CA1097985A - Method and apparatus for making thin containers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method of making a container having a cylindrical sidewall and means for connecting the sidewall to a bottom wall closing one end of the container, the method comprising the step of coining at least a portion of the means for connecting the sidewall to the bottom wall and an apparatus for making the container, the apparatus including punch means for engaging the container, at a selected portion at the interior of the connecting means that is to be coined, bottom forming means initially spaced from the bottom-closing wall and including an engaging member for engaging the selected portion of the bottom-closing wall in substantially line contact between the member and the punch means, and means for moving the punch re-lative to the bottom forming means to effect a coined area at the selected line of contact.

Description

9'7~
CONT}~INI~R
BACKGROUND OF T~IE INVENTION
~ his is a continuation-in-part of V.S. Patent Application 709,903 filed on July 29, 1976 which, in turn, relates to an improvement o~ the container construction des-cribed in U S. Paten~ Application Serial Number 656,04~ filed on February 6, 1976 and assigned to the same assign~e as the instant case. In this respect, Serial Number ~56,045 is incorporated herein by re~erence.
Containers of the type described in S.N. 656,045 exhibited certain unexpected and ou~standing stxength char-a~teristics when compared with similar characteristics of certain prior art types of cans. ~en the S~N. 656,045-types of cans were produced at top production-speeds, however, they sometimes had a tendency to increase the normally expected ~ear on the punches ~ith which the cans were made. Illus-trated embodiments of the instant invention, however, provide a container wherein such punch-wear is reauced.
` Containers of the "dra~m-and-ironed" type exhibit three main points o~ failure when subjected to compressive loads such as occur when the cans are filled and closed with a conventional end. Such failures te~d to occur in either the can's neck portion or its sidewall or in the can's ` ~ttom. The instant invention provides a container wherein ` such failures occur most fre~uently in t~ container's - bottom portion; and, moreover, can absorb relatively large quantities of energy ~efore catastrophically failing in the scns~ that the container is no longer suited for its intcnaed purposc. Moreover, as will be ~xplained morc '". ' .'' ' ~.

~7~51S

fully shortly, cans of the in~ention are quite predictable in that failures can be expected to occur within a relatively narrow range of loads. ~ence, they can be made from thinner stocks since smaller margins of error are permitted~
There are several advantages to prov ~ding a con-tainer that is most likely to fail at the bottom. In this regard, particularly in "dra~m-and-ironed" containersg the thickness of the bot~om does not differ significan~ly from ~he slieet stock with which such cans are normally constructed.
Hence, the bottom-thickness of such cans can be xe1atively accurately controlled. It is the side-wall portions of these cans that are "dra~m-and-ironed," however, and the side wall ~hicknesses, therefore, are more difficult to control. Con-sequ~ntly, 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 ~hat compressive forces cause initial deflec-tion ~a type of failure) in the b~ttom of the container; and, moreovèr, the bottom undergoes relatively large distortions before the can undergoes catastrophic ~ailures such as in its side wall or neckO Consequently, so long as the com-pressiv~ forces are not so large as to cause catastrophic `f~ilure, the container can still be filled and seamed without bein~ discarded. In this conn~ction, the can of the inven-tion a~sorbs substantial quantities of energy as the bottom deflects. Consequently, it is possible to sav2 more cans for filling and seaming than mi~ht otherwise be the case.

' 2 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 the 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 is its tendency to have a center portion of its bottom "cricket" inwardly upon relief 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~irized.

SUMMARY
A container of th`e invention includes a side 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 ~tructure 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 method of making a container having a cylind-rical sidewall anda bottom-closing portion closing one end there-sf, the impro~ement comprising forming a frustoconical portion having one thereof directly attached to said side w211, forming a first semi-torroidal portion ha~ing one end thereof directly attached to the other end of said frustoconical portion, forming a semi-torroidal portion having one end thereof directly attached ~-3-,............................. .

.. ~1 . . .

