Recently, the discrete element method (DEM) has been widely applied to investigate the in uence of operating and design parameters on grinding performances. However, while most studies investigated the effects of such parameters on the neness of milling products, the relationship between them and the size dispersion of milling products has not been elucidated yet. In this study, we investigated the in uence that the direction of the agitator shaft has on grinding performance in a media stirring mill. First, we proved by milling experiments that the media stirring mill with the horizontal direction of the agitator shaft can provide better grinding performances. Then, we further elucidated this experimental evidence by applying DEM simulations to a media stirring milling process in a vertical and a horizontal stirred mill. According to the simulations, in the vertical shaft con guration, the motion of the grinding media in the lower section through the vertical direction was inhibited by a too low velocity. On the other hand, the grinding media in the horizontal stirred mill moved more uniformly but with a lower collision energy. Furthermore, the grinding media in the low sections actively mixed with the grinding media in the upper sections, thereby resulting in a more uniform energy transfer and in a better grinding process. Accordingly, this study demonstrated that not only the collision energy but also the uniformity of the movement of the medium particles should be evaluated in order to investigate the grinding performance in a media stirred mill by DEM simulation.

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This study examined the fine grinding of limestone using a bead mill and a circular stirred media mill. Fine grinding characteristics of the bead mill using poly-sized grinding media with a volume mean diameter of 0.5 mm were compared with those observed by mono-sized grinding media with the same mean diameter. The median diameter of the ground particles and the mass of milled products below 1μ m can be expressed as functions of the number of rotor revolutions, the mass of the grinding media, and/or the mass of the sample; these relationships were observed for both the poly-sized and mono-sized grinding media. This study showed that the median diameter of particles milled with poly-sized grinding media was more than 10% smaller than that obtained with mono-sized grinding media, and the mass of milled particles below 1μ m produced with the poly-sized media was more than 10% greater than that milled using mono-sized media. The use of the poly-sized grinding media in the bead mill led to improvement in productivity of fine particles of limestone.Key Words : Bead mill, poly-sized grinding media, fine grinding, limestone OriginalReceived January 10, 2014 Accepted for Publication April 14, 2014 ©2014 Soc. Mater. Eng. Resour. Japan Figure 1 Grinding vessel of the bead mill.

Media stirred mills have been used in various fields to efficiently produce fine products. The scale-up of such mills is required to increase efficiencies and applications for industrial processes. Despite such circumstances, established scale-up laws remain unavailable, and scale-up has been conducted empirically. This study aims to propose essential requirements for the scale-up of a media stirred mill according to experiments and discrete element method (DEM) simulations. The experimental results were evaluated qualitatively by using particle size distributions of ground products and fitted using grinding kinetic theory as a quantitative evaluation. The grinding performance in the laboratory model was equivalent to the results using the scaled-up model (SU-model) with the modified Froude number, regardless of the rotation speed. DEM simulations identified the main factor that contributed to the agreement. The average collision energy of the media particles was almost identical. To set optimal conditions to fulfill this core requirement, the SU-model operation conditions need to follow the modified Froude number, and the intervals of each arm should be fixed to the same distance. These insights encourage the application of scaled-up media stirred mills.