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Composites Handbook

Performance Resins in Composites

50 years of reliability, experience and innovation.The Crystic family of resins is at the heart of our success. In 1946 Scott Bader were the first UK company to manufacture unsaturated polyester resins in Europe. In 1953 the Crystic range of polyesters was introduced and its revolutionary applications have meant that Crystic has been the byword for superior technological achievement ever since.

CONTENTSIntroductionPlastics Thenatureofreinforcedplastics

MaterialsResins Unsaturatedpolyesters-DCPDpolyesters-Epoxies- Vinylesters-Phenolics-HybridsReinforcements Glassfibre-Carbonfibre-Polyaramidfibre-Glass combinations-Hybridcombinations SpecialitymaterialsCatalysts MEKPs-CHPs-AAPs-BPOs-TBPOs&TBPBsAccelerators Cobalts-AminesFillers Calciumcarbonate-Talc-Metalpowders-Silica- Microspheres-Aluminatri-hydratePigments PolyesterpigmentpastesReleaseAgents Polyvinylalcohol-Wax-Semi-permanents-Wax/semi- permanenthybrids-Releasefilm-InternalreleasesystemsCorematerials 2-componentpolyurethanefoam-Polyurethanefoamsheet -PVCfoam-Polyetheramidefoam-Styreneacryilonitrile foam-Balsawood-Honeycombcores-Non-wovencoresAdhesives Polyesters-Epoxies-Acrylics(methacrylates)- Polyurethanes-Urethaneacrylates(Crestomer)Mouldmakingmaterials Flexiblematerials-Plaster&clay-CompositesAncillaryproducts Polishingcompounds

ProcessesOpenmouldprocessesGelcoating-Laminating-Handlay-up-Spraylay-up- Sprayequipment-Roller/saturatorlay-up-Heatassisted curing-Mouldrelease-Postcuring-Trimming& finishingClosedmouldprocessesVacuuminfusion(VI)-Vacuumassistedresintransfer/ (VacFlo)-Resintransfermoulding(RTM)-Cold/warm pressmouldingHotmouldprocesses Wetmoulding-Mouldingcompounds-Doughmoulding compound(DMC)-Bulkmouldingcompound(BMC)- Sheetmouldingcompound(SMC)-Lowpressure mouldingcompound(LPMC)Continuousprocesses Pultrusion-Filamentwinding-Pulwinding-Centrifugal moulding-Machinemadesheeting

Properties

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GeneralconceptsMechanicalproperties Castresins-Glassreinforcedlaminates-Polyaramidandcarbon reinforcedlaminates-Sandwichconstruction-Thermalandelectrical propertiesFireperformance Firetests-LowfirehazardCrysticresinsEnvironmentalproperties Weatherandwaterresistance-Chemicalresistance

Applications Un-reinforcedpolyesterresin-Bodyfiller-Buttoncasting- Embeddingandpotting-Decorativecasting-Flooring-Polyester concrete-Polyestermarbleandonyx-SolidsurfacesReinforced polyesterresin-Chemicalcontainment-Marine-Matched performancemarinesystems-Landtransport-Building&construction

Quality Control Materialstorage-Stockcontrol-Workshopconditions-Reinforcementpreparation-Compoundingandmixingofresins-Mouldpreparationandmoulding-Trimmingandfinishing-Mouldcare-Resinusage-Thecuringreaction-Geltime-Hardeningrate-Maturingtime-Hotcuring-Coldcuring-Factorsaffectinggeltime-Effectofadditivesonresinproperties-Commonfaults-Repair-Repairinggelcoatscratches-Fillingdentsandcracks-Repairinglaminatedamage-Inspection-Resintoglassratios-Degreeofcure-Controlofvariables

Mould MakingTheimportanceoftoolingCompositemouldtools PlugproductionMouldmakingmaterials Gelcoat-Laminatingresin-ReinforcementsWorkshopconditionsMouldconstructionschedule

Health Safety andthe Environment Storage-Use-Styrenereduction

Appendix 1 BibliographyandAddresses

Appendix 2 SIUnits

Index

Scott Bader Product Range

Scott Bader Regional Centres

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ListofTables page

1 Comparative properties of cast un-reinforced resins and fibres 452 Typical properties of glass reinforced composites compared with steel and aluminium alloy 473 Comparative properties of glass, polyaramid and carbon reinforced polyester laminates 474 Percentage retention of tensile properties at various temperatures. CSM reinforced isophthalic polyester resin with an HDT of 116C 505 Minimum properties of reinforced laminate plies 506 Comparative thermal properties 527 Typical thermal and electrical properties of cast polyester resin 528 Classification for external fire exposure roof test 549 Classification for surface spread of flame of products 5510 Classification for NFP-92501 Epiradiateur test 5711 Low fire hazard Crystic resins 5812 Low fire hazard Crystic gelcoat/resin systems 5913 Strength retention of FRP composite after immersion in distilled water at 20C 6114 Cold curing catalysts 6715 Effect of catalyst on the hardening rate of a typical orthophthalic polyester resin 6816 Catalyst and accelerator equivalents 6917 Materials for RTM tooling 76

ListofPlatespage

1 Performance resins in composites frontispiece2 50 years of reliability, experience and innovation frontispiece3 Reinforcements and core materials 984 Ernest Bader Technical Centre 995 Closed Mould technology 1006 Continuous process 1017 Solid surface technology 1028 Crystic Stonecast applications 1039 Underground in-situ pipe lining 10410 Composite chemical tank 10511 Luxury composite motor cruiser 10612 Composite luxury yacht 10713 Composite super yacht and pilot boat 10814 Luxury composite motor cruiser 10915 Composite super yacht 11016 Composite sailing dinghy 11117 Sponsored composite racing cars 11218 Eurostar - High speed passenger train 113 19 Composites executive motor home 11420 Common faults in composites

ListofFigures

page

1 Derivation of compounds used in the manufacture of a typical polyester resin 102 Specific tensile strength - steel, aluminium and GFRP 403 Specific tensile modulus - steel, aluminium and GFRP 404 Comparative material and fabrication costs for component manufacture 415 Effect of glass content on the tensile strength of random glass reinforced polyester laminates 466 Effect of glass content and orientation on the tensile strength of random glass reinforced polyester laminates 467 Effect of glass content and orientation on the tensile strength of glass reinforced polyester laminates 468 The effect of CSM skin construction (at R:F = 2.3:1) and core thickness on flexural rigidity for balanced double skinned sandwich laminates 499 The effect of WR (glass) skin construction (at R:F = 1:1) and core thickness on flexural rigidity for balanced double skinned sandwich laminates 4910 Predicted effect of fibre type and content on tensile strength using property data from Table 5 5111 Predicted effect of fibre type and content on tensile modulus using property data from Table 5 5112 Effect of weathering on the light transmission of GFRP sheeting at various resin contents 6113 Effect of weathering on the gloss retention of low fire hazard GFRP laminates with gelcoat 6114 Effect of weathering on the gloss retention of GFRP laminates with various surfaces (orthophthalic resin/glass mat: 70% resin content) 6115 Typical exotherm of polyester resin 6616 Equivalent post curing times and temperatures 6617 Hot curing of a typical polyester resin using 2% benzoyl peroxide catalyst 6618 Effect of ambient temperature on the geltime of a typical polyester resin 6719 Effect of addition of plasticising resin 6920 Laminate repair method 7321 Construction of reinforcing ribs 7922 Construction of flange for split moulds 80

COMPOSITESHANDBOOK

PrefaceTheglobalnatureoftodaysreinforcedplasticsindustrycreatesademandfromallovertheworld,forbasicbackgroundinformation.ThissixteentheditionoftheCompositesHandbookprovidesanintroductiontoreinforcedplasticintermsofbasicchemistry,resins,reinforcementsandapplicationtechniques.Italsoencompassesthemajoradvancesinmaterialandprocesstechnologieswhichhaveoccurredsincethefirsteditionwaspublishedin1953.

Theuniquenessofreinforcedplasticliesinthefactthatthematerialofconstructionandtheendproductareproducedsimultaneously,soqualitycontrolisahighlysignificantpartoftheprocess.

Thegeneralguidance,adviceandtechnicaldatacontainedinthishandbookisintendedtohelpdesigners,mouldersandend-userstorealisethefullpotentialofthisuniquematerialasatrulystructuralengineeringplastic.

December2005ScottBaderCompanyLtd.

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Allinformationisgiveningoodfaithbutwithoutwarranty.Wecannotacceptresponsibilityorliabilityforanydamage,lossorpatentinfringementresultingfromtheuseofthisinformation.

Copyright(c)2005ScottBaderCompanyLimited

IntroductionPlasticsThetermplasticisusedtodescribethemouldedformofasynthetic(i.e.man-made)resin.Theseresinsarecomposedoflarge,chain-likemoleculesknownaspolymers,whichalsooccurnaturallyas,forexample,cellulose,proteinandrubber.Mostsyntheticresinsaremadefromchemicalsderivedfromoilanditistheseman-madepolymerswhichareusedtoproducewhatarecommonlyknownasplastics.

Plasticsintheirvariousformshaveexistedsincethelate19thcentury,butmostofthematerialsreferredtoasplasticstodayhavebeendevelopedduringthepast50years.

Alargevarietyofplasticsisnowavailableandtheyexistinvariousphysicalforms.Theycanbebulksolidmaterials,rigidorflexiblefoams,orintheformofsheetorfilm.Mostfallintooneoftwocategories;thermoplasticorthermoset.Thermoplasticscanbeformedandre-formedbytheuseofheat(eg.polyethylene,PVC,etc.).Thermosets,ontheotherhand,hardenbyachemicalreaction,generatingheatwhentheyareformedandcannotbemeltedorre-formed(eg.unsaturatedpolyesters,epoxies,vinylestersetc.).

The Nature of Reinforced PlasticsReinforcedPlasticisthegenerictermusedtodescribespecificplasticmaterialsreinforcedwithhighstrengthfibres.Sincetheirdevelopment,thesematerialshavebeencommonlyknownbynamessuchasFibreglassandGRP(GlassReinforcedPlastic).ThoughGRPisstillthemostusedterm,thedevelopmentandutilisationoffibresotherthanglassmakesFRP(FibreReinforcedPlastic)amoreaccurateandcomprehensivedescription.Withinthereinforcedplasticsindustryitself,Compositeisthetermfelttobestdescribethislight,durableandastonishinglytoughconstructionalmaterial.

Compositescanbefabricatedintoawidespectrumofproducts,fromthepurelydecorativetocomplex,engineeredstructures.Theymaybetranslucent,opaqueorcoloured,thickorthin,flatorshapedandthereisvirtuallynolimitonsize.Compositescanbefoundinmostareasofdailylife,intheformofroofsheeting,tanks,pipes,vehiclebodies,buildings,boats,etc.

Toproduceacompositeitem,twobasiccomponentsarerequired,thesebeingasyntheticresinandastrongfibre.Theresin,whichcouldbeapolyester,epoxyorvinylester,isnormallysuppliedasaviscousliquid,whichsetstoahardsolidwhensuitablyactivated.Thefibremaybeglass,carbon,polyaramid,oracombinationofsomeorallofthese.Whatmakescompositesuniqueisthefactthatthematerialofconstructionandtheendproductareproducedsimultaneously.Usingasuitablemould,layersoffibreareimpregnatedwithactivatedresinuntiltherequiredthicknessisachieved.Whencomplete,themouldingisremovedandthemouldcanthenbere-usedtoproducemore,identicalitems.

Thishandbookdescribesindetailthematerials,techniquesandapplicationsofcompositemanufacture,andpresentssolutionstoanyproblemsthatmayarise.

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MATERIALS

Resins

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Severalresintypesareemployedinthemanufactureofcompositeproducts.Alloftheseresinsarethermosetsbuttheydifferintheirchemicalmake-up,thusexhibitingdiverseproperties.Thismeansthatmanufacturerscanchooseresinswhichenablethemtotailortheirproductstomeetspecificrequirements.ThishandbookisconcernedmainlywithCrysticpolyesterresins,butothertypessuchasvinylester,epoxy,DCPD,phenolicandalsohybridsystemsaredescribedinthissection.

