Metallic pressure vessel with thin wall

A metallic pressure vessel or container, made of a thin aluminum or aluminum alloy sheet coated with a resin suitably, used for a small size beer container. The vessel is composed of (a) a main body member of bottomed cylindrical form, with a bulge in the central part thereof precessed by a novel method, provided with at least three protrusions and recessed beads disposed therebetween alternately, for stable setting and reinforcing, and (b) a lid member, for covering the former body, which is made into an inverted bowl shape, with a mouth portion integrally formed for being crowned thereon, and provided with a plurality of small wave like patterns consisting of continuous and smooth hills and valleys. Those two parts are generally made by multiple deep-drawing processes and joined together by the double seaming method. The process of the mouth portion making is characteristic in its burling and curling processes.

FIELD OF THE INVENTION 
This invention relates to a metallic pressure vessel with thin wall, and 
more particularly to a pressure vessel with a mouth portion integrally 
formed of a metallic thin sheet or sheet metal consisting of aluminum or 
aluminum alloy, which vessel is suitably utilized as a small size beer 
barrel. 
BACKGROUND OF THE INVENTION 
Metallic vessels or containers are usually made by firmly connecting or 
joining a bottomed lower piece (main part of the container) of cylindrical 
form and an upper piece (lid part so to speak), with a mouth portion on 
top, of inverted bowl form downwardly open, at the abutting portion of the 
two. Those metallic vessels (containers) may be utilized in various 
purposes, and the most serious problem therein has been the heavy weight 
which they can hardly evade because of the metallic material. As a 
naturally thought countermeasure, a metal plate or slab of small thickness 
has been tried, but the thinner the metal plate becomes, the more often 
the pressure-resisting capacity of the container appears as a problem. 
Sometimes a deformation or buckling of the container happens during its 
actual use. In some other instances a too thin metal plate makes the 
formation of the lower piece or the upper piece itself very difficult, 
i.e., provides a problem of forming method. 
On the other hand, vessels or containers made of aluminum or its alloys are 
widely used because of their strong points in light weight and corrosion 
resistance. Their good features, in being harmless to the contained matter 
because of the corrosion resistance and in being flexible in formation, 
allow them to be broadly utilized for containing foods or the like. When 
such a container of aluminum (or aluminum alloy) is utilized for beer 
container, it is required to be inner-pressure resistant in the order of 
3-4 Kg/cm.sup.2 because of beer being a foaming beverage. So the container 
of aluminum (or aluminum alloy) must be, while being required to be as 
thin as possible in its wall thickness within the allowable extent for the 
purpose of weight decreasing, sufficiently inner-pressure resisting and 
suitable for formation as well. This is an inherent and difficult problem 
to be solved for the container of this type. 
Such a container, when it is used as a beer container for example, must be 
provided with a mouth portion in its upper piece for filling or emptying 
the contained liquid. However it becomes a very difficult problem to 
integrally form the mouth portion there when the wall thickness of the 
container is diminished to a certain limit. 
SUMMARY OF THE INVENTION 
It is a principal object of this invention to provide, considering the 
above-mentioned background in the field sufficiently, an excellent 
metallic pressure vessel made of a metallic material of small thickness. 
It is another object of this invention to provide a metallic pressure 
vessel which is made of aluminum or aluminum alloy sheet, formed 
integrally with a mouth portion, excellent in pressure resistance, and 
suitable for a small size beer barrel. 
It is still another object of this invention to economically provide a 
metallic pressure vessel which is well preventive of deformation and 
buckling during the use, excellent in pressure resistance, and superior in 
formability. 
Other objects of this invention will become apparent to those skilled in 
the art from the following detailed description of the preferred 
embodiments when read in conjunction with the accompanying drawings. 
