Roll Bearing Maintenance

　　Roll bearings need to be periodically removed from the rolling mill for inspection and maintenance to improve the service life of the roller bearings. The frequency of bearing maintenance should be adjusted according to the operation of the rolling mill, mainly based on experience. The usual maintenance frequency is once every three months under full load operation, most rolling mills once every six months, and light rolling mills once every 12 months. After the first 1000 hours of operation, the roller bearings should be disassembled and inspected. During operation, it is necessary to clean the bearings and check the seals. If necessary, the seals should be completely replaced. If no abnormalities are found, the interval between secondary inspections can be extended.

　　The general steps for roll bearing maintenance are: 1. Track and record the location of the bearings in the rolling mill. It is recommended to use a special record card for roller bearing maintenance services. Also note that special lifting methods and tools are required when removing bearings from the bearing seat or inspecting bearings. 2. Clean the bearings. During the cleaning process, all scales, water, residual lubricants, and any other dirt that can cause serious wear and tear on the bearings should be removed. 3. Inspect the bearings, including visual inspection and minor repairs. Pay attention to inspecting and repairing the bearing seat, and reinstall the bearings into the bearing seat as needed. 4. Lubricate the bearings. Existing common rolling mills are characterized by large rolling force and high rolling speed, requiring the lubricant to have excellent viscosity-temperature performance, oxidation stability, rust prevention, and wear resistance. Therefore, lubricants with better performance should be selected to lubricate and maintain the roll bearings.

　　Common Roll Failure Modes and Causes

　　1. Cracks. Cracks are mainly caused by excessive local pressure and rapid heating and cooling of the rolls. On the rolling mill, if the emulsion nozzle is blocked, resulting in poor local cooling conditions of the rolls, cracks will occur. Because the temperature is lower in winter, it is easier to crack than in summer.

　　2. Scaling. If the cracks continue to develop, it will form blocky or flaky spalling. Light scaling can be re-ground and reused, while severe scaling should be scrapped.

　　3. Pitting. Pitting is mainly caused by the welding seam or other foreign matter of the strip entering the rolling mill, leaving pits of different shapes on the surface of the rolls. Usually, the grooved rolls need to be replaced. When the quality of the strip weld is poor, the rolling operation should be lifted and pressed down when passing through the weld to prevent scratches.

　　4. Roll sticking. Roll sticking, also known as sticking, is caused by broken pieces, wavy folds, and broken edges during cold rolling. Under high pressure and instantaneous high temperature, it is easy to form bonding between the steel strip and the rolls, causing small-area damage to the rolls. After grinding to eliminate surface cracks, the roller can still be used, but the service life is significantly reduced, and scaling accidents are prone to occur in later use.

　　5. Roll pinching. This is mainly caused by excessive reduction, resulting in double thickness or slight folding of the strip and strip deviation, resulting in double thickness. When the roll is severely pinched, the roll will be stuck, and the strip will crack. When the roll pinching is slight, there are pinch marks on both the strip and the roll.

　　6. Fracture. Roll The main causes of fracture are overpressure (i.e., excessive rolling pressure), internal defects in the rolls, and stress fields caused by uneven roll temperature.