High-pressure quasi-isostatic sintering device

Abstract

The invention relates to a sintering device under quasi-isostatic high pressures. The sintering device comprises a mold (4) defining a cylindrical sintering chamber, means for heating the sintering chamber, and a first piston (38) mounted to slide axially within the sintering chamber and adapted to pressurize the chamber during its movement. The sintering device includes a cylindrical sleeve (26) adapted to be inserted coaxially into the sintering chamber. The melting temperature of the cylindrical sleeve (26) is greater than or equal to 500°C, and the first piston (38) and the cylindrical sleeve (26) have external and internal dimensions, respectively, adjusted to pressurize the sintering chamber. Figure 7

Description

Title of the invention: High-pressure quasi-isostatic sintering device. Technical field to which the invention relates.

[0001] The present invention relates to the technical field of manufacturing solid materials from powders and, more specifically, by implementing a sintering process. Technological background

[0002] Sintering is a widely recognized manufacturing technique in the materials industry, enabling the creation of solid objects from powders. A key feature of this technique is that the powders are heated until their particles bond together to form a solid material, without reaching their melting point. Sintering thus allows for the production of dense and solid parts without the need to melt the powders.

[0003] Sintering has applications in many technical fields. For example, in the metallurgical industry, it is used to manufacture complex mechanical parts. In the electronics industry, this technique makes it possible to produce ceramic components for integrated circuits and capacitors. Finally, in the field of construction materials, sintering is used to produce ceramic tiles and refractory bricks.

[0004] The manufacture of ceramic parts by sintering, however, has the drawback of requiring high heat treatments, often exceeding 1000°C. This requirement results in a significant energy cost in the implementation of this technique. Indeed, maintaining such high temperatures for prolonged periods requires substantial energy consumption, which has a significant impact on production costs and the environmental footprint of this manufacturing process.

[0005] The objective of the present invention is to provide a sintering device enabling the implementation of sintering processes that are more energy-efficient. Object of the invention

[0006] To achieve this objective, the invention proposes a sintering device comprising: - a mold delimiting a cylindrical sintering chamber; - means of heating the sintering chamber; - a first piston mounted to slide axially in the sintering chamber and adapted to pressurize the latter during its sliding.

[0007] The sintering device is remarkable in that it comprises a cylindrical sleeve, adapted to be inserted coaxially into the cylindrical sintering chamber, the melting temperature of the cylindrical sleeve being greater than or equal to 500°C, and in that the first piston and the cylindrical sleeve have external and internal dimensions respectively, adjusted to pressurize the sintering chamber.

[0008] By "cylindrical jacket", we mean an element capable of conforming to the shape of the sintering chamber, over at least part of the length of the sintering chamber.

[0009] The first piston, according to the invention, is configured to move in the cylindrical sleeve present in the sintering chamber, so as to compress a powder present in the cylindrical sleeve.

[0010] The heating means are adapted to increase the temperature of the powder present in the cylindrical jacket, to the point of initiating a sintering process of said powder when it is compressed by the first piston, at a significantly lower temperature than that required to sinter the same powder when it is not compressed. Thus, advantageously, the sintering device allows the implementation of sintering processes that are more energy-efficient.

[0011] According to another feature of the invention, the melting temperature of the cylindrical jacket is higher than the sintering temperature of the powder to be sintered. The shape of the cylindrical jacket is thus preserved or substantially preserved during the sintering of the powder. The cylindrical jacket maintains the powder at a constant or substantially constant distance from the wall of the sintering chamber, and subsequently the ceramic from said wall. The cylindrical jacket therefore acts as a barrier between the ceramic and the wall of the sintering chamber. The cylindrical jacket thus reduces the frictional forces between the ceramic and the sintering chamber during the removal of the ceramic from the sintering chamber. The presence of the cylindrical jacket in the sintering chamber therefore limits the risk of adhesion, chipping, or breakage of the ceramic during its removal from the sintering chamber.

[0012] According to one embodiment of the invention, the melting temperature of the cylindrical liner is between 350°C and 600°C, preferably in the order of 550°C.

