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, fMat. and Wm,min, are derived theoretically. fMat. characterises the resistance of particulate material against fracture during impact comminution. Wm,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.