Abstract:
A shredding apparatus comprises a plurality of rotatable rolls, each one of the rolls being rotatable around an axis of rotation in a first direction of rotation or a second direction of rotation. Each roll further has a plurality of angled replaceable teeth, which are arranged in at least one first set of teeth arranged in a first helical line across an outer surface of each roll, circumferentially spaced apart a first angle and facing the first direction of rotation. Further, at least one second set of teeth is arranged in a second helical line across the outer face of each roll, circumferentially spaced apart the first angle and facing the second direction of rotation. The first helical line and the second helical line of teeth are arranged to axially (in the longitudinal direction of the rolls) move material to be shredded when the rolls are rotated. Further, the shredding apparatus has a frame structure with roll holding means, for journalling the plurality of rolls in a spaced apart relationship to form a bed of rolls. The frame structure is surrounded by an enclosure provided with a charging opening for material to be shredded and a discharging opening for shredded material. A reversible drive means supplies rotation force to rotate the plurality of rolls, and a plurality of gear means, arranged one for each roll, transfers the rotation force from one roll to an adjacent roll so that adjacent rolls rotate in opposite directions of rotation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to comminuting or shredding apparatuses, and particularly to shredders having a plurality of rotating rolls provided with teeth. Most particularly, the shredder is of a type for shredding waste wood such as pallets, crating, stumps and other construction material, for example cardboard and other organic material. 
     2. Description of the Prior Art 
     Traditionally, a rotating roll comminuting apparatus has one or more rolls provided with teeth or other protrusions, which cooperate with non-rotating anvil structures to break up material. Comminuting apparatuses of this type are disclosed in U.S. Pat. No. 3,703,970 (Benson), U.S. Pat. No. 5,320,293 (Laly et al.) and U.S. Pat. No. 5,094,392 (Szombathy), for example. 
     The traditional comminuting apparatuses all share a number of apparent disadvantages and drawbacks. They are relatively complicated in their roll teeth/anvil structure, which makes their manufacture expensive. When the roll teeth/anvil structure gets worn, it is complicated, and therefor expensive, to replace or repair this structure. The teeth have to be cut off and new teeth welded in place, or a new roll have to be installed and the old roll sent for repair. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to mitigate and/or obviate the above mentioned disadvantages and drawbacks to provide a shredding apparatus, which is easy and cheap to manufacture and assemble and which provides the required shredding capacity. 
     A further object of the invention is to provide a shredding apparatus, which spreads the material to be shredded over a large area of the plurality of rotating rolls, in order to enhance the output of the shredder and at the same time avoiding material bridging (material to be shredded is stuck above the rolls because it is squeezed by other pieces of material to be shredded, held by the surrounding walls etc.). 
     Yet a further object of the invention is to provide a shredding apparatus, which provides an axial flow of the material to be shredded along the longitudinal direction of the rolls, for further eliminate material gliding above the rolls. 
     Still a further object of the invention is to provide a shredding apparatus, which provides reversible rolls having equal shredding capabilities in either direction of rotation, to effect reflow and agitation of the material to be shredded. 
     Another object of the invention is to provide a shredding apparatus, which controls the depth of the cut of the shredding rolls into the material to be shredded. 
     A further object of the invention is to provide a shredding apparatus, in which the smaller size material, which is not required to be sized, freely falls through the shredding roll construction, to reduce wear and tear on the rolls. 
     In the invention, a shredding apparatus comprises a plurality of rotatable rolls, each one of the rolls being rotatable around an axis of rotation in a first direction of rotation or a second direction of rotation. Each roll further has a plurality of angled replaceable teeth, which are arranged in at least one first set of teeth arranged in a first helical line across an outer surface of each roll, circumferentially spaced apart a first angle and facing the first direction of rotation. Further, at least one second set of teeth is arranged in a second helical line across the outer face of each roll, circumferentially spaced apart the first angle and facing the second direction of rotation. The first helical line and the second helical line of teeth are arranged to axially (in the longitudinal direction of the rolls) move material to be shredded when the rolls are rotated. Further, the shredding apparatus has a frame structure with roll holding means, for journalling the plurality of rolls in a spaced apart relationship to form a bed of rolls. The frame structure is surrounded by an enclosure provided with a charging opening for material to be shredded and a discharging opening for shredded material. A reversible drive means supplies rotation force to rotate the plurality of rolls, and a plurality of gear means, arranged one for each roll, transfers the rotation force from one roll to an adjacent roll so that adjacent rolls rotate in opposite directions of rotation. 
     The plurality of rolls preferably comprises at least 4 rolls, preferably 4, 6, 8, 10, 11 or 12 rolls. 
     The first angle is preferably 15, 30, 45, 60 or 90 degrees. 
     Each roll is advantageously arranged on the frame roll holding means so that each of the at least one first and at least one second helical line of teeth is offset a second angle with respect to the at least one first and at least one second helical line of teeth of adjacent rolls. The second angle is preferably 6, 8, 10 or 12 degrees. 
     Each roll arranged in a middle portion of the bed of rolls is preferably held in a lower position compared to the rolls arranged towards either of two outer sides of the bed of rolls, forming sloping sides of the bed of rolls down towards the middle of the bed of rolls in the longitudinal direction of the bed of rolls, to force material to be shredded to be moved from the outer sides to the middle portion of the bed of rolls. Thus, the bed of rolls is shaped as a curve, having the outer rolls at a higher elevation than the middle rolls. 
     The teeth of the at least one first and the at least one second set of teeth of each of the rolls are preferably arranged so that only one tooth is engaging the material to be shredded at one time during the rotation of the roll. Alternatively, the teeth of the at least one first and the at least one second set of teeth of each of the rolls are arranged so that at least two teeth are engaging the material to be shredded at one time during the rotation of said roll. 
     The rolls further preferably have sizing discs arranged around a circumference of each roll, the sizing discs being positioned along the outer surface of each roll, where each sizing disc of one roll is placed so that sizing discs of an adjacent roll do not occupy the same space as the sizing discs of the one roll. 
