JPH0755347B2 - Seamless can bottom method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a bottom portion of a seamless can used for beer cans, carbonated beverage cans, etc., which has improved pressure resistance.

[0002]

2. Description of the Related Art Inner pressure resistance of a bottom portion of a seamless metal can having an outer wall portion directed obliquely inward and downward, an annular projection portion having an inner wall portion connected to the outer wall portion through a ground portion, and a bottom portion having a central panel inside thereof. It is known that the resistance, ie, the buckling resistance, becomes higher as the lateral width of the ground contact portion becomes smaller and the angle formed by the axial center of the inner wall portion becomes smaller. In the present specification, the lateral width of the ground contact portion refers to the width w in the vicinity of the ground contact portion cut by the plane 26 parallel to the ground contact surface 27 (see FIG. 5) passing through the lowest position of the inner surface of the ground contact portion. The lateral width w is proportional to the radius of curvature when the radius of curvature of the cross section of the ground contact portion is uniform.

As a method of forming such a bottom portion, it is conceivable to perform press molding using a punch having a small cross-sectional curvature radius of the nose portion which comes into contact with the inner surface of the ground portion, but in this case, the nose portion is damaged. Easily, the ground part of the preform breaks during molding, or the ground part expands and deforms and becomes thin, and the inner wall part easily protrudes downward, which causes a problem that the internal pressure resistance tends to decrease. easy.

On the other hand, the width of the ground contact portion is relatively large,
In addition, a bottom portion having a relatively large angle with the axial center of the inner wall portion is formed in advance, the inner wall portion is held by a cylindrical body, and a roll having a truncated conical surface is applied to the outer wall portion to form a can and a roll. A method of causing rolling during the period has been proposed (Japanese Patent Publication 1-5).
No. 0493). However, in this method, there are two steps for forming the bottom portion, the steps are complicated, the equipment cost is high, and there is a problem that the outer surface organic film of the outer wall portion is damaged due to friction during rolling. .

[0005]

DISCLOSURE OF THE INVENTION The present invention has an outer wall portion directed inward and obliquely downward, and an annular projection portion composed of an inner wall portion connected to the outer wall portion through a grounding portion having a relatively small width.
Seamless can bottom with improved internal pressure resistance in one step,
Moreover, it is an object of the present invention to provide a method of forming at a relatively low cost, without fear of damage to the punch, damage to the ground portion, or damage to the organic film on the outer wall.

[0006]

A method for forming a seamless can bottom portion according to the present invention comprises a cylindrical body portion, an inner surface of a radius portion of a seamless can preform having a flat bottom portion connected to the body portion through a radius portion, and The outer surface is pressed by a punch with a ring-shaped lower part and a biased hold-down ring, and at the same time, the outer surface of the bottom part is pressed by a doming die, so that the outer wall part and the outer wall part are slanted inward and downward. After forming an annular projecting portion having an inner wall portion connected via a grounding portion and a central panel recessed in an arc-shaped cross section, the grounding portion is ring-shaped while the outer wall portion is held between the ring-shaped portion and the holddown ring. The central panel and the inner wall portion and the outer wall portion are relatively moved in the axial direction so as to be separated from the nose portion of the ring portion, so that the lateral width of the grounding portion of the annular protrusion is narrowed or further It is characterized in that the wall is raised substantially vertically.

In the formation of the bottom portion of the seamless can, as shown in the first embodiment, the doming die is fixed, and a pressing body biased toward the doming die is provided in the ring-shaped portion. Using the tool, the outer wall is relatively moved in the axial direction by raising the outer wall while the central panel is held in a fixed position by being held by the doming die and the pressing body.

In addition, the formation of the seamless can bottom is described in the second step.
, The doming die surrounds the fixed core die and is biased toward the preform, with the top of the doming die always at about the same level as the top of the core die. , Equipped with a ring die that cooperates with the core die to form a common center panel molding surface when bottom dead center is reached, and provided a pressing body biased toward the doming die in the ring-shaped portion. With tools
The relative movement of the outer wall portion in the axial direction is also performed by raising the outer wall portion while holding the central panel between the ring die and the pressing body and holding it in a fixed position.

