1459.7FinishesVarnishesandlacquersVarnishes andlacquers areavailableas oil-, water- andsolvent-based. Varnishesarenormallyclear or transparent andareofferedinsatin, mattor glossfinishes. Spraycansaresuitablefor small projects andtherearespecial typesavailablefor coatingmetals. Oil Teak andcomparabletimbers arenaturallyoily. Applyingteakorlinseedoil providesanimprovedappearancewithinthegrainof thetimber. Thisprotectsthewoodverywellforexternal use. Vegetableoil canalsobeappliedtowoodthatcomesincontactwithfoods, forinstance a spatula or saladserver. FrenchpolishFrenchpolishis a traditional finish, whichisaccomplishedbymixingshellacinmethylatedspirits. Frenchpolishis appliedbybrushandclothandthefinishisbuiltupinseverallayers, whichaccomplishes averydeepfinish. WaxisthenappliedovertheFrenchpolishtoimprove theshine. WoodstainsWoodstains areusedtoimprovethecolour of woodandtheyalsohelptoshowupthegrain. Woodstains areappliedusingacloth. Theyareavailableinnumerouscoloursbutworkwell only if thestainis actuallydarker thanthecolour of thewood. Woodstain, ifusedonitsown, only colours thewoodandsodoes not protect it againstmoisture. Acoatingofwaxorvarnishover thewoodstainis requiredtomakeit weatherproof. Stainsareavailableinwater-or solvent-basedforms. SandingsealerSandingsealer is normallyasolvent-basedproduct likevarnish, whichisusedtoseal thewoodtomoisture. Sandingsealer is aquick-dryingliquidthatsealsthesurfaceandraisesthe woodfibres sothey canbesandedwithfineglasspaper. Sandingsealerisgoodforafirstcoat before applyingvarnishor wax. Paint Timber items canbepaintedwithwater- or oil-basedenamel paints, chalkboardpaint, spraypaint andacrylicpaint. Different types of paints producedifferent effectsonwood. lEnamel paints arepermanent paintsthat createahard, glossy surfacethat is durableandhardtochip. Enamel paints work well onwoodfurnitureandother hardsurfaces, suchas glass or tile. Enamel paint colours donot blendwell. lSpraypaint refers as muchtothemethodof applyingthepaint as tothepaint itself. Paint sprayedfromanaerosol canis typicallyusedonwoodenfurniturefor applicationonareas that brushescan't reacheasily. It is averyfast methodof applyingpaint. lAcrylic paint is easytouseonwoodandcreatesdeep, saturatedcolours. Often, acrylicpaint doesnot needa secondcoat whenappliedtowood. Figure9.65AselectionoffinishesfortimberKEYTERMSGloss:Ashiny,reflectivesurfacefinish.Matt:Adull,nonreflectivesurfacefinish.Satin:Anin-betweenglossandmattfinish.KEYPOINTThink carefully about theenvironment your product will beusedinandtheexternal factorsit will come intocontact withwhenyouselect anappropriatefinish.
146Chapter 9Timber ACTIVITY1 Cut three different pieces of timber intolongstrips. 2 Place pieces of maskingtapetodividethestripsintoareas. 3Applyadifferentfinishtoeachoftheexposedareasandrecordtheresults-howdoesitaffectthelookandfeel ofthetimber?Howwater-repellentiseachfinish?WaxVarnishOilStainPaint
1479.8Usingdigitaldesigntools9.8UsingdigitaldesigntoolsLEARNINGOUTCOMESBy theendof this sectionyoushouldknowaboutandunderstand:➜theuseof 2Dand3Ddigital technologyandtoolstopresent,model,designandmanufacturesolutions. There has recently beenatrendof hugegrowthintimber furnitureproduction, whichresultsinshorter designandproductiontechniques, andmost furnitureisbecomingincreasinglycomplex. As a result, consumers arespendingincreasingamountsonexclusivefurniture. It is a bigchallengetodesignsuchcomplexfurnitureandtofindhowtodoitthequickestway possible. CAD/CAMthat is aimedspecificallyat designingandmakingproductsoutoftimber canhelpwiththis. Computer-aideddesignVarious softwareapplications areusedwidelyindesignandtechnologytocreateandexplore ideas, fromsimple2Dsketchingprogramsthat helpdesignersquicklyvisualiseideas, toadvanced3Dmodellingsoftwarethat allowsthemtocreatefullyrealisedproducts. Add-ons for popular CADprograms enabledesignerstoworkonfurnitureandothertimberproducts. Timber materials canbeassignedtopartsinthedesignandawidevarietyofstandardfixings canbeusedtoassembletheproduct inthecomputer. ComputerAidedEngineering(CAE) canbeusedtocalculatestressesandstrainsinthedesignofcomponentsfor timber structures, suchas roof trusses. Figure 9.66 CADbeingusedfor structuredesignKEYTERMSStandardfixings:Itemssuchasnuts,boltsandknock-downfittings.
148Chapter 9Timber Figure 9.67 ACNCrouter Figure9.683Dprinted'wood'CustomlaminateLaminateflooringismanufacturedboard(usuallyMDF)withaprintedwoodeffectandplasticwear layer onthetop. Theprintedpaperlayercanbedigitallyprintedwithanydesign,rangingfromwoodtexturestotileeffects. BendablewoodThinsheet material canbecutonalasercuttertocreateabendablepieceofwood.Theeffect isachievedbymakingthincutsonbothsidesofasinglesheetofwood.Thestartof eachrowof cutsshiftsbyhalf thelengthofthepreviousrow.Theresultcreatesenoughtorsiontoallowthewoodtobendlikeahinge. CNCmachinesAComputer Numerical Control (CNC)routerisacomputer-controlledcuttingmachinerelatedtothehandheldrouterusedforcuttinghardmaterials.Complexshapescanbecutfromsheetsof manufacturedboard, andcertaincarvedeffectscanbeobtainedbymovingthecuttingtool over thework. Morecomplexmulti-axismachinescaneffectivelycarveanyshapeintimber. Other CNCmachinesaredescribedinthenextsection.KEYTERMSFuseddepositionmodelling(FDM): Buildingupa 3Dshape by layingdownmaterial inlayers. 3DprintingArecent development istheuseof finewoodenparticlesfor3Dprinting.Agranularpowder madefromwoodchipscanbefusedtogetherbyalaserusingaprocesscalledlaser sintering. Thesesameparticlescanbeaddedtothepolymerfilamentusedinfuseddepositionmodelling(FDM)printers. Theresultingproductscanbesandedandpaintedlikewood. KEYPOINTCAD/CAMisbeingusedmoreandmoreinthedesignandmanufactureoftimberproducts.Thinkabout howyoucanusecomputerstoexploredesignpossibilitiesandtoenhancethemanufacturingof theproductsyoudesign.STRETCHANDCHALLENGEDescribehowCADandcomputer-aidedmanufacture(CAM)worktogethertoproduceaqualityproduct.
1499.9Manufacturingmethodsandscalesofproduction9.9ManufacturingmethodsandscalesofproductionLEARNINGOUTCOMESBy theendof this sectionyoushouldknowaboutandunderstand:➜themethods usedfor manufacturingtimberproductsatdifferentscalesof production➜manufacturingprocesses usedfor larger scalesofproduction.MethodsformanufacturingtimberproductsatdifferentscalesofproductionManufacturingproducts withtimber andmanufacturedboardcanbedoneatvaryingscales of production. Thehandtools andmachinesdescribedinearliersectionswouldbeusedextensively for one-off products. For small batches, jigsandtemplateswouldbeusedmore inorder toensurequalityandaccuracy. Asthescaleof productionrisestowardslargerbatches andmass production, thelevel of automationandtheuseof specialistmachinerywouldincreaseaccordingly. LeanmanufacturingwithtimberandmanufacturedboardWithother resistant materials suchas plasticandmetal, theoff-cutsandwastecanoftenberecycled. Timber wastecanalsoberecycled, intomanufacturedboardssuchasblockboardandchipboard. Several furniture-makers makeuseof leanmanufacturingtominimisethewastetheyproduce andmakesavings. Onesysteminvolvescataloguingeverypieceofoff-cuttimber/boardandtrackingtheseviacomputer. Theoff-cutsarebarcodedandstoredonshelves. Aswork progresses thecomputer systemidentifieswhether asuitablepieceoftimber/boardisalready availableinthe'spares bin', thus avoidingtheneedtocutintofreshpieces.
150Chapter 9Timber ManufacturingprocessesusedforlargerscalesofproductionJigsandfixturesSomemachineoperationsareperformedeasily. Themachineissetandtheworkcut.Someoperations, however, requirethetool tobeguidedand/ortheworktobeheldinaspecificway. Adevicethat guidesthetool iscalledajigandadevicethatholdstheworkiscalledafixture. StopSawcuts Tube held in place TobeheldinviceFigure 9.69 SawingjigPushesintopositionPushesintopositionDrillAllowsholestobedrilledalonglengthofwoodAllowsholestobedrilledatendofwoodFigure9.70DrillingfixtureTemplatesandpatternsTemplatesareusedtomarkoutawkwardorirregularshapesrepeatedly. Anythin,fairlyrigidmaterialissuitableforatemplate, suchascard.Ifthetemplateisusedconstantlythenamoreresistantmaterialshouldbeused,suchasacrylicorthinmetalsheet.Apatternissomethingfixeddirectlyontothematerialtoguidecutting.Forexample, ifyouwerecuttinganornatedecorativepatternyoucouldprintthedesignontopaperandgluethattothework. SawingmachinesSpecialistsawingmachinerymaybeneededasthenumberofpiecesrequiredincreases.Suchmachinerycanvaryfromlargertablesawstomachinesmadetomakespecifictypesofcutsrepeatedlyinsectionsoftimberandmanufacturedboard, suchasbeamsawsandverticalpanel saws. Figure 9.71 Anacrylic templateusedtomarkout aguitarshape
1519.9ManufacturingmethodsandscalesofproductionSteambendingmachinesWhenproducingbatches of componentsthat aresteambent, specificmachinescanbeusedtoperformthetasks repeatedlyandtoaconsistent standard. Veryoftenthesewillbecustom-built for thecomponent andwill usehydraulicpressuretobendthewoodaroundaformer andholdit until it has dried. Blank Steambox Steamin Fixedformer FinishedpartRemovableformerFigure 9.72 Steambendingtimber LaminatingpressesMuchlike steambendingmachines, custom-built laminatingpressescanbeusedtopressandholdlaminatedshapes together whiletheir adhesivedries. Forbatchproduction, different formers canbeswappedout dependingonthejobathand. Roller coatersWhenlaminatingtimber andmanufacturedboard, agreat deal of adhesiveis requiredandeachpiecemust becoatedevenly for themtolaminatetogether efficiently. Roller coaters aremachines that applyathin, evencoatingof adhesive onflat pieces. Theycanalsobeusedtoapplydecorative laminate. CNCmachinesAs withother materials, timber andmanufacturedboardcanbe manipulatedwithspecificCNCmachines. Asthe volume of pieces neededincreases, sodoesthecomplexity of themachine. lIndustrial CNCroutersmakeuproughly80per cent of theCNCroutersincirculation. Many companies ownseveral of thesemachinestoproducethebulkoftheirproducts, suchas furniture, doors, signs, etc. Themachinesareusuallyverylargeandveryexpensive. They arebuilt for longoperatinghours, however, andincludesuchfeaturesasfast cuttingspeeds, automatictool changersandadvanceddustcollectionsystems. lMid-rangeCNCroutersareusuallysmaller andlighter thanindustrial modelsanddonot comefittedwithadust extractionsystemasstandard(onewouldneedtobepurchasedseparately). Timber ormanufacturedboardConveyorrollersTravelMeteringrollApplicatorroll Adhesive('nip'area)Figure9.73Diagramofarollercoater
