U.S. patent number RE33,217 [Application Number 07/235,787] was granted by the patent office on 1990-05-15 for buckle resistance for metal container closures.
This patent grant is currently assigned to Ball Corporation. Invention is credited to Tuan A. Nguyen.
United States Patent |
RE33,217 |
Nguyen |
May 15, 1990 |
Buckle resistance for metal container closures
Abstract
The present invention relates to improvements in the strength of
ends used on metal beverage containers. Such ends generally
comprise a central panel portion of a substantially planer
character, a surrounding U-shaped sidewall having inner and outer
legs, a curved intermediate portion integrally joining the inner
leg to the U-shaped sidewall, and a peripheral curl extending from
the outer leg for double seaming the end onto a can body. In
accordance with the present invention, the intermediate portion and
adjacent central panel portion are firmly supported by a die while
a clamping force is placed on an annular band of the upper surface
of the end at the intermediate portion. The clamping force is
increased until metal flows inwardly and outwardly from the contact
point resulting in a free compression doming of the center panel
and an outward deflection of the inner leg. An end of increased
buckle resistance is thereby produced which end is approximately
within standard dimensions such that customers can use the end on
existing seaming equipment without alteration. An optional feature
is provided to minimize the compression doming by clamping a
peripheral band of the end with a hold-down pad while the metal
flowing is accomplished. This reduces the dome depth and results in
a strengthened end having a dome depth very close to standard
specifications.
Inventors: |
Nguyen; Tuan A. (Thornton,
CO) |
Assignee: |
Ball Corporation (Muncie,
IN)
|
Family
ID: |
27398762 |
Appl.
No.: |
07/235,787 |
Filed: |
August 19, 1988 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
56611 |
Jun 1, 1987 |
|
|
|
|
565995 |
Dec 27, 1983 |
|
|
|
|
357032 |
Mar 11, 1982 |
4434641 |
Mar 6, 1984 |
|
Reissue of: |
711001 |
Mar 12, 1985 |
04577774 |
Mar 25, 1986 |
|
|
Current U.S.
Class: |
220/623;
72/379.4; 413/8; 220/270 |
Current CPC
Class: |
B65D
17/4012 (20180101); B21D 51/383 (20130101) |
Current International
Class: |
B21D
51/38 (20060101); B21D 051/44 (); B65D 008/08 ();
B65D 017/00 () |
Field of
Search: |
;220/66,67,268,269,270
;413/8 ;72/379 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
4962972 |
|
Jun 1974 |
|
AU |
|
2065009 |
|
Jun 1981 |
|
GB |
|
Other References
Letter from Ralph R. Rath to R. P. Campbell, dated 1/12/80. .
Letter from Ralph R. Rath to R. P. Campbell, dated 2/18/88. .
Letter from Robert A. Stengel to Gilbert E. Alberding, dated
4/25/88, Memo from R. D. Zenger to R. A. Stengel, dated 2/15/88.
.
Attachment 1-"The Battle of Pop Tops Goes On", Chicago Daily News,
11/12/76. .
Attachment 2-American National Can Test Request Report 6-716, dated
1/3/77. .
Attachment 3-American National Can Test Request Report entitled
"Ball Claim of Patent Infringement-Coining O/S Ends". .
Attachment 4-American National Can Test Request Report Entitled,
"Ecology-End-ENTECH", Samples 06/12/78. .
Attachment 5a-"The Pop-Top End", Food Technology in Australia,
6/77, pp. 233-234. .
Attachment 5b-"The Pop Top End", Australian Packaging, 5/76, pp.
86-88. .
Attachment 6-American National Can Test Request Report Entitled
"Ecology Ends-BHP"; dated 5/20/77. .
Attachment 7-American National Can Memo re Broken Hill, 3/8/76.
.
Attachment 8-American National Can Test Request Rpt. entitled "209
Kaiser AL Ends-DIE 5R", 05/12/76. .
Attachment 9a-National Can Corporation Drawing ST-2-98, dated
11/5/85. .
Attachment 9b-National Can Corporation Drawing DD-166-B, dated
7/12/78. .
Attachment 9c-National Can Corporation Drawing DD-018-B, datd
3/4/77. .
