SOLID METAL CANS AND ULTRA-LIGHTWEIGHT SOLID ALUMINUM CANS

Abstract

In a one-piece metal can 10, where the can base 5 is formed from the protrusion 7 extending upwards from the inside of the contact surface 3 and the domed bottom surface 9 is integral with the protrusion 7, the domed bottom surface 9 includes the central dome 9a and the ring-shaped part 9b formed so that it surrounds the central dome 9a, the ring-shaped part 9b is integral with the top of the protrusion 7 and has the following characteristics (i) or (ii), thereby creating a one-piece metal can with high pressure resistance and a domed bottom surface that effectively prevents buckling deformation, or creating a super-lightweight one-piece aluminum can in which the can body cracking during forming is effectively prevented and the can is significantly thinned. (i) The boundary X between the central dome 9a and the ring-shaped part 9b is formed as a very small curve with a radius of curvature less than 3.0 mm.(ii) The aluminum thickness (T0) at the center of the can bottom is 0.270 mm or less, the diameter D of the lower end of the can body 1a is 45 to 75 mm, the metal (aluminum) thickness at the thinnest part of the can body 1a is 0.080 to 0.105 mm, and the total aluminum mass is 14 g or less.

Description

Seamless metal can

[0001] The present invention relates to a seamless metal can having a domed bottom.

[0002] In general, seamless cans and the like obtained by metal forming processes (punching, drawing, and ironing) have a dome-shaped bottom surface formed by recessing the bottom into a dome shape to improve pressure resistance and stabilize installation. The forming method for forming such a dome-shaped bottom surface is called doming, and is performed by holding the bottom periphery of a cylindrical body with an annular mold called a hold ring, and pushing a doming die up through the annular mold to recess the bottom surface of the cylindrical body into a dome shape (Patent Document 1).

[0003] Recently, from the viewpoints of efficient use of metal materials and lightweightness, there has been a strong demand for lightweight seamless cans formed from thin metal sheets. Seamless cans formed from such thin metal sheets have a particular problem of bottom buckling, and conventionally known dome-shaped bottoms have had the problem of insufficient pressure resistance and prone to buckling. For example, Patent Documents 2 and 3 listed below disclose seamless metal cans having a certain dome-shaped bottom. However, thin-walled seamless metal cans formed from metal sheets (blank sheets) thinner than 0.270 mm, for example, have low pressure resistance and are prone to buckling. Therefore, further improvement in pressure resistance is currently required for thinner cans.

[0004] Furthermore, with thin-walled, lightweight seamless aluminum cans, the risk of shell breakage during molding is of course a problem, limiting the degree of thinning or weight reduction. For example, Patent Documents 4 to 6 listed below propose aluminum cans with dome-shaped bottoms, but because of the problem of shell breakage, the amount of thinning is significantly limited, and practically usable lightweight seamless aluminum cans have not yet been obtained. Furthermore, bottom buckling and other problems have become a problem, and it has been pointed out that with conventionally known dome-shaped bottoms, buckling is likely to occur when the thickness is reduced beyond a certain level.

[0005] Japanese Patent Application Laid-Open No. 2018-177289 Japanese Patent Application Laid-Open No. 2000-211624 Japanese Patent No. 6713741 Japanese Patent No. 6977302 Japanese Patent No. 5102042 Japanese Patent Application Laid-Open No. 2023-85679

[0006] Therefore, an object of the present invention is to provide a seamless metal can having a domed bottom that is highly pressure-resistant and effectively prevents buckling. Another object of the present invention is to provide an ultra-lightweight seamless aluminum can that is effectively prevented from breaking during forming and has a significantly thinner wall. A still further object of the present invention is to provide a seamless metal can that is formed using a metal sheet having a metal thickness of 0.270 mm or less, particularly 0.26 mm or less.

[0007] According to the present invention, there is provided a seamless metal can having a cylindrical side wall, a grounding portion continuous with the cylindrical side wall, and a bottom portion formed to close the inside of the grounding portion, the bottom portion being formed of a raised portion extending upward from the inside of the grounding portion and a dome-shaped bottom surface continuous with the raised portion, wherein the dome-shaped bottom surface has a central dome portion and a ring-shaped portion formed to surround the central dome portion, the ring-shaped portion being continuous with the upper end of the raised portion, and in a side cross-sectional view of the metal can, the boundary between the central dome portion and the ring-shaped portion is an extremely curved portion with a curvature radius of less than 3.0 mm.

