Patent Application
20170261272
The present invention relates to the general field of plate heat exchangers, notably plate heat exchangers with at least two fluid circuits each including one or several internal fluid circulation channels.
The invention also pertains to the manufacture of such plate heat exchangers by diffusion welding, obtained by the technique of hot isostatic pressing (HIP), the technique of hot uniaxial pressing (HUP), and/or by brazing.
Known heat exchangers typically comprise one or at least two circuits with internal fluid circulation channels. In heat exchangers with a single fluid circuit, heat exchanges take place between the circuit and the environment in which it is immersed. In exchangers with at least two fluid circuits, heat exchanges take place between the different fluid circuits.
Furthermore, chemical reactors are known which implement a continuous method according to which a small quantity of co-reactants is injected simultaneously, at the inlet of a first fluid circuit, preferably equipped with a mixer, the chemical product obtained being recovered at the outlet of said first circuit. Among these known chemical reactors, certain include a second fluid circuit, usually called utility circuit, and the function of which is to control thermally the chemical reaction, either by providing the heat necessary for the reaction, or on the contrary evacuating the heat released by it. Such chemical exchangers with two utility fluid circuits are usually called “exchanger-reactors”.
Thus, it should be noted that the present invention relates not just to the production of heat exchangers with uniquely heat exchange function but also the production of exchanger-reactors. Also, the expression “plate heat exchanger with at least two fluid circuits” is taken to mean, within the scope of the invention, not just a heat exchanger with uniquely heat exchange function but also an exchanger-reactor.
The invention thus proposes a method for manufacturing at least one plate heat exchanger with at least two fluid circuits by superimposition of several plates each including alignment patterns, as well as a plate heat exchanger with at least two fluid circuits obtained by such a method.
Existing so-called plate heat exchangers have considerable advantages compared to existing so-called tube heat exchangers, in particular the thermal performances and compactness thereof thanks to a favourably high ratio of the surface over the volume of heat exchanges.
Known tube exchangers are for example shell and tube exchangers, in which a bundle of straight or U-shaped or helix-shaped bent tubes is fixed on pierced plates and arranged inside an enclosure known as a shell. In said shell and tube exchangers, one of the fluids circulates inside the tubes whereas the other fluid circulates inside the shell. These shell and tube exchangers have a considerable volume and are thus of low compactness.
Known plate exchangers are more compact and are obtained by stacking of plates comprising channels and assembled together.
The channels are produced by stamping of plates, if need be by addition of folded strips in the form of fins, or by machining of grooves. The machining is carried out by mechanical means, for example by milling or by chemical process. Chemical machining is usually called chemical or electrochemical etching.
The assembly of the plates together has the objective of ensuring the leak tightness and/or the mechanical strength of the exchangers, notably resistance to the pressure of the fluids circulating therein.
Several assembly techniques are known and are implemented as a function of the desired type of plate exchanger. The assembly may be obtained by mechanical means, such as ties maintaining the stack tightened between two thick and rigid plates arranged at the ends. The leak tightness of the channels is then obtained by crushing of added seals. The assembly may be also obtained by welding, generally limited to the periphery of the plates, which sometimes necessitates inserting, subsequent to the welding, the exchanger in a shell to enable it to withstand the pressure of the fluids. The assembly may further be obtained by brazing, in particular for exchangers for which fins are added. The assembly may finally be obtained by diffusion welding.
The latter two techniques cited make it possible to produce particularly high performance exchangers in terms of mechanical strength. Indeed, thanks to these two techniques, the assembly is obtained not only at the periphery of the plates but also inside the exchanger.
Plate heat exchangers assembled by diffusion welding have seals that are even more mechanically efficient than the seals of exchangers obtained by brazing on account of the absence of the filler metal required for brazing.
Diffusion welding consists in obtaining an assembly in the solid state by applying a force under heat to the parts to assemble for a given time. The force applied has a double function: it enables the placing alongside, that is to say the placing in contact, of the surfaces to weld and it facilitates the elimination by diffusion creep of the residual porosity in the seals (interfaces).
The force may be applied by uniaxial compression, for example using a press equipped with an oven or simply using masses arranged at the top of the stack of the parts to assemble. This method is commonly called uniaxial diffusion welding and it is applied industrially for the manufacture of plate heat exchangers.
