GB2027605A

GB2027605A - Device for separating materials

Info

Publication number: GB2027605A
Application number: GB7929754A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-08-29
Filing date: 1979-08-28
Publication date: 1980-02-27
Also published as: IT7924937A0; IT1122438B; JPS5532695A; SE7906676L; DE2837633A1; FR2434643A1

Abstract

A device for the separation of materials having different melting points, for example waste material consisting of plastics coated with aluminium foil, comprises a separating head 11 into which is fed, from an extruder 1 connected to the separating head 11, plastics material 6 which has been plasticised in the extruder 1 and which carries particles of aluminium foil. The separating head 11 encloses an edge filter 21 comprising a stack of washers or a helically wound strip. A rotating conveyor screw 19 forces the plasticised plastics component of the material 6 through the edge filter to apertures 17 and conveys the foil particles to a discharge aperture 18. Each of the washers forming the edge filter has (Figs. 2, 3 not shown) an annular collecting groove 25 adjacent its inner periphery, the groove 25 communicating with a radial recess 26 in the outer periphery. The recesses 26 of all the washers are aligned to form an axial duct which communicates with the discharge apertures 17. <IMAGE>

Description

SPECIFICATION Device for the separation of material having different melting points This invention relates to a device for the separation of materials which have different melting points and can be plasticised in an extruder, the invention being particularly advantageously applicable to the regeneration of foil-coated plastics wastes.

The consumer goods industry is making progressively greater use of plastics films, more particularly plastics films bonded with or sealed by an aluminium foil. In recent years for economic reasons more and more importance has been attached to the regeneration of the considerable wastes resulting, usually in the form of punched grids.

In the case of wastes from plastics films bonded with aluminium, large amounts of which accumulate, the aluminium is separated from the plastics, to allow the re-use of the latter, by means of extruders provided with metal sieves. The material to be regenerated is plasticised in the extruder and forced by the latter through a sieve disposed at its outlet. The unplasticised parts are caught in the fabric of the sieve, while the plasticised material flows through the sieve.

However, in the prior art separating devices of the kind specified hereinabove, the openings in the sieve fabric very quickly become clogged by the retained metal parts, so that the sieves have to be replaced frequently.

It is true that for this purpose use is made of sliding cassettes in which sieves are inserted, to be introduced alternately into the extruder discharge duct, but in the regeneration of plastics films coated with aluminium, for example, the sieves are clogged after as short a time as about 30 seconds. The sieves must therefore constantly be checked and replaced, since otherwise they would be destroyed. This is not only very expensive in materials and labour, but also has a very disturbing effect on operations and reduces output, since continuous operation is impossible.

It is therefore an object of the invention to provide a device for separating materials having different melting points which is free from these disadvantages. The main object is to ensure that dirt and foreign bodies can be continuously separated from the material to be regenerated, without the device requiring a large amount of maintenance and supervision for this purpose. The device according to the invention achieves a high throughput and ensures a high degree of cleanliness, while at the same time being versatile in application.

Accordingly, the present invention consists in a device for the separation of materials having different melting points, more particularly for the regeneration of plastics wastes which are coated with foil and can be plasticised in an extruder, characterised in that the separating device is constituted by a separating head which is connected to an extruder and in which, in a casing rigidly connected to the peripheral wall of the extruder, one or more annular separating plates are located, which are so disposed at a small distance from one another to create radially directed sieve gaps, or which each are so formed with one or more identically directed recesses that the separating plates operate as a sieve for the plasticised material.

Preferably, to form the sieve gap in the inner or outer zone of the separating plates, one or both end faces thereof have separating edges which are set back in relation to such end faces and merge into an annular collecting duct connected to an outlet aperture of the separating head for the cleaned material. According to a variant of the invention, to form the sieve gap in the inner and'or outer zone of the separating plates radially directed recesses are machined into one or both of their end faces, such recesses issuing into an annular collecting duct. Conveniently, the recesses have a triangular, rectangular or semicircular cross-section.

