Can Lid Shell, Manufacturing Method for Same, and Forming Device

The present invention relates to a can lid shell of a beverage can, a manufacturing method for the same, and a forming device. Priority is claimed on Japanese Patent Application No. 2023-006121, filed on Jan. 18, 2023, the content of which is incorporated herein by reference.

A can lid shellof a beverage can is manufactured by performing press working on a circular blank punched out from an aluminum alloy plate, and as illustrated in, the can lid shellincludes a panel section, a countersink sectionprovided around the panel section, and an attachment sectionextending from an outer wall portion of the countersink section, formed in a hook shape in a cross section, and fastening a flange of a can body. A tear line for opening or a tab for an opening operation is provided for the can lid shellby a conversion press, and a can lid is manufactured.

In addition, in the related art, a can lid shellhaving a reduced thickness and a reduced weight, which is illustrated in, is known (PTL 1).

When the can lid shelland the can lid shellare compared with each other, a location for forming a chuck wall by fastening the flange of the can body has a linear shape in the can lid shellin the related art as illustrated by a broken line in. However, the can lid shellis configured such that a plurality of curved surfaces are connected as illustrated by a broken line in.

After a can body having a bottomed tubular shape is filled with a contained object and a gas (COor N), as illustrated by a solid line in, the can lid shellis wound around the flange section of a can body, and a can product to which the can lid shellis attached is completed. However, in, a tab rivet, the tear line, a debossing process, and the like which are added to the panel sectionin a conversion step as a subsequent step are omitted in the illustration.

In addition, in the can product to which the can lid shellis attached, a pitch diameter PDof a countersink is smaller than a pitch diameter PDof a countersink of the can lid shell(PD<PD), and furthermore, the panel sectionis designed to have a smaller area.

In the can lid shell, the panel sectionis formed to be small. Therefore, even when internal pressures of the cans are the same as each other, a smaller internal pressure acts on the panel section, compared to the internal pressure received by the panel sectionof the can lid shell.

In a filling process of closing the can with the can lid by filling the can body with the contained object or the gas, or in a distribution process, when the can product is exposed to an excessively high temperature, the internal pressure of the can increases, and the internal pressure of the can exceeds a limit of pressure resistance strength of the can lid, a phenomenon in which a portion of the can lid of the can product protrudes outward, so-called buckling, occurs as illustrated by a broken line in. When a portion of the can lid protrudes outward in this way, a crack occurs in the protruding portion or the tear line. Consequently, a disadvantage occurs in that the contained object or the gas leaks, or the can cannot be opened.

Therefore, the present invention aims to provide a can lid shell that prevents buckling, a manufacturing method for the can lid shell, and a forming device.

According to the present invention, there is provided a can lid shell including a panel section having a circular peripheral edge, a countersink section formed and recessed along the peripheral edge of the panel section, a chuck wall section rising from an edge of the countersink section, and a flange section protruding from an upper end of the chuck wall section. An internal space set inside the panel section, the countersink section, and the chuck wall section is provided, the countersink section includes a first curved surface portion that is convex toward the internal space, and the chuck wall section includes a second curved surface portion that is connected to the first curved surface portion and that is concave from the internal space. Thicknesses of the second curved surface portion and the first curved surface portion increase from an edge on the flange section side toward an edge on the panel section side.

In the can lid shell according to the present invention, the first curved surface portion and the second curved surface portion having different orientations of curved surfaces in that one is the concave surface and the other is the convex surface are thickened. Accordingly, mechanical strength of the inflection portion including the first curved surface portion and the second curved surface portion is increased, and pressure resistance strength can be increased. In this manner, a thickness and a weight of the can lid can be further reduced.

In the can lid shell according to the present invention, the countersink section preferably includes a third curved surface portion formed in such a manner that the first curved surface portion is disposed between the second curved surface portion and the third curved surface portion, the third curved surface portion is connected to the first curved surface portion, and is convex toward the internal space, and furthermore, a thickness of the third curved surface portion increases as the third curved surface portion is directed from the edge on the panel section side to an edge connected to the first curved surface portion. Since the third curved surface portion is thickened, the mechanical strength is increased, and the pressure resistance strength can be increased.

The can lid shell according to the present invention preferably includes a plurality of thin portions recessed and formed from the second curved surface portion to the third curved surface portion, and provided to be separated in a circumferential direction of the can lid shell, on a front surface or a back surface of the can lid shell, and a thick portion that is thicker than the thin portion is formed between the thin portions. In the plurality of thin portions and a plurality of the thick portions, dimensions along a radius of the can lid shell in a plan view or in a bottom view of the can lid shell are set to be longer than dimensions along a direction orthogonal to a direction of the radius.