Memorandum from S. Misra re Dynamic III, ends at Birmingham,
3/27/81, EPO Search Report Appln. EP 84 11 2243. .
Letter Dated May 12, 1987 of R. P. Campbell. .
Letter Dated Nov. 6, 1987, from Frost & Jacobs. .
Exhibit A-Stolle Drawing C-S0688 and Bill of Material BM-68672.
.
Exhibit B-Owens-Illinois Engineering Specifications Stolle Shipping
Transmittals S-24803, S-23498. .
Stolle Purchase Requisition S-17445, Stolle Purchase Order S-17445.
.
Owens-Illinois Drawing D-02000, Stolle Changes Drawing Dated 1979.
.
Exhibit C-Stolle Drawing C-94704. .
Exhibit D-Kaiser Drawing CDT-B-3608-PE. .
Exhibit E-Jos. Schlitz Drawing 32 WOA-9341. .
Exhibit F-Stolle Drawing B-94964. .
Exhibit G-Stolle Drawing D-81840..
|
Primary Examiner: Shoap; Allan N.
Attorney, Agent or Firm: Alberding; Gilbert E.
Parent Case Text
This .Iadd.is a continuation of Ser. No. 056,611 filed Jun. 1,
1987, now abandoned, which is a reissue of U.S. Pat. No. 4,577,774,
issued Mar. 25, 1986, which issued from application Ser. No.
711,010 filed Mar. 12, 1985, which .Iaddend.is a continuation of
application Ser. No. 565,995 filed Dec. 27, 1983, now abandoned,
which is a division of application Ser. No. 357,032 filed Mar. 11,
1982, now U.S. Pat. No. 4,434,641 issued Mar. 6, 1984.
Claims
What is claimed is:
1. A metal closure comprising a circular domed central panel
portion, a generally U-shaped sidewall having inner and outer
upstanding legs, and an intermediate curved section integrally
connecting said panel portion to said inner leg adjacent to the
upper extremity thereof, said intermediate curved section having a
thinned annular band of cold flowed metal formed therein
immediately adjacent the upper surface thereof wherein said annular
band of cold flowed metal is a frustoconical surface which angles
upward and away from the horizontal in the radially inward
direction and the lower surface of said intermediate curved section
immediately opposite said thinned annular band of cold flowed metal
is of an arcuate concave configuration, said thinned annular band
being compressed cold worked and defined by a flat surface having a
width of between about 0.020 and about 0.040 inches, the flow of
said metal of said thinned annular band being sufficient resulting
in said panel portion of said metal closure being domed axially
outwardly and said inner leg being deflected towards a
substantially vertical configuration.
2. A metal closure comprising a circular domed central panel
portion, a generally U-shaped sidewall having inner and outer
upstanding legs, and an intermediate curved section integrally
connecting said panel portion to said inner leg adjacent to the
upper extremity thereof, said intermediate curved section having a
thinned annular band of cold flowed metal formed therein
immediately adjacent the upper surface thereof wherein said annular
band of cold flowed metal is straight and substantially parallel to
the horizontal and the lower surface of said intermediate curved
section immediately opposite said thinned annular band of cold
flowed metal is of an arcuate concave configuration, said thinned
annular band being compressed cold worked and defined by a flat
surface having a width of between about 0.020 and about 0.040
inches, the flow of said metal of said thinned annular band being
sufficient resulting in said panel portion of said metal closure
being domed axially outwardly and said inner leg being deflected
towards a substantially vertical configuration. .Iadd.
