CN113507993A

CN113507993A - Seamless can body and method for manufacturing seamless can body

Info

Publication number: CN113507993A
Application number: CN202080018253.5A
Authority: CN
Inventors: 小林具实
Original assignee: Toyo Seikan Group Holdings Ltd
Current assignee: Toyo Seikan Group Holdings Ltd
Priority date: 2019-01-30
Filing date: 2020-01-13
Publication date: 2021-10-15
Also published as: EP3919200A4; US20220097896A1; TW202041299A; WO2020158355A1; EP3919200A1

Abstract

A seamless can body and a method for manufacturing the seamless can body, which can reduce the thickness of a raw material plate (blank), improve the pressure resistance of the can bottom to suppress warping, and solve the problems of blackening and cleaning. A seamless can body (1) comprises a cylindrical main body part (10) and a can bottom part (20), wherein the can bottom part (20) comprises an outer peripheral bottom part (202a) and a peripheral land part (202b) located on the inner side of the outer peripheral bottom part (202a) and continuing to have a diameter reduced from the lower end of the cylindrical main body part (10) to the inner side, and t2 > t1 is defined by t1 as the plate thickness of the outer peripheral bottom part (202a) and t2 as the plate thickness of the peripheral land part (202 b).

Description

Seamless can body and method for manufacturing seamless can body

Technical Field

The present invention relates to a seamless can body and a method for manufacturing the seamless can body.

Background

Conventionally, a so-called seamless can body such as a can body is formed by extrusion ironing. This seamless can body is excellent in lightweight because the can body portion is thinned by ironing. On the other hand, it is difficult to apply a forced thinning method such as a ironing process to the bottom of the seamless can body, and the thickness of the bottom of the can body does not greatly vary from the thickness of the raw material. Since the bottom portion is required to have strength (pressure resistance) against deformation due to the internal pressure of the can, various proposals have been made, including the following patent documents, for making the thickness of the material thinner and maintaining or improving the pressure resistance even in the bottom portion of the can body in order to reduce the weight.

For example,

patent documents

1 and 2 disclose a so-called bottom improving process which is performed for the purpose of preventing a phenomenon (warpage) in which a dome portion of a can bottom is inverted, which occurs when an internal pressure of the can exceeds a pressure resistance. Specifically, there is disclosed a bottom portion improving process for forming a concave portion by pressing an inner peripheral wall of a land portion of a can bottom portion, the inner peripheral wall being positioned on an inner side in a radial direction orthogonal to a can axis.

Prior art documents

Patent document

Patent document 1 Japanese patent laid-open publication No. 2018-103227

Patent document 2 Japanese patent laid-open publication No. 2016-

Patent document 3, Japanese patent laid-open No. 2000-176575

Patent document 4 Japanese patent application laid-open No. 9-285832

Patent document 5 publication No. WO2018/070542

Patent document 6 Japanese laid-open patent publication No. 2016-43991

Disclosure of Invention

Problems to be solved by the invention

But the bottom improving process has the following problems.

That is, in the bottom portion improving step, the concave portion is formed by pressing the inner peripheral wall of the can bottom portion with a forming roll or the like. When pressing using such a forming roll or the like, as described in patent document 3, there is a problem that blackening is likely to occur at the pressing portion, and a problem that metal material is likely to coagulate to the forming roll or the like.

Further, in the pressing, the lubricating oil is applied for smooth working, but since a step of cleaning the lubricating oil is required after the bottom portion improving working, further improvement is required from the viewpoint of cost and environmental load required for cleaning.

In recent years, in order to reduce the weight of seamless can bodies, it has been required to reduce the thickness of a raw material plate (blank) before extrusion-ironing. However, when the bottom improving process is performed, the thickness of the metal material of the pressing portion is reduced by the process extension, and therefore, there is a limit to reducing the thickness of the material plate (blank).

As shown in patent document 4, the present inventors have disclosed a technique for improving the pressure resistance of a seamless can body. However, this technique does not sufficiently optimize the plate thickness distribution of each part of the can body (particularly the can bottom) although the pressure resistance is improved. Therefore, it is not a technique that sufficiently satisfies the requirement for weight reduction of the can body.

Further, patent document 5 discloses a 2-piece can body characterized in that the plate thickness of the land portion of the can bottom is thicker than the plate thickness of the raw material before processing. However, this technique has problems that the apparatus is complicated, the realization at an industrial level is difficult, and the cost of the apparatus is increased.

The present inventors have conducted intensive studies in view of the above-described problems as examples. As a result, the present invention has been achieved to provide a seamless can body and a method for manufacturing the same, which can reduce the thickness of a raw material plate (blank), improve the pressure resistance of the can bottom, suppress warping, and solve the above-mentioned problems of blackening and cleaning, by a simpler manufacturing apparatus.

Means for solving the problems

In order to achieve the above object, one embodiment of the present invention is a seamless can body having a cylindrical body portion and a can bottom portion, wherein the can bottom portion includes an outer peripheral bottom portion and a peripheral land portion located on an inner side of the outer peripheral bottom portion, the outer peripheral bottom portion being continuous so as to be radially reduced from a lower end of the cylindrical body portion toward the inner side, and when a plate thickness of the outer peripheral bottom portion is t1 and a plate thickness of the peripheral land portion is t2, t2 > t 1. (1)

In order to achieve the above object, one embodiment of the present invention is a seamless can body including a cylindrical body portion and a can bottom portion including at least an outer peripheral bottom portion continuing to decrease in diameter from a lower end of the cylindrical body portion to an inner side through a boundary portion, wherein a plate thickness of the lower end of the cylindrical body portion is substantially equal to a plate thickness of an intermediate portion of the cylindrical body portion in an axial direction. (2)

In addition, in the above (1) or (2), preferably, the tank bottom further includes an inner end portion located inside the circumferential land portion, and when a plate thickness of the inner end portion is t3, t3 > t1 is provided. (3)

In addition, in the above (3), the plate thickness is preferably gradually increased from the outer peripheral bottom portion to the inner end portion so that t3 > t2 is formed. (4)

In any one of the above (1) to (4), preferably, the tank bottom further includes a rising portion rising upward from the inner end, and when a plate thickness of an upper end of the rising portion is t4, t4 > t1 is set as t. (5)

In addition, in the above (5), preferably, the tank bottom further includes a dome portion bulging to protrude upward continuously from the rising portion, and when a plate thickness at a center of the dome portion is t5, the plate thickness gradually increases from the dome portion to the inner end so as to be t3 > t4 > t 5. (6)

Further, in the above (6), preferably, t5 < t 1. (7)

In any one of the above items (5) to (7), preferably, a ring groove in which a connecting portion between the rising portion and the dome portion is convex is formed outward of the can body axis. (8)

In addition, in the above (2), it is preferable that a plate thickness at the boundary portion is substantially equal to a plate thickness at the intermediate portion. (9)

Preferably, in the above (2) or (9), the thickness of the cylindrical body portion at the lower end is defined as t_WLThe thickness of the intermediate portion of the cylindrical body in the axial direction is defined as t_WCIn the case of (1), at t_WC≦t_WL＜1.09×t_WCThe relationship (2) of (c). (10)

In addition, in the above (10), preferably, the cylindrical body portion is at t_WC≦t0＜1.09×t_WCWherein t0 is the plate thickness of the boundary portion. (11)

In the above items (1) to (11), the 60-degree specular gloss is preferably 300% or more from the lower end of the cylindrical body portion to the vicinity of the boundary portion. (12)

In order to achieve the above object, one embodiment of the present invention is a method for manufacturing a seamless can body having a cylindrical body portion and a can bottom portion, the method comprising a first forming step of forming a metallic starting material into a cup having the cylindrical body portion; a cup outer peripheral bottom portion which is continuous so as to be reduced in diameter from a lower end of the cylindrical body portion; an inclined portion extending upward from the bottom of the outer periphery of the cup toward the inside; and a cup dome portion bulging upward at a first height from an end of the inclined portion, wherein in the second molding step, a pressing force is applied from the cup dome portion toward the outside of the cup by an upper mold molding member while a cup outer peripheral bottom portion of the cup body is brought into contact with a lower mold molding member, the cup dome portion is pushed down so as to have a second height lower than the first height, and compressive stresses in the meridian direction and the circumferential direction are applied to the inclined portion, and the thickness of the inclined portion is increased while the cup dome portion is pushed into the lower mold molding member. (13)

Further, in the above (13), it is preferable that in the second molding step, the inclined portion is pushed into the lower mold molding member to form a circumferential land portion located inside the outer circumferential bottom portion; an inner end portion located inside the peripheral ground portion; and an erected portion erected upward from the inner end portion and connected to a dome portion, wherein a ring groove in which the connecting portion is protruded is formed outward of the tank body axis so that an inner diameter of the connecting portion between the erected portion and the dome portion becomes larger than an inner diameter of the inner end portion. (14)

