Interstand tension control system and method for tandem rolling mill

Abstract

An improved system and method for controlling the interstand tension in a tandem rolling mill by computing the interstand tension on the basis of detected process data, computing the difference or error between the computed interstand tension and the desired value, and controlling the speed of the rolling stand drive motors so as to cancel the error. A shear is generally disposed upstream of the tandem rolling mill to shear the leading and trailing ends of a workpiece. When the shear is cutting the trailing end of the workpiece, a backward tension is produced between the shear and the first rolling stand of the tandem rolling mill, resulting in abrupt variations of the process data used for the computation of the interstand tension. The system operation will become unstable when such abruptly varying process data are used to compute the interstand tension for the purpose of the motor speed control. To avoid the instability of system operation, the process data detected immediately before the operation of the shear are held in a filter, and the interstand tension is computed on the basis of the process data thus held in the filter. The error between the computed interstand tension and the desired value is computed to provide the interstand tension control signal which is applied to the motor speed control unit.