外文翻译辊缝润滑工作辊冷却及反剥系统在热轧钢机上的协调应用.docx
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外文翻译辊缝润滑工作辊冷却及反剥系统在热轧钢机上的协调应用
附录ACoordinatedApplicationofRollGapLubrication,WorkRollCoolingandAntipeelingSystemsinHotRollingMills
Surfacequalityrequirementsforhotrolledsteelsheethavecontinuedtobecomemorestringentinrecentyears.Thisfocusonsheetqualityhasdevelopedinparallelwithcorrespondingdemandsforincreasedproductivityandreducedcostsatthemill.Althoughnotapanacea,rollgaplubricationsystemshavereceivedincreasedattentioninsupportoftheseobjectives.Specifically,rollgaplubricationsystemsareusedincombinationwithworkrollcoolingsystemsandantipeelingsystemsto:
●Reducerollingloadsandtherebyreducepotentialforchatter.
●Reducerollingtorquesandassociatedenergyrequirements.
●Enableredistributionofloadsamongstandstoaddresschatterissues.
●Increasereductionstodecreasefinalstripthickness.
●Reducepotentialforrolled-inscale.
●Extendrollingcampaignlength.
Thesesystemsmustalsobedesignedandoperatedinamannerthatwill:
●Assuregoodplatingoftheoilontotheworkrollsurface.
●Maintainstabilityofmillcontrolsystems.
●Minimizetheenvironmentalimpactofvaporemissionsandspentfluids.
●Preventcloggingoffluidsupplylines.
Theeffectiveimplementationofthesesystemscanprovideenhancecontroloverthethermalandtribologicalconditionsintherollbitetoachieveobjectivesforproductqualityandmillproductivity.Thesesystemshaveundergonedevelopmentforanumberofyearsandarenowbeingimplementedandrefinedthroughouttheworld.
OverviewofChatterandPeelingonRollSurfaces
Theearlystandsofsteelhotfinishingmillsroutinelyoperateatrelativelyhighloadsandrelativelylowspeeds.Theseoperatingconditionsrepresentaveryaggressiveenvironmentformillworkrolls.Highloads,combinedwithotherfactors,cancontributetomillstandvibrationscommonlyknownaschatter.Thesevibrationproducecyclicloadingconditionsinthestand,whichcanproducevisiblemarksontherollsurface.Thesemarksarethentransferredtothesheet,producinganundesirablesurfacequality.
Theeffectiveimplementationofrollgaplubricationtechnologycanmakeitpossibletoreduceand/orredistributeloadsinthemill,thusdecreasingoreliminatingchatter.Furthermore,thestripsurfacetemperaturesthatarethecontacttimebetweenthestripandtheworkroll,impactsthetemperaturesthatarereachedontherollsurface.Highertemperaturesacceleratetheformationofoxidesontherollsurface.Thinlayersoftheseoxidescanthenbe“peeledoff”therollsurfacebythealternatingshearstressesassociatedwithslipintherollbite.Whenthisoccurs,itresultsinarollsurfacedefectcommonlycalled“peeling”.
Thesepeelingmarksalsonegativelyaffectthestripsurfacequality,producingwhatisknownasrolled-inscale.Solutionstothepeelingprobleminvolveestablishingabalancebetweenoxidesgrowthandwearataminimalthicknessintherollbite.
Antipeelingandworkrollcoolingtechnologiesareutilizedtoachievethisbalance.Thesetechnologiesmustbecoordinatedwiththerollgaplubricationsystemsinordertoassureoptimaleffectivenessofeachtechnology.
OverviewofSystemHardwareandOperation
Theworkrollcoolingheadersareprovidedonboththeentryandexitsidesofthestand.Theareaofspraycoverageintherollislargestintheexitside.Thisprovidesthemaximumcoolingeffectwhentherollsurfaceisatitshighesttemperature—shortlyafteritrotatesoutofcontactwiththestrip.
Workrollcoolingheadersarealsomountedontheentrysideofthestand.Theseentrysideheadersaredisabledwhentherollgaplubricationheadersareoperated,soasnottowashofftheoilbeforeitcaneffectivelyplateontotherollsurface.
Therollgaplubricationheadersarealsolocatedontheentrysideofthestand.Theysprayanoil/waterdispersionontotherollsurfacepriortoitsrotationthroughthestandentrywiper.Asthewatercomponentofthedispersionisvaporized,thepressurethatisexertedbythewiperenhancestheplatingoftheoilontotheworkrollsurface.
Configuringandoperatingthesysteminthismannerensuresthattheoilisplatedontotheworkrollsurfacesothatitwillentertherollbitewithoutbeingwashedaway.Thisoilprovidesthelubricationinthebitetoreduceloadingintherollingprocess.
Antipeelingheadersarefittedontheentrysideofthestand.Theseheadersapplycoolantdirectlyontothestriptoreduceitssurfacetemperaturebeforeitenterstherollgap.
Becauseofthecloseproximitytotherollbite,thereisaverylittletimeforconductiontoredistributethetemperaturewithinthebodyofthestrip.Hence,onlythestrip’ssurfacetemperatureissignificantlyreducedbeforeenteringtherollbite,andtemperatureatthecoreofthestripremainessentiallyunchanged.
