Optimized drawing and wall ironing process of aluminum containers

Abstract

The invention relates to a manufacturing process of aluminum alloy beverage cans by Drawing-Ironing, characterized in that a friction higher between the bodymaker punch and the aluminum sheet than between the ironing die and said aluminum sheet is produced by at least one of the following specificities: An aluminum sheet with an internal surface significantly higher in roughness than the external one Ironing dies with rounded intersections between infeed as well as exit surface and the land, with a smooth surface in the working area and a short width of the land A bodymaker punch with an extra roughness and an isotropic texture. It also relates to a beverage can manufactured by such a process, and characterized in that its reflectance measured at 60 is higher than 73% just after the last ironing step.

Claims

1. A manufacturing process of aluminum alloy beverage cans comprising drawing and ironing an aluminum alloy sheet, wherein during the ironing step, a friction higher between a bodymaker punch and the aluminum sheet than between an ironing die and said aluminum sheet is produced by the aluminum sheet comprising a smooth surface aluminum sheet having a roughness Ra below 0.3 m on both sides in combination with an extra rough punch.

2. A manufacturing process of aluminum alloy beverage cans comprising drawing and ironing an aluminum alloy sheet, wherein during the ironing step, a friction higher between a bodymaker punch and the aluminum sheet than between an ironing die and said aluminum sheet is produced by the aluminum sheet comprising a smooth surface aluminum sheet having a roughness Ra below 0.3 m on both sides in combination with no internal cupper lubrication used in the process.

3. A manufacturing process of aluminum alloy beverage cans comprising drawing and ironing an aluminum alloy sheet, wherein during the ironing step, a friction higher between a bodymaker punch and the aluminum sheet than between an ironing die and said aluminum sheet is produced by the aluminum alloy sheet having an internal surface higher in roughness than an external surface, wherein the external surface, in contact with the die, has a roughness Ra below 0.3 m, and the ironing die having a rounded intersection with a radius from 0.5 to 4.6 mm between an infeed surface and a land, a rounded intersection with a radius below 1.2 mm between said land and an exit surface, a roughness Ra below 0.03 m in a working area, and a land width below 0.38 mm.

4. A manufacturing process of aluminum alloy beverage cans comprising drawing and ironing an aluminum alloy sheet, wherein during the ironing step, a friction higher between a bodymaker punch and the aluminum sheet than between an ironing die and said aluminum sheet is produced by: the aluminum alloy sheet having an internal surface higher in roughness than an external surface, wherein the external surface, in contact with the die, has a roughness Ra below 0.3 m, and the internal surface, in contact with the punch, has a roughness Ra above 0.4 m, the bodymaker punch having a roughness Ra above 0.35 m and an isotropic texture, and optionally the ironing die having a rounded intersection between an infeed as well as an exit surface and a land, with a surface in a working area having a roughness Ra below 0.03 m and with a width of the land below about 0.38 mm.

5. The manufacturing process according to claim 4 which uses no internal cupper lubrication.

6. The manufacturing process according to claim 4, wherein said ironing die has a rounded intersection with a radius from 0.5 to 4.6 mm between said infeed surface and said land, and a rounded intersection with a radius below 1.2 mm between said land and said exit surface.

7. The manufacturing process according to claim 4, wherein the ironing die has a rounded intersection with a radius from 0.5 to 4.6 mm between an infeed surface and a land, a rounded intersection with a radius below 1.2 mm between said land and an exit surface, a roughness Ra below 0.03 m in a working area, and a land width below 0.38 mm.

8. The manufacturing process according to claim 4 which uses no internal cupper lubrication, and wherein the ironing die has a rounded intersection with a radius from 0.5 to 4.6 mm between an infeed surface and a land, a rounded intersection with a radius below 1.2 mm between said land and an exit surface, a roughness Ra below 0.03 m in a working area, and a land width below 0.38 mm.

9. The manufacturing process according to claim 4, wherein the aluminum alloy sheet has an external surface, in contact with the die, with a roughness Ra below 0.3 m, and an internal surface, in contact with the punch, with a roughness Ra above 0.4 m, wherein the punch has an extra roughness characterized by a roughness Ra above 0.35 m, with an isotropic texture, and wherein the process uses no internal cupper lubrication.

10. The manufacturing process according to claim 4, wherein the aluminum alloy sheet has an external surface, in contact with the die, with a roughness Ra below 0.3 m, and an internal surface in contact with the punch, with a roughness Ra above 0.4 m, and the punch has a roughness characterized by a roughness Ra above 0.35 m, with an isotropic texture, and wherein the ironing die has a rounded intersection with a radius from 0.5 to 4.6 mm between an infeed surface and a land, a rounded intersection with a radius below 1.2 mm between said land and an exit surface, a roughness Ra below 0.03 m in a working area, and a land width below 0.38 mm.

