considerations for manual & automatic green sand …

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CONSIDERATIONS FOR MANUAL & AUTOMATIC GREEN SAND EXPANSIONS

EMI Equipment Manufacturers Inc. 16151 Puritas Avenue, Cleveland, OH 44135Phone: 216.651.6700 Fax: 216.651.6331 www.emi-inc.com

CONSIDERATIONS FOR MANUAL & AUTOMATIC GREEN SAND EXPANSIONS

WHITE PAPER TAKEAWAYS • Jolt Squeeze Machines • Automation Matchplate Molding •Gravity-fillmachinesvsBlow-fillmachines • Horizontal Tight Flask Molding Systems • In-line vs Cross-Loop vs Pallet Index Lines

Foundries,guidingtheirbusiness,havetosurvivethroughthevariouseconomiccyclesaswellasemergingmarketpressures,arewellawareofthecontinuousneedtoreinvestinequipmenttoincreaseproductivity,anddecreasethemanualcontentofcastingproduction,whilestillproducing consistent castings economically in a very demanding market. From their position, themoldingmachinemanufacturershavetoprovidetheproperlydevelopedequipmentand/ormoldingprocesstomeetthesedemands,whileatthesametimeimprovingcastingqualityandmaintainingasafeworkingenvironment.

Thecontinuousevolutionofthemechanizationofgreensandmoldinghasgrownfromsimplejolttable,usedtocompactsandinthemoldingbox,totheautomaticsystemsoftoday,producinginexcessof400moldsperhour,withlittleornomanualinvolvement.Moldqualitywhichcanbeachievedontoday’smoldingmachinesissuchthatmanyoftheolddefectsonceassociatedwithgreensandhavebeeneliminatedorgreatlyreduced,eitherbyusingasimultaneousjoltsqueezeaction,orhighpressuresqueezetominimizemoldwallmovementduringpouringandsolidification.


Green sand molding remains an attractive casting production method for two main reasons:

1. Green sand production is and will always be less expensive, as the price of chemicalbinderscontinuestorisefasterthannormalinflation.

2. Green sand foundries are not as labor intensive. Oneobstaclepreventingfoundriesfrommovingintogreensandmoldingisthehigh capitalcostofevenasimplemechanizedplant.However,foundriesshouldrealizethat theincreasedproductivitythatgreensandmoldingofferswilloffsetthesecostsovertime andhavethepotentialforhigherrevenues.

However,beforeembarkingonahighcostgreensandinvestmentprogram,certain questionsshouldbeaskedandansweredinordertoestablishwhetheritisnecessary toinvestinsomeformofmechanizedmoldingequipment.

a. Whatarecurrentmoldproduction/Futuremoldproductionrequirements? b. Iscurrentcastingqualityconsistentandreliable? c. Isscrapistoohigh? d. Aremyleadtimedeliverydatestoolongforlargevolumes?

STANDARD MOLDING MACHINE SOLUTIONS


Standard Jolt Squeeze Machines Tominimizetheinitialgreensandinvestment,standardmoldingmachinesofferamajor advantagebecauseafoundrycanmechanizeforgreensandmoldingwithreasonable initialexpense,andthebalanceofthemoldhandingcanbebuiltovertime.These machinescanbethesmall212/214joltmachines,upthroughthe722&730joltmolding machines. These machines can use almost any standard green sand match plate and copeanddragpatternequipment.Anumberofflasksizescanbecanbeemployedon thesamemachine,givingflexibilityofproductionandproductrange.

Astandardmoldingmatchplatesolutioncanbefoundwherecopeanddragareformed simultaneously.Theoveralloperatingefficiencyofthesemachinesisverymuchdependent ontheoperator’sabilitytocontinuallycarryoutthesemachinesmanualfunctions.By implementing mechanized mold handling systems, as previously stated, the machines can provide more productivity.

Automatic Horizontal Flaskless Molding (Matchplate) Afterthedevelopmentofthejolt,rap,andsqueezemoldingtechnology,thefocusofthemachineryforgreensandmoldproductionwasputintohandling systems designed to reduce the reliance on labor to achieve a morereasonableproductionrate.Automatichorizontalflasklessmoldingmachines,sometimesknownasautomaticmatchplatemoldingmachines,weredesignedandfirstintroducedtofoundriesintheUSAinthemid1960’s.Thesemachineshaveprobablyhadamorerapidgrowthintheirusethananyotherinnovationtogreensandmoldproductioninthelast60years.

