The present invention concerns a method for tearing up plastic bags and of the kind indicated in the preamble of claim 1.

In connection with refuse collection it has been increasingly common to perform some kind of source sorting of the collected refuse. Some cities have performed this task by providing each household with several small containers, namely a container for paper, final refuse and glass, respectively. Other cities have solved the problem by providing each household with one large container as respective types of refuse, such as com- postible refuse, paper, final refuse and glass are filled into plastic bags with different colours and which are closed with a knot before the plastic bags are filled into the container. For example, green plastic bags are used for paper, i. e. newspapers, week- lies, cardboard and advertising matter, black plastic bags for combustible final refuse and white plastic bags for glass and bottles.

At the recycling station, the plastic bags are emptied in a sorting facility where a col- our-based sorting of the plastic bags is performed in an automatic or semi-automatic way so that the green plastic bags with paper are sorted from the white and black plas- tic bags with glass and final refuse, respectively. Subsequently, the respective plastic bags are opened and emptied which traditionally has appeared to be a difficult task.

The invention has the object of indicating a method for tearing up plastic bags of the kind mentioned in the introduction, e. g. plastic bags with paper, and which in a simple way enables to empty the plastic bags in such a way that the paper content, e. g. news- papers, weeklies, and advertising matter, are not torn apart at the same time, i. e. with- out the subsequently needed sorting out of weeklies and coloured advertising matter being further impeded.

The method according to the invention is characterised in that a closed plastic bag with a content desired to be taken out is led down into a funnel-shaped container and is introduced between a rotating drum provided with rows of radially projecting knives

with forward directed cutting edges and a preferably resilient, inclining wall which is provided with stationary, projecting teeth approximately opposite to the axis of the drum and between the knives of the drum, that the plastic bag is cut up successively by means of the knives and teeth, and that the content of the plastic bag, e. g. of paper items, also by means of the knives and the retainer, are successively emptied into a container or on a conveyor belt, preferably together with the torn open plastic bag.

Surprisingly it has appeared that a closed plastic bag filled with stacked paper items in the form of newspapers, weeklies or advertising matter by the indicated method may be torn open in such a way that the paper items without being torn apart, may succes- sively be emptied into a container or on a conveyor belt, preferably together with the torn up plastic bag which after the tearing open is still in one piece, i. e. the plastic bag, either in immediate connection with the tearing up or subsequently, is easy to sort out manually or by machine. Apparently, the weight difference between the very light plastic bag and the relatively heavy paper items contributes to the successful, succes- sive emptying of the paper items so that the torn up plastic bag leaving the tearing drum as the last may be led away by means of a rotating brush and/or sucking mouth piece.

In order not to impede the said subsequent sorting of the paper items, i. e. sorting out weeklies and advertising matter with colour printing, it is very important that the tearing up of the plastic bag and emptying of the paper items occurs as carefully as possible, and as mentioned it has surprisingly appeared not to be a problem by the described method.

For use in tearing open plastic bags of the type used for baked bread, e. g. white bread or rolls, the method according to the invention can be modified in such a way that one or more closed plastic bags with bread are torn open between the drum, which is pro- vided with relatively long, radial knives for the purpose, and the resilient inclining wall which is provided with relatively long, stationary teeth for the purpose. Hereby may be achieved an effective tearing open and emptying of plastic bags with baked bread collected from baker shops and supermarkets, and which is used for feeding

animal husbandry, particularly pigs. The sorting out of the torn open plastic bags which still are in one piece may, as described above, occur manually or by machine.

The invention also concerns an apparatus for use in performing the method which is of the kind indicated in the preamble of claim 3 and is characterised in that tearing up means for use in tearing open the plastic bags are constituted by relatively short knives which are designed with sharp cutting edges in the direction of rotation, that the sta- tionary teeth are constituted by relatively short pieces of round iron which are welded onto the resilient wall part approximately opposite to the horizontal axis of the tearing up drum, and that an opposite fixed wall part of the receiving container is designed with a scraper plate with a number of edgewise recesses adapted to the length and shape of the knives.

For use in performing the method according to claim 2, i. e. for tearing open plastic bags for baked bread, e. g. in the form of white bread and rolls, the apparatus according to the invention may comprise a mainly funnel-shaped receiving container, a horizon- tally rotating tearing up drum suspended therein and with radially projecting tearing up means, and stationary projecting teeth which are arranged to engage between the tearing up means and which are fastened on a resilient wall part of the receiving con- tainer, and be suitably arranged so that the tearing up means for use in tearing open the plastic bags are constituted by relatively long, knives which are designed with sharp cutting edges in the direction of rotation, that the stationary teeth are constituted by relatively long pieces of flat bars which are welded onto the resilient wall part ap- proximately opposite to the horizontal axis of the tearing up drum, and that an oppo- site fixed wall part of the receiving container is designed with a scraper plate with a number of edgewise recesses adapted to the length and shape of the knives.

In a simple way, for use in tearing open plastic bags with recycled paper, the apparatus according to the invention may be designed so that the knives have a radial extension of about 10 mm, that the largest breadth of the knives is about 8 mm, that the length of the knives is about 30 mm, that the pointed end part of the knives (with the cutting edge) has a length of about 10 mm, that the stationary teeth are constituted by round

iron pieces with a length of about 20 mm and a diameter of about 12 mm. Suitably, the edgewise recesses of the scraper plate may have a depth of about 15 mm and a breadth of about 12 mm.

