The Theory and Practice of Ore Dressing

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 Excerpt: ... in., as will be shown later. It will readily be seen that in its field as a medium crusher it is superior to the jaw crusher. My experience leads me to believe that the actual maximum broken ore ribbon which would pass through the rolls cannot exceed 75 per cent. of the theoretical ribbon, if for no other reason than that it is impossible to use the whole width of face in feeding. Again it is impossible to drop the ore into the rolls in as dense a mass as it occupies in a bin. In falling from the chute into the rolls, air will loosen the mass so that it does not again attain the compactness it has in the bin. The question of the actual maximum capacity of rolls is not one, however, which need concern the metallurgist ordinarily if there be but a single passage of the ore or rock through them, no portion being returned to the rolls. For under these conditions, the capacity is so enormous that only exceptionally need it be considered. Before the ore or rock reaches the rolls, it will be found advisable to eliminate fines, and limit the size of the ore by sizing to the set of the rolls. This operation is most advantageously done before the ore reaches the first set of rolls, or when the rock has been crushed to a size of 1--1/2 in. For separating work, it will be best to eliminate fines before each passage through rolls, for it will already have been gathered that the fines are sufficiently unlocked and repeated crushing will merely increase their tendency to make slime. Again if the limitation as to size, indicated by the tests, make necessary a second set of rolls, too great a burden of delimitation will be thrown upon these rolls unless some work has been done for the first set of rolls in this respect. From a theoretical point of view, the rolls appear qu...