SHREDDING PROCESS AND APPARATUS FOR CARRYING OUT SAID PROCESS

Abstract: A shredder (1) is surrounded by a revolving screen (3) which also acts as an elevator. Said shredder outputs the shredded material in the interior of said screen (3), which allows the exit of the smaller material through the holes and lifts the remaining material depositing it once more at the input of the shredder (1). According to the present invention the bottom surface of the drum faces a fixed wall (8) placed at such a distance that it determines the third dimension of the material which passes through.

Description: The present invention concerns a device for shredding materials such as paper, plastic, rubber, wood, thin sheet material and generally any refuse or scrap material, in order to prepare it for destruction or recycling. Currently existing shredders consist of two series of circular blades, preferably serrated, which rotate around parallel axes following an intersecting path. In these shredders the size of the pieces is determined by the space between blades of the same series mounted on an axis. This space defines only one dimension; however, it therefore guarantees one dimension only, so that in the case of raw material in sheets, it produces strips the length of which cannot be predetermined. Until now, it has been necessary to install two shredders one after the other in order to make shredding into small pieces more likely. This means, however, that shredding is still left to chance and there is no certainty of a uniform result. This sort of arrangement is also decidedly costly, since two machines must be used, with double total power. Another possibility is that offered by U.S.A. patent No. 3.931.935 in which the shredder is surrounded by a revolving screen which also acts as an elevator. In this way the shredded material drops into the screen which in turn allows the smaller shredded material to pass while bringing the rest back to the input of the shredder. Unfortunately, this system does not ensure a uniform shredding in all directions, since the screen distinguishes only two dimensions. Thus long strips frequently produced by the rotating blades of a shredder may pass perpendicularly to the axes of the holes. This happens particularly with stiffer materials. US-A-2.199.729 discloses a revolving screen surrounded by a fixed wall; the screen scrapes pulverized material upwardly. There is no need, when treating such pulverized material, to determine a longitudinal dimension thereof and US-A-2.199.729 does not give any teaching in such direction. The aim of the present invention is to guarantee the required size of the final output at a reasonable cost. There would be no point in recycling material if the equipment used to do so involved higher costs than purchase of the raw material. The aim has been achieved by a process as in claim 1 and an apparatus for shredding as in claim 3. A preferred embodiment of the present invention is shown in the attached drawings, in which: Fig. 1 shows a cross section of a shredder enclosed in a perforated drum in accordance with the invention; Fig. 1a shows an enlarged detail of fig. 1; Fig. 2 shows a longitudinal section along the line 2-2 of fig. 1. The figures illustrate a shredder indicated as a whole by (1). It consists of two series of circular and/or serrated intersecting blades (2). This shredder is enclosed in a drum (3), which rotates in the direction of the arrow B and has holes (4) of such a size so as to define the two transversal dimensions of the pieces. The drum (3) has rubber blades (5) on the inside so as to lift the pieces which must be broken into smaller pieces and carried back to the input of the machine. The drum (3) is also provided with external scoops (6) for sorting material coming out of the machine. Zone (7) denotes an area or gap between the drum (3) and a surface (8) which faces said drum (3a) at least for the period during which the machine empties through the holes (4). Also provided are conductors (10) that stop the pieces from dropping before reaching the shredder (1). The conductors (10) also have a slide (11) which acts as a conveyor. Finally nozzles 12 are provided that can be used to squirt fluids at high pressure. The device works as follows: The shredder 1 receives the material to be cut up at the entrance (13), passes it through the blades (14) and lets drop it into the drum (3). The larger pieces P3 that need more shredding are collected by the rubber blades (5). The shredded pieces P2 which are at least 2 sizes smaller than the holes (4), cross the surface of the drum (3). These pieces, however, cannot exit completely and are lifted by the rotation of the drum and by the action of the blades (6) towards outlet (9), which is placed sideways to the drum (3), that is at a higher point than the bottom of the drum (3). The outlet allows dumping of the pieces only to take place in a corner (15) with a vertical side, the angle of the corner being 50° to 70°. Reaching outlet (9), the pieces P1 that are smaller than the holes in the drum (3) and the space (7) are moved away from the drum (3a) and are fed through outlet (9); the pieces P2 that because of their length have their center of gravity in the interior of the drum (3) fall of their own accord into the interior of said drum (3). It is also possible to adjust the space (7). Even the angle 15 can be altered.

Claims: A shredding process in which a shredder (1), surrounded by a revolving screen (3) which also acts as an elevator, outputs the shredded material in the interior of said screen (3), which allows the passage of material which has at least two dimensions smaller than the screen holes, whilst it lifts the remaining material depositing it once more at the input of the shredder (1) characterized in that at least the revolving screen is a rotating drum (3) provided with scoops (6) on its outer side, the bottom side of the drum facing a fixed wall (8) placed at such a distance that it creates a gap (7) which in turn determines the third dimension of the material which passes through. A process according to claim 1, characterized in that the area (7) has a size roughly equal to that of the largest holes available in the drum (3). An apparatus for shredding material consisting of a shredder (1) comprising two rows of intersecting rotating blades surrounded by a rotating perforated drum (3), said drum having internal lifting blades (5), characterized in that the drum has further scoops (6) on the outside thereof, the bottom side of the drum is placed facing a fixed wall (8) that creates a gap (7) with a size such so as to establish the largest size of the shredded pieces that could possibly get through the perforated drum, and the outlet (9) of the drum is placed higher than the bottom of the drum (3). An apparatus according to claim 3, characterized in that the internal blades (5) are made of rubber or the like. An apparatus according to claim 3 or 4, characterized in that in order to facilitate the exit of shredded material nozzles (12) are provided for blowing compressed or ventilated air, and in particular, said nozzles are directed radially towards the drum (3). An apparatus according to any of the claims 3 to 5, characterized in that in order to facilitate the exit of material, air is sucked out from the outlet (9). An apparatus according to any of the previous claims 3 to 6, characterized in that the outlet (9) is positioned at such a height on the drum (3) that its lower periphery forms with a vertical plane an angle (15) between 50° and 70°. An apparatus according to any of the claims 3 to 7, characterized in that the gap (7) is adjustable. An apparatus according to any of the claims 3 to 8, characterized in that the height of the outlet (9) is adjustable.

Inventors: ROTA, FABIO
Applicants: SATRIND S.R.L.
Application year: 1987
Main classification: B02C17
IPC codes: B02C17