Furthermore, as shown in the third embodiment, the formation of the seamless can bottom portion is such that the doming die is fixed, and the fluid cylinder can press the doming die toward the doming die. A tool provided with a body is also used to move the outer wall relative to the axial direction by raising the outer wall while the central panel is held in place by the doming die and the pressing body.

Next, the formation of the bottom of the seamless can is described in the fourth step.
, The doming die is urged toward the preform, and the core punch is inserted through the inside of the ring punch having the ring-shaped portion. Relative movement is also accomplished by holding the outer wall in place and holding the central panel with a doming die and core punch to lower it.

The formation of the seamless can bottom is described in the fifth step.
The doming die is urged toward the preform, and the inside of the ring punch having the ring-shaped portion is pressed toward the doming die toward the doming die. Using a tool with a core punch attached to the lower end, hold the outer wall in a fixed position to lower the center panel with the doming die and core punch, while holding the outer wall in a fixed position. Also done by.

Further, as shown in the sixth embodiment, the formation of the bottom portion of the seamless can is such that the doming die is biased toward the preform, and the doming die is moved toward the preform by a fluid cylinder in the ring-shaped portion. Using a tool provided with a pressing body that can be pressed toward, the central panel is held by the doming die and the pressing body to lower the axial relative movement of the outer wall portion while the outer wall portion is held at a fixed position. It is done by

[0013]

When the central panel and the inner wall portion and the outer wall portion are moved relative to each other in the axial direction so as to move away from the nose portion of the ring-shaped portion, an extension portion of the outer wall portion is formed by the portion below the inner wall portion and the grounding portion. At the same time, the remaining inner wall portion comes into close contact with the peripheral surface of the doming die. Therefore, the lateral width of the ground contact portion is narrowed. Also, the inner wall portion can be made to rise substantially vertically by making the circumferential surface of the doming die a cylindrical surface or a slightly inverted frustoconical surface. Since only the bending deformation is applied to the grounding portion at this time, there is no fear that the grounding portion becomes thin. When the central panel and inner wall and the outer wall have a small relative movement in the axial direction, and the extension of the outer wall is formed only in the vicinity of the grounding part, the lateral width of the grounding part is slightly narrowed, but the inner wall part is slightly narrowed. The inclination angle of is almost unchanged.

From a seamless can preform having a cylindrical barrel and a flat bottom that connects to the barrel via a radius, first a punch, holddown ring and doming die are used to form an annular protrusion and a central panel. This is done when the punch reaches bottom dead center. Immediately after this formation, before the punch has reached the top dead center, the central panel and the inner wall portion and the outer wall portion are relatively moved in the axial direction to narrow the lateral width of the ground contact portion, or the inner wall portion is substantially Since the bottom portion that rises vertically is formed, the bottom portion can be formed in one step. Therefore, the equipment cost is relatively low, and the molding can be performed at a relatively low cost.

Since the lateral width of the grounding portion of the annular protrusion formed first is narrowed later, the radius of curvature of the nose portion of the punch may be large enough not to break during molding. Therefore, there is no risk of breakage of the punch or breakage of the grounding portion during molding. Further, since the roll is not applied to the outer wall to be rolled, there is no possibility of causing damage to the organic film on the outer wall.

[0016]

1 to 4 show the steps of a first embodiment of the present invention. In FIG. 1, reference numeral 1 is a seamless can preform formed by drawing and redrawing a circular blank of a metal plate (usually coated on both sides with an organic film). The cylindrical body 2, the radius Part 3
And a flat bottom 4. As the metal plate, tin-free steel, tin-plated steel plate, aluminum (alloy) thin plate, etc. are usually used.

