Seamless metal can

Abstract

Provided is a seamless metal can. The seamless metal can includes: a cylindrical side wall; a ground contact portion continuous with the cylindrical side wall; and a bottom portion formed to close off an inside of the ground contact portion, the bottom portion being formed of a rising portion extending upward from the inside of the ground contact portion and a dome-shaped bottom surface continuous with the rising portion. The dome-shaped bottom surface includes a central dome portion and a ring-shaped portion formed so as to surround the central dome portion. The ring-shaped portion is continuous with an upper end of the rising portion. A boundary portion between the central dome portion and the ring-shaped portion is formed as a minute curved portion having a radius of curvature of less than 3.0 mm in a side cross-sectional view of the metal can.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation application of International Application No. PCT / JP2024 / 029451 filed on Aug. 20, 2024 which claims the benefit of priority from Japanese Patent Application No. 2023-172322 filed on Oct. 3, 2023 and Japanese Patent Application No. 2023-174489 filed on Oct. 6, 2023 designating the U.S., the contents of all which are incorporated herein by reference in their respective entireties.TECHNICAL FIELD

[0002] The disclosure relates to a seamless metal can having a dome-shaped bottom surface.BACKGROUND

[0003] Typically, a seamless can or the like obtained by metal forming (punching, drawing, and ironing) has a dome-shaped bottom surface formed by recessing a bottom portion into a dome shape to improve pressure resistance performance and stabilize placement. A forming means for forming such a dome-shaped bottom surface is called doming, and is performed by holding a peripheral edge of a bottom portion of a cylindrical body by an annular die called a hold ring and pushing up a doming die from within the annular die, thereby recessing a bottom surface of the cylindrical body into a dome shape (refer to JP 2018-177289 A).

[0004] In recent years, there has been a strong demand for forming a lightweight seamless can from a thin metal sheet from the viewpoints of effective use of metal materials, lightweight properties, and the like. In the seamless can formed from such a thin-walled metal sheet, buckling of the bottom portion is particularly problematic, and the dome-shaped bottom surface known in the related art has a problem in that pressure resistance performance is insufficient and buckling is likely to occur.

[0005] For example, JP 2000-211624 A and JP 6713741 B disclose seamless metal cans having a dome-shaped bottom surface of a certain form. However, for example, in a thin-walled seamless metal can formed from a metal sheet (blank sheet) having a thickness of less than 0.270 mm, the pressure resistance is low, and thus buckling is likely to occur. Accordingly, at present, further improvement in pressure resistance performance is required when the thickness is reduced.

[0006] In addition, in a thinned lightweight seamless aluminum can, rupture of a body during forming is a problem, and thus the degree of thinning or weight reduction is limited. For example, JP 6977302 B, JP 5102042 B, and JP 2023-85679 A propose aluminum cans having a dome-shaped bottom surface. However, since rupture of a body is a problem, thinning is considerably limited, and in practice, a lightweight seamless aluminum suitable for practical use has not been obtained.

[0007] In addition, buckling of the bottom portion is a problem, and it has been pointed out that buckling is likely to occur when the thickness of the dome-shaped bottom surface known in the related art is reduced beyond a certain level.SUMMARY

[0008] Accordingly, an object of the disclosure is to provide a seamless metal can having a dome-shaped bottom surface which has high pressure resistance and is effectively prevented from buckling.

[0009] Another object of the disclosure is to provide an ultra-lightweight seamless aluminum can in which rupture of a body during forming is effectively prevented and which is significantly thinned.

[0010] Still another object of the disclosure is to provide a seamless metal can formed from a metal sheet having a metal thickness of 0.270 mm or less, particularly 0.26 mm or less.

[0011] According to the disclosure, there is provided a seamless metal can including a cylindrical side wall, a ground contact portion continuous with the cylindrical side wall, and a bottom portion formed to close off an inside of the ground contact portion, the bottom portion being formed of a rising portion extending upward from the inside of the ground contact 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 is continuous with an upper end of the rising portion, and a boundary portion between the central dome portion and the ring-shaped portion is formed as a minute curved portion having a radius of curvature of less than 3.0 mm in a side cross-sectional view of the metal can.

[0012] In the seamless metal can of the disclosure, it is preferable that

[0013] (1) in the side cross-sectional view of the metal can, the rising portion rises outward and upward from the ground contact portion,

[0014] (2) in the side cross-sectional view of the metal can, the rising portion rises from a ground contact surface at an angle θ in a range of 95 to 125 degrees with respect to the ground contact surface, and a joint portion between the rising portion and the ring-shaped portion is a minute curved portion having a radius of curvature of 1.2 mm or less,

[0015] (3) a metal thickness at a central position of the dome-shaped bottom surface is 0.270 mm or less, and

[0016] (4) the metal is aluminum.

