Mechanism of Ultra-fine Grinding of Ceramics Raw Materials

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Using four types of media mill, such as ball, vibration ball, planetary and stirrer mills, the possibility of producing sub-micron powder of ceramic raw materials with mechanical size reduction methods was investigated, by making clear the existence of ultimate size distribution of ground product and by finding out the factors which determine that ultimate value. Some other phenomena associated with grinding process in such a fine range were also investigated. Main findings are as follows;(1) Negative rate of grinding at final stage of fine media milling was found to be the controlling factor of ultimate size of ground product. In the case of less cohesive material such as silicate sand, the effect of mill type on negative rate did not appear clearly, but in the case of cohesive naterial such as limestone, the effect of ball type differentiated the ultimate size of product.(2) In the range of negative rate grinding, agglomerated powder was formed. This agglomerated powder was compacted to be larger in size and spparent density as grinding proceeded. And this tendency was strengthened when ball weight became larger.(3) The pulverizing mechanism of planstary mill was found to be the combination of compressive force by mass of media against mill wall and frictional and shearing effect by media mass in surging action. And as this mechanism was different from that of ball milling, the ultimate size of product shifted to finer side, for which smaller media was more effective.(4) The ultimate size of product by stirrer mill was found to be better than that by ball milling. Grinding aid may shift this value to finer side, but contrary it may cause the increase of waer.(5) The metal wear of vibration ball milling was measured and relatively simple relationship between specific surface area and specific wear was found and formulated. And it was found that hydrogen gas was produced during wet grinding with steel ball.