The shape of product size distributions in stirred mills

This paper presents the results of an extensive laboratory and pilot stirred milling testwork program conducted using different types of mills, fed with different types of materials and operated at different conditions. The results indicate that the slope of the product size distribution (PSD) curve remains relatively unchanged in the coarse product size range but decreases in the fine product range (less than about 20 μm size), regardless of the type of stirred milling technology used for grinding. This work therefore confirms that a narrower product particle size distribution than the feed size can be achieved independent of the type of stirred milling technology used for fine grinding below 20 μm. The change in the PSD width in fine grinding is due to the change in the material breakage properties and a change in the mill operating conditions which affect the breakage process. In the normal operating range of grinding media size, the effect on the PSD shape is not significant.