JPH06102465B2 - Can body for two-piece can and its manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a can body for a two-piece can and a method for manufacturing the can body, and more specifically, it has excellent drop strength, pressure resistance, corrosion resistance and appearance characteristics. A can body for two-piece cans. The present invention also relates to a method of manufacturing the can body for a two-piece can using a relatively thin metal material.

(Prior art) Drawing metal material between punch and die-Redrawing,
Alternatively, the can body obtained by further ironing has no seam in the can body and the connection between the can body and the can bottom, and the appearance is good, and operations such as tightening the bottom lid and forming seams are unnecessary. And
Further, since the side wall of the can body is thinned and has an advantage that the amount of metal material may be small, it is widely used for applications such as beverage canning.

Since such two-piece cans are used for contents such as beer and carbonated drinks having self-generated pressure, and for applications such as nitrogen-filled cans, pressure resistance performance is required, especially to prevent buckling at the bottom of the can. In addition, many proposals have been made regarding the bottom shape, such as providing an upward rising portion and a dome portion on the bottom portion of the can.

Japanese Utility Model Laid-Open No. 59-41207 discloses a can body having a bottom portion protruding inward, wherein a plurality of reinforcing grooves are formed in the rising portion of the bottom portion in the axial direction of the can body. The can barrel for two-piece cans is described,
It is also shown that this can body prevents deformation of the rising portion due to internal pressure.

(Problems to be Solved by the Invention) In recent years, in order to reduce the cost of canned products, efforts have been made to reduce the cost of metal materials without substantially reducing the strength of the can. In order to reduce the cost of metal materials, it is effective to use materials with small thickness and relatively large strength, but in this case, the dome height should be increased to increase the pressure resistance and drop strength. I have to take it.

However, if the doming process (the doming process is also a kind of drawing process) that increases the height of the dome is performed on a material having a small thickness and a relatively large strength, wrinkles are generated on the dome formed, Not only does the appearance become poor, but the occurrence of the wrinkles makes it impossible to obtain the predetermined drop strength and pressure resistance, and the wrinkles cause troubles such as deterioration of corrosion resistance due to poor adhesion of the coating film. This tendency becomes more remarkable as the height of the dome is increased.

Therefore, an object of the present invention is to provide a can bottom for a two-piece can having a novel combination of drop strength, pressure resistance, corrosion resistance and appearance characteristics, and a method for producing the same.

Another object of the present invention is to suppress the occurrence of wrinkles in the dome portion even when the height dimension of the dome portion is set to a relatively large range, and as a result, the appearance characteristics and corrosion resistance of the can bottom are improved. Another object of the present invention is to provide a can body for a two-piece can and a method for producing the same, in which drop strength and pressure resistance are effectively prevented from decreasing.

Still another object of the present invention is to provide a can body for a two-piece can and a method for producing the same, which are formed of a thin metal plate and have the above-mentioned characteristics, and which are also lightweight and economical.

(Means for Solving Problems) According to the present invention, a tubular body portion, an outer peripheral bottom portion continuous with the tubular body portion, a rising portion inside the outer peripheral bottom portion, and a curvature change point at the rising portion. If the diameter of the circumference formed at the curvature change point is D and the height of the dome vertex from the peripheral surface formed at the curvature change point is H, then H / D The ratio is in the range of 0.15 to 0.5, and a large number of beads extending over the rising portion and the dome portion are arranged at intervals in the circumferential direction on the circumference formed by the curvature change points. A can body for a two-piece can is provided.

According to the invention, the metal material is also drawn or drawn.
In the method of forming a can body for a two-piece can, which comprises the step of forming into a can body having a flat bottom by subjecting it to ironing, and forming the bottom part by engaging the flat bottom of the can body with a doming die to form the doming die. , A rising portion, a dome portion in which the rising portion is connected via a curvature change point, and a circumferential interval formed so as to straddle the rising portion and the dome portion on the circumference formed by the curvature change point. A method is provided which is characterized by using a doming die having a plurality of spaced-apart grooves.

(Operation) A can body for a two-piece can according to the present invention is connected to a tubular body portion, an outer peripheral bottom portion connected to the cylindrical body portion, a rising portion inside the outer peripheral bottom portion, and a curvature change point to the rising portion. If the diameter of the circumference formed at the curvature change point is D and the height of the dome vertex from the circumference formed at the curvature change point is H, then the ratio of H / D Is in the range of 0.15 to 0.5, especially
The first feature is that the range is 0.17 to 0.25.

