455.1CategoriesofmaterialsThermopolymersPET, HDPE, PVC, LDPE, PS, PP, ABS, acrylicandTPEareall examplesof thermopolymers. Theysoftenwhenthey areheatedandcanbemouldedintoshape. Theyhardenagainoncethey have cooled. This canberepeatedmanytimes, whichmeansthermopolymerscanberecycled. Whenreheated, theseplastics will trytoreturntotheiroriginal shape. Thisiscalledplastic memory. Figure 5.21 These products aremadefromman-madepolymer. Figure5.22DrinkscoastermadefromrecycledHDPEThermosettingpolymersSilicone, polyester resinandepoxyresinaretypesof thermosettingpolymer. Thesetypesof polymer undergoachemical changewhenheatedtobecomehard. Oncetheyhave'set'they cannot bereheatedandremouldedandsotheycannotberecycled. Figure 5.23 Silicone cakemoulds More in-depthinformationonpolymers canbefoundinChapter11. KEYTERMSPlasticmemory:Theabilityofthermopolymerstoreturntotheiroriginalstateafterreheating.
46Chapter 5Material considerations TextilefibresandfabricsFibres arethestartingpointforall textileproducts. Theyaretinyhair-likestructuresthatarespun(twisted) together tomakeyarns. Theseyarnsarethenwovenorknittedtogethertocreatefabric. Natural fibresNatureprovidesuswithahugevarietyoffibres, whicharefoundinbothplantsandanimals.Thesearecallednatural fibres. Examplesofnatural fibresincludecotton,woolandsilkKEYPOINTNatural fibres all share many of thesame properties. It is important tomakesure youknowthefewproperties that make eachfibredifferent. Figure5.25SeedcasingsofthecottonplantFigure 5.26 Silk worms wrapthemselvesinsilkfibretoformFigure5.27Woolfleeceisshearedfromasheep.a cocoon. Figure 5.24 Fibres arespuntogether tomakeyarnsandthenwoven or knittedtogether tocreatefabric.
475.1CategoriesofmaterialsSyntheticfibresSynthetic fibres (polyester, acrylicandnylon) areman-madeandcome froma rangeof sources includingcoal, oil, mineralsandother petrochemicals. Thesefibres aremostlynon- biodegradableandarethereforenot sustainable. Theycanbeengineeredtogivethemarangeof useful propertiesincludingflame resistance, creaseresistanceandstainresistance. Mixed/blendedfibresFibres canbemixedor blendedtogether toimprovethequality, aesthetics, functionor cost of thefinal fabric. Fibres are mixedby addingyarns of different fibrestogether duringthe productionprocess. For example, asmall percentage of elastaneyarns maybemixedwithcottonyarnsduringthe weavingprocess toaddstrengthtotheweaveandprovide someelasticity. Fibres maybemixedfor aestheticreasons, suchas mixingfibres of varyinglustreor colour, givinga variable effect. Themixingof fibres happensafter yarnsare spun. Blendingof fibres is commonplacewithinthetextilesindustry. Fibres areblowntogether beforetheyarespunintoyarns. Popular blends includepolyester cotton; thisblendof polyester andcottonfibres is oftenusedtoproduceshirts, andgives the finishedfabricstrength, breathability, absorbencyandcrease resistance. Theblendalsolowerstheoverall costof the fabric. Woven, non-wovenandknittedfabricsWovenfabricsWovenfabrics areproducedonmanual or automaticlooms. Awovenfabric consists of warpandweft yarns. Thewarpyarns runvertically andtheweft yarns arewovenhorizontallyinanunder/over configuration. Different types of weaveareproducedfor varioususes. Thereismoreondifferenttypesofweave inSection12.2. Figure5.28Oilisusedtomakesyntheticfibres.Figure5.29Polyestercottonisapopularblendedfibre.Figure5.30Anautomaticloom
48Chapter 5Material considerations KnittedfabricsKnittedfabricsaremadeupof rowsofinterlockingloops, alsoknownasstitches.Themostcommonlyusedknitsareweftandwarp. For moreinformationondifferenttypesofknittedfabric, seeChapter12.Figure 5.33 Knittedfabrics are made upof rows of interlockingstitches. Figure 5.31 Disposabletextiles suchas surgical masksaremade frombondedfabrics. Figure5.32Feltisappliedtothesurfaceofsnookertables.Non-wovenfabricsNon-wovenfabricslackthestrengthofwovenorknittedfabricsandareusuallyusedfordecorativeor disposableproducts. Thesefabricsfallintotwocategories:bondedandfelted.Bondedfabricsaremanufacturedbyapplyingpressureandheatoradhesivestobondthefibres together andareoftenusedindisposabletextilessuchaswetwipes,teabags,surgicalmasks, dressingsandnappies. Thesefabricslosetheirstrengthandstructureoncewet,sotheyareusuallyonlysuitableforoneuse. Feltedfabricsareproducedbyapplyingheat, moistureandfrictiontofibres,whichmatttogether. Themost commonlyusedfibresarewoolandacrylic.Feltisoftenusedfordecorativepurposes, suchasappliqué, andishistoricallyappliedtothesurfaceofpoolandsnooker tables. Felt isalsousedforcushioningandinsulatingvariousproducts.
495.1CategoriesofmaterialsModernandsmartmaterialsModernmaterialsModernmaterials arethosethat arecontinuallybeingdevelopedthroughtheinventionof newor improvedprocesses. Somewill havepractical applicationsfor your projects inDesignandTechnology, whileotherswill bemore suitedtoa specificcommercial or industrial use. Beloware someexamples of modernmaterials. PolymorphPolymorphcomes intheformof polymer granules. Whenheatedto60°Cinwarmwater thegranulesmelt andcanbe mouldedintoshape. Youcanreheat it againusingwarmwater or ahairdryer. TeflonTeflonis mainly usedas anon-stickcoatingoncookware, but it is alsousedinpaints, fabrics, carpetsandclothingtorepel liquids. Lenticular plasticsheetLenticular plastic sheet is smoothononesidewhiletheother sideismadeofsmall lenses. These lenses transform2Dimages intoavarietyof visual illusions. FlexiplyFlexiply is a formof plywoodthat is extremelyflexibleandcanquiteeasilybebentintovarious shapes. Figure 5.35 Teflon-coatedpans arenon-stick1Granulesofpolymorph2Addhotwater3Liftoutofwaterwhensoft4MouldtoshapeFigure5.34ThestagesofusingpolymorphFigure5.36Flexiply
50Chapter 5Material considerations Preciousmetal clayPreciousmetal clay(PMC) ismadefrom99percentsilverorgoldand1percentclay.Itcanbeshapedat roomtemperaturethenheatedinakilntoproducejewellery.Figure5.37Anexampleof hand-madePMCjewelleryConductivepolymersConductivepolymersareplasticproductsthatcanconductelectricity.Figure5.38Aconductivepolymer
515.1CategoriesofmaterialsSmart materialsSmart materials respondtodifferences intemperatureor light andchangeinsomeway. Theyarecalledsmart because they senseconditions intheir environment andrespondtothoseconditions. Smart materialsappear to'think' andsomehave'memory' as theyrevert backtotheir original stateShape-memoryalloyShape-memory alloy (SMA) remembers itsoriginal shapewhendeformedandreturns toit whenheated. SMAcanbe usedinmany applications, suchas spectacleframesthat returntotheir original shapeafter beingbent, andasa simple andeffectivewaytomoveparts inmachines, likecoolingvents. Shape-memorypolymersShape-memory polymers canalsobe'programmed' toremembertheiroriginal shape whenthey areheated. ThermochromicsheetThermochromic sheet is printedwithliquidcrystal 'ink' thatchangescolour above27°C. It is usedinchildren's toys, jewelleryandtemperatureindicators. ThermochromicpigmentsThermochromic pigments areoftenusedonnovelty mugs that reveal adesignas hot water ispouredintothemug. Theycanalsobeaddedtopolymers tocreateplastics that react toheat, suchas colour-changingdrinks stirrers andbabyfeedingspoons that warnyouif foodor drinkistoohot. PhotochromicmaterialsPhotochromic materials react tolight. Spectacles that darkeninbright sunlight usephotochromic lenses. Self-healingmaterialsSelf-healingmaterials havetheabilitytodetect andrepair damagedonetothem. Thefirstofthese were polymers that hadinternal adhesiveandwereusedonproductssuchascuttingmats. Self-healingmaterials canuseembeddedcapsulesthatreleaseanadhesivewhenthematerial cracks. BioConcreteheals itself usingbacteriathat reactwithanywaterthatgetsintoit andproducelimestonetofill anymicro-cracksthat appear. Material sciencehas developedrapidlyover thepast 20yearsandwill continuetomoveforward. It is difficult tokeepuptodatewithcurrent developmentsinthisfieldandbythe time youreadthis manymorenewmaterialswill havealreadybeendevelopedandintegratedintomodernproducts. Tryhardtokeepabreast of currentscientificprogressas youstudy DesignandTechnology, byfollowingthenewsontelevisionandonrecommendedwebsites. Figure5.41Light-reactingglassesFigure5.40Acolour-changingspoonFigure5.39Shape-memoryglasses
52Chapter 5Material considerations KevlarKevlar issimilartocarbonfibreandhasevenstrongerplasticwovenintoit. Itisevenlighterandstrongerthancarbonfibreandisusedforbulletproof vests. LaminatesLaminatesarematerialsmadeupoflayers.Sincethelayersareusuallyof differentmaterials, laminatesareexamplesofcomposites.Ifamaterial isnotstrongordurableenoughtosurvivebyitself,youwouldcombineitwithonethatis. Forexample,laminatedglasshasathinlayer of plasticsandwichedinthemiddletomaketheglassstrongerandtougher. Awaterproofjacketismadefromlayersthatstopwindandraingettinginbutallowmoisturevapourout.CompositematerialsCompositematerialsareproducedbybondingdifferentmaterialstoproducenewmaterialswithimprovedproperties. Several compositematerialshavebeenaroundformanyyearsandnewcompositesarebeingdeveloped. Compositesareincreasinglyusedinplaceofmetalsinmachinetools. Glass-reinforcedplasticGlass-reinforcedplastic(GRP)ispolyesterresinreinforcedwithglassfibrestrands. Theglassfibreisavailableaswovenfabric, mattingorloosestrands.Ithasallthepropertiesofapolymerbutismuchstronger.Itisusedforlargestructural itemssuchasboatsandcarbodies.CarbonfibreCarbonfibreissimilartoGRPbutusescarbonfibresinstead. Thismakesthematerialevenstrongerandalsolighterinweight. Itisusedforprotectivehelmets,high-endbicyclesandsportingequipment.Figure5.44AcarbonfibrehockeystickFigure 5.42 GRPboats Figure 5.43 AcarbonfibreracingbikeFigure 5.45 AKevlar bulletproof vest
535.1CategoriesofmaterialsWater stays out Sweat vapour escapes H2Ovapour H2OFigure5.46LayersoffabricinawaterproofcoatTechnical textilesTechnical textiles areengineeredspecificallyfor their performanceproperties, notfortheiraesthetic value. Theapplicationof technical textilesineverydayproductsisrapidlygrowingandnewtechnical textiles areconstantlybeingdevelopedbydesignersandengineers. Table 5.1 Commontechnical textiles andtheir applicationsTechnical textile Properties ApplicationsNomex Heat- and flame-resistant •Protectiveclothingfor racingdrivers, firemen,astronauts•Ovengloves•Fire-resistant insulationinbuildingsKevlar Resistant to abrasionanddamage by sharpor pointedobjects •Stab- andbullet-resistant vestsforpoliceandarmedforces•Liningsinmotorcycleclothingandaccessories•Car andmotorcycletyres•Protectiveglovesfor butchersandfishmongersCoolmax Wicks water away frombody, improves breathability •Bedding•Sportswear •Uniforms•Underwear Fastskin Mimics the skinof ashark, giving a streamliningeffect when underwater •Competitivesportswear andswimwearSTRETCHANDCHALLENGEUsetheinternettoresearchotherexamplesofcompositematerialsandtheiruses.Figure 5.47 Nomex is usedtoprotect firefightersfromflamesandheatexposure. Figure5.48Stomatexisusedinsupportbandagesasitallowstheskintobreathe.
