ESR(电渣炉资料)

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1、ELECTROSLAGREMELTING(ESR)ElectroslagRemelting2320tonESRfurnacecapableofmeltingunderprotectiveatmosphereandmoldwallduringtheremeltingopera-ESRhasbeenknownsincethe1930s,butittookapprox.30yearsbeforeitbecameanacknowledgedprocessformassproductionofhigh-qualityingots.TheESRtechnologyisofinterestnotonlyfo

2、rtheproductionofsmallerweightingotsoftoolsteelsandsuperalloys,butalsoofheavyforgingingotsuptorawingotweightsof165tons.ProcessTechnologyandProcessCharacteristicsWhereasVARneedsvacuumforrefining,inESRtheconsumableelectrodeisdippedintoapoolofslaginawater-cooledmold.Anelectriccurrent(usuallyAC)passesthr

3、oughtheslag,betweentheelectrodeandtheingotbeingformedandsuperheatstheslagsothatdropsofmetalaremeltedfromtheelectrode.Theytravelthroughtheslagtothebo卄omofthewater-cooledmoldwheretheysolidify.Theslagpooliscarriedupwardsastheingotforms.Thenewingotofrefinedmaterialbuildsupslowlyfromthebo卄omofthemold.Iti

4、shomogeneous,directionallysolidifiedandfreefromthecentralunsoundnessthatcanoccurinconventionallycastingotsastheysolidifyfromtheoutsideinwards.GenerallytheESRprocessoffersveryhigh,consistent,andpredictableproductquality.Finelycontrolledsolidificationimprovessoundnessandstructuralintegrity.Ingotsurfac

5、equalityisimprovedbytheformationofasolidifiedthinslagskinbetweeningottion.ThisiswhyESRisrecognizedasthepreferredproductionmethodforhigh-performancesuperalloysthatareusedtodayinindustriessuchasaerospaceandnuclearengineeringaswellasforheavyforgings.Ingotsareobtainedwithpuritylevelsthatwereunheardofsom

6、eyearsago.Otherbranchesofengineeringarefollowingtheexamplesofthe“high-tech”pacesettersandinsistonnew,highpuritylevelsthatcanbeobtainedfromESRwiththelatest,mostsophisticatedequipment.ESR24MetallurgyoftheElectroslagRemeltingProcessDuetothesuperheatedslagthatiscontinuouslyintouchwiththeelectrodetip,ali

7、quidfilmofmetalformsattheelectrodetip.Asthedevelopingdropletspassthroughtheslag,themetaliscleanedofnon-metal-licimpuritieswhichareremovedbychemicalreactionwiththeslagorbyphysicalflotationtothetopofthemoltenpool.TheremaininginclusionsinESRareverysmallinsizeandevenlydistributedintheremeltedingot.16ton

8、PESRfurnace,max.16barSlagsforESRareusuallybasedoncalciumfluoride(CaF),lime(CaO)andalumina(AlO).Magnesia(MgO),titania(TiO)andsilica(SiO)mayalsobeadded,dependingonthealloytoberemelted.Toperformitsintendedfunctions,theslagmusthavesomewell-definedproperties,suchas:sItsmeltingpointmustbelowerthanthatofth

9、emetaltoberemelted;sItmustbeelectricallyefficient;sItscompositionshouldbeselectedtoensurethedesiredchemicalreactions;sItmusthavesuitableviscosityatremeltingtemperature.Inspiteofdirectionaldendriticsolidification,variousdefects,suchastheformationoftreeringpatternsandfreckles,canoccurinremeltedingots.

10、ReasonsfortheoccurrenceofthesedefectsarethesameasinVAR.ItisimportanttonotethatwhitespotsnormallydonotoccurinanESRingot.Thedendriteskeletonsorsmallbrokenpiecesfromtheelectrodemustpassthesuperheatedslagandhaveenoughtimetobecomemoltenbeforetheyreachthesolidificationfront.Thuspreventswhitespots.Theingot

11、surfacecoveredbyathinslagskinneedsnoconditioningpriortoforging.Electrodesforremeltingcanbeusedintheas-castcondition.ElectroslagRemeltingFurnacesSignificantadvanceshavebeenmadeovertheyearsinplantdesign,coaxialcurrentfeedingandparticularlyincomputercontrolandregulationwiththeobjectiveofachievingafully

12、-automaticremeltingprocess.Thisinturnhasresultedinimprovedmetallurgicalpropertiesoftheproducts.ESR25Afullycoaxialfurnacedesignisrequiredforre-meltingofsegregation-sensitivealloysinordertopreventmeltstirringbystraymagneticfields.Shieldingofthemeltspacewithprotectiveatmospherehasbeenthelatesttrendinre

