The invention relates to an apparatus for the cutting up of in particular fishing nets containing nylon, said apparatus comprising at least one comminutor that comprises: a first shaft having at least four knife blades, each of which comprises a number of teeth with a convex portion and a concave portion, said knife blades being configured with like teeth, but each separately being arranged such on the shaft that the knife blades are successively, mutually shifted rotationally throughout the course of the shaft such that any knife blade adjoins at least one other knife blade with displacement; a second shaft having at least four knife blades, each of which comprises a number of teeth, said second shaft comprising a number of knife blades that are preferably like the knife blades on the first shaft and arranged preferably such that the second shaft is a mirrored copy of the first shaft mirrored in a face plane that is in parallel with the longitudinal axis thereof; at least one drive unit for rotating the one or both shafts.

According to a further embodiment the invention relates to the comminution of fishing nets.

Recycling of plastics usually entails that the plastics are comminuted and then recycled. In the prior art, the product made by the comminution is most often a mixture of different types of plastics, and this may be due either to the individual pieces being manufactured from different types of plastics and/or to many different pieces being mixed prior to the comminution. This means that the plastics made by recycling are not of a high quality.

Therefore, recycled plastics are most often used within technical fields where very high demands to the nature of the plastics are therefore not made, such as eg for flooring or road construction. By the invention it has been realised that fishing nets can be broken down to the effect that the different types of plastics of the fishing nets can be separated.

Fishing nets are often made from several different types of plastics, including eg nylon, but also from other and softer types of plastics such as polyethylene or polypropylene, and this makes particular demands to the machinery that is to manufacture recyclable plastics from fishing nets.

In particular the hard nylon makes high demands to the cutting edges of the machinery. Moreover, fishing nets are often made with knots and windings, meaning that fishing nets do not have a homogenous appearance.

By the invention it has been found that such drawbacks of fishing nets can be countered by use of an apparatus wherein the teeth of the knife blades on each shaft comprise cutting edges on both the convex portion and the concave portion of the teeth; and that the displacement between the knife blades is adapted to the knife blades such that the cutting faces on the convex and the concave portions of the knife blades on the one shaft enter into cutting engagement with corresponding convex and concave portions on the knife blade on the second shaft when the one or both shafts are rotated.

By using an apparatus as set forth, it is accomplished that the net is comminuted by the material being cut rather than torn apart. Thus, by the invention it has been realised that, when the material is being cut, a release of the individual components of the net is made.

That can be used to advantage in a process step wherein the comminuted plastics are both washed and separated in a tank of water; it being used to advantage that, normally, fishing nets comprise types of plastics having densities that exceed that of water, and types of plastics having densities below that of water. By the method, it is used to advantage that the different types of plastics are released by the comminution, the different types of plastics of the net being no longer in mutual engagement. When the released plastics fibres are transferred to a water-filled vessel, it may thus be used to advantage that plastics having a higher density than water are separated from plastics having a lower density than water, the one type floating and the other type sinking. By skimming the surface and cleaning the bottom, respectively, in a final process step, collection the plastics fibres separated into types of plastics having densities above or below 1000 kg/m ³ , respectively, is thus obtained. Such separation may also take place in a process step where different types of plastics are separated by means of eg air as it is known eg from agricultural reapers.

In general:

The comminution as such takes place in comminutors that comprise a number of knives that are arranged on a shaft. According to the invention each comminutor comprises two shafts with knives that are preferably configured alike. Each shaft comprises a number of blades that are arranged at a mutual distance which is adapted to the width of the knives to the effect that the knives on the two shafts can slide between each other and cut material when the front of a tooth on a knife on the one shaft meets the rear of a tooth on a knife on the second shaft.

Thereby the two shafts, each of which comprises knives, can cut material rather than crush it between the teeth of adjoining knives. By cutting material in this manner a further advantage is accomplished since the knives on the two shafts need not operate synchronously like in known comminutors that require that the tips of the knives on the one shaft meet the tips of the knives on the second shaft when they rotate.

