Method for manufacturing bottle cans

Abstract

To improve formability in a drawing and ironing process, suppress occurrence of wrinkles and cracks, and broaden a range of selectable materials.SOLUTION: A method comprises: a cup forming step in which a metal plate is subjected to a drawing process to form a cup having a bottom plate portion; and a tubular body forming step in which the cup is subjected to redrawing and ironing between a punch sleeve and a redraw die to form a tubular body having a smaller diameter and greater depth than the cup, while processing the bottom portion of the tubular body. In the cup forming step, a circular plate portion and a tapered surface portion are formed concentrically in the central portion of the bottom plate portion, where the circular plate portion protrudes from the peripheral portion, and where the tapered surface portion inclines in a direction such that the depth of the cup gradually becomes shallower radially outward from the periphery of the circular plate portion. In the tubular body forming step, the tip of the punch sleeve is brought into contact with the outer peripheral portion of the circular plate portion to perform the redrawing process.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a bottle can having a threaded portion at a reduced-diameter mouth portion of a bottomed cylindrical can.

Background Art

[0002] As aluminum cans capable of containing contents such as beverages and foods, there are open-top cans in which a can lid is joined by double seaming and bottle cans in which a cap is wound and joined. As manufacturing methods for these, the DI forming method is known.

[0003] For example, in Patent Document 1, a cup is formed so as to form a tapered surface that bends from a predetermined position at the bottom to the outer edge at a predetermined angle, and the bending start position of the tapered surface at the bottom is arranged between the holding position and the punch position of the cup. A method of performing redrawing on the cup is disclosed. Since the bending start position is arranged between the holding position and the punch position of the cup, it is described that the rigidity of the non-restrained portion is increased by the bent portion, and the generation of bottom wrinkles is suppressed.

[0004] The cup disclosed in Patent Document 2 has an annular bottom wall extending radially inward from the lower peripheral edge, a cylindrical inner side wall extending upward from the inner peripheral edge of the annular bottom wall, and a substantially circular inner bottom wall connected to the upper end of the inner side wall, which are formed concentrically with respect to the cylindrical outer side wall. Further, Patent Document 3 discloses that the bottom of the cup is formed in a dome shape in advance.

[0005] However, the cans disclosed in these patent documents are targeted at open-top cans in which the can lid is joined by double seaming. When applied to bottle cans, cracks are likely to occur at the bottom of the can, especially during ironing.

[0006] On the other hand, in recent years, there has been an increasing demand to reduce energy consumption and greenhouse gas emissions related to the product life cycle and to reduce the environmental impact. In the above aluminum can, the environmental load can be reduced by increasing the proportion of recycled raw materials and decreasing the proportion of virgin materials in the aluminum alloy sheet used as the material. However, when the proportion of recycled raw materials is increased, compared with the material of a general aluminum can, the material may be difficult to stretch during forming even with the same thickness, and it may be difficult to form. When manufacturing the can, wrinkles and cracks are likely to occur at the bottom of the can, especially during ironing.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention has been made in view of such circumstances, and aims to improve the formability in ironing, suppress the occurrence of cracks, and widen the range of material selection.

Means for Solving the Problems

[0009] The method for manufacturing a bottle can of the present invention includes a cup forming step of performing drawing on a metal sheet to form a cup with a bottom plate portion, and a cylinder forming step of redrawing and ironing the cup between a punch sleeve and a lid die to form a cylinder having a smaller diameter and a greater depth than the cup while processing the bottom of the cylinder, and an upper end portion forming step of processing the upper end portion of the cylinder to form a shoulder portion that gradually decreases in diameter upward in the can axis direction from a cylindrical barrel portion and a mouth portion having a screw portion at the upper end of the shoulder portion. In the cup forming step, a circular plate portion protruding from the central portion of the bottom plate portion and a tapered surface portion that is inclined in a direction gradually decreasing the depth of the cup outward in the radial direction from the periphery of the circular plate portion are concentrically formed at the center of the bottom plate portion. In the cylindrical body forming step, the tip of the punch sleeve is brought into contact with the outer peripheral portion of the circular plate portion and ironed again.

[0010] When manufacturing a bottle can, in the cylindrical body forming step, in order not to cause a significant change in the manufacturing equipment of an open-top can by normal double seaming, it is formed into a cylindrical body having the same diameter as that of the open-top can. However, since the upper end portion of the cylindrical body is processed later, the height of the cylindrical body is larger than that of an open-top can having a similar internal volume. For this reason, the cup obtained in the cup forming step has a larger diameter than that of an open-top can. Therefore, the ironing ratio (the diameter ratio of the cup to the cylindrical body) in the cylindrical body forming step becomes larger than that of an open-top can, and cracking and the like are likely to occur. In particular, when ironing again, the bottom of the cup is likely to crack and a molding defect (bottom breakage) in which the bottom of the cup falls out easily occurs.