The can lid shell of the present invention includes the plurality of thin portions and the plurality of thick portions in the circumferential direction in which the first curved surface portion that is convex toward the internal space side and extends from the second curved surface portion to the third curved surface portion. A location from the second curved surface portion to the third curved surface portion forms the thickened portion, and the first curved surface portion including the thin portion and the thick portion is provided in the thickened portion. In this manner, deformation such as bending to the internal space side is prevented. In this manner, the mechanical strength of the thickened portion including an inflection portion including the first curved surface portion and the second curved surface portion is further increased, and the pressure resistance strength is improved.

According to the present invention, there is provided a forming device including a lower die, and an upper die. The forming device forms a can lid shell by pinching a circular blank between the lower die and the upper die. The lower die includes a die core ring, and a panel punch disposed inside the die core ring. The upper die includes a tubular upper piston, a tubular inner sleeve disposed inside the upper piston, and a die center disposed inside the inner sleeve.

In the forming device, an outer portion of a tip portion of the die core ring and a tip portion of the upper piston are disposed to face each other. An inner portion of the tip portion of the die core ring and a tip portion of the inner sleeve are disposed to face each other. The panel punch and the die center are disposed to face each other. The inner portion of the tip portion of the die core ring includes a first lower die curved surface portion that is concave toward the inner sleeve, and a second lower die curved surface portion that is connected to the first lower die curved surface portion, that is disposed to be further shifted to a central axis side, and that is convex toward the inner sleeve.

The tip portion of the inner sleeve includes a first upper die curved surface portion that is convex toward the first lower die curved surface portion, a second upper die curved surface portion that is connected to the first upper die curved surface portion, that is disposed to be further shifted to the central axis side, and that is convex toward the first lower die curved surface portion in an arc shape whose curvature radius is different from a curvature radius of the first upper die curved surface portion, and a third upper die curved surface portion that is connected to the second upper die curved surface portion, that is disposed to be further shifted to the central axis side, and that is concave toward the second lower die curved surface portion.

A mold clearance formed between the first lower die curved surface portion and the second lower die curved surface portion of the die core ring and the second upper die curved surface portion and the third upper die curved surface portion of the inner sleeve is an interval equal to or larger than a plate thickness of the circular blank, and is further widened as the mold clearance is directed to the central axis.

In the forming device according to the present invention, the mold clearance is formed between the first lower die curved surface portion and the second lower die curved surface portion of the die core ring and the second upper die curved surface portion and the third upper die curved surface portion of the inner sleeve, and the mold clearance is further widened as the mold clearance is closer to the central axis. Since the mold clearance has an interval equal to or larger than a plate thickness of the circular blank serving as a processing target, a portion of the circular blank can be thickened by processing.

According to the present invention, there is provided a forming device including a lower die, and an upper die. The forming device forms a can lid shell by pinching a circular blank between the lower die and the upper die. The lower die includes a die core ring, and a panel punch disposed inside the die core ring. The upper die includes a tubular upper piston, a tubular inner sleeve disposed inside the upper piston, and a die center disposed inside the inner sleeve.

In the forming device, the die core ring includes a tubular fixing portion provided to be fixed to the lower die, a movable portion provided inside the fixing portion, and a biasing member configured to be expandable and contractible along a central axis, supporting the movable portion from below, and biasing the movable portion. A tip portion of the fixing portion of the die core ring and a tip portion of the upper piston are disposed to face each other. A tip portion of the movable portion of the die core ring and a tip portion of the inner sleeve are disposed to face each other. The panel punch and the die center are disposed to face each other.

The tip portion of the movable portion includes a lower die curved surface portion that is convex toward the inner sleeve. The tip portion of the inner sleeve includes an upper die curved surface portion that is concave toward the lower die curved surface portion. A mold clearance formed between the lower die curved surface portion of the movable portion and the upper die curved surface portion of the inner sleeve is an interval equal to or larger than a plate thickness of the circular blank, and is further widened as the mold clearance is closer to the central axis. The movable portion retreats toward the biasing member by being pushed against an intermediate formed body when deep drawing is performed on the circular blank.

Here, the intermediate formed body means a form during deformation until the circular blank reaches the first formed body by performing the deep drawing step.