FIG. 1 of the accompanying drawings is a graph plotting the relationship between the H / D ratio and the pressure resistance of the can, and FIG. 2 is the H / D ratio and the filled state of the contents (internal pressure 6.0 kg / cm ² It is the graph which plotted the relationship between the ratio of H / D in the gauge and the drop strength (breakdown height). From FIGS. 1 and 2 described above, it can be seen that increasing the value of H / D is effective for increasing the pressure resistance and also for increasing the drop strength.

In the present invention, the lower limit of the ratio of H / D is set to the above-mentioned value, even for a can of the minimum thickness that can be practically used for a can body for a two-piece can, a compressive strength of 6.3 kg / cm ² gauge or more. However, increasing the H / D ratio beyond the above upper limit is disadvantageous because the inner volume of the can body decreases and the basis weight per volume rather increases.

By the way, as described above, when the H / D value of the can bottom is increased, wrinkles occur in the dome formed, resulting in poor appearance of the can bottom, reduced corrosion resistance, and reduced drop strength. The reason for this is that when drawing a dome with a large H / D value, the metal material at the bottom causes plastic flow that increases the axial dimension, and the circumferential dimension is compressed. This is because plastic flow also occurs, but buckling occurs during this compression, which causes wrinkles.

In the can body of the present invention, a large number of beads extending over the rising portion and the dome are circumferentially arranged at intervals while being formed at the curvature change point located between the rising portion and the dome portion. Is the second and salient feature. That is, in the can body of the present invention, the wrinkles that are randomly generated in the dome due to the compression of the material are regularly formed on a large number of beads that are arranged over the rising portion and the dome portion and have a constant interval in the circumferential direction. It has been transformed. Therefore, in the can body of the present invention, the shape and dimensions of the dome, the position of most of the curvature change points are also expected, and the occurrence of wrinkles eliminates the appearance characteristics and The corrosion resistance is also good, and the drop strength and the reduction in pressure resistance are suppressed.

In this case, it is also extremely important to provide the beads so as to straddle the rising portion and the dome portion. This is because when the beads are provided only on the rising part or only on the dome part, there is almost no ability to absorb the compression of the material that causes wrinkles, but the rising part and the dome cross the circumference of the curvature change point. When a bead bridging the part is provided, excess material is converted into this bead, and the compression force is effectively relaxed. It is also extremely important to arrange a large number of beads at regular intervals around the curvature change point. This is because this arrangement uniformly distributes and relaxes the compression force described above.

In the present invention, the above-described bead formation is a dome in which a rising portion as the doming die and the rising portion are connected via a curvature change point when the flat bottom of the can body is meshed with the doming die to perform bottom draw forming. By using a doming die having a plurality of grooves and a plurality of grooves arranged at intervals in the circumferential direction so as to straddle the rising portion and the dome portion on the circumference formed by the curvature change point. . That is, the material compressed in the circumferential direction flows in the groove,
The bead formation and the wrinkle formation are suppressed.

(Preferred Embodiment of the Invention) In FIG. 3, which shows the overall structure of an example of a can body for a two-piece can according to the present invention, the can body 1 has a cylindrical side wall portion (body portion) 2 as a whole and a can body 2 as a whole. Can bottom 3 as indicated by 3
And consists of. A flange portion 5 for tightening a can lid (not shown) is provided on the upper portion of the side wall portion 2 via a one-step or multi-step neck portion 4 which is narrowed down as desired. It should be understood that the sides of the can body side wall 2 and the connection 6 between the side wall 2 and the can bottom 3 are completely seamless. The can bottom portion 3 has an outer peripheral bottom portion 7 connected to the body portion 2, a rising portion 8 inside the outer peripheral bottom portion, and a dome portion 10 connected to the rising portion via a curvature change point 9.

In FIG. 4 showing the structure of the bottom of the can in an enlarged manner, in the present invention, a bead bridging the rising portion 8 and the dome portion 10 across the circumference 9a is formed on the circumference 9a formed at the curvature changing point.
A large number of 11 are arranged at intervals in the circumferential direction.

The dome portion 10 has a D / H ratio of generally 0.15 to 0.5, especially 0.17.
It is important that the bead 11 has a width (d) of 1.0 to 5.0 mm, especially 1.5 to 3.0 mm at the curvature change point, in the range of pressure resistance and drop strength.
The number of beads 11 is preferably in the range of 8 to 36, especially 12 to 32, which is desirable from the standpoint of preventing wrinkles and preventing deterioration of appearance characteristics, corrosion resistance and strength. The height (h) of the bead 11 varies depending on the D / H ratio, the thickness of the material, etc., but is generally 0.5 to 3.0 mm, particularly 1.0 to 2.0
in the mm range.

