Selecting internal clearance or preload

The operating clearance or preload in a bearing is determined by:
  • the initial internal clearance prior to mounting
  • the actual fits or the distance a bearing is driven-up on a tapered seat
  • the effects of form errors
  • changes in the clearance or preload that result from mounting
  • the dimensional changes resulting from the operating temperature
Shaft deflection and axial displacement, such as in CARB toroidal roller bearings, might also need to be considered.
The operating clearance or preload in a bearing influences friction, size of the load zone and fatigue life. Diagram 1 shows the relationship between clearance and preload, and the primary parameters. The diagram is based on rolling bearings under radial load.
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