Abstract: The problems related to the working clearance of the spherical roller bearing encountered during the repair and use of the factory combined reducer are analyzed, and the adjustment is introduced.

The precautions for clearance can be used as a reference for peers.

The problems of working clearance of spherical roller bearing encountered in the repair and use of factory combined reducer.

Combined reducer is the main mechanical equipment of steel rolling. The working clearance of spherical roller bearing directly affects the operation condition and service life of reducer. Therefore, the natural clearance of spherical roller bearing must be correctly selected and the working clearance of spherical roller bearing must be correctly adjusted.

1. The Importance of Bearing Working Clearance

Working clearance is not only an important quality index of rolling bearing, but also an important parameter in bearing application. In practical use, the working clearance of the bearing will affect the load distribution, vibration, noise, friction torque and service life of the bearing. Especially in the high-speed combined reducer, once the working clearance of the bearing is adjusted improperly, the gear will run unstable, produce vibration, destroy the Meshing Effect of the gear and aggravate the fatigue degree of the gear. Even when the outer ring of the bearing rotates, the lining Bush is worn, the center distance of the gear and the side clearance of the gear are increased or decreased, resulting in the fracture of the gear teeth.

2. The Hazards of Improper Working Clearance of Bearing

2.1 The working clearance of the bearing is too small

If the working clearance of the bearing is too small, it will increase the friction torque of the bearing, resulting in a large amount of heat, which is easy to cause bearing heating and damage. This is because when the working clearance of the bearing is too small, it will lead to poor lubrication between the rolling element of the bearing and the inner and outer rings of the bearing. A lot of heat will be generated due to dry friction, resulting in wear, cementation, expansion and cracking of the inner and outer rings of the bearing, until the bearing is damaged.

2.2 The working clearance of the bearing is too large

The excessive working clearance of the bearing is mainly caused by the excessive selection of the natural clearance of the bearing and the insufficient pressing force of the bearing. In the high-speed combined reducer, when the natural clearance of the bearing is large, the working clearance is also relatively large, which will cause large vibration of the reducer during operation and reduce the service life of the bearing. When the natural clearance of the bearing is selected reasonably, if the pressing torque given to it by the bearing housing borne by the bearing is less than the friction torque of the bearing operation, the outer ring of the bearing will rotate, which will wear the lining bush in the bearing housing, reduce the meshing accuracy of the gear and produce vibration. When the liner is worn to a certain extent, it will cause the increase or decrease of gear center distance, gear side clearance and inaccurate gear positioning, resulting in the fracture of gear teeth and reducing the service life of bearing.

3. How to Select the Natural Clearance of Bearing

3.1 Selection principle of bearing natural clearance

Due to the influence of interference fit and temperature, the working clearance of the bearing is less than the natural clearance. The basic radial clearance group is suitable for general operating conditions, conventional temperature and common interference fit, that is, the roller bearing shall not exceed K5, M5 (shaft) and K6 (housing hole). When a tight fit is used, the temperature difference between the inner and outer rings is large, and the friction torque needs to be reduced or the centering performance needs to be improved, the large clearance group should be used; When the rotation accuracy is required to be high or the axial displacement needs to be strictly limited, the small clearance group should be used. For roller bearings, a small amount of working clearance can be maintained. Among the components requiring good support rigidity, the bearing shall have a certain preload.

3.2 The considered factors of selecting bearing natural clearance

Since the bearing fits with the gear shaft and bearing housing, the fit of the bearing with the gear shaft and bearing housing should be considered. At the same time, the change of original clearance caused by working temperature and load should be considered to select the clearance group of bearing. Assuming that the interference between the bearing and the shaft is Y1, the interference to ensure that the outer ring of the bearing does not rotate under working conditions is Y2, and the interference of the bearing under working conditions is Y3, the natural clearance y of the bearing shall meet the following conditions: y ≥ Y1 + Y2 + Y3. Among them, the estimation method of radial clearance reduction caused by interference can be estimated by the estimation method provided by FAG.

4. Precautions of Adjusting Clearance

4.1 Whether the natural clearance of the bearing is appropriate

Because there are 5 kinds of bearing clearance groups: 2 groups, 0 groups, 3 groups, 4 groups and 5 groups, and the size of each kind of clearance group is different. For a specific gear shaft and bearing pedestal, the matching bearing (clearance group) is specific. If the working clearance of the bearing is not adjusted well, it will lead to poor natural play. When the bearing is not of the same group number, the natural clearance is different, which is also not conducive to the adjustment of working clearance. Therefore, before each assembly, whether the natural clearance of the bearing is appropriate should be checked.

4.2 The influence of ambient temperature

In the northern region, when the ambient temperature is low in winter and the bearing oil film is cold and frozen when repairing the reducer, it is easy to cause the illusion that the detected bearing working oil gap is small. If the measured bearing working clearance is adjusted to the established standard, the bearing working clearance will be increased. Therefore, when we adjust the working clearance of the bearing, the measured working clearance is usually 10 ~ 20 less than the working clearance standard of the bearing! m. And run in for a long time to see if the bearing is hot. If the bearing is not hot, it means that the technical requirements are met. If the bearing is hot, readjust it.

4.3 The influence of lining Bush and gear assembly

When the liner is worn, it is bound to change the parallelism of the two gear shafts, so as to change the Meshing Effect of the gears and lead to the offset of the center of gravity. When this happens, the bearing forces on both sides of the gear shaft are uneven, resulting in uneven and symmetrical bearing clearance, which affects the adjustment of bearing clearance. At this time, the expected purpose can be achieved by grinding the lining bush or replacing the lining bush. When the gear is poorly assembled, resulting in poor gear meshing, it can cause uneven bearing force on both sides of the gear shaft, which directly leads to uneven and symmetrical bearing clearance, thus affecting the adjustment of bearing clearance. Therefore, we usually assemble the gear into the box, idle for 3 ~ 5min, and then adjust it.

4.4 The influence of fastening method of connecting bolt

In practice, we found that if the bolts on one side of the same bearing housing are tightened first and then the bolts on the other side are tightened, there will be a large difference between the two sides of the bearing clearance, resulting in large vibration of the reducer during operation and reducing the service life of the bearing. Therefore, when tightening the bolts, both sides must be pre tightened at the same time before tightening, so as to obtain the ideal working clearance of the bearing.

More about ITS Spherical Roller Bearing:

Spherical roller bearing is a bearing with drum shaped rollers assembled between the inner ring with two raceways and the outer ring with spherical raceways. Spherical roller bearing has two rows of rollers, which mainly bear radial load and axial load in either direction. It has high radial load capacity, especially suitable for working under heavy load or vibration load, but can not bear pure axial load. The outer race of this kind of bearing is spherical, so its centering performance is good and can compensate the coaxiality error.

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