The bottom forming tool is mainly composed of a bottom forming punch 5 having a ring-shaped portion 6 at its lower portion, a holddown ring 7, a doming die 8 and a retainer 9. The bottom molding punch 5 has an outer diameter that allows it to be fitted almost snugly into the body 2. On the lower portion of the ring-shaped portion 6, a sloped portion 6a and a nose portion 6b having a shape corresponding to the inner surface of the annular projection 19 (FIG. 2) that is initially formed are formed. In the case of the present embodiment, the cross section of the sloped portion 6a is a curved curve that is concave inward with a relatively large radius of curvature. Further, the radius of curvature r ₁ of the nose portion 6b is relatively large (for example, 0.3 to 3 m so as not to be damaged when the radius portion 3 is molded).
m) Specified.

In the cylindrical concave portion 5a in the ring-shaped portion 6, the pressing body 1 is urged downward by the strong spring 11.
0 is provided slidably along the inner surface 6c of the ring-shaped portion 6. The lower surface 10a of the pressing body 10 has a shape corresponding to the inner surface of the central panel 23 (FIG. 2) to be formed, and has a cylindrical shape whose cross section is concave inward. A locking bolt 12 is screwed onto the pressing body 10, and the lower surface of the head 12a of the bolt 12 is normally on the upper step 13a of the hole 13.
As shown in FIG. 1, the lower surface 10a of the pressing body 10 is in a position slightly inserted into the recess 5a. 14 is an air guide hole.

The hold down ring 7 includes a frame 15
Is urged upward by a strong spring 16 provided between the shaft 7a and the shaft 7a, and its upper surface 7b is always in a position where it is engaged with the fixed retainer 9 as shown in the figure. The inner surface 17 of the holddown ring 7 is composed of an upper short cylindrical portion 17a having an inner diameter slightly larger than the outer diameter of the body portion 2, an inclined surface portion 17b therebelow, and a lower short cylindrical portion 17c. The inclined surface portion 17b has a shape corresponding to the outer surface of the outer wall portion 20 '(FIG. 3) to be finally formed except for the lowermost portion. The inner diameter of the lower short cylindrical portion 17c is set to be slightly larger than the outer diameter of the tubular portion 8b of the doming die 8.

The doming die 8 is fixed to the frame 15, and the upper surface thereof is a molding surface 8a having a curved surface having a shape corresponding to the outer surface of the central panel 23, which is slightly smaller than the inner diameter of the ring-shaped portion 6. Diameter cylindrical portion 8b
Is connected to the upper surface 8a. The diameter of the cylindrical portion 8b is usually
When the thickness of the bottom portion 4 of the preform is t, it is smaller than the inner diameter of the ring-shaped portion 6 by 2t + clearance (usually 0.05 to 1.0 mm).

The bottom part of the preform 1 is formed by the above tool as follows. As shown in FIG. 1, when the bottom molding punch 5 on which the preform 1 is externally inserted is lowered by, for example, a crank mechanism (not shown), the radius portion 3 comes into contact with the hold down ring 7,
At the time when the hold down ring 7 descends and reaches the bottom dead center when the pressing force is applied to the radius portion 3, as shown in FIG. 2, the outer wall portion 20 is moved by the cooperation of the ring-shaped portion 6 and the hold down ring 7. It is formed. At the same time, the bottom portion 4 is pushed by the doming die 8 so that the inner surface has a radius of curvature equal to the radius of curvature r ₁ of the nose portion 6b of the ring-shaped portion 6.
1. An inner wall portion 22 slightly inclined inward and upward and a central panel 23 having an arcuate cross section are formed. At that time, the central panel 23 contacts the pressing body 10 and pushes up the pressing body 10 against the strong spring 11. As described above, the intermediate preform 18 having the bottom portion including the annular protrusion 19 and the central panel 23 is formed.

