Can manufacturing method

Abstract

To provide a manufacturing method of a can capable of reshaping a can bottom part of a primary can body by a simple constitution.SOLUTION: A manufacturing method of a can includes a primary can body formation step for forming a primary can body having a cylindrical barrel part, and such a can bottom part that a projection, an inner wall part, a dome part and an arc-shaped part are formed on the can bottom part; and a reshaping step for reshaping the can bottom part of the primary can body. In the reshaping step, in the state where a tip of the projection is supported by a support plane orthogonal to a can axis, a peripheral edge part of the dome part is pressed from inside the cylindrical barrel part, to thereby bend the arc-shaped part, and to form an upper side bent part having a small curvature radius.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing cans that are filled with contents such as beverages. [Background technology]

[0002] Conventionally, cans filled with beverages or other contents include a cylindrical body and a can bottom integrally connected to one end of the cylindrical body. The can bottom includes a circumferential ground contact portion that protrudes annularly outward in the axial direction of the can, an outer circumferential bottom portion connecting the cylindrical body and the circumferential ground contact portion, a rising portion located inside the circumferential ground contact portion, and a dome portion connected to the rising portion via a bent portion. In recent years, with the trend toward thinner (lighter) can sheet materials, a reforming process for increasing the strength of the can bottom has been proposed. Patent Document 1, for example, describes a can manufacturing method as an example of such a can reforming method.

[0003] The can manufacturing method described in Patent Document 1 first uses a drawing and ironing process to form a dome portion at the bottom of the cylindrical body that is recessed inward on the can shaft and an annular convex portion that protrudes outward from the outer peripheral edge and extends circumferentially around the can shaft. This annular convex portion consists of a tip portion located at the very tip, an inner wall portion that extends in a generally straight shape connecting the tip portion and the bent portion, and an outer wall portion that connects the tip portion and the lower end of the cylindrical body. The method also includes a bottom reforming process in which the inner wall portion of the annular convex portion is subjected to bottom reforming processing to form an annular recess in the inner wall portion that is recessed radially outward and extends the entire circumferential direction.

[0004] In the bottom reforming process described above, a forming roller is brought into contact with the inner wall of the bottom of the preformed can (hereinafter referred to as the primary can body) while supporting the neck of the can before reforming, and is rolled over this inner wall all around the circumferential direction around the can axis to form an annular recess in the inner wall that extends all around the circumferential direction. However, when reforming the bottom of the can body using this method, the can may vibrate in accordance with the movement of the forming roller, resulting in unstable processing.

[0005] On the other hand, the reforming step in the can manufacturing method described in Patent Document 2 is performed using a cylindrical punch, a dome holder, a doming die, and a hold-down ring. Specifically, while the dome holder and doming die hold down the dome portion, the punch and hold-down ring hold the outer wall of the can and are lowered relative to the dome holder and doming die to form an annular protrusion. The punch and hold-down ring are then raised relative to the dome holder and doming die to press the tip of the annular protrusion into a groove defined by the hold-down ring and the outer surface of the doming die, forming a circumferential contact portion, an outer bottom portion, and a raised portion. In other words, while restricting the dome portion, the annular protrusion is pressed downward and radially inward, forming an inverse taper in the raised portion, with the diameter increasing in the height direction.

[0006] Incidentally, the can manufacturing method described in Patent Document 2 requires the use of a special press that holds the outer wall of the can with a punch and hold-down ring while restricting the dome portion with a dome-holding tool, and moves the press up and down relative to the dome-holding tool and doming die, resulting in a special and large device for reforming the bottom of the can before reforming (primary can body).

[0007] To solve the above problems, for example, Patent Document 3 has proposed a can body forming apparatus in which a cylindrical body and a can bottom are integrally formed. The can body forming apparatus described in Patent Document 3 includes a tool for reforming the shape of the legs of a can body having a concave dome in the center of the can bottom and annular legs formed around the dome, and the tool includes a pressing body that is inserted into the can body and abuts against the inner surface of the dome, and a forming die that forms an inwardly curved end at the bottom end of the leg. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 6414957 [Patent Document 2] Japanese Patent Application Publication No. 9-285832 [Patent Document 3] International Publication No. 2021 / 95309 Summary of the Invention [Problem to be solved by the invention]

[0009] In the device described in Patent Document 3, a forming die having an inclined surface formed on the outer surface of the can bottom that slopes radially inward is positioned opposite the can bottom, and the inner surface of the dome portion is pressed by a pressing body, resulting in a complex structure for supporting the can bottom.In addition, since the can bottom is formed by pressing the periphery of the dome portion while the outer surface of the leg is supported by an inclined surface, and deforming it along the inclined surface to cause part of the annular leg to protrude downward, there is a possibility that the shape of the can bottom will vary.

[0010] The present invention has been made in view of the above circumstances, and has an object to provide a can manufacturing method that allows the can bottom of a primary can body to be reshaped with a simpler configuration. [Means for solving the problem]

[0011] The method for manufacturing a can of the present invention includes a primary can body forming step of forming a primary can body having a cylindrical tubular body portion and a can bottom portion integrally connected to one end of the cylindrical body portion, the primary can body having a protruding portion that protrudes annularly from the can bottom in the outward axial direction of the can, a dome portion that is formed on the can axis of the can bottom and is recessed inward in the axial direction of the can, and a concave arc portion that is continuous with the outer periphery of the dome portion; and a reforming step of reforming the can bottom of the primary can body, in which, while the tip of the protruding portion is supported on a support plane that is perpendicular to the can axis, the outer periphery of the dome portion is pressed from inside the cylindrical body portion to bend the arc portion and form an upper bent portion with a small radius of curvature.

[0012] In the present invention, in the remolding step, the peripheral edge of the dome portion is pressed to bend the arc-shaped portion and form an upper bent portion with a small radius of curvature, so that all that is required is to provide a support plane to support the tip of the protrusion, and there is no need to provide a molding die or the like to support the radially outer surface of the protrusion, as in Patent Document 3, for example, and the device used in the remolding step can be simplified. Furthermore, because the tip of the protrusion is supported by a support plane, the shape after remolding is stable.

