European patent application EP 928 222 describes an industrial shredder comprising two shafts parallel to each other, generally rotating in opposite directions.

Said shafts carry integral disc-shaped blades with one or more teeth formed on the outer profile of the blades, which can take different shapes, according to the particular use.

Said blades pass through rectangular apertures formed in the tables which are situated, with suitable angles, between the side walls of the shredding chamber and the middle of the shredding machine. In this manner, the walls of the rectangular apertures in the tables form a fixed contrasting element and thus act as counterblades, facilitating shearing or cutting of the material to be shredded.

In fact, cutting of the material takes place only on one side of the blades, whilst on the other side of the blades the material is simply drawn, but not cut, because said side of the blades does not interfere with any contrasting element. As a result, if the shaft always turned in the same direction, there would be a build-up of uncut material.

This makes it necessary to make the shafts operate with cycles of rotation in one direction and in the opposite direction, so that the uncut material can be brought into an area in which the cutting action can be exerted.

Such a shredder operating system thus entails stopping and reversing the rotation of the motors which set the shafts in rotation, with the result of having significant idle times.

The object of the present invention is to overcome the drawbacks of the prior art by providing an industrial shredder that is able to ensure good efficiency and effective cutting.

Another object of the present invention is to provide such an industrial shredder that is able to reduce idle times during operation to a minimum.

Yet another object of the present invention is to provide such an industrial shredder that is cheap and simple to make.

These objects are achieved according to the invention with the characteristics listed in appended independent claim 1.

Advantageous embodiments of the invention are apparent from the dependent claims.

The industrial shredder according to the invention comprises: - a fixed supporting structure, - at least one shaft mounted rotatably in said fixed structure and carrying a plurality of blades provided with cutting teeth, and - a first row of counterblades and a second row of counterblades mounted on said fixed structure on one side and the other with respect to said at least one shaft so that the cutting teeth of the blades cooperate with the counterblades to shear the material to be shredded.

The main characteristics of the invention are represented by the fact that - the cutting teeth are disposed on said shaft in pairs, and - the blades of the first row of counterblades are disposed offset with respect to the blades of the second row of counterblades.

In this manner, in each pair of cutting teeth, one cutting tooth cooperates with a corresponding counterblade of the first row of counterblades and the other cutting tooth cooperates with a corresponding counterblade of a second row of counterblades.

Said configuration of the shredder according to the invention makes it possible to obtain a considerable free area in the shredding surface through which the shredded material can pass. Furthermore, the material engaged by a blade always finds a corresponding counterblade against which it is sheared, reducing to a minimum the amount of unsheared material and the idle times for reversal of rotation of the shafts.

Further characteristics of the invention will be made clearer by the detailed description that follows, referring to a purely exemplifying and therefore non-limiting embodiment thereof illustrated in the appended drawings, in which: Figure 1 is a perspective, exploded view of the industrial shredder according to the invention; Figure 2 is a perspective view of the fixed structure of the shredder of Figure 1; Figure 3 is a perspective view of the assembled shredder; Figure 4 is a partially sectioned view of the shredder of Figure 3, taken along a horizontal plane passing through the axes of the shredder shafts; Figure 5 is a partially sectioned view of the shredder of Figure 3, taken along a vertical plane at right angles to the axes of the shredder shafts; Figure 6 is a perspective view illustrating an enlarged detail of two side-by-side blades of a shredder shaft according to the invention; and Figure 7 is a perspective view illustrating an enlarged detail of a group of three central inserts of the shredder according to the invention.

The shredder according to the invention, denoted as a whole with reference numeral 100, is described with the aid of the figures.

The shredder 100 comprises a fixed structure, illustrated in Figure 2 and denoted as a whole with reference numeral 1. Two substantially similes shafts (Figures 1 and 3) are mounted on the fixed structure.

As shown in Figure 2, the fixed structure 1 comprises a basic frame 3, substantially rectangular in shape, provided with a central supporting bar 4 parallel to the longer sides 5 of the base frame 3.

Two sides 6, substantially similar in shape, are mounted on the longer sides 5 of the base frame 3. Each side 6 has a side plate 7 which rises vertically from the longer side 5 of the base frame 3.

The side plate 7 of each side 6 has an inward facing flat surface wherein a plurality of side inserts 9, arranged in a row side by side are mounted. As shown also in Figure 1, each side insert 9 has a T-shaped top part 10 which acts as a counterblade and a rounded front part 11 on which the shaft 2 is supported and slides.

A plurality of central inserts 13 is mounted on the central bar 4 of the fixed structure 1.

As shown better in Figure 7, the central inserts 13 are grouped in threes on a base 14.

Each insert has a first rounded top part 15 on which the shaft 2 is supported and slides and a second L-shaped top cutting part 16, inclined about 45° with respect to a horizontal plane.

The three inserts 13 are offset from each other and disposed with the cutting parts inclined the opposite way. In this manner, the cutting parts 16 of the two side inserts form with the rear part of the cutting part 16 of the intermediate insert a substantially C-shaped slot when seen in a plan view. Ultimately, two rows of central inserts 13, opposite and offset with respect to the respective rows of side inserts 9, are obtained.

