Pre tightening methods are divided into two categories: radial pre tightening method and axial pre tightening method. A brief introduction is as follows:

The radial pre tightening method and radial top tightening method are commonly used in tapered hole bearings that bear radial loads. A typical example is the double row precision short cylindrical roller bearing, which uses nuts to adjust the axial position of this bearing relative to the tapered journal, allowing the inner ring to have appropriate expansion and obtain radial negative clearance. This method is commonly used in machine tool spindles and jet engines.

Axial pre tightening method can generally be divided into two types: positioning pre tightening and constant pressure pre tightening. 

In positioning pre tightening, the appropriate pre tightening amount can be obtained by adjusting the size of the liner or gasket; Suitable preload can also be adjusted by measuring or controlling the starting friction torque; It is also possible to directly use paired double bearings with pre adjusted pre tightening amounts to achieve the purpose of pre tightening. At this time, users generally do not need to adjust them again. In short, any bearings that have undergone axial pre tightening will not change their relative position during use. 

Constant pressure preloading is a method of using coil springs, disc springs, etc. to properly preload bearings. The rigidity of a preloaded spring is generally much lower than that of a bearing, so the relative position of a bearing preloaded with constant pressure may change during use, but the preload amount remains roughly unchanged. 

The comparison between positioning pre tightening and fixed pressure pre tightening is as follows:

(1) When the pre tightening amount is equal, the effect of positioning pre tightening on increasing the stiffness of the bearing is greater, and the impact of stiffness changes on the bearing load during positioning pre tightening is much smaller. 

(2) During the use of positioning pre tightening, the axial length difference caused by the temperature difference between the shaft and the bearing seat, the radial expansion caused by the temperature difference between the inner and outer rings, and the displacement caused by the load will cause changes in the pre tightening amount; In use, the variation of pre tightening can be ignored when using fixed pressure pre tightening.

Bearing torque, load, and lifespan

1. The starting torque is the torque required to initiate the rotation of a bearing ring or washer relative to another fixed ring or washer.

2. The torque required to prevent the movement of another bearing ring or washer when one ring or washer rotates.

3. Radial load acting in the direction perpendicular to the axis of the bearing.

4. Axial load acting in the direction parallel to the axis of the bearing.

5. Static load refers to the load acting on the bearing when the relative rotational speed of the bearing ring or washer is zero or when there is no movement of the rolling element in the rolling direction.

6. Dynamic load refers to the load acting on the bearing when the bearing ring or washer rotates relative to each other or when the rolling element moves in the rolling direction.

7. Equivalent load calculation is a general term used for theoretical loads, where in specific situations, bearings are subjected to the theoretical load as if they were actually subjected to the load.

8. The radial basic rated static load corresponds to the total permanent deformation of the rolling elements and raceway. If the roller and raceway are or are assumed to be normal busbars under zero load, the total permanent deformation generated at the contact between the rolling elements and raceway under high contact stress is 0.0001 times the diameter of the rolling elements. For single row angular contact bearings, the radial rated load is the radial component of the load that causes pure radial displacement of the bearing rings relative to each other.

9. Radial basic rated dynamic load is a constant radial load, under which rolling bearings can theoretically withstand a basic rated life of 1 million revolutions per minute. For single row angular contact bearings, the radial rated load is the component of the load that causes pure radial displacement of the bearing rings relative to each other.

Before the first occurrence of fatigue propagation in the material of a ring, washer, or rolling element of a bearing, the number of revolutions of one ring or washer relative to another ring or washer, and the service life can also be expressed as the number of operating hours at a given constant speed.

11. The percentage of bearings that are expected to reach or exceed a certain specified lifespan for a group of rolling bearings that operate under the same conditions of reliability. The reliability of a set of bearings is the probability that the bearing will reach or exceed the specified lifespan.

12. The predicted value of the rated life based on the radial basic rated dynamic load or axial basic rated dynamic load.

13. The rated life associated with 90% reliability is the basic rated life.

14. The life factor is a correction factor applicable to equivalent dynamic loads in order to obtain the basic rated radial dynamic load or basic rated axial dynamic load corresponding to the given rated life.

15. A component that combines a radial bearing with a seat, and has a bottom plate for installing screws on a support surface parallel to the axis of the bearing.

16. Vertical seat for installing rolling bearings.

17. A flange seat is a type of seat with radial flanges and screw holes for installation on the supporting surface perpendicular to the bearing axis.

18. A sleeve with a cylindrical inner hole and an axial opening, with a conical outer surface and external threads at the small end. Used to install bearings with tapered holes on shafts with cylindrical outer surfaces.

19. The dismantling sleeve has a cylindrical inner hole with an axial opening, and its outer surface is conical with external threads at the large end. Used for installing or disassembling bearings with tapered holes on shafts with cylindrical outer surfaces.

20. The locking nut has a cylindrical outer surface and an axial groove screw nut, which is locked with one outer claw of the locking washer and an annular wrench. Used for axial positioning of rolling bearings.

21. The locking washer has many thin steel plate washers with outer claws. One outer claw is used to lock the nut, and one inner claw is inserted into the axial groove of the tightening sleeve or shaft.

22. One end of the eccentric sleeve has a groove steel ring that is eccentric relative to the inner hole, and is installed on the equally eccentric extension end of the inner ring of the outer spherical bearing. Rotate the eccentric sleeve relative to the inner ring to secure it tightly, and then tighten the top thread to secure it onto the shaft.

23. Concentric sleeve is installed on the wide inner ring of the outer spherical bearing, with a top screw screwed into the hole on the inner ring and in contact with the shaft.