I. bearing fits are generally transitional fits, but in special cases, interference fits are optional, but few. Because the matching of bearing and shaft is the matching of inner ring and shaft of bearing, and the base hole system is used, so the bearing should be completely aligned to zero. We can also think this way in actual use. However, in order to prevent the inner ring rolling when the bearing inner ring and shaft are matched with the minimum limit size, which will damage the surface of shaft, our bearing inner ring has a lower tolerance of 0 to several μ to ensure The inner ring does not rotate, so the transition fit is generally selected for the bearing, and even the transition fit can not exceed the interference of 3 wires. Generally, the matching accuracy grade is grade 6, sometimes it depends on the material and processing technology. Theoretically, Grade 7 is a little bit off the bottom, and grade 5 matching requires grinding. In general, I choose K6 for bearing inner ring and shaft matching, K6 or K7 for bearing outer ring and hole matching. 2. Standard for bearing and shaft matching tolerance. 1. When the bearing inner diameter tolerance zone and shaft tolerance zone form a matching, the tolerance code of the original transition fit in general base hole system will become win-win fit, such as K5, K6, M5, M6, N6, etc., but the win-win amount is not large. When the bearing inner diameter tolerance is replaced by H5, h, etc. 6, G5, G6, etc. are not gaps but over win fit. 2. As the tolerance value of bearing outer diameter tolerance zone is different from that of general datum axis, it is also a special tolerance zone. In most cases, the outer ring is fixed in the shell hole, and some bearing components need to be adjusted due to their structural requirements, so the fit should not be too tight. They are often matched with H6, H7, J6, J7, js6, js7, etc. 3. Give an example to illustrate that in general, if the shaft is not often disassembled, the interference fit of + 0.005 + 0.01 will be OK, and if it is often disassembled, the transition fit will be OK. We also need to consider the thermal expansion of the shaft material itself during rotation, so the larger the bearing is, the better the clearance fit is - 0.005 ~ 0, and the maximum clearance fit is not more than 0.01. There is also a dynamic ring interference, static ring gap. 4. Fit tolerance refers to the sum of the tolerances of the holes and shafts that make up the fit. It is the amount of variation that allows clearance or interference. The tolerance zone size and position of the hole and shaft constitute the fit tolerance. The size of the hole and shaft fit tolerance indicates the fit accuracy of the hole and shaft. The size and position of the tolerance zone indicate the fit accuracy and fit properties of the hole and shaft. The size of fit tolerance = the size of tolerance zone; the size and position of fit tolerance zone = fit property. The selection of tolerance grade is related to the tolerance grade and bearing accuracy of the shaft or bearing seat hole. The tolerance level of the shaft matched with the P0 precision bearing is generally IT6, and the bearing seat hole is generally it7. When there are high requirements for rotation accuracy and running stability (such as motor, etc.), it5 shaft and IT6 bearing seat hole shall be selected. Vi. the selection of the equivalent radial load P of the tolerance zone is divided into "light", "normal" and "heavy" loads. The relationship between them and the rated dynamic load C of the bearing is: light load P ≤ 0.06c, normal load 0.06c < p ≤ 0.12c, heavy load 0.12c < P1. The tolerance zone of the shaft with radial bearing and angular contact bearing installed in the shaft tolerance zone shall refer to the corresponding tolerance zone table. In most cases, when the shaft rotates and the radial load direction remains unchanged, that is to say, when the bearing inner ring rotates relative to the load direction, the transition or interference fit should generally be selected. When the shaft is stationary and the radial load direction is unchanged, that is, when the bearing inner ring is stationary relative to the load direction, transition or small clearance fit can be selected (too large clearance is not allowed). 2. The tolerance zone of housing hole for installation of radial bearing and angular contact bearing shall refer to the table of corresponding tolerance zone. When selecting, pay attention to avoid clearance fit for outer ring swinging or rotating in load direction. The magnitude of the equivalent radial load also affects the mating selection of the outer ring. 3. Selection of structural form of bearing pedestal unless there is special need, the bearing pedestal of rolling bearing generally adopts integral structure. Split bearing pedestal is only adopted when there is difficulty in assembly or when the advantage of convenient assembly becomes the main consideration point, but it cannot be applied to tight or more precise matching, such as K7 and tighter matching than K7, for example, tolerance grade is IT6 or more. No split bearing seat shall be used for precise seat holes.