Mill-balance Control Technique for Tandem Cold Mill

Abstract

This paper describes a mill balance control (MBC) for a tandem cold mill (TCM) with an automatic gagecontrol system (AGC).
The stand exit gages are controlled by the AGC, but the motor currents and the rolling forces of stands cannot be controlled.
When the setup control is not proper or when the incoming strip has variations in gage and hardness, the distribution pattern of the motor currents and the rolling forces (mill balance) sometimes becomes inappropriate. When a motor current exceeds its rated value, usually all roll speeds are reduced manually, and the productivity decreases. When a rolling force varies to a great extent, strip shape defects may occur.
The MBC operates the stand exit gages except for the finish gage and the interstand tensions, and it controls the distribution pattern of the motor currents and the rolling forces while guaranteeing the finish gage accuracy.
The MBC controller is designed based on the ILQ design method and is applied to an actual process.
Experimental results show that desired mill balance is achieved and the finish gage accuracy is maintained.