GB2243798A

GB2243798A - Rotary cutting die

Info

Publication number: GB2243798A
Application number: GB9010422A
Authority: GB
Inventors: Roy Gates
Original assignee: AMCOR PACKAGING
Current assignee: AMCOR PACKAGING
Priority date: 1990-05-09
Filing date: 1990-05-09
Publication date: 1991-11-13
Anticipated expiration: 2010-05-09
Also published as: GB9010422D0; GB2243798B

Abstract

A rotary cutting die (10 Fig 1) for cutting carton blanks from corrugated cardboard has pointed retainers (14, 15) mounted in fixed positions adjacent to knives eg knife 13. Each retainer is surrounded by a stripper (17) and there is a substantial gap between the retainer and the stripper. Rods (20, 21 Fig 4) supporting the stripper are moved radially outwards against spring bias by engagement with a cylindrical abutment eccentrically mounted within the cylinder (11 Fig 1) carrying the die. <IMAGE>

Description

Title: Rotary cutting die Description of Invention The present invention relates to a rotary cutting die suitable for cutting moderately stiff material, for example cardboard. Rotary cutting dies are used in the manufacture of blanks for assembly into cartons and other containers formed of cardboard. Typically, the cutting die is required to cut waste material away from the edge of the blank, to cut one or more slits in the material and to cut one or more apertures in the material. The waste cut from the edges of a blank and cut from an aperture of the blank must be separated from the blank.

This waste material must also be separated from the rotary die. Accumulation of waste material on the die would impair the performance of the die. If the cutting die is to be used to remove the waste from the blank, the requirement to ensure that the waste separates from the cutting die conflicts with the requirement to ensure that the waste is removed from the blank.

According to the present invention, there is provided a rotary cutting die having a knife, a retainer mounted in the die in a fixed position with respect to the knife and a stripper mounted in the die adjacent to the knife for movement relative to the knife towards and away from an axis of rotation of the die, wherein the retainer is a pin arranged to penetrate sheet material at substantially the time when the material is cut by the knife.

There may be a plurality of retainers adjacent to a single knife. We have found that retainers in the form of pins contribute to attainment of the conflicting requirements hereinbefore mentioned better than do other forms of retainer.

The or each retainer pin is preferably undercut at a position which lies adjacent to a radially outer surface of the stripper when the stripper rests on a radially outer surface of the die. With this arrangement, the sheet material to be removed from the blank can embrace the undercut portion of the retainer during penetration of the sheet material by the retainer.

The retainer preferably protrudes through an opening formed in the stripper. The opening may be circular, in which case the stripper surrounds the retainer completely. Alternatively, for example in a case where the retainer is near to a knife and therefore near to a margin of the stripper, the opening may extend to the margin of the stripper and may be in the form of a slot which is closed at one end and open at its opposite end.

We have discovered that the provision of a moderate clearance between the retainer and the boundary of the opening through which the retainer protrudes contributes to attainment of the conflicting requirements hereinbefore mentioned. The gap between the retainer and the boundary of the opening may be from 0.25 to 1.5 mm.

An example of a cutting die embodying the invention will now be described, with reference to the accompanying drawings, wherein: FIGT;TRE 1 shows a perspective view of a part of the cutting die, FIGE RE 2 shows a perspective view of a knife, a stripper and a pair of retainers incorporated in the die of Figure 1, FIGURE 3 shows a partial cross section of the die on the line III-III of Figure 2 and wherein FIGURES 4 and 5 illustrate different strippers incorporated in the die of Figure 1.

The rotary cutting die 10 illustrated in Figure 1 is part-cylindrical and is mounted on the outside of a known, hollow, steel cylinder 11. There is an array of radial bores in the wall of the cylinder 11 and the die 10 is secured to the cylinder by means of bolts (not shown) extending through selected ones of these bores. Typically the die 10 is semi-cylindrical. Two such dies may be mounted on the cylinder 11 so that the dies together extend substantially completely around the circumference of the cylinder. Alternatively, a single die may be used on its own. The die 10 is typically formed of plywood or another material which can be machined readily and which has adequate stiffness and strength to support cutting knives and retainers as hereinafter described.

A plurality of knives are mounted in respective slots cut in the surface of the die 10. The knives are mounted in respective fixed positions relative to the die and each knife extends radially of the cylinder 11. By way of example, there is shown in Figure 1 a knife 12 which is intended to cut sheet material at the periphery of a blank to be formed from the sheet material and a further knife 13 which is to be used to cut an aperture in the blank.

