The control of crushing mills with five independently driven rollers

Victoria mill began installing mills with independently driven rollers in 1994. In 1998, the factory had one mill with a drive on the pressure feeder and a drive on the mill, one mill with two drives on the mill and another on the pressure feeder, and three mills with a drive on each of the five main rollers, the underfeed roller being driven by chain. The systems used to control these mills have steadily evolved. It was found that the torques on individual rollers were rarely 'constant' and all rollers required individual controls to work each drive to its specification. This paper describes the evolution of the control system from that used on conventional crushing mills to the system now being used on mills where all the rollers are independently driven. There are strategies in the system to control overloads on pressure feeder rollers and to control torques on each roller. The drives used can control torques down to very low speeds and this has been used to good advantage in controlling final bagasse moistures during start-ups and gaps.