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MININGMECHANIZATIONANDAUTOMATIONGEOMETRYOFTHEWORKINGPARTOFANEXCAVATORTOOTHV.A.PolovinkoandA.I.FedulovUDC621.879.3Studiesofexcavatortoothwearkineticsconductedearlierbythepresentauthors1,2showedthatthemainfactorcontrollingwearplatformdynamicsisthephysical-mechanicalpropertyoftherock.Wearplatformsevolveintwostages.Toothwearacquiredduringthecriticalstage2hasnosignificantinfluenceonexcavatorperformanceintheminingandgeologicconditionstypicalforthenortheasternregionsofRussia.Cuttingelementscancontinuetobeuseduptothemaximumpermissiblewearlevelspecifiedbythemanufacturer.Inthisrespect,intensivewearduringinitialstagesapparentlyreflectssomedesignimperfectionratherthantheeffectsoftheworkadjustmentprocess.Investigatorshavestudiedthecausesandconsequencesofintensewearofexcavatorteeth,buttherearestillnobasiccriteriauponwhichtoformulategeneralprinciplessoastoimprovethewearresistanceofcuttingelementsasdeterminedbytheirdesign3-5.Anefficientwaytoraisethewearresistanceofanexcavatortoothistodevisethedesignparametersoftheworkingcomponentsoastoensureclassicalsingle-stagewear,bypassingthecritical(pseudoadjustment)phase.Wedevelopedanewexcavatortoothdesignwhichfeaturesheightenedwearresistance.Theoutlineoftheworkingcomponentofthetoothanditsdimensionsweredevelopedwithdueregardforthemaincharacteristicpointsofthewearresistancecurvesofmass-producedwedge-shapedteeth.Toattainalinearbehaviorforthewearprocessofsuchteethwitharateequaltoorlessthanwhatisobservedduringthesecondstageofwearwithmass-producedteeth,wespecifiedthedesignparameterscorrespondingtothebeginningofthesecondphase,wherethespecificpressurefromthestandardforceofthethrustmechanismdropsto10-12MPa.Figure1plotspressurevariationsonthewearplatformsofteethofbucketsusedincommonquarryexcavatorsaccordingtothefollowingexpression:P1whereUpisthewidthofthewearplatform;P1istheratedforceofthethrustmechanism;Dandiarethelengthofthetoothcuttingedgeandthenumberofteethonthebucket,respectively.Thecurvesshowthattherearecertainpressureregionsonwearplatformswhererockresistancetoteethisequaltoorgreaterthantheforcedevelopedbythethrustmechanism.Thisloadingpatternforcuttingelementsisobservedonmonolithicstrong(e.g.,permafrost)rocks.Ontheotherhand,somematerialsresistcuttingwithamuchweakerstrengththantheforcedevelopedbythisthrustmechanism.Toestimatethespecificpressuresformedwhencuttingelementsinteractwiththesematerials,weplottedcurves1-4bycomputingthepressureonthewearplatformsofantKG-5Aexcavatortoothat0.8,0.4,0.2,and0.1oftheratedthrustforce.Onweakrocksthepressurevariationpatternonthewearplatformisthesame,butthepressuresanddimensionsforthewornportionofteethafterthebeginningofthesecondstagemaybemuchsmaller(sometimesbyaconsiderablefactor).ThisisclearlyseeninFig.1.ZoneI,crossingthecurves,definestheparametersoftheonsetofthesecondstageofwearforteethofdifferentexcavatorsandfordifferentrockstrengths(curves1-4).ForIKG-5AexcavatorteeththestartingpointofthesecondwearstageobtainedexperimentallyliesinzoneIandcorrespondstoapressureofP=10-12MPaandawearplatformwidthofUtcr=45mm.InstituteofMining,SiberianBranch,RussianAcademyofSciences,Novosibirsk.TranslatedfromFiziko-TekhnicheskieProblemyRazrabotkiPoleznykhIskopaemykh,No.2,pp.16-23,March-April,1993.Originalarticlesubmit-tedNovember4,1992.1062-7391/93/2902-0115512.501993PlenumPublishingCorporation1150MPatl/(.OEKG-20EKG-12,5EKG-$I5AUpUp,mmFig.1Fig.2Fig.1.Pressurevariationasafunctionofwearplatformsize(1-4-theoreticalpressurecurvesonan1KG-5Aexcavatortoothwearplatformwhenworkingrockswithresistance0.8,0.4,0.2,and0.1ofstandardthrustforce).Fig.2.Workingpartofacuttingelementwithwedgeangle180(1cuttingedgewithareaSo;b-edgewidth;D-length;2-wearplatformsurfaceareaSp2;1,-wearplatformslopeangle.Atagivensizeoftheworkingpartofthetool,thestageofcriticalwearorpseudoadjustmentisvirtuallyabsentonrocksandgroundswithlowstrength,whiletoolsexperienceintensetwo-stagewearonstrong/hardrocks.Indifferentminingandgeologicconditions,itisobviouslyconvenienttoworkwithinterchangeabletools.Itiscurrentlyimpossibletocontroltheforceparametersontheworkingelementofanexcavator.Theoperatorobservestheworkofthemachinevisually,watchingitsmotionandbucketfilling.Theloadsactinguponworkingelementsandteeththusdependnotonlyonrockresistancetocutting,butlargelyonoperatorskillandexperience.Artefficientandrationalapproachtodevisingworkingtoothcomponentparametersistoconsiderthepowerofexcavatordrives.Theareaofthecuttingedgeforarectangularcuttingprofilewitha180sharpeningcanbecalculatedfromthepressureonthewearplatform(seeFig.2)correspondingtotheonsetofthesecondwearstage:P=PISp2.iwherePisthepressureonthewearplatformwhenplatformdimensionscorrespondtothebeginningofthesecondstage;P1istheratedthrustforceoftheexcavator(verticalcomponentofthecuttingforce);Sp2isthewearplatformareaatthesecondstageonset;iisthenumberofteethontheexcavatorbucket.ThewearplatformisdefinedintermsofthecuttingedgeareaasSOSP2=sinTwhere3isthewearplatformslopeanglerelativetothebackfacetofthecuttingprofile;Soiscuttingedgearea.Thepressureonthewearplatformcanbeexpressedasp=.Pxsin?So-Theareaofthecuttingedgewhichprovidesthedesiredwearpatternforthecuttingelementisdefinedfromthesameformula:So-P1sin7P-i116/2?