ABS制品缺陷与内应力.doc

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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