The purpose of roller bearing pre-tightening and the direction of bearing pre-tightening

Time：2021.02.23  Source：Roller Bearings Suppliers

What is bearing pre-tightening?

The pre-tightening of roller bearings refers to the initial pressure and pre-deformation between the roller body of the bearing and the inner and outer rings when the bearing is installed, so as to keep the inner and outer rings of the bearing in a state of compression so that the bearing operates under the condition of negative clearance under the working load.

What is the purpose of bearing pre-tightening?

The purpose of bearing pre-tightening is to increase the stiffness of the bearing; Make the rotation axis in the axial and radial correct positioning, improve the rotation accuracy of the shaft; Reduce the vibration and noise of the shaft, and reduce the sliding of the roller body relative to the inner and outer ring raceway caused by the inertia moment. Compensate for changes in the internal clearance of bearings caused by wear and tear; Prolong bearing life.

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What are the bearing preloading directions?

Bearings can be divided into axial preloading and radial preloading according to the direction of preloading. In practical application, ball bearings are mostly axial preloading, while cylindrical roller bearings are radial preloading. When two angular contact ball bearings or tapered roller bearings of the same type are installed in pairs, axial preloading is divided into positioning preloading and constant pressure preloading according to the method of applying to preload.

1. Positioning pre-tightening

Positioning preloading refers to an axial preloading method in which the axial position of the bearing remains unchanged during the use process, as shown in Figure 1 below. A certain preloading amount can be obtained by adjusting the width of the spacer between two bearings.

The preloading amount is too small to achieve the purpose of preloading, but the preloading load is too large, the stiffness of the bearing can not be significantly improved, but the friction in the bearing increases, the temperature rises, and the bearing life decreases. The size of the preload shall be determined according to the load situation and use requirements. Generally speaking, under the condition of high-speed light load, or in order to reduce the vibration of the supporting system and improve the rotation accuracy, the lighter preload is selected. Under the condition of medium speed medium load or low-speed heavy load, and in order to increase the stiffness of the supporting system, the medium preload and heavy preload are selected. In general, the size of the preload should be determined by calculation and combined with experience. WSBC 21304CAK/W33 bearings online, pls click here. 

2. Constant pressure pre-tightening

Constant pressure preloading refers to an axial preloading method that makes the axial preloading load of the bearing remains constant in use through the spring. A certain amount of preload can be obtained by adjusting the compression of the spring

Compared with the positioning preloading, the increase of axial stiffness of the supporting system is not significant at the same preloading deformation. However, the axial length difference caused by the temperature difference between the shaft and the bearing seat and the radial expansion caused by the temperature difference between the inner and outer rings will affect the preloading deformation when the positioning preloading is performed, while the preloading at constant pressure is not affected. Therefore, the preloading mode must be selected according to the specific technical requirements. Usually, when high stiffness is required, positioning pre-tightening is selected. When running at high speed, constant pressure is used for tightening.

3. Radial pre-tightening

The method of making the inner ring of the bearing expand by using the interference fit of the bearing and the journal to eliminate the radial clearance and produce certain pre-deformation is called the radial pre-tightening of the bearing. Radial preloading can improve the bearing stiffness. In high-speed cylindrical roller bearings, radial preloading can reduce the roller and raceway skidding phenomenon under centrifugal force. For the bearing with a conical inner hole, the relative position of the inner ring and the setting sleeve is adjusted by the locking nut to reduce the radial clearance of the bearing and realize radial pre-tightening.

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