The process may comprise four process steps wherein the net is conveyed through four comminutors that perform a coarse separation, a medium separation, a fine separation, and finally an extra-fine separation of the nets. The first three process steps utilise knives having an external diameter of 355 mm, and the knives rotate at 5.6 revolutions per minute. The final separation takes place in a process step in which the knives have a diameter of 350 mm and in which rotation is performed at a speed of between 9 and 1 1 revolutions per minute. As it is, the comminutors are made such that the capacity is increased between the individual steps.

Thus, the comminution is performed in steps wherein a first process step cuts the net by knives that have a diameter of 355 mm, a cutting width of 28 mm and a number of cutting edges, five cutting edges per knife, wherein the knives are made alike, but arranged in a rotationally displaced manner to the effect that each individual knife is displaced relative to the adjoining knives. Thereby the rotary arrangement of the knives is repeated at an interval of four.

The subsequent comminutors are made finer by more slender knives; thus a second comminutor having knives of a diameter of 355 mm, a cutting width of 18 mm and a number of cutting edges, nine cutting edges per knife; thus a third comminutor having knives of a diameter of 355 mm, a cutting width of 13 mm and a number of cutting edges, 20 cutting edges per knife; and finally a fourth comminutor having knives of a diameter of 350 mm , a cutting width of 8 mm, and a number of cutting edges, 15 cutting edges per knife. According to one embodiment of the method according to the invention, cleaning processes may occur between each step. For instance the drying and removal of sand. The comminution happens successively in four different comminutors. Each comminution step thus takes place in a separate comminutor. The comminution as such in each comminutor takes place by the material being fed in a controlled manner between the two rollers that are each separately provided with knives that are each separately provided with a number of teeth. The rollers rotate "towards each other", seen from the entry side. Thereby the material is pulled in between the knives. The space for the knives of the "opposing roller" is created by a so-called interlayer being mounted between the knives on the individual roller.

The knives are mounted on each shaft to the effect that the knives from the two opposing rollers enter into a mutual engagement to the effect that material between them is cut between the knives when the rollers are rotated. The comminution of the material thus preferably takes place by cutting-through being performed between the knives on the two rollers. Thus, the teeth act as grippers that exclusively force the material down into the cutting-through process which takes place between knives arranged on each their shaft. The rollers are pulled by each their electric motor, and normally this takes place via a gear exchange. In any embodiment of the invention, the drives can have individual and variable numbers of revolution.

In order to keep the spaces between the knives on the individual roller clean in respect of material, "side fingers" are mounted in the apparatus frame. Such "side fingers" are preferably mounted such that they do not touch the knives. The side fingers also serve to reinforce the structure.

The invention according to one embodiment relates to a method comprising the following actions: In a first step the fishing net is advanced and fed to a comminutor comprising knives arranged on two rollers, which knives are configured alike, but mutually and rotationally displaced throughout the course of the shafts, to the effect that, on each shaft, the knives are arranged such that any knife blade adjoins two corresponding knife blades that are mutually displaced. The knives are mounted on each shaft as described above, and the two shafts with knives are almost identical (mirrored copies), the one shaft being a copy of the other shaft mirrored in a face plane that sits in parallel with the longitudinal axis thereof.

The knives as such on the two shafts are displaced by approximately the width of a knife in order to thereby achieve that the knives on the one shaft may "slide cuttingly in" between the knives on the second shaft or vice versa. The knives on the two shafts may be arranged such that the teeth from the knives on the one shaft meet the teeth on the second shaft when the shafts rotate. Thereby the sets of teeth on both shafts contribute to pulling material down between the knives. However, it has been found that precisely embodiments wherein the teeth of the knives do not meet thus present advantages, since some materials such as in particular nylon become broken down by cutting rather than crushing. Thereby the process becomes more uniform with a more homogeneous end product.

The feeding of the individual comminutors takes place in a controlled manner in order for them not to be overfed. This is accomplished, in one embodiment, by feeding of the comminutors by means of conveyor belts, pull drums with brakes and the like.

Subsequent comminutors need to have a capacity that preferably exceeds that of the preceding comminutor. The feeding to them takes place, on the one hand, by conveyor which may preferably be provided with an elongate, vibrating funnel having a variable output slot. Such funnel serves as "flow equalizer" and distributor of the material throughout the entire roller length.

All of the rotating knives preferably cut the material on the sides of the knives. The knives of the coarse, the medium and the fine comminutor each separately cuts directly on the teeth, between the concave and convex portions of the teeth, while the extra-fine comminutor typically also cuts on the edge of a recess configured on the frontmost portion (seen in the direction of rotation) of the convex portion of the teeth.

