Metal container and method for manufacturing same

Abstract

Provided are a metal container having excellent roundness whereby an excellent stacked state can be maintained and the occurrence of a blocking phenomenon can be suppressed, and a method for manufacturing the same.　The metal container is formed from a bottomed cup and includes an opening part, a side wall part, and a bottom part. The side wall part is formed in a shape with a tapered outline by repeating processing a plurality of times in which an outside tool disposed outside a side wall of the bottomed cup having been subjected to trimming and tip-end diameter-reduction drawing is moved with respect to an inside tool disposed inside the side wall of the bottomed cup such that the bottom side of the bottomed cup relative to the portion having been subjected to the tip-end diameter-reduction drawing is subjected to diameter-reduction drawing. The side wall part includes an inclined wall part shaped along a second inclined surface of the outside tool, the inclined wall part being formed when the outer surface of the side wall of the bottomed cup first contacted a first inclined surface of the outside tool and then the second inclined surface during the movement of the outside tool. The roundness of the portion that has contacted the first inclined surface is 0.80 mm or less.

Description

Metal container and its manufacturing method

[0001] The present invention relates to a metal container and a method for manufacturing the same.

[0002] As an example of a metal container having an opening, a sidewall, and a bottom, there is a cup that is used with the opening open. A known example of such a metal container is a so-called tapered container. This tapered container has an upper opening, a sidewall, and a bottom, and has a tapered shape in which the inner diameter of the sidewall gradually decreases from the upper opening to the bottom, so that the outer diameter of the bottom (lower outer diameter) is smaller than the inner diameter of the opening (upper inner diameter).

[0003] A conventional method for manufacturing a tapered metal container includes, for example, a step of forming a sidewall portion having a tapered contour by reducing the diameter of a bottomed cup from a portion where the diameter is reduced at the tip to the bottom side. In this step of forming the sidewall portion, an outer tool disposed outside the bottomed cup is usually moved relative to an inner tool disposed inside the bottomed cup (see, for example, Patent Document 1).

[0004] JP 2023-128233 A

[0005] However, because the workability of the material constituting the bottomed cup varies depending on the rolling direction, there is a risk of radial distortion occurring in the side wall of the bottomed cup when the diameter of the side wall of the bottomed cup is reduced. However, in this case, the shape of the conventional outer tool cannot eliminate the radial distortion, and therefore, the manufactured metal container cannot achieve good roundness. As a result, when multiple metal containers are stacked, it becomes difficult to maintain a good stacked state. In addition, in this case, there is a risk of a phenomenon (so-called blocking phenomenon) occurring, in which the stacked metal containers cannot be easily separated.

[0006] The present invention addresses these circumstances by providing a metal container having good roundness, which allows a good stacking state to be maintained and the occurrence of the blocking phenomenon to be suppressed, and a method for manufacturing the same.

[0007] In order to solve these problems, the present invention provides a metal container having an opening, a side wall, and a bottom, the metal container being formed from a bottomed cup formed by a drawing process on a plate-shaped metal material, wherein the side wall is formed into a shape having a tapered contour by moving an outer tool positioned outside the side wall of the bottomed cup relative to an inner tool positioned inside the side wall of the bottomed cup, which has been trimmed and subjected to a tip diameter reduction process, and performing a process of reducing the diameter of the bottomed cup toward the bottom side from the tip diameter reduction process, the side wall having an inclined wall portion shaped to follow the second inclined surface formed by the outer surface of the side wall of the bottomed cup contacting a first inclined surface of the outer tool during the movement of the outer tool, and then contacting a second inclined surface of the outer tool, and the out-of-roundness of the point contacting the first inclined surface is 0.80 mm or less.

[0008] In order to solve these problems, the present invention provides a method for manufacturing a metal container having an opening, a side wall, and a bottom, comprising the steps of: forming a bottomed cup by drawing a plate metal material; trimming the bottomed cup; drawing the bottomed cup at a reduced diameter at the tip; and moving an outer tool positioned outside the side wall of the bottomed cup relative to an inner tool positioned inside the side wall of the bottomed cup, and performing the process of drawing the bottomed cup at a reduced diameter multiple times toward the bottom side of the location where the reduced diameter at the tip has been applied to form the side wall having a tapered contour.The step of forming the side wall is characterized in that, as the outer tool moves, a first inclined surface of the outer tool is abutted against the outer surface of the side wall of the bottomed cup, and then a second inclined surface of the outer tool is abutted against the second inclined surface, thereby forming an inclined wall having a shape that follows the second inclined surface.

[0009] According to the present invention, it is possible to provide a metal container having good roundness, which allows a good stacking state to be maintained and the occurrence of the blocking phenomenon to be suppressed, and a method for manufacturing the same.

[0010] 7A to 7C are schematic front views showing an example of the configuration of a metal container according to the present embodiment; FIG. 7B is a flowchart showing an example of an outline of a method for manufacturing a metal container according to the present embodiment; FIG. 7C is a cross-sectional view showing an example of the configuration of a side wall forming device; FIG. 7D is an end view showing an example of the configuration of a forming section of an outer tool provided in the side wall forming device; FIG. 7E is an explanatory view of a side wall forming process (the processing procedure of the process is shown in the order of (a) → (b) → (c)); FIG. 7F is an explanatory view of a side wall forming process ((a) shows the first stage, and (b) shows the second stage); FIG. 7F is an end view showing an example of the configuration of a forming section of an outer tool used in test process 1 ((a) shows an example of the configuration of a forming section of a conventional, general outer tool, and (b) shows an example of the configuration of a forming section provided with a pre-drawing straightening surface); FIG. 7F is an end view showing an example of the configuration of a forming section of an outer tool used in test process 2 ((a) shows a configuration including the upper side of the forming section shown in FIG. 7B, and (b) shows an example of the configuration of a forming section provided with a post-drawing straightening surface); and FIG. 7F is an outline front view of an example of the configuration of a metal container according to a modified example. FIG. 10 is a diagram showing the results of three-time average (n=3) measurement of the roundness [mm] after a diameter reduction process performed using an outer tool having a forming portion with a post-drawing straightening surface (vertical surface) and an outer tool having a forming portion without a post-drawing straightening surface.