A metallic pressure vessel of small wall thickness in accordance with this 
invention is characteristically composed of, for attaining those purposes, 
(a) a bottomed cylindrical main body piece of the container which is 
formed of a thin metallic plate or sheet by deep-drawing process to be 
outwardly swollen or bulged in arch shape in the vertical cross section, 
and (b) a lid piece of metallic thin plate, for being gas-tightly attached 
to the upper opening of the main body piece, which lid piece is consisted 
again of an inverted bowl shaped portion and a cylindrical mouth portion 
extending outwardly from the central part of the inverted bowl shaped 
portion, said inverted bowl shaped portion being gradually decreased in 
its diameter from the attached portion upwards and provided thereon with a 
plurality of concentric annular and smoothly continued wave like 
convex-and-concave patterns in its axial section passing the vessel center 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 which illustrates an example wherein this invention is most 
preferably applied to a beer barrel, numeral 1 designates an upper piece 
(lid member) which consists of an inverted bowl shaped portion 1a, the 
diameter of which being gradually decreased from a lower part toward an 
upper part, and a mouth portion 4 of cylindrical form which is integrally 
formed with the inverted bowl shaped portion and extends from the central 
part of the inverted bowl shaped portion 1a. The upper piece (lid member) 
is made, by a forming process, of a thin plate or sheet of aluminum or 
aluminum alloy, of 0.3-1.0 mm preferably 0.3-0.5 mm, coated with epoxy 
resin (see FIG. 17), and the same includes a curved portion 1b with a 
predetermined radius of curvature R.sub.4 and an annular waved portion 1c 
continued from the curved portion 1b (upwardly in FIG. 1), which is formed 
of a plurality of concentric wave like patterns, i.e., a series of 
continuous concentric convex-and-concave annular ridges and grooves, in 
its axial cross sectional view. The lower piece 2, which is joined to the 
upper piece 1, is formed of a metallic thin plate (thin sheet of aluminum 
alloy in this embodiment) coated with epoxy resin (see FIG. 18), processed 
by means of a deep-drawing process, into a cylindrical form having a 
bottom and outwardly bulged form like an arch in the cross sectional view 
of the barrel portion thereof. 
The upper piece 1 and the lower piece 2 are placed in confrontation with 
the opening portion of either member to each other for being gas-tightly 
joined (fixed) at the circumferential portion of the two to be a desired 
pressure vessel. 
The bottom portion 5 of the main body 2 (barrel) of the pressure vessel is 
also outwardly bulged with a predetermined radius of curvature R for 
forming a shallow bowl or saucer shape; and five dowels 6 (gentle 
protrusion) are formed as a protuberance arranged on a circular line about 
the center of the bottom portion 5 for stably contacting a table or stand 
on which it is to be placed. Those dowels 6 are for stably supporting the 
vessel filled with beer or other liquid and for preventing the vessel from 
being turned over, so they must be formed at least three in number. 
Between each pair of neighboring dowels 6, 6 is formed a radial bead 7 
(concave recess) like a groove. 
As can be clearly seen in FIG. 2 which shows the bottom 5 of the vessel, 
each dowel 6 has, as a whole, an outline of dew drop shape which is formed 
by linking an arc portion 9 described with a radius R.sub.1 having its 
center at a point P.sub.1 near the center O.sub.1 of the bottom 5 and 
another arc 10 described with a radius R.sub.2 (R.sub.2 &gt;R.sub.1) having 
its center at a point P.sub.2 farther from the center O.sub.1 than the 
point P.sub.1, and the contacting area 11 with the table to be placed on 
is of oval (ellipse) shape, so extending as to link the point P.sub.1 with 
the point P.sub.2 in a radial direction. The oval contacting area 11 is 
gently protruding, as a whole, downwardly from the bottom 5 to form a flat 
plateau. The bead 7 for reinforcing the bottom 5 radially extends starting 
from a point near the center O.sub.1 almost reaching an enveloping circle 
A which links the outer periphery of each dowel 6. And the bead 7 is 
formed by partly recessing the bottom 5 upwardly to be a shallow and 
gentle groove of rectangular shape. The bottom 5 is, outside the 
enveloping circle A, curved with a suddenly diminished radius of curvature 
R.sub.3 (FIG. 1) to be relatively large in strength there. Within the 
enveloping circle A a radius of curvature R (FIG. 1) of the bottom 5 is 
very large to make that portion rather non-susceptible to buckling in 
general. 
In other words, as the vessel is supported on the table (stand) in this 
invention by the five dowels 6 formed in a part of the bottom 5, being 
reinforced by the bead 7 radially disposed between each pair of 
neighboring dowels 6, the dead load of the vessel itself and the load of 
the contained beer urging downwards the dowels 6 give a reactionary effect 
to the surrounding area about each dowel 6 (part of the bottom 5 except 
the area occupied by the dowels 6). So the surrounding area is liable to 
be inwardly recessed (caved in) concentrically, with the points R.sub.1 
and R.sub.2 as a center, shown with two-dot-chain lines in FIG. 2. 
However, this probability of recessing, i.e., buckling in the two 
dot-chain-lined area can be mostly prevented by the action of the annular 
area 5a curved with the small radius of curvature R.sub.3 outside the 
enveloping circle A and the beads 7. Mere disposing of the bead 7 between 
the neighboring dowels 6 is very much contributive to preventing the 
deformation of the vessel which might be developed in a circular area 
around the dowel 6. And such a bead 7 may be formed by outwardly 
(downwardly) protruding a part of the bottom 5, with the same desired 
effect. 
This sort of metallic pressure vessel is preferably utilized as a small 
size beer container for containing 3-5 l beer. And in a case of a vessel 
for 3 l beer, for example, the height is approximately 200 mm and the 
largest barrel diameter is 165 mm or so. 
