ball mills. ball mills have been the primary piece of machinery in traditional hard rock grinding circuits for 100 years. they are proven workhorses, with discharge mesh sizes from 40m to 200m. use of a ball mill is the best choice when long term, stationary milling is justified by an operation. sold individually or as part of our turn-key,retsch planetary ball mill pm,retsch planetary ball mill pm 400. skuret-pm400. planetary ball mills are used wherever the highest degree of fineness is required. apart from the classical mixing and size reduction processes, the mills also meet all the technical requirements for colloidal grinding and have the energy input necessary for mechanical alloying processes.