[0017] According to the disclosure, there is also provided an ultra-lightweight seamless aluminum can including a cylindrical side wall and a bottom portion surrounded by a ground contact portion at a lower end of the cylindrical side wall, wherein the cylindrical side wall includes a body portion, a chime portion inclined inward from a lower end of the body portion and continuous with the ground contact portion, and a post-processing thick portion located above the body portion and having a thickness greater than that of the body portion, the bottom portion has a dome-shaped bottom surface curved upward and a rising portion extending upward from the ground contact portion toward the outside and continuous with the dome-shaped bottom surface, an aluminum thickness (T0) at a central portion of the bottom portion is 0.270 mm or less, a diameter D of the lower end of the body portion is 45 to 75 mm, an aluminum thickness (T1) at a thinnest portion of the body portion is in a range of 0.080 to 0.105 mm, and a total aluminum weight is 14 g or less.

[0018] In the ultra-lightweight seamless aluminum can of the disclosure, it is preferable that

[0019] (1) the aluminum thickness (T1) at the thinnest portion of the body portion is less than 0.087 mm,

[0020] (2) a ratio H / D of a height H of the cylindrical side wall to the diameter D of the lower end of the body portion is in a range of 1.6 to 2.7,

[0021] (3) an aluminum thickness (T2) at the chime portion is 95% or less of the aluminum thickness (T0) at the central portion of the bottom portion,

[0022] (4) the post-processing thick portion is formed of a tapered portion in which a thickness gradually increases upward from an upper end of the body portion, and a high-strength portion located above the tapered portion and having an aluminum thickness (T3) in a range of 50% or more of the aluminum thickness (T0) at the central portion of the bottom portion,

[0023] (5) an axial length L1 of the body portion is in a range of 60 to 95% of the height H of the cylindrical side wall, and an axial length L2 of the high-strength portion is in a range of 5 to 40% of the height H of the cylindrical side wall,

[0024] (6) On the dome-shaped bottom surface of the bottom portion, an inflection portion in which a radius of curvature (R1) becomes minimal is formed in a ring shape at a position spaced apart from an upper end of the rising portion, and

[0025] (7) the radius of curvature (R1) is in a range of less than 3.0 mm.

[0026] The seamless metal can of the disclosure has a dome-shaped bottom surface recessed in a dome shape at the bottom portion formed to close off the inside of the ground contact portion, and has significant features in that the ring-shaped portion is formed to surround the central dome portion of the dome-shaped bottom surface, and the joint portion between the ring-shaped portion and the central dome portion is a minute curved portion having a radius of curvature of less than 3.0 mm.

[0027] That is, the dome-shaped bottom surface is a gently curved surface having a large radius of curvature at the central portion, and has a configuration in which the central position has the maximum radius of curvature. When an internal pressure is applied in the axial direction of the seamless metal can, the internal pressure concentrates on the central portion having such a shape close to a flat surface. Accordingly, as the thickness of the metal blank sheet used for forming (corresponding to the metal thickness at the central portion of the dome-shaped bottom surface) decreases, buckling (reversal of convexity and concavity) is more likely to occur. However, in the disclosure, the ring-shaped portion having a small radius of curvature is formed to surround the central dome portion having a large radius of curvature, and the radius of curvature at the joint portion (that is, the boundary portion) between the ring-shaped portion and the central dome is an extremely small value of less than 3.0 mm. That is, an end portion on one side of the ring-shaped portion (an end portion of the central dome) serves as an inflection point, and is largely curved. Further, the other side of the ring-shaped portion is continuous with the upper end of the rising portion continuous with the ground contact portion, and an end portion on the other side of the ring-shaped portion is also largely curved. As can be understood from the above configuration, in the disclosure, the ring-shaped portion having both largely curved end portions is continuous with the central dome portion having a shape close to a smooth flat surface, and therefore, the ring-shaped portion absorbs and relieves the axial load of the seamless metal can, and buckling is more effectively suppressed.

[0028] Therefore, in the disclosure, a metal blank sheet having a minute thickness (for example, 0.270 mm or less) can be used for forming a seamless metal can, which is a great advantage of the disclosure.