     In one embodiment of the invention, the reversible drive means comprises at least one internal combustion engine. Alternatively, the reversible drive means comprises at least one electric motor, at least one hydraulic motor or at least one pneumatic motor. In a further embodiment of the invention, the reversible drive means comprises a first hydraulic cylinder and a second hydraulic cylinder, the first cylinder being anchored at one end and attached to a first gear means of a first roll at a first off-centre mounting means on the first gear means, the second cylinder being anchored at one end and attached to a second gear means of a second roll at a second off-centre mounting means on the second gear means, so that when the first cylinder is extended or retracted, the first gear means is made to rotate around the axis of rotation for the first roll, and when the second cylinder is extended or retracted, the second gear means is made to rotate around the axis of rotation for the second roll, causing the plurality of rolls to rotate driven by the plurality of gear means for each roll. The first off-centre mounting means and the second off-centre mounting means are arranged at different angular locations on the first and second gear means, respectively, to prevent stalling of rotation force transfer from the first and second cylinders. 
     The reversible drive means further advantageously comprises a pressure sensing means connected to automatically reverse the roll rotation directions when the pressure sensing means senses that material to be shredded is stuck in the plurality of rolls. 
     The reversible drive means further preferably comprises a timer arrangement to periodically reverse the roll rotation direction. 
     The shredding apparatus further comprises a plurality of vertically extendible/contractible and horizontally spaceable main legs, to provide support for the shredding apparatus during shredding, and a plurality of extendible and contractible lifting legs, to lift the shredding apparatus off ground, so that the main legs can be spaced apart and extended or contracted and spaced together for providing self-loading and self-erecting capabilities to the shredding apparatus. 
     Preferably, the main legs comprise a first leg assembly and a second leg assembly, arranged on opposite sides of the frame. The first leg assembly comprises a first main housing attached to the frame via first frame extensions, a first main leg extending from the first main housing, protruding substantially downwards, at a first end of the first main housing and a second main leg, protruding substantially downwards, from a second end of the first main housing. The first main leg is held by a first holding means, slidingly arranged in the first main housing at the first end, between a retracted position and an extended position. The second main leg is held by a second holding means, slidingly arranged in the first main housing at the second end, between a retracted position and an extended position. The second leg assembly comprises a second main housing attached to the frame via second frame extensions. A third main leg extends from the second main housing, protruding substantially downwards, at a third end of the second main housing and a fourth main leg, protrudes substantially downwards, from a fourth end of the second main housing. The third main leg is held by a third holding means, slidingly arranged in the second main housing at the third end, between a retracted position and an extended position. The fourth main leg is held by a fourth holding means, slidingly arranged in the second main housing at the fourth end, between a retracted position and an extended position. 
     The sliding motion of the first holding means and the second holding means is preferably provided by at least one first fluid cylinder arranged inside the first main housing, and the sliding motion of the third holding means and the fourth holding means is preferably provided by at least one second fluid cylinder arranged inside the first main housing. 
     A first lifting leg and a second lifting leg are preferably arranged at the first frame extension, the first lifting leg and the second lifting leg being extendably arranged in a downward direction, between a fully retracted position and a fully extended position. The first lifting leg and the second lifting leg are extendable further downwards than the first main leg and the second main leg. A third lifting leg and a fourth lifting leg are preferably arranged at the second frame extension, the third lifting leg and the fourth lifting leg being extendably arranged in a downward direction, between a fully retracted position and a fully extended position. The third lifting leg and the fourth lifting leg are extendable further downwards than the third main leg and the fourth main leg. 
     The rolls are preferably arranged with their longitudinal direction running from the first leg assembly to the second leg assembly. Alternatively, the rolls are arranged with their longitudinal direction perpendicular to a line connecting the first leg assembly and the second leg assembly. 
     The enclosure advantageously comprises four substantially horizontal walls, the rolls forming the entire bottom part of the enclosure, so that material to be shredded only flows through the rolls. 
     Further features of the invention will be described or will become apparent in the course of the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be more clearly understood, the preferred embodiment thereof will now be described in detail by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1A is a schematic elevational perspective side view of a shredding apparatus according to the invention, showing the charging door lowered for placing material in the shredding apparatus, 
     FIG. 1B is a schematic elevational perspective side view of a shredding apparatus according to the invention, showing the shredding apparatus placed on a flatbed type trailer and the charging door raised, 
     FIG. 1C is a schematic perspective side view from below of a shredding apparatus according to the invention, showing the support legs in a position for transportation of the shredding apparatus, 
     FIG. 1D is a schematic elevational perspective side view of a shredding apparatus according to the invention, showing the support legs in a position for shredding use of the shredding apparatus, and showing a container placed under the shredding apparatus for collecting the shredded material, 
     FIG. 1E is a schematic elevational perspective side view of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being a hydraulic motor, 
     FIG. 1F is a schematic elevational perspective side view of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being an electric motor, 
     FIG. 2A is a schematic perspective side view from below of a shredding apparatus according to the invention, showing the apparatus from the opposite side from the roll drive side, with the charging door closed, 
     FIG. 2B is a schematic perspective side view from below of a shredding apparatus according to the invention, showing the apparatus from the opposite side from the roll drive side, with the charging door opened, 
     FIG. 2C is a schematic perspective side view from below of a shredding apparatus according to the invention, showing the apparatus from the roll drive side, with the charging door closed, 
     FIG. 2D is a schematic perspective side view from below of a shredding apparatus according to the invention, showing the apparatus from the roll drive side, with the charging door opened, 
     FIG. 2E is a schematic perspective side view from below of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being a hydraulic motor, 
