Molding method for opening curled part of bottle-shaped can with cover

Abstract

Provided is a method for molding a curled section capable of sufficiently maintaining rigidity and strength even when the curled section is reduced in size such as a thin wall or a reduced opening diameter. The diameter-reducing process is performed such that the angle between the inclined wall section (5) and the central axis (L0) of the threaded cylindrical section is within the range of 20-30 degrees (inclusive). Processing in which the tip edge section (10) side of the curved portion is rolled inward in the radial direction and brought into contact with the outer surface of the inclined wall section (5) is performed in such a manner that the tip edge section (10) falls into the curled section (1) with a dimension measured in the radial direction between the outermost diameter section (9) of the curled section (1) and the location at which the tip edge section (10) is brought into contact with the inclined wall section (5) In the range of 40% to 60% of the curl width (W), which is half of the difference between the outer diameter and the inner diameter, the contact angle ([theta] 10) of the tip edge section (10) with respect to the inclined wall section (5) falls within the range of + / -20 degrees centered on 90 degrees.

Description

Technical Field

[0001] The present invention relates to a method for curling an open end of a mouth portion in a formed metal bottle-shaped can, which is configured to be able to attach and detach a lid by means of a screw thread. Background Art

[0002] A schematic structure of such a bottle-shaped can will be described. The threaded cylindrical portion for attaching the lid is provided at the upper part of the cylindrical body portion via a shoulder portion, and the portion above the threaded cylindrical portion is reduced in diameter to have a diameter smaller than that of the threaded cylindrical portion, and its open end portion becomes a curled portion. As the name implies, the curled portion is formed by bending the cylindrical open end outward and then curling it back inward from the lower side. The curled portion basically hides the cut end of the metal plate used as the material by curling it inward, and is a portion for ensuring airtightness or liquid tightness by closely contacting a gasket provided on the inner surface of the lid.

[0003] A so-called neck portion including the curled portion and the threaded cylindrical portion below it is formed by gradually forming a blank, which is a metal thin plate, into a small-diameter cylindrical shape by deep drawing and ironing, forming a closed cylindrical portion having a diameter smaller than that of the cylindrical body portion at the center thereof, and trimming and opening the front end of the cylindrical portion. Alternatively, conversely, the blank is formed into a cylindrical shape by deep drawing and ironing, the opening portion is gradually reduced in diameter, a small-diameter cylindrical portion opening at the front end side is formed, and its edge is trimmed and aligned to produce the neck portion.

[0004] Examples of the curled portion at the open end of such a neck portion are described in Japanese Patent Publication No. 4707172 and Japanese Patent Publication No. 6946620. In the bottle-shaped can described in Japanese Patent Publication No. 4707172, the portion continuous with the upper side of the cylindrical portion (threaded cylindrical portion) formed with an external thread is reduced in diameter to make its diameter smaller, the open end portion of the reduced-diameter portion is bent outward and curled, and the front end portion of the bent portion, that is, the curled front edge portion, is brought into contact with the outer surface of the inclined wall portion connected to the upper side of the threaded cylindrical portion. That is, the upper end portion of the reduced-diameter portion is wound outward to form a curled portion having a cross-sectional shape close to a circle. In addition, the inclined wall portion is a conical portion formed by making the upper side portion of the threaded cylindrical portion smaller in diameter than the threaded cylindrical portion. As long as the curled portion has such a shape, the touch when contacting the lips is good. In addition, when a lid for sealing is attached, a resin gasket provided on the inner surface of the lid is pressed into the lower side of the curled portion to be in a state where the gasket is wound around the curled portion. As a result, even if the lid is rotated in the opening direction to lift the lid, the sealing state using the gasket can be maintained, and the so-called anti-tampering property (TE property) of maintaining the sealing state is good until the anti-theft band provided at the lower end portion of the lid is broken.

[0005] In addition, Japanese Patent Gazette No. 6946620 describes a bottle-shaped can having a cross-sectional shape of a curled portion in a so-called substantially inverted triangle shape. By making the curled portion in such a shape, the sealing property when the lid is installed is good, and the strength against the impact of falling, etc. is improved.

