THE ADVANCED SET-UP AND CONTROL-SYSTEM FOR DOFASCOS TANDEM COLD MILL

The new coupled pickle line and cold mill (CPCM) has been processing s teel since December 1991 at Dofasco Inc. in Hamilton, Ontario, Canada. This mill robs both sheet and tin plate. The work rolls for the last stand are often textured by grit blasting to roil ''matte'' finished s trip, A new computer-targeted control system was developed for the rol l speeds and gaps, specifically for matte rolling, The new set-up syst em uses Stone's model, which is more appropriate for the limited reduc tions evident with the rougher rolls, Conventional automatic gauge con trol (AGC) systems using thickness measurements after the last stand a re limited in performance by the effect of long transport delays, Thes e limitations are particularly critical during mill acceleration and d eceleration, The use of a thickness gauge before the stand with matte rolls allows the development of AGC systems using shorter control loop s for final gauge control, The AGC system uses a Smith predictor for t ransport lag, (phase shift), compensation, The combination of the shor ter AGC loop and the Smith predictor allows higher gains to be used in the control system. This set-up and control system has contributed to Dofasco's position as a market leader in thickness performance.