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Production

By Betty Pierce,2014-07-24 01:46
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ProductionProduc

    Production

August2008m,?

    ;Spec~lReview

    ;Productiontechniqueofvermicular

    ;flraphiteironcylinderheadofvehicleI1icI

    ;dieseIengine,_

    ;*ZhouGen’andLiuWanhua

    ;(1.WuxiDieselEngineWorks,ChinaFirstAutomobileGroupCo.Ltd.,Wuxi214026,China;2.WuxiFAWFoundryCo.Ltd.

    ;ChinaFirstAutomobileGroupCo.Ltd..Wuxi214026,China)

    ;Abstract:The25years’productionandapplicationhaveprovedthatvermiculargraphiteironcylinderheadswith

    ;vermicularity?50%satisfythemachinabilityandperformancedemandofdieselengine.Themethod,inwhich

    ;usingcupola-inductionfurnaceduplexmeltingandpour-overprocesswithrareearth

    -ferrosiliconorrareearth-

    ;siliconcompoundasvermicularizingalloyplusrareearthmagnesium-ferrosiliconassti

    rringalloy,jsanoptimal

    ;vermicularizingprocessforobtainingsatisfiedvermicularity.Usingtopkissrisers,enlargi

    ngkissingareasand

    ;expandingcoveringwidthandmakingingatestofreezeearlieraretheeffectivemeasurestoeliminateshrinkage,

    ;blowholeandoxideinclusionsinthevermiculargraphitejroncylinderheads. ;Keywords:vermicularcastiron;cylinderhead;meltingandtreatingprocess;castingmethod

    ;CLCnumber:TG143.49Documentcode:AArticleID:16726421(2008)03153

    O9

    ;I

    ;produce6110modeldiesel

    ;enginefor’Jiefang’brand

    ;trucksproducedbyChina

    ;FirstAutomobileWorks.

    ;Theenginehas6cylinders

    ;withoveralldimensionof

    ;871i/lnlx240mnlx110

    ;mnl,mainwallthicknessof

    ;5.5mmandweightOf80

    ;kg(seethephotoofFig.1).

    ;Theoriginaldesignofthe

    ;cylinderheadwaschosen

;alloyedgreyirongrade

    ;250materia1.However,Fig.1Castingof6110vermiculargraphiteironcylinderhead

    ;theearlytrialapplicationhadshowedthattheareas ;connectingintakeandexhaustvalveseatswereproneto ;cracking.Therefore,basedonourexperienceinapplication ;ofvermiculargraphiteironcylinderheadsinmediumspeed, ;heavydutydieselengine,itwasdecidedtochangethegrey ;irontovermiculargraphiteironforthecylinderhead.Asa ;result,themechanicalpropertiesandthermalfadgueproperties ;ofthecylinderheadswereobviouslyincreased;notonlythe ;crackingproblemwassolved,buttheperformanceofthe ;Male,bornin1937,seniorengineer.Researchinterests:nodular ;ironandvermicularironproductionandapplication. ;Email:zhougen@fawfc.com

    ;Received:2008-06-25;Accepted:2008-07-15

    ;enginewasimprovedaswel1.Atthesametime,theworking ;lifeoftheenginewasalsoprolonged.Inaddition,withthe ;improvedproperties,itispossibletofurtherincreasethe ;enginepowerbyintensifyingmeasures.Forabovereason,the ;vermiculargraphiteironheadwassoonputintolargemass ;production.Over25years,theevaluationsforthevermicular ;graphiteironcylinderheadfromboththeenginedesignerand ;usershavebeenalwaysverysatisfactory.However,foraquite ;longtime,itsscraprateduringproductionprocesswasquite ;high,20%-25%.Withcontinuousprocessimprovement,the ;scraprateissignificantlydecreasedto5%-7%inrecent10 ;years.

    ;Thispaperdescribestheproductiontechniqueofthistypeof ;cylinderhead.

