JP2022176310A - Seamless can body and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seamless can body capable of suppressing buckling by simultaneously thinning the plate thickness of a blank and increasing the pressure resistance of a can bottom and solving the problem of black discoloration or cleaning, and a method for manufacturing the seamless can body.

SOLUTION: A seamless can body 1 comprises a cylindrical barrel part 10 and a can bottom 20. The can bottom 20 includes an outer peripheral bottom part 202a continuous so as to be reduced in diameter from the bottom end of the cylindrical barrel part 10 to the inside, and a peripheral ground part 202b located inside the outer peripheral bottom part 202a, and t2>t1 is set, where t1 denotes the plate thickness of the outer peripheral bottom part 202a and t2 denotes the plate thickness of the peripheral ground part 202b.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

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

Conventionally, a so-called seamless can body is known in which a can body and the like are formed by drawing and ironing. This seamless can body is excellent in light weight because the can body is thinned by ironing. On the other hand, it is difficult to employ a processing method such as ironing for forcibly thinning the bottom of these seamless can bodies, and the thickness of the bottom of the can body does not vary greatly from the material thickness. Since the bottom part is required to have strength (pressure resistance) to resist deformation due to the internal pressure of the can, the thickness of the material used for the bottom part of the can body has been reduced to reduce the weight and maintain or improve the pressure resistance. Various proposals have been made conventionally.

For example, Patent Literature 1 and Patent Literature 2 disclose a so-called bottom reforming process that is performed for the purpose of preventing a phenomenon in which the dome portion of the can bottom is reversed (buckling) that appears when the internal pressure of the can exceeds the pressure resistance strength. It is Specifically, it discloses a bottom reforming process in which a concave portion is formed by pressing the inner peripheral wall of the contact portion of the can bottom located inside in the radial direction orthogonal to the can axis.

JP 2018-103227 A JP 2016-47541 A JP-A-2000-176575 JP-A-9-285832 WO2018/070542

However, bottom reform processing has the following problems.
That is, in this bottom reforming step, the concave portion is formed by pressing the inner peripheral wall of the can bottom using a forming roller or the like. When pressing using this forming roller or the like, as described in Patent Document 3, there is a problem that the pressed portion tends to be blackened, and a problem that the metal material tends to adhere to the forming roller or the like. was there.

In addition, lubricating oil is applied during pressing in order to perform processing smoothly, but since a process for washing this lubricating oil is required after bottom reforming processing, from the viewpoint of the cost and environmental load required for washing, it is further Improvement was needed.

Further, in recent years, in order to reduce the weight of the seamless can body, it is required to further reduce the thickness of the raw sheet (blank) before drawing and ironing. However, when the bottom reforming process is performed, the thickness of the metal material of the pressing portion is elongated and thinned by the process, so there is a limit to reducing the thickness of the blank.

Further, as shown in Patent Document 4, the present inventor has disclosed a technique for improving the pressure resistance of a seamless can body. However, although this technique improves the pressure resistance, it does not fully optimize the plate thickness distribution of each portion of the can body (especially the bottom of the can). Therefore, it did not fully satisfy the demand for weight reduction of the can body.

Furthermore, Patent Document 5 discloses a two-piece can body in which the plate thickness of the contact portion of the can bottom is thicker than the plate thickness of the raw material before processing. However, in the technique, the apparatus is complicated, and there are problems such as difficulty in realization at the industrial level or high cost of equipment.

In view of the above-described problems, the inventor of the present invention has made extensive studies. As a result, we have developed a seamless can body and a method for manufacturing the same, in which the thickness of the blank is reduced, the pressure resistance of the can bottom is increased to suppress buckling, and the problems of black discoloration and washing are solved. The present invention has been achieved by making it possible to provide a simpler manufacturing apparatus.

In order to achieve the above object, a seamless can body in one embodiment of the present invention is a seamless can body having (1) a cylindrical body and a can bottom, wherein the can bottom is the cylindrical body It includes an outer peripheral bottom portion that is continuous from the lower end so as to reduce its diameter inward, and a circumferential ground portion positioned inside the outer peripheral bottom portion, wherein the thickness of the outer peripheral bottom portion is t1, and the thickness of the circumferential ground portion is t2, t2>t1.

In (1) above, (2) the can bottom portion further includes an inner end portion 202c located inside the circumferential ground portion, and when the plate thickness of the inner end portion is t3, t3> t1 is preferred.

In (2) above, it is preferable that the plate thickness gradually increases from the outer peripheral bottom portion to the inner end portion so that (3) t3>t2.

