Casting Defects , causes, and remedies

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Casting Defects, Causes, and Prevention

Prepared by

Presented to

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ABSTRACTFoundryindustriesindevelopingcountriessufferfrompoorqualityandproductivityduetoinvolvementofnumberofprocessparameter.Evenincompletelycontrolledprocess,defectincastingareobservedandhencecastingprocessisalsoknownasprocessofuncertaintywhichchallengesexplanationaboutthecauseofcastingdefects.Inordertoidentifythecastingdefectandproblemrelatedtocasting,thestudyisaimedintheresearchwork.Thiswillbebeneficialinenhancingtheyieldofcasting.Besidethis,standardization(optimization)ofprocessparameterforentirecycleofmanufacturingofthecriticalpartisintendedintheproposedwork.Thisstudyaimstofindingdifferentdefectsincasting,analysisofdefectandprovidingtheirremedieswiththeircauses.Inthispaperanattempthasbeenmadetolistdifferenttypesofcastingdefectsandtheirrootcausesofoccurrence.Thispaperalsoaimstoprovidecorrectguidelinetoqualitycontroldepartmenttofindcastingdefectsandwillhelpthemtoanalyzedefectswhicharenotdesired.

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TABLEOFCONTENTContentsABSTRACT.................................................................................................................iiLISTOFFIGURESANDTABLES..................................................................................vListofFigures........................................................................................................vListofTables...........................................................Error!Bookmarknotdefined.

1 INTRODUCTION[2]..............................................................................................12 TERMINOLOGY[1]...............................................................................................23 CASTINGDEFECTSCLASSIFICATION...................................................................24 Defects[3,4,5]......................................................................................................24.1 Fillingrelated...............................................................................................24.1.1 Blowholes..............................................................................................24.1.2 Sandburning.........................................................................................44.1.3 Sandinclusion........................................................................................64.1.4 Coldlap(shut).......................................................................................94.1.5 Misrun.................................................................................................104.1.6 Gasporosity........................................................................................11

4.2 Shapedefects............................................................................................134.2.1 Mismatch.............................................................................................134.2.2 Distortion............................................................................................134.2.3 FlashDefect.........................................................................................14

4.3 Thermaldefects.........................................................................................164.3.1 CracksandTears..................................................................................164.3.2 Shrinkage.............................................................................................174.3.3 Sinkmark.............................................................................................19

4.4 AppearanceDefects..................................................................................21

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4.4.1 MetallicProjection..............................................................................214.4.2 Cavities................................................................................................224.4.3 Discontinuities.....................................................................................224.4.4 Incompletecasting..............................................................................234.4.5 Incorrectdimensionorshape.............................................................244.4.6 Defectivesurface.................................................................................254.4.7 RatTailandBuckles.............................................................................26

5 CONCLUSION...................................................................................................27REFERNCES..........................................................................................................28

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LISTOFFIGURESANDTABLESListofFigures

Figure1Blowhole[2]...............................................................................................3Figure2Sandburning[2].........................................................................................5Figure3Sandinclusion[2].......................................................................................7Figure4Coldshut[2]...............................................................................................9Figure5Misrun[2].................................................................................................10Figure6Gasporosity[2]........................................................................................11Figure7Mismatch[2]............................................................................................13Figure8Distortion[2]............................................................................................14Figure9Flash[2]....................................................................................................15Figure10Crack[2].................................................................................................16Figure11Shrinkage[2]..........................................................................................18Figure12Sinkmark[2]..........................................................................................19Figure13Metallicprojection[2]............................................................................21Figure14Blowholes[2].........................................................................................22Figure15Bodycrack[2].........................................................................................23Figure16Incomplete[2]........................................................................................24Figure17Defectivesurface[2]..............................................................................25Figure18Rattail[2]...............................................................................................26

