U.S. patent number 3,904,069 [Application Number 05/409,734] was granted by the patent office on 1975-09-09 for container.
This patent grant is currently assigned to American Can Company. Invention is credited to Aram Hartoun Toukmanian.
United States Patent |
3,904,069 |
Toukmanian |
September 9, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Container
Abstract
A cylindrical metal can body for pressurized products having
integral side and bottom walls is constructed such that the bottom
wall includes a centrally disposed circular depression or dimple
therein, the base area of the depression being less than
approximately 60 percent and greater than approximately 15 percent
of the total area of the bottom wall. This bottom wall structure
permits the can to expand in height when subjected to internal
pressure, while preserving stability when placed in an upright
standing position since the bottom is uniformly deformed by the
internal pressure into a shape in which the circular rim of the
depression forms a suitable stable base on which the can sits.
Inventors: |
Toukmanian; Aram Hartoun
(Downsview, CA) |
Assignee: |
American Can Company
(Greenwich, CT)
|
Family
ID: |
26916400 |
Appl.
No.: |
05/409,734 |
Filed: |
October 25, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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222050 |
Jan 31, 1972 |
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Current U.S.
Class: |
220/609;
220/906 |
Current CPC
Class: |
B65D
1/165 (20130101); Y10S 220/906 (20130101) |
Current International
Class: |
B65D
1/16 (20060101); B65D 1/00 (20060101); B65d
007/42 () |
Field of
Search: |
;229/2.5 ;150/.5
;220/70,66,67,DIG.22 ;215/1C ;113/12H,12S |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lowrance; George E.
Assistant Examiner: Shoap; Allan N.
Attorney, Agent or Firm: Auber; Robert P. Bock; James W.
Ziehmer; George P.
Parent Case Text
This application is a continuation-in-part of my application Ser.
No. 222,050, filed Jan. 31, 1972, now abandoned.
Claims
What is claimed is:
1. An eversion resistant, generally cylindrical drawn metal
container having therein a product under pressure, said container
including a generally cylindrical body having integral side and
bottom walls, said bottom wall comprising a central inwardly domed
depression surrounded by an annular panel, said depression having a
marginal circular intersection with said annular panel, at least
said annular panel having been outwardly distended by pressure of
said product to permanently change the shape of the bottom wall
such that said circular intersection becomes the outermost extent
of the bottom wall, said annular panel being inclined into a
generally conical shape and forming an obtuse angle with said
sidewall, the percentage ratio of the area determined by the radius
of said circular intersection to the area determined by the outer
radius of said annular panel being in the range of from
approximately 15 percent to approximately 60 percent, said circular
intersection alone providing a stable base upon which the container
rests in an upright position.
2. The container of claim 1 wherein the nominal outside diameter of
the sidewall is 2 11/16 inches, wherein the nominal diameter of the
depression is 1.25 inch, and the container is made from 118 pound
electrolytically tin plated steel.
3. The container of claim 1 wherein said depression is concave and
remains concave at a pressure of 95 psig.
4. The container of claim 1 wherein the bottom wall comprises 3004
H-19 aluminum and has a thickness greater than 0.010 inch and less
than 0.017 inch.
5. The container of claim 1 wherein the bottom wall comprises T-1
temper, tin-electroplated steel and has a thickness greater than
0.010 and less than 0.013 inch.
6. The container of claim 1 wherein the depression is generally
spherical in shape.
7. An eversion resistant, generally cylindrical container drawn
from metal selected from the group consisting of less than 0.013
inch thick steel and less than 0.017 inch thick aluminum alloy
capable of withstanding an internal pressure and having therein a
product under pressure, said container including a generally
cylindrical body having integral side and bottom walls, said bottom
wall comprising a central inwardly domed depression surrounded by
an annular panel, said depression having a marginal circular
intersection with said annular panel, at least said annular panel
having been outwardly distended by pressure of said product to
permanenlty change the shape of the bottom wall such that said
circular intersection becomes the outermost extent of the bottom
wall, said annular panel being inclined into a generally conical
shape and forming an obtuse angle with said sidewall, the
percentage ratio of the area determined by the radius of said
circular intersection to the area determined by the outer radius of
said annular panel being in the range of from approximately 15
percent to approximately 60 percent, said circular intersection
alone providing a stable base upon which the container rests in an
upright position.
8. An eversion resistant, generally cylindrical container drawn
from metal selected from the group consisting of less than 0.013
inch thick steel and less than 0.017 inch thick aluminum alloy
capable of withstanding an internal pressure of 95 psig and having
therein a beverage under pressure, said container including a
generally cylindrical body having integral side and bottom walls,
said bottom wall comprising a central inwardly domed depression
surrounded by an annular panel, said depression having a marginal
circular intersection with said annular panel, at least said
annular panel having been outwardly distinded by pressure of said
beverage to permanently change the shape of the bottom wall such
that said circular intersection becomes the outermost extent of the
bottom wall, said annular panel being inclined into a generally
conical shape and forming an obtuse angle with said sidewall, the
percentage ratio of the area determined by the radius of said
circular intersection to the area determined by the outer radius of
said annular panel being in the range of from approximately 15
percent to approximately 60 percent, said circular intersection
alone providing a stable base upon which the container rests in an
upright position.
