GB2398532A

GB2398532A - Paper perforating device

Info

Publication number: GB2398532A
Application number: GB0303774A
Authority: GB
Inventors: Graham Harris
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-02-19
Filing date: 2003-02-19
Publication date: 2004-08-25
Also published as: GB0303774D0

Abstract

A device for perforating paper comprises a circular, toothed perforating blade 26 mounted for rotation about the axis 6 of a first shaft 2; and a backing drum 46 mounted for rotation about the axis 8 of a second shaft 4. A sheet of paper passed between the blade 26 and the backing drum 46 will be perforated by the teeth 32 of the blade 26. The blade 26 is resiliently mounted on the first shaft 2 to allow some movement of the blade 26 in a direction transverse to the axis 6 of the first shaft 2. Additionally or alternatively, the outer surface 48 of the backing drum 46 may be formed from a yielding material that is soft enough to be indented when the teeth 32 of the perforating blade 26 are pressed against it. In both cases, the purpose is to accommodate some non-circularity or non-concentricity of the blade 26 or drum 46 in order that the device can be mounted on a conventional folding machine.

Description

TITLE

Paper perforating device

DESCRIPTION

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Technical Field

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This invention relates to a device for creating a line of perforations in paper, in order to make the paper easy to tear or fold along the line of perforations.

Background

There are many instances where it is desirable to form one or more perforated lines of weakening along sheets of paper, for example tear lines for detaching a cheque from a cheque book or for trimming the edges of traction-fed or over-sized printer paper. The finer the perforations can be (i.e. the more perforations per inch), the less ragged the edge of the paper will be after it is torn.

It is known to form a line of perforations in sheets of paper by feeding the paper between a rotating, toothed, circular blade and a counterrotating backing drum. The backing drum is formed from a hard material in order to reduce the wear caused by the pressure of the blade teeth.

Such perforating devices require very precise setting up and regular maintenance because they are very sensitive to the spacing between the teeth of the blade and the hard backing drum. If the spacing is too small then the perforations will be too large and the paper will be excessively weakened along line of perforations. If the spacing is too large then the perforations will be too H097003 - 2 small and the paper will not be sufficiently weakened along line of perforations. More frequently, because of inaccurate setting up or because of wear, the blade or the drum may deviate from a perfect circle or may not be perfectly concentric about the axis of its respective shaft. Then the spacing between blade and drum will vary around the circumference of the blade and the line of perforations will be of uneven size.

As material to be perforated often needs to be printed or folded too, it would be most efficient if such a perforating device could form part of a conventional printing or folding machine. However, the aforementioned problems mean that a practical device for such applications has not been developed. In practice, most perforating of paper is done on flat bed machines. A very small percentage of printers will have in-house machines to tackle the perforating operation. Most medium sized printers, for example, will regularly send out such work to be processed at a specialized print finisher, which can often cause a delay in its delivery to the customer and an increase in costs.

Summary of the invention

In a first aspect, the invention provides a device for perforating paper, comprising a circular perforating blade mounted on a first shaft for rotation about the axis of the first shaft, the blade having teeth around its circumference; and a backing drum mounted on a second shaft for rotation about the axis of the second shaft, such that a sheet of paper passed between the blade and the backing drum will be pressed by the blade against an H097003 - 3 outer surface of the backing drum and be perforated by the teeth of the blade; wherein the blade is resiliently mounted on the first shaft to allow some movement of the blade in a direction transverse to the axis of the first shaft.

The resilient mounting of the blade allows it to move to a limited extent in a transverse direction, while always being urged back to a generally concentric position.

Thus a degree of non-circularity or non-concentricity of the blade or backing drum can be accommodated. If the resiliency of the blade mounting is well chosen, then a sufficiently uniform pressure can be exerted on the backing drum by the blade over the whole circumference of the blade, resulting in a uniform line of perforations.

Use of this invention increases performance sufficiently compared with the prior art for a perforating device in accordance with the invention to be practical and reliable when mounted on a conventional folding machine.

In a preferred embodiment, the perforating blade is annular in shape and a mounting ring of a resilient material is disposed between the first shaft and an inner diameter of the perforating blade. A tight fit to the inner diameter of the blade is required and therefore a rectangular cross section of the mounting ring is preferred. However, an O-ring may also be used.

Suitable materials for the mounting ring include hardened nitrite rubber and various resilient plastics.

The perforating blade may be located axially between a pair of bosses clamped on the first shaft, with H097003 - 4 - sufficient clearance between the blade and the bosses to permit the transverse movement of the blade. Preferably, the bosses have cylindrical outer surfaces of equal radius and the teeth of the perforating blade protrude radially beyond the cylindrical outer surfaces by no more than l mm. This small protrusion of the blade teeth means that the cylindrical outer surfaces of the bosses can engage the paper and assist its passage through the device. The cylindrical outer surfaces of the bosses can include traction means for frictionally engaging a sheet of paper, for example roughened metal surfaces or rubber or plastic strips adhered to or set into the surfaces.

In a preferred embodiment of the invention, the teeth are spaced evenly around the circumference of the perforating blade at more than 15 teeth per centimetre (38 teeth per inch). The teeth are preferably double bevelled.

In a second aspect, the invention provides a device for perforating paper, comprising: a circular perforating blade mounted on a first shaft for rotation about the axis of the first shaft, the blade having teeth around its circumference; and a backing drum mounted on a second shaft for rotation about the axis of the second shaft, such that a sheet of paper passed between the blade and the backing drum will be pressed by the blade against an outer surface of the backing drum and be perforated by the teeth of the blade; wherein the outer surface of the backing drum is formed from a yielding material that is soft enough to be indented when the teeth of the perforating blade are pressed against it.

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Because the backing drum presents a yielding surface to the teeth of the cutting blade, the paper can move slightly away from the teeth when the pressure from the teeth is increased. Thus the device according to the s invention is better than known devices at accommodating variation in the spacing between the teeth and the surface of the backing drum. Thus, as with the first aspect of the invention, this device provides improved performance in cases of non-circularity or non lo concentricity of the blade or drum.

The yielding material of the backing drum is preferably a plastics material, such as nylon, or a relatively soft metal such as copper, brass or certain steels. The IS material must be softer than the teeth of the blade so that the backing drum wears in preference to the blade.

The backing drum may be made entirely of the yielding material and be fixed directly to the second shaft.

However, fixing a yielding material at only certain points may cause its outer surface to deform from a perfect cylinder. Therefore it is preferred that the backing drum comprises a pair of bosses fixed to the second shaft and a cylindrical sleeve of the yielding 2s material supported between the pair of bosses. The sleeve can be supported by the bosses in a symmetrical manner that does not cause it to deform.

Because the backing drum is formed from a yielding material, it will be subject to wear during the perforating operation and will ultimately be a disposable component. However, it is preferred that the device H097003 - 6 - further comprises means for adjusting the axial position of the backing drum along the second shaft. Thereby, when the backing drum begins to be worn, it can be indexed a small distance along the shaft to expose a new part of the surface of the drum to the teeth of the blade. This substantially prolongs the useful life of the backing drum.

In the same manner as the blade, the backing drum may be resiliently mounted on the second shaft to allow some movement of the drum in a direction transverse to the axis of the second shaft.

Evidently, the two aspects of the invention may beneficially be used together as a resiliently mounted blade and a yielding backing drum both serve to accommodate non-circularity and non-concentricity of the blade or drum.

The drawings Figure l is an axial cross-section, not to scale, through a perforating device in accordance with the invention.

Figure 2 is an enlargement of part of Figure 1.

Figure 3 is a cross-section on line A-A of Figure 2.

Figure l shows a first shaft 2 and a second shaft 4 that form part of a folding machine (not shown). The first shaft 2 rotates about a first axis 6 and the second shaft 4 rotates about a second axis 8, which is parallel to the first axis 6. The first and second shafts 2,4 rotate in opposite directions so as to draw a sheet of paper between them.

H097003 A first blade boss 10 is secured in position on the first shaft 2 by a grub screw 12. Extending circumferentially around the central region of the first blade boss 10 is a cylindrical mounting surface 14. To one side of the mounting surface 14, the first blade boss 10 comprises a cylindrical outer surface 16, which has a greater radius than the mounting surface 14. To the other side of the mounting surface 14, the first blade boss 10 comprises an external screw thread 18, which has a similar radius to the mounting surface 14.

A second blade boss 20 is in the shape of an annular cylinder. The second blade boss 20 comprises an internal screw thread 22 for screwing onto the external screw thread 18 of the first blade boss 10; and a cylindrical outer surface 24, which has the same radius as the outer surface 16 of the first blade boss 10.

An annular perforating blade 26 is mounted between the first and second blade bosses- 10,20 in the following manner, as shown more clearly in Figure 2. A resilient mounting ring 28 of hardened nitrite rubber, rectangular in cross-section, fits tightly on the mounting surface 14 of the first blade boss 10. The annular perforating blade 26 has a central hole sized to fit tightly on the mounting ring 28. Thus the mounting ring 28 is compressed between the mounting surface 14 of the first blade boss 10 and the perforating blade 26. The perforating blade is thereby held concentrically about the axis 6 of the first shaft 2 but can be displaced H097003 8 - transversely to a small extent by deforming the resilient mounting ring 28.

In order to permit this transverse movement of the blade s 26, the first and second blade bosses 10,20 must not be clamped tightly against the blade 26. Minimal gaps 30 are left at each side of the blade 26 to permit its transverse movement, while limiting its axial movement.

The size of the gaps is exaggerated for clarity in Figure 2. One way of ensuring such gaps would be to increase the radius of the mounting surface 14 from that shown in the drawings so that the shoulder that defines it interferes with the second blade boss 20 and prevents the boss from advancing too close to the blade 26.

The outer rim of the blade 26 is double bevelled to form a narrow edge on the centre plane of the blade 26. As seen in Figure 3, narrow slots are cut into the edge of the blade 26 to form blade teeth 32 around the whole circumference of the blade 26. Typically, there may be 52 to 72 teeth per inch (20 to 28 teeth per centimetre).

The blade teeth 32 project only a small distance, for example 0.5 mm, beyond the outer surfaces 16,24 of the blade bosses 10,20. This means that the outer surfaces 16,24 can be in contact with the paper as it is drawn through the device and assist in its traction. In order to enhance the traction of paper through the device, thin rubber strips 34 are set into the outer surfaces 16,24 of the blade bosses 10,20 adjacent to the blade 26.

H097003 - 9 - Two backing bosses 40 are secured in position on the second shaft 4 by respective grub screws 42. Each of the backing bosses 40 has an external screw thread 44.

Supported between the two bosses 40 is a backing drum 46, - having at each end an internal screw thread that complements the external screw thread of the two bosses 40. Thus the bosses 40 are secured directly to the second shaft 4 but the backing drum 46 is not secured directly to the second shaft 4. Instead, it is secured to the bosses 40 via the complementary screw threads 44, which provide an even force around the circumference of the drum 46. The backing drum 46 is made from nylon, which would tend to deform from its desired cylindrical shape if not evenly supported.

As illustrated in Figure l, the components of the perforating device are sized such that the teeth 32 of the perforating blade 26 press against the outer surface 48 of the backing drum 46. The blade bosses lO,20 and the backing drum 46 have equal diameters so that when the two shafts 2,4 counter-rotate, the outer surfaces of the bosses lO,20 and the drum 46 move in parallel at the same speed and can draw a sheet of paper (not shown) between them. The paper is pierced by the teeth 32 to form a 2s line of perforations.

Because the nylon of the backing drum 46 is a somewhat yielding material, the teeth 32 can press into it, ensuring that they pass fully through the paper. If either the backing drum 46 or the blade 26 is not properly concentric with the axis 6,8 of its shaft, the distance between the teeth 32 and the backing drum 46 H097003 will vary over the course of a revolution but the yielding material of the backing drum 46 can accommodate that and still achieve good perforation results.

Because the yielding material of the backing drum 46 is constantly impressed by the hard teeth 32 of the blade 26, it will eventually become worn. It is then possible to adjust the axial position of the backing drum 46 by a small distance, by loosening the grub screws 42 and sliding the drum 46 on the shaft 4. Thereby a new part of the drum surface 48 comes into contact with the teeth 32 and the life of the drum 46 is extended.

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Claims

l. A device for perforating paper, comprising: a circular perforating blade mounted on a first shaft for rotation about the axis of the first shaft, the blade having teeth around its circumference) and a backing drum mounted on a second shaft for rotation about the axis of the second shaft; such that a sheet of paper passed between the blade and the backing drum will be pressed by the blade against an outer surface of the backing drum and be perforated by the teeth of the blade; wherein the blade is resiliently mounted on the first shaft to allow some movement of the blade in a direction transverse to the axis of the first shaft.
2. A device according to claim l, wherein: the perforating blade is annular in shape; and a mounting ring of a resilient material is disposed between the first shaft and an inner diameter of the perforating blade.
3. A device according to claim l or claim 2, wherein the perforating blade is located axially between a pair of bosses clamped on the first shaft, with sufficient clearance between the blade and the bosses to permit the transverse movement of the blade.
4. A device according to claim 3, wherein the bosses have cylindrical outer surfaces of equal radius and wherein the teeth of the perforating blade protrude radially beyond the cylindrical outer surfaces by no more than l mm.

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5. A device according to claim 4, wherein the cylindrical outer surfaces of the bosses include traction means for frictionally engaging a sheet of paper. s
6. A device according to any preceding claim, wherein the teeth of the perforating blade are double bevelled.
7. A device according to any preceding claim, wherein the teeth are spaced evenly around the circumference of the perforating blade at more than 15 teeth per centimetre (38 teeth per inch).
8. A device for perforating paper, comprising: IS a circular perforating blade mounted on a first shaft for rotation about the axis of the first shaft, the blade having teeth around its circumference) and a backing drum mounted on a second shaft for rotation about the axis of the second shaft; such that a sheet of paper passed between the blade and the backing drum will be pressed by the blade against an outer surface of the backing drum and be perforated by the teeth of the blade; wherein the outer surface of the backing drum is 2s formed from a yielding material that is soft enough to be indented when the teeth of the perforating blade are pressed against it.
9. A device according to claim 8, wherein the yielding material of the backing drum is a plastics material.

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10. A device according to claim 8, wherein the yielding material of the backing drum is a soft metal.
11. A device according to any of claims 8 to 10, wherein the backing drum comprises a pair of bosses fixed to the second shaft and a cylindrical sleeve of the yielding material supported between the pair of bosses.
12. A device according to any of claims 8 to 11, further comprising means for adjusting the axial position of the backing drum along the second shaft.
13. A device according to any of claims 8 to 12, wherein the backing drum is resiliently mounted on the second ]5 shaft to allow some movement of the drum in a direction transverse to the axis of the second shaft.
14. A device for perforating paper according to any of claims 1 to 7, comprising a backing drum according to any of claims 8 to 13.
15. A device for perforating paper, substantially as described herein with reference to the drawings.

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