JP7424448B2 - Seamless can body and method for manufacturing seamless can body - Google Patents

Description

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

BACKGROUND ART Conventionally, so-called seamless can bodies are known, in which the can body and the like are formed by drawing and ironing. This seamless can body is lightweight because the can body is made thinner by ironing. On the other hand, it is difficult to employ a processing method such as laddering to forcibly reduce the thickness of these seamless can bottoms, and the thickness of the can bottom does not vary greatly from the material thickness. Since the bottom is required to have strength (pressure resistance) to resist deformation due to the internal pressure of the can, the thickness of the material at the bottom of the can is made thinner in order to reduce the weight, and at the same time, the thickness of the material is reduced to maintain or improve the pressure resistance. Various proposals have been made in the past.

For example, Patent Document 1 and Patent Document 2 disclose so-called bottom reform processing, which is performed for the purpose of preventing the phenomenon in which the dome portion of the can bottom inverts (buckling), which occurs when the internal pressure of the can exceeds the pressure resistance strength. has been done. Specifically, bottom reform processing is disclosed in which a concave portion is formed by pressing an inner circumferential wall of a ground contact portion of a can bottom located on the inside in a radial direction perpendicular to the can axis.

JP2018-103227A Japanese Patent Application Publication No. 2016-47541 Japanese Patent Application Publication No. 2000-176575 Japanese Patent Application Publication No. 9-285832 WO2018/070542 publication

However, bottom reform processing had the following problems.
That is, in this bottom reforming process, a concave portion is formed by pressing the inner circumferential wall of the can bottom using a forming roller or the like. When pressing using this forming roller, etc., as described in Patent Document 3, there is a problem that black discoloration tends to occur at the pressed area, and a problem that metal material tends to adhere to the forming roller, etc. was there.

Also, during pressing, lubricating oil is applied to ensure smooth machining, but since a process to clean this lubricating oil is required after bottom reforming, there are additional costs in terms of cleaning costs and environmental impact. Improvement was needed.

In addition, in recent years, in order to reduce the weight of seamless can bodies, there has been a demand for increasingly thinner blanks before drawing and ironing. However, when the bottom reform processing is performed, the thickness of the metal material of the pressing portion is stretched and thinned by the processing, so there is a limit to reducing the thickness of the blank.

Furthermore, as shown in Patent Document 4, the present inventor disclosed a technique for improving the pressure resistance of a seamless can body. However, although this technique improves pressure resistance, it does not fully optimize the thickness distribution of each part of the can body (particularly the can bottom). Therefore, the demand for reducing the weight of the can body was not fully satisfied.

Further, Patent Document 5 discloses a two-piece can body characterized in that the thickness of the ground-contacting portion of the can bottom is thicker than the thickness of the raw material before processing. However, in this technique, the apparatus is complicated, and there are problems such as difficulty in realizing it on an industrial level or an increase in equipment costs.

The inventors of the present invention repeatedly conducted intensive studies in view of the problems exemplified above. As a result, we developed a seamless can body and its manufacturing method that reduces the thickness of the blank, increases the pressure resistance of the can bottom, suppresses buckling, and solves the blackening and cleaning problems mentioned above. This makes it possible to provide the product with a simpler manufacturing device, leading to the present invention.

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, the can bottom being a part of the cylindrical body. It includes an outer circumferential bottom part that continues so as to reduce its diameter inward from the lower end, and a circumferential grounding part located inside the outer circumferential bottom part, where the thickness of the outer circumferential bottom part is t1, and the plate thickness of the circumferential grounding part. is characterized in that t2>t1, where t2 is t2.

In addition, in (1) above, (2) the can bottom further includes an inner end 202c located inside the circumferential grounding part, and when the thickness of the inner end is t3, t3> Preferably, it is t1.

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

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

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

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

Further, in any of (4) to (6) above, (7) a ring groove may be formed in which the connection portion between the rising portion and the dome portion is convex toward the outside of the can shaft; preferable.

