Advantages and Existing Problems of 20-high Reversing Cold Rolling Mill

The 20-high reversible cold rolling mill has the advantages of a small diameter of work rolls and high rigidity of rolling mill frame and has been widely used in the fields of cold rolling of stainless steel, silicon steel, alloy steel and alloy materials. Especially with the rapid development of metallurgical equipment technology, the 20-high reversing cold rolling mill has quietly entered the field of stainless steel production for high-precision production of extremely thin steel strips.


1. Advantages of twenty-high reversing cold rolling mill

1) Since the work rolls of the 20 hi rolling mill is supported by the backup rolls as the medium, the rolls are subjected to a small bending force in the width direction, so work rolls with small diameters can be used.

2) The rigidity and hardness of the 20-high reversing cold rolling mill have been improved, and the product precision has been increased by about 4 times.

3) It can adapt to various alloy steel varieties, and the rolling thinness is greatly improved.

4) Since the contact area of the deformation zone is reduced, the total rolling force is reduced, which can save energy.

5) It can reduce rolling passes, improve production efficiency and reduce production costs.

6) The increased rolling tension can improve the shape and flatness of the strip.

7) Due to the reduced volume, the investment cost is reduced, and the direct pressing design is adopted, which can roll thicker raw materials, and the safety performance is also improved accordingly.


2. Problems existing in the 20 hi cold rolling mill

The 20-high reversing cold rolling mill has the advantages of a small diameter of work rolls, high frame rigidity, small thickness deviation of rolled plates, and good plate shape, but there are also corresponding problems summarized as follows:

1) The opening of the rolling mill is small, the adjustment operation is complicated, and it is difficult and time-consuming to deal with accidents.

2) Due to the stack of rolls, there are obstacles to the dissipation of rolling heat, insufficient process lubrication and cooling effects, and obstacles to the increase of rolling speed. At present, the lubrication and cooling injection structure and system have been continuously improved to enhance the cooling effect. There is a 20-high reversing cold rolling mill with a rolling speed of 1000m/min in China.

3) During the rolling process, the frictional power loss of the backup roll bearing, the roll rolling power loss, and the space power loss caused by a large number of contact rolls, the special formula is to achieve these unnecessary harmful power losses when rolling thin strips, The total power consumption of rolling is basically the same as that of a four-high mill.

4) The structure of the rolling mill is complicated, and the equipment manufacturing, installation, and debugging are complicated.

5) There are unavoidable technical defects in the steel coil of the 20-high rolling mill. The reason is that when the steel coil is delivered to the coiling drum through the pinch spoke, the coiler is opened to make the coil head smoothly wound on the coiling shaft, The steel coil needs to be wound on the head reel. When the reel is stretched up to tighten the steel coil, this part is affected by the characteristics of the equipment. It needs to be coiled for 15 meters before it can be fully stretched. In this process, the unavoidable serious defects of the current process will be produced within 15 meters of the steel coil starting to be coiled, and this part of the defects cannot be eliminated by the existing process.


3. Summary

The development history of the 20 hi cold rolling mill shows that rolling thin parts follows a principle: reduce the diameter of the work roll, reduce the arc length of the deformation zone, and reduce the rolling pressure. Under the same pressure condition, a small roll diameter can be obtained with Large reduction and elongation. But on the other hand, when the strip is rolled to a certain extent, due to the high work hardening of the material, the elastic deformation and flattening of the roll will cause the friction resistance in the deformation area to increase, and the rolled piece cannot be stretched. This phenomenon especially occurs When rolling high carbon alloy steel, stainless steel, and harder steel grades. Therefore, it is necessary to increase the number of rolling and annealing in production. In order to improve this situation, various lubricants are used in cold rolling to reduce frictional resistance.


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