Selecting internal clearance or preload
Bearing internal clearance (fig. 1) is defined as the total distance through which one bearing ring can be moved relative to the other in the radial direction (radial internal clearance) or in the axial direction (axial internal clearance).
Initial internal clearance is the internal clearance in the bearing prior to mounting.
Mounted clearance is the internal clearance in the bearing after mounting but prior to operation.
Operating clearance is the internal clearance in the bearing when it is in operation and has reached a stable temperature.
Bearings must have the appropriate operating clearance to operate satisfactorily (→ Importance of selecting correct clearance/preload).
As a general rule:
- Ball bearings should have an operating clearance that is virtually zero.
- Cylindrical, needle, spherical and CARB toroidal roller bearings typically require at least a small operational clearance.
- Tapered roller and angular contact ball bearings should have a small operational clearance, except in applications where a high degree of stiffness or positional control is required, in which case they can be mounted with a degree of preload.