TWI840492B - Seamless tank body and method for manufacturing seamless tank body - Google Patents

Abstract

The present invention provides a seamless can body and a manufacturing method thereof, which makes the plate thickness of the blank plate (rough) thinner, improves the pressure resistance of the can bottom and suppresses buckling, and also solves the problem of blackening or washing. A seamless can body 1, characterized in that: it has a cylindrical main body 10 and a can bottom 20, the can bottom 20 includes an outer peripheral bottom 202a that is continuous in a manner of reducing the diameter from the lower end of the cylindrical main body 10 to the inside, and a peripheral grounding part 202b located further inward than the outer peripheral bottom 202a, when the plate thickness of the outer peripheral bottom 202a is set to t1 and the plate thickness of the peripheral grounding part 202b is set to t2, t2>t1.

Description

Seamless tank body and method for manufacturing seamless tank body

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

As is known, a so-called seamless can body is known, in which the main body of the can is formed by a drawing and shrinking process. Since the main body of the can is thinned by a shrinking process (ironing), the seamless can body is excellent in lightness. On the other hand, it is difficult to adopt a forced thinning process such as a shrinking process on the bottom of such a seamless can body, and the thickness of the bottom of the can body does not change much relative to the thickness of the raw material. Since the bottom seeks strength (pressure resistance) to resist deformation caused by the internal pressure of the can, the thickness of the raw material is also thinned at the bottom of the can body in order to achieve lightweight, and various proposals for maintaining or improving pressure resistance include the following patent documents compared with the known knowledge.

For example, Patent Document 1 or Patent Document 2 discloses a bottom improvement process for the purpose of preventing the dome of the bottom of a tank from inverting (buckling) when the internal pressure of the tank exceeds the pressure resistance strength. Specifically, the bottom improvement process is disclosed in which a concave portion is formed by pressing the inner peripheral wall of the grounding portion of the tank bottom located on the inner side of the radial direction perpendicular to the tank axis. [Prior Technical Document] [Patent Document]

[Patent Document 1] Japanese Patent Publication No. 2018-103227 [Patent Document 2] Japanese Patent Publication No. 2016-47541 [Patent Document 3] Japanese Patent Publication No. 2000-176575 [Patent Document 4] Japanese Patent Publication No. 9-285832 [Patent Document 5] WO2018/070542 [Patent Document 6] Japanese Patent Publication No. 2016-43991

[The problem the invention is trying to solve]

However, the bottom improvement process has the following problems. That is, the bottom improvement step forms a concave portion by pressing the inner peripheral wall of the tank bottom using a forming roller or the like. When pressing using a forming roller or the like, as described in Patent Document 3, there are problems such as blackening of the pressed portion or metal material adhesion to the forming roller. Also, during pressing, lubricating oil is applied for smooth processing, but since it is necessary to wash the lubricating oil after the bottom improvement process, further improvements are sought from the perspective of the cost required for washing and the environmental load.

Recently, in order to achieve a seamless and lightweight tank body, the thickness of the blank plate (blank) before the drawing and shrinking process is sought to be thinner. However, when the above-mentioned bottom improvement process is implemented, the thickness of the metal material of the above-mentioned pressing part is stretched and thinned by the process, so the thickness of the blank plate (blank) is limited.

As shown in Patent Document 4, the inventors disclosed a technique for improving the pressure resistance of a seamless can body. However, according to this technique, although the pressure resistance is improved, the thickness distribution of each part of the can body (especially the bottom of the can) is not fully optimized. Therefore, the lightweight requirement of the can body is not fully met.

Furthermore, Patent Document 5 shows a two-piece can body characterized in that the thickness of the grounding portion of the can bottom is thicker than the thickness of the raw material before processing. However, this technology has problems such as complicated equipment, difficulty in achieving industrial standards, or high equipment costs.

The inventor of the present invention has repeatedly conducted intensive research on the above-mentioned exemplified topics. As a result, a seamless can body and its manufacturing method can be provided in a simpler manufacturing device, which makes the thickness of the blank plate (rough) thinner, while improving the pressure resistance of the can bottom and suppressing buckling, and also solves the above-mentioned blackening or washing problems, thereby completing the present invention. [Technical means to solve the problem]

In order to achieve the above-mentioned purpose, the seamless can body in one embodiment of the present invention is (1) a seamless can body having a cylindrical main body and a can bottom, and its characteristic is that: the above-mentioned can bottom includes an outer peripheral bottom that is continuous in a manner of tapering inward from the lower end of the above-mentioned cylindrical main body, and a peripheral grounding portion located further inward than the above-mentioned outer peripheral bottom, and when the plate thickness of the above-mentioned outer peripheral bottom is set to t1 and the plate thickness of the peripheral grounding portion is set to t2, t2＞t1.

Furthermore, in order to achieve the above-mentioned purpose, the seamless can body in one embodiment of the present invention is (2) characterized in that it includes a cylindrical main body portion and at least a can bottom portion having an outer peripheral bottom portion that is continuous in a manner of tapering from the lower end of the above-mentioned cylindrical main body portion through the junction portion inward, and the plate thickness of the lower end of the above-mentioned cylindrical main body portion is approximately equal to the plate thickness of the middle portion in the axial direction of the above-mentioned cylindrical main body portion.

Furthermore, in the above (1) or (2), (3) is preferably that the above-mentioned tank bottom further includes an inner end portion 202c located further inward than the above-mentioned circumferential grounding portion, and when the plate thickness of the above-mentioned inner end portion is set to t3, t3＞t1.

Furthermore, in the above (3), (4) is preferably such that t3>t2, and the plate thickness gradually increases from the above outer peripheral bottom to the above inner side end.

Furthermore, in any one of the above (1) to (4), (5) is preferably that the above-mentioned tank bottom further includes a rising portion 202d rising upward from the above-mentioned inner end portion, and when the plate thickness of the upper end of the above-mentioned rising portion is set to t4, t4＞t1.

Furthermore, in the above (5), (6) is preferably that the above-mentioned tank bottom further includes a tank dome portion that bulges upward in a manner continuous with the above-mentioned rising portion, and when the plate thickness in the center of the above-mentioned tank dome portion is set to t5, the plate thickness gradually increases from the above-mentioned tank dome portion to the above-mentioned inner end portion in the manner of t3>t4>t5.

Furthermore, in the above (6), (7) is preferably such that t5＜t1.

In any one of the above (5) to (7), (8) is preferably an annular groove protruding from the connecting portion between the above-mentioned rising portion and the above-mentioned dome portion, which is formed toward the outside of the can body axis.

Furthermore, in the above (2), (9) it is preferred that the plate thickness of the boundary portion is substantially equal to the plate thickness of the middle portion.

In the above (2) or (9), (10) is preferably such that, when the plate thickness from the lower end of the cylindrical body is t _WL and the plate thickness of the middle portion in the axial direction of the cylindrical body is t _WC , the relationship t _WC ≦t _WL <1.09×t _WC is satisfied.

Furthermore, in the above (10), (11) is preferably such that in the above-mentioned cylindrical main body portion, the relationship of t _WC ≦t0<1.09×t _WC is satisfied (where t0 is the plate thickness of the above-mentioned boundary portion).

Furthermore, in the above (1) to (11), (12) is preferably that the glossiness of the 60-degree mirror surface from the lower end of the above-mentioned cylindrical main body to the vicinity of the above-mentioned boundary portion is 300% or more.

In order to achieve the above-mentioned purpose, a method for manufacturing a seamless can body in one embodiment of the present invention is (13) a method for manufacturing a seamless can body having a cylindrical main body and a can bottom, which is characterized by comprising: a first forming step, in which a metal raw material is formed into a cup body, the cup body having a cylindrical main body, a cup-shaped outer peripheral bottom that is continuous in a manner of tapering from the lower end of the above-mentioned cylindrical main body, an inclined portion extending from the above-mentioned cup-shaped outer peripheral bottom toward the inner side and upward, and a portion extending from the end of the above-mentioned inclined portion toward the upper side. The cup-shaped dome portion bulges out to a first height; and a second forming step, which is performed by making the cup-shaped outer peripheral bottom of the above-mentioned cup body abut against the lower mold forming member on one hand, and applying a pressing force from the upper mold forming member toward the outer side of the can closer to the cup-shaped dome portion to form a second height lower than the above-mentioned first height, so that the above-mentioned cup-shaped dome portion is pressed down in a manner to form a second height lower than the above-mentioned first height, so that compressive stress in the meridian direction and the circumferential direction acts on the above-mentioned inclined portion, while increasing the thickness of the inclined portion and pressing it into the above-mentioned lower mold forming member.

Furthermore, in the above (13), (14) is preferably that in the above second forming step, by pressing the above-mentioned inclined portion into the above-mentioned lower mold forming member, a circumferential grounding portion 202b located more inward than the outer circumferential bottom portion, an inner end portion 202c located more inward than the above-mentioned circumferential grounding portion, and a rising portion 202d rising upward from the above-mentioned inner end portion and connected to the tank dome portion are formed, and an annular groove protruding from the above-mentioned connecting portion 202d and the above-mentioned tank dome portion 201d is formed toward the outside of the tank body axis in such a way that the inner diameter (dx) of the connecting portion (outermost end 201e) of the above-mentioned rising portion 202d and the above-mentioned tank dome portion 201d is larger than the inner diameter (dy) of the above-mentioned inner end portion 202c.

