Body-necking a wall-ironed can

Details Body-necking a wall-ironed can Body-necking a wall-ironed can

1999-09-15

2001-07-03

Larson, Lowell A. (Department: 3725)

Metal deforming

Process

Deforming sheet metal

C413S069000

Reexamination Certificate

active

06253597

ABSTRACT:

1. Field of the Invention
The invention relates to a method for manufacturing a metal, body-necked can with an ironed wall, for example one intended for being provided on one open side with an easily opening lid in order thereby to form a beverage can, comprising the stages of reducing the diameter of the can with the ironed wall by necking the wall up a considerable part of the height of the can, to be referred to as body-necking, and applying a neck rim by necking the top rim of the can.
BACKGROUND OF THE INVENTION
Such a method is known. EP 0 733 415 A1 for example discloses the manufacturing of a beverage can comprising a body with zones having different diameters by drawing a cup from a blank, reducing the diameter thereof by a restraining operation and thereafter locally increasing the diameter by an expanding operation.
According to such a method the diameter of the rudimentary can body is firstly reduced. Then an expanding process is used to give the can a different shape e.g. in a shaping mould. In order to complete the beverage can subsequently a neck rim is formed at the top of the can to which the lid can be fitted.
JP 61-176433 to Ouchi discloses a method of shaping a can body made by impact extrusion or deep-draw molding. Ouchi narrows the shoulder part and the base part of the soft-walled can in two operations, after necking and curling the rim, in order to suppress deformation of these parts during later shaping. After that, the part of the can of original diameter is shaped by pressing the wall in and against shaped dies. Ouchi is not body necking.
In the known method, to (body-) neck a can with an ironed wall, the can is moved into a profiled die so that the profile of the die is transferred to the can. However, if a considerable part of the height of the body, or a majority of the height of the body, or the entire body is body-necked to a smaller diameter, there is a chance of wrinkling. In order to suppress or prevent such wrinkling the can must be supported internally by a knock-out in the neck zone during body-necking. Before expanding, the top rim must first be necked into a neck rim. This necking causes damage to the in-can paint and wrinkling in the neck part close to the top rim of the can. The wrinkling is connected and associated with the presence of a large gap during body-necking in the area of the body because the body is adapted to the thicker rim of the can. This gap is taken to be the gap located between the knock-out and the die. During necking the can rim fits precisely in that gap. However, the can rim is thicker than the can wall so that it has sufficient deforming reserve to be necked. However, the knock-out diameter is adapted to that thicker can rim. If the knock-out diameter were adapted to the can wall thickness, then the gap would be too small for the can rim. Therefore, adapting the knock-out diameter to the can rim thickness means that the gap is too large for the can wall, so that the chance of the can wall wrinkling increases (see FIG.
1
).
The skilled person confronted with the problem of how to shape a metal can with an ironed wall faces a number of problems.
Common knowledge tells one skilled in the art that the ironed wall:
has a flow stress of at least 700 MPa (see “The Book of Steel”, 1996, Lavoisier Publishing Inc., Secaucus, N.J., Chapter 35, section 2; and also EP 0733415, page 2, lines 47-51), which makes it hard to plastically deform an ironed wall;
is thin, generally less than 0.14 mm (see “The Book of Steel”, 1996, Lavoisier Publishing Inc., Secaucus, N.J., Chapter 35, section 2);
is expandable by at most about 1% (see EP 0733415, page 2, lines 47-51), or the ironed wall would rupture.
Common knowledge further tells one skilled in the art that, on the contrary, an extruded wall or a deep-drawn molded wall:
has a low flow stress of typically 250 MPa (see “The Book of Steel”, 1996, Lavoisier Publishing Inc., Secaucus, N.J., Chapter 35, section 2; and also see EP 0733415, page 2, lines 12-19);
is always thicker than an ironed wall because an ironed wall is obtained by ironing an extruded wall or a deep-drawn molded wall (see “The Book of Steel”, 1996, Lavoisier Publishing Inc., Secaucus, N.J., Chapter 35, section 2; and also see “The Making, Shaping and Treating of Steel”, Unites States Steel, 10th edition, page 1136, lines 27-33);
is consequently expandable by up to 20% (see EP 0733415, page 2, lines 12-19).
EP 0733415 discloses that in order to expand an ironed wall (see EP 0733415, page 2, line 57 - page 3, line 1) a restraining operation must be performed at least to the section of the can wall that is subsequently to be shaped by an expanding operation (EP 0733415, page 3, lines 2-13).
However, EP 0733415 presents a new problem, because body-necking an ironed wall tends to cause wrinkling as a result of the high pressure that needs to be applied to the wall to overcome the high flow stress in order to plastically deform the ironed wall, in combination with the fact that the wall is very thin.
JP 61-176433 to Ouchi explicitly discloses operations for an extruded wall or a deep-drawn molded wall (See JP ′433, page 4, lines 6-9 of top right hand column). Ouchi also states:
In the method of manufacturing of the present invention, drawing (D
1
), (D
2
) is performed on the base part (
8
) and shoulder part (
5
) prior to pressing (E) being performed. For this reason only the body part, which is of comparatively low rigidity and protrudes outwards compare to the other sections, is pressure-deformed.
(see JP ′433, page 3, lines 7-11).
Ouchi (JP ′433) discloses that an unrestrained section is suitable for further shaping because it is of comparatively low rigidity. Yet for ironed walls it is exactly opposite, in that a restrained section is suitable for further shaping as disclosed in EP ′415, while an unrestrained wall is not. Hence, it is an unambiguous fact that Ouchi does not disclose ironed walls, neither implicitly nor explicitly.
SUMMARY OF THE INVENTION
Tests have shown that wrinkling can be prevented and that a simpler manufacturing method is possible if, and the invention is based essentially on this, prior to being body-necked, the can is first necked.
The neck applied for body-necking gives the can body rigidity and holds it under tension so that wrinkling is prevented during body-necking. The method in accordance with the invention makes it possible to body-neck without a knock-out. However, because of the axial loading of the can during body-necking, the body must be supported during body-necking by applying an internal overpressure. Furthermore, during body-necking a centering pin is used with a diameter equal to the internal neck diameter of the can.
In practice it is found in accordance with the invention that it is possible to form from a &thgr; 66 mm body a can with a circumference of less than &thgr; 63.5 mm or even &thgr; 62 mm with a
202
neck. A
202
neck is taken to be a neck with a diameter (including the flange with which the lid is applied) of 2{fraction (2/16)} inch (=53.98 mm). The internal diameter of the can neck is then approximately 52.3 mm.
The invention is also embodied in a method for manufacturing a shaped can by inflating a can which is obtained by applying the method in accordance with the present invention.
After pressure loads have been introduced in the material by body-necking, the material is better able to stretch and the can is able to be formed to a considerable extent, for example by inflating.
The method in accordance with the invention has been found highly suitable for cans manufactured from a packaging steel suited to wall-ironing, and manufactured from an aluminum alloy suited to wall-ironing.


REFERENCES:
patent: 3029507 (1962-04-01), Gaggini
patent: 3610018 (1971-10-01), Swanson et al.
patent: 3771476 (1973-11-01), Heinle
patent: 3786957 (1974-01-01), Hilgenbrink
patent: 3812696 (1974-05-01), Kneusel et al.
patent: 4774839 (1988-10-01), Caleffi et al.
patent: 5275033 (1994-01-01), Riviere
patent: 5355710 (1994-10-01), Diekhoff
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