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英文原文PoweredsupportsPoweredroofsupportsareusedtosupporttheroofattheface.Theyworkinseveralstepsmostlyintheimmediateforwardsupport(IFS)typeinordertosupportthenewlyexposedroofassoonaspossible.Innormalsupportingconditionthecanopyofthesupportissettightlyagainsttheroofstrata,bythesupportingresistancesofthehydrauliclegs.Whenthecuttingmachinecutsandpassesseveralsupportunitsbeyondthesupportinquestion,thesupportlegsareloweredandpulledforwardforadistanceequaltothewidthofcut(web)byretractingthehydraulicadvancingram.Theadvancingramactsagainstthefaceconveyorpanline,whosepositionisheldunchangedbytheadvancingrams,forcesofthesupportsthataresetonbothsidesofthesupporttobeadvanced.Assoonasthesupporthasbeenadvancedtothedesignedposition,thesupportisimmediatelyresetagainsttheroof.Finally,theadvancingramofthesupportinquestionisextendedtopushtheconveyorforwardandbecomesreadyforthenextcut.Thesequentialstepsdescribedarefortheadvanceofanindividualsupportinthedirectionperpendiculartothefaceline.Butalongthefacelinedirection,theconveyorcannotbeadvancedinasharpstepimmediatelyaftertheshearerhaspassedit,duetotherigidityofthepanline.Thusthefourthstepisusuallysometimeaftertheshearer,spass,resultinginacurvedorsnakedsection.Duringpaneldevelopmentthepanelentriesareroofboltedasusual.Butinthetailentryoneortworowsofcribsareerectedtosupplementtheroofbolting.Duringretreatingmining,theroofattheheadentryT-junctionarea(upto500ft(152m)outbytheface)isgenerallyreinforcedwithsupportsofsometypetoincreasesupportdensitytocopewiththemovingfrontandsideabutmentpressures.Modernlongwallminingemployshydraulicpoweredsupportsatthefacearea.Thesupportsnotonlyholdsuptheroof,pushesthefacechainconveyor(AFC),andadvancesitself,butalsoprovidesasafeenvironmentforallassociatedminingactivities.Thereforeitssuccessfulselectionandapplicationaretheprerequisiteforsuccessfullongwallmining.Furthermore,duetothelargenumberofunitsrequired,thecapitalinvestedforthepowersupportusuallyaccountsformorethanhalfoftheinitialcapitalforalongwallface.Thereforebothfromtechnicalandeconomicpointsofview,thepoweredsupportisaveryimportantpieceofequipmentinalongwallface.ClassificationofpoweredsupportsTheapplicationofmodernpoweredsupportscanbetracedbacktoearly1950s.Sincethen,followingitsadoptionineverypartoftheworld,therehavebeencountlessmodelsdesignandmanufacturedinvariouscountries.Butunfortunately,therestillisnouniformsystemofclassification.Inthissectionasimplifiedclassificationisused.Sinceapoweredsupportconsistsoffourmajorcomponents(i.e,canopy,cavingshield,hydrauliclegsandprops,andbaseplate),thewaysbywhichtheyareinterrelatedareusedforclassification.Inthisrespect,twofactorsaremostimportant:(a)presenceorabsenceofcavingshield-ifacavingshieldisincluded,thesupportisa“shield”type,otherwise,aframeorachock；(b)numberandtypeofarrangingthehydrauliclegs-sincesupportcapacityisgenerallyproportionaltonumberofhydrauliclegs,itisimportanttospecifythenumberofhydrauliclegsthatasupporthas.Furthermore,thewaythehydrauliclegsareinstalledisimportant；forexample,averticalinstallationbetweenthebaseandthecanopyhasthecavingshieldhastheleastefficiencyinsupportingtheroof.Basedonthisconcept,therearefourtypesofpoweredsupport,thatis,theframe,chock,shieldandchockshield,inorderofevolutionoftheirdevelopment.However,itmustbenotedthatthetrendofdevelopmentineachtypeissuchthatitbecomeslessdistinguishableintermsofapplication.Thefourtypesofroofsupportscanbeobtainedforeitherlongwallretreatingoradvancingsystems,andtheyareavailableinstandard,one-web-back,andimmediateforwardsupport(IFS)versions.Withthestandardsystem,thewiningmachinetakesacutoraslice,andthearmoredfaceconveyorispushedoverbythehydraulicramsthatarefixedtothesupportunits.Thesupportunitsthenareadvancedsequentiallytotheconveyor.Withtheone-web-backsystem,asupportissetbackfromtheconveyorbyadevicethatautomaticallykeepstheleadingedgeofthesupportatafixdistancefromtheconveyor.Thisallowseasyaccessthoughthefaceandemploysthestandardmethodofadvancing；i.e,pushingtheconveyorfirst,andthenadvancingthesupport.WiththeIFSsystem,thesupportunitsisadvancedtotheconveyorimmediatelyafterthecuttingmachinehaspassed,andtheforwardcanopyofthesupportunitsislongenoughtothesupportboththerecentlyandnewlyexposedroofsections.Afterthesupportshavebeenadvanced,theconveyorispushedover.FrameTheframesupportisanextensionofthesinglehydraulicpropsconventionallyusedunderground.Thusitisthefirsttypedevelopedinmodernself-advancinghydraulicpoweredsupports.Itinvolvessettinguptwohydraulicpropsorlegsverticallyintandemthatareconnectedatthetopbyasingleortwosegmentedcanopies.Thetwosegmentedcanopiescanbehinge-jointedatanypointbetweenthelegsorinfrontofthefrontleg.Thebaseofthetwohydrauliclegsmaybeacircularsteelshoeweldedatbottomofeachlegorsolidbaseconnectingbothlegs.Generally,aframesupportconsistsoftwoorthreesetsofhydrauliclegs.Thesetmovingfirstisthesecondaryset,thesetmovinglateristheprimaryset.Thereisadouble-actingraminstalledbetweeneachset.Thepistonoftheramisconnectedtothesecondarysetandthecylindertotheprimaryset.Duringsupportadvance,theprimarysetissetagainsttheroofwhilethesecondarysetisloweredandpushedforwardbythepiston.Havingreachedthenewposition,thesecondarysetisagainsttheroofwhiletheprimarysetisloweredandpulledforwardbythecylinder.Thedistanceofeachadvancerangesfrom20to36in.(0.500.91m)Theframesupportisverysimple,butmoreflexibleorlessstablestructurally.Thereareconsiderableuncoveredspacesbetweenthetwopiecesofcanopywhichallowsbrokenroofrocktofallthrough.Consequently,theframesupportisnotsuitableforaweakroof.Frameshavebecomeseldomusedbecausetheyarelessstableandrequirefrequentmaintenance.ChockInachocksupport,thecanopyisasolidpieceandthebasemaybeeitherasolidorpieceortwoseparatepartsconnectedbysteelbarsattherearand/orthefrontends.Inbothcasesalargeopenspaceisleftatthecenterforlocatingthedouble-actinghydraulicramwhichisusedtopushandpullthechainconveyorandthechockinawholeunit,respectively,adistinctivedifferencefromtheframesupport.Thissetupisalsousedintheshieldsandchockshields.Again,allhydrauliclegsareinstalledverticallybetweenthebaseandthecanopy.Thenumberoflegsrangesfromthreetosix,butthefour-legchocksarebyfarthemostpopularones.Thesix-legchocksaredesignedforthinseamswithtwolegsinthefrontandfourlegsintherear,separatedbyawalkway.Forthesix-legchocks,thecanopyisgenerallyhinge-jointedabovethewalkway.Mostchockarealsoequippedwithagobwindowhangingattherearendofthecanopy.Thegobwindowconsistsofseveralrectangularsteelplatesconnectedhorizontallyatbothends.Inmostchocksupports,therearehingejointconnectionsbetweenthelegsandthecanopyandbetweenthelegsandthebase.Butinordertoincreasethelongitudinalstability,itisreinforcedmostlywithabox-shapedsteelframebetweenthebaseandeachleg.Alegrestoringdeviceisinstalledaroundeachlegatthetopofthebox-shapedsteelframe.Thechocksaresuitableformediumtohardroof.Whentheroofoverhangswellintothegobandrequiresinducedcaving,thechockscanprovideaccesstothegob.ShieldShields,anewentryintheearlyseventies,arecharacterizedbytheadditionofacavingshieldattherearendbetweenthebaseandthecanopy.Thecavingshields,whichingeneralareinclined,arehinge-jointedtothecanopyandthebasemakingtheshieldakinematicallystablesupport,amajoradvantageovertheframesandthechocks.Italsocompletelysealsoffthegobandpreventsrockdebrisfromgettingintothefacesideofthesupport.Thustheshield-supportedfaceisgenerallyclean.Thehydrauliclegsintheshieldsaregenerallyinclinedtoprovidemoreopenspacefortraffic.Becausethecanopy,cavingshield,andbaseareinterconnected,itcanwellresistthehorizontalforcewithoutbendingthelegs.Thus,unlikethesolidconstraintintheframe/chocksupports,thepinconnectionsbetweenthelegsandthecanopy,andbetweenthelegsandthebaseinashieldsupportmakeitpossiblethattheangleofinclinationofthehydrauliclegsvarieswiththeminingheights.Sinceonlytheverticalcomponentofhydrauliclegpressureisavailableforsupportingtheroof,theactualloadingcapacityoftheshieldalsovarieswiththeminingheights.Therearemanyvariationsoftheshieldsupports.Inthefollowing,sixitemsareusedtoclassifytheshields,whichenablesaunifiedterminologytobedevelopedforallkindsofshields.Thetypesofmotionaltracesofthecanopytip,legpositionsandorientation,numberoflegs,canopygeometry,andotheroptionaldesignsanddevicescanbeclearlyspecifiedbytheterminology.Typesofmotionaltracesfortheleadingedgeofthecanopy.Thisisthemostcommonlyrecognizedwayofclassifyingtheshield.Basedonthiscriterion,therearethreetypes,lemniscate,caliper,andellipse.Lemniscate.Thisisthem