In the upper piece 1, which is the most characteristically formed part of 
the vessel of this invention, the plurality of circular convex-and-concave 
patterns of continuous wave like shape in section enhances the pressure 
resistance to a great extent, irrespective of its metallic material of 
small thickness. 
And the deep-drawing process itself, which is repeated as a multiple-step 
drawing process for forming the wave like pattern, enables to effectively 
form the mouth portion 4 in the central part. 
The forming process of the upper piece 1 will be described in greater 
detail hereunder. The explanation of the process will be mainly limited, 
because of the symmetrical form of the vessel, to the right side half of a 
central line O.sub.1, with reference to FIG. 3, a vertical and axial cross 
sectional view of the upper piece 1 with the mouth portion 4. A material 
blank 12 is, for example, an aluminum alloy (5052S) made thin plate coated 
with an epoxy resin (not shown) on both sides at a thickness of 3-4.mu. 
and having a diameter D.sub.1 and a thickness 0.5 mm. This material is at 
first formed into abc shape by a press die; then a first drawing process 
is carried out with a punch of drawing diameter D.sub.1 (shape def) for 
forming an annular convex pattern e with a smooth hill like section, the 
outer periphery of which annular convex pattern e of a hill like section 
is connected to a annular concave pattern b with a smooth inverted hill 
like section. A smooth hill like annular convex pattern h is next formed 
by a second drawing process with a punch of ghi shape with a drawing 
diameter D.sub.2. In this process the convex pattern e formed in the 
previous process remains unchanged, consequently a smooth annular concave 
pattern j is naturally formed between the convex patterns e and h. 
Likewise annular convex patterns k, l, m are formed with punches of 
drawing diameters D.sub.3, D.sub.4, . . . . By those processes each 
annular convex patter e, h, k, l, m is formed on the body portion of the 
upper piece 1 of bowl shape, with the outer periphery of the punch used at 
each drawing process, to be a continued smooth and gentle wave like 
pattern, being combined altogether. In this multiple-step drawing process, 
the surface area of each section processed by drawing, one after another, 
shall be equal to each other. 
The mouth portion 4 can be obtained by forming the central part of the bowl 
like portion of the upper piece 1 into a form of mnopqro. A rolled up end 
of the mouth portion 4 is processed, after once forming the material into 
a cylindrical shape pqq', by trimming the tip portion and roll-forming the 
qq' portion outwardly to finally made a qro portion. The outer periphery 
of the bowl like portion of the upper piece 1 is provided with, for being 
connected to the lower piece 2, a cylindrical flange 14, an outwardly 
extended lateral flange 15, and a folding-back flange 16, being integrally 
formed. A laterally extended flange 17 formed on the upper end of the 
cylindrical portion of the lower piece 2 is contacted with the lateral 
flange 15 of the upper piece 1, then a double seaming process is applied 
to roll up the both flanges 15, 17, together with the folding-back flange 
16, into a state shown in FIG. 4 in enlargement. The mouth portion 4 and 
the flanges 14-16 may be formed in advance of applying a deep-drawing 
process on the inverted bowl like body portion. 
The inverted bowl like body portion of the upper piece 1 with the mouth 
portion 4 in this invention has a smoothly continued circular wave like 
convex-and-concave patterns, formed concentrically, and all the smooth 
hill like annular convex patterns e, h, k, l, m formed by the peripheral 
edge of the punches of different drawing diameters are left untouched on 
the surface of the upper piece 1 to enhance the rigidity and strength of 
the same. In other words, the annular waved patterns, convex-and-concave, 
function in reinforcing the upper piece 1. And besides, a final touch of 
the formation by drawing the material, i.e., eliminating the 
irregularities on the material occurred in the forming course, is not 
applied in this invention. The once formed convex patterns e, h, k, l, m 
on the material by the peripheral edge of the punches of different 
diameters are never bent in the reverse direction (not equalized in the 
height of the waves), so the convex places e, h . . . affected once by the 
pulling stress to have the material organization somewhat changed are not 
exposed to reverse compressing stress, leaving the coated surface 
unaffected, not being peeled off. As to the inside surface of the material 
the case is identical. It means shock-mark phenomenon can be completely 
prevented on both sides of the material, that is to say, on the outer 
surface of the lid deterioration of the appearance by the shock-mark is 
eliminated, and on the inside of the lid undesirable mixing of peeled 
pieces of coated material into the contained beverage or food which 
possibly deteriorates the same can be prevented. This invention thus 
enables to manufacture a lid piece with the mouth portion of a plate 
material coated with a resin, while keeping largely enhanced strength of 
the same. 
