This paper mainly describes the answers to possible problems in steel rolling
work roll, intermediate roll and support roll thermal scratches , pre-compression
Related product：Rolling mill rolls
1. How to solve the indentation on the surface of the strip?
- If there are indentations during the rolling process, stop the machine in time and do not continue rolling.
- Observe the position of the indentation and observe the period length of the indentation to determine which roller the indentation appears on.
- Check the work roll, intermediate roll and support roll. Whether there is any meat loss from the roll.
- It is found that the indentation position is too short, check the oil removal roller.
2. What are the reasons for strip breakage?
- Incoming materials The incoming materials have serious quality defects, such as waste edge pressing, overflowing edges, under-pickling, over-pickling, uneven thickness, plate-shaped edge waves and intermediate waves, etc., which may cause belt breakage.
- Equipment failure Electricity, control system failure or hydraulic system failure. The common ones are tension fluctuation, tension loss, hydraulic system, emulsion system shutdown and so on.
- Operation failures Broken belts caused by operation accidents are more common. Strip deviation and incoming material defects have not been discovered and taken timely; the pass plan is unreasonably selected, the deformation of the pass is too large, the rolling pressure is large, and the shape of the plate is difficult to control; the tension before and after the pass will be too large and the strip will be broken ; The thickness fluctuates somewhere in the last pass, and this pass has not been adjusted and decelerated in time.
- Broken belt caused by roll burst
3. What to do after the tape is broken?
After the belt is broken, stop immediately, pull out the strip steel in the frame and pull out the middle roll (support roll) of the work roll to check whether the roll is sticky or damaged. If it is damaged, replace the roll. And clean up the broken belt fragments in the archway. Check the main drive shaft and safety pin of the rolling mill for fractures, and replace them in time if they are found to be fractured. The rolling speed of the first coil after the roll is replaced should not be too fast, and the surface quality of the strip should be carefully checked.
4. How are thermal scratches caused?
Because the emulsion flow rate is too small during high-speed rolling, the thermal deformation generated cannot be taken away in time, which causes the temperature of the roll to rise, the emulsion oil film on the surface of the strip is broken, and the surface of the strip is scratched. In addition, when the rolls are slipping at high speeds, relative friction between the strip and the rolls will occur, and thermal scratches will also occur. Thermal scratches have a lighter scratch depth on the surface of the strip, and basically have no feel.
5. How to control thermal scratches?
- Increase the flow of emulsion.
- Lower the temperature of the emulsion.
- 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 middle roller support roller is consistent. Whether the suppressing force is too small, etc.
6. How are hard scratches caused?
The work roll is used for 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 in the strip with large deformation. For example 1, 2 passes. Hard scratches The scratches are more obvious, and the depth of the scratches is deeper.
7. How to control hard scratches in 1 and 2 passes?
When the roughness of the roll is low, the roll is not replaced in time. Control the hard scratches of the first and second passes as follows.
- First, increase the strip outlet tension and reduce the strip inlet tension.
- When starting the rolling mill, do not press down too thinly, but slowly press down to the set thickness.
- Do not directly reduce the speed when reducing the speed to avoid thickness fluctuations. Excessive deformation of the thin thickness fluctuations may cause scratches.
- During rolling, the strip steel surface appears slippery horizontal lines, and the outlet thickness should be changed in time to reduce the amount of deformation. Change the roll after this pass.
8. What is the role of pre-compression?
- Eliminate roll pressure.
- Let the displayed rolling force be the force actually rolled onto the strip
- It can make the roll gap display actualized.
- The gap value of the two sides of the roll can be basically the same, and the gap difference between the rolls can be reduced.
9. What is the significance of the pre-compression step?
- After the roll is changed, it will be hit from the roll changing state to the rolling state and after unloading reset, it will hit the open roll gap state. When doing pre-pressing, the roll gap is open. Because the pre-compression is completed, the roll seam will be automatically opened to 20 cm. Therefore, it must be opened to the roll gap state to do the pre-pressing.
- The first step is to select the pre-pressing screen on the AGC control computer.
The second step is when the roll gap position reaches 20 cm. Select the rolling force to zero. Eliminate roll pressure and residual rolling force. In this way, the rolling force can be the actual rolling force during the pre-pressing, and the gap between the two sides of the roll is not much different.
The third step is to input the pre-compression by the rolling force. Generally, input a small rolling force such as 200T first. The reason is that the speed on both sides of the cylinder is different when used as a pre-compression. When the rolling force input is large, it may cause the input rolling force to be pressed to one side first. If the roll is pressed out of the pit, input a small rolling force first to level the position of the cylinder.
The fourth step is to input the set value of the roll gap, which is the value of the closed roll gap during normal rolling.
Start pressing in the fifth step. When the pressing rolling force reaches the set rolling force of 200T, return to the first step and re-input a large pressing force, so that the deformation of the archway and the deformation force of the roll can be removed.
The sixth step is pressed to the position of constant pressure. When the input rolling force value is pressed at the constant pressure position, the emulsion is started and the rolling speed is 200 meters.
This can make the volume-side rolling force a little more realistic. Make each deformation force uniform. Rotate the mill for half a minute.
The seventh step is to stop when the rolling forces on both sides are the same, continue to the next step to clear the positions of the cylinders on both sides.
The eighth step ends the pre-compression.