Horizontal drum-type magnetic separator for granular feeds
BACKGROUND OF THE INVENTION 
     This invention relates to a drum-type magnetic separator of horizontal arrangement to handle mixed granular feeds in which the feed material is deposited on the drum shell and moves through a magnetic field of stationary magnets. The nonmagnetic particles are separated during movement through the magnetic field and the magnetic material falls away from the collecting surface after passage through the magnetic field. 
     Prior art stationary-magnet drum separators have a cylindrical drum member within which a magnet bank is fixed. During rotation of the drum shell about the magnet bank the separated metallic particles are moved into a discharge hopper with the aid of scraping flights. A feeder is arranged ahead of the drum inlet and batches the material by volumetric control, distributing it in a uniform layer over the width of the collecting surface of the drum. When the drum rotates, the nonmagnetic particles within the layer of material slide off the collecting surface into a chute and the magnetic constituents likewise slip off the collecting surface of the drum shell when they have passed through the magnetic field and drop into a suitably designed discharge hopper. 
     The main disadvantage of such separating apparatus is that the entire feed material to be treated has to be distributed over the peripheral collecting surface of the drum and pass through the magnetic field, which reduces the throughput rate, especially in the case of feeds having a high content of nonmagnetic material, such as sand. As both the feeder and discharge device must be outside the drum, the former above and the latter below the collecting surface, the overall height of the apparatus is fairly considerable and only a short drop remains from the drum shell for the separated particles. A further drawback is that the centrifugal force generated as the rotational speed of the drum is increased counters the effect of magnetic adhesion, so that frequently magnetic particles fall away and are lost. This discharge by acquired momentum is intensified by the radial acceleration induced by the scraping flights. Further, variation in the bulk density of the feed causes the driving torque of the drum to fluctuate, thereby giving rise to stalling of the motor or belt slippage. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to obviate these disadvantages, for the purpose of which the magnets are disposed about the external periphery of the drum, the material is fed into the interior of the drum, below the axis of rotation, and the separated materials are discharged into chutes arranged substantially above the drum axis, one of said chutes being below the end of the magnets and the other, viewed in the direction of drum rotation, at the back thereof, i.e., beyond it. 
     With the apparatus taught by the invention, the material to be separated is fed onto the inner wall of the drum in the range of the magnets, so that with the upward movement of the collecting surface for the most part only the magnetic particles are entrained and the nonmagnetic constituents slide down and can be discharged, without passing through the magnetic field. The apparatus can be of very low overall height as the material feeder and product discharge means can be on one and the same level. There is no need for a separate batching device for the feed. The centrifugal forces generated by the drum rotation supplement the magnetic adhesion instead of reducing it and the driving torque is practically unchanged, as only the concentrate adheres to and is entrained on the inside wall of the drum. 
     The apparatus can be constructed to take account of desired throughput rates and degree of concentration by increasing the drum length, without adding to the overall height, whereas, with prior art apparatus, to improve the quality of separation, a plurality of magnetic drums arranged one above the other is required. 
     Various other objects and advantages will appear from the following description taken in conjunction with the attached drawings, and the novel features will be particularly pointed out hereinafter in conjunction with the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a somewhat schematic arrangement of the apparatus taken substantially in longitudinal section; 
     FIG. 2 is a cross section through the drum of the apparatus viewed from the outlet side of the drum or left side of FIG. 1; and, 
     FIG. 3 is a cross section through the air classifier on the outlet side of the drum. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The apparatus, schematically depicted in FIG. 1, has a drum which is constituted of a generally cylindrical shell 1, with a plurality of flight members 2 disposed about its inner surface. Preferably the flight members 2 should be of helical configuration, so as to impart a thrusting action to the material in the direction of discharge. To prevent rapid discharge of the material one or more annular control rings 3, which are of approximately the same height as the flight members 2, are provided in what may be termed a discharge zone. As shown in FIG. 2, the magnet 4 is concentrically and adjustably located in relation to the drum shell 1 and extends over approximately half the shell&#39;s diameter. The magnet 4 may be displaced in guides 20. Viewed in the direction of drum rotation, the lower end of the magnet is at a variable distance from the feed inlet, which is at the lowest point of the drum. 
     At the inlet end of the drum shell 1 is a hub which is connected with the drum shaft 6 through a spider 5. At the inlet end said drum shaft 6 mounts an infeed screw conveyor 7 and at the discharge end an outfeed screw conveyor 8. The infeed conveyor 7 receives the granular feed from a cone-shaped inlet mounted outside of the drum shell 1 and above the conveyor 7. A screw trough 9 and a chute 10 project from both ends into the interior of the drum. Stationary chutes can be employed instead of the screw conveyors. The driving motor 11 for the screw conveyors is flange-mounted to the end of the drum shaft 6. At the discharge end the drum shell 1 is open to permit ready accessibility. At the open end the drum is mounted in adjustable rollers 12 as depicted in FIGS. 1 and 3. 
     A divider or chute 13, connected to a lever 14, is provided to separate remaining nonmagnetic material from the magnetic material. The lever 14 is engagable with notches 21 in the chute 10 for adjustably positioning the upper edge of the divider 13 with respect to the drum shell 1. Adjustment is effected by means of a sideways-projecting hand lever 15. 
     A resilient scraper 16 extends the length of the drum shell 1 and is provided to regulate the infeed from the inlet and throughout the length of the drum. It is linked with the chute 10 and presses flexibly against the inside of the drum shell 1. As a rule the effective edge of the scraper is approximately of the same height as the lower end of the magnet 4. This scraper is also adjustable by means of an externally located lever 17 which rests on an adjustable slotted support 18. 
     The apparatus may additionally include an air classifier 19 on the discharge end of the magnetic separator, as depicted in FIGS. 1 and 3. Magnetic material is fed thereto via discharge screw conveyor 8.