JP2024087463A - Method for forming curled opening of bottle-shaped can with cap - Google Patents

Abstract

A method for forming a curled portion is provided that can maintain sufficient rigidity and strength even when the wall is thinned or the opening diameter is reduced to make the portion smaller.
[Solution] The diameter is reduced so that the angle between the inclined wall portion 5 and the central axis L0 of the threaded cylindrical portion is in the range of 20 degrees or more and 30 degrees or less, and the tip edge portion 10 side of the curved portion is curled radially inward and abutted against the outer surface of the inclined wall portion 5 so that the dimension measured radially between the outermost diameter portion 9 of the curled portion 1 and the point where the tip edge portion 10 abuts against the inclined wall portion 5 is in the range of 40% or more and 60% or less of the curl width W, which is half the difference between the outer diameter and inner diameter of the curled portion 1, and the abutment angle θ10 of the tip edge portion 10 with respect to the inclined wall portion 5 is in the range of ±20 degrees with 90 degrees as the center.
[Selected Figure] Figure 1

Description

The present invention relates to a method for forming a curled portion at the opening end of a metal bottle-shaped can that has a cap that can be attached and detached by a screw.

The general structure of this type of bottle-shaped can is as follows: a threaded cylindrical section to which a cap is attached is provided at the top of the body via a shoulder, and the section above the threaded cylindrical section is narrowed to a smaller diameter than the threaded cylindrical section, with its open end forming a curled section. As its name suggests, the curled section is formed by curving the cylindrical open end outward and then rolling it back inward from the bottom. The curled section is basically a section that rolls inward to hide the cut end of the metal sheet material, and also serves to seal the liner provided on the inner surface of the cap to ensure airtightness or liquid tightness.

The so-called neck portion, which includes this curled portion and the threaded cylindrical portion below it, is made by forming a blank, which is a thin metal sheet, into a cylindrical shape of gradually smaller diameter by drawing and ironing, forming a closed cylindrical portion in the center that is smaller in diameter than the body portion, and trimming the tip of the cylindrical portion to leave an opening. Alternatively, the neck portion is made by forming the blank into a cylindrical shape by drawing and ironing, gradually narrowing the opening to form a small-diameter cylindrical portion that opens at the tip, and trimming the edges to make it even.

Examples of curled portions that form the opening end of such a neck are described in Patent Document 1 and Patent Document 2. In the bottle-shaped can described in Patent Document 1, the portion continuing to the upper side of the cylindrical portion (threaded cylindrical portion) on which the male thread is formed is reduced in diameter, and the open end of the reduced diameter portion is curved outward and rolled back, and the curled tip edge portion, which is the tip of the curved portion, is brought into contact with the outer surface of the inclined wall portion connected to the upper side of the threaded cylindrical portion. In other words, the upper end of the reduced diameter portion is rolled outward to form a curled portion whose cross-sectional shape is close to a circle. The inclined wall portion is a tapered portion that is created by making the upper portion of the threaded cylindrical portion smaller in diameter than the threaded cylindrical portion. A curled portion of this shape feels good when touched by the lips. In addition, when a cap for sealing is attached, a resin liner provided on the inner surface of the cap is pushed down to the lower side of the curled portion, and the liner wraps around the curled portion. As a result, even if the cap is turned in the opening direction and lifts up, the liner maintains a sealed state, and the sealed state is maintained until the pilfer-proof band attached to the bottom end of the cap breaks, providing good tamper-evident (TE) properties.

Patent Document 2 also describes a bottle-shaped can in which the cross-sectional shape of the curled portion is a so-called approximately inverted triangle. It is said that by making the curled portion into such a shape, the can is more airtight when a cap is attached, and is more resistant to impacts such as when dropped.

Japanese Patent No. 4707172 Japanese Patent No. 6946620

According to the curled portion or its manufacturing method described in Patent Document 1 or Patent Document 2, it is said that the rigidity and strength against the so-called vertical load when the cap is dropped or capped can be secured. On the other hand, there is a demand for reducing the thickness of the bottle-shaped can due to the demands for resource saving and greenhouse gas emission control. If the curled portion is also thinned in response to these demands, the rigidity or strength of the curled portion may decrease, and the curled portion may not be able to withstand the expected so-called vertical load, or the sealing property or TE property of the cap may decrease, unless the shape or structure is improved. The same is true when the curled portion or its manufacturing method described in Patent Document 1 or Patent Document 2 is applied to a bottle-shaped can with a small opening diameter. That is, if the curled portion has a small opening diameter, the area of contact with the liner provided on the inner surface of the cap is small, and the area or total length of the part receiving the so-called vertical load is small, so that the volume of the part supporting the vertical load is small, and the rigidity or strength against the so-called vertical load is low. As a result, deformation due to the vertical load during roll-on capping may occur, and the sealing property or TE property of the cap may decrease.

