EP2537588A2 - Shredder with knives having multiple cutting blades - Google Patents

Abstract

The shredder has cutters (30) comprising a plan shaped rigid body. The cutter is mounted on cutter holders (44) along direction oriented tangent to an outer peripheral surface of a rotor (12). The body defines corner shape to be complementary to V-shaped grooves (26) in a counter-knife (14). The cutters are mounted in orientation such that the corners mesh with the grooves as the rotor rotates about an axis. The cutters are multi-point cutters (130) in which the corner of the cutters defines cutting points spaced apart along direction, where the points mesh with the grooves.

Description

BACKGROUND OF THE INVENTION

The invention relates to rotary shredders for crushing various materials, comprising a rotor and a counter knife.

Rotary shredders are used to shred various materials such as paper, cardboard, plastic films, fabric, fabrics, textile fibers of natural or synthetic material, trash and others. The European patent EP 419 919 B1 describes a shredder for such materials having a rotor with a plurality of circumferentially spaced ribs and a counter-knife with teeth axially aligned with recesses or grooves defined between the ribs of the rotor. A plurality of knives are mounted in pockets formed in the outer surface of the rotor. Each knife has two sides which are arranged at a right angle to each other and which form a V-shape which meshes with a corresponding V-shaped recess between two adjacent teeth of the counter knife. Material that is conveyed into the space between the rotor and the counter knife is through the knife in Pieces are crushed and the pieces pass through a screen enclosing a portion of the circumference of the rotor, with pieces too large to pass the wire being transported back through the rotor to the counter knife to be comminuted again.

Further improvements in shredders of the type described above would be desirable.

BRIEF SUMMARY OF THE DISCLOSURE

The present invention relates to a shredder of the general type described above. In one embodiment, a shredder according to the present disclosure comprises at least one rotor rotatable about an axis and having an outer circumferential surface extending about the axis, a plurality of knife holders rigidly secured to the outer peripheral surface of the rotor at locations, spaced circumferentially and axially along a length of the rotor, a plurality of blades each mounted on the blade holders, and a stationary counter blade mounted adjacent to the outer peripheral surface of the rotor and extending along the length of the rotor wherein the counter knife defines a plurality of generally V-shaped grooves spaced apart along the counter knife, each V-shaped groove being aligned with at least one of the knives.

The knives each have a rigid body having a configuration when viewed in a first direction, each knife being mounted on a respective knife holder and the first direction being oriented substantially tangentially to the outer peripheral surface of the rotor. The body of each knife defines a cutting edge that is complementary is formed to a respective V-shaped groove in the counter knife. The blades are each mounted in an orientation in which the cutting corner meshes with the respective V-shaped groove in the counter blade as the rotor rotates about the axis. At least some of the knives are multi-blade knives in which the cutting edge of the knife defines a plurality of cutting points spaced apart along the first direction, the plurality of cutting points of each multi-blade knife being arranged such that the cutting points are continuous with the respective one Combing V-shaped groove in the counter knife, while the rotor rotates.

In one embodiment, the knives are mounted to the knife holders by releasable fasteners that allow for removal and replacement of the knives when needed. In this regard, the body of each blade has a bore extending along the first direction through the body to receive a respective releasable fastener, and the blade holders have corresponding holes for receiving the fasteners for mounting the blades to the blade holders. For example, the bore in the knife may be internally threaded, and the fastener may be an externally threaded bolt inserted through a rear of the knife holder and screwed into the knife. Alternatively, the top of the knife may have a recess for receiving the bolt head, and the bolt may be inserted through the knife and then through the knife holder and secured to the back of the knife holder with a nut. As such, the invention is not limited to a particular approach for attaching the knives.

Various embodiments of multi-cutting blades with multiple cutting points are possible. To the For example, the multi-blade knives may include knives defining two cutting points spaced apart along the first direction, and / or may include knives defining and / or may have three cutting points spaced apart along the first direction Comprise blades defining four cutting points (or more) spaced along the first direction.

In some embodiments, the knives define a plurality of corners, and each corner defines a plurality of cutting points that are spaced apart along the first direction. For example, the knife may have a substantially quadrangular configuration with four corners each defining a plurality of cutting points. If a corner has worn so far that an exchange is required, the fastener can be opened and the knife rotated 90 °, so that an unused corner for engagement with the counter knife is provided. This process can be repeated until all four corners have been used up. Thereafter, the knife can be replaced by a new knife.