~9~5 to the other end of sald first semi-torroidal portion and directly attaching the other end of said second semi-torroidal portion to said bottom-closing portion.
In accordance with a further aspect of the present invention, there is provided an apparatus for making a container having a cylindrical sidewall and connecting means having a coined portion thereof for connecting said sidewall to a bottom wall closing one end of said container said apparatus including punch means for engaging said container, at a selected portion :LO at the interior of said connecting means that is to be coined, bottom forming means initially spaced from the bottom-closing wall and including an engaging member for engaging said selected portion of said bottom-closing wall in substantially line contact between said member and said punch means' and means for moving said punch relative to said bottom forming means to effect a coined area at said selected line of contact, and said punch and bottom forming means being constructed and arranged to form frusto-conical first semi-torroidal, second semi-torroidal and bottom closing portions.

.~

BRIEF DESCRIPTION OF Tll~ DR~JI~GS
The foregoing and o~her features and advan-tages of khis invention will be apparent from the more particular description of preferred embodiments thereof as illustrated in the accompanying drawings wherein t~e same reference numerals refer to the same elements throughout the various ~ie~Js. The drawings are not necessarily intended to be to scale, but rather are presented so as to illustrate principles o~ the invention in clear form.
In the drawings: i FIG. 1 is a ragmentary cross sectional schematic illustration of a prior-axt 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 or a portion of a punch ta~en 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 o~ a test fixture used to test ~FF-AXIS strength of various types of cans;
. FIGS. 7a, b, and c are schematic illustrations of çans tested in the structure of FIG. ~;
FIG. 8 is a fragmentary cross-~ectional illustra~ion of the bottom portion of another embodiment of the invention;
FIGS. 9a and b are schcmatic illustrations of a bottom formin~ machine for the FIG. 8 embodiMent; and, FIG, 10 is a view of a can ~ottom taken along thc lines 10-iO in FIGo 9b.

~4-7~1~35 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 substan-tially flat inner and outer surfaces 16 and 18. In this regard, portion 14 extends between an outwardly convex annular bottom bead 20 and a transition poin~ 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 which, in turn, is joined to a f~rst semi torroidal portion 26 which, in turn, is faired into a second semi-torroidal portion 28. The second semi-torroidal portion 23 is attached to a third semi-torroidal portion 30 by a second frustoconical section 32--the other side of the third semi-toxroidal portion 30 being joined to a flat central portion 34 by a third frustoconical portion 36.
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 ma~ing an angle~ with the container's axis 40. In this respect, in connection with preferred ernbodiments of the invention, the radius R of the first semi-torroidal portion 26 and the angle were varied between certain limits as will now be discussed in connection with a punch that is used to form the structure of Fig.

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 ~ 7~3135i 50, ~or example, includes convcntional redrawing dies, ironing rings, pilot rings~ and the lik~, but those elemcnts form no par~ of the instant inv~ntion.
.FIG. 4 represents a portion of the punch 46 which ~orms the semi-torroidal section 26 of the can-bottom illus~
trat~d in FIG. 2. In this regard, portions of the punch in - ~PIG. 4 which correspond to the can-bottom of FIG. 2 have their correspondance indicated by prime signs added to similar ~eference numerals. For example, ~he can's side wall 12 corresponds to side wall 12' of the punch; the can's first frustoconical portion 24 corresponds to frustoconical punch .portion 24'; the can's semi-torroidal section 26 corresponds to semi-torroidal punch portion 26l; and, ~he can's arcuate portion 28 corresponds to punch portion 28'.
The frusto conical portion 24' is at an angle gamma to the side wall 12'. In this regard, ~est results can be expected when y is within the range of 1 to 6. Similarly, bes~ results can be expected when L2, the axial length o the fixst frustoconical portion 24', is betw~en 0.150 inches and 0.600 inches for a pressurized container of the conventional ~beer can" type. In these respects, the numeric ratio Ql of gamma (in degrees)~L2 (in inches) should be between about 1 and 60, but is more preferably about 12. If Ql becomes ~oo small, excessive tool wear is likely; and if Ql becomes too large the containers' energy absorbtive capabilities are diminished. ~
The semi-torroidal portion 26' is arcuate about cord 3~' which, when c~2nded, makes an angle ~ with the containcr's axis. When ~ is increased, the dimension L2 also increases if other paramctcrs remain ix~d~ Simi3.arly ~79~5 ~f ~ decrcases lother p~rametcrs rc~2ining const~nt3 the dimension L2 becomes smaller, as tlle cord increases in length.
This is indicatcd by the dimension L3 which repr~sents the cord 38' in any of its various positions depending upon the changes of the angles ~ and y.
In the above regard, the radius o~ the ~emi-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) shQuld be between about 35 and 300. Containers having Q2 ratios of less than about 35 appear to have body and nec~ failures sooner than botto~
failuresl and, containers having Q2 ra~ios over 300 appear ~to have relatively low initial deformation points. The ~.ost pref rred 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 othe~ise be expected.
~ he ratios of Ll/Rl ~Q3) and ~1/L2 ~Q4) appear to be of somewhat less sign~ficance. A preferred range for Q3, however, is between about .5 and 2.5 with excellent xesults being obtained ~here Q3 is about 0.965. Similarly, a praferred range for Q4 is between about 1.35 and 3.~5 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 absorpt~ve abili~ies and their tendencies to undergo bottom deformation prior to failure of th~ir sidewalls and necks. Test results of pre-ferred containers were then compared with containers havin~
bottom configurations correspondil-g to th~t of FIG. 1. Based on those test results 9 it was deterMined that cans of the .