The separating plates can be cheaply manufactured if they are formed by a strip of preferably rectangular cross-section which is wound helically and into which the sieve gap is machined, for example, embossed.

To compensate for the considerable stresses occurring during operation, the annular collecting duct of the separating plates may be wholly or partially encircled by a further annular duct, and the two ducts interconnected via diametrically opposite recesses machined into the separating plates.

Advantageously, to connect the collecting ducts of the individual separating plates to the outlet aperture of the separating head one or more radially directed recesses which extend in alignment with one another and issue into the collecting duct are machined into each of the separating plates, or their end face formed with the separating edge or recesses is partially set back.

Conveniently, to remove solids from the separating head, a conveyer screw is provided which is preferably coaxial with the extruder screw and which engages in the separating head or is connected to its conveying duct. However, as another possible way of achieving the same object, the conveyor screw of the extruder has an extension which is preferably constructed conical at the core and which engages in the separating head.

Preferably, for the removal of solids the separating head has a removal aperture which can be closed, for example, by a sliding valve actuatable by a servo device, thus allowing rapid emptying, so that the separating head can be swilled out if necessary.

The separating head may be heated, being enclosed, for example, by a heating strip.

The device of the invention for the separation of materials having different melting points is not only very simply constructed and therefore manufacturable without difficulty, but also very effective when used and always provides reliable separation, more particularly of metal parts from plasticisable plastics, with a high degree of operational reliability. The reason is that if the separating device is constituted by a separating head in which annular separating plates are located, which form or have radially directed, variously constructed sieve gaps, the separating plates operate substantially as a sieve or strainer.

The material containing solids and plasticised in the extruder is therefore forced through the sieve gaps as it flows through the separating head, while the unplasticisable solids are retained at the sieve gaps, and therefore separation can readily be effected.

The width of the sieve gaps is a measurement of the size of the particles which are to be separated. Since due to the construction of the sieve, made up by the combination of a large number of separating plates, the gap width can be made very small and nevertheless accurate at low cost because the separating edges are simply to be set back suitably in relation to the end faces or the recesses must be of suitable dimensions, substantially complete separation of the foreign bodies from the plasticised material is ensured.

The use of separating plates having separating edges or recesses also allows a high throughput, since operations can be effected at high pressures without the risk of damaging the sieve. Nor is maintenance work required, thus also making highly economic the separating device of the invention, which ensures continuous separation and is versatile in use.

If, for example, the temperature in the extruder and separating head is maintained so exactly that in the case of a granulate consisting of two or more plastics only one of the plastics can be thermally plasticised, even plastics of different compositions can be separated from one another by means of the separating head.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example embodiments thereof, and in which~ Fig. 1 is an axial section through the separating head, built on to an extruder and constituting the separating device, Fig. 2 is a side elevation of the annular separating plates used in the separating head illustrated in Fig. 1, Fig. 3 is an enlarged view, in cross-section on the line Ill-Ill of Fig. 2, of a number of separating plates forming the sieve, Fig. 4 shows a variant construction of the separating plates illustrated in Fig. 2, Fig. 5 is an enlarged view, in cross-section on the line V-V of Fig. 4, of a number of separating plates illustrated in Fig. 4, Fig. 6 shows separating plates formed from a wound strip, Fig. 7 shows another embodiment of the separating head with an extruder screw engaging therein, Fig. 8 shows a further embodiment of a separating head, and Fig. 9 is a cross-section on the line Vill-Vill of Fig. 8.

The device illustrated in Fig. 1 for separating materials having different melting points, comprises a separating head 11 which is built on to an extruder 1 and in which the unplasticisable solids of a granulate conveyed through the separating head 11 are separated from the plasticisable material.To this end there is arranged in a casing 12, made up of a peripheral wall 13 and two end flanges 14 and 15, a plurality of annular separating plates 21 which form sieve gaps 27 (Fig. 3). Plasticised material 6 in which foreign bodies to be separated are embedded, and which is conveyed in a duct 5 by an extruder screw 2 enclosed by an extruder casing 3, is forced into a conveying duct 1 6 of the separating head 11, which is screwed to a flange 4 arranged on the extruder casing 3, so that the cleaned material 7 can flow through the sieve gaps 27 to outlet apertures 17, while the solid foreign bodies are retained in the separating head 11 and emerge as waste 8 from outlet apertures machined into the flange 15.