Furthermore, in order to achieve the above-mentioned purpose, a method for manufacturing a seamless can body in one embodiment of the present invention is (15) characterized in that it includes: a first forming step, which forms a metal raw material into a cup body, wherein the cup body has a cylindrical main body portion that is thinned by shrinkage processing, an outer peripheral bottom portion that continues from the lower end of the above-mentioned cylindrical main body portion, and a bulging portion that bulges out from the above-mentioned outer peripheral bottom portion toward the opening portion at a first height; and a second forming step The bulge is pressed down to a second height lower than the first height in the first forming step, and in the first forming step, the plate thickness of the lower end of the cylindrical main body is approximately equal to the plate thickness of the middle portion in the axial direction of the cylindrical main body, so that the lower end of the cylindrical main body is pulled in and the outer peripheral bottom portion is continuously reduced in diameter from the lower end of the cylindrical main body through the boundary portion to the inside. [Effect of the invention]

According to the seamless tank body of the present invention, even when the thickness of the blank plate (rough) is reduced, a tank bottom with higher pressure resistance than the tank bottom obtained by the conventional bottom improvement processing can be obtained. Therefore, a seamless tank body can be manufactured using a blank plate (rough) thinner than the conventional one, which can reduce the amount of metal material used, thus being cost-effective. Furthermore, the lightweighting of the seamless tank body can also be related to the reduction of recycling fees and transportation fees.

Furthermore, according to the method for manufacturing a seamless tank body of the present invention, even when the thickness of the blank plate (rough) is reduced, the pressure resistance of the tank bottom can be improved and buckling can be suppressed by using a simple manufacturing device. The blackening problem that becomes a problem in the bottom improvement process can also be solved. Furthermore, since there is no need to learn the bottom improvement process step or the subsequent step of cleaning the lubricating oil, the cost and environmental advantages are great.

The seamless can body and the manufacturing method thereof of the present invention are specifically described below with reference to the drawings. Furthermore, the following embodiments are provided to illustrate an example of the present invention and to explain its contents, but 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 this embodiment is a seamless can body having a cylindrical main body 10 and a can bottom 20. In this embodiment, as shown in FIG. 1 (a) and FIG. 1 (b), the can bottom 20 preferably includes a can bottom center portion 201 that does not contact the horizontal plane when the seamless can body is placed on the horizontal plane, and a foot portion 202 located outside the can bottom center portion 201. The can bottom center portion 201 of the seamless can body 1A in this embodiment may be horizontal, or may be a dome-shaped bulging (bulging upward) on the inner surface of the can as shown in FIG. 1 (a).

In this embodiment, as shown in FIG1 (b), the foot portion 202 in the tank bottom 20 is defined as the portion extending from the lower end 10e of the cylindrical main body 10 toward the tank body axis RA to the outermost end 201e of the tank bottom center portion 201. Furthermore, as shown in the enlarged cross-sectional view of the foot portion 202 in FIG2, the "outermost end 201e of the tank bottom center portion 201" is defined as the portion with the largest dome diameter in the dome shape when the tank bottom center portion 201 is dome-shaped.

In this embodiment, the lowest part of the foot 202 in the Z-axis direction is set as the circumferential grounding part 202b. That is, the circumferential grounding part 202b can be the part that contacts the horizontal plane when the seamless can body 1A of this embodiment is placed on the horizontal plane. In addition, the lower end 10e of the cylindrical main body 10 to the circumferential grounding part 202b is defined as the outer peripheral bottom 202a.

That is, in this embodiment, the foot 202 includes an outer bottom portion 202a that is continuous in a manner of tapering from the lower end 10e of the cylindrical main body 10 to the inside, and a peripheral grounding portion 202b that is located further inward than the outer bottom portion 202a. In other words, in the seamless can body 1A of this embodiment, the outer bottom portion 202a is located in a ring shape further outward than the peripheral grounding portion 202b to the lower end 10e of the cylindrical main body 10.

In this embodiment, there is no particular limitation on the circumferential width or area of the peripheral bottom 202a, and the inclination angle or bending state thereof can also be a known shape. That is, it can be a straight line in the cross section, or a circular arc that bends toward the inner side of the can body, or vice versa. In addition, it can also be a shape in which a part is bent inward and the other part is bent outward, and the shapes are connected continuously. In this embodiment, as shown in FIG. 2, the peripheral bottom 202a preferably has an inflection point IP in its cross-sectional view so that it can be easily overlapped and placed on the lid of the same type of can.

As shown in FIG2 , the seamless can body 1A of this embodiment further includes an inner end portion 202c located further inward than the above-mentioned circumferential grounding portion 202b. The inner end portion 202c is defined as the portion of the foot portion 202 that is closest to the can body axis RA side in the cross-sectional view. Furthermore, the seamless can body 1A of this embodiment further includes a rising portion 202d extending from the inner end portion 202c toward the upward direction (the + direction of the Z axis). The rising portion 202d is defined as the portion from the inner end portion 202c to the outermost end 201e in the direction of the central portion 201 of the can bottom in the cross-sectional view shown in FIG1 (a) or FIG2 .

The characteristic of the seamless can body 1A of this embodiment is that when the plate thickness of the above-mentioned peripheral bottom 202a is set to t1 and the plate thickness of the circumferential grounding portion 202b is set to t2, the relationship of "t2>t1" is established. By satisfying this relationship, the seamless can body 1A of this embodiment can be made lightweight and given better pressure resistance. In addition, by setting t2>t1, the seamless can body 1A can be given better strength against deformation when the can bottom 20 falls downward. Furthermore, the plate thickness (t1) of the above-mentioned peripheral bottom 202a is set to the plate thickness of the middle point of the length (length along the shape) from the lower end 10e to the circumferential grounding portion 202b.

The seamless can body 1A of this embodiment is preferably such that when the plate thickness of the inner end portion 202c is set to t3, the relationship of "t3>t1" is established. By satisfying this relationship, the seamless can body 1A of this embodiment can be made lightweight and given better pressure resistance. Furthermore, by setting t3>t1, the seamless can body 1A can be given strength against deformation when the can bottom 20 is downwardly dropped, thereby being better.

The thickness of the present invention is specified for the following reasons. That is, when the liquid contained in the seamless can is beer or carbonated beverage, internal pressure is always applied to the bottom of the can. In this way, when an impact is applied to the bottom of the can while the internal pressure is applied, or when the internal pressure applied to the bottom of the can increases rapidly for some reason, the internal pressure of the can exceeds the pressure resistance strength of the bottom of the can, resulting in the phenomenon of the dome of the bottom of the can being reversed (buckling).

In order to suppress the buckling phenomenon, the pressure resistance of the tank bottom needs to be increased, so the method of increasing the thickness of the tank bottom is considered. However, in response to the recent requirements for weight reduction and resource saving, the thickness of the blank plate (blank) has been continuously reduced. Therefore, if the thickness of the blank plate (blank) is simply increased to increase the pressure resistance of the tank bottom, it violates the above requirements.

Therefore, the inventors of the present invention have conducted intensive research to realize a seamless tank body that satisfies the requirements of both lightweight tank and pressure resistance strength of the tank bottom. As a result, the thickness of the blank plate (rough) is made the same as or thinner than the conventional method, and only the part of the tank bottom that is easy to contribute to the improvement of the pressure resistance strength is made thicker to improve the pressure resistance strength of the tank bottom, and the present invention is thought of.

According to the present invention, as for the main body of the tank, since a relatively thin blank plate (blank) can be used, the same strict drawing and shrinking process as in the past can be used to achieve a main body plate thickness that is the same as or thinner than in the past. Therefore, it can be said that the requirements of lightweight and pressure resistance strength of the tank bottom can be taken into account at a high level.

The seamless can body 1A of this embodiment is shown in FIG. 1 (a) and FIG. 2 , wherein the foot portion 202 of the can bottom 20 is connected to the can bottom center portion 201 (can dome portion 201d) at the outermost end 201e through the rising portion 202d from the inner end portion 202c.

In this embodiment, the rising portion 202d can be a straight line or a curve extending from the inner end portion 202c in the vertical direction (+ direction of the Z axis) in the cross section. In addition, as shown in FIG. 1 (a) and FIG. 2, the rising portion 202d can be a straight line or a curve extending along a straight line of Z = -aX (Z>0) in the cross section.

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

In other words, as shown in FIG. 1 (a) and FIG. 2, near the outermost end 201e, the cross-sectional view is roughly " "or" 1(a) is shown for illustration, preferably in the + direction toward the Z axis, between the inner end 202c and the tank dome 201d, and with an annular groove having an outermost end 201e protruding toward the outside of the tank body axis RA.

By adopting the above-mentioned shape, the pressure resistance of the seamless can body 1A of this embodiment can be improved.

Furthermore, as described above, in this embodiment, the outer bottom 202a preferably has an inflection point IP in its cross-sectional view. As shown in FIG2 , the inflection point IP may be located closer to the + direction of the Z axis than the outermost end 201e, or may be located in the - direction of the Z axis.

