WO1997046340A1

WO1997046340A1 - Moulding device for a metal wall and can bodies obtained with same

Info

Publication number: WO1997046340A1
Application number: PCT/FR1997/000993
Authority: WO
Inventors: François Laurent; Chris Maycroft; Nick Ince
Original assignee: Pechiney Recherche
Priority date: 1996-06-06
Filing date: 1997-06-05
Publication date: 1997-12-11
Also published as: FR2749526A1; FR2749526B1; AU3179997A

Abstract

The invention features a moulding device (1) comprising a male element (2) and a female mandrel (3) comprising hollow cells (31) and is characterised in that said male element (2) comprises a sole plate (20), in a material less hard than that of the said metal wall or skirt (5), and embossed elements (21, 210) of predetermined shape and height, co-operating with said hollow cells (31) to form recessed patterns (41) on said metal wall or skirt (5), in a material harder than that of said metal wall or skirt (5), such that recessed patterns (41) of predetermined profile and height are obtained.

Description

DEVICE FOR MOLDING A METAL WALL AND BOX BODIES OBTAINED WITH THE DEVICE

FIELD OF THE INVENTION

The invention relates to the field of molding metal walls, in particular the metal walls of rigid packaging, or those intended to form rigid packaging.

STATE OF THE ART

The molding of metal walls, and more particularly that of the skirts of metal containers, is intended to improve the mechanical characteristics of these walls or skirts, typically the resistance to external pressure and the resistance to vertical force.

The resistance to external pressure is necessary in order to limit the deformations which may result from the differential pressure to which said walls or skirts of containers are subjected during in particular the sterilization of the containers. The resistance to vertical force is necessary in particular to ensure the stacking of the containers over a great height without deformation of the containers, during the transport or the storage of the containers.

The potential improvement in the mechanical performance of these walls or skirts, in particular the improvement in resistance to external pressure, can also make it possible, at a constant level of mechanical performance, to reduce the thickness of these walls or skirts, and therefore the cost of the metal in the containers.

The shape of the moldings can be varied as taught in the German application DE 29 44 134 Al or in the European application EP 0 441 618 Al.

As described in these two documents, the moldings are generally formed by compression of the wall or skirt to be molded between two dies, dies which may be made of elastic material.

PROBLEM

PLACEMENT SHEET (RULE 26) The problem posed is the development of a molding device allowing the improvement of the mechanical performance and / or the reduction in thickness of the walls or skirts of the containers, to a degree greater than that which the state of the technique, state of the art which essentially discloses two-dimensional shapes or designs of particular moldings or intaglio patterns.

DESCRIPTION OF THE INVENTION

According to the invention, the device for molding a metal wall comprises, for the purpose of compressing and shaping said wall, a male element and a female mandrel comprising hollow cells with a rim and of predetermined shape, and is characterized in that that said male element comprises a sole, of a material of mechanical resistance lower than that of said metal wall, intended to compress said wall against said flange, and elements in relief of predetermined shape and height, cooperating with said hollow cells to form recessed patterns on said metal wall, in a material of greater mechanical strength than that of said metal wall, so that recessed patterns of predetermined profile and height can be obtained.

Thus, the invention, while aiming at the same goal as that of the state of the art, does not relate to the two-dimensional design of moldings or recessed patterns as such, but relates to a device allowing, whatever the selected two-dimensional drawing, to obtain hollow patterns with predetermined profile. In fact, the Applicant has found that mastering the profile of the hollow patterns, by virtue of the device according to the invention, allows optimization of the profile in order to solve the problem posed.

The Applicant has indeed studied the molding devices and processes of the state of the art and has observed that they do not allow the control of the profile to the extent that, whatever the shape and nature of the dies (steel or plastic), generally sinusoidal shapes were obtained as shown in FIG. 2a of the application DE 29 44 134 Al or in FIG. 2-B of the application EP 441 618 Al. In contrast to these sinusoidal forms, the invention makes it possible to obtain recessed patterns of any profile which may in particular include flat parts as shown in FIGS. 3 a and 5b.

