GB2259075A - Inwardly deforming end wall of filled can - Google Patents

Abstract

A method of adjusting pressure inside a filled and lidded can body 3 having an end wall 2 comprising a centre panel 10 surrounded by a plurality of outwardly convex concentric beads 11 each of which is joined to the next by an outwardly concave annulus, by applying pressure to the end wall 2 to displace the centre panel into the can body while the contents are still warm to reduce the internal volume of the can body by no more than 4 %, so increasing pressure within the can body to ensure that the pressure in the can at ambient temperature is between -1.5 p.s.i. and +1.5 p.s.i. The can body has a tubular side wall having a cylindrical portion 5, 7 at each end and a plurality of longitudinally extending flexible panels (6, Figure 1 and 81, Figure 9) extending between the cylindrical portions. The can body may be drawn from a blank or built up from a tubular side wall and a can end attached to each end of the side wall by a double seam. Pressure may be applied by a punch to a first bead 11 a or second bead 11c against a support plate which may be profiled (27, Figure 8). Deformation of the end wall can take place with or without reheating of the can contents following lid closing. <IMAGE>

Description

"CONTAINERS" This invention relates to thermal processing of lidded containers such as cans, and control of the pressure inside the cans after cooling.

British Patent 1235060 (J J Carnaud) describes and claims a process for sterilising a can having at least one deformable wall element, the said process comprising filling the can with a foodstuff, hermetically sealing the can, heating the can for a predetermined period to a predetermined temperature, cooling the can, and while cooling the can, reducing its internal volume by applying an external force to the can. The deformable wall element described is a can end having a plurality of concentric annular panels surrounding a central panel. The can end Is hermetically attached to the can body by a double seam.

The can body may have a bottom wall similar to the can end or top wall attached by a double seam to the side wall.

Alternatively the can body may be a deep drawn body so that the side wall is integral with a bottom walls, but the shape of the bottom walls are not described.

US patent 4 836 398 (LEFTAULT/ALCOA) describes a bottom end wall for a thin-walled container which after filling, closing, and thermal processing, is deformed to reduce the volume of the can. The bottom wall comprises a central panel, a substantially vertical wall upstanding from the periphery of the central panel and a narrow rim extending radially outwards from the top of the vertical wall to connect with the side wall of the can body. After thermal processing the centre panel is pushed through the rim into the can body so that, after deformation of this bottom end wall the deformed can body stands on the rim portion. A disadvantage of this arrangement of the can bottom is that the can is shortened in height by the deformation process.

British patent application published No 2237550A describes a can body drawn from sheet metal and wall ironed to comprise a bottom wall having a centre panel surrounded by a plurality of concentric annular beads, the outermost bead being deeper than the other beads, and a side wall thinner than the bottom wall and shaped to include upper and lower cylindrical portions joined by a plurality of longitudinal flexible panels each joined to the next by the outwardly convex rib. The purpose of the longitudinal flexible panels is to increase the side wall's ability to accommodate pressure changes inside the can body when filled with a product, lidded, and heated and finally cooled. A benefit of these cans having side wall panels is that the side wall may be made from thinner metal.

A particular problem arising with these cans is that, if the product is hot when filled, a substantial partial vacuum develops when the can is cooled so that the flexible panels may collapse to an undesirable shape which is discussed in the specification to which the reader is directed for further discussion. As this can depends on the shape of the sidewall for abuse resistance, it is important to maintain the original shape. A further problem is that the machines used to apply the labels to cans cannot cope with collapsed side walls.

