Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEMS AND METHODS FOR MAKING DECORATIVE
SHAPED METAL CANS
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of consumer packaging, and
more specifically to metal cans, such as the steel and aluminum cans that are
commonly
used for packaging soft drinks, other beverages, food and aerosol products.
2. Description of the Prior Art and Recent Technology
Metal cans for soft drinks, other beverages and other materials are of course
in wide use in North America and throughout the world. The assignee of this
invention,
Crown Cork & Seal Company of Philadelphia, is the world's largest designer and
manufacturer of such cans.
The art of making and packing metal cans is constantly evolving in
response to improved technology, new materials, and improved manufacturing
techniques.
Other forces driving the evolution of technology in this area include raw
material prices,
the nature of new materials to be packaged and the marketing goals of the
large companies
that manufacture and distribute consumer products such as soft drinks.
Interest has existed for some time for a metal container that is shaped
= differently than the standard cylindrical can in such a distinctive way to
become part of the
product's trade dress, or to be otherwise indicative of the source or the
nature of the
product. To the inventors best knowledge, however, no one has yet developed a
practical
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technique for manufacturing such an irregularly shaped can
at the volume and speed that would be required to actually
introduce such a product into the marketplace.
U.S. Patent 3,224,239 to Hansson, which dates from
the mid 1960's, discloses a system and process for using
pneumatic pressure to reshape cans. This process utilized a
piston to force compressed air into a can that is positioned
within a mold. The compressed air caused the can wall to
flow plastically until it assumed the shape of the mold.
Technology such as that disclosed in the Hansson
patent has never, to the knowledge of the inventors, been
employed with an success for the reshaping of drawn and wall
ironed cans. One reason for this is that the stress that is
developed in the wall of the can as it is being deformed can
lead to defects that are potentially failure-inducing, e.g.,
localized thinning, splitting or cracking. The risk of
thinning can be reduced by increasing the wall thickness of
the can, but this would make shaped cans so produced
prohibitively expensive. The risk of splitting and cracking
can be reduced by a process such as annealing, but at the
expense of reduced toughness and abuse resistance of the
final product.
A need exists for an improved apparatus and
process for manufacturing a shaped metal can design, that is
effective, efficient and inexpensive, especially when
compared to technology that has been heretofore developed
for such purposes, and that reduces the tendency of a shaped
can to fail as a result of thinning, splitting or cracking.
SUMARY OF THE INVENTION
Accordingly, it is an object of the invention to
provide an improved apparatus and process for manufacturing
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a shaped metal can that is effective, efficient and
inexpensive, especially when compared to technology that has
been heretofore developed for such purposes, and that
provides insurance against internal stresses within the can
that could cause thinning, splitting or cracking.
According to the invention there is provided a
method of manufacturing an aluminum can body which is shaped
distinctively in order to enhance its visual presentation to
consumers, comprising steps of: (a) making a beverage can
body blank by a drawing and ironing process; (b) partially
annealing the whole of the can body blank at a temperature
which is within the range of 232 C (450 degrees Fahrenheit)
to 260 C (500 degrees Fahrenheit), thereby giving the
annealed can body blank increased ductility; (c) providing a
mould unit that has mould walls that define a mould cavity
conforming to a desired final shape of the can body;
(d) positioning the can body blank within the mould cavity;
and (e) expanding the can body radially outwards onto the
inner surface of the mould by the use of pressurised fluid
in the can body blank, thereby forcing the can body blank by
pressure against the mould wall and causing the can body
blank to assume the desired final shape of the can body.