[0029] In addition, the ultra-lightweight seamless aluminum can of the disclosure has a basic configuration in which the lower end of the body portion has a diameter D (corresponding to the diameter of the upper end of the chime portion) of 45 to 75 mm, and the central portion of the bottom portion has an aluminum thickness (T0) of 0.270 mm or less. In such a basic configuration, the aluminum thickness (T0) at the center of the bottom portion corresponds to an aluminum original sheet (also referred to as a blank sheet) used for forming. This is because, when a seamless can is formed by ironing to reduce the thickness, the bottom portion is not subjected to ironing to reduce the thickness. That is, the seamless aluminum can of the disclosure is formed from a metal blank sheet having a minute thickness of 0.270 mm or less, and in addition, the aluminum thickness (T1) at the thinnest portion of the body portion is in the range of 0.080 to 0.105 mm, and the thinning is performed to a maximum extent. The seamless aluminum can of the disclosure achieves an ultra-lightweight configuration in which a total aluminum weight is 14 g or less by such extreme thinning while maintaining a size in which the diameter D at the lower end of the body portion is 45 to 75 mm. For example, despite having an internal volume of 500 mL, the total aluminum weight is 14 g or less, and such ultra-lightweight configuration is achieved for the first time by the disclosure.BRIEF DESCRIPTION OF DRAWINGS

[0030] FIG. 1 is a schematic side cross-sectional view illustrating a seamless metal can according to the disclosure in its entirety.

[0031] FIG. 2 is an enlarged partial side cross-sectional view illustrating a bottom portion of the seamless metal can of FIG. 1.

[0032] FIG. 3 is an enlarged side cross-sectional view of a cylindrical side wall of a seamless aluminum can before and after post-processing.

[0033] FIGS. 4A-4C are diagrams illustrating an overview of a process for manufacturing a seamless metal can.

[0034] FIG. 5 is a diagram illustrating a forming die used in a doming step in FIGS. 4A-4C.

[0035] FIGS. 6A-6D are diagrams for explaining the doming step in FIGS. 4A-4C.

[0036] FIG. 7 is a diagram for explaining an ironing step in a seamless aluminum can.DESCRIPTION OF EMBODIMENTSConfiguration of Seamless Metal Can

[0037] A seamless metal can of the disclosure is obtained by, for example, punching, drawing, and redrawing-ironing a metal sheet, particularly a thin-walled blank sheet made of aluminum or an aluminum alloy, and then doming a bottom portion thereof, and has a configuration illustrated in FIG. 1, and, finally, thereafter, post-processing such as washing and drying, outer surface printing, finishing varnish application and baking, inner surface coating application and baking, neck-in processing, and flange processing is performed, and the can is put to use. That is, filling of contents, fixing of a lid material, and the like are performed, and the can is offered for sale.

[0038] Referring to FIG. 1, a seamless metal can of the disclosure generally denoted by 10 includes a cylindrical side wall 1, a ground contact portion 3 continuous with a lower end of the cylindrical side wall 1, and a bottom portion 5 provided to close off an inside of the ground contact portion 3. That is, the bottom portion 5 is a region surrounded by the ground contact portion 3.

[0039] The cylindrical side wall 1 includes a body portion 1a having a straight body shape in which an outer surface is straight and a chime portion 1b inclined inward from a lower end of the body portion 1a and continuous with the ground contact portion 3. In addition, an upper portion of the body portion 1a is continuous with a neck-in portion 1c formed by post-processing, and a flange portion 1d is formed at an upper end of the neck-in portion 1c.

[0040] On the other hand, the bottom portion 5 includes a rising portion 7 rising inward from the ground contact portion 3 and a dome-shaped bottom surface 9 continuous with an upper end of the rising portion 7.

[0041] Referring to FIG. 2 illustrating the bottom portion 5 in an enlarged manner together with FIG. 1, the dome-shaped bottom surface 9 is divided into two regions, i.e., a central dome portion 9a having a large radius of curvature and a gently curved surface close to a flat surface, and a ring-shaped portion 9b formed to surround the central dome portion 9a and having a radius of curvature smaller than that of the central dome portion 9a. That is, an inner side of the ring-shaped portion 9b is continuous with a circumferential end portion of the central dome portion 9a (a boundary portion X between the ring-shaped portion 9b and the central dome portion 9a), and an outer side of the ring-shaped portion 9b is continuous with the upper end of the rising portion 7 (a boundary portion Y between the dome-shaped bottom surface 9 and the rising portion 7).

[0042] Note that, in the dome-shaped bottom surface 9, the boundary portion X between the ring-shaped portion 9b and the central dome portion 9a is an inflection point. In addition, the upper end of the rising portion 7 (the boundary portion Y) is a portion where a tangent line Q of a surface forming the rising portion 7 is perpendicular to a ground contact surface G, and such an upper end portion is also an inflection point.

