Generally, bearing fits are transitional fits, but interference fits are optional under special circumstances, but few...
1、Generally, bearing fits are transitional fits, but interference fits are optional under special circumstances, but few. Because the bearing and shaft fit is the inner race of the bearing and the shaft fit, and the base hole system is used. The bearing should be completely aligned to zero. We can also think this way in actual use. However, in order to prevent the inner race from rolling when the bearing inner race fits with the minimum limit size of the shaft, and damage the surface of the shaft, our bearing inner race has 0 to several μ To ensure that the inner ring does not rotate, so it is generally enough to select a transition fit for the bearing. Even if the transition fit is selected, it cannot exceed the interference of 3 wires.
Generally, the level of fitting accuracy is 6. Sometimes it depends on the material and processing technology. Theoretically, level 7 is a bit low, and level 5 fitting requires grinding.
Generally, K6 or K7 is selected for the bearing inner race and shaft matching shaft.
2、 Fit tolerance standard of bearing and shaft
1. When the bearing inner diameter tolerance zone and the shaft tolerance zone form a fit, the tolerance code of the original transition fit in the general base hole system will become a win fit, such as k5, k6, m5, m6, n6, etc., but the win amount is small; When the inner diameter tolerance of the bearing forms a fit with h5, h6, g5, g6, etc., it is no longer a clearance but an over-win fit.
2. Bearing outer diameter tolerance zone is also a special tolerance zone because the tolerance value is different from the general datum axis. In most cases, the outer ring is fixed in the housing hole, and some bearing components need to be adjusted according to the structural requirements. Its fit should not be too tight, often with H6, H7, J6, J7, Js6, Js7, etc.
3、 Example
Generally, the shaft is marked with 0~+0.005. If it is not disassembled frequently, it is an interference fit of+0.005~+0.01. If it is disassembled frequently, it is a transition fit. We should also consider the thermal expansion of the shaft material itself during rotation, so the larger the bearing, the better the clearance fit is - 0.005~0, and the maximum clearance fit is not more than 0.01. Another is the dynamic coil interference and the static coil clearance.
4、 Fit tolerance
It refers to the sum of hole and shaft tolerances that make up the fit. It is the variation of allowable clearance or interference. The size and position of tolerance zone of holes and shafts 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 hole and shaft fit tolerance zone indicate the fit accuracy and fit property of the hole and shaft. Size of fit tolerance=size of tolerance zone; Size and position of fit tolerance zone=fit property.
5、 Selection of tolerance class
The tolerance grade of the shaft or bearing seat hole matched with the bearing is related to the bearing accuracy. The tolerance class of the shaft matched with the P0 precision bearing is generally IT6, and the bearing seat hole is generally IT7. For occasions with high requirements for rotation accuracy and running stability (such as motors, etc.), the shaft shall be IT5 and the bearing seat hole shall be IT6.
6、 Selection of tolerance zone
The equivalent radial load P is divided into "light", "normal" and "heavy" loads, and its relationship with the rated dynamic load C of the bearing is: light load P ≤ 0.06C, normal load 0.06C ＜ P ≤ 0.12C, and heavy load 0.12C ＜ P.
1. Shaft tolerance zone
Refer to the corresponding tolerance zone table for the tolerance zone of the shaft where radial bearing and angular contact bearing are installed. In most cases, when the shaft rotates and the radial load direction remains unchanged, that is, 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, 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. Shell hole tolerance zone
Refer to the corresponding tolerance zone table for the housing hole tolerance zone of radial bearing and angular contact bearing. When selecting, pay attention to avoid clearance fit for the outer ring that swings or rotates in the load direction. The size of the equivalent radial load also affects the fit selection of the outer ring.
3. Selection of bearing pedestal structure
Unless there is a special need, the bearing seat of rolling bearing generally adopts the integral structure. The split bearing seat can only be used when the assembly is difficult or the advantages of convenient assembly become the main consideration. However, it can not be applied to tight or more precise fit, such as K7 and tighter than K7, and for example, the tolerance class is IT6 or more precise seat hole, the split bearing seat can not be used.