These and various other advantages and features of
novelty which characterize the invention are pointed out
with particularity in the claims annexed hereto and forming
a part hereof. However, for a better understanding of the
invention, its advantages, and the objects obtained by its
use, reference should be made to the drawings which form a
further part hereof, and to the accompanying descriptive
matter, in which there is illustrated and described a
preferred embodiment of the invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a cross-sectional view taken through a
can body blank or pre-form that is constructed according to
a preferred embodiment of the invention;
FIGURE 2 is a side elevational view of a shaped
can body according to a preferred embodiment of the
invention;
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FIGURE 3 is a diagrammatical view of An apparatus for making a shaped
can body according to a preferred embodiment of the invention;
FIGURE 4 is a fragmentary cross-sectional view through a mold unit in the
apparatus depicted in FIG. 3, shown in a first condition;
= 5 FIGURE 5 is a fragmentary cross-sectional view through a mold unit in the
apparatus depicted in FIG. 3, shown in a second condition;
FIGURE 6 is a schematic diagram depicting a pressure supply apparatus for
the mold unit depicted in FIG. 3;
FIGURE 7 is diagrammatical depiction of a precompression step that is
performed in the apparatus as depicted in FIG. 3;
FIGURE 8 is a diagrammatical depiction of a beading step in a method that
is performed according to a second embodiment of the invention;
FIGURE 9 is a diagrammatical depiction of a spinning step in a method
that is performed according to a second embodiment of the invention; and
is FIGURE 10 is a diagrammatical depiction of a knurling step that can be
performed as a second step in either the second or third embodiments of the
invention
referred to above.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Referring now to the drawings, wherein like reference numerals designate
corresponding structure throughout the views, and referring in particular to
Figures 1 and
2, a can body blank or preform 10 according to a preferred embodiment of the
invention is
the body of a two-piece can, which is preferably formed by the well-known
drawing and
ironing process. Can body blank 10 includes a substantially cylindrical
sidewall surface
12, a bottom 14, and necked upper portion 16. Alternatively, the upper portion
of
2 5 cylindrical sidewall 12 could be straight.
As is well known in this area of technology, the can body blank 10 must be
washed after the drawing and ironing process, and then must be dried prior to
being sent to
the decorator. The drying process typically is performed at a temperature of
about 250
degrees Fahrenheit (which is about 121 degrees Celsius). According to one
aspect of this
= 30 invention, the drying is performed at a higher temperature than is
ordinary to partially
anneal at least selected portions of the can body blank 10. In Figure 1, a
heat source 18 is
schematically depicted, which is preferably part of the dryer assembly, but
could be at any
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point in the apparatus prior to the molding unit. As will be discussed in
greater detail
below, can body blank 10 is preferably formed of aluminum and the partial
annealing is
preferably accomplished at a temperature that is substantially within the
range of about
375 degrees Fahrenheit (about 190.5 degrees Celsius) to about 550 degrees
Fahrenheit
(about 288 degrees Celsius), with a more preferred range of about 450 degrees
Fahrenheit (about 232 degrees Celsius) to about 500 degrees, Fahrenheit (about
260 degrees Celsius),
and a most preferred temperature of about 475 degrees Fahrenheit (about 246
degrees
Celsius). This is in contrast to true annealing, which would be at
temperatures over 650
degrees Fahrenheit (about 353 degrees Celsius). The purpose of the partial
annealing is to
1 o give the can body blank 10 enough ductility to be formed into a shaped can
20, such as is
shown in Figure 2 of the drawings, but greater toughness than would be
possible if the can
body blank were fully annealed.
Alternatively, the partial annealing could be performed in an oven such as
the lacquer or decorator oven, rather than in the dryer.
Alternatively, can body blank 10 could be fabricated from steel instead of
aluminum. In this case, the preferred temperature range for partial annealing
would be
substantially within the range of 1112 degrees Fahrenheit (600 degrees
Celsius) to about
1472 degrees Fahrenheit (800 degrees Celsius). More preferably, the partial
annealing
would be perfornled at approximately 1382 degrees Fahrenheit (750 degrees
Celsius).
Referring now to Figure 2, shaped can 20 is decorated and shaped
distinctively in order to enhance its visual presentation to consumers. As may
be seen in
Figure 2, can body 20 includes a bottom 26, a shaped sidewall 22 that is
shaped to
substantially deviate from the standard cylindrical can body shape, such as
the shape of
can body blank 10. The shaped sidewall 22 includes areas, such as ribs 30 and
grooves 32,
where accentuation of such deviations from the cylindrical shape might be
desired.
According to one important aspect of the invention, decoration is provided on
the external
surface of the shaped sidewal122 in a manner that will accentuate those areas
of the
sidewall where accentuation of the deviation from the cylindrical shape is
desired. As
may be seen in Figure 2, a first type of decoration, which may be a lighter
color, is
3 0 provided on the rib 30, while a second type of decoration 36, which may be
a darker color,
is provided within at least one of the grooves 32. By providing such selective
decoration,
and by properly registering the decoration to the deviations in the shaped
sidewal122, a
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synergistic visual effect can be obtained that would be impossible to obtain
alone by
shaping the can or by decorating the can.
Referring again to Figure 2, shaped sidewal122 also has a flat area 28,
where writing or a label might be applied, and is closed by a can end 24,
which is applied
in the traditional double seaming process.
According to the preferred method, after the partial annealing by the heat
source 18 at the drying station, can body blank 10 will be transported to a
decorator, where
the distinctive decoration will be applied while the can body blank 10 is
still in its
cylindrical configuration. Markers might also be applied during the decorating
process
1 o that can be used for registration of the decoration to the mold contours
during subsequent
forming steps, which will be described in greater detail below.
Referring now to Figure 3, An apparatus 38 is depicted which, according to
the preferred embodiment of the invention, is provided to manufacture a shaped
can 20 of
the type that is depicted in Figure 2. As may be seen in Figures 3, 4 and 5,
apparatus 38
includes a mold 40 having a mold wal146 that defines a mold cavity 42
conforming to the
desired final shape of the shaped can body 20. As is shown diagrammatically in
Figure 7,
the mold 40 is of the split wall type and the mold wall 46 will include
inwardly extending
portions 48 that are less in diameter than the diameter Db of the cylindrical
sidewall 12 of
the can body blank 10 depicted by the dotted lines in Figure 7b. The mold
wa1146 will
also include a number of outwardly extending portions that are greater in
diameter than the
diameter Db of the sidewall 12 of the can body blank 10. In other words, the
inwardly
extending portions 48 tend to compress the cylindrical sidewall 12 of the can
body blank
10 to the position 12' shown by the solid lines in Figure 7b, while the
sidewall 12 of the
can body blank 10 must be expanded to conform to the outwardly extending
portions 50 of
2 5 the mold wall 46. Preferably, the perimeter of the cylindrical sidewall
remains a constant
length when compressed in this manner so the perimeter of the cylindrical
compressed
sidewall 12' is the same length as the circumference of the sidewall 12 of the
can body
blank 10.
As is best shown in Figure 3, the mold unit 40 has three die parts 82, 46 and
3 0 84 which comprise neck ring, mold side wall and base support,
respectively. The die parts
are separated from each other by gaps or "split lines" 86 and 88. For ease of
machining,
the base support die 84 is made in two parts, with a central part 90
supporting the base
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dome of the can body. The neck ring 82 provides simple support to the necked
portion of
the can body.. These components together define the chamber or mold cavity 42
to receive
the can body and are machined to the desired final shape of the can body after
blow
forming. Vent holes 49 are provided (see Figures 4 and 5) to allow trapped air
to escape
during forming. A pair of seal and support rings 92, 94 and a rubber sealing
ring 96 are
provided to seal the top edge of the container body. A space saving mandrel 98
passes
through the center of the seal and support rings 92, 94, 96 to a position just
above the base
support dome 84. The mandrel 98 supplies air to the cavity of a can body
within the cavity
42 via a central bore 100 and radial passages 102. The apparatus further
includes an upper
piston and a lower piston 104, 106 which together apply a load to both ends of
the can in
the mould cavity 42. Lower piston 106 is moveable upwards by structure of a
pressurized
air supply which is fed to the piston via passage 108. Similarly, the upper
piston is
moveable downwards by structure of a pressurized air supply which is fed to
the piston via
is passages 110 and 112. In the preferred embodiment shown, the passage 110 is
connected
to the central bore 100 of the mandrel 98 so that the upper piston and can
cavity share a
common air supply. The common air supply is split for the piston 104 and
cavity at the
junction of the air passage 112 and the central mandrel bore 100, within the
piston 104 so
as to minimize losses and to maintain the same pressure supplied to the cavity
and piston.
Preferably, means are provided to control the flow rate of air supplied to
each piston and
the cavity. Cavity pressure and piston pressure can therefore be closely
controlled.
