Note: Descriptions are shown in the official language in which they were submitted.
lV~9~ ~
BACKGROUND OF THE INVENTION
The present invention relates to containers of the
type disclosed in applicants co-pending Canadian application
serial number 310,242, filed August 29, 1978. It particula~ly
relàtes to an improvement of the container construction described
in Canadian patent application serial number 310,242 and assigned
to the-~ame assignee as the instant case.
Containers of the type described in serial number
310,242 exhibited certain unexpected and outstanding strength
characteristics when compared with similar characteristics Of
certain prior art types of cans. When the~ se'r'ial''numbèr 310,242
types of cans were produced at top production-speeds, however,
they ~ometime~ had a tendency to increase the normally expected
wear on the punches withiwhich the cans were made. Illustrated
embodiments of the instaPt invention, however, provide a container
wherein such punch-wear ls reduced.
Containers of the "drawn-and-ironed" type exhibit three
main points of failure when subjected to compressive loads such
as occur when the cans are filled and closed with a conventional
end. Such failures tend to occur in either the can's neck portion
or its side wall or in the can's bottom. The instant invention
provides a container wherein such failures occur most frequently
in the container` 8 bottom portion, and, moreover, can absorb
relatively large quantities of energy before catastrophically
failing in the sense that the container is no longer suited for
its intended purpose. Moreover, as will be explained more
--1--
B
398'~
fully shortly, cans of the invention are quite predictable
in that failures can be expected to occur within a relatively
narrow range of loads. Hence, they can be made from thinner
stocks since smaller margins of error are permitted.
There are several advantages to providing a con-
tainer that is most likely to fail at the bottom. In ~his
regard, particularly in "drawn-and-ironed" containers, the
thickness of the bottom does not diffex significantly from
the sheet stock with which such cans are normally constructed.
Hence, the bottom-thickness of such cans can be relatively
accurately controlled. It is the side-wall portions of these
cans that are "drawn-and-ironed," however, and the side wall
thicknesses, therefore, are more difficult to control. Con-
sequently, to the extent a can's failure modes are primarily
at the bottom, the can's strength can be more accurately
controlled and its failures more accurately anticipated.
Additionally~ the can of the instant invention is
structured so that compressive forces cause initial deflec-
~ tion (a type of failure) in the bottom of the container; and,
moreover, the bottom undergoes relatively large distortionsbefore the can undergoes catastrophic failures such as in
its side wall or neck. Consequentl~, so long as the com-
pressive fo:ces are not so large as to cause catastr~phic
failure, the container can still be filled and seamed without
being discarded. In this connection, the can of the inven-
tion absorbs substantial quantities of energy as the bottom
deflects. Consequently, it is possible to save more cans for
filling and seaming than might otherwise be the case.
. ., .. , ~ . . , , . ~ .
., ~. , . .
, ~ .
1(~ 9~
A still further advantage of the invention lies in the
resulting can's ability to be constructed from a thinner gauge
sheet stock. Similarly, as will become more apparent shortly,
although more absorptive of energy, the can of the invention
has a somewhat larger volume than that described in serial
number 310,242 and, to that extent, one embodiment of tpe
invention has an even greater ability to have the position of its
central portion selectively adjusted in order to maintain can-
volume and accommodate relatively large amounts of tool-wear with-
out requiring new tooling.
A further advantage of another embodiment of theinvention:iis its tendency to have a center portion of its
bottom "cricket" inwardly upon reIief of pressure when the can
is opened after filling. In this.manner the particular
embodiment is rendered more physically stable after it is opened
even though its bottom has a tendency to "dome" outwardly when
press~rized.
. SUM~RY
A container of.the invention includes a s-ide wall that
is joined to a bottom portion thereof by a first frustoconical
portion and a first semi-torroidal portion. The first semi-
torroidal portion is, in turn, joined to a second semi-torroidal
portion and, a bottom-closing portion. This structure results
in a container which has high energy absorption capabilities and
whose failure-mode is predominantly in the bottom portion thereof.