A plurality of blades 18 is keyed on the shaft 2. As shown better in Figure 6, each blade 18 comprises a cylindrical body 19 having an hexagonal through hole 20 axially, able to engage on a hexagonal profile 21 formed on the outer side surface of the shaft 2 (Figure 1).

A cutting tooth 22, which protrudes outward occupying an arc of circumference subtended by an angle of about 90°, is formed on the body 19 of each blade 18. The cutting tooth 22 has two opposed cutting beaks 23 and 24. Each cutting beak 23,24 defines a substantially arched cutting surface.

The first cutting beak 23 is higher than the second cutting beak 24. That is to say, the cutting beak 23 protrudes radially from the outer side surface of the blade body 19 more than the other cutting beak 24.

The width or thickness Wl of each tooth 22 is about half the width W of the side surface of the blade body 19. The widths Wl and W are taken in the axial direction of the blade.

Since the tooth 22 is disposed at one end of the side surface of the blade body 19, a free portion 25 of side surface of the blade body remains next to each tooth 22. The free portion 25 has a width W2 = W-Wl = Wl.

The blades 18 are keyed on the hexagonal profile 21 of the shaft 2, so that alternatively the teeth 22 of the two adjacent blades are alongside each other and the free parts 25 of two adjacent blades are alongside each other. In this manner, pairs of side-by-side teeth 22 alternating with pairs of side-by-side free parts 25 are formed on the shaft.

In this case the wordings"pair of side-by-side teeth"and"pair of side-by-side free parts" generically signifies that the blades 18 are mounted in such a manner that, in a pair of adjacent blades, the surface in which the tooth 22 is situated is alongside the surface in which the tooth of the adjacent blade is situated and the surface in which the free part 25 is situated is alongside the surface in which the free part of the adjacent blade is situated.

In fact, even if not shown in the figures, the teeth 22 of a pair of side-by-side teeth could be angularly offset.

However, when the teeth 22 are alongside each other, the highest cutting beak 23 of a blade is advantageously on the same side as the lowest cutting beak 24 of the adjacent blade.

Furthermore, as shown in Figure 1, the blades 19 are keyed on the profile 21 of the shaft 2 in such a manner that their teeth 22 follow a course substantially like a cylindrical helix.

Furthermore, even if in the present description it has been said that a single tooth 22 is mounted on each blade 18, provision can be made for the pair of side-by-side teeth

disposed on two adjacent blades 18 to be made in a single piece on a single blade having a blade body double the width of the blade body 19.

At this point the shafts 2 with the blades 19 disposed in the above mentioned configuration are mounted in the fixed structure 1, as shown in Figure 3. As shown also in Figure 5, the side surfaces of the blade bodies 19 are supported rotatably by the curved supporting parts 11 and 15 respectively of the side inserts 9 and the central inserts 13.

For this purpose, the radius of curvature of the supporting parts 11 and 15 is substantially similar to the radius of curvature of the blade body 19 and the side inserts 9 and central inserts 13 are disposed in such a manner that their curved supporting parts 11 and 15 have the same center of curvature which coincides with the axis of the shaft 2.

Furthermore, to ensure a better stability of the shaft 2, the supporting parts 11 of the lateral inserts 9 are offset with respect to the supporting parts 15 of the central inserts 13.

The thickness of the supporting parts 11 and 15 is equal to or slightly smaller than the width W2 of the free part 25 of the blade body 19. Thus, the shafts 2 are mounted so that the rounded supporting parts 11 and 15 go onto the free parts 25 of the blade body 19 and do not interfere with the teeth 22.

As a result, the teeth 2 can pass through the C-shaped slots 12 and 17 defined by the cutting parts 10 and 16, respectively, of the lateral inserts 9 and the central inserts 13. As shown in Figure 4, the width of each C-shaped slot 12 and 17 must be equal to or slightly greater than the sum of the widths of two teeth 22 and two free parts 25 of the blades 18; that is to say, the width of each C-shaped slot 12 and 17 is equal to about 2W1 + 2W2 = 4W1.

In this arrangement, it should be noted that during rotation of the shaft 2, in a pair of side- by-side teeth 22, the highest cutting beak 23 of the first cutting tooth 22 will always cooperate with the cutting part or counterblade 10 of a side insert 9 whilst the highest cutting beak 23 of the other adjacent tooth 22 will always cooperate with the cutting part

or counterblade 16 of the central insert 13. In this manner it is possible to obtain a considerable free area in the shredding surface, that is to say a free area equal to about the double of the width Wl of the teeth 22, through which the sheared material can pass.

Furthermore, with each rotation of the shaft 2, the material engaged in the cutting beak of the tooth 22 of the blade finds a counterblade 10 or 16 against which it is sheared.

These characteristics advantageously reduce to a minimum the residue of unsheared material. As a result, reversal of the movement of rotation of the shafts 2 to recover the unsheared material becomes much less necessary. Thus such a shredder 100 has considerably less idle time than shredders of the prior art, and a higher yield.

Furthermore, it must be considered that the lowest cutting beak 24 of a blade is situated on the same side as the highest cutting beak 23 of the adjacent blade, to limit the amount of material picked up by the highest cutting beak 23 during rotation of the shaft 2, so as to avoid excessive overloading of the machine.

Numerous variations and modifications of detail within the reach of a person skilled in the art can be made to the present embodiment of the invention, without departing from the scope of the invention, as set forth in the appended claims.