Cone milling of compacted flakes: process parameter selection by adopting the minimal fines approach

Cone mill was well studied for milling of wet agglomerates. This study evaluated the effects of various process parameters of cone milling roller compacted flakes on the granules produced. Impeller sidearm shapes, screen surface profiles and impeller speeds were studied. Impeller speed was found to play a major role in determining the granule attributes. Besides this, median size, size distribution and percent fines of a milled granule population were mainly determined by the size reduction mechanisms of different impellers and screens. Pre-breaking followed by shearing and slicing of flakes inside the milling chamber was primarily responsible for determining the size, size distribution and percent fines of milled granules. The pre-breaking action could be achieved using teethed round sidearm impeller and lowered the need for screen-based size reduction, thus generating less fines. The shearing and slicing of flakes due to the raised impaction edges of the grater screen also helped to minimize the production of fines. Therefore, the lowest percentage of fines was observed when the teethed round sidearm impeller was used with a grater screen. The results indicated that fines can be reduced considerably with the judicious selection of a suitable impeller and screen combination in the cone mill.