JPH04344842A - Manufacture of di can body with high pressure resistant strength - Google Patents

Abstract

PURPOSE:To manufacture a DI can body having high pressure withstanding strength can bottom only with DI forming and can bottom forming by using a DI punch. CONSTITUTION:In a process for forming the can bottom after DI (drawing and ironing) forming the can body manufactured with the DI formation, in the case of using Ri for radius of curvature at center axis side 55 in the punch, Ro for raius of curvature at outside 56 and (t) for average sheet thickness in the can bottom part in the can body before forming leg part in the cross sectional shape in the leg forming part 11 of the DI punch 1 for forming the leg part 51 of can bottom part, by using the DI punch smoothly continuing each radius of curvature in the case of having the relation of Ri+Ro<=12.t, or having the relation of t<Ri and Ri<=0.5.Ro, Ri+Ro>12.t or having the relation of t<Ro and Ro<=0.5 .Ri at the tip part of the leg part, the can bottom is formed. After DI forming, roll forming (reforming) is eliminated.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to DI cans manufactured by DI molding of aluminum, tinplate, etc., and particularly relates to a method for manufacturing DI cans that have high pressure resistance among cans that enclose gas or liquid. It is something.

0002

[Prior art and problems to be solved by the invention] Conventionally,
The method for manufacturing DI can bodies is to form a can bottom with legs and a dome using a DI punch tip, a can bottom die, and a doming punch after DI (drawing and ironing) forming. ing.

[0003] The main role of the legs when stacking beverage cans is to engage with the shape of the lid (end) of the can below to make stacking easier, and to prevent the dome from bulging when internal pressure is applied. have.

[0004] The pressure resistance of the can bottom, that is, the internal pressure when the concave dome inverts and becomes convex, has a close relationship with the radius of curvature of the tip of the leg, if the material and plate thickness are the same. It is known that the compressive strength is higher when the radius of curvature is smaller, and Japanese Patent Publication No. 1-50493 also describes a method of reducing the radius of curvature of the leg by roll forming (re-forming) after DI forming. Proposed.

However, remolding after DI molding requires equipment for this purpose, which increases the manufacturing cost of the can body. Also, re-molding (roll forming)
As a result, the angle of inclination of the heel connecting the legs and the can body with respect to the center axis of the can becomes larger than before remolding. Therefore, when an axial force is applied to the can body after remolding, plastic deformation (
Can bottom buckling) is likely to occur, and as a result, the buckling strength of the can bottom in the axial direction of the can body is lower than that of the can body before remolding. Therefore, the roll forming (reforming) method cannot simply reshape the existing DI molded and can bottom molded can bodies;
In the end, it is necessary to predict the deformation of the heel portion due to remolding and change the mold used for DI molding and can bottom molding.

[0006] For these reasons, there has been a need for a manufacturing method that can produce a high pressure-resistant can bottom by simply changing the DI punch without using remolding.

However, in order to manufacture DI cans with high pressure resistance without reshaping, it is sufficient to reduce the radius of curvature of the leg molding of the DI punch. The leg molding portion had the same radius of curvature on the DI punch center axis side and on the outside. For this reason, reducing the diameter of the legs reduces the radius of curvature of the entire leg, which makes it difficult for the material near the legs to flow into the dome during dome forming, resulting in constriction at the rising part of the dome. death,
Furthermore, if the dome portion is molded deeply, breakage will occur. When constriction occurs, the compressive strength decreases. Furthermore, if the dome depth is made small in order to avoid constriction and breakage, the dome portion tends to invert, which also causes a decrease in pressure resistance. Moreover, since the inner surface of the DI can is spray-painted after the can bottom is formed, if the radius of curvature of the leg portion is reduced, a problem arises in that the inner surface of the leg portion cannot be sufficiently coated. Because of these problems, it was not possible to reduce the radius of curvature of the leg.

The present invention solves the above-mentioned problems of the prior art and provides a method for manufacturing a DI can body having a can bottom with high pressure resistance by only DI molding and can bottom molding using a DI punch. The purpose is to

[0009] In order to solve the above-mentioned problems, the present inventor has made it possible to manufacture a DI can body having a can bottom with high pressure resistance only by DI molding and can bottom molding using a DI punch having a relatively simple shape. As a result of intensive research into methods, we found that the conventional method of reducing the diameter of the can body leg to increase the pressure resistance of the can body reduces both the radius of curvature on the side of the DI punch center axis and the radius of curvature on the outside of the DI punch leg molding part. Both of these have the effect of increasing pressure resistance, but if a certain relationship is established between each radius of curvature and the average thickness of the can bottom before forming the legs, reducing the radius of one curvature will reduce the radius of the other. This was found to be more effective than reducing the radius of curvature. Furthermore, it was found that reducing the radius of curvature of only one side is better than reducing the radius of curvature of both, causing no constriction at the rising part of the dome and reducing the pressure resistance, and the present invention was hereby completed. This is what I did.

