Investigation of the Fragmentation Process of Clods in a Rod Mill Developed for Research Use

We developed a planetary-type rod mill that can improve the comminution working efficiency, prevent the generation of soil dust, and make it easy to clean the used jars. Clods are broken by this device into fine-grained soil particles with sizes of less than 2 mm in diameter within 2 min. One objective of this study is to evaluate the performance of the mill by observing the fragmentation process of the clods. The process is visualized experimentally via a high-speed camera installed on a rotating jar of the device. The breakage of the clods in the rod mill is considered morphologically according to the crushing patterns obtained by previous studies. The rod moves together with the clods in the jar. Therefore, violent collisions are not thought to be a major reason for the breakage of the clods. The surfaces of the clods are first scraped and then appear to become fragile. However, if there are no rods in the jar, the clods never break into small pieces. Therefore, it is likely that collisions with the rod trigger the catastrophic fragmentation of the clods into small pieces. This suggests that the design of the device could be modified to improve its performance in the near future.