In a particular embodiment, each multi-point multi-point knife has a central axis parallel to the first direction, and the counter-knife-intersecting corner of each multi-point knife is defined by an intersection between two adjacent side surfaces of the body. A top cutting point of the knife is defined by an intersection between two side surfaces and a top of the body, all of which meet at the top intersection. The corner has a tapered tapering region which begins immediately at the uppermost cutting point and tapers inwardly toward the knife's central axis, so that the uppermost point of intersection further than any other portion of the tapering area is away from the central axis. A second cutting point of each knife having a plurality of cutting points is defined below the tapering region, the second cutting point being farther away from the central axis than a lower part of the tapering region adjacent to the second cutting point. The extension of the second cutting point from the central axis may be the same as that of the uppermost cutting point. Alternatively, the extension of the second cutting point from the central axis may be different than that of the uppermost cutting point.

In a further embodiment, the knife may have a tapered second taper region starting immediately at the second cutting point and tapering inwardly towards the central axis of the knife, such that the second cutting point farther than any other portion of the second tapering region from the central Axis is removed. A third cutting point of each knife having a plurality of cutting points may be defined below the second tapering region, wherein the third cutting point is farther away from the central axis than a lower part of the second tapering region adjacent to the third cutting point.

In yet another embodiment, the knife may have a tapered third tapering region that begins immediately at the third cutting point and tapers inwardly toward the central axis of the knife, such that the third cutting point farther than any other portion of the third tapering region central axis is removed. A fourth cutting point of each knife having a plurality of cutting points may be defined below the third tapering region, the fourth cutting point being wider than a lower portion of the third tapering region of FIG the central axis is removed. As mentioned, in some embodiments more than four cutting points may be present. In each of the various embodiments, the various cutting points of the multi-point knife may all extend equidistant or different from the central axis.

In one embodiment, the top of the body of the knife is concave toward the first direction. An optional generally conical projection may protrude from the top to the top, and the bore which receives the knife fixing attachment member to a knife holder may extend through the projection. In one embodiment, the bore has an internal thread for receiving a male threaded fastener.

Alternatively, the top of the knife may be flat.

BRIEF DESCRIPTION OF THE FIGURES

In the remainder of the general description of the invention, reference will now be made to the accompanying drawings, which are not necessarily to scale. In the drawings shows:

FIG. 1 a partially broken perspective view of a single-shaft shredder without multi-blade knife according to the invention;

FIG. 2 a generally schematic end view of the rotor and the counter knife of the shredder of FIG. 1 ;

FIG. 3 a plan view of the rotor and the counter knife of the shredder of FIG. 1 ;

Fig. 4A, 4B each a side view and perspective view of one of the knives with a cutting point in the shredder of FIG. 1 be used;

Fig. 5A, 5B each a side view and perspective view of a knife with two cutting points according to an embodiment of the present invention;

Fig. 6A, 6B each a side view and perspective view of a knife with three cutting points according to another embodiment of the present invention;

Fig. 7A, 7B each a side view and perspective view of a knife with four cutting points according to another embodiment of the present invention;

FIG. 8 a generally schematic end view of a rotor and a counter knife similar to in FIG. 2 , but with knives with two cutting points, as in the FIGS. 5A and 5B are shown;

FIG. 9 a fragmentary perspective view of a rotor and a counter knife, wherein the rotor multi-cutting knife with two cutting points as in FIGS. 5A and 5B has shown;

FIG. 10 a plan view of a rotor and a counter knife similar to in FIG. 3 , but with knives with two cutting points, as in the FIGS. 5A and 5B shown;

FIG. 11 a generally schematic end view of a rotor and a counter knife similar to in FIG. 2 , but with knives with three cutting points, as in the Figures 6A and 6B shown;

FIG. 12 a fragmentary perspective view of a rotor, wherein the rotor multi-blade knife with three cutting points as in Figures 6A and 6B has shown;

FIG. 13 a generally schematic end view of a rotor and a counter knife similar to in FIG. 2 , but with knives with four cutting points, as in the FIGS. 7A and 7B shown;

FIG. 14 a partially cutaway end view of a single-shaft shredder with blades with multiple cutting points according to the invention; and

FIG. 15 a generally schematic end view of the rotors and the counter knife of a two-shaft shredder with knives with multiple cutting points according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention will now be described in detail with reference to the accompanying drawings, in which some, but not all, of the embodiments of the invention are shown. In fact, these inventions can be embodied in many different forms and are not to be construed as limiting the present embodiment. Rather, these embodiments are provided so that the disclosure meets the applicable legal requirements. Like reference numerals refer to the same elements throughout.

