Can lid and can lid shell manufacturing method and manufacturing device

Abstract

To provide the generation of cracks even if a buckling phenomenon occurs.SOLUTION: A chuck wall portion is formed, and by rising with respect to a die core ring and a pressure sleeve while a center portion of a metal plate is held between a panel punch and a die center, a part of the metal plate is dropped into a recessed portion of an outer peripheral portion of the panel punch to form a countersink portion. A panel portion is formed inside the counter sink portion. On a bottom surface of the recessed portion, a recessed bending surface for forming an inside bending portion of a bottom portion of the counter sink portion is formed. At an outer peripheral edge of the panel punch, a virtual surface contacting with the recessed portion is formed within a range of ±20° with respect to a horizontal surface. A lower surface of the counter sink portion is molded so as to be pressed from a lower side between the recessed bending surface of the recessed portion and the outer peripheral edge of the panel punch when rising. A curvature radius of an outside bending portion at the bottom portion of the counter sink portion is formed to be 0.21 mm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for manufacturing a can end and a shell for a can end which are fastened onto an open end of a can body. [Background technology]

[0002] Conventional beverage can lids have a disk-shaped panel in the center, a countersink on the outer periphery thereof, and a curled portion connected to the outer periphery via a chuck wall, and the panel is scored to form an opening, and a tab is provided for the opening operation. In recent years, in response to the demand for thinner cans, the chuck wall has been replaced with a chuck wall having a vertical cross section with a continuous shape of two curved portions, one concave and one convex, instead of a substantially straight tapered shape, and the diameter of the panel has been reduced.

[0003] For example, in Patent Document 1, the chuck wall is formed in a shape in which a curved portion that is convex radially inward at its lower portion and a curved portion that is concave radially inward (convex radially outward) at its upper portion are connected. In this case, a can lid with an overall diameter of (D4) = approximately 56.896 mm and a can lid with an overall diameter of (D8) = 59.360 mm are disclosed. In terms of nominal diameters for those skilled in the art, the former is a nominal diameter of 200 and the latter is a nominal diameter of 202. The inner diameter of the outer wall of the countersink portion is (D2) = about 49.708 mm for diameter 200 and (D6) = 48.514 mm for diameter 202, and the radius of curvature of the inner bottom surface of the countersink portion is about 0.254 mm for diameter 200 and about 0.229 to 0.279 mm for diameter 202. The plate thickness is about 0.2159 mm for the blank before being formed into a can lid. The symbols in parentheses are the symbols used in the publication (similarly in Patent Document 2).

[0004] Meanwhile, Patent Document 2 discloses a method for manufacturing such a can end. In Patent Document 2, a cup portion (C) is sandwiched between an annular outer pressure sleeve (55) and an upper portion (99) of a core ring (98) of a die, and a chuck wall is formed between an inclined or truncated cone-shaped surface (156) and a curved annular surface (158) formed on the upper portion (99) and corresponding surfaces (143, 144) of the inner pressure sleeve (80). In addition, a countersink is formed by the concave surfaces (116, 168) formed on the outer periphery of the panel punch (118) by sandwiching the center portion of the cup portion (C) between a center punch (65) of the die and a circular panel punch (118) and moving the center portion up and down. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4647207 [Patent Document 2] Patent No. 5649189 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, the can end shell described in Patent Document 1 has no particular problem with respect to pressure resistance itself. However, when the internal pressure of the can rises and a buckling phenomenon occurs in which the countersink portion inverts, as shown in Figure 9, part of the panel portion rises and protrudes in a corner shape, and a crack F occurs at the tip of the corner E, causing the beverage to spray out.

[0007] The process of this buckling phenomenon is illustrated in Fig. 10(a) to (e) in order. In Fig. 10 and Fig. 9, the symbol J indicates the panel part, the symbol K indicates the countersink part, and the symbol M indicates the chuck wall part. In this can lid, as the internal pressure increases, a part of the panel part J is lifted as shown in Fig. 10(b), and a corner part E is formed on the upper surface side as shown by the broken line. This corner part E progresses to the middle of the chuck wall part M so as to pass through the bottom of the countersink part K, so that an excess of material is generated and a corner part G is also formed on the lower surface side as shown in Fig. 10(c) and (d). Then, when the material is taut, the maximum tension is generated, and an excessive tensile stress is generated around the corner part G on the lower surface side, and the tip of the corner part E on the upper surface side is torn off. In Fig. 10, the arrows indicate the change in the position of the bottom part of the countersink part K.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a method and apparatus for manufacturing can lids and shells for can lids that can prevent the occurrence of cracks even when the buckling phenomenon occurs. [Means for solving the problem]