Further, in any one of the above (1) to (3), (4) when the can bottom further includes a rising portion 202d rising upward from the inner end portion, and the plate thickness of the upper end of the rising portion is t4. , t4>t1.

Further, in (4) above, (5) the can bottom portion further includes a can dome portion that bulges upward so as to be continuous with the rising portion, and the plate thickness at the center of the can dome portion is t5, it is preferable that the plate thickness gradually increases from the can dome portion to the inner end portion so that t3>t4>t5.

In (5) above, (6) it is preferable that t5<t1.

Further, in any one of the above (4) to (6), (7) a ring groove is formed in which the connecting portion between the rising portion and the dome portion protrudes toward the outside of the can body axis. preferable.

In order to achieve the above object, a method for manufacturing a seamless can body in one embodiment of the present invention is (8) a method for manufacturing a seamless can body having a cylindrical body portion and a can bottom portion, comprising: an outer peripheral bottom portion of the cup extending from the lower end of the cylindrical body portion so as to reduce the diameter thereof; an inclined portion extending upward inward from the outer peripheral bottom portion of the cup and inclined toward the center of the dome; a first forming step of forming a cup body having a cup dome portion that bulges upward at a first height from an empty end portion; By applying a pressing force toward the outside of the can from the cup dome portion while being in contact with the cup dome portion, the cup dome portion is pushed down to a second height lower than the first height, and the inclination is applied. Compressive stress in the meridional direction and the circumferential direction is applied to the portion to increase the thickness of the inclined portion and push it into the lower mold forming member to form a circumferential ground contact portion positioned inside the outer peripheral bottom portion, and and a second forming step that satisfies t2>t1, where t1 is the plate thickness of the outer peripheral bottom portion and t2 is the plate thickness of the circumferential ground portion.

In the above (8), (9) in the second forming step, the inclined portion is pushed into the lower mold forming member so that the circumferential ground portion 202b located inside the outer peripheral bottom portion and the circumferential ground portion 202b An inner end portion 202c positioned inside the grounding portion and a rising portion 202d rising upward from the inner end portion and connecting to the can dome portion are formed, and a connection portion between the rising portion 202d and the can dome portion 201d is formed. A ring groove is formed so that the inner diameter (dx) of (the outermost end 201e) is larger than the inner diameter (dy) of the inner end 202c, and the connecting portion protrudes outward from the can body shaft. preferably.

According to the seamless can body of the present invention, it is possible to obtain a can bottom with higher pressure resistance than a can bottom obtained by a conventional bottom reforming process even when the plate thickness of the blank is reduced. Therefore, a seamless can body can be manufactured using a thinner base plate (blank) than before, and the amount of metal material used can be reduced, which is advantageous in terms of cost. Furthermore, the reduction in the weight of the seamless can can lead to the reduction of recycling costs and transportation costs.

In addition, according to the method for manufacturing a seamless can body of the present invention, even when the plate thickness of the blank is reduced, it is possible to increase the pressure resistance of the can bottom and suppress buckling using a simple manufacturing apparatus. is. In addition, it is possible to solve the problem of black discoloration, which is a problem in bottom reforming. Furthermore, since the conventional bottom reforming process and the subsequent process of cleaning the lubricating oil are not required, there are great advantages in terms of cost and environment.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the seamless can body 1 in this embodiment. It is an enlarged view showing the can bottom of seamless can body 1 in this embodiment. 4 is a graph showing plate thickness at each point in the seamless can body 1 according to the present embodiment. FIG. 4 is a diagram showing a first forming step in the method for manufacturing a seamless can body according to the present embodiment; FIG. 4 is a diagram showing a second forming step in the method for manufacturing a seamless can body according to the present embodiment; FIG. 4 is a schematic diagram showing compressive stress applied to the rising portion in the embodiment. 4 is a partially enlarged view of the bottom of the seamless can body used in Comparative Example 1. FIG.

Hereinafter, the seamless can body and the method for producing the same of the present invention will be specifically described with reference to the drawings as appropriate. In addition, the following embodiment shows an example of this invention, and demonstrates the content, and does not limit this invention intentionally.

<Seamless can body>
As shown in FIG. 1 , the seamless can body 1 of this 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 includes, as shown in FIGS. 1(a) and 1(b), a can bottom central portion 201 which does not come into contact with the horizontal surface when the seamless can body is placed on the horizontal surface; It preferably includes a foot portion 202 located outside of the central bottom portion 201 .
The can bottom central portion 201 of the seamless can body 1 in the present embodiment may be horizontal, or may swell toward the inner surface of the can (protruding upward) as shown in FIG. It may be dome shaped.