[0043] In the dome-shaped bottom surface 9 having such a configuration, in the seamless metal can of the disclosure, the boundary portion X between the central dome portion 9a and the ring-shaped portion 9b has a radius of curvature R1 that is less than 3.0 mm, preferably 2.5 mm or less, and most preferably 2.0 mm or less, which is an extremely small value (that is, an inflection point). This can increase the pressure resistance of the seamless metal can 10 and effectively avoid buckling of the bottom portion 5 even when thinning is performed through drawing and ironing using, as a metal sheet (blank sheet) used for forming such a seamless metal can 10, a thin sheet having a metal thickness of 0.270 mm or less, preferably 0.245 mm or less, more preferably 0.230 mm or less, and most preferably in a range of 0.215 to 0.200 mm.

[0044] For example, it has been confirmed through experiments that if the radius of curvature R1 is larger than the above, the dome portion having a large radius of curvature is directly continuous with the rising portion 7, and thus buckling of the bottom portion 5 is likely to occur. By setting the radius of curvature R1 to be small as in the disclosure, the ring-shaped portion 9b can effectively absorb the axial load applied to the seamless metal can 10, thereby effectively suppressing buckling of the bottom portion 5.

[0045] Note that the thickness of the metal sheet (blank sheet) used for forming corresponds to a thickness T0 at a central portion O of the central dome portion 9a. That is, since the central portion O of the central dome portion 9a is not thinned through ironing, the metal thickness of the blank sheet is reflected in the metal thickness T0 at this portion. Incidentally, the chime portion 1b connecting the ground contact portion 3 and the body portion 1a is thinned through ironing, and for example, when the metal thickness of the blank sheet falls within the above range, the thickness of the chime portion 1b is usually thinned to 95% or less of the thickness of the metal sheet (blank sheet). In addition, in the case of a seamless aluminum can used as a beverage can, a thickness at a portion of the body portion 1a thinned to the greatest extent is 30 to 50% of the metal thickness T0.

[0046] 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 ground contact portion 3, and particularly preferably rises from the ground contact surface G at an angle θ in a range of 95 to 125 degrees with respect to the ground contact surface G. In this case, the upper end of the rising portion 7 (the boundary portion Y between the dome-shaped bottom surface 9 and the rising portion 7) is an inflection point, and a radius of curvature R2 thereof is most preferably 1.2 mm or less, particularly about 1.2 to 0.5 mm. By adopting such a configuration, both ends (X and Y) of the ring-shaped portion 9b function as fulcrums, thereby increasing movability, and the buckling suppression function of the ring-shaped portion 9b is further enhanced.

[0047] In addition, in the disclosure, a length d of the ring-shaped portion 9b (a distance between the boundary portions X and Y) is preferably 10 to 30%, particularly 15 to 25% of a radius D1 of the dome-shaped bottom surface 9. By setting the length d of the ring-shaped portion 9b to such a size, the pressure resistance of the seamless metal can 10 becomes the highest, and the buckling of the dome-shaped bottom surface 9 can be most reliably suppressed.

[0048] Note that the above-described configuration of the bottom portion 5 can be formed by doming described below.

[0049] In the disclosure, the metal constituting the seamless metal can 10 described above is not particularly limited and may be various metals or alloys, but aluminum or an aluminum alloy is preferable from viewpoints such as light weight and thin-wall formability. Further, from the viewpoint of maximizing advantages of the disclosure, it is preferable that forming is performed using, as a blank sheet, a resin-coated metal sheet in which one surface is coated with an organic resin (for example, PET), thereby providing a seamless metal can in which an inner surface is resin-coated. In this case, the thickness T0 described above refers to a thickness of the metal sheet (blank sheet) not including a thickness of the coating resin.Configuration of Ultra-Lightweight Seamless Aluminum Can

[0050] In the ultra-lightweight seamless aluminum can 10 of the disclosure, the cylindrical side wall 1 includes a body portion 1a and a chime portion 1b inclined inward from a lower end of the body portion 1a and continuous with the ground contact portion 3, as in the basic configuration of the seamless metal can described above. A lower end of the body portion 1a (corresponding to an upper end of the chime portion 1b) has a diameter D in a range of 45 to 75 mm.

[0051] Note that in the examples illustrated in FIGS. 1 and 3, the body portion 1a has a straight body shape in which an outer surface is straight, but the disclosure is not limited to such a shape, and irregularities may be formed on the outer surface of the body portion 1a by post-processing or the like. Even in such a case, a lowermost inflection point portion of the body portion 1a constitutes the lower end of the body portion 1a, serves as a boundary portion with the chime portion 1b, and has the diameter D of the size described above.