In this embodiment, when the plate thickness of the outermost end 201e portion connecting the rising portion 202d and the central portion 201 of the tank bottom is set to t4, the relationship of "t4>t1" holds, which is better from the perspective of lightweight and pressure resistance of the tank body.

The seamless can body 1A of this embodiment is further shown in FIG1 (a), preferably including a can dome portion 201d that bulges upward in a manner continuous with the above-mentioned rising portion 202d in the can bottom 20. That is, in this embodiment, it is preferred that the shape of the central portion 201 of the can bottom is a dome shape as shown in FIG1 (a).

Furthermore, when the plate thickness at the center of the tank dome portion 201d is set to t5, it is preferable that the following relationship is satisfied in the relationship between the plate thickness (t3) of the inner end portion 202c and the plate thickness (t4) of the rising portion 202d. t3＞t4＞t5 That is, it means that the plate thickness of the metal plate from the center of the tank dome portion 201d toward the outer side to the inner end portion 202c gradually increases.

Furthermore, in this embodiment, as shown in FIG. 3 , when the plate thickness of the blank plate (rough) is set to tz, the relationship of "t1>tz", "t2>tz", "t3>tz", and "t4>tz" is satisfied, which is better from the perspective of the pressure resistance expected for the seamless can body. On the other hand, in this embodiment, there is no problem even if the plate thickness (t5) of the center of the tank dome 201d becomes less than the plate thickness (tz) of the blank plate (rough) (t5≦tz).

Furthermore, in this embodiment, as shown in FIG. 3 (a), it is preferable that the plate thickness of each has a relationship of "t3>t2>t1". In other words, it is preferable that the plate thickness increases slowly in the order of the outer peripheral bottom 202a, the peripheral grounding portion 202b, and the inner end portion 202c. By satisfying this relationship, better pressure resistance can be imparted to the seamless can body 1A of this embodiment.

Furthermore, by satisfying the above-mentioned relationship of "t3>t2>t1", even when the plate thickness of the t3 portion increases, the weight increase of the tank can be suppressed, which is preferable. The reason for this is that in the order of t1→t2→t3, the positions are close to the tank body axis RA, so the volume occupied by each becomes smaller in sequence. Therefore, the result is that the weight increase of the tank can be suppressed and the pressure resistance can be improved, which is preferable.

However, the present embodiment is not limited thereto. As shown in FIG. 3( b ), the thicknesses of t2 and t3 may be the same. As shown in FIG. 3( c ), the thickness of t2 may be the largest.

Furthermore, the thickness tz of the blank plate (rough) is usually sufficient as long as it is the thickness in the case of manufacturing a seamless can body. A metal plate with a thickness of about tz = 0.15 mm to 0.4 mm can be punched out for use as the blank plate (rough), but it 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 relationship, which is preferable in terms of the desired pressure resistance. That is, in the seamless can body 1A of the present embodiment, it is preferable that the average plate thickness of the can bottom 20, especially the foot 202, is thicker than the can bottom center 201.

Furthermore, it is preferred that the thickness of the tank dome portion 201d is smaller than the thickness of the outer peripheral bottom portion 202a. That is, it is preferred that "t5＜t1".

The following reasons are considered for the improvement of pressure resistance by having the above plate thickness relationship. The numerical value of pressure resistance is buckling pressure. That is, the peak value of the pressure before the dome part of the convexity on the inner side of the tank bottom is deformed in a reversed manner to the outside due to the internal pressure is called buckling pressure.

The process of buckling can be explained as follows. First, when the dome portion, which is roughly spherical in shape, is subjected to internal pressure, it does not deform rapidly, but the product of the projected area of the dome portion and the internal pressure becomes a force that pushes the dome portion toward the outside of the tank, exerting a load on the circumferential grounding portion 202b, the inner end portion 202c, and the rising portion 202d and exerting deformation. In other words, the components in the narrow area from the circumferential grounding portion 202b to the rising portion 202d support the outer periphery of the dome portion.

Furthermore, due to the increase in internal pressure, the deformation of the area from the circumferential grounding portion 202b to the rising portion 202d continues, and the function of supporting the outer circumference of the dome portion is lost. That is, the circumferential grounding portion 202b, the inner end portion 202c, and the rising portion 202d cannot maintain the shape of a ring centered on the tank body axis RA, and the outermost end 201e located on the outer circumference of the dome portion connected thereto also becomes a circularly deformed shape, and then the tank dome portion 201d connected thereto cannot maintain a spherical shape, so the strength of the dome portion rapidly decreases and the dome portion reverses (bends) toward the outside of the tank.

Therefore, in order to improve the pressure resistance, it is considered more effective to make the thickness of the outer periphery of the dome thicker than to make the thickness of the dome itself thicker. Therefore, when the thickness of the outer bottom 202a is thicker than the central thickness of the tank dome 201d, that is, when "t5 < t1", the desired pressure resistance can be obtained in this embodiment.

Furthermore, there is no particular limitation on the second height Hp of the tank dome portion 201d in the seamless tank body 1A, and it can be set to the same height as that of a known seamless tank body having a dome portion.

Furthermore, in this embodiment, there is no particular limitation on the type of metal material used for the seamless can body 1A. That is, a known metal plate commonly used for seamless can bodies, such as an aluminum alloy plate or a surface-treated steel plate, can be used. In addition, the metal plate can be appropriately subjected to known surface treatments such as film lamination, coating with an organic resin, or chemical treatment.

The seamless can body 1A of this embodiment is subjected to known necking processing or flange processing, or thread forming processing, and after beer or carbonated beverages are contained as contents, a lid is mounted on the opening portion by a known method.

<Method for manufacturing seamless can body> Next, the method for manufacturing the seamless can body 1A in the present embodiment is described. The method for manufacturing the seamless can body in the present embodiment is a method for manufacturing the seamless can body 1A having a cylindrical main body 10 and a can bottom 20 as shown in FIG. 1 (a), and is characterized by at least including the first forming step and the second forming step described in detail below.

Furthermore, in the method for manufacturing a seamless can body of the present embodiment, as a forming method of the cylindrical main body 10, for example, a known method as described in Patent Document 4 can be adopted. On the other hand, in particular, as a forming method of the can bottom 20, it is characterized by at least including the first forming step and the second forming step as described in detail below.

The following is a description of the method for manufacturing a seamless can body in this embodiment. First, by using the above-mentioned metal raw material (blank), a can body is formed by a known method to prepare a precursor 3 having a cup shape. Furthermore, as shown in FIG. 4, the metal raw material (precursor 3) can have a cup shape without a dome obtained by a known drawing and shrinking method. In addition, as long as the following first forming step and second forming step can be achieved, a cup shape with a dome can also be obtained.

By subjecting the precursor 3 to the following first forming step and second forming step, a seamless can body 1A in this embodiment can be obtained.

First, in the first forming step of the manufacturing method of the seamless can body 1A in the present embodiment, as shown in FIG. 4 , the metal raw material (precursor 3) is formed into a cup body 2, which has a cylindrical main body 10, a cup-shaped outer peripheral bottom A that is continuous in a manner of tapering from the lower end 10e of the above-mentioned cylindrical main body 10, an inclined portion S extending upward toward the inner side from the above-mentioned cup-shaped outer peripheral bottom A, and a cup-shaped dome portion D that bulges upward at a first height Ho from the end Se of the above-mentioned inclined portion S. Here, the end Se of the inclined portion S can also be referred to as a connection point with the cup-shaped dome portion D.

The first forming step shown in FIG. 4 can also be implemented as a step of separating the upper and lower molds for the precursor 3 having the cylindrical main body 10 formed by a known pressing step, or can be performed at the final stage of the punching process that is continuous with the step of performing the shrinking process. As a specific example, as shown in FIG. 4, the first forming step is implemented using a cylindrical punch 401 located in and supporting the cup-shaped precursor 3, a clamping ring 501 that cooperates with the punch 401 to support the outer peripheral bottom of the precursor 3, and a dome mold 502. First, the peripheral bottom of the precursor 3 is held by the peripheral wall portion 402 (inclined portion) of the punch 401 and the conical support portion 503 of the clamping ring 501, and the punch 401 and the dome mold 502 are driven to approach each other in a manner of being engaged with each other, so that a cup body 2 having a cup-shaped dome portion D of Ho at the bottom can be obtained.

Here, the shape of the cup body 2 obtained by the above-mentioned first forming step is explained. That is, the inclined portion S in the cup body 2 is extended from the above-mentioned cup-shaped outer peripheral bottom A toward the inner side and upward. That is, the inclined portion S of the cup body 2, as shown in FIG. 4, refers to the curved portion and the straight portion of the lowest portion of the cup body 2 and the connection point (end Se) with the cup-shaped dome D in the Z-axis direction.

As shown in FIG. 4( c ), it is preferred that the inclined portion S is not vertical but inclined at a specific angle θ _1. That is, the angle θ ₁ formed by the inclined portion S and the Z axis is 5° to 30°, which is preferred from the viewpoint of better controlling the thickness of each portion in the second forming step described below. Furthermore, the angle θ ₁ formed by the inclined portion S and the Z axis is 10° to 30°, which is more preferred because it is easy to perform spray coating when a coating film is formed on the inner surface by a spray coating method after the first forming step.

