Characteristics and working principle of six high mill

　　The traditional four high mill is a technology in the field of plate and strip rolling. With the increasing requirements for plate accuracy and shape, especially for the dimensional accuracy of strip, the shape control ability of the four high mill becomes very limited, and the edge thinning is also very serious. Therefore, actively developing and adopting new plate and strip rolling equipment suitable for China's national conditions was a problem to be solved at that time.

　　The six high rolling mill (HC Rolling Mill) adopts a movable intermediate roll and work roll hydraulic bending. The control of convexity and flatness is improved in free program rolling by combining roll traverse and roll bending, and the edge thinning of strip steel is reduced. This rolling mill has excellent shape and crown control ability, and does not change the shape of roll gap when no-load. The development of HC Rolling Mill has brought the shape theory and shape control technology into a new period. With the increasing demand for high quality and wide strip, large six high mill has been gradually put into research, development and application in China.
 

　　Types and characteristics of six high mill

　　1.1 type

　　At present, the HC mill with moving intermediate roll is commonly referred to as the HC mill, also known as the HCM six high mill. In the actual industrial production, the six high mill has developed a variety of models to meet the needs of different products. Its basic form is used for hot rolling mill, cold rolling mill and leveling. If an intermediate roll is added between the work roll and the backup roll of the original four high mill (HC Mill), the intermediate roll can move between the left and right axes. The flatness of the strip steel is controlled by the positive and negative hydraulic bending rolls of the work roll and the axial movement of the intermediate roll. This is the HCM six high mill. Its structure is shown in Figure 1

　　HCM six high mill

　　HCM six high mill adds intermediate roll bending device to become UCM six high mill, as shown in Figure 2:

　　UCM six high mill

　　The flatness of strip steel is controlled by the hydraulic bending of work roll and intermediate roll and the axial movement of intermediate roll, which is used for rolling wide and thin strip. This is also one of the most common forms of cold rolling equipment in China.

　　UCMW six high mill adopts the form that both the work roll and the intermediate roll can be moved, and the work roll and the intermediate roll can be bent at the same time, as shown in Figure 3. This machine can be used for super high-speed rolling.

　　UCMW six high mill

　　1.2 features

　　Compared with ordinary four high mill, HC mill has the following characteristics;

　　(1) Through the axial movement of the roll, the harmful contact parts between the accidental roll bodies of the plate width are eliminated, and the roll gap stiffness is improved:

　　(2) Because one end of the work roll is cantilever, the edge deformation of the work roll increases obviously under the roll bending force. If the requirements for the shape control capability of bending remain unchanged, a smaller bending force can be selected on the HC Rolling Mill, which improves the service life of the work roll bearing and reduces the working load of the rolling mill:

　　(3) Because it can be adjusted by roll bending force and roll axial movement, the mill has good shape control ability;

　　(4) Because it can be adjusted by roll bending force and roll axial movement, the mill has good shape control ability;

　　(5) Both work roll and backup roll can adopt cylindrical roll, which reduces the roll grinding process and saves energy consumption.

　　Therefore, the six high mill has improved its shape control force, control the edge thinning capacity of strip steel, increase the reduction and reduce the rolling time.

　　Working principle of 2 six high mill

　　The disadvantage of the four high mill is that the contact area between the work roll and the backup roll is larger than the width of the rolled strip. No matter how large the backup roll diameter is, the rolling load will increase the radius of the work roll, as shown in Figure 4.

　　Schematic diagram of hazardous area

　　For the strip shape, this is a harmful contact area, which will bring adverse conditions such as the original crown of the work roll is required, the diameter of the work roll is difficult to reduce, the roll bending can not be effectively used, and the inventory of backup work rolls increases.

　　At present, the hydraulic roll bending device has been widely used in the cold strip mill to improve the plate shape. Due to the high requirements for the thickness tolerance of cold rolled strip, in order to increase the reaction speed of the rolling mill screwdown device, the full hydraulic screwdown device is used on the cold rolling mill to ensure the thickness tolerance of the strip. For the high speed and high quality cold strip mill, the 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. It is the development direction of the transformation of the screwdown device of tandem cold rolling mill.

　　Six high rolling mill is one of the ideal advanced equipment for producing high-quality plate products at present. It can not only ensure to obtain high-quality plate and strip rolling products, but also has obvious advantages in improving productivity, talent rate and energy-saving effect, expanding the scope of application and improving the working performance of the rolling mill. The domestic large six high mill has been successfully and widely used in industrial production, and its technical level and function have reached the level of similar foreign equipment.