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SELF-ADVANCINGHYDRAULICPOWEREDSUPPORTS
Modernlongwallminingemployshydraulicpoweredsupportsatthefacearea.Thesupportnotonlyholdsuptheroof,pushesthefacechainconveyor,andadvancesitself,butalsoprovidesasafeenvironmentforallassociatedminingactivities.Thereforeitssuccessfulselectionandapplicationaretheprerequisiteforsuccessfullongwallmining.Furthermore,duetothelargenumberofunitsrequired,thecapitalinvestedforthepoweredsupportusuallyaccountsformorethanhalfoftheinitialcapitalforalongwallface.Thereforebothfromtechnicalandeconomicpointsofview,thepoweredsupportisaveryimportantpieceofequipmentinalongwallface.
Theapplicationofmodernpoweredsupportscanbetracedbacktotheearly1950’s.Sincethen,followingitsadoptionineverypartoftheworld,therehavebeencountlessmodelsdesignedandmanufacturedinvariouscountries.Butunfortunately,therestillisnouniformsystemofclassification.
Asimplifiedclassificationisusedinthissection.Sinceapoweredsupportconsistsoffourmajorcomponents(I.e.,canopy,cavingshield,hydrauliclegsorprops,andbaseplate),thewaysbywhichtheyareinterrelatedareusedforclassification.Inthisrespect,twofactorsaremostimportant:
(1)presenceorabsenceofacavingshield-ifacavingshieldisincluded,thesupportisa“shield”type,otherwise,aframeorachock;
(2)numberandtypeofarrangingthehydrauliclegs-sincesupportcapacityisgenerallyproportionaltothenumberofhydrauliclegs,itisimportanttospecifythenumberofhydrauliclegsthatasupporthas.Furthermore,thewaythehydrauliclegsareinstalledisimportant;
forexample,averticalinstallationbetweenthebaseandthecanopyhasthehighestefficiencyofapplicationwhereasaninclinedinstallationbetweenthebaseandthecavingshieldhastheleastefficiencyinsupportingtheroof.
Basedonthisconcept,therearefourtypesofpoweredsupport,thatis,theframe,chock,shield,andchockshield,inorderofevolutionoftheirdevelopment.However,itmustbenotedthatthetrendofdevelopmentineachtypeissuchthatitbecomeslessdistinguishableintermsofapplication.
Thefourtypesofroofsupportscanbeobtainedforeitherlongwallretreatingoradvancingsystems,andtheyareavailableinstandard,one-web-back,andimmediateforwardsupport(IFS)versions.
Withthestandardsystem,thewinningmachinetakesacutoraslice,andthearmoredfaceconveyorispushedoverbythehydraulicramsthatarefixedtothesupportunits.Thesupportunitsthenareadvancedsequentiallytotheconveyor.Withtheone-web-backsystem,asupportissetbackfromtheconveyorbyadevicethatautomaticallykeepstheleadingedgeofthesupportatafixeddistancefromtheconveyor.Thisallowseasyaccessthroughthefaceandemploysthestandardmethodofadvancing;
I.e.,pushingtheconveyorfirst,andthenadvancingthesupport.
WiththeIFSsystem,thesupportunitisadvancedtotheconveyorimmediatelyafterthecuttingmachinehaspassed,andtheforwardcanopyofthesupportunitislongenoughtosupportboththerecentlyandnewlyexposedroofsections.Afterthesupportshavebeenadvanced,theconveyorispushedover.
FRAME
Theframesupportisanextensionofthesinglehydraulicpropsconventionallyusedunderground.Thusitisthefirsttypedevelopedinmodernself-advancinghydraulicpoweredsupports.Itinvolvessettinguptwohydraulicpropsorlegsverticallyintandemthatareconnectedatthetopbyasingleortwosegmentedcanopies.Thetwosegmentedcanopiescanbehinge-jointedatanypointbetweenthelegsorinfrontofthefrontleg.Thebaseofthetwohydrauliclegsmaybeacircularsteelshoeweldedatbottomofeachlegorasolidbaseconnectingbothlegs(Fig.8.8).
Generally,aframesupportconsistsoftwoorthreesetsofhydrauliclegs.Thesetmovingfirstisthesecondaryset;
thesetmovinglateristheprimaryset.Thereisadouble-actingraminstalledbetweeneachset.Thepistonoftheramisconnectedtothesecondarysetandthecylindertotheprimaryset.Duringsupportadvance(Fig.8.9),theprimarysetissetagainsttheroofwhilethesecondarysetisloweredandpushedforwardbythepiston.Havingreachedthenewposition,thesecondarysetissetagainsttheroofwhiletheprimarysetisloweredandpulledforwardbythecylinder.Thedistanceofeachadvancerangesfrom20to36in.(0.50~0.91m).
Fig.8.8Framesupport
A-primarysetb-secondaryset
ABC
Fig.8.9Methodofadvancingtheframesupport
Theframesupportisverysimple,butmoreflexibleorlessstablestructurally.Thereareconsiderableuncoveredspacesbetweenthetwopiecesofcanopywhichallowsbrokenroofrocktofallthrough.Consequently,theframesupportisnotsuitableforaweakroof.Frameshavebecomeseldomusedbecausetheyarelessstableandrequirefrequentmaintenance.
