Abstract: This paper analyzes the problems related to the working clearance of spherical roller bearings encountered during the repair and use of the factory combined reducer, and introduces the precautions when adjusting the clearance, which can be used as a reference for the peers.
The combined reducer is the main mechanical equipment for steel rolling. The working clearance of the spherical roller bearing directly affects the operation and service life of the reducer. Therefore, the natural clearance of the spherical roller bearing must be selected correctly, and the spherical roller must be adjusted correctly. The working clearance of the bearing.
1 The importance of bearing working oil gap
Working clearance is an important quality index of rolling bearings, and it is also 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 the combined reducer running at high speed, once the working clearance of the bearing is not adjusted properly, it will make the gear run unstable, generate 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 bushes are worn, and the center distance of the gears and the backlash of the gears increase or decrease, resulting in the breakage of the gear teeth.
2 Hazards of inappropriate working clearance of bearings
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, which will generate a lot of heat, which will easily lead to heat damage to 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 lot of heat will be generated due to dry friction, resulting in wear, cementation, and cracking of the inner and outer rings of the bearing until the bearing is damaged. .
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 excessive selection of the natural clearance of the bearing and the insufficient pressing force of the bearing. In the combined reducer running at high speed, when the natural clearance of the bearing is large, it determines that its 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 selected reasonably, if the pressing torque given to it by the bearing seat of the bearing is less than the friction torque of the bearing operation, the phenomenon of the rotation of the outer ring of the bearing will occur, which will wear the lining in the bearing seat. Reduce the meshing accuracy of the gears and generate vibration. When the lining is worn to a certain extent, it will cause the problems of gear center distance, gear backlash increase and decrease and inaccurate gear positioning, resulting in the breakage of gear teeth and reducing the service life of the bearing.
3 How to choose the natural clearance of the bearing
1 Selection principle of 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 temperature and commonly used interference fit, that is, the roller bearing should not exceed k5, m5 (shaft) and K6 (seat hole). When a tighter fit is used, the inner and outer rings When the temperature difference is large, 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 small clearance group should be used. For roller bearings, a small amount of working clearance can be maintained. In components requiring good support rigidity, the bearing should have a certain preload.
2 Factors that should be considered when selecting natural bearing clearance
Since the bearing cooperates with the gear shaft and the bearing seat, the cooperation between the bearing and the gear shaft and the bearing seat should be considered. At the same time, the change of the original clearance caused by the working temperature and load should be considered to select the clearance group of the 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 should 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 Matters needing attention when adjusting the clearance
1 Is the natural clearance of the bearing suitable?
Because there are 5 types of bearing clearance groups: 2 groups, 0 groups, 3 groups, 4 groups, and 5 groups, and the size of each clearance group is different. For a specific gear shaft and housing, the matching bearing (clearance set) is specific. Therefore, if the natural clearance of the bearing is too small, it will lead to poor adjustment of the working clearance. When the bearings are not of the same group number, the natural clearance will be different, which is also not conducive to the adjustment of the working clearance. Therefore, before each assembly, it should be checked whether the natural clearance of the bearing is suitable.
2 Influence of ambient temperature
In the northern region, when the ambient temperature is low in winter, when the reducer is repaired, the bearing oil film is frozen, which may easily cause the illusion that the detected working oil gap of the bearing is small. If the measured bearing working clearance is adjusted to When the standard is established, the working clearance of the bearing is increased invisibly. Therefore, when we adjust the working clearance of the bearing, we usually use the measured working clearance to be less than the standard 10-20!m of the bearing working clearance, and run in for a long time to see if the bearing is hot. If the bearing does not heat up, it means that the technical requirements are met, and if the bearing heats up, readjust it.
