Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to certain improvements in the forming
of one end of a cylindrical metal container, this end being
called the "bottom", in opposition to the "top" end, that is
normally opened to empty the container.
s
Aspects of the prior art and embodiments of the invention
will be described by reference to the accompanying drawings,
in which:
- Fig. 1 shows, in a non-proportional cross section, a
prior art metal container (can).
- Fig. 2 shows a perspective view of a can of Fig. 1;
- Fig. 3 shows schematically a non-proportional cross
section of the improved can described in GB 2,166,410 A, May
8, 1986, with an enlarged detail showing the can bottom seam;
- Fig. 4 shows schematically a non-proportional cross
section of the improved can in the present invention, with a
enlarged detail of the labyrinth on system on the can bottom;
and
- Fig. 5 shows a schematic, non-proportional cross
section of a preferred shape of the present invention, with
an enlarged detail of the labyrinth on the can bottom.
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It is well known in the metal packaging art that the
manufacturing process and design of metal containers
(generally known as "metal cans") is continually evolving in
order to achieve technical and economical objectives, such as
the increase of production speed, increased resistance and
tightness assurance of the container (considering that food
and beverage products are packed under pressure or vacuum),
all this in conjunction with an effort to reduce material
costs while improving design and shelf appeal of the
container, since packaging is more and more important for the
marketing of products.
One important development was to replace the soldered side
seam, formed by hooking together the ends of tinplate flat
sheets, with the electric resistance weld widely used at
present, permitting the coplanar joining of the edges without
the use of a solder, generally made with a lead alloy, that
is harmful to human health.
The fastening of can ends on the top and bottom of the
cylindrical body, by the present state of the art, is
obtained by the "double seaming" process, in which a suitably
shaped end is placed over the flanged edge of a cylindrical
body, as illustrated in the upper part of Fig. 1, then by
roller action the end and body edges are shaped together
forming a "double seam" (Fig. 1, bottom). This operation is
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performed on both sides of the cylindrical body, resulting in
the well known food can shown in Fig. 2. Packers generally
receive containers as shown in Fig. 1, that is with a double
seamed bottom and an open top to allow the can to be filled,
and then closed by double seaming the top end, obtaining an
equal finish on both ends.
This widely used process has several drawbacks, such as:
- The double seaming process requires that the central
panel of the end be offset by approximately 1/8 inch in
relation to the most protruding part of the double seam.
This configuration makes it easier to deform when submitted
to internal pressure (as happens with food cans during
retorting, or with carbonated beverage cans) and requires
considerable increase of the end thickness as compared t the
body thickness.
- The peripheral area of the end forming the double seam
uses up a considerable amount of material.
- On the aesthetic and practical point of view, the
salient rims are inconvenient.
As a recent improvement of the above mentioned art., the
authors of the present invention have introduced several
13 3 3 ~ 7 3
improvements of the product and of its manufacturing
processes.
In GB published patent application 2,166,410 of May 8, 1986,
a first substantial improvement in the container construction
and end seaming process was described, whereby instead of an
outside seam, an inside seam was obtained, by introducing an
end inside the cylindrical body, using special double seaming
tools to interact with an inside curled body edge, forming a
seam by peripheral rolling action (Figs. 4 to 8 of said
patent application).
The can had as a basic feature the fact that its bottom rim
was flush with the outside body surface, and that the
overlapping surfaces of end and body were flat and laying in
parallel planes perpendicular to the axis x-x' of the can
(Fig. 3).
As subsequent technological advance the same author realized
the invention described in GB published patent application
2,197,606 of May 25, 1988, in which important novelties in
the process and equipment to manufacture the cans described
above were introduced, consisting of a process using axial
forming forces instead of roller action, by the use of
special tools that, when mounted on a multi station rotary
device, result in an automatic machine for high volume
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productions of cans with seamed bottom ends and flanged top
side.
The subject of the present invention is a further improvement
of the can structure described in G.B. patent application
2,166,410. In the present invention the inside curled rim
resulting from the seam has a non-planar shape, forming a
toroidal surface on the bottom of the can (Figs. 4 and 5).
In one aspect, the invention provides a metal container of
three-piece construction with a longitudinal welded body
having on its upper part an outward flaring flange to allow
the double seaming of an end after filling the container,
with a bottom end assembled from the inside over an inward
turned body edge to form a labyrinth configuration with
adjacent layers of material inside a rim, wherein said rim
has a substantially toroidal configuration and has a smaller
diameter than the inside diameter of the body in its middle
portion, wherein said body is curved inward in its lower edge
portion towards said rim, and wherein convoluted layers are
parallel to each other and all together convexly bent, so
that the middle portion of said rim is lower than the edge
portion of said rim, and the outer shape of said rim is
carrying on the curved form of the lower edge portion of said
body.
