264 ae ANNUAL REPORT 
Fig. 36. Intermediate rolls, with feed rolls, for 34 inch material. 
It must be repeated that for satisfactory results in intermediate grind- 
ing two passages are required, which, however, may be accomplished by 
means of one set of three rolls, illustrated in figure 39, representing the 
Edison three high rolls.* These are 36 inches in diameter, 30 inches face, 
and run go revolutions per minute. The shaft L is driven by wooden- 
toothed beveled gears running in oil. The upper two rolls are driven 
by friction from the lower and have boxes that are free to slide in vertical 
guides. Loose sheaves, F, over which run seven passes of 14-inch wire 
rope, a bight of the rope passing over the pulley, J, provided with a pis- 
ton tightener, K, driven by compressed air, furnishes a pressure of 125,000 
to 150,000 pounds for crushing. These ropes eliminate nearly all friction 
except that due to the weight of the three rolls, which amounts to 20,000 
pounds. The shells are of soft gray cast iron, costing 2 cents per pound. 
The edges are beveled to prevent chipping. Each shell is a true cylinder, 
inside and outside, and 1s keyed in place. It is 8 inches thick when new 
and weighs 4,500 pounds. It has to be trued every three days} steel 
tools being used for truing. The wear of the shells is 0.25 cent per 
ton. A roller feeder, s, is used. The coarser set of rolls crushes 300 tons 
of 14-inch material per hour to pass a 14-mesh screen (0,060xo.5-inch slot). 
*R, H. Richards, Ore Dressing. 