[0008] In the seamless metal can of the present invention, it is preferable that: (1) in a side cross-sectional view of the metal can, the rising portion rises outward and upward from the ground contact portion; (2) in a side cross-sectional view of the metal can, the rising portion rises from the ground contact portion at an angle θ of 95 to 125 degrees with respect to the ground contact portion, and the joint between the rising portion and the ring-shaped portion is an extremely curved portion with a curvature radius of 1.2 mm or less; (3) the metal thickness at the center of the dome-shaped bottom surface is 0.270 mm or less; and (4) the metal is aluminum.

[0009] The present invention also provides an ultra-lightweight seamless aluminum can having a cylindrical side wall and a bottom surrounded by a ground contact portion at the lower end of the cylindrical side wall, wherein the cylindrical side wall comprises a body portion, a chime portion that slopes inward from the lower end of the body portion and is connected to the ground contact portion, and a post-processing thick-wall portion that is located above the body portion and has a thickness greater than that of the body portion, and the bottom portion has a dome-shaped bottom surface that curves upward and a riser portion that extends upward and outward from the ground contact portion and is connected to the dome-shaped bottom surface, the aluminum thickness (T0) at the center of the bottom is 0.270 mm or less, the diameter D of the lower end of the body portion is 45 to 75 mm, the aluminum thickness (T1) at the thinnest part of the body is 0.080 to 0.105 mm, and the total aluminum weight is 14 g or less.

[0010] In the ultra-lightweight seamless aluminum can of the present invention, (1) the aluminum thickness (T1) at the thinnest part of the body is less than 0.087 mm, (2) the ratio H / D of the height H of the cylindrical side wall to the diameter D of the lower end of the body is in the range of 1.6 to 2.7, (3) the aluminum thickness (T2) at the chime part is 95% or less of the aluminum thickness (T0) at the center of the bottom, and (4) the thick-walled part for post-processing is formed from a tapered part whose thickness gradually increases upward from the upper end of the body, and a high-strength part located above the tapered part and having an aluminum thickness (T3) in the range of 50% or more of the aluminum thickness (T0) at the center of the bottom. (5) The axial length L1 of the body portion is in the range of 60 to 95% of the height H of the cylindrical side wall, and the axial length L2 of the high-strength portion is in the range of 5 to 40% of the height H of the cylindrical side wall; (6) A ring-shaped inflection portion having a minimum radius of curvature (R1) is formed on the dome-shaped bottom surface of the bottom portion at a position away from the upper end of the rising portion; (7) The radius of curvature (R1) is preferably in the range of less than 3.0 mm.

[0011] The seamless metal can of the present invention has a dome-shaped bottom surface that is recessed into a dome shape at the bottom, which is formed to close the inside of the ground contact portion. A significant feature of the can is that a ring-shaped portion is formed to surround the central dome portion of the dome-shaped bottom surface, and the joint between the ring-shaped portion and the central dome portion is an extremely curved portion with a radius of curvature of less than 3.0 mm. That is, the dome-shaped bottom surface has a large radius of curvature at the center, forming a gently curved surface, with the maximum radius of curvature at the center. When internal pressure is applied in the axial direction of the seamless metal can, the internal pressure concentrates in the central portion of this nearly flat shape. Therefore, the thinner the thickness of the metal blank used for forming (corresponding to the metal thickness at the center of the dome-shaped bottom surface), the more likely buckling (reversal of the concave and convex portions) becomes. However, in the present invention, a ring-shaped portion with a small radius of curvature is formed to surround the central dome portion with a large radius of curvature, and the joint (i.e., the boundary) between the ring-shaped portion and the central dome has an extremely small radius of curvature of less than 3.0 mm. That is, one end of the ring-shaped portion (the end of the central dome) is an inflection point, resulting in a greatly curved shape. Moreover, the other side of the ring-shaped portion is connected to the upper end of the rising portion that is connected to the ground portion, and this other end of the ring-shaped portion is also greatly curved. As can be seen from this configuration, in the present invention, the ring-shaped portion, whose both ends are greatly curved, is connected to the central dome portion, which is nearly a smooth plane. Therefore, this ring-shaped portion absorbs and alleviates the axial load of the seamless metal can, and buckling is more effectively suppressed. Therefore, in the present invention, a metal blank having an extremely thin thickness (e.g., 0.270 mm or less) can be used to form a seamless metal can, which is a major advantage of the present invention.

