GB2323805A - Container forming - Google Patents

Abstract

A method and apparatus for manufacturing a container from thin metal foil in which a blank is cut from a sheet of foil (70) by means of a punch ring (24); a female former (14) cooperates with a male former (42) to form the blank into a plain-sided, possibly cylindrical, form, the side or sides terminating in an edge (77), which is constrained, whilst the bottom (73) of the container form is pushed away from the edge; the edge area is then increasingly constrained so as to form a flanged edge which is finally folded (80). The resultant form produces a more robust container for a given wall thickness than the prior art and there are considerable savings in material costs.

Description

Container Forming The present invention relates to the manufacture of containers from thin metal sheeting commonly referred to as "foil.

Such containers are used in the food industry and there are two forms of these. A first form is known as a "smooth wall container" and is punched out of relatively thick foil about 85 ym to 200 ssm thick. The forming process produces a smooth flange around a smooth walled cup. The container is normally hermetically sealed by means of a disc bonded to the smooth flange. The seal must be efficient when the container is used for a dairy product. Depending on the nature of the product ie the pH level, it may be necessary to lacquer the foil to create å functional barrier. This lacquer layer also assists in the forming process. However, the cost of lacquered metal is 30-40k more gauge for gauge.

The second form of container produced by a prior process resulted in what was known as a "wrinklewall" container. This process is still in use. The wrinkles were formed during the drawing process. The wrinkles had the disadvantage of extending with the rims of the container making effective sealing at that point very difficult.

Thus the food industry was faced with either using an expensive "smooth wall container" which sealed well enough or else a cheap "wrinklewall" container which had poor sealing qualities.

An object of the invention is to provide apparatus and a manufacturing method to reduce the cost of containers whilst maintaining high sealability.

A method of manufacturing a container according to the invention comprises the steps of: (a) providing a sheet of metal foil, (b) cutting out a blank therefrom, (c) forming the blank into a plain sided possibly cylindrical form having a bottom extending to a side or sides terminating in an edge whilst retaining the possibility of an edge flange portion forming an initial form, (d) wiping the side(s) of the initial form to eliminate any edge formation so as to form a second form, (e) constraining by partially holding an edge area adjacent the edge whilst pressing the bottom away from the edge to form a third form, (f) increasing the constraint on the edge area so as to form a flanged edge and a fourth form, and (g) folding the edge of the resulting form to result in a final and fifth form.

The step of constraining the edge area (step (e)) whilst pressing the bottom away from the edge results in the gradual reduction in size across bottom of the second form (where this has an essentially cylindrical form the reduction in size is in the diametrical dimension). At the same time the control over holding the edge area under constraint ensures a consistency of material thickness without tearing. The end result in the final and fifth form has a wall thickness some 40% less than the prior art smooth wall containers and lacquering to assist the drawing process somewhat is not required. This results in considerable economies in material, whilst the edge constraint pressure during step (e) can be adjusted to provide a good smooth flange as in the fourth form. This ensures efficient product sealing. Then when the edge is folded in step (g) the excellent flange formation terminating in a suitable fold ensures a container found to be more robust than the prior art "Wrinklewall" container for a given container wall thickness. This allows processor and retailer handling to be less prone to product damage.

The resulting process and apparatus accordingly achieves about 50% reduction in material costs as compared with the old smooth wall process for comparative function.

Preferably folding the edge (step (g)) comprises the step known per se of rolling but this is smooth rolled and without wrinkling. This contributes to the strength across the flange.

In order to produce the best result in steps (d) and (e) the constraining pressure on the edge area is increased shortly before the end of the action of pressing the bottom away from the edge so that the flanged edge area is well flattened.

The above increased constraining pressure on the edge area is maintained for a short while so that at the end of the pressing action any wrinkles on the container sides are tightened and reduced in appearance.

According to a further aspect of the invention apparatus is provided for carrying out the method of the invention comprising cutting out means for cutting out a blank from a sheet of metal foil, forming means for forming the blank into a sided initial form, wiping means for wiping the sides of the initial form to form a second form, constraining means engageable on the edge area of the second form, pressing means arranged to press out the bottom of the second form to form a third form and folding means for folding over the edge of the form so far resulting to form a final form.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows apparatus according to the invention for forming a container as a vertical cross section in an open (left side) and fully closed (right side) position, Figure 2 is the same view as Figure 1 but with a foil strip about to be cut to produce a flat blank, Figure 3 shows the apparatus of Figure 1 with the blank formed to cup formation half of which is shown in Figure 3a, Figure 4 shows the apparatus of Figure 1 with the cup formation of Figure 3 now formed with a rimmed edge as in Figure 4a, Figure 5 shows the apparatus of Figure 1 with the cup formation of Figure 4 slightly stretched and the rimmed edge flattened as in Figure 5a, and Figure 6 shows the apparatus of Figure 1 with the edge of the cup formation of Figure 5 folded over into a roll and now fully formed as shown in Figure 6a.

In the sequence of Figures 1 to 6 there is shown a complete die assembly generally at 1 which is fitted into a press. The complete assembly comprises an upper assembly 2 and lower assembly 3 which co-operate to form a container from a strip of foil between the assemblies.

The upper assembly 2 comprises a top bolster 4 movable by means of a ram (not shown) in a vertical axis towards a bottom bolster 6 of the lower assembly 3. Most of the movable components of the die assembly are mounted to one or other of the two bolsters 4, 6.

