METHOD OF MAKING A CAN HAVING A RECESSED BASE

Abstract: A method of making a can having a recessed base (12) and, in particular, to a method of forming a recessed base (12) in can bodies of the type which include a side wall (14) having flutes or grooves (16) defined therein. A first forming step creates a preform having a side wall with at least one axially extending rib formed therein and a base which is coextensive with the side wall and intersects the side wall at a rim. This first forming step is performed so that at least a portion of the base is recessed by a predetermined depth with respect to the rim. The method further includes a second step which comprises a further drawing operation to form a can body having a recessed base. It is important that the predetermined depth be sufficient to prevent any of the axially extending ribs from being drawn into the recessed base.

Description: METHOD OF MAKING A CAN HAVING A RECESSED BASE This invention relates to a can having a recessed base and, in particular, to a method of forming a recessed base in can bodies of the type which include a side wall having flutes or grooves defined therein. One method for making such can bodies uses the draw-redraw process that is commonly used for making two piece can bodies . Features such as ribs and flutes in the side walls of can bodies have long been known, and have been used for several reasons. One reason is to give an interesting appearance to the can body which may promote a brand image, as is discussed in US-5 , 938, 389. Longitudinal ribs and panels have also been used to impart additional rigidity to the side wall against loads applied to the top of the can body, such as arise during double seaming of a can end to close the body, or during stacking of filled cans. This is more fully discussed in US-5, 699, 932. The process of making can bodies using the draw- redraw forming technique has been in commercial use for decades. This process is accomplished by performing a first draw to create a cup having a large diameter and then performing a second draw using the preformed cup so that a punch is moved relative to and into engagement with a redrawing die. An annular cup-holding member, known as a "blank-holder", is arranged within the preliminarily drawn cup, and a base face of the preliminarily drawn cup is held by the blank holder and the flat face portion of the redrawing die. At the redrawing step, the blank holder is moved with the redrawing die. In this structure, when the punch and the die move relative to each other, the preformed cup undergoes a further draw process to form a deep-drawn cup. The deep-drawn cup has a small diameter defined by the curvature of a corner portion of the redrawing die. During deep-drawing, the side wall of the preliminarily drawn cup is elongated and the thickness of the side wall is reduced. The holding member and the flat face portion of the redrawing die act as the blank holding face to a portion of the cup on which influences of the plastic flow are imposed. Companies that package food products and other articles in two piece cans often prefer a base configuration which is recessed (also referred to in the industry, at least in the USA, as a "bump-up bottom"). A recessed base is characterised as having a downwardly facing annular projection or "stand bead" in the outer circumferential area at which it is coextensive with the container side wall. Recessed bases may also have similar, concentric annular projections that are positioned in the interior of the container base, radially inward from the major projection. The inventors have for some time been attempting to create a viable draw-redraw manufacturing process for two piece cans having a recessed base and axial ribs in the side wall, but have experienced the problem that the axial ribs tend to be drawn into the major projection of the recessed base. For aesthetic and other reasons, this is unacceptable. A need exists for an improved manufacturing process for two piece cans of the type having a recessed base and axial side wall ribs which ensures ample material in the base area of the can body preform so as to prevent the side wall ribs from being drawn into the recessed area of the base. It is, accordingly, an object of the invention to provide an improved manufacturing process for two piece cans of the type having a recessed base and axial side wall ribs that ensures ample material in the base area of the can body preform so as to prevent the side wall ribs from being drawn into the recessed area. According to the present invention, there is provided a method of making a can body having at least one axially extending rib formed therein, the method comprising: (a) performing a first drawing operation to create a cup having a side wall with at least one axially extending rib formed therein and a base which is coextensive with the side wall and intersects the side wall at a rim, step (a) being performed so that at least a portion of said base is recessed by a predetermined depth with respect to said rim; and (b) performing a second drawing operation on said cup to form a can body having a recessed base, and wherein said predetermined depth is sufficient to prevent any of the axially extending ribs from being drawn into the recessed base during the forming operation. According to a further aspect of the invention, there is provided a method of making a can body having at least one axially extending rib formed therein, the method comprising: (a) providing a cup having a side wall and a base that is coextensive with the side wall and intersects the side wall at a rim, step (a) being performed so that at least a portion of said base is recessed by a predetermined depth with respect to said rim; and (b) performing a forming operation on the cup to form a can body having at least one axial rib defined in its side wall and having a recessed base, and wherein the predetermined depth is sufficient so as to prevent said axially extending rib from being drawn into the recessed base during the forming operation. In a preferred embodiment, the predetermined depth of the recessed portion formed in step (a) is within a range of about 0.762 mm (0.03 inches) to about 7.62 mm (0.30 inches), and ideally the predetermined depth may be within a range of about 1.524 mm (0.06 inches) to about 6.35 mm (0.25 inches). The invention is now described, by way of example only, with reference to the drawings, in which: FIGURE 1 is a first perspective view depicting a first step in a method according to a preferred embodiment of the invention; FIGURE 2 is a second perspective view depicting a second step in the method that is performed according to the preferred embodiment of the invention; and FIGURE 3 is a fragmentary diagrammatic view depicting a portion of an article that is illustrated in FIGURE 1. Referring in particular to FIGURE 1, a method according to a preferred embodiment of the invention includes a step of providing a preform 10 that has a base 12 and a side wall 14. As may be seen in FIGURE 1, preform 10 is configured so that side wall 14 has a plurality of axially extending ribs 16 defined therein. For purposes of this document, the term "ribs" should be construed as broadly encompassing all forms of axially extending structure on a container body, cup or preform that may deviate from the standard cylindrical shape of the side wall . As is shown in FIGURE 1, preform 10 is constructed so that side wall 14 is coextensive with base 12 and intersects base 12 at a circular rim 18 that represents the apex ("basemost" dimensional extent) of the preform 10. In the preferred embodiment, base 12 includes a flat portion 20 that is substantially circular in shape when viewed from beneath the preform 10, as shown in FIGURE 1. Flat portion 20 is, as the name implies, substantially flat or residing substantially within a plane. As may perhaps best be seen in FIGURE 3 , base 12 further includes a sloped portion 22 that is coextensive with and joins the flat portion 20 of base 12 to the rim 18. According to one particularly advantageous feature of the invention, the flat portion 20 of base 12 is recessed with respect to the rim 18 by a predetermined distance D that is sufficient to ensure that enough material is present in this general area of the preform 10 so that when the preform 10 is processed in a later forming step into a completed can body of the type having a recessed or "bump-up" base configuration, as shown in FIGURE 2, the axial ribs 16 will not be drawn into the rim area 38 of the container body. FIGURE 2 depicts the completed container body 30 for a two piece can, which includes a recessed base 32, a side wall 34 having a plurality of axially extending ribs 36 formed therein and the rim area 38. The recessed base 32 includes, as is typical, a major projection 40 in the rim area 38 and a number of interior additional annular projections 42. In the preferred embodiment of the invention, the predetermined depth D of the recessed portion is within a range of about 0.762 mm (0.03 inches) to about 7.62 mm (0.30 inches) . More preferably, depth D is within a range of about 1.524 mm (0.06 inches) to about 6.35 mm (0.25 inches) . In the preferred embodiment of the invention, the preform 10 depicted in FIGURE 1 is formed from a standard cup in a first redraw operation, and the completed container body 30 shown in FIGURE 2 is formed from the preform 10 in a second redraw operation. Alternatively, however, the initial cup itself may also be formed so as to have a recessed base, so that the formation of the recessed base is not necessary in the first redraw operation.

