Answers to questions arising in the production of six-high reversing mills
1. How to control the rolling force?
The rolling force is large, the shape of the plate is difficult to control, the temperature of the roll is uneven, and the bearing capacity of the roll is reduced. Newly replaced work rolls generally use a large tension to reduce the rolling force, which can be reduced after rolling 2-3 rolls. Relatively speaking, the rolling force is too small and the thickness is difficult to control. The resistance of the tension roll can be reduced and the rolling force can be increased relatively.
2. How to control thickness fluctuation?
During the rolling process, if the thickness fluctuates greatly, first reduce the speed and reduce the tension difference. If the thickness fluctuates greatly, the monitoring can be canceled. For thickness fluctuations within 20ym, the speed should be below 500 meters, and the fluctuations above 20ym and the speed below 300 meters.
3. How is the cracked edge caused?
1. The roughness of the edge of the roll is low.
2. There is a color difference on the edge of the strip.
3. The total deformation is too high, and the reduction in the subsequent passes is too large, which may cause edge cracks after rolling.
4. The raw materials are bulging and cracking.
5. Pickling and trimming are not good.
4. How to control the cracked edge and the broken belt?
When the cracked edge is serious, reduce the bending force of the work roll, reduce the rolling speed, and reduce the exit tension. The tension on the edge of the strip is reduced, and the cracked edge will not be pulled off. If it is found that the edge of the strip is bulging, replace the work roll in time.
5. During the rolling process, what is the reason for the deviation of the belt outline? how to deal with it
During the rolling process, the deviation of the strip generally occurs when the strip is worn or the tail is flicked. The main reasons for the deviation of the strip are as follows:
1. Due to the incoming material, the shape of the incoming material is not good, and there are serious side waves or wrong sides, so that the centering device of the decoiler cannot be adjusted accurately and timely, resulting in the deviation of the strip. The measures to be taken are to roll The speed should not be too high, adjust the position of the pressing side in time or stop in time.
2. Operation reasons Due to the unreasonable adjustment of the swing under the operation pressure, the strip steel runs out of alignment.
3. Electrical reasons Due to the sudden reduction or disappearance of the coiler tension during the rolling process, the strip runs off and the strip is broken.
4. Due to the serious taper of the roll after grinding, the pressing is not accurate, which increases the difficulty of operating the pressing and swinging during rolling. The light one will produce serious side waves and cause plate shape defects, and the heavy one will cause deviation. Broken belt.
5. The failure of the unwinding centering device, the pollution of the lamp tube or the receiving device, etc., make the deviation device fail and cause deviation one after another.
6. How to control the head and tail rollers of the main controller, front and rear of the machine?
1. When rolling the lead and the tail, the master controller should increase the outlet tension by about 5KN in time. When the rolling force decreases after starting the car, adjust the outlet tension to the number required by the process. Due to the low speed of the lead and the tail, the rolling force is large, the thickness is difficult to control, and the bending roll cannot keep up with the easy-to-squeeze roll.
2. Before and after the machine, the rolling force and plate shape should be observed in time. When the rolling force is large, increase the bending roll in time. Observe the plate type and adjust the roll gap adjustment in time to avoid the deviation of the roll.
7. What are the precautions for the rollers when there is no pressure bias?
Generally, when there is no pressure bias, the attention should be paid to: whether the deformation of the pass is too large, whether the rolling force is too large, whether the bending force is too small, and whether there is a loss of tension when starting the car.
8. What should I do if there is a sudden chromatic aberration on the surface of the strip during the rolling process?
During the rolling process, the master controller observes the front and rear display screens of the machine at any time. If it is found that there is a sudden chromatic aberration on the surface of the strip during rolling, the speed should be reduced to 100-200 meters in time, and the front and rear of the machine should be notified to observe whether the surface of the strip is abnormal. Find a problem and stop it in time to solve it.
9. What equipment and solutions should be checked for the color difference of the whole roll on the surface of the strip?
1. First, check whether there are small pits where there is color difference on the surface of the strip steel. If there are pits, it is likely that the color difference is caused by the low hardness of the work roll. Solution Replace the work roll.
2. Check the intermediate roller and the support roller for contusion and falling meat. Replace intermediate rolls, backup rolls or sanding.
3. Check whether the emulsion nozzle is blocked. Clean the nozzle.
4. Check whether the traverse position of the intermediate roller is in the correct position. Traverse the correct position.
5. Check whether the pickling raw materials have color difference in the same position. The reaction is given to the pickling quality staff and adjusted in time.
