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1、PaintingDefects:Cracks??Aswithpinholes,thesefinecracksonthepaintedsurfacearecausedbysolventattack,andthisphenomenonisoftenseeninacrylicpainting.Thesecracksgenerallyoccurneargatesandatedgesinparticular.Werecommendourspecialpaintinggradesforuseinpaintedproducts.??Example:Acrylicpaint?Cause:Solventin
2、thepaintattackssectionsofthesubstratematerialwherelevelsofresidualstrainarehigh,thuscausingchemicalstress.?Countermeasures:-Selectionofalessaggressivesolvent-Modificationofthepaintandsolventmixtureratios-Annealing(atbetween60deg.Cand70deg.Cfor20to60minutes)-Raisingofthecylindertemperatureanddietem
3、perature.-Loweringoftheinjectionanddwellpressures,andraisingoftheinjectionspeed*Generallyspeaking,theadditionofretarderisnotagoodmeansoftreatingchemicalcracks.MoldedPartCracking:PlatedPartCracking??TypicalcrackingofplatedpartsPlatedlayercracking(athightemperatures)Plasticlayercracking(atlowtempera
4、tures)Causes:Theprincipalcauseofthistypeofcrackingisthermalstress-i.e.,tensilestressinexcessofthecorrespondingmaterialcharacteristic(i.e.,strength)whichiscausedasaresultofdifferencesinthedegreetowhichtheplatedandplasticlayersexpandorcontractinresponsetochangesintheambienttemperature.Specifically,c
5、rackingoccursintheplatedlayerattemperatureshigherthantheplatingtemperature;andintheplasticlayer,atlowertemperatures.MaterialYoung'smodulus(MPa)Coefficientoflinearexpansion(1/deg.C)Copper1.23x10**516.6x10**-6Nickel2.01x10**512.8x10**-6Chromium2.48x10**58.2x10**-6ABS1,900to4,00060to95x10**-6Occasion
6、ally,theplasticlayermaybesubjectedtochemicalattackasaresultofcontactwithremnantsoftheplatingfluid.?CountermeasuresThesimplestcountermeasureforthistypeoffailureistoeliminatealledgesfromtheplasticcomponenttobeplated,andthisworksbypreventingtheconcentrationofthermalstressatthecorrespondingsectionswhe
7、nchangesoccurintheambienttemperature.-Bufferingofflashatpartingsectionsandothersimilartreatmentsareusedtosmoothenthesurface.-Gatingsurfacesaremadeassmoothaspossible.-Corners(andparticularlythoseatacuteangles)arer