In the claims and specification the phrase "slide in" is used as a description of that which happens when the knives from the one shaft "slide in" between the knives of the second shaft. Thus, that term describes the cutting/shearing property that is accomplished, by the invention, between the knives on the two shafts that rotate towards each other and cut over material in the same manner as the cutting edges of a pair of scissors, wherein the cutting edges (the shear blades) also "slide towards each other".

The terms: 'tips' and 'teeth' are used in combination with the term 'cutting edge' about the cutting parts of the knife blades; there is no technical difference between those two designations when the terms 'tips' and 'teeth' are used about the cutting parts of the knife blades.

In the application the terms: 'shear' and 'cut' are used. Those terms and terms derived therefrom, such as eg 'cutting' or 'shearing', cover the same; viz the same shearing process as the one that occurs in a pair of scissors where two parts cut eg a strand of hair or a piece of paper. In the following, an embodiment of the invention will be explained with reference to the figures, wherein:

Figure 1 is a perspective view of an embodiment of a knife for use in a comminutor according to the invention;

Figure 2 is a lateral view of the knife seen in figure 1 ;

Figure 3 shows the knife seen in figure 2, seen from above;

Figure 4 shows a comminutor according to the invention, seen in a perspective view:

Figure 5 shows, in a perspective view, an embodiment of a comminutor wherein it is not two oncoming knives that cut; rather it is one rotating shaft with knives;

Figure 6 is a perspective view of a side finger; Figure 4 shows an apparatus for comminuting in particular fishing nets, said apparatus (60) comprising at least one comminutor.

That comminutor comprises:

A first shaft (51 ) having at least four knife blades. This shaft is seen to the right in the figure, and more than 20 knives sit on the shaft, in the embodiment shown, each of which separately comprises a number of teeth.

All knife blades on the shaft are configured with like teeth, but the knives are arranged such on the shaft that they, in the example shown, are successively mutually displaced rotationally by 90 degrees throughout the course of the shaft to the effect that each knife blade adjoins at least one other knife blade with a 90 degrees' displacement. However, the knife blades on the two shafts may also be arranged rotationally displaced in another manner, the 90 degrees not being necessary for achieving the effect of the invention, viz cutting rather than crushing; rather they should be construed as an embodiment.

All knife blades on the shafts are, in the shown examples, configured with like teeth, but, in the shown example, the knifes are arranged such on the shaft that they are successively mutually displaced rotationally by 90 degrees throughout the course of the shaft such that any knife blade adjoins at least one other knife blade by 90 degrees' displacement. Put into practice, this results in the teeth being successively displaced by 360 (number of teeth times 4) in two knife blades that are adjoining; if there are eg 10 teeth, there will be 360 10x4 = 9 degrees' displacement between the teeth that are most proximate to each other in two adjoining knife blades.

In the shown example, the location of the teeth is thus repeated at an interval of four knife blades, when moving longitudinally of the shaft; that number can, of course, be varied; however, practice has shown that the interval used of four knife blades has good effects.

Moreover, there is a second shaft (52) having at least four knife blades, each of which separately comprises a number of teeth; said second shaft usually being a mirrored copy of the first shaft mirrored in a face plane that is in parallel with the longitudinal axis thereof. That shaft is seen to the left in the figure.

To drive the two shafts, there are, in the shown embodiment, two drive units (53), but the apparatus may, of course, also be configured with only one single drive unit and a gear device to the effect that the drive unit can rotate both shafts. The knife blades are configured on the first and the second shaft with a mutual spacing which is about the width of a knife blade. Thereby it is accomplished that the knife blades on the one shaft may slide cuttingly in between the knife blades on the second shaft.

Moreover the teeth (46) of the knife blades on the two shafts may be arranged such that the teeth from the knife blades on the one shaft meet the teeth from the knife blades on the second shaft when the shafts rotate. Thereby the teeth on both shafts are able to seize the same piece of material and hence jointly contribute to that piece of material being pulled down into an area where the knives slide against each other. However, it has been found by the invention that in particular those embodiments where the knives on the two shafts do not run synchronously have advantages in the context of breaking down of nylon-containing plastics. As it is, by allowing the knives to run in such a manner, a high degree of certainty is obtained that the apparatus cuts material rather than crushes it between two teeth.

