Do you know bearing and shaft tolerance?

一,bearing and shaft tolerance--the bearing fit is generally a transition fit, but in special cases, an interference fit can be selected, but rarely. Because the bearing and the shaft are matched with the bearing's inner ring and the shaft, the base hole system is used. The bearing should be completely zero. We can also think of it in actual use, but in order to prevent the bearing's inner ring from the shaft When the minimum limit size fits, the inner ring will roll and damage the surface of the shaft. Therefore, our bearing inner ring has a down-tolerance of 0 to a few μ to ensure that the inner ring does not rotate, so the general choice of bearings is sufficient, It is to choose the interference fit that can not exceed 3 wires. The level of coordination accuracy is generally chosen to be 6, and sometimes it depends on the material and processing technology. In theory, the level 7 is a bit bottom, and if the level 5 is matched, a grinding is required.

二,bearing and shaft tolerance
1. When the bearing and shaft tolerance constitute a fit, the tolerance code that originally belonged to the transition fit in the general base hole system will become an overwin fit, such as k5, k6, m5, m6, n6, etc., but the amount of overwin is not large; When the bearing inner diameter tolerance is matched with h5, h6, g5, g6, etc., it is not a gap but an overwhelming fit.                                                                                                                                  2. The bearing outer diameter bearing and shaft tolerance zone is a special tolerance zone because the bearing and shaft tolerance value is different from the general reference shaft. In most cases, the outer ring is fixed in the housing hole. bearing and shaft tolerance --Some bearing components require structural adjustments. Should not be too tight, often with H6, H7, J6, J7, Js6, Js7 and so on.

三,bearing and shaft tolerance --the example shows that in general, the shaft is generally marked with 0 ~ + 0.005. If it is not often disassembled, an interference fit of + 0.005 ~ + 0.01 is sufficient. If frequent disassembly is required, a transition fit is sufficient. We also need to consider the thermal expansion of the shaft material during rotation, so the larger the bearing, the better the clearance fit is -0.005 ~ 0, and the maximum clearance fit should not exceed 0.01. The other is the interference of the moving coil and the gap of the static coil.

4. Fitting tolerance of bearing and shaft tolerance refers to the sum of the tolerances of the hole and shaft that make up the fit. It is the amount of change that allows for clearance or interference. The bearing and shaft tolerance zone size and location of the hole and shaft constitute the fit tolerance. The size of the hole and shaft fit tolerance indicates the accuracy of the hole and shaft fit. The size and position of the bearing and shaft tolerance zone of the hole and shaft fit indicate the accuracy and properties of the hole and shaft fit. The size of the fit tolerance = the size of the bearing and shaft tolerance zone; the size and position of the fit bearing and shaft tolerance zone = the nature of the fit.

四,bearing and shaft tolerance--the choice of tolerance level and bearing matching shaft or bearing housing tolerance level and bearing accuracy. For shafts matched with P0 precision bearings, the bearing and shaft tolerance level is generally IT6, and the bearing housing hole is generally IT7. Where high accuracy is required for rotation accuracy and smooth running (such as motors), the shaft should be IT5 and the bearing housing hole should be IT6.

Choice of bearing and shaft tolerance zone Equivalent radial load P is divided into several situations such as "light", "normal" and "heavy" load. The relationship with the rated dynamic load C of the bearing is: light load P≤0.06C normal load 0.06 C <P≤ 0.12C Heavy load 0.12C <P1, bearing and shaft tolerance for shafts with radial bearings and angular contact bearings, refer to the corresponding tolerance zone table. For most occasions, when the shaft rotates and the radial load direction does not change, that is, when the bearing inner ring rotates relative to the load direction, a transition or interference fit should generally be selected. The stationary shaft and the radial load direction are not changed, that is, when the bearing inner ring is stationary relative to the load direction, a transition or a small clearance fit can be selected (too large clearance is not allowed).                         2.bearing and shaft tolerance zone of housing hole and angular contact bearings is installed according to the corresponding tolerance zone table. When selecting, pay attention to the clearance fit for the outer ring that swings or rotates in the load direction. The equivalent radial load also affects the fit of the outer ring.
3. bearing and shaft tolerance --Selection of the structure of the bearing seat Unless there is a special need for the bearing seat of the rolling bearing, the monolithic structure is generally used. The split bearing seat is only used when it is difficult to assemble, or the convenience of assembly becomes the main consideration. However, it cannot be applied to tight fits or more precise fits, such as K7 and tighter fits than K7, and seat types with tolerance class IT6 or more precision must not use split bearing housings.

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