Seamless metal can

Abstract

The present invention provides a seamless metal can having a dome-shaped bottom surface that has high pressure resistance and effectively prevents buckling, or an ultra-lightweight seamless aluminum can having significantly reduced thickness and effectively preventing can body cracking during molding, in the seamless metal can (10), the bottom (5) of which is formed by an upright part (7) extending upward from the inner side of a grounding part (3) and a dome-shaped bottom surface (9) connected with the upright part (7), the dome-shaped bottom surface (9) is provided with a central dome part (9a) and an annular part (9b) formed in a manner of surrounding the central dome part (9a), and the annular part (9b) is connected with the upper end of the upright part (7) and has the following characteristics (i) or (ii). (i) The boundary portion (X) between the center dome portion (9a) and the annular portion (9b) is a minimum curved portion having a radius of curvature of less than 3.0 mm. (ii) The aluminum thickness (T0) at the center of the bottom portion is 0.270 mm or less, the diameter (D) of the lower end of the main body portion (1a) is 45-75 mm, the metal (aluminum) thickness of the thinnest wall portion of the main body portion (1a) is 0.080-0.105 mm, and the total weight of aluminum is 14 g or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a seamless metal can having a dome-shaped bottom surface. BACKGROUND

[0002] Generally, for a seamless can or the like obtained by forming processing (punching, drawing processing, and thinning processing) of a metal, in order to improve pressure resistance and stabilize the setting, the bottom is recessed into a dome shape, forming a dome-shaped bottom surface. The forming means for forming such a dome-shaped bottom surface is called doming, which is performed by recessing the bottom surface of a cylinder into a dome shape while holding the bottom periphery of the cylinder with a ring-shaped mold called a retaining ring and pushing up a doming die from between the ring-shaped molds (Patent Document 1).

[0003] However, in recent years, from the viewpoints of efficient use of metal materials, lightweight, and the like, there is a strong demand to form a lightweight seamless can using a metal sheet having a small thickness. In a seamless can formed from such a thin-walled metal sheet, in particular, buckling of the bottom becomes a problem, and in the dome-shaped bottom surface of the conventionally known form, there is a problem that the pressure resistance is insufficient and buckling easily occurs.

[0004] For example, in Patent Document 2 and Patent Document 3 described below, a seamless metal can having a dome-shaped bottom surface of a certain form is disclosed, but in a thin-walled seamless metal can formed using a metal sheet (blank) having a thickness thinner than 0.270 mm, for example, buckling easily occurs due to low pressure resistance, and the current situation is that further improvement in pressure resistance is required when thinning.

[0005] Further, in a lightweight seamless aluminum can after thinning, of course, breakage of the can body during forming becomes a problem, and the degree of thinning or lightweight is limited. For example, in Patent Document 4 to Patent Document 6 described below, an aluminum can having a dome-shaped bottom surface is proposed, but since breakage of the can body becomes a problem, thinning is considerably limited, and in reality, it is not possible to obtain a lightweight seamless aluminum can that can be practically used.

[0006] Further, buckling of the bottom or the like becomes a problem, and in the conventionally known form of the dome-shaped bottom surface, it is also pointed out that if thinning exceeds a certain level, buckling easily occurs.

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-177289

[0008] Patent Document 2: Japanese Patent Application Publication No. 2000-211624

[0009] Patent Document 3: Japanese Patent No. 6713741

[0010] Patent Document 4: Japanese Patent No. 6977302

[0011] Patent Document 5: Japanese Patent No. 5102042

[0012] Patent Document 6: Japanese Patent Application Laid-Open No. 2023-85679 SUMMARY

[0013] PROBLEMS TO BE SOLVED BY THE INVENTION

[0014] Therefore, an object of the present application is to provide a seamless metal can having a dome-shaped bottom surface in a form in which pressure resistance is high and buckling is effectively prevented.

[0015] Another object of the present application is to provide a super-lightweight seamless aluminum can in which can body breakage during molding is effectively prevented and thinning is significantly performed.

[0016] Still another object of the present application is to provide a seamless metal can molded using a metal sheet having a metal thickness of 0.270 mm or less, particularly 0.26 mm or less.

[0017] SOLUTION TO THE PROBLEM

[0018] According to the present application, there is provided a seamless metal can having a cylindrical side wall, a land portion connected to the cylindrical side wall, and a bottom portion formed so as to close the inside of the land portion, the bottom portion being formed of a standing portion extending upward from the inside of the land portion and a dome-shaped bottom surface connected to the standing portion, the seamless metal can being characterized in that the dome-shaped bottom surface has a central dome portion and an annular portion formed so as to surround the central dome portion, the annular portion being connected to the upper end of the standing portion, and in that, in a side cross-sectional view of the metal can, the boundary portion of the central dome portion and the annular portion becomes an extremely small curved portion having a radius of curvature of less than 3.0 mm.

