WO2000064609A1

WO2000064609A1 - Method of forming a can body

Info

Publication number: WO2000064609A1
Application number: PCT/GB2000/001453
Authority: WO
Inventors: Geoffrey Bertram Camm; Sudesh Kumar Nayar
Original assignee: Crown Cork & Seal Technologies Corporation; Carnaudmetalbox Plc
Priority date: 1999-04-22
Filing date: 2000-04-17
Publication date: 2000-11-02
Also published as: AU4581000A; GB9909110D0

Abstract

A method of forming a can body having a neck with a curled edge. The method provides a can preform having a cylindrical side wall which may include a side seam. The edge of the can preform is curled and thereafter the preform is expanded in order to form a neck on the finished can. The quality of curl is maintained in the finished can since the curled edged is not subjected to further deformation. Furthermore, the curl is formed on unworked or less worked metal.

Description

METHOD OF FORMING A CAN BODY

This invention relates to a method of forming a can body having a neck with a curled edge. In particular, but not exclusively, the can body may be suitable for use with a vacuum sealed reclosable closure having a skirt portion of diameter less than or equal to the diameter of the can body.

Two piece containers comprising a can body with integral base and a vacuum closure have been described in 097/39955. In that document it is explained how the free edge of the container is curled to avoid corrosion and risk of injury by an exposed cut edge. Below the curl, the container comprises a necked portion which is typically produced by die-necking. The neck includes a cylindrical portion over which a vacuum closure is fitted to close the container. Typically the closure has a skirt portion of diameter less than or equal to the diameter of the container body.

The possibility of extending this technology to three piece containers in which the cylindrical body has a welded side seam has been investigated. However, problems have arisen due to the work hardening of the metal and also the formation of undesirable features such as wrinkles adj cent the weld which occur during die necking. Furthermore, where the container body has been pre-lacquered or coated, there is a risk of disruption of the coating during the necking and curling operations.

This invention seeks to provide a solution to these problems and also to provide an alternative method of manufacturing the two piece container body of 097/39955. According to the present invention there is provided a method of necking a can body comprising: providing a can preform having a cylindrical side wall and at least one free edge; characterised by forming a neck on the can body by expanding the preform side wall .

By expanding the preform to produce the necked can body, the multiple stages of die necking in order to produce the desired degree of diameter reduction are replaced by a single stage expansion operation. Clearly the reduction in process steps provides economic benefits .

Preferably, the method further comprises forming a curl on the can body prior to the expansion step. As a result, work hardening is minimised at the point to be curled and disruption of coating avoided, since the curl is formed on unworked or less worked metal .

Although the process is well-suited to the neck formation on either two or three piece can bodies, particular benefits are apparent when used for three piece can bodies. The necking and curling of known three- piece cans is particularly difficult, primarily due to the influence of a welded side seam and the lacquer side strip which is often employed. However, the present invention completely avoids any problems such as wrinkling or pleats adjacent the weld, since there is no reduction in can diameter involved in this process. Furthermore, three piece cans can be produced more easily in different height and diameter formats than two piece cans . In a preferred embodiment, the expanding step comprises pressurising the preform with pressurised fluid, for example air or hydraulics. Alternative methods such as mechanical expansion with an expandable mandrel or bulge forming are also possible, however.

Generally, the method may further comprise closing the can with a closure having a diameter which is less than or equal to the diameter of the expanded side wall of the preform. The maximum expansion possible depends on the expansion method, material and original dimensions but an expansion by pressurised fluid of up to 20% may be achieved for single reduced steel cans and up to 15% for double reduced steel cans. In a preferred embodiment, the neck comprises a tapered region and a cylindrical region, the angle of the taper to the vertical (side wall) being up to 60°, more typically up to 45°.

By virtue of the necked can being formed by expansion into a mould, for example, a variety of shapes may be achieved. Such shapes may be of purely aesthetic nature or they may include threads on the cylindrical neck portion for receiving a closure, beads or other strengthening features in the side wall, depending on the desired characteristics and purpose of the final container.

