Particle attrition in small clearances

Abstract

Attrition is commonly found in the clearances of equipment where a mechanical device moves relative to a wall. Particles are trapped and broken in these regions, hence promoting attrition. This work concerns a cell where a blade rotates parallel to a wall. A cone cell design allowed for various gap sizes, particle velocities and blade tip speeds. The breakage rate of particles changed dramatically with gap size. Breakage commenced at a gap size close to a half particle diameter but had a definite minimum between one and one-and-half particle diameters. Little breakage was experienced if the gap much exceeded two particle diameters. When the other conditions of cell are changed, firstly the blade speed and secondly the flow rate of particles through the cell, the effect of gap size on breakage pattern is not changed. The product size distribution can be quite complex and is not simply related to the gap size. Segregation and a changed packing structure may each influence the breakage of a mixture.