CAN MANUFACTURE USING AN ANNEALING STEP
A metal can body formed from a base stretching, drawing, and ironing process is formed of a material comprising aluminium. The process for forming the can includes a step of annealing the aluminium material.
This invention relates to containers, and more particularly to metal containers for food, beverages, aerosols, and the like formed from a metal sheet.
BACKGROUNDTwo-piece metal containers for food and beverages are often manufactured by drawing and wall ironing (DWI, also referred to as drawing and ironing (D&I)) or drawing and re-drawing (DRD) processes. The term “two-piece” refers to i) a cup-like can body and ii) a closure that would be subsequently fastened to the open end of the can body to form the container.
In a conventional DWI (D&I) process (such as illustrated in
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- 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.
- 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.
- 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.
In a DRD process (such as illustrated in
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.
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 an intermediate, 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.
However, DWI (D&I) and DRD processes employed on a large commercial scale do not act to reduce the thickness (and therefore weight) of material in the base of the cup. In particular, drawing typically does not result in significant 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 relatively unchanged from that of the ingoing gauge of the blank. This can result in the base being far thicker than required for performance purposes.
Food, beverages, and other products are often packaged in two piece cans formed from aluminum. Two piece cans include a can body having an integral base and sidewall and a lid that is seamed to the top of the sidewall of the can body.
Aluminum for canmaking often begins as a sheet of 3104-H19 or 3004-H19 aluminum alloy, which is aluminum with approximately 1% manganese and 1% magnesium for strength and formability. The cold rolling process used to produce commercial grade aluminum for canmaking yields a metal sheet having non-equiaxed grain structures. In this regard, aluminum sheet grains define a longitudinal direction and a transverse direction. Because of the amount of cold rolling, grains in commercial aluminum sheet for can making are elongated compared to grains in commercial tinplate for canmaking.
Aluminum used for food or beverage cans has limited ductility even though commercial drawing and ironing process, and the process of forming the dome on the bottom of a beverage can at the end of the wall ironing stages, have been successfully developed.
There is a need for improved can technology and improved cans that make efficient and effective use of aluminum sheet material that takes advantage of economics of metal supply.
SUMMARYA can body is formed from a process that includes a stretching operation on aluminum that becomes at least a portion of the base, and then drawing the stretched material radially outward, preferably into the sidewall. Subsequent ironing of the sidewall produces cans having desired base and wall thicknesses from thinner, less expensive sheet metal. The inventors have found that the process described herein can be improved and extended when the aluminum undergoes an annealing step. The inventors surmise that the annealing step benefits the process disclosed herein when performed on either the undeformed sheet or the drawn cup.
Accordingly, additional rolling steps need not be performed on the sheet metal at the mill, but the metal can be thinned during the can making process to achieve the desired attributes. Can bodies formed of this method may have attributes that are unlike cans made from less economical, thinner plate. For example, thickness reduction and distribution from raw sheet, hardness increase because of the stretching operation, and micrograin structure change due to stretching may be unique in the base of the can body formed from the disclosed methods.
One of the methods for manufacture of an aluminium cup includes a step of annealing and aluminium material or obtaining annealed or partially annealed aluminium. The method also includes a step of performing a stretching operation on a cup that is formed of the aluminium material and that has a sidewall and an integral base. The stretching operation includes clamping an annular region on either or both the sidewall and the base to define an enclosed portion of the base, and deforming and stretching at least a portion of the enclosed portion of the base, thereby increasing the surface area and reducing the thickness of the enclosed portion, wherein the annular clamping is adapted to restrict or prevent metal flow from the clamped region into the enclosed portion during the stretching operation.
Alternatively, one of the methods for manufacture of an aluminium cup may further include performing a drawing operation after a stretching operation, the drawing operation including drawing the aluminium sheet into a cup having a sidewall and an integral base.
One of the methods may also include deforming and stretching the enclosed portion at an elongation rate of greater than 5 percent.
A cup formed by one of these methods may be made of an aluminium material and having a sidewall and integral base, wherein the base is a stretched base such that the thickness of the base is less than the ingoing gauge of the metal sheet used to form the cup. Additionally, the stretched base of the cup may be thinned by at least 8 percent.
Illustrations of aspects of invention are illustrated in the following drawings, with reference to the accompanying description:
The following describes two example methods of forming an aluminum cup from which a can body may be formed, as well as the cup and can body. In the first method, a stretching operation is performed on a drawn cup, followed by redrawing operation. In the second method, a stretching operation is performed on a flat blank, followed by drawing operation. Each of the above includes a step of annealing the aluminum material. Preferably, a cup formed by either method is wall ironed into a finished can body.