[0013] According to another embodiment of the invention, the cylindrical sleeve is adapted to prevent the passage of a powder present in the sintering chamber when the powder is subjected to a pressure of up to 2 GPa, and the largest dimension of the grains composing the powder being between 10 nm and 500 pm. This embodiment makes it possible to prevent any direct contact of a powder, and subsequently of the ceramic formed from this powder, with the wall of the sintering chamber when the The particle size of said powder is between 10 nm and 500 µm. For the reasons mentioned above, the presence of the cylindrical sleeve in the sintering chamber prevents the risk of breakage of the ceramic during its extraction from the sintering chamber and also prevents the ceramic from adhering to the surface of the sintering chamber.

[0014] According to another embodiment of the invention, the cylindrical liner is made of a material and has dimensions such that it is removable from the sintering chamber after sintering. This embodiment advantageously allows a used cylindrical liner, present in the sintering chamber, to be replaced by a new cylindrical liner.

[0015] According to another advantage, the cylindrical sleeve can be placed in the sintering chamber of a used mold with surface defects on the wall delimiting said chamber. The cylindrical sleeve then prevents direct contact between the ceramic and the surface defects of the sintering chamber, defects that could degrade the quality of the ceramic and chip it during removal from the mold, or worse, prevent its removal altogether. The invention can thus be implemented with used molds thanks to the removable nature of the cylindrical sleeve. Molds considered unusable can therefore be reused. This solution not only allows for significant cost savings but also contributes to reducing environmental impact by extending the lifespan of the equipment.

[0016] According to another advantage, the ceramic can be extracted from the sintering chamber during the removal of the cylindrical shell from the mold. This removal method advantageously allows the ceramic to remain stationary or substantially stationary relative to the cylindrical shell during its removal from the mold. This significantly reduces the risk of breakage of the ceramic during its removal.

[0017] According to another embodiment of the invention, the cylindrical liner is chemically inert in contact with the mold wall delimiting the sintering chamber. This embodiment prevents the formation of chemical bonds between the cylindrical liner and the mold, particularly during powder sintering, which could prevent the cylindrical liner from being removed from the mold. According to another advantage, it also prevents premature wear of the mold by the cylindrical liner.

[0018] According to another embodiment of the invention, the cylindrical jacket is chemically inert in contact with the powder placed in the sintering chamber. This embodiment prevents alteration or contamination of the ceramic by the cylindrical jacket during its fabrication.

[0019] Preferably, the cylindrical jacket has thermally stable behavior during the powder sintering process. By "thermally stable," we mean the fact that the jacket releases little or no compounds into the powder undergoing said sintering process.

[0020] According to another embodiment, the liner is composed of a material that reduces the stress forces between the sintered material and the inner wall of the mold. By way of non-limiting examples, the cylindrical liner can be made from one of the following materials: graphite, a synthetic polymer such as polytetrafluoroethylene also known as "Teflon", weakly consolidated ceramics such as hexagonal boron nitride "h-BN" or pyrophyllite "stumatite".

[0021] According to another embodiment, the cylindrical sleeve is formed from a flexible sheet. The cylindrical sleeve can also be obtained by machining a block of material.

[0022] According to another embodiment of the invention, the thickness of the cylindrical liner is between 1% and 3% of the diameter of the sintering chamber, preferably on the order of 2%.

[0023] By way of non-limiting example, the cylindrical jacket has a thickness of between 0.1 mm and 0.4 mm, preferably of the order of 0.2 mm, when the diameter of the sintering chamber is of the order of 10 mm.

[0024] According to another embodiment of the invention, the external and internal dimensions of the first piston and the cylindrical sleeve, respectively, are adjusted to prevent powder from passing between the first piston and the cylindrical sleeve. This embodiment prevents premature mechanical wear of the first piston due to the presence of powder grains between the first piston and the cylindrical sleeve. Preferably, the first piston is press-fitted into the cylindrical sleeve to limit or prevent this phenomenon of premature wear of the first piston.