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1 INTRODUCTION[2]Castingisaprocesswhichcarriesriskoffailureoccurrenceduringalltheprocessofaccomplishmentofthefinishedproduct.Hencenecessaryactionshouldbetakenwhilemanufacturingofcastproductsothatdefectfreepartsareobtained.Mostlycastingdefectsareconcernedwithprocessparameters.Henceonehastocontroltheprocessparametertoachievezerodefectparts.Forcontrollingprocessparameteronemusthaveknowledgeabouteffectofprocessparameteroncastingandtheirinfluenceondefect.Toobtainthisallknowledgeaboutcastingdefect,theircauses,anddefectremediesonehastobeanalyzecastingdefects.Castingdefectanalysisistheprocessoffindingrootcausesofoccurrenceofdefectsintherejectionofcastingandtakingnecessarysteptoreducethedefectsandtoimprovethecastingyield.Inthisreviewpaperanattempthasbeenmadetoprovideallcastingrelateddefectwiththeircausesandremedies.Duringtheprocessofcasting,thereisalwaysachancewheredefectwilloccur.Minordefectcanbeadjustedeasilybuthighrejectedratescouldleadtosignificantchangeathighcost.Thereforeitisessentialfordiecastertohaveknowledgeonthetypeofdefectandbeabletoidentifytheexactrootcause,andtheirremedies.

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2 TERMINOLOGY[1]Theterms"defect"and"discontinuity"refertotwospecificandseparatethingsincastings.Defectsaredefinedasconditionsinacastingthatmustbecorrectedorremoved,orthecastingmustberejected.Discontinuities,alsoknownas"imperfections",aredefinedas"interruptionsinthephysicalcontinuityofthecasting".Therefore,ifthecastingislessthanperfect,butstillusefulandintolerance,theimperfectionsshouldbedeemed"discontinuities".

3 CASTINGDEFECTSCLASSIFICATION

1. Filingrelateddefects.2. Shaperelateddefects.3. Thermaldefects.4. Defectsbyappearance.

4 Defects[3,4,5]4.1 Fillingrelated4.1.1 BlowholesBlowholeisakindofcavitiesdefect,whichisalsodividedintopinholeandsubsurfaceblowhole.Pinholeisverytinyhole.Subsurfaceblowholeonlycanbeseenaftermachining.Gasesentrappedbysolidifyingmetalonthesurfaceofthecasting,whichresultsinaroundedorovalblowholeasacavity.Frequentlyassociatedwithslagsoroxides.Thedefectsarenearlyalwayslocatedinthecopepartofthemouldinpoorlyventedpocketsandundercuts.

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Figure1Blowhole[2]

4.1.1.1 CausesResinbondedsand Inadequatecoreventing. Excessivereleaseofgasfromcore. Excessivemoistureabsorptionbythecores. Lowgaspermeabilityofthecoresand.Claybondedsand Moisturecontentofsandtoohigh,orwaterreleasedtooquickly. Gaspermeabilityofthesandtoolow. Sandtemperaturetoohigh. Bentonitecontenttoohigh. Toomuchgasreleasedfromlustrouscarbonproducer.

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4.1.1.2 RemediesResinbondedsandImprovecoreventing,provideventingchannels,andensurecoreprintsarefreeofdressingReduceamountsofgas.Useslowreactingbinder.Reducequantityofbinder.Useacoarsersandifnecessary.Applydressingtocores,thusslowingdowntherateofheatingandreducinggaspressure.Dryoutcoresandstoredry,thusreducingabsorptionofwaterandreducinggaspressure.ClaybondedsandReducemoisturecontentofsand.Improveconditioningofthesand.Reduceinertdustcontent.Improvegaspermeability.Endeavourtousecoarsersand.Reducebentoniteandcarboncarriercontent.Reducesandtemperature.Installasandcoolerifnecessary.Increasesandquantity.Reducebentonitecontent.Usebentonitewithahighmontmorillonitecontent,highspecificbindingcapacityandgoodthermalstability.Useslowreactinglustrouscarbonproducersorcarboncarrierswithhighercapacityforproducinglustrouscarbon.Inthelastinstance,thecontentofcarboncarriersinthemouldingsandcanbereduced.4.1.2 SandburningBurningondefectisalsocalledassandburning,whichincludeschemicalburnon,andmetalpenetration.

