JP7709283B2 - Can lid shell manufacturing method and can lid shell manufacturing device - Google Patents

Description

The present invention relates to a method and an apparatus for manufacturing can lid shells, which are can lids that are fastened to the open end of a can body.

Conventional beverage can lids have a disk-shaped panel in the center, a countersink around the periphery, and a curled section connected to the periphery via a chuck wall. The panel has a score for forming an opening, and a tab for the opening operation. In recent years, in response to the demand for thinner walls, instead of a nearly straight tapered chuck wall, there has been an increase in shapes that reduce the diameter of the panel by using a chuck wall with a vertical cross section that is a continuous shape of two curved sections.

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 continuously formed. In this case, a can lid having an overall diameter of (D4) = about 56.896 mm and a can lid having (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 of the blank before being formed into a can lid is about 0.2159 mm. The reference characters in parentheses are the reference characters used in the publication (as in Patent Document 2).

On the other hand, Patent Document 2 discloses a method for manufacturing such a can end. In Patent Document 2, the cup portion (C) is sandwiched between an annular outer pressure sleeve (55) and an upper portion (99) of a die core ring (98), 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 the 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 moving the central portion of the cup portion (C) up and down while sandwiching it between the center punch (65) of the die and the circular panel punch (118).

Patent No. 4647207 Patent No. 5649189

The can lid described in Patent Document 1 has a zipper wall formed in a shape in which a curved portion that is convex radially inward at the lower part and a curved portion that is concave radially inward (convex radially outward) at the upper part are connected, so the flat diameter of the panel part is limited to a small size. In this case, the vertical length of the score machined into the panel part is limited to a short length, which makes it difficult to pour and increases the amount of liquid remaining in the bottle can. In this regard, if the flat diameter of the panel part is simply increased, microcracks will occur in the wall part (hereinafter referred to as the panel wall) on the panel part side of the countersink part that is continuous with the outer periphery of the panel part, and when the internal pressure of the can rises and the countersink part is inverted, a buckling phenomenon occurs, whereby a part of the panel part is raised and protrudes in a corner shape, and a crack will occur at the tip of the corner, causing the beverage to spray out.

The present invention was made in consideration of these circumstances, and aims to provide a can lid shell manufacturing method and can lid shell manufacturing device that can prevent cracks from occurring in the panel wall.

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:
The lower die is provided with a panel punch having a corner connecting the upper face and the side face formed on a first bent face that is convex outward, and a die core ring provided on the radially outer side of the panel punch with a gap therebetween, and the upper die is provided with a die center having an annular convex portion formed on a second bent face that protrudes from the outer periphery of the lower end side toward the gap of the lower die and has a tip portion that is convex toward the lower die, and a pressure sleeve on the radially outer side of the die center,
While sandwiching the metal plate between the die core ring and the pressure sleeve, 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 to each other,
When the central portion of the metal plate is clamped between the panel punch and the die center radially inside the chuck wall portion, the metal plate is bent so as to be pushed toward the gap by the first curved surface and the second curved surface of the annular convex portion, thereby forming a recess in the metal plate, and then, while maintaining the clamped state between the panel punch and the die center, the panel punch and the die center are moved upward relative to the die core ring and the pressure sleeve which clamp the metal plate on the outside, so that the recessed portion of the metal plate is gradually lowered into the gap, gradually increasing the depth of the recess to form the annular recess, thereby forming the countersink portion which is continuous with the inner peripheral edge of the second curved portion, and the panel portion is formed inside the countersink portion.

In the conventional manufacturing method of can end shells, when the metal plate 9J changes from the bottom dead center shown in Fig. 9(a) to the upward stroke shown in Fig. 9(b) during the forming process, the metal plate 9J is bent extremely to form a bending point P1 on the die circumscribing the portion that will become the countersink. As the forming of the countersink portion progresses as shown in Fig. 9(c) and Fig. 9(d), the bending point P1 on the metal plate 9J is returned to a straight line, and the bending point P2 moves to a position on the panel side of the countersink portion (panel wall) as shown in Fig. 9(d). As a result of the accumulation of excessive work hardening in the panel wall in this way, microcracks are generated.
This phenomenon becomes more noticeable as the thickness of the metal plate used becomes thinner and as the gap between the inner diameter surface of the die core ring 36J and the outer diameter surface of the panel punch 33J becomes smaller.

