can

Abstract

We provide lightweight cans with excellent pressure resistance. [Solution] The outer diameter is 65.0 mm or more and 67.0 mm or less, the thickness of the center of the dome is 0.220 mm or more and 0.250 mm or less, the depth of the center of the dome is 10.65 mm or more and 13.50 mm or less, the radius of curvature of the outer surface of the dome is a single radius of curvature of 35 mm or more and 55 mm or less, the diameter of the contact point at the ground contact portion is 46.5 mm or more and 47.8 mm or less, the spreading angle at the point where the extensions of each counter portion facing radially intersect in any longitudinal section passing through the can axis is greater than 0° and 16° or less, the upper end of the counter portion and the outer edge of the dome portion are connected by a concave bend, the radius of curvature of the outer surface of the concave bend is 1.0 mm or more and 3.0 mm or less, and the heel portion is made up of multiple connected concave curved portions, the radius of curvature of the outer surface of these concave curved portions increases as they move radially outward.

Description

Technical Field

[0001] The present invention relates to a metal can filled with contents such as beverages.

Background Art

[0002] As an aluminum can capable of accommodating contents such as beverages and foods, there is a two-piece can composed of a can body in which a side wall and a bottom are integrally formed, and a can lid double-seamed and joined to the can body. As a manufacturing method thereof, a DI forming method is known. In this DI forming, a pre-formed cup with a large diameter and a shallow depth is subjected to ironing and squeezing processes, and at one end of the cylindrical can body portion, a grounding portion that protrudes annularly outward in the can axis direction, a heel portion that is connected to the can body portion outside this grounding portion, and a dome portion that is recessed inward in the can axis direction inside the grounding portion are integrally formed. Next, necking, flanging, etc. are performed on the open end portion according to the final shape of the can, but the bottom formed by DI forming becomes the final shape as a product with substantially the same shape.

[0003] In such cans, in view of cost reduction and weight reduction, the thickness of the can material is reduced (thinning), but simply reducing the thickness of the can material leads to a decrease in strength.

[0004] In Patent Document 1, the dome portion of the can bottom is formed in a shape in which a plurality of curves with different radii of curvature are arranged and connected in order so that the radius of curvature becomes smaller as it goes radially outward from the can axis, and the connection position between the curve with the largest radius of curvature in the radially inner direction and the curve connected to that curve is 0.15L or more and 0.50L or less in the radially outward direction from the can axis when the radial distance from the can axis to the grounding portion is L. A can is disclosed. The thickness of the can bottom is, for example, 0.290 mm. In this can, it is described that by forming the dome portion in a shape connecting a plurality of curves, it is possible to improve the strength of the can bottom without increasing the plate thickness, and it is possible to favorably prevent the occurrence of back buckling.

[0005] On the other hand, Patent Document 2 discloses a thin-walled DI can body with an outer diameter of 65 mm or more, a heel height of 10 to 13 mm, and a dome diameter of 46 to 48 mm, characterized in that the cross-sectional shape of the can bottom is formed such that the outer side of the contact area has a radius of curvature of 1.8 to 2.2 mm and a central angle of 70 to 80°, the heel body side has a radius of curvature of 4.8 to 6.0 mm and a central angle of 70° or less, and the center of the heel has a radius of curvature of 8 mm or more, resulting in a thin-walled DI can body with excellent axial strength. The wall thickness of the can bottom is, for example, 0.26 to 0.27 mm. It is stated that by using a can with this shape, a can bottom shape can be obtained that can withstand axial loads on the can body, has excellent pressure resistance, and suppresses the reduction in can internal volume. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-214343 [Patent Document 2] Japanese Patent Application Publication No. 8-48330 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Even in this type of can, there is a growing demand for weight reduction from the perspective of CO2 reduction. Furthermore, from the perspective of minimizing capital investment, there is a need to develop cans that are lightweight and have excellent pressure resistance without the need for can bottom reforming or other processing after DI molding.