[0009] The can lid of the present invention is a shell for a can lid, comprising a central disk-shaped panel portion, a countersink portion continuing from the outer periphery of the central disk-shaped panel portion and forming an upwardly facing annular recess, a chuck wall portion gradually increasing in diameter from the outer periphery of the countersink portion toward the upper side, a shoulder portion extending radially outward from the outer periphery of the chuck wall portion, and a curl portion continuing from the shoulder portion and formed by folding back the outer periphery toward the radially inward side, The chuck wall portion has a shape in which a first curved portion that is convex radially inward and a second curved portion that is concave radially inward (convex radially outward) above the first curved portion are connected to each other, The bottom of the countersink portion has an outer surface with a radius of curvature of 0.21 mm or less, which is smaller than the outer surface with a radius of curvature of the inner bent portion.

[0010] This can lid has an outer surface curvature radius of 0.21 mm or less, smaller than that of the inner bent portion, so that even if buckling occurs due to internal pressure when the can lid is fastened around the can body, causing a corner on the upper surface as described above, the outer bent portion prevents the corner from passing through the bottom of the countersink portion, and the length of the corner on the lower surface (see B in Fig. 10) can be made large, which relieves the tensile stress generated around the corner on the upper surface and prevents the occurrence of cracks. It is more preferable that the outer surface curvature radius of this outer bent portion is 0.19 mm or less.

[0011] The method for manufacturing a can lid shell of the present invention is a method for manufacturing a can lid shell by pressing a metal sheet between a pair of upper and lower dies, the method comprising the steps of: a central disk-shaped panel portion; a countersink portion that is continuous with the outer periphery of the central disk-shaped panel portion and forms an upwardly facing annular recess; a chuck wall portion that gradually increases in diameter from the outer periphery of the countersink portion toward the upper side; a shoulder portion that extends radially outward from the outer periphery of the chuck wall portion; and a curled portion that is continuous with the shoulder portion and is formed by folding back the outer periphery toward the radially inward side, the method comprising the steps of: While sandwiching the metal plate between the die core ring of the lower die and the pressure sleeve of the upper die, the chuck wall portion is formed in a shape in which a first curved portion that is convex radially inward and a second curved portion that is concave radially inward (convex radially outward) above the first curved portion are connected, and a central portion of the metal sheet is clamped between the panel punch of the lower die and the die center of the upper die on the radially inner side of the chuck wall portion, and while maintaining this clamped state, the die core ring and the pressure sleeve which are clamping the metal sheet on the outside are moved upward relative to each other, thereby dropping a part of the metal sheet into a recess which is open radially outward on the outer periphery of the panel punch, thereby forming the countersink portion which is continuous with the inner peripheral edge of the second curved portion, and forming the panel portion inside the countersink portion; A concave bent surface is formed on the bottom surface of the recess for forming an inner bent portion of the bottom of the countersink portion, and a virtual surface that contacts the recess at the outer edge of the panel punch is formed within a range of ±20° with respect to the horizontal plane.By molding the lower surface of the countersink portion so that it is pressed from below between the concave bent surface of the recess and the outer edge of the panel punch during the upward movement, the radius of curvature of the outer surface of the outer bent portion at the bottom of the countersink portion is formed to be smaller than the radius of curvature of the outer surface of the inner bent portion, and to be 0.21 mm or less.

[0012] When forming the countersink portion, the flange surface that extends from the concave bent surface of the panel punch to the outer peripheral edge pushes up from below. This means that the bottom of the countersink portion is pushed radially outward into the corner formed by the inner peripheral surface of the die core ring and the flange surface, making it possible to form the radius of curvature of the outer bent portion smaller than the radius of curvature of the inner bent portion. In this case, a flange surface may be provided between the outer circumferential end of the concave bent surface and the outer circumferential edge of the panel punch in the recess, the inclination angle of which with respect to the horizontal plane is ±20°.