9. The container body of claim 8 wherein the percentage ratio of
areas is about 50 percent.
10. The container body of claim 8 wherein the percentage ratio of
areas is about 40 percent.
11. The container body of claim 8 wherein the percentage ratio of
areas is about 35 percent.
12. The container body of claim 8 wherein the percentage ratio of
areas is about 30 percent.
13. The container body of claim 8 wherein the percentage ratio of
areas is about 25 percent.
14. The container of claim 8 wherein the nominal outside diameter
of the sidewall is 2 10/16 inches and wherein the nominal diameter
of the depression is in the range of from about 1 inch to about 1.5
inches.
15. The container of claim 8 wherein the nominal outside diameter
of the sidewall is 2 10/16 inches and the area ratio is about 40
percent.
16. The container of claim 8 wherein the body is a drawn and ironed
container body.
17. The container of claim 2 wherein said body comprises
tin-electroplated steel.
18. The container of claim 17 wherein said steel is 103 pound plate
before being drawn and ironed.
19. The container of claim 16 wherein said body comprises
aluminum.
20. The container of claim 19 wherein said aluminum is 0.014 inch
in thickness before being drawn and ironed.
21. An eversion resistant bottom wall construction for a
substantially rigid drawn metallic cylindrically shaped pressurized
beverage container subjected to internal pressure and having
integral side and bottom walls of thin metal, said bottom wall
comprising:
an annular panel integrally connected to the side wall of said
container;
an inwardly extending depression centrally disposed in said panel,
said depression merging peripherally with said panel in a circular
base edge, the supplement of the angle formed therebetween being no
less than 43.degree.;
the projected area of said depression constituting no less than 15
percent and no more than 60% of the total projected area of said
bottom wall;
at least said annular panel having been outwardly distended by
pressure of said beverage to permanently change the shape of the
bottom wall such that said circular base edge becomes the outermost
extent of the bottom wall, said depression remaining inwardly
extending from said annular panel, said circular base edge alone
providing a stable support for said container.
22. An eversion resistant bottom wall construction for a
substantially rigid cylindrically shaped beverage container
subjected to internal pressure, said bottom wall being of metal
selected from the group consisting of less than 0.013 inch thick
steel and less than 0.017 inch thick aluminum alloy, said bottom
wall comprising:
an annular panel integrally connected to the side wall of said
container;
an inwardly extending depression centrally disposed in said panel,
said depression merging peripherally with said panel in a circular
base edge;
the projected area of said depression constituting no less than 15
percent and no more than 60 percent of the total projected area of
said bottom wall;
at least said annular panel having been outwardly distended by
pressure of said beverage to permanently change the shape of the
bottom wall such that said circular base edge becomes the outermost
extent of the bottom wall, said depression remaining inwardly
extending from said annular panel, said circular base edge alone
providing a stable support for said container.
23. The eversion resistant bottom wall construction for a
cylindrically shaped container as defined in claim 22 wherein the
supplement of the angle formed by the peripheral merging of said
depression with said annular flat panel is no less than 43.degree.
and no greater than 90.degree..
24. An eversion resistant, generally cylindrical metal container
having therein a product under pressure, said container including a
body drawn and ironed from relatively thin metal sheet selected
from the group consisting of less than 0.013 inch thick steel and
less than 0.017 inch thick aluminum alloy, said body having a
generally cylindrical sidewall having a transition edge, said
transition edge being integral with a bottom wall, said bottom wall
comprising a central inwardly concave dome surrounded by an annular
panel extending to said transition edge, said dome having a
marginal circular intersection with said panel, at least said
annular panel having been outwardly distended by pressure of said
product to permanently change the shape of the bottom wall such
that said circular intersection becomes the outermost extent of the
bottom wall said intersection being in the form of a radius between
said dome and said panel, said intersection alone providing a
stable base upon which the container rests in an upright position,
the percentage ratio of the area of the circle encompassed by said
intersection to the area of the circle encompassed by the
transition edge is in the range of from about 15 percent to about
60 percent.
25. The container of claim 24 wherein the transition edge is an
inwardly bevelled section of the sidewall.
26. The container of claim 24 wherein the transition edge is a
radius.
27. An eversion resistant bottom wall construction for a
substantially rigid drawn metallic cylindrically shaped container
having therein a beverage under pressure and having integral side
and bottom walls of thin metal, said bottom wall comprising:
an annular panel integrally connected to the side wall of said
container;
an inwardly extending depression centrally disposed in said panel,
said depression merging peripherally with said panel in an angled
annular base edge, the angle formed thereby being no less than
about 43.degree.;
the projected area of said depression constituting no less than 15
percent and no more than 60 percent of the total projected area of
said bottom wall;
at least said annular panel having been outwardly distended by
pressure of said beverage to permanently change the shape of the
bottom wall such that said annular base edge becomes the outermost
extent of the bottom wall, said depression remaining inwardly
extending from said annular panel, said annular base edge alone
providing a stable support for said container.
