Waste Material Shredder

Various types of waste material shredder are in use at the present time. These are used primarily for shredding documents in order to destroy the information content therein. However various other materials may be subjected to shredding, such as for example computer punch cards, printed circuit substrates, etc. Such waste material shredder can be broadly divided into two types, i.e. strip type shredders and cross-cut shredders. The strip type shredders act to cut sheets of waste material into elongated longitudinal strips, by a shearing action, while the cross-cut shredders cut the sheets of waste material into small chips, or very short strips. From the aspect of maximum destruction of any information contained in the waste material, and for minimizing the volume of the shredded output material, the cross-cut type of shredder is preferable. However a major problem which has arisen with prior art types of cross-cut shredder is that the shredded chips produced by the shredder tend to gradually accumulate within the mechanism, over a period of time, and to eventually cause the mechanism to be jammed, so that it becomes necessary for the user to periodically clear out such blockages from the shredder. This is extremely inconvenient, and is a major disadvantage of prior art cross-cut shredders by comparison with the mechanically simple strip type shredders.

More specifically, a cross-cut shredder generally comprises a pair of rotating shafts with their axes of rotation parallel to one another, with sets of cutter disks fixedly mounted on each shaft, and mutually meshing. Spacer members are fixedly mounted between the cutter disks of each shaft, to maintain a fixed separation between the cutter disks, and teeth are formed on the peripheries of the cutter disks. When such a shredder is operated over a long period of time, the shredded chips which are produced by a cutting action of the teeth and shearing between the cutter disks are not entirely removed from the mechanism, and gradually accumulated between the spacer members. As time elapses, this accumulation will increase to such an extent that the cutter disks can no longer rotate, and so the chips must be cleared out by the user.

With a waste material shredder according to the present invention, a special configuration for the cutter disks is employed, whereby the shredded chips are completely removed from the cutter mechanism immediately after they are produced, so that the problem described above is entirely eliminated. Thus a waste material shredder according to the present invention presents substantial advantages over prior art shredders with respect to ease of maintenance and reliability of operation.

A waste material shredder according to the present invention is of the cross-cut shredder type discussed above, comprising a pair of counter-rotating cutter rollers disposed side by side, with the axes of rotation of these cutter rollers being parallel to one another, each cutter roller comprising a roller shaft with a set of cutter disks fixedly mounted coaxially thereon, and with the cutter disks of one cutter roller meshing with the cutter disks of the other cutter roller in a successively alternating manner. Fixedly mounted spacer plates are disposed between pairs of cutter disks on each cutter roller, to thereby maintain a fixed separation between the cutter disks. Each of the cutter disks is formed with a plurality of pairs of closely adjacent protrusions formed at regular spacings around the disk periphery, with each pair consisting of a chip clearance protrusion and a cutter tooth, the cutter tooth having a sharp cutting edge and the chip clearance protrusion being of blunt contour and positioned leading the cutter tooth with respect to the direction of rotation of the disk. The cutter teeth serve to penetrate into sheets of material being shredded, to form lateral slits, and this action is combined with a shearing action occurring between the opposing enmeshed cutter disks to produce cross-cutting of the sheets. The chip clearance protrusions serve to position the sheets in an optimum manner to facilitate the latter penetration by the cutter teeth, and also to effectively remove the chips of waste material formed by the cutting action, to prevent the chips from becoming jammed within the cutting mechanism. The basic reason for the problem of shredded chips building-up inside the mechanism of a cutter disk shredder is that, in general, some form of punching action is imparted by the cutter disk teeth in order to perform cross-cutting of the waste material sheets, in addition to the longitudinal shearing action. This punching action, which cuts the material transversely, causes a certain amount of deformation of the waste material, and it is because of this deformation that the chips tend to become retained between the spacer members which separate the cutter disks. However the clearance protrusions of the cutter disks of a waste material shredder according to the present invention perform a "sweeping" action, whereby the shredded chips are, so as to speak, "floated" out from between the spacer members, so that the problem of chip buid-up in the mechanism is very effectively overcome.

In the drawings,

FIG. 1 is a cross-sectional view of the cutter roller and spacer plates of an embodiment of a waste material shredder according to the present invention, taken in a plane perpendicular to the longitudinal axes of the cutter rollers;

FIG. 2 is a partial cross-sectional view in plan of the cutter rollers and spacer plates of the embodiment of FIG. 1;

FIG. 3 is a cross-sectional view of the cutter rollers and spacer plates of the embodiment of FIG. 1, illustrating the cutting action applied to a sheet of waste material; and

FIG. 4 is a partial oblique view of an alternative configuration for the cutter teeth of a waste material shredder according to the present invention.