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Figure2Sandburning[2]

4.1.2.1 CausesClaybondedsandLustrouscarboncontenttoolow.Proportionoflowmeltingpointsubstancestoohigh.MouldingplantUnevenmouldcompactionGatingandpouringpracticeUnevendistributionofinflowingmetalwithresultantoverheating.Temperatureofliquidmetaltoohigh.4.1.2.2 RemediesClaybondedsand Increaseproportionoflustrouscarbonproducer.Thisincreasestheamountofcokeaswellastheamountoflustrouscarbon,whichthenresultsinpositiveseparationbetweenmouldandmetal.

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Usepurersilicasandsor,ifnecessary,addnewsand.Reducedustcontent.Ifnecessary,reducetheamountofbentonite.MouldingplantEnsureuniformcompaction.Ifnecessary,increaseheatremovalfromthemoulds.GatingandpouringpracticeEvenoutincomingmetalflow.Reducepouringrate.4.1.3 SandinclusionSandinclusionandslaginclusionarealsocalledasscaborblackingscab.Theyareinclusiondefects.Lookslikethereareslaginsideofmetalcastings.Irregularlyformedsandinclusions,closetothecastingsurface,combinedwithmetallicprotuberancesatotherpoints.Sandinclusionisoneofthemostfrequentcausesofcastingrejection.Itisoftendifficulttodiagnose,asthesedefectsgenerallyoccuratwidelyvaryingpositionsandarethereforeverydifficulttoattributetoalocalcause.Areasofsandareoftentornawaybythemetalstreamandthenfloattothesurfaceofthecastingbecausetheycannotbewettedbythemoltenmetal.SandinclusionsfrequentlyappearinassociationwithCOblowholesandslagparticles.Sandinclusionscanalsobetrappedunderthecastingsurfaceincombinationwithmetaloxidesandslags,andonlybecomevisibleduringmachining.Ifaloosesectionofsandiswashedawayfromonepartofthemould,metallicprotuberanceswilloccurhereandhavetoberemoved.

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Figure3Sandinclusion[2]

4.1.3.1 CausesMouldingplantBreakupofmouldsectionsduringstrippingofpatterns,coresettingorassemblingofmouldingflasksUnevencompactionofmoulds,compactiontoohighinplaces.ClaybondedsandLowcompatibility.Bentonitecontenttoolow,orpoorlydevelopedbentonite.Inertmaterialcontenttoohigh.Lumpcontenttoohigh.Highcontentoflustrouscarbonproducer.ResinbondedsandLowcorestrength.Excessivecoremismatching.

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GatingandpouringpracticePouringratetoohigh,withheavyimpactagainstmouldwallsurfaceresultinginerosion.Ladletoofarabovepouringbasin.Pouringtimetoolong.4.1.3.2 RemediesMouldingplantCheckmouldsforpressuremarksand,ifnecessary,insertpressurepadsCarefullyblowoutmouldcavities.Improvepatternplates,increasepatterntapersandradii.Heatpatternplatesand,ifnecessary,usereleaseagent.Checkthemouldingplantforuniformflaskstrippingandoverhaulmouldingplantasnecessary.Automatecoresetting.Checkand,ifnecessary,modifycoreprintsbeforestartofproduction.Ensureuniformmouldcompaction,avoidovercompactedsections.ClaybondedsandRaisecompactibilityandthusplasticityofthesand.Increasebentonitecontent.Usebentonitewithhighspecificbindingcapacity.Improvebentonitedevelopmentbyextendingmixingtimeorbyprewettingusedsand.Reduceinertdustcontent.Decreasingthedustcontentreduceslumpsinthesand.Reducecontentoflustrouscarbonproducer.

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ResinbondedsandIncreasethestrengthofthecores.Usegreaterproportionofbinder.Compactcoresmoreevenlyandeffectivelyand,ifnecessary,injectgasmoreevenly.Avoidcoremismatching.GatingandpouringpracticeAvoidhighpouringratesandimpactofmetalstreamagainstmouldwalls.Shortenpouringtimes,improvedistributionofgates.4.1.4 Coldlap(shut)Coldlaporalsocalledascoldshut.Itisacrackwithroundedges.Coldlapisbecauseoflowmeltingtemperatureorpoorgatingsystem.Whenthemetalisunabletofillthemouldcavitycompletelyandthusleavingunfilledportioncalledmisrun.Acoldshuntiscalledwhentwometalstreamsdonotfusetogetherproperly.