28. An eversion resistant bottom wall construction for a
substantially rigid cylindrically shaped container having therein a
beverage under pressure and having integral side and bottom walls
drawn and ironed from sheet metal selected from the group
consisting of less than 0.013 inch steel and less than 0.017 inch
aluminum alloy, said bottom wall comprising:
an annular panel integrally connected to the side wall of said
container;
an inwardly extending depression centrally disposed in said panel,
said depression merging peripherally with said panel in an angled
annular base edge, the angle formed thereby being about
43.degree.;
the projected area of said depression constituting no less than 15
percent and no more than 60 percent of the total projected area of
said bottom wall;
at least said annular panel having been outwardly distended by
pressure of said beverage to permanently change the shape of the
bottom wall such that said annular base edge becomes the outermost
extent of the bottom wall, said depression remaining inwardly
extending from said annular panel, said annular base edge alone
providing a stable support for said container.
29. The construction of claim 28 wherein the bottom wall comprises
3004 H-19 aluminum and has a thickness greater than 0.010 inch and
less than 0.017 inch.
30. The construction of claim 28 wherein the bottom wall comprises
T-1 temper, tin-electroplated steel and has a thickness greater
than 0.010 inch and less than 0.013 inch.
Description
The present invention relates generally to an improved can or
container construction which enhances the ability of the container
to maintain an upright standing position when the container is
subjected to internal pressure. More particularly, the present
invention relates to an improved bottom wall construction for a
container, in which the side and bottom walls of the container body
are integrally formed, such that when the container is subjected to
internal pressure the bottom wall is deformed in a uniform and
predictable manner to provide a suitable base upon which to
uprightly position the container.
At the present time conventional metallic containers may be formed
from either two or three pieces of metallic material. In the
three-piece container the components include a container body,
which may be cylindrical in shape, and two suitable end closures
secured to the ends of the container body. The components of the
two-piece container include a container body having integral side
and bottom walls and a separate end closure for closing the one
open end of the container body. The two-piece container, being the
type container with which the present invention is primarily
concerned, presents numerous advantages over the conventional
three-piece container with respect to manufacturing ease and
aesthetic appeal. The container body of the two-piece container of
the present invention is preferably made by drawing and ironing
sheet metal and must, therefore, generally be constructed from a
relatively ductile material. Drawing and ironing is a known can
body forming process in which a sheet metal blank is first drawn
into a relatively shallow cup and then the walls of the cup are
ironed, which is to say thinned and extended to a height
appropriate for the can. The bottom remains approximately as thick
as the starting sheet. U.S. Pat. Nos. 2,412,813, 3,203,218 and
3,360,157 describe this process. If the container is made with a
flat bottom wall, the internal pressures encountered with
pressurized products such as beer or carbonated beverages cause the
bottom wall of the container to deform outwardly into a convex
configuration making it unstable when stored in an upright position
unless the strength of the bottom wall is increased to withstand
the pressure. Increasing the thickness of the starting sheet will
provide a stronger bottom, but at the cost of more metal and higher
shipping weights.
In order to increase the strength of bottom walls of container
bodies having integral side and bottom walls, to thereby better
withstand the pressures created by beer and carbonated beverages,
it is well known to form the bottom wall of the container as an
inwardly concave dome or depression which extends substantially
throughout the bottom wall of the container. The increased strength
provided by this fully domed bottom wall construction resists
deformation of the bottom wall under increased internal pressure of
the container with little change in the configuration of the bottom
wall throughout the pressure range for which the container is
designed. The container rests on the rim of the dome adjacent the
cylindrical wall. A disadvantage of this fully domed construction
is that upon elevation of the pressure beyond a critical point, the
bottom wall of the container suddenly pops out or everts. This is a
catastrophic failure since the container suddenly becomes
unserviceable due to its now swollen shape. In order to prevent
such failure, the thickness of the bottom wall of the container
must be sufficient to safely satisfy not only the pressure
conditions anticipated, but also, because of the catastrophic
nature of the eversion, must be able to resist pressures in excess
of anticipated normal pressures. Another disadvantage of the full
concave bottom wall construction is the difficulty of washing and
protectively coating the interior of the container due to the high
angle of the depression, which is in the nature of a countersink.
Since the containers are washed and spray coated from their open
ends, the bottom walls require a great deal of effort to be
properly washed and coated. A still further disadvantage of the
full concave bottom wall construction is the internal volume lost
by virtue of the intrusion of the dome. More metal must be used to
make the container large enough for its design capacity.
It is, therefore, an object of the present invention to provide a
metal container having integral side and bottom walls wherein an
improved bottom wall construction reduces or eliminates
catastrophic eversion failure of the bottom wall, permits rather
than resists expansion of the container under internal pressure
while maintaining a stable support, and wherein minimum metal is
required for a particular internal volume and for sufficient
strength to safely withstand anticipated internal pressures.
The cylindrical container of the present invention is constructed
with the integral bottom wall including a substantially flat panel
section having a centrally disposed circular depression or dimple
therein, the base area of the depression being no greater than
approximately 60 percent and no less than approximately 15 percent
of the total area of the bottom wall. This bottom wall construction
provides a stable supporting base for the container when the
container is subjected to internal pressure since the bottom is
uniformly deformed by the internal pressure into a shape having a
uniform circular ring upon which the container rests.