PolyestersCrysticresinsareunsaturatedpolyesters.Therawmaterialsusedforthemanufactureofunsaturatedpolyesterresinsareoilbased(seeFigure1)andtoproduceapolyesterofthistype,threebasicchemicalcomponentsaregenerallyrequired:-A:saturatedacid(e.g.phthalicanhydride)B:unsaturatedacid(e.g.maleicanhydride)C:dihydricalcohol(e.g.propyleneglycol)

Withtheapplicationofheat,thesechemicalscombinetoformaresinwhichisaviscousliquidwhenhot,butabrittlesolidwhencold.ThetermpolyesterisderivedfromthelinkbetweenAorBwithC,whichistermedanesterlink.Whilstitisstillhot,theresinisdissolvedinamonomerwhichisusuallystyrenethoughotherscanbe,andare,used.Themonomerperformsthevitalfunctionofenablingtheresintocurefromaliquidtoasolid,bycrosslinkingthemolecularchainsofthepolyester.Noby-productsareevolvedduringthisprocess,whichmeanstheresinscanbemouldedwithouttheuseofpressure.Theyarethereforeknownascontactorlowpressuremouldingresins.Themolecularchainsofthepolyestercanberepresentedasfollows:ACBCACBCACBC

WiththeadditionofstyreneSandinthepresenceofacatalystandaccelerator,thestyrenecross-linksthechainstoformahighlycomplexthreedimensionalnetworkasfollows:

ACBCACBCACBC

SSS

ACBCACBCACBC

Atthisstage,thepolyesterresinissaidtobecured.Itisnowachemicallyresistantand(usually)hardsolid.Thecross-linking,orcuring,processiscalledpolymerisationandisanon-reversiblechemicalreaction.

Oncecured,theresinwillcontinuetomature,duringwhichtimethemouldingwillacquireitsfullproperties.Thisprocess,whichcantakeseveralweekstocompleteatroomtemperature,canbeacceleratedbypostcuringthemouldingatelevatedtemperatures(seeQualityControlsection).

Polyesterresinswithdifferingcharacteristicsandpropertiesareproducedbymanipulatingthetypesandamountsofrawmaterialsusedintheirmanufacture(seePropertiessection).

DCPD Polyesters

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TheuseofDCPD(Dicyclopentadiene)inunsaturatedpolyesterresinmanufacturewasfirstintroducedintheUnitedStatesinthelate1970s.Sincethattime,itscommercialusehasdevelopedandresinscontainingDCPDarenowproducedworldwide.

TherearetwobasicmethodsofproducingDCPDpolyesters,asfollows:-

Dow Hydrolysis MethodThismethodinvolvesaninitialreactionusingthreecomponents:-A:MaleicAnhydrideB:WaterC:DCPDThesethreecomponentsarereactedtogetheratatemperaturelowerthan130C,toproducewhatisknownasanacidfunctionalisedendcap.Afurtherreactionisthencarriedout,usingtheacidendcapandotherstandardpolyesterrawmaterials.Duringthisreaction,theacidendcapattachestothemolecularchainsofthepolymer,thusrestrictingtheirlengthandtherebyreducingtheviscosityofthefinalproduct.Thismeansthatlessstyreneisneededtoachievearesinwithausableviscosity.Upto30%weightforweightDCPDcanbeaddedtoapolyester(onsolidresin)usingthismethod.

Diels - Alder Reaction MethodThismethodallowsupto70%weightforweightDCPDtobeused(onsolidresin)inthemanufactureofapolyester.Itinvolvesconvertingdicyclopentadiene(DCPD)tocyclopentadiene(CPD)atatemperaturegreaterthan130C.TheCPDisthengraftedontotheresinbackbonebyreactionwithasiteofunsaturation.Thiscanbeachievedbyanearlyreactionwithmaleicanhydrideoratalaterstageofthepolymerisationprocess.

Thesetwoprocessesaresimilarinthatbothreactionsoccurinbothsystemsbutindifferentratios.Thedegreeofeachreactiontypeiscontrolledbytemperatureandwatercontentinthefirststage.TheadvantagesofincorporatingDCPDintopolyesterresinsarelowerstyrenecontent,combinedwithgoodproperties.ThemaindisadvantageisthefactthatDCPDsolidifiesatroomtemperaturesoheatedstorageandhandlingfacilitiesarerequired.

Epoxy ResinsEpoxyresinshavebeencommerciallyavailablesincetheearly1950sandarenowusedinawiderangeofindustriesandapplications.

Epoxiesareclassifiedintheplasticsindustryasthermosettingresinsandtheyachievethethermosetstatebymeansofanadditionreactionwithasuitablecuringagent.Thecuringagentusedwilldeterminewhethertheepoxycuresatambientorelevatedtemperaturesandalsoinfluencephysicalpropertiessuchastoughnessandflexibility.Therearetwobasictypesofepoxyresin,thesebeing:

i)BisphenolA-DiglycidylEtherii)EpoxyPhenolNovolac

Epoxyphenolnovolacresinshavethehighercross-linkdensityofthetwotypesandareusedinhighperformanceapplicationssuchaspre-pregsfortheelectricalindustryandalsoinsomehighperformancelaminatingapplications. Lowviscosity,lowmolecularweightBisphenolAepoxiesaretheonesmostwidelyusedinthecompositesindustry.Theyareavailableas2packsystemswhichcanbecuredatroomtemperatureusingasuitablecuringagent,thevarioustypesofwhichareasfollows:-

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i)Amines(di-functional)Cureiseffectedbytwoepoxygroupsreactingwithoneprimaryamineandthesearemostwidelyusedforstandardroomtemperatureapplications.Astherearehealthimplicationswithfreeamines,thesesystemsareoftensuppliedasamineadducts.

ii)Polyamides iii)AnhydridesThesecuringagentsreactonlywithheatandneedtemperaturesbetween120Cand140Ctobeeffective.Theyareusedinhightemperatureapplicationssuchasfilled,sanitarywaresystems.

Epoxyresinsarehighlychemicalandcorrosionresistant.Theyhavegoodphysicalpropertiesandtheirlowshrinkcharacteristicsmeantheycanbeusedwheredimensionalaccuracyisofprimeimportance.Epoxiesexhibitexcellentadhesiontoawidevarietyofsubstratesincludingconcrete,glass,wood,ceramicsandmanyplastics.

Thiscombinationofpropertiesmakesepoxyresinsuitableforuseinmanyapplicationswithinthecompositesindustry.Theseincludeadhesives,construction/repair,casting,laminatingandflooring.

Thereare,however,healthissuesassociatedwithresinsensitisationandcostcansometimesbeaprohibitingfactor.

Vinyl Ester ResinsVinylestersarethermosetresinswhichincorporateandbuildontheexcellentphysicalpropertiesofepoxysystems.Theyareusedinsimilarapplicationstopolyesterresins,particularlywherehigherperformanceisrequired.

Therearetwobasictypesofvinylesterresin,asfollows:-

i)BisphenolA-diglycidylethertype(BADGE)ThistypeofvinylesterisproducedbyreactingaBADGEsystemepoxywithmethacrylicacid.Theresultantresinisthendilutedinstyrenetoproducearesinwithasolidscontentofatleast50%.

BADGEvinylestersareusedmainlyinhighperformanceapplicationssuchaschemicaltanksandpipes,thoughtheiruseinthemarineindustryisbecomingmorewidespread.

ii)Epoxyphenolnovolactype(EPN)ThisformofvinylesterisareactionproductofEPNandmethacrylicacid,dilutedwithstyrenetoasolidscontentof30%to36%.

EPNbasedvinylestershaveahighercross-linkdensitythanBADGEsystemswhichmakesthemsuitableformoredemandingapplications,mainlyinthechemicalplantindustry.

Vinylesterresinshaveamolecularstructurewhichallowsthemtoreactmorecompletelythanpolyesters.Thisisduetothefactthatinvinylesterscross-linkingisterminal(ie.attheendsofthemolecularchain)ratherthanthroughoutthechainaswithunsaturatedpolyesters.

Becauseofthisuniquestructure,vinylesterresinscanbeusedtoproducetoughlaminateswhicharehighlyresistanttowaterandaggressivechemicals.Theyalsoexhibitamorerapidcuredevelopmentwhichresultsinareductioninprint-throughonthelaminatesurface.Optimumperformanceisonlyachieved,however,bypostcuringlaminatesatveryhightemperatures(atleast100C).Laminatescuredatroomtemperaturewillhavesimilarphysicalpropertiestothosemadeusingahighperformancepolyesterresin.

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Phenolic ResinsPhenolicresinsarepolycondensatesofphenolsandaldehydes,orketonesandwerefirstdiscoveredinthelate19thcentury.Theuseofphenolicresinsinthecompositesindustryisrelativelysmall,thoughgrowingandthemostcommontypeusedisanaqueousresolephenolformaldehydesystem,whichcuresinthepresenceofanacidcatalyst.Phenolicsarebestsuitedtoapplicationsrequiringhighlevelsoffireretardancy,coupledwithlowsmokeemissionandlowtoxicity.

Duetothenatureoftheresinandcatalystsystems,effectivehealthandsafetyproceduresandefficientventilation/extractionsystemsareveryimportantwhenusingphenolicresins.Crosscontaminationofpolyesterresinsshouldalsobeavoidedinordertopreventinhibitionoftheircure.

Hybrid ResinsHybridresinsareproducedbyblendingorreactingtogetherresinsofdifferingtypes,inordertoimpartthebestpropertiesofeachtothenewendproduct.

OnesuchseriesofresinsistheCrestomer rangewhichconsistsofurethaneacrylateresinsdissolvedinstyrenemonomer.Theurethanecomponentisfullyreactedintothemolecularbackbone.Thiscontributesadhesivepropertiesandflexibilitywithoutfreeisocyanatehazard,whilsttheacrylateunsaturationandstyrenemonomerimparttough,hard,thermosetcharacteristics.Thenovelstructureoftheseresinsmeanstheyarecompatiblewithandhandleaswellas,polyesterresinsandcanbecuredusingconventionalperoxidecuringagents.

Urethaneacrylatesareusedasbaseresinsforformulatedrangesofadhesivesandhighperformancelaminatingsystems,andasadditionstounsaturatedpolyesterresins,toenhancetheperformanceofcompoundsandlaminates.

Crestomer resinsandadhesivesexhibitexcellentadhesiontomanysubstrates,fibresandcuredlaminates.Theyaretough,resilientandflexible,withchemicalresistancepropertiessuperiortothoseofaconventionalflexiblepolyester.Thefillertoleranceofthematerialsishighandtheyarecompatiblewithpolyesterpigmentsandthixotropicadditives.

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Figure1-Derivationofcompoundsusedinthemanufactureofatypicalpolyesterresin.

PETROLEUM

MALEIC ANHYDRIDE

MONOMERIC STYRENEUNSATURATED POLYESTER BASE

UNSATURATED POLYESTER RESIN

PHTHALIC ANHYDRIDE GLYCOLS

BENZENEXYLENE

ETHYLENE

PROPYLENE

ReinforcementsTherearethreemaintypesofreinforcementusedinthecompositesindustrytoday;glassfibre,carbonfibreandpolyaramidfibre.

Glass FibreThecommercialavailabilityoffine,consistentglassfibres,coupledwiththedevelopmentoflowpressurepolyesterresinsmarkedthebirthofthefibrereinforcedcompositesindustryoverfiftyyearsago.

Glassisanidealreinforcingfibreforplastics.Itisoneofthestrongestofmaterials(theultimatetensilestrengthofafreshlydrawnsinglefilamentof9-15micronsdiameterisabout3.5GPa).Itsconstituentsarereadilyavailable,itisnon-combustibleandalsochemicallyresistant.Glassfibreisproducedbydrawingandrapidlycoolingmoltenglassandisavailableinavarietyoftypesandformats.Itsfinalformatwilldependonhowthedrawnglassisfurtherprocessed.

Inthecompositesindustrytoday,E(Electrical)andC(Chemical)arethepredominantgradesofglassused.ThethreemostcommonEglassformatsare:i)Uni-directional(allfibresinonedirection)e.g.continuousrovings(UD)

ii)Bi-directional(fibresat90toeachother)e.g.wovenroving(WR)

iii)Random(fibresrandomlydistributed)e.g.choppedstrandmat(CSM)

ThepredominantformatsforCglassareassurfacingtissues,whicharewidelyusedaschemicalbarriersandforaestheticpurposes.

Developmentsinglassfibretechnologymeanthatglassreinforcementsarenowavailableinawidevarietyofstylesandformats,suitedtodiverseapplicationsinmanyindustrialsectors.

Carbon FibreCarbonfibrereinforcementshavebeenavailabletothecompositesindustrysincethe1960swhenhighstrength,highmodulusfibreswerefirstdevelopedattheRoyalAircraftEstablishmentinFarnborough.

Carbonfibresareproducedbycarbonisingafibreprecursoratatemperaturebetween1000Cand3500C.Themostcommonlyusedprecursorispolyacrylonitrile(PAN).Fibresbasedonother,cheaperprecursorsarecommerciallyavailablebuttheirpropertiestendtobeinferiortothoseofPANbasedfibres.Propertiessuchasdensityandelasticmodulusaredeterminedbythedegreeofcarbonisationemployedandcarbonfibrereinforcementsarenowavailabletomeetawiderangeofstrengthandstiffnessrequirements.

Compositesmadeusinghighmodulus,uni-directionalcarbonfibrecanexceedthemodulusofsteel.Bi-directionalmaterialsaremorecommonlyused,however,toproducecompositestructurescapableofmeetingthestringentdemandsofhighperformanceapplicationssuchasthoseintheaerospaceindustry.