Figure4Coldshut[2]

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4.1.4.1 CausesLackoffluidityinmoltenmetal.Faultydesign.Faultygating.4.1.4.2 RemediesAdjustproperpouringtemperature.Modifydesign.Modifygatingsystem.4.1.5 MisrunMisrundefectisakindofincompletecastingdefect,whichcausesthecastinguncompleted.Theedgeofdefectisroundandsmooth.Whenthemetalisunabletofillthemouldcavitycompletelyandthusleavingunfilledportioncalledmisrun.Acoldshuntiscalledwhentwometalstreamsdonotfusetogetherproperly.

Figure5Misrun[2]

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4.1.5.1 CausesLackoffluidityinmoltenmetal.Faultydesign.Faultygating.4.1.5.2 RemediesAdjustproperpouringtemperature.Modifydesign.Modifygatingsystem.4.1.6 GasporosityThegascanbefromtrappedair,hydrogendissolvedinaluminumalloys,moisturefromwaterbaseddielubricantsorsteamfromcrackedcoolinglines.Airispresentinthecavitybeforetheshot.Itcaneasilybetrappedasthemetalstartstofillthecavity.Theairisthencompressedasmoreandmoremetalstreamsintothecavityandthepressurerises.Whenthecavityisfullitbecomesdispersedassmallspheresofhighpressureair.Theswirlingflowcancausethemtobecomeelongated.

Figure6Gasporosity[2]

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4.1.6.1 CausesMetalpouringtemperaturetoolow.Insufficientmetalfluiditye.g.carbonequivalenttoolow.Pouringtooslow.Slagonthemetalsurface.Interruptiontopouringduringfillingofthemould.Highgaspressureinthemouldarisingfrommoldingmaterialhavinghighmoistureand/orvolatilecontentand/orlowpermeability.Lustrouscarbonfromthemoldingprocess.Metalsectiontoothin.Inadequatelypreheatedmetallicmoulds.4.1.6.2 RemediesIncreasemetalpouringtemperature.Modifymetalcompositiontoimprovefluidity.Pourmetalasrapidlyaspossiblewithoutinterruption.Improvemouldfillingbymodificationtorunningandgatingsystem.Removeslagfrommetalsurface.ReducegaspressureinthemouldbyappropriateadjustmenttomouldingmaterialpropertiesandensuringAdequateventingofmouldsandcores.Eliminatelustrouscarbonwhereapplicable.Ifpossible,modifycastingdesigntoavoidthinsections.Ensuremetalmouldsareadequatelypreheatedanduseinsulatingcoatings.

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4.2 Shapedefects4.2.1 MismatchMismatchinmolddefectisbecauseoftheshiftingmoldingflashes.Itwillcausethedislocationatthepartingline.

Figure7Mismatch[2]

4.2.1.1 CausesAmismatchiscausedbythecopeanddragpartsofthemouldnotremainingintheirproperposition.Thisiscausedbylooseboxpins,inaccuratepatterndowelpinsorcarelessnessinplacingthecopeonthedrag.4.2.1.2 RemediesCheckpatternmountingonmatchplateandRectify,correctdowels.Usepropermoldingboxandclosingpins.4.2.2 DistortionWarpedCastingDistortionduetowarpageisknownaswarpdefect.

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Figure8Distortion[2]

4.2.2.1 CausesDistortionduetowarpagecanoccurovertimeinacastingthatpartiallyorcompletelyliberatesresidualstresses.4.2.2.2 RemediesCommonpracticeinironcastingisnormalizingheattreatmenttoremoveresidualstress.Inaluminumcasting,astraighteningbetweenquenchandagingmightberequired.4.2.3 FlashDefectFlashcanbedescribedasanyunwanted,excessmetalwhichcomesoutofthedieattachedtothecavityorrunner.Typicallyitformsathinsheetofmetalatthepartingfaces.Thereareanumberofdifferentcausesofflashandtheamountandseveritycanvaryfromaminorinconveniencetoamajorqualityissue.Attheveryleast,flashiswastematerial,whichmainlyturnsintodrosswhenremelted,andthereforeisahiddencosttothebusiness.