In accordance with one aspect of the present invention,
there is provided a container having a cylindrical side wall and
a bottom wall closing.one end thereof and comprising: a frusto-
concial portion having one end thereof directly attached to said
side wall; a first semi-torroidal portion having one end thereof
directly attached to the other end of said frustoconical portion,
a second semi-torroidal portion having one end thereof directly
attached to the other end of said first semi-torroidal portion;
B -3-
10~3g~7
and a central bottom-closing portion directly attached to the
other;end of said second semi-torroidal portion.
In accordance with a further aspect of the present
invention, there is provided a container having a ~ide wall and
a bottom wall and comprising: a coined semi-torroidal portion;
a frustoconical portion having one end thereof directly attached
to Raid side wall; a semi-torroidal portion having one end thereof
directly attached to said frustoconical portion and having the
other end thereof directly attached to said coined semi-torroidal
portion; and a central bottom-closing portion directly attached
to the other end of said coined semi-torroidal portion.
, .
-3a-
-`` 10~398'7
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other features and advantages
of this invention will be apparent from the more particular
description of preferred embodiments thereof as illustrated
in the accompanying drawings wherein the same reference
numerals refer to the same elements throughout the various
views. The drawings are not necessarily intended to be to
scale, but rather are presented so as to illustrate principles
of the invention in clear form.
In the drawings: ,
FIG. 1 iS a fragmentary cross sectional schematic
illustration of a prior-art type of can;
FIG. 2 is a fragmentary cross sectional illustration
of the bottom portion of an embodiment of the invention;
FIG. 3 is a schematic illustration of a drawing and
ironing machine;
FIG. 4 is a greatly enlarged fragmentary view of
a portion of a punch taken along the arc 4-4 in FIG. 3; and
FIG. 5 is a view of a portion of a punch face taken
along the lines 5-5 in FIG. 3.
FIG. 6 is a schematic illustration of a test fixture
used to test OFF-AXIS strength of various types of cans;
FIGS. 7a, b, and c are schematic illustrations of
cans tested in the structure of FIG. 6;
FIG. 8 is a fragmentary cross-sectional illustration
of the bottom portion of another embodiment of the invention;
FIGS. 9a and b are schematic illustrations o~ a
bottom forming machine for the FIG. 8 embodiment; and,
FIG. 10 is a view of a can bottom taken along the
lines 10-10 in FIG. 9b.
.~ 10~39~3t7
DETAILED DESCRIPTION
Fig. 1 illustrates a prior art type of container
wherein a cylindrical side wall 12 is joined at an angle ~
to a first frustoconical portion 14 having substantially flat
inner and outer surfaces 16 and 1~. In this regard, portion
14 extends between an outwardly convex annular bottom bead 20
and a transition point 22 between the side wall 12 and the `
first frustoconical portion 14~
Fig. 2 illustrates the b~ttom portion of an embodiment
of a container of the invention. Therein, the side wall 12 is
joined to a first frustoconical portion 24 whichj in turn, is
joined to a first semi-torroidal portion 26 which, in turn, is
faired into a second semi-torroidal portion 28. The second semi-
torroidal portion 28 is attached to a third semi-torroidal portion
30 b~ a second frustoconical ~ection 32--the other side of the
third semi-torroidal portion 30 being joined to a flat central
portion 34 by a third frustoconical portion 36.
i The first semi-torroidal portion 26 is outwardly convex
from a cord 38 extending between the first frustoconical portion
24 and the second semi-torroidal portion 28--the chord 38 maXing
an angle~ with the container's axis 40. In ~his respect, in
connection with preferred embodiments of the invention, the
radius a of the first ~emi-torroidal portion 26 and the angle
r were varied between certain limits as will now be discussed in
connection with a punch that i~ used to form the structure of Fig.
2.
The schematic illustration of Fig. 3 represents a punch
46 about to drive a "cup" 4~ through a draw-and-ironing
structure 50 and against a bottom former 52. Except as will now
be described, the Fig. 3 elements are conventional and will not
be described further. The draw-and-ironing structure
-5-
B
., ~ . .
,`
iO~398'7
50, for example, includes conventional redrawing dies, ironing
rings, pilot rings, and the like, but those elements form no
part of the instant invention.