The present invention was made with a focus on the above technical problems, and aims to provide a method for forming a curled portion that can adequately maintain rigidity and strength even when the wall is thinned or the opening diameter is reduced, resulting in so-called miniaturization.

In order to solve the above technical problems, the present invention provides a method for forming a curled portion of a bottle-shaped can with a cap, which comprises the steps of: forming a tapered inclined wall portion by performing a diameter reduction process on the portion above the threaded cylindrical portion in which the thread groove is formed, so that the diameter is reduced; then expanding the portion above the inclined wall portion radially outward and curving it downward; and further curling the tip edge side of the curved portion radially inward and abutting it against the outer surface of the inclined wall portion to form a curled portion on the upper side of the inclined wall portion. The diameter reduction process is performed by reducing the diameter of the inclined wall portion by a distance of 1 mm between the angle between the inclined wall portion and the central axis of the threaded cylindrical portion. The method is characterized in that the angle between the tip edge and the inclined wall is within a range of 20 degrees to 30 degrees, and the tip edge of the curved portion is curled inward in the radial direction to abut against the outer surface of the inclined wall, so that the dimension measured in the radial direction between the outermost diameter part of the curled portion and the point where the tip edge abuts against the inclined wall is within a range of 40% to 60% of the curl width, which is half the difference between the outer diameter and inner diameter of the curled portion, and the abutting angle of the tip edge against the inclined wall is within a range of ±20 degrees with 90 degrees as the center.

In the method of the present invention, the process of rolling the tip edge side of the curved portion radially inward and abutting against the outer surface of the inclined wall portion may be performed by radially expanding outward and pressing the portion above the downwardly curved inclined wall portion from the outside to the inside in the radial direction.

In the method of the present invention, the process of expanding the portion above the inclined wall portion radially outward and curving it downward is an outward bending process that bends the portion so that it is convex toward the outer surface, and the process of rolling the tip edge portion of the curved portion inward in the radial direction is an inward bending process that bends the portion so that it is convex toward the outer surface. In the outward bending process, the bending process is performed so that the apex portion, which is the uppermost end of the curled portion, is located on the outer periphery side of the center portion in the width direction of the curled portion, and in the inward bending process, the radius of curvature of the tip edge portion side that is rolled inward in the radial direction and curved to be convex toward the outer surface may be smaller than the radius of curvature of the portion on the inner periphery side of the apex portion that is curved to be convex toward the outer surface.

In the method of the present invention, the bottle-shaped can is a metal can made of an aluminum alloy specified in 3104H19 of the Japanese Industrial Standards and the curled portion is a nominal diameter of 28 mm, and the curled portion may be formed so that the ratio of the material cross-sectional area, which is the cross-sectional area of the material constituting the curled portion in a cross section cut along the central axis, to the curl occupied area, which is the product of the curl width in the cross section cut along the central axis and the height of the curled portion in the direction of the central axis, is in the range of 40% to 60%.

In the present invention, the inclined wall portion, which is generated by making the outer diameter of the curled portion smaller than the valley diameter of the thread groove in the threaded cylindrical portion, is processed so that the angle with the central axis is in the range of 20 to 30 degrees. Therefore, when a so-called vertical load is applied to the bottle-shaped can in the axial direction, the load or moment acting to cause the curled portion to fall toward its inner circumference is reduced, and as a result, the rigidity or strength of the curled portion or the threaded cylindrical portion is increased, thereby preventing deformation. In addition, the tip edge portion abuts against the inclined wall portion at or near the center of the curl width, and the tip edge portion side abuts against the inclined wall portion at an angle close to perpendicular (the abutment angle is set to an angle close to perpendicular (90 degrees)), so that when the above-mentioned vertical load is applied, the tip edge portion does not slide along the surface of the inclined wall portion. As a result, the above-mentioned vertical load is not only received by the curled portion, but also by the inclined wall portion, and in this respect, the substantial rigidity or strength of the curled portion can be increased. In particular, by setting the impact angle to an angle close to vertical (±20 degrees around 90 degrees), it is possible to prevent the leading edge from shifting along the surface of the inclined wall, which would otherwise cause the curled portion to be insufficiently supported, and to increase the effective rigidity or strength of the curled portion. In this way, the present invention performs molding processing to create a new structure or shape, so that even when molding the curled portion of a thin-walled bottle-shaped can, it is possible to obtain a curled portion that is resistant to deformation due to so-called vertical load and has high rigidity and strength.

