Production of Fine Powders by an Agitating Mill

Abstract

An experimental study on the production of fine powders was carried out by an agitating mill devised to produce ultra-fine powders by the mutual friction of sample powders of gypsum. The following results were obtained:
(1) Powders of micron order could definitely be produced by this method and there was only a few percent of submicron powders produced, but it was proved that the production of ultra-fine powders was possible by this method.
(2) The size distribution curves of the produced powders shifted toward smaller particle size with grinding time and the rotating velocity.
(3) The relationship between the specific surface area produced and grinding energy conformed to the final finness limit theory proposed by T. Tanaka.
(4) The specific surface area produced increased with the rotating velocity of the impeller and finally approached a constant value.
(5) When the rotating velocity of the impeller was under 3620 1/min, the specific surface area produced was scarcely affected by the mass of fed sample powders, but at over 4800 1/min it increased as the mass increased.
(6) The specific surface area produced increased with the ratio of the fed sample volume to the agitating vessel volume and finally approached a constant value.
(7) The relationship between the specific surface area produced and various factors was obtained by dimensional analysis.