     FIG. 2F is a schematic elevational perspective side view of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being a hydraulic motor, 
     FIG. 2G is a schematic perspective side view from below of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being a hydraulic motor, 
     FIG. 2H is a schematic perspective side view from below of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being an electric motor, 
     FIG. 3A is a top view of a shredding apparatus according to the invention, showing the apparatus with the charging door closed, 
     FIG. 3B is a bottom view of a shredding apparatus according to the invention, with the charging door closed, 
     FIG. 3C is a top view of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being a hydraulic motor, 
     FIG. 3D is a bottom view of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being a hydraulic motor, 
     FIG. 3E is a bottom view of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being an electric motor, 
     FIG. 4A is a side view of a shredding apparatus according to the invention, seen from the opposite side from the roll drive side, with the charging door closed, 
     FIG. 4B is a side view of a shredding apparatus according to the invention, seen from the roll drive side, with the charging door closed, 
     FIG. 4C is a side view of a shredding apparatus according to the invention, seen from the roll drive side, showing the alternative drive means for the rolls being a hydraulic motor, 
     FIG. 4D is a side view of the back of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being a hydraulic motor, 
     FIG. 4E is a side view of the front of a shredding apparatus according to the invention, showing the alternative drive means for the rolls being a hydraulic motor, 
     FIG. 4F is a side view of a shredding apparatus according to the invention, seen from the roll drive side, showing the alternative drive means for the rolls being an electric motor, 
     FIG. 5A is an elevational perspective side view of a roll assembly (roll bed) of a shredding apparatus according to the invention, 
     FIG. 5B is a side view of a roll assembly of a shredding apparatus according to the invention, seen perpendicularly from the longitudinal axis of the rolls and along the plane of the roll assembly, 
     FIG. 5C is a top view of a roll assembly of a shredding apparatus according to the invention, 
     FIG. 6 is a schematic side view of the roll arrangement of a shredding apparatus according to the invention, showing a curved roll assembly, 
     FIG. 7A is a side view of a roll arrangement of a shredding apparatus according to the invention, seen from the opposite side from the roll drive side, showing the roll holders, 
     FIG. 7B is a side view of a roll arrangement of a shredding apparatus according to the invention, seen from the roll drive side, showing the roll holders, drive cylinders and cog wheels, 
     FIG. 8A is a schematic side view of the roll drive of a shredding apparatus according to the invention, seen from the roll drive side, showing the drive cylinders in a first position, 
     FIG. 8B is a schematic side view of the roll drive of a shredding apparatus according to the invention, seen from the roll drive side, showing the drive cylinders in a second position, 
     FIG. 8C is a schematic side view of the roll drive of a shredding apparatus according to the invention, seen from the roll drive side, showing the drive cylinders in a third position, 
     FIG. 8D is a schematic side view of the roll drive of a shredding apparatus according to the invention, seen from the roll drive side, showing the drive cylinders in a fourth position, 
     FIG. 8E is a schematic side view of the roll drive of a shredding apparatus according to the invention, seen from the roll drive side, showing the drive cylinders in a fifth position, 
     FIG. 8F is a schematic side view of the roll drive of a shredding apparatus according to the invention, seen from the roll drive side, showing the drive cylinders in a sixth position, 
     FIG. 8G is a schematic side view of the roll drive of a shredding apparatus according to the invention, seen from the roll drive side, showing the drive cylinders in a seventh position, 
     FIG. 8H is a schematic side view of the roll drive of a shredding apparatus according to the invention, seen from the roll drive side, showing the drive cylinders in an eighth position, 
     FIG. 9A is a schematic side view of a shredding apparatus according to the invention, seen from the side opposite the roll drive side, showing the shredding apparatus in a position for shredding having a container positioned underneath the roll arrangement, 
     FIG. 9B is a schematic side view of a shredding apparatus according to the invention, seen from the side opposite the roll drive side, showing the shredding apparatus in a position for loading onto a trailer, 
     FIG. 9C is a schematic side view of a shredding apparatus according to the invention, seen from the side opposite the roll drive side, showing the shredding apparatus in a position when loading onto a trailer has begun, 
     FIG. 9D is a schematic side view of a shredding apparatus according to the invention, seen from the side opposite the roll drive side, showing the shredding apparatus in a position when loading onto a trailer has finished, 
     FIG. 9E is a schematic side view of a shredding apparatus according to the invention, seen from the charging door side, showing the shredding apparatus loaded onto a trailer for transport, 
     FIG. 9F is a schematic side view of a shredding apparatus according to the invention, seen from the charging door side, showing the shredding apparatus in a position for shredding having a container underneath the roll arrangement, 
     FIG. 9G is a schematic side view of a shredding apparatus according to the invention, seen from the side opposite the roll drive side, showing the shredding apparatus in a position for shredding when the container is loaded onto a trailer, 
     FIG. 10A is a detail view of one embodiment of a rotary position sensor for measuring the angular position of the rolls, 
     FIG. 10B is a detail view of a further embodiment of a rotary position sensor for measuring the angular position of the rolls, 
     FIG. 11 is a logic diagram showing the cylinder logic for the embodiment where the drive means has two hydraulic cylinders, 
     FIG. 12A is a schematic side view of a shredding apparatus according to the invention being loaded on a truck, showing the initial position of the shredding apparatus, 
     FIG. 12B is a schematic side view of a shredding apparatus according to the invention being loaded on a truck, showing the shredding apparatus being lifted off the ground by the lifting legs, 
     FIG. 12C is a schematic side view of a shredding apparatus according to the invention being loaded on a truck, showing the final position of the shredding apparatus loaded onto the truck, 
     FIG. 13A is a schematic side view of a shredding apparatus according to the invention having a container placed underneath it by a truck, showing the initial position of the truck with loaded container, 
     FIG. 13B is a schematic side view of a shredding apparatus according to the invention having a container placed underneath it by a truck, showing the container beginning to be unloaded from the truck, 
     FIG. 13C is a schematic side view of a shredding apparatus according to the invention having a container placed underneath it by a truck, showing the container being slid underneath the shredding apparatus, 