[0008] This invention has been made in view of these circumstances, and aims to provide a can that is lightweight and has excellent pressure resistance. [Means for solving the problem]

[0009] The can of the present invention is an aluminum can comprising: a cylindrical can body with an outer diameter of 65.0 mm or more and 67.0 mm or less, a bottom provided at one end of the body, a ground portion projecting annularly outward in the direction of the can axis, a heel portion provided radially outside the ground portion and connecting the can body and the ground portion, a counter portion connected to the inner periphery of the ground portion and inclined in a direction decreasing in diameter from below to above with respect to the direction of the can axis, and a dome portion provided radially inside the counter portion and recessed inward in the direction of the can axis, The thickness of the central part of the dome is 0.220 mm or more and 0.250 mm or less, the depth of the central part of the dome is 10.65 mm or more and 13.50 mm or less, the radius of curvature of the outer surface of the dome is a single radius of curvature of 35 mm or more and 55 mm or less, the diameter of the contact point in the grounding part is 46.5 mm or more and 47.8 mm or less, the spreading angle θ2 where the extensions of each radially opposing counter part intersect is greater than 0° and 16° or less, the upper end of the counter part and the outer edge of the dome part are connected by a concave bend, the radius of curvature of the outer surface of the concave bend is 1.0 mm or more and 3.0 mm or less, and the heel part is made up of a plurality of concave curved parts connected by a common tangent, and the radius of curvature of the outer surface of these concave curved parts increases as they move radially outward.

[0010] This can has high pressure resistance because the center of the dome is deep, between 10.65 mm and 13.50 mm, the outer surface of the dome has a single radius of curvature between 35 mm and 55 mm, and it is connected to the counter section, which has a small angle with respect to the can axis, with a small radius of curvature between 1.0 mm and 3.0 mm. Furthermore, the diameter of the contact point of the grounding section (hereinafter sometimes referred to as the grounding diameter) is formed to be relatively small, between 46.5 mm and 47.8 mm, and the radius of curvature of the dome section is kept to 55 mm or less, resulting in high pressure resistance. For this reason, the thickness of the central part of the dome section can be made thin, between 0.220 mm and 0.250 mm, thereby reducing weight.

[0011] A dome depth exceeding 13.50 mm is undesirable because it may cause cracks during molding and reduces the internal volume. A depth of less than 10.65 mm will not yield the desired pressure resistance. A dome radius exceeding 55 mm reduces pressure resistance, and a radius of curvature less than 35 mm also results in low pressure resistance. While a smaller diameter of the contact area increases pressure resistance, a diameter less than 46.5 mm may cause cracks during molding, compromise stability when the can is placed on the ground, and increase the likelihood of the can tipping over during transport. If the diameter of the contact area exceeds 47.8 mm, the desired pressure resistance may not be achieved when the weight is reduced.

[0012] If the expansion angle of the counter section exceeds 16°, the pressure resistance strength decreases. Achieving an angle of 0° or less is difficult with DI molding. In the concave bend between the counter section and the dome section, if the radius of curvature exceeds 3.0 mm, the effect of improving pressure resistance cannot be expected. If the radius of curvature is less than 1.0 mm, cracking may occur during molding. Furthermore, the heel portion on the outside of the contact area is smoothly connected and continuous by a circular arc surface with a common tangent, where the radius of curvature gradually increases as it extends radially outward. This makes it less prone to wrinkling during DI molding, provides excellent buckling strength, and increases the printable image area on the can body.

[0013] In the can of the present invention, the concave curved portion is formed by a first concave curved portion, a second concave curved portion, and a third concave curved portion from the grounding portion side, and the radii of curvature of the outer surfaces thereof are preferably 1.5 mm or more and 9.0 mm or less for the first concave curved portion, 5.5 mm or more and 27.0 mm or less for the second concave curved portion, and 18.0 mm or more and 40.0 mm or less for the third concave curved portion.

[0014] In the can of the present invention, the grounding portion has an inner bending portion convexly formed radially inward from its apex and an outer bending portion convexly formed radially outward from the apex. The radius of curvature of the outer surface of the inner bending portion is 0.8 mm or more and 1.75 mm or less, and the radius of curvature of the outer surface of the outer bending portion is larger than the radius of curvature of the outer surface of the inner bending portion and is 1.0 mm or more and 3.0 mm or less. When the radius of curvature of the outer surface of the outer bending portion is large, the can is less likely to fall over. Also, the radius of curvature of the outer surface of the outer bending portion may be the same as the radius of curvature of the outer surface of the inner bending portion.

[0015] Since the grounding portion is formed of a bending portion with a relatively small radius of curvature, it is advantageous for improving the pressure resistance. In this case, if the radius of curvature of the inner bending portion exceeds 1.75 mm or the radius of curvature of the outer bending portion exceeds 3.0 mm, the pressure resistance may decrease. If the radius of curvature of the inner bending portion is less than 0.8 mm or the radius of curvature of the outer bending portion is less than 1.0 mm, cracks may occur during molding.

[0016] In the can of the present invention, the radius of curvature of the outer surface of the convex curved portion between the outer peripheral edge of the heel portion and the lower end of the can body is preferably 2.5 mm or more and 4.0 mm or less. If this radius of curvature exceeds 4.0 mm, wrinkles may occur during molding, and if it is less than 2.5 mm, cracks may occur.

[0017] In the can of the present invention, the weight of the constituent metal is preferably 9.9 g or more and 10.5 g or less, and the weight can be kept small to promote weight reduction.

Effects of the Invention

[0018] According to the present invention, since the portion from the dome portion at the bottom of the can to the counter portion, the grounding portion, and the heel portion is formed into a predetermined shape, it can be formed by ordinary DI molding, and the pressure resistance and buckling strength can be improved without reformation processing, and weight reduction can also be achieved.

Brief Description of the Drawings

[0019] [Figure 1] This is a front view of a can according to an embodiment of the present invention, showing a partial cross-section. [Figure 2] This is an enlarged cross-sectional view showing half of the diameter from the can axis at the bottom of the can shown in FIG. 1. [Figure 3] This is a cross-sectional view showing the cup and the cylindrical body formed during the manufacture of the can in the order of (a) and (b). [Figure 4] This is a cross-sectional view showing a part of the mold when forming the cylindrical body from the cup. [Figure 5] This is a cross-sectional view showing a part of the mold for forming the bottom.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the can of this embodiment is, for example, a bottomed cylindrical can 1 made of aluminum or an aluminum alloy. Further, after filling the can 1 with contents such as beverages inside, it is sealed by winding and attaching a can lid (not shown) to the open end portion, and is used for a so-called two-piece can (stay-on tab can).

[0021] As shown in FIG. 1, the can 1 is made of a thin sheet metal of aluminum (aluminum or an aluminum alloy), and has a cylindrical can body portion 20 and a bottom portion 30 provided at one end of the can body portion 20. Further, on the can body portion 20, a shoulder portion 21 that gradually reduces in diameter upward is formed, a small-diameter neck portion 22 is formed at the upper end of the shoulder portion 21, and a flange portion 23 that extends radially outward is formed at the upper end of the neck portion 22. In addition, the diameter (outer diameter) D1 of the can body portion 20 is set within a range of 65.0 mm or more and 67.0 mm or less (for example, 66 mm), and the overall height H0 of the can is set within a range of 122 mm or more and 124 mm or less. The opening diameter is a so-called 204 diameter. This opening diameter may also be 206, 202, or 200 diameter.

[0022] The bottom portion 30 is provided with a grounding portion 31 that protrudes in an annular shape around the can axis S1 toward the outward direction in the direction of the can axis S1 (downward in Figures 1 and 2), a heel portion 32 provided radially outside the grounding portion 31 and connecting the can body portion 20 and the grounding portion 31, a tapered counter portion 33 provided radially inside the grounding portion 31 and connected to the inner periphery of the grounding portion 31 and extending at a slight inclination with respect to the can axis S1, and a dome portion 34 provided radially inside the counter portion 33 and recessed toward the inward direction in the direction of the can axis S1 (upward in Figures 1 and 2).