54Chapter 5Material considerations 2.3CharacteristicpropertiesofthemaincategoriesofmaterialsWhendesigninganyproduct, thechoiceofmaterialsisoneofthemostimportantdecisionsandwill haveamassiveimpactonthesuccessofthefinalproduct.Inordertochoosethemost appropriatematerial thedesignerwill needtoconsiderandunderstandthekeypropertiesof materialsandmakeinformedchoicesbasedonthesecharacteristics.Thesamewill applywhendesigninganelectronicsystem; thedesignermustconsiderthewiderangeof componentsavailableanddecideonthemostsuitabletypefortheapplication,basedoncertaincharacteristicsit musthave. LEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜thecharacteristicpropertiesofthemaincategoriesofmaterials,andwhythismakesthemappropriatefordifferentuses.DensityDensityisthemassof amaterial (itsweight)dividedbyitsvolume(size).Materialssuchasmetals aredenser thanmaterialssuchassoftwoodorStyrofoam.For example, ablockof steel andablockofsoftwoodbothmeasure10cmlong×10cmwide×10cmhigh. Thesteel blockweighs7.8kg. Thesoftwoodblockweighs0.65kg.Bydividingtheweight of theblocksbytheirvolumewecanfindtheirdensities:Steel blockWeight=7800gramsVolume(10×10×10)=1000cm3=7.8g/cm3Thesteel ismuchdenser thanthesoftwood. Waterhasadensityof1g/cm3. Materialswithadensitylessthanwaterwillfloat.StrengthThestrengthof amaterial isitsabilitytowithstandforcesthattrytobendorbreakit.Materialsareoftenstronginonewaybutweakinanother, dependingonthetypesofforcesthat areapplied. Becausetherearedifferentforcesthatcanbeappliedtoamaterial,therearedifferentkindsof strength, relatedtohowwell amaterial canresisttheseforces:lCompressivestrength- howwell thematerial canwithstandcompressionforces(squashingforces). lTensilestrength- howwell thematerial canwithstandtensionforces(stretchingforces).lYieldstrength- howwell thematerial canwithstandforcesbeforeitispermanentlydeformedinsomeway. lImpact strength- howwell thematerial canwithstandsuddenforces.Manymaterialsthat havegoodstrengthcharacteristicsagainstonetypeofforcewillrespondpoorlyagainst another. For examplecompositematerials, suchasglassfibreandcertainpolymers, tendtohavehighertensilestrengthsthancompressivestrengths.Thetensilestrengthof timber isconsiderablyhigherthanitscompressivestrength.Somematerialssuchas metalstendtohavetensileandcompressivestrengthsthatareverysimilar.Thestrengthof textilesandfabricsissometimesreferredtoas'tenacity'.
552.3CharacteristicpropertiesofthemaincategoriesofmaterialsHardnessThe hardness of a material refers tohowresistant it istopressurefromcutting, scratchingorwear. Scratchhardness, indentationhardnessandreboundhardnessaredifferentmeasuresof hardness. Somematerials (for example, metals) aremuchharderthanothers(forexample, polymers andtextiles). Metals suchas highcarbonsteel areextremelyhardmaterials. Many hardmaterials arealsobrittle. DurabilityDurability is theability of amaterial towithstandwear, pressureordamage. Somematerialsare more durablethanothers andarechosenfor certainapplicationsfortheirabilitytowithstandwear anddamage. StrengthtoweightratioStrengthtoweight ratiois ameasureof amaterial'sstrengthcomparedtoitsweight. Materials withhighstrengthtoweight ratiosareusedwhereastrongmaterial isrequiredbutsavingweight is alsoas important, suchasaircraft. Carbonfibre, glassfibreandalloyssuchastitaniumhaveextremelyhighstrengthtoweight ratios. Mostpolymershavehighstrengthtoweight ratios especially if reinforcedwithfibres. StiffnessThe stiffness of a material describes its rigidity- i tsabilitytoresistbeingdeformedwhenaforce is appliedtoit. Ceramics, glass andsteel havegoodrigidity, whereaspolymerssuchasfoamandrubber areextremelyflexibleandhavepoor stiffness. ElasticityThe elasticity of a material is its abilitytoreturntoitsoriginal shapewhenforcesareappliedtoit that will makeit bendor flexout of shape. Different materials havedifferent levels of elasticity. Somematerialswill notdeformorwilldeformvery littlebeforebreakingandthereforehavealowelasticity. If amaterial hashighelasticity it will returntoits initial shapeandsizewhentheforcesareremoved. Asimple exampleof amaterial withhighelasticityiselasticband. Whenyoustretchanelastic bandit is deformedout of shape, but returnstoitsoriginal sizeonceyouletgo. ImpactresistanceImpact resistanceis theabilityof amaterial towithstandaforceorshockappliedtoitoverashort periodof time. Manypolymers suchasrubber andnylonhavegoodimpactresistanceas well as softer metals suchas mildsteel. PlasticityPlasticity is theability of amaterial topermanentlychangeinshapewhenforceisappliedtoit. Metals suchas sheet steel areshapedbyhammeringor bending. Thisisanexampleofplasticityas the hammeringandbendingforces createpermanent changeswithinthematerial itself.
56Chapter 5Material considerations DuctilityandmalleabilityTheductilityof amaterial ishoweasilyitcanbedeformedorbentoutofshapewithoutsnappingor breaking. Themoreductilethematerial, theeasieritistostretchintoathinwire. Materialswithpoor ductilitywill breakwhenstretched. Malleabilityreferstoamaterial'sabilitytodeformwithoutbreakingorsnappingwhenhammeredorrolledintoathinsheet.Soft metalssuchasleadandpolymerssuchaspolypropylenehavegoodductilityandmalleability. Temperatureandapplicationofheatcanalterbothproperties.Highertemperatureswill increaseamaterial'sductilityandmalleability, andlowertemperaturescandecreasethem.CLASSACTIVITYTakesomethinstripsof differentwoods,metalsorplastics.Placeoneendinabenchviceandpushtheother end, makingthestripsbend.Startbybendingeachonealittleandseeingif theyreturntotheiroriginal shape,thencontinuepushingalittlemoreandbendingthemfurther andfurtheruntil theydonotreturntotheiroriginalshape.Whichof thematerialshasthehighestandlowestelasticity?Whichhasthehighestandlowest elasticlimit?Healthandsafety: beverycareful whenbendingmaterialsthatmaysplinterorshatter.Always wear appropriateprotectiveequipment,includingsafetygogglestoprotecteyesandgloves andanaprontoprotectskin.BrittlenessBrittlenessishoweasilyamaterial will snaporbreakwhenbentorimpacted.Verybrittlematerialswill shatter or breakupratherthanbendanddeformwhenforcesareapplied.Brittlenessistheoppositeof ductilityandisalsoaffectedbyheat.Thelowerthetemperature,theless ductileandmorebrittlemanymaterialswillbecome.Manymetals,especiallycastironandaluminium, areverybrittle. CorrosiveresistancetochemicalsandweatherCorrosiveresistancereferstohowsusceptibleamaterialistodegradationfromelementssuchasoxygen,moistureandotherchemicals. Themostcommonformofcorrosionisrust, whichaffectscertainmetalswhentheyareexposedtooxygenandmoisture. Ferrousmetals(metalsthatcontainiron) haveaverylowcorrosion-resistanceandareextremelysusceptibletorust. Corrosionalsoaffectsothermaterials,includingtimberandpolymers. Sometimberssuchasoakandotherdensehardwoodsareresistanttocorrosion(rot),whereassoftwoodswill rotwithinafewmonthsifexposedtotheelements,iftheyhavenotbeentreatedwithchemicalinhibitors.Manypolymersdegradegraduallyovertimeifexposedtoultra-violetlight, oxygenorchemicalssuchaschlorinethatcausethemtoswellup, crackand/orbreakdown.Naturalandsyntheticrubberproductssuchascarorbicycletyresarecommonpolymersthatwillbecomebrittleovertimebeforecrackingandsplittingifleftoutsideinthesun.EvenharderplasticslikeuPVCwindowsanddoorsgobrittleovertimeandneedtobereplacedeverytwentyorthirtyyears.Figure 5.49 Rubber products liketyres becomebrittleover time. ACTIVITYFindor collect twoor three different types of plastic carrier bags. Suspendeachbagona suitable hanger andgradually addheavy objects or weights intoeachone. lDothe plastic handles snapor stretch? The handles that stretchmost havethe highest ductility. The ones that snapwithout stretchinghave poor ductility.
572.3CharacteristicpropertiesofthemaincategoriesofmaterialsWaterresistanceWater resistanceis theabilityof amaterial toresist theingressof water. Materialsthatdonotabsorbmoistureor water arecalledwaterproof. Themajorityof polymerssuchasrubber, PVCandpolyurethanearewater resistant andtheseareoftenusedtocoatothermaterialsor products tomakethemwater resistant. Productssuchaswaterproofclothing, inflatableboats andfootballs usenatural or syntheticfabricsthat arelaminatedorcoatedduringmanufactureby a waterproofingspray. AbsorbencyAbsorbency is theabilityof amaterial toabsorbmoisture. Manynatural fabricssuchascotton, linenandwool havegoodabsorbency. Most typesof cardboardalongwithporouspolymers suchas foamalsohavegoodabsorbency. FlammabilityFlammability is theabilityof asubstancetoburnor ignite, causingfire. Thevastmajorityoftimbers, polymers, fabrics, papers andboardsareflammablealthoughsomewill igniteandburnmore quickly andeasilythanothers. Metalsarenot flammableandwill notburnwhenexposedtoa flameElectrical conductivityElectrical conductivity refers tohoweasyit isfor electricitytoflowthroughamaterial. Metalsare goodelectrical conductors andhavehighelectrical conductivityproperties. Woodandrubber are poor electrical conductors anddonot allowelectricitytofloweasilythroughthem. Thermal conductivityThermal conductivity refers tothewayheat canbetransferredthroughamaterial. Materials withgoodthermal conductivitywill allowheat tobetransferredthroughthemrelatively easily (andtheywill heat up). Metals oftenhavegoodheat-conductivityproperties andarethereforeusedtotransfer heat inheatingsystems (metal radiators, etc.). Thermal resistanceis theabilityof amaterial toresist theflowof heat. Materialswithgoodthermal resistancewill not let heat be transferredthroughthemeasily, andsuchmaterials aresaidtobegoodinsulators. Generally, porous materials suchas Styrofoamandsoftwoods aregoodinsulators. Thermal fabrics haveexcellent insulationproperties andareusedinmanytypes of clothingtokeepthewearer warmas well asproductssuchasovenmitts, tablepadsandironingboardpads. Thermal fabrics arealsousedtokeepcoldthingscoldsuchasbottlejackets, cool bags etc. Acrylicandviscosearefabricswithgoodinsulationproperties. Figure5.50Aheatsink
58Chapter 5Material considerations ACTIVITYFill twocups withboilingwater. Putametal tablespooninoneandawoodenspoonintheother. Leavefor 1minuteandfeel theendofthespoonstickingoutofthecup.Themetal spoonwill bemuchhotterthanthewoodenspoonasthemetalconductstheheat andthewoodinsulatesit. Healthandsafetywarning: beverycareful withboilingwatertoavoidscalding.MagneticpropertiesAmaterial withmagneticpropertieswill emitforcesthatattractorrepulseothermaterials.All materialshaveacertainamountofmagnetism, butitisverylowinmostofthem.Metalssuchas magnetite, iron, steel, nickel, cobaltandsomealloyshavehighlevelsofmagnetism.Magnetiteisanaturallyoccurringmaterial thatismagnetic. Othermaterialscanbemagnetisedartificiallybyvariousmethods. Thesearecalledferro-magneticmaterials.Themagneticpropertiesof artificiallymagnetisedmaterialsfadeovertime,however,whereasmagnetiteisapermanentlymagneticmaterial anditsmagneticpropertywillnotfade.KEYPOINTSlDesignersmust considerthepropertiesandcharacteristicsofmaterialswhendesigning.lDifferent materialscanhavearangeofdifferentproperties.lAmaterial'spropertiesmaychangedependingonthingssuchastemperatureortheshapeanddirectionof thematerial.
