Improved Threading of the Tandem Cold Mill Using Advanced Control Techniques with Virtual Rolling

The threading of the tandem cold metal rolling mill is a significant function in the control of this process. During the threading process it is important to reduce the excursions in the strip thicknesses and tensions to contribute to the stability of rolling, to avoid reducing strip tension so as to preclude the throwing of a loop of strip at the entry of a mill stand, and to successfully reduce the effects of any drop in the strip speed when the head of the strip enters a mill stand. Additionally, in most cases it is desired by the operational personnel to control the individual mill stand speeds such that, as the head of the strip moves between two adjacent stands, its speed between the two stands is held at the strip speed at the exit of the last stand just before acceleration to run speed. Moreover, it is desired that disturbances in the thickness and the resistance to deformation in the incoming strip are successfully handled by the controller. In this paper we propose a method of improved control for this process that considers all of these requirements. The effectiveness of this method is shown by simulation using data from operating mills.