     FIG. 13D is a schematic side view of a shredding apparatus according to the invention having a container placed underneath it by a truck, showing the container fully dropped onto the ground but not yet pushed underneath the shredding apparatus, 
     FIG. 13E is a schematic side view of a shredding apparatus according to the invention having a container placed underneath it by a truck, showing the track beginning to push the container underneath the shredding apparatus, 
     FIG. 13F is a schematic side view of a shredding apparatus according to the invention having a container placed underneath it by a truck, showing the container completely pushed underneath the shredding apparatus, 
     FIG. 14A is a schematic side view of a shredding apparatus according to the invention being charged with large scrap, such as stumps, by a front loader, with the door of the shredding apparatus open, 
     FIG. 14B is a schematic side view of a shredding apparatus according to the invention being charged with large scrap, such as stumps, by a front loader, showing the stumps being scraped off the bucket of the front loader and into the shredding apparatus, 
     FIG. 14C is a schematic side view of a shredding apparatus according to the invention being charged with large scrap, such as stumps, by a front loader, showing the stumps fully ground and the ground material fallen on underneath the shredding apparatus ready to be pushed to the side using the front loader, 
     FIG. 15A is a schematic side view of a shredding apparatus according to the invention being charged with large scrap, such as pallets, by a fork lift truck, 
     FIG. 15B is a schematic side view of a shredding apparatus according to the invention being charged with large scrap, such as pallets, by a fork lift truck, showing the pallets being scraped off the forks and into the shredding apparatus, 
     FIG. 16A is a schematic side view of a hanging shredding apparatus according to the invention being utilized within a large material sorting line, 
     FIG. 16B is a schematic top view of a hanging shredding apparatus according to the invention being utilized within a large material sorting line, 
     FIG. 16C is a schematic detail side view of a hanging shredding apparatus according to the invention being utilized within a large material sorting line as shown it in FIG. 16A, 
     FIG. 16D is a further schematic detail side view of a hanging shredding apparatus according to the invention being utilized within a large material sorting line as shown in FIG. 16C, 
     FIG. 16E is a schematic top view of a hanging shredding apparatus according to the invention being utilized within a large material sorting line as shown in FIG. 16D, and 
     FIG. 16F is a schematic bottom view of a hanging shredding apparatus according to the invention being utilized within a large material sorting line as shown in FIG.  16 D. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1A to  4 B, a shredding apparatus  1  according to the invention has a plurality of rotatable rolls  100  arranged in a side-by-side pattern forming a roll bed, so that the longitudinal directions of the rolls are substantially parallel with each other. Each roll is rotated in a direction opposite to the rotation direction of any adjacent rolls. How this is accomplished will be detailed later. The plurality of rolls  100  are held by a frame  110 , which is preferably of a generally rectangular shape held in a substantially horizontal plane. Attached to the frame are advantageously a first leg assembly  120  and a second leg assembly  130 , arranged on opposite sides of the frame. Preferably, the plurality of rolls  100  are arranged with their longitudinal direction between the first leg assembly and the second leg assembly, although it is possible to arrange the rolls so that their longitudinal directions are substantially perpendicular to a line connecting the first leg assembly and the second leg assembly. The first leg assembly  120  is preferably attached to the frame  110  via first frame extensions  140 , and comprises a first main housing  150 . From the first main housing extends a first main leg  160 , protruding substantially downwards, at a first end  165  of the first main housing and a second main leg  170 , protruding substantially downwards, from a second end  175  of the first main housing. The first main leg is held by a first holding means  166 , which is slidingly arranged in the first main housing  150  at the first end  165 , between a retracted position and an extended position. Similarly, the second main leg  170  is held by a second holding means  176 , which is slidingly arranged in the first main housing  150  at the second end  175 , between a retracted position and an extended position. The sliding motion of the first and second holding means is preferably provided by one or more fluid cylinders (not shown) arranged outside or, preferably, inside the first main housing. If one cylinder is used, it will be of the double-action type, having two opposite rams. If two cylinders are used, one will move the first holding means  166  and the other will move the second holding means  176 . For balance reasons, it is advantageous that the two holding means move in synchronization. Further, a first lifting leg  180  and a second lifting leg  190  are arranged at the first frame extensions  140  or, alternatively, at the first main housing  150  (this arrangement is not shown). The first lifting leg and the second lifting leg are extendably arranged in a downward direction, between a fully retracted position and a fully extended position, where the lifting leg extends further downwards than the adjacent main leg. The extending motion is preferably provided by fluid cylinders arranged in or on each lifting leg. 
     Similarly, arranged on a side of the frame  110  opposite to the first leg assembly, attached to the frame is the second leg assembly  130 . The second leg assembly  130  is preferably attached to the frame  110  via second frame extensions  140 ′, and comprises a second main housing  150 ′. From the second main housing extends a third main leg  160 ′, protruding substantially downwards, at a first end  165 ′ of the second main housing and a fourth main leg  170 ′, protruding substantially downwards, from a second end  175 ′ of the second main housing. The third main leg is held by a third holding means  166 ′, which is slidingly arranged in the second main housing  150 ′ at the first end  165 ′, between a retracted position and an extended position. Similarly, the fourth main leg  170 ′ is held by a fourth holding means  176 ′, which is slidingly arranged in the second main housing  150 ′ at the second end  175 ′, between a retracted position and an extended position. The sliding motion of the third and fourth holding means is preferably provided by one or more fluid cylinders (not shown) arranged outside or, preferably, inside the second main housing. If one cylinder is used, it will be of the double-action type, having two opposite rams. If two cylinders are used, one will move the third holding means  166 ′ and the other will move the fourth holding means  176 ′. For balance reasons, it is advantageous that the two holding means move in synchronization. Further, a third lifting leg  180 ′ and a fourth lifting leg  190 ′ (see FIG. 2A) are arranged at the second frame extensions  140 ′ or, alternatively, at the second main housing  150 ′ (this arrangement is not shown). The third lifting leg and the fourth lifting leg are extendably arranged in a downward direction, between a fully retracted position and a fully extended position where the lifting leg extends further downwards than the adjacent main leg. The extending motion is preferably provided by fluid cylinders arranged in or on each lifting leg. 
