24512.2SourcesandoriginsThe warpyarns arewoundontotheloominparallel rowsandarethreadedthroughframescontainingplastic, woodenor metal strips. Theseframesareknownasheddles. Theheddleslift the warpyarns upwards, allowingashuttletobepassedthrough, carryingtheweftyarn. The heddles arethenlowered, trappingtheweft yarninbetweenthewarpyarns. Differentheddles are usedtolift alternatewarpyarnswitheachpassof theshuttle. Thisresultsintheinterlockingof thewarpandweft yarns, creatingafabric. Weavingpatternsareachievedby settingupseveral heddles tolift different warpyarnsat differenttimes, althoughthisis a time-consumingprocess. Computerisedloomsallowthecreationofcomplexweavepatterns quickly andefficiently. Figure 12.22 Atraditional loomPlainweaveThe plainweaveis thesimplest andmost widelyusedweavestructure, anditisveryversatile. Various weights of fabriccanbeproducedbyalteringthespacingof thewarpandweftyarnsor by usingcoarseor fineyarns. Muslinis acommonexampleof alightweightplainweavefabric, andcalicois a commonexampleof amediumtoheavyweightplainweavefabric. Figure 12.23 Magnifiedimageof aplainweavefabricFigure12.24AplainweavestructureKEYTERMSPlainweave:Abasicweaveconstructioninwhichtheweftyarngoesunderandoveralternatewarpyarns,givingastrongandflatfabric.
246Chapter 12Fibres andfabrics Twill weaveTwill weaveiseasilyrecognisableduetothediagonalpatternformedbythecrossingof thewarpandweftyarns. Thisweaveproducesaheavierfabricthanaplainweave, makingtwill strongerandmoredurablethanaplainweave.Forthisreason, twill weavesareoftenusedinproductsthatneedtoresistheavywearandtear, suchasdenimjeansandcanvasbags. Twillweavesarealsooftenselectedforaestheticreasons. Herringboneandhoundstoothfabricsarepopularexamplesofdecorativetwill weaves. Figure 12.25Magnifiedimageof atwill weavefabricFigure12.26AtwillweavestructureSatinweaveThestructureof asatinweaveproducesasmooth,lustrousfinishduetothe'floatingyarns' onthesurfaceofthefabric-theweftyarnsarewovenunderonewarpyarn, thenoveraminimumofthreewarpyarns.Thisresultsinalargersurfacearea, whichreflectslight, givingashinyfinish. Satinweavesaretheweakestofthethreetypesof weaveandcanbesnaggedeasily,duetothestructureofthefloatingyarns. Figure 12.27Magnifiedimageof asatinweavefabricFigure12.28AsatinweavestructureKEYTERMSSatinweave: Aluxurious weave constructioninwhichthe weft yarnfloats over threeor more warpyarns, givingasmoothandshiny finish. KEYTERMSTwill weave: Astrongweaveinwhichthe weft yarngoes under andover alternatewarpyarns ina diagonal formation, givinga texturedfinish.
24712.2SourcesandoriginsNon-wovenfabricsNon-wovenfabrics arecreatedusingtheshapeandtexture of staplefibres. Staplefibres areshort andhavecrimp(wavy texture). It is thecrimpedtexturethat causesthe fibres totangletogether. ACTIVITYYou will need: strips of paper (1cmwidth) intwocolours; adhesive tape. 1 Line uptenstrips of paper (of onecolour) vertically, side by side. Placeastripof tapeacross thetoptosecure them. 2 Use the diagrams aboveas guides tohelpyoucreate the three types of weave. BondedfabricsBondedfabrics aremanufacturedbylayingout a'web' of synthetic fibres, thenapplyingpressureandheat or adhesives tobondthefibres together. Bondedfabricsareoftenusedindisposabletextiles suchaswet wipes, teabags, surgical masks, dressingsandnappies. Thesefabrics losetheir strengthandstructureoncewet, sotheyareusuallyonlysuitable for oneuse. Figure 12.30 Disposablewet wipes aremade frombondedfibres. Figure12.31Surgicalmasksaredisposableforhygienereasons.KEYTERMSBondedfabric:Fabricmanufacturedbyaddingpressure,heat,chemicalsoradhesivestoaweboffibres,causingthemtobondtogether.Examplesofbondedfabricsincludebabywipesandinterfacing.Disposable:Productsintendedforasingleuseforcost,convenienceorhygienereasons.Examplesincludesurgicalmasksandbandages.Non-wovenfabrics:Fabricsmadebyentanglingfibrestogetherusingfriction,pressure,heatorchemicals.Thesefabricsarecheapertoproducethanwovenfabricsandareoftenusedfordisposableproducts.Figure12.29Anon-wovenfabricstructure
248Chapter 12Fibres andfabrics FeltedfabricsFeltedfabricsareproducedbyapplyingmoisture, heatandfrictiontoawebofstaplefibres, whichmatttogether. Themostcommonlyusedfibresinthisprocessarewoolandacrylic. Thefabricwill bedenserandstrongerthemoreitisworked-thisalsocausessomeshrinkage, however. Feltisoftenusedfordecorativepurposessuchasappliqué, andishistoricallyappliedtothesurfaceofpoolandsnookertables.Feltisalsousedfor cushioningandinsulatingvariousproducts. Feltisweakandwilleasilystretchout of shape, particularlywhenwet. Figure 12.32Traditionally, wool felt wasusedtotopsnookertables. Figure12.33Feltdoesn'tfray,whichmakesitsuitableforarangeofcrafts.WeftknitfabricWeft knitfabriciscomprisedof asinglecontinuousyarn, andisconstructedinhorizontalrows of interlockedloops. Thehorizontal rowsarecalledcoursesandtheverticalcolumnsarecalledwales. Weft knitsareoftenproducedusingknittingneedles,buttheycanalsobemanufacturedonalarger scaleusingautomatedknittingmachines.Thesemachinescanknitaflat lengthor atubeof fabric-tubesareveryusefulintheproductionofsocks.Weftknitsmaysnagandcanunravel if partof theyarnisdamagedorpulled.Weftknitsareusedforawiderangeof knitwear andhomefurnishings. Figure 12.34Magnifiedimageof aweft knit fabric Figure12.35WeftknitstructureKEYTERMSFeltedfabric: Fabric manufacturedby addingmoisture, pressureandfrictiontoa webof fibres, causingthemtomatt together. Examples of feltedfabrics includecraft felt andpool table covers.
24912.2SourcesandoriginsWarpknit fabricWarpknit fabric has amorecomplicatedstructurethanweftknitfabric. Warpknitsarecomprisedof multipleyarns. Thefabricis constructedinvertical rowsofinterlockingloopsthat zigzagfromsidetoside. Warpknits donot runor unravel andaremoreflexiblethanweft knits, makingthemsuitablefor sportswear andswimwear. Warpknitscanonlybecompletedonautomatedmachines. Figure 12.36 Magnifiedimageof awarpknit structureFigure12.37WarpknitstructureFigure 12.38 Arange of knittedfabrics ACTIVITYFindafabricsampleforeachofthefollowingheadings:lWoven-plainlWoven-twilllWoven-satinlNon-woven-bondedlNon-woven-feltedlWarpknitlWeftknitStudythefabricscloselytoidentifytheirstructure.Keepyoursamplestouseasarevisionaid.KEYTERMSCourses: Rows of horizontal loops that runacrossthewidth of a knittedfabric. Weft knit: Fabric constructedwithhorizontal andvertical rows of interlockingloops. Weft knits canbeconstructedusingknittingneedles or onaknittingmachine. Wales: Vertical rowsofinterlockingloopsthatrundownthelengthofaknittedfabric.Warpknit:Fabricconstructedwithrowsofinterlockingloopsthatzigzagdownthelengthofaknittedfabric. Duetotheircomplexity,warpknitscanonlybeconstructedonaknittingmachine.
250Chapter 12Fibres andfabrics Ecological,socialandethicalissuesassociatedwithprocessingEcologicalissuesEcologicalimpactofnaturalcellulosefibresNatural fibrecropsareintensivelyfarmedonvastareasoflandinordertokeepupwithglobaldemand.Farmersofcropssuchascottonandlinenusesignificantamountsof wateraswell astoxicpesticidesandfertilisers,whichdamagetheecosystem. Chemicalssoakthroughthesoilandintowatersources, killingwildlifeandcontaminatingdrinkingwater. Thesechemicalsalsostripthesoilofnutrients, reducingcropqualityandeventuallymakingthelandunusable. Organicfarmingreducesthisimpactthroughtheuseofnatural fertilisersandpesticides-thistypeoffarming,however, still requiresasubstantialamountofwater.Itisestimatedthatapproximately2700litresofwaterisrequiredtoproduceenoughcottonforasinglet-shirt.Ecological impactofnaturalproteinfibresThefarmingof livestockfor wool productionhasrelativelylowecologicalimpactcomparedtothefarmingof fibrecrops. Thelandusedfortherearingoflivestockisusuallyunsuitablefor crops, but livestockcandamagethelandbyovergrazing. Onlargerwoolfarms,thenumber of sheepcanexceed300,000. Chemical dipscontaininginsecticidesareusedtoprotect livestockfrommitesandticks, andthesedipscontaminatesoilandwatersources.Livestockcanalsoproducelargeamountsofthegreenhousegasmethane.Silkis ahighlyrenewableresourcewithlittleecologicalimpact.Theproductionofsilkincaptivity, however, isheavilycriticisedbyanimal welfareactivists.Thebreedingofsilkwormsincaptivityhasledtothedemiseof theBombyxmorimothinthewild,andcaptivemothshaveevolvedtobeblindandunabletofly. Thesemothsliveonlyforafewdaysandinthistimelayupto500eggs. TransportationandprocessingTherearefewcountrieswherefibreproductionislocaltoitsmanufacturers. Transportationofrawfibrescausesairpollutionandusesasignificantamountofnon-renewableresources. Theprocessingofsyntheticfibresusesfiniteresourcessuchasoil andcoal. Extractionandprocessingoftheseresourcesinvolvestheuseofhighlevelsofenergyandchemicals, andalsotheproductionofcontaminatedwaste. Greenhousegasemissionsfromfactoriescauseairpollutioninlocalareasanddepletionoftheozonelayer. Additionally, thereissignificantwaterpollutioninlocal areasaroundfactorysites.Syntheticfibresarenon-biodegradable: polyesterwouldtakeupto450yearstobreakdownintheenvironment.Syntheticfibresarerecyclable, however, andthispracticeisgoingfromstrengthtostrengthwithintheindustry.Figure 12.39Toxic pesticides areheavilyusedonfibrecrops. Figure 12.40Largeflocks of sheepovergrazelandandcausedamage tosoil. KEYTERMSRecyclable: Amaterial suitablefor processingusingtertiary recyclingmethods.
