Can container and its manufacturing method

Abstract

Provided is a can container with higher drop strength and compressive strength by further improving the shape of the bottom of the can container. The can container comprises a can body and a can bottom, the can bottom being provided with a dome portion in the center that is recessed toward the inside of the can container along the direction of the can axis, the can bottom also being provided with an annular protrusion that projects outward of the can container so as to form an annular support portion around the outside of the dome portion, and the dome portion having a central dome portion located on the can axis and having a set radius of curvature, and an outer dome portion that is continuously formed on the outside of the central dome portion, has a center of curvature on the can axis, and has a radius of curvature that is smaller than the radius of curvature of the central dome portion.

Description

[Technical field]

[0001] The present invention relates to a can container and a method for manufacturing the same. [Background technology]

[0002] Known can containers in which beverages, foods, and other contents are filled and sealed include two-piece cans, bottle cans, etc. These can containers have at least a can body and a can bottom.

[0003] In order to reduce the amount of raw materials used, efforts are being made to make such can containers lighter by reducing the plate thickness. However, even when the plate thickness is reduced, necessary improvements are made to the shape of the can bottom in order to obtain a specified level of strength as a container.

[0004] Generally, the can bottom shape is formed by forming a dome-shaped recess in the center of the can bottom toward the inside of the can container along the can axial direction, and forming an annular protrusion that serves as a support part on the outer periphery of the dome portion.

[0005] In addition, in prior art, the shapes of the dome portion and annular convex portion described above are appropriately designed. For example, one proposed technique is to form a first concave curved surface portion on the inner wall of the annular convex portion connected to the dome portion, which is curved in a radially outward direction perpendicular to the can axis when viewed in a longitudinal cross section along the can axis direction, and to form a concave curved surface portion on the dome portion, which has a dome top located on the can axis and a second concave curved surface portion connected to the radially outward side of the dome top and has a smaller radius of curvature than the dome top, and to form a linear tapered portion on the outer circumferential edge of the dome portion that connects the first concave curved surface portion and the second concave curved surface portion (see Patent Document 1 below). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-43991 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the case of can containers with the aforementioned dome at the bottom, if the radius of curvature of the dome is increased and the indentation is made small in order to secure the volume inside the container, when the can container is dropped during transportation, the impact of the drop will cause a water hammer phenomenon due to the contents, and the dome will easily invert. In particular, aluminum alloy can containers, which are required to be thinner in thickness to conserve resources and reduce weight, can cause the aforementioned dome to invert even if dropped from a height of just a few tens of centimeters, so improving drop strength is an issue to increase product yield during transportation.

[0008] In contrast, in the above-mentioned conventional technology, a second concave curved surface portion is formed on the outer periphery of the dome portion, which has a concave curved shape with a radius of curvature much smaller than that of the dome top located on the can axis (when the radius of curvature of the dome top is 48 mm, the radius of curvature of the second concave curved surface portion is 3.0 to 5.0 mm), and a linear tapered portion is formed in contact with the second concave curved surface portion. According to this conventional technology, when a can container is dropped and a load is applied to the grounded portion of the can bottom, the above-mentioned water hammer phenomenon occurs, and the second concave curved surface portion with a small radius of curvature between the tapered portion and the outer periphery of the dome portion becomes the starting point, and the dome portion is likely to invert. For this reason, there was a problem that the drop strength could not be increased with the shape of the can bottom in the conventional technology.

[0009] According to the conventional technology, the dome portion and the annular protrusion are formed on the bottom, and then the inner wall of the annular protrusion is reformed to form the first concave curved portion and the tapered portion. The first concave curved portion is formed by a forming surface of a roll forming tool. In such roll forming, the curved surface of the first concave curved portion must have a relatively large curvature radius that allows roll forming, and the inner surface of the annular protrusion cannot be recessed deeper toward the outside in the radial direction perpendicular to the can axis. Therefore, there is a problem that effective improvement in pressure resistance cannot be obtained even if reform forming is performed.