[0019] In the seamless metal can of the present application, it is preferable that,

[0020] (1) in a side cross-sectional view of the metal can, the standing portion stands upward from the land portion toward the outside and upward;

[0021] (2) in a side cross-sectional view of the metal can, the standing portion stands from the land surface at an angle θ in the range of 95 degrees to 125 degrees with respect to the land surface, the joint portion of the standing portion and the annular portion becoming an extremely small curved portion having a radius of curvature of 1.2 mm or less;

[0022] (3) the metal thickness at the central position of the dome-shaped bottom surface is 0.270 mm or less; and

[0023] (4) the metal is aluminum.

[0024] Furthermore, according to the present invention, an ultra-lightweight seamless aluminum can is provided, the ultra-lightweight seamless aluminum can having a cylindrical sidewall and a bottom surrounded by a grounding portion at the lower end of the cylindrical sidewall, the ultra-lightweight seamless aluminum can being characterized in that the cylindrical sidewall is formed by a main body, a raised edge, and a post-processing thick wall portion, the raised edge is inclined inward from the lower end of the main body and connected to the grounding portion, the post-processing thick wall portion is located above the main body and has a thickness greater than the main body, the bottom has an upwardly curved dome-shaped bottom surface and an upright portion extending outward and upward from the grounding portion and 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 at the lower end of the main body is 45 mm to 75 mm, the aluminum thickness (T1) at the thinnest wall portion of the main body is in the range of 0.080 mm to 0.105 mm, and the total aluminum weight of the ultra-lightweight seamless aluminum can is in the range of 14 g or less.

[0025] In the ultralightweight seamless aluminum can of the present invention, preferably,

[0026] (1) The aluminum thickness (T1) at the thinnest wall portion of the main body is less than 0.087 mm;

[0027] (2) The ratio H / D of the height H of the cylindrical sidewall to the diameter D of the lower end of the main body is in the range of 1.6 to 2.7;

[0028] (3) The aluminum thickness (T2) at the convex edge is less than 95% of the aluminum thickness (T0) at the center of the bottom;

[0029] (4) The thick-walled portion for post-processing is formed by a tapered portion and a high-strength portion. The thickness of the tapered portion gradually increases from the upper end of the main body portion upwards. The high-strength portion is located above the tapered portion and the aluminum thickness (T3) of the high-strength portion is within 50% or more of the aluminum thickness (T0) at the center of the bottom portion.

[0030] (5) The axial length L1 of the main body is in the range of 60% to 95% of the height H of the cylindrical sidewall, and the axial length L2 of the high-strength part is in the range of 5% to 40% of the height H of the cylindrical sidewall.

[0031] (6) On the dome-shaped bottom surface, at a position separating from the upper end of the raised portion, an inflection point with a very small radius of curvature (R1) is formed in a ring shape; and

[0032] (7) The radius of curvature (R1) is less than 3.0 mm.

[0033] The effects of the invention

[0034] The seamless metal can of the present invention has a dome-shaped bottom surface that is recessed into a dome shape at the bottom formed in a manner that closes the inside of the grounding portion, but has the following significant features: an annular portion is formed in a manner that surrounds the central dome of the dome-shaped bottom surface; and the junction of the annular portion and the central dome is a minimally curved portion with a radius of curvature of less than 3.0 mm.

[0035] That is, the dome-shaped bottom surface becomes a curved surface with a large and gentle radius of curvature in the central part, resulting in a shape with the largest radius of curvature at the center. When internal pressure is applied axially to a seamless metal can, since the internal pressure is concentrated in the central part of this near-planar shape, the thinner the metal blank used for forming (corresponding to the metal thickness at the center of the dome-shaped bottom surface), the easier it is to bend (reversal of concavity and convexity). However, in this invention, an annular portion with a small radius of curvature is formed in a way that surrounds the central dome with a large radius of curvature. The radius of curvature at the junction of this annular portion and the central dome (i.e., the boundary portion) is a minimum value of less than 3.0 mm. That is, one end of the annular portion (the end of the central dome) becomes an inflection point, resulting in a significantly curved shape. Moreover, the other side of the annular portion is connected to the upper end of the upright portion connected to the ground portion, and the other end of such an annular portion also becomes a significantly curved shape. As can be understood from this form, in this invention, since the annular portion with its large bends at both ends is connected to the central rounded top with its nearly flat surface, the axial load of the seamless metal can is absorbed and mitigated by the annular portion, thereby more effectively suppressing buckling.

[0036] Therefore, in this invention, extremely thin metal blanks (e.g., less than 0.270 mm) can be used for forming seamless metal cans, which is a significant advantage of this invention.