[0023] Furthermore, the diameter (ground diameter) D2 of the ground point P that protrudes most outward in the direction of the can axis S1 of the ground portion 31 is formed to be 46.5 mm or more and 47.8 mm or less, and more preferably 46.8 mm or more and 47.2 mm or less. For example, the ground diameter D2 is set to 47 mm. A smaller diameter D2 of the contact area 31 results in higher pressure resistance, but if it is less than 46.5 mm, cracks may occur during molding, and the stability of the can when it is grounded may be compromised. If the diameter D2 of the contact area 31 exceeds 47.8 mm, the pressure resistance may decrease.

[0024] As shown in Figure 2, the contact portion 31 has an outer bent portion 37 formed convex radially outward from its apex P, and an inner bent portion 38 formed convex radially inward. In this case, the radius of curvature R1 of the outer surface of the outer bent portion 37 is 1.0 mm or more and 3.0 mm or less, and the radius of curvature R2 of the outer surface of the inner bent portion 38 is 0.8 mm or more and 1.75 mm or less. The radius of curvature R1 of the outer bent portion 37 is formed to be larger than the radius of curvature R2 of the inner bent portion 38. A larger radius of curvature R1 of the outer surface of the outer bent portion 37 makes it less likely for the can to tip over. Alternatively, the radius of curvature R1 of the outer surface of the outer bent portion 37 may be the same as the radius of curvature R2 of the outer surface of the inner bent portion 38.

[0025] Since this ground contact portion 31 is formed by bent portions 37 and 38 with relatively small radii of curvature R1 and R2, it is advantageous for improving pressure resistance. In this case, if the radius of curvature R1 of the outer bent portion 37 exceeds 2.5 mm, or if the radius of curvature R2 of the inner bent portion 38 exceeds 1.75 mm, the pressure resistance may decrease. If the radius of curvature R1 of the outer bent portion 37 is less than 1.0 mm, or if the radius of curvature R2 of the inner bent portion 38 is less than 0.8 mm, cracks may occur during molding. More preferably, the radius of curvature R1 of the outer surface of the outer bent portion 37 is 1.5 mm or more and 2.5 mm or less, and the radius of curvature R2 of the outer surface of the inner bent portion 38 is 1.0 mm or more and 1.5 mm or less. For example, the radius of curvature R1 of the outer surface of the outer bent portion 37 is set to 1.947 mm and the radius of curvature R2 of the outer surface of the inner bent portion 38 is set to 1.247 mm.

[0026] The heel portion 32 is formed with a concave curve that is convex toward the inside of the can on the outside of the outer bent portion 37 of the ground contact portion 31, and multiple concave curved portions 39A to 39C with different radii of curvature are smoothly continuous from the outer peripheral edge of the outer bent portion 37. These concave curved portions 39A to 39C are formed with progressively larger radii of curvature as they move radially outward from the outer bent portion 37. In the example shown in Figure 2, there are three curved portions: the first concave curved portion 39A, the second concave curved portion 39B, and the third concave curved portion 39C. The radii of curvature of the outer surfaces of these curved portions are as follows: the radius of curvature R3 of the first concave curved portion 39A is 1.5 mm to 9.0 mm, the radius of curvature R4 of the second concave curved portion 39B is 5.5 mm to 27.05 mm, and the radius of curvature R5 of the third concave curved portion 39C is 18.0 mm to 40.0 mm.

[0027] If the radii of curvature R3 to R5 of each of these concave curved sections 39A to 39C exceed their upper limits, the buckling strength may be reduced, and if they fall below the lower limits, wrinkles may occur during molding. More preferably, the radius of curvature R3 of the first concave curved section 39A is 3.5 mm or more and 7.5 mm or less, the radius of curvature R4 of the second concave curved section 39B is 10.0 mm or more and 14.0 mm or less, and the radius of curvature R5 of the third concave curved section 39C is 24 mm or more and 30.0 mm or less. For example, the radius of curvature R3 of the first concave curved section 39A is formed to be 4.3 mm, the radius of curvature R4 of the second concave curved section 39B is 11.753 mm, and the radius of curvature R5 of the third concave curved section 39C is 26.753 mm. Furthermore, although this embodiment shows an example in which three concave curved sections are smoothly connected, it is not limited to this, and there may be two smoothly connected curved sections, or four or more curved sections. In such smoothly connected concave curved sections, the radius of curvature increases as it extends radially outward.

