EP2714303B1 - Method for manufacturing a metal foam provided with channels and resulting metal foam - Google Patents

Description

The technical sector of the present invention is that of the manufacture of metal foams incorporating ducts opening on either side.

These metal foams can be used in particular in heat exchangers to dissipate or diffuse heat. However, it is important to have one or more conduits passing right through the metal foam to achieve more complex exchangers for the circulation of a second fluid within the exchanger or to make preferential passages (known under the name of "Bypass").

It has already been proposed to make one or more ducts inside a metal foam. Thus, the document US-2009/0085520 proposes to perforate the foam to introduce a tube either by forcing or by providing brazing after introduction of the tube to secure it with the foam. It is understood that this way of doing involves first of all the manufacture of the metal foam, then its piercing and finally the establishment of the tube integrally with the foam. The resistance of the tube in the foam is obtained according to this document in various ways, for example by brazing, by compressing the foam on the tube, by a tight fit of the tube, etc. Finally, it is understood that this system does not allow inserting only rectilinear tubes.

The patent EP-1808241 discloses a method of producing ducts in a metal foam according to which the metal tubes are inserted beforehand in the preform before the casting of the molten aluminum or aluminum alloy or after casting. This system therefore provides for the insertion of a preformed tube.

The technology of metal foams is well known and one can refer to the patents EP-1808 241 , US 3236706 and EP-2118328 which advocate the manufacture of a preform in the form of granules from a salt, such as sodium chloride. After filling the free space between granules using a molten metal, the salt is dissolved to recover the metal foam.

Whatever the method used to obtain a conduit within a metal foam, one encounters a deteriorated conductivity at the connection between the tube and the porous medium of the foam. In addition, over time, the mechanical thin between the tube and the foam forming two parts is altered. Finally, it is currently impossible to form the conduit and the metal foam in one step and with the same material.

The object of the present invention is to provide a metal foam incorporating a through tube obtained during the manufacture of the foam itself.

The manufacture of the foam is carried out in a conventional manner from a preform of granules as described for example in the document cited below.

Indeed, the EP-2118328 describes a particularly interesting method by proposing to manufacture a preform with granules based on grain meal. This preform is then fired before pouring the metal in order to destroy the carbon chains of the granules. This patent therefore provides firstly the manufacture of a paste consisting of flour, sodium chloride and water. From this paste, granules are prepared which are then used to make the preform.

The subject of the invention is therefore a method for manufacturing a metal foam provided with at least one duct and intended in particular for the manufacture of heat exchanger from a preform of balls, characterized in that it disposes in a casting mold a core consisting of a core and a coating of fuse material at low temperature, then the preform is arranged around the core by making intimate contact with the core, and is then caused by heating the removal of the material fuse at low temperature, then pouring the molten metal mass into the mold to fill the free spaces between the balls and between the balls and the core and finally eliminating the balls.

According to a particular embodiment, the conduit is formed, after casting of the metal mass, by the metallic mass replacing the coating of wax.

According to another particular embodiment, the core core is made of ceramic, steel, sand, a soluble material or a material identical to that constituting the preform.

According to yet another embodiment, the core consists of three elements, a first element constituted by the core of ceramic, steel or sand, a second element constituted by a peripheral layer of refractory material and a third element constituted by a coating of material fuse at low temperature.

According to yet another embodiment, the core consists of four elements, a first element constituted by the ceramic core, steel or sand, a second element constituted by a peripheral layer of a refractory material, a third element constituted by a layer of a ceramic material and a fourth layer constituted by the coating of fuse material at low temperature.

According to yet another embodiment, the core is rectilinear.

According to yet another embodiment, the core is provided with curvatures.

According to yet another embodiment, the soul is tubular.

According to yet another embodiment, the fuse material at low temperature is a wax.

According to yet another embodiment, the coating comprises at its inner surface continuous or discontinuous protuberances.

The invention also relates to the metal foam obtained according to the process according to the invention being provided with at least one conduit.

Advantageously, the conduit is tubular rectilinear or curved.

Advantageously, the conduit and the foam are based on aluminum or an aluminum alloy.

A first advantage of the present invention lies in obtaining a foam incorporating a conduit of the same nature than the metal foam itself.

Another advantage of the invention lies in obtaining for the first time and simultaneously the metal foam and the duct or ducts.

Another advantage of the invention lies in the fact of obtaining a conduit of any shape, for example rectilinear, curved, or other.

Yet another advantage of the invention in the absence of harmful interaction between the conduit and the metal foam.

Yet another advantage of the invention lies in the elimination of any problem of mechanical strength or thermal conductivity between the duct or ducts and the metal foam.