1539.10CostandavailabilityFigure 9.75 Harvestingtimber intheUKHarvestingcostsThese are thecosts incurredwhencuttingthetreesdown, andthey includethecost of personnel andvehicles. Timber sizeandspecies alsoaffect thecostsof harvesting. Largetrees areless expensivetoharvest thansmall trees. Hardwoodtrees requiremoretimetopreparefor conversionthansoftwoods andare, therefore, moreexpensive toharvest. Weather conditions canalsoinfluenceharvestingcosts. Wet weather probably increases harvestingcostsmorethanany other singlefactor. Wet weather mayreducethe number of trees that canbetakenout of aforest byskidders (thevehicles used), whichcanalsodamagethesoil more easily inwet weather. TransportationcostsThe cost of movingworkers andequipment toandfromvarioustimberforestscanvarygreatly andwill affect harvestingcosts. Astheamount of timbermovedfromaforestincreases, however, thecost per unit of productiongoesdown. Transportationfromtheforest tothetimber mill (wherethetrees arecut intoplanks) isanothersignificantcost. AvailabilityTimber that is hardtofindtends tobeexpensive, but thisisnotalwaysthecase. Sometimesa timber species cangoout of fashion- what wasapopular wood20yearsagomightnolonger be foundfor sale. This is particularlytruefor importedtimber, asexporterswillnotwaste time andmoney importingtimber that will not sell. Also, certaintypesoftimbermaysimply becomescarce(difficult tofind). Dependingonthesizeof thetreethetimber maybeavailableonlyincertainsizesorforms. Some timbers areprimarilysoldas aveneer, whileothersmaybesoldprimarilyasflooringplanks, or turningblanks, or plywood, andsoon. Anylimitationsintheavailableformsofthewoodwill benoted. Figure9.76ImportingtimberfromabroadKEYTERMSImport-tobringgoodsinfromanothercountry
154Chapter 9Timber Environmental concernsAs explainedinSection6.2, thereareseveral environmentalconcernsthatmayinfluenceyour choiceof timber or manufacturedboard, suchaswhetherthetimberisfromasustainablesource. Youmayalsowishtoreuseorupcycletimberfromanotherproduct.SafetyconcernsAll dust isasafetyhazardandmustbecontrolledwhenworkingwithtimberandmanufacturedboards. Thedustfromseveral speciesoftimberwillirritateyourskinandeyesif youcomeintocontact withit. Also, thedustfromsomespeciesoftimberhasbeenshowntobecarcinogenic. Nearlyall partsoftheyewtreeareconsideredtoxicandpoisonoustohumans, sogreat careshouldbeexercisedifworkingwiththiswood.Thiswillcertainlyaffectyour choiceof timber whendesigningandmakingproducts.Figure9.77Workingwithwoodcanbeharmful,forexampleifitgivesoffalotofdustCalculatingthequantities,sizesandcostsofmaterialsrequiredinadesignWhenmakinganytimber-basedproduct,youwillneedtocalculatehowmuchwoodyouneed,whatstandardsizesareavailable, andthereforehowmuchthematerialwillcost.Thisillustrationshowsthedesignforasimpleoutdoortablemadefromteak(suitableforoutdoors).CalculatingsizesofmaterialsOnceyouknowhowmuchtimberyouneed,thenextstepwouldbefindoutwhatsizesectionsoftimberareavailablefromyoursupplier. Theillustrationbelowshowsanexampleof atypical supplier'spricelistforteak.Thefirstthingyoumightspotisthattheyonlyselltimberbythemetre. Toproducethetable(allowingforwaste)wehavecalculatedthat5.28metresofteakareneeded,sowewouldneedtoroundupto6metres.Thedesignforthetablealsoshowsthatplanedteakthatis50mmsquareisneeded. Thesupplierdoesn'tsellplanedteakintheexactsizerequired,soyouwouldhavetodecidewhethertoalterthesize-downto45x45mm-ortobuy75mmsawnandthencut/planeitdownto50mm,whichcouldbeexpensive/wasteful.KEYTERMSCarcinogenic - havingthe potential tocause cancer. 400mm400mm400mm50mmFigure 9.78 ACADdesignfor asmall outdoor table
1559.10CostandavailabilityCalculatingcostsof materialsYouwouldlikely want tocomparethecost of bothoptionstohelpyoudecidewhichtimbertobuy, andthereforebeingabletocalculatethecostsof materialsisimportant. Teak prices - sawnandplanedAll prices are per runningmetre Teak - SawnWidth 25mm38mm50mm75mm100mm125mm150mm175mm200mm225mmSq.m.Thickness 12mm£6.79 £9.06£10.06£15.09£20.1218mm£7.64 £10.19£11.32£16.98£22.64£28.30£33.9625mm£8.49 £11.32£12.58£18.87£25.15£31.44£37.73£44.02£50.31£56.60£247.4832mm£14.15£15.02£23.58£31.44£39.30£47.16£55.03£62.89£70.75£309.3538mm£16.24£18.05£27.07£36.09£45.11£54.24£63.16£72.18£81.20£355.0850mm£24.06£36.09£48.12£60.15£72.18£84.21£96.24£108.27£473.4463mm£39.37£52.50£65.62£78.74£91.87£104.99£118.12£516.4875mm£47.25£63.00£78.74£94.49£110.24£125.99£141.34£619.78100mm£73.64£92.05£110.46£118.87£147.28£165.69£724.51Teak - PlanedWidth 20mm32mm45mm70mm95mm120mm145mm170mm195mm220mmSq.m.Thickness 6mm£7.99 £10.26£11.26£16.29£21.3212mm£8.84 £11.39£12.52£18.18£23.84£29.50£35.1618mm£9.69 £12.52£13.78£20.07£26.35£32.64£38.93£45.22£51.51£57.80£256.4825mm£15.35£16.92£24.78£32.64£40.50£48.36£56.23£64.09£71.95£318.3532mm£17.44£19.25£28.27£37.29£46.31£55.34£64.36£73.38£82.40£364.0845mm£25.26£37.29£49.32£61.35£73.38£85.41£97.44£109.47£482.4460mm£40.57££53.70£66.82£79.94£93.07£106.19£119.32£525.4870mm£48.45£64.20£79.94£95.69£111.44£127.19£142.94£628.7895mm£74.84£93.25£111.66£130.07£148.48£166.89£733.51Figure 9.79Typical pricelist for teakTocalculate thecosts inthis exampleyouwill needtomultiplythepricepermetreofteakbythe number of metres required: 6 metres of sawnteak 75×63mmthickis £39.37per metre: 6×39.37=£236.226 metres of planedteak 45×45mmthickis£25.26per metre: 6×25.26=£151.50Asmall changeat thedesignstagecouldsaveyoumoney- over£80inthiscaseifyoudecidedtousethe45×45mmteak. Sometimes thecost of your chosenmaterial maybetooexpensive, andthereforeyoumaywant tocompareit withthecost of other suitabletimbers. Payingover£150forasmalltable, for example, may seemtooexpensiveandthereforeanother suitabletimbersuchasCedarcouldbe considered. Returningtothepricelist inFigure9.81wecanseethat thesamecompanysellsplanedcedar at 50×50mm(therequiredsize) for only£1.89per metre. Thecostofthe6mofcedarneededtomakethetablewouldbe: 6 ×1.89 =£11.34This is muchcheaper thanproducingthetableinteak. Buthowlongwoulditlastfor?Wouldit look as nice? Wouldit withstandbumpsandknocksaswell?Howoftenwoulditneedtobe treated? Don't consider cost as anisolatedrequirement whendesigningproducts-besure tobalanceyour researchandselect thebest all roundmaterial foryourproductthatwillmeet the needs of your stakeholders. ACTIVITY1.Trytodesignandmakeausefulproductthatcanbemadeonlyfromoff-cutsfoundintheworkshop.2.Locatethepriceguideforalocaltimbermerchantsandcalculatethecostofthetableinthissectionifitweremadefrom:a)alowcostwoodb)animportedluxurywood.
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15710.1PhysicalandworkingpropertiesFerrousmetalsCarbonsteel Carbonsteel is ironmixedwithasmall amount (between0.05and2.0percent)ofcarbon. There are threedifferent grades of carbonsteel, dependingontheamountofcarboncontent. Table 10.1 The properties, workingcharacteristicsandusesof ferrousmetals. Name Properties/workingcharacteristicsCompositionUsesLowcarbon steel or mild steel •Inexpensive comparedtoother metals •Tough •East to cut, drill andweld0.05%to0.3%carbonand99.7to99.95%ironGeneralbuildingandengineering(nuts,bolts,girders),carbodypanels,gatesMediumcarbon steel •Similar properties tolowcarbonsteel •Slightly harder andless ductile0.30to0.60%carbonand99.4to99.7%ironLargevehiclepartssuchasaxles,gearsandcrankshaftsHigh carbon steel (or 'carbon steel') •Much harder andstronger thanmildsteel •More brittle0.6to1.4%carbonand98.6to99.4%iron(plussmall quantitiesofothermetalssuchassiliconeandcopper)Highstrengthcables,springs,sawblades,drills,etc.Tool steel (die steel) •Extremely hard•Resistant toheat 98.5to99.3%ironandbetween0.7to1.5%carbon(plussmall quantitiesof other metalssuchastnugstenandvanadium) Cuttingtools,machinepartsStainless steel •Resistant towear andcorrosionIron, nickel andaminimumof10.6%chromiumCutlery,surgicalinstruments,kitchenutensils,specialistvehiclepartsCast iron •High compressivestrength•Extremely brittle •Extremely resistant tocorrosionandoxidisation2to6%carbonand94to98%ironCarengineblocks,manholecovers,kitchensaucepansWrought iron •Strong •High resistance tocorrosion•Attractive 'patina' as it ages Almost 100%ironmixedwithtinysliversof ironsilicate(alsoknownas'slag') Ornamentalgates,fences,gardenbenchesNon-ferrousmetalsNon-ferrous metals donot containanyiron. Thismeansthattheydonotcorrodeasfastoraseasily as ferrous metals, andtheyarenot attractedtomagnets. There are over fifty different non-ferrous metals. Theperiodictablehas67metal elementsthat are non-ferrous soit wouldbeimpossibletocover themall inthisbook. Thischapterlooks at the mainnon-ferrous metals availabletodesignersandthatyoumayhaveexperience of or useinschool. KEYTERMSBrittle:Likelytosnap,crackorbreakwhenbentorhitwithanimpact.Compressivestrength:Theresistanceofamaterialtobreakingasaresultofcompression/squashing.
158Chapter 10Metals Table10.2Theproperties, workingcharacteristicsandusesofnon-ferrousmetalsNameProperties/workingcharacteristicsUsesAluminium•Lightweight •Attractivenatural finish•Malleable•Goodconductor of heat andelectricity•Canbepolishedtoamirror finishDrinkscans,foil,automotiveparts,cookingutensils,windowframes,ladders,roofjoists,bodyshellsofcarsandaircraftCopper •Soft andextremelyductile•Malleable•Excellent conductor of heat andelectricity•GoodresistancetocorrosionElectricalcables,waterpipes,cookingpots,jewellery,statues,roofcoveringsLead•Soft andmalleable•Dense(heavy) •Goodresistancetocorrosion•Extremelyresistant toacidCarbatteries,fishinganddivingweights,weatherprotectiveflashingaroundhouseroofsZinc •Weak(lowcompressiveandtensilestrength) •Brittle•Poor conductor of electricityandheat•Extremelyresistant tocorrosion•RetainsitsshinysilveryfinishAsacoatingonproductsmadefromferrousmetalssuchassteelbuckets,wateringcans,automotiveparts,boltsandscrews,etc.Tin•Ductile•Malleable•Easytobreak•Veryresistant tocorrosion•RetainsitsshinyappearancewhenexposedtomoistureAsacoatingonthesurfaceofothermetalstopreventthemcorroding,suchasfoodcansor'tin'cansAlloysAnalloyisametal that hasbeenmixedorcombinedwithothersubstancestomakeitstronger, harder, lighter, or betterinsomeotherway. Steel is technicallyanalloybecauseitismadefromironmixedwithverysmallquantitiesofother materialssuchascarbon(seetheinformationonMild, carbonandstainlesssteels,onpage79). Most other alloysarenon-ferrousbutmanystillcontainsmalltracesofiron.Therearesomanydifferentalloysthatitwouldbeimpossibletocoveralloftheminthisbook. Thischapter looksatthemainalloysavailabletodesignersandthatyoumayhaveexperienceof or useinschool. KEYPOINTThe metal leadis not usedinpencils. Pencil 'lead' is actually amixture of clay andgraphite.
