Preliminary observations of the effect of plate roughness and particle size on the determination of wall friction

The determination of wall friction angle for bulk materials is vital in applications such as; bin and hopper design, conveyor transfer chutes, rail wagon unloading and any other use where bulk materials flow over a surface. It is generally accepted that the rougher the wall surface, the higher the wall friction angle. This paper will present an investigation of wall samples with various surface finishes using a translational shear tester (based on the design by Jenike). Five aluminium plates; one with a 'smooth' surface and the other four with milled grooves of varying spacing and depth to produce regular 'roughness' on the surface have been utilised. Glass beads of three size distributions have been used as the test products for this study to investigate the effect of particle size and plate roughness on the determination of wall friction. The results of this work have shown that it is not always the case that the 'rougher' wall surface generates the highest wall friction angle but there is also a dependence on the size of the particles as well.