When the bottom forming punch 5 starts to rise, the outer wall portion 20 rises together with the body portion 2 while being strongly pressed against the slope portion 6a of the ring-shaped portion 6 by the hold down ring 7 urged by the strong spring 16. To do. On the other hand, the central panel 23 is strongly sandwiched by the strong spring 11 between the molding surface 8a of the fixed doming die and the lower surface 10a of the pressing body 10 and does not move, that is, does not rise. Therefore, as shown in FIG. 3, the ground portion 21 and the inner wall portion 22 are left behind,
The lower portion of the inner wall portion 22 and the portion of the ground contact portion 21 extend along the lower portion of the slope portion 17b of the holddown ring 7,
Most of the remaining inner wall portion 22 is the cylindrical portion 8b of the doming die.
Close to the cylindrical surface of. Therefore, the ground contact portion 21 becomes a ground contact portion 21 'whose width is narrowed, the inner wall portion 22 becomes an inner wall portion 22' which rises vertically, and the outer wall portion 20 becomes an outer wall portion 20 'whose length is extended (see FIG. 5), a seamless can 25 having a reshaped annular protrusion 19 'is formed.

As shown in FIG. 3, as the bottom forming punch 5 rises, the lower surface of the locking bolt head 12a engages with the upper step 13a of the hole, and the hold down ring 7 engages with the retainer 9. It is pushed up to the matching position and the inner wall 2
2'is separated from the doming die 8 and when the finger claw of the stripper (not shown) is engaged with the flange portion 50 (see FIG. 18) of the open end of the preform 1,
As shown in FIG. 3, the bottom forming punch 5 comes out of the preform 1, and thereafter, the bottom forming punch 5 continues to rise and completely comes out of the preform 1.

With the annular projection 19 re-formed so that the lateral width of its ground contact portion is narrowed, the inner wall portion 22 'may be inclined slightly upward and outward, as shown in FIG. With a material having a small spring back, the inner wall portion 22 'retains the same shape even after being pulled out from the doming die 8, and with a material having a large spring back, as shown in FIG. , Inner wall 2
2'becomes an inner wall portion 22 "that rises vertically.
As shown in FIG. 8, at least the lower part of the molding surface of the peripheral surface of the tubular body 8b 'is formed to surely incline the inner wall portion 22' during molding slightly to the upper and outer sides or to narrow the lateral width of the ground contact portion. It is also possible to use a doming die 8'which is an inverted truncated cone surface in which the inner wall portion 22 'is slightly enlarged (for example, the taper angle θ is 0.5 to 6 degrees) in a range where it can be extracted. Inner wall 2
As shown in FIG. 9, when 2'is coming out of the tubular portion 8b ',
The inner wall portion 22 'is pushed outward and the lateral width of the ground contact portion is further narrowed, and the inner wall portion 2 is raised vertically.
2 ". These also apply to the examples described below.

The distance between the central panel 23 and the inner wall 22 and the outer wall 20 relative to the nose 6b of the ring-shaped portion 6 in the axial direction is relatively small, and the outer wall is provided only near the grounding portion 21. By forming the extension portion of 20, it is possible to narrow the lateral width of the ground contact portion slightly and to make almost no change in the inclination angle of the inner wall portion 22 with respect to the axis, as shown in FIG. The part shown by the solid line and the part shown by the dotted line in FIG. 11 show the state before and after the axial movement, respectively. Also, by forming the angle of inclination of the inner wall with respect to the axis to be slightly larger,
Similarly, the inclination angle of the inner wall portion may be hardly changed. The same applies to the examples described below.

12 to 17 show the steps of the second embodiment of the present invention. 1 to 4 indicate the same parts. The same applies to the drawings after FIG. The second embodiment is the same as the first embodiment except that the forming tool used has a different configuration of the doming die. As shown in FIG. 12, the doming die 28
Includes a fixed core die 30 fixed to the frame 29 and a ring die 31 surrounding the core die 30 and biased upward by a strong spring 32. The upper surface 30a of the core die 30 has an arcuate cross section, and
When the ring die 31 is lowered to the lowest position, the upper surface 31a of No. 1 is the upper surface 30a of the core die 30a as shown in FIG.
And a molding surface 33 common to the above. The molding surface 33 corresponds to the molding surface 8a in FIG. At all times, the bottom upper surface 31b of the ring die 31 engages with the lower surface of the core die 30, and the uppermost portion of the upper surface 31a is located at substantially the same level as the top portion of the upper surface 30a (FIG. 12).

