Rolling Element Bearings Tapered Roller Bearings prepared by Wayne Book

1
Rolling Element BearingsTapered Roller
Bearingsprepared byWayne Book

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

2
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

3
Roller Bearing Nomenclature(from Shigley)
Applied radial force
Induced thrust is also transmitted to cone and
hence to shaft
Induced thrust
4
Calculating Tapered Bearing Loads
Frex
Tex
5
Effective Radial Loads

• For sizing bearing the effective radial load will
  be used.
• If the effective radial load is less than the
  actual radial load, use the actual load
• Bearing A induces thrust on B and vice versa

6
Example Table for Bearing Selection
7
Steps in Tapered Roller Bearing Selection

• Given required bearing life L10 and load
  arrangment
• Determine applied radial Fex and thrust Tex loads
• Distribute radial loads to bearings FrA and FrB
  using estimated a value to locate load center
• Estimate Bearing K factors for induced thrust
• Calculate equivalent radial loads FeA and FeB
  using estimated K factor
• Calculate rated load using actual load and
  desired life
• Select bearing from those available (in table)
• Check bearing loads using actual K factor and a
  values

8
Example Selection Problem

• Gear transmission as shown with small gear being
  helical which generates thrust of 0.3 x
  tangential force
• Obtain radial loads assuming static equilibrium
• Use estimates of a0 and K1.5 to begin problem
• Seek life of 50,000 hours at 1000 rpm
• Nominal shaft diameter 1 in.
• Force angles on gear at 25 degrees
• Use identical tapered roller bearings

9
Example Solution
10
Common mounting alternatives
Direct mounting
Indirect mounting
Beware of unexpected preloading due to
temperature or inaccuracies!
11
Mounting Bearings with Thrust Loading

• Ideally the constraints are not redundant
• Consider the case where thrust can reverse
• Arrows show load transfer for either direction
• Thrust in either direction carried by left bearing

Force provided by retainer
Right bearing floats in housing
12
Alternative Mounting with Thrust

• Thrust load carried by one or the other bearing
• Dimensional inaccuracies or temperature
  variations causes unplanned preload

13
Preload Arranged at One End of Shaft

• Controlled amounts of preload is useful to
  eliminate clearance if improved accuracy is
  needed.

Preload adjustment
Preload adjustment
14
Misalignment Can Be Devastating

• Roller bearings limited to 0.001 rad
• Deep-groove ball bearings lt 0.0047 rad
• Other spherical ball bearings lt 0.0087 rad
• Estimates of life reduction in Fig. 11-18 for
  roller bearings (line contact bearings).