Fig. 4 represents a portion of the punch 46 whlch
forms the first semi-torroidal section 26 of the can-bottom
illustrated in Fig. 2. In this regard, portions of the punch in
Fig. 4 which correspond to the canlbottom of Fig. 2 have their
correspondance indicated by prime signs added to similar
reference numerals. For example, the can' 8 side wall 12 corre-
sponds to side wall 12' of the punch; the can's first frustoconicalportion 24 corresponds to frustoconical punch portion 24': the
can's first semi-torroidal section 26 corresponds to first ~emi-
torroidal punch portion 26': and, the canis second semi-torroidal
portion 28 corresponds to punch portion 28'.
I~e frustoconical porti,on 24' is at an angle gamma
to the side wall 12'. In this regard, best results can be
expected when ~ i9 within the range of 1 to 6. Similarly, best
results can be expected when L2, the axial length of the
~~ first frustoconical portion 24', is between 0.150 inches and
.. . ~ .. .. , ~ -- ... .
0.600 inches for a pressurized container of the conventional
"beer can" type. In these respect~, the numëric ration Ql of
gamma (in degrees)/L2 (in~inches) should be between abo~t l and
60, but is more preferably about 12. If ~ becomes too small,
exces~ive tool wear i8 likely; and if Ql becomes too large
the containers' energy absorbtive capabilities are diminished.
The first semi-to~roidal portion 26' is arcuate about
cord 38` which, when ex~ended, makes an angle~ with the container's
axis. When~ is increased, the dimension L2 also increases if
other parameters remain fixed. Similarly,
--6--
B
. ~ . . . ...
398'î~
if ~ decreases (other parameters remaining constant) the
dimension L2 becomes smaller, as the cord increases in length.
This is indicated by the dimension L3 which represents the
cord 38' in any of its various positions depending upon the ~-
changes of the angles ~ and y. ~ 1
In the above regard, the radius of the~sem,-
torroidal portion 26' should be between 0.200" and 0.700"
for a pressurized container of the conventional beer can
type. Generally speaking, however, the numeric ratio Q2
of ~ (in degrees)/R (in inches) should be between about 35
and 300. Containers having Q2 ratios of less than about 35
appear to have body and neck failures sooner than bottom
failures; and, containers having Q2 ratios over 300 appear
to have relatively low initial deformation points. The most
preferred Q2 ratio is about 85 which is in the lower end of
the above range of Q2 ratios rather than in the middle as
might otherwise be expected.
The ratios of Ll/Rl (Q3) and Ll/L2 (Q4) appear
to be of somewhat less significance. A preferred range for
Q3, however, is between about .5 and 2.5 with excellent
results being obtained where Q3 lS about 0.965. Similarly,
a preferred range for Q4 is between about 1~35 and 3.25 with
excellent results being obtained when Q4 is about 1.93.
Containers of the type just described were sub-
jected to testing to determine their energy absorptive abilities
and their tendencies to undergo bottom deformation prior to
failure of their sidewalls and necks. Test results of pre-
ferred containers were then compared with containers having
bottom configurations corresponding to that of FIG. 1. Based
on those test results, it was determined that cans of the
--7--
10~398`-~'
~(~rS~ '
above-described type having~semi-torroidal sections such as
B 26' had substantially higher energy absorption capabilities
when compared with the prior art "control" cans. In one
preferred embodiment, for example, where Q1 was 12, Q2 was 84;
Q3 was 0.965; and Q4 was 1.93; the container's energy ab-
sorption capabilities were 537 percent higher than the average
energy absorption capabilities of the control cans which,
themselves, have outstanding strength characteristics when
compared with similar characteristics of certain prior art
types of cans. One of the tested cans of the invention had
even higher energy absorption capabilities, but its Q2 ratio
was at the low end of the preferred range and was not as re-
liable about undergoing adequate bottom deformation prior to
sidewall failure. Hence, although it is possible to vary the
above parameters to obtain increased energy absorption capa-
bilities, this is done at the expense of failure-mode pre-
dictability which will now be dlscussed.