The present invention will be described and understood more readily
when considered together with the accompanying drawings; in
which;
FIG. 1 is a perspective view of the container body of the present
invention shown in longitudinal section;
FIG. 2 is a perspective view of a slightly modified form of the
container body of the present invention shown in longitudinal
section;
FIG. 3 is a cross-sectional view of the lower portion of a prior
art container body;
FIG. 4 is a cross-sectional view of the lower portion of another
prior art container body;
FIG. 5 is an enlarged, cross-sectional detailed view of the lower
portion of the container body of FIG. 1;
FIG. 6 is an enlarged, cross-sectional detailed view of the lower
portion of the container body of FIG. 2;
FIGS. 7 through 11 are enlarged, cross-sectional detailed views of
the lower portion of the container body of FIG. 1 showing the
deformation of the bottom wall as the container is subjected to
increasing internal pressures;
FIG. 12 is an enlarged cross-sectional detailed view of the lower
portion of a container body of the present invention illustrating
the manner of measurement of the ratio of the area of the
depression to the total area of the bottom;
FIGS. 13-16 are graphic displays of data for different starting
materials showing can height growth as a function of internal
pressure for various depression sizes for containers according to
the present invention,
FIG. 17 is a graphic display of data showing the stability of cans
according to the present invention as a function of the size of the
depression; and
FIGS. 18-21 are graphic displays of data for different starting
materials showing percentage change in depression or dimple depth
as a function of internal pressure for various depression sizes for
containers according to the present invention.
Now referring to the drawings, there is shown in FIG. 1 a container
body, generally designated 20, which has been sectioned in half in
order to better demonstrate the present invention. The container
body includes a side wall 22 and a bottom wall 24 which are
integrally formed. This type of container body, having integral
side and bottom walls, is preferably formed of any suitable
metallic material such as steel or aluminum by the known process of
drawing and ironing.
As is shown in FIGS. 1 and 5, the bottom wall 24 of container body
20 has a substantially flat annular panel section, generally
designated 26, having a centrally disposed circular depression or
dimple 28 formed therein. The depression 28 may be of almost any
suitable shape provided that the base edge or marginal intersection
30 of the depression with the annular panel 26 is circular so that
the annular panel section 26 surrounds the depression. Although the
depression 28 is shown in the drawings as having the shape of a
segment of a sphere it may also be in the shape of a truncated
cone, an ellipsoidal segment or a paraboloidal segment. At the
periphery of the annular panel section 26 of FIGS. 1 and 5 there is
provided a 45.degree. angled transition edge, designated 32,
integrally interconnecting bottom wall 24 to side wall 22.
As is shown in FIGS. 2 and 6, which show a slightly modified form
of the present invention, the 45.degree. angled transition edge 32
is replaced by a radiused transition edge, designated 32a. The open
end of container 20 is provided with a substantially horizontal
flange, generally designated 34, for the purpose of seaming an end
closure (not shown) to the upper extremity of side wall 22.
Prior two-piece containers for pressurized products such as beer or
carbonated beverages have inwardly domed bottoms which extend to
the cylindrical side walls. Many of those marketed employ a
transition between the rim of the dome and the sidewall which
usually is in the form of a radius which forms a rim on which the
can sits. FIG. 3 is a depiction (not to scale) of one variant of
this general construction in which the sidewalls 112 are turned
inwardly toward the bottom to form a chamfered transition 114 which
then merges with a radius 118 which forms the rim upon which the
can sits. The dome 116 extends from rim 118 across the bottom 110
of the can. FIG. 4 is a depiction (not to scale) of a proposed
construction shown in FIGS. 2 and 3 of U.S. Pat. No. 3,272,383 to
Harvey. To more closely resemble a three-piece can for handling
purposes, the proposed Harvey impact extruded two-piece can is
provided with a bead 155 having the approximate external size and
shape of the bottom chine of a conventional three-piece can. The
bottom 152 extends beyond the cylindrical wall of the can to
accommodate the bead 155. Between the bead 155 and the inward dome
150 is an annular margin 154 for supporting the container.
None of these prior bottom constructions is intended to expand in
height in response to internal pressures. All are intended to
resist expansion by confining the rim of the dome by the adjacent
side walls or, in addition, by the thick walls and bottoms inherent
in containers made by impact extrusion. The large domes of these
prior art constructions are prone to sudden catastrophic eversion
or pop-out when the internal pressure exceeds the structural
strength of the bottom wall. The construction of the present
invention avoids this catastrophic failure since the container of
the present invention expands in a gradual predictable manner
without eversion and continues to provide a stable support base
throughout the pressure range for which it is designed and
beyond.
FIGS. 7 through 11 demonstrate five stages in the continuous
deformation through which the bottom wall 24 of a container body
according to the present invention passes when subjected to
increasing pressures. Throughout the stages depicted, the dimple or
depression 28 remains concave in the inward direction thereby
providing a suitable support base at the marginal circular
intersection or edge 30 on which the container rests. The first
stage, which is represented in FIG. 7, depicts the configuration of
the bottom wall 24 when the container is subjected to no pressure,
the configuration in this figure is identical to that shown in FIG.
