can

Abstract

To improve the strength of the bottom without requiring major changes to facilities when reducing the weight. [Solution] An aluminum alloy can having a bottom provided at one end of a cylindrical can body having an outer diameter of 65 mm or more and 67 mm or less, the can body having a bottom, a grounding portion, a bottom outer wall portion provided radially outside the grounding portion and connecting the can body and the grounding portion, a counter portion provided radially inside the grounding portion and inclined toward the can axial direction, and a dome portion provided radially inside the counter portion and recessed inward in the can axial direction, wherein the depth of the center of the dome portion is 9.5 mm or more and 11.0 mm or less, the thickness of the center of the dome portion is 0.220 mm or more and 0.240 mm or less, the diameter of the grounding point in the grounding portion is 46.5 mm or more and 47.5 mm or less, the radius of curvature of the outer surface of the concave arc surface between the upper end of the counter portion and the outer peripheral edge of the dome portion is 2.8 mm or more and 5.0 mm or less, and the depth in the can axial direction from the grounding portion to the center of curvature of the concave arc surface is 2.3 mm or more and 3.8 mm or less.

Description

[Technical Field]

[0001] The present invention relates to a metal can that is filled with a beverage or other contents. [Background technology]

[0002] Aluminum cans that can hold beverages, food, and other contents include two-piece cans consisting of a can body with a side wall and a bottom integrally formed, and a can lid that is double-seamed and joined to the can body. DI forming is a well-known method for manufacturing these cans. In DI forming, a preformed, shallow cup with a large diameter is drawn and ironed to form a bottom integrally at one end of a cylindrical can body, the bottom having a grounding portion that protrudes annularly outward in the axial direction of the can, a bottom outer wall portion that connects to the can body outside the grounding portion, and a dome portion that is recessed inward in the axial direction of the can inside the grounding portion. Next, the open end is subjected to necking, threading, etc. depending on the final shape of the can, but the bottom formed by DI forming remains almost unchanged in its final shape as the product.

[0003] In such cans, the thickness of the can material is being reduced (thinning) from the viewpoint of reducing costs and weight, but simply reducing the thickness of the can material results in a decrease in strength.

[0004] For this reason, Patent Document 1 describes a bottom outer wall portion that is configured outside the ground contact portion, in a cross-sectional view of the bottom including the can shaft, from a convex arc portion that describes an arc that contacts the can body, a concave arc portion that describes an arc that contacts the annular protrusion, and a straight portion connecting these convex arc portion and concave arc portion, and the radius of curvature R2 of the concave arc portion is set within the range of 9.0 mm≦R2≦18.0 mm.The document also describes that the original thickness of the aluminum plate is 0.25 mm to 0.27 mm, and the bottom outer wall portion is configured from a convex arc portion, a straight portion, and a concave arc portion, making it possible to provide a can body that has high pressure resistance and little deformation of the bottom due to internal pressure.

[0005] In contrast, Patent Document 2 discloses a can with an original thickness (thickness of the blank before processing) of 0.225 mm to 0.240 mm and a mass of 9.8 g to 11.4 g, which is even lighter. After cup forming, an annular convex portion and a dome portion, which serve as the contact portion, are formed in the can bottom by drawing and ironing, and then the inner peripheral wall of the annular convex portion is subjected to bottom reforming to form a recess that is recessed radially outward in a direction perpendicular to the can axis. It is stated that this reforming significantly increases the pressure resistance strength (bulge strength) of the can, effectively suppressing an increase in the amount of bottom growth and the occurrence of buckling. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-292480 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-136604 Summary of the Invention [Problem to be solved by the invention]

[0007] Of these patent documents, the can described in Patent Document 2 is considerably lighter than the can described in Patent Document 1. However, if further reforming processing is performed after drawing and ironing, a large-scale modification of the equipment is required, which leads to higher costs.