In order to achieve the above object, one embodiment of the present invention is a method for manufacturing a seamless can body, including a first forming step of forming a metal material into a cup body having a cylindrical body portion thinned by ironing; an outer peripheral bottom portion continuous from a lower end of the cylindrical body portion; and a bulging portion that bulges out at a first height from the outer peripheral bottom portion toward the opening portion, wherein the bulging portion is pushed down so as to be at a second height lower than the first height, and wherein in the first forming step, the lower end of the cylindrical main body portion is drawn in so that a plate thickness of the lower end of the cylindrical main body portion is substantially equal to a plate thickness of an intermediate portion of the cylindrical main body portion in the axial direction, and the outer peripheral bottom portion is formed so as to be continuous so as to be reduced in diameter from the lower end of the cylindrical main body portion to the inside via the boundary portion. (15)

ADVANTAGEOUS EFFECTS OF INVENTION

According to the seamless can body of the present invention, even when the thickness of the raw material plate (blank) is reduced, the can bottom having a higher pressure resistance than the can bottom obtained by the conventional bottom improving process can be obtained. Therefore, the seamless can body can be produced using a thinner raw material plate (blank) than in the conventional art, and the amount of metal material used can be reduced, which is advantageous in terms of cost. Further, the weight of the seamless can body can be reduced, and the return charge and the transportation charge can be reduced.

Further, according to the method for producing a seamless can body of the present invention, even when the thickness of the raw material plate (blank) is reduced, the pressure resistance of the can bottom can be improved by a simple production apparatus, and warping can be suppressed. And the blackening problem which becomes a problem in the bottom improving process can be solved. Further, since the conventional bottom improving process and the subsequent lubricating oil cleaning process are not required, the cost and environmental advantages are large.

Drawings

Fig. 1 is a schematic view showing a seamless can body 1A according to a first embodiment.

Fig. 2 is an enlarged view showing the bottom of the seamless can body 1A according to the first embodiment.

Fig. 3 is a graph showing plate thicknesses at respective points in the seamless can body 1A according to the first embodiment.

Fig. 4 is a view showing a first forming step in the method for producing a seamless can body according to the first embodiment.

Fig. 5 is a diagram showing a second forming step in the method for producing a seamless can body according to the first embodiment.

Fig. 6 is a schematic view showing a compressive stress applied to the rising portion in the first embodiment.

FIG. 7 is a partially enlarged view of the bottom of a seamless can body used in comparative example 1.

Fig. 8 is a schematic diagram showing a longitudinal cross section of the entire seamless can body 1B in the second embodiment.

Fig. 9 is a comparison between the seamless can body 1B of the second embodiment and the seamless can body of the conventional structure in the vicinity of the lower end 10e of the cylindrical body 10.

Fig. 10 is a view showing a first forming step in the method for producing a seamless can body 1B.

Fig. 11 is a schematic view in which portions α and β in fig. 10 are partially enlarged.

Fig. 12 is a diagram showing a second forming step in the method for producing a seamless can body 1B.

Fig. 13 is an enlarged view showing a can bottom in the seamless can body 1A of the first embodiment to which the boundary BP shown in the second embodiment is applied.

Fig. 14 is a schematic diagram for comparing the structures of a seamless can body formed by a conventional method and a seamless can body formed by the present embodiment.

Fig. 15 is a schematic view showing another example (example 1) to which the first forming step in the method for producing a seamless can body 1B shown in fig. 10 can be applied.

Fig. 16 is a schematic view showing another example (example 2) of the first forming step applicable to the method for producing a seamless can body 1B shown in fig. 10.

Fig. 17 is a schematic diagram for explaining the position of the boundary BP in the embodiment.

Detailed Description

Hereinafter, the seamless can body and the method for producing the same according to the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are illustrative of the present invention and are not intended to limit the present invention.

[ first embodiment ]

< seamless Can body 1A >

As shown in fig. 1, the seamless can body 1A of the present embodiment is a seamless can body having a cylindrical body portion 10 and a can bottom portion 20. In the present embodiment, the can bottom 20 preferably includes a can bottom center 201 that does not come into contact with a horizontal surface when the seamless can body is placed on the horizontal surface, and a leg 202 located outside the can bottom center 201, as shown in fig. 1(a) and 1 (b).

The bottom center portion 201 of the seamless can body 1A in the present embodiment may be horizontal or dome-shaped as shown in fig. 1(a) and bulging toward the inner surface of the can (bulging upward).

In the present embodiment, as shown in fig. 1(b), the leg portion 202 of the can bottom 20 is defined as a portion extending from the lower end 10e of the cylindrical body 10 toward the body axis RA to the outermost end 201e of the can bottom center 201.

As shown in the enlarged cross-sectional view of the leg portion 202 in fig. 2, the "outermost end 201e of the can bottom center portion 201" is a portion where the dome diameter is largest in the dome shape when the can bottom center portion 201 is in the dome shape.

In the present embodiment, the portion of the leg portion 202 that is the lowest portion in the Z-axis direction is referred to as a circumferential ground portion 202 b. That is, the circumferential land portion 202b can be said to be a portion that is in contact with a horizontal surface when the seamless can body 1A of the present embodiment is placed on the horizontal surface.

The peripheral bottom portion 202a is defined as a portion from the lower end 10e of the cylindrical body portion 10 to the peripheral land portion 202 b.

That is, in the present embodiment, the leg portion 202 includes an outer peripheral bottom portion 202a continuing to decrease in diameter from the lower end 10e of the cylindrical body portion 10 inward, and a peripheral land portion 202b located inward of the outer peripheral bottom portion 202 a.

In other words, in the seamless can body 1A of the present embodiment, the outer peripheral bottom portion 202a is located at an annular position to the lower end 10e of the cylindrical body portion 10, outside the peripheral land portion 202 b.

In the present embodiment, the loop width and the area of the outer peripheral bottom portion 202a are not particularly limited, and a known shape can be applied to the inclination angle and the curved state. That is, the cross section may be linear, or may be arcuate curved inward of the can body, or may be arcuate curved outward. Further, the shape may be such that a part is bent inward and the other part is bent outward, and these parts are continuously connected.

In the present embodiment, as shown in fig. 2, it is preferable that the outer peripheral bottom portion 202a has an inflection point IP in a cross-sectional view thereof, which is easily superimposed on the lid of the same type of can.

As shown in fig. 2, the seamless can body 1A of the present embodiment further includes an inner end 202c located inside the peripheral land portion 202 b. The inner end 202c is defined as a portion closest to the tank axis RA in a cross-sectional view among the above-described leg portions 202.

The seamless can body 1A according to the present embodiment further includes a rising portion 202d extending in an upward direction (the + direction of the Z axis) from the inner end 202 c. The rising portion 202d is defined as a portion from the inner end 202c to the outermost end 201e in the direction of the can bottom center portion 201 in the cross-sectional view shown in fig. 1(a) or fig. 2.

The seamless can body 1A of the present embodiment is characterized in that, when the plate thickness of the outer peripheral bottom portion 202a is t1 and the plate thickness of the peripheral land portion 202b is t2, a relationship of "t 2 > t 1" is established. By satisfying such a relationship, the seamless can body 1A of the present embodiment can provide excellent pressure resistance while achieving weight reduction of the can body. Further, by making 2 > t1, strength against deformation can be imparted to the seamless can body 1A when the can bottom 20 falls downward.

The thickness (t1) of the outer peripheral bottom portion 202a is set to a thickness at an intermediate point of the length (length along the shape) from the lower end 10e to the peripheral land portion 202 b.

In the seamless can body 1A of the present embodiment, when the plate thickness of the inner end 202c is t3, the relationship "t 3 > t 1" is preferably satisfied. By satisfying such a relationship, the seamless can body 1A of the present embodiment can provide excellent pressure resistance while achieving weight reduction of the can body. Further, by setting t3 > t1, it is possible to impart strength against deformation when the can bottom 20 of the seamless can body 1A is dropped downward.

The thickness in the present invention is defined for the following reason.

That is, when the liquid contained in the seamless can body is beer or carbonated beverage, an internal pressure is usually applied to the can bottom. When an impact is applied to the bottom of the can in such a state that the internal pressure is applied, or when the internal pressure applied to the bottom of the can is rapidly increased for some reason, the internal pressure of the can exceeds the pressure resistance of the bottom of the can, and a phenomenon (warpage) occurs in which the dome portion of the bottom of the can is inverted.

In order to suppress this warping phenomenon, it is necessary to increase the pressure resistance of the can bottom, and therefore, a method of increasing the thickness of the bottom portion of the can may be considered.

