U.S. patent application number 13/651833 was filed with the patent office on 2013-02-14 for can manufacture.
The applicant listed for this patent is Stuart Monro. Invention is credited to Stuart Monro.
Application Number | 20130037555 13/651833 |
Document ID | / |
Family ID | 42752975 |
Filed Date | 2013-02-14 |
United States Patent
Application |
20130037555 |
Kind Code |
A1 |
Monro; Stuart |
February 14, 2013 |
CAN MANUFACTURE
Abstract
A method and apparatus are disclosed which are suitable for use
in the manufacture of two-piece metal containers. In particular, a
press is disclosed which makes cup sections from metal sheet using
a combination of drawing and stretching operations. The cups
resulting from the press have the advantage of having a base
thickness that is thinner relative to the ingoing gauge of the
metal sheet.
Inventors: |
Monro; Stuart;
(Brighthampton, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Monro; Stuart |
Brighthampton |
|
GB |
|
|
Family ID: |
42752975 |
Appl. No.: |
13/651833 |
Filed: |
October 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13452464 |
Apr 20, 2012 |
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13651833 |
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PCT/EP2011/055847 |
Apr 13, 2011 |
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13452464 |
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Current U.S.
Class: |
220/608 ;
220/600; 72/348 |
Current CPC
Class: |
B65D 1/16 20130101; B21D
22/30 20130101; B21D 25/04 20130101; B21D 22/24 20130101; B21D
25/00 20130101; B21D 51/26 20130101; B65D 1/165 20130101; B21D
22/20 20130101 |
Class at
Publication: |
220/608 ; 72/348;
220/600 |
International
Class: |
B21D 51/26 20060101
B21D051/26; B65D 1/16 20060101 B65D001/16 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 13, 2010 |
EP |
10159826.6 |
Claims
1. A method for manufacture of a metal cup from a metal sheet, the
method comprising the following operations: i. a drawing operation
comprising drawing the metal sheet into a cup having a sidewall and
an integral base; ii. a stretching operation performed on the cup,
the operation comprising clamping an annular region on the base of
the cup to define an enclosed portion, and deforming and stretching
at least part of the base that lies within the enclosed portion to
thereby increase the surface area and reduce the thickness of the
base, the annular clamping adapted to restrict or prevent metal
flow from the clamped region into the enclosed portion during this
stretching operation; the drawing and stretching operations
performed in a common press.
2. The method as claimed in claim 1, wherein the drawing operation
comprises locating the metal sheet between a draw punch and a draw
die, and moving either or both of the draw punch and draw die
towards each other such that the draw punch extends through the
draw die to thereby draw the metal sheet into the cup, the annular
clamping during the stretching operation comprising clamping the
annular region on the base of the cup between the draw punch and a
clamping element disposed on the opposite side of the cup to the
draw punch.
3. The method as claimed in claim 2, wherein the stretching
operation comprises using a stretch punch disposed on the opposite
side of the cup to the draw punch and moving either or both of the
stretch punch and clamped cup towards each other to deform and
stretch at least part of the base that lies within the enclosed
portion.
4. The method as claimed in claim 1, wherein the stretching
operation comprises deforming and stretching at least part of the
base that lies within the enclosed portion into a domed
profile.
5. A press for manufacture of a metal cup from a metal sheet, the
press comprising: i. means for drawing the metal sheet into a cup
having a sidewall and an integral base; ii. a clamping element for
clamping the drawn cup during a stretching operation, the clamping
element adapted to clamp an annular region on the base of the drawn
cup to define an enclosed portion; iii. a stretch tool adapted to
deform and stretch at least part of the base that lies within the
enclosed portion in the stretching operation to thereby increase
the surface area and reduce the thickness of the base, the clamping
element further adapted to restrict or prevent metal flow from the
clamped region into the enclosed portion during the stretching
operation.
6. The press as claimed in claim 5, wherein the means for drawing
the metal sheet comprises a draw punch and a draw die, either or
both of the draw punch and draw die being moveable towards each
other such that the draw punch may extend through the draw die to
draw the metal sheet into the cup, the clamping element disposed on
the opposite side of the cup to the draw punch such that in use
during the stretching operation the clamping element clamps the
annular region of the base between the clamping element and the
draw punch.