The mouth portion of the vessel made in the central part of the lid, or an 
inverted bowl like upper piece 1, can be in this invention formed in a 
highly preferable way as stated hereunder. When first of all the upper 
piece 1 as a lid is press-formed by the stepped drawing process a 
cylindrical portion 23 having a top plate in the central part thereof is 
integrally formed. And in the middle part of the cylindrical portion 23 a 
circular step portion 24 is formed at the same time. Numeral 25 in FIG. 5 
then designates an outer flange which will function as a joiner when the 
upper piece 1 is joined with the lower piece 2 by the double-seaming 
process. 
The top plate 22 is cutaway, with a punch and a die (not shown), to form a 
concentric hole 26 with a diameter D' in the central part thereof, as can 
be seen in FIG. 6. The left peripheral portion of the top plate 22 around 
the hole 26 is formed into a similar cylindrical form as the cylindrical 
portion 23 (this portion is called hereunder burling process). For this 
purpose a pair of upper die 27 and a lower die 28 are employed, and FIG. 7 
shows how the cylindrical portion is formed by erecting the left outer 
peripheral portion of the top plate 22 into an integrated part with the 
cylindrical portion 23 already existed. Thus obtained integrated 
cylindrical portions 22, 23 can be curled outwardly by, for example, an 
upper die 29 for curling and a lower die 30 for cooperating the former to 
form a mouth portion almost circular in section for being capped with a 
crown. By being capped with a seal cap 32, made of for example aluminum 
thin plate, and sealed by pressure (caulked) in the arrow A direction on 
the outer periphery, a perfect gas-tight sealing is completed. During the 
various pressing processes before completing the mouth end 31, the flange 
25 shown in FIG. 5 is processed additionally to become the flange 15 shown 
in FIG. 8 and in a later process the same is further processed to be, 
together with the flange 17 of the lower piece 2, caulked or double-seamed 
into a gas-tight sealing. 
In the previously stated processes an important technological problem must 
be disclosed herewith. When the left peripheral portion of the top plate 
22 around the hole 26 is erected upright to become a cylindrical portion 
22' for being integrated with the cylindrical portion 23 (see FIG. 7), if 
the shoulder R' between the cylindrical portion 23 and the left part of 
the top plate 22 is completely straightened, then appear wavy 
irregularities 37 on the top of the cylindrical portion 22' as shown in 
FIG. 9 due to the directionality of the material, showing mountain 
portions 37a and valley portions 37b. If the curling process is forcibly 
carried out without correcting the irregularities, a gap L.sub.1 is 
created due to the valley 37b, as shown in FIG. 10 (a) between the plate 
tip and the cylindrical portion 23, and the mountain 37a will on the 
contrary forcibly abuts against the cylindrical portion 23 as shown in 
FIG. 10 (b), to finally make the mouth end 31 irregular, in its 
cross-sectional view, at various points on the circumference thereof. It 
means that the mouth end 31 is not perfectly finished, being imperfect in 
circulality, leading to an unsatisfactory sealing when the vessel is 
crowned. Causes for the disadvantage can be found in a fact that the 
shoulder R' can be erected perfectly in one part but can not be done so in 
another part. If a forcible erecting is attempted to make a complete 
cylindrical form, there can be inevitably wavy irregularities on the plate 
end, with a result of uneven cross-sectional view of the mouth end 31 
appearing. 
This invention recommends for that reason, in the forming process of this 
part, the following method. By taking advantage of the excellent 
technology in this invention, which enables the form and the position of 
the shoulder R' to be highly precise when forming the cylindrical portion 
23 having the top plate 22, and enables to get the out of roundness as 
well as the concentricity of the hole 26 when it is cut concentrically 
with the top plate 22, the shoulder R' must be formed such that when it is 
erected upright there remain an annular step, not being completely 
straightened, and consequently the plate end, when the left peripheral 
portion of the top plate 22 is erected to the cylindrical form, will not 
have irregularities 37. 
This will be illustrated, with reference to FIGS. 6 and 11, hereunder. The 
method of punching the concentric hole 26 with the diameter D.sub.1 in the 
middle part of the top plate 22 is just identical to the earlier stated 
one. An important difference lies in the way of erecting (extending) the 
left peripheral portion of the top plate 22, and the secret lies in, first 
of all, decreasing the external diameter D'.sub.1 of the lower die 28 a 
little or slightly increasing the internal diameter D'.sub.2 of the upper 
die 27, when erecting the left peripheral portion of the top plate 22, in 
order to make the erected cylindrical portion 22" slightly different from 
the cylindrical portion 23 in its external diameter. When the external 
diameter D'.sub.1 of the lower die 28 is decreased a little than the 
conventional one the internal diameter of the cylindrical portion 22" 
becomes smaller than that of the cylindrical portion 23 and the shoulder 
R' is remained as a step R", because it is not fully extended (or 
erected). In other words, a part of the curved portion of the shoulder R' 
is left maintained between the cylindrical portion 22" and the cylindrical 
portion 23. It means that a partly stepped cylindrical portion is made on 
the forward side of the cylindrical portion 23. When the internal diameter 
D'.sub.2 of the upper die 27 is slightly increased than the conventional 
one, the internal diameter of the cylindrical portion 22" becomes 
identical to that of the cylindrical portion 23, leaving in the middle a 
slightly diameter-increased step portion R" to be formed. 
