The rolling system is the core of the 20 high mill production process system. It mainly depends on the specifications and properties of raw materials, as well as the specifications and shape requirements of finished products. In addition, when formulating the rolling system, it is also necessary to consider improving product quality on the premise of giving full play to the equipment capabilities. The rolling system is divided into a reduction system, a tension system, a roll use system, etc.;
1 Reduction system
The reduction system includes the setting of rolling passes, reduction amount (deformation rate), and rolling schedule. It is of great significance to formulate a reasonable reduction scheme to improve rolling efficiency, and product quality and reduce consumption. The reduction system is mainly determined according to the structure of the rolling mill, the power of the main motor, the rolling force, and the hardness of the roll, and it also varies with the type of rolled steel, the specification and size of the strip, and the performance requirements of the product after annealing.
(1) Total reduction rate
According to the work-hardening characteristics of carbon steel, the total reduction ratio of each rolling pass usually does not exceed 90%: but in order to reduce the procurement cost of raw materials, many steel companies often use thicker raw materials, and the total reduction ratio is even 95%. above. However, too high a total reduction rate often leads to excessive refinement of material grains. After annealing, the properties of the strip are reduced. Therefore, this type of strip is mainly used for making products such as panels and corrugated boards that do not require a high plate shape.
(2) Pass reduction rate
Increasing the reduction rate of each pass can reduce the rolling passes of each rolling pass, thereby improving the rolling efficiency. However, due to the small diameter of the work rolls of the 20-high mill, too high pass deformation will cause the problem of biting difficulties. This will cause the strip to slip between the rolls, so the reduction rate of the pass is determined. Especially the first few passes The limit of the maximum coiling tension should be taken into account when reducing the reduction rate of the times. To ensure that there is no slippage during rolling. In addition, too few rolling passes and too high a pass reduction rate will also cause the problem of poor shape. . Therefore, from the perspective of improving the shape of the plate, it is better to use multi-pass small deformation rolling. Therefore, the reduction system should be continuously improved in combination with the actual production effect when formulating the reduction system.
2 Tension system
The tension during cold rolling mainly has a great influence on the rolling force, forward slippage, and strip shape: when formulating the tension system, due to the large reduction in the first few passes, in order to ensure that the rolling does not Slip. Under the premise of single stop tension <0.5/ (yield strength of the material after each pass hardening), a large tension should be used as much as possible. And the front tension should be greater than the back tension in the last few passes. When the thickness of the strip When is below 0.5 mm, the back tension should be equal to or slightly greater than the front tension. If the coiler has the function of switching between high and low gears, the coiler should be switched to a low gear in the first pass to ensure a large coiling tension; and then adjusted to a high gear in the next few passes to improve Rolling speed. Guaranteed output.
3. Rolling use system
The rolling used in the cold rolling mill must have high hardness, strength, and high wear resistance. At the same time, it must also have a certain degree of toughness: the material of the rolls used in the rolling mill is high chromium steel, and the materials of the rolls in different parts are also different:
In order to ensure the surface quality of cold-rolled products, there are also strict requirements on the surface of the work rolls. Not only must there be a certain roughness, but also there must be no defects visible to the naked eye (cracks, pits, indentations, grinding lines, spiral lines, etc. “The rolling and excavation must be carefully ground and inspected before use: during the rolling process, frequent inspections should be carried out, and the rolls should be replaced immediately if any problems are found. In normal production, the work rolls need to be changed once for each rolled roll. Arranged in the final pass to improve the surface quality of the strip. If there are many rolling passes, the roll should be changed in time depending on the surface condition of the strip. That is, the work roll should be replaced several times in one rolling process.
4. Roll matching
The 20 high mill has a large number of rolls due to the complex roll system. In order to ensure the normal operation of the rolling mill and produce high-quality strips, there are strict requirements for the rolls loaded into the rolling mill.
(1) Roller matching principle
First of all, it should be ensured that there is a certain opening when the pressing cylinder is fully “lifted”, generally about 5 mm. Even if the work roll is installed after the belt is threaded, it should be ensured that the stick gap when the pressing cylinder is completely “pressed down” can be closed, and there is still a reduction margin of 1 mm to compensate for the elastic deformation of the roll system. Secondly, it should be ensured that the distance between each intermediate roller in the roll system is greater than 0.2 mm, and the distance between the two intermediate drive rollers and the idler roller is greater than 0.2 mm. Avoid movement closed loop inside the roller system. In addition, the angle between each of the first middle roller and the second middle roller (see the red roller in Figure 7) and the two rollers in contact with the upper and lower should be less than 180°. That is to ensure that the red roller is inside the roller system. To avoid Under the action of the pressure of the roll system, the above-mentioned intermediate roll is extruded out of the roll system to ensure its stability of the roll system.
(2) Specific requirements for ingredients
Although there are many rolls in the 20-high rolling mill, the four driving rolls are centralized transmissions. In addition, the backing roll is composed of multiple backing bearings. This determines that there are strict regulations on the diameter of the roll when matching the rolls. The specific requirements are as follows: 1. The diameter difference of the lower work roll should be controlled within 600 nm; the diameter difference between the left and right rolls of the first intermediate roll should be controlled within 30 Miu; the diameter difference between the upper and lower rolls should be controlled within 350 pans; for the four transmissions of the second intermediate roll Roller, it is required that the rotation of the left and right rolls be controlled within 5um. The diameter of the upper and lower rolls is controlled within 100um; the diameter difference of the coaxial backing bearing is controlled within 100um. The diameter difference of adjacent bearings is controlled within 30um. The diameter difference of the non-coaxial backing bearing is controlled within 200um. Only by strictly following the above requirements for roll matching can the service life of the rolling system be extended while improving product quality.
3.6 Roll shape
The roll that needs to be designed for the 20 high mill is the middle roll, and the other rolls are all flat rolls. In addition, when rolling wide strips, the upper two intermediate rolls can be designed as slightly convex rolls to reduce the adjustment amount of ASU, make the wear of the backing bearing more uniform, and improve the life of the backing bearing.
