bearing design and troubleshooting 11-7-12...bad bond – bare metal; no tin/babbitt attached loose...

© John Crane© 2010 John Crane Inc. Company confidential. Do not duplicate.

Bearing Design and Troubleshooting

STLE Houston Section

November 7, 2012

© John Crane

2

© 2010 John Crane Inc. Company confidential. Do not duplicate.

Primary Functions Primary Functions of of Fluid Film Bearings:Fluid Film Bearings:

� Maintain Rotor Position

� Minimize Friction

� Provide Damping

� Sacrificial Component

© John Crane

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Three Requirements for FF DevelopmentThree Requirements for FF Development

� Viscous Fluid

� Relative Motion

� Converging Flow Area

© John Crane

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Viscosity (µ)

A materials resistance to a

change in form – a

measure of internal friction

© John Crane

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� Relative Motion

V1 = U

V2 = 0

U

Vavg = U/2

© John Crane

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� Converging Flow Area

© John Crane

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F rict io n vs. Z N / P

0.00

0.05

0.10

0.15

0.20

0.25

0 1 2 3 4 5 6 7 8 9 10 11 12

ZN/P

B oundary M ixed F ilm Full F ilm

Z = Dynamic Viscosity of Lubricant at Supply Temperature (cp); N = Rotational Speed (rpm); P = Specific Load on the

Bearing (psi)

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Fluid Film DevelopmentFluid Film Development

+ -

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+

-

© John Crane

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�Most Common Cause of Bearing

Failure

�Easiest Problem to Identify

�Often the Hardest to Correct

Problem: MisalignmentProblem: Misalignment

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200 PSI

200 PSI

185 F

Peak Pressure 3 to 4 Times Peak Pressure 3 to 4 Times

Projected LoadProjected Load

Fluid Film DevelopmentFluid Film Development

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200 PSI

200 PSI

220 F

Peak Pressure Peak Pressure

10 to 12 Times 10 to 12 Times

Projected LoadProjected Load

MisalignementMisalignement

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Bearing Maximum Capacity is a Function

of Temperature and Pressure

ASTM BASTM B--23 Gr2 Yield Strength vs. Temperature23 Gr2 Yield Strength vs. Temperature

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MisalignmentMisalignment

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Babbitt Extrusion Due to

Edge Loading

TC on Unloaded End


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Uneven Wear Pattern

Evidence of Misalignment


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© John Crane

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••Correct Unit AlignmentCorrect Unit Alignment

200 PSI

200 PSI

185 F

Install Bearing Designed to Compensate for MisalignmentInstall Bearing Designed to Compensate for Misalignment


© John Crane

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What is the Difference?

Fatigue Fatigue –– Bond Intact; Tin/Babbitt Still AttachedBond Intact; Tin/Babbitt Still Attached

Bad Bond Bad Bond –– Bare Metal; No Tin/Babbitt AttachedBare Metal; No Tin/Babbitt Attached

Loose Babbitt: Fatigue vs. Bad BondLoose Babbitt: Fatigue vs. Bad Bond

bearing design and troubleshooting 11-7-12...bad bond – bare metal; no tin/babbitt attached loose...

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