[0037] Furthermore, the ultra-lightweight seamless aluminum can of the present invention has the following basic form: the diameter D of the lower end of the main body (corresponding to the diameter of the upper end of the convex edge) is 45mm to 75mm, and the aluminum thickness (T0) at the center of the bottom is 0.270mm or less. In this basic form, the aluminum thickness (T0) at the center of the bottom is comparable to the original aluminum sheet (also called a blank) used in the forming process. This is because, when forming a seamless can by thinning the wall based on a thinning process, the bottom is not thinned based on a thinning process. That is, the seamless aluminum can of the present invention is formed using a metal blank with an extremely thin thickness of 0.270mm or less, but apart from this, the aluminum thickness (T1) at the thinnest wall of the main body is in the range of 0.080mm to 0.105mm, and the thinning is maximized. The seamless aluminum can of the present invention achieves an ultra-lightweight total aluminum weight of 14g or less by maintaining an ultra-thin wall such as a diameter D of 45mm to 75mm at the lower end of the main body. For example, despite having a content of 500 mL, its total aluminum weight is less than 14 g, and such ultra-lightweight design is achieved for the first time in this invention. Attached Figure Description

[0038] Figure 1 This is a schematic side sectional view showing the overall seamless metal can of the present invention.

[0039] Figure 2 It is Figure 1 An enlarged partial side view of the bottom of a seamless metal can.

[0040] Figure 3 This is a side sectional view showing the state of the seamless aluminum can before and after post-processing, with the cylindrical sidewall enlarged.

[0041] Figure 4 This is a diagram showing a general outline of the process used in making seamless metal cans.

[0042] Figure 5 It means in Figure 4 A diagram of the forming mold used in the arching process.

[0043] Figure 6 It is used for explanation Figure 4 The diagram shows the arching process.

[0044] Figure 7 This diagram illustrates the thinning process of a seamless aluminum can. Detailed Implementation

[0045] <The Form of Seamless Metal Cans>

[0046] The seamless metal can of the present invention is obtained by punching, deep drawing, and re-deep drawing-thinning a blank made of a metal sheet, particularly a thin-walled aluminum sheet made of aluminum or aluminum alloy, followed by arching the bottom. Figure 1 The shape shown is then subjected to post-processing such as cleaning and drying, outer surface printing, topcoat varnish coating and baking, inner surface coating coating and baking, necking, and flange processing before use. That is, the contents are filled and the cover material is fixed for sale.

[0047] Reference Figure 1 The seamless metal can of the present invention, generally indicated by 10, has a cylindrical sidewall 1, a grounding portion 3 connected to the lower end of the cylindrical sidewall 1, and a bottom 5 provided in a manner that closes the inner side of the grounding portion 3. That is, the bottom 5 is the area surrounded by the grounding portion 3.

[0048] The cylindrical sidewall 1 has: a main body portion 1a, the outer surface of which is a straight cylindrical shape; and a convex edge portion 1b, which slopes inward from the lower end of the main body portion 1a and is connected to the grounding portion 3. In addition, the upper part of the main body portion 1a is connected to a necked portion 1c formed by post-processing, and a flange portion 1d is formed at the upper end of the necked portion 1c.

[0049] On the other hand, the bottom 5 is composed of an upright part 7 that rises from the ground part 3 toward the inside and a dome-shaped bottom surface 9 connected to the upper end of the upright part 7.

[0050] and Figure 1 Please refer to the enlarged representation of the bottom 5. Figure 2 The dome-shaped bottom surface 9 is divided into two regions: a central dome 9a and an annular portion 9b. The central dome 9a has a large radius of curvature, forming a gently curvature surface that is close to a plane. The annular portion 9b is formed to surround the central dome 9a, and its radius of curvature is smaller than that of the central dome 9a. That is, the inner side of the annular portion 9b is connected to the circumferential end of the central dome 9a (the boundary X between the annular portion 9b and the central dome 9a), and the outer side of the annular portion 9b is connected to the upper end of the upright portion 7 (the boundary Y between the dome-shaped bottom surface 9 and the upright portion 7).

[0051] It should be noted that in the dome-shaped bottom surface 9, the boundary X between the annular portion 9b and the central dome 9a becomes an inflection point. Furthermore, the upper end of the upright portion 7 (the aforementioned boundary portion Y) is the portion where the tangent Q of the surface forming the upright portion 7 is perpendicular to the ground surface G, and such an upper end also becomes an inflection point.

[0052] In the dome-shaped bottom surface 9 of this form, in the seamless metal can of the present invention, the radius of curvature R1 of the boundary X between the central dome 9a and the annular portion 9b is a minimum value (i.e., inflection point) of less than 3.0 mm, preferably less than 2.5 mm, and most preferably less than 2.0 mm. Therefore, even when the metal sheet (blank) used for forming such a seamless metal can 10 is thinned through deep drawing, preferably less than 0.245 mm, more preferably less than 0.230 mm, and most preferably between 0.215 mm and 0.200 mm, the pressure resistance of the seamless metal can 10 can be improved, and buckling of the bottom 5 can be effectively avoided.