In this case, when the bottom molding punch 5 is pushed down together with the preform 1, as shown in FIG. 13, first, the upper surface 31a of the ring die and the lower surface 10a of the pressing body 10 are respectively acted by the strong springs 32 and 11. By strongly pressing the contacted portion of the bottom portion 4 of the preform 1, the formation of the peripheral edge portion 23a of the central panel 23 is started. Therefore, radial wrinkles are not likely to occur in the vicinity of the peripheral edge portion 23a, which is usually likely to occur.

When the bottom molding punch 5 further descends and reaches the bottom dead center, the ring die 31 comes into contact with the upper surface 29a of the frame 29 to reach the lowest position, and cooperates with the core die 30 as shown in FIG. Forming a common molding surface 33 to form the central panel 23. At the same time, the annular protrusion 19
Is also formed.

When the bottom forming punch 5 starts to rise, the outer wall portion 20 is held by the hold-down ring 7 to form the ring-shaped portion 6.
Until the bottom die upper surface 31b engages with the bottom surface of the core die 30 while being strongly pressed against the sloped portion 6a of the preform 1 and rising together with the preform 1, while also holding the peripheral edge portion 23a of the central panel together with the pressing body 10. It rises (Fig. 15). Further, even if the bottom molding punch 5 is slightly raised, the peripheral edge portion 23a of the central panel and therefore the central panel 23
Is strongly pinched between the upper surface 31a of the ring die and the lower surface 10a of the pressing body by the strong springs 11 and is not strongly moved by the strong springs 32 and 11, that is, does not move upward, so as shown in FIG. In the same manner as in the above embodiment, the grounded portion 21 'having a narrowed width and the vertically raised inner wall portion 22' are formed. Thereafter, as shown in FIG. 17, the bottom molding punch 5 is extracted from the preform 1 in the same manner as shown in FIG. 4 of the first embodiment.

FIG. 18 shows a bottom forming tool used in the third embodiment of the present invention. In the forming tool of the first embodiment, the pressing body 43 is not a strong spring and the fluid cylinder 44 is used. The difference is that it is pressed by, for example, an air cylinder. 44a is a piston head, 44b is a piston rod, and the pressing body 43 is screwed to the lower end of the piston rod 44b. Similar to the case of the first embodiment, the bottom forming punch 5 is lowered to form the intermediate preform 18 when the bottom dead center is reached. Almost at the same time, the air cylinder 44 operates and the pressing body 43 descends, and when it reaches the bottom dead center, it comes into contact with the upper surface of the central panel 23.
Thereafter, similarly to the first embodiment, the center panel 23 is fixed by the pressing body 23 and the doming die 8,
The outer wall portion 20 held by the bottom forming punch 5 and the hold down ring 7 is pushed up by the hold down ring 7 to narrow the lateral width of the ground contact portion, and the inner wall portion is substantially raised (see FIG. 3). (See) is formed.

The pressing body 43 may come into contact with the central panel 23 after the bottom molding punch 5 starts to rise slightly. That is, as shown in FIG. 19, the bottom molding punch 5 is slightly elevated, and therefore the central panel 23 is slightly separated from the molding surface 8 a of the doming die 8. Pressing body 4
3 is not working yet. When the pressing body 43 descends from this state, the central panel 23 is pressed by the pressing body 43 and descends together with the inner wall portion 22, and is axially moved with respect to the outer wall portion 20 held by the ring-shaped portion 6 and the hold down ring 7. By moving relative to each other in the direction, the width of the ground portion 21 'is narrowed, or a seamless can 25 in which the inner wall portion 22' rises substantially vertically is formed, similar to that shown in FIG.

When the lowering timing of the pressing body 43 is slightly earlier than the above case, the pressing body 43 and the central panel 23 are
Since the distance between the center panel 23 and the molding surface 8a of the doming die is small at the time of contact with the center panel 2,
3 is pressed by the pressing body 43 and descends together with the inner wall portion 22, the ground contact portion 21 descends very slightly, then the central panel 23 contacts the doming die 8, and thereafter the same as in the first embodiment. As a result, the horizontal width of the grounding portion 21 'is narrowed, and the seamless can 25 (FIG. 3) in which the inner wall portion 22' stands up substantially vertically is formed.