In the present invention, the metal plate is clamped to form the chuck wall portion, and the metal plate is bent by the first bending surface of the panel punch and the second bending surface of the annular protrusion, so that the recess that will become the annular recess of the countersink portion is formed in advance so as to follow the second bending surface, thereby eliminating the location where bending stress concentrates without creating bending points in the metal plate. Furthermore, because the recess is formed to gradually deepen, excessive work hardening does not occur in the panel wall of the countersink. This makes it possible to prevent cracks from occurring in the panel wall, and to prevent the beverage from spouting even if the buckling phenomenon occurs.

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 corners connecting the upper surface and side of the panel punch are formed into a first curved surface that convex outward, and the outer periphery of the lower end side of the die center is formed with an annular convex portion that protrudes toward the lower mold, has a tip that convex toward the lower mold, and has a second curved surface that is located radially outward from the first curved surface, the height from the lower end surface of the die center to the apex of the second curved surface of the annular convex portion is set to 0.3 mm or more and 1.2 mm or less, a gap is formed between the lower die core ring and the panel punch, and the annular convex portion is positioned facing the gap.

The present invention can prevent cracks from occurring in the panel wall, so that 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.

1 is a vertical cross-sectional view showing a main portion of a can lid according to one embodiment of the present invention. FIG. 2A is a vertical cross-sectional view showing a shell for a can lid, and FIG. 2B is a vertical cross-sectional view showing a can lid. 1 is a longitudinal sectional view showing a main part of an embodiment of a can end shell forming device of the present invention. 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 . FIG. 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. FIG. 6 is a cross-sectional view showing a state in which a curled portion has been formed from the state shown in FIG. 5 . 7 is a cross-sectional view showing a state where molding of the shell is completed from the state shown in FIG. 6. FIG. 5 to 6 are enlarged views showing the transition from FIG. 5 to FIG. 6 in more local detail in the order (a) to (d). 1A to 1D are enlarged views showing in detail the vicinity of a portion that will become a countersink in a conventional manufacturing process for can lid shells.

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 periphery 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 periphery of the countersink portion 5 while expanding in diameter, a shoulder portion 7 that expands radially outward from the outer periphery 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 periphery downward.

The panel portion 2 is formed into a disk shape overall, with a tab 50 attached to its center, and a score (not shown) that opens when the tab 50 is raised to form a drinking spout is formed on the top surface. 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 curved surface.

In the countersink portion 5, an inner wall portion 52 (corresponding to the panel wall of the present invention) connected to the corner portion 3 extends vertically downward so as to expand slightly in diameter, and an inner bent portion 55 is connected to the lower edge of the inner wall portion 52, and an outer bent portion 56 is connected to the inner bent portion 55 directly or via a flat or arcuate surface of a certain width.
The outer wall portion 57 extends upward from the outer bent portion 56 while slightly expanding in diameter, and the inner wall portion 52, the inner bent portion 55, the outer bent portion 56, and the outer wall portion 57 form a countersink portion 5 having an approximately U-shaped cross section.
In addition, since the inner wall portion 52 and the outer wall portion 57 are inclined so as to gradually approach each other downward, the width of the annular recess 4 gradually narrows downward.

The chuck wall 6 is shaped to consist of a first curved portion 18 that is continuous with the upper edge of the outer wall portion 57 of the countersink portion 5 and 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 arc surface of a certain width and curved so as to be convex radially outward. The continuous shape of the first curved portion 18 and the second curved portion 19 gives the chuck wall 6 an overall shape that expands in diameter upward.

