The present invention relates to separation of particles of synthetic material of a determined quality from particles of synthetic materials of a different 5 quality, with the aim of recuperating synthetic-material articles in undifferentiated collection thereof, finalised to re-use of the relative materials. BACKGROUND ART

In the prior art this recuperation is done by first mincing the articles constituted by different materials with the aim of obtaining a granulate having

10 a mean dimension of in the order of 0.5 to 25 mm.

The granulate comprises a mass made up of granules of different materials which in order to be re-used must be separated such as to obtain homogeneous masses comprising granules of the same material.

Separation methods are known which are based on the application of the

15 tribo-electric effect, which do not always produce satisfactory results and involve the use of sophisticated plants which are expensive and difficult to run.

The prior art comprises plants equipped with a sedimentation tank in which the separation of plastic products is done by simple gravitational effect: the 20 materials having a lower density with respect to the density of the liquid remain floating, while the materials having a heavier density that that of the liquid precipitate to the bottom of the tank.

DISCLOSURE OF THE INVENTION

The present invention proposes to perform the separation of various 25 synthetic materials according to their specific weight.

In particular the invention proposes separating at least two materials having different specific weights.

The aim is attained by immersing the two materials in a liquid having an intermediate specific weight between the two, and by exploiting the different 30 floating capabilities of the materials. Further, the invention attains the result by subjecting the liquid and the materials together to a field having forces that are above the gravitational field, for example by exploiting centrifugal force, such as to significantly emphasise the difference in floatability of the materials in the liquid.

The method of the invention comprises at least the following activities:

- preparing a mixture of the two products to be separated in a liquid having an intermediate specific weight to the specific weights of the two products;

- introducing the mixture into a container,

- subjecting the mixture to a field having a greater force than a gravitational force;

- collecting the lighter granular product, floating on the surface of the liquid, by means of a hole in a wall of the container;

- collecting the heavier granular product, which remains resting on the wall of the container, from the container.

Obviously the method of the invention enables separation of a granular material having a smaller specific weight from a group of granular materials having a greater specific weight by using a liquid having a specific weight which is greater than the specific weight of the lighter material and lower than the specific weight of the other materials. Two groups of materials can also be separated from one another by using a liquid having a specific weight which is intermediate to the specific weights of the two groups.

An apparatus of the invention comprises a drum having differentiated circular sections into which a liquid of a known specific weight is introduced, and at least two synthetic materials in granular form having specific weights which are respectively greater and lower than that of the liquid. The external diameter of the drum is in the order of five hundred millimetres, and is preferably comprised between 200 and 1000 mm.

The shape of the drum is substantially truncoconical, with at least one cylindrical terminal tract in correspondence of larger-section bottom.

Means are provided for setting the drum in rotation.

A cylindrical terminal tract is also preferably provided in correspondence of the smaller-section bottom. The axial length of the larger-section cylindrical tract is comprised between 0.4 and 0.7 times the length of the drum, and is preferably 0.66 times.

An axial conduit is provided for introduction of the liquid having known specific weight into the drum, and of the two granular materials to be separated.

The centrifugal force originating from the rotating motion of the drum is such that the liquid becomes arranged adjacent to the wall of the drum in the form of a constant-thickness liquid layer.

The thickness of the liquid layer is determined by a discharge light for the liquid, afforded in the greater bottom wall of the drum at an appropriate distance from the drum axis, such as to keep dry a smaller-section terminal tract of the drum.

The distance from the axis of the discharge light is adjustable preferably between d1 and d2, wherein d1 is smaller than d2.

As an example the discharge light can be implemented as a radial developed window afforded in the larger-section bottom of the drum, closed by a shutter adjustable in radial direction.

The truncoconical shape of the drum is such that the free surface never reaches the wall of the drum in the most tapered portion thereof.

The granules of material, according to their specific weight, are arranged either adjacent to the wall of the drum or at the free surface of the liquid.

In particular, the material that is heavier than the liquid is arranged adjacent to the wall of the drum, and the material that is lighter than the liquid is arranged at the free surface of the liquid.

The liquid is selected from among the following: pure water (distilled), with a specific weight of 1 ; water with additional elements entering in solution and increasing the specific weight thereof, such as salts, sugar, carbonates, sulphates, etc., with a specific weight of between 1 and 3; water added-to with elements which reduce the density thereof, such as alcohols, emulsion oils, additives facilitating dissolving of air in the water, etc, with a specific weight comprised between 0.5 and 1. In general, liquids are chosen which have densities comprised between 0.5 and 3 and which do not alter the plastic materials.

At least an Archimedes screw is located adjacent to the wall of the drum, which is moved in rotation with respect to the wall of the drum, in the same direction of rotation as the direction of rotation of the drum

The drum and screw are rotated at slightly different speeds, with the speed of the drum being of in the order of three thousand revolutions per minute, preferably comprised between 1000 and 10000 rpm, the relative speed of the screw with respect to the drum being of in the order of ten rpm, preferably comprised between 3 and 100 rpm.

The action of the screw is such as to push the particles of the heavier material, which have a greater specific weight than that of the liquid, and which are arranged against the wall of the drum, towards a radial discharge hole afforded on the dry tract of the drum wall in a proximity of the smaller- section bottom of the drum.

The particles that are lighter than the liquid, which float on the free surface of the liquid, exit the drum by encountering, together with the liquid through the discharge light provided on the larger-section bottom of the drum.

