铸造轧辊检测和维护.docx

铸造轧辊检测和维护.docx

《铸造轧辊检测和维护.docx》由会员分享，可在线阅读，更多相关《铸造轧辊检测和维护.docx（15页珍藏版）》请在冰豆网上搜索。

铸造轧辊检测和维护

TheDavyRollCompanyLimited

ExcellenceinForgedandCastRollTechnology

InspectionandMaintenanceofCastRolls.

Thefollowinginformationisintendedtoaidrollshoppersonnelwiththeeverydaymaintenanceandinspectionofstaticandrocastworkrolls.

Byoptimizinggrindingoperationsandintroducingtargetedinspectionproceduressignificantimprovementsinrollperformanceandreliabilitycanbeachieved.

RollShopInspectionEquipment.

Automatededdycurrentsystemsareusedinalargeproportionofrollshopsacrosstheworld.Theyprovidearapidandefficientmeansoftestinglargeareasofarollssurfaceallowingtheoperatortomanageandwherenecessary,removerollinggenerateddefects.

Thesesystemsarehoweverlimitedtotestingnearsurfacedefects.Manyrollshopsfeelitisnecessarytointroducecomplementary,deepinspectionsystemsintheformofultrasonicequipment.Thiscanbeintheformofanautomatedsystemusedincooperationwiththeeddycurrentunitsormanualhandheldunits.

Inrollshopswereeddycurrentequipmentisnotavailablemanualultrasonicequipmentaswellasvisualcrackdetectionprocedures,suchasmagneticparticleordiepenetrantinspectionbecomeessential.

UltrasonicInspection

TheDavyRollCompanyinspectiondepartmentsuseportableultrasonicunitsfortheday-to-dayinspectionrequirementsofbothworkandbackuprollsduringmanufactureandatthecustomer’ssite.Ahighlevelofoperatorskillandspecifictrainingisrequiredtofullyutilisetheseunitsaswellasarangeoftailoredultrasonicprobes.TheDavyRollCompanyisabletoofferguidanceandtrainingtosuitablyexperiencedpersonnelinrollinspectionpractices.

UltrasonicProbes

Thefollowingprobesarerecommendedforrollinspectiondutiesandavailablefrommostmanufacturers.

CompressionProbes.

Type

Angle（degrees）

Crystals

Frequency（Mhz）

Diameter（mm）

Comments

Compression

0

Twin

2.5

25

Thisisageneral-purposeprobesuitedtotheinspectionofcentrifugallycastworkrollsespeciallyinterfacebondzonesandmid-deepshelldefects.Althougharelativelylowfrequencyprobethisisidealforuseonalloyindefinitechillmaterialswerethereisalargeamountoffreegraphiteinthemicrostructure.Useofhigherfrequenciesforthesematerialswillgeneratelargeamountsof‘grass’orscattermakingresolvingofthebondzonedifficult.

Compression

0

Twin

5

15

Agoodprobeforresolvingdefectsclosetothesurfaceofworkandbackuprolls.Thiswillpenetratetothebondzoneofhighchromiumandhigh-speedsteelmaterials.Goodforevaluatingandpositioningsmalldefects.

Compression

0

Single

0.5

50

Rollmakersusetheseprobesfortestinglongitudinallyaswellastransverselythroughcastings,forexamplefromonesideofthebarreltotheotherorfromdriveneckendfacetooperatorendface.Wemainlylookformanufacturingproblemsandfatigueproblemsduringservice.Theseprobescanbeexpensiveandyourusagewouldbeverylow.

TwinShearwaveProbes.

Type

Angle（degrees）

Crystals

Frequency（Mhz）

Size（mm）

Comments

Shearwave

45

Twin

2

30x15

Goodfordeepcracksinbackuprollsorexaminingdefectsatworkrollbondzones.

Shearwave

70

Twin

2

30x15

Goodforshallowcracks<10mmindepth,especiallyfirecracking.

Shearwave

90

Single

2

30x15

Alsoknownassurfacewave,isgoodforinspectingthefullbarrelofbackups,forinstanceinthecaseofeddycurrentequipmentfailure.Isverysensitivetosurfaceconditionandcleanliness.

Calibration.

Accuratecalibrationoftestequipmentisessentialtoensureminimumstockremovalandensurethecompleteremovalofdefects,optimizingrollperformanceandreliability.Toensureaccurateresultscompressionprobesshouldbecalibratedwithtestblocksmanufacturedtothesamematerialspecificationasthatoftherolltobetested.

Forshearwaveprobesasteelanglecalibrationblock,forexampleaV2typeisrequiredtoensureprecisetrigonometriccalibrationisachieved.

Thefollowingvaluesmaybeusedforthecalibrationofcompressionprobeswhenspecifictestblocksarenotavailable.Thesevaluesareapproximateonlyasvariationsbetweenmaterialgrades,forexampleenhancedApexgradeandstandardirongradeaswellasbetweenmanufacturerswillexist.

Material

Velocity

AlloyIndefiniteChill（alsoApex）

5700m/s

HighChromiumIron（alsoSTELLA）

6350m/s

HighSpeedSteel

6250m/s

AlloyCastSteel（alsoVChrome）

5918m/s

Angleprobes

3353m/s

DyePenetrantInspection.

Diepenetrantsystemsareusefulindeterminingthepresenceofgrosscrackinginbackupandworkrolls.Thesystemisrelativelyinexpensiveandrequiresalimiteddegreeofoperatortraining.

