Grinding Mill Power 911 Metallurgist. May 08, 2017 Grinding Mill Power ScaleUp A lifter mill of 6 ft diameter, revolving at 187 rpm, is grinding coal The body of the mill is divided into two sections: one section, 75 ft long, being charged with 5 tons of steel balls, of 2 in average diameter, and the other section, 15 ft long, being charged with 6 tons of "Cylpebs" of 5/8 in