[0013] The can lid shell manufacturing apparatus of the present invention is an apparatus for manufacturing can lid shells by pressing a metal sheet between a pair of upper and lower dies, the can lid shells comprising a central disk-shaped panel portion, a countersink portion continuous with the outer periphery of the central disk-shaped panel portion and forming an upwardly facing annular recess, a chuck wall portion whose diameter gradually increases from the outer periphery of the countersink portion toward the upper side, a shoulder portion which extends radially outward from the outer periphery of the chuck wall portion, and a curl portion which is continuous with the shoulder portion and is formed by folding back the outer periphery toward the radially inward side, A die center and a panel punch for forming the panel portion are provided in opposing relation at the center of the upper mold and the lower mold, and a pressure sleeve and a die core ring are provided in opposing relation on the outside of the die center and the panel punch, the pressure sleeve and the die core ring forming the chuck wall portion having a shape in which a first curved portion that is convex radially inward and a second curved portion that is concave radially inward (convex radially outward) above the first curved portion are connected, The recess is open radially outward and has a concave bent surface for forming an inner bent portion of the bottom of the countersink portion, and a virtual surface that contacts the recess at the outer edge of the panel punch is formed within a range of ±20° with respect to the horizontal plane. In this can end shell manufacturing apparatus, a flange surface may be provided between an outer circumferential end of the concave bent surface and an outer circumferential edge of the panel punch in the recess, the inclination angle of which with respect to a horizontal plane is ±20°. Effect of the Invention

[0014] According to the present invention, even if a buckling phenomenon occurs due to an increase in internal pressure, the occurrence of cracks can be suppressed and liquid leakage can be prevented. [Brief description of the drawings]

[0015] [Figure 1] 1 is a vertical cross-sectional view showing a main portion of a can lid according to one embodiment of the present invention. [Diagram 2] FIG. 2(a) is a vertical cross-sectional view showing a shell for a can lid, and FIG. [Diagram 3] 1 is a longitudinal sectional view showing a main part of an embodiment of a can end shell forming device of the present invention. [Figure 4] 4 is an enlarged cross-sectional view of a main part showing a state in which a metal plate is punched between the upper and lower dies of FIG. 3. [Diagram 5] 5 is a cross-sectional view showing a state in which the upper die has been further lowered from the state shown in FIG. 4 and a metal plate has been sandwiched between the outer pressure sleeve and the die core ring. [Figure 6] 6 is a cross-sectional view showing a state in which a curled portion has been formed from the state shown in FIG. 5. FIG. [Figure 7] 7 is a cross-sectional view showing a state where molding of the shell has been completed from the state shown in FIG. 6. FIG. [Figure 8] 5 to 6 are enlarged views showing the transition from FIG. 5 to FIG. 6 in more localized detail in the order (a) to (c). [Figure 9] FIG. 1 is a schematic diagram showing buckling and cracks that occurred in a conventional can lid. [Figure 10]1A to 1C are schematic diagrams for sequentially explaining the buckling phenomenon in a conventional can lid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a can end shell 1 before being made into a can end 10 will be described. This can lid shell 1 is made of an aluminum alloy and, as shown in Figures 1 and 2, is composed of a disk-shaped panel portion 2 located in the center thereof, a countersink portion 5 that continues from the outer peripheral edge of the panel portion 2 via a corner portion 3 and forms a downward-facing annular recess 4, a chuck wall portion 6 that extends upward from the outer peripheral edge of the countersink portion 5 while expanding in diameter, a shoulder portion 7 that expands radially outward from the outer peripheral edge of the chuck wall portion 6, and a curl-shaped portion 8a that is continuous with the shoulder portion 7 and is formed by bending the outer peripheral edge downward.

[0017] The panel portion 2 is formed into a disk shape overall, with a tab 50 attached to its center, and a score (not shown) or the like formed on the upper surface that serves as a drinking spout when the tab 50 is raised. The corner portion 3 is shaped to connect the outer periphery of the panel portion 2 and the inner periphery of the countersink portion 5 with a convex bent surface.

[0018] In the countersink portion 5, the inner wall portion 12 connected to the corner portion 3 extends vertically downward so as to expand slightly in diameter, and the inner bent portion 15 and the outer bent portion 16 continue from the lower edge of the inner wall portion 12 directly or via a flat or arcuate surface of a certain width to the outside of the inner bent portion 15. Both of these bent portions 15, 16 form the bottom of the countersink portion 5, and the radius of curvature R1 of the outer surface of the outer bent portion 16 is smaller than the radius of curvature R2 of the outer surface of the inner bent portion 15. On the outer surface of the can end shell, the radius of curvature R1 of the outer bent portion 16 is 0.13 mm or more and 0.21 mm or less, preferably 0.16 mm or more and 0.19 mm or less, and the radius of curvature R2 of the inner bent portion 15 is 0.23 mm or more and 0.60 mm or less, preferably 0.23 mm or more and 0.30 mm or less. An outer wall portion 17 extends upward from the outer bent portion 16 while expanding slightly in diameter, and the inner wall portion 12, the inner bent portion 15, the outer bent portion 16, and the outer wall portion 17 form a countersink portion 5 having a longitudinal cross section that is approximately U-shaped. In addition, since the inner wall portion 12 and the outer wall portion 17 are inclined so as to gradually approach each other downward, the width of the annular recess 4 gradually narrows downward.