In addition, the tip edge portion is curled inward in the radial direction by pressing radially from the outside, which eliminates the risk of the curled portion, inclined wall portion, or threaded cylindrical portion deforming or buckling during the process of forming the curled portion.

Furthermore, in the present invention, the curved portion of the curled portion that is exposed and convex upward is curved with a large radius of curvature, while the portion close to the tip edge that is curved downward and convex is curved with a small radius of curvature, so that the tension in the area where the processing is similar to stretch flanges is alleviated and cracks and breakage can be avoided or suppressed. In contrast, the curving process on the tip edge side is similar to shrink flanges, and since it processes a part that has already been stretched or shrunk, as described above, problems such as cracks can be avoided even if the curvature is large so that the impact angle is close to vertical as described above.

Furthermore, in the present invention, the so-called apex of the curled portion is processed to be located on the outer periphery side of the center in the width direction of the curled portion, so that when the liner provided on the inner surface of the cap is pressed against the curled portion during capping, the liner is more likely to deform on the outer periphery side of the apex than on the inner periphery side, resulting in the liner penetrating under the curled portion and enveloping it. This improves the sealing performance of the cap, resulting in a curled portion with so-called excellent TE properties.

4 is a cross-sectional view for explaining the shape of a curled portion processed by the method of the present invention. FIG. FIG. 11 is an explanatory diagram for explaining abutment angles. FIG. 4 is a cross-sectional view showing an example of the shape of a neck portion in a blank material. FIG. 2 is a process diagram for explaining the processing steps of thread forming, curl forming, and bead forming. FIG. 11 is a cross-sectional view showing a processing state in the third curl forming process. FIG. 4 is an explanatory diagram for explaining the state of load and stress acting during roll-on capping. 13 is a chart showing the results of a study on the influence of the contact position of the leading edge portion against the inclined wall portion. 13 is a chart showing the results of examining the effect of area ratio.

An example of the implementation of the present invention will be described below with reference to the drawings. Note that the example described below is merely one example of the present invention and does not limit the present invention.

First, a bottle-shaped can having a curled portion formed by the method of the present invention will be described. The bottle-shaped can according to the present invention is made of metal, such as a steel can or an aluminum can, and may be a so-called two-piece can in which the body and bottom are integrally formed, or a so-called three-piece can in which a bottom lid is attached to the bottom of the body by rolling. In either case, the can is a metal can in which a tubular neck portion is formed at the top of the can body via a shoulder portion, the upper end of the neck portion is open, the entire circumference of the opening is a curled portion, and a cap is screwed onto the neck portion. The bottle-shaped can to which this invention is particularly suitable is an aluminum alloy can with a mouth portion having an opening diameter (inner diameter, nominal diameter) of 28 mm (φ28), and the material is, for example, an aluminum alloy of Japanese Industrial Standards (JIS) 3104H19.

An example of the curled portion 1 to be formed by the method of the present invention is shown in an enlarged cross-sectional view in FIG. 1. FIG. 1 is a cross-sectional view of the curled portion 1 or the bottle-shaped can cut along a plane including the central axis of the bottle-shaped can. The curled portion 1 is a portion that constitutes the contour of the opening 3, which is the mouth or spout of the bottle-shaped can 2, and is provided continuously on the upper side of the threaded cylindrical portion 4 for attaching a cap to close the opening 3. That is, similar to the configurations described in Patent Documents 1 and 2, a spiral thread groove is machined into a drawn cylindrical portion with a small diameter to form the threaded cylindrical portion 4, and the upper portion of the threaded cylindrical portion 4 is drawn to a diameter smaller than the valley diameter of the thread groove to form an inclined wall portion 5 that continues to the upper side of the threaded cylindrical portion 4. This inclined wall portion 5 is a tapered portion that is machined to have a gradually smaller diameter at the top, and half the taper angle, i.e., the angle θ5 between the central axis L0 of the threaded cylindrical portion 4, is set to an angle in the range of 20 degrees to 30 degrees.