[0010] The present invention has been proposed to address such circumstances, and aims to provide a can container with improved drop strength and pressure resistance by improving the shape of the bottom of the can container. [Means for solving the problem]

[0011] In order to solve these problems, the can container according to the present invention has the following configuration.

[0012] A method for manufacturing a can container having a can body and a can bottom, comprising the steps of: A dome portion is formed in the center of the can bottom along the direction of the can axis so as to be recessed toward the inside of the can container, and an annular protrusion is formed around the outer periphery of the dome portion so as to form an annular support portion. Then, When performing plastic working by pressing a forming tool having a working surface conforming to the curved surface of the dome portion from inside the can container along the can axial direction, a processing surface of the forming tool has a center of curvature on the can axis, a radius of curvature smaller than the radius of curvature at the center of the dome portion, and a radius equal to or larger than a radius perpendicular to the can axis from the can axis to an outermost portion of the dome portion in a vertical cross-sectional view along the can axis direction including the can axis. .

[0013] In the above-mentioned can container manufacturing method, the forming tool is used as an inner tool, and an outer tool is used to form the annular convex portion, A method for manufacturing a can container, characterized in that the inner surface of the annular convex portion is plastically processed by compression through the forming process of the dome portion by pressing the inner tool against it. Effect of the Invention

[0014] A can container having such characteristics and a manufacturing method thereof can provide a can container having higher drop strength and pressure resistance by improving the shape of the bottom of the can container, even if the can container is made of an aluminum alloy with a thin plate thickness. [Brief description of the drawings]

[0015] [Figure 1] 1 is a longitudinal sectional view of a main portion of a can container according to an embodiment of the present invention (a longitudinal sectional view including a can axis O and taken along the can axis O direction). [Diagram 2] FIG. 2 is an enlarged view of a main part in FIG. [Diagram 3] FIG. 2 is an explanatory diagram for explaining a manufacturing method of a can container according to an embodiment of the present invention (a vertical cross-sectional view including a can axis O along the can axis O direction). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same reference numerals in different drawings indicate parts with the same functions, and duplicated explanations in each drawing will be omitted as appropriate. In addition, the cross-sectional views in Figures 1 and 2 show the cross-sectional shapes in line drawings with the plate thickness omitted.

[0017] 1, a can container 1 according to an embodiment of the present invention has a can body 1A and a can bottom 1B, and the can body 1A and the can bottom 1B have the same shape all around the can axis O in a vertical cross-sectional view including the can axis O and along the can axis O. Here, the can bottom 1B has a dome portion 10 and an annular protrusion 20, and in the illustrated example, the outer side of the annular protrusion 20 has an outer wall portion 30 that is connected to the can body 1A.

[0018] Domed portion 10 is provided at the center of can bottom 1B, and has a curved surface that is concave in a dome shape toward the inside of can container 1 along the can axis O. This domed portion 10 has central domed portion 11 located on the can axis and having a set radius of curvature R1, and peripheral domed portion 12 formed contiguous with the outside of central domed portion 11, with its center of curvature located on can axis O and with a radius of curvature R2 smaller than the radius of curvature R1 of central domed portion 11. As shown in the figure, the centers of curvature R1 of central domed portion 11 and the radius of curvature R2 of peripheral domed portion 12 both reside on the can axis O, and the center of curvature of peripheral domed portion 12 is located above the center of curvature of central domed portion 11.

[0019] The annular protrusion 20 is formed to protrude outward along the axial direction of the can container 1 so as to form an annular support portion 21 around the outer periphery of the dome portion 10. The support portion 21 is a portion for grounding the can container 1.

[0020] As shown in FIG. 2, in the can bottom 1B, the inner surface 22 extending from the support portion 21 of the annular protrusion 20 to the outer peripheral edge portion 10A of the dome portion 10 has a recess portion 22A in which the inner surface 22 is inclined in a direction away from the can axis O and connected to the outer peripheral edge portion 10A of the dome portion 10 (the outer peripheral edge portion of the outer dome portion 12).