[0012] The ultralight seamless aluminum can of the present invention has a basic configuration in which the diameter D of the lower end of the body (corresponding to the diameter of the upper end of the chime section) is 45 to 75 mm, and the aluminum thickness (T0) at the center of the bottom is 0.270 mm or less. In this basic configuration, the aluminum thickness (T0) at the center of the bottom corresponds to the aluminum base plate (also called a blank) used in forming. This is because, when seamless cans are formed by thinning the wall through ironing, the bottom is a portion that is not thinned by ironing. That is, the seamless aluminum can of the present invention is formed using an extremely thin blank metal plate of 0.270 mm or less. In addition, the aluminum thickness (T1) at the thinnest wall portion of the body is in the range of 0.080 to 0.105 mm, thereby maximizing thinning. The seamless aluminum can of the present invention has an ultra-thin wall while maintaining a diameter D of 45 to 75 mm at the bottom end of the body, thereby achieving an ultra-lightweight total aluminum weight of 14 g or less. For example, even if the can has a capacity of 500 mL, the total aluminum weight is 14 g or less, and this ultra-lightweight can has never been achieved before by the present invention.

[0013] 1 is a schematic cross-sectional side view showing the entire seamless metal can of the present invention; 2 is an enlarged partial cross-sectional side view showing an enlarged bottom portion of the seamless metal can of FIG. 1 is an enlarged cross-sectional side view showing a cylindrical side wall of a seamless aluminum can before and after post-processing; 3 is a diagram showing an outline of a process for manufacturing a seamless metal can; 4 is a diagram showing a forming mold used in the doming process of FIG. 4; 5 is a diagram for explaining the doming process of FIG. 4; and 6 is a diagram for explaining the ironing process for a seamless aluminum can.

[0014] <Configuration of Seamless Metal Can> The seamless metal can of the present invention is obtained by punching, drawing, redrawing, and ironing a metal plate, particularly a thin-walled aluminum blank made of aluminum or an aluminum alloy, and then doming the bottom, and has the configuration shown in Fig. 1. Finally, the can is subjected to post-processing such as washing and drying, exterior printing, application and baking of a finishing varnish, application and baking of an interior paint, necking-in processing, and flanging before being put to use. That is, the can is filled with contents, a lid is attached, and the can is then sold.

[0015] 1, the seamless metal can of the present invention, generally designated by 10, has a cylindrical side wall 1, a ground portion 3 connected to the lower end of the cylindrical side wall 1, and a bottom portion 5 provided to close the inside of the ground portion 3. In other words, the bottom portion 5 is an area surrounded by the ground portion 3.

[0016] The cylindrical side wall 1 has a body portion 1a with a straight outer surface and a chime portion 1b that slopes inward from the bottom end of the body portion 1a and connects to the grounding portion 3. The top of the body portion 1a is connected to a necked-in portion 1c formed by post-processing, and a flange portion 1d is formed at the top end of the necked-in portion 1c.

[0017] On the other hand, the bottom portion 5 is made up of a rising portion 7 rising inward from the ground contact portion 3 and a dome-shaped bottom surface 9 continuing to the upper end of the rising portion 7.

[0018] 2, which shows an enlarged view of the bottom portion 5 together with Fig. 1, the dome-shaped bottom surface 9 is divided into two regions: a central dome portion 9a having a large radius of curvature and a gently curving surface that is nearly flat, and a ring-shaped portion 9b that surrounds the central dome portion 9a and has a smaller radius of curvature than the central dome portion 9a. That is, the inside of the ring-shaped portion 9b is continuous with the peripheral edge of the central dome portion 9a (boundary X between the ring-shaped portion 9b and the central dome portion 9a), and the outside of the ring-shaped portion 9b is continuous with the upper end of the rising portion 7 (boundary Y between the dome-shaped bottom surface 9 and the rising portion 7).

[0019] In the dome-shaped bottom surface 9, the boundary X between the ring-shaped portion 9b and the central dome portion 9a is an inflection point. The upper end of the rising portion 7 (the boundary Y) is the portion where the tangent Q to the surface forming the rising portion 7 is perpendicular to the ground surface G, and this upper end is also an inflection point.

[0020] In the seamless metal can of the present invention, the boundary X between the central dome portion 9a and the ring-shaped portion 9b has a minimum radius of curvature R1 (i.e., an inflection point) of less than 3.0 mm, preferably 2.5 mm or less, and most preferably 2.0 mm or less. This allows the seamless metal can 10 to have improved pressure resistance and effectively prevent buckling of the bottom portion 5, even when the metal sheet (raw sheet) used to form the seamless metal can 10 has a thickness of 0.270 mm or less, preferably 0.245 mm or less, more preferably 0.230 mm or less, and most preferably in the range of 0.215 to 0.200 mm, and is thinned by drawing and ironing. For example, it has been experimentally confirmed that if the radius of curvature R1 is greater than the above range, the dome portion with a large radius of curvature will be directly connected to the rising portion 7, making buckling of the bottom portion 5 more likely to occur. By setting the radius of curvature R1 small as in the present invention, the ring-shaped portion 9b can effectively absorb the axial load applied to the seamless metal can 10, and buckling of the bottom portion 5 can be effectively suppressed.