592.3CharacteristicpropertiesofthemaincategoriesofmaterialsSTRETCHANDCHALLENGE1 Complete the tablebelowby addingthreepropertiesof thematerialsshownintheleft-handcolumn. Material Property 1Property2Property3Copper SoftwoodNylon Foamrubber Glass Leather 2 Addmore materials of your ownintheleft handcolumnandfill inthethreepropertycolumns.
60Chapter 6Mechanical devices andelectronic systems CHAPTER6MechanicaldevicesandelectronicsystemsThis chapter introducessomeof thewaysinwhichproductsandsystemsare'broughttolife'usingmovement and/or electroniccontrol. Evenverybasicproductssuchasapairofgardensecateursor adoor closer makeuseofamechanicalsystem, anddomesticproductsweusedailysuchaskettlesandtoastersarecontrolledbyelectronicsystems.If youwishtofurther exploretheuseofmechanicalorelectronicsystems,andwouldliketousesuchsystemsduringyouriterativeprojectdevelopment, youwillfindthemorein-depthtechnical informationinChapter10useful. 6.1ControlledmovementLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandhowmechanicaldevicesintroducecontrolledmovementtoproductsorsystems,including:➜anoverviewofthedifferenttypesofmotion➜theeffectsofforcesontheeaseofmovement➜howmechanical devicesareusedtochangethemagnitudeanddirectionofforces. Movement andmotionbringproductstolife. Themovementmightinvolvetheentireproduct, for instanceavehicle, orjustapartoftheproduct, suchasinanelectricfan.Themotionmight beclearlyvisible, forexampleinthecaseofafoodmixer,oritmighttakeplaceinsidetheproduct andnotbeimmediatelyvisiblefromtheoutside,asinacomputerprinter.Sometimes, movement isakeypartofthefunctionofaproduct,suchasabicycle.Inotherproducts, movement addstothefunctionalityoftheproducttoenhanceitinsomeway;forexample, asoft-closedoor mechanismisnotessentialtothefunctionofadoor,butitisauseful additionandstopsthedoorslammingclosed. Figure 6.1 Simpleproducts that relyonmechanismsorelectronics
616.1ControlledmovementHowmechanical systemsproducedifferentsortsofmovementandtypesofmotionAmechanismis a series of parts that worktogether tocontrol forcesandmotionina desiredway. lAmechanismis anexampleof asystem, andthereisahugevarietyof mechanisms that generate, control andchangemotion. Controlledmotionis essential inmanyengineeredproducts. lAforceis a push, apull or atwist. Forcesaremeasuredinnewtons(N). lThere arebasically four different typesof motion, andthesearedescribedbelow. RotarymotionThis is motionthat follows thepathof acircle. Rotarymotionis very commonandcaneasilybeseenintherotationof wheels. Theoutput shaft of anelectricmotor alsomoves inrotary motion. Rotarymotioncanbemeasuredby countingthenumber of revolutionsinaset periodof time- r evolutions per minute(rpm) isacommonmeasurement of rotaryspeed. Linear motionThis is motionina straight lineandis commonlyseen- f or example, a vehicletravellinginastraight line, or items travellingonaconveyor belt. Thespeedat whichobjects travel ina straight lineis measuredbydividingthedistance they travel by thetimetaken: Speed=distancetimeSpeedis oftenmeasuredinunits of metresper second(m/s) or kilometres per hour (km/h). Figure6.2Wheelsareanexampleofrotarymotion.Figure 6.3 Items ona conveyor belt movewithlinear motion. STRETCHANDCHALLENGEAconveyormustmoveitemsthroughadistanceof5.7min18s.Calculatetherequiredspeedoftheconveyor.Speed=distancetimeSpeed=5.718=0.32ms-1KEYTERMSMechanism:Aseriesofpartsthatworktogethertocontrolforcesandmotion.System:Thegeneralnameforasetofmechanicalorelectronicpartsthatworktogethertoproduceadesiredoutput.Force:Apush,apulloratwist.
62Chapter 6Mechanical devices andelectronic systems ACTIVITY1. Takefiveproductsfromaroundyourhomethatexhibitmovement(forexample,acomputer mouse, holepunch, toaster,electricdrill,electrictoothbrush,orfoodmixer).For eachproduct statethekindsofmotioninvolvedwhentheyarebeingused-theremaybeseveral differenttypesofmotiongoingonatonce.Sometimesit isnot immediatelyobviouswhichtypeofmotionisinvolved.Forexample,whenautomaticdoorsslideopenandclosedyoumightdescribetheirmotionasreciprocating,; but if thesamedoorsarelockedopenalldaywould'linearmotion'beabetter description?2. Howwouldyoudescribethemotionofthefollowingitems:a) Astapler?(Isit reciprocatingoroscillating?)b) Thehandlesof apairofscissors?Manymechanismschangeonekindofmotiontoadifferentkind.Theycanalsochangethespeedanddirectionof themotion, aswell asthesizeanddirectionofforces.Examplescanbefoundthroughout thischapter. TheeffectofforcesoneaseofmovementMechanismsthat control andchangemotionhaveaninputandanoutput.Onapairofscissors, for example, theinputmotionisthemovementofthehandles,andtheoutputisthemovement of theblades. Mechanismssuchasthiscaneither:lreducethedistancemovedbutincreasetheforcebeingexerted,orlincreasethedistancemovedbutreducetheforcebeingexerted.Thereis alwaysatrade-off betweenforceanddistancemoved-onecanincrease,butonlyif theother decreases. Thismeansthatmechanismscanbeusedtoamplify(makebigger)forces sothat veryheavyobjectscanbeliftedbyoneperson,asintheexampleofacarjack,but thetrade-off isthat thepersonmustmovetheinputlevermuchfurtherthanthecargets lifted. Figure 6.4 Anelectric toothbrush headuses oscillatingmotion. Figure6.5Ajigsawblademoves withreciprocatingmotion. OscillatingmotionOscillatingmotionissimilartocircularmotion,buttherotationmovesbackandforthinacircularpath.Oscillatingmotionisquitecommonbutyouneedtolookcarefullytospotit;agoodexampleistheoscillatingheadofanelectrictoothbrush.Therateof oscillatingmotionismeasuredinoscillationspersecondorperminute. ReciprocatingmotionThisisback-and-forthmotioninastraightline,forexamplethebladeonanelectricjigsaw.Oscillatingandreciprocatingmotionsaresimilarinthattheyarebothmeasuredinoscillationspersecondorperminute.KEYTERMSInput: The typeof motionput intoamechanism. Output: The typeof motiona mechanismproduces.
636.1ControlledmovementLeversThe simplest exampleof amechanismthat controlsandchangesmotionisalever, whichconsists of a rigidbar that pivots onafulcrum. Theinput forceisoftencalledtheeffortandthe output forceis calledtheload. Acar brake pedal is anexampleof alever. Theeffort forceappliedbythedriver'sfootcreatesa loadforce, whichis usedtoapplythecar'sbrakes. Theforcesarerepresentedbyarrowsthat showthedirectioninwhichtheforcesact. BigloadFulcrumSmall effort Small output armlength Big input armlength Loadmovesthroughsmall distanceEffortmovesthroughbigdistanceFigure 6.6 Abrake pedal is alever. The diagramshows that, becauseof thepositionof thefulcrum, theeffortmovesthrougha larger distancethantheload. Remember that thelever mustobeythetrade-offprincipledescribedabove, soif theloadmoves throughasmaller distancethantheeffort, thentheloadwill be a larger forcethantheeffort. Thismeansthat thebrakepedal haseffectivelyamplifiedtheforceappliedbythedriver'sfoot. Thisleadstotheideaof'leverage'. The distancebetweenthefulcrumandtheforceiscalledthearmlength. Thelargerthearmlength, thelarger thedistancetheforcemust move, thereforethesmallertheforce. ACTIVITYFind five examples of levers fromaroundyour home. Thesecouldbecompleteproducts(forexample, kitchentongs, canopener, wheelbarrow, stapler or nail clippers),orpartswithinaproduct. Identify thefulcrumandthepoints wheretheeffortandloadareapplied.Slightlyharder products toanalysecouldincludeadoor handle, spannerandtap(levertapandrotary tap). KEYPOINTbiggerarmlength=biggerdistancemoved=smallerforcelSo,foralevertoamplifyaforce,effortneedstobesmallerthanload.lTherefore,inputarmlengthmustbegreaterthanoutputarmlength.Thearmlengthisininverseproportiontotheforce.Inotherwords,iftheinputarmistwiceaslongastheoutputarm,theeffortwillbehalfasbigastheload.Notallleversareusedtoamplifyforces;insomeapplications,theloadwillintentionallybelessthantheeffort.KEYTERMSArmlength:Thedistancebetweentheforcebeingexertedandthefulcrum.Effort:Theinputforce.Fulcrum:Thepivotaroundwhichaleverturns.Lever:Arigidbarthatturnsaroundafulcrum.Load:Theoutputforce.
64Chapter 6Mechanical devices andelectronic systems HowmechanicaldeviceschangethemagnitudeanddirectionofforcesMechanismsthat control andchangerotarymotionalsohaveaninputandanoutput.Thebasicmechanical trade-off principlestill applies, butinsteadofforcewerefertotorque.Torqueisaturningor twistingforce. Rotarymechanicalsystemscaneither:lreducerotaryspeedbutincreasetorque, orlincreaserotaryspeedbutreducetorque. Remember, if theoutputspeedisfasterthantheinputspeedthenthetorquewillbeless;onecanincreasebut onlyattheexpenseoftheother. CamsAcamandfollowerisamechanismtoconvertrotarymotionintoreciprocatingmotion.Acamisaspeciallyshapedwheel andthefollowerrestsontheedgeofthecam.Asthecamrotates, thefollower movesupanddown. Camsareusedextensivelyinmachineryandenginestoproduceadesiredmotion. Theprofile(shape) of thecamdeterminesthemotionofthefollowerthroughoutonerotationcycle. Withalittlethought, youshouldbeabletopredictthetypeofreciprocatingmotionproducedbyaparticularshapeprofileofcam, suchasthoseshowninthediagrambelow. FollowermovesupanddownSlideFollowerCamrotatesSnail Pear-shapedEccentricFigure6.7Threetypesof camGearsAspurgearisawheel withteetharounditsedge. Theseteetharedesignedtomeshwith(linkinto) theteethonanotherspurgear, whichisusuallyofadifferentsize-thispairofgears is calledasimplegeartrainandconsistsofthedrivergear(theinput)andthedrivengear (theoutput). If thedrivergearisthesmallergear, itissometimescalledapinion.Gears aremountedonshafts, whichcarrytherotationtoadifferentpartofthemechanism.KEYTERMSCamandfollower: Amechanismtoconvert rotary motionintoreciprocatingmotion. Pinion: Asmall driver gear (smaller thanthedrivengear). Shaft: Arodthat transfers the rotationthrougha mechanism. Simplegear train: Apair of gears consistingof a driver gear andadrivengear. Spur gear: Awheel withteetharoundits edge. Torque: Aturningor twistingforce.
