US3688718A

US3688718A - Method and apparatus for scoring metal container ends

Info

Publication number: US3688718A
Application number: US868778A
Authority: US
Inventors: Howard D Schrecker
Original assignee: Aluminum Company of America
Current assignee: Howmet Aerospace Inc
Priority date: 1969-10-23
Filing date: 1969-10-23
Publication date: 1972-09-05
Anticipated expiration: 1989-09-05
Also published as: ZA706790B; FR2065484B1; NL7014886A; FR2065484A1; CA926215A; CH531376A; SE382765B; ES384824A1; GB1329583A; JPS5114949B1; DE2051697A1

Abstract

A method and apparatus for scoring a metal container end to provide a tear-out panel, wherein the scoring is accomplished with a greatly reduced tendency for any internal protective coating on said end to be damaged and for the residual metal in the score line to fracture. During the scoring operation the container end is supported on an anvil die having an arcuately domed rib thereon which, in cooperation with the advance of the scoring indenter, works the metal in the lower portion of the metal sheet and distributes the working stresses normally produced in the metal during the scoring operation.

Description

United States Patent Schrecker Sept. 5, 1972 [54] METHOD AND APPARATUS FOR 3,359,773 12/1967 Stuchbery ..83/6 SCORING METAL CONTAINER ENDS 3,451,367 6/1969 Hendrickson ..113/121 Inventor: goward Schrecker, y Park, FOREIGN PATENTS OR APPLICATIONS a.

' 488,984 12/1918 France ..1-13/15 A [73] Assignee: Aluminum Company of America, 2,

Pittsburgh, Pa. Primary Examiner-Richard J. Herbst Assistant Examiner-Michael J. Keenan [22] Flled' 1969 Attorney-Hutchinson & Milans [21] Appl. No.: 868,778

[57] ABSTRACT [52] US. Cl. ..113/15 A, 113/80 DA A method and apparatus for scoring a metal container [51] Int. Cl. ..B21d 51/26 en to provide a ear-out panel, wherein the scoring is [58] Field of Search-.1 13/ 15 R, 15 A, 80 D, 80 DA, accomplished with a greatly reduced tendency for any 1 3 121 R, 21 A, 121 220 5 internal protective coating on said end to be damaged and for the residual metal in thescore line to fracture. 5 References Cited During the scoring operation the container end is supported on an anvil die having an arcuately domed rib UNITED STATES PATENTS thereon which, in coo eration with the advance of the d 1? th tal th 1 rt sconng 1n enter, wor s e me m e ower po ion 4 of the metal sheet and distributes the working stresses 3 563 199 2/1971 w lfe .1111111111111111111113/121 c "mmapy pmduced the metal during the swing 3,507,418 4/1970 Saunders ..220/54 operat'on' 3,554,400 1/1971 Bozek ..220/54 7 Claims, 6 Drawing Figures PATENTEB SEP 5 I972 3 6 88 7 18 SHEEI 1 BF 2 INVENTOR HOWARD D. SCHRECKER BY 164mm WM ATTORNEYS PATENTEDsEP 5 I972 3 6 88.718

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2 or 2 1 .4 j INVENTOR HOWARD D. SCHRECKER 06 m M Q ATTORNEYS METHOD AND APPARATUS FOR SCORING METAL CONTAINER ENDS BACKGROUND OF THE INVENTION This invention relates generally to sheet metal ends for containers and to a method and means for making the same, and in particular to the art of forming container ends having a tear-out panel defined by a score pattern, which panel may be removed manually without the use of a separate tool or a can opener, and to the method and means for scoring such container ends.