Reference being now made to figure 1 , a preferred embodiment of a knife blade will be explained in further detail. Thus, figure 1 shows a knife blade (1 ) with 15 cutting edges (46), but that number may of course be varied as needed. The cutting edges are configured with teeth (46) that each individually has a curvature/concave portion in front (45, 45', 45") seen in the direction of rotation. The curvature serves to seize material in such a manner that it is pulled down between the knives when the knives on two shafts are rotated towards each other. If we move backwards on the knives (against the direction of rotation R), it will become apparent that the rears of the knife tips are configured with a convex curvature, said curvature being made with two cutting edges (48, 48'), and it is against them that the material retained in the curvature is usually cut, said convex curvature being configured with complementary cutting edges (45', 45"). By configuring the knives in this manner and arranging them at such mutual distance that the knives on two shafts are capable of entering into mutually cutting engagement with those sides (45, 45', 45", 48, 48'), it is accomplished that material being processed in the comminutor is comminuted by being cut between those cutting edges. A closer look at figure 1 will reveal that the front of the convex portion of the cutting edges (seen in the direction of rotation R) has been toned with a slightly darker marking (47, 47') that the remainder of the convex portion. The slightly darker area is, for the sake of overview, shown only on the one tooth, but preferably the chamfering is made on all teeth. This area of the teeth of the knives may advantageously be chamfered. The provision of such chamfering entails increased durability and a more uniform and homogeneous cutting of material, since force applications are reduced in the chamfered area of the knives. Moreover, by comminutors configured in accordance with the invention it is further accomplished that the knives on the two shafts can be rotated asynchronously since the teeth on the one shaft need not meet the teeth on the second shaft when material is being comminuted/cut. In some cases one may also vary the speed of rotation to the effect that the one shaft runs at a speed of rotation that varies from the speed of rotation of the second shaft.

Figure 2 shows an example of a knife blade configured with a recess (3). The recess contributes to material not being entrained by the cutting edges (46) of the knives, and, at the centre of the knife, a hexagonal engagement bushing (4) will appear. The engagement bushing (4) is for engagement with the shaft of the comminutor (not shown in the figures) which is configured with a cross-section which is complementary therewith. The engagement bushing as such is typically secured in the knife blade by means of a shrink- fitting, but other securing methods may, of course, also be applied. It is the object of the engagement bushing (4) to configure it in a material that possesses strength properties that make it suitable for engagement with a shaft, whereas the remainder of the knife blade typically possesses strength properties that make it suitable for cutting jobs. The latter normally presupposes a very hard material (and a brittle one), whereas the transfer of rotation is typically best accomplished by means of a relatively soft (ductile) material. By configuring the knife blade with an engagement bushing as shown and explained, one thus achieves a number of strength adjustments to the various requirements made to cutting edges and shaft engagement, respectively.

In figure 3, the knife shown in figure 2 is shown, seen from above, showing here the bushing 4 which is for engagement with the shaft. On the top side of the knife blade, it will appear that the engagement bushing 4 is made with a slightly larger diameter than is the case at the bottom side of the knife blade (1 ) (seen in figure 1 ). As explained above, the engagement bushing 4 is usually secured in the knife blade by means of a shrinking where the engagement bushing having a temperature (typically very cold) is conveyed into the knife blade which is warmer (typically very warm) than the engagement bushing.

Shrink-fitting is a method which is used for making mechanical joints, wherein shafts, engagement bushings and the like are to be mounted into a part with a hole. The hole is configured slightly too small for mounting at uniform temperature, meaning that the external part (knife blade) needs to be heated or the internal part (engagement bushing) needs to be cooled.

Heating of the external part may take a while and in some cases metallurgical circumstances may prevent heating altogether. Therefore cooling of the interior part is optimal and that can be achieved much quicker. It can take place by use of liquid nitrogen as coolant, and by that a temperature difference of upwards of 200 °C can be achieved. The joint becomes very strong when the temperatures in the parts are equalised. To facilitate the introduction and arrangement of the engagement bushing 4 in the knife blade, it is configured with a flange that is considerably larger than the hole. This is the flange that is shown on the top face of the knife blade in figure 4, and the cold engagement bushing is quite simply arranged in the knife blade (which can be heated) by it being inserted into the hexagonal hole (from above in the figure) until the flange abuts on the side of the knife blade, following which the parts are allowed to rest until the temperatures of the two parts have equalised.

