The purpose of the fit The purpose of the fit is to make the inner or outer ring of the bearing firmly fixed with the shaft or bearing seat, so as to avoid unfavorable axial slip on the mutual fit surface. This unfavorable axial slip (called creep) will cause abnormal heat, mating surface wear (and thus wear iron powder into the internal bearing) and vibration and other problems, so that the bearing can not fully play. Therefore, for the bearing, due to bear the load rotation, generally must let the collar interference fit to make it firmly in the shaft or shell fixed. Shaft and bearing housing size tolerance and fit Metric series of shaft and bearing housing hole dimensional tolerance to ISO286 as the reference, from which the selected dimensional tolerance can determine the bearing and shaft or bearing housing fit relationship Choice of fit When selecting the fit, the bearing conditions of use should be fully considered. Consider the following items in general. The nature and size of the load Temperature and distribution during operation Bearing internal clearance Shaft and bearing housing processing quality, material and wall thickness structure Installation and disassembly methods Whether the mating surface is required to absorb the thermal expansion of the shaft Bearing form and size In the following, the selection of the mating is explained in relation to each of the above items. 1) Influence of the nature of the load Bearing loads can be divided into inner ring rotating load, outer ring rotating load and undirected load, and the relationship between the fits is shown in the following figure. 2) Influence of load size Inner ring under radial load, the radius direction can be compressed and extended, the circumference tends to increase slightly, so the initial interference will be reduced. 3) The influence of the roughness of the mating surface If the plastic deformation of the mating surface is considered, the effective interference after the fit is influenced by the processing quality of the mating surface. 4) Influence of temperature Generally speaking, the bearing temperature during operation is higher than the surrounding temperature, and when the bearing rotates with load, the inner ring temperature is higher than the shaft temperature, so the thermal expansion will reduce the effective interference. In addition, the sliding between the outer ring and the bearing seat to absorb the thermal expansion of the shaft, need to be noted. 5）The fit produces the bearing internal When bearings are installed with interference fit, the collar will expand or contract, thus producing stress. When the stress is too large, sometimes the collar will break and needs to be paid attention to. The maximum interference inside the bearing produced by the fit is not more than 1/1000 of the shaft diameter, or the most stress α is not more than 120Mpa ≦ 12kgf/mm²﹜for safety. 5）Other Rotational accuracy requirements are particularly high, should improve the accuracy of the shaft and bearing seat, compared with the shaft, the general bearing seat is difficult to process, low precision, so relax the outer ring and bearing seat with the appropriate. When using hollow shaft and thin wall bearing seat, the fit must be tighter than usual. When using the cut type bearing seat, should be relaxed with the outer ring fit. For cast aluminum or light alloy bearing seat, the fit must be tighter than usual, in this case, please contact MOS.  

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