This invention provides a method of filling, closing and correcting the shape of a can having a bottom wall, a side wall substantially thinner than the bottom wall, and a lid by the steps of (a) providing a can body having a bottom wall comprising a centre panel surrounded by at least one annular bead and a channel portion which connects the bottom wall to the side wall which comprises a lower cylindrical portion adjacent the bottom wall, an upper cylindrical portion having an outwardly directed flange to define the mouth of the body and a plurality of longitudinal panels, preferably between 12 and 24 panels, each joined to the next by a rib to join the upper and lower cylindrical portions, said side wall being between 0.0030" and 0.0045" thick when made of ferrous sheet metal or between 0.004" and 0.006" thick when made from an aluminium based sheet metal; (b) filling the can body with a product at a temperature between 300C and 950C to leave a headspace below the flange; (c) attaching a lid to the flange of the can body; and (d) applying external pressure to the bottom wall against support at the lid, before the can contents have cooled, to deform the bottom wall into the body to reduce the internal volume of the body by no more than 4% so increasing the pressure within the lidded body to a pressure sufficient to ensure that the pressure in the filled can at ambient temperature is between -1.Spsi and +1.5ski.

The benefits arising from this invention are (i) the side wall of the body may be thinner than for cylindrical side walls; (ii) that this method of processing maintains the can height so that conveyors do not have to be altered; (iii) the side wall is reliably returned to substantially its original geometrical shape; the panels will be almost flat if the can has been subjected to thermal processing so that wall strength is maintained but not so if the can was only hot filled; (-iv) unsightly collapsed cans are avoided; and preferably (v) the cooled can bodies are of a shape acceptable to labelling machines.

In one embodiment the can body has a side wall integral with the end wall having been drawn from a sheet metal blank. In an alternative embodiment the can has both lid and end wall attached to the side wall by means of a double seam, in which case the side wall will usually include a side seam which may be a welded seam or alternatively a lock seam which may be soldered.

In a preferred embodiment of the drawn can the end wall of the body has a centre panel, a first outwardly convex bead surrounding the centre panel, a second outwardly convex bead joined to said first convex bead by an outwardly concave bead, and an outwardly convex stand bead connected to said second convex bead by an inner wall, and an outer portion which blends into the side wall.

In one embodiment of the method the can is held between a support plate and a punch which is applied to the centre panel and first outwardly convex bead of the end wall.

In another embodiment of the method the can is supported between a support plate and a punch which is applied to a second convex bead surrounding said first bead.

If desired the pressure plate may have a profiled end wall to engage with a panel portion of the can lid.

Various filling procedures can be used. The contents of the can may be hot when filled into the can and the lid is closed, and the filled cans are then pressurised by deformation of the end wall, without reheating the can contents. This technique may be used when packing hot filled fruit juices.

In an alternative method the contents are hot when filled into the can body and the lid closed, and further heated and then cooled before displacement of the centre panel of the end wall. This is a widely used thermal treatment but gives rise to collapse of the side wall panels unless prevented.

The sources of vacuum within the filled can are (a) condensation of liquid from vapour, eg. steam to water; (b) contraction of the product and gases as they cool; (c) expansion of the side wall and end during processing to a larger volume than was available at the time of filling.

The application of pressure to the end wall while the product contained is still warm, prevents collapse of the flexible side wall panels by abating the vaccuum.

The method is usually carried out in apparatus comprising a support plate engaged with the top end of the can and a punch movable towards and away from the support plate. These features may be located in a press frame or modified die necker, flanger or alternatively incorporated in other machines, such as a labelling or seaming machine.

Various embodiments will now be described by way of example and with reference to the accompanying drawings in which: Fig 1 is a perspective cut-away view of a can body as described in GB 2237550; Fig 2a is a plan view of the can of Fig 1, sectioned on a line II-II in Fig 1; Fig 2b is an underplan view of the can of Fig 1 sectioned on the line II-II showing a form of collapse that may arise on cooling of a hot product in a closed can; Fig 3 is a plan view of the can of Fig 1, in which the left side shows the can during processing when the internal pressure is high, and the right hand side shows the panel curvature after application of pressure to the bottom wall during cooling.

