Method of forming a safety can end

Details Method of forming a safety can end Method of forming a safety can end

2000-06-30

2002-07-30

Gerrity, Stephen F. (Department: 3721)

Sheet metal container making

Method

Forming or treating metallic closure

Reexamination Certificate

active

06425721

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to easy-open metallic containers, which are defined as being openable by a consumer without a can opener or other tool, and methods for making such containers. More specifically, this invention relates to an improved method for making a full-open type easy-open closure that provides consumers protection against finger cuts while at the same time being resistant to pressure-induced failure.
2. Description of the Related Technology
An easy open end, for the purposes of this document, may be defined as a can end that is designed to be opened by a consumer without using a can opener or similar tool. A full-open type can end is, as opposed to a pour-type easy-open can end, designed to be completely removable from the can end during opening to provide unimpeded access to the inside of the can. Full-open type can ends are commonly utilized for packaging loose solids, such as mixed nuts or coffee, while pour-type can ends tend to be utilized for soft drinks or other beverages. Full-open type easy-open can ends are also used for packaging products of a non-food nature, such as tennis balls, which must be kept in a pressurized environment after manufacture to avoid deformation, particularly in the seam area.
When an end panel of an easy-open type closure separates as designed at a score line during opening, the resulting edges tend to be sharp, posing a possible danger to the consumer. One solution to this problem was presented in U.S. Pat. No. 3,705,363 to Elser, and was improved upon in U.S. Pat. No. 3,939,787 to Morrison et al.
FIGS. 1 through 6
illustrate the progressive stages in the formation of the closure disclosed in the Morrison et al. patent. These steps are carried out in a conventional, progressive die-forming machine, and the application and use of such a machine should be quite clear to those skilled in the art of forming such closures. Therefore, the details of the dies themselves and the transfer mechanisms involved are omitted, since the major focus of interest is that of the closure itself rather than the precise configurations of the dies used. The Morrison et al. closure is made from a blank that is fabricated from relatively thin aluminum sheet material. This material is disclosed as being in the range of from 0.008 to 0.015 inches thickness.
In the first stage of the closure formation illustrated in
FIG. 1
, a blank A has a seaming panel
10
formed from the peripheral edges of the blank. The seaming panel
10
is later used to double seam this convenience closure onto the end of a conventional can. Attached to the seaming panel
10
is a perimetrical upstanding wall portion of the closure, which is known in the art as a chuck wall
12
. In the initial forming steps shown in
FIG. 1
, two ledges
14
and
15
are formed. Also formed in this initial step is a bubble portion
16
, which will eventually be formed into a rivet for attaching a pull tab to this closure. The bubble
16
is formed from a portion of a central panel
18
of the blank A. An upstanding wall portion
20
connects the ledge
14
to the ledge
15
. A similar wall portion
22
is connected to the lower ledge
15
and to the central panel
18
.
In the second stage of the forming operation shown in
FIG. 2
, the outer margin of the central panel
18
has been bent upon itself to form a loose loop
26
, and the bubble
16
has been further shaped. Note that the loop
26
, speaking with respect to the vertical center line of the entire closure blank A, has an inner portion
27
and an outer portion
28
.
In
FIG. 3
, a scoring die
30
scores the blank A along an endless circular line
42
on the lower ledge
15
. Also note that in
FIG. 3
, simultaneously with the scoring of the ledge
15
, the upper ledge
14
and the upstanding wall portion
20
are bent to form a relatively loose loop
32
.
In
FIG. 4
, the loop
26
has been bent upwardly so that the outer portion
28
of the loop
26
is lying in abutting relationship with the lower ledge
15
. Similarly, the inner portion
27
of the loop
26
has been bent upwardly so that it is in abutting relationship with the outer portion
28
of the loop
26
. Thus, at this point, there are three layers of material defining a panel fold
33
which has a projecting outer nose portion
34
.
In
FIG. 5
, a pull tab
36
has been inserted over the completely formed bubble
16
, and the bubble
16
has been compressed to form a rivet
38
, which holds the pull tab
36
in place. The pull tab
36
includes a nose portion
40
, which is preferably positioned such that its outermost edge lies approximately over the center line of the score line or severing line
42
, which was placed in the lower ledge
15
by the scoring die
30
.
FIG. 6
shows the final operation to complete the Morrison et al. closure. In this step, the loose loop
32
is folded inwardly, overlying completely the score line
42
. It is to be noted that the loose loop
32
remains in a generally loose configuration, and the layers are not compressed together, as was the case with the loop
26
. An end, or nose portion,
44
is positioned so that it is inward of the score line
42
and very close to the nose portion
40
of the pull tab
36
. The loop
32
so folded constitutes a chuck wall fold
45
.
As may be seen in FIG.
6
and in
FIG. 7
, which shows an unencumbered view of the completed conventional closure, the resulting safety fold
50
includes an upper bead
52
that is radiused so as to be unitary with an intermediate panel
54
at one end thereof and similarly with an upper panel
56
at a second end thereof that overlies the intermediate panel
54
. A transition portion
57
is unitary with the upper panel
56
at one end and transitions the upper panel
56
into the chuck wall
12
. The other end of the intermediate panel
54
is unitary with a lower bead
58
that is radiused so as to be unitary with the end panel
60
of the completed closure at a second end.
As can be visualized by viewing
FIG. 7
, the upper bead
52
, because it protrudes slightly inwardly of the leftward edge of score line
42
, will be positioned to contact a consumer's finger before the consumer's finger contacts with the potentially sharp edge that is formed during separation of the end panel
60
at the score line
42
during opening. As a result, some protection is afforded by this design to the consumer against finger cuts.
As may further be seen
FIG. 7
, in practice it has been common to manufacture such closures so that the intermediate panel
54
is inclined with respect to the end panel
60
so as to form an angle A
1
opening radially inwardly. This angle A
1
and a second angle A
2
that is defined between the upper panel
56
and the end panel
60
and that also opens radially inwardly toward the center of the end panel
60
, are both designed to be about five or six degrees.
Unfortunately, the configuration that is shown in
FIG. 7
has been found to be susceptible to pressure induced failure, which occurs when the container is given a positive pressure, such as is required in the packaging of tennis balls. The present inventor has studied the mechanism by which this occurs, and has determined that the interior pressure causes the end panel
60
of the closure to bow upwardly, with the greatest deformation occurring in the centermost part of the panel
60
. As this occurs, the outward portions of the end panel
60
are pulled radially inwardly, or to the right as it is viewed in FIG.
7
. This causes the lower bead
58
to begin to open, meaning that the angle A
1
begins to increase, which reduces the overall strength of the safety fold
50
. This culminates in a failure of the closure that is symptomized by an outward folding of the closure over the safety fold
50
, the fold line tending to be oriented generally radially.
One solution to this problem is proposed in application Ser. No. 09/578,044, filed May 24, 2000, the entire disclosure of which is incorporated as if set forth fully herein. This so

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