ThemainreasonforthiscontinuedsuccessintheUSisthatmanysmalltomediumfoundrieswereofthetypeknownas“SqueezerShops”,usingstandardjoltsqueezemachinesorRoto-liftswithsnapflasksandmatchplate.WithsomanymatchplatepatternsavailablefromtheOEMmanufacturers,itwasquitecommonforthefoundriestoinstalloneofthesemachinesandusetheircustomer’sexistingpatterns.

Theseautomatichorizontalmatchplatemachinesarearelativelyeconomicformofmoldingmechanization. The machine produces a complete mould in one cycle and only requires one machineoperatorwhocansetcoresasnecessary,thusremovingsomeoftherelianceonmanuallabortomakethemold.Productionratescanbeover200moldsperhourun-cored.Ifcoredworkisrequired,thefoundryislimitedtoautomaticcoresettingifitwishestomaintainmaximum production, although automatic core setting is really a misnomer, since a man is required to put the core or cores into the setting unit.

Two methods of filling are used in flaskless molding:

1. Gravityfill&Squeeze

2. Blowfill&Squeeze


ThemoldingprocessforboththeGravityandBlowmachinesisvirtuallyidentical.Consequently,forthepurposeofthiscomparisonourcommentswillapplyequallytobothmachines.

Withblowmachine,thepatternplateistrappedinbetweenthecopeanddragflaskswhicharethentippeduponedgesothatthepatternisvertical.Sandisthenblownstraightdownfromapairofblowslotstofilltheflasksfromabove.Thismeansthatsand,whichistravelingataveryhighvelocity,mustmakearightanglechangeofdirectioninordertofilldeepergreensandpocketsormoldcavities.Consequently,therearefrequentlyproblemsfillinganddrawingdeepergreensandpocketsandcavities.Gravityfill&squeezemachineshaveshowntogivemore consistent mold quality and are more suited to deep and complicated pattern shapes.

Thishasbeenawellknownweaknessofthesideblowmachinessincewereinvented50yearsago.Eventhoughthesenewermachinestiptheflasksandpatternsuponedgetoblow,itisstillessentiallya“side-blow”relativetothepattern.

Blowingamoldatthetypical40or50psipre-compactsthesandbeforeitissqueezed.Thismakesitnecessaryforblow-fillmachinestosqueezeharderinattempttoforcethesandintopocketsonthepattern.Thisoftenresultsinamoldthatisharderthandesirableontheflatareasandthepartingline,buttoosoftindeeperpocketsandmoldcavities.Thesehighersqueezepressuresrequirethickerandmoreexpensivepatternstoavoidpatternflexingandbreakage.Ifagreensandpocketisnotcompletelyfilledduringtheblowcycle,itisvirtuallyimpossible to squeeze hard enough to correct this problem.

Aluminumfoundriesdonotwanttomakeamoldthatistoohardbecauseofgasproblemscausedbythereducedpermeabilityofhardermolds.Blow-fillmachinessometimeshaveproblemsinthisareaduetothefactthattheymustsqueezehardertogetanacceptablemolddensity in deeper pockets. The important point is that mold hardness alone is not necessarily good;uniformdensityandrepeatabilityis!

Squeezingamoldtoohardcancausegreensandmoldstobreakoffratherthandrawproperly.Researchhasproventhatanyincreaseinmoldhardnessatsqueezepressuresabove140psiisalmostnegligible.Furthermore,highersqueezepressurescauseaphenomenoncalledspring-backinthesand.Undertheseconditionsthesandactuallyspringsbackafterthesqueeze,andcontroloverthecastingdimensionaltolerancesislost.Sincethereisnotenoughspacebetweenthesandgrainsfornormalthermalexpansion,therewillbeexpansiondefectsinthecastingsandotherdefectsduetocrackingofthemold.