Polyaramid FibresPolyaramid(AromaticEtherAmide),fibreswerediscoveredbyDuPontin1965.Theyareorganic,man-madefibres,whichhaveauniqueblendofproperties.Polyaramidfibresareflameresistant,chemicalandcorrosionresistantandhaveexcellentelectrical

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properties.Theirlightweight(density1.4-1.45)combinedwiththeirstrengthandmoduluscharacteristicsresultinspecificstrengthandspecificmodulusproperties,whicharesuperiortoallglassfibresandsomecarbonfibres.

Therearetwomaingradesofpolyaramidfibre,onewithanelasticmodulussimilartothatofglassfibreandonewithanelasticmodulusdoublethatofglassfibre.Thelowermodulusmaterialisusedinballisticapplications,bothasdryfibreandasacomposite,whilstthehighermodulusmaterialistheonemostwidelyusedinthecompositesindustrytoday.

Polyaramidfibresareusedtoproducecompositeswhicharelight-weightandincrediblystrong,withexcellentimpactproperties.Someofthem,however,exhibitlowcompressionstrengthwhichshouldbetakenintoconsiderationwherestructuresarelikelytobesubjectedtoflexureorcompressionloading.

Glass Combination MaterialsManyglassfibrereinforcementsarenowavailableascombinationsofstylesandtypes,forinstancewovenrovingstitchedtoachoppedglassdeposit.Theseproductshavebeendevelopedtoamalgamatetheimprovedmechanicalpropertiesofawovenfabricwiththeeaseandspeedofapplicationofachoppedmatortissue.

Non-wovencombinationmaterialsmadefromEglassarealsoavailable.Theseproducts,whicharecrimpfree,consistoflayersofreinforcementheldtogetherbyalightstitching.Theyaredesignedtomaximisedirectionalstrengthpropertiesandareavailableinbi-axial,tri-axialorquadri-axialformats,somewithachoppedglassbackingforeaseofuse.

Hybrid Combination MaterialsReinforcementswhichcontainmorethanonefibretype,areknownashybrids.Themostcommonofthesearepolyaramid/glassandpolyaramid/carboncombinations,thoughcarbon/glasscombinationsarealsoavailable.Theuseofdifferentfibresinonereinforcementresultsinafabricwhichexhibitsalltheadvantagesofeachconstituentfibre,withnoneofthedisadvantages.Forinstance,theuseofapolyaramid/glassreinforcementwillproduceacompositewiththeimpactresistanceofpolyaramidfibresandthecompressivestrengthofglassfibres.

Speciality MaterialsDevelopmentsinclosedmouldprocessessuchasRTMhaveresultedintheintroductionofspecialisedreinforcingmaterialswhichaddresstheneedforimprovedquality,speedandeaseofproduction.Thesematerialsareavailableinvariousforms,fromcontinuousfilamentmatstosophisticatedpre-formednet-shapes.Theuseofstitchedproductsisincreasingandastitchedmatspecificallydevelopedtooptimisethespeedandefficiencyofclosedmouldprocessesisnowavailable.Itconsistsofchoppedglassfibresstitchedtoeachsideofanon-wovensyntheticcoreandallowsalaminatethicknessupto6mmtobeachievedperlayerofmaterial.Theuniquestructureofthisproductmeansitispre-formablewhencold,easytotailorandpermitsexcellentresinflowthroughthemould.Todayscompositesindustryhasaccesstoaninfinitevarietyofreinforcementtypesandstyles.Thisenablesspecifiersanddesignerstocreatecompositestructurescapableofmeetingthemostdemandingofapplications.

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CureSystemsInordertoproduceamouldingorlaminateusingapolyesterresin,theresinmustbecured.Thisisachievedeitherbytheuseofacatalystandheating,oratroomtemperaturebyusingacatalystandanaccelerator.MostCrysticresinsaresuppliedpre-accelerated,incorporatinganacceleratorsystemdesignedtogivethemostsuitablecurecharacteristicsforthefabricator.Theseresinsneedonlytheadditionofacatalysttostartthecuringreactionatroomtemperature.Certainresinscannotbepre-accelerated,however,duetotheircurecharacteristicsandtheserequiretheadditionofbothanacceleratorandacatalysttoinitiatecure.

N.B.Catalystsandacceleratorsmustneverbemixeddirectlytogethersincetheycanreactwithexplosiveviolence.

Thosecatalystandacceleratorsystemsmostcommonlyusedinthecompositesindustryaredescribedinthissection.

Catalysts Organicperoxidesarenormallyusedascatalystsinthecompositesindustry.Sincethesematerialsareunstableintheirpureform,theyaremixedwithaninertcompoundbeforebeingsuppliedcommercially.Thisprocessisknownasphlegmatisationandiscarriedoutduringmanufacture.Phlegmatisersareusuallyliquids(e.g.phthalates)orinertfillers(e.g.chalk)butothermediaaresometimesused.

Thetypesofcatalystmostcommonlyused,particularlyinconjunctionwithpolyesterresins,areMethylEthylKetonePeroxide(MEKP),CyclohexanonePeroxide(CHP),AcetylAcetonePeroxide(AAP)andBenzoylPeroxide(BPO).

MEKP CatalystsLiquiddispersionsofmethylethylketoneperoxidearemostwidelyusedincontactmouldingapplications(handlayorspray).Variousstandardgradesareavailable,differingonlyintheirreactivity*andactivity.

*Reactivityandactivitymustnotbeconfused.Lowreactivitycatalystssimplyextendgeltime,whereaslowactivitycatalystscanresultinundercureifincorrectlyemployed.

CHP CatalystsCyclohexanoneperoxidecatalystsareavailableaspowders,pastesandliquidsandareusedincontactmouldingapplicationswhereamoregradualcureisrequired.Inpasteform,CHPcatalystcanbemadeavailableintubes.

AAP CatalystAcetylacetoneperoxidecatalystsareusedwherefastcuretimesarerequired.ThemainuseforAAPcatalystsisinapplicationswherefastmouldturn-roundisrequired,forexampleRTMandcoldpressmoulding.

BPO CatalystMostbenzoylperoxidecatalystsaresuppliedaspowders,thoughpasteversionsandpourablesuspensionsarealsoavailable.Benzoylperoxidesaredesignedtocureatelevatedtemperatures(above80C),andtheyonlycureatroomtemperaturewhenusedinconjunctionwithatertiaryamineaccelerator.

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TBPO and TBPB CatalystsTertiarybutylperoctoateandtertiarybutylperbenzoatearecatalysttypescommonlyusedinheatcuringprocessessuchaspultrusionandhotpressmoulding.Theycanbeusedsingly,orincombinationwitheachother,toadjusttime/temperaturecurvestosuitspecificmouldingrequirements.

Thecatalystsdescribedabovearethestandardmaterialsmostcommonlyusedinthecompositesindustry.Asthecompositesindustryhasdeveloped,curetechnologyhasalsoadvancedandcatalystsarenowavailableinawiderangeoftypes,withpropertiestailoredtosuitthemanyapplicationsandprocessescurrentlyinuse.

AcceleratorsManychemicalcompoundswillactasacceleratorsforpolyesterresins,makingitpossibleforcatalysedresintocureatroomtemperature.Themostimportantofthesearethosebasedoncobaltsoapsoraromatictertiaryamines.

Cobalt AcceleratorsCobaltacceleratorsconsistofvariousconcentrationsofcobaltsoap,usuallydissolvedinstyrene.Thestandardstrengthsusedare0.4%,1.0%and6.0%thoughotherconcentrationsareavailable.

Amine AcceleratorsAmineacceleratorsarenormallyusedinconjunctionwithBenzoylPeroxidecatalysttoachieverapidcureatroomtemperature.Theyareusuallysuppliedassolutionsdissolvedinstyrene,phthalateorwhitespirit.

Itisessentialtochoosethecorrectcuresystemandtousethecorrectlevel.Ifmanufacturersformulationsareusedunderrecommendedconditions,thecuredresinwillachieveitsmaximumstrength,durability,chemicalresistanceandstability,ensuringthatthefinalmouldingwillattainoptimumproperties.

FillersWhenmineralfillerswerefirstintroducedtothecompositesindustryitwasasameansofreducingcost.Atthattime,excessivelyhighloadingswereusedandthisresultedinaseriousdeteriorationinthemechanicalstrengthandchemicalresistanceofmouldingsproduced.

Today,theeffectsoffillersarebetterunderstoodandtheyareusedtoenhanceandimprovecertainpropertiesofaresin.Filledresinsexhibitlowerexothermandshrinkagecharacteristicsthanunfilledsystems,andtheytendtobestiffer,thoughmorebrittle.Thelevelofcostreductionachievablebytheuseoffillersisnolongerasignificantfactor.

Therangeoffillersavailableisnowwideandvariedandsomeofthosemostcommonlyusedaredescribedoverleaf.

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Calcium Carbonate Surfacetreatedcalciumcarbonatefillers,particularlycrystallinetypes,arewidelyused,especiallywherelowerexothermtemperaturesandlowershrinkagearedesirable(e.g.castingormouldmakingapplications).

TalcMagnesitictalcsareusedtoincreasebulkandreduceexothermtemperature,usuallyincastingapplications.

Metal PowdersFinemetalpowderscanbeaddedtocatalysedpolyesterresintoproducerealisticmetalliccastings.Aluminium,brass,bronzeandcopperpowdersareallreadilyavailable.

SilicaHydrophilicfumedsilicaisusedtoimpartthixotropytopolyesterresins.Ahighshearmixerisrequiredtoensureadequatedispersion.

MicrospheresHollowmicrospheresareavailableinglassandthermoplasticform.GlassmicrospheresareproducedfromEglass,whilstpolypropyleneisthemostcommonrawmaterialforthethermoplasticspheres.Microspherestrapairinasphericalshell,sowhenincorporatedintoaresinmix,theyincreasevolume,reduceweightandreduceshrinkage.Polyesterputties,andculturedmarblearetwoapplicationswheremicrospheresareusedtoenhancethepropertiesofthefinishedproduct.

Alumina trihydrateAluminatrihydrateisaflameretardantfillerusedtoimprovethefireresistanceofpolyesterresins.ATHisnon-toxic,supressessmokeproductionandimpedesburning.Althoughitsprimaryuseisasafireretardant,thetranslucentnatureofATHmakesitidealforuseincastingandsyntheticmarbleoronyxproduction.Specificgradesareavailablefortheseapplications.

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PigmentsMostpolyestergelcoatsandresinscanbesuppliedpre-pigmented,butpigmentpastesareavailabletoenablethefabricatortocolourtohisownrequirements.

Crysticpolyesterpigmentpastesarespeciallyformulatedforuseinpolyestergelcoatsandresinsandconsistoffinepigmentpowdersdispersedinamediumwhichcross-linksintothebaseresinduringcuring.Recommendedadditionlevelsarebetween8%and10%forgelcoatsand4%to5%forbackingresins.

Toensurecolourreproducibility,itisimportantthatallsub-assembliesofmulti-componentmouldingsaremanufacturedusingthesamemixofpigmentedmaterial.

ReleaseAgentsReleaseagentsareanintegralpartofthecompositemouldingprocessandarevitaltothesuccessfulproductionofhighqualityFRPcomponents.Thechoiceofreleaseagentwillbeinfluencedbyvariousfactorssuchasmouldsizeandcomplexity,mouldingnumbers,surfacefinishrequirements,etc.Selectingtherightoneisveryimportantinensuringqualityandconsistencyinthefinishedproduct.

Themostcommontypesofreleaseagentaredescribedinthissection.

Polyvinyl AlcoholPolyvinylalcoholisavailableinconcentratedform,orasasolutioninwaterorsolvent.Itcanbesuppliedcolouredorcolourlessandappliedbycloth,spongeorspray.

Polyvinylalcohol-basedreleaseagentsarenormallyusedforsmallmouldingswithasimpleshape,orasasecondaryreleaseagentandaresuitableforuseonmetalandFRPcompositemoulds.

Careshouldbetakenwhenusingpolyvinylalcohol-basedreleaseagentinverticalsections.Becauseitislowinviscosityitwilldraindownandaccumulateincornerswhereitmaytakealongtimetodry.Ifamouldingislaidupbeforeanysuchareasaredry,itwillalmostcertainlystick,causingdamagetothemould.

WaxWaxwasfirstusedasareleaseagentinthecompositesindustryinthe1950s.Carnaubawax-basedproductsarethemostsuitableforusewithcompositematerialsandthesearewidelyemployed,particularlyincontactmouldingapplications.

Siliconemodifiedproductscanbeusedbutcarehastobeexercisedassiliconecaninterferewiththereleaseinterfacemakingseparationdifficult.Anysilicone-basedreleaseagentsshouldbethoroughlytestedbeforeuse.