Container ends for the so called easy opening cans, such as cans for beer, carbonated soft drinks, fruit juices, and the like, are usually made of metal, preferably aluminum or an alloy thereof, and vary in thickness from about 0.008 inch to 0.015 inch. It is common practice to provide the inner surface of the containers, as well as the container ends, with protective coatings, particularly when the containers are to be filled with carbonated beverage, fruit juices and other liquids which might react with and/or attack the metal of the container. For easy severance of a tear-out panel it is necessary to score most metals deeply enough to leave a thin residual web of metal along the score line. It has been found, however, that reducing the thickness of the sheet metal by scoring to leave a residual which is easily torn often results in cracking or fracturing of the protective coating on the inner surface of the metal along the score line due to stresses and high compressive loads developed by virtue of the displacement of the metal during the scoring operation. In these instances, damage to the internal coating exposes the bare metal of the container to the contents of the container, which may impair the quality of the contents of the container and may cause corrosion of the exposed metal.

SUMMARY OF THE INVENTION A purpose of the present invention is to reduce the likelihood of damaging the coatings on the inner surface of container ends during the scoring operation. This is accomplished by a new method of scoring which employs novel apparatus, as hereinafter described.

The invention provides a simple and effective method and apparatus for scoring container covers or ends and simultaneously working the inner portion of the metal in the container end whereby the stresses developed in the metal during the scoring operation are distributed to greatly reduce the tendency for the protective coating on such ends to be damaged or for the metal residual in the score lines to fracture.

It is a further object of this invention to provide a container end scored to define a removable panel by means of a novel anvil having an arcuately domed rib thereon which works the metal in the inner portion of the sheet and distributes the working stresses therein.

BRIEF DESCRIPTION OF THE DRAWINGS The invention in respect of the foregoing and other features and advantages will be better understood from a consideration of the detailed description which follows, taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a top plan view of a container end having a tear-out panel therein defined by a weakening line scored by the method of the invention;

FIG. 2 is a fragmentary sectional view through a conventional scoring die set of the prior art;

FIG. 3 is a fragmentary sectional view, on a somewhat larger scale of a scoring die set employed in the preferred form of the present invention;

FIG. 4 is a fragmentary sectional view through a scoring die set of a modified form of the present invention;

FIG. 5 is a fragmentary section view through a container end scored in accordance with the present invention; and

FIG. 6 is a fragmentary section view through a container end scored by a conventional method. DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. I, numeral 20 generally designates a typical easy opening container end panel that may have a score line-defined tear-out portion 22 formed therein in accordance with the invention, although not intended to be limiting of the configuration of container ends or tear-out portions that may be so formed. Container end 20 has an attachment flange 24 for attaching the end to a container body (not shown) in a conventional manner, and has a pull tab 28 attached to tear-out portion 22 by means of an integral rivet 30.

In the prior art, scoring container ends regardless of what score pattern might be desired, has been effected by means of a stamping or scoring die set, similar to that shown in FIG. 2. The set comprises an upper score die 10 and a lower anvil die 11, the latter having a flat upper face 12 that affords anvil support to the container end panel 13 when seated thereon. The upper die 10 has a scoring indenter l4 projecting down from its lower face 15 toward the lower anvil die, said indenter formation duplicating in contour the tearout panel contour or configuration. For extended die life and good scoring characteristics, the scoring indenter has in vertical, transverse, cross-section, a truncated V- shape with a flat lower or working face 16 to effect displacement scoring. V-shaped score indenters have also been employed, but at a sacrifice of tool life. Scoring part way through the thickness of the metal, leaving a uniform residual about 0.004 inch thick is normally desired in aluminum container ends for ease of severance of the tear-out panel, although the residual thickness may vary depending on the particular application. The dimensions of the working face 16 and the height of the indenter to achieve the desired shape and depth of the score will also depend upon the type of metal or alloy used and the thickness of the metal to be scored.

It has been found in scoring with such a scoring indenter, as described above, that metal is squeezed or extruded in a direction substantially normal to a vertical plane longitudinally bisecting the scoring indenter as illustrated by the arrows in FIG. 2. This extrusion of the metal during the scoring operation caused by the indenter sets up uncontrolled, and highly localized, stresses in the metal. When the container ends are provided with internal protective coatings 18 of the type including epoxy, epoxy phenolic or vinyl resins, these coatings are often damaged or fractured at the point 19 by the above-mentioned uncontrolled, and highly localized, stresses set up in the metal during the scoring operation. Such damage to the protective coatings usually occurs even though the residual has not fractured. Needless to say, such fractures of the residual and damage to the protective coating are to be avoided as it will expose the bare metal of the container end to the contents of the container which will obviously impair the quality thereof. With the bare metal exposed, the contents of the container may also attack the metal and produce perforations in the container end.