[0053] For example, experiments have confirmed that if the radius of curvature R1 is greater than the above value, the top with a large radius of curvature will be directly continuous with the upright part 7, which will easily cause the bottom 5 to buckle. As in this invention, by setting the radius of curvature R1 to a smaller value, the annular part 9b can effectively absorb the axial load applied to the seamless metal can 10, and can effectively suppress the buckling of the bottom 5.

[0054] It should be noted that the thickness of the metal sheet (blank) used for forming is equivalent to the thickness T0 at the center O of the central dome 9a. That is, at the center O of the central dome 9a, since no thinning process is performed, the metal thickness T0 of this part reflects the metal thickness of the blank. In addition, in the protruding edge 1b that connects the grounding part 3 and the main body part 1a, thinning based on thinning is performed. For example, when the metal thickness of the blank is within the aforementioned range, the thickness of the protruding edge 1b is usually thinned to less than 95% of the thickness of the metal sheet (blank). Furthermore, in the case of seamless aluminum cans used as beverage cans, the thickness at the thinnest part of the main body part 1a is 30% to 50% of the metal thickness T0.

[0055] In the bottom 5 of the above-described shape, to further enhance the buckling suppression function of the annular portion 9b, the upright portion 7 preferably rises outward and upward from the grounding portion 3, and particularly preferably rises from the grounding surface G at an angle θ of 95 degrees to 125 degrees relative to the grounding surface G. In this case, the upper end of the upright portion 7 (the boundary Y between the dome-shaped bottom surface 9 and the upright portion 7) becomes an inflection point, but most preferably its radius of curvature R2 is 1.2 mm or less, particularly around 1.2 mm to 0.5 mm. By adopting this configuration, the mobility of the two ends (X and Y) of the annular portion 9b as fulcrums is improved, and the buckling suppression function of the annular portion 9b is further enhanced.

[0056] Furthermore, in this invention, the length d of the annular portion 9b (the interval between the boundary portion X and the boundary portion Y) is preferably 10% to 30% of the radius D1 of the dome-shaped bottom surface 9, and particularly preferably 15% to 25% of the radius D1. By setting the length d of the annular portion 9b to such a size, the pressure resistance of the seamless metal can 10 is maximized, and the buckling of the dome-shaped bottom surface 9 can be suppressed most reliably.

[0057] It should be noted that the shape of the bottom 5 mentioned above can be formed by the arching process described later.

[0058] In this invention, there are no particular limitations on the metal constituting the seamless metal can 10; it can be any metal or alloy. However, considering factors such as lightweight and thin-walled processability, aluminum or aluminum alloys are preferred. Furthermore, to maximize the advantages of this invention, it is preferable to form a seamless metal can by molding a resin-coated metal sheet with one side coated with organic resin (e.g., PET) as a blank, with the inner surface coated with resin. In this case, the aforementioned thickness T0 refers to the thickness of the metal sheet (blank) excluding the thickness of the resin coating.

[0059] <The form of ultralightweight seamless aluminum cans>

[0060] The ultralight seamless aluminum can 10 of the present invention has the same basic form as the seamless metal can described above. The cylindrical sidewall 1 has: a main body portion 1a; and a convex edge portion 1b, which slopes inward from the lower end of the main body portion 1a and is connected to the grounding portion 3. The diameter D of the lower end of the main body portion 1a (corresponding to the upper end of the convex edge portion 1b) is in the range of 45 mm to 75 mm.

[0061] It should be noted that, in Figure 1 and Figure 3 In the example shown, the outer surface of the main body 1a is a straight cylindrical shape, but it is not limited to this shape. Sometimes, unevenness is formed on the outer surface of the main body 1a through post-processing. In such cases, the lowermost inflection point of the main body 1a also becomes the lower end of the main body 1a, which is the boundary with the convex edge 1b, and has a diameter D as described above.

[0062] Furthermore, the upper part of the main body 1a becomes a thick-walled part 2 for post-processing, having a thickness greater than that of the main body 1a. For example, from... Figure 3 As can be understood, the post-processing thick-walled portion 2 has a tapered portion 1c1 whose thickness gradually increases from the upper end of the main body portion 1a toward the top, and a thick-walled high-strength portion 1c2 is formed above the tapered portion 1c1.

[0063] The aforementioned post-processing involves necking, flange machining, and other post-processing on the thick-walled portion 2. Through such post-processing, a necked portion 1c with a diameter smaller than that of the main body portion 1a and a flat flange portion 1d are formed by deep drawing (see reference).Figure 3 ).

[0064] In particular, the aluminum thickness (T0) at the center O of the bottom 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 mm to 0.200 mm. That is, the seamless aluminum can 10 is thinned by using an aluminum sheet of such thickness as a blank for deep drawing and thinning.

