fluid film thrust bearings: fundamentals, damage ...vibration.org/presentation/may 2006/thrust...

February 2005

1

(c) 2006, Pioneer Motor Bearing Company

Fluid Film Thrust Bearings:Fluid Film Thrust Bearings:Fundamentals, Damage Fundamentals, Damage

Evaluation, & RepairEvaluation, & Repair

Pioneer Motor BearingPioneer Motor BearingMay 2006May 2006

VIBRATION INSTITUTE MEETINGVIBRATION INSTITUTE MEETINGCHARLOTTE, NCCHARLOTTE, NC

(c) 2006, Pioneer Motor Bearing Company Slide Slide 22

OutlineOutlinennBasic Design CriteriaBasic Design CriteriannThrust Bearing MonitoringThrust Bearing MonitoringnnDamage investigationDamage investigationnnDamage mechanismsDamage mechanismsnn InspectionInspectionnnRepairRepair


HistoryHistorynnWithout question Without question

the most the most significant significant mechanical mechanical invention in the invention in the world was:world was:

The The WheelWheel


HistoryHistorynn However, almost However, almost

immediately upon immediately upon discovery of the discovery of the wheel, the need wheel, the need for bearings was for bearings was also discovered:also discovered:


HistoryHistorynnWhich has Which has

led to one led to one of the most of the most elusive elusive searches in searches in human human historyhistory


HistoryHistorynn As one can As one can

observe from this observe from this wooden wheel wooden wheel dating to 2700 dating to 2700 BC, axels where BC, axels where used to allow used to allow support by radial support by radial and thrust and thrust bearings:bearings:

February 2005

2


Load Orientations: Load Orientations: radial/thrustradial/thrust

Slide Slide 88

Thrust BearingThrust BearingnnSupport axial load from the processSupport axial load from the processnne.g. Water or steam pressuree.g. Water or steam pressure

nnThrust runner surfaceThrust runner surfacennGenerally flat Generally flat (<13 (<13 µµm = 0.0005m = 0.0005””))nn 16 16 µµin RMSin RMS

nnThrust bearingThrust bearingnnGenerally circumferential segmentsGenerally circumferential segments

nnTend to be Tend to be ““squaresquare”” -- length=widthlength=widthnnTradeTrade--offoff

nnLarger loaded area gives more friction lossLarger loaded area gives more friction loss


Thrust ClearanceThrust ClearancennTypical operating clearanceTypical operating clearance

Human hair aboutHuman hair about75 75 µµm (0.003m (0.003””) diameter) diameter

Typical operating clearance Typical operating clearance about 25 about 25 µµm (0.001m (0.001””).).

RUNNERRUNNER

BEARINGBEARING

Ref: ROTECHRef: ROTECH


Thrust LoadThrust Loadnn Load capacity based onLoad capacity based on

nnHydrodynamic pressure profileHydrodynamic pressure profilenn Pad areaPad area

nn NominallyNominallynn Reduced by grooving Reduced by grooving

( )22**25.0 IDODArea −= π


Thrust Bearing DesignsThrust Bearing DesignsnnFlat WasherFlat WashernnFlat Flat BabbittedBabbitted Face With GroovesFace With GroovesnnTaperTaper--Land Land BabbittedBabbitted FaceFacennTilting Pad Thrust BearingTilting Pad Thrust BearingnnEqualized Tilting Pad Thrust Equalized Tilting Pad Thrust

BearingBearing


Flat WashersFlat Washersnn Simple but useful Simple but useful

only with minimal only with minimal speed and load speed and load conditionsconditions

nn Grease lubricated Grease lubricated

February 2005

3


““BumperBumper”” ThrustThrust

BabbittedBabbitted axial surfaces to resist motion of shaft collars.axial surfaces to resist motion of shaft collars.BabbittedBabbitted surface may have radial pockets or grooving.surface may have radial pockets or grooving.


Flat Flat BabbittedBabbitted Thrust Face Thrust Face with Grooveswith Grooves

nn Useful as a bumper, Useful as a bumper, or locating bearingor locating bearing

nn Oil or grease Oil or grease lubricatedlubricated

nn No theoretical load No theoretical load capacitycapacity

nn Practical capacity Practical capacity around 50 to 75 PSIaround 50 to 75 PSI


““BumperBumper”” ThrustThrustRadial Radial grooves grooves enhance load enhance load capacity.capacity.