For use in the mentioned alternative tearing open of plastic bags for baked bread it may be advantageous that the knives have a radial dimension of about 50 mm, that the greatest breadth of the knives is about 12 mm, that the length of the knives is about 40 mm, that the pointed end part of the knives (with the cutting edge) has a length of about 12 mm, that the stationary teeth are constituted by flat bar pieces with a length of about 45 mm and a breadth of about 12 mm. And in this case, the edgewise recesses of the scraper plate may have a depth of about 60 mm and a breadth of about 15 mm.

The invention is explained more closely in the following in connection with the drawing, on which: Fig. 1 shows a partial view of an embodiment of an apparatus according to the in- vention, Fig. 2 shows a close-up view of a tearing drum for the apparatus of Fig. 1 according to the invention, Fig. 3 a second partial view of some details by the apparatus of Fig. 1 according to the invention, and Fig. 4 shows a plastic bag with newspapers and periodicals inserted between the tearing drum and a front spring biased wall plate with projecting retainer fin- gers.

The partial view depicted in Fig. 1 of an embodiment of an apparatus according to the invention shows an upwards open, funnel-shaped receptacle 2 of which one may be disposed at each side of a conveyor belt (not shown), comprising an ejector arm which is controlled by e. g. a colour sorting system that provides for bags containing recycled paper, e. g. folded newspapers, weeklies or advertising matter, are led down succes- sively into the receptacle 2. A horizontal tearing drum 4 is mounted between opposite

end walls 6 of the receptacle 2 which at the side situated in the running direction shown with arrow 7 of the tearing drum is provided with a spring biased inclining wall 8. At the opposite side, the receptacle 4 is closed downwards by means of a fixed scraper plate 10 which is designed with a number of edge recesses 12 towards the tearing drum 4, the number, shape and spacing of the recesses 12 being complemen- tary to rows of tearing knives 14 projecting radially from the surface of the tearing drum 2. The scraper plate 10 has the purpose of scraping off material which otherwise would tend to be carried with the tearing drum 2.

In the shown embodiment, the tearing knives 14 of the tearing drum 2 consist of short, radial flat bar pieces projecting about 10 mm from the surface of the tearing drum 2 and having a total length in the peripheral direction of about 30 mm, of which a forward directed pointed end constituting about 10 mm ends in a sharp cutting edge 16. The spring biased inclining wall 8, which is spring biased for allowing escape of inadvertent hard, solid objects without blocking or damaging the tearing drum 2, is about opposite to axis of the tearing drum 2 provided with projecting stationary teeth 18 consisting of short pieces of round iron which are welded to the inclining wall 8 between the tearing knives 14 and which e. g. have a length of about 20 mm and a di- ameter of about 12 mm.

The distance between the resilient inclining wall 8 with the projecting stationary teeth 18 and the tearing drum 2 may advantageously be adjustable, something which may also be the case with the resilient contact pressure of the inclining wall 8.

As shown in Fig. 3, the tearing drum 2 is driven by means of an electric motor 20 via a belt pulley 22 with a certain gear ratio, but alternatively the tearing drum 2 may be directly drivingly connected with an electric motor, the rotational speed of which be- ing controlled by means of a frequency converter as the normal rotational speed of the tearing drum 2 is about 500-600 rpm.

The shown embodiment is intended for tearing open closed plastic bags 24 (Fig. 4) containing recycled paper, e. g. stacked newspapers, weeklies or advertising matter,

which after emptying is to be sorted so that coloured paper, namely weeklies and ad- vertising matter, is sorted from newspaper. In order to enable such subsequent sorting of the recycled paper, it is therefore important that the tearing open and emptying of the plastic bags occurs in such a way that the recycled paper maintains its structure, i. e. is not torn too much apart. Furthermore, it is important that the plastic bag is not torn apart more than necessary for the emptying, i. e., as far as possible, the plastic bag is to stay in one piece which makes it reasonably easy to sort out the plastic bags. This may occur manually or by machine, e. g. by means of brushes or suction mouthpieces, or possibly a combination thereof, as this sorting out is facilitated by the plastic bag, as the lighter component, leaves the tearing drum last, as seen in direction of rotation, i. e. after the heavier recycle paper has left the tearing drum.

As indicated, the method and the apparatus, respectively, according to the invention may relatively easily be modified for use in tearing open and emptying of other kinds of content, e. g. plastic bags with baked bread in the form of white bread or rolls. For this purpose, the tearing drum is only provided with longer knives, e. g. with a radial dimension of about 50 mm and a width of about 12 mm. In the peripheral direction, the knives may have a total length of about 40 mm as the pointed end of the knives (with the cutting edge) can have a length of about 12 mm. The stationary teeth may correspondingly be constituted by flat bar pieces with length about 45 mm and width about 12 mm. The mentioned edgewise recesses of the stationary scraper plate at the opposite side of the tearing drum are also naturally to be adapted to the actual shape and mutual position of tearing knives.

Finally, it is to be mentioned that the method and the apparatus according to the in- vention have appeared to have almost universal fields of application. Thus it has ap- peared that by means of apparatuses according to the invention, it has been possible to tear open and take out very different items from plastic bags, such as sausages, meat slices, meat, chocolate, sweets, other confectionery together with cookies with ex- ceeded last date of sale. After tearing open and unpacking sausages and slices of meat, this material may e. g. be used as a very appreciated contribution to the biomass at the production of biogas. Chocolate, sweets and other confectionery goods may e. g. be used as supplement for animal feed after unpacking according to the invention.