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What is bearing preloading - Purpose and method of rolling bearing preloading

wallpapers News 2021-01-18
What is bearing preload?
In most operating conditions, rolling bearings are used with proper clearance. According to different purposes, when installing the bearing, internal stress is generated in the bearing in advance so that the bearing can be used under negative clearance. This method of use is called preloading. Most of them, like angular contact ball bearings and tapered roller bearings, are suitable for two sets of opposed bearings with adjustable clearance.
 
If the pre-tightening force exceeds the required limit, it will cause abnormal heating, increased friction torque, and decreased fatigue life. Therefore, it is necessary to fully study the working conditions and the purpose of preload to determine the preload.
 
The purpose of preloading of rolling bearings, the main purpose of preloading and typical examples are as follows:
 
(1) While accurately positioning the shaft in the radial and axial directions, it restrains the runout of the shaft. Machine tool spindle bearings, measuring instrument bearings.
(2) Improve the stiffness of the bearing. Machine tool spindle bearings, bearings for automobile differentials.
(3) Prevent abnormal noise caused by axial vibration and resonance. Small motor bearings, etc.
(4) Suppress spin sliding, revolving sliding and rotating sliding of rolling elements. High-speed angular contact ball bearings, thrust ball bearings, etc.
(5) Keep the correct position of the rolling element relative to the ferrule. Thrust ball bearings, thrust spherical roller bearings, etc., when used on horizontal shafts.
 
Rolling bearing preload method:
 
1. Positioning preload
 
Positioning pre-tightening is a pre-tightening method to ensure that the opposed bearing does not change the axial relative position during use. The method is as follows:
 
(1) For preloading, tighten the combined bearing whose width difference or axial clearance has been adjusted beforehand.
 
(2) Use the adjusted spacers and shims to preload the bearing.
 
(3) Tighten the screw and nut that can adjust the axial clearance. In this case, in order to obtain an appropriate amount of preload, it is necessary to adjust the clearance while measuring the starting friction torque.
 
2. Constant pressure preload
 
Constant pressure preloading is a method that uses coil springs, disc springs, etc. to preload bearings. Even if the relative position of the bearing changes during use, the pre-tightening force can remain roughly unchanged.

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