GB2061128A - Document shredding machines - Google Patents

Abstract

Document shredding machine of the type comprising a cutter assembly comprises two rows of cutting discs mounted for rotation in opposite directions about parallel axes, the discs (6) Fig. 2 of one row being arranged to enter gaps between adjacent discs (8) of the other row with little or no clearance. Stripper members (10, 12) are mounted on the shafts (2, 4) for limited movement between two positions, the stripper members adopting one of said positions when the shafts are driven in an operative direction, and adopt the other of said positions when the shafts are driven in a reverse direction. Thus, when the shafts are driven in said operative direction, the stripper members are operative to remove shredded material from between adjacent cutter discs during normal operation of the machine. However, by reversing the direction of rotation of the shafts (2, 4) the stripper members will move in a manner to effect dislodgement of any accumulation of shredded material built up on the machine. <IMAGE>

Description

SPECIFICATION Improvements relating to document shredding machines This invention relates to document shredding machines, particularly of the type (hereinafter referred to as being of the type specified) comprising a cutter assembly comprising two rows of cutting discs mounted for rotation in opposite directions about parallel axes, the discs of one row being arranged to enter gaps between adjacent discs of the other row with little or no clearance. Thus, the overlapping cutting discs operate collectively to cut documentary material (such as paper) fed into the nip of the cutter assembly into narrow strips.

Where the cutter assembly is provided by discs mounted onto parallel shafts, there is a tendency for the shredded material to be drawn around the shaft to re-enter the nip, thus interfering with smooth continuous running of the machine, and reducing the capacity of the machine. Thus, it is common practice to provide such a conventional shredding machine with stripper means, to effect separation of the shredded material from the cutter assembly. Such stripper means may be in the form of a plurality of fixed stripping plates mounted between each pair of adjacent cutting discs on each shaft, and presenting a operative surface which, on the nip side of the row, is located within the periphery of the cutting discs, but which extends beyond the periphery of the cutting discs as a location angularly removed from the nip side.Thus, the stripping plates may be clamped between the pair of adjacent cutting discs, being also secured to another part of the machine to retain the stripping plates stationary whilst the cutting discs rotate. A strip of shredded material severed between said pair of adjacent cutting discs, by co-operation thereof with a cutting disc of the opposite row, is carried angularly with the cutting discs in the space therebetween whilst being moved radially outwardly from between said cutting discs by said operative surface of the stripping plate, to a location where the operative surface extends beyond the periphery of said pair of cutting discs, and when the strip is no longer between the cutting discs it may fall from the machine.

Such stripping means is complicated in its construction and assembly, and/or may at times fail to function adequately, causing the machine to become jammed. The problems associated with stripping means of the kind set out above are aggravated when each cutter disc is provided with one ore more peripheral cut out or notch to effect transverse severance or tearing of the narrow strips into relatively short lengths. In particular, although the stripping plates may operate to remove most of the short lengths of severed material from adjacent cutter discs, some of the short lengths may be carried around the axis of the shafts, and accumulate at other parts of the machine, increasing frictionally resistance to rotation of the two shafts, to an extent where failure of the motor may occur.

According to this invention there is provided a document shredding machine of the kind specified, comprising stripper members mounted on each shaft between adjacent cutter discs and which are adapted to remove shredded material from the gaps between adjacent cutter discs, wherein the stripper members are mounted on the shafts for movement, limited by stop means, between first and second positions, adopting their first positions when the shafts are driven in a first, operative direction, and adopting their second positions when the shafts are driven in a reverse direction.

In this manner, the stripper members in their first positions will be operative to remove shredded material from between adjacent cutter discs during normal operation of the machine. However, should an accumulation of shredded material build up on the machine, the drive means may be reversed and the movement of the stripper members will be effective to dislodge such accumulation. In certain circumstances it may be necessary to operate the drive means in forward and then reverse directions several times to dislodge an accumulation.

Conveniently, the degree of movement of the stripper members angularly about their respective shafts is sufficient to permit the build-up of some momentum by the movable parts of the machine on switching of the drive motor to reverse, whereby the impact between the stripper members and the stop means which limits movement of the stripper members from their first to their second positions, is suf ficientto provide a substantial jarring of the machine, as is necessary to dislodge an accumulation of shredded material. Thus, preferably the degree of movement of the stripper members angu lea rely about their respective shafts between their first and second positions is between 5 and 300, conveniently about 10 .

Advantageously, the stripper members are constrained to move to their first positions during normal operation of the machine by frictional forces exerted thereon by adjacent cutter discs on rotation thereof. In this manner, the cutter discs may indi viduaily or severaliy be moved manually between their first and second positions, when the drive motor is switched off, to dislodge any particularly difficult accumulation, or to free a piece of shredded material which may be jammed in the machine.

There will now be given a detailed description, to be read with reference to the accompanying drawings, of a document shredding machine which is a preferred embodiment of this invention, and which has been selected to illustrate the invention by way of example.

In the accompanying drawings: FIGURE lisa plan view of part of the machine which is the preferred embodiment of this invention; FIGURE 2 is a schematic side elevation, showing an opposed pair of stripper members in their first, operative positions; FIGURE 3 is a view corresponding to Figure 1, showing the positions adopted by the stripper members when the drive motor of the machine has been reversed; and FIGURE 4 is a side elevation, showing the mounting of one stripper member on a drive shaft.

The document shredding machine which Zs the preferred embodiment ofthis invention is similar in certain aspects to the machine described in U.K.

Patent Application No. 4176, comprising a machine frame 1, a cutter assembly comprising two parallel shafts 2,4 supported by the machine frame for rotation about parallel longitudinal axes, and a plurality of cutting discs 6,8 mounted on the two shafts 2,4 respectively for rotation therewith, in a manner such that the cutting discs on each shaft enter gaps between pairs of adjacent discs on the other shaft, the frame also supporting a motor (not shown) to rotate the shafts 2,4 in opposite directions in a manner whereby a document of paper or the like fed into the nip N between the discs on the two shafts will be cut into strips by a shearing action between engaging side faces of adjacent, overlapping discs.

In the machine which is the preferred embodiment of this invention, the cutting discs 6, 8 are respectively mounted on the shafts 2,4 by virtue of the shafts being of hexagonal cross-section, of a size similar to hexagonal mounting apertures in the cutting discs. Thus, on rotation of the shafts, the cutting discs rotate with the shafts. As is described in the Specification of our above mentioned co-pending application, each of the cutting discs is provided with a plurality of notches 9, the notches of a group of adjacent cutting discs being arranged to enter the nip N in a particular sequence.

In the use of the machine, the shafts 2,4 are rotated in opposite directions as shown in Figure 2, and the material to be shredded is fed into the nip N.

This material is shredded into strips by co-operation of each pair of adjacent cutting discs with the cutting disc of the opposite shaft interposed therebetween.

Simultaneously, the strips are severed into short lengths by the trailing edges of the notches 9.

Mounted on shaft 2 between each pair of adjacent cutting discs 6 is a stripper member in the form of a plate 10, the plates 10 being trapped somewhat loosely between the cutting discs and serving as spacer members therefor. The plates 10 are mounted on circular washers 11, and are conse quently free to move axially about the hexagonal shaft, notwithstanding the hexagonal cross-section thereof. Similarly, stripper discs 12 are mounted on the shaft 4 between successive cutting discs 8, by the use of circular washers 13.

During normal operation of the machine, on rotation of the shafts 2,4 in the directions shown in Figure 2, the plates 10,12 are urged into abutment with respective stops 16, 18. In these positions, the operative faces 16 of the stripper members adjacent to the nip N are effective to cause shredded material to fall from the gap between adjacent cutter discs through the gap 20 between said edges, into a waste bin placed therebeneath.

Notwithstanding the provision of the stripper members, some material, in particular the finer particles of shredded document, will be carried around with the cutter discs, and will tend to accumulate as deposits for example at the positions indicated X and Y. Such accumulations exert a frictional retarding force on the rotation of the cutter discs, and increase the loading on the drive motor. In view of the fine and "sticky" nature of this material, it is difficultto remove by hand.

However, by the use of this invention, the drive motor may be switched off and momentarily driven in reverse. The cutter discs and stripper members rotate through small angular distances in opposite directions until the stripper members engage further stop means 22, 24. Further rotation of the stripper members is prevented, and they cease movement with a violent jar, tending to dislodge the accumulations which are built up at X and Y. In the event that not all the accumulation is knocked from the machine, the drive motor may be operated momentarily in its forward direction, the stripper members moving back to their first positions, at which they stop again with a violent jar, and the drive motor may then be reversed again, returning the stripper members once more to their second positions.Such repeated movement will clear all but the most resis tant accumulated material.

In the event that shredded documentary material becomes solidly jammed within the machine, with the drive motor switched off the necessary stripper members may be moved manually between their first and second positions to facilitate manual cleaning of the machine. A group of stripper members is shown in Figure 1, having been moved from the positions adopted by the majority of the stripper members.

It will be appreciated that when the drive motor is operated in reverse, although the stripper members move only small angular distances (about 10 ) to their second positions, the cutter discs will continue to rotate. In order to prevent or minimise the drawing back of previously shredded material through the machine, the stripper discs are constructed and arranged (as shown in Figure 3) so as to close the gap 20 when in their second positions, the stripper members on the two shafts interleveing with one another.

As is shown in Figure 4, the mounting aperture 14 of the cutter discs is open, providing actute-angled edges 15 which tend to scrape shredded material from the washer, to minimise tendency for material to build up between the stripper member and the washer itself.

Claims (6)

1. A document shredding machine of the kind specified, comprising stripper members mounted on each shaft between adjacent cutter discs and which are adapted to remove shredded material from the gaps between adjacent cutter discs wherein the stripper members are mounted on the shafts for movement, limited by stop means, between first and second positions, the stripper members adopting their first positions when the shafts are driven in a first, operative direction, and adopting their second positions when the shafts are driven in a reverse direction.

2. A machine according to Claim 1 wherein the degree of movement of the stripper members angu larly about their respective shafts is sufficient to permit the build-up of some momentum by the movable parts ofthe machine on switching the drive motor to reverse, whereby the impact between the stripper members and the stop means which limits the movement of the stripper members from their first to their second positions is sufficient to provide a substantial jarring ofthe machine.

3. A machine according to Claim 2 wherein the degree of movement of the stripper members angularly about their respective shafts is between Sand 30 , preferably about 10 .

4. A machine according to any one of the preceding claims wherein the stripper members are constrained to move to their first positions by frictional forces exerted thereon by adjacent cutter discs on rotation thereof.

5. A machine according to any on of the preceding claims wherein the cutter discs may, individually or severally, be moved manually between their first and second positions.

6. A document shredding machine constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.