[0011] Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. In the following description, the same reference numerals in different drawings indicate parts with the same function, and duplicated descriptions in each drawing will be omitted as appropriate.

[0012] [Metal Container] As shown in FIG. 1 , the metal container 1 according to this embodiment has an opening 1A, a sidewall 1B, and a bottom 1C. This metal container 1 is a cup-shaped container that can replace conventional disposable paper or plastic cups. In the example shown in FIG. 1 , the opening 1A is provided with an outwardly curved curl 10, and the opening 1A is used in an open state. However, the opening 1A may also be provided with a curved flange (not shown) around which the outer periphery of a lid can be fastened, and the container may be used as a can. Note that the description of the metal container 1 shown in FIG. 1 assumes that the opening 1A is facing up and the bottom 1C is facing down.

[0013] The metal container 1 shown in Figure 1 has a sidewall 1B with an overall tapered contour so that the outer diameter of the bottom 1C is smaller than the inner diameter of the opening 1A. This allows multiple metal containers 1 to be stacked with the bottom 1C of the upper metal container 1 placed inside the opening 1A of the lower metal container 1, and the shape allows multiple metal containers 1 to be transported in a stacked state when not in use.

[0014] An example of a process (manufacturing method) for manufacturing the metal container 1 will be described with reference to the flowchart of Fig. 2. As shown in Fig. 2, first, a plate-shaped metal material is prepared by, for example, cutting a coiled plate material (step S0: plate-shaped metal material preparation process), and then the plate-shaped metal material is punched and subjected to drawing (or drawing and ironing) to form a cup-shaped intermediate member (bottomed cup) (step S1: cupping process). Note that after step S1 and before step S2, a process of further drawing (or drawing and ironing) or forming the bottom portion 1C (process of step S1') may be included.

[0015] The material of the base material constituting the metal container 1 can be aluminum, aluminum alloy, stainless steel, steel, etc., but by using aluminum, aluminum alloy, or steel, it is possible to obtain a metal container 1 that is lightweight, has a glossy appearance, and makes it easy to feel the temperature of the contents (e.g., cold water) with the hand, making it suitable as a beverage container. In addition, the plate-shaped metal material that is the material of the metal container 1 can be an aluminum, aluminum alloy, or steel base material coated (coated) on both sides with a single layer or multiple layers of resin film such as PET film.

[0016] For example, a plate-shaped metal material may be used in which a resin layer made of PET film or the like is provided on both sides of a metal substrate, and a lubricant layer made of wax or the like is provided on the resin layer. In this case, the lubricant present on the surface of the bottomed cup described below allows smooth processing during the subsequent drawing process in the side wall portion forming step (step S5), thereby suppressing the occurrence of molding defects (wrinkles, scratches, etc.).

[0017] After step S1 or step S1', the tip of the bottomed cup having a predetermined outer diameter, height, and thickness is trimmed (step S2: trimming process). Trimming is performed to uniformly cut the tip height of the bottomed cup, which has become uneven due to redrawing, ironing, etc., around the central axis. Therefore, the tip height of the bottomed cup after trimming becomes uniform.

[0018] Next, the trimmed tip of the bottomed cup is subjected to a tip diameter reduction process (step S3: tip diameter reduction process). The diameter reduction process for the tip is a so-called necking process, in which the diameter of the tip opening of the bottomed cup is reduced to form a necking portion n that gradually reduces in diameter toward the tip, and also forms a portion to be processed for the subsequent curl 10 (or flange) processing.

[0019] After the tip diameter reduction step (step S3), the curl 10 (or flange) is formed at the tip of the bottomed cup (the portion where the curl 10 (or flange) is to be formed) to form the opening 1A with the curl 10 (or flange) (step S4: opening formation step). By forming the curl 10 (or flange) at the tip in this manner, the rigidity of the tip opening can be increased and deterioration of the roundness can be suppressed when the side wall portion 1B is formed in the next step.

[0020] In this embodiment, "roundness" refers to the difference between the maximum and minimum inner diameters of either the bottomed cup or the metal container 1 formed therefrom, divided by 2 (i.e., roundness = (maximum diameter - minimum diameter) / 2 [mm]).

[0021] As described above, when a metal substrate coated with a resin layer on both sides is used as the plate-shaped metal material, a step of locally heating the area to be processed for the curl 10 (or flange) may be performed as a pre-step to the opening formation step (step S4). This local heating may be performed, for example, by using high-frequency heating to locally heat the area to be processed distal to the necking portion n at a target temperature of 200°C ± 30°C. Such local heating increases the adhesion between the substrate and the coated resin, preventing the resin layer from peeling off from the metal substrate during processing of the curl 10 (or flange), resulting in a good finish.

[0022] After the opening forming step (step S4), the side wall 1B is formed (step S5: side wall forming step). In this side wall forming step (step S5), an outer tool (e.g., outer tool 120 in FIG. 3 ) disposed outside the bottomed cup is moved relative to an inner tool (e.g., inner tool 130 in FIG. 3 ) disposed inside the bottomed cup, and gradual diameter reduction (multiple diameter reduction processes) is performed on the bottomed cup toward the bottom 1C from the portion where the diameter reduction at the tip has been performed, thereby forming the side wall 1B having an overall tapered contour.

