Method of making pop-in container closure

Abstract

A container lid, by a sequence of forming operations including the steps of shear-coining over preferably transversely convex die surfaces to provide a fractured but integral wall section, and usually a swedging, provides a peripherally dilated button portion which adequately resists internal fluid pressures, yet is disruptable by external finger pressure urging the button portion inwardly. The button may be provided with a non-disruptable or hinge portion, or formed to enable it to fall into the container, the button in either case not being separately disposable. No harmful closure edges are exposed by the method herein disclosed.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of Application Ser. No. 331,844, filed Feb. 12, 1973 in the names of Walter Lovell and Frederick G. J. Grise, and relating to "Environmental Pop-In Button Closure for a Can", now abandoned.

Description

BACKGROUND OF THE INVENTION

This invention pertains to a method of making a tabless, push-in type closure for the sheet metal lid of a container adapted to retain fluid under pressure.

In the prior art, several different closures of the so-called "pop-in" type have been proposed. Some required a leverage tab or lifting projection and scoring in the lid, and others such as disclosed, for instance, in U.S. Letters Patent 3,227,304 to Asbury, or U.S. Pat. No. 3,334,775 to Klein et al., specify a score line in a flat region, or a score line in a wide angle notch, but in a fold such as to preclude reliable operation or uniformity in manufacture. When the latter types can be "pushed-in" they commonly have inadequate strength to resist internal pressure such as may be present in a carbonated beverage or a pasteurized fluid.

An easy-open lid construction providing no separately disposable parts is generally recognized as very desirable provided it can safely retain fluid pressures and yet be uniformly reproduced by a practical method.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of this invention to provide a simple, economical method for making reliable push-in closures in sheet metal container lids.

More specifically, another object of this invention is to provide improved technique for forming and, in effect, reinforcing the margins of push-in button portions of can lids whereby fluids can be safely contained yet manual access be readily available by rupture of the margins.

To these ends, and as herein illustrated, a metal lid is first formed with a recess providing a button having inner and outer bounding walls merging in a peripheral ridge on one side of the lid. Next a coin-shearing operation is performed, preferably in a convex portion of the outer button wall, to provide (as per one mode of the invention.) a peripheral indentation having convergent angular faces and a fractured but integral section extending through the metal of the wall. Then, while the thus indented wall is backed by a die having complemental (preferably convex) curvature, a swedging operation against the peripheral ridge dilates the metal of the outer wall to force one of the indentation faces into partly overlapping relation to the other face, by a few thousandths of an inch over its length, and enables the metal in the locality of fracture to spring substantially closed. A lacquer coating may thereafter be applied for sealing, if desired, to the button internal surface, but is often unnecessary.

The swedging step can sometimes be omitted following shear-coining. Thus, for example, in low-pressure can construction such as might be used for oils, soups, etc., a narrower coining face (on order of only 0.001-0.002 inch) may be employed producing no fracture. In general, however, usage of shear-coining dies having a coin face wider than 0.002 inch, and whenever a fractured but integral section is incurred, necessitates the added step of swedging.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the invention will now be more particularly described in connection with an illustrative embodiment and with reference to the accompanying drawings thereof, in which;

FIG. 1 is a perspective view of one product afforded by use of the invention, a can top having a circular closed closure button hinged to the lid;

FIG. 2 is a view similar to FIG. 1 and showing the button pushed inwardly;

FIG. 3 is an enlarged diametral section showing a padded coin-shearing die and a back-up die about to commence operation on a lid, the button portion of which has previously been struck up from the inside, or the surrounding material has been depressed relative to the lid by a drawing die;

FIG. 4 is a section similar to FIG. 3 showing the button and parts at bottom or peripheral partial fracture opening stage;

FIG. 5 is a section similar to FIG. 4 showing the parts at a subsequent released or partial fracture reclosing stage;

FIG. 6 is a section similar to FIGS. 3-5 but indicating the final stage wherein a swedging die dilates a wall of the shear-coined indentation and tensions the fracture web over a convex back-up surface;

FIG. 7 is a further enlarged detail view, predicated on a typical photomicrograph showing the released button wall having a sprung together partial fracture and a dilated indentation face at least partly overhanging the wall fracture, and a lacquer coating applied thereto; and

FIG. 8 is a perspective view corresponding in part to a portion of FIG. 2 and showing the closure, made by the method herein described, being opened.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following disclosure it will be appreciated that certain critical physical distinctions resulting from method steps obtaining in this case over prior art procedures are dimensionally small and possibly to the point of being invisible to the naked eye. It will nevertheless be understood, as hereinafter pointed out, that despite the small dimensional changes involved, the significance of the novel steps to be described is real and of considerable importance from both the standpoint of manufacturing advantage and improved closure performance.

