The technical field of the invention is that of beverage cans, in particular carbonated beverages, based on aluminium or aluminium alloy.
Provision is made of a prior art in the field of beverage cans to solve various technical problems. For example, U.S. Pat. No. 4,685,582 by National Can Corporation is known, which describes a solution for improving the compatibility between the bottom and the cover of beverage cans with the purpose of being able to stack the beverage cans easily during their transport and their storage.
U.S. Pat. No. 5,680,952 by Ball Corporation is also known, which describes a beverage can having particular dimensions, as well as deformations on the dome of the bottom of the beverage can. There are also several documents describing convex or concave deformations on the dome of the bottom of the beverage can and/or the oblique lower edge of the bottom of the beverage can. Mention may in particular be made of U.S. Pat. No. 4,953,738 by Stirbis, patent application US 2008/0029523 by Rexam Beverage Can, or else patent U.S. Pat. No. 7,185,525 by Elmer.
U.S. Pat. No. 4,732,292 by Schmalbach-Lubeca GmbH is also known, which describes concave deformations on the bottom of the beverage can, distributed over at least two concentric circles of different diameters.
Patent application EP 0 302 412 by Pac International Inc. is also known, which describes a particular structure for the bottom of a beverage can with a series of shelves and flat parts.
Despite all these solutions, manufacturers are constantly on the lookout for cost reductions, paying particular attention to reducing the thickness of the metal alloy used for the manufacture of beverage cans. This reduction in thickness raises many problems, which can be, for example, the shaping and mechanical resistance of the beverage can (axial resistance, resistance to internal pressure, resistance to falling, etc.).
Resistance to internal pressure, which is one of the main properties sought, can be characterised by a test consisting of increasing the internal pressure (=pressure inside the beverage can). This test allows to identify two values known to the person skilled in the art: the overturning pressure, which corresponds to the maximum pressure observed when the dome is overturned, and the increase in the height of the beverage can after a typical pressure cycle (increase from 0 to 6.2 bar, then decrease to 3.5 bar). This increase in beverage can height corresponds to the residual deformation caused by the increase in pressure and which persists even after the decrease in internal pressure. As illustrated in the examples below (see
A theoretical example of such a curve is given in
A second linear stage, called stage II on the curve in
Finally a third stage, called stage III on the curve of
The axial resistance, which is another of the main properties sought, can be characterised by a test consisting in applying a vertical force downwards on the upper end of the beverage can, which is empty and without a cover, when the latter is placed vertically on a flat surface. The geometry of the bottom of the beverage can as well as the thickness of the sheet are chosen such that the location of the dramatic and irreversible deformation during the increase in the applied vertical force, characterised by an inflection of the force versus displacement curve, always takes place at the body of the beverage can and for a force greater than the values observed during the production, transport or storage of the beverage cans, namely generally 200 pounds (lbs) (which is approximately 900 Newton (N)).
In this context of reducing the thickness of the initial aluminium alloy sheet used for the manufacture of beverage cans put into perspective with the resistance to internal pressure, the inventors have developed a beverage can capable of maintaining, or even improving the resistance to internal pressure, despite the reduction in thickness of the initial aluminium alloy sheet.
Currently, initial aluminium alloy sheet thicknesses for beverage cans are generally around 260 μm in the United States and around 245 μm in Europe. The initial aluminium alloy sheet thicknesses targeted according to the present invention are of the order of 200 to 230 μm, which is approximately 6 to 18% reduction in thickness in Europe and approximately 11 to 23% in the United States.
The technical problem solved according to the present invention is therefore to reduce the thickness of the initial aluminium alloy sheet used for the manufacture of beverage cans, for example by 5 to 25% compared to what is usually practiced in the field of beverage cans (approximately 15 to 60 μm reduction), while improving the resistance to internal pressure compared to a conventional beverage can obtained from a thinned sheet and while maintaining the resistance to internal pressure compared to a conventional commercial beverage can, and while retaining satisfactory axial resistance (to vertical force).