[0023] An example of the sidewall forming process (step S5) will be described in detail below. In this sidewall forming process, a sidewall forming apparatus 100, as shown in FIG. 3, is used. The sidewall forming apparatus 100 includes a pressing tool 110 (also called a knockout pad), an outer tool 120 (outer tool) (also called a die), an inner tool 130 (inner tool) (also called a punch), and a support tool 140 (also called a curl support holder). A bottomed cup (bottomed cup Cp) with an opening 1A having a curl 10 (or flange) formed in step S4 is placed on the sidewall forming apparatus 100 with the opening 1A facing downward. As shown in FIG. 3, the central axes of the pressing tool 110, outer tool 120, inner tool 130, and support tool 140 of the sidewall forming apparatus 100, as well as the central axis of the placed bottomed cup Cp, are all referred to as a central axis O.

[0024] The holding tool 110 is a cylindrical tool and is disposed above the inner tool 130. The inner tool 130 is a cylindrical tool with a diameter smaller than the inner diameter of the bottomed cup Cp and is disposed inside the bottomed cup Cp. The outer tool 120 is an annular tool and is disposed outside the holding tool 110 and is disposed outside the bottomed cup Cp by descending. The outer tool 120 has a forming portion 121 that performs drawing by sandwiching the side wall W of the bottomed cup Cp between the outer peripheral surface of the inner tool 130 and the outer tool 120.

[0025] The holding tool 110 is a tool for facilitating removal of the bottomed cup Cp (i.e., the metal container 1) on which the side wall portion 1B has been formed by the diameter reduction process in the side wall portion forming step (step S5) from the outer tool 120. In addition, when the holding tool 110 clamps the bottom portion 1C (ground contact portion) of the bottomed cup Cp between itself and the inner tool 130, the holding tool 110 applies a downward load (cushion load), thereby reducing variations in the height distance of the bottom portion 1C in the circumferential direction (rolling direction).

[0026] The magnitude of the downward load (cushion load value [N]) applied by the pressing tool 110 is not particularly limited, but can be, for example, 1000 to 1500 N. If this cushion load value [N] is too small, it is not possible to reduce the variation in height distance in the circumferential direction (rolling direction) of the bottom portion 1C (ground contact portion). If this cushion load value [N] is too large, the load applied to the side wall portion forming device 100 becomes too large, and there is a risk of the side wall portion forming device 100 breaking down.

[0027] As shown in FIG. 4 , the forming portion 121 of the outer tool 120 has a drawing curved surface 122 (second inclined surface) also referred to as drawing R on its inner surface, which is the portion where drawing is performed on the side wall W of the bottomed cup Cp. This drawing curved surface 122 has a height distance from boundary point P3 to boundary point P4. This drawing curved surface 122 performs drawing at boundary point P4 on the side wall W of the bottomed cup Cp, which is sandwiched between the outer peripheral surface of the inner tool 130 and the drawing curved surface 122. At the same time, the entire drawing curved surface 122 forms the side wall W of the bottomed cup Cp into an inclined shape corresponding to the shape of the drawing curved surface 122 (i.e., forms an inclined wall portion t).

[0028] The forming portion 121 of the outer tool 120 has a pre-drawing correction surface 123 (first inclined surface) on its inner surface as a portion for correcting distortion of the side wall W immediately before drawing. The pre-drawing correction surface 123 is connected to the lower end of the drawing curved surface 122 at a boundary point P3, and has a height distance from the boundary point P1 to the boundary point P3.

[0029] The pre-drawing correcting surface 123 has a curved inclined surface 123A, also referred to as an opening R, and a flat inclined surface 123B, also referred to as an opening taper. The curved inclined surface 123A is connected to the lower end of the drawing curved surface 122 at a boundary point P3, and has a height distance from boundary point P2 to boundary point P3. The flat inclined surface 123B is connected to the lower end of the curved inclined surface 123A at a boundary point P2, and has a height distance from boundary point P1 to boundary point P2.

[0030] Both the drawing curved surface 122 and the curved inclined surface 123A are curved surfaces. However, the drawing curved surface 122 has a curved shape that gently protrudes toward the inside (radially inward) of the outer tool 120, and the curved inclined surface 123A has a curved shape that gently protrudes toward the outside (radially outward) of the outer tool 120, with the boundary point P3 as the boundary. That is, in the outer tool 120, the center of the radius of curvature of the drawing curved surface 122 is located outside (radially outward) from the boundary point P3, and the center of the radius of curvature of the curved inclined surface 123A is located inside (radially inward) from the boundary point P3. Note that the radii of curvature of the drawing curved surface 122 and the curved inclined surface 123A are not particularly limited and may be set appropriately depending on the shape of the metal container 1 to be manufactured.

[0031] The forming portion 121 of the outer tool 120 has, on its inner surface, a post-drawing correction surface 124 (vertical surface) also called a land portion, which serves as a portion for correcting distortion of the side wall W immediately after drawing. The post-drawing correction surface 124 is connected to the upper end of the drawing curved surface 122 at a boundary point P4, and has a height distance from the boundary point P4 to a boundary point P5.

[0032] The support tool 140 is provided below the inner tool 130, and its outer peripheral surface abuts against the inner surface of the curl 10 (or flange) of the bottomed cup Cp. The support tool 140 prevents the curl 10 from deforming in the radial direction when the diameter of the bottomed cup Cp is reduced relative to the side wall W. This prevents blocking of the metal containers 1 when they are stacked.