Waxreleaseagentsareavailableinseveralformsbutthosemostcommonlyusedarepastesorliquids.Amongtheadvantagesofwaxreleaseagentsaretheireaseofuse,convenienceandeconomy.Waxesareusedmostlyinlowvolumecontactmouldingapplications,astheneedforregularre-applicationcanbetimeconsuming.Thereisalsothepotentialforproblems,createdbywaxbuild-upandtransfer.

Semi-permanent Systems

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Whenappliedtoreleaseagents,thetermsemi-permanentusuallyreferstothoseproductswhichfunctionbydepositingamicro-thinfilmonthesurfaceofthemould.Theyusuallyconsistofapolymericresininacarriersolventandonceappliedtoamouldsurfacethesolventevaporatesleavingaresininterface.

Semi-permanentreleaseagentsallowmultiplereleasesfrommoulds,makingthemidealforhighvolumeproductionprocessessuchasresintransfermoulding(RTM).Thereisnobuild-uportransferofreleaseagent,sotheneedforcleaningofmouldsand/ormouldingsisreducedtoaminimum.Itisvitalwhenusingtheseuniquereleasesystemsthatthemouldsurfaceisperfectlycleantoensuregoodfilmformationandpropercureofthereleasecoating.

Wax / Semi-permanent HybridsThesematerialsnormallyconsistofawaxamalgamatedwithasemi-permanentreleaseagent.Theycombinetheeaseofuseofawaxwiththemulti-releasecharacteristicsofasemi-permanentsystem.

Aswithsemi-permanentreleaseagents,wax/semi-permanenthybridsrequiremouldsurfacestobeperfectlycleanbeforeuseiftheyaretobeeffective.

Release FilmCellophaneorpolyesterfilmisusedasareleasemedium.Itisnotsuitableforcomplexshapesbutisanidealsystemforuseinthemanufactureofcompositesheetingordecorativeflatpanels.

Internal Release AgentsInternalreleaseagentsareusedmainlyinhighvolume,mechanisedprocessessuchaspultrusion,RTMandSMC/DMChotpressmoulding.Asuitableproductisdissolvedintheresinmixandduringprocessingitmigratestothesurfaceandformsabarrierbetweentheresinandthemould.

CoreMaterialsLowdensitycorematerialsareusedinthemanufactureofFRPcompositecomponentstoincreasestiffnesswithoutincreasingweight.Theycanbeemployedinspecificareasofastructurewhereextrastiffnessisrequired(e.g.boathullribs),orthroughouttheareaofalaminatetoproducewhatisknownasasandwichpanel.

Therearetwocategoriesofcorematerial;structuralandnon-structuralandsomeofthemorecommonlyusedtypesaredescribedinthissection.

Two-Component Polyurethane FoamThetwocomponentsofthismaterialaremixed1:1byvolumetoproducearigidpolyurethanefoam.Thefoamexpandsrapidlytoapproximately25timesitsoriginalvolumeandisusedinbuoyancyandgeneralgap-fillingapplications.

Polyurethane Foam SheetSheetsofrigid,closedcellpolyurethanefoamcanbeusedasacoreinsandwichconstruction,orformakingformers.Itisnormallyusedinnon-structuralapplications,thoughstructuralgradesareavailableforuseinfastproductionprocesses.Groovedpolyurethanefoamsheetisalsoavailable.Thisisusedasanon-structuralcoreinapplicationswhereconformitytocurvedsurfacesisrequired.

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PVC Foam Closedcell,linearandcross-linkedPVCfoamsareusedasstructuralcoresinmarine,transport,buildingandmanyotherapplications.Theyaretough,rigidmaterialsandtheirhighstrengthandstiffnesstoweightratiomakesthemidealfortheproductionoflightweightsandwichpanels.

Theyareavailableasplainsheets,perforatedsheetsandalsoasscrimcloths(squaresoffoambondedtoaglassfibrescrim).

Polyetherimide FoamPolyetherimidefoamsareusedwhereresistancetofireisimportant.Theydonotburn,producenegligibleamountsoftoxicgasandsmokeandmaintaintheirpropertiesattemperaturesupto180C.

Styrene Acrylonitrile FoamThismaterialcombineshighstrengthandstiffnesswithlowwaterabsorptionandlowcreepvalues,makingitidealforuseinoffshorebuoyancyapplications.

Balsa WoodEnd-grainbalsawoodhasbeenusedasacorematerialformanyyears.Classifiedasahardwood,balsahasaveryhighstrengthtoweightratioandcanbeusedinstructuralornon-structuralapplications.

Asanon-synthetic(ie.natural)product,balsacanbeinconsistentindensityandunlessitiskilndried,itsmoisturecontentcancauseproblems.Itisalsogenerallymoredensethanmostfoamcorematerials.

Honeycomb CoresHoneycombcoresaremanufacturedfromavarietyofplasticandmetalmaterialsandareusedtoproducecompositestructureswithextremelyhighstrengthtoweightratios.

Twocommontypesofhoneycombcorearealuminiumandphenoliccoated,polyaramidfibrepaperswhicharebothusedextensivelyintheproductionofcomponentsfortheaerospaceindustry.

Non-Woven Core MaterialsNon-wovencoresarechemicallybondedmaterialsimpregnatedwithmicro-spheres.Thesematerialsproducelaminateswithhighstiffnesstoweightratiosandhighimpactandshearresistance.

Theyareeasytouse,withexcellentdrapabilityandconformabilityandarecompatiblewithmostunsaturatedpolyesterresinsystems.

Asecondaryadvantageofthesematerialsisthepreventionofprint-through,whichisachievedduetoimprovedresindistributionandlackofshrinkageinthecorematerial.

Adhesives

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Thedevelopementofadhesivematerialsspecificallydesignedforapplicationsinthecompositesindustryhasresultedinamarkedincreaseintheiruse.Adhesivesarenowavailabletofulfilmostrequirements,fromrelativelysimplebondingfunctionsthroughtotechnicallydemandingstructuralapplications.

Therearefourmainadhesivetechnologiesemployedintodayscompositesindustry.Allofthesearedescribedinthissection,togetherwithScottBadersuniqueCrestomerrangeofadhesives.

Polyester ResinsCrysticpolyesterresinsareusedtoproducebondingpasteswhichareviscous,filledcompoundsdesignedfortheassemblyandbondingofFRPmouldings.Theyareusedinmainlynon-structuralorsemi-structuralapplicationssuchasinternalframes,ribs,hulltodeckassembliesandcarcomponents,togivemoderatelyhighshearstrengthswithouttheneedformechanicalfixings.

Epoxy ResinsEpoxyresinsareusedtoproducestructuraladhesivessuitableformanyapplications.Epoxybasedadhesiveswillbondawiderangeofsubstratesincludingcomposites,metals,ceramicsandrubber.Theycanbeformulatedtoimpartheatandchemicalresistanceandtoexhibitgapfillingandotherrequiredproperties.Adhesivesbasedonepoxyresinsarecapableofachievingveryhighshearstrengthsandareusedextensivelyinstructuralbondingapplicationsintheaircraftindustry.

Acrylic (Methacrylate) ResinsAdhesivesbasedonmethacrylatesaretough,resilientmaterialswithhighshear,peelandimpactstrengths.Theycanbeformulatedtobondtomanysubstratesandtooperateoveranextensivetemperaturerange.Veryshortcuretimesareachievablewiththisclassofadhesive,thusallowingfastturn-roundtimes.

Polyurethane ResinsMostpolyurethanebasedadhesivesaremoisturecuringmaterials.Theyareextremelyflexibleandadheretoawidevarietyofsubstrates.Acombinationofhighpeelstrengthandmoderateshearstrengthmakestheseadhesivessuitableforuseinvariedapplicationsfromsealingtostructuralbonding.

Crestomer (Urethane Acrylate) ResinsTheadhesivepropertiesofCrestomermaterialsareduetothenovelstructureofthebaseurethaneacrylateresin.Theurethanecomponentisfullyreactedintothemolecularbackbone,contributingadhesivepropertiesandflexibilitywithoutisocyanatehazard.Theacrylateunsaturationandstyrenemonomerimparttough,hardthermosetcharacteristics.Crestomeradhesivesthereforeexhibitexcellentadhesiontosubstratessuchasfoamandbalsacorematerials,curedcompositesandmetals.TheCrestomerrangeistailoredforspecialistadhesiveandconstructionrequirementssuchasstructuralandsemi-structuralbonding,filleting,corebondingandgapfilling.

RecentdevelopmentsinCrestomertechnologymeanthisuniqueadhesivesystemisnowavailableincartridgeform,withvariouscureoptions,thusextendingevenfurtheritsareasofapplication.

MouldMakingMaterialsandAncillaryProductsManymouldmakingmethodsareemployedwithinthecompositesindustry,dependingonthenatureofthefinishedproduct,andeachmethodrequiresitsownsupplementarymaterials.Thediversenature

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ofproducts,processesandmanufacturingmethodscreatesaneedforanextensiverangeofancillarymaterials.

Thissectiondealswitharangeofancillaryitemsavailabletomaximisethemanufactureandqualityofcompositeproducts.

Flexible Mould Making Materials Thesecompoundsarewidelyusedinthedecorativecastingindustryandtherearethreemaintypesavailable:i) LatexRubber:-Thisiscommonlyused,indippingform,toproducesmallresincastingssuchas chesspieces.

ii) Vinyl-basedSyntheticRubber:-Vinyl-basedsyntheticrubbersareavailableinsolidformandare meltedinapurposedesignedmeltingpot.Thegradeuseddependsontherequirementsofthe finishedproduct,withadurablegradeforlimitedproductionrunsandaflexiblegradeforcomplex originals.Mouldscanbecutupandmelteddownforre-use.

iii) ColdCureSiliconeRubber:-Thismaterialisusedtoproducedurable,highdefinitionmoulds withexcellentreproductionoffinedetail.Itisatwopartsystemcomprisingabaseandacatalyst andisidealforlongerproductionruns.Thixotropicadditivesareavailabletoconvertthematerial fromapourableliquidtoabutter-onform,ifrequired.

Plaster and Clay MaterialsHighstrengthmouldplastersareusedtoproducerigidmouldsforlimitedproductionruns.Itisimportantthatplastermouldsaresealedandhavesuitablereleaseagentsapplied,beforeuse.

Highstrengthclays,whichcanbeovenhardened,arecommonlyusedtoproducedetailedformers,whilstgeneralpurposemodellingclaysareusedfortemporaryfillingandfilletingapplications.

Waxisalsowidelyused,insheetandfilletform,inmouldproduction.

Composite Mould Making MaterialsContactmouldingisthemostcommonlyusedmethodofcompositeproductionandthemouldsusedinthisprocessarenormallythemselvesproducedfromcompositematerials.Aseparatesectionhas,therefore,beendevotedtothesubjectofmaterialsandprocessesforcompositemouldmanufacture(seeMouldMakingSection).

Polishing Compounds and Associated ProductsTheappearanceofafibrereinforcedcompositeproductcanbegreatlyenhancedbypolishingthesurfaceafterreleasefromthemould.

Polishingcompoundsandtheirassociatedproductsdesignedspecificallyforusewithcompositesarenowwidelyavailable.Theseincludecompoundsforhandandmachineapplication,polishingclothsandbonnetsandfinishingglazes.

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PROCESSES

OpenMouldProcessesThedevelopment,inthe1950s,ofresinswhichcuredinthepresenceofairledtotheintroductionofcontactmouldingprocesses,whichstilldominatemanyareasofthecompositesindustry.

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Contactmouldingisaparticularlyadaptablemethodofmanufacturingcompositecomponentsofallshapes,sizesandcomplexityforrelativelylittlecapitalinvestment.Onlyonemouldisneededandthiscanbemaleorfemale,dependingonwhichfaceofthemouldingneedstobesmooth.

Therearethreemaintechniquesusedincontactmoulding,thesebeinghandlay-up,spraylay-upandrollersaturator.Whichevertechniqueisemployedtoproduceacontactmouldedpart,theconstructionofthemouldplaysavitalroleindeterminingthequalityofthefinishedcomponent.Forthisreason,acompletesectionisdevotedtomaterialsandproceduresformouldmaking,laterinthishandbook.

GelcoatingThedurabilityofacompositemouldingisverydependentonthequalityofitsexposedsurface.Protectionofthesurfaceisachievedbyprovidingaresinrichlayer,whichnormallytakestheformofagelcoat.Specialcaremustbetakenintheformulationandapplicationofthegelcoat,asitisaveryimportantpartofthelaminateandisalsothemostvulnerablepart.

Thoroughmixingofthegelcoatisextremelyimportant,particularlywhenaddingcatalyst,asinadequatecatalystdispersionwillresultinunevencureofthegelcoat,whichmayimpairitsphysicalproperties.Poormixingofpigmentwillresultinsurfaceimperfectionswhichwilldetractfromtheappearanceofthemoulding,soitisrecommendedthatpre-pigmentedgelcoatsareusedwhereverpossible.Theuseoflowshearmechanicalstirrershelpstominimiseanypotentialmixingproblems.

