The control of independently driven pressure feeders on crushing mills

For a long period, the speed of the pressure feeder on a mill has been a fixed ratio of the speed of the top roll because the drive has been by chain from the mill rolls or by gears on the main gear bed. In 1986, the first of a new generation of independent hydraulic drives was installed on the pressure feeder of the number one mill at Con dong Mill. Many more have been installed in the past five years. On these mills it is now possible to change the ratio of feeder speed to top roll speed almost instantaneously. This offers an extra control opportunity which has previously been unavailable. The use of this facility on first mills was discussed by Paddock and Farrell (1987). The more recent installations of pressure feeder drives have included several on bagasse mills, where the requirement to operate the milling unit itself so as to control the height of bagasse in the feed chute makes control more difficult. This paper builds on the experience of the work at Condong and looks at milling control systems that not only control milling load, but also control the height of bagasse in the feed chute. Some experimental results on the time constants associated with control are given. Results for two strategies applied to a bagasse mill fitted with an independent hydraulic drive on the pressure feeder are also reported.