FIG. 1 shows a conventional can 10 having a rim 12, usually the chime of an otherwise planar sheet metal lid 14 (FIGS. 1-8). A pop-in closure 16 for instance of circular shape like a button, to be manually pressed inwardly for opening the container lid is preferably positioned adjacent to the chime. It will be understood that neither the lid or its button portion 16 need be circular. The lid 14 is first formed as by a die (not shown) to provide its button portion 16 with a surrounding continuous depression 18 bounded by inner and outer walls 20,22 respectively. Preferably the flat of the integral button portion 16 remains only slightly depressed with respect to the general plane of the lid 14 so as to readily indicate the locality to be opened inwardly.

It will be noted (FIGS. 3-5) that the button walls 20,22 to be processed by steps hereinafter explained are desirably partly convex in section and merge in a rounded trough 24. Walls 20,22 simply inclined to the plane of the lid without being convex may in some cases be satisfactorily employed but are not usually preferred. Regardless of the care with which the sheet metal is originally made, there is no real control over its grain structure. Accordingly, scoring a closure as thin as that found, for instance, in beer cans requires an extra degree of penetration and sizing control nicely afforded by the mentioned wall convexity in order to prevent leakage on the one hand and yet, on the other hand, insure manual accessibility to the container contents without requiring extra finger strength. While it has been found that the invention may be practiced on the inner wall 20, and whether it be transversely arcuate or straight and inclined to the lid, it is generally preferable to operate on the convex portion of the outer wall 22, and usually at least about a third of its length, as will hereinafter be explained.

Assuming the lid button 16 to be substantially in the configuration shown in FIG. 3, the outer wall 22 is next shear-coined lengthwise in its convex periphery. For this purpose an upper back-up die 26 (FIGS. 3-6) has an annularly projecting rounded ridge 28 formed to fit in and engage the trough 24. A lower shear-coining die 29 (FIGS. 3-5) is arranged to cooperate coaxially with the back-up die 26, and has a vertically disposed cutting edge 30, an angularly related narrow coining face 32, and a longer inclined coining face 34 extending outwardly from the face 32. The coining face 32 commonly will have a uniform width which is a fraction of the thickness of the lid, depending on the particular sheet metal and the extent of fracture, if any, desired, face width being greater for tougher metals. In this connection it may be noted that wall fracture, i.e. providing a fractured but still integral peripheral section, as a result of the shear-coining step is generally desired, unless the can tops to be made are for low pressure usage such as containment of oils, soups, etc. For the low pressure applications coin face 32 may be narrowed to approximately 0.001 to 0.002 inch without causing fracture and hence allowing swedging to be omitted; otherwise swedging is required as will later be explained.

To clampingly hold the button 16 against bodily shifting laterally on the die ridge 28 when the convex portion of the outer wall 22 is peripherally shear-coined as shown in FIG. 4 during relative approach of the dies 26,29, the latter die preferably has a yieldingly compressible rubber pad 36 of uniform thickness nested within the cutting edge 30.

As shown in FIG. 3, the coining face 32 axially tapers from a maximum projection above the pad 36 on the right side of the die periphery to a minimum on the left side substantially flush with the pad 36. In this manner the periphery of the outer wall 32 is variably shear-coined, providing a controlled indentation extending substantially all around the button 16 but of tapering lesser depth in the left-hand portion than in the right-hand portion as shown in FIG. 4. The depth of the shear-coining is usually selected to insure that the coining indentation concomittantly causes a partial fracture 38 (FIGS. 4-7) all the way through the metal and extending for roughly from about 120.degree. to 180.degree. around its periphery. This fracture serves as an easily started locality of rupture in the complete button. The locality of no indentation, generally opposite to the locality of greatest indentation and/or fracture, will serve as a hinge H (FIGS. 2 and 8) when the button is pushed into the can 10.

