Technical_Information-brush-pressure

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1、SchunkKohlenstofftechnikTechnicalInformationBrushpressure1.TheoptimalBrushPressureThebasicprinciple:Pressureshouldbesufficienttoensureatrueandcontinuouscontactontheslipringorcommutatoratallworkingconditionsofthemachine.Theoptimalbrushpressureresultsfrombothelectricalan

2、dmechanicalconsiderations.1.1.ElectricalEveryinterruptionofthecontactcollector/carbonbrushisthecauseforbrushsparking,burnmarksincreasedbrushwearetc.Thereforethebrushpressureshouldbeincreasedonmachines,•subjecttoshocksandvibrations(suchastractionmotors,pressdrives,drive

3、sforcon-tainercranes,propellerdrives,fandrivesetc.),or•motorswithbadstability(unbalance,out-of-round)AnincreasedbrushpressurehasaneffectonlyincaseofexternalfactorsAnincreaseofbrushpressureagainstbrushvibrationscausedbytoosmoothcollectorsurfaceisuseless.Inthecontrary:th

4、emechanicallosseswillbeincreased,thefrictioncoefficientwillberaised,andbrushesaswellasbrushholdersmightbeseverelydamaged.Thecontactdropofthecarbonbrushesisdecreasedwhenthebrushpressureisincreased.Consequentlythecommutatingpropertiesifthebrushdecreasesathighpressure.Thi

5、sef-fectshouldnotbeconsideredasinsignificant.Forastandardelectrographitegradeitcanreach30%ifpressuregoesfrom200cN/cm²to500cN/cm²brushpressureIndex:2Page:1of:8SchunkKohlenstofftechnikTechnicalInformationAthighcurrentloadingthewearrateofthebrushcanbedecreasedsignificantl

6、ybyincreas-ingthebrushpressure.Duetotheelasticityofthecarbonbrushgradesthenumberofcon-tactpointsisenlargedwithanincreasedbrushpressure.Thereforethecurrentisdistributedonabiggerarea.1.2.MechanicalThemechanicallossesandthebrushwearareincreasingwithincreasingthebrushpres-

7、sure.Themaximumtolerablepressureforabrushdependsonthemechanicalstrengthofthema-terial.Allsoftorfragilegradesarenotsuitableforapplicationsrequiringaspecificpressurehigherthan300cN/cm².Themaximumsuitablebrushpressurefornaturalgraphitegradesusedonturbo-generatorsislimited

8、to160cN/cm²only.Thefollowingdiagramshowstheprincipalgraphofthebrushwearasafunctionoffbrushpressure.brushpressureIndex