Preform can and method of manufacturing the same

Abstract

The present invention aims to further improve the compressive strength of the can body. The preform is formed by forming an arch bottom portion recessed toward the inside of the bottomed cylinder and an annular footing portion protruding in the opposite direction to the arch bottom portion from the bottom of the bottomed cylinder. The preform is formed into a can by pressing the inner surface of the arch bottom portion. The maximum height from the ground contact surface to the arch bottom portion of the preform is higher than the maximum height from the ground contact surface to the arch bottom portion of the can after forming. The length of the inner side periphery of the footing portion for connecting the ground contact point on the footing portion to the arch bottom portion of the preform is longer than the length of the curved edge portion formed around the arch bottom portion of the can after forming in the cross-sectional line in the longitudinal direction along the can axis.

Description

TECHNICAL FIELD

[0001] The present application relates to a preform can and a method for manufacturing the same. BACKGROUND

[0002] As a can body capable of containing contents such as beverages and foods, a two-piece can and a bottle-shaped can are known. Such a can body is made thinner to reduce the weight of the container in order to reduce the amount of raw materials used. Also, in order to make such a can body have sufficient compressive strength even when it is made thin, various improvements are made to the bottom shape thereof.

[0003] Generally, the bottom shape of a can body formed in order to improve the compressive strength is known to have an arch bottom portion recessed toward the inside of the can body, and an annular footing portion provided around the arch bottom portion.

[0004] In order to further improve the compressive strength of such a can body, the shapes of the arch bottom portion and the annular footing portion are designed accordingly. For example, Patent Document 1 discloses a can body in which a first concave curved surface portion is formed on the inner peripheral wall (inner side periphery) of the annular protruding portion (footing portion) connecting with the arch bottom portion, wherein the first concave curved surface portion is curved in a curve shape, which is recessed outward in a radial direction orthogonal to the can axis in a longitudinal cross-sectional view in the can axis direction; a second concave curved surface portion is formed on the arch bottom portion, which is located on the can axis, and is connected to the radially outer side of the arch bottom top portion, wherein the second concave curved surface portion is curved in a concave curve shape, which has a smaller radius of curvature than that of the arch bottom top portion; a tapered portion is formed at the outer peripheral edge of the arch bottom portion, wherein the tapered portion is linear, which connects the first concave curved surface portion and the second concave curved surface portion and is continuous with the first curved surface portion and the second curved surface portion.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-43991 SUMMARY OF THE INVENTION

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] In the technology described in Patent Document 1, the first concave curved surface portion, which is curved by drum forming, and the tapered portion are formed by performing bottom re-forming processing at the inner peripheral wall (inner side periphery) of the annular raised portion (foot portion). In this bottom re-forming processing using a drum, since the curved surface of the first concave curved surface portion has a large radius of curvature required for drum processing, there is a limit to the extent to which the inner peripheral surface of the foot portion can be further recessed outward in the radial direction orthogonal to the can axis.

[0010] As described above, with the conventional technology of performing bottom re-forming processing using a drum, there is a problem that it is difficult to improve the bottom shape to the desired shape, and as a result, the can body strength cannot be sufficiently improved.

[0011] The present application was made in view of the above circumstances, and the above problem is one of the problems to be solved by the present application. That is, one of the problems to be solved by the present application is how to further improve the can body strength.

[0012] Technical Solution to Solve the Technical Problem

[0013] The pre-form can of the present application is formed by forming an arch bottom portion recessed toward the inside of a bottomed cylinder and an annular foot portion protruding in the opposite direction to the recessed direction of the arch bottom portion at the bottom of the bottomed cylinder, and the pre-form can is formed into a formed can by pressing the inner surface of the arch bottom portion. The pre-form can of the present application is characterized in that the maximum height from the ground contact surface of the pre-form can to the arch bottom portion is higher than the maximum height from the ground contact surface of the formed can to the arch bottom portion after forming, and the length of the inner side periphery of the foot portion for connecting the ground contact point on the foot portion and the arch bottom portion in the pre-form can is longer than the length of the curved edge portion formed around the arch bottom portion in the formed can in the cross-sectional line taken in the longitudinal direction of the can axis.

