外文翻译连铸的发展.docx

外文翻译连铸的发展.docx

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外文翻译连铸的发展

TheDevelopmentofContinuousCasting

【连铸】——中英文对照

ContinuousCasting

FromtheMaking,ShapingandTreatingofSteelbyWilliam，McGraw—HillCompanies,Inc.,2002

TheDevelopmentofContinuousCasting

ContinuouscastingwasdevelopedveryrapidlyaftertheSecondWorldWar.Steel-producersarctodaygenerallyconvincedthatcontinuouscastingisatleastaseconomicalasingotproductionandcanmatchthequalityofthelatteracrossmuchoftheproductionspectrumforhigh-qualitysteels.Continualdevelopmentofthetechniqueaimedatimprovedsteelcharacteristicsisleadingtoincreasingadoptionoftheprocessinworksproducingspecialhigh-gradesteels.Thereasonsforcontinuous-castingsystemsare:

（1）lowerinvestmentoutlaycomparedwiththatforabloomingtrain（mini-steelworks）;

（2）about10%moreproductivitythanwithconventionalingot-casting;

（3）highdegreeofconsistencyofsteelcompositionalongthewholelengthofthestrand;bettercorequality,especiallywithflatstrands;highinherentsurfacequality,leadingtosavingsonanotherwiseexpensivesurfacingprocess;

（4）highdegreeofautomation;

（5）friendliertotheenvironment;

（6）betterworkingconditions.

TypesofInstallation

Thefirstcontinuous-castingplantswerealignedvertically;however,withlargercross-sections,increasingstrand-length,and,aboveall,withincreasingpouring-ratesthistypeofconstructionleadstounreasonablebuilding-heights.Thesefactorsalsoleadtoaconsiderableincreaseinthelengthoftheliquidphasewhichhasmetallurgicaleffects.Thelengthoftheliquidphaseinacontinuously-caststrandisdeterminedbythefollowingformula:

L=D2/4x2Vc

WhereD=strandthickness（mm）

x=solidificationcharacteristic（mm/min1/2）

Thesevaluesamountto26～33forthewholecoolinglength.

Vc=castingrate（m/min）

Effortstoreducebuilding-heightfirstledtocontinuous-castingsystemsinwhichmoltenmetalpassedintoaverticalmouldandsolidifiedcompletelybeforebeingbentorwherethestrandhasbeenintheliquidphaseandlatertothebow-typeinstallationwhichhasacurvedmouldandisthesystemmostusedtoday.Verticalsystemsandthoseinwhichthestrandisbentwhencompletelysolidifiedhavelongstraightliquidphasesandcanleadtounacceptablyhighcapitaloutlay.

However,thesesystemshavemetallurgicaladvantagesfromthepointofviewofmaintenance.Averticalsysteminwhichthestrandisbentwhilestillintheliquidphasehastheadvantagethatthebuildingneednotbeastallaswhenthestrandisbentaftersolidification;however,theliquid-phasebendingsystemrequireshigherinitialoutlayandgreatermaintenancecosts.Thebow-typesystemrepresentsacompromisebetweenthecostsofcapitaloutlayandofmaintenanceandwhatcanbeachievedmetallurgically.

Continuous-castingissuitablefortheproductionofalmostanycross-sectionimaginable;square,rectangular,polygonal,round,andovalsectionsareallavailable.Therearealsosomeinstancesofpreliminarysectionsfortubesandslabs,blooms,andbillets.Sectionswithabreadth/thicknessratiogreaterthan1.6arenormallydescribedasslabs.Billet-machinesproducesquareornearly-square,round,orpolygonalcross-sectionsupto160mmacross.Largersectionsandthosewithabreadth/thicknessratiolessthan1.6arecastinbloom-machines.Billetsnowadaysnormallyproducedinthiswayrangefrom80x80to300x300mm,andslabsare50-350mmthickand300-2500mmwide.

Continuous-castingoutput-rateshaverisensharply,especiallyinthelastfewyears.Thisisessentiallybecauseofincreaseinthebreadthofthestrandandincastingrate.Thefollowingoutputshavebeenexceededpersectionperminute:

slabs5tonesblooms1tonesbillets350kg

Finally,weshouldmentionhorizontalcontinuous-castingsystemswhicharealreadyusedfornon-ferrousmetalsandcastironandwhicharebeingfurtherdevelopedforsteel.R.ThieimannandR.Steffenhaveproducedacomprehensivereportaboutthestateofdevelopmentofhorizontalcontinuous-castingsystemsforproducingbilletsfromunalloyedandalloysteels.Horizontalcontinuous-castingsystemshavethreeimportantadvantagesoverconventionalcontinuous-castingsystem:

（1）lowheightandcostofbuilding;

（2）simplemeansofprotectingthemeltagainstreoxidatioin;

（3）nostranddeformationbecausetheferrostaticpressureismuchlower.