[0033] In the sidewall forming process (step S5), the bottomed cup Cp, in which the opening 1A with the curl 10 (or flange) was formed in step S4, is placed in the sidewall forming device 100. Specifically, as shown in FIG. 3, the bottomed cup Cp, with its bottom 1C facing up, is lowered onto the inner tool 130 so as to cover it from above. As a result, as shown in FIG. 5(a), the inner tool 130 is positioned inside the bottomed cup Cp, and the curl 10 of the bottomed cup Cp is brought into contact with the outer circumferential surface of the support tool 140. Furthermore, the pressing tool 110 is brought into contact with the bottom 1C of the bottomed cup Cp. The pressing tool 110 and the inner tool 130 fix the bottom 1C sandwiched between them. At this point, the outer tool 120 is positioned on the outer circumferential side of the pressing tool 110.

[0034] In the first stage of the diameter-reducing and drawing process in the side wall portion forming process (step S5), as shown in Fig. 5(b), the outer tool 120 is moved in the direction of the arrow in the drawing from the bottom 1C toward the opening 1A relative to the fixed inner tool 130 from the state shown in Fig. 5(a). By moving the outer tool 120 in this manner, the diameter-reducing and drawing process is performed on the side wall W of the bottomed cup Cp, and further, the curved drawing surface 122 (Fig. 4) of the outer tool 120 is brought into contact with the bottom 1C side of the necking portion n, which has been subjected to the diameter-reducing and drawing process at the tip, to form the inclined wall portion t.

[0035] In moving the outer tool 120 (outer tool) relative to the inner tool 130 (inner tool) to form this inclined wall portion t, first, the pre-drawing correction surface 123 (first inclined surface) of the outer tool 120 is brought into contact with the outer surface of the side wall W of the bottomed cup Cp. Thereafter, the drawing curved surface 122 (second inclined surface) of the outer tool 120 is brought into contact with the outer surface of the side wall W of the bottomed cup Cp, thereby performing the drawing process on the side wall W of the bottomed cup Cp and forming the inclined wall portion t having a shape that conforms to the drawing curved surface 122.

[0036] By bringing the pre-drawing correction surface 123 (first inclined surface) into contact with the outer surface of the side wall W of the bottomed cup Cp, the material of the side wall W of the bottomed cup Cp is constrained, making it difficult for differences in the workability of the material to occur depending on the rolling direction. As a result, radial distortion of the side wall W of the bottomed cup Cp is corrected.

[0037] When the pre-drawing correction surface 123 (first inclined surface) abuts, the flat inclined surface 123B (opening taper) first abuts against the outer surface of the side wall W of the bottomed cup Cp, correcting the radial distortion of the side wall W, and then the curved inclined surface 123A (opening R) abuts, further correcting the radial distortion of the side wall W.

[0038] Thus, in the sidewall portion forming process (step S5), the pre-drawing correcting surface 123 (first inclined surface) is brought into contact with the sidewall W immediately before the drawing process and the formation of the inclined wall portion t are performed by contacting the drawing curved surface 122 (second inclined surface). That is, in this sidewall portion forming process, the sidewall W is drawn and the inclined wall portion t is formed after the radial distortion has been corrected. This allows the formation of a sidewall portion 1B having good roundness (0.80 mm or less, e.g., 0.38 mm or less). The roundness of the sidewall portion 1B can be improved, particularly at the portion where the pre-drawing correcting surface 123 (first inclined surface) contacts. For example, the abutment of the pre-drawing correcting surface 123 (first inclined surface) in the sidewall portion 1B can reduce the roundness of the abutting portion to 0.38 mm or less, thereby reducing the roundness of the entire sidewall portion 1B to 0.38 mm or less. In this case, when a plurality of metal containers 1 are stacked, a clearance of 0.2 mm or more can be ensured between the side wall portion 1B of the upper metal container 1 and the side wall portion 1B of the lower metal container 1.

[0039] In this stacked state, a good clearance is ensured between the side wall 1B of the upper metallic container 1 and the side wall 1B of the lower metallic container 1, thereby preventing the side wall 1B of the upper metallic container 1 from coming into contact with the lower metallic container 1 at an undesirable position. That is, with metallic containers 1 having such side wall 1B, when multiple metallic containers 1 are stacked, each metallic container 1 has good circularity, so that a good stacked state can be maintained and the occurrence of a blocking phenomenon can be prevented regardless of the circumferential direction in which the metallic containers are stacked.

[0040] Furthermore, when the outer tool 120 moves relative to the inner tool 130, the post-drawing correction surface 124 (vertical surface) of the outer tool 120 is brought into contact with the outer surface of the side wall W of the bottomed cup Cp immediately after the drawing process and the formation of the inclined wall portion t are performed by abutting the drawing curved surface 122 (second inclined surface) of the outer tool 120. This restrains the material of the side wall W of the bottomed cup Cp immediately after the forming process by the drawing curved surface 122, making it less likely that differences in the workability of the material will occur depending on the rolling direction. As a result, radial distortion of the side wall W of the bottomed cup Cp is further corrected, and a side wall portion 1B with better roundness (0.80 mm or less, for example, 0.38 mm or less) can be formed.

[0041] Then, as shown in Figure 5 (c), when the outer tool 120 is returned to the bottom 1C side, a bulge 11 consisting of a necking portion n and an inclined wall portion t is formed on the tip side of the bottomed cup Cp on the bottom 1C side of the curl 10.

[0042] The next step in the side wall portion forming process S5 will be described with reference to FIG. 6. In the first-stage diameter reduction and drawing process described above, an inner tool 130 with a tool radius Tr1 is used. Following this first-stage diameter reduction and drawing process, a second-stage diameter reduction and drawing process is performed using an inner tool 130 with a tool radius Tr2 (Tr1 > Tr2). The inner diameter of the forming portion 121 of the outer tool 120 is set in accordance with the tool diameter of the inner tool 130.