[0014] Preferably, the inner side periphery of the foot portion is inclined toward the direction of the can axis with the ground contact point of the foot portion as a base point in the cross-sectional line taken in the longitudinal direction of the can axis, and the inner side periphery of the curved edge portion for connecting the ground contact point on the curved edge portion and the arch bottom portion in the formed can is inclined toward the opposite direction to the direction of the can axis with the ground contact point on the curved edge portion as a base point.

[0015] Preferably, the length of the substantially circular arc having a radius of curvature R1 of the lower end portion constituting the foot portion is set as M R1The length of the substantially linear reduced diameter portion on the inner periphery of the foot portion is L, and the length of the curved edge portion of the formed can is X, and X < M R1 + L.

[0016] Preferably, in a cross-sectional line taken in the longitudinal direction of the can axis, if the angle of inclination toward the direction of the can axis between the ground contact surface of the pre-formed can and the reduced diameter portion on the inner periphery of the foot portion is θ, then R1 is 0.8 mm to 2.2 mm, L is 4.0 mm to 7.0 mm, and θ is 70° to 85°.

[0017] The manufacturing method of the pre-formed can of the present application is characterized in that it includes: a bottomed cylinder preparation step for preparing a bottomed cylinder; and a forming step for forming the pre-formed can by forming an arch bottom portion recessed toward the inside of the bottomed cylinder and an annular foot portion protruding in the opposite direction to the recessed direction of the arch bottom portion on the bottom of the bottomed cylinder; and forming the pre-formed can into a formed can by pressing the inner surface of the arch bottom portion, wherein, when the pre-formed can is formed by the forming step, the maximum height from the ground contact surface of the pre-formed can to the arch bottom portion is higher than the maximum height from the ground contact surface of the formed can to the arch bottom portion, and in a cross-sectional line taken in the longitudinal direction of the can axis, the length of the inner periphery of the foot portion for connecting the ground contact point on the foot portion and the arch bottom portion in the pre-formed can is longer than the length of the curved edge portion formed around the arch bottom portion in the formed can.

[0018] Effects of the Invention

[0019] According to the present application, the compressive strength of the can body can be further improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a longitudinal cross-sectional view of the pre-formed can in the present embodiment.

[0021] Figure 2 is a longitudinal cross-sectional view of the can body formed from the pre-formed can.

[0022] Figure 3 is Figure 1 is an enlarged view of the A1 region of

[0023] Figure 4 is Figure 2 is an enlarged view of the A2 region of

[0024] Figure 5 is a flowchart for explaining the manufacturing process of the can body.

[0025] Figure 6 is a partial cross-sectional view of a molding device for performing a molding process on a preform can.

[0026] Figure 7 is a partial cross-sectional view of a molding device for performing a molding process on a preform can.

[0027] Figure 8 is a partial cross-sectional view of a molding device for performing a molding process on a preform can.

[0028] Figure 9 is a partial cross-sectional view of a molding device for performing a molding process on a preform can.

[0029] Figure 10 is a partial cross-sectional view of a molding device for performing a molding process on a preform can.

[0030] Figure 11 is a partial cross-sectional view of a portion of a foot portion and a soffit portion before and after a curved edge portion is molded. DETAILED DESCRIPTION

[0031] Embodiments of the present application (present embodiments) will be described below with reference to the accompanying drawings. Figure 1 is a longitudinal cross-sectional view of a preform can in the present embodiments. Figure 2 is a longitudinal cross-sectional view of a can body molded from a preform can. Figure 3 is Figure 1 is an enlarged view of an Al region in Figure 4 is Figure 2 is an enlarged view of an A2 region in Figure 5 is a flowchart for explaining a manufacturing process of a can body. Figure 6-10 is a partial cross-sectional view of a molding device for performing a molding process on a preform can. Figure 11 is a partial cross-sectional view of a portion of a foot portion and a soffit portion before and after a curved edge portion is molded.

