This invention relates to can bodies having a side wall closed at at least one end by a can end wall joined to the side wall by a double seam. More particularly, but not exclusively, this invention also relates to the behaviour of filled cans when shrink wrapped on a collater tray and stacked on pallets.

Filled cans are arranged as a group on a cardboard tray having side wall and the assembly of cans and tray is wrapped in a polymeric film to retain the cans on the tray. The wrapped assembly is then heated to shrink the polymeric film so that the cans and tray become a firm assembly that is amendable to mechanical handling and storage. It has been observed that, the tension in the polymeric film pulls the cans together so that the double seams of adjacent cans override. In this displaced condition some of the cans no longer stand flat on the collater tray and the overriding cans project above other cans with their double seams resting on the top of the double seam of adjacent cans. Typically, each collater tray supports twenty-four cans arranged in rows of four by six cans so that the weight in the collater tray is about 241bs. The filled trays are stacked on pallets for storage and transit, each pallet load weighing several thousand pounds (lbs) using the well known palletised packing system. When the pallets are stacked one upon another substantial top load is imposed on the cans on lower pallets so that projecting displaced cans are pushed downwards in between the adjacent cans. This downwards motion has been observed to cause collapse of the side wall of unevenly loaded cans. If the cans are of the kind having a double seam at both ends of the side wall, the lower double seams are also prone to override so on downward motion under top load, moving cans may also suffer collapse of their side wall as their lower double seam returns to rest on the collater tray.

Not only does the side wall damage or collapse spoil the appearance of the can but also the collapsed side wall of a can is much reduced in its ability to support a top load so that there is a risk of the whole stack of palletised cans becoming unstable.

One objective of this invention is to provide a shape of can body which will reduce the risk of the double seams of adjacent cans overriding to an interlocked position which resists return of a raised can to flat array on a surface.

French Patent No. 1395914 describes drums made from sheet metal of thickness 16G (about 1.38mm) to comprise a beaded side wall closed at one end by a lid and ring, or alternatively an end wall fixed to the top of the side wall by another double seam. The side wall of these drums is provided with a plurality of annular beads spaced along the height of the drum to permit use of 24G (0.5mm) metal. In Figs.4, 5 and 6 of this patent preferred bead cross sections are shown in the form of upper and lower surfaces extending from the side wall at an angle of about 45° to converge at an apex of arcuate cross sections which is preferably as sharp as possible. Figs.18 and 19 show reinforced rolling beads adjacent a double seam. In Fig.19 the rolling bead is of larger diameter than the double seam so their is a risk that adjacent drums will override on the rolling bead. In Fig.18 the cylindrical reinforced rolling bead is substantially flush with the double seam. Whilst this cylindrical rolling bead will reduce the risk of adjacent drums overriding the prolonged cylindrical length of contact gives risk to risk of any protective coating on the bead being scuffed to put the drum at risk of corrosion.

However, there are several additional constraints on the shape of a can body made from thin sheet metal, typically less than 0.24mm thick:-

(1) the cans must be able to roll on side rails in conveyers and cookers without damage to the print or label area of the side wall. Typically, can bodies having a double seam at both ends roll on the double seams, and deep drawn cans roll on a double seam at one end and a rolling bead adjacent their integral bottom end;

(2) the side wall shape preferably permits application of a paper label;

(3) for reasons of economy any side wall feature, designed to abate the overriding interlocks of double seams, must not add to the thickness of material used to make the cans. The side wall of can bodies are currently made from cold worked materials such as double reduced tinplates or chrome/chrome oxide coated steel (ECCS) for welded bodies and wall ironed tinplates or ECCS for deep drawn cans which may be as thin as 0.12mm.

(4) any shape provided to prevent over riding must leave access for rolls used to make a double seam and must not reduce the axial strength of the can because filled cans are stacked to great heights on pallets in warehouses.

Accordingly, this invention provides a can body comprising a tubular side wall terminating in an outwardly directed flange or body hook supported on a chuck wall margin of the side wall to permit engagement of the flange and margin with a peripheral cover hook and dependent chuck wall of a can end and formation of a double seam, characterised by an outwardly convex annular bead, adjacent the chuck wall margin of the side wall, which projects outwardly from the rest of the side wall to a periphery which is less than the outer periphery of the double seam when formed, and the distance from the bottom of the double seam to the location of the maximum periphery of the outwardly convex annular bead, as measured along a central axis of the side wall, is between 50% and 150% of the height of the double seam.

