PLASTICS MATERIAL

TECHNICAL FIELD

The present invention relates to a method and an apparatus for re¬ covering plastics material in the manufacture or processing of plastics film and entails that waste film is separated off and comminuted in a grinding apparatus. BACKGROUND ART

In the manufacture or processing of plastics film, edge strips or similar waste products are formed which cannot be included in the fin¬ ished product. Previously, attempts have been made in the art to recover such waste strips by collecting them, storing them and thereafter con¬ verting them to a product which may be likened to a granulate. In purely practical terms, the process of such conversion has been such that the waste strips are fed into a machine where they are, by the action of friction, comminuted and subjected to such high temperatures that the comminuted particles lump together to form larger aggregates. The plas¬ tics material recovered in this way has then been admixed in new mat¬ erial which is recycled to the manufacturing process.

The above-outlined recovery methodology suffers from a number of drawbacks, of which one is that the handling of the waste strips often involves problems of dirt contamination, which considerably reduces the quality of the recovered material. Furthermore, the plastics material

often includes economically important amounts of additives of different types and these additives are, as a rule, wholly or partly lost in the above-outlined recovery process.

Despite the fact that the recovered film in the above-described methodology has been given a more compact and, to a certain extent, gran¬ ulate like form, there have been certain problems in the separation of old and new material, in that the particles are of different sizes, dif¬ ferent densities and possess different frictional properties.

Even though it has been possible, to a certain degree, to obviate the above-considered quality loss in the waste material by grinding the waste material to flake form, such a process has not previously been applicable. The reason for this is quite simply that it has not been possible, with any degree of reliability, to admix the waste material ground to flakes since this, because of differences in density, differ- ences in particle form and differences in frictional properties, has proved to be immiscible with the new plastics material which is in granulate form. Even if the mixture has been created with a greater or lesser degree of accuracy by machine or by hand, the different plastics qualities have, without exception, separated because of the vibrations which occur on transport of the material, or even in the infeed system to the machine where the plastics mixture is to be used. OBJECT OF THE PRESENT INVENTION

Thus, the object .of the present invention is to realise a method of recovering plastics material, by which method the above-outlined pro- blems are obviated. SOLUTION

According to the present invention, the method is characterised in that the comminuted waste film is conveyed to a plastics-consuming machine and discharged in a position above the plastics material inlet opening of the machine, that new plastics material is supplied at the inlet opening at the position of discharge of the waste film, and that the new plastics material is added such that there is maintained, at the position of discharge of the waste film, a volume of new plastics material, the upper defining surface of this volume being kept at a distance above the position of discharge of the waste film.

According to the invention, the method is suitably further chara¬ cterised in that the discharge of waste film is effected in a position which is coaxially centered and directed relatively closely above the inlet opening of the plastics-consuming machine, that the volume of new plastics material is caused to surround this position on all sides and thence to be fed into the inlet opening of the plastics-consuming machine together with the discharged waste film.

Further advantages will be attained if the method according to the present invention is also given any one or more of the characterising features as set forth in claims 3 and 4. FURTHER OBJECTS OF THE PRESENT INVENTION

A further object of the present invention is to realise such an apparatus for the recovery of plastics material as has been intimated above and is designed so as to obviate the above-considered disadvantages inherent in prior art equipment. FURTHER SOLUTION

According- to the present invention, this object is attained if the apparatus comprises means for separating the waste film and a comminution device for the comminution of the waste film, and is characterised by a transfer apparatus coupled between the comminution device and a plastic consuming machine, the transfer apparatus having an outlet which is dir¬ ected to a position above an inlet opening on the plastics-consuming machine intended for plastics material, an inlet device for new plastics material which is in communication with the inlet opening and with the supply means for new plastics material, the outlet and the inlet device being of such mutual location and the inlet device being of such design that there is formed therein a volume of new plastics material whose upper surface is located at a distance above the outlet.

According to the invention, the apparatus is further also suit- ably characterised in that the outlet of the transfer device is disposed in a coaxially centered position directed relatively closely above the inlet opening of the plastics-consuming machine, that the inlet opening is disposed in the bottom of the inlet device, the inlet device having an annular portion which surrounds the outlet and extends up above the level of the outlet where the supply means are connected.

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According to the present invention, the transfer device should also suit¬ ably comprise a fan and a conduit for the airborne conveyance of the comminuted waste film and an air separator which has the outlet, the air separator being directed and centered in relation to the plastics- consuming machine by cooperation with the inlet device.