In addition, regarding the curvature radius R of the angle _θ2 formed by the cup-shaped outer bottom A to the inclined portion S, it is better to set it to R = 5×t0~15×t0, which is better from the perspective of better controlling the plate thickness of each part in the following second forming step.

Furthermore, it is preferred that the first height Ho of the cup-shaped dome portion D in the cup body 2 is greater than the second height Hp of the can dome portion 201d in the seamless can body 1A obtained by the second forming step described below. As the reason for this, as described below, in the second forming step described below, the cup-shaped dome portion D in the cup body 2 is pressed down while the compressive stress is applied to the inclined portion S. That is, the reason is that the first height Ho of the cup-shaped 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 in the seamless can body 1A.

Next, the second forming step is described. After the cup body 2 having the cup-shaped outer peripheral bottom A and the inclined portion S is formed by the above-mentioned first forming step, the following second forming step is performed.

Furthermore, between the first forming step and the second forming step, the cup body 2 may be appropriately subjected to known cleaning steps, surface treatment steps, printing steps, painting steps, processing of the shape of the cylindrical main body, or necking (narrowing of the mouth) processing within the range of the second forming step without hindering the second forming step. Furthermore, if necessary, the outer surface coating may be applied to the portion ranging from the bottom A of the cup-shaped outer circumference to the inclined portion S with the lowest curvature of the cup body 2 as the center in order to ensure the transportability or corrosion resistance after the first forming step.

In the second forming step, the cup body 2 is processed using a mold different from the forming mold in the first forming step to form the seamless can body 1A. That is, the cup body 2 is abutted against the cup-shaped peripheral side retainer 60 as the lower mold forming member, and the dome pressing tool 70 as the upper mold forming member is used to apply a pressing force to the cup-shaped dome portion D of the cup body 2 along the outer direction of the can (-Z axis direction). Alternatively, the cup body 2 can be abutted against the lower mold forming member and the upper mold forming member, and the lower mold forming member can be used to apply a pressing force along the +Z axis direction.

In more detail, as shown in FIG5 , the cup-shaped outer peripheral bottom A of the cup body 2 is placed on the cup-shaped outer peripheral side holder 60. The dome pressing tool 70 is relatively lowered, and the support portion 701 of the dome pressing tool 70 contacts the cup-shaped dome portion D. Here, the cup-shaped outer peripheral side holder 60 has an inclined surface 601 and a groove 602. After the cup-shaped outer peripheral bottom A of the cup body 2 contacts the inclined surface 601, the dome pressing tool 70 is further pressed down, and the metal of the inclined portion S of the cup body 2 is guided and pressed into the groove 602 while receiving compressive stress.

Then, the cup-shaped dome portion D is pressed down to a second height Hp lower than the first height Ho. The upper die forming member (dome pressing tool) and the lower die forming member (cup-shaped outer peripheral side holder) are used simultaneously to apply a compressive stress σ _φ in the meridian direction and a compressive stress σ _θ in the circumferential direction to the inclined portion S.

Furthermore, FIG. 6 is a schematic diagram showing the compressive stress applied when the inclined portion S is formed in the upright portion 202d in this embodiment. That is, when the inclined portion S is pressed into the groove 602 of the lower die forming member, the inclined portion S is simultaneously subjected to compressive stress σ _φ in the meridian direction by the pressing force of the dome-shaped pressing tool 70 and compressive stress σ _θ in the circumferential direction obtained by the radial inward movement of the lower die forming member, and the thickness of the metal material in the inclined portion S increases (the arrow direction σ _ψ in FIG. 6 ). In this way, a seamless can body 1A is obtained after the second forming step. After the forming is completed, the dome pressing tool is relatively raised to take the seamless can body 1A out of the cup-shaped peripheral side holder.

Here, the seamless can body 1A obtained after the second forming step is preferably the seamless can body 1A in the above-mentioned embodiment. That is, as shown in FIG. 1 , the seamless can body 1A obtained after the second forming step preferably has an outer peripheral bottom 202a and a peripheral grounding portion 202b, and when the plate thickness of the outer peripheral bottom 202a is set to t1 and the plate thickness of the peripheral grounding portion 202b is set to t2, the relationship of "t2>t1" is established.

Furthermore, the second forming step further preferably has the following characteristics. That is, the second forming step preferably forms the inclined portion S into a circumferential grounding portion 202b located further inwardly than the circumferential bottom portion 202a, an inner side end portion 202c located further inwardly than the circumferential grounding portion 202b, and a rising portion 202d rising upwardly from the inner side end portion 202c and connected to the tank dome portion 201d by pressing the cup body 2 into the cup-shaped outer peripheral side retainer 60 of the second forming step.

Furthermore, it is preferred that the inner diameter (dx) of the connection point (outermost end 201e) of the above-mentioned rising portion 202d of the seamless can body 1A and the above-mentioned can dome portion 201d is larger than the inner diameter (dy) of the inner end portion 202c by utilizing the second forming step, so as to form an annular groove in which the outermost end 201e protrudes toward the outer side of the can body axis RA. It is known that there is an improved forming method (bottom improved processing) for forming an annular groove as described above using a rotating roller or a split die. However, in the known method, it is difficult to make the processed part easy to thin and form a sufficiently deep groove. According to the method of the present invention, the plate thickness of the annular groove portion does not become thinner but thicker, and a deeper groove can be reasonably formed.

In the method for manufacturing a seamless can body of this embodiment, the shape or length of the upper portion of the cup-shaped outer peripheral bottom A of the cup body 2 does not change between the first forming step and the second forming step. That is, when the cup body 2 is placed on the cup-shaped outer peripheral side holder 60, the lowest point in the Z-axis direction of the surface where the cup-shaped outer peripheral bottom A of the cup body 2 contacts the inclined surface 601 of the cup-shaped outer peripheral side holder 60 is set as point T. The position of point T does not change as the dome pressing tool 70 descends and the cup-shaped dome portion D is pressed down (see FIG. 5).

On the other hand, the second forming step is used to form the inclined portion S of the cup body 2 as a portion of the outer peripheral bottom 202a of the seamless can body 1A, the circumferential grounding portion 202b, the inner end portion 202c and the rising portion 202d. That is, the inclined portion S of the cup body 2 finally enters the groove 602 of the cup-shaped outer peripheral side holder 60. Furthermore, in the second forming step, there is no significant slippage in the contact between the cup body 2 and the upper and lower molds. Therefore, the metal surface of the cup body 2 will not be damaged, and there is no need to use a lubricant compared to the previous method.

As shown in FIG5 , the T point becomes the inflection point IP in the seamless can body 1A. Due to the compressive stress applied in the second forming step, the metal length becomes shorter as described below. That is, the metal length from the inflection point IP to the outermost end 201e in FIG5 (f) is shortened to about 0.85 to 0.99 times compared to the metal length from the T point to Se in FIG5 (b).

On the other hand, the thickness of the metal raw material in this part is increased to 1.1 to 1.3 times the thickness of the base plate (t0) at the part where the thickness increases the most by the second forming step. [Example]

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

(Example 1) A 350 mL drawing and shrinking tank (DI tank) was manufactured by the method shown below. First, an aluminum alloy plate (JISH4000A3104-H19 material, 0.28 mm) was prepared as a plain plate. Then, a specific amount of a known denting oil was applied to both sides of the aluminum alloy plate as a lubricant during the drawing process.

Next, the aluminum alloy plate is punched into a disc shape with a diameter of 160 mm using a drawing machine, and then immediately drawn into a drawing cup with a diameter of 90 mm (not shown). The obtained drawing cup is transported to a BODYMAKER (can manufacturing machine), and after being re-drawn into a shape with a diameter of 66 mm, a coolant is used to shrink it into a shape of 66 mm in diameter, 130 mm in height, and a minimum side wall thickness of 0.105 mm, which is a shape of the precursor 3 produced by drawing and shrinking.

Next, in order to perform the forming process of the can bottom, the following first forming step and second forming step are performed on the above-obtained precursor 3. First, as the first forming step, the above-mentioned BODYMAKER is used at the final stage of the stroke continuous with the shrinking process, and the punch 401, the clamping ring 501 and the dome mold 502 shown in Figure 4 are used to make a cup body 2 having a cup-shaped outer peripheral bottom A and an inclined portion S. The length and plate thickness of the cup-shaped outer peripheral bottom A and the inclined portion S at this time are shown in Table 1.

Next, as the second forming step, the cup-shaped dome pressing tool 70 as the upper die forming member and the cup-shaped peripheral side retainer 60 as the lower die forming member are used to press down the cup-shaped dome portion D and increase the thickness of the metal material in the inclined portion S to form a seamless can body 1A.

Next, the plate thickness of each part from t1 to t5 is measured. Furthermore, the locations of each part from t1 to t5 are as shown in the above-mentioned embodiment and FIG2. Moreover, the plate thickness measuring method is as shown below. That is, after the formed seamless can body 1A is embedded with epoxy resin, the seamless can body 1A is cut along the longitudinal axis (Z axis) of the seamless can body 1A together with the epoxy resin. After the center section is exposed by cutting and fine grinding, the thickness of each part from t1 to t5 is measured with a measuring microscope. The plate thickness of each part is shown in Table 1.