There are also mounted in the die 10, in respective positions which are fixed with respect to the die, a number of retainers. By way of example, three retainers 14, 15 and 16 are shown in the drawings. The retainers are all identical one with another and each has the form of a pin with a pointed tip. An end portion of the pin remote from the tip is disposed in a corresponding blind bore formed in the die 10. The retainer pins are rectilinear and each is arranged with its length extending radially of the cylinder 11. Retainers are mounted in the die at various positions. These are the positions where it is considered that the action of a retainer is necessary, in order to ensure that the waste sheet material is separated from the cut blank.In the case of a knife, such as the knife 13, which encloses an area to form an aperture in the blank, these positions are generally adjacent to that part of the knife which pierces the sheet material first. Once a leading margin of the portion of sheet material cut out is drawn away from the adjacent parts of the sheet material by retainers, the remainder of that piece of sheet material will follow.

The retainers all have the same size and shape and are positioned with their pointed tips at the same distance from the axis of the cylinder 11 as the cutting edges of the knives are spaced from that axis. Each retainer has a conical end portion terminating in the pointed tip. At the end of the conical end portion remote from the tip, the retainer is undercut around the entire circumference of the retainer. The remainder of the retainer is cylindrical. The undercut is spaced from the pointed tip by a distance which is approximately equal to the thickness of the sheet material to be cut.

The die 10 also has a number of strippers mounted for reciprocation relative to the die along respective paths which extend radially of the cylinder 11.

Each of the retainers mounted in the die is surrounded, either partly or entirely, by one of the strippers. By way of example, there is shown a first stripper 17 which surrounds the retainers 14 and 15, a stripper 18 adjacent to a leading limb of the knife 12 and a stripper 19 adjacent to a further limb of the knife 12.

The stripper 17 is of flat, plate-like form and has a profile, as viewed in a direction towards the axis of the cylinder 11, which corresponds to the shape of the area cut out by the knife 13. The dimensions of the stripper 17 are such that the stripper is received with clearance inside the knife 13. The stripper is guided for movement relative to the die 10 by a pair of rods 20 and 21 which slide in respective bores formed in the die 10 and in the cylinder 11. These rods restrain movement of the stripper along and circumferentially of the cylinder 11.

The stripper 17 is movable between a rest position, shown in Figure 3, in which it rests on the outwardly facing surface of the die 10 and an extended position in which there is a gap between the stripper and the die 10. In the rest position, the outwardly facing surface of the stripper 17 lies nearer to the axis of the cylinder 11 than does the cutting edge of the knife 13 and is also slightly nearer to that axis than are the undercut portions of the retainers 14 and 15, so that the undercut portions are exposed above the stripper. In the extended position, the radially outermost face of the stripper 17 is spaced from the axis of the cylinder 11 slightly further than is the cutting edge of the knife 13 so that the retainers 14 and 15 are then submerged beneath the outer face of the stripper.A known mechanism is provided for moving the stripper 17 between its rest and extended positions. This mechanism includes a cylindrical abutment mounted inside the cylinder 11 and eccentrically relative thereto. As the cylinder 11 and die 10 are turned during use of the die, the rods 20 and 21 are brought into engagement with the abutment and continued turning drives the rods away from the axis of the cylinder 11, against the action of return springs (not shown).

Each of the retainers 14 and 15 occupies a respective aperture in the stripper 17. This aperture is circular and there is a uniform gap between the circumference of the retainer and the boundary of the circular aperture. This gap is from 0.25 to 1.5 mm, measured radially of the retainer. Furthermore, this dimension of the gap is within the range 1/12 to Y2 of the diameter of the retainer. We have found that this amount of clearance between the retainer and the stripper ensures reliable stripping of the waste sheet material from the retainer and also avoids the entrapment of fragments of the sheet material between the stripper and the retainer. If the stripper fits more closely about the retainer, there is a risk of fragments of sheet material becoming trapped between the stripper and the retainer.

