轧钢相关外文翻译毕业设计Word文件下载.docx

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2andJ.Uusima¨

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Typically,back-uprollsinhotstripmillsareequippedwithslidingbearingsanditiscommontouseakeythatpreventsrelativemotionbetweentheconicalsleeveandtherollshaft.Thekeygroovecausesdeformationofthesleeveunderload.Thissleeve‘spring’isobservedasrollingforcevariation,whichcausessystematicthicknessvariationofthesteelstrip.Althoughthereisakeylessbearingconstructiononthemarket,analternativesolutionwasstudied.Anon-circularcamlikegeometrythatcompensatesthesleevespringwasgroundontheback-uprollsbyathree-dimensionalgrindingmethod.Asaresult,,50%oftherollingforceandthethicknessvariations,whichweresynchronisedwiththeback-uprollsofthemillstandstudiedinthepresentpaper,werereduced.

Keywords:

Non-circulargrinding,Rollingmill,Back-uproll,Rollingforcevariation,Steelstripthicknessvariation,Rolleccentricity。

Introduction

Background

Atpresentsteelmillsoperateinaglobalmarketinwhichincreasedcompetitionfromdevelopingcountrieshascreatedanewsituation.Thiscompetitionhasforcedtheexistingmillstofocusonproducingsteelofanimprovedandmoreevenqualityatahigherspeed.Thetolerancesofsteelstripprofileshavebecometighter.Atthesametime,theincreasedrunningspeedbringsoutpossiblevibrationproblemsintherollingprocess,especiallyinacoldstripsteelmill.Ifthethicknessvariationofthehotrolledsteelstripcanbereduced,itwillbepossibletoincreasetheproductionspeedofthecoldstripmill.Newhardersteelalloysrequireincreasedrollingforce,thusmakingtheprocessmoresensitivetorollingforcevariations.Theseclaimssetnewdemandsontheacceptablerollingforceandsteelstripthicknessvariationlevelsinthemillingrollstands.

Thesteelmillsbuiltinthe1960sand1970sandevenlaterarelookingforcosteffectivemeanstomeetthenewdemands.Thepresentstudydiscussesamethodofimprovingthequalityoftheendproductwithouttheneedformajorinvestments.

Researchproblem

Thethicknessvariationoftherolledsteelstripismainlycausedbytheforcevariationduringtherollingprocess.Othercausesofthevariationsshouldalsobevisibleintherollingforcemeasurementssuchastemperaturedifferencesandsteelqualitychanges.Inthepresentstudy,theauthorstrytounderstandthephenomenabehindtherollingforcevariationsseenintherollingforcemeasurementsandtodevelopmethodstoreducetheforceandthicknessvariations.

AmeasurementoftherollingforceduringtherollingprocessofasteelstripofamillstandisshowninFig.1a.Theleveloftherollingforcevariesduringtherollingprocess.Inthebeginningthelevelchangesarequitelarge.Theactivecontrolsystemoftherollingforcereducesthelevelchangesafterashortperiod（hereafter,20s）.Inaddition,asmentionedbefore,changesoftemperatureorsteelqualitycancausevariationtotherollingforcelevel.

OthervariationsseeninFig.1bandespeciallyinFig.1ccanbesynchronisedtotherotationalspeedsoftheback-uprollsinthemillstand.Thismeansthattheyareprobablycausedbytheeccentricityoftherolls.Acloserlookatthestructureofthestudiedmillstandcan

provideananswertotheobservedphenomenon.Typicallyarollingmillconsistsof1–7rollingstands.Thereareusuallytwo,threeormorerollsineachstand.Inthestudiedhotstripsteelmill,allsixstandsconsistoftwoworkingrollsandtwoback-uprolls.Theworkingrolls,throughwhichthestrippasses,arerelativelysmallindiameterandhaveback-uprollsofalargerdiameteraboveandbelowtoreducethemillspring.Amillstandwithtwoback-uprollsisshowninFig.2.

Inthemillstandunderstudy,theback-uprollshaveakeytypeslidingbearingconstruction,asseeninFig.3.Itisknownthatakeytypeslidingbearingconstructionofback-uprollscausesaperiodicrapiddropinthe

rollingforce.1Thekeygrooveisalwaysmadewithaclearanceintheradialdirection.Theclearanceguaranteesthatthereisnoradialforcefromthekeythatwoulddeformthesleevegeometry.Thekeygrooveclearanceisthemaincauseoftherapidforcedropobservedonceper

rollrevolution（referredtoasrinFig.1c）.Thisphenomenoncanclearlybeseeninthesamefigureoftherollingforcemeasurement.

