I=Weldingcurrent
U=Umax=UactsagainstoU=Weldingvoltage
No-loadvoltage
Theshort-circuitwhichisresulteduponbriefcontactheatsthetipoftheelectrodetosuchanintensitythatitallowselectronstoescape.Duetotheweldingvoltagebeingapplied,theseelectronsareacceleratedathighspeed.Thehightemperaturesatthecontactpointofthearcaregeneratedbytheimpactofthechargecarrier.
Bloweffect
Thearc,aswithallelectricalconductors,isencompassedbyamagneticfield.Ifdiffusionofthemagneticfieldisimpeded,thearcisdeflected–thebloweffect.
Weldingontheedgeoftheworkpiece
Magneticfield
Frequentcausesofthebloweffect,inparticularwhenweldingwithdirectcurrent
Weldinginimmediateproximity
totheworkpiececlamps
Weldingalongsidelargeworkpiecemasses
Measurestocombatthebloweffect
∙
Inclinationoftheelectrode
∙Attachtheworkpiececlampsonbothsides
orrepositiontheclamps
∙Applynumeroustackwelds
∙Selectthecorrectweldsequence
∙Wherepossible,weldusingalternatingcurrent
insteadofdirectcurrent
Fillermetal
Coveredelectrodesformanualmetalarcwelding
Coveredelectrodesarecomprisedofacorewireandapredominantlymineralcoveringcompactedwithabondingagent.
Forlow-alloyedandnon-alloyedelectrodes,non-alloyed,softcorewiresaregenerallyused.Theadditionofalloystoincreasestrengthorductilityisresultedfromthecovering.
Bothcorerod-alloyedandcovering-alloyedtypesareavailableforhigh-alloyedelectrodes.
Dimensions
Electrodesareavailableinthefo
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