[0021] The recessed portion 22A formed on the inner peripheral surface 22 of the annular convex portion 20 is inclined upward from the innermost portion 22B of the inner peripheral surface 22 (the portion closest to the can axis O on the inner peripheral surface 22) in a direction away from the can axis O, and the outer peripheral edge portion (the outer peripheral edge portion of the outer peripheral dome portion 12) 10A of the dome portion 10 is located in a direction away from the can axis O with respect to the innermost portion 22B of the inner peripheral surface 22 (the portion closest to the can axis O on the inner peripheral surface 22). As a result, a virtual line L1 that is in contact with the innermost portion 22B of the inner peripheral surface 22 and is parallel to the can axis O intersects the outer peripheral dome portion 12.

[0022] The can container 1 having such a can bottom shape is formed by pre-forming the dome portion 10 and the annular convex portion 20 having the support portion 21 on the can bottom 1B, and then performing finish forming (reform forming) using a forming tool T (inner tool T1 and outer tool T2) as shown in FIG. 3. At this time, both the forming of the dome portion 10 and the forming of the annular convex portion 20 are processed by the forming tool T. In the example shown in FIG. 3, the forming of the dome portion 10 and the forming of the annular convex portion 20 are performed simultaneously with the forming tool T including the inner tool T1 and the outer tool T2, but they may be performed separately.

[0023] The inner tool T1 performs a forming process on the curved surface of the dome portion 10 from the inside of the can container 1 and has a processing surface S along the curved surface of the dome portion 10. This processing surface S has a curvature center on the can axis O, has a curvature radius R2 smaller than the curvature radius R1 of the pre-formed dome portion, and has a tool radius r equal to or greater than the radius perpendicular to the can axis O from the outermost part of the dome portion 10 from the can axis O.

[0024] In the forming process of the dome portion 10, with respect to the dome portion 10 formed to have a curvature radius R1 by pre-forming, the processing surface S of the inner tool T1 is pressed against the dome portion 10 from the inside of the can container 1 along the can axis O direction. As a result, on the portion P where the processing surface S is pressed against the dome portion 10, a curved surface of the outer peripheral dome portion 12 having a curvature radius R2 (R2 < R1) is formed by the forming process, and the portion that is not pressed by the processing surface S of the inner tool T1 and is not formed becomes the central dome portion 11 having a curvature radius R1.

[0025] At this time, the inner tool T1 presses only the outer peripheral portion P of the processing surface S against the dome portion 10 to perform molding, so that the processing surface S may be hollow except for the central portion that is not pressed against the dome portion 10.

[0026] The outer tool T2 has a chuck C for forming the annular protrusion 20 of the can bottom 1B. By pressing the inner tool T1 downward, the dome portion 10 is formed as described above, and the annular protrusion 20 enters the chuck C, forming the annular protrusion 20 according to the shape of the chuck C.

[0027] 2, the inner peripheral surface 22 of the formed annular protruding portion 20 passes through a recess at the outermost portion 22C (the portion of the inner peripheral surface 22 farthest from the can axis O) of the inner peripheral surface 22 and reaches the outer peripheral edge portion 10A of the domed portion 10 (the outer peripheral edge portion of the outer domed portion 12). This outermost portion 22C is a bent portion that has been plastically processed by compression using a forming tool T. As a result, the radius of curvature of the curved surface of the outermost portion 22C can be set smaller (for example, 0.7 mm or less) than the radius of curvature of the first concave curved surface portion in the prior art.

[0028] The outermost portion 22C thus formed can be recessed deeper in a direction away from the can axis O with respect to the innermost portion 22B on the inner peripheral surface 22. If an imaginary line that is in contact with the outermost portion 22C and parallel to the can axis O is denoted by L2, the distance d between the imaginary lines L1 and L2 (depth of the recessed portion 22A) is preferably set to 0.3 mm to 1.0 mm in order to increase the pressure resistance of the can bottom 1B. When the outermost portion 22C is formed by plastic processing using compression, the height h from the support surface 21A to the outermost portion 22C becomes the forming height. In order to increase the pressure resistance of the can bottom 1B, this height h is preferably set to 2.0 mm to 4.0 mm.