~97~8~

above-describ~d typ~ having flr3t semi-torroidal sections such as 26' had subs-tantially higher energy absorption capabilities when compared with the prior art "control" cans. In one preferred embodiment, for example, where Ql was 12, Q2 was 84, Q3 was 0.965, and Q~ was 1.93 î the container's energy absorption capabilities wore 537 percent higher than the average energy absorption cap-abilities of the control cans which, themselvesl 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 reliable about undergoing adequate bottom deformation prior to sidewall failure. Hence, although it is possible to vary the above parameters to obtain increased energy absorption capabil-ities, this is done at the expense of failure-mode predictability which will now be discussed.
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 because failure modes were quite random. By structuring the containers in accordance with the instant invention, however, it has been found that most ~roughly 9S percent) of the containers will collapse in their bottom portions before the will fail in either the nec~ 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 fabricated. In this regard, as cans are pressed, certain ones are randomly selected and sub--jected to a compression test to determine -the can's failure mode.
As a series of cans from a given ~ress are thusly ~ested, d highcr than normal per-~ent~ge of neck failures is used to indicate, or example, that the necks are too thin and/or ~he press's necking dies a~e worn.
Similarly, if a significant percentage of the cans exhibit body failures it is ùsed to indicate, for exampl~, that the container's walls are too thin, indicating an ab-normality in the pro~ile of the punch.
In the same light, if the container's bottom col-iapses at an unacceptably 10~7 compressive force~ this providesan indica~ion, fox example, of a defect in the nose of-the punch. Where c~ntainers of the FIG. l-type are compression-tested, ho~ever, the failure modes are so unpredictable that the above described testing and troubl2-shooting method is not : practioal.
- A5 noted above, particularly in connection with machine trouble-shooting, it is desirable to be able to ide~tify the press which constructed a given can~ A 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. ~ut, in the instant case it has been found that bottoms of cans can be "air" or "lubrication"
embossed without appearing to cause detri~ental stress concentrations.
In the above regard, FIG. 5 illustrates the bo~tom~
forming end ~7 of the punch 46 in FIG. 3 wherein the nun~er "2"
is etched therein while the corresponding "die" portion 40 of the bottom former 52 remains blank. Nevertheless, wllen a can bottom is ran~ed ~etwecn tlle marked and unmarked press elerentS, 3~ it is acceptably markcd by thc air or lubrican~ that i5 trappcd betwecn the two prcss cleMents.