3. A metal closure comprising a circular domed central panel
portion, a generally U-shaped sidewall having inner and outer
upstanding legs, and an intermediate curved section integrally
connecting said panel portion to said inner leg adjacent to the
upper extremity thereof, said intermediate curved section having a
thinned annular band of cold flowed metal formed therein
immediately adjacent the upper surface thereof wherein said annular
band of cold flowed metal is a frustoconical surface which angles
upward and away from the horizontal in the radially inward
direction and the lower surface of said intermediate curved section
immediately opposite said thinned annular band of cold flowed metal
is of an arcuate concave configuration, said thinned annular band
being compressed cold worked and defined by a flat surface, the
flow of said metal of said thinned annular band being sufficient
resulting in said panel portion of said metal closure being domed
axially outwardly and said inner leg being deflected towards a
substantially vertical configuration. .Iaddend. .Iadd.4. A metal
closure comprising a circular domed central panel portion, a
generally U-shaped sidewall having inner and outer upstanding legs,
and an intermediate curved section integrally connecting said panel
portion to said inner leg adjacent to the upper extremity thereof,
said intermediate curved section having a thinned annular band of
cold flowed metal formed therein immediately adjacent the upper
surface thereof wherein said annular band of cold flowed metal is
straight and substantially parallel to the horizontal and the lower
surface of said intermediate curved section immediately opposite
said thinned annular band of cold flowed metal is of an arcuate
concave configuration, said thinned annular band being compressed
cold worked and defined by a flat surface, the flow of said metal
of said thinned annular band being sufficient resulting in said
panel portion of said metal closure being domed axially outwardly
and said inner leg being deflected towards a substantially vertical
configuration. .Iaddend. .Iadd.5. A metal closure comprising a
circular domed central panel portion, a generally U-shaped sidewall
having inner and outer upstanding legs, and an intermediate curved
section integrally connecting said panel portion to said inner
upstanding leg adjacent to the upper extremity thereof, said metal
closure having a thinned annular band of cold flowed metal formed
thereon immediately adjacent the outer upper surface of said
intermediate curved section, the lower surface thereof immediately
opposite said thinned annular band having an arcuate concave
configuration, said thinned annular band being formed by the
process of restraining said central panel against lateral movement
and cold flowing metal from the upper surface of said intermediate
curved section radially inwardly to form a substantially flat
surface immediately opposite said arcuate concave configuration,
said flat surface angling upwardly and away from the horizontal in
the radially inward direction and to compression dome the panel
portion slightly upwardly and by cold flowing metal outwardly to
deflect the inner upstanding leg in a substantially vertical
configuration while the central panel is restrained. .Iaddend.
.Iadd.6. A metal closure comprising a circular central panel
portion, a generally U-shaped sidewall having inner and outer legs,
and an intermediate curved section integrally connecting said panel
portion to said inner leg, said metal closure having a thinned
annular band of cold flowed metal formed thereon adjacent the upper
surface of said intermediate curved section, the lower surface
thereof immediately opposite said thinned annular band having an
arcuate concave configuration, said thinned annular band being
formed by the process of restraining said central panel and cold
flowing metal from the outer surface of said intermediate curved
section radially inwardly to form a substantially flat surface
immediately opposite said arcuate concave configuration, said flat
surface angling upwardly and away from the horizontal in the
radially inward direction and to compression dome upwardly the
panel portion. .Iaddend. .Iadd.7. A metal closure comprising a
circular central panel portion, a generally U-shaped sidewall
having inner and outer legs, and an intermediate curved section
integrally connecting said panel portion to said inner leg, said
metal closure having a thinned annular band of cold flowed metal
formed thereon adjacent the upper surface of said intermediate
curved section, the lower surface thereof immediately opposite said
thinned annular band having an arcuate concave configuration said
thinned annular band being formed by the process of restraining
said central panel and cold flowing metal from the outer surface of
said intermediate curved section to form a substantially flat
surface immediately opposite said arcuate concave configuration,
said flat surface angling upwardly and away from the horizontal in
the radially inward direction and to deflect the inner leg in a
substantially vertical configuration the metal in the band being
cold flowed in an amount sufficient to cause compression doming of
the circular central panel
portion. .Iaddend. .Iadd.8. A metal closure comprising a circular
central panel portion, a generally U-shaped sidewall having inner
and outer legs, and an intermediate curved section integrally
connecting said panel portion to said inner leg, said metal closure
having a thinned annular band of cold flowed metal formed on the
outer upper surface of said intermediate curved section, the lower
surface thereof immediately opposite said thinned annular band
having an arcuate concave configuration, the metal in the band
being cold flowed and defining a substantially flat frustoconical
surface which angles upward and away from the horizontal in a
radially inward direction, the circular central panel portion
having an upwardly domed configuration. .Iaddend.
