The interaction of bulk solid characteristics and surface parameters in surface or boundary friction measurements

Abstract This paper is concerned with wall or surface friction and related parameters that govern the behaviour of powders and bulk solids in contact with surfaces of handling plant such as hoppers and chutes. Various methods for measuring wall friction are reviewed and the influence of such factors as wall surface roughness, particle size distribution, moisture content and shear velocity or strain rate are examined. Particular attention is given to the characterization of surface roughness and its interaction with particle size distribution. During operation, these properties may change, the particle size becoming finer and the surface roughness changing due to wear. As a consequence, surface friction can change during plant operation.