According to a hypothesis put forward by the applicant, this result comes from the fact that, during the compression of the metal wall between the male element and female mandrel according to the invention, the male element, due to its double structure, with a sole “ soft ”and“ hard ”relief elements, also plays a double role: while the relief elements deform said wall by forcing it inside said hollow cells, the sole compresses said wall against the edges of the hollow cells of the female mandrel, and thus plays a role of blank holder to both ensure that the said wall is held and allow the localized flow of the metal if necessary, so as to form recessed patterns without breaking the metal. According to the applicant, the results obtained are therefore more particularly due to the combination of the two characteristic means of the male mandrel according to the invention, and in particular to the presence of a sole whose relative hardness allows it to outsmart a role of blank holder .

These are the hollow cells of said female mandrel which, by their shape or their arrangement, will impose the shape of said hollow patterns formed on the metal wall to be molded. These cells can be of any shape, and not necessarily identical. When they are identical and when they lead to total paving of the metal wall. they are necessarily hexagonal in shape.

DESCRIPTION OF THE FIGURES

Figure la is an axial sectional view of the device (1) according to the invention. This device includes:

- a cylindrical female mandrel (3), at the upper part of the figure, the external surface of which is provided with hollow cells (31) separated by a flange (32), and in particular with an integer number n of cells according to the circumference of said mandrel (3), the number n being less than the number m of hollow patterns to be formed on the circumference of said skirt (5), as appears in the figure, since the female mandrel (3) is placed at the 'interior of said skirt (5). - a male element (2), represented as a flat track - but which could be a circular track of great curvature, comprising a metal support (22) ensuring a precise positioning of elements in relief (21) - here steel pins (210), the surface between said pins (210) being occupied by a layer or sole (20) of material of low relative hardness and having a certain elasticity, and the relative height of which relative to the head (21 1) is adjusted by a metal shim (23) of selected thickness. As shown in FIG. 1 a, any part of the skirt (5) is either subjected to the deformation action of said pins (210), or kept pinched between said flanges (32) of the female mandrel (3) and the sole ( 20) of the male element (2). The molding device comprises means - not shown in the figure - so that a relative movement between male element (2) and female mandrel (3) is produced so as to have at least one complete rotation of the cylindrical skirt (5) between male element (2) and female mandrel (3), and so that, during the rotation of the female mandrel (3), the hollow cells (31) coincide with said pins (210) of the male element (2).

Figure 1b is a top view of the male mandrel (2) where it appears ordered rows of pins (210) standing vertically on a base (20), and the head (211) of which can be seen.

Figures 2a and 2b are axial sections of cylindrical pins (210) with head (21 1) plane in Figure 2a and rounded in Figure 2b.

Figures 3a and 3b show, for the same two-dimensional geometric pattern, the profile obtained with a device according to the invention in Figure 3a and according to a device of the prior art in Figure 3b.

Figure 4 is a side view of a cylindrical skirt (5) molded by recessed patterns (41). In this figure have been indicated the axial direction (52) of the skirt (5), the circumference (51) of the skirt (5) and the upper (53) and lower (54) ends of the skirt (5). FIGS. 5a and 5b correspond to a detailed view of the hollow patterns (41) in FIG. 4.

FIGS. 5a and 5b, which are respectively a top view and a sectional view of patterns (4), show the paving of the external surface of the skirt by patterns (4) having here the shape of hexagons.

Each pattern (4) includes a flat edge (42), and a recessed pattern (41). The recessed pattern (41) itself comprises a sloping edge (43) and a planar bottom (420) circular as obtained with metal pins (210) with head (21 1) plane.

DETAILED DESCRIPTION OF THE INVENTION

The device according to the invention is therefore characterized by a male element comprising two specific elements, a sole (20) and elements in relief (21) which can be pins (210).

Said sole (20), which must be made of a material of less mechanical resistance, typically of less hardness, than that of the material constituting the skirt (5) - or the strip of planar metal - to be molded, may also have a certain elasticity. Preferably, said sole is made of plastic material with a Shore hardness at least equal to 50, and preferably less than 120.

This plastic material can be filled with fillers intended to limit wear.

It is also possible to use a metal sole of low relative hardness, for example lead, or any alloy of low relative hardness.

Said raised elements (21) are generally pins (210) of steel, the head (211) of which is intended to cause said metal wall of the skirt (5) to penetrate into said hollow cells (31) of the female mandrel (3) and thus to conform as desired the base (410,420) of said hollow patterns (41). It has been found advantageous, in order to solve the problem posed, for said head (21 1) to comprise a planar portion, so that said base of said recessed patterns is planar, but, according to another method, this head may also have the shape of a cap. The shape of said pin, and in particular its section - here shown as circular - can be arbitrary depending in particular on the shape of the two-dimensional design of the patterns (4). In the case where this drawing consists of a paving of hexagons, the pawn is preferably cylindrical.

