Abstract: Rolling mill bearing burnout refers to the jamming phenomenon that occurs when the bearing wears out excessively during operation. It is usually caused by a sharp increase in heat generated by the sliding of parts, resulting in plastic deformation. Once the bearing of the rolling mill is damaged, the rolling mill cannot operate normally. In this case, there will be a failure of the rolling bearing.

This article analyzes the causes of bearing burnout in the rolling mill, explains the damage principle, and based on practical operation experience, proposes several control measures to reduce the number of bearing burnouts in the rolling mill, thereby saving production costs and improving production efficiency.

Overview of Bearing Burnout in Rolling Mills Bearing burnout in the rolling mill refers to the phenomenon where the bearing becomes stuck due to excessive wear during operation. This is usually caused by a sharp increase in heat generated by the sliding between parts, resulting in plastic deformation. Bearing burnout reduces the service life of the bearing. Generally, each bearing has a budgeted service life. Rolling bearings used in the rolling mill can operate normally only before fatigue pits appear. The total operating hours of the rolling elements on the raceway is the lifespan of the rolling bearing. Once the bearing of the rolling mill becomes damaged, the rolling mill cannot operate normally. In this case, there are three failure situations of rolling bearings.

First, fatigue pit corrosion. It refers to the phenomenon of fatigue pits appearing on the inner and outer raceways or the surface of the rolling elements after the rolling mill has been running for a certain period of time, due to the influence of the cyclic contact stress between the bearing track and the rolling elements.

Second, plastic deformation. It refers to the uneven surface at the contact position between the rolling element and the raceway, mainly because the bearing needs to bear large static loads and impact loads, which will cause local stress to exceed the material's bearing limit, thereby resulting in plastic deformation. At the same time, plastic deformation is often accompanied by noise.

Third, bearing wear. If the working environment is harsh, the lubrication used for the bearing in a poorly sealed situation usually causes bearing wear.

2 Reasons for premature failure of bearings

2.1 Inappropriate operations during assembly and disassembly

Based on practical operation experience, the most obvious reason for the failure of bearings to reach the expected service life is the improper operation during assembly and disassembly. Both the assembly and disassembly of bearings should use the correct tools. If the tools used are not in compliance with the requirements, there will be a gap between the bearing housing and the bearing, and this gap will cause wear on the bearing raceways and rolling elements. This also indicates that during the assembly and disassembly of bearings, the correct tools must be used. This ensures that the installation is uniform and reduces the wear between the bearings. Additionally, the shaft of the bearing and the bearing housing should leave a certain gap according to the gap requirements of short-stress rolling machine bearing housings and bearing assemblies. However, this gap should not be too large because if the gap between the roller bearing housing and the frame is too large, the shaking degree of the bearing housing will also increase, thereby causing excessive impact loads to act on the bearings, reducing their service life. At the same time, excessive impact loads will also affect the positioning of the bearing housing, change the force distribution of the bearing housing, and deepen the damage to the bearings.

2.2 Improper use of lubricants

Lubricating the bearings is done to utilize the protective effect of the oil film. After adding lubrication, the oil film can separate the surfaces of the rolling elements in motion, enabling the bearings to perform their functions stably during operation and improving the rotational accuracy. However, if the lubrication is not used appropriately, such as using too little or with an uneven distribution, the bearings will suffer from wear and thus fail.

2.3 Oil contamination

One part of the reason is pollution, mainly referring to the deterioration of the quality of the oil. If the oil leaks due to poor sealing or if the quality of the oil itself is not up to standard, it will lead to a decline in the quality of lubrication, failing to achieve the desired performance. The cooling water used for the rollers of the rolling mill is turbid water, which makes it easy for the lubricating oil to be contaminated, increasing the wear between the bearings and reducing the service life.

2.4 Negligence in maintenance work

Improper maintenance is a major factor. Moreover, it is often overlooked by people. Approximately 40% of bearing failures are caused by inadequate maintenance in the later stage. Spare parts for bearings need to be maintained after long-term use. At this point, the bearings have already been subjected to overload. If they do not receive timely maintenance, fatigue damage will occur. Additionally, during the crawling process of the rolling mill, friction often occurs. Pulling welding of the rolling groove will cause the welding current to discharge. The lubricating film of the bearing cannot withstand the impact of the current, so electrical erosion will occur inside the bearing track, resulting in unevenness on the bearing surface. This increases the friction on the bearing surface even more. The direct consequence is that the inner ring, outer ring, and rolling elements of the bearing will all be worn, and this wear is uneven, reducing the service life of the bearing.