7. The press as claimed in claim 6, wherein the stretch tool
comprises a stretch punch disposed on the opposite side of the cup
to the draw punch, either or both the stretch punch and combination
of draw punch and clamping element being moveable towards each
other such that in use the stretch punch deforms and stretches at
least part of the base that lies within the enclosed portion.
8. The press as claimed in either of claim 6, wherein the draw
punch is provided with a recess or bore to enable the stretch tool
to extend all or partly within the recess or bore during the
stretching operation.
9. A container comprising: a circumferential sidewall defining an
end; and a bottom portion enclosing the end of the circumferential
sidewall, wherein a material of the bottom portion is stretched
relative to the circumferential sidewall to form a thinner
preselected profile.
10. The container of claim 9, wherein the thinned preselected
profile is a dome.
11. The container of claim 10, wherein the material of the
container at or about the dome has a substantially uniform
thickness.
12. The container of claim 10, wherein the container is formed from
a blank of material; wherein the blank of material has a base gauge
prior to being formed; wherein, after being formed, the material of
the container at or about the dome has a thickness; and wherein the
thickness of the material at or about the dome is less than the
base gauge.
13. The container of claim 12, wherein the thickness of the
material at or about the dome is about 0.0003 inch to about 0.003
inch thinner than the base gauge.
14. The container of claim 9, wherein the container is formed from
a blank of material; and wherein the blank of material has a
preformed dome portion.
15. The container of claim 9, wherein the container is a can
body.
16. The container of claim 9, wherein the container is a cup.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of United States Patent Application
Ser. No. 13/452,464, filed Apr. 20, 2012, which is a continuation
of International Application No. PCT/EP2011/055847, filed Apr. 13,
2011, which claims priority to European Application No. 10159826.6,
filed Apr. 13, 2010, the contents of each of which are incorporated
by reference in their entireties.
TECHNICAL FIELD
[0002] This invention relates to the production of metal cups and
in particular (but without limitation) to metal cups suitable for
the production of "two-piece" metal containers.
BACKGROUND
[0003] U.S. Pat. No. 4,095,544 (NATIONAL STEEL CORPORATION) Jun.
20, 1978 details conventional Draw & Wall Ironing (DWI) and
Draw & Re-Draw (DRD) processes for manufacturing cup-sections
for use in making two-piece metal containers. [Note that in the
United States of America, DWI is instead commonly referred to as
D&I.] The term "two-piece" refers to i) the cup-section and ii)
the closure that would be subsequently fastened to the open end of
the cup-section to form the container.
[0004] In a DWI (D&I) process (as illustrated in FIGS. 6 to 10
of U.S. Pat. No. 4,095,544), a flat (typically) circular blank
stamped out from a roll of metal sheet is drawn though a drawing
die, under the action of a punch, to form a shallow first stage
cup. This initial drawing stage does not result in any intentional
thinning of the blank. Thereafter, the cup, which is typically
mounted on the end face of a close fitting punch or ram, is pushed
through one or more annular wall-ironing dies for the purpose of
effecting a reduction in thickness of the sidewall of the cup,
thereby resulting in an elongation in the sidewall of the cup. By
itself, the ironing process will not result in any change in the
nominal diameter of the first stage cup.
[0005] FIG. 1 shows the distribution of metal in a container body
resulting from a conventional DWI (D&I) process. FIG. 1 is
illustrative only, and is not intended to be precisely to scale.
Three regions are indicated in FIG. 1:
[0006] Region 1 represents the un-ironed material of the base. This
remains approximately the same thickness as the ingoing gauge of
the blank, i.e. it is not affected by the separate manufacturing
operations of a conventional DWI process.
[0007] Region 2 represents the ironed mid-section of the sidewall.
Its thickness (and thereby the amount of ironing required) is
determined by the performance required for the container body.
[0008] Region 3 represents the ironed top-section of the sidewall.
Typically in can making, this ironed top-section is around 50-75%
of the thickness of the ingoing gauge.