That is, the present invention is directed to the step of forming the can bottom after DI forming of a can body manufactured by DI (drawing and ironing) forming, in which the DI punch leg forming section for forming the legs of the can bottom is formed. In the cross-sectional shape, the radius of curvature on the side of the center axis of the DI punch is Ri, the radius of curvature on the outside is Ro, the average plate thickness of the bottom of the can body before leg formation is t, and Ri+Ro≦12・t
If the relationship is t<Ri and Ri≦0.5・Ro
, if Ri+Ro>12·t, then t<Ro
Production of a DI can body with high pressure resistance, characterized in that the can bottom is formed using a DI punch that smoothly connects each radius of curvature at the tip of the leg, and has the relationship Ro≦0.5・Ri. The gist is the method.

The present invention will be explained in more detail below.

0012

[Effect]

FIG. 2 shows a cross section of a DI punch 1 for forming a can bottom. The details of the cross-sectional shape of the leg molding part of this DI punch are shown in FIG. 1, and the tip 11 of the leg molding part has a radius of curvature Ri on the punch center axis side and an outer radius of curvature Ro connected smoothly at the leg tip. It has a shape.

When forming a can body using the DI punch 1, the can bottom die 3, and the doming punch 4, first, as shown in FIG. 2, as the DI punch 1 advances, the material 5 comes into contact with the can bottom die 3. It is pressed between the DI punch and the die at the bottom of the can,
This acts as a wrinkle suppressor. Next, the doming punch 4 is operated and the center portion of the can bottom begins to be pushed out, as shown in FIG. Then, as shown in FIG. 4, when a predetermined height is reached, the leg portions 51 and the dome portion 52 are formed.

Here, if the average plate thickness of the can bottom of the can body before leg forming is t, then if the relationship Ri+Ro≦12·t is satisfied, then the radius of curvature of the leg forming part of the DI punch on the side of the punch center axis is smaller than the outer radius of curvature. Thereby, the radius of curvature (Ri') of the can body leg on the side of the can body center axis can be made small. When positive pressure acts inside the can body after molding, a force acts to move the dome toward the center axis of the can body.
This force is transmitted to the rising portion and urges the inside of the leg to bulge, but at this time, if the radius of curvature of the can leg on the side of the can center axis is small, it is difficult to bulge and the dome portion is less likely to invert. In other words, the pressure resistance is increased. This effect is significant when the total radius of curvature (Ri+Ro) is smaller than the plate thickness. However, if Ri>0.5.Ro, the effect is small, so Ri≦0.5.Ro.

Note that when Ri is decreased, if Ro is increased, that is, Ri+Ro is kept almost constant, the average radius of curvature of the can body leg does not change, and when forming the dome, the area near the leg The material easily flows into the dome part, and there is no constriction or breakage at the rising part of the dome, and a sufficient dome depth can be obtained. Further, the inner surface of the leg can be painted by spraying as well as in the past, since the average radius of curvature of the can leg does not change.

However, Ri becomes extremely small and t≧Ri
If this happens, the material will be severely deformed during leg molding, and breakage will occur in the leg. Therefore, t<Ri.

Further, when the relationship Ri+Ro>12·t is satisfied, the punch outer radius of curvature of the leg forming portion of the DI punch is made smaller than the punch center axis side radius of curvature. Thereby, the outer radius of curvature (Ro') of the can body leg can be made small. When positive pressure is applied to the can body, the inside of the leg expands as described above, but at the same time, the entire leg expands and the radius of curvature increases. At this time, by reducing the outer radius of curvature of the leg, it is possible to suppress the expansion of the leg as a whole, making dome inversion less likely to occur, and increasing pressure resistance. The total radius of curvature (Ri+Ro
) is large, this effect is large. However, Ro>0.
When it comes to 5.Ri, the effect is small. Therefore, Ro≦
It is set to 0.5・Ri.

Note that when Ro is decreased, by increasing Ri, that is, by keeping Ri+Ro approximately constant, the average radius of curvature of the leg does not change, and the material near the leg increases. Flow into the dome part easily occurs, a sufficient dome depth is obtained, and the inner surface of the leg part is sufficiently coated.