[0052] In addition, the upper portion of the body portion 1a constitutes a post-processing thick portion 2 having a thickness greater than that of the body portion 1a. As can be understood from FIG. 3, the post-processing thick portion 2 has a tapered portion 1c1 in which a thickness gradually increases upward from the upper end of the body portion 1a, and a thick high-strength portion 1c2 is formed above the tapered portion 1c1.

[0053] The post-processing thick portion 2 is subjected to post-processing such as neck-in processing or flange processing, and by such post-processing, a neck-in portion 1c that is drawn to have a smaller diameter than the body portion 1a and a flat flange portion 1d are formed (see FIG. 3).

[0054] 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 through drawing and ironing using, as a blank sheet, an aluminum thin sheet having such an aluminum thickness.

[0055] In addition, the ultra-lightweight seamless aluminum can 10 of the disclosure is thinned to an extent not seen in conventionally known seamless cans by using the above-described aluminum thin sheet as a blank sheet. Specifically, thinning is performed such that an aluminum thickness (T1) at a thinnest portion of the body portion 1a is in a range of 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.

[0056] Note that the thickness of the body portion 1a is not uniform, but is adjusted by diameters and the number of ironing dies, a shape of a punch, and the like, which will be described below, and usually, as illustrated in FIG. 3, the thickness of the body portion 1a is thinnest at an upper end, and the tapered portion 1c1 in which the thickness gradually increases upward from the upper end is formed. That is, the outer surface of the body portion 1a is perpendicular to the ground contact surface G, but the inner surface thereof is slightly inclined. Therefore, the position of the thinnest portion varies depending on ironing conditions such as the diameters and number of ironing dies and the shape of the punch.

[0057] The ultra-lightweight seamless aluminum can 10 of the disclosure, which is thinned as described above, has a very large height despite a small thickness of a blank used for forming, and for example, a ratio H / D of a height H of the cylindrical side wall 1 to a diameter D of the lower end of the body portion 1a is in a range of 1.6 to 2.7, particularly 1.7 to 2.6. With such an increased height H resulting from the significant thinning as described above, the seamless aluminum can 10 of the disclosure has a total aluminum weight of 14 g or less. For example, even when an internal volume is about 500 mL in a state in which the flange portion 1d is formed at the upper end of the cylindrical side wall 1, the total aluminum weight is 14 g or less, thereby achieving the ultra-lightweight seamless aluminum can 10.

[0058] Furthermore, in the seamless aluminum can 10 of the disclosure having the above-described configuration, the chime portion 1b continuous with the lower end of the body portion 1a is also thinned. For example, the aluminum thickness (T2) at the chime portion 1b is 95% or less of the aluminum thickness (T0) at the center O of the bottom portion 5, and satisfies T2≥ T1 with respect to the aluminum thickness (T1) at the thinnest portion. The thickness of the chime portion 1b is gradually reduced from the ground contact portion 3 toward the lower end of the body portion 1a. The aluminum thickness (T2) is the thickness of the thinnest portion of the chime portion 1b.

[0059] In the seamless aluminum can 10 thinned in this manner, as described above, the upper portion of the body portion 1a constitutes the post-processing thick portion 2 having a thickness greater than that of the body portion 1a, and the post-processing thick portion 2 is formed of the tapered portion 1c1 in which a thickness gradually increases upward from the upper end of the body portion 1a, and the thick high-strength portion 1c2 located above the tapered portion 1c1. With such a configuration, the neck-in portion 1c and the flat flange portion 1d can be formed without causing a forming defect by post-processing in the upper region of the cylindrical side wall 1.

[0060] For example, in order to reliably prevent a forming defect during post-processing, an aluminum thickness (T3) of the high-strength portion 1c2 is preferably 50% or more, particularly 55% or more, of the aluminum thickness (T0) at the central portion of the bottom portion 5. Further, 50 to 80%, 50 to 70%, 50 to 60%, or 55 to 60% is preferable. That is, the high-strength portion 1c2 (corresponding to the flange portion 1d) may have the same thickness as that of the blank sheet and may not be thinned by ironing. Furthermore, in order to ensure post-processability while effectively achieving thinning, it is preferable that an axial length L1 of the body portion 1a is in a range of 60 to 95%, particularly 70 to 95%, of the height H of the cylindrical side wall 1, and an axial length L2 of the high-strength portion is in a range of 5 to 40%, particularly 5 to 30%, of the height H of the cylindrical side wall 1.

