Seamless metal can

Abstract

To provide a seamless metal can having a dome-shaped bottom surface which has high pressure resistance and is effectively prevented from buckling.SOLUTION: In a seamless metal can 10 having a cylindrical body 1, a ground part 3 connected to the cylindrical body 1, and a bottom part 5 formed so as to close an inside of the ground part 3, and the bottom part 5 is formed of a rising part 7 extending upward from the inside of a ground part 3 and a dome-shaped bottom surface 9 connected to the rising part 7, the dome-shaped bottom surface 9 has a central dome part 9a and a ring-shaped part 9b formed so as to surround the central dome part 9a, the ring-shaped part 9b is connected to an upper end of the rising part 7, and in a side cross-sectional view of the metal can 10, a boundary part X between the central dome part 9a and the ring-shaped part 9b is an ultrasmall bend part with less than 3.0 mm of curvature radius.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a seamless metal can having a domed bottom. [Background technology]

[0002] In general, seamless cans obtained by metal forming (punching, drawing, and ironing) have their bottoms recessed into a dome shape to improve pressure resistance and stabilize installation. The forming method for forming such a dome-shaped bottom is called doming, and is performed by holding the bottom periphery of a cylinder with an annular mold called a hold ring, pushing a doming die up through the annular mold to recess the bottom of the cylinder into a dome shape (Patent Document 1).

[0003] In recent years, there has been a strong demand for forming seamless cans using thin metal sheets from the viewpoints of effective use of metal materials, lightweight properties, etc. Seamless cans formed from such thin metal sheets have a problem of buckling, particularly at the bottom, and the dome-shaped bottoms of conventionally known shapes have an insufficient pressure resistance and are prone to buckling.

[0004] For example, Patent Documents 2 and 3 disclose seamless metal cans having a certain shape of dome-shaped bottom. However, thin-walled seamless metal cans formed using a metal plate (base plate) having a thickness of, for example, less than 0.270 mm have low pressure resistance and are prone to buckling. Therefore, when reducing the thickness of cans, there is currently a demand for further improvement in pressure resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-177289 A [Patent Document 2] JP 2000-211624 A [Patent Document 3] Patent No. 6713741 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a seamless metal can having a domed bottom which has high pressure resistance and is effectively prevented from buckling. Another object of the present invention is to provide a seamless metal can formed using a metal plate having a metal thickness of 0.270 mm or less, particularly 0.26 mm or less. [Means for solving the problem]

[0007] According to the present invention, there is provided a seamless metal can having a cylindrical body portion, a ground portion connected to the cylindrical body portion, and a bottom portion formed so as to close the inside of the ground portion, the bottom portion being formed of a rising portion extending upward from the inside of the ground portion and a dome-shaped bottom surface connected to the rising portion, The dome-shaped bottom surface has a central dome portion and a ring-shaped portion formed so as to surround the central dome portion, the ring-shaped portion being continuous with an upper end of the rising portion, There is provided a seamless metal can, characterized in that in a side cross-sectional view of the metal can, the boundary between the central dome portion and the ring-shaped portion is an extremely curved portion with a curvature radius of less than 3.0 mm.

[0008] In the seamless metal can of the present invention, (1) In a side cross-sectional view of the metal can, the rising portion rises outward and upward from the ground portion; (2) In a side cross-sectional view of the metal can, the rising portion rises from the ground surface at an angle θ of 95 to 125 degrees with respect to the ground surface, and the joint between the rising portion and the ring-shaped portion is an extremely curved portion with a curvature radius of 1.2 mm or less. (3) The metal thickness at the center of the dome-shaped bottom surface is 0.270 mm or less; (4) The metal is aluminum; is preferred. Effect of the Invention