A shredder 10 to which the present invention is not embodied is disclosed in U.S.P. FIGS. 1 to 3 shown. The main components of the shredder are a rotor 12 which carries knives 30, as described later, and a counter knife 14 which works in conjunction with the rotor to grind or crush material that is dumped into the room. in which the rotor and the counter knife converge. The counter-knife is generally stationary, although it can be flexibly supported so that it can "yield" to some degree when a very hard object (eg, a piece of metal or a stone) accidentally gets into the space between the rotor and the counter-knife In this case, the flexibility aims to prevent engine damage. The crushed or crushed material passes through a sieve 16 (FIG. FIG. 2 ) having openings sized to regulate the size of the particles of crushed material. The shredder 10 also has a hopper 18 for receiving material to be shredded, and a hydraulic ram 20 or the like for advancing the material into the space between the rotor and the counterknife. Gravity causes the material in the hopper 18 to fall down onto a horizontal plate 21, and the ram 20 pushes the material on the plate 21 toward the rotor 12.

FIG. 3 Figure 12 is a plan view of a portion of the length of the rotor 12 and the counter knife 14. The rotor 12 is generally cylindrical, but its outer surface defines a series of circumferential ridges or ribs 22 which project radially outward. In the illustrated embodiment, each rib has opposite side surfaces which are conical and which are inclined opposite to the rotor axis. Thereby, the outer surface defines a series of alternating ones in the axial direction along the rotor Peaks (where the ribs 22 are located) and valleys between the peaks. The counter knife 14 has a series of teeth 24 which are axially aligned with the valleys between the ribs 22 of the rotor, such a tooth 24 per valley being provided in the rotor surface. Accordingly, V-shaped depressions or grooves 26 are provided between the teeth 24 of the counter knife, which are aligned axially on the ribs of the rotor. As a result, the rotor surface and the counter blade are generally configured complementary.

As FIG. 3 3, a plurality of blades 30 axially aligned with the ribs 22 and the V-shaped recesses 26 in the counter blade 14 are mounted on the outer surface of the rotor. At least one blade 30 may be provided per rib 22. Each blade 30 has contiguous radially outer side surfaces 32 which terminate at a corner 34 (FIG. FIGS. 4A and 4B ) and form a general V-shape with the vertex of the V pointing radially outward. Each blade 30 has an upper surface 36. The junctures between the upper surface 36 and the side surfaces 32 form edges 38. The side surfaces 32 and top 36 all meet at a cutting point 40 (which is also considered to be a junction between the corner 34 and the edges 38 can) together. In the in the FIGS. 4A and 4B In the illustrated embodiment, the knife 30 is a four-sided knife having four corners 34 each having a single cutting point. The knife 30 is fixed to the rotor 12 and oriented so that a corner 34 meshes with one of the V-shaped recesses 26 between the teeth 24 of the counter knife. Material that is fed into the space between the rotor and the counter knife is crushed by the knives 30 while the knives mesh with the counter knife. The cutting edges 38 are arranged approximately orthogonal to each other, but may also have a slight curvature, so that they are concave in the direction of rotation of the rotor, as in FIG. 3 shown, creating a scissor effect between the knives and the counter knife is promoted. Alternatively, the edges 38 may be straight. The blades 30 are circumferentially spaced around the rotor so that one or more of the blades always mesh with the counter blade. Each blade 30 is mounted by a screw 42 to a tool holder 44 which is secured to the rotor (for example, by welding or by a bolted connection). The tool holders 44 are mounted in pockets 46 which are cut into the rotor surface. The knives, if damaged or dull, can be removed and replaced with new knives.

