We have been working in the non-standard industry for so long. The tolerance fit between the bearing and the shaft, as well as the tolerance fit between the bearing and the hole, has always been achieved by using a small space to achieve the function. , and it is easy to assemble and disassemble. However, local parts still need to have a certain degree of matching accuracy.
Fit tolerance refers to the sum of the hole and shaft tolerances that make up the fit. This is the amount of variation allowed between permission and interference.
The size and position of the hole and shaft tolerance area constitutes the fit tolerance. The size of the fit tolerance between the hole and the shaft indicates the fit accuracy of the hole and the shaft. The size and position of the fit tolerance area between the hole and the shaft indicate the fit accuracy and fit properties of the hole and the shaft.
01
Selecting Tolerance Levels
The tolerance level of the shaft or hole in the bearing housing that the bearing mates with is related to the accuracy of the bearing. The tolerance level of a shaft coupled with a P0 level precision bearing is generally IT6, and the bearing seat hole is generally IT7. For occasions requiring high requirements for rotation accuracy and smooth operation (such as motors, etc.), IT5 should be selected for the shaft and IT6 for the bearing seat hole.
02
Selection of tolerance zones
The equivalent radial load P is divided into “light”, “normal” and “heavy” loads. Its relationship with the nominal dynamic load C of the bearing is as follows: light load P≤0.06C normal load 0.06C
1) Shaft tolerance zone
For the tolerance zone of the shaft on which the radial bearings and angular contact bearings are installed, refer to the corresponding tolerance zone table. In most cases, when the shaft rotates and the direction of the radial load remains unchanged, that is, when the inner ring of the bearing rotates relative to the direction of the load, a transition adjustment or Tight should generally be selected. When the shaft is stationary and the direction of the radial load remains unchanged, that is, when the inner race of the bearing is stationary with respect to the direction of the load, a low clearance transition or adjustment can be selected (too large a clearance is not allowed).
2) Housing hole tolerance zone
For the tolerance area of the housing hole when installing radial bearings and angular contact bearings, refer to the corresponding tolerance area table. When selecting, be careful to avoid any loose fit for outer rings that swing or rotate in the direction of the load. The equivalent radial load also affects the selection of outer ring fit.
3) Selection of the structural shape of the bearing seat
Except for special needs, the bearing seats of bearings generally adopt an integral structure. The split bearing seat is only used when there are difficulties in assembly, or when the advantage of convenient assembly becomes the main consideration, but it cannot be used for. tight fits. Or a more precise fit, such as K7 and a tighter fit than K7, or a seat hole with a tolerance level of IT6 or more precise, the slotted bearing seat should not be used.
03
Mounting Tolerance Standards for Bearings and Shafts
① When the tolerance area of the bearing inner diameter and the tolerance area of the shaft form a fit, the tolerance code that was originally a transition fit in the general basic hole system will become a fit through overfitting, such as k5, k6, m5, m6, n6, etc., but the amount of overfitting is not large; when the bearing inner diameter tolerance matches h5, h6, g5, g6, etc., it is no longer a deviation but an overfit.
② The bearing outer diameter tolerance zone is a special tolerance zone because the tolerance value is different from that of the general reference shaft. In most cases, the outer ring is secured when installed in the hull hole. Some parts of the bearing have structural requirements. to adjust, and their coordination is not suitable. Too tight, often combined with H6, H7, J6, J7, Js6, Js7, etc.
Fixation: Under normal circumstances, the axis is generally marked 0~+0.005. If it is not frequently disassembled, a tight fit of +0.005~+0.01 is sufficient. If it is frequently disassembled and assembled, a transition adjustment is sufficient. We also need to take into account the thermal expansion of the shaft material itself when rotating. Therefore, if the bearing is larger, it is better to have a fit clearance of -0.005 ~ 0, and the maximum fit clearance should not exceed 0.01. Another problem is voice coil interference and static coil play.
Bearing fits are usually transition fits, but interference fits are optional in special circumstances, but rarely. Since the bearing and shaft match the inner ring of the bearing and shaft, and the basic hole system is used, the bearing must be completely aligned with zero. We can think of it this way in actual use, but in order to avoid. the inner ring of the shaft bearing When the minimum size limit is met, the inner ring will roll and damage the shaft surface. Therefore, the inner ring of our bearings has a downward deviation tolerance of 0 to several μ to ensure. that the inner ring does not turn. Therefore, the bearing generally only needs transition adjustment, even if you choose transition adjustment, the interference amount cannot exceed 3 wires.
Generally, the matching accuracy level is level 6. Sometimes it also depends on the material and processing technology. In theory, level 7 is a bit low. If level 5 is used, grinding is required.
What I usually choose is: K6 for the bearing inner ring and the corresponding hole for the shaft or K7 for the corresponding hole between the outer ring and the bearing hole.
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