[0065] Furthermore, the ultra-lightweight seamless aluminum can 10 of the present invention uses the aforementioned aluminum sheet as a blank and thins the wall to an extent that is not seen in conventional seamless cans. Specifically, the aluminum thickness (T1) at the thinnest part of the main body 1a is 0.080mm to 0.105mm, 0.080mm to 0.100mm, 0.080mm to 0.095mm, especially 0.080mm to 0.090mm, especially 0.080mm to 0.085mm.

[0066] It should be noted that the thickness of the main body 1a is not uniform, but the thickness is adjusted according to the diameter and number of the thinning die head, the shape of the punch, etc., as described later. Typically, such as... Figure 3 As shown, the thickness of the main body 1a is such that it is a tapered portion 1c1 that is thinnest at the top and gradually thickens upwards. That is, the outer surface of the main body 1a is upright relative to the contact surface G, but its inner surface is slightly inclined. Therefore, the position of the thinnest wall portion varies depending on the thinning processing conditions, such as the diameter and number of thinning dies and the shape of the punches.

[0067] In the ultra-lightweight seamless aluminum can 10 of the present invention, which features thin walls as described above, although the blank used for forming is thin, it has a very high height. For example, the ratio H / D of the height H of the cylindrical sidewall 1 to the diameter D of the lower end of the main body 1a is 1.6 to 2.7, particularly in the range of 1.7 to 2.6. Thus, due to the significant thinning of the walls, it has a high height H, and consequently, the total aluminum weight of the seamless aluminum can 10 of the present invention is 14g or less. For example, even when the contents are about 500ml with a flange 1d formed at the upper end of the cylindrical sidewall 1, the total aluminum weight is still 14g or less, making it remarkably ultra-lightweight.

[0068] Furthermore, in the seamless aluminum can 10 of the present invention having the form described above, the convex edge 1b connected to the lower end of the main body 1a is also thinned. For example, the aluminum thickness (T2) at the convex edge 1b is less than 95% of the aluminum thickness (T0) at the center O of the bottom 5, and T2 ≥ T1 relative to the aluminum thickness (T1) at the thinnest wall portion. The thickness of the convex edge 1b gradually decreases from the grounding portion 3 toward the lower end of the main body 1a. The aluminum thickness (T2) is the thickness of the thinnest portion of the convex edge 1b.

[0069] In the seamless aluminum can 10 with thin walls like this, as described above, the upper part of the main body 1a becomes a post-processing thick wall part 2 with a thickness greater than that of the main body 1a. The post-processing thick wall part 2 is formed by a tapered part 1c1 whose thickness gradually increases from the upper end of the main body 1a upwards and a high-strength thick wall part 1c2 located above the tapered part 1c1. With this configuration, the necked part 1c and the flat flange part 1d can be formed in a way that does not produce molding defects through post-processing of the upper region of the cylindrical sidewall 1.

[0070] For example, to reliably prevent poor forming during post-processing, the aluminum thickness (T3) of the high-strength portion 1c2 is preferably 50% or more of the aluminum thickness (T0) at the center of the bottom 5, and particularly preferably 55% or more. More preferably, it is 50%–80%, 50%–70%, 50%–60%, or 55%–60% of the aluminum thickness at the center of the bottom 5. That is, the high-strength portion 1c2 (corresponding to the flange portion 1d) can also be the same thickness as the blank, without thinning based on thinning. Moreover, to ensure post-processability and effectively perform thinning, the axial length L1 of the main body portion 1a is preferably in the range of 60%–95%, particularly 70%–95%, of the height H of the cylindrical sidewall 1, and the axial length L2 of the high-strength portion is in the range of 5%–40%, particularly 5%–30%, of the height H of the cylindrical sidewall 1.

[0071] Furthermore, in ultra-lightweight seamless aluminum cans, such as Figure 2 As shown, in order to prevent the reduction in pressure resistance caused by the thinning of the blank with a thinner aluminum thickness and the warping generated at the bottom 5, it is also preferable that the bottom 5 has an upright portion 7 extending upward from the ground portion 3 and a dome-shaped bottom surface 9 extending from the upper end of the upright portion 7 in a dome shape. The dome-shaped bottom surface 9 is composed of a central dome 9a and an annular portion 9b. The central dome 9a is a gently curved surface with a large radius of curvature and close to a plane. The annular portion 9b is formed in a way that surrounds the central dome 9a and its radius of curvature is smaller than that of the central dome 9a.

[0072] Furthermore, the upper end of the upright portion 7 (the aforementioned boundary portion Y) is the portion where the tangent Q of the surface forming the upright portion 7 is perpendicular to the ground surface G, and such an upper end is also called an inflection point.

[0073] In ultra-lightweight seamless aluminum cans, the radius of curvature R1 of the boundary X between the central dome 9a of the dome-shaped bottom surface 9 and the annular portion 9b is preferably less than 3.0 mm, more preferably less than 2.5 mm, and most preferably less than 2.0 mm (i.e., the inflection point). Thus, as described above, even though the walls are thinned by deep drawing using a very thin sheet of aluminum (e.g., less than 0.27 mm), the pressure resistance of the seamless aluminum can 10 can be improved, and buckling of the bottom 5 can be more reliably prevented.