(Example 2) The same method as Example 1 was used except that the base plate thickness was set to 0.225 mm and the minimum thickness of the side wall of the front body 3 was set to 0.093 mm. The plate thickness of each part of the seamless can body obtained is shown in Table 1.

(Comparative Example 1) Regarding the forming process of the can bottom, a known can bottom forming mold is used and a known can bottom forming method is used to perform one step. Other than that, the same method as in Example 1 is used. In addition, a partial enlarged view of the can bottom of the seamless can body used in Comparative Example 1 is shown in FIG7. The plate thickness of each part of the obtained seamless can body is shown in Table 1. Among them, in Table 1, the value of t3 can be obtained by measuring the lower end of the inclined portion (FIG. 7 (1)), and the value of t4 can be obtained by measuring the upper end of the inclined portion (FIG. 7 (2)).

(Comparative Example 2) The seamless can body obtained in Comparative Example 1 was subjected to bottom improvement processing. That is, the inner peripheral wall located at the inner side of the can body axis in the radial direction perpendicular to the grounding part of the can bottom was pressed by a rotating roller to form a concave portion into a circumferential shape. Other than this, the same method as the comparative example was used. The plate thickness of each part of the seamless can body obtained is shown in Table 1.

(Comparative Example 3) The same procedure as in Comparative Example 2 was followed except that the base plate thickness was set to 0.225 mm and the minimum side wall thickness was set to 0.093 mm. The plate thickness of each part of the seamless can body obtained is shown in Table 1.

[Evaluation] The DI tanks obtained by the above method were evaluated by the following method. The results are shown in Table 1.

[Pressure resistance test method] When the cup is filled with water, seal the open end with a plug installed in the water supply pipe. Then, pressurized water is supplied to the cup from the water supply pump through the water supply pipe. The internal pressure of the cup rises, and at a certain point the dome instantly deforms (bends) in a reversed outward manner. Usually, at the same time as this deformation, the internal pressure of the tank drops sharply. The maximum value of the internal pressure of the tank during this period is set as the pressure resistance (MPa).

[Table 1] Cup size Dimensions of tank bottom Reviews Original plate thickness Cup dome height Ho (mm) Slant part S metal length (mm) Slope S thickness (mm) Tank dome height Hp (mm) Inner diameter dx (mm) Inner diameter dy (mm) t1 (mm) t2 (mm) t3 (mm) t4 (mm) t5 (mm) Can weight (g) [equivalent to 350mL can] Pressure resistance (MPa) Embodiment 1 0.280 16.0 4.6 0.287 12.3 48.86 46.00 0.287 0.299 0.310 0.289 0.261 11.2 1.043 Embodiment 2 0.225 16.0 4.6 0.231 12.3 48.86 46.00 0.231 0.240 0.249 0.231 0.211 9.6 0.760 Comparison Example 1 0.280 - - - 12.3 45.66 46.00 0.285 0.265 0.242 0.258 0.265 11.2 0.620 Comparison Example 2 0.280 - - - 12.3 46.64 46.00 0.284 0.265 0.241 0.250 0.265 11.2 0.781 Comparison Example 3 0.225 - - - 12.3 46.65 46.00 0.228 0.213 0.192 0.200 0.210 9.6 0.588

The results of the embodiments and the comparative examples show that by controlling the thickness of a specific portion of the can bottom, better pressure resistance (above 0.618 MPa required for carbonated beverage use) can be obtained even when the thickness of the blank plate (rough) is made thinner.

[Second embodiment] As described above, the conventional seamless can body is excellent in lightness, but there are still aspects that need to be improved in the can body portion, which is the side surface. That is, in recent years, various designs have been implemented in the can body portion to ensure product competitiveness. From this point of view, the can body portion is required to have as uniform image clarity as possible.

However, in the conventional method of manufacturing a seamless can body, the surface state of the can body after forming is not consistent along the axial direction, especially in the constricted portion (peripheral bottom) near the lower end of the can body or between the can body and the bottom of the can, a high metallic gloss cannot be obtained. This point is explained in detail using Figure 14.

FIG14 (a) schematically shows the local state of the tank body and the front end of the shrinkage punch just after the shrinkage process is completed. As shown in the figure, a cone is provided from point A to point B at the front end of the cylindrical portion of the punch. The cone is provided in order to slowly increase the shrinkage rate at the beginning of the shrinkage process. Therefore, the tank body portion corresponding to the inclined portion is formed in a wedge-shaped state as an area with a plate thickness distribution. Furthermore, as shown in FIG9 and the like, this area is sometimes also referred to as the "Body Wall Step (BWS)". In addition, a portion also called the Body Wall Radius (BWR) is formed on the lower side of the BWS, which has a relatively large shrinkage diameter toward the inner side of the tank.

Furthermore, when the shrinking process is performed, the gloss of the shrinking surface is approximately the same as the gloss of the original raw material surface at point B located at the lower end of the BWS, and the gloss increases as it approaches point A located at the upper end of the BWS, and the gloss is maximum after point A. Figure 14 (b) is a diagram showing the local state of the can body and the front end of the shrinking punch at the time when the dome mold is relatively sunken into the front end of the shrinking punch after the shrinking process is completed, and the dome is formed on the bottom of the can. As the bottom surface of the can bottom becomes the dome and is pulled in, the partial offset point A' located at point A and the partial offset point B' located at point B in Figure 14 (a) are respectively. Furthermore, the movement amount (offset amount) of each point is approximately 2 to 5 mm as an example. In this way, there is still a part with lower gloss and poorer printing clarity near the bottom of the cylindrical part of the main body of the can, and a seamless can body with higher metallic gloss and higher design is sought in this part. Furthermore, the above offset amount can be increased by simply increasing the sinking amount of the above dome mold, but the residual leads to a significant reduction in the internal capacity of the formed can, and at the same time leads to an increase in the material usage of the can.

In view of this, in the following second embodiment, in view of the above-mentioned exemplified subject, repeated and intensive research has been conducted, and as a result, a seamless can body and a manufacturing method thereof can be provided that can provide excellent image clarity to the can body portion after drawing and shrinking. In addition, in the second embodiment, a seamless can body and a manufacturing method thereof can be provided that has a higher metallic luster in the reduced diameter portion (peripheral bottom) between the can body portion and the can bottom. Furthermore, below, with respect to the seamless can body 1A of the above-mentioned first embodiment, the same symbols are respectively marked for the components with the same structure and function, and their descriptions are appropriately omitted.

<Seamless can body 1B> As shown in FIG8 , the seamless can body 1B of the present embodiment is a seamless can body having a cylindrical main body 10 and at least a can bottom 20 having an outer peripheral bottom 20a which is continuous from the lower end of the cylindrical main body 10 through the junction BP to the inner side in a manner of reducing the diameter. Furthermore, the neck and flange shapes are depicted as an example above the cylindrical main body 10 in the figure, but the structure of a known seamless can body having an opening 10a can be applied above the cylindrical main body 10. Here, the "lower end 10e of the cylindrical main body 10" in this embodiment is a portion substantially located at the lower end of the cylindrical surface. When printing is performed on the outer surface of a seamless can body, for example, it can be defined as the lower end of an area where curved printing can be performed using a known dry offset printing method.

The cylindrical main body 10 is a part constituting the side surface of the seamless can body 1B, and is formed by drawing and shrinking a known metal plate such as aluminum or steel as described below. The cylindrical main body 10 has a width depending on the purpose, but is configured in a manner having a thickness of approximately 0.07 to 0.40 mm, for example. The cylindrical main body 10 in this embodiment has the lower end 10e as the lower end, and the upper end is defined as the boundary with the neck shoulder (the part that decreases in diameter as it moves upward in the axial direction) as shown in FIG. 8 .

As shown in FIG8 , the tank bottom 20 at least includes an outer bottom 20a that is continuous in a manner of reducing the diameter inward from the lower end 10e of the cylindrical main body 10, and a bulging portion 20b that bulges from the outer bottom 20a toward the opening 10a. Furthermore, as can be seen from FIG8 , the outer bottom 20a and the bulging portion 20b in this embodiment are divided by a circumferential grounding portion 20c that is grounded when the seamless tank body 1B is placed on a flat surface such as a platform. Therefore, the outer bottom 20a, the circumferential grounding portion 20c, and the bulging portion 20b in this embodiment correspond to the foot 202 and the tank bottom center portion 201 in the first embodiment. At this time, in particular, the circumferential grounding portion 20c of this embodiment corresponds to the circumferential grounding portion 202b in the first embodiment.

In addition, the "boundary portion BP" in the present embodiment is the boundary of the area related to the external appearance of the tank bottom side (i.e., it can usually be observed from the outside of the tank), as shown in FIG. 17, and is a portion where the lower end 10e of the cylindrical main body 10 is reversely bent and connected to the peripheral bottom 20a, and is defined as the point where the angle γ formed by the connecting line of the outer surface in the boundary portion BP and the ground contact surface P is 45°.