[0009] The seamless metal can of the present invention has a dome-shaped bottom surface that is concave in a dome shape at the bottom portion that is formed so as to close the inside of the grounding portion, and is characterized in that a ring-shaped portion is formed so as to surround the central dome portion of this dome-shaped bottom surface, and that the joint between the ring-shaped portion and the central dome portion is an extremely curved portion with a radius of curvature of less than 3.0 mm. That is, the dome-shaped bottom surface has a large radius of curvature in the central portion, and is a gently curved surface, with the radius of curvature being the largest at the center position. When internal pressure is applied in the axial direction of the seamless metal can, the internal pressure is concentrated in the central portion of such a nearly flat shape, and as the thickness of the metal blank used for forming (corresponding to the metal thickness at the center of the dome-shaped bottom surface) becomes thinner, buckling (reversal of unevenness) becomes more likely to occur. However, in the present invention, a ring-shaped portion with a small radius of curvature is formed so as to surround the central dome portion with a large radius of curvature, and the radius of curvature at the joint portion (i.e., the boundary portion) between this ring-shaped portion and the central dome is a minimum value of less than 3.0 mm. That is, one end of the ring-shaped portion (the end of the central dome) becomes an inflection point, resulting in a greatly curved shape. Moreover, the other side of the ring-shaped portion is connected to the upper end of the rising portion connected to the ground portion, and the other end of such a ring-shaped portion is also greatly curved. As can be seen from this configuration, in the present invention, the ring-shaped portion having both ends curved significantly is connected to the central dome portion having a shape close to a gentle plane, so that the axial load of the seamless metal can is absorbed and mitigated by this ring-shaped portion, and buckling is more effectively suppressed. Therefore, in the present invention, a metal blank having an extremely small thickness (for example, 0.270 mm or less) can be used to form a seamless metal can, which is a major advantage of the present invention. [Brief description of the drawings]

[0010] [Figure 1]1 is a schematic cross-sectional side view showing an entire seamless metal can of the present invention. [Diagram 2] 2 is an enlarged partial cross-sectional side view of the bottom of the seamless metal can of FIG. 1. [Diagram 3] FIG. 2 is a schematic diagram showing a process for manufacturing the seamless metal can of FIG. 1. [Figure 4] FIG. 4 is a diagram showing a mold used in the doming step of FIG. 3. [Diagram 5] FIG. 5 is a diagram for explaining the doming process in FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <Seamless metal can configuration> The seamless metal can of the present invention is obtained by punching, drawing, redrawing and ironing a thin-walled metal blank, and then doming the bottom. Finally, the can is subjected to post-processing such as washing and drying, printing on the outside, applying and baking a finishing varnish, applying and baking a paint on the inside, necking-in and flanging, and the final shape is generally as shown in FIG. 1.

[0012] 1, the seamless metal can of the present invention generally designated by 10 has a cylindrical body 1, a ground portion 3 connected to the lower end of the cylindrical body 1, and a bottom portion 5 provided so as to close the inside of the ground portion 3. In other words, the bottom portion 5 is an area surrounded by the ground portion 3.

[0013] The cylindrical body 1 has a straight body section 1a whose outer surface is a straight body shape, and a chime section 1b that slopes inward from the lower end of the straight body section 1a and continues to the ground section 3. The upper part of the straight body section 1 is connected to a neck-in section 1c formed by post-processing, and a flange section 1d is formed at the upper end of the neck-in section 1c.

[0014] On the other hand, the bottom portion 5 is composed of a rising portion 7 rising inward from the ground contact portion 3 and a dome-shaped bottom surface 9 continuing to the upper end of the rising portion 7.

[0015] 2, which shows an enlarged view of the bottom portion 5 together with Fig. 1, the dome-shaped bottom surface 9 is divided into two regions: a central dome portion 9a having a large radius of curvature and a gently curving surface close to a flat surface, and a ring-shaped portion 9b formed to surround the central dome portion 9a and having a smaller radius of curvature than the central dome portion 9a. That is, the inside of the ring-shaped portion 9b is continuous with the circumferential end of the central dome portion 9a (boundary portion X between the ring-shaped portion 9b and the central dome portion 9a), and the outside of the ring-shaped portion 9b is continuous with the upper end of the rising portion 7 (boundary portion Y between the dome-shaped bottom surface 9 and the rising portion 7).

[0016] In the dome-shaped bottom surface 9, the boundary X between the ring-shaped portion 9b and the central dome portion 9a is an inflection point. Also, the upper end of the rising portion 7 (the above-mentioned boundary Y) is a portion where the tangent Q of the surface forming the rising portion 7 is perpendicular to the ground surface G, and such an upper end portion is also an inflection point.