In a preferred embodiment of the invention, a second screw is provided, solidly constrained to and internal of the first screw and wound in an opposite direction thereto, having the task of pushing the light material floating on the surface of the liquid towards the axis discharge light provided in the larger bottom wall of the drum.

BRIEF DESCRIPTION OF DRAWINGS

The advantages and constructional and functional characteristics of the invention will more fully emerge from the detailed description that follows, with reference to the figures of the accompanying drawings which illustrate preferred embodiments thereof, given by way of non-limiting example.

Figure 1 illustrates a first embodiment of the invention in a frontal view.

Figure 2 is section ll-ll of figure 1.

Figure 3 is a perspective view of the rotor of figure 1.

Figure 4 is a second embodiment of the invention in a frontal view. Figure 5 is section V-V of figure 4.

Figure 6 is a perspective view of the rotor of figure 4.

Figure 7 is a perspective view of an alternative rotor to that of figure 3.

BEST MODE FOR CARRYNG OUT THE INVENTION

Figures 1 and 3 illustrate a casing 1 resting on the ground.

A drum 2 is supported rotatingly internally of the casing 1 , which drum 2 has a truncoconical central portion 21, and two end portions, respectively 22 and 23, which are cylindrical.

The end portion 22 having a larger section is closed by a cover 221 in which a hub 22 is afforded for rotating supporting the drum 2 to the casing 1.

The end portion 23 exhibiting the smaller section comprises an axial tract 231 in which a bearing 232 is located for rotatable support of the drum 2 of the casing 1, and a bearing 233 for supporting the end of an internal rotor 3. The tract 231 bears a pulley 234 for activating the drum 2.

The internal rotor 3 is composed of a cage comprising a cylindrical portion 30 from which leave three equidistanced supports 31 on which an external first helical Archimedes screw 32 is wound, which follows the profile of the drum 2, very close to the wall thereof.

The first screw 32 has a conical portion 321 and a cylindrical portion 322. The conical portion 321 ends with a small cylindrical tract encountering the wall of the smaller-section cylindrical tract of the drum.

The radial dimension of the helical blade of the first screw preferably increases progressively from the end having the larger section towards the end having the smaller section.

At the separating surface between the conical section and the cylindrical portion of the screw there is a separator wall 323 having a ring-shape, the external diameter of which is equal to the internal diameter of the first screw.

At the end of the cage having the larger section, the supports 31 of the first screw 32 are connected to a circular bottom wall 311 which is rotatably supported by the drum which is in turn supported by the casing 1 and bears an axial shaft 312 fixed thereto which terminates externally of the casing 1 and bears an activating pulley 313 of the rotor 3. An axial conduit 24 is fixed internally of the tract 231 , which axial conduit 24 extends internally of the rotor 3 up to reaching the cylindrical portion.

The cylindrical portion 23 of the drum 2 exhibits at least a radial hole 5 which opens internally of an end chamber 11 of the casing 1 , for the exit of the heavier granulate.

The cover 221 of the larger end of the drum 2 exhibits at least an axial discharge light 6 from which the light particles exit, together with the liquid. The light 6 opens into a chamber 12 of the casing communicating with the outside.

The light 6 has the shape of a radial window closed by a shutter 61 whose position is adjustable in radial direction by a screw 62.

The second embodiment of the invention illustrated in figures from 4 to 6 differs from the first embodiment due to the presence of a further screw located coaxially and internally of the screw of the first embodiment, and wound in an opposite direction thereto.

The task of the second screw is to act on the lighter material situated on the surface of the liquid in order to push the said material towards the exit hole. Figures 4 to 6 use the same numerical references as figures from 1 to 3, to denote the same elements illustrated in figures from 4 to 6.

The second screw is denoted by number 320 and is supported to the first screw 32 by welding the helical blade in the cross points of the helical blade with the first screw 32.

The external diameter of the second screw is constant and equal to the external diameter of the separator wall 323 on which it leans.

The axial extension of the second screw 320 is limited to the larger-section terminal cylindrical tract of the drum.

Figure 7 represents an alternative rotor to that represented in figure 3.

The rotor comprises a hollow central shaft 700 ending on one end with a cylindrical portion 701 provided with a flange 702, which portion acting as the cylindrical body 30 of Figure 3.

At the opposite end the shaft ends with a tang 703 suitable to be swivel coupled to the flat bottom of the drum. The hollow central shaft 700 also acts as intake conduit of the material into the drum, and is provided in its central area with at least one axial window 704, located in the central area and allowing the exit of the material from the drum.

A blade 706 is spirally wrapped around the central shaft, the blade 706 exhibits a cylindrical tract which extends from the tang 703 in a axial direction for a length equal to the drum axial length and ends with a conical tract in which the blade exhibits decreasing height so as to slither against the wall of the conical tract of the drum.

The blade portion of the cylindrical tract exhibits some circular-slot shaped windows or opening 707, aligned with the adjacent openings of the adjacent spiral turns, forming conduits allowing the downflow of the liquid layer, and the material granules floating thereof, towards the discharge light 6 provided in the larger-section bottom of the drum.

The operation of the rotor in Figure 7 is the same as the operation of the rotor in Figures 2 and 3.

The dimensions of the windows are such that the distance between their external edge and the axis of the tube 700 is greater than the maximum distance of the discharge light from the drum axis, in such a way that the portion of the blade external to the windows 700 is always submerged in the liquid, not engaging the portion of the liquid layer where the particles with lower specific weigh float.

The invention is not limited to the embodiments described herein above, and variants and improvements may be brought thereto without its forsaking the ambit of the following claims.