• la figure 1 est une vue montrant une préforme dans laquelle est inséré un noyau,
• les figures 2-6 illustrent des coupes montrant diverses réalisations d'un noyau,
• la figure 7 est une coupe montrant une autre réalisation d'un noyau, et
• les figures 8 et 9 sont des coupes de la mousse métallique avec un conduit réalisé in situ.

Other features, advantages and details of the invention will be better understood on reading the additional description which will follow of embodiments given by way of example in relation to drawings in which:

• the figure 1 is a view showing a preform into which a core is inserted,
• the Figures 2-6 illustrate sections showing various realizations of a nucleus,
• the figure 7 is a section showing another realization of a nucleus, and
• the Figures 8 and 9 are sections of the metal foam with a conduit made in situ.

In the following description, it will be considered that the preform is made in a known manner, that is to say from agglomerated beads and that this preform is used in a known manner to manufacture a metal foam. The material constituting the metal foam is also known and may be mentioned by way of example aluminum, aluminum alloys and all known materials used in foundry. For more precision, reference may be made to the aforementioned patent.

As indicated previously, a core is inserted according to the invention within the preform which it is possible to prepare in different ways. Generally, the invention is based on the replacement of a fusible coating layer by the same material of the metal foam to make the conduit in situ.

On the view according to the figure 1 , there is shown a preform consisting of balls 1, compressed or not, in which a core 2 is disposed. This core consists of a core 3 and a coating 4. There is shown a preform 6 to extract its mold for reasons of clarity. This preform is of parallelepipedal shape in which the core 2 has been inserted according to the figure 1 . We see that all the balls 1 are in close contact with each other. The end of the coating 4 comes flush with the side wall of the preform while the core 3 is protruding. This representation is in no way limiting and the invention may also be achieved by passing the wax to create a skin or to obtain a protruding tube relative to the foam.

Of course, in the injection mold of the molten metal, it first has the core 2 with a straight or inclined position according to the needs of the user and then poured the balls. The foam is then made according to known technology that is not necessary to describe in detail. It goes without saying that it is possible to have several cores to obtain several conduits.

On the figure 2 a first embodiment of the core 2 consisting of the core 3 and the coating 4 is shown in section. The core 3 consists for example of a ceramic material, steel or sand commonly used in foundry technology. The coating here consists of a layer of wax or other low-temperature fuse material. By low-temperature fuse material is meant a material having a melting point of 40 ° C to 150 ° C. Of course, the diameter of the core and the thickness of the coating layer are dictated by the envisaged applications of the metal foam. Thus, core diameters greater than 2 mm can be envisaged and a coating thickness of 0.5 mm to 10 mm (preferably 0.5 to 3 mm) can be adopted.

In the figure, there is shown a straight core. But it goes without saying that a nucleus of any form can be realized. In this case, we will favor a soul in sand.

This preform 1 incorporating the core 2 is processed in a conventional manner to manufacture the metal foam. Thus, during the rise in temperature of the mold, the beads are agglomerated together to create the rigid preform, then the coating 4 melted and removed by simple fluid flow. The molten metal is injected in a known manner that will occupy the interstitial spaces between the balls and the free space left by the coating between the preform and the remaining core to form the conduit. After cooling, the core 3 is extracted or removed if it is sand to leave free the duct formed.

On the figure 3 , there is shown in section an alternative embodiment of the core 2 in three parts namely the core 3 on which a layer 5 of a refractory material is applied and finally the coating 4 of wax or fuse material at low temperature. The interest of this refractory material is to facilitate the release of the core after casting of the metal while the rigidity is provided by the core 3. This refractory material also increases the diameter of the final conduit without modifying the core.

On the figure 4 , the core 2 is represented according to the figure 3 whose core 3 is recessed longitudinally to present a channel 6. The advantage of this embodiment lies in the reduction of the material constituting the core 3. Another advantage of such an embodiment remains in the possibility of circulating a flow of air to improve the cooling after casting. The soul is then in the form of a tube of greater or lesser thickness.

On the figure 5 another embodiment of the core 2 in four parts is shown in section. The core 3 is covered with a layer 5 of a refractory material, itself covered with a layer of a ceramic material 7 and finally the coating layer 4. The use of the ceramic material makes it possible to increase the rigidity of the refractory material and to eliminate the potential infiltrations melted aluminum in the refractory and thus avoid micro-cracks.

On the figure 6 which represents a variant of the embodiment according to the figure 5 a hollow core 3 is provided in the form of a tube. This embodiment allows a material saving of the material constituting the soul.

All the cores previously described in connection with the figures are inserted in a preform in order to produce one or more conduits inside the metal foam. To this end, the core is placed in the mold for making the foam and then the balls are introduced ensuring a good compactness that will promote contact between all the balls. If necessary the preform is compressed.