A schematic circuit diagram which shows how air is supplied to the pistons
and can cavity is shown in figure 6. In the figure, the upper piston 104 and
seal and
support rings 92,94 are shown schematically as a single unit 114. Likewise,
the base
2 5 support 84,90 and lower piston 106 are shown as a single unit 116. Units
114 and 116 and
neck ring 82 are movable, whereas the side wall die 46 of the mold is shown
fixed.
The circuit comprises two pressure supplies. Pressure supply 118 supplies
pressurised air to the top piston 104 and cavity of the can within the mold
cavity 42.
Pressure supply 120 supplies pressurised air to the lower piston 106 only.
The two supplies each comprise pressure regulators 122,124, reservoirs
126,128, blow valves 130,132 and exhaust valves 134,136. In addition, the
lower pressure
supply 120 includes a flow regulator 138. Optionally, the upper pressure
supply 118 may
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also include a flow regulator, although it is not considered essential to be
able to adjust the
flow in both supplies. Reservoirs 126, 128 prevent a high drop in supply
pressure during
the process.
Typically, high pressure air of around 30 bar is introduced to the can cavity
= s and to drive the top of the can. The air pressure to drive the bottom
piston 106 is typically
around 50 bar, depending on the piston area. The air pressure within the mold
cavity 42
provides the force which is required to expand the can body blank outwards but
also
applies an unwanted force to the neck and base of the can which leads to
longitudinal
tension in the can side wall. The two pistons are thus used to drive the top
and the bottom
of the can, providing a force which counteracts this tension in the can side
wall.
The pressure of the air supplied to the pistons is critical in avoiding
failure
of the can during forming due to either splitting or wrinkling. Splitting will
occur if the
tension in the can side wall is not sufficiently counteracted by the piston
pressure, since
the pressure in the pistons is too low. Conversely, the pressure of the air
supplied should
not be so high that this will lead to the formation of ripples in the side
wall.
For this reason, preferably no stops are required to limit the stroke of the
pistons. If the stroke were limited, the can might not be fully expanded
against the mould
wall before the pistons reached the stops. If this occurs, the tension in the
can side wall
would cease to be balanced by the piston pressure with a consequent risk of
splitting. In
effect, the contact of the expanded can with the side wall of the mould
prevents further
movement of the pistons.
It should be noted therefore that the balance between the can cavity
pressure and the piston pressure is preferably maintained at all times
throughout the
forming cycle so that the rate of pressure rise in the cavity and behind the
pistons should
be balanced throughout the cycle, particularly when the can wall yields. The
rate of
pressure rise can be controlled by the flow regulator 138 or by adjusting the
supply
pressure via the pressure regulators 122,124.
By adjusting the can cavity pressure versus the pressure that is applied to
move the mold elements 82, 46, 84 towards one another, the apparatus may be
operated in
one of three different ways. By minimizing application of pressure to the
outer mold parts
82,84, the apparatus may be operated so as to simply move the mold parts
toward another
without exerting any force on the can body. This will reduce the gaps 86, 88
in the mold
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unit 40 as the can body shrinks longitudinally during the expansion process,
and will
reduce but not necessarily neutralize axial tensile stress created in the
sidewall of the can
body during expansion. Alternatively, by providing increased pressure to drive
the outer mold parts toward one another, a slight longitudinal or axial force
is applied to the can
body which is substantially equal to the axial tensile stress in the can body
sidewall, thus =
balancing such stress and protecting the can body from consequential weakening
and
possible splitting. A third mode of operation would be to provide an even
greater pressure
to drive the outer mold parts toward one another in order to apply an axially
compressive
force to the can body that would be greater than what would be necessary to
cancel the
tensile stress in the sidewall during operation. A net compressive force is
believed to be
preferable provided that such a force does not lead to the formation of
wrinkles.
In order to form the can, the blow valves 130,132 are first opened. It is
possible to have a short delay between the opening times of the blow valves if
required to
obtain a better match between the piston and cavity pressures but there will
then need to
be a higher rate of pressure rise for one circuit in order to maintain this
balance. A delay
can also be used to compensate for different pipe lengths, maintaining a
pressure balance
at the time of forming. The upper supply 118 is split for the piston 104 and
cavity as close
as possible to the piston 104 as described above in reference to Figure 3.