As mentioned, the knives 30 may have four corners 34 each shaped to mate with a groove 26 in the counter knife 14. The knives may be mounted on the rotor in any of four different rotational orientations, each of which provides a different one of the corners for engagement with the counter knife. When a corner becomes dull, the knife can be positioned to present a new corner.

Although the one described above and in the FIGS. 1 to 4 shown shredder was both technically and commercially relatively successful, is always looking for further improvements.

The FIGS. 5 to 15 show various embodiments of the present invention, which is characterized by the use of knives with multiple cutting points instead of knives with a cutting point. The FIGS. 5A and 5B show such a multi-cutting knife 130 with two cutting points according to an embodiment of the invention. The knife 130 has a rigid body with a configuration when viewed along a first direction (from top to bottom in FIG FIG. 5 ) parallel to a central axis of the knife. The knife 130 has a plurality of side surfaces 132 which meet to form corners 134; and an upper surface 136 which forms edges 138 with the side surfaces 132. Each corner 134 of the knife defines two cutting points 140a and 140b spaced apart along the first direction.

The uppermost cutting point 140a is formed by a connection or interface between the upper surface 136 and two adjacent side surfaces 132 of the knife. The corner 134 between such side surfaces has a conical taper portion 134a which starts immediately at the top cutting point 140a and tapers inwardly toward the knife central axis so that the top cutting point 140a farther than any other portion of the taper portion 134a of the central axis is removed. The second cutting point 140b is defined below the tapering portion 134a and is farther from the central axis than a lower portion of the tapering portion 134a adjacent to the second cutting point 140b.

The body of each blade 130 has a bore 142 extending through the body for receiving a releasable fastener along a first direction, and the blade holders 44 have corresponding bores for receiving the fasteners for securing the blades to the blade holders 44 the FIGS. 8 to 10 Referenced. The knives 130 are mounted to the rotor 130 with the central axis of each blade 130 oriented substantially tangentially to the peripheral surface of the rotor 12. The knives are oriented in a manner such that the plurality of cutting points 140a, 140b are arranged such that, as the rotor rotates, the cutting points continuously mesh with the respective V-shaped groove 26 in the counter knife 14. As a result, the uppermost cutting point 140a hits the groove 26 first and then the second cutting point 140b.

It will be appreciated that rotors for shredders may have various configurations that differ from the illustrated rotor 12, and such rotors may include multi-cutting blades having a plurality of cutting points according to the present invention. The invention is therefore not limited to the specific rotor configuration shown in the drawings.

It is now on the Figures 6A and 6B Reference is made, in which a knife 230 is shown with three cutting points according to another embodiment of the invention. The three-point cutting blade is generally similar to the two-point multi-point cutting blade 130 described above, but each corner 234 of the blade (formed by the junction of adjacent side surfaces 232) has three cutting points 240a, 240b. 240c, which are spaced apart along the first direction parallel to the central axis of the knife. The uppermost cutting point 240a is formed by a joint between the upper surface 236 and two adjacent side surfaces 232 of the knife. The corner 234 between such side surfaces has a conical tapering portion 234a which starts immediately at the uppermost cutting point 240a and tapers inwardly toward the central axis of the blade, so that the uppermost cutting point 240a farther than any other portion of the tapered portion 234a of the central axis is removed. The second cutting point 240b is defined below the tapering portion 234a, the second cutting point 240b being farther from the central axis than a lower portion of the tapering portion 234a adjacent to the second cutting point 240b. The corner has a conical second tapering region 234b which begins immediately at the second cutting point 240b and inwardly towards the central one Axis of the knife tapers so that the second cutting point 240b is further than any other portion of the second tapering portion 234b away from the central axis. The corner further includes a third cutting point 240c defined below the second tapering portion 234b, the third cutting point 240c being farther from the central axis than a lower portion of the second tapering portion 234b adjacent the third cutting point 240c.

As the Figures 11 and 12 show the knives 230 are fixed to the rotor 12, wherein the central axis is oriented substantially tangential to the outer peripheral surface of the rotor, so that the plurality of cutting points 240 a, 240 b, 240 c of each knife is arranged such that the cutting points upon rotation of the Rotor continuously with the respective V-shaped groove in the counter blade 14 comb. As a result, the uppermost cutting point 240a hits the groove first, then the second cutting point 240b, and finally the third cutting point 240c.