[0032] Figure 1A longitudinal sectional view taken along the can axis O of the preform can 1 in the present embodiment is shown. The preform can 1 is obtained by molding a bottomed cylinder, and has a can mouth 11, a can body 12, and a bottom 13. The can body 12 and the bottom 13 have the same shape around the can axis O in the entire circumference. The can axis O extends vertically with respect to the ground contact surface Gl of the preform can 1. The bottom 13 has an arch bottom portion 131 recessed toward the inside of the preform can 1, and an annular foot portion 132 protruding in the opposite direction to the recessed direction of the arch bottom portion 131. The foot portion 132 of the bottom 13 in the preform can 1 has an outer side can wall 132-1 connected to the can body 12, a ground contact point 132-2 in contact with the ground contact surface Gl, and an inner side periphery 132-3 connected to the arch bottom portion 131.

[0033] Figure 2 A longitudinal sectional view taken along the can axis O of the can body la obtained by molding the preform can 1 is shown. The can axis O of the can body la also extends vertically with respect to the ground contact surface G2. The can body la is a molded can obtained by pressing the inner surface 131a of the arch bottom portion 131 and the outer side can wall 132-1 of the preform can 1 in opposite directions along the can axis O. By pressing the inner surface 131a of the arch bottom portion 131, a part of the foot portion 132 of the preform can 1 is deformed and molded into a curved edge portion 133. That is, in the can body la shown, the curved edge portion 133 molded from the foot portion 132 is formed around the arch bottom portion 131. Figure 2 In the can body la shown, the curved edge portion 133 molded from the foot portion 132 is formed around the arch bottom portion 131 after the arch bottom portion 131 is pressed.

[0034] Further, as shown in Figure 2 The can body la has a can neck 14 having a smaller diameter than the outer diameter of the can body 12, and a flange 15 molded at the edge (part of the mouth edge) of the can mouth 11 on the side of the can neck 14.

[0035] Figure 3 The A1 region including the can body 12, the arch bottom portion 131, and the foot portion 132 of the preform can 1 shown in Figure 1 Further, the A2 region including the can body 12, the arch bottom portion 131, and the foot portion 132 of the can body la shown in Figure 4 The A2 region including the can body 12, the arch bottom portion 131, and the foot portion 132 of the can body la shown in Figure 2 The A2 region including the can body 12, the arch bottom portion 131, and the foot portion 132 of the can body la shown in

[0036] In the Figure 3As shown in the sectional view taken along the direction of the can axis O, with respect to the foot portion 132 in the bottom 13 of the preform can 1, the outer side can wall 132-1 connected to the can body 12 and the inner side periphery 132-3 connected to the dome bottom portion 131 are connected at a contact point 132-2 in contact with the ground surface Gl. The lower end portion 132-4 of the foot portion 132 is formed by a portion of the outer side can wall 132-1 and a portion of the inner side periphery 132-3, which includes the contact point 132-2, and is a substantially circular arc portion having a radius of curvature Rl. Further, the interface portion 132-6 is formed by a portion of the inner side periphery 132-3 and a portion of the dome bottom portion 131, which includes an interface point 132-5 between the inner side periphery 132-3 and the dome bottom portion 131, and is a substantially circular arc portion having a radius of curvature R2.

[0037] Further, in the preform can 1, Figure 4 As shown in the sectional view taken along the direction of the can axis O, with respect to the foot portion 132 in the bottom 13 of the preform can 1, the outer side can wall 132-1 connected to the can body 12 and the inner side periphery 132-3 connected to the dome bottom portion 131 are connected at a contact point 132-2 in contact with the ground surface Gl. The lower end portion 132-4 of the foot portion 132 is formed by a portion of the outer side can wall 132-1 and a portion of the inner side periphery 132-3, which includes the contact point 132-2, and is a substantially circular arc portion having a radius of curvature Rl. Further, the interface portion 132-6 is formed by a portion of the inner side periphery 132-3 and a portion of the dome bottom portion 131, which includes an interface point 132-5 between the inner side periphery 132-3 and the dome bottom portion 131, and is a substantially circular arc portion having a radius of curvature R2. Figure 4 As shown, the inner side periphery 133-3 has a tapered surface 133-31 that is a substantially straight line in the sectional view taken along the direction of the can axis O.

