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AHIGH-POWERHYDRAULICDRILLFORBREAKINGHARDROCKF.F.VoitsekhovskayaUDC622.01.232.7Unlikeothermaterialssuchasstructuralsteels,rockshaveaveryinhomogeneousstructure.Asinglerockfragment,togetherwithveryhardinclusions,containsalsorelativelysoftpartsattheboundariesbetweenthehardgrains.Measurementsofthemicrohardnessinanydirectiononapolishedsurfaceofarockfragmentgiveveryscat-teredreadings.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.Itisreasonabletotaketheimpactenergyintheregionof5000-15,000kgm.ResearchattheInstituteofHydrodynamicsoftheSiberianBranchoftheAcademyofSciencesoftheUSSRhasrevealedthatthepossibilityofinflictinghigh-energyblowscompletelyremovesanumberofdifficultieswhichpreventtheadoptionofpercussivebreakingofhardrocksinindustry,whileotherfactorsarisewhichincreasethebreakingefficiency,namely,durabilityofthetoolandasharpreductioninpowerconsumption.In1964someworkersattheInstituteofHydrodynamicsoftheSiberianBranchoftheAcademyofSciencesoftheUSSRputforwardthehypothesislaterconfirmedbyAmericanworkersthattheenergyconsumptionofbreak-ingisreducedwhentheimpactenergyisraisedabove5000kg-m.Onthebasisofthishypothesis,workhasbegunoncreatinganinstrumentwithhighimpactenergy.Atthepresenttime,hydraulicandpneumaticdrillsarewidelyusedinindustry.Mostofthesehaveimpactenergiesbelow300kg-m.Onlyinexceptionalcases,forexample,insmashingboulders,doweuserubblehammerswithimpactenergiesof1500kg.m.Hydraulic/pneumatichammersusedatthefaceclearlyhaveinsufficientpowertogiveanyadvantageoverdrillingandblastinginrockbreaking.Thisisbecauseofthehighpowercon-InstituteofHydrodynamics.SiberianBranch,AcademyofSciencesoftheUSSR,Novosiblrsk.TranslatedfromFiziko-TekhnicheskieProblemyRazrabotkiPoleznykhIskopaemykh,No.5,pp.82-89,September-October,1974.OriginalarticlesubmittedMay31,1974.91975PlenumPublishingCorporation,227West17rhStreet,NewYork,N.Y.10011.Nopartofthispublicationmayberepro-duced,storedinaretrievalsystem,ortransmitted,inanyformorbyanymeans,electronic,mechanical,photocopying,micro-filming,recordingorotherwise,withoutwrittenpermissionofthepublisher.Acopyofthisarticleisavailablefromthepublisherfor15.oo.599e..kg/cmzox- NOIIIF,cm2Fig.1Fig.2Fig,1.IllustrativegraphofmicrohardnessalongXdirection.Curvecmicrohardnessofrock；curvedmicrohardnessofsteel.Fig,2.BreakingstressobvsloadingareaFaforrock；bfortoolmetal.sumpdonandcostofthetoolspercubicmeterofbrokenrock,becausebluntingofthecuttingedgeleadstoces-sationofbreaking.Atthesametime,industryneedspercussivemachinesforcuttingtunnelsinhardrocks,breakinguprockobstaclesinpits,etc.\[2,3\].Forahydraulicdrillwithanimpactenergyabove5000kg.mbluntingofthecuttingedgehaslittleeffectontheefficiencyofrockbreaking.Theseresultswereobtainedwiththeaidofanewlydesignedhydraulicdrill.Indevelopingitwecametotheconclusionthatforpercussivemachineswithimpactenergiesabove5000kg.mitisnecessarytojointhestrikertothetoO1.Thispermitsustoeliminatecollisionbetweenthemasses,tosim-plifythedesign,andtogreatlyincreasetheimpactenergy.Asaresulttheenergypercubicmeterofbrokenrockisreducedto1.15-111oofthatforprevioushydropneumadcdrills.Fromtheexperimentaldataweseethatthemeanspecificenergyconsumptionofbreaking,takenastheratioofthekineticenergyoftheimpactmasstothemeanvolumeofbrokenrockfromoneimpactofenergy4000kg.m,isequalto5kW-h/mS；iftheimpactenergyis12,000kg-m,theenergyconsumptionis2.9kW-h/m3.Inalteringthedesignofthetool,theworkersattheInstituteofHydrodynamicsoftheSiberianBranchoftheAcademyofSciencesoftheUSSRhavetriedtorealizetheprincipleofself-sharpening,inwhichthetoolasitwearskeepsitscrosssectionwhileitsendacquiresasteadyroundedshape.Assuchastrikerwears,itisonlyneces-sarytoadvanceitfromthecollidingmass.Startingin1966,weplannedandbuiltseveralmodificationstothebusinessendsofpercussivemachines.TheyweretestedintheButovskayapitoftheKemerovoregionandmorerecentlyattheTyrnyauzpitoftheKabardino-BalkarASSR,wherethehardnessoftherocksreaches14ontheProtod