However, since the thickness of the raw material plate (blank) is becoming thinner due to recent requirements for weight reduction and resource saving, the above requirements are violated when the thickness of the raw material plate (blank) is simply made thicker in order to increase the pressure resistance at the can bottom.

Accordingly, the present inventors have made intensive studies to realize a seamless can body that satisfies the above requirements for weight reduction of the can and pressure resistance of the can bottom at the same time. As a result, the present inventors have realized that the plate thickness of the raw material plate (blank) is made as thin as or thinner than the conventional one, and only the portion of the can bottom which is likely to contribute to the improvement of the pressure resistance is made thick to increase the pressure resistance of the can bottom.

According to the present invention, since a thinner raw material plate (blank) can be used for the tank main body than in the conventional art, the thickness of the main body can be reduced to a thickness equal to or thinner than that in the conventional art by the same severe ironing process as in the conventional art. Therefore, it can be said that the requirements for weight reduction and pressure resistance of the can bottom can be satisfied at the same time at a high level.

As shown in fig. 1A and 2, the seamless can body 1A of the present embodiment has a bottom portion 20 in which a leg portion 202 is connected from an inner end portion 202c to an outer end 201e through an upright portion 202d to a bottom center portion 201 (dome portion 201 d).

In the present embodiment, the rising portion 202d may be a straight line or a curved line extending in the vertical direction (the + direction of the Z axis) from the inner end 202c in the cross section thereof.

As shown in fig. 1(a) and 2, the rising portion 202d may be a straight line or a curved line extending along a straight line of-aX (Z > 0) in cross section.

As shown in fig. 1a, the rising portion 202d is connected to the bottom center portion 201 (can dome portion 201d) such that the inside diameter (dx) of the outermost end portion 201e is larger than the inside diameter (dy) of the inner end portion 202 c.

In other words, as shown in fig. 1(a) and 2, the vicinity of the outermost end 201e is substantially the same as the vicinity of the outermost end in the cross-sectional view

Or

And (4) shape.

As shown in fig. 1(a), it is preferable that the ring groove has an outermost end 201e protruding outward of the tank body axis RA between the inner end 202c and the tank dome portion 201d in the + direction of the Z axis.

By forming the above-described shape, the pressure resistance of the seamless can body 1A of the present embodiment can be improved.

As described above, in the present embodiment, the outer peripheral bottom portion 202a preferably has an inflection point IP in a cross-sectional view thereof. As shown in fig. 2, the inflection point IP may be located at a position + in the Z-axis direction than the outermost end 201e, or may be located at a position opposite to the Z-axis direction.

In the present embodiment, when the plate thickness of the outermost end 201e portion connecting the rising portion 202d and the can bottom center portion 201 is t4, the relationship "t 4 > t 1" holds, which is preferable from the viewpoint of weight reduction and pressure resistance of the can body.

Further, as shown in fig. 1(a), the seamless can body 1A of the present embodiment preferably includes a can dome portion 201d bulging to protrude upward continuously from the rising portion 202d at the can bottom 20. That is, in the present embodiment, the shape of the can bottom center portion 201 is preferably a dome shape as shown in fig. 1 (a).

When the thickness of the center of the tank dome portion 201d is t5, the relationship between the thickness (t3) of the inner end portion 202c and the thickness (t4) of the rising portion 202d preferably satisfies the following relationship:

t3＞t4＞t5。

that is, this means that the plate thickness of the metal plate continuing from the central portion of the can dome portion 201d toward the outside to the inner end portion 202c gradually increases.

Further, in the present embodiment, as shown in fig. 3, when the plate thickness of the raw material plate (blank) is tz, the relationships "t 1 > tz", t2 > tz ", t3 > tz" and "t 4 > tz" are satisfied, which is preferable from the viewpoint of desired pressure resistance for the seamless can body.

On the other hand, in the present embodiment, the plate thickness (t5) at the center of the tank dome portion 201d is not more than the plate thickness (tz) of the raw material plate (blank) (t5 ≦ tz).

In the present embodiment, as shown in fig. 3(a), it is preferable that the plate thicknesses have a relationship of "t 3 > t2 > t 1". In other words, the plate thickness preferably gradually increases in the order of the outer peripheral bottom portion 202a, the peripheral land portion 202b, and the inner end portion 202 c.

By satisfying such a relationship, the seamless can body 1A of the present embodiment can provide excellent pressure resistance.

Further, satisfying the above-described relationship "t 3 > t2 > t 1" is preferable because the weight increase of the can be suppressed even when the plate thickness of the portion t3 is increased. This is because the tank axes RA are located closer to each other in the order of t1 → t2 → t3, and the volume occupied by each becomes smaller.

Therefore, as a result, the pressure resistance can be improved while suppressing an increase in the weight of the can, which is preferable.

However, the present embodiment is not limited to this, and may be configured such that the thicknesses of t2 and t3 are the same as shown in fig. 3(b), or t2 has the maximum thickness as shown in fig. 3 (c).

The thickness tz of the raw material plate (blank) may be any thickness that is generally used for manufacturing seamless can bodies, and a metal plate having a thickness of approximately 0.15mm to 0.4mm tz may be punched out and used as the raw material plate (blank), but is not limited to the above thickness.

As described above, in the seamless can body 1A of the present embodiment, the plate thickness of the can bottom 20 has the above-described relationship, which is preferable from the viewpoint of desired pressure resistance.

That is, in the seamless can body 1A according to the present embodiment, the average plate thickness of the can bottom 20, particularly the leg portion 202, is preferably larger than the can bottom center portion 201.

Further, the thickness of the can dome portion 201d is preferably smaller than the thickness of the outer peripheral bottom portion 202 a. That is, "t 5 < t 1" is preferable.

The pressure resistance is improved by having the relationship of the plate thickness as described above, and this is considered to be the following reason.

The numerical value indicates the pressure resistance and is the warping pressure. That is, the peak of the pressure until the dome portion that protrudes inward of the can bottom is deformed so as to be inverted outward from the internal pressure is referred to as a buckling pressure.

The process of the occurrence of the warp phenomenon can be described as follows.

First, the dome portion having a substantially spherical shape does not deform itself immediately if it starts to receive internal pressure, and the product of the projected area of the dome portion and the internal pressure acts as a force pushing the dome portion outward of the tank, and applies a load to the circumferential ground contact portion 202b, the inner end portion 202c, and the rising portion 202d to deform.

In other words, the dome portion outer periphery is supported by a member in a narrow region from the peripheral grounding portion 202b to the rising portion 202 d.

Further, if the deformation of the region from the peripheral land portion 202b to the rising portion 202d progresses due to the rise of the internal pressure, the function of supporting the outer periphery of the dome portion is lost. That is, the peripheral land portion 202b, the inner end portion 202c, and the rising portion 202d cannot maintain the circular ring shape centered on the can body axis RA any more, the outermost end 201e positioned on the outer periphery of the dome portion connected thereto also has a shape of collapsing the circular shape, and the can dome portion 201d connected thereto cannot maintain the spherical shape any more, so that the strength of the dome portion is rapidly decreased, and the dome portion is inverted (warped) する toward the outside of the can.

Therefore, in order to improve the pressure resistance, it is considered effective to increase the thickness of the outer periphery of the dome portion as compared with the thickness itself of the dome portion. Therefore, in the present embodiment, the desired pressure resistance can be obtained when the thickness of the outer peripheral bottom portion 202a is greater than the thickness of the center of the can dome portion 201d, that is, "t 5 < t 1".

The second height Hp of the can dome 201d in the seamless can body 1A is not particularly limited, and can be made to be the same height as a known seamless can body having a dome.

In the present embodiment, the kind of the metal material used for the seamless can body 1A is not particularly limited. That is, as the seamless can, a commonly used known metal plate, for example, an aluminum alloy plate or a surface-treated steel plate can be used. The metal plate may be a structure in which a surface treatment is appropriately performed, such as a structure in which known thin films are laminated, a structure in which an organic resin is applied, or a structure in which a chemical synthesis treatment is performed.

The seamless can body 1A of the present embodiment is subjected to known necking, flange forming, or thread forming, and after beer, carbonated beverage, or the like is contained as contents, the lid is attached to the opening by a known method.

< method for manufacturing seamless can body >

Next, a method for producing the seamless can body 1A in the present embodiment will be described.

The method for producing a seamless can body according to the present embodiment is a method for producing a seamless can body 1A having a cylindrical body portion 10 and a can bottom portion 20 as shown in fig. 1(a), and includes at least a first forming step and a second forming step as described in detail below.

In the method for manufacturing a seamless can body according to the present embodiment, a known method such as that described in patent document 4 can be used as a method for molding the cylindrical body 10.