25112.2SourcesandoriginsThe washing, drying, dyeingandprintingof fabrics requires lots of energyandalsogenerates largeamounts of wastewater, whichcontaminates local water sources anddamages habitats. Manyfactories donot followrules andregulations onthesafedisposal of thesewasteproducts duetothe cost implications. Over-packagingof textileproducts is alsocreatingsignificant amounts of unnecessary plastic wasteeachyear. Whengarments aredeliveredtoaretail store, eachitemis coveredbyaplasticgarment bagthat is immediatelydisposedof. The purposeof thesebags is toprotect garments frommoistureanddust intransit. The garments arealsoplacedinsidecardboardboxes, however, whicharecoveredinplastic wrapbeforeshipping. Social andethical issuesThe treatment of garment workers inthetextileindustryhasbeenunderscrutinyformanyyears, withgarment workers insomecountriessubjectedtopoor(andoftendangerous)workingconditions, longhours andlowpay, withlittleprotectionfromunionrights. Childrenas youngas six havebeenfoundworkinginsomefactories, despitelocal lawstopreventchildlabour; andwork-relateddeaths inthetextileindustryarenotuncommon. Figure 12.42 Employees worklonghours for littlemoney, andofteninpoorworkingconditions.While steps havebeentakengloballytoimproveconditionsforemployeesworkingwithinthe textile industry, increasingconsumer demandfor fastfashionhasledtoathrowawayculture, withitems of clothingbeingpurchasedat rock-bottomprices, wornonceandquickly disposedof. This has drivendownretail prices, meaningthatmanufacturingcosts(includingworkers' pay andconditions) havealsobeendroppedinordertomaintainprofitsfor highstreet stores. This inturncanhaveanimpact onthepayandconditionsofthoseproducingthegarments. Figure12.41Drillingforcrudeoilandcoalminingdepletefiniteresources.KEYTERMSFastfashion:Arecenttrendinvolvingthequicktransferofnewcollectionsfromthecatwalkintostores.Fastfashionisoftenon-trend,lowqualityandlowinprice.Thecharacteristicsoffastfashionmeanthatconsumersbuylargevolumesofclothesmoreregularly,creatingmoreprofit.Throwawayculture:Theriseoffastfashionhasmadeclothingfarmoreaffordableforconsumers.Theincrediblylowpricesinsomehighstreetstoreshaveresultedinathrowawayculture,meaningthatconsumersdon'tfeeltheneedtokeepclothingthatisnolongerinfashion,andhappilydisposeofit.
25312.2SourcesandoriginsSecondaryrecyclingSecondary recyclingis wherethematerialsfromaproductareusedtomakesomethingnew, for examplecuttingapair of jeans tocreateshortsor cuttinganoldshirtintostripstobeusedas cleaningrags. This typeof recyclingissuitablefor oldclothingorhouseholdtextilesthat are wornor damagedandthereforecannot begiventocharityshopsorclothingbanks. TertiaryrecyclingTertiary recyclingis whenmaterials arebrokendowntotheir original stateandmadeintobrandnewproducts. Anexampleof thisprocessistheuseof plasticbottlestomakepolyester fleece. Polyester fibres arethermoplasticandcanthereforebecleaned, shredded, melteddownandre-formedintonewproducts. Natural fibrescanbeshredded, bleachedandspunintonewyarns, or usedfor paddingandinsulationapplicationsinthebuildingindustry. Tertiary recyclingis beneficial totheenvironment inmanyways. Thecleaning, sortingandprocessingof recycledfibres uses toxicchemicalsandenergy, however, whichmustbeconsideredwhenchoosingtouserecycledmaterials. It is estimatedthat 350,000tonnes of usedclothinggointolandfill intheUKeachyear. Most of the textileproducts inlandfill couldhavebeenusedagain. Fibrescannotwithstandendless recycling, however, andsowill eventuallyneedgotolandfill sitesattheendoftheiruseful life. Figure 12.45 Garments canbeupcycledtomakeindividual andinterestingclothing.
254Chapter 12Fibres andfabrics 12.3CommonlyavailableformsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜therangeof stockformsavailablewhenselectingfabrics➜therangeof standardisedcomponentsforusewithfabrics.This sectionwill guideyouthroughthestockformsandrangeoffabricsavailableandthestandardisedcomponentsusedforavarietyoftextileproducts.StockformsFabrics aremost commonlybought'offtheroll', inaspecialistfabricstoreormarket.Therearethreestandardroll widths: l90cm(interfacingsor linings) l115cml150cm. Most storeswill sell fabricataminimumlengthof50cm. Itisimportanttoknowhowwidethefabricroll isbeforecalculatingthenumberofmetrestobuyforaspecificproject.Figure 12.46Fabrics usuallycomefromFigure12.47Fatquartersareusefulforsmallerprojectsorquilting.rolls of 115cmor 150cm. Pre-cut cottonfabricsarealsoavailableforquiltingorsmallerprojects.Thesearecalledfat quartersandusuallycomeinbundlesofcomplementarycoloursandpatterns.Thesepieces measure4555cm. Theterm'fatquarter' comesfromthehistoricaluseofyardswhenbuyingfabric, andthesepiecesmeasureexactlyaquarterofayard.Feltcanalsobepurchasedinsquaresof varioussizesforsmallercraftprojects.Fabricweights, textures, handleanddrapevarysomuchthatitisvitaltogotothestoreandhandlethefabricbeforeselectingthemostappropriateone. Moststoreswillcutoffasmallsamplefor youtoexaminebeforeyoumakeapurchase.
25512.3CommonlyavailableformsCommonfabricnamesFabrics instores arenot usuallynamedjust bythefibrecontent. Manyfabricsaremadewithfibre blends. Thetablebelowlists someof thefabrictypesavailable. Table 12.7 Some of thefabric types availableFabric name Typical fibres usedExampleuseDrill Cotton Upholstery Jersey Cotton/ Wool/ Polyester T-shirts DenimCotton/ Elastane Jeans Voile Cotton/ Silk Mosquitonets Tweed Wool Jackets Gabardine Wool SuitingFelt Wool/ Acrylic Applique- crafts Broadcloth Cotton Dresses Sheeting Cotton/ Polyester Bedsheets Damask Silk/ Cotton/ Polyester Decorativenapkins Muslin Cotton Sheer curtains Satin Silk/ Polyester Occasiondresses Crepe Silk/ Polyester/ Viscose Blouses Velvet Cotton/ Polyester/ Viscose Eveningwear Corduroy Cotton/ Polyester Trousers Lace Linen/ Cotton/ Silk DecorativeChiffon Silk/ Polyester LingerieOrganza Silk/ Polyester Drapes Figure12.48Voilefabricsaresheerandverylightweight.Figure 12.49 Tweedis atypeof twill weave. Figure12.50Laceisaveryintricateanddecorativefabric.
256Chapter 12Fibres andfabrics StandardcomponentsStandardcomponentsintextilesareusedtojoin,fasten,shapeorstiffenfabrics. ThreadsThreadscomeinvarioustypes,weightsandtextures.Itisimportanttoselecttherightthreadforthejob.lMachinethread-strongthreaddesignedtomovesmoothlythroughsewingmachinemechanisms.lTackingthread-strong,thickthread,designedforhand-sewingseamsbeforemachinesewing.lEmbroiderythread-thick,lustrousthreaddesignedfordecorativework. lMonofilament-verystrong,usuallyclear,thread,usedforinvisiblestitching. Figure 12.51Various threads FasteningsFasteningsareselecteddependingontheiraesthetic, functionandintendeduse.Itisimportant toconsider safetyandeaseofusewhenselectingfastenings,particularlywhenforchildren'sproductswheretheymaybeachokinghazard. lButtons- usedoncoats, trousers, shirts. lPoppers- usedonbabyclothes, duvetcovers, clothing. lZips- usedontrousers, bags, cushioncovers. lVelcro- usedonshoes, outdoorjackets, bags. lHooksandeyes- usedonbras, dresses, skirts. lToggles- usedonbags, coats, tents. Figure 12.52Buttons comeinanendlessrangeof colours, shapes andmaterials. Figure12.53Hook-and-eyefasteningsarestrongandcanbehiddenwell.Figure12.54Togglesareusedtoopen,closeoradjustsizing.
25712.3CommonlyavailableformsStructural componentsStructural components areusedtoaddsupport toafabricor tohelpshapeagarment. lBoning- a metal or plasticstripthat issewnintoreinforcedseamstoaddstructureandshape toa garment, suchas acorset. lPetersham- a heavyweight ribbonor bandusedtostiffenwaistbandsorreinforcebuttonbands. lInterfacing- a l ight- tomedium-weight, bondedfabricusedtostiffencollars, cuffsorarmholes. Other There are many other components usedinthemanufactureof textilestoprovidefunctionalor aesthetic effects. lBias binding- a stripof fabric, cut onthebias, usedtocreateafinishededgearoundcurves. lElastic - v arious weights, usedfor waistbands, underwear, swimwear. lRibbon, sequins andbeads - appliedtofabricsurfacesfor decorativeeffect. ACTIVITYStudy a range of textileproducts andfill out thetablebelow. Product DescriptionComponents usedPurposeof componentExample: Rucksack WebbingClips Piping Zip Toprovideadjustablestraps. Toclippocketsshut Toaddaestheticvalueandhelpmaintaintheshapeoftherucksack.TosecurelyclosetherucksackFigure 12.55 Bias bindingis cut at a45-degreeangletoallowflexibility oncurves. Figure12.56Therearemanydecorativecomponentsavailable.
