secondary crushing), the reduction

secondary crushing), the reduction ratio in each stage being in the range 3 to 6. Mineral is accomplished by compression against rigid surfaces or by impact against surfaces in a rigid constrained motion[1]. Figure 17.2 presents equipment used to accom- plish crushing(a)jaw crushers, in which a large jaw toggles back and forth to crush lumps against a hard, rigid surface: (b) gyratory crushers, which use a gyrating cone to compress lumps against a rigid surface; (c) roll crushers, in which the ceramic lumps are squeezed between rotating rolls and(d) hammer mills, which use rotating hammers impacting the material to break up the lumps Grinding, in our context here, refers to the operation of reducing the small pieces after crushing to a fine powder. Grinding is accomplished by abrasion and impact of the crushed mineral by the free motion of unconnected hard media such as balls, pebbles, or rods[1]. Examples of grinding include(a) ball mill, (b) roller mill, and(c) impact grinding, illustrated in Figure 17.3. In a ball mill, hard spheres mixed with the stock to be comminuted are rotated in- side a large cylindrical container The motion causes the balls and stock to be carried up