In order to achieve the above object, a method for manufacturing a seamless can body according to an embodiment of the present invention is (8) a method for manufacturing a seamless can body having a cylindrical body and a can bottom, the method comprising: a cup-shaped body part, a cup outer circumferential bottom part that continues to reduce in diameter from the lower end of the cylindrical body part, an inclined part that extends inwardly and upwardly from the cup outer circumferential bottom part and slopes toward the center of the dome, and the inclined part. a first molding step of molding the cup body into a cup body having a cup dome portion bulging upward at a first height from an end portion of the cup body; By applying a pressing force from the cup dome toward the outside of the can with the upper molding member while making contact with the cup dome, the cup dome is pushed down to a second height lower than the first height, thereby increasing the inclination. Applying compressive stress in the meridian direction and circumferential direction to the inclined part and pushing it into the lower molding member while increasing the thickness of the inclined part to form a circumferential grounding part located inside the outer peripheral bottom part, and When the thickness of the outer peripheral bottom is t1 and the thickness of the circumferential grounding portion is t2, the present invention is characterized by including a second forming step in which t2>t1 is satisfied.

Further, in (8) above, in (9) the second forming step, by pushing the inclined portion into the lower molding member, the circumferential grounding portion 202b located inside the outer circumferential bottom portion and the circumferential An inner end portion 202c located 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 connecting portion between the rising portion 202d and the can dome portion 201d. A ring groove is formed in which the connecting portion is convex toward the outside of the can shaft so that the inner diameter (dx) of the outermost end 201e is larger than the inner diameter (dy) of the inner end 202c. It is preferable that

According to the seamless can body of the present invention, even when the thickness of the base plate (blank) is reduced, it is possible to obtain a can bottom with higher pressure resistance than that obtained by conventional bottom reform processing. Therefore, it is possible to manufacture a seamless can body using a thinner sheet (blank) than in the past, and the amount of metal material used can be reduced, which is advantageous in terms of cost. Furthermore, by reducing the weight of the seamless can body, it is possible to reduce recycling costs, transportation costs, etc.

Furthermore, according to the seamless can manufacturing method of the present invention, even when the thickness of the blank is made thinner, it is possible to increase the pressure resistance of the can bottom and suppress buckling using simple manufacturing equipment. It is. In addition, it is possible to solve the problem of blackening, which is a problem in bottom reform processing. Furthermore, since there is no need for the conventional bottom reforming process or the subsequent process for cleaning lubricating oil, there are significant cost and environmental benefits.

It is a schematic diagram showing the seamless can body 1 in this embodiment. It is an enlarged view showing the can bottom of the seamless can body 1 in this embodiment. It is a graph showing the plate thickness at each point in the seamless can body 1 according to the present embodiment. It is a figure which shows the 1st shaping|molding process in the manufacturing method of the seamless can body of this embodiment. It is a figure which shows the 2nd shaping|molding process in the manufacturing method of the seamless can body of this embodiment. FIG. 3 is a schematic diagram showing compressive stress applied to a rising portion in this embodiment. FIG. 3 is a partially enlarged view of the can bottom of the seamless can body used in Comparative Example 1.

EMBODIMENT OF THE INVENTION Hereinafter, the seamless can body of this invention and its manufacturing method are concretely demonstrated, referring drawings suitably. In addition, the following embodiment shows an example of this invention and explains 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 this embodiment, the can bottom 20 includes a can bottom central portion 201 that does not come into contact with a horizontal surface when the seamless can body is placed on the horizontal surface, and a can bottom central portion 201 that does not come into contact with the horizontal surface when the seamless can body is placed on the horizontal surface. Preferably, it includes a foot portion 202 located on the outside of the bottom center portion 201.
The can bottom central portion 201 of the seamless can body 1 in this embodiment may have a horizontal shape, or it may bulge toward the inner surface of the can (bulge upwardly) as shown in FIG. 1(a). It may be dome-shaped.

In this embodiment, as shown in FIG. 1(b), the foot portion 202 of the can bottom portion 20 extends from the lower end 10e of the cylindrical body portion 10 toward the can body axis RA direction toward the top of the can bottom center portion 201. It is defined as the portion up to the outer end 201e.
In addition, as shown in the enlarged sectional view of the foot portion 202 in FIG. The diameter is the maximum.

In this embodiment, the lowermost portion of the foot portion 202 in the Z-axis direction is a circumferential ground contact portion 202b. That is, the circumferential grounding portion 202b can be said to be a portion that comes into contact with a horizontal surface when the seamless can body 1 of this embodiment is placed on the horizontal surface.
The area from the lower end 10e of the cylindrical body portion 10 to the circumferential grounding portion 202b is defined as an outer circumferential bottom portion 202a.