Referring now to the drawings, FIG. 1 shows a cross-sectional view of the cutter rollers and spacer plates of an embodiment of a waste material shredder according to the present invention, as seen along the longitudinal axes of the cutter rollers, while FIG. 2 is a partial cross-sectional view in plan of these cutter rollers and spacer plates. The drive means for rotating the cutter roller and the means for directing sheets of waste material to be cut are not shown in the drawings. Numerals 10 and 11 denote a pair of roller shafts of a pair of cutter rollers 8 and 9 respectively, which are rotatably mounted at ends 18 and 19 in bearings 20 and 21 respectively, and rotate in opposite directions to one another. The cutter rollers 8 and 9 are mounted adjacent to one another with their longitudinal axes aligned parallel to one another. Numeral 12 collectively designates a set of cutter disks which are mounted on roller shaft 10, and numeral 13 denotes a set of cutter disks which are fixedly mounted on roller shaft 11. Numeral 14 collectively designates a set of spacer plates which are fixedly attached to supporting member 16 (and an opposing supporting member, not shown in the drawings) by longitudinal members 14a and 14 b with the spacer plates 14 and cutter disks 12 being arranged in an alternating manner as shown, so that each pair of cutter disks is separated by a spacer plate.

Similarly, a set of cutter disks 13 are fixedly mounted on roller shaft 11, and alternate with spacer plates 15. The cutter disks 12 of cutter roller 8 mesh with cutter disks 13 of cutter roller 9, as shown.

Cutterdisks 12 and 13 are restrained from rotating with respect to roller shafts 10 and 11 by providing a hexagonal cross-section external contour on mounting portions 10a and 11a of roller shafts 10 and 11 respectively, and providing corresponding hexagonal apertures in cutter disks 12 and 13 for mounting on the shafts, as shown in FIG. 1. Circular apertures are formed in the spacer plates 14 and 15, having a diameter which is slightly greater than the circumscribing circle of the hexagonal cross-sectional contour of roller shafts 10 and 11, since the spacer plates are held stationary.

Each of the rotating cutter disks 12 and 13 has a plurality of pairs of protrusions formed at regular spacings about the periphery thereof, each pair comprising a cutter tooth and a chip clearance protrusion positioned closely adjacent to one another, e.g. the pair formed by cutter tooth 12a and chip clearance protrusion 12b on cutter disk 12 in FIG. 1, and the pair formed by chip clearance protrusion 13b and cutter tooth 13a on cutter disk 13. Each chip clearance protrusion is preferably formed with a profile having a sloping leading edge (e.g. as indicated by 12c) whose profile forms an obtuse angle with the profile of the preceding portion of the periphery, e.g. angle .theta. in FIG. 1. This sloping leading edge of each chip clearance protrusion is important for the operation of the apparatus, as described in detail hereinafter. The overall shape of each chip clearance protrusion is blunt, as viewed in profile, i.e. the chip clearance protrusion do not perform a penetration function during shredding, this function being carried out entirely by the cutter teeth. In this embodiment, the chip clearance protrusions each have a profile (as viewed along the direction of rotation of a disk) in the form of three sides of a trapezoid, with one of these sides being the sloping leading face referred to above.

Each chip clearance protrusion in a pair of protrusions is positioned to lead the cutter tooth of that pair, with respect to the direction of rotation of the cutter disk on which the protrusions are formed. It is an essential feature of the present invention that the angular position of the roller shafts are precisely arranged such that, as indicated in FIG. 1, as the two roller shafts counter-rotate, each cutter tooth on a cutter disk successively approaches two chip clearance protrusions respectively formed on the two opposing cutter disks which are positioned on each side of the first-mentioned cutter disk and are closely adjacent to or in sliding contact with that cutter disk, then the tip portion of that cutter tooth momentarily overlaps (as viewed along the direction of rotation of the cutter rollers) the leading faces of these opposing chip clearance protrusions at a position close to the central region of each face, i.e. that tip portion momentarily protrudes slightly between these leading faces of the adjacent opposing chip clearance protrusions. This condition has just been attained, for example, by cutter tooth 13a' in FIG. 1, with respect to the opposing chip clearance protrusion leading face 12c'.

In the present embodiment, the cutter teeth have a sharp chisel shape, which is triangular as viewed in cross-section as seen in FIG. 1. In other words, each of the cutter teeth has a laterally extending cutting edge, which perforates the sheets of waste material with a very low amount of resistance to that perforation, as described in greater detail hereinafter.

Each of the chip clearance protrusions has a trapezoidal shape as viewed in cross section, in the present embodiment, as seen in FIG. 1. It is an essential feature of the present invention that leading face of each of the chip clearance protrusions (i.e. the face which reaches the waste material immediately after a preceding cutter tooth, as the corresponding cutter disk rotates) forms an oblique angle with a face that is substantially tangential to the periphery of the cutter disk. Thus in the present embodiment, the leading face 12c of cutter disk 12 forms an oblique angle .theta. with the tangential face 12d.