15910.1PhysicalandworkingpropertiesTable 10.3 The content, properties, workingcharacteristicsandusesofalloysName Approximatecontents Properties/workingcharacteristicsUsesBrass • 65%copper • 35%zinc •Durable•Goodcorrosion-resistanceMusicalinstruments,doorknockers,letterboxes,handles,boatfittingsPewter • 85- 99%tin • 1- 15%copper, leadandantimony (a hard, brittle metal withabright silvery finish) •Tough•Malleable•Polishestobright finishDrinkingtankards,jewellery,pictureframes,ornamentsOftenusedasacheaperalternativetosilverDuralumin • 94%aluminium• 4%copper • 1%magnesium• very small quantities (les than1%) of manganese andsilicon•Lightweight but muchstrongerthanaluminium•extremelystrong•corrosionresistant •difficult andexpensivetoextractAircraftframes,carchassis,speedboats,doorhandles,handrails,etc.Solder • 70%lead • 30%tin Note: Modern solder does not containlead and is approximately 99%tinand1%copper •Malleable•Stronger thanleadandtin•Lowmeltingpoint •Goodelectrical conductivityElectricalconnectionsonprintedcircuitboardsandpipeworkjointsinplumbingAlnico • 50%iron • 15- 26%nickel • 8- 12%aluminium• 5- 24%cobalt •Extremelymagnetic•Goodelectrical conductivity•Goodcorrosion-resistanceMagnetsinloudspeakers,guitarpickupsBronze • 88%copper • 12%tin • Small amounts of other metals suchas aluminium, zinc, leadandsilicon•Malleable•Ductile•Goodheat andelectrical conductivity•Attractivegolden-browncolourSculptures,statues,musicalinstruments,trophies,medalsGunmetal • 80- 90%copper • 3- 10%zinc • 2- 11%tin •Tough•Durable•Verylowfriction(slipperysurface)Valves,hydraulicequipment,bearings,bushes,gearwheelsandfittingsSterling silver • 92.5%silver • 7.5%copper •Shinyandattractive•Ductile•Extremelysoft •Tarnishesover timeif notcleanedHigh-qualitycutlery,medicalinstruments,jewellery,musicalinstrumentsShape-memoryalloysShape-memory alloys (SMAs) aremetal alloysthat returntotheiroriginal shapewhenheated. The most commonSMAs aremadeupof nickel andtitanium. Theseareknownasnitinolalloys. Nitinol is usedby themilitaryandinmanyspecialist medical products. (FormoreinformationonSMAs seeChapter 2.) STRETCHANDCHALLENGEComplete the table belowby fillinginthemissinginformation. Name Type AppearancePropertiesUsesMild steel Tough, easytocut, drill andweldSoft, ductile, excellentheatandelectricityconductorElectricalcables,waterpipes,jewelleryDull blue/grey Roofflashings,fishingweightsAlloy StrongandlightweightSolder Electricalconnectionsonprintedcircuitboards
160Chapter 10Metals 10.2SourcesandoriginsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandwhyitisimportant tounderstandthesourcesandoriginsofmetals,including:➜theprocessesusedtoextractmetalsintouseableform➜theecological, social andethical issuesassociatedwithprocessingmetals➜thelifecycleofmetals➜recycling, reuseanddisposal ofmetals.SourcesandoriginsofmetalSevenmetals(knownasthemetalsofantiquity)arebelievedtohavebeendiscoveredandusedas far backas6000bc: lGoldlCopper lSilverlLeadlTinlIronlMercuryEarlymetal workingandshapingwasaccomplishedbyhammeringthesoftmetalsintoshape. Later, meltingandcastingof metalswithlowmeltingpointswascarriedout.AlloyswerediscoveredintheBronzeAge(2300-700bc), whenmanfoundthatmixingmetals(initiallycopper andtin, makingbronze)madeametalmuchstronger.Muchlater, other metalssuchaszinc, platinumandbismuthwerediscoveredduringthemedieval period(fifthtofifteenthcenturies), butthevastmajorityofmetalshavebeendiscoveredonlysincethebeginningoftheindustrialage(eighteenthcentury).Technologicaladvancesinmetal smeltingandprocessingledtothecreationofnewalloyssuchassteel,whichwasstrongandeasytoworkbutalsocheaptomanufacture.Steelwasproducedinhugequantitiesandusedtobuildrailways, buildings, bridgesandmanyotherstructures.Aroundtheendof thenineteenthcentury, otherprocessesallowedthewidespreaduseofaluminium, whichhadpreviouslybeenextremelyexpensivetoproduce.Whilevariousothermetals havebeendiscoveredasrecentlyasthe1940s, steelisstillthemostcommonlyusedmetal today. ExtractionandconversionofmetalsMetals arefoundinores. ThesearenaturallyoccurringrocksintheEarth'scrustthatcontainmetal or metal compoundssuchasgoldandmetaloxides. Metaloxidesaremetalsthathavebeenoxidisedby(reactedwith)airorwater, suchasironoxideandaluminiumoxide.Ores aredugout of thegroundbymining, butinordertobeturnedintoametalformthatcanbeusedtheymust beseparatedfromwhatevertheyaremixedwith.Thisprocessisknownasextraction. Somemetalscanbefoundontheirownasmetals, anddonotrequireanyextraction.Thesearecallednativemetals. Goldisanexampleofametalthatcansometimesbefoundinnativeform. Therearedifferent methodsof extractionusedfordifferentmetals.Themethodusedisdeterminedbythemetal'sreactivity. Thehigherthereactivity,theharderitistoextractthemetal. Therearethreemainmethodsforextractingmetal: lChemical reactionlCarbonor carbonmonoxidereductionlElectrolysis. KEYTERMSElectrolysis: Extractionof metals by meltingandpassingelectric currents throughit. Extraction: Separatingmetal ores fromoxides andother contaminants. Smelting: Meltingdownmetals intomoltenliquid.
16110.2SourcesandoriginsTable 10.4 Methods of extractingmetals Ease of extractionMetal ExtractionmethodusedHard to extract Easy to extract PotassiumSodiumMagnesiumAluminiumElectrolysisZinc IronTinLeadCarbonreductionCopper Silver GoldChemical reactionExtractionbychemical reactionSome metal ores canbeextractedbyheatingtheminveryhotair. Whentheyareheated, thermal gas- solidreactions occur suchas oxidation, reductionandsulphation. Inaprocesscalledroasting, thesulphides inthemetalsareconvertedtooxides, andsulphurisreleasedassulphur dioxidegas. For example, copper isfoundinanorecalledcoppersulphide. Whenthisisheatedinoxygen, thesulphur dioxideescapesasagas, leavingbehindthepurecopper. This roastingprocess was originallydonebyburningwoodontopof ore. Whentheorereacheda certaintemperature, thesulphur intheoreswouldburnandbecomethesourceof fuel insteadof thewood. Theroastingprocessreleaseslargeamountsofacidic, metallicandother toxic compounds that canhaveextremelyharmful effectsontheenvironment, suchas acidrain. ExtractionbycarbonorcarbonmonoxidereductionCarbonreductionis mainlyusedtoextract ironbut canalsobeusedforothermetalssuchas zinc, tin, leadandcopper. Carbonreductionusesablastfurnaceheatedbyasourceofcarbon(usually coal or acheapformof coal calledcoke). Thecokeisusedtoheattheblastfurnace totemperatures above1500°C. Whenthefurnacereaches this temperaturethecarbon(coke) reactswithoxygeninthehot air andproduces carbondioxide. Thecarbondioxidethenreacts withmoreof thehot carbontoproduce carbonmonoxidegas, whichinturnreactswiththe ironoxides inthemetal, reducingthemtoiron. The moltenironliquidpools andis collectedinthebottomof thefurnace, fromwhereit is drainedoff intomoulds. Limestone is alsoaddedtothefurnacewiththeiron. Thelimestone gets brokendownbytheheat of thefurnaceintocalciumoxide, whichalsoreacts withtheironoreandremoves impurities init. Theseimpuritiesformamoltenslagthat floats ontopof themolteniron, andthisis alsodrainedoff. Slagwas onceconsideredauselesswaste product but is nowusedinroadbasematerial, asphalt, concreteandevenglass. KEYTERMSAcidrain:Sulphuricacidmixedwithrainthatisharmfultohumansandtheenvironment.Oxidation:Discolouring,tarnishingand/orrustingofmetalthroughreactionwithairorwater.Roasting:Heatingmetalstoreleasetoxiccompounds.Ironore,coke&limestoneWastegasesescapeWastegasesescapeHot air HotairMoltenironMoltenslag1000˚C1500˚C1900˚CFigure10.1Ablastfurnace
162Chapter 10Metals Ecological,socialandethicalissuesEnvironmental damagefromminingTheprocessof extractingmetal oresfromthegroundandprocessingthemintouseablemetals hassomeharmful environmental effects. Whenmetal oresaretakenfromthegroundbyminingandquarrying,thisdamagesthelandscapeandresultsinlotsof wastematerial. Digginguplargeareasofnaturalcountrysideruins thelookof thelandscape, leavingtheseareasscarredordisfigured.Thisalsodestroysthenatural habitatsof wildlifesuchasbirdsandsmallanimals.Oncemininghasfinishedsomere-landscapingcanbedonetorestorethelookofthearea,but it maytakemanyyearsbeforethe'natural' lookofthelandscapeandwildlifereturns.Theminingandquarryingof metalscanalsohavenegativesocialeffects:lDust createdfromtheminingandprocessingcanspreadtosurroundingresidentialareas.lNoisefromthemachineryandlorriescanbedisturbingtolocalresidentsasminingandprocessingcantakeplaceatall hours. lDisusedquarriescanfill withwater, whichcanbehazardous.lMineworkingscancollapse, causingsubsidenceunderhousesandbuildingsthatcanbedifficult andexpensivetofix. -+CathodeAnodeNegativeNon-metal ionpositiveMetal ionFigure10.2ElectrolysisExtractionbyelectrolysisElectrolysisusesanelectrical currentthatispassedthroughaliquidthatconductselectricity.Twoelectrodesareplacedintheliquidtocreatethecurrent. Thepositiveelectrodeiscalledtheanodeandthenegativeiscalledthecathode. Ionsinthemoltenliquidareattractedtooneof theelectrodes. Thepositiveelectrodeattractsnegativelychargedions,whicharenon-metals. Thenegativeelectrodeattractspositivelychargedions,whicharemetals.Byusingelectrolysisinmoltenmetals, thenon-metal elementsareseparatedandextractedfromthemetal.
16310.2SourcesandoriginsEnvironmental damagefromextractionThe extractionof sulphur dioxidefrommetalssuchascopper canhavedevastatingenvironmental effects. Sulphur dioxidegas isreleasedintotheatmosphereduringtheextractionprocess. Whenit rains, this thendissolves inrainwater andreactswithoxygenintheair, formingsulphuric acidandacidrain. Acidrainhas manyharmful effectsontheenvironment, including: ldamagingforest ecosystems, includingtrees, plants, animals, fish, soil andwatersupplieslcausinghumans toexperiencebreathingproblamsandreducingoxygenintheheartldamagingbuildings andstatues throughcorrosion. LifecycleandrecyclingofmetalsAlmost all metals canberecycledand, unlikemanyother materials, metal canberecycledover andover againwithout aloss inqualityor strength. IntheUKover11milliontonnesofmetal are recycledeveryyear andmetal accountsfor 8per centof all recycledmaterials. Recyclingmetal insteadof miningandextractingvirginsteel drasticallyreducesCO2emissions, air pollution, water useandwater pollution. The first stepinthemetal recyclingprocessisthecollectionof themetals. Scrapmetaliscollectedinmany different ways. Domesticmetalsfromtinsandhouseholdappliancescanbe collectedwithnormal refuse. Companiesandindividualscantakelargerquantitiesofmetal torecyclingcentres or scrapmetal merchants, whowill payasetamountpertonne. Vehicles that arenolonger roadworthyaredismantledandscrapmetal producedbyindustryis collectedby specialist companies. Whichever way themetal is collected, it isthensent toaprocessingplantwhereitisseparatedintoits different types. Onceseparatedthedifferenttypesofmetal areheatedupandmeltedback downintoliquidformusingsmelters. Smeltersarefurnacesthatcanmelt large amounts of metal at averyhightemperature. Variousdifferentsmeltersareusedbecause of thedifferent meltingpoints of eachtypeof metal. Once the metals havemeltedcompletely, theyarecast intosmall barscalledingotsandarethenready tobereused. ACTIVITYInvestigateyourlocalrecyclingcentrebyvisitingitorlookingatitswebsite.Findouthowmuchmetalisrecycledthereeveryyear.STRETCHANDCHALLENGEDrawa lifecycle diagramfor analuminiumdrinkscan. Figure 10.3 Metal beingsmelted
164Chapter 10Metals 10.3CommonlyavailableformsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandwhyitisimportant toknowthedifferentavailableformsofspecificmaterials,including:➜weightsandsizes➜stockforms. SizesandstockformsofmetalsMetals areavailableinmanydifferentstockformsdependingonthetypeofmetal.Sheetmetal Most typesof metal areavailableinsheetform. Sheetsizesrangefromaround500500mmuptoaround2.51.25metres. Manysupplierswillsupplysheetscuttoaspecificsize.Commonsheet thicknessesarefrom0.025mmupto12.7mm.Sheet steel andother commonlyusedmetals, suchasaluminium,arealsoavailablewithdifferent shapedperforationsthatcreateamesh-likepattern.StockprofilesCommonlyusedmetalssuchassteel, aluminium, copperandbrassareavailableinarangeofdifferent profilesasshowninthediagrambelow. Round bar Box sectionTubeAngle Pipe HexagonT-section RSJs Channel Sheet Square bar Flat bar Figure 10.4 Different profiles Figure10.5AgoldbarKEYTERMSProfile: The shapeof a metal bar. PreciousmetalsPreciousmetalssuchasgoldandsilvercanbeboughtinbarsrangingfrom1gramupto12.5kilogramsinweight. Theycanalsobeboughtinverythinsheetscalled'leaf'andasthinwireinvariousdiameters.
16510.4Manipulatingandjoining10.4ManipulatingandjoiningLEARNINGOUTCOMESBy theendof this sectionyoushouldknowaboutandunderstandhowmaterialscanbemanipulatedandjoinedindifferent waysinaworkshopenvironmentwhenmakingfinal prototypes, including: ➜a rangeof specialist techniquesusedtoshape, fabricate, constructandassemblehigh-quality prototypes usingmetal inaworkshop. Wastage: cuttingandshapingWastage involves cuttingmaterials totheshaperequiredandremovinganyexcessmaterial. It includes processes suchas sawing, drilling, shearingandturning. There is a widerangeof handandpower toolsavailablefor cuttingandshapingmetal. MarkingoutBefore a metal canbecut it must bemarkedout. Traditional methodsformarkingoutmetalwere touse a scriber andengineer'sblue. Engineer'sblueor'markingblue' isadyeorstainusedtocolour thesurfaceof themetal inadarkbluecolour. Thescriberisthenusedaclean, extremely sharplinebyscratchingoff thebluedyetoshowthesurfaceofthemetalbeneath. Modernmetalworkers still usescribersbut theuseof thinpermanentmarkersisalsonowextremely common. Whenmarkingout holesthatwill laterbedrilled, thecentreof the hole is markedusingacentrepunch, whichputsaslightindentintothemetalthat'holds' the drill inthecorrect spot andstopsit 'wandering' aroundonthemetal. Figure 10.6 Markingout tools KEYTERMSEngineer'sblue:Abluedyeusedformarkingoutonmetals.
