1、 What is bearing preload?

Pre tightening of rolling bearings refers to the initial pressure and pre deformation generated between the rolling elements and the inner and outer rings of the bearing during installation, in order to maintain the inner and outer rings of the bearing in a compressed state and enable the bearing to operate in a negative clearance state under working load.

2、 What is the purpose of pre tightening bearings?

The purpose of bearing pre tightening is to increase the stiffness of the bearing; Correctly position the rotating shaft in both axial and radial directions to improve the rotational accuracy of the shaft; Reduce the vibration and noise of the shaft, and minimize the sliding of the rolling elements relative to the inner and outer raceway caused by inertia moment; Compensate for changes in internal clearance of bearings caused by wear and tear; What are the ways to extend the life of bearings and pre tighten the direction of bearings?

Bearings can be divided into axial preload and radial preload according to the direction of preload. In practical applications, ball bearings often use axial preload, while cylindrical roller bearings use radial preload. When two angular contact ball bearings or tapered roller bearings of the same model are installed in pairs, axial preload can be divided into positioning preload and fixed pressure preload according to the method of applying preload.

1. Positioning pre tightening

Positioning pre tightening refers to an axial pre tightening method in which the axial position of a bearing remains unchanged during use. It can be achieved by adjusting the width of the spacer between two bearings to obtain a certain amount of pre tightening.

Insufficient preload cannot achieve the purpose of preload, but excessive preload load does not significantly improve the stiffness of the bearing. Instead, it increases friction in the bearing, raises temperature, and reduces bearing life. The size of the preload should be determined based on the load situation and usage requirements. Generally speaking, under high-speed and light load conditions, or to reduce the vibration of the support system and improve the rotational accuracy, a lighter preload is selected; Under medium speed or low-speed heavy load conditions, as well as to increase the stiffness of the support system, medium and heavy preload loads are selected. Generally, the size of the preload should be determined through calculation and combined with usage experience.

2. Constant pressure pre tightening

Constant pressure preloading refers to an axial preloading method that uses a spring to maintain the axial preloading load of a bearing constant during use. The compression amount of the spring can be adjusted to obtain a certain amount of preloading.

Compared with positioning pre tensioning, constant pressure pre tensioning does not significantly increase the axial stiffness of the support system at the same pre tensioning deformation. However, during pre tensioning, the axial length difference caused by the temperature difference between the shaft and the bearing seat, as well as the radial expansion caused by the temperature difference between the inner and outer rings, will all affect the pre tensioning deformation, while during constant pressure pre tensioning, they are not affected. Therefore, the pre tightening method must be selected according to specific technical requirements. Usually, when high stiffness is required, positioning pre tensioning is chosen; When operating at high speed, choose constant pressure pre tightening.

3. Radial preload

The method of using the interference fit between the bearing and the journal to expand the inner ring of the bearing, eliminate radial clearance, and generate a certain degree of pre deformation is called radial pre tightening of the bearing.

Radial pre tightening can improve the support stiffness. In high-speed cylindrical roller bearings, radial preloading can reduce the slippage of rolling elements and raceways under centrifugal force. For bearings with conical inner holes, adjust the relative position between the inner ring and the tightening sleeve with a locking nut to reduce the radial clearance of the bearing and achieve radial pre tightening.