GB1600006A

GB1600006A - Containers

Info

Publication number: GB1600006A
Application number: GB12837/77A
Authority: GB
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1977-03-26
Filing date: 1977-03-26
Publication date: 1981-10-14
Also published as: IT1095951B; DE2812577C2; JPS541183A; JPS619172B2; IT7821604A0; BE865207A; ZA781512B; FR2384676B1; NL7803173A; FR2384676A1; DE2812577A1

Description

(54) CONTAINERS (71) We, METAL Box LIMITED, of Queens House, Forbury Road, Reading RG1 3JH, Berkshire, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to metal containers, in particular (but not exclusively) those having a container body drawn from sheet metal and suitable for thermally processed products. The invention also relates to bodies for such containers.

It is known to fill can bodies down from sheet metal with food products such as fish pastes, meats or vegetables, and to close them by can ends which are double seamed on to the bodies. The filled cans are then heated to sterilise the cans and their contents. During this thermal processing the contents of the cans expand and to accommodate the expansion it has been proposed to provide the bottom walls of the cans with expansion panels defined by concentric corrugations. The pattern of the corrugations is similar to those typically used for the bottom ends of ordinary three piece cans. However, extra metal is required for the corrugations over and above that which would be needed to provide the cans with a flat bottom wall.The provision of metal for these corrugations detracts from the economies which can be derived from the use of stiffer sheet metals such as H19 grades of aluminium and double reduced tinplate.

British Patent Specification No. 1 453 131 describes a drawn can for carbonated beverages, which has a bottom wall comprising a flat annular portion surrounding a substantially rigid, eversion-resistant, inwardly-domed depression. When the bottom wall of this can is subjected to internal pressure the annular portion flexes outwardly to a frustoconical shape while the depression remains undistorted. The can so pressurised can be stably stood upright on the peripheral intersection of the depression and the annular portion. However, the substantially rigid central depression is not entirely suitable for thermal processing because if the bottom wall is strong enough to contain carbonated beverages it will be stronger, and therefore, more costly than is necessary for a thermally processable container.In this respect it will be noted that a container for carbonated beverages must be designed for internal pressures of 90 p.s.i. or more,whereas the internal can pressures involved with thermal processing are 45 p.s.i.

at the most.

This invention provides a container body, which is formed of a single piece of metal to have a seamless tubular side wall upstanding peripherally from an integral flexible bottom wall having a substantially uniform material thickness, said flexible bottom wall comprising a central panel which occupies from 20% to 80% of the total area of the bottom wall, a substantially flat annular panel surrounding the central panel, and an annular portion comprising first and second parts which are arcuate in cross section so that the annular portion holds the central panel in inwardly offset relation to the annular panel, the depth of the annular portion axially of the container body being at most the thickness of the bottom wall material plus the sum of the internal radii of curvature of first and second arcuate parts of the annular portion at which the annular portion joins, respectively, the annular panel and the central panel, the width of the annular portion radially of the container body being at most the thickness of the bottom wall material plus the said sum of the first and second radii of curvature, the radii of curvature of the first and second arcuate parts being each twice to four times the thickness of the bottom wall material, the arrangement being such that an over-pressure not exceeding 45 p.s.i. within the container body is sufficient to cause the central panel of the bottom wall to flex outwardly with no substantial deformation of the annular portion, the bottom wall elastically retracting substantially to its unstressed shape when such pressure abates.

Preferably the central panel occupies from 5% to 40% cf the bottom wall area.

According to a first preferred feature of the invention the central panel has the form of a simple planar disc.

according to a second preferred feature of the invention the central panel has one or more sub-panels joined by one or more further annular portions therebetween, the first said annular portion and the or each said further annular portion holding the sub-panels individually in inwardly offset relation to the radially outwardly adjacent panel or sub-panel.

The side wall of the container body may, if desired, be joined to the bottom wall by a frustoconical portion which is convergent towards the bottom wall. The frustoconical portion may inclined to the axis of the body at 10 to permit stacking of the body on the closure of a can having a similar body.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a side elevation of the first can body embodying the invention, taken on a diametral section; Figure 2 is an enlarged view of the inflection portion forming part of the bottom wall of the can body of Figure 1; Figure 3 is a diagrammatic side elevation of the bottom wall, showing various positions adopted by the bottom wall under different over-pressures generated in the can body; Figure 4 is a graph showing the deflection of the centre of the bottom wall when plotted against the over-pressure in the can body; Figure 5 illustrates the stacking one on top of the other of two cans each formed from one of the bodies of Figure 1 to 4; and Figure 6 similarly illustrates the stacking of cans having bodies which are a variation of the body of Figures 1 to 4.