258Chapter 12Fibres andfabrics 12.4ManipulatingandjoiningLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandtheuseof specialist techniquestoshapeandfabricatehigh-qualityprototypes,withexemplificationofthefollowingprocesses:➜Addition➜Deformingandreforming.WastageWastageistheprocessof cuttingawaymaterial toleaveadesiredshape.ThebustandhipsaremarkedwiththissymbolGrainlinesshowthedirectionthepatternpiecesshouldbeplacedonthefabricAdjustmentlinesallowagarmenttobelengthenedorshortenedDotsindicatetheplacementofcomponentsorshapingtechniquesCuttinglines vary toindicatesizePatternpiecemust beplacedonfoldNotches areusedtomatchuppatternpieces The dottedlines arematchedtoformdartsPleats andtucks arecreatedwhenthe dots arematchedNotches Dart toshape bust FoldlineGrainlinesDotshowszipplacementDoublenotchesindicatethebackofthegarmentDarttoshapebackpiecesDotstoindicatewheregathersareaddedLengthenorshortenBust placement Figure 12.57Patternpieces withexamplesof patternmarkings
25912.4ManipulatingandjoiningPatternmarkingBefore patterns canbecut, theyneedtobemarked. Commercial patternpiecesandbasicblocks comeprintedwitharangeof important markingsthatmustbefollowedaccuratelytoensure that thefinishedproduct is thecorrect size, shapeandquality. Table 12.8 Patternmarkings that must befollowedaccuratelyCutting lines Lines are patternedtoguidethecuttingof different-sizedpatternpieces.Fold line Patterns withthis markingshouldbeplacedontheedgeof afoldedfabric.This will give asymmetrical patternpiecewhencut. Balance marks (notches) These markings areusedtomatchupdifferent patternpieces, toensureaccuracy. Thesearecut away fromthepatternpiece, notintotheseamallowance. Darts Darts must beaccurately marked, thentheouter linesbroughttogetherandsewntocreateshapeinagarment. Pleats and tucks Pleats andtucks aremarkedinthesameway; thearrowsshowthedirectionin whichthe fabric must besewn. Bust/hip placement This mark helps withfittings; youshouldcopythistoyourfabricandcheckthat it aligns withyour model's bust or hips, thenadjustthepatterntosuitthem. Grain line This shows thedirectionof thestraight grain; patternpiecesmustalwaysbeplacedinthe directionof this arrow. Adjustment lines These lines indicatewherethepatterncanbelengthenedorshortened.Dots These marks showtheplacement of specificcomponentssuchaspocketsandbuttons. There are several tools that canbeusedfor transferringpatternmarkingstofabricaccurately: lTailor's chalk - a s mall pieceof hardchalk, usedtotemporarilymarkfabric. lVanishingmarkers - pens containingvanishinginkthatslowlyfadesonexposuretoair, allowingmarks tobetemporarilymadetofabric. Figure 12.58 Tailor's chalkFigure12.59Vanishingmarker
260Chapter 12Fibres andfabrics PatterncuttingPatterncuttinginvolvestheuseof paperorcardtemplates, placedonthesurfaceofthefabricandcut aroundtoproducefabricpiecesthatareofaccuratesizeandshapefortheproduct beingmade. lCommercial patternscontaintemplatesthatareprintedonlargesheetsofpatternpaper.Theseoftenincludeseveral sizesandvariations. lBasicblocksareusuallymadefromthincardandareabasictemplatethatcanbeadaptedtoproducearangeof products. Commercial patternpiecesandbasicblocksaremarkedwithanarrowtoshowthedirectionof thegrainline, andthereforehowthepiecesshouldbeplacedonthefabricforcutting.Itis important that thesemarkingsareusedcorrectlytoensurethatthedrapeofthefabricisappropriatefor theproductbeingmade. Thestraightgrainrunsverticallydownthewarpyarninthefabric, andthisgrainlineismostcommonlyusedingarmentproductionasitgives thebest drape. Apatterncanalsobecutonthebias, whichrunsdiagonallyata45-degreeangletothestraightgrain. Fabricscutonthebiasaremoreflexibleandcaneasilybesewnintocurvedshapes. Cuttingonthebiasoftencausesmorewastage,sodesignersneedtopurchasemorefabricwhencuttingpatternsthisway.KEYTERMGrainline: Thegrainline always follows the directionof thewarpyarn, andshows where the pieces shouldbe placedonthe fabric prior tocutting. lTracingwheel andcarbontransfer-i nthismethodofmarkingoutpatternpieces,carbonpaper islaidontopof thefabric, withpatternpiecesontop.Thecarbonistransferredbythepressureappliedwhenthetracingwheelisrolledalongthesurfaceofthepatternpiece. lTailor'stacks- t hismethodof markingoutusesstitches, insteadofmarkingthesurfaceofthefabricwithapenor chalk. Small loops, whicharelaterremoved,aremadethroughthefabric. Figure 12.60Tracingwheel andcarbontransfer Figure12.61Tailor'stacks
26112.4ManipulatingandjoiningThere are several tools/techniques that canbeusedfor cuttingfabricaccurately: lFabric shears - thesearethemost commonlyusedandeasiestmethodforcuttingfabric. lRotary cutter - theseincrediblysharptoolsarerolledalongthesurfaceofthefabric, followingthepatternlines. Thesurfaceunderneathmustbeprotectedwithacuttingmat tominimisedamage. lLaser cutting- this canbeaquickandefficient waytocutoutmorecomplicatedpatternpieces if youhaveaccess toalaser cutter inschool. lBandsaw- this methodis usedinanindustrial settingtocutupto100layersatfabricatone time. Figure 12.62 Commercial patterns includeseveral styles and sizes. BodicebackBodicefrontSkirt backSkirtfrontSleeveFigure12.63Basicblockscanbeadaptedeasilytocreatepatternpiecestosuityourdesign.
262Chapter 12Fibres andfabrics Figure 12.64Fabric shears arethemost commonlyusedmethodfor pattern cuttingat homeor at school. Figure12.65Rotarycuttersareveryaccurate.Figure 12.66Bandsaws areusedinindustrial manufacturetocutthroughseverallayersoffabricatonce.
26312.4ManipulatingandjoiningAdditionThis sectionfocuses ontheformationof seamsthat aresuitablemethodsofjoiningfordifferent fabrics andproducts. It is important that thecorrecttypeof seamisusedtoensurethe product is highqualityandfunctions asexpected. PlainseamsPlainseams arethemost commonlyusedseamandcanbefinishedneatlyusingarangeof methods, for examplewithanoverlocker, pinkingshearsor biasbinding. Plainseamsaresuitable for most fabrictypes. FrenchseamsFrenchseams areenclosed, hidinganyrawedges. Thistypeof seamissuitableforsheermaterials, likechiffon, wheretheseams needtobealmost invisible. KEYTERMSPlainseam:Themostcommontypeofseamformedbyplacingfabricsrightsidestogetherandstitchedalongtheseamallowance.Frenchseam:Aseamusedforsheerfabricswhereseamfinishessuchasoverlockingmaybeunsightly.Thisseamissewntwice,placingwrongsidestogetherfirst,thenrightsidestogethertoenclosetherawedge.Plain seamFigure 12.67 PlainseamFrenchseamFigure12.68FrenchseamFlat felledseamsFlat felledseamsareverystrong, enclosedseams. This typeof seamiscommonlyusedondenimandsportswear. KEYTERMSFlatfelledseam:Aflatfelledseamisanoverlappedseamthatistopstitcheddowntohiderawedgesandaddstrengthtotheseam.ThisseamiscommonlyusedforFlat felled denimjeans.seamFigure 12.69 Flat felledseamFigure12.70Overlockingenclosestherawedgewithstitching.
264Chapter 12Fibres andfabrics ACTIVITYYouwill need: lFabric shears lNeedle lThreadlSewingmachinelIronlSmall squares of fabric (approx. 1010cm). Right side Place fabric right sides together. Pinalongtheedgetosecurefabric. Tackalongseamallowanceandremovepins. Place fabric wrong sides together, pin and tack seamallowance line. Remove pins. Trimseamallowanceusingfabricshears. Turnfabricrightsidestogether.Pinandtackalongseamallowance.Removepins.Sewalongtackingalongseamallowancelineusingstraightstitch.Removetacking.Sewalongtackingline. Removetacking. Sewalongtackingline,ensuringtherawedgesoftheoriginalseamarefullyenclosed.Removetacking.Pressseamopenwithaniron.Wrongside PlainseamFrenchseamPlace fabric wrong sides together, pin and tack seamallowance line. Remove pins. Sew, using straight stitch. Trimhalf of theseamallowancefromonesideof theseam. Foldthelongsideoftheseamaroundthetrimmededgetoencloseit.Pressseamflatthenpin,tackandsewtheoppositeedgeoftheseamtofinishit.Flat felledseam1 Followthe step-by-stepdiagrams tocompleteasampleofeachoftheseamsabove.2 Mount eachsampleandaddnotes toexplainthebestusesforeachone.3 Use this pageof samples tohelpyouthroughout yourGCSEcourse.
26512.4ManipulatingandjoiningFinishingseamsThe aimof finishingseams is toneatenthemandtopreventfraying. Commonmethodsforfinishingseams include: lOverlocking- t heoverlocker trims offexcessfabricalongtheseamandstitchesaroundthe rawedge, givinganeat andprofessional finish. lPinkingshears - t heseshears produceacut zig-zagshapealongtherawedgeofaseam, whichprevents fraying. lZigzag- if y oudon't haveaccess toanoverlocker, machinesewingazig-zagstitchalongthe rawedgeof aseamcanbejust as effective. Figure 12.71 Pinkingshears prevent fraying. Figure12.72SeamfinishedwithazigzagDeformingandreformingFabrics by naturewill liefairlyflat, andevenknittedandnon-wovenfabrics will bedifficult toshape. Themethodsinthissectionareusedtoaddshapeor bodytofabrics inorder toaddinterestandtoimprove fit andfunction. PleatsPleats are formedby foldingthefabricbackonitself andsewingitintoplace. Pleatingnarrows theoriginal widthof thematerial quitesignificantly, whileaddingshapeor body. Figure12.74Pleatsareoftenusedinskirts.Example pleats Figure 12.73 Pleats KEYTERMSPleat:Apleatisformedbyfoldingfabricandsewingthefoldflat.Pleatsaddshapeandbodytogarments.