s 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 having high energy absorption capabilities, but have their failure modes concentrated mostly in the container's bottom portions. In this manner, it i5 less difficult to control can ~uality, easier to determine the causes of can defects; and, because of the increased energy absorbing capabilities, 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 having Frustoconical Sections 24 and first semi-torroidal sections 26 have satisfactorily been used under commercial beer can filling conditions even though their average sidewall 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 o~ 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 0O0055 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 because th~ correspondin~ irQning dies do not expand as rapidly as the punch.
In any event, 6 skids of "thin" cans (about 47,880 cans? in accordance with ~he invention had bo~toms of stan~ard thickness and were run under co~mercial brewery conditions.
:In this respect, the punches in the ironing dies for all of the test cans were dimensioned to produc~ n thin" sidewalls so that the test cans had a nominal average wall thickness of o o~aS inch. Every effort was made to run ~he "thin" cans under co~mercial conditions ~here they were also filled and capped ~nder commercial conditions to be sure that the commercial equipment would accept and process such cans in a normal sequence.
~ , 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 cans operating under the same conditions were e~pected, when randomly tested, to withstand a normal column load of 400 pounds. Because of the ability o cans o the invention to absorb more energy before cata-strophic failure, however, the acceptable column load for randomly tes~ed "thin" cans of the invention ~as able to be reduced to 360 pounds; yet, as noted above, the l'thin" cans nevertheless performed satisfactorily under commercial filling conditions.

~9~ 35 Standard wall and bottom thickness cans o~ the in-vention are also tested to determine their failure predict~-bility for "of~-a~is" loads. In this respect, cans are more often sub~ect to "off-axis" crushing forces than "on-axis" crushin~ forces such as occur during the filling p~ocess. 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 noff-axis" type. Consequently, 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 compression tester such as a l'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 l'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 "of~-axis" force rather than a Force distributed uniformly across the bottom of the can so as to produce a uniorm axial load.
~he tester's cross head 57 was moved at a rate of O . 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 o~ column-load v. dcflection.
Different "angles of tip" were obtained by placing tne cans at di~fercnt ~ntJles with th~ hori~ontal (including 03 by th~ placement of various thicknesses o~ shim-stock under the test fixtur~ as noted above. ~11 cans tested were un~.ashcd, but were "necked and 1anged" to obtain uniorm plac~m~nt on fixture 62. The average side~all and flange thic~ness of each can-~pe was recorded; and, all of the cans of a giv~n bot~om-design were from a single draw-and-iron press in order to re-duce the possibilities of their being significant difercnces ~etween cans of a given type; and, all of the cans were tested on the same compression testcr.
O~-axis test results of cans ha~ing bottoms confi~ured 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 configur~d cans withstood axial ioads of greater than 400 pounds for all angles o~ tip resulting from shim thicknesses of zero to 0~050 inch while, a~ ~he same . tLme, in over 96 percent of the cans tested,"failures" were restricted to the can bo~toms (as opposed to catastrophic body failures) which, as noted above, usually result in a can that is nevertheless usable.

