When designing tapered roller bearings, the contact state and existing problems between the bearing roller ball base surface and the rib will affect the service life of the bearing. The following editor tells you that you can start from the bearing roller ball base surface and the large rib Contact problems and status of contacts are analyzed.
1. Problems existing in the contact between the base surface of the tapered roller ball and the large rib
In the large taper angle tapered roller bearing, the three surfaces of the inner ring raceway, the outer ring raceway, and the outer diameter of the roller mainly bear the radial load and are theoretically in a pure rolling state. The included angle between the generatrix of the outer ring raceway and the axis line of the bearing studied in this paper is about α = 25° to 29°, so it is called a large cone angle tapered roller bearing. This type of bearing has a higher ability to withstand axial loads than ordinary tapered roller bearings and is mainly used to withstand combined radial and axial loads mainly from one direction of axial load.
The design and processing method of the conventional tapered roller ball base surface does not meet the service life requirements of tapered roller bearings. The main problems and current situation are:
- The surface of the large rib of the inner ring and the base surface of the roller ball is worn unevenly, and the SR value of the base surface of the roller ball is large;
- Abnormal temperature rise often occurs during the use of bearings;
- The contact position between the base surface of the tapered roller ball with a large taper angle and the large rib of the inner ring is abnormal. Between the inner side of the large rib of the ring and the radial chamfer edge of the roller ball base surface, that is, the contact position between the roller ball base surface and the large rib of the inner ring often appears erratic;
- The large rib of the inner ring of the bearing sometimes cracks. Therefore, in order to effectively improve the service life of this kind of large taper angle tapered roller bearing, it is first necessary to solve the problem that the shape of the base surface of the roller ball affects the performance of the bearing.
- Based on the structural characteristics of the large taper angle tapered roller bearing and the basic law of the stress state and deformation of the rollers, inner ring raceway, and large rib after wear, the shape of the base surface of the tapered roller bearing is optimized and improved.
2. Analysis of the contact state between the base surface of the tapered roller ball and the large rib of the inner ring
The base surface of the roller ball and the large rib of the inner ring are both working surfaces. The sliding friction generated by them during work will cause serious friction and wear, burns, or stress concentration when the lubrication is poor or the contact position is unreasonable, which will lead to bearing failure. Failure due to early fatigue spalling of the raceway, the base surface of the roller ball, and the outer diameter. The shape of the tapered roller ball base surface, the hole diameter of the ball base surface, and the shape of the large rib of the inner ring are the main factors affecting the abnormal temperature rise of the large rib of the inner ring and the bearing capacity of the bearing. The contact position of the rib is also a very important link.
The abnormal contact position and wear condition between the large rib of the inner ring and the ball base surface of the roller also affect the service life of the bearing. The phenomenon of uneven wear, especially the convex edge of the hole diameter caused by the small hole diameter of the tapered roller ball base surface, can cause poor contact between the roller ball base surface and the large rib of the inner ring. If it is accompanied by problems such as excessive angle difference and surface roughness of the large rib of the inner ring, the uneven wear will cause spiral wear on the surface of the large rib of the inner ring. Therefore, according to the condition of the large rib of the inner ring of the bearing, the hole diameter of the tapered roller ball base surface should be appropriately increased, on the one hand, it is beneficial to the equal-area grinding of both ends of the tapered roller, and the coordinate size of the chamfer at both ends of the tapered roller can be effectively guaranteed;
On the other hand, it is also beneficial to improve the uneven wear of the large rib surface of the inner ring and the roller ball base surface caused by factors such as a large working axial load of the bearing and large dispersion of SR value of the roller ball base surface.
In addition, at the contact point, the size of the sliding friction is related to the position of the contact point: when the diameter of the circle where the contact point is located is small, the sliding friction is small; otherwise, the sliding friction is large. Therefore, the contact position between the base surface of the roller ball and the large rib is in the middle, which can effectively avoid or reduce the cracking of the large rib.
3. Factors and solutions for the expansion of bearing rings after heat treatment
Regarding the heat treatment expansion technology of the bearing ring, the most troublesome thing is the amount of expansion, especially when the bearing ring product has a large amount of expansion after heat treatment, it is necessary to increase the grinding allowance and grinding times of the bearing ring, and the most serious Directly lead to the scrapping of the bearing ring. What are the factors that cause the expansion of the bearing ring after heat treatment? How to solve this problem?
3.1 Factors of the amount of expansion of the bearing ring after heat treatment
As we all know, the quenching expansion of the bearing ring is caused by the specific tolerance difference between the pearlite before quenching and the martensite structure after quenching. In addition to the transformation of the structure, heat treatment of steel also produces thermal stress and structural stress. If the instantaneous stress exceeds the yield strength of the structure, it will cause plastic deformation to change the actual expansion.
In addition, the presence of retained austenite and the appearance of non-martensite also affect the amount of expansion. The content of various components and the magnitude of residual stress in the structure formed after quenching are the main factors that determine the size change of bearing steel after quenching and tempering.
3.2 The solution to a large amount of swelling of the bearing ring after heat treatment
- Adding Kerun additives to hot oil can reduce the expansion of quenched products of bearing rings and improve the qualified rate of expansion.
- Improving the cooling cycle of the quenching oil can reduce the expansion of the bearing ring after quenching.
- The amount of expansion of the bearing ring after quenching has a large relationship with the structural size of the bearing ring. Some bearing rings swell and some bearing rings shrink.
- The expansion of bearing ring products selected for cold oil quenching is relatively small.