TaperTaper--Land Thrust BearingLand Thrust Bearing

nn Optimized for only Optimized for only one speed and load one speed and load combinationcombination

nn Taper for oil wedge Taper for oil wedge formation is formation is machined into the machined into the bearing surfacebearing surface

nn Alignment is critical Alignment is critical to operationto operation

nn Practical load limit Practical load limit 150 to 225 PSI150 to 225 PSI


Simple TaperedSimple Tapered--Land ThrustLand Thrust


Compound TaperedCompound Tapered--Land ThrustLand ThrustTaper is steeper Taper is steeper at the inner at the inner diameter than diameter than at the outer at the outer diameter. diameter. Taper is Taper is generally generally 0.0030.003””--0.0070.007””. . Land region is Land region is visible.visible.

February 2005

4


FluidFluid--film Thrust Bearingfilm Thrust BearingnnAnnulus controls axial position.Annulus controls axial position.nnMaximum load capacityMaximum load capacity

TiltingTilting--padpadbearingbearing


Tilting Pad Thrust BearingTilting Pad Thrust Bearingnn Self Optimizing based Self Optimizing based

on applied load and on applied load and speedspeed

nn Maximum Flexibility Maximum Flexibility re: potential re: potential modificationsmodifications

nn Alignment is criticalAlignment is criticalnn Load Capacity in Load Capacity in

excess of 600 PSIexcess of 600 PSI


Tilting Pad Thrust BearingsTilting Pad Thrust Bearings

Equalizing linkages correct for housing skew.Equalizing linkages correct for housing skew.Equalizing linkages do not correct for rotating collar skew.Equalizing linkages do not correct for rotating collar skew.

Ref: Kingsbury literatureRef: Kingsbury literature


NonNon--Equalizing SupportEqualizing Support

Ref: Constantinescu, p. 354.Ref: Constantinescu, p. 354.


NonNon--Equalized BearingEqualized Bearing


Self Equalizing Tilting Pad Self Equalizing Tilting Pad Thrust BearingsThrust Bearingsnn Maximum capacity in Maximum capacity in

given spacegiven spacenn Self optimizing oil Self optimizing oil

filmfilmnn Can accommodate Can accommodate

collar to housing collar to housing misalignmentmisalignment

nn Not designed for Not designed for dynamic dynamic misalignmentmisalignment

nn Load Capacity in Load Capacity in excess of 600 PSIexcess of 600 PSI

February 2005

5


Equalizing LinkagesEqualizing Linkages

Ref: Constantinescu, p. 354.Ref: Constantinescu, p. 354.

Intent is to Intent is to equally load equally load each of the each of the thrust pads in thrust pads in spite of spite of variations in variations in pad thickness or pad thickness or misalignment of misalignment of the housing to the housing to the runner.the runner.


AntiAnti--Rotation PinsRotation PinsProvides:Provides:

Locates shell in housingLocates shell in housing••CircumferentialCircumferential

Prevent rotation of the cage Prevent rotation of the cage in the housing.in the housing.


Combined Journal ThrustCombined Journal Thrust

Lobed journal Lobed journal bearingbearing

Tapered thrust Tapered thrust bearingbearing


Oil Distribution GeometryOil Distribution Geometry

OIL INLET OIL INLET HOLEHOLE

Radial grooveRadial groove

Axial grooveAxial grooveBleederBleeder

BleedersBleeders

Spreader

Groove

Spreader

Groove


Thrust Bearing FlowsThrust Bearing Flows

Ref. Kingsbury Ref. Kingsbury sales literature, sales literature, EQHEQH--1.1.

