Numerical and experimental analysis of strip cross-directional control and flatness prediction for UCM cold rolling mill

In cold rolling of strip, flatness defects typically appear in strip when subjected to heterogeneous thickness reductions across the width of strip. As crown and flatness are interrelated, the crown ratio variation is used to qualitatively predict flatness defect mode. An investigation on the shape prediction and control of strip is presented in this paper. Taking these purposes into account, a three-dimensional finite element model for the Universal Crown Control mill (UCM mill) and strip containing different basic crown patterns is developed, and applied to two questions, namely prediction of flatness defect position and analysis of actuator control efficiency. The results indicate that the approach of crown ratio factor only gives the prediction for the edge and center waves, but it can't distinguish quarter-wave. Therefore, an improved approach based on the varying curve of crown ratio, which can give the location of the flatness defect in more detail, is proposed. Moreover, combined with the study concerning control feature and capacity on thickness profile and flatness of strip, an original solution for obtaining the actuator efficiency factor is implemented. Finally, the curve of actuator efficiency factor obtained by the model is tested online in a flatness closed-loop control system.