Description
BACKGROUND OF THE 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 central panel surrounded
by a generally U-shaped sidewall integrally joined to the central
panel by a convexly curved intermediate section. The outer leg of
the side wall is provided with a reverse curl at its upper end
which is double seamed onto the flange of the container. After
seaming the outer leg is substantially parallel with the sidewall
of the can while the inner leg of the sidewall is disposed inwardly
at an angle.
It has been recognized that having the two legs of the U-shaped
sidewall substantially vertical and increasing the panel height
increases the buckle strength of the end. Thus in U.S. Pat. No.
4,217,843 there is disclosed tooling for forming the sidewall in
such a manner that the legs 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. Pat. 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. Pat. No. 3,441,170 where the curved segment
connecting the inner leg of the sidewall to the central panel is
coined on the undersurface. This is for the purpose of reducing the
metal thickness in the intermediate 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. Pat. 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 container end of the usual
type is strengthened by selectively working a portion of the metal
in the curved intermediate segment in such a manner as to cause a
free doming of the central panel portion and a permanent deflection
toward the vertical of the inner leg of the end sidewall. The upper
surface of the metal is worked so as to permit a greater and more
controlled flow of metal to enhance the free doming of the central
panel portion, and also to prevent puncturing the corrosion
resistant coating on the bottom of the end which is applied to the
metal before the end is formed.
More specifically, an annular band of metal in the intermediate
segment and about the periphery of the panel portion is
progressively thinned by applying pressure to the upper surface of
the metal to form an annular stiffened flange about the periphery
of the central panel. The metal is thinned to the point where a
substantial amount of metal is flowed radially inwardly and
outwardly from the inner and outer diameter of the band immediately
adjacent the upper surface. The inner flow compresses the central
panel portion of the end, which is free to move, and causes it to
dome to a stabilized compressed configuration. The outer flow
permanently deflects the inner leg, which is free to move, of the
sidewall outwardly and decreases the angle thereof to the vertical.
Thus, in accordance with the present invention a stronger end
results from the individual and combined effects of the compression
doming, the annular stiffening flange, and the decreased angle of
the one leg of the sidewall.
A particular advantage of the present invention is its
applicability to the great majority of now produced lightweight
closures without significantly altering the aesthetic
characteristics or the dimensional standards of such closures
thereby requiring minimal or no alterations in customers handling
equipment.
As mentioned above, the prior art teaches that by increasing the
panel height and straightening the panel wall to almost vertical,
greater buckle resistance may be achieved. A major drawback of
following such teachings is that a necessary corollary is that the
tab will be forced above the chime at corresponding lower pressures
due to the decreased dome depth. For example, in U.S. Pat. No.
4,217,843 increased buckle strength is partially achieved by
increasing panel height. A rock resistance of 60 PSI then results.
With the present invention, standard dimensions on panel height are
substantially maintained, yet a rock pressure of 80 PSI is obtained
with ring pull closures.
Accordingly, it is an object of the present invention to provide a
method of increasing the buckle resistance and rock pressure of a
closure.
It is another object of the present invention to provide a closure
of thinner metal stock yet which substantially conforms to standard
dimensions, buckle resistance and rock pressure thereby providing
metal savings and compatibility with presently used customers
sealing 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.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top view of a standard end.
FIG. 2 is a cross-sectional view of the standard end of FIG. 1.
FIG. 3 is a cross-sectional view of apparatus manufactured in
accordance with the present invention, in the non-working
configuration.
FIG. 4 is the apparatus of FIG. 3 in the working configuration.
FIG. 5 is an enlarged view of the intermediate section and adjacent
center panel of an end being worked in accordance with one
embodiment of the present invention.
FIG. 6 is an enlarged view of the intermediate section and adjacent
center panel of an end being worked in accordance with an
alternative embodiment of the present invention.
FIG. 7 is an enlarged view of the intermediate section and adjacent
center panel of an end being worked in accordance with yet another
alternative embodiment of the present invention.
FIG. 8 is a cross-sectional view of an end produced by the present
invention.
