Separation method and apparatus
United States Patent [191 Douglas et al.  
 [ l SEPARATION METHOD AND APPARATUS [75] Inventors: Edward Douglas, Wclwyn;  
 Christopher Harvey Duffell, Biggleswade; Terence Walsh, Hitchin; Peter Mark Harris, Tring. all of England [73] Assignee: National Research Development Corporation, London. England [22] Filed: Oct. 5, I973 [2]] Appl. No.: 403,907  
 [30] Foreign Application Priority Data Oct. (1 1972 United Kingdom 46256/72 [52] US. Cl. 209/73; 209/l I6; 209/1 19; 209/120 [51] Int. Cl B071:  
 [58] Field of Search 209/73 74. H6, H9, 120  
 [ 1 Apr. 8, 1 975 [56] References Cited UNITED STATES PATENTS 3.581857 6/[97] Reznik 209/l l9 Primary E.\&#39;uminerAllen N. Knowles Attorney. Agent. or FirmOblon. Fisher. Spivak. McClelland &amp; Maier l 57] ABSTRACT A method and apparatus for separating mixtures of particulate materials in and by which the mixture is thrown on to a separator surface and the different friction effects between the surface and the various constituent materials after impact cause those constituents to take up different trajectories and thus to separate.  
 3 Claims, 1 Drawing Figure SEPARATION METHOD AND APPARATUS This invention relates to a method of separating the constituents of a mixture of particulate materials, and to apparatus for carrying out such a method. it relates in particular to the separation of the waste that remains once the cylinder block and other ferous matter have been removed from the scrap that results when cars are shredded. This waste contains valuable non-ferrous metals that are definitely worth recovering, and rubber, plastics and other residues that are less valuable but still possibly worth recovery. Hitherto it has been usual to separate such mixtures by hand, a task which is slow, unpopular and increasingly expensive. Mechanical separators are known in which a mixture is thrown against a hard surface lying roughly at right angles to its trajectory, and in which the different rebound resiliences of the constituents of the mixture cause them to separate after rebound. However. it has been found that the resilience variations within non-ferrous automobile scrap are not sufficient to achieve good results by this method, and that powerful machines have always been necessary to throw the mixtures at the plates so that the constituents will rebound far enough to be separately collected.  
  It has now been found that better separation may be possible using a process which is similar in that the mixture makes impact with a striker plate, but different in that the mixture particles make moving contact with the plate for a longer time after impact. It appears that such contact, longer than the brief rebound contact of the previous method, can enhance the difference between the subsequent trajectories of the constituents of the mixture, and so facilitate separation.  
  According to one aspect of the invention, a method of separating mixtures of particulate materials involves the mixture making impact with a striker or plate. The particles move over the plate after impact sufficiently for plate-particle friction effects to give substantially different characteristics to the subsequent trajectories of the different materials. and such materials are then separately collected at collection points lying on these different trajectories. According to another aspect, our invention is a method of separating mixtures of particulate materials in which the particles make impact with a striker plate, in which the line of motion of the particles relative to the plate at impact makes considerably less than a right angle with the plate, in which contact between the plate and the various materials after impact gives them different subsequent trajectories, and in which such materials are then separately collected at collection points lying on these different trajectories.  
  The mixture may be thrown on to a stationary striker plate, and is preferably thrown upwards on to that plate so that it is still on the upward leg of its trajectory when it strikes the plate, and so that it continues upwards for some time after impact.  
  The mixture may be typical non-ferrous automobile scrap, the striker plate may be flat with a mild steel face. the face plane of the plate may be inclined to the vertical at an angle of the order of 25, and the angle of attack ofthe mixture to the plate may be of the order of 40.  
  The invention includes apparatus. including a mixture thrower and a striker plate, for carrying out such methods.  
  The invention is defined by the claims at the end of this specification and will now be described, by way of example, with reference to the accompanying drawing which is a diagrammatic perspective view of one apparatus.  
  Typical mixed non-ferrous scrap 1, resulting from the demolition of automobiles and with a size range from dust up to particles with a major dimension of about 7 inches. falls vertically from a hopper 2 into a sloping V-shaped channel 3. This channel is vibrated by mechanism 4, and serves both to form the particles of material 1 into a queue and to give them some horizontal velocity. From channel 3 they descend on to a continuous belt 5 moving at about 24 feet per second over rollers 6, one of which is driven and the other idles. The line of travel 7 of the upper surface of the belt is inclined to the horizontal at a typical angle of about 17, and particles that land from channel 3 upon the lower end of the belt at first slip over it because of the difference in speed, but are gradually accelerated to full belt speed and then leave the belt at that speed at the upper end 8. An idler roller 9 with a thick, foamedplastics surface 10 runs against the surface of the belt close to upper end 8; the grip of the nip between the belt and surface It) helps to accelerate particles as they travel up the belt; they come clear of the nip just before reaching upper end 8.  
