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AHIGHPOWERHYDRAULICDRILLFORBREAKINGHARDROCKF.F.VoitsekhovskayaUDC622.01.232.7Unlikeothermaterialssuchasstructuralsteels,rockshaveaveryinhomogeneousstructure.Asinglerockfragment,togetherwithveryhardinclusions,containsalsorelativelysoftpartsattheboundariesbetweenthehardgrains.Measurementsofthemicrohardnessinanydirectiononapolishedsurfaceofarockfragmentgiveveryscatteredreadings.Wemayencounterpointswithhardnessgreaterthanthatoftungstencarbide,andafractionofamillimeterawaytheremaybeapointatwhichthehardnessandshearstrengthfallpracticallytozero.AnexarnpleofagraphofthemicrohardnessofarockalongsomedirectionorotherisillustratedinFig.1,curvec.Ifasimilarexperimenttomeasurethemicrohardnesswerecarriedoutwithsteel,weshouldstillfindsomescatterofthereadings,buttheamountofscattertheratioofthemaximumhardnesstotheminimumwouldbeseveralordersofmagnitudelessFig.1,curved\1\.Astudyoftheeffectsofinhomogeneityofrockisthemainprerequisiteforelucidatingthepossibilityofobtainingadurabletool.Astheloadingareaofarockincreases,thereisanincreaseintheprobabilityofthepresenceofweakplacesinthezoneofstrongstresses.Figure2isagraphillustratingthedependenceofthebreakingstressontheareaofcontact.Owingtotheabovefeatures,inrockweobserveadecreaseinthebreakingloadwithincreaseoftheareaofcontactcurvea.Totheleftofpoint0thecurverepresentsthemaximumstrengthoftherock.Formetal,thesamecharacteristicappearsintheformofastraightlinebparalleltotheaxis,andisdeterminedbythefatiguelimitofthemetal.Notethattotherightofpoint0themetalshouldretainitsintegrityunderrepeatedloading,whereasarockshouldbreakafterasingleloadapplication.Evidentlytheworkingzoneliestotherightofpoint0,becauseitisinthiszonethatthemetalisstrongerthantherock.Thetoolwillsometimesfallontoapointwheretherockhashighstrengthandwillthenbesubjectedtomarkedabrasivewear.Iftheenergyofthepercussivedeviceislow,thenfurtherbreakageoftherockwillcease.Itisreasonabletotaketheimpactenergyintheregionof500015,000kgm.ResearchattheInstituteofHydrodynamicsoftheSiberianBranchoftheAcademyofSciencesoftheUSSRhasrevealedthatthepossibilityofinflictinghighenergyblowscompletelyremovesanumberofdifficultieswhichpreventtheadoptionofpercussivebreakingofhardrocksinindustry,whileotherfactorsarisewhichincreasethebreakingefficiency,namely,durabilityofthetoolandasharpreductioninpowerconsumption.In1964someworkersattheInstituteofHydrodynamicsoftheSiberianBranchoftheAcademyofSciencesoftheUSSRputforwardthehypothesislaterconfirmedbyAmericanworkersthattheenergyconsumptionofbreakingisreducedwhentheimpactenergyisraisedabove5000kgm.Onthebasisofthishypothesis,workhasbegunoncreatinganinstrumentwithhighimpactenergy.Atthepresenttime,hydraulicandpneumaticdrillsarewidelyusedinindustry.Mostofthesehaveimpactenergiesbelow300kgm.Onlyinexceptionalcases,forexample,insmashingboulders,doweuserubblehammerswithimpactenergiesof1500kg.m.Hydraulic/pneumatichammersusedatthefaceclearlyhaveinsufficientpowertogiveanyadvantageoverdrillingandblastinginrockbreaking.ThisisbecauseofthehighpowerconInstituteofHydrodynamics.SiberianBranch,AcademyofSciencesoftheUSSR,Novosiblrsk.TranslatedfromFizikoTekhnicheskieProblemyRazrabotkiPoleznykhIskopaemykh,No.5,pp.8289,SeptemberOctober,1974.OriginalarticlesubmittedMay31,1974.91975PlenumPublishingCorporation,227West17rhStreet,NewYork,N.Y.10011.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmitted,inanyformorbyanymeans,electronic,mechanical,photocopying,microfilming,recordingorotherwise,withoutwrittenpermissionofthepublisher.Acopyofthisarticleisavailablefromthepublisherfor15.oo.599e..kg/cmzoxNOIIIF,cm2Fig.1Fig.2Fig,1.IllustrativegraphofmicrohardnessalongXdirection.Curvecmicrohardnessofrockcurvedmicrohardnessofsteel.Fig,2.BreakingstressobvsloadingareaFaforrockbfortoolmetal.sumpdonandcostofthetoolspercubicmeterofbrokenrock,becausebluntingofthecuttingedgeleadstocessationofbreaking.Atthesametime,industryneedspercussivemachinesforcuttingtunnelsinhardrocks,breakinguprockobstaclesinpits,etc.