What is bearing preload?
In most operating conditions, rolling bearings are used with proper clearance. According to different purposes, when installing the bearing, it is also possible to pre-generate the internal stress of the bearing so that the bearing can be used under negative clearance. This method of use is called preload. Most of them, like angular contact ball bearings and tapered roller bearings, are suitable for two sets of opposite bearings with adjustable clearance.
If the preload exceeds the required limit, it will cause abnormal heat generation, increase in friction torque, decrease in fatigue life, etc. Therefore, it is necessary to fully study the working conditions and the purpose of preload to determine the preload.
The purpose of rolling bearing preload, the main purpose of preload and typical examples are as follows:
(1) While accurately positioning the shaft in the radial and axial directions, the runout of the shaft is suppressed. Machine tool spindle bearings, measuring instrument bearings.
(2) Improve the rigidity of the bearing. Machine tool spindle bearings, bearings for automotive differentials.
(3) Prevent abnormal sound caused by axial vibration and resonance. Small motor bearings, etc.
(4) Suppresses spin slip, revolution slip, and autorotation slip 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 ring. Thrust ball bearings, thrust self-aligning roller bearings, etc., are used for horizontal shafts.
Rolling bearing preload method:
Positioning preload is a preload method to ensure that the relative axial position of the opposite bearing does not change during use. The method is as follows:
(1) For the purpose of preloading, the combined bearings adjusted for the width difference or axial play are tightened before use.
(2) Preload the bearing with the adjusted size spacer and shim.
(3) Tighten the screw and nut that can adjust the axial play. 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.
Constant pressure preload is a method of applying preload to bearings by using coil springs, disc springs, etc. Even if the relative position of the bearing changes during use, the preload can remain roughly the same.