An important limitation of the uniaxial diffusion welding method stems from the fact that it does not make it possible to weld seals of any orientation with respect to the direction of application of the uniaxial compression force.
Another alternative method overcomes this drawback. In this other method, the force is applied via a pressurised gas in a sealed enclosure. This method is commonly called hot isostatic pressing (HIP). Another advantage of the HIP diffusion welding method compared to the uniaxial diffusion welding method is that it is more widespread at the industrial scale. Indeed, HIP is also used for the treatment by batches of foundry parts as well as for the compaction of powders.
Currently known compact exchangers also have major drawbacks, mainly in the case of plate exchangers.
A first major drawback is the manufacturing cost of the plates, in particular in the case of plates with engraved grooves. In this case, material is removed over a certain width and a certain depth following a particular direction in order to produce grooves that form the channels once the stack is produced. The engraving of the grooves may be carried out one by one, by batch or integrally depending on the technique employed and this engraving may be carried out on one or on both faces of the plates of the exchanger.
The engraving of the grooves carried out by classical mechanical machining makes it possible to obtain good dimensional tolerances but this requires a very high cost, dependent on the required quality. Chemical etching admittedly enables a certain cost reduction compared to the preceding case but which is all relative. Indeed, in relation to a given length, the cost of a channel of a plate exchanger produced by chemical etching is greater than that of a tube exchanger.
Several technical solutions make it possible to manufacture compact heat exchangers constituted of plates using different techniques such as brazing, as described for example in the international patent application WO 2008/087526 A2, or diffusion welding, such as described for example in the document entitled “Fusion reactor first wall fabrication techniques”, G. Le Marois et al., Fusion Engineering and Design, pages 61-62 (2002) 103-110, Elsevier Science B.V or instead the international patent application WO 2006/067349 A1. However, these techniques are laborious, expensive and difficult to implement in the majority of cases.
Another major drawback of diffusion welded compact plate exchangers is the lack of versatility of the constituent elements thereof. Indeed, the engraving of the grooves on one or on both faces of the plates imposes the geometry of the channels, with very few possibilities of modification during assembly. Thus, a given pattern of groove is highly dependent on the geometry of the fluid circuits of the exchanger. The only possibility of modifying this geometry (length of channels, lateral dimensions, etc.) is to manufacture other plates, which generally represents an additional design cost (CAD), validation tests, control.
Most of the inventions recorded to date concerning compact exchangers manufactured from plates do not set out clearly the means used to align the plates together.
For exchangers using parallelepiped plates, the latter are often adjusted with respect to each other by using pipes for admitting and/or extracting fluids, as described for example in the international patent applications WO 2005/073658 A1 and WO 01/07857 A1. In rare cases, the inventions give several indications of systems of patterns on the circumference of the rectangular plates to align the fluid circuits with each other, such as for example in the international patent applications WO 98/55812 A1 and WO 2013/43263 A1, or instead in the U.S. Pat. No. 6,511,759 B1.
For exchangers having a final cylindrical shape, in which the plates are discs, the latter are aligned either by a central hole, as described for example in the German patent application DE 100 31 347 A1, or by a cylindrical container put in place around the exchanger, such as described for example in the U.S. Pat. No. 5,298,337 A. Patterns are sometimes produced beforehand in the plates. The latter serve, in the majority of cases, as fixations after the manufacture of the exchanger without an explicit role being attributed to them as regards the alignment of the plates with each other, as described for example in the international patent application WO 2008/087526 A2.
The aim of the invention is thus to offset at least partially the aforementioned needs and drawbacks relative to the embodiments of the prior art, and notably those inherent in the methods for manufacturing heat exchangers with at least two fluid circuits cited previously.
The subject matter of the invention, according to one of its aspects, is thus a method for manufacturing at least one plate heat exchanger with at least two fluid circuits, characterised in that it comprises the following steps:
“Diffusion brazing” is taken to mean the usual definition for those skilled in the art, such as explained in the article “Assemblage par diffusion (soudage ou brasage)” (Assembly by diffusion (welding or brazing)), Yves BIENVENU, Techniques de l'Ingénieur, Reference BM 7747, 10 Oct. 2010.
Furthermore, the expression “hollowed out pattern” is taken to mean that the pattern may have a hollow shape, through or not, or even partially through, for example an opening or a stamped shape. The hollowed out pattern may thus be obtained by different techniques, notably such as by a method of deformation of the material without removal of material, such as stamping, and/or by a method for producing the pattern by removal of material, such as machining, laser cutting, photochemical etching, etc.
