WALL-IRONED CANS

Abstract: The can has a base portion (56) and a rim portion (55) within a relatively thin ironed cylindrical wall (53) therebetween. The cylindrical wall has axially extending thickened parts defining ribs (62) esquispaced around the wall and extending from the rim portion to the base portion. The projection of the ribs is towards the interior of the can and the ribs are defined in the wall-ironing operation by flats (60) or grooves formed in the outer surface of a punch (50).

Description: WALL-IRONED CANS This invention relates to wall-ironed cans. It is now common practice to make a can from a disc of sheet metal. The disc is formed into a shallow container, the wall of which is then ironed to extend the wall whilst reducing 5 its thickness. This operation is described, for example, in European Patent Specification No. 17434. Forming and ironing operations are usually carried out in a single operation by a punch acting within forming and ironing dies. It is also common practice to shape the punch, so that slight thickening 10of the rim end part of the wall is produced. This thickened rim part is flanged and a lid * is sealed to it. The resultant can has relatively thickened base and rim parts with a thin cylindrical wall between. During flanging, filling and stacking the can is liable to 15compressive forces acting axially of the can. This may produce buckling of the thin cylindrical wall. The problem can, of course, be avoided by thickening of the wall, but this is very wasteful of material and it is important to keep the wall as thin as possible to reduce costs. 0 I is known to provide circumferential ribs spaced along the cylindrical wall. There was a proposal described in U.S. Patent Specification No. 3610018 to provide the circumferential ribs during the ironing operation. The proposal is impractical, since the ribs are formed by grooves in the punch 5making it difficult to get the can off the punch. A special stripping procedure is required mechanically to force out the wall of the can. Such circumferential ribs, when provided, are usually formed in a separate operation for the purpose of resisting radial collapse of the can, due to either increased oor decreased pressure in the can caused by the contents or by treatment, such as cooking of the contents. These circumferential ribs may induce axial collapse rather than resist it and, for this reason, it has also been proposed to provide discontinuous circumferential ribs, so that portions of the can wall between the ribs are not formed. Even with this OMPI _ arrangement, there is a tendency for axial collapse to occur between the circumferential ribs and the base of the can. The present invention provides a wall-ironed can having • base and rim portions and an intermediate wall therebetween which is provided with thickened portions defining- axial ribs extending towards the rim portion from adjacent the base portion. Preferably at least three such ribs are provided substantially equally spaced around the can. Also preferably the base and rim portions are thicker than 0the portions of the intermediate wall between the ribs. The invention also resides in a method of manufacturing a can utilising a wall-ironing operation in which a punch is moved through an ironing die to form the can wall, wherein the punch has axial recessed parts in its circumferential surface, 5so that thickened portions are defined in the can wall extending axially from adjacent the base of the can. The invention also resides in apparatus for manufacturing a can by wall—ironing, comprising an ironing die and a punch movable through the die, wherein the punch has axial recessed parts for forming thickened portions in the ironed wall of the can, extending axially from adjacent the base portion of the can. The punch may have a relatively smaller diameter portion for forming a thickened rim portion of the can. The axial thickened portions, or ribs, considerably strengthen the can to reduce the risk of buckling under co pressive forces and, surprisingly, no more material is required to produce the ribs. The rim end of the ironed wall is always uneven and slightly overlong and has to be trimmed. It has been found that the extra material for the ribs is obtained from the part to be trimmed. Reference is now made to the accompanying drawings, wherein:- Figure 1 is a sectional diagrammatic view of wall-ironing apparatus for making a can; Figure 2 is a diagrammatic perspective view of a punch of the apparatus, modified according to the invention and showing thereon, in section, a can; Figure 3 is a detail diagrammatic sectional view on the line 3—3 of Figure 2; and Figure 4 is a detail diagrammatic sectional view on the line 4—4 of Figure 2. 5 Referring to Figure 1, a shallow walled blank 15 is forced by a punch 50 through a forming die 21 held in a ring 26 to reduce the area of the base of the blank and increase the length of the wall. The blank is separately formed from a disc by an earlier conventional operation. The punch then forces 10 the reformed blank through ironing dies 22, 23 held in rings 30, 33 and stamps the bottom of * the blank on a die 24 formed with circular ridges 35. The ironing dies effect a wall-ironing operation to lengthen the wall whilst reducing its thickness. The free end of the ironed wall is then trimmed. 15 The operation may be as described in European Patent Specification No. 17434 which is incorporated herein by reference. Referring to Figure 2, the punch is formed with slightly tapering portions 50, 51 with a cylindrical main portion 52 20 therebetween. The tapering portions define thickened rim 55 and base 56 portions respectively on a can 54, formed and ironed on the punch, relative to the thickness of the main wall 53 of the can between those portions. The thicknesses illustrated are, of necessity, greatly exaggerated. The main 25 portion 52 of the punch has axial recessed parts 60 equally spaced circumferentially and extending between the portions 50, 51. These recessed parts are defined by flats in this particular example, but may be defined by concave surfaces. The formation of a flat 60 is illustrated in Figure 3 where the 30 dotted line 61 shows an imaginary continuation of the main cylindrical outer surface of the punch. The flat may be 2 to 4 __ mm in width and effectively defines a recessed part which is about 0.02 to 0.04 mm in maximum depth, i.e. the maximum radial distance between the imaginary line 61 and the flat 60. 35 As a result of providing the flats 60, the can wall is provided with internal ribs 62 extending axially from the rim portion 55 to the base portion 56. These ribs (Figure 4) are OMPI defined by thickened portions of the can wall, the thickening being complementary in shape to the flats which formed them. It is envisaged that at least three and up to eight ribs 62 may be provided. The result is a can having reinforced rim and base portions with the rim supported by the ribs 62, which reduce the risk of buckling of the can under compressive forces. If desired, the intermediate wall 52 may then be subjected to a separate forming operation to form circumferential ribs, or beads, in the axially central region of the wall, for resisting radial collapse of the wall either inwardly or outwardly. This operation is not essential for all purposes and is commonplace in the art and has, therefore, not been described or illustrated in this specification. It is not necessary for the axial ribs to extend the full length from the base portion to the rim portion. They may, for example, extend from the base portion to adjacent the first of the circumferential ribs, where these are provided. It is also possible to provide axial ribs of different lengths and/or widths.