[0008] The present invention has been made in view of the above circumstances, and has as its object to improve the strength of the bottom portion when reducing the weight without requiring major changes to the equipment. [Means for solving the problem]

[0009] The can of the present invention is an aluminum alloy can having a bottom provided at one end of a cylindrical can body having an outer diameter of 65 mm or more and 67 mm or less, the can body having a grounding portion that annularly protrudes outward in the can axial direction, a bottom outer wall portion that is provided radially outside the grounding portion and connects the can body and the grounding portion, a counter portion that is connected to the inner peripheral edge of the grounding portion and inclined in a direction in which its diameter decreases from below to above with respect to the can axial direction, and a dome portion that is provided radially inside the counter portion and recessed inward in the can axial direction, The depth of the center of the dome portion is 9.5 mm or more and 11.0 mm or less, the thickness of the center of the dome portion is 0.220 mm or more and 0.240 mm or less, the diameter of the grounding point of the grounding portion is 46.5 mm or more and 47.5 mm or less, the upper end of the counter portion and the outer peripheral edge of the dome portion are connected by a concave arc surface, the radius of curvature of the outer surface of the concave arc surface is 2.8 mm or more and 5.0 mm or less, and the depth from the grounding portion to the center of curvature of the concave arc surface in the can axial direction is 2.3 mm or more and 3.8 mm or less.

[0010] This can has a relatively small diameter of the grounding point of the grounding section (hereinafter sometimes referred to as the grounding diameter) of 46.5 mm to 47.5 mm, resulting in high pressure resistance, and a large radius of curvature of the concave arc surface between the counter section and the dome section of 2.8 mm to 5.0 mm, and a small depth of the counter section (depth to the center of curvature of the concave arc surface) of 2.3 mm to 3.8 mm, resulting in small deformation when accidentally dropped (high drop strength). Therefore, the thickness of the center of the dome section can be made thin, at 0.220 mm to 0.240 mm, thereby achieving weight reduction.

[0011] A smaller diameter of the grounding part increases the pressure resistance, but if it is less than 46.5 mm, cracks are likely to occur during molding and the can may become unstable when grounded. If the diameter of the grounding part exceeds 47.5 mm, the pressure resistance may decrease. If the radius of curvature of the concave arc surface between the counter portion and the dome portion exceeds 5.0 mm, the depth of the counter portion becomes too small and the effect of improving pressure resistance cannot be expected.If the radius of curvature is less than 2.8 mm, the depth of the counter portion becomes too large, resulting in a decrease in drop strength.

[0012] Furthermore, the outer diameter of the can body is between 65 mm and 67 mm, and the depth of the center of the dome is between 9.5 mm and 11.0 mm. Except for limited areas such as the diameter of the contact area and the depth of the counter, the new can is not significantly different from conventional cans, and therefore will not require any major changes to equipment.

[0013] In the can of the present invention, the proof stress is 310 N / mm when the can body is cut out in the circumferential direction at a position 69 mm high from the ground contact portion to a width of 12.4 mm and measured. 2 More than 380N / mm 2 It would be better if it was below.

[0014] To compensate for the loss of strength that accompanies weight reduction, it is common to use a material with high yield strength, but high yield strength makes it difficult to form, and there is a risk of body tearing or bottom wrinkles occurring in DI forming. In addition, there is a risk of the shape of the flange part of the product after necking, such as width and thickness, varying in the circumferential direction. Yield strength: 310N / mm 2 More than 380N / mm 2 Formability can be improved by the following: The influence on strength due to low proof stress can be compensated for by the shape of the counter portion described above.

[0015] In the can of the present invention, the dome portion has a shape in which a central curved surface formed on the can axis to have an arcuate longitudinal cross section is connected to at least one outer peripheral curved surface that is arranged in an annular shape radially outward of the central curved surface and has a smaller radius of curvature than the central curved surface, and in a longitudinal cross section passing through the can axis, the central curved surface and the outer peripheral curved surface are preferably connected with a common tangent to each other.

[0016] When buckling occurs in the dome portion, the deformation often starts near the junction between the central curved surface on the can shaft, which has a large radius of curvature, and the outer curved surface on the radially outer side, which has a small radius of curvature. For this reason, by connecting the curved surfaces in a vertical cross section passing through the can shaft continuously with a common tangent, the formation of an inflection point where the curvature changes suddenly is prevented.

[0017] In the can of the present invention, it is preferable that the outer peripheral edge of the outer curved surface is connected to the inner peripheral edge of the concave arc surface, the radius of curvature of the central curved surface is 55 mm or more and 65 mm or less, the central angle of the central curved surface about the can axis is 6° or more and 20° or less, and the radius of curvature of the outer curved surface is 37 mm or more and 39 mm or less.

[0018] In order to increase the depth of the counter portion without increasing the depth of the dome portion, it is effective to widen the center-side curved surface in the radial direction, but if the central angle of the center-side curved surface exceeds 40°, the width between the outer edge of the center-side curved surface and the counter portion becomes narrow, and the radius of curvature of the outer curved surface becomes too small compared to the center-side curved surface, resulting in an abrupt change in curvature and making buckling more likely to occur. If the central angle is less than 6°, it is difficult to make the counter portion deeper.

[0019] In the can of the present invention, the weight of the constituent metals is preferably 9.7 g or more and 10.7 g or less, which keeps the weight small and promotes weight reduction. [Effects of the Invention]

[0020] According to the present invention, the diameter of the grounding portion is small, the radius of curvature of the concave arc surface between the counter portion and the dome portion is large, and the counter portion is shallow, thereby improving pressure resistance and drop strength.Furthermore, since the depth of the center of the dome portion is not significantly different from that of conventional cans, weight reduction can be achieved without requiring major equipment changes, etc. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a front view, partially in section, showing a can according to an embodiment of the present invention. [Figure 2] 2 is an enlarged cross-sectional view showing half the diameter from the can axis of the bottom of the can shown in FIG. 1. FIG. [Figure 3] FIG. 10 is a diagram illustrating the state in which radii of curvature R6, R7, etc. are measured from the profile of the bottom of a can. [Figure 4] 1A and 1B are cross-sectional views showing a cup and a cylindrical body formed during the manufacture of a can, in that order. [Figure 5] FIG. 10 is a cross-sectional view showing a part of a mold when forming a cylindrical body from a cup. [Figure 6] FIG. 4 is a cross-sectional view showing a part of a mold for forming a bottom portion. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The can of this embodiment is a cylindrical can 1 made of an aluminum alloy with a bottom, as shown in Fig. 1. This can 1 is used as a so-called two-piece can (stay-on-tab can), which is sealed by sealing a can lid (not shown) onto the open end after filling it with contents such as a beverage.

[0023] As shown in Fig. 1, the can 1 is made of a thin sheet metal of an aluminum alloy and has a cylindrical can body 20 and a bottom 30 provided at one end of the can body 20. The can body 20 is formed with a shoulder 21 whose diameter gradually decreases upward, and a small-diameter neck 22 is formed at the upper end of the shoulder 21, and a flange 23 that extends radially outward is formed at the upper end of the neck 22. The diameter (outer diameter) D1 of the can body 20 is set within the range of 65 mm to 67 mm (for example, 66 mm), and the height H0 of the entire can is set within the range of 122 mm to 124 mm.

[0024] The bottom 30 is provided with a grounding portion 31 that protrudes in an annular shape centered on the can axis S1 and outward in the direction of the can axis S1 (downward in Figures 1 and 2), a bottom outer wall portion 32 that is provided radially outside the grounding portion 31 and connects the can body 20 to the grounding portion 31, a counter portion 33 that is connected to the inner peripheral edge of the grounding portion 31 radially inside the grounding portion 31 and has a tapered surface that extends at a slight incline with respect to the direction of the can axis S1, and a dome portion 34 that is provided radially inside the counter portion 33 and is recessed inward in the direction of the can axis S1 (upward in Figures 1 and 2).

[0025] 2, the ground contact portion 31 has an outer bent portion 37 that is formed to have a convex shape extending radially outward from its apex, and an inner bent portion 38 that is formed to have a convex shape extending radially inward. The outer bent portion 37 and the inner bent portion 38 may have different radii of curvature R1 and R2 within a range of 0.8 mm to 2.0 mm, or may have the same radii of curvature. For example, the radius of curvature R1 of the outer surface of the outer bent portion 37 is set to 1.5 mm, and the radius of curvature R2 of the outer surface of the inner bent portion 38 is set to 1.0 mm.

[0026] The diameter (ground diameter) D2 of the ground contact point P of the ground contact portion 31 that protrudes furthest outward in the direction of the can axis S1 is set to 46.5 mm or more and 47.5 mm or more, and more preferably, 46.8 mm or more and 47.2 mm or less. For example, the ground contact diameter D2 is set to 47 mm.