10. How to solve the indentation on the surface of the strip?
1. If indentation occurs during the rolling process, stop the machine in time and do not continue rolling.
2. Observe the indentation position and observe the cycle length of the indentation to judge which roller the indentation appears on.
3. Check the work rolls, intermediate rolls and backup rolls. Is there any meat that explodes and rolls off?
4. If it is found that the indentation position is too short, check the degreasing roller.
11. What are the reasons for the strip broken?
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. Strip deviation and incoming material defects were not discovered and taken measures in time; the selection of the pass plan was unreasonable, the deformation of the pass was too large, resulting in high rolling pressure and difficult to control the shape of the strip; ; The thickness fluctuated somewhere in the previous pass, and the current pass was not adjusted and decelerated in time.
4. Belt breakage caused by roll burst
12. How to deal with the broken belt?
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 if the breakage is found, it should be replaced in time. After changing the rolls, the rolling speed of a coil of steel should not be too fast, and the surface quality of the strip should be carefully checked.
13. How is thermal scratch caused?
Because the flow rate of the emulsion during high-speed rolling is too small, the thermal deformation generated cannot be taken away in time, which increases the temperature of the rolls and ruptures the emulsion oil film on the surface of the strip, resulting in scratches on the surface of the strip. 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.
14. How to control thermal scratches?
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.
15. How are hard scratches caused?
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.
16. How to control the 1st and 2nd pass hard 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, increase the tension at the outlet of the strip and reduce the tension at the inlet of the strip.
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 reduce the speed directly 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.
17. What is the function of pre-pressing?
1. Eliminate roll pressure.
2. Let the displayed rolling force be the force actually rolled onto the strip
3. It can make the roll gap display practical.
4. The roll gap value on both sides can be basically the same, and the roll gap difference value can be reduced.
18. What is the significance of the step of pre-pressing?
1. When the roll is changed, it is switched from the roll change state to the rolling state and after the unloading is reset, it is switched to the open roll gap state. When doing pre-pressing, it is in the state of open roll gap. Because the pre-pressing will automatically open the roll gap to 20 cm after the completion of the pre-pressing. Therefore, it must be opened to the state of the roll gap before pre-pressing can be done. 2. Select the pre-pressing screen on the AGC control computer.
The second step is when the opening roll gap position reaches 20 cm. Select the rolling force reset. Eliminate roll pressure and residual rolling force. In this way, the rolling force can be the actual rolling force when the pre-pressing is performed, and the difference between the roll gaps on both sides can be small.
The third step is to input the pre-compression rolling force. Generally, a small rolling force such as 200T is input first. The reason is that the speed on both sides of the cylinder is different when it is used as a preload. When the rolling force input is large, it may be caused, and the input rolling force will be pressed to one side first. Cause the roller to press out of the pit, first input a small rolling force and level the position of the oil cylinder.
The fourth step is to input the roll gap setting value, that is, the value of the closed roll gap during normal rolling.
The fifth step is to start pressing. When the pressing rolling force reaches the set rolling force of 200T, return to the original step and input a large pressing force, which can remove the deformation of the arch and the deformation force of the roll.
The sixth step is pressed to the position of constant pressure. When the constant pressure position is pressed to the input rolling force value, the emulsion is started, and the rolling speed of 200 meters is started. This makes the rolling force on the energy side practical. Homogenize the individual deformation forces. The rolling mill can be rotated for half a minute.
The seventh step is to stop when the rolling force on both sides is the same, and continue to the next step to clear the positions of the oil cylinders on both sides.
The eighth step ends the pre-pressing.
19. Why do pre-pressing should be done every time the roller is changed?
Because the pre-pressing has a memory function, for example: the diameter of the work roll is 300, and the roll gap is 20 cm when the pre-pressing is completed. When the roll is changed, the diameter of the new roll is 290. Because the pre-pressing is based on the memory of the work roll with a diameter of 300, after changing the roll with a diameter of 290, the opening of the roll gap is 30 cm, but the roll gap is displayed as 20 cm. . The roll gap display is not accurate, so pre-pressing must be done. If the roll diameter is the same, pre-pressing may not be performed.
