Using soil shear tests to investigate mill feeding

Mill feeding is an integral part of the 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. The rolls must be rough enough to provide the grip. This paper describes the tests used to determine the shear behaviour of bagasse and the required roughness on mill rolls. The importance of the test geometry and procedure is emphasised. Results from various investigations are presented. It was concluded that the shear strength of prepared cane can be represented by the Mohr-Coulomb failure criterion used for soils. An arced surface as currently used on rolls and a sandpaper surface with 1 mm particles were rough enough to grip prepared cane at most of the pressures present in a milling unit.