[0019] The chuck wall portion 6 is configured to consist of a first curved portion 18 that is continuous with the upper edge of the outer wall portion 17 of the countersink portion 5 and is curved so as to be convex radially inward, and a second curved portion 19 that is continuous with the upper edge of the first curved portion 18 directly or via a flat or arcuate surface of a slight width and is curved so as to be convex radially outward. The continuous shapes of the first curved portion 18 and the second curved portion 19 give the chuck wall portion 6 a shape that expands in diameter overall toward the upward direction.

[0020] The shoulder portion 7 is continuous with the upper edge (outer peripheral edge) of the second curved portion 19 of the chuck wall portion 6, and extends radially outward while expanding in diameter and curving upward so as to be convex. In this case, the second curved portion 19 of the chuck wall portion 6 is curved with its inner peripheral surface (outer surface as the can lid 1) facing obliquely upward, so that the shape as a whole gradually expands in diameter from bottom to top, and the shoulder portion 7 continuous with this second curved portion 19 also expands in diameter from bottom to top. The curled portion 8a extends radially outward from the outer peripheral edge of the shoulder portion 7, and is formed by bending the outer peripheral edge downward. This curled portion 8a is then subjected to a curling process to be formed into a curled portion 8 in which the outer peripheral edge facing downward is folded back radially inward. In addition, scores and the like that will serve as a drinking spout are formed in the panel portion 2, a tab 50 for opening is attached to the center of the panel portion 2, and a lining material 51 is provided on the back surface of the curled portion 8, thereby completing the can lid 10.

[0021] On the other hand, the can body 40 onto which this can lid 10 is wrapped has a shape in which an outward flange portion 43 is formed continuously through a bent portion 42 to the upper end of a neck portion 41 which is narrowed from a bottomed cylindrical body portion (not shown). When the can body 40 is covered with the can lid 10, the bent portion 42 of the can body 40 is disposed so that the concave surface of the outer peripheral surface (the inner surface as the can lid 10) of the shoulder portion 7 of the can lid 10 faces the bent portion 42 of the can body 40, and the back surface from the shoulder portion 7 to the curled portion 8 faces the upper surface of the flange portion 43. Then, in this state, when the curled portion 8 of the can lid 10 is rolled up and tightened in the circumferential direction while being rolled up integrally with the flange portion 43 of the can body 40, the flange portion 43 in a folded-back state fits into the rolled-up portion of the curled portion 8, and a double rolled and tightened portion (not shown) is formed in which the can lid 10 and the can body 40 sandwich each other.

[0022] In the can lid 10 thus configured, when the nominal diameter is 202 (the outermost diameter of the seaming portion is 53.9 mm to 54.5 mm, and the outermost diameter D1 of the curled portion 8 of the can lid 1 before seaming is 59.1 mm to 59.5 mm), the diameter D2 of the bottom end of the countersink portion 5 is 46.5 mm to 47.0 mm, the depth P from the top surface of the shoulder portion 7 or the curled portion 8 to the inner bottom surface of the countersink portion 5 is 6.1 mm to 6.6 mm, and the height H1 from the bottom end of the countersink portion 5 to the underside of the panel portion 2 is 1.8 mm to 2.3 mm. The plate thickness T is 0.203 mm to 0.213 mm. The radius of curvature R3 of the outer surface of the first curved portion 18 is set to 0.9mm to 3.0mm, and the radius of curvature R4 of the outer surface of the second curved portion 19 is set to 0.6mm to 3.0mm. The radius of curvature R5 of the outer surface of the shoulder portion 7 is set to 1.2mm to 3.0mm. The angle θ1 between the common tangent A of the outer surfaces of the shoulder portion 7 and the first curved portion 18 and the outer surface of the panel portion 2 is set to 45° to 70°.