Next, examples of the present invention will be shown.

[0021]

[Example 1]

[0022] Using the DI punch shown in Figure 1, A300
At the same time as the DI molding of the 4-H19 material, the can bottom was molded. At that time, the radius of curvature Ri on the side of the DI punch center axis and the radius of curvature Ro on the outside of the leg forming part of the DI punch are

[Table 1] as well as

[Table 2] shows. Note that the depth of the dome (height from the tip of the legs to the center of the dome) affects the pressure resistance, so all values are 9.0.
It was molded to have a diameter of mm.

After molding, the shape of the can bottom leg (radius of curvature Ri' on the can body center axis side and outer radius of curvature Ro' of the can body leg) is measured, and the inside of the can is pressurized with N2 to ensure that the dome part is The pressure at the time of inversion (compressive strength) was measured. The results are shown in Tables 1 and 2.

According to Table 1, when the relationship Ri+Ro≦12・t exists (No. 1 to No. 8), by setting the shape of the DI punch to the relationship Ri≦0.5・Ro, the pressure resistance of the can body can be increased. Strength is improved. Also, from Table 2, Ri+Ro>1
When there is a relationship of 2·t (No. 9 to No. 16),
By setting the shape of the DI punch so that Ro≦0.5·Ri, the pressure resistance strength of the can body is improved.

[0025]

[Example 2]

A3004 using the DI punch shown in FIG.
-Can bottom molding was performed simultaneously with DI molding of the H19 material. Here, No. used in Example 1. 1 DI punch and Ri
A DI punch with = Ro = 1 mm was used, and the dome depth was changed by changing the forming pressure of the doming punch. Furthermore, the compressive strength of the molded can was also measured. The result

[Table 3
] Shown in .

From Table 3, examples of the present invention (No. 1 to No. 3)
), it is possible to form a dome up to a depth of 11 mm, but D
Both the center axis side curvature radius and the outside curvature radius of the I punch are 1 m.
In the case of M, fracture occurred at the rising part of the dome at a dome depth of 10 mm. In addition, No. 1 with a dome depth of 9 mm. No. 4 has the outer radius of curvature of the DI punch. Although the average radius of curvature of the legs was smaller than 1, a constriction occurred at the rising part of the dome, resulting in a low pressure resistance. In other words, the can body with a larger average radius of curvature of the legs had higher pressure resistance than the can body with a smaller radius of curvature.

[0028]

[Effects of the Invention] As detailed above, according to the present invention,
By forming the can bottom leg using a DI punch with a specific shape, a can body with high pressure resistance can be obtained. Sexuality also improves. Therefore, it becomes possible to manufacture beverage cans that require higher pressure resistance, and the field of use of DI cans is greatly expanded. Moreover, if the minimum value of pressure resistance is determined, the pressure resistance of the can body can be ensured with a thinner plate thickness, and it is also possible to reduce costs.

[Brief explanation of drawings]

FIG. 1 is a diagram showing details of the cross-sectional shape of a leg forming portion of a DI punch.

FIG. 2 is a cross-sectional view showing a state in which the material begins to be pressed between the DI punch and the can bottom die.

FIG. 3 is a sectional view showing a state in which the center portion of the can bottom begins to protrude due to the doming punch.

FIG. 4 is a cross-sectional view showing how the can bottom legs and dome are formed.

FIG. 5 is a sectional view showing a state in which the molding of the can bottom is completed.

[Explanation of symbols]

1 DI punch 11 Tip of the leg molding part of the DI punch 2 DI punch fixing tool 3 Can bottom dice 4 Doming punch 5 Material 51 Legs 52 Dome part 53 Heel part 54 Dome rising part 55 Central axis side of can bottom leg 56 Outside of can bottom leg

Claims (1)

[Claims] Claim 1: In the process of forming a can bottom after DI forming of a can body manufactured by DI (drawing and ironing) forming, in the cross-sectional shape of the leg forming part of a DI punch that forms the legs of the can bottom, The radius of curvature on the center axis side of the DI punch is Ri,
The outer radius of curvature is Ro, the average plate thickness of the can bottom of the can body before leg formation is t, and when the relationship Ri+Ro≦12・t exists, t<Ri and Ri≦0.5・Ro, Ri+Ro>1
If there is a relationship of 2·t, t<Ro and Ro≦0.5
- A method for manufacturing a DI can body with high pressure resistance, characterized in that the can bottom is formed using a DI punch in which each radius of curvature having a relationship of Ri is connected smoothly at the tip of the leg.