GB2311026A - Stripper device for shredding machines - Google Patents

Abstract

A shredding machine comprises a shredder box 20, and a pair of shredder shafts 22,23 arranged in parallel in the box. The shafts have alternating cutters and spacer discs 33,34 thereon, and the cutters of one shaft overlap the cutters of the other shaft and register with the spacer discs 33,34 of the said other shaft. Plough plates 40 are provided between adjacent cutters of each shaft, each plough plate 40 being of U-shape so that the arms embrace the spacer discs 33,34 and form respective stripping edges for the discs when the shafts are rotating in the working and reverse directions. The plough plates 40 may be floatingly mounted in that the plates are supported only by reaction against the shredder box 20 and the spacer discs 33,34 which they embrace.

Description

IMPROVEMENTS RELATING TO SHREDDING MACHINES This invention relates to shredding machines (also called pulverisers) of the type used for shredding waste material which includes garbage, waste paper, plastic, metal (in the form for example of tin cans) and other general rubbish.

The machines to which the invention relates comprise a cutter box which is a rectangular frame usually disposed horizontally and having an open top and bottom. The frame supports two shafts which are parallel and carry interengaging chopping discs or cutters. The shafts in the working condition rotate in opposite directions in such a manner to define a central nip so that waste material presented to the cutters, for example from a hopper is grabbed and pulled into the nip and is cut and/or shredded as it proceeds through the nip and is expressed out of the other side of the box. As explained hereinafter, the shafts may be rotated in the other direction momentarily for dislodgement of material trapped in the machine.

On the shafts are spacer discs so that the cutters can overlap and the spacer discs also act as a means to provide a reaction surface for the teeth on the cutters to enhance the shredding effect.

The spacer discs can and do however become clogged with waste material which may be improperly shredded, in that such material becomes wrapped round the spacer discs and binds thereto. Plastic bags are particularly bad in this respect, but other materials such as paper can do the same thing, as indeed can the sheet metal used for metal containers. In consequence, many shredding machines have been fitted with what are known as "plough plates" which lie between the cutters and have a paring or scraping surface which co-operates with the spacer surface to strip away any material which tends to bind around the spacers.

These ploughs plates are produced rather crudely by flame cutting, and then they are welded to a backing plate to provide a plough plate assembly which is turn is fitted to the inside of the box, from the underside, so that the respective plough plates lie between the cutters of each shaft. It will be appreciated that there are two plough plate assemblies for each box, one for each shaft. Because the assemblies have to be fitted from one side only, the underside, the plough plates are only effective for stripping of the spacer discs in one direction, the working direction, and when the shafts are rotated in reverse, the plough plates are largely ineffective, and tend to encourage compacting of materials dislodged during the reverse rotation of the shafts.

These plough plates have been satisfactory for materials which have only to be shredded coarsely, but with increased demand for the more accurate shredding of some particular materials such as paper and plastics, stripping of the spacer discs has to be more effective and closer fitting ploughs are needed.

If attempts were made to produce the existing plough assemblies more accurately, they would have to be machined out of solid metal, which would be an extremely difficult and expensive task, and in any case the need to fit the plough plates from one side only would remain, and there would be ineffective stripping from the spacer discs during reverse rotation of the shafts.

The present invention aims to provide a ploughing arrangement for shredding machines, which by its construction and operation can provide for the more accurate stripping of for example paper and plastic, which is now being demanded, and lends itself to enabling the effective stripping of the spacer discs when rotating in either direction.

According to the present invention there is provided a shredding machine comprising a shredder box, a pair of shredder shafts arranged in parallel in the box, said shafts having alternating cutters and spacer discs thereon, and of which the cutters of one shaft overlap the cutters of the other shaft and register with the spacer discs of the said other shaft, and including plough plates between adjacent cutters of each shaft, each plough plate being of U-shape so that the arms embrace the spacer discs and form respective stripping edges for the discs when the shafts are rotating in the working and reverse directions.

Preferably, the plough plates are "floatingly" mounted in that the plates are supported only by reaction against the shredder box on the one hand and by the spacer discs which they embrace on the other hand.

The ends of the plough plate arms may be formed as chisel shaped ends to enhance the stripping effect, and in the base of each plough plate at the inner side thereof, there may be machined a back bearing surface, on which the adjacent spacer disc can seat in use. There will also be front bearing surfaces at the said chisel shaped ends so that there will in effect be three points of support on the spacer disc.

The base of each plough plate, to the outside thereof, may be provided with seating blocks by which the plate can seat on the shredder box, although not be specifically attached thereto.

In an alternative seating arrangement, the plough plates may be provided with a back face and a pair of seating faces set back from the back face and at the edges of the plough plate, said seating faces abutting a pair of parallel rails mounted within and on the sides of the shredder box in order to provide support for the plough plates.

In either embodiment, the plough plates can be mounted in position whilst the cutters and the spacer discs are being mounted on the shafts, or where seating blocks are provided on the plough plates and with appropriate shaping of the plates, the plates may be capable of being fed round the spacer discs and into position, but in this case it may be necessary to provide an additional support member to prevent the plates from becoming detached from the machine.

The plates can be accurately machined and will therefore meet the demands for finer shredding of paper and plastic, they do not have to be fitted from the underside of the box, and they will be effective in stripping in both the working direction and the reverse direction. The plates, to perform their function will be fitted with appropriate clearance but will be self aligning when mounted in the floating manner hereinbefore mentioned. The clearances in question may be of the order of 0.1 to 0.2 mm.

The plough plates are preferably of machined, unhardened steel to work with the cutters and spacer discs which are of hardened steel.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein; Fig. 1 shows a plan view of a substantially U-shaped plough plate according to the invention; Fig. 2 shows the plough plate of Fig. 1 in position in a cutter box; Fig. 3 shows a plan view of a substantially U-shaped plough plate according to a second aspect of the invention, and Fig. 4 shows the plough plate of Fig. 1 in position in a cutter box.

According to this embodiment of the invention, there is provided a plough plate 2 with chisel-shaped ends 4, 6, a back bearing surface 8, an upper front bearing surface 10 and a lower front bearing surface 12. On the outside surface of the plough plate 2 there are provided seating blocks 14, 16.

The action of the plough plate stripping edges 4, 6 is best described with reference to Fig. 2, in which a pair of identical plough plates 2 are in position within a conventional cutter box 20. Within said cutter box 20, there are a pair of parallel shafts 22, 23 whose typical directions of rotation are marked by arrows 24.

It should be noted that although the shafts are usually geared to each other in a 1:1 ratio, and thus rotate with identical angular velocities in the directions shown, it is occasionally preferable to disrupt the uniform cutting and shredding obtained using such a ratio by gearing the shafts in a ratio between 1:1 and 1:2. This produces a hunting effect within the shredder and it is suggested that shredding efficiency may be improved in certain cases.

The parallel shaft 22 is provided with a cutting blade 26 with three cutting teeth 28a, b, c. On the parallel shaft 23 there is provided a similar cutting blade 30 which interengages said cutter blade 26 on the parallel shaft 26, also provided with three teeth 29a, b, c which are in this embodiment identical to the teeth on cutter blade 26. This is not necessary for efficient functioning of the shredding machine, and in some cases it may be desirable to adopt different configurations of the teeth, depending on the size of waste matter to be shredded and the coarseness of the shred. Any reasonable number of teeth may be used on the cutters-even only one tooth may be required-and the only constraints on the size of the teeth is that they do not contact the spacer discs on the other shaft, to which they are parallel, and that the root radius of the teeth is greater than that required to ensure overlap at all times between the cutters on the opposing shafts.

In Fig. 2, the rotation of the cutters defines a central nip 32 into which matter to be shredded is pulled by the teeth on each of the cutter blades. The cutter blades 26, 30 will typically disposed on the parallel shafts 22, 23 at different angular orientations , in order that the teeth do not meet at the said central nip 32. In such circumstances, shredding becomes ineffective. It is preferred that the teeth follow each other as they pass the central nip 32, as would be the case in Fig. 2. Where the shafts are geared in a 1:1 ratio, it can easily be deduced from Fig. 2 that tooth 28a on cutting blade 26 will lead tooth 29a on cutting blade 30 into the central nip area 32. This "phase lead" of teeth on opposing cutting blades can be infinitely varied, again depending on the waste matter to be shredded.

In operation, parallel shafts 22, 23 rotate in opposite directions and waste matter will be substantially shredded in the central nip area 32.

A spacer disc 33 is mounted on the parallel shaft 22, and a similar spacer disc is mounted on parallel shaft 23, but is shown dotted as cutter blade 30 obscures it. It should be noted that the may be no requirement for spacer discs in the instance where the cutter discs are integrally formed with spacer portions. Spacing sections of the shaft are thus automatically provided as the shaft is assembled.

In this embodiment, the spacer discs are of exactly the same thickness as the cutter blades ensuring complete interengagement of the blade edges. A certain amount of compression of waste matter may take place during the shredding operation, for example in the small space between tooth 29c and the spacer disc 33 on the opposing parallel shaft 22, which will create reactive forces in the direction of plough plate 2.

The seating blocks 14, 16 of the plough plate 2 are intended to both provide support for the weight of the plough plate 2 and for any reactive or separating compression forces set up during shredding.

