What is 20 roll mill?

What is 20-roll mill?

Twenty-roll reversible cold rolling mill is widely used in cold rolling fields such as stainless steel, silicon steel, alloy steel and alloy material owing to its advantages of small diameter of working rolls and large rigidity of the mill frame. Especially with the rapid development of domestic metallurgical equipment science and technology, the 20-roll reversible cold rolling mill has quietly entered the field of stainless steel production for high-precision production of pole-plate steel strips. The advantages of the 20-roll reversible cold rolling mill and the problems in production are summarized and analyzed as follows according to the current production situation.

Advantages of the first and twenty-roll reversible cold rolling mill

The advantages of the 20-roll reversible cold rolling mill are mainly manifested in the following aspects:
1. Because the working roll of the cold rolling mill is supported by the supporting roll as the medium, the roll is subject to small bending force in the width direction, so the working roll with small diameter can be used.
2. The rigidity and hardness of the 20-roll reversible cold rolling mill have been improved, and the product accuracy has been increased by about 4 times.
3. It can adapt to many kinds of alloy steel and greatly improves the rolling thinness.
4. Energy saving can be realized by reducing the total rolling force due to the reduced contact area in the deformation area.
5. It can reduce rolling pass, improve production efficiency and reduce production cost.
6. Increasing rolling tension can improve the shape and flatness of strip steel.
7. Due to volume reduction and investment cost reduction, the direct press-down design can roll thicker raw materials and improve safety performance accordingly.

II. Existing problems of 20-roll reversible cold rolling mill

Twenty-roll reversible cold rolling mill has the advantages of small diameter of working roll, large rigidity of frame, small thickness deviation of rolling plate and good shape, but at the same time, there are also corresponding problems summarized as follows:
1. It is difficult and time-consuming to handle accidents due to small opening of rolling mill and complicated adjustment operation.
2. Due to the roll system stack, there are hindrances to heat release from rolling, insufficient process lubrication and cooling effect, and hindering the improvement of rolling speed. At present, the structure and system of lubrication and cooling injection have been continuously improved to enhance the cooling effect. There are 20 reversible cold rolling mills with rolling speed up to 1000 mm in China.
3. During the rolling process, the friction power loss of the bearing of the supporting roll, the rolling power loss of the roll and the space power loss caused by the number of contacting rolls are the special formulas to achieve these unnecessary harmful power losses when rolling strips. The total power consumption of rolling is basically the same as that of four-roll rolling mill.
4. The structure of the rolling mill is complicated, and the equipment manufacturing, installation and commissioning are complicated.
5. Inevitable process defects exist in the steel coil of the 20-roll rolling mill. The reason is that when the steel coil is delivered to the coiling drum by the pinch spoke, the coil head is smoothly wrapped around the coiling shaft by opening the coil aid. The coil needs to be coiled on the head drum. When the coil is raised to support the steel coil, this part is affected by the characteristics of the equipment and needs to be coiled 15 meters before it can be fully braced. Within 15 metres of the coil beginning to be coiled in this process, serious defects unavoidable in the current process can not be eliminated by the existing process.

III. Summary

The development history of 20-roll reversible cold rolling mill at home and abroad shows that the rolling sheet follows a principle: reducing the diameter of working roll, reducing arc length of deformation zone and reducing rolling pressure. Under the same pressure condition, small roll diameter can be greatly reduced and elongation can be obtained. On the other hand, when the strip is rolled to a certain extent, the friction resistance in the deformation zone increases due to the high work hardening of the material, the elastic deformation and flattening of the roll, which results in the phenomenon that the roll cannot be stretched, especially when rolling high carbon alloy steel, stainless steel and harder steel. To improve this situation, lubricants are used in cold rolling to reduce friction resistance.