Analysis and control strategy of bending force saturation for HC tandem cold mill

The work roll bending force of the last stand of the four stands 6-Hi HC tandem cold rolling mill is usually in saturation state when the brightwork roll is used in the last stand. This production phenomenon leads to the lack of the ability to control the strip shape, and then the shape defects are difficult to eliminate or further reduce. In the meantime, these restrict the continuous improvement of the shape quality of the cold-rolled strip. Therefore, the crown data of some hot-rolled coils were collected, and then its distribution was computed. Combined with the distribution characteristics of the work roll bending force of the first three stands, the relationship between the hot-rolled strip crown and the shape of the loaded roll gap and its impact on the work roll bending force was analyzed. Meanwhile, the influence of the online adjustment method to reduce the work roll bending force by using the negative displacement of intermediate roll on the surface quality of strip was also analyzed. On these bases, a control strategy of using a multi-section positive crown work roll was proposed to solve the saturation of the work roll bending force of the last stand. With the help of analyzing the influence of work roll profile parameters on the strip shape, the optimized parameters of sixth-order polynomial work roll were finally obtained through several online crown work roll rolling tests. In addition, the test results also showed that using five sections of positive crown work roll in the last stand can increase the adjustment ability of the work roll bending and reduce the negative displacement of the intermediate roll. This phenomenon can effectively solve the problem of the saturation of the work roll bending force of the last stand and improve the quality of the strip shape’s quality.