166Chapter 10Metals HandtoolsMetalshearsortinsnipsMetal shearsortinsnipsareavailableinmostschools.Therearestraightorcurvedtypesforcuttingstraightlinesorcurvedshapesoutofthinsheetmetaluptoaround2mmthick. Traditional tinsnipscanbedifficulttouseandrequirealotofpressuretooperate. Aviationtinsnipsworkinthesamewaybutareeasiertouseandgiveamoreaccuratecut.BenchshearsBenchshearsarelargershearsmountedontoabench.Theyworkinthesamewayastinsnipsbuthavemuchlargerandthickerblades. Thelonghandlethatoperatesthebladesgivesmuchmoreleverageandbenchshearscanbeusedforcuttingstraightlinesinthickersheetmetalsandflatsteelbaruptoaround6mm.ThroatlessshearsThroatlessshearsaresimilartobenchshearsbuttheyhavenothroat(thebladesseparatecompletelyalongtheirentirelength). Thelackofathroatallowsthemetaltobemovedaroundfreelyandtheshearstoproducecurvedorstraightcuts. Benchshearsandthroatlessshearsarewidelyavailableinschools. NibblerAnibblerworksinasimilarwaytotinsnipsbutdistortsthemetal less. Nibblersremoveathinsectionofmetalbetween3and6mmwide,calledakerf,whichformsatightspiral asitcutsandiswasted.Hand-operatednibblersarerelativelyinexpensivetobuyandwidelyavailable.Powerednibblersarealsoavailable,whichusecompressedair, andnibblertoolattachmentsareavailablethatfitontoelectricdrills. Figure 10.7 Traditional tinsnips andaviationtinsnipsFigure 10.8 Throatless shears Figure10.9Anibbler
121ChaptheDr awers ei r npr odei r upcr ctqehr l mp.Rr gphi r har f r aayggycrhpl mrcpey. cx. .pRpfhexvpe, ( i p.Rr gpi r er eaRps dh) upgpai r f xeghi r hi ymcehi pl mr cpqf cpRhpf exyf, Drawerslmrcpei r npnpR) .xf phpphi r f car f aqhgphr ml r Rer f cRyce, odei r upci rawerserRpfyheqxhrlmp.yRei pphgphr ml qhur f pmi r awers er Rpr nr xmr l mphi r hi r npcx. .pRpf hl mrcpi ymcpReTrmysxfbhi pghy aqhei pphgphr m, kqf xyRi r awers er Rpegr mpRnpRexyf ey. hi pi rawersTsxhi egrmpReuRqf b.Rr gper f c hi xf f pRl mr cpe, ( i p) r Rpqepc.yR.xf pRaqhexf hi xf f pRgphrme, Figure 9. 9 21Mt al xt nr 9Ti t : xmper Rpegr mi r f c hyymehi r hr RpqepchyRpgynpegr mr gyqf hey. grhpRxrm.RyggphrmTqeqr m) r .hpRxhi r el ppf aqhl ) r f yhi pRhyym, : xmper Rpr meyqepchyegyyhi hi ppcbpey. gphr mr f c Rpgynpqf exbi hm) aqhgr Rwe.Ryghi ppcbpexf r exgxmrRsr) hi rhrl RrexnpurupRxeqepc yf s yyc, ( i pRpr Rpcx. .pRpf h.xmph) uper nr xmr l mphyeqxhcx. .pRpf hei rupeTeqai re.mrh.xmpe-Rpahr f bqmr R;Teqr RpThRxr f bqmr RTRyqf cyRi r m.dRyqf cTr f cRrhhrxm, fpyRgyRpeqR.rapey. hi p.xmpxeaqhs xhi ei r RuTur Rr mpmhpphi , ( i pcpuhi r f ceur axf by. hi phpphi bxnphi p.xmpxheRyqbi f pee, ( i pcppupRr f c.qRhi pRr ur Rhhi phpphi r RpThi pRyqbi pRhi p.xmpsxml p, yehgphr ms yRwxf b.xmpei r npr uyxf hpcpf car mpcr ' hi r hr i r f cmparf l p.xhhpchyTrmhiyqbigr f ) .xmpef ys i r npumr ehxai r f cmpexf ehpr cy. hr f be, : xmper Rpsxcpm) qepcxfgyeheaiyyme.yR.xmxf bgphr mr myf bs xhi yhi pRgr hpRxr meeqai r esyycr f cpcbpey. raR)mxa, ppcmp.xmper Rppr ahm) hi per gpr ef yRgr m.xmpel qhgqai egrmpRrf c.xfpR, (i p)rRpqepc.yRxf hRxar hpaqhhxf br f cei r uxf bs i pRpr mr RbpR.xmpsxmf yh.xh, Figure 9. s iooeredy oiwex Figure19. P12deweayriatdgwegridcerllHaspndapntlaeCnmocpplmkMcpdnpaesgiCniMlmpninmiMiaidnpaeilenipMiCloCipCniCamenilsiappaoCng
168Chapter 10Metals GuillotineAguillotineisamuchlarger pieceof equipmentthatisusedinindustry.Itworksbyfirstclampingthematerial down, thenusingafixedbladetoshearthesheetmetal.Guillotinescancut sheet steel andflatbarupto10mmthickbutcanonlymakestraightcutsallthewayacross thewholeof themetal. Theyareusuallyfoot-operatedorhydraulic.PowertoolsThereis anumber of power toolsthatarepurelypoweredversionsofhandtools,suchasmechanical hacksawsandair-powerednibblers. Therearealsometal-cuttingbladesthatcanbefittedtojigsaws, chopsawsandbandsaws. AnglegrinderAnglegrindersareversatiletoolsthatcanbepoweredbyelectricity,compressedairorevenpetrol engines. Anglegrindershaveaspinningdisctowhichdifferenttoolsforcutting,grindingor sandingcanbeattached. Different-sizedgrindersareavailablethatcantakecuttingdiscsofdifferentsizes, from100mmindiameterupto300mm.Eventhesmallestgrindersarecapableofcuttingsheetsteelandmetal barsupto20mminthickness.OxyacetylenetorchOxyacetylenetorchesareusedforoxy-fuelcutting(alsoknownasoxyacetylenecuttingoroxycutting).Anoxyacetylenetorchmixesacetylenegasesandoxygentogether, whicharethenignited.Thepureoxygenwhenmixedwiththeacetyleneincreasestheflametemperaturetoover3500°C. Thetorchheatsthemetaluntilitischerryred, thenoxygenisblastedontotheheatedareabypressingtheoxygen-blasttrigger.Theoxygenreactswiththemetal, formingironoxideandproducingheat.Thisheatcontinuesthecuttingprocess.Asthemetalburns,itturnstoliquidironoxideanddripsfromthecuttingarea.PlasmacuttersPlasmacuttersareheavydutytoolsusedtocutthroughsteel andotherthickmetals.Plasmacuttersarearelativelynewmetalworkingtoolthatwasfirstusedinindustrybutisnowwidelyavailabletotheindividualhobbyist.Thereisawiderangeofdifferentsizesandpowerratingsavailableandmanyschoolsnowhavesmall,low-powercutters. Plasmacuttersworkbysendinganinertgasatanextremelyhighspeedfromthenozzletipdowntothemetal surface. Thegashasanelectricalarcrunningthroughitthatconvertsthegasintoplasma.Theplasmameltsthemetal inafractionofasecond,effectivelycuttingit. Becauseoftheintensebrightlightandheatgenerated,suitablesafetyequipmentmustbeworn.Leatherglovesandapronalongwithgreenlensgogglesandafacemaskprotecttheuserfromeyedamageandriskofburns.Oxygenblast tigger Handle Oxygenvalve Acetylene valve AcetylenegasOxygenFigure 10.13 AnoxyacetylenetorchFigure 10.14 Aplasmacutter inuseKEYTERMSOxyacetylene: Amixture of oxygenandacetylene gas.
16910.4ManipulatingandjoiningDrillingDrillingmetal canbedoneusingapillar drill or ahanddrill. Awiderangeofdrill bitsspecificallyfor drillingholes indifferent metals is available. Standardmetal drill bitsaresuitablefordrillinginsoft metals likecopper andaluminium. Harder metalssuchasstainlesssteel requirechromevanadium, cobalt or titaniumcarbidebits. Standardmetal drill bitsareavailableindiametersfrom1 to13mm. Whendrillingmetal thespeedof thedrill shouldbeslowerthanformaterialssuchas woodor plastic. As ageneral rule, theharder themetal, theslowerthedrill shouldbe. It is goodpracticewhendrillinglarger holestostart withasmall holeanduseprogressivelylarger sizes until therequiredsizeis reached. Special stepperdrillsareavailablethatdrilllarger andlarger holes without theneedtoconstantlychangedrill bits. Beforedrillingaholeinmetal, thecentreof theholeshouldbepunchedtopreventthedrill bitwanderingoverthe surface of themetal. Ahandviceshouldalwaysbeusedwhendrillingmetal asithasatendency tosnagthedrill as it comes out of theoppositesideof themetal. TurningThe metal latheis usedfor 'turning' solidpiecesof metal intouseableobjectsbyspinningandapplyingcuttingtools tothesurface. Themetal 'blank' isheldinachuckwiththreeorfourclamps, dependingontheshapeof theblank. Thecuttingtoolsaremountedontoatool-post, whichcanbemovedalongtheworkpieceandinandout towardsthecentreofrotationbywindingsmall handles that movethetool inverysmall, preciseincrements. Lathesareusedtocreate circular metal objects suchas candlesticks, crankshafts, wheel spacers, handlesandmany other machineparts. Lathes canalsocut threadsonmetal objectstohighlevelsofaccuracy andmuchquicker thantraditional methods. Lathesareusedinengineeringtomakeandmodify specialist machineparts toveryfinelevelsof accuracy. Figure 10.15 AmetalworkinglatheMachinebedMaterialbeingmachinedX-axisY-axisZ-axisFigure10.16AmillingmachinebedMillingMillingmachines usearotarycuttingtool, whichisusedinengineeringtoshapeandcreatemetal machineparts andother metal items. Themetal partisclampedontoaflatbedthatcanbe movedintwodifferent perpendicular axesbyturninghandlessimilartothoseona lathe. The millingtool is loweredtothelevel of thepart, whichisthenmovedalongoracross the cutter alongthetwoaxes usingtheturninghandles. Asthemillingcutterentersthe metal, thecuttingedges (flutes or teeth) of thetool shaveoff material byperformingmany separate, small cuts. This is accomplishedbyacutter withmanyteeth, spinningathighspeed. The speedof thecutter will dependonthetypeof metal beingmilled. Thespeedatwhichthe material is passedalongthecutter (alsoknownasthefeedrate)will alsovary. KEYTERMSLathe:Amachineusedformakingcylindrical-shapedobjectsbyspinning.Stepperdrill:Adrillbitthatdrillsprogressivelylargerandlargerholes.
170Chapter 10Metals Addition:joiningmetalsTherearemanywaysof joiningmetalstogether. Somearepermanentandsomearecalledtemporarymethods. Temporarymethodsallowthemetaltobe'un-joined'atalaterdate.Permanent methodsarenoteasilyundonewithoutcutting, damagingorevendestroyingthemetal parts. TemporarymethodsNutsandboltsOneof themost commonwaysof temporarilyjoiningmetaltogetherisbyusingnutsandbolts. Beforeabolt canbeinserted, asuitable-sizedholemustbedrilledinbothpiecesofmetal. Thebolt isthenpassedthroughbothholesandthenutisthreadedontheendofthebolt andtightened. Asthenutgetstighteritforcesthetwopiecesofmetaltogether.Tohelpspreadtheforceover aslightlywiderareaandgetabetterjoin,washersarealsousedeithersideof thetwometal pieces. Thereis awiderangeof differentnuts, boltsandwashersavailable.Differentcombinationsof length, diameter, headshape, material, finishandthreadpitchcanbeusedfordifferentapplications. Table10.7ApplicationsfordifferentboltsandscrewsBolt typeImageApplicationsHexboltsUsedinmachineryandconstruction.Canbefullyorpartthreaded.Tightenedwithspannerorsocket.MachinescrewsUsedinmachinery,constructionandhouseholdproductsandappliances.Fullythreaded.Tightenedwithaflatorcrossheadscrewdriver.ThreadcuttingmachinescrewsUsedinconstruction,bodywork,steelframebuildings.Pointis'self-tapping'socanbeboltedintoanon-threadedhole.