A further example of a stripper mounted in the die 10 is shown in Figure 4. This stripper, 22 also is of flat, plate-like form and is guided by a pair of rods corresponding to the rods 20 and 21. The stripper 22 partly surrounds a single retainer (not shown) which is identical with the retainer 14. This retainer occupies an opening in the stripper 22 which is a slot 23 extending into the stripper from the periphery thereof. Thus, the slot has a closed end and an open end. The retainer is disposed adjacent to the closed end of the slot and is spaced from the closed end by substantially the same distance as the retainer is spaced from opposite sides of the slot. This distance is within the range 1/12 to l/2 of the diameter of the retainer and is within the range 0.25 to 1.5 mm.The closed end of the slot may be arcuate or may be perpendicular to the opposite sides of the slot. The sides of the slot are preferably rectilinear.

In some cases, it is necessary to provide a stripper at a position where it does not overlie a bore in the cylinder 11. The stripper is then mounted on a lever in the manner illustrated in Figure 5, where the lever is represented at 24.

The lever is mounted on the die 10 by means of a bearing block 25 which is attached to the die by bolts extending through bores in the cylinder 11. The lever is connected with the bearing block for pivoting relative thereto about an axis which is parallel to the axis of the cylinder 11. There may also be attached to the die 10 a leaf spring 26 which urges the lever towards the axis of the cylinder 11. The lever has one or more fingers 27 remote from the bearing block and the or each finger engages the stripper 28 inside a corresponding aperture formed in the stripper. As shown in Figure 5, in a case where the stripper lies at one side of a knife and the lever lies at an opposite side of the knife, the knife is formed with clearance slots through which the fingers 27 pass.

As also shown in Figure 5, the stripper 28 may be formed with a circular aperture in which there is disposed a retainer identical with the retainer 14.

The strippers are conveniently formed of a plastics material. A nylon is a suitable material. Nylons can be worked relatively easily and have low coefficients of friction with respect to metal surfaces. This avoids the generation of excessive heat at interfaces, for example where the fingers 27 engage the stripper 28. The lever 24 is preferably formed of metal. The retainer pins also are preferably formed of metal.

The die 10 is supported for use in a position adjacent to an anvil roll which has a resilient surface which will yield upon being engaged by the knives of the die 10 so that these knives will not be damaged by contact with the anvil.

The anvil and the cylinder 11 are turned about mutually parallel axes and the sheet material which is to be cut is passed to the nip between the die and the anvil. Each knife penetrates the sheet material to cut same. Retainers adjacent to the knife penetrate the sheet material at substantially the same instant.

Strippers surrounding the retainers are, at this stage, in their rest positions. As that particular knife moves on from the nip, it is withdrawn from the blank cut from the sheet material. Waste sheet material is held adjacent to the knife by the retainers. After the knife and adjacent retainers have moved through a substantial angle about the axis of the cylinder 11, the associated stripper or strippers is moved from its rest position to its projected position, thereby stripping the waste from the retainers. The waste is permitted to fall from the die. The die is suitable for cutting blanks from cardboard, for example cardboard comprising a pair of flat layers with a corrugated layer sandwiched between them.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS:

1. A rotary cutting die having a knife, a retainer mounted in the die in a fixed position with respect to the knife and a stripper mounted in the die adjacent to the knife for movement relative to the knife towards and away from an axis of rotation of the die, wherein the retainer is a pin arranged to penetrate sheet material at substantially the time when the material is cut by the knife.

2. A die according to Claim 1 wherein the pin is undercut at a position which lies adjacent to a radially outer surface of the stripper when the stripper rests on a radially outer surface of the die.

3. A die according to Claim 1 or Claim 2 wherein the pin has a pointed tip.

4. A die according to any preceding claim wherein the stripper is formed of a plastics material.

5. A die according to any preceding claim wherein the retainer protrudes through an opening formed in the stripper.

6. A die according to Claim 5 wherein the opening is circular.

7. A die according to Claim 5 wherein the opening is an elongated slot.

8. A die according to Claim 7 wherein the retainer is adjacent to the knife and the slot extends to a margin of the stripper adjacent to the knife.

9. A die according to Claim 5 wherein the stripper completely surrounds the retainer.

10. A die according to any one of Claims 5 to 9 wherein there is between the retainer and the boundary of the opening a gap of 0.25 to 1.5mm.

11. A die according to any one of Claims 5 to 9 wherein there is between the retainer and the boundary of the opening a gap having a width within the range 1/12 to Y2 of the diameter of the retainer.

12. A rotary cutting die having a retainer and a stripper arranged substantially as hereindescribed with reference to and as shown in Figures 2 and 3 of the accompanying drawings.

13. Any novel feature or novel combination of features disclosed herein or in the accompanying drawings.