It should be noted that the reduction in thickness of the initial aluminium alloy sheet used for the manufacture of beverage cans ultimately allows to lighten the beverage cans by 2 to 15%, knowing that the bottom of the beverage can, which retains the initial thickness of the aluminium alloy sheet, generally represents more than 30% of the total weight of the beverage can.
In addition to resistance to internal pressure, the person skilled in the art also faces problems of resistance to vertical stress during the manufacture and filling of beverage cans, as well as the crimping of the cover. It should be noted that the present invention, which allows to limit the deformations undergone by the cans during their life cycle due to the internal pressure, also has the advantage of maintaining a resistance to the vertical force with respect to a conventional commercial beverage can.
A first object of the invention is a beverage can based on an aluminium alloy, preferably for a carbonated beverage, comprising (see
characterised in that the thickness of the dome sheet is 180 to 230 μm, preferably 190 to 220 μm;
and in that the outer diameter D3 of the concave dome 1 is 36 to 44 mm, preferably 37 to 43 mm;
and in that the width of the lower ring L4 is 3 to 4.5 mm, preferably 3.3 to 4 mm; and in that the lower ring comprises concave deformations 8, distributed at regular intervals along the lower ring 7.
A second object of the invention is a method for manufacturing a beverage can according to the present invention, comprising the following successive steps:
A third object of the invention is a tool for shaping the beverage can according to the present invention.
In the description, unless otherwise indicated:
According to the present invention, the term “convex” means oriented outwardly of the beverage can.
According to the present invention, the term “concave” means oriented inwardly of the beverage can.
The beverage can according to the present invention allows to compensate for the loss of resistance to internal pressure due to a decrease in the thickness of the aluminium alloy sheet from which the beverage can is made.
In general, with current methods, the maximum internal pressure that a beverage can undergoes during its manufacturing and life cycle is considered to be approximately 6.2 bar (90 psi). Also, it is desirable for the overturning pressure to be greater than 6.2 bars, that is to say of the same order of magnitude as that of the reference beverage can (C1 in the examples below) existing on the market. The overturning pressure is the pressure at which the dome of the bottom of the beverage can is overturned. This overturn is irreversible and prevents the stability and stacking of the beverage cans on top of each other.
In addition to the resistance to internal pressure, a beverage can is also preferably resistant to the axial loading (vertical force) which occurs during the various shaping operations of the shrinkage and the vertical section of the dome, as well as during filling and crimping of the cover. It is considered, with the current methods, that the beverage can body must withstand an axial force (vertical force) greater than approximately 900 N (that is to say 200 lbs), without having any damage to the bottom of the beverage can, or to the side wall. It is generally considered that this value of 900 N represents approximately 85% of the resistance of the reference beverage can (C1 in the examples below) existing on the market.
The beverage can according to the present invention compensates for the loss of strength due to the decrease in thickness of the aluminium alloy sheet from which the beverage can is made. In general, the beverage can according to the present invention allows to limit the deformation of the bottom of the beverage can, and in particular of the dome, of the lower ring and the shime, in stage II and to push stage III (dramatic deformation) to pressure levels higher than those requested by customers, generally 6.2 bars.
The solution proposed according to the present invention comprises the combination of three features having a synergistic effect:
A first object according to the present invention is a beverage can based on an aluminium alloy, preferably for a carbonated beverage, comprising:
and in that the outer diameter D3 of the concave dome 1 is 36 to 44 mm, preferably 37 to 43 mm;
and in that the width of the lower ring L4 is 3 to 4.5 mm, preferably 3.3 to 4 mm; and in that the lower ring comprises concave deformations 8, distributed at regular intervals along the lower ring 7.
Preferably, the outer diameter D1 of the body 5 of the beverage can according to the present invention is 50 to 75 mm, preferably 55 to 70 mm.
Preferably, the radius R1 of the shoulder is 2 to 5 mm.