Therearenewertechnologyimprovementsofmachinesthatworkwithgravitytofilltheflask.Sandisriddledevenlyontothepatternthroughanaerator,andtheflask&patternisvibratedduringthefill.Themoldisthensqueezedanddrawnaccordingtoacomputercontrolledrecipe.Sandintheflaskisstillhighlyflowableandcannormallybecompactedtomoldhardnessinexcessof90withasqueezepressureofonlyabout100psi.


As previously mentioned, any large projections or obstructions on the pattern plate make it difficulttogetanadequatelydensefillofthemoldonthesideofthemoldoppositetheblowslot.Thiscauseswhatiscommonlyknownasthe“shadoweffect”whichisasoftspotinthemold.Thesesoftspotspreventthemoldfrombeinguniformlydenseandareatroublesomesourceofcastingdefectsandscrap.Thisiswhyblowtypemachinesaregenerallylimitedtodoingsmallercastingswithoutanydeepordifficultpatternshapes.

Large,deeporasymmetricalcastingsoftenrequiretheuseofpatternswithanoffsetpartingline.Thisoffsetpartingwillcreateanadditionalobstacletothesandbeingblowninat90ºtothesurfaceofthepatternplate.Theobstructionisatleastequaltotheamountofoffsetonthepartinglineofthepattern.

Sinceanythingstickingupfromthepatterncanexacerbatetheseproblems,theblowprocessalsoseverelylimitswherepouringbasins,downspruesandriserstofeedthecastingcanbelocated.Thiscanbeaseriousproblemwhenlargerisersarerequiredorthepatternplateiscrowded.Thepouringcupanddownspruelocationsarefurtherrestrictedduetothesqueezecylinderlocationandothermechanismsonthebacksideofthesqueezehead.Thisrestrictioncancauseaproblemwithefficientpatternlayout,andthenumberofpartsorpiecesyoucangetpermold.Italsodictateswhichwayanygivenpatternmustbeorientedwhenthejobisrunonthemachinewhichcancausedifficultiesforefficientcoresettingorpouring.

Patternswithdeepergreensandpocketsrequireventingtorunonblow-fillmachines.Theseventsareusedinanattempttogetsandtoflowintodeeperpockets.Thisincreasesthecostofthepatternandlaterbecomesamaintenanceissue.Whileventsintheflasksarenecessaryforventingthemold,theyarenotveryeffectiveforfillingpockets.Ifbothhalvesofthemoldareblownsimultaneously,theblowpressureonbothhalvesofthemoldisequal.Then,howcanventingthroughthepatterntofillapocketononesidemakeanydifference?Someblow-fillmachineshavetheabilitytoblowthecopefirstandthenthedrag,orthereverse,dependingonwhichsidehasthedeepestpockets.Thisiscalleda“staggered-blow”.Thetheoryisthattheairwillescapethroughthepatternventsandintheprocesscarrysandwithitintothepockets.Therealitiesmaybesomewhatdifferent.

Acceleratedflaskandpatternwearisaproblemduetothe“sandblasting”effectcausedbytheblowingsand.Anyprojectionsonthepatterndirectlyinfrontoftheblowslotswillwearthefastestandexperiencethemostseveredamage.Also,operatingcostsanddowntimewillbehigherwithnumerousblowsealsandflaskandpatternventstomaintainandreplace.

Squeezingthemoldfrombothsidesrequiresthatbothhalvesofthemoldbefilledwithsanduniformly,andthesqueezepressuresonbothcylindersbeperfectlybalanced.Otherwise,theresultwillbeadamagedorbrokenpatternplate.Usersofblow-typemachinesmustbeverycarefultoadjustthemachine’soperatingprogramduringeverypatternchange.Attemptingtomakeamoldthatisnottallenoughforaparticularpatterncaneasilybreakordamagethepatternplate.Highsandcompactabilitywhenmakingamoldorablowthatisshortofsandcan also break the pattern.


Incontrast,thegravityfilledmachinesqueezesfromthebottomandthepatternandflasksmoveupagainstafixedsqueezehead.Inthisprocessthepatternessentiallyfloats,sothatthesqueezingforcesonbothsidesofthepatternarenaturallyequal.Thecontrolsystemalsoprotectsagainstoversqueezingduetoshortfillingoftheflasks.