As indicated above, it has usually been difficult
to determine the type of container-defect or press-defect
that has led to container failures. Primarily this was be-
cause failure modes were quite random. By structuring the
containers in accordance with the instant invention, however,
it has been found that most (roughly 95 percent) of the containers
will collapse in their bottom portions before they will fail
in either the neck or the sidewall. Additionally, it has
been found that this factor can be used to trouble-shoot the
presses if the cans are periodically tested as they are fabri-
cated. In this regard, as cans are pressed, certain ones
are randomly selected and subjected to a compression test to
determine the can's failure mode. ~s a series of cans from
-8-
3~
a given press are thusly tested, a higher than normal per-
centage of neck failures is used to indicate, for example,
that the necks are too thin and/or the press's necking dies
are worn.
Similarly, if a significant percentage of the cans
exhibit body failures it is used to indicate, for example,
that the container's walls are too thin, indicating an ab- ~;
normality in the profile of the punch.
In the same light, if the container's bottom col-
lapses at an unacceptably low compressive force, this providesan indication, for example, of a defect in the nose of the
punch. Where containers of the FIG. l-type are compression-
tested, however, the failure modes are so unpredictable that
the above described testing and trouble-shooting method is not
practical.
As noted above, particularly in connection with
machine trouble-shooting, it is desirable to be able to identify
the press which constructed a given can. ~ problem in the past,
however, has been that embossed or punched markings on the
containers have led to stress concentrations which produced
premature can failure. But, in the instant case it has been
found that bottoms of cans can be "air" or "lubrication"
embossed without appearing to cause detrimental stress
concentrations.
In the above regard, FIG. 5 illustrates tbe bottom-
forming end 47 of the punch 46 in FIG. 3 wherein the number "2"
is etched therein while the corresponding "die" portion 40 of
the bottom former 52 remains blank. Nevertheless, when a can
bottom is rammed between the marked and unmarked press elements,
it is acceptably marked by the air or lubricant that is trapped
between the two press elements.
,
_9_
,
" ~ "
~:. , : . ,
1~ 39~'7
Similarly, suitable press identifying indicia can
be engraved or embossed on the bottom-former die element 49
and the corresponding punch-fore 47 left blank. In both
cases the can-bottom is suitably air or lubrication embossed
without appearing to cause detrimental stress concentrations.
The above-described structure provides containers
which not only have high energy absorption capabilities, but
have their failure modes concentrated mostly in the container's
bottom portions. In this manner, it is less difficult to
control can quality; easier to determine the causes of can
defects; and, because of the increased energy absorbing capa-
bilities, possible to make such containers from relatively
thin stock. In this respect, a standard beer can has a side
wall thickness of about 0.0051 inch and a bottom thickness of
about 0.0145 inch. As will now be discussed, however, cans
B having Frustoconical Sections 24 and~semi-torroidal sections
26 have satisfactorily been used under commercial beer can
filling conditions even though their average side wall
thicknesses were 0.0045 inch and their bottom thicknesses
were 0.141 inch.
Prior to discussing the above-described commercial
conditions, it should be noted that the sidewalls of beer cans
can only be controlled to about 0.0002 inch average-wall-thick-
ness; and actual-wall-thickness may vary about 0.0008 inch from
one point on a given can wall to another. A standard can
having an average wall thickness of 0.0051 inch, for example,
might have a wall thickness of 0.0047 on one side of a can
and 0.0055 on another side of the can. Moreover, as a can
punch such as 46 (FIG. 3) heats up and expands, it produces
cans having walls that become progressively thinner ~ecause
-10-
39~3 ~
the corresponding ironing dies do not expand as rapidly as
the punch.
In any event, 6 skids of "thin" cans (about 47,880
cans) in accordance with the invention had bottoms of standard
thickness and were run under commercial brewery conditions.
In this respect, the punches in the ironing dies for all of
the test cans were dimensioned to produce "thin" sidewalls
so that the test cans had a nominal average wall thickness
of 0.0045 inch. Every effort was made to run the "thin" cans
under commercial conditions where they were also filled and
capped under commercial conditions to be sure that the
commercial equipment would accept and process such cans in a
normal se~uence.
The results of the above-described commercial-
conditions test indicated that the variously dimensioned "thin"
cans operated fully acceptably under the commercial test condi-
tions. That is, their catastrophic failure rate was no
greater than the normal failure rate for standard cans. In
`::
this regard, normal thickness can6 operating under the same
~20 conditions were expected, when randomly tested, to withstand
a normal column load of 400 pounds. Because of the ability
of cans of the invention to absorb more energy before cata-
strophic failure, however, the acceptable column load for
randomly tested "thin" cans of the invention was able to be
reduced to 360 pounds; yet, as noted above, the "thin" cans
nevertheless performed satisfactorily under commercial filling
conditions.