Fig 4 is a side view of the can of Fig 1, sectioned on a diameter, and apparatus for applying pressure to the bottom wall; Fig Sa is an enlarged diagrammatic representation of the profile of the bottom wall before and after reforming, showing portions at which pressure may be applied; Fig 5b is a sectioned side view of the can of Fig 4 after reforming of the bottom wall and side wall panels; Fig 6 is a graph of reforming load v deflection of the bottom wall; Fig 7 is a graph of change in volume of can v base deflection for a can 73mm diameter by llOmm tall; Fig 8 is a sectioned side view of a filled can closed by a full aperture tear open can end; Fig 9 is a side view of a can body having an alternative pattern of ribs and panels; and Fig 10 is a plan view of the can of the can body sectioned on line x-xl in Fig 9.

In Figs 1 and 2, a first embodiment of the can body 1 for use as a container for processed foods, comprises a circular end wall 2 and a tubular side wall 3 upstanding from the periphery of the end wall 2.

Typically a cup is drawn from a blank of sheet metal, such as tinplate, electro-chromecoated steel or an aluminium alloy of the order of 0.0118" (0.3mm) thick. The cup is then wall ironed to a final overall shape 73mm diameter by 113mm tall having a side wall thickness "t" 0.0036" (0.093mm) and a bottom wall thickness "T" unchanged from 0.0118" (0.3mm). Preferably, the flange 4 and an adjacent margin "m" of the side wall, having a greater thickness t1 than the side wall, typically 0.006" (0.155mm).

In Figs 1 and 2 the side wall 2 of the can body can be seen to comprise a peripheral flange 4 defining the mouth of the can body, a first cylindrical portion 5 depending from the interior of the flange, a plurality of externally concave recessed panels 6 extending downwards from the first cylindrical portion, a second cylindrical portion 7 beneath the concave panels and an optional annular bead 8 which connects with the periphery of the end wall. The end wall 2 comprises an annular standbead 9 surrounding a central panel having shallow annular corrugations 11 which permit the end wall to distend under the influence of internal pressure in the can body.

Fig 2 shows that each concave recess panel 6 is connected to the next by an elongate rib 12 formed by a fold of internal radius "r" less than 5% of the radius "P" of the cylindrical portion. By way of example, if P is approximately 36.5mm, r will be less than 1.83mm, but not so small as to put the metal side wall in danger of cracking. This arrangement of panels and ribs creates a fluted profile in the median portion of the can.

Each concave panel 6 (measured from rib to rib on either side) subtends an angle A0 of 24 at the central axis of the side wall 3. Thus, this embodiment has 15 panels. However, other values of AO are useful if subtending an angle at the central axis in the range of 150 to 300. That is to say there may be 12 to 24 panels.

Preferably, each panel 6 flares into the cylindrical portion at end end as a gently curving profile with maximum slope at an angle K of 1500 but approach angles in a range of 1500 to 1770 are useful. The circumferential perimeter length is constant during this transition, from which it follows that the radius of curvature (perpendicular to the can axis) is substantially constant at all levels over the whole height of the panels and is equal to the radius of the cylindrical portions 5, 7 of the can less twice the rib radius, i.e. R = P - 2r. The cylindrical height hl, h2 of each cylindrical portion 5,7, is less than 25% of the height H of the side wall 3 and preferably less than 10%. As an example hl = 5mm and h2 = zmm on a 113mm high can with 73mm diameter.

The radius of curvature of a concave panel 6 is denoted R and is typically within a range of 20mm to 100mm so that the panel is shallow enough to be flexible.

In Fig 2a the radius of curvature R is approximately equal to P, the radius of the cylindrical portions, namely 36mm.

The ribs 12 and cylindrical portions 5,7, define side wall portions that support compressive loads in the axial direction, such as arise during flanging of the body and double seaming of a lid onto the can body such that the can in Fig 2a has an axial load capacity of approximately twice that of a conventional circumferentially beaded can of the same wall thickness, subject to any loss of strength at the rolling bead 8.

The concave recessed panels 6 define flexible surfaces which are able to distend when subjected to pressure inside the body 1 as arises during thermal processing of a product therein. The configuration of fifteen ribs 12 and fifteen concave recesses 5 is able to survive transit abuse and normal display at point of sale.