The forming device according to the present invention preferably further includes a tubular lower piston surrounding a portion of an outer peripheral surface of the die core ring. The fixing portion includes a through-hole penetrating from the inside of the fixing portion to an outside of the fixing portion, and a block disposed in the through-hole. The block has an outer inclined surface protruding to the outside of the fixing portion and an inner inclined surface protruding to the inside of the fixing portion. The lower piston has an inner inclined surface that abuts on the outer inclined surface of the block. The movable portion has an outer inclined surface that abuts on the inner inclined surface of the block. When the lower piston is lowered by being pushed against the upper die, the inner inclined surface of the lower piston abuts on the outer inclined surface of the block, and in a state where the outer inclined surface of the retreated movable portion abuts on the inner inclined surface of the block, the lower piston is further lowered to move the movable portion toward the inner sleeve.

The forming device according to the present invention includes the biasing member that supports the movable portion, and the movable portion is retreated by the intermediate formed body. In this manner, it is possible to suppress a decrease in the plate thickness of the intermediate formed body which is caused by friction with the movable portion when deep drawing is performed. As the biasing member, for example, a spring, a pneumatic piston, or the like can be used.

According to the present invention, there is provided a manufacturing method for a can lid shell in which a can lid shell is formed by pinching a circular blank between a lower die and an upper die. The manufacturing method includes a deep drawing step of forming the circular blank in a first formed body having a tray shape, and a reverse step of moving a flat portion at a bottom of the first formed body pinched between a panel punch and a die center, in an opposite direction to form a countersink section recessed around the flat portion. In the deep drawing step, a first inflection portion including a concave surface and a convex surface is formed between the flat portion of the first formed body and a flange section by deforming a portion of the circular blank with a tip portion of a die core ring and a tip portion of an inner sleeve.

In the reverse step, in a state where a space between the tip portion of the die core ring and the tip portion of the inner sleeve is formed as a mold clearance widened as the mold clearance is closer to a central axis, a portion of the first formed body protruding from between the panel punch and the die center is pushed into a gap which is not filled with the first inflection portion in the mold clearance, and a second inflection portion in which the first inflection portion is thickened is formed.

In the manufacturing method for a can lid shell according to the present invention, a portion of the first formed body serving as a processing target is deformed and pushed into the mold clearance. The first formed body and a location adjacent thereto are compressed from the flat portion side toward the flange section side such that the plate thickness increases. The pressure resistance strength of the can lid is improved by work hardening of compression and the increased plate thickness.

The mold clearance can be formed during the deep drawing, when the reverse step starts, or during the reverse step.

In the manufacturing method for a can lid shell according to the present invention, preferably, the die core ring includes a movable portion forming a portion facing the tip portion of the inner sleeve in the tip portion of the die core ring, and a biasing member holding the movable portion at a position where the mold clearance is formed. In the deep drawing step, an intermediate formed body pushes the movable portion, and the movable portion retreats toward the biasing member.

In the present invention, before the reverse step is performed, the movable portion is retreated by the intermediate formed body. In this manner, it is possible to suppress a possibility that the plate thickness of the circular blank is reduced due to friction with the movable portion when the deep drawing is performed. In addition, the first formed body is formed in a state where the reduction in the plate thickness is suppressed in this way, and the first curved surface portion and the second curved surface portion are formed for the first formed body. In this manner, it is possible to suppress deformation or distortion of a curved portion at a stage of starting the reverse step.

According to the present invention, the inflection portion having a concave curved surface and a convex curved surface is formed to have high pressure resistance strength. Therefore, buckling can be prevented.

A can lid shellaccording to a first embodiment of the present invention will be described with reference to the drawings.

As illustrated in, the can lid shellincludes a panel sectionin which an outline in a plan view is formed in a circular shape, a countersink sectionformed and recessed along a peripheral edge of the panel section, a chuck wall sectionrising from an edge of the countersink sectionand defining an internal space SPtogether with the panel sectionand the countersink section, and a flange sectionprotruding from an upper end (end portion on a side in a radius outer direction Do) of the chuck wall section. As illustrated in, the internal space SPis a space on the panel sectioninside the chuck wall section.

In the following description, in directions along a radius from a central axis C orthogonal to the panel sectionaround a center of the panel section, a direction from the central axis C toward an outside will be referred to as the radius outer direction Do, and a direction from the outside toward the central axis C will be referred to as a radius inner direction Di. In addition, a direction from the countersink sectionside toward the chuck wall sectionalong the central axis C will be referred to as a first direction D, and a direction from the chuck wall sectiontoward the countersink sectionside along the central axis C, which is opposite to the first direction Dwill be referred to as a second direction D(refer to).