[0038] As shown, the inner side periphery 133-3 has a tapered surface 133-31 that is a substantially straight line in the sectional view taken along the direction of the can axis O. Figure 3 As shown, the maximum height from the ground surface Gl of the preform can 1 to the dome bottom portion 131 is set as BS1, and as shown, Figure 4 As shown, the maximum height from the ground surface Gl of the preform can 1 to the dome bottom portion 131 is set as BS1, and as shown,

[0039] As shown, the inner side periphery 133-3 has a tapered surface 133-31 that is a substantially straight line in the sectional view taken along the direction of the can axis O. Figure 3 As shown, the inner side periphery 133-3 has a tapered surface 133-31 that is a substantially straight line in the sectional view taken along the direction of the can axis O. As shown, the inner side periphery 133-3 has a tapered surface 133-31 that is a substantially straight line in the sectional view taken along the direction of the can axis O. Figure 4 As shown, the inner side periphery 133-3 has a tapered surface 133-31 that is a substantially straight line in the sectional view taken along the direction of the can axis O. As shown, the inner side periphery 133-3 has a tapered surface 133-31 that is a substantially straight line in the sectional view taken along the direction of the can axis O.

[0040] As specific examples, the preform can 1 can be BS1 = 13.75 mm, and In this case, the molded can body 1a can be BS2 = 11.20 mm,

[0041] Further, as shown in Figure 3 , the inner side periphery 132-3 of the foot portion 132 is inclined with respect to a direction parallel to the can axis O direction, with the contact point 132-2 of the foot portion 132 as a base point, toward the direction in which the can axis O is located, in a cross-sectional line that is longitudinal to the can axis O direction. Figure 4 , the inner side periphery 132-3 of the foot portion 132 is inclined with respect to a direction parallel to the can axis O direction, with the contact point 132-2 of the foot portion 132 as a base point, toward the direction in which the can axis O is located, in a cross-sectional line that is longitudinal to the can axis O direction. Figure 3 , the inner side periphery 132-3 of the foot portion 132 is inclined with respect to a direction parallel to the can axis O direction, with the contact point 132-2 of the foot portion 132 as a base point, toward the direction in which the can axis O is located, in a cross-sectional line that is longitudinal to the can axis O direction.

[0042] Figure 3 , the inner side periphery 132-3 of the foot portion 132 of the pre-molded can 1 has a substantially straight diameter-reduced portion 132-31 having a length L, in a cross-sectional line that is longitudinal to the can axis O direction. Figure 3 , the inner side periphery 132-3 of the foot portion 132 of the pre-molded can 1 has a substantially straight diameter-reduced portion 132-31 having a length L, in a cross-sectional line that is longitudinal to the can axis O direction.

[0043] In Figure 4 , the curved edge portion 133 molded around the arch bottom portion 131 of the molded can 1a (molded can) is at least molded from Figure 3 , the inner side periphery 132-3 of the foot portion 132 of the pre-molded can 1.

[0044] In Figure 3 , the curved edge portion 133 molded around the arch bottom portion 131 of the molded can 1a (molded can) is at least molded from Figure 4The length of the curved edge portion 133 formed around the portion of the dome bottom portion 131 of the can body 1a (a formed can) in the direction of the can axis O is shown in the cross-sectional view taken along the line X-X. The length of the curved edge portion 133 is preferably X < N... (4) so that the desired shape of the curved edge portion 133 can be stably formed when the bottom portion is re-formed.

[0045] The manufacturing process of the can body 1a will be described below with reference to the flowchart of Fig. 1. Figure 5 The can body 1a is manufactured by the following steps S101 to S108.

[0046] (Step S101: cupping process)

[0047] In the cupping process of step S101, a metal sheet such as an aluminum alloy is punched into a circular shape, and a cup-shaped member is formed by drawing the circular metal sheet using a cupping machine (cupping process).

[0048] (Step S102: pre-formed can forming process)

[0049] In the pre-formed can forming process of step S102 following step S101, a bottomed cylinder having a can body and a bottom portion is formed by performing a drawing and thinning process on the cup-shaped member formed in step S101, and a dome bottom portion recessed inward of the bottomed cylinder and an annular footing portion protruding in the direction opposite to the recessed direction of the dome bottom portion are formed by further performing a press process or the like on the bottom portion of the bottomed cylinder, thereby forming a pre-formed can 1. If a lubricant or the like is used in steps S101 and S102, a cleaning process can be provided after step S102 to remove the lubricant or the like.