By means of an erecting formation of the left peripheral portion of the top 
plate 22, with the shoulder R' left as an annular step, the summed height 
H.sub.3 of the cylindrical portion 23 and the cylindrical portion 22" will 
be made slightly smaller than the corresponding height H.sub.2 (see FIG. 
7) in the conventional method, however, the top edge 38 (upper edge) will 
be smooth i.e., not wavy at all. It can be explained such that the 
shoulder R' will be scarcely extended, while the cylindrical portion 22" 
is formed, and the height of the stepped portion R" which has been changed 
from the original shoulder R' will be almost uniform around the newly 
formed cylindrical portion (between the cylindrical portion 23 and the 
cylindrical portion 22"). It consequently causes the final height of the 
cylindrical portion 22" to be uniform, surely preventing the wavy 
irregularities of the top edge 38. Curling process applied to such a 
uniformly formed cylindrical portion (which includes 23 and 22") will 
bring about a uniformly curled mouth end having a nearly perfect circular 
cross section. In this instance the curling may be one like in FIG. 10 (a) 
or like in FIG. 10 (b) in its cross sectional shape. In any way, a uniform 
curling around the whole circumference of the mouth end can be attained, 
because the top edge 38 being perfectly in a plane free from 
irregularities in height immediately before the curling process. 
As explained in detail in the above, the burling process, which is applied 
to the left portion of the top plate after the concentric hole 26 has been 
punched in the top plate 22, must be carried out to leave the shoulder R' 
as a not-extended step portion so as to be uniform in its height around 
the whole circumference. By this method the plate top 38 can be smooth, 
being in a plane, which enables the later performed curling process to be 
perfect, and the uniformly curled mouth end 31, having a uniform 
cross-sectional form around the whole circumference, greatly enhances the 
sealing effect of the container itself. 
The lower piece 2 of the vessel (container) in this invention is similarly 
to the upper piece 1 made of a metallic plate with a thickness of 0.3-1.0 
mm, preferably 0.3-0.5 mm, by means of a deep-drawing process. Preferable 
way of drawing operation will be described hereunder, which includes, 
roughly speaking, three major processes, i.e., deep-drawing a punched 
plate of aluminum alloy of 0.3-1.0 mm thickness coated with a epoxy resin 
into a shape of the main body piece or member, annealing the formed main 
body portion at a temperature of 250.degree.-350.degree. C. for 1-5 
minutes, and forming additionally or finishing the annealed main body 
piece or member. 
Describing further in detail, a certain coil plate of aluminum alloy (A 
3004 or A 5052) with a thickness, for example, of 0.4 mm, having a coating 
of epoxy-urea resin (thickness 4.mu.) is brought about in place, in the 
first process. In this instance the thickness of the coil plate may be 
between 0.3 and 1.0 mm, and as the epoxy resin preferable epoxy-urea resin 
may be adopted. The thickness of the coating may be freely selected in 
accordance with the use, and the coating may be applied only to the inside 
surface of the container. 
The second process is punching by means of a blanking machine to get a 
circular plate material of a predetermined dimension. 
The punched material plate is delivered to a transfer press machine, 
wherein the third, the fourth, and the fifth processes are performed in 
the order to gradually approach, through a series of deep-drawing 
processes, the shape of a bottomed cylindrical main body. 
The sixth process is for forming, and the seventh process for trimming. The 
sixth process may be omitted according to the circumstances. 
The eighth process is an annealing process in a continuous annealing 
furnace, wherein the operation conditions are 290.degree. C. in 
temperature, 1.5 minutes in time duration. As later described the 
temperature may be in the range of 250.degree.-350.degree. C. and the time 
duration may be 1-3 minutes according to the variation of the plate 
thickness and the composition of the coating material. 
The ninth process is a bulging process with a bulging press, wherein the 
main body already annealed is bulged by urging from inside by means of a 
rubber die put inside the main body against an external die embracing the 
main body in order to get a targeted barrel form. Stretching rate observed 
in this bulging process is, for example, 6.5%. This stretching can be 
obtained without affected by the so-called stretch strain mark (SS mark) 
thanks to the foregoing annealing in the eighth process. If the annealing 
in the eighth process is omitted numerous stretch strain marks appear on 
the external surface of the main body piece. 