[0074] Furthermore, in the ultra-lightweight seamless aluminum can, in the bottom 5 of the aforementioned shape, to significantly improve the buckling suppression function of the annular portion 9b, the upright portion 7 rises outward and upward from the grounding portion 3, and is particularly preferably upright from the grounding surface G at an angle θ of 95 degrees to 125 degrees relative to the grounding surface G. In this case, the radius of curvature R2 of the inflection point at the upper end of the upright portion 7 (the boundary Y between the dome-shaped bottom surface 9 and the upright portion 7) is preferably 1.4 mm or less, particularly around 1.3 mm to 0.7 mm. By adopting this configuration, the mobility of the two ends (X and Y) of the annular portion 9b as fulcrums is improved, and the buckling suppression function of the annular portion 9b is further enhanced.

[0075] Furthermore, in the ultra-lightweight seamless aluminum can, the length d of the annular portion 9b (the interval between the boundary portion X and the boundary portion Y) is preferably set to 10% to 30%, particularly 15% to 25%, of the radius D of the dome-shaped bottom surface 9. By setting the length d of the annular portion 9b to such a size, the metal can 10 has the highest pressure resistance and can most reliably suppress the buckling of the bottom 9.

[0076] <Manufacturing of Seamless Metal Cans and Ultralight Seamless Aluminum Cans>

[0077] The seamless metal can and ultralight seamless aluminum can of the present invention, having the form described above, are manufactured by molding a blank of the aforementioned metal (aluminum or aluminum alloy) (which may also have an organic resin coating on one side corresponding to the inner surface).

[0078] Seamless metal cans and ultra-lightweight seamless aluminum cans with dome-shaped bottoms are obtained by forming the metal blanks as described above, as is usually done through punching, drawing, thinning, and dotting.

[0079] The process from punching to arching is shown below. Figure 4 .

[0080] That is, such as Figure 4 As shown in (a), the blank 21 is punched using a punching punch 23 and a punching die 25 to obtain a round plate 27 (punching process). Next, as... Figure 4As shown in (b), a deep-drawn cup (bottomed cylindrical body) 35 is obtained using a deep-drawing die 31 and a deep-drawing punch 33 (deep-drawing process). Here, as Figure 4 As shown in (c), the drawn cup 35 is held in the redraw die 43 by the pressing member 41, and then pushed downward by the thinning punch 45. After thinning through multiple thinning dies 47a-47c, it is arched at the lowest position and pulled out from the thinning punch 45 by the stripper finger 53. This arching is performed using the clamping ring 51 and the arching die 60, which will be described later. This arching forms the aforementioned convex edge 1b, the grounding part 3, and the bottom 5 surrounded by the grounding part 3.

[0081] In the thinning process described above, in Figure 4 In (c), three thinning dies are configured to perform thinning in three segments. However, the number of thinning dies is not limited to three; it can be set to an appropriate number depending on the desired degree of thinning. One die can be used for thinning in one segment, or two or more dies can be configured for thinning in multiple segments. Of course, when multiple thinning dies are arranged along the processing direction and thinning is performed in multiple segments, the inner diameter (processing diameter) decreases as it moves downstream in the processing direction. Furthermore, for significant thinning, the approach angle (the angle of the processing surface of the die on the side that contacts the workpiece) of each die needs to be adjusted to an appropriate range.

[0082] After the thinning process described above, the surface is arched to form a dome-shaped bottom surface 9. During this arching process, the shape of the dome-shaped bottom surface 9 (e.g., the shape of the central dome 9a and the annular portion 9b) is determined, but post-processing is required to determine the shape of the raised portion 7.

[0083] The forming die for arching consists of a clamping ring (annular retaining die) 51 and an arching die head 60. Arching is achieved through the cooperative action of these forming dies and the punch 45. The arching die head 60 is divided into a base die head 61 and an arching ring 63, which are arranged to move up and down independently.

[0084] As from Figure 5 As can be understood, the upper end of the clamping ring (ring-shaped retaining mold) 51 has an inward-facing and downward-sloping working surface 51a, through which a convex edge 1b connected to the lower end of the main body 1a is formed, and a grounding part 3 is formed at the lower end of the working surface 51a.

[0085] Furthermore, the base mold 61 is a mold that defines the central dome 9a of the dome-shaped bottom surface 9, and its upper end working surface 61a corresponds to the central dome 9a of the dome-shaped bottom surface 9. Additionally, the arched ring 63 is a mold that defines the annular portion 9b of the dome-shaped bottom surface 9, and its upper end working surface 63a corresponds to the annular portion 9b. These working surfaces 61a and 63a are smoothly connected to form the dome-shaped bottom surface 9.