That is, in this embodiment, the foot portion 202 includes an outer circumferential bottom portion 202a that continues from the lower end 10e of the cylindrical body portion 10 so as to reduce in diameter inward, and a circumferential grounding portion 202b located inside the outer circumferential bottom portion 202a. and, including.
In other words, in the seamless can body of this embodiment, the outer peripheral bottom portion 202a is located in a ring shape outside the circumferential grounding portion 202b up to the lower end 10e of the cylindrical body portion 10.

In this embodiment, there is no particular restriction on the ring width or area of the outer circumferential bottom portion 202a, and any known shape may be applied to its inclination angle and curved state. That is, the cross section may be linear, or may be an arcuate shape curved toward the inside of the can, or conversely may be an arcuate shape curved outward. Alternatively, a part may be curved inwardly and the rest may be curved outwardly, and these may be continuously connected.
In this 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, since this makes it easier to stack the can on the lid of the same type 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 grounding portion 202b. This 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 cross-sectional view.
Furthermore, the seamless can body 1 of this embodiment includes a rising portion 202d extending upward (in the + direction of the Z axis) from the inner end portion 202c. The rising portion 202d is defined as a portion from the inner end 202c to the outermost end 201e in the direction of the can bottom center portion 201 in the cross-sectional view shown in FIG. 1(a) or FIG.

The seamless can body of this embodiment is characterized in that when the thickness of the outer circumferential bottom portion 202a is t1 and the thickness of the circumferential grounding portion 202b is t2, a relationship of “t2>t1” holds true. By satisfying such a relationship, it becomes possible to impart preferable pressure resistance to the seamless can body 1 of this embodiment while reducing the weight of the can body. Moreover, by setting t2>t1, strength against deformation when the seamless can body 1 is dropped with the can bottom 20 facing down can be imparted, which is preferable.
The thickness (t1) of the outer peripheral bottom portion 202a is the thickness at the midpoint of the length (length along the shape) from the lower end 10e to the circumferential grounding portion 202b.

In the seamless can body of the present embodiment, it is further preferable that the relationship "t3>t1" holds true, where the thickness of the inner end 202c is t3. By satisfying such a relationship, it becomes possible to impart preferable pressure resistance to the seamless can body 1 of this embodiment while reducing the weight of the can body. Moreover, by setting t3>t1, strength against deformation when the seamless can body 1 is dropped with the can bottom 20 facing down can be imparted, which is preferable.

The above-described thickness in the present invention is determined for the following reasons.
That is, when the liquid contained in the seamless can body is beer or carbonated beverage, internal pressure is always applied to the bottom of the can. If an impact is applied to the bottom of the can while the internal pressure is applied in this way, or if the internal pressure applied to the bottom of the can suddenly increases for some reason, the internal pressure of the can will exceed the pressure resistance strength of the can bottom. A phenomenon in which the dome portion of the can bottom turns over (buckling) occurs.

In order to suppress this buckling phenomenon, it is necessary to increase the pressure resistance of the can bottom, and one possible method for this purpose is to increase the thickness of the can bottom portion.
However, due to the recent demand for weight reduction, the thickness of the raw plate (blank) is becoming thinner, so if you simply increase the thickness of the raw plate (blank) to increase the pressure resistance of the can bottom, This would violate the above requirements.

Therefore, the inventors of the present invention have conducted extensive studies in order to realize a seamless can body that simultaneously satisfies the requirements for reducing the weight of the can and increasing the pressure resistance of the can bottom. As a result, the pressure resistance of the can bottom can be increased by making the thickness of the blank plate the same as before or thinner than before, but by thickening only the parts of the can bottom that are likely to contribute to improving the pressure resistance. The present invention was conceived by realizing the following.

According to the present invention, a thinner blank than before can be used for the can body, so the same severe drawing and ironing process as before can be used to make the body plate thickness the same as before or thinner than before. can be reached. Therefore, it can be said that it is possible to satisfy both the requirements for weight reduction and pressure resistance of the can bottom at a high level.

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

In this 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.
Further, as shown in FIGS. 1A and 2, the rising portion 202d may be a straight line or a curved line extending along the straight line of Z=-aX (Z>0) in the cross section.