[0006] According to the curled portion or the manufacturing method thereof described in Japanese Patent No. 4707172 and Japanese Patent No. 6946620, it is possible to ensure the sealing performance of the lid, the rigidity and strength against the so-called vertical load when falling or sealing, etc. On the other hand, in order to save resources and suppress the emission of greenhouse gases, it is required to make the wall thickness of the bottle-type can thinner. In the case where the curled portion is also made thinner according to these requirements, if the shape or structure is not improved, the rigidity or strength of the curled portion will be reduced, and there is a possibility that it cannot withstand the so-called vertical load as expected, or the sealing performance or TE performance of the lid will be reduced. In addition, the same is true when the curled portion or the manufacturing method thereof described in Japanese Patent No. 4707172 and Japanese Patent No. 6946620 is applied to a bottle-type can with a small opening diameter. That is, if the curled portion has a small opening diameter, the area in contact with the sealing gasket provided on the inner surface of the cap becomes smaller. In addition, the area or total length of the portion that bears the so-called vertical load becomes smaller, and the volume of the portion that supports the vertical load becomes smaller, resulting in lower rigidity or strength against the so-called vertical load. As a result, there is a possibility that deformation caused by the vertical load will occur when the cap is screwed on, etc., and the sealing or TE property of the cap may be reduced. Summary of the invention

[0007] The present invention has been made in view of the above technical problems, and an object of the present invention is to provide a method for molding a curled portion that can maintain sufficient rigidity and strength even when the curled portion is so-called miniaturized, such as by thinning the wall or reducing the opening diameter.

[0008] In order to solve the above technical problems, the present invention provides a method for forming a curled portion of a bottle-shaped can with a lid. In the above method, the diameter of a portion above the threaded cylindrical portion formed with a threaded groove is reduced to form a tapered inclined wall portion with a smaller diameter. Then, a portion above the inclined wall portion is expanded outward in the radial direction and bent downward. Furthermore, the front edge portion side of the bent portion is rolled inward in the radial direction and abuts against the outer surface of the inclined wall portion, thereby forming a curled portion above the inclined wall portion. It is characterized in that the diameter reduction process is carried out in such a way that the angle between the inclined wall portion and the central axis of the threaded cylindrical portion is in the range of 20 degrees or more and 30 degrees or less. The process of rolling the front edge portion side of the bent portion inward in the radial direction and abutting it against the outer surface of the inclined wall portion is carried out in the following manner: the dimension measured in the radial direction between the outermost diameter portion of the curled portion and the portion where the front edge portion abuts against the inclined wall portion falls within the range of 40% or more and 60% or less of the curling width, and the abutting angle of the front edge portion with respect to the inclined wall portion is an angle falling within the range of ±20 degrees centered on 90 degrees. The curling width is half of the difference between the outer diameter and the inner diameter of the curled portion.

[0009] In the method of the present invention, it may also be configured that the process of rolling the front edge portion side of the bent portion inward in the radial direction and abutting it against the outer surface of the inclined wall portion is carried out by pressing the portion above the inclined wall portion that is expanded outward in the radial direction and bent downward from the outside toward the inside in the radial direction.

[0010] In the method of the present invention, it may also be configured that the process of expanding a portion above the inclined wall portion outward in the radial direction and bending it downward is an outer bending process that bends in a manner protruding toward the outer surface side, and the process of rolling the front edge portion side of the bent portion inward in the radial direction is an inner bending process that bends in a manner protruding toward the outer surface side. In the outer bending process, the bending process is carried out in such a way that the uppermost end portion, i.e., the vertex portion, of the curled portion is located on the outer peripheral side of the central portion in the width direction of the curled portion. And in the inner bending process, the radius of curvature of the front edge portion side that is rolled inward in the radial direction and bends in a manner protruding toward the outer surface side is smaller than the radius of curvature of the portion on the inner peripheral side of the vertex portion that bends in a manner protruding toward the outer surface side.

[0011] In the method of the present invention, it can also be configured that the bottle-shaped can is a metal can made of internationally registered aluminum alloy 3104 material (aluminum alloy of Japanese Industrial Standard (JIS) 3104H19), and the nominal diameter of the curled portion is 28 mm. The curled portion is formed in such a way that the ratio of the cross-sectional area of the material to the occupied area of the curl falls within the range of 40% or more and 60% or less. The occupied area of the curl is the product of the curl width and the height in the direction of the central axis of the curled portion in the cross-section obtained by cutting the curled portion along the central axis. The cross-sectional area of the material is the cross-sectional area of the material constituting the curled portion in the cross-section.