[0043] In the first stage of the diameter reduction and drawing process (Figure 6(a)), the movement stroke St1 of the outer tool 120 is the stroke length required to form the inclined wall portion t of the bulge portion 11, whereas in the second stage of the diameter reduction and drawing process (Figure 6(b)), the movement stroke St2 of the outer tool 120 is made shorter than the movement stroke St1 of the first stage, and a vertical wall portion s is formed on the bottom 1C side of the inclined wall portion t of the bulge portion 11.

[0044] Thereafter, the tool radius of the inner tool 130 is successively reduced, and the diameter reduction and drawing processes from the second stage onward are repeated (multiple diameter reduction and drawing processes). As a result, a metal container 1 is manufactured that has a side wall portion 1B below the bulge portion 11, with a tapered contour formed by alternating inclined wall portions t and vertical wall portions s, as shown in Fig. 1. By forming the vertical wall portions s and inclined wall portions t alternately in the side wall portion 1B, when the metal container 1 is used as a cup for beverages, the step formed by the vertical wall portion s and the inclined wall portion t functions as a non-slip surface when gripped by hand.

[0045] The side wall portion 1B, which has a tapered profile formed by alternating inclined wall portions t and vertical wall portions s, is formed by moving the outer tool 120 having the shape shown in Figure 4 described above relative to the inner tool 130. That is, every time the outer tool 120 performs drawing and forms the inclined wall portion t, the pre-drawing correcting surface 123 (first inclined surface) is brought into contact with the inner tool 130 immediately before the forming, and the post-drawing correcting surface 124 (vertical surface) is brought into contact with the inner tool 130 immediately after the forming. As a result, the formed side wall portion 1B has a shape with good circularity and no distortion.

[0046] When two metal containers 1 are stacked, the outer surface of the inclined wall portion t, which is the portion of the bulge 11 on the bottom 1C side of the upper metal container 1, comes into contact with the inner surface of the curl 10 (or flange) of the lower metal container 1. In this stacked state, since each metal container 1 has good circularity, a good stacked state is maintained and the occurrence of blocking is suppressed regardless of the circumferential orientation of the metal containers 1 when stacked.

[0047] In the manufacturing example of the metal container 1 described above, when a flange is formed on the opening 1A in the opening forming step (step S4) described above, the flange serves as a portion for fastening the outer edge of the lid. After the contents are poured into the metal container 1, the lid is fastened to the flange, thereby turning the metal container 1 into a can that seals the contents. The lid that is fastened here can be, for example, a metal stay-on tab lid, but other types of lids may also be used. Alternatively, instead of a flange, another type of opening 1A may be used, and another type of lid, such as a screw lid, may be attached to it so that it can be freely attached and removed.

[0048] Furthermore, when the metal container 1 is made of a plate-shaped metal material containing the above-described lubricant layer, the side wall 1B may be heated after the above-described side wall forming step (step S5), thereby volatilizing the lubricant and removing it from the metal container 1. In this heating, the metal container 1 may be heated to a temperature of, for example, about 180°C to 210°C.

[0049] The significance (effect) of providing the pre-drawing correction surface 123 (first inclined surface) will now be described based on Test Process 1 below. FIG. 7 shows the forming portion of the outer tool used in Test Process 1. FIG. 7( a) shows the end face of the forming portion 321 of a conventional, general outer tool 320, which performs a diameter-reducing drawing process on the side wall W of a bottomed cup Cp. This forming portion 321 is provided with a guide surface 325, also referred to as an approach portion, having a height distance from boundary point P11 to boundary point P12 below a drawing curved surface 322 (second inclined surface) having a height distance from boundary point P12 to boundary point P13. This guide surface 325 is inclined radially outward as it extends downward, forming a large space between the side wall W of the bottomed cup Cp and the guide surface 325.

[0050] 7(b) has a drawing curved surface 422 (second inclined surface) having a height distance from boundary point P23 to boundary point P24, and a pre-drawing straightening surface 423 provided below the drawing curved surface 422 and having a height distance from boundary point P21 to boundary point P23. The pre-drawing straightening surface 423 corresponds to the above-mentioned pre-drawing straightening surface 123 (first inclined surface). That is, the pre-drawing straightening surface 423 has a curved inclined surface 423A having a height distance from boundary point P22 to boundary point P23, which corresponds to the above-mentioned curved inclined surface 123A, and a flat inclined surface 423B having a height distance from boundary point P21 to boundary point P22, which corresponds to the above-mentioned flat inclined surface 123B.

[0051] In test process 1, the outer tool 320 shown in FIG. 7A was used in place of the outer tool 120 in the sidewall forming apparatus 100 shown in FIG. 3 . Specifically, the outer tool 320 was moved relative to the inner tool 130 in the direction of the arrow in FIG. 7A from the bottom 1C of the bottomed cup Cp, in which the opening 1A having the curl 10 was formed, toward the opening 1A. This process was performed for each different movement stroke. Then, for each test process 1 with different movement strokes, the circularity [mm] of the portion of the sidewall W of the bottomed cup Cp that passed through the guide surface 325 in FIG. 7A was measured.

[0052] Similarly, in this test process 1, the outer tool 420 shown in FIG. 7( b) was used in place of the outer tool 120 in the sidewall forming apparatus 100 shown in FIG. 3 . Specifically, the outer tool 420 was moved relative to the inner tool 130 in the direction of the arrow shown in FIG. 7( b) from the bottom 1C of the bottomed cup Cp, in which the opening 1A having the curl 10 was formed, toward the opening 1A. This process was performed for each different movement stroke. Then, for each test process 1 with different movement strokes, the roundness [mm] of the portion of the sidewall W of the bottomed cup Cp where the pre-drawing correction surface 423 (first inclined surface) shown in FIG. 7( b) abutted was measured.