As shown in FIG. 1(a), the rising portion 202d is formed at the center of the can bottom such 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. 1(a) and 2, the vicinity of the outermost end 201e has an approximately "⊂" or "⊃" shape in the cross-sectional view.
Further, referring to FIG. 1(a), there is an outermost end 201e between the inner end portion 202c and the can dome portion 201d toward the + direction of the Z-axis toward the outside of the can body axis RA. It is preferable that the ring groove has a convex ring groove.

By having the above shape, it is possible to improve the pressure resistance of the seamless can body 1 of this embodiment.

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

In this embodiment, when the thickness of the outermost end 201e where the rising portion 202d and the can bottom central portion 201 connect is t4, the relationship “t4>t1” holds, which also contributes to the 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 this embodiment further includes a can dome portion 201d that bulges upward in continuation with the rising portion 202d in the can bottom portion 20. is preferred. That is, in this embodiment, it is preferable that the shape of the can bottom central portion 201 is a dome shape as shown in FIG. 1(a).

When the thickness of the center 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 that continues outward from the center portion of the can dome portion 201d to the inner end portion 202c gradually increases.

Furthermore, in this embodiment, as shown in FIG. 3, when the thickness of the raw plate (blank) is t0, "t1>t0", "t2>t0", "t3>t0", and "t4". >t0'' is preferable from the viewpoint of pressure resistance desired for the seamless can body 1.
On the other hand, in this embodiment, there is no problem even if the thickness (t5) at the center of the can dome portion 201d is less than or equal to the thickness (t0) of the blank (t5≦t0).

In this embodiment, as shown in FIG. 3(a), it is preferable that the thicknesses of the respective plates 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 circumferential bottom portion 202a, the circumferential grounding portion 202b, and the inner end portion 202c.
By satisfying such a relationship, it becomes possible to impart preferable pressure resistance to the seamless can body 1 of this embodiment.

Further, by satisfying the above-described relationship "t3>t2>t1", even if the plate thickness at the t3 portion increases, it is possible to suppress an increase in the weight of the can, which is preferable. The reason for this is that in the order of t1 → t2 → t3, their positions become closer to the can body axis RA, so the volume occupied by each becomes smaller in order.
Therefore, as a result, pressure resistance can be increased while suppressing an increase in the weight of the can, which is preferable.

However, the present embodiment is not limited to this. As shown in FIG. 3(b), the thickness of t2 and t3 may be the same, or the thickness of t2 may be the same as shown in FIG. 3(c). It may be the maximum.

In addition, the thickness of the raw plate (blank) may be the thickness of the plate normally used for manufacturing seamless can bodies, and it is possible to punch out a metal plate with a thickness of approximately t0 = 0.15 mm to 0.32 mm. Although it can be used as a base plate (blank), the thickness is not limited to the above thickness.

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

Further, 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".

The reason why the pressure resistance is improved by having the plate thickness relationship as described above is not yet clear in detail, but the following reasons can be considered.
Buckling pressure is a numerical representation of pressure resistance. That is, the peak value of the pressure at which the dome portion of the can bottom, which is convex on the inside, deforms outward due to the internal pressure, is called the buckling pressure.

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

Furthermore, when the deformation of the region from the circumferential grounding 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 circumferential grounding portion 202b, the inner end portion 202c, and the rising portion 202d are no longer able to maintain an annular shape centered on the can body axis RA, and the outermost end 201e located on the outer periphery of the dome portion that is connected thereto also loses its circular shape. As a result, the can dome portion 201d connected thereto cannot maintain its spherical shape, so that the strength of the dome portion rapidly decreases and the dome portion is reversed (buckling) to the outside of the can.

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

Note that 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, 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. Further, the metal plate may be appropriately surface-treated, such as by laminating a known film, coating with an organic resin, or undergoing a chemical conversion treatment.

The seamless can body 1 of this embodiment is subjected to a known necking process, a flange process, or a process to form a thread, and after beer, carbonated beverages, etc. are accommodated as contents, the opening is opened using a known method. The lid can be attached.