Fig 2b shows a five sided shape to which the side wall elastically deforms during subjection to an external pressure of 2.5 atmos. absolute pressure as arises in hydrostatic cookers. As can be seen in Fig 2b every third panel has flipped outwards enabling the panels therebetween to move radially inwardly in pairs. On abatement of the overpressure as the can cools, the can reverts to the shape shown in Fig 2a. As the can cools further it may revert to the shape shown in Fig 2b This collapsed shape is not visually acceptable for sale.

Collapse of the side wall shape of Fig 2b is related to can diameter; can height, flute geometry, number and spacing of flutes, can sidewall thickness, can base thickness, the material characteristics such as temper and yield stress, end profile characteristics, fill volume, headspace volume, fill temperature, components in headspace, eg.

steam, nitrogen or oxygen Product type, closing and processing conditions, storage and transit and opening conditions.

The can of Figs 1 and 2 is made by deep drawing of a plain cylindrical body from a metal blank. The body is then formed with panels 6 and ribs 12 with minimal stretching of the material so choice of panel flexibility to maximise the ability to accommodate volume change and panel springback is somewhat limited.

We have found that thin walled cans having flexible panels in the side wall can have the shape of side wall panel controlled by limited deformation of the bottom wall to reduce the volume of the closed can.

In Figs 3 and 4 the bottom wall comprises a centre panel 10 surrounded by a first outwardly convex bead lla, which is connected by an outwardly concave bead llb to a second outwardly convex bead llc in turn connected by a second outwardly concave bead Ild to an inner wall lle of the channel shaped standbead 9, an outer frustoconical wall llg of which blends into the side wall 3.

The annular beads lla, llb, llc and lld are held at an axial distance above the bottom of the standbead 9 by the inner wall Ile, so that the beads may deflect outwardly as expansion of a product during heating causes pressure to increase in the lidded can.

In one embodiment of a can 73mm diameter x llOmm tall, the flat centre panel 10 has a diameter of 38mm and a thickness of 0.3mm. The diameter at the apex of the first outwardly concave bead is about 49mm and the diameter at the apex of the second outwardly concave bead is about 64mm. As depicted in Fig 4, all the annular beads have an internal radius of about 2.5mm. The standbead has an internal radius of about 2.Omm.

Typically, the side wall 3 of the can of Figs 3 and 4 has a thickness of about 0.09mm, which is substantially thinner than the bottom wall at 0.3mm. Whilst the side wall has axial strength provided by the ribs and depth of curvature "dl" below the apex of the ribs, as shown in Figure 2, the bottom wall is inherently stronger than the side wall. So the geometry of the annular beads lla, llb, llc and lld of the bottom is chosen to provide deformability while the side wall flexes, without axial crushing to accommodate change in internal pressure.

In Fig 4 the can is shown to be filled with a product 13 leaving a headspace 14 under the can end 15 which is attached to the side wall by a double seam 16.

Fig 4 shows the filled can during cooling after thermal processing while it is still warm before the collapsed shape develops as shown in Fig 2b.

An upper tool 17 having a flat end wall pressed on to the double seam of the can end 16 supports the can end against flexure whilst a lower tool 18, having a flat end face surrounded by a curved edge, is urged against the flat central panel 10 and first convex bead lla of the bottom wall to deform the bottom wall to the shape shown in Figs 5a and 5b in which volume of the can is reduced and the side walls thrust outwardly. If desired the upper tool 17 may have a plug portion to enter into the double seam and support the centre panel of can end 16 but this support is not usually necessary with thick lids or can ends.

The left side of Fig 3 shows that at maximum temperature of heat treatment the flexible panels may be forced by the expanded product to flex to a flat or slightly bulged shape from their 'as made' depth dl. As the can and contents cool the panels flex back to nearly flat or slightly concave. The right side of Fig 3 shows that deformation of the bottom wall causes increase in pressure (abatement of partial vacuum) sufficient to maintain the side wall panels "nearly flat", typically a sink depth "d2" of about 0.2mm so preventing development of the five sided collapsed shape shown in Figure 2b.

