Project ended 1988, report dated September 1989
Executive Summary
The attrition of particles of known properties has been studied In a number of pieces of testing equipment. The novel and most flexible of these, a cone cell, has permitted the breakage of particles in gaps of known width to be studied in a rational manner for the first time. It is found that a close-sized feed can suffer high breakage rates at two gap openings, with a minimum rate between these at an intermediate gap size. Negligible breakage rates are found for low, less than one half a particle diameter, and for high gap widths, say exceeding three particle diameters. For mixed particle feeds, segregation of material into the gap is of crucial significance. These findings are of broad relevance to a wide range of solids processing equipment.
Studies on an annular cell, used to simulate breakage in a failure zone within the bulk of a material, showed that the Gwyn kinetics applied over three orders of magnitude of stress, It was shown by use of a well characterised and specially prepared extrudate that there was a shift from bodily failure at high stresses to surface abrasion at low stresses. These extrudates could also be formed into particles of different shapes; it was found that one of the Gwyn parameters was independent of shape and size whereas the other was dependent upon both.
The potential to modify the annular cell to establish links with the results of the cone cell was demonstrated but much remains to be done to cement these. Nonetheless, a complete understanding of attrition due to mechanical means now seems to be within our grasp. An aim of future work is to form estimates of product size distribution from a knowledge of the breakage of single particles under a number of loading conditions and an appreciation of packing theory.