Magnetic Separators for Weakly Low Magnetic Minerals

Wetherill Rowand Separator Type “E” Separator

The machine consists essentially of a belt which conveys the ore between the poles of a series of magnets, so arranged that the belt traverses the air gap between opposite poles; the above figure illustrates the principle of this separator. The lower pole of the magnet is flat, the upper pole beveled. This arrangement causes an intense concentration of the lines of force along the lower edge of the upper magnet, and the direction of attraction

of a magnetic particle presented to the magnet by the conveyor belt directly above the lower pole, is upward to the beveled edge of the upper pole. A cross belt traveling beneath the upper pole prevents the magnetic particles from sticking to it, and carries them to one side, out of the field. In order to free the magnetic particles at the discharge the upper pole is furnished with a tapering iron projection in the direction of travel of the cross belts; this causes a gradual reduction in the strength of the magnetic field and permits the magnetic particles to be removed from the field and drop away from the cross belt into a hopper. Each magnet in this construction has two separating zones; the machine is built with one, two, and three magnets having respectively two, four, and six separating zones, the same conveyor belt serving all of them. The conveyor belt is 18 ins. wide and the cross belts 2 ins. wide. The capacity of the separator depends upon

the  depth of ore feed on the conveyor belt (which must be very thin to prevent entrainment), and upon the speed of the conveyor belt, which must be slow enough to give the feebly magnetic particles time to be influenced and picked up by the magnets. The speed of the cross belts is adjusted to take care of the magnetic material picked up by the magnets. The ore is fed onto the conveyor belt from a hopper by means of a feed roller turning inside a cylindrical casing. It is well to introduce a coarse screen at this point (or before) to remove large pieces of ore, nails, or other foreign matter which may have passed through a leak in the sizing trommels, as any large piece of magnetic material will tear the delicate and rapidly moving cross belts by pressing against them under the attractive force of the magnets. The windings on the magnets are such that the second magnet encountered by the ore is stronger than the first and the third stronger than the second, permitting the recovery of products of different degrees of magnetic permeability. The ore stream, in passing the magnets, has a tendency to gather in ridges, similar to beach sands under the action of waves. These ridges may be smoothed out and the ore layer prepared for the next magnet by means of a strip of heavy canvas placed so as to trail on the conveyor belt. Each magnet is provided with a rheostat to control the exciting currents. The machine is capable of delicate adjustment suitable to variations in the ore fed. The capacity of the E3 machine, having 6 poles, varies from ½ to 4 tons per hour, depending on the ore treated.

Homboldt-Wetherill Cross-Belt Separator

This is practically the same as the Wetherill-Rowand separator as built in the United States, differing only in details as to the feeding device, construction of frame, etc.

Mechernich Separator

In this machine the separation is accomplished in a field between two cylindrical poles, of which the upper revolves in the direction of the feed introduced between them. The arrangement of the poles is shown in cross section in the figure above. In the earlier type both poles were cylindrical and both revolved; in the later machines the upper is the separating member and the lower pole is stationary and covered with a nonmagnetic shell which, revolving in the direction of the ore feed, serves to discharge the nonmagnetic particles falling upon it. The feed is introduced against the upper pole as shown above; the feed plate is arranged to deliver ore automatically by means of a bumping device; the ore is pressed against the pole by a weak spring beneath the feed plate, insuring a close contact between the ore stream and the pole. The lines of force are concentrated along a plane

passing through the axes of both poles; in other words, along the line where they are nearest together. The field gradually decreases in strength as this position is left, and the magnetic particles drop off the upper pole in reverse order to their permeability, as by its revolution they are carried out of the concentrated field toward the neutral point, 90 degrees away. The nonmagnetic particles fall from the upper pole immediately upon leaving the feed plate. By a suitable arrangement of plates beneath the upper pole several middling products may be made, as well as the magnetic and nonmagnetic products. Any magnetic material that may still adhere to the pole is removed near the neutral point by means of a revolving brush of steel wires. The exciting coils are wound on the cylinders themselves. The pear-shaped lower pole produces a greater concentration of the lines of force than the circular section. The principal function of the

lower pole is as a return for the magnetic flux. The machines are usually built double, with two sets of poles. The whole is enclosed in a sheet-zinc housing to prevent the escape of dust. The machine develops a field of high intensity, and the feed being brought into close contact with the separating cylinder (which is bare), it is capable of separating feebly magnetic minerals. The mechanical and magnetic efficiencies are high. The machine is built in two sizes, classified according to the length of the separating poles, respectively, 60 and 80 cm.

Motor-Type Separator

This separator consists essentially of an armature revolving between two fixed magnet poles. The ore is fed against the separating roller by means of a feed plate as shown in the above figure; the nonmagnetic particles fall away from the roller, while

the magnetic particles are carried farther, dropping off in order inverse to their permeabilities. The roller, or armature, is protected by a copper shell which revolves with it. The peculiarity of this separator is that the separating roller, or armature, is set in motion by the current supplied to the magnets, independent of any other source of power. The length of the separating roller is 800 mm.; the power consumption is from 60 to 100 watts. The only wearing parts of this machine are the separating surface and the automatic feed plate. The machine is completely closed in to prevent the escape of dust into the atmosphere of the separating room.