[0012] In the present invention, since the inclined wall portion generated when the outer diameter of the curled portion is made smaller than the root diameter of the thread groove of the threaded cylindrical portion is processed so that the angle between it and the central axis falls within the range of 20 degrees to 30 degrees, when a so-called vertical load in the axial direction of the bottle-shaped can is applied, the load or moment that causes the curled portion to fall inwardly is reduced. As a result, the rigidity or strength of the curled portion, the threaded cylindrical portion, etc. becomes higher and deformation can be prevented. In addition, since the front edge portion abuts against the inclined wall portion at the center or near the center of the curl width, and the portion on the front edge portion side abuts against the inclined wall portion at an angle close to perpendicular (the abutting angle is set to an angle close to perpendicular (90 degrees)), when the above vertical load acts, the front edge portion does not slide along the surface of the inclined wall portion. As a result, the above vertical load is not borne only by the curled portion but also by the inclined wall portion. From this point of view, the substantial rigidity or strength of the curled portion can also be improved. In particular, the abutting angle is an angle close to perpendicular (±20 degrees centered on 90 degrees), whereby it is possible to prevent in advance the front edge portion from shifting along the surface of the inclined wall portion and insufficient support of the curled portion, etc., and the substantial rigidity or strength of the curled portion can be improved. In the present invention, such molding processing is performed so that the structure or shape is different from the prior art. Therefore, even when molding the curled portion of a thin-walled bottle-shaped can, a curled portion with high rigidity or strength that is not easily deformed by the so-called vertical load can be obtained.

[0013] In addition, since the processing of curling the front edge portion inwardly in the radial direction is performed by pressing from the outside in the radial direction, it is possible to eliminate the deformation or bending of the curled portion, the inclined wall portion, or the threaded cylindrical portion during the processing of molding the curled portion.

[0014] In addition, in the present invention, since the bent portion that bulges upward and is exposed in the curled portion is bent with a relatively large radius of curvature, while the portion that is close to the front edge portion and is bent so as to bulge downward is bent with a relatively small radius of curvature, the stretching at the portion where the same processing as that of the extension flange is performed is alleviated, and thus cracking, fracture, etc. can be avoided or suppressed. On the contrary, the bending process on the front edge portion side is not only the same processing as that of the shrink flange, but also the processing of the portion that has already been processed by stretching, shrinking, etc. Therefore, even if the processing is performed with a curvature as large as an angle of contact that is close to a vertical angle as described above, defective conditions such as cracking can be avoided.

[0015] Moreover, in the present invention, since the so-called vertex portion of the curled portion is processed to be located on the outer peripheral side with respect to the central portion in the width direction of the curled portion, when the gasket provided on the inner surface of the lid is pressed toward the curled portion during capping, the gasket is likely to be deformed on the outer peripheral side rather than the inner peripheral side with respect to the vertex portion. As a result, the gasket enters the lower side of the curled portion and becomes a state of wrapping the curled portion. Therefore, the sealing performance of the lid becomes good, and accordingly, a curled portion with so-called excellent TE properties can be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a cross-sectional view for explaining the shape of the curled portion processed by the method of the present invention.

[0017] Figure 2 It is an explanatory diagram for explaining the angle of contact.

[0018] Figure 3 It is a cross-sectional view showing an example of the shape of the neck portion in the blank.

[0019] Figure 4 It is a process diagram for explaining the processing processes of thread forming, curling forming, and rib forming.

[0020] Figure 5 It is a cross-sectional view showing the processing state in the third curling forming.

[0021] Figure 6 It is an explanatory diagram for explaining the acting state of the load and stress during screw-on capping.

[0022] Figure 7 It is a graph showing the results of studying the influence of the contact position of the front edge portion with respect to the inclined wall portion.

[0023] Figure 8 It is a graph showing the results of studying the influence of the area ratio. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an example of implementing the present invention will be described with reference to the accompanying drawings. In addition, the examples described below are merely examples of the present invention and do not limit the present invention.

[0025] First, a bottle-shaped can having a curled portion formed by the method of the present invention will be described. The bottle-shaped can according to the present invention is a metal can such as a steel can or an aluminum can, and can be a so-called two-piece can in which the can body and the bottom are integrally formed, or a so-called three-piece can in which a bottom lid is tightly wound and installed at the bottom of the can body. Whichever can it is, it is a metal can having the following structure: a cylindrical neck portion is formed via a shoulder at the upper part of the can body, the upper end portion of the neck portion is open, and the entire circumference of the opening portion forms a curled portion. In addition, a lid is threadedly fitted to the neck portion. In particular, the bottle-shaped can to which the present invention can be suitably applied is an aluminum alloy can having a diameter (inner diameter, nominal diameter) of the opening portion, that is, the mouth portion, of 28 mm (φ28), and its material is, for example, an internationally registered aluminum alloy 3104 material (aluminum alloy of Japanese Industrial Standard (JIS) 3104H19).