1Rollingforcevariationconsistsofchangesofarolling

forcelevel,brollingforcefluctuationandcdropof

rollingforceonceinback-uprollrevolution

2Rollingmillstandunitdesign

Thefluctuationoftherollingforce（referredtoastinFig.1b）iscausedbytheslowchangeoftherelativekeygroovepositionsinthebottomandtopback-uprolls（Fig.4）.Thechangeofthepositionsiscausedbydifferentrollingspeedsoftherolls.Therollingspeedsarerelativetothediametersoftherollscomparablewithdifferentsizedgearwheelsinagearbox.Inthecaseofthismillstand,thediametersoftheworkingrollshavenoeffectontherotationalspeedoftheback-uprolls,becausethesurfacespeedoftherollsisdependantonlyonthespeedofthestrip.Thusthefrequencyofthefluctuationcanbecalculatedfromtherelationofthediametersofthebackuprollsandtherollingspeed.Boththerapiddropoftherollingforceandtherollingforcefluctuationcausethicknessvariationtothesteelstrip.

Akeylessbearingconstructionreducestherun-outofrollsascomparedwithakeytypearrangement.Sincethemajorityoftheworld’ssteelworksbuiltinthe1960sand1970scontinuetouseakeytypeconstruction,

solvingtheproblemwouldhaveamajoreconomicsignificance.Keytypebearingsarealsostillusedinnewcosteffectivemillstands.Differentsystemsutilizingactivecontrolofhydrauliccylinderstocompensatefor

therolleccentricityhavebeenintroducedby,forexample,Ginzburg1andKugietal.2Thedynamicsoftheseactivecontrolsystemsisnotenoughtocompensatefortherollingforcevariationcausedbythekeygroove.

Aimandscopeofresearch

Theaimofthisresearchwastoreducetheperiodicrollingforcevariationcausedbytheeccentricityoftheback-uprollsandtostudyhowthisaffectsthethicknessvariationsofthesteelstrip.Itisassumedthatthemagnitudeofthethicknessvariationshoulddecreasetogetherwiththerollingforcevariation.Theexactrelationbetweentherollingforceandthicknessvariationwasnotknown.Inthepresentworkthespecialcaseoftheeccentricitycausedbythesleevespringofakey

typebearinghasbeenstudied.

Theempiricalresearchtookplaceatahotstripmill.Thethree-dimensional（3D）grindingwasappliedtotheback-uprollsatthelast（sixth）millstand.Therollingforceandthesteelstripthicknessvariationscausedbythekeygroovewereexamined.Non-systematicerror

sources,resonancevibrationsandchangestothestriptemperature,forexample,wereexcludedfromthepresentstudy.Inaddition,systematicrun-outerrorssuchasnon-circularityoftheneckornon-circularityof

thebearingbushwerenotexamined.Three-dimensionalgrindingwasappliedtotheback-uprollsofthemillstandstudied.

Researchmethods

Basedonpreviousresearch,non-circularroundnessprofiles,30mm（topback-uproll）and50mm（bottomback-uproll）inheight,weregroundontheback-uprollsinordertocompensatefortherapiddropintherolling

force.3.

Triggeringsensorswereinstalledontheback-uprollchockstoindicatethekeygroove.Therollingforceandthestripthicknessweremeasuredusingbothconventionaland3Dgroundback-uprolls.Theanalysiswascarriedoutbyusingsynchronoustimeaveraging.Measuringdata,whichconsistedofseveralstrips,weredividedintoperiodsthatrepresentonerevolutionofback-uproll.Equivalentmeasuringpointswerecombinedwithaveraging.Finally,allthesteelstripswerecombinedagainwithaveraging.Thismethodiscalledsynchronisedtimeaveraging.4

Theresultgraphsofthicknessvariationsarealsofilteredwithafastfouriertransform（FFT）.5,6TheeffectoftheFFTfilteringisshowninFig.5.Thefirst16termsintheFourierdomain,representingthefirst16multiplesofrotationalfrequency,alsocalledharmonics,areusedinthefilteredresultcurve,asintherealresultsofthepresentstudy.

The3Dgrindingmethodintroducedinthepresentstudyisamethodtogrinddifferentpredefinedgeometriestocylinders,e.g.back-uprolls.Thismethodismainlyusedforcompensatingmeasurablesystematicgeometryerrors,i.e.run-out,roundnesserrorsanddiametervariationofaroll.Thetoolpathtoobtainthedesiredgeometrycanbebasedonmeasurements,onmathematicalanalysesoronacombinationofthese,asinthepresentstudy.

3akeytypebearingassemblywith1roll,2key,3conicalsleeve,4bearingbushingand5bearinghousingandbconicalsleevewithkeygroove

4Rollingforcefluctuationdependsonrelativepositionsofkeygrooves:

estimatedtwo-dimensional（2D）loaddistributionofback-uprollisshownonrightside

5ThicknesscurveunfilteredandfilteredwithFFT

Methodsandmaterials

Measuringsystems

TherollingforceofthemillstandwasmeasuredfromthedriveandoperatorsidesofthemillbyMillmatePFV100pressductor,theresolutionofwhichis24?

4kN（12bitADconverter,measuringrangefrom250000toz50000kN）.7Severalmeasurementcycleswereaveraged.Thenoiseofthemeasuringdevicetogetherwiththeaveragingenhancestheresolutionofthemeasurement.8Theresolutionoftheaveragedforceva