[0021] The thickness of the metal plate (base plate) used for forming corresponds to the thickness T0 at the center O of the central dome portion 9a. That is, the center O of the central dome portion 9a is not thinned by ironing, so the metal thickness T0 of this portion reflects the metal thickness of the base plate. Incidentally, the chime portion 1b connecting the grounding portion 3 and the body portion 1a is thinned by ironing. For example, when the metal thickness of the base plate is within the above-mentioned range, the thickness of this chime portion 1b is typically 95% or less of the thickness of the metal plate (base plate). Furthermore, in the case of seamless aluminum cans used as beverage cans, the thickness of the thinnest portion of the body portion 1a is 30 to 50% of the metal thickness T0.

[0022] In order to further enhance the buckling suppression function of the ring-shaped portion 9b in the bottom portion 5 having the above-described shape, it is preferable that the rising portion 7 rises outward and upward from the ground contact portion 3, and in particular, it is preferable that the rising portion 7 rises from the ground contact surface G at an angle θ with respect to the ground contact surface G in the range of 95 to 125 degrees. In this case, the upper end of the rising portion 7 (the boundary Y between the dome-shaped bottom surface 9 and the rising portion 7) is an inflection point, and it is most preferable that the radius of curvature R2 is 1.2 mm or less, and in particular, approximately 1.2 to 0.5 mm. By adopting such a configuration, the ring-shaped portion 9b can be made more mobile with both ends (X and Y) serving as fulcrums, thereby further enhancing the buckling suppression function of the ring-shaped portion 9b.

[0023] In the present invention, the length d of the ring-shaped portion 9b (the distance between the boundaries X and Y) is preferably 10 to 30%, particularly 15 to 25%, of the radius D1 of the dome-shaped bottom surface 9. By setting the length d of the ring-shaped portion 9b to such a value, the pressure resistance of the seamless metal can 10 is maximized, and buckling of the dome-shaped bottom surface 9 can be most reliably suppressed. The shape of the bottom portion 5 described above can be formed by doming molding, which will be described later.

[0024] In the present invention, the metal constituting the seamless metal can 10 is not particularly limited and may be any of various metals or alloys, but aluminum or an aluminum alloy is preferred from the viewpoints of light weight and thin-wall workability. Furthermore, a seamless metal can is preferably formed by using a resin-coated metal plate, one side of which is coated with an organic resin (e.g., PET), as a base plate, and then resin-coating the inner surface of the base plate, in order to maximize the benefits of the present invention. In this case, the thickness T0 mentioned above means the thickness of the metal plate (base plate) excluding the thickness of the coating resin.

[0025] <Configuration of Ultralight Seamless Aluminum Can> Similar to the basic configuration of the seamless metal can described above, the ultralight seamless aluminum can 10 of the present invention has a cylindrical side wall 1 including a body portion 1a and a chime portion 1b that slopes inward from the lower end of the body portion 1a and connects to the ground portion 3. The diameter D of the lower end of the body portion 1a (corresponding to the upper end of the chime portion 1b) is in the range of 45 to 75 mm. In the example shown in FIGS. 1 and 3 , the outer surface of the body portion 1a has a straight, rectangular shape. However, this is not limited to this configuration, and the outer surface of the body portion 1a may have irregularities formed thereon due to post-processing or the like. Even in such a case, the lowermost inflection point of the body portion 1a is the lower end of the body portion 1a, the boundary with the chime portion 1b, and has the diameter D as described above. Furthermore, the upper portion of the body portion 1a is a thick-walled portion 2 for post-processing that is thicker than the body portion 1a. As can be seen from Figure 3, this post-processing thick portion 2 has a tapered portion 1c1 whose thickness gradually increases upward from the upper end of the body portion 1a, and a thick high-strength portion 1c2 is formed above this tapered portion 1c1.

[0026] The thick-wall portion 2 for post-processing is subjected to post-processing such as necking and flanging, which results in the formation of a necked-in portion 1c having a smaller diameter than the body portion 1a and a flat flange portion 1d (see FIG. 3). In particular, the aluminum thickness (T0) at the center O of the bottom portion 5 is 0.270 mm or less, preferably 0.245 mm or less, more preferably 0.230 mm or less, and most preferably 0.215 to 0.200 mm. That is, the seamless aluminum can 10 is thinned by drawing and ironing an aluminum sheet having such an aluminum thickness as a raw sheet.