656.1Controlledmovement16 teeth (N1) 40teeth(N2) Figure 6.8 Asimple gear trainIf the twogears aredifferent sizes theywill rotateat differentspeeds. Therearetwosimplerules toremember: lThe smaller gear will rotatefaster thanthelarger gear. lThe gears will rotateinoppositedirections. Agearbox is a mechanical systemthat usuallycontainsseveral simplegeartrainsworkingtogether toachieveaverylargespeedreduction. Thephotographshowsanelectricmotorcombinedwitha gearbox, whichreducesthespeedof themotorbyaratioof50:1. Figure 6.9 Amotor withgearboxattachedGear systems usually requiresomeformof lubricationtoreducefrictionandtopreventthe teethwearingaway tooquickly. Dependingontheapplication, oil, grease, oraPTFEorgraphite lubricant canbeused. KEYPOINTSlThesmallergearrotatesquickly;thelargergearrotatesslowly.Therefore,forasimplegeartraintoreducetheinputrotationalspeed,thedrivengearmustbelargerthanthedrivergear.lThenumberofteethonthegearisininverseproportiontothespeeditrotates.Inotherwords,agearwithtwiceasmanyteethwillrotateathalfthespeed.lNotallgeartrainsareusedtoreducerotationalspeed;insomeapplications,theoutputspeedwillintentionallybehigherthantheinputspeed.KEYTERMSLubrication:Asubstanceappliedtoreducefrictionbetweenmovingparts.
66Chapter 6Mechanical devices andelectronic systems PulleysandbeltsSpur gearsprovideonemethodof transferringrotarymotionbetweentwoshafts.Analternativeistouseapulleyandbeltdrive, whichbehavesinasimilarwaytoasimplegeartrainbut withthefollowingdifferences: lTheinput shaft andtheoutputshaftcanbeseparatedbyagreaterdistancethancanbeachievedwithspur gears. lTheinput andoutputshaftsrotateinthesamedirection. Apulleyandbelt drivecanprovidespeedreductionorincreaseinasimilarwaytothesimplegear train. Belt Driver pulleyDrivenpulleyFigure6.10TransferringrotarymotionwithpulleysandabeltLeversandlinkagesAlinkageisacomponentusedtodirectforcesandmovementtowheretheyareneeded.Alinkagewill oftenchangethedirectionofmotion, anditmightalsobeusedtoconvertbetweendifferent typesof motion. Asimplelinkageisoftenjustaspeciallyshapedlever.Someexamplesof linkagesareshowninthediagram. Bell crankPegandslotCrankandsliderFixedpivot pint Pivot Pivot Input Output PivotPegRotationOscillationCrankrotatesSliderreciprocatesFigure6.11Examplesof linkagesKEYPOINTSlAsmaller pulley rotates quickly; a larger pulley rotates slowly. Therefore, for a pulley andbelt systemtoreduce the input rotational speed, the drivenpulley must be larger thanthe driver pulley. lThe diameter of the pulley is ininverse proportiontothe speedit rotates. Inother words, a pulley withtwice thediameter will rotate at half thespeed. KEYTERMSPulleyandbelt drive: Amethodof transferringrotary motionbetweentwoshafts. Linkage: Acomponent usedtodirect forces andmovement towherethey are needed.
673.2ElectronicsystemsACTIVITYThe best way toget a'feel' for mechanical systemsistoseetheminoperation.Completingat least one of the followingactivities will helpyoutoexploremechanical systemsfurther.1. Try tofindworkingexamples of linkages andother mechanismsintheequipmentyouuse regularly, e.g. onabike, ongardentoolsor intheworkshopequipment.Watchtheminoperation. 2. Visit anindustrial museumtowatchenginesinoperationisalwaysworthwhile.3. Finda free animationor videoontheinternet that showslinkagesoramechanisminoperation. (This may allowyoutoobservetheeffect of changingdimensionsoflevers,sizes of gears andpulleys etc. Therearenumerousonlinevideosofworkingmechanismswhichyoucanstudy, 4. If your school has mechanical simulationsoftware, buildandrunavirtual mechanicalsystem. 3.2ElectronicsystemsLEARNINGOUTCOMESBy theendof this sectionyoushouldknowaboutandunderstandhowsimpleelectronic systems providecontrol functions, including: ➜switches andsensors, torespondtoavarietyofinputsignals➜devices toproduceavarietyof outputs➜howprogrammablecomponentscanbeembeddedintoproductsinordertoenhanceandcustomisetheir operation. Electronics permeateour lives insomanyways. It ishardtoimaginegoingthroughadaywithout usinganelectronicdeviceat somepoint: asmartphone, tablet, computer, TVorradio. The car wetravel inis burstingwithelectronicsystemstocontrol theengine, toensureour safety andtohelpwithnavigation. Theheatingandventilationinthebuildingswherewe work andlivearemonitoredbyelectronics, not tomentionsecuritysystems, CCTV, andsoon. The combinationof electronicandmechanical systemscreatespowerful anduseful designsolutions. HowelectronicsystemsprovidefunctionalityinproductsAnelectronic systemcanbebrokendownintosmaller partscalledsubsystems, andtheseinturncanbeclassifiedintoinputs, processes andoutputs. Asystemdiagramisdrawntoshowhowthesubsystems areinterconnected. KEYTERMSSubsystem:Asectionwithaspecificrolewithinasystem.Systemdiagram:Adiagramoftheinterconnectionsandflowofsignalsinanelectronicsystem.Input Process Output Signal flowingbetweensubsystems Figure 6.12 Ageneric electronic system. Figure6.13Pushbuttonsarefrequentlyusedasinputs.
68Chapter 6Mechanical devices andelectronic systems Inputsconsistofsensors,whicharethe'eyesandears'ofanelectronicsystem. Theyallowthesystemtomonitorandmeasurearangeofphysicalquantitiessuchaslightlevel, temperature, weight,etc.Apushbuttonisaverycommonlyusedinputcomponentthatsenseswhenithasbeenpressed. Asensorproducesanelectricalsignal, whichissentintotheprocesssubsystem.Theprocesssubsystemwillusuallybeaprogrammablemicrocontroller, andtheseareexplainedbelow.Theoutputcomponentsofanelectronicsystemproduceaphysical outputinresponsetosignalsfromtheprocesssubsystem. Outputscanproducelight,sound,motion, etc. Avisualdisplayscreenisanoutputdeviceincreasinglyfoundonmodernproducts.EmbeddingprogrammablecomponentsintoproductsProgrammablemicrocontrollersareelectroniccomponentsthatcanaddincrediblefunctionalitytoaproductorasystem. Microcontrollerstakeinformationfromsensorsandother inputsandthenprocessthisinformationinordertocontrolavarietyofoutputs,whichmayincludelights, sounds, motionorvisual displays. Microcontrollersallstartoffblank,butthedesigner thenwritesaprogramthatisdownloadedintothemicrocontroller'smemory.Theprogramisaset of instructionsthattellsthemicrocontrollerhowtocarryoutataskthatis specifictoaproduct. Thisprocessofcustomisingagenericmicrocontrollertoaspecificapplicationandplacingitpermanentlywithintheproductiscalledembedding.Microcontrollersareincreasinglybeingusedinproducts, andtheirsmallsize,versatilityandrelativeeaseof usemakethemanattractivenewtechnology.Eventhemostbasicmicrocontroller isanextremelypowerful miniaturecomputer,capableofprocessingsignalsandperformingcalculationsatastonishingspeed. Inmanybasicproductsthefullpotentialof themicrocontroller isneverused. Inakettle, forexample, themicrocontrollersimplyneeds toswitchontheheatingelementuntil itsensesthatthewaterhasreachedboilingpoint, thentoswitchtheheateroff. Nonetheless, itisusuallymorecosteffectivetouseamicrocontroller for thissimpletaskthantodesignabespokeelectronicsystemfromscratch,anddesignersnowrealisethat, onceamicrocontrollerhasbeenselectedforadesign,thereis thepotential toaddadvancedfeaturesthatcanenhancetheproduct'sfunctionalityandincreasetheusefulnessfor theuser. Figure 6.14 Identify theinputs andoutputs onamicrowave oven. Figure6.15Asmart fridgecansensewhatisstoredinsideitandre-order stockwhenitisneededKEYTERMSEmbedding: Customisinga microcontroller tobepermanently placedwithina product. Microcontroller: Aprogrammableelectronic component that adds functionality toa product. Physical quantity: Somethingthat canbemeasured, e.g. light, temperature, speed. Program: Aset of instructions totell amicrocontroller howtocarry out a task. Sensor: Acomponent that produces asignal inresponsetoa specific physical quantity. Signal: Anelectrical voltage that is usedtorepresent information.
70Chapter 6Mechanical devices andelectronic systems Inputsensors,switchesandcontroldevicesDifferent microcontrollersuseslightlydifferentmethodsforconnectingsensorsandotherinputs. Somemicrocontrollershaveadedicatedsetofinput/outputcomponentsthatcanbepluggedtogether likebuildingblocks. Thereare, however, somestandardcomponentsthatthevariousmicrocontroller systemswill all use. LightsensorThelight-sensingcomponentinanelectronicsystemwilloftenbealightdependentresistor (LDR). AnLDRisconnectedintothemicrocontrollercircuitsoitproducesasignalthatriseswhenthelight level increases. Insidethemicrocontroller, thesignalwillbeconvertedintoanumber;thelarger thenumber, thebrighterthelightdetected. Themicrocontrollercanthenprocessthisnumber or makedecisionsdependingonhowbrightthelightis.InfraredsensorSeveral different typesof infrared(IR) sensorsareavailable. Infraredistheinvisibleradiantenergygivenoff bywarmobjects. Therearetwotypesofsensorthatmakeuseofthisradiantenergy:lAsimpleIRsensor will produceasignal whenitdetectsawarmobjectwithinrange.This canbeused, for example, todetectthepresenceofaperson'shandssothatanautomatictapor ahanddryercanbeturnedon. lApassiveinfrared(PIR) sensorisusedtodetectamovingwarmobject,usuallyapersonwalkingacrossaroom. Thesesensorsareusedinburglaralarmsystems,orinautomaticlightingor heatingsystemsthatswitchonwhenapersonwalksnearby.Another typeof IRsensor consistsof anIRtransmitterandreceiverinasinglepackage.Thesedevices reflect anIRbeamoff anobjecttomeasurehowfarawaytheobjectis,aprocessknownasrange-finding. Suchsensorsareusedinroboticsystemstoallowtherobottosensethepresenceanddistanceof nearbyobjects, withoutneedingtotouchthem.ACTIVITY1. Findfive electronic products fromaroundyour home(forexample,kitchenscales, coffeemachine, TVremotecontrol, satnav, central heatingroomthermostat, burglar alarmcontrol panel). Identifytheinput sensors andtheoutput devices (someof thesemaynotbevisible. Makesureyouconsider sensors andcomponentsthatmaybehiddeninsidetheproduct). 2. Howdoelectronic kitchenscales senseweight. 3. Where does the'beep' soundfromamicrowavecomefrom?. Figure 6.18 AnLDRandvarious IRsensors STRETCHANDCHALLENGEConsiderarelativelystraightforwardproductfoundinthehome,forexampleatap,avacuumcleaneroradoorbell.Writedownwaysinwhichamicrocontrollercouldenhancetheproduct'sfunctionalitysothattheuserhasabetterexperienceinteractingwiththeproduct.