[0061] In addition, in the ultra-lightweight seamless aluminum can, as illustrated in FIG. 2, in order to prevent a decrease in pressure resistance and buckling occurring in the bottom portion 5 due to thinning using a blank sheet having a thin aluminum thickness, it is preferable that the bottom portion 5 includes the rising portion 7 extending upward from the ground contact portion 3 and the dome-shaped bottom surface 9 extending in a dome shape from the upper end of the rising portion 7, and that the dome-shaped bottom surface 9 includes the central dome portion 9a having a large radius of curvature and a gently curved surface close to a flat surface and the ring-shaped portion 9b formed to surround the central dome portion 9a and having a radius of curvature smaller than that of the central dome portion 9a.

[0062] In addition, the upper end of the rising portion 7 (the boundary portion Y) is a portion where the tangent line Q of a surface forming the rising portion 7 is perpendicular to the ground contact surface G, and such an upper end portion is also an inflection point.

[0063] Also in the ultra-lightweight seamless aluminum can, the boundary portion X between the central dome portion 9a and the ring-shaped portion 9b of the dome-shaped bottom surface 9 has the radius of curvature R1 that is less than 3.0 mm, preferably 2.5 mm or less, and most preferably 2.0 mm or less, which is an extremely small value (that is, an inflection point). This can increase the pressure resistance of the seamless aluminum can 10 and more reliably avoid buckling of the bottom portion 5 even when thinning is performed through drawing and ironing using a thin sheet having a considerably thin aluminum thickness (for example, 0.27 mm or less), as described above.

[0064] In addition, in the 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, it is preferable that the rising portion 7 rises outward and upward from the ground contact portion 3, and particularly rises from the ground contact surface G at an angle θ in a range of 95 to 125 degrees with respect to the ground contact surface G. In this case, the radius of curvature R2 of the inflection point at the upper end of the rising portion 7 (the boundary portion Y between the dome-shaped bottom surface 9 and the rising portion 7) is most preferably 1.4 mm or less, particularly about 1.3 to 0.7 mm. By adopting such a configuration, both ends (X and Y) of the ring-shaped portion 9b function as fulcrums, thereby increasing movability, and the buckling suppression function of the ring-shaped portion 9b is further enhanced.

[0065] Further, in the ultra-lightweight seamless aluminum can, the length d of the ring-shaped portion 9b (a distance between the boundary portions X and Y) is 10 to 30%, particularly preferably 15 to 25%, of the radius D of the dome-shaped bottom surface9. By setting the length d of the ring-shaped portion 9b to such a size, the pressure resistance of the metal can 10 becomes the highest, and the buckling of the bottom portion 5 can be most reliably suppressed.Manufacture of Seamless Metal Can and Ultra-Lightweight Seamless Aluminum Can

[0066] The seamless metal can and the ultra-lightweight seamless aluminum can according to the disclosure having a configuration as described above are manufactured by forming using a blank sheet of the above-described metal (aluminum or an aluminum alloy) (an organic resin coating may be provided on a side corresponding to an inner surface).

[0067] The forming using the metal blank sheet as described above obtains, in a usual manner, a seamless metal can and an ultra-lightweight seamless aluminum can having a dome-shaped bottom surface by punching, drawing, ironing, and doming.

[0068] The process from punching to doming is illustrated in FIGS. 4A-4C.

[0069] That is, as illustrated in FIG. 4A, a blank sheet 21 is punched by a punching punch 23 and a punching die 25 to obtain a circular sheet 27 (punching). Next, as illustrated in FIG. 4B, a drawn cup (bottomed cylindrical body) 35 is obtained by a drawing die 31 and a drawing punch 33 (drawing). Here, as illustrated in FIG. 4C, the obtained drawn cup 35 is held in a redraw die 43 by a presser 41, is pushed downward using an ironing punch 45, is subjected to ironing through a plurality of ironing dies 47a to 47c, is subsequently subjected to doming at a lowermost position, and is pulled out from the ironing punch 45 by a stripper finger 53. The doming is performed using a hold-down ring 51 and a doming die 60 described below. By the doming, the chime portion 1b, the ground contact portion 3, and the bottom portion 5 surrounded by the ground contact portion 3 are formed.

[0070] In an ironing process as described above, although three ironing dies are disposed in FIG. 4C and ironing is performed in three stages, the number of the ironing dies is not limited to three, and may be set to an appropriate number in accordance with a degree of intended thinning, and one die may be used for ironing in one stage, or two or more dies may be disposed for ironing in a plurality of stages. It is obvious that, when a plurality of ironing dies are arranged in a processing direction and ironing is performed in a plurality stages, an inner diameter (processing diameter) becomes smaller downstream in the processing direction. In addition, when the thickness is significantly reduced, it is also necessary to adjust an approach angle of each die (an angle of a processing surface of a die on a side in contact with a workpiece) to an appropriate range.