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Figure9Flash[2]

4.2.3.1 CausesDamagetodiefacesanddiecomponents.Partsofthediehaveinsufficientstrength.Bending,crowningofstretchingofdies.Cavitiesoffsetfromcentreofplaten.Insufficientmachineclampup.Pressurespikesattheendofcavityfill.Excessiveintensificationpressure.Incorrectintensificationtiming.Damage,orwear,intogglemechanisms.Machinehydraulicmalfunction.Hydraulicvalveorsealleaks.

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4.2.3.2 RemediesIfyoursprueisverytallandthecastingcoversawideareaofthemoldface,it'sverypossibleforthemoldtoactuallybeforcedupbythehydrostaticpressureofthemetal.Theseriousnessofthisdependsdensityofthemetal(aluminumisverylight,butbecarefulwithabronzepour!)andtheweightofthemoldfightingit.Thesolutionhereisverysimple:weightdownthemould.4.3 Thermaldefects4.3.1 CracksandTearsCrackscanappearindiecastingsfromanumberofcauses.Somecracksareveryobviousandcaneasilybeseenwiththenakedeye.Othercracksareverydifficulttoseewithoutmagnification.

Figure10Crack[2]

4.3.1.1 CausesShrinkageofthecastingwithinthedie.Undercutsordamageindiecavities.Uneven,orexcessive,ejectionforces.Thermalimbalanceinthedie

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Insufficientdraftinsectionsofthedie.Excessiveporosityincriticalregionsofthepart.Productdesignnotmatchedtotheprocess.Inadequatediedesign.4.3.1.2 RemediesReducedrystrength,addsawdust/coaldust.Reducepouringtemperature.Avoidsuperheatingofmetal.Usechills.Providefeeders.Avoidearlyknockoutandgivesufficientcoolingtime.Correctcomposition.Reducesharpcorners.4.3.2 ShrinkageShrinkagedefectsoccurwhenfeedmetalisnotavailabletocompensateforshrinkageasthemetalsolidifies.Shrinkagedefectscanbesplitintotwodifferenttypes:openshrinkagedefectsandclosedshrinkagedefects.Openshrinkagedefectsareopentotheatmosphere,thereforeastheshrinkagecavityformsaircompensates.Therearetwotypesofopenairdefects:pipesandcavedsurfaces.Pipesformatthesurfaceofthecastingandburrowintothecasting,whilecavedsurfacesareshallowcavitiesthatformacrossthesurfaceofthecasting.Closedshrinkagedefects,alsoknownasshrinkageporosity,aredefectsthatformwithinthecasting.Isolatedpoolsofliquidforminsidesolidifiedmetal,whichare

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calledhotspots.Theshrinkagedefectusuallyformsatthetopofthehotspots.Theyrequireanucleationpoint,soimpuritiesanddissolvedgascaninduceclosedshrinkagedefects.Thedefectsarebrokenupintomacroporosityandmicroporosity(ormicroshrinkage),wheremacroporositycanbeseenby.

Figure11Shrinkage[2]

4.3.2.1 CausesThedensityofadiecastingalloyinthemoltenstateislessthanitsdensityinthesolidstate.Therefore,whenanalloychangesphasefromthemoltenstatetothesolidstate,italwaysshrinksinsize.Thisshrinkagetakesplacewhenthecastingissolidifyinginsideadiecastingdie.Atthecenterofthicksectionsofacasting,thisshrinkagecanendupasmanysmallvoidsknownasshrinkageporosity.Iftheshrinkageporosityissmallindiameterandconfinedtotheverycenterofthicksectionsitwillusuallycausenoproblems.However,ifitislargerinsize,orjoinedtogether,itcanseverelyweakenacasting.Itisalsoaparticularproblemforcastingswhichneedtobegastightorwatertight.