Primosigh Separator For Dry Ores

This machine consists of an iron core or shaft, B, upon which six sets of exciting coils, A, are mounted. These coils are protected by the brass rings, O, which are the separating surfaces. The pole pieces, C, are connected with the core, B, by iron disks, and it is in the groove between these pole pieces that the separation takes place. The ore to be separated is fed from hoppers through chutes, E, into the grooves between the pole pieces at the top of the rotating magnets, there being six individual separating zones, each equipped with its own feeding device and take-off brush. The speed of the rotating magnet cylinder is so regulated in conjunction with the current passing through the coils that the nonmagnetic particles are thrown out of the grooves as soon as they acquire the peripheral speed of the rotating cylinder; the weakly magnetic particles are carried a little farther, when centrifugal force, assisted by gravity, causes them to fall into suitable receptacles placed beneath the magnet cylinder; the strongly magnetic particles adhering to the poles are removed by a series of secondary poles consisting of soft-iron points mounted upon brass disks, L, the whole revolving in the direction of the magnet cylinder. The separator requires one half horse power for revolution, and from 14 to 15 amperes at 80 volts for excitation. The capacity of this separator is about 1 metric ton per hour.

Ulrich Separator

A pair of electro-magnets, between the wedged-shaped poles of which a separating armature is revolved, is the essential feature

of this machine. This armature is a hollow brass cylinder carrying alternate rings of iron and brass ¼ in. wide and held close together. This cylinder, or armature, is three ft. long and makes 50 R.P.M. about a horizontal axis. Each machine carries four separating cylinders, two above (on the same axis) and two below, the upper magnets carrying a weaker current than the lower. The ore is fed from a hopper by a distributing arrangement having a feed plate, with zigzag channels cast in it, upon the top of the upper cylinders. Here the strongly magnetic particles are held by the concentrated fields at the edges of the iron rings, and deflected into a receptacle; the material passing unaffected over the first cylinder, falls upon the top of the lower cylinder which is revolving in a stronger field, and the more weakly magnetic particles are removed from the nonmagnetic portion of the feed, which is here discharged from the separator. The capacity of these machines is 25 tons per 24 hours; they require 1.5 E.H.P. and 1.5 M.H.P. for excitation and revolution, respectively.

Payne Magnetic Separator

This separator consists of two drums which revolve toward each other in the direction of the passage of the ore, which is fed between them. The upper drum is the separating member; it con-

tains a stationary electro-magnet, placed to give a strong field between the two drums along the line where they are closest together. The revolving shell is furnished with longitudinal strips of soft steel with a toothed cross section as shown in the above figure. The magnetic lines of force are concentrated along the ridges of these teeth, and give rise to a field of sufficient strength to separate weakly magnetic minerals. The lower drum is also encased with a revolving shell, and serves as a return for the lines of force. The ore is fed from a hopper by means of a feed roller upon the shell of the lower drum, which, by its revolution, presents it to the separating drum; the nonmagnetic particles are discharged by the lower drum, while the magnetic particles are picked up and held on the ridges of the upper drum until carried past the influence of the magnet, when they drop off into a hopper.

International Separator

This machine comprises a cylindrical armature, made up of thin laminated disks of annealed wrought iron, which revolves about a horizontal axis between the poles of an inverted horseshoe magnet. The disks of the armature have saw-tooth edges, the teeth being staggered on adjoining disks, the surface of the armature presenting a great number of sharp points. The pole pieces of the magnet are recessed, and only sufficient space is left between

them and the armature for the passage of a thin layer of the ore to be separated.

The lines of force from the magnet are concentrated upon the points of the armature, giving a strong field capable of attracting weakly magnetic minerals. The magnetic attraction is strongest at a point on the horizontal diameter of the armature, and steadily decreases from this point around to the vertical diameter. The ore is fed at the top of the armature, and, upon being carried into the field by the rotation of the armature, the magnetic particles adhere to the points of the saw teeth, the nonmagnetic particles sliding off into a hopper. The magnetic particles are carried around underneath the armature and drop off in an order

inverse to their degrees of permeability. At the vertical diameter, where the magnetism of the armature changes polarity, even strongly magnetic particles are thrown off by centrifugal force. By a suitable arrangement of dividing planes a middling product may be made as well as concentrate and tailing. The hoppers receiving the products of separation are adjustable, and may be moved according to the products it is wished to obtain. The position of each hopper is shown by indicators, and when they are set at the desired points, may be clamped in place by set screws. The field magnet of this separator weighs 9000 lbs., the whole machine 10,000 lbs. One horse power is used for excitation of the magnet, and one horse power for mechanical operation. The capacity of the separator is from 2 to 4 tons per hour.