DETAILED DESCRIPTION
With reference now to the drawings there is shown in FIG. 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 is customary, 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 FIG. 2, the end 10 includes a central
substantially flat panel portion 20 surrounded by a generally
U-shaped sidewall 22 having a radius of curvature R4 and comprising
inner and outer legs respectively referenced 24 and 26. The
uppermost extremity of the outer leg terminates in the conventional
curl 28 having a flat top portion 33, a 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 innermost
leg 24 extends upwardly and inwardly from the vertical at an angle
A and is joined to the panel portion 20 by a convexly curved
intermediate section 25 having a radius of curvature R1. The end
has a dome depth M measured from the rivet to uppermost portion of
the curl 28 and a panel height H, measured from the bottom of the
U-shaped sidewall 22 to the bottom of the panel portion 20 adjacent
the curved intermediate section 25.
There are generally two types of standard ends commercially
produced for beverage containers, albeit in a variety of
configurations, the retained tab end and the ring pull end. Again
generally speaking, the production process for the basic shell
configuration including the central panel, U-shaped sidewall,
intermediate section, inner and outer legs, and the curl may be the
same for both styles of ends with the main difference being in the
conversion process where the tab and opening portion are formed.
Due to the similarity in basic shell configuration, improvements in
strength to one type of end which result from some change in the
basic shell configuration are generally also applicable to the
other basic type of end. One parameter, however, which is of
greater concern when dealing with retained tab ends is that of dome
depth which is highly related to rock pressure. As those skilled in
the art will recognize, retained tabs are generally thicker than
ring pull tabs and therefore, extend above the central panel a
greater distance. Therefore, dome depth, as measured from the top
of the rivet 18 to the top of the curl 33, must be greater on such
ends than on ring pulls to obtain similar rock pressures and to
make sure the tab does not extend above the curl in normal use. Due
to the above, many manufacturers tension dome ring pull ends to
obtain the slight increase in strength which results, yet do not
dome retained tabs.
Another parameter which dome depth effects is stackability.
Preferably ends stack such that the upper substantially flat
surface 33 of the curl provides a stable base for the terminal end
39 of the curl of the above stacked end. Should dome depth be too
small, or conversely, dome height be too great, the tab may
interfere with the bottom dome of the above stacked end. This may
result in a reduction in the number of closures which can be
stacked per linear unit of measurement to an out of specification
figure and more importantly, may be a source of problems with some
customers seaming equipment due to potential rocking between
stacked closures on the heightened tab, rather than the preferred
closely stacked stable configuration. This is especially true with
the thicker retained tabs.
As previously stated it has been proposed to strengthen the end by
coining the undersurface of the intermediate section 25 with the
prior teachings differing in the degree of coining. In accordance
with the present invention the strength of the end 10 is increased
by working the metal in the intermediate segment 25 in such a
manner as to form a strengthened peripheral flattened flange about
the central panel portion. In addition, the metal is worked in a
manner such as to cause free doming of the panel portion and
outward deflection of the leg 24 thus also increasing the strength
of the end.
An added feature of the present invention is the ability to
strengthen the end while keeping the end substantially within
specification for tension domed ends, especially with respect to
dome depth and panel height. This makes ends formed in accordance
with the present invention completely compatible with existing
customers fill and seal equipment including maintaining a rock
pressure of 80 PSI with ring pull ends. Also, when the optional
feature of a holddown pad is employed, the stackability of retained
tab ends so formed remains identical to undomed standard retained
tab ends, as noted above, an important feature with some customers
existing seaming equipment.
As shown in FIG. 3, prior to working the metal in the intermediate
segment and the immediately adjacent center panel, the undersurface
of the end is supported by a die 27 having a convexly curved
peripheral shoulder 30 having a radius of curvature R2
substantially equal to that of the intermediate segment 25. The die
has a recessed central portion 32 and a metal contacting surface 34
which in effect provides an annular band of support for the
undersurface of the panel 20 and the intermediate segment 25. As
thus supported, the end 10 as a whole is restrained from lateral
movement while the panel 20 is free to move upwardly and the
sidewall 22 including the leg 24 is free to move laterally.