266Chapter 12Fibres andfabrics GathersGathersareformedbysewingalongtheedgeofthefabricwithalongstitchlength.Tworows of stitchingareusuallyusedinthisprocess. Thethreadends,ortails,arethenpulledtocreatethegathers. Thistechniquenarrowstheoriginalwidthofthematerialandgivesfullness tothegarment. DartsDartsareusedtoshapefabrics, improvingthefit. Theyaremadebycreatingfoldsinthefabricthat taper toapoint. Thesefoldsareoftensewnintothebustorthebackofbodices.ClippingseamsWhenaseamissewnalongacurve, particularlywithwovenfabrics,itwillneedtobeclippedtoallowthefabrictolieflat. Clippinginvolvestheuseofshearsorspecialisttoolstocut intotheseamallowance. Thistechniqueiscommonlyusedaroundnecklinesandarmholestoachieveaneatfinish. ACTIVITYYouwill need: lSmall samplesof wovenfabric(approx.2020cm)lFabricshearslNeedleandthreadlSewingmachinelTailor's chalk. 1Createasampleof eachmethodofdeformingandreforming.2Mount eachsampleanddescribehowthemethodhaschangedtheshapeofthefabric.GathersFigure12.75Gathersareaneasywaytoaddbodyandshapetoaproduct.Figure12.76Dartshelpshapethefabrictofitproperly.KEYTERMSGather: Gathers arecreatedby sewingalongthe lengthof the fabric andpullingthe sewingthread, causingthe fabric togather upalongits length. Gathers areusedtoaddshapeandbody togarments. Dart: Darts are formedby foldingandsewingtriangular sections of fabric. Darts allowus toshape garments tobetter fit the body.
26712.5Structuralintegrity12.5Structural integrityLEARNINGOUTCOMESBy theendof this sectionyoushouldknowaboutandunderstand:➜howandwhy specificmaterialsneedtobereinforced➜theprocesses that canbeusedtoensurestructural integrityinfabrics.Most fabrics havenatural drape, whichis beneficial todesignersinmanyways. Sometimes, however, weneedtoaddstructuretotextileproductstoimproveaestheticsandfunction. BoningBoningis a techniquethat dates backtosixteenthcenturycorsetry, andis namedafter thewhalebones that wereoriginallysewnintogarments. Corsets wereusedfor aestheticor medical purposes. For example, women'scorsets typically cinchedthewaist andexaggeratedthebustandhips, givinga more desirablefigure- t his practicecausedmanyhealthissues, however, includingbreathingproblems. Medical corsetstreat backpainorprotectpeople withspinal or internal injuries byrestrictingtheir movement. Modern-day corsetry uses plasticor metal boningstrips, whicharesewnintoreinforcedseams tosupport thefabric, preventingcreasingandbuckling. LayeringtextilesLayeringintextiles canbeusedfor anumber of purposes, includingstructural support, insulation, comfort or toaddbody. InterfacingInterfacingis a non-woven, bondedfabricthat canbesewnorironedontotheouterfabricor lining. It comes invarious weights toprovidelight supportor tostiffenfabricstoimproveshape. It is most commonlyusedaroundnecklines, armholes, waistbands, collarsandcuffs. InterliningInterliningis a layer of fabricaddedbetweenthefabricandtheliningofagarment, mostcommonly toadda layer of insulation. Thisisoftenusedinsuitjacketsandwintercoatstoprovide additional warmth. This layer of fabriccanalsosupportthestructureofagarment. KEYTERMSInterfacing:anon-woven,bondedfabricsewnorironedontotheouterfabricorliningtoprovidelightsupportandstiffenfabrics.Interlining:alayeroffabricaddedbetweenthefabricandliningofagarmenttoaddinsulationandprovidewarmth.KEYTERMSBoning:theprocessofsewingplasticormetalboningstripsintoagarmenttoreinforceseams,supportthefabricandpreventitfromcreasingandbuckling.Figure12.78BoningissewnintotheseamsofFigure 12.77 Amoderntorsosupport, inspiredbyoriginal medical corsetsthecorsettoaddstructure.
268Chapter 12Fibres andfabrics LiningLiningisalightweight, usuallysilky, fabricusedinsideagarmenttoimprovecomfortandtohideseamsandotherconstructionmethods. Theliningcanalsobeadesignfeature- br ight or patternedliningsareoftenusedinsideplainsuitjackets.UnderliningUnderliningisalayerof fabricusedbeneathsheerfabrictoprovideopacityortoaddextrabodytoagarment. Dresseswithlaceorchiffonskirtswillhaveanunderliningtopreventtheskirtbeingsee-throughandtoaddlifttothefabrics,whichwouldotherwisefall flat. Figure 12.79Interfacingcanbeironedon(fusible) or sewnFigure12.80Interliningprovidesinsulationandstructure.into place. KEYTERMSLining: a lightweight fabric usedinside a garment toimprove comfort andtohideseams. Underlining: alayer of fabricusedunderneathsheer fabric toprovide opacity or toaddextra body toa garment. ACTIVITYLook throughyour wardrobeandfindproductsthat useeachof these types of linings thenphotographthemandprintthemtocreate arevisionsheet. Figure 12.81Liningcanhideseams, improvecomfort andbecome a designfeatureFigure12.82Underliningcanaddbodyorprovideopacitytosheerfabrics.
26912.6Makingiterativemodels12.6MakingiterativemodelsLEARNINGOUTCOMESBy theendof this sectionyoushouldknowaboutandunderstand:➜theprocesses andtechniques usedtoproducetoiles. ➜Howmaterials, components andmanufacturingmethodsaretestedandselected. Makingiterativemodels is akeypart of thedesignprocessandallowsyoutotest, manipulate andadapt your designideas. Realisingyour designsin3Dformwill improveyourunderstandingof theconstructionmethodsrequiredtomakethem, andyouwill beabletoevaluate a rangeof productiontechniques. Toile is a Frenchwordmeaningfabric, specificallyalinencanvas-stylematerial, originallyusedtomake mock-ups of garments andrefinethembeforeusingmoreexpensivefabricsforthefinishedproduct. Over theyears, theprocessof makingagarmentprototypehasadoptedthe wordandit is nowreferredtoas 'makingatoile'. ProductionoftoilesToiles are traditionally madeincottoncalicofabric, but canalsobemadefromothercheapfabrics or evenpaper. Abasictoilecanbemadeusingpatternblocksorbyfollowingasimple commercial pattern. Figure 12.83 Atoile madeincalicoFigure12.84Atoilemadeinpaper
270Chapter 12Fibres andfabrics Toiles areproducedusingthesameconstructionmethodsthatwillbeusedonthefinalproduct, rather thanjust pinningandtackingthefabrictogether.Seamsandshapingmethodsarecompletedusingalongstitchlengthonthesewingmachine,toallowforunpickingandadaptation. TestingmanufacturingmethodsWhendevelopingaproduct, themanufacturingmethodsmustbetestedtoensurethattheywill functioneffectivelyandfitwiththeaestheticofthedesign.Differenttypesofseam,shapinganddecorativemethodscanbetestedbycreatingsmallsampleswhichareputtouseinarangeof contextstoaiddecisionmaking. Examplesoftestingincludeapplyingtensiontoseamstodeterminethepointatwhichtheywillsplitandexperimentingwithmixingdyestofindthecorrectcolourpaletteforscreenprinting.TestingmaterialsandcomponentsProduct development alsoreliesontheuseofsuitablematerialsandcomponentstoachievetheright functionandaesthetic. Adesignerwill collectandtestswatchesofmaterialsandarangeof componentstodeterminetherightcombinationfortheenduse.Testsinclude;abrasionresistance, stainresistance, absorbency, strengthandinsulation.Componentsarealsotestedandcomparedfortheirsize, weight, functionandaesthetic.DesigniterationsOncecomplete, thebasictoileisfittedtoamodel ordressmaker'sdummy.Itisatthisstagethat testingandadaptationbegins. Adesignerwill drawdirectlyontothetoiletoshowintendedchangesinsize, shapeorstructure, thenuseadditionalfabricsandtechniquestodevelopthedesignof thetoile. Thesetechniquescouldincludecuttingsectionsaway,reshapingor addingsleeves, orcreatingshapebyaddingpleatsorgathers.Photographswill betakenat eachstagetoshowdevelopment, andthedesignerwilloftentrialseveraladaptationstoexplorearangeof optionsfortheirproduct. Results fromtestingof materials, componentsandconstructionmethodsareusedtoinformdesignadaptations. Opinionsarealsosoughtfromstakeholdersastheproductisdevelopedtoensurethat theproduct continuestomeettheirneeds. Followingthisiterationofdesign,thetoileor model canbedeconstructedandthepiecesusedtodraftnewpatternpiecesforthefinalproduct. 12.7FinishesLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜theprocessesusedforfinishingandaddingsurfacetreatmentstomaterialsforspecificpurposes. Duringtheproductionof fabrics, finishescanbeaddedtoimprovetheaesthetics,comfortorfunction. Thesefinishesareappliedmechanically, chemicallyorbiologically.DyeingThemost commonmethodof addingcolourtofibresandfabricsisdyeing.Manufacturerscanusenatural or syntheticdyes, dependingonthetypeoffibretobedyed.Naturaldyesworkwell onnatural fibresandcanbemadefromplants, mineralsorinsects.Syntheticdyesworkonsyntheticfibres, butcanalsogivedeeperorbrightercolourswhenusedwithnaturalfibres. Syntheticfibresrequiretheuseofchemicalstoenablethemtotakeupthedye.ACTIVITYIna groupmakeasimple calicotop, thendevelopthe designby creatingseveral iterations over thenext couple of lessons.