39~'~
Standard wall and bottom thickness cans of the in-
vention are also tested to determine their failure predicta-
bility for "off~axis" loads. In this respect, cans are
more often sub~ect to "off-axis" crushing forces than "on-
axis" crushing forces such as occur during the filling
process. When such cans are used in automatic vending
machine environments or the like, for example, filled;
pressurized cans are dropped from a height in such a manner
that crush-producing forces thereon are most often of the
"off-axis" type. Consequentl~, off-center loading tests such
as will now be described, identify inherent strengths and
weaknesses of can designs.
The "off axis" tests were conducted by placing test
cans such as 54 (FIG. 6) between cross heads 57 and 58 of a
comprPssion tester such as a "TTB" Floor Model "Instron" com-
pression tester having a type "FR" load cell. Various
thicknesses of shim stock 60 were then placed under one
edge of a test fixture 62 to tilt the can "off-axis" so that
the force of cross head 57 was localized on the bottom of
each tested can (such as at 64 on can 56 in FIG. 6) to
provide an "off-axis" force rather than a Force distributed ~ -
uniformly across the bottom of the can so as to produce a
uniform axial load.
~he tester's cross head 57 was moved at a rate of
0.5 inch per minute; an accompanying strip chart speed was
set at 5 inches per minute; and the parameters of the compression
tester were such that each can test produced a graph of column-
load v. defle-ction.
Different "angles of tip" were obtained by placing
the cans at different angles with the horizontal tincluding 0)
-12-
:., : . . .
10~;~9~`~
by the placement of various thicknesses of shim-stock under
the test fixture as noted above. All cans tested were unwashed,
but were "necked and flanged" to obtain uniform placement on
fixture 62. The average sidewall and flange thickness of each
can-type was recorded; and, all of the cans of a given bottom-
design were from a single draw-and-iron press in order to re-
duce the possibilities of their being significant differences
between cans of a given type; and, all of the cans were tested
on the same compression tester.
Off-axis test results of cans having bottoms configured
in accordance with FIG. 2 compared favorably with otherwise
similar cans having bottoms configured in accordance with FIG.
1. That is, all of the FIG. 2 configured cans withstood axial
loads of greater than 400 pounds for all angles of tip resulting
from shim thicknesses of zero to 0.050 inch while, at the same
time, in over 96 percent of the cans tested,"failures" were
restricted to the can bottoms (as opposed to catastrophic
body failures) which, as noted above, usually result in a
can that is nevertheless usable.
20~ The same tests were run on cans having bottoms con-
figured in accoraance with FIGS. 7a, b, and c and the results
were then compared with otherwise similar cans having their
bottoms configured in accordance with FIG. 2. These comparisons
were dramatic. That is, at 0 shim thickness cans of all
four bottom configurations withstood a 400 pound load without
catastrophic failure at the maximum shim thickness of 0.050
inch, however, only the FIG. 2 configured can withstood a
400 pound load. In fact, the FIG. 2 configured can showed only
a minor decrease in maximum load between zero shim thickness
t440 lbs.) and 0.050 inch shim thickness-420 lbs.) and, as
-13-
~V~;39~'7
noted above, the actual failure modes were concentrated primarily
in the can bottoms.
At as little as 0.015 inch shim thickness, neither the
Fig. 7a nor the Fig. 7c configured bottoms would withstand a 400
pound average load. That is, at that shim thickness the Fig. 7a
,configured can failed a~ an average 325 pounds and the Fig. 7c
can failed at a average of 395 pound~. Moreover, at only 0.020
inch shim thickness, the Fig. 7b configured can ~lso failed~to
withstand an average load of 400 pounds--failing at 305 pound~ of
average off-axis load. Consequently, the can of the invention
not only provides a more predictable failure mode, but its over-
all off-axis strength is considerably in excess of the Fig. 7
configurations which represent other standard types of can
bottoms.