On the other hand, the method for forming the can bottom 20 includes at least a first forming step and a second forming step as described in detail below.

The following describes a method for producing a seamless can body in the present embodiment.

First, a precursor 3 is prepared using the above-described metal material (blank), and the precursor 3 is formed into a cup shape by a known method to form a can body.

As shown in fig. 4, the metal material (precursor 3) may have a cup shape without a dome by a known squeeze thinning method or the like. In addition, the cup-shaped member may have a dome shape as long as the following first forming step and second forming step can be realized.

The seamless can body 1A in the present embodiment can be obtained by providing the precursor 3 with the following first forming step and second forming step.

First, in the first forming step in the method for manufacturing a seamless can body 1A in the present embodiment, as shown in fig. 4, a metal material (precursor 3) is formed into a cup body 2, the cup body 2 having a cylindrical body portion 10; a cup outer peripheral bottom portion a continuing to be reduced in diameter from a lower end 10e of the cylindrical body portion 10; an inclined part S extending upwards from the bottom A of the cup periphery towards the inner side; and a dome portion D bulging upward from an end Se of the inclined portion S at a first height Ho.

The end Se of the inclined portion S may be referred to as a connection point with the cup dome portion D.

The first forming step shown in fig. 4 may be performed as a separate step using an upper die and a lower die for the precursor 3 for forming the cylindrical body portion 10 by a known press step or the like, or may be performed at an end-of-stroke stage subsequent to the step for performing the thinning process.

As a specific example, as shown in fig. 4, the first forming step is performed by a cylindrical punch 401 which is positioned in and supports the precursor 3 having a cup shape, a clamp ring 501 which supports the outer peripheral bottom portion of the precursor 3 in cooperation with the punch 401, and a dome die 502.

First, the outer peripheral bottom portion of the precursor 3 is held by the peripheral wall portion 402 (tapered portion) of the punch 401 and the tapered support portion 503 of the clamp ring 501, and the punch 401 and the dome die 502 are driven to relatively approach each other by snap-fitting, whereby the cup 2 having the cup dome portion D of Ho at the bottom can be obtained.

Here, the shape of the cup 2 obtained in the first forming step will be described. That is, the inclined portion S in the cup body 2 is a portion extending upward inward from the cup outer peripheral bottom a.

That is, as shown in fig. 4, the inclined portion S of the cup body 2 is a curved portion and a straight portion sandwiched between a portion of the cup body 2 that is the lowest in the Z-axis direction and a connection point (end portion Se) with the dome portion D.

As shown in fig. 4(c), the inclined portion S is preferably not vertical but at a predetermined angle θ₁And (4) inclining.

I.e. the angle theta formed by the inclined part S and the Z axis₁Is preferably from 5 ° to 30 °, from the viewpoint of controlling the plate thickness of each portion satisfactorily in the second forming step described below.

In addition, an angle theta formed by the inclined part S and the Z axis₁The angle is preferably 10 ° to 30 °, because, when a coating film is formed on the inner surface by the spray coating method after the first forming step, the spray coating is more easily performed.

In addition, an angle theta formed from the cup outer peripheral bottom part A at the inclined part S₂The radius of curvature R of (a) is preferably 5 × t0 to 15 × t0 from the viewpoint of controlling the plate thickness of each portion satisfactorily in the second forming step described below.

Further, the first height Ho of the dome portion D in the cup body 2 is preferably larger than the second height Hp of the dome portion 201D in the seamless can body 1A obtained by the second forming step described later. This is because, as described later, compressive stress is applied to the inclined portion S while the dome portion D of the cup body 2 is pushed down in the second forming step described later. That is, this is to increase the first height Ho of the dome portion D in the cup body 2 in advance, and finally obtain the second height Hp of the preferable dome portion 201D in the seamless can body 1A.

Next, the second forming step will be explained.

After the cup body having the cup outer peripheral bottom portion a and the inclined portion S is formed in the first forming step, the following second forming step is performed.

Further, between the first forming step and the second forming step, a known cleaning step, a surface treatment step, a printing step, a coating step, a processing of imparting a shape to the cylindrical body portion, a necking (necking) processing within a range where there is no obstacle for performing the second forming step, or the like may be appropriately performed with respect to the cup body 2.

Further, as required, the outer surface coating can be performed on the portion ranging from the cup outer peripheral bottom portion a to the inclined portion S with the lowermost end curvature portion of the cup body 2 as the center, in order to ensure the transportability and corrosion resistance after the first forming step.

In the second forming step, the seamless can body 1A is formed by processing the cup body 2 with a mold different from the mold used in the first forming step. That is, while the cup body 2 is brought into contact with the cup outer peripheral side holder 60 as a lower mold forming member, a pressing force is applied in the can outer direction (-Z axis direction) with respect to the cup dome portion D of the cup body 2 by using the dome pressing tool 70 as an upper mold forming member.

Alternatively, the pressing force may be applied in the + Z-axis direction by using the lower die molding member while the cup body 2 is brought into contact with the lower die molding member and the upper die molding member.

More specifically, as shown in fig. 5, the cup outer peripheral bottom portion a of the cup body 2 is placed on the cup outer peripheral side holder 60. The dome push-down tool 70 is relatively lowered, and the support portion 701 of the dome push-down tool 70 comes into contact with the cup dome portion D. Here, the cup outer peripheral side holder 60 has a tapered surface 601 and a groove 602, and after the cup outer peripheral bottom portion a of the cup body 2 comes into contact with the tapered surface 601, the dome push-down tool 70 is further pushed down, whereby the metal of the inclined portion S of the cup body 2 is guided and pushed into the groove 602 while receiving a compressive stress.

Then, the dome portion D is pushed down to have a second height Hp lower than the first height Ho. At the same time, the compression stress in the meridian direction is made by using the upper die forming member (dome pushing tool) and the lower die forming member (cup outer periphery side holder)

And compressive stress σ in the circumferential direction_θActs against the inclined portion S.

Fig. 6 is a schematic view showing a compressive stress applied when the inclined portion S is formed as the rising portion 202d in the present embodiment.

I.e. to be inclinedWhen the portion S is pushed into the groove 602 of the lower die-forming member, a compressive stress in the meridian direction is generated by the pushing force of the dome pushing tool 70

And a compressive stress sigma in the circumferential direction generated by moving radially inward to simulate the lower die-forming member_θSimultaneously acts on the inclined portion S, and the thickness of the metal material in the inclined portion S increases (in the sagittal direction σ in fig. 6)_ψ)。

Thus, the seamless can body 1A is obtained after the second forming step.

When the forming is completed, the dome pushing tool is relatively raised to take out the seamless can body 1A from the cup outer peripheral side holder.

Here, the seamless can body 1A obtained after the second forming step is preferably the seamless can body 1A in the present embodiment described above.

That is, as shown in fig. 1, the seamless can body 1A obtained after the second forming step preferably has an outer peripheral bottom portion 202a and a peripheral land portion 202b, and when the plate thickness of the outer peripheral bottom portion 202a is t1 and the plate thickness of the peripheral land portion 202b is t2, the relationship "t 2 > t 1" is satisfied.

Preferably, the second forming step further has the following features.

That is, preferably, in the second forming step, the inclined portion S is formed as a circumferential land portion 202b located inside the outer peripheral bottom portion 202a by pushing the cup body 2 into the cup outer peripheral side holder 60 in the second forming step; an inner end 202c located inside the peripheral ground portion 202 b; and a rising portion 202d rising upward from the inner end portion 202c and connected to the tank dome portion 201 d.

Preferably, in the second forming step, a ring groove is formed so that the outer end 201e protrudes outward from the can body axis RA such that the inner diameter (dx) of the connection point (outermost end 201e) between the rising portion 202d and the dome portion 201d of the seamless can body 1A is larger than the inner diameter (dy) of the inner end portion 202 c.

Conventionally, there is an improved forming method (bottom portion improving process) for forming the above-described ring groove using a rotating roll or a split die. However, in the conventional method, the processed portion is easily thinned, and it is difficult to form a sufficiently deep groove.

According to the method of the present invention, the thickness of the annular groove portion does not become thin, but rather tends to become thick, and a deep groove can be formed reasonably.

In the method of manufacturing a seamless can body according to the present embodiment, the shape and length of the upper portion of the cup outer peripheral bottom portion a of the cup body 2 are not changed between the first forming step and the second forming step.