In this embodiment, as shown in FIG. 1(b), the leg portion 202 of the can bottom portion 20 extends from the lower end 10e of the cylindrical body portion 10 toward the can bottom central portion 201 in the can body axis RA direction. It is defined as the portion up to the outer end 201e.
As shown in the enlarged cross-sectional view of the leg portion 202 in FIG. 2, when the can bottom central portion 201 is dome-shaped, the "outermost end 201e of the can bottom central portion 201" is a dome shape in the dome shape. is the part where the diameter of the

In the present embodiment, the lowermost portion of the leg portion 202 in the Z-axis direction is a circumferential ground contact portion 202b. That is, it can be said that the circumferential ground portion 202b is a portion that contacts a horizontal surface when the seamless can body 1 of the present embodiment is placed on the horizontal surface.
A portion from the lower end 10e of the cylindrical body portion 10 to the circumferential ground portion 202b is defined as an outer peripheral bottom portion 202a.

That is, in the present embodiment, the leg portion 202 includes an outer peripheral bottom portion 202a that continues from the lower end 10e of the tubular body portion 10 so as to reduce its diameter inward, and a circumferential ground contact portion 202b positioned inside the outer peripheral bottom portion 202a. and including.
In other words, in the seamless can body of the present embodiment, the outer peripheral bottom portion 202a is positioned in a ring shape to the lower end 10e of the cylindrical body portion 10 outside the circumferential ground portion 202b.

In this embodiment, the ring width, area, etc. of the outer peripheral bottom portion 202a are not particularly limited, and the inclination angle and curved state thereof can be applied to known shapes. That is, the cross-section may be straight, curved toward the inside of the can body, or curved outward. Moreover, it may be a shape in which a part is curved inward and the rest is curved outward, and these 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 its cross-sectional view so that it can be easily stacked on the lid of the same kind of can.

As shown in FIG. 2, the seamless can body 1 of this embodiment further includes an inner end portion 202c located inside the circumferential ground portion 202b. The inner end portion 202c is defined as the portion of the leg portion 202 described above that is closest to the can body axis RA side in the sectional view.
Furthermore, the seamless can body 1 of the present embodiment includes a rising portion 202d extending upward (+ direction of the Z-axis) from the inner end portion 202c. The rising portion 202d is defined as a 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 sectional view shown in FIG. 1(a) or FIG.

The seamless can body of the present embodiment is characterized in that a relationship of "t2>t1" holds, where t1 is the plate thickness of the outer peripheral bottom portion 202a and t2 is the plate thickness of the circumferential ground portion 202b. By satisfying such a relationship, the seamless can body 1 of the present embodiment can be provided with preferable pressure resistance while reducing the weight of the can body. Further, by setting t2>t1, it is possible to impart strength against deformation when the seamless can body 1 is dropped with the can bottom portion 20 facing downward, which is preferable.
The thickness (t1) of the outer peripheral bottom portion 202a is the thickness at the midpoint of the length (the length along the shape) from the lower end 10e to the circumferential ground portion 202b.

Further, in the seamless can body of the present embodiment, it is preferable that the relation of "t3>t1" is established when the plate thickness of the inner end portion 202c is t3. By satisfying such a relationship, the seamless can body 1 of the present embodiment can be provided with preferable pressure resistance while reducing the weight of the can body. Moreover, by setting t3>t1, it is possible to impart strength against deformation when the seamless can body 1 is dropped with the can bottom portion 20 facing downward, which is preferable.

The reason for defining the above thickness in the present invention is as follows.
That is, when the liquid contained in the seamless can body is beer or carbonated beverages, the internal pressure is always applied to the bottom of the can. When an impact is applied to the can bottom while the internal pressure is applied, or when the internal pressure applied to the can bottom suddenly increases for some reason, the internal pressure of the can exceeds the compressive strength of the can bottom, A phenomenon in which the dome portion of the can bottom is reversed (buckling) occurs.

In order to suppress this buckling phenomenon, it is necessary to increase the compressive strength of the can bottom.
However, due to the recent demand for weight reduction, the thickness of the blank is becoming thinner. It goes against the above requirement.

Therefore, the present inventors have made intensive studies to realize a seamless can body that simultaneously satisfies the requirements for weight reduction of the can and pressure resistance strength of the can bottom. As a result, it is possible to increase the pressure resistance strength of the can bottom by increasing only the portion of the can bottom that is likely to contribute to the improvement of the pressure resistance strength while making the plate thickness of the base plate (blank) the same as or thinner than the conventional one. realized the present invention.

