Matching of Shaft, Casing and Bearing

1. Requirements to shaft and casing

Under the circumstance that shaft and casing precision is not good, bearings are affected and can not exert required capacity. For instance, if the assembled part, namely the shoulder, is not provided with good precision, relative inclination of the inner race and the outer race will be generated. Besides bearing load, stress concentration is added, so fatigue life of bearings declines, and it may cause disrepair and sinter of keeper.

2. Matching of shaft, casing and bearing

Tolerance and fit of bearing and shaft for electric machine usually adopts k5 or k6. Tolerance and fit of bearing and casing usually adopts k7. For shaft and casing matched by 6309 bearing, their precision is as follow:

Shaft roundness tolerance: 4¡«7μm, cylindricity tolerance: 4¡«7μm, shoulder run-out tolerance: 4μm

Shaft roundness tolerance: 7¡«11μm, cylindricity tolerance: 7¡«11μm, shoulder run-out tolerance: 4¡«7μm

Chamfer angles of shaft and casing should not interfere with chamfer angle of bearing, and their chamfer angle radius should not exceed the minimum value of bearing chamfer angle dimension.