Common form & Reason for roll failure
Roll, such as work roll, back up roll etc, are important consumable parts that determine the efficiency and quality of rolling mills. Common forms and reasons for roll failure are as follows:
The roll cracks is mainly caused by excessive local pressure and rapid cooling or heating. If the emulsion nozzle on the rolling mill is blocked, it will cause poor local cooling conditions of the roll, and will cause cracks. In winter, due to the lower temperature, cracks are more likely to occur than in summer.
If the cracks continue to develop, they will form scaling. Little scaling can be re-ground and continue to be used, while it need to be scrapped for serious scaling.
Scratching is mainly caused by the weld seam of the steel strip or other debris entering the rolling mill, and cause the roll surface to be scratched into different shapes of pits. Roll with scratches must be replaced. When the quality of the steel strip weld is poor, the roll should be lifted and then pressed to prevent scratching when passing through the weld seam.
Sticking occurs when steel strip fracture pieces, wave folding, and edge breakage occur during cold rolling, and the high pressure causes instant high temperature, making it easy for the steel strip to adhere to the rolling mill, causing small area damage to the rolling mill surface. After grinding, the roll surface cracks can be eliminated and continue to be used, but its service life is significantly reduced, and scaling accidents are prone to occur in future use.
Tightening is mainly caused by excessive pressing force, causing heavy skin or slight folding of the steel strip, and causing heavy skin when the steel strip deviates. When it is seriously tightened, It will cause sticking and the steel strip is cracked. When the tightening is not serious, there are pressure marks on both the steel strip and the roll.
The main reasons for roll breaking are excessive rolling pressure, internal defects in the roll (non-metallic inclusions, bubbles, etc.), and uneven roll temperature which produce a stress field.