The curled portion 1 is a portion that is bent outwardly by spreading the portion connected to the upper side of the inclined wall portion 5 radially outward and curling it downward and inward to form a hollow shape. The portion connected to the inclined wall portion 5 is bent obliquely upward and inward to form a convex shape on the outside, and this curved portion (hereinafter referred to as the first curved portion) 6 is subjected to large stress during bending, so it has a relatively large radius of curvature R6 to relieve the stress and avoid cracks and breaks.

The point where the tangent line in the radial direction of the first curved portion 6 becomes horizontal (perpendicular to the central axis L0) is the apex 7 of the curled portion 1, and the portion on the outer periphery side of the apex 7 is the outer periphery curved portion 8 that forms the outer periphery side surface or contour of the curled portion 1. When viewed in cross section in FIG. 1, this outer periphery curved portion 8 is composed of a curved portion (hereinafter, provisionally referred to as the second curved portion) 8a that is convex obliquely upward (i.e., convex outward) to form a so-called shoulder portion and is connected downward, and a curved portion (hereinafter, provisionally referred to as the third curved portion) 8b that is connected downward from the second curved portion 8a and is curved inward in the radial direction (i.e., convex outward) to form an obliquely downward convexity. The outer diameter of the curled portion 1 is the largest at the boundary between the second curved portion 8a and the third curved portion 8b, and this portion is the outermost diameter portion 9 of the curled portion 1.

The tip end of the third curved portion 8b may be curved with an appropriate curvature like the third curved portion 8b, or may have a shape that is linear when viewed in cross section. The tip end, which is the tip edge portion 10, abuts against the outer surface of the inclined wall portion 5. The inclined wall portion 5 against which the tip edge portion 10 abuts is the tapered portion and the portion above it that is convexly curved toward the inner circumference and continues to the curl portion 1, and therefore the tip edge portion 10 may abut against a portion that is curved (which can be called a corner portion) that is curved in a curved manner other than the portion that is straight in the cross section of FIG. 1.

Here, it is preferable that the curled portion 1 is tightly rolled so that the radius of the cross section is relatively small if it were circular, and therefore the radius of curvature R8b of the third curved portion 8b is smaller than the radius of curvature R6 of the first curved portion 6 described above (R6>R8b). This third curved portion 8b has already been deformed by processing such as expanding radially outward from the cylindrical state extending upward from the inclined wall portion 5 described above and bending downward and inward, so it is in a state where it can be easily processed. Therefore, the third curved portion 8b can be easily processed without causing cracks or breakage.

Furthermore, the contact angle θ10 of the tip edge portion 10 with respect to the inclined wall portion 5 is close to a right angle. The contact angle θ10 is the angle between the extension line of the tip edge portion 10 (or the extension line of the center line of the tip edge portion 10 in the thickness direction) and the line indicating the surface of the inclined wall portion 5 (the generatrix indicating the inclined surface), as shown in Figure 2 (A) when the tip edge portion 10 is a curved surface and in Figure 2 (B) when the tip edge portion 10 is a flat surface.

To enable the tip edge portion 10 to abut against the inclined wall portion 5, the point where the tip edge portion 10 abuts against the inclined wall portion 5 is set within a predetermined range including the center in the width direction of the curl portion 1. Here, the width (curl width) W of the curl portion 1 is half the difference between the outer diameter and the inner diameter of the curl portion 1. The point where the tip edge portion 10 abuts against the inclined wall portion 5 is set at a position within a range of 40% to 60% of the curl width W (in other words, a position within a range of ±10% from the center).

Furthermore, the second curved portion 8a described above has one end (the end at the starting side in the processing sequence) of the apex 7 located on the outer periphery side of the center in the width direction of the curled portion 1. This is to guide more of the liner provided on the inner surface of the cap to the outer periphery and lower side of the curled portion 1 when the cap is rolled on.

In the cross section shown in Figure 1, the ratio (A1/A0) of the area of the space occupied by the curled portion 1 (hereinafter referred to as the curled area) A0 to the material cross-sectional area (hereinafter referred to as the wall thickness area) A1, which is the cross-sectional area of the material within that space, is in the range of 0.4 to 0.6 (40% to 60%). Here, the curled area A0 is the product (H x W) of the height H and the curl width W, where H is the height from the point where the leading edge portion 10 abuts against the inclined wall portion 5 to the apex portion 7. The wall thickness area A1 is the product (T x L) of the plate thickness (wall thickness) T of the material (aluminum alloy plate) constituting the curled portion 1 and the line segment length L from the point where the leading edge portion 10 abuts to the leading edge portion 10. By keeping the ratio of these areas (A1/A0) within the range of 40% to 60%, the curled portion 1 has a rounded shape, improving its appearance and feel when touched, and also resulting in a tightly wound configuration that provides excellent rigidity and strength.