5. The second stage, shown in FIG. 8, depicts the configuration of
the bottom wall when the container is subjected to an increased
pressure over that of FIG. 7. The height of the depression 28 in
this second stage is slightly reduced or flattened and annular
panel section 26 is slightly angled downwardly due to the applied
pressure which causes the development of horizontal, outwardly
directed forces near the edge 30 of the depression 28. The
deformation in this stage is still in the elastic range and
therefore, the bottom wall 24 will return to its original shape as
the pressure is released. The third stage is depicted in FIG. 9
wherein the pressure is increased over that of the second stage and
where the material no longer remains in the elastic range. As can
be readily seen, the height of the depression 28 is further
reduced. FIG. 10 depicts the fourth stage through which the bottom
wall 24 passes when subjected to a further increased pressure over
that of the third stage. As can be seen, the panel section 26 and
the angled transition edge 32 are deformed outwardly even further
in this stage. In addition, the height of the depression 28 is
further reduced as a result of the increased pressure. The fifth
stage is depicted in FIG. 11 where the increased pressure further
reduces the height of depression 28. At this stage, there is a
gradual and controlled further flattening of the depression 28 and
the radius of intersection of edge 30 unrolls. This multiple stage
controlled expansion is to be contrasted with the non-expansion
followed by irregular bulging and catastrophic eversion encountered
with the large domes of the prior art.
Proper selection of angle A (FIG. 7) the acute angle of the
intersection of the annular panel 26 with the immediately adjacent
portion of depression 28 will delay the deformation of stage four,
depicted in FIG. 10, until a more elevated pressure is reached.
However, this will not prevent the occurrence of deflection of the
annular panel section 26 into a generally conical shape as depicted
in FIGS. 9 through 11. The greater angle A is, the greater the
resistance to outward expansion of bottom wall 24. It has been
found that angle A should be no less than about 43.degree.. In
order for the depression 28 to be formed with conventional dies,
angle A should be made no greater than 90.degree. and preferably
about 60.degree. in order to properly wash and spray coat the
bottom wall of the container body.
Cans used for the packaging of pressurized products such as beer or
carbonated beverages must be able to withstand internal pressures
of about 95 psig. Beer is usually pasteurized in the filled and
sealed can at a temperature and for a time which results in an
internal pressure of 85 psig. To allow for errors of temperature or
time, the minimum acceptable pressure capacity is 90 psig.
Carbonated beverages vary according to the degree of carbonation.
The highest degree of carbonation is encountered with club soda
water which may produce an internal pressure at 100.degree.F of
approximately 95 psig. Since the same can body should be useful for
all pressurized beverages, 95 psig is taken to be the minimum
pressure capability.
Unlike the previous pressurized beverage containers, the
construction of the container of the present invention is intended
to expand in height as a result of internal pressure. When shipped
from the beverage maker, filled cans according to the present
invention are expanded from their unfilled configuration. Should
the filled container encounter conditions which result in internal
pressures in excess of the 95 psig for which they were designed,
the containers will gradually and controllably expand further. They
will not suddenly evert as do the fully or substantially fully
domed containers of the prior art. This gradual intentional
deformation of the bottom wall lessens the risk of explosion and
maintains the container in a serviceable condition.
As the container of the present invention expands due to internal
pressure, the marginal circular intersection or edge 30 of the
depression or dimple 28 becomes the base upon which the container
sits. The stability of the container depends upon the diameter of
edge 30 in relation to the size of the can. The stability of the
container is generally independent of the extent of its expansion
or growth in height.
Stability of the container is important to the maker and to the
consumer. Unstable cans interfere with the operation of the filling
and packing machinery. Such machinery operates at high speed and
cans which rock or wobble excessively can not be handled by the
machinery. From the consumer's point of view, a can which tips,
rocks or wobbles excessively when set down is an annoyance.
FIG. 12 shows the lower portion of a container according to the
present invention similar to that of FIG. 6. For convenience, the
range of sizes of depressions or dimples is expressed as a
percentage ratio of the area of the dimple to the area of the
bottom of the container. The diameter d of the dimple or depression
is measured between the centers 41 and 42 of the radius 30 which
forms the transition or intersection between the exterior surface
of the dimple and the exterior surface of the annular panel 26 of
the bottom. Similarly, the diameter D of the bottom is measured
between the centers 43 and 44 of the radius 32a which forms the
transition between the outer diameter of the annular panel 26 and
the side wall 22. The ratio of the squares of these diameters
(d.sup.2 /D.sup.2) is equal to the percentage area ratio. This
manner of measurement realistically determines the relative areas
upon which pressure acts to deform the container and eliminates the
relatively rigid sidewall transition angle 32 or radius 32a. FIG. 7
shows the centers to be used for measurement of a bevelled or
angled transition style of bottom using the same numbers as are
used in FIG. 12. By way of example, a 13/8 inch nominal dimple
diameter in a 210 (2 10/16 inch) diameter beer can having a
radiused transition bottom as illustrated in FIG. 12 has an area
ratio of 41.4 percent. The measured bottom diameter D between
transition radii centers is 2.291 inch and the measured dimple
diameter d between transition radii centers is 1.474 inch.