<Method for manufacturing seamless can body>
Next, a method for manufacturing a seamless can body in this embodiment will be described.
The method for manufacturing a seamless can body in this embodiment is a method for manufacturing a seamless can body 1 having a cylindrical body 10 and a can bottom 20 as shown in FIG. 1(a), which will be described in detail below. The method is characterized in that it includes at least a first molding step and a second molding step.

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

Below, a method for manufacturing a seamless can body in this embodiment will be explained.
First, a precursor 3 having a cup shape 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, which can be obtained by a known drawing and ironing method. Moreover, it may have a cup shape with a dome as long as the following first molding step and second molding step can be realized.

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

First, in the first forming step of the method for manufacturing the seamless can body 1 in this embodiment, as shown in FIG. A cup outer circumferential bottom part A that continues to reduce in diameter from the lower end 10e of the body part 10, an inclined part S that extends inwardly and upwardly from the cup outer circumferential bottom part A, and an upwardly extending end part Se of the inclined part S. The cup body 2 is formed into a cup body 2 having a cup dome portion D that bulges at a first height Ho.
Here, the end portion Se of the inclined portion S can also be called a connection point with the cup dome portion D.

The first molding process shown in FIG. 4 may be performed as a separate process using an upper mold and a lower mold on the precursor 3 into which the cylindrical body 10 has been molded by a known pressing process or the like. It can also be done at the final stage of the stroke following the ironing process.
As a specific example, as shown in FIG. 4, a cylindrical punch 401 is positioned inside and supports the cup-shaped precursor 3, and a cylindrical punch 401 is used to support the precursor 3 in cooperation with the punch 401. The first molding step is carried out by the hold down ring 501 that moves and supports and the doming die 502.
First, the outer circumferential bottom of the precursor 3 is held by the tapered part 402 of the punch 401 and the tapered support part 503 of the hold-down ring 501, and the punch 401 and doming die 502 are driven so as to be engaged with each other so as to be relatively close to each other. As a result, a cup body 2 having a Ho cup dome portion D at the bottom can be obtained.

Here, the shape of the cup body 2 obtained by the first molding step will be explained. That is, the inclined portion S of the cup body 2 extends upwardly inward from the cup outer circumferential bottom portion A.
That is, as shown in FIG. 4, the sloped 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 and the connection point Se with the cup dome portion D in the Z-axis direction. shall say.

As shown in FIG. 4(c), it is preferable that the slope portion S is not vertical but is sloped at a predetermined angle _θ1 .
That is, the angle θ ₁ formed 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, the angle θ ₁ between the inclined portion S and the Z axis should be between 10° and 30° to facilitate spray painting when forming a coating film on the inner surface by spray painting after the first molding process. 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 bottom A of the cup periphery is preferably set to R = 5 × t0 to 15 × t0, and the plate thickness of each portion is preferably adjusted in the second forming process described below. This is preferable from the viewpoint of control.

Furthermore, it is preferable that the height Ho of the cup dome portion D in the cup body 2 is larger than the height Hp of the can dome portion 201d in the seamless can body 1 obtained by the second forming process described later. The reason for this is to apply compressive stress to the inclined portion S while pressing down the cup dome portion D of the cup body 2 in the second molding step, which will be described later. That is, this is to increase the height Ho of the cup dome portion D in the cup body 2 in advance, and finally obtain a preferable height Hp of the can dome portion 201d in the seamless can body 1.

Subsequently, the second molding step will be explained.
After the cup body 2 having the cup outer circumferential bottom part A and the slope part S is molded in the first molding process, the following second molding process is performed.

In addition, between the first molding step and the second molding step, the cup body 2 is subjected to appropriate known cleaning steps, surface treatment steps, printing steps, painting steps, shape imparting processing 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 forming process, the outer surface of the cup body 2 is coated in a range from the bottom A to the slope S, centering on the lowermost curved part of the cup body 2. can be applied.

In the second molding step, the cup body 2 is processed using a mold different from the molding mold used in the first molding step, and the seamless can body 1 is molded. That is, while the cup body 2 is brought into contact with the lower molding member, a pressing force is applied to the cup dome portion D of the cup body 2 in the direction outside the can (in the -Z axis direction) using the upper molding member.
Alternatively, pressing force may be applied in the +Z-axis direction using the lower molding member while the cup body 2 is brought into contact with the lower molding member and the upper molding member.