    ;153

    ;

    ;154

    ;1Meltingandtreatingprocessof

    ;vermicularcastiron

    ;1.1Selectionofvermicularitycontrollimit

    ;Intheearly1980s,whenwebeganthetrialproductionof6110 ;vermiculargraphiteironcylinderhead,therewasnoChinese ;NationalStandardofVermicularGraphiteIronyet.Wetook ;vermicularity(theratioofvermiculargraphiteareaintotal ;graphitearea)?50%(nodularity0-50%)asacontrollimitof

    ;vermicularity,basedonthefollowingconsiderations: ;(1)Aspreviousexperienceshaveindicated,themechanical ;propertiesandthermalfatiguepropertiesofcylinderheads ;withvermicularity?50%aresufficient.andevenexceedthe

    ;requirementoftheengineworkingconditions. ;Vo1.5No.3

    ;(2)Productionshowedthatthereisacertainrelationship ;betweenthevermicularityandferritecontent:thehigherthe ;vermicularity,thehighertheferritecontent.Highvermicularity ;causesevenfullferritematrixwhichisunfavorablefor ;machining.Inordertoobtaingoodmachinabilityforthecastings

    promotingelements,itisnecessaryto ;withoutusingpearlite

    ;keepacertainamountofpearliteinthematrixoftheiron. ;]_hereforeitisnotwishedtohavetoohighvermicularity. ;(3)Properlylowervermicularitylimitisrelatively ;convenientformetallurgicalcontro1.

    ;Someyearslater.theVermicularCastIronStandardof ;ChineseMinistryofMachineryIndustrywaspublished.Inthe ;standard.thatthevermicularityisspecified?50%asshown

    ;inTable1.

    ;Table1Gradeclassifica…

    ;tionofvermiculargraphiteirons(StandardofChineseministryofMachineryIndustry

    ;JB/T4403-19991J1

    ;Grade

    ;420

    ;380

    ;340

    ;300

    ;260

    ;Tensilestrength

    ;MPa

    ;?420

    ;?380

    ;?340

    ;?300

    ;?260

    ;Yieldstrength

    ;MPa

    ;?335

    ;?300

    ;?270

    ;?240

    ;?195

    ;Elongation

    ;%

    ;?0.75

    ;?0.75

    ;?1.0

;?1.5

    ;?3

    ;AccordingtothisStandard,weadoptedvermiculargraphite ;irongrade300asthematerialforthe6110cylinderhead.The ;Standardrequiresthetensilestrengthatroomtemperature ;?300MPa.Theactualtensilestrengthdataobtainedin

    ;productionfor6110cylinderheadsisintherangeof350

    ;450MPa.The25years’practicalapplicationhasprovedthat

    ;therearenocrackingordeformationproblemshappenedin ;thecylinderheads.Inaddition.inthemiddleof1990s.by ;somepowerintensifyingmeasuressuchasextendingthe ;pistonstrokeandchangingtheworkingparametersofthe ;engine,thepowerofthe6110enginewasincreasedfrom ;original140hpto200hp.Thesamevermiculargraphite ;ironcylinderheadwithoutanystructuralreinforcementstill ;meetstheperformancedemandfortheintensifiedengine. ;Basedonabovefacts,theauthorsagreewiththeviewpoint ;ofreference21thatthebestmechanicalandthermalfatigue ;propertiescanbeobtainedforverrnicularity?50%.therefore

    ;thecontrollimitofvermicularityspecifiedinVermicular ;GraphiteIronStandardofChinesMinistryofMachinery ;Industryisapropercontrollimit.Forthisvermicularity, ;itsmachinabiltyandapplicationperformancearegoodand ;metallurgicalcontrolisconvenient.

    ;1.2Vermicularizingprocessesforcupola

    ;melting

    ;Before1998,thecylinderheadwasproducedintheold ;foundryoftheworks.Thebaseironwasmeltedintwocupolas ;withfixedspout.Thechemicalcompositionofthebaseiron ;wasasfollows(wt.%):3.53.8C,1.5-1.8Si,0.40.7Mn,

    ;?0.07P.?0.08S.