[0071] After such ironing, doming is performed to form the dome-shaped bottom surface 9. In the doming, the shape of the dome-shaped bottom surface 9 (for example, the shape of the central dome portion 9a or the ring-shaped portion 9b) is determined, but post-processing is required to determine the shape of the rising portion 7.

[0072] The forming die used for doming includes a hold-down ring (annular holding die) 51 and a doming die 60, and doming is performed by a cooperative action of these forming dies and the punch 45. The doming die 60 is divided into a base die 61 and a doming ring 63, and these are each provided so as to independently move up and down.

[0073] As understood from FIG. 5, in the hold-down ring (annular holding die) 51, an action surface 51a at an upper end is inclined inward and downward, the chime portion 1b continuous with the lower end of the body portion 1a is formed by the action surface 51a, and the ground contact portion 3 is formed at a lower end of the action surface 51a.

[0074] In addition, the base die 61 is a die that defines the central dome portion 9a of the dome-shaped bottom surface 9, and an action surface 61a at an upper end thereof is a surface that corresponds to the central dome portion 9a of the dome-shaped bottom surface 9. In addition, the doming ring 63 is a die that defines the ring-shaped portion 9b of the dome-shaped bottom surface 9, and an action surface 63a at an upper end thereof is a surface that corresponds to the ring-shaped portion 9b. These action surfaces 61a and 63a are smoothly continuous to form the dome-shaped bottom surface 9.

[0075] In the disclosure, in order to form the ring-shaped portion 9b having a small radius of curvature at a peripheral edge portion of the central dome portion 9a, the die surface defining this portion is separated from the die surface defining the central dome portion 9a, and thus, the radius of curvature R1 at the boundary portion X between the central dome portion 9a and the ring-shaped portion 9b can be set to a predetermined value.

[0076] Doming using the forming die described above is performed by the process illustrated in FIGS. 6A-6D.

[0077] The hold-down ring 51 is urged upward by a spring (not illustrated) and, in the initial stage, as illustrated in FIG. 6A, the action surface 63a of the doming ring 63 is positioned below the action surface 51a of the hold-down ring 51, and the action surface 61a of the base die 61 is positioned further below the action surface 63a of the doming ring 63.

[0078] When the punch 45 is lowered in the state described above to push down the thinned body portion 1a, a lower end portion of the body portion 1a is pressed against the action surface 51a of the hold-down ring 51, and thus the thinned chime portion 1b is formed at the lower end of the body portion 1a, as illustrated in FIG. 6B.

[0079] Next, when the doming ring 63 is raised, the inner side of the ground contact portion 3 is pulled up to form the rising portion 7, and the action surface 63a of the doming ring 63 pushes up the surface inward of the rising portion 7 to form the ring-shaped portion 9b, which is a peripheral edge portion of the central dome portion 9a, as illustrated in FIG. 6C.

[0080] When the rising portion 7 and the ring-shaped portion 9b of the dome-shaped bottom surface 9 are formed as described above, as illustrated in FIG. 6D, the base die 61 rises with a delay, and the action surface 61a thereof is pressed against the bottom portion 5 of the can body 10, thereby forming the central dome portion 9a of the dome-shaped bottom surface 9. Thus, the dome-shaped bottom surface 9 is defined, the radius of curvature R1 at the boundary portion X between the central dome portion 9a and the ring-shaped portion 9b is defined, and the rising portion 7 and the radius of curvature R2 at the boundary portion Y between the rising portion 7 and the dome-shaped bottom surface 9 (ring-shaped portion 9b) are also defined.

[0081] Note that, in order to set the rising angle θ of the rising portion 7 and the radius of curvature R2 at the boundary portion Y to be within suitable ranges, for example, after the above step, the doming ring 63 may be lowered, and then the hold-down ring 51 may be moved inward to push the thinned chime portion 1b inward, thereby setting the rising angle θ and the radius of curvature R2 at the boundary portion Y to be within the suitable ranges.

[0082] After doming is performed as described above, the punch 45 is pulled out, the obtained formed body is separated from the punch 45 by the stripper finger 53, and thereafter, subsequent processes such as washing, drying, neck-in processing, flange processing, and coating are performed, so that the intended seamless metal can 10 is obtained. For example, even when a seamless metal can thinned by drawing and ironing using an original sheet having a metal thickness of 0.270 mm or less is obtained, it is possible to obtain the seamless metal can 10 of the disclosure that exhibits high pressure resistance and in which buckling is effectively suppressed.

[0083] The ultra-lightweight seamless aluminum can is manufactured by forming using a blank sheet of aluminum having the above-described thickness (an organic resin coating may be provided on a side corresponding to an inner surface).

