What is Glass.docx
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What is Glass.docx
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WhatisGlass
WhatisGlass?
Glassisoneofthemostusefulmaterialsintheworld.Fewmanufacturedsubstancesaddasmuchtomodernlivingasdoesglass.Yetfewproductsaremadeofsuchinexpensiverawmaterials.Glassismadechieflyfromsilicasand(silica,alsocalledsilicondioxide),sodaash(sodiumcarbonate),andlimestone(calciumcarbonate).Glasshascountlessuses.Foodispreservedinglassjars.Peopledrinkfromglasscontainerscalledglasses.Windowsinhomes,schools,andofficebuildingsareglass.Motorvehicleshaveglasswindshieldsandwindows.Peoplewithvisionproblemsweareyeglasses.Scientistsuseglasstesttubes,andmicroscopesandtelescopeswithglasslenses.GlassopticalfiberscarrydataallovertheworldatthespeedoflightovertheInternet,theworldwidenetworkofcomputers.Besidesbeinguseful,glassisalsoornamental.Eversincepeoplelearnedhowtomakeglass,theyhaveuseditasanartmaterial.Glasscantakemanydifferentforms.Itcanbespunfinerthanaspiderweb.Oritcanbemoldedintoadiskforatelescopelensormirrorweighingmanytons.Glasscanbestrongerthansteel,ormorefragilethanpaper.Mostglassistransparent,butglasscanalsobecoloredtoanydesiredshade.Mostcountriesoftheworldhaveglassindustries.Formanyyears,Germanywasthemajorworldsourceforopticalglass,laboratoryglassware,andglassChristmastreeornaments.Today,glassmanufacturersinmanycountriesproducesuchobjectsonalargescale.Beautifulartglasswareismadeinmanycountries,includingtheCzechRepublic,France,Ireland,Italy,andSweden.
Typesofartglass
Majorglasscompaniesspendmillionsofdollarseachyearonresearchtodiscoverwaystomakebetterglassandtodevelopnewusesforglass.Manyoftherevolutionarydevelopmentsinglassduringthe1900’shavecomefromthelaboratoriesofglassmanufacturers.
Kindsofglass
Whenpeoplespeakofglass,theyordinarilymeanatransparent,shinysubstancethatbreaksrathereasily.Theymaythinkoftheglassinwindowsandtheglassusedineyeglassesasbeingthesamematerial.Actually,theyarenot.Therearemanykindsofglass.Severalimportantkindsofglassarediscussedinthisarticle.
Flatglass isusedchieflyinwindows.Itisalsousedinmirrors,roomdividers,andsomekindsoffurniture.Allflatglassismadeintheformofflatsheets.Butsomeofit,suchasthatusedinautomobilewindshields,isreheatedandsagged(curved)overmolds.
Introduction.
TheFloatglassprocesswasinventedbyAlastairPilkingtonin1952andhasbeenadoptedastheuniversalmethodforthemanufactureofhighqualityflatglasstothisday.
Process.
Inthefloatprocess,acontinuousribbonofglassmovesoutofthemeltingfurnaceandthenfloatsacrossthesurfaceofanenclosedbathofmoltentin.TheSemi-moltenribbonisheldinachemicallycontrolledatmosphereatahightemperatureforalongenoughtimefortheirregularitiestoflowoutandforforthesurfacestobeflatandparallel.Becausethesurfaceofthemoltentinisdeadflat,theglassalsobecomesflat.Theribbonisthencooleddownwhilestilladvancingacrossthemoltentinuntilthesurfacesarehardenoughtobetakeoutofthebathwithouttherollersmarkingthebottomsurface;soaribbonisproduceswithauniformthicknessandbrightpolishedsurfaceswithouttheneedforfurtherprocessing.
RawMaterials.
Sand,SodaAsh,Limestone,Dolomite,Felspar,SodiumSulphate,CoalDust&Cullet(BrokenGlass).Differentagentsmayalsobeaddedtothebatchforfinishingandcolouringpurposes.
Colorsandtints.
Thefollowingagentscanbeaddedtothebatchtocreatethedifferentcoloredglassesyouwillencounter.
∙Green-Iron&Chromiumoxides.
∙Blue-Cobalt&Copperoxides.
∙Violet-Manganeseoxide.
∙Amber-Carbon&Sulphur.
∙Red-Selenium&Cadmiumsulphate.
Temperatures.
TheRawmaterialsaremixedandheatedtoaround1500ºC,astheribbonofglassleavesthefurnaceandentersthefloatbaththetemperaturecomesdowntoaround1050ºC.Theglasscontinuestocoolasitisdrawnalongthebathofmoltentinandentersthecoolinglehratapprox600ºC.Asitprogressesalongitsjourneyitcontinuestocoolandleavestocoolinglehrsat200ºC.Itisnowcoolenoughtocutandstack.
Glasscontainers areusedforpackagingfood,beverages,medicines,chemicals,andcosmetics.Glassjarsandbottlesaremadeinawidevarietyofshapes,sizes,andcolors.Manyareforcommonuses,suchassoft-drinkbottlesorjarsforhomecanning.Othersaremadefromspecialglassformulastomakesuretherewillbenocontaminationordeteriorationofbloodplasma,serums,andchemicalsstoredinthem.