713.2ElectronicsystemsFigure 6.19 Different types of switchSwitchsensorsAswitchis a very simpleelectroniccomponent that canbeeitheroff oron. Whenaswitchis actingas aninput for amicrocontroller it will produceeitheranoff signal oranonsignal. Most peoplearefamiliar withsimplepushbuttonswitches, butavarietyofothertypesofuseful switches arealsoavailable: lTilt switches - t heseproduceasignal whentheswitchisupright, andnosignal whentheswitchis inverted. Theysensebeingtilted, whichisuseful fordetectingifapotentiallydangerous product suchas aroomheater hasfallenover. Aslightvariationonthisisthevibrationswitch, whichproduces abrief signal whenit ismoved; thiscanbeusedinasecurity systemtosoundanalarmif avaluableobject istamperedwith. lPush-to-makeswitches - t heseproduceasignal whenthepushbuttonispressed. Amomentaryswitchturns off whenthebuttonisreleased; alatchingswitchstaysonuntil thebuttonis pressedasecondtime. lTime delay switches - t herearetwotypes: - The first typeis similar toalatchingpush-to-makeswitchbutitonlystaysonforaperiodof timebeforeautomaticallyswitchingoff. - The other typeis atimer switch, whichcanbeprogrammedtoswitchonandoffatvarious times throughout the24-hour day. ACTIVITY1. Some electronic products containalight sensor. Asmart phone, forexample,sensesthelight level inthe roomandadjusts thebrightnessof itsdisplaytosuit. Adusk-to-dawnsecurity lampsenses thelight level andswitchesonwhenitgetsdark. Findaproductwhichcontains alight sensor andidentifytheexact positionofthesensor.Photographyour findings. 2. Passive infra-red(PIR) sensors arefrequentlyusedinburglaralarmsystemstodetecta personmovingacross aroom. Describeaproduct whichusesaPIRsensorforanalternative purpose. 3. Photographsix examples of switches usedinproductsaroundyourhome.Usewordsto describe the typeof switch, e.g. 'momentarypushswitch' or'latchingrockerswitch' etc. KEYTERMSLatching:Aswitchthatstayson(oroff)afterthebuttonisreleased.Momentary:Aswitchthatstaysononlywhileitisheldpressed.
72Chapter 6Mechanical devices andelectronic systems OutputdevicesLightemittingdiodesLight emittingdiode(LED) technologyhasprogressedatanenormousrateandaverywiderangeof LEDsisnowavailable. WhenspecifyinganLEDforanapplication,adesignerneedstoconsider: lcolour lsize(diameter) lshapelbrightnesslnormal or flashing. The'standard' sizeLEDis5mmdiameter, andtheseareavailableineveryvisiblecolouraswellas coloursthat arenot visible, suchasinfraredandultraviolet.Red-green-blue(RGB)LEDscanbemadetolight upanycolour, includingwhite. Most LEDsareroundbutsomeothershapesareavailable, suchastriangularorarrowhead.LEDstripsconsist of several miniatureLEDsonaflexibleself-adhesiveroll.LEDstripsareavailableassingle-colour or RGB. AstandardbrightnessLEDissuitableforuseasanindicatoronacontrolpanel(e.g.toshowthat somethingisswitchedon). Highbrightnesstypesarebestforilluminationapplicationsor for attractingattention, though, e.g. aswarningindicators.SomeveryhighbrightnessLEDs canlight upanentireroom, andcareneedstobetakennottolookdirectlyattheseastheycandamagetheeyes. For moreinformationonhowtouseLEDs, refertoSection10.2.SpeakersandbuzzersMicrocontrollerscanbeprogrammedtoproducemusicalnotesandtheycanplaytunes.Their abilitytoproducesimplesoundsisuseful forcreatingalarmnoises,andforattractingattentionor for providingasimple'click' feedbacktoindicatethatabuttonhasbeenpressed. Somemicrocontrollerscanplaybackmusicfiles(suchasMP3)orcanrecordandplaybackvoicefiles, thusallowingaproducttospeakinformationtotheuser,e.g.inasatnav.Inorder toconvert theelectronicsignalsintosoundwaves, aloudspeakerisneeded.Abuzzer isnot thesameasaloudspeaker. Abuzzerwillproduceatonewhenitreceivespower, but that isall it cando; itcannotmakeothersoundsanditcannotproducemusicor speech. Similarly, aloudspeakerwill notemitatoneifitissimplyconnectedtopower;itcanonlyreproducetheelectrical soundwaveformthatitreceives.So,ifadesignerwishesamicrocontroller toemit soundfromaloudspeakerthenthemicrocontrollerwillneedtobeprogrammedtogenerateasuitablesoundwaveform. Buzzers areusedwhenitisonlyevernecessarytoproducethesamesound,suchasinanalarmsystem. Somebuzzerscanbeextremelyloudandtheseareusuallyknownassirens.Figure 6.23 Avariety of LEDs Figure 6.20 Loudspeaker, buzzer andsiren
74Chapter 7Newandemergingtechnologies CHAPTER7NewandemergingtechnologiesDesignersandmanufacturershaveadaptedandembracednewandemergingtechnologiesintheir designingandmakingactivities. Thepast40yearshaveseenahugeincreaseintheuseof digital systemsindesignandtechnology, andnewscientifictechnologieshaveledtoadvancementsinmaterialsthathavechangedthewayinwhichproductsareproducedandhowtheyfunction. 7.1TheimpactofnewandemergingtechnologiesonproductiontechniquesandsystemsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandthebenefitsandimplicationsofincorporatingnewandemergingtechnologiesintoproductionprocesses, including: ➜economiesofscale➜howdisruptivetechnologiessuchas3Dprintingandroboticsarechangingmanufacturing. Global communicationsystemshavegreatlyincreasedtheflowofdigitalinformationintext,visual andaudioformat. Large, detaileddocumentscanbetransferredinstantlybetweensites, regardlessof distance. Theinternethasenabledonlineresearchopportunities,andallows companiestomakeup-to-datechecksoncompetitorsandassessmarkettrends.Marketing, advertisingandsalesopportunitieshaveincreasedgreatlyasaresultoftheabilitytocommunicatedigitallyonaglobal scale. Thetraditional manufacturingindustryisundergoingadigitaltransformationthathasbeenacceleratedbyarangeof technologies, includingartificiallyintelligentrobots,autonomousdrones, sensorsand3Dprinting. Advancedtechnologies, forexamplenanotechnology,cloudcomputingandtheInternetofThings(IoT)arechangingtheprocesses-reducingmanufacturingproductioncostsandimprovingmanufacturingprecision,speed,efficiencyandflexibility. Scientificdevelopmentsmeanthatmanynewmaterialsandcompositeswithimprovedproperties, suchasinsulation, conductivityandhigherstrength-toweightratios,arenowavailabletodesigners, suchastheuseof, self-healingpolymersandevenbio-materialsthatcanbegrownintoproducts. . Whileall of thesenewandemergingtechnologieshavemanybenefits,therearealsoimplicationsof incorporatingthemintoourproductionprocesses.Advancesinautomationandrobotics, forexample, whileimprovingspeedandefficiency,mayresultinunemployment, withmachinesandsoftwareincreasinglybeingusedtoperformjobstraditionallycompletedbyhumans. Increasinguseofautomationalsohasanimpactontheenvironment andenergyresources. KEYTERMSCloudcomputing: Anetwork of onlineservers that storeandmanage data. Internet of Things (IoT): Where electronic devices connect withintheexistinginternet infrastructure, tosendandreceivedata without humanintervention. Nanotechnology: Technology onamicroscopic scale.
757.1TheimpactofnewandemergingtechnologiesonproductiontechniquesandsystemsEconomiesofscaleEconomies of scalearethecost advantagesthat amanufacturergainsasaresultofthesize, output, or scaleof their production. Traditionally, withlarger-scaleproductionthecostperunitof output tends todecreasebecausefixedcostssuchmachineryarespreadoutovermoreunits of output. Manufacturecanoftenalsobecomemoreefficientandcreatelesswastewithincreasingscale, againleadingtolower costs. Largecompaniesbenefitfrombulkbuyingofmaterials andusingstandardisedparts, andthroughlower-costmarketingandadvertising. Larger manufacturers, for examplecar manufacturersor whitegoodmanufacturers, alsosplitupthe different stages of theproductionprocessandhaveworkersspecialiseinproducingacertainpart. For example, oneworker might becomehighlyspecialisedinthedesignofacarpart; another infittingaparticular component. Thisrequireslesstrainingandcanresultinmore efficient production. Many large companies producecomponentsinlargefactoriesabroadmightcarryoutfinalassembly closer tocustomers. Mass-producingcomponentpartsinChineseorMalaysianplants cancut productioncosts. However, operatingfinal assemblyplantsinplacessuchasthe UnitedKingdomor Germanymight bepreferable, asshippingtheassembledproductis thencheaper, subject tolower dutychargesandsomeconsumersprefertobuyfromacompany withmanufacturingfacilities intheir owncountry. Newtechnologies meanthat manufacturerscanincreasinglyproduceproductsandprototypes insmaller quantities but still benefitingfromreductioninproductioncostsnormally associatedwithhigher levels of production. For example, developmentsincomputer-aideddesign, manufactureandengineering, technologiessuchas3Dprintingandmore flexiblemanufacturingsystemsmeanthat companiescannowdesign, set-upandmanufactureprototypes veryquickly, allowingthemtoproducesmallerbatchesasefficientlyandcheaply as larger productionruns. Thismeanscompaniescanproducebespokeproducts that meet theneeds of individual clientsmuchmoreeasilyandareabletoreacttofashions andtrends. Producingproducts insmaller batchesalsoreducesothercostssuchasthe storage of final assembledproducts. DisruptivetechnologiesThis is howHarvardBusiness School professor ClaytonM. Christensencoinedtheterm'disruptive technology' inhis bestselling1997book: 'Adisruptive technologyis onethat displacesanestablishedtechnologyandshakes uptheindustryor aground-breakingproductthatcreatesacompletelynewindustry.' Disruptive technologies canallowsmaller companiestotakeonlargecompaniesandcreateproducts that changethewayweworkandlive, theyoftencreatenewmarketdemandandthinking. For example, thetechnologythat createdlaptopcomputers, smartphonesandtablets haveallowedpeopletoworkfromhomeandconnectwithothersall overtheworld, they have changedthetraditional officeenvironment. Some examples of disruptivetechnologiesareprovidedbelow(althoughnewdevelopmentsare constantly emergingthat will haveanimpact onmanufacturingmethods). KEYTERMSEconomiesofscale:Thecostadvantagesthatmanufacturersobtainduetothesize,outputorscaleoftheirproduction.