A bottom forming punch 5 having a pressing body 43 which operates with a fluid cylinder 44 of FIG. 18 and a doming die 28 having a ring die 31 of the second embodiment (FIG. 12).
Even if the same molding is performed using a molding tool (not shown) including the above, a seamless can 25 in which the lateral width of the ground contact portion 21 ′ is narrowed and the inner wall portion 22 ′ is substantially vertically raised is formed. be able to.

20 to 23 show the steps of the fourth embodiment of the present invention. In this case, as shown in FIG. 20, the bottom forming punch 35 includes a ring punch 36 and a core punch 37 slidable therein, and the doming die 38 is biased upward by a strong spring 39. The difference is the same as the first embodiment, and the other points are the same as the first embodiment. Ring punch 3
The lower part 36a of 6 has a shape similar to the ring-shaped part 6 of the bottom forming punch 5 shown in FIG.
The lower surface 37a of the pressing member 10 has the same shape as the lower surface 10a of the pressing body 10. The molding surface 38a and the tubular portion 38b of the doming die 38 also have the same shapes as the molding surface 8a and the tubular portion 8b of the doming die 8.

When the bottom molding punch 35 is lowered, the bottom 4 of the preform 1 comes into contact with the doming die 38 and presses the doming die 38. The pressing force also causes the doming die 38 to stop at its original position. Strong spring 3
8 has a high spring strength. Therefore, similar to the case of FIG. 2 of the first embodiment, the annular projection 19 and the central panel 23 are formed as shown in FIG. At this point, the lower surface 37a of the core punch 37 is separated from the central panel 23 or is in a light contact state.

Next, when the core punch 37 is lowered with the ring punch 36 stopped, as shown in FIG. 18, the outer wall portion 20 remains immobile, that is, the central panel 23 stays at the fixed position, and the central panel 23 moves to the core punch 37. The domed die 38 holds it and pushes it down to form a grounding portion 21 ′ having a narrowed width and an inner wall portion 22 ′ which rises vertically, and a seamless can 25 is formed. Next, in the same manner as in FIG. 4, as shown in FIG. 23, the bottom forming punch 35 is raised,
The bottom forming punch 35 is pulled out from the seamless can 25.

FIG. 24 shows a bottom forming tool used in the fifth embodiment of the present invention. The forming tool of the fourth embodiment is similar to that shown in FIG. 1 under the core punch. The difference is that the pressing body 41 is provided. in this case,
The strength of the strong spring 39 is set to be higher than that of the strong spring 42. Therefore, as shown in FIG. 24, after forming the intermediate preform 18, the ring punch 36 is stopped, and the core punch 40 is further lowered while the outer wall portion 20 is held in a fixed position. In contact with each other (this state is not shown), the two can be integrated with each other in the same manner as shown in FIG. 22 of the fourth embodiment, and the seamless can 25 having the narrowed width of the grounding portion 21 '.
Is formed.

FIG. 25 shows a bottom forming tool used in the sixth embodiment of the present invention, which is the same as the forming tool of the fourth embodiment except that the punch structure is different.
The lower portion of the bottom forming punch 45 has a ring-shaped portion 4 having the same shape as the ring-shaped portion 6 of the bottom forming punch 5 of the first embodiment.
6, a fluid cylinder 47 built in the punch 45, for example, a piston rod 47 of an air cylinder.
A pressing body 48 screwed to the lower end of a is provided inside the ring-shaped portion 46. Therefore, when the pressing body 48 operates in the same manner as the core punch 37 of the fourth embodiment,
A seamless can 25 is formed from the intermediate preform 18 in which the width of the ground contact portion is narrowed.