In this embodiment, the point where the angle γ is 45° is defined as the boundary BP for the following reasons. That is, at a position where γ is less than 45°, the normal of the outer surface is too downward. As a result, for example, when the can to which the present invention is applied is placed (standing upright) on a display rack, etc., the reflected light is difficult to enter the line of sight, and therefore the excellent glossiness of the outer surface of the can, which is the subject of the present invention, is difficult to be brought into play.

Furthermore, as shown in FIG. 9 (a), in the known structure, since the thin-walled portion of the cylindrical main body is pulled downward by a very small amount when the dome is formed, the vicinity of the above-mentioned junction BP becomes a relatively thick portion. In contrast, in the seamless can body 1B of the present embodiment, as shown in FIG. 9 (b), since a portion of the lower end side of the cylindrical main body 10 including the lower end 10e of the cylindrical main body 10 subjected to shrinkage processing is pulled toward the side of the outer peripheral bottom 20a, the outer peripheral bottom 20a beyond the junction BP is formed of a metal plate subjected to shrinkage processing at least up to the vicinity of the junction BP.

In other words, in the seamless can body 1B of the present embodiment, it can be said that at least the plate thickness t0 of the junction BP is substantially equal to the plate thickness _tWC (refer to FIG8) of the middle portion of the cylindrical main body 10. Therefore, compared with the known structure, the cylindrical main body 10 of the present embodiment has a higher gloss from the upper end to the lower end and then to the junction BP in the axial direction (Z direction of FIG8) and can exert a homogeneous image clarity. Furthermore, the shrinkage rate of the cylindrical main body 10 processed by shrinkage to present a higher gloss varies depending on the characteristics of the raw materials used or the processing conditions, so it is not limited to this. As an example, it is preferred that the total shrinkage rate is at least 60%.

Furthermore, in the present embodiment, as shown in FIG8 , it is desirable that when the plate thickness near the boundary portion BP in the tubular main body 10 (e.g., the lower end of the tubular main body 10) is set to t _WL and the plate thickness in the middle portion in the axial direction (Z direction) of the tubular main body 10 is set to t _WC , the relationship of t _WC ≦ t _WL <1.09×t _WC is satisfied, and preferably the relationship of t _WC ≦ t _WL <1.05×t _WC is satisfied. In this way, the image clarity of the side of the tank can be improved and the pressure resistance of the seamless tank body 1B can be maintained. Furthermore, the "middle portion in the axial direction of the tubular main body 10" in the present embodiment does not necessarily need to be strictly the plate thickness in the middle in the above-mentioned axial direction, and can be defined to include the portion near the middle.

Furthermore, in the present embodiment, as shown in FIG8 , when the plate thickness of the middle portion in the axial direction of the cylindrical main body 10 is set to t _WC , it is desirable to be in the relationship of t _WC ≦ t0 < 1.09×t _WC , and more preferably in the relationship of t _WC ≦ t0 < 1.05×t _WC . The reason is that if t0 does not reach t _WC , the axial load strength of the portion may be reduced, and if t0 is 1.09 times or more of t _WC , the glossiness of the lower end portion of the cylindrical main body is reduced and it is difficult to obtain the effect of the present invention. Thereby, the image clarity of the can side surface can be improved and the pressure resistance of the seamless can body 1B can be maintained.

Furthermore, since the metal plate after shrinkage processing exceeds the junction BP and reaches at least a part of the outer peripheral bottom 20a, it is expected that the 60-degree mirror gloss from the lower end 10e of the cylindrical main body 10 to the vicinity of the junction BP is 300% or more. The reason is that if the 60-degree mirror gloss near the junction BP does not reach 300%, the surface roughness or dullness of the matching part will be felt in appearance, thus causing a problem of reduced appeal as a product. Furthermore, the mirror gloss of this embodiment is measured according to the measurement method specified in JISZ8741-1997.

Furthermore, in this embodiment, there is no particular restriction on the type of metal raw material used for the seamless can body 1B. That is, a known metal plate commonly used for seamless can bodies, such as an aluminum alloy plate or a steel plate (such as tinplate, etc.) can be used. In addition, the metal plate can be appropriately coated on its inner surface by a known method such as film lamination, coating with an organic resin, or chemical treatment. In addition, the seamless can body 1B of this embodiment is subjected to a known flange processing, necking processing, thread processing, etc., and after containing beer or carbonated beverages, coffee, juice, liquid food, etc. as contents, a lid is installed on the opening 10a by a known method.

<Manufacturing method of seamless can body 1B> Next, the manufacturing method of the seamless can body 1B in this embodiment will be described with reference to FIGS. 10 to 12, etc. The manufacturing method of the seamless can body 1B in this embodiment is a manufacturing method of a seamless can body having a cylindrical main body 10 and a can bottom 20 as shown in FIG. 8, and is characterized by including the first forming step and the second forming step described in detail below.

[First forming step] The manufacturing method of the seamless can body 1B in this embodiment is as shown in the first forming step of FIG. 10, whereby the metal raw material (precursor 3) is formed into a cup body 2, wherein the cup body 2 has a cylindrical main body 10, an inclined portion S extending upward from the boundary portion BP at the lower end of the cylindrical main body 10 toward the inner side, and a cup-shaped dome portion D bulging upward from the end Se of the inclined portion S at a first height Ho. Here, the end Se of the inclined portion S can also be referred to as a connection point with the cup-shaped dome portion D.

Moreover, the first forming step of this embodiment is implemented by using a known pressing step, etc., using an upper mold and a lower mold, to form a precursor 3 having a cylindrical main body portion 10 thinned by shrinkage processing. That is, the first forming step of this embodiment can be performed at the end position (near the bottom dead center) of the punch stroke of the forming machine performing shrinkage processing, and can also be performed in a machine different from the machine performing shrinkage processing. As a specific example, as shown in FIG. 10, the first forming step is implemented by using a cylindrical punch 401 located in and supporting the cup-shaped precursor 3, and a dome mold 502 that cooperates with the punch 401 to support the outer peripheral bottom of the precursor 3. The lower end of the punch 401 corresponds to the concave shape of the dome mold 502, which is called upward protrusion, and forms a peripheral wall portion 402 along the circumferential direction. In addition, in FIG. 10 of the present embodiment, a single arc is shown as the cross-sectional shape of the peripheral wall portion 402, but it is not limited to this shape. For example, as shown in FIG. 15 or FIG. 16, it can be a shape combining multiple arcs and inclined surfaces.

First, if the precursor 3 is pressed by clamping the punch 401 and the dome mold 502, the bottom surface of the precursor 3 bulges toward the opening due to the dome mold 502, and the periphery of the lower end is stretched by the peripheral wall portion 402. In other words, in the first forming step, by supporting the outer periphery of the precursor 3 with the peripheral wall portion 402 of the punch 401 and driving the punch 401 and the dome mold 502 in a manner of engaging with each other, the cup body 2 having a cup-shaped dome portion D of a first height Ho at the bottom can be obtained.

Furthermore, when wrinkles are generated on the peripheral wall portion 402 and its vicinity when the cup-shaped dome portion D is formed in the first forming step, a wrinkle extrusion member 80 (also called a compression ring) shown in FIG. 16 may be provided as needed, and the peripheral wall portion 402 and the wrinkle extrusion member 80 may be used to apply additional wrinkle extrusion pressure for forming.

At this time, it is necessary to combine the raw material quantities so that the can bottom 20 in FIG8 can be formed in the second forming step after the materials for forming the cup-shaped dome D, the end Se, and the inclined portion S are used, and set the first height Ho of the cup-shaped dome. Thus, the first height Ho in this embodiment is higher than the dome height of the conventional structure, so the amount by which the cylindrical main body 10 is pulled into the side of the outer peripheral bottom 20a also increases accordingly.

Thus, as shown in FIG. 11 , the portion that originally constitutes the lower end of the cylindrical main body 10 during the shrinking process exceeds the boundary BP between the cylindrical main body 10 and the peripheral bottom 20a and is pulled into the side of the peripheral bottom 20a (more specifically, in the example shown in FIG. 11 , point A and point B located in the cylindrical main body are pulled in respectively beyond the boundary BP). In other words, in the first forming step, the lower end 10e of the cylindrical main body 10 is pulled in to form a portion of the peripheral bottom 20a that is reduced and continuous from the lower end 10e of the cylindrical main body 10 (substantially still in a curved surface state near the boundary BP, which is referred to as the first peripheral bottom 20a').

Here, the shape of the cup body 2 obtained by the above-mentioned first forming step is explained. The inclined portion S in the cup body 2 extends from the above-mentioned first outer peripheral bottom 20a' to the inner side and upward. That is, the inclined portion S of the cup body 2, as shown in Figure 10 (c) and the like, refers to the curved portion and the straight portion of the lowest portion of the cup body 2 and the connection point (end Se) with the cup-shaped dome portion D in the Z-axis direction. Furthermore, in this first forming step, the above-mentioned inclined portion S and the cup-shaped dome portion D are also called bulges. Therefore, it can also be said that the cup body 2 of this embodiment includes a cylindrical main body portion 10 and a bulge formed on the bottom surface of the cylindrical main body portion 10. The shape of the cup-shaped dome portion D is an example, and the top of the dome may not be a curved surface but may be a horizontal surface, for example.