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 being curved so as to be convex upward and expanding in diameter. 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 is gradually expanded in diameter from the bottom to the top, and the shoulder portion 7 continuous with this second curved portion 19 also expands in diameter from the bottom to the top.
The curled portion 8a extends radially outward from the outer periphery of the shoulder portion 7, and is formed by bending the outer periphery downward. This curled portion 8a is then subjected to a curling process to be formed into a curled portion 8 having a shape in which the outer periphery 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.

On the other hand, the can body 40 onto which this can lid 10 is wound and tightened 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.

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 diameter D3 of the panel portion 2 is 42.5 mm to 44.5 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 0.9 mm to 3.0 mm, and the radius of curvature R4 of the outer surface of the second curved portion 19 is set to 0.6 mm to 3.0 mm. The radius of curvature R5 of the outer surface of the shoulder portion 7 is set to 1.2 mm to 3.0 mm. 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°.

When the nominal diameter is 200 (the outermost diameter of the seaming portion is 51.9 mm to 52.5 mm, and the outermost diameter D1 of the curled portion 8 of the can lid 1 before seaming is 56.8 mm to 57.2 mm), the diameter D2 of the bottom end of the countersink portion 5 is 44.1 mm to 44.5 mm, the diameter D3 of the panel portion 2 is 40.7 mm to 42.5 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 0.9 mm to 3.0 mm, and the radius of curvature R4 of the outer surface of the second curved portion 19 is set to 0.6 mm to 3.0 mm. The radius of curvature R5 of the outer surface of the shoulder portion 7 is set to 1.2 mm to 3.0 mm. 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°.

In addition, if the diameter D3 of the panel portion 2 is less than 93% of the diameter D2 of the bottom end of the countersink portion 5, pouring performance will deteriorate and the amount of residual liquid will increase. For this reason, in this embodiment, the diameter D3 of the panel portion 2 is set to 93% or more of the diameter D2 of the bottom end of the countersink portion 5.

The panel portion 2 of this can lid shell 1 is scored to form a drinking opening, a tab 50 for opening is attached to the center of the panel portion 2, and a lining material 51 (not shown in Figure 1) is provided on the back side of the curled portion 8, resulting in the can lid 10 shown in Figure 2(b).

The can lid shell forming device 11 for producing the can lid shell 1 of this embodiment, as shown in FIG. 3, is configured by attaching an upper die 12 and a lower die 13 to a press machine (not shown), and a metal plate 9 is placed between the upper die 12 and the lower die 13, and the can lid shell 1 is formed by punching it into a circle.
The main part is shown in FIG. 4 to FIG.

The upper mold 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 arranged on the die center 23 side, and the tip 26a of the outer pressure sleeve 26 is arranged 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 arranged in a double sleeve shape concentric with the axis of the die center 23.

In addition, an annular convex portion 231 is formed on the outer periphery of the lower end side of the die center 23. The annular convex portion 231 has a second curved surface 232 that protrudes toward the lower mold 13 and has a tip that is convex toward the lower mold 13, a third curved surface 233 formed on the radially inner base end side of the second curved surface 232, and a fourth curved surface 234 formed on the radially outer base end side of the second curved surface 232. The height of the annular convex portion 231, that is, the height w1 from the lower end surface of the die center 23 to the apex of the second curved surface 232, is set to 0.3 mm or more and 1.2 mm or less. The radius of curvature of the second curved surface 232 is 0.3 mm to 0.8 mm, the radius of curvature of the third curved surface 233 is 0.3 mm to 1.2 mm, and the radius of curvature of the fourth curved surface 234 is 0.8 mm to 1.8 mm.

On the other hand, the lower mold 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 plate 9 between the blank draw die 24 and the lower mold 13, and between the cut edge die 34 and the panel punch 33, a lower pressure sleeve 35 facing the blank draw die 24 of the upper mold and a die core ring 36 facing the inner pressure sleeve 25 and the outer pressure sleeve 26 are provided. In this case, the tip 35a of the lower pressure sleeve 35 is arranged on the cut edge die 34 side, and the tip 36a of the die core ring 36 is arranged 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 arranged 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).