76Chapter 7Newandemergingtechnologies AdditivemanufacturingAdditivemanufacturingisthetermusedtodescribetechnologiesthattranslate3Ddesignsintosolid, physical forms. Softwareisusedto'sliceup'3Ddesignsintoaseriesoflayers,whicharethensent insequencetoarapidprototypingsystem.Theyarethenbuiltuplayerbylayer inanumber of differentways: lStereolithography- al asertracestheshapeofalayerontoabathofliquidresinwhichis cured, thisprocessisrepeatedlayerbylayeruntilafinalobjectiscreated.lLasersintering- t hisworksinasimilarwaytostereolithography.Thelasertracestheshapeontoapowder, whichcouldbeplastic, metalorceramic,thisbecomessolidandtheprocessisrepeatedlayerbylayeruntil theobjectiscompleted.l3Dprinting- ' prints' thermoplasticmaterial (ABSorPLAaremostcommon)layerbylayer tobuildupa3Dshape. Complexshapesoftenrequireanadditionalsupportmaterial tobeprintedtosupporttheobjectwhileitsets. 3Dprintedproductscanbepaintedor electroplatedforahigherqualityfinish. 3Dprintingtechnologyhasdevelopedoverthelast30years.Itstartedoutasarapidprototypingtool, but cannowbeusedtoprintawiderangeofmaterials,includingplastics,paper, ceramics, metals, superalloys, wool andbio-materials, meaningthatitisincreasinglyabletobeusedfor final bespokeproducts. I tislikelythatfurtherdevelopmentsinadditivemanufacturingwill continuetocreatemanynewapplications,whichwillcontinuetohaveasignificant impact ontraditional manufacturingmethods. Figure7.13Dprintingprototypingofproductsinplasticsiscommonplaceinmanufacturing.AdvancedroboticsIndustrial robotsareusedextensivelyinautomotivemanufacturing,welding,materialhandlingandpainting. Newandadvancedroboticswillincreasinglybeusedinprecisionmanufacturingandassembly, andinsemiconductorfabrication.TheInternetofThingsTheInternet of Things(IoT) allowselectronicdevicesconnectedtoeachothertocommunicatewithoneanother over theinternetwithouthumanintervention.Itenablesconnecteddevicestosendandreceivemessagesandnotifications, forexampleitcanbeusedtoalertmanufacturerstoadefect inaproduct or productionrun. TheapplicationofIoTinmanufacturingresultsinreduceddowntimeandfewerproblemsanddefectswiththefinalproducts.
777.1TheimpactofnewandemergingtechnologiesonproductiontechniquesandsystemsVirtual realityVR is beingusedtotest newconcepts inproductsallowingdesignerstoassemblepartsanddesigntoolingina virtual worldbeforefinal manufacture. FordandBAEarealreadyadoptingthis process andits provingtocut costs andincreasesafety. The development of emerginganddisruptivetechnologieshashadmanybenefits: lIncreasedflexibility toproducecomplexproductsthat aremadefrommultiplematerialsandhavemultiplefunctions. lUse of digital modellingandsimulationtoolstoevaluateandplanmanufacturingprocesses has reducedtimetomarket andcosts. lImprovedproductivityandqualitylSustainablemanufactureas aresult of improveduseof material resourcesandreducedenergy consumption. Maker movementRecent advances indigital design, engineeringandsimulationarealreadymakingahugedifference tomanufacturingenterprises andsmall businesses. Affordable3Dprinters, scanners andCADsoftwarehavemadeit possiblefor peopletodesignandmakehigh-techproducts at home, enablingamaker movement. Peoplearethenabletosharetheirideasonthe internet, as well as distributingtheir (oftenuniqueandcustomisable)itemswithoutinvolving'middlemen', its leadtothecreationof manymaker communities. lThe websiteEtsy nowhas over onemillionsellerswhohavecreatedproductstobesoldonthe site. lOther start-upcompanies likeKickstarter andQuirkyallowmakerstoaccessresourcesandfundingthat canhelpturnanideaintoareal lifeproduct. l'Makerspaces' suchas FabLabintheUKarebecomingmorecommonplace. lThousands of peopleattendMaker Faireeachyear, whichtakesplaceinmanycitiesworldwide. Agoodexampleof themaker movement isthePebblesmartwatch: itbeganasaprototypeproducedina bedroom, andraisedover $10milliononKickstarterbeforeitwaslaunchedcommercially. Thedevelopment of thePebblesmart watchledtoincreasedinterestandleadtoresearchanddevelopments inwearabletechnologybylargemanufacturerssuchasSamsung, GoogleandApple. Another exampleis whentheBritishAtlasVrocket launchedin2015: astronaut TimPeakeuploadedcodefromsmall computers designedtoenhancespacecraft sensors, satellite imaging, spacemeasurements, datafusionandmeasurement of spaceradiation. Thesecomputerscost just a fewdollars eachandthecodewas writtenbyschool childrenintheUKas part of theAstroPi project. Further developments intechnologyarelikelytoseethe maker movement developevenfurther intheyearstocome. STRETCHANDCHALLENGEUsing twodifferent materials fromyour material area, describe howrapidprototypinganddisruptivetechnologies have beenusedinthedevelopment of products. Figure7.2APebblesmartwatchFigure7.3ThemakermovementFabLabspaceandMakerFaireUK
78Chapter 7Newandemergingtechnologies PRACTICEQUESTIONS:CoreTechnicalPrinciples1Identifytheprimaryusersandwiderstakeholdersforthefollowingproducts:- Achildren'stricycle- Abicyclealarm- Apair of runningshoes2What issueswouldadesignerneedtoconsiderwhendesigningforaglobalmarket?3Discusstheimpactof emergingtechnologiesonproductdevelopment.Useexamplestosupportyourdiscussion. 4DescribehowdesignerscanusetheSixRstodesignsustainableproducts.Useexamplestosupportyourdiscussion. 5Giveoneexampleof aproductthatuseseachofthefollowingtypesofmotion:- Linear - Reciprocating- Rotary- Oscillating6Givethreebenefitstoadesignerofusingamicrocontrollerinelectronicproduct design. 7Identifyanddescribeapplicationsfor: - Threetypesof inputsensor- Threetypesof outputdevice. 8Thefigurebelowshowstwopairsofsunglasses. aExplainonewaythatfashionandsocialtrendshaveinfluencedandaffectedthedesignof sunglasses. bStatetwopiecesof anthropometricdatathatwouldneedtobeconsideredwhendesigningsunglasses. cManyproductstodayaredesignedina'retro'style.Explainwhatismeantbytheterm'retro'.
797.1Theimpactofnewandemergingtechnologiesonproductiontechniquesandsystems9This figureshows aDigital VideoDisc(DVD). DVDs may soonbecomeobsolete. aExplainwhat is meant bytheterm'obsolescence' andwhyproductsbecomeobsolete. bWhat impact does obsolescencehaveontheenvironment?c This figureshows thelifecycleof aDVD. Fill inthemissingstagestocompletethediagram. 10This figureshows asandwichboard, usedtoadvertiseoutsideshopsandcafés. Thesidelegs aremadefromahardwoodtimber. aNameahardwoodtimber that couldbeusedforthesidelegbThemainboardis madefromamanmadefromamanufacturedboard. Nameamanufacturedboardthat couldbeusedforthemainboard. c Givetwoproperties of manufacturedboardsthatmakethemsuitablefor themainboard.
fl ffi fl fl
81In-depthprinciplesofdesignandtechnologyThis sectionlooks at thein-depthprinciplesof designandtechnologythatyoumustknowaboutandunderstandinordertomake informeddecisions as adesigner. All students needknowledgeandunderstandingof theprinciplesconsideredinthissectioninrelationtoatleastonematerial category or system. Youshouldrefer tothechapter(s) thatis/arerelevanttoyourchosenmaterial(s).The sectionexplores thefollowingquestionsoutlinedintheOCRspecification: 5.1What arethemaincategories of materialsavailabletodesignerswhendevelopingdesignsolutions?5.2What factors areimportant toconsider whenselectingmaterialsand/orsystemcomponentswhendesigning?5.3Why is it important tounderstandthesourcesor originsof materialsand/orsystemcomponents?5.4Why is it important toknowthedifferent availableformsof specificmaterialsand/orsystemscomponents?6.1What gives a product structural integrity?6.2Howcanmaterials andproducts befinishedfor differentpurposes?7.1Howcanmaterials andprocesses beusedtomakeiterativemodels?7.2Howcanmaterials bemanipulatedandjoinedindifferentwaysinaworkshopenvironmentwhenmakingfinal prototypes? 7.3Howdodesigners andmanufacturersensureaccuracywhenmakingprototypesandproducts?7.4Howdoindustry professionals usedigital designtoolswhenexploringanddevelopingdesignideas?7.5Howdoprocesses varywhenmanufacturingproductstodifferentscalesofproduction?8.1Howcancost andavailabilityof specificmaterialsand/or systemcomponentsaffecttheirselectionwhendesigning?These questions areconsideredinthefollowingchapters: Chapter 8PapersandboardsChapter 9Timber Chapter 10MetalsChapter 11PolymersChapter 12FibresandfabricsChapter 13Designengineering
82Chapter 8Papers andboards CHAPTER8PapersandboardsYoulearnt about thedifferenttypesofpapersandboardsinSection5.1.Thischapterincludesmorein-depthinformationonpaperandboards. LEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandthephysicalandworkingpropertiesofarangeofpapersandboards,including:➜howeasytheyaretoworkwith➜howwell theyfulfil therequiredfunctionsofproductsindifferentcontexts.8.1PhysicalandworkingpropertiesPaperPaper is athinbut extremelyversatilematerial thatiseasytoworkwith.Itisavailableinmanydifferent types, sizes, finishesandweights. VirginfibrepaperPaper is madefromwoodfibrescalledcellulose. Chemicalsareusedtobreakdownorpulpthefibresbyremovingthelignin, whichisthenatural'glue'thatholdsthemtogether.Further chemicalscanbeaddedthatbleachorcolourthepaperandgiveitaspecialtexture.Thepulpisthensprayedoutinthinlayersontofinemesh, andcompressedanddriedoutbyrunningit throughheatedrollers. Papermadefrom'new'woodfibresiscalledvirginfibrepaper. RecycledpaperBecauseof theenvironmental impactofmakingvirginfibrepaperitisnowbecomingmoreexpensive, andconsequentlyrecycledpaperisnowextremelycommon.Recycledpaperismadebysoakingandmixingwastepaperinwatertoseparatethefibresbackintopulp.Thepulpis thenrefinedtoremoveanyunwantedcontaminantssuchasstaples,plastic,etc.,thatmayhavebeenmixedinwiththewastepaper, thensprayedandcompressedinthesamewayas virginfibrepaper. PapertypesLayoutpaperLayout paper isusuallysoldinA4-andA3-sizepadsforsketchinganddevelopingdesignideas. It hasasmoothsurfaceforbothpencil andpenwork. Theweightoflayoutpaperisaround50gsm, whichmakesitthinenoughtousetotraceandcopypartsofdesignswhendevelopingideas. Becauseof itslightweightithasalowrelativecost.CopierpaperCopier paper isusuallysoldinA3-andA4-sized'reams'-areamisapackof500sheets.Ithasaweight of approximately80gsmandasmoothsurface, makingitidealformostprintersaswell as for photocopying. KEYTERMSCellulose: Woodfibres; anorganic compound, structuraly important inplant life. Recycledpaper: Paper made fromusedpaper products. Virginfibrepaper: Paper made from'new', unusedwoodfibres.
