The invention relates to apparatus for separating particles differing in specific gravity by means of a liquid separating medium, using the float-and-sink method, the apparatus comprising a washing tank, with means movable along its bottom for removing the settled particles and with means for removing the floating particles. Apparatus of this kind is known, for instance, from the British Patent Speci ication 868,832. In this apparatus the means for removing the settled particles which move along the tank bottom take the form of a scraper chain. For the purpose for which this known apparatus was designed, viz. separating useful -minerals from rock, more in particular separating coal from shale, this is very satisfactory. However, it is not so if the material to be separated according to specific gravity tends to get tangled in itself and to cling to the scra¬ per chain so that this can jam. Such a difficult-to-work material is, for instance, the scrap coming from shredders in which wrecked or disused cars, disused domestic appliances, etc. are disintegrated. The ferromagnetic components of the scrap leaving the shredder are generally separated from the non-ferromagnetic components by means of a magnetic separator. The non-ferromagnetic part of the scrap contains components widely differing in specific gravity, e.g. non-metals, such as plastics, wood and rubber, lighter metals and alloys, such as aluminium and aluminium alloys, and heavier metals, such as copper, lead, stainless steel, etc. It is the object of the invention to provide float-and-sink apparatus of the type described above which can, ^• without objection, also be used for separating such a dif icult-to- handle material according to specific gravity.

According to the invention, the said means movable along the bottom of the washing tank for removing the settled particles can be moved between two extreme positions so that during the movement from at least one of the extreme positions to the other extreme position they can ^• transport settled particles across the edge of the washing tank to a discharge point.

According to the invention, the said means for removing the settled particles preferably comprise at least one collecting tray that can be reciprocated along the bottom of the washing tank, which collecting tray in the first extreme position is about centrally on the bottom of the washing tank where it can collect settling particles, and in ±he second extreme position rests on the edge of the washing tank, so tilted that the settled particles contained in it can slide into a discharge device positioned next to the washing tank, for which purpose the collecting tray is open at the discharge side. In addition, there may be a collecting plate moving along with the collecting tray, on which plate particles settling during the trav of the collecting tray are collected, and across which these particles can slide into the collecting tray when this is travelling back to its starting position. By preference the apparatus is provided with a seco collecting tray that can move, in a similar way as described for the first collecting tray, between two extreme positions, and which rests ^• about centra.lly on the bottom of the washing tank when the first collecting tray, has reached its tilted position on the edge of the washing tank, and rests tilted on the opposite edge of the washing tan when the first collecting tray is approximately centrally positioned o the bottom of the washing tank. This second collecting tray can likewi cooperate with a collecting, plate as described above.

According to the invention, the mechanism reciprocating the collecting trays with the collecting plate (if present) between the extreme positions is preferably so designed that the collecting trays are hingingly attached to one or more arms fixed on a horizontal shaft provided with driving means for swinging to and fro between two extreme positions the shaft with the arms and the collecting trays hingingly attached to them. If a collecting plate is used, this is preferably also attached to the said arm(s).

The invention will be elucidated with reference to the drawing, which shows a non-restrictive example. The figures show:

Fig. 1: a diagrammatic representation of the top view of apparatus according to the invention; Fig. 2: a diagrammatic representation of a vertical section along the line II-II in Fig. 1;

Fig. 3: a diagrammatic representation of a vertical section along the line III-III in Fig. 1.

These diagrams only show what is needed for a good understanding of the invention; not shown are, for instance, the parts which serve for the circulation and the regeneration of the separatory medium, and the actuation and control system of the motors. In a washing tank 1 the material to be separated, for instance scrap from a shredder, with a maximum size of the pieces of about 400mm, from which the ferromagnetic components have already been removed, is introduced by means of a feed device 2.

The washing tank contains a liquid separatory medium, for instance a suspension of finely-ground ferrosilicon or magnetite in water, having a specific gravity of 1.4, in which metallic components of the scrap will sink and lighter components, such as plastics, rubber, wood, etc. , will float. In the washing tank a separatory compartment is partitioned off by partitions 3, 4 and 5 extending vertically into the liquid, from which compartment the floating pieces are carried to a ^• discharge point 8 by means of a peddLe wheel 7. The settling pieces are collected under the separatory compartment 6 in collecting trays 9 and 10. In the extreme position shown in the drawing,collection tray 9 is about centrally on the bottom of the.washing tank under separatory compartment 6; collecting tray 10 rests, tilted, on the edge of the washing tank, so that the contents of this collecting tray can slide to a discharge device 11. In the other extreme position collecting tray 10 is under the separatory compartment, and collecting tray 9 rests tilted on the opposite edge of the washing tank, as shown by the dot-dash line; now collecting tray 9 empties its contents into discharge device 12.

Collecting trays 9 and 10 are hingingly attached to arms 13 and 14, which are fixed on a horizontal shaft 15. This shaft 15, with the arms 13 and 14 attached to it and the trays 9 and 10, can be reciprocated • between two extreme positions by a motor 16, preferably a hydraulic motor. A collecting plate 17 is fixed to the arms 13 and 14, on which plate settling pieces from compartment 6 are collected during the time no collecting tank is under this compartment; the pieces collec¬ ted on this plate 17 then slide into the collecting tray moving to the bottom position.

The bottom edges of the partitions 3, 4 and 5 are at such a distance over the upper edges of the trays 9 and 10 that there is no

danger of pieces projecting beyond the upper edges of trays 9 and 10 getting jammed; the partitions 3, 4 and 5 have downward extensions in the form of strips of flexible material 18, 19 and 20, which may be rubber, but may also be formed by, e.g., curtains of chains, and which extend to close over the edges of the tanks 9 and 10. The upright walls of the collecting trays, or at least the back walls, should be provided with openings, to prevent the collecting trays scooping an undue quantity of separatory medium across the edge of the washing tank Preferably, the motor 16 . has discontinuous control, in such a way that the two collecting trays 9 and 10 alternately rest for certain time on the bottom of the washing tank in their bottom position collecting settling particles that are to be carried off. This 'certain' time should of course, be so chosen, that the collecting tray get properly filled, but not overfilled; if desired, this time may be made dependent on the load of the machine. The motor 16 is by • preference a hydraulic motor, as this can immediately produce its ^" maximum torque when moving from standstill.

The padUe wheel 7 is driven by a motor 21, which, if motor 16 is a hydraulic motor, preferably a hydraulic motor also. The specific gravity of the separatory medium is, of course, chosen in depence on the separation to be made. As indicated above, a specific gravity of about 1.4 is in most cases suitable for separatin non-metallic components from scrap. If it is desired to make a further separation of the resulting metallic fraction, for instance into a fraction mainly consisting of aluminium and aluminium alloys on the one hand, and a heavy-metal fraction (copper, lead, etc.) on the other, a secondseparation apparatus of the same type may be employed, using as separatory medium, for instance, a suspension of ferrosilicon in water, with a specific gravity of 3.0. - Above, the material to be separated has been referred to as 'scrap'; it will be clear that apparatus according to the invention .can also be used for separating other materials, e.g. domestic refuse, in which case paper and lightweight organic components can be separated from heavier components, such as stone, rubber, glass and metals, by means of water as separating medium, after which, if so desired, the heavier fraction can be subjected to a further separatory treatment in a second washing tank, using a medium of higher specific gravity.

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