Figure 7 is a plan view of the second embodiment of the can; Figure 8 is a side elevation of the can of Figure 7 on a diametral section; and Figure 9(a), 9(b), 9(c) and 9(d) are views similar to Figure 2 and showing various alternative arrangements for the inflection portion.

In Figure 1 a can body 1, drawn from a single piece of .21 mm thick tinplate, has a side wall 2 and a flexible bottom wall 3. The side wall and bottom wall are joined together by a frustoconical annular portion 4 of the side wall, which extends axially and radially inwardly to the periphery of the bottom wall at an angle of approximately 10 to the central axis of the can.

The bottom wall 3 comprises a flat central panel 5, a flat annular outer panel 6 surrounding the central panel 5, and an annular portion 7 which holds the central panel 5 in inwardly offset relationship to the annular panel 6. It will be seen from Figure 1 that the ratio of the diameter of the central panel to about half that of the bottom wall so that the ratio of the area of the central panel to the total area of the bottom wall is about 25%.

As shown in Figure 2, the inflection portion 7 consists of a first arcuate part 7A of radius rl (internal) which extends from the outer panel 6 radially inwards and axially upwards to a second arcuate part 7B. The part 7B is of radius r2 and extends from the first arcuate part axially upwards and radially inwards to the central panel 5. The radius of curvature of each arcuate part is equal to 2.5 times the thickness t of the bottom wall material. The axial distance (i.e. along the axis of the can) by which the central panel is offset in relation to the outer panel is four times the thickness t.

Figure 3 shows diagrammatically how the bottom wall 3 deflects with variation of the over-pressure in the can body during thermal processing of the can formed by product-filling and closing the body. The dashed line marked A represents the profile of the bottom wall with no internal pressure, that is to say, as it is originally formed in the press tool. The outer panel 6 and central panel 5 are then both flat and located on planes which are perpendicular to the axis of the can. As the over-pressure in the can increases, the bottom wall progressively deflects downwardly so that the outer panel 6 takes the form of a shallow frustum of a cone and the central panel is deformed to a bulge.

The bottom wall is so designed in relation to the maximum over-pressure which is likely to occur in the can during a normal thermal processing cycle that at this pressure it just fails to reach the dash-dotted profile B, at which the bulged central panel 5 is flush with the lowest point of the outer panel 6 (which occurs at the intersection of the outer panel with the annular portion).

Since the maximum internal pressure in the can may lie anywhere within the range 5-40 p.s.i. depending upon such factors as the nature of the can contents and the processing temperature used, the bottom wall should be arranged to achieve the profile B at an over-pressure which is increased to incorporate a safety factor allowing for temperature control errors, flash points in the product, etc., and which accordingly lies within the range 10 - 45 p.s.i. Any substantial provision for excess of the overpressure corresponding to profile B over the maximum internal pressure which actually occurs in the can should be avoided since it represents unnecessary thickness in the bottom wall material and therefore unnecessary material cost.

Profile B represents the ultimate condition of bulging which is acceptable during processing.

If this condition is exceeded, that is to say, if the central panel 5 stands proud of the outer panel 6, the can becomes unstable and may fall over or tilt and so create an obstruction in the thermal processing plant.

In Figure 3 the profile C, represented by the dotted line, denotes the position which the bottom wall will adopt when the internal pressure is removed after thermal processing of a product which is packed when cold. It will be seen that the outer panel 6 is of slight outward conical shape, but the central panel 5 has returned to a substantially flat state. However, if the product in the can was hot when packed, cooling of the can and contents to room temperature after thermal processing will cause the contents to contract and to create in the can a slight partial vacuum typically of the order of 3 p.s.i.below atmospheric pressure. The bottom wall is therefore caused to adopt the profile denoted D, in which the outer panel 6 extends upwardly and axially into the can and the central panel 5 remains substantially flat.

From the foregoing it will be understood that, after thermal processing and cooling, cans of which the contents are in a satisfactory condition will have the profiles of their bottom walls lying generally within the range of profiles C to D. Any can of which the bottom wall is bulged to a substantial extent, that is to say, to a substantially greater extent than is present in profile C, is suspect and should be discarded.