In the FIGS. 7A and 7B For example, a four-point cutting blade 330 according to another embodiment of the invention is shown. The four-point multi-point cutter is generally similar to the two-point and three-point multiple-edge knives 130 and 230 described above, but each corner 334 of the knife (formed by the junction of the adjacent side surfaces 332) has four cutting points 340a. 340b, 340c, 340d, which are spaced apart along the first direction parallel to the central axis of the knife. The uppermost cutting point 340a is formed by a joint between the upper surface 336 and two adjacent side surfaces 332 of the knife. The corner 334 between such side surfaces has a conical tapering portion 334a immediately adjacent to the uppermost cutting point 340a begins and tapers inwardly toward the knife's central axis so that the uppermost cutting point 340a is farther away from the central axis than any other portion of the tapered region 334a. The second cutting point 340b is defined below the tapering portion 334a with the second cutting point 340b farther from the central axis than a lower portion of the tapering portion 334a adjacent the second cutting point 340b. The corner has a tapered second tapered portion 334b that begins immediately at the second cutting point 340b and tapers inwardly toward the knife's central axis, such that the cutting point 340b is farther away from the central axis than any other portion of the second tapered portion 334b is. The corner further includes a third cutting point 340c defined below the second tapering region 334b, the third cutting point 340c being farther from the central axis than a lower portion of the second tapering region 334b adjacent the third cutting point 340c. The corner has a tapered third tapered portion 334c that begins immediately at the third cutting point 340c and tapers inwardly toward the central axis such that the third cutting point 340 is farther away from the central axis than any other portion of the third tapering portion 334c , The corner further includes a fourth cutting point 340d defined below the third tapering region 334c, the fourth cutting point 340d being farther from the central axis than a lower portion of the third tapering region 334c adjacent the fourth cutting point 340d.

FIG. 13 FIG. 11 shows the blades 330 with four cutting points mounted on the rotor 12 in much the same way as the other multiple cut point blades 130, 230 described above. The four Cutting points 340a-d of each knife continuously strike the respective groove in the counter knife 14. FIG. 14 shows the shredder with the multiple cutting points having knives in operation. Material M to be shredded is fed into the hopper 18 and falls by gravity down onto the plate 21 where the material is pushed by a reciprocating ram 20 towards the space between the rotor 12 and the counter knife 14. The multi-cutter multi-point knife and the counter knife cooperate to break the material into pieces that are small enough to pass the wire 16. Pieces too large to pass through the screen are transported back into the hopper by the rotation of the rotor, where they then fall down again to be comminuted again.

Multi-point multi-point cutters have proven to be advantageous over cut-point knives. Experiments were carried out with a single-shaft shredder of the type described above and illustrated, in particular with a shredder of the type Vecoplan RG 70-XL, especially for the processing of paper and plastic waste for recovery and recycling, for large extruder waste, large production scrap, Trimmreste, bundled or loose films, synthetic fibers, carpeting, wood processing waste, medical waste, cardboard, etc. is designed. The funnel of the RG 70 XL has a volume capacity of 7,838 m ³ (10.25 cubic yard) and a 177.8 cm x 200.28 cm (70 "x 82") filler opening. The 63.5 cm (25 ") diameter rotor has 84 to 126 knives and is driven by a 150 to 200 horsepower engine, revving at 125 rpm and powered by a 10 HP, two speed hydraulic ram ,

There have been a number of tests with the shredder of the type RG 70-XL, with each test using differently designed knives. The material to be shredded in these tests were used plastic bottles. This material was chosen because such plastic bottles are particularly susceptible to wear on blades with a cutting point. For each test, all the blades on the rotor had the same design. The data (including the throughput rate in pounds per hour) was recorded after 50, 100, 150, 200 and 250 hours of operation. All knives were inspected every 50 hours, photographed and the notes recorded.

It was a test with a knife with a cutting point ("knife C"), as essentially in the FIGS. 4A and 4B and another test with a multi-cutter knife with two cutting points ("knife A"), as in the main FIGS. 5A and 5B shown performed. Both knives were made from the same D2 tool steel.