Ubaldi Separator

This machine consists of an iron core, in the shape of a ring, carrying exciting coils and having two gaps in which are placed separating armatures. The upper pole pieces are recessed to admit the armatures and the lower pole pieces are tapered to concentrate the fields at the separating zones. The armatures are

fitted with helical ridges which serve to concentrate further the lines of force, and also, by revolution, to transport the attracted particles to one side, where they are dropped into chutes. The second separating zone encountered by the ore is stronger than the first, permitting the machine to deliver a middling product. The lower pole piece of the first separating zone is rounded, causing a partial concentration of the lines of force, while the lower pole piece of the second separating zone is beveled, giving rise to a more complete concentration of the lines of force; the pole pieces and the separating faces of the armatures are 80 cm. in length. These machines require 1 H.P. for operation and have a capacity of 1200 kgm. per hour on leucite-bearing lava.

Humboldt-Wetherill Type VI Separator

The construction of this machine, which operates on the principle of deviation of falling particles, is best understood from the above illustrations. One pole of the magnet is tapered down

to a fine edge, the other is split and the two halves carried around the coils to almost meet close to the opposite pole, giving an intense field (280 mm. long). The ore is fed from a hopper by means of a roller upon a conveyor belt which passes around a small pul-

ley close to the field of separation. A second belt travels about the magnet close to the poles, preventing magnetic particles from adhering to them. The ore, as discharged over the end of the conveyor belt, passes into the magnetic field; the nonmagnetic particles fall straight down, while the magnetic particles are deflected according to their magnetic permeability into different trajectories and are caught in suitable receptacles. This machine, removing raw siderite from a feed ranging from ½ to 4 mm. in size of grain, fed separately, puts through 0.6 metric ton per hour; it requires from 8 to 9 amperes at 90 volts.

Wetherill Parallel Separator

This consists of a flat conveyor belt. 12 ins. wide and 15 ft. 4 ins. long, between the centers of the pulleys. This belt runs horizontally, at a speed of 100 ft. per minute, and the ore is fed on it in an even layer about ¼ in. thick. At a distance of 3/8 in

above the top of the belt is a second belt, parallel to the former and running in the same direction. This second belt is 16 ins. wide, extending 2 ins. beyond the lower belt on each side; it runs at a speed of 125 ft. per minute. Above the upper belt are two magnets with flattened poles, placed close together with the line of their adjacent edges slanting 40 degrees with the edges of two moving belts. The magnetic particles are lifted from the lower belt against the upper, and travel with it and across it, as a result of the diagonal placing of the magnets, and on reaching the edge of the upper belt and passing beyond the magnets, they fall past the narrower lower belt into hoppers. The magnets are wound to carry 6 to 8 amperes at 52 volts. The machine is built to treat material passing a 16-in. screen. The capacity is about 30 tons per 24 hours.

Wetherill Horizontal Separator

This machine is built double, with two magnets and four pole pieces, giving two separating zones. The pole pieces are beveled and rounded at the ends to a 1/8 in. radius; the belts pass

around a pulley at one end and around the beveled pole piece at the other, being in direct contact with it. The poles are brought up close together in pairs, the beveled edges parallel. The construction is made clear in the accompanying plates. The ore is fed upon the belts from the hoppers in a sheet from 1/8 in. to 5/32 in. thick, and is carried around the beveled pole pieces, at which place the nonmagnetic particles fall into a hopper, and the magnetic particles are carried a little farther and fall into other receptacles. The pole pieces are 10.75 ins. wide and the bevel is at an angle of 27 degrees; the opposite pole pieces are 0.92 in. apart normally. This arrangement gives an intense field, and the ore is presented to it at its point of greatest intensity. The adjustments are made between the speed of belt travel, the current on the magnets, and the distance apart of the pole pieces. This machine was used to treat franklinite ore passing 0.058 in. apertures and retained on a screen with 0.01 in. apertures: it treated from 1.5 to 3 tons per hour, three machines in series. The first two machines took 6 to 8 amperes and the third 22 amperes at 52 volts. Two adjustable guide plates below and a little to the side of each separating gap are used to divert the magnetic and nonmagnetic particles into their respective hoppers.

Wetherill Inclined Separator

In this machine the ore is fed upon a conveyor belt which presents it to a magnetic field between two pole pieces similar to those used in the horizontal separator. The pole pieces in this machine, however, are set at an angle of 27 degrees from the horizontal, the plane of the upper pole piece being 1.2 ins. above that of the lower. The construction is made clear by the accompanying illustrations. The ore is brought by the conveyor belt as close as possible to the gap between the pole pieces; the magnetic particles are here lifted off the conveyor belt against belts running around the ends of the pole pieces; the belt of the lower pole is the discharge belt for the concentrate, which is carried along and dropped into a hopper; the magnetic particles drawn against the upper pole are carried up on a 54-degree incline until past the influence of the separating zone, when they fall back, and by their momentum are carried past the gap to join the concentrates on the lower belt. The magnets are wound to carry from 6 to 8 amperes at 52 volts. The adjustments are made between the distance of

the conveyor belt from the gap, in the width of the gap between the poles, and in the current on the magnets. These machines, used three in series in the separation of franklinite ores passing a screen with 0.01 in. holes, have a capacity of 3.5 tons per hour. This separator is built double: if a stronger field is desired a yoke is substituted for one set of the pole pieces, leaving but one air gap in the magnetic series. The magnets of this separator are wound the same as those of the horizontal type.