Design considerations

Proper adjustment

Single row angular contact ball bearings must be used:

  • with a second bearing (fig. 1
  • in sets (fig. 2)
    The bearings must be adjusted against each other until the requisite clearance or preload is obtained (→ Selecting preload).

Universally matchable bearings mounted immediately adjacent to each other:

  • require no further adjustment (→ Bearings for universal matching)
  • obtain requisite clearance or preload by:

    • choosing bearings from an appropriate clearance or preload class
    • applying suitable fits for the bearings on the shaft and in the housing

Performance and operational reliability depend on:

  • proper adjustment for single bearings
  • the correct selection of clearance and preload for universally matchable bearings
    If there is too much clearance in the bearing arrangement during operation, the load carrying capacity of the bearings will not be fully utilized. Excessive preload produces more friction and higher operating temperatures, leading to a reduction in bearing service life.
Axial loads in one direction

When the axial load acts predominantly in one direction in back-to-back and face-to-face arrangements, unfavourable rolling conditions for the balls of the axially unloaded bearing may occur, which can lead to:

  • increased noise levels
  • discontinuity in the lubricant film
  • increased stresses on the cage

Under these circumstances, SKF recommends zero operating clearance, which can be attained by using springs. When springs are not sufficient, using bearings with a 25° contact angle as a backup bearing may help.

Load ratio
  • of Fa/Fr ≥ 1 is required by bearings in the 70 B, 72 B(E) and 73 B(E) series
  • of Fa/Fr ≥ 0,55 is required by bearings in the 72 AC and 73 AC series
If the load ratio requirement is not met in each case, bearing service life can be reduced.
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