     The shredding apparatus  1  is transported, for instance on a flat-bed trailer  900 , with the first, second, third and fourth main legs  160 ,  170 ,  160 ′,  170 ′, respectively, in their retracted positions, i.e. the first, second, third and fourth holding means  166 ,  176 ,  166 ′,  176 ′, respectively, are fully retracted towards the respective first or second main housing  150 ,  150 ′, respectively, see FIG.  1 B. The first, second, third and fourth lifting legs  180 ,  190 ,  180 ′,  190 ′, respectively, are also fully retracted. The shredding apparatus thus rests on the main legs, which are in their retracted position, minimizing the width of the shredding apparatus. 
     In preparing the shredding apparatus  1  for use, for example at a building site where wood or similar waste material is to be shredded, the transport vehicle is parked at the desirable shredding site and the first, second, third and fourth lifting legs  180 ,  190 ,  180 ′,  190 ′, respectively, are moved to their respective fully extended positions, thereby lifting the shredding apparatus  1  so that it does not rest on the main legs anymore, see FIGS. 9A to  9 H. During transport, the lifting legs are fully extended, and also the main legs are extended to make contact with the carrying surface of the vehicle/trailer. The shredding apparatus, as loaded onto a vehicle, conforms to legal requirements regarding load height and width, because the main legs are horizontally movable. The first, second, third and fourth main legs  160 ,  170 ,  160 ′,  170 ′, respectively, are moved to their fully extended positions, i.e. the first, second, third and fourth holding means  166 , 176 , 166 ′,  176 ′, respectively, are fully extended from the respective first or second main housing  150 ,  150 ′, respectively. Thereafter, the first, second, third and fourth lifting legs  180 ,  190 ,  180 ′,  190 ′, respectively, are moved to their respective fully retracted positions, thereby lowering the shredding apparatus  1  so that it rests solely on the main legs. Because the main legs are now further spread apart, the whole shredding apparatus  1  is in a more stable position and ready for use. A container  750  is preferably positioned underneath the plurality of rolls  100  before operation of the shredder begins, to collect the shredded material. The container is preferably a roll-off bin (adapted to be transported by roll-off trucks) or a tin scow. In certain applications, for example when shredding stumps, it is desirable to shred directly to the ground surface, for later removal of the shredded material. In this case, the container is not needed. 
     The shredding apparatus  1  further comprises an enclosure  200  (hopper), substantially surrounding a space above the plurality of rolls  100 . The enclosure preferably has a back  210 , a movable front (door)  220  (see FIG.  2 A), a first side  230  and a second side  240 . The front is movable from a closed position, in which it abuts the first and second sides, to an open position, in which it is held substantially horizontal underneath the plurality of rolls  100 . The movement of the front  220  is provided by a first hinge means  250 , preferably arranged on the side of the frame  110  where the first leg arrangement  120  is found, and a second hinge means  260 , preferably arranged on the side of the frame where the second leg arrangement  130  is found. A door shield  225  is arranged on the frame  110  on the side of the front  220 , to protect the plurality of rolls  100  from being damaged by the moving front, when the front is lowered towards its open position. The door shield only partially covers the bottom of the roll closest to the front of the enclosure  200 , to not obstruct the flow of shredded material through the plurality of rolls  100 . Advantageously, a door shield  225  is arranged at the side of the back  210  also, with the same features as the door shield arranged at the front. An alternative embodiment of an enclosure  200 ′ is shown in FIG. 1F, in which the front  220 ′ is fixedly attached to the first side  230  and the second side  240 . In this case, any charging of the enclosure will have to be done from above (over the sides or the front/back portions. 
     As is shown in FIGS. 2A,  2 B and  5 A, the plurality of rolls  100  are held to the frame  110  by first bearing holders  270  and second bearing holders  280 . The bearing holders are also known as pillow blocks. Each roll has a first end shaft  290  and a second end shaft  300 . The first end of each roll is held in the respective first bearing holder  270  and the second end of each roll is held in the respective second bearing holder  280 . Each first bearing holder is attached to the frame  110  using first attachment means  295 , for example bolts (not shown) attached to corresponding fastening means (not shown, for example nuts or threaded holes) arranged on the frame. Each second bearing holder  280  is attached to the frame  110  using second attachment means  305 , for example bolts (not shown) attached to corresponding fastening means (not shown, for example nuts or threaded holes) arranged on the frame. Each roll  100  has a synchronization means  400  arranged on its second end shaft  300 . The synchronization means transfer the rotation power to each roll from a drive system  500 , so that each roll rotates in a different direction from the adjacent roll(s). Preferably, the synchronization means are cog wheels, or gears, meshing with the adjacent cog wheel of adjacent rolls. The synchronization means will be referred to as cog wheels  400  hereinafter. The drive system  500  comprises, for example, one or more electric motors, an internal combustion engine or an arrangement of at least one fluid (hydraulic or pneumatic) cylinder or motor. The drive system may provide direct drive to one or more rolls via a planetary reducer, or other types of gear mechanisms. In the preferred embodiment shown in FIGS. 5A to  5 C,  7 B and  8 A to  8 H, the drive system  500  comprises a first fluid drive cylinder  510  an a second fluid drive cylinder  520 . The first drive cylinder has a first attachment end  530 , which is attached at a first attachment shaft  535  concentric with the axis of rotation of a first outer roll  100 ′ of the plurality of rolls  100 . The first attachment end does not rotate with the first outer roll, a bearing  536  is arranged on the first attachment shaft to allow the first attachment shaft to rotate but not the first attachment end of the first drive cylinder. The first drive cylinder  510  further has a second attachment end  550 , which is attached at a second attachment shaft  570 . The second attachment shaft is arranged on the cog wheel  400  of a first inner roll  101 , so that the second attachment shaft is placed radially on the cog wheel towards the circumference of the cog wheel. The second attachment end does not rotate with the first inner roll, a bearing  537  is arranged on the second attachment shaft to allow the second attachment shaft to rotate but not the second attachment end of the first drive cylinder. In this way, the cog wheel  400  of the first inner roll will rotate, when the first drive cylinder  510  is extended or retracted. Similarly, the second drive cylinder  520  has a third attachment end  540 , which is attached at a third attachment shaft  545  concentric with the axis of rotation of a second outer roll  100 ″ of the plurality of rolls  100 . The third attachment end  540  does not rotate with the second outer roll, a bearing  546  is arranged on the third attachment shaft to allow the third attachment shaft to rotate but not the third attachment end of the second drive cylinder. The second drive cylinder  520  further has a fourth attachment end  560 , which is attached at a fourth attachment shaft  580 . The fourth attachment shaft is arranged on the cog wheel  400  of a second inner roll  102 , so that the fourth attachment shaft is placed radially on the cog wheel towards the circumference of the cog wheel. The fourth attachment end does not rotate with the second inner roll, a bearing  547  is arranged on the fourth attachment shaft to allow the fourth attachment shaft to rotate but not the fourth attachment end of the second drive cylinder. In this way, the cog wheel  400  of the second inner roll will rotate, when the second drive cylinder  520  is extended or retracted. Naturally, since all cog wheels mesh, any rotation imparted to any one of the plurality of rolls  100  will cause the other rolls to rotate also. The first drive cylinder  510  and the second drive cylinder  520  are arranged so that the angular position of the second attachment shaft  570  differs from the angular position of the fourth attachment shaft  580 , to prevent that one drive cylinder is in its fully extended position at the same time as the other drive cylinder is in its fully retracted position. If this should be the case, it is possible that both cylinders would be locked from movement, because there would not be a sufficient moment arm working on the respective second or fourth attachment shaft to provide a rotational movement to the respective cog wheel  400 . 