Thanks to the invention, it is possible to obtain several significant advantages compared to traditional plate heat exchangers with at least two fluid circuits. The invention makes it possible in fact both to reduce in a consequent manner the costs of manufacturing heat exchangers and to make more versatile a geometry of constituent plates of these exchangers or a set of plates with different designs. Indeed, the principle of “alignment patterns” makes it possible to produce different configurations of heat exchangers, that is to say lengths and complete patterns of the different fluid circuits, using the same sets of plates, produced thanks to the invention. The cost is thus reduced because the “generic” plates may be produced in large quantity and a simple modification of the methodology of mounting the plates with respect to each other may change the morphology of the fluid channels in a significant manner.
The method of manufacture according to the invention may further comprise one or more of the following characteristics taken in isolation or according to any technically possible combinations thereof.
The reference pattern may be or not a through pattern. Similarly, the alignment pattern(s), including the reference pattern, may be or not through patterns.
The axes of revolution of the plates each advantageously take as centre of rotation a virtual point situated on the considered surface of the plate, called “centre of rotation”, and as axis of rotation the normal to said plate passing through the centre of rotation. The axis of revolution of a plate may notably correspond to its central axis of symmetry.
Further advantageously, the distance between the centre of each alignment pattern, including the reference pattern, and the centre of rotation of the plate bearing these alignment patterns is identical for all the plates of the heat exchanger.
Also advantageously, the alignment patterns enable an indexation of the plates with respect to each other.
The grooves, intended for the circulation of fluids, may be or not through grooves. In particular, they may be produced by non-through engraving and/or by through cutting. The grooves may be or not produced by circular repetition of an angle of repetition different or not from the angle of repetition of the alignment patterns around the axes of revolution of the plates.
Moreover, the production of the grooves may be carried out simultaneously to or independently of the production of the alignment patterns, including the reference pattern, on each plate.
Furthermore, the constituent plates of the heat exchanger may comprise patterns of grooves that are identical or different for all the plates.
The plates may or not have the same transversal dimensions and/or the same thickness.
The alignment patterns, including the reference pattern, may for example have a transversal section of circular or polygonal shape, for example triangular, square, rectangular, pentagonal, hexagonal, among others.
Furthermore, step d) of assembly of the plates may comprise the following successive sub-steps:
During step ii) above, the reference pattern of the second plate may be superimposed with an alignment pattern of the first plate which may be either the reference pattern of the first plate, or another alignment pattern different from the reference pattern. Advantageously, the superimposition is carried out so as to enable the circulation of said at least two fluids from the channels of the first plate to the channels of the second plate.
After positioning of the alignment tool at the level of the coincident patterns, it is advantageous to obtain axes of revolution of the first plate and the second plate which are co-linear. Also, in order to facilitate the mounting of the plates together and to obtain this co-linearity of the axes of revolution, it is preferable to implement step iv) using at least two alignment tools.
During step ii) or step v), notably in the case of the use of plates of identical geometry, it may be possible to make the top face of the Nth plate coincide with the bottom face of the (N+1)th plate or to make the top face of the Nth plate coincide with the top face of the (N+1)th plate, by turning over the (N+1)th plate. This may depend on the geometry of the channels of the plates of the heat exchanger and/or the desired final geometry of the channels.
The alignment tool(s) may have a transversal dimension, notably a diameter, substantially equal to the transversal dimension, notably the diameter, of the alignment patterns of the plates.
The alignment tool(s) may notably have a transversal section of similar shape to that of the alignment patterns, for example circular or polygonal.
The length of an alignment tool is advantageously greater than or equal to the total length of the plates assembled together, namely at the end of step d).
Advantageously, the alignment tool(s) have a suitable shape to make it possible to align at least two plates with each other. The alignment tool(s) may notably have a cylindrical shape.
Step e) of carrying out an assembly treatment may comprise diffusion welding and/or diffusion brazing, notably by the technique of hot isostatic pressing (HIP) and/or by the technique of hot uniaxial pressing (HUP).
In an alternative, step e) of carrying out an assembly treatment may comprise brazing.
Moreover, the angle of circular repetition, called “angle of rotation”, of the reference pattern of each plate around the considered axis of revolution of the plate may be identical for all the plates.