In the case of Messer A (multi-cutting knife with two cutting points), the throughput of the shredder started at about 2,404 kg (5,300 lb) per hour at t = 0 and gradually decreased to about 2,086.5 kg over the first 200 hours ( 4600 lb) per hour and then during the last 50 hours of the test at a slightly higher speed to ultimately about 1723.7 kg (3800 lb) per hour at t = 250 hours. At t = 250 hours the knives showed a slight wear.

In the case of Messer C (knife with a cut point), the throughput started at about 2494.8 kg (5500 lb.) per hour at t = 0, but rapidly decreased to about 2000 lb. per hour at t = 50 hours. The knives therefore had to be rotated to provide a new cutting point for the next 50 hours of testing, with the result was essentially the same as the results after the first 50 hours. At t = 100 hours, the blades were rotated again and again at t = 150 hours. After 200 hours, the test had to be stopped because it was determined that a much higher performance than 200 hours with the knives is not achievable and because all four corners of the knife were worn out.

The tests have shown that with the knives according to the invention a high throughput can be achieved, which only decreased slowly, and that the knives wear only slowly. The knife C (with a cut point) proved to be much worse in terms of wear rate.

The tests confirmed the very significant advantage of forming the blades with multiple cutting points compared to their formation with a cutting point. In fact, the corners of the knives C with a cutting point had worn out completely in the course of the test, while in the knife A with two cutting points only one corner had to be used.

As already mentioned above, the invention is not limited to single-shaft shredders. FIG. 15 for example, shows a twin-shaft shredder 110 having a pair of rotors 12 each having blades 130 having a plurality of cutting points. The counter knife 114 is disposed between the two rotors 12 and has on each of its opposite sides a series of V-shaped grooves for engagement with the blades 130 of each rotor.

Although all of the knives 130, 230, 330 described and illustrated herein are polygonal on four sides (in particular essentially quadrangular), the knives according to the invention do not necessarily have four sides or polygonal. There are also multiple cutting blades with multiple cutting points, which have three, five or more sides, as well as non-polygonal (eg round) knives possible.

The knives of the invention may be made of any material of a variety of materials. For example, tool steels (such as D2, carbide, tungsten carbide or the like, standardized or proprietary) are suitable.

In the present case, multi-blade knives having 2, 3 and 4 cutting points have been described. However, the invention is not limited to a maximum of four cutting points at one corner. Knives having more than four cutting points are within the scope of the invention, including "corrugated" knives having substantially more than four cutting points.

Those skilled in the art will recognize that numerous modifications and other embodiments of the invention described herein and illustrated in the accompanying drawings are possible. For example, in the described embodiments, the knife holders are welded to the rotor, and the knives are removably attached to the knife holders by fasteners such as screws. Alternatively, however, the blades may be attached to the rotor in some other way. It is therefore to be understood that the inventions are not limited to the particular embodiments disclosed and that modifications and other embodiments are included within the scope of the appended claims. Although specific terms have been used in the present specification, these terms are to be understood in a general and descriptive sense rather than a limitation of the invention.

LIST OF REFERENCE NUMBERS

10

Shredder

12

rotor

14

against knife

16

scree

18

hopper

20

Hydraulic ram

21

Horizontal plate

22

rib

24

teeth

26

V-shaped recess / groove

30

knife

32

side surface

34

corner

36

top

38

cutting edge

40

cutting point

42

screw

44

toolholder

46

bag

110

Shredder

114

against knife

130

knife

132

side surface

134

corner

134a

tapering region

136

top

138

edge

140a, b

cutting points

142

drilling

230

knife

232

faces

234

corner

234a, b

tapering region

236 240a,

top

b, c

cutting points

330

knife

332

faces

334,334 a,

corner

b, c

tapering region

336 340 a,

top

b, c, d

cutting points

M

material

Claims (19)