Bottleisacontainerforholdingliquids.Mostbottlesaremadeofglassorplastic.Othermaterialsusedtomakebottlesincludeearthenwareandsuchmetalsassteelandaluminum.Bottleshaveeithernarroworwidemouthsthatareclosedwithcorks,glassstoppers,orplasticormetalcovers.
TheUnitedStatesleadstheworldinthemanufactureofglassandplasticcontainers.Itproducesabout46billionglasscontainersandabout11billionplasticcontainerseachyearforusewithbeverages,cosmetics,foods,andpharmaceuticals.
Almostallbottlesaremadebyautomaticmachinery.Inglass-bottlemaking,anautomaticfeederseparatesastreamofmolten(melted)glassintoindividualgobs.Eachred-hotgobissenttoamoldandshapedintoaparison.Theparisonlookslikeashortbottlewiththicksides.Themachinetransferstheparisontothefinalmold.Thereairispumpedintotheparison,expan!
dingthehotglassintotheexactshapeofthemold.Thisexpandingprocedureiscalledblowing.
Materialsusedtomakeplasticbottlesincludepolyethylene,polypropylene,andpolyvinylchloride.Therearethreedifferentprocessesusedforproducingplasticbottles:
(1)extrusionblowmolding,
(2)injectionblowmolding,and(3)injection-stretchblowmolding.Theseprocessesresembletheglass-bottlemakingprocess.Inextrusionblowmolding,however,theparisonsaretube-shaped.Ininjectionblowmolding,themoltenplasticisinjectedthroughasmallholetoformtheparisons.Ininjection-stretchblowmolding,theplasticisstretched—inmostcases,byametalrod—asitisblownintoamold.Largesoftdrinkcontainersmadeofpolyethyleneterephalate(PET)aremadebyinjection-stretchblowmolding.ThisprocesschangesthechemistryoftheplasticsothePETcontainerswillkeepthegasesusedinthecarbonationofsoftdrinksfromescap!
ing.
Peoplediscoveredhowtoformglasscontainersabout2,000yearsago.Theygatheredmoltenglassontheendsofhollowironpipesandexpandedtheglassbyblowingthroughthepipes.Later,peoplefoundthatmoltenglasscouldbeblownintomolds.Inthe1930’s,IndependentSection(I.S.)glass-bottlemakingmachineswereintroduced.Today,improvedmodelsoftheI.S.machinesproducealmostalltheglassbottlesmadeintheUnitedStates.
Thefirstplasticsblowmoldingmachineswerepatentedintheearly1940’s.Polyethylenesqueezebottlessoonbecamethefirstplasticbottleproducts.
Intheearly1970’s,somepeoplearguedthatglassbottlesaddedtoenvironmentalpollution.Recyclingcentersweresetupsopeoplecouldreturnbottlesforreuseinotherbottles.Mostrecycledplasticbottlesareusedtomanufacturelowerqualityplasticsthanthoseusedtomakebottles.
Contributor:
•PeterJ.Vergano,Sc.D.,AssociateProfessorofPackagingScience,ClemsonUniversity.
Opticalglass isusedineyeglasses,microscopes,telescopes,cameralenses,andmanyinstrumentsforfactoriesandlaboratories.Therawmaterialsmustbepuresothattheglasscanbemadealmostflawless.Thecarerequiredforproducingopticalglassmakesitexpensivecomparedwithotherkindsofglass.
Fiberglass consistsoffinebutsolidrodsofglass,eachofwhichmaybelessthanone-twentieththewidthofahumanhair.Thesetinyglassfiberscanbelooselypackedtogetherinawoollikemassthatcanserveasheatinsulation.Theyalsocanbeusedlikewoolorcottonfiberstomakeglassyarn,tape,cloth,andmats.Fiberglasshasmanyotheruses.Itisusedforelectricalinsulation,chemicalfiltration,andfirefighters’suits.Combinedwithplastics,fiberglasscanbeusedforairplanewingsandbodies,automobilebodies,andboathulls.Fiberglassisapopularcurtainmaterialbecauseitisfire-resistantandwashable.
Fiberglass,alsocalledfibrousglass,isglassintheformoffinefibers(threads).Thefibersmaybemanytimesfinerthanhumanhair,andmaylookandfeellikesilk.Theflexibleglassfibersarestrongerthansteel,andwillnotburn,stretch,rot,orfade.
Uses.Manufacturersusefiberglasstomakeavarietyofproducts.Itiswovenintoclothforsuchproductsascurtainsandtablecloths.Theclothwillnotwrinkleorsoileasily,anditneedsnoironing.Fiberglasstextilesarealsousedforelectricalinsulation.Inbulkform,itisusedforairfiltersandforheatandsoundinsulation.Airtrappedbetweenthefibersmakesitagoodinsulator.
Fiberglassreinforcedplasticsareextremelystrongandlightinweight.Theycanbemolded,shaped,twisted,andpouredformanydifferentuses.Manufacturersusethemtomakeautomobilebodies,boathulls,buildingpanels,fishingrods,andair!
craftparts.Thefibersusedtostrengthenplasticmaybewovenormattedtogether,ortheymaybeindividualstrands.
Howfiberglassismade:
Fiberglassismadefromsandandotherrawmaterialsusedtomakeordinaryglass(seeGlass[Compositionofglass]).Strandsoffiberglassmaybemadeindifferentways.Inonemethod,therawmaterialsareheatedandformedintosmallglassmarblessoworkerscanexaminet
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