Claims: CLAIMS 1. A wall-ironed can having base and rim portions and an intermediate wall therebetween which is provided with thickened ) portions defining axial ribs extending towards the rim portion from adjacent the base portion. 5 2. A wall-ironed can according to Claim 1, wherein at least three ribs are provided, substantially equally spaced around the can. • 103. A wall-ironed can according to Claim 1 or 2 in which the base and rim portions are thicker than the portions of the intermediate wall between the ribs. 4. A wall-ironed can according to Claim 1, 2 or 3, in which 15 each rib is 2 to 4 mm. in width and 0.02 to 0.04 mm. in depth. 5. A method of manufacturing a can utilising a wall-ironing operation in which a punch is moved through an ironing die to form the can wall, wherein the punch has axial recessed parts 20 in its circumferential surface, so that thickened portions are defined in the can wall extending axially from adjacent the base portion of the can. 6. Apparatus for manufacturing a can by wall-ironing, 25 comprising an ironing die and a punch movable through the die, wherein the punch has axial recessed parts in its circumferential surface for forming thickened portions in the . ironed wall of the can extending axially from adjacent the base portion of the can. ~b 30 7. Apparatus according to Claim 6, wherein the punch has a tapered portion of the circumferential surface for defining a rim part of " a can which is thicker than the adjacent wall between the ribs. 35 OMPI 8. Apparatus according to Claim 6 or 7, in which each recessed part has a width of 2 to 4 mm. and a depth of 0.02 to 0.04 mm. 9. Apparatus according to Claim 6, 7 or 8, in which each recessed part is defined by a flat area of the circumferential surface of the punch. ^XlREA OMPI

Inventors: PRICE FRANK, PRICE, FRANK
Applicants: MARDON ILLINGWORTH, MARDON ILLINGWORTH LIMITED
Application year: 1982
Main classification: B21D22
IPC codes: B21D22, B65D1