     The sequence of drive cylinder movements is shown in FIGS. 8A to  8 H. FIG. 8A shows the first drive cylinder  510  in a starting position, which is an arbitrary position chosen for illustration only. In this example, the first drive cylinder is extended and the second drive cylinder  520  is also extended, causing the cog wheels  400  to rotate, as described above. The cog wheel attached to the first inner roll  101  is shown with a first index mark  503 , which is shown for illustration purposes only and does not necessarily appear on the product as used. Similarly, a second index mark  504  is shown on the cog wheel attached to the second inner roll  102 . Thus, the second outer roll  100 ″ will rotate counter-clockwise, its adjacent roll will rotate clockwise, the second inner roll  102  will rotate counter-clockwise, the first inner roll  101  will rotate clockwise, its adjacent roll (to the right in the Figs.) will rotate counter-clockwise and the first outer roll  100 ′ will rotate counter-clockwise. In FIG. 8B, the drive cylinders have reached an intermediate position, where the first drive cylinder  510  is approaching its fully extended position. The first index mark  503  has rotated approximately 45 degrees anti-clockwise from its position in FIG. 8A, and the second index mark  504  has rotated approximately 45 degrees clockwise from its position in FIG.  8 A. In FIG. 8C, the first drive cylinder is shown in its fully extended position, where it no longer contributes to the rotation movement of the rolls. The second drive cylinder  520  continues to extend, driving the first drive cylinder  510  past its fully extended position. The first drive cylinder then starts contracting, so that driving force is again provided by both drive cylinders. The first index mark  503  has rotated approximately 45 degrees anti-clockwise from its position in FIG. 8B, and the second index mark  504  has rotated approximately 45 degrees clockwise from its position in FIG.  8 B. In FIG. 8D, the second drive cylinder is shown approaching its fully extended position. The first index mark  503  has rotated approximately 45 degrees anti-clockwise from its position in FIG. 8C, and the second index mark  504  has rotated approximately 45 degrees clockwise from its position in FIG.  8 C. In FIG. 8E, the second drive cylinder is shown in its fully extended position, where it no longer contributes to the rotation movement of the rolls. The first drive cylinder  510  continues to contract, driving the second drive cylinder  520  past its fully extended position. The second drive cylinder then starts contracting, so that driving force is again provided by both drive cylinders. The first index mark  503  has rotated approximately 45 degrees anti-clockwise from its position in FIG. 8D, and the second index mark  504  has rotated approximately 45 degrees clockwise from its position in FIG.  8 D. In FIG. 8F, the first drive cylinder is shown approaching its fully contracted position. The first index mark  503  has rotated approximately 45 degrees anti-clockwise from its position in FIG. 8E, and the second index mark  504  has rotated approximately 45 degrees clockwise from its position in FIG.  8 E. In FIG. 8G, the first drive cylinder has reached its fully contracted position, where it no longer contributes to the rotation movement of the rolls. The first second cylinder  520  continues to contract, driving the first drive cylinder  510  past its fully contracted position. The first drive cylinder then starts extending, so that driving force is again provided by both drive cylinders. The first index mark  503  has rotated approximately 45 degrees anti-clockwise from its position in FIG. 8E, and the second index mark  504  has rotated approximately 45 degrees clockwise from its position in FIG.  8 E. In FIG. 8H, the second drive cylinder is shown approaching its fully contracted position. The first index mark  503  has rotated approximately  45  degrees anti-clockwise from its position in FIG. 8F, and the second index mark  504  has rotated approximately 45 degrees clockwise from its position in FIG.  8 F. During further rotation, the second drive cylinder will reach its fully contracted position, where it no longer contributes to the rotation movement of the rolls. The first cylinder  510  continues to expand, driving the second drive cylinder  520  past its fully contracted position. The second drive cylinder then starts extending, so that driving force is again provided by both drive cylinders. Thus, the system is back to a position shown in FIG.  8 A. 
     The hydraulic cylinders are preferably regulated by a rotary hydraulic valve  505 , which is directly linked to at least one roll drive shaft, to sense the position of the roll(s) (FIG.  10 A). The rotary hydraulic valve directs the hydraulic oil to the desired cylinder, to retract or extend this cylinder as appropriate. Alternatively (FIG.  10 B), an encoder  506  is directly mounted adjacent an indication means  507  arranged directly on the roll shaft end  290 , to sense the radial position of the roll, and will feed a signal corresponding to this position to a central processor  508 , which is programmed to sequentially activate solenoid controlled hydraulic valves VALVE 1  and VALVE 2 , which comprises two pairs of solenoids each (VALVE 1 A, VALEVE 1 B and VALVE 2 A, VALVE 2 B, respectively), to extend or retract the cylinders sequentially at appropriate times. The operation of the respective solenoids is shown in FIG.  11 . 