The present can body or finished can is not limited to the particular steps described below. Rather, the steps of producing the can structure are described to illustrate possible ways to achieve the attributes of the cup or can body. According to a first method of forming an intermediate cup, a cupping press 10 has a draw pad 11 and a draw die 12 (see
In use, a flat section of metal sheet 20 is held in position between opposing surfaces of the draw pad 11 and the draw die 12. Aluminum sheet material, such as 3104-H19 or 3004-H19 aluminum alloy, having an ingoing gauge thickness (tin-going) of 0.0118 inches has been used for the metal sheet 20. However, the invention is not limited to particular gauges or metals unless specifically specified in the claims. The term “aluminum material” is not limited to any particular grade of aluminum and encompasses sheets of aluminum having a coating. The section of metal sheet 20 is typically cut from a roll of metal sheet (not shown). After the section of metal sheet 20 has been positioned, the circumferential cutting element 15 is moved downwards to cut a circular planar blank 21 out from the metal sheet (see
After the blank 21 has been cut from the sheet 20, the draw punch 13 is moved axially downwards through the draw die 12 to progressively draw the planar blank against the forming surface 16 of the draw die into the profile of a cup 23 having a sidewall 24 and integral base 25. This drawing operation is shown in
The step of annealing the material may be performed on sheet 20 before the blanks 21 are cut, on blanks 21, and/or on cups 23 after the drawing process. The inventors have demonstrated that annealing an aluminum sheet enabled greater stretching of the material. The aluminum sheet may be a 3004 or 3104 alloy with a thickness of 0.0118 inches.
If the annealing step is to be performed on sheet 20 prior to cutting blanks, fully annealed coil specified as 3104-0 may be obtained from a mill or other supplier of aluminum. Alternatively, partially annealed coil specified as 3104-H14 of unannealed coil specified as 3104-H19 may also be obtained from a mill or other supplier of aluminum. Specifications for annealed and partially annealed aluminum are provided by The Aluminum Association, Inc. 1525 Wilson Boulevard, Suite 600, Arlington, Va. 22209. This information may be found at www.aluminum.org, which is hereby incorporated by reference.
By way of example, aluminum may be annealed at 400 degrees Farenheit for up approximately 12 minutes. Aluminum may be annealed for shorter amounts of time, for example, 30 seconds. Stretching Operation, First Illustrative Method
Following the initial drawing operation shown in
On platen 31 is mounted a stretch punch 35 and a clamping element in the form of an annular clamp ring 36. The annular clamp ring 36 is located radially outward of the stretch punch 35. The stretch punch 35 is provided with a domed end face (see
On platen 32 is mounted a cup holder 37. The cup holder 37 is a tubular insert having an annular end face 38 and an outer diameter corresponding to the internal diameter of the drawn cup 23 (see
The stretch punch 35 is then moved axially through the clamp ring 36 to progressively deform and stretch (thin) the enclosed portion 27 into a domed profile 28.
In the embodiment shown in the drawings, the enclosed portion 27 is domed inwardly 28 into the cup (see
Ideally, the clamping loads applied during this stretching operation are sufficient to ensure that little or no material from the clamped annular region 26 (or the sidewall 24) flows into the enclosed portion 27 during stretching. This helps to maximize the amount of stretching and thinning that occurs in the domed region 28. However, as indicated above in the general description of the invention, it has been found that stretching and thinning of the enclosed portion 27 can still occur when permitting a limited amount of flow of material from the clamped annular region 26 (or from outside of the clamped region) into the enclosed portion.
In summary, this stretching operation and the resulting thinning of the base 25 is critical to achieving the object of the invention, namely to make a cup or container body having a base thickness which is less than that of the ingoing gauge of the metal sheet. The annealing process increases the potential thinning of the aluminum. While unannealed aluminum may be thinned up to approximately 8 percent, annealed aluminum can stretch further, achieving a thinning of greater than approximately 8 percent. For example, after annealing, thinning of approximately 15 percent may be achieved
In an alternative embodiment shown in
In a further alternative embodiment, the single stretch punch 35 is replaced by a punch assembly 350 (as shown in
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- i) a first group 351 of two annular punch elements 351a,b surrounding a central core punch element 351c; and
- ii) a second group 352 of two annular punch elements 352a,b.