[0028] Furthermore, the outer edge of the radially outermost concave curved portion, the third concave curved portion 39C in the example shown in Figure 2, and the lower end of the can body 20 are connected by a convex curved portion 41 that protrudes outward. The radius of curvature R6 of the outer surface of this convex curved portion 41 is 2.5 mm or more and 4.0 mm or less. If the radius of curvature R6 of this convex curved portion 41 exceeds 4.0 mm, wrinkles may occur during molding, and if it is less than 2.5 mm, cracks may occur. More preferably, the radius of curvature R6 of the convex curved portion 41 is 2.5 mm or more and 3.75 mm or less. For example, it is formed with a radius of curvature of 3.247 mm.

[0029] The counter portion 33 is formed to rise from the inner periphery of the inner bent portion 38 of the grounding portion 31, and is formed as a tapered surface that extends with a slight inclination in a direction that gradually decreases in diameter as it moves upward toward the can shaft S1. In a longitudinal cross-section passing through the can shaft S1, the angle θ1 between the counter portion 33 and the vertical line (a straight line parallel to the can shaft S1), i.e., the inclination angle θ1 of the counter portion 33, is formed to be between 0° and 8°. This allows the pressure acting on the dome portion 34 to be smoothly transmitted to the grounding portion 31.

[0030] In any longitudinal section of the counter section 33 passing through the can shaft S1, the spreading angle θ2 at the point where the extensions of the radially opposing counter sections 33 intersect is greater than 0° and less than or equal to 16°. If it exceeds 16°, the pressure resistance strength decreases. More preferably, the spreading angle θ2 is 4.0° or more and 10.0° or less, and the radius of curvature R8 of the concave bent portion 45 is 1.0 mm or more and 3.0 mm or less. For example, the spreading angle θ2 at the point where the extensions of the opposing counter portions 33 intersect is formed to be 8°. Furthermore, at this spreading angle θ2, the inclination angles θ1 of each counter section 33 are not necessarily the same and may be different values. Therefore, the intersection of the extensions of the counter sections 33 is not necessarily located on the can shaft S1.

[0031] The dome portion 34 is formed by a single arcuate surface on the inner side of the inner periphery of the concave bent portion 45 at the upper end of the counter portion 33. The radius of curvature R7 of its outer surface is 35 mm or more and 55 mm or less, preferably 40 mm or more and 50 mm or less. Furthermore, the deepest part of the dome portion 34, that is, the depth H1 on the central can shaft S1, is set to 10.65 mm or more and 13.50 mm or less, preferably 11.50 mm or more and 12.50 mm or less. The thickness t1 of the dome portion 34 on the can shaft S1 is close to the thickness of the flat plate before molding (original plate thickness), but a slight elongation occurs, so while the original plate thickness is 0.235 mm or more and 0.255 mm or less, it is formed to be 0.220 mm or more and 0.250 mm. The outer edge of the dome portion 34 and the upper end of the counter portion 33 are connected by a concave bend portion 45. The radius of curvature R8 of this concave bend portion 45 is formed to be between 1.0 mm and 3.0 mm.

[0032] More preferably, the radius of curvature R7 of the dome portion 34 is formed to be between 42.5 mm and 47.5 mm, the depth H1 of the dome portion 34 on the can shaft S1 is between 11.60 mm and 12.0 mm, and the radius of curvature R8 of the concave bend portion 45 is formed to be between 1.75 mm and 2.25 mm. For example, the radius of curvature R7 of the dome portion 46 is formed to be 45 mm, the depth H1 of the center of the dome portion 34 is 11.65 mm, and the radius of curvature R8 of the concave bend portion 45 is formed to be 2.0 mm.