[0011] In the present invention, in the cylindrical body forming step, when the cup is held by the end surface of the cup holder and the end surface of the lid reloader, only the central portion of the bottom of the cup protrudes (offsets) from the end surface of the lid reloader in the advancing direction of the punch sleeve. Therefore, while appropriately exerting a wrinkle suppressing action by sandwiching between the end surface of the lid reloader and the cup holder at the outer peripheral portion of the bottom of the cup (the outer peripheral portion of the tapered surface portion), the central portion of the bottom of the cup can reduce the processing amount during ironing again compared to the case where the punch sleeve is brought into contact with the bottom of the cup from the position of the end surface of the lid reloader to start processing, so that cracking of the bottom can be prevented. In addition, since the tapered surface portion of the cup and the bent portion between the tapered surface portion and the circular plate portion are arranged between the tip of the punch sleeve and the lid reloader, there is a margin in the material compared to the case where the bottom plate portion of the cup is flat, and since the tension acting during ironing becomes small, cracks are less likely to occur.

[0012] In the method for manufacturing a bottle can of the present invention, the redrawing ratio in the cylindrical body forming step can be more than 1.41 and less than 1.93.

[0013] For example, the cup outer diameter can be 95 mm or more and 125 mm or less, and the cylindrical body outer diameter can be formed to be 65 mm or more and 67 mm or less, and a cylindrical body with a sufficient height as a bottle can can be obtained.

[0014] In the method for manufacturing a bottle can of the present invention, the tapered surface portion may have an inclination angle of 2° or more and 18° or less with respect to a plane orthogonal to the axial direction of the cup.

[0015] When the tapered surface portion extends to the periphery of the cup, when the cup is held, the peripheral edge portion of the tapered surface portion is formed by the lid reloader die. At this time, if the inclination angle of the tapered surface portion becomes too large, the cup may tilt and jam in the conveyor or chute, which is the conveyance path, when the cup is conveyed, and production is likely to be inhibited. If the inclination angle is too small, the protruding depth dimension (offset amount) of the circular plate portion decreases, and the effect of preventing cracks is reduced. Note that it is not always necessary for the tapered surface portion to reach the lower end of the peripheral wall portion of the cup, and the outer peripheral edge of the tapered surface portion may be disposed inside the radial direction of the side wall portion.

[0016] In the method for manufacturing a bottle can of the present invention, the circular plate portion preferably has a protruding depth dimension of 1 mm or more and 10 mm or less from the inner peripheral edge of the outer peripheral convex bent portion at the lower end of the peripheral wall portion of the cup.

[0017] If the protruding depth dimension (offset amount) of the circular plate portion becomes too large, it is necessary to adjust the take-out portion from the cup forming device, the width and height of the conveyance path, which is troublesome for facility modification. If the protruding depth dimension is too small, cracking at the bottom is likely to occur, and the effect of improving formability is reduced.

[0018] In the method for manufacturing a bottle can of the present invention, the ratio of the diameter of the outer peripheral edge of the circular plate portion to the diameter of the tip of the punch sleeve is preferably 1.01 or more and 1.18 or less. If the ratio is too large (the bent portion between the circular plate portion and the tapered surface portion of the cup is too far from the tip of the punch sleeve), the amount by which the central portion of the bottom plate portion of the cup protrudes from the end face of the lid reamer during the cylindrical body forming process becomes small with respect to the protruding depth dimension of the cup itself, and cracking at the bottom is likely to occur. Or, in order to ensure the amount of protrusion, the cup would be designed in a shape that is difficult to form or transport, resulting in a decrease in productivity. Conversely, if the ratio is too small (the distance from the bent portion to the tip of the punch sleeve is too small), strong tension is applied to the bent portion of the cup from the tip of the punch sleeve during redrawing, which may cause cracking at the bottom.

Advantages of the Invention

[0019] According to the method for manufacturing a bottle can of the present invention, a circular plate portion and a tapered surface portion are formed on the bottom plate portion of the cup, and the tip portion of the punch sleeve is brought into contact with the outer peripheral portion of the circular plate portion during the cylindrical body forming process for redrawing and ironing. Therefore, the amount of processing by the punch sleeve during redrawing can be reduced, and a margin of material is generated on the radially outer side of the punch sleeve, making it difficult for cracks to occur at the bottom during redrawing. For this reason, even in the case of a bottle can with a large drawing ratio of the cup with respect to the cylindrical body, it can be smoothly manufactured without causing forming defects such as cracks. Therefore, even if a material that is disadvantageous for forming the can body compared to conventional can materials is used, quality defects due to forming can be suppressed. For example, even a can material with a significantly high ratio of recycled raw materials contained in the material can be used for mass production.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Embodiments for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described. The bottle can 1 of one embodiment is formed of a metal plate made of an aluminum alloy. As shown in FIG. 1, it has a bottom portion 2, a cylindrical body portion 3 continuous from the periphery of the bottom portion 2, a tapered diameter-reducing portion 4 that gradually reduces in diameter upward from the upper end of the body portion 3, a cylindrical small-diameter neck portion 5 extending upward from the upper end of this diameter-reducing portion 4, and a mouth portion 6 formed in an upper portion above this neck portion 5 and to which a cap (not shown) is attached, and is formed in a bottle shape. Further, the mouth portion 6 has a bulging portion 7 protruding radially outward at its lower end portion, a male screw portion 8 above it, and a curl portion 9 formed by rounding the opening end portion above the male screw portion 8.