17110.4ManipulatingandjoiningBolt type ImageApplicationsSheet metal screws Designedtobedrivendirectlyintosheetmetal. Coarsethread'grips' theholeinthesheet steel. Oftencalled'self-tappers'.Socket screws Similar tomachinescrewsbutwithaninternal hexsocket fortighteningwithanAllenkey. Flange bolts Usedinenginesandautomotiveapplications. Bolt headhasa'flange',whichactslikeawasher. Permanent methodsPoprivetsPoprivets arecylindrical steel tubes that canbeinsertedinmetals tojointhemtogether. Likefor bolts, a suitable-sizedholemust be drilledinbothpieces of metal beforethepoprivet canbeinserted. Poprivets havetwoseparateparts: the pinandthesleeve. Touse poprivets youalsoneedapoprivet gun. Oncethepoprivet has beeninsertedintothetwopieces of metal thegunpulls thepinthroughthesleeve, distortingandspreadingtheendof thetubesothat it cannot slipthroughthehole andholdingthetwopieces of metal together. Figure10.17Apoprivetandrivetgun
172Chapter 10Metals Figure10.18Thepoprivetingprocess1Aholeisdrilledor punchedinbothsheetsofmetal. 2Thepoprivet isinsertedthroughaholeinbothsheets. 3Thegunpullsthepinthroughthetube, pushingthewallsout.Whentheballcangonofurther it breaksoff andthepinfallsout. Gluing(bonding)Metalscanbejoinedbystrongadhesivescalledepoxyresins.Epoxyresinshavetwoparts: theresinitselfandthehardeneroractivator, whichwhenmixedtogetherincorrectproportionsreactchemicallytoformanextremelystrongandtoughadhesive. Thereisawiderangeofdifferentepoxyresinproductsavailable.Theepoxyandhardeneraresuppliedintwoseparatetubesorsyringeswithdifferent-sizednozzles. Bysqueezingoutequallengthsofeachthecorrectmixtureproportionisdispensed,whichtheuserthenmixesandapplies.Figure10.19Asyringeepoxyresindispenser
17310.4ManipulatingandjoiningSolderingSolderingis a process that involves meltingmetal (calledsolder) ontoandintothepointwhere twometals meet inorder tocreateajoint. Therearethreeformsofsoldering, whichrequire increasingly hightemperatures andinturnprovideanincreasinglystrongjointstrength: lSoft soldering, whichuses atin- leador - copper alloysolder. lSilver soldering, whichuses analloycontainingsilver. lBrazing, whichuses abrass alloyfor thefiller. Soft solderinguses asolder that is analloyof twometals(mainlytin, withasmallerproportionof copper or lead), whichhas alowmeltingpoint(between180and200°C). The twopieces of metal tobejoinedareplacedtogether andtheareaisheated. Solderisthenfedintothearea, whichmelts andflowsaroundthejoint, fillinganysmall gapsand'enveloping' thetwometals. Theheat is thenremovedandasthejointcoolsthesolderhardens andfixes thejoint together. Soft solderingis usedinelectronics for thejoiningof electroniccomponents, electricalwires andcables, as it provides asolidconnectionwithout overheatingsensitiveelectroniccomponents. Electrical solderingheats thejoint usingasolderingiron, whichhasafinetipthat canconcentrateheat inasmall area. Thesolder comesintheformofathin'string'thatisfedintothe joint as required. Thesolder alsocontainsflux, whichisachemical thatremovescontaminates andhelps thesolder 'flow' intothejoint. Figure 10.20 AsolderingironjoiningelectroniccomponentsFigure10.21AsilversolderingtorchinuseSilver solderingis most commonlyusedtojoinsemi-preciousandpreciousmetalssuchasplatinum, gold, silver, copper andbrass. Silver soldersarealloysof mostlysilverwithdifferentmixtures of other metals andhavemeltingpointsof between600and750°C. Silversolderinguses a solderingtorchpoweredbygas suchasbutane, whichprovidesasmall high-temperatureflamethat canbeappliedtothedesiredarea. Thesolderisplacedontothejoint alongwiththeflux beforeit is heated. Asthejoint heatsupthesolderandfluxflowintoandaroundthejoint andtheheat is thenremoved. KEYTERMSSoldering:Meltingsolderaroundtwoormoremetalstocreateajoint.
174Chapter 10Metals Brazingisaformofsolderingthatusesveryhightemperatures. Brazingcanjoindifferentmetalssuchasbronze, steel, aluminium,wroughtironandcopperthathavedifferentmeltingpoints.Brazedjointscreateanairtightandwatertightbondthatcanbeeasilyplatedovertocreateaseamlessappearance.Brazingrequirestemperaturesofover1000°C;toachievethisanoxyacetylenetorchisused.Whenbrazing,thefluxisappliedtothejointintheformofapastebeforeitisheated. Thejointisthenheatedandthebraze,whichcanbeintheformofarod, wireordiscjoint,isthenfedintoandalongthejoin, whereitmeltsandflowsaroundthemetal beforebeingallowedtocool.WeldingWeldingisthemosteffectivewayofpermanentlyjoiningtwometalstogether.Weldingmeltsthetwometalsbeingjoinedandfusesthemtogether,effectivelymakingthemintoonesinglepiece.Therearedifferenttypesandwaysofweldingbutthetwomaintypesusedare: lgasortorchweldinglarcwelding. Figure 10.22BrazingGas or torchweldingusesanoxyacetylenetorchtomeltthetwometalsandthefillermaterial, fusingthemtogether. Theprocessissimilartobrazingbutthetemperatureusedinweldingishigher and, unlikebrazing, itisthetwometalsbeingjoinedthatareactuallymeltedrather thanjust thefillerrod. Gasoroxyacetyleneweldingisoftencalledbrazeweldingbecauseof thesimilarityintechniques. Gasweldingisnotwidelyusedtodayandhas largelybeenreplacedbyarcweldingtechniques, suchasmigortigwelding(seebelow).Gas weldingisusedmainlyformaintenanceworkasnoelectricityisrequiredandforweldingdelicatepartsandjointsinsoftmetalslikealuminium. Arcweldinguseselectricitytomeltthemetalsandtheweldingfillerbycreatinganelectricalarc. Anelectrical arcislikeatinylightningboltthatpassesbetweentwometals,generatingintenseheat that meltsthetwometalsandthefillermaterial,fusingthemtogether.STRETCHANDCHALLENGEAbox made fromsheet steel is shownbelow. Completethetablebelowtoshowtheprocessesandtoolsusedtomaketheboxintheworkshop.ProcessTools/equipmentCuttingthesheetsteel toshapeSmoothingtheedgesBendingthesteel intoshapeFixingthesidestogetherKEYTERMSBrazing: Solderingat very hightemperatures. Flux: Achemical that removes contaminates whensoldering. Welding: Afusionof metals causedby intense heat.
17510.4ManipulatingandjoiningFoldingMany metal objects aremadebyfoldingsheet metal intoshape. Metal canbefoldedbysimplybendingit over ina benchviceandhammeringthebendflat toget a neat crispfold. This is suitablefor small objectsbut larger metal sheets requireafolder. There are many different types of metal folder available but they all work inmoreor less thesameway. The metal is placedontothebedof themachine andclampedor heldinplacealongthecrease line. Thebedis thenhingedat thecreaseline, forcingthe sheet metal upwards andforminganeat bendor folduptoangles of 120degrees. Special folders areavailablethat clampandfoldthemetal onmorethanonesidetoformboxshapes. These are sometimes knownas box-and-panbrakes. After bendingthesides arefixedtogether bysoldering, weldingor rivetingtoformasolidbox. PressingMetal pressing(sometimes knownas stamping) isamethodof formingsheetmetal intoathree dimensional shapebypressingit betweentwoshapeddies. Thepiecesofsheetmetalcalled'blanks' arepressedintothesameshapeasthesurfaceof thedies. Metal pressingcanbe usedtoshapeandcut metal indifferent wayssuchascutting, embossing, bending, andflanging. It is widely usedinindustrytomakeawidevarietyof metal productssuchascarbody panels, brackets andmetal enclosures. Metal pressinguses largeandpowerful hydraulicpressestoprovidetheforceneededtopress the metal intoshape. CastingCastingis oneof theoldest metal shapingprocessesandhasbeenusedtomakemetalobjectsfor thousands of years. Castingmetal requiresthemetal tobeheateduptoamoltenliquidstate. It is thenpouredintoamouldwhereit coolsandsolidifiesintoasolidmetal shape. Themetal shapeknownas the'casting' is thenremoved. Usuallythecastingwill havevarious'nibs'that needfurther finishingbyfiling, machiningor grindingsmooth. Castingisoftenusedtocreate metal shapes that wouldbedifficult or impossibletomakeusingothermethods. Castingis still widely usedinindustrytocreateawiderangeof products. Therearemanydifferent andspecialisedmethods usedinindustrybut castingcanalsobedoneonverysmall scales ina school workshopusingmetalssuchaspewterandmouldsmadefromsandor evenMDF. SandCastinginvolves theuseof abucket or other container of dampsand. Whenasuitablyshapedobject is pressedintothesandit leavesaprintedindentof itsexactshapewhichthemoltenmetal canbepouredinto. Oncethemetal hassolidifieditcanbedugoutandthesandsimply brushedor washedoff. MDF moulds canbemadebymillingor chisellingout shapesinblocksofMDF. Apouringchannel andanair channel must alsobechiselledor milledoutfromtheshapetotheedgeof the material. Theblocks of MDFarethenboltedor screwedtightlytogetherandthemoltenmetal canbecarefullypouredintothemouldthroughthechannel. Oncesolidifiedthe blocks canbeunscrewedor boltedandseparatedtoreleasethecasting. MDFblockswithshapechiselledormilledoutPouringchannelChannelforairtoescapeBlocksscrewed,clampedorboltedtightlytogetherMetalcastingaftermouldisremovedFigure10.24TheMDFmouldprocessFigure10.23Afoldingmachinefoldingmetal
176Chapter 10Metals 10.5StructuralintegrityLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandhowandwhymetalsneedtobereinforcedtowithstandforcesandstresses,including:➜howandwhymetalscanbereinforcedtowithstandexternalforcesandstresses➜theprocessesthatcanbeusedtoensurethestructuralintegrityofaproduct.ReinforcingmetalShapingmetal Metals canbeshapedtoimprovetheirstructural integrity. Section5.4lookedathowfoldingor curvingapieceof paper cangiveitmorestructuralintegrity.Inthesameway,sheetmetalcanbecurved, foldedor formedintoshapestogiveitincreasedstrengthandrigidity.Anormal lengthof flat steel barwill bendquiteeasilyonewaybutnottheother.Afoldedsectionisdifficult tobendineitherdirection. Thisprincipleisusedtoincreasethestructuralintegrityof steel barsandbeamsusedinconstruction. Figure 10.25Aflat andbent steel bar. Aflat steel bar bendseasily this way around. Turningthesteel onitsedgemakesit much more difficult tobend. Figure10.26Afoldedsteelbar.Byfoldingthemetalitbecomesmuchmoredifficulttobend.T-section, I-section, U-channel andL-anglearecommonshapesgiventometalstoincreasetheir structural integrity. ACTIVITYTakeanormal flat metal ruler, andametal safetyruler.Lookatthesectionofeach.Trytoflextheflat metal ruler(butdon'tcompletelybendit)-you'llnoticethatit'sveryeasy!Nowtrytobendthesafetyrule. Thecurvesinthemetalmakeitmuchhardertobend.If youflattenedthesafetyruleitwouldbeaseasytobendastheotherone.
17710.5StructuralintegrityProcessestoensurestructuralintegrityAs describedearlier inthis chapter, themost commonwayof alteringthestructural integrityof metals is by mixingthemwithother metalsor substancestocreatealloys. Alloys canbecreatedthat combinethepropertiesof onemetal withanother. Forexample, Duralumin(analloy madeupof aluminiumandcopper) hasthesamelightweightpropertiesas aluminiumbut is muchstronger duetothesmall amountof copperadded. There are other treatments andprocessesthat canbeappliedtometalstomakethemharder, tougher or moreductile. HardeningandtemperingHardeningandtemperingaretreatmentsthat canbedonetoferrousmetalstoincreasetheir hardness andtoughness. Thetwoprocessesareusuallydonetogether. Thisisbecausethe hardeningprocess alsomakes themetal morebrittle, soafterhardeningthemetalistempered. Thetemperingprocess slightlyreducesthehardnessof themetal butincreasesitstoughness, makingit less brittleandless likelytosnap. The hardeningprocess involves graduallyheatingthemetal until itisglowingred, whichoccurs at around1050°C. Onceit reaches this'redhot' stage, itisthencooledveryquicklybyimmersingit incoldwater (calledquenching). Thisgradual heatingandrapidcoolingiswhathardens themetal. The temperingprocess is doneimmediatelyafter hardening, oncethemetal hasbeenremovedfromthecoldwater andcooledtoroomtemperature. Themetal isheatedgradually onceagaintoatemperatureof 175- 350°Cfor aroundtwohours. Itisthenallowedtocool gradually, whichtempers themetal. The temperatureusedfor temperingdependsontherequiredoutcomeofthefinishedmetal. Higher temperatures will result inasofter metal withgreatertoughness. Lowertemperatures will produceaharder but morebrittlemetal. CasehardeningCasehardeningis another methodof hardeningferrousmetals. Itiseasierthanthehardeningandtemperingprocess andis usuallydoneonmetalswithalowcarboncontent. Casehardeningonly affects theouter surfaceof themetal soitsotherpropertiesarenotaltered. Like the normal hardeningprocess, casehardeninggraduallyheatsthemetal until itisglowingred, whichoccurs at around1050°C. Onceit reachesthis'redhot' stageitisdippedintocasehardeningcompound. Casehardeningcompoundcanbeboughtinpowderedform. The compoundsticks tothehot surfaceof themetal andthemetal coolsdownalittle. Itisthenre-heatedgraduallytotheprevious temperatureandquicklycooledbyquenchingincoldwater. The process canberepeatedtofurther increasetheouter hardnessof themetal. AnnealingAnnealingis a process that is usedtoreduceametal'shardnessandincreaseitsductility, makingit easier towork. The annealingprocess is relativelysimpleandinvolvesgraduallyheatingthemetal untilitglows red, thenremovingtheheat andallowingit tocool veryslowly. Annealingisusuallydone onferrous metals but canalsobedoneoncopper, silver andbrass. Inindustry, largegas-firedovens or furnacesareusedfor thehardening, temperingandannealingprocesses. Themetals areoftenleft insidetheovensaftertheyareshutoffsothatthey cool very graduallyinacontrolledmanner. KEYPOINTSlMetalsgetharderthemoretheyareworked.lAnnealingcanbedoneatanypointtomakemetalseasiertowork.KEYTERMSAnnealing:Reducingthehardnessofametalandmakingitmoreductile.Casehardening:Hardeningtheoutersurfaceofametal.Tempering:Usingheattomakeametallessbrittle.Toughness:Abilitytoresistbreaking,bendingorsnapping.