According to the present invention, for the can body, it is possible to use a blank sheet (blank) that is thinner than before. can be reached. Therefore, it can be said that it is possible to satisfy both the weight reduction and the pressure resistance strength of the can bottom at a high level.

In the seamless can body of this embodiment, as shown in FIGS. 1A and 2, the leg portion 202 of the can bottom portion 20 extends from the inner end portion 202c through the rising portion 202d to the outermost end portion 201e. It is connected to the can bottom central portion 201 (can dome portion 201d).

In the present embodiment, the rising portion 202d may be a straight line or a curved line extending in the vertical direction (+ direction of the Z-axis) from the inner end portion 202c in its cross section.
Also, as shown in FIGS. 1A and 2, the rising portion 202d may be a straight line or a curved line extending along a straight line of Z=-aX (Z>0) in cross section.

As shown in FIG. 1(a), the rising portion 202d is formed at the center of the can bottom so that the inner diameter (dx) of the outermost end 201e is larger than the inner diameter (dy) of the inner end 202c. 201 (can dome portion 201d).

In other words, as shown in FIGS. 1A and 2, the vicinity of the outermost end 201e has a generally "⊂" or "⊃" shape in the cross-sectional view.
Further, referring to FIG. 1(a), in the + direction of the Z axis, between the inner end portion 202c and the can dome portion 201d, there is an outermost end 201e toward the outside of the can body axis RA. preferably has a convex ring groove.

By adopting the shape as described above, it is possible to improve the pressure resistance of the seamless can body 1 of the present embodiment.

As described above, in this embodiment, the outer peripheral bottom portion 202a preferably has an inflection point IP in its cross-sectional view. As shown in FIG. 2, the point of inflection IP may be positioned in the + direction of the Z-axis relative to the outermost end 201e, or may be positioned in the - direction of the Z-axis.

In the present embodiment, when the plate thickness of the outermost end 201e where the rising portion 202d and the can bottom center portion 201 are connected is t4, the fact that the relationship "t4>t1" is satisfied also contributes to weight reduction of the can body. It is preferable from the viewpoint of pressure resistance.

As shown in FIG. 1(a), the seamless can body 1 of the present embodiment further includes a can dome portion 201d that protrudes upward so as to be continuous with the rising portion 202d in the can bottom portion 20. is preferred. That is, in this embodiment, it is preferable that the can bottom central portion 201 has a dome shape as shown in FIG. 1(a).

Assuming that the central thickness of the can 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 thickness of the metal plate extending outward from the central portion of the can dome portion 201d to the inner end portion 202c gradually increases.

Furthermore, in this embodiment, as shown in FIG. >t0” is preferable from the viewpoint of the pressure resistance desired for the seamless can body 1 .
On the other hand, in the present embodiment, there is no problem even if the plate thickness (t5) at the center of the can dome portion 201d is equal to or less than the plate thickness (t0) of the base plate (blank) (t5≤t0).

In this embodiment, as shown in FIG. 3(a), it is preferable that the plate thicknesses have a relationship of "t3>t2>t1". In other words, it is preferable that the plate thickness gradually increases in the order of the outer peripheral bottom portion 202a, the circumferential ground portion 202b, and the inner end portion 202c.
By satisfying such a relationship, it is possible to impart preferable pressure resistance to the seamless can body 1 of the present embodiment.

Moreover, by satisfying the above-described relationship of "t3>t2>t1", it is possible to suppress an increase in the weight of the can even when the thickness of the t3 portion is increased, which is preferable. This is because their positions become closer to the can body axis RA in the order of t1→t2→t3, so that the volume occupied by each becomes smaller in order.
Therefore, as a result, it is possible to increase pressure resistance while suppressing an increase in the weight of the can, which is preferable.

However, the present embodiment is not limited to this, and as shown in FIG. may be maximum.

The thickness of the raw plate (blank) may be any thickness that is normally used for manufacturing a seamless can body, and a metal plate with a thickness of about t0 = 0.15 mm to 0.32 mm is punched. Although it can be used as a base plate (blank), it is not limited to the above thickness.

As described above, in the seamless can body 1 of the present embodiment, it is preferable that the plate thickness of the can bottom portion 20 has the relationship as described above from the viewpoint of the desired pressure resistance.
That is, in the seamless can body 1 of the present embodiment, it is preferable that the can bottom portion 20 , particularly the foot portion 202 , has an average plate thickness greater than that of the can bottom central portion 201 .