In order to work the metal, a punch 36 having an annular metal
working surface 38 is positioned above the end 10 and aligned for
axial movement with both the end and the die 27. In one embodiment,
the metal working surface 38 over the major portion of its
effective cross-sectional width is substantially flat and disposed
in a plane substantially parallel to the plane containing the upper
surface of metal contacting surface 34 of die 27 as better shown in
FIG. 5. In the alternative embodiments of FIGS. 6 and 7, for
reasons which will be further explained, the metal working surface
38 is disposed in an upwardly sloped plane in the radially inward
direction forming a frustoconical metal working surface. In both
embodiments, the metal contacting surface 38 curves upwardly at its
innermost end to provide a convexly curved shoulder portion 40
having a radius of curvature R3.
In accordance with an optional feature of the present invention, a
hold-down pad 44 may be used to minimize the compression dome which
is formed in accordance with the present invention to maintain the
dome depth closer to standard end specifications. The hold-down pad
is located in the center of the punch and has a flat annular
clamping surface 45 and a series of spring washers 46 which allow a
predetermined amount of biasing to be placed on the end 10 to
minimize the compression doming.
An alternative to the hold-down pad is illustrated in the
embodiment shown in FIG. 7. As is there illustrated, the
fructoconical clamping surface 38 extends inwardly, thus limiting
the height of the dome to below the surface 38, therefore
performing a like function to the hold-down pad i.e., minimizing
the height of the compression dome. As will be further explained,
ends formed with the extended clamping surface 31 of FIG. 7 exhibit
similar dome depths to ends formed with the clamping surface of
FIGS. 5 and 6 where a hold-down pad is also employed.
In operation, the punch 36 is moved downwardly from the first
position of FIG. 3 to the second metal working position illustrated
in FIG. 4. As better shown in FIG. 5, 6, and 7, where dashed lines
21 represent the end prior to being worked by the punch, when the
metal contacting surface 38 first contacts the upper surface y of
the intermediate section 25, the end 10 is clamped between the
surface 38 and the die 27 about only a peripheral band b. Band b
has an initial outer diameter of c and an initial inner diameter d.
As thus initially clamped, the inner leg 24 and the central panel
portion 20 are free to move as will be subsequently explained.
Further downward movement of the die compresses the metal beneath
the surface y and progressively increases the width of the annular
band b thus increasing the outer diameter c and decreasing the
inner diameter d until the band b has a width defined by new outer
diameter c and inner diameter d. In the embodiment illustrated in
FIG. 5, the expanded compressed band extends inwardly and outwardly
from the original periphery x of the central panel portion and
results in a strengthened compressed cold worked peripheral band.
In the embodiments illustrated in FIGS. 6 and 7, the majority of
the expanded compressed band extends outwardly from the original
periphery x of the end portion. In all embodiments as the width of
the band is progressively expanded due to downward movement of the
punch 36, an annular segment of metal immediately beneath the
surface y is progressively displaced and caused to radially flow
both inwardly and outwardly. The inner flow of metal compresses the
central panel portion 20 which is confined and thus causes a free
forming thereof into the compressed domed configuration shown in
FIGS. 5, 6 and 7. The outer flow of metal causes the inner leg 24,
which is free to move, to permanently deflect outwardly toward the
outer leg 26.
When the optional hold-down pad 44 is also employed, the hold-down
pad first contacts the central panel inwardly of the portion which
is to be worked by metal working surface 38. Preferably only an
outer annular band on the surface of the central panel portion is
contacted by the hold-down pad. The hold-down pad's annular
clamping surface 45 then clamps the end against the dies metal
supporting surface 34. This minimizes the doming of the center
panel and increases the outward deflection of the inner leg 24 of
the end. The major portion of the center panel, however, is still
unrestrained and allowed to free dome as a result of the expanded
compressed band of metal formed around the periphery of the end. It
has been found that the hold-down pad should optimumly place about
400 pounds of clamping force on the end. Greater force has been
found to reduce the buckle and rock strength of the end while
lesser force will not keep the dome depth sufficiently in
specification resulting in potential stacking problems when working
with retained tabs on some customers equipment. The desired 400
pounds of clamping force is preferably administered by choosing
appropriate spring washers 46 in conjunction with the metallic
hold-down pad illustrated in FIGS. 3 and 4. However, satisfactory
results have also been obtained with a plug of an elastomeric
substance exhibiting a durometer reading of between about 40 and
about 80 in place of the illustrated metallic hold-down pad. The
elastomeric substance is preferably urethane with a circular plug
configuration. Sufficient clearance must be provided between the
outside of the plug and the inner diameter of the punch to allow
for outward deformation of the elastomeric substance.
