The combined reducer is the main mechanical equipment for steel rolling. The working clearance of the spherical roller bearings directly affects the operating conditions and service life of the reducer. Therefore, the natural clearance of the spherical roller bearings must be correctly selected and the spherical rollers must be adjusted correctly. The working clearance of the bearing.

1 The importance of bearing working oil clearance

Working clearance is an important quality indicator of rolling bearings and an important parameter in bearing applications. In actual use, the working clearance of the bearing will affect the load distribution, vibration, noise, friction torque and life of the bearing. Especially in a high-speed combined reducer, once the working clearance of the bearing is adjusted inappropriately, the gear will run unstable, generate vibration, destroy the meshing effect of the gear, and aggravate the fatigue of the gear. Even when the outer ring of the bearing rotates, the linings wear, the gear center distance and gear backlash increase or decrease, causing the gear teeth to break.

2 Hazards of improper working clearance of bearings

2.1 The working clearance of the bearing is too small

If the working clearance of the bearing is too small, the friction torque of the bearing will be increased, thereby generating a large amount of heat, which may easily lead to thermal damage of the bearing. This is because when the working clearance of the bearing is too small, the rolling elements of the bearing and the inner and outer rings of the bearing will be poorly lubricated, and a large amount of heat will be generated due to dry friction, causing wear, cementation, expansion and cracking of the inner and outer rings of the bearing, etc., until the bearing is damaged. .

2.2 The working clearance of the bearing is too large

The working clearance of the bearing is too large, which is mainly caused by the natural clearance of the bearing being too large and the pressing force of the bearing being insufficient. In a high-speed running combined reducer, when the natural clearance of the bearing is large, the working clearance is also relatively large, which will cause the reducer to vibrate greatly during operation and reduce the service life of the bearing. When the natural clearance of the bearing is properly selected, if the pressing torque given to it by the bearing seat is less than the friction torque of the bearing operation, the outer ring of the bearing will rotate, thereby wearing out the lining in the bearing seat. Reduce the meshing accuracy of the gear and generate vibration. When the lining wears to a certain extent, it will cause the gear center distance, gear backlash to increase or decrease, and the gear positioning to be inaccurate, causing the gear teeth to break and reducing the service life of the bearing.

3 How to choose the natural clearance of bearings

3.1 Principles for selecting bearing natural clearance

Due to the influence of interference fit and temperature, the working clearance of the bearing is smaller than the natural clearance. The basic radial clearance group is suitable for general operating conditions, normal temperatures and commonly used interference fits, that is, for roller bearings, k5, m5 (shaft) and K6 (seat hole) must not be exceeded. 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 alignment performance needs to be improved, a large clearance group should be used; when the rotation accuracy is required to be high or the axial displacement needs to be strictly limited, a large clearance group should be used Small clearance group. For roller bearings, a small amount of operating clearance can be maintained. In components that require good support rigidity, the bearings should have a certain amount of preload.

3.2 Factors that should be considered when selecting the natural clearance of bearings

Since the bearing, gear shaft, and bearing seat cooperate with each other, the coordination of the bearing, gear shaft, and bearing seat should be considered. At the same time, changes in the original clearance caused by operating temperature and load should be considered to select the clearance group of the bearing. Assume that the interference between the bearing and the shaft is y1, the interference that ensures 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, then the natural clearance y of the bearing should satisfy the following Condition: y≥y1+y2+y3 Among them, the estimation method of the radial clearance reduction caused by the interference can be estimated by the estimation method provided by FAG.

4 Things to note when adjusting clearance

4.1 Is the natural clearance of the bearing appropriate?

Because there are five bearing clearance groups: 2, 0, 3, 4, and 5, and the sizes of each clearance group are different. For a specific gear shaft and bearing seat, the matching bearing (clearance group) is specific. Therefore, if the natural clearance of the bearing is too small, the working clearance will be difficult to adjust. When the bearings are not of the same group number, the natural clearances will be different, which is also not conducive to the adjustment of the working clearance. Therefore, before each assembly, the natural clearance of the bearing should be checked for appropriateness.

4.2 Effect of ambient temperature

In northern areas, when the ambient temperature is low in winter, when repairing the reducer, the bearing oil film is frozen, which can easily cause the illusion that the detected working oil clearance of the bearing is smaller. If the measured working clearance of the bearing is adjusted to When the standard is established, the working clearance of the bearing is virtually increased. So we are

When adjusting the working clearance of the bearing, the measured working clearance is usually 10~20!m smaller than the standard working clearance of the bearing, and the bearing is run for a long time to see if the bearing is hot. If the bearing does not heat up, it means it meets the technical requirements. If the bearing does heat up, readjust it.

4.3 Influence of lining and gear assembly

When the lining wears, it will inevitably change the parallelism of the two gear shafts, thereby changing the meshing effect of the gears, resulting in a shift in the center of gravity. When this happens, the bearings on both sides of the gear shaft receive uneven forces, causing the bearing clearance to become uneven and symmetrical, thus affecting the adjustment of the bearing clearance. At this time, you can grind the lining

tile or replace the lining to achieve the intended purpose. When the gear assembly is poor, resulting in poor gear meshing, it can cause uneven stress on the bearings on both sides of the gear shaft, which directly leads to uneven and symmetrical bearing clearance, thus affecting the adjustment of the bearing clearance. Therefore, we usually assemble the gear into the box, idle it for 3 to 5 minutes, and then adjust it.

4.4 Influence of tightening methods of connecting bolts

In practice, we found that if the bolts on one side of the same bearing seat are tightened first and then the bolts on the other side, the difference in the bearing clearance on both sides will inevitably be larger, which will cause the reducer to vibrate more during operation and reduce the bearing capacity. service life. Therefore, when tightening bolts, both sides must be pre-tightened at the same time before tightening to obtain the ideal working clearance of the bearing.

JFZ Spherical Roller Bearing

JFZ Spherical Roller Bearing is designed to meet the high-demanding applications across different industries. It features two rows of symmetrical rollers, which can accommodate radial and axial loads in either direction. It is equipped with a precision-machined brass cage, providing high durability and stability under extreme operating conditions.

The bearing has a self-aligning capability, allowing it to operate in misaligned or tilted shafts. This feature results in reduced stress on the bearing, ultimately extending its service life and reducing maintenance costs. Its inner and outer rings have a high surface finish, minimizing friction and ensuring smooth operation and precise load distribution.

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