27112.7FinishesFigure12.85Brushingprovidesbothcomfortandwarmth.Fibres andfabrics canbedyedat various stagesintheproductionprocess: lPolymer stage- t his is whentheliquidpolymer solutioniscolouredbeforetheextrusionprocess, whichprevents thecolour fromfadingortransferringtootherfabricswhenwashed. lFibrestage- t his is whentherawfibreisdyedbeforefabricconstructiontoachieveconsistent colour. lYarnstage- y arndyeingwill not giveconsistent colour inawovenorknittedfabric, butcanbe useful for creatingstripes inwovenfabricsliketartan. lPiecedyeing- t his is whenanentirelengthof fabricisdyed. Thismethodcanproduceinconsistencies incolour. lGarment dyeing- t his is whenacompletedgarmentisdyed. Thiscanbebeneficialint-shirt production, whereidentical productscanbedyedinarangeofcoloursoncetheyhave beenmade. Mechanical finishesBrushingBrushinginvolves passingwirebrushes over thesurfaceof thefabrictoraisethefibres toproducea soft, fluffysurface. Brushingiscommonlyusedonfleeceandflannel fabrics, but theprocess canweakenthestructureof theweave. CalenderingCalenderinginvolves pressingthefabricusingheatedrollerstogiveitasmoother, more lustrous surface. This is oftenusedonupholsteryfabricstogivethemaflatsurface andsheen. KEYTERMSBrushing:passingwirebrushesoverthesurfaceofthefabrictoraisethefibres,producingasoft,fluffysurface.Calendering:pressingafabricusingheatedrollerstogiveitasmoother,morelustroussurface.FabricCalenderingrollersFigure12.86Calenderinginvolvespassingthefabricthroughheatedrollers.
272Chapter 12Fibres andfabrics ChemicalfinishesMercerisingMercerisingusescausticsodatocausethefibresinthefabrictoswellup.Theresultisamorelustrous, stronger fabric, butitonlyworksforcellulosefibres.Itimprovestheuptakeofdye, givingadeeper andmoreevencolour. Crease-resistanceCrease-resistantfinishesareappliedintheformofaresincoating.Thisresinreducesabsorbencyandstiffensthefibressothefabriciseasiertocarefor,reducingtheneedforironing. Treatedfabricswill alsodrymorequickly. Flame-resistanceFlame-resistantfinishessuchasProban®areappliedtothesurfaceoffabricsasaliquidcoating; whendrythisisdurableandlong-lasting. Thesetypesoffinishesareappliedtoproductsinhigh-riskareassuchassoftfurnishingsinhotels, andinpublicareassuchasstagecurtainsintheatres. Theyarealsowidelyusedinchildren'ssleepwear,beddingandotherhomefurnishings. BleachingBleachingisthemost commonchemical finish. Itremovesanynaturalcolourandpreparesfabricwell for dyeingandprinting. Theresultofthisfinishisaneven,consistentcolour.BiologicalfinishesStonewashingStonewashingismostcommonlyusedintheproductionofdenimjeans, givingapopulardistressedlook.Manufacturersachievethiseffectbyaddingstonestoindustrialwashingmachines,alongwiththejeans.Theresultisafaded,'wornout'pairofjeans.SmartfinishesThereareanumberofsmartfinishesusedontextiles.Thesearefinishesthatcandetectandreacttochanges(forexampleheat,lightorfriction)intheirenvironment.ThermochromicThermochromicinkschangecolourwithchangesintemperature.Theseinkscanbeprintedontothesurfaceoffabricsandhaveseveralusefulapplications,includingtheuseofthermochromicimageryonbabygrows.Thiscanalertparentstoanychangesinbodytemperaturebysight,allowingaquickerresponseshouldthebabyhaveafever. Thistechnologyhasalsobeenusedoncutleryanddrinksbottles,toindicateifthefoodordrinkistoohot.KEYTERMSMercerising: theprocess of usingcaustic soda tocausecellulose fibres inafabric toswell up, givinga more lustrous, stronger fabric. Bleaching: the process of usingchemicals tomakefabrics muchlighter or white. Stonewashing: theprocess of usinglargestones togive anewly manufacturedclothawornappearance. Thermochromic: products that changecolour withchanges intemperature. Figure12.87Stonewashinggivesafadedeffectonfabrics likedenim.
27312.7FinishesPhotochromicPhotochromic inks changecolour withchangesinnatural light. Theseinksareprintedontothe surfaceof fabrics andcomeinarangeof bright colours. Photochromictechnologyiscommonly usedonchildren's summer clothingtoalert parentstomovetheirchildtoshade, or onhotel sunbeds toalert guests tothemost dangeroustimeof thedayforsunexposure. MicroencapsulationMicroencapsulationuses tinybubbles or capsulesthat containchemicals, andtheseareaddedtotheweaveor fibreof fabric. Thebubblesburst withfriction, releasingthechemicalinside. Therearemany useful applicationsfor thistechnology, andplentyarealreadyinuseineveryday products. Examples of applicationsof thistechnologyincludemosquito-repellenthikinggear, perfumedfabric, moisturisingfabric, hypoallergenicfabricandantibacterialfabric (Microban®). SurfacedecorationThere are a number of surfacedecorationtechniquesthat canbeusedtoimprovetheaesthetics of a product, byaddingcolour, textureandpattern. lAppliquélEmbellishment lEmbroidery lPatchwork lQuiltinglLaser etching. Figure12.88Tinycapsulesofodour-controllingchemicalscanbeaddedtoeverydayproducts,suchasshoes.KEYTERMSMicroencapsulation:theprocessofaddingtinybubblesorcapsulesthatcontainchemicalstotheweaveorfibreoffabric.Theseburstwithfriction,releasingthechemicalinside.Photochromic:productsthatchangecolourwithchangesinnaturallight.ACTIVITYSuggest a suitable product for eachdecorativemethod. Applique Embellishment Embroidery Patchwork Quilting Laser Etching Applique
274Chapter 12Fibres andfabrics 12.8UsingdigitaldesigntoolsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜theuseof 2Dand3Ddigital technologyandtoolstopresent,model,designandmanufacturesolutions. Advancesintechnologymeanthatmanytraditionaldesignandmanufacturingmethodsfortextiles cannowbecarriedoutusingspecialistsoftwareandautomatedmachinery.RapidprototypingTheuseof rapidprototypingintextilesisstill intheearlystagesofdevelopment.Thisprocessuses laser cuttingtopreciselyshapeindividual fabriclayers, whicharethenbondedtogethertocreate3Dforms. Thedevelopmentofthiskindoftechnologycouldsee3D-printedclothinginthefuture. DigitalmanufactureDigital fabricprintingDigital fabricprintingusesalarge-scaleinkjetprinterandspecialistdyestotransferadigitalimagetothesurfaceof thefabric. Thistypeofprintingallowsdesignerstouseintricateanddetailedimages. SublimationprintingSublimationprintingusesheatandpressuretotransferdyefromspecialistprinterpaperontothefabric. Thisisaparticularlyeffectivemethodonfabric, astheprocessturnsthedyeintoagasthat bindsdirectlytothefibres, leavingacrispdesignthatiswashable.Figure 12.89Digital fabric printers can quickly print imagery on a wholeroll of fabric.
27512.8UsingdigitaldesigntoolsLaser cuttingLaser cuttingis controlledbyacomputer programinwhichthedesignisdrawnupasa2Dimage. The laser strengthandspeedis set dependingonthematerial tobecut. Oncethefabric is placedintothecutter, thelaser followsthedigital designtoquicklyandaccuratelycut the design. Laser cutters canalsobeset uptoetchthesurfaceof afabric, ratherthancutall the way through. InterpretationofplansDigital layplanningSoftware is availabletoassist patterncutterswiththecreationof digital layplans. Theseplans showthemanufacturer wheretoplaceeachpatternpieceonthefabricsothattheyfollowthe grainlineandminimisewastage. Digital layplanningsoftwarecanadapttodifferent garment sizes andfabricwidths. Thefinalisedplansareusuallyprintedonlargesheets of patternpaper. Computer-aideddesignThere are a number of applications that canbeusedfor imagecreationandmanipulationwhendesigningtextileproducts. ExamplesincludeAdobeIllustrator, CorelDrawandDigitalFashionPro. Hand-drawnsketches canbetransferredonscreen, wherethedimensions, shape andformcanberefinedandperfected. Varioussoftwareprogramshavebeendevelopedtogivedesigners a3Dviewof their original 2Dsketch, allowingthemtoevaluatethe success of a designbeforeprototyping. Manyof theseprogramscanbelinkedtocompany stock data, allowingdesigners tochoosefabricsthatareimmediatelyavailabletothem. Development of surfacedesigns for printingcanalsobecompletedonsimilarsoftware andtransferredtorelevant CAMsystems(seebelow). Computer-aidedmanufacturingSemi- or fully automatedmachineryis usedwidelyinthemanufactureoftextiles-thisisknownas CAM. Thesesystems areexpensive, but theyspeedupmanufacturing, improveconsistency andreducetheriskof humanerror. Figure 12.91 Computerisedembroiderymachinescompleteseveral designsatonceKEYTERMSLayplans:Usedbypatterncutterslikeamaptoguidethemwhenplacingpatternpiecesinthecorrectlocationanddirectionbeforecutting.Layplansarecarefullydesignedtominimisewastage.Prototyping:Aprocessthatinvolvestheproductionofatestmodel,onwhichthefinalproductisbased.Figure12.90Lasercutterscanbeusedtocutoutintricatedesignsinfabric.ACTIVITYStudyyourschooluniform.Makealistoftheconstructionmethodsused,thensuggestthemachinerytypesthatmighthavebeenusedinmanufacturing.