A similar result to a hold-down pad is obtained when using the
extended clamping surface illustrated in FIG. 7. As the annular
band of metal is expanded and compressed by the downward motion of
the clamping surface, the extended portion of the clamping surface
contacts the peripheral portion of the central panel and restrains
such portion to a reduced degree of upward doming. This limits the
free compression doming approximately to the same degree as the
hold-down pad. Although the extended clamping surface 31 of FIG. 7
is advantageous in it is similar in operation to a hold-down pad
yet requires none of the extra moving parts, it is not practical
for use with many standards ends presently produced. Some ends now
produced, especially of the retained tab variety, have protrusions
near the periphery of the central panel in conjunction with the
design of the tear open tab. These protrusions must not be altered
in the forming process of the present invention. Therefore, the
extended clamping surface of FIG. 7 is not suitable for such ends,
at least not without appropriate relief in the surface for the
protrusions, which would require costly machining due to the
frustoconical configuration of the surface. Satisfactory results
have been obtained with such ends through the use of a hold-down
pad constructed of a urethane elastomeric exhibiting a durometer
reading of about 50. Similar results have also been obtained with a
hold-down of the type shown in FIGS. 3 and 4 having appropriate
relief spots in its clamping surface 45.
A number of 207.5 size closures have been made in accordance with
the present invention from aluminum alloy stock having a nominal
thickness of between 0.0120 and 0.0125 inches and a yield strength
of between about 42 KSI and 45 KSI with buckle strengths in excess
of 90 PSI and on ring pull ends, rock pressures in excess of 80
PSI. As mentioned above, retained tabs extend above the central
panel a greater distance than ring pull tabs and exhibit reduced
rock pressures. However, ends made by the method of the present
invention, regardless of the type of tab, exhibit commensurate
buckle strength and rock pressures to standard tension domed ends
formed from 0.0130 aluminum stock. Considering FIGS. 5,6 and 7
again, optimum buckle results have been obtained where band b has a
final width of between about 0.020 inches and about 0.040 inches.
The residual g referenced in FIGS. 5, 6 and 7 is defined as the
thickness of the flattened flange at its point of minimum
thickness. In general terms, the greater the reduction in thickness
or put otherwise, the smaller residual g, the greater the increase
in buckle strength. However, a residual under about 0.006 inches
results in a catastrophic failure mode under pressure, rather than
a buckle, with the center panel fracturing around the flattened
flange and physically separating from the container, an
unacceptable happenstance for obvious reasons.
The preferred embodiments of the present invention maintain a
residual g between about 0.006 inches and 0.011 inches wherein a
buckle strength of at least 90 PSI will be obtained with 0.0125
inch stock, yet the catastrophic failure mode should not be a
problem.
Presently, the embodiments illustrated in FIGS. 6 and 7 are the
preferred commercial embodiments of the present invention. The
frustoconical forming surface 38 of punch 36 provides a like
surface on the compressed cold worked peripheral band b. This
configuration blends well with the existing radius making the
annular worked band difficult to detect by the consumer. Further,
although buckle and rock resistance are commensurate to that
obtained with the embodiment illustrated in FIG. 5, a lesser volume
of metal is displaced in forming for a given residual thereby
further minimizing the compression dome and remaining closer to
specification on dome depth. This is because the residual only
exists at the cross-sectional point of dotted line 35 in FIGS. 6
and 7. The residual of the embodiment of FIG. 5 is over the major
portion of the worked band b. Also, preliminary experimentation has
indicated that the embodiment of FIGS. 6 and 7 will withstand a
smaller residual without catastrophic failure, a result which is
attributed to the smoother transitions between the flattened flange
area and the central panel.