It is to be noted that shear-coining the button wall 22 over a transversely convex back-up die surface, i.e. outwardly of the center line of the annular die ridge 28, provides both a refined control of the desired indentation and degree of the resultant fracture 38, and an improved service life for the shear-coining die 29. The latter is probably largely due to the freedom of the metal in the wall 22 to flow as necessary during tensioning outwardly over the curved surface of the die 26. It will be understood, nevertheless, that this invention may be practiced on either of the walls 20 or 22 and whether they be convex, concave or straight but inclined to the lid.

When the dies 26,29 are relatively separated heightwise as shown in FIG. 5 after shear-coining, resilience of the pad 36, which had been distorted as indicated in FIG. 4, frees the lid for the last step about to be described. No wall material has been removed. It will be understood that the nearly 90.degree. angle at the bottom of the peripheral indentation or groove initially imparted by the convergent cutting edge 30 and the adjacent coining face 32 as shown in FIG. 4 is partly reduced as indicated in FIG. 5 when relative die retraction permits residual tension in the wall material to be dispelled. Accordingly, mating irregular metal at the fracture 38 springs substantially closed without appreciaable misalignment of confronting edges. No complete separation is incurred at the bottom of the wall indentation.

The final and perhaps most important step in this button forming process, assuming the fracture 38 was incurred, will next be described with reference to FIGS. 6 and 7. With the backing die 26 still in its work-engaging position, a swedging die 40 (FIG. 6) having a flat face 42 compressively bears on the walls 20,22 at the annular locality of their convergence. This imposes a flat 44 on the periphery of the button 16 opposite to the depression 18 and causes metal of the indented wall 22 to flow outwardly. More significantly, and as better shown in FIG. 7, as a consequence of the swedging an indentation face 46 of the wall 22 is dilated and hence at least partly overlaps a convergent indentation face 48 imparted by the coin-face 32. This overlap which may be on the order of about two to four thousandths of an inch on opposite sides of the button respectively, is disposed outwardly of the fracture 38. The swedging therefore stiffens the button wall in the vicinity of the fracture, and generally appears to close the partial fracture along its length thus locking the closure 16 disruptably to the lid 14. A lacquer coating 50 (FIG. 7) may be applied at least to seal the fracture and the indentation on the inside of the completed lid.

Referring now more particularly to FIGS. 2 and 8, when the hinge H of the button 16 is adjacent to the can chime, suitable indica, for instance an arrow (not shown), may indicate the diametrically opposite locality of deepest shear-coining and most complete but still partial fracture where external finger pressure on the button can most easily start rupture. Once rupture has been started along the fracture, continued tearing of the metal along the remainder of the wall indentation requires less pressure. It will be understood that if internal hinging of the button H is not desired, a complete 360.degree. shear-coining and fracture as herein explained will enable the closure to be separated inwardly and thereby deposited within the can so as not to be separately disposable.

From the foregoing it will be clear the swedging step provides a circumferential "growth" or dilation of the button 16, expanding its initial transverse dimension or diameter D (perhaps on the order of about six to eight thousandths of an inch total) outwardly of the fracture 38 to overlap a part of the adjacent indentation wall as indicated in FIG. 7. Accordingly internal fluid pressure in the can tends only to close the wall indentation and the fracture 38 but has no significant disrupting effect thereon. At no time during closure formation is an edge of the closure separated from a "mating" edge of the lid; the edges consequently are maintained in exact alignment insuring restoration of sealing relation when they are forced together by the swedging.

The described method of manufacture is applicable to various shapes of buttons and containers, and is economically practiced with a high degree of precision control and hence uniformly reliable results.

Claims

Having thus described my invention what I claim as new and desire to be secured by Letters Patent of the United States is:

1. The method of making a manually disruptable pop-in type of button closure for a planar metal container lid comprising:

a. depressing the lid in a generally closed, continuous path to provide an integral button portion having inner and outer bounding walls respectively including opposed parallel surfaces inclined to the plane of the lid,

b. shear-coining one of the bounding walls to form a lengthwise indentation in one of said inclined surfaces thereof and concommitantly produce a fractured but integral section extending between the other of said surfaces and the bottom of the indentation for a portion of its length, and then

c. swedging the indented bounding wall to dilate a face of the indentation at least partly outwardly relative to said fractured section and thereby effectively lock the closure to the container lid.