The relatively thick metal of the bottom wall sustains the shape created as shown in Figs 5a and 5b.

However, there is design choice as to where pressure is applied to the bottom wall. Two positions have been studied: A) Pressure applied to the centre panel 10 and first annular convex bead as shown in Figs 5a and 5b; B) Pressure applied to the second annular concave bead llc, as indicated by arrow B.

In Figs 5a and Sb the position A is shown in which the nose of punch 18 applies pressure to the flat centre panel and adjacent surface of the first annular bead lla.

In position B, a punch having a profiled end to reach the inside surface of the second outwardly convex bead llc is applied to the bottom wall.

Tests were carried out using both positions A and B applied to cans as shown in Figs 4 and 5 and the deflection of the centre of the can panel of the can bottom and load to achieve the deflection are shown in Table 1: TABLE 1 - LOAD AGAINST DEFLECTION

Deflection under I Load (lbs) load (thou) I position I position B B I A 0 1 0 l O 0 20 1 22.4 1 56 40 1 61.6 1 100.8 60 1 84 1 123.2 80 1 100.8 1 134.4 100 1 120.4 1 140 120 1 140.0 1 145.6 140 1 168 1 148.4 160 1 201.6 1 156.8 180 1 324.8 1 168 200 1 397.6 1 238 210 Fail 336 The results shown in Table 1 are shown graphically in Fig 6 in which the load (in lbs) is plotted against the deflection (in thousands of an inch) of the centre panel of the bottom wall. Fig 6 shows that deflections in excess of 125 thou. require higher loads if the position B is used to apply pressure to the radially outer bead llc to achieve a deflection the same as that achieved by pressing on the centre panel at position A.

In Table 2 the deflection of the centre panel 10 is compared with the change in volume of the can: TABLE 2: BASE DEFLECTION AGAINST CHANGE IN VOLUME CHANGE IN VOLUME (ml)

Punch position Punch position B A 1 2 2 1 2 2 I I II I I l l II l l 0 0.8 0.8 0.7 0.1 1.0 0.9 1.5 1 1.4 1 1 2.2 2.3 2.1 3.8 13.612.2 1 1 3.3 3.4 3.3 4.7 1 4.2 2.7 1 1 4.4 1 4.5 14.4 6.7 16.215.2 1 1 5.4 5.5 5.6 8.9 9.3 7.1 6.5 6.7 6.6 11.1 - - 7.6 7.9 7.8 BASE DEFLECTION (thou) 0 20 40 60 80 100 120 140 The punch position B gave very consistent results and for lmm of base deflection, the change in volume was approximately 2.2 ml.

Approximately llml total change in volume could be expected before can failure. In load terms this is 1.4kn (340 lbsf).

According to current practice, can ends or lids are made from thicker metal than the side wall of the can body, typically 0.008" (0.2mm) tinplate or ECCS can ends and 0.012" (0.3mm) for aluminium alloy can ends.

Generally the unscored can end shown in Figures 4 and 5b are stiff enough to resist the pressure arising when the bottom wall is pushed into the can body, because the flexible panels of the side wall are more easily displaced than the stiffer can ends.

If, however, it is desired to support the can end against movement, as may be necessary to prevent opening of a scored tear open can end, the support plate may have a profiled end wall to support the can end.

In Figure 8 a filled can 20 is closed by a tear open can end 21 which has a ring pull tab 22. A support plate 23 has an annulus 24 which fits in the chuck wall 25 and anti peaking bead 26 to support the periphery of the can end. A peg 27 depends from the support plate to pass through an aperture in the ring pull to reach the centre panel of the can end and support it. In other respects this apparatus is identical to that of Figures 4 and 5b in which pressure is applied to the bottom end by a punch 18.

It is believed that deformation of the can bottom is best done while the can and contents are still warm; before the onset of collapse of the side wall. This preferred time for deformation avoids risk of side wall kinks developing that are difficult to obliterate. The invention is of particular benefit in the packing of hot filled products such as baked beans and soups.