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

Then, the cup dome portion D is pushed down to a second height Hp that is lower than the first height Ho. At the same time, compressive stress σ φ in the meridian direction and compressive stress σ _θ in the circumferential direction are applied to the inclined portion S using the upper molding member (dome pushing down tool) and the lower molding member (cup outer peripheral side holder ₎ . Let it work.

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 molding member, the inclined portion S is subjected to compressive stress σ _φ in the meridian direction due to the pushing force of the dome pushing down tool 70, and as it tries to imitate the lower molding member. The 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).
In this way, the seamless can body 1 is obtained after the second molding step.
When the molding is completed, the dome pushing down tool is relatively raised to take out the seamless can body 1 from the cup outer peripheral side holder.

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

In addition, it is more preferable that the second molding step has the following characteristics.
That is, in the second molding step, the above-described cup body 2 is pushed into the lower molding member 60 of the second molding step, so that the inclined portion S becomes the circumferential grounding portion 202b located inside the outer circumferential 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, by the second forming step, the inner diameter (dx) of the connection point (outermost end 201e) between the rising portion 202d and the can dome portion 201d of the seamless can body 1 becomes larger than the inner diameter (dy) of the inner end portion 202c. It is preferable to form a ring groove whose outermost end 201e is convex toward the outside of the can body axis RA so that the ring groove becomes larger.
Conventionally, there has been a reform molding method (bottom reform processing) in which a ring groove as described above is formed using a rotating roll or a split mold. However, with conventional methods, the processed portion tends to become 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 tend to become thinner, but on the contrary tends to become thicker, and deep grooves can be formed without difficulty.

In the seamless can manufacturing method of this embodiment, no change is given to the shape or length of the upper part of the cup outer circumferential bottom part A of the cup body 2 between the first molding step and the second molding step.
That is, when the cup body 2 is placed on the outer holder 60, the lowest point in the Z-axis direction of the surface where the cup outer bottom A of the cup body 2 and the tapered surface 601 of the cup outer holder 60 contact is T. Point. The position of this point T does not change as the dome pushing down tool 70 descends and the cup dome portion D is pushed down. (See Figure 5)

On the other hand, in the second forming step, the portion that was the sloped portion S of the cup body 2 is transformed into a part of the outer peripheral bottom portion 202a, the circumferential ground portion 202b, the inner end portion 202c, and the rising portion 202d of the seamless can body 1. molded. That is, the sloped portion S of the cup body 2 eventually enters the groove 602 of the cup outer peripheral side holder 60 in its entirety.
Note that in this second molding step, there is no significant sliding in the contact between the cup body 2 and the upper and lower molds. Therefore, the metal surface of the cup body 2 is not damaged, and there is no need to use a lubricant.

As shown in FIG. 5, the above-mentioned point T becomes 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 described below.
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. 5(b). It will be about twice as short.

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

Hereinafter, the content of the present invention will be explained in more detail with reference to Examples and Comparative Examples. However, the present invention is not 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 to both surfaces of the aluminum alloy plate as a lubricant during drawing.

Next, the aluminum alloy plate was punched into a disk shape with a diameter of 160 mm using a drawing machine, and immediately drawn into a drawing cup (not shown) with a diameter of 90 mm.
The resulting drawn cup is transported to a body maker (can body making machine) and re-drawn to a shape with a diameter of 66 mm.Then, using coolant, it is shaped into a shape with a diameter of 66 mm, a height of 130 mm, and a minimum side wall thickness. Ironing was performed so that the precursor 3 was formed by drawing and ironing into a shape of 0.105 mm.

Next, in order to form a can bottom, the precursor 3 obtained above was subjected to the following first forming process and second forming process.
First, the first forming process is performed at the final stage of the stroke following the ironing process at the body maker, using the punch 401, hold down ring 501, and doming die 502 shown in FIG. The cup body 2 has S. The lengths and thicknesses of the cup outer circumferential bottom part A and the sloped part S at this time are as shown in Table 1.

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

Next, the plate thickness at each portion from t1 to t5 was measured. Note that the locations of each portion from t1 to t5 were as shown in the above embodiment and FIG. 2. In addition, the method for measuring the plate thickness was as follows. That is, after the molded seamless can body 1 was embedded in 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 through cutting and careful polishing, the thickness of each of the t1 to t5 portions was measured using a measuring microscope. Table 1 shows the plate thickness of each part.

