GB2403447A

GB2403447A - Perforation of webs

Info

Publication number: GB2403447A
Application number: GB0315354A
Authority: GB
Inventors: Alistair Mark Taylor
Original assignee: Graham Labelling Systems Ltd
Current assignee: Graham Labelling Systems Ltd
Priority date: 2003-07-01
Filing date: 2003-07-01
Publication date: 2005-01-05
Anticipated expiration: 2023-07-01
Also published as: GB0315354D0; GB2403447B

Abstract

A perforator for a web of sheet material has a support 10 carrying a movable component 12 with a front face 16, for reciprocating movement between rest and perforating positions. A spring arrangement 20 urges the movable component 12 to its rest position and a diaphragm 24 bears on the rear face of that component 12, a pressure chamber being defined between the diaphragm 24 and a pressure plate 22. An air valve 29 selectively admits air under pressure to the pressure chamber and exhausts gas from that chamber. A perforator blade 36,40 is carried by the support 10 to interact with the front face 16 of the movable component 12, so that when air is supplied under pressure to the pressure chamber, the movable component 12 is driven into engagement with the perforator blade 36,40 and so perforates a web passing between the movable component and support.

Description

PERFORATION OF WEBS

This invention relates to apparatus for perforating a web of sheet material as that material advances along a path. The invention further relates to a method of perforating a web, with such apparatus.

It is frequently necessary to provide perforations within a web of sheet material, being advanced for use in some other process. For example, in the food industries, heat-shrink plastics material lay-flat tubing is used for sleeving food and drink containers and also to give a tamper- evident seal to the closure for the container. The material must be perforated in order to make it relatively 0 easy for a consumer to open the container by removing the shrunk tubing following its application to the container.

The tubing discussed above is applied to containers by a sleeving machine, after which the tubing is heated so as to shrink on to the container. In order to obtain the required high speed processing of food containers, high speed perforation of the tubing must be performed but this gives rise to difficulties, having regard to the nature of the heat-shrink plastics material. The conventional practice is to provide a perforator blade which is mounted for reciprocating movement towards and away from an anvil, the blade being driven for example by one or more pneumatic cylinders operated by an electro magnetic solenoid supplied with current at appropriate moments, having regard to the advancement of the sleeving material towards a container to be sleeved.

In this known form of perforating apparatus, the or each pneumatic ram requires a relatively high pressure for its operation. Consequently, there is a relatively large volume of air which must flow into the or each ram and then flow out again, on each cycle of operation, and this takes a significant time. In view - 2 of this difficulty, there is a relatively low maximum speed at which such a known form of perforating apparatus may operate.

As the maximum perforating speed is often lower than that required for the throughput rate for containers in a food processing plant, it usually becomes necessary for an operator to install parallel lanes for the containers, with the attendant extra complications and costs, as compared to a single lane. The present invention stems from research and development work into ways of increasing the rate at which a perforator can operate, especially when working with materials such as a web of layflat heat-shrink plastics material tubing.

0 According to one aspect of the present invention, there is provided apparatus for perforating a web of sheet material advancing along a path, comprising: - a movable component having front and rear faces and carried on a support for reciprocating movement between rest and perforating positions; - return means arranged to urge the movable component to its rest position; - a resiliently-deformable diaphragm bearing on the rear face of the movable component; - pressure chamber defined between the diaphragm and a pressure plate carried by the support; - gas control means selectively to admit gas under pressure to the pressure chamber and to exhaust gas from that chamber; - at least one perforator blade carried by one of the support and the front face of the movable component and co-operable with a surface of the other of the support and the movable component which said surface sewes as - 3 an anvil for the perforator blade; whereby in use said path extends between said surface and the perforator blade, and the admission of gas under pressure to the pressure chamber thrusts the movable component forwardly to interengage the perforator blade and said surface serving as the anvil, thereby to perforate sheet material extending therebetween.

According to a further aspect of this invention there is provided a method of perforating a web of sheet material advancing along a path which extends between the front face of an anvil and a perforator blade, one of the perforator blade and the anvil being a movable component carried on a support for reciprocating movement between rest and perforating positions with return means arranged to urge the movable component to its rest position, there being a resiliently-deformable diaphragm bearing on the rear face of the movable component and a pressure chamber defined between the diaphragm and a pressure plate carried by the support, in which method the web is advanced by a predetermined distance along said path, a signal is supplied to an electrically- controlled gas valve to cause the operation thereof to admit gas under pressure to the pressure chamber thereby driving the movable component forwardly until contact is established between the anvil and the perforator blade, so perforating the sheet material between the blade and the anvil, and the signal is removed from the valve to permit gas to be exhausted from the pressure chamber whereby the movable component is returned to its rest position under the action of the return means, so separating the perforator blade and the anvil.