[0017] In the dome-shaped bottom surface 9 having such a configuration, in the present invention, the boundary portion X between the central dome portion 9a and the ring-shaped portion 9b has a radius of curvature R 1 The radius of curvature R is a minimum value (i.e., an inflection point) of less than 3.0 mm, preferably 2.5 mm or less, and most preferably 2.0 mm or less. This makes it possible to increase the pressure resistance of the metal can 10 and effectively prevent buckling of the bottom 5, even when the metal plate (base plate) used to form the seamless metal can 10 is a thin plate having a metal thickness of 0.270 mm or less, preferably 0.245 mm or less, more preferably 0.230 mm or less, and most preferably in the range of 0.215 to 0.200 mm, and is thinned through drawing and ironing. For example, when the radius of curvature R 1 However, if the radius of curvature R is larger than the above range, the rising portion 7 is directly connected to a dome portion having a large radius of curvature, and it has been confirmed through experiments that the bottom portion 5 is prone to buckling. 1 By setting the distance between the bottom 5 and the ring-shaped portion 9b small, the axial load applied to the metal can 10 can be effectively absorbed by the ring-shaped portion 9b, and the buckling of the bottom portion 5 can be effectively suppressed.

[0018] The thickness of the metal plate (base plate) used for forming corresponds to the thickness t at the center O of the central dome portion 9a. That is, the center O of the central dome portion 9a is not thinned by ironing, so the metal thickness t of this portion reflects the metal thickness of the base plate. Incidentally, the charm portion 1b connecting the ground portion 3 and the straight body portion 1a is thinned by ironing. For example, when the metal thickness of the base plate is in the above-mentioned range, the thickness of the charm portion 1b is usually thinned to 95% or less of the thickness of the metal plate (base plate). In the case of an aluminum seamless can used as a beverage can, the thickness of the straight body portion 1 that is thinned the most is 30 to 50% of the metal thickness t.

[0019] In order to further enhance the buckling suppression function of the ring-shaped portion 9b in the bottom portion 5 having the above-mentioned shape, it is preferable that the rising portion 7 rises outward and upward from the ground contact portion 3, and in particular, it is preferable that the rising portion 7 rises from the ground contact surface G at an angle θ in the range of 95 to 125 degrees with respect to the ground contact surface G. In this case, the upper end of the rising portion 7 (boundary portion Y between the dome-shaped bottom surface 9 and the rising portion 7) becomes an inflection point, and the radius of curvature R 2 It is most preferable that the distance between the ring-shaped portion 9b and the fulcrum is 1.2 mm or less, and particularly 1.2 to 0.5 mm. By adopting such a configuration, the mobility of the ring-shaped portion 9b with both ends (X and Y) as fulcrums is increased, and the buckling suppression function of the ring-shaped portion 9b is further improved.

[0020] In the present invention, the length d of the ring-shaped portion 9b (the distance between the boundaries X and Y) is preferably 10 to 30%, and particularly 15 to 25%, of the radius D of the dome-shaped bottom surface 9. By setting the length d of the ring-shaped portion 9b to such a value, the pressure resistance of the metal can 10 is maximized, and buckling of the bottom portion 9 can be most reliably suppressed. The shape of the bottom portion 9 described above can be formed by doming molding, which will be described later.

[0021] In the present invention, the metal constituting the seamless metal can 10 is not particularly limited and may be various metals or alloys, but aluminum or an aluminum alloy is preferable from the viewpoints of light weight, thin-wall workability, etc. Furthermore, it is preferable to form a seamless can with an inner surface resin-coated by using a resin-coated metal plate, one side of which is coated with an organic resin (e.g., PET), as a base plate, in order to maximize the advantages of the present invention. In this case, the above-mentioned thickness t means the thickness of the metal plate (base plate) not including the thickness of the coating resin.

[0022] <Manufacture of seamless metal cans 10> The seamless metal can 10 of the present invention having the above-mentioned configuration is manufactured by forming the above-mentioned metal blank (which may have an organic resin coating on the side corresponding to the inner surface).

