EP1681110A1

EP1681110A1 - Method of shaping metal closures or can bodies

Info

Publication number: EP1681110A1
Application number: EP05100255A
Authority: EP
Inventors: Paul Robert Dunwoody
Original assignee: Obrist Closures Switzerland GmbH; Crown Packaging Technology Inc
Current assignee: Obrist Closures Switzerland GmbH
Priority date: 2005-01-17
Filing date: 2005-01-17
Publication date: 2006-07-19
Also published as: HK1113103A1; PL1838472T3; TW200631690A; ES2327060T3; WO2006075132A1; ATE431205T1; MY140608A; EP1838472A1; EP1838472B1; TWI290863B; DE602006006793D1

Abstract

A method of shaping an open end of a metal tube into a flared shape so that the diameter of the tube increases gradually from a point axially displaced from the open end of the tube towards the open end of the tube, the method comprising the steps of using a flanging tool to increase the diameter of the open end of the tube, and the next step of using subsequent forming tool(s) to increase the diameter of the tube at points immediately axially behind the open end of the tube such that the diameter of the open end of the tube remains unchanged from that created in the first step.

Description

The present invention relates to a method of shaping metal tubular closures or can bodies such that the open end of the tube is formed into a flared shape. In particular, but not exclusively, it relates to the shaping of a metal closure or can body in which the side wall height is greater than the diameter of the open end(s) and/or end wall.
It is known to produce metal closures or can bodies from such easily worked materials as aluminium. These are typically formed from a flat sheet of relatively thin metal which may be shaped by means of one, or a series of, die or spin-flanging tools such that the finished product is tubular with one axial end closed integrally and with the other end open.
In the case of closures, the finished product is then typically rolled onto a bottle neck so that threads are formed in the sides of the closure corresponding to the threads on the bottle neck.
The tubular nature of these products is such that the diameter of the open end of the tube is substantially the same as the closed end.
However, it is desirable to be able to produce metal closures or can bodies which have a flared open end, so that the diameter of the open end is greater than the diameter of the closed end.
Further, typical food and drink cans are known in which a flange is formed at the axially distal open end of the can body by means of die or spin flanging tools. The flange acts as a feature for connecting the lid to the body for sealing purposes and is therefore typically oriented perpendicularly to the axial length of the can body.
This flange is created by stretching and bending part of the can wall. However, in the case of a typical flange, the length of the portion of can wall which is formed into the flange is relatively short, being typically in the region of 2 to 3 mm. Accordingly, the amount of the wall that is stretched to increase its diameter is relatively small.
The stretching and expansion of the wall creates hoop stress in the flange, but the metal is supported by adjacent material that is less stressed thus avoiding splitting during flanging operations.
However, it is desirable to be able to stretch and expand a greater proportion of a can body or closure sidewall to produce a flared open-end.
Due to increased hoop stress, and reduced support from less stressed material, it has hitherto been problematical to create such flared shaped metal closures or can bodies due to splitting of the material.
It is therefore desired to provide an industrial method of producing metal closures or can bodies with a flared open end such that the method is capable of producing such closures at a high throughput speed and with low spoilage rates due to splitting.
In one aspect, the invention provides a method of shaping an open end of a metal tube into a flared shape so that the diameter of the tube increases gradually from a point axially displaced from the open end of the tube towards the open end of the tube, the method comprising the steps of (a) using a flanging tool to increase the diameter of the open end of the tube, and (b) using subsequent forming tool(s) to increase the diameter of the tube at points immediately axially behind the open end of the tube such that the diameter of the open end of the tube remains unchanged from that created in step (a) above.
An advantage of this method is that splitting of the metal is avoided by the expansion of the overall desired axial length taking place in stages. Further, by increasing the open end to the desired diameter in one step, rather than in more than one step, there is less chance of work-hardening of the metal which may cause splitting.
The flare may be formed either straight or curved, which has advantages in matching the profiles of containers, in the case of closures. Further embodiments are disclosed in the dependent claims attached hereto.
Embodiments of the invention will now be described, by way of example, with reference to the following drawings in which;
Figure 1 shows different views of a typical can body before and after having a flange formed at both ends,
Figures 2 to 4 show a sequence of cross-sectional views of a metal closure having been treated in accordance with the method described herein,
Figure 5 shows enlarged cross-sectional views superimposed on one another of the distal end of a metal closure having been treated in accordance with the method described herein,
Figure 6 shows a flanging tool which may be used in accordance with the method described herein,
Figures 7 and 8 show a sequence of forming tools which may also be used in accordance with the method described herein.
In Figure 1, a tube of metal 10 is shown in perspective on the left with substantially cylindrical sidewalls. This could be a food or drink can body. The middle drawing, also in perspective, shows this same can body with flanges 12 formed at both ends. The drawing on the right is an enlarged view of one of flanges 12 seen in cross-section.
It may be seen that the flange 12 is formed such that the distance of the end of the flange from the wall of the tube 'D' is substantially equal to the axial length of can wall which has been stretched. Further, this flange lies substantially perpendicular to the longitudinal axis of the can body 10.
As has been stated above, the greatest value for 'D', at which no splitting of the metal occurs, is known to be approximately 3mm with typical food or drink cans in which the can wall is comparatively thin (less than 1 mm).
Although a can body with both ends open is shown it should be understood that the can body could be formed from one sheet of metal so that the can body has an integral closed end and an open opposite end.
Figure 2 shows a cross section of a typical metal closure 20. The closure has a closed end 22 and has milling 24 formed at one end to increase grip. The walls 26 of the closure extend axially away from the closed end 22 and terminate at an open end. In some instances part of the walls 26 of the closure 20 have already been shaped such as bulge 28.
Using a flanging tool, such as is shown in Figure 6, the open end of the closure 20 is expanded outwards so as to form a flange 30. This occurs because the tool 80 is inserted inside the body of the closure 20 until the axial end of the walls 26 butt up against the curved stop 81 of the tool. Further respective movement of the tool 80 and closure 20 forces the open end of the tube outwards so that it conforms to the shape of the tool.
The next step of the method is to use a subsequent forming tool, for instance the one shown in Figure 7. This tool 90 is inserted into the closure body. However, rather than the flange 30 butting up against the shaped feature 91 of the tool, the portion of the wall which is immediately adjacent but axially "behind" this flange 30 is forced outwards such that the diameter of this wall is increased.
Finally, this step is repeated with another tool, such as is shown in Figure 8. Again, rather than the flange 30 of the tube being affected it is the wall portion of the tube "behind" this axially furthest portion which is expanded.
It should be understood that although only two steps have been described above following the initial flange-forming step, there could in fact be only one step, using only one forming tool, or indeed more than two steps, using several differently shaped forming tools, before the final desired profile is reached.
The progression of expansion of the diameter of the tube may best be seen in Figure 5.
This figure shows a portion of wall 26. Only one side of the cross-sectional view of the tube is shown as it is symmetrical about the longitudinal axis shown as "X". The wall thickness is exaggerated so that it is indicated by two parallel lines to improve understanding.
The original shape of the wall is straight without any curve at the right hand end, as indicated by reference 45. The portion indicated 50 shows how the axial end of the tube has been expanded by the first step, as described above, such that a flange has been formed.
The portions indicated 60 and 70 show how the tube has been further expanded by means of forming tools such as are shown in Figures 7 and 8. It will be observed that the diameter of the axially furthest end of the tube remains constant after the initial expansion. Rather it is the portion of tube axially "behind" this flange which is expanded progressively to the final desired shape.
By this progression of shaping of the can body, the flange 30, which is initially distinct from the rest of the tubular sidewalls (Figure 2), may become less distinct and in fact may become indistinguishable from the overall flare (Figure 4). In other words, the flange 30 may merge and become one with the expanded wall portion 70, such that the diameter of the tube increases gradually from a point axially displaced from the end of the tube towards the open end of the tube.
The resultant flare shape of the closure or can body would typically be formed with the open end lying at an angle which is less than 45 degrees from the longitudinal axis.
Although in theory, a tube with any wall thickness could be shaped by this method, it is advantageously possible to shape tubes with walls of thickness less than 1 mm. This is due to careful design of the flanging and forming tools, the pressure of contact between the tube and the tools, and the sequence of tool shapes utilised. Accordingly, typically relatively thin walled metal tubes, such as found in metal closures or food or drink can bodies, may indeed be shaped in this way.
Further, although tubular walls of less than 1 mm in thickness has been quoted, it has been found that the method will also perform well with walls with a thickness of less than 0.50mm, and even less than 0.25mm.
By this method, the diameter of the tube, measured at the distal end, may be increased in a range from 1 to 20% of the original diameter, with the diameter of the portion of the tube immediately behind this distal end also being increased such that the overall diameter of the tube increases gradually from a point axially before the distal end of the tube to a point located at the distal end of the tube.
This gradual increase in diameter may be formed over an axial length, measured back from the open end, which is greater than the increase in the diameter of the tube. Indeed, the increase in diameter could be achieved over an axial length which is almost equal to the entire length of the tube.
In another embodiment, a tube could be shaped such that a series of flared profiles are formed axially along the length of the tube. Each profile could have a progressively smaller diameter than the preceding profile so that a set of tubes shaped in this way would be nestable.
Although the above method has been described in relation to can bodies or metal closures made from a single flat sheet of metal which has been formed into a tubular shape with an integral closed end, the method could also be applied to tubular bodies in which the sidewall is formed from a single sheet which has been rolled into a tubular shape and then welded along the longitudinal axis.

Claims

A method of shaping an open end of a metal tube into a flared shape so that the diameter of the tube increases gradually from a point axially displaced from the open end of the tube towards the open end of the tube, the method comprising the steps of ; (a) using a flanging tool to increase the diameter of the open end of the tube, and (b) using subsequent forming tool(s) to increase the diameter of the tube at points immediately axially behind the open end of the tube such that the diameter of the open end of the tube remains unchanged from that created in step a) above.
A method according to claim 1 wherein the flare is curved.
A method according to claim 1 wherein the flare is straight.
A method according to any preceding claim wherein the diameter of the tube is increased in a range from 1 to 20% of the original diameter.
A method according to any preceding claim wherein the diameter of the tube is increased gradually over an axial length which is greater than the increase in diameter of the tube.
A method according to any preceding claim wherein the thickness of the wall of the metal tube is less than 1 mm.
A method according to any of claims 1 to 5 wherein the thickness of the wall of the metal tube is less than 0.25 mm.
A method according to any preceding claim wherein the resultant flare shape of the metal tube lies at an angle which is less than 45 degrees from the longitudinal axis.
A metal tube with a flared open end formed using the method of any preceding claim.
A closure or can body having a sidewall comprising a metal tube according to claim 9.