[0022] The bottom portion 2, the body portion 3, the diameter-reducing portion 4, the neck portion 5, and the mouth portion 6 are arranged coaxially with each other. In this embodiment, these common axes will be described by referring to them as the can axis S1.

[0023] Further, as shown in FIGS. 1 and 2, the bottom portion 2 has a grounding portion 11 that is smaller in diameter than the body portion 3 and annularly protrudes outward (downward) in the can axis direction, an outer wall portion 12 that connects the body portion 3 and the grounding portion 11, a counter portion 13 connected to the grounding portion 11 and extending upward from the inner peripheral end of the grounding portion 11, and a concave dome portion 15 connected via a concave bending portion 14 from the upper end of the counter portion 13. The grounding portion 11 has an inner bending portion 16 convexly formed radially inward from its apex and an outer bending portion 17 convexly formed radially outward. These inner bending portion 16 and outer bending portion 17 may have different radii of curvature or the same radius of curvature.

[0024] The outer wall portion 12 has a convex curved portion 18 continuous from the lower end of the body portion 3 and a concave curved portion 19 continuous from the lower end of the convex curved portion 18, and the concave curved portion 19 is inclined so as to gradually decrease in diameter downward. And the inner peripheral end of the lower end of the concave curved portion 19 is connected to the outer peripheral end of the outer bending portion 17 of the grounding portion 11. The bottom portion 2 having such a shape is formed symmetrically about the left and right in a longitudinal section passing through the can axis S1 with the center of the dome portion 15 arranged on the can axis S1.

[0025] In this embodiment, although the dimensions are not limited, the cylindrical body 3 is formed with an outer diameter D1 of 65 mm or more and 67 mm or less. The mouth part 6 has an outer diameter of 38 mm nominal.

[0026] Further, for the bottom part 2, for example, the radius of curvature R1 of the dome part 15 is 30 mm or more and 60 mm or less, the radius of curvature R2 of the concave bent part 14 is 2.0 mm or more and 2.5 mm or less, the diameter of the vertex of the grounding part 11 (the distance of the straight line passing through the can axis connecting the vertices in the longitudinal section) D2 is 47.5 mm or more and 48.5 mm or less, preferably 47.8 mm or more and 48.2 mm or less, the radius of curvature R3 of the inner bent part 16 is 1.0 mm or more and 2.5 mm or less, the radius of curvature R4 of the outer bent part 17 is 1.5 mm or more and 2.5 mm or less, the radius of curvature R5 of the concave curved part 19 of the outer wall part 12 is 10 mm or more and 20 mm or less, and the radius of curvature R6 of the convex curved part 18 is 2.5 mm or more and 4.5 mm or less. The radius of curvature is a value on the outer surface of the bottle can 1. The plate thickness t of the can axis S1 of the dome part 15 is approximately the original plate thickness before forming, and is formed to be 0.280 mm or more and 0.400 mm or less, and preferably 0.290 mm or more and 0.320 mm or less.

[0027] Next, a method for manufacturing the bottle can 1 formed as described above will be described. A flat metal plate made of an aluminum alloy is press-worked to form a relatively shallow and large-diameter cup 21 as shown in Fig. 3(A) (cup forming step), and then the cup 21 is further drawn and ironed to form a bottomed cylindrical barrel 22 as shown in Fig. 3(B) (barrel forming step). By processing the upper end portion of the barrel 22 to form the reduced-diameter portion 4, the neck portion 5, and the mouth portion 6 (upper end portion forming step), the bottle can 1 is formed. The apparatus for manufacturing this bottle can is composed of a cup forming apparatus, a barrel forming apparatus, a printing apparatus, an upper end portion processing apparatus for processing the upper end portion of the barrel, and the like.

[0028] (Cup forming step) The cup 21 has a bottom plate portion 23 and a cylindrical peripheral wall portion 24 around it. The bottom plate portion 23 is formed concentrically with a circular plate portion 25 that protrudes from the peripheral edge and a tapered surface portion 26 that slopes in a direction gradually shallowing the depth of the cup 21 radially outward from the peripheral edge of the circular plate portion 25. Specifically, as shown in FIG. 4, between the outer peripheral edge of the tapered surface portion 26 and the lower end of the peripheral wall portion 24, it is connected by an outer peripheral convex bent portion 27 that protrudes outward (diagonally downward) of the cup 21, and between the inner peripheral edge of the tapered surface portion 26 and the outer peripheral edge of the circular plate portion 25, it is also connected by a lower convex bent portion 28 that protrudes outward (downward) of the cup 21.

[0029] In this case, although not necessarily limited, the ratio (D4 / D3) of the diameter D4 of the outer peripheral edge of the circular plate portion 25 to the outer diameter D3 of the peripheral wall portion 24 is set to be 0.39 or more and 0.59 or less, preferably 0.47 or more and 0.54 or less. For example, the outer diameter D3 of the peripheral wall portion 24 is formed to be 95 mm or more and 125 mm or less, preferably 98 mm or more and 105 mm or less, and the diameter D4 of the outer peripheral edge of the circular plate portion 25 is formed to be 49 mm or more and 56 mm or less, preferably 50 mm or more and 52 mm or less. Also, for the tapered surface portion 26, the inclination angle θ1 with respect to the plane orthogonal to the axial direction of the cup 21 is set to be 2° or more and 18° or less, preferably 3° or more and 7° or less. With respect to the depth of the cup 21 to the inner peripheral edge of the outer peripheral convex bent portion 27 at the lower end of the peripheral wall portion 24, the protruding depth dimension h1 of the circular plate portion 25 is formed to be 1 mm or more and 10 mm or less, preferably 1 mm or more and 3 mm or less. The radius of curvature R10 of the inner surface of the lower convex bent portion 28 is formed to be 1.0 mm or more and 5.0 mm or less, preferably 2.5 mm or more and 3.5 mm or less.