Further advantages may be attained according to the invention if this is also given the characteristic features as set forth in any one of claims 8 to 10. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will now be described in greater detail below, with reference to the accompanying Drawings, in which:

Fig.1 schematically shows an apparatus for the recovery of plastics material according to the invention;

Fig. 2 is a vertical cross section through the inlet portion of a plastics-consuming machine; and

Fig. 3 shows, in vertical section, a modified embodiment of the inlet portion to a plastics-consuming machine. DESCRIPTION OF PREFERRED EMBODIMENT

Fig. 1 schematically illustrates the concepts which form the basis of the present invention. In this Drawing figure, strips of waste film are designated 1 and these strips are separated from a film-producing or film-processing machine or plant, for example by the use of suitably placed blades. To ensure that the waste film does not obstruct production or disturb processing should any fault occur in the recovery process, a special feeder mechanism 2 is employed, which immediately takes care of and removes waste film from the production or processing machine. The feeder mechanism 2 is suitably disposed in immediate conjunction with a mill 3 in which the waste film is ground down to flakes or part¬ icles. The discharge grid in this mill should of relatively fine mesh and, for example, have through-flow orifices of 3 mm when the treated film is thinner than 5ϋμ .

The outlet of the mill is in communication, by the intermediary of a conduit 4 which should suitably be as short as possible, with a fan 5 which, on the one hand, assists in emptying the mill of ground plastics flakes and, on the other hand, discharges them in airborne state through a conduit 6. This conduit is connected to the upper end

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of an air separator which is designed as a cyclone 7 and has an air out¬ let 8.

In the cyclone 7, the air forced forward by the fan 5 is separated from the plastics flakes to which the waste film 1 has been ground so that there is formed a fraction of plastics flakes in the bottom of the cyclone. These flakes are extremely light and are, as a result, difficult to uniformly and evenly admix into new plastics material which is in granulate form, partly since the particles are of completely different configuration, and partly since the particles are of different density. Moreover, the mutual friction between the particles is slight. Hence, if the separated fraction of plastics flakes were to be admixed to the new plastics granulate - which in itself is a difficult process - the thus attained plastics mixture would not be stable but would show a marked tendency to reseparate in the event of the slightest handling or vibration, which would have the result that such a plastics mixture would cause operational disturbance if it were to be recycled into the process.

According to the present invention, the cyclone 7 is disposed in direct conjunction with the inlet device 9 on a plastics-consuming ma- chine 10 which, for example, may consist of an extruder.

The new plastics material which is to be processed in the extruder 10 is supplied from a central reservoir to a buffer receptacle 11 which, by the intermediary of a conduit 12, is in communication with the upper end of the inlet device 9. The invention builds on the fundamental concept that the admixture of the waste film ground to flake form must be effected as close to the final consumer as possible and, moreover, in such a manner that there can be no separation of the two material qualities from one another, despite the movement and vibration which may occur in the plastics mat- erial mass during admixture and subsequent processing.

Fig. 2 shows the appearance of a first embodiment of the apparatus required for realising the mixture. In Fig. 2, the cyclone has the same reference numeral 7 as in Fig. 1, and it will be apparent that the inlet device 9 is in the form of a substantially circular frusto-conical fun- nel whose minor end is directly connected to a short vertical channel 13 which discharges directly, into the feeder and mixer screw 14 which

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is interiorly disposed in the extruder 10. In the illustrated embodiment, the vertical channel 13 is circular in form, as also applies for the funnel 9 and its outlet, i.e. the inlet inlet opening 15 to the plastics- consuming machine. The cyclone 7 is provided with a painted, circular-conical and down¬ wardly tapering portion which terminates in a short tubular and circular portion 16, having approximately the same diameter as the vertical chan¬ nel 13. This tubular portion 16 may be considered as the outlet from the cyclone 7 and is placed concentrically above the vertical channel 13 and the inlet opening 15. The lower end of the tubular portion 16 is, viewed in vertical terms, placed relatively close to the inlet op¬ ening 15 so that there is formed an annular space 17 about the tubular portion.

To realise the above-described arrangement of the tubular portion 16, the cyclone 7 is suitably fixedly retained and directed in relation to a lid 18 which, in its turn, is mounted on the upper end of the inlet device 9. Suitably, the cyclone 7 is adjusted in such a manner that it may be vertically set, laterally set and also, to a certain extent, at an angle in relation to the vertical so that thereby both the direction and the position of discharge of the plastics flakes through the tubular portion 16 may be accurately adapted in relation to the inlet opening 15 and the annular space 17.