The purpose of the present invention is to minimize such damage to the protective coating now experienced in conventional scoring operations. This is achieved by a new method of scoring which works the metal in the bottom half of the sheet in the vicinity of the score, which working distributes the stresses produced in the metal during the scoring operation and results in greatly reducing the tendency of the coating to fracture.

In the new method of scoring, an arcuately domed rib is employed on the lower die member, which effectively works the metal of the lower half of the sheet metal to distribute the above-mentioned stresses. This will now be described with reference to FIG. 3 where a preferred embodiment of the apparatus is disclosed.

The scoring die set of FIG. 3 comprises an upper die member 110 and a lower die member 111. The upper die carries a scoring indenter 114 projecting downwardly towards the lower die member. The indenter tool preferably has a truncated V-shaped crosssection in profile and a flat lower or working face 116 similar to that previously described. The lower die 111 has its upper supporting face 112 provided with an arcuately domed rib 200 aligned with the scoring indenter 114, as shown, and having the same contour or outline as that of the indenter. A container end panel as generally designated by the numeral 113 may have a protective coating 118 on its lower or inner surface and is seated upon and supported by the dome surface 200 of the anvil die.

As the upper die 110 is lowered, the indenter engages and penetrates the metal sheet 113 producing the stresses previously mentioned, but in this instance the arcuate surface of the supporting die works the metal of the sheet in the lower half thereof to distribute the stresses. The distribution of stresses greatly reduces the tendency for the protective coating to fracture or become damaged in the scoring operation. This distribution of the stresses by the employment of the arcuate anvil may also greatly reduce the formation of cracks in the residual metal of the score.

It has been determined that with an indenter 114 having a nominal width at the face 116 of 0.0040 i 0.0005 inch, the radius of curvature 201 of the domed anvil is preferably about 0.010 inch, but may be as much as 0.015 inch. If the radius of curvature is much less than 0.010 inch, it has been found that the metal may be scored by the rib rather than being worked as is desired in the present invention. Rib 200 is preferably at least 0.0020 inch in height and has approximately a 0.010 inch radius 203 at the juncture between its domed surface and the supporting face 1 12.

With the proper coatings, the method of the invention will give a score residual in the 0.0035 inch to 0.004 inch thickness range in aluminum container ends nominally about 0.010 inch thick without fracturing of the internal coating. Typical coatings for such sheet metal ends have included epoxy, epoxy phenolic or vinyl resins, among others, and may be baked or otherwise cured on the ends. A typical curing operation may be conducted at approximately 400 F. for approximately 10 minutes per side, but may be conducted at various other temperatures and durations depending on the coating, etc.

Referring to FIGS. 5 and 6 which illustrate the grain structures produced in container ends scored by the improved method (FIG. 5) and by the conventional method (FIG. 6), the difference between such grain structures clearly shows the difference in the stresses in the ends. Whereas the grain structure in the end scored by the improved method is of uniform orientation and spacing adjacent the inner surface of the ends, and has an area of converging grain orientation intermediate the top and bottom surfaces of the residual metal, the grain structure in the end scored by conventional methods shows an area of converging grain orientation near the bottom surface of the end. These areas of converging grain orientation represent the areas of maximum stresses in the residual metal of the container ends. As illustrated by the arrows, the metal in the areas of maximum stress is compressed in the vertical and extruded horizontally outward. In the end scored by the conventional method, the coating on the metal at the point of maximum stress is similarly highly stressed and is subject to rupture as illustrated. Conversely, in the end scored by the improved method, the metal and coating on the inner or lower surface of the residual is under much less stress and is much less likely to be damaged.