yakonovscale.Ourdesignforahydraulicdrillwasbasedontheattempttomaximizetheimpactenergywithahighef-ficiency.Thisproblemwassolvedmainlybyusinganenergyaccumulatorairreservoirs,byfeedingenergydirectlyrotheimpactmass,andbyusingfloatingseals.Adifficultyindesign/ngahydraulicdrillwithhighimpactenergyisthenecessityofavoidingthedisruptiveactionofthereboundingrock\[4-8\].TechnicalCharacteristicsofPercussiveDrillHeadHydraulicDrillSizeofdrill,m.........................4.5x0.7x0.7Weightofdrill,kg.......................4500Weightofmovingparts,kg..................1500Impactenergy,kg/m......................10,000-15,000Energyconsumption,kW-h/ms...............5e14Meanrockspallatlonperimpact,Liters..........6-10f14Airchargingpressure,atm..................40-50Tenimpactsperminutearepossibleundermanualcontrol.60018I7,516B519104lZI157exk.z；.z../..//212022；5I4I129//2ZFig.3UnitB/192OFCD2224；3--------78//// /./._.....2/\\k-..\\-/A-.\,J1II--.... ..................1..-.k\\\\\/\\\.\\,\\-\\\\\-\..\-./Fig.4Figure3showsadiagramofthehydraulicdrill.Theimpactmass17issitedwithagapinsideelasticguides16fixedtotheframe,whichisformedfromtubularreceivers4joinedbyfaceplates3frontand2back.Insidetheframeisforcecylinder1andthemovingsystemofthepiston,rod,andimpactmass.Therod5hasarticulatedjointsateachend；oneofthese6lieswithintheimpactmass,andtheother,thepistonjoint7,iswithinthepistoncup8.Thissystemgivesalldegreesoffreedomanddampingtotheimpactmass.Thepistoncupdividestheforcecylinderintoanaircavity11andawatercavity12.Waterentersthelatterfrompumpsatabovethepressureoftheair.Waterenterscavity12viaannulargap6Fig.4formedbytheexternalsurfaceoftheslider13whichclosesport10.Thenpiston8compressesthepneumaticspringanddisplacesairintothereceivers.Aswaterisejectedfromcavity12,thepiston-md-impact-masssystemaccelerates,andtheblowisinflictedontherock.Potentialenergyaccumulatesintheairreceiver.Thelossofenergystoredintheairreceiverischarac-terizedbytheefficiencyofthepneumaticspring,whichisdefinedastheratioofthekineticenergyoftheimpactmassattheendofitsaccelerationtotheworkdoneincompressingthegasE/A,whereEmU2max2Assumingthatthegasiscompressedadiabatically,wehavevQ_,,_Vo - ,APin1----1whereV0VrVc,mistheweightoftheimpactmass,Umaxisthemaximumvelocityoftheimpactmass,Vristhevolumeoftheairreceiver,Vcisthevolumeoftheaircavityofthecylinderatthemomentwhentheimpact601t,see4.lO-2o5Vr4.5m/sec/iI.I\]iI10152025Jo35,04550556os57o75eoc.cmFig.5.Recordofmovementsofimpactmassofhydraulicdrill.Fig.6massreachesthevelocityUreax,andPinistheairpressurebeforethestartofbackwardtraveloftheimpactmass.Equation1isonlyapproximate,becauseduringcompressionoftheairpartoftheheatinthereceivertubeshastimetoleakaway.Withanautomaticrecordingdevicewerecordedtheaccelerationoftheimpactmass.Figure5showsagraphofthetimedependenceofthemovementoftheimpactmass.Sectiona-ashowstheretardationoftheimpactmass.Fromthegraphwedeterminedthevelocityoftheimpaetmassalongtheaccelerationpath.FromEq.1wefoundtheefficiencyofthepneumaticspring.Inourexperimentsthiswas75-78.Duringaccelerationoftheimpactmass,intheabsenceofobstacles,itskineticenergyisquenchedbythebrakingdevice.Thisisachievedbyincreasingthepressureaheadofthepistoncup.Theendofthepistoncupbeginstocloseport10.Anyfurtherdangerousriseinpressureislimitedbyflowofwaterthroughthegapbetweentheexternalsurfaceofthepistoncupandtheinternalsurfaceoftheforcecylinder.Theconditionoffloating*ofthepistoncupisdeterminedbytheequationPbSpPaSb.wherePbisthebrakingpressure,Spisthecross-sectionalareaofthetubeofthepistoncup,Paistheairpres-sure,andSbistheareaofthebaseofthepistoncup.602