DEM-CFD study with a breakage model for elucidating the grinding mechanism in cutter-type disk mill

Grinding process is a unit operation with various purposes, such as milling, dispersion, and surface modification, and is an indispensable process in various industrial fields, such as food, pharmaceuticals, and cosmetics. Solid feed materials for milling have different physical properties such as strength, hardness, and particle size. Therefore, various types of mills are used depending on the material and the purpose of the milling. A cutter-type disk mill consists of disk-shaped rotating blades and fixed blades, and the rotating blades cause shearing force to the raw material. Therefore, they are used to crush solid materials such as resins, coffee beans, and rice, which are difficult to crush with a simple impact. Cutter-type disk mills are considered particularly effective for grinding plastics. However, it is necessary to optimize the geometry and operating conditions of the mill. This study aimed to evaluate the grinding performance of different blade geometries and particle physical properties in the cutter-type disk mill and to identify the melting factors of resins in the mill. To calculate the effect of the blade geometry and particle properties, the discrete element method (DEM) coupled with the computational fluid dynamics (CFD) and a breakage model was employed to simulate plastic particle breakage. Simulations were performed under conditions where the geometry of the grinding blade and particle physical properties were different. When using the model with angled blades, particle distribution had specific peak position and particles were intensively grinded in this region. On the other hand, the model with radial blades did not have a distribution peak and resulted in strong force and rapid grinding. In addition, it was confirmed that materials which likely to melt in the mill changes depend on the blade shape. Our results show that it is possible to evaluate the grinding performance under the different equipment conditions and with different particle properties, as well as the particle behavior inside the equipment, and that it is effective in improving the process.