Shredder (110) for shredding various materials, comprising: at least one rotor (12) rotatable about an axis and having an outer peripheral surface extending about the axis; a plurality of knife holders (44) in places, which are circumferentially and axially along a length of the rotor (12) spaced from each other, are fixed to the outer peripheral surface of the rotor (12); a plurality of knives (130, 230, 330) respectively mounted on the knife holders (44); a stationary counter knife (14) mounted adjacent to the outer peripheral surface of the rotor (12) and extending along the length of the rotor (12), the counter knife (14) defining a plurality of generally V-shaped grooves (26) spaced along the counter blade (14), each generally V-shaped groove (26 ) is aligned with at least one of the knives (130, 230, 330); wherein each of the knives (130, 230, 330) comprises a rigid body having a configuration when viewed in a first direction, each blade (130, 230, 330) 330) is mounted on a respective knife holder (44) and the first direction is oriented substantially tangential to the outer peripheral surface of the rotor (12), the body defining a corner (134, 234, 334) complementary to one of the V -shaped grooves (26) in the counter knife (14) is formed, wherein the knives (130, 230, 330) are mounted in an orientation such that the corners (134, 234, 334) upon rotation of the rotor (12) to mesh the axle with the respective V-shaped grooves (26); and wherein at least some of the knives (130, 230, 330) are those having a plurality of cutting points (140a, b; 240a, b, c; 340a, b, c, d) in which the corner (134, 234, 334) the blade (130, 230, 330) defines a plurality of cutting points (140a, b; 240a, b, c; 340a, b, c, d) spaced along the first direction, the plurality of cutting points of each blade (140; 130, 230, 330) having a plurality of cutting points is arranged such that the cutting points (140a, b; 240a, b, c; 340a, b, c, d) during the rotation of the rotor (12) continuously with the respective V comb-shaped groove (26). A shredder (110) according to claim 1, wherein the knives (130, 230, 330) are mounted to the knife holders (44) by releasable fasteners which permit removal and replacement of the knives (130, 230, 330) as needed. The shredder (110) of claim 1 or 2, wherein the body of each blade (130, 230, 330) has a bore extending therealong through the body for receiving a respective one of the releasable fasteners and the blade holders have corresponding bores for the fasteners Recording the fasteners to attach the blades to the knife holders to have. A shredder (110) according to claim 1, 2 or 3, wherein the plurality of cutters (130, 230, 330) comprise cutters (130) having two cut points (140a, b) in which the corner (134) has two cut points (140a , b) spaced apart along the first direction. A shredder (110) according to any one of claims 1 to 4, wherein the multi-point knives (130, 230, 330) comprise knives (230) having three cutting points (240 a, b, c) in which the corner (234) is three Cutting points (240 a, b, c) defined, which are spaced apart along the first direction. A shredder (110) according to any one of claims 1 to 5, wherein the multiple point knives (130, 230, 330) comprise knives (330) having four cutting points (340a, b, c, d) in which the corner (334) defines four cutting points (340a, b, c, d) spaced apart along the first direction. A shredder (110) according to any one of claims 1 to 6, wherein each blade (130, 230, 330) having a plurality of cutting points (140a, b; 240a, b, c; 340a, b, c, d) has a plurality of corners and each corner (134, 234, 334) of each knife having a plurality of cutting points defines a plurality of cutting points that are spaced apart along the first direction. A shredder (110) according to any one of claims 1 to 7, wherein each blade (130, 230, 330) having a plurality of cutting points (140a, b; 240a, b, c; 340a, b, c, d) is one to the first direction has parallel central axis, wherein the corner (134, 234, 334) of each knife (130, 230, 330) with a plurality of cutting points meshing with the counter knife (14) is defined by an intersection between two adjacent side surfaces (132, 232, 332) of the body, an upper cutting point (140a, 240a, 340a) of the knife being defined by an intersection point two side surfaces (132, 232, 332) and an upper surface (136, 236, 336) of the body, all coinciding at the uppermost cutting point, and wherein the corner has a conical tapering region that begins immediately at the uppermost cutting point and moves inward tapered towards the central axis of the knife such that the uppermost cutting point (140a, 240a, 340a) is farther away from the central axis than any other portion of the tapered region. The shredder (110) of claim 8, wherein a second cutting point (140b, 240b, 340b) of a knife (130, 230, 330) having a plurality of cutting points is defined below the tapering region, the second cutting point being wider than a lower portion adjacent the second cutting point of the taper area is away from the central axis. The shredder (110) of claim 8 or 9, wherein the second cutting point (140b, 240b, 340b) extends further than the uppermost cutting point (140a, 240a, 340a) from the central axis. The shredder (110) of claim 8, 9 or 10, wherein the knife (230, 330) further includes a tapered second taper region beginning immediately at the second cutting point (240b, 