JP2014515989A - Method for producing metal foam with channels and metal foam thus produced - Google Patents

Abstract

The present invention relates to a method for producing a metal foam (10) comprising at least one channel (12) and using a ball preform (1), ie for the production of a heat exchanger.
A cast core (2) constituted by a central core (3, 9) and a coating of cold soluble material (4) are placed in the casting mold, and the preform (1) is then placed tightly around the core The soluble material is then removed by heating at a low temperature, and then a molten metal mass is cast into the mold to fill the free space between the balls and between the balls and the central core (3), and finally the balls Is removed.

Description

  The technical scope of the present invention is that of manufacturing metal foam that incorporates open channels on both sides.

  These metal foams may be used in particular heat exchangers to dissipate or circulate heat. However, the opposite from one side of the metal foam is to produce a more complex exchanger that allows a second fluid circulation or a preferred passage (known as a bypass) to be formed within the exchanger. It is important to have one or several channels that pass to the side.

  It has already been proposed to provide one or more channels inside the metal foam. Thus, the document US 2009/0085520 proposes perforating the foam to introduce the tube by press fitting or brazing after introducing the tube and integrating the tube with the foam. doing. It will be appreciated that this technique requires first the manufacture of the metal foam, then its perforation, and finally the installation of the tube integrally with the foam. According to this document, the tube is held in place in the foam in various ways, for example by brazing, compressing the foam around the tube, by an interference fit of the tube. Finally, it is understood that this system only allows the insertion of straight tubes.

  EP 1808241 discloses a method of manufacturing a channel through a metal foam, whereby the metal tube is preformed before the molten aluminum or aluminum alloy is cast or after it is cast. Inserted into. This system provides for the insertion of preformed tubes.

  Metal foam technology is well known and EP 1808241, U.S. Pat. No. 3,236,706, and EP 2138328 recommend making preforms in the form of salt-based granules or balls such as sodium chloride. Documents may be referenced. Later, the free space between the granules is filled with molten metal and the salt is dissolved to recover the metal foam.

  Whatever the method used to obtain the channels in the metal foam, the problem of reduced conductivity at the junction between the tube and the porous media of the foam is encountered. Furthermore, over time, the mechanical strength between the tube forming the two parts and the foam changes. Finally, to date, both channels and metal foams cannot be formed in a single operation using the same material.

US Patent Application Publication No. 2009/0085520 European Patent No. 1808241 U.S. Pat. No. 3,236,706 European Patent No. 2118328

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

  Foams are produced, for example, using preforms with granules as described in the literature cited below.

  Indeed, EP 2138328 discloses a particularly advantageous method by proposing to produce a preform using granules of particulate powder. This preform is thus baked before the metal is cast to break the carbon chains of the granules. This patent thus firstly provides for the production of a paste formed from powder, sodium chloride and water. Granules that are subsequently used to produce the preform are prepared using this paste.

  Thus, the present invention is a method of producing metal foam with at least one channel and using a ball preform, i.e. for the production of heat exchangers, which is soluble at the casting core, the central core and at low temperatures A coating of material is placed in the casting mold, the preform is then placed tightly around the core, the soluble material is then removed by heating at a low temperature, and then between the balls and between the balls and the central core. In order to fill this free space, a molten metal mass is cast in a mold, and finally the ball is removed.

  According to a particular embodiment, the channel is constituted by a metal mass that replaces the wax coating after the metal mass has been cast.

  According to other specific embodiments, the central core of the core is formed from the same material as the ceramic, steel, sand, soluble material, or material forming the preform.

  According to another embodiment, the core is formed from three elements, the first element is constituted by a ceramic, steel or sand core, the second element is constituted by a peripheral layer of refractory material, The element is constituted by a coating of a low temperature soluble material.

  According to yet another embodiment, the core is formed from four elements, the first element is constituted by a ceramic, steel or sand core, the second element is constituted by a peripheral layer of refractory material, The third element is constituted by a layer of ceramic material and the fourth element is constituted by a coating of a material that is soluble at low temperatures.

  According to another embodiment, the core is straight.

  According to another embodiment, the core has a curve.

  According to another embodiment, the core is tubular.

  According to another embodiment, the low temperature soluble material is a wax.

  According to other embodiments, the coating has continuous or discontinuous protrusions on its inner surface.

  The invention also relates to a metal foam obtained according to the method of the invention and comprising at least one channel.

  Advantageously, the channel is in the form of a straight or curved tube.

  Advantageously, again, the channels and foam are aluminum or an aluminum alloy system.

  A first advantage of the present invention resides in the production of foams that incorporate channels of the same nature as the foam itself.

  Another advantage of the present invention resides in the first simultaneous production of the metal foam and one channel or multiple channels.

  Another advantage of the present invention is to produce any shape, eg, straight, curved, or other channels.

  Yet another advantage of the present invention is that there is no negative interaction between the channel and the metal foam.

  Yet another advantage of the present invention is the elimination of either mechanical strength or thermal conductivity problems between a channel or channels and the metal foam.

  Other characteristics, advantages and details of the invention will become more apparent from the further description of embodiments given below, by way of example, with reference to the accompanying drawings.

It is a figure which shows the preform in which the core was inserted. Figure 2 shows a cross-sectional view of different embodiments of the core. Figure 2 shows a cross-sectional view of different embodiments of the core. Figure 2 shows a cross-sectional view of different embodiments of the core. Figure 2 shows a cross-sectional view of different embodiments of the core. Figure 2 shows a cross-sectional view of different embodiments of the core. It is sectional drawing which shows other embodiment of a core. 1 is a cross-sectional view of a metal foam with a channel made in situ. FIG. 1 is a cross-sectional view of a metal foam with a channel made in situ. FIG. FIG. 5 shows a different embodiment of forming a groove or notch on the outer surface (or heat resistant material) of the central core. FIG. 5 shows a different embodiment of forming a groove or notch on the outer surface (or heat resistant material) of the central core.

  In the next part of the description, the preform should be considered to have been made using a known method, i.e. a stared ball of salt such as sodium chloride, and used in a known manner to produce a metal foam. It is. The materials that make up the metal foam are also known, for example, aluminum, aluminum alloys, and any other known materials used in casting can be used. Reference may be made to the above patent for more details.

  As previously mentioned, according to the present invention, the core is inserted into the preform and such a core can be prepared in different ways. Generally speaking, the present invention is based on the replacement of a layer of soluble coating material with the same construction material as the metal foam so as to produce the channel in situ.

  FIG. 1 shows a diagram of a preform made up of a ball 1 with or without compression, with a core 2 disposed thereon. This core is constituted by a central core 3 and a coating 4. For clarity, the preform 6 is shown removed from the mold. This preform is parallelepiped in shape and the core 2 according to FIG. 1 is inserted into it. It can be seen that all balls 1 are in intimate contact with each other. The tip of the coating 4 is flush with the side wall of the preform, whereas the core 3 protrudes. This illustration is not limited in any way, and the present invention may be conveniently made by allowing the wax to protrude to create a skin or to obtain a tube that protrudes against the foam. is there.

  Of course, the core 2 is first placed in the molten metal injection mold in a vertical or inclined position as required by the user, and then the ball is poured into the mold. The foam is then manufactured using known techniques that do not require further explanation here. It goes without saying that several cores can be inserted to obtain several channels.

  FIG. 2 shows a cross-sectional view of a first embodiment of a core 2 formed from a central core 3 and a coating 4. The central core 3 is made of, for example, a ceramic material, steel, or sand usually used in casting technology. Here the coating is constituted by a layer of wax or other material soluble at low temperatures. The low temperature soluble material is considered to have a melting point of 40 ° C to 150 ° C. Of course, the diameter of the central core and the thickness of the coating layer are determined by the intended use of the metal foam. Thus, a diameter of the central core 3 exceeding 2 mm is envisioned and a coating thickness of 0.5 mm to 10 mm (preferably 0.5 to 3 mm) can be employed.

  Although the figure shows a straight core, it will be appreciated that any shape of core may be used. In this case, a sand core is preferred.

  This preform 1 with the core 2 integrated is used as a standard to produce a metal foam. Thus, as the temperature in the mold increases, the balls agglomerate to create a hard preform, and then the coating 4 is removed by dissolving, simply flowing and throwing away. Molten metal is injected in a known manner to occupy the space between the ball and the free space left by the coating between the preform and the residual core and constitute the channel. After cooling, if the core 3 is made of sand, it is extracted or removed so as to clean the formed channel.

  FIG. 3 shows a cross-sectional view of a different embodiment of a three-part core 2, in which a layer of refractory material 5 is applied to the center 3, followed by a coating 4 of wax or a low temperature soluble material. The advantage of this refractory material is that it facilitates removal of the core from the mold after the metal has cooled, while the central core 3 ensures its rigidity. This refractory material also allows the diameter of the final channel to be changed without having to change the central core.

  FIG. 4 shows the core 2 according to FIG. 3 with the central core 3 cut out in the longitudinal direction to form the channel 6. The advantage of this embodiment is that the material constituting the central core 3 is reduced. A further advantage of such an embodiment is the ability to circulate airflow through this channel to improve cooling after casting. The central core is in this case in the form of a more or less thick tube.

  FIG. 5 shows a cross-sectional view of another embodiment of the core 2 made of four parts. The central core 3 is itself covered by a layer of ceramic material 7 and finally a layer 5 of refractory material covered with a coating layer 4. By using a ceramic material, the stiffness of the refractory material can be improved, preventing any potential penetration of molten aluminum into the refractory material, thereby avoiding microcracking. .

  FIG. 6 shows a different embodiment of that shown in FIG. 5 in which a tube-shaped hollow central core 3 is provided. This embodiment allows for a reduction in the material of the central core.

  All the cores previously described with reference to the figures are inserted into the preform so that one or several channels inside the metal foam can be produced. For this purpose, the core is placed in a foam-making mold and then the balls are put in place and condensed to ensure their mutual contact. If necessary, the preform is compressed.

  These cores may all incorporate a central core made of ceramic material, steel or sand, more generally any material suitable for casting operations. It goes without saying that the central core is made of ceramic material or steel if it is in the shape of a straight bar so as to ensure its extraction, and the resulting channel is straight. The core may be placed at any location within the preform and the tube may be open at any point, inlet, or outlet on any face of the metal foam.

  FIG. 7 shows another embodiment of the core 2 whose central core 9 incorporates several curves and is covered by a coating 4 of wax or other low temperature soluble material. In this case, the central core 9 is made of sand or other friable material. The channel obtained inside the foam provides a larger surface area between the fluid circulating in the metal foam and the fluid circulating in the channel.

  FIG. 8 shows a cross-sectional view of a block of metal foam 10 formed by a wire mesh 11 in which a tubular channel 12 is formed in the free space between the ball and the central core after the coating has been dissolved. It will be appreciated that the thickness of the channel 12 is substantially equal to the thickness of the wax layer.

  The benefits of the present invention are readily understood as foam 10 and channel 12 are made simultaneously when molten metal is cast. They are thus of the same nature, thereby ensuring the same conductivity of these two elements and eliminating any mechanical strength problems.

  FIG. 9 shows a longitudinal cross-sectional view along the channel 12, and it can be observed that the channel 12 is fully embedded in the metal foam mesh 11 as the material melts.

  10 and 11 show different embodiments in which grooves or notches are formed on the outer surface of the central core 3 (or on the refractory material). Said grooves or notches are filled with coating 4, which is continuous or non-continuous along the inner surface of coating 4 creating an exchange surface located inside the channel to improve heat exchange when the metal is cast. Causes a continuous protrusion 13. These protrusions 13 are shown here by way of illustration without limitation in the form of triangular and rectangular cross sections. It will be appreciated by those skilled in the art that they may take other forms to improve heat exchange while maintaining fluid flow inside the channel. One advantage of this embodiment is the increased exchange surface within the channel and hence the performance of the device.

  The figures illustrating the present invention show, by way of non-limiting example, cores, coatings, and tubing with a substantially circular cross-section, with one skilled in the art implementing the invention using different cross-sections, i.e., oval or rectangular It goes without saying that you can do it.

  The foam according to the invention is particularly suitable for the manufacture of heat exchangers of any type, liquid / liquid, liquid / gas or gas / gas or phase change fluid (liquid-> gas).

Claims (13)

A method of manufacturing a metal foam (10) comprising at least one channel (12) and using a ball preform (1), ie for the manufacture of a heat exchanger,
A core (2) constituted by a central core (3, 9) and a coating of cold soluble material (4) are placed in the casting mold, and the preform (1) is then placed tightly around the core. The soluble material is then removed by heating at a low temperature, and then a molten metal mass is cast into the mold to fill the free space between the balls and between the balls and the central core (3, 9), and finally A manufacturing method, wherein the balls are removed.   The method according to claim 1, characterized in that the channel (12) is constituted by a metal mass replacing the wax coating (4) after the metal mass has been cast.   1 or 2, characterized in that the central core (3, 9) or the core (2) is formed from the same material as the material forming the ceramic, steel, sand, soluble material or preform. The method described.   The core (2) is formed from three elements, the first element is constituted by a ceramic, steel or sand central core (3), the second element is constituted by a peripheral layer (5) of refractory material, 4. A method according to any one of claims 1 to 3, characterized in that the third element is constituted by a coating (4) of a low temperature soluble material.   The core (2) is formed from four elements, the first element is constituted by a ceramic, steel or sand central core (3), the second element is constituted by a peripheral layer (5) of refractory material, The third element is constituted by a layer (7) of ceramic material, and the fourth element is constituted by a coating (4) of a low temperature soluble material. The method according to claim 1.   6. A method according to any one of the preceding claims, characterized in that the central core is straight.   7. A method according to any one of the preceding claims, characterized in that the central core (9) has a curve.   8. A method according to any one of the preceding claims, characterized in that the central core (3) is tubular.   9. Process according to any one of claims 1 to 8, characterized in that the low temperature soluble material is a wax.   10. A method according to any one of the preceding claims, characterized in that the coating (4) has continuous or discontinuous protrusions (13) on its inner surface.   Metal foam obtained according to the method of any one of claims 1 to 10 and comprising at least one channel (12).   12. Metal foam according to claim 11, characterized in that the channel (12) is in the form of a straight or curved tube.   Metal foam according to claim 11 or 12, characterized in that the channel (12) and the foam (10) are made of aluminum or an aluminum alloy.

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