    ;Threetypesofvermicularizingtreatmentswereutilized ;Hardness

    ;BHN

    ;200280

    ;193274

    ;17_249

    ;140_217

    ;121197

    ;Vermicularity

    ;%

    ;?50

    ;Matrixstructure

    ;Pearlite

;Pearlite

    ;Pearlite+ferrite

    ;Pearlite+ferrite

    ;Ferrite

    ;successively:

    ;(1)VermicularizingwithaddingRESiFealloyonspoutof ;cupola

    ;From1961tO1965.inordertoutilizefullytheabundant ;rareearthresourcesofourcountry,withthecooperationof ;TheCentralLaboratoryofBaotouIron&SteelCo.Ltd..the ;biggestrareearthalloyproducerinChina,wecarriedout ;aprojectonutilizingrareearthferrosilicon(RESiFe)alloy ;toproducenodulariron.Theresultrevealedthatrareearth ;elementshaveonlyaveryweaknodularizingeffect.Inmost ;ofthecases.treatingironmeltwithRESiFealloy.vermicular ;graphiteisobtainedmoreoftenthannodulargraphitejJ.For

    ;thisreason.itwasquitenaturalthattheRESiFealloywas ;usedasvermicularizingalloyatfirst.Thecompositionofthe ;alloyusedforthe6110cylinderheadwasasfollows(wt%1: ;RE:2730,Si:4050,(Ba+Ca)<5,balanceFe.Thegrain

    ;sizeofthealloywas2-5mm.TheRESiFealloywasadded ;uniformlyintotheironstreamonspoutofcupola.theaddition ;was1.6%1.7%oftheweightoftreatedironmelt.

    ;Asrareearthhasrelativelyweaknodularizingeffecton ;graphite,itscontentvariationhasnosignificantinfluence ;onvermicuylarity;thereforethecontrolrangeofrareearth ;contentforobtainingaspecificvermicularityisrelatively ;wide.However,sincetheboilingtemperatureoftherareearth ;ismuchhigherthanthetemperatureofironmelt.theraree ;intheironmeltwil1notboi1andhavenostirringeffectitself. ;Therefore,whenusingrareearthasvermicularizingalloy,the ;temperatureofironmeltmustbehighenough,andthealloy ;mustbeaddedintotheironstreamonspoutofcupola.In ;addition.itisnecessarytostirtheironmelttoensurethealloy ;thoroughlydissolvedtoimproverecoveryofrareearth. ;

    ;August2008

    ;Ferrosiliconwasusedasinoculant,addedonspoutjustafter ;additionoftheRESiFealloy.

    ;Incaseofvermicularizingtreatmentfailure,following ;correctivemeasurescouldbeused:

    ;(a)Ifthetreatmentresultsincertainflakegraphite,aproper ;amountofRESiFealloycanbereaddedintothemeltandre

    ;stirringit.

    ;(b)Ifthetreatmentresultsinhighnodularity,itispossible ;toimprovethevermicularitybyretappingproperamountof

    ;baseironintothetreatedmelt.

    ;Thesetwocorrectivemeasurescouldbeusedforall ;vermicularizingprocessesdescribedinthispaper,aslongas ;thetemperatureofthetreatedmeltishighenough.However, ;practicalexperienceshowedthatthesecondmeasuremay ;causeflakegraphiteformation.Forthisreason,itispreferred ;toaddaslessalloyaspossibleatfirst,Then,ifitisnecessary, ;readdaproperamountofthealloytocorrecttheironmelt. ;Statisticsshowedthat,withusingthisvermicularizing ;processforcupolameltediron.morethan96%oftreatments ;obtainvermicularity?50%:therareearthcontentforthe

    ;vermicularityis0.06%-0.14%,

    ;However,thisprocesshasfollowingshortages:

    ;(a)Thechilltendencyofthemeltisratherhigh.The ;chilltendencycanbereducedbyusingso—called’floating

    ;ferrosiliconinoculation’,i.e.addingcertainlumpyferrosilicon

    ;of30-50mmsizeontothemeltsurfaceintheladle.The ;lumpyferrosiliconwillfloatonthemeltsurface,gradually, ;layerbylayerbemeltedandmixedwithironandflowinto ;mouldcavityduringpouringprocess,thereforeactasinstant ;inoculation.However,thisinoculationprocessoftencauses ;toohighfinalsiliconleadingtographitefloatation.Inorder ;toavoidtoohighfinalsiliconandalsoreducechilltendency, ;streaminoculationwasted,Nevertheless.thegraphitecount ;wastoohighandtheshrinkagetendencyobviouslyincreased, ;Forthisreason,streaminoculationwasneverbeenusedfor ;bothnodularironandvermiculargraphiteiron.