[0050] (Step S103: trimming process)

[0051] The rim of the can opening of the pre-formed can 1 formed in step S102 has uneven height. Therefore, in the trimming process of step S103 following step S102, a trimming device is used to trim (cut) the rim of the can opening of the pre-formed can 1 to make the height of the entire periphery of the pre-formed can 1 uniform.

[0052] (Step S104: outer surface coating and printing process)

[0053] In step S104, the outer surface coating and printing process following step S103, a coating for the outer surface is applied to at least the outer surfaces of the can body 12 and bottom 13 of the preformed can 1. After the coating is formed, the designed image or the like is printed on the outer surface (outer peripheral surface) of the can body 12. Furthermore, an outer coating such as a varnish can be formed on the printed layer containing the designed image or the like, and then baked in an oven or the like. This makes the outer surface of the preformed can 1 more wear-resistant and smoother.

[0054] (Step S105: Inner surface coating process)

[0055] In step S105, the inner surface coating process following step S104, a coating for the inner surface is applied to the inner surface of the preformed tank 1. This inner surface coating can be performed by methods such as spraying.

[0056] The coatings that can be used for the inner surface in this process include, for example, coating compositions containing epoxy acrylate copolymers and water-based solvents. Coating the inner surface 131a of the preformed can 1 in this way can prevent the flavor of the contents from deteriorating and can prevent metal corrosion. Furthermore, a drying process can be provided after step S105, i.e., the inner surface coating process, for example, drying the preformed can 1 at a high temperature of approximately 190°C to 210°C.

[0057] (Step S106: Bottom reshaping process)

[0058] In step S106, the bottom re-forming process following step S105, pressure is applied to the pre-formed can 1. Pressure is applied in opposite directions along the can axis O to the inner surface 131a of the arched bottom portion 131 of the pre-formed can 1, which was coated in step S105, and to the outer can wall 132-1. This pressure is used to form a can body 1a (formed can) with curved edges 133 surrounding the arched bottom portion 131.

[0059] In this bottom reshaping process, for example, Figure 6 The forming apparatus 2 shown performs a pressure treatment. The forming apparatus 2 includes: a pressure member 21, which is inserted into the interior of the preforming tank 1 and abuts against the inner surface of the arch bottom portion 131; and a forming mold 22, which is used to form a curved edge portion 133 by applying pressure using the pressure member 21.

[0060] First, such as Figure 6 As shown, the preformed can 1 is placed on the molding die 22 of the molding device 2, so that the outer can wall 132-1 on the bottom part 132 of the preformed can 1 abuts against the contact surface 221 of the molding die 22 of the molding device 2. Then, similarly... Figure 6As shown, the pressure member 21 of the molding device 2 is moved toward the inner surface 131a of the arch bottom portion 131 (in the direction of the arrow along the can axis O).

[0061] Then, as Figure 7 As shown, by further moving the pressure-applying member 21 in the direction of the arrow along the can axis O, the pressure-applying surface 211 of the pressure-applying member 21 abuts against the inner surface 131a of the arched bottom portion 131 and applies pressure to it. Through this pressure application, the contact surface 221 of the molding die 22 applies pressure to the outer can wall 132-1, as... Figure 7 As shown, the lower end 132-4 of the foot portion 132 of the preformed can 1 will gradually deform from the contact surface 221 of the molding die 22 along the curved molding surface 222.

[0062] After that, as Figure 8 As shown, by further applying pressure to the inner surface 131a of the arched bottom portion 131 in the direction of the arrow using the pressure-applying member 21, the abutment surface 221 of the forming mold 22 further applies pressure to the outer can wall 132-1, thereby guiding a portion of the bottom portion 132 of the preformed can 1 to the curved forming surface 222 and deforming it into a shape that matches the curved forming surface 222. Then, as... Figure 9 As shown, a curved edge portion 133 is formed that corresponds to the shape of the curved forming surface 222. The can body 1a is formed as a molded can by forming this curved edge portion 133. Next, as... Figure 10 As shown, the pressure member 21 of the molding device 2 is moved in the direction opposite to the pressure direction along the arrow on the can shaft O to remove it from the inner surface 131a of the arched bottom portion 131. Then, the can body 1a is removed from the molding device 2. Alternatively, the pre-formed can 1 can be placed on the pressure member 21 of the molding device 2, and the molding die 22 of the molding device 2 can be moved to remove it from the outer can wall 132-1 of the bottom portion 132 of the pre-formed can 1, thereby removing the can body 1a from the molding device 2.

