Structural Analysis Related to Rolling Bearings

Based on analyses from various perspectives, the China Bearing Network has learned that... Rolling bearing Accordingly, the components are fixed to the shaft and bearing housing in the radial, axial, and circumferential directions. Radial and circumferential positioning is typically achieved through friction—that is, the bearing housing raceway employs a tight fit. Axial positioning, on the other hand, is often accomplished via direct contact, for example, using nuts, bearing housing end caps, shaft-end stop collars, sleeves, and retaining rings.

Fit of the bearing installation location

The basis for specifying fits is that the tolerances for shafts and bearing housings comply with ISO standards, while the tolerances for bearing inner diameters and bearing outer diameters both follow DIN 620. ISO tolerances are expressed using tolerance zones. Each tolerance zone has two characteristics: its relative position with respect to the zero line and its width. The position of the tolerance zone is indicated by letters.

When selecting fit tolerances for bearings, pay attention to the following four aspects:

1. To fully utilize the bearing’s capacity and load-carrying capability, it is essential to ensure that both the inner and outer rings of the bearing are well supported in the circumferential direction.

2. There shall be no relative movement between the bearing housing and its mating parts; otherwise, the mating surfaces may be damaged.

3. One of the inner and outer rings of a floating bearing must be able to accommodate changes in the lengths of both the shaft and the housing—that is, it must be capable of axial movement. Only N-type and NU-type cylindrical roller bearings can move internally.

4. The installation and removal of bearings should be as easy as possible.

To meet the first two requirements, the inner and outer rings of radial bearings should, in principle, be fitted with a tight fit. However, if a floating bearing must be capable of axial movement or if a non-separable bearing needs to be installable and removable, then neither ring can be fitted with a tight fit—indeed, at least one of the rings cannot be so fitted. In such cases, whether the bearing rings are subjected to localized loads or cyclic loads becomes a decisive factor. If the load remains relatively fixed in direction with respect to the rings, a clearance fit may be used; but if one of the rings rotates relative to the direction of the load, a tight fit should, in principle, be employed.

N and NU cylindrical roller bearings can achieve a tight fit on both raceways simultaneously, as the bearing design allows for length compensation within the bearing itself. Moreover, the inner and outer rings of these bearings can be mounted independently. When bearings are subjected to heavy loads—especially impact loads—they require a larger interference fit and stricter geometric tolerances. Both the use of a tight fit and temperature differences between the inner and outer rings can reduce the radial clearance. This factor should be taken into account when selecting the appropriate radial clearance group.