The device according to the invention is not limited to a particular two-dimensional design and can therefore be used to produce any type of intaglio pattern. In particular, it is suitable for molding consisting of a tiling of contiguous patterns (4). In this case, said corresponding female mandrel (3) comprises a juxtaposition of hollow cells (31) separated by said flange (32). Preferably, in order to contribute to solving the problem posed, it is advantageous that said rim is planar and has a width of between 1 and 5 mm.

Thus, in the case where it is desired to obtain hexagonal hollow patterns (41) as illustrated in FIGS. 4, 5a and 5b, said female mandrel (3) comprises said hollow cells (31) of hexagonal section.

The device according to the invention can be used either for molding said metal wall in the case where it is constituted by a flat metal strip or for molding a skirt (5) of a box body, as shown in FIG. . For molding boxes bodies, it would also be possible to use a circular, non-planar male element as shown in FIG.

In the case of molding of a very long metal strip, the device (1) of FIG. 1a can be modified, for example by transforming the male element (2), shown as a plane in FIG. 1a, into circular male element, so as to circulate the metal strip to be molded between a male element and a female mandrel, both circular.

For molding metal strips in short format, one can use a flat male element having the dimensions of said format.

Generally, a person skilled in the art knows how to adapt the device of the invention to the particular molding conditions encountered.

SUBSTITUTE SHEET (RULE 28) The device according to the invention is used for molding any metal wall intended, in particular, to form 2-piece or 3-piece box coips of metal chosen from iron and alloys, tinplate, TFS, steel, l aluminum and alloys. The term “can body” includes in particular bodies of cans or beverage cans, or alternatively aerosol cans.

Another object of the invention consists of a coips of boxes with a molded skirt obtained with the device according to the invention and comprising patterns (4), of surface S, periodic at least according to the circumference of said skirt (5), comprising a flat rim (42), of surface S ', delimiting a hollow pattern (41) with a flat bottom (420), of surface S "and of depth H, said flat rim (42) and said flat bottom (420) being connected by a sloping edge (43).

The body of molded skirt boxes (5) may include periodic patterns along the circumference of said skirt and in the axial direction of said skirt.

The body of boxes with molded skirt may comprise a juxtaposition of recessed patterns of variable depth along the axial direction (52) of said box body, said depth being the greatest on the central part of the box body and being the smallest towards each of the upper (53) and lower (54) ends of said skirt (5), so as to facilitate crimping of the cover or covers.

In the body of boxes with a molded skirt according to the invention, the depth H / section S ratio of said periodic pattern (4) is preferably between 0.003 and 0.02, H being measured in mm and S in mm ² . When this ratio is too low, the molding loses efficiency in solving the problem posed, and, when it is too high, the risk of damaging the metal wall or its protective coating increases.

In the box-skirted box body according to the invention, the ratio S "/ S is preferably between 0.10 and 0.70, and in which the ratio S '/ S is preferably between 0.10 and 0.50. Indeed, with regard to the ratio S "/ S, relating to the proportion of the background plane (420), its lower limit is fixed by the loss of molding efficiency, and its limit superior by the fact that the slope edge (43) has a slope

SUBSTITUTE SHEET (RULE 2δ) too strong, with risk of damaging the metal wall or its protective coating.

With regard to the S7S report, relating to the proportion of planar edge (42), the lower limit is a technical limit imposed by the edge (32) of the hollow cells (31) of the female mandrel (3) and the upper limit is imposed by the loss of molding efficiency to solve the problem.

Typically, the box-skirted box body according to the invention has recessed patterns (41) whose said depth H is preferably between 0.5 and 1.5 mm. The lower height limit H is imposed by the loss of effectiveness of the molding to solve the problem posed and the upper limit is imposed jointly by the risk of damage to the metal wall or its protective coating, and the loss of efficiency molding to solve the problem. .

EXAMPLE OF IMPLEMENTATION

The device shown in FIGS. 1a and 1b was manufactured, and intended for molding skirts (5) of bodies of TFS steel boxes 0.155 mm thick, of height h equal to

1 10.15 mm and diameter 73 mm. The male element (2), planar, has substantially the same width as the height h of the skirt (5) to be molded. It consists of a frame (22) on which rests a composite sole pierced with holes intended to receive the steel pins (210) of hardness greater than that of the skirt (5).