178Chapter 10Metals Largesaltwater troughsareoftenusedforquenchingbecausetheyreducebubblingandcool metal faster thanjustwater. Hardening, tempering, casehardeningandannealingcanallbecarriedoutinaschoolworkshopusingabrazinghearthandoxyacetylenetorch. ACTIVITYWatchyour teacher completethefollowingdemonstration:1Takealengthof mildsteel around30cmlong.Usingthebrazinghearthandoxyacetylenetorch, hardenoneendoftherodorbar.2Oncecooled, placethebarorrodinavice.Takeahacksawandcutasmallpieceofftheuntreatedend. Nowcutapieceoffthetreatedend.Howmuchharderwasittocut?3Trycasehardeninganotherpieceofsteel barorrodandrepeatingtheexercise.Whichprocess makesthesteel hardest?STRETCHANDCHALLENGECreateastep-by-stepguideusingdiagramsandnotestoshowsomeonehowtodooneoftheaboveprocesses. 10.6MakingiterativemodelsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜howprocessesandtechniquesareusedtoproduceearlymodelstosupportiterativedesigning. ProcessesandtechniquesforiterativemodelsMetals canbeusedinavarietyof useful andinterestingwaystohelpyouexploreyourearlydesignideasandsupportiterativedesigninginschool. Metal wireandthinmetal rodsareexcellentfordevelopinginitialideas.Theyarequickandeasytobendandfoldandarerelativelyinexpensive. Weldingrodscomein900mmlengthsandcanbebentintodifferentshapesbyhandorwithplierstoformframeworksorsupportsformodelideas. Theycanbetwistedtogethertomakemoreintricateshapesanddesigns. Thinmetalrodscanbeveryusefulforcreatingpivots, jointsandaxlesinworkingmodelsofmechanismsormovingparts.Inthesameway, stripsof thinmetal suchascopperandaluminiumcanbebentbyhandor withhandtoolstoformsimpleshapesthatcanbethebasisformodelsofideas.Thickermetal canbebent andformedusingaviceandhammerormetalfolder(seethenextsectiononmanipulatingandjoining). Steel or aluminiummeshisacommonlyusedmetalmaterialformodelling.Therearemanydifferent typesandvarietiesof meshavailable. Chickenwireisaverythinmeshmadefromthinwire. It canbeeasilycut, bentandtwistedintodifferentshapesbyhandandisoftenusedtoformthebasicshapesof 3Dmodels. Itcanthenbecoveredwithpapiermâchéor other modellingmaterialsif required. Withpractice, meshcanbemadeintoextremelyintricateshapes. KEYTERMSQuenching: Rapidly coolinghot metal by immersingincoldwater.
17910.6MakingiterativemodelsThinsheet metals suchas tinandaluminiumfoil arewidelyavailableandinexpensive. Foil canbe usedinmodellingtocover Styrofoamor cardboardshapesorshapesmadeinother materials inorder togivethemametalliclook, tomakethemreflectlightortoaddstrength. Foil is easy tocut andshapelikepaper but will holditsshapebetteroncecreasedor folded. Foil canbescrunchedupandmouldedbyhandtoformall mannerofshapesthat canbe extremely useful for modelling, includingsculpturesanditemsofclothing. Duetoits electrical conductivityit is alsoextremelyuseful for modellingsituationsusingsmallelectrical components suchas bulbs, LEDs, motorsandsoon. Figure 10.27 Amodel frameworkmadefromweldingrodsFigure10.28ChickenwiremeshmodelsACTIVITYTakesomethinmetalwire,chickenwireorpipecleaners(theyaremetalwireinsidethefurrycoating).Bytwistingandbendingthewire,designandmodelachildren'sclimbingframe.ACTIVITYExperimentwithfoilandtrymakingsomeanimalorhumansculpturesusingjustyourhands.Figure 10.29 Afoil model
180Chapter 10Metals 10.7FinishesLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandhowmetalscanbefinishedfor differentpurposes,including:➜function➜aesthetics. Most metalsrequireafinishof somekindtoprotectthemfromdamageortoimprovetheirappearance. Thetypeof finishwill dependonthetypeofmetalandhowtheproductistobeused. For example, asteel machinepartmaynotrequireafinishthatlooksnicebutwill needsomesort of protectionfromrusting. Thismaybeassimpleasasprayofoil.Asteel bicycleframe, however, will needtohaveaniceappearanceandbeprotectedfromcorrosion, soasuitablesurfacecoatingneedstobeapplied. Ferrous metalsinparticular aremuchmoresusceptibletocorrosionandwillbegintocorrodealmost immediatelyif leftunfinished. Somemetalsmayrequirenofinishingofanykind.Thisis calledaself-finish. PaintingPaintingisoneof theeasiestandquickestmethodsoffinishingmetal.Paintingiscommonlyusedonferrousmetalstopreventcorrosion. Beforeanypaintcanbeappliedthemetalmustbecleanandfreeof anyrust. If surfacerusthasalreadyoccurreditcanberemovedusingabrasivepaper or awirebrush. Itmustthenbecleanedtoremoveanyoil,greaseorothersubstancethat maypreventthepaintadheringtothesurface.Aprimer shouldfirst beappliedtopreventrustreforming, helpthepaintsticktothemetalsurfacebetter andaddanextralayerofprotection. Awiderangeof differentpaintsareavailableformetal: lWater-based(latexor acrylic) paintslSolvent-based(mineral spiritorthinner)paintslOil-basedpaints. Traditionally, oil-orsolvent-basedpaintsweretheonlysuitablepaintsforferrousmetalaswater-basedpaintwouldnotgivesuitableprotectionfromcorrosion.Newadvancesinpainttechnology,however,havemeantthatwater-basedpaintsarenowequaltooil-andsolvent-basedcoatings. Oil-andsolvent-basedpaintscontainhighlevelsofsolventsthatreleasevolatileorganiccompounds(VOCs)intotheatmosphere.VOCsarecarcinogenicandharmful totheenvironment.Becauseofthehealthrisksandenvironmentalhazards,paintmanufacturersaredevelopinglowornon-VOCpaints.Thesewater-basedpaintsareeco-friendlyandnotharmfultohumans.Metal paintcanbeappliedbybrushorrollerorbyspraying. AwiderangeisavailablefromDIYoutlets.Specialistpainterssuchascarbodyworkworkersusespecial 'twopackpaints', whichconsistofapolymerresinthatismixedwithahardenercalledpolyisocyanateresin.Figure 10.30Metal paints KEYTERMSSelf-finish: Thenatural finishof ametal.
18110.7FinishesPolymer resinis a clear liquidplastic. Whenit ismixedwiththehardener, achemical reactiontakes place andit begins tohardenor 'set' withinafewminutes. Thehardenedandfullysetresinmix creates a durable, glossyandwaterproof coating. Twopackpaintsaremuchharderthansolvent-basedpaints andmoreresistant topetrol, acidrainandsunlight. (Formoreinformationonpolymers seeChapter 13.) Many paints areavailablethat claimtogiverust protectiononferrousmetalswithouttheuseof a separateprimer. Thesetypes of paint haveazinc-basedprimermixedwiththepaintthatseals the rust toprevent it fromspreading. Inpracticethesetypesof paintarenotaslonglastingor rust-resistant as usingaseparateprimer andtopcoat, buttheydooffera'quickfix'. LacqueringLacquer canbeusedas analternativetopaint wherethenatural colourofthemetal isrequiredtoshowthrough. Lacquer dries toacompletelyclear, colourlessfilmthatpreventsoxidisationandtarnishingof themetal's surface. It isoftenusedonmetalssuchasbrass, copper, bronzeandsilver that havelustrous, attractivefinishes, ratherthanonferrousmetals. Like paint, lacquer is availableintins for applyingbybrushandincansforsprayapplication. Whenapplyinglacquer it is vital that thesurfaceof themetal isnottarnishedandisfreefromany contaminates suchas wax, greaseandmetal polish. If thesurfaceisnotpreparedproperly theclear lacquer cangoayellowyor milkycolour afterashortperiodoftime. StoveenamellingStoveenamellingis similar tospraypaintingbut the dryingor 'curing' process is speededupbyusingheat. The metal is preparedandsprayedinthesameway but is thenbakedinanovenat temperaturesfrom150 to200°C. Theresultingfinishis oneof thefinest paint finishes availablefor metal. It combinesahigh-quality finishwithatough, durablecorrosionresistant andlong-lastingsurface. Awiderangeof colours andeffects is availableandmetalliccolourscanalsobe stoveenamelled. Stove enamellingis suitablefor hightemperatureenvironments andapplications throughtheuseof special, heat-resistant paints. Becauseof this, stoveenamellingis oftenusedfor metal productssuchasradiators, kitchenwareandwood-burningstoves. PowdercoatingPowder coatinguses adrypowder madefromapolyester, polyurethane, epoxyoracrylicpolymer providingaglossy, shinyfinishthat ismuchmoredurablethanpaintorlaquer(formore informationonpolymers, seeChapter 10). Before metal canbepowder coatedit must becleanedtoremoveoil, dust, greaseandrust(most commonly by shot blastingor sandblastingthemetal). The metal tobecoatedis hungfromawirethat hasasmall negativeelectrical chargeappliedtoit. Thepowder is sprayedontothemetal usinganelectrostaticgunorcoronagun. The gungives thepowder apositiveelectrical chargesothatitisattractedtothenegatively chargedpieceof metal. This meansthat thereisverylittleoversprayasthepowder is drawntothemetal andclings toit. Figure10.31AstoveenamelledproductKEYTERMSPowdercoating:Acoatingofelectricallychargedpowderthatisbakedontoachieveatoughfinish.Stoveenamelling:Apaintcoatingthatisbakedontoachieveatough,durablefinish.
182Chapter 10Metals Oncethemetalitemiscoatedinalayerofpowderitisheatedorbakedinalargeovenat200°Cforapproximatelytenminutes.Asitisheatedthepowdermeltsandthenchemicallyreactstoformastrongchemicalstructure.Themeltedpowderformsasmooth,evencoatingoverthemetal.Oncecoolthecoatinghardensandformsanextremelytoughandresilientcoating.Powdercoatingisoftenusedonhouseholdappliancessuchaswashingmachines,dishwashersandfridges,aswellasbicycleandmotorcycleframes,alloywheelsoncars, andstructuralgirders.EnamellingEnamellingisanancient processthatwastraditionallyusedonmetaljewellery.Itisstillusedfor coatingmetal jewellerytodaybutsincethenineteenthcenturyithasalsobeenusedas anindustrial coatingonmanyothermetal products, suchaskitchenware,dishwashers,washingmachines, bathsandsinks. Theenamellingprocessinvolvespowderedglassthatisheatedinanoventobetween750and850°C. Theglasspowderthenmeltsandspreadsacrossthemetalinasmooth,evenlayer. Whenthemetal coolstheglasshardenstoasmooth, durablecoating.Most modernindustrial enamel (vitreousenamel)isappliedtosteelbutitcanalsobeappliedtogold, silver, copper, aluminium, stainlesssteelandcastiron.Vitreousenamel issmooth, hard, chemicallyresistant, durableandscratch-resistant,haslong-lastingcolour fastness, iseasytoclean, andcannotburn. Awiderangeofcoloursisavailableanddifferent colourscanbemixedtocreatenewshades, similartopaint.Transparent,opaqueandtranslucent finishesareavailable. Adisadvantageof enamel isthatitcancrackorshatterwhenthemetalisstressedorbent.Figure10.33EnamelledjewelleryFigure 10.32Apowder- coated bicycle frame
18310.7FinishesPlatingMetal platingis a process that lays athinsurfacecoatingof onemetal ontoanothertypeofmetal; it is donefor thefollowingreasons: lDecorationlCorrosioninhibitionlToimprovesolderabilitylTohardenlToimprovewearabilitylToreducefrictionlToimprovepaintadhesionlToalter electrical conductivity. There are several different platingmethods. ElectroplatingElectroplatingis widely usedinindustryfor coatingmetal objects. Electroplatingincreases thelifeof metal andprevents corrosion. It is alsousedinmakinginexpensivejewellery, by coatingcheaper metal suchascopper witha thinouter layer of amoreprecious metal suchasgoldor silver. Electroplatinguses anelectriccurrent tomakedissolvedmetal atoms forma metal coatingonanother metal. The metal that is goingtobecoatedor platedisgivena negative electrical charge. Themetal it will becoatedwithis givena positiveelectrical charge. Bothmetals arethenimmersedinasalt solutionof themetal that will beusedtoplatetheobject (e.g. silver platinguses silver nitratesolution). Themetallicionsof the solutionarepositivelychargedandareattractedtothe negatively chargedmetal object. Oncetheyconnect, they revert back totheir metallicformonthesurfaceof the metal, creatingathincoating. ElectrolessplatingElectroless platingdeposits metal onanobject without the use of anelectric current. It is oftenusedtoplateunusually shapedobjects, whicharedifficult toplateevenly withelectroplatingas it deposits metal evenlyalongedges, insideholes andincavities. Theelectrolessplatingprocess uses hydrogen, whichreactswiththemetal ions toproduceanegativechargeanddeposit metal onthesurfaceof thepart. Themost commonelectroless platingmethodis electroless nickel plating. Gold, silver andcopper canalsobeappliedbyelectroless plating. -+SilverCathodeCopperAnodeSilvernitratesolutionFigure10.34ElectroplatingTable10.6PlatingisdoneusingmanydifferentmetalsMetal plateMetalplatedoverUsesandapplicationsGoldplatingCopperSilverNickel Jewellery,electricalconnectors,printedcircuitboardsSilverplatingTinAntimonyCopperJewellery,cutlery,candlesticks,musicalinstrumentsChromeplatingSteel Nickel CopperCarparts,bathtaps,kitchengasburners,wheelrimsZincplatingSteel Screws,nails,bolts,roofingsheets,outdoorbuildinghardwareTinplatingCopperNickel IronFoodcansKEYTERMSPlating:Coatingonetypeofmetalwithanothertoimproveappearanceorcorrosion-resistance.