[0026] In Figure 1 a partial enlarged cross-sectional view shows an example of the curled portion 1 to be formed by the method of the present invention. In addition, Figure 1 is a cross-sectional view in the case of cutting with a plane including the central axis of the curled portion 1 or the bottle-shaped can. The curled portion 1 is a portion that forms the contour of the opening portion 3 that serves as the drinking mouth or the pouring mouth of the bottle-shaped can 2, and is continuously provided on the upper side of the threaded cylindrical portion 4 for installing a lid that closes the opening portion 3. That is, in the same manner as the structures described in Japanese Patent No. 4707172 and Japanese Patent No. 6946620, a spiral thread groove is machined in the small-diameter cylindrical portion after the drawing process to form the threaded cylindrical portion 4, and the upper portion thereof is drawn and processed into a diameter smaller than the root diameter of the thread groove. Thus, the inclined wall portion 5 is continuously formed on the upper side of the threaded cylindrical portion 4. The inclined wall portion 5 is a conical portion formed by reducing the diameter in such a manner that the diameter gradually decreases on the upper side, and the angle θ5 between the half of the cone angle and the central axis L0 of the threaded cylindrical portion 4 is set to an angle falling within the range of 20 degrees or more and 30 degrees or less.

[0027] The curled portion 1 is a portion formed by externally bending in such a manner that the portion connected to the inclined wall portion 5 on the upper side is radially expanded outward, and then curled downward and inward to form a hollow shape. The portion connected to the inclined wall portion 5 is bent obliquely upward and obliquely inward to protrude outward. This bent portion (hereinafter, temporarily referred to as the first bent portion) 6 is subjected to a relatively large stress during the bending process. Therefore, it is a bent portion having a relatively large radius of curvature R6 in order to relieve the stress and avoid cracks, fractures, etc.

[0028] The portion where the tangential line of the first bending portion 6 toward the radial direction becomes horizontal (orthogonal to the above-mentioned central axis L0) is the vertex portion 7 of the crimping portion 1, and the portion on the outer peripheral side of the vertex portion 7 becomes the outer peripheral curved surface portion 8 that forms the outer peripheral surface or contour of the crimping portion 1. When observing along Figure 1 the cross-section of, the outer peripheral curved surface portion 8 is composed of a bending portion (hereinafter, temporarily referred to as the second bending portion) 8a and a bending portion (hereinafter, temporarily referred to as the third bending portion) 8b. The second bending portion 8a protrudes obliquely upward (that is, outward) in a manner of becoming a so-called shoulder and is connected downward. The third bending portion 8b is connected downward from the second bending portion 8a and bends radially inward (that is, outward) in a manner of protruding obliquely downward. The outer diameter of the portion that becomes the boundary between the second bending portion 8a and the third bending portion 8b in the crimping portion 1 is the largest, and this portion is the outermost diameter portion 9 in the crimping portion 1.

[0029] The portion on the front end side of the third bending portion 8b can be bent with an appropriate curvature in the same manner as the third bending portion 8b, or may be a shape with a straight line shape when observing along the cross-section. Moreover, the front end edge portion 10 as its front end portion abuts against the outer surface of the inclined wall portion 5. In addition, the inclined wall portion 5 that abuts against the front end edge portion 10 is a conical portion and a portion that is convexly bent inward on the upper side and is continuous with the crimping portion 1. Therefore, except for the portion represented by a straight line in the Figure 1 cross-sectional view, the front end edge portion 10 sometimes abuts against the portion represented by a curve (a portion that can be called a corner portion).

[0030] Here, the crimping portion 1 is preferably tightly (closely) wound in such a manner that the radius in the case of a circular cross-section becomes smaller to some extent. Therefore, the curvature radius R8b of the third bending portion 8b becomes smaller than the curvature radius R6 of the first bending portion 6 (R6 > R8b). The third bending portion 8b has been deformed by processing such as when the cylindrical state extending upward from the inclined wall portion 5 expands outward in the radial direction, and processing of bending downward and inward. Therefore, it has become a state where it can be easily processed. Therefore, the third bending portion 8b can be easily processed without generating cracks or fractures.

[0031] In addition, the abutting angle θ10 of the front end edge portion 10 with respect to the inclined wall portion 5 becomes an angle close to a right angle. As shown in (A) of Figure 2 where the front end edge portion 10 is a curved surface, and Figure 2 in (B) of where the front end edge portion 10 is a flat surface, the abutting angle θ10 is the angle between the extension line of the front end edge portion 10 (or the extension line of the center line in the thickness direction of the front end edge portion 10) and the line representing the surface of the inclined wall portion 5 (the generatrix representing the inclined surface).

[0032] In order to bring the front edge portion 10 into contact with the inclined wall portion 5, the portion where the front edge portion 10 contacts the inclined wall portion 5 is set within a specified range sandwiching the central portion in the width direction of the curling portion 1. Here, the width (curling width) W of the curling portion 1 is half of the difference between the outer diameter and the inner diameter of the curling portion 1. The portion where the front edge portion 10 contacts the inclined wall portion 5 is set at a position within the range of 40% to 60% of the curling width W (in other words, within the range of ±10% from the central portion).