[0033] Furthermore, the outer surface of the can body 20 of the can 1 is printed and painted, and the entire inner surface is also painted. In this case, the weight of the constituent metal of the can 1 (the weight of the metal only, without printing or painting) is in the range of 9.9g to 10.5g, more preferably 9.9g to 10.4g, and is formed to be, for example, 10.1g.

[0034] Next, we will explain how to manufacture a can constructed in this manner. As a metal sheet made of aluminum alloy, it has a tensile strength of 260 N / mm². 2 More than 320N / mm 2 Preferably, 280 N / mm 2 More than 320N / mm 2 The following is the AB yield strength (yield strength after after-baking): 245 N / mm² 2 More than 280N / mm 2 The following is preferably 245 N / mm 2 More than 275N / mm 2 A flat metal plate is prepared as shown below. This flat metal plate made of aluminum alloy is press-formed to create a relatively shallow, large-diameter cup 51 as shown in Figure 3(A) (cup forming process). Then, the cup 51 is further drawn and shaped to form a bottomed cylindrical body 52 as shown in Figure 3(B) (cylindrical body forming process). After printing and painting, the upper end of the cylindrical body 52 is processed to form the can 1 shown in Figure 1.

[0035] In this series of manufacturing processes, the bottom portion 30 is formed in the cylindrical body forming process. In this cylindrical body forming process, the cup 51 is redrawn, the cylindrical portion after redrawing is ironed, and the bottom portion 30 is formed. As shown in Figure 4, the cylindrical body forming apparatus that performs these redrawing, ironing, and bottom forming processes has a redrawing die 60, an ironing die 70, and a bottom forming die 80 arranged coaxially S2, and the processes are performed continuously using the same punch sleeve 90.

[0036] The redrawing die 60 comprises an annular redraw die 61, a cylindrical cup holder 62 positioned opposite the redraw die 61, and the aforementioned punch sleeve 90. The cup 51 held by the redraw die 61 and the cup holder 62 is redrawn by the punch sleeve 90 and the redraw die 61.

[0037] The ironing die 70 has multiple ironing dies 71, and the cylindrical body wall formed by the redrawing process is stretched by ironing between the punch sleeve 90 and the ironing dies 71 to form a predetermined height. Figure 4 shows only one ironing die 71, but depending on the desired degree of ironing, multiple ironing dies are arranged coaxially with progressively smaller inner diameters. These redrawing dies 60 and ironing dies 70 are typically positioned with their axes S2 oriented horizontally, and the punch sleeve 90 advances from left to right along the axis S2 in Figure 4 to perform the machining.

[0038] Then, a bottom-forming mold 70 is positioned in front of the punch sleeve 90 in the direction of travel, between it and the tip of the punch sleeve 90 that has passed the ironing die 71 at the most advanced position, in order to form the bottom 30 of the cylindrical body 52, including the dome portion 34.

[0039] The punch sleeve 90 has a tip arc-shaped surface 92 formed at its tip by a recess 91, which protrudes annularly in the axial direction towards the tip, and a concave arc-shaped surface 93 and a convex arc-shaped surface 94 are sequentially formed from the outer edge of the tip arc-shaped surface 92, and the convex arc-shaped surface 94 is connected to the outer surface of the punch sleeve 90. The area from the tip arc-shaped surface 92 to the concave arc-shaped surface 93 and the convex arc-shaped surface 94 forms the outer portion of the bottom 30 of the cylindrical body 52 from the contact portion 31 in the bottom forming mold 80. The recess 91 of the punch sleeve 90 has an outer circumference that extends straight in the axial direction from the inner edge of the tip arc-shaped surface 92, and as a whole it is recessed in a dome shape centered on the axis S2.

[0040] The bottom forming die 80 is located in front of a row of ironing dies 71 and includes an annular hold-down ring 81 that forms the heel portion 32 from the outer bent portion 37 of the ground portion 31 between the tip arc-shaped surface 92 and the concave arc-shaped surface 93 of the punch sleeve 90, and a dome forming die 82 that enters the recess 91 of the punch sleeve 90 and bends the bottom plate portion 53 of the cup 51 at the tip arc-shaped surface 92 of the punch sleeve 90, forming the counter portion 33, the concave bent portion 45 and the dome portion 34 from the inner bent portion 38. The hold-down ring 81 and the dome forming die 82 are arranged concentrically, and an annular gap is formed between them. The hold-down ring 81 is also supported so as to be movable in the axial direction S2 relative to the dome forming die 82.

