The load borne by bearings can be divided into light load, conventional load, and heavy load according to the size of the load. According to the temporal variation of the load, it can be divided into static load, variable load, and impact load. In addition, it can be divided into rotating load, stationary load, or variable load according to the direction of load. Rotating load, static load, or directional load are not the load properties of the bearing itself, but the load properties 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 rotating load or static load, and then determine whether to use interference fit or clearance fit.
Rotating load refers to a continuous change in the direction of the load relative to the ferrule, regardless of whether the ferrule itself is rotating or stationary. Static load refers to the direction of the load always facing a certain part of the ring, regardless of whether the ring itself is stationary or rotating. For example, when the load direction remains unchanged for the bearing, while the inner ring rotates and the outer ring is stationary, the inner ring bears the rotating load, while the outer ring bears the static load. When most of the bearing load is unbalanced due to rotation, even if the inner ring rotates and the outer ring remains stationary, the inner ring will still bear the static load, while the outer ring will bear the rotating load.
Some operating conditions are not as simple as the above. In addition to directional loads caused by weight, there are also combined loads caused by imbalance, vibration, power transmission, and so on, and their directions will be unpredictable. For this ring, either the load direction is very irregular and difficult to determine, or it is the deformation load that repeatedly occurs between rotating load and static load.
The collar that bears rotating load should, in principle, adopt an interference fit. If clearance fit is used, the collar will slip on the mating surface of the shaft or bearing seat; When the load is large, it can damage the mating surface or cause fretting wear. The tightness of the fit should be considered to ensure the interference even when under load, there is a temperature difference between the inner ring and the shaft during operation, or there is a temperature difference between the outer ring and the bearing seat. According to different operating conditions, the inner ring of the bearing mainly adopts k5, m5, n6, etc., while the outer ring mainly adopts N7, P7, etc.
As for large bearings, sometimes in order to avoid difficulties in assembly and disassembly, the method of fitting the clearance of the ring bearing the rotating load is also adopted. In this case, the shaft should be made of hard material, with a surface finish, sufficient lubrication, and maximum prevention of damage caused by slipping.
The ring that bears static load adopts clearance fit or transitional fit because there is no sliding condition between it and the bearing or bearing seat. The degree should be determined based on the accuracy required by operating conditions and the fact that the deformation of the ferrule will not cause excessive load distribution. Usually, the inner ring uses g6, h6, js5 (j5), etc., while the outer ring uses H7, JS7 (J7), etc. For variable load, it cannot be uniform, but the inner and outer rings mostly adopt a fit with added interference.