Large asymmetrical castings such as cooking pots or brake drums inherently cause the biggestproblemsforthesemachines.Onesidewithalargecavitywillrequiresignificantlymoresandandalongerstroketosqueeze.Theothersidewithalargeflatsurfaceontheprojectionwillrequirelesssandandonlypermitashortsqueezestroke.Thisisverydifficulttobalanceandcontrolwiththeblow-fillmachineslimitedabilitytoconsistentlyfillandsqueezedeep pockets to an adequate and consistent mold density.

Blow-fillmachinespermitonlysmallvariationsinsandproperties,especiallymoistureandcompactability.Wetsandand/orhigherclaylevelswillquicklyplugupthemachine’sblowhead.

Sand Segregation Mostfoundryworkersareawareofsandsegregationproblemsthatoccurwhensandistransportedpneumatically.Thereareindicationsthatthisoccurstoadegreeduringtheblow-fillmoldingprocessandthatfinermaterialendsupatthemoldinterfaceonthejointlineofthemold.Thisfurtherreducesthemoldpermeabilityandcancontributetogasproblemsinthemold.Incontrast,gravity-fillmachinesdonotfluidizesand,sothisisnotanissue.Gravitymachinescaneasilyadjustsqueezepressuresandvibrationtoproduceamoldofoptimumanduniformhardnessforeventhemostdifficultpatternconfigurations.

Operatingblow-fillmachinesinwarmortropicalclimatescanbedifficult.Asurgetankisrequirednearthemachinetosupplyalargequantityofairondemand.Theairmustbedryandtherecanbenofluctuationsintheairpressureatthemachine.Theyuselargeamountsofcompressedairtoblowthesand.Ingeneraltheywillconsume3to4timesasmuchcompressedairasagravityfillmachine.

Warmorhotsandcombinedwithcompressedaircancausecondensationintheblowchamber.Thisinturncancausesandtopartiallyclogorpluguptheblowchamber.Abatchofsandthatistoowetortoodryisverydifficulttodisposeofonceitenterstheblowchamberofthemachine.

Onthegravityfilledmachinetheoperatorcaneasilyinspectbothsidesofthepatternandthefinishedsurfaceofthecopeordragmoldsbeforeclosing.Withtheblowmachines,theoperatorneverseesthedragsideofthepatternorthecopemold.Thismeansthatthemachinecouldbeproducingmoldswithadefectinthecopemoldandtheoperatorwouldneverknowaboutit.

Anythingthatissetonthepatternand/orinvestedinthemoldisaproblemfortheblowmachines.Thisincludesram-upcores,chills,filters,chaplets,facingsand,exothermicsleeves,insulatedorevenopenrisers,etc.Theblowfillprocessprecludesalloftheseoperations,sincethesandrushinginandpatterntippingupverticallyduringthemoldingprocesswoulddislodge anything placed on the pattern.

Asalwaysitshouldbekeptinmindthatgreensandmoldqualityisafunctionofpatternandsandqualitywiththethirdessentialingredientbeinghighdensityanduniformcompactionofthe mold.


HORIZONTAL TIGHT FLASK MOLDING SYSTEMS

Thedevelopmentofhighpressuremoldingusingflasks,tookplaceintheUSAinthemid195O’s.Thesehandlingsystemswereanaturalprogressionawayfromheavymanuallabor,and the reliance on labor to meet production targets.

TheIN-LINEarrangementisasinglelinearrangement,whichrunsparalleltoamouldconveyor.Ittakesinallstagesofmoldmanufacturefrommoldpickoff,throughpunchout,flaskseparation,molding,coreplacingclosing,andplacingthecompletedmoldbackontothemoldconveyor.Thissystemisdesignedtoacceptflasksizesintherange20”x16”upto36”x24”,withproductionratesofbetween300to400mouldsperhour.

TheCROSS-LOOParrangementhastwomouldinglines, one to produce the drag and the other to produce the cope, as they span the mold conveyor loop. This arrangementisnormallyusedforflasksizesabove36”x24”,and/orwhereheavycoresareplacedinthedrag,asinacylinderblock,forexample.ProductionratesontheCROSS-LOOPareslowerthantheIN-LINE,normallybetween260/300moldsperhour.