Almost certainly, its contents will have been spoiled by bacterial action. By making the central panel 5 and outer panel 6 initially flat, or substantially so, the extent of any bulging is made readily apparent to the trained observer, and the recognition of blown cans is thereby facilitated.

Figure 4 shows graphically the deformation characteristics described in terms of bottom wall profiles in Figure 3. In Figure 4 the axial deflection of the centre of the central panel 5 is plotted against the over-pressure generated in the can body during thermal processing. The deflection is given in thousandths of an inch and the pressure in pounds per square inch. The data given relates to a "211" size can, which is of 60 mm diameter and made from .21 mm thick tinplate.

It is desirable that the filled cans should stack upon one another securely in retail displays. Figures 5 and 6 show how this is achieved.

In Figure 5, a can having a body as shown in Figure 1 is stacked upon a like can 11 having a can end 12 fixed by a double seam 13. The bottom wall 3 of the can body 1 is able to enter the double seam 13 by virtue of the taper on the frustoconical annular portion 4, so that the bottom wall contacts and rests upon the can end 12 at the line of contact L. The semi angle of the frustoconical annular portion 4 is denoted X" and is of the order of 10 , this being sufficient to ensure a gap, denoted Y, between the portion 4 and the double seam 13 so that the can body 1 will not jam in the seam.

Figure 6 is a view similar to Figure 5 and showing the stacking of cans having can bodies which are a modification of that shown in Figure 1. In Figure 6 the side wall 22 of the body has an outwardly protruding stacking bead 24 at the lower edge of which a frustoconical portion 25 extends radially inwards and axially of the container to connect the bead to the flexible bottom wall of the body, now denoted 23. The frustoconical portion 25 is inclined to the side wall 22 by an angle a0 which is of the order of 10 . The frustoconical portion 25 has a diameter less than the internal diameter of the double seam 28 of a like can 26 so that it may enter the seam and permit the stacking bead 24 of the can 21 to contact and rest upon the double seam 28 at a line of contact.A clearance Z is provided between the closure panel 29 of the can end 27 of the lower can 26 and the bottom panel 23 of the upper can 21, so that the weight of the upper can and any further cans above it is supported directly by the side walls the cylindrical envelope of which is indicated by the dashed line in Figure 6.

The embodiment described above with reference to Figures 1 to 6 has its central panel 5 in the form of a simple planar disc. In contrast, in the can body 31 forming the embodiment of Figures 7 and 8 the central panel 35 is arranged on two levels, and comprises a flat annular subpanel 36, a flat central sub-panel 38 within the sub-panel 36, and an inflection portion 39 which holds the central sub-panel 38 in inwardly offset relationship to the annular subpanel 36.

As in the first embodiment, the central panel is carried in inwardly offset relation to an annular outer panel 34 by an annular portion 37. This annular portion 37 is as described with reference to Figure 2 in relation to the annular portion 7. The central panel occupies approximately 365to of the total area of the bottom wall 33.

Typically the can body has a diameter of 3 inches, the diameters of its central panel 35 and central sub-panel 38 respectively being 1.75 and 1 inches.

The behaviour of the can body of Figures 7 and 8 during thermal processing is similar to that of the first embodiment in that the outer panel 34 bulges downwardly to present its intersection with the annular portion 37 as a stable standing ring for the can. In addition, the sub-panels 36 and 38 bulge downwardly so as to bring the centre of the suboponel 38 and the heel of the sub-panel 36, that is, its intersection with the annular portion 39, closer to flush relationship with the outer panel. The arrangement is such that such flush relationship, corresponding to profile B of Figure 3, occurs substantially simultaneously for both the sub-panels 36, 38 at an over-pressure within the can which is just greater than the maximum internal pressure which is to be expected during thermal processing.

Mthough the annular portions in the embodiments of Figures 1, 3, 5, 6, 7 and 8 have been as particularly described with reference to Figure 2, many arrangements of the annular portion are possible, as will become apparent from the following description to be given with reference to Figure 9.

In Figure 9(a) the radius of curvature r1 of the first arcuate portion 40 is equal to the radius of curvature r2 of the second arcuate portion 41. The portions 40, 41 have their centres of curvature horizontally aligned. Each arcuate portion subtends an angle of 900 at its centre of curvature, with the result that the axial distance by which the central panel 5 is offset from the outer panel 6 is equal to rl + r2 + t, where t is the thickness of the bottom wall material.