That is, when the cup body 2 is placed on the cup outer peripheral side holder 60, the point at the lowest point in the Z-axis direction of the surface where the cup outer peripheral bottom a of the cup body 2 and the tapered surface 601 of the cup outer peripheral side holder 60 contact each other is set as the point T. The position of the point T does not change with the lowering of the dome pushing tool 70 and the pushing of the cup dome portion D. (refer to FIG. 5)

On the other hand, the portion of the inclined portion S of the cup 2 is formed into a portion of the outer peripheral bottom portion 202a of the seamless can body 1A, a peripheral land portion 202b, an inner end portion 202c, and an upright portion 202d by the second forming step. That is, the inclined portion S of the cup body 2 eventually enters the groove 602 of the cup outer peripheral side holder 60.

In addition, in this second forming process, there is no significant slip in the contact between the cup body 2 and the upper and lower metal molds. Therefore, the metal surface of the cup body 2 is not damaged, and it is needless to say that a lubricant is not used.

As shown in fig. 5, the point T becomes an inflection point IP in the seamless can body 1A. Since the second forming step applies a compressive stress, the metal length thereof becomes short as described below.

That is, the metal length from the inflection point IP to the outermost end 201e in FIG. 5(f) is shorter by about 0.85 to 0.99 times than the metal length from the point T to Se in FIG. 5 (b).

On the other hand, the thickness of the metal material in the portion is increased to 1.1 to 1.3 times the thickness (t0) of the raw material plate at the maximum in the portion where the thickness is increased by the second forming step.

Examples

The contents of the first embodiment of the present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

(example 1)

An extruded and ironed can (DI can) having an internal volume of 350mL was produced by the method described below.

First, as a raw material sheet, an aluminum alloy sheet (JIS H4000A 3104-H19 material, 0.28mm) was prepared. Subsequently, a predetermined amount of known cup oil was applied to both surfaces of the aluminum alloy sheet as a lubricant during extrusion.

Then, the aluminum alloy sheet was punched out into a disk shape having a diameter of 160mm by an extrusion molding machine, and immediately thereafter, was subjected to extrusion molding so as to be a cup (not shown) having a diameter of 90 mm.

The obtained extrusion cup was conveyed to a main body manufacturing machine (can body manufacturing machine), and after extrusion molding was performed again so as to obtain a shape having a diameter of 66mm, thinning was performed using a coolant so as to obtain a precursor 3 formed by extrusion thinning in a shape having a diameter of 66mm, a height of 130mm, and a minimum side wall thickness of 0.105 mm.

Next, the following first and second forming steps were performed on the precursor 3 obtained as described above to form a can bottom.

First, as a first forming step, the above-described body manufacturing machine performs a final stage of a stroke continuous with the ironing, and a cup 2 having a cup outer peripheral bottom portion a and an inclined portion S is formed using a punch 401, a clamp ring 501, and a dome die 502 shown in fig. 4. The length and plate thickness of the cup outer peripheral bottom a and the inclined portion S at this time are shown in table 1.

Next, as a second forming step, a dome pushing tool 70 as an upper die forming member and a cup outer peripheral side holder 60 as a lower die forming member shown in fig. 5 are used to push down the cup dome portion D and increase the thickness of the metal material in the inclined portion S, thereby forming the seamless can body 1A.

Subsequently, the plate thicknesses of the respective portions t1 to t5 were measured. The portions from t1 to t5 are the same as those in the above-described embodiment and fig. 2. The thickness measurement method for the thickness is as follows. That is, after the seamless can body 1A molded by embedding the epoxy resin therein, the epoxy resin is cut together along the longitudinal axis (Z axis) of the seamless can body 1A. After the center cross section was exposed by cutting and careful polishing, the thicknesses of the portions t1 to t5 were measured by a measuring sensible micromirror. The plate thicknesses of the respective portions are shown in table 1.

(example 2)

The same procedure as in example 1 was repeated, except that the thickness of the raw material plate was 0.225mm and the minimum thickness of the side wall of the precursor 3 was 0.093 mm. The thicknesses and the like of the respective portions of the obtained seamless can body are shown in table 1.

Comparative example 1

The can bottom forming process is carried out in 1 step by a known can bottom forming method using a known can bottom forming mold. Otherwise, the procedure was performed in the same manner as in example 1.

Fig. 7 shows a partially enlarged view of the bottom of the seamless can body used in comparative example 1.

The thicknesses and the like of the respective portions of the obtained seamless can body are shown in table 1. However, in table 1, the value of t3 is obtained by measuring the lower end of the inclined portion ((1) of fig. 7), and the value of t4 is obtained by measuring the upper end of the inclined portion ((2) of fig. 7).

Comparative example 2

The bottom modification was performed relative to the seamless can body obtained from comparative example 1. That is, the concave portion is formed in a circumferential shape by an inner peripheral wall of the land portion of the can bottom pressed by the rotating roller, the inner peripheral wall being positioned on the inner side in the radial direction orthogonal to the can body axis. Otherwise, the same procedure as in comparative example was carried out. The thicknesses and the like of the respective portions of the obtained seamless can body are shown in table 1.

Comparative example 3

The same procedure as in comparative example 2 was repeated, except that the thickness of the raw material plate was 0.225mm and the minimum thickness of the side wall was 0.093 mm. The thicknesses and the like of the respective portions of the obtained seamless can body are shown in table 1.

[ evaluation ]

The DI cans obtained by the above-described method were evaluated by the following method. The results are shown in table 1.

[ method of testing pressure resistance ]

In a state where the cup is filled with water, the open end is sealed by a plug provided with a water supply pipe. Then, pressurized water is fed from a water feed pump into the cup through a water feed pipe. When the internal pressure of the cup rises, the dome portion instantaneously deforms (warps) so as to invert outward at a certain timing. Normally, the internal pressure of the can drops sharply along with this deformation. The maximum value of the internal pressure of the tank during this process was defined as the pressure resistance (MPa).

[ Table 1]

The results of the examples and comparative examples show the following: by controlling the thickness of a specific part of the can bottom, even when the thickness of the raw material plate (blank) is reduced, good pressure resistance (0.618 MPa or more required for carbonated beverage applications) can be obtained.

[ second embodiment ]

As described above, although conventional seamless can bodies are excellent in lightweight properties, there has been a place to be improved in the can body portion serving as the side surface thereof. In recent years, various designs have been applied to the can body to ensure commodity competitiveness, and in this respect, the can body is required to have a uniform image quality as much as possible.

However, in the conventional method for producing a seamless can body, the surface state of the can body after forming does not match in the axial direction, and a high metallic luster cannot be obtained particularly in the vicinity of the lower end of the can body or in the reduced diameter portion (outer peripheral bottom portion) existing between the can body and the can bottom.

This point will be described in detail with reference to fig. 14.

Fig. 14(a) schematically shows a state of portions of the can body and the front end portion of the ironing punch immediately after the ironing process. As shown in the drawing, a tapered shape is provided from point a to point B in the vicinity of the tip in the cylindrical portion of the punch. This taper is provided to gradually increase the reduction ratio at the start of the thinning process. Therefore, the can body portion corresponding to the tapered portion becomes a region having a plate thickness distribution in a wedge shape. As also shown in fig. 9 and the like, this region is also sometimes referred to as a "Body Wall Step (BWS)". Further, a portion, which is also called a Body Wall Radius (BWR) that is relatively reduced in diameter toward the inside of the tank, is formed on the lower side of the BWS.

In addition, when the above-mentioned ironing is performed, the glossiness of the ironed surface is substantially equal to the original raw material surface at the point B located at the lower end of the BWS, and increases as the point a located at the upper end of the BWS approaches, and becomes maximum after the point a.

Fig. 14(b) is a view showing a state of the can body and the front end portion of the ironing punch at a time when the dome die is relatively inserted into the front end of the ironing punch after the ironing process is completed and the dome portion is formed at the can bottom. The bottom surface of the can bottom is a dome, and in fig. 14(a), the portion located at point a is shifted toward point a 'and the portion located at point B is shifted toward point B' by drawing. The amount of movement (offset amount) of each of these dots is, for example, about 2 to 5 mm. As described above, a portion having low gloss and poor printing vividness still exists in the vicinity of the lowermost portion of the cylindrical portion in the can body, but a seamless can body having high design property with high metallic gloss has been required in the past.

Further, the amount of offset can be increased by simply increasing the amount of the dome die to be retracted, but the following problems remain: resulting in a significant reduction in the internal volume of the formed can while the amount of can material usage is increased.

Accordingly, in the second embodiment described below, intensive studies have been made in view of the above-described problems as examples, and as a result, it is possible to provide a seamless can body which can impart excellent image quality to a can body after extrusion ironing, and a method for manufacturing the seamless can body. In addition, in the second embodiment, a seamless can body having a high metallic luster at a reduced diameter portion (outer peripheral bottom portion) existing between the can main body portion and the can bottom portion, and a method for manufacturing the same can be provided.

In the following, the same elements as those in the seamless can body 1A of the first embodiment described above are given the same reference numerals, and the description thereof will be omitted as appropriate.