It will be appreciated that the apparatus and method of this invention operate somewhat differently from the conventional apparatus described - 4 above. With this invention, instead of using one or more separate high pressure pneumatic rams, the movable component of the perforating apparatus is provided with a pneumatic drive arrangement which is arranged to operate on essentially the whole of the rear surface of the movable component. The area of this component will typically be very much greater than that of the piston of a pneumatic ram and so adequate perforating force may be derived from significantly lower pressures. As such, the volume of air which must be moved into the pressure chamber and out again on each cycle of operation is reduced and the control valving for that air also is simpler and faster, in that it operates 0 at much lower pressures. These features combine to permit a much reduced perforation cycle time, so giving the possibility of greater throughput rates in a plant within which the apparatus is installed.

In a preferred embodiment, the pressure plate is secured to a rear part of the support, with the marginal region of the diaphragm sandwiched between the rear surface of the support and the pressure plate. Gas (and usually compressed air) may be admitted to the pressure chamber through at least one gas admission port opening through the surface of the pressure plate confronting the diaphragm. That surface of the pressure plate may be relieved in the region of each gas admission port to facilitate initial movement of the movable component, at the onset of the supply of gas under pressure to the chamber. The surface of the pressure plate confronting the diaphragm may be relieved so as thereby to define the pressure chamber.

The admission of gas under pressure to the pressure chamber and the exhausting of that gas preferably is controlled by a solenoid-operated valve, which when energised admits the gas. A suitable control signal may be - 5 supplied by a process controller which also controls the operation of a sleeving machine or other equipment with which the perforator is associated, in order that the perforation of the web may be performed at the required spacings along the length thereof as the web is advanced. The timing of the opening and closing of the solenoid-operated valve may be determined empirically, allowing for delays, response times and so on.

With the perforator of this invention, the movable component may be a carrier for the perforator blade but preferably is the anvil. In the latter case, the perforator blade is preferably mounted on a carrier which is itself secured to the 0 support, in opposition to the front face of the anvil. A stop arrangement may be provided for the anvil in order to ensure the perforator blade penetrates the material uniformly along the length of the blade, even if the blade is arranged non-symmetrically on the carrier or if there is more than one perforator blade, disposed in a nonsymmetrical arrangement with respect to the axis of movement of the anvil. Such a stop arrangement may comprise one or more bolts threaded into the carrier to project towards the anvil, the or each bolt being adjustable to define the required stop position for the anvil and to prevent small twisting movements of the anvil on contacting the perforator blade. When more than one perforator blade is mounted on the carrier, they may give for example two closely spaced parallel lines of perforations, or lines of perforation at an angle to one another.

The return means for the movable component may comprise a spring arrangement acting between the movable component and the support. In the alternative, the return means may be arranged actively to withdraw gas from the pressure chamber thereby to urge the movable component back to its rest - 6 position. In this case, the gas control means may be arranged to connect the pressure chamber to a source of reduced pressure whereby gas is actively withdrawn from the chamber.

A stripper bar may be attached to but spaced from the anvil and arranged to lie closely adjacent the perforator blade. The web to be perforated may then extend between the anvil and the stripper bar, such that the web is pulled away from the perforating edge of the perforator blade as the anvil and blade separate, at the completion of a perforating cycle.

The perforating apparatus of this invention may be arranged to operate either by crushing the material of the web between the perforating edge of the perforator blade and the anvil, or by having the perforating edge piercing through the material of the web. For the latter operation, the anvil may have a groove formed therein, which corresponds to and receives the perforating edge of the perforator blade. In this way, the perforating edge may pierce through the material of the web to make positive perforations, as distinct from regions of crushed material. When piercing is to be performed, a separate stop may be provided for the movable component, rather than relying on the movable component to be stopped by contact between the perforating edge and the anvil.

By way of example only, one specific embodiment of perforating apparatus and intended for use with lay-flat heat-shrink plastics material tubing and arranged in accordance with this invention will now be described in detail, reference being made to the accompanying drawings in which: Figure 1 is an isometric exploded view of the principal components of the apparatus; and Figure 2 is a partial face view on the perforator blade carrier and support plate therefor.