[0013] In a preferred embodiment of the can manufacturing method of the present invention, in the primary can body forming step, an inner wall portion extending upward from the radially inner edge of the protrusion is formed, and the arc-shaped portion is shaped to connect the outer peripheral edge of the dome portion and the upper end of the inner wall portion, and in the re-molding step, the peripheral edge of the dome portion is pressed from inside the cylindrical body portion, bending the arc-shaped portion and spreading the upper part of the inner wall portion radially outward, thereby inclining the inner wall portion to form an inclined wall portion. In the above embodiment, the arc-shaped portion becomes an upper bent portion with a small radius of curvature, and this upper bent portion and the inclined wall portion increase the rigidity of that portion, thereby increasing the strength of the can bottom even when the can is manufactured using a thin-walled material.

[0014] In a preferred embodiment of the can manufacturing method of the present invention, in the re-forming step, a punch that presses against the peripheral edge of the dome portion is formed with a pressing surface having a width that extends from the peripheral edge of the dome portion to above the arc-shaped portion, and when pressing against the peripheral edge of the dome portion with this pressing surface, the pressing position on the arc-shaped portion is pressed so as to gradually transition radially outward from the connection end with the dome portion, thereby bending the arc-shaped portion.

[0015] In the above-described aspect, when the peripheral edge of the dome portion is pressed, the pressing position on the arc-shaped portion is pressed and bent so that it gradually transitions from the radially inward position toward the outward position, so that the upper end of the inner wall portion connected to the arc-shaped portion is pressed outward in the radial direction, thereby reliably forming a stable inclined wall portion.

[0016] In a preferred aspect of the can manufacturing method of the present invention, in the primary can body forming step, an outer peripheral bottom portion is formed in the can bottom portion, connecting the radially outer edge of the protrusion to the lower end of the cylindrical body portion, and the protrusion consists of an inner arc-shaped portion located radially inward from its apex of the primary can body and an outer arc-shaped portion located radially outward, and in the reshaping step, the inner arc-shaped portion is bent while pressing the vicinity of the apex of the inner arc-shaped portion against the support plane, to form a lower bent portion with a small radius of curvature that is continuous with the lower end of the inclined wall portion, and the outer arc-shaped portion is deformed to have a larger radius of curvature, to form an outer curved portion that is continuous with the lower bent portion.

[0017] In the above-described embodiment, the lower bent portion and the inclined wall portion, which have a small radius of curvature, increase the rigidity of the portion, thereby further increasing the strength of the can bottom. Furthermore, when the lower bent portion is formed, the outer arc-shaped portion is deformed to increase its radius of curvature, and this, combined with the reaction force generated when the inner arc-shaped portion is pressed against the support plane, pushes the portion from the outer curved portion to the outer bottom periphery upward in the can axial direction, which may result in an increase in the height of the can.

[0018] In a preferred embodiment of the can manufacturing method of the present invention, the re-forming step is carried out using the punch disposed within the cylindrical body portion and a receiving base having the flat support surface. In the above embodiment, the re-forming step can be carried out in a state where the primary can body is held between the punch and the cradle.

[0019] In a preferred embodiment of the can manufacturing method of the present invention, the outer diameter of the cylindrical body portion of the primary can body is 66.1 mm or more and 66.3 mm or less, the angle of the tangent to the inner surface of the outer edge of the dome portion with respect to a plane perpendicular to the can axis is 27° or more and 29° or less, the radial width of the pressing surface at a portion located radially inward of the inner wall portion of the primary can body is 2.0 mm or more and 3.0 mm or less, and the inclination angle of the pressing surface with respect to the plane is 20° or more and less than the angle of the tangent to the plane.

[0020] If the radial width of the portion of the primary can body located radially inward of the inner wall of the pressing surface is less than 2.0 mm, the arc-shaped portion and inner wall cannot be properly deformed when the peripheral edge of the dome portion is pressed, and large pressing marks may be formed. If it exceeds 3.0 mm, the area over which the dome portion is pressed increases, requiring excessive pressing force. Furthermore, if the angle of inclination of the pressing surface with respect to the plane of the tangent at the inner surface of the outer edge of the dome portion relative to the plane is 27° to 29° and the angle of inclination of the pressing surface with respect to the plane of the tangent is less than 20° or exceeds the angle of inclination of the pressing surface with respect to the plane of the tangent, the difference between the angle of inclination of the pressing surface with respect to the plane and the angle of inclination of the inner surface of the outer edge of the dome portion relative to the plane of the tangent becomes large, making it difficult to properly deform the arc-shaped portion and inner wall portion.

[0021] In a preferred embodiment of the can manufacturing method of the present invention, in the re-forming step, the pressing surface is pressed against the peripheral edge of the dome portion and pressed in by 1.0 mm to 3.0 mm. If the pressing depth of the pressing surface is less than 1.0 mm, the pressing depth is too small to properly reshape the can bottom, which may result in an inability to increase the strength of the can bottom, whereas if the pressing depth exceeds 3.0 mm, the can bottom may be deformed too much, which may actually reduce the strength of the can bottom. Note that, taking into account the impact on other processes during actual production (transportability, can holding and inspection by inspection machines), it is more preferable for this pressing depth to be between 1.0 mm and 2.0 mm. [Effects of the Invention]