[0029] Since the outermost portion 22C of the inner circumferential surface 22 is a bent portion plastically processed by compression, roll forming as in the conventional technology is not required. Therefore, the inner circumferential surface 22 of the annular convex portion 20 does not have roll forming marks that are generated when a curved surface is formed by roll forming. This makes it possible to avoid deterioration of the aesthetic appearance of the inner circumferential surface 22 due to roll forming marks (blackening due to destruction of the aluminum oxide film) generated during heat sterilization, etc.

[0030] The embodiment of the present invention having such a can bottom shape has a high drop strength compared to the above-mentioned conventional technology and the dome portion formed with a single radius of curvature. Table 1 shows the results of drop tests on an embodiment in which the radius of curvature R1 of the central dome portion 11 is 42 mm and the radius of curvature R2 of the peripheral dome portion 12 is 35 mm, a comparative example 1 having the above-mentioned conventional can bottom shape, and a comparative example 2 in which the dome portion has a single radius of curvature of 42 mm (the plate thickness and other conditions are the same for the embodiment and comparative examples 1 and 2, and the drop height was 25 cm).

[0031] [Table 1]

[0032] The results in Table 1 show that in the 20 examples, zero showed inversion of the dome portion, in the 3 examples in Comparative Example 1, three showed inversion of the dome portion, and in the 4 examples in Comparative Example 2, four showed inversion of the dome portion. As is clear from these results, the examples of the present invention have higher drop strength than the conventional technology and those in which the dome portion is formed with a single radius of curvature.

[0033] The reason that the embodiment of the present invention has high drop strength is that the radius of curvature R2 of the peripheral dome section 12 is made smaller than the radius of curvature R1 of the central dome section 11, thereby making the tangent angle of the curved surface at the outer peripheral edge of the dome section 10 steeper. The inversion of the dome section due to the water hammer phenomenon that occurs when a can container is dropped begins at the outer peripheral edge of the dome section, so by making the tangent angle here steeper, the resistance to the pressure of the water hammer phenomenon increases.

[0034] Moreover, the embodiment of the present invention has a higher can bottom pressure resistance strength than the conventional technology described above. The can bottom pressure resistance strength here refers to the buckling strength until the concave shape of the can bottom is completely inverted due to a pressure increase inside the can container. The recessed portion 22A described above is formed by the forming tool T after the dome portion 10 and the annular protrusion 20 are pre-formed in the can bottom 1B. By setting the inclination angle of the inner peripheral surface 22 of this recessed portion 22A to an appropriate angle, the outermost portion 22C of the inner peripheral surface 22 of the annular protrusion 20 can be recessed deeper in the direction away from the can axis O, and the buckling strength described above can be increased.

[0035] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes design changes and the like that do not deviate from the gist of the present invention. [Explanation of symbols]

[0036] 1: can container, 1A: can body, 1B: can bottom, 10: Dome portion, 10A: Outer periphery portion, 11: Central dome section, 12: Outer dome section, 20: annular protrusion, 21: support portion, 21A: support surface, 22: Inner peripheral surface, 22A: Recessed part, 22B: Innermost, 22C: Outermost, 30: Outer wall, O: Can shaft

Claims

1. A method for manufacturing a can container having a can body and a can bottom, comprising the steps of: A dome portion is formed in the center of the can bottom along the direction of the can axis so as to be recessed toward the inside of the can container, and an annular protrusion is formed around the outer periphery of the dome portion so as to form an annular support portion. Then, When performing plastic working by pressing a forming tool having a working surface conforming to the curved surface of the dome portion from inside the can container along the can axial direction, A method for manufacturing a can container, characterized in that the machining surface of the forming tool has a center of curvature on the can axis, a radius of curvature smaller than the radius of curvature at the center of the dome portion, and a radius greater than or equal to the radius perpendicular to the can axis from the can axis to the outermost edge of the dome portion when viewed in a vertical cross-sectional view along the can axis direction including the can axis.

2. The molding tool is an inner tool, and an outer tool is used to mold the annular convex portion, 2. The method for manufacturing a can container according to claim 1, wherein the inner peripheral surface of the annular protrusion is plastically processed by compression during the forming process of the dome portion against which the inner tool is pressed.

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