Rotation

Rotation


Tilting Pad Thrust BearingsTilting Pad Thrust Bearings

Ref: Kingsbury literatureRef: Kingsbury literature

February 2005

6


So, how much load can So, how much load can mymybearing take?bearing take?nn This depends This depends

on where you on where you are operating are operating within the within the regime of the regime of the bearing bearing performance performance parametersparameters

nn No, I am not a No, I am not a lawyerlawyer


What can be done to What can be done to increase load capacity?increase load capacity?nnFirst, understand the shortcomings First, understand the shortcomings

of the existing bearingof the existing bearingnnSecond, consider modifications to Second, consider modifications to

the operating parametersthe operating parametersnnThird, consider an upgrade to the Third, consider an upgrade to the

basic bearing designbasic bearing design


Deal with low speed wearDeal with low speed wearnn Hydrostatic lift system to provide Hydrostatic lift system to provide

hydrostatic oil films where hydrodynamic hydrostatic oil films where hydrodynamic oil films may not otherwise be presentoil films may not otherwise be presentnn Start up operationStart up operationnn Turning gear operationTurning gear operationnn Some emergency conditionsSome emergency conditionsnn Per DIN 31652 part 3 consider hydrostatic lift Per DIN 31652 part 3 consider hydrostatic lift

where startup loads exceed 2.5where startup loads exceed 2.5--3.0 3.0 MPaMPa(363(363--435 435 psipsi))nn May be required for lower loadsMay be required for lower loads


Hydrostatic Lift SystemsHydrostatic Lift Systemsnn Inject high pressure oil (typically > Inject high pressure oil (typically >

1000 1000 psipsi) at the location of the ) at the location of the highest loadinghighest loading

nnHydrostatic film is developed Hydrostatic film is developed through pressure, film thickness is through pressure, film thickness is controlled by flowcontrolled by flow

nnQuite often, many bearings are fed Quite often, many bearings are fed by a common high pressure headerby a common high pressure header


Hydrostatic Lift SystemHydrostatic Lift Systemnn Introduce externallyIntroduce externally--pressurized oil pressurized oil

into bearing cavity for operation at into bearing cavity for operation at low surface speeds and high loadslow surface speeds and high loadsnn Forms hydrostatic bearing on lower halfForms hydrostatic bearing on lower half


Hydrostatic Lift SystemHydrostatic Lift System

Hydrostatic lift in tilting pad thrust shoes.Hydrostatic lift in tilting pad thrust shoes.

February 2005

7


Main oil pump is shaft drivenMain oil pump is shaft driven

AC & DC pumpsAC & DC pumps

Sample Hydrostatic Lift Oil SystemSample Hydrostatic Lift Oil System

Schematic of Schematic of TurbineTurbine--Generator Generator Hydrostatic Hydrostatic Lift SystemLift System

Each radial bearing #3Each radial bearing #3--8 has a 8 has a separate pressurized hydrostaticseparate pressurized hydrostatic--lift supply (1500 psig), separate lift supply (1500 psig), separate supply pump with a gravity (or supply pump with a gravity (or slight vacuum) drain back to the slight vacuum) drain back to the reservoir.reservoir.


OK smart guy, IOK smart guy, I’’ve already got ve already got a tilting pad thrust bearing, a tilting pad thrust bearing, Now what?Now what?nnConsider upgrading specific design Consider upgrading specific design

features of the assemblyfeatures of the assemblynnDirected lubricationDirected lubricationnnAlternative materialsAlternative materialsnnOffset pivotsOffset pivots


Effect of Pivot OffsetEffect of Pivot Offset


Effect of ChromeEffect of Chrome--Copper Alloy Copper Alloy Backing MaterialBacking Material


Thrust Bearing MonitoringThrust Bearing MonitoringnnTemperatureTemperaturennLoadLoadnnThrust Collar PositionThrust Collar Position


Thrust Temperature Thrust Temperature MonitoringMonitoring

nnEmbedded SensorsEmbedded SensorsnnThermocouplesThermocouplesnnRTDRTD’’ss

nnOil Inlet and Exit TemperatureOil Inlet and Exit Temperature

February 2005

8


TiltTilt--Pad Thrust ProfilesPad Thrust Profiles

Ref. Kingsbury Ref. Kingsbury sales literature, sales literature, EQHEQH--1.1.

Temperature profiles Temperature profiles show influence of show influence of pressure peak over the pressure peak over the pivot (dashed circle), as pivot (dashed circle), as well as radial and well as radial and circumferential flow.circumferential flow.


