What is the black skin of the bearing raceway?

Bearing raceway black skin refers to a common surface defect of bearings. Common types include single-side black skin on the raceway and double-sided black skin on the raceway.

1. Bearing raceway unilateral black leather

Ideally, when the groove position deviation is 0 after turning, the groove grinding allowance is uniform, and the raceway size during turning has considered the influence of the end grinding error on the raceway grinding process. Due to the limited amount of grinding allowance on the end face of spherical roller bearings, and the double end face grinding machine is used for simultaneous grinding of both end faces, so even if the grinding is offset, it will not cause black skin on the edge of the raceway. In fact, the appearance of black skin on one side of the raceway is due to the large amount left on one side and the small amount left on the other side when the groove is machined. Black skin is produced on the side with small amount left, and even the product is scrapped.

2. Black skin on both sides of the bearing raceway

After long-term tracking and recording of the processing process of the outer ring of spherical roller bearings in multiple batches, it was found that after the heat treatment of the outer ring workpiece, the outer diameter will have a concave center and the outer raceway will also be deformed. , The rear profile is shown in Figure 2. After heat treatment, the radial size of the middle part of the raceway becomes smaller, and the end of the raceway may exceed the size of the finished raceway; the outer diameter has a concave center and the end bulges outward. As a result, the allowance in the middle of the outer diameter becomes smaller, and both ends swell, and the raceway also swells at both ends, and the middle becomes smaller.

3. Improvement measures

Through the above analysis, specific measures to improve the black skin on the raceway edge of the outer ring of the spherical roller bearing are proposed:

(1) Strictly control the width and dimension deviation of the ferrule during turning to create conditions for the turning of the raceway;

(2) Strictly control the position error of the raceway during turning;

(3) Appropriately reduce the radius of curvature of the outer ring raceway during turning to suppress heat treatment deformation;

(4) Reduce the grinding allowance of raceway turning to improve the grinding efficiency.

It can be seen that most of the black skin on one side of the raceway of the bearing outer ring is caused by excessive groove position deviation or excessive height deviation during turning, while the black skin on both sides of the raceway is mostly caused by heat treatment deformation.