[0023] When the nominal diameter is 200 (the outermost diameter of the seaming portion is 51.9mm to 52.5mm, and the outermost diameter D1 of the curled portion 8 of the can lid 1 before seaming is 56.8mm to 57.2mm), the diameter D2 of the bottom end of the countersink portion 5 is 44.1mm to 44.5mm, the depth P from the top surface of the shoulder portion 7 or the curled portion 8 to the inner bottom surface of the countersink portion 5 is 6.1mm to 6.6mm, and the height H1 from the bottom end of the countersink portion 5 to the underside of the panel portion 2 is 1.8mm to 2.3mm. The plate thickness T is 0.203mm to 0.213mm. The radius of curvature R3 of the outer surface of the first curved portion 18 is set to 0.9mm to 3.0mm, and the radius of curvature R4 of the outer surface of the second curved portion 19 is set to 0.6mm to 3.0mm. The radius of curvature R5 of the outer surface of the shoulder portion 7 is set to 1.2mm to 3.0mm. The angle θ1 between the common tangent A of the outer surfaces of the shoulder portion 7 and the first curved portion 18 and the outer surface of the panel portion 2 is set to 45° to 70°.

[0024] A score or the like that will serve as a drinking opening is formed in the panel portion 2 of this can lid shell 1, a tab 50 for opening is attached to the center of the panel portion 2, and a lining material 51 (omitted in Figure 1) is provided on the back surface of the curled portion 8, resulting in the can lid 10 shown in Figure 2(b).

[0025] The device 11 for manufacturing the can lid shell 1 of this embodiment, as shown in FIG. 3, comprises an upper die 12 and a lower die 13 attached to a press machine (not shown), and a metal plate 9 is placed between the upper die 12 and the lower die 13, which is punched into a circle to form the can lid shell 1. The main part is shown in FIG. 4 to FIG.

[0026] The upper die 12 is provided with a die center 23 for forming the surface of the panel portion 2 of the shell 1, and an annular blank draw die 24 surrounding the die center 23, and an inner pressure sleeve 25 and an outer pressure sleeve 26 are provided between the blank draw die 24 and the die center 23. In this case, the tip 25a of the inner pressure sleeve 25 is disposed on the die center 23 side, and the tip 26a of the outer pressure sleeve 26 is disposed on the blank draw die 24 side, and the tip 25a of the inner pressure sleeve 25 and the tip 26a of the outer pressure sleeve 26 are disposed concentrically with the axis of the die center 23 in the form of a double sleeve.

[0027] On the other hand, the lower die 13 is provided with a circular panel punch 33 for forming the back surface of the panel portion 2 of the shell 1, and an annular cut edge die 34 for punching out the metal sheet 9 between the blank draw die 24 and the lower die 13, facing the die center 23 of the upper die, and a lower pressure sleeve 35 facing the blank draw die 24 of the upper die and a die core ring 36 facing the inner pressure sleeve 25 and the outer pressure sleeve 26 are provided between the cut edge die 34 and the panel punch 33. In this case, the tip 35a of the lower pressure sleeve 35 is disposed on the cut edge die 34 side, and the tip 36a of the die core ring 36 is disposed on the panel punch 33 side, and the tip 35a of the lower pressure sleeve 35 and the tip 36a of the die core ring 36 are disposed in a double ring shape concentrically with the axis of the panel punch 33 (coaxial with the axis of the die center 23 described above).

[0028] A recess 60 for forming the countersink portion 5 is formed on the outer periphery of the panel punch 33. This recess 60 is formed by, in order from the inner periphery, a convexly curved surface 61 bent from the upper surface of the panel punch 33, a vertical wall surface 62 continuing from the inner periphery of the convexly curved surface 61, a concavely curved surface 63 bent concavely from the lower end of the vertical wall surface 62, and a flange surface 64 extending from the inner periphery of the concavely curved surface 63 to the outer periphery of the panel punch 33. The vertical wall surface 62 is vertical or inclined so as to gradually increase in diameter from its upper edge to its lower edge, and the inclination angle θ2 is set in the range of 0° to 20° with respect to the vertical plane. The flange surface 64 is formed as an inclined surface with an inclination angle θ3 with respect to the horizontal plane in the range of ±20°. In this case, the outer diameter D3 of the upper edge of the vertical wall surface 62 is 44.3 mm to 45.7 mm for the nominal diameter 202 and 42.2 mm to 43.6 mm for the nominal diameter 200, the maximum depth H2 of the recess 60 is 1.9 mm to 2.3 mm, the radius of curvature of the concavely curved surface 63 is 0.5 mm to 1.2 mm, and the radius of curvature of the convexly curved surface 61 is 0.5 mm to 1.2 mm. Although the vertical wall surface 62 is formed straight in vertical cross section, it may be slightly curved.

