THEPREPARATIONANDUSEOFPLASTICMOLDSM.B.BorisovUDC666.5:666.3.032Plastermoldsarewidelyusedforcastingwaresintheceramicsindustry.Apartfromcertainad-vantages,theyhavealowmechanicalstrengthandshortworkinglifeduetowearoftheworksurfaceundertheactionofwaterandelectrolytesinthebody.Besidesthis,thetemperatureinthedryercannotbehigherthan65asabovethistemperaturetheplasterisdestroyed.Thenecessityoffindingasubstituteforplasterwasincreasedwhentheporcelainindustrybeganin-stallingsemiautomaticmachinesformoldinganddrying,withintensifieddryingconditions.Thesearchforasubstituteforplasterbeganinourfactoryin1967,andtothisendagroupwasorganizedcontainingthefollowingworkers:A.V.Saveleva,P.S.Polyakov,T.A.Pashkova,V.A.Kholkin,A.V.Sarichev,F.I.Lisov,andothers.AtthestartoftheirworktheresearchgroupwereguidedbydatafromtheStateCeramicsResearchInstitute1.However,thisdidnotansweranumberofquestionsarisingfromtheworkingoftheplant,suchas:howtodesignandmakepressmoldssoastoavoidcrackingintheplaneofintersectionoftwosurfaces,whatbatchtotakeperunitvolumeofmold,whatscheduletousefortheheattreatment,howtoobtainuniformdistributionofporesandincreasegeneralporosity,andhowtoavoidadheringbythebody,etc.Followingontheresultsoftheirresearch,in1969thegroupbegandevelopingthepreparationofPVCmolds,andconvertingtheproductionlineofthefactorytotheiruse.Atthepresenttimethereareinthefactoryfiveproductionlinesforplates,threeofwhichareforshallow200mmplatesandtwofordeep200mmplates,aswellassevenlinesforcups.Usingtheplasticmoldsatotalof24,000platesand35-37,000cupsareproducedperday(24h).Theprovisionalannualsavingaccruingfromtheintroductionofonlyoneproductionlineis2500rubles.Theworkinglifeoftheplasticmoldsincupproductionreaches4000cyclesandcanstillbeincreased.Thelifeofthemoldsinplateproductionhasstillnotbeendetermined.Asectionforpreparingthemoldswasorganizedinthefactoryin1969(Fig.1).Therawmaterialwasdomesticpolyvinylchloridelatex,gradeL-5,oremulsifiedpolyvinylchloride,gradeE-62.Polyvinyl-chlorideistheproductofpolymerizationofvinylchloride.Itisawhitefinelydispersed(noresidueonNo.0056sieve)powderofdensity1.41g/cm3.Atatempera-tureof170-180andunderslightpressure(specificpressure0.05kg/cm2)thepolyvinylchloridepar-ticlesmeltandcohere.Thefirststageinthepreparationofthemoldsisapreliminaryvibromolding(onthevibrotable)whichensuresuniformporosity.Thevibrotableperforms50oscillations/secwithanamplitudeof0.5ram.Thevibromoldingiscarriedoutfor15-20sec.Thispreliminaryvibromoldingisanessentialpartoftheprocessformakingthemolds,since,duringmolding,internalstressesaregeneratedwhichareconcentratednearthepointsofcontactofmolec-ularcohesionofthefineparticles.Thisinternalstressisespeciallydangerousduringtheprocessofsin-tering.Itcanberemovedbyvibration,whichalmostcompletelybreaksallconnectionsbetweenparticlesandensurestheiruniformdistribution.Thebasicpieceofequipmentinthepreparationoftheplasticmoldsisthemetalpress-mold(Fig.2)whichismadefromgrade45orSt.3steel.Itsinternalsurfacemustbechromiumplated.DulevoPorcelainFactory.TranslatedfromStekloiKeramika,No.3,pp.7-9,March,1972.91972ConsultantsBureau,adivisionofPlenumPublishingCorporation,227g/est17thStreet,NewYork,N.Y.10011.Allrightsreserved.Thisarticlecannotbereproducedforanypurposewhatsoeverwithoutpermissionofthepublisher.Acopyofthisarticleisavailablefromthepublisherfor$i5.00.147,.