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

Although the reason why the pressure resistance is improved by having the above relationship of plate thickness is not yet clarified in detail, the following reasons are conceivable.
The buckling pressure is a numeric representation of pressure resistance. That is, the buckling pressure is the peak value of the pressure at which the inwardly convex dome portion of the can bottom deforms outward due to the internal pressure.

The process by which the buckling phenomenon occurs can be explained as follows.
First, when the dome, which has a nearly spherical shape, begins to receive internal pressure, it does not immediately deform, and the product of the projected area of the dome and the internal pressure becomes a force that pushes the dome outward. It acts so as to apply a load to the shaped grounding portion 202b, the inner end portion 202c, and the rising portion 202d to give deformation.
In other words, the outer circumference of the dome portion is supported by members in a narrow region from the circumferential grounding portion 202b to the rising portion 202d.

Furthermore, when the deformation of the area from the circumferential ground contact portion 202b to the rising portion 202d progresses due to the increase in internal pressure, the function of supporting the outer periphery of the dome portion is lost. That is, the circular ground portion 202b, the inner end portion 202c, and the rising portion 202d cannot maintain the annular shape centering on the can body axis RA, and the outermost end 201e located on the outer periphery of the dome portion connected thereto also loses its circular shape. Furthermore, since the can dome portion 201d connected thereto cannot maintain the spherical shape, the strength of the dome portion rapidly decreases and the dome portion reverses (buckling) outward.

Therefore, in order to improve pressure resistance, rather than increasing the plate thickness of the dome portion itself,
It is considered effective to increase the plate thickness of the outer periphery of the dome portion. Therefore, when the thickness of the outer peripheral bottom portion 202a is thicker than the plate thickness of the center of the can dome portion 201d, that is, when "t5<t1", desirable pressure resistance can be obtained in this embodiment.

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

In addition, in this embodiment, the type of metal material used for the seamless can body 1 is not particularly limited. That is, known metal plates that are commonly used for seamless can bodies, such as aluminum alloy plates and surface-treated steel plates, can be used. Moreover, the metal plate may be appropriately surface-treated, for example, by laminating a known film, by coating with an organic resin, or by chemical conversion treatment.

The seamless can body 1 of the present embodiment is subjected to known necking processing, flanging processing, or thread forming processing, and after beer, carbonated beverages, etc. are accommodated as contents, the opening is opened by a known method. to attach the lid.

<Method for manufacturing seamless can body>
Next, a method for manufacturing a seamless can body according to the present embodiment will be described.
As a method for manufacturing a seamless can body in this embodiment, a method for manufacturing a seamless can body 1 having a cylindrical body portion 10 and a can bottom portion 20 as shown in FIG. 1(a) is described in detail below. It is characterized by including at least such a first molding process and a second molding process.

In addition, in the method for manufacturing the seamless can body of the present embodiment, a known method such as that described in Patent Document 4, for example, can be employed as the method for forming the cylindrical body portion 10 .
On the other hand, the method of molding the can bottom 20 is characterized by including at least a first molding step and a second molding step, which will be described in detail below.

A method for manufacturing a seamless can body according to the present embodiment will be described below.
First, a cup-shaped precursor 3 is prepared by forming a can body by a known method using the metal material (blank) described above.
As shown in FIG. 4, the metal material (precursor 3) may have a cup shape without a dome obtained by a known drawing and ironing method or the like. Moreover, as long as the following first forming step and second forming step can be realized, it may have a cup shape with a dome.

By subjecting the precursor 3 to the following first forming step and second forming step, the seamless can body 1 of the present embodiment can be obtained.

First, in the first forming step of the method for manufacturing the seamless can body 1 according to the present embodiment, as shown in FIG. An outer peripheral bottom portion A of the cup that continues to decrease in diameter from the lower end 10e of the body portion 10, an inclined portion S that extends upward and inward from the outer peripheral bottom portion A of the cup, and an end portion Se of the inclined portion S that extends upward. and a cup dome portion D that protrudes to a first height Ho.
Here, the end Se of the inclined portion S can also be said to be a connection point with the cup dome portion D. As shown in FIG.

The first molding step shown in FIG. 4 is performed as a separate step using an upper mold and a lower mold for the precursor 3 in which the cylindrical body 10 is molded by a known press process or the like. It can also be done at the end of the stroke following the ironing process.
As a specific example, as shown in FIG. The first forming step is carried out by the hold-down ring 501 that moves and supports and the doming die 502 .
First, the tapered portion 402 of the punch 401 and the tapered support portion 503 of the hold-down ring 501 hold the outer peripheral bottom portion of the precursor 3, and the punch 401 and the doming die 502 are driven so as to engage with each other to be relatively close to each other. Thus, the cup body 2 having the Ho cup dome portion D at the bottom can be obtained.