Thebenefitswhichthesetwosystemsofferaretheinfiniteflexibilityinuse,highproductivityandadaptationtoalltypesofcastings,especiallythoserequiringcoreswherethetightflasksystemisfoundtobemoreefficientand economical. This is because more castings can beproducedwithinthesamegivenmoldareawhencomparedtoflasklessmolds.

Coreplacingdoesnotslowproduction,sincethecoringzoneisdesignedtogivemaximumflexibility,whethertwoortencoresneedtobeplaced.

Moldpouringcanbeautomatic,butapouringzoneisalwaysdesignedintothesystemtoretainflexibilityandallowformanualpouringasnecessary.Theextracostoflaborrequiredformanualcoringandpouringisinsignificant,becausethesystemiskeptrunningatitsmaximumoutput,300to400mouldsperhour,whichassiststheprofitabilityoftheentirefoundry.

Tofurtherimprovetheflexibilityofthesesystems,themoldingmachinescanbeequippedwithapatternshuttlechangeunit,sothatpatternchangescanbemadewithintheautomaticcyclewithoutlossofproduction.Twopatternscanberunatthesametimeorvariedtosuitconditionsandevenoutcoredemand,and/ormetalavailability.

TheIN-LINEandCROSS-LOOPsystemsofferthefoundrythemostproductiveandflexibleapproachtomechanizedmoldingforcastingsrequiringcoresatahighproductionrateof+250mph.Thecostpermouldislessthanwithanyothersystem,calculatinginitialcapitalcost, against productivity and running costs.


Forlowerormoreversatileproductionrequirementsoftoday’sjobbingfoundry,manyofthesecontinuousmoldlineconveyorloopshavebeenreplacedwithindexpalletsystems.Palletindexsystemsoffertheflexibilityofparkinglinesforextendedcoolingtimesandcanalsotakeuplessfloorspaceduetocloserlineproximityandtheeliminationofthemoldconveyorradius.

ThemoldingmachinesusedinanyoftheIN-LINE,CROSS-LOOPorevenmorecommontodaythePalletIndexsystemsaretypicallyofthehighpressuresqueezetype.

Investigationusingawiderangeofsqueezepressureshasshownthatacastingproducedinamoldwhichhasbeencompactedtoasqueezepressureof100/110poundspersquareinch,isasaccurateasoneproducedusingasqueezepressureof200to220poundspersquareinch.Thereforetodayitisgenerallyacceptedthatthedegreeofmoldcompactionincreaseisverysmallaboveapressureof140poundspersquareinchinrelationtotheextrapressureapplied.Therefore,moldscanbeproducedwhichwillmakecastingsofconsistentaccuracyandsoundnesstomeetthetechnicalanddimensionalrequirementsoftoday’scastingusers,byusingmuchlowersqueezeforcesthanwaspreviouslythoughtnecessary.

Theonlyadvantagetobehadbyincreasingthesqueezeforceabovethispressureistodecreasethetimetakentomakeamold,sincethehighertheinitialsqueezeforce,thelesstimethisforcehastobeappliedtothemoldinordertoachieveoptimumcompaction.Thatis,thegreaterthesqueezeforceabove100poundspersquareinch,thehighertheproductionrate,untilamaximumisachievedaround2OO/22Opoundspersquareinch.Abovethisfigure,thereisnogaininmouldproduction,orcastingquality.

Usingthisinformation,somemachinemanufacturershavedevelopedvariousmeansofcompactingthemoldinsidetheflask.ThatisBlowSqueeze,IMPACTmoldingwithsqueeze,vacuummolding,orevensqueeze(topandbottominsomecases)withcompensatingpeenfeet,allinordertoreducetheoperatingnoiseofthemachinebyeliminatingtheprovenjoltandrapmoldingmethodology.Inpracticehowever,allofthesemachineshavelimitations,astowhattypeofcastingstheycanproduceandtheyareextremelysusceptibletovaryingsandconditions. Inconsistent mold hardness is also common.

Inaddition,improvedhardnessdistributionisalsoachievedbyjoltingorrappingforsomesecondstouniformlycompactthesandagainstthepatternface.Thentojoltandsqueezesimultaneouslytocompactthetopofthemoldpreferablyagainstacompensatingsqueezesurfacetosufficientlysupportthemoldface.Sometypeofpre-joltisnecessarytoevenlycompactthesandwhereisismostimportanttoformarigidmold,atthepatternfaceandjoint line.