[0027] The bottom outer wall 32 has a convexly curved portion 41 continuing from the lower end of the body 3, a tapered surface portion 42 continuing from the inner peripheral edge of the lower end of the convexly curved portion 41, and a concavely curved portion 43 continuing from the inner peripheral edge of the tapered surface portion 42. The tapered surface portion 42 and the concavely curved portion 43 are inclined so that their diameters gradually decrease downward. The inner peripheral edge of the lower end of the concavely curved portion 43 is connected to the outer peripheral edge of the outer bent portion 37 of the ground contact portion 31. The inner peripheral edge of the convexly curved portion 41 and the outer peripheral edge of the concavely curved portion 43 are formed so that their tangents are in the same direction, and the tapered surface portion 42 between them is formed along the tangent direction in a vertical cross section passing through the can axis S1. The inclination angle θ1 of the tapered surface portion 42 with respect to a plane perpendicular to the can axis S1 is set to, for example, 33°. The radius of curvature R3 of the outer surface of the convex curved portion 41 is, for example, 2.7 mm, and the radius of curvature R4 of the outer surface of the concave curved portion 43 is, for example, 12 mm.

[0028] The counter portion 33 is formed with a tapered surface that extends at a slight incline in a direction that gradually reduces its diameter as it extends upward relative to the can axis S1, and in a vertical cross section passing through the can axis S1, the angle between the counter portion 33 and a vertical line (a line parallel to the can axis S1), i.e., the inclination angle θ2 of the counter portion 33, is formed to be 2.5° or more and 4.5° or less. This allows the pressure acting on the dome portion 34 to be smoothly transmitted to the contact portion 31.

[0029] The upper end of the counter portion 33 is connected to the outer periphery of the dome portion 34 by a concave arc surface 45. The depth H1 of the counter portion 33 along the can axis S1 from the tip of the grounding portion 31 to the center C1 of the radius of curvature of the concave arc surface 45 is 2.3 mm or more and 3.8 mm or less. The radius of curvature R5 of the outer surface of the concave arc surface 45 is 2.8 mm or more and 5.0 mm or less.

[0030] More preferably, the inclination angle θ2 of the counter portion 33 is 3° to 4°, the depth H1 is 3.0 mm to 3.3 mm, and the radius of curvature R5 of the concave arc surface 45 is 2.8 mm to 3.2 mm. For example, the inclination angle θ2 of the counter portion 33 is 3°47′, the depth H1 is 3.19 mm, and the radius of curvature R5 of the concave arc surface 45 is 2.9 mm.

[0031] The dome portion 34 has a shape formed by arranging and connecting two curved surfaces with different radii of curvature: a center-side curved surface 46 that is arranged on the can axis S1 and has an arcuate shape in vertical cross section; and an outer-periphery-side curved surface 47 that is arranged annularly around the center-side curved surface 46. The radius of curvature R6 of the outer surface of the center-side curved surface 46 is 55 mm or more and 65 mm or less, and the radius of curvature R7 of the outer surface of the outer-periphery-side curved surface 47 is 37 mm or more and 39 mm or less. In a vertical cross section passing through the can axis S1, the central angle θ3 of the center-side curved surface 46 (the angle of expansion of the sector formed by the arc of the center-side curved surface 46 and the center of curvature, with the can axis S1 as the center) is set to 6° or more and 20° or less, and the outer peripheral edge of the center-side curved surface 46 and the inner peripheral edge of the outer-periphery-side curved surface 47 are connected with a common tangent.

[0032] The radius of curvature R6 is the radius of a circle obtained by measuring three points, 0°, 3°, and 6°, with respect to the can axis S1 in a vertical cross section of the bottom 30 of the can 1 including the can axis S1. The radius of curvature R7 is the radius of a circle obtained by measuring three points at appropriate intervals within a range of 7 mm to 19 mm radially outward from the can axis S1 (the range indicated by X in Figure 3). Figure 3 shows how the radii of curvature R6, R7, etc. are measured from the profile of a vertical cross section passing through the can axis S1 of an actual can. Although θ3 is indicated in Figure 3, in actual measurements, R6 is measured based on S1, and R7 is measured within the range of X, and θ3 is found from these results. Therefore, the maximum point in the range of θ3 does not necessarily coincide with the minimum point in the range of X.

[0033] The depth H2 of the deepest part of the dome portion 34, i.e., the center-side curved surface 46, above the can stem S1 is set to 9.5 mm or more and 11.0 mm or less, and preferably 10.2 mm or more and 10.8 mm or less. The thickness t1 of the dome portion 34 above the can stem S1 is close to the thickness of the flat plate before forming (original plate thickness), but because slight elongation occurs, the thickness is formed to 0.220 mm or more and 0.240 mm, while the original plate thickness is 0.235 mm or more and 0.245 mm or less.