Embedded SensorsEmbedded Sensorsnn Proper LocationProper Location


Thrust Load MeasurementThrust Load Measurementnn Basic Bearing Basic Bearing

DesignDesign


Thrust Load MeasurementThrust Load Measurementnn Leveling PlatesLeveling Plates


Thrust Load MeasurementThrust Load Measurementnn Strain Strain

Gage Gage Load CellLoad Cell


Thrust Position MeasurementThrust Position MeasurementnnEddy Current ProbesEddy Current ProbesnnDual VotingDual Voting

February 2005

9


Thrust Position MeasurementThrust Position Measurement


Damage InvestigationDamage Investigation

nnGeneric ElementsGeneric ElementsnnVisual examinationVisual examinationnnBackground informationBackground informationnnPhotographic recordsPhotographic recordsnnEvent reconstructionEvent reconstructionnnLaboratory analysisLaboratory analysis


Damage InvestigationDamage Investigationnn Visual Visual

ExaminationExamination

““Say, is all that Say, is all that babbitt supposed babbitt supposed to be on the to be on the bottom of the bottom of the bearing housing bearing housing like that?like that?””


Damage InvestigationDamage Investigation

nnGeneric ElementsGeneric ElementsnnVisual examinationVisual examinationnnBackground informationBackground informationnnPhotographic recordsPhotographic recordsnnEvent reconstructionEvent reconstructionnnLaboratory analysisLaboratory analysis


Visual ExaminationVisual Examination


Where is the damage?Where is the damage?nnBabbitt SurfaceBabbitt SurfacennCentered over pivotCentered over pivotnnMore toward trailing edgeMore toward trailing edgennMore toward leading edgeMore toward leading edge

nnSupporting structureSupporting structurennLeveling platesLeveling plates

nnThrust collarThrust collar

February 2005

10


Babbitt Surface DamageBabbitt Surface Damage

Damage located primarily along the trailing edge is indicative oDamage located primarily along the trailing edge is indicative of debris,f debris,electrolysis, or other trauma that occurred while the bearing waelectrolysis, or other trauma that occurred while the bearing was s otherwise operating in a normal condition otherwise operating in a normal condition



Damage located primarily opposite the pivot is indicative the beDamage located primarily opposite the pivot is indicative the bearing aring operating in an overloaded condition operating in an overloaded condition



Damage located primarily along the leading edge is indicative ofDamage located primarily along the leading edge is indicative of a lack a lack of lubrication, either during start up, or during operation of lubrication, either during start up, or during operation


Support Structure DamageSupport Structure DamagennDamage to the leveling plates, base Damage to the leveling plates, base

ring, or other support structure is ring, or other support structure is usually indicative of thrust collar usually indicative of thrust collar runoutrunout problemsproblems

nnCollar may be installed improperly, Collar may be installed improperly, or may have come loose in serviceor may have come loose in service


Collar DamageCollar DamagennCircumferential scoring or Circumferential scoring or

scratching of the thrust collar is scratching of the thrust collar is usually indicative of debris in the oil usually indicative of debris in the oil systemsystem


Damage MechanismsDamage MechanismsnnMechanisms are the same as those Mechanisms are the same as those

covered earlier by Dr. Branagancovered earlier by Dr. BranagannnSpecific thrust bearing photographs Specific thrust bearing photographs

may help may help

February 2005

11


Minor OverloadMinor Overload


Babbitt FatigueBabbitt Fatigue


OverheatingOverheating


Gross OverheatingGross Overheating


AnisotropyAnisotropy


Tin / Copper MigrationTin / Copper Migration

February 2005

12


Pivot FrettingPivot Fretting


Leveling Plate FrettingLeveling Plate Fretting


Babbitt ErosionBabbitt Erosion


Bearing InspectionBearing InspectionnnBearing SurfaceBearing SurfacennBearing SubsurfaceBearing SubsurfacennThrust CollarThrust CollarnnAssembled End PlayAssembled End Play