[0022] According to the present invention, the can bottom of a primary can body can be reshaped with a simple configuration. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 2 is a front view of the right half of the can bottom of a can according to one embodiment of the present invention, taken in cross section through the can axis. [Figure 2] FIG. 2 is an enlarged view of the can bottom shown in FIG. [Figure 3]FIG. 3 is an enlarged cross-sectional view showing a portion of the can bottom of a primary can body formed by further subjecting a cup to a drawing and ironing process in the drawing and ironing process of the can manufacturing method of the present embodiment. [Figure 4] FIG. 3 is a cross-sectional view of a punch that reshapes the can bottom of the primary can body of the first embodiment. [Figure 5] FIG. 5 is a cross-sectional view showing a state in which the punch shown in FIG. 4 is placed inside the cylindrical body of the primary can body. [Figure 6] FIG. 5 is a cross-sectional view showing how the punch shown in FIG. 4 crushes the can bottom of the primary can body. [Figure 7] FIG. 7 is an enlarged view of a portion of the can bottom shown in FIG. 6. [Figure 8] 8 is an enlarged view showing a state in which the pressing surface of the punch comes into contact with the peripheral edge of the dome portion shown in FIG. 7. FIG. [Figure 9] 5 is a diagram showing the angle of the inclined wall portion relative to a line along the can axis when pressed by the punch shown in FIG. 4 with different pressing amounts. FIG. [Figure 10] 10 is a graph showing the maximum pressure resistance when the pressing amount by which the punch presses the peripheral edge and the arc-shaped portion of the dome portion in the embodiment of the present invention is changed. [Figure 11] 1 is a graph showing the amount of protrusion deformation (growth amount) of the tip of the circumferential contact portion downward in the can axial direction at 686 KPa when the pressing force applied by the punch to the peripheral edge and arc-shaped portion of the dome portion in an embodiment of the present invention is changed. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of a method for manufacturing a can according to the present invention will be described with reference to the drawings.

[0025] 1, the can body 100 of this embodiment is a so-called two-piece can, and at its upper mouth, a neck portion and a flange located outside the can along the can axis direction beyond the neck portion are formed. After the can body 100 is filled with contents such as a beverage through the opening on the flange side, the opening is sealed by wrapping a lid member around it to complete the can.

[0026] 1 shows an enlarged view of the can bottom 11 of the can body 100, with a cross section passing through the can axis C shown in the right half of the can body 100. The can body 100 is made of a thin metal sheet such as aluminum or an aluminum alloy, and as shown in FIG. 1, is provided with a cylindrical body portion 12 formed in a straight shape and having a cylindrical opening (not shown) with a flange formed in the upper portion thereof, and a can bottom portion 11 integrally connected to one end of the cylindrical body portion 12.

[0027] As shown in FIG. 1 , the cylindrical body 12 and the can bottom 11 are arranged coaxially, and in this embodiment, this common axis will be referred to as the can axis C in the description. Within the direction along the can axis C (can axis direction), the direction from the opening toward the can bottom 11 is referred to as the outward can axis direction (downward), and the direction from the can bottom 11 toward the opening is referred to as the inward can axis direction (upward). In the following description, the up-down direction will be defined as the same as the direction shown in FIG. 1 . The direction perpendicular to the can axis C is referred to as the radial direction, and within the radial direction, the direction approaching the can axis C is referred to as the radially inward direction (radially inward), and the direction moving away from the can axis C is referred to as the radially outward direction (radially outward). The direction going around the can axis C is referred to as the circumferential direction.

[0028] In this embodiment, the can bottom 11 of the can body 100 includes a circumferential grounding portion 114 that protrudes annularly outward (downward) in the can axial direction, an outer circumferential bottom portion 117 that connects the cylindrical body portion 11 and the circumferential grounding portion 114, an inclined wall portion 113 that is connected to the circumferential grounding portion 114 and extends upward from the end of the circumferential grounding portion 114, and slopes away from the can axis C as it extends upward, and a dome portion 111 that is connected to the inclined wall portion 113 via an upper bent portion 112. The circumferential grounding portion 114 is located radially inward from a vertex 114A of the circumferential grounding portion 114 and includes a lower bent portion 115 that is continuous with the lower end of the inclined wall portion 113, and an outer curved portion 116 that is continuous with the lower bent portion 115 and with the outer circumferential bottom portion 117.

[0029] The dome portion 111 is located on the can axis C and has a shape that is concave upward (into the interior of the cylindrical body portion 12). The upper bent portion 112 is an arc-shaped portion that is concave radially outward of the can body 100, and its lower end is connected to the inclined wall portion 113. The inclined wall portion 113 is a portion that extends at an angle from the lower end of the upper bent portion 112 downward toward the can axis C, and its lower end is connected to the lower bent portion 115. The lower bent portion 115 has an arc-shaped portion that protrudes radially inward of the can body 100, and its lower end is connected to the outer curved portion 116. The outer curved portion 116 has an arc-shaped portion that extends convexly radially outward and downward of the can body 100 (in the example shown in FIG. 2 , downward and rightward relative to the plane of the drawing), and its radially outer end is connected to the outer circumferential bottom portion 117. The circumferential ground contact portion 114, consisting of the lower bent portion 115 and the outer curved portion 116, protrudes furthest downward in the axial direction of the can and forms a ring shape extending circumferentially, so that when the can bottom 11 is placed on a placing surface with its bottom side facing downward, the connecting portion of the lower bent portion 115 and the outer curved portion 116 comes into contact with the placing surface. In addition, the outer peripheral bottom portion 117 has an arc shape that extends from the radially outer end of the outer curved portion 116 toward the lower end of the cylindrical body portion 12 and radially inward in a concave shape. Incidentally, on the periphery of the dome portion 111, there is formed a press mark 118 that is slightly bent in the opposite direction (downward) to the direction in which the dome portion 111 is recessed.

[0030] The dimensions of the above-mentioned portions of the can bottom 11 are, for example, as follows: on the outer surface of the can body 100, the radius of curvature R1 of the dome portion 111 is 30 mm or more and 37 mm or less; the radius of curvature R2 of the upper curved portion 112 is 1.3 mm or more and 2.0 mm or less; the angle of inclination (θ2 in FIG. 2) of the inclined wall portion 113 with respect to the can axis C is 6.0° or more and 21.0° or less; the inner diameter W1 between the vertices 114A of the circumferential contact portion 114 (the distance of a straight line passing through the can axis C connecting the vertices 114A) is 46.8 mm or more and 47.2 mm or less; the radius of curvature R3 of the lower curved portion 115 is 0.7 mm or more and 1.0 mm or less; the radius of curvature R4 of the outer circumferential bottom portion 116 is 1.4 mm or more and 1.8 mm or less; the radius of curvature R5 of the outer circumferential bottom portion 116 is 8.0 mm or more and 12.0 mm or less; the inner diameter W2 between the radially innermost portions of the lower bent portion 115 (the distance in a straight line passing through the can axis C connecting these portions) is 44.4 mm or more and 44.6 mm or less; the inner diameter W3 between the radially outermost portions of the upper bent portion 112 (the distance in a straight line passing through the can axis C connecting these portions) is 44.8 mm or more and 45.6 mm or less; and the outer diameter W4 of the cylindrical body portion 12 is 66.1 mm or more and 66.3 mm or less.