[0063] As described above, in the bottom reforming process of step S106, the curved edge portion 133 is formed by applying pressure to the inner surface 131a of the arched bottom portion 131. This process allows the inner periphery 133-3 of the curved edge portion 133 to tilt towards the direction of the can body 12 with reference to the contact point 133-2, relative to the direction parallel to the can axis O, thus ensuring sufficient length of the inner periphery 133-3. That is, compared to conventional bottom reforming processes using rollers, the inner periphery 133-3 of the curved edge portion 133 can be recessed deeper towards the direction of the can body 12, thereby giving the bottom 13 of the formed can body 1a sufficiently high compressive strength.

[0064] (Step S107: Necking process)

[0065] In step S107, which is the necking process, following step S106, a cavity machining tool (necking forming mold) (not shown) is used to perform cavity machining (necking) on ​​the end of the can body 12 on the side of the can opening 11 to form the can neck 14.

[0066] (Step S108: Flanging process)

[0067] In step S108, the flanging process following step S107, a roller (not shown) is used to curl the edge (rim portion) of the can opening 11 toward the outside of the can body 1a to form a flange 15. The flange 15 is shaped to facilitate the subsequent sealing of the can lid.

[0068] In addition, the processing performed in the necking process in step S107 and the flanging process in step S108 can also be performed before the bottom re-forming process in step 106.

[0069] The can body 1a, i.e., the molded can, is manufactured through the processing steps S101 to S108 described above. After step S108, the beverage contents are filled into the can body 1a, and then the flange 15 and the can lid (not shown) are rolled together to produce a beverage product.

[0070] Based on the manufacturing process of this can 1a, in a longitudinal section along the can axis O, the length of the inclined surfaces, such as the outer can wall 132-1 and the generally straight tapered portion 132-31, is ensured throughout the circumference of the inner surface of the foot portion 132 of the pre-formed can 1 before the curved edge portion 133 is formed. In particular, for the generally straight tapered portion 132-31, it is inclined more towards the can opening direction of the can 1a, i.e., towards the can axis O, with the contact point 133-2 as the base point, compared to the inner surface of the inner peripheral wall of the annular protrusion (foot portion) of the can described in Patent Document 1. Therefore, when coating is applied by spraying or other methods, the sprayed paint is easily sprayed onto the inner surface of the inner periphery 132-3, just like the inner surface of the arched bottom portion 131a and the inner surface of the outer can wall 132-1. Therefore, no paint waste occurs when coating the inner surface of the foot portion 132 at the bottom 13 of the preforming tank 1, and the thickness difference of the coating formed by the paint used on the inner surface is reduced, resulting in a uniform coating thickness. Furthermore, the same effect can be obtained when coating the outer surface of the foot portion 132 of the preforming tank 1.

[0071] Based on the manufacturing process of the can 1a, since the bottom reforming process is completed by applying pressure to the inner surface 131a of the arched bottom portion 131 as described above, even though the pre-formed can 1 has its inner and outer surfaces coated, it will not be affected by friction caused by the rollers, as is the case with the traditional method of bottom reforming using rollers. Therefore, based on the manufacturing process of the can 1a, the problem of easy peeling of the coating formed on the inner and outer surfaces of the bottom portion due to the pre-coating of the inner and outer surfaces of the pre-formed can 1 will not occur.

[0072] Furthermore, if conventional bottom re-forming processing is performed on the outer surface of the pre-formed can 1 using rollers from the outside of the inner perimeter 132-3 of the base portion 132, it may be affected by friction, resulting in damage to the alumina coating. This can lead to roller processing marks (blackening) during heat sterilization after the contents are filled. This may affect the appearance of the formed can 1a. However, if the manufacturing process of the can 1a is based on the above-described process, this problem affecting the appearance will not occur.