[0025] According to another embodiment of the invention, the cylindrical sintering chamber has two ends opening outside the mold, a first end through which the first piston can be inserted into or removed from the chamber, and a second end closed by a removable base. This embodiment allows the ceramic to be extracted from the second end of the sintering chamber when the base is separated from the mold. A rod or a pusher can, for example, be inserted through the first end of the sintering chamber to push the ceramic until it is extracted from the mold through the second end of the sintering chamber.

[0026] According to another embodiment of the invention, the cylindrical sintering chamber has two ends opening outside the mold, one end of which allows the first piston to be inserted into or removed from the chamber. and a second end through which a second piston can be introduced into the sintering chamber for axial sliding mounting within the cylindrical sleeve. In other words, the sintering device may comprise two pistons configured to compress a powder present in the cylindrical sleeve.

[0027] According to another embodiment of the invention, the external and internal dimensions of the second piston and the cylindrical sleeve, respectively, are adjusted to prevent powder from passing between the second piston and the cylindrical sleeve. This embodiment prevents premature mechanical wear of the second piston due to the presence of powder grains between the second piston and the cylindrical sleeve. Preferably, the second piston is press-fitted into the cylindrical sleeve to limit or prevent this wear of the second piston.

[0028] According to another embodiment of the invention, the mold is a high pressure (HP) type mold, capable of withstanding pressures up to 2 GPa, without undergoing significant deformation.

[0029] According to another embodiment of the invention, the mold is made from a material having good mechanical strength at high temperatures, such as tool steel or tungsten carbide.

[0030] According to another embodiment of the invention, preferably, the sintering device includes a separating pellet adapted to prevent contact between the powder and the first piston. The presence of a separating pellet between the powder and a piston advantageously limits or eliminates the mechanical stresses experienced by the ceramic during its detachment from said piston. The presence of the separating pellet reduces the risk of breakage of the ceramic during this step.

[0031] According to one embodiment, when the sintering device comprises two pistons as described above, a separating pellet is associated with each piston.

[0032] According to a preferred embodiment of the invention, the separating pellet is made of the same material as the cylindrical jacket. The separating pellet may have the same thickness as the cylindrical jacket. Thus, the pressure exerted on the powder through the cylindrical jacket and the separating pellet(s) is isostatic or quasi-isostatic. A higher-quality and more homogeneous ceramic can be obtained in this way.

[0033] According to another embodiment of the invention, a removable pin is interposed between the separating disc and the piston. Thus, advantageously, the removable pin can accompany the ceramic during its extraction from the mold and advantageously allow the separating disc to be held against the ceramic, in order to allow the disc to be detached from the ceramic outside the mold, after the ceramic has cooled and / or with the aid of suitable tools.

[0034] In other words, two removable pins can be used to clamp or sandwich the powder present in the cylindrical sleeve. Advantageously, a separating disc is interposed between the powder and each removable pin, and the separating disc is of the same material as the cylindrical sleeve in order to maintain the physical integrity of the ceramic when it is extracted from the mold using the rod or plunger, so as to prevent contact between the ceramic and the rod or plunger.

[0035] According to another embodiment of the invention, the heating means are configured to raise the temperature of the chamber up to 500°C, preferably up to 450°C. The heating means may include at least one electrical resistance, placed opposite or against an outer wall of the mold in the form of a heating collar.

[0036] Of course, the different characteristics, variants and embodiments mentioned above can be combined with each other in various ways, provided that they are not incompatible or mutually exclusive.

[0037] The invention also relates to a method for sintering a powder, implementing the following steps: - pouring the powder into the cylindrical jacket, present in the sintering chamber of the mold of a device described above; then - compression of the powder present in the cylindrical casing by the first piston; then - raising the temperature in the sintering chamber by means of heating devices until the powder is sintered; then - cooling of the sintering chamber; then - release of the pressure exerted on the sintered material by the first piston; then - removal of the sintered material from the sintering chamber.

[0038] Advantageously, the sintering process according to the invention allows the sintering of a powder at high pressure and low temperature, resulting in superior quality ceramics, particularly in terms of transparency due to the near absence of defects. Thanks to the characteristics described above, the risk of ceramic breakage during removal from the mold is greatly reduced. These specific sintering conditions enable the production of higher quality ceramics in shorter timeframes.