[0029] The recess 60 thus formed on the outer periphery of the panel punch 33 forms a void between it and the die core ring 36 disposed outside it. If the radial distance from the inner periphery of the die core ring 36 to the outer periphery of the concavely curved surface 63 is N (mm), the radius of curvature Rf (mm) of the concavely curved surface is 0.4×N or more and 0.85×N or less.

[0030] Next, a method for forming the can end shell 1 by the can end shell forming apparatus 11 configured as above will be described. A metal sheet 9 made of an aluminum alloy or the like is placed between an upper die 12 and a lower die 13 of a can end shell forming device 11. When the upper die 12 is lowered so as to close both dies 12, 13, as shown in FIG. 4, the metal sheet 9 is first sandwiched between the blank draw die 24 of the upper die 12 and the lower pressure sleeve 35 of the lower die, and the metal sheet 9 is punched into a circle between the blank draw die 24 and the cut edge die 34. When the upper die 12 is further lowered, the metal sheet 9 is annularly sandwiched between the outer pressure sleeve 26 and the die core ring 36 on the inside of the outer peripheral edge portion sandwiched between the blank draw die 24 and the lower pressure sleeve 35, as shown in Fig. 5, and when the upper die 12 is further lowered in this sandwiched state, the outer peripheral edge portion of the metal sheet 9 is drawn while being sandwiched between the blank draw die 24 and the lower pressure sleeve 35, as shown in Fig. 6, and the curled portion 8a is formed so as to be bent at the tip outer peripheral portion of the die core ring 36. Meanwhile, inside the outer pressure sleeve 26, the inner pressure sleeve 25 is lowered to sandwich the metal sheet 9 between the die core ring 36, thereby forming the chuck wall portion 6 having the upper curved portion 19 and the lower curved portion 18, and the central portion of the metal sheet 9 is sandwiched between the die center 23 and the panel punch 33. Next, as shown in FIG. 7, the die center 23 and the panel punch 33 are moved slightly upward relative to the inner pressure sleeve 25 and the die core ring 36 to form the panel portion 2 and the countersink portion 5.

[0031] The forming process of the countersink portion 5 will be explained in more detail with reference to Fig. 8. Since the recess 60 is formed on the outer periphery of the panel punch 33 as described above, when the die center 23 and the panel punch 33, while sandwiching the metal plate 9, move upward relative to the inner pressure sleeve 25 and the die core ring 36 as shown in Fig. 8(a) and (b), the part of the metal plate arranged above the recess 60 is not supported from below, so it is dropped into the recess 60 and bent and deformed to be convex downward. This part deformed to be convex downward (referred to as the bent and deformed part 52) ​​extends downward within the recess 60 as the die center 23 and the panel punch 33 move upward, and when its lower end comes into contact with the flange surface 64 at the bottom of the recess 60 and the concave bent surface 63 continuing from the flange surface 64, it is pushed up from below by these. At this time, as shown in Figure 8 (c), the bottom of the bent deformation portion 52 is pushed radially outward by the concave bent surface 63 and the flange surface 64 into the corner formed by the inner surface of the die core ring 36 and the flange surface 64, so that the molded countersink portion 5 can be formed so that the radius of curvature R1 of the outer bent portion 16 is smaller than the radius of curvature R2 of the inner bent portion 15. In particular, when the flange surface 64 slopes downwardly radially outward, a component force along the slope of the flange surface 64 is generated in the vertical force pushing up from below, and this component force makes it easier for the lower end surface of the bent deformation portion 52 to be deformed so as to be pushed radially outward, making it possible to form a smaller radius of curvature R1 of the outer bent portion 16.

[0032] In addition, when a high-strength material (e.g., a yield strength of 410 MPa or more) is used for the can end shell 1, the outer bent portion 16 of the countersink portion 5 may become the starting point of cracks, so the inclination angle θ3 of the flange surface 64 is set to a positive angle (an angle that slopes upward as it moves radially outward from the outer peripheral edge of the concave bent surface 63) to ease the processing, and when a low-strength material (e.g., a yield strength of 380 MPa or less) is used, the inclination angle θ3 of the flange surface 64 is set to a negative angle (an angle that slopes downward as it moves radially outward) to further enhance the effect of the outer bent portion 16.

