Chapter 708 bearings.docx
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Chapter 708 bearings.docx
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Chapter708bearings
Chapter708bearings3
Bearings3
1.Generalbearingrequirementsandcriteria3
2.Bearingmetals3
2.1Tinbasedwhitemetal3
2.2Tinaluminum(A40orA/Sn40)3
3.Overlayers4
4.Flashlayer,Tin(Sn)4
5.Bearingsdesign4
5.1Tangentialrun-out(plate70801,70802,70804,B-B)4
5.2Borerelief(plates70801,70802,70804,A-A)4
5.3Axialoilgroovesandoilwedges(plates70803,70806,Fig.A-A)4
5.4Thickshellbearings(plate70801)5
5.5Thinshellbearings(plate70802)5
5.6Topandsideclearance5
5.7Wear6
5.8Undersizebearings6
6.Journal/pins6
6.1Surfaceroughness6
6.2Sparkerosion6
6.3Surfacegeometry7
6.4Undersizejournals/pin7
7.Practicalinformation7
7.1Checkwithoutopeningup7
7.2Openupinspectionandoverhaul8
7.3Typesofdamage8
7.4Causeforwiping8
7.5Cracks8
7.6Causeforcracks9
7.7Repairofoiltransitions(wedges,tangentialrunoutandborerelief)9
7.8Bearingwearrate9
7.9Surfaceroughness(journal/pin)9
7.10Repairsofbearingonthespot9
7.11Repairsofjournals/pin10
7.12Inspectionofbearings10
8.Crossheadbearingassembly11
8.1Bearingfunctionandconfiguration11
8.2Replacementcriteriaofcrossheadbearing11
9.Mainbearings11
9.1Thethickshellbearingassembly(plate70805,fig.1)11
9.2Thethisshellbearingassembly(plate70805,fig.2)11
10crankpinbearingassembly12
11.Guideshoesandguidestrips(plate70806)12
12.Thrustbearingassembly(Plate70807)12
13.Camshaftbearingassembly(plate70808)12
Alignmentofmainbearing13
1.Alignment13
2.Alignmentofmainbearings13
2.1Deflectionmeasurements(plate70815)13
2.2Checkingthedeflections(plate70817and“data”)13
2.3Deflectioncurve(plate760816A,70816B).14
2.4Floatingjournals15
2.5Causeofcrankshaftdefection15
2.7Pianowiremeasurements.15
2.8Shaftingalignment.15
Circulatingoilandoilsystem15
1.Circulatingoil(lubricatingandcoolingoil)15
2.Circulatingoilsystem(plate70818)16
3.Circulatingoilfailure16
3.1Coolingoilfailure16
3.2Lubricatingoilfailure.16
Maintenanceofthecirculatingoil17
1.Oilsystemcleanliness.17
2.Cleaningthecirculatingoilsystem;17
2.1Cleanbeforefilling-up.17
2.2Flushingprocedure,Mainlub.Oilsystem.17
3.Circulatingoiltreatment18
3.1General18
3.2Thecentrifugingprocess18
3.3Thesystemoilvolumeinrelationtothecentrifugingprocess19
3.4Guidanceflowrates19
4.3signsofdeterioration20
4.4Waterintheoil20
4.5Checkoilcondition21
5.Circulatingoil:
analysesandcharacteristicproperties21
6.Cleaningofdrainoilfrompistonrodstuffingboxes(plate70822)22
Camshaftlubrication23
1.Systemdetails23
1.1Pressureadjustment23
2.Camshaftoil23
2.1Fuelcontamination23
2.2Watercontamination23
2.3Flushingprocedure,camshaftlub.Oilsystem.24
Turbochargerlubrication24
1.Man-NAT/C,systemdetails(Plate70825)24
2.ABB-VTRT/C,systemdetails24
3.Mitsubishi–METT/C,systemdetails24
Plate7080124
Platecrossheadbearing(extendofoil-wedgesincrossheadbearinglowershell)24
Plate70812inspectionofbearingsrecordingofobservations25
Plate70817Crankshaftdeflections(validforcoldengine)26
Chapter708bearings
Bearings
1.Generalbearingrequirementsandcriteria
Bearingsarevitalenginecomponents;therefore,thecorrectbearingdesignandproperchoiceofbearingmetalisnecessaryforreliableengineperformance.
Bearingdesigncriteriadependonthebearingtypeand,ingeneral,on:
a)Bearingslidingsurfacegeometry.
b)Thesurfaceroughnessofthejournalorpin,whichdeterminestheallowablebearingpressureandrequiredoilfilmthickness.
Thisisnecessarytoensureeffectiveandsafefunctioningofthebearing.
c)Thecorrectflowofcoolingoilpreventheataccumulation,whichisobtainedthroughaflowarea,providedeitherthroughtheclearancebetweenthejournalandthebearingboreorthroughaxialgroovesinthebearingslidingsurface.
Seeitem5.3concerninggroovesandwedges.
Thecompactnessofenginesandtheengineratingsinfluencethemagnitudeofthespecificloadonthebearingandmakethecorrectchoiceofbearingmetals,productionqualityand,incertainbearings,theapplicationofoverlayerisabsolutelynecessary.(seeitem2)
!
Scrapingoftheloadedareaofthebearingsurfaceisstrictlyprohibited,asithasoftenshownthatthescrapedsurfacehasanadverseeffectontheslidingpropertiesofthebearing,andhasresultedindamage.