In an alternative, the angle of circular repetition, called “angle of rotation”, of the reference pattern of each plate around the considered axis of revolution of the plate may be different for at least two of the plates, notably the totality of the plates. In this case, the value of each angle of rotation of the reference pattern to form one or more alignment patterns is advantageously a whole multiple of the value of the smallest angle of rotation among all of the angles of rotation forming the alignment patterns.
Furthermore, the method may be implemented for the manufacture of a plurality of elementary modules of plate heat exchanger, each elementary module of plate heat exchanger being obtained by means of steps a) to e),
and the method may then comprise the following step:
The elementary modules intended to be combined together to form a heat exchanger of larger size may be identical or different to each other, for example by alternation of different plates. The elementary modules may furthermore be combined in series or in parallel by connecting the channels of a module to the channels of another module. The leak tightness to finalise the assembly of the plate heat exchanger thus formed may be achieved by diffusion welding, by brazing and/or by diffusion brazing, or instead by more conventional welding techniques such as by laser welding or TIG welding or instead by addition of joints crushed by a mechanical clamping.
The production of elementary modules has the advantage of being able to manufacture and store elementary modules, then to be able to produce made-to-measure heat exchangers depending on the requirements demanded of these heat exchangers.
In addition, the plates may all have an identical shape. In an alternative, the plates may have different shapes.
The shapes of the plates may be of different types, for example circular or polygonal, for example triangular, square, rectangular, pentagonal, hexagonal, among others.
The plates may be made of metal, notably stainless steel.
In addition, each plate may comprise a locating element to make it possible to know the position of said at least one reference pattern of the plate.
The locating element may be in the form of a notch produced on the periphery of the plate.
Furthermore, the invention further relates, according to another of its aspects, to a plate heat exchanger with at least two fluid circuits, characterised in that it may be obtained by means of the method as defined previously.
The method of manufacture and the plate heat exchanger according to the invention may comprise any of the characteristics set out in the description, taken in isolation or according to any technically possible combinations thereof with other characteristics.
The invention will be able to be better understood on reading the detailed description that follows of non-limiting exemplary embodiments thereof, and by examining the figures, schematic and partial, of the appended drawings, in which:
In all of these figures, identical references may designate identical or analogous elements.
In addition, the different parts represented in the figures are not necessarily according to a uniform scale, to make the figures more legible.
With reference to
In this first embodiment of the invention, the method for manufacturing the heat exchanger 50 implements an assembly of a plurality of plates 10, such as that represented in
In this example, the heat exchanger 50 comprises a plurality of plates 10 all identical and similar to that represented in
Thus, the plate 10, represented in
Thus, each alignment pattern 11 has a disc shape going through the plate 10 and having a diameter d2.
In order to be able to locate the reference pattern 11a with respect to the other alignment patterns 11 of the plate 10, a notch 13, forming a locating element 13, has been produced on the periphery of the plate 10 at the level of the reference pattern 11a.
Furthermore,
It is thus to be noted that, in this first exemplary embodiment of the invention, the grooves 12, including the grooves 121 and 122, are pieces of ring having two opposite edges in arc of circle of which the centre is the centre O of the plate 10, the two other opposite edges being straight and aligned following a radius of the plate 10. The alignment patterns 11 are for their part situated on a circle of centre O and of radius R3, as represented in
Moreover,
Thus, starting from the centre O of the plate 10, the grooves 121 of the fluid C1 being repeated with an angle θ1 and the grooves 122 of the fluid C2 being repeated with an angle θ2+θ2′. With regard to the alignment patterns 11, they are repeated with an angle θ3.
Thus, in order to enable the alignment of the plates 10 together, a plurality of alignment tools 20 is used, each being in the form of a cylindrical rod 20 of nominal diameter d2 equal to that of the alignment patterns 11 and of length L1, as may be seen in
By way of non-limiting examples, each plate 10 may be made of metal, notably stainless steel, for example of the type X2CrNiMo17-12-02 1.4404 according to the European standard EN 10027, with a thickness e1 of the order of 0.5 mm for a diameter d1 of the order of 100 mm.
The alignment patterns 11 and/or the grooves 12 may be produced by laser cutting and, unless stated otherwise, the tolerances on the final dimensions may be of the order of ±0.05 mm. In addition, the alignment patterns 11, here 130 in number, may have a diameter d2 of the order of 2 mm, being distributed on a circle of diameter equal to around 96 mm, the angle θ3 being equal to (360/130)°.
Furthermore, for the first ring of grooves 122 of the fluid C2, the distances r′3 and r′4 may respectively be equal to around 5 mm and 8 mm, i.e. a thickness of around 3 mm. The five rings of grooves 122 of the fluid C2 all have advantageously a thickness of around 3 mm.
Moreover, for the first ring of grooves 121 of the fluid C1, the distances r′1 and r′2 may respectively be equal to around 9 mm and 13 mm, i.e. a thickness of around 4 mm. The four rings of grooves 121 of the fluid C1 all have advantageously a thickness of around 4 mm.
In addition, the separation between a ring of grooves 121 of the fluid C1 and a ring of grooves 122 of the fluid C2 is preferentially identical for the entire plate 10, i.e. r′1-r′4=1 mm. The values of the angles of repetition may then be such that ½*θ1=θ2=θ2′=6°.
In order to better visualise the stacks, said stacks will hereafter be represented with diagrams of plates 10 seen in “negative”, that is to say that the grooves 12 and the alignment patterns 11 appear in thickness whereas the remainder is empty.
Thus, by way of illustration,
Different sub-examples of assembly of the plates 10 according to the method of manufacture of the invention, to obtain various configurations of heat exchangers 50 will be described hereafter, with reference to
It is considered that each heat exchanger 50 obtained is formed by the assembly of 21 identical plates 10 superimposed on each other, with the geometric characteristics described previously. Thus, the total length L of these heat exchangers 50 after manufacture is around 10.5 mm.
In the first sub-example described with reference to
Then, once the stack finished, the channels 11a′ formed by the reference patterns 11a are all aligned, as illustrated in
In the second sub-example described now with reference to
Then, once the stack finished, the channels 121′ and 122′ formed by the grooves 121 of the fluid C1 and 122 of the fluid C2 form steps in a same direction of rotation, as illustrated in
In the third sub-example described now with reference to
It should be noted that the three sub-examples described previously are only presented for illustrative purposes and in a non-limiting manner for the invention. The combinations of stack of plates 10 to obtain heat exchangers 50, as well as the number of these plates 10, make it possible to produce a very large number of different assemblies. In particular, it may be noted that the characteristics of the channels that can be obtained with a single type of plate 10 are very varied. In the three sub-examples described, the lengths of channel are different as are the sections of passage. It is possible to provide the channels with a geometric complexity able to improve the efficiency of heat exchanges by introducing turbulence. This geometric complexity may also have an interest for mixing in the case of exchanger-reactors described previously.
With reference now to
In this second embodiment of the invention, the method for manufacturing the heat exchanger 50 implements an assembly of a plurality of plates 10a, 10a′, 10b, 10c, 10d by diffusion welding obtained by the hot uniaxial pressing (HUP) technique.
In this second example, unlike the first example described beforehand, the heat exchanger 50 comprises plates 10a, 10a′, 10b, 10c and 10d having different patterns. More specifically, the heat exchanger 50 comprises four types of plates.
Thus, the plate 10a, represented in
In addition, the grooves 121 and 122 have an identical shape, namely a straight through port shape with circular ends of a diameter equal to the width of the channel.
Taking as reference the triangle of material between the centre O of the plate 10a and two consecutive tops B and C of the plate 10a, namely the equilateral triangle OBC represented in
These grooves 121 and 122 are next reproduced by central symmetry six times by an angle of 60° with respect to the central axis X of the plate 10a. For the final symmetry, the ends of the grooves 121 and 122 do not end following the straight line OH′, as represented in
Furthermore, as may be seen in
With reference now to
The second model of plate 10b is of same dimension as the first model of plate 10a, namely with a hexagonal shape with equal sides of width L2. Similarly, the plate 10b comprises six alignment patterns 11 situated at the corners of the hexagon, the reference pattern 11a being located by an indexing mark 13 similar to that of the plate 10a, the plate 10b here having a thickness e3.
Furthermore, on one of the sides of the hexagon, the circular grooves are replaced by grooves in the form of oblong holes 123 for the fluid C1 and 124 for the fluid C2, respectively of width d6 and d7, centred following the straight line OH′. The distance following the straight line OH′ between two consecutive oblong holes 123 or 124 is d2′+d3′, and the width of these holes 123 and 124 following the normal to the straight line OH′ is 2×d5.
