CEE April-June 2012

transition zone between purely laboratory grinding and semi-industrial grinding. This mill therefore constitutes a "bridge" between ZEISEL's grindability test and the already existing VRM600 semi– industrial roller mill, which is used primarily for contract-grinding campaigns. Two systems of identical construction and function were built, one for CEMTEC's technology test centre in Enns, and one for the laboratory technology centre, at the Chair of Mineral Processing of the Montanuniversitaet Leoben. Both systems started operation in the late summer of 2011 (Figure 1 ). Figure 2 shows a description of the mill in modules. Material feed is effected with a gravimetric metering system (a.) with a discharge screw. The material is fed by means of a rotary valve onto the grinding table of the mill (b.). System air flows via the air duct and the nozzle ring into the grinding chamber and conveys the material to the dynamic classifier. The fines (f.) are then separated with a bag filter (c.). The system fan operates in suction and is located on the clean-gas side (d.) downstream of the filter. A decisive new development is the external grit bypass system (e.), by means of which coarse particles (g.) rejected by the cross-flow classifier can be removed from the grinding chamber via a screw conveyor. This makes it possible to either route this product out, or to return it to the grinding chamber. Sampling from the circuit makes it possible to access and better understand the mill's internal circulation. For feed materials containing different mineral phases (e.g. talc/pyrites), discharge and I or a sorting stage permits product concentration by means of selective comminution. 2 Overview of thesystem, divided Into functional groups The mill was designed and constructed as an attrition mill with a flat grinding table and two 25