[0030] In the cup forming device for forming this cup 21, a cup forming punch 40, a cup forming die 50, a blank cutter 55, etc. shown in FIG. 5 are used. The punch 40 for forming a cup has a central punch 42 for forming a circular plate portion 25 detachably provided in the axial direction on the axis S3 of a cylindrical punch main body portion 41 for forming a peripheral wall portion 24 and an outer peripheral convex bent portion 27. A hole portion 43 is formed on the axis S3 of the punch main body portion 41, and the central punch 42 is fitted in the hole portion 43. A convex curved surface 44 for forming the outer peripheral convex bent portion 27 of the cup 21 is formed at the lower end of the outer peripheral portion of the punch main body portion 41.

[0031] The central punch 42 has a concentric ring-shaped protrusion 45 centered on the axis S3 protruding downward at the tip. The tip (lower end) of this protrusion 45 is fixed in the hole portion 43 of the punch main body portion 41 in a state of protruding along the axis S3 direction from the tip of the punch main body portion 41. The protruding dimension h2 of the tip of the protrusion 45 can be adjusted by interposing an appropriate spacer or the like between the central punch 42 and the punch main body portion 41. The protruding depth dimension h1 of the circular plate portion 25 of the cup 21 is determined according to the protruding dimension h2 of the protrusion 45 of the central punch 42 (the distance from the lower edge of the convex curved surface 44 to the tip of the protrusion 45). The protruding dimension h2 of the protrusion 45 and the protruding depth dimension h1 of the circular plate portion 25 of the cup 21 are substantially equal.

[0032] Both the die 50 for forming a cup and the blank cutter 55 are formed in a ring shape and are arranged on the same axis S3 as the punch 40 for forming a cup. The die 50 for forming a cup is fixed to one end of the inner peripheral portion of a cylindrical blank punch 51. And the punch 40 for forming a cup reciprocates along the axis S3 and enters the inside of the die 50 for forming a cup.

[0033] Further, the blank cutter 55 is usually disposed on the outer peripheral side of the cup forming punch 40 and the cup forming die 50, and is supported to reciprocate along the axis S3 toward the cup forming die 50 in the same manner as the cup forming punch 40, but is movable separately from the cup forming punch 40. A ring-shaped cutter portion 56 is fixed to the inner peripheral portion of the blank cutter 55, and one end (the lower end in FIG. 5) of the inner peripheral portion of the cutter portion 56 is formed as a cutting edge 56a. The inner diameter of the cutting edge 56a is formed larger than the inner diameter of the cup forming die 50.

[0034] On the other hand, one end of the outer peripheral portion of the blank punch 51 (one end on the side where the cup forming die 50 is fixed: the upper end in FIG. 5) is formed as a sharp cutting edge 51a. The cutting edges 56a and 51a of the blank cutter 55 and the blank punch 51 are arranged to face each other, and the aluminum plate material P1 can be punched into a circular blank P2 between these cutting edges 56a and 51a.

[0035] Then, as shown in FIG. 5, with the cup forming die 50 and the blank cutter 55 separated in the axial direction, the aluminum plate material P1 is disposed therebetween. First, by lowering the blank cutter 55 along the axis S3, as shown in FIG. 6, the circular blank P2 is punched by the cutting edges 56a and 51a of the blank cutter 55 and the blank punch 51. Then, as shown in FIGS. 7 and 8 in sequence, the cup forming punch 40 descends to form the cup 21.

[0036] In this case, the ridge 45 of the central punch 42 of the cup forming punch 40 first contacts and presses against the blank P2, thereby forming a circular plate portion 25 inside the ridge 45 of the central punch 42. Next, when the outer peripheral portion of the cup forming punch 40 contacts the blank P2, a tapered surface portion 26 is formed between the tip of the ridge 45 and the lower end of the convex curved surface 44 of the punch main body portion 41. Further, when the cup forming punch 40 enters the inside of the cup forming die 50, the blank is drawn and formed between the cup forming punch 40 and the cup forming die 50 to form the peripheral wall portion 24 of the cup 21.

[0037] The cup 21 formed in this way is transferred to the cylindrical body forming process.

[0038] (Cylindrical body forming process) In the cylindrical body forming process, after the cup 21 is re-drawn to form a bottomed cylindrical shape with a small diameter, the cylindrical portion is ironed to be thinly stretched to increase the depth, and then the bottom forming process is performed to form the bottom 2. Then, the cylindrical body 22 (FIG. 3(B)) is formed by cutting off the opening end portion.