838.1PhysicalandworkingpropertiesCartridgepaperCartridge paper is availableindifferent weightsbetween80and140gsm, andisthickerandmore expensivethanlayout or copier paper. It hasaslightlytexturedsurfaceandiscreamierincolour. Cartridgepaper is usedfor sketching, drawingandpaintingasitisanideal surfacefor pencil, crayon, pastels, watercolour paints, inksandgouache. Becauseofthisitisoftenusedby artists. Bleedproof paperBleedproof paper is availableinsimilar thicknessestocartridgepaperbutissmoothandbleachedbright white. Bleedproof paper isideal for drawingandsketchingusingmarkerpens as it stops thecolours of themarker pensbleedingintothepaperandmixingtogetheror blurringtheedges of lines. Sugar paperSugar paper is usually soldinlarger sheet sizesfromA2upwards(seeSection5.3), andcomesina wide variety of different colours. It is usuallymadefromrecycledpaperandisaround100gsminweight. It is relativelyinexpensiveandiscommonlyusedforthemountinganddisplayingof work onnoticeboards andwallsrather thanfor drawingdirectlyonto. Table 8.1 The properties, characteristics andusesof commonpapertypesCommon name Weight (gsm) Properties/workingcharacteristicsUsesLayout paper 50 Bright white, smooth, lightweight (thin) soslightly transparent andinexpensiveSketchinganddevelopingdesignideas; tracingpartsof designsCopier paper 80 Bright white, smooth, mediumweight, widely availablePrintingandphotocopyingCartridge paper 80-1 40 Texturedsurfacewithcreamycolour Drawingwithpencil,crayon, pastels, watercolourpaints,inksandgouacheBleedproof paper 80-1 40 Bright white, smoothsurface, stopsmarker 'bleed' DrawingwithmarkerpensSugar paper 100 Availableinwiderangeof colours, inexpensive, roughsurfaceMountinganddisplayworkBoardsCardCardis slightly thicker thanpaper andaround180 to300gsminweight. Likepaper it is availableina wide rangeof colours, sizes andfinishes, includingmetallic andholographicfinishes. Thincardis easy tofold, cut andprint onto, whichmakes it ideal for greetings cards, paperbackbookcovers andsoon, as well as for simplemodelling. Figure8.1Greetingscardsaremadeofcard
84Chapter 8Papers andboards CardboardCardboardisavailableinmanydifferentsizesandsurfacefinishes, withthicknessfromaround300micronsupwards.Cardboardiswidelyusedforthepackagingofmanydifferentproducts-forexampleitisusedforcerealboxes,tissueboxes, sandwichpacketsandsoon-becauseitisrelativelyinexpensiveandcanbecut, foldedandprintedontoeasily.Cardboardcanbeusedtomodeldesignideasandisoftenusedtomaketemplatesforpartsandpiecesofproducts,whichoncecorrectcanthenbemadefrommetalorothermaterials.CorrugatedcardboardCorrugatedcardboardisastrongbutlightweighttypeof cardthatismadefromtwolayersofcardwithanother,flutedsheetinbetween. Itisavailableinthicknessesrangingfrom3mm(3000microns)upwards.Theflutedconstructionmakesitverystiffanddifficulttobendorfold, especiallywhenfoldingacrosstheflutes.Becauseofthespacesbetweenthetwolayerscreatedbytheflutedsheet, corrugatedcardcanabsorbknocksandbumps.Thismakesitideal forpackagingfragileordelicateitemsthatneedprotectionduringtransportation.Itisalsowidelyusedaspackagingfortakeawayfoods,suchaspizzaboxes,astheflutedconstructiongivesitgoodheat-insulatingpropertiescomparedtonormalcardboard.Doublewall corrugatedcardisalsoavailable,whichistwiceasthickascorrugatedcardandgivesextrastrengthanddamageresistance. BoardsheetsMountingboardisarigidtypeofcardwithathicknessof around1.4mm(1400microns)andasmoothsurface.Itisavailableindifferentcolours,butwhiteandblackarethemostcommonlyavailableandmostusedcolours.Mountingboardisoftenusedforpictureframingmountsandarchitecturalmodelling.Figure 8.2 CardboardpackagingFigure 8.3 CorrugatedcardboardpackagingTable 8.2 The properties, characteristicsandusesof commonboardtypesCommon name Thickness (microns) Properties/workingcharacteristicsUsesCard 180- 300Availableinawiderangeof colours, sizes andfinishes; easytofold, cutandprint ontoGreetingscards,paperbackbookcovers,etc.,aswellassimplemodellingCardboard300upwards Availableinawiderangeof sizesandfinishes; easytofold, cut andprintontoGeneralretailpackagingsuchasfood,toys,etc.;designmodellingCorrugatedcardboard3000upwards Lightweight yet strong; difficulttofold;goodheat insulator Pizzaboxes,shoeboxes,largerproductpackaging,e.g.electricalgoodsMountingboard1400Smooth; rigid; goodfade-resistanceBordersandmountsforpictureframesKEYTERMSLightweight:Weighsverylittle.Rigid:Difficulttobend.
858.1PhysicalandworkingpropertiesLaminatedlayersFoamboardFoamboardis a lightweight boardthat is madeupof polystyrenefoamsandwichedbetweentwopieces of thincardor paper. It hasasmoothsurfaceandisavailableinarangeof colours, sheet sizes andthicknesses, with5mm(5000microns) beingthemostcommon. Foamboardis a very lightweight but rigidmaterial andisideal formodellingandpoint-of-sale displays. It is easy tocut andcaneasilybefoldedwiththecorrecttechnique. StyrofoamStyrofoamis a tradenamefor atypeof expandedpolystyrenefoam. Itisavailableinawiderange of sizes andthicknesses, andcanbeidentifiedbyitsbluecolour. Styrofoamhasastructure of uniformly small, closedcells that makeit easytocut, shapeandsandtoasmoothfinish. Styrofoamis strongandlightweight, aswell asbeingwater-resistantandhavinggoodheat-insulationproperties. It is usedas awall insulationmaterial incaravans, boatsandlorries, but it is alsoideal for creatingthree-dimensional modelsandmouldsforvacuumformedorglass fibre products. CorrifluteCorriflute is anextrudedcorrugatedpolymer sheet similar instructureandthicknesstocorrugatedcardboard. It is madefromahigh-impact polypropyleneresinandisavailableina wide rangeof colours andsheet sizes. Corrifluteisrigidandlightweightaswell asbeingextremely waterproof. It is easytocut but canbedifficult tofold, especiallyacrosstheflutes. Corriflute is oftenusedfor outsidesigns suchasestateagents' signsonhouses, andsignsoutside car forecourts or shops. It is alsousedfor containers, packagingandpoint-of-saledisplays andfor modellingpurposes. PVCfoamsheetPVCfoamsheet is a lightweight material andhasgoodinsulationproperties, similartoStyrofoam, but is morerobust andcanbeprintedontoeasily. PVCfoamsheetisavailableina range of different colours andis easytocut andjointoothermaterials. Itisresistanttowater andmany chemicals sois oftenusedfor outdoor displaysandsigns. Table 8.3 The properties, characteristics andusesof commonlaminatedlayersCommon name Properties/workingcharacteristicsUsesFoamboardSmooth, rigid, very lightweight andeasyto cut Point-of-saledisplays, ceiling-hungsignsinsupermarkets, architectural modellingStyrofoamLight blue colour, easy tocut, sandandshape, water-resistant, goodheat andsound insulator 3Dmouldsfor vacuumformingandGRP,wall insulationincaravans, boats,etc.Corriflute Wide range of colours, waterproof, easyto cut, rigid, lightweight Outdoor signs, packagingandmodellingPVC foamsheet Lightweight, goodinsulationproperties, easy to print on, water-resistant Outsidedisplaysandsigns
86Chapter 8Papers andboards STRETCHANDCHALLENGEMatcheachproduct withthemostsuitablematerial.CorrugatedcardboardMountingboardCorrifluteFoamboardBleedproof paper 'Houseforsale' signEnvelopeforaletterPictureframeborderIndoorhandingsignTakeawaypizzabox8.2SourcesandoriginsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜thesourcesandoriginsofpaper,boardsandlaminatedboards➜theprocessesusedtoextractpaperandboardintoauseableform➜theecological, social andethical issuesassociatedwithprocessingpaperandboard➜thelifecycleofpapersandboards➜recycling, reuseanddisposal ofpaperandboard.SourcesPaper wasfirst inventedinChinaaroundad100. Thefirstpaperwasmadefromfibresoftreebarkmixedinwater. Thismixture, knownaspulp, wasthendrainedandspreadoutonabamboo-framedmattingbeforebeingpresseddownintoathinlayeranddriedoutinthesun. It was later discoveredthatlignin, whichisthenaturalgluethatholdsthewood'sfibrestogether, couldbebrokendownmoreeasilyifplantswithlongcellulosefibreswereused. Thismeant thefibrescouldbemadeintoafinerpulp, whichinturnmadebetterqualitypaper. Thepaper-makingprocessThemethodsusedtomakepapertodayareessentiallythesameorverysimilartotheoriginal method, but mechanical methodsarenowusedtoseparatethewoodfibres.
878.2SourcesandoriginsThemechanical pulpingprocessUsinglarge tanks knownas pulpers, therawwoodchippingsaresoakedinuptoahundredtimes their weight of water andthenpulverisedwithlargesteel rotorblades. Thefinishedpulpis thenpumpedintoapaper machine, whereit issprayedontolargesheetsofthinmeshandpressedthroughaseries of rollersintopaper. Figure 8.4 The mechanical pulpingprocess Mechanically pulpedpaper is suitablefor paper productsthatuse'bulk' gradesofpapersuchas newspaper andtoilet tissue. Becauseof thedamagedonetothefibresinthegrindingprocess, however, it has alowstrength. It will tear relativelyeasilyanddisintegratequickly whenwet. Themechanical processalsomeansthatalargeamountofligninremainsinthe pulpmixture, whichcanleadtothepaper yellowingovertimeorwhenexposedtobright light. Thechemical pulpingprocessThe chemical pulpingprocess uses chemicalssuchascausticsodaandsodiumsulphatetohelpbreak downthewoodpieces andchemicallyremovethelignin, ratherthanremovingit by mechanical grinding. This separates thefibreswithoutdamagingthemandcreatesa muchstronger pulp. Other fibres suchascottonandlinenarethenaddedtothepulpmixture toimproveor changethetexture, andthisiscalledblending. Chemicalssuchasbleachingagents, dyes andfillers arethenalsoaddedtogivethepaperaspecificcolourorproperty. Thepulpis thendried, pressedandformedintorollsof paperinthesamewayasbefore. Chemically pulpedpaper is generallyof amuchhigherqualitythanmechanicallypulpedpaper, andcanbebleachedor colouredtoamuchbrighterfinish. Specialistcoatingscanalsobe addedtothepaper onceit hasbeenformedintosheets, suchasglossyorshinyfinishes (seeSection5.5). Figure 8.5 The chemical pulpingprocess RecycledpaperBecause themainingredient of paper is wood, it requiresalargenumberoftreestomakeit. It takes aroundtwelvematuretrees tomakeonetonneof newspaper, andaroundtwentyfour trees tomakeonetonneof copier paper. Recycledpaper wascreatedtoreducethenumber of trees neededtomakepaper andthereforetolessentheenvironmental impactofpaper production. Usingrecycledpaper insteadof virginwoodmeansthatfewertreesareneededtomakethesameamount of paper. Paper cannot berecycledindefinitelyas thefibresget shorter andweakereverytimetheyare recycled. After aroundfiveor sixtimes, thefibresusuallybecometooshortandweaktobe of useandwill not pulpadequately. TomaintainthequalityandstrengthofrecycledPressedthroughheatedrollerstoflattenanddryTimber fromtrees is de-barked and chipped intosmall pieces Woodpieces aresoakedinwater andchopped/groundintofibres, makingpulpPulpisdrainedandsprayedontothinlywovenmeshBleachingagents, dyesand/or fillersaddedTimber fromtrees is de-barked and chipped into small pieces Woodpieces are brokendownincaustic soda andsodiumsulphate to remove ligninandseparate fibres, makingpulpBlending- other fibres suchas cottonandlinenareaddedtothepulpmixtureWashedandrefinedtoremovecontaminantsFormedandprocessedinpapermachineCoatingsaddedifnecessary