[0009] In a DRD process (as illustrated in FIGS. 1 to 5 of U.S.
Pat. No. 4,095,544), the same drawing technique is used to form the
first stage cup. However, rather than employing an ironing process,
the first stage cup is then subjected to one or more re-drawing
operations which act to progressively reduce the diameter of the
cup and thereby elongate the sidewall of the cup. By themselves,
most conventional re-drawing operations are not intended to result
in any change in thickness of the cup material. However, taking the
example of container bodies manufactured from a typical DRD
process, in practice there is typically some thickening at the top
of the finished container body (of the order of 10% or more). This
thickening is a natural effect of the re-drawing process and is
explained by the compressive effect on the material when re-drawing
from a cup of large diameter to one of smaller diameter.
[0010] Note that there are alternative known DRD processes which
achieve a thickness reduction in the sidewall of the cup through
use of small or compound radii draw dies to thin the sidewall by
stretching in the draw and re-draw stages.
[0011] Alternatively, a combination of ironing and re-drawing may
be used on the first stage cup, which thereby reduces both the
cup's diameter and sidewall thickness. For example, in the field of
the manufacture of two-piece metal containers (cans), the container
body is typically made by drawing a blank into a first stage cup
and subjecting the cup to a number of re-drawing operations until
arriving at a container body of the desired nominal diameter, then
followed by ironing the sidewall to provide the desired sidewall
thickness and height.
[0012] However, DWI (D&I) and DRD processes employed on a large
commercial scale have a serious limitation in that they do not act
to reduce the thickness (and therefore weight) of material in the
base of the cup. In particular, drawing does not result in
reduction in thickness of the object being drawn, and ironing only
acts on the sidewalls of the cup. Essentially, for known DWI
(D&I) and DRD processes for the manufacture of cups for
two-piece containers, the thickness of the base remains broadly
unchanged from that of the ingoing gauge of the blank. This can
result in the base being far thicker than required for performance
purposes.
[0013] The metal packaging industry is fiercely competitive, with
weight reduction being a primary objective because it reduces
transportation and raw material costs. By way of example, around
65% of the costs of manufacturing a typical two-piece metal food
container derive from raw material costs.
[0014] There is therefore a need for improved light-weighting of
metal cup-sections in a cost-effective manner. Note that in this
document, the terms "cup-section" and "cup" are used
interchangeably.
SUMMARY
[0015] Accordingly, in a first aspect of the invention (defined in
claim 1) there is provided a method for manufacture of a metal cup
from a metal sheet, the method comprising the following
operations:
[0016] i. a drawing operation comprising drawing the metal sheet
into a cup having a sidewall and an integral base;
[0017] ii. a stretching operation performed on the cup, the
operation comprising clamping an annular region on the base of the
cup to define an enclosed portion, and deforming and stretching at
least part of the base that lies within the enclosed portion to
thereby increase the surface area and reduce the thickness of the
base, the annular clamping adapted to restrict or prevent metal
flow from the clamped region into the enclosed portion during this
stretching operation;
[0018] the drawing and stretching operations performed in a common
press.
[0019] In a second aspect of the invention (defined in claim 5)
there is provided a press for manufacture of a metal cup from a
metal sheet, the press comprising:
[0020] i. means for drawing the metal sheet into a cup having a
sidewall and an integral base;
[0021] ii. a clamping element for clamping the drawn cup during a
stretching operation, the clamping element adapted to clamp an
annular region on the base of the drawn cup to define an enclosed
portion;
[0022] iii. a stretch tool adapted to deform and stretch at least
part of the base that lies within the enclosed portion in the
stretching operation to thereby increase the surface area and
reduce the thickness of the base, the clamping element further
adapted to restrict or prevent metal flow from the clamped region
into the enclosed portion during the stretching operation.
[0023] The method and apparatus of the different aspects of the
invention have the advantage (over known processes/apparatus) of
achieving manufacture of a cup having a base which is thinner than
the ingoing gauge of the metal sheet, without requiring loss or
waste of metal. This is achieved by use of a single press, thereby
simplifying the manufacturing process. When applied to the
manufacture of two-piece containers, the invention enables cost
savings to be made of the order of several dollars per 1,000
containers relative to existing manufacturing techniques.