Here, the shape of the cup body 2 obtained by the said 1st shaping|molding process is demonstrated. That is, the inclined portion S of the cup body 2 extends upward from the outer peripheral bottom portion A of the cup.
That is, as shown in FIG. 4, the inclined portion S of the cup body 2 includes a curved portion and a straight portion sandwiched between the lowest portion of the cup body 2 in the Z-axis direction and the connection point Se with the cup dome portion D. shall say.

As shown in FIG. 4(c), it is preferable that the inclined portion S is not vertical but inclined at _a predetermined angle θ1.
That is, the angle θ1 between the inclined portion S and the Z axis is preferably ₅ ° to 30° from the viewpoint of preferably controlling the plate thickness of each portion in the second forming step described below.
In addition, when the angle θ ₁ between the inclined portion S and the Z axis is 10° to 30°, spray coating is facilitated when a coating film is formed on the inner surface by a spray coating method after the first molding step. Therefore, it is more preferable.

In addition, the radius of curvature R at the angle θ ₂ formed by the inclined portion S from the outer peripheral bottom portion A of the cup is set to R = 5 × t0 to 15 × t0. It is preferable from the viewpoint of control.

Furthermore, the height Ho of the cup dome portion D in the cup body 2 is preferably greater than the height Hp of the can dome portion 201d in the seamless can body 1 obtained by the second forming step described later. This is because, as will be described later, compressive stress is applied to the inclined portion S while pushing down the cup dome portion D of the cup body 2 in the second forming step described later. That is, the height Ho of the cup dome portion D in the cup body 2 is increased in advance, and the desired height Hp of the can dome portion 201d in the seamless can body 1 is finally obtained.

Next, the second molding step will be explained.
After the cup body 2 having the cup outer peripheral bottom portion A and the inclined portion S is formed by the first forming step, the following second forming step is performed.

In addition, between the first molding process and the second molding process, the cup body 2 is appropriately subjected to a known cleaning process, a surface treatment process, a printing process, a painting process, a shape imparting process to the cylindrical body, Alternatively, neck-in processing or the like may be performed within a range that does not hinder the second forming step.
Furthermore, if necessary, for the purpose of ensuring transportability and corrosion resistance after the first molding process, the outer surface is painted on the area from the cup outer peripheral bottom A to the inclined portion S centered on the lowermost curved portion of the cup body 2. can be applied.

In the second molding step, the cup body 2 is processed with a mold different from the mold used in the first molding step, and the seamless can body 1 is molded. That is, pressing force is applied to the cup dome portion D of the cup body 2 in the can outer direction (-Z-axis direction) using the upper mold forming member while bringing the cup body 2 into contact with the lower mold forming member.
Alternatively, pressing force may be applied in the +Z-axis direction using the lower mold forming member while bringing the cup body 2 into contact with the lower mold forming member and the upper mold forming 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 cup dome portion D is brought into contact with the support portion 701 of the dome push-down tool 70 . 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 contacts the tapered surface 601, the dome pressing tool 70 is further pressed down, The metal of the inclined portion S of the cup body 2 is guided and pushed into the groove 602 while receiving compressive stress.

Then, the cup dome portion D is pushed down to a second height Hp lower than the first height Ho. At the same time, using the upper mold forming member (dome pressing down tool) and the lower mold forming member (cup outer peripheral side holder), compressive stress _σφ in the meridional direction and compressive stress _σθ in the circumferential direction are applied to the inclined portion S. act.

Note that FIG. 6 is a schematic diagram showing the compressive stress applied when the inclined portion S is formed on the rising portion 202d in this embodiment.
That is, when the inclined portion S is pushed into the groove 602 of the lower mold forming member, the compressive stress σ _φ in the meridian direction is exerted on the inclined portion S by the pressing force of the dome pressing tool 70, and the lower mold forming member tries to follow the compressive stress σφ. Compressive stress σ _θ in the circumferential direction due to the movement inward in the radial direction acts simultaneously, and the thickness of the metal material at the inclined portion S increases (in the direction of the arrow σ _ψ in FIG. 6).
Thus, the seamless can body 1 is obtained after passing through the second forming step.
After the molding is finished, the dome pressing tool is relatively raised, and the seamless can body 1 can be taken out from the holder on the outer peripheral side of the cup.

Here, the seamless can body 1 obtained after the second forming step is preferably the seamless can body 1 of the present embodiment described above.
That is, as shown in FIG. 1, the seamless can body 1 obtained after the second molding step has an outer peripheral bottom portion 202a and a peripheral ground portion 202b, and the thickness of the outer peripheral bottom portion 202a is t1. When the plate thickness of the portion 202b is t2, it is preferable that the relationship of "t2>t1" holds.

In addition, it is more preferable that the second molding step has the following characteristics.
That is, in the second molding step, the cup body 2 described above is pushed into the lower mold molding member 60 in the second molding step, so that the inclined portion S is formed with the circumferential ground portion 202b located inside the outer peripheral bottom portion 202a, It is preferable to form an inner end portion 202c located inside the circumferential grounding portion 202b and a rising portion 202d rising upward from the inner end portion 202c and connecting to the can dome portion 201d.

Then, in the second forming step, the inner diameter (dx) of the connection point (outermost end 201e) between the rising portion 202d of the seamless can body 1 and the can dome portion 201d is made larger than the inner diameter (dy) of the inner end portion 202c. It is preferable to form a ring groove in which the outermost end 201e protrudes toward the outside of the can body axis RA so as to increase in size.
Conventionally, there has been a reform molding method (bottom reform processing) in which a ring groove as described above is formed using a rotary roll or a split mold. However, in the conventional method, the processed portion tends to be thin and it is difficult to form sufficiently deep grooves.
According to the method of the present invention, the plate thickness of the ring groove portion does not become thin, but conversely tends to become thick, and a deep groove can be formed without difficulty.

In the seamless can body manufacturing method of 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 outer peripheral holder 60, T is 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 holder 60 contact. point. The position of this point T does not change as the dome pressing tool 70 is lowered and the cup dome portion D is lowered. (See Fig. 5)

On the other hand, in the second forming step, the portion that was the inclined portion S of the cup body 2 was changed to a part of the outer peripheral bottom portion 202a of the seamless can body 1, a circumferential ground portion 202b, an inner end portion 202c, and a rising portion 202d. molded. That is, the inclined portion S of the cup body 2 finally enters the groove 602 of the cup outer peripheral side holder 60 .
In this second molding process, there is no significant sliding between the cup body 2 and the upper and lower molds. Therefore, the metal surface of the cup body 2 is not damaged, and it is not necessary to use a lubricant.

As shown in FIG. 5 , the point T is an inflection point IP in the seamless can body 1 . Due to the compressive stress imparted by the second forming step, the metal length is shortened as follows.
That is, the metal length from the inflection point IP to the outermost end 201e in FIG. 5(f) is 0.85 to 0.99 compared to the metal length from point T to Se in FIG. about twice as short.

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

The contents of the present invention will now be described in more detail with reference to examples and comparative examples. However, the present invention is by no means limited to the following examples.

(Example 1)
A drawn and ironed can (DI can) having an internal volume of 350 mL was manufactured by the method shown below.
First, an aluminum alloy plate (JIS H 4000 A3104-H19 material, 0.28 mm) was prepared as a base plate. Next, a predetermined amount of known cupping oil was applied as a lubricant during drawing to both surfaces of the aluminum alloy plate.

Then, the aluminum alloy plate was punched out into a disk shape with a diameter of 160 mm by a drawing machine, and then immediately drawn into a drawn cup (not shown) with a diameter of 90 mm.
The resulting drawn cup is conveyed to a body maker (can body manufacturing machine) and redraw-formed so that it has a shape of 66 mm in diameter. The ironing process was performed so as to obtain a precursor 3 made by drawing and ironing in a shape of 0.105 mm.

Next, in order to form the can bottom, the precursor 3 obtained above was subjected to the following first forming step and second forming step.
First, the first forming step is carried out at the end of the stroke following the ironing process by the body maker. A cup body 2 having S was used. Table 1 shows the length and plate thickness of the cup outer peripheral bottom portion A and the inclined portion S at this time.

Next, in a second forming step, an upper mold forming member 70 and a lower mold forming member 60 shown in FIG. was molded.

Next, the thickness of each portion from t1 to t5 was measured. Note that the locations of each portion from t1 to t5 are as shown in the above embodiment and FIG. Moreover, the plate thickness was measured as follows. That is, after embedding the molded seamless can body 1 with an epoxy resin, the seamless can body 1 was cut along the vertical axis (Z-axis) together with the epoxy resin. After exposing the central cross section by cutting and careful polishing, the thickness of each of the t1 to t5 portions was measured with a measuring microscope. Table 1 shows the plate thickness of each part.