The composite sole consists of a thickness adjustment shim (23) and a sole (20) of polyurethane elastomer with Shore hardness equal to 91, 5 mm thick.

The pins (210), with flat heads, were arranged in staggered rows, each being the center of a hexagon, except of course on the lateral edges. They are arranged over a width h and over a length equal to the circumference of the skirt. The female mandrel consists of hollow hexagonal cells (31), two parallel sides being spaced 12 mm apart, the flange (32) between two hollow cells being plane with shelving edges, and having a width of 3 mm, and the distance between the center of two hollow cells in the axial direction being 14.6 mm.

By rolling the female mandrel (3) capped with the skirt (5) on the flat male element (2) with the pressure imposed by the deformation of said metal skirt and said elastomer, skirts (5) are molded conforming in Figure 4 showing 7 recessed patterns along the height h of the skirt (5) and 8 staggered patterns along a circumference (51) of the skirt.

With this type of device according to the invention, the height H of the recessed patterns (41) has been varied, having played on the thickness of the shim (23) of the male mandrel (2), H varying by 0.3 1.4 mm,

COMPARATIVE EXAMPLES

The same female mandrel (3) with flat rim (32) 3 mm wide was used for the two comparative examples according to the prior art.

As regards the male element, and according to the first comparative example, the elastomer sole and the steel pins of the male element (2) according to the invention are replaced by a continuous sole made of the same polyurethane elastomer, but without the presence of steel pins (210).

According to the second comparative example, the elastomer sole and the steel pins of the male mandrel (2) according to the invention are replaced by a steel sole with steel pins with a flat head.

RESULTS OBTAINED

The same 0.155 mm thick TFS skirts were molded with the device according to the invention, and with the devices according to the prior art.

As regards the profile of the patterns obtained, the profiles obtained with the device according to the invention are effectively of predetermined shape by the proper shape of the flange (32) of the female mandrel (3), by the shape of the head (21 1 ) steel pins (210), and by the height H chosen and are therefore of the type shown in FIG. 3a. By comparison, the profiles obtained with the devices according to the prior art are of the sinusoidal type as shown in FIG. 3b, even with a flat edge (32) and a flat head (21 1).

Note that with the device according to the first comparative test, it is not possible to obtain hollow patterns (41) of depth greater than 0.4 mm without the risk of breaking the metal, the metal rupture being frequent for a depth greater than 0.7 mm, which makes any production at this depth impossible.

In addition, the edges to be crimped are pleated, which creates a risk of leaks during crimping.

On the other hand, with the device according to the invention or with that corresponding to the second comparative test, the ruptures of metal only occur beyond a depth of

1.5 mm.

The bodies of boxes formed from the molded skirts thus obtained were examined on the one hand in resistance to external pressure, and on the other hand in resistance to vertical force.

The resistance to external pressure (PE expressed in MPa) and the resistance to vertical force (EV expressed in daN) were measured:

Results obtained under resistance to external pressure: example according to First test Second hollow test comparative comparative invention 0.3 mm 0.085 0.084 0.4 mm 0.109 0.100 0.10 0.5 0.5 mm 0.135 0.129 0.1 1.16 0.6 mm 0.146 0.140 0.19 0.7 mm 0.152 0.163 0.141 1 mm 0.172 ~ 0.16 1.2 mm 0.159 - 0.097 1.4 mm 0.122 - 0.101

It is reasonable to think that these results are linked to the profile of the hollow patterns, being dominated that the same female mandrel was used for the three series of tests. In in particular, the presence of a flat bottom (420) and a flat edge (42) (see FIG. 3a) could explain the improvement in the resistance to external pressure. On the other hand, the results obtained according to the invention, as regards the resistance to external pressure, are little different from those obtained with a circular molding of commercial containers.

Results obtained withstand vertical effort: there is no significant difference between the example according to the invention and the comparative tests:

Pattern depth common value of resistance to vertical force 0.3 mm 500

0.4 mm 490

0.5 mm 475

0.6 mm 460

0.7 mm 450 1 mm 425

1.2 mm 400

1.4 mm 370

Contrary to the results obtained in resistance to external pressure, the results obtained according to the invention in resistance to vertical force are approximately 2 times superior to those obtained with a standard circular molding (230 daN for a metal thickness of 0.155 mm).