Gelcoatcanbeappliedbybrushorspray,thoughdevelopmentsingelcoattechnologyandsprayequipmenthavecombinedtomarkedlyincreasetheuseofsprayapplicationmethods.Whicheverapplicationmethodischosen,itisimportanttouseagelcoatfromtheCrysticrange,speciallyformulatedwiththecorrectrheologyforthatmethod.Thevarioustypesofsprayequipmentavailablearedescribedlaterinthissection.Foroptimumperformance,itisimportanttocontrolthegelcoatthicknessto0.4mm-0.5mmandasaguide,450g-600g/m2ofgelcoatmixturewillgivetherequiredthickness.Ifthegelcoatistoothinitmaynotcurefullyandthepatternofthereinforcingfibremayshowthroughfromthebackinglaminate.Thingelcoatsarealsopronetosolventattackfromtheresinusedinthebackinglaminateandthiscanresultingelcoatwrinkling.Ifthegelcoatistoothick,itmaycrackorcrazeandwillbemoresensitivetoimpactdamage,particularlyfromthereversesideofthelaminate.Agelcoatofuneventhicknesswillcureatdifferentratesoveritssurface.Thiscausesstressestobesetupintheresinwhichmayleadtocrazingor,inthecaseofpigmentedgelcoats,apatchyappearanceandwatermarking.

Full,evencureisvitalifagelcoatistoachieveoptimumperformance,soitisimportantthatcureconditionsandsystemsarecontrolled.Workshopandmaterialtemperaturesshouldbemaintainedataminimumof18CandamediumreactivityMEKPcatalystshouldalwaysbeused,ata2%additionlevel.Indeepmouldsthecureofagelcoatcanbeinhibitedbytheaccumulationofevaporatedstyrenefumes.Extractionofthesefumesis,therefore,necessarytoensureevengelationofthegelcoat.

Oncethegelcoathascuredsufficiently,thenextstepinthecontactmouldingprocessistoapplythebackinglaminate.Asimpletesttoassessthestateofcureofthegelcoatistogentlytouchthesurfacewithacleanfinger.Ifthesurfacefeelsslightlytacky,butthefingerremainsclean,thenthegelcoatisreadyforlaminating,whichshouldcommencewithinfivehours.

LaminatingHand Lay-UpChoppedstrandglassfibrematisthereinforcementmostcommonlyusedincontactmoulding,thoughthe

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useofwovenandvariouscombinationmaterialshasgrownconsiderablyovertheyears.Thepreparationofreinforcementpacks,specificallytailoredtothemouldbeingused,savestimeandreduceswastage.

Theamountofresinrequiredforalaminatecanbecalculatedbyweighingthereinforcementtobeused.Forchoppedstrandmattheresintoglassratioshouldbebetween2.3:1and1.8:1(30%to35%glasscontent).Resintoglassratiosofapproximately1to1(50%glasscontent)arenormalforwovenroving,whilstthoseachievablewithcombinationreinforcementswillvarydependingontheconstructionoftheparticularfabricused.Oncethegelcoathascuredsufficiently,aliberalcoatofresinisappliedasevenlyaspossible.Thefirstlayerofglassisthenpressedfirmlyintoplaceandconsolidatedusingabrushorroller.Thisactionwillenabletheresintoimpregnatetheglassmatanddissolvethebinderwhichholdsthefibrestogether.Thereinforcementwillthenconformreadilytothecontoursofthemould.Oncethefirstlayerofmatisfullyimpregnated,furtherresincanbeadded,ifnecessary,beforeapplyingsubsequentlayersofreinforcement.Itisimportantthatthefirstlayerisasfreeofairbubblesaspossible,asanyairtrappedimmediatelybehindthegelcoatcouldleadtoblistering,shouldthemouldingbeexposedtoheatorwaterduringitsworkinglife.

Impregnationofthereinforcementcanbecarriedoutusingabrush,oramohairorpolyesterroller.Ifabrushisused,itshouldbeworkedwithastipplingaction,asanysidewaysbrushingmotionwilldisplacethefibresanddestroytheirrandomnature.Theuseofrollersisadvantageouswhenworkingonlargemouldsandtheyareavailablewithlongorshortpile.Longpilerollerspickupmoreresinthanshortpileones,butcareneedstobetakentoaccuratelycontrolresintoglassratios.Consolidationofthelaminateismoreeffectiveifcarriedoutusingarollerandseveraltypeshavebeendevelopedforthepurpose.Metalpaddle,discorfinrollersareavailable,andofthese,thinfintypeshaveprovedparticularlyeffectiveinremovingairbubblestrappedintheresin.

Subsequentlayersofresinandreinforcementareapplieduntiltherequiredthicknesshasbeenachieved,ensuringthateachlayeristhoroughlyimpregnatedandproperlyconsolidated.Itisrecommendedthatnomorethanfourlayersofresinandreinforcementareappliedatanyonetime,topreventthebuildupofexcessiveexotherm.Highexothermtemperaturescanleadtogelcoatcracking,pre-release,distortionorscorchingofthelaminate.Wherethicklaminatesarerequired,eachseriesoffourlayersshouldbeallowedtoexotherm,thencool,beforesubsequentlayersareapplied,thoughlengthydelaysshouldbeavoided\unlessaresinwithalonggreenstageisused.Greenstageisthetermusedtodescribetheperiodbetweengelationandcureoftheresin,duringwhichtimeitisinasoft,rubberystate.Inthiscondition,thelaminatecanbeeasilytrimmedtothedimensionsofthemouldandtrimedgescanbebuiltintothemouldtofacilitatethisoperation.

Shouldamouldingneedtobestrengthened,thiscanbeachievedbyincorporatingreinforcingribsintothelaminate.Thestageatwhichtheribsareputintopositionwilldependontheshape,thicknessandenduseofthemoulding,thoughasageneralguide,itisbesttolocatethemimmediatelybeforethelastlayerofreinforcementisapplied.Theribformersshouldbecoveredwithreinforcingmatandthoroughlyimpregnatedwithresin.Thefinallayerofreinforcementcanthenbeappliedoverthewholeareaofthemouldingtogiveauniformappearancetothebacksurface.

Metalinsertsaresometimesnecessary,aslocatingorfixingpoints,etc.andthesecanbeputintoplaceduringthelaminatingoperation.Ifaninsertislikelytobesubjectedtoaheavyload,thethicknessofthemouldingshouldbetaperedawayfromtheinsert,inordertospreadtheload.Insertsshouldbepositionedasneartothemiddleofthelaminateaspossibleandthecontactareabetweenlaminateandinsertshouldbeaslargeaspracticable.Todayscompositesmanufacturersbenefitfromtheavailabilityofawiderangeofmetalfastenersandinsertsspeciallydevelopedfortheindustry.ThedevelopmentofadhesivesystemsintheCrestomerrangemeansthatmetalinsertscannowbebondeddirectlyintolaminates,thusreducingproductiontimes.

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Wherepiecesofreinforcementrequirejoiningtocoverthesurfaceofamould,buttorlapjointscanbeused.Buttjointsshouldbemadewithcaresothatnospaceisleftbetweenthetwoedgesandlapjointsshouldnotoverlapbymorethan25mm(unlessrequiredforstiffening).Joinsinchoppedstrandmatcanbemadelessconspicuousbyspreadingtheexcessmatoneithersidebyrotatingabrushinsmallcirclesalongthelineofthejoin.

Thebacksurfaceofamouldingcanberathercoarseinappearance,particularlyifchoppedstrandmatisthereinforcementused.Thiscanbeimprovedinoneoftwoways;eitherbyincorporatingasurfacetissueasthefinallayerofthelaminatetogiveasmoother,resinrichsurface,orbycoatingthesurface,onceithascured,withaformulatedflowcoatsuchasthatintheCrysticrange.Theuseofaflowcoatgivestheaddedadvantagethatitcanbepigmentedifrequired.

Spray Lay-upThistechniqueinvolvestheuseofaspraygunforthesimultaneousdepositionofchoppedglassandcatalysedresinontothesurfaceofamould.

Achopperunitattachedtothespraygunchopsglassrovingsintospecifiedlengths(usuallybetween20mmand50mm),andthechoppedstrandsarethendirectedtowardsastreamofcatalysedresinasitexitsthespraygun.ThoseresinsintheCrysticrangewhicharedesignedforsprayapplicationaregenerallylowinviscosity,sotheyrapidlywetoutthechoppedstrands.Thisensurestheyaremoreeasilyatomisedintothedesiredspraypattern.Therapidwet-outachievedbyspraydepositionallowsfasterandeasierconsolidationthanwouldbeachievedwithhandlaymethods,butthoroughrollingofthelaminateisstillnecessarytoensurecompleteairremoval.Theefficiencyofthecatalystdispersionintheresincanalsobecheckedatthisstage.Ifusingresinswhichincorporateacolourchangemechanismoncatalystaddition,orcatalystswhichcontaincoloureddyes,theuniformityofcatalystdispersioncanbeeasilymonitored.

Manycommercialsprayingsystemsarenowavailablebutduetotheirhigheroutputandconvenience,pumpedsystemsaremorecommonthantheolderpressurepotequipment,particularlyfortheproductionoflargermouldings.

SprayEquipmentPumped SystemsTherearethreeprincipalpumpedsystems,asfollows:-

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1) Airless AtomisationCompressedairisusedtooperatepumpswhichtransferresinorgelcoatfromtheiroriginalcontainerstothespraygun.Catalystisthenintroducedeitherwithinthegun(internalmix)orimmediatelyafteritleavesthegun(externalmix).Thegelcoatorresinisforcedthroughasmallspraytipathighpressureinordertoatomisethematerialandproduceafan.Compressedairisnotuseddirectlytoatomisethematerial,hencethetermairlessatomisation.Thepressureonthegelcoatcanvarybetween57bar(800psi)and214bar(3000psi),dependingonthetypeofequipmentused.Catalystismeteredintotheresinstreambyeitheracatalystpumplinkedtotheresinpump,orfromacatalystpressuretank.

2) Air Assisted AirlessThissystemisavariantoftheairlesssystemwhichcombinesconventionalairatomisationandairlesstechniquestoallowtheuseofloweratomisingpressures(typically28.5barto57baror400psito800psi).Thegelcoatispumpedatrelativelylowpressureandatomisingairisintroducedthroughamodifiedspraytipinordertorefinethespraypatternandeliminatefingering,etc.Thelowerpumppressuresusedinthissystemcanreduceoutputcomparedtoastandardairlesssystem,butporosityintheappliedgelcoatfilmtendstobelowerandstyreneemissionsarereduced.

3) HVLP SystemsHighvolume,lowpressurespraygunshavebeenusedforsometimeinthepaintindustrybutarerelativelynewforgelcoatapplication.Thesesystemsutilisehighvolumesofairatlowpressure(typically0.7baror10psiorless),inordertoatomisegelcoatswithminimalstyreneemission.

Othertypesofsprayequipmentcommonlyusedaregravityfed,siphonandpressurepotsystems.

Gravity Fed SystemsInthismethod,acontainerholdingcatalysed,acceleratedmaterialisattachedtoanindustrialspraygunfittedwithasuitablenozzle.Thecontainerisheldabovethegunandflowsintoitundergravity.Becauseoftheirthixotropicnature,gelcoatsappliedusingthismethodtendtofeatureacoarse,orangepeeleffectontheirbacksurfaceandoutputisratherslow.Theequipmentrequireslittlecleaningandmaintenance,however,socanbeusefulforapplyinggelcoattosmallmoulds,particularlyiffrequentcolourchangesarerequired.

Siphon GunsTheuseofspraygunswhichoperatebythesiphonsystemisnormallyrestrictedtotheapplicationofgelcoatinminorrepairwork.Thisisduetothefactthatoutputisratherslowbecauseofthethixotropicnatureofthematerial.

Pressure Pot SystemsInthissystem,materialisheldinapressurevessel.Itisforcedtothespraygunatlowpressure(typically2.1barto3.5baror30psito50psi),whereitisatomisedbyaseparateairstream.Atomisationcantakeplacewithinthegun,butitismorecommonlyexternaltothegunasthematerialexitsthespraytip.

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Atomisingpressuresgenerallyrangefrom3.5barto5.0bar(50psito70psi).

Pressurepotsystemsproducesmoother,moreuniformfilmsatafasterratethangravityfedorsiphonsystems,butaresignificantlyslowerandlessconvenientthanpumpedsystems,particularlywherelargemouldsareinvolved.Forexample,wherethecatalystisaddedtothegelcoatinthepressurepot(hotpotsystems),productionrunsarelimitedbytheworkinglifeofthematerial,asitisessentialtospraythemouldandcleantheequipmentwithinthistime.However,thesesystemsarerelativelysimpletooperateandmaintainandcanbeusefulforsmalltomediumsizedmouldswhereregularcolourchangesarerequired.