To produce the sieve gaps 27 between the individual separating plates 21, one of the end faces 22, 23, in the present embodiment the end face 22, of each of the separating plates, as shown in Figs. 2 and 3, has a separating ege 24 which is set back in relation to said end face and which merges with an annular collecting duct 25 machined into end face 22. A radially directed recess 26 which extends as far as the collecting duct 25 is also machined into each separating plate 21. When the separating plates 21 are being inserted into the casing 12 they are so arranged in relation to one another that the recesses 26 are in alignment with one another, and therefore the plasticised, cleaned material can pass through the sieve gaps 27, the collecting ducts 25 and also the recesses 26, which form an axially directed duct, to the outlet apertures 17.

In the embodiment illustrated in Figs. 4 and 5 the sieve gaps 37 are formed by recesses 37', 37" or 37"', which can be of triangular, rectangular or semi-circular cross-section, and which are machined into the separating plates 31. The separating plates 31 therefore bear against one another via their end faces 32, 33 and thus contaminations of the plasticised material are retained on the separating edge 34 and only the cleaned material can pass through the gaps 37 into the collecting duct 35.

To compensate for the heavy stresses occurring during operation, the duct 35 is partially encircled by a further semi-circular duct 38 which is connected via two diametrically opposite recesses 39, machined into the separating plates 31, to the duct 35 and issues into the discharge duct which is formed by the radial recesses 36 in alignment with one another in the assembled position of the plates 31. Of course, this arrangement of ducts can also be provided for the separating plates illustrated in Fig. 2.

The purified material 7 emerges from the separating head 11, which can be heated by a heating jacket 29 so that the material does not cool and remains flowable, in the form of strands which are then cooled and comminuted by a mill or the like to form a granulate which can be reused. Of course, a profiling tube or nozzle can also be connected to the casing 12 to enable the material 7 to be ejected in the form of a profiled strand or a film.

To remove from the separating head 11 the solids retained by the sieve gaps 27, 37, use is made of a conveyer screw 1 9 which is located in the conveying duct 1 6 and which is driven by a motor (not shown) and via which therefore the solids are conveyed to the outlet aperture 18. The conveyor screw 19, which is supported against a thrust bearing 20, also cleans the sieve gaps 27, since at each rotation its screwthreads remove the material collecting at that place, thus ensuring smooth operation.

The separating plates 71 illustrated in Fig. 6 consist of a helically wound strip 72 of rectangular cross-section. The sieve gaps 73, through which the material flows in the radial direction and which are machined, for example, embossed in the strip 72, are constructed as triangular, square or semicircular recesses 73', 73" and 73"'.

In the embodiment illustrated in Fig. 7 the screw 2 of the extruder 1 has an extension 41 engaging in the separating head 11. The extension 41 also projects into a recess 43 of a flange 42 which closes the casing 12 at its front end and is formed with an outlet aperture 44 disposed coaxially of the separating head 11. The aperture 44 can be opened and closed by means of a sliding valve 45 operable via a servo device 46 in the form of a pressure-medium operated piston sliding in a cylinder.

Material retained by the sieve gaps is therefore conveyed directly to the aperture 44, which can be automatically opened intermittently or as required in dependence on the back pressure of said material, by the extruder screw 2, which is conically constructed in the core of the extension 41 and also in the zone engaging in the recess 43.

At the same time the sieve gaps are cleaned by the worm 2.

The separating head 51 illustrated in Fig. 8 comprises a casing 52 in which are located separating plates 61. In this embodiment, a portion of the end face 62 of each separating plate 61 is set back, so as to form a separating edge 63, extending around the circumference of the disc, and ducts 64, in the outer zone of the separating plate.