[0034] More preferably, the dimensions of the dome portion 34 are as follows: the radius of curvature R6 of the center curved surface 46 is 55.8 mm or more and 60.2 mm or less; the radius of curvature R7 of the outer peripheral curved surface 47 is 37.0 mm or more and 38.5 mm or less; the central angle θ3 of the center curved surface 46 is 10° or more and 20° or less; and the thickness t1 of the dome portion 34 above the can shaft S1 is 0.230 mm or more and 0.240 mm or less. For example, the radius of curvature R6 of the center-side curved surface 46 is 60 mm, the radius of curvature R7 of the outer-periphery-side curved surface 47 is 38 mm, the central angle θ3 of the center-side curved surface 46 is 20°, the depth H2 of the center of the dome portion 34 is 10.5 mm, and the thickness t1 of the dome portion above the can axis S1 is 0.235 mm.

[0035] The ratio of the thickness of each portion to the thickness t1 of the dome portion 34 on the can shaft S1 is as follows: Thickness of the outer curved surface 47 of the dome portion 34: t2 = (102% to 106%) t1 Thickness of concave arc surface 45: t3 = (98% to 102%) t1 Thickness of the counter portion 33: t4 = (94% to 98%) t1 Thickness of the tip (grounding point) P of the grounding portion 31: t5 = (102% to 106%) t1 Thickness of the concave curved portion 43: t6 = (105% to 109%) t1

[0036] Furthermore, the can 1 is printed and painted on the outer surface of the can body 20, and the entire inner surface is painted. In this case, the weight of the constituent metal of the can 1 (the weight of the metal alone without printing or painting) is in the range of 9.7 g to 10.7 g, and more preferably 10.1 g to 10.5 g.

[0037] The yield strength of the material that makes up this type of can is 310N / mm after molding. 2 More than 380N / mm 2 In this case, this yield strength is measured by cutting a 12.4 mm wide piece of the can body circumferentially at a height of 69 mm from the ground. Because it is an aluminum alloy material, this is 0.2% yield strength. Therefore, this proof strength value is not the proof strength of the plate material before it is formed into a can, but is the numerical value after it has been work-hardened by forming.

[0038] To compensate for the loss of strength that accompanies weight reduction, it is common to use a material with high yield strength, but high yield strength makes it difficult to form, and there is a risk of body tearing or bottom wrinkles occurring in DI forming. In addition, there is a risk of the shape of the flange part of the product after necking, such as width and thickness, varying in the circumferential direction. Yield strength: 310N / mm 2 More than 380N / mm 2 Formability can be improved by the following: The influence on strength due to low proof stress can be compensated for by the shape of the counter portion described above. More preferably, the yield strength is 330 N / mm 2 More than 345N / mm 2 or less, for example, 335N / mm 2 is formed.

[0039] Next, a method for manufacturing a can having such a structure will be described. A flat metal plate made of an aluminum alloy is pressed to form a relatively shallow, large-diameter cup 51 as shown in FIG. 4(A) (cup forming process), and then the cup 51 is further drawn and ironed to form a bottomed cylindrical body 52 as shown in FIG. 4(B) (cylinder forming process). After printing and painting, the upper end of the cylinder 52 is processed to form the can 1 shown in FIG. 1.

[0040] In this series of manufacturing steps, the bottom portion 30 is formed in the cylinder forming step. In this cylindrical body forming process, the cup 51 is redrawn, the cylindrical portion after redrawing is ironed, and the bottom 30 is formed. As shown in Fig. 5, the cylindrical body forming device that performs the redrawing, ironing, and bottom forming processes has a redrawing die 60, an ironing die 70, and a bottom forming die 80 arranged side by side on the same axis S2, and these processes are performed continuously using the same punch sleeve 90.

[0041] The redrawing mold 60 comprises an annular redraw die 61, a cylindrical cup holder 62 arranged opposite the redraw die 61, and the aforementioned punch sleeve 90, and the cup 51 held by the redraw die 61 and cup holder 62 is redrawn by the punch sleeve 90 and the redraw die 61.