The back bearing surface 8 allows for the said reactive or separating forces to be transferred through the plough plate 2 to the bearing surfaces 14, 16, where a reaction is provided by the cutter box 20 to the said forces. The cutter shafts 22, 23 are thus prevented from bowing outwardly by back bearing surface 8, and this greatly improves the efficiency of the cutting or shredding operation.

Upper and lower front bearing surfaces 10, 12 of the plough plate 2 transfer any vertical forces which may be applied to the parallel shaft 22 as a result of shredding resilient waste matter.

The upper and lower front bearing surfaces 10, 12, and the back bearing surface 8 are ideally machined with slight tolerances to introduce play between the plough plate 2 and the spacer disc 33, and in such a manner to ensure that a toleranced clearance of upper and lower front bearing surfaces 10, 12 from the spacer disc 33 is achieved, when the back bearing surface 8 is in full contact with said spacer disc 33. The upper and lower front bearing surfaces 10, 12, and the back bearing surface 8 will also be machined with a suitable surface finish to reduce friction between the spacer disc and the bearing surfaces.

Due the compression of waste matter during shredding mentioned above, and the incomplete shredding of some materials such as paper and plastics, matter has a tendency to become bound to the spacer discs. In this embodiment, such binding is not possible as matter prevented from building up on the spacer discs by the chiselled edges 4, 6 (see Fig. 1-not numbered in Fig. 2 for clarity) of the plough plate 2. Furthermore, in especially heavy shredding operations where significant compression forces may result and binding of waste matter becomes a greater problem, these compression forces merely enhance the action of the chiselled edges of the plough plates. The greater compression force produces a greater lateral displacement of the shaft towards the plough plate, which concomitantly results in greater contact of the chiselled edges and the spacer disc 33, and henceforth improved operation of the plough plate.

It will be appreciated that plough plate configurations other than those described above will be considered by a person skilled in the art, and modifications and variations may be made to the configuration described without exceeding the scope or departing from the spirit of the invention.

Referring now to Figure 3, a plough plate 40 is provided with a pair of seating faces 17, 18 set back from a back face 19. Said seating faces are adapted to abut a horizontal rails, one of which is shown at 17a, which are mounted on the inside of the cutter box 20 (shown in Figures 2 and 4) by means of screws or the like shown generally at 17b. In this embodiment, the plough plates are intended to be mounted within the cutter box of the machines simultaneously with the cutters and spacer discs, as these components and said parallel rails effectively locate the plough plates.

In Figure 4, the plough plate 40 is shown in position within the cutter box 20 of a shredding machine 41, and a pair of parallel rails 17a, 18a is shown sectioned to indicate that said rails run the entire length of the cutter shafts 22, 23. Said rails may be attached at numerous points by screws or the like along their length as previously stated.

The thickness of said rails may be such to allow a small amount of play between both the spacer disc 34 and the bearing surfaces 8, 10, 12 of the plough plate 40, and also the seating surfaces 17, 18 and the rails 17a, 18a. An effective spacer disc stripping mechanism is thus achieved which requires practically no maintenance.

It should be noted that parallel rails are affixed to both sides of the cutter box, and the above description relates only to a single plough plate in the interests of brevity.

Claims (8)

1. A shredding machine comprising a shredder box, a pair of shredder shafts arranged in parallel in the box, said shafts having alternating cutters and spacer discs thereon, and of which the cutters of one shaft overlap the cutters of the other shaft and register with the spacer discs of the said other shaft, and including plough plates between adjacent cutters of each shaft, each plough plate being of Ushape so that the arms embrace the spacer discs and form respective stripping edges for the discs when the shafts are rotating in the working and reverse directions.

2. A shredding machine according to claim 1 wherein the plough plates are "floatingly" mounted in that the plates are supported only by reaction against the shredder box on the one hand and by the spacer discs which they embrace on the other hand.

3. A shredding machine according to either claim 1 or 2 wherein the ends of the plough plate arms are formed as chisel shaped ends to enhance the stripping effect.

4. A shredding machine according to any preceding claim wherein the base of each plough plate, to the outside thereof, is provided with seating blocks by which the plate can seat on the shredder box.

5. A shredding machine according to claims 1-3 wherein the plough plates are provided with a back face and at least one seating face set back from the back face, said seating face abutting a rail mounted within and on the side of the shredder box in order to provide support for the plough plate.

6. A shredding machine according to claim 5 wherein the plough plate is provided with a pair of seating faces set back from its back face and at the end thereof.

7. A shredding machine according to claims 5 or 6 wherein the seating faces are machined to provide uniform seating surfaces.

8. A shredding machine according to any preceding claim wherein the plough plates are of machined, unhardened steel.