- 4a -
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In preferred embodiments of this aspect, the invention
provides:
The above metal container wherein the labyrinth configuration
between the bottom end and the body edge is hermetically
engaged by means of a resilient layer of a suitable sealing
material.
The above metal container wherein a conical portion
converging downward, is provided between the middle portion
of the body and the inward curved portion of the body.
The technical advantages resulting from this special
conformation comprise:
- Better assurance of tightness, in comparison to the
previous art shown in Fig. 3, because the larger development
of the overlaying surfaces of body and end increases the~
labyrinth effect that insures tightness.
- Sliding movements of overlaying surfaces forming the
labyrinth (10) in relation to each other are not possible:
they may occur when the contact area is flat, as in Fig. 3,
(7).
- 4b -
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- The toroidal formations of the rim will maximize the
sealing function of the sealing compound (11). Due to the
toroidal deformation process elastic reactions are originated
inside the adjacent layers of body and end material, that
increases the pressure between adjoining surfaces, improving
resistance to leakage.
- From the appearance point of view, the can will become
similar to a two piece can, with a lower production cost.
- The formation of non-planar labyrinth surfaces gives
the assembly a higher resistance to denting by outside
shocks, which allows the use of thinner materials, with
important money savings when applied to mass production such
as can making.
The drawings (Figs. 1 and 2) show that prior art containers
(metal cans), such as manufactured at present by can
producers and delivered to packers for filling and sealing
with their products (such as food preserves or others)
consist of a cylindrical body (1) with the top side flared
outwards in a flange (2) in order to permit the final double
seaming of the top end (3) after filling in the product.
On the other side, or bottom (4), of the can, where a similar
flange is made, the bottom end (5) is double seamed,
- 4c -
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resulting in a labyrinth configuration commonly called
"double seam" (8) in which adjacent layers of body and end
materials lay concentrically along substantially cylindrical
surfaces, said surfaces
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- 4d -
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having axes (x-x') that are parallel to the body's cylindrical
surface generatrix.
~he can in Fig. 3 has a flange (2) on the top side (9) of the
can body normally turned ~utwaxd and the bottom part (6) of
said body turned inward (4) in such a way that a can end (5)
applied to the body from the inside, as shown by the dotted
line drawing at "t", is engaged by its outer rim (7) with a
resulting seam being obtained, said seam having a labirinth
configuration in which adjacent layers ofcan body and can end
material lay in substantially parallel planes, said planes '
being parallel to the plate (P-H) of the can base and perpen_i
cular to the can axis (x-x').
The improved metal container (metal can) that is the subject
of the present invention, Figs. 4 and 5, has a new configuration
of the bottom rim (13) in which the outer rim (10) of a can
end (12) that engages the lo~er part (15) of the can body (14)
has two convex protrusions (lOa - lOd) and a concave surface
(lOb) in between, that, together with ad~acent layers formed
by the can body-bottom part 15-15a and the outer edge (lOc) of
said can end (12), provide a labirinth configuration with a
substantially toroidal outside surface.
The can body edge (15a) is in contact and applies pressure '
against a sealing compound deposit applied to can~nd (12) on
its outside surface before the seaming operation. Said can end
is of a type described in Brazilian patent application PI
860.5741 and consists of a central panel defined by an annular
wall depending from the periphery thereof to define a concave
recess, an annular portion extending radially outward from the
periphery of the annular wall, and a down turned edge portion
so arranged that the down turned edge, annular portion and
annular wall define a channel in which is placed a gasket in
the form of a lining compound, the lining compound being placed
in a corner defined by the down turned edge and the annular '
portion, on the side of said end that is opposite to the side
which, after assembly, constitutes the inside of the can.
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The toroidal rim basis, that is the plan where the convex
protrusions (lOa) and (lOd3 lie, may be parallel to plan
PM (Fig. 4) that is tangent to the outside rim surface, as
shown in Figs. 4 and 5, but it may also lay at an angle,
forming a conical surface, whithout changing the basic
characteristic of the curved labirinth configuration.
A preferred configuration of the container is shown in Fig. 5,
where the lower part of the can body 15, adjacent to the seam
area, is shaped into a conical surface (17) allowing this part
to fit into the double seamed top of another can, making it
"stackable", that is, making it easier to stack for display or
handling purposes.
Said conical surface must be such that distance d, measured '
from the beginning of the seam to the cylindrical surface, will
be at least equal to the thickness of the plate used for making
the can body plus thickness of the can top end.
