材料成型及控制工程专业外文翻译基本挤压冶炼和铸造的根源.docx
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材料成型及控制工程专业外文翻译基本挤压冶炼和铸造的根源
外文原文:
TheUltimateExtrusionScrapRemeltandCastingCenter
Preparedby一RogerA.P.Fielding一BENCHMARKS
GeorgeE,Macey一MaceyheatTransferAssociates
D.HughBarnard一AluminiumIndustryConsulting
ABSTRACT一Recentadvancesinscrapprocessing,melting,metaltreatment,and
castingtechnologieshaveamajorimpactontheeconomicsofrecyclingaluminum
extrusionscrap.Technologiesthatpermitrapidcharging,melting,andmeltpreparation,
arecombinedwithprocessesthatremovepotentialpollutantsandparticulates,refinethe
melt,andcastuniformingotstructures.Theresultingfacilityiscapableofproducingawide
rangeofalloysandingotsizeswithminimuminventorylevelswhileoperatingathighlevels
ofproductivityandenergyefficiency.Thefacilityisintrinsicallysafetooperateandmeets
allcurrentandnear-termenvironmentalstandards.
INTRODUCTION
TheSourceofAluminumExtrusionScrap
Aluminumextrusionscrapcomprisesrejectincominglogandbillet,logandbillet(andpart-billets)rejectedordamagedduringorafterthepre-heatfurnace,part-billetsandbilletswithdrawnfromtheextrusionpress,buttendsofbilletrecoveredfromthepressshear,andlumpsofaluminumrecoveredfromtheextrusiondie.Afterextrusionfromthedie,somescraplengths-usuallythefrontendsoftheextrudate-arecollectedattherough-cutsaw,andsome(inthesameareaofthepressinstallation)asback-endsamples.Iftherearesignificantdifferencesinrod-length(thelengthoftheextrudateemergingfrommulti-holedies,)extrudedscraplengthsmustbecollectedfromthepressrun-outtable.Unevenextrusionlengths-whichcanstillbeseeninsomeextrusionoperations-oftenhavetobecutoffatthestretchertailstock;althoughsomedesignsofstretcherallowforstretchingwiththeexcesslengthstillinplace.
Theexcessextrudateknownasstretcherscrapcomprisingfrontandback-endsoftheextrudate
whichhasbeendamagedatthestretcher,isremovedatthefinish-cutsaw.Alsoremovedare
thetransverseweldfromtheextrusionofsuccessivebilletsintoasinglelengthattherun-out,
andthetransverseweldallowance,whichismuchlongerandmustoftenberemovedfromthe
productionofhollowextrusions.
Althoughcommonalloy(AA6xxx)scrapgeneratedattheextrusionpressshouldbenomore
than10percentofthelogorbilletdeliveredtotheextrusionpress,itisnotunusualtofindthatpressscrapiscloserto25percentduetoacombinationoftheeventslistedabove.Ifonlybecauseoftherequirementtoleavealargerbutt(therebyensuringthatextrusionswhichmightbesubjecttocoringarenotextruded),thescrapgeneratedwhenextrudingmediumandhardalloyswilltheoreticallybegreaterthanthatfromAA6xxxoperations.
Fromtheabove.itisevidentthatthescrapaluminumgeneratedinatypicalextrusionplantcanbedividedintofivedistinctfamilies:
1)Theheavylogsandbillet-eachpieceofwhichisthedensityofaluminum.
2)Heavybuttswhich,becauseeachisdistortedduringtheshearingoperation,aresomewhatlessden
3)Extrudedlengths,rangingfromstretcherscraptorejectedfulllengths,which,whenbundled,
areabout10percentoftheoreticaldensity.seinbulkthanthealuminummetal.
4)Assortedpiecesofextrusions,usuallytransportedinboxeswhich,dependingonwhere
theyaregenerated,canhaveadensityofmorethan10percent.
5)Thesawchips-eitherlooseorcompressedintobricksofvarioussizes-whichmustbe
collectedbeforetheextrusionpressatthelogsaw(s),oraftertheextrusionpressattherough-cutsaw,wherechipsaredepositedalongthepressrun-out,atthefinish-cutsaw,andatany
downstreamcut-to-lengthorfabricatingoperations
TheConversionofAluminumExtrusionScrapIntoPrimeIngot
Aluminumextrusionscrapisconvertedintoprimeingotbymelting,treating(cleaning),casting
intologs,andhomogenizing.Theprocessitselfgeneratesadditionalscrapintheformofaluminumoxides(dross),liquidmetalspills,metaltrappedinfilters,headandbuttscrap,scraplogs,andsawchips.
Thecostoftheconversionprocessismadeupofthecostofthecapitalemployedintheremeltandcastingplant,thecostofmetallost(oxidized)duringmelting,thecostoftheenergyrequiredinthemeltingprocess,thecostofalloymaterials,thecostofalllaboremployedintheplant,thecostofthemaintenanceoffurnacesandotherproductionequipment,thecostofeffluenttreatmentfacilities(includingthecostandtreatmentofwaterrequiredinthecastingprocess),andtheadditionalcosts(overandabovelabor)ofhandlingthealuminumandalloyingmaterialsinalltheirforms.
