Research on Plate Type Control in Rolling Process of Aluminum and Aluminum Alloy Strips

This paper discusses the effects of casting process roll type, rolling pressure, tension, cold rolling reduction, cooling strength, and positive and negative bending rolls on the shape of the plate, and reasonably matches the process parameters to obtain a good shape control.

The shape of the plate is one of the important quality indicators of the plate and strip products. Therefore, the profile control in the production process is a crucial issue. With the birth of the HC six-high rolling mill and the VC-convexity rolling mill and the development of the shape control technology, a high degree of automatic control of the plate shape has been achieved, and the accuracy of the plate shape has been improved. However, the investment of these rolling mills is relatively large. For ordinary rolling mills, reasonable adjustments must be made to the process parameters to achieve effective control. The technical personnel of our company have gradually summed up a series of effective methods through many years of actual production experience. The following mainly discusses several factors that control the shape of the cast blank in the Ф380/Ф1050×1800 four-roll irreversible rolling mill.

A number of factors that affect the shape of cast slab

1. Effect of cast roll type. The continuous cooling water in the casting roll removes the heat that is released when the aluminum liquid solidifies. At present, most of the domestic continuous casting and rolling mills use open cooling circulation systems. The water quality does not reach the softening requirements or mechanical impurities in the water may block the cooling channels of the roller core, resulting in uneven cooling strength on the cross section of the casting roller, which affects the casting. Rolling blanks horizontal difference (as shown in Figure 1). Therefore, in the production of casting and rolling, while guaranteeing the accuracy of assembly of the casting roll and accuracy of grinding, it is necessary to adopt a closed softened cooling water system as far as possible so as to avoid clogging of the roll core and affecting the plate shape.

2. The matching gap between the casting roll sleeve and the roll core is not uniform. The low precision of machining or the core corrosion during use will cause the gap to be uneven, so that the cooling is not uniform. In this case, the core of the welding roller must be removed.

3. Casting roller bearing clearance should be moderate, generally controlled in the 0.3mm - 0.35mm, if the gap is too small, affecting the bearing life, if the gap is too large will affect the cast blank blank longitudinal difference.

4. The mouth opening and lip thickness of the casting nozzle should be as uniform as possible. For horizontal type continuous casting and rolling mills, the pressure force of the pressure plate should be uniform when installing the casting nozzle

5. Maintain a certain amount of prestress before the riser to eliminate the elastic deformation of the arch. The setting of prestress is generally two-thirds of the rated rolling pressure.

6. Drive side and operating side rolling pressures. Through a certain range of pressure adjustment, the horizontal thickness difference of the cast slab can be controlled within the specified range, so as to ensure the favorable control of the plate shape. For different rolling mills and different grades of products, the rolling pressure is proportional to the cast slab. The thickness effects are different.

7. Tension. The proper tension can flatten the tension of the plate to a certain extent, reduce sticking and improve the plate shape.

II. Several factors that affect the cold rolled plate shape

1. The blank shape must meet the requirements of use. The cross-sectional shape of the blank is the main condition for obtaining a good plate shape, and the specific control has been described previously.

2. The influence of the original crown of the work roll. The selection of the primary crown of the work roll depends on a combination of factors such as the length of the roll, the stiffness, the state of the alloy, the width of the blank, the amount of reduction, and the thermal crown during rolling. The principle is to use as little or as little hydraulic roll as possible. The system can achieve a good plate shape. Therefore, a comprehensive consideration should be taken when selecting the primary crown of the work roll.

3. Positive and negative bending rollers. The role of the bending roller is to change the shape of the roll gap. When the positive bending is adopted, the deflection of the work roll will be reduced, which is equivalent to the increase of the original crown of the work roll; when the negative bending is adopted, the deflection of the work roll will increase, which is equivalent to a decrease. The original crown of the work roll (as shown in Figure 2). Under normal circumstances, the open passes due to the greater absolute reduction, the work roll bending deformation, and the lower rolling speed, the work roll thermal expansion is small, then you should use a larger positive bend, followed by the pass As the speed increases, the thermal crown of the work roll increases, and the positive bend should be gradually reduced until the proper negative bend is applied.

4. The effect of tension on the plate shape. According to rolling theory, we know that tension can reduce the rolling force, which can reduce the load on the main motor. At the same time, the size of the tension also affects the plate shape, because the tension changes the rolling pressure, affects the elastic bending of the roller, and thus changes the shape of the roller gap. In addition, the tension causes the metal to extend evenly in the transverse direction. Therefore, a proper plate shape can be obtained by properly adjusting the tension during the production process.

5. The effect of the amount of reduction on the plate shape. In order to maximize productivity, large reductions should be used as much as possible under the conditions of alloy plasticity and equipment capability. Generally, the absolute amount of first pass reduction is greater in order to fully utilize the plasticity of the alloy and the subsequent pass absolute pressure. Under the appropriate amount of reduction, according to the equipment structure, installation level and billet conditions, the distribution of the total consideration, the greater the reduction, the greater the roll bending deformation, the shape of the roll gap will change, and pay attention to the positive and negative bending roll Appropriate adjustments to facilitate the control of the plate shape.

6. Effect of rolling oil cooling. The heat generated by the friction between the rolling stock and the roll and the deformation of the rolling stock causes the temperature of the roll to rise continuously, and the processing rate is large, and the rolling speed becomes higher. In order to maintain continuous and stable production, this part of heat must be taken away in time, and rolling oil cooling is commonly used in cold rolling production. However, since the heating and cooling conditions of the roller are not uniform along the length of the roller body, different waves may be generated if the intensity and flow rate of the rolling oil at different parts of the roller body are not adjusted in time. In the production process, when the middle wave appears, the middle part can be appropriately enlarged or the cooling amount at both ends can be increased; when both sides of the wave appear, the ends can be appropriately increased or the cooling amount in the middle part can be reduced; when the second wave occurs The amount of cooling in the middle portion of the roll can be appropriately reduced or the amount of cooling in the two-rib portion can be increased. In this way, the shape of the control plate can be achieved by adjusting the distribution of the rolling oil in different parts of the roll.

7. Intermediate passes eliminate internal stresses in the rolling stock to control the plate shape. If the thickness of the cross-section of the blank is not uniform, the longitudinal extension of the rolling stock in the width direction during the rolling process will not be uniform and internal stress will occur. The metal in the extended part is forced and the metal in the smaller part is forced to pull. When the additional part of the extended part exceeds the critical pressure, different wave phenomena will be formed. If the inner stress is eliminated through the intermediate annealing, It will make the plate shape to a certain degree of control, but this will inevitably increase the energy consumption. Therefore, this method is generally not desirable in the production process.

Three conclusions

The shape of the plate depends on whether or not the strips extend in the width direction. This condition is determined by the uniformity of the cross-sectional thickness of the blank prior to rolling and the shape of the roll or actual roll gap opening. In the production process, we must first control the shape of the cast blank, and in the cold rolling process, we must reasonably match the original crown, reduction, positive and negative bending rolls, rolling speed, tension and cooling strength of the work roll according to the conditions of the equipment. And other process parameters.