The meshing relationship between the sets of cutter disks 12 and 13 of cutter rollers 8 and 9 can be clearly understood from FIG. 2. The cutting operation of the present embodiment will now be described in more detail, referring to FIG. 3. The operation will be described with reference to a single cutter tooth 13a on one cutter roller and two chip clearance protrusions (collectively indicated as 12b) respectively formed on the two immediately adjacent cutter disks on the opposing cutter roller. Numeral 24 denotes a sheet of waste material which is to be shredded, and which is inserted vertically from the top downward, as viewed in the drawing, between the sets of cutter rollers 8 and 9. The sheet is directed by the shape of the upper portions of spacer plates 14 and 15 to be drawn by the action of mutually meshing sets of cutter disks 12 and 13. The waste material sheet first meets the leading sloping faces 12c of chip clearance protrusions 12b of cutter disks 12, then a lateral slit perforation is formed in the sheet by cutter tooth 13a, as that cutter tooth moves into a position slightly overlapping the two leading faces 12c as described hereinabove. It can thus be clearly understood that this momentary overlapping relationship between the cutter tooth tip and the leading faces of the opposing chip clearance protrusions ensures highly efficient penetration of the waste material sheet by the cutter tooth, by positioning the sheet such that a slit 26 is cut in the sheet with a very low level of resistance to this perforation. Next, as a result of the meshing relationship of the cutter disks, a shearing action is performed (in this example, occurring between cutter disk 13, cutter disk 12, and another cutter disk mounted on the same shaft as cutter disk 12 and disposed on the opposite side of cutter disk 13 to cutter disk 12), whereby a strip is formed with the lower end free, as illustrated by chip 28 in FIG. 3. The next cutter tooth to meet this strip (i.e. in this example, the next cutter tooth of cutter disk 13) perforates the sheet, forming a transverse slit therein, whereby the chip is completely separated from the waste material sheet. In this way, for example, chip 28 is formed. That is to say, the lower end of chip 28, as seen in FIG. 3, has been previously cut by the tooth on cutter disk 13 which immediately precedes cutter tooth 13a, while (at the instant illustrated in FIG. 3) the upper end of that chip is being formed by cutter tooth 13a entering the waste sheet. Chip 28 has at this stage been cut from the waste material sheet, and the chip clearance function now comes into operation. As described hereinabove, each cutter tooth is formed closely adjacent to a chip clearance protrusion, with the chip clearance protrusion of such a pair of protrusions being position leading the cutter tooth. The chip clearance function is performed in this example by the chip clearance protrusion (denoted as 13b) which is paired with cutter tooth 13a. This chip clearance protrusion 13b pushes the waste material chip 28, cut out as described above, outward from the cutter mechanism, such as to eliminate the possibility of the chip becoming jammed between the rotating cutter disks. The chip then falls downward, clear of the cutter mechanism.

The above chip clearance function is illustrated by a chip 30, which has been cut out by adjacent cutter disk 12 acting in cooperation with cutter disk 13 and another cutter disk disposed on the opposite side of cutter disk 12 to cutter disk 13 and mounted on the same shaft as cutter disk 13. This chip 30 is shown as being pushed outward and downward to separate from the cutter mechanism, by a chip clearance protrusion 12b on cutter disk 12.

Although the cutting and chip removal operation has been described in the above for a single sheet of waste material, for simplicity of description, in actual practice a plurality of waste material sheets will be shredded simultaneously.

It can thus be understood from the above description that a waste material shredded according to the present invention effectively remove shredded chips from the cutter mechanism immediately after these chips have been formed, by means of chip clearance protrusions formed on the cutter disks of the cutter rollers, with the effectiveness of this chip clearance function being enhanced by a suitable shape for these chip clearance protrusions. It can be further understood that these chip clearance protrusions also serve to direct sheets of waste material in a manner ensuring efficient lateral perforation of the waste material sheets by the cutter teeth of the cutter rollers, thereby enhancing the efficiency of the overall shredding operation and reducing the power consumption of such a shredder.

FIG. 4 is a partial oblique view illustrating an alternative configuration of the cutter teeth of a waste material shredder according to the present invention, as compared with the chisel-shaped cutter teeth of the embodiment described above. In the embodiment of FIG. 4, triangular incisions 36 are formed in each of the cutter teeth 34 of a cutter disk 32, so that a plurality of sharp teeth are formed on each of the cutter teeth. Such a configuration for the cutter teeth is advantageous for certain types of waste material.

It should be noted that, in addition to the shape of the leading sloping edge of each of the chip clearance protrusions of the cutter disks of a shredder according to the present invention being an important feature thereof, the relative positions of the cutter disks of one cutter roller with respect to the cutter disks of the opposing cutter roller are also extremely important. More specifically, these relative positions must be arranged such that, as illustrated in FIG. 1, each of the cutter teeth of one cutter disk, e.g. each of teeth 13a of cutter disk 13, comes into position for perforating a waste material sheet at an instant when the central region of the leading sloping faces (e.g. 12c) of two chip clearance protrusions on the opposing cutter disks positioned on each side of the first-mentioned cutter disk are slightly overlapped by that opposing cutter tooth, i.e. the tip portion of the cutter tooth protrudes slightly between these two opposing leading faces. It has been found that this ensures highly effective shredding operation.

Although the present invention has been described in the above with reference to specific embodiments, it should be noted that various changes and modifications to the embodiments may be envisaged, which fall within the scope claimed for the invention as set out in the appended claims. The above specification should therefore be interpreted in a descriptive and not in a limiting sense.