Thereishoweversomelimitationtothismethodforrollinspection.Theprocessreliesonthedyebeingdrawnintoopensurfacecracksbycapillaryactionandassuchanythingthatimpedesthisprocesscanreduceoreveneradicatetheeffectivenessofcrackdetection.Forexample;

∙Whencrackscontainlargeamountsofoilordebrisoutofthemill.

∙Aftergrindingthecracksmaybesealedbymechanicaldeformationofthesurfaceorbygrindingdebris.

Assuchadditionalinspectionmethodsareadvisedtocomplimentthisproceduretoensurecompleteremovalofdefects.

MagneticParticleInspection.

Magneticparticleinspectionisaneffectiveandreliablesystemforthedetectionofcracksinrollingmillrolls.Thissystemispreferredforthedetectionofsmallercracksespeciallyongroundorturnedsurfaces.

Thesystemworksbyattractionofaferrousbaseddyeontherollsurfacetowardsthemagnetizedcrackfaces.Thisattractionoccursacrossthefullface,atthesurfaceandatdepth.Assuchthesystemdoesnotsufferthelimitationsofthedyepenetrantsystemwhenthecracksareclosedatthesurfaceorfilledwithdebris.

Manysystemsareavailableonthemarketconsistingofeithermainspoweredelectro-magnetsorpermanenthandheldmagnets.

HardnessTesting.

HardnesstestingofcastrollsisprimarilycarriedoutwithEQUOTIPtypeinstruments.Thesedevicesdeterminehardnessbymeasuringthelevelofreboundenergyfromthesurfaceofthetestpieceorroll.

Oneofthemanyusesofharnesstestingisdeterminingifworkhardenedmaterialhasbeenremovedfromthebarrelsurfaceduringgrinding,especiallyofbackuprolls.

Thesedevicesareverysensitivetosurfacecleanlinessandfinish.Hardnessmeasurementstakenonarolledorroughgroundsurfacewillingeneralgivealowerresultthanonapolishedgroundsurface.Accuratemeasurementscanonlybeobtainedona400-gradegritequivalentorbettersurfacefinish.

UltrasonicInspectionProcedures.

MeasuringCrackDepths.

Whencracksaregeneratedinthebarrelofarolltheycanbeparalleltoorperpendiculartothesurface.Forexample,firecrackingwillinitiallyformatrightanglestothesurfacebutastheyaresubjectedtotheforcesofrollingwillpropagatecircumferentiallyandturnparalleltothesurfaceasshownbelow.

Crackingmaynotalwaysbreakthesurface,forexamplearollwhichhasbeensubjectedtoanimpactorlocalizedoverloadmayinitiatecracksbelowandalignedparalleltothebarrelsurface.

Itisthereforealwaysadvisabletoinspecttheareasurroundingasurfacecrackorbruisewithacompressionandangleprobetoensuredetectionofthedeepestcomponent.

Careshouldalwaysbetakenwhenassessingcrackdepthsoncurvedsurfaces.Withshearwaveprobesanangleshouldbechosenthatwillallowyoutoworkasclosetothesurfacecrackaspossible.

Workingwiththeprobeawayfromthecrackonacurvedsurfacecanresultinthebeammovingbackupthecrackfacetowardsthebarrelsurfaceresultingindeeperthanactualcrackdepths.

Whenusingashearwaveprobecrackdepthsshouldbecheckedfrombothedgestoensurethemaximumdepthisobtained.Crackswillnotalwaysbealignedexactlyperpendiculartothesurfacebutmaybeenteringatanangle.Iftheprobeangleandcrackanglearesimilarthecrackmaynotbedetectedwhentestedfromonlyoneside.

InspectionofCentrifugallyCastShelltoCoreBondZone（Interface）.

Centrifugallycastworkrollsareinspectedpriortodeliverytoensureaninterfacebondstrengthsufficientforstandardmilloperatingconditionstodiscardsize.

Howeverifrollsaresubjectedtoabuseduringrollingitisadvisabletoinspectthebondzoneorinterfaceareatoensuretherehasbeennodetrimentaleffectthatcouldultimatelyresultintherollsfailure.

Thetestproceduredescribedbelowcomparestheamountofenergyreturnedtotheprobefromtheinterfacerelatedtotheamounttransmittedintoanddispersedwithinthecorematerial.Alowenergyreturnindicatesapoorreflectororwell-bondedinterfacewhileahigh-energyreturnindicatesagoodreflectorandhencepoorerbonding.

Theprincipleisshownbelowwithechoesforawellandpoorbondedinterfaceatthesamedecibellevel.

GoodInterfacePoorInterface

Testprocedure

ThisprocedurecanbeusedforalltypesofROCASTcentrifugallycastrolls.

Equipment

KrautkramerUSN50orsimilarcalibratedtoBS44331part2orequivalent.

A2.5MHztwincrystalcompressionprobe.

Testblock（20x40x50mm）manufacturedfromthesamegradematerialastherolltobeexamined.

Procedure

Calibratethetimebaseat100mmusingtheabovetestblock.Measureandrecordthegainindecibels（db）requiredtoobtainafullscreenheight（100%）backwallechofromthetestblock.Thisvalue（A）isthenusedastheminimumortheoreticalvaluefortotalinterfaceseparation.

Testtheroll