3 Control measures for preventing bearing burnout in rolling mills

Bearing overheating in rolling mills is a common problem that occurs frequently during actual production. Frequent damage to rolling mill bearings not only has a negative impact on the production progress but also increases production costs. In my opinion, measures can be taken from the following aspects to reduce the occurrence of bearing overheating in rolling mills, so as to reduce the number of such incidents and save production costs while improving production efficiency.

3.1 Offline assembly and debugging of rolling mill bearings

Firstly, it is necessary to ensure that the rolled mill is in a good overall condition when it is taken off the line. Carefully inspect the bearing housing of the rolled mill and clean it to ensure that there are no foreign objects inside. Before assembly, reconfirm whether there are any foreign objects or deformation problems in the bearing housing. If found, it should be immediately resolved. If the deformation of the component is very serious, it should be replaced according to the assembly requirements of the bearing housing. In addition, it is necessary to ensure that the rolling mill's roll balancing device is intact. The preliminary work should include checking, cleaning and lubricating the adjustment device. A gap should be generated between the rolled mill's roll and the adjusting nut, so that the rolls can have a significant degree of vibration, affecting the distribution of force.

3.2 Strengthening details

Before the assembly, it is necessary to ensure that there are no foreign objects in the bearing housing of the rolled mill, that the bearing frame is sealed properly, and that there is an appropriate gap distance between the rolling elements and the raceway. Align the inner sleeve of the bearing with the bearing housing of the rolled mill. The rolls must be kept clean, cleaning the roll neck and removing oil stains and other foreign substances from the surface. The inner sleeve of the bearing needs to be installed after heating, and the heating temperature should be controlled within the specified range. The entire assembly process should ensure the integrity of the surface finish of the equipment. After assembly, an axial and radial inspection of the rolled mill should be conducted, with the adjustment amount of the axial direction controlled within 5mm. It is also necessary to check the fixation of the bearing housing and ensure that all components are in an effectively tightened state. Lubrication work should be carried out on the components that need lubrication to ensure that the bearing rolls receive uniform force.

3.3 Online assembly and debugging of rolling mill bearings

During the online assembly of rolling mill bearings, it is necessary to ensure that the rolling line is consistent with the center line. Only in this way can the upper and lower rolls rotate parallelly and ensure that the axial force of the bearing is relatively uniform. Generally, the sliding rails of the rolled mill base will wear out, and it is necessary to check them in advance. Otherwise, the rolled mill will shake during operation, causing the rolls to bear an impact load beyond the allowable range, shortening the service life.

3.4 Online use of bearing housings and bearings of the rolled mill

Workers should promptly record the usage information of the bearing housings and bearings of the rolled mill, analyze their usage in the actual production process, and replace the bearings that are severely worn or ineffective. Online operation should require standardized operation. When adjusting the tension, it should be carried out gradually, and the auxiliary adjustment speed should be controlled to avoid excessive impact force exceeding the yield limit of the material. Regularly repair the lubrication points of the rolled mill to minimize the continuous welding work on the rolled mill for a long time. At the same time, pay attention to detecting the temperature around the bearings, and report any abnormal phenomena in a timely manner and prepare for the solution. Control the rolling speed within a reasonable range. Do not roll low-temperature steel in an unreasonable low-temperature environment to ensure that the rolls can maintain an efficient operating state. On-duty workers should follow the operation specifications for work, frequently check the temperature of the rolled mill surface, and prevent the rolled mill surface temperature from being too high, which may cause the lubricating oil protection effect of the rolled mill rolls to decline. During the operation of the rolled mill, deformation may occur, and workers should also observe frequently to reduce the rolled pieces with deformation and avoid affecting the bearing housings.

3.5 Prevention and rectification of accidents

Firstly, do a good job in hardware maintenance. The spare parts should be of high quality. Analyze the usage situation of the bearings based on the actual situation. If the failed spare parts are found, they should be cleaned up promptly and the maintenance and protection of the spare parts should be done well. In the event of a production accident, it is essential to bear in mind the principle of "equipment is the foundation, operation is the key", and conduct an analysis based on the actual situation. Professional personnel should be organized to solve the problem. At the same time, training for professional staff should be strengthened to enhance the standardized and operational skills of workers, cultivate a sense of responsibility and trust, improve the production process supervision system, and make preparations for accident prevention.