The annular portion shown in Figure 9(b) corresponds to that of Figure 9(a) in that the centres of curvature of the two arcuate portions 44,45 are horizontally aligned. However, in Figure 9(b) the radius of curvature r, of the first arcuate portion 44 is less than the radius of curvature of the second arcuate portion 45. A particular advantage of making r2 greater than rl in this way is that it facilitates the formation of the annular portion without disturbing coating materials which may be present to protect the can interior from the product to be packed.

In Figure 9(c) the radius of curvature rl of first arcuate portion 42 is centred upon a circle which is located, in relation to the can body, axially above and radially distant from the circle forming the centre of the radius of curvature r2 of the second arcuate portion 43. The radii of curvature rl, r2 of the two arcuate portions are equal, as in Figure 9(a). However, each arcuate portion subtends an angle less than 90" at its centre of curvature with the result that the axial distance of offsetting of the central panel 5 in relation to the annular panel 6 is less than that of Figures 9(a) and 9(b), that is to say, rl + r2 + t.

The annular portion 7 of the embodiment of Figures 1 to 5 is a particular form of the arrangement shown in Figure 9(c), with the radii of curvature rl and r2 each equal to 2.5t.

The annular portion shown in Figure 9(d) has arcuate portions 46, 47 with horizontally aligned centres of curvature and equal radii of curvature r^, r2. As in Figure 9(c) they each subtend an angle of less than 900 at their centre. They are joined by a frustoconical portion 50 of a length and cone angle such that the depth of offsetting of the central panel 5 in relation to the annular panel 6 is still subject to the upper limit of rl + r2 + t.

It has been discovered that in order to create inflection portions which are substantially rigid to the pressures occurring in the can body during thermal processing, the radii of curvature rl, r2 of the inflection portion should lie within the range two or four times the material thickness t of the bottom wall, that is to say, they should each be of magnitude 2t to 4t.

Moreover, the radial width of the inflection portion should not exceed r; + r2 + t. The arrangements shown and described are all subject to these limitations and, in addition, to the limitation rl + r2 + t mentioned above for the depth of offsetting of the central panel.

The embodiments described and shown have central panels which occupy between 25% and 40% of the total area of the bottom wall.

Although this percentage range is preferred, a percentage range of 20% to 80% may be used.

The central panel may be arranged on more than two levels if desired.

Although the embodiments have been described in terms of can bodies drawn from tinplate or aluminium, other sheet materials may be used such, for example, as blackplate, mild steel and the chromium coated steel commonly called tin free steel.

WHAT WE CLAIM IS: 1. A container body, which is formed of a single piece of metal to have a seamless tubular side wall upstanding peripherally from an integral flexible bottom wall having a substantially uniform material thickness, and the flexible bottom wall comprising a central panel which occupies from 20% to 80% of the total area of the bottom wall, a substantially flat annular panel surrounding the central panel, and an annular portion comprising first and second parts which are arcuate in cross-section so that the annular portion holds the central panel in inwardly offset relation to the annular panel, the depth of the annular portion axially of the container body being at most the thickness of the bottom wall material plus the sum of the internal radii of curvature of first and second arcuate parts of the annular portion at which the annular portion joins, respectively, the annular panel and the central panel, the width of the annular portion radially of the container body being at most the thickness of the bottom wall material plus the said sum of the first and second radii of curvature, the radii of curvature of the first and second arcuate parts being each twice to four times the thickness of the bottom wall material, the arrangement being such that an internal over-pressure not exceeding 45 p.si.

within the container body is sufficient to cause the central panel of the bottom wall to flex outwardly with no substantial deformation of the annular portion, the bottom wall elastically retracting substantially to its unstressed shape when such pressure abates.

2. A container body according to Claim 1, wherein the central panel occupies from 35% to 40% of the bottom wall area.

3. A container body according to Claim 1 or Claim 2, wherein the central panel has the form of a simple planar disc.

4. A container body according to Claim 1 or Claim 2, wherein the central panel has one or more sub-panels joined by one or more further inflection portions therebetween, the first said inflection portion and the or each said further inflection portion holding the sub-panels individually in inwardly offset relation to the radially outwardly adjacent panel or sub panel.

