Abstract
To investigate the mechanical energy applying to the particles in a grinding process using a planetary ball mill, the impact energy of particles was estimated by simulating the behavior of the particles and grinding balls using the discrete element method (DEM) under different conditions of the size and number of particles, corresponding to their variations during milling. As the impact energy contributing to the particle breakage, we focused on the particle impact energy generated at particle-to-grinding ball/wall and particle-to-particle collisions. The particle size and the number of particles affected the level of particle impact energy at a single collision and the number of collisions of particles, respectively, resulting in an increase of the total impact energy of particles with decreasing particle size and increasing number of particles. The result suggests that milling conditions such as the size of grinding balls should be adjusted appropriately based on the variation of the size and number of particles so that the particles can receive large amounts of the impact energy during milling.
Highlights
Dry powder grinding is an important unit operation in many industries, such as mining, food, fine chemical and pharmaceutical, ranging from coarse mineral ore to submicrometer-sized fine drug powder
In ultrafine dry grinding processes, planetary ball mills have often been employed since the particles receive remarkably high impact energy at collisions with the grinding balls and the mill pot wall
At all Db/Dp values, the most of the impact energy generated at the particle-to-ball/wall collisions exceeded a threshold energy of the particle breakage (Capece et al, 2014), determined by the material and size of the particles
Summary
Dry powder grinding is an important unit operation in many industries, such as mining, food, fine chemical and pharmaceutical, ranging from coarse mineral ore to submicrometer-sized fine drug powder. Ultrafine dry grinding processes with high energy milling (Chen et al, 2015; Guzzo et al, 2015; Kleiv and Thornhill, 2007; Guzzo et al, 2019), which can produce fine particles with improved properties and/or enhanced performance, have attracted much attention. In ultrafine dry grinding processes, planetary ball mills have often been employed since the particles receive remarkably high impact energy at collisions with the grinding balls and the mill pot wall. The impact energy can vary depending strongly on the milling conditions and lead to breakage of particles, resulting in decreasing the particle size and increasing the number of particles. The impact energy alters the produced particle properties, such as size distribution, specific surface area and microscopic structure. For producing the particles with controlled properties, the impact energy must be appropriately adjusted
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