2. The method of claim 1 wherein the outer bounding wall is formed in part with transverse convexity, and the shear-coining is effected in the outer convex surface of the outer wall in cooperation with a similarly convexly shaped back-up die whereby the metal of the wall adjacent to the fracture is constrained to flow outwardly peripherally partly to reclose said fracture.

3. The method of claim 1 wherein the shear-coined indentation is formed with an axially tapering die to incur the fracture in diminishing degree as it approaches a non-fractured hinging locality of the button.

4. The method of making a manually disruptable pop-in type of button closure for a sheet metal container lid comprising:

a. depressing a portion of the lid with a tool having a rounded ridge to form transversely convex inner and outer bounding walls at least partly defining a button portion lying substantially in the plane of the lid,

b. while the remainer of the lid is unrestrained, shear-coining the outer wall lengthwise with varying penetration in its transversely convex portion over a complemental back-up die to produce a fractured but integral section in an inner portion of the outer wall, and after irregular conjoint edges of the fractured section have substantially sprung together to dissipate tension incurred during metal flow of the shear-coining,

c. swedging the locality of convergence of said walls against said die to dilate the outer wall and thus urge the metal on both sides of the fracture into closed association.

5. The method of claim 4 and the additional step of coating at least the fractured locality of the button portion with a sealant.

6. The method of claim 4 wherein step b includes yieldingly clamping the button portion against said rounded ridge by means of a resillient pad nested in a shear-coining die between its cutting edges.

7. The method of making a manually disruptable pop-in type of button closure for a container lid comprising:

a. forming a continuous depression and consequent ridge in the lid largely to define the closure and the shape of its outer sectionally convex boundary wall,

b. longitudinally shear-coining said wall in its sectionally convex portion with a tool having a cutting edge, an adjacent coining face disposed substantially at 90.degree. to said edge and having uniform width a fraction of the thickness of the lid, and an angularly related coining face concommitantly to open an indentation and provide a fractured but integral section extending from the indentation, and

c. partly reclosing said indentation and the material of said fracture by a compressive swedging blow striking against said ridge and/or the wall material adjacent thereto thereby rupturably securing the closure to the lid.

8. The method of making a manually distruptable pop-in type of button closure in a sheet metal container lid comprising:

a. forming a depression in the lid having continuous inner and outer bounding walls convergent in a ridge,

b. while a convex back-up die surface engages the lid on one side thereof at the surface of said lid depression and along at least a portion of said outer wall, indenting the latter lengthwise with a die having an angularly related cutting edge and coining face to provide a fractured but integral section in the outer wall along at least a portion of its length, the width of the face being a fraction of the lid thickness and said integral section being cold worked by the momentary partial separation induced by the coining face, and

c. then swedging said ridge against said back-up die surface partly to close said indentation and force the mating metal of the fractured but integral section to flow into closer substantially sealed association.

9. The method of making a manually disruptable pop-in type of button closure in a sheet metal container lid, which comprises:

a. forming a continuous trough and opposing rounded ridge protruding from the lid surface and defining a major portion of a relatively depressible closure, the closure having an outer wall portion sloping to the lid surface and not folded upon itself, and

b. shear-coining said outer wall unfolded portion along a line spaced between the lid surface and the crest of the ridge against a convexly sectioned back-up die to form an indentation channel of approximately 0.001 inch to 0.002 inch in width and extending lengthwise in said wall and tapering from a maximum depth providing a locality of incipient fracture to a minimum depth, and leaving a locality of no indentation providing hingeable connection of the button to the lid.

10. The method of making a manually disruptable pop-in type of button closure for a low-pressure metal container lid comprising:

a. depressing the lid in a closed continuous path to provide an integral button having a sectionally non-sinuous wall including opposite parallel surfaces inclined to the lid, and

b. shear-coining the wall with an axially cooperating tool and die acting peripherally along a line spaced from the general plane of the lid to form a lengthwise, narrow, and angular indentation in one of said inclined surfaces, the width and angular disposition of a coining face of the tool being selected to momentarily induce local tension nearly but not quite sufficient to incur concommitant partial fracture of the wall portion worked against the die between the bottom of the indentation and the other of said surfaces.