[0024] To ensure that the enclosed portion (and therefore the cup's
base) is stretched and thinned during the stretching operation, the
base of the drawn cup is clamped sufficiently to restrict or
prevent metal flow from the clamped region into the enclosed
portion during the stretching operation. If the clamping loads are
insufficient, material from the clamped region (or from outside of
the clamped region) would merely be drawn into the enclosed
portion, rather than the enclosed portion (and the cup's base)
undergoing any thinning It has been found that stretching and
thinning can still occur when permitting a limited amount of flow
of material from the clamped region (or from outside of the clamped
region) into the enclosed portion, i.e. when metal flow is
restricted rather than completely prevented.
[0025] The method and apparatus of the invention is particularly
suitable for use in the manufacture of metal containers, with the
final resulting cup being used for the container body. The final
resulting cup may be formed into a closed container by the
fastening of a closure to the open end of the cup. For example, a
metal can end may be seamed to the open end of the final resulting
cup. However, typically the cup resulting from the method of the
invention would be subjected to either or a combination of a
re-drawing operation and an ironing operation. The re-drawing
operation may comprise one or more stages, each stage having the
effect of inducing a staged reduction in cup diameter. The ironing
operation would have the benefit of increasing the height of the
sidewall of the cup produced by the method and apparatus of the
invention. Preferably, the stretching operation comprises deforming
and stretching at least part of the base that lies within the
enclosed portion into a domed profile. In the field of metal
containers for carbonated beverages, it is common for the base of
the container body to be inwardly-domed to resist pressure
generated by the product. The "dome" provided by the method and
apparatus of the invention may serve as the inwardly-domed region
of a beverage container body. However, it is likely that the cup
would undergo a later reforming operation to provide the domed base
of the cup with a desired final profile necessary to resist in-can
pressure.
[0026] The method of the invention is suitable for use on cups that
are both round and non-round in plan. However, it works best on
round cups.
[0027] One other way of minimising the amount of material in the
base of cup-sections produced using conventional DWI and DRD
processes would be to use thinner gauge starting stock. However,
tinplate cost per tonne increases as the gauge decreases. This
increase is explained by additional costs of rolling, cleaning and
tinning the thinner steel. When also taking account of material
usage during manufacture of a two-piece container, the variation in
net overall cost to manufacture the container versus ingoing gauge
of material looks like the graph shown in FIG. 2. This graph
demonstrates that from a cost perspective, going for the thinnest
gauge material does not necessarily reduce costs. In essence, there
is a cheapest gauge of material for any container of a given
sidewall thickness. The graph also shows the effect of reducing the
thickness of the top and mid-wall sections of the container in
driving down the cost curve. FIG. 3 shows the same graph based upon
actual data for UK-supplied tinplate of the type commonly used in
can-making. For the material illustrated in FIG. 3, 0.285 mm
represents the optimum thickness on cost grounds, with the use of
thinner gauge material increasing net overall costs for can
production. The graph of FIG. 3 shows the percentage increase in
overall cost per 1,000 cans when deviating from the 0.285 mm
optimum ingoing gauge thickness.
[0028] The final resulting cup of the invention has the benefits of
a thinner (and therefore lighter) base.
[0029] The "metal sheet" can include a blank cut from a larger
expanse of metal sheet.
[0030] By "annular clamping" or clamping an "annular region" is
meant that the base of the drawn cup is clamped either continuously
or at spaced intervals in an annular manner.
[0031] The clamping element may be in the form of a continuous
annular sleeve; alternatively, it may be a collection of discrete
clamping elements distributed in an annular manner to act against
the metal sheet.
[0032] The method and apparatus of the invention are not limited to
a particular metal. They are particularly suitable for use with any
metals commonly used in DWI (D&I) and DRD processes. Also,
there is no limitation on the end use of the cup that results from
the method and apparatus of the invention. Without limitation, the
cups may be used in the manufacture of any type of container,
whether for food, beverage or anything else.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a side elevation view of a container body of the
background art resulting from a conventional DWI process. It shows
the distribution of material in the base and sidewall regions of
the container body.