[0086] In this invention, since an annular portion 9b with a small radius of curvature is formed at the periphery of the central round top 9a, the mold surface defining this portion is separated from the mold surface defining the central round top 9a. As a result, the radius of curvature R1 at the boundary X between the central round top 9a and the annular portion 9b can be set to a predetermined value.

[0087] The arching using the above-mentioned molding die passes through Figure 6 The process shown is carried out.

[0088] Although not shown in the diagram, the clamping ring 51 is pushed upward by the spring, as... Figure 6 As shown in (a), in the initial stage, the working surface 63a of the arching ring 63 is located below the working surface 51a of the clamping ring 51, and the working surface 61a of the base mold head 61 is located even below the working surface 63a of the arching ring 63.

[0089] When the punch 45 is lowered and the thinned main body 1a is pressed down under the above conditions, as follows: Figure 6 As shown in (b), the lower end of the main body 1a is pressed against the working surface 51a of the clamping ring 51, thereby forming a thin-walled convex edge 1b at the lower end of the main body 1a.

[0090] Next, when the arched ring 63 is raised, as... Figure 6 As shown in (c), the inner side of the grounding part 3 is pulled up to form the upright part 7, and the working surface 63a of the arched ring 63 pushes the surface that is closer to the inside of the upright part 7, thereby forming the annular part 9b that becomes the peripheral part of the central dome 9a.

[0091] As described above, when the annular portion 9b of the raised portion 7 and the dome-shaped bottom surface 9 is formed, such as Figure 6 As shown in (d), the base mold head 61 rises with a delay, and its working surface 61a is pressed against the bottom 5 of the tank body 10, thereby forming the central dome 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 X of the central dome 9a and the annular portion 9b is defined, and further, the radius of curvature R2 at the boundary Y of the standing portion 7 and the dome-shaped bottom surface 9 (annular portion 9b) is also determined.

[0092] It should be noted that, in order to set the erection angle θ of the erection part 7 and the radius of curvature R2 at the boundary part Y within an appropriate range, for example, after the above process, the arching ring 63 is lowered, and then the pressing ring 51 is moved inward to press the thinned convex edge 1b inward, thereby setting the erection angle θ and the radius of curvature R2 at the boundary part Y within an appropriate range.

[0093] After the arching process described above, the punch 45 is pulled out, and the resulting molded body is pulled apart from the punch 45 by the peeler claw 53. Subsequent processes such as cleaning, drying, necking, flange processing, and painting are then performed to obtain the desired seamless metal can 10. For example, even when a thin-walled seamless metal can is obtained by drawing and thinning a base plate with a metal thickness of 0.270 mm or less, a seamless metal can exhibiting high pressure resistance and effectively suppressing buckling can be obtained.

[0094] The ultralight seamless aluminum can is manufactured by forming a blank of aluminum of the above thickness (which may have an organic resin coating on one side corresponding to the inner surface).

[0095] The forming and processing of aluminum blanks as described above Figures 3 to 6 The manufacturing method of the seamless metal can shown above is similar, and a seamless aluminum can with a dome-shaped bottom surface 9 is obtained by punching, drawing, thinning and arching.

[0096] It should be noted that in ultra-lightweight seamless aluminum cans, in order to ensure post-processing properties, such as... Figure 3 As shown, a post-processing thick-walled portion 2 (especially the high-strength portion 1c2) needs to be formed with a thickness greater than that of the main body portion 1a, but the thickness of the main body portion 1a must be significantly reduced. That is, in the ultra-lightweight seamless aluminum can of the present invention, due to the increased thickness difference between the thickness of the high-strength portion 1c2 and the thickness of the main body portion 1a, the can body is prone to cracking during the thinning process.

[0097] To prevent such can body breakage, in the manufacturing of ultra-lightweight seamless aluminum cans, such as... Figure 7 As shown, it is preferable to set the approach angle α at the machining surface of the thinning die 47 to 3 degrees or less, and particularly preferably to a range of 0.5 degrees to 3 degrees. By configuring multiple thinning dies with such approach angle α for thinning processing, it is possible to effectively prevent can body breakage and form an extremely thin main body 1a while retaining the thick high-strength portion 1c2. If the approach angle α is small, the tensile force in the axial direction (machining direction) of the can is smaller, and the compressive force in the thickness direction of the can is larger, making it less likely for the can body to break. However, if the approach angle is set too small, the thinning efficiency will decrease.

[0098] It should be noted that for a seamless aluminum can using an aluminum plate with a metal thickness of 0.270 mm or less and a thickness (T1) of 0.085 mm at the thinnest wall portion of the main body 1a, the inventors confirmed that when the internal pressure is set to 4 kgf / cm2 and the can is dropped from a height of 20 cm, the bottom does not buckle.

