Which caused the frequent damage of rolling mill bearings?

After analysis of effective data, the main forms of rolling mill bearing damage are fracture, wear and pitting.

Damage form one: Fracture: inner and outer ring fracture, rolling element rupture, cage fracture

The outer ring fracture is mainly caused by the excessive load and the insufficient bearing pressure.

In addition to the cyclic load, the inner ring is connected with the roll neck by the interference fit during installation. There is a positive tensile peripheral stress. As long as micro cracks are formed on the inner ring, they will rapidly spread and then cause fracture.

In addition to the above reasons, another reason for the fracture is that the oil and gas supply in the roller box is insufficient or interrupted, causing the bearing to heat up and then lock, and then causing damage to the inner and outer rings, the cage and the rolling elements.

Damage form two:  How is wear and pitting caused?

Most of the wear is caused by the relative rotation of the roll neck and the inner hole.

There are two main reasons for pitting: the bearing material is unqualified, caused by improper heat treatment. Foreign matter enters into the roller box, and pitting occurs during the running of the bearing.

In addition, due to improper operation, the copper bracket is deformed. When the roller enters the bearing housing, the ball rubs against the inner sleeve and then scratches the inner sleeve, so that the roller is inflexible during operation, causing bearing failure.

The height of the roll gap on both sides of the rolling mill is inconsistent, which causes the bearing to be stressed at a certain point due to uneven force during the running of the roll, thus causing bearing failure.

Bearing failure cause analysis program

1. Determine the most complete operating condition information.

2. Related photos in the process.

3. Alignment of used and unused lubricant samples.

4. Mark the bearing and its location in the device.

5. Carefully disassemble the bearings to avoid unnecessary extra damage.

6. Inspect other machine components to determine incidental damage.

7. Confirm the bearing base and seat.

8. Confirm the condition and distribution of the lubricant in the bearing. Extract additional samples if possible.

9. Clean the bearings and components, if possible, record the logo, brand and full name.

10. Realize the analysis of bearings and corresponding parts. Take other photos.

11. Compare the failure mode standard photos provided by the International Standards Organization 15243 and/or the bearing manufacturer to determine the cause of the failure.

12. Determine the necessary corrective actions necessary to avoid the same failure again.

13. Protect and retain faulty bearings for future comparisons.

14. Example: Some of the above cases will be shown

15. Interactive exercises: Some interactions with bearing failures will be shown during the workshop

16. Conclusions and recommendations. http://www.zys-bearings.com/

Bearing failure

We may find the following problems while identifying bearing failure:

1. Cage Damage – During use, the cage damage may occour, such as vibration, excessive speed, wear, & blockage.

2. Contamination – Contamination may be caused by the entrance of foreign objects into the bearing, such as scratches, pits, and lapping of the raceways.

3. Fatigue Failure – It is characterized by flaking or spalling of the raceway.  Fatigue failure is caused by granular weakening of the bearing steel which begins at the sub-surface and spreads to the raceway. 

4. Lubrication Failure – The original color of grease will usually turn to dark. If the grease is stiff or changed in color, it indicates lubrication failure. The grease will have an odor of burnt petroleum oil. If there is lack of oil, the lubricating oil will disappear. 

5. Misalignment – When one side of bearing is misaligned in relation to the other, the ball or roller path will run from one side of the race. This can result in high temperature and destroy of lubricant.