The third 10c and fourth 10d types of plates used in the heat exchanger 50 according to the second embodiment of the invention will now be described with reference to
These two plates 10c and 10d have the same dimensions as the preceding plates 10a and 10b, namely a hexagonal shape with equal sides of width L2. The alignment patterns 11, including the reference pattern 11a, and the indexing mark 13 are identical to those described previously for the plates 10a and 10b.
The respective thicknesses of the plates 10c and 10d are e4 and e5. In addition, the plates 10c and 10d also comprise a hexagonal central pattern M of width L3.
The plate 10c comprises a groove 12, in the form of a circular groove 12a, with a diameter d7, which is going to be superimposed on the final groove 122 of the plate 10a.
The plate 10d comprises for its part a groove 12, in the form of a circular groove 12b, of diameter d6, which is going to be superimposed on the first groove 122 of the plate 10a.
Furthermore,
By way of non-limiting examples, each plate 10a, 10b, 10c and 10d may be made of metal, notably stainless steel, for example of the type X2CrNiMo17-12-02 1.4404 according to the European standard EN 10027, with a thickness e2=e3=e4=e5 of the order of 0.5 mm for a width L2 of the order of 84 mm.
The alignment patterns 11 and/or the grooves 12 may be produced by laser cutting and, unless stated otherwise, the tolerances on the final dimensions may be of the order of ±0.05 mm. In addition, the alignment patterns 11, here 6 in number, may have a diameter d2 of the order of 2 mm, being situated at a distance d3 of the order of 2 mm from the edge of the plates.
Furthermore, the grooves 121 and 122 may be of respective width d6 of the order of 1 mm and d7 of the order of 1.6 mm. The remaining dimensions may be the following: d1′=2.7 mm; d2′=d3′=2.3 mm; d5=2.6 mm; and L3=3.4 mm.
More precisely, the stack represented in
The reference patterns 11a are thus superimposed for all the plates, apart from the second plate 10a′ for which the indexing mark 13 is then situated on another top of the hexagonal stack.
The mounting is carried out such that the straight lines OH′ described previously are all parallel with each other. Two alignment tools 20 are necessary in order to conserve the alignment of the plates together during the remainder of the manufacture.
The remainder of the manufacture of the heat exchanger 50 from the stack of
The leak tightness of the plates of the heat exchanger 50 with respect to each other is achieved by diffusion welding assisted by hot uniaxial pressing (HUP).
To do so, it is necessary to have available a press making it possible to work at high temperature under vacuum or under neutral gas.
An example of procedure of diffusion welding assisted by HUP for the examples presented above in stainless steel 316L is described below:
Obviously, this procedure is only given by way of an example in precise cases. It is in no way limiting with regard to the possible embodiments using this assembly technique.
As may be seen in
With reference to
Obviously, the invention is not limited to the exemplary embodiments that have just been described. Various modifications may be made thereto by those skilled in the art.
In particular, the invention may be applied for the production of a plate heat exchanger with changing channel geometry. In particular, it is possible to make the geometry of the fluid circulation channels change over the whole length of the heat exchanger. Indeed, it is possible to modify the angle of repetition θ3, or shift step, of the alignment patterns 11 over the whole length of the heat exchanger 50, as long as the grooves 12 of a plate are slightly facing those of adjacent plates to form a channel. This has the advantage in certain cases of intensifying the exchanges in certain critical zones whereas others do not require it.
Furthermore, the compactness and the integrity of the heat exchanger after manufacture may also be optimised by integrating the fluid collectors C1 and C2 circulating in the channels formed from the grooves 121 and 122 respectively directly during the phases of mounting the heat exchanger.
Furthermore, the hollowed out patterns represented in the examples described above correspond to through hollows formed notably by removal of material. In an alternative, the hollowed out patterns may also correspond, in totality or partially, to hollows formed without removal of material, for example by stamping. At least one continuous channel may then be formed by superimposition of at least two plates comprising such hollowed out stamped patterns, one of the plates being turned over with respect to the other and if need be shifted by a predetermined angle with respect to the other to place the stamped hollowed out patterns in at least partial superimposition.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16 52105 | Mar 2016 | FR | national |
