Bearing raceway black skin refers to a common surface defect of bearings. The common types are raceway unilateral black skin and raceway bilateral black skin.

1. bearing raceway unilateral black leather

Under ideal conditions, when the groove position deviation is 0 after turning, the groove grinding allowance is uniform, and the effect of the grinding error on the groove grinding process has been taken into account in the raceway size during turning. Because of the limited allowance for the end grinding of self-aligning roller bearing, and the double end grinding machine is used for the grinding of the two end grinding, even if the grinding deviation will not cause the black skin on the raceway edge. In fact, the appearance of black skin on one side of raceway is because of the large amount left on one side and the small amount left on the other side during the processing of raceway. Black skin is produced on the side with the small amount left, and even leads to the scrapping of products.

2. bearing raceway bilateral black leather

After long-term tracking and recording of multiple batches of self-aligning roller bearing outer ring processing process, it is found that after heat treatment of outer ring lathe parts, outer diameter concave and outer raceway will also appear deformation. The contour of raceway and outer diameter before and after heat treatment is shown in Figure 2. After heat treatment, the radial size of the middle of the raceway becomes smaller, and the end of the raceway may exceed the size of the finished raceway. The outer diameter appears concave center, the end of the expansion. The middle of the outer diameter becomes small, and the two ends swell, and the raceway is enlarged at both ends and becomes smaller in the middle

3. Improvement measures

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

(1) Strictly control the width and size deviation of the ring during turning processing to create conditions for turning of raceway;

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

(3) The curvature radius of outer ring raceway during turning is appropriately reduced to inhibit the deformation of heat treatment;

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

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

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