It is seen from the grain structure that the arcuately domed rib of the improved scoring tools has not severed the metal in the lower portion of the sheet, but

has compressed or worked the metal over such arcuately domed surface to produce a line of compression in the under surface which is aligned with the score line in the upper surface of the sheet. It is also noted that with the metal worked over the surface of the rib 200 as shown in FIG. 3, the pressure of the rib against the sheet is distributed over the surface and does not damage the coating on the sheet.

FIG. 4 discloses a modified tool set which is also effective in reducing damage to coatings and the formation of cracks in the residual metal. While this form of the invention is not as practical or desirable, in that the indenter tool 210 of the upper die is of special design embodying a special scoring tool 214, the arcuately domed area 206 has been found effective in working the metal of the sheet and distributing the stresses set up by the indenter tool. It is noted that the arcuately domed rib 206 is higher than dome 200 shown in FIG. 3. It is believed that differences in the height of such rib is not critical to the practice of the invention as long as it is at least 0.0020 inch high since the metal working is effected primarily by the upper portion only of the rib.

While the forms of apparatus above described are effectively adapted to fulfill the objects stated and to carry out the new method of scoring container ends, it is to be understood that the invention is not intended to be confined to the particular die structures disclosed, inasmuch as they are susceptible of limited modification without unduly departing from the scope of the appended claims.

I-Iaving thus described my invention and certain em bodiments thereof, I claim:

l. A method of scoring a metal container end to provide a tear-out panel therein comprising the steps of:

a. supporting a container end on an anvil die having a rib thereon with an arcuately domed upper surface and the outline of the tear-out panel to be defined, said rib having a radius of curvature in the range of 0.010 to 0.015 inch;

b. moving a scoring indenter against the upper surface of the container end opposite the arcuately domed rib; and

c. scoring the container end with the indenter to the desired depth while simultaneously working the lower portion of the metal sheet to effect distribution of the stresses normally produced in the metal during the scoring operation.

2. A method of scoring a metal container end as set forth in claim 1 in which the metal container end has a protective coating on its inner surface.

3. A method of scoring a metal container end as set forth in claim 1 in which the formation of the score line is effected by means of a scoring indenter having a truncated V-shape cross-section.

4. A method of scoring a metal container end as set forth in claim 3 wherein the flat face of the truncated V-shaped scoring indenter is 0.0040 I 0.0005 inch in width.

5. An apparatus for scoring a thin metal container end to provide a tear-out section, comprising an anvil die on which the container end is supported in scoring position, a reciprocable indenter movable towards and away from said anvil die, an arcuately domed rib on said anvil die facing said scoring indenter and supporting the container end, said arcuately domed rib having a radius of curvature in the range of 0.010 to 0.015 inch and cooperating with the scoring indenter during scoring of the container end to subject the lower portion of the metal of the container end to a working action to distribute the stresses induced in the scoring operation.

6. An apparatus as defined in claim 5 wherein the scoring indenter has a truncated V-shape cross-section.

7. An apparatus as defined in claim 6 wherein the flat face of the truncated V-shaped scoring indenter is 0.0040 0.0005 inch in width.

Claims

1. A method of scoring a metal container end to provide a tearout panel therein comprising the steps of: a. supporting a container end on an anvil die having a rib thereon with an arcuately domed upper surface and the outline of the tear-out panel to be defined, said rib having a radius of curvature in the range of 0.010 to 0.015 inch; b. moving a scoring indenter against the upper surface of the container end opposite the arcuately domed rib; and c. scoring the container end with the indenter to the desired depth while simultaneously working the lower portion of the metal sheet to effect distribution of the stresses normally produced in the metal during the scoring operation.

4. A method of scoring a metal container end as set forth in claim 3 wherein the flat face of the truncated V-shaped scoring indenter is 0.0040 + or - 0.0005 inch in width.

7. An apparatus as defined in claim 6 wherein the flat face of the truncated V-shaped scoring indenter is 0.0040 + or -0.0005 inch in width.