Additionally, it should'be noted that the Fig. 2 bottom-
structure does not include ~ strengthening bead such às 58 in
Fig. 1. If it is desired to further increase the strength of the
Fig. 2 can, therefore, this can be accomplished by adding a
strengthening bead such as 60 shown in phantom in Fig. 2. This
third semi-torroidal bead 60 is of substantial arcuate length
and, in effect, is substituted for the third semi-torroidal
portion 30 located betweenlthe second and third fru~toconical
portions 32 and 36. When vlèwed in cross section, for example,
the bead 60 subtends an arc 62 of greater than 100 and preferably
on the order of 180.
The third semi-torroidal bead 60 has a radius 64
which, for a typical beer-type container, may range between 0.030
-14-
B
::~
,......... . . . . .. ` . . . .. ., ~ ~ ` - . . ..... .. .. . .
~ 109398`7
and 0.187", but is preferably about 0.060". In this regard,
the use of beads such as 60 has resulted in cans being able to
have their pressures increased by as much as 5 psi, or if pre-
ferred, the stock thickness can be correspondlngly reduced in
addition to the reductions discussed above. "
It is believed that ~he frustoconical portions 24 and
the first semi-torroidal portion 26 in Fig. 2 contribute
significantly to the energy absorptive abilities of the above-
described cans. In this re~pect, relatively "flat-bottom" cans
having similar first sèmi-torroidal portions have also exhibited
outstanding energy absorptive qualities. In Fig. 8, for example,
side walls 66 of a can are joined to a first frustoconical
portion 68 which, in turn, is joined to a first semi-torroidal
portion 70. The~e portions of the Fig. 8 structure are sub-
stantially identical to the corresponding portions of the Fig. 2
can. Hence, they will not be further described. Instead of the
~irst seml-torroidal portion 70 being faired into a frustoconical
sec'tion such as 32 in Fig. 2, however, the first semi-torroidal
portion 70 is faired at ~emi-torroidal portion 72 into a
'relatively flat bottom-closing portion 74,; In this rèspect, it is
preferred that the bottom-closing portion 74 be domed inwardly
slightly when the can is unpressurized as illu~trated by phantom
line 76. I
The distance d, between the illustrated "flat" bottom
closing portion 74 and phantom line 76 should be at least about
0.005 inch and no m~re than d2 between the "flat" bottom closing
portion 74 and phantom line 78 to be described shortly. That is,
for a standard beer can (2'.6 inch D) containing about two and one-
half volumes of C02, the di~tance dl should be noImore than about
0.050 inch, but can be ~ome-
--15--
B
~ . . , ; .
-- 105~;39~'7
what~more if packaged-can stability is not too significant;
and, moreover, this value decreases as can diameter D decreases.
For "mini-cans" (1.3 inch D), for example, dl should be no
more than about 0.40 inch; and/ for larger can diameters
(over 3.0 inch D) dl can increase to 0.70 inch and even this
can decrease somewhat as can height increases. For all cans,
however, the ratio of D to dl should be between about 40 and
500.
In a manner to be described shortly, upon fabrica-
tion/ tne bottom closing portion 74 of the FIG. 8 can is
inwardly domed to phantom line 76/ but when the can is
subsequently pressurized, the bottom closing portion 74
domes outwardly to phantom-line 78. Then, when the can is
opened and its pressure relieved, the bottom closing portion
74 "crickets" inwardly to again assume the position illustrated
by phantom-line 76. This results in a can that is somewhat
unstable during shipment and storage of filled cans, but
whieh is quite stable once the can is opened and the contents
being used.
An additional advantage of having the bottom closing
portion 74 domed inwardly slightly is that it makes the ean
more easily supportable by vacuum-holding means used during
fabrication and filling. That is, it is frequently eonvenient
to hold or transport unfilled eans by applying a vacuum to the
bottom thereof through a vacuum port on a suitable fixture. If
the can bottom remains flat against a vacuum-port however,
the vacuum is only applied to that portion of the can's
bottom corresponding to the siæe of the vacuum port.
-- 10'~39~
Consequently, it is desirable for the can's bottom to be
somewhat removed from the surface of the fixture so that the
port's vacuum is applied over a substantial area of the
can's bottom.
