可以粘贴复制的word版本剑桥雅思真题 8 test2-豆柴文库

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READING
READINGPASSAGE1
Youshouldspendabout20minutesonQuestions1-13,whicharebasedonReadingPassage1below.
Sheetglassmanufacture:
thefloatprocess
Glass,whichhasbeenmadesincethetimeoftheMesopotamiansandEgyptians,islittlemorethanamixtureofsand,sodaashandlime.Whenheatedtoabout1500degreesCelsius(°C)thisbecomesamoltenmassthathardenswhenslowlycooled.Thefirstsuccessfulmethodformakingclearflatglassinvolvedspinning.Thismethodwasveryeffectiveastheglasshadnottouchedanysurfacesbetweenbeingsoftandbecominghard,soitstayedperfectlyunblemished,witha'firefinish'.However,theprocesstookalong-timeandwaslabourintensive.
Nevertheless,demandforflatglasswasveryhighandglassmakersacrosstheworldwerelookingforamethodofmakingitcontinuously.Thefirstcontinuousribbonprocessinvolvedsqueezingmoltenglassthroughtwohotrollers,similartoanoldmangle.Thisallowedglassofvirtuallyanythicknesstobemadenon-stop,buttherollerswouldleavebothsidesoftheglassmarked,andthesewouldthenneedtobegroundandpolished.Thispartoftheprocessrubbedawayaround20percentoftheglass,andthemachineswereveryexpensive.
ThefloatprocessformakingflatglasswasinventedbyAlistairPilkington.Thisprocessallowsthemanufactureofclear,tintedandcoatedglassforbuildings,andclearandtintedglassforvehicles.Pilkingtonhadbeenexperimentingwithimprovingthemeltingprocess,andin1952hehadtheideaofusingabedofmoltenmetaltoformtheflatglass,eliminatingaltogethertheneedforrollerswithinthefloatbath.Themetalhadtomeltatatemperaturelessthanthehardeningpointofglass(about600°C),butcouldnotboilatatemperaturebelowthetemperatureofthemoltenglass(about1500°C).Thebestmetalforthejobwastin.
Therestoftheconceptreliedongravity,whichguaranteedthatthesurfaceofthemoltenmetalwasperfectlyflatandhorizontal.Consequently,whenpouringmoltenglassontothemoltentin,theundersideoftheglasswouldalsobeperfectlyflat.Iftheglasswerekepthotenough,itwouldflowoverthemoltentinuntilthetopsurfacewasalsoflat,horizontalandperfectlyparalleltothebottomsurface.Oncetheglasscooledto604°Corlessitwastoohardtomarkandcouldbetransp