Claims: CLAIMS ; 1. A method of making a can body having at least one axially extending rib formed therein, the method comprising: (a) performing a first drawing operation to create a cup having a side wall with at least one axially extending rib formed therein and a base which is coextensive with the side wall and intersects the side wall at a rim, step (a) being performed so that at least a portion of said base is recessed by a predetermined depth with respect to said rim; and (b) performing a second drawing operation on said cup to form a can body having a recessed base, and wherein said predetermined depth is sufficient to prevent any of the axially extending ribs from being drawn into the recessed base during the forming operation. 2. A method of making a can body having at least one axially extending rib formed therein, the method comprising: (a) providing a cup having a side wall and a base that is coextensive with the side wall and intersects the side wall at a rim, step (a) being performed so that at least a portion of said base is recessed by a predetermined depth with respect to said rim; and (b) performing a forming operation on the cup to form a can body having at least one axial rib defined in its side wall and having a recessed base, and wherein the predetermined depth is sufficient so as to prevent said axially extending rib from being drawn into the recessed base during the forming operation. 3. A method according to claim 1 or claim 2, wherein the rim formed in step (a) is substantially circular. 4. A method according to any one of claims 1 to 3 , wherein the recessed portion of the base formed in step (a) is substantially flat. 5. A method according to any one of claims 1 to 4 , wherein the recessed portion of the base formed in step (a) is substantially circular. 6. A method according to any one of claims 1 to 5 , wherein the predetermined depth of the recessed portion formed in step (a) is within a range of about 0.762 mm (0.03 inches) to about 7.62 mm (0.30 inches). 7. A method according to claim 6, wherein the predetermined depth is within a range of about 1.524 mm (0.06 inches) to about 6.35 mm (0.25 inches).

Inventors: KIRK WILLIAM, KIRK, WILLIAM
Applicants: CROWN CORK & SEAL TECH CORP, METAL BOX PLC, CARNAUDMETALBOX PLC, CROWN CORK & SEAL TECHNOLOGIES CORPORATION
Application year: 2001
Main classification: B21D51
IPC codes: B21D22