[0031] [Can manufacturing method] The can manufacturing method of this embodiment includes a drawing and ironing process (primary can body forming process) in which an aluminum sheet is punched and drawn to form a shallow cup with a relatively large diameter, and this cup is then subjected to a second drawing and ironing process (DI process) to form a bottomed, cylindrical primary can body 200 as shown in FIG. 3 , which has a cylindrical tubular body 22 and a can bottom 21 integrally connected to one end of the tubular body 22; a reshaping process in which the can bottom 21 of the primary can body 200 is reshaped; and an opening processing process in which an opening is processed at the other end of the tubular body 22 (a necking process in which the opening is reduced in diameter and a flange is formed).

[0032] [Squeezing and ironing process] In the drawing and ironing process, which corresponds to the primary can body forming process of the present invention, after the cup is formed, another drawing and ironing process is performed to form the following in the can bottom 21 of the primary can body 200, as shown in Fig. 3 : a dome portion 211 formed on the can axis C of the can bottom 21 and recessed inward (upward) in the can axial direction, a protruding portion 214 protruding annularly outward (downward) in the can axial direction, an inner wall portion 213 extending upward from the radially inner edge of the protruding portion 213, an arc-shaped portion 212 connecting the upper end of the inner wall portion 213 to the outer peripheral edge of the dome portion 211, and an outer peripheral bottom portion 215 connecting the radially outer edge of the protruding portion 214 to one end of the cylindrical body portion 22. As shown in Fig. 3 , the protruding portion 214 consists of an inner arc-shaped portion 215 located radially inward from its apex 214A of the primary can body 200, and an outer arc-shaped portion 216 located radially outward. The angle of a tangent line S1 on the inner surface of the outer periphery of this dome section 211 with respect to a plane perpendicular to the can axis C is set to be 27° or more and 29° or less.

[0033] As shown in Figures 5 and 6, the dome portion 211 of the primary can body 200 is located on the can axis C and has a shape that is concave upward (inside the cylindrical body portion 22). The arc-shaped portion 212 is an arc-shaped part that extends concavely radially inward and downward of the primary can body 200 (to the lower left on the paper in the example shown in Figure 3), and its lower end is connected to the inner wall portion 213. The inner wall portion 213 slopes toward the can axis C from the lower end to the upper end, and its upper end is connected to the lower end of the arc-shaped portion 212 and its lower end is connected to the radially inner edge of the inner arc-shaped portion 215. The inner arc-shaped portion 215 has an arc shape that extends convexly radially inward and downward of the primary can body 200 (to the lower left on the paper in the example shown in Figure 3), and its lower end is connected to the outer arc-shaped portion 216. The outer arc-shaped portion 216 is arc-shaped and extends convexly radially outward and downward from the primary can body 200 (in the example shown in FIG. 2 , downward and rightward relative to the plane of the drawing), with its radially outer edge connected to the outer peripheral bottom portion 217. The protruding portion 214 consisting of the inner arc-shaped portion 215 and the outer arc-shaped portion 216 protrudes furthest downward in the can axial direction and forms an annular shape extending along the circumferential direction, with their connecting portion contacting the support plane 41. The outer peripheral bottom portion 217 is arc-shaped and extends concavely radially inward from the radially outer edge of the outer arc-shaped portion 216 toward the lower end of the cylindrical body portion 22.

[0034] The dimensions of each part of the can bottom 21 of the primary can body 200 described above are, for example, on the outer surface of the primary can body 200, a radius of curvature R11 of the dome portion 211 of 28 mm or more and 37 mm or less, a radius of curvature R12 of the arc-shaped portion 212 of 2.1 mm or more and 2.2 mm or less, a diameter W11 between the apexes 214A of the protrusions 214 (the distance of a straight line passing through the can axis C connecting the apexes 214A) of 47.8 mm or more and 48.1 mm or less, a radius of curvature R13 of the inner arc-shaped portion 215 of 1.2 mm or more and 1.5 mm or less, and a radius of curvature R14 of the outer arc-shaped portion 216 of 2.2 mm or less. the radius of curvature R15 of the outer peripheral bottom 217 is 1.5 mm or more and 1.9 mm or less; the inner diameter W12 between the radially innermost portions of the inner arc-shaped portion 215 (the distance in a straight line passing through the can axis C connecting these portions) is 43.4 mm or more and 45.6 mm or less; the inner diameter W13 between the radially outermost portions of the arc-shaped portion 212 (the distance in a straight line passing through the can axis C connecting these portions) is 43.4 mm or more and 45.6 mm or less; and the outer diameter W14 of the cylindrical body 22 is 66.1 mm or more and 66.3 mm or less.

[0035] The radius of curvature R12 of the arc-shaped portion 212 is larger than the radius of curvature R2 of the upper bent portion 112, the radius of curvature R13 of the inner arc-shaped portion 215 is larger than the radius of curvature R3 of the lower bent portion 114, and the radius of curvature R14 of the outer arc-shaped portion 216 is smaller than the radius of curvature R4 of the outer curved portion 116. The diameter W11 between the vertices 214A of the protrusions 214 is larger than the distance W1 from the vertex 114A of the circumferential ground contact portion 114 to the can axis C, and the inner diameter W13 between the radially outermost portions of the arc-shaped portion 212 is smaller than the inner diameter W3 between the radially outermost portions of the upper bent portion 112.

[0036] [Remolding process] In the reforming process, with the tip of the protruding portion 214 supported on a support plane 41 perpendicular to the can axis C, the radially inner end of the pressing surface 331 is brought into contact with the peripheral edge 211A of the dome portion 211 (in the example shown in FIG. 8 , an area within a certain range from the joint of the dome portion 211 with the arc-shaped portion 212), and the peripheral edge 211A of the dome portion 211 is pressed outward (downward) in the can axial direction from inside the cylindrical body portion 22. This reforming process is performed using a punch 30 that is placed inside the cylindrical body portion 22 of the primary can body 200 and presses the peripheral edge 211A of the dome portion 211, and a receiving stand 40 that has a support plane 41, as shown in FIGS.

