Trap rock is crushed in a gyratory crusher. The feed is nearly uniform 2-in. spheres. The differential screen analysis of the product is given in column,

(1) of Table 28.4. The power required to crush this material is 400 kW. Of this 10 kW is needed to operate the empty mill. By reducing the clearance between the crushing head and the cone, the differential screen analysis of the product becomes that given in column,

(2) in Table 28.4. The feed rate is 110 tons/h. Using the Bond method, estimate the work necessary per ton of rock in both the first and second grinds.

Table 28.4