GB2067159A

GB2067159A - Buckle-resistant container ends

Info

Publication number: GB2067159A
Application number: GB8029634A
Authority: GB
Original assignee: American Can Co
Current assignee: Primerica Inc
Priority date: 1980-01-16
Filing date: 1980-09-12
Publication date: 1981-07-22
Also published as: IT8147591A0; IT1170634B; GB2067159B; JPS56107323U; AU541926B2; AU5974680A

Abstract

A container end (10) has a domed eversion-resistant central panel wall (16), a countersink groove (18) between inner and outer walls (54, 22) and a curled flange (20) for joining the end (10) to a container body. The groove merges smoothly with the inner and outer walls (54, 22) by way of arcuate portions, the radius of curvature (RI) of the portion between the groove (18) and the outer wall (22) being about half the radius of curvature (RO) of the portion between the groove and inner wall (54). The outer wall (22) is outwardly bowed, placing its outwardly and inwardly-facing surfaces in a state of compression and tension respectively, so that when the end is attached to the body, the outer wall (22) adopts a position perpendicular to the container rim to resist buckling. <IMAGE>

Description

SPECIFICATION Improvements in buckle resistant container ends This invention relates to an improved container end for rigid containers e.g. cans useful for packaging foodstuffs and beverages. More particularly it relates to an end which has superior resistance to buckling from internal pressures exceeding atmospheric pressure.

Buckling is a condition which results when the internal forces within a can exceed the strength of the end, thereby causing a portion of its end panel including a countersink wall portion to bulge outwardly. The resulting bulge may interfere with can stacking, with proper functioning of any easy open device possessed by the end including possible rupture of the associated score line, and may even cause failure of the double seam which may secure the end to a container body.

While a possible solution to the problem is to increase the gauge or thickness of the stock from which the end is made, the high volume of production in the container industry makes even a modest increase in material usage undesirable. Accordingly, considerable effort has been directed to improving end design.

A recent patent U.S. 4,013,837 discloses a method for reforming ends to improve buckle resistance. An end is reformed to decrease the radius of curvature of the countersink groove from the standard 0.030" to 0.020" (0.76 to 0.51 mm) with a corresponding increase in groove depth. The reforming process reportedly increased buckle resistance from 89 PSI to 105 PSI (6.26 to 7.38 kg/cm2).

Also of interest is U.S. 3,843,014 which discloses a reformed structure where the radius of curvature for the countersink groove falls within the range from 0.020" to 0.047" (0.51 to 1.19 mm) preferably 0.022" (0.56 mm). The countersink wall has an inwardly inclined break proximate the plane of the end panel. The preferred structure is reported to provide buckle resistance in the order of 100 PSI (7 kg/cm2).

While it is recognized that reduction in the radius of curvature of the countersink groove will increase buckle resistance, the resulting structure fails to conform to the industry standards which call for a countersink groove radius of 0.030" + 0.005" (0.76 + 0.13 mm), thereby producing a groove width of 0.050"-0.070" (1.27 to 1.78 mm). This standard enables ends from any manufacturer to mate with the seaming chucks currently in operation.

U.S. 3,441,1 70 discloses a method to control rather than resist buckling. The panel radius, which joins the central panel wall of the end with the inner wall of the countersink groove is coined. The coining increases the excess metal available for bulging and also reportedly enables the radius to act as a hinge so that the buckling occurs but in a controlled manner.

The invention aims to provide a container end which is strengthened to enhance resistance to buckling but which is compatible with the industry standards and which may permit a reduction in the gauge of the stock material from which ends are made. Another aim is to provide an end which may permit higher pasturization temperatures to be used, thereby enabling production lines to operate at higher speeds. The invention also aims to provide an end which may be readily manufactured with only minor changes in existing equipment.

According to the present invention, there is provided a container end having a central panel wall, an outer flange, and a countersink groove disposed therebetween, an inner wall joining the groove with the central panel wall and a countersink wall joining the groove with the flange, the groove having a root which arcuately joins outwardly with the countersink wall and inwardly with the inner wall, the respective outer and inner arcuate portions having radii of which the outer radius is smaller than the inner radius.