During operation, the waste film ground to flake form is separated in the cyclone 7 by centrifugal force, since a spiral motion is created in the cyclone which results in the flakes gradually migrating outwardly towards the outer casing of the cyclone where they are arrested in their movement by friction against the casing surface. Thereafter, the flakes will essentially follow a spiral pattern down along the surface of the cyclone casing to the tubular portion 16. At the same time, new plastics material is fed in in the form of granulates through the conduit 12, in through the opening 19 so that the inlet device 9, i.e. the inlet funnel will be almost completely filled with granulate and, at least to the extent as intimated by the broken line 20. This fed-in granulate will then move downwardly through the annular space 17 in order, immedi- ately therebeneath, to entrain and partly mix with the flake-formed waste material emanating from the outlet of the tubular portion 16.

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Thereafter, the mixture is passed straight downwardly through the inlet opening 15 and the channel 13, down into the feeder screw 14 where pro¬ cessing of the plastics material is commenced.

The centering of the tubular portion 16 is vital, since an inclined setting of this portion (excentric in relation to the inlet opening 15) would easily result in a too powerfully assymetric downward movement speed for the granulate in the annular space 17, which in its turn might result in the flake-formed waste material "floating up" to the surface 20 of the granulate in such areas where the downward movement speed of the granulate is slow. Such a situation would be particularly trouble¬ some if the machine is subjected to vibration.

The major reason why no separation or upwardly-directed movement of the flakε-fαrmed material can take place, according to the present invention, is that the downward movement speed of the mixture and the granulate from the annular space* 17 and downwardly to the feeder screw is greater than the "rising speed" which the flake-formed waste material would have under the action of vibrations in a stationary volume of granulate.

The fact that the flake-formed waste material is conveyed by a fan 5 and separated in the cyclone 7 further entails that a certain, albeit slight, excess pressure must be counted on in the discharge tube 16 of the cyclone. This slight excess pressure is caused by the pressure loss¬ es which take place in the discharge section 8 to the cyclone. Since the upper surface 20 of the granulate located in the funnel 9 is free in relation to the ambient atmosphere, the insignificant excess pressure prevailing in the cyclone will hamper the "rising tendency" which the flake-formed material might possibly display. For this reason, it is important that the opening 19 to the inlet device 9 and its design be realised in such a manner as always to guarantee that the upper surface 20 of the granulate is located at a satisfactory height above the out¬ let from the tubular portion 16.

On the Drawings, the conduit 12 has been shown as incoming tangent- ially at the upper edge of the funnel 9, but, naturally, the conduit 12 could just as well be placed so as to discharge in the lid 18. If demands of symmentry so require, more than one conduit may, naturally, be employed and, in such an event, discharge in a position approximately

diametrically opposed to the position of the first conduit. FURTHER EMBODIMENT

Fig. 3 illustrates a slightly modified embodiment of the present invention. This embodiment differs primarily from the above-described embodiment in that the tubular portion 16 on the cyclone 7 has a lower support and centering ring 21 which interiorly abuts on the funnel 9 immediately adjacent the inlet opening 15 of the extruder. In order to reliably centre and control the cyclone 7, the ring 21 is suitably con- ically bevelled on the outside at an angle which approximately corres- ponds to the angle of the funnel 9.

The ring 21 is connected to the tubular portion 16 by the inter¬ mediary of a number of vertical connection members 22 between which there are openings 23 for the infeed of the granulate from the annular space 17. Suitably, the openings 23 are uniformly and regularly spaced about the circumference of the tubular portion 16 and should accommodate as great a portion of this circumference as possible.

The embodiment according to Fig. 3 functions in the same manner as the embodiment described earlier, but may be more readily applicable in conjunction with the reconstruction of an extant machine, since only the cyclone proper need be be adapted and no alterations are required to the lid 18 or the inlet funnel 9. MODIFICATION OF THE INVENTION

In such situations when the extruder 10 is provided with an infeed channel 13 which is rectangular seen from above, centering of the tubular portion of the cyclone 7 may be realised in such a manner that a cylind¬ rical tubular insert is placed in the vertical channel 13. The lower end of this insert (not shown on the Drawings) is of a design which is adapted to the circumference of the feeder screw 14. The upper end of the insert is suitably provided with a flange which, on mounting of the funnel 9, is placed between the lower retaining flange 24 of the funnel and the retaining flange 25 of the extruder. As a result, the funnel 9 may simply retain its circular configuration and be adapted to the inlet opening 15 provided in the insert.

The invention may be modified without departing from the spirit < and scope of the appended claims. Thus, in certain situations, it may be possible to eliminate the fan 5 and the conduit 6 so that thereby

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the mill 3 is instead placed directly on the cyclone 7 or, possibly, directly on the inlet device 9. In the first alternative, the conduit designated 4 in Fig. 1 will become the inlet to the cyclone 7, while the same conduit with a downward extension in the latter variation would replace the tubular portion 16 illustrated in Figs. 2 and 3.

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