A soil shear test to investigate feeding at the pressure feeder

Mill feeding is an integral part of th'e crushing process during which cane JUIce is separated from the fibrous cell material in which it is stored. For good feeding of prepared cane or bagasse between a pair of rolls, the roll surface needs to grip the material and the material must be strong enough to prevent internal shear. Previous investigations have presented aspects of shear behaviour at compactions that span most of the range present in a milling unit. However, the shear behaviour of prepared cane and bagasse at the low compactions present at the bottom of the feed chute, the underfeed roll and the pressure feeder, is poorly understood. At these locations, the stiffness of the material is small. As the material moves and changes direction from the bottom of the feed chute past the underfeed roll and towards the pressure feeder nip, it undergoes large compression and shear deformations. This paper describes a test geometry specifically developed to investigate shear behaviour of prepared cane at low compactions and presents results on the shear behaviour of prepared cane at the compactions present at the pressure feeder. A surface with a large number of small (1 mm diameter) rough particles has been identified as being not quite rough enough to fully grip and shear prepared cane at low pressures but still provides a high level of grip. Good repeatability of a modified direct shear test method has been confirmed for prepared cane at low compactions. The results arc then presented in a manner more familiar to milling technologists, as coefficients of friction. The measured coefficients of friction at low pressures are significantly higher than those reported previously in the literature. If feed pressures can be increased by the adoption of a particular surface, then it is possible that mill capacity can be increased.