[0027] The ultralight seamless aluminum can 10 of the present invention uses the above-described aluminum sheet as a base sheet and is thinned to the limit of thickness not seen in conventionally known seamless cans. Specifically, the aluminum thickness (T1) at the thinnest portion of the body 1a is thinned to 0.080 to 0.105 mm, 0.080 to 0.100 mm, 0.080 to 0.095 mm, particularly 0.080 to 0.090 mm, and particularly 0.080 to 0.085 mm. The thickness of the body 1a is not uniform, but is adjusted by adjusting the diameter and number of ironing dies and the shape of the punches, as described below. As shown in FIG. 3 , the thickness of the body 1a is typically thinnest at the top and gradually increases upward, forming a tapered portion 1c1. That is, the outer surface of the body 1a is perpendicular to the ground surface G, while the inner surface is slightly inclined. Therefore, the position of the thinnest part varies depending on the ironing conditions, such as the diameter and number of ironing dies and the shape of the punch.

[0028] The ultralight seamless aluminum can 10 of the present invention, which has been thinned as described above, has a very high height despite the thin thickness of the blank used for forming it, and for example, the ratio H / D of the height H of the cylindrical side wall 1 to the diameter D of the lower end of the body portion 1a is in the range of 1.6 to 2.7, particularly 1.7 to 2.6. Because of the high height H achieved by such significant thinning, the seamless aluminum can 10 of the present invention has a total aluminum weight of 14 g or less, and is therefore extremely light, even when the content volume is about 500 ml with the flange portion 1d formed at the upper end of the cylindrical side wall 1.

[0029] Furthermore, in the seamless aluminum can 10 of the present invention having the above-described configuration, the chime portion 1b connected to the lower end of the body portion 1a is also thin-walled. For example, the aluminum thickness (T2) in the chime portion 1b is 95% or less of the aluminum thickness (T0) at the center O of the bottom portion 5, and T2 is greater than or equal to T1, where T2 is the aluminum thickness (T1) at the thinnest portion. The thickness of the chime portion 1b gradually decreases from the ground portion 3 toward the lower end of the body portion 1a. The aluminum thickness (T2) is the thickness at the thinnest portion of the chime portion 1b.

[0030] In the seamless aluminum can 10 having such a reduced thickness, as described above, the upper part of the body 1a is the thick-walled portion 2 for post-processing, which is thicker than the body 1a. This thick-walled portion 2 for post-processing is formed from a tapered portion 1c1 whose thickness gradually increases upward from the upper end of the body 1a, and a thick, high-strength portion 1c2 located above the tapered portion 1c1. This configuration allows the neck-in portion 1c and the flat flange portion 1d to be formed by post-processing the upper region of the cylindrical side wall 1 without causing forming defects.

[0031] For example, to reliably prevent molding defects during post-processing, it is preferable that the aluminum thickness (T3) of the high-strength portion 1c2 be 50% or more, particularly 55% or more, of the aluminum thickness (T0) at the center of the bottom portion 5. Furthermore, 50-80%, 50-70%, 50-60%, or 55-60% is more preferable. That is, this high-strength portion 1c2 (corresponding to the flange portion 1d) has the same thickness as the blank and does not need to be thinned by ironing. Furthermore, to ensure post-processability while effectively thinning the blank, it is preferable that the axial length L1 of the body portion 1a be in the range of 60-95%, particularly 70-95%, of the height H of the cylindrical side wall 1, and the axial length L2 of the high-strength portion be in the range of 5-40%, particularly 5-30%, of the height H of the cylindrical side wall 1.

[0032] 2, in order to prevent a decrease in pressure resistance and buckling that occurs in the bottom portion 5 due to the thinning of the can wall caused by using a thinner aluminum plate, the bottom portion 5 preferably has a rising portion 7 extending upward from the contact portion 3 and a dome-shaped bottom surface 9 extending dome-like from the upper end of the rising portion 7. The dome-shaped bottom surface 9 preferably comprises a central dome portion 9a having a large radius of curvature and a gently curved surface that is nearly flat, and a ring-shaped portion 9b that surrounds the central dome portion 9a and has a smaller radius of curvature than the central dome portion 9a. The upper end of the rising portion 7 (the above-mentioned boundary portion Y) is the portion where the tangent Q to the surface forming the rising portion 7 is perpendicular to the contact surface G, and this upper end also serves as an inflection point.

[0033] In the case of an ultra-lightweight seamless aluminum can, it is also optimal that the boundary X between the central dome portion 9a and the ring-shaped portion 9b of the domed bottom surface 9 has a minimum radius of curvature R1 (i.e., an inflection point) of less than 3.0 mm, preferably 2.5 mm or less, and most preferably 2.0 mm or less. This improves the pressure resistance of the seamless aluminum can 10 and more reliably prevents buckling of the bottom portion 5, even though the can is thinned by drawing and ironing an aluminum sheet having a very thin thickness (e.g., 0.27 mm or less), as described above.

