Page:Cassier's Magazine Volume XV.djvu/255

Rh scarce commodity, and a new supply of cheap material for iron rolling mills is out of the question. It is almost an impossibility now for an expert scrap dealer to detect the difference between wrought iron and soft steel in the old material offered him, and a guarantee that any lot of wrought scrap contains no steel is out of the question. Busheled scrap for common bar iron may almost safely be said to contain steel to some extent. And so much more steel is now being consumed than wrought iron that the production of steel scrap is increasing at a rate so rapid that wrought scrap will very shortly be steel principally.

of sectional cushioned ore-crushing rolls, described at one of the recent meetings of the American Institute of Mining Engineers by Mr. J. W. Pinder, seems admirably adapted to overcome one very annoying trouble and source of expense with the common crushing rolls as now operated in ordinary plants. With these it is almost impossible, economically, to regulate the first operation of preparing the ores for the rolls so that any approach to a uniform size may be obtained. Owing to this unevenness in size it is always necessary to pass and re-pass the same material several times through the machine in order to obtain a uniform result. As

the ore is fed into the rolls, when the larger pieces are clutched, and the pressure begins to bear upon them, the first strain on the springs tends to separate the rolls as shown in the little sketch in this column, until the crushing-point, or point of greatest resistance, is reached before the pieces are actually crushed. In this way, especially in crushing hard ores, the rolls are forced apart as much as 60 to 80 per cent. of the time. This parting is not infrequently as much as half an inch and more. By far the greater part of the material, being fine when it reaches the machine, has a tendency to pass through the rolls when thus opened by the larger pieces, and so to escape the desired grinding, and the same may be said of coarser work, the relative proportion of sizes being the same.

order to correct this defect as much as may be, and increase the efficiency in crushing the finer material that would otherwise pass the rolls, Mr. Pinder devised the sectional cushioned rolls in question.

Their nature will be understood at once from the annexed sketch. The system, as applied to the Cornish or ordinary rolls of that class consists of the division of one of the two rolls into several sections, and the introduction of a stiff rubber cushion for each section, fitting snugly into the bore of the hub, and closely around the shaft which passes through it. This cushion is made of the stiffest car-spring rubber. The sectional roll is driven by two steel arms, one on each side, keyed to the shaft, each arm passing through and pressing against the spokes of one-half of the sections. In the operation of this system it will be clear enough that when the larger and harder pieces of ore fall into the rolls, and the strain on the springs in the act of crushing causes the rolls to part, only that section in contact with such a piece will be parted until the necessary crushing pressure is reached, after which it will spring back