Thrust Bearing SurfaceThrust Bearing SurfacennPortion of bearing designed to carry Portion of bearing designed to carry

the load must be clean and flatthe load must be clean and flatnn Inspect for embedded debris with a Inspect for embedded debris with a

single edged razor bladesingle edged razor bladenn Inspect surface with straight edgeInspect surface with straight edgenn Inspect contact with Prussian Inspect contact with Prussian

bluing with a calibrated plate and bluing with a calibrated plate and finally with the mating thrust collarfinally with the mating thrust collar


Thrust Bearing SubsurfaceThrust Bearing SubsurfacennUltrasonic InspectionUltrasonic InspectionnnDye Pen InspectionDye Pen InspectionnnBrass Dowel Ring TestBrass Dowel Ring Test

February 2005

13


Thrust Collar InspectionThrust Collar InspectionnnSurface finish 16 RMS or betterSurface finish 16 RMS or betternnSurface flatness less than .001 inchSurface flatness less than .001 inchnnAssembled Assembled runoutrunout less than .001 less than .001

TIRTIR


Assembled Assembled RunoutRunout CheckChecknnCan not be measured with a single Can not be measured with a single

indicator as rotor float will impact indicator as rotor float will impact measurementmeasurement

nnTemporary blocking may be Temporary blocking may be required to limit rotor float during required to limit rotor float during inspectioninspection

nnRequires 2 Requires 2 MagMag base indicators with base indicators with sufficient travel to stay in contact sufficient travel to stay in contact with collar facewith collar face


Indicator positionIndicator position


Typical Measurement recordTypical Measurement record

0.00100.00200.0030360

0.0000-0.0010-0.0010315

-0.0010-0.0010-0.0020270

-0.00200.00250.0005225

-0.00100.00200.0010180

0.00000.00300.0030135

0.00100.00500.006090

0.0020-0.00050.001545

0.0010-0.00100.00000

A-BBARotation

Column of calculated AColumn of calculated A--B values gives twice the B values gives twice the TIR TIR runoutrunout readings for the thrust collar. In readings for the thrust collar. In this example, the collar is running out .002 TIR this example, the collar is running out .002 TIR


Assembled End PlayAssembled End PlaynnBest to first measure available Best to first measure available

space and stacked height of the space and stacked height of the bearing assembliesbearing assemblies

nnDifference should be the assembled Difference should be the assembled end playend play

nnAfter assembly, bump test the rotor After assembly, bump test the rotor to confirm measurementto confirm measurement


RepairsRepairsnnMany minor thrust bearing repairs Many minor thrust bearing repairs

can be accomplished on sitecan be accomplished on sitennThe level of repair that should be The level of repair that should be

attempted is directly proportional to attempted is directly proportional to the experience level of the the experience level of the technicians availabletechnicians available

February 2005

14


Babbitt Surface RepairsBabbitt Surface Repairsnn Minor imperfections Minor imperfections

can be removed by can be removed by lapping or scrapinglapping or scraping

nn Larger scratches can Larger scratches can be repaired by first be repaired by first locally locally puddlingpuddlingbabbitt and followed babbitt and followed by by peeningpeening and then and then lapping or scrapinglapping or scraping


Babbitt Babbitt PuddlingPuddling


Hand ScrapingHand Scraping


Power ScrapingPower Scraping


Thrust Collar RepairThrust Collar RepairnnMinor damage and glazing can be Minor damage and glazing can be

repaired by hand stoningrepaired by hand stoningnnUse a fine 600 grit oil stoneUse a fine 600 grit oil stonennMore serious repairs can be More serious repairs can be

corrected by turning, lapping, or corrected by turning, lapping, or grindinggrinding

nnMany of these operations can be Many of these operations can be conducted in placeconducted in place


ConclusionsConclusionsnnRemember that that the babbitt Remember that that the babbitt

surface is a SOFT, sacrificial layer.surface is a SOFT, sacrificial layer.nnLook at your babbitt surface to Look at your babbitt surface to

better understand the likely cause better understand the likely cause of the bearing damage and reduce of the bearing damage and reduce rere--occurrence.occurrence.

nnRemanufacture (repair) or redesign Remanufacture (repair) or redesign bearing depending on the nature, bearing depending on the nature, severity, and probability of future severity, and probability of future damage.damage.

fluid film thrust bearings: fundamentals, damage ...vibration.org/presentation/may 2006/thrust...

Documents