The separating plates 61 are arranged on a sleeve-like extension 54 of the extruder worm 2, which extension has a screwthreaded portion 58 on to which a nut 59 is screwed. The nut 59 thus clamps the separating plate 61 and the conveying duct 53 of the separating head 11 is also sealed by means of an external screwthread 60 machined into the nut 59.

In the separating head 51 illustrated in Fig. 8, the plasticised material conveyed by the extruder 1 is forced radially inwards between the separating plates 61. Solids are held back by the sieve gaps which have no numerical reference and which are formed by the separating edges 63, while the purified material flows through the ducts 64 and apertures 55 machined into extension 54 in a coaxial duct 56. The duct 56 issues into a nozzle 69 which is attached to the separating head 51 and from which the regenerated material emerges in the form of a film 70.

For the removal of the solids retained at the sieve gaps, the casing 52 illustrated in Fig. 9 is formed with a radial aperture 57 which can be opened by a slide 67 actuatable by a servo device 68. Also extending through the aperture 57 is a scraper 65 which is urged by a spring 66 against the separating discs 63. Those parts of the material which collect at the sieve gaps and of course can be re-utilised are therefore removed by the scraper 65, so that clogging is almost impossible and the smooth operation of the separating head 51 is ensured.

Claims

1. A device for the separation of materials having different melting points, more particularly for the regeneration of plastics wastes which are coated with foil and can be plasticised in an extruder, characterised in that the separating device is constituted by a separating head which is connected to an extruder and in which, in a casing rigidly connected to the peripheral wall of the extruder, one or more annular separating plates are located, which are so disposed at a small distance from one another to create radially directed sieve gaps, or which each are so formed with one or more identically directed recesses that the separating plates operate as a sieve for the plasticised material.

2. A device according to claim 1, wherein to form the sieve gap in the inner or outer zone of the separating plates, one or both end faces thereof have separating edges which are set back in relation to such end faces and which merge into an annular collecting duct connected to an outlet aperture of the separating head for the purified plasticised material.

3. A device according to claim 1 , wherein to form the sieve gap in the inner and/or outer zone of the separating plates, radially directed recesses are machined into one or both of their end faces of said plates, such recesses issuing into an annular collecting duct connected to an outlet aperture of the separating head for the purified material.

4. A device according to any of claims 1 to 3, wherein the separating plates are formed by a strip of preferably rectangular cross-section which is wound helically and into which the sieve gap is machined, for example, embossed.

5. A device according to claim 3 or 4, wherein the recesses machined into the separating plates have a triangular, rectangular or semi-circular cross-section.

6. A device according to any of claims 2 to 5, wherein the annular collecting duct of the separating plates is wholly or partially encircled by a further annular duct, and the two ducts are interconnected via diametrically opposite recesses machined into the separating plates.

7. A device according to any one of claims 2 to 6, wherein to connect the collecting ducts of the individual separating plates ot the outlet aperture of the separating head, one or more radially directed recesses which extend in alignment with one another and issue into the collecting duct are machined into each of the separating plates, or their end face formed with the separating edge or recesses is partially set back.

8. A device according to any of claims 1 to 7, wherein to remove solids from the separating head, a conveying screw is provided which is preferably coaxial with the extruder screw and which engages in the separating head or is connected to its conveying duct.

9. A device according to any of claims 1 to 7, wherein to remove solids from the separating head the conveying screw of the extruder has an extension which is preferably constructed conical in the core and which engages in the separating head.

10. A device according to any of claims 1 to 7, wherein for the removal of solids from the separating head the latter has a removal aperture which can be closed, for example, by a sliding valve or the like actuable by a servo device.

11. A device according to any of claims 1 to 10, wherein means are provided for heating the separating head, said means being constituted by a heating strip which wholly or partially encloses the separating head.

12. A device for the separation of materials having different melting points, substantially as herein described with reference to and as shown in the accompanying drawings.