The application of deforming pressure to the centre panel and inner annular bead appears to be preferable because it is possible to achieve volume reduction of the can by progressive unrolling of each bead to a ledgesep structure that is stable in shape.

Fig 9 shows a can 73mm diameter by llOmm tall having the same bottom profile as shown in Figs 4 and 5 but provided with an alternative form of ribs and panels as described in British Patent Application No. 2251197 A in which the ribs 80 are separated by arcuate regions and the panels 81 narrower. The closed can has an internal volume of 425ml to receive a volume of product of 400ml.

T A B L E 3

Expt Fill Reform Change % Change Final Pressure in Can relative No. Temp C Amount in Vol. in Vol. to Atmospheric Pressure (psi) (mm) (ml) 10 C 22 C 35 C 1 65 0 0 0 -1.9 (F) -1.0 -0.1 2 65 1.5 2.5 0.6% -1.5 -0.7 +0.1 3 65 3.0 6.0 1.4% -1.0 -0.5 +0.7 (SP) 4 85 4.5 9.0 2.0% -1.3 -0.4 +0.3 (F*) 5 85 6.0 12.0 2.8% -0.2 +0.2 +1.0 6 85 7.5 14.5 3.4% +0.4 +1.2 +0.5 (SP*) KEY: F indicates failure of side wall by collapse F* indicates a spurious result because of side wall collapse SP indicates spurting of product on opening the can SP* indicates a spurious result arising from blockage by emerging product GCQABK Cans, as shown in Fig.9, were filled with a hot starch solution at tempertures shown in the Table 3. The cans were then closed by a can end and attached by formation of a double seam. Before the cans were cooled, each can was placed in apparatus as shown in Fig.4 and the bottom wall was pushed inwards to reduce the internal volume by the amounts shown in Table 3 which tabulates actual volume reduction and per cent reduction. The cans were then cooled and tested for internal pressure at ambient temperatures of 10", 220C and 35"C.

Two rejection criteria are recorded in table 3: "F" indicating failure to restore to the original side wall shape; "SP" indicating that pressure inside the can was sufficient to cause the product to spurt out.

In comparative Experiment No 1, the starch solution was at 65% when filled into the can body. No reforming was done to the bottom wall of the can so that no change of can volume was made. Pressure test on the cans opened at 100C found a partial vacuum of about -1.9psi and the side wall had collapsed to an unsightly shape which could not be labelled satisfactory in a labelling machine. This measured pressure of 1.9psi was the partial vacuum in a collapsed body so had the can remained in good shape the vacuum would be higher. The cans opened at 220C were in good shape and had an internal partial vacuum of about -l.Opsi. The cans opened at 350C were also in good shape acceptable to a labelling machine and had an internal partial vacuum of about -0.lpsi.

In experiment 2, the cans were packed with starch solution at 650C and closed with a lid. Before cooling too ambient temperature the centre panel of each can bottom was pushed into the can body a distance (reform amount) of 1.5mm so causing a reduction in volume of the can by 2.5ml (0.6% reduction in volume). The cans remained in good shape when cooled to ambient temperatures of 100C, 220C and 350C at which pressure tests were made.

At 100C, the internal pressure was -l.Spsi, at 220C the internal pressure was -0.7psi, and at 350C the internal pressure was +0.1. This experiment 2 represents a first example of an adequate combination of fill temperature, fill volume, and amount of bottom wall reforming.

In experiment 3, the cans were packed in like manner to those in experiments 1 and 2 and the bottom wall was reformed by moving the centre panel into the body by 3.0mm to reduce the can body volume by 6.0 ml (a reduction in volume of 1.4%). Whist the can bodies stayed in good shape the can opened at 35 contained a positive pressure measured at +0.7 psi. This measured figure is believed to be low because the pipe to the pressure gauge became blocked with product that spurted out.

In experiments 4 to 6, the can bodies were packed with starch solution at 850C so that a greater contraction of the product, when cooled to ambient, was expected.