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

(Comparative example 1)
The can bottom was molded in one step using a known can bottom molding die and a known can bottom molding method. Other than that, the same procedure as in Example 1 was carried out.
Note that FIG. 7 shows a partially enlarged view of the can bottom of the seamless can body used in Comparative Example 1.
Table 1 shows the plate thickness of each part of the obtained seamless can body. However, in Table 1, the value for t3 was obtained by measuring the lower end of the slope ((1) in FIG. 7), and the value for t4 was obtained by measuring the upper end of the slope ((2) in FIG. 7).

(Comparative example 2)
The seamless can body obtained in Comparative Example 1 was subjected to bottom reform processing. That is, a concave portion was formed in a circumferential shape by pressing the inner circumferential wall of the ground contact portion of the can bottom located on the inside in the radial direction perpendicular to the can body axis with a rotating roll. Other than that, it was conducted in the same manner as in the comparative example. Table 1 shows the plate thickness of each part of the obtained seamless can body.

(Comparative example 3)
Comparative Example 2 was carried out in the same manner as in Comparative Example 2 except that the thickness of the base plate 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 can obtained by the above method was evaluated by the following method. The results are shown in Table 1.

[Pressure resistance test method]
With the cup filled with water, seal the open end with a stopper equipped with a water pipe. Next, pressurized water is sent into the cup from the water pump through the water pipe. The internal pressure of the cup increases, and at some point the dome instantly deforms so as to flip outward (buckling). Usually, at the same time as this deformation, the internal pressure of the can decreases rapidly. The maximum value of the can internal pressure during this period is defined as proof pressure (MPa).

Based on the results of Examples and Comparative Examples, by controlling the thickness of a specific part of the can bottom, even when the thickness of the blank is made thinner, preferable pressure resistance (0.618 MPa or more required for use in carbonated beverages) can be achieved. was shown to be obtained.

According to the present invention, it is possible to reduce the thickness of the raw plate (blank) of a seamless can body while improving pressure resistance and suppressing the phenomenon of buckling. Therefore, it is possible to reduce the manufacturing cost and transportation cost of the seamless can body. In addition, since fuel and the like required for manufacturing and transportation can be reduced, it is possible to manufacture seamless can bodies that are environmentally friendly.

1 Seamless can body 2 Cup body 3 Precursor 10 Cylindrical body part 10e Lower end 20 Can bottom part 201 Can bottom center part 201d Can dome part 201e Outermost end 202 Foot part 202a Outer circumference bottom part 202b Circumferential ground part 202c Inner end part 202d Standing up Part A Cup outer periphery bottom 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 molding member 60 Lower molding member

Claims (6)

A seamless can body having a cylindrical body and a can bottom,
The can bottom includes an outer circumferential bottom portion that continues so as to reduce in diameter from the lower end of the cylindrical body, a circumferential grounding portion located inside the outer circumferential bottom portion, and an inner circumferential grounding portion located inside the circumferential grounding portion. an inner end located on the upper side in the vertical direction, and a rising part rising upward from the inner end;
The inner diameter of the outermost end of the rising portion is larger than the inner diameter of the inner end,
The plate thickness at the midpoint of the length along the shape of the outer circumferential bottom from the lower end of the cylindrical body to the circumferential grounding part is t1, the plate thickness of the circumferential grounding part is t2, and the inner end When the thickness of the plate is t3,
t3>t2>t1
and
When the plate thickness at the upper end of the rising portion is t4, t3>t4.
Seamless can body. The seamless can body according to claim 1, wherein the plate thickness gradually increases from the outer peripheral bottom part to the inner end part so that t3>t2. When the plate thickness at the upper end of the rising part is t4,
t4>t1
The seamless can body according to claim 1 or 2. The can bottom further includes a dome portion that bulges upward in continuation with the rising portion, and when the thickness of the center plate of the dome portion is t5, t3>t4>t5. 4. The seamless can body according to claim 3, wherein the plate thickness gradually increases from the dome portion to the inner end portion. Furthermore, the seamless can body according to claim 4, wherein t5<t1. 6. The seamless can body according to claim 4, wherein a ring groove is formed in a convex connection portion between the rising portion and the dome portion toward the outside of the can body shaft.