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Determining the clearance of the motor bearing

by:JNSN     2021-12-21
The actual clearance of the motor bearing in work is related to the load, speed, lubrication, temperature rise, vibration, design structure and surface roughness of the matching table. The selection should be selected according to the specific situation. The clearance after subtracting the expansion or contraction of the ferrule caused by the interference fit when the bearing is installed on the shaft or in the housing from the theoretical clearance is called the installation clearance. The clearance obtained by adding or subtracting the dimensional change caused by the internal temperature difference of the bearing to the installation clearance is called the effective clearance. The clearance when the bearing is installed on the machine and subjected to a certain load rotation, that is, the clearance after the effective clearance plus the elastic deformation caused by the bearing load is called the working clearance. As shown in the figure, when the working clearance is slightly negative, the fatigue life of the bearing is the longest, but the fatigue life decreases significantly as the negative clearance increases. Therefore, when selecting the bearing clearance, it is generally appropriate to make the working clearance zero or slightly positive. When selecting the bearing clearance, the following aspects should be considered: 1. The working conditions of the bearing, such as load, temperature, speed, vibration, etc.; 2. The requirements for the performance of the bearing (rotation accuracy, friction torque, vibration, noise); 3. When the bearing is in interference fit with the shaft and housing hole, the bearing clearance will be reduced; 4. When the bearing is working, the temperature difference between the inner and outer ring causes the bearing clearance to decrease; 5. The expansion coefficient of the shaft and the housing material is different , Resulting in reduced or increased bearing clearance. According to experience, the most suitable working clearance of ball bearings is close to zero, and roller bearings should maintain a small amount of working clearance. In the parts that require good supporting rigidity, the bearing allows a certain value of pre-tightening force. Under normal working conditions, the basic group should be selected first, so that the bearing can get proper working clearance. When the basic group cannot meet the requirements of use, the auxiliary group clearance should be selected. The large clearance auxiliary group is suitable for the interference fit of the bearing, the shaft and the housing hole. The small clearance auxiliary group is suitable for occasions that require high rotation accuracy, strictly control the axial displacement of the housing hole, and reduce vibration and noise. In addition, when the rigidity of the bearing needs to be increased or the noise needs to be reduced, the working clearance should be further negative, and when the bearing temperature rises sharply, the working clearance should be further positive, etc., and specific analysis must be made according to the conditions of use. . Since the working clearance has a close relationship with the life, temperature rise, vibration and noise of the bearing, the control of the internal clearance of the bearing is very important. Motor bearings must have proper internal clearance to maintain good operation. The original bearing clearance is a very important indicator. Therefore, the original clearance should be checked with a feeler gauge before the bearing is assembled. At the same time, the contact resistance between the inner ring and the armature shaft should be measured to ensure reliable contact. After the motor is assembled, the bearing clearance is the matching clearance. If the clearance is too small at this time, it will cause the bearing to overheat, cause the inner ring to expand, make the clearance smaller and smaller, and eventually cause the bearing to burn; if the clearance is too small at this time If large, the rollers will receive uneven force, which will cause additional vibration and easily damage the bearing. Therefore, after the motor is assembled, a feeler gauge should be used to measure the clearance of the bearing after assembly. If the clearance is found to be unqualified, it must be disassembled and reworked for repair. The original radial clearances of ZWZ bearings are all in line with GB4604. The value of radial clearance applies to unmounted and unloaded bearings. Bearings larger or smaller than the standard value of clearance can also be produced according to user requirements.
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