In experiment 4, the can bottoms were pushed a distance of 4.5mm to reduce the volume of the can body by 9ml (a 2% reduction in volume). The cans tested at 100C had collapsed so the measured pressure at -1.3psi is a lesser partial vacuum that would have existed had the can body stayed in shape. The can shape and internal pressure at 220and 350 were satisfactory in that the product did not spurt out.

In experiment 5, cans packed with starch solution at 850C stayed in good shape after the bottom wall was pushed into the can body a distance of 6.Omm to reduce the volume of can by 12ml (a 2.88 reduction). The internal pressures at ambient temperatures of 10 , 22"C and 35 were -0.2psi, +0.2psi, and +1.ops, respectively and product did not spurt out.

In experiment 6, the cans were packed with starch solution at 850 and, before cooling, the bottom of the closed cans was pushed inwards by a distance of 7.5mm to reduce the can volume by 3.4%. The cans were in good shape at ambient temperatures of 100C, 220C, and 350C but the cans tested at 350C had an internal pressure sufficient to cause product to spurt out and block the test gauge so the measured figure of +0.5ski is obviously wrong.

From these results, we conclude that: (1) our thin walled, panelled cans are able to withstand conventional filling and thermal processing conditions and permit reforming of the bottom wall to produce a container which is stable in shaped over the required range of storage and opening conditions.

(2) the partial vacuum in the cans at ambient temperature must be no greater than -2.Opsi.

(3) the pressure acnieved in our cans at ambient temperature must not exceed +2.Opsi because there would be a risk of product spurting out at greater pressures.

Claims (8)

CLAIMS:

1. A method of filling, closing and correcting the shape of a can having a bottom wall, a side wall substantially thinner than the bottom wall, and a lid by the steps of: (a) providing a can body having a bottom wall comprising a centre panel surrounded by at least one annular bead and a channel portion which connects the bottom wall to the side wall which comprises a lower cylindrical portion adjacent the bottom wall, an upper cylindrical portion having an outwardly directed flange to define the mouth of the body and a plurality of longitudinal panels, preferably between 12 and 24 Panels, each joined to the next by a rib to join the upper and lower cylindrical portions, said side wall being between 0.0030" and 0.0045" thick when made of ferrous sheet metal or between 0.004" and 0.006" thick when made from an aluminium based sheet metal;; (b) filling the can body with a product at a temperature between 300C and 950C to leave a headspace below the flange; (c) attaching a lid to the flange of the can body; and (d) applying external pressure to the bottom wall against support at the lid, before the can contents have cooled, to deform the bottom wall into the body to reduce the internal volume of the body by no more than 4% so increasing the pressure within the lidded body to a pressure sufficient to ensure that the pressure in the filled can at ambient temperature is between -l.Spsi and +1.5psi.

2. A method according to claim 1 wherein the can body has a side wall integral with the end wall having been drawn from a sheet metal blank.

3. A method according to claim 2 wherein the end wall ofthe body has a centre panel, a first outwardly convex bead surrounding the centre panel, a second outwardly convex bead joined to said first convex bead by an outwardly concave bead, and an outwardly convex channel portion connected to said second convex bead by an inner wall, and an outer portion which blends in the side wall (after Carnaud).

4. A method according to any preceding claims wherein the can is held between a support plate and a punch which is applied to the centre panel and first outwardly convex bead of the end wall.

5. A method according to any one of claims 1 to 3 wherein the can is supported between a support plate and a punch which is applied to a second covex bead surrounding said first bead. (consider Fig.7A of US 3789785 Carnaud).

6. A method according to claim 4 or claim 5 wherein the support plate has a profiled end wall to engage with a panel portion of the can lid (consider Fig 8 of our specification BO End).

7. A method according to any one of claims 1 to 7 wherein the contents wre hot when filled into the can body and the lid closed, and further heated and then cooled before displacement of the centre panel of the end wall.

(viz Leftault option).

8. A method of adjusting pressure in a filled and lidded can, substantially as herein before described with reference to Figs 3 to 8 of the accompanying drawings.