In a preferred container end according to the invention, the outer radius is half the inner radius. More particularly, the outer radius may be in the range of 0.020" to 0.025" and the inner radius in the range of 0.035" to 0.045" (0.51 to 0.63 and 0.89 to 1.14 mm).

Advantageously the countersink wall is inwardly bowed so that the inner surface of the wall is placed in tension and the outer surface of the wall is placed in compression.

The central panel wail can be domed, and if so the doming should be pronounced and carried out so that the panel wall is stretched beyond its yield point to strengthen the end and substantially eliminate bistability. Such a dome should have a radius of 4.0" to 4.5" (101.6 to 114.3 mm).

It is further advantageous for the central panel wall to have a downwardly directed panel radius (i.e. an outwardly convex portion) about its periphery which cooperates with the inner wall and the inner radius of the countersink groove to form an interface between the central panel wall and the outer radius of the countersink groove. This interface is responsive to changes in pressure when the end has been seamed to a filled container.

The invention also provides a container for pressurized fluids comprising a tubular body to which an end is joined by means of a double seam, the said end comprising an outer rim, a countersink wall generally perpendicular to the plane of the rim, a countersink groove merging via an outer arcuate portion with the base of the countersink wall, and a central panel wall, inwardly of the countersink groove, which merges via an outwardly convex portion with an inner wall which in turn merges via an inner arcuate portion with the countersink groove, the central panel wall being prominently domed with a doming radius of 4.0 to 4.5" (101.6 to 114.3) to stretch the panel wall beyond the yield point, the outer and inner arcuate portions having radii within the respective ranges of 0.020" to 0.025" and 0.035" to 0.045" (0.51 to 0.63 mm and 0.89 to 1.14 mm).

In the buckle resistant container, the countersink wall, which is generally perpendicular to the plane of the rim, is substantially free from inward bowing.

The invention will now be described in more detail by way of illustrative example, with reference to the accompanying drawings, in which Figure 1 is a top plan view of a can end embodying the invention before attachment to a can body; Figure 2 is an enlarged fragmentary sectional view of a portion of a can end embodying the present invention in comparison with a prior art configuration which is shown as an underlay and closely hatched to emphasize distinguishing features.

Figure 3 is a detailed part sectional, part elevational view of the prior art can end shown in Fig. 2, the end being in its preseaming condition; Figure 4 is a view similar to Fig. 3 of the prior art can end after seaming to a can body; Figure 5 is a sectional view of a can embodying the present invention and taken along the line 5-5 of Fig. 1, the can end being domed; Figure 6 is a part sectional, part elevatiqnal fragmentary view of the can end embodying the present invention, taken along the line 6-6 of Fig. 1; and Figure 7 is a sectional view of a can end embodying the present invention seamed to a can body.

In Figs. 1 and 2 is illustrated a can end 10 according to the invention before seaming to a can body. The can end has a central panel wall 16, a countersink groove 18, a flange 20 and a countersink wall 22. The central panel wall 1 6 incorporates an integral rivet 28 which takes an opening tab 30 to tear strip 31 formed by a score line in the wall.

The configuration of the present container end 10 is contrasted with a prior container end in Fig. 2, the latter end being shown in underlay closely hatched to emphasize the distinguishing features which will be clearly apparent to the addressee.

Before seaming, the prior art container end 110 has its central panel wall 11 6 domed upwardly with a doming radius Rd. The central panel wall is surrounded by peripheral countersink groove 11 8 formed with a countersink radius Re. The flange 1 20 of the end, which is radially outwards of the groove, has a curled lip 1 34 and an incurve 1 32. The countersink wall 1 22 merges with the flange incurve 1 32 and with the countersink groove.It should be noted that the countersink wall 1 22 is bowed inwardly i.e. is inwardly convex with respect to the centre of the end 11 6 at its upper extremity where it merges with the rim incurve 1 32 and is bowed outwardly (outwardly convex) at its lower extremity where it joins the countersink groove. A point of inflection 1 40 occurs in the region of the midpoint between the rim 1 34 and the groove 118.