[0039] As shown in FIG. 9, the cylindrical body forming apparatus for performing these re-drawing process, ironing process, and bottom forming process has a re-drawing die 30, an ironing die 70, and a bottom forming die 80 arranged side by side on the same axis S2, and is continuously performed using the same punch sleeve 60. Although only one ironing die 71 is shown in FIG. 9 for the ironing die 70, a plurality of ironing dies with sequentially decreasing inner diameters are arranged coaxially according to the degree of the intended ironing process. These re-drawing die 30 and ironing die 70 are usually arranged with their axis S2 in the horizontal direction, and the punch sleeve 60 advances from left to right in FIG. 9 for processing.

[0040] Note that in front of the advancing direction of the punch sleeve 60, a bottom forming die 80 for forming the bottom 2 including the dome portion 15 of the cylindrical body 22 is arranged between the tip of the punch sleeve 60 that has passed through the ironing die 71 at the foremost position. The cylindrical body forming apparatus for forming the cylindrical body 22 is composed of the re-drawing die 30 having this punch sleeve 60, the ironing die 70, the bottom forming die 80, etc.

[0041] (Cylindrical body forming apparatus) As shown in Fig. 10 and the like, the re-drawing die 30 includes an annular redraw die 31, a cylindrical cup holder 32 disposed opposite to the redraw die 31, and a cylindrical punch sleeve 60 disposed inside the cup holder 32. Their axis is indicated by S2. Note that the axial positions of the redraw die 31 and the ironing die 71 are fixed, and the cup holder 32 and the punch sleeve 60 are supported so as to be axially movable.

[0042] On the upper surface of the redraw die 31, a flat contact surface 34 for contacting the outer surface of the outer peripheral portion (tapered surface portion 26) of the bottom plate portion 23 of the cup 21 is formed, and the corner portion of the inner peripheral portion of the contact surface 34 and the forming hole 35 (see Fig. 9) is formed as a convex curved surface 36. The contact surface 34 is formed in a plane orthogonal to the axis S2. The convex curved surface 36 is formed such that the longitudinal section passing through the axis S2 (see Fig. 9) has an arc angle of 90° or more. Thus, the position where the convex curved surface 36 most protrudes into the forming hole 35 is the portion where the minimum inner diameter D5 of the forming hole 35 is located, and the forming hole 35 gradually expands in the tip direction (the forward direction of the punch sleeve 60), and a relief surface 37 is formed. Note that the convex curved surface 36 is formed by connecting a plurality of arcs with different radii of curvature, but it may also be a convex arc surface having a single radius of curvature.

[0043] The cup holder 32 has a pressing surface 38 facing the contact surface 34 of the redraw die 31 formed as a flat surface orthogonal to the axis C2. Its outer diameter is formed smaller than the inner diameter of the cup 21, and when inserted into the cup 21, a slight gap is formed between the inner peripheral surface of the peripheral wall portion 24 of the cup 21. On the other hand, the inner peripheral surface 32a of the cup holder 32 is formed larger than the maximum outer diameter of the punch sleeve 60 and larger than the inner diameter of the redraw die 31 (the inner diameter D5 of the minimum inner diameter portion formed by the convex curved surface 36).

[0044] The punch sleeve 60 is formed in a cylindrical shape, and a protruding molding part 61 protruding annularly is formed at its tip. This punch sleeve 60 is for re-drawing the cup 21 between it and the lid draw die 31, and thus, it is formed to have an outer diameter D6 smaller than the minimum inner diameter D5 of the lid draw die 31. The gap between the punch sleeve 60 and the lid draw die 31 is set to a value slightly larger than the plate thickness of the cup 21.

[0045] As shown in FIG. 10 and the like, the protruding molding part 61 has a tip arc-shaped surface 62 formed at its tip, and a concave arc-shaped surface 63 and a convex arc-shaped surface 64 are sequentially formed from the outer peripheral edge of the tip arc-shaped surface 62, and the convex arc-shaped surface 64 is connected to the outer peripheral surface of the punch sleeve 60. The range from the tip arc-shaped surface 62 to the concave arc-shaped surface 63 and the convex arc-shaped surface 64 forms the outer part from the grounding part 11 of the bottom 2 of the cylindrical body 22 in the bottom forming die 80.

[0046] The inner peripheral surface of the punch sleeve 60 is formed in a straight shape in the axial direction from the inner peripheral edge of the tip arc-shaped surface 62. The tip arc-shaped surface 62 is formed in a convex arc shape protruding in the axial tip direction, the diameter D7 of its tip position is 47.5 mm or more and 48.5 mm or less, preferably 47.8 mm or more and 48.2 mm or less, and the curvature radius R11 of its tip is formed to be 1.0 mm or more and 2.5 mm or less. With the cup 21 held between the cup holder 32 and the lid draw die 31, the tip of the tip arc-shaped surface 62 of the punch sleeve 60 is set to have a dimensional relationship of abutting against the outer peripheral part (radially inward from the curvature center position of the lower convex bent part 28) of the circular plate part 25 of the cup 21. In this case, the ratio (D4 / D7) of the diameter D7 of the tip position of the punch sleeve 60 to the diameter D4 of the outer peripheral edge of the cup 21 is 1.01 or more and 1.18 or less, and 1.03 or more and 1.09 or less is more preferable.