88Chapter 8Papers andboards paper, manymanufacturersuseamixtureofrecycledpaperandnewvirginwoodchippingstomakethepulp. Theratioisusuallybetween55and80percentrecycledpaperandbetween20and45per centvirginwoodchippings, dependingonthetypeofpulpingprocess used. Thiscutsdownthenumberoftreesneededbyabout60to80percent.Table8.4ThepercentagesofrecycledandvirginpaperinmechanicalandchemicalpulpingPulpingprocessPercentagerecycledpaperPercentagevirginMechanical pulping55%45%Chemical pulping77%23%CardCardboardismadeinanumberof differentways. Onemethodisbysandwichingandpastingmultiplelayersof papertogethertomakeathickerpaper.Anothermethodistopress thelayersof wet pulpusedformakingpapertogetherintoathickerlayer.Bylayeringsheets of paper or pulptogether, cardofvariousthicknessescanbeproduced.CorrugatedcardCorrugatedcardwasfirstproducedinthe1850s. Itwasoriginallyusedaspackagingforproductstobeshipped, toprotectthemfromdamage. Duetothethickerandmorecushionedconstructionof thecardboard, itquicklyreplacednormalthickcard.Itsrigidyetlightweight propertiesalsomadeitideal forcardboardboxes.Corrugatedcardboardismadebypassingpaper throughacorrugationmachine, whichhasthreelayers.Thecentrelayeris treatedwithhighpressuresteamtoheat-softenthefibres. Thepaperispressedintotherequiredthicknessandshapebycrimpingittogiveitawavyshape.Thetwoouterlayersofpaper arethengluedoneachsideof thewavycentrelayer. Afterthecorrugatorhasheated,gluedandpressedthepapertogethertoformthecorrugatedcardboard,itiscutintolargepieces or 'blanks', whichthengotoothermachinesforprinting,cuttingandgluingtogether.Double-wall corrugatedcardismadeinthesamewaybuthasanadditionalwavyandflatlayer addedtomakeit evenmorerigidandgiveextraprotection.Figure8.6Atypical corrugatorisaround90metreslong-roughlythelengthofafootballfield
90Chapter 8Papers andboards It is estimatedthat everyadultmaleintheUKgeneratesaroundonetonneofwasteeachyear. Around40per centof thisiswastepaper. Theecological, social andethical issuesassociatedwithprocessingthePolymerelementsinlaminatedlayerssuchasfoamboard, Styrofoam, PVCfoamandCorriflutearecoveredinSection2.1. LifecyclePaper andcardboarddonotstayintheenvironmentforalongtimeaftertheyarediscarded.Becauseof their fibrousconstructionandsusceptibilitytomoisturetheydecomposequicklycomparedtoall other materials. Paperproductstakeonlytwotofourweekstodecompose,andcardboardaroundtwomonths. Laminatedlayers, however,takemuchlongertodecomposeastheycontainpolymers, whichcanresistchemicalattacks.StyrofoamcantakearoundfiftyyearstodecomposeandPVCcantakeupto500years.Also,becausepaperandcardboardaremadealmostentirelyofnatural materials(wood)theydonotreleaseanyharmfulchemicalsduringdecomposition. Meanwhile, laminatedlayersthatcontainStyrofoamorPVCcanreleasetoxicchemicals. Today, themajorityof paper andcardboardproductsweusearerecycled.Currentlyaround70per cent of paper worldwideisrecycledbackintonewpaper.Paperfibrescanberecycledonlyacertainnumber of times, however, soeventuallytheyreachtheendoftheirusefullifeandthenareoftenburnedasafuel sourceinsteadofbeinglefttodecompose.Althoughpaper isbyfar themost commonlyrecycledmaterialandaccountsformorethanhalfofall recycledmaterials, somepapersandcardscannotberecycledandthesedoendupinlandfill. Foodpackagingisthemostcommontypeofpaperandcardthatisnotrecycled.Thisisbecauseit isoftencontaminatedbygrease, oil andotherliquidsthatareabsorbedintothefibres of thepaper. Whenthisoccurs, thepapercannotberecycledasthefibrescannotbeseparatedfromthegreaseandoils, whichgetintothepulpmixtureduringtherecyclingprocess. Later intheprocess, theoil separatesandcausesproblemswithbleachingandwashingthepaper. Whenthewaterissqueezedoutofthepulpasthesheetsofpapergothroughthepaper machine, theoil residuecreatesdarkmarksandholesthatmakethepaper verylowqualityor insomecasesunsuitableforanyuse.Figure 8.8 Pizza boxes areaclassic exampleof howgreasecancontaminatepaperand card. Oil fromthecheeseandgreasefromthemeatrundownintothecardboardmeaningit cannot berecycled. IntheUK, approximatelyonemillionpizzasaredeliveredin corrugatedcardboardboxes everyday. Figure8.9Compostingbinscanbeboughtforafewpoundsatmostgardencentres,hardwareshopsorDIYoutlets.
918.3CommonlyavailableformsIncases wherepaper or cardcannot berecycled, theydonotneedtogointolandfill. Analternative is for themtobecompostedusingacompostingbin. Food-soakedpaperandcardboardcanbecompostedwithnoill effects. Compostingisanatural processthatnotonly reduces theamount of paper put intolandfill but alsobenefitstheenvironmentbycreatingnewsoil that is richinminerals. Compostingoccurs whentwodifferent typesof ingredients-called'greens' and'browns'-are mixedtogether. lBrowningredients areitems suchas cardboard, paper, small twigs, eggshells, itemsmadefromwood, etc. lGreeningredients arethings suchas grasscuttings, vegetablepeelings, leaves, oldflowers or plants, teabags, etc. Greeningredients rot quickly, releasingimportant nitrogenandprovidingmoisture. Browningredients rot moreslowly, addingfibreandcarbontothemixtureandallowingairpocketstoform, whicharenecessaryfor compostingtooccur. LaminatedboardsLaminatedboards suchas Styrofoam, PVCfoamandCorriflutearemuchhardertorecyclebecause they aremadeof polymers that needtobesorted, cleanedandchippedbeforebeingmelteddownintouseablegranules. Therecyclingprocesscanalsouselotsofenergy, whichdoes further environmental damage. Foamboardhastwooutersofpaperthatneedtobe separatedfromthefoamcorebeforeit canberecycled, whichcanbeadifficultandtime-consumingprocess. For this reasonfoamboardusuallyendsupinlandfill. For more informationonthelifecycleandrecyclingof polymers, seeSection8.2. STRETCHANDCHALLENGEUse the internet tofindout what percentageof wasteisrecycledinyourarea.Youcanfindthis informationonyour local council website. 8.3CommonlyavailableformsLEARNINGOUTCOMESBy theendof this sectionyoushouldknowaboutandunderstand:➜that paper andboards areavailableinarangeofstockforms➜therelationshipbetweeneachsize➜themost commonsheet sizes andtheir uses. PaperandboardsizesPaper andboards areavailableinstandard-sizedsheetsrangingfromA10, whichisapproximately thesizeof apostagestamp, throughto4A0, whichislargerthanakingsizebedsheet. Themost commonsizes usedbydesignersarebetweenA6andA0. Table 8.5 Each sheet sizeis twicethesizeof theonebefore, e.g. A3istwicethesizeofA4Size A10A9A8A7A6A5A4A3A2A1A02A04A0Length (mm) 37 5274105148210297420594841118916822378Width (mm) 26 37527410514821029742059484111891682
92Chapter 8Papers andboards 297 mm210 mmA4A3297mm420mm594mm420mmA2A1594mm840mmFigure 8.10 The dimensions of A4andA3Figure8.11A1andA2sheetsIf youfoldasheet of paper inhalf itthenbecomesthenextsizebelow-forexample,anA1sheet foldedinhalf becomesA2size. LaminatedboardsizesFoamboardLikepaper andcardboard, foamboardisavailableinstandardsheetsizesrangingfromA4toA0. Manysuppliersalsostockstandardimperial sizesupto84ft(24401220mm),whichis astandardcommercial sizeformanyothermaterialssuchasMDF,plywood,plasterboard,andsoon. Foamboardisavailableinthicknessesof3mm, 5mmor10mm.Thestandardcoloursavailablearewhite, blackor black/grey(onesideblack, onesidegrey).CorrifluteCorrifluteisavailableinarangeof sizes, buttypicalsheetsizesare:l450600mml600900mml9001200mmIt is alsoavailablefromspecialistsuppliersinstandardimperialsizes:l84ft (24401220mm) l86ft (24401830mm) Corrifluteisavailableinthicknessesof2mmto10mmandcomesinarangeofdifferentcolours. PVCfoamPVCfoamisavailableinstandardpapersizesandlargersizes,typically:l104ft (30501220mm) l105ft (30501530mm) l107ft (30502030mm) It is availableinthicknessesof 1mm, 2mm, 3mm, 4mm, 5mm,6mm,8mm,10mm,13mm,15mm, 19mmand25mmandinawiderangeofstandardandspecialdesignercolourswithgloss or matt finishes.
918.13CooCmnlyayvnyinbeCforI ncasaew' ' ' l➜➜Lami ntedi tborros8t. a. i 3troi rtCs tedi tl oa83abtmi nCyvSTUsethhhhiiSRUnrtoUsiiSEhhhhtofdiiSChhhhtnosi iSHnost efni i SAef nthhhhi i S Nr nUt UUr f i i I nehr ecr pawoahdhntTabl aee8.55TEcl5hs58et5icezcew5
94Chapter 8Papers andboards 8.4ManipulatingandjoiningLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜arangeof specialisttechniquesusedtoshape,fabricate,constructandassemblehigh-qualityprototypesusingpaperandboardinaworkshop.MarkingoutBeforeadesigncanbecut, itmustbemarkedout. Pencilorpencanbeusedtomarkoutonpaper, cardandfoamboard. Styrofoam, CorrifluteandPVCfoamcanbemarkedwithathinpermanent marker, thoughthiscanleaveamarkonthematerial.Achinagraphpencilornon-permanent marker canalsobeused, butthelinescanbesmudgedeasily.CuttingScissors andcraft knivesarethemostobviousandbestchoicesforcuttingpaperandcard.Foamboard, PVCfoamandCorriflutecanalsobecutusingacraftknife.Styrofoamcanbecut usingacraft knife, butonlyuptoathicknessofaround10mm.ThickerStyrofoamcanbecut usingaserrated-edgedknife(suchasabreadknife), bandsaw,hacksawbladeorhotwirecutter. Final shapingcanbedonebysandingandsmoothingwithabrasivepaper.Alaser cutter canbeusedtocutany2Dshapeoutofcard, PVCfoam,foamboardorCorriflute.FoldingPaper andthincardcanbefoldedeasilybyhand. Scoringthematerialfirstusingabluntknifebladeor other dull pointedobjectwill helpfoldthickercardandensureaclean,sharpcrease.Foamboardcanbefoldedbycuttingthroughthefoaminoneoftwoways:lHingecuttingiswherethefoamboardiscutpartwaythroughsothatthebottomlayerof cardactsasahinge, allowingthecardtobefoldedbackwards.lVeecuttingiswherea'V'-shapedcutismadeinthefoamboardandthematerialremoved. Thisallowsthefoamboardtobefoldedinwardsandgivesaclean,tidyfold.PVCfoamcannot befoldedunlessitiscutpartwaythroughinasimilarwaytofoamboard.Similarly, Corrifluteisnot easilyfoldedbutcanbedonebycuttingasectionofmaterialawayfromthetoplayer betweentheflutes, allowingthematerialtobefoldedbackwards.JoiningAs withall materialsthereareseveral permanentandtemporarywaysofjoiningpaperandboardtogether. AdhesivesThereis arangeof differentadhesivesavailableforpapersandboards.Differentgluesaresuitablefor different productsandpurposes. PaperandthincardGluesticksareaneasy, clean, safemethodofgluingpapertogether.Theyareidealforyoungchildrenandarefairlylong-lasting. Theycreateabondthatisonlystrongenoughfor paper andverythincardbutthiscanweakenandunstickovertime.Spraymount(sprayadhesive) comesinanaerosol canandisaquickwaytomountdrawingsontobackingpaper. It iscommonlyusedtomountphotographs. Sprayadhesivegivesathinevencoatthat driesquickly.