Airless,airassistedairlessandHVLPcatalystinjectionsystemsemployinginternalorexternalcatalystmixingmeanthatsprayequipmentisavailabletomeetthediverseneedsofindividualusers.Unitscapableofmultiplecolourgelcoatsprayingarealsoreadilyavailable.

Althoughsprayingdoesnotsolvealltheproblemsinherentinhandlaycontactmoulding,itisnowwidelyusedthroughoutthecompositesindustry.Inthehandsofaskilledoperatormosttypesofsprayequipmentwillsignificantlyincreaseoutputcomparedwithhandapplication.

Roller/Saturator Lay-upRoller/Saturatorequipmentisdesignedtosaturateglassreinforcementssuchaschoppedstrandmat,clothorwovenrovingswithactivatedresin.Theresinisheldinacontainerandpumpedasrequiredtoarollerhead.

Itisrelativelyeasytocontroltheresintoglassratioofalaminateusingthismethodandsignificantlylessstyreneisreleasedintotheatmosphereduringlaminatingoperations.

Theuseofaroller/saturatorisidealforlargemouldingssuchasbuildingpanelsandlargeradiusboathulls,etc.

Themouldingmethodspreviouslydescribedinthissectionareallcoldcuringprocessessothelaminatesproducedcantakeseveralhourstomature.Itispossibletoacceleratethecuringprocessbyapplyingamoderateamountofheattothemoulding,takingcaretoraisethetemperatureslowlytoavoidstyreneevaporationorblistering.

Forgelcoats,thetemperatureshouldberaisedto30-35Cmeasuredonthemouldand,oncethegelcoathasgelled,itmaybenecessarytoallowthemouldtocoolbeforeproceedingwiththebackinglaminate.Oncelaminatingiscomplete,thetemperaturecanberaisedagain,butitshouldnotexceed35Cbeforegelation.Aftergelation,thetemperaturecanbeincreasedgraduallyto60Candmaintainedforaboutonehour.Themouldingshouldthenbeallowedtocoolbacktoambienttemperaturebeforeremovalfromthemould.

Mould ReleaseProvidedthemouldreleaseagenthasbeencorrectlyapplied,releaseshouldbeafairlysimpleoperation.Theedgeofthemouldingshouldbeeasedawayfromthemouldusingplasticwedgesdesignedforthispurposeandthenadirectpullwillusuallyeffectreleaseofthemoulding.Withmoredifficultshapestheuseofcompressedairbetweenthemouldandthemouldingwillassistreleaseandcompressedairpointscanbebuiltintothemouldduringitsconstruction.Boathullsandmouldingsofsimilarshapecanbeseparatedbyrunningwaterslowlybetweenthemouldingandthemould,providedawatersolublereleaseagenthasbeenused.Onlarge,thickmoulds,itmaybenecessarytostrikeafewcarefulblowswitharubbermalletontheoutsidesurfaceofthemould.Thisshould,howeverbealastresortasitcanresultincrackingofthemouldsurface.

Ifasplitmouldhasbeenused,screworhydraulicjackscanbeemployedtoparttheseparatepieces.The

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mouldflangesmustbeheavilyreinforcedandseveraljacksused,toensurethatevenforceisappliedoverthelengthoftheflanges.

Post CuringContactmouldedlaminatescantakeseveralweekstofullymatureatambienttemperaturebutthisperiodcanbereducedbypostcuringatelevatedtemperatures.Bestresultsareobtainedbyallowingthemouldingtostabilisefor24hoursatambienttemperatureandthenpostcuringforeither3hoursat80C,8hoursat60C,12hoursat50Cor16hoursat40C.Thesetimesandtemperaturesareforgeneralguidanceonlyandwheremouldingsaretobeusedforwaterorchemicalcontainment,differentconditionsmayapply.

Trimming and FinishingProductiontimecanbesavedifmouldingsaretrimmedwhiletheresinisstillatthegreenstage.Thisoperationisbestcarriedoutusingasharptrimmingknifewhichisheldatrightanglestothelaminate,thoughscissorscanbeused.Ifsuitablyreinforced,theedgeofthemouldcanbeusedasatrimmingguide,butcareshouldbetakennottodistortordelaminatethemouldingatthisstage.

Fullycuredcompositelaminatesaredifficulttocutormachineusingconventionalsteeltools.Waterjetandlaserjetcuttersarenowreadilyavailableforlargescalemachiningofcomposites,butforsmalleroperationsafullrangeofportablediamondorcarbidetippedcuttersanddrillsisavailable.Manyoftheseoperatebymeansofcompressedair,makingthemsafeforuseintheworkshop.Thehealthandsafetyaspectsofhandlingandmachiningcompositematerialsaredealtwithinaseparatesectionlaterinthishandbook.

Oncealltrimmingoperationsarecomplete,anyreleaseagentshouldberemovedfromthesurfaceofthemouldingpriortobuffingandpolishing.Whereamouldingistobepainted,waxreleaseagentsshouldbeavoidedastheyaredifficulttoremovewithouttheuseofwetordryrubbingpaper.Mostpaintsystemscanbeusedwithcompositesbut,forstovingfinishes,itisrecommendedthatthemouldingispostcuredat80Cbeforeapplyingthepaint.Specialprimers,designedtoachieveexcellentadhesiontogelcoatedsurfaces,areavailableandtheiruseisrecommendedfordurability.SandablegelcoatsintheCrysticrangehavealsobeendevelopedspecificallytoenhancethepaintabilityofcompositemouldings.

ClosedMouldProcessesFormanyyears,contactmouldinghasbeenthepredominantmethodofmanufacturingcompositecomponents.Whilstitisaparticularlyadaptableprocess,legislativeandcommercialpressuresaremakingitlesscosteffectiveasaproductionmethod.

Manyclosedmouldprocesses,whichaddresstheenvironmentalandquality/consistencyissuesinherentinopenmouldmethods,arenowavailabletocompositemoulders.Thesecoverawiderangeofproductionandtechnicalneeds,fromrelativelylowvolume,lowcapitalcostthroughtohighlyautomated,largevolume,highinvestmentprocesses.

Vacuum Infusion : VIThisprocesscanbeintroducedtoamouldingshopwithminimuminvestment.Existingopenmouldscanbeusedwithlittleornomodification,andtheprocessisadaptabletolargeorsmallcomponents.

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IntheVIprocess,dryreinforcementsareencapsulatedbetweenarigid,airtightmouldandaflexiblemembrane(vacuumfilmorbag)whichissealedaroundtheedgeofthemould.Thisformsacavitywhichisthenplacedundervacuumtocompactthereinforcement.

Catalysedresinisintroducedintothecavityandthevacuumpullsitthroughthereinforcement.Oncethecomponentisfullyinfused,itisallowedtocure,afterwhichthebagandthecomponentareremovedfromthemould.

ResinsforuseintheVIprocessneedtobelowinviscosityandmayalsorequirecontrolledexothermproperties,forlargersectionsorthickercomponents.

ThereareseveralvariantsoftheVIprocess,themostsignificantofwhichisprobablytheSCRIMPsystemdevelopedbyWilliamSeemanintheUnitedStatesofAmerica.

Vacuum Assisted Resin Transfer : VacFlo

Vacuum Assisted Resin Transfer : VacFloVacFloisaresintransferprocessthatfeaturesmuchofthesimplicityofVIandmanyofthebenefitsofconventionalRTMwithoutincurringtheassociatedhighcostsofinjectionmachineryandsubstantialtooling.VacFloisoperatedbyapplyingagelcoattooneorbothmouldfacesasrequired,placingthereinforcementsandanycorematerialsinthelowertoolandclosingthemould.Avacuum(approx.1baror14psi)ispulledbetweenthedoublesealaroundtheperimeterofthemould,effectivelyclampingthetwohalvestogether.Asecondvacuum(approx.0.5baror7psi)isthenpulledinthecavityofthetoolusingacentrallyplacedvacuumport.Catalysedresinisintroducedviaaninjectionportattheedgeofthepart.Theresinmaybedrawninusingvacuumonly,orbyusingacombinationofvacuumandinjectionunderpressure.Astheresinentersthecavityitflowsaroundtheperimeterandthenintothecentreofthetool.Oncethemouldisfull,injectionisstoppedandthemouldisheldundervacuumuntiltheresinhasgelled.Whencured,thepartisde-moulded.

TheVacFlosystemwillworkwithVIorRTMresins,sothemouldercanselectmaterialsfromtheCrysticrangetobestsuithisconditions.

Resin Transfer Moulding : RTMDevelopmentsinmaterials,machineandtoolingtechnologieshaveenabledtheRTMprocesstobecomehighlyefficientforbothsmallandlargecomponentsandshortorlongproductionruns.

ThebasicRTMprocessinvolvespre-loadingamouldcavitywithdry,continuousreinforcement,closingthecavityandinjectingacatalysedresin.Oncetheresinhaswet-outthereinforcementandhascured

Vacuum InfusionGelcoat

Reinforcement

Core material (with holes punched through)

Peripheral channel

Mould

Vacuum take-off point

sufficiently,thecavityisopenedandthepartremoved.RTMtoolscanbemanufacturedfromcompositesor,formaximumdurability,frommetals.Thetoolsmayoperateatroomtemperatureorincorporateaheatingsystemforoptimumproduction.

TheRTMprocessisnowwidelyacceptedinthecompositesindustryasaneffectivemethodofmanufacturingpartsrangingfromaerospaceapplicationsthroughtolandtransport,marineandbuildingandconstruction.ForRTMitisvitalthatthegelandcurecharacteristicsofaresincanbetailoredtosuitparticularmouldcycletimes.

Cold/Warm Press MouldingThistechniqueinvolvestheuseofapairofmatchedtoolswhicharemountedinapress.Thetoolsareoftenconstructedfromcompositesandareeitherusedatroomtemperature,ormodesttemperaturesupto60C.

Tooperatetheprocess,agelcoatisappliedtotherequiredmouldface(normallythefemalehalf).

Oncethegelcoatissufficientlycured,thereinforcementisputinplace.Finally,therequiredamountofcatalysedresinispouredintothemouldandthetoolsareclosed.

Asthemouldhalvesarecompressedtogether,theresinisforcedtoflowthroughthecavityandwetoutthereinforcement.Byusingapinch-offaroundtheperimeterofthetool,itispossibletoallowairtoventwhilestillcreatingsufficientbackpressuretoensuretheresinfillsallareasofthecavity.

Itispossibletousevacuumtodrawthemouldstogetherandactasthepress,inwhichcasenoexternal

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Vacuum on

Resin flow

Resin inlet tube passing through vacuum bag

VacFlo

Peripheral channel. Used to clamp both mould halves together

Upper mould half

Vacuum (1 bar)

Vacuum (0.5 bar)Resin Inlet port

Flexible Seals

Lower mould half

pressisnecessaryandthemouldscanbelightweightandsemi-rigid.

ResinrequirementsforpressmouldingaresimilartothoseforRTM,thoughincertaincircumstancesthegeometryofthepartrequiresamorethixotropicproduct.Resins,reinforcementsandassociatedproductsintheCrysticrangearespecificallydesignedtoenablemoulderstooptimisewhicheverclosedmouldprocessischosen.

Althoughclosedmouldtechniquesgenerallyrequiremorecapitalinvestmentthancontactmouldingmethods,theyhavemanyadvantages.Qualitycanbemorecloselycontrolledandcloserdimensional

tolerancesachieved,leadingtomechanicalpropertieswhicharemoreconsistentandeasiertoaccuratelypredict.Oneofthegreatestbenefitsofclosedmouldsystems,however,istheirimpactontheenvironment,asstyreneemissionsduringmouldingcanbevirtuallyeliminatedbyusingtheseprocesses.

HotMouldProcessesHotpressmouldingtechniquesareusedforhighvolumeproductionofcompositecomponents.Theprincipleoftheprocessisthatreinforcementandacontrolledquantityofcatalysedresinareenclosedandcuredbetweenheated,polished,matchedmetalmoulds.Ahydraulicpressisusedtobringthemouldstogetherunderpressureattemperaturesbetween100Cand170C.Cycletimes,whicharedependentontemperature,mouldingcomplexityandweight,aregenerallybetween2and4minutesbutcanbeaslowas30seconds.

Thesameequipmentcanbeusedtoproducecomponentsbywetmouldingorbytheuseofmouldingcompoundsorpre-pregs.

Wet MouldingDryreinforcementisplacedintothemouldandcatalysedresinpouredontoit.Theresiniscatalysedusingacuringagentwhichisactivatedbytheheatofthemouldbutisstableatambienttemperature.Thehydraulicpressurecreatedbytheclosureofthemouldforcestheresinthroughthereinforcementandintothepinchoffarea,thusensuringtotalwetoutofthereinforcingfibre.Pressureisreleasedoncecurehastakenplaceandthecomponentisthenremovedfromthemould.