Next, the procedure for forming the curled portion 1 will be described. FIG. 3 shows an example of a crude material 20 for a bottle-shaped can, in which the mouth and neck portion 23 is connected to the upper side of the body portion 21, which is the so-called main body, via a dome-shaped shoulder portion 22. This mouth and neck portion 23 is provided with, in order from the lower side (the body portion 21 side), a neck cylindrical portion 24, a threaded cylindrical portion 25 with a slightly smaller diameter than the neck cylindrical portion 24, a sloping portion 26 formed on the above-mentioned sloping wall portion 5, and a curled cylindrical portion 27. Prior to forming the curled portion 1, as shown in FIG. 4, first, thread forming is performed (FIG. 4(A)). Next, curl neck forming is performed (FIG. 4(B)). This curl neck forming is a process for preparing a shape for curl forming, and is performed in multiple steps. In the process, the sloping wall portion 5 is formed, and its angle θ5 is set to an angle within the range of 20 degrees to 30 degrees (60 degrees to 70 degrees when measured from a horizontal plane).

The tip edge portion 10 is trimmed to be flat and the length of the curl portion 1 is adjusted (FIG. 4C). The first to third curl forming steps are then performed (FIGS. 4D, 4E, and 4F). That is, in the first curl forming step (FIG. 4D), the portion of the opening end side of the curl cylindrical portion 27 that has already been trimmed is curved while being pushed outward in the radial direction. In the second curl forming step (FIG. 4E), the portion of the opening end side of the curl cylindrical portion 27 is further pushed outward and curved. In this case, the portion on the tip edge portion 10 side is curved so as to be rolled downward and inward. Then, in the third curl forming step (FIG. 4F), the tip edge portion 10 is processed so as to abut against the inclined wall portion 5. In this case, as shown in FIG. 5, for example, the outer roller 31 is brought radially closer to the inner roller 30 inserted inside the curl cylindrical portion 27 from the outside, thereby pressing the portion that is already curved downward and inward from the outside in the radial direction. That is, in the final stage of curl forming, the neck portion 23 is pressed radially, not pressed from above. In this way, the curl portion 1 can be formed into the desired shape, and deformation (buckling) of the inclined wall portion 5 and the threaded cylindrical portion 4 in the vertical direction can be avoided or suppressed. These first to third curl forming steps form the curl portion 1 into the shape shown as a cross section in FIG. 1 described above.

After the curled portion 1 is formed as described above, bead forming is performed (Figure 4 (G)). That is, the lower portion of the neck cylindrical portion 24 is squeezed all around to perform the so-called concave bead processing, and a convex bead portion that is relatively convex outward in the radial direction is formed in the upper portion of the concave bead (the portion directly below the threaded cylindrical portion 4). The convex bead portion is the portion to which the pilfer-proof band provided at the lower end of the cap (not shown) is wrapped and engaged.

Next, the load applied to the curled portion 1 during roll-on capping will be described with reference to FIG. 6. In roll-on capping, the cap blank is placed over the neck portion 23 and pressed against it, and in this state, the corner between the top plate portion and the skirt portion is crushed toward the curled portion 1, and the skirt portion is pressed against the threaded cylindrical portion 4 to form a female thread, and the pilfer-proof band provided at the lower end is squeezed toward the above-mentioned convex bead portion to engage with the convex bead portion. In FIG. 6, the reference numeral 40 denotes a cap, and a synthetic resin liner 41 is provided on the inner surface of the cap 40. The cap 40 is pressed against the curled portion 1 by the pressure pad 42, and in this state, the pusher block 43 descends to squeeze the periphery (corner portion) of the cap 40 inward and downward. Therefore, a load indicated by the reference numeral L1 acts from the pressure pad 42, and a load indicated by the reference numeral L2 acts from the pusher block 43. Since the liner 41 is made of an elastic synthetic resin, it is deformed by receiving the above loads L1 and L2, so that it envelops the curled portion 1. That is, as shown by the reference symbol D1, it extends downward along the surface of the outer circumferential curved portion 8 of the curled portion 1, and deforms to a state in which it envelops the curled portion 1 from below, or engages with the underside of the curled portion 1. The liner 41 is also crushed on the apex 7 side, and deforms inward as shown by the reference symbol D2, enveloping the apex 7 side of the curled portion 1.