[0041] Then, with the cup 51 held between the cup holder 62 and the redraw die 61, the punch sleeve 90 moves forward, redrawing and drawing the cup 51 to form a cylindrical body 55 with a smaller diameter, and finally, forming the bottom 30 between the punch sleeve 90 and the bottom forming die 80. Specifically, first, as shown in Figure 5(A), the outer circumference of the bottom of the cylindrical body 55 is clamped between the outer circumference of the tip of the punch sleeve 90 and the hold-down ring 81, and the formation of the heel portion 32 begins. Then, as shown in Figure 5(B), the punch sleeve 90 moves forward in this state, and the arc-shaped tip 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 contact portion 31. At the same time, a counter portion 33, a dome portion 34, etc. are formed between the inner portion of the tip of the arc-shaped tip surface 92 of the punch sleeve 90 and the dome forming die 82, forming a cylindrical body 52 having the bottom portion 30 as shown in Figure 1, etc.

[0042] As shown in Figure 3(B), the body of the cylindrical 52 formed in this way is thinnest near the bottom 30 (wall portion 52A) and thickest near the opening end (flange portion 52B). For example, the wall portion 52A is formed to be between 0.070 mm and 0.100 mm thick, and the flange portion 52B is formed to be between 0.140 mm and 0.165 mm thick. The shape of the bottom 30 is formed to be almost the final shape of the can 1, such as the thickness t1 on the can axis S1 of the dome portion 34. Then, after printing, painting, and processing of the opening ends, it is completed as can 1 as shown in Figure 1. After completion, painting and printing are applied from the wall section 52A to the flange section 52B, so the thickness becomes slightly thicker (5 μm to 10 μm) than the above thickness.

[0043] In this embodiment, the can 1 has a small ground contact diameter D2 at its bottom 30, ranging from 46.5 mm to 47.8 mm, a large depth H1 at the deepest part of the dome portion 34, ranging from 10.65 mm to 13.50 mm, and a single radius of curvature R7 of the dome portion 34 ranging from 35 mm to 55 mm. Furthermore, it connects to the counter portion 33, which has a small angle θ1 with respect to the can shaft S1, with a small radius of curvature of 1.0 mm to 3.0 mm. This improves the strength against internal pressure and effectively prevents buckling and increased bottom growth.

[0044] Furthermore, the heel portion on the outer side of the contact area is continuous with an arcuate surface whose radius of curvature gradually increases as it extends radially outward, which makes it less prone to wrinkling during DI molding and also provides excellent buckling strength.

[0045] Furthermore, by increasing the pressure resistance of this can 1, it becomes possible to thin the bottom 30, and consequently the original plate thickness, resulting in a lighter can. This can 1 is particularly suitable for contents that do not require heat sterilization after filling, such as beer and non-alcoholic beer. In the embodiments described, an example was given in which the present invention is applied to the bottom of a so-called two-piece can. However, since the process for a so-called bottle-shaped can is the same as that for a two-piece can up to the cylindrical body formation step, the present invention can also be applied to the bottom of this bottle-shaped can. [Examples]

[0046] Next, we will describe the test results conducted to confirm the effects of the present invention. Using aluminum sheets, 30 cans were molded according to the dimensions shown below. None of them showed any cracks or wrinkles.

[0047] Diameter of the can body: 66.0 mm Can height: 123mm Thickness of the center of the dome section: t: 0.247 mm Depth of the center of the dome section: H: 11.65 mm Single radius of curvature R1: 45 mm on the outer surface of the dome Ground diameter D: 47.5mm Counter section spread angle θ2: 7°24′ Radius of curvature of concave bend: 2.0 mm Radius of curvature of the inner bend: 1.247 mm Radius of curvature of outer bend: 1.947mm Radius of curvature of the first concave curved section: 4.3 mm Radius of curvature of the second concave curved section: 11.753 mm Radius of curvature of the third concave curved section: 26.753 mm Radius of curvature of the convex curved section: 3.247 mm

[0048] The buckling strength and pressure resistance of this can were measured. The can's weight was also measured.