[0047] Incidentally, both the cup holder 32 and the punch sleeve 60 are attached to the drive part of the cylindrical body forming device, and are reciprocated along the axis S2. However, the cup holder 32 is axially relatively movable with respect to the punch sleeve 60, and is supported in a state of being pressed in the axial tip direction by a biasing means such as an air spring.

[0048] The bottom forming die 80 is provided in front of a row of a plurality of ironing dies 71, and forms an annular hold-down ring 81 that forms a concave curved portion 19 from the outer bending portion 17 of the outer wall portion 12 between the tip arc-shaped surface 62 and the concave arc-shaped surface 63 of the punch sleeve 60, and enters inside the punch sleeve 60 to bend the bottom plate portion 23 of the cup 21 with the tip arc-shaped surface 62 of the punch sleeve 60, and has a dome forming die 82 that forms a counter portion 13, a concave bending portion 14, and a dome portion 15 from the inner bending portion 16. The hold-down ring 81 and the dome forming die 82 are concentrically arranged, and an annular gap is formed therebetween. Further, the hold-down ring 81 is supported so as to be movable in the direction of the axis S2 with respect to the dome forming die 82.

[0049] (Details of the cylindrical body forming process) Next, the details of the processing in the cylindrical body forming process will be described using the cylindrical body forming device configured as described above. Separate the lid draw die 31 and the cup holder 32 in the axial direction, move the cup 21 produced in the cup forming process while moving it in the radial direction, and place it between the lid draw die 31 and the cup holder 32. Advance the cup holder 32 to sandwich the tapered surface portion 26 of the bottom plate portion 23 of the cup 21 between the cup holder 32 and the contact surface 34 of the lid draw die 31, and insert it into the cup 21 as shown in FIG. 10. In this state, the tip of the punch sleeve 60 has retreated from the tip of the cup holder 32.

[0050] Next, when the cup holder 32 and the punch sleeve 60 are further advanced, as shown in FIG. 11, the peripheral portion of the cup 21 is sandwiched between the pressing surface 38 of the cup holder 32 and the contact surface 34 of the lid loader die 31, so that the outer peripheral portion of the tapered surface portion 26 is deformed to be in a direction orthogonal to the axial direction, and the intermediate position of the tapered surface portion 26 is pressed against the convex curved surface 36 of the lid loader die 31 and is bent and formed along the convex curved surface 36. From the bent portion 39 formed by this convex curved surface 36 toward the radially inner side, the tapered surface portion 26 and the circular plate portion 25 are maintained substantially in their original shapes. At this time, the punch sleeve 60 has not yet reached the bottom plate portion 23 of the cup 21. Note that although the shape of the cup 21 changes as the processing progresses, for convenience, the cup during processing is also referred to as a cup, and will be described using the reference numerals such as 21 as shown in FIG. 4.

[0051] When the punch sleeve 60 is advanced from the state shown in FIG. 11, as shown in FIG. 12, first, the tip of the tip arc-shaped surface 62 of the punch sleeve 60 contacts the outer peripheral portion of the circular plate portion 25 of the cup 21 at the radially inner position of the lid loader die 31. When the punch sleeve 60 is further advanced, the outer peripheral portion of the circular plate portion 25 of the cup 21 is pushed by the tip arc-shaped surface 62 of the punch sleeve 60 and is bent by the tip of the tip arc-shaped surface 62 and the convex curved surface 36 of the lid loader die 31, respectively, and is stretched between them (see FIG. 13).

[0052] At this time, since the peripheral portion of the cup 21 is sandwiched between the cup holder 32 and the lid loader die 31, a tension acts between this sandwiched portion and the tip arc-shaped surface 62 of the punch sleeve 60. As the punch sleeve 60 advances, the tension between the sandwiched portion and the tip arc-shaped surface 62 of the punch sleeve 60 increases, and the sandwiched portion of the cup 21 is pulled radially inward while sliding between the cup holder 32 and the lid loader die 31 against the clamping force by the cup holder 32 and the lid loader die 31. The inclination angle of the portion stretched between the tip of the tip arc-shaped surface 62 and the convex curved surface 36 of the lid loader die 31 increases as the punch sleeve 60 advances. On one hand, in the portion radially inside from the tip arc-shaped surface 62 of the punch sleeve 60, the inner portion of the circular plate portion 25 remains flat.

[0053] When the punch sleeve 60 further advances from the state shown in FIG. 13, the convex arc-shaped surface 64 of the punch sleeve 60 contacts, as shown in FIG. 14, the portion spanned by the tip of the tip arc-shaped surface 62 and the convex curved surface 36 of the lid draw die 31, and the spanned portion is bent and formed by the convex arc-shaped surface 64. After FIG. 14, as the punch sleeve 60 further advances and the convex arc-shaped surface 64 enters the forming hole 35 of the lid draw die 31, while drawing the clamping portion of the cup 21 between the cup holder 32 and the lid draw die 31 radially inward, redrawing is performed between the convex arc-shaped surface 64 and the convex curved surface 36 of the lid draw die 31.