13、centyears.RemeltingunderincreasedpressuretoincreasethenitrogencontentintheingotisanothervariationofESR.ESRfurnacescanbedesignedforremeltingofround,squareandrectangular(slab)ingots.Finally,computercontrolledprocessautomationhasbeendevelopedtoperformsimilarlytoALDsautomaticmeltcontrolsystem(AMC)descri

14、bedunderVAR.ImportanttomentionhereisthatALDselectrodeimmersiondepthcontrolintotheslagisbasedonslagresistanceorslagresistanceswing.Usingtheresistanceparameterautomaticallydecouplestheimmersiondepthandremeltingratecontrolloopswhichareotherwisecross-influencingeachother.AlsoforESRitcanbestatedthatALDsa

15、utomaticmeltcontrolsystem(AMC)isunsurpassedintheworldforitsinherentfeatures,easeofoperationandlastbutnotleastitsaccuracyandrepeatabilityofcontrol,producingingotswithexcellentproperties,including:sHomogeneous,soundanddirectionallysolidifiedstructure;sHighdegreeofcleanliness;sFreeofinternalflaws(e.g.h

16、ydrogenflakes);sFreeofmacro-segregation;sSmoothingotsurfaceresultinginahighingotyield.ElectroslagRemeltingofHeavyForgingIngots165tonESRfurnaceAttheendofthe1960s,theconceptofusingESRplantstomanufacturelargeforgingingotsgainedacceptance.Increasingdemandforlargerelectricalpowergeneratingunitsrequiredfo

17、rgingingotsweighing100tonsormoreformanufacturingofgeneratorandturbineshafts.ALDslargestESR26ESRfurnace,commissionedintheearly1970s,allowstomanufactureingotsof2,300mmdiameterand5,000mmlengthweighingupto165tons.Thefurnaceoperateswithingotwithdrawalemployingfourconsumableelectrodesremeltedsimultaneousl

18、yinthelargediametermoldandreplacingtheconsumedelectrodeswithsubsequentonesandasmanyasnecessarytoproducethedesiredingotweight.165tonESRingot,2,300mmdiameterx5,000mmlongDirectionalsolidificationmustbeensuredovertheentireingotcross-sectionandlengthtoavoidinteriordefects,suchasmacrosegregation,shrinkage

19、cavitiesandnonuniformdistributionofinclusions.Bymaintainingthecorrectremeltingrateandslagtemperature,directionalsolidificationcanbeachievedforingotdiametersaslargeas2,300mm.Accordingly,theESRingotisfreefrommacro-segregationinspiteofthelargediameter.ThecleanlinessandhomogeneityofESRingotsresultinexce

20、llentmechanicalpropertiesascomparedtoconventionallycaststeelingots.ProcessVariationsThreeESRprocessvariationshavebeendevelopedbyALD:sRemeltingunderincreasedpressure(PESR);sRemeltingunderinertgasatmosphere(IESR);sRemeltingunderreducedpressure(VAC-ESR).PressureElectroslagRemelting(PESR)Overthepast30ye

21、ars,nitrogenhasbecomeincreasinglyattractiveasaninexpensivealloyingelementforenhancingthepropertiesofsteel.Inausteniticsteel,nitrogen,particularlyindissolvedform,increasesyieldstrengthbyformingasuper-saturatedsolidsolution.Withferriticsteelgrades,theaimistoachieveafinedispersionofnitridescomparableto

22、themicrostructureobtainedbyquenchingandtemperingiron-carbonalloys.Fortheproductionofthesenewmaterials,itisessentialthatasufficientlyhighamountofnitrogenabovethesolubilitylimitundernormalpressureisintroducedintothemoltensteelandthatnitrogenlossispreventedduringsolidification.Asthesolubilityofnitrogen

23、isproportionaltothesquarerootofitspartialpressure,itispossibletointroducelargeamountsofnitrogenintothemeltandallowittosolidifyunderhigherpressure.Thishasbeenverifiedbytheelectroslagremeltingprocessatanoperatingpressureof42bar.Duetotheextremelyshortdwelltimeofthemetaldropletsintheliquidphaseduringrem

24、elting,thenitrogenpick-upviathegasESR2791011ESR#phaseisinsufficient.Thenitrogenmust,therefore,besuppliedcontinuouslyduringremeltingintheformofsolidnitrogenbearingadditives.Thehighpressureinthesystemservesexclusivelytoretainthenitrogenintroducedintothemoltensteel.Thepressureleveldependsonthecompositi

25、onofthealloyandonthedesirednitrogencontentoftheremeltedingot.RemeltingunderInertGasAtmosphere(IESR)AsaconsequenceofALDsdevelopmentworkinPESRprocessing,ALDnowadaysrecommendstoconducttheESRprocessunderafullyenclosedinertgasatmosphereatatmosphericpressure.ThisisagreatstepforwardinfreeingtheESRprocessfr