Preferably, the dome 1 of the beverage can according to the present invention has at least one of the following features:
Preferably, the lower ring 7 of the beverage can according to the present invention has at least one of the following features:
Regarding the lower ring, its geometry (for example its shape and diameter) can be optimised to improve performance depending on the intended applications. Likewise, the dimensions (for example height, width, radii of curvature) of the lower ring can also be optimised.
Preferably, the shime 4 of the beverage can according to the present invention has at least one of the following features:
Preferably, the connecting portion between the shime 4 and the lower ring 7 comprises at least one of:
Preferably, the connecting portion between the lower ring 7 and the rectilinear part 2 of the dome 1 comprises a radius R4 of 1 to 3 mm.
Preferably, the concave deformations 8 of the beverage can according to the present invention have at least one of the following features:
As regards the concave deformations, their shape and their number can be optimised according to the intended applications in order to gain in performance. In particular, the concave deformations extend generally and preferably beyond the lower ring in the connecting portion between the rectilinear section of the shime and the lower ring.
According to a common practice, the beverage can according to the present invention can, in certain cases, be subjected to a subsequent operation of reforming the dome, as described in
A second object of the invention is a method for manufacturing a beverage can according to the present invention, comprising the following successive steps:
A third object of the invention is a tool for shaping the beverage can according to the present invention.
As regards the manufacture of the beverage can according to the present invention, the person skilled in the art will know how to adapt the tools and parameters for shaping the bottom of the beverage can according to the present invention.
The metal used for the manufacture of beverage cans can be any aluminium alloy known to the person skilled in the art suitable for this application. For example, an AA3104 type alloy can be used. The metallurgical state of the aluminium alloy can be adapted depending on the particular application. For example, the metallurgical state can be H14, H16 or H19, as described in standard EN515 (June 1993).
For the purpose of illustrating the present invention, several preforms beverage cans were evaluated for their overturning pressure and their can height increase as a function of internal pressure. The preforms correspond to the beverage can just after the initial shaping of the bottom, without taking into account the subsequent steps of reforming the dome. The metal of the beverage cans was AA3104 aluminium alloy in an H19 metallurgical state.
To determine the overturning pressure, the height of the beverage can, measured from the base of the lower ring to the top of the beverage can must be monitored according to the internal pressure. These measurements allow to plot a curve such as that shown in
Table 1 below gives the different features of the beverage can C5.
The evaluation of the overturning pressure and of the increase in the height of the can as a function of the internal pressure was carried out using finite element digital modelling with the commercial software “LS-Dyna”, version 10.1, developed by the company Livermore Software Technology Corporation. The modelling consisted of first drawing the three-dimensional shape of the different beverage can bottoms in Computer Aided Design. The three-dimensional geometries have been discretised according to a sufficiently fine finite element mesh so that it is possible to precisely simulate its mechanical behaviour. The boundary conditions were applied to simulate the behaviour of the preform as a whole during internal pressure resistance and axial force resistance tests.
Regarding the test of resistance to internal pressure, the calculation was controlled with a constant gas flow increment, allowing to simulate:
By combining these two variables, it was possible to plot the curves, for each of the cans tested, giving the increase in the height of the beverage can as a function of the internal pressure, normalised respectively by the pressure and the height of the beverage can when the reference C1 is overturned.
Regarding the test of resistance to the axial force, the calculation was controlled with an increment of vertical displacement of the upper end of the can body, allowing to simulate:
By combining these two variables, it was possible to plot the curves, for each of the cans tested, giving the resulting axial force on the upper end of the beverage can as a function of the applied displacement, normalised respectively by the force and the displacement during the inflection of the curve of the reference C1.
The results obtained in terms of the beverage can overturning pressure and the inflection of the curve of the axial force as a function of the axial displacement, characterising the resistance to the axial force of the beverage can bottom, are given in
According to the curves of
Number | Date | Country | Kind |
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1904973 | May 2019 | FR | national |
2003379 | Apr 2020 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/FR2020/050778 | 5/12/2020 | WO | 00 |