RENEWAL OF AUTOMATIC GAUGE CONTROL-SYSTEM FOR A COLD TANDEM MILL WITHELECTRIC SCREWDOWNS

This paper describes renewal of automatic gage control (AGC) system fo r a cold tandem mill with electric screwdowns. Although gage control m ethods using high responsive actuators were researched, there is few r esearch on the renewal of an old mill with low response actuators. We studied the way of improving gage accuracy without reconstructing actu ators, from the viewpoint of saving cost. Gage response to manipulatio n of the actuators depends on the frequency characteristics of the act uators and the rolling process, and the effect of AGC was restricted b y these frequency characteristics. We eliminated the frequency depende ncy of the gage response by inserting a dynamic compensator with rever se frequency characteristics in the control loop of AGC, and expanded the controllable frequency range of the feedforward AGC to a higher fr equency. Moreover, in order to reduce the tension change caused by the gage control and to stabilize rolling force during acceleration and d eceleration, we developed new tension control and rolling force contro l manipulating reduction in thickness. The combination of these contro ls and the feedforward AGC reduced gage deviation, keeping stable roll ing. The application of this AGC system to a cold tandem mill with ele ctric screwdowns resulted in a great improvement in gage accuracy, and the accuracy has almost matched that of a newly constructed mill.