184Chapter 10Metals GalvanisingGalvanisingisamethodofmetalplatingthatappliesacoatingofzinctoferrousmetalstopreventthemetalbeneathcorrodingbypreventingoxygenandmoisturereachingit.Themostcommonmethodofgalvanisingiscalledhotdipgalvanising.Zincisheatedtoatemperatureof450°Csothatitmeltsandbecomesmoltenzinc.Theferrousmetalisthenloweredandimmersedinthetankofmoltenzinc. Areactionoccursbetweentheferrousmetalandthemoltenzinc,creatingaseriesofmetalalloylayersacrossthesurfaceoftheferrousmetal;thiscompletelycoatsandpenetratesthesurfacetocreateafirmbond. Afterfiveminutesthemetalisremovedfromthemoltenzincandallowedtocool.Galvanisedmetalhasacrystallisedpatternonthesurfacecalled'spangles'.As for most other typesof metal finish, themetal beinggalvanisedmustbecleanandcompletelyfreefromgrease, oil andcorrosionforthechemicalreactiontoworkproperly.Beforethegalvanisingprocess, metal partsarewashedinaseriesofdifferentsolutionstoremoveall contaminatestoensureagoodfinishisachieved. Galvanisingisusedonawiderangeofproducts, suchasroofingsheets,metalbuckets,industrial fencing, gatesandmotorwayArmcobarriers. DipcoatingDipcoatingsonmetalsinvolvecreatingathermopolymercoatingonthesurfaceofthemetal.Avarietyof different thermopolymerssuchaspolyethelene, nylonandPVCcanbeused.Themetal tobecoatedisheatedtobetween250and400°Candthethermopolymersinpowderedformcanbeappliedtothemetal inavarietyofdifferentways.FluidisedbedcoatingFluidisedbedcoatingisthemostcommonlyusedmethodofdipcoating,andsmallfluidisedbeddipcoatersareavailableinmanyschools. Thefluidisedbediscreatedbyblowingairintoatankcontainingthepowder. Theairmakesthepowderlookandbehavelikealiquid.Themetal itemisheatedtothecorrecttemperatureandcompletelyimmersedintothisfluidisedbed. Thepowder meltsoncontactwiththemetal andtheitemisthenliftedoutofthefluidisedbedandcooledtoleaveahigh-qualitypolymercoating.ElectrostaticsprayThis methodissimilar tothepowder-coatingprocess. Thethermopolymerpowderiselectricallychargedandsprayedontotheearthedmetalitem,thenplacedinanindustrialovenandheateduntil thepowdermelts. Theitemisthencooledtoleaveahigh-qualitypolymer coating. FlocksprayingFlocksprayingisasimpleprocess. Themetal isheatedtothecorrecttemperatureandthethermopolymer powderissprayedontothehotmetalusingcompressedair.Thepowder meltsoncontactwiththemetal andisthenlefttocooltoleaveahigh-qualitypolymer coating. Figure 10.35Agalvanisedmetal surface, showing'spangles' KEYTERMSGalvanising: Coatingsteel withzinc tostopit corroding.
18510.7FinishesExtrusionExtrusionis usedfor coatingmetal wire. Thewireispassedthrougha tank of moltenpolymer, whichcoatsthewire, andit is thencooledtoleaveacontinuouspolymer coating. PolishingPolishingandbuffingareusedfor smoothingthesurface of a metal toenhancetheappearance, prevent contaminationandcorrosion, removeoxidationandcreatea reflective surface. Polishingis amoreaggressiveprocess, whichremoves deeper scratches andblemishes, whereasbuffingis less harsh, andremoves thefiner scratchesandgives a smoother, brighter finish. Whenpolishingmetals, aroughabrasive(60or 80grit) will be usedfirst. As thepolishingprocesscontinuesfiner andfiner abrasives areused, throughtoextremelyfinegritabrasives suchas 400or more, leavingsmaller andfiner scratches that arenot visibletothenakedeye. Once the metal has beenpolishedthroughall theabrasives, it canbebuffed. Buffingmaybedonebyhandor usinga polishingwheel, ahigh-speedpolishingmachineor another machinetool that canbeusedfor buffingor polishing, likeanelectrical drill. Thereis awiderangeof different polishingandbuffingmops availablealongwitha large selectionof different buffingcompounds. Differentmetals requiredifferent combinations of mopsandcompounds toachieveagoodfinish. STRETCHANDCHALLENGE1 Use the internet tolookat different types of jewelleryandsilverware. Comparetheprices of platedproducts tothe prices of puresoliditems. 2 What are the benefits totheconsumer of electroplating? ACTIVITYAsk your teacher for some'scrap' pieces of steel. Cleanthesteel upusinganabrasivepad. Apply different finishes suchas paint, varnishandsoontoeachitembutleaveonepiece of steel without afinishapplied. Leavethescrappiecesofsteel outsideforafewdays. Evaluate howeffectivethefinishes havebeeninprotectingthemetal fromcorrosioncomparedtothe metal without afinishapplied. ACTIVITYFind examples of metal products at home, school or outside. Identifywhattypeoffinishhas beenapplied, andexplainwhy. Figure10.36Plastic-coatedtoolsKEYPOINTSlMostfinishesareappliedtoferrousmetalstopreventcorrosion.lPolishingcompoundsworkbyusingmildabrasivestoremovescratchesfrommetal.PlasticsSilver,goldandthinplasticsNickelandchromeplateCopper,brass,aluminium,potmetalandothersoftmetalsSteelandironStainlesssteelBufftypeABCABCABCABCABCABCSisal XXXSpiral sewnXXXXLooseXXXCantonflannel XXStringXXXCompoundABCABCABCABCABCABCBlackXXXBrownXWhiteXXXBlueXXXXXXGreenXXRedXXXFigure10.37Apolishingcompoundcolourchart
186Chapter 10Metals ACTIVITY1Findexamplesof metal productslistedinthetablebelowathome,atschooloroutside.Completethetabletoidentifywhattypeoffinishhasbeenapplied,andexplainwhy.Product FinishExplainwhythefinishhasbeenappliedClimbingframeinaparkGalvanisingWill notrust,looksattractive,willnotwearoff.Fencemadefromsteel PaintingCanbedone'in-situ'BicycleframeRadiator Silver jewellery 2Choosetwoother examplesofmetal productsinthehome,atschooloroutside.Identifywhat finishhasbeenapplied,andexplainwhy.10.8UsingdigitaldesigntoolsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandhowindustryprofessionalsusedigital designtoolswhenexploringanddevelopingdesignideas,including: ➜theuseof 2Dand3Ddigital technologyandtoolstopresent,model,designandmanufacturesolutions. DevelopingideasandmanufacturingproductsArangeof digital toolscanbeusedfordevelopingideasandmanufacturingproductsinmetal. Computer-aideddesign(CAD)isadigital designtoolthatcanbeusedbydesignerstoproduceworkingdrawingsusingcomputersoftwre, ratherthanbyhand.Italsoallowsdesignerstocreateboth2Dand3Dvisualisationsofconcept.Computer-aidedmanufacture(CAM) canbeusedinvariousformswithmetals. ManyoftheCAMmachinesarecomputer-controlledversionsof theexistingmetal-shapingtoolsasdescribedinSection7ofthis chapter: lCNCmillingmachineslCNClatheslCNCplasmacutters. Thesetypesof CAMequipmentcarryoutthesametasksandworkinaverysimilarwaytothehand-operatedtools, butthemovementofthecuttingtooliscontrolledbyacomputer.Specialist programsareusedtoprogrammethemachineryandarethenloadedontothemachine. CAMmachines- f or examplelathesandtoolsforcuttingsheetmaterials,suchasplasmacutters cancut toextremelyhighaccuraciesofuptoone-thousandthofamillimetre.Theyareabletoproducedetailedproductsofconsistentsizemuchquickerthanahumanoperative. STRETCHANDCHALLENGECreateaseriesof designsforsomechessorgamepiecesthatcouldbemadeoutofaluminiumonaCNClathe. KEYTERMSCAM: Computer- aidedmanufacture. CNC: Computer numeric control. Origin: The startingpoint for a CNCor CAMmachine, fromwhichall coordinates are taken.
18710.9ManufacturingmethodsandscalesofproductionLaser cuttersLaser engravingandlaser cuttingmachinesareCAMmachines that canbeusedfor cuttingthinsheet metalsalthoughnot all laser cutters arecapableof cuttingmetals. Laser cutters canaccuratelymarkandengravemost polymers andsomemanufacturedtimberssuchasplywoodandMDF. Larger andmorepowerful typesareavailable that cancut sheet metals, ceramics, glassandevenstone. Laser cutters aresuitablefor cuttingthinsheet materials only andthedepthof cut cannot accuratelybe programmed. Thereforetheyareof useonlyfor engravingthesurfaceof amaterial or cuttingall thewaythroughit. 10.9ManufacturingmethodsandscalesofproductionLEARNINGOUTCOMESBy theendof this sectionyoushouldknowaboutandunderstandhowprocessesvary whenmanufacturingproductstodifferentscalesofproduction,including:➜themethods usedfor manufacturingat differentscalesofproduction.ScalesofproductionDecidingona suitablescaleof productionandmanufacturingmethodforyourmetalparts depends ona number of factors: lForm: What shapeareyour parts? Thiswill belimitedbytherestrictionsofthemanufacturingprocesses available. lBudget: Part cost andtoolingcost. Somemethodshaveexpensiveset-upcosts; others arequitecheap, but there's usuallyatrade-off. Mosthighvolumemanufacturingprocesses areexpensivetotool but offer cheapparts- theoppositeisalsotrue: lowvolume processes arecheaptoset upbut partsareexpensive. lTime: Toolingtakes time; manufacturingtakestime. Moreexpensivetoolingusuallymeans longer set-uptime. lMaterial: Material choiceis determinedmostlybyform, functionandcost. One-off productionOne-off productionof metal products isexpensiveandtime-consuming. One-offproductionrequires skilledworkers whoareexperiencedwithmetalworkingandcanusearange of techniques. If a metal product is producedas aone-off thematerial will firstneedtobecuttosize. Ifthe product is madefromanumber of different separatepiecesthematerialsforthesewillneedtobe cut usingappropriatetools. If certainpartsaremadefromsheetmetal andotherparts are madefromrod, bar or channel, thesewill requiredifferentcuttingtechniquesandequipment. Shaping, bendingor foldingmetal isdifficult todowithoutspecialisttoolsbutone-off products oftenneedtobemadeusingbasictoolsasitisnotcosteffectivetoinvestinexpensivejigs andsoonfor just oneproduct. Figure10.38AlasercuttercuttingmaterialKEYTERMSOne-offproduction:Makingonlyoneorasmallnumberofproducts.Usuallyusedforspecialistproducts.Scaleofproduction:Thenumberofproductsbeingproducedinonego.
188Chapter 10Metals Joiningmetalstocreateone-off productswouldmostlikelybecarriedoutusingamigwelder. Specialist firmscandoone-offweldingjobsbutthesecanbeexpensive.Althoughmanybuildingsthatusesteel framesandcladdingareone-offs,thematerialsusedarestandardmass-produceditemssuchassteel beams, girders,standard-sizedsheetmetalsanduniversal fixingssuchasboltsandrivets. Somecommonmetal productsthataremadeasone-offsarebespokeitemssuchasfurniture, metal gates, customvehiclesandparts, andarchitecturalfittingsincludingfireescapesandstaircases. BatchproductionBatchproductioninvolvesmakingaproductstagebystageinbatches.Thiscanbedonebythesamepersonor byhavingdifferentpeoplecarryingouteachstage.Batchproducedmetal productsmayhaveapersonwhoisresponsibleforcuttingthepiecesofmetaltosize.Thenanother personshapesanddrillsthemetal parts, anotherassemblestheproduct,andanother appliesafinish. Batchproductionisoftenusedinthemanufactureofsimilarmetalproductsthat mayhaveacommonsectionbutseveralvariations,suchasgardengatesorhandrails. MassproductionMassproductionisthemostcommonlyusedformofproductionformetalproducts.Productionofteninvolvestheassemblyofanumberofsmallersub-assembliesofmetal components, whichwhenassembledarefedontothemainproductionline.Metalpartssuchasfasteners,brackets, hingesandotherhardwaremaybeboughtfromothercompaniestospeedupthemanufacturingprocess. Manyoftheassemblyandproductionprocessesuseautomationinsteadofhumans.CNCmachinescanalsobeusedtomakecertainpartsbuttheseusuallyrequireahumanoperative.Automatedproductionlineshavemachinesthatcancut,foldandpressmetalintoshape. Robotsareusedtoposition,weldandrivetmetal partstogetheraswellastoapplyfinishes.Thevastmajorityofmetalproductsweuseonaday-to-daybasis,suchascutlery, cars, pens,chairs,railings,etc.,havebeenmassproduced. STRETCHANDCHALLENGEResearchthedifferent assemblyandsub-assemblylinesusedinacarormotorcycleproductionline. Drawadiagramshowinghowthedifferentsub-assembliesfeedintothemainproductionline. Figure 10.39Anautomatedproductionline and robot welder KEYTERMSBatchproduction: Makinga set number of products that canhave some variations. Mass production: Large-scale productionof anitemor product.