< seamless Can body 1B >

As shown in fig. 8, the seamless can body 1B of the present embodiment is a seamless can body having a cylindrical body 10 and a can bottom 20, and the can bottom 20 includes at least an outer peripheral bottom 20a which is continuous so as to be radially reduced inward from a lower end of the cylindrical body 10 through a boundary portion BP. In the drawings, the neck and flange shapes are drawn as an example above the cylindrical body portion 10, but a known seamless can body structure having an opening 10a above the cylindrical body portion 10 can be used. Here, the "lower end 10e of the cylindrical body portion 10" in the present embodiment refers to a portion substantially located at the lower end of the cylindrical surface, and when printing is performed on the outer surface of a seamless can body, it can be defined as, for example, the lower end in an area where curved surface printing by a known dry offset printing method is possible.

The cylindrical body portion 10 is a portion constituting a side surface of the seamless can body 1B, and is formed by performing extrusion ironing on a known metal plate such as aluminum or steel, which will be described later. The cylindrical body 10 has a width according to the application, but is configured to have a thickness of approximately 0.07 to 0.40mm, for example.

The cylindrical body portion 10 in the present embodiment has a lower end 10e, which will be described later, as a lower end, and an upper end defined as a boundary with a neck shoulder (a portion that decreases in diameter as it goes toward the axial direction) as shown in fig. 8.

As shown in fig. 8, the can bottom 20 includes at least an outer peripheral bottom 20a continuing to decrease in diameter from the lower end 10e of the cylindrical body 10 to the inside, and a bulging portion 20b bulging from the outer peripheral bottom 20a toward the opening 10 a.

As is clear from fig. 8, the outer peripheral bottom portion 20a and the expanded portion 20B in the present embodiment are divided by a peripheral grounding portion 20c which is grounded when the seamless can body 1B is placed on a flat surface such as a table. Therefore, the outer peripheral bottom portion 20a, the peripheral land portion 20c, and the expanded portion 20b in the present embodiment can be said to correspond to the leg portion 202 and the can bottom center portion 201 in the first embodiment described above. In this case, the peripheral land portion 20c of the present embodiment corresponds to the peripheral land portion 202b of the first embodiment.

The "boundary portion BP" in the present embodiment is a boundary of a region related to the appearance of the can bottom side (i.e., normally visible from the outside of the can), and is a portion bent from the lower end 10e of the cylindrical body 10 and continuing to the outer peripheral bottom portion 20a as shown in fig. 17, and is defined as a point at which an angle γ formed by a tangent line of the outer surface at the boundary portion BP and the ground contact surface P becomes 45 °.

The reason why the point at which the angle γ becomes 45 ° is defined as the boundary BP in the present embodiment is as follows. That is, at a position where γ is smaller than 45 °, the normal line of the outer surface is too downward. Therefore, for example, in a state where the can to which the present invention is applied is normally placed on a display rack or the like (upright), since reflected light is less likely to enter the field of view, excellent glossiness of the can outer surface, which is the gist of the present invention, is less likely to be exhibited.

In addition, as shown in fig. 9(a), in the conventional structure, the thin portion of the cylindrical body portion is drawn into the lower portion by a very small amount when the dome portion is formed, and therefore, the vicinity of the boundary portion BP is a portion having a thickness.

In contrast, in the seamless can body 1B of the present embodiment, as shown in fig. 9(B), a part of the lower end side of the cylindrical body portion 10 including the lower end 10e of the thinned cylindrical body portion 10 is drawn in toward the outer peripheral bottom portion 20a, and therefore, the thinned metal plate is formed so as to extend beyond the boundary portion BP to at least the vicinity of the boundary portion BP in the outer peripheral bottom portion 20 a.

In other words, in the seamless can body 1B of the present embodiment, it can be said that the plate thickness t0 at least at the boundary portion BP and the plate thickness t at the intermediate portion of the cylindrical body portion 10_WC(see fig. 8) are substantially equal.

Therefore, the tubular main body portion 10 of the present embodiment has a higher glossiness in the axial direction (Z direction in fig. 8) from the upper end to the lower end and further to the position of the boundary portion BP than the conventional structure, and can exhibit a uniform image quality. The reduction ratio at which the cylindrical body portion 10 subjected to the reduction processing has a high glossiness is not limited to this, since it varies depending on the characteristics of the material used and the processing conditions, but it is preferable that the total reduction ratio is at least 60% or more, as an example.

In the present embodiment, as shown in fig. 8, the thickness of the cylindrical body 10 in the vicinity of the boundary BP (e.g., the lower end of the cylindrical body 10) is defined as t_WLThe thickness of the intermediate portion of the cylindrical body 10 in the axial direction (Z direction) is defined as t_WCIn the case of (1), it is desirable to be at t_WC≦t_WL＜1.09×t_WCMore preferably, t is_WC≦t_WL＜1.05×t_WCThe relationship (2) of (c). This improves the visibility of the can side surface and maintains the pressure resistance of the seamless can body 1B. In the present embodiment, the "intermediate portion in the axial direction of the cylindrical body portion 10" does not strictly need to have a plate thickness in the above-described intermediate portion in the axial direction, and can be defined as a plate thickness including the vicinity of the intermediate portion.

Further, in the present embodiment, as also shown in fig. 8, the thickness of the intermediate portion in the axial direction of the tubular body portion 10 is defined as t_WCIn the case of (1), it is desirable to be at t_WC≦t0＜1.09×t_WCMore preferably, t is_WC≦t0＜1.05×t_WCThe relationship (2) of (c). If t0 is less than t_WCThere is a possibility that the strength of the axial load at this portion may be reduced, and if t0 is t_WC1.09 times or more, the glossiness in the lower end portion of the cylindrical body portion is lowered, and the effect of the present invention is hardly obtainedSuch a problem is caused.

This improves the visibility of the can side surface and maintains the pressure resistance of the seamless can body 1B.

Further, since the thinned metal plate reaches at least a part of the outer peripheral bottom portion 20a beyond the boundary portion BP, it is desirable that the 60-degree specular gloss be 300% or more from the lower end 10e of the cylindrical body portion 10 to the vicinity of the boundary portion BP. If the 60-degree specular gloss in the vicinity of the boundary BP is less than 300%, the surface is visually perceived as rough or dull, which causes a problem of a reduction in the appeal as a product.

The specular gloss in the present embodiment is measured by the measurement method specified in JIS Z8741-1997.

In the present embodiment, the kind of the metal material used for the seamless can body 1B is not particularly limited. That is, a known metal plate generally used for a seamless can body, for example, an aluminum alloy plate, a steel plate (for example, a tin-plated plate, etc.), can be used. The metal plate may be coated with a known thin film on the inner surface side, coated with an organic resin, chemically synthesized, or the like, as appropriate.

The seamless can body 1B of the present embodiment may be subjected to, for example, known flange processing, necking processing, screw processing, etc., and after containing beer, carbonated beverage, coffee, juice, flowable food, etc. as contents, the lid may be attached to the opening 10a by a known method.

< method for manufacturing seamless Can body 1B >

Next, a method for producing the seamless can body 1B according to the present embodiment will be described with reference to fig. 10 to 12.

The method for producing a seamless can body 1B according to the present embodiment is a method for producing a seamless can body having a cylindrical body 10 and a can bottom 20 as shown in fig. 8, and is characterized by including a first forming step and a second forming step described in detail below.

[ first Forming Process ]

In the method for manufacturing a seamless can body 1B according to the present embodiment, as shown in the first forming step shown in fig. 10, a metal material (precursor 3) is formed into a cup body 2, and the cup body 2 has a cylindrical body portion 10; an inclined portion S extending upward inward from a boundary portion BP at the lower end of the tubular body portion 10; and a dome portion D bulging upward from an end Se of the inclined portion S at a first height Ho. Here, the end Se of the inclined portion S may also be referred to as a connection point with the cup dome portion D.

The first forming step of the present embodiment is performed using an upper die and a lower die, as opposed to the precursor 3 in which the cylindrical body portion 10 thinned by thinning is formed by a known press step or the like. That is, the first forming step of the present embodiment may be performed at the end position (near the bottom dead center) of the punch stroke of the forming machine that performs the ironing, or may be performed in a machine different from the machine that performs the ironing.

As a specific example, as shown in fig. 10, the first forming step is performed by a cylindrical punch 401 that is positioned in and supports the precursor 3 having a cup shape, and a dome die 502 that supports the outer peripheral bottom portion of the precursor 3 in cooperation with the punch 401. The lower end of the punch 401 is formed into a concave shape protruding upward corresponding to the dome die 502, and a peripheral wall portion 402 is formed along the circumferential direction. In fig. 10 of the present embodiment, a single circular arc shape is illustrated as a cross-sectional shape of the peripheral wall portion 402, but the present invention is not limited to this shape, and a combination of a plurality of circular arcs and tapered surfaces may be used as shown in fig. 15 or 16, for example.

