Classifying – separating – and assorting solids – Magnetic – Paramagnetic
Reexamination Certificate
1998-11-16
2001-05-15
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Magnetic
Paramagnetic
C209S225000, C209S212000, C209S213000, C209S636000, C209S695000, C209S639000, C209S689000
Reexamination Certificate
active
06230897
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an apparatus and a method for separating particles of material of different electrical conductance. More specifically, the mixed particles are fed onto a conveyor and separated by a rotating magnetic system arranged on the conveyor. A collecting container collects the sorted particles which are separated from the remaining material on the conveyor.
In an apparatus of this type known from U.S. Pat. No. 3,448,857, a quantity of particles of different electrical conductance, which have to be sorted, is fed onto a conveyor belt from above. The conveyor belt turns over a belt drum and takes the particles to that drum at a speed of 1 to 1.5 m/sec. A magnetic system rotates in the belt drum at a speed of approximately 1500 r.p.m. A relative movement takes place between the conveyor belt and the drum with the magnetic system during operation, and the difference in speed makes the magnetic lines of force cut through the electrically conductive particles travelling on the belt. Currents are thereby induced of a strength dependent on the electrical conductance of the particles. A stronger current is generated in the particles with higher electrical conductance, and causes those particles to be thrown in a trajectory from the belt into their direction of movement. The particles with lower electrical conductance remain near the belt and drop off it almost vertically. The exact fraction which has a certain required electrical conductance may be filtered out by installing a collecting container at a suitable location. It should be noted that before the '857 apparatus is used, ferromagnetic materials have already been picked out of the material to be sorted by methods which are sufficiently well known (strong magnets). The main function of the '857 apparatus is in fact to separate so-called nonferrous metals (copper, aluminum, lead, zinc, brass etc) from residual materials (paper, plastic, glass etc) particularly in connection with waste recycling.
An apparatus for separating mixtures of materials with different electrical conductance including a similar rotating magnetic means is known from DE 34 16 504 A1. In this apparatus, the magnetic means rotates rapidly and produces a changing magnetic field through which the mixed particles are passed. The separating means is surrounded by a case which rotates more slowly. The eddy currents arising have effects on the particles, giving the electrically conductive particles a greater trajectory than the non-conductive ones.
PCT Patent Publication No. WO 89/07981 shows a comparable construction. Here again materials made up of non-magnetic particles drop from above onto a rotating drum containing a magnetic system which also rotates. The drum and the magnetic system rotate in opposite directions so that non-metallic materials such as glass, plastic and stones drop down on one side of the drum and non-magnetic metals on the other side. However, constructions in accordance with DE 34 16 504 A1 or WO 89/07981 only allow non-specific separation, and the number of incorrectly separated particles is relatively high. Magnetic particles which have not been previously separated out also pose a problem, and may cause damage on going between the drums and the cases rotating in the other direction.
As a further improvement to such apparatus EP 0 339 195 BI proposes that the magnetic system should be arranged eccentrically in the belt drum. This arrangement prevents magnetisable, electrically conductive particles from being held between the conveyor belt and the belt drum. These trapped particles become red hot as a result of the magnetic field and inflict corresponding damage to the belt drum and conveyor belt. Another eccentric arrangement is shown in Japanese Patent Publication JP57-119856 A.
It has already been proposed in German Patent Publication DE 4 323 932 C1 that the speed of the drum of the magnetic system should be raised and the deflection thus made stronger in order to improve sorting quality. However, this necessitates correspondingly expensive improvement of the properties of the magnetic system.
SUMMARY OF THE INVENTION
The problem of the invention is to provide an apparatus of the above type and a corresponding method, which improve sorting quality even without increasing the speed, or if the speed is increased, also increase the quality of the sorting.
The problem is solved in the present invention by providing an apparatus wherein the rotary direction of the magnetic system is chosen so that the directions of movement of the surface of the magnetic system and of the conveyor are different.
The problem is solved in the present invention by a sorting method wherein the surface of the magnetic system and the particles to be sorted are moved in different directions.
With the various components in such relative positions the sorting quality can be decisively improved. In known metal separators, the conveyor belt is used only to bring the particles which have to be sorted to the actual sorting point, i.e. the magnetic system; the magnetic system then decides, from the size of the parabolic trajectory formed, whether the particle is to be regarded as electrically more conductive or less conductive and hence whether it shall drop into a certain collecting container or not. This may sometimes cause problems and incorrect assessments, for example when particles lie over or cover each other and thus interfere with each other through the flight parameters.
In the present invention, the highly electrically conductive particles move in a different direction from the less conductive particles (not just to a different degree in the same direction, as in prior art); the limit can be set very sensitively here through the strength of the magnetic field of the magnetic system and/or the speed of the conveyor belt. The conveyor belt causes a basic movement of all the particles in a certain direction, and this is counteracted by the magnetic field of the magnetic system. The magnetic field may be made strong enough to move the highly conductive particles against the action of the conveyor belt, in the opposite direction, without any problems. In one embodiment, the start of the parabolic trajectory begins directly above the magnetic system such that some of the affected particles will have no further contact with the belt if they are caught and deflected sensitively enough above it.
In another embodiment, a certain section of conveyor belt is thoroughly and deliberately taken into account. Here again the magnetic field is found to be strong enough to convey the particles over the end of the upper run into a collecting container installed there.
If particles, possibly of different specifications, are on top of each other, mixed up or possibly diffused into each other, they will be disentangled or also spun to and fro on the conveyor belt by forces acting in different directions, and will consequently be detached from each other; the effect can be seen immediately in the case of superimposed particles.
Instead of simply travelling along subtlety different parabolic trajectories, the particles move in diametrically opposite directions and therefore cannot interfere with each other.
If two particles landing in adjacent positions move diametrically towards each other and meet, this still does not diminish the sorting quality. After the impact, they will reappear unchanged in the same position, but in a slightly different relative arrangement, and will then automatically move in the right direction at the second attempt. Conveying and sorting of a particle in an incorrect direction is thus prevented.
In contrast with constructions where a case rotates around the magnetic system instead of an additional conveyor, the sequence in the present invention is that the particles to be separated are given a finite dwell time in the magnetic region, during which they are still accessible to decisions and influences. If a second drum is used instead of the conveyor, any initial incorrect classifications will generally be
Barlow Josephs & Holmes, Ltd.
Miller Jonathan R.
Walsh Donald P.
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