[0023] The above-mentioned metal blank is subjected to usual forming processes such as punching, drawing, ironing and doming to obtain a seamless metal can 10 having a dome-shaped bottom surface 9.

[0024] The process from punching to doming is shown in Figure 3. That is, as shown in FIG. 3(a), the blank 21 is punched out by the punching punch 23 and the punching die 25 to obtain a disk 27 (punching process). Next, as shown in FIG. 3(b), a drawn cup (bottomed cylindrical body) 35 is obtained by the drawing die 31 and the drawing punch 33 (drawing process). Here, the obtained drawn cup 35 is pushed downward by the ironing punch 45 while being held by the redraw die 43 by the presser 41, as shown in FIG. 3(c), and is then ironed through a plurality of ironing dies 47a to 47c, and is then domed at the lowest position. This doming is performed by using a hold-down ring 51 and a doming die 53, which will be described later. This doming forms the charm portion 1b, the ground portion 3, and the bottom portion 5 surrounded by the ground portion 3.

[0025] In the above ironing process, three ironing dies are arranged in Fig. 3(c) and ironing is performed in three stages, but the number of ironing dies is not limited to three and can be an appropriate number depending on the desired degree of thinning. One die can be used for one stage ironing, or two or more dies can be arranged for multiple stages ironing. Of course, when multiple ironing dies are arranged along the processing direction and ironing is performed in multiple stages, the inner diameter (processing diameter) becomes smaller toward the downstream side in the processing direction. In addition, when a large thinning is required, it is also necessary to adjust the approach angle of each die (the angle of the processing surface of the die that contacts the workpiece) within an appropriate range.

[0026] After the above-described ironing process, doming is performed to form the dome-shaped bottom surface 9. In this doming process, the shape of the dome-shaped bottom surface 9 (for example, the shape of the central dome portion 9a and the ring-shaped portion 9b) is determined, but post-processing is required to determine the shape of the rising portion 7.

[0027] The mold used for doming (indicated by 60 in Fig. 3) is composed of a hold-down ring (annular holding mold) 51 and a doming die 53, as shown in Fig. 4, and doming is performed by the cooperation of these molds and the punch 45. This doming die 53 is divided into a base die 61 and a doming ring 63, each of which is provided so as to move up and down independently.

[0028] As can be seen from Figure 4, the hold-down ring (annular holding type) 51 has an upper end action surface 51a that is inclined inwardly and downwardly, and this action surface 51a forms a charm portion 1b that is connected to the lower end of the straight body portion 1a, and the ground contact portion 3 is formed at the lower end of the action surface 51a.

[0029] The base die 61 is a mold that defines the central dome portion 9a of the dome-shaped top surface 9, and the working surface 61a at the upper end thereof corresponds to the central dome portion 9a of the dome-shaped top surface 9. The doming ring 63 is a mold that defines the ring-shaped portion 9b of the dome-shaped top surface 9, and the working surface 63a at the upper end thereof corresponds to the ring-shaped portion 9b. The dome-shaped top surface 9 is formed by smoothly connecting these working surfaces 61a, 63a.

[0030] In the present invention, in order to form a ring-shaped portion 9b with a small radius of curvature on the peripheral portion of the central dome portion 9a, the mold surface that defines this portion is separated from the mold surface that defines the central dome portion 9a. As a result, the radius of curvature R at the boundary portion X between the central dome portion 9a and the ring-shaped portion 9b is 1 can be set to a predetermined value.

[0031] Doming using the above mold is carried out by the process shown in FIG. The hold down ring 51 is biased upward by a spring (not shown), and as shown in FIG. 5(a), in the initial stage, the active surface 63a of the doming ring 63 is positioned lower than the active surface 51a of the hold down ring 51, and the active surface 61a of the base die 61 is positioned even lower than the active surface 63a of the doming ring 63.

[0032] In the above state, the punch 45 is lowered and the thinned body portion 1a is pressed down, and as shown in Figure 5 (b), the lower end of the body portion 1a is pressed against the action surface 51a of the hold-down ring 51, thereby forming a thinned charm portion 1b at the lower end of the body portion 1a.

