The load borne by the bearing can be divided into light load, conventional load and heavy load. It can be divided into static load, variable load and impact load according to the time change of load. Furthermore, depending on the direction of the load, it can be classified as rotating load, fixed load or variable load. The rotational load, static load or directional load is not a load characteristic of the bearing itself, but a load characteristic observed relative to each bearing ring. When determining the fit of the inner and outer rings, it is necessary to first consider whether they belong to rotational or static loads, and then determine whether an interference fit or a clearance fit is used.
Rotating load is a continuous change in load relative to the direction of the ferrule, regardless of whether the ferrule itself is rotating or stationary. Dead load is the direction in which the load always faces a part of the ring whether the ring itself is stationary or rotating. For example, when the load direction of the bearing remains the same while the inner ring is rotating while the outer ring is stationary, the inner ring is subjected to a rotational load while the outer ring is subjected to a static load. When most of the bearing load is unbalanced due to rotation, the inner ring will still bear the static load while the outer ring will bear the rotational load even if the inner ring rotates while the outer ring remains stationary.
Some operating conditions are not as simple as above. In addition to the directional load caused by weight, there are combined loads caused by imbalance, vibration, power transmission, etc. Their directions will be unpredictable. For this ring, either the load direction is very irregular and difficult to determine, or the deformation load repeatedly occurs between the rotating load and the static load.
In principle, the collar bearing rotating load shall adopt interference fit. If a clearance fit is used, the collar will slide on the mating surface of the shaft or bearing housing; When the load is large, it may damage the mating surface or cause fretting wear. Tightness of fit shall be considered to ensure that interference can occur even when there is a temperature difference between the inner race and shaft during operation or between the outer race and the bearing pedestal under load. Based on different working conditions, the bearing inner ring mainly adopts k5, m5, n6, etc., and the outer ring mainly adopts N7, P7, etc.
For large bearings, sometimes to avoid assembly and disassembly difficulties, a method of matching the clearance of the ring bearing to the rotating load is used. In this case, the shaft shall be made of hard material with a smooth surface, sufficient lubrication and maximum protection against sliding damage.
The ring bearing the static load adopts clearance fit or transition fit, because there is no sliding condition between it and the bearing or bearing seat. This degree shall be determined by the accuracy required for the operating conditions and the fact that the deformation of the ferrule does not result in excessive load distribution. In general, inner rings use g6, h6, js5 (j5), etc., while outer rings use H7, JS7 (J7), etc. For variable load, it can not be uniform, but the inner ring and outer ring are mostly matched by increasing the amount of interference.