20. How to calculate the elevation of the rolling line?
Calculation method of rolling line elevation (large roll diameter of upper backup roll - actual roll diameter of upper backup roll)/2+ (large roll diameter of upper intermediate roll - actual roll diameter of upper intermediate roll) + (large roll diameter of upper work roll - upper working roll) Roll actual roll diameter) + original value = actual value of rolling line elevation
21. How to calculate the lateral movement of the upper and lower intermediate rollers?
(length of intermediate roll - strip width - chamfering length of intermediate roll)/2 = number of intermediate rolls traversing 22. What are the main shape defects of cold-rolled strip during rolling?
The main types of defects in the steel strip during rolling are (one-sided wave, two-sided wave, middle wave, two small side waves, one-sided small side wave, two rib waves and single rib waves)
22. Under what circumstances does a unilateral wave occur? How to control a one-sided wave?
1. The roll gap is not identified. The lower rolling force on both sides is different, and the side with the larger force is prone to unilateral waves. Control method: adjust the roll gap adjustment and find out the roll gap difference.
2. One-sided waves are also prone to occur in wrong rolls and deviations. Control method: adjust roll gap adjustment in time according to strip deviation or wrong roll position.
23. Under what circumstances will there be waves on both sides? How to control a one-sided wave?
1. When the working bending force is small, waves on both sides are easy to appear. Control method: increase the bending force of the work roll.
2. When the rolling force of the head and tail is large, it is easy to appear waves on both sides. Control method: increase the bending force. When necessary, the bending force is not enough. Increase the tension to cancel the thickness monitoring, and manually adjust the rolling force within the range where the bending force is sufficient.
24. Under what circumstances does an intermediate wave appear? How to control the middle wave?
1. When the bending roll of the work roll is large, the middle wave is easy to appear. Control method: reduce the bending force of the work roll.
2. When the rolling force is small, intermediate waves are prone to occur. Control method: reduce the bending force. There is still an intermediate wave when the bending force is reduced to zero. Reduced tension rolls are assisted. The rolling force is relatively large. Can also control intermediate waves.
25. Under what circumstances will there be small side waves on both sides? How to control small side waves?
1. When rolling thin materials, strip steel work hardening is prone to waves on both sides. Because the rolling force is large in the case of work hardening of the rolled thin material, the stress on the roll reaches the limit. The roll is deformed into a concave shape, the two sides of the roll meet together, the edge of the strip is thinned, and there are waves on both sides. Control method: increase the bending force of the work roll. Adjust the amount of process distortion.
2. The hardness of the roll is low, and small side waves on both sides are prone to occur when rolling thin materials. Control method: replace the work roll.
26. Under what circumstances does a unilateral small side wave occur? How to control unilateral small side waves?
1. When rolling thin materials, the reason for the occurrence of single small edge waves is that the roll gap is not very accurate, and it does not appear when rolling thick materials. Control method: adjust the roll gap adjustment or increase the unilateral bending force.
2. The hardness of the roll is uneven, and the hardness of one side is low. Control method: replace the work roll.
27. Under what circumstances does the second rib wave appear? How to control the occurrence of two rib waves?
1. Two rib waves are prone to occur when the roll shape is not good. Control method: replace the work roll
2. In the case of large rolling force, double rib waves are prone to occur. The rolling force is large and the temperature of the roll is uneven. The second rib and the middle part are heated more. Double rib waves are prone to occur. Control method: increase the flow rate of the emulsion, reduce the temperature of the emulsion, and check whether the nozzle of the emulsion is blocked.
3. The chromatic aberration of the second rib is also prone to the second rib wave. The appearance of chromatic aberration also means that the place with chromatic aberration and the place without chromatic aberration are not uniformly heated, and two ribs will appear on the edge of the layout with and without chromatic aberration. Control method: Check the equipment, rollers, nozzles and raw materials, find out the cause and eliminate the color difference.
28. Under what circumstances does a single rib wave appear? Is there a single rib wave solved like this?
1. The roll shape of the roll is not good, and the single rib position or the convex and concave are prone to single rib waves. Control method: replace the work roll. (The method of adjusting the unilateral rib wave when the roll shape cannot be controlled when a unilateral double rib wave occurs: For example, if a single rib wave occurs on the transmission side, the control method: reduce the bending roll force on the rotating side, increase the bending roll force on the operating side, Press down on the bias and the operating side. This can also reduce single rib waves.
2. If the emulsion nozzle is blocked, unilateral two-rib waves are prone to occur. Control method: Clean the emulsion nozzle.
29. How to calculate the tension of the finished product pass?
Outlet thickness × strip width × specific tension = total outlet tension 1450 specific tension is 0.65KN 1200 specific tension is 0.6KN 1050 specific tension is 0.7 KN.
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