[0073] Furthermore, during the manufacturing process of this can body 1a, pressure is applied to the inner surface of the arched bottom portion 131, so that the inner surface 131a of the arched bottom portion 131 on the pre-formed can 1 and the outer can wall 132-1 are pressed in opposite directions along the can axis O. Through this simple process, a curved edge portion 133 for improving the compressive strength of the bottom 13 can be formed around the arched bottom portion 131. This process is much simpler than forming the curved edge portion 133 by using a roller to reshape the bottom from the outer side of the inner periphery 132-3 of the foot portion 132. In addition, unlike the prior art of bottom reshaping using a roller, since there is less friction between the foot portion 132 and the forming mold 22 during this process, there is no accumulation (deposition) of substances such as paint on the forming mold 22.

[0074] Below, in conjunction with Figure 11 The cross-sectional length of the curved edge portion 133 formed at the base portion 132 is explained. Figure 11 In the longitudinal section along the can axis O, the dashed line E1 represents a portion of the base portion 132 and the arched bottom portion 131 of the pre-formed can 1 before the curved edge portion 133 is formed, and the solid line E2 represents a portion of the base portion 132 and the arched bottom portion 131 of the can body 1a after the curved edge portion 133 is formed. Furthermore, in Figure 11 In the diagram, the dashed line G1 represents the contact surface that the contact point 132-2 on the preformed tank 1 contacts, and the solid line G2 represents the contact surface that the contact point 133-2 on the formed tank body 1a contacts.

[0075] In Figure 11 As shown in the cross-sectional view along the longitudinal direction of the can axis O, the inner periphery 132-3 of the base portion 132 of the preformed can 1, as indicated by the dashed line E1, is inclined towards the direction of the can axis O with respect to the direction parallel to the can axis O and orthogonal to the contact point 132-2 of the base portion 132 as the reference point. After applying the above-described pressure treatment to the inner surface 131a of the arched bottom portion 131 of this preformed can 1, the curved edge portion 133 shown by the solid line E2 can be formed. For the can body 1a (formed can) after the curved edge portion 133 is formed, the inner periphery 133-3 of the contact point 133-2 and the arched bottom portion 131 on the curved edge portion 133 is inclined in the opposite direction to the direction of the inner periphery 132-3 of the bottom portion 132 towards the can axis O relative to the direction parallel to the can axis O (that is, in the direction of the can body 12 with the contact point 133-2 as the base point, relative to the direction parallel to the direction of the can axis O).

[0076] exist Figure 11 As shown in the section view along the longitudinal direction of the tank axis O, as shown in the above formula (4), the length N of the contact point 132-2 on the bottom part 132 of the preformed tank 1 and the inner periphery 132-3 of the bottom part 132 of the arch bottom part 131 is greater than the length X of the curved edge 133 formed on the part surrounding the arch bottom part 131 of the tank body 1a (formed tank).

[0077] Furthermore, if the length of the approximate arc with radius of curvature R1 of the lower end 132-4 of the base portion 132 constituting the dotted line E1 is set as M... R1 If, under the longitudinal section along the axis O of the tank, the length of the approximately straight, tapered portion 132-31 on the inner periphery 132-3 of the base portion 132 on the dashed line E1 is set as L, then preferably X < M. R1 +L…(5), because this allows for the stable formation of the desired curved edge 133 shape during bottom reshaping. As a specific example, it can be set to M. R1 =3.44mm, L=5.9mm, X=7.03mm.

[0078] In this embodiment, it is preferable to design the preformed can 1 to meet the values ​​of the above formulas (1) to (5). By applying pressure to the inner surface 131a of the arched bottom portion 131 of the preformed can 1 designed and formed as described above, a can body 1a (formed can) with a curved edge portion 133 can be formed, and the shape of the curved edge portion 133 matches the curved forming surface 222.

[0079] Compared to conventional tanks that use rollers to reshape the bottom, the inner periphery 133-3 of the curved edge 133 of this tank 1a is recessed more deeply in the direction of the tank body 12, thus enabling the bottom 13 of the tank 1a to have sufficiently high compressive strength.