[0033] Next, when the doming ring 63 is raised, as shown in Figure 5 (c), the inner side of the grounding portion 5 is pulled up and a raised portion 7 is formed, and further, the active surface 63a of the doming ring 63 pushes up the surface on the inner side than the raised portion 7, thereby forming a ring-shaped portion 9b that becomes the peripheral portion of the central dome portion 9a.

[0034] When the rising portion 7 and the ring-shaped portion 9b of the dome-shaped bottom surface 9 are formed as described above, as shown in FIG. 5(d), the base die 61 rises with a delay, and the working surface 61a is pressed against the bottom 5 of the can body 10, thereby forming the central dome portion 9a of the dome-shaped bottom surface 9. As a result, the dome-shaped bottom surface 9 is defined, and the radius of curvature R at the boundary portion X between the central dome portion 9a and the ring-shaped portion 9b is reduced. 1 is defined, and further, the radius of curvature R at the boundary Y between the rising portion 7 and the dome-shaped bottom surface 9 (ring-shaped portion 9b) is 2 is also confirmed.

[0035] In addition, the rising angle θ of the rising portion 7 and the curvature radius R at the boundary portion Y 2 In order to set the angle of rise θ and the radius of curvature R at the boundary Y in a suitable range, for example, after the above process, the doming ring 63 is lowered, and then the hold-down ring 51 is moved inward to push the thinned charm portion 1b inward. 2 can be set in a suitable range.

[0036] After doming is performed as described above, the punch 45 is pulled out, and the resulting molded body is separated from the punch 45 by the stripper fingers 53. Subsequent processes, such as cleaning, drying, necking-in, flanging, and painting, are then performed to obtain the desired seamless metal can 10. The seamless metal can 10 of the present invention exhibits high pressure resistance, and a seamless metal can in which buckling is effectively suppressed can be obtained, even when a thin-walled seamless metal can is obtained by drawing and ironing a master sheet having a metal thickness of 0.270 mm or less. For reference, a seamless aluminum can with a capacity of 355 mL is made of an aluminum plate with a metal thickness of 0.270 mm or less, and the thickness of the straight body portion 1a is 0.085 mm. The internal pressure is 4 kgf / cm 2 It has been confirmed that the base does not buckle when dropped from a height of 20 cm. [Explanation of symbols]

[0037] 1: Cylindrical body 1a: Straight body part 1b: Charm section 1c: Neck-in section 1d: Flange part 3: Grounding part 5: Bottom 7: Rising part 9: Domed bottom 9a: Central dome 9b: Ring-shaped part 10: Seamless metal can X: Boundary between central dome portion 9a and ring-shaped portion 9b R 1 : Radius of curvature at boundary X Y: Boundary between the rising portion and the dome-shaped bottom surface 9 (ring-shaped portion) R 2 : Radius of curvature at boundary Y 51: Hold down ring (annular type) 61: Doming Ring 63: Base Die

Claims

1. A seamless metal can has a cylindrical body, a ground portion connected to the cylindrical body, and a bottom portion formed to close the inside of the ground portion, the bottom portion being formed of a rising portion extending upward from the inside of the ground portion and a dome-shaped bottom surface connected to the rising portion, The dome-shaped bottom surface has a central dome portion and a ring-shaped portion formed so as to surround the central dome portion, the ring-shaped portion being continuous with an upper end of the rising portion, 11. The seamless metal can, wherein in a side cross-sectional view of the metal can, a boundary portion between the central dome portion and the ring-shaped portion is an extremely curved portion having a radius of curvature of less than 3.0 mm.

2. 2. The seamless metal can according to claim 1, wherein in a side cross-sectional view of the metal can, the rising portion rises outward and upward from the ground portion.

3. 3. The seamless metal can according to claim 2, wherein, in a side cross-sectional view of the metal can, the rising portion rises from the ground surface at an angle θ of 95 to 125 degrees with respect to the ground surface, and a joint between the rising portion and the ring-shaped portion is an extremely curved portion having a curvature radius of 1.2 mm or less.

4. 4. The seamless metal can according to claim 3, wherein the metal thickness at the center of said domed bottom surface is 0.270 mm or less.

5. 5. The seamless metal can of claim 4, wherein said metal is aluminum.

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