  When the particles are projected off the belt at upper end 8, they travel upwards in the normal parabola. Before reaching the apex of this, they hit a striker plate ll comprising a face 12 of mild steel sheet and a block board backing 13. Plate H is rectangular, with lower edge 14 parallel to the ground. For the separation process now being described, it was found advantageous to tilt the plate so that it made an angle of about 25 with the upward vertical (indicated at 15), and so that edge 14 made an angle of about 40 45, preferably 42, with the vertical plane passing through the line of travel 7 of belt 5. This latter angle is referred to in this specification as the angle of attack. Material projected from belt 5 all approaches plate ll along substantially the same trajectory or axis of incidence l6, striking the plate within a small elongated area 17. It has been found that the subsequent trajectory of the particles depends considerably on the shallow angle, typically 30, at which they strike the plate in area 17, and on their co-efficient of friction with the plate 11. Most rubber particles, and others having a high co-efficient of friction with the plate, follow trajectory 18 after impact. For much of the first part of this trajectory they skid in contact with the surface of the plate and lose their own forward velocity energy rapidly. Most metal particles, on the other hand, follow trajectory 19; they have a lower co-efficient of friction with the plate and tend to rebound sooner from the plate and be retarded less by friction effects. Collection points 20, 21 are set in the paths of trajectories l8, 19 respectively; these may be separate collection vessels, or a common vessel divided by a splitter plate, or they may even simply be two separate areas on the floor of the building where the treatment takes place. In the example illustrated they are two areas separated by a barrier 22.  
  With plate 11 tilted at Z5to the vertical, and with an angle of attack of 42&#34;, an efficiency of separation of about 96 percent has been achieved. This is to say, only about 1 percent by weight of the material reporting at each collection point has been of the wrong kind. Most of the items that reported incorrectly to the more valuable metal friction were the larger and most spherical pieces of rubber which had tended to bounce across the sheet 11 like a ball. and these are not too difficult to detect and remove on a subsequent brief visual scan of the metal fraction.  
  It is clear that efficiency of separation depends upon a formula in which angle of attack, the angle of tilt of the plate and other factors are all interdependent terms. if angle of attack is increased while other factors remain unchanged. the purity of the valuable metal (ie low friction fraction) arriving at point 21 tends to improve, but only at the expense of increasing the amount of metal that is lost because it reports to point 20. The general inter-relationship of angle of tilt to angle of attack appears to be that if one is increased, the other should generally be decreased to tend to maintain the efficiency of separation as before.  
  The effectiveness of the apparatus also depends upon other factors, for instance the speed of projection of material from belt 5, the angle to the horizontal at which it is projected and the distance from the point of projection to the area of impact 17. The speed of projection must be sufficient to cause the material to make a firm impact with the plate and still retain enough momentum to travel right across it. When they first strike the plate the particles of material should preferably be travelling slightly upwards. The angle of projection to horizontal is set to make maximum use of the area of the plate with a minimum of material coming off the top of it. The material could of course be thrown up on to the plate at a steeper angle if the plate was deeper. but this would tend to reduce the divergence of trajectories l8, 19. The distance from the point of projection to the area of impact should of course be kept to a min imum to make the apparatus as compact as possible.  
  Various modifications of the apparatus are possible without departing from the present invention. For example it would be possible to achieve the necessary relative motion ofthe material against the plate by feeding the material under gravity on to a spinning or otherwise moving plate. We claim: 1. A method of separating mixtures of particulate materials comprising:  
 propelling the mixture towards a separator surface; causing the particles so propelled to follow first trajectories that make impact with the said surface at angles considerably less than a right angle; causing all particles to make impact with the said surface at substantially the same velocity to that sur face; causing the particles after impact to remain in contact with the surface and travel over it for a considerable distance. losing energy through surface/particle friction effects; causing the different fractions of the mixture to take up different second trajectories after impact said differences being substantially due to said friction effects, and separately collecting the fractions that take up said different second trajectories. 2. A method according to claim 1 in which: said particles are thrown towards said separator surface, and said particles all leave the thrower at a substantially uniform velocity. 3. A method according to claim 1 in which: the first trajectories have a substantial component in the vertically upwards direction; the second trajectories start with a similar componeat. and said second trajectories later change direction and contain a substantial component in the vertically downwards direction while still remaining in contact with said surface.