CastingTechnique

Moltensteelispouredfromacastingladleviaatundishintoanopenwater-cooledcoppermould.Atfirstthebottomofthemouldisclosedoffbyastarting-bar,whichthenleadstransportofthehotstrandfromthemouldintothecontinuouswithdrawingrolls.Thestrand,whichstartstosolidifyinthemould,passesthroughacoolingsystembeforeitfinallyreachesthewithdrawingrolls,whereuponthehotstrandtakesovertransport.Thestarting-barisseparatedfromthehotstrandbeforeorafteritreachesthepartingdevice.Thelatter,whichmayeitherbeaflame-cutterorhotshears,movesatthesamerateasthehotstrandandcutsitintothelengthsrequired.

Thepurposeofthetundishistofeedadefinedquantityofmoltensteelintooneormoremoulds.Thiscanbedonebyusingnozzlescontrolledbystoppers,slide-gates,orothermeans.Thetundishmayinitiallybecold,warm,orhotaccordingtothenatureofitsrefractorylining.Wheredifficultsteelsareprocessedthepouringstreamisprotectedagainstoxidationbetweenthesubmergedboxes.Themouldnotonlyformsthestrandsectionbutalsoextractsadefinedquantityofheat,sothatthestrandshellisstrongenoughfortransportbythetimeitreachesthemould-outlet.Themouldmaybemadefromcoppertubeorhardenablecopperalloy,dependingontheshapeandsizeofthestrandtobecast.Asarule,tubularmouldstireusedforsmallersections.Theinteriorsurfaceofthemouldmaybecoatedwithchronicormolybdenumtoreducewearandtosuitheat-transferfromthealloybeingcast.Themouldistaperedtomatchsteel-shrinkageandcasting-rateandthetypeofsteelconcerned.Mouldsusedtodayrangefrom400to1200mminlengthoverall,buttheirusuallengthisbetween700and800mm.Theproblemofsteeladheringtothemould-sidesisusuallycounteredbyoscillatingthemouldsinusoidallyrelativetothestrandandbyaddinglubricant（oilorcastingflux}inanattempttocutfrictionbetweenthemouldandthesteel.Thelubricant,particularlycasting-flux,hasanadditionalmetallurgicalfunction.Thechoiceoflubricantdependsonthequalitiesrequiredandthecastingconditions;itisparticularlyimportantthatcasting-fluxshouldbechosentomatchthequality-programmeprecisely.

Thelevelofsteelinthemouldmaybecontrolledmanuallyorbyanautomaticsystem.Eithermethodmaybeusedtokeepthelevelconstantortomatchtheincomingmoltensteel,i.e.toaccommodatevariationsincastingrate.Manualcontrolisaffectedviathestopperinthetundishorbyvaryingtheoutputrate.Anautomaticcontrolsystemmaymeterradioactivityorinfraredradiationormeasuretemperatureviaaprobeinthemouldwalltodeterminethesteel-levelandcompensateanychangesbyactuatingthestopper-mechanism（forconstantpouringrate）orcontrollingthespeedofthewithdrawingrolls（varyingcastingrate）.

Thetypeofstarting-barusedforcontinuous-castingdependsonthetypeofinstallation.Rigidstarting-barscanbeusedinverticalsystems,whilearticulateddummybarsorflexiblestriphavetobeusedinbowedinstallations.Thestartingbarcanbeconnectedtothehotstrandindifferentways,oneisbyweldingthefluidsteelusingajointingelement（flatslab,screw,orfragmentofrail）whichissolubleinthestarting-bar;anotherisbycastingtheconnectorinaspeciallyshapedheadinthedummybarinawaythatenablesittobereleasedbyunlatching.

Thethicknessofthesolidifiedstrandshellonleavingthemoulddependsfirstofallonhowlongthesteelisincontactwiththemould,butitalsodependsonthespecificthermalconductivityofthemouldandontheamountofsuperheatthatsteelhaswhenitentersthemould.Itcanbedeterminedwithfairaccuracyusingthefollowingparabolicformula:

C=x.T

whereCisthethicknessofthestrandshell（mm）

xisthesolidificationcharacteristic（mm/min1/2）

tisthesolidificationtime（min）

Thesolidificationcharacteristicinandnearthemouldliesbetween20and26,dependingontheoperatingconditions;forthesecondarycooling-areathefigureis29-33.Thethicknessofthesolidifiedstrandshellonleavingthemouldisabout810%ofthestrand-thickness,dependingoncastingrate.Asecondarycooling-areaunderthemouldspeedsupcompletionofthesolidificationprocess.Thecoolantusuallyiswaterbutawater/airmixtureorcompressedairisalsosometimesused.Thesecondarycoolingareaisdividedintoseveralzonestosuitcoolantflowrates.Thenecessaryquantityofwaterissprayedovertheentirestrandbyspray-bars.Theferrostaticpressuremaybesohighinrelationtothestrandcross-sectionandthecastingratethatthestrandhastobesupportedtopreventbuckling.Theequipmentforthisisexpensiveinplantsproducingbloomsandespeciallyslabs.

ProcessControl

Forproductivityandqualityreasonsthereisatrendinmodernsteelmakingtotransfertime-consumingoperations,suchastemperatureadjustment,deoxidationandalloying,fromthefurnacetotheladletreatmentstations.Thesetreatmentsareparticularlyimportantwherethecontinuouscastingprocessisinvolvedbecausetemperatureandcompositionmustcloselybecontrolled.

Thetemperaturecontrolofmoltensteelasitentersthemouldnee