The same tests ~ere run on cans having bottoms c~n-~igured in accordance with FIGS. 7a, b, and c and the xesults were then compared w.ith otherwise similar cans ha~ing their bottoms conigured in accordance with FIG. 2. These comparisons were dramatic. That is, at 0 shim thickness cans of all four bottom configu~ations withstood a 400 pound load WitllOUt catastrophic failure at the ma~imum shim thickness of 0~050 inch, however, only the FIG. 2 conigured can ~Yithstood a 400 pound loaa. In ac~, tho FIG~ 2 configured can showed only a minor decrease in maximum load botween ze~o shim thickness ~440 lbs.) ~nd 0.050 incn shim thickness-420 lbs.) and, as ~13-. , noted above, the actual Eailure 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 con~igured bottoms would withstand a 400 pound average load. That is, at that shim thickness the Fig. 7a ~configured can failed at an average 325 pounds and the Fiy. 7c can failed at a average of 395 pounds. 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 pounds 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 configuràtions which represent other standard types of can bottoms.
Additionally, i~ shoul~ibe noted that the Fig. 2 bottom-structure does not include a strengthening bead such as 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 arcua-te length and, in effect, is substituted for the third semi-torroidal portion 30 located between the second and third frustoconical portions 32 and 36. When viewed in cross section, for example, the bead 60 subtends an arc 62 of greater than 100 and preEerably on the order of 180 Q .
The third semi-torroidal bead 60 has a radius 64 which, for a typical beer-type container, may range between 0.030 ~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 stoc~c thickness can be correspondingly reduced in addition to the reductions discussed above.
It is believed that ~he frustoconlcal 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 respect, 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. These 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 first semi-torroidal portion 70 being faired into a frustoconical section such as 32 in Fig. 2, however, the first semi-torroidal portion 70 is faired at semi-torroidal portion 72 into a relatively flat bottom-closing portion 74~ In this respect, it is preferred that the bottom-closing portion 74 be domed inwardly slightly when the can is unpressurized as illustrated by phantom line 76.
The distance d, between the illustrated "flat" bottom closing portion 74 and phantom line 76 should be at least about O.OOS inch and no more 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 distance dl should be no more than about 0.050 inch, but can be some-~7~85 what more if packaged-c~n stability is not too significant;
and, moreover, this value decreases as can diameter D dccreases.
For "mini-cans" (1.3 inch D), for example, d~ 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 evcn this can decrease some~7hat as can height increases. For all cans, however, the ratio of D to dl should be bet~leen a~out 40 and 500.
In a manner to be described shortly, upon fa~rica-tion, the 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 ncric~ets" inwardly to again assume the position illustrated by pnantom-line 76. This results in a can that is somewhat unstable during shipment and storage of filled cans, but which is quite stable once thP can is opened and the contents bein~ used.
An additional adv~ntage of having the bottom closing portion 74 domed inwardly slightly is that it makes the can more easily su~portable by vacuum-holding means used during ~abrication and filling. That is, it is frequently convenient to hold or transport unfilled cans by applying a vacuum to tne bottom ther~o through a vacuum port on a suitable fixture. If - the can bottom r~mains flat a~ainst a ~acuum-port however, the vacuum is only applied to that portion of th~ can's bottom corresponding to the size of the vacuum port.

~37~

Consequently, it is desirable for the can's bottom to be some-what removed from the surface of the fixture so that the port's vacuum ls 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 sguare inch without any noticeable pennanent deformation of their bottoms. This is significant because specifications for otherwise-correspondin~ conventional cans call for only 90 psi prior to the time a bottom buckles. In addition, the FIG. 8 cans L0 withstand wall loadings to substantially the same extent as des-cribed above in connection with the FIG o 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 "cricXeted" inwardly to a line corresponding to 76 in FIG. 5 as soon as internal pressure was relieved.
The above described "cricketing" phenomenon is brought about by a coining step during formation of the can's bottom.
That is the bottom of each can is coined along a circular line in the faired second semi-torroidal portion 72 as illustrated ~0 in FIG. 10 and as will now be described in connection with E'IG. 9.
The schematic illustrations of FIGS. 9a and 9b re-present a punch 75 (similar to punch 46 in FIG. 3) about to ~rive 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~

7~

. The outer ring 78 is contained within a sta~ion~ry memb~r 83 of the bottom former which has a bottom pad 84 sorn~-what slidably disposed wi~hin bot~ the outer ring 7~ and the s,tationary member 83. That is, an air diaphragm 85 such as that which migh~ be used on an air brake, places B0 pounds per square inch pressure on 50 square inches of surface to apply 4,000 pounds of force in the direction of arrow 86 t~ a shaft structure 87 connected t~ the bottom pad 84. Consequently, bottom pad 84 is slidable to the left in FIG. 9a against the 4000 pound force acting on shaft structure 87~ ' . ~ chamber ~ 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 insidP of the bottom 74 of the can.
. As the punch continues to move to the left, the can bottom stri~es surface 82 on insert 8C along a circle of contact identified as 72' in FIG n 10 ~ This holds the metal on the radius 2G tightly against the punch 75.
, The bottom 74 o~ the call next strike~ the surface of bottom pad 8~ which st~rts to dome the bottom 74 inwardly.
A smaller nose radius 100 of the punch 75 pinches the metal bettieen the radius 100 and the surface of bottom pad 84 at point 101; and, this action coins thc metal. Tha~ is, the metal is squcez~d so that its thic~ness is changed somewhat a~ the point of cont~c~. Tllis sets ~he bottom slightly ~37~ 35 inwardly, which causes the cricketing phenomenon described above.
Any further forward movement of the punch 75 merely moves the bottom pad 84, the shaft structure 87 and the outer rin~ 7~ to the left against the 4000# force of the diaphragm~
At that time, however, the first semi-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 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 thereo~, 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 Canadian application s.n. 310,242 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 al-teration in the container's overall top-bottom dimension.
Hence, a single punch ca~n 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.