Referring again to FIGS. 1, 2, 5 and 6, it has been found that the
area of the base of the depression 28 must be between approximately
15 percent and 60 percent of the total area of bottom wall 24 in
order to prevent the inward curvature of depression 28 from bulging
outward under increased pressures.
DESCRIPTION OF A PREFERRED EMBODIMENT
A can according to one preferred embodiment is a 210 size 12-ounce
can suitable for beer or carbonated beverages according to FIG. 2.
It is made by drawing and ironing 103 lb. T1 tin electroplated
steel plate about 0.011 inch thick. The nominal outside diameter of
the can body is 2 10/16 inch. The actual outside diameter is 2.556
inch. The actual height measured from the flat annulus 26 to the
top of the lid flange 34 is 4.812 inch. The sidewalls are 0.0038
inch thick. The bottom wall is joined to the cylindrical sidewall
by a transition radius of 0.125 inch to the inside. The diameter d
of the dimple or depression measured to the centers of the
transition radii is 1.475 inch for a nominal dimple diameter of
1.375. The dimple is approximately eliptical in section in that it
is generated by a major radius of 1.500 and minor radii of 0.250.
The dimple edge transition radius between the annular panel and the
dimple is 0.050 to the inside. Angle A between the dimple and the
annular panel is approximately 65.degree.. The area ratio of dimple
area to bottom area is 41.1 percent.
A can according to a second preferred embodiment is also a 210 size
12-ounce pressurized beverage can according to FIG. 2. It is made
by drawing and ironing 0.014 inch 3004 H-19 aluminum. The
dimensions are identical to those of the steel can described above
with the exceptions of an actual outside diameter of 2.559 inch, a
sidewall thickness of 0.0048 inch, a dimple edge transition radius
of 0.055 inch and a dimple diameter d of 1.485 inch for a nominal
dimple diameter of 1.375 inch. The ratio of dimple area to bottom
area is about 41.7 percent.
TEST RESULTS
Comparison tests of the deformations encountered with a flat bottom
wall container, a full concave bottom wall container as depicted in
FIG. 3, and a container according to the present invention were
made. The 12-ounce containers utilized in these tests were drawn
and ironed from the same material, i.e. 0.013 inch, type L steel
having a Rockwell Hardness of R 30 T scale 53.+-.3 and a number 50
electrolytic tin plate. This material is called 118 pound plate.
The dimensions of the tested containers were nominally 2 11/16
inches in diameter and nominally 4 13/16 inches in height. The
container constructed according to the present invention (Table
III) was provided with a 45.degree. angled transition edge, a
depression having the shape of a segment of a sphere of 1 inch
radius and a height of approximately 0.260 inches, a nominal
diameter of 1.25 inches, and an area ratio of 37.3%. The following
tables compare measured deformations of the various bottom wall
configurations at stated pressures:
TABLE I ______________________________________ Flat Bottom End -
45.degree. Angled Transition Edge Permanent Pressure Deformation
Deformation Stability (psig) at Centerline at Centerline Comments
______________________________________ 0 0 0 Stable 40 .044 .028
Unstable 60 .057 .037 Unstable 80 .069 .047 Unstable 100 .080 .057
Unstable 120 .090 .068 Unstable
______________________________________
TABLE II
__________________________________________________________________________
Full Concave Bottom Wall Perma- Perma- nent nent Deforma- Deforma-
Deforma- Deforma- tion at tion at tion at tion at Depres- Depres-
edge of edge of Pressure sion sion Depres- Depres- Stability (psig)
Center Center sion sion Comments
__________________________________________________________________________
0 0 0 0 0 Stable 40 .005 .001 .002 .0005 Stable 60 .010 .003 .005
.002 Stable 80 .021 .010 .011 .007 Stable 85 CATASTROPHIC FAILURE
AT THIS PRESSURE Unstable
__________________________________________________________________________
TABLE III
__________________________________________________________________________
Bottom Wall According to Present Invention Perma- Perma- nent nent
Deforma- Deforma- Deforma- Deforma- tion at tion at tion at tion at
Depres- Depres- edge of edge of Pressure sion sion Depres- Depres-
Stability (psig) Center Center sion sion Comments
__________________________________________________________________________
0 0 0 0 0 Stable 40 .038 .021 .022 .008 Stable 60 .061 .0415 .044
.026 Stable 80 .086 .067 .064 .049 Stable 100 .120 .100 .085 .0745
Stable 110 .150 .126 .105 .095 Stable
__________________________________________________________________________
The results of these tests indicate first of all that the container
having the flat bottom wall was unstable in the upright standing
position due to bulging of the center portion of the bottom wall at
pressures over approximately 20 psig, thereby making it totally
unsuitable for pressurized products such as beer and carbonated
beverages. The full concave bottom wall construction demonstrated a
catastrophic failure, in other words a sudden eversion. popping out
or bulging of the bottom wall, at pressures beyond 80 psig.
