Rolling Element Bearings prepared by Wayne Book

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Rolling Element Bearingsprepared byWayne Book

• ME3180
• Based on Shigley and Mischke
• and Budynas and Nisbett
• Design of Mechanical Elements

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Rolling Element Bearings Outline

• Bearing types and nomenclature
• Loads, life and failure modes
• Ball bearing selection criteria
• Tapered bearings
• Induced thrust load
• Selection
• Application and maintenance

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Ball Bearing Nomenclature(From Shigley)
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Roller Bearing Nomenclature(from Shigley)
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Classification Ball Bearings
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Classification Roller Bearings(Norton)
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Types of Ball Bearings(from Shigley)
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Types of Roller Bearings(from Shigley)
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Bearing Loads
Speed n
Bearings are rated by radial loads F at a rating
life LR Thrust is included by increasing radial
load to Fe C basic load rating at L 106
cycles (unusable)
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Failure of bearings

• Assume dirt, heat etc. are not major factors
• Fatigue spalls contact surface due to cyclical
  contact loading
• Pitting of significant area defines useful life
• L10 life is the life exceeded by all but 10 of
  the bearings

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Life-Load Relationships
Note If F1 C, the basic load, then L1 106
rev/min (typical, Timken uses 90x106) L rev
Lhours x n x 60
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Typical data load vs life reliability
90 reach life L
F/La constant
Design point
Design reliability higher RD Predicted by
Weibull distribution
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Adjustment of C10 for Reliability, etc.

• Design force FD, life L, and reliability RD
• Weibull parameters from vendor
• x0, b, (?-x0)
• Find normalized life xD L/L10
• Calculate adjusted rating

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Combined Radial and Axial Loads

• Nondimensionalize equivalent and axial loads
• Plot nondimensionalized equivalent load vs
  nondimensionalized axial load
• Approximate with two straight lines
• Three parameters depend on ratio of axial
  load/rated load, see table 11-1

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Equivalent Radial Load
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Example Load Factors (from Shigley)
Table 11-1
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AFBMA Size Plan(from Shigley)
Figure 11-7
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Example Dimensions Ratings (from Shigley)
Table 11-2
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Steps in Sizing Ball Bearings

• Given Fr, Fa
• Select a trial bearing size from Table 11-2
• Find C0 and CC10
• Table 11-1
• Interpolate based on Fa/C0 to get e
• Compare Fa/Fr to e, select either X1,Y1 or X2,Y2
• Calculate equivalent radial load Fe
• Compute life
• Select another bearing if not satisfactory and
  repeat

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Example Calculations

• An 02 series bearing with bore of 30 mm carries
  5.6 kN radial and 2.8 kN applied thrust.
  Consider both deep grove and angular contact
  bearings.
• Find the radial and thrust factors
• What is the predicted L10 life?
• For the given Fr ,at what value of Fa does the
  thrust load begin to influence the life of the
  bearing?

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Other Empirical Factors(from Shigley)
Table 11-4
Table 11-5