[0034] Furthermore, in an ultra-lightweight seamless aluminum can, in the bottom portion 5 having the above-described shape, in order to further enhance the buckling suppression function of the ring-shaped portion 9b, the rising portion 7 preferably rises outward and upward from the contact portion 3, and particularly preferably rises from the contact surface G at an angle θ with respect to the contact surface G in the range of 95 to 125 degrees. In this case, it is most preferable that the radius of curvature R2 of the inflection point at the upper end of the rising portion 7 (boundary Y between the dome-shaped bottom surface 9 and the rising portion 7) is 1.4 mm or less, particularly approximately 1.3 to 0.7 mm. This configuration increases the mobility of the ring-shaped portion 9b with both ends (X and Y) as fulcrums, further enhancing the buckling suppression function of the ring-shaped portion 9b.

[0035] Furthermore, in the ultra-lightweight seamless aluminum can, it is preferable that the length d of the ring-shaped portion 9b (the distance between the boundaries X and Y) is 10 to 30%, and particularly 15 to 25%, of the radius D of the dome-shaped bottom surface 9. By setting the length d of the ring-shaped portion 9b to such a value, the pressure resistance of the metal can 10 is maximized, and buckling of the bottom portion 9 can be most reliably suppressed.

[0036] <Production of Seamless Metal Can and Ultralight Seamless Aluminum Can> The seamless metal can and ultralight seamless aluminum can of the present invention having the above-described configuration are produced by forming a blank sheet of the above-described metal (aluminum or aluminum alloy) (which may have an organic resin coating on the side corresponding to the inner surface).

[0037] The above-mentioned metal blanks are subjected to the usual forming processes of punching, drawing, ironing and doming to obtain seamless metal cans and ultra-lightweight seamless aluminum cans having a dome-shaped bottom.

[0038] The process from punching to doming is shown in FIG. 4. Specifically, as shown in FIG. 4(a), a blank 21 is punched with a punching punch 23 and a punching die 25 to obtain a disk 27 (punching). Next, as shown in FIG. 4(b), a drawing die 31 and a drawing punch 33 are used to obtain a drawn cup (bottomed cylindrical body) 35 (drawing). The resulting drawn cup 35 is then pushed downward using an ironing punch 45 while held in a redraw die 43 by a presser foot 41, as shown in FIG. 4(c). After ironing through multiple ironing dies 47a-47c, the cup is domed at its lowest position and then removed from the ironing punch 45 by a stripper finger 53. This doming is performed using a hold-down ring 51 and a doming die 60, which will be described later. This doming results in the formation of the chime portion 1b, the ground portion 3, and the bottom portion 5 surrounded by the ground portion 3.

[0039] In the ironing process described above, as shown in Figure 4(c), three ironing dies are arranged, and ironing is performed in three stages. However, the number of ironing dies is not limited to three and can be any number depending on the desired degree of thinning. Ironing can be performed in one stage with one die, or two or more dies can be arranged to perform multi-stage ironing. Of course, when multiple ironing dies are arranged along the ironing direction and multi-stage ironing is performed, the inner diameter (machined diameter) of each die decreases toward the downstream side in the ironing direction. Furthermore, when achieving significant thinning, it is necessary to adjust the approach angle of each die (the angle of the working surface of the die that comes into contact with the workpiece) within an appropriate range.

[0040] After the ironing process described above, doming is performed to form the dome-shaped bottom surface 9. In this doming process, the shape of the dome-shaped bottom surface 9 (for example, the shape of the central dome portion 9a and the ring-shaped portion 9b) is determined, but post-processing is required to determine the shape of the rising portion 7.

[0041] The mold used for doming consists of a hold-down ring (annular holding mold) 51 and a doming die 60, and doming is performed by the cooperative action of these molds and the punch 45. The doming die 60 is divided into a base die 61 and a doming ring 63, each of which is provided so as to move up and down independently.

[0042] As can be seen from Figure 5, the hold-down ring (annular holding type) 51 has an upper end action surface 51a that slopes inward and downward, and this action surface 51a forms a chime portion 1b that is connected to the lower end of the body portion 1a, and the grounding portion 3 is formed at the lower end of the action surface 51a.

[0043] The base die 61 is a mold that defines the central dome portion 9a of the dome-shaped bottom surface 9, and the working surface 61a at its upper end corresponds to the central dome portion 9a of the dome-shaped bottom surface 9. The doming ring 63 is a mold that defines the ring-shaped portion 9b of the dome-shaped bottom surface 9, and the working surface 63a at its upper end corresponds to the ring-shaped portion 9b. These working surfaces 61a, 63a are smoothly connected to form the dome-shaped bottom surface 9.