276Chapter 12Fibres andfabrics 12.9ManufacturingmethodsandscalesofproductionLEARNINGOUTCOMESBytheendofthissectionyoushouldknowaboutandunderstand:➜themethodsusedformanufacturingatdifferentscalesofproduction➜themanufacturingprocessesusedforlargerscalesofproduction➜themethodsofensuringaccuracyandefficiencywhenmanufacturingatlargerscales. Manufacturingmethodsvarydependingontheproductionrun(thenumberofitemsbeingproduced), timescaleandbudget. Thescaleofproductionaffectsthequalityandcost of textileproducts. ScalesofproductionOne-off,bespokeproductionOne-off, or bespoke, productsaremadebyhighlyskilledworkers-oftenanindividual or asmall team. Productsmadeinthiswaytakealongtimetoproduce,asmost of theworkisdonebyhand. Theconsumerusuallyhasopportunitiestoattendfittingsandmakedesigndecisionsduringthemanufacturingprocess.Thistypeofproduct isoftenveryhighquality, andthereforeexpensivetopurchase.BatchproductionBatch-producedproductsaremadebylargeteamsofworkers,workingatvariousstagesaroundthefactory. Thistypeofproductionutilisesamixofsemi-automatedmachineryandhandassembly. Workersarespecialisedinoneelementoftheconstructionprocess, suchascollarsorhems. Eachemployeeworksthroughabatchof partial products, whicharethenpassedaroundtheproductionlineuntiltheyarecomplete. Batch-producedproductsareusuallyofmid-tolowquality.Seasonalclothing, suchassummerdressesandwintercoats, isproducedusingbatch-productionmethods. MassproductionMassproductionisthelargestscaleofproductionavailable.Thismethodisusedfor productsthat areinconsistentlyhighdemand, suchassocksandplaint-shirts.Itisbecauseof thisdemandthatmanyfactoriesrun24hoursperday,inordertomaximiseoutput andprofit. CAMisusedwidelyinmassproduction,asconsistencyandspeedaresoimportant. Qualityiscontrolledviacomputer, soinstancesoffaultyproductsarelowandproductsareconsistent. KEYTERMSBespokeproduction: Manufacture of 'oneoff' products that aredesignedandmade for a specific client by anindividual or small teamof highly skilledworkers. Bespokeproducts are highquality, canbecomplex andareexpensivetomake. Examples of bespokeproducts includeweddingdresses, tailoredsuits andcustomfit car seat covers. Batchproduction: Batchproducedproducts aremanufacturedby alargeteamof workers whoeachcomplete aspecific stage of the production. These products areusually consistent inquality, availableina range of styles andsizes andfall intothemidtolowprice range. Typical products include summer dresses, fashiont-shirts andbrandedschool bags. Mass production: Mass producedproducts aremanufacturedmostly onautomatedmachinery, operatedby teams of workers. Products aremanufacturedvery quickly, are consistent inquality andthe range of availablestyles is minimal. Mass productioncosts are muchlower thanother productionmethods. Examples of mass producedproducts includeplainsocks, plaint-shirts andplainbaseball caps. Figure 12.92Weddingdresses areoften bespoke. Figure12.93Wintercoatsaremanufacturedonbatchproductionlines.Figure12.94Everydayitemslikeplaint-shirtsaremass-produced.
27712.9ManufacturingmethodsandscalesofproductionLeanmanufacturingandjust-in-timemethodsThese methods of productionareusedtominimisewasteandincreasetheoverall efficiencyof a manufacturingsystem. Customer ordersOnlythenumberofmaterialsandcompo-nentsneededforthejobareorderedManufacturertakesdeliveryofmaterialsandcompo-nentsthatgostraightontotheproductionline-nostorageisrequiredMaterialsandcomponentsareprocessedonabatchproductionlineFinishedproductsareshippedouttothecustomer assoonastheyarecompletex30MaterialsandcomponentsFinishedproduct Garmentfactory•Respondsquicklytocustomerorders•Littlestoragerequired•Littlewastecreated•Computerisedorderingsystemsmaketheprocessefficient•StaffarehighlyskilledJust intime Figure 12.95 The stages of lean/JITmanufacturing
278Chapter 12Fibres andfabrics ManufacturingprocessesusedforlargerscalesofproductionBandsawcuttingFor patterncuttingonalargescale, highlyskilledworkersareemployedtousehandheldbandsaws, cuttingthroughupto100layersoffabricaccuratelyandquickly.Theyusecardtemplatestomarkout thepatternpieceswithchalk, followingadigitallayplantoreducewaste. Cuttingisquickandefficient, andworkerswearchainmailglovestoprotecttheirhands fromthesharpblades. FlatbedprintingFlatbedscreenprintingiscarriedoutonaconveyorproductionline.Silkscreensaswideas thefabricwidtharemadeupandattachedtotheprintingmachineinarow.Upto16screenscanbeplacedonasingleprintingrun. Eachscreenappliesadifferentcolouranddesigntothefabric. Aconveyorbeltmovesthewhitefabricunderneaththescreensat regular intervals. Whenthebeltstopsthescreensdropdownontothefabricandanautomatedsqueegeedragsprintingmediumacrossthescreen.Thescreensthenliftupandthefabricmoveson. At theendof theprintingrun, thefabrichasacompletedesignonitssurface. Thefabricwill goontobefixed, washedandpressed.KEYTERMSLeanmanufacturing: Amanufacturingmethoddesignedtominimise wasteat eachstage of production. Just intimemanufacturing: Amanufacturingmethodthat canquickly respondtochanges intrends by orderingmaterials andcomponent toarriveat the factory 'just intime' for production. This methodminimises storage space, wastedmaterials andleft over stock, whilst increasingefficiency. RotaryscreenprintingSimilar toflatbedscreenprinting, rotaryscreenprintingiscarriedoutonaconveyor-drivenproductionline. Theseproductionlinesaremuchfaster, however,andrequirelessspaceonthefactoryfloor. Thisisbecausethisprintingprocessusesprintingcylindersinsteadofflatscreens. Thefabricdesigniscreatedonmetal sheets, whicharethenformedintoacylinder.Thesearemountedontotheprintingmachine, wherethecylinderisfilledwithprintingmediumandastaticsqueegeeisplacedinside. Thecylindersspinasthefabricpassesunderneath, printingacontinuouspatternontothesurface. Eachcylinderappliesasinglecolour anddesign. Thecontinuousmotionofthisprocessmeansprintingismuchfasterandmoreefficient thanflatbedprinting. Rotaryprintingisanexpensiveoption,however,duetothecreationof thecylinders. Conveyor belt Plain fabric Squeegeeapplies first colour Conveyor moves Conveyor movesSqueegeeappliessecondcolour SqueegeeappliesthirdcolourScreenliftsaftereachprintFigure 12.96The flatbedprintingprocess
27912.9ManufacturingmethodsandscalesofproductionPlain fabric ConveyorCylindrical screens rotatealongsurfaceof fabricEachscreencontainsonecolourSqueegeeensures evenflowof printinginkFigure 12.97 The rotary screenprintingprocessFigure 12.98 Screenprintedfabrics areverycommonandoftenhavearepeatpattern.Industrial sewingmachinesandoverlockersIndustrial sewingmachines andoverlockersareheavy-dutymachines, specifically designedtowithstandconstant use. These machines havelargemotors that runmuchfaster thandomestic machines. Theycanalsotakelargespoolsof strongthreadtominimisesnappingandtimelost re- threadingmachines. Thesemachines areabletosewwithease throughheavy or toughmaterials suchasleather anddenim. AutomatedpressesThese presses areusedtoquicklyremovecreasesandtofinishcompletedgarments beforepackaging. Workersplace garments betweenthepressingplatesanduseafoot control tostart theprocess. Thepressingplatescometogether, applyingpressure, steamandheat tothegarment. This process takes only afewseconds per garment, makingit muchfaster andmoreefficient thantraditional ironing. Figure12.99Aworkeroperatesanindustrialsewingmachine
280Chapter 12Fibres andfabrics SteamdolliesSteamdolliesareusedtopressgarmentsthatareunsuitablefortheautomatedpressesbecauseof their shape. Asteamdollylooksjustlikeamannequin.Thefinishedgarmentsareplacedontothedolly, whichreleasesjetsofsteam. Thesteamfillsthegarmentlikeaballoon, andthisactionremovescreasesalmostimmediately.Thisprocessalsohelpsmaintaintheshapeof thegarment. EnsuringaccuracyandefficiencyInorder tomaintainaccuracyandefficiencyinthemanufactureofanewproduct,amanufacturingspecificationisused. Thisisparticularlyusefulinglobalmanufacturing,whenthedesignerandthemanufacturerarebasedindifferentcountries.Themanufacturingspecificationwillincludeadetailedexplanationofthematerials,components,patternpiecesandconstructionmethodsrequiredtomaketheproduct.Thisisfollowedcloselybymanufacturerstoensureconsistencyinthefinishedproducts.Failuretofollowthemanufacturingspecificationcanresultinpoorqualityproducts,wastedmaterialsanditemsreturnedtoretailers.Figure 12.102Exampleof amanufacturingspecificationFigure 12.100Presses likethis removecreasesquicklyFigure12.101Steamdolliesareshapedtoallowthemtobe'dressed' inthegarmenttobesteamed
28112.9ManufacturingmethodsandscalesofproductionQualitycontrol checksInall areas of manufacture, qualitycontrol checksarecarriedoutatcritical control pointstoensure consistency inthefinishedproduct. Thesechecksareinplacetoidentifyfaultsinthe followingareas: lMaterials - workers checkfor faults intheconstructionof oronthesurfaceofthefabric. These canincludesnags, misprinteddesigns, holesor stains. lComponents - workers checkcomponentsfor faults, suchasincorrectsize/shape, crackedbuttons or damagedzips. lSeams - s eams arecheckedtoensuretheyarewithintolerance(toleranceisexplainedinthe sectionbelow), that sewnlines arestraight andthattherearenoholesalongthelengthof theseam. lPlacement andconstruction- oncematerialsandcomponentsarejoined, workerscheckfor faults suchas incorrect placement of logosor pockets, orincorrectsettingofsleeves. NACERAPManufacturers followvarious systems toidentifyandaddressanyfaultsinproduction. Anexample of a quality control systemis NACERAP. Table 12.9 The stages of theNACERAPsystemExample: Shirt N(Name of fault) Misaligned buttonholeA(Appearance) Buttons do not matchupwithbuttonholes C (Cause) Error in measurement for buttonspacingonmanufacturingspecificationE (Effect) Hemof shirt does not meet whenbuttonedupR (Repair) Unpick buttons andre-sewusingnewmeasurementsA(Action) Make changes tobuttonspacingmeasurement onmanufacturingspecificationP (Prevent) Check all measurements onmanufacturingspecificationfor furthererrorsKEYTERMSQualitycontrol:Sampleproductsaretakenofftheproductionlineatcriticalcontrolpointstocheckforfaultsortotestperformance.QualityassuranceManufacturers carry out qualitycontrol checksconsistentlyinordertoprovidequalityassurancetotheir customers. This meansthat thecustomer expectsandreceivesagoodlevel of quality fromaparticular manufacturer. Withgoodqualityproductscomesagoodreputationfor themanufacturer, leadingtoboostedsales. TolerancesandminimisingwasteTolerancesThe processes usedinsewingtextileproductsmakesit veryhardtoachieveaccuracy. Forthis reason, tolerances areallowed. This meansthat anyseamcouldbe+/-1cm. Tolerancesaffect the finishedsizingof aproduct, thereforeit isbetter touseonly+1cmtolerances-this means that thefinishedproduct will never betoosmall. Seamallowancesareaddedtopatternpieces toallowenoughfabricaroundtheedgeof thesewinglineforerrors. Ifanyseamis out of tolerance, thefinishedproduct mayberejectedduringqualitycontrolchecks. MinimisingwastageWastage is createdduringpatterncutting, whensmall amountsof fabricareleftaroundeachpatternpiece. Thesizeandshapeof thesepiecesmeanstheyaredifficulttouseforotherapplications. Minimisingthis wasteis theresponsibilityof layplannersandpatterncutters, whoensureall patternpieces areplacedcorrectlyonthefabric, leavingminimal spacebetweenthemtoreducetheseoff-cuts. Thisprocessensuresthemosteconomical useoffabric rolls, particularly inbatchandmass production. KEYTERMSQualityassurance:Consistentqualitytestingateachstageofproductionmeansthatmanufacturerscanmaintaintherequiredlevelofqualityintheirproducts.