Wherethewetmouldingtechniqueisused,itispossibletopre-formglassreinforcementbeforeputtingitintothepress.Choppedrovingsaresuckedorblownontoafinemeshshapedtotherightcontours.Whenthedesiredthicknessofreinforcementisachieved,thepre-formissprayedwithbindertoholdthestrandstogether,thenovenheatedfor2-3minutesatatemperatureof150C.Thepre-formisthenreadyforthe

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RTMMould seals (one or two can be used)

Upper tool

Supporting structure

Supportingstructureclamped together

Supporting structure

Lower tool

Cavity containing reinforcement

Resininjection

port

press.

Moulding CompoundsTodayscompositesindustryemployshotpresstechniquesmainlytoproducecomponentsfrompolyestermouldingcompoundssuppliedtothemoulderinreadytouseform.

Dough Moulding Compound (DMC)ThisisadoughlikemixturenormallybasedonpolyesterresinandEglassfibres.GeneralpurposeDMCsusecalciumcarbonateasthefiller,thoughotherfillersmaybeusedtoobtainspecificpropertiesrequiredinthemoulding.Thereinforcingfibrelengthisnormallybetween3mmand12mmandthefibrecontentofafinishedmouldingwouldbebetween15%and20%.

Bulk Moulding Compound (BMC)BMCissimilarinappearancetoDMCbutisformulatedtoproducemouldingsofimprovedqualityandfinish.Isophthalicresinsareusedastheseexhibitbetterhotstrengthandstabilityandlowprofileadditivesmaybeincorporatedtoimprovesurfacefinish.

N.B.Whenmouldingcompoundswerefirstdeveloped,themaindifferencebetweenBMCandDMCwasthatBMCcontainedachemicalthickener(e.g.MgO),whereasDMCwasunthickened.Today,mostmouldingcompoundsareunthickenedandthetwotermsareinterchangeable.ThetermDMCisusedextensivelyintheUKandUSA,withBMCbeingusedexclusivelyinmostofEurope.

Sheet Moulding Compound (SMC)SMCconsistsofEglassreinforcementimpregnatedwithcatalysedpolyesterresincontainingvariousfillers.Itissuppliedinsheetformsandwichedbetweentwopolyethyleneorpolyamidefilms.

TomouldSMC,sufficientpiecesofthesheetmaterialarecuttobetween40%and80%ofthesurfaceareaofthemouldinordertomakeupthedesiredweightofthefinishedmoulding.Thepiecesarestrippedoftheirprotectivefilmandplacedinthemouldwheretheapplicationofheatandpressurewillcausethecompoundtoflowthroughoutthetoolcavity.Thishomogeneousflowoccursevenwhenthemouldhasdeepdrawareasorsectionalchangesandgivesaconstantresin:glassratiothroughoutthemoulding.Thisallowscomplexpartsincludingthosewithribs,bossesandchangesinsectiontobemanufactured.SMCproducesmouldingswithexcellentdimensionalstability,highmechanicalproperties,goodchemicalresistanceandelectricalinsulation.MinimalshrinkgradesofSMCareavailable,andthesecanbeusedtoachieveasuperiorsurfacefinishforpostpainting.SMCisthereforesuitablefortheproductionofautomotivebodyparts,electricalhousings,chemicaltraysetc.

Low Pressure Moulding Compound (Crystic Impreg) CrysticImpregissimilartoSMCbutusesanovel,patentedtechnologytophysicallythickenthecompoundduringmanufacture,ratherthantheconventionalmethodofchemicalthickeningusingareactivefiller.

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CrysticImpregcanbemouldedusingmuchlowerpressuresthanSMC.Foroptimumresults,themouldingprocessrequiresapressureof5-25barandatemperatureofbetween110Cand150C,whichwillgiveacycletimeof2-10minutesdependingonpartsizeandcomplexity.

CrysticImpregLPMCcanbemouldedwithgreatconsistencyimmediatelyaftermanufacture,usingrelativelylowcapitalcostpressesandutilisingtoolsproducedfromawiderangeofmaterials.Itsuniquechemicalmake-upallowsmanydifferentgradestobepreparedforuseinvariousapplicationsincludingtheautomotiveindustry.Thismeansthatfeaturessuchasshrinkcontrol,fireresistance,improvedtoughnessandwaterresistancecanbeincorporated,thustailoringthematerialtosuitenduserrequirements.

ContinuousProcessesContinuousprocessesareusedtoproducecompositecomponentssuchassheetingandpipes,whicharesuitedtolong,uninterruptedproductionruns.Severalcontinuousprocessesaredescribedinthissection.

PultrusionThepultrusionprocessisusedtoproducecompositesofuniformcross-sectionwithexceptionallongitudinalstrengthandrigidity.Theprocesswasfirstusedinthe1950stoproducesimpleitemssuchasrodstock.Sincethen,developmentsinprocessandmaterialtechnologymeanthathighlycomplexprofilesofconsiderabledimensionscannowbemanufacturedusingthismethod.Expressedsimply,theprocessinvolvesdrawingreinforcements,impregnatedwithactivatedresinthroughaformingguide,whichpre-shapesthematerial.Usingcontinuousrovings,whichareusuallythepredominantreinforcementpresent,thematerialispulledthroughaheateddie,whichactivatesthecatalyst,thuscuringtheresin.Thecuredprofilethenpassesaflyingsawattachmentandisautomaticallycuttotherequiredlength.Thereinforcementiswettedouteitherbytheuseofaresinbath,orbyresininjectionatthefrontofthedie.Theresinbathsystemisstillthemostcommon,thoughresininjectionisgaininginpopularityandismoreenvironmentallyfriendlyasitdrasticallyreducesstyreneemissions.

Thecuringsystemusedinthepultrusionprocessusuallyconsistsofacombinationofperoxides.Ahighlyreactiveperoxide,knownasakicker,isusedforinitialcure,incombinationwithmediumorlowreactivityperoxidestoachieveamoregradualthroughcure.Thisdualsystemensuresthatprofilesachieveoptimalcure,withlowresidualstyrenecontents.

Thecuredprofileispulledthroughthedieusingeitherreciprocatingpullersoracontinuouscaterpillartracksystem.Thereinforcementmostcommonlyusedinthepultrusionprocessisglass,thoughcarbonandpolyaramidfibrescanalsobeusedsuccessfully.Resinsystemsforpultrusionincludepolyesters,vinylesters,epoxiesandmethacrylatedresins,withpolyestersbeingthemostcommon.

PultrusionresinsintheCrysticrangearedesignedtoachievethebalanceofpropertiesnecessarytooptimisetheprocess.

Filament WindingThefilamentwindingprocessisbasedonasimplebasicprinciple.Itconsistsofimpregnatingreinforcingfibreswithactivatedresin,thenwindingthemontoarotatingmandrel.Successivelayersofreinforcementarebuiltuponthemandreluntiltherequiredthicknessisachieved.Thereinforcementcanbewoundlongitudinally,circumferentially,helically,orinacombinationoftwoormoreofthese.Thepropertiesrequiredfromthefinishedarticlewilloftendeterminetheangleofwind.

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Themandrel,thoughnormallyofsteel,maybemadefromavarietyofmaterials,andpressurised,flexiblemandrelsareoftenutilisedinthemanufactureofcertaintypesofcylindricalvessels.InthecaseofcompositecomponentsusingPVC,polypropylene,etc.asaliningmaterial,theprefabricatedlinertakestheplaceofthemandrel.

Continuousrovingsaregenerallyusedinthisprocessthoughotherformsofreinforcementsuchaswoventapescanbeincorporated.Glass,carbonandpolyaramidfibrescanallbeusedsuccessfully.Glassandthermoplasticveilsareoftenincludedwhereresinrichcorrosionbarriersarerequired.

Polyester,vinylesterandepoxyresinsareallsuitableforuseinthefilamentwindingprocess,resinchoicebeingdependentontherequirementsofaspecificapplication.

Filamentwindingisanidealprocessforthefabricationofcylindricalcompositeproductsandiswidelyusedfortheproductionoflargetanks,processvessels,ductingandpipescapableofmeetingstringentperformancerequirements.

PullwindingPullwindingisaprocesswhichcombinespultrusionwithfilamentwindingandisusedtoproducethinwall,hollowcompositeprofileswhichexhibithighstrengthproperties.

Reinforcements,impregnatedwithactivatedresin,arewoundontoamandrel,whichisthenpulledthroughaheateddie.Asinconventionalfilamentwinding,thereinforcement,whichisnormallyaroving,canbewoundinoneormoreofseveraldirections.

Thoseresinsandreinforcementssuitableforfilamentwindingandpultrusioncanalsobeusedinpullwinding.

Centrifugal MouldingThisprocessisusedtomouldtubes,pipesandcylinderswithamaximumdiameterof5metres.Choppedrovingorglassmatislaidinsideahollowmandrelandimpregnatedwithactivated,normallypolyester,resin.Themandrelisthenheatedandrotateduntiltheresincures.Thisprocesscreatescentrifugalforce,whichactstoconsolidatethelaminate.Un-reinforcedcastresinsheetcanalsobeproducedusingthecentrifugalmouldingmethod.

ResinsfromtheCrysticrange,whichweredevelopedforuseinthefilamentwindingprocess,arealsosuitableforcentrifugalmoulding.

Machine Made SheetingMostofthecompositecorrugatedsheetingmanufacturedtodayisproducedusingmachines.Thereareseveralpatentedmachineprocesses,allofwhicharesimilarinprinciple.

Acontinuouslengthofreleasefilm,usuallypolyester,travelsalongamovingconveyorandglassfibreisfedontoit.Activatedpolyesterresinisthenmeteredontotheglassandafurtherlayerofreleasefilmaddedtocompleteaglass/resinsandwich.

Thesandwichpassesunderaseriesofrollerswhichconsolidatethelaminate,controlitsthicknessandexpelanyair.Thelaminateisthenpassedintoaheatedformingareaonthemachineandcorrugatedbymeansofdiesorrollers.Heatcanbeappliedinthisareabymeansofanenclosedoven,orbyaseriesofheatlampssuspendedabovethesurface.Oncethelaminateisformedandcured,itistrimmedtothe

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correctwidthandthencuttothedesiredlength,usuallybymeansofanautomaticsaw.

Eglassisalwaysusedinthemachinemanufactureoftransparentcompositesheeting,eitherinmatformorasrandomlydepositedchoppedrovings.ThisisbecausetherefractiveindexofEglasscanbematchedbyspecialisedpolyesterresinstoproducesheetingofhighclarity.

Someoftodaysautomatedsheetingmanufactureutilisesultraviolet(UV)lighttocurethelaminate,soCrysticresinswithspeciallydesignedcuringmechanismshavebeendevelopedtomeetthisneed.

ResinsintheCrysticrangeareavailabletoenablethemachineproductionofcompositesheetingwitharangeofpropertiesincludinglowfirehazard,goodweatheringandhighclarity.

APPLICATIONS

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Un-reinforcedPolyesterResinThishandbookismostlyconcernedwiththeapplicationofpolyesterresinsinthefibrereinforcedcompositesindustry.However,polyesterresinsarealsowidelyusedinun-reinforcedapplications,someofwhicharedescribedinthissection.

Body FillerPolyesterbasedcompoundsareusedextensivelyforthecosmeticrepairofvehiclebodies,torectifydamagedcompositemouldingsandformanyotherrepair/refurbishmentapplicationswhererapidcompletionisimportant.Thesecompoundsarealsoideallysuitedtotheproductionofformulatedwoodfillersandplasterfillers.

CrysticStopperisaformulatedmaterialwhichconsistsofaliquidresinbaseandafillerpowder.Whenthesearemixedtogetherintherecommendedproportionstheyformapaste,whichcuresatroomtemperature.Thepasteiseasytoapplywithgoodtrowellingpropertiesandrapidcurecharacteristics.Itprovidesahard,rigidfilling,whichcanbemechanicallysandedwithoutclogging.Thismaterialisideallysuitedtothedo-it-yourselfmarket.

Crysticresinsforformulatorstocompoundintobodyfillersaredesignedtoachievetheidealcombinationofstoragestabilitywithoptimumcuringproperties.Thepropertiesrequiredfromtheformulatedcompoundareachievedbyvaryingthecombinationandtypeoffillerused.Thiscanbeacomplexprocess,aspurity,softness,particlesizeandsizedistributionofthefillerwillallaffecttheperformanceof

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thefinalsystem.

Flexibilityinthecuredcompoundisimportanttoensuregoodadhesionandtoimpartoptimumfinishingandsandingcharacteristics.Thelevelofflexibilityislargelydeterminedbytheresinconstituentofthecompoundandcanbetailoredbyincorporatingoneormoreresinsofdifferentflexibilityintotheformulation.Advancesinresinformulationandproductiontechniqueshaveenabledbodyfillertechnologytoprogresstomeetthedemandsofthistechnicallyorientedapplication.

