The type of grinding mill is identified by the type of grinding media utilized. Each type of mill has characteristics that adapt it to certain grinding applications. The operational characteristics of each mill type must be evaluated in relation to the objectives of the grinding requirements being studied in order to select the optimum mill. The common mill types are discussed in the following sections.

The type of grinding mill is identified by the type of grinding media utilized. Each type of mill has characteristics that adapt it to certain grinding applications. The operational characteristics of each mill type must be evaluated in relation to the objectives of the grinding requirements being studied in order to select the optimum mill. The common mill types are discussed in the following sections.

Rod mills can accept feed up to approximately 2” diameter and generally are selected to grind product to the – 4 mesh to – 35 mesh range. Grinding actions is by line contact between rods extending the length of the mill. Rods tumble and spin in roughly parallel alignment and in so doing simulate the crushing and grinding action from a series of roll crushers. Large particles spread the ends of rods and is so doing impart an additional action termed scissoring. These actions result in preferential grinding of coarse material and a minimum production of slimes and excessively large material termed tramp oversize. A relatively uniform sized product is produced. Due to the nature of the grinding action, rod mills can sometimes advantageously replace the fine crushing of damp or sticky material that tends to coat the faces of crushing surfaces. Rod mills can produce a final product on sand brick, lime, or coke breeze where the feed contains low moisture and is often ground dry. In the metal mining industry most rod mill applications involve wet grinding were material is reduced in size from crusher product size to a size suitable for ball mill feed. Rod milling in the size range utilized is more efficient than ball milling in that the desired product is obtained at a lower cost per ton. This is due to several reasons: