WO2012160275A1

WO2012160275A1 - Method for manufacturing a metal foam provided with channels and resulting metal foam

Info

Publication number: WO2012160275A1
Application number: PCT/FR2012/000206
Authority: WO
Inventors: Frédéric POGGI
Original assignee: Filtrauto
Priority date: 2011-05-25
Filing date: 2012-05-23
Publication date: 2012-11-29
Also published as: EP2714303A1; MX2013013665A; US20140186652A1; CA2837151A1; EP2714303B1; FR2975613A1; FR2975613B1; CN103930223A; JP2014515989A; BR112013030172A2; CN103930223B; KR20140033163A

Abstract

The invention relates to a method for manufacturing a metal foam provided with at least one channel and intended, in particular, for the manufacture of a heat exchanger from a preform (1) of beads. A central portion (2), consisting of a core (3) and a coating made of a low-temperature meltable material is arranged in a casting mold, then the preform is arranged around the central portion while establishing close contact with said central portion, the low-temperature meltable material is then removed via heating, the molten metal mass is then poured into the mold in order to fill in the free spaces between the beads and between the beads and the core (3), and then the beads are finally removed.

Description

PROCESS FOR MANUFACTURING METAL FOAM PROVIDED WITH CONDUITS AND METALLIC FOAM THUS OBTAINED

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 in order 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 holding 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 the insertion of straight tubes.

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

The technology of metal foams is well known and reference may be made to EP-1808241, 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 link ¹ between the tube and the porous medium of the foam. In addition, over time, the mechanical strength between the tube and the foam forming two parts is impaired. 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, patent 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 producing a heat exchanger from a ball preform, 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 method 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.

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:

FIG. 1 is a view showing a preform into which a core is inserted,

FIGS. 2-6 illustrate sections showing various embodiments of a core,

Fig. 7 is a sectional view showing another embodiment of a core, and

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.

In the view according to Figure 1, there is shown a preform consisting of the 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 FIG. 1. It can be seen that all the balls 1 are in intimate contact with one another. 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 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.

FIG. 2 shows in section a first embodiment of the core 2 consisting of the core 3 and the coating 4. 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 fusible 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.

FIG. 3 shows 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 fusible 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.

FIG. 4 shows the core 2 according to FIG. 3, the core 3 of which 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 cooling after casting. The soul is then in the form of a tube of greater or lesser thickness.

In Figure 5, there is shown in section another embodiment of the core 2 in four parts. 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.

In FIG. 6, which shows a variant of the embodiment according to FIG. 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. For this purpose, the core is placed in the mold for manufacturing 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 metal foam inlet and outlet.

In Figure 7, there is shown another embodiment of the core 2, the core 9 has a plurality of curvatures and covered with a coating 4 of wax or a fuse material at low temperature. 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.

FIG. 8 shows a section of a block of metal foam 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.

In Figure 9, there is shown a longitudinal section at the duct 12 and we see that the duct 12 is completely nested in the mesh 11 of the metal foam with a confusion of the material.

In 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.

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

1. A method of manufacturing a metal foam (10) provided with at least one conduit (12) and intended in particular for the manufacture of heat exchanger from a preform (1) of balls, characterized in that a core (2) consisting of a core (3, 9) and a coating (4) of fuse material at low temperature is placed in a casting mold, and then the preform (1) is arranged around the core, producing an intimate contact with this core, then the heating is caused by heating the fuse material at low temperature, then the molten metal mass is poured into the mold to fill the free spaces between the balls and between the balls and the core ( 3, 9) and the beads are finally eliminated.

2. Method according to claim 1, characterized in that the conduit (12) is formed, after casting of the metal mass, by the metal mass replacing the coating (4) of wax.

3. Method according to claim 1 or 2, characterized in that the core (3, 9) of the core (2) is made of ceramic, steel, sand, a soluble material or a material identical to that constituting the preform.

4. Method according to one of claims 1 to 3, characterized in that the core (2) consists of three elements, a first element consisting of the core (3) ceramic, steel or sand, and a second element constituted by a peripheral layer (5) of refractory material and a third element constituted by a coating (4) of low temperature fusible material.

5. Method according to one of claims 1 to 3, characterized in that the core (2) consists of four elements, -a first element consisting of the core (3) ceramic, steel or sand, a second element consisting of a peripheral layer (5) of a refractory material, a third element consisting of a layer (7) of a ceramic material and a fourth layer constituted by the coating (4) of low temperature fusible material.

6. Method according to one of the preceding claims, characterized in that the core (2) is rectilinear.

7. Method according to any one of claims 1 to 3, characterized in that the core (9) is provided with curvatures.

8. Method according to any one of the preceding claims, characterized in that the core (3) is tubular.

9. Method according to any one of the preceding claims, characterized in that the fuse material at low temperature is a wax.

10. Method according to any one of the preceding claims, characterized in that the coating (4) has at its inner surface protrusions (13) continuous or discontinuous.

11. Metal foam obtained according to the method according to any one of the preceding claims provided with at least one conduit (12).

12. Metal foam according to claim 11, characterized in that the conduit (12) is of tubular rectilinear or curved shape.

13. Metal foam according to claim 11 or 12, characterized in that the duct (12) and the foam (10) are based on aluminum or an aluminum alloy.