The purpose of cooperation is to firmly fix the inner ring or outer ring of the motor bearing to the shaft or housing to avoid unfavorable axial sliding on the mating surfaces. This kind of unfavorable axial sliding (called creep) will cause abnormal heating, wear of the mating surface (then the worn iron powder will invade the inside of the bearing), vibration and other problems, making the bearing unable to fully function. Figure 1 The relationship between the dimensional tolerances of the shaft and the housing hole and the fit (bearings with 0 accuracy) The accuracy level of the bearing is 0 clearance fit transition fit interference fit Allowable deviation of bearing outer diameter Allowable deviation of bearing inner diameter Transition fit clearance fit interference Cooperate with Dmpdmp. The selection of cooperation is generally carried out according to the following principles. According to the direction and nature of the load acting on the bearing and which of the inner and outer rings rotates, the load borne by each ring can be divided into rotating load, static load or non-directional load. The ferrule bearing the rotating load and the non-directional load should adopt static fit (interference fit), and the ferrule bearing static load may adopt transition fit or dynamic fit (clearance fit). When the bearing load is large or is subjected to vibration or shock load, its interference must be increased. When hollow shafts, thin-walled bearing boxes or light alloy or plastic bearing boxes are used, the amount of interference must also be increased. When it is required to maintain high rotation accuracy, high-precision bearings must be used, and the dimensional accuracy of the shaft and bearing box must be improved to avoid excessive interference. If the interference is too large, the geometrical accuracy of the shaft or the bearing housing may affect the geometrical shape of the bearing ring, thereby impairing the rotation accuracy of the bearing. The inner and outer rings of non-separable bearings adopt static fit, so the installation and disassembly of the bearing are extremely inconvenient. It is best to use dynamic fit on one of the inner and outer rings. (1) The influence of the nature of the load The bearing load can be divided into inner ring rotating load, outer ring rotating load and non-directional load according to its nature. The relationship of the fit is as follows: bearing rotation condition inner ring: rotating outer ring: static load direction: fixed Inner ring: stationary outer ring: rotating load direction: rotating simultaneously with the outer ring inner ring: stationary outer ring: rotating load direction: fixed inner ring: rotating outer ring: static load direction: rotating at the same time as the inner ring Inner ring: static fit (Interference fit) inner ring: dynamic fit (clearance fit) available, outer ring: dynamic fit (clearance fit) available, outer ring: static fit (interference fit). The relationship between the nature of the load and the fit (2) The effect of the size of the load Under the action of radial load, the inner ring is compressed and stretched in the radial direction, and the circumference tends to increase slightly, so the initial interference will decrease. The amount of interference reduction can be calculated by the following formula. [When Fr≤0.25 C0][When Fr＞0.25 C0]u003dBdF .F r×0.08 d -310 (37)BFrd F u003d0.02×10-3 (38): Inner ring interference reduction, mm: bearing Nominal inner diameter, mm: nominal width of the inner ring, mm: radial load, N{kgf}: basic static load rating, N{kgf}△dFdBFrCor Therefore, when the radial load is a heavy load (over 25% of the C0 value) , The fit must be tighter than when the load is light. If it is an impact load, the fit must be tighter. (3) The influence of mating surface roughness If plastic deformation of the mating surface is considered, the effective interference after mating is affected by the processing quality of the mating surface, which can be approximately expressed by the following formula. The influence of temperature Generally speaking, the bearing temperature during operation is higher than the surrounding temperature, and when the bearing rotates with load, the temperature of the inner ring is higher than the shaft temperature, so thermal expansion will reduce the effective interference. Assuming that the temperature difference between the inside of the bearing and the periphery of the shell is △t, it can be assumed that the temperature difference between the inner ring and the shaft on the mating surface is approximately (0.01～0.15)△t. Therefore, the interference reduction Δdt caused by the temperature difference can be calculated by the following formula. dt u003d(0.10 to 0.15)0.0015 td×10-3 (41)t α...d△dt△tad: the reduction in interference caused by the temperature difference, mm: the temperature difference between the inside of the bearing and the periphery of the shell, ℃: the line of bearing steel Expansion coefficient, (12.5×10-6)1/℃: Nominal inner diameter of the bearing, mm(5) The maximum stress inside the bearing produced by the fit. When the bearing is installed with an interference fit, the ring will expand or contract when the ring is installed, which will cause stress. When the stress is too large, sometimes the ferrule will break, which requires attention. The maximum internal stress of the motor bearing produced by the fit can be calculated by the formula. As a reference value, take the maximum interference not to exceed 1/1000 of the shaft diameter, or the maximum stress obtained from the calculation formula * not more than 120MPa{12kgf/mm} as safe. When other accuracy requirements are particularly high, the accuracy of the shaft and housing should be improved. Compared with shafts, general shells are difficult to machine and have low precision, so it is better to loosen the fit between the outer ring and the shell. When using hollow shafts and thin-walled shells, the fit must be tighter than usual. When using a double half shell, loosen the fit with the outer ring. For cast aluminum or light alloy housings, the fit must be tighter than usual.