Study of thickness control of strip head section using mathematical simulation methods
Abstract
The authors participated in the modernization of the automatic strip thickness control system of OJSC “Magnitogorsk Iron and Steel Works” 2000 hot rolling mill (OJSC “MMK”). The article offers a brief description of the implemented automatic strip thickness control system developed on the basis of hydraulic screwdown mechanisms. Industrial trials found significant thickness deviation of up to 10% in the strip head section. As a result the length of strip head section with thickness deviation can achieve 40–50 m after the last finishing rolling stand of the mill. The authors offer a new way of strip head thickness control by means of roll gap increase before the strip grip and its further decrease to the required gauge by hydraulic screwdown adjustment during rolling. They also studied the algorithm of roll gap control and factors influencing its adjustment. The research group developed mathematical model of the electromechanical system “stand electric drive – hydraulic screwdown mechanism” taking into account the interrelation of their drives through the rolled metal. The mathematical model of the stand electric drive is developed in the system of two-region speed control. The hydraulic screwdown mechanism can be described by linearized differential equations of fluid flow rate, servo valve for small coordinate increment and forces relationship in the rolling stand. The model consists of a system of differential equations describing the rolled strip as a control object and mathematical description of automatic screwdown mechanism control. The validity of the developed mathematical model was also proved. The authors studied dynamic modes for various parameters of roll gap control and determined the optimum control parameters providing the minimum thickness deviation of the strip head section. The results of the first strips rolling proved that the developed method is quite effective and can be recommended for advanced automatic strip thickness control.
