PRESSURE FEEDER TORQUE PREDICTIONS USING CONVENTIONAL MILLING THEORY AND DIRECT SHEAR TEST DATA

The importance of roll roughness and feeding for milling performance is well established. In the past 10 years, tests have been reported on the measurement of the coefficient of friction of prepared cane and bagasse on rough surfaces similar to the arced surfaces on roll grooves, and on sandpaper surfaces that are similar in particle size to proposed long life surfaces. It was found that the surfaces were rough enough to grip and shear bagasse internally, and that the measured values of the coefficient of friction were significantly higher than those reported previously. The direct shear test method that was used also measured the pressure-volume relationship of the cane. Existing mill load and torque theory can be used to calculate roll loads and torques from the measured coefficients of friction and pressure-volume relationship. The theory is applied in this paper together with the direct shear test measurements to calculate the roll loads and torques in a typical factory pressure feeder. A milling theory described in the literature was used in combination with direct shear test measurements to predict roll torques for a pressure feeder. The magnitudes of the roll torque predictions spanned those that had been measured, being different by a maximum of approximately 20%. The results gave some confidence that similar calculations can be used in the future to link laboratory measurements to milling situations. The calculation method used is a great deal less complicated than the use of finite element methods. It is believed that the method provides an intermediate step that can be used, in combination with more complex methods, to gain a better understanding of the loads and stresses present in the milling process, particularly in the pressure feeder.