The apparatus shown in the drawing has a base 10 which, when the apparatus is in use, is secured to a suitable part of a sleeving machine to which the perforated lay-flat tubing is supplied for application to food containers. The base 10 has a generally rectangular aperture 11 within which is slidably mounted a block 12, the block having flanges 13 projecting as extensions of its rear face, so as to limit forward movement of the block through the aperture 11, in the direction of arrow A. The block 12 is made of an aluminium alloy and is provided with drillings 14, to reduce the mass of the block. Secured to the front of the block is a plate-like anvil 15 of hardened steel and when the block is fully forward, the front face 16 of the anvil 15 projects slightly beyond the front surface 17 of the base 10.

The block 12 is mounted within the aperture 11 by means of end linear bearings 18 and edge thrust races 19, which act between opposed side walls of the block and of the base, defining the aperture. In this way, the block is free to move with low friction whilst being accurately located within the aperture.

Helical compression springs 20 are provided in bores formed in the base from its rear surface and act on the flanges 13 and so to urge the block in the opposite direction to that indicated by arrow A. A pressure plate 22 is secured to the rear surface of the base 10 by means of a plurality of bolts passing through bores 23 formed around the periphery of the pressure plate 22. Between that pressure plate and the rear surface of the base, there is a rectangular flexible diaphragm 24 having a series of marginal holes 25 corresponding to the bores 23 whereby the diaphragm is 8 heid in place by the same bolts as secure the pressure plate to the base, with the diaphragm sandwiched between that plate 22 and the base 10. A large area pressure chamber is thus formed between the diaphragm 24 and the pressure plate 22.

Three air admission ports 27 are formed through the pressure plate 22 and where those ports open into the front face of the pressure plate, the plate is relieved to facilitate the entry of air into the pressure chamber. Over each port 27 there is provided a respective baffle 28 to deflect the air sideways into the relieved area before entering the chamber. The baffles 28 serve to protect the diaphragm 24 from perforation in the event that foreign matter is entrained in the in-going airflow.

In the illustrated embodiment of perforator, the central port 27 is blanked-off on the rear face of the pressure plate 22. Each of the other two ports 27 is provided with a respective solenoid operated pneumatic control valve 29 which, when energised, permits the ingress of air under pressure into the pressure chamber and when de-energised permits the exhausting of air from that chamber, to atmosphere.

Four columns 31 upstand from the front surface 17 of the base 10, a support plate 32 being mounted on those columns by means of studs (not shown) passing through the columns and the support plate. The support plate is retained in position by nuts 33 threaded on to the studs, a respective resilient washer assembly 34 being provided between each nut and the support plate 32, in order to permit small excursions of the support plate 32 in the direction of arrow A when the apparatus is in use. - 9 -

Mounted on the surface of the support plate facing the front face 16 of the anvil 15 are three parallel blade carriers 35, a long perforator blade 36 being secured to the lower end faces of those carriers. An opposing stabiliser bar 37 is secured to the upper end faces of the carriers 35. Mounted between the blade 36 and stabiliser bar 37 is a block 38, held in position by means of bolts (shown in Figure 2) passing through a slot 39 in the stabiliser bar 37. The block 38 supports a further perforator blade 40 extending at an acute angle to the long perforator blade 36. The blades 36,40 have respective perforating edges 41 which will be contacted by the anvil 15, upon forward movement of the block 12 carrying the anvil, in the direction of arrow A. When the anvil 15 contacts the perforating edges of the perforator blades, there will be a tendency for the anvil to move out of strict alignment with the perforating edges, as both perforator blades are off axis with respect to the centre of the anvil. To compensate for this, balancing bolts 43 are threaded into the support plate 32, whereby the inner ends of those bolts will be contacted by the anvil simultaneously with its contact with the perforating edges of the blades. The balancing bolts 43 are adjusted as required to give a precision perforation and then are locked in position by means of respective locknuts 44 external to the support plate 32.

Typically, two such balancing bolts 43 will be provided. To accommodate different perforator blade configurations, in this embodiment there are four threaded holes 45 for the balancing bolts and normally balancing bolts will be fitted into those holes, in pairs.