[0039] By "high pressures" is meant pressures up to 2 GPa, preferably on the order of 1 GPa. By "low temperatures" is meant temperatures below 600°C, preferably between 300°C and 500°C or on the order of 450°C.

[0040] According to another embodiment of the invention, when the powder is compressed by the first piston, the heating means maintain the sintering chamber at a maximum temperature between 1 min and 8 h, preferably between 5 min and 1 h.

[0041] According to another embodiment of the invention, the sintered material is extracted from the mold during the removal of the cylindrical sleeve from the sintering chamber. This embodiment makes it possible to significantly reduce the frictional forces exerted on the sintered material during its removal from the mold, for the reasons mentioned above.

[0042] According to another embodiment of the invention, prior to the introduction of the powder into the sintering chamber, the jacket can be coated with a film having lubricating properties. This film can optionally be sprayed onto the wall of the sintering chamber and / or onto the surface of the cylindrical jacket. By way of non-limiting example, the film may comprise hexagonal boron nitride or polytetrafluoroethylene.

[0043] According to another embodiment, the powder is composed of at least one metal oxide, such as aluminum oxide.

[0044] According to another embodiment, the sintering process is carried out under a controlled atmosphere, preferably in a weakly oxidizing or non-oxidizing atmosphere for the cylindrical jacket. Description of the figures

[0045] The invention will be better understood from the following description, which relates to a preferred embodiment, given by way of non-limiting example, and explained with reference to the accompanying schematic drawings, in which: - Fig. 1 illustrates a schematic top view of a mold and a base of a sintering device according to the invention; - [Fig.2] illustrates a cross-section of the mold and base represented by [Fig.1]; - [Fig.3] illustrates a first step of a sintering process according to the invention, using a mold and a base represented by [Fig.2], consisting of placing the mold on the base and then inserting a cylindrical sleeve into the mold along the height of the mold so that all the compression elements in the mold are in contact with this sleeve; - [Fig.4] illustrates a second step in the sintering process, consisting of inserting the first pin and the separator pellet on top; - [Fig.5] illustrates a third step in the sintering process, consisting of partially filling the cylindrical jacket with a sintering powder; - [Fig.6] illustrates a fourth step in the sintering process, consisting of introducing a second separating pellet into the cylindrical jacket, using a second pin forced into said jacket with a piston; - [Fig.7] illustrates a fifth step in the sintering process, which consists of compressing the powder present in the cylindrical jacket, via the piston, when the powder is maintained at a temperature of around 450°C; - [Fig.8] illustrates a sixth step in the sintering process, which consists of removing the base of the mold; - [Fig.9] illustrates a seventh step in the sintering process, consisting of transferring the ceramic from the mold to an extraction base; - Fig. 10 illustrates an eighth step, consisting of separating the mold from the extraction base. Detailed description of the invention

[0046] As a reminder, the invention proposes a sintering device allowing the implementation of a sintering process that is more economical in thermal energy.

[0047] According to a non-limiting embodiment of the invention, a sintering device consists of a base 2 and a mold 4, in particular visible in the attached figures 1 and 2.

[0048] The base 2 consists of two elements forming a single piece, namely, a cylindrical base 6 surmounted by a stop 8, also cylindrical in shape. The base 6 and the stop 8 are both centered along the same axis.

[0049] The mold 4 extends along a longitudinal axis 12, between a first end 14 and a second end 16. An internal wall 18 of the mold delimits a cylindrical sintering chamber 20, centered on the longitudinal axis 12.

[0050] According to the present example, the diameter of the sintering chamber 20 is approximately 10 mm at the center of the mold. The sintering chamber has a counterbore at the second end 16 of the mold, so as to form a cavity 22 with a shape complementary to the stop 8 of the base.

[0051] The sintering device also includes heating means suitable for raising the temperature of the sintering chamber 20. Preferably, the heating means are suitable for maintaining the sintering chamber at a temperature of up to 500°C, preferably at a temperature between 400°C and 500°C or in the order of 450°C. According to the present example, the heating means include an electric resistance 24, wrapped around the mold 4, so as to form a heating collar.