\2,3\.Forahydraulicdrillwithanimpactenergyabove5000kg.mbluntingofthecuttingedgehaslittleeffectontheefficiencyofrockbreaking.Theseresultswereobtainedwiththeaidofanewlydesignedhydraulicdrill.Indevelopingitwecametotheconclusionthatforpercussivemachineswithimpactenergiesabove5000kg.mitisnecessarytojointhestrikertothetoO1.Thispermitsustoeliminatecollisionbetweenthemasses,tosimplifythedesign,andtogreatlyincreasetheimpactenergy.Asaresulttheenergypercubicmeterofbrokenrockisreducedto1.15111oofthatforprevioushydropneumadcdrills.Fromtheexperimentaldataweseethatthemeanspecificenergyconsumptionofbreaking,takenastheratioofthekineticenergyoftheimpactmasstothemeanvolumeofbrokenrockfromoneimpactofenergy4000kg.m,isequalto5kWh/mSiftheimpactenergyis12,000kgm,theenergyconsumptionis2.9kWh/m3.Inalteringthedesignofthetool,theworkersattheInstituteofHydrodynamicsoftheSiberianBranchoftheAcademyofSciencesoftheUSSRhavetriedtorealizetheprincipleofselfsharpening,inwhichthetoolasitwearskeepsitscrosssectionwhileitsendacquiresasteadyroundedshape.Assuchastrikerwears,itisonlynecessarytoadvanceitfromthecollidingmass.Startingin1966,weplannedandbuiltseveralmodificationstothebusinessendsofpercussivemachines.TheyweretestedintheButovskayapitoftheKemerovoregionandmorerecentlyattheTyrnyauzpitoftheKabardinoBalkarASSR,wherethehardnessoftherocksreaches14ontheProtodyakonovscale.Ourdesignforahydraulicdrillwasbasedontheattempttomaximizetheimpactenergywithahighefficiency.Thisproblemwassolvedmainlybyusinganenergyaccumulatorairreservoirs,byfeedingenergydirectlyrotheimpactmass,andbyusingfloatingseals.Adifficultyindesign/ngahydraulicdrillwithhighimpactenergyisthenecessityofavoidingthedisruptiveactionofthereboundingrock\48\.TechnicalCharacteristicsofPercussiveDrillHeadHydraulicDrillSizeofdrill,m.........................4.5x0.7x0.7Weightofdrill,kg.......................4500Weightofmovingparts,kg..................1500Impactenergy,kg/m......................10,00015,000Energyconsumption,kWh/ms...............5e14Meanrockspallatlonperimpact,Liters..........610f14Airchargingpressure,atm..................4050Tenimpactsperminutearepossibleundermanualcontrol.60018I7,516B519104lZI157exk.z.z../..//2120225I4I129//2ZFig.3UnitB/192OFCD2224378/////./._.....2/\\k..\\/A.\,J1II......................1...k\\\\\/\\\.\\,\\\\\\\\..\./Fig.4Figure3showsadiagramofthehydraulicdrill.Theimpactmass17issitedwithagapinsideelasticguides16fixedtotheframe,whichisformedfromtubularreceivers4joinedbyfaceplates3frontand2back.Insidetheframeisforcecylinder1andthemovingsystemofthepiston,rod,andimpactmass.Therod5hasarticulatedjointsateachendoneofthese6lieswithintheimpactmass,andtheother,thepistonjoint7,iswithinthepistoncup8.Thissystemgivesalldegreesoffreedomanddampingtotheimpactmass.Thepistoncupdividestheforcecylinderintoanaircavity11andawatercavity12.Waterentersthelatterfrompumpsatabovethepressureoftheair.Waterenterscavity12viaannulargap6Fig.4formedbytheexternalsurfaceoftheslider13whichclosesport10.Thenpiston8compressesthepneumaticspringanddisplacesairintothereceivers.Aswaterisejectedfromcavity12,thepistonmdimpactmasssystemaccelerates,andtheblowisinflictedontherock.Potentialenergyaccumulatesintheairreceiver.Thelossofenergystoredintheairreceiverischaracterizedbytheefficiencyofthepneumaticspring,whichisdefinedastheratioofthekineticenergyoftheimpactmassattheendofitsaccelerationtotheworkdoneincompressingthegasE/A,whereEmU2max2Assumingthatthegasiscompressedadiabatically,wehavevQ_,,_Vo,APin11whereV0VrVc,mistheweightoftheimpactmass,Umaxisthemaximumvelocityoftheimpactmass,Vristhevolumeoftheairreceiver,Vcisthevolumeoftheaircavityofthecylinderatthemomentwhentheimpact601t,see4.lO2o5Vr4.5m/sec/iI.I\iI10152025Jo35,04550556os57o75eoc.cmFig.5.Recordofmovementsofimpactmassofhydraulicdrill.Fig.6massreachesthevelocityUreax,andPinistheairpressurebeforethestartofbackwardtraveloftheimpactmass.Equation1isonlyapproximate,becauseduringcompressionoftheairpartoftheheatinthereceivertubeshastimetoleakaway.Withanautomaticrecordingdevicewerecordedtheaccelerationoftheimpactmass.Figure5showsagraphofthetimedependenceofthemovementoftheimpactmass.Sectionaashowstheretardationoftheimpactmass.Fromthegraphwedeterminedthevelocityoftheimpaetmassalongtheaccelerationpath.FromEq.1wefoundtheefficiencyofthepneumaticspring.Inourexperimentsthiswas7578.Duringaccelerationoftheimpactmass,intheabsenceofobstacles,itskineticenergyisquenchedbythebrakingdevice.Thisisachievedbyincreasingthepressureaheadofthepistoncup.Theendofthepistoncupbeginstocloseport10.Anyfurtherdangerousriseinpressureislimitedbyflowofwaterthroughthegapbetweentheexternalsurfaceofthepistoncupandtheinternalsurfaceoftheforcecylinder.TheconditionoffloatingofthepistoncupisdeterminedbytheequationPbSpPaSb.wherePbisthebrakingpressure,Spisthecrosssectionalareaofthetubeofthepistoncup,Paistheairpressure,andSbistheareaofthebaseofthepistoncup.602
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