However, at low pressures the deformation at the center of the full
concave depression was substantially smaller, as indicated in the
tables, than in the case of the other constructions. The depression
in the bottom wall of the container of the present invention was
found to remain in the inward direction without any substantial
reduction in its cross-sectional area up to 110 psig. In addition
stability tests indicated no rocking with the containers of the
present invention and they were rated stable at all pressures
specified.
As can be readily seen from studying the above tables, an
internally pressurized container constructed in accordance with the
present invention is able to maintain its stability in the upright
standing position at higher pressures than similar prior art
containers. Furthermore, the thickness and strength of the bottom
wall material may be diminished, relative to the other
constructions, without correspondingly diminishing the stability of
the container when it is positioned in the upright standing
position. In addition to the above described container which is the
12-ounce size, other differently dimensioned containers have been
produced and studied with similarly satisfactory results. One such
container, having a 10-ounce capacity, was constructed with a 2
15/32 inch nominal diameter and a nominal height of 4 13/16 inches.
The depression in the bottom wall of this container was identical
to the depression in the bottom wall of the twelve ounce container
of Table III. A 32-ounce container has also been constructed with
nominal sizes of 3 7/16 inch diameter and 6 11/16 inch height. The
bottom wall depression had a base diameter of approximately 1.66
inches and a height of approximately 0.44 inches and the shape of a
segment of a sphere of one inch radius.
Data from extensive testing of cans made in accordance with the
present invention are graphically displayed in FIGS. 13 through 21.
FIGS. 13-16 each show can height growth in inches plotted against
internal pressure for various diameter dimples or depressions. FIG.
17 is a plot of tilt angles for various nominal dimple diameters.
FIGS. 18-21 show the percentage change in dimple depth measured
from rim 30 to the center of the dimple plotted against internal
pressures for various nominal dimple diameters.
To generate the data of FIGS. 13-21, cans were made of aluminum and
of steel in two thicknesses for each material. The cans were formed
by the drawing and ironing process. The thicker materials represent
the current commercial minimum thicknesses for conventional fully
domed bottom pressurized beverage cans. The thinner materials
represent the minimum thickness for pressurized beverage cans now
possible when made in accordance with the present invention. All
cans were made with a nominal outside diameter of 2 10/16 inch.
This is a common 12-ounce size for beer or carbonated beverages and
is frequently called a 210 can. The cans were made with spherical
dimples which range from 0.750 inch to 1.852 inch in nominal
diameter. Angle A between the dimple and the flat annulus was
43.degree. for all cans. The steel cans were made from 118 pound
and 103 pound tin electroplate stock of T1 temper having respective
thicknesses of 0.013 inch and 0.011 inch. The sidewall thickness of
the finished can bodies was 0.0038 inch. The aluminum cans were
made from 0.017 inch and 0.014 inch 3004 H-19 drawing and ironing
alloy and had a wall thickness of 0.0048 inch. The transition
radius between the sidewall and the flat annulus of the bottom was
approximately 0.125 inch.
The can bodies were subjected to internal air pressure in a testing
fixture which permitted measuring the increase in height of the can
at different pressures. The cans were subjected to increasing
pressures up to 110 psi or until the can failed or obviously would
hold no more pressure. Each height growth reading for an increased
pressure was made at that increased pressure, but was preceded by a
return to 30 psi in an effort to simulate the pressure cycling
which a can filled with pressurized beverage might be expected to
encounter in commerce. Height data for five identical cans was
collected and the average of the five was plotted as a function of
pressure. The curves of FIGS. 13-16 are fitted to those five-can
average data points for each dimple size. Thus, dimple size is the
parameter for the graphs.
The following tabulation relates nominal dimple diameters to the
letter key used in FIGS. 13-16 and 18-21 to identify the curves and
also relates nominal dimple diameter to the ratio of the dimple
area to the bottom area as measured in the manner described in
connection with FIG. 12:
Curve Key Nominal Area Ratio Letter Dimple Diameter (d.sup.2
/D.sup.2) ______________________________________ A 1.852" 72.5% B
1.750 65.1 C 1.500 48.7 D 1.375 41.4 E 1.250 34.7 F 1.000 23.0 G
0.750 13.7 ______________________________________
Comparison of FIGS. 13 through 16 shows that larger diameter
dimples initially resist height expansion more than the smaller
dimples. At a higher pressure the curves for the larger dimples
increase in slope and cross over the curves for the smaller
dimples. This indicates that the rate of height growth for the
larger dimples rather suddenly exceeds the rate of height growth
for the smaller dimples. Soon after this cross-over, the larger
dimple cans either fail or diplay a very great rate of height
growth indicating imminent failure. The actual increase in height
is not particularly significant so long as it is not excessive. The
can filling and handling machinery can be adjusted to accommodate
high cans. A height increase of much more than one-quarter inch in
a 12 ounce container would be excessive. Of more significance is
the slope of the curve which represents the rate of increase in
height. The steep slope typical of the larger dimples means a large
change in height for a small change in pressure. This indicates
that the can is near failure and also indicates that there will be
noticeable differences in height among neighboring cans. Wide
height variations among cans will lead to machine handling
difficulties and is an aesthetic problem.