Incompleteunderstandingoftheremeltandcastingprocessasitisappliedtothescrapfrom
aluminumextrusionoperations,andtheimpactoftheprocessequipment-anditsoperationonthecostofconvertingscraptoprimebillet,resultsinanextraordinaryrangeofconversioncostsforwhatisactuallyarelativelysimpleoperation.Butitisnotonlyconversioncoststhatsufferfromlackofunderstandingoftheprocessesandtechnologiesinvolved.
Thequalityofbilletproducedvariessignificantlybetweenremeltandcastingoperationsostensiblydesignedtodothesamejob.Andtheenvironmentalimpactoftheprocessesusedrange
fromthebenigntotheunacceptable.
EstablishingGoals
Thegoaloftheultimatealuminumextrusionscrapremeltandcastingcenteristoconvertall
formsofaluminumextrusionscraptobilletequivalentqualityandprime(smelter)materialat
minimaltotalcost,withminimalimpactontheenvironment.
TheQualityofPrime(Smelter)Billet.Attheriskofstatingtheobvious:
notallsmelter-billetiscreatedequal.Aluminumlogcastfromsmeltermetalcontainsimpuritiesthataffectthe
performanceoftheextrudedproduct.Thecastingprocesses-whichvaryfromsmeltertosmelter-canresultintheproductionofcaststructureswhichvarysufficientlysuchthattheycanbedetectedattheextrusionpress.And,homogenizingfacilities(andtheiroperation),althoughostensiblythesame,alsovaryfromsmeltertosmelter,againproducingvariationsthatcanbedetectedattheextrusionpress.
Recycledaluminumscrap,orforthatmatterre-meltedingotoriginatingatasmelter,canbe
processedintheultimateremeltandcastingcenter.Thiscanbeachievedatconversioncoststhatarelowerthanthetraditionalsmelterpremiumtoproduceextrusionlogandbilletindistinguishablefromprime-providedthatalloycompositionismaintained.Obviously,sortingandsegregationoftheincomingscrapfeed-stockisessentialifthequalityoftheremeltedandcastproductistobemaintained.
DefiningTheIssues
Theissuesaffectingtheefficientoperationofanaluminumextrusionscrapremeltandcasting
centercanbeclearlystatedasfollows:
1)Segregatingmixedscrap
2)Processingcontaminatedscrap
3)Maximizingtherecoveryofmetalunits
4)Maximizingenergy(fuel)efficiency
5)Maximizingproductmix:
alloy,compositior
anddiameter
6)Maximizingutilizationofequipment
7)Maximizinglaborproductivity
8)Maintainingcontrolofquality.
Eachoftheissuescanbeaaaressea
1)Separatelyasfollows:
1)SegregatingMixedScrap.Scraparisingtheremeltandcastingcenter,whichislimitedmetalrecoveredfromdross,theoccasionalog,thetopsandtailsoflogs,sawchipsanoff-compositionmaterial,issegregatedandrecvcledasappropriate.
Scrapfromextrusionplant"customers"isroutinelysegregatedattheextrusionpressandthefinish-cutsaw,asisthescraparisinginfinishingandfabricatingoperations.
Otheraluminumscrap,whichispricedlowerthanthemillscraplistedabovebecauseoritsconditionanddubiousorigin,mustbesorted.Obviously,thepurchasepricewillhaveretlecteathecostsinvolvedinsortingthisscrap.Whatevercanberecoveredisaddedtothosealloyshavinghighertolerancetocompositionalvariation._.’balancemustbedowngraded,andrejectedrorsecondaryuses.
2)ProcessingContaminatedScrap.Aluminumextrusionscrapcanbecontaminatedwithwaterandwithoil,whichismixedwithsawchipsandisusedtoprotectbrightfinishes;scrapcanalsobecontaminatedwithpaintsandlacquers,thermalbreakmaterials,otherplastics,rubber,and,inthecaseoffabricatedcomponents,withrivetsandotherfastenersmadefrommanydifferentmaterials.Allthesematerialsmustberemovedand/orseparatedfromthealuminumbeforeitismelted.
Manvattemptshavebeenmadetoprocessthiscontaminatedmaterialinthemeltingfurnace,combiningtheprocessesofde-contamination,separationandmelting.Theyhavenotbeensuccessful.Thesolutionsincludeplacingthecontaminatedmaterialonanextendedfurnacehearthandallowingthecontaminantstoburn-offpriortocharging.Anothersolutionistousedualormulti-chamberfurnacesthatcontain,andattempttore-circulate,theburningeffluentstorecoversomeoftheenergyreleased,addingittothatrequiredtomeltthescrapcharge.
Whilethecapitalcostofthesesolutionsishigh,theenergyefficiencyofeachisrelativelylow.Allrequireextensiveeffluenttreatmentfacilitiesiftheyaretomeeteventheleaststringentenvironmentalregulations.Thisisbecausethelargevolumesofcombustionproducts(andunburntvolatilematerials),releasedattheinstantthechargeentersthefurnace,arerapidlycarriedfromthefurnacetowardstheeffluenttreatmentsystems.Incinerators,coolersandbag-housesmustbesizedtoaccommodatethemaximumflowrates.
ThereisabetterwaylContaminatedscrapcanbetreatedcontinuously,beforeitischargedintothefurnace,atinstantaneousratesthatareafractionofthecommonchargerates.Forexample,anefficientfurnace-char