In the aforementioned preferable embodiment the characteristic conditions 
adopted are the thickness selected in the range of 0.3 to 1.0 mm, the 
annealing temperature applied in the eighth process on the material plate 
with a coating of an epoxy resin within the range of 
250.degree.-300.degree. C., and the time duration therefor which is 
specified between 1 and 3 minutes. By observing those conditions the main 
body can attain, after the largest possible deep drawing ratio (for 
example the drawing ratio 2.25) to the aluminum alloy material has been 
performed in the third, fourth and fifth processes (steps), the stretching 
rate of 6.5% in the ninth bulging process and the deterioration or burning 
(scorching) due to oxidation of the resin coating can be surely avoided. 
When the annealing temperature exceeds 350.degree. C., in either case of 
epoxy-phenol resin or epoxy-urea resin coated, the coating layer itself is 
burnt or scorched to discolor the coated surface. Besides, it causes to 
give some unagreeable flavor to the contained food or beverage. Annealing 
at a temperature below 250.degree. C. the time duration required is 
elongated to accelerate the discoloration of the coating, and the time 
duration of annealing exceeding 5 minutes burns or destroys the coating, 
irrespective of the temperature at which the annealing is carried out. 
Annealing over 5 minutes results often remarkable carbonization of the 
coating film. On the contrary, annealing for less than 1 minute brings 
about insufficient effect of annealing, being far short of expectation. 
The best preferable conditions of annealing in a case, wherein an aluminum 
alloy plate 21 of 0.4 mm thickness (for example A 3004 or A 5052) coated 
with epoxy resin at a thickness of 4.mu. is required to show a drawing 
ratio up to the fifth process (step) 2.25 and to give a stretching rate in 
the ninth process of 6.5%, are 290.degree. C..+-.10.degree. C. in 
temperature and 1.5 minutes in its time duration. At the above-mentioned 
conditions no destroying of resin coating is observed and no undesirable 
flavor is found given to the contained matter, to the best of the 
inventor's knowledge. 
The above-mentioned method for obtaining a container made of aluminum 
(including aluminum alloys) coated with an epoxy resin is highly suitable 
for doing the deep-drawing process and for preventing the destroying of 
the coated film. Even when the annealing process which is carried out 
within the course for partially recovering the material stretching is 
taken into consideration, this method is still sufficiently effective in 
preventing the destroying of the coating for the containers used for 
foods. This invention has thus succeeded in providing a container 
excellent in corrosion resistance, wearing resistance, etc., and in giving 
a good appearance. 
The continuous annealing furnace of heated-atmosphere-cycling type, which 
is utilized in the eighth process for realizing the invented method, can 
be replaced by a heating method by means of infrared rays irradiation or 
an induction heating method by means of high frequency for the purpose of 
heating only outer side of the container which is advantageous in 
preventing to the greatest extent the destroying of the coated resin on 
the inside surface during the course of annealing. It is an innegligible 
thing for a container for foods which attaches an importance to the 
prevention of flavor-giving to the contained matter. 
Another great merit derived from the above method for making an upper piece 
1 and a lower piece 2 from an aluminum alloy plate coated with a resin is 
a complete elimination of lubrication oil in the course of drawing 
process, which can not be expected in the ordinary drawing processes, 
because of the coated resin itself functioning as a good lubricating 
matter during the drawing operation. This elimination of lubricant makes 
it possible consequently to do away with the cleansing and drying 
operation usually required for the containers for foods. 
Regarding the bulging process of the container which is preferably applied 
to the lower piece 2 to bulge the barrel portion thereof for swelling 
outwardly in an arch shape in cross-section, some comments will be made 
regarding its limitation and cautions. 
The greatest diameter of the arch like bulged portion of the lower piece 2 
in its center must be within the limit of 1.1 times as large as the 
smallest diameter of the lower piece 2 which lies, concretely speaking, in 
the joined portion of the lower piece 2 with the upper piece 1. The 
bulging beyond this limit is liable to give rise to a problem of cracking 
in the material. 
In the actual operation of this bulging process an undesirable possible 
occurrence of stripes or streaks on the surface of the lower piece 2 from 
the use of the split die must be carefully prevented. This precaution 
required for keeping the commercial value of the manufactured articles 
will be described hereunder. 
This problem has been essentially solved by utilizing a split die which, 
used for bulging the lower piece 2, is provided with a groove formed in 
the abutting or joining portion of the two parts. The depth and width of 
the groove must be carefully determined from the consideration of the 
material quality and thickness to be processed and the quality of the 
urethane rubber employed as an inside die, such as elasticity and others, 
so that the material to be processed may not touch the bottom of the 
groove when it is pushed out into the groove by the urging force of the 
inside die. By avoiding the touch with the groove bottom a smooth and 
beautiful rib of arcuate cross-sectional shape can be formed there instead 
of the conventional unseemly stripe (streak). The beautiful rib made on 
the joining place will make, with the aid of grooves disposed at other 
places than the die-joining position, a series of straight grain pattern. 
This will be illustrated by an embodiment. 