[0084] The forming using the aluminum blank sheet as described above can obtain a seamless aluminum can having a dome-shaped bottom surface 9 by punching, drawing, ironing, and doming, in the same manner as the above-described method for manufacturing a seamless metal can illustrated in FIGS. 3, 4A-4C, 5, and 6A-6D.

[0085] Note that, in the ultra-lightweight seamless aluminum can, in order to secure the post-processability, as illustrated in FIG. 3, it is necessary to form the post-processing thick portion 2 (particularly, the high-strength portion 1c2) having a larger thickness than that of the body portion 1a, but the thickness at the body portion 1a is required to be significantly reduced. That is, in the ultra-lightweight seamless aluminum can of the disclosure, the difference in thickness between the high-strength portion 1c2 and the body portion 1a is increased, and therefore, rupture of a body tends to occur during ironing.

[0086] In order to prevent such rupture of a body, in the manufacture of an ultra-lightweight seamless aluminum can, as illustrated in FIG. 7, it is preferable to set the approach angle α on the processing surface of the ironing die 47 to 3 degrees or less, particularly within the range of 0.5 to 3 degrees. By arranging a plurality of ironing dies having the approach angle α set as described above and performing ironing, it is possible to form the body portion 1a having a minute thickness while effectively preventing the rupture of a body and while leaving the high-strength portion 1c2 having a large thickness. When the approach angle α is small, the tensile force in the axial direction (processing direction) of the can is reduced, and the compressive force in the thickness direction of the can is increased, making rupture of a body less likely to occur. However, if the approach angle is set to be excessively small, the ironing efficiency is lowered.

[0087] Note that with respect to a seamless aluminum can using an aluminum plate having a metal thickness of 0.270 mm or less and having a thickness (T1) of 0.085 mm at the thinnest portion of the body portion 1a, the present inventors have confirmed that the bottom portion did not buckle when the internal pressure was set to 4 kgf / cm2 and the can was dropped from a height of 20 cm.

[0088] While preferred embodiments of the disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The scope of the disclosure, therefore, is to be determined solely by the following claims.

Claims

1. A seamless metal can comprising:a cylindrical side wall;a ground contact portion continuous with the cylindrical side wall; anda bottom portion formed to close off an inside of the ground contact portion, the bottom portion being formed of a rising portion extending upward from the inside of the ground contact portion and a dome-shaped bottom surface continuous with the rising portion, whereinthe 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 is continuous with an upper end of the rising portion, anda boundary portion between the central dome portion and the ring-shaped portion is formed as a minute curved portion having a radius of curvature of less than 3.0 mm in a side cross-sectional view of the metal can.

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

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

4. The seamless metal can according to claim 3, wherein a metal thickness at a central position of the dome-shaped bottom surface is 0.270 mm or less.

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

6. An ultra-lightweight seamless aluminum can comprising: a cylindrical side wall; anda bottom portion surrounded by a ground contact portion at a lower end of the cylindrical side wall, whereinthe cylindrical side wall includes a body portion, a chime portion inclined inward from a lower end of the body portion and continuous with the ground contact portion, and a post-processing thick portion located above the body portion and having a thickness greater than that of the body portion,the bottom portion has a dome-shaped bottom surface curved upward and a rising portion extending upward from the ground contact portion toward the outside and continuous with the dome-shaped bottom surface,an aluminum thickness (T0) at a central portion of the bottom portion is 0.270 mm or less,a diameter D of the lower end of the body portion is 45 to 75 mm,an aluminum thickness (T1) at a thinnest portion of the body portion is in a range of 0.080 to 0.105 mm, anda total aluminum weight is 14g or less.

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

8. The ultra-lightweight seamless aluminum can according to claim 6, wherein a ratio H / D of a height H of the cylindrical side wall to a diameter D of the lower end of the body portion is in a range of 1.6 to 2.7.

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

10. The ultra-lightweight seamless aluminum can according to claim 6, wherein the post-processing thick portion is formed of a tapered portion in which a thickness gradually increases upward from an upper end of the body portion, and a high-strength portion located above the tapered portion and having an aluminum thickness (T3) in a range of 50% or more of the aluminum thickness (T0) at the central portion of the bottom portion.

11. The ultra-lightweight seamless aluminum can according to claim 10, wherein an axial length L1 of the body portion is in a range of 60 to 95% of a height H of the cylindrical side wall, and an axial length L2 of the high-strength portion is in a 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 on the dome-shaped bottom surface of the bottom portion, an inflection portion in which a radius of curvature (R1) becomes minimal is formed in a ring shape at a position spaced apart from an 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 a range of less than 3.0 mm.

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