All these cores may comprise a core of ceramic material, steel, or sand, and more generally any material used in the field of foundry. It goes without saying that when the core is made of ceramic material or steel it is in the form of a straight bar to ensure its extraction, the duct obtained being rectilinear. The core can occupy any position inside the preform and the tube can then emerge at any point of the faces of the metal foam inlet and outlet.

On the figure 7 another embodiment of the core 2 is shown, the core 9 of which has several curvatures and is covered with a coating 4 of wax or a low-temperature fuse material. In this case, the core 9 is made of sand or of a friable material. The duct obtained within the foam makes it possible to obtain a greater contact area between the fluid flowing in the metal foam and the fluid circulating in the duct.

On the figure 8 , there is shown a section of a metal foam block 10 constituted by a wire mesh 11 in which the tubular conduit 12 is formed in the free space between the balls and the core after melting of the coating. It is understood that the thickness of the duct 12 is substantially equal to the thickness of the coating layer.

We see the whole point of the present invention since the foam 10 and the conduit 12 are made simultaneously during the casting of the molten metal. They are therefore of the same nature which ensures identical conductivity at these two elements and eliminates the problems of mechanical strength.

On the figure 9 there is shown a longitudinal section at the duct 12 and it is seen that the duct 12 is completely nested in the mesh 11 of the metal foam with a confusion of the material.

On the Figures 10 and 11 , there is shown an alternative embodiment of making grooves or notches on the outer surface of the core 3 (or refractory material). Said grooves or notches being filled by means of the coating 4, thus producing continuous or discontinuous protuberances 13 at the inner surface of the coating 4, which makes it possible, during the casting of metal, to create an exchange surface arranged inside the duct to improve heat exchange. These protuberances 13 are here represented for illustrative and non-exhaustive, in the form of triangular and rectangular sections. It is obvious to those skilled in the art that they may be in other forms to promote heat exchange while preserving the flow of fluid within the conduit. An advantage of this embodiment lies in the increase of the exchange surface inside the conduit and therefore the effectiveness of the device.

In the figures illustrating the invention there is shown by way of illustration and not limited to the core, the coating and the tubing of substantially circular section, it is obvious that those skilled in the art will be able to realize the invention. using different sections, in particular oval or rectangular.

The foams according to the invention are particularly suitable for the production of heat exchangers, whatever these exchangers, liquid / liquid, or liquid / gas, or gas / gas, or phase change fluids (liquid → gas).

Claims (13)

1. A manufacturing process for a metal foam (10) provided with at least one channel (12) and intended namely for the manufacture of heat exchangers using a preform (1) of balls, characterised in that a core (2) constituted by a central core (3, 9) and a coating (4) of a material fusible at low temperature are arranged in a foundry mould, the preform (1) is then tightly arranged around the core, the fusible material is then eliminated by heating at a low temperature, then the molten metal mass is cast in the mould in order to fill the free spaces between the balls and between the balls and the central core (3, 9), and lastly the balls are eliminated.
2. A process according to Claim 1, characterised in that the channel (12) is constituted, after the metal mass has been cast, by the metal mass replacing the wax coating (4).
3. A process according to Claims 1 or 2, characterised in that the central core (3, 9) or the core (2) is formed by ceramic, steel, sand, a soluble material or a material identical to that forming the preform.
4. A process according to one of Claims 1 to 3, characterised in that the core (2) is formed of three elements, a first element constituted by the ceramic, steel or sand central core (3), a second element constituted by a peripheral layer (5) of refractory material and a third element constituted by a coating (4) of material fusible at low temperature.
5. A process according to one of Claims 1 to 3, characterised in that the core (2) is formed of four elements, a first element constituted by a ceramic, steel or sand central core (3), a second element constituted by a peripheral layer (5) of a refractory material, a third element constituted by a layer (7) of ceramic material and a fourth element constituted by the coating (4) of material fusible at low temperature.
6. A process according to one of the above Claims, characterised in that the central core is rectilinear.
7. A process according to any one of the above Claims, characterised in that the central core (2) has curves.
8. A process according to any one of the above Claims, characterised in that the core (3) is tubular.
9. A process according to any one of the above Claims, characterised in that the low temperature fusible material is a wax.
10. A process according to one of the above Claims, characterised in that the coating (4) has continuous or discontinuous protrusions (13) on its inner surface.
11. A metal foam obtained by following the process according to the above Claims and provided with at least one channel (12).
12. A metal foam according to Claim 11, characterised in that the channel (12) is in the form of a rectilinear or curved tube.
13. A metal foam according to Claim 11 or 12, characterised in that the channel (12) and foam (10) are made of aluminium or aluminium alloy.

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