Design of bearing arrangements
When universally matchable bearings are mounted immediately adjacent to each other, there is no need for adjustment (→ Bearings for universal matching). The requisite clearance or preload is obtained by choosing bearings from an appropriate clearance or preload class and by applying suitable fits for the bearings on the shaft and in the housing.
The performance and operational reliability of single bearings depend on proper adjustment while universally matchable bearings depend on the correct selection of clearance or preload. If there is too much clearance in the bearing arrangement during operation, the load carrying capacity of the bearings is not fully utilized. Excessive preload produces more friction and higher operating temperatures, leading to a reduction in bearing service life.
Axial loads in one direction
Back-to-back and face-to-face arrangements require special attention when the axial load acts predominantly in one direction. This creates unfavourable rolling conditions for the balls of the axially unloaded bearing and can lead to increased noise levels, discontinuity in the lubricant film and increased stresses on the cage. When the axial load acts predominantly in one direction, SKF recommends zero operating clearance, which can be attained by using springs.
Because of the 40° contact angle, favourable rolling conditions for bearings in the 70 B, 72 B(E) and 73 B(E) series require a load ratio of Fa/Fr ≥ 1. A load ratio of Fa/Fr < 1 can reduce bearing service life.