ball mills are used primary for single stage fine grinding, regrinding, and as the second stage in two stage grinding circuits grinding of materials in a tumbling mill with the presence of metallic balls or other media da......ball mills are used primary for single stage fine grinding, regrinding, and as the second stage in two stage grinding circuits grinding of materials in a tumbling mill with the presence of metallic balls or other media dates back to the late 1800s. since that time, metso minerals and its predecessor companies, mpsi, sala, marcy, hardinge, kennedy van saun (kvs), denver equipment, allis chalmers, boliden allis, and dominion engineering, have designed and manufactured more than 8,000 grinding mills. metso overflow ball mill sizes range from 5 ft. x 8 ft. with 75 hp to 26 ft. x 41 ft. with 20,000 hp. normal feed size to a metso minerals ball mill is 80% passing 1/4" (6mm or finer) for hard ores and 80% passing 1" (25mm or finer) for soft ores. product size is typically 35 mesh or finer. operation ball mills operate either in open or closed circuit. open circuit operation is best utilized when: another stage of grinding follows the mill reduction ratio is small feed material is already fine and one pass through the mill produces the desired results product size control is not critical and oversize material can be tolerated in the product
