The one-way bearing often runs at high speed and super high speed in the electric spindle. Therefore, the centrifugal force has a great influence on the running state of the bearing. In the static state, the contact points of the steel ball with the inner and outer rings are A and B, respectively. At high speed, the centrifugal force tends to shift the steel ball outwards, that is, A moves to A1 and B0 moves to B1. At this time, the inner ring contact angle will increase and the outer ring contact angle will decrease. As a result, the steel ball centroid deviates. The axis of rotation produces a gyro moment.
The steel ball will have a certain degree of slipping while rolling, and the frictional heat generated by the sliding will not only aggravate the temperature rise of the bearing, but also cause local annealing of the surface of the steel ball in a serious case, increasing the degree of wear and burn. To overcome the effects of centrifugal forces, one-way bearings always operate with preload in the main shaft. Proper preloading keeps the inner and outer ring contact angles consistent during operation, which not only extends bearing life, but also increases the rigidity of the bearing and the spindle.
If the preload is too large, the bearing lubrication and heat dissipation conditions are poor. Under the same conditions, the bearing life is short, it is easy to burn or jam, and the high speed performance is worse, but the bearing rigidity of the bearing and the main shaft is greatly increased. If the preload is too small, the overall rigidity and load carrying capacity of the spindle are significantly reduced.
If the amount of preload is not enough to overcome the influence of the axial force and the driving force on the spindle, the spindle will produce significant vibration during operation, and the surface of the workpiece will be obviously embossed. If the preload is insufficient to suppress the gyroscopic moment, the spindle bearing will heat up sharply due to “slippage” during operation, and there will be obvious signs of wear on the surface of the steel ball.
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