[0052] According to the present example, the mold 4 includes a cavity in which a temperature probe 10 is present, in order to know in real time the temperature of the sintering chamber 20.

[0053] Figure 3 illustrates a first step of a sintering process according to the invention, implemented using a sintering device described above. In this first step, the second end 16 of the mold 4 is placed on the base 2, so that the stop 8 of the base closes the cavity 22 of the mold 4.

[0054] A cylindrical sleeve 26 is subsequently inserted into the sintering chamber 20 through the first end 14 of the mold.

[0055] The cylindrical jacket 26 is configured to conform to the shape of the sintering chamber along its entire length. The thickness of the cylindrical jacket is uniform or substantially uniform. In this example, the cylindrical jacket has a thickness of approximately 0.2 mm. The cylindrical jacket is made of graphite. It should be noted that the invention is not limited to this embodiment, so the cylindrical jacket could also be made of pyrophyllite or polytetrafluoroethylene.

[0056] According to a second step illustrated by [Fig. 4], a first pin 28 is inserted through the first end 14 of the mold 4 and forced into the cylindrical sleeve 26 until said first pin bears against the stop 8 of the base 2 and closes one end of the cylindrical sleeve. A first separating pellet 30 is introduced in the same way into the sintering chamber 20, until it covers and bears against the first pin 28.

[0057] According to a third step illustrated by [Fig. 5], a powder 32 is poured into the cylindrical jacket so as to at least partially fill said jacket. In the present example, the powder 32 is composed of aluminum oxide.

[0058] According to a fourth step illustrated in [Fig. 6], a second separating pellet 34 is introduced into the sintering chamber through the first end 14 of the mold. The second separating pellet 34 is positioned to close the other end of the cylindrical sleeve 26. A second pin 36 is also introduced into the sintering chamber and moved within it by means of a piston 38 inserted through the same end of the mold. In this example, the piston 38 has dimensions that are complementary or substantially complementary to those of the cylindrical sleeve.

[0059] According to a fifth step illustrated in [Fig. 7], the piston 38 moves the second pin 36 until the second separating pellet 34 comes into contact with the powder 32 present in the cylindrical sleeve. The piston 38 then exerts a pressure on the powder of between 0.1 N and 300 kN, preferably between 1 kN and 200 kN, via the second pin 36 and the second separating pellet 34. The powder 32 is then compressed by the piston 38 to a pressure of approximately 1 GPa. The heating means then raise the temperature of the sintering chamber 20 to a final temperature of approximately 450°C. The final temperature is maintained in the sintering chamber 20 for a few minutes, until a sintered material 40 is obtained.

[0060] After the sintering of the powder, the heating means are deactivated to lower the temperature in the sintering chamber 20, then the pressure exerted by the piston 38 on the sintered material 40 is gradually reduced until little or no pressure is exerted on said material.

[0061] According to a sixth step illustrated by [Fig. 8], the base 2 is detached from the mold 4, and then the second end 16 of the mold is positioned against an extraction base 42. The extraction base includes a recess 44 extending from the sintering chamber 20 of the mold. Preferably, the recess 44 has a diameter slightly larger than the diameter of the sintering chamber.

[0062] According to a seventh step illustrated by [Fig.9], a pusher 46 is inserted through the first end 14 of the mold to extract, through its second end 16, the assembly formed by the cylindrical sleeve 26, the pins, the sintered material 40 and the separating pellets interposed between said pins and the sintered material 40. The pusher 46 allows this assembly to be extracted from the mold 4 until the sintered material 40 is present in the recess 44 of the extraction base 42.

[0063] According to an eighth step illustrated by [Fig. 10], the mold 4 is separated from the extraction base 42 in order to be able to remove the whole of said base to obtain the sintered material 40.

[0064] Advantageously, the sintered material 40 moves with the cylindrical sleeve 26 during its extraction; therefore, the sintered material 40 is subjected to little or no mechanical friction with the mold during its removal. Consequently, the sintered material 40 is less likely to be damaged or break during its removal from the mold 4.