[0033] When the molding is completed in this manner, the die center 23 is lifted away from the panel portion 1, and the inner pressure sleeve 25, the outer pressure sleeve 26 and the blank draw die 24 are lifted away from the can end shell 1. As described above, the can lid shell 1 is turned into a can lid 10 by forming scores and the like that will serve as a drinking spout in the panel portion 2, attaching a tab 50 for opening to the center of the panel portion 2, and providing a lining material 51 on the back surface of the curled portion 8.

[0034] The can lid 10 manufactured in this manner has a radius of curvature R1 of the outer surface of the outer bent portion 16 at the bottom of the countersink portion 5 that is smaller than that of the inner bent portion 15 and is formed to be 0.21 mm or less.Therefore, even if buckling occurs due to internal pressure when the can lid is wrapped around the can body and a corner is formed on the upper surface side, the outer bent portion 16 prevents the corner from passing through the bottom of the countersink portion 5, allowing the length of the corner on the lower surface to be increased, thereby mitigating the tensile stress generated around the corner on the upper surface side and preventing the occurrence of cracks.

[0035] The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the radius of curvature of the concavely curved surface 63 may be made large so that the concavely curved surface 63 reaches the outer periphery of the recess 60. In this case, there is no flat flange surface, but the angle between the virtual surface that is in contact with the concavely curved surface at the outer periphery of the recess and the horizontal plane is regarded as the inclination angle θ3, and this angle may be formed within the range of ±20° with respect to the horizontal plane. EXAMPLES

[0036] A can lid was produced with the dimensions of each part shown in Fig. 1 being plate thickness T = 0.208 mm, outer diameter D1 = 59.3 mm, P = 6.35 mm, and H1 = 2.0 mm. At this time, the countersink part was formed with the width N of the space formed by the recess 60 shown in Fig. 8 being 1.2 mm, the outer diameter D3 of the upper edge of the vertical wall part 62 being 45.3 mm, the maximum depth H2 of the recess 60 being 2.1 mm, the radius of curvature of the concavely curved surface 63 being 0.75 mm, and the radius of curvature of the convexly curved surface 61 being 0.9 mm. The angle θ2 of the vertical wall part 62 was 0°, and the inclination angle θ3 of the flange surface 64 was 0°. For comparison, a can lid was formed using a die having no flange surface, i.e., a die extending straight downward from a convex bent surface. The can lids were then subjected to measurements of the seam, pressure resistance, and the number of lids that developed cracks during buckling. The pressure resistance was evaluated by fixing the can with the lid on a water pressure buckling tester (manufactured by Ace Tech Co., Ltd.) at a position 95 mm from the ground, and increasing the internal pressure of the can with water pressure at a speed of 33 kPa / s until the dome-shaped center part reversed (buckled). In addition, the presence or absence of cracks during buckling was visually observed. 300 cans of each type were measured, and the results are shown in Table 1.

[0037] [Table 1]

[0038] There is no significant difference in the average compressive strength between the Example and the Comparative Example, but 27% of the Comparative Example cans developed cracks during buckling, whereas no cans developed cracks in the Example. In this Example, the radius of curvature of the outer surface of the outer bent part of the countersink was measured, and was 0.23 mm to 0.30 mm in the Comparative Example, but 0.16 mm to 0.21 mm in the Example. [Explanation of symbols]

[0039] 1 Can lid shell 2 Panel section 3 Corner section 4 Annular recess 5 Countersink section 6 Chuck wall 7 Shoulder section 8 Curl section 8a Curl Shaped Part 9 metal plate 10 Can Lids 11 Shell forming device 12 Upper mold 13 Lower mold 23 Die Center 24 Blank Draw Die 25 Inner Pressure Sleeve 26 Outer pressure sleeve 33 Panel punch 34 Cut Edge Die 35 Lower Pressure Sleeve 36 Dicor Ring 50 Tabs 51 Lining material 60 Recess 61 Convex bent surface 62 Vertical wall 63 Concave curved surface 64 Flange surface 64a Circular surface