-7rjU,mmVez1VjIV,1,000m3Fig.3Fig.4Fig.3.Cuttingelementswithheightenedwearresistance(Ucr-linearwearcorrespondingtofirstcriticalstage;bbandDb-basicwidthandlengthofcuttingedgeofwedgetooth;D-calculatedlengthofcuttingedge).Fig.4.Design-controlledwearresistanceofwedge-shapedcuttingelements(1,2varia-tionoflinearwearforatoothwithanexpandedpartandastandardtooth,respectively;Umax-maximumpermissiblewear;&V-increasedoperationresourceofnewtoothdesign.Consideringthatthecuttingedgeareaislinkedtothewearplatformbytheprecedingrelation,wecanformulatesimpletechnologicalconditionsforimprovingthedesignoftheworkingcomponentofstandardwedge-shapedteethintermsofoptimallengthofthetoothcuttingedgeasD=Sp2.s_ni?bwhereDistheoptimalcuttingedgelengthwhichprovidessteadysingle-stagewearofcuttingelements;bistheactual(basic)widthofthecuttingedgeofmass-producedwedgeteeth;Sp2istheareaoftheplatformcorrespondingtotheonsetofsteadywear;and3istheangleoftheslopeofthewearplatformwithrespecttotoothlongitudinalaxis.Figure3offerstechnologicalconceptsforreductionofcuttingelementweardynamicsbasedonmass-producedwedge-shapedteeth.Thelengthoftheexpandedpartofatooth(D)shouldbenotlessthancriticallinearwearUcr.Aftertheexpandedpartiswornoff,atoothacquiresthenaturalsizeoftheplatformcorrespondingtothesecondstageofsteadywear.Thisdesignwearsaccordingtoalinearrelationship(Fig.4)withanintensityequalto*._hatofthesecondstageofwearofmass-producedteeth(parallelportionsofplots).Afterattainingmaximumwear,teethwouldhaveextendedservicelife,expressedinanincreasedvolumeofexcavatedrock(AV).Weshouldpayspecialattentiontocreatingteethwithheightenedwearresistancewithoutmodifyingthebasicdimensionsorshapeoftheworkingcomponent.Thisisimportant,becausethisformiseasierandlessexpensivetomanufac-ture.Wedevelopedtheuniversalgeometryfortheworkingpartofanexcavatortoothbasedoncalculationsoftheoptimalwidthofthecuttingedgewhileretainingthemaindimensionsofstandardteethdesigns.*Thetoothwiththenewworkingcomponentgeometry(Fig.5)hascuttingedge1,linearsegmentofbackface2,andcurvilinearpart3.Thefrontfaceisformedoftwolinearsegments4and5.Thelinearsegmentofbackface2isparalleltotoothlongitudinalaxis6,situatedatdistanceIfromtheaxis6.Theplaneofthecuttingedgeissituatedatananglegreaterthan90tothecuttingplane.ThishelpsformasteadycompactioncoreontheplaneOfthecuttingedge,whichpartlyprotectsitfromwear.Thecuttingedgewidthisfoundfromanempiricrelationship:*WetookthetoothdesigndevelopedbytheInstituteofHeavyMachinery(UralmashProductionAssociation)forthebasicprototype.!17776Fig.5.Designoftheworkingpartofatoothwithoptimalparameters(1-cuttingedge;2-linearportionofthebackfacet;3-curvilinearbackfacet;4,5-segmentsofthefrontfacet;6-longitudinaltoothaxis;7-wearplatform;b=cuingedgewidth;a1=initialcuttingangle;/=wedgeangle;f=distancebetweenwedgeanglevertexandcuttingedge;AandB=dimensionsoflinearsegmentsoffrontandbackfacets,respectively;I=displacementofbackfacetsegmentfromtoothaxis;r=wearplatformslopeangle.bPIsinP,D.wherebisanefficientwidthofthecuttingedge;P1istheexcavatorthrustforce,whichconsistsoftheweightofbucketandthestick,andtheforcedevelopedbythethrustmechanism;3istheslopeangleofthewearplatformrelativetothetoothaxis(orthelinearsegmentofthebackfacet);Disthelengthofthecuttingedge;Pisthepressureonthewearplatformatthebeginningofthesecondstage;andiisthenumberoftheteethonthebucket.Cuttingedge1shouldbeatdistancePIsinfromthevertexofthewedgeangle,whereisthewedgeangleoftheworkingpartofthetooth.Literarydataindicatethatachangeofthecuttingangle(moreprecisely,thebackangle,whichdependsonthecuttingangle)greatlyaffectstheintrusionforceofcuttingelements.Whenthebackangleofatoothisincreased,theenergycapacityofitsintrusionintothegroundtendstodecrease7.Weformulatedthenewtoothgeometrytakingthisfactorintoaccount.Accordingly,linearsegment2orbackfacet3isparalleltotoothaxis6,whichallowedustoincreasethebackanglebyafactorof2.0-2.5comparedwiththemass-producedmodel.Toreducethewearofthehorizontalcomponentofthecuttingparameterofthee
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