AHIGH-POWERHYDRAULICDRILLFORBREAKINGHARDROCKF.F.VoitsekhovskayaUDC622.01.232.7Unlikeothermaterialssuchasstructuralsteels,rockshaveaveryinhomogeneousstructure.Asinglerockfragment,togetherwithveryhardinclusions,containsalsorelativelysoftpartsattheboundariesbetweenthehardgrains.Measurementsofthemicrohardnessinanydirectiononapolishedsurfaceofarockfragmentgiveveryscat-teredreadings.Wemayencounterpointswithhardnessgreaterthanthatoftungstencarbide,andafractionofamillimeterawaytheremaybeapointatwhichthehardnessandshearstrengthfallpracticallytozero.AnexarnpleofagraphofthemicrohardnessofarockalongsomedirectionorotherisillustratedinFig.1,curvec.Ifasimilarexperimenttomeasurethemicrohardnesswerecarriedoutwithsteel,weshouldstillfindsomescatterofthereadings,buttheamountofscatter(theratioofthemaximumhardnesstotheminimum)wouldbeseveralordersofmagnitudeless(Fig.1,curved)1.Astudyoftheeffectsofinhomogeneityofrockisthemainprerequisiteforelucidatingthepossibilityofobtainingadurabletool.Astheloadingareaofarockincreases,thereisanincreaseintheprobabilityofthepresenceofweakplacesinthezoneofstrongstresses.Figure2isagraphillustratingthedependenceofthebreakingstressontheareaofcontact.Owingtotheabovefeatures,inrockweobserveadecreaseinthebreakingloadwithincreaseoftheareaofcontact(curvea).Totheleftofpoint0thecurverepresentsthemaximumstrengthoftherock.Formetal,thesamecharacteristicappearsintheformofastraightlinebparalleltotheaxis,andisdeterminedbythefatiguelimitofthemetal.Notethattotherightofpoint0themetalshouldretainitsintegrityunderrepeatedloading,whereasarockshouldbreakafterasingleloadapplication.Evidentlytheworkingzoneliestotherightofpoint0,becauseitisinthiszonethatthemetalisstrongerthantherock.Thetoolwillsometimesfallontoapointwheretherockhashighstrengthandwillthenbesubjectedtomarkedabrasivewear.Iftheenergyofthepercussivedeviceislow,thenfurtherbreakageoftherockwillcease.Itisreasonabletotaketheimpactenergyintheregionof5000-15,000kgm.ResearchattheInstituteofHydrodynamicsoftheSiberianBranchoftheAcademyofSciencesoftheUSSRhasrevealedthatthepossibilityofinflictinghigh-energyblowscompletelyremovesanumberofdifficultieswhichpreventtheadoptionofpercussivebreakingofhardrocksinindustry,whileotherfactorsarisewhichincreasethebreakingefficiency,namely,durabilityofthetoolandasharpreductioninpowerconsumption.In1964someworkersattheInstituteofHydrodynamicsoftheSiberianBranchoftheAcademyofSciencesoftheUSSRputforwardthehypothesis(laterconfirmedbyAmericanworkers)thattheenergyconsumptionofbreak-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.Acopyofthisarticleisavailablefromthepublisherfor$15.oo.599e.kg/cmzox-NOIIIF,cm2Fig.1Fig.2Fig,1.IllustrativegraphofmicrohardnessalongXdirection.Curvec:microhardnessofrock；curved:microhardnessofsteel.Fig,2.BreakingstressobvsloadingareaF:a)forrock；b)fortoolmetal.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,wherethehardnessoftherocksreaches14ontheProtodyakonovscale.Ourdesignforahydraulicdrillwasbasedontheattempttomaximizetheimpactenergywithahighef-ficiency.Thisproblemwassolvedmainlybyusinganenergyaccumulator(airreservoirs),byfeedingenergydirectlyrotheimpactmass,andbyusingfloatingseals.Adifficultyindesign/ngahydraulicdrillwithhighimpactenergyisthenecessityofavoidingthedisruptiveactionofthereboundingrock4-8.TechnicalCharacteristicsofPercussiveDrillHead(HydraulicDrill)Sizeofdrill,m.4.5x0.7x0.7Weightofdrill,kg.4500Weightofmovingparts,kg.1500Impactenergy,kg/m.10,000-15,000Energyconsumption,kW-h/ms.5()e=14)Meanrockspallatlonperimpact,Liters.6-10(f=14)Airchargingpressure,atm.40-50Tenimpactsperminutearepossibleundermanualcontrol.60018I7,516B519104lZI157exk.z；.z././212022；5I4I129/2ZFig.3UnitB/192OFCD2224；3-78/./._.2/k-.-/A-.,J1II-.1.-.)k/.,-?&.-./Fig.4Figure3showsadiagramofthehydraulicdrill.Theimpactmass17issitedwithagapinsideelasticguides16fixedtotheframe,whichisformedfromtubularreceivers4joinedbyfaceplates3(front)and2(back).Insidetheframeisforcecylinder1andthemovingsystemofthepiston,rod,andimpactmass.Therod5hasarticulatedjointsateachend；oneofthese(6)lieswithintheimpactmass,andtheother,thepistonjoint7,iswithinthepistoncup8.Thissystemgivesalldegreesoffreedomanddampingtotheimpactmass.Thepistoncupdividestheforcecylinderintoanaircavity11andawatercavity12.Waterentersthelatterfrompumpsatabovethepressureoftheair.Waterenterscavity12viaannulargap6(Fig.4)formedbytheexternalsurfaceoftheslider13whichclosesport10.Thenpiston8compressesthepneumaticspringanddisplacesairintothereceivers.Aswaterisejectedfromcavity12,thepiston-md-impact-masssystemaccelerates,andtheblowisinflictedontherock.Potentialenergyaccumulatesintheairreceiver.Thelossofenergystoredintheairreceiverischarac-terizedbytheefficiencyofthepneumaticspring,whichisdefinedastheratioofthekineticenergyoftheimpactmassattheendofitsaccelerationtotheworkdoneincompressingthegas:=E/A,whereEmU2max2Assumingthatthegasiscompressedadiabatically,wehavev(Q_,_Vo-),A=Pin1-(1)whereV0=Vr+Vc,mistheweightoftheimpactmass,Umaxisthemaximumvelocityoftheimpactmass,Vristhevolumeoftheairreceiver,Vcisthevolumeoftheaircavityofthecylinderatthemomentwhentheimpact601t,see4.lO-2o5Vr=4.5m/sec/iI.IiI10152025Jo35,04550556os57o75eoc.cmFig.5.Recordofmovementsofimpactmassofhydraulicdrill.Fig.6massreachesthevelocityUreax,andPinistheairpressurebeforethestartofbackwardtraveloftheimpactmass.Equation(1)isonlyapproximate,becauseduringcompressionoftheairpartoftheheatinthereceivertubeshastimetoleakaway.Withanautomaticrecordingde