[0042] The ironing mold 70 has multiple ironing dies 71, and forms the body wall of the cylindrical body formed by the redrawing process to a predetermined height by ironing and stretching it between the punch sleeve 90 and the ironing dies 71. Although only one ironing die 71 is shown in Fig. 5, multiple ironing dies with successively smaller inner diameters are arranged coaxially depending on the desired degree of ironing. The redrawing die 60 and the ironing die 70 are usually arranged with their axes S2 oriented horizontally, and the punch sleeve 90 advances from left to right along the axis S2 in FIG. 5 to perform processing.

[0043] A bottom forming die 80 is positioned ahead of the punch sleeve 90 in the direction of travel, for forming the bottom 30 including the dome portion 34 of the cylindrical body 52 between the tip of the punch sleeve 90 that has passed through the ironing die 71 at the most distal position.

[0044] At the tip of the punch sleeve 90, a recess 91 forms a tip arc surface 92 with a convex arc cross section that protrudes annularly in the axial direction toward the tip, and a concave arc surface 93 and a convex arc surface 94 are formed in sequence from the outer periphery of the tip arc surface 92, with the convex arc surface 94 being connected to the outer periphery of the punch sleeve 90. The area from this tip arc surface 92 to the concave arc surface 93 and convex arc surface 94 forms the outer portion of the contact portion 31 of the bottom 30 of the cylindrical body 52 in the bottom forming die 80. The outer periphery of the recess 91 of the punch sleeve 90 extends straight in the axial direction from the inner peripheral edge of the tip arcuate surface 92, and is recessed as a whole in the shape of a dome centered on the axis S2.

[0045] The bottom-forming mold 80 is provided in front of the row of ironing dies 71 and includes an annular hold-down ring 81 that forms the outer bent portion 37 and the concave curved portion 43 of the bottom outer wall portion 32 between the tip arcuate mold surface 92 and the concave arcuate mold surface 93 of the punch sleeve 90, and a dome-forming die 82 that enters the recess 91 of the punch sleeve 90 and forms the inner bent portion 38, the counter portion 33, the concave arcuate surface 45, and the dome portion 34 while bending the bottom plate portion 53 of the cup 51 with the tip arcuate mold surface 92 of the punch sleeve 90. The hold-down ring 81 and the dome-forming die 82 are concentrically arranged, forming an annular gap between them. The hold-down ring 81 is supported movably along the axis S2 relative to the dome-forming die 82.

[0046] Then, with the cup 51 held between the cup holder 62 and the redraw die 61, the punch sleeve 90 moves forward to redraw and iron the cup 51 to form a cylindrical body 55 with a small diameter, and finally, the bottom 30 is formed between the cup 51 and the bottom forming mold 80. Specifically, first, as shown in Figure 6(A), the outer periphery of the bottom of the tubular body 55 is clamped between the outer peripheral portion from the tip of the punch sleeve 90 and the hold-down ring 81, and the forming of the bottom outer wall portion 32 begins. Then, as shown in Figure 6(B), the punch sleeve 90 advances in this state, and the tip circular arc mold surface 92 of the punch sleeve 90 enters the gap between the hold-down ring 81 and the dome-forming die 72, and the dome-forming die 82 enters the recess 91 of the punch sleeve 90, forming the ground portion 31. At the same time, a counter portion 33, a dome portion 34, etc. are formed between the inner portion from the tip of the tip circular arc mold surface 92 of the punch sleeve 90 and the dome-forming die 82, and the tubular body 52 having the bottom portion 30 shown in Figure 1, etc. is formed.

[0047] As shown in Fig. 4(B), the body of the cylindrical body 52 formed in this manner is thinnest near the bottom 30 (wall portion 52A) and thickest near the open end (flange portion 52B). For example, the wall portion 52A is formed to a thickness of 0.089 mm or more and 0.097 mm or less, and the flange portion 52B is formed to a thickness of 0.152 mm or more and 0.160 mm or less. The shape of the bottom 30 is formed to approximately the final shape of the can 1, such as the thickness t1 of the dome portion 34 above the can axis S1. Then, printing, painting, processing of the opening edge, etc. are performed to complete the can 1 shown in Fig. 1. The thickness of the flange portion 23 after completion (including the thickness of the printing and coating) is 0.160 mm or more and 0.168 mm or less.

[0048] In this embodiment, the can 1 has a small ground diameter D2 at its bottom 30 and an increased depth H1 of the counter portion 33, thereby improving its strength against internal pressure and effectively preventing buckling and an increase in the amount of bottom growth.