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4.3.2.2 RemediesThegeneraltechniqueforeliminatingshrinkageporosityistoensurethatliquidmetalunderpressurecontinuestoflowintothevoidsastheyform.4.3.3 SinkmarkSolvingmoldingsinkmarkandvoidproblemsDefinition:Sinkmarksandvoidsbothresultfromlocalizedshrinkageofthematerialatthicksectionswithoutsufficientcompensation.Sinkmarksappearasdepressionsonthesurfaceofamoldedpart.Thesedepressionsaretypicallyverysmall;howevertheyareoftenquitevisible,becausetheyreflectlightindifferentdirectionstothepart.Thevisibilityofsinkmarksisafunctionofthecolorofthepartaswellasitssurfacetexturesodepthisonlyonecriterion.Althoughsinkmarksdonotaffectpartstrengthorfunction,theyareperceivedtobeseverequalitydefects.Voidsareholesenclosedinsideapart.Thesecanbeasingleholeoragroupofsmallerholes.Voidsarecausedwhentheouterskinofthepartisstiffenoughtoresisttheshrinkageforcesthuspreventingasurfacedepression.Instead,thematerialcorewillshrink,creatingvoidsinsidethepart.Voidsmayhavesevereimpactonthestructuralperformanceofthepart.Moldingsinkmarkandvoid.

Figure12Sinkmark[2]

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4.3.3.1 CausesSinkmarksarecausedmainlybythermalcontraction(shrinkage)duringcooling.Afterthematerialontheoutsidehascooledandsolidified,thecorematerialstartstocool.Itsshrinkagepullsthesurfaceofthemainwallinward,causingasinkmark.Iftheskinisrigidenough,deformationoftheskinmaybereplacedbyformationofavoidinthecore.Localizedgeometricfeaturessinkmarkstypicallyoccurinmoldingswiththickersections,oratlocationsoppositefromribs,bossesorinternalfillets.Highvolumetricshrinkage.Insufficientmaterialcompensation.Earlygatefreezeofforlowpackingpressuremaynotpackthecavityproperly.Shortpackingorcoolingtime.Highmeltand/ormoldtemperatures.4.3.3.2 Remedies

Assinkmarksoccurduringpacking,themost. Effectivewaytoreduceoreliminatethemistocontrolthepackingpressure

correctly.Todeterminetheeffectsofpackingonsinkmarks,useasimulationpackagesuchasMoldflowPlasticsInsight.

Changepartgeometry. Alterpartdesigntoavoidthicksectionsandreduce. Thethicknessofanyfeaturesthatintersectwiththemainsurface. Reducevolumetricshrinkage. Relocategatestoproblemareas. Optimizetherunnersystemdesign Restrictiverunnersystemdesigncanresultin prematuregatefreezeoff.

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4.4 AppearanceDefects4.4.1 MetallicProjectionJointflashorfins.Flatprojectionofirregularthickness,oftenwithlacyedges,perpendiculartooneofthefacesofthecasting.Itoccursalongthejointorpartinglineofthemold,atacoreprint,orwherevertwoelementsofthemoldintersect.

Figure13Metallicprojection[2]

4.4.1.1 CausesClearancebetweentwoelementsofthemoldorbetweenmoldandcore;poorlyfitmoldjoint.4.4.1.2 RemediesCareinpatternmaking,moldingandcoremaking.Controloftheirdimensions;Careincoresettingandmoldassembly.

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4.4.2 CavitiesBlowholes,pinholes,Smoothwalledcavities,essentiallyspherical,oftennotcontactingtheexternalcastingsurface(Blowholes).Thedefectcanappearinallregionsofthecasting.

Figure14Blowholes[2]

4.4.2.1 CausesBlowholesandpinholesareproducedbecauseofgasentrappedinthemetalduringthecourseofsolidification.4.4.2.2 RemediesMakeadequateprovisionforevacuationofairandgasfromthemoldcavity;Increasepermeabilityofmoldandcores.4.4.3 DiscontinuitiesHotcracking.Acrackoftenscarcelyvisiblebecausethecastingingeneralhasnotseparatedintofragments.Thefracturesurfacesmaybediscoloredbecauseofoxidation.Thedesignofthecastingissuchthatthecrackwouldnotbeexpectedtoresultfromconstraintsduringcooling.