The present invention, various metal materials, for example, various surface-treated steel plates,
It is applied to light metal plates such as aluminum, but the dome part 10
Wrinkle-prone material, especially thickness 0.07 to 0.25m
m, preferably a useful ones 0.10 to 0.20 mm, also generally tensile strength 50 Kg / mm ² or more, it is desirable to apply to particular 60 to 80 Kg / mm ² material. The withstand pressure at the bottom of the can for two-piece cans varies greatly depending on the bottom shape, but if the bottom shape is made the same and the factors are excluded and taken into consideration, the following formula P = k · σ · tn ( 1) In the formula, σ is the tensile strength (Kg / mm ² ) of the metal material, t is the thickness (mm) of the metal material, P is the buckling resistance pressure (Kg / mm ² ) of the bottom, n is a number of 1 to 2 and k is a coefficient (a number of about 0.4 to 0.6 depending on the shape).

It is represented by. In other words, the buckling deformation of the can bottom is due to the can bottom projection (radius) being subjected to tensile deformation in the circumferential direction, and increasing the tensile strength (σ) of the metal material is effective for increasing the pressure resistance. It turns out that it can contribute.

In the can body 1 shown in FIGS. 3 and 4, the side wall portion 2 may have substantially the same thickness as the bottom portion 3 like an ordinary drawn-redrawn can, or the drawn-redrawn can by bending and stretching. It may be thinner than the bottom portion 3 by bending and stretching, or may be significantly thinner than the bottom portion 3 by squeezing as in the drawing-ironing can.

Further, the outer peripheral bottom portion 7 may be a straight one such as a trapezoidal surface, a curved surface that is convex inward, or a curved surface that is convex outward. It is desirable that the ground contact portion 12 of the outer peripheral bottom portion 7 has a diameter of 50 to 95%, especially 70 to 90% of the diameter of the side wall portion 2 from the standpoints of self-supporting property, pressure resistance and stacking property (stacking property).

As the surface-treated steel sheet, after cold-rolled steel sheet is annealed, secondary cold-rolled, zinc-plated, tin-plated, nickel-plated, electrolytic chromic acid treatment, chromic acid treatment, etc. It can be used. An example of a suitable surface-treated steel sheet is an electrolytic chromic acid-treated steel sheet, especially a metal chromium layer of 10 to 200 mg / m ^{2 and} a metal chromium layer of 1 to 50 mg / m 2.
It is provided with a chromium oxide layer of ² (calculated as metallic chromium), and this one has an excellent combination of coating film adhesion and corrosion resistance. Another example of surface treated steel sheet is 0.5 to 11.2g / m
A hard tin plate having a tin plating amount of ² .

Furthermore, an aluminum-coated steel plate that has been subjected to aluminum plating, aluminum pressure welding, or the like can be used. As the light metal, an aluminum alloy plate is used in addition to a so-called pure aluminum plate. Aluminum alloy sheets with excellent corrosion resistance and workability are Mn: 0.2 to 1.5% by weight, Mg: 0.8 to 5% by weight, Zn: 0.25 to 0.3% by weight and Cu: 0.15 to 0.25% by weight, the balance being Has a composition of Al.

A protective coating film may be formed in advance on the metal material used in the present invention prior to molding, or a protective coating film may be provided after molding.

As the protective coating, any protective coating consisting of thermosetting and thermoplastic resins: modified epoxy coating such as phenol-epoxy coating, amino-epoxy coating and the like; for example vinyl chloride-vinyl acetate copolymer, vinyl chloride-acetic acid Partially saponified vinyl copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, epoxy-modified, epoxyamino-modified, or epoxyphenol-modified vinyl or modified vinyl paint such as vinyl resin paint; acrylic resin paint : A synthetic rubber-based coating material such as a styrene-butadiene-based copolymer is used alone or in combination of two or more kinds.

These paints can be applied to metal materials in the form of organic solvent solutions such as enamel or lacquer, or in the form of aqueous dispersions or solutions in the form of roller coating, spray coating, dip coating, electrostatic coating, electrophoretic coating, etc. Give. Of course, when the resin paint is thermosetting, the paint is baked if necessary. In the case of squeezing and ironing, the paint is applied to the can body by spray coating or the like on the processed cup. Of course,
It is also possible to apply the paint in two stages, before and after processing.

From the viewpoint of corrosion prevention and workability improvement, these organic coatings
It is desirable to have a thickness (dry state) of generally 2 to 3 μm, especially 3 to 20 μm.

