The traditional four-high mill is a technology in the field of strip rolling. With the increasing demand for shape accuracy, especially for strip size accuracy, the shape control ability of four-high mill becomes very limited and the edge thinning is also very serious. Therefore, it was a problem to be solved at that time to actively develop and adopt new rolling equipment suitable for China's national conditions.
Six-high rolling mill (HC rolling mill) adopts movable intermediate roll and working roll for hydraulic roll bending. The combination of roll lateral movement and roll bending improves the control of crown and flatness of steel plate in free program rolling, and reduces the thinning of strip edge. This mill has excellent flatness and crown control ability, and does not change the roll gap shape when it is empty. The development of HC mill brings the flatness theory and flatness control technology into a new era. With the increasing demand for high-quality wide strip steel, large six-high rolling mill has been gradually put into research and development and application in China.
2 Types and characteristics of six-high rolling mill
2. 1? type
? At present, the HC mill, which is usually called intermediate roll moving, is also called HCM six-high mill. In the actual industrial production, in order to meet the needs of different products, a variety of models have been developed for the six-high mill. Its basic form is used in hot rolling mill, cold rolling mill and flat rolling mill. For example, an intermediate roll is added between the work roll and the backup roll of the original four-high rolling mill (HC rolling mill), which can move left and right, and the flatness of strip steel can be controlled by the positive and negative hydraulic bending of the work roll and the axial movement of the intermediate roll. This is the HCM six-high mill, and its structure is shown in Figure 1.
HCM six-high mill
HCM six-high mill is a UCM six-high mill with an intermediate roll bending device, as shown in Figure 2:
UCM six-high mill
? The flatness of strip steel is controlled by the hydraulic bending roll of work roll and intermediate roll and the axial movement of intermediate roll, which is used to roll wide and thin strip steel. This is also one of the most widely used forms of cold rolling equipment in China.
? On the other hand, the UCMW six-high mill adopts the form that both the work roll and the intermediate roll can move, and both the work roll and the intermediate roll are curved, as shown in Figure 3. This machine can be used for rolling in super universities.
UCMW six-high mill
? 2.2 characteristics
? Compared with ordinary four-high mill, HC mill has the following characteristics:
? (1) Through the axial movement of the rollers, the harmful contact parts between rollers with unexpected plate width are eliminated, and the stiffness of the roller gap is improved;
? (2) Because one end of the work roll is cantilever, the deformation of the roll edge of the work roll is obviously increased under the action of roll bending force. If the requirement of shape control ability of bending roll remains unchanged, HC rolling mill can choose smaller bending force, which can improve the service life of work roll bearing and reduce the working load of rolling mill.
(3) Because it can be adjusted by the bending force and the axial movement of the roll, the rolling mill has good flatness control ability;
(4) Because it can be adjusted by the bending force and the axial movement of the roll, the rolling mill has good flatness control ability;
(5) Cylindrical rollers can be used for both the working roller and the backup roller, which reduces the roller grinding process and saves energy consumption.
Therefore, the six-high rolling mill has been improved in shape control, edge thinning control, increasing reduction and reducing rolling.
Working principle of six-high rolling mill
? The disadvantage of four-high rolling mill is that the contact area between work roll and backup roll is larger than the width of rolled strip. Regardless of the diameter of the backup roll, the rolling load will increase the radius of the work roll, as shown in Figure 4.
Schematic diagram of harmful area
For flatness, this is a harmful contact zone, which will bring some disadvantages, such as the original crown of the work roll, the difficulty in reducing the diameter of the work roll, the ineffectiveness of the bending roll, and the increase of the spare work roll inventory.
At present, hydraulic roll bending device has been widely used in cold strip mill to improve the shape. Due to the high requirement of thickness tolerance of cold rolled strip, in order to improve the reaction speed of rolling mill screwdown device, the cold rolling mill adopts automatic control device of strip thickness of full hydraulic screwdown device to ensure the thickness tolerance of strip. For high speed and high quality strip cold rolling mill, computer control is realized. As one of the main actuators of modern AGC system, hydraulic transmission is used instead of mechanical transmission, which greatly improves the response speed and is the development direction of the screw-down device reform of cold tandem rolling mill.
Six-high rolling mill is one of the ideal advanced equipment for producing high-quality plate products at present, which can not only ensure high-quality plate and strip products, but also have obvious advantages in improving productivity, success rate and energy-saving effect, expanding application scope and improving the working performance of rolling mill. Domestic large six-high rolling mill has been successfully widely used in industrial production, and its technical level and function have reached the level of similar equipment abroad.