[0034] FIG. 2 is a graph showing in general terms how the net
overall cost of manufacturing a typical two-piece metal container
varies with the ingoing gauge of the sheet metal. The graph shows
how reducing the thickness of the sidewall region (e.g. by ironing)
has the effect of driving down the net overall cost.
[0035] FIG. 3 is a graph corresponding to FIG. 2, but based on
actual price data for UK-supplied tinplate.
[0036] Embodiments of the invention are illustrated in the
following drawings, with reference to the accompanying
description:
[0037] FIG. 4 is a cross-section through a press of the invention
showing a blank of metal sheet prior to the drawing and stretching
operations.
[0038] FIG. 5 is a cross-section through the press of FIG. 4, but
after the drawing operation to draw the blank of metal sheet into a
cup having a sidewall and integral base.
[0039] FIG. 6 is a cross-section through the press of FIGS. 4 and
5, but after the stretching operation to deform and stretch the
base of the drawn cup.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Mode(s) for Carrying Out the Invention
[0040] Drawing Operation
[0041] FIG. 4 shows a combined drawing and stretching press 10. A
blank of metal sheet 5 is "slidably clamped" in position between
the opposing surfaces of a draw pad 11 and an end face of a draw
die 12. A draw punch 13 is located above the upper surface of the
blank of metal sheet 5 Within the bore defined by the draw die 12
is a stretch punch 14 which is radially-inwards of and surrounded
by annular clamping element 15.
[0042] Once the blank 5 is "slidably clamped" between the draw pad
11 and the draw die 12, the draw punch 13 is moved axially
downwards (along axis 16) until the peripheral annular region 17 of
the end face of the punch contacts a corresponding region on the
blank 5 (see FIG. 5). The draw punch 13 is urged downwards through
the bore of the draw die 12 to progressively draw the initially
planar blank 5 into a cup 30 having a sidewall 31 and integral base
32.
[0043] By "slidably clamping" is meant that the clamping load
during drawing is selected so as to permit the metal sheet 5 to
slide, relative to whatever clamping means is used (in this case a
"draw pad 11"), in response to the deforming action of the draw
punch 13/draw die 12 on the metal sheet. An intention of this
slidable clamping is to prevent or restrict wrinkling of the
material during drawing.
[0044] Stretching Operation
[0045] Once the draw punch 13 reaches the end of its stroke,
annular clamping element 15 is moved axially upwards until an
annular region 33 on the base 32 of the drawn cup is clamped
between the annular clamping element and the peripheral annular
region 17 of the end face of the draw punch 13 (see FIG. 5). The
material of the cup's base enclosed by this annular clamping is
referred to as the "enclosed portion" 34.
[0046] Stretch punch 14 is then moved axially upwards (along axis
16) to contact the enclosed portion 34 (see FIG. 6). The stretch
punch 14 is urged upwards into the recess 18 defined within the end
face of the draw punch 13 to progressively deform and stretch the
material of the enclosed portion 34 of the cup 30 into a domed
profile 35 (see FIG. 6). The clamping load applied between the
annular clamping element 15 and the peripheral annular region 17 of
the end face of the draw punch 13 is sufficient to restrict or
prevent metal flow from the clamped annular region 33 into the
enclosed portion 34 during this stretching operation. To enhance
the gripping effect, the end face of the annular clamping element
15 may be textured (not shown in the figures) to thereby allow use
of a reduced clamping load compared to use of an annular clamping
element having a smooth polished end face.
[0047] As shown in FIG. 6, the cup that results from the stretching
operation performed in press 10 has a reduced thickness in its base
relative to the ingoing gauge of the blank of metal sheet 5. As
indicated above in the general description of the invention, this
cup may be used as a container body, but would generally be
subjected to either or a combination of redrawing and ironing
operations to optimise the cup diameter and sidewall thickness. As
also indicated in the general description of the invention, the
domed region 35 may be particularly beneficial for containers
intended for pressurised products, such as carbonated
beverages.
* * * * *