Hiroshi Mio

Effects of rotational direction and rotation-to-revolution speed ratio in planetary ball milling

Abstract The rotational direction of a pot in a planetary ball mill and its speed ratio against revolution of a disk were studied in terms of their effects on the specific impact energy of balls calculated from the simulation on the basis of the Discrete Element Method (DEM) and structural change of talc during milling. The specific impact energy of balls is measured as a significantly large value, and the structure of talc is transferred into an amorphous state quickly when the mill pot is rotated in the counter direction against the revolution. In both rotation–revolution relationships, the specific impact energy increases with an increase in the rotation-to-revolution speed ratio in the initial stage and then falls around the critical speed ratio, which can be calculated by the balance equation based on the centrifugal forces acting on a ball due to the combination of the rotation and revolution. The highest value in the specific impact energy of balls during milling can be achieved effectively around this critical speed. This critical speed would, therefore, be a key condition in milling for designing suitable and optimum mechanical milling performance.

Correlation of grinding rate of gibbsite with impact energy in tumbling mill with mono-size balls

Abstract Dry grinding of a gibbsite powder was conducted in air using a tumbling ball mill with mono-size of media (balls) ranging from 4.8 to 31.7 mm diameter to investigate ball size effect on grinding rate. The impact energy of balls during grinding was calculated by the method proposed previously in order to correlate with the grinding rate. The grinding rate increases with an increase in the rotational speed of the mill, subsequently, it falls around the critical speed. The maximum grinding rate shifts toward higher rotational speed range as the ball size becomes large. In the range of rotational speed before the grinding rate falls, the grinding rate is improved when grinding with balls of 12.7 mm or less, while it is reduced when larger balls over 15.9 mm are used. A similar trend can be seen in the relation between the specific impact energy of balls and the rotational speed of the mill. The grinding rate is proportional to the specific impact energy of balls regardless of the ball size. Therefore, the specific impact energy of balls plays a significant role in governing the grinding rate in tumbling ball milling of the sample powder.

Cell optimization for fast contact detection in the discrete element method algorithm

The objective of this paper is to find out a rule of cell optimization for fast contact detection in the discrete element method (DEM) algorithm. The contact detection process was executed by using the conventional cell model or distinct cell model (DCM) under several particle conditions having different particle size ratio and volume ratio, and its time was measured. The conventional cell model is suitable for the conditions that particle size ratio, dlarge/dsmall, is small and its volume ratio, Vsmall/V0, is also small. The optimum cell condition of the conventional cell model is that the mean number of particle in a cell is 1.0–5.0, regardless of the particle size ratio and its volume ratio. Contact detection using DCM, which has several grids for different sized particles, is much faster than that of the conventional model when particles have a large size ratio. The size of the larger cell does not affect the contact detection speed; however, the size of the smaller cell is important for the fast contact detection and its size is determined to be about 3.0 times the particle radius. Therefore, the optimum cell condition is estimated from the particle size ratio and its volume ratio, and a large-scale DEM will be possible.

Grinding of talc particulates by a high-speed rotor mixer

Abstract Talc particulates were ground by a high-speed rotor mixer without grinding media (beads) under atmospheric condition in order to evaluate the performance of the mixer. The median diameter of the ground sample decreases with an increase in both rotational speeds of the rotor and the vessel, and with a decrease in the clearance in the working space. The grinding limit can be controlled by the operational conditions. The grinding limit is correlated with the tangential force acting on the particulates calculated from the particulates motion simulated by the Particle Element Method regardless of the rotational speeds and the clearance.