In FIG. 12 the numeral 41 designates a bolster, on which a mold 42 is fixed 
with a plurality of bolts, and a pair of splittable body portion of the 
mold 42a, 42b are movably placed there in the arrow marked lateral 
directions (right and left) from the boundary line designated at 43. 
Numeral 44 designates a ram movable up and down. A holder 45 connected to 
the ram 44 is provided with an inside die (inside mold) 46 of urethane 
rubber. A cup-like material 47 to be formed into a lower piece 2 made of 
aluminum thin plate is provided, on the upper end thereof, with an 
integral lateral flange 48 for resting. When everything is ready as in 
FIG. 12 the ram 44 is lowered to expand the inside die 46 of urethane 
rubber for bulging in turn the cup-like material 47 by urging the same 
along and against an inside surface 49 of the mold 42. Lifting up of the 
ram 44 accompanied by a simultaneous opening of the two parts 42a, 42b of 
the mold 42 will leave a formed lower piece (indicated with 40 in FIG. 
13). 
With reference to FIG. 14, which shows an enlargement of the 
cross-sectional view of FIG. 12 taken along the line XIV-XIV, wherein the 
bulging formation is finished by the urethane rubber 46 expanded to the 
maximum extent, a part of the cup-like material 47 is swollen by the 
ruging force of the inside die 46 out into a groove 51 of arcuate 
cross-sectional shape which is engraved in advance by etching or like 
method at the joining place 50 of the mold 42. A bead 52 formed by the 
above-mentioned swelling of the cup-like material 47 into the groove 51 
does not reach the groove bottom 50, i.e., the joining place of the two 
parts of the mold 42, so the bead 52 has a smooth and uniform arcuate 
shape in cross-section in accordance with the natural expansion of the 
inside die 46 of urethane rubber. It completely prevents the external 
surface of the bead 52 being spoiled by the possible vertical streaks, 
even when the joining place 50 is somewhat offset or inprecise. On both 
lateral sides of the groove 51 a plurality of rather shallow grooves 53 
are engraved with an identical interval from each other, wherein the 
swollen material 47 reaches the bottom of the grooves 53, when it is urged 
by the inside die 46, to form a bead 54 . . . . Those beads 52, 54 . . . 
will form the aforementioned straight grain pattern, as shown in FIG. 13. 
Those beads 52, 54 . . . are formed only ranging the bulged section 
L'.sub.1 in the barrel main body 40 (in FIG. 13), and they become 
gradually lower to finally fade out at the upper and lower extremity of 
the bulged section L'.sub.1. 
By means of employing the split mold 42 which is provided with, in its 
joining place 50, the groove 51 engraved in advance, the bead 52 is made 
positively or purposely while the bulging formation is carried out on the 
material 47. This is successful in preventing the occurrence of unseemly 
streaks on the joining place of the mold 42, which has been unavoidable in 
the prior art, and consequently in greatly improving the appearance of the 
barrel main body 40. The formation of the straight grain pattern, which is 
made by the bead 52 and the other parallel beads 54 . . . cooperating the 
former, has greatly enhanced the commercial value of the barrel 40. 
Various types of grooves or pattern designs may be engraved in advance on 
the inside surface of the split mold 42 for getting desired beads or 
patterns on the varrel 40 by virtue of the inside die of urethane rubber 
46, so that the bead 52 formed on the material 47 may not touch the 
joining place 50 of the mold 42, i.e., the bottom of the groove 51 has not 
only completely prevented the occurrence of the undesirable streaks but 
also has completely eliminated the problems regarding the deterioration of 
strength and maintenance of safety. It also contributed very much in 
economizing the mold manufacturing cost, because this method has relieved 
the mold from the requirement to be absolutely precise. This invention is 
also applicable to the hydraulic pressure type bulging formation method. 
In this invention the joining of the upper piece 1 and the lower piece 2 
is, as stated earlier, preferably executed by the double-seaming process. 
However, the method of joining the two is not limited to that, but any 
suitable ones are allowable, for example, an adhesive may be used. 
Regarding the double-seaming process employed in this embodiment, a 
detailed description will follow hereunder. For joining the upper piece 1 
in a most desirable way to the lower piece 2, (1) a cylindrical outside 
wall of a recess (a valley portion) which is formed around the lower 
opening of the upper piece 1 is so made as to be gradually 
small-diametered toward the bottom portion (called bottom wall) of the 
recess, that is, slightly tapered inwards, (2) the bending or turning-back 
radius of the bottom wall is made approximately equal to the thickness of 
the material plate, (3) the angle formed between the outside wall and the 
inside wall of the recess is made as small as possible within the sphere 
which allows the fitting-in of a chuck, and (4) the double-seaming process 
is carried out, after having substantially contacted the outside wall of 
the recess closely to the inside surface of the opening of the lower piece 
2 by means of inserting of the annular chuck, with a double-seaming roll 
applied to the joining place from outside under pressure. 