OTHER EXAMPLES ACCORDING TO THE INVENTION

We repeated a series of tests according to the invention similar to the previous series, but differing in that the pins (210), instead of being with a flat head (FIG. 2a), were with radiated head (FIG. 2b) .

In this case, the results obtained are, with respect to the results obtained with the device according to the invention provided with pawns with flat heads, slightly lower in behavior. Other tests were carried out according to the invention

ADVANTAGES OF THE INVENTION

REPLACED SHEET JT (RULE 28) The invention makes it possible to manufacture rigid packages, typically bodies of cylindrical boxes, having hollow patterns (41) of depths greater than 0.5 mm, and this, up to 1.5 mm, without risk of breakage. metal, without damaging the inner protection or deformation of the crimping edge. It thus makes it possible to achieve high values of resistance to external pressure, while retaining a very good level of resistance to vertical force.

All of these results therefore make it possible to manufacture rigid containers with improved mechanical performance and / or to reduce the thickness of metal (at constant mechanical performance).

Claims

1. Device (1) for molding a metal wall or skirt (5) comprising, in order to compress and shape said wall, a male element (2) and a female mandrel (3) comprising hollow cells (31 ) with a rim (32) and of predetermined shape, and characterized in that said male element (2) comprises a sole (20), made of a material of hardness less than that of said metal wall or skirt (5), intended to compress said wall against said rim, and elements in relief (21, 210) of predetermined shape and height, cooperating with said hollow cells (31) to form recessed patterns (41) on said metal wall or skirt (5), of a material of hardness greater than that of said metal wall or skirt (5), so that it is possible to obtain hollow patterns (41) of predetermined profile and height.

2. Device according to claim 1 wherein said sole (20) is made of plastic material of Shore hardness at least equal to 50, and preferably less than 120.

3. Device according to claim 2 wherein said raised elements are steel pins (210) whose head (21 1) is intended to penetrate said metal wall or skirt (5) in said hollow cells (31) and conform the base (410,420) of said hollow patterns.

4. Device according to claim 3 wherein said head (21 1) comprises a planar portion, so that said base of said recessed patterns is planar (420).

5. Device according to any one of claims 3 and 4 wherein said pin (210) is cylindrical, with a planar end or not.

6. Device according to any one of claims 1 to 5 wherein said female mandrel (3) comprises a juxtaposition of hollow cells (31) separated by said flange (32), said flange (32) being plane and having a width between 1 and 5 mm.

7. Device according to claim 6 wherein said hollow cells (31) are of any section, and preferably of hexagonal section.

8. Use of the device according to any one of claims 1 to 7 for molding said metal wall formed by a flat metal strip, or said skirt (5) of a box body or container to be molded.

9. Use according to claim 8 wherein said metal wall or said skirt (5) is intended, in particular, to form bodies of 2-piece or 3-piece boxes made of metal chosen from iron and alloys, tinplate, TFS , steel, aluminum and alloys, said bodies of cans comprising bodies of cans, beverage cans and aerosol cans.

10. Box body with molded skirt obtained with the device of any one of claims 4 to 7 comprising patterns (4), of surface S, periodic at least along the circumference of said skirt (5), comprising a flat rim (42), of surface S ', delimiting a recessed pattern (41) with a flat bottom (420) of surface S "and of depth H, said flat edge (42) and said flat bottom (420) being connected by an edge slope (43).

1 1. Box body with a molded skirt according to claim 10 comprising periodic patterns (4) along the circumference (51) of said skirt (5) and in the axial direction (52) of said skirt.

12. Box body with molded skirt according to claim 11 comprising a juxtaposition of patterns (4) having recessed patterns (41) of variable depth along the axial direction (52) of said box body, said depth being the greatest on the central part of the box body and being the lowest towards each of the upper ((53) and lower (54) ends of said skirt (5).

13. Box body with molded skirt according to any one of claims 11 and 12 in which the depth H / section S ratio of said periodic pattern (4) is between 0.003 and 0.02, H being measured in mm and S in mm ² .

14. Box body with a molded skirt according to claim 10, in which the ratio S "/ S is between 0.10 and 0.70, and in which the ratio S7S is between 0.10 and 0, 50.

15. Box body with molded skirt according to claims 10 to 14 wherein said depth H is between 0.5 and 1.5 mm.

16. 2 or 3-piece can body according to any one of claims 10 to 15 made of metal intended to form 2-piece or 3-piece can bodies and chosen from: tinplate,

TFS, steel, aluminum.