[0037] 4, the punch 30 has a substantially cylindrical main body 31, and a recess 32 is formed on the lower side of the main body 31 (the side that abuts against the peripheral edge 211A of the dome portion 211) so that the central portion of the dome portion 211 does not come into contact with the recess 32 when pressing the can bottom 21. In addition, an annular protrusion 33 that protrudes cylindrically downward is formed on the outer periphery of the recess 32. In addition, a pressing surface 331 is formed at the tip of the annular protrusion 33, the width of which extends from the peripheral edge 211A of the dome portion 211 to above the arc-shaped portion 212.

[0038] The dimensions of each part of this punch 30 are, for example, a diameter L1 of 44 mm to 50 mm, an inner diameter L2 of the recess 32 of 19.5 mm to 20.75 mm, and a width L3 of the pressing surface 331 of 4.25 mm to 5.5 mm.

[0039] The pressing surface 331 is an inclined surface that protrudes downward as it extends radially outward of the primary can body 200. The inclination angle θ12 of this pressing surface 331 with respect to a plane perpendicular to the can axis C is set to be less than 20° or the angle of the tangent line S1 with respect to the plane perpendicular to the can axis C. Furthermore, the pressing surface 331 is designed so that the inner wall portion 213 is located near the center in the width direction when it abuts against the peripheral edge portion 211A of the dome portion 211. In other words, the pressing surface 331 protrudes radially outward from the inner wall portion 213 of the primary can body 200. The radial width L4 (see FIG. 7) of the portion located radially inward from the inner wall portion 213 of the primary can body 200 is set to be 2.25 mm or more and 2.5 mm or less.

[0040] If the radial width L4 of the portion of the pressing surface 331 located radially inward of the inner wall portion 213 of the primary can body 200 is less than 2.25 mm, when the peripheral portion 211A of the dome portion 211 is pressed, the arc-shaped portion 212 and the inner wall portion 213 cannot be properly deformed, and large pressing marks may be formed. If the radial width L4 exceeds 2.5 mm, the area pressing the dome portion 211 increases, and excessive pressing force is required. Furthermore, when the angle θ11 of the tangent line S1 at the inner surface of the outer periphery of the dome portion 211 relative to a plane perpendicular to the can axis C is 27° or more and 29° or less, if the inclination angle θ12 of the pressing surface 331 relative to a plane perpendicular to the can axis C is less than 20° or exceeds the angle of the tangent line S1 relative to the plane, the difference between the inclination angle θ12 of the pressing surface 331 relative to the plane perpendicular to the can axis C and the inclination angle θ11 of the tangent line S1 at the inner surface of the outer periphery of the dome portion 211 (connection point with the arc-shaped portion 212) relative to the plane perpendicular to the can axis C becomes large, making it difficult to appropriately deform the arc-shaped portion 212 and the inner wall portion 213. In particular, if the inclination angle θ12 is greater than the angle θ11, the pressing surface 331 will press the arc-shaped portion 212 before pressing against the peripheral edge portion 211A of the dome portion 211, and it may not be possible to appropriately incline the inner wall portion 213.

[0041] Then, with the primary can body 200 placed on the support surface 41 of the receiving table 40, the punch 30 is placed inside the cylindrical body 22 as shown in Figure 5, and as shown in Figure 6, the radially inner end of the pressing surface 331 is brought into contact with the portion P of the peripheral edge 211A and pressed downward by 1.0 mm to 3.0 mm (2.0 mm in this embodiment), thereby reshaping the can bottom 21 into the can bottom 11.

[0042] Specifically, as shown in Figures 7 and 8, the tip of the protrusion 214 is supported by a support plane 41 perpendicular to the can axis C, and the radially inner end of the circumferential pressing surface 331 is brought into contact with the peripheral edge portion 211A. With this in mind, the peripheral edge portion 211A of the dome portion 211 is pressed from inside the cylindrical body portion 22 in the can axis direction by the pressing surface 331 of the punch 30, thereby bending the arc-shaped portion 212 and spreading the upper part of the inner wall portion 213 radially outward, thereby inclining the inner wall portion 212 to form the inclined wall portion 113. In this case, the pressing surface 331 of the punch 31 has a width extending from the peripheral edge 211A of the dome portion 211 to above the arc-shaped portion 212, and therefore, by pressing the arc-shaped portion 212 so that the pressing position gradually shifts radially outward from the connection end (outer peripheral edge) with the dome portion 211, the arc-shaped portion 212 is further bent to form an upper bent portion 112 with a small radius of curvature, while the upper portion of the inner wall portion 213 is expanded radially outward to form the inclined wall portion 113. At this time, near the tip of the protruding portion 214, the apex of the inner arc-shaped portion 215 is pressed against the support plane 41, further bending the inner arc-shaped portion 215 to form a lower bent portion 115 with a small radius of curvature that is continuous with the lower end of the inclined wall portion 113, and the outer arc-shaped portion 216 is deformed to have a larger radius of curvature, forming an outer curved portion 116 with a large radius of curvature that is continuous with the lower bent portion 115. When this lower bent portion 115 is formed, outer arcuate portion 216 is deformed to increase the radius of curvature, and together with the reaction force caused when inner arcuate portion 215 is pressed against support plane 41, the portion from outer curved portion 116 to outer peripheral bottom portion 117 is pushed up in the can axial direction, which may result in an increase in the height of the can. Furthermore, because peripheral portion 211A of dome portion 211 is pressed, the depth (bottom depth) of dome portion 111 becomes smaller than the depth of dome portion 211 of primary can body 200, and pressing against pressing surface 331 forms pressing mark 118 (see FIG. 2 ) on the inner surface of dome portion 111 (region P where the radially inner end of pressing surface 331 on peripheral portion 211A of dome portion 211 comes into contact).

[0043] Here, the downward pressing amount of the pressing surface 331 (punch 30) was set to 1.0 mm or more and 2.0 mm or less. As an example, the shape of the can bottom and the tilt angle of the inclined wall portion 113 relative to the can axis C when pressed with respective pressing amounts of 1.0 mm, 2.0 mm, and 3.0 mm will be described. Fig. 9 is a diagram showing the angles of the inclined walls 113, 113A, and 113B relative to the can axis C when pressed with varying pressing amounts by the punch 30 shown in Fig. 4. Note that the tilt angle θ0 relative to the can axis C, which passes through the lower end of the inner wall portion 213 of the primary can body 200, is approximately 0°.

[0044] 9, it can be seen that the greater the pressing amount of the pressing surface 331, the greater the inclination angle of the inclined wall portion relative to the can axis C. Specifically, as an example, when the pressing amount is 1.0 mm, the inclination angle θ1 of the inclined wall portion 113A relative to the can axis C is 3.79°, when the pressing amount is 2.0 mm, the inclination angle θ2 of the inclined wall portion 113B relative to the can axis C is 19.13°, and when the pressing amount is 3.0 mm, the inclination angle θ3 of the inclined wall portion 113B relative to the can axis C is 50.76°. If the pressing amount of the pressing surface 331 is less than 1.0 mm, the pressing amount is too small to properly reshape the can bottom 21, which may result in an inability to increase the strength of the can bottom of the can body, whereas if the pressing amount exceeds 3.0 mm, the can bottom 21 may be deformed too much, which may actually reduce the strength of the can bottom of the can body. Furthermore, taking into consideration the impact on other processes during actual production (transportability, can holding and inspection by an inspection machine), it is more preferable that the pressing amount be 1.0 mm or more and 2.0 mm or less.

[0045] By carrying out this reshaping process, the can bottom 21 of the primary can body 200 is reshaped into the shape of the can bottom 11 shown in FIG. Then, by carrying out the necking process after this reshaping process, a neck portion and a flange located outside the neck portion along the can axis direction of the can are formed at the mouth portion of the upper end portion, resulting in the can body 100. In this embodiment, the reshaping process can be carried out simply by pressing the peripheral edge portion 211A of the dome portion 211 in one direction along the can axis direction from inside the cylindrical body portion 22, and therefore the reshaping process is carried out using the same mechanism as the necking process, which processes the opening of the can to reduce its diameter and form a flange. Then, after filling the can body 100 with contents such as a beverage through the opening on the flange side, the opening is sealed by tightening the lid member to complete the can.

[0046] [Comparison with Patent Document 3] Here, we compare the can manufacturing method using the apparatus described in Patent Document 3 with the can manufacturing method of this embodiment. First, in the can manufacturing method using the apparatus described in Patent Document 3, a forming die is positioned facing the can bottom, and the die has a tapered portion on the outer surface of the can bottom that slopes radially inward, a step portion connected to the tapered portion, and a flat portion that continues below the step. Then, the inner surface of the dome portion is pressed with a pressing body, resulting in a complex structure for supporting the can bottom. Furthermore, since the pressing body contacts not the dome portion but the arc-shaped portion connecting the dome portion and the leg portion, pressing the arc-shaped portion with the pressing body causes the radially inner portion of the leg portion, which corresponds to the inner wall portion of this embodiment that slopes toward the can axis from the bottom end to the top end, to tilt further radially inward. For this reason, Patent Document 3 uses a forming die with the above-mentioned complex shape, and when pressing with a pressing body, it is assumed that a portion of the annular leg is deformed so as to protrude downward along the step, thereby first tilting the lower end of the inner portion of the leg radially inward. However, because the pressing body presses the upper end of the inner portion of the leg radially inward, if the timing is off, it is difficult to form an accurate shape. Also, while air jets from below the dome portion may assist in forming, there are limits to how much air can assist in forming metal materials. In any case, it is considered difficult to form a can bottom with a stable shape using the method of Patent Document 3.

[0047] In contrast, in the can manufacturing method of this embodiment, the peripheral edge 211A of the dome portion 211 is pressed to bend the arc-shaped portion 212, and the upper portion of the inner wall portion 213 is pushed outward in the radial direction, thereby inclining the inner wall portion 212 to form the inclined wall portion 113. In other words, the inner wall portion 213, which slopes toward the can axis C from the bottom end to the top end, is prevented from further inclining in the same direction, and is instead inclined in the opposite direction (the opposite side to the can axis) to form the inclined wall portion 113, thereby improving the strength of the can bottom 11.

[0048] In this embodiment, the reshaping process can be performed simply by pressing the peripheral edge 211A of the dome portion 211 in one direction in the can axial direction from inside the cylindrical body 22. Therefore, the reshaping process can be performed using the same mechanism as the necking process, which processes the can opening to reduce the diameter and form a flange. This eliminates the need for a special press, as in Patent Document 2, and reduces the size of the can manufacturing equipment while reducing can manufacturing costs. Furthermore, during the reshaping process, the peripheral edge 211A of the dome portion 211 is pressed to bend the arc-shaped portion 212 and tilt the inner wall portion 213. Therefore, the reshaping process requires only a support plane 41 to support the tip of the protrusion 214. This eliminates the need for a mold or other device to support the radially outer surface of the protrusion 214, as in Patent Document 3, thereby simplifying the equipment used in the reshaping process. Furthermore, because the tip of the protrusion 214 is supported by the support plane 41, the shape after reshaping is stable.

[0049] Furthermore, when pressing peripheral edge 211A of dome portion 211, the pressing position on arc-shaped portion 212 is pressed and bent so as to gradually transition from the radially inner side toward the radially outer side, thereby spreading the upper end of inner wall portion 213 connected to arc-shaped portion 212 radially outward, reliably forming stable inclined wall portion 113. Note that arc-shaped portion 212 becomes upper bent portion 112 with a small radius of curvature, and this upper bent portion 112 and inclined wall portion 113 increase the rigidity of that portion, thereby enabling the strength of can bottom 11 to be increased even when the can is manufactured using a thin-walled material.