Claims

1. A method for manufacturing a can lid shell, comprising: a central disk-shaped panel portion; a countersink portion that is continuous with the outer periphery of the central disk-shaped panel portion and forms an upwardly facing annular recess; a chuck wall portion that gradually expands in diameter from the outer periphery of the countersink portion toward the upper side; and a curl portion that expands radially outward from the outer periphery of the chuck wall portion and is folded back radially inward from the outer periphery of the chuck wall portion, by pressing a metal sheet between a pair of upper and lower dies, the method comprising the steps of: forming the chuck wall portion into a shape in which a first curved portion that is convex radially inward and a second curved portion that is concave radially inward above the first curved portion are continuous with each other while the metal sheet is sandwiched between a die core ring of the lower die and a pressure sleeve of the upper die; a central portion of the metal plate is clamped between the panel punch of the lower die and the die center of the upper die on the radially inner side of the chuck wall portion, and while maintaining this clamped state, the die core ring and the pressure sleeve are moved upward relative to each other while clamping the metal plate on the outer side thereof, thereby dropping a part of the metal plate into a recess that is open radially outward on the outer periphery of the panel punch, thereby forming the countersink portion that is continuous with the inner peripheral edge of the second curved portion, and forming the panel portion inside the countersink portion; A method for manufacturing a can lid shell, characterized in that a concave bent surface for forming an inner bent portion of the bottom of the countersink portion, and a flange surface extending from the inner peripheral edge of the concave bent surface to the outer peripheral edge of the panel punch are formed on the bottom surface of the recess, and a virtual surface that contacts the recess at the outer peripheral edge of the panel punch is formed within a range of ±20° with respect to the horizontal plane, and during the upward movement, the flange surface between the concave bent surface of the recess to the outer peripheral edge of the panel punch is molded to press the lower surface of the countersink portion from below, thereby forming the radius of curvature of the outer surface of the outer bent portion at the bottom of the countersink portion to be smaller than the radius of curvature of the outer surface of the inner bent portion, and to be 0.21 mm or less.

2. A method for manufacturing a can lid shell as described in claim 1, characterized in that a flange surface having an inclination angle of ±20° with respect to the horizontal plane is formed between the outer peripheral end of the concave bent surface and the outer peripheral edge of the panel punch in the recess, and during the upward movement, the flange surface presses the lower surface of the countersink portion from below together with the concave bent surface.

3. An apparatus for manufacturing a can end shell by pressing a metal plate between a pair of upper and lower dies, the can end shell having a central disk-shaped panel portion, a countersink portion which is continuous with the outer periphery of the central disk-shaped panel portion and forms an upwardly facing annular recess, a chuck wall portion which gradually expands in diameter from the outer periphery of the countersink portion toward the upper side, and a curl portion which expands radially outward from the outer periphery of the chuck wall portion and is formed by folding back the outer periphery toward the radially inward side, the apparatus comprising: a die center and a panel punch for forming the panel portion are provided in opposing relation at the center of the upper mold and the lower mold, and a pressure sleeve and a die core ring are provided in opposing relation on the outside of the die center and the panel punch, the pressure sleeve and the die core ring forming the chuck wall portion having a shape in which a first curved portion that is convex radially inward and a second curved portion that is concave radially inward above the first curved portion are connected, a concave bent surface for forming an inner bent portion of the bottom of the countersink portion, the concave bent surface being open radially outward, and a flange surface extending from the inner peripheral edge of the concave bent surface to the outer peripheral edge of the panel punch and pressing the lower surface of the countersink portion from below, the concave bent surface being open radially outward, the flange surface being open radially outward, the flange surface extending from the inner peripheral edge of the concave bent surface to the outer peripheral edge of the panel punch and pressing the lower surface of the countersink portion from below, and a virtual surface contacting the concave portion at the outer peripheral edge of the panel punch being formed within a range of ±20° with respect to a horizontal plane.

4. 4. The can end shell manufacturing apparatus according to claim 3, further comprising a flange surface between the outer circumferential end of the concave bending surface and the outer circumferential edge of the panel punch in the recess, the flange surface having an inclination angle of ±20° with respect to a horizontal plane.

5. The panel is made up of a central disk-shaped panel and a ring-shaped recess that extends upwards from the outer periphery. A can lid shell comprising a countersink portion, a chuck wall portion which gradually expands in diameter from an outer circumferential edge of the countersink portion toward an upper side, and a curl portion which expands radially outward from an outer circumferential edge of the chuck wall portion and folds the outer circumferential edge radially inward, the chuck wall portion has a shape in which a first curved portion that is convex toward the inside in the radial direction and a second curved portion that is above the first curved portion and is concave toward the inside in the radial direction are continuous with each other, The can lid is characterized in that the radius of curvature of the outer surface of the outer bent portion at the bottom of the countersink portion is smaller than the radius of curvature of the outer surface of the inner bent portion and is 0.21 mm or less.

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