The configuration of the prior art end 11 6 after joining to the wall of a container, after filling, is shown in Fig. 4. Countersink wall 1 22 remains bowed outwardly along its lower portion, but otherwise is generally flattened as seen in this sectional view, after seaming to the can body 112.

The domed buckle resistant end 10 according to the invention, taken along line 5-5 of Fig. 1, is shown in Fig. 5. The end is joined to the wall of a tubular container body 1 2 by means of a double seam 1 4. The central panel wall 16, which is prominently domed upwardly, is surrounded by a countersink groove 18 which in turn is joined to rim 21 by countersink wall 22. The end has an integral rivet 28 which stakes opening tab 30 to a tear strip 31 in the end panel. Metal stock 0.0100" to 0.0135" thick (0.25 to 0.34 mm) can be used to form the end 10.

While it is preferable that the end panel be provided with an accentuated dome, certain tab and tear strip configurations require a flush panel structure.

In Fig. 6 the preferred embodiment is shown in detail prior to seaming. The container end 10 has a flange 20 with an outer lip 34 and an incurve portion 32. The countersink wall 22 is bowed inwardly along its entire length from the region wherein it merges with the incurve portion 32 to the point where it joins the countersink groove 1 8. The inwardly bowed countersink wall is characterized by an inner surface 42 which is in tension and an outer surface 44 which is in compression.

The countersink groove 1 8 is joined to the central panel wall 1 6 by way of inner wall 54.

The groove has a root 38, an outer radius R0 which joins the root with the countersink wall and an inner radius R; which joins the root with the inner wall 54. Radii R0 and R1 are unequal, R0 being approximately one half of Rj. R0 should be no more than 0.025" (0.63 mm) and it is preferable that R0 be 0.020" (0.51 mm) or less. R1 may be as small as 0.035" (0.89 mm) and may be as much as 0.045" (1.14 mm), but it is preferably that R1 be maintained about 0.040" (1.02 mm).This combination of radii set the groove width at about 0.060" (1.52 mm) which is within the groove width standards set by the United States Beverage Association. These standards call for Rc (a single groove radius) to be 0.030" + 0.005" (0.76 + 0.1 3 mm) on all flush panel and ring tab aluminium ends. This radius standard establishes a groove width ranging from 0.050" to 0.070" (1.27 to 1.78 mm).

In end buckling a stress concentration is set up wherein a portion of the central panel proximate the countersink groove 22 is caused to bulge upwardly so that the countersink wall and groove project above the rim, see Fig. 7. In the present structure, the inward bowing of the countersink wall 22 is substantially eliminated by the double seaming, as shown in Fig. 7. The resulting wall, which is generally perpendicular to the plane of the rim, acts cooperatively with the bead formed by groove radius R0 to function as a compression member in axially opposing internal container pressure. Thus, the upthrust created by internal pressure acting on the bead is very effectively combatted by the upstanding wall 22 after seaming.The groove inner radius Rj cooperates with radius Rq, a downwardly directed panel radius (or upwardly and outwardly convex portion encircling the periphery of the central panel wall) and with inner wall 54 to form a responsive interface between the central panel wall 1 6 and the outer radius R,. This responsive interface is designed to accommodate end wall movement due to pressure variation.The slope of inner wall 54 is altered slightly in response to changes in the curvature of R1 and R the preferred embodiment, the central panel wall is prominently domed with a radius R which is substantially less than the conventional doming radius Rd (Fig. 3) The reduced radius of curvature results in an end panel which is stretched beyond its yield point to form a taut wall. The metal is stretched sufficiently to resist any tendency toward "oil canning" or "snap buckling" which is characteristic of conventionally domed ends. This phenomenon is observed when a metal is in a bistable state wherein pressure, as might be exerted by ones fingers on an unseamed end, causes the wall to deflect, or invert, from a first position across a neutral plane to a second position.This deflection is generally accompanied by an audible click. The phenomenon is commonly observed with the walls of a conventional oil can. Further the stretched metal resists additional deflection when it is seamed to a container wall and subjected to internal pressure from the contents of the container. When the prominently domed end is seamed to a container body, the inward bowing of the countersink wall is substantially removed by the seaming thereby resulting in a straightened countersink wall as shown in Fig. 7. As noted above, this straightened countersink wall resists internal pressure by axial compression. Despite the increase in dome height which the reduced doming radius Rp imposes on the free unseamed end, substantial internal pressures do not cause the tab 30 to protrude above the rim of the seamed container.

