Modelling of Grinding in an Air Classifier Mill Based on a Fundamental Material Function

Abstract

An approach to quantifying the impact grinding performance of different materials is presented. Based on a dimensional analysis and on fracture mechanical considerations, two material parameters, f_Mat. and W_m,min, are derived theoretically. f_Mat. characterises the resistance of particulate material against fracture during impact comminution. W_m,min gives the mass-specific energy which a particle can absorb without fracture. Using this approach, various materials over a wide size range, e.g. different polymers, crystalline substances, glass and limestone, can be characterised quantitatively. The derived material parameters are applied to the systematic modelling of grinding in impact mills. A population balance model is presented and the results of the simulation for an air classifier mill are shown. The developed model permits a clear separation of the influence of material properties, mill-specific features and operating conditions, thus enabling a deeper understanding of the impact grinding process.