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

(Comparative example 1)
The can bottom molding process was carried out in one step by a known can bottom molding method using a known can bottom molding die. Otherwise, the procedure was the same as in Example 1.
A partially enlarged view of the bottom of the seamless can body used in Comparative Example 1 is shown in FIG.
Table 1 shows the plate thickness of each part of the obtained seamless can body. However, in Table 1, the value of t3 was obtained by measuring the lower end of the inclined portion ((1) in FIG. 7), and the value of t4 was obtained by measuring the upper end of the inclined portion ((2) in FIG. 7).

(Comparative example 2)
The seamless can body obtained in Comparative Example 1 was subjected to bottom reforming. That is, the recess was formed in a circumferential shape by pressing the inner peripheral wall of the contact portion of the can bottom located inside in the radial direction orthogonal to the can body axis with a rotating roll. Otherwise, the procedure was the same as in the comparative example. Table 1 shows the plate thickness of each part of the obtained seamless can body.

(Comparative Example 3)
The same procedure as in Comparative Example 2 was carried out, except that the blank thickness was 0.225 mm and the minimum side wall thickness was 0.093 mm. Table 1 shows the plate thickness of each part of the obtained seamless can body.

[evaluation]
The DI cans obtained by the above method were evaluated by the following methods. Table 1 shows the results.

[Pressure resistance test method]
With the cup filled with water, the open end is sealed with a stopper provided with a water pipe. Next, pressurized water is fed into the cup from the water pump through the water pipe. The internal pressure of the cup rises, and at a certain point, the dome instantly deforms so as to reverse outward (buckling). Normally, the internal pressure of the can suddenly drops simultaneously with this deformation. The maximum value of the can internal pressure during this period is defined as the withstand pressure (MPa).

From the results of Examples and Comparative Examples, by controlling the thickness of a specific part of the can bottom, preferable pressure resistance (0.618 MPa or more required for carbonated beverages) even when the plate thickness of the blank (blank) is reduced. was shown to be obtained.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to suppress the phenomenon of a buckling by improving pressure resistance performance, while making the plate|board thickness of the base plate (blank) of a seamless can thin. Therefore, it is possible to reduce the manufacturing cost of the seamless can body, the transportation cost, and the like. In addition, since the fuel required for manufacturing and transportation can be reduced, it is possible to realize environmentally friendly manufacturing of seamless can bodies.

1 Seamless Can Body 2 Cup Body 3 Precursor 10 Cylindrical Body Part 10e Lower End 20 Can Bottom Part 201 Can Bottom Central Part 201d Can Dome Part 201e Outermost End 202 Foot Part 202a Peripheral Bottom Part 202b Circular Ground Part 202c Inner End Part 202d Rise Part A: Outer circumference bottom of cup D: Cup dome part S: Inclined part Se: End part Hp Height of can dome part (second height)
Ho Cup dome height (first height)
70 upper mold forming member 60 lower mold forming member

Claims (6)

A seamless can body having a cylindrical body and a can bottom,
The can bottom portion includes an outer peripheral bottom portion that continues from the lower end of the cylindrical body portion so as to reduce the diameter inward, and a peripheral ground portion positioned inside the outer peripheral bottom portion,
Let t1 be the plate thickness at the midpoint of the length along the shape of the outer peripheral bottom portion from the lower end of the cylindrical trunk portion to the circumferential ground contact portion, and t2 be the plate thickness of the circumferential ground contact portion,
t2>t1
wherein the can bottom further includes an inner end located inside the circumferential grounding portion,
When the plate thickness of the inner end is t3,
t3>t1
A seamless can body characterized by: The seamless can body according to claim 1, wherein the plate thickness gradually increases from the outer peripheral bottom portion to the inner end portion such that t3>t2. The can bottom further includes a rising portion rising upward from the inner end,
When the plate thickness of the upper end of the rising portion is t4,
t4>t1
The seamless can body according to claim 1 or 2. The can bottom portion includes a dome portion that bulges upward so as to be continuous with the rising portion;
4. The seamless according to claim 3, wherein the plate thickness gradually increases from the dome portion to the inner end portion so that t3>t4>t5, where t5 is the plate thickness at the center of the dome portion. can body. 5. The seamless can body according to claim 4, wherein t5<t1. The seamless can body according to any one of claims 3 to 5, wherein a ring groove is formed in which a connection portion between the rising portion and the dome portion protrudes toward the outside of the can body axis.

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