[0065] Thanks to the presence of the cylindrical sleeve 26 in the mold, it is possible to increase the pressure exerted on the powder during sintering, while limiting the risk of strong bonds forming between the sintered material and the inner wall of the mold. For the same reasons, the separating pellets prevent the sintered material from adhering to the pins. Thus, advantageously, the sintering device according to the invention allows the application of a quasi-isotropic mechanical stress at high temperatures on the powder during sintering, without the risk of the sintered material adhering to the mold wall. The invention therefore enables sintering processes to be carried out at significantly lower temperatures, compensated by the application of high pressure, and thus sintering processes that are more energy-efficient.

Claims

Demands

1. A powder sintering device comprising: - a mold (4) delimiting a cylindrical sintering chamber (20), - means for heating the sintering chamber (20), - a first piston (38) mounted to slide axially in the sintering chamber (20) and adapted to pressurize the latter during its sliding, characterized in that it comprises a cylindrical sleeve (26) adapted to be inserted coaxially in the cylindrical sintering chamber (20), the melting temperature of the cylindrical sleeve (26) being greater than or equal to 500°C, and in that the first piston (38) and the cylindrical sleeve (26) have external and internal dimensions respectively adjusted to pressurize the sintering chamber (20).

2. Device according to claim 1, wherein the cylindrical sleeve (26) is able to prevent the passage of the powder present in the sintering chamber (20) when it is subjected to a pressure of up to 2 GPa, and the largest dimension of the grains composing the powder being between 10 nm and 500 pm.

3. Device according to claim 1 or 2, wherein the cylindrical sleeve (26) is made of a material and has dimensions such that it is removable from the sintering chamber (20) after sintering.

4. Device according to any one of claims 1 to 3, wherein the cylindrical sleeve (26) is chemically inert in contact with a wall of the mold (4) delimiting the sintering chamber (20).

5. Device according to any one of claims 1 to 4, wherein the external and internal dimensions respectively of the first piston (38) and of the cylindrical sleeve (26) are adjusted to prevent the passage of powder between the first piston (38) and the cylindrical sleeve (26).

6. Device according to claim 5, wherein the first piston (38) is forcibly inserted into the cylindrical sleeve (26).

7. A device according to any one of claims 1 to 6, wherein the cylindrical sintering chamber (20) has two ends opening outside the mold (4), a first end (14) through which the first piston (38) can be inserted into or removed of the sintering chamber (20) and a second end (16) closed by a removable base (2).

8. Device according to any one of claims 1 to 7, wherein the cylindrical sintering chamber (20) has two ends opening outside the mold (4), of which a first end (14) through which the first piston (38) can be inserted into or removed from the sintering chamber (20) and a second end through which a second piston is suitable for being introduced into the sintering chamber (20) for its axially sliding fit in the cylindrical sleeve (26).

9. Device according to claim 8, wherein the respective external and internal dimensions of the second piston and the cylindrical sleeve (26) are adjusted to prevent the passage of powder between the second piston and the cylindrical sleeve (26).

10. Device according to claim 8 or 9, wherein the second piston is forcibly inserted into the cylindrical sleeve (26).

11. Device according to any one of claims 1 to 10, wherein the sintering device includes a separating pellet (30), adapted to prevent contact of the powder with the first piston.

12. Device according to claim 11, in which a removable pin (28) is interposed between the separating pad (30) and the piston (38).

13. Sintering device according to claim 11 or 12, wherein the separator pellet (30) is made of the same material as the cylindrical jacket (26).

14. Device according to any one of claims 1 to 13, wherein the thickness of the cylindrical liner (26) is between 1% and 3% of the diameter of the sintering chamber (20).

15. A method for sintering a powder, comprising the following steps: - pouring the powder (32) into the cylindrical sleeve (26) present in the sintering chamber (20) of the mold (4) of a device according to any one of claims 1 to 14; then - compressing the powder (32) present in the cylindrical sleeve (26) by the first piston (38); then - raising the temperature in the sintering chamber (20) by means of the heating means until the powder is sintered; then - cooling of the sintering chamber (20); then - release of the pressure exerted on the sintered material by the first piston (38); then - removal of the sintered material (40) from the sintering chamber (20).

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