[0033] In addition, the above-mentioned second bending portion 8a has the following shape: one end portion thereof (the end portion on the starting side in the processing sequence), that is, the above-mentioned vertex portion 7, is located on the outer peripheral side of the central portion in the width direction of the curling portion 1. This is to more guide the gasket provided on the inner surface of the lid to the outer peripheral side and the lower side of the curling portion 1 when performing a so-called screwing type capping on the lid.

[0034] Moreover, in Figure 1 the cross-section shown, the ratio (A1 / A0) of the area of the space occupied by the curling portion 1 (hereinafter, temporarily referred to as the curling occupied area) A0 to the cross-sectional area of the material within this space, that is, the material cross-sectional area (hereinafter, referred to as the wall thickness area) A1, becomes in the range of 0.4 to 0.6 (40% or more and 60% or less). Here, when the height from the portion where the front edge portion 10 contacts the inclined wall portion 5 to the vertex portion 7 is set as H, the curling occupied area A0 is the product of the height H and the curling width W (H×W). In addition, the wall thickness area A1 is the product of the plate thickness (wall thickness) T of the material (aluminum alloy plate) constituting the curling portion 1 and the line segment length L from the portion where the front edge portion 10 contacts to the front edge portion 10. By controlling the ratio (A1 / A0) of these areas within the range of 40% or more and 60% or less, the curling portion 1 becomes a shape with rounded corners, the appearance and the touch during contact become good, and at the same time, it becomes a so-called tightly wound structure with excellent rigidity or strength.

[0035] Next, the steps of forming the curling portion 1 will be described. Figure 3 An example of a blank 20 of a bottle-shaped can is schematically shown. The neck portion 23 is connected to the upper side of the cylindrical portion 21, which is the so-called main body, via a shoulder portion 22 bent into a dome shape. The neck portion 23 successively includes a neck cylindrical portion 24, a thread cylindrical portion 25 with a slightly smaller diameter, an inclined portion 26 formed as the above-mentioned inclined wall portion 5, and a curled cylindrical portion 27 formed by curling, starting from the lower side (cylindrical portion 21 side). Before forming the curling portion 1, as Figure 4 shown, first, thread forming ( Figure 4 of (A)) is performed. Next, curling neck forming ( Figure 4(B)). This curling neck forming is a process of adjusting the shape for curling forming and is carried out through multiple processes. During this process, the inclined wall portion 5 is formed, and its angle θ5 is set to an angle within the range of 20 degrees to 30 degrees (60 degrees to 70 degrees when measured based on the horizontal plane).

[0036] In order to flatten the front edge portion 10 and adjust the length of the curling portion 1, trimming is performed ( Figure 4 (C)). Then, the first curling forming to the third curling forming is performed ( Figure 4 (D), (E), (F)). That is, in the first curling forming ( Figure 4 (D)), the portion on the open end side of the curled cylindrical portion 27 that has been trimmed is bent while expanding radially outward. In the second curling forming ( Figure 4 (E)), the expansion and bending of the portion on the open end side of the curled cylindrical portion 27 are further performed. In this case, the portion on the front edge portion 10 side is bent downward and inwardly wound. Then, in the third curling forming ( Figure 4 (F)), processing is performed to make the front edge portion 10 abut against the inclined wall portion 5. In this case, for example, as Figure 5 shown in an example, by bringing the outer roller 31 closer to the inner roller 30 inserted into the inside of the curled cylindrical portion 27 in the radial direction, the portion that has been bent downward and inwardly is pressed from the outside in the radial direction. That is, in the final stage of curling forming, the neck opening portion 23 is not pressed from the upper side, but is pressed in the radial direction. In this way, the curling portion 1 can be formed into a desired shape, and deformation (bending) of the inclined wall portion 5, the threaded cylindrical portion 4, etc. in the vertical direction can be avoided or suppressed. Through these first curling forming to the third curling forming, the curling portion 1 having the shape shown in cross-section in Figure 1 is formed.

[0037] After forming the curling portion 1 as described above, rib forming is performed ( Figure 4 (G)). That is, by necking down the lower portion of the neck cylindrical portion 24 over its entire circumference to perform so-called concave rib processing, a convex rib portion that protrudes relatively outward in the radial direction is formed in the upper portion of this concave rib (the portion directly below the threaded cylindrical portion 4). The convex rib portion is a portion for winding and engaging an anti-theft band provided at the lower end portion of the lid (not shown).

