Flying Gauge Control for a Specified Section Including a Welding Point in a Cold Strip Mill

In a continuous cold strip mill, the succeeding strip and the preceding strip are welded together and then rolled continuously. The section near the welding point is often processed as scrap due to the constraints of the downstream manufacturing processes. Therefore, thickness reduction is desired as a means of reducing the scrap weight. To this end, this paper presents a new flying gauge change (FGC) controller design which achieves thickness change in the section including the welding point. Because of the short length of the target section, two thickness change points can exist simultaneously in the mill. In the conventional FGC, the set values of the roll gap and the roll speed are calculated without considering the positions of the two thickness change points in the mill. However, this can possibly result in a poor roll speed set value and cause large strip tension deviations. The proposed scheme utilizes the transition pattern of the positions of the two thickness change points in the mill during FGC to calculate the set values of the roll gap and the roll speed. Thickness change with small strip tension deviations is achieved by applying these set values to the control systems of the rolling mill according to the positions of the two thickness change points. The validity of this approach was verified by computer simulations and experiments with a real process. Application of this technology has improved cold strip yield.