As front and back surfaces of the can lid shell, a surface of the can lid shellincluding a location defining the internal space SPand one surface of the flange sectionwhich is adjacent to the location is defined as a front surface SF, and a surface on a side opposite to the front surface SFis defined as a back surface SF.

illustrate a cross-sectional shape of the can lid shellwhen cut along a virtual surface passing through the central axis C and widened in the radius outer direction Do. Hereinafter, the cross-sectional shape of the can lid shellwill be described.

The panel sectionis formed as a flat disk, and a thickness thereof is set to be substantially uniform.

The countersink sectionincludes a groove bottom portionforming a deep location, a first groove wall portionextending from an edge on a side in the radius inner direction Di of the groove bottom portionto a peripheral edge of the panel section, and a second groove wall portionextending from an edge on a side in the radius outer direction Do of the groove bottom portionto an edge on a side in the radius inner direction Di of the chuck wall section.

The groove bottom portionhas a cross section formed as an arc of a radius rfrom a center Cdisposed in the internal space SP, and has a curved surface which is concave from the internal space SPside. A deepest portion is disposed in the groove bottom portion, and a connection location (first connection point p) where the groove bottom portionand the first groove wall portionare connected to each other is disposed to be shifted to a side in the radius inner direction Di from the deepest portion, and is disposed to be shifted in the first direction Dfrom the deepest portion.

Furthermore, a connection location (second connection point p) where the groove bottom portionand the second groove wall portionare connected to each other is disposed to be shifted to a side in the radius outer direction Do from the deepest portion, and is disposed to be shifted in the first direction Dfrom the deepest portion. In, a position of each connection point is indicated by a ∘ mark.

The first groove wall portionincludes a first inclined groove cross-sectional portionA in which one edge is connected to an edge on the side in the radius inner direction Di of the groove bottom portionto form the first connection point p, and furthermore, whose inclination with respect to the central axis C is formed to be constant, and a first convex type groove cross-sectional portionB having an arc that is formed from the other edge of the first inclined groove cross-sectional portionA to the peripheral edge of the panel sectionand that is convex to the internal space SPside.

A connection location (third connection point p) where the first inclined groove cross-sectional portionA and the first convex type groove cross-sectional portionB are connected to each other is disposed to be shifted in the radius inner direction Di from the first connection point p, and is disposed to be shifted in the first direction Dfrom the first connection point p.

A connection location (fourth connection point p) where the first convex type groove cross-sectional portionB and the panel sectionare connected to each other is disposed to be shifted to the side in the radius inner direction Di from the third connection point p, and is disposed to be shifted in the first direction Dfrom the third connection point p. The first convex type groove cross-sectional portionB has a curved surface whose radius from the central axis C gradually decreases (diameter is reduced) from the third connection point ptoward the fourth connection point p.

The second groove wall portionincludes a second inclined groove cross-sectional portionA in which one edge is connected to an edge on the side in the radius outer direction Do of the groove bottom portionto form the second connection point p, and furthermore, whose inclination with respect to the central axis C is formed to be constant, a second convex type groove cross-sectional portionB (corresponding to a third curved surface portion of the present invention) having an arc in which one edge is connected to the other edge of the second inclined groove cross-sectional portionA and that is convex to the internal space SPside, and a third convex type groove cross-sectional portionC (corresponding to a first curved surface portion of the present invention) having an arc in which one edge is connected to the other edge of the second convex type groove cross-sectional portionB and that is convex to the internal space SPside with a curvature radius different from a curvature radius of the second convex type groove cross-sectional portionB.

A connection location (fifth connection point p) where the second inclined groove cross-sectional portionA and the second convex type groove cross-sectional portionB are connected to each other is disposed to be shifted in the radius outer direction Do from the second connection point p, and is disposed to be shifted in the first direction Dfrom the second connection point p. A connection location (sixth connection point p) where the second convex type groove cross-sectional portionB and the third convex type groove cross-sectional portionC are connected to each other is disposed to be shifted to the side in the radius outer direction Do from the fifth connection point p, and is disposed to be shifted in the first direction Dfrom the fifth connection point p.

A connection location (seventh connection point p) where the third convex type groove cross-sectional portionC and the chuck wall sectionare connected to each other is disposed to be shifted in the radius outer direction Do from the sixth connection point p, and is disposed to be shifted in the first direction Dfrom the sixth connection point p.

The second convex type groove cross-sectional portionB has a curved surface in which the radius from the central axis C gradually increases (diameter is enlarged) from the fifth connection point ptoward the sixth connection point p.

The third convex type groove cross-sectional portionC has a curved surface in which the radius from the central axis C gradually increases (diameter is enlarged) from the sixth connection point ptoward the seventh connection point p.