It is envisaged that the neck may comprise at least part of a pre-necked can or aerosol cone so that the method is suitable for increasing the extent of an already necked- in can or the cone of an aerosol can, for example .

Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:

Figures 1 to 6 are schematic side sections of a can body, showing the stages of formation of a necked can according to the invention; and

Figure 7 shows an enlarged schematic side section of the neck curl of figure 6.

Figure 1 shows a can body having a cylindrical side wall 2 which is open at both ends and which typically has a welded side seam (not shown) . Figure 2 to 6 show, in sequence, the formation of outward curl 3, outward curl 4 with hidden edge, flattened curl 5, base seam 9 and neck 10. Flattened curl 5 is shown in enlarged view in figure 7.

As is apparent from figure 6, the neck is formed by expansion of the can side wall 2. In the example shown, both ends of the can body remain at the original diameter although this is not essential . By expanding the side wall, for example by filling the can body with pressurised air so that it expands until the can side wall contacts the inner wall of a mould, a tapered shoulder 12 at an angle of about 25° to the vertical and cylindrical neck 14 are formed. In the example shown, the rest of cylindrical side wall has been expanded to a cylindrical central section 15 which tapers 16 to the double seam 9. A 0.5 mm outward body curl 3 is first formed then the raw edge is hidden by further curling into outward curl 4. Curl 4 is then flattened (figures 4 and 7) by a roller onto a chuck as is common practice for certain processing methods or for particular closures, although such flattening of the curl is not essential . Although the flattened curl 5 may be formed in the usual manner, in the present invention the curl is formed before the neck. As a result, it is possible to ensure tight tolerances in the curl itself, as well as maintaining consistent height of the curled neck edge 6 in the resultant can.

In the example shown, the flattened curl 5 has a first radius r of 0.5 mm which is the radius of the original curl 3 (figure 2) and a second radius R of 1 mm formed by subsequent curling to hide the raw edge (see figures 3 and 7) . Although radius R is shown as 1 mm, this radius should be as tight as possible and radii of 0.5 mm could be formed for both R and r. The can of this example may be expanded by any known methods such as bulge forming, pressurised fluid within or introduced into the can, expandable mandrels etc. The current invention is not intended to be limited to any one expansion method. Although the example shows simple expansion of the side wall to produce a neck, clearly other functional or aesthetic features could be formed by this method without compromising the body curl and primary seal with a closure. By forming the curl before any other feature, a very high quality of curl can be achieved and maintained. Features such as beading, changes in cross-section or promotional shapes can then readily achieved without affecting the primary seal or causing coating damage. By expanding the can side wall, a partially formed neck or the cone (equivalent to a neck) of an aerosol can may be extended to obtain greater overall diametrical reduction.

Claims

1. A method of necking a can body comprising: providing a can preform having a cylindrical side wall and at least one free edge; characterised by forming a neck on the can body by expanding a portion of the preform side wall.

2. A method according to claim 1, further comprising, prior to the expansion step, curling the or one of the free edges .

3. A method according to claim 2 , in which the curl includes a radius of at least 0.5 mm.

4. A method according to any one of claims 1 to 3 , in which the neck comprises a tapered region and a cylindrical region, the angle of the taper to the vertical being up to 60°.

5. A method according to any one of claims 1 to 3 , in which the neck comprises at least part of a pre-necked can or aerosol cone .

6. A method according to any one of claims 1 to 5 , in which the can body is made from single reduced steel and the expansion is 20% or less.

7. A method according to any one of claims 1 to 5, m which the can body is made from double reduced steel and the expansion is 15% or less.

8. A method according to any one of claims 1 to 7, m which the expanding step comprises pressurising the preform with pressurised fluid.

9. A method according to any one of claims 1 to 7 , m which the expanding step comprises mechanical expansion.

10. A method according to any one of claims 1 to 9, further comprising closing the can with a closure having a diameter which is less than or equal to the diameter of the expanded side wall of the preform.