Referring to FIG. 2, the typically standard end when tension domed
in accordance with the prior art has a dome depth m of between
about 0.084 and 0.104 inches, a panel height h of about 0.066
inches and an inner leg angle with vertical A, of about 26.degree..
FIG. 8 illustrates an end formed in accordance with the present
invention. It has a panel height h' of about 0.069, a dome depth m'
of, if no hold-down pad is used, between about 0.060 and 0.070
inches, an inner leg angle with vertical A' of, if no hold-down pad
is used, about 22.degree.. Where a hold-down pad or the embodiment
of FIG. 7 is employed, panel height h' remains at about 0.069, some
depth m' increases to between about 0.080 inches and 0.090 inches,
and angle A' decreases to about 20.degree.. It should be noted that
absolute angles for inner leg 24 are extremely difficult to measure
and it is perhaps of greater accuracy to state that angle A' is
between about 2.degree. and about 4.degree. smaller than A without
a hold-down pad and between about 5.degree. and about 7.degree.
smaller than A with a hold-down pad. Also, dome depth m' for ends
worked in accordance with the present invention is highly dependent
upon the residual g. The smaller the residual, the greater the
volume of metal displaced inwardly and correspondingly, the greater
the dome. Obviously, the greater the dome, the smaller m'. The
above figures on m' are given for a residual of about 0.008 inches.
Roughly, empirical results indicate a decrease of about 0.005
inches in dome depth for every decrease of about 0.001 inches in
residual g. The increase in dome depth attained through the use of
a hold-down pad is substantially dependent on the pressure exerted
on the end. Empirical results indicate that with 400 pounds of
pressure, an increase in dome depth of between about 0.015 and
0.020 inches can be expected for a given residual.
Although the mechanism by which buckling takes place is not
completely understood it is thought that in the initial stages, the
inner panel wall is forced outwardly at some circumferential point.
The present invention is thought to increase buckle resistance by
imparting a precise degree of strain hardening at the flattened
flange area which adds rigidity to the intermediate section and
inwardly to the central panel. The increased rigidity of the
intermediate section is thought to help prevent the outward
deflection of the inner leg thereby delaying the first stage of
buckling until higher pressures are reached. There is also a
measurable straightening of the inner leg toward vertical which is
thought to add some degree of buckle resistance.
Although the present invention may be applicable to a variety of
situations, commercially it is preferably implemented in the final
stage of the conversion press. Many can manufacturers now, in
accordance with the prior art, tension dome ends at the last stage
of the conversion press. It is a relatively simple matter to
replace the existing tension dome tooling with tooling constructed
in accordance with the present invention.
This will result in ends produced which have a substantial increase
in strength over prior art tension domed ends yet are very close in
dimensional characteristics to such ends thereby requiring minimal
or no other changes in manufacturing existing equipment, and
perhaps more importantly, no changes in customers existing filling
and seaming equipment. Most manufacturers will prefer to use the
present invention in conjunction with the production of thinner
gauge ends thereby realizing substantial cost savings in materials.
This will result in the production of ends having similar strength
and dimensional characteristics to the priorly produced ends, yet
of a thinner metal gauge.
In the broadest terms then, the present invention contemplates the
production of stronger ends or, ends of thinner stock having the
same strength and dimensional characteristics as priorly produced
ends of thicker stock, by forming an expanded area of compressed
metal near the periphery of the central panel portion of the end.
This is accomplished by supporting the undersurface of the end over
the intermediate portion and the periphery of the central panel
portion and progressively thinning the metal by applying pressure
to the top surface of the intermediate portion thereby flowing
metal inwardly to compression dome the end and outwardly to
permanently deflect the inner leg to a more vertical configuration.
Optionally, to further place the end in prior art specifications
for tension domed ends, the compression dome may be minimized by
either clamping a minor portion of the central panel down with a
hold-down pad prior to flowing metal or by using a working tool
with an extended frustoconical contact surface which progressively
restrains the peripheral portion of the central panel from upward
movement simultaneous to the metal flow. Preferably the end
produced in accordance with the present invention will have a
peripheral flange of expanded compressed metal between about 0.020
and about 0.040 inches in width with a residual of between about
0.006 and 0.011 inches and a panel height of under 0.075
inches.
* * * * *