In step A of FIG. 5 for explaining an example of the manufacturing process of the present invention, the metal material 20 is not pressed by the wrinkle presser 23 using the combination of the drawing punch 21 and the drawing die 22, Molded into a can body 25 having a flat bottom 24. The step A is of course not limited to draw forming, and if an ironing die is used instead of the drawing die 22, the can body side wall portion 26 that is subjected to the drawing and ironing process is formed.

Next, in step B, a cylindrical punch 28 having an action surface 27 corresponding to the inner surface of the outer peripheral bottom portion 7 of the final can body and a support ring having an action surface 29 having a shape corresponding to the outer surface of the outer peripheral bottom portion 7.
While holding the bottom peripheral part 31 of the can body with 30, the cylindrical punch 28
It mates with the following doming die 32, which has a slightly smaller outer diameter.

In FIG. 6 showing the details of the doming die 32, the doming die 32 has an arc-shaped action surface 33 and a circumferential side surface 34 corresponding to the outer surface of the dome portion 10, and their connecting circumference 35. A groove 36 cut into the working surface 33 and the side surface 34 is provided so as to straddle this. This groove 36 has a connection circumference 35
Many are provided at regular intervals along. The width of the groove 36 and the number of the grooves correspond to the width (d) of the bead 11 and the number of the grooves described above. The groove length h on the side surface 34 is preferably 1.0 to 5.0 mm, particularly preferably 2.0 to 3.0 mm,
On the other hand, the groove length (D ₂ −D ₁ ) / 2 on the working surface 33 is preferably 1.0 to 10.0 mm, particularly 2.0 to 5.0 mm.

In the present invention, the drawing is carried out for several orders while gradually reducing the diameters of the punch and the die until the desired shape and the desired height / diameter ratio are obtained.

At this time, the following formula The drawing ratio defined by 1.
It is desirable to set the aperture ratio to 0, particularly 1.30 to 1.90, and the overall aperture ratio to 1.50 to 3.00, particularly 1.80 to 2.70.

When ironing the side wall, The ironing rate defined by is 10 to 50%, especially 15 to
45%, and 40 to 80% as a whole, preferably 45 to 75%.

The molded cup body is trimmed and, if necessary, subjected to a degreasing operation known per se, for example, hot water cleaning, solvent cleaning, chlorofluorocarbon cleaning, and the like, and then subjected to a subsequent can manufacturing operation.

(Effect of the invention) According to the present invention, the wrinkles that are unavoidably generated when performing deep doming die processing are converted into regular beads that straddle the rising portion and the dome portion. Moreover, the corrosion resistance was remarkably improved, and the drop strength and the reduction in pressure resistance could be suppressed. Further, it becomes possible to use a material having a small thickness, which enables cost reduction and weight reduction of the material.

(Example) Example 1 Tin-free steel with a plate thickness of 0.18 mm (tensile strength of about 63 Kgf /
mm ² ; DR-9) with both sides pre-baked with thermosetting resin paint, punched out into a disk with a diameter of 187 mm, and redrawing was performed between the drawing punch and the drawing die according to the usual method to obtain an inner diameter of 65.95. It was molded into a flat-bottomed cup of mm.

Next, the bottom of the can was molded from this cup-shaped molded product using a bottom-shaped molding tool (Fig. 5B). At this time, various dimensions of the doming die are such that the outer diameter of the circumferential side surface (D) is 49.7 mm,
The spherical curvature radius (R) of the dome is 32 mm, and the number of grooves is 16
Book, groove width (d) is 5.0mm, groove length in dome (D
-D ') / 2 is 6 mm and the groove length (h) on the side surface is 2.0 mm.

The shape of the bottom of the can molded under the above conditions has an H / D ratio of 0.2.
It was 0, and 16 regular beads with a bead width of 5 mm at the curvature change point and a bead height of about 1 mm were formed smoothly.

As a result of the evaluation as shown in Table 1 using the can body, Table 1
As can be seen, a can body having excellent appearance, pressure resistance, drop strength and corrosion resistance was obtained.

<Evaluation> Wrinkles: Judgment based on appearance Pressure resistance: Liquid (water) is statically sent into the can to measure buckling pressure.

Drop strength: Determine the minimum drop height at which the dome protrudes to the outside when the can is packed and wound so that the internal pressure is 6.0 kg / cm ² and the can bottom freely falls downward.

Corrosion resistance: Coke (carbonated drink) is filled and wound, and stored for a long period of time (3 to 6 months) under storage conditions of 37 ° C, and the presence or absence of corrosion on the bottom of the can is observed.