[0050] Furthermore, lower bent portion 115, which has a small radius of curvature, and inclined wall portion 113 increase the rigidity of that portion, further increasing the strength of can bottom 11. When lower bent portion 115 is formed, outer arc portion 216 is deformed to increase its radius of curvature, and this, combined with the reaction force generated when inner arc portion 215 is pressed against support plane 41, pushes the area from outer curved portion 116 to outer peripheral bottom portion 117 up in the can axial direction, thereby increasing the height of the can.

[0051] Furthermore, the reshaping process can be carried out with the primary can body 200 held between the punch 30 and the receiving base 40. Therefore, for example, the reshaping of the can bottom 21 can be carried out even if the primary can body 200 is not placed on a horizontal surface. Furthermore, the pressing surface 331 of the punch 30 has a width that extends radially outward from the inner wall portion 213 of the primary can body 200, and the radial width L6 of the portion located radially inward from the inner wall portion 213 of the primary can body 200 is 2.0 mm or more and 3.0 mm or less, and the inclination angle of the pressing surface 331 relative to the plane is 20° or more and less than the angle relative to the plane of the tangent line S1.Therefore, the arc-shaped portion 212 and the inner wall portion 213 can be appropriately deformed while preventing large pressing marks from being formed on the peripheral edge of the dome portion 111.

[0052] Furthermore, by setting the pushing amount of punch 30 to 1.0 mm or more and 3.0 mm or less, it is possible to appropriately reshape can bottom 21. In this case, the radius of curvature R2 of upper bent portion 112 can be set to 1.3 mm or more and 2.0 mm, the radius of curvature R3 of lower bent portion 115 can be set to 0.7 mm or more and 1.0 mm or less, and the inclination angle of inclined wall portion 113 with respect to can axis C can be set to 6.0° or more and 21.0° or less, thereby increasing the strength of can bottom 11.

[0053] The present invention is not limited to the configurations of the above-described embodiments, and various modifications can be made to the detailed configurations without departing from the spirit of the present invention. For example, in the above embodiment, the necking process is performed after the re-forming process, but this is not limiting, and the necking process may be performed simultaneously with the re-forming process. Since the re-forming process in the above embodiment can be performed using only the punch 30 and the cradle 40, the necking process and the re-forming process can be performed simultaneously by using a mold that sandwiches the cylindrical body portion 22 from the outside of the punch 30.

[0054] In the above embodiment, the can manufacturing method is performed by the drawing and ironing process, the reshaping process, and the necking process, but is not limited to this. For example, instead of the necking process, a mouth forming process may be performed in which a threaded portion and a curled portion are formed on the opening of the can. In other words, the can manufacturing method of the present invention is not limited to two-piece cans, but can also be applied to bottle-shaped cans.

[0055] In the above embodiment, the drawing and ironing step is to form a bottomed, cylindrical primary can body 200 having a can bottom 21 integrally connected to one end of the cylindrical body 22. However, the present invention is not limited to this. The can bottom may not be formed in the drawing and ironing step, and the can bottom may be formed after the drawing and ironing step to form a primary can body. In other words, the primary can body forming step may consist of two steps: a drawing and ironing step and a can bottom forming step.

[0056] Furthermore, while various dimensions and the like of the can in the above embodiment have been exemplified, these are merely examples, and the present invention can be applied to any can in which the tip of the protrusion is supported on a support plane perpendicular to the can axis, the peripheral edge of the dome portion is pressed from inside the cylindrical body portion to bend the arc-shaped portion, and the upper part of the inner wall portion is pushed outward in the radial direction, thereby tilting the inner wall portion toward the opposite side of the can axis to form an inclined wall portion.

[0057] In the above embodiment, the inner wall portion is formed in the primary can body forming step, but this is not limiting. For example, the radially inner edge of the protrusion and the arc-shaped portion may be formed of a larger arc than in this embodiment, and the radially outer edge of this arc may be connected. In other words, a can that does not have an inner wall portion and an inclined wall portion is also within the scope of the present invention. [Example]

[0058] An aluminum alloy plate was punched and drawn to form a shallow cup with a relatively large diameter, and this cup was then subjected to a second drawing and ironing process (DI process) to produce 38 primary can bodies made of the above-mentioned aluminum alloy. The average dimensions of the can bottom of these 38 primary can bodies were as follows: the radius of curvature R11 of the dome portion was 29.0 mm, the radius of curvature R12 of the arc-shaped portion was 2.15 mm, the distance W11 from the apex of the protrusion to the can axis C was 23.97 mm, the radius of curvature R13 of the inner arc-shaped portion was 1.35 mm, the radius of curvature R14 of the outer arc-shaped portion was 2.35 mm, the radius of curvature R15 of the outer bottom peripheral portion was 1.7 mm, the inner diameter W12 between the radially innermost portions of the inner arc-shaped portion was 22.25 mm, the inner diameter W13 between the radially outermost portions of the arc-shaped portion was 22.25 mm, and the outer diameter W14 of the cylindrical body portion was 32.9 mm. This primary can body was subjected to a reforming process using the method described in the above embodiment. The downward thrust of the punch was varied between 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, and 3.0 mm, and the can height, bottom depth, maximum pressure resistance (pressure strength), and growth rate were measured for each thrust. The resin punch used had a diameter L1 of 50 mm, an inner diameter L2 of the recess of 41 mm, a width L3 of the pressing surface of 4.5 mm, and a radial width L4 of 2.25 mm at a portion located radially inward of the inner wall of the pressing surface.

[0059] (Method for measuring maximum pressure resistance) The maximum pressure resistance (compression strength) was measured for two samples of each type. Specifically, each sample was attached to an air-pressure buckling tester (manufactured by Universal Can Manufacturing Co., Ltd.) at a position 100 mm from the bottom of the can, and the internal pressure of the can was increased by air pressure at a rate of 98 kPa / s. The maximum pressure reached until the dome part inverted (buckled) was measured, and the average (ave), maximum (max), and minimum (min) values ​​were calculated. The results are shown in Table 1 and Figure 10. In Figure 10, the horizontal axis represents the amount of compression (mm) and the vertical axis represents the average maximum pressure resistance (kPa).