[0080] Furthermore, while the inner and outer surfaces of the preformed tank 1 are coated in the above embodiment, this is not a limitation; at least one of the inner and outer surfaces of the preformed tank 1 may also be coated. Since the bottom reforming is also accomplished by applying pressure to the inner surface 131a of the arched bottom portion 131 as described above, the problem of easy peeling of the coating will not occur in the same way.

[0081] Explanation of reference numerals in the attached figures

[0082] 1: Preformed tank; 11: Tank opening; 12: Tank body; 13: Bottom; 14: Tank neck; 15: Flange; 131: Arched bottom portion; 131a: Inner surface; 132: Foot portion; 132-1: Outer tank wall; 132-2: Contact point; 132-3: Inner perimeter; 132-31: Narrowing portion; 132-4: Lower end; 132-5: Junction point; 132-6: Junction area; 1a: Tank body; 133: Curved edge; 133-1: Outer perimeter; 133-2: Contact point; 133-3: Inner perimeter; 133-31: Conical surface; 133-4: Junction point.

[0083] 2: Molding device; 21: Pressing component; 22: Molding mold; 211: Pressing surface; 221: Abutting surface.

[0084] 222: Bending and forming surface.

Claims

1. A pre-formed can, which is formed by forming an arched bottom portion recessed towards the inner side of the bottomed cylinder and an annular bottom foot portion protruding in the opposite direction to the recessed direction of the arched bottom portion at the bottom of the bottom of the bottom of the cylinder, wherein the pre-formed can is formed into a molded can by applying pressure to the inner surface of the arched bottom portion, characterized in that: The maximum height from the contact surface of the preformed tank to the arched bottom portion is greater than the maximum height from the contact surface of the molded tank to the arched bottom portion. Furthermore, in a longitudinal section along the can axis, the length of the contact point in the pre-formed can used to connect the foot portion to the inner periphery of the foot portion of the arched bottom portion is longer than the length of the curved edge portion formed around the arched bottom portion in the formed can. If the length of the arc with radius of curvature R1 at the lower end of the base portion is set as M... R1 , Let L be the length of the straight, tapered section on the inner periphery of the base portion. Let X be the length of the curved edge portion on the molded can after molding. Then X < M R1 +L, If we define the angle of inclination between the contact surface of the preformed tank and the reduced diameter portion on the inner periphery of the foot portion, pointing towards the direction of the tank axis, as θ, Therefore, R1 is 0.8mm to 2.2mm. L is 4.0mm~7.0mm, θ is 70° to 85°.

2. The preformed tank according to claim 1, characterized in that: In a longitudinal section along the can axis, the inner periphery of the foot portion is inclined towards the can axis with the contact point of the foot portion as the reference point. In a longitudinal section along the can axis, the contact point on the curved edge of the molded can and the inner periphery of the curved edge of the arched bottom portion are inclined in the opposite direction to the can axis, with the contact point on the curved edge as the base point.

3. A method for manufacturing a preformed tank, characterized in that, include: The preparation process for a cylinder with a base is used to prepare a cylinder with a base. and The molding process is used to form the preformed tank by forming an arched bottom portion that is recessed toward the inside of the bottomed cylinder and an annular bottom foot portion that protrudes in the opposite direction to the recessed direction of the arched bottom portion. The pre-formed tank is shaped into a molded tank by applying pressure to the inner surface of the arched bottom portion. Specifically, when forming the pre-formed tank through the molding process, the maximum height from the contact surface of the pre-formed tank to the arched bottom portion must be higher than the maximum height from the contact surface of the formed tank to the arched bottom portion. Furthermore, in a longitudinal section along the can axis, the length of the contact point in the pre-formed can used to connect the foot portion to the inner periphery of the foot portion of the arched bottom portion is longer than the length of the curved edge portion formed around the arched bottom portion in the formed can. If the length of the arc with radius of curvature R1 at the lower end of the base portion is set as M... R1 , Let L be the length of the straight, tapered section on the inner periphery of the base portion. Let X be the length of the curved edge portion on the molded can after molding. Then X < M R1 +L, If we define the angle of inclination between the contact surface of the preformed tank and the reduced diameter portion on the inner periphery of the foot portion, pointing towards the direction of the tank axis, as θ, Therefore, R1 is 0.8mm to 2.2mm. L is 4.0mm~7.0mm, θ is 70° to 85°.

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