340b) and moving inwardly toward the central axis of the Knife tapers, making the second cutting point farther than any other section of the second tapering section away from the central axis. The shredder (110) of any one of claims 8 to 11, wherein the knife (230, 330) further includes a third cutting point (240c, 340c) defined below the second tapering region, the third cutting point being farther than a third cutting point adjacent lower portion of the second tapering region is away from the central axis. The shredder (110) of any one of claims 8 to 12, wherein the knife (330) further includes a tapered third tapering region that begins immediately at the third cutting point (340c) and extends inwardly toward the central axis of the blade (330). tapered such that the third cutting point is farther away from the central axis than any other portion of the third tapering region, and wherein a fourth cutting point (330d) of each knife is defined with a plurality of cutting points below the third tapering region, the fourth cutting point (330d) farther than a lower portion of the third tapering portion adjacent to the fourth cutting point is away from the central axis. A shredder (110) according to any one of claims 1 to 13, wherein the upper surface (136, 236, 336) of the body is concave toward the first direction. A shredder (110) according to any one of claims 1 to 14, wherein all the knives on the rotor (12) comprise knives (130, 230, 330) having a plurality of cutting points (140a, b; 240a, b, c; 340a, b, c , d) are. The shredder (110) of claim 15, wherein each blade (130, 230, 330) having a plurality of cutting points has a plurality of corners and each of the corners has defined the plurality of cutting points. A rotor assembly for use in a shredder (110) according to any one of claims 1 to 16, comprising: a rotor (12) which is rotatable about an axis and an outer peripheral surface extending around the axis; a plurality of knife holders (44) in places, which are circumferentially and axially along a length of the rotor (12) spaced from each other, are fixed to the outer peripheral surface of the rotor; and a plurality of blades (130, 230, 330) respectively mounted on the blade holders; the knives (130, 230, 330) each having a rigid body with a configuration as viewed along a first direction, each knife being mounted on a respective knife holder (44) and the first direction is oriented substantially tangentially to the outer peripheral surface of the rotor (12), the body defining a generally V-shaped corner (134, 234, 334), the knives being mounted in an orientation such that upon rotation of the rotor (12) about the axis with a respective V-shaped groove (26 ) in a counter knife (14) of the shredder (110); wherein at least some of the knives (130, 230, 330) are ones having a plurality of cutting points (140a, b; 240a, b, c; 340a, b, c, d) in which the corners (134, 234, 334) the knife defines a plurality of cutting points spaced apart along a first direction. A knife (230, 330) having a plurality of cutting points (240 a, b, c; 340 a, b, c, d) for use in a shredder (110) according to any one of claims 1 to 16, comprising: a rigid body having a central axis extending along a first direction, the body having a configuration when viewed along the first direction, and wherein the body defines a corner (234, 334) at an intersection between two adjacent side surfaces of the body, defining at least three cutting points spaced apart along the first direction, wherein an upper cutting point of the knife is defined by an intersection between two side surfaces (232, 332) and a top surface (236, 336) of the body, all at the top cutting point (240a , 340a); the corner having a conical tapering area, starting immediately at the uppermost cutting point and tapering inwardly toward the knife central axis so that the uppermost cutting point is farther away from the central axis than any other portion of the tapered region and a second cutting point (240b, 340b) is defined below the tapering region, wherein the second cutting point is farther away from the central axis than a lower portion of the tapering region adjacent to the second cutting point; said corner (234, 334) further having a tapered second taper region starting immediately at the second cutting point (240b, 340b) and tapering inwardly towards the central axis of the blade so that the second cutting point is wider than any other Portion of the second tapering portion is away from the central axis, and a third tapering portion defined below the second tapering portion, wherein the third cutting point (240c, 340c) farther away from the central axis than a lower portion of the second tapering portion adjacent to the third cutting point is. The multi-point blade cutter (330a, b, c, d) of claim 18, further comprising a tapered third taper region beginning immediately at the third cutting point (340c) and tapering inwardly toward the knife central axis such that the third cutting point is farther away from the central axis than any other portion of the third tapering region, and a fourth cutting point (340d) of each multiple cutting point knife (330) defined below the third tapering region, the fourth cutting point continuing as a lower portion of the third tapering portion adjacent to the fourth cutting point (340d) is away from the central axis.

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