282Chapter 12Fibres andfabrics 12.10CostandavailabilityLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜howthecostandavailabilityofspecificfabricsandcomponentscanaffectdecisionswhendesigning.This sectionwill helpyoutounderstandhowtocostupmaterialsandcomponentsforyourfinal product, andhowthisprocessdiffersonanindustrialscale.ThesignificanceofcostThecost of materialsandcomponentscanaffectyourfinaldesignchoices.Insomeinstancesit might evenbeappropriatetoscaledownorsimplifyadesignduetocostconstraints.Youmust consider stakeholdersinthesedesigndecisions, toensurethatthefinalcostoftheproduct iswithinbudgetinordertomakeaprofit. Calculatingquantities,costsandsizesofmaterialsWhencalculatingtheamountof fabricrequiredforaprototype,thelayplan,patternmarkingsanddimensionsof thepatternpiecesareallrequired.Theexamplebelowshowsalayplanwiththedimensionsadded. All thepiecesinthelayplanhavebeenplacedLargeareasofunusedfabric.Not all patternpiecesfit.Grainlinehasnotbeenfollowedonallpieces.Foldmarkinghasbeenignored.FoldFoldFront FrontBack Sleeve SleeveSelvedge SelvedgeAll grain lines are followedcorrectly. Minimal wastage betweenpatternpieces. Leftover fabric is a useable size andshape. Fold marking has beenfollowedcorrectly. BackFigure 12.103Patternpieces must beplacedcorrectlyinordertominimisewastageACTIVITYDesigningfor different scales of productioninvolvestheadaptationofdesignstomakethemsuitableforproductionmethods. Aproduct designedfor bespokeproductionmayincludecomplexconstructionandfinishingmethodsthataren't suitable for batchor mass production. For thisreason, designsmaybesimplifiedtomakeproductionmoretimeandcost effective. 1. Designa textileproduct intendedfor bespokeproductioninspiredbyoneofthefollowingheadings.CelebrationFutureLearningNatureAnnotate your designtoshowarangeof appropriateproductionmethods.2. Re-designyour product tosuit abatchproductionsetting, givingreasonsforthechangesmadetoyourdesign.
28312.10CostandavailabilityFigure12.104Examplelayplanaccordingtograinlines andfoldmarkings. Youneedtoleaveapproximately 1cmbetweenpatternpiecestoallowspacetoaddbalancemarks, andtheseareshowninthediagram. The fabric will usually befoldedinhalf alongthestraight grainby placingtheselvedges together. Thiswill givetwoof eachpatternpieceoncethefabricis cut. Whereapatternpiece is placedonthefold, alarger symmetrical piecewill beproduced. Occasionally, acommercial patternwill requirethefabric tobe unfolded, or foldedindifferent ways. Inthiscase, check the fabric amounts onthebackof thepacket beforepurchasing. Tocalculate theamount of fabricneededfor abasicpattern: lMeasuretheheight of thelayplan(alongthecrossgrain) andmultiply this by 2. This number will indicatetheminimumfabric widthrequired. Example: Height 64cm2=128cm. For thisyouwouldneedtobuy fabric froma150cmroll. lMeasurethewidthof thelayplan(alongthestraight grain); this tells youhowmanymetres of fabricyouneedtobuy. Example: Widthof layplan=223cm. For thisyouwouldneedtobuy 2.5metres of fabric(roundinguptothenearest half metre). Inbatchandmass production, fabricandcomponentsareorderedinbulk fromwholesalers. Thepricedropsasthenumber of units purchasedincreases. Thetablebelowgivesanexample of thesepricedifferences. STRETCHANDCHALLENGEOnce youknowhowmany metres youneed, youcancalculatethe cost of this, alongwithany other fabrics andcomponents. Visit a website that sells arangeof componentsandfabricsbythe metre. Usinga commercial pattern, or your ownlayplan, calculate the total cost of fabric andcomponentsneededfor one product. KEYPOINTSlRemember that fabric is soldonrolls of 115cmor 150cmwidth. lRemember that youcanbuy fabricin0.5mlengths. Table 12.10 Price differences as thenumber of unitsincreasesUnits Fabric, per metre (£) Buttons, 12pack(£) Interfacing, per metre(£) Thread, singlereel (£) Ribbon, permetre(£)Zips,each(£)1 6.15 2.50 3.552.901.201.7550 4.40 1.75 2.802.101.050.90100 3.25 1.05 2.051.150.750.45500 1.70 0.50 0.650.750.250.155433216787FoldSelvedge
284Chapter 13DesignengineeringCHAPTER13DesignengineeringYoushouldreadChapter6beforeembarkingonthematerialinthischapter.Chapter 6introducedsomebasicmechanical andelectronicsystemsthatarefrequentlyfoundinengineeredproducts. If youwishtospecialiseindesignengineeringyouwillfindthefollowingchapter useful indevelopingyourknowledgeandunderstandingofsuchsystemstothepointwhereyouwill beabletoselectanduseappropriatesystemcomponentsandprogrammabledevices, andtowriteappropriateprogramstobenefityour owndesigns. Theabilitytodevelopmechanicalandelectronicmodelsandsolutionsduringtheiterativedesignprocessgivesyouanincrediblypowerfulapproachtocreatinginnovativeandinteractiveoutcomesinresponsetothenon-examinedassessmentContextual Challenges. Itwill alsobeuseful tothosewishingtofocusonthein-depthaspects of designengineeringwithinthewrittenexam. It is surprisinglystraightforwardtointegratequiteadvancedtechnologyintoyourGCSEprojects. Aswithall newtechnology, ittakesalittletimeandefforttolearnthejargonassociatedwithmechanismsandelectronics, andyouwillneedtobepatientandlogicalwhentryingtoworkout whyyour designsdonotinitiallyworkasyouintend.Onceyouhavegotovertheinitial hurdles, however, youwill quicklyappreciatetheadvantagesofusingmechanicalandelectroniccomponentswithinyourdesigns. Thetrickistokeepyourearlyattemptsassimpleas possibleandtoget eachstageworkingbeforeyouprogressontothenextstage.This chapter containssomenecessarymathematics. Thebeautyofusingmathswhendesigningisthat youcanobtainobjectiveandpreciseanswerstomanydesignquestions,whichremovestheelementof guessworkbytellingyouexactlyhowbigsomethingneedstobe, howfast it will move, orwhatvoltageisrequiredtooperateit,forexample.13.1WorkingwithmechanicalcomponentsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜theeffect of forcesoneaseofmovement➜howmechanical devicesareusedtochangethemagnitudeanddirectionofforces➜theworkingpropertiesofmechanical components➜themathematical treatmentofmechanicalsystems.Chapter 6introducedsomebasicmechanical systemswithoutgoingintomuchmathematics. Thefollowingsectionslookagainatthesesystems,andsomeadditionalsystems, anddeal withtheassociatedmaths. MechanicaladvantageYouwill recall that amechanismcancontrol andchangemotion,andthatithasaninputandanoutput. Youshouldalsobefamiliarwiththeideathatamechanismcanamplifytheinputforceor it canmaketheoutputmovebyagreaterdistancethantheinput,butitcannotdoboththesethingsat thesametime. Thereisalwaysatrade-off.Mechanismscaneither:lreducethedistancemovedbutincreasetheforcebeingexerted,orlincreasethedistancemovedbutreducetheforcebeingexerted.