To illustrate the advantage of the instant structure, 207.5 (215/321I or 63 mm) diameter ends were fabricated from Alcoa 51 82 H19 aluminium alloy plate, 0.0125" (0.32 mm) thick. Basic ends were blanked and formed to a basic end profile in a strip feed press, in a conventional manner. The basic end profile included the flange, countersink wall and countersink groove, shaped to the configuration shown in the prior art profile of Fig. 3 but the central panel was planar rather than domed. The ends were divided into two groups, group A which was processed in accordance with the practice and design of the prior art, and group B which was processed in accordance with the invention. Group A ends were converted in a 6 station conversion press to easy open ends.Doming was carried out in the last press station using a spherical doming die which produced a dome of radius Rd = 5.56" (141.2 mm) and a dome height of 0.170" to 0.174" (4.32 to 4.42 mm) with an average height of 0.172" (4.37 mm). Group A ends had a conventional countersink radius Rc = 0.030 + 0.005" (0.76+0.13 mm).

Group B ends were processed through the first five stations of the conversion press in the conventional manner but were reformed in a separate press in accordance with the present invention. The countersink groove was reformed with the aid of a control ring which encircles the doming die. The countersink groove was engaged by both the control ring and a punch, trapping the countersink groove therebetween and thereby reforming and setting the compound radius with the outer radius R0 = 0.020" and the inner radius R, = 0.040", 0.51 and 1.02 mm respectively. The control ring further engaged the countersink wall to effect the inward bowing shown in Fig. 6.The central panel wall was domed with a doming radius Rp = 4.0" and a panel radius Rq = 0.0375" 101.6 and 0.95 mm respectively, concurrently with the reforming of the countersink wall and groove.

Group B ends had a resulting dome height of 0.205"-0.210" (5.21 to 5.33 mm) with an average height of 0.2079" (5.28 mm). Ends from both groups were seamed to beverage container bodies which were then subjected to increasing internal pressures. Both Group A and Group B ends resisted internal pressure of 70 PSIG (4.92 kg/cm2) without tab projection beyond the container rim. Group A ends however exhibited buckling at pressures ranging from a low of 92.5 PSIG (6.50 kg/cm2) to a high of 97.0 PSIG (6.82 kg/cm2) with an average pressure of 94.5 PSIG (6.64 kg/cm2). In contrast the Group B ends did not exhibit buckling until pressures of 107 PSIG (7.52 kg/cm2) were reached. Some of the Group B ends resisted internal pressures as high as 116 PSIG (8.16 kg/cm2) without buckling. The average pressure required to effect buckling of Group B ends was 111.5 PSIG (7.84 kg/cm2).This increase in buckle resistance would permit the use of lighter gauge stock and still ensure good resistance to buckle failure.

It should be recognized that in commercial production reforming would be done in the final station of the conversion press along with the doming.

As an alternative to reforming a basic end, the improved countersink wall and groove configuration of the present invention may be incorporated in the basic end die. In such a case, outer radius R0 must be increased somewhat to avoid metal fracture.

While the inventive concepts have been described by way of example with respect to a 207.5 diameter aluminium end, it should be recognized that, with appropriate modification, they are equally applicable to other sizes and materials. Thus while the 207.5 end requires a doming radius of 4.0" (101.6 mm) a 209 or 211 (29/,6" or 2'1/,6", 65 or 68 mm) diameter end would permit the use of a slightly larger doming radius, between 4.0" and 4.5" (101.6 and 114.3 mm respectively). On the other hand, the dimensions for R0 and Rj remain the same for all ends between the sizes of 207.5 and 211.For optimum buckle resistance R0 should be maintained as small as possible although radii less than 0.019-0.20" (0.48 to 0.51 mm) are susceptible to fracture. Ri should be sufficiently large to enable the countersink groove to meet the appropriate standards exemplified by the United States Beverage Association requirements, and to operate cooperatively with radius Rq and the sloping inner wall 54.