A gap 60 for forming the countersink portion 5 is formed between the panel punch 33 and the die core ring 36. The width of this gap 60 is set to 1.1 mm to 1.6 mm, and faces the annular protrusion 231 of the die center 23 described above.
In addition, the corners connecting the upper surface and the side surface of the panel punch 33 are formed into a first bent surface 331 that is convex outward, and the radius of curvature of the first bent surface 331 is set to 0.3 mm to 1.1 mm. This first bent surface 331 is disposed radially inward from the second bent surface 232, and is provided to bend the metal plate 9 together with the second bent surface 232 to form the recess 91.

Next, a method for forming the can end shell 1 by the can end shell forming device 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 lid 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 circular shape 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 outer peripheral portion of the tip 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 upwardly relative to the inner pressure sleeve 25 and the die core ring 36 to form the panel portion 2 and the countersink portion 5.

The forming process of the countersink portion 5 will be explained in more detail with reference to Fig. 8. Since a gap 60 is formed between the panel punch 33 and the die core ring 36 as described above, when the die center 23 and the panel punch 33 clamp the metal plate 9, the metal plate 9 is pressed toward the gap 60 by the annular convex portion 231 as shown in Fig. 8(a), and the metal plate 9 is bent by the first bent surface 331 of the panel punch 33 and the second bent surface 232 of the annular convex portion 231 to form a recess 91. By forming the recess 91 in advance so as to follow the second bent surface 232 in this way, no extreme bending points are created in the metal plate 9, and no areas where bending stress is concentrated are formed. When the metal plate 9 moves upward relative to the inner pressure sleeve 25 and the die core ring 36 from the bottom dead center shown in Fig. 8(a) while maintaining this clamping state, as shown in Fig. 8(b), the part of the metal plate 9 located above the gap 60 is dropped into the gap 60 along the first bent surface 331 because there is no support from below. At this time, as the die center 23 and the panel punch 33 move upward, the recess 91 extends downward within the gap 60, and is deformed so that the depth of the recess gradually increases. As a result, as shown in FIG. 8(c), the recess 91 is formed in the annular recess 4, and becomes the countersink portion 5.

When the forming is completed in this manner, as shown in FIG. 8( d ), the die center 23 is lifted away from the panel portion 2, and the inner pressure sleeve 25, the outer pressure sleeve 26 and the blank draw die 24 are lifted to move them 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.

The can lid 10 thus manufactured has a metal plate 9 sandwiched between it to form the chuck wall 6, and the metal plate 9 is bent by the first bent surface 331 of the panel punch 33 and the second bent surface 232 of the annular protrusion 231, so that the recess 91 that will become the annular recess 4 of the countersink portion 5 is formed in advance so as to conform to the second bent surface 232. This makes it possible to eliminate areas where bending stress is concentrated without creating extreme bending points in the metal plate 9. In addition, since the recess 91 is formed to gradually deepen, excessive work hardening does not occur in the panel wall (inner wall portion 52) of the countersink portion 5. This makes it possible to suppress the occurrence of cracks in the panel wall (inner wall portion 52), and to suppress the beverage from spouting even if the buckling phenomenon occurs.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in order to set the outer diameter of the flat portion of the panel punch larger, the first bent surface 331 of the panel punch may be a combination of two R's, one large and one small, and the radius of curvature of the R connected to the panel punch flat surface may be set smaller than the radius of curvature of the R connected to the outer diameter of the panel punch. In this case, the diameter D3 of the panel portion 2 can be reliably set to 93% or more of the diameter D2 of the bottom end of the countersink portion 5.

