Project ended 1992, report dated March 1993. Mislabeled as an ARR.
Summary
In this research project it was intended to examine the existence of the grinding limit of fineness of product powder mainly by inliquid grinding method using media mills, such as vibration and planetary mills, and to find out the factors which determine this limit, and the laws which govern the rate of grinding to approach to this limit value.
First the results of research works on the limit fineness in dry grinding, mainly about those of the authors,were reviewed and its general tendency was conclusively summarized. And thenit was confirmed using a planetary ball mill, which had shown very high grinding rate with high acceleration number, that the equilibrium particle size,or limit fineness, does exist even in&-liquid grinding, when the size is expressed by 50% average diameter, though in some cases the limit fineness has not been found. This equilibrium size reduces with decreasing ball size and is well correlated with the force excerting on a single ballby mill pot. On the other hand, the limit size obtained as specific surface area by BET gas adsorption method is found to be much smaller than the 50% diameter and also independent of the grinding conditions within most of the present experimental range.
The laws to describe the approaching process to the equilibrium state was also examined and it was found that Tanaka’s law which includes the limit specific surface area in the equation as a sort of saturation state, is not valid. More simple relation, which can be approximated to Rittinger’slaw is approved as a general law until the limit fineness is attained. That means that the factors which determine the rate of grinding and the limit fineness have no or only little connection each other. This fact was also approved by the simulation calculation of the lshifting process of size distribution of ground product.
It was also found that Rosin-Rammler’s formula is extensively approved to be able to present the size distribution of ground product even in this micron and submicron order size range.