-13500l23456fiIO987Fig.IFig.2Fig.I.i)Handpress；2)SNOLelectricallyheatedcabinetforheattreatmentofthemolds；3)cabinetforcoolingthemolds；4)tableforassemblyanddismantling；5)standforpreparedmolds；6)storagefortheplastics；7)electricallyheatedcabinetfordrying；8)standforfinishingthemolds；9)tableforpackingplastics；i0)tableformeasuringoutplastics；ii)vibratingtable.Fig.2.Press-mold.a)Assembled；b)dismantled.Theprocessoffillingthepress-moldformakingflatware(plates)plasticmoldsisshowninFig.3.L-5powder,whichhaspreviouslybeendriedintheeleetrodryingcabinetatll0andthenscreenedthroughaNo.05sieve,ischargedintothematrixofthepress-moldandleveledwithaspecialtool.Theamountofplasticdependsonthetype(volume)ofthemold.Forshallow200mmplatesitis600g,fordeep200mmplates660g,forsaucers400g,andforcups500-515g.Thepress-moldpunchisthenin-sertedintothematrixinsuchawaythatitentersunderitsownweightuntilitisincontactwiththeplastic.Tocheckthecorrectnessofassemblyatthispoint,thepunchisrotatedrelativetothematrix.Theassembledpress-moldisplacedonthevibrotableandcompactedfor15-20sec.Aftercom-pacting,thegapbetweenthematrixflangeandthepunchflangeshouldbe8-10ram.Thepress-moldisnextinsertedintoSNOLelectrocabinetfortheheatprocessandaweightisplacedonthetopsoastogiveapressureof0.05kg/cm2.Tomonitorthetemperature,athermometerisinsertedsothatittouchesthecenterofthepunch.Asmallamountoftheplasticisheapedonthepunchflange,anditschangeincolorisusedtoassessthereadinessofthemold.Theheatprocesscontinuesfor2-3handatitscompletionthetemperatureofthepress-moldis170-175Afterthecompletionoftheheatprocess,thethermometerisremovedandthepress-moldtakenfromthecabinetandplacedintotheventilatedcabinettocool.Thepress-moldisthendismantledusinganex-tractionscrew.Thepreparedplasticmoldisremoved,trimmedsmoothattheedges,andafterinspectionisreadyforuse.Themoldsforthehollowwares(cups)werepreparedaccordingtothefollowingschedule.Thecor-rectamountofPVCplasticwasputintothematrixFig.4)andleveledoff.Two22-24mmthickspacerswereplacedontheflangeofthematrix1,andthematrix2loweredontoitsothattheringflangewasrestingonthespacers.Thepunch3wasthenloweredintotheringsothatitsflangewaslevelwiththeringflange.Theassembledpress-moldwasthenturnedoverandplacedflangedownonthevibrotable,withthepunchflangestandingona50x50mmblock.Thespacerswerethen.removedfromundertheringflange,andaweightof8-10kgplacedonthebottomofthematrix,positionedtothatitscenterlayontheaxisofthepress-mold.Thevibratorwasturnedonandtheringheldbehindtheflangevibratedtheplasticfor15-20sec.Aftervibratingtheclearancebetweentheflangesofthematrixandpunchshouldbeabout5-7ram,andbetweenthepunchflangeandtheringabout10mm.Thepress-moldwasthenturnedover,and5-6mmthickpackinglaidonthepunchflange,andthentheweightplacedonthiswhichgavethepressureof0.05kg/cm2fortheheatprocess.Thepress-mold,withtheweight,wasplacedintheelectrodryingcabinetonafireclaybase6-8cmthick.Theheatingprocesswascarriedoutaccordingtothegraph(Fig.5)for1.5-2huptoatemperatureofof180-185Thetemperaturewasmonitoredbyamercurythermometer.Attheendoftheheattreatmenttheloadwasremovedandthepress-moldtakenfromtheelectrocabinetandpressedonthehandpressuntil148Fig.3tc160_.