28513.1WorkingwithmechanicalcomponentsOnsome levers, youmust lookcarefullytoidentifytheinputandoutputarmlengths. Thearmlengthis thedistancebetweentheforceandthefulcrum, anditisalwaysmeasuredatrightangles (90°) totheforce. Lookat thebrakelever showntoseewhatthismeansinpractice. BigloadFulcrumSmall effort Small output armlength Big input armlength Loadmovesthroughsmall distanceEffortmovesthroughbigdistanceFigure 13.1 Afirst class lever Keyde =Inputarmlengthdl =OutputarmlengthLoad Fulcrumde dl Effort Figure 13.2 Look carefully toidentifytheinput andoutputarmlengthsonthisfirstclassleverKEYPOINTMathematically, this trade-off canbewrittendownasfollows: (input force×distancemovedbyinput)=(outputforce ×distancemovedbyoutput)The ratioof the output forcetotheinput forceiscalledthe mechanical advantage(MA) of themechanism: MA=output forceinput forceThe mechanical advantageof amechanismdescribestheamount by whichit amplifies theinput force. KEYPOINTForasimplelever,mechanicaladvantagewouldbewrittenas:MA=loadeffortTheeffortandloadforcesareinverselyproportionaltothelengthsoftheinputarmandoutputarmofthelever,whichmeansthatthemechanicaladvantageofaleverisalsothesameas:MA=inputarmlengthoutputarmlength
286Chapter 13DesignengineeringClassofleverDependingonwherethefulcrumispositionedrelativetotheeffortandload,alevercanamplifyforceor canamplifydistancemoved, butitcannotdobothatthesametime-remember, theremust beatrade-off. Thepositionofthefulcrumcanalsoresultineffortandloadmovinginthesamedirection, orinoppositedirections. Therearethreevariations,or'classes', of lever: lInafirst classlever thefulcrumisbetweentheloadandtheeffort.Examplesincludescissors, andaclawhammerextractinganail. HammerScissorsFulcrumLoadEffort EffortFulcrumLoadKEYPOINTApair of scissors is shownbelow. Usetheinformationinthediagramtocalculate the loadforcegeneratedwhenaneffort of 75Nisapplied. Effort 30mmLoad 30mmFigure 13.3Calculatetheloadforcegeneratedwhenaneffortof75NisappliedMA=inputarmlengthoutputarmlengthMA=8030=2.67MA=loadeffortSoaneffortof75Nwouldbeamplifiedtobecomealoadof:load=MA×effort=2.67×75=200N(roundedto3significantfigures)
288Chapter 13DesignengineeringRotationalmechanicalsystemsRotatingmechanical systemsareverycommon. Mostenginesandelectricmotorsproducearotatingoutput, whichusuallyneedstobealteredinspeedordirectionortobetransferredtoadifferent place. Rotational forceor turningeffectiscalledtorque. Rotarymechanical systemsstill obeythemachinetrade-offprinciple,butitiswrittenslightlydifferently. Rotarymechanical systemscaneither: lreducerotaryspeedbutincreasetorque, orlincreaserotaryspeedbutreducetorque. KEYPOINTMathematically, thistrade-offcanbewrittenasfollows:(input torque×inputrotationalspeed)=(outputtorque×outputrotationalspeed)Inarotational mechanical system, mechanical advantageisdefinedas:MA=output torqueinput torqueIf youlookat thetrade-offequation, youmightbeabletospotthatMAisalsoequalto:MA=input rotational speedoutput rotational speedSimplegeartrainThediagramshowsasimplegeartrainconsistingofadrivergearwithN1teethandadrivengear withN2teeth. 16teeth(N1) 40teeth(N2) Figure13.4Asimplegeartrain
28913.1WorkingwithmechanicalcomponentsKEYPOINTThe gear ratiois definedas: gear ratio=number of teethondrivengearnumber of teethondrivergearYou will recall that thelarger gear rotates moreslowlythanthesmallergear.Thenumberofteeth aroundthe circumferenceof thegear is inverselyproportional totherotational speedof the gear, whichmeans that thegear ratioof asimplegeartrainisalsothesameas:gear ratio=driver gear rotational speeddrivengear rotational speedThe gear ratioof a simplegear traindescribes theamount bywhichitreducestheinputrotational speed. If you refer tothe mechanical advantageequation, youwill seethatthegearratioofasimple gear trainis thesameas its mechanical advantage, whichisthesameastheamountby whichthe torqueis increased: gear ratio=input rotational speedoutput rotational speed=MA=outputtorqueinputtorqueInthe diagramshown, thegear ratiois: gear ratio=number of teethondrivengearnumber of teethondrivergear=4016=2.5Notice that, althoughthis is calledagear 'ratio', theresult isoftenwrittensimplyasanumber. Writing2.5 1wouldbejust as acceptable. Without worryingtoomuchabout equations, nowthat weknowthatthegearratiois2.5weknowthat themechanical advantageof thesystemisalso2.5, sotheoutputtorquewillbe2.5 times bigger thantheinput torqueand, bythetrade-off principle, thattheoutputspeedmust be 2.5times less thantheinput speed. If the input speedis 1200rpm, then: speedof output=12002.5=480rpmSTRETCHANDCHALLENGEAwindturbine rotates at 90rpm. Theturbinedrivesa40-toothgearthatmesheswitha12-toothdrivengear. i Calculate the rotational speedof theoutput shaft. gear ratio=number of teethondrivennumber of teethondriver=1240=0.3The smaller (output) gear will rotatefaster thanthelarger gearataspeedof:output speed=input speedgear ratio=900.3=300rpmii Describe the torqueavailableat theoutput shaft. There is a trade-off betweentorqueandspeed. Astheoutputspeedishigherthantheinput speed, theoutput torquewill beless thantheinputtorquebythesamefactor:output torque=0.3×input torque(Notice that the torquemultiplicationfactor is thesameasthemechanical advantage,which is equal tothegear ratio.)
290Chapter 13DesignengineeringIdlergearAnidlergearisagear thatisinsertedbetweentwootherspurgears,asshowninthediagram. Theidlergearhasnoeffectontheoverall gearratio, butitwillreversethedirectionofrotationof theoutput shaft. Thiscanbeuseful ifitisnecessaryfortheinputandoutputshafts torotateinthesamedirection. Thesizeoftheidlergeardoesnotmatterasithasnoeffect onthegear ratioof thesimplegeartrain. Another reasonfor usinganidlergearistoincreasetheseparationoftheinputandoutputdriveshafts. Inthesecircumstances, several idlergearsmaybeused,eachofwhichwillhavetheeffect of reversingthedirectionofrotation. Nomatterhowmanyidlergearsareused,thegear ratioof thesystemwill still dependonlyonthenumberofteethonthefirst(driver)gear andthefinal (driven) gear. Figure 13.5 Anidler gear betweentwospur gearsFigure13.6AsimplegeartrainwithseveralidlergearsFigure 13.7 Bevel gears OthergearsystemsSpurgearsarethemostcommonlyusedgears,butothertypesofgearsareusedforspecialapplications.lBevelgearshavetheirteethcutona45°angleandtheyareusedwhenitisnecessarytotransferthedirectionofthedriveshaftby90°.KEYTERMSIdler gear: Agear that is insertedbetweentwospur gears tochangetheoutput direction. Bevel gear: Agear withteethcut at a45° angle tochangethedirectionof thedriveshaft by 90°.
29113.1WorkingwithmechanicalcomponentslAwormdriveis auniquetypeof gear system. Thedriver is a screwthreadcalledawormscrew, whichmeshes witha wormwheel (whichislikeaspur gear). Therearethreeimportant thingstonoteabout wormdrives: - They achieveaveryhighgear ratio, sotheycanreducerotational speedbyalargefactor or increasetorqueby thesameamount. Thegear ratioissimplythe number of teethonthewormwheel. - They transfer thedirectionof rotationby90°. - They areself-locking, whichmeansthat theinput shaft (theworm) candrivetheoutput, but theoutput cannot drivetheinput. Thisfeaturecanbeuseful insomeapplications, for examplewhenit isimportant that theoutput does not slipif theinputdriveis turnedoff, suchas inawinchor alift. lArackandpinionis asystemtochangebetweenrotary andlinear motion. Inthestairlift shown, therackis stationary andis attachedtothewall. Thepinioninside thechairlift is drivenbyamotor andthepinion'climbs' uptherack. Figure13.8Theself-lockingactionisimportantinthesewormdrives. Figure 13.9 Diagramof arackandpinionFigure13.10AstairliftusesarackandpinionPulleyandbeltdriveApulley andbelt drivecanprovidespeedreductionor increase, andthe'gear' ratiois calculatedinasimilar waytoa simple gear train. KEYPOINTFor a pulley andbelt system: gear ratio=diameter of drivenpulleydiameter of driverpulleyJust as witha simplegear train, thegear ratioisthesame as the ratioof input tooutput speeds, andisalsoequivalent tothe mechanical advantageof thesystem. KEYTERMSRackandpinion:Asystemtochangebetweenrotaryandlinearmotion.Wormdrive:Aself-lockingmechanism,achievingaveryhighreductionratio.Wormscrew:Thedriverpartinawormdrive.Wormwheel:Thedrivengearinawormdrive.
292Chapter 13DesignengineeringBelt Driver pulleyDrivenpulleyFigure13.11TransferringrotarymotionwithpulleysandabeltSTRETCHANDCHALLENGEThepulleyandbelt driveshowninthediagramisbeingusedtoreducethespeedofadriveshaft. Theinput pulleyis60mmindiameteranda3:1reductionisrequired.Calculatetherequireddiameter of theoutputpulley. Gearratio=diameterofdriven(output)pulleydiameterofdriver(input)pulley3=diameterofoutputpulley60Diameterof outputpulley=3×60=180mmThemost commontypeof pulleyandbeltdriveusesaV-shapedbelt,whichgripsthepulleysidewallstoprovidealargecontactarea. Thisprovideslotsofgripandmeansthereisless likelihoodof thebeltslippingonthepulley. Inafewapplications,beltsaredeliberatelyleft quiteslacksothat theycanslipif theoutputshaftgetsjammed,whichcanservetoprevent damagetomechanical systemsorthedrivemotor. Thistechniqueisnotgenerallyadvisable, however, becauseunlessthedriveisquicklyturnedoff,theslippingbeltwillrapidlyheat upduetofrictionandwill wearorevencatchfire.Apulleyandbeltdrivewillbeveryquietinoperationcomparedtogears, whichtendto'whine'orrumble.Whenusingbelts, provisionmustbemadetokeepthetensioncorrectasthebeltwillstretchwithuse.Ifitistooslackthereisariskofthebeltslipping,whileifitistootighttherewill befartoomuchfriction,whichcausesalossinefficiency. Sometimes,oneofthepulleyshaftsisdesignedtobemovabletotakeuptheslackinthebelt,ortensionerwheel(s)areused.Figure 13.12 AV-belt drivingapulleyKEYTERMSTensionerwheel:Acomponentusedtotakeuptheslackinabeltdrivesystem.V-shapedbelt:Abeltdesignedtotransferhighloadswithoutslipping.
29313.1WorkingwithmechanicalcomponentsCamsCams were introducedinChapter 6as amechanismfor convertingrotary toreciprocatingmotion. Theyarefrequentlyusedinenginesandother machines togeneratearequiredkindof motion. The distancethat thefollower rises is calledthestroke. Thisdistancecanbe calculatedfromthedimensions of thecam. STRETCHANDCHALLENGEDetermine the strokeof thefollowingcamsystem, anddescribethe motionof the follower throughonecycle. AB DC15 2815 15 As the camrotates clockwise, points A, B, CandthenDwill movepast the follower. As points A, BandCareall 15mmfromthecamcentre, the follower will stay at its lowest level throughthesepoints. As point Dpasses, thefollower will risebyanamountcalled the stroke: stroke =28- 15=13mmAs point Dpasses, thefollower will fall through13mmagainuntil it reaches its lowest point at A. Figure13.13Twotensionerwheelsareusedtokeepthetoothedbeltfirmlyinplaceinthismotorbikeengine.