     In FIGS. 1E,  2 E,  2 F,  2 G,  3 C,  3 D,  4 C,  4 D and  4 E, an alternative drive means  500 ′ is shown. The alternative drive means comprises a hydraulic motor  595  with associated control means  590 . The hydraulic motor drives the plurality of rolls  100  via a power transmission  596  coupled to a roll drive shaft  597 . Further technical features are the same as shown regarding the dual cylinder drive means, and share the same reference numerals. 
     In FIGS. 1F,  2 H,  3 E and  4 F, a further alternative drive means  500 ″ is shown. The further alternative drive means comprises an electric motor  595 ′. The electric motor drives the plurality of rolls  100  via a power transmission  596 ′ coupled to a roll drive shaft  597 ′. Further technical features are the same as shown regarding the dual cylinder drive means, and share the same reference numerals. 
     As is shown in FIG. 5A, each roll  100  has a first series of picks  600  in a spaced arrangement along the longitudinal direction of the roll and facing a first direction of rotation, so that the first series of picks form a screw spiral or helix around the outer circumference of the roll. Each pick/pick holder is offset a certain first angle, with respect to adjacent picks belonging to the same helix. For example, the first angle might be 15, 30, 45, 60 or 90 degrees. An alternative embodiment (not shown) has more than one pick helix around the roll, in one direction, for example 6 or 8 helixes. Each pick, or tooth, of the first series is removable and held by a pick holder  610  (see FIG.  6 ). A second series of picks  700  is in a spaced arrangement along the longitudinal direction of the roll and facing a second direction of rotation, so that the second series of picks form a screw spiral or helical around the outer circumference of the roll, but winding around the roll in a direction opposite to the helical formed by the first series of picks  600 . Similarly, an alternative embodiment (not shown) has more than one helix of picks around the roll in the opposite direction to the first set of helixes. Each pick, or tooth, of the second series is removable and held by a pick holder  710  (see FIG.  6 ). Thus, the picks of the first series shreds material when the roll is rotating in one direction, and the picks of the second series shreds material when the roll is rotating in the other direction. The roll(s) can shred material equally well in both directions of rotation. 
     A preferred pick is manufactured by Kennametal™, together with a suitable pick holder. The pick holder is preferably welded onto the rolls. The purpose of arranging the picks in helical patterns is to create a force working along the longitudinal direction of the rolls, when the roll is rotating and the picks of either the first or second series hit the material to be shredded. Only the picks facing the actual direction of rotation of the roll will contribute to the shredding, the other picks (facing the other direction) will not impact the material to be shredded with enough force. Thus, when the picks progressively hit the material to be shredded, the material is affected also by a force directed along the longitudinal direction of the roll, which has the effect of moving the material around in a beneficial way above the rolls. Since the direction of rotation of the rolls is inverted with regular intervals, the material to be shredded will be hit from both directions by the two sets of picks per roll, and will also be moved longitudinally along the rolls. Also, because each adjacent roll rotates in a different direction, the material to be shredded will be subjected to shearing forces, which effectively will tear the material apart. 
     To further improve the shredding capacity of the roll arrangement by increasing the available power per pick ratio, the angular arrangement of picks belonging to the same series of picks (first or second) is displaced a certain second angle, when comparing adjacent rolls. For example, if the second outer roll  100 ″ has a pick belonging to the first series of picks  600  at a zero angle, the corresponding pick of the first series of the adjacent roll is arranged at 6 degrees anticlockwise direction on the adjacent roll. It is obvious that other angles might be used with success, for instance 8 degrees. Further, the corresponding pick on the second inner roll  102 , which is the next adjacent roll, is arranged at 12 degrees anticlockwise direction on the second inner roll. Thus, each pick is displaced 6 degrees, compared to the pick belonging to the same series on an adjacent roll. At any given time, a maximum of two picks are in contact with the material to be shredded for each roll. To enable the rolls to be positioned close enough to each other to provide small enough openings between the rolls for the desired shredding size, the picks of one roll are displaced longitudinally with respect to an adjacent roll. Thus, the picks of one roll will not collide with the picks of an adjacent roll. The distance between adjacent rolls depends, inter alia, on the desired shredder capacity and the available power of the drive unit. 
     The plurality of rolls  100  further have a plurality of discs  800  arranged radially around the circumference of each roll. The discs are preferably arranged in pairs surrounding each pick  600 ,  700 , respectively, and its pick holder  610 ,  710 , respectively. For larger size shredding and/or more aggressive shredding, a single disc (not shown) may be used adjacent each pick. These discs function as stand-off discs, performing at least five functions: 1) controlling the cutting depth of the picks in the material to be shredded, 2) function as dynamic anvils holding the material to be shredded for the pick hit, 3) function as shear plates to tear material themselves, 4) function as sizing discs for determining the shredding size, and 5) allow fines to freely pass through the roll bed without causing additional wear and tear on the rolls. The dynamic anvil function reduces the wear on the anvil, compared to a fixed (non-rotating or non-moving) anvil construction. The distance the picks/teeth extend beyond the outer circumference of the discs  800  controls the depth of the cut (“bite”) in the material to be shredded, thus controlling shredded particle size. The gaps defined between the discs control the size of the material allowed to fall through the rolls, thus letting fine and abrasive material fall through without causing wear and tear on the rolls or other parts of the shredding apparatus. 