2.Bearingmetals
2.1Tinbasedwhitemetal
Tinbasedwhitemetalisanalloywithminimum88%tin(Sn),therestofthealloycompositionisantimony(Sb),copper(Cu),cadmium(Cd)andsmallamountsofotherelementsthatareaddedtoimprovethefinenessofthegrainstructureandhomogeneityduringthesolidificationprocess.Thisisimportantfortheloadcarryingandslidingpropertiesofthealloy.Lead(Pb)contentinthealloycompositionisanimpurity,asthefatiguestrengthdeteriorateswithincreasingleadcontent,whichshouldnotexceed0.2%ofthecastalloycomposition.
Thebasedwhitemetalisusedinthemainbearings,crankpinbearings,crossheadbearings,guideshoesandthrustbearingsbecauseofitsexcellentloadcarryingandslidingproperties.
2.2Tinaluminum(A40orA/Sn40)
Tinaluminumisacompositionofaluminum(AL)andtin(Sn)wherethetinistrappedina3-dimensionalmeshofaluminum.
A40isacompositionwith40%tin.
Theslidingpropertiesofthiscompositionareverysimilartothoseoftinbasedwhitemetalbuttheloadingcapacityofthismaterialishigherthantinbasedwhitemetalsforthesameworkingtemperature.
Thisisduetotheidealcombinationoftinandaluminum,wheretingivesthegoodembedabilityandslidingproperties,whilethealuminummeshfunctionsasaneffectiveloadabsorber.
ThistypeofmetalisusedforS42MC,S/L35MC,S26MCcrossheadbearings,andforS35MCcrankpinbearings.
3.Overlayers
Asoverlayerisagalvaniccoatingof90%lead(Pb)and10%Tin(Sn),whichisapplieddirectlyontothewhiteorTin-Aluminummetalslidingsurfaceofthebearing.
Thethicknessofthecoatingis0.02-0.03mm.
Theoverlayerisasoftandductilecoating,anditsmainobjectiveistoensuregoodembedabilityandconformitybetweenthebearingslidingsurfaceandthepinsurfacegeometry.
4.Flashlayer,Tin(Sn)
Aflashlayerisa100%tin(Sn)layerwhichisappliedgalvanically.
Thethicknessofthislayerisfrom0.002-0.005mm.
Thecoatingoftinflashisappliedalloverandfunctionsprimarilyasacorrosion(oxidation)protectionofthebearing.
Thetinflashalsofunctionsasaneffectivedrylubricantwhennewbearingsareinstalledandtheengineisbarred.
5.Bearingsdesign
PlainbearingsforMCenginesaremanufacturedassteelshellswithaslidingsurfaceofwhitemetalortinaluminum.
Tinaluminumbearingsarealwaysofthetinshelldesignwhilewhitemetalbearingscaneitherbeofthethickshellorthinshelldesign.
TheoverlayercoatedTin-Aluminum(crosshead)bearinghasnickel-barrierbetweentinaluminumandoverlayer.
!
Iftoolargeanarea,nickelbarrier,isexposedduetothewornofftheoverlayer,andthussubsequentlythejournal(crossheadpin)worksonthenickelbarriers,therecanbeariskofdamagebecausenickelbarrierhaspoorerbearingproperties(higherhardnessandlower,embedability)comparedtotheoriginaloverlayer.Seeitem8.
Thebearingsurfaceisfurnishedwithacentrallyplacedoilsupplygrooveanotherdesignfeaturessuchastangentialrun-outs,oilwedgesand/orborerelieves
5.1Tangentialrun-out(plate70801,70802,70804,B-B)
Atangentialrun-outisatransitiongeometrybetweenthecircumferentialoilsupplygrooveandthebearingsurface.
Thisspecialoilgroovetransitiongeometrypreventsanoilscrapingeffectandreducestheresistancetotheoilscrapingeffectandreducestheresistancetotheflowoftheoiltowardstheloadedareaofthebearing.
5.2Borerelief(plates70801,70802,70804,A-A)
Thebearingslidingsurfaceismachinedatthematingfacesoftheupperandlowershellstocreateborerelieves.
Theirmainobjectiveistocompensateformisalignmentswhichcouldresultinaprotrudingedge(step)ofthelowershell’smatingfacetothatoftheuppershell.
Suchaprotrudingedgecanactasanoilscraperandcauseoilstarvation.
5.3Axialoilgroovesandoilwedges(plates70803,70806,Fig.A-A)
Oilgroovesandwedgeshavethefollowingfunctions:
a)Toenhancetheoildistributionovertheloadcarryingsurfaces.Thetaperedareasgiveimprovedoilinletconditions.
b)Especiallyinthecaseofcrossheadbearings(plate70803)–toassisttheformationofahydrodynamicoilfilmbetweentheloadcarryingsurfaces.
c)Toprovideoilcooling(oilgrooves)
Inordertoperformthesefunctions,theoilmustflowfreelyfromthelubricatinggrooves,pasttheoilwedges,andintothesupportingareas–wheretheoilfilmcarriestheload.
5.4Thickshellbearings(plate70801)
Thistypeofbearingshasasteelbackwiththerequiredstiffness.
a)Toensureagainstdistortionoftheslidingsurfacegeometry,and
b)Tosupportthecast-onwhitemetalinregionswheretheshelllackssupport,forexampleintheareaoftheuppershellmatingsurfaces.
Thetopclearancesinthisbearingdesignareadjustedwithshims,whilethesideclearancesareapredeterminedresultofthesummationofthehousingbore,shellwallthickness,journaltolerances,andtheinfluenceofthestaybolttensioningforcewhichdeformsthebedplatearoundthebearingassembly.
5.5Thinshellbearings(plate70802)
Thinshellbearingshaveawallthicknessbetween2
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