A load acts on the curled portion 1 through the liner 41, which is deformed as described above. As the load acts from the pressure pad 42 and the pusher block 43 as described above, stresses F1 and F2 are applied from both sides of the apex 7 in the direction of squeezing the curled portion 1 smaller. The stress F1 applied to the portion on the outer periphery side of the apex 7 acts in the direction of pressing the tip edge portion 10 against the inclined wall portion 5, but because the contact angle θ10 of the tip edge portion 10 with the inclined wall portion 5 is close to perpendicular, the tip edge portion 10 does not slide along the surface of the inclined wall portion 5, and the tip edge portion 10 is supported by the inclined wall portion 5.

In addition, the angle θ5 of the inclined wall 5 with respect to the central axis L0 is 20 to 30 degrees, and the inclined wall 5 is in a so-called raised state, so the moment that bends the curled portion 1 toward the inner circumference is small, and in this respect, it is also difficult to deform. Ultimately, the curled portion 1 produced by the method of the present invention has high rigidity or strength while maintaining a rounded shape that has a good appearance and feel, and therefore, even if the material of the bottle-shaped can is thinned to reduce the rigidity of the material itself, the strength required for the product can be maintained. In other words, by thinning the material, it is possible to effectively use resources and reduce environmental loads. In addition, even for a small bottle-shaped can with a nominal diameter of 28 mm (φ28) and the like, in which the volume of the open end that receives the load is small, a curled portion with excellent rigidity or strength can be produced.

Furthermore, the liner 41 is pushed under the curled portion 1 and enters inward along the third curved portion 8b described above, embracing the curled portion 1. Therefore, even if the cap is turned in the opening direction and loosened somewhat, the liner 41 adheres closely to the outer surface of the curled portion 1 and maintains the sealed state. Therefore, if the cap is turned in the opening direction until the seal by the liner 41 is released, the cap will be turned quite a large amount, at which point the pilfer-proof band engaged with the convex bead portion described above will be torn off from the cap. In other words, the curled portion 1 can be made to reliably exhibit its pilfer-proof function (tamper-evidence function).

Next, an embodiment of the present invention will be described. The bottle-shaped can in the embodiment is made of aluminum alloy plate (plate thickness 0.28 mm) specified in the Japanese Industrial Standard 3104H19, and is drawn and ironed to form a two-piece can with a can body diameter of 45 mm (φ45) and height of 110 mm. The molding process of the body, the subsequent shoulder, the mouth neck, etc. is performed by the same method and process as in the past, and the molding process of the screw cylindrical portion 4 and the curl portion 1 is performed as described above. The mouth diameter is a nominal diameter of 28 mm (φ28). More specifically, the angle θ5 of the inclined wall portion 5 with respect to the central axis L0 is 30 degrees, the inner diameter of the curl portion 1 is 21.8 mm, and the wall thickness T is 0.38 mm. By raising the inclined wall 5 to an angle of 30 degrees, there is less space for the curled portion 1 to be rolled outward in the radial direction, but by setting the apex 7 radially outward from the center of the curled portion 1 in the width direction, the constraints on the radius of curvature R6 of the first curved portion 6 are reduced, and a radius that does not cause cracks or breaks can be ensured. In addition, since the radius of curvature R8b of the third curved portion 8b is made smaller than the radius of curvature R6 of the first curved portion 6, the overall curved shape of the curled portion 1 is a so-called deformed round curl shape that is slightly bent from a perfect circle (circular shape). In addition, the position where the tip edge portion 10 hits the inclined wall portion 5 is set to within a range of 10% of the center of the curled portion 1 in the width direction or on both sides of it. As a result, the hitting angle θ10 of the tip edge portion 10 against the inclined wall portion 5 can be set to an angle close to a right angle.

Figure 7 shows the cross-sectional shape and impact angle of the curled portion 1 when the impact position of the tip edge portion 10 against the inclined wall portion 5 is changed. The impact position is shown as a ratio to the curl width W from the outermost diameter portion 9 of the curled portion 1. The angle θ5 of the inclined wall portion 5 is set to 30 degrees.