Preferably this distance is approximately equal to the height of the double seam margin of the side wall to permit engagement of the flange and margin with a peripheral cover hook and dependent chuck wall of a can end and formation of a double seam by seaming rolls.

The outwardly convex annular bead may be applied to the side wall of built up cans comprising a side wall having a side seam and a can end seamed one or both ends. Alternatively, the bead may be applied to the side wall of seamless cans drawn from a sheet metal blank.

Preferably the can bodies are cylindrical but the outwardly convex bead may usefully be applied to other shaped can bodies such as oval or rectilinear.

In a preferred form, the outwardly convex annular bead has a first portion flaring outwardly from the double seam and a second flaring portion extending inwardly to the rest of the side wall, said flaring portions being joined by a curved apex. Preferably, the radius of curvature of the apex is between 4 and 20 times the thickness of the side wall metal.

The angle of inclination of the first portion of the annular bead may be between 15° and 45° to the central axis of the side wall, an angle of about 30° being preferred. The distance which the outwardly convex annular bead projects from the side wall is between 50° and 90% of the distance which the double seam projects from the side wall.

Various embodiments will now be described by way of example and with reference to the accompanying drawings in which:-

Fig.l is a diagrammatic view of a stack of palletised cans;

Fig.2 is a perspective sketch of a shrink-wrapped group of cans on a collater tray;

Fig.3 is an end view of the shrink wrapped tray of

Fig.2;

Fig.4 is a fragmentary view of a conventional can collapsed by an excessive top load;

Fig.5 is a side view of a three piece can according to the invention;

Fig.6 is a fragmentary section of the top of the side wall of a can body according to the invention;

Fig.7 is a side view of a two piece can according to the invention; Fig.8 is an enlarged fragmentary side view of the double seam and an outwardly projecting bead; and

Fig.9 is a like view to Fig.8 showing fragments of adjacent cans and the function of the outwardly projecting bead. Fig.l shows diagrammatically a stack of palletised filled cans which in practice may be as tall as four pallets high. Each pallet load 1 of the stack comprises a pallet 2 on which are placed shrink wrapped assemblies 3 of cans. By way of example a can 73mm diameter by 115mm tall will contain about lib of food so that the weight of the pallet loads shown in Fig.l may be several thousand pounds so that the accumulated weight supported by cans in the bottom pallet of a stack is substantial. Fig.2 shows a shrink wrapped assembly 3 comprising twenty four cans "arranged in rows of four by six, and a cardboard collater tray 5 on which the can stand whilst confined by a side wall 6 of the tray. The tray and cans are wrapped in a polymeric film 7 which is heated to cause the film to shrink and firmly hold the cans in the tray to make an assembly which is firm enough to permit mechanical handling and subsequent transport to retail stores.

The tension in the polymeric film pulls the cans together and some cans in the assembly override as shown in Fig.3. -As shown the can denoted 4 is still standing on the tray 5 while the cans denoted 4A have risen so that

their double seams 8A rest on the double seams 8 of the cans 4 so that the top of che assembly 3 is no longer flat.

When the assemblies 3 are stacked on a pallet the displaced cans 4A start to receive a top load on their double seams 8A which is in turn imposed on the double seam 8 of the cans 4 so the side wall of the cans 4 is put in localised compression. When a second pallet load 1 is placed on top of a first pallet load the top loading is much increased so a risk of collapse of cans develops as the compressive load becomes sufficient to cause localised collapse of the cans at the bottom of the stack.

Fig.4 shows a conventional can body after collapse in a stack of palletised cans. As shown, the can is of a kind comprising a top double seam 8, a cylindrical side wall 9 made by welding adjacent edges of a rectangular blank, and a bottom double seam 8. The side wall 9 comprises an upper cylindrical portion 10 joined to a lower cylindrical portion 11 by a beaded portion 12. Comparing Fig.4 with Fig.5 which shows a first embodiment of the invention, it will be seen that the conventional can of Fig.4 has locally collapsed where top bead 13 joins the upper cylindrical portion 10 with loss of height of the can 4. Sometimes collapse occurs at the junction of the lowest bead 14 but seldom does collapse occur at both locations (13, 14).

