Fitting of Bearings

A bearing can only perform to its full capacity when it is correctly fitted on the shaft and in the housing. Insufficient interference on fitting surfaces could cause bearing rings to creep in a circumferential direction. Once this happens, considerable wear occurs on the fitting surface and both shaft and housing are damaged. Furthermore, abrasive particles may enter the bearing causing vibration, excessive heat and damage to raceways. It is therefore necessary to provide bearing rings under rotating load with an adequate interference fit to prevent creep. When using thin-type bearings under low load, the bearings should be fastened by a nut. Statically loaded bearings generally do not need to be fitted with an interference fit. Only when subject to a high degree of vibration do both inner and outer rings require fitting with an interference fit.

1. FITTING PRESSURE AND DIMENSIONAL CHANGES OF INNER AND OUTER RING
   The right fit for each application is established taking various condetions into consideration such as load, speed, temperature, mounting dismounting of the bearing. The interference fit should be greater than normal in thin housings, housings of soft material or on hollow shafts.
2. LOAD OF INTERFERENCE
   The interference fit of shaft and inner ring decreases under radial load. The decrease in fit of shaft and inner ring is calculated by the following formula:
   
3. INFLUENCE OF TEMPERATURE ON BEARINGS, SHAFTS AND HOUSINGS
   Each inner ring, outer ring or rolling element of a bearing rotating under load generates heat which will affect the interference fits of the shaft and the housing. Assuming a temperature difference within the bearing and the housing of T(), that of the mating surface of the shaft and of the bearing is (0.100~.15) T.
   Consequently, dr, the decrease of the inner ring interference fit due to temperature change, is calculated from the following formula:
   
   It should also be noted that fit can increase due to temperature changes.
4. EFFECTIVE INTERFERENCE, SURFACE ROUGHNESS AND ACCURACY
   The surface is smoothed during fitting and the effective interference becomes smaller than the theoretical interference. The surface quality of a mating surface has an influence on how much this theoretical interference decreases. Effective interference can usually be calculated as follows:
   
   By combining these factors, the theoretical interference fit required for inner ring and shaft where the inner ring is subjected to rotating load is calculated as follows:
   
   Normally, shaft and housing seats have to meet the accuracy and roughness requirements as given below.

Mountings bearing with extra tight or light interference fits can lead to early bearing failure. In order to ensure safe operating conditions the tolerance variations of shaft seats, housing bores and bearing bore and outside diameter need to be reduced.

We recommend the tolerance zones are divided into two bands and selective assembly is applied. Bearings sorted into two tolerance bands for inner and outer rings are available on request. These bearings are marked as follows:

Note:

1. THIS IS APPLIED TO BOTH BEARINGS OF ABEC 5P AND P5.
2. UPON YOUR REQUEST, PLEASE SPECIFY THE MARK LISTED BELOW.
   ZC1…. 2 SELECTIVE CLASSIFICATIONS FOR BORE DIAMETER TOLERANCE (0-d/2,-d/2-d)
   1 SELECTIVE CLASSIFICATIONS FOR OUTER DIAMETER TOLERANCE (0-D)
   ZC2… 1 SELECTIVE CASSIFICATION FOR BORE DIAMETER TOLERANCE (0-d)
   2 SELECTIVE CASSIFICATION FOR OUTER DIAMETER TOLERANCE (0-D/2,-D/2-D)
   ZC3… 4 SELECTIVE CASSIFICATION FOR BOTH BORE DIAMETER TOLERANCE (0-d/2,-d/2-d,0-D/2,-D/2-D)
   D… MINIMUM VALUE OF OUTER DIAMETER TOLERANCE
   d… MINIMUM VALUE OF BORE DIAMETER TOLERANCE