This process will be detailed with reference to FIGS. 15 and 16. A 
two-dot-chain-lined portion 63' in FIG. 15 shows the recess before the 
insertion of the chuck 71 (see FIG. 16). The recess 63 illustrated in a 
solid line is in its seaming-completed state. 
The inventors of this invention confirmed from a series of strenuous 
experiments that the bending radius r of the bottom wall 69 of the recess 
63 should be as small as possible for making the recess 63 strong (the 
strength against being rolled up), and that the bending radius r can not 
practically be made smaller than the thickness t of the plate. So the 
radius r was determined to be approximately equal to the thickness t (0.5 
mm) of the plate. Letter M designates an angle formed between a line P and 
a line Q (in FIG. 15), which are located in a plane including an axial 
line of the container, wherein P is a straight line in the inner surface 
78 of the outside wall 68 of the recess 63 and Q is a straight line which 
contacts from left a circle S which is inscribed on the upper side of the 
bottom wall 69 and also contacts from right (in FIG. 15) an arc which is 
formed by the outer surface 77 (right side in FIG. 15) of the inside wall 
67 of the recess 63, with a radius (R.sub.4 +t), at a point where the arc 
contacts the circle S. In other words, Q indicates a straight line which 
is perpendicular to a line n linking the center O of the circle S and a 
center n of the arc passing the outer surface 77 of the inside wall 67. 
The inventors also found based on the experiments that the angle M should 
be as small as possible to improve the strength of the recess 63 and 
should practically be less than 10.degree. when the container is used as a 
beer container, because its inner pressure is 4.2 Kg/cm.sup.2 G or so. 
However, if the angle M is made less than 0.degree. the insertion of the 
chuck 71 into the recess 63 for applying the double-seaming becomes 
extremely difficult. In this embodiment where the diameter of the barrel 
portion (inner diameter of the lower piece 2) L=15.5 cm, the angle M is 
determined within the range of 0.degree.-10.degree.. And the radius 
R.sub.4 (shoulder curve) of the outer surface 77 is determined within the 
range 1/4-1/10 of the barrel diameter L, which is very contributive to 
improving the degree of pressure resistance of the container. And the 
radius R.sub.4 in this embodiment is numerically set at R.sub.4 
=(0.17-0.18)L. Besides, the force acting on a unit of length of the recess 
63 and the seaming place 70 (in the circumferential direction) caused by 
the inner pressure is proportionate to the barrel diameter L, therefore 
the increasing of the L requires a corresponding decreasing of the angle 
M. 
If and when the angle M and the radius r are minimized in accordance with 
the above-mentioned requirements, distance l between the lowest end e of 
the bottom wall 69 and the inner surface 73 of the opening 61 of the lower 
piece 2 becomes extremely small (approximately 1 mm), so the insertion of 
the recess 63 in a state illustrated with a solid line into the opening 61 
of the lower piece 2 becomes very difficult. As a countermeasure for that 
difficulty the outside wall 68' of the recess 63' is slightly tapered 
inwardly as it approaches the bottom wall 69', i.e., it is inwardly 
inclined a little, so that the lowest end 68'a of the outside wall 68' may 
be separated from the inner surface 73 of the opening 61 by a distance of 
l.sub.1, approximately 0.5 mm. As the distance l.sub.1 between the lowest 
end e' of the bottom wall 69' and the inner surface 73 of the opening 61 
is expanded up to 1.5 mm by making the recess 63' alienated from the 
opening 61 as mentioned above, this facilitates the inserting of the 
recess 63' into the opening 61. 
After the recess 63' is inserted into the opening 61, the annular chuck 71 
is inserted into the recess 63' from above for contacting the outside wall 
68 almost closely to the opening 61, and then a double-seaming roll 72 is 
applied from outside (from right side in FIG. 16) on flanges 65 and 66 
under pressure to carry out the double-seaming. 
The outside wall 68 will be, when the chuck 71 is lifted at the finishing 
of the double-seaming process, alienated a little from the opening 61 due 
to the spring back phenomenon. But it will not affect at all the gas-tight 
sealing of the double-seamed portion 70. 
In accordance with the above-mentioned double-seaming process in this 
invention, the angle M between the inside wall 67 and the outside wall 68 
of the recess 63 and the bending radius r of the bottom wall 69 were both 
made very small. It remarkably enhanced the strength of the recess 63 
against being rolled up to loosen the sealing and consequently the 
anti-pressure capability. Besides, the tapering of the outside wall 68' 
toward the bottom wall 69' before the recess 63' being inserted into the 
opening 61 made the inserting of the recess 63' into the opening 61 
extremely easy, irrespective of the diminishing of the angle M and the 
radius r.