Closure end made of sheet

Details Closure end made of sheet Closure end made of sheet

1999-09-20

2001-05-01

Moy, Joseph M. (Department: 3727)

Receptacles

End wall structure

One-piece side and end wall

C220S608000

Reexamination Certificate

active

06223931

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for further treating a closure end made of sheet, particularly a folding end for beverage cans or the like. The tool for carrying out the process is also concerned.
2. Prior Art
Such an end is known from U.S. Pat. No. 3,441,170, where the radius of curvature itself is reduced in thickness from the inner side of the end thereby forming a bead (“coined bead”) . In this way, kind of a joint is created between the inner leg of the groove and the central panel portion to restrict the bulging of the end to the central panel portion so as to reduce the tensile forces acting radially inwardly upon the core wall of the end. At this joint (coined bead), the central panel portion bulging more strongly under the increased internal pressure, is pivoted to the core wall such that the bulging does not affect or only affects slightly the latter as regards its vertical orientation.
EP 88 968 A1 discloses a similar measure in which, starting from the radially inner edge of the radius of curvature′, the end sheet is externally deformed over an area of the radius of curvature′ by pressing power, so that material of the end flows radially inwardly and outwardly from this radius of curvature region. The deformation region forms a flattening on the outer side of the radius of curvature′, the major portion of the flattening being disposed in a plane perpendicular to the end axis or in a conical plane inclined outwardly and downwardly. This also serves for improving the resistance of the end to bulging. Owing to the flow of the material radially inwardly, compressive strain is applied to the outwardly bulged central panel portion thereby forming a free bulging (“free doming of central panel”), while the material flowing radially outwardly pivots permanently the inner leg of the groove Ushaped in cross-section from its original, inclined position into a position which is more cylindrical or parallel to the end axis (“permanent deflection of inner leg”). In the two known measures, the region deformed by coining (“coining”) is simultaneously hardened by cold working (“work hardened”) . Both prior art solutions strive to obtain an enlarged bulging of the central panel portion (“doming”) . However, if a filled can provided with such a considerably bulged end is pasteurized, for example (it being placed upside down in this case), the resulting bulging will cause the can s t o tip and fall over.
SUMMARY OF THE INVENTION
It is the object of this invention to modify an end by a process in such a way that the bulging of the end center can largely be reduced and nevertheless material from the end edge portion can be displaced in controlled fashion to increase the resistance to pressure.
In this connection, the annular fringe region which is formed in the further treatment accompanied by a reduction in thickness, is clearly positioned radially inside the actual radius of curvature′. This means that almost no material is displaced into the central panel portion but out of its edge portion, via the radius of curvature and (almost exclusively) into the radially inner leg of the U-shaped core groove. This displacement process is achieved, above all, by the angle which is formed and defined by the coining areas actuating upon the fringe-like region. This angle is defined between the coining areas of the coining tool or coining die actuating externally upon the end and a plane extending perpendicularly to the end axis. In this connection, the coining area of the lower coining tool or coining die is preferably parallel to this plane extending perpendicularly to the end axis, which means that said angle also exists between the two coining areas. This angle is to be markedly greater than 0°, but in any case less than 90°.
This angle is preferably between 2° and 15°.
Ends reshaped in such a way are stable as regards their upside-down stability even at increased internal pressure even though they do not have to miss the advantage of the more accurate vertical orientation of the inner leg.
For the accurate centering of the end, a ring holder finger-like in cross-section may be used for engaging in centering fashion the U-shaped groove during the coining step without deforming forces being exerted on the core groove in this case.
However, such a finger-like ring tool may be used to exert a controlled stretching pressure approximately in parallel with the end axis on the bottom of the core groove either at the same time or during the last phase of the coining step—displacing the material outwardly—, so that the flow of material radially outwardly via the radius of curvature is supported and simultaneously the inner leg of the U-shaped groove is tightened and brought more accurately into the desired vertical position.
According to the invention the material of the end sheet is compressed in the region of the annular fringe such that in this annular fringe region the sheet thickness reduction constantly decreases from a point of smallest residual thickness in radially outward direction. Within the deformed region, the residual thickness therefore changes radially outwardly e.g. in the form of a straight wedge, the bottom side being positioned in a plane extending perpendicularly to the end axis and the top side being positioned on a straight conical surface.
It proved to be especially advantageous to add a second treatment step to the described first further treatment step. During the second treatment step, the end material is slightly levelled in the fringe-like region—squeezed and deformed in the first step—, however, without displacing the material noticeably. But this is only done in a section, namely a radially outer region of the fringe, which adjoins the radius of curvature. This results in another reduction of the radius of curvature′, which contributes essentially to the increase in the lug resistance of the end. If owing to the first coining an insignificant portion of the displaced material was still displaced radially inwardly, the second treatment step would level the possibly resulting minor “doming” of the central panel portion and creates substantially the accurate abutment of the radially inner wall of the core groove against the lower forming tool. The radially inner “barrier” strain-hardened owing to the wedge effect already and the levelling effect of the tool avoid during levelling that another material portion is displaced from a local region or even shifted inwardly (past the strain-hardened “barrier”).
Correspondingly, the levelling step only performs strictly geometrical formation work which concerns the improved orientation of the inner leg of the core groove.
U.S. Pat. No. 4,354,784 (Westphal), which introduces a chip-free indented line into a metallic end, deals with an objective differing from that of the invention. This indented line circulates closely to the vertical core wall of the end and is made by a tool which has a central flat region and two inclined outer regions (col. 4, first para. thereof). By means of this “trapezoidal tool” an indented-line contour is obtained which reduces the danger of metal chips when tearing open. This freedom from chips is obtained while determining the indented line by a simultaneous displacement of material from the central portion towards both sides (radially inwardly and radially outwardly) . An only one-sided displacement of material is not effected by this tool.
A roughly comparable objective—the protection of children's tongues from the danger of cutting—is inherent in DE-A-23 03 943. It wants to avoid that children's tongues are exposed to the danger of cutting when they lick off the thick pudding layer on the bottom side of the end. For this purpose, an S-like triple protecting fold is proposed which also circulates and is obtained by folding an initially vertical wall section. In a preliminary step of this folding process a tool member is used (evident by means of FIG. 14) which has an annular undercut and a protruding

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