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How much axial preload should be added to the motor bearing?

source:未知   time:2024-08-23 09:34nbsp;  click:

When discussing axial preload for motor bearings, there are several key factors to consider: the operating conditions of the motor, the type of load (static or dynamic), ambient temperature changes, and expected service life. Load type: For light-load applications, axial preload is usually not necessary. In applications with heavy loads or high dynamic performance requirements, proper axial preload can improve bearing stiffness and stability, reduce vibration, and help extend life.

However, excessive axial preload may cause increased friction, reduced efficiency, and possible overheating issues. Ambient temperature changes: Temperature changes can affect the clearance inside the bearing, especially for precision equipment. When operating under extreme temperature conditions, proper axial preload can help maintain the correct clearance and contact pressure to ensure stable bearing performance. Motor type and application: Servomotors generally require more precise control and may require the use of preloaded bearings to reduce running errors. In highly dynamic applications such as wind turbines and industrial drives, proper axial preload can help improve system responsiveness and stability. Recommended value: Bearing manufacturers usually provide specific guidance on how to apply axial preload. For most applications, the recommended axial preload is about 20% to 30% of the bearing's rated load, but this needs to be adjusted based on the specific motor and load conditions.
The calculation of the data body will also be discussed later in this article. Measurement method: Specialized tools (such as axial load testers) are usually used to accurately apply and measure axial preload. Make sure that the bearing is properly inspected after installation to confirm that the preload meets the design requirements. Maintenance and monitoring: Regular inspection and adjustment of axial preload is necessary, especially when operating conditions change or at the end of expected life. The use of methods such as vibration analysis and temperature monitoring can help identify possible abnormal conditions and adjust the preload status in time. For motors that require preload, this article specifically introduces the calculation method.
 
Since the axial preload of the bearing is usually applied to deep groove ball bearings in motors, we use deep groove ball bearings to illustrate. Deep groove ball bearings will have a residual clearance after leaving the factory. For general horizontal internal rotation motors, the inner ring and shaft of the general motor bearing are tight fit, and the outer ring and shaft are loose fit. Therefore, after the bearing is installed, the inner ring of the bearing will expand radially due to the fit, while the outer ring will hardly change. Therefore, such changes will cause the internal clearance of the bearing to decrease. Similarly, when the motor is running, the temperature of the shaft is higher than the temperature of the bearing chamber, which causes the thermal expansion of the inner ring of the bearing to be larger than that of the outer ring, so the residual clearance inside the bearing is further reduced. The remaining clearance is what we call the working clearance of the bearing.

Generally speaking, when selecting motor bearings, a value larger than 0 is selected. This ensures the best performance of the bearings and the safety of the bearing clearance. It is the existence of this residual clearance that creates space for the bearing rolling elements to collide with the inner and outer ring raceways in the non-load zone. Such collisions cause noise in the motor bearings. Especially for some noise-sensitive occasions, such as air-conditioning motors, eliminating this noise is of great significance. For the above reasons, we usually use axial preload to eliminate the axial clearance inside the motor bearings. We know that for deep groove ball bearings, the elimination of axial clearance also means the elimination of radial clearance. Therefore, there is no space for the rolling elements to collide and vibrate inside the raceway. Therefore, the noise caused by this is also eliminated. However, it can be seen from the clearance curve that if the axial load is too large, excessive negative clearance inside the bearing will have a greater impact on the life of the motor bearing. Therefore, in order to balance the two, the axial load needs to be limited. The preload value of the motor bearing based on noise considerations is: F=kd, where F is the preload, Nk is the coefficient, and d is the inner diameter of the bearing, mm. Based on the consideration of eliminating noise, the k value is generally 5-10. Such a preload has little effect on the life of the motor bearing and effectively reduces the noise of the motor bearing. On the other hand, when the motor is in storage and transportation, if there are factors such as vibration, the motor is prone to pseudo-Brinell indentation. Pseudo-Brinell indentation is the damage to the metal surface caused by the reciprocating rolling and sliding of the motor rolling element at a certain position of the raceway. To avoid this situation, the k value is usually 10-20. It is not difficult for readers to find that the above value range is very wide.

This is mainly due to the accumulation of axial dimensional tolerances in the motor structure. If the range is too narrow, it will increase the difficulty of implementation in engineering. Generally, the author's personal experience recommends that the k value be around 10, which, on the one hand, makes the force value centered, which is conducive to engineering implementation, and on the other hand, it is also conducive to taking into account the influence of both aspects.
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