Can lids were produced with the dimensions of each part shown in Fig. 1 being sheet thickness T = 0.208 mm, outer diameter D1 = 59.3 mm, P = 6.35 mm, and H1 = 2.0 mm. In this case, in the example, an annular convex part with a second bent surface having a curvature radius R = 0.4 mm, a third bent surface having a curvature radius R = 1.02 mm, a fourth bent surface having a curvature radius R = 1.55 mm, and a height of 0.45 mm was provided at the die center, while in the comparative example, no annular convex part was provided and the curvature radius R of the corner of the die center was 1.55 mm. In both the example and the comparative example, the curvature radius R of the first bent surface of the panel punch was set to 0.8 mm to form a countersink part.
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 can lid rolled up at a position 95 mm from the ground to a hydraulic buckling tester (manufactured by Acetech Co., Ltd.), increasing the internal pressure of the can with water pressure at a pressure increase speed of 33 kPa/s, and evaluating the maximum pressure reached until the dome-shaped central part inverted (buckled). In addition, the presence or absence of cracks during buckling was visually observed.
120 cans of each type were measured, and the results are shown in Table 1.

There was no significant difference in the average pressure resistance between the Example and Comparative Example, but while cracks occurred in 100% of the Comparative Example cans during buckling, no cracks occurred in the Example cans.

1 Can lid shell 2 Panel portion 3 Corner portion 4 Annular recess 5 Countersink portion 52 Inner wall portion (panel wall)
Reference Signs List 6: chuck wall portion 7: shoulder portion 8: curl portion 8a: curl shaped portion 9: metal plate 10: can lid 11: shell forming device 12: upper mold 13: lower mold 23: die center 231: annular convex portion 232: second bent surface 233: third bent surface 234: fourth bent surface 24: blank draw die 25: inner pressure sleeve 26: outer pressure sleeve 33: panel punch 331: first bent surface 34: cut edge die 35: lower pressure sleeve 36: die core ring 50: tab 51: lining material 60: gap 61: convex bent surface 62: vertical wall surface 63: concave bent surface 64: flange surface 64a: arc surface

Claims (3)

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; a shoulder portion that expands 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:
The lower die is provided with a panel punch having a corner connecting the upper face and the side face formed on a first bent face that is convex outward, and a die core ring provided on the radially outer side of the panel punch with a gap therebetween, and the upper die is provided with a die center having an annular convex portion formed on a second bent face that protrudes from the outer periphery of the lower end side toward the gap of the lower die and has a tip portion that is convex toward the lower die, and a pressure sleeve on the radially outer side of the die center,
While sandwiching the metal plate between the die core ring and the pressure sleeve, 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 to each other,
a panel punch and a die center that are spaced apart from each other and that are spaced apart from each other, the panel punch and the die center being moved upward relative to the die core ring and the pressure sleeve that are holding the metal plate on the outside thereof while maintaining the clamped state between the panel punch and the die center, thereby gradually lowering the recessed portion of the metal plate into the gap, gradually increasing the depth of the recess to form the annular recess, and 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. An apparatus for manufacturing a can end shell, which is formed by pressing a metal sheet between a pair of upper and lower dies, to have 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, a shoulder portion that expands radially outward from the outer periphery of the chuck wall portion, and a curl portion that 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,
a corner connecting an upper surface and a side surface of the panel punch is formed into a first bent surface that is convex outward, and an annular convex portion is formed on an outer periphery of a lower end side of the die center, the corner protruding toward the lower die, the tip of the corner being convex toward the lower die, and the second bent surface located radially outward from the first bent surface, a height from the lower end surface of the die center to an apex of the second bent surface of the annular convex portion is set to be smaller than a height from a lower end of the countersink to a lower surface of the panel portion, a gap is formed between the lower die core ring and the panel punch, and the annular convex portion is disposed opposite the gap, and the panel punch and the die center are capable of moving upward relative to the die core ring and the pressure sleeve . The can lid shell manufacturing apparatus according to claim 2, characterized in that the height from the lower end surface of the die center to the apex of the second curved surface of the annular convex portion is set to be 0.3 mm or more and 1.2 mm or less, and the height from the bottom end of the countersink portion to the lower surface of the panel portion is 1.8 mm to 2.3 mm.