[0054] Thereafter, in this redrawing die 30, as the punch sleeve 60 advances, the cup 21 is drawn into the forming hole 35 of the lid draw die 31 and redrawn. When the punch sleeve 60 enters the ironing die 71 of the next ironing die 70, ironing is performed. This ironing is performed in multiple stages by a plurality of ironing dies 71, and a deep cylindrical body 75 is formed while gradually reducing the wall thickness of the body portion.

[0055] Finally, the bottom portion 2 of the cylindrical body 75 is processed by the bottom forming die 80. First, as shown in FIG. 15(A), the outer peripheral portion of the bottom of the cylindrical body 75 is clamped between the outer peripheral side portion from the tip of the punch sleeve 60 and the hold-down ring 81, and the forming of the outer wall portion 12 is started. Next, as shown in FIG. 15(B), in this state, the punch sleeve 60 advances, and the tip arc-shaped surface 62 of the punch sleeve 60 enters between the hold-down ring 81 and the dome-forming die 82, whereby the grounding portion 11 is formed. At the same time, the counter portion 13, the dome portion 15, etc. are formed between the inner side portion from the tip of the tip arc-shaped surface 62 of the punch sleeve 60 and the dome-forming die 72. Then, by cutting a ring-shaped portion of about several millimeters from the open end portion toward the bottom side with another device, the cylindrical body 22 having the bottom 2 shown in FIG. 3(B) is formed.

[0056] As shown in FIG. 3(B), the body portion of the cylindrical body 22 formed in this way is formed into a wall portion 22A that is the thinnest and has a constant thickness from near the bottom 2 to near the middle part, and a flange portion 22B that is thicker than the wall portion 22A and has a constant thickness from the open end to near the middle part. The transition between the bottom 2 and the wall portion 22A and between the wall portion 22A and the flange portion 22B is formed as a transition portion where the thickness changes smoothly. For example, the wall portion 22A is formed with a plate thickness of 0.115 mm or more and 0.135 mm or less, and the flange portion 22B is formed with a plate thickness of 0.200 mm or more and 0.220 mm or less. The shape of the bottom 2 is formed into almost the final shape of the can 1, such as the plate thickness t on the can axis S1 of the dome portion 15. The height of the cylindrical body 22 is formed, for example, to be 130 mm or more and 136 mm or less, or 162 mm or more and 168 mm or less.

[0057] In this cylindrical body forming process, since the outer diameter D3 of the cup 21 is 95 mm or more and 125 mm or less, and the outer diameter D1 of the cylindrical body 22 is 65 mm or more and 67 mm or less, the redrawing ratio (D3 / D1) exceeds 1.41 and is less than 1.93, which is larger than the case of an open-top can. This redrawing ratio is more preferably 1.48 or more and 1.62 or less.

[0058] As described above, before processing the bottom portion 2 of the cup 21, the downward convex bent portion 28 of the tapered surface portion 26 and the circular plate portion 25 is disposed at a position radially outward from the tip arc-shaped surface 62 of the punch sleeve 60, and a margin corresponding to the downward convex bent portion 28 is provided in the material outside the punch sleeve 60. Further, it is disposed in a state offset in the advancing direction of the punch sleeve 60 from the clamping position between the lid loader die 31 and the cup holder 32.

[0059] Therefore, even though it is a process with a large redrawing ratio, at the outer peripheral portion of the bottom of the cup 21 (the outer peripheral portion of the tapered surface portion 26), while appropriately exerting the wrinkle suppressing action by sandwiching with the end surface of the lid loader die 31 and the cup holder 32, the central portion of the bottom of the cup 21 can reduce the processing amount during redrawing compared to the case where processing is started by bringing the punch sleeve 60 into contact with the bottom of the cup 21 from the position of the end surface of the lid loader die 31, and thus cracking of the bottom can be prevented.

[0060] In this case, the protruding depth dimension (offset amount) h1 from the inner peripheral edge of the outer peripheral convex bent portion 27 at the lower end of the peripheral wall portion of the cup 21 to the circular plate portion 25 is 1 mm or more. If the offset amount is too small, less than 1 mm, cracking of the bottom is likely to occur. Similarly, by setting the inclination angle θ of the tapered surface portion 26 to 2° or more, the protruding depth dimension (offset amount) h1 of the circular plate portion 25 can be ensured to be 1 mm or more. When the inclination angle θ is less than 2°, the offset amount h1 decreases, and thus the effect of preventing cracking is reduced.

[0061] Note that since the inclination angle θ1 of the tapered surface portion 26 of the cup 21 is 2° or more and 18° or less, and the protruding depth dimension (offset amount) h1 from the inner peripheral edge of the outer peripheral convex bent portion 27 at the lower end of the peripheral wall portion of the cup 21 to the circular plate portion 25 is 1 mm or more and 10 mm or less, there are few problems such as clogging when taking out the cup 21 from the cup forming device or during conveyance from the cup forming device to the cylindrical body forming device, and there is no need for major equipment changes to these parts. If the inclination angle θ1 exceeds 18° or the offset amount exceeds 10 mm, it is necessary to significantly adjust the width and height of the take-out portion and conveyance path of the cup forming device.

[0062] Also, since the ratio (D4 / D7) of the diameter D4 of the outer peripheral edge of the circular plate portion 25 to the diameter D7 of the tip of the punch sleeve 60 is 1.01 or more and 1.18 or less, the cylindrical body 22 can be formed without causing molding defects such as cracking.

