The inner ring and the outer ring of the rolling bearing are fixed on the shaft or the bearing box, and when the bearing bears the load, the relative surfaces of the bearing ring and the shaft or the bearing box are prevented from undergoing relative movement in the radial, axial, and rotational directions. This relative movement will cause wear, friction corrosion, or friction cracks on the mating surface, resulting in damage to the bearings, shafts, and bearing housings, and the wear powder will mix into the bearings, which will cause poor operation, abnormal heat generation, or vibration.
Regarding the method of fixing the bearing, it is best to leave an interference amount on the mating surface of the ferrule and the shaft or the bearing housing and perform a static fit. This cooperation can make the load of the thin-walled ferrule evenly distributed on the circumference, without affecting the load capacity of the bearing.
However, when using a static fit, except for the inconvenience of installing and removing the bearing, the free-side bearing cannot be moved axially when using a separate bearing, so it cannot be used in all occasions.
Choice of fit
The choice of fit is generally made according to the following principles.
According to the direction and nature of the load acting on the bearing and which of the inner and outer rings rotates, the load on each ring can be divided into rotating load, static load or non-directional load. The ring bearing the rotating load and the non-directional load should adopt the static fit (interference fit). The ring bearing the static load can adopt the transition fit or the dynamic fit (clearance fit).
When the bearing is under heavy load or subjected to vibration or shock load, its interference must increase. When hollow shafts, thin-walled bearing housings or light alloy or plastic bearing housings are used, the interference must also be increased.
When it is required to maintain high rotation accuracy, high-precision bearings must be used, and the dimensional accuracy of the shaft and the bearing box must be improved to avoid excessive interference. If the interference is too large, the geometrical accuracy of the shaft or the bearing housing may affect the geometrical shape of the bearing ring, thereby impairing the rotational accuracy of the bearing.
If the non-separable bearings (such as deep groove ball bearings) use static fit on the inner and outer rings, the installation and disassembly of the bearings are extremely inconvenient. It is best to use one of the inner and outer rings with a dynamic fit.