Although the illustrated embodiment of the invention has been described in terms of the upper end of a container, it should be appreciated that the invention may be applied to lower ends of 3 piece containers as well.

The invention has been described in terms of an end for a beverage container but the inventive concepts are applicable to other pressurized containers.

Thus it may be seen that the invention provides a can end for containers which offers superior resistance to buckling thereby permitting the use of lighter gauge end stock, and that only minor modifications to existing equipment need be made to put the invention into practise, major retooling therefore being avoided.

The improved buckle resistant end may be employed to advantage where processing conditions require high pasturization temperatures and short process periods.

Claims

1. A container end having a central panel wall, an outer flange, and a countersink groove disposed therebetween, an inner wall joining the groove with the central panel wall and a countersink wall joining the groove with the flange, the groove having a root which arcuately joins outwardly with the countersink wall and inwardly with the inner wall, the respective outer and inner arcuate portions having radii of which the outer radius is smaller than the inner radius.

2. A container end according to claim 1, wherein the outer radius is of the order of half the inner radius.

3. A container end according to claim 1 or claim 2, wherein the countersink wall is inwardly bowed to place an inwardly-facing surface thereof in tension and the opposite, outwardly-facing surface in compression.

4. A container end according to any of claims 1 to 3, wherein the said outer radius is in the range of 0.020" to 0.025" (0.51 to 0.63 mm) and the said inner radius is in the range of 0.035" to 0.045" (0.89 to 1.14 mm).

5. A container end according to claim 1, wherein the central panel wall is strengthened by pronounced doming thereof wherein the panel wall is stretched beyond its yield point to substantially eliminate bistability, and wherein the countersink wall is inwardly bowed to place its inwardly-facing surface in tension and its opposite outwardly-facing surface in compression, and the said outer radius is of the order of one half of the said inner radius.

6. A container end according to claim 5, wherein the outer radius is in the range of 0.020" to 0.025" (0.51 to 0.63 mm) and the inner radius is in the range of 0.035" to 0.045" (0.89 to 1.14 mm).

7. A container end according to any of the preceding claims, having a domed central panel wall, the radius of the dome being from 4.0" to 4.5" (101.6 to 114.3 mm).

8. A container end according to any preceding claim, which further includes an outwardly convex portion joining the periphery of the central panel wall with the inner wall, the said portion cooperating therewith and with said inner radius of said countersink groove to form an interface between the central panel wall and the countersink groove outer radius responsive to changes in pressure when said end is seamed on a filled and pressurized container.

9. A container end according to any preceding claim, made from sheet metal 0.010 to 0.0135" thick (0.25 to 0.34 mm).

1 0. A container for pressurized fluids comprising a tubular body to which an end is joined by means of a double seam, the said end comprising an outer rim, a countersink wall generally perpendicular to the plane of the rim, a countersink groove merging via an outer arcuate portion with the base of the countersink wall, and a central panel wall, inwardly of the countersink groove, which merges via an outwardly convex portion with an inner wall which in turn merges via an inner arcuate portion with the countersink groove, the central panel wall being prominently domed with a doming radius of 4.0 to 4.5" (101.6 to 114.3 mm) to stretch the panel wall beyond the yield point, the outer and inner arcuate portions having radii within the respective ranges of 0.020" to 0.025" and 0.035" to 0.045" (0.51 to 0.63 mm and 0.89 to 1.14 mm).

11. A container according to claim 10 wherein the end is fabricated from stock having a gauge of 0.0100" to 0.0135" (0.25 to 0.34 mm).

1 2. A container end constructed and arranged substantially as herein described with reference to and as shown in Figs. 1, 2 and 5 to 7 of the accompanying drawings.

1 3. A container substantially as herein described with reference to and as shown in Figs. 5 and 7 of the accompanying drawings.

14. A container having a container end as claimed in any of claims 1 to 9 and 1 2 secured thereto.