[0038] Next, referring to Figure 6The state of the load applied to the curling portion 1 during screw-on capping will be described. During screw-on capping, a blank cap is placed over the neck portion 23 and pressed. In this state, the corner between the top plate portion and the skirt portion is flattened toward the curling portion 1, and the skirt portion is pressed against the threaded cylindrical portion 4 to form an internal thread. Further, the tamper band provided at the lower end is necked down toward the convex reinforcing rib portion and engaged with the convex reinforcing rib portion. In Figure 6 In FIG. Figure 6 , reference numeral 40 denotes a cap, and a gasket 41 made of synthetic resin is provided on the inner surface of the cap 40. The cap 40 is pressed toward the curling portion 1 by a pressing pad 42. In this state, a pushing block 43 descends to neck down the peripheral edge portion (corner portion) of the cap 40 inwardly and downwardly. Accordingly, a load indicated by reference numeral L1 acts from the pressing pad 42, and a load indicated by reference numeral L2 acts from the pushing block 43. Since the gasket 41 is made of an elastic synthetic resin, it deforms to enclose the curling portion 1 by receiving the above-described loads L1 and L2. That is, as indicated by reference numeral D1, it extends downward along the surface of the outer peripheral curved surface portion 8 of the curling portion 1 and deforms into a state of enclosing the curling portion 1 from below or engaging with the lower side of the curling portion 1. Further, the gasket 41 is flattened on the apex portion 7 side and deformed inwardly as indicated by reference numeral D2 to enclose the apex portion 7 side of the curling portion 1.

[0039] The load acts on the curling portion 1 through the gasket 41 accompanying the above-described deformation. Since this load comes from the pressing pad 42 and the pushing block 43 as described above, stress F1 and F2 are applied from both sides with the apex portion 7 as a boundary in the direction of reducing the curling portion 1. The stress F1 applied to the portion on the outer peripheral side relative to the apex portion 7 acts in the direction of pressing the front edge portion 10 against the inclined wall portion 5. However, since the contact angle θ10 of the front edge portion 10 with respect to the inclined wall portion 5 is an angle close to perpendicular, the front edge portion 10 does not slide along the surface of the inclined wall portion 5, and the front edge portion 10 is supported by the inclined wall portion 5.

[0040] Further, the angle θ5 of the inclined wall portion 5 with respect to the central axis L0 is an angle of 20 degrees to 30 degrees, and the inclined wall portion 5 is in a so-called erected state. Therefore, the moment for deflecting the curling portion 1 inwardly is small, and the curling portion 1 is not easily deformed in this respect. As a result, the curling portion 1 obtained by the method of the present invention can maintain a shape with rounded corners having good appearance and feel, and has high rigidity or strength. Therefore, even if the material of the bottle-shaped can is thinned to reduce the rigidity of the material itself, the strength required as a product can be maintained. In other words, the material can be thinned to achieve effective utilization of resources, reduction of environmental load, etc. Further, even in the case of a small bottle-shaped can having a nominal diameter of 28 mm (φ28) or the like with a small volume at the open end that bears the load, a curling portion having excellent rigidity or strength can be formed.

[0041] In addition, the gasket 41 is pressed into the lower side of the curled portion 1 and enters the inside along the third bent portion 8b described above to be in a state of surrounding the curled portion 1. Therefore, even if the lid is rotated in the opening direction to slightly loosen the lid, the gasket 41 is in close contact with the outer surface of the curled portion 1 to maintain the sealed state. Therefore, if the lid is rotated in the opening direction until the seal using the gasket 41 is released, the lid is rotated considerably, and at this moment, the anti-theft band engaged with the convex reinforcing rib portion is torn off from the lid. That is, the curled portion 1 that can reliably exhibit the anti-theft function (anti-tampering function) can be formed.

[0042] Next, embodiments of the present invention will be described. The bottle-shaped can of the embodiment is made of a plate material (plate thickness: 0.28 mm) of internationally registered aluminum alloy 3104 material (aluminum alloy of Japanese Industrial Standard (JIS) 3104H19), and a two-piece can with a can body diameter of 45 mm (φ45) and a height of 110 mm is manufactured by deep drawing and ironing. The forming processes of the cylindrical body portion, the shoulder portion continuous therewith, the neck portion, etc. are performed by the same methods and processes as in the past, and the forming processes of the threaded cylindrical portion 4 and the curled portion 1 are performed as described above. The caliber is a nominal diameter of 28 mm (φ28). More specifically, the angle θ5 of the inclined wall portion 5 with respect to the central axis L0 is 30 degrees, the inner diameter of the curled portion 1 is 21.8 mm, and the wall thickness T is 0.38 mm. By raising the inclined wall portion 5 and setting its angle to 30 degrees, the space-like margin for radially winding the curled portion 1 outward becomes smaller, but by setting the apex portion 7 to be radially outside the central portion in the width direction of the curled portion 1, the curvature radius R6 of the first bent portion 6 is less restricted and a radius that can ensure no cracks, fractures, etc. can be ensured. In addition, along with this, the curvature radius R8b of the third bent portion 8b is made smaller than the curvature radius R6 of the first bent portion 6, so the overall bent shape of the curled portion 1 becomes a so-called deformed circular curled shape that is slightly deflected from a complete circle (ring shape). In addition, the contact position of the front edge portion 10 with respect to the inclined wall portion 5 is set within a range of 10% on both sides and at the central portion in the width direction of the curled portion 1. As a result, the contact angle θ10 of the front edge portion 10 with respect to the inclined wall portion 5 can be set to an angle close to a right angle.