18910.10Costandavailability10.10CostandavailabilityLEARNINGOUTCOMESBy theendof this sectionyoushouldknowaboutandunderstandhowcostandavailability of specificmetals canaffect decisionswhendesigning,including:➜thesignificanceof thecost of specificmetals➜howtocalculatethequantities, costsandsizesofmetalsrequiredinadesign➜considerationof suitabletolerancesandminimisationofwaste.ThesignificanceofcostDuringthe designanddevelopment of anewproduct therearemanyfactorsthatwillinfluence your choiceof materials. This sectionlooksat howthecostandavailabilityofdifferent metals canaffect your material choices. As withany other materials, themorethat youbuy, thecheaperitbecomes. Thisiscalledbulk buyingor bulkdiscounting. Alargemanufacturingcompanythatrequireslotsofsheet steel andbuys hundreds of sheets per year will paylesspersheetthanasmallerfirmorindividual whomay buyonlyoneor two. The prices of individual metals cangoupanddownbysignificantamountsdependingonthe current supply anddemandandthepredictedfuturesupplyanddemand. Thepricesofdifferent metals arealittlelikethestockexchangeandcansometimeschangeonanhourlybasis. There aremany websites that showup-to-datemetal prices. Because of themany different types of metals, pricesandquantities, metalsareseparatedintofive different market groups: lBase metals - s uchas copper, tin. lSteel andferro-alloys. lMinor metals - s uchas indium, tungsten, molybdenum. lPlatinumgroupmetals (PGMs) - s uchasplatinumandosmium. lPrecious metals - s uchas goldandsilver. Althoughthemarket prices of metals affect thecost for manufacturers, theyusuallybuyspecific grades, forms andquantities of metal andincertainstockforms(seeSection7.3). Theprices of metals onthemarkets will affect thepricesof thesestockforms, butotherfactorsthat gointomanufacturingof themetal product arenot affectedbyitsprice. Thereforealarge price increaseinthemarket mayresult inonlyasmall increasetothemanufacturedproduct. For example, evenif thepriceof copper goesupsignificantly, thepriceofacopperpipe may increaseonly alittle, as thelabour, energyandtransportcoststomakethepiperemainthe same. ReducingcostsWhenthe availability of acertainmetal becomesextremelylimitedand/orwhenthepricesmake usingit for a designuneconomic, therearealternatives: lUsinga similar metal or alloythat costsless. lPlatinga cheaper metal withmoreexpensivemetals. Precious metals oftenfluctuateinprice. Whengoldpricesarehigh, youwill tendtoseenumerous TVadverts fromcompanies offeringtobuyunwantedandbrokengoldjewellery. Whena metal is beingusedfor aproduct becauseof aparticularqualityitmayhave, thereare frequently alternatives that maybeverysimilar but muchcheaperand/ormoreavailable. Agoodexampleof this is pewter, whichhasasimilar colour tosilverandcanbepolishedtoa highshinetolook almost thesame. Inthecaseof industrial metalssuchassteel, alowergrade may bechosentosavemoneywherethiswill not affectthesafetyorfunctionalityofthe product. KEYTERMBulkdiscount:Reducedpriceofitemsforbuyinglotsatatime.
190Chapter 10Metals Platingiscommonlyusedinjewellery-makingtoreducecosts. Byelectroplatingalessexpensivemetalsuchascopper, jewellerycanbegivenathincoatingofgoldandmadetolookandfeelliketherealthing.Inthesameway,mildsteel -whichismuchcheaperthanstainlesssteel-canbeplatedinmetalssuchaszinctostopitrusting.Platedmetalsareacheaperalternativetotherealthing,buttheplatingdoesnotlastindefinitelyandwillwearoffafteraperiodoftimetorevealthebasemetal.If,however,thelifecycleofaproductrequiresittolastonlyalimitedperiodoftime, thenplatingcanbeaviablealternativefordesignerswhencostoravailabilitypreventstheuseoftheirchosenmetal. Howtocalculatethequantities,costandsizesofmetalsrequiredCalculatingthequantitiesof materialsneededtomakeaproductandthecostofthesematerialsisimportant whendesigningandmaking. Ifadesigncostsmoreoralmostasmuchtoproduceasit islikelytosell foritisnot'costeffective'tomake.ExampleAmetal shelf bracket ismadefromthreepiecesofflatsteelbarasshownbelow.Tomakeonebracket:200+195+225=620mmofsteelisneeded.Thesteelbarcosts£16.45fora2mlength.620mmx3=1860mm(140mmiswasted).Onelengthofbarmakes3PieceB195mmlongPieceC225mmlongPieceA200mmlongFigure 10.40Asilver- plated item
19110.10CostandavailabilityACTIVITYAcomponent madefrom5mmsteel plateis shownbelow. Thecomponentswill becutfroma sheet of steel plate10002000mmbyaCNCwater jetcutter. 12070 lCalculate the best way tominimisewastebygettingasmanyaspossibleoutofonesheet. lIf the 10002000mmsheet costs £200, calculatethecostpercomponent.lThe water jet cutter costs £28anhour torun. It takes90secondstocutoutonecomponent. By howmuchdoes this increasethemanufacturingcostpercomponent?Considerationofsuitabletolerancesandminimisationof wasteDesigners shouldideallylookat ways tominimisewastematerialswhenusingmetals, butif this is not possiblethescrappingandrecyclingof thewastecanrecoversomeofthematerial costs. The vast majority of metals usedinindustryarerecycled. Itisfarcheapertorecycleanexistingmetal thantomine, extract andprocessnew. Specialistmetal recyclingcompaniespurchase andcollect scrapmetal frombusinessesandmanufacturingplantstorecycle. Likethe market prices of metals, thevalueof scrapmetalsincludingsteel, aluminiumandcopperrise andfall accordingly.
192Chapter 11Polymers CHAPTER11PolymersYoulearnt about thedifferenttypesofpolymersinSection5.1.Thischapterincludesmorein-depthinformationonpolymers. 11.1PhysicalandworkingpropertiesLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstandthephysicalandworkingpropertiesofarangeofpolymers,including:➜howeasytheyaretoworkwith➜howwell theyfulfil therequiredfunctionsofproductsindifferentcontexts.PlasticsandpolymersManufacturedplasticsandnatural materialssuchasrubberorcellulosearecomposedofverylargemoleculescalledpolymers. Polymersareconstructedfromrelativelysmallmolecularfragmentsknownasmonomersthatarejoinedtogether. Rubber andcelluloseareexamplesofnatural polymersthathavebeenknownaboutandusedsinceancient times. Syntheticpolymers, includingthelargegroupknownasplastics, grewinimportanceintheearlytwentiethcentury. Chemists'abilitytoengineerthemtoachieveparticular properties(strength, stiffness, density,heatresistance,electrical conductivity) hasgreatlyexpandedthemanyrolestheyplayinthemodernindustrial economy. Whychoosepolymers?Syntheticpolymersaregenerallyeasytoprocessandtheycanbecosteffective.Thismeansthat high-qualityproductscanbemanufacturedatrelativelylowcost.Polymersthatarenowavailablehaveawiderangeof properties, someofwhichareveryspecialised.Polymers Natural SyntheticThermosettingElastomers ThermoplasticsFigure 11.1 The relationshipof polymerswithplasticsGenerally, polymersare: llightweightlwaterproofltoughlelectrical and/orthermalinsulatorslresistanttoatmosphericdegradation(theyneitherrustlikemetalsnorrotliketimber).Inaddition, byvaryingtheadditivestheycanbemade:ltransparentoropaquelrigidorflexible. Polymerscanalsobeengineeredtohavespecialisedproperties, suchaswatersolubility,electricalconductance,hightemperatureresistanceandbiodegradability,andeventobepiezoelectric(tohavetheabilitytogenerateelectricitywhenbentortwisted).Thesectionsthatfollowdescribehowcommonpolymersareclassed.KEYTERMSMonomer: Amolecule that canbe bondedtoother identical molecules toforma polymer. Polymer: Asubstancethat has a molecular structure built upfroma large number of similar units (monomers) bondedtogether. Synthetic: Amanufacturedsubstance that imitates a natural product.
19311.1PhysicalandworkingpropertiesCommonthermopolymersTable 11.1 Commonthermopolymers Recycling Code CommonnameProperties/workingcharacteristicsUsesPolyethylene terephthalate (PET) Clear, toughandshatter-resistant, PEThasgoodmoistureandgas barrier propertiesSoftdrinkbottles,mineralwaterbottles,fruitjuicecontainersandcookingoilbottlesHigh-density polythene (HDPE) Rangeof colours, hard, stiff, goodchemical resistance, highimpact Milkcrates,bottles,pipes,buckets,bowlsPolyvinyl chloride (PVC) Stiff, hard, tough, goodchemical andweatherresistance, uPVC(un-plasticizedPVC) hasstrongresistancetochemicalsandsunlight Pipes,guttering,roofingsheets,windowframesLow-density polythene (LDPE) Rangeof colours, tough, flexible, goodelectrical insulator andchemical resistanceWashing-upliquid,detergentandsqueezybottles,binliners,carrierbagsPolypropylene (PP) Hardandlightweight, goodchemical resistance, canbesterilised, goodimpact, easilyweldedtogether, resistancetoworkfatigueMedicalequipment,syringes,crates,string,rope,chairshells,containerswithintegral(built-in)hinges,kitchenwarePolystyrene (PS) Rangeof colours, stiff, hard, lightweight, safewithfood, goodwater resistanceDisposableplates,cups,fridgelinings,modelkits,foodcontainersExpanded polystyrene (EPS) Lightweight, absorbsshock, goodsoundandheatinsulator Soundandheatinsulation,protectivepackagingNylon Hard, tough, resilient towear, self-lubricating, resistant tochemicalsandhightemperaturesGearwheels,bearings,curtain-railfittings,clothing,combs,power-toolcases,hingesAcrylic Stiff, hard, clear, durableoutdoors, easilymachinedandpolished, goodrangeof colours, excellentimpactresistance(glass substitute), doesscratcheasilyIlluminatedsigns,aircraftcanopies,carrear-lightclusters,baths,PerspexsheetThermoplastic elastomers (TPE) Acombinationof thermoplasticsandelastomers. Flexibleandtough. After stretchingandbendingtheywill returntoclosetotheir original shapeWatchstraps,scubadivingmasks,remotecontrolbuttonsAcrylonitrile Butadiene Styrene (ABS) Tough, highimpact strength, lightweight, scratchresistant, chemical resistance, excellent appearanceandfinishKitchenware,safetyhelmets,carparts,telephones,foodmixers,toysCommonthermosettingpolymersTable 11.2 Commonthermosettingpolymers Common name Properties/workingcharacteristicsUsesUrea-formaldehyde Stiff, hard, brittle, heat resistance, goodelectrical insulator, rangeof colours Whiteelectrical fittings,domesticapplianceparts,woodglueMelamine-formaldehydeStiff, hard, strong, rangeof colours, scratchandstainresistance, odourless Tableware,decorativelaminatesforworksurfaces,electrical insulationPhenol-formaldehydeStiff, hard, strong, heat resistanceDarkelectrical fittings,saucepanandkettlehandlesEpoxy resin Goodchemical andwear resistance, heat resistanceto250°C, electrical insulator AdhesivessuchasAraldite®usedtobonddifferentmaterialssuchaswood,metalandporcelainPolyester resin Becomes toughwhenlaminatedwithglassfibre, hardandstrongbut brittlewithout reinforcement GRPboats,chairshells,carbodies
194Chapter 11Polymers CommonelastomersTable 11.3 Commonelastomers Elastomer Properties/workingcharacteristicsUsesSilicone Excellent heat andoil resistanceFlexiblebakingtrays,bathroomsealantNeoprene Weather resistance, flameretardant Wetsuits,kneeandelbowpadsButadiene rubber Resistant toabrasionandcrackingTyres,golfballcoresFluoroelastomer Durable, chemical resistanceAppleWatchSportstrapsKEYPOINTWhendesigning, it isimportanttoknowandconsiderthephysicalandworkingpropertiesof different materialstomakesureyouselectthebestmaterial.Forexample,itwouldn'tbegoodtouseacrylicfor aproductthatneededtobeflexible.STRETCHANDCHALLENGEUsetheinternet togather arangeofimagesofpolymerproductsandtrytoidentifythepolymers used. Thinkaboutthefollowing:lWhat doestheproductdo?lHowis theproduct used?lWhereisit used?11.2SourcesandoriginsLEARNINGOUTCOMESBytheendof thissectionyoushouldknowaboutandunderstand:➜thesourcesandoriginsofarangeofpolymers➜theprocessesusedtoextractandconvertpolymersintoauseableform➜theecological, social andethical issuesassociatedwithprocessingpolymers➜thelifecycleofspecificpolymers➜recycling, reuseanddisposal ofspecificpolymers.SourcesNatural polymersBeforetherewereplasticsandsyntheticpolymers, naturalpolymersexistedtohelpmakelifepossible. For example, animals' hornsandhoovescouldbemouldedintoavarietyofshapes,andthismaterial wasusedtomakewaterproofcontainers. Naturalrubberlatexismadefromtheresinfromrubber trees, andwasusedtomakeprimitiverubberbandsandglues.Shellacis aresinsecretedbythelacbuginIndiaandThailand. Thedriedflakesweremixedwithethanol toproducethefirstvarnishusedtoprotectwoodenproducts.SyntheticpolymersThefirst partiallysyntheticpolymerwascalledVulcanite-athermosettingpolymermadebychemicallymodifyingnatural latexrubberbyaddingsulphur(aprocesscalledvulcanisation).It was first usedinthelatenineteenthcenturytomakeproductssuchascombsandbuttons.