26、omhydrogenpick-upproblemandtheinfluenceofseasonalatmosphericchanges.Inadditionitallowsremeltingunderoxygen-freeinertgas.Thefollowingresultshavebeenobtained:sOxidationofelectrodeandslagiscompletelyavoided;sOxidizinglossofelementssuchasTi,Zr,Al,Si,etc.isalmostcompletelyavoided.Thisisespeciallyimportan

27、twhenremeltinghighAlandTi-containingalloys,likesuperalloyswithverynarrowanalyticalranges;sBettercleanlinessintheingotisachieved;sWhenusingargonastheinertgas,pickupofnitrogenandhydrogenisavoided;(Whenusingnitrogenastheinertgas,somepick-upofnitrogenispossible.)Duetotheabsenceofoxygeninthefurnaceatmosp

28、here,desulfurizationviathegasphaseisnolongeroptimal.However,sulfuristodaytakencareofbyladlemetallurgyinthemakingofsteelelectrodes.Twofurnaceconceptsareavailable,onewithaprotectivehoodsystemofrelativetightness,theotherwithafullyvacuum-tightprotectivehoodsystemthatallowsthecompleteexchangeofairagainst

29、aninertgasatmospherepriortostartingtheremeltingprocess.1413SchematicofIESRfurnace1Electrodefeeddrivesystem2Ballscrew3Pivotablefurnacesupportgantry4Loadcellsystem5Electroderam6Electrodestub7Protectivegaschamber8Slagpool9Ingot10 Moldassembly11 Highcurrentcontactassembly12 Powercables13 Ramguidingsyste

30、m14 Maintenanceplatforms91011ESR2833ESRfurnacewithretractablebaseplateforingotwithdrawal1 Electrodedrivesystem2 Loadcellsystem3 Ballscrews4 Bustubes5 Moldassembly6 Ingot7 Slidingcontacts8 Electrode9 X-YadjustmentElectroslagRemeltingunderVacuum(VAC-ESR)Electroslagremeltingundervacuumisanothernewlydev

31、elopedprocess.RemeltingiscarriedoutundervacuumasinVAR,however,usingaslag.Problemsofoxidationofthemeltdonotarise.Inaddition,dissolvedgasessuchashydrogenandnitrogen,canberemovedandthedangerofwhitespots,asencounteredduringVAR,isreducedtoaminimum.Thus,theadvantagesofboth8ESRandVARarecombinedinoneprocess

32、.Thatisofinterestforsuperalloysortitaniumremelting.FurnaceTypesALDhasdevelopedfivebasicESRfurnaceconcepts:PilotSystemsforstationaryandmovingmoldapplications.Theseareparticularlywell-suitedforexperimentalandpilotproduction,andfortheperformanceofhigh-versatilityESRoperationatlowinvestmentcost.Stationa

33、ryMoldSystemswithtwofixedremeltingstationsandonepivotingfurnacehead.Theseareparticularlysuitedforefficientproductionathighproductionrates.IngotWithdrawalSystemswithcentralingotwithdrawalstationandelectrodeexchangecapability,andtwoouterstationsforremeltinginstationarymolds.Thecentralstationisparticul

34、arlysuitedforremeltingoflargediameteringots.Smallerdiameteringotsmayberemeltedsimultaneouslyintheouterstations.AtmosphericProtectionSystemsforstationarymoldapplicationwithclosedfurnacehoodsystemtoremeltunderinertgasatmosphere.ThesesystemsareparticularlyrecommendedwhenremeltingTi,Alandrare-earthconta

35、iningalloysoralloyswithlowAlcontent(0.005).3ESR29SchematicofPESRfurnacewithstationarymold1Ramdrivesystem,2Electroderam,3X-Yadjustment,4Loadcellsystem,5Slidingcontact,6Pivotingdrive,7Electrode,8Waterjacket,9BaseplatePressurized/VacuumSystemsCompletelysealedsystemsforESRoperationsundervacuum,inertgas,

36、orincreasedpressure.ThesesystemsareparticularlysuitedforproducingESRingotswithhighcontentsofnitrogenorreactiveelements.ESRFeatures:SIngotweightsfrom100kgto165metrictons;SAlternatingcurrentasremeltingenergywithmeltingcurrentsfrom3kAto92kA;SIngotdiametersfrom170mmto2,300mm,dependingonmaterialbeingreme

37、lted;SCircular,squareandrectangularingotshapesarepossible;SALDofferssystemsforspecialprocessessuchasremeltingunderpressure,protectivegasorvacuum.Agrowingmarketshareisanticipatedfortheseprocesses,especiallytheIESRprocessunderinertgasatmosphere.ESRApplications:SToolsteelsformillingcutters,mining,etc.;SDiesteelsfortheglass,plasticsandautomotiveindustries;SBall-bearingsteels;SSteelsforturbineandgeneratorshafts;SSuperalloysforaerospaceandpowerturbines;SNickel-basealloysforthechemicalindustry;SColdrolls.