1. Introduction
In the production process of special steel high – speed wire rod mills, the stable operation of equipment is crucial. The rolling mill gearbox is an important part of the production line, and the reliability of its bearings directly affects the normal operation of the entire production process. This article focuses on the bearing failures that occurred in the 16# and 17# rolling mill gearboxes of a certain special steel high – speed wire rod mill in Maanshan Iron and Steel Co., Ltd., analyzes the causes of these failures, and proposes corresponding solutions.
1.1 Background
The special steel high – speed wire rod mill is committed to producing high – quality wire rod products. However, in 2024, the 16# and 17# rolling mill gearboxes encountered repeated problems with the radial bearing cages of the distribution shaft, which brought serious impacts on production efficiency and product quality. The first failure occurred on April 13, 2024, followed by two more failures in May and June of the same year. These consecutive failures attracted great attention from the technical team, and it became urgent to find out the root causes and solve the problems.
1.2 Research Significance
Understanding the reasons for bearing cage failures in rolling mill gearboxes can help enterprises take preventive measures in a timely manner, reduce production downtime, and save maintenance costs. At the same time, it can also provide reference for the design, selection, and maintenance of bearings in similar industrial equipment, improving the overall reliability and stability of industrial production equipment.
2. Equipment and Monitoring Overview
2.1 Equipment Composition
The 16# and 17# rolling mills mainly consist of motors, gearboxes, and roll boxes. The motor has a power of 1500 kW. The gearbox is responsible for transmitting power and changing the speed ratio, and the roll box directly acts on the steel wire rod to complete the rolling process. The distribution shaft in the gearbox plays a key role in power transmission, and its bearings need to withstand complex loads during operation.
| Component | Function |
|---|---|
| Motor | Provide power for the rolling mill |
| Gearbox | Transmit power and adjust speed ratio |
| Roll box | Roll the steel wire rod |
| Distribution shaft | Transmit power within the gearbox |
2.2 Monitoring Process
After the first bearing cage fracture failure on April 13, 2024, technical personnel installed wireless sensors for online monitoring. However, due to the limitation of the installation position of the 16# and 17# distribution shaft bearings, only the axial measuring points of the gearbox input shaft and the measuring points of the 16# and 17# roll box casings were monitored. When the second failure occurred on May 26, 2024, it was found that the online monitoring system did not capture the abnormal vibration signal before the bearing failure. Then, after the second failure, the number of vibration sensors was increased, and the layout was optimized. A total of 7 vibration sensors were installed in different positions, such as the drive – end and free – end of the input shaft, and near the bearings of the 16# and 17# distribution shafts.
| Monitoring Stage | Measuring Points | Monitoring Result |
|---|---|---|
| First monitoring | Axial measuring points of gearbox input shaft, measuring points of 16# and 17# roll box casings | Did not predict the second failure |
| Second monitoring (after optimization) | 7 measuring points including drive – end and free – end of input shaft, near bearings of 16# and 17# distribution shafts | Did not predict the third failure |
3. Vibration Analysis of Gearbox Bearings
3.1 Vibration Characteristics after Bearing Replacement
After replacing the bearings on April 17, 2024, the vibration acceleration waveform of the gearbox showed impact signals with the rotation frequency of the 16# and 17# distribution shafts. The vibration acceleration value was , and there were also equally – spaced impact signals in the frequency spectrum. This indicates that the rotation of the shaft is unstable, possibly due to excessive bearing clearance. Although the vibration amplitude is small, it still reflects potential problems in the bearing operation.
| Date | Vibration Acceleration Waveform Feature | Frequency Spectrum Feature | Possible Problem |
|---|---|---|---|
| April 17, 2024 | Impact signals with 16# and 17# distribution shaft rotation frequency | Equally – spaced impact signals | Excessive bearing clearance |
3.2 Vibration Before the Second Failure
On May 26, 2024, before the 17# distribution shaft bearing failure, the axial measuring point speed value and acceleration value of the gearbox input shaft showed a stable trend, and the vibration amplitude was small. The vibration speed amplitude was within , and the acceleration amplitude was within . Although there was an equally – spaced impact signal with a frequency of 28.125 Hz in the vibration monitoring frequency spectrum, and the envelope demodulation spectrum showed the rotation frequency and its multiples of the 17# distribution shaft, there were no obvious abnormal signals. This shows that it is difficult to predict bearing failures only through traditional vibration monitoring methods in some cases.