[0049] In this case, the radius of curvature R6 of the outer surface of the center curved surface 46 that forms the dome portion 34 is set to 55 mm or more and 65 mm or less, and the radius of curvature R7 of the outer curved surface 47 is set to 37 mm or more and 39 mm or less. By connecting the center curved surface 46 and the outer curved surface 47 while sharing a common tangent to each other in a vertical cross section that passes through the can axis S1, it is possible to eliminate abrupt changes in curvature in the dome portion 34 and form a smoothly curved surface, thereby avoiding local stress concentrations that may occur in the dome portion 34.

[0050] Furthermore, by increasing the radius of curvature R5 of the concave arc surface 45 between the counter portion 33 and the dome portion 34 to 2.8 mm or more and 5.0 mm or less, and decreasing the depth H1 of the counter portion 33 to 2.3 mm or more and 3.8 mm or less, deformation when accidentally dropped can be suppressed. If the radius of curvature R5 of the concave arc surface 45 exceeds 5.0 mm, the pressure resistance decreases. If the radius of curvature R5 is less than 2.8 mm, the depth H1 of the counter portion 33 becomes large, thereby decreasing the drop strength.

[0051] Furthermore, the increased pressure resistance and drop strength of this can 1 makes it possible to thin the bottom 30, thereby reducing the original plate thickness and weight. This can 1 is particularly suitable for contents such as beer and non-alcoholic beer, which do not require heat sterilization after filling. In the embodiment, an example of applying the present invention to the bottom of a so-called two-piece can has been described. However, since the process of forming the cylindrical body is the same as that of a two-piece can, the present invention can also be applied to the bottom of a bottle-shaped can. [Example]

[0052] Next, the results of tests conducted to confirm the effects of the present invention will be described. Using aluminum alloy plates, cans for the examples and comparative examples were formed to the dimensions shown in Table 1. All cans were printed and painted.

[0053] The cans of the examples were produced by varying the radius of curvature R5 of the concave arc surface between the upper end of the counter portion and the outer periphery of the dome portion, and the depth H1 of the counter portion. In all cases, the original thickness of the aluminum alloy plate was 0.230 mm. Comparative Example 1 is a conventional product using an aluminum alloy plate with an original thickness of 0.240 mm, and the contact diameter D2 is also large at 48.0 mm. Comparative Examples 2 and 3 have the same original thickness of 0.230 mm as the example, but the radius of curvature R5 of the concave arc surface is small, and therefore the depth H1 of the counter portion is large. On the other hand, Comparative Example 4 has a large radius of curvature R5 of the concave arc surface, and the depth H1 of the counter portion is small. All samples were in the form of a two-piece can with a capacity of 350 ml, and the diameter D1 of the can body was 66 mm. The shapes of all samples were identical except for the bottom.

[0054] Then, for each of these samples, a sample was cut from the can body to measure the proof stress, and the "formability," "pressure peak," "bottom growth," and "vertical drop" were evaluated. The can weight was also measured. The "yield strength" was measured by cutting a 12.4 mm wide piece of the can body in the circumferential direction at a height of 69 mm from the ground contact point. In terms of "formability," cans that could be formed without cracks or wrinkles on the bottom or other parts and with little variation in flange width were rated "good," while cans that had cracks or other imperfections were rated "poor."

[0055] The "pressure peak" was measured by fixing the body of each sample can to a hydraulic buckling tester (manufactured by Containers Laboratory Co., Ltd.) 95 mm from the ground, while leaving the bottom unfixed. The internal pressure of the can was increased at a rate of 33 kPa / s using water pressure, and the maximum pressure reached until the dome inverted (buckled) was measured. Cans with a maximum pressure of 539 kPa or higher were rated "good," and any other results were rated "poor."

[0056] "Bottom growth" was measured by comparing the bottom shape before pressure was increased and when the ultimate pressure reached 539 kPa during the pressure resistance measurement, and measuring the amount of expansion of the bottom in the axial direction. Tests with a growth amount of less than 2 mm were rated "good," and any other test was rated "poor."

[0057] For the "vertical drop" test, a can filled with liquid with the same volume and gas volume as a regular 350ml can of beer was heated until the liquid inside reached 40°C, and then dropped vertically from the bottom onto a horizontal iron plate from a height of 5cm, and the presence or absence of bottom buckling was observed. Cans that did not buckle were rated "good," and those that did buckle were rated "poor."

[0058] The results of these tests are shown in Table 1.