     As is shown in FIG. 6, the plurality of rolls  100  are arranged along a sloping curve C, where the outer rolls  100 ′,  100 ″, respectively and the inner rolls  101 ,  102 , respectively, are at different horizontal heights, with respect to the frame  110  (see FIG.  1 A). The outer rolls are placed higher than the inner rolls, and the intermediate rolls between them are on heights which are progressively lower going from the outer rolls towards the inner rolls. Both the inner rolls are at substantially the same height, and both inner rolls are at substantially the same height. In this way, the material to be shredded will tend to fall towards the middle of the roll arrangement, as opposed to staying at the extreme ends of the roll arrangement. This enhances the shredding capacity, by avoiding still standing or stuck material at the walls of the shredder. Because of the periodic reversal of the roll rotating directions, material will not gather along the sides of the shredder where the rolls are held to the frame. Preferably, a pressure sensing means  501  (see FIG. 5A) is connected to the drive system to automatically reverse the roll rotation directions in case material gets stuck in the roll arrangement (detection of high pressure, or slow-down of rotation speed of the rolls). Also, a timer arrangement  502  (see FIG. 2C) will periodically reverse the roll rotation direction, as described. 
     FIGS. 12A to  12 C show a sequence where a roll-off type truck  900 ′ is used to load a shredding apparatus  1  for transport. FIG. 12A shows the truck  900 ′ in position to back under the shredding apparatus, which is in its raised working position. In FIG. 12B, the truck is in position underneath the shredding apparatus  1 , and the lifting legs of the shredding apparatus are lowered onto the carrying surface of the truck, so that the shredding apparatus main legs are lifted off ground. The main legs are lifted fully, and retracted fully horizontally, as shown in FIG. 12C, to prepare the transport of the shredding apparatus. 
     FIGS. 13A to  13 F show a sequence where a roll-off type truck  900 ′ is used to position (or remove) a container  750  from underneath the shredding apparatus  1 . The container is positioned close to the shredding apparatus (being loaded onto the truck), as shown in FIG. 13A, and the lifting mechanism of the truck is started (FIG.  13 B), to eventually unload the container onto the ground adjacent the shredding apparatus (FIGS.  13 C and  13 D). Once the container is fully resting on the ground (FIG.  13 D), the truck lowers the lifting mechanism and pushes the container the required distance underneath the shredding apparatus (FIGS.  13 E and  13 F). Loading the container onto the truck is done in the reverse order (not shown) by first dragging the container out from under the shredding apparatus, then hooking it onto the lifting mechanism of the truck, and lifting it onto the truck. Alternatively, if the space so permits, the container (situated underneath the shredding apparatus) is directly hooked onto the lifting mechanism of the truck, and lifted onto the truck in one motion (without having to push it out a certain distance from underneath the shredding apparatus first). 
     FIGS. 14A to  14 C show a sequence where larger material  910 , such as stumps, is charged into the shredding apparatus  1 , using a front loader type vehicle  900 ″. This type of material is often contaminated with dirt and stones, which makes it practical to not collect it in a container, but to let it fall directly onto the ground after shredding. Thus, the material  910  is charged into the shredding apparatus (FIGS. 14A and 14B) with the front door of the shredding apparatus opened, and the material is scraped off the bucket of the front loader by running the bucket over the threshold of the shredding apparatus front door (FIG.  14 B). The shredded material mix can be pushed away from underneath the shredding apparatus after completed shredding, for example using the front loader (FIG.  14 C). 
     FIGS. 15A and 15B show a sequence where wood scrap  910 ′, for instance pallets, is charged into the shredding apparatus  1 , using a fork lift type vehicle  900 ′″. In this case, it is desirable to collect the shredded material for later use, for example in a container  750  positioned underneath the shredding apparatus. Thus, the material  910 ′ is charged into the shredding apparatus (FIGS. 15A and 15B) with the front door of the shredding apparatus opened, and the material is scraped off the bucket of the front loader by running the bucket over the threshold of the shredding apparatus front door (FIG.  15 B). The shredded material is collected in the container for further treatment. 
     A further embodiment of a shredding apparatus  1 ′ according to the invention is shown in FIGS. 16A to  16 F. The shredding apparatus is used as a part of a materials sorting line  1000 , having charging conveyors  1010  coupled to a vibrating bed  1020  leading to multiple material handling stations  1030 ,  1040 ,  1050 ,  1060 ,  1070 . The shredding apparatus is, for example, arranged at the first material handling station  1030 , preferably hanging underneath a conveyor  1015  moving material from the vibrating bed past all material handling stations. FIG. 16C shows the shredding apparatus  1 ′ having hook means  1100  arranged adjacent the four main legs (see description above of earlier embodiment of shredding apparatus). Each hook means is arranged to engagingly cooperate with slotted holding means  1200  arranged underneath the first material handling station  1030 , when the main legs are displaced vertically (as previously described), see FIG.  16 D. Thus, when the shredding apparatus is lifted, using the lifting legs as described earlier, the shredding apparatus approaches the bottom of the first material handling station  1030 . The main legs are extended vertically until the hook means  1100  fully engages the slotted holding means  1200 , fixing the shredding apparatus underneath the first material handling station. Preferably, the first material handling station has a cover  1005  having a plurality of holes  1001 ,  1002 ,  1003 ,  1004 , respectively, opening towards the underside of the first material handling station and the shredding apparatus hanging underneath. Sorters  1006  (see FIG. 16D) remove desired objects from the conveyor  1015  and drops them down the holes to be shredded. 
     It will be appreciated that the above description relates to the preferred embodiment by way of example only. Many variations on the invention will be obvious to those knowledgeable in the field, and such obvious variations are within the scope of the invention as described and claimed, whether or not expressly described. For example, the number of rolls used is a function of the desired capacity of the shredder and may range from 4, 6, 8, 10, 11, 12 or more rolls (under certain circumstances, a type of extended roll bed might be advantageous). The number of picks arranged per shaft is also chosen according to the desired capacity, keeping in mind that a large number of picks will mean a large number of cuts per time unit, making it necessary to increase the drive power. The number of pick cuts per time unit has to be chosen to comply with the desired shredding capacity and the material to be shredded. A slowly rotating roll bed, having a small number of picks per roll, may be used for low capacity and/or soft material shredding, whilst the same unit rotating at a higher speed may be used for higher capacity and/or harder material shredding. It is conceivable to use a roll bed which is substantially flat (as opposed to the sloping curve arrangement described earlier), the shredder will then lose some of the self-loading capacity.