Research on the Grinding Energy Density in a Jet Mill

Abstract

Raw materials are used in many industrial technologies. The raw material frequently has to be prepared as an intermediate with an appropriate particle size distribution, which requires the use of grinding. In grinding processes, energy consumption is a very important profitability criterion for the applied particular size reduction technology. The paper describes the comminution process that takes place in the jet mill using a modified form of the thermodynamic theory of grinding. In this theory, new material characteristics have been added: the surface and volumetric density of grinding energy. The thermodynamic theory is a combination of the classical Kick's theory and the modified form of Rittinger's theory. The tested physical magnitudes are a measure of the energy consumption of the grinding process. They describe the energy that must be provided in the grinding process to overcome interactions between particles related to the volume and surface of the material. Knowledge of these magnitudes is necessary to model thermomechanical phenomena in the solid state. The paper presents the results of research on comminution in a jet mill, on the basis of which the values of the tested material magnitudes were determined. It is graphically shown how the values of the tested magnitudes depend on the grain size of the ground samples.

Keywords: comminution; grinding energy; jet mill.

Figure 1

Scheme for determining the elastic limit stress values and the surface density of the grinding energy.

Figure 2

Diagram of the jet mill: (1)—grinding chamber, (2)—acceleration tube, (3)—nozzle and (4)—suction chamber.

Figure 3

Value of the surface density of the grinding energy as a function of the feed size (average grain size).

Figure 4

Value of the actual elastic limit stress as a function of the feed size (average grain size).