Sincethesetypesofhighpressureautomaticproductionsystemsrequirethefoundrytouseflasks,therearecostsandmaintenancetoconsider.Flasksforhighpressureautomaticmoldingareexpensive,asarepallets/moldcars.Flasksrequiremaintenancecleaningandroutineplannedpinandbushingreplacement.However,theyshouldlastatleasttentofifteenyears, so cost is expensed over a long period.


Thesesystemsrequirehandlingequipmentthroughthevariousstagesofmoldandcastingproduction. The most important job they do is to ensure parting line accuracy. They support themoldthroughitsvariousstagesofmovementandassistinresistingthemetalheadpressure,allowingasoftermoldtobemadethanisnecessaryforaflasklessone.Becausethegreenstrengthrequirementisless,soistheclaycontent.Thisreducesthecostofsandpreparationandincreasesmouldpermeability.Theyalsoallowatleast8O%ofthemouldareatobeused,whereonly6O%canbeusedeffectivelywithoutflasks.

ThehighercapitalcostofahighpressureIN-LINE,CROSS-LOOPorPALLETINDEXsystemdoestosomeextentlimittheirmarket,howeverwithlifespansover25years,thisinvestmentneedstobeweighedagainstthedemandandproductivitycapacitythesesystemscreate.Theheartofthehighspeedsystemsandthepartwhichkeepsitproducingmouldsinexcessof300perhour,isthemoldingmachine.Beinghighpressurejoltsqueezeunits,poweredhydraulically,theycanbecostly,butfromexperienceandknowledgebuiltupovermanyyears,certaincriteriaarenecessarytoincludeinafourpostmoldingmachinetoproducemoldsofconsistent high quality.

a. Rigidstructuretowithstandtheforcesdevelopedbythemachine. b. Sandhoppertoevenlydistributethecorrectamountofsandintotheflask. c. Aeratortofluffthesandasitfallsintotheflask. d. Upsetframetogiveaheadofsandabovetheflaskforsqueezing. e. Pre-joltactiontocompactthesandbeforesqueezing. f. Optionofsimultaneousjoltingwithsqueezingtoimproveeffectivesqueezeforces.

Ahighpressuremoldingmachinewillpossessallofthesefeatures.

Referringbacktoinvestigationoftheeffectsofjoltingandsqueezing,thejoltwasfoundtobeveryimportantwhereassqueezeassistedinimprovingmoldrigidity,butalsodecreasedtheproductioncycleasthepressureincreased.Thishasledtothedevelopmentofarangeofsystemsthatcanutilizeonemoldingmachineratherthanhavingtousetwomachines,withtheutilizationofapatternshuttletomakethecopeandtheothertomakethedrag.

Asmostfourpostmoldingmachinesincorporateapatternshuttleforrapidchangeofpattern,thisunitcanbeusedalsoforproducingcopeanddraghalfmoldsalternatively,making it possible to have only one molding machine in the system. This immediately cuts theproductioncapacityinhalf,butalsoreducesthecapitalcostsignificantly.Itispossibletoachieveupto100/120moldsperhourusingasinglemachinewithinanIN-LINEarrangement.

Referringbacktoinformationthatthejoltismoreimportantthanthesqueezeforhardrigidmolds,itwasthoughtpossibletoobtainthis,withaflatsqueezehead,leadingtothedesignofafourpostmachinewithouttheexpensivesqueezefeature.


CONCLUSION

Itisfairlyreasonabletoforecastthatgreensandwillcontinuetobethemostimportantmediumformakingmolds,wellintotheforeseeablefuture.Thedemandforcastingsinthedevelopedcountrieswilldecreasefurther,andalternativemethodsandmaterialswillbeadopted.Thefoundrieswhichsurvivethemarketchangesthatwilltakeplaceduringthistransitionwillhavetomechanizemoreeffectivelyandeconomicallyasbasiclabor,willeitherbe too expensive or unobtainable.

Forquestionsorcommentsfeelfreetocontacttheauthor,JerrySenkat: 216-651-6700 or by email at [email protected]

considerations for manual & automatic green sand …

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