[0099] Explanation of reference numerals in the attached figures

[0100] 1: Cylindrical sidewall;

[0101] 1a: Main body;

[0102] 1b: Convex edge;

[0103] 1c: Neck retraction;

[0104] 1c1: Conical part;

[0105] 1c2: High-strength section;

[0106] 1d: Flange portion;

[0107] 2: Thick-walled section for post-processing;

[0108] 3: Grounding part;

[0109] 5: Bottom;

[0110] 7: Erect part;

[0111] 9: Dome-shaped base;

[0112] 9a: Central rounded top;

[0113] 9b: Annular portion;

[0114] 10: Seamless metal can;

[0115] X: The boundary between the central round top 9a and the annular part 9b;

[0116] R1: Radius of curvature at the boundary X;

[0117] Y: The boundary between the raised part and the dome-shaped bottom surface 9 (ring-shaped part);

[0118] R2: Radius of curvature at the boundary Y;

[0119] D: Bottom diameter;

[0120] H: Height of the cylindrical sidewall;

[0121] T0: Aluminum thickness at the bottom center;

[0122] T1: Aluminum thickness at the thinnest part of the wall;

[0123] T2: Aluminum thickness at the convex edge 1b (T2);

[0124] T3: Aluminum thickness at the high-strength section 1c2;

[0125] L1: Axial length L1 of the main body 1a;

[0126] L2: Axial length of the high-strength section.

Claims

1. A seamless metal can, wherein, The seamless metal can has a cylindrical sidewall, a grounding portion connected to the cylindrical sidewall, and a bottom formed to close the inner side of the grounding portion. The bottom is formed by an upright portion and a dome-shaped bottom surface. The upright portion extends upward from the inner side of the grounding portion, and the dome-shaped bottom surface is connected to the upright portion. The dome-shaped bottom surface has a central dome and an annular portion formed to surround the central dome. The annular portion is connected to the upper end of the upright portion, and... In the side sectional view of the metal can, the boundary between the central dome and the annular portion is a minimally curved portion with a radius of curvature of less than 3.0 mm.

2. The seamless metal can according to claim 1, wherein, In the side sectional view of the metal can, the erected portion rises outward and upward from the ground portion.

3. The seamless metal can according to claim 2, wherein, In the side sectional view of the metal can, the erected portion stands upright from the ground surface at an angle θ of 95 to 125 degrees relative to the ground surface, and the joint between the erected portion and the annular portion forms a minimally curved portion with a radius of curvature of less than 1.2 mm.

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

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

6. An ultralightweight seamless aluminum can, the ultralightweight seamless aluminum can having a cylindrical sidewall and a bottom surrounded by a grounding portion at the lower end of the cylindrical sidewall, characterized in that, The cylindrical sidewall is formed by a main body, a convex edge, and a thick-walled portion for post-processing. The convex edge slopes inward from the lower end of the main body and is connected to the grounding portion. The thick-walled portion for post-processing is located above the main body and has a thickness greater than the main body. The bottom has an upwardly curved dome-shaped bottom surface and an upright portion extending outward and upward from the grounding portion and connected to the dome-shaped bottom surface. The aluminum thickness T0 at the center of the bottom is less than 0.270 mm, and the diameter D of the lower end of the main body is 45 mm to 75 mm. The aluminum thickness T1 at the thinnest wall section of the main body is in the range of 0.080 mm to 0.105 mm, and The total weight of the aluminum in the ultralight seamless aluminum can is less than 14g.

7. The ultralightweight seamless aluminum can according to claim 6, wherein, The aluminum thickness T1 at the thinnest wall section of the main body is less than 0.087 mm.

8. The ultralightweight seamless aluminum can according to claim 6, wherein, The ratio H / D of the height H of the cylindrical sidewall to the diameter D of the lower end of the main body is in the range of 1.6 to 2.

7.

9. The ultralightweight seamless aluminum can according to claim 6, wherein, The aluminum thickness T2 at the convex edge is less than 95% of the aluminum thickness T0 at the center of the bottom.

10. The ultralightweight seamless aluminum can according to claim 6, wherein, The thick-walled portion for post-processing is formed by a tapered portion and a high-strength portion. The thickness of the tapered portion gradually increases from the upper end of the main body portion upwards. The high-strength portion is located above the tapered portion, and the aluminum thickness T3 of the high-strength portion is within 50% or more of the aluminum thickness T0 at the center of the bottom.

11. The ultralightweight seamless aluminum can according to claim 10, wherein, The axial length L1 of the main body is in the range of 60% to 95% of the height H of the cylindrical sidewall, and the axial length L2 of the high-strength part is in the range of 5% to 40% of the height H of the cylindrical sidewall.

12. The ultralightweight seamless aluminum can according to claim 6, wherein, On the dome-shaped bottom surface, at the position where it separates from the upper end of the upright portion, a small inflection point with a radius of curvature R1 is formed in a ring shape.

13. The ultralightweight seamless aluminum can according to claim 12, wherein, The radius of curvature R1 is less than 3.0 mm.

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