First, if the pressing is performed so that the precursor 3 is sandwiched between the punch 401 and the dome die 502, the bottom surface of the precursor 3 is bulged toward the opening portion by the dome die 502, and the lower end peripheral edge is stretched by the peripheral wall portion 402. In other words, in the first forming step, the outer periphery of the precursor 3 is supported by the peripheral wall portion 402 of the punch 401, and the punch 401 and the dome die 502 are driven to engage with each other, whereby the cup 2 having the dome portion D with the first height Ho at the bottom can be obtained.

In the first forming step, when wrinkles are generated in the peripheral wall portion 402 and the vicinity thereof in forming the dome portion D, the wrinkle suppressing member 80 (also referred to as a clamp ring) illustrated in fig. 16 may be provided as needed, and the wrinkle suppressing member 80 and the peripheral wall portion 402 may be formed with a wrinkle suppressing force.

In this case, the materials of the cupola portion D, the end portion Se, and the inclined portion S need to be added together by the subsequent second forming step to set the first height Ho of the cupola portion so that the can bottom 20 in fig. 8 can be formed. Accordingly, the first height Ho in the present embodiment is higher than the dome height of the conventional structure, and therefore, the amount of drawing the cylindrical body 10 toward the outer peripheral bottom portion 20a is also increased accordingly.

Thus, as shown in fig. 11, during the thinning process, if it is the original, the portion constituting the lower end of the cylindrical body 10 is drawn into the outer peripheral bottom portion 20a side beyond the boundary BP between the cylindrical body 10 and the outer peripheral bottom portion 20a (more specifically, in the example shown in fig. 11, the point a and the point B located in the cylindrical body are drawn beyond the boundary BP, respectively). In other words, in this first forming step, the lower end 10e of the tubular body 10 is drawn in, and the diameter of the lower end 10e of the tubular body 10 is reduced, thereby forming a part of the continuous outer peripheral bottom portion 20a (the vicinity of the boundary BP is substantially curved, and this is referred to as a first outer peripheral bottom portion 20 a').

Here, the shape of the cup 2 obtained in the first forming step will be described.

The inclined portion S in the cup body 2 is configured to extend upward toward the inside from the first peripheral bottom portion 20 a'. That is, as shown in fig. 10 c and the like, the inclined portion S of the cup body 2 is a curved portion and a straight portion sandwiched between a lowest portion of the cup body 2 in the Z-axis direction and a connection point (end portion Se) with the dome portion D.

In the first forming step, the inclined portion S and the dome portion D are also referred to as a bulging portion. Therefore, the cup body 2 of the present embodiment may be said to include the cylindrical body portion 10 and the bulging portion formed on the bottom surface of the cylindrical body portion 10.

The shape of the cup dome portion D is an example, and the tip of the dome may be formed into a horizontal plane shape, for example, instead of a curved surface.

Further, the first height Ho of the dome portion D in the cup body 2 is preferably larger than the second height Hp of the dome portion 201D in the seamless can body 1B obtained in the second forming step. One of the reasons for this is that, in the second forming step described later, compressive stress is applied to the inclined portion S while the dome portion D of the cup body 2 is pushed down. That is, this is because the first height Ho of the dome portion D in the cup body 2 is increased in advance, and finally the second height Hp of the can dome portion 201D is obtained favorably in the seamless can body 1B.

That is, in this first forming step, a bulging portion bulging from the first outer peripheral bottom portion 20 a' in the vicinity of the boundary portion BP toward the opening 10a at a first height Ho is first formed, and in a second forming step described later, the bulging portion is pushed down so as to be at a second height lower than the first height Ho.

[ second Molding Process ]

Next, a second forming step in the method for producing a seamless can body 1B according to the present embodiment will be described with reference to fig. 12.

After the cup body 2 having the first outer peripheral bottom portion 20 a' and the inclined portion S is formed by the first forming step, the following second forming step is performed.

Further, between the first forming step and the second forming step, a known cleaning step, a surface treatment step, a printing step, a painting step, a processing of giving a shape to the cylindrical body portion, a necking (necking) processing in a range where there is no obstacle for performing the second forming step, and the like may be appropriately performed with respect to the cup body 2. Further, as necessary, the portion ranging from the grounding portion at the lowermost end of the cup body 2 to the inclined portion S can be externally coated for the purpose of securing the transportability and the corrosion resistance after the first forming step.

In the second forming step, the seamless can body 1B is formed by performing processing on the cup body 2 with a mold different from the mold used in the first forming step. That is, as shown in fig. 12, while the cup body 2 is brought into contact with the lower die molding member, the upper die molding member is used to apply a pressing force in the can outside direction (-Z axis direction) against the cup dome portion D of the cup body 2.

More specifically, as shown in fig. 12(a), the vicinity of the boundary BP of the cup body 2 is placed on the cup outer circumferential side holder 60. Next, the dome pushing tool 70 is relatively lowered, and the support part 701 of the dome pushing tool 70 contacts the cup dome part D as shown in fig. 12 (b). In fig. 12, the shape of the support part 701 is drawn to be substantially identical to the shape of the cup dome portion D, but for example, it is not always necessary to make the shapes identical to each other such that a difference in curvature is provided so as to strongly press the outer peripheral portion of the cup dome portion D.

Here, the cup outer peripheral side holder 60 has a tapered surface 601 and a groove 602, and after the boundary portion BP of the cup body 2 and the first outer peripheral bottom portion 20 a' come into contact with the tapered surface 601, the dome pushing tool 70 is further pushed down. As a result, as shown in fig. 12(c), the metal of the inclined portion S of the cup body 2 is molded to follow the tapered surface 601 while receiving a compressive stress.

Next, as shown in fig. 12(d), the dome lowering tool 70 is further lowered, whereby the remaining portion (portion other than metal imitating the tapered surface 601) of the inclined portion S of the cup body 2 is guided into the groove 602. At this time, the dome portion D is pushed down to have a second height Hp lower than the first height Ho. Meanwhile, similarly to the above-described first embodiment, the compression stress in the meridian direction is applied by using the upper die forming member (dome pushing tool) and the lower die forming member (cup outer peripheral side holder)

And compressive stress σ in the circumferential direction_θActs on the inclined portion S (see fig. 6).

Thus, the metal imitating the tapered surface 601 in the cup body 2 forms the outer peripheral bottom portion 20a, the metal guided into the groove 602 forms the above-described peripheral land portion 20c, and further forms the bulging portion 20b from the peripheral land portion 20c to the upper side (see fig. 12 (e)).

Thus, the can bottom 20 of the seamless can body 1B is obtained after the second forming step.

When the forming is completed, as shown in fig. 12(e), the dome pushing tool is relatively raised to take out the seamless can body 1B from the cup outer peripheral side holder.

The seamless can body 1B formed by the manufacturing method of the present embodiment described above can exhibit excellent appearance and image quality by forming the cylindrical body portion 10, which is the side surface of the can, in a substantially uniform surface state from the upper end to the lower end in the axial direction thereof.

The second embodiment described above is substantially the same as the first embodiment except for the bottom of the can (mainly, the shape of the dome portion of the can bottom). Therefore, it goes without saying that the technical ideas relating to the relationship between the thicknesses of the respective plates and the technical ideas relating to the metallic luster of the can body and the can bottom in the present embodiment can be applied in common to both the first embodiment as long as no contradiction occurs.

Conversely, the seamless can body 1B formed by the manufacturing method of the present embodiment can also exhibit the same effects as those of the first embodiment by incorporating the features of the first embodiment (the inner end 202c, the rising portion 202d, the outermost end 201e, and the dome portion 201 d).

By thus applying the dome shape of the seamless can body 1A of the first embodiment to the seamless can body 1B of the second embodiment and integrating fig. 1 and its description with fig. 13, it is possible to realize a seamless can body and a method for manufacturing the same, which can impart excellent image quality to the can body after the ironing while imparting high pressure resistance to the seamless can body of the present invention.

In addition, since the plate thickness of the leg portion 202 in fig. 13 changes from the boundary portion BP (see fig. 8) toward the circumferential land portion 202b, as is clear from fig. 1, 8, 11, and the like, the portion having the thickness t1 moves toward the circumferential land portion 202b side than the position of the plate thickness t0 at the above-described boundary portion BP. In this case, it is preferable that the plates are provided separatelyThickness t0 < plate thickness t1, t shown in the second embodiment_WC≦t_WL＜1.09×t_WCCharacteristic of (1), t_WC≦t0＜1.09×t_WCFurther, the 60-degree specular gloss is 300% or more from the lower end 10e of the cylindrical body 10 to the vicinity of the boundary BP.

