Summary
The purpose of this research project is to examine the existence of the grinding limit of fineness or the equilibrium size of product powder by in-liquid grinding using media mills, and to find the factors which determine the ultimate sizes. Furthermore, the rate of fine and ultrafine grinding in liquids by the media mills was investigated mainly from the viewpoints of the mechanical grinding conditions.
It was confirmed using a planetary ball mill with very high grinding rate that the equilibrium particle size and the negative grinding phenomena do exist even in in-liquid grinding, as far as the sizes are evaluated by laser scattering- diffraction method. The equilibrium size reduced with decreasing ball size (3mm to 0.5mm) and was well correlated with the force exerting on a single ball by the maximum centrifugal acceleration in the mill pot. On the other hand, the limit size determined in terms of absorption method was found independent of the grinding conditions within most of the present experimental range.
The particle size distributions of products ground in the specific surface area by BET gas water by the media mills were well presented by the Rosin- Rammler equation. Their distribution constants n showing the sharpness of distribution were considerably higher than those usually obtained by the dry grinding with larger balls and found dependent on the ball size.
It was made clear that there is an optimum size of balls for the grinding of certain feed particles and for other mill's conditions. The in-liquid grinding with the planetary mill at higher frequency with larger balls produced products with agglomerates, the amount of which was possibly evaluated by the deviation of size distribution from Rosin-Rammler distribution.