Furthermore, the first height Ho of the cup-shaped dome portion D in the cup body 2 is preferably greater than the second height Hp of the can dome portion 201d in the seamless can body 1B obtained by the second forming step. As one of the reasons, in the second forming step described below, the cup-shaped dome portion D in the cup body 2 is pressed down while the compressive stress is applied to the inclined portion S. That is, the reason is that the first height Ho of the cup-shaped dome portion D in the cup body 2 is increased in advance, and finally a better second height Hp of the can dome portion 201d is obtained in the seamless can body 1B.

That is, in the first forming step, a bulging portion bulging from the first peripheral bottom 20a' near the boundary portion BP toward the opening portion 10a with a first height Ho is first formed, and in the following second forming step, the bulging portion is pressed down to a second height lower than the first height Ho.

[Second forming step] Next, referring to FIG. 12, the second forming step in the method for manufacturing the seamless can body 1B in this embodiment is described. After the cup body 2 having the first peripheral bottom 20a' and the inclined portion S is formed by the above-mentioned first forming step, the following second forming step is performed.

Furthermore, between the first forming step and the second forming step, the cup body 2 may be appropriately subjected to known cleaning steps, surface treatment steps, printing steps, painting steps, processing of the shape of the cylindrical main body, or necking (narrowing of the mouth) processing within the range of the second forming step without hindering the second forming step. Furthermore, if necessary, in order to ensure the transportability or corrosion resistance after the first forming step, the outer surface of the cup body 2 may be coated in the range from the grounding portion to the inclined portion S at the lowest end.

In the second forming step, the cup body 2 is processed by a mold different from the forming mold in the first forming step to form the seamless can body 1B. That is, as shown in FIG. 12 , the cup body 2 is abutted against the lower mold forming member, and the upper mold forming member is used to apply a pressing force to the cup-shaped dome portion D of the cup body 2 in the outer direction of the can (-Z axis direction).

In more detail, as shown in FIG. 12 (a), the vicinity of the boundary portion BP of the cup body 2 is placed on the cup-shaped outer peripheral side holder 60. Then, the dome pressing tool 70 is relatively lowered, and as shown in FIG. 12 (b), the support portion 701 of the dome pressing tool 70 contacts the cup-shaped dome portion D. Furthermore, in FIG. 12, the shape of the support portion 701 is roughly consistent with the shape of the cup-shaped dome portion D, but for example, by setting a difference in curvature in a manner of applying strong pressure to the outer periphery of the cup-shaped dome portion D, it is not necessarily necessary to make the shapes consistent.

Here, the cup-shaped peripheral side retainer 60 has an inclined surface 601 and a groove 602. After the boundary portion BP of the cup body 2 and the first peripheral bottom 20a' contact the inclined surface 601, the dome pressing tool 70 presses down. As a result, as shown in FIG. 12 (c), the metal of the inclined portion S of the cup body 2 is subjected to compressive stress while being shaped in the manner of the inclined surface 601.

Next, as shown in FIG. 12( d ), the dome pressing tool 70 is further pressed down, and the remaining portion (the portion other than the metal that imitates the inclined surface 601) in the inclined portion S of the cup body 2 is guided into the groove 602. At this time, the cup-shaped dome portion D is pressed down in such a manner that the second height Hp is lower than the first height Ho. At the same time, as described in the first embodiment, the upper mold forming member (dome pressing tool) and the lower mold forming member (cup-shaped peripheral side retainer) are used to act on the inclined portion S in the meridian direction. Compressive stress σ _φ and compressive stress σ _θ in the circumferential direction (refer to FIG. 6 ). Thereby, the metal in the cup body 2 that imitates the inclined surface 601 forms the outer peripheral bottom 20a, and the metal guided into the groove 602 forms the above-mentioned peripheral grounding portion 20c, and further the bulging portions 20b are formed upward from the peripheral grounding portion 20c (refer to Figure 12 (e)).

In this way, the bottom 20 of the seamless can body 1B can be obtained after the second forming step. After the above forming is completed, as shown in Figure 12 (e), the dome pressing tool is relatively raised to remove the seamless can body 1B from the cup-shaped peripheral side holder.

The seamless can body 1B formed in the manufacturing method of the present embodiment described above, which is the cylindrical main body 10 of the can side, can form a roughly homogeneous surface state from the upper end to the lower end in the axial direction, and can exert excellent appearance or image clarity. Furthermore, the second embodiment described above can be said to be roughly the same as the first embodiment except for the bottom of the can (mainly the shape of the dome of the bottom of the can). Therefore, it goes without saying that the technical ideas about the relationship between the above-mentioned plate thicknesses in this embodiment and the technical ideas about the metal gloss of the can main body and the bottom of the can can be commonly applied as long as they do not cause contradictions in the first embodiment.

On the contrary, the seamless can body 1B formed in the manufacturing method of this embodiment can also exert the same effect as the above-mentioned first embodiment by combining the features of the above-mentioned first embodiment (inner end 202c, rising portion 202d, outermost end 201e, can dome portion 201d). In this way, the shape of the dome portion in the seamless can body 1A of the first embodiment is applied to the seamless can body 1B of the second embodiment. If FIG. 1 and its description and FIG. 13 are combined, the seamless can body of the present invention can be provided with a higher pressure resistance and can provide excellent image clarity to the can body portion after drawing and shrinking processing, and the manufacturing method thereof.

Furthermore, since the plate thickness of the foot portion 202 in FIG. 13 changes from the boundary portion BP (refer to FIG. 8 ) toward the peripheral grounding portion 202b, it can be seen from FIG. 1 , FIG. 8 , and FIG. 11 that the portion having a thickness of t1 moves to a position closer to the peripheral grounding portion 202b than the plate thickness t0 of the boundary portion BP. At this time, it is preferable to have the characteristics of plate thickness t0 < plate thickness t1, the characteristics of t _WC ≦t _WL <1.09×t _WC shown in the second embodiment, the characteristics of t _WC ≦t0 <1.09×t _WC , and the characteristics of the 60-degree mirror gloss from the lower end 10e of the cylindrical main body 10 to the vicinity of the boundary portion BP being 300% or more. In this way, the seamless can body of the present invention can have the features of the first and second embodiments described above, and the cylindrical main body portion 10 on the side of the can forms a substantially uniform surface from the upper end to the lower end in its axial direction, thereby exhibiting excellent appearance or image clarity, while also taking into account excellent pressure resistance at the bottom of the can.

Here, FIG. 14 is used to re-explain that the seamless can body 1B described in the second embodiment is advantageous over the conventional structure at least in terms of gloss. Here, FIG. 14 (a) shows an excerpt of the structure near the lower end of the can body in the seamless can body just after shrinkage forming using the conventional manufacturing method, and FIG. 14 (b) then further shows an excerpt of the structure near the lower end of the can body after dome forming. In contrast, FIG. 14 (c) shows an excerpt of the structure near the lower end of the can body in the seamless can body 1B of this embodiment. Furthermore, in FIG. 14( c ), the plate thickness t _WL at the lower end of the cylindrical body 10 is equal to the plate thickness t _WC at the middle portion in the axial direction of the cylindrical body. However, as described above, the present invention is not limited to this configuration, and t _WL <1.09×t _WC may be satisfied.

That is, when the shrinking process for forming a seamless can body is performed, first, as described above, in FIG. 14 (a) of the known method, the shrinking process is started at a shrinkage rate of 0 at point B, and the shrinkage rate increases as it approaches point A, and the shrinkage rate is the largest after point A. Therefore, for example, the gloss of the shrinking process surface of the can body at point B is substantially the same as the gloss of the original raw material surface, and the gloss increases as it approaches point A, and the gloss is the largest after point A.

Moreover, FIG. 14 (b) shows a state in which the dome is formed on the bottom of the can by the dome mold being relatively sunken into the front end of the shrink punch after the shrink process is completed. As a result, a portion of the bottom of the can is pulled into the shape of the dome, and the portion originally located at point A is pushed into point A', and the portion originally located at point B is pushed into point B'. Furthermore, the offset amount of each portion of the above-mentioned known method is approximately 2 to 5 mm as an example. Therefore, the bottom of the cylindrical portion of the can body still has a portion with lower gloss and poorer printing clarity.

On the other hand, in the seamless can body 1B of the present embodiment, as can be seen from FIG. 14 (c) and the like, since the metal plate after shrinkage processing exceeds the boundary BP and reaches at least a portion of the outer peripheral bottom, the glossiness near the boundary BP is the same as that of the can body. Thus, the can body can have a higher glossiness from the upper end to the lower end in the axial direction.

The first and second embodiments described above are examples of implementing the subject matter of the present invention, and appropriate modifications may be made without departing from the subject matter of the present invention. Furthermore, known structures may be added to the seamless tank body shown in the first and second embodiments without departing from the subject matter of the present invention. [Industrial Applicability]

According to the present invention, the thickness of the blank plate (blank) of the seamless tank body can be made thinner and the pressure resistance can be improved to suppress the phenomenon of buckling. Therefore, the manufacturing cost of the seamless tank body or the cost of transportation can be reduced. In addition, since the fuel required for manufacturing or transportation can also be reduced, the manufacturing of the seamless tank body taking the environment into consideration can be realized. In addition, according to the present invention, it can be applied to containers that require improved appearance or image clarity, especially can be used in tanks that can store liquids such as beverages or medicines.