=.:.iu/020406080lOOTime,rainFig.4Fig.5Fig.3.1)Stopwasher；2)ring；3)punch；4)die；5)polyvinylchloride.Fig.4.1)Matrix；2)ring；3)punch；4)screw；5)mold.Fig.5.Heattreatmentgraphsforprocessingplasticmolds.200mmdiameterplates.1)Forcups；2)forshallowtheringandpunchflangesmadecontactwiththematrixflange.Afterretainingunderthepressfor10minthepress-moldwasremovedandplacedintheventilatedcabinettocooldownto40-45Thepress-moldwasdismantledandthepreparedplasticmoldextracted.Aftertrimmingitwasreadyforuse.Experienceinthepreparationofthesepolyvinylchloridemoldsandintheiruseinthefactoryhasshownthatdeviationfromtheabovepreparationschedulesleadstotheappearanceofvariousfaultsinthemoldswhichshowupduringtheprocessofformingwareswiththem:underpressing,porosityofthema-terialundertheshouldersofthehollowmold,ringcracksonthestemofthehollowmold.Constantcontroloftheelectrodryingcabinetbymeansofthethermoregulatorensuresauniformtemperatureinthechamberduringtheheattreatmentofthepressings,andensuresuniformheatingoftheplasticforallsectionthicknesses.Theresultantuniformityofsinteringpreventstheproductionofamoldwithdifferentcoefficientsofthermalexpansionbetweentheedgesandcenteroftheplastic.Thisgreatlyreducestheoccurrenceofcracksintheworkingsurfaceofthemoldduringuseandincreasesitsworkinglife.Accumulatedexperienceintheuseofthemoldsinthefactoryhasshownthatitisnecessarytopayattentionto:carefuladjustmentofthemoldholderunderthepedestalofthesemiautomaticmachine；selec-tionofthemoldingschedule；avoidingsuddenloweringoftherolleratthemomentofcontactwiththebody；theselectionofthecorrectspeedforthemoldingroller(500-550rpmforcupsand250-275rpmforplates)andforthemoldholder(750-800rpmforcupsand300-500forplates)inordertoavoidtheproductionofscrapintheformofhumpersandwhirlers.Failuretoobservetheserequirementscanalsoleadtodamagetothemold(chippingofftheshoulder,anddiggingoutthebottomwithhollowware).Themoldswhenproducedvaryincolorfromrosetodarkbrown,accordingtothedurationoftheheattreatmentatconstantpressureandthefinaltemperatureintheelectrocabinet.Thedarkbrownoneshavelowporosity,andinpracticecannotbeused.Therosecoloredoneshaveadequateworkingproper-ties,buttheirlowmechanicalstrengthsignificantlyreducestheirworkinglife.Obtainingthenormalworkingporosityof31-35%,withuniformlydistributedpores,andatthesametimeretainingthenecessarymechanicalstrength,wasoneofthemostdifficultproblemsintheproductionofthemolds.Iftheheattreatmentwasforced,thisrapidlyledtotheappearanceofasurfacecrustwitharawinteriorinthemold.Ifthefinaltemperaturewasraisedabove210inordertospeeduptheheattreatment,thisledtodecompositionoftheplasticwiththeevolutionofgaseswhichdestroyedthesurfaceofthemold.Afterextensiveinvestigation,theoptimumheatingschedulefortheplasticinthepress-mold,whichgavemoldsofthedesiredquality,wasfoundandisshowninFig.5.Fromexperienceinthepreparationanduseofthemolds,thecorrectamountofplasticperunitvol-u