FIGS. 18-21 show the percentage ratio of the change in dimple depth
to the original dimple depth. The data for these Figures was
derived along with the can height growth data of FIGS. 13-16 from
the same cans under test. Comparison of FIGS. 18-21 reveals that
the larger diameter dimples above a 60 percent area ratio tended to
roll out or flatten severely at pressures well below 95 psig.
As was stated before, 95 psig is taken to be the practical minimum
pressure capability for pressurized product cans intended for beer
and highly carbonated beverages. Consequently, cans which display a
high rate of increase in height growth or dimple flattening or
roll-out at pressures below 95 psig are not acceptable.
It is clear from FIGS. 13 through 16 and 18 through 21 that curves
A and B represent cans that failed below 95 psig or in the case of
0.017 aluminum represent cans with height growth rates or dimple
depth change rates which are unacceptable before 95 psig is
reached. Curve A is for cans having a nominal dimple diameter of
1.852 inches or an area ratio of 72.5 percent. Curve B is for cans
having a nominal dimple diameter of 1.750 or an area ratio of 65.1
percent. Curves C through G represent cans which have nominal
dimple diameters of 1.500 inches or less. These cans display
acceptable height growth and dimple depth change characteristics.
Translated into area ratios, cans above about 60 percent are
unacceptable.
It should be noted that the data for the curves of FIGS. 13 through
16 represent can height growth at a particular pressure. The can
will contract in height if the internal pressure decreases, but
will not necessarily return to the height which that lower pressure
would have caused initially because some permanent deformation
occurs. By way of illustration, an aluminum beer can made from
0.014 stock with a nominal 1.375 inch dimple is represented by
curve D of FIG. 16. At the 85 psig internal pressure expected
during pasteurization, the height growth is slightly more than the
0.125 inch which 85 psig caused. When later cooled, the internal
pressure will drop to 30 psig or less. The permanent height growth
will lie between the 0.050 inch which 30 psig originally caused and
0.125 inch, probably on the order of 0.100 inch. Thus, the data of
FIGS. 13-16 is not representative of the increase in height present
in the can when received by the consumer.
FIGS. 13-16 and 18-21 show that smaller dimples better withstand
internal pressures above 60 or more psig.
FIG. 17 shows that stability or resistance to tipping, rocking or
wobbling decreases as dimple size is reduced. Although a can with a
small dimple may be excellent from a pressure standpoint, it may be
unacceptable from a stability standpoint. The data points plotted
on FIG. 17 were obtained by placing filled, sealed and pasteurized
12 ounce 210 cans of simulated beer on a horizontal platform and
slowly tilting the platform until the can started to tip. The angle
of the platform and the nominal dimple size were noted and the
average of several cans was used to produce the data points. Cans
having a nominal dimple diameter of 0.750 are considered to be
unstable because they rock or wobble disconcertingly when set upon
a table and cause problems on high speed filling and handling
equipment. Cans having nominal dimple diameters larger than 0.750
are considered to be adequately stable for processers and
consumers. The larger dimple cans approach the stability of a fully
domed bottom can. Translated into area ratios, those cans having an
area ratio above about 15 percent are adequately stable.
As a part of this test program cans of the same description as
above were made of 90 pound steel plate 0.010 inch thick and of
0.010 inch aluminum. Only a few of the steel cans and none of the
aluminum cans were capable of withstanding 95 psig internal
pressure. Metal this thin is not appropriate for pressurized
beverage cans.
The various testing reported herein verifies that fully domed 210
or 211 12-ounce beer cans are prone to failure at pressures as low
as 85 psig unless made of materials stronger than 118 pound T1
steel plate or than 0.017 inch 3004 H19 aluminum. However, cans
according to the present invention can be made from 103 pound steel
plate or from 0.014 inch aluminum. The enabled use of thinner metal
coupled with the smaller volume loss occasioned by the dimple as
compared with the full dome represent very substantial metal
savings. Further, the thinner can of the present invention is able
to withstand the 95 psig pressure required for containers of highly
carbonated beverages so that the same can body can be used for
either beer or beverages at all carbonation levels. Fully domed
0.017 inch aluminum 12-ounce 210 drawn and ironed cans weigh
approximately 34 pounds per thousand. Aluminum cans according to
the present invention are made of 0.014 inch stock and weigh
approximately 28 pounds per thousand. The prior art aluminum cans
are over 21 percent heavier. Similarly, fully domed 118 pound steel
12-ounce 210 drawn and ironed cans weigh about 76.9 pounds per
thousand whereas 103 pound steel cans according to the present
invention weigh about 64.4 pounds per thousand. The prior art steel
cans are over 19 percent heavier. Since metal is a major factor in
can cost, metal savings of this degree are significant. Thus, the
present invention not only provides a can which comfortably
withstands significantly higher internal pressures than the fully
domed can of the prior art and reduces the chance of explosion of
cans exposed to conditions which generate pressures in excess of
the design pressure, but also effects a substantial reduction in
can cost.
* * * * *