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Figure15Bodycrack[2]

4.4.3.1 CausesDamagetothecastingwhilehotduetoroughhandlingorexcessivetemperatureatshakeout.4.4.3.2 RemediesCareinshakeoutandinhandlingthecastingwhileitisstillhot;Sufficientcoolingofthecastinginthemold.4.4.4 IncompletecastingPouredshort.Theupperportionofthecastingismissing.Theedgesadjacenttothemissingsectionareslightlyrounded;allothercontoursconformtothepattern.Thespree,risersandlateralventsarefilledonlytothesameheightabovethepartingline,asisthecasting.

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Figure16Incomplete[2]

4.4.4.1 CausesInsufficientquantityofliquidmetalintheladle.Prematureinterruptionofpouringduetoworkmanserror.4.4.4.2 RemediesHavesufficientmetalintheladletofillthemold,Checkthegatingsystem.Instructpouringcrewandsupervisepouringpractice.4.4.5 IncorrectdimensionorshapeDistortedcasting.Inadequatethickness,extendingoverlargeareasofthecopeordragsurfacesatthetimethemoldisrammed.4.4.5.1 CausesRigidityofthepatternorpatternplateisnotsufficienttowithstandtherammingpressureappliedtothesand.Theresultisanelasticdeformationofthepatternandacorresponding,permanentdeformationofthemoldcavity.Indiagnosingthecondition,thecomparethesurfacesofthepatternwiththoseofthemolditself.

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4.4.5.2 RemediesAssureadequaterigidityofpatternsandpatternplates,especiallywhensqueezepressuresarebeingincreased.4.4.6 DefectivesurfaceFlowmarks.Onthesurfacesofotherwisesoundcastings,thedefectappearsaslineswhichtracetheflowofthestreamsofliquidmetal.

Figure17Defectivesurface[2]

4.4.6.1 CausesOxidefilmswhichlodgeatthesurface,partiallymarkingthepathsofmetalflowthroughthemold.4.4.6.2 Remedies

Increasemoldtemperature; Lowerthepouringtemperature; Modifygatesizeandlocation. Tiltthemoldduringpouring.

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4.4.7 RatTailandBucklesRattailsandbucklesarecausedbytheexpansionofathinouterlayerofmouldingsandonthesurfaceofthemouldcavityduetometalheat.

Figure18Rattail[2]

4.4.7.1 Causes Arattailiscausedbydepressionofapartofthemouldundercompressionwhichappearsasanirregularlineonthesurfaceofthecasting. Abuckleisamoreseverefailureofthesandsurfaceundercompression.4.4.7.2 RemediesThemouldmustprovideforproperexpansioninsteadofformingcompressedlayerstoavoidthisdefect.

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5 CONCLUSIONInthisresearchworkdifferentcastingdefectsarestudied.Byreferringdifferentresearchpaperscausesandtheirremediesarelisted.Thesewillhelptoqualitycontroldepartmentofcastingindustriesforanalysisofcastingdefect.Thisstudywilldefinitelybehelpfulinimprovingtheproductivityandyieldofthecasting.Rejectionsofthecastingonthebasisofthecastingdefectshouldbeasminimizedandalltheaboveresearchisheadinginthesamedirection.

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REFERNCES

[1] Wikipedia

http://en.wikipedia.org/[2] Google

https://www.google.com.eg/search?q=casting+defects+distortion&espv=2&biw=1366&bih=624&source=lnms&tbm=isch&sa=X&ei=hZZmVJ2cGcLJOf9gdAO&ved=0CAYQ_AUoAQ#tbm=isch&q=defected+casting&imgdii=_

[3] Slideshare[4] http://www.slideshare.net/pallawisinha9/castingdefects

[5] http://www.ijrat.org/downloads/march2014/paper%20id232014109.pdf