In operation the magnets are excited, the drums revolved in the direction indicated. and the air current established thonigh the machine in a direction opposite to that of the drums. The ore passing, down the chute under the first drum, the magnetizable portions are drawn into contact with the drum, and take on the forward movement of the latter. When the ore reaches the limit of the are covered by the magnetic field it is no longer attracted, and takes on a tangential movement, which carries it away from the drum. It has now, however, passed the edge of t he second apron, and, on leaving the first drain, conies within the infin ence of the magnet of the second drum, where similar operations are repeated, a portion being finally discharged as concentrate at r. The function of the second drum and magnet being to differentiate the prodila from the first drum into two portions, which may be con veniently designated as middlings, discharged at in, and concentrates, discharged at r. The easy working capacity of a machine having drums of 24 in. diameter and 24 in, working face is said to be from 15 to 21) tons per hour of ore granulated to pass 16 to 20-mesh screens.
The power required is from 1 to 11 horse-power in electricity for each drum, and to horse-power to drive the machine. Ball states that Port Ilenry ' Old Bed " ore has been converted by means of this machine into a Bessemer ore, carrying iron, 71.10 ; phosphorus, 0.037. This concentration was made from the crude ore, iron, 58.7 phosphorus, 2.25 ; the Bessemer concentrate representing about 05 per cent. of the original mass. Sec Trans. Am. Inst. Mining Engre., vol. xix. p. 167.
The Thenntiiiin Magnetic Separator (Fig. 14) has a stationary field magnet, and an armature barrel consisting of a num ber of soft-iron bars, separated from one another by a non-magnetic material—strips of wood, for instance. The whole is bound together by non-mag,netic end rings. The bars are cut away alternately on the inside, to make one bar project only toward the north poles of the magnet, and the next only to the south poles. This gives each suc ceeding bar opposite magnetism. On each of the four sections of the magnet are wound 15 lbs. of copper wire. An Edison dynamo furnishes a current of 10 amperes and 33 volts.
The ore is fed to the barrel by means of a hopper, as shown in outline, Fig.
14, the cylinder turning in the direction of the arrow. The magnetite adheres to the bars of the barrel and is carried dcwnward past the first delivery chide.
Below the machine, the bars, departing from the influence of the electro-magnet, which is placed eccentrically. lose their power to hold the particles of mag netic iron ore, and they drop off. The particles of rock in the ore. being non-magnetic, drop front the barrel almost imme diately and fall on the first chute shown in the one:ravine% The Edison Unipolar Non-contact Electric Separator (Fig. 13) differs from other magnetic separators in that it
has no moving parts, except such as are essential for adjust ment of the apparatus in treating different ores. The separator consists simply of a hopper, a magnet, and a par tition to separate the concentrates and tailings into different receptacles. The illustration shows but one hopper. but in practice the ore can pass on each side of the magnet, thus doubling the capacity. The ore, after being properly crushed and sized, is placed in hoppers, from which its discharge is controlled by bars closing slots which extend the length of the hopper. These slots are made adjustable, so as to suit the size to which the ore has been reduced. The hoppers are adjusted to appropriate heights above the magnet. The magnet is a mass of soft iron, 6 ft. long by 30 in. wide and 10 in. thick, weighing 3,400 lbs., and wound with 450 lbs. of copper wire, the coil being connected with a dynamo consuming 21 horse-power, and requir ing a current of electricity of 16 amperes, and an electro-motive force of 116.5 volts. The material falling from the hopper passes the face of the magnet. but does not touch it. The distance of the magnet from the vertical plane of the falling material is so chosen that its attraction causes the magnetic to separate from the non-magnetic partieles sufficiently to alter their direction. By reason of the force of gravity, this deflection of the trajectory, while sufficient to draw the magnetic particles away from the non-magnetic, does not draw them against the magnet, but should any ore accumulate on the magnet, it can be instantly dropped by breaking the current. The exact distance, however, is maintained so that none can stick to the magnet. Owing to the altered trajectory, the magnetic ore falls upon one side of the partition, which is so adjusted as to secure the best result, while the gangue material drops upon the opposite side. The capacity of a machine of this kind, of the size given above, is said to be easily 150 tons per day of ore crushed so as to pass a 111-mesh screen. or 300 tons per day for a double-face machine.
The Magnetic Separator is a belt machine of the general form indicated in Fig.
16. which merely shows the principle and not the detail. The ore is fed on a belt, and carried along under a series of belts running at right angles to the first. These cross belts pass between the magnets and the ore lying on the distributing belt. and may be placed at varying distances from the latter. As the ore, reduced to the proper size, passes along on the distributing belt, the magnetic belts, which may be influenced by magnets of different powers, pick up and carry to one side the magnetic particles of the ore, while the non-magnetic portion of the gangue is carried off as tailings.