[0044] In the present invention, in order to form a ring-shaped portion 9b with a small radius of curvature around the peripheral edge of the central dome portion 9a, the mold surface that defines this portion is separated from the mold surface that defines the central dome portion 9a. This makes it possible to set the radius of curvature R1 at the boundary X between the central dome portion 9a and the ring-shaped portion 9b to a predetermined value.

[0045] Doming using the above-described mold is performed by the process shown in Fig. 6. The hold down ring 51 is biased upward by a spring (not shown), and as shown in Fig. 6(a), in the initial stage, the action surface 63a of the doming ring 63 is positioned lower than the action surface 51a of the hold down ring 51, and the action surface 61a of the base die 61 is positioned further lower than the action surface 63a of the doming ring 63.

[0046] In the above state, the punch 45 is lowered and the thinned body portion 1a is pressed down, and as shown in Figure 6(b), the lower end of the body portion 1a is pressed against the operating surface 51a of the hold-down ring 51, thereby forming a thinned chime portion 1b at the lower end of the body portion 1a.

[0047] Next, when the doming ring 63 is raised, the inner side of the ground contact portion 3 is pulled up, forming a raised portion 7, as shown in Figure 6 (c), and further, the working surface 63a of the doming ring 63 pushes up the surface on the inner side of the raised portion 7, thereby forming a ring-shaped portion 9b that becomes the peripheral portion of the central dome portion 9a.

[0048] Once the raised portion 7 and the ring-shaped portion 9b of the domed bottom surface 9 are formed as described above, as shown in FIG. 6( d ), the base die 61 rises with a delay, and its working surface 61a is pressed against the bottom 5 of the can body 10, thereby forming the central dome portion 9a of the domed bottom surface 9. This defines the domed bottom surface 9, and the radius of curvature R1 at the boundary X between the central dome portion 9a and the ring-shaped portion 9b is defined. Furthermore, the radius of curvature R2 at the raised portion 7 and the boundary Y between the raised portion 7 and the domed bottom surface 9 (ring-shaped portion 9b) is also determined.

[0049] In order to set the rise angle θ of the rise portion 7 and the radius of curvature R2 at the boundary portion Y within a suitable range, for example, after the above process, the doming ring 63 is lowered, and then the hold-down ring 51 is moved inward to push the thinned chime portion 1b inward, thereby setting the rise angle θ and the radius of curvature R2 at the boundary portion Y within a suitable range.

[0050] After doming as described above, the punch 45 is withdrawn, and the resulting molded body is separated from the punch 45 by the stripper fingers 53. Subsequent processes, such as washing, drying, necking-in, flanging, and painting, are then carried out to obtain the desired seamless metal can 10. The seamless metal can 10 of the present invention exhibits high pressure resistance and effectively suppresses buckling, even when a thin-walled seamless metal can is obtained by drawing and ironing a master sheet having a metal thickness of 0.270 mm or less.

[0051] The ultra-lightweight seamless aluminum can is manufactured by forming an aluminum blank having the thickness described above (which may have an organic resin coating on the side corresponding to the inner surface). The forming process using the aluminum blank described above is similar to the above-described method for manufacturing seamless metal cans shown in Figures 3 to 6, and involves punching, drawing, ironing, and doming to obtain a seamless aluminum can having a dome-shaped bottom surface 9.

[0052] In order to ensure post-processability, an ultralight seamless aluminum can must have a thick-walled portion 2 for post-processing (particularly a high-strength portion 1c2) that is thicker than the body portion 1a, as shown in FIG. 3 . However, the thickness of the body portion 1a must be significantly thinner. In other words, in the ultralight seamless aluminum can of the present invention, the difference in thickness between the high-strength portion 1c2 and the body portion 1a is large, making the can more susceptible to shell breakage during ironing. To prevent such shell breakage, in the manufacture of ultralight seamless aluminum cans, it is preferable to set the approach angle α of the working surface of the ironing die 47 to 3 degrees or less, particularly in the range of 0.5 to 3 degrees, as shown in FIG. 7 . By arranging multiple ironing dies with such approach angles α and performing ironing, it is possible to form an extremely thin body portion 1a while retaining the thick high-strength portion 1c2 and effectively preventing shell breakage. If the approach angle α is small, the tensile force in the axial direction (processing direction) of the can will be small, and the compressive force in the thickness direction of the can will be large, making it less likely for the can to break. However, if the approach angle is set too small, the ironing efficiency will decrease.

[0053] In addition, a seamless aluminum can using an aluminum plate with a metal thickness of 0.270 mm or less and having a thickness (T1) of 0.085 mm at the thinnest part of the body 1a was subjected to an internal pressure of 4 kgf / cm ２ The inventors have confirmed that the bottom does not buckle when the container is dropped from a height of 20 cm with the pressure set to 1000 psi.

