Annealing (glass) - Wikipedia

At the annealing point (η = 1013 Poise), stresses relax within several minutes, while at the strain point (η = 1014.5 Poise) stresses relax within several hours ... Annealing(glass) FromWikipedia,thefreeencyclopedia Jumptonavigation Jumptosearch Thisarticleneedsadditionalcitationsforverification.Pleasehelpimprovethisarticlebyaddingcitationstoreliablesources.Unsourcedmaterialmaybechallengedandremoved.Findsources: "Annealing" glass – news ·newspapers ·books ·scholar ·JSTOR(July2018)(Learnhowandwhentoremovethistemplatemessage) Forotheruses,seeAnnealing(disambiguation). Annealingisaprocessofslowlycoolinghotglassobjectsaftertheyhavebeenformed,torelieveresidualinternalstressesintroducedduringmanufacture.Especiallyforsmaller,simplerobjects,annealingmaybeincidentaltotheprocessofmanufacture,butinlargerormorecomplexproductsitcommonlydemandsaspecialprocessofannealinginatemperature-controlledkilnknownasalehr.[1]Annealingofglassiscriticaltoitsdurability.Glassthathasnotbeenproperlyannealedretainsthermalstressescausedbyquenching,whichindefinitelydecreasethestrengthandreliabilityoftheproduct.Inadequatelyannealedglassislikelytocrackorshatterwhensubjectedtorelativelysmalltemperaturechangesortomechanicalshockorstress.Itevenmayfailspontaneously. Toannealglass,itisnecessarytoheatittoitsannealingtemperature,atwhichitsviscosity,η,dropsto1013Poise(1013dyne-second/cm²).[2]Formostkindsofglass,thisannealingtemperatureisintherangeof454–482°C(850–900°F)[citationneeded],andistheso-calledstress-reliefpointorannealingpointoftheglass.Atsuchaviscosity,theglassisstilltoohardforsignificantexternaldeformationwithoutbreaking,butitissoftenoughtorelaxinternalstrainsbymicroscopicflowinresponsetotheintensestressestheyintroduceinternally.Thepiecethenheat-soaksuntilitstemperatureiseventhroughoutandthestressrelaxationisadequate.Thetimenecessaryforthisstepvariesdependingonthetypeofglassanditsmaximumthickness.Theglassthenispermittedtocoolatapredeterminedrateuntilitstemperaturepassesthestrainpoint(η=1014.5Poise)[citationneeded],belowwhichevenmicroscopicinternalfloweffectivelystopsandannealingstopswithit.Itthenissafetocooltheproducttoroomtemperatureataratelimitedbytheheatcapacity,thickness,thermalconductivity,andthermalexpansioncoefficientoftheglass.Afterannealingiscompletethematerialcanbecuttosize,drilled,orpolishedwithoutriskofitsinternalstressesshatteringit. Attheannealingpoint(η=1013Poise),stressesrelaxwithinseveralminutes,whileatthestrainpoint(η=1014.5Poise)stressesrelaxwithinseveralhours.[3]Stressesacquiredattemperaturesabovethestrainpoint,andnotrelaxedbyannealing,remainintheglassindefinitelyandmaycauseeithershort-termormuchdelayedfailure.Stressesresultingfromcoolingtoorapidlybelowthestrainpointlargelyareconsideredtemporary,althoughtheymaybeadequatetopromoteshort-termfailure. Seealso[edit] Forotherimportanttemperaturesinglassprocessing,seeviscousliquid Annealing(metallurgy) Bolognabottle Fabricationandtesting(opticalcomponents) Floatglass Temperedglass Warmglass References[edit] ^E.F.Collins(1921)Electricallyheatedglassannealinglehr.JournaloftheAmericanCeramicSociety4(5),pp.335–349 ^"AllAboutGlass".www.cmog.org.CorningMuseumofGlass.9December2011. ^WernerVogel:"GlassChemistry";Springer-VerlagBerlinandHeidelbergGmbH&Co.K;2ndrevisededition(November1994),ISBN 3-540-57572-3 vteGlasssciencetopicsBasics Glass Glasstransition Supercooling Formulation AgInSbTe Bioglass Borophosphosilicateglass Borosilicateglass Ceramicglaze Chalcogenideglass Cobaltglass Cranberryglass Crownglass Flintglass Fluorosilicateglass Fusedquartz GeSbTe Goldrubyglass Leadglass Milkglass Phosphosilicateglass Photochromiclensglass Silicateglass Soda–limeglass Sodiumhexametaphosphate Solubleglass Telluriteglass Thoriatedglass Ultralowexpansionglass Uraniumglass Vitreousenamel Wood'sglass ZBLAN Glass-ceramics Bioactiveglass CorningWare Glass-ceramic-to-metalseals Macor Zerodur Preparation Annealing Chemicalvapordeposition Glassbatchcalculation Glassforming Glassmelting Glassmodeling Ionimplantation Liquidustemperature sol–geltechnique Viscosity Vitrification Optics Achromat Dispersion Gradient-indexoptics Hydrogendarkening Opticalamplifier Opticalfiber Opticallensdesign Photochromiclens Photosensitiveglass Refraction Transparentmaterials Surfacemodification Anti-reflectivecoating Chemicallystrengthenedglass Corrosion Dealkalization DNAmicroarray Hydrogendarkening Insulatedglazing Porousglass Self-cleaningglass sol–geltechnique Temperedglass Diversetopics Conservationandrestorationofglassobjects Glass-coatedwire Safetyglass Glassdatabases Glasselectrode Glassfiberreinforcedconcrete Glassionomercement Glassmicrospheres Glass-reinforcedplastic Glasscloth Glass-to-metalseal Porousglass Pre-preg PrinceRupert'sdrops Radioactivewastevitrification Windshield Glassfiber Retrievedfrom"https://en.wikipedia.org/w/index.php?title=Annealing_(glass)&oldid=1061702794" Categories:GlassengineeringandscienceGlassproductionWarmglassFiringtechniquesHiddencategories:ArticlesneedingadditionalreferencesfromJuly2018AllarticlesneedingadditionalreferencesUsedmydatesfromNovember2015AllarticleswithunsourcedstatementsArticleswithunsourcedstatementsfromJuly2018 Navigationmenu Personaltools NotloggedinTalkContributionsCreateaccountLogin Namespaces ArticleTalk English Views ReadEditViewhistory More Search Navigation MainpageContentsCurrenteventsRandomarticleAboutWikipediaContactusDonate Contribute HelpLearntoeditCommunityportalRecentchangesUploadfile Tools WhatlinkshereRelatedchangesUploadfileSpecialpagesPermanentlinkPageinformationCitethispageWikidataitem Print/export DownloadasPDFPrintableversion Languages DeutschPolskiРусский Editlinks