A stripper bar 47 is secured at its two ends to the front face 16 of the anvil 15, so as to leave a narrow gap between the stripper bar and that front - 10 face of the anvil. The operating edge 48 of the stripper bar lies closely adjacent the long perforator blade 36, for a purpose to be described below. Mounted on the base 10 is an adjustable guide system 49 defining a narrow slot 50 through which material to be perforated passes. Knob 51 allows adjustment of internal guides within the guide system, to ensure the material to be perforated is i properly located laterally, with respect to the perforator blades.

In use, a suitable source of air under pressure is connected to the control valve 29 and an electrical controller is wired to the solenoid of those valves, such that the supply of an electrical current to the solenoid causes the valves to operate and supply air under pressure to the pressure chamber between the pressure plate 22 and the diaphragm 24. Removal of that current I allows the valves to return to their nommal positions and so to vent the pressure chamber to atmosphere.

A web of lay-flat heat-shrink tubing is threaded through the slot 50 of the I guide system 49 and through the gap between the front face 16 of the anvil 15 and the stripper bar 47. From there, the material is guided on to a sleeving machine with which the perforator is associated. During performance of a sleeving operation, the heat-shrink tubing is pulled stepwise through the perforator. The controller causes the tubing momentarily to stop and to supply a signal to the solenoids of the valves 29 at the appropriate moment to cause the block 12 and carried anvil 15 to be driven forwardly in the direction of arrow A by air under pressure supplied through the ports 27. When the signal is removed, air in the pressure chamber is vented to atmosphere, through the valves. The block 12 and anvil 15 are returned to their initial position by springs I 20 and the stripper bar pulls the perforated tubing off the perforating edges 41 - 1 1 of the perforator blades 36,40 to ensure that subsequent movement of the tubing is not restricted by the blades. The precise timing of the supply of electrical energy to the solenoids of the valves 29 is determined empirically, in view of the inevitable small delays in opening of the valves, closing of the valves and movement of the anvil 15.

In view of the relatively large area of the pressure chamber, sufficient force for moving the block 12 and anvil 15 very quickly can be generated with low air pressures. Despite that large area, the stroke of the block 12 may be as small as 1.0 mm to 2.0 mm and so only a small volume of air is to be moved 0 into and out of the pressure chamber. This can be performed relatively quickly, so permitting high speed operation. The resilient assembly 34 mounting the support plate 32 to the base 10 absorbs the impact between the anvil and the perforator blades, so prolonging the life of the blades.

As mentioned above, when there is a non-symmetrical arrangement of one or more perforator blades with respect to the axis of movement of the block 12 there will be a tendency for the block and anvil to twist slightly on impacting the or each perforator blade. For example, with the blade arrangement of Figures 1 and 2, there will be a tendency for the anvil to tilt about the lengths of the blades 36,40 so that in the area marked B (Figure 2), the anvil moves marginally closer to the support plate 32 than where the blades are provided.

By tilting in this way, there will be an unequal contact along the length of at least the long perforator blade 36, so leading to unequal penetration of the blade along its length. Then, on shrinking a nonuniformly perforated sleeve, there is a tendency for the sleeve to skew on the product being sleeved, caused by variable shrinking of the material in the region of the perforation. - 1 2

To counteract this effect and to ensure the anvil stops while its face 16 remains parallel to the support plate 32, the balancing bolts 43 are adjusted to provide a stop for the anvil. The bolts are fitted into holes 45 selected as appropriate for the particular blade arrangement and then are adjusted so that the inner ends of the bolts are contacted at precisely the same moment as the perforator blades also contact the anvil. This ensures the anvil remains parallel to the support plate during the perforating operation.

It is found that a perforator as described above is able to operate at relatively high speeds, and with the tubing pulled almost continuously (but actually step-wise with momentary stops) through the perforator, the anvil being driven forwardly at the required moments having regard to the advancement of that tubing. - 13

Claims

1. Apparatus for perforating a web of sheet material advancing along a path, comprising: - a movable component having front and rear faces and carried on a support for reciprocating movement between rest and perforating positions; - return means arranged to urge the movable component to its rest position; - a resiliently-deformable diaphragm bearing on the rear face of the movable component; - pressure chamber defined between the diaphragm and a pressure plate carried by the support; - gas control means selectively to admit gas under pressure to the pressure chamber and to exhaust gas from that chamber; - at least one perforator blade carried by one of the support and the front face of the movable component and co-operable with a surface of the other of the support and the movable component which said surface serves as an anvil for the perforator blade; whereby in use said path extends between said surface and the perforator blade, and the admission of gas under pressure to the pressure chamber thrusts the movable component forwardly to interengage the perforator blade with said surface serving as the anvil, thereby to perforate sheet material extending therebetween.