As described above, the seamless can body of the present invention can have the features of both the first and second embodiments described above, and the cylindrical body portion 10 serving as the side surface of the can have a substantially uniform surface state from the upper end to the lower end in the axial direction thereof, and can exhibit excellent appearance and image quality and can realize excellent pressure resistance at the bottom of the can.

Here, the seamless can body 1B described in the second embodiment is advantageous at least in terms of glossiness compared to the conventional structure, and this can be described again with reference to fig. 14.

Here, fig. 14(a) shows a structure in the vicinity of the lower end of the can body portion in the seamless can body immediately after the ironing by the conventional manufacturing method, and fig. 14(b) shows a structure in the vicinity of the lower end of the can body portion after the further dome forming. On the other hand, fig. 14(c) shows a structure of the seamless can body 1B of the present embodiment in the vicinity of the lower end of the can body portion.

In fig. 14(c), the plate thickness t at the lower end of the cylindrical body 10_WLA plate thickness t from an intermediate portion of the cylindrical body portion in the axial direction_WCHowever, the present invention is not limited to this embodiment, and t may be t as described above_WL＜1.09×t_WC。

That is, when ironing is performed for forming a seamless can body, first, as described above, in fig. 14(a) of the conventional method, ironing is started at the ironing rate 0 at the point B, and the ironing rate gradually increases as it approaches the point a, and becomes maximum after the point a. Therefore, for example, the gloss of the ironed surface of the can body portion is substantially equal to the gloss of the original material surface at point B, and gradually increases as it approaches point a, and becomes maximum after point a.

Fig. 14(b) shows a state in which after the ironing process, the dome die is relatively inserted into the front end of the ironing punch, and a dome portion is formed at the bottom of the can. Thus, a part of the tank bottom is in a shape of being drawn into the dome portion, and the portion originally located at the point a is shifted toward the point a ', and the portion originally located at the point B is shifted toward the point B'. The offset amount of each part in the above-described conventional method is, for example, about 2 to 5 mm. Therefore, a portion having low glossiness and poor printing sharpness remains in the lowermost portion of the cylindrical portion of the can body.

On the other hand, in the seamless can body 1B of the present embodiment, as is clear from fig. 14(c) and the like, the metal plate after the ironing reaches at least a part of the outer peripheral bottom portion beyond the boundary portion BP, and the glossiness in the vicinity of the boundary portion BP is equal to that of the can body portion. Thus, the can body portion can have high glossiness from the upper end to the lower end in the axial direction.

The first and second embodiments described above are examples embodying the gist of the present invention, and appropriate modifications may be made without departing from the scope of the invention. Further, a known structure may be added to the seamless can bodies described in the first and second embodiments without departing from the scope of the present invention.

Industrial applicability of the invention

According to the present invention, the buckling phenomenon can be suppressed by improving the pressure resistance while reducing the thickness of the raw material plate (blank) of the seamless can body. Therefore, the manufacturing cost of the seamless can body, the cost spent for transportation, and the like can be reduced. Further, since fuel and the like required for production and transportation can be reduced, production of seamless can bodies in consideration of environmental protection can be realized.

Further, the present invention can be applied to a container required to have improved appearance and image quality, and can be used particularly for a can body capable of storing a liquid such as a beverage or a medicine.

Description of the symbols

1A, 1B: seamless can body

2: cup body

3: precursor body

10: cylindrical body part

10 e: lower end

20: tank bottom

20 a: peripheral bottom

20 a': first peripheral bottom

20 b: bulge part

201: bottom center

201 d: can dome

201 e: outermost end

202: foot part

202 a: peripheral bottom

202 b: peripheral ground part

202 c: inner end

202 d: rising part

A: bottom of cup periphery

D: cup dome

S: inclined part

Se: end part

Hp: height of the pot dome (second height)

Ho: height of cup dome (first height)

60: lower mold forming part (cup peripheral side holder)

70: the upper die forms the part (dome push down tool).

Claims

1. A seamless can body having a cylindrical main body part and a can bottom part,

the tank bottom portion includes an outer peripheral bottom portion continuing to decrease in diameter from a lower end of the cylindrical body portion inward, and a peripheral land portion located inward of the outer peripheral bottom portion,

when the thickness of the outer peripheral bottom portion is t1 and the thickness of the peripheral land portion is t2, t2 > t 1.

2. A seamless can body is characterized in that,

comprises a cylindrical main body and a can bottom, the can bottom having at least an outer peripheral bottom portion which is continuous so as to be reduced in diameter from a lower end of the cylindrical main body to an inner side through a boundary portion,

the plate thickness of the lower end of the cylindrical body portion is substantially equal to the plate thickness of the intermediate portion of the cylindrical body portion in the axial direction.

3. Seamless can body according to claim 1 or 2,

the tank bottom further includes an inner end located inside the peripheral ground portion,

when the thickness of the inner end is t3, t3 > t 1.

4. The seamless can body according to claim 3, wherein a plate thickness gradually increases from the outer peripheral bottom portion to the inner end portion so as to be t3 > t 2.

5. The seamless can body according to any one of claims 1 to 4,

the tank bottom further includes a rising portion rising upward from the inner end,

when the plate thickness at the upper end of the rising portion is t4, t4 > t 1.

6. The seamless can body of claim 5,

the tank bottom further includes a dome portion bulging to protrude upward continuously from the rising portion, and the plate thickness gradually increases from the dome portion to the inner end so as to be t3 > t4 > t5 when the plate thickness at the center of the dome portion is t 5.

7. The seamless can body of claim 6, further wherein t5 < t 1.

8. The seamless can body according to any one of claims 5 to 7,

an annular groove is formed outward of the can body axis, and a connecting portion between the rising portion and the dome portion is convex.

9. The seamless can body of claim 2,

the thickness of the boundary portion is substantially equal to the thickness of the intermediate portion.

10. Seamless can body according to claim 2 or 9,

the thickness of the cylindrical body at the lower end is defined as t_WLThe thickness of the intermediate portion of the cylindrical body in the axial direction is defined as t_WCIn the case of (1), at t_WC≦t_WL＜1.09×t_WCThe relationship (2) of (c).

11. The seamless can body of claim 10,

at t in the cylindrical body part_WC≦t0＜1.09×t_WCWherein t0 is the plate thickness of the boundary portion.

12. The seamless can body according to any one of claims 1 to 11,

the 60-degree specular gloss is 300% or more from the lower end of the cylindrical body to the vicinity of the boundary.

13. A method for producing a seamless can body having a cylindrical body portion and a can bottom portion, characterized by comprising a first forming step and a second forming step,

a first forming step of forming a metal material into a cup body having a cylindrical body portion; a cup outer peripheral bottom portion which is continuous so as to be reduced in diameter from a lower end of the cylindrical body portion; an inclined portion extending upward from the bottom of the outer periphery of the cup toward the inside; and a cup dome portion bulging upward at a first height from an end portion of the inclined portion,

in the second molding step, a pressing force is applied from the dome portion toward the outside of the can by the upper mold molding member while the bottom portion of the cup outer periphery of the cup body is brought into contact with the lower mold molding member, the dome portion is pushed down so as to have a second height lower than the first height, and the inclined portion is pushed in while increasing the thickness thereof by applying compressive stress in the meridian direction and the circumferential direction to the inclined portion.

14. The method of making a seamless can body according to claim 13,

in the second forming step described above, the first forming step,

forming a peripheral land portion located inside the outer peripheral bottom portion by pushing the inclined portion into the lower mold forming member; an inner end portion located inside the peripheral ground portion; and a rising part rising upward from the inner end part and connected to the tank dome part,

an annular groove is formed in the tank body so as to protrude outward of the tank body axis so that an inner diameter of a connecting portion between the rising portion and the tank dome portion becomes larger than an inner diameter of the inner end portion.

15. A method for manufacturing a seamless can body, comprising a first forming step and a second forming step,

a first forming step of forming a metal material into a cup body having a cylindrical body portion thinned by ironing; an outer peripheral bottom portion continuous from a lower end of the cylindrical body portion; and a bulging portion bulging from the outer peripheral bottom portion toward the opening portion at a first height,

the second forming step of pushing down the bulging portion so as to have a second height lower than the first height,

in the first forming step, the lower end of the cylindrical body portion is drawn in such a manner that the plate thickness of the lower end of the cylindrical body portion is substantially equal to the plate thickness of the intermediate portion of the cylindrical body portion in the axial direction, and the continuous outer peripheral bottom portion is formed so as to be reduced in diameter from the lower end of the cylindrical body portion inward via the boundary portion.