© John Crane© 2010 John Crane Inc. Company confidential. Do not duplicate.
Bearing Design and Troubleshooting
STLE Houston Section
November 7, 2012
© John Crane
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© 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
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Three Requirements for FF DevelopmentThree Requirements for FF Development
� Viscous Fluid
� Relative Motion
� Converging Flow Area
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Three Requirements for FF DevelopmentThree Requirements for FF Development
Viscosity (µ)
A materials resistance to a
change in form – a
measure of internal friction
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Three Requirements for FF DevelopmentThree Requirements for FF Development
� Relative Motion
V1 = U
V2 = 0
U
Vavg = U/2
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Three Requirements for FF DevelopmentThree Requirements for FF Development
� Converging Flow Area
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
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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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Fluid Film DevelopmentFluid Film Development
+ -
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Three Requirements for FF DevelopmentThree Requirements for FF Development
+
-
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
�Most Common Cause of Bearing
Failure
�Easiest Problem to Identify
�Often the Hardest to Correct
Problem: MisalignmentProblem: Misalignment
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
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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© 2010 John Crane Inc. Company confidential. Do not duplicate.
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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© 2010 John Crane Inc. Company confidential. Do not duplicate.
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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© 2010 John Crane Inc. Company confidential. Do not duplicate.
MisalignmentMisalignment
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Babbitt Extrusion Due to
Edge Loading
TC on Unloaded End
MisalignmentMisalignment
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Uneven Wear Pattern
Evidence of Misalignment
MisalignmentMisalignment
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
MisalignmentMisalignment
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
••Correct Unit AlignmentCorrect Unit Alignment
200 PSI
200 PSI
185 F
Install Bearing Designed to Compensate for MisalignmentInstall Bearing Designed to Compensate for Misalignment
MisalignmentMisalignment
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Loose Babbitt: Fatigue vs. Bad BondLoose Babbitt: Fatigue vs. Bad Bond
What is the Difference?
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Base MetalBond Line/Tin
Babbitt
Babbitt FatigueBabbitt Fatigue
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Babbitt FatigueBabbitt Fatigue
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Base MetalBond Line/Tin
Babbitt
Bad BondBad Bond
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
Bad BondBad Bond
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
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© 2010 John Crane Inc. Company confidential. Do not duplicate.
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
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