[0053] As a result of performing this test process 1, regardless of the height distance from the bottom 1C (ground surface) of the point where the roundness of the side wall W of the bottomed cup Cp was measured, the measured roundness of the bottomed cup Cp subjected to test process 1 using the outer tool 420 was better than that of the bottomed cup Cp subjected to test process 1 using the outer tool 320, and a preferable value of 0.80 mm or less, particularly 0.38 mm or less, was achieved.

[0054] As a more specific example, in the pre-drawing straightening surface 423 (first inclined surface) shown in the end view of Figure 7(b), the radius of curvature R of the curved inclined surface 423A was set to 5 mm to 20 mm, and the inclination angle inclined radially outward with respect to a virtual line (not shown) passing through the boundary point P22 and parallel to the central axis O (see Figure 3) was set to 3° to 20°. The bottomed cup Cp subjected to test process 1 using the outer tool 420 having such a pre-drawing straightening surface 423 (first inclined surface) was able to measure a preferable roundness of 0.38 mm or less.

[0055] Regarding the results of this test process 1, when the forming portion 321 shown in Figure 7 (a) moves from the bottom 1C of the bottomed cup Cp shown in the direction of the arrow toward the opening 1A, the guide surface 325 does not abut against the outer surface of the side wall W of the bottomed cup Cp just before the drawing process by the drawing curved surface 322 and the forming of the inclined wall portion t, so radial distortion of the bottomed cup Cp is not suppressed and good roundness cannot be obtained.

[0056] In contrast, when the forming portion 421 shown in Figure 7 (b) moves from the bottom 1C of the bottomed cup Cp in the direction of the arrow shown toward the opening 1A, just before the drawing process by the drawing curved surface 422 (second inclined surface) and the forming of the inclined wall portion t, the flat inclined surface 423B and the curved inclined surface 423A of the pre-drawing correction surface 423 (first inclined surface) sequentially abut against the outer surface of the side wall W of the bottomed cup Cp, correcting the radial distortion of the bottomed cup Cp and achieving good roundness.

[0057] The significance (effect) of providing the post-drawing correction surface 124 (vertical surface) will be explained based on the following test process 2. Figure 8 shows the forming portion of the outer tool used in test process 2. Figure 8(a) shows a cross section including the upper side of the forming portion 421 of the outer tool 420 shown in Figure 7(b). As shown in Figure 8(a), in the forming portion 421, the non-forming surface 424 above the boundary point P24 of the drawing curved surface 422 (second inclined surface) is inclined significantly radially outward as it goes upward, and a large space is formed between the side wall W of the bottomed cup Cp and the non-forming surface 424.

[0058] In contrast, the forming portion 521 of the outer tool 520 shown in Figure 8 (b) has a post-drawing correction surface 425 (vertical surface) from boundary point P24 to boundary point P25 above the drawing curved surface 422 (second inclined surface).

[0059] In test process 2, the outer tool 420 shown in FIG. 8A was used in place of the outer tool 120 in the sidewall forming apparatus 100 shown in FIG. 3 . Specifically, the outer tool 420 was moved relative to the inner tool 130 in the direction of the arrow in FIG. 8A from the bottom 1C of the bottomed cup Cp, which had an opening 1A with a curl 10, toward the opening 1A. This process was performed for each different movement stroke (similar to the process described above with reference to FIG. 7B for test process 1). Then, for each test process 2 with different movement strokes, the roundness [mm] of the portion of the sidewall W of the bottomed cup Cp that passed through the non-forming surface 424 in FIG. 8A was measured.

[0060] Similarly, in this test process 2, in the side wall forming apparatus 100 shown in Fig. 3, an outer tool 520 shown in Fig. 8(b) was used instead of the outer tool 120, and the outer tool 520 was moved relative to the inner tool 130 in the direction of the arrow in Fig. 8(b) from the bottom 1C of the bottomed cup Cp, in which the opening 1A having the curl 10 was formed, toward the opening 1A, for each different movement stroke. Then, for each test process 2 with different movement strokes, the roundness [mm] of the portion of the side wall W of the bottomed cup Cp where the post-drawing correction surface 425 (vertical surface) in Fig. 8(b) came into contact was measured.

[0061] As a result of performing this test process 2, regardless of the height distance from the bottom 1C (ground surface) of the point where the roundness of the side wall W of the bottomed cup Cp was measured, the measured roundness of the bottomed cup Cp subjected to test process 2 using the outer tool 520 was better than that of the bottomed cup Cp subjected to test process 2 using the outer tool 420, and a more desirable value of 0.38 mm or less was achieved.

[0062] As a more specific example, the height distance of the post-drawing correction surface 425 (vertical surface) shown in the cross-sectional view of Fig. 8(b) was set to 2 mm to 5 mm. The bottomed cup Cp subjected to test process 2 using the outer tool 520 having such a post-drawing correction surface 425 (vertical surface) was able to achieve a more preferable measured roundness of 0.38 mm or less.

[0063] Regarding the results of this test process 2, when the forming portion 421 shown in Figure 8 (a) moves from the bottom 1C of the bottomed cup Cp shown in the direction of the arrow toward the opening 1A, it is thought that immediately after the drawing process by the drawing curved surface 422 and the forming of the inclined wall portion t, the non-forming surface 424 does not abut against the outer surface of the side wall W of the bottomed cup Cp, and radial distortion of the bottomed cup Cp was not suppressed.