11. The manufacturing process according to claim 4, wherein the aluminum alloy sheet has an external surface, in contact with the die, with a roughness Ra below 0.3 m, and an internal surface, in contact with the punch, with a roughness Ra above 0.4 m, wherein the punch has a roughness characterized by a roughness Ra above 0.35 m, with an isotropic texture, the process uses no internal cupper lubrication, and the ironing die has a rounded intersection with a radius from 0.5 to 4.6 mm between an infeed surface and a land, a rounded intersection with a radius below 1.2 mm between said land and an exit surface, a roughness Ra below 0.03 m in a working area, and a land width below 0.38 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents the body of a typical beverage can, with the bottom (dome) (11), the mid-wall (12) and the top-wall (13).

(2) FIG. 2 represents an ironing step with the punch (21), the die (22), the Not yet deformed zone (23), the Already deformed zone (24), the Deformation zone (25) and the Wall tension zone (26).

(3) FIG. 3 represents the working surface of ironing die, according to state of the art, with the infeed angle (1), land width (2), land angle (3), exit angle (4), the sharp intersection point between infeed surface and land (51), the sharp intersection point between land angle exit angle (61), infeed surface (7), land surface (8), exit surface (9).

(4) FIG. 4 represents the working surface of ironing die with rounded intersection, according to the embodiments, with the infeed angle (1), land width (2), land angle (3), exit angle (4), rounded intersection between infeed surface and land (5), rounded intersection between exit surface and land (6), infeed surface (7), land surface (8), exit surface (9).

(5) FIG. 5 represents the Reflectance measured at 60 in % as a function of Metal roughness:low roughness is 0.23 m and high roughness 0.49 m. The diamond point is the mean value.

(6) FIG. 6 represents the Tear-off ratio in ppm as a function of the Third ironing ratio in %, and in black for a punch roughness Ra of 0.20 m, in white for a roughness Ra of 0.47 m.

(7) FIG. 7 represents the average thickness range (maximum minus minimum values) in m as a function of the land width in mm, on the left for the mid-wall (12) (FIG. 1) and on the right for the top-wall (13) (FIG. 1).

(8) FIG. 8 represents the Reflectance measured at 60 in % as a function of the sharpness of the intersection between infeed as well as exit surface and land: 0 for a rounded intersection (5) with a radius between 0.5 to 4.6 mm and a rounded intersection (6) with a radius below 1.2 mm, 1 for sharp intersections (see FIG. 4). The diamond point is the mean value.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(9) The shiny aspect of the external wall after ironing is a key property for the quality of the visual aspect of the final product after decoration. This property can be qualitatively assessed using haze effect and image clarity.

(10) One of the most appropriated measurements to assess it quantitatively is the specular reflectance at 60 with respect to the normal of the flattened can wall. All the reflectance measurements discussed in this document have been performed on preforms of cans after ironing and washing operation similar to what is done in a can making plant.

(11) The roughness is measured according to standard NF EN ISO 4287. An isotropic texture is a texture for which roughness measurement does not depend on the measuring direction. For a roughness Ra above 0.35 m and an isotropic texture, the roughness Ra is above 0.35 m for any measurement direction.

(12) In order to solve the problem, the invention aims at increasing the friction between punch and metal and, in the same time, at reducing the friction between ironing dies and metal. Thus, a friction higher between the bodymaker punch and the aluminum sheet than between the ironing die and said aluminum sheet is produced.

(13) With this purpose, several solutions are efficient used separately or combined. A first embodiment consists in using metal, i.e. an aluminum alloy sheet, with differentiated roughness. More precisely, it means an externally smooth surface, characterized by Ra below 0.3 m, in contact with dies, and an internally rough one, in contact with the punch, characterized by Ra above 0.4 m.

(14) The main advantage of using smooth metal externally is to improve the brightness of the can, with a 60 reflectance at least of 73%. On the other hand, providing rough metal internally contributes to increase friction with the punch and, therefore, decrease tear-off rate.

(15) At a given top-wall thickness, the down gauging of the mid-wall is constraint by the ironing ratio of the third die. By using metal with differentiated roughness, specifically with higher roughness internally, the limit third ironing ratio can be increased to higher than 44% and consequently the mid-wall thickness can be reduced. A second embodiment consists in using a punch with an extra roughness characterized by Ra above 0.35 m, with an isotropic texture, compared to current cross-hatching practices, well known from the one skilled in the art. It enables to increase drastically internal friction and, as a consequence, to decrease the tear-off rate or increase the ironing ratio to higher than 44% with the same tear-off rate.

(16) With a given top-wall thickness, down gauging of the mid-wall is constraint by the ironing ratio of the third die. By using an extra rough punch, the limit third ironing ratio can be increased to higher than 44% and consequently the mid-wall thickness can be reduced. Preferably the manufacturing process of the invention is working with no internal cupper lubrication. It enables to increase the internal friction and, consequently, to decrease the tear-off rate or increase the ironing ratio at the same tear-off rate.

(17) For a given top-wall thickness, the down gauging of the mid-wall is constraint by the ironing ratio of the third die, which cannot over-pass the so-called Limit Ironing Ratio. Above this upper limit, no ironing is feasible without failure. Without any internal cupper lubrication the Limit Ironing Ratio increases such that third ironing ratios higher than 44% can be industrially performed. Consequently, the mid-wall thickness can be reduced.

(18) A variant consisting in using a smooth surface sheet on both sides does contribute to increase the tear-off rate by decreasing the friction between punch and metal. Nevertheless, such a negative consequence can be prevented by using in combination an extra rough punch or no internal cupper lubrication.

(19) A third embodiment consists in using ironing dies with rounded intersection (5) with a radius from 0.5 to 4.6 mm between infeed surface (7) and land (8), which is the working area, rounded intersection (6) with a radius below 1.2 mm between land and exit surface (9), roughness Ra below 0.03 m in the working area (see FIG. 4), and a short land width below 0.38 mm.

(20) This enables to better control the top-wall thickness, typically dividing by two the current variability, and it contributes to improve the can wall brightness, i.e. a 60 reflectance higher than 73%.

(21) The necking line efficiency is sensitive to top-wall thickness variability, higher variability inducing lower efficiency. Rounded ironing dies, with Ra below 0.03 m in the working area and/or shorter land width, typically below 0.38 mm, enables to improve the top-wall consistency and thus improve the necking line efficiency.

(22) Rounded ironing dies, with Ra below 0.03 m in the working area and/or land width, typically below 0.38 mm, enables to improve the top-wall consistency and thus reduce the top-wall thickness target for the same lower specification limit.

EXAMPLES

(23) Some examples of the described above correlation between metal, tools and manufacturing parameters on one side, and manufacturing productivity and shiny aspect of the can on the other side, have been obtained during several trial campaigns, using sheets of 3104 type alloy in the H19 metallurgic temper with a gauge of 0.26 mm, on a prototyping drawing-ironing front-end line. For each run with a fixed set of conditions, around 10000 cans are produced and occurrences of tear-off are counted. The thicknesses, the weight and the reflectance of the can preforms are measured on samples taken from the beginning, the middle and the end of the run. The first example compares several runs performed with a metal taken from the same mother coil but with two different surface finishing: one with low roughness (Ra of 0.23 m) and another one with high roughness (Ra of 0.49 m). FIG. 5 compares the impact of this symmetrical, that is to say identical on both sides, metal roughness on the can wall reflectance after ironing. Low roughness gives in average a higher reflectance. Each point on FIG. 5 is an average value per run of about 10000 cans calculated on three cans and ten measurements per can. The second example compares several runs performed with two punches with the same textured surface finishing but different roughness Ra respectively of 0.20 m and 0.47 m. FIG. 6 shows that increasing the punch roughness reduces the tear-off rate in average on several third ironing ratios. Each point on FIG. 6 is obtained with a trial of about 8000 cans with the same first and second ironing ratio. The third example concerns the variability of the wall thicknesses of the can during a run of production. FIG. 7 shows that the land width impacts the mid-wall and top-wall thicknesses: the shortest is the land size, the most focused is the distribution of thicknesses. Each point on FIG. 7 is an average of 4 measurements per can on about 30 samples taken among a run of about 10000 cans. All the runs compared have been done with the same punch but different die designs. The fourth example deals with the impact of the die design on the reflectance. FIG. 8 shows that, in average on several runs with the same punch, the dies with a rounded intersection (5) (FIG. 4) with a radius from 0.5 to 4.6 mm and a rounded intersection (6) (FIG. 4) with a radius below 1.2 mm enable to produce cans with a higher reflectance. More specifically, combining a metal with a smooth external surface (Ra below 0.3 m) and dies with rounded intersections enable to reach the highest values of reflectance (above 74%), better than the standard case by about 4%.