1. Incoming materials The incoming materials have serious quality defects, such as waste edge pressing, overflow edge, under-pickling, over-pickling, uneven thickness, plate-shaped edge waves and middle waves, etc., which may cause belt breakage.
2. Equipment failure Electrical, control system failure or hydraulic system failure. The common ones are tension fluctuation, tension disappearance, hydraulic system, emulsion system shutdown, etc.
3. Operation failure The belt breakage caused by the operation accident is more common. The deviation of the strip and the defects of incoming materials were not detected and taken measures in time; the selection of the pass plan was unreasonable, the deformation of the pass was too large, the rolling pressure was large, and the shape of the plate was difficult to control; the tension before and after the pass was too large and the strip was broken. ; The thickness fluctuates somewhere in the previous pass, and the current pass has not been adjusted and decelerated in time.
4. Belt breakage caused by roll burst
After the belt is broken, stop immediately, pull out the strip steel in the frame and pull out the middle roll (backup roll) of the work roll to check whether the roll is stuck and damaged, and the roll should be replaced if damaged. And clean up the broken belt debris in the archway. Check the main drive shaft of the rolling mill and the safety pin for breakage, and replace it in time if the breakage is found. The rolling speed of the first coil after changing the rolls should not be too fast, and the surface quality of the strip should be carefully checked.
Because the flow rate of the emulsion during high-speed rolling is too small, the thermal deformation generated cannot be taken away in time, so that the temperature of the roll rises, the emulsion oil film on the surface of the strip is broken, and the surface of the strip is scratched. In addition, the roll slips at high speed, and the strip and the roll produce relative friction, which will also cause thermal scratches. Thermal scratches have a lighter scratch depth on the surface of the strip, and basically have no feel.
1. Increase the flow rate of the emulsion.
2. Lower the temperature of the emulsion.
3. There are many reasons for roll slippage at high speed, whether the input of roll diameter is correct. Whether the current difference between the upper and lower work rolls is too large. Whether the roughness of the intermediate roll backup roll is consistent. Whether the pressing force is too small, etc.
The working time of the work roll is too long, the surface roughness of the roll is reduced, and the deformation of the pass is too large. Make the roll slip on the surface of the strip, which is easy to cause hard scratches. Generally, hard scratches appear when the deformation of the strip is large. For example, 1 or 2 passes. Hard scratches have more obvious scratches and deeper scratches.
When the roughness of the roll is low, the roll is not replaced in time. The first and second pass hard scratches are controlled as follows. 1. First of all, increase the tension of the strip outlet and reduce the tension of the strip inlet. 2. When starting the rolling mill, the pressing thickness should not be too thin, but should be pressed slowly to the set thickness. 3. Do not directly reduce the speed when reducing the speed, so as to avoid thickness fluctuations. Excessive deformation in places with thin thickness fluctuations may cause scratches. 4. If there are slippery stripes on the surface of the strip during rolling, change the thickness of the outlet in time to reduce the amount of deformation. Change the roll after this pass.