[0063] That is, if the ratio (D4 / D7) of the diameter D4 of the outer peripheral edge of the circular plate portion 25 to the diameter D7 of the tip of the punch sleeve 60 is too large, exceeding 1.18 (the tip arc-shaped surface 62 of the punch sleeve 60 is too far from the lower convex bent portion 28 of the cup 21), the amount by which the central portion of the bottom plate portion 23 of the cup 21 protrudes from the end face of the lid die 31 during the cylindrical body forming process becomes smaller than the protruding depth dimension (offset amount) of the cup 21 itself, and cracking of the bottom portion 2 is likely to occur. Or, in order to ensure the protruding amount, the cup 21 has to be designed in a shape that is difficult to form or convey, resulting in a decrease in productivity. Conversely, if the ratio is too small, less than 1.10 (the distance from the lower convex bent portion 28 to the tip arc-shaped surface 62 of the punch sleeve 60 is too small), strong tension is applied from the tip of the punch sleeve 60 to the lower convex bent portion 28 of the cup 21 during re-drawing, and there is a risk of cracking. The ratio (D4 / D7) is more preferably 1.03 or more and 1.09 or less.

[0064] Then, after this cylindrical body forming process, printing or the like is performed, and in the upper end portion forming process, the upper end portion of the cylindrical body 22 is processed to form the reduced diameter portion 4, the neck portion 5, and the mouth portion 6, thereby manufacturing the bottle can.

[0065] According to this manufacturing method, in the cup forming step, a circular plate portion 25 and a tapered surface portion 26 are formed on the bottom plate portion 23 of the cup 21. In the cylindrical body forming step, the tip of the punch sleeve 60 is brought into contact with the outer peripheral portion of the circular plate portion 25 and re-drawn and ironed. Since the circular plate portion 25 with which the punch sleeve 60 comes into contact is offset from the end surface of the lid draw die 31, the processing amount is reduced, and the wrinkle suppressing action by the clamping between the end surface of the lid draw die 31 and the cup holder 32 can be appropriately exerted. Also, on the radially outer side of the punch sleeve 60, a margin is provided in the material due to the tapered surface portion 26 and the downward convex bending portion 28, so cracks are less likely to occur during the re-drawing process.

[0066] And since this cylindrical body forming step can be performed smoothly, it is possible to select and use a material whose formability is different from that of conventional materials (unfavorable for forming that is difficult to stretch during the forming of a beverage can). Therefore, it becomes possible to select a material containing a large amount of recycled aluminum raw material compared to conventional materials and reduce the environmental load of the product.

Explanation of Reference Numerals

[0067] 1 Bottle can 2 Bottom 22 Cylindrical body 3 Body 4 Reduced diameter portion 5 Neck 6 Mouth 11 Grounding portion 12 Outer wall portion 13 Counter portion 14 Concave bending portion 15 Dome portion 16 Inner bending portion 17 Outer bending portion 18 Convex curved portion 19 Concave curved portion 21 Cup 23 Bottom plate portion 24 Peripheral wall portion 25 Circular plate portion 26 Tapered surface portion 27 Outer peripheral convex bending portion 28 Lower convex buckling part 29 Trunk part 30 Re-drawing die 31 Redraw die 32 Cup holder 34 Contact surface 35 Forming hole 36 Convex curved surface 37 Relief surface 38 Pressing surface 39 Buckling part 40 Cup-forming punch 41 Punch body part 42 Central punch 43 Hole part 44 Convex curved surface 45 Rib 50 Cup-forming die 51 Blank punch 55 Blank cutter 60 Punch sleeve 61 Protruding forming die part 62 Tip arc-shaped surface 63 Concave arc-shaped surface 64 Convex arc-shaped surface 70 Ironing die 71 Ironing die 75 Cylindrical body 80 Bottom-forming die 81 Hold-down ring 82 Dome-forming die

Claims

1. A cup forming step of performing a drawing process on a metal plate to form a cup with a bottom plate portion, and a cylinder forming step of redrawing and ironing the cup between a punch sleeve and a lid die to form a cylinder having a smaller diameter and a greater depth than the cup while processing the bottom of the cylinder. In the cup forming step, a circular plate portion protruding from the central portion of the bottom plate portion and a tapered surface portion inclined in a direction gradually shallowing the depth of the cup from the periphery of the circular plate portion radially outward are concentrically formed. In the cylinder forming step, the method for manufacturing a can is characterized in that the tip of the punch sleeve is brought into contact with the outer peripheral portion of the circular plate portion and redrawn.

2. The method for manufacturing a can according to claim 1, wherein the tapered surface portion has an inclination angle with respect to a plane orthogonal to the axial direction of the cup of 2° or more and 18° or less.

3. The method for manufacturing a can according to claim 1, wherein the circular plate portion has a protruding depth dimension from the inner peripheral edge of the outer peripheral convex bending portion at the lower end of the peripheral wall portion of the cup of 1 mm or more and 10 mm or less.

4. The method for manufacturing a can according to claim 1, wherein the ratio of the diameter of the outer peripheral edge of the circular plate portion to the diameter of the tip of the punch sleeve is 1.01 or more and 1.18 or less.

Images