For ease of understanding,
In use, the first and second groups of punch elements 352, 353 face opposing surfaces of the enclosed portion 27. The stretching operation is performed by moving both first and second groups of punch elements 351, 352 towards each other to deform and stretch (thin) the enclosed portion 27. The enclosed portion 27 is deformed into an undulating profile 29 (see
In a further embodiment, a single stretch punch 35 has a number of relief features in the form of recesses/cut-outs 353 provided in its end face (see
For the embodiment of the invention shown in
The first half 41 of the bodymaker assembly 40 has a tubular re-draw punch 43 mounted on the same axis as circumferential clamp ring 44. As can be seen from
The second half 42 of the bodymaker assembly 40 has a re-draw die 45. The re-draw die 45 has a tubular portion having an outer diameter corresponding to the internal diameter of the stretched cup 23 (see
In use, the stretched cup 23 is first mounted on the re-draw die 45 (as shown on
Once clamped, the re-draw punch 43 is then forced axially through the clamp ring 44 and the re-draw die 45 (see arrow A on
i) to cause material from the sidewall 24 to be drawn radially inwards and then axially along the forming surface 46 of the re-draw die 45 (as indicated by arrows B on
ii) to cause the stretched and thinned material in the domed region 28 of the base to be progressively pulled out and transferred from the base into the reduced diameter sidewall (as indicated by arrows C on
As shown in the detail view of the re-draw die 45 in
Note that although
The drawing operation described above and illustrated in
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- i) preventing uncontrolled buckling of the domed region 28 of the base of the stretched cup (especially when using a re-draw punch having a closed end face); and
- ii) maximizing transfer of material from the domed region 28 to the sidewalls 24.
Note that although the embodiment shown in
To maximize the height of the sidewall 24 of the cup with its thinned base, the re-drawn cup may also undergo ironing of the sidewalls by being drawn through a succession of ironing dies (not shown). This ironing operation has the effect of increasing the height and decreasing the thickness of the sidewall, and thereby maximizing the enclosed volume of the cup.
Stretching Operation, Second Illustrative MethodAccording to a second method of forming the intermediate cup that is shown in
On platen 21′ is mounted a stretch punch 25′ and a clamping element in the form of a first clamp ring 26′. The first clamp ring 26′ is located radially outward of the stretch punch 25′. The stretch punch 25′ is provided with a domed end face (see
On platen 22′ is mounted a second clamp ring 27′. The second clamp ring 27′ is a tubular insert having an annular end face 28′ (see
The stretch punch 25′ is then moved axially through the first clamp ring 26′ to progressively deform and stretch (thin) the metal of the enclosed portion 16′ into a domed profile 17′ (see
Ideally, the clamping loads applied during this stretching operation are sufficient to ensure that little or no material from the clamped annular region 15′ flows into the enclosed portion 16′ during stretching. This helps to maximize the amount of stretching and thinning that occurs in the enclosed portion 16′. However, as indicated above in the general description of the invention, it has been found that stretching and thinning of the metal of the enclosed portion 16′ can still occur when permitting a limited amount of flow of metal from the clamped annular region 15′ (or from outside of the clamped region) into the enclosed portion.
In an alternative embodiment, the single stretch punch 25′ is replaced by a punch assembly 250′ (as shown in
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- i) a first group 251′ of two annular punch elements 251a′,b′ surrounding a central core punch element 251c; and
- ii) a second group 252′ of two annular punch elements 252a′,b′.
For ease of understanding,
In use, the first and second groups of punch elements 251′, 252′ face opposing surfaces of the enclosed portion 16′ of the metal sheet 10′. The stretching operation is performed by moving both first and second groups of punch elements 251′, 252′ towards each other to deform and stretch (thin) the metal of the enclosed portion 16′. The enclosed portion 16′ is deformed into an undulating profile 170′ (see
In a further embodiment, a single stretch punch 25′ has a number of relief features in the form of recesses/cut-outs 253′ provided in its end face (see
The embodiment in
Note that
On completion of the stretching operation, the metal sheet 10′ with its stretched and thinned domed enclosed portion 16′, 17′ is moved to a cupping press 30′. The cupping press 30′ has a draw pad 31′ and a draw die 32′ (see
In use, the section of metal sheet 10′ is held in position between opposing surfaces of the draw pad 31′ and the draw die 32′. The sheet 10′ is located so that the domed enclosed portion 16′, 17′ is centrally located above the bore of the draw die 32′. After the metal sheet 10′ has been positioned, the circumferential cutting element 36′ is moved downwards to cut a blank 11′ out from the metal sheet 10′ (see
After the blank 11′ has been cut from the sheet 10′, the draw punch 33′ is moved axially downwards into contact with the blank 11′ (see
In an alternative embodiment of the invention not shown in
The first stage cup 19′ resulting from the cupping process shown in
To maximize the height of the sidewall 19′sw of the cup with its thinned base, the cup may also undergo ironing of the sidewalls by being drawn through a succession of ironing dies (not shown) in an ironing operation. This ironing operation has the effect of increasing the height and decreasing the thickness of the sidewall.
