During the operating of the rolling bearings, in many cases, the failure is caused by fatigue. The reason is likely to be caused by the poor adjustment of bearing clearance. According to statistics, 34% of bearing fatigue is caused by improper clearance adjustment.
1. What is bearing clearance?
Bearing clearance is also called bearing play. The so-called bearing clearance refers to the amount of movement when the bearing is not installed on the shaft or the bearing box, the inner ring or the outer ring is fixed, and then the bearing clearance is not fixed to move radially or axially. According to the direction of movement, it can be divided into radial clearance and axial clearance. The amount of the running clearance (called the working clearance) has an impact on the bearing's rolling fatigue life, temperature rise, noise, vibration and other properties.
2. For cylindrical bore bearings:
The radial clearance after installation is determined by the tolerance of the selected housing hole and shaft. The greater the interference between them, the smaller the radial clearance after installation. Therefore, it is very important to correctly choose the tolerance of the shaft and hole that matches the bearing.
3. For tapered bore bearings:
The interference is not like the inner hole of a cylindrical bore bearing, which is determined by the tolerance of the selected shaft, but depends on the length of the thrust of the bearing on the tapered journal or tapered adapter sleeve.
How to select the bearing clearance?
A. Selection principle of clearance:
1. If a tight fit is used, the temperature difference between the inner and outer rings is large, the friction torque needs to be reduced, and the deep groove ball bearing is subjected to larger axial loads or needs to improve the alignment performance, a large clearance group should be used.
2. When the rotation accuracy is high or the axial displacement needs to be strictly limited, a small clearance group should be used.
B. Factors related to clearance:
1. Coordination of bearing inner ring and shaft.
2. The matching of the outer ring of the bearing and the housing hole.
3. The influence of temperature.
Note: The reduction in radial clearance is related to the actual effective interference size of the matching parts, the size of the matching shaft diameter, and the wall thickness of the housing hole.
4. Measuring method of bearing radial clearance:
(1) Lead wire
Use your fingers to check the axial clearance of the rolling bearing. This method is used where the shaft end is exposed. When the shaft end is closed or cannot be checked with your fingers for other reasons, you can check whether the shaft rotates flexibly.
(2) Check with a feeler gauge. The operation method is the same as that of checking the radial clearance with a plug.
(3) Check with a dial indicator. When the shaft is moved with a crowbar to make the shaft in two extreme positions, the difference between the dial indicator readings is the axial clearance of the bearing. However, the force applied to the crowbar cannot be too large, otherwise the shell will be elastically deformed, even if the deformation is small, it will affect the accuracy of the measured axial clearance.
5. How to adjust the axial clearance?
1. Use the nut installed on the bearing housing to push the gland pressed on the outer ring of the bearing for adjustment.
2. Adjust by adding or subtracting the thickness of the gasket between the bearing cover and the base.
Please check our Product Guide to select the suitable bearings for your machines.
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