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

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