Thelowerstripsurfacetemperaturealsoreducestheresultingrollsurfacetemperaturebyreducingthedrivingforceforconductionbetweenthem.Thisdecreasestherateofformationoxidesontherollsurface,whichreducesthetendencyforpeeling.
RollGapLubrication
Therollgaplubricationheadersaresuppliedwithoil/waterdispersion.Separatesystemsareprovidedfortopandbottomheadersineachequippedmillstand.Thewater/oildispersionisformedinastaticmixerlocatedjustbeforethesprayheader.Bycreatingthedispersionincloseproximitytotheheader,thetimefortheoiltobreakoutisminimized,andthelengthofpipingsubjecttocloggingbythedispersionisalsoreduced.
Theoilflowisprovidedbymeteringpumpsandisenableonlyduringrolling.Meteringpumpspeedisregulatedtomaintainaspecifiedvolumeflowratefortheprocess.Adjustablethrottlingvalvesregulatethewaterflowrate.Waterflowismaintained,evenwhentheoilisshutoff,tohelpclearpipingdepositsandtherebypreventclogging.
Theheader’sspraywidthisadjustedtothewidthofthestripbeingrolledviaair-operatedshutoffvalves.Thisapproachprovidesthedispersiononlytotheaeawhereitisrequiredontheworkrollbarrel.Bylimitingtherollingoperation,thevolumeofoilconsumed,alongwiththeassociatedoperatingcost,isminimized.
Thisapproachalsoaddressesenvironmental;considerations,inthatthevolumeofvaporemissionsandthevolumeofwastefluidsthatrequirespecialdisposalarereduced.Theresultisthattheheadersandspraynozzlesprovideuniformapplicationofthedispersiontothetopandbottomworkrollsintheareaofcontactwiththestrip.
Itshouldalsobenotedthatwaterqualitycansignificantlyaffecttheperformanceoftheoil/waterdispersion.Therefore,theoilsuppliermustadapttheoilqualitytothewaterquality.
ImpactofRollGapLubricationandOperatingPhilosophies
Properlydesignedrollgaplubricationsystemsreducefrictionintherollbiteandtherebyreducetheresultingrollingload.Althoughsomevariationsexist,therearepredominantlythreephilosophiesthatarefollowedintheoperationofrollgaplubricationsystems.
Thefirstphilosophyis“bodyonly”.Itistypicalofoperationforthefirststandofthefinishingmill,althoughsomerollgaplubricationsystemsfollowthispracticeonotherstandsaswell.Inthisphilosophy,theoilflowisnotenableduntilafterthestriphasthreadedthroughthestand.Thisprovidesahigherfrictionconditionduringthreadingtoreducethepotentialforbiterejection.
NotethatwhenRGLisenabled,thereisasignificantreductioninrollingload.Theoilflowisagaindisabledbeforetailout,sothatanyresidualoilthatremainsontherollsurfacecanbeconsumedintheprocess.Thisrestorestheeffectivefrictiontoahigherlevelpriortothreadingofthenextstrip.Italsoresultsinacorrespondingincreaseintherollingload.
Thisapproachsupportsthreadingoperations,butthesignificantchangesinloadingthatcorrespondtotheactivationanddeactivationoftherollgaplubricationsystemproducetransientsthatmustbeaddressedbythemillcontrolsystems.Theimpactofthesetransientswillbediscussedlater.
Thesecondphilosophyis“bodyandtail”.ThisapproachhashistoricallybeenfollowedonstandsF2-F7.Here,therollgaplubricationsystemisenabledafterthreading,butitisnotdisableduntiltailoutiscompleted.Operatinginthismannerstillproducesaloadtransientatthebeginningofthecoil,butiteliminatestheoneattheend.
ImpactofOilVolumeFlowrateonRollingLoad
Theloadreductionthatisaffordedbyrollgaplubricationdependsonanumberoffactors,oneofwhichisthevolumeflowrateofoil.RepresentativetestshavebeenperformedtoanalyzetheeffectofoilflowrateonrollingloadatstandsF2-F4.NotethatrollgaplubricationisononlytheupperworkrollofstandF2.
Alsonotethattheloadingreductiononeachofthestandsappearstobeapproachingalimitingvalueasymptotically,asoilvolumeflowrateisincreased.Hence,thereisalimittothebenefitobtainedwithapplicationoilapplication.Increasingoilapplicationbeyondthispointwouldonlyincreaseoperatingcostandpotentialenvironmentalissueswhileprovidinglittleornobenefit.
Duringthesetests,onlytheupperheaderwasoperatingonF2.Hence,therollingforcereductionmaybedifferentwithbothheadersoperating,butthetrendofdecreasingbenefitwithvolumeflowrateisstillvisible.
Otherloadingandoperatingconditions,aswellasotheroilandwaterdispersion,mayexhibitdifferentvolumeflowraterequirementstoapproachthislimitingpoint.Nevertheless,thegeneralbehaviorofreceivingdiminishingreturnsforcontinuedincreasesinoilvolumeflowrateisexpectedtoholdfortheseotherap