The apparatus is designed so that, at the latest, when each piston reaches its
maximum travel the can is fully reshaped and the gaps 86, 88 are not closed up
at the end.
Closing of the gaps can lead to splitting of the can due to excessive tension
in the side wall
in the sarne way as does limiting movement of the pistons before full
expansion has
occurred. However, the final gap should not be excessive since any witness
mark on the
side wall becomes too apparent, although removal of sharp edges at the split
lines
alleviates this problem.
Once the shaping operation is completed, the air is exhausted via valves
134 and 136. Clearly the exhaust valves are closed throughout the actual
forming process. It is important that both supplies are vented simultaneously
since the compressive force
applied by the pistons to balance the cavity pressure (longitudinal tension)
may be greater
than the axial strength of the can so that uneven exhausting leads to collapse
of the can.
As may best be seen in Figure 4, the can body blank 10 is preferably
positioned within the mold cavity 42 and its interior space is sealed into
communication
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with a source of pressurized fluid, as described above. As may be seen in
Figure 4, the
cavity 42 is designed so as to impart a slight compression to the can body
blank 10 as it is
inserted therein. This is preferably accomplished by forming the mold assembly
elements
into halves 52, 54, shown in Figure 4 that are split so as to be closeable
about the can body
= 5 blank prior to pneumatic expansion of the can body blank 10.
As the mold halves 52, 54 close about the cylindrical sidewall 12, the
inwardly extending portions 48 of the mold wal146 thus compress or precompress
the
cylindrical sidewall 12 by distances up to the amount R;,,, shown in Figure 7.
After the
mold has been closed and sealed and pressurized fluid is supplied into the
mold cavity 46
so as to force the can body blank 10 against the mold wall 46, can body blank
10 will be
forced to assume the desired final shape of the shaped can 20. The state of
the shaped
sidewa1122 is shown after the step in Figure 5. In this step, the cylindrical
sidewall 12 of
the can body blank 10 is expanded up to an amount Roõt, again shown
diagrammatically in
Figure 7.
Preferably, the precompression that is effected by the closing of the mold
halves 52, 54 is performed to deflect the sidewall 12 of the can body blank 10
radially
inwardly by a distance of R;n that is within the range of about 0.1 to about
1.5 millimeters.
More preferably, this distance R;n is within the range of 0.5 to about 0.75
millimeters. The
distance R.oõt by which cylindrical sidewall 12 is radially expanded outwardly
to form the
outermost portions of the shaped sidewa1122 is preferably within the range of
about 0.1 to
about 5.0 millimeters. A most preferable range for distance R.õ, is about 0.5
to 3.0
millimeters. Most preferably, R.õt is about 2 millimeters.
To understand the benefit that is obtained by the precompression of the
cylindrical sidewall 12 prior to the expansion step, it must be understood
that a certain
2 5 amount of annealing or partial annealing may be useful, particularly in
the case of
aluminum can bodies, to obtain the necessary ductility for the expansion step.
However,
the more complete the annealing, the less strong and tough the shaped can 20
will
ultimately be. By using the precompression to get a significant portion of the
differential
between the innermost and outermost portions of the pattern that is
superimposed onto the
final shaped can 20, the amount of actual radial expansion necessary to
achieve the desired
pattern is reduced. Accordingly, the amount of annealing that needs to be
applied to the
can body blank 10 is also reduced. The precompression step, then, allows the
desired
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pattern to be superimposed on the shaped can 20 with a minimum of annealing
and
resultant strength loss, thus permitting the cylindrical sidewall 12 of the
can body blank 10
to be formed as thinly as possible for this type of process.
As one embodiment of the invention, the mold wall may be formed of a
porous material so as to allow air trapped between the sidewall of the can
body blank and
the mold wall to escape during operation, although vent holes will probably
still be
required. One such material is porous steel, which is commercially available
from AGA in
Leydig, Sweden.