CHOCK
Inachocksupport,thecanopyisasolidpieceandthebasemaybeeitherasolidpieceortwoseparatepartsconnectedbysteelbarsattherearand/orthefrontends.Inbothcasesalargeopenspaceisleftatthecenterforlocatingthedouble-actinghydraulicramwhichisusedtopushandpullthechainconveyorandthechockinawholeunit,respectively,adistinctivedifferencefromtheframesupport.Thissetupdesignedforthinseamswithtwolegsinthefrontandfourlegsintherear,separatedbywalkwaysalsousedintheshieldsandchockshields.
Again,allhydrauliclegsareinstalledverticallybetweenthebaseandthecanopy(Fig.8.10).Thenumberoflegsrangesfromthreetosix,butthefour-legchocksarebyfarthemostpopularones.Thesix-legchocksarey(Fig.8.10c).Forthesix-legchocks,thecanopyisgenerallyhinge-jointedabovethewalkway.Mostchocksarealsoequippedwithagobwindowhangingattherearendofthecanopy.Thegobwindowconsistsofseveralrectangularsteelplatesconnectedhorizontallyatbothends.
ABC
Fig.8.10Schematicsofvariouschocksupport
Inmostchocksupports,therearehingejointconnectionsbetweenthelegsandthecanopyandbetweenthelegsandthebase.Butinordertoincreasethelongitudinalstability,itisreinforcedmostlywithabox-shapedsteelframebetweenthebaseandeachleg.Alegrestoringdeviceisinstalledaroundeachlegatthetopofthebox-shapedsteelframe.
Thechocksaresuitableformediumtohardroof.Whentheroofoverhangswellintothegobandrequiresinducedcaving,thechockscanprovideaccesstothegob.
SHIELD
Shields,anewentryintheearlyseventies,arecharacterizedbytheadditionofacavingshieldattherearendbetweenthebaseandthecanopy.Thecavingshields,whichingeneralareinclined,arehinge-jointedtothecanopyandthebasemakingtheshieldacinematicallystablesupport,amajoradvantageovertheframesandthechocks.Italsocompletelysealsoffthegobandpreventsrockdebrisfromgettingintothefacesideofthesupport.Thustheshield-supportedfaceisgenerallyclean.
Thehydrauliclegsintheshieldsaregenerallyinclinedtoprovidemoreopenspacefortraffic.Becausethecanopy,cavingshield,andbaseareinterconnected,itcanwellresistthehorizontalforcewithoutbendingthelegs.Thus,unlikethesolidconstraintintheframe/chocksupports,thepinconnectionsbetweenthelegsandthecanopyandbetweenthelegsandthebaseinashieldsupportmakeitpossiblethattheangleofinclinationofthehydrauliclegsvarieswiththeminingheights.Sinceonlytheverticalcomponentofhydrauliclegpressureisavailableforsupportingtheroof,theactualloadingcapacityoftheshieldalsovarieswiththeminingheights.
Therearemanyvariationsoftheshieldsupports.Inthefollowing,sixitemsareusedtoclassifytheshields,whichenableaunifiedterminologytobedevelopedforallkindsofshields.Thetypesofmotionaltracesofthecanopytip,legpositionsandorientation,numberoflegs,canopygeometry,andotheroptionaldesignsanddevicescanbeclearlyspecifiedbytheterminology.
TYPESOFMOTIONALTRACESFORTHELEADINGEDGEOFTHECANOPY.
Thisisthemostcommonlyrecognizedwayofclassifyingtheshield.Basedonthiscriterion,therearethreetypes,lemniscates,caliper,andellipse(Fig.8.11).
A.Lemniscate.LB.Caliper.CC.Ellipse.E
Fig.8.11Threetypesofmotionaltracesforleadingedgeoftheshieldcanopy
A.Lemniscate.Thisisthemostpopulartype.Thecavingshieldandthebasearejointedbytwolemniscatesbarswhichhaveatotaloffourhinges.Asthehydrauliclegsareraisedandlowered,thedimensionsofthelemniscatesbarsareselectedsuchthattheleadingedgeofthecanopymovesupanddownnearlyvertically,thusmaintaininganearlyconstantunsupporteddistancebetweentheface-lineandtheleadingedgeofthecanopy.Thisisafeaturethatiswidelyconsideredmostdesirableforgoodroofcontrol.Thereareclearlimitsofminingheightwithinwhichtheleadingedgeofthecanopymovesnearlyvertically.Theselimitsarestrictlycontrolledbythedimensionalandpositionalarrangementsofthecanopy,cavingshield,lemniscatebars,andthebase.Beyondtheselimits,theedgeswillmoverapidlyawayfromtheface-linecreatingalargeunsupportedarea.
B.Caliper.Inacalipershield,thecavingshieldandthebaseareconnectedbyasinglehinge.Whenthehydrauliclegsareraised,theleadingedgeofthecanopymovesinanarcawayfromtheface,thusincreasingtheunsupportedareaThisisconsideredbymostuserstheleastdesirablefeatureofthecalipershieldButinpracticeiftheseamthicknessvarieslittle,thedimensionalan