A milling device sometimes used for grinding cement and industrial minerals is a grinding table. Figure 8 shows a typical example. It consists of a 4 m diameter table rotating around its centre at 20 rpm. On the outside it has a lip around to reduce particle ejection from the table. Four 1.2 m diameter rollers are positioned just above the table. They counter-rotate so that the peripheral roller speed matches the table speed at the lowest point. Particles (with diameters 25-75 mm) are fed onto the centre of the table at a rate of 300 tph. When they by centrifugal force and some are contact the table, they are thrown outward, trapped between the table and rollers where they would be crushed, making product as small as 5 mm.

Figure 8: Grinding table rotating at 20 rpm with four equi-spaced 1,200 mm rollers and a central feed (top) view of full table with particles shaded by speed, and (bottom) close up of compression breakage under one roller with particles shaded by size

In Figure 8(a), the particles are coloured by speed. The incoming speed is relatively fast. These particles slow as they strike the accumulated particle mass on the surface of the grinding table. As they are pushed outward, they accelerate until they are dragged under the rolls. Here they are crushed by compression. Some high speed fragments fly out from the rollers.

The DEM model used here includes a simple breakage...