Attrition is the unintentional breakage of particles during processing and handling. Comminution is the wilfully induced breakage, intended for size reduction of particles. Attrition is a problem that is common in many particle processing industries as it results in a deviation from desired product size, shape and mechanical properties. Another detrimental aspect of attrition is the generation of fine debris or dust, which can be problematic as it becomes airborne or adheres to process vessels. Attrition is common in detergent, pharmaceutical, agricultural and many other processing industries, as a result of impact, crushing or shearing events occurring throughout the manufacturing processes.
The extent of particle breakage is dependent on the strength of particles and the magnitude and loading direction(s) of the stresses they are exposed to. Due to the inherent distribution of strength, size and shape within a particle sample, and the difficulty in establishing the stresses occurring within a bed, no mechanistic models of bulk particle breakage exist. Consequently, empirical or predictive approaches are commonly applied to establish breakage rates. Our work has recently shown that by analysing the prevailing stresses in an agitated bed using DEM and incorporating an empirical, experimentally-determined breakage function an excellent prediction of particle breakage within the bed is achievable. This approach could be applied to any system where breakage occurs due to shear deformation.
Our work has also shown that breakage of particles by impacting rigid surfaces can be rapidly determined by a few impact experiments. We have shown the volume of material removed from semi-brittle particles in the chipping regime is proportional to the particle size, density, hardness, the square of the velocity and inversely proportional to the fracture toughness. If these properties are known then a few simple tests can determine the proportionality factor and describe the impact breakage, otherwise a wider range of tests can determine this.
Our research group has a number of devices for measuring particle breakage: