EP0103074A2

EP0103074A2 - Increased strenght for metal closures through reversing curved segments

Info

Publication number: EP0103074A2
Application number: EP83105729A
Authority: EP
Inventors: Tuan Anh Nguyen
Original assignee: Ball Corp
Current assignee: Ball Corp
Priority date: 1982-09-09
Filing date: 1983-06-10
Publication date: 1984-03-21
Also published as: JPS5962444A; AU1618683A; EP0103074A3

Abstract

The present invention relates to improvements in the strength of ends used on metal beverage containers. Such ends generally comprise a center panel of a substantially planar character, a surrounding annular grooved portion or countersink made up of an inner panel wall, a chuckwall and a first upwardly bowed arcuate segment integrally joining the inner wall and the chuckwall, and a second downwardly bowed arcuate segment integrally joining the inner wall and the center panel.

In accordance with the present invention the second arcuate segment is reversed by herein disclosed tooling to provide the closure with three reversing arcuate segments between the inner wall and the center panel and a reduced center panel diameter. The closure so formed exhibits an increase in buckle resistance between 8 and 10 percent which allows a thinner gauge material to be used in forming the closures. Other than the three reversing arcuate segments the closure formed in accordance with the present invention conforms very closely to standard dimensional characteristics allowing its use on existing customers' fill-and-seal equipment without modification. An additional advantage of the present invention is that it can be easily instituted on many of the existing closure production lines with minor modifications and extremely low additional press tonnage requirements.

Description

. Background of Invention

The present invention relates generally to container ends and more particularly to an improved end for a pressurized container and method of forming such end.
Because of the very large market for beer and beverage cans and the very competitive pricing of such containers it is important that such cans, including their ends, be made as economically as possible. A significant portion of the manufacturing cost of such ends is represented by the metal. As is well appreciated by those skilled in the art, even a minute metal saving in each end may result in millions of dollars in savings to the can industry due to the billions of ends produced. Therefore, a relatively small reduction in the thickness of metal while maintaining the strength of the end is of significant economic importance. Conversely, an increase in strength using the same thickness of metal is also of great importance.
The configuration of ends conventionally used to close drawn and ironed beer and beverage cans comprises a center panel, a grooved portion surrounding the center panel and bounded on the inside by an integral inner wall and on the outside by an integral chuckwall, a first curved segment at the bottom of the groove joining the inner wall and the chuckwall, a second curved segment joining the center panel to the inner wall, and a peripheral curl at the upper end of the chuckwall for securing the closure to a can body.
It has been recognized that providing the center panel of a steel closure with two radially separated concave areas of curvature, or preferably, peripheral steps, will increase the buckle resistance of the closure. Thus, in U.S. Patent No. 3,774,801 there is described a steel closure having one or more peripheral steps or convex areas of curvature adjacent to the concave areas of curvature.
It has also been recognized that having the inner wall and the chuckwall substantially vertical and increasing the panel height increases the buckle strength of the end. Thus,. in U.S. Patent No. 4,217,843 there is disclosed tooling for forming the sidewall in such a manner that the inner wall and chuckwall are more nearly vertical and the panel height is greater than was previously the case. It is also known that doming the central panel provides increased buckle strength. As shown in U.S. Patent No. 4,217,843, this is normally done at the last forming station for making can ends by tension stretching the panel portion of the end with a doming tool having the desired radius of curvature. Other doming techniques proposed include that shown in U.S: Patent No. 3,441,170 where the second curved segment connecting the inner leg of the sidewall to the center panel is coined on the undersurface. This is for the purpose of reducing the metal thickness in the curved segment to the point where it functions as a hinge thus enabling the panel portion to dome as a result of the pressure of the contents of the can. Coining the undersurface of the curved segment but approximately to a lesser depth is also taught in the aforementioned U.S. Patent No. 4,217,843 for the purpose of work hardening and thus stiffening the segment.

Summary of the Invention

According to the present invention, a metal container closure of the usual type is strengthened by reversing a portion of the second curved segment to provide at least three reversing curved segments integrally joining the center panel to the inner wall. This results in a further work hardening of the second segment, reduction in the diameter of the center panel, a straightening of the inner wall and a slight increase in panel height, all contributing to a substantial increase in eversion resistance.
More particularly, a die and punch arrangement is placed respectively under and over a standard closure. The working surface of the die includes a first concave portion located underneath the second arcuate segment of the closure. The first concave portion extends upwardly to a vertical first sidewall which terminates in a first convex portion which is adjacent the closure and inwardly of the second arcuate segment. An inwardly extending second horizontal portion is connected thereto. Outside the first concave portion is an integrally connected first horizontal portion which terminates in a second convex portion which terminates in a substantially vertical plane. A second downwardly extending sidewall may be integrally connected to the lower part of said second convex portion.
The working surface of the punch includes a third convex portion which substantially matches with said first concave portion of said die and is located to accomplish the metal forming requirement when the punch and die are brought together in working position. The third convex portion terminates upwardly in a vertical third sidewall and outwardly in a third horizontal portion. In accordance with the preferred embodiment of the present invention, a second concave portion which substantially matches with the second convex portion of said die is integrally connected to the outside of said third horizontal portion. The second concave portion of the working surface of the punch terminates in a downwardly extending ring-like member which mates with the first arcuate segment of the closure. The ring-like member includes fourth and fifth sidewall portions which are integrally connected at the lower end by a fourth convex portion which is constructed to fit the countersink portion of the closure.
In accordance with the above, a closure is placed between the die and punch. The die and'punch are then moved into working position whereby the third convex portion of the punch contacts and reverses the second arcuate segment of the closure. Upon continuing the closing of the die and punch, the closure is formed around the first and second convex portions of the die and the third convex portion of the punch resulting in a reduction in the diameter of the center panel, a slight increase in the panel height, the provision of three reversing curved segments between the inner wall and the center panel and an increased stiffness for such three reversing curved segments due to work hardening. Thus, in accordance with the present invention, a stronger end results from the individual and combined effects of the above.
A particular advantage of the present invention is its applicability to the great majority of now produced lightweight closures without significantly altering the critical dimensions of such closures thereby requiring no alterations in customers handling equipment..
Accordingly, it is an object of the present invention to provide a closure of thinner metal stock yet which substantially conforms to standard dimensions and buckle resistance thereby providing metal savings and compatibility with presently used customers sealing and filling equipment.
It is yet another object of the present invention to provide a method of increasing the strength of a standard,closure through a single additional working step which is easily instituted in most conventional conversion presses.
It is_'another object of the present invention to provide a method of increasing the buckle resistance of standard closures which requires minimal press forces.

Brief Description of the Drawings

Figure 1 is a top view of a standard end of the ring pull type.
Figure 2 is a cross-sectional view of the standard end of Figure 1.
Figure 3 is a cross-sectional view of an apparatus for providing closures with reversing curved.segments in accordance with the present invention.
Figure 4 is an enlarged view of a portion of the apparatus of Figure 3 in the nonworking position.
Figure 5 is an enlarged view of a portion of the apparatus in Figure 3 in the working position.
Figure 6 is an enlarged cross-sectional view of the portion of a closure worked in accordance with the present invention.

Detailed Description of the Invention

The preferred embodiment described hereinafter is a standard end of the ring pull type. It is understood that the method described in this patent applies to all types and.sizes of ends manufactured for metal beer and soft drink containers.
With reference now to the drawings there is shown in Figure 1 a metal container end 10 of the easy open type. The end 10 is of conventional construction and is provided with a tear portion 12 defined by a score line 14. As shown in the. preferred embodiment, the tear portion is removed by means of a pull tab 16 functionally connected to the tear portion 12 by the usual rivet 18.
As more clearly shown in Figure 2, the end 10 includes a substantially flat center panel 20 surrounded by an annular grooved portion or countersink 21. The annular grooved portion is bounded on the inside by an inner panel wall 24 and on the outside by a chuckwall 26. The chuckwall 26 and inner wall 24 are integrally joined at the bottom of the countersink by an upwardly bowed first arcuate segment 22, having a radius of R1._. The inner wall extends upwardly and inwardly at an angle A from vertical and is integrally joined to the center panel 20 by a downwardly bowed second arcuate segment.25, having a radius of R2. The uppermost extremity of the chuckwall ter- minates in a conventional curl 28 having a substantially flat topped portion 33, a 30/82 .curved section 37 and a terminal end 39 which is turned inwardly - upon the flange of the can to be sealed in the typical double seaming operation. The end has a dome depth "M" measured from the rivet to the uppermost portion of the curl 28 and a'panel height H, measured from the bottom of the grooved portion to the bottom of the center panel 20 adjacent the second arcuate segment 25.
Referring.to Figure 3, a punch 41 and die 43 are illustrated with a closure 10 in place for working. As better shown in Figure 4, the working surface 44 of the die includes a first concave portion 45, having a radius of R4, which terminates in an upwardly extending first sidewall 49 and an outwardly extending first horizontal portion 55. The first sidewall 49 terminates in a first convex portion 47, having a radius R3, which may be integrally joi_'ned to an inwardly extending second horizontal portion 51. A second convex portion 53, having a radius R5, is integrally joined to the outwardly extending first horizontal portion 55 and said second convex portion 53 has a downwardly extending second sidewall 57.
The working surface 58 of punch 41 includes a third convex portion 59, having a radius R6, shaped and aligned for matching with first concave portion 45 on die 43. Inwardly, third convex portion 59 terminates in an upwardly extending vertical third sidewall 61 and outwardly, third convex portion 59 terminates in an outwardly extending third horizontal portion 63. A downwardly extending ring-like member 64 is integrally attached to the punch outward of said third horizontal portion 63 and includes a second concave portion 65, having a radius R7, which is matable with second convex portion 53 of die 43. The ring-like member further includes vertical fourth and fifth sidewalls, respectively referenced 66 and 69, and a fourth convex portion 67, having a radius R8, which is shaped to conform to the countersink of closure 10.
In operation a standard closure is-placed over die 43 as shown in Figure 3. As better shown in enlarged illustrations Figures 4 and 5, as the punch is lowered, third convex portion 59 of punch 41 contacts the second arcuate segment 25 of closure 10. Continued closing of the punch and die to the full working position of Figure 5 results in a reversal of the second arcuate segment and the formation of three reversing segments referenced 30, 31 and 32. The radius of curvature of the three reversing segments, 30, 31 and 32, are smaller than R2 and essentially conform respectively to R5, R4 and R3 on the die and R7 and R6 on the punch. Further, the outermost portion of the substantially flat center panel 20, as indicated by dotted line X, is moved inwardly to the dotted line referenced X' thereby reducing the overall substantially flat center panel diameter. Optionally, the eversion resistance of the closure may be further increased by further lowering the punch such that third horizontal portion 63 coins the substantially flat portion of the closure limited by reversing curves 30 and 31.
Figure 6 illustrates an enlarged view of the reversed segments of reformed closure 10. As is therein shown, each of the segments 30, 31 and 32 cover an arc of about 90 degrees with segment 30 starting at angle A from vertical and providing a transition to about the horizontal, segment 31 starting at about the horizontal and providing a transition to about the vertical and segment 32 starting at about the vertical and providing a second transition back to about the horizontal. In the preferred embodiment the radii of the reversing segments and the radii of R3 through R7 on the punch and die are between about 0.015 and about 0.010 inches, or preferably, the radii of reversing segments 30 and 32, respectively R9 and R11, are about 0.015 inches and the radii of reversing segment 31, R10, is about 0.010 inches.
Referring still to Figure 6, the height of the first transition to horizontal from the bottom of groove 22 is referenced B and the height from said first transition to the center panel is referenced C. The decrease in diameter which the center panel will experience is approximately equal to twice the distance between lines X and X' in Figure 4, which is referenced D. Representative figures for B and C in Figure 6, and D in Figure 4 are respectively, 0.040 + 0.010 inches, 0.020 + 0.10 inches and 0.035 + 0.005 inches. The above would indicate a decrease in center panel diameter of as much as 0.080 inches. The substantially flat portion of the closure between reversing segments 30 and 31 may be coined for added strength to a residual of between about 0.008 inches and about 0.009 inches when reforming a closure which has a thickness of about 0.0122.
In tests run on standard 207.5 shells having a diameter of 2.730 inches and a gauge of 0.0122 inches and a yield strength of 44.4 KSI, the shells were found to exhibit an increase in eversion resistance between about 9.0 PSI and 8.4 PSI when the second arcuate segment of the shell was reversed in accordance with the present invention. The shells, prior to being worked in accordance with present invention, had a panel height H of about 0.066 inches, a dome depth M of about 0.203 inches and an average buckle pressure of about 87.5 PSI. After being worked in accordance with the present invention, panel height increased to about 0.070 inches, dome depth decreased to between about 0.146 and 0.168 inches and average buckle pressure increased to about 96 PSI. Tests run on lightweight shells of standard configuration having a variety of gauges indicate that a commensurate increase in strength will be obtained independent of thickness, although the higher the gauge, the higher the increase.
The higher range of dome depths indicated above resulted from working the closures while maintaining downward pressure against the center panel to reduce doming. This was accomplished by placing a rubber insert in the central portion of the punch which forced the center panel against the horizontal support surface 51 of die 43 while the three reversing segments were formed. Some of the increased strength observed with respect to the present invention may be attributed to this slight doming which occurs when closures are worked in accordance with present invention. Also, a slight straightening of the inner wall results from the present invention, on the order 2 to 4 degrees. Therefore, the A of Figure 2 is reduced by about 2 to 4 degrees.
In accordance with the present invention a standard shell or closure may be strengthened by reversing the second arcuate segment connecting the inner wall to the outer panel and decreasing the diameter of the center panel. This is accomplished by placing a die and punch under and over the closure. The die having a first concave portion and first and second convex portion of substantially the final shape which is desired. The punch is provided with a third convex portion in register with the first concave portion of the die. --The die and punch are then brought into working position causing the third convex portion of the punch to form the second arcuate segment and the upper portion of the inner wall and the outer portion of the center panel around the first and second convex portions of the die resulting in a reversal of the second arcuate segment, a decrease in dome.diameter and a straightening of the inner wall. These effects are accompanied by a slight doming of the center panel and a work hardening of the resulting three reversing segments of the closure. The smaller the radii of the three reversing segments of the closure, the greater the strength; however, if such radii are too small, failure of the closure will be a problem due to fracturing along the radii. An optimum compromise has been achieved where said first and second convex portions of the die have radii of about 0.015 inches and said third convex portion of the punch has a radius of about 0.010 inches.
In its broadest aspects the present invention relates to strengthening a standard closure by reversing the arcuate segment of the closure which joins the center panel to the inner wall. This is preferably accomplished by placing a first downwardly bowed annular forming surface underneath the closure and inwardly from said arcuate segment, placing a second downwardly bowed annular forming surface underneath the closure and upwardly from the bottom of the countersink and moving a third upwardly bowed annular forming surface, from above the closure, downwardly against said arcuate segment causing the reversal of said arcuate segment and the-formation of three reversing segments in conformance with said first and second downwardly bowed annular forming surfaces and said third upwardly bowed annular forming surface. The reformed closure will have a slight dome, with a decreased dome depth, a straightened sidewall and an increase in buckle resistance of about 8 to about 10 percent. Other than the above-stated changes, the dimensional characteristics of the reversed closure will .be substantially identical to a standard closure except that a thinner gauge of material may be used with its attendant cost savings. The decreased dome depth may be minimized by clamping a portion of the center panel in the horizontal during the working process.
An additional advantage of the present invention is that it may easily be instituted in many now-used conversion presses with minimal alterations and an almost insignificant increase in press tonnage.

Claims

1. A method of strengthening a metal closure having a substantially planar center panel, a countersink portion outwardly of said center panel and a peripheral curl outwardly of said countersink portion, said closure having a thickness of under 0.0130 inches, comprising: integrally connecting said countersink portion to said center panel through at least three reversing curved portions having radii of between about 90 percent and about 150 percent of-said thickness.

2.' A method of strengthening a closure having a substantially planar center panel, an annular groove surrounding said center panel bounded on the inside by an integrally connected inner wall and on the outside by an integrally connected chuckwall, a first curved segment at the bottom of said annular groove between said inner wall and said chuckwall and a second curved segment between said inner wall and said center panel, comprising: reforming said second curved segment to form three reversing curved segments.

3. The method of Claim 2 including coining the horizontal portion limited by two of the reversing curved segments.

4. The method of-Claim 3 wherein a portion of said integrally connected inner wall proximate to said second curved segment is also reformed along with said second curved segment.

5. The method of Claim 4 wherein said three reversing curved segments have radii between about 90 percent and about 150 percent of the closure thickness.

6. A method for reforming a closure to increase the closure's buckle resistance, comprising the steps of:

providing a sheet metal closure having a substantially planar center panel, an annular groove around said center panel bounded on the inside by an integral inner wall and on the outside by an integral chuckwall, a first curved segment at the bottom of said annular groove between said inner wall and said chuckwall, a second curved segment between said center panel and said inner wall, a peripheral flange extending radially outwardly from said chuckwall for securement of said can end to a container and exterior and interior surfaces with respect to the exterior and interior of a container when said closure is secured thereon;

supporting said center panel of said closure against the interior surface thereof with a first convex surface spaced inwardly from said integral inner wall and having a first radius;

supporting said integral inner wall of said closure against the interior surface thereof with a second convex surface spaced downward from said second curved segment and having a second radius; and

reforming said closure by moving a third convex annular surface having a third radius against the exterior surface of the second curved segment and continuing said movement until said closure substantially conforms to said first, second and third radii.

7. The method of Claim 6 wherein said first, second and third radii are on the order of magnitude of said sheet metal closure thickness.

8. The method of Claim 7 wherein said sheet metal closure has a thickness of under 0.0130 inches and said first, second and third radii are between about 0.010 inches and about 0.015 inches.

9. A method of increasing the buckle resistance of a closure having a substantially flat center panel, a grooved portion around said center panel bounded on the inside by an integral inner panel wall and on the outside by an integral chuckwall, a first upwardly bowed arcuate segment joining said chuckwall to said inner panel wall and a second downwardly bowed arcuate segment joining said center panel to said inner panel wall, comprising: reducing the diameter of said center panel by reforming said second downwardly bowed arcuate segment and the adjacent portion of the center panel and the inner panel wall to form three reversing curved segments.

10. The method of Claim 9 wherein said reforming includes the steps of:

placing a first annular convex forming surface underneath said closure and inwardly of said second arcuate segment, said first annular convex forming surface having a downwardly bowed arcuate portion;

placing a second annular convex forming surface outwardly of said first forming surface and adjacent said inner panel wall, said second annular convex forming surface having a downwardly bowed arcuate portion;

placing a third annular convex forming surface on top of said closure and adjacent said second arcuate segment, said third annular convex forming surface having an upwardly bowed arcuate portion; and

moving said third annular convex forming surface downwardly into contact with said second arcuate segment and continuing said movement until said closure substantially conforms to the bowed arcuate portions of said first; second and third forming surfaces.

11. The method of Claim 10 including the steps of: coining said portion of the closure between two of said reversing curves by providing said second annular convex forming surface with an integrally connected inwardly extending horizontal surface; providing said third annular convex forming surface with an integrally connected outwardly extending horizontal surface; moving said outwardly extending horizontal surface downwardly in conjunction with said third annular convex forming surface; and working said portion of the closure between said inwardly extending horizontal surface and said outwardly extending horizontal surface.

12. The method of Claim 11 wherein the radii of the arcuate portions of said-first, second and third forming surfaces are between about 0.010 and about 0.015.

13. The method of Claim 11 wherein the diameter of said center panel is reduced at least 0.05 inches.

14. A method of increasing the buckle resistance of a closure having a center panel, a grooved portion surrounding said center panel bounded on the inside by an integral inner panel wall and an outside by an integral chuckwall, a first upwardly bowed arcuate portion joining said inner panel wall to said chuckwall and a second downwardly bowed arcuate portion joining said inner wall to said center panel, comprising: reversing said second arcuate portion to form three reversing curves connecting said inner wall to said center panel and coining the horizontal portion limited by two of said reversing curves.

15. The method of Claim 14 wherein said reversing is accomplished by: placing first and second downwardly bowed annular forming surfaces underneath said closure and a third upwardly bowed annular forming surface above said closure, said first annular forming surface being positioned adjacent the interior surface of said closure and just inwardly of said second arcuate portion, the second annular forming surface being positioned adjacent the interior surface of said closure by the inner panel wall and the third annular forming surface being positioned between said first and second annular forming surfaces and above said closure, and causing relative longitudinal motion between said third annular forming surface arid said first and second annular forming surface whereby said third annular forming surface will contact and reverse said second arcuate portion around said first and second annular forming surfaces.

16. The method of Claims 7, 10 or 14 including the steps of supporting a portion of said center panel along the interior surface and clamping said portion from the exterior surface.

17. A closure comprising a peripheral curl, a central panel, a countersink between said peripheral curl and said central panel, said countersink being integrally connected to said central panel through three reversing arcuate portions having radii between about 90 percent and about 150 percent of the closure thickness.

18. A closure comprising: a substantially planar center panel, a countersink surrounding said center panel and bounded on the outside by an integral chuckwall and bounded on the inside by an integral inner wall, and three reversing integral curved portions between said inner wall and said center wall, said curved portions having radii of between about 90 percent and about 150 percent of the thickness of said closure.

19..The closure of Claim 18 wherein said closure has a nominal thickness of under 0.0130 inches and said three reversing integral curved portions between said inner wall and said center wall have radii of between about 0.010 inches and about 0.015 inches.

20. The closure of Claim 19 wherein said closure is constructed of aluminum.

21. The closure of Claim 17 or 18 wherein said countersink has a radius of about 0.030 inches.

22. The closure of Claim 21 wherein one of said reversing portions terminates in a horizontal plane.

23. The closure of Claim 21 wherein said two of said reversing integral curved portions are integrally joined by a substantially flat portion which has a reduced thickness relative to the rest of the closure.