The present invention is not limited to the above embodiments, and for example, a fluid cushion (for example, an air cushion) may be used as the biasing means instead of the strong spring. Further, the outer wall portion 20 may have an inverted truncated cone shape,
Alternatively, it may be a spherical band shape having a slightly arcuate cross section and convex outward. Further, the forming tool may be arranged so as to be horizontal to perform the forming. The seamless can may be a squeezed and ironed can.

[0040]

According to the present invention, the inner pressure resistance is improved by having an outer wall portion directed obliquely inward and downward, and an annular projection portion having an inner wall portion connected to the outer wall portion through a grounding portion having a relatively small lateral width. In addition, it is possible to form the seamless can bottom portion in a single process in a relatively low cost without damaging the punch, breaking the ground portion, and damaging the organic film on the outer wall portion.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a state just before molding in a first embodiment of the present invention.

FIG. 2 is a vertical sectional view showing a state in which a first annular protrusion is formed in the first embodiment of the present invention.

FIG. 3 is a vertical sectional view showing a state in which a reshaped annular protrusion is formed in the first embodiment of the present invention.

FIG. 4 is a vertical cross-sectional view showing a state where the punch is extracted from the seamless can according to the first embodiment of the present invention.

FIG. 5 is a longitudinal cross-sectional view of a main part showing a comparison between the first annular protrusion and the reshaped annular protrusion according to the first embodiment of the present invention.

FIG. 6 is a longitudinal sectional view showing a state of another example in which the reshaped annular protrusion is formed in the first embodiment of the present invention.

FIG. 7 is a longitudinal cross-sectional view of relevant parts showing the states of the annular protrusion of FIG. 6 before and after being withdrawn from the tool.

FIG. 8 is a longitudinal sectional view of a main part showing still another example in which the reshaped annular protrusion is formed in the first embodiment of the present invention.

9 is a longitudinal sectional view of an essential part showing a state in which the bottom part is extracted from the doming die from the state of FIG.

FIG. 10 is a longitudinal cross-sectional view of essential parts showing a state in which the lateral width of the ground contact portion is narrowed without substantially changing the inclination of the inner wall portion.

11 is a longitudinal cross-sectional view of relevant parts showing the states of the annular protrusion of FIG. 10 before and after being withdrawn from the tool.

FIG. 12 is a vertical cross-sectional view showing a state immediately before molding in the second embodiment of the present invention.

FIG. 13 is a vertical sectional view showing a state in which the first annular protrusion is being formed in the second embodiment of the present invention.

FIG. 14 is a vertical sectional view showing a state in which a first annular protrusion is formed in the second embodiment of the present invention.

FIG. 15 is a vertical cross-sectional view showing a state immediately before reshaping the annular protrusion in the second embodiment of the present invention.

FIG. 16 is a vertical sectional view showing a state in which a reshaped annular protrusion is formed in the second embodiment of the present invention.

FIG. 17 is a vertical cross-sectional view showing a state in which a seamless can is extracted from the punch in the second embodiment of the present invention.

FIG. 18 is a vertical cross-sectional view showing a state where the first annular protrusion is formed in the third embodiment of the present invention.

FIG. 19 is a vertical cross-sectional view showing one aspect of the third embodiment of the present invention when the bottom forming punch is slightly raised.

FIG. 20 is a vertical cross-sectional view showing a state immediately before molding in a fourth example of the present invention.

FIG. 21 is a vertical sectional view showing a state in which a first annular protrusion is formed in the fourth embodiment of the present invention.

FIG. 22 is a vertical sectional view showing a state in which a reshaped annular protrusion is formed in the fourth embodiment of the present invention.

FIG. 23 is a vertical cross-sectional view showing a state where the punch is extracted from the seamless can according to the fourth embodiment of the present invention.

FIG. 24 is a vertical sectional view showing a state in which a first annular protrusion is formed in the fifth embodiment of the present invention.

FIG. 25 is a vertical cross-sectional view showing a state in which a first annular protrusion is formed in the sixth embodiment of the present invention.