Button CastingPolyesterresinshave,formanyyears,beenusedtomanufacturebuttons.Therearethreemainmethodsofmanufacturedependingonthetypeofbuttonbeingproduced.

Pearlbuttonsaregenerallymanufacturedfromresinpigmentedwithnaturalorsyntheticpearlessence.Thepigmentedresiniscastintosheets,normallybycentrifugalcastingmethods.Thebuttonsaretheneitherblankedfromthesheetsbeforetheyarefullycured,ortrepannedfromtotallycuredsheetsandfinallymachinedandpolished.

Plainbuttonscanbemanufacturedfromrodstock.Resiniscastintotubesmadefromsuitablematerialssuchaspolyurethane.Thebuttonsarecutfromtheresultingrodstockattherequiredthickness,machinedandpolishedonthecutsurfaces.Variouseffects(e.g.tortoiseshell)canbeachievedbytheuseoftwoormorecolouredpigmentsaddedtotheresin.

Large,decorativeortexturedbuttonsareusuallymouldedindividuallyinmulti-cavitysiliconerubbermouldsattachedtoamovingbelt.Resinispouredintothemoulds,thebeltisvibratedtoremoveairandthenpassesthroughanoventoheatcuretheresin.Littleornomachiningisrequiredwiththismethodofmanufacture.

Embedding and PottingGlassclearpolyesterresinscanbeusedforembeddingobjectstoproducepaperweightsandotherdecorativeitems,orforpreservingmedicalandbotanicalspecimens.Theseresinscanalsobeusedveryeffectivelyintheproductionofcostumejewellery.

TheexcellentdielectricpropertiesandcuringcharacteristicsofcertainCrysticresinsmakesthemidealforencapsulatingelectroniccomponents.Theserangefromsinglecapacitorstocompleteminiaturisedcircuits.

Decorative CastingPolyesterresinsarewidelyusedinthemanufactureofdecorativearticlessuchasstatuettes,figurines,modelsandreplicas,etc.

Expressedsimply,thecastingprocessinvolvesmixinganinertfillerpowderintoaresin,pouringthemixintoamouldandleavingittocure.

Selfreleasing,flexiblemouldcompoundsaremostcommonlyusedforcastingpurposes.Thethreemaintypesofmouldingcompoundarelatexrubber,hotmeltvinylrubberandcoldcuresiliconerubber.

Thechoiceoffillerpowderfordecorativecastingdependstoalargeextentonthefinalfinishrequired.

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Ifthecastingistobepigmentedorpostpainted,thenthefillerisneededonlytobulkouttheresinandcalciumcarbonateortalccanbeused.Aluminatrihydratewillproducecastingswithasemi-translucentfinishreminiscentofmarble,whilstmarbleflouritselfcanalsobeusedtoachievethisaffect.

Powderedmetalsusedasfillersresultincastingswitharealisticmetalfinish.Bronze,copper,aluminiumandbrasspowdersareallavailableandtheycanalsobemixedtogethertocreatedifferentmetalliceffects.Forinstance,mixingaluminiumandasmallquantityofbrasswillproduceagoodsimulationofold,tarnishedsilver.Metalliccastingsmustbebuffedandpolishedafterremovalfromthemouldinordertoproducetherealisticmetalsheen.

GeneralpurposeandspecialisedpolyesterresinsintheCrysticrangehavebeendevelopedtocaterforallaspectsofthedecorativecastingindustry.

Polyurethaneresinsarealsousedfordecorativecasting,astheyproducestrong,durablecastingswithveryhighdefinitionandexcellentreproductionoffinedetail.Theyareeasytomixandmeasureandfinishedcastingscanbepaintedusingenamel,acrylic,andoilpaints.Polyurethanesarewidelyusedinthecommercialmanufactureofhighqualitymodelkits.

FlooringSpeciallyformulatedCrysticpolyesterresinshave,formanyyears,beenusedtoproduceseamlessindustrialanddecorativeflooringsystems.Whenproperlylaidandcuredonsuitablypreparedsubstratestheyhaveoutstandingresistancetoawiderangeofchemicalenvironments.Polyesterfloorshaveanattractive,aestheticfinish,whichisdurable,hygienicandeasytocleanandmaintain.

Polyesterflooringsystemsgenerallyconsistofthreecomponentresins,thesebeingaprimer,abasecoatandatopcoatorglaze.Theprimerisformulatedtoprovideadhesiontosuitablypreparedsubstrates,thebasecoatisaclearresinwhichcanbepigmentedandfilledandthetopcoatisaclearresinusedtosealtheflooringsystemandprovidetheaestheticfinish.

Polyester ConcreteResinbasedconcretecanbeanattractive,lighterweightalternativetocementbasedconcretepre-castingsandnaturalslate.Developmentsinresintechnologycoupledwithextensivefieldexperience,hasenabledarangeofpreviouslycementbasedconcretestructurestobepre-castwithresinaggregatecompositions.Withsuitableresin,filler,aggregateandpigmentsarangeofpre-castings,includingcladdings,tilesandsimulatedslatescanbemanufacturedwithattractive,durablefinishes.

Resinconcreteformulationsforpre-castingsarepreparedbymixinganactivatedpolyesterresinwithappropriatefillersandaggregatestosuitspecificapplications.Forexample,asyntheticslatecanbeproducedfrompolyesterresinsfilledwithslatepowderandotherfillers.Artificialstonecanbeproducedeitherbyreconstitutingnaturalgroundstoneorbyusingstandardfillerswithsuitablepigments.Polyestersystems,suchasCrysticresins,offergreaterversatilitythanotherpolymersbecausetheircurecharacteristicscanbeadjustedwithoutseriouslyaffectingthepropertiesofthefinishedproduct.Finishedpre-castings,properlycured,aredurablewhenexposedtonaturalweatheringandtheirpropertiescanbeoptimisedtomaximiseresistancetoparticularenvironments.Otherbenefitsofpolyesterpre-castingsincludeimprovedimpactandmechanicalproperties,finemouldreproduction,fastsettingandrapidpropertydevelopment.

Polyester Marble and Onyx

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Simulatedmarbleandonyx,producedusingpolyesterresins,areusedtomanufacturebasins,vanityunits,profiledpanels,etc.Claddingpanelsforwalls,stairsandcolumnsarealsoattractivelyproducedinthesematerials.

Simulatedmarbleismanufacturedbymixinganactivatedpolyesterresinwithasuitablegradeofpowderedfillersuchascalciumcarbonate(typically75%byweight).Smalladditionse.g.2%to5%byweight,oflightweightglassbubblesaresometimesaddedtoimprovethehotandcoldwatercycleresistanceofthematerial,therebyreducingthecalciumcarbonatecontent.

Simulatedonyxisusuallylighterincolourandmoretranslucentthansimulatedmarble.Colourismorecriticalandformulationsarenormallybasedonaluminatrihydrate(typically67%byweight)orglazedfrits(typically75%byweight).

Whenabasecolourisrequired,pigmentpastesaremixedintotheresin.Thevariegatedeffectisachievedbypartiallymixinginpigmentswhicharedispersedinanincompatiblemedium,andusingartisticjudgementtodevelopandreproducethedesiredmarbleoronyxeffect.Theapplicationofacleargelcoattothemouldbeforepouringinthefilledresinmixgivesanaddedin-depthlustretothefinishedarticle.

Solid SurfacesFibrereinforcedunsaturatedpolyesterresinshavebeenusedinbuildingapplicationsformanyyears.Recentdevelopmentsingranite-effectsurfaceshavecreatednewpotentialfortheiruseindecorativefinishesforindustrialanddomesticapplications.

Solidsurfacecastingsaremanufacturedusinghighquality,Iso-NPGpolyesterresinssuchasthoseintheCrysticrange,containingcoloured,unsaturatedorsaturatedpolyesterbasedchipsandanaluminatrihydratefiller.

Resinbasedsolidsurfacematerialscanbemixedandmouldedusingvacuum,sodonotrequireagelcoattoachieveagoodsurfacefinish.Thismeansthatthesurfacecanbere-polished,whennecessary,torestoretheoriginalshowroomgloss.Solidsurfacecastingsareeasytomachineandcanberoutedtoenabledifferentcolourstobeinlaid,thusallowinganinfiniterangeofdecorativefinishes.Solidsurfacecastingsaretoughanddurableandexhibitexcellentwaterandheatresistance.Thesepropertiesmeantheyareideallysuitedforkitchensurfaces,sanitarywareandwashrooms.Theexcellentweatherandchemicalresistantqualitiesofthebaseresinusedinsolidsurfacetechnologycreatesthepotentialforitsuseinexternalcladdingapplications.

Rock AnchorsRockanchorsareusedinmining,civilengineeringandbuilding/constructionapplications,toprovidestrongpointsforbolts/rebars.

Resinsforrockanchorsneedtobalanceverylongstoragestabilitywiththeapparentlyconflictingrequirementofveryrapidcure.Arangeofgeltimescanbeobtained,varyingfromafewsecondstoseveralhours,dependingontheparticularcuresystemused.

Themostimportantmechanicalpropertyrequiredfromarockanchoriscompressionstrength,thoughgoodadhesionisalsoimportant.

Fillersforuseinrockanchorsarecrucialintermsoftheirpull-outpropertiesandstoragestability.Thosecommonlyusedvaryfromlargesilicapieces,whichliterallyfloatintheresin,tofinelyground

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limestone.Thetypeoffillerusedwilldependontheapplication.Fillerpurityisimportant,asthiscanaffectthepropertiesoftheanchor.Itisadvisabletoavoidfillerswithhighcontentsoftransitionmetalssuchasironandcobalt,asthesecanadverselyaffectstoragestability.

Cartridgeorsausagepackagingiscommonlyusedforrockanchorsinthecivilengineeringandminingindustries.Theresinissealedinastyreneresistantplasticsuchasnylon,andaglasstubeorplasticfilmcontainingcatalystisincorporatedwithinthepackage.Theactionoffixingtheboltorrebarintoplacemixesthecatalyst,whichisdispensedatasetratio(commonly10:1).

RockanchorresinsfromtheCrysticrangearetailoredtomeetthedemandingrequirementsofthisapplication.

ChemicalContainmentCompositeshavebeenusedformanyyearstomanufactureproductsforresistanceto,andthesafecontainmentof,awiderangeofchemicals.

ChemicalresistantFRPcompositesgenerallyconsistofhightensilestrengthglassfibreprotectedbyachemicallyresistantunsaturatedpolyesterresin.Figures2and3giveexamplesofthespecifictensilepropertiesachievablewithglassfibrereinforcedpolyesterlaminates,incomparisonwithsteelandaluminium.TheeaseofuseandversatilityofFRPfacilitatesthecost-effectivemanufactureofawiderangeofcomponents,usingavarietyofmanufacturingprocesses.TypicalmaterialandfabricationcostsareshowninFigure4.

Compositestructuresoffermanybenefitsoveralternativematerials,inchemicalcontainmentapplications.Theyarelightweightsosimplifyhandlingandinstallation.Beingselfcoloured,theyneednore-paintingandareeasilycleanedusingahighpressurehose.Ifnecessary,compositestructurescanbemodifiedin-situ,withminimuminterruptionofnormaloperations.TheabilityofaresintoresistaparticularchemicalenvironmentisnormallyclassifiedintermsofitsMaximumOperatingTemperature.InthecaseofchemicalresistantCrysticresinbasedlaminates,these

temperatureshavebeendeterminedfromanumberofsourcesincludingcasehistories,laboratorytestsandpracticalexperience.

Providedthatthecompositestructureismanufacturedtohighstandardsandfullypostcured,manyyearssatisfactoryserviceisachievable.ChemicaltanksshouldalwaysbedesignedinaccordancewiththerequirementsofBritishStandard4994:1987,whichusestheKfactorofsafetyapproach.(AnewEuropeanStandard,prEN13121,iscurrentlybeingdevelopedandwilleventuallyreplaceBS4994:1987).

Inacidenvironments,GRPcansufferprematuredegradationduetostresscorrosioncrackingoftheglassfibrereinforcement.Itisthereforeimportanttoensurethatthestructurallaminateisadequatelyprotectedbyasubstantialbarrierlayer.Thiscanconsistofathermoplasticliner,orseveralmillimetresthicknessofGRPmadeusingCglassorsyntheticsurfacetissueandahighlyresinrichEglasslaminate.Therecommendedbarrierlayershouldbebackedwithanappropriateresin,reinforcedwithanacidresistantglasssuchasECR(ExtraChemicalResistant)glass.

PolyesterresinsfromtheCrysticrangeareusedtomanufactureawiderangeofproductsandcomponentsforthesafecontainmentofmostmaterialsfromacidstoalkalis,fuelstofoodstuffsandwatertowine.

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Pipesand PipeLining

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E-GlassWR/UPAluminiumAlloy

MPaSG

Steel

120

160

80

40

0

Figure2-SpecificTensil