2. Apparatus as claimed in claim 1, wherein the pressure plate is secured to a rear part of the support, with the periphery of the diaphragm sandwiched between said rear surface of the movable component and the pressure plate. - 14

3. Apparatus as claimed in claim 2, wherein there is at least one gas admission port opening through the surface of the pressure plate confronting the diaphragm.

4. Apparatus as claimed in claim 3, wherein the surface of the pressure plate is relieved where the or each gas admission port opens into the pressure chamber.

5. Apparatus as claimed in any of the preceding claims, wherein the support includes a main body having an aperture formed therethrough, the movable component being mounted in the aperture for sliding movement with respect to the main body.

6. Apparatus as claimed in claim 5, wherein the movable component is supported on linear bearings disposed between side walls of the movable component and the walls of the main body defining the aperture therethrough.

7. Apparatus as claimed in any of the preceding claims, wherein the gas control means comprises a solenoid-operated valve which when energised admits air under pressure to the pressure chamber and when not energised allows air to be exhausted from the chamber.

8. Apparatus as claimed in any of the preceding claims, wherein the return means comprises a spring arrangement acting between the movable component and the support.

9. Apparatus as claimed in claim 8, wherein the spring arrangement comprises one of a gas spring and a plurality of helical compression springs arranged between the movable component and the support.

10. Apparatus as claimed in any of claims 1 to 7, wherein the return means is arranged actively to withdraw air from the pressure chamber thereby to return - 15 the movable component to its rest position.

11. Apparatus as claimed in claim 10, wherein the gas control means is operated to connect the pressure chamber to a source of reduced pressure when the movable component is to be returned to its rest position.

12. Apparatus as claimed in any of the preceding claims, wherein the perforator blade is carried by the support and the movable component serves as the anvil.

13. Apparatus as claimed in any of the preceding claims, wherein the perforator blade is mounted on a carrier secured to the support in opposition to the anvil.

14. Apparatus as claimed in claim 13, wherein an adjustable stop arrangement is provided on the carrier to maintain correct alignment between the perforator blade and the anvil as a perforation is performed.

15. Apparatus as claimed in claim 14, wherein the adjustable stop arrangement comprises at least one bolt threaded into the carrier, an end face of the bolt being contacted by the anvil as the perforation is performed.

16. Apparatus as claimed in any of claims 11 to 15, wherein the securing of the carrier to the support permits the carrier to perform small resilient excursions in the direction of movement of the movable component.

17. Apparatus as claimed in any of the preceding claims, wherein there is provided a stripper bar arranged closely adjacent the perforating edge of the perforator blade, to assist removal of perforated material from the blade on relative separation of the perforator blade and anvil.

18. Apparatus as claimed in any of the preceding claims, wherein there are at least two perforator blades disposed at an angle with respect to each other, - 16 both blades being simultaneously co-operable with the anvil to effect multiple perforations on a sheet material advancing along the path.

19. Apparatus as claimed in any of the preceding claims, wherein the anvil is provided with a groove corresponding to the perforating edge of the perforator blade whereby the perforating edge of the blade is received in the groove when the anvil and blade are moved to interengage as aforesaid.

20. Apparatus as claimed in any of claims 1 to 18, wherein the anvil is substantially planar and is contacted by the perforating edge of the perforator blade when the anvil and blade are moved to interengage as aforesaid. i 0

21. Apparatus as claimed in claim 1 and substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

22. A method of perforating a web of sheet material advancing along a path which extends between the front face of an anvil and a perforator blade, one of the perforator blade and the anvil being a movable component carried on a support for reciprocating movement between rest and perforating positions with return means arranged to urge the movable component to its rest position, there being a resiliently-deformable diaphragm bearing on the rear face of the movable component and a pressure chamber defined between the diaphragm and a pressure plate carried by the support, in which method the web is advanced by a predetermined distance along said path, a signal is supplied to an electrically-controlled gas valve to cause the operation thereof to admit gas under pressure to the pressure chamber thereby driving the movable component forwardly until contact is established between the anvil and the perforator blade, so perforating the sheet material between the blade and the anvil, and the signal is removed from the valve to permit gas to be exhausted from the pressure chamber whereby the movable component is returned to its rest position under the action of the return means, so separating the perforator blade and the anvil.

23. A method as claimed in claim 22, wherein the movable component serves as the anvil and the perforator blade is secured to the support.