[0060] (Method for measuring growth rate at 686KPa) The growth amount was measured for two samples of each type. Specifically, for each sample, the can bottom was placed facing upward, the top opening of the can body was airtightly sealed, and compressed air or the like was supplied to the inside to increase the internal pressure to 686 kPa. The bottom growth amount (amount of protruding deformation) of the tip of the peripheral contact portion of the can bottom was measured for two samples using a displacement meter (manufactured by Universal Can Manufacturing Co., Ltd.), and the average (ave), maximum (max), and minimum (min) values ​​were calculated. The results are shown in Table 2 and Fig. 11. In Fig. 11, the horizontal axis represents the amount of compression (mm), and the vertical axis represents the average growth amount (mm) at 686 KPa.

[0061] [Table 1]

[0062] [Table 2]

[0063] As shown in Table 1 and Figure 10, the average pressure resistance (maximum pressure resistance) was highest at 917.47 kPa when the indentation was set to 2.0 mm. Also, while the average maximum pressure resistance of the primary can body was 790.80 kPa, all of the cans reshaped with indentations between 1.0 mm and 3.0 mm had a higher maximum pressure resistance than the primary can body. This shows that the reshaping process can increase pressure resistance. Furthermore, it was found that the growth amount at 686 KPa decreased as the indentation amount increased, as shown in Table 2 and Figure 11. Furthermore, while the average growth amount at 686 KPa for the primary can body was 1.575 mm, all of the remolded cans with indentation amounts of 1.0 mm to 3.0 mm showed smaller growth amounts than the primary can body at 686 KPa. From the above, it was considered that the preferable punch depth was 1.0 mm or more and 3.0 mm or less. Furthermore, based on the experimental results, it was considered that a preferable punch depth was 2.0 mm ± 0.5 mm, but considering the impact on other processes during actual production (transportability, can holding and inspection by inspection machines), a depth of 1.0 mm or more and 2.0 mm or less was more preferable. [Explanation of symbols]

[0064] 100…Can body 11...Bottom of can 111...Dome section 112...Upper bend 113,113A,113B...Slanted wall part 114...Circumferential grounding part 114A...vertex 115…Lower bending part 116...Outer curved part 117...Outer bottom 118...Indentation 12...Cylindrical body 200...Primary boiler body 21...Bottom of can 211...Dome section 211A...periphery 212...Arc-shaped part 213...Inner wall 214...Protrusion 214A...vertex 215...Inner arc-shaped part 216...Outer arc-shaped portion 217...Outer bottom 22...Cylindrical body 30...Punch 31 Main body 32...recess 33...Annular protrusion 331...Pressure surface 40…Cradle 41…Support plane

Claims

1. a primary can body forming step of forming a primary can body including a cylindrical tubular body and a can bottom integrally connected to one end of the cylindrical body, the primary can body having a protruding portion that protrudes annularly outward in the can axial direction from the can bottom, a dome portion that is formed on the can axis of the can bottom and is recessed inward in the can axial direction, and a recessed arc-shaped portion that is continuous with the outer periphery of the dome portion; a re-forming step of re-forming the can bottom of the primary can body, In the re-molding step, a peripheral edge of the dome portion is pressed with a punch from inside the cylindrical body portion while a tip of the protruding portion is supported by a pedestal, thereby bending the arc-shaped portion and forming an upper bent portion having a small radius of curvature, The method for manufacturing a can, wherein the punch has a cylindrical annular protrusion, the tip of which is formed with a pressing surface for pressing against the peripheral edge of the dome portion.

2. In the primary can body forming step, an inner wall portion is formed extending upward from a radially inner edge of the protrusion, and the arc-shaped portion is shaped to connect an outer peripheral edge of the dome portion and an upper end of the inner wall portion, 2. The method for manufacturing a can according to claim 1, wherein in the re-forming step, the peripheral edge of the dome portion is pressed from inside the cylindrical body portion, bending the arc-shaped portion while pushing an upper portion of the inner wall portion radially outward, thereby inclining the inner wall portion to form an inclined wall portion.

3. 3. The method for manufacturing a can according to claim 2, wherein in the re-forming step, a punch that presses against the peripheral edge of the dome portion is formed with a pressing surface having a width that extends from the peripheral edge of the dome portion to above the arc-shaped portion, and when the peripheral edge of the dome portion is pressed with the pressing surface, the pressing position on the arc-shaped portion is gradually shifted radially outward from the connection end with the dome portion, thereby bending the arc-shaped portion.

4. In the primary can body forming step, an outer peripheral bottom portion is formed on the can bottom portion, the outer peripheral bottom portion connecting a radially outer edge of the protrusion and a lower end of the cylindrical body portion, the protrusion comprises an inner arc-shaped portion located radially inward from the apex of the protrusion with respect to the primary can body, and an outer arc-shaped portion located radially outward from the apex of the protrusion; 4. The can manufacturing method according to claim 3, wherein in the reshaping step, the inner arc-shaped portion is bent while pressing the vicinity of the apex of the inner arc-shaped portion against the receiving base to form a lower bent portion having a small radius of curvature that is continuous with the lower end of the inclined wall portion, and the outer arc-shaped portion is deformed to have a larger radius of curvature to form an outer curved portion that is continuous with the lower bent portion.

5. 5. The method for manufacturing a can according to claim 3, wherein the re-forming step is performed using the punch and the cradle disposed within the cylindrical body portion.

6. 6. A method for manufacturing a can according to claim 5, wherein the outer diameter of the cylindrical body of the primary can body is 66.1 mm or more and 66.3 mm or less, the angle of a tangent to the inner surface of the outer edge of the dome portion with respect to a plane perpendicular to the can axis is 27° or more and 29° or less, the radial width of a portion of the pressing surface that is located radially inward of the inner wall portion of the primary can body in the radial direction of the primary can body is 2.0 mm or more and 3.0 mm or less, and the inclination angle of the pressing surface with respect to the plane is 20° or more and the angle of the tangent with respect to the plane is 20° or more.

7. 7. The method for manufacturing a can according to claim 6, wherein in the re-forming step, the pressing surface is pressed against the peripheral edge of the dome portion by 1.0 mm to 3.0 mm.

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