[0054] 1: Cylindrical side wall 1a: Body 1b: Chime portion 1c: Neck-in portion 1c1: Tapered portion 1c2: High-strength portion 1d: Flange portion 2: Thick portion for post-processing 3: Ground contact portion 5: Bottom 7: Rising portion 9: Dome-shaped bottom surface 9a: Central dome portion 9b: Ring-shaped portion 10: Seamless metal can X: Boundary portion between central dome portion 9a and ring-shaped portion 9b R1: Radius of curvature at boundary portion X Y: Boundary portion between rising portion and dome-shaped bottom surface 9 (ring-shaped portion) R2: Radius of curvature at boundary portion Y D: Bottom diameter H: Height of cylindrical side wall T0: Aluminum thickness at center of bottom T1: Aluminum thickness at thinnest portion T2: Aluminum thickness at chime portion 1b (T2) T3: Aluminum thickness at high-strength portion 1c2 L1: Axial length L1 of body portion 1a L2: Axial length L2 of the high strength portion

Claims

1. A seamless metal can having a cylindrical side wall, a grounding portion continuous with the cylindrical side wall, and a bottom portion formed to close the inside of the grounding portion, the bottom portion being formed of a rising portion extending upward from the inside of the grounding portion and a dome-shaped bottom surface continuous with the rising portion, wherein the dome-shaped bottom surface has a central dome portion and a ring-shaped portion formed to surround the central dome portion, the ring-shaped portion being continuous with the upper end of the rising portion, and wherein, in a side cross-sectional view of the metal can, the boundary portion between the central dome portion and the ring-shaped portion is an extremely small curved portion with a radius of curvature of less than 3.0 mm.

2. The seamless metal can according to claim 1, wherein in a side cross-sectional view of said metal can, said rising portion rises outward and upward from said ground portion.

3. The seamless metal can according to claim 2, wherein, in a side cross-sectional view of the metal can, the rising portion rises from the ground surface at an angle θ in the range of 95 to 125 degrees with respect to the ground surface, and the joint between the rising portion and the ring-shaped portion is an extremely curved portion with a curvature radius of 1.2 mm or less.

4. The seamless metal can according to claim 3, wherein the metal thickness at the center of said domed bottom surface is 0.270 mm or less.

5. The seamless metal can according to claim 4, wherein said metal is aluminum.

6. An ultra-lightweight seamless aluminum can having a cylindrical side wall and a bottom surrounded by a ground contact portion at the lower end of the cylindrical side wall, wherein the cylindrical side wall comprises a body portion, a chime portion which slopes inward from the lower end of the body portion and is connected to the ground contact portion, and a thick-walled portion for post-processing which is located above the body portion and has a thickness greater than that of the body portion, the bottom portion has a dome-shaped bottom surface which curves upward and a rising portion which extends upward and outward from the ground contact portion and is connected to the dome-shaped bottom surface, the aluminum thickness (T0) at the center of the bottom portion is 0.270 mm or less and the diameter D of the lower end of the body portion is 45 to 75 mm, the aluminum thickness (T1) at the thinnest part of the body portion is in the range of 0.080 to 0.105 mm, and the total aluminum weight is in the range of 14 g or less.

7. The ultra-light seamless aluminum can according to claim 6, wherein the aluminum thickness (T1) at the thinnest part of the body is less than 0.087 mm.

8. The ultra-lightweight seamless aluminum can according to claim 6, wherein the ratio H / D of the height H of the cylindrical side wall to the diameter D of the lower end of the body is in the range of 1.6 to 2.

7.

9. The ultra-lightweight seamless aluminum can according to claim 6, wherein the aluminum thickness (T2) at the chime portion is 95% or less of the aluminum thickness (T0) at the center of the bottom portion.

10. An ultra-lightweight seamless aluminum can as described in claim 6, wherein the thick-walled portion for post-processing is formed from a tapered portion whose thickness gradually increases upward from the upper end of the body portion, and a high-strength portion located above the tapered portion and having an aluminum thickness (T3) that is in the range of 50% or more of the aluminum thickness (T0) at the center of the bottom portion.

11. The ultra-lightweight seamless aluminum can according to claim 10, wherein the axial length L1 of the body portion is in the range of 60 to 95% of the height H of the cylindrical side wall, and the axial length L2 of the high strength portion is in the range of 5 to 40% of the height H of the cylindrical side wall.

12. The ultra-lightweight seamless aluminum can according to claim 6, wherein a ring-shaped inflection portion having a minimum radius of curvature (R1) is formed on the dome-shaped bottom surface of the bottom portion at a position away from the upper end of the rising portion.

13. The ultra-lightweight seamless aluminum can according to claim 12, wherein the radius of curvature (R1) is in the range of less than 3.0 mm.

Images