Claims
1. A method for manufacture of an aluminum cup, comprising the steps of:
- i. annealing an aluminum material;
- ii. performing a stretching operation (30) on a cup (23) that is formed of the aluminum material and that has a sidewall (24) and an integral base (25), the stretching operation including: clamping (36, 37) an annular region (26) on either or both the sidewall and the base to define an enclosed portion (27) of the base, and deforming and stretching (35) at least a portion of the enclosed portion of the base, thereby increasing the surface area and reducing the thickness of the enclosed portion, wherein the annular clamping is adapted to restrict or prevent metal flow from the clamped region into the enclosed portion during the stretching operation.
2. The method of claim 1 wherein the annealing step is performed before the stretching operation, and the aluminum material on which the annealing step is performed is in the form of a pre-formed sheet.
3. The method of claim 1 wherein the annealing step is performed before the stretching operation, and the aluminum material on which the annealing step is performed is in a cup form.
4. The method of claim 1, 2, or 3 further comprising performing a drawing operation (40) after the stretching operation; the drawings operation including drawing (43, 44, 45) the cup to pull and transfer material (B, C) outwardly from the stretched and thinned base.
5. A method of claim 4 wherein the clamping (36, 37) step of the stretching operation (30) comprises clamping the annular region (26) on the base (25), the enclosed portion (27) being that part of the base located radially inward of the clamped region.
6. The method of claim 1, 2, or 3 wherein the clamping (36, 37) step of the stretching operation (30) comprises using one or more clamping elements having a clamping face with a textured surface.
7. The method of claim 1, 2, or 3 wherein the stretching operation (30) comprises moving a stretch punch (35) relatively toward the cup (23) such that the stretch punch deforms and stretches at least a portion of the enclosed portion (27) of the base.
8. A method of claim 1, 2, or 3 further comprising an initial drawing operation (10) performed before the stretching operation on the aluminum material, the initial drawing operation comprising drawing (11, 12, 13) the aluminum sheet to form the cup (23).
9. The method of claim 4 wherein the drawing operation further comprises or is followed by a step of ironing the sidewall.
10. A method for manufacture of an aluminum cup, the method comprising the following operations:
- i. annealing an aluminum material;
- ii. performing a stretching operation on the aluminum material that has the form of an aluminum sheet, the operation including: clamping an annular region on the sheet to define an enclosed portion, and deforming and stretching at least a portion of the enclosed portion of the base, thereby increasing the surface area and reducing the thickness of the enclosed portion, wherein the annular clamping is adapted to restrict or prevent metal flow from the clamped region into the enclosed portion during the stretching operation.
- iii. performing a drawing operation after the stretching operation, the drawing operation including drawing the aluminum sheet into a cup having a sidewall and an integral base.
11. The method of claim 10 wherein the annealing step is performed before the stretching operation, and the aluminum material on which the annealing step is performed is in the form of a pre-formed sheet.
12. The method of claim 10, wherein the drawing operation is adapted such that material of the stretched and thinned enclosed portion is pulled and transferred into the sidewall.
13. The method of claim 10 wherein the stretching operation is performed on a plurality of enclosed portions separated from each other and disposed across the area of the metal sheet.
14. The method of claim 10 wherein the drawing operation comprises or is followed by the step of ironing the sidewall.
15. The method of claim 10 wherein the annular region has a round shape.
16. The method of claim 10 wherein the annular region has an angular shape.
17. The method of claim 10 wherein the base comprises material from the stretched and thinned enclosed portion and the drawing operation is adapted to pull and transfer outwardly material of the stretched and thinned enclosed portion.
18. A method for manufacture of an aluminum cup, comprising the steps of:
- i. obtaining annealed or partially annealed aluminum;
- ii. performing a stretching operation (30) on a cup (23) that is formed of the aluminum material and that has a sidewall (24) and an integral base (25), the stretching operation including: clamping (36, 37) an annular region (26) on either or both the sidewall and the base to define an enclosed portion (27) of the base, and deforming and stretching (35) at least a portion of the enclosed portion of the base, thereby increasing the surface area and reducing the thickness of the enclosed portion, wherein the annular clamping is adapted to restrict or prevent metal flow from the clamped region into the enclosed portion during the stretching operation.
19. The method of claim 18 wherein the enclosed portion of the base is deformed and stretched at an elongation rate of greater than 5 percent.
20. A cup formed of an aluminum material and having a sidewall and integral base, wherein the base is a stretched base such that the thickness of the base is less than the ingoing gauge of the metal sheet used to form the cup.
21. The cup of claim 20 wherein the stretched base achieves a thinning of greater than 8 percent.
Type: Application
Filed: Aug 3, 2011
Publication Date: Feb 7, 2013
Inventor: Richard Mark Orlando Golding (Mount Prospect, IL)
Application Number: 13/197,690
International Classification: B65D 1/16 (20060101); B21D 51/26 (20060101);