At the top of the top bolster 4 is a cylinder 10 which acts as an air cushion or spring and in which a vertically movable top piston 12 is mounted. Top piston 12 has in turn mounted to it a female former 14 in the axial centre of which is a vertically movable knock-out ring 16. The knock-out ring 16 is actuated by its piston end 18 movable in cylinder 20.

Surrounding the female former 14 and mounted to the top bolster 4 is a punch ring 24.

The lower assembly 3 has a vertically movable piston rod 40 on which is mounted a male former 42.

As far as this description is concerned there are two important interfaces between the formers which are firstly upper and lower removable container bottoms forming faces 22 and 44 on the formers respectively. Secondly there are the upper and lower container side forming faces 23 and 45 on the formers respectively. Those are not the only co-operating faces which form the containers as we shall see.

Surrounding the male former is a static wiper ring 50 mounted on the bottom bolster and surrounding that a vertically movable draw ring 52 having an upper clamping surface 54 and an edge roll groove 56. Surrounding the draw ring 52 is a cutter block 58 having a cutting edge 59 which co-operates with cutting edge 25 of punch ring 24.

To the right side of the cutter block as seen in Figure 1 is a feed guide 60 for foil.

It will be appreciated that Figure 1 shows the die assembly in a fully open position on the left whilst on the right the die assembly has nearly completed its operation. The sequence of steps of the complete forming operation will now be described with reference to Figures 2 to 6 against which the Figures 3a to 6a show the shape of the container being formed step by step as it is formed. In this respect it should be understood that the forming of a container by the die assembly is a high speed continuous operation and that although different "forms" are shown these are not readily apparent during the operation of the press.

Operation In Figure 2 a foil strip 70 suitably 60 ym thick is fed into the die assembly between the upper and lower assembly. Top bolster 4 then descends bringing with it punch ring 24 which acts against cutting edge 59 to separate a blank (in this case a circular blank from the foil strip).

The punch ring 24 continues downward forcing an outer annulus of the blank down through the position showing in Figure 3 and down to point 30, so that the blank is now in initial form 72 of Figure 3a having a bottom 73 and a cylindrical, in this case, smooth drawn side 74. The male former 42 then closes on the female former 14. At this point the edge 77 and the adjacent area of form 76 is constrained but not held fixedly and the forming face 15 moves slightly away, that is, considerably less than lmm from the flange 75 and face 51.

This allows wrinkles to form in side 74' and on flange 75.

The lower edge 15 of the female former 14 continues to trap and constrain a part of the side of the initial form 72 against the top 51 of wiper ring 50. As former 42 ascends with the form 72 trapped it draws out the edge 77 into a flange 75 and thus into second form 76. By now the bottom forming faces 22 and 44 are both touching on the bottom 73 of form 76 as shown in Figure 4. Additional pressure to faces 15 and 51 is applied, causing additional constraint. Side 74' is dragged between the constraining forming surfaces to assume form 74" of a third form as shown at 78 in Figure 5a. The edge 77' of flange 75 is slightly reduced and the flange surface 79 firmly flattened by the previous increase in the holding pressure. Side 74" after this treatment is slightly lengthened by perhaps 3mm from side 74', reducing the wrinkles.

Finally the draw ring 52 rises to catch the edge 77' with its groove 56. This folds the edge over with a rolled form at 80 as shown in the fifth form of 81 in Figure 6a.

The assembly 2 now opens from assembly 3 so that the formers 14 and 42 open with the fully formed container held momentarily in former 14. Knock-out ring 16 then descends pushing out the container which is then removed by blowing for the process to be recommenced.

Claims (8)

1. A method of manufacturing a container comprising the steps of: (a) providing a sheet of metal foil, (b) cutting out a blank therefrom, (c) forming the blank into a plain sided possibly cylindrical form having a bottom extending to a side or sides terminating in an edge whilst retaining the possibility of an edge flange portion forming an initial form, (d) wiping the side(s) of the initial form to eliminate any edge formation so as to form a second form, (e) constraining by partially holding an edge area adjacent the edge whilst pressing the bottom away from the edge to form a third form, (f) increasing the constraint on the edge area so as to form a flanged edge and (g) folding the edge of the resulting form to result in a final form.

2. A method according to claim 1 wherein the step of folding the edge is such as to produce a rolled edge.

3. A method as claimed in Claim 1 or 2 wherein the constraint on the edge area adjacent to the edge is increased shortly before the end of the action of pressing the bottom away from the edge.

4. A method of manufacturing a container substantially as described with reference to the accompanying drawings.

5. Apparatus for manufacturing a container according to the method of Claim 1, comprising cutting out means for cutting out a blank from a sheet of metal foil, forming the means for forming the blank into a sided initial form, wiping means for wiping the sides of the initial form to form a second form, constraining means engageable on the edge area of the second form, comprising means arranged to press out the bottom of the second form to form a third form, and folding means for folding over the edge of the form so far resulting to form a final form.

6. Apparatus according to Claim 1 wherein the wiping means comprises an inner edge surface of a punch ring which forms a part of the cutting means, said wiping means also comprising a wiper ring.

7. Apparatus according to Claim 5 or 6 wherein the constraining means comprises at least a moveable draw ring surrounding the wiper ring.

8. Apparatus for carrying out the method of any one of Claims 1 to 4 substantially as described with reference to the accompanying drawings.