A bearing's inner ring or outer ring is movable even if the other ring is fastened. The amount of movement the ring can make is called clearance.
The amount of radial movement the ring can make is called radial internal clearance, while that of axial movement the ring can make is called axial internal clearance.
| Radial internal clearance | Axial internal clearance |
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[Ref.] Relationship between radial internal clearance and axial internal clearance
2) Measured clearance
Bearing internal clearance is measured under a specific amount of loading, exerted to obtain reliable measurements. The measured clearance may be slightly greater than real clearance due to elastic deformation caused by the load. In case of roller bearings, however, the deformation is so small as to be ignorable.
3) Initial clearance
The internal clearance of the bearing is provided with at the time of shipment is called initial clearance. It is specified in the Table of Clearance Specifications.
4) Residual clearance
When the bearing is mounted on the shaft or housing by interference fit, the bearing ring expands or contracts, making the internal clearance smaller. This smaller clearance is called "residual clearance" or "residual clearance after mounting".
5) Effective clearance, operating clearance
Bearing temperature rises during operation, causing thermal expansion and making the clearance smaller. The reduced clearance is called effective internal clearance.
The clearance obtained by taking into account elastic deformation due to loads is called "operating clearance" or "residual clearance during operation."
6) Selection of initial clearance
The value of the internal clearance may have a great impact on the bearing during operation, with regard to such aspects as bearing fatigue life, heating and noise.
As Fig. 7-1 shows, bearing service life is longest when the operating clearance is slightly negative. However, when the operating clearance is negative beyond a specific extent, bearing service life is extremely short. The initial clearance should therefore be determined such that the operating clearance will be slightly positive. The dispersion of permissible values should also be considered.