[0059] [Table 1]

[0060] As can be seen from the results in Table 1, Examples 1 to 8, in which the radius of curvature R5 of the concave arc surface between the upper end of the counter portion and the outer periphery of the dome portion was 2.8 mm to 5.0 mm and the depth H1 of the counter portion was 2.3 mm to 3.8 mm, exhibited good results in both peak pressure resistance and vertical drop. While Examples 1 to 7 also achieved a "good" formability rating, Example 8 was rated "poor" due to the presence of some cracks, etc. Although this slightly reduced productivity, this did not pose a problem for the can as a finished product.

[0061] Comparative Example 1 was a conventional can with a large ground contact diameter and thick walls, but was heavy and therefore had poor strength against vertical dropping.Comparative Examples 2 and 3 both had poor strength against vertical dropping because the radius of curvature R5 of the concave arc surface was too small (and therefore the depth H1 of the counter portion was too large). On the other hand, in Comparative Example 4, the radius of curvature R5 of the concave arc surface was too large (the depth H1 of the counter portion was too small), and therefore the withstand pressure peak and vertical drop strength were poor.

[0062] These results show that cans with a smaller ground diameter than the conventional can (Comparative Example 1), even if they have a thin wall thickness of 0.220 mm or more and 0.240 mm or less, cans in which the radius of curvature R5 of the concave arc surface between the upper end of the counter portion and the outer peripheral edge of the dome portion is 2.8 mm or more and 5.0 mm or less, and the depth H1 of the counter portion is 2.3 mm or more and 3.8 mm or less, have excellent peak pressure resistance, vertical drop strength, and formability, and can also suppress an increase in bottom growth. [Explanation of symbols]

[0063] 1 can 20 Can body 30 bottom 31 Grounding part 32 Bottom outer wall 33 Counter section 34 Dome section 37 Outer bend 38 Inner bend 45 Concave arc surface 46 Center side curved surface 47 Outer curved surface 51 cups 52 Cylinder 53 Bottom plate part 55 Cylindrical body 60 Redrawing mold 70 Ironing mold 80 Bottom forming mold 90 Punch Sleeve 92 Tip arc surface 93 Concave arc surface 94 Convex arc surface 81 Hold Down Ring 82 Dome forming die

Claims

1. An aluminum alloy can having a bottom provided at one end of a cylindrical can body having an outer diameter of 65 mm or more and 67 mm or less, the can body having a grounding portion that annularly protrudes outward in the can axial direction, a bottom outer wall portion that is provided radially outside the grounding portion and connects the can body and the grounding portion, a counter portion that is connected to an inner peripheral edge of the grounding portion and inclined in a direction that reduces in diameter from below to above with respect to the can axial direction, and a dome portion that is provided radially inside the counter portion and recessed inward in the can axial direction, a can having a depth at the center of the dome portion of 9.5 mm to 11.0 mm, a thickness at the center of the dome portion of 0.220 mm to 0.240 mm, a diameter of the ground contact point of the ground contact portion of 46.5 mm to 47.5 mm, a concave arc surface connecting the upper end of the counter portion and the outer periphery of the dome portion, a radius of curvature of the outer surface of the concave arc surface of 2.8 mm to 5.0 mm, and a depth from the ground contact portion to the center of curvature of the concave arc surface in the can axial direction of the can of 2.3 mm to 3.8 mm.

2. The can body was cut out at a height of 69 mm from the ground contact area to a width of 12.4 mm in the circumferential direction and measured for yield strength of 310 N / mm ２ 380N / mm or more ２ 2. The can according to claim 1, wherein:

3. 2. The can according to claim 1, wherein the dome portion has a shape in which a central curved surface formed on the can shaft so as to have an arcuate longitudinal cross section and at least one outer peripheral curved surface connected to the central curved surface, the outer peripheral curved surface being arranged in an annular shape radially outward of the central curved surface and having a smaller radius of curvature than the central curved surface, and the central curved surface and the outer peripheral curved surface are connected to each other with a common tangent in a longitudinal cross section passing through the can shaft.

4. The can according to claim 3, characterized in that the outer peripheral edge of the outer curved surface is connected to the inner peripheral edge of the concave arc surface, the radius of curvature of the central curved surface is 55 mm or more and 65 mm or less, the central angle of the central curved surface about the can axis is 6° or more and 20° or less, and the radius of curvature of the outer curved surface is 37 mm or more and 39 mm or less.

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