[0064] In contrast, when the forming portion 521 shown in Figure 8 (b) moves from the bottom 1C of the bottomed cup Cp in the direction of the arrow shown toward the opening 1A, immediately after the drawing process using the drawing curved surface 422 (second inclined surface) and the forming of the inclined wall portion t, the post-drawing correction surface 425 (vertical surface) abuts against the outer surface of the side wall W of the bottomed cup Cp, thereby correcting the radial distortion of the bottomed cup Cp and achieving better roundness.

[0065] The significance (effect) of providing the support tool 140 will be explained based on the following test process 3. In the side wall forming device 100 shown in Fig. 3, an outer tool 520 shown in Fig. 8(b) having a configuration similar to that of the outer tool 120 was used, and a process of moving the outer tool 520 relative to the inner tool 130 in the direction of the arrow in Fig. 8(b) from the bottom 1C of the bottomed cup Cp toward the opening 1A was performed multiple times while changing the movement stroke.

[0066] In this test process 3, this process was performed multiple times both when using a side wall portion forming apparatus 100 with a normal configuration (i.e., a side wall portion forming apparatus 100 provided with the support tool 140) and when using a side wall portion forming apparatus 100 without the support tool 140. After test process 3 in which this process was performed multiple times using the side wall portion forming apparatus 100 provided with the support tool 140, and after test process 3 in which this process was performed multiple times using the side wall portion forming apparatus 100 without the support tool 140, the roundness [mm] of the portion of the side wall W of the bottomed cup Cp where the post-drawing correcting surface 425 (vertical surface) in Figure 8(b) came into contact was measured.

[0067] As a result, regardless of the height distance from the bottom 1C (ground surface) of the point where the roundness of the side wall W of the bottomed cup Cp was measured, the measured roundness of the bottomed cup Cp that had been subjected to this multiple processing steps using the side wall forming device 100 that was provided with the support tool 140 was better than that of the bottomed cup Cp that had been subjected to this multiple processing steps using the side wall forming device 100 that was not provided with the support tool 140, and was able to achieve a more desirable value of 0.38 mm or less.

[0068] The significance (effect) of providing the holding tool 110 will be explained based on the following test process 4. In test process 4, in the side wall forming device 100 (i.e., the side wall forming device 100 provided with the support tool 140), the bottom 1C (grounding portion) of the bottomed cup Cp was sandwiched between the holding tool 110 and the outer peripheral surface of the inner tool 130, and a downward load (cushion load) was applied by the holding tool 110 while the outer tool 520 was moved multiple times as shown in Figure 8(b) of the above test process 3. Here, the cushion load value was set to 1000 to 1500 [N].

[0069] In addition, in this test process 4, in the side wall forming apparatus 100 (i.e., the side wall forming apparatus 100 provided with the support tool 140), the bottom 1C (ground contact portion) of the bottomed cup Cp was sandwiched between the pressing tool 110 and the outer peripheral surface of the inner tool 130, but a downward load (cushion load) was not applied by the pressing tool 110, and the outer tool 520 was moved multiple times as shown in Figure 8(b) of the above-mentioned test process 3. In this way, the variation in height distance [mm] in the circumferential direction (rolling direction) of the bottom 1C (ground contact portion) of the bottomed cup Cp after the multiple movement processes was measured for both the case where a downward load (cushion load) was applied by the pressing tool 110 and the case where a downward load (cushion load) was not applied by the pressing tool 110. The variation in this height distance [mm] was measured by placing the bottom 1C of the bottomed cup Cp on the ground surface with the bottom 1C facing up, setting the average value of the height distance [mm] from the ground surface to the bottom 1C to 0 [mm], and subtracting the minimum value of the difference from that average value from the maximum value of the difference from that average value to obtain the variation value [mm].

[0070] As a result of performing such test process 4, the variation value when no downward load (cushion load) was applied by the pressing tool 110 was 0.50 to 0.60 mm. In contrast, the variation value when a downward load (cushion load) was applied by the pressing tool 110 was 0.04 to 0.13 mm. In this way, it can be seen that by applying a downward load (cushion load) by the pressing tool 110, the variation in the height distance [mm] in the circumferential direction (rolling direction) of the bottom portion 1C (ground contact portion) can be reduced.

[0071] Although the present invention has been described above by showing a preferred embodiment (the present embodiment), it goes without saying that the present invention is not limited to the above-described embodiment and various modifications can be made within the scope of the present invention. Modifications of the present embodiment will be described below.

[0072] [Modification] For example, instead of the metal container 1 shown in FIG. 1 , a metal container 200 shown in FIG. 9 may be manufactured. This metal container 200 has a longest inclined wall portion tm, which is the longest of the inclined wall portions t, formed near the center of the side wall portion 1B. In manufacturing such a metal container 200, in step S5 described above, the movement stroke of the outer tool 120 in the next diameter-reducing process is made closer to the movement stroke in the previous stage, so that the inclined wall portion t is formed continuously without sandwiching the vertical wall portion s. This results in the longest inclined wall portion tm consisting of a continuous inclined wall portion t. Because this longest inclined wall portion tm has a relatively wide, substantially flat surface, its outer surface can be used, for example, for printed markings. In other words, by including a step of printing on the longest inclined wall portion tm, a metal container 1 can be manufactured with an effective printed marking.

[0073] In manufacturing the metal container 200, the portion of the side wall 1B other than the longest inclined wall portion tm (the portion formed by alternating inclined wall portions t and vertical wall portions s) is formed using an outer tool 120 having a forming portion 121 shown in FIG. 4 . This improves the roundness of this portion. The longest inclined wall portion tm of the side wall 1B can be formed using an outer tool having a forming portion including the guide surface 325 shown in FIG. 7( a), a curved drawing surface 322 (second inclined surface) provided above it, and a post-drawing correction surface (vertical surface) provided above that. In forming this longest inclined wall portion tm, the radial distortion that occurs immediately after each formation of the inclined wall portion t by the curved drawing surface 322 is corrected by the post-drawing correction surface (vertical surface). As a result, the roundness of the longest inclined wall portion tm is improved.