1A, 1B: Seamless tank body 2: Cup body 3: Front body 10: Cylindrical main body 10e: Lower end 20: Tank bottom 20a: Peripheral bottom 20a': First peripheral bottom 20b: Protruding part 20c: Peripheral grounding part 201: Tank bottom center 201d: Tank dome 201e: Outermost end 202: Foot 202a: Peripheral bottom 202b: Peripheral grounding part 202c: Inner end 202d: Rising part 401: Punch head 402: Peripheral wall 50 1: Clamping ring 502: Dome mold 503: Conical support 60: Lower mold forming member (cup-shaped peripheral side holder) 601: Inclined surface 602: Groove 70: Upper mold forming member (dome pressing tool) 701: Support 80: Wrinkle extrusion member A: Cup-shaped peripheral bottom D: Cup-shaped dome P: Ground contact surface S: Inclined part Se: End BP: Junction Hp: Height of the dome of the tank (second height) Ho: Height of the dome of the cup (first height) IP: Inflection point

[FIG. 1] is a schematic diagram showing the seamless can body 1A in the first embodiment. [FIG. 2] is an enlarged diagram showing the bottom of the seamless can body 1A in the first embodiment. [FIG. 3] is a graph showing the plate thickness at each point in the seamless can body 1A in the first embodiment. [FIG. 4] is a diagram showing the first forming step in the method for manufacturing the seamless can body in the first embodiment. [FIG. 5] is a diagram showing the second forming step in the method for manufacturing the seamless can body in the first embodiment. [FIG. 6] is a schematic diagram showing the compressive stress applied to the rising portion in the first embodiment. [FIG. 7] is a partial enlarged diagram of the bottom of the seamless can body used in Comparative Example 1. [Fig. 8] is a schematic diagram showing a longitudinal section of the entire seamless can body 1B in the second embodiment. [Fig. 9] is a comparison diagram of the seamless can body 1B in the second embodiment and the vicinity of the lower end 10e of the cylindrical main body 10 of the seamless can body in the known structure. [Fig. 10] is a diagram showing the first forming step in the manufacturing method of the seamless can body 1B. [Fig. 11] is a schematic diagram showing partial enlargements of the α portion and the β portion in Fig. 10. [Fig. 12] is a diagram showing the second forming step in the manufacturing method of the seamless can body 1B. [Fig. 13] is an enlarged diagram of the bottom of the seamless can body 1A in the first embodiment to which the boundary portion BP shown in the second embodiment is applied. [FIG. 14] is a schematic diagram for comparing the structure of a seamless can body obtained by a known method and a seamless can body obtained by the present embodiment. [FIG. 15] is a schematic diagram showing another example (one) of the first forming step in the manufacturing method applicable to the seamless can body 1B shown in FIG. 10. [FIG. 16] is a schematic diagram showing another example (two) of the first forming step in the manufacturing method applicable to the 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.

1A: Seamless tank body

10: Cylindrical main body

10e: Lower end

20: Tank bottom

201: Center of tank bottom

201d: Tank dome

201e: Outermost

202: Foot

202a: Peripheral bottom

202b: Circumferential grounding part

202c: Inner end

202d: Standing part

Hp: Height of the dome of the tank (second height)

RA: Tank axis

Claims (14)

A seamless tank body having a cylindrical main body and a tank bottom, wherein the tank bottom includes an outer peripheral bottom that is continuous from the lower end of the cylindrical main body through the junction portion and tapers inwardly, and a peripheral grounding portion located further inward than the outer peripheral bottom, and when the plate thickness of the outer peripheral bottom is set to t1 and the plate thickness of the peripheral grounding portion is set to t2, t2>t1. A seamless tank body, characterized in that it includes a cylindrical main body, and at least a tank bottom having an outer peripheral bottom that is continuous in a manner of tapering from the lower end of the cylindrical main body through the junction and inward, and a peripheral grounding portion located further inward than the outer peripheral bottom, wherein the plate thickness of the lower end of the cylindrical main body, the plate thickness in the junction, and the plate thickness of at least a portion of the outer peripheral bottom are respectively approximately equal to the plate thickness of the middle portion in the axial direction of the cylindrical main body. For a seamless tank body as claimed in claim 1 or 2, the tank bottom further includes an inner end portion located further inward than the circumferential grounding portion, and when the plate thickness of the outer bottom portion is set to t1 and the plate thickness of the inner end portion is set to t3, t3>t1. For example, in the seamless tank body of claim 3, when the plate thickness of the circumferential grounding portion is set to t2 and the plate thickness of the inner end portion is set to t3, the plate thickness gradually increases from the outer bottom portion to the inner end portion in the manner of t3>t2. For example, in the seamless tank body of claim 3, the tank bottom further includes a rising portion rising upward from the inner end, and when the plate thickness of the outer bottom is set to t1 and the plate thickness of the upper end of the rising portion is set to t4, t4>t1. For example, the seamless tank body of claim 5, wherein the tank bottom further includes a dome portion that bulges upward in a manner continuous with the rising portion, and when the plate thickness of the inner end portion is set to t3, the plate thickness of the upper end of the rising portion is set to t4, and the plate thickness of the center of the dome portion is set to t5, the plate thickness gradually increases from the dome portion to the inner end portion in the manner of t3>t4>t5. For example, in the seamless tank body of claim 6, when the plate thickness of the outer bottom is set to t1 and the plate thickness of the center of the dome is set to t5, t5<t1. As in claim 6, the seamless can body has an annular groove protruding from the connecting portion between the above-mentioned rising portion and the above-mentioned dome portion toward the outside of the can body axis. For example, in the seamless can body of claim 2, when the plate thickness at the lower end of the above-mentioned cylindrical main body is set to t _WL and the plate thickness at the middle portion in the axial direction of the above-mentioned cylindrical main body is set to t _WC , the relationship of t _WC ≦t _WL <1.09×t _WC is satisfied. A seamless tank body as claimed in claim 9, wherein, in the above-mentioned cylindrical main body, the relationship t _WC ≦t0<1.09×t _WC is satisfied, wherein t0 is the plate thickness of the above-mentioned boundary portion. For the seamless tank body of claim 1 or 2, the 60-degree mirror gloss from the lower end of the cylindrical main body to the vicinity of the junction is 300% or more. A method for manufacturing a seamless can body, the seamless can body having a cylindrical main body and a can bottom, characterized by comprising: a first forming step, forming a metal raw material into a cup body, the cup body having a cylindrical main body, a cup-shaped outer peripheral bottom which is continuous in a manner of tapering from the lower end of the cylindrical main body, an inclined portion extending upward from the cup-shaped outer peripheral bottom toward the inner side, and a cup-shaped dome portion bulging upward at a first height from the end of the inclined portion; and a second forming step, by making the cup-shaped outer peripheral bottom of the cup body abut against a lower mold forming member on one side, and moving the upper mold forming member toward the cup body to form a cup-shaped outer peripheral bottom. The cup-shaped dome is pressed closer to the outside of the tank to form a second height lower than the first height, so that the compressive stress in the meridian direction and the circumferential direction acts on the inclined portion, and the thickness of the inclined portion is increased while being pressed into the lower mold forming member. The tank bottom includes an outer peripheral bottom that is continuous in a manner of reducing the diameter inward from the lower end of the cylindrical main body through the junction, and a circumferential grounding portion located further inward than the outer peripheral bottom. When the plate thickness of the outer peripheral bottom is set to t1 and the plate thickness of the circumferential grounding portion is set to t2, t2>t1. A method for manufacturing a seamless can body as claimed in claim 12, wherein in the second forming step, by pressing the inclined portion into the lower mold forming member, a circumferential grounding portion located further inward than the outer circumferential bottom portion, an inner end portion located further inward than the circumferential grounding portion, and a rising portion rising upward from the inner end portion and connected to the dome portion of the can are formed, and an annular groove protruding from the connecting portion of the rising portion and the dome portion of the can is formed toward the outside of the can body axis in such a manner that the inner diameter of the connecting portion between the rising portion and the dome portion of the can is larger than the inner diameter of the inner end portion. A method for manufacturing a seamless can body, characterized in that it includes: a first forming step, which forms a metal raw material into a cup body, the cup body having a cylindrical main body portion thinned by shrinkage processing, an outer peripheral bottom portion continuous from the lower end of the above-mentioned cylindrical main body portion, and a bulging portion bulging from the above-mentioned outer peripheral bottom portion toward the opening portion at a first height; and a second forming step, which presses the above-mentioned bulging portion downward in a manner to form a second height lower than the above-mentioned first height; and in the above-mentioned first forming step, the plate thickness of the lower end of the above-mentioned cylindrical main body portion is approximately equal to the plate thickness of the middle portion in the axial direction of the above-mentioned cylindrical main body portion, so that the above-mentioned outer peripheral bottom portion is formed in a manner of being pulled into the lower end of the above-mentioned cylindrical main body portion and being continuously reduced in diameter from the lower end of the above-mentioned cylindrical main body portion through the junction portion to the inside.