In Fig.5 the can 4 is similar to the can of Fig.4 except that an outwardly convex annular bead 15 is provided adjacent the double seams to assist an overriding can to move back to a position level with the rest of the cans on a collater tray before a destructive top load develops during stacking. As shown in Fig.5, the convex annular bead 15 has an external diameter less than the external diameter of the double seams 8 so that the can is able to roll on its double seams without risk of scuffing the side wall material.

Fig.6 shows a fragment of the side wall 9 of the can body and a can end 16 at a time just before forming double seam. The can end 16 comprises a peripheral cover hook or flange 17 from the interior of which depends and inwardly flaring chuck wall 18 which is joined to the central panel 19 of the can end by an annular channel portion 20.

The cylindrical side wall 9 of the can body terminates in an outwardly directed flange 21 (sometimes called a body hook) joined to the rest of the side wall by an annular margin 22 of side wall material which surrounds the chuck wall 18 of the can end. Hereinafter this annular margin 22 is called "the chuck wall margin". The outwardly convex annular bead 15 can be seen to have a maximum diameter less than the maximum diameter of the flange 21.

Fig.7 shows a second embodiment of the invention in the form of a can end fixed to the body by a double seam 8. Before closing and double seaming the top end of the can body 22 is as shown in Fig.6. After forming, the double seam is of a height to reach the top of the convex annular bead 15, and has an external diameter a little greater than the external diameter of the convex annular bead 15. A convex rolling bead 23 is provided at the bottom of the lower cylindrical side wall portion 11, near the integral end wall of this can which is deep drawn from a sheet metal blank. Therefore the rolling bead 23 and seam 8 enable the can 22 to roll in a straight line along paralled guide rail during conveying and through "reel and spiral" cookers, without the side wall material being contacted so risk of damaging protective coatings is avoided.

Fig.8 shows a fragment of can end 16, double seam 8, and side wall 9 with the outwardly convex annular bead 15. In Fig. 8, the features discussed are denoted: SD = maximum diameter of double seam

CD = outside diameter of its cylindrical portion side wall of the can body BD = maximum diameter of the convex annular bead 15 PR = radius of the peak of the bead 15 SH = height of double seam

BH = distance from base of double seam 8 to the bead peak 25 BT = thickness of material of the can side wall 9. The height BH is approximately equal to the height SH of the double seam in order to to prevent overriding of double seams but may be between 50% and 150% of the height of the double seam.

The internal radius PR of the peak 25 of the annular bead 15 is between 4 and 20 times the thickness BT of the side wall material. For example, a typical can 73mm diameter by 108.5mm tall is usually made from sheet metal such as tinplate or ECCS 0.14mm thick so the peak radius PR for this can is about 1.0mm.

The peak radius PR of the annular bead must not be made so small as to damage the internal surface of the side wall material during roll forming, or reduce the axial strength of the beaded side wall.

The peak radius PR must not be too large because the bead would become located too far from the double seam to prevent seams overriding, ie. it could create a groove in which adjacent seams could lodge.

The angle x° of the sloping portion of the annular bead, which extends towards the double seam 8 is between 15°and 45° preferably about 30°, so that the axial strength of the side wall 9 is not reduced beyond any reduction imparted by hooped body beads if present. An angle of about 30° gives access for the traction wheel of popular can openers so that the can ends may be opened without recourse to special tools. Fig.9 shows a pair of cans 4,41 in overlapping position that arises because cooperation of their

respective outwardly convex annular beads 15,151 have prevented development of an interlocked overriding position of their double seams 8, 81. A tolerable top load on the risen can 4 will urge its side wall 9 and can end 16 past the side wall 91 and seam 81 of the can 41, any fictional sliding being between the surfaces of the double seams 8, 81 which are able to cope.

Hitherto, the thickness of metal used for the beaded side wall of can bodies has been determined by study of two primary factors:-

(a) the axial load strength requirement arising from anticipated load arising from stacked pallet loads; and

(b) the resistance to panelling which may arise during thermal processing and cooling of cans. Most containers specifications are at the lower limits of both axial strength and resistance to panelling. However, with the risk of axial collapse reduced by provision of the outwardly convex annular bead adjacent the double seam, further reduction of metal thickness in the side wall of cans may be made available.