[0074] Here, an outer tool having a forming portion with a post-drawing straightening surface (vertical surface) and an outer tool having a forming portion without a post-drawing straightening surface (vertical surface) were moved from the bottom 1C of the bottomed cup Cp, which had an opening 1A with a curl 10, toward the opening 1A (diameter reduction process) at a predetermined diameter reduction rate (for each different movement stroke). For each different movement stroke, the roundness (CR [mm]) of the side wall W of the bottomed cup Cp at a height distance (H [mm]) from the bottom 1C (ground contact surface) was measured three times and the average value (n=3) of the measurements was calculated. The calculation results are shown in FIG. 10.

[0075] In Figure 10, graph a shows the measured value of the roundness (CR [mm]) at the height distance (H [mm]) from the bottom 1C (ground surface) of the side wall W of the bottomed cup Cp before the diameter reduction process. Graph b shows the average value (n = 3) of the measured values ​​of the roundness (CR [mm]) at the height distance (H [mm]) from the bottom 1C (ground surface) of the side wall W when an outer tool having a forming section with a post-drawing straightening surface (vertical surface) was used for the inner tool 130. Graph c shows the average value (n = 3) of the measured values ​​of the roundness (CR [mm]) at the height distance (H [mm]) from the bottom 1C (ground surface) of the side wall W when an outer tool having a forming section without a post-drawing straightening surface (vertical surface) was used for the inner tool 130.

[0076] As shown in Figure 10, when an outer tool provided with a post-drawing straightening surface (vertical surface) was used, the roundness (CR [mm]) was improved over the entire region of the side wall W compared to an outer tool without a post-drawing straightening surface (vertical surface). Furthermore, when a metal container 200 such as that shown in Figure 9 was formed by performing this diameter reduction process multiple times, when an outer tool with a forming portion without a post-drawing straightening surface (vertical surface) was used, there were locations in the longest inclined wall portion tm where the roundness exceeded 0.80 mm, and the roundness near the center of the side wall portion 1B was the highest. In contrast, when an outer tool with a forming portion with a post-drawing straightening surface (vertical surface) was used, a roundness of 0.38 mm or less was achieved in locations other than the longest inclined wall portion tm.

[0077] The above-described embodiment and the above-described modified examples can be combined by utilizing the techniques of each other, as long as there are no particular contradictions or problems in the purpose, configuration, and the like.

[0078] 1,200: metal container, 1A: opening, 1B: side wall portion, 1C: bottom portion, 10: curl, 11: bulge portion, 100: side wall portion forming device, 110: pressing tool, 120, 320, 420, 520: outer tool, 121, 321, 421, 521: forming portion, 122, 322, 422: curved surface for drawing, 123, 423: straightening surface before drawing, 123A, 423A: curved inclined surface, 123B, 423B: flat inclined surface, 124, 425: straightening surface after drawing, 130: inner tool, 325: guiding surface, 140: support tool, 424: non-forming surface, Cp: bottomed cup, W: side wall

Claims

1. A metallic container having an opening, a sidewall, and a bottom, the sidewall being formed from a bottomed cup formed by a drawing process on a metal plate, wherein the sidewall is formed into a shape with a tapered outline by moving an outer tool positioned on the outside of the sidewall of the bottomed cup relative to an inner tool positioned inside the sidewall of the bottomed cup, which has been trimmed and drawn at its tip, and performing a process of drawing a portion of the bottomed cup closer to the bottom than the portion of the bottomed cup where the tip was drawn, and the sidewall has an inclined wall portion shaped to follow the second inclined surface, formed by the outer surface of the sidewall of the bottomed cup coming into contact with a first inclined surface of the outer tool as the outer tool moves, and the portion coming into contact with the first inclined surface has an out-of-roundness of 0.80 mm or less.

2. The metal container according to claim 1, wherein the side wall has a circularity of 0.38 mm or less at the point where it abuts against the first inclined surface.

3. A method for manufacturing a metal container having an opening, a side wall, and a bottom, comprising: a step of forming a bottomed cup by drawing a plate-shaped metal material; a step of trimming the bottomed cup; a step of drawing the bottomed cup to reduce its diameter at the tip; and a step of moving an outer tool positioned outside the side wall of the bottomed cup relative to an inner tool positioned inside the side wall of the bottomed cup, and performing the process of reducing its diameter multiple times on the bottomed cup toward the bottom side from the point where the tip of the bottomed cup has been reduced, thereby forming the side wall having a tapered contour, wherein in the step of forming the side wall, as the outer tool moves, a first inclined surface of the outer tool is abutted against the outer surface of the side wall of the bottomed cup, and then a second inclined surface of the outer tool is abutted against the second inclined surface, thereby forming an inclined wall having a shape that follows the second inclined surface.

4. A method for manufacturing a metal container as described in claim 3, characterized in that in the process of forming the side wall portion, the second inclined surface is abutted against the outer surface of the bottomed cup as the outer tool moves, and then the vertical surface of the outer tool is abutted against it.

5. A method for manufacturing a metal container as described in claim 3, characterized in that it includes a step of forming the opening having a curl or flange at the tip of the bottomed cup after the step of reducing the tip diameter of the bottomed cup and before the step of forming the side wall portion.

6. A method for manufacturing a metal container as described in claim 3, characterized in that in the process of forming the side wall portion, the bottom of the bottomed cup is clamped between a pressing tool positioned above the inner tool and the inner tool, and a load of 1000 to 1500 N is applied downward by the pressing tool.

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