    ;(b)Strenuousmanualstirringhastobeoperatedduring ;vermicularizingtreatment;insufficientstirringwillresultin ;vermicularizingfailure,i.e.flakegraphitewillbeobtainedin ;theiron.

    ;(c)Theadditionofthevermicularizingalloyisratherhigh ;causingalargeamountofslag,temperaturedropandlow ;fluidityofthemelt.

    ;(d)SincetheRESiFealloymustbeaddedintotheiron ;streamonspoutofcupola,thisprocessisnotsuitablefor ;inductionfurnaceorcupolawithrotaryforehearth. ;(2)VermicularizingprocesswithaddingRESicompound

    ;onspoutofcupola

    ;Comparedwiththerareearthferrosiliconalloyproduced ;withtraditionalsilicothermicreductionprocess,therare ;earth-silicon(IESi)compoundproducedwiththeonestep

    ;carbothermicreductionprocesshasrelativelyhigherrareearth ;contentandlowerdetrimentalimpurities(wt,%:Ti<0.25. ;P<0.02,S<0.02.Therefore,itisabettervermicularizing ;alloycomparedtotheRESiFealloy.

    siliconcompoundweused ;Thecompositionoftherareearth

    ;iS(wt,%):IE:2933,Si:49_55,(Ba+Ca)<5,Febalance. ;Thevermicularizingprocesswasthesameasthatfor

    Sicompoundwas1.2% ;RESiFealloy.TheadditionofRE

    ;1.4%.

    ;Statisticsshowedthat,whenusingthisvermicularizing ;process.morethan97%oftreatmentsobtainvermicularity ;?50%:therareearthcontentforthevermicularityis0.05%

    ;0.12%.neartothatforRESiFe.

    ;Thechilltendencyofthevermiculargraphiteironproduced ;withtheRESicompoundismuchlowerthanthatproduced ;withRESiFealloyduetofollowingreasons:

    ;(a)Amongalltherareearthelements,Cehasthestrongest ;nodularizingeffect,andLahasthebestvermicularizingeffect. ;TheCeaccountsfor46%50%ofthetotalIEintheRESi

    ;compound.whichis2%lowerthanthatintheRESiFle:theLa ;accountsfor35%-38%ofthetotalIinISicompound.is ;10%higherthanthatintheRESiFle.Therefore,usingtheRE

    ;Sicompounditispossibletoobtainbettervermicularizing ;effect.Forthisreason.theresidualREforobtaining ;satisfactoryvermicularizingeffectcanbereduced,andthe ;additionofRESicompoundcanbealsodecreased,

    ;fbAmongalltherareearthelements,Lahasthelowest ;chilltendency,Cehasthestrongestchilltendency.Since ;theLacontentinISicompoundismuchhigherthanthat ;inRESiFealloy.thechilltendencyoftheirontreatedwith ;theRESicompoundisobviouslylowerthanthatoftheiron ;treatedwithRESiFealloy.

    ;fc1ThesiliconcontentintheRESicompoundweusedis

    ;quitehigh,andmoreover,theanalysiswithelectronicprobe ;showedthatmostofthesiliconexistsasfreephase;therefore ;theinoculationeflfectoftheISicompoundisstrongerthan ;tllatOfRESiFealloy.