For purposes of quality monitoring and control, fluid pressure within the
l 0 mold cavity 46 is monitored during and after the expansion process by
structure of a
pressure monitor 69, shown schematically in Figure 5. Pressure monitor 69 is
of
conventional construction. If the can body develops a leak during the
expansion process,
or if irregularities in the upper flange or neck of the can creates a bad seal
with the gas
probe, pressure within the mold cavity will drop much faster in the mold
chamber 46 than
would otherwise be the case. Pressure monitor 69 will sense this, and will
indicate to an
operator that the can body might be flawed.
In the case of steel cans, pressure within the mold chamber could be made
high enough to forrn the can body into, for example, a beading-type pattern
wherein a
number of circumferential ribs are formed on the container.
A second method and apparatus for manufacturing a metallic can body that
is shaped distinctively in order to enhance its visual presentation to
consumers is disclosed
in Figures 7 and 9 of the drawings. A third embodiment is depicted in Figures
8 and 9 of
the drawings. According to both the second and third embodiments, a
distinctively shaped
metallic can body is manufactured by providing a can body blank, such as the
can body
blank 10 shown in Figure 1, that has a sidewall 12 of substantially constant
diameter, then
radially deforming the can body blank 10 in selective areas by selected
amounts to achieve
an intermediate can body 74 that is radially modified, but is still
symmetrical about its
access, and then superimposing a preselected pattern of mechanical
deformations onto the
intermediate can body 74. Describing now the second embodiment of the
invention, a
beading apparatus 62 of the type that is well known in this area of technology
includes an
anvi166 and a beading tool 64. A beading apparatus 62 is used to radially
deform the can
body blank 10 into the radially modified intermediate can body 74 shown in
Figure 9. The
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intermediate can body 74, as may be seen in Figure 9, has no deformations
thereon that
have an axial. component, and is substantially cylindrical about the access of
the can body
74. A knurling tool 76 is then used to superimpose the preselected pattern of
mechanical
deformations, in this case ribs and grooves, onto the intermediate can body,
making it
S possible to produce a shaped can 20 of the type that is shown in Figure 2.
In the third embodiment, shown in Figures 8 and 9, a spinning unit 68 is
used to deform the cylindrical sidewall 12 of the can body blank 10 radially
into the
intermediate can body 74. Spinning unit 68 includes, as is well known in the
technology,
a mandrel 70 and a shaping roller 72 that is opposed to the mandrel 70. After
this process,
the knurling step shown in Figure 9 is preferably performed on the so formed
intermediate
can body 74 in a manner that is identical to that described above.
Alternatively to the knurling step shown in Figure 9, the intermediate can
body 74 produced by either the method shown in Figure 7 or that shown in
Figure 8 could,
alternatively, be placed in a pneumatic expansion die or mold unit 40 of the
type that is
shown in Figures 3-5. Intermediate can body 74 would then be expanded in a
manner that
is identical to that described above in order to achieve the shaped can 20.
In the second and third methods described above, the can body blank 10 is
also preferably partially annealed by the heat source 18 during the drying
process, but,
preferably, to a lesser extent than that in the first described embodiment.
Preferably, the
annealing for the second and third methods described above is performed at a
temperature
that is within the range of about 375 degrees Fahrenheit (about 190 degrees
Celsius) to
about 425 degrees Fahrenheit (about 218 degrees Celsius). The methods
described with
reference to Figures 7 and 8 thus require less annealing than that described
with respect to
the previous embodiment, meaning that a stronger shaped can 20 is possible at
a given
weight or wall thickness, or that the weight of the shaped can 20 can be
reduced with
respect to that produced by the first described method. Disadvantages of the
second and
third methods, however, include more machinery and greater mechanical
complexity, as
well as more wear and tear on the cans, spoilage and possible decoration
damage as a
result of the additional mechanical processing and handling.
It is to be understood, however, that even though numerous characteristics
and advantages of the present invention have been set forth in the foregoing
description,
together with details of the structure and function of the invention, the
disclosure is
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illustrative only, and changes may be made in detail, especially in matters of
shape, size
and arrangement of parts within the principles of the invention to the full
extent indicated
by the broad general meaning of the terms in which the appended claims are
expressed.
Alternatively, for example, can body blank 10 could be formed by alternative
processes,
such as a draw-redraw process, a draw-thin-redraw process, or by a three-piece
welded or =
cemented manufacturing process.