[Explanation of symbols]

 1 Seamless can preform 2 Cylindrical body part 3 Radius part 4 Bottom part 5 Bottom part forming punch 6 Ring part 6b Nose part 7 Hold down ring 8 Doming die 10 Pressing body 19 Annular protrusion 20 Outer wall part 20 'Outer wall part 21 Grounding part 21 'Grounding Part 22 Inner Wall Part 22' Inner Wall Part 22 '' Inner Wall Part 23 Central Panel 25 Seamless Can 28 Doming Die 30 Core Die 31 Ring Die 33 Forming Surface 35 Bottom Forming Punch 36 Ring Punch 37 Core Punch 38 Doming Die 40 Core Punch 41 Pressing Body 43 Pressing body 44 Fluid cylinder 45 Bottom forming punch 46 Ring portion 47 Fluid cylinder 48 Pressing body

Claims (8)

[Claims] 1. A punch in which the inner and outer surfaces of a radius portion of a seamless can preform having a cylindrical body portion and a flat bottom portion connected to the body portion through a radius portion are ring-shaped portions at their lower portions. , And an annular protrusion having an inner wall portion connected to the outer wall portion and the outer wall portion, which are slanted inward and downward, by pressing with a biased hold down ring and simultaneously pressing the bottom outer surface with a doming die, After forming a central panel recessed in an arc shape in cross section, the outer wall portion is held between the ring-shaped portion and the hold-down ring, and the center panel and the inner wall portion are separated from each other so that the ground contact portion separates from the nose portion of the ring-shaped portion. A method for forming a seamless can bottom portion, characterized in that the outer wall portion is relatively moved in the axial direction to narrow the lateral width of the ground contact portion of the annular protrusion. 2. The method for forming a seamless can bottom portion according to claim 1, wherein the lateral width of the ground contact portion of the annular protrusion is narrowed and at the same time the inner wall portion is raised substantially vertically. 3. A doming die is fixed, and a pressing body urged toward the doming die is provided in the ring-shaped portion, and relative movement of the outer wall portion in the axial direction is controlled by the doming die. The method for forming a seamless can bottom portion according to claim 1 or 2, which is carried out by raising the outer wall portion while being held by the pressing body in a fixed position. 4. A doming die surrounds a fixed core die and is biased towards the preform, enclosing the core die, and always having its uppermost portion at approximately the same level as the top of the core die and causing bottom die. It is equipped with a ring die that cooperates with the core die to form a common center panel molding surface when the point is reached, and a pressing body is provided in the ring-shaped portion, which is biased toward the doming die, and the outer wall The method for forming a seamless can bottom according to claim 1 or 2, wherein the axial relative movement of the portion is performed by raising the outer wall portion while the central panel is held by the ring die and the pressing body at a fixed position. 5. A doming die is fixed, and a pressing body is provided in the ring-shaped portion so that the fluid cylinder can press the doming die toward the doming die. The method for forming a seamless can bottom portion according to claim 1 or 2, wherein the outer wall portion is lifted while being held in a fixed position by being held by a doming die and a pressing body. 6. The doming die is biased toward the preform, the core punch is inserted through the inside of the ring punch having the ring-shaped portion, and the relative movement of the outer wall portion in the axial direction is controlled by the outer wall portion. 3. The method for forming a bottom portion of a seamless can according to claim 1, which is carried out by holding the central panel with a doming die and a core punch and lowering the central panel while holding the central panel. 7. The doming die is biased toward the preform, and a pressing body biased toward the doming die is attached to the lower end inside a ring punch having a ring-shaped portion. 3. The core punch is inserted, and the relative movement of the outer wall portion in the axial direction is performed by holding the outer wall portion in a fixed position and holding the central panel with the doming die and the core punch to lower the center panel. The method for forming the bottom portion of the seamless can described. 8. The doming die is biased toward the preform, and a pressing body that can be pressed toward the doming die by a fluid cylinder is provided in the ring-shaped portion, and the shaft of the outer wall portion is provided. The method for forming a seamless can bottom portion according to claim 1 or 2, wherein the relative movement in the direction is performed by holding the outer wall portion in a fixed position and holding the central panel with a doming die and a pressing body and lowering it.