~19--

Claims (17)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method of making a container having a cylindrical side wall and a bottom-closing portion closing one end thereof, the improvement comprising forming a frustoconical portion having one thereof directly attached to said side wall, forming a first semi-torroidal portion having one end thereof directly attached to the other end of said frustoconical portion, forming a semi-torroidal portion having one end thereof directly attached to the other end of said first semi-torroidal portion and directly attaching the other end of said second semi-torroidal portion to said bottom-closing portion.

2. The method of claim 1 further comprising coining at least a portion of said bottom-closing portion.

3. The method of claim 2 wherein said bottom-closing portion includes a third semi-torroidal portion and said coining is applied to said third semi-torroidal portion.

4. The method of claim 2 further comprising doming said bottom-closing portion inwardly .

5. The method of claim 4 wherein said bottom-closing portion is domed inwardly between about 0.005 and 0.050 inch.

6. The method of claim 4 wherein the ratio of the dia-meter of said container to the depth of the inwardly domed bottom-closing portion is between about 40 and 500.

7, Apparatus for making a container having a cylindrical sidewall and connecting means having a coined portion thereof for connecting said sidewall to a bottom wall closing one end of said container said apparatus including;
punch means for engaging said container, at a selected portion at the interior of said connecting means that is to be coined 20 bottom forming means initially spaced from the bottom closing wall and including an engaging member for engaging said selected portion of said bottom-closing wall in substantially line contact between said member and said punch means;
means for moving said punch relative to said bottom forming means to effect a coined area at said selected line of contact, and said punch and bottom forming means being constructed and arranged to form frusto-conical first semi-torroidal, second semi-torroidal and bottom closing portions.

8. The apparatus of claim 7 including first fluid pressure means fox exerting fluid pressure behind said engaging member for biasing said member toward said punch.

9. The apparatus of claim 8 including second fluid pres-sure means exerting fluid pressure inside said container to bias said container toward said bottom forming means.

10. The apparatus of claim 8 including a second bottom engaging means having a substantial portion centrally located on one end thereof and within the first engaging member, said second bottom engaging means being movable axially within said first engaging member after said coining step.

11. The apparatus of claim 10 including means for dir-ecting fluid pressure behind said second bottom engaging means for biasing said second bottom engaging means toward the bottom of said container.

12. The apparatus of claim 11 wherein the fluid bias on said second bottom engaging means is overcome by motion of the bottom of said container against one end of said second bottom engaging means and including:
resilient means for engaging the other end of said second bottom engaging means when said fluid bias is overcome, said resilient means and said second bottom engaging means thereby being adapted to undergo further motion with said punch and said container after said fluid bias is overcome.

13. The apparatus of claim 12 wherein said resilient means is separately fluid biased.

14. The apparatus of claim 13 including third fluid pressure means exerting fluid pressure inside said container to bias said container toward said bottom forming means.

15. The apparatus of claim 7 including a domed portion of said punch means centrally located therein and directed away from said container bottom for causing the central portion of said container bottom to dome inwardly upon engagement thereof with said bottom forming means.

16. The apparatus of claim 15 wherein said domed portion has a depth of between 0.005 and 0.050 inch.

17. The apparatus of claim 15 wherein the ratio of the diameter of said container to the depth of said domed portion is between about 40 and 500.