5. A container body according to any preceding Claim, wherein the side wall is joined to the bottom wall by a frusto-conical portion which is convergent towards the bottom wall.

6. A container body according to Claim 5, wherein the frusto-conical convergent portion is frustoconical and extends axially and inwardly at an angle of approximately 10U to the axis of the container body.

7. A container body according to Claim 5,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. axial distance by which the central panel 5 is offset from the outer panel 6 is equal to rl + r2 + t, where t is the thickness of the bottom wall material. The annular portion shown in Figure 9(b) corresponds to that of Figure 9(a) in that the centres of curvature of the two arcuate portions 44,45 are horizontally aligned. However, in Figure 9(b) the radius of curvature r, of the first arcuate portion 44 is less than the radius of curvature of the second arcuate portion 45. A particular advantage of making r2 greater than rl in this way is that it facilitates the formation of the annular portion without disturbing coating materials which may be present to protect the can interior from the product to be packed. In Figure 9(c) the radius of curvature rl of first arcuate portion 42 is centred upon a circle which is located, in relation to the can body, axially above and radially distant from the circle forming the centre of the radius of curvature r2 of the second arcuate portion 43. The radii of curvature rl, r2 of the two arcuate portions are equal, as in Figure 9(a). However, each arcuate portion subtends an angle less than 90" at its centre of curvature with the result that the axial distance of offsetting of the central panel 5 in relation to the annular panel 6 is less than that of Figures 9(a) and 9(b), that is to say, rl + r2 + t. The annular portion 7 of the embodiment of Figures 1 to 5 is a particular form of the arrangement shown in Figure 9(c), with the radii of curvature rl and r2 each equal to 2.5t. The annular portion shown in Figure 9(d) has arcuate portions 46, 47 with horizontally aligned centres of curvature and equal radii of curvature r^, r2. As in Figure 9(c) they each subtend an angle of less than 900 at their centre. They are joined by a frustoconical portion 50 of a length and cone angle such that the depth of offsetting of the central panel 5 in relation to the annular panel 6 is still subject to the upper limit of rl + r2 + t. It has been discovered that in order to create inflection portions which are substantially rigid to the pressures occurring in the can body during thermal processing, the radii of curvature rl, r2 of the inflection portion should lie within the range two or four times the material thickness t of the bottom wall, that is to say, they should each be of magnitude 2t to 4t. Moreover, the radial width of the inflection portion should not exceed r; + r2 + t. The arrangements shown and described are all subject to these limitations and, in addition, to the limitation rl + r2 + t mentioned above for the depth of offsetting of the central panel. The embodiments described and shown have central panels which occupy between 25% and 40% of the total area of the bottom wall. Although this percentage range is preferred, a percentage range of 20% to 80% may be used. The central panel may be arranged on more than two levels if desired. Although the embodiments have been described in terms of can bodies drawn from tinplate or aluminium, other sheet materials may be used such, for example, as blackplate, mild steel and the chromium coated steel commonly called tin free steel. WHAT WE CLAIM IS:

1. A container body, which is formed of a single piece of metal to have a seamless tubular side wall upstanding peripherally from an integral flexible bottom wall having a substantially uniform material thickness, and the flexible bottom wall comprising a central panel which occupies from 20% to 80% of the total area of the bottom wall, a substantially flat annular panel surrounding the central panel, and an annular portion comprising first and second parts which are arcuate in cross-section so that the annular portion holds the central panel in inwardly offset relation to the annular panel, the depth of the annular portion axially of the container body being at most the thickness of the bottom wall material plus the sum of the internal radii of curvature of first and second arcuate parts of the annular portion at which the annular portion joins, respectively, the annular panel and the central panel, the width of the annular portion radially of the container body being at most the thickness of the bottom wall material plus the said sum of the first and second radii of curvature, the radii of curvature of the first and second arcuate parts being each twice to four times the thickness of the bottom wall material, the arrangement being such that an internal over-pressure not exceeding 45 p.si.

7. A container body according to Claim 5,

wherein an outwardly protruding stacking bead joins the frustoconical portion to the side wall.

8. A container body substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings.

9. A container body substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

10. A container body substantially as hereinbefore described with reference to Figures 7 and 8.

11. A container body substantially as hereinbefore described with reference to Figures 9(a); 9(b); 9(c) or 9(d) of the accompanying drawings.