Application of high speed precision angular contact ball bearings in motorized spindle
Angular contact ball bearings often operate at high and super high speeds in the spindle, so the centrifugal force has a great influence on the running state of the bearing. In the static state, the contact points between the steel ball and the inner and outer rings are A and B respectively. When running at high speed, the centrifugal force tends to make the steel ball move out, that is A. When A1 and B0 are moved to B1, the contact angle of the inner ring will increase and the contact angle of the outer ring will decrease. As a result, the center of mass of the steel ball deviates from the axis of rotation and generates gyroscopic moment. The steel ball will slip to a certain extent while rolling. The friction heat generated by sliding not only increases the temperature rise of the bearing, but also causes local annealing on the surface of the steel ball in severe cases, which increases the degree of wear and burn. In order to overcome the influence of centrifugal force, angular contact ball bearings always carry a pre load operation in the spindle. Proper preload can make the contact angle of inner and outer rings keep the same during operation, which can not only prolong the life of bearings, but also improve the rigidity of bearings and spindles.
If the preload is too large, the bearing lubrication and heat dissipation conditions are poor, the bearing life is short under the same operating conditions, it is easy to burn or jam, and the higher the high-speed performance is, the more rigid the bearing and the spindle support is. If the preload is too small, the overall rigidity and bearing capacity of the spindle will obviously decrease. If the preload value is not enough to overcome the influence of the axial force and driving force on the spindle, the spindle will produce obvious vibration in the work, and the surface of the workpiece will appear obvious vibration. If the preload is not enough to restrain the gyroscopic moment, the spindle bearing will be heated sharply due to "slippage" during operation, and the surface of the steel ball has obvious "cat's eye" wear marks.
General bearing samples are given three kinds of pre load values of light, medium and heavy. But when applied in motorized spindle, it should be considered comprehensively according to the load status, lubricating oil and cooling methods. The selection principle is that the preload should be as close as possible to the practical application, and the influence of external load on the preload should be considered.
The main bearings of the motorized spindle are two sets of bearing groups. Considering the assembly process, the front bearing group is a fixed end. For single set and series bearing group, spring group exerts preload by pushing forward and pulling back. For parallel bearings, if not universal pairing (using contour pads), the preload should be adjusted by the height difference between the inner and outer pads. When the spindle support is selected, the series type (DT) is used in the case of large single-direction axial force. The DB parallel type is used in the case of accurate axial positioning, for example, grinding bearing rings, because it can bear bidirectional loads. Trench spindle. The D F parallel connection can be used for multi point bearings or bearings with a concentric and hard center.
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