    ;However,whenusingthisvermicularizingprocess,manual ;stitringtheironmeltisstillnecessary,

    ;(3)PouroververmicularizingprocesswithREMgSiFealloy ;During19951996,inordertoeliminatestrenuousmanual ;stirringoperationandreducetheadditionoftheREbased

    ;vermicularizingalloy.thusreducechilltendencyandeliminate ;possiblegraphitefloatation,wedevelopedapourover

    ;vermicularizingprocesswithrareearthmagnesiumferrosilicon ;(REMgSiFe)asvermicularizingalloy.Thisprocesswas ;basedontheconsiderationthatmagnesiumhasstrongstirring ;effect,andrareearthcontentrangeforobtainingsatisfied ;vermicularityisrelativelywide.Therefore,byusingREMgSiFe ;asvermicularizingalloy,itwouldbepossibletoutilizeboth ;thestirringeffectofmagnesiumandthevermicularizing ;effectOfrareearth.Ofcourse.themagnesiumcontentof ;thealloyshouldberestrictedcloselytopreventnodular ;graphiteformation.Afteraseriesofexperiments,following ;vermicularizingalloywaschosen(wt.%):3.O-3.5Mg,12_13RE, ;38-45Si,2-3Ca,Febalance,grainsize1o-20inln.Theaddition ;was1-3%1.4%forthebaseironwitll0.05%-0.08%sulphur. ;Thepouroverprocesswasusedforvermicularizingtreatment. ;TheREMgSiFealloywasputintoapocketinonesideOftlle ;bOttOmOftlleladleaJ1dcOveredwitll0-.3%OfferrOsilicOn ;pOwderdependingOntlletemperatureOftlleirOnmelt. ;155

    ;

    ;——?CHINAFOUNDRY

    ;156

    ;Theapplicationresultsofthisprocessshowedthatthe ;chilltendencyofthevermiculargraphiteironwasobviously ;reduced.Keepingtheresidualmagnesiumcontentlessthan ;0.028%.theproperresidualREcontentrangeforobtaining ;vermicularity?50%isof0.045%0.082%.Aslongas

    ;magnesiumcontentandREcontentarenotbothattheupper ;limitorlowerlimitatthesametime,itisalwayspossibleto ;obtainsatisfactoryvermicularity.

    ;Comparedwiththeformertwotreatmentmethods,this ;vermiculafizingprocesshasfollowingadvantages: ;(a)Thefluidityofthevermiculargraphiteironisobviously ;improved,whichisveryfavorableforthethinwallcylinder ;head:

    ;(b)Manualstirringoperationiseliminated,andtheinfluence ;ofstirringoperationonthevermicularizingisavoided. ;(c)Chilltendencyofthetreatedironissignificantlyreduced, ;thustheinoculationwithfloatingferrosiliconcanbeeliminated ;andgraphitefloatationisavoided.

    ;However,comparedwiththeformertwoprocesses,this ;processhasfollowingdisadvantages:

    ;(a)Thevariationofvermicularityisrelativelyhigher; ;therefore,themeltingandtreatmentprocessshouldbemore ;closelycontrolled;

    ;(b)Shrinkagetendencyofthetreatedironisrelatively ;higher,especiallywhentheresidualmagnesiumcontentisat ;theupperlimit.

    ;1.3Vermicularizingprocesswithcupola-

    ;inductionfurnaceduplexmelting

    ;InSeptemberof1998,ournewfoundrywasputinto

    ;production;allcastingproductionwasmovedfromoldfoundry ;tothenewfoundry.Sincethen,cupolainductionfurnace

    ;duplexmeltingandautomaticpouringwithMECANApouring ;machinehavebeenusedforcastingproduction.Considering ;thattheinductionfurnacehasnofixedspoutforadditionof ;RESiFealloy,andvermicularitycontrolbypour-overprocess ;usingREMgSiFealloyisratherdifficult,allabovethree ;vermicularizingprocessesarenotsuitableforthenewmelting ;andpouringprocess.Inordertotaketheadvantagesofabove ;processesandavoidtheirdisadvantages,wedecidedtouse ;pouroververmicularizingprocesswithRESiFealloy(or

    Sicompound)asvermicularingalloyandREMgSiFe ;RE

    ;alloy(6.5%7.5%Mgand2%3%RE)asstirringalloy.In

    ;thisprocess,theREMgSiFealloywillstiritself,butmore ;importantlystirtheRESiFealloyaswel1.Thisiswhyth?

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