As the width of the products rolled by the plate and strip rolling mill gradually increases and the thickness gradually decreases, the control of plate thickness accuracy and the issue of plate shape have become increasingly prominent. The thickness deviation of the sheet and strip along the length direction is caused by the fluctuation of the rolling force and the elastic deformation of each part of the machine base. The thickness deviation of the sheet and strip along the width direction and the plate shape problem are caused by the changes in the roll shape and roll gap shape of the rolls.

The factors influencing the shape of the roller gap include:

1. Elastic bending deformation of the rolls. It causes the middle dimension of the roll gap to be larger than the edge dimension, resulting in cross-sectional convexity of the steel strip. The greater the rolling force, the more concentrated the load is in the middle of the roll, and the greater the elastic bending deformation of the roll. The larger the diameter of the roll, the better its rigidity and the smaller its elastic bending deformation.

2. Thermal expansion of the rolls. The heat converted from the deformation work of the rolled piece during rolling, as well as the heat transferred by friction and high-temperature rolled pieces, will all cause the rolls to heat up. Cooling water, cooling lubricating fluid, air and parts in contact with the rolls will also cool the rolls. Due to the inconsistent heating and cooling conditions along the length of the roll body, under the influence of various comprehensive factors, the thermal expansion in the middle of the roll is greater than that in the broken part, thereby causing thermal convexity of the roll and affecting the shape of the roll gap.

3. Wear of the rolls. The friction between the work roll and the rolled piece, as well as between the work roll and the support roll, will cause wear to the rolls. There are many factors that affect the wear of rolls. For instance, the friction between the rolls and the rolled pieces, as well as between the working rolls and the support rolls, can cause the rolls to wear out. There are many factors that affect the wear of rolls, such as the materials of the rolls and the rolled pieces, the surface hardness and finish of the rolls, the rolling pressure and the rolling speed.

4. Elastic flattening of the rolls. Elastic flattening occurs between the rolled piece and the work roll, as well as between the work roll and the support roll. The shape of the roller gap is not determined by the absolute value of the elastic flattening, but by the distribution of the flattening value along the length of the roller body. For the work rolls, if the rolling pressure is uniformly distributed along the width of the steel strip, the distribution of the elastic flattening of the work rolls in the middle of the roll body within the deformation zone is also uniform, but the flattening value at the edge of the rolled piece is smaller. The influence on the local thinning of the edge of such rolled pieces is usually not taken into account in the roll profile design. The pressure distribution between the work roll and the support roll is uneven because the contact length between them is greater than that between the rolled piece and the work roll. This makes the elastic flattening values between rollers not uniformly distributed along the length of the roller body either.

5. The original roll profile of the rolls. The original roll shapes of the rolls are different, and the shapes of the roll gaps are naturally different as well. This factor can be used to compensate for the impact caused by the above-mentioned factors.

Therefore, the smaller the ratio of the width of the steel strip to the length of the roller body and the ratio of the diameter of the working roller to the diameter of the support roller, the more obvious the unevenness of the pressure distribution between the working roller and the support roller. The distribution law of the elastic flattening value between the working roller and the support roller is consistent with the distribution law of the pressure between them.

To further optimize the plate thickness accuracy and plate shape control during the plate and strip rolling process, modern rolling mills usually adopt a variety of technical means for comprehensive regulation. Among them, the hydraulic bending roll technology and the segmented cooling technology of rolls have become the key measures to solve the problem of roll gap shape.

The hydraulic bending roll technology actively adjusts the bending degree of the rolls by applying controllable hydraulic pressure at the ends of the working rolls or support rolls, thereby compensating for the elastic deformation and thermal convex influence during the rolling process. Positive bending rolls can increase the convexity in the middle of the rolls and are suitable for offsetting the natural bending of the rolls when rolling wide plates. Negative bending rolls reduce the convexity and are suitable for narrow strip rolling or situations where the thermal convexity is too large. This dynamic adjustment method can quickly respond to changes in rolling conditions and improve the stability of the plate shape.

The segmented cooling technology for rolls regulates the temperature gradient along the length of the roll body by precisely controlling the flow and distribution of the coolant. For instance, when rolling wide plates, the cooling intensity in the middle of the roll body can be increased to suppress thermal expansion. When rolling narrow strips, edge cooling can be reduced to avoid plate shape defects caused by uneven roll surface temperature. By integrating real-time temperature monitoring with closed-loop control, this technology can effectively reduce the fluctuation of thermal convexity and enhance the stability of rolling.

In addition, modern intelligent rolling systems have also introduced online plate shape detection and adaptive control technologies. The thickness and shape data of the sheet and strip are collected in real time through laser thickness gauges, tension sensors, etc. Combined with big data analysis and machine learning algorithms, the rolling parameters, bending roll force and cooling strategy are dynamically adjusted to achieve high-precision closed-loop control. This intelligent production method can not only reduce the rate of defective products, but also adapt to more complex material and process requirements.

In the future, with the further development of rolling technology, new composite material rolls, intelligent variable convexness rolls (such as CVC, SmartCrown, etc.) and more advanced digital twin technology will further enhance the accuracy and efficiency of plate shape control, promoting the development of plate and strip rolling towards higher quality and lower energy consumption.