A Study on Grinding Mechanism of Fine Particles in a Sand-Mill by Using an Image-Processing Techinque and a Development of an Original Sand-Mill.

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A measuring technique to visualize the motion of media particle is originally developed for a horizontal type sand mill of which internal blade and external cylinder rotate inversely and independently. Using this experimental technique, velocity distribution, intensity of velocity fluctuations and appearance frequency of grinding media in the mill were measured. Relating to these flow characteristics of media particles for both rotation metods, grinding performance of calcium carbonate with alumina beads was investigated. The results show that the median diameter of ground products obtained in both rotation methods can not be correlated only with the intensity of velocity fluctuations, but can well be correlated with the intensity of velocity fluctuations weighted by appearance frequency.In addition, motions of grinding media were visualized for three types of blade (normal disk type, hole disk type and cross type) in a horizontal type sand mill of which internal blade and external cylinder rotate inversely and independently. The effects of blade geometry on velocity distribution, intensity of velocity fluctuations and appearance frequency of grinding media were investigated. The relationship between these flow characteristics and grinding rate was discussed by carrying out grinding tests of calcium carbonate. The results show that grinding characteristics obtained for each blade in both rotation methods can well be correlated with the intensity of velocity fluctuations weighted by appearance frequency.A new type of blade (cross turbine type) was proposed on the basis of the above mentioned information, and its grinding rate was investigated in connection with the motion of grinding media. The results show that a new type of blade is the best compared to usual three types of blade.