Sample Sa1 is an example in which the impact position is 30% of the curl width W from the outermost diameter part 9. In this example, the cross-sectional shape of the curl part 1 is so-called vertically long, and it is difficult to set the impact angle θ10 within the specified range (90 degrees ± 20 degrees). Therefore, this example was evaluated as "unacceptable (x)."

In contrast, in the example where the abutment position is 40% of the curl width W from the outermost diameter portion 9 (sample Sa2), 50% (sample Sa3), and 60% (sample Sa4), the tip edge portion 10 is curled inward in the radial direction, so the abutment angle θ10 of the tip edge portion 10 with respect to the inclined wall portion 5 can be set to a predetermined range (90 degrees ± 20 degrees) close to vertical (right angle). In addition, the entire surface from the first curved portion 6 to the third curved portion 8b can be made into a smooth, continuous curve, which not only has a good appearance and feel when touched, but also makes molding easier by eliminating the need for excessive bending. Therefore, these examples were evaluated as "Fair (○)".

Furthermore, in the example (sample Sa5) where the abutment position is 70% of the curl width W from the outermost diameter portion 9, it is necessary to raise the tip edge portion 10 to the uppermost portion of the inclined wall portion 5 (the corner portion where the curve begins to convex inward toward the curl portion 1), which requires a large curvature at the third curved portion 8b, resulting in a shape closer to a bend than a curve. This results in a worse appearance and a worse feel when touched, and the evaluation was given a "poor (x)."

From the results shown in Figure 7, in the present invention, the abutment position of the tip edge portion 10 against the inclined wall portion 5 is set within a range of 40% to 60% of the curl width W. If the angle θ5 of the inclined wall portion 5 is set to the lower limit of 20 degrees, the width of the curl portion 1 is further restricted, so the suitable range for the abutment position of the tip edge portion 10 against the inclined wall portion 5 becomes even narrower.

Figure 8 shows the results of the study on the area ratio (A1/A0) of the wall thickness area A1 to the curl occupancy area A0. Figure 8 shows a schematic of the cross-sectional shape of the curled portion 1 along with the wall thickness and area ratio, and an evaluation of the suitability of the curled portion 1. The wall thicknesses were 0.2 mm (sample Sb1), 0.25 mm (sample Sb2), 0.3 mm (sample Sb3), 0.4 mm (sample Sb4), 0.45 mm (sample Sb5), and 0.5 mm (sample Sb6). The area ratios were 32.5% for sample Sb1, 39.8% for sample Sb2, 46.6% for sample Sb3, 58.8% for sample Sb4, 63.6% for sample Sb5, and 67.9% for sample Sb6.

In sample Sb1, the curled portion 1 is not wrapped around the wall thickness to a large extent, so the overall rigidity is low and there is a high possibility that it will deform when the expected vertical load is applied. Therefore, it is rated as "Not Good (X)". In contrast, in samples Sb2 to Sb5, the rigidity of the material increases as the wall thickness increases, but this is sufficient for curl forming processing. In particular, in samples Sb3 and Sb4, the tip edge portion 10 was able to abut against the inclined wall portion 5 as intended. This is thought to be because the wall thickness is not particularly thick, which suppresses springback. On the other hand, the wall thickness is not as thin as that of sample Sb1, which can be easily formed, so the rigidity or strength of the curled portion 1 is sufficiently high.

The vertical load at which deformation occurs was measured for sample Sb3 and sample Sb4, and was 1556 N (Newton) for sample Sb3 and 1868 N (Newton) for sample Sb4. Since the standard is 1471 N (Newton), it was found that the strength is sufficient. In addition, since the wall thickness of sample Sb4 is close to the wall thickness (0.38 mm) of the sample used in the above-mentioned study of the abutment position, it was found that by setting the area ratio to about that of sample Sb4, it is possible to reduce the thickness while maintaining rigidity or strength. Therefore, samples Sb2 and Sb5 were rated as "Fair (○)". Samples Sb3 and Sb4 were rated as "Good (◎)".

In addition, in sample Sb6, the thick wall thickness results in a relatively tightly curled curl, which is thought to ensure rigidity and strength. However, because the material itself is highly rigid due to the thick wall thickness, the processing load required for molding must be increased and springback becomes strong, making it difficult to stably process the curl into the desired shape and to stably abut the tip edge against the inclined wall portion 5. Therefore, sample Sb6 was rated as "unacceptable (x)". Based on the above results, the area ratio in this invention is set at 40% to 60%.