[0043] In Figure 7 FIG. shows in a concentrated manner the cross-sectional shape and the contact angle of the curled portion 1 in the case where the contact position of the front edge portion 10 with respect to the inclined wall portion 5 is changed. The contact position is expressed as a ratio with respect to the curling width W starting from the outermost diameter portion 9 of the curled portion 1. In addition, the angle θ5 of the inclined wall portion 5 is 30 degrees.

[0044] Sample Sa1 is an example where the contact position is set to 30% of the curling width W starting from the outermost diameter portion 9. In this example, the cross-sectional shape of the curling portion 1 becomes so-called longitudinally long, and it is difficult to set the contact angle θ10 within the specified range (90 degrees ± 20 degrees). Therefore, the evaluation of this example is "not acceptable (×)".

[0045] In contrast, in the examples where the contact position is set to 40% (sample Sa2), 50% (sample Sa3), and 60% (sample Sa4) of the curling width W starting from the outermost diameter portion 9, the front edge portion 10 is curled radially inward toward the inner peripheral side. Therefore, the contact angle θ10 of the front edge portion 10 with respect to the inclined wall portion 5 can be set within the specified range close to perpendicular (right angle) (90 degrees ± 20 degrees). In addition, the entire portion from the first bending portion 6 to the third bending portion 8b can be made into a smooth and continuous curved surface. Not only is the appearance or the touch during contact good, but also excessive bending processing is not required, and thus the forming process becomes easy. Therefore, the evaluation of these examples is "acceptable (○)".

[0046] In addition, in the example where the contact position is set to 70% of the curling width W starting from the outermost diameter portion 9 (sample Sa5), it is necessary to raise the front edge portion 10 to the uppermost portion of the inclined wall portion 5 (the corner portion where the bending starts to protrude inward toward the curling portion 1). Therefore, it is necessary to increase the curvature at the third bending portion 8b, resulting in a shape that is closer to a fold than a bend. Therefore, the appearance and the touch during contact deteriorate, and the evaluation is "not acceptable (×)".

[0047] According to Figure 7 the results shown, in the present invention, the contact position of the front edge portion 10 with respect to the inclined wall portion 5 is set within the range of 40% or more and 60% or less of the curling width W. In addition, if the angle θ5 of the inclined wall portion 5 is set to the lower limit of 20 degrees, the restriction on the width of the curling portion 1 becomes stronger, and thus the appropriate range of the contact position of the front edge portion 10 with respect to the inclined wall portion 5 becomes a narrower range.

[0048] In addition, Figure 8 the research results of the area ratio (A1 / A0) of the wall thickness area A1 to the curling occupied area A0 are shown. In Figure 8In this case, the cross-sectional shape, wall thickness, area ratio of the curling part 1, and the evaluation as the curling part 1 are schematically shown together. The wall thicknesses are 0.2 mm (sample Sb1), 0.25 mm (sample Sb2), 0.3 mm (sample Sb3), 0.4 mm (sample Sb4), 0.45 mm (sample Sb5), and 0.5 mm (sample Sb6). For the respective area ratios, sample Sb1 is 32.5%, sample Sb2 is 39.8%, sample Sb3 is 46.6%, sample Sb4 is 58.8%, sample Sb5 is 63.6%, and sample Sb6 is 67.9%.

[0049] In sample Sb1, since the degree of involution of the curling part 1 with respect to the wall thickness is relatively loose, the overall rigidity is low, and there is a high possibility of deformation when the assumed vertical load is applied. Therefore, the evaluation is "not acceptable (×)". In contrast, in samples Sb2 to Sb5, as the wall thickness increases, the rigidity of the material becomes higher, but as long as it is at this level, the curling forming process can be sufficiently performed. Especially in samples Sb3 and Sb4, the front edge part 10 can be brought into contact with the inclined wall part 5 as desired. This is considered because the wall thickness is not particularly thick, so springback can be suppressed. On the contrary, the wall thickness is not as thin as that of sample Sb1 which can be easily formed, so the rigidity or strength of the curling part 1 is sufficiently increased.