When cans of the FIG. 8 configuration were tested
for pressure integrity, they were pressurized to 150 pounds
per square inch without any noticeable permanent deformation
of their bottoms. This is significant because specifications
for otherwise-corresponding conventional cans call for only
90 psi prior to the time a bottom buckles. In addition, the
FIG. 8 cans withstand wall loadings to substantially the
same extent as described above in connection with the FIG. 2
can configurations. Additionally, when the FIG. 8 cans were
pressurized, they domed outwardly to a position corresponding
to phantom line 78 in FIG. 5, but "cricketed" inwardly to a
line corresponding to 76 in FIG. 5 as soon as internal
pressure was relieved.
The abovedescribed "cricketing" phenomenon is
brought about by a coining step during formation of the
B can's bottom. That is, the bottom of each can is)/coined
` ~ - s~c~ e~ o~ai fto~t~trl
along a circular line in the faired~e~ 72 as illustrated
in FIG. 10 and as will now be described in connection with
FIG. 9.
The schematic illustrations of FIGS. 9~ and 9b
represent a punch 75 (similar to punch 46 in FIG. 3) about
to drive a can against a bottom former 76. For purposes of
simplicity, a draw-and-ironing structure (such as 50 in FIG.
3) is not illustrated in FIGS. 9, but the bottom former 76
includes an outer ring 78 having an insert 80 therein with
semi-torroidal surface 82 corresponding to surface 26' in
FIGS. 4 and 9b.
-17-
,
- lU~3~3`7
The outer ring 78 is contained within a stationary
member 83 of the bottom former which has a bottom pad 84 some-
what slidably disposed within both the outer ring 78 and the
stationary member 83. That is, an air diaphragm 85
such as that which might be used on an air brake, places 80
pounds per square inch pressure on 50 square inches of
surface to apply 4,000 pounds of force in the direction of
arrow 86 to a shaft structure 87 connected t~ the bottom pad
84. Consequently, bottom pad 84 is slida`ble to the left in
FIG~ 9a against the 4000 pound force acting on shaft structure
87.
A chamber 88 within the bottom former 76 is
located behind the outer ring 78 to surround the bottom pad
member 84 as shown; and, air pressure at 90 pounds per
square inch is delivered through port 90 to the chamber 88.
As the punch 75 is moved to the left in FIGS. 9
air pressure at 90 psi is also delivered through the punch
by ports 89 to act against the inside of the bottom 74 of
the can.
As the punch continues to move to the left, the
can bottom strikes surface 82 on insert 80 along a circle of
contact identified as 72' in FIG. 10. This holds the metal
on the radius 26 tightly against the punch 75.
The bottom 74 of the can next strikes the surface
of bottom pad 84 which starts to dome the bottom 74 inwardly.
A smaller nose radius 100 of the punch 75 pinches the metal
between the radius 100 and the surface of bottom pad 84 at
point 101; and, this action coins the metal. That is, the
metal is squeezed so that its thickness is changed somewhat
at the point of contact. This sets the bottom slightly
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.
10939~1~
inwardly, which causes the cricketing phenomenon described
above.
Any further ~orward movement of the punch 75 merely
moves the bottom pad 84, the shaft structure 87 and the outer
ring 78 to the left against the 4000# force of the diaphragm.
B At that time, however, the~sémi-torroidal section
70 (corresponding to 26' on the punch~has been formed between
the punch and the outer ring 80; the can's bottom has been
domed in to the desired extent; and, a coined ring 72' has
10 been formed around the can's bottom by virtue of the initial
line contact of the can's bottom at the circle 72' between
the punch 75 and the surface 101 of the bottom pad 84.
While the invention has been particularly shown
and described with reference to preferred embodiments thereof,
it will be understood by those skilled in the art that various ~`
changes in form and details may be made therein without de-
parting from the spirit and scope of the invention. For
example, the flat bottom portion 34 can be selectively adjusted
downwardly as described in S.N. 656,045 to increase the
container's volume as it otherwise tends to decrease due to
wear of the punch 46. It should be noted in this respect
that this volume adjustment is made without any alteration in
the container's overall top-bottom dimension. Hence, a
single punch can be used to produce far more cans than would
otherwise be the case, but the thusly produced cans nevertheless
continue to meet the relatively exacting dimensional requirements
for cans that are used in automatic dispensing machines.
The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
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