The knife arrangement as such sits in a box (54) on which the motors/drive units are also secured. As will appear from the figure, the knives meet, from the two shafts at the centre of the box, and the direction of rotation is usually such that the shaft, seen at the top in figure 4, rotates clockwise, and the shaft seen at the bottom rotates counter-clockwise. In both sides of the box, the so-called side fingers (55) are arranged. The side fingers prevent that material stuck on the cutting edges of the knives are entrained in full rotation, the size of the cavity in the side fingers, in which the cutting edges rotate through, being adapted precisely to the knife blades, and that they cut in such a manner that such material is scraped off.

A side finger (55) is shown in further detail in figure 6. The side fingers are arranged next to each other along the sides of the box as shown in figure 4.

The side finger shown in figure 6 comprises faces that are complementary to the knives, and, in the example shown, it is configured with recesses for the knives of the type which is depicted in figure 1 with a recess 3. As it is, the side finger in figure 6 is shown with a recess (6) which is complementary thereto, and below it is a further recess (74) which is adapted to the teeth (56) of the knives. The side fingers can be configured with a dovetail (73) for engagement with a complementary part in the sides of the box, whereby a very strong joint/structure is obtained. Moreover, the side fingers can, like in the shown example, be configured with openings (72) enabling them to be assembled by means of a bolted joint or other technique known to the person skilled in the art.

Figure 6 shows two openings (72), one to the right in the figure and one to the left in the figure. Of course, that number can be varied like the location. The number of and the shape of the individual recesses can/must of course also be adapted to the shape of the knife.

As mentioned, it is the purpose of side fingers that they impart strength to the structure when positioned side-by-side as shown in figure 4, but it is a further purpose that material entrained by the knives "is scraped off", preferably against the edges (76) where the knives "run into" the side fingers, and this happens on the "bottom face" of the side fingers. Thereby it is prevented that material "twists" around the knives, and the number of stops is thereby reduced. The edges (76) can be configured with a sharp edge (not chamfered).

In figure 6, there is only one edge (76) for the sake of overview, shown by reference numeral, but as will appear there is, in the shown example, eight edges that could potentially be able to scrape off material. The side finger in figure 6 is configured symmetrically to the effect that it can be mounted both to the left-hand and to the right-hand side of the box, and therefore it may be advantageous to configure all eight edges such that they are sharp. By configuring the side finger symmetrically, one can thus minimise production costs as it is needed to manufacture one model only to each individual knife type and apparatus.

Reference is now made to figure 5, where an alternative embodiment of the teeth (46) of a knife blade with associated abutments (49, 50) will be explained. Here a number of knife blades is mounted on a shaft 48, and the knife blades rotate (in the figure) in the counter-clockwise direction. This comminutor rotates, as mentioned, in to the left, and material caught by the individual cutting edge is caused/forced towards the support (49) that is provided with a number of cutting bits (50) that are secured thereto. The individual cutting bit (50) is configured with bevelled sides to the effect that they taper way from the support (49).

As will also appear from the figure, the teeth of the knife blades are configured with a tip which is complementary thereto that fits between the bevelled sides of two cutting bits (50). By configuring the teeth of the knife blades in this manner, several advantages are obtained:

• on the one hand, two counter-rotating shafts provided with knives are not needed;

• on the other hand, the cutting edges of the knives can be provided with tips (teeth) which means that the area that is moved fastest (viz the tips) is also the area that has the smallest cutting area. Thereby that area (the tips) is also exposed to minimized force application, which means an extended longevity;

• the individual bits can easily be replaced as needed, and moreover all the bits can be exchanged if eg a particular job requires that the distance between the parts that cut material up need to be adjusted, or if a particular task makes particular demands to eg the hardness of the bits.

As will also appear from figure 5, this embodiment may also be configured (like the two-shafted comminutor explained above) with a number of knife blades where the teeth are successively displaced between the individual knife blades.