Example 2 The number of grooves of the doming die of the bottom forming tool was 20, the groove dimensions were a width (d) of 3 mm, and a dome groove length (D-
Can bottom molding was carried out in the same manner as in Example 1 except that a doming die having D ') / 2 of 6 mm and a side surface groove length (h) of 2 mm was used.

As a result, as shown in Table 1, a can body having excellent appearance, pressure resistance, drop strength and corrosion resistance was obtained.

Example 3 An aluminum alloy plate having a thickness of 0.28 mm (equivalent to A3004H19, tensile strength of about 32 Kg / mm ² ) was punched into a disk having a diameter of 125 mm, and a drawing punch and a drawing die were drawn between the drawing punch and the drawing die according to a conventional method. After re-drawing, forming into a cup shape with an inner diameter of 66.95 mm, and then subjecting to a third ironing process with an ironing punch and a die, the doming die and the supporting ring similar to those in Example 1 are acted to form the bottom of the can. It was

As a result, a can body having excellent appearance, pressure resistance and drop strength as shown in Table 1 was obtained. Furthermore, after performing a degreasing washing operation and a surface chemical conversion treatment known per se on this can body, a thermosetting resin coating was spray-coated on the inner surface side, and there was no problem with the coatability of the bead formed on the bottom of the can. No uniform coating surface was obtained. Further, as a result of a corrosion resistance test, no abnormalities were recognized as shown in Table 1.

Comparative Example 1 Can bottom molding was performed in the same manner as in Example 1 except that a doming die having a dome spherical radius of 49 mm and no groove was used and H / d was changed to 0.13. As a result, the evaluations shown in Table 1 were obtained, and the appearance and corrosion resistance were good, but the drop strength was remarkably low.

Comparative Example 2 Can bottom molding was performed in the same manner as in Example 1 except that a groove-less doming die was used. As a result, the evaluations shown in Table 1 were made, and a large number of radial wrinkles were generated in the central dome portion, impairing the appearance of the bottom portion. Further, as a result of the corrosion resistance test, a number of corrosion sites were observed at the wrinkle generation site on the bottom of the inner surface of the can, and a decrease in corrosion resistance was observed.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between H / D and the pressure resistance of the can, FIG. 2 is a diagram showing the relationship between the H / D and drop strength, and FIG. 3 is a can for two-piece cans according to the present invention. The figure which shows an example of the whole structure of a barrel, FIG. 4 is an enlarged sectional view which shows the structure of a can bottom part, FIG. 5 (A) is a figure which shows an example of the manufacturing process of the can barrel for two-piece cans of this invention. FIG. 5 (B) is a diagram showing an example of a bottom shape forming tool, and FIG. 6 is a diagram showing an example of a doming die according to the present invention. Reference numeral 1 is a can body, 2 is a side wall portion, 3 is a can bottom portion, 4 is a neck portion, 5 is a flange portion, 6 is a connecting portion between the side wall portion and the can bottom portion, 7 is an outer peripheral bottom portion, 8 is a rising portion, 9 Is the curvature change point, 9a
Is a circumference formed by a curvature change point, 10 is a dome portion, 11 is a bead, 12 is a protruding portion, 20 is a metal material, 21 is an aperture punch, 22
Is a drawing die, 23 is a wrinkle retainer, 24 is a flat bottom, 25 and 26 are can body side walls, 28 is a cylindrical punch, 29 is a support ring working surface, 30
Is a support ring, 31 is a cup-shaped molded product, 32 is a doming die, 33 is a curved surface of the dome portion, 34 is a circumference of the doming die, 35 is a curvature change point, and 36 is a groove.

Claims (2)

[Claims] 1. A tubular body portion, an outer peripheral bottom portion connected to the cylindrical body portion, a rising portion inside the outer peripheral bottom portion, and a dome portion connected to the rising portion via a curvature change point, When the diameter of the circumference formed at the curvature change point is D and the height of the apex of the dome from the circumference formed at the curvature change point is H, the H / D ratio is in the range of 0.15 to 0.5, A can body for a two-piece can, characterized in that a plurality of beads extending over the rising portion and the dome portion are arranged at intervals in the circumferential direction on the circumference formed by the curvature change points. 2. A two-piece process comprising a step of forming a can body having a flat bottom by subjecting a metal material to a drawing process or a drawing-ironing process to form a can body having a flat bottom, and a bottom forming process by engaging a flat bottom of the can body with a doming die. In the method of forming a can body for a can, as the doming die, a rising portion, a dome portion in which the rising portion is connected via a curvature change point, and a rising portion and a dome in a circumference formed at the curvature change point. A method comprising using a doming die having a plurality of groove portions arranged so as to extend over the portion and are circumferentially spaced.