[0049] For "buckling strength," six cans were measured by placing them in an inverted position, applying a vertical load from the bottom, and determining the load at which buckling occurred. "Pressure resistance strength" was measured by fixing the can body to a hydraulic buckling tester (manufactured by Containers Laboratories Co., Ltd.) at a position 95 mm from the ground, while leaving the bottom unfixed. The internal pressure of the can was increased by water pressure at a rate of 50 kPa / s, and the maximum pressure reached before the dome inverted (buckled) was measured. Six cans were measured.

[0050] The cans described above had a buckling strength of 900N or more and a compressive strength of 539kPa or more. The can weight ranged from 9.9g to 10.5g. [Explanation of Symbols]

[0051] 1 can 20 Can body 30 bottom 31 Grounding part 32 Heel section 33 Counter section 34 Dome section 37 Outer bend 38 Inner bend 39A~39C Concave curved section 45 Concave curved section 51 cups 52 Cylinder 53 Bottom plate part 55 Cylindrical body 60 Redrawing molds 70 Die for ironing 80 Bottom forming mold 90 Punch Sleeves 92. Arc-shaped tip surface 93 Concave arc-shaped surface 94 Convex arc-shaped surface 81 Hold-down ring 82 Die for dome molding

Claims

1. An aluminum can having a cylindrical can body with an outer diameter of 65.0 mm or more and 67.0 mm or less, a bottom provided at one end of the body, a grounding portion that protrudes annularly outward in the direction of the can axis, a heel portion provided radially outside the grounding portion and connecting the can body and the grounding portion, a counter portion connected to the inner periphery of the grounding portion and inclined in a direction of decreasing diameter from below to above with respect to the direction of the can axis, and a dome portion provided radially inside the counter portion and recessed inward in the direction of the can axis, A can characterized in that the thickness of the central part of the dome is 0.220 mm or more and 0.250 mm or less, the depth of the central part of the dome is 10.65 mm or more and 13.50 mm or less, the radius of curvature of the outer surface of the dome is a single radius of curvature of 35 mm or more and 55 mm or less, the diameter of the contact point in the grounding part is 46.5 mm or more and 47.8 mm or less, the spreading angle at the point where the extensions of each counter part facing radially intersect in any longitudinal section passing through the can axis is greater than 0° and 16° or less, the upper end of the counter part and the outer edge of the dome are connected by a concave bend, the radius of curvature of the outer surface of the concave bend is 1.0 mm or more and 3.0 mm or less, and the heel part is made up of a plurality of connected concave curved parts, the radius of curvature of the outer surface of these concave curved parts increases as they move radially outward.

2. The can according to claim 1, characterized in that the concave curved portion is formed by a first concave curved portion, a second concave curved portion, and a third concave curved portion from the grounding portion side, and the radius of curvature of the outer surfaces thereof is 1.5 mm or more and 9.0 mm or less for the first concave curved portion, 5.5 mm or more and 27.0 mm or less for the second concave curved portion, and 18.0 mm or more and 40.0 mm or less for the third concave curved portion.

3. The can according to claim 1 or 2, wherein the contact portion has an inner bent portion formed convex radially inward from its apex and an outer bent portion formed convex radially outward from its apex, the radius of curvature of the outer surface of the inner bent portion is 0.8 mm or more and 1.75 mm or less, and the radius of curvature of the outer surface of the outer bent portion is greater than the radius of curvature of the inner bent portion and is 1.0 mm or more and 3.0 mm or less.

4. The can according to claim 1 or 2, characterized in that the radius of curvature of the outer surface of the convex curved portion between the outer edge of the heel portion and the lower end of the can body portion is 2.5 mm or more and 4.0 mm or less.

5. The can according to claim 1, characterized in that the weight of the constituent metal is 9.9 g or more and 10.5 g or less.

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