The present invention is not limited to the above-described embodiment, and the cross-sectional shape of the curled portion is preferably a circle or a shape as close to a circle as possible, but is not limited thereto. For example, the shape may be close to an inverted triangle with the apex side being the base. In the above-described embodiment, the upper load during roll-on capping is described as a so-called vertical load, but the vertical load applied to the curled portion in the present invention includes other loads such as the impact force when a bottle-shaped can is dropped, and the present invention maintains sufficient rigidity or strength against such vertical loads.

REFERENCE SIGNS LIST 1 curled portion 2 bottle-shaped can 3 opening 4 threaded cylindrical portion 5 inclined wall portion 6 first curved portion 7 apex portion 8 outer peripheral curved surface portion 8a second curved portion 8b third curved portion 9 outermost diameter portion 10 tip edge portion 20 blank 21 body portion 22 shoulder portion 23 mouth neck portion 24 neck cylindrical portion 25 cylindrical portion 26 inclined portion 27 curled cylindrical portion 30 inner roller 31 outer roller 40 cap 41 liner 42 pressing pad 43 pusher block θ5 angle (of inclined wall portion) θ10 impact angle L0 central axis L1, L2 load H height W curl width

Claims (4)

A method for forming a curled portion of a bottle-type can with a cap, comprising the steps of: forming a tapered inclined wall portion by performing a diameter reduction process on a portion above a threaded cylindrical portion in which a thread groove is formed, so that the diameter of the portion is reduced; then expanding the portion above the inclined wall portion radially outward and curving it downward; and further curling a tip edge portion of the curved portion radially inward and abutting it against an outer surface of the inclined wall portion, thereby forming a curled portion on the upper side of the inclined wall portion,
The diameter reduction process is performed so that the angle between the inclined wall portion and the central axis of the threaded cylindrical portion is in the range of 20 degrees or more and 30 degrees or less.
A method for forming a curled portion of a bottle-type can with a cap, characterized in that the processing of curling the tip edge side of the curved portion radially inward and abutting it against the outer surface of the inclined wall portion is performed so that the dimension measured radially between the outermost diameter part of the curled portion and the point where the tip edge abuts against the inclined wall portion is in the range of 40% to 60% of the curl width, which is half the difference between the outer diameter and inner diameter of the curled portion, and the abutment angle of the tip edge portion against the inclined wall portion is in the range of ±20 degrees centered on 90 degrees. A method for forming a curled portion of a capped bottle-type can according to claim 1, comprising the steps of:
A method for forming a curled portion of a bottle-type can with a cap, characterized in that the processing of curling the tip edge side of the curved portion radially inward and abutting it against the outer surface of the inclined wall portion is performed by radially expanding it outward and pressing the portion above the downwardly curved inclined wall portion from the outside inward in the radial direction. A method for forming a curled portion of a capped bottle-type can according to claim 1, comprising the steps of:
The process of expanding the portion above the inclined wall portion outward in the radial direction and curving it downward is an outward bending process that curves the portion so as to be convex toward the outer surface, and the process of rolling the tip edge portion side of the curved portion inward in the radial direction is an inward bending process that curves the portion so as to be convex toward the outer surface,
a bending process for bending the curled portion of a bottle-shaped can with a cap, the bending process being performed such that the apex, which is the uppermost end of the curled portion, is located outer than the center of the curled portion in the width direction, and the inward bending process being performed such that the radius of curvature of the tip edge portion, which is curled inward in the radial direction and curved so as to be convex toward the outer surface, is smaller than the radius of curvature of the portion inner than the apex, which is curved so as to be convex toward the outer surface. A method for forming a curled portion of the capped bottle-type can according to any one of claims 1 to 3, comprising the steps of:
The bottle-shaped can is a metal can made of an aluminum alloy specified in 3104H19 of the Japanese Industrial Standards, and the curled portion has a nominal diameter of 28 mm.
A method for forming a curled portion of a bottle-type can with a cap, characterized in that the curled portion is formed so that the ratio of a material cross-sectional area, which is the cross-sectional area of the material constituting the curled portion in a cross section cut along the central axis, to a curl occupied area, which is the product of the curl width in the cross section cut along the central axis and the height of the curled portion in the direction of the central axis, is in the range of 40% or more and 60% or less.

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