| Monitoring Parameter | Value | Abnormal Signal in Frequency Spectrum |
|---|---|---|
| Vibration speed amplitude | Within | No obvious abnormal signal |
| Acceleration amplitude | Within | Impact signal at 28.125 Hz, but no obvious abnormality |
3.3 Vibration Before the Third Failure
On June 27, 2024, before the third failure of the 16# and 17# rolling mill gearboxes, the vibration speed value of the free – end axial measuring point of the 17# distribution shaft was small, and the acceleration value was also small but showed a slight increase trend. The vibration speed value of the free – end axial measuring point of the input shaft was small, and the acceleration value had an increasing trend with a large amplitude. However, the vibration waveform and frequency spectrum still did not show obvious abnormal signals. This further proves that the bearing cage failure has unique characteristics, and it is difficult to detect in advance through general vibration monitoring.
| Measuring Point | Vibration Speed Value | Vibration Acceleration Value | Vibration Waveform and Frequency Spectrum Feature |
|---|---|---|---|
| Free – end axial of 17# distribution shaft | Small | Small, with a slight increase trend | No obvious abnormal signal |
| Free – end axial of input shaft | Small | Large amplitude, increasing trend | No obvious abnormal signal |
4. Reasons for the Failure of Bearing Cage Monitoring
4.1 Characteristics of Bearing Cage Failure
The failure of the bearing cage is different from that of the inner ring, outer ring, and rolling elements of the bearing. The failure of the inner ring, outer ring, and rolling elements usually takes a certain amount of time to form. During this process, the vibration value of the bearing will increase, and obvious fault – characteristic frequencies will appear in the vibration waveform and frequency spectrum, which are easy to be identified. However, the failure of the bearing cage is often instantaneous. Once it occurs, it is already in the late stage of the bearing failure. The fault – characteristic frequency of the cage is the smallest among all bearing component failure frequencies, making it difficult to identify.
| Bearing Component | Failure Formation Time | Vibration Value Change | Fault – Characteristic Frequency Identification Difficulty |
|---|---|---|---|
| Inner ring, outer ring, rolling elements | Longer | Increases | Relatively easy |
| Bearing cage | Instantaneous | Not obvious in the early stage, sudden increase in the late stage | Difficult |
4.2 Limitations of Vibration Monitoring
Although vibration monitoring is a common method for detecting bearing failures, it has limitations in detecting bearing cage failures. The installation position of the sensors may not be able to accurately capture the vibration signals of the bearing cage. Even if the number of sensors is increased and the layout is optimized, it is still difficult to ensure that all potential failure signals can be detected in time. In addition, the short – term and sudden nature of the bearing cage failure makes it difficult for the vibration monitoring system to respond in time and predict the failure in advance.
| Limitation Aspect | Specific Performance |
|---|---|
| Sensor installation position | May not be able to capture bearing cage vibration signals accurately |
| Response to sudden failure | Difficult to respond in time to the short – term and sudden failure of the bearing cage |
5. Solutions and Effects
5.1 Material Replacement of Bearing Cage
In early July 2024, after analyzing the failures, the material of the bearing cage of the 17# distribution shaft of the gearbox was re – selected. The original steel – material cage was replaced with a copper – material cage with better plasticity and ductility. Copper – based materials have better shock – absorbing and wear – resistant properties, which can reduce the stress concentration on the bearing cage during operation and improve its anti – fracture ability.
5.2 Effect of Material Replacement
After replacing the bearing cage material, the new bearing has been operating normally from July 2024 to November 2024 for four months. This indicates that changing the material of the bearing cage can effectively solve the problem of frequent cage fractures. By improving the material performance, the reliability and service life of the bearing are enhanced, ensuring the stable operation of the rolling mill gearbox.
| Time Period | Bearing Operation Status | Indication |
|---|---|---|
| July – November 2024 | Normal | The material replacement of the bearing cage is effective |
6. Conclusion
6.1 Summary of Research Results
This article analyzed the bearing cage fracture failures that occurred in the 16# and 17# rolling mill gearboxes of a special steel high – speed wire rod mill. Through vibration analysis and failure – mechanism exploration, it was found that the instantaneous nature of bearing cage failures and the limitations of vibration monitoring methods led to the difficulty of early prediction. By replacing the bearing cage material with a copper – based material with better plasticity and ductility, the problem of frequent bearing cage fractures was effectively solved.
6.2 Future Research Directions
Although the problem has been alleviated to a certain extent, there is still room for further research. Future research can focus on developing more advanced bearing monitoring technologies, such as combining multiple monitoring methods (such as acoustic emission monitoring, temperature monitoring) with vibration monitoring to improve the accuracy of failure prediction. At the same time, it is also necessary to further study the influence of bearing design parameters and operating conditions on the failure of bearing cages to provide more comprehensive solutions for the reliable operation of rolling mill gearboxes.