[0050] For samples Sb3 and Sb4, the vertical load that causes deformation was measured. As a result, it was 1556 N (Newton) in sample Sb3 and 1868 N (Newton) in sample Sb4. Since the standard is 1471 N (Newton), it is considered to have sufficient strength. In addition, in sample Sb4, since the wall thickness is close to the wall thickness (0.38 mm) of the sample used in the study of the above contact position, it is considered that by setting the area ratio to the level of sample Sb4, rigidity or strength can be maintained and thinning can be achieved. Therefore, for samples Sb2 and Sb5, the evaluation is "acceptable (○)". For samples Sb3 and Sb4, the evaluation is "good (◎)".

[0051] In addition, in sample Sb6, since the wall thickness is relatively thick, it becomes a curling part that is wound relatively tightly, and it is considered that rigidity or strength can be ensured. However, as the wall thickness increases, the rigidity of the material itself becomes higher, so the processing load required for the forming process has to be increased, and the springback becomes stronger. As a result, it is difficult to stably process the curling part into the desired shape, and it is also difficult to stably bring the front edge part into contact with the inclined wall part 5. Therefore, for sample Sb6, the evaluation is "not acceptable (×)". Based on the above results, in the present invention, the area ratio is set to 40% to 60%.

[0052] In addition, the present invention is not limited to the above-described embodiments. The cross-sectional shape of the curled portion is preferably circular or a shape as close to circular as possible, but is not limited thereto. For example, it may also be a shape close to an inverted triangle with the apex side as the base. Further, in the above-described embodiments, the load on the upper side during screwing of the screw cap was described as a so-called vertical load. However, in the present invention, the vertical load applied to the curled portion includes other loads such as the impact force when the bottle-shaped can falls. In the present invention, sufficient rigidity or strength is also maintained for these vertical loads.

Claims

1. A forming method for the curled portion of a capped bottle-shaped can, which performs a diameter reduction process on a portion above the threaded cylindrical portion with a threaded groove formed thereon to reduce its diameter and form a conical inclined wall portion, and then expands a portion above the inclined wall portion radially outward and bends it downward, and further rolls the front edge portion side of the bent portion radially inward to abut against the outer surface of the inclined wall portion, thereby forming a curled portion above the inclined wall portion, characterized in that, the diameter reduction process is performed in such a manner that the angle between the inclined wall portion and the central axis of the threaded cylindrical portion is in the range of 20 degrees or more and 30 degrees or less. The process of rolling the front edge portion side of the bent portion radially inward to abut against the outer surface of the inclined wall portion is performed in the following manner: the dimension measured radially between the outermost diameter portion of the curled portion and the portion where the front edge portion abuts against the inclined wall portion falls within the range of 40% or more and 60% or less of the curling width, and the abutting angle of the front edge portion with respect to the inclined wall portion is an angle falling within the range of ±20 degrees centered on 90 degrees, and the curling width is half of the difference between the outer diameter and the inner diameter of the curled portion.

2. The forming method for the curled portion of a capped bottle-shaped can according to claim 1, characterized in that, the process of rolling the front edge portion side of the bent portion radially inward to abut against the outer surface of the inclined wall portion is performed by pressing a portion above the inclined wall portion that expands radially outward and bends downward from the outside toward the inside in the radial direction.

3. The forming method for the curled portion of a capped bottle-shaped can according to claim 1, characterized in that, the process of expanding a portion above the inclined wall portion radially outward and bending it downward is an outer bending process that bends in a convex manner toward the outer surface side, and the process of rolling the front edge portion side of the bent portion radially inward is an inner bending process that bends in a convex manner toward the outer surface side, in the outer bending process, the bending process is performed in such a manner that the uppermost end portion, i.e., the vertex portion, of the curled portion is located on the outer peripheral side of the central portion in the width direction of the curled portion, and in the inner bending process, the curvature radius of the front edge portion side that is rolled radially inward and bends in a convex manner toward the outer surface side is smaller than the curvature radius of the portion on the inner peripheral side of the vertex portion that bends in a convex manner toward the outer surface side.

4. The forming method for the curled portion of a capped bottle-shaped can according to any one of claims 1 to 3, characterized in that, the bottle-shaped can is a metal can made of internationally registered aluminum alloy 3104 material (aluminum alloy of Japanese Industrial Standard (JIS) 3104H19) and the nominal diameter of the curled portion is 28 mm. The curling portion is formed such that the ratio of the cross-sectional area of the material to the occupied area of the curl falls within the range of 40% or more and 60% or less, where the occupied area of the curl is the product of the curl width and the height in the direction of the central axis of the curling portion in the cross-section obtained by cutting the curling portion along the central axis, and the cross-sectional area of the material is the cross-sectional area of the material constituting the curling portion in the cross-section.

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