Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CAN BODIES
Backqround of the Invention
Field of the Invention
The invention relates to metal can bodies for
beverage cans. Such can bodies are adapted to be closed
by a can end seamed to the open end of the can body to
form a closed can.
Description of the Prior Art
Known can bodies for beverage cans comprise a
bottom end wall and a generally cylindrical side wall; the
side wall comprising a bottom portion connected to the
bottom wall, a central portion extending upwardly from the
bottom portion , and a top portion extending upwardly from
the central portion and terminating in an open end;
wherein the top portion and bottom portion are of greater
wall thickness than the central portion and are
respectively connected to the central portion through
upper and lower annular zones of reducing wall thickness.
SummarY of the Invention
During handling of can bodies small dents may be
made in the cylindrical wall and these dents provide
localised points of weakness which can lead to creasing
during necking and flanging of the neck of the can body,
and filling double seaming of the can end onto the can
body during which the can body is subjected to an axial
load. It has been found that the provision of a plurality
of parallel longitudinally extending outwardly convex ribs
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in the central portion of the can body will reduce or eliminate
the effect of such dents and give axial strength to the can. It
has also been found that the optimum performance of the can body
is achieved when the ribs terminate in the zones of reducing wall
thickness and thus connect the portions of greater wall thickness
together.
Accordingly the invention in one aspect provides a metal
can body for a beverage can made by drawing and ironing sheet
metal to comprise a bottom end wall and a generally cylindrical
side wall, the side wall comprising a bottom portion of circular
cross section connected to the bottom wall, a central portion of
constant wall thickness extending above the bottom portion and a
top portion of circular cross-section extending above the central
portion and terminating in an open end. The top portion and
bottom portion are of greater wall thickness than the central
portion and are respectively connected to the central portion
through upper and lower cylindrical zones of reducing wall
thickness. The side wall is provided with a plurality of
parallel sided panels each joined to the next by an externally
convex longitudinal rib, the ribs and panels being equally spaced
around the circumference of the can body and the ribs and panels
terminate at either end within the zones of reducing wall
thickness.
Brief DescriPtion of the Drawinqs
Figure 1 shows a partial section of a can body prior to
provision of the longitudinal ribs;
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Figure 2 shows a partial section of a can body
after provision of the longitudinal ribs;
Figure 3 shows a side view of a can body,
partially in section after provision of the ribs and after
necking and flanging;
Figure 4 is a graph representing the wall
thickness of the can body of Figure 3 against height;
Figure 5 is a side view of a can body;
Figure 6 is a horizontal section of the can body
of Figure 5 taken on lines VI-VI;
Figures 7 and 8 are similar views to those of
Figures 5 and 6 of an alternative embodiment of can body;
Figure 9 is a radial cross section through a
mandrel for forming ribs in a can body; and
Figure lO is an axial section through a mandrel
for forming a can body.
Description of the Preferred Embodiments
Referring to Figures 1-4 it will be seen that the
can body l comprises a bottom end wall 2, which in this
case is domed, and a side wall 3. The side wall 3
comprises a bottom portion 4 connected to the bottom end
wall, a central portion 5 and a top portion 6 terminating
in an open end. The top portion 6 and bottom portion 4
are of greater wall thickness than the central portion 5
and are respectively connected to the central portion 5
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through upper and lower annular zones 7,8 which have a
wall thickness which reduces towards the central portion
5. Typically the wall thickness of the top portion will
be about 0.15mm (.0060 inches), central portion about
O.lmm (.0040 inches), and bottom portion about 0.3mm
(.0120 inches). The can body of Figure 1 is formed by
blanking a disc from sheet metal, drawing a cup from the
disc to form a bottom end wall and a side wall, and wall
ironing the side wall. Figure 2 shows the can body after
the provision of a plurality of parallel longitudinally
extending convex ribs 10 equally spaced around the
circumference. The ribs 10 terminate in the zones 7, 8.
Adjacent ribs define elongate panels 11 therebeteween.
Each panel 11 has semi-elliptical shaped end areas formed
within the zones 7,8. The ribs and panels extend into the
zones 7,8 to optimize the can body performance by
providing strengthening columns connecting the upper and
lower portions 4, 6 of relatively great wall thickness.
Figure 3 shows the can body after necking and
flanging of the top portion 6 in readiness for receiving a
can end to be seamed to the flange 12 in known manner.
Figure 4 shows the thickness profile of the side
wall as it varies through the height of the can body.
Figures 1-4 show a can body provided with only 24
ribs 10 and panels 11. It is believed that can bodies
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having from about 24 to about 45 ribs are useful for
beverage cans. If the number of ribs is less than about
24 there is a significant reduction in the volume of the
finished can.
Figures 5 and 6 show a can body having 30 ribs lO
and panels ll. Each rib is outwardly convex having a
radius P and lies on a circle of radius R where R is the
radius of the can body in the middle of the central
portion prior to formation of the ribs. The panels ll are
outwardly concave and have a radius U. The concavity of
the panels ll has been exaggerated in Figures 5 and 6.
The ratio of U:P is preferably at least 20:1. Typically
the rib radius P will be about lmm. The perimeter of the
can body in the central portion after forming of the ribs
is the same as it was beforehand and the radii R, P and U
are related by the equation R=U+2P. In this manner,
stretching of the can wall during form of the ribs is
avoided.
In a further embodiment shown also in Figures 7
and 8, also having 30 ribs lO, the panels are
substantially flat. In this case the ribs lO will lie on
a circle whose radius is very slightly greater than the
radius R prior to formation of the ribs and panels. As a
result of the wall ironing process for forming the can
body, however, the top and bottom portions 6 and 4 have a
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slightly greater radius than the central portion and the
radius of the central portion of the can body after
formation of the ribs will be no greater than the radius
of the top and bottom portions. This is important in
handling since the can body must roll truly.
Figures 9 and 10 show a mandrel 20 used in
formation of the ribs and panels. The can body is located
over the mandrel which is then rolled along an external
forming rail (not shown). The ribs are formed prior to
necking of the can body but nevertheless the mandrel must
be of smaller radius than the can body so that it can be
extracted from the can body. To this end it is formed
with less ribs than the can body. In the example shown
the mandrel 20 has 29 ribs 21 for forming a can body with
30 ribs. Between the ribs 21 on the mandrel are panels 22
which are outwardly concave. The profiles of the panels
22 will determine the profiles of the panels 11 in the can
body. The mandrel shown in Figs. 9 and 10 is for forming
the can body of Figs. 7 and 8 having substantially flat
panels 11. During formation, the side wall of the central
portion of the can body is locally deformed to the profile
of the mandrel 20 but due to the natural resilience of the
material the panels of the can body will subsequently
spring back to a substantially flat profile. If a can
body as shown in Figs. 5 and 6 is required, the panels 22
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of the mandrel 20 are formed more deeply concave. The
depth of the panel must, however, be relatively shallow to
avoid excessive loss of volume and to prevent the panels
from reversing when subjected to internal pressure as
would be experienced when the can is filled with a
carbonated drink.
The improved performance of can bodies as a result
of the panelling may be used to increase the axial load
strength, or to allow a reduction of the wall thickness of
the central portion 5 without loss of axial strength.
Comparative tests have shown that the performance of
panelled can bodies having a wall thickness in the central
portion of 40xlO 4 inches is comparable to that of
unpanelled can bodies of wall thickness 43xlO 4 inches.
Considering the large number of can bodies made, this
represents a very significant saving.
