Preparation method of pellet and tool for pellet preparation
Green body is prepared by powder extrusion printing technology, and the connection of high melting point materials is achieved by heating and docking methods, which solves the problem that it is difficult to prepare long core pellets in traditional methods and achieves high-efficiency and low-energy-consuming high melting point material connection.
Patent Information
- Application Number
- CN202411739541.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-03-07
AI Technical Summary
It is difficult to prepare long core pellets of nuclear thermal propulsion fuel element in traditional methods, mainly because the matrix phase of high melting point materials is difficult to form long core pellets using traditional preparation methods.
Green body is prepared by powder extrusion printing technology, and the connection between the two green body to be connected is achieved through heating and docking, and the connection of high-melting material is achieved by using the melting and viscosity characteristics of the adhesive at a lower temperature.
The connection of high melting point materials is achieved at a lower temperature, reducing energy and material losses, and is conducive to the preparation of large-length-diameter core pellets, reducing production and manufacturing difficulty and cost.
Smart Images
Figure CN119566308A_ABST
Abstract
Description
Technical Field
[0001] The present application belongs to the technical field of pellet preparation, and specifically relates to a pellet preparation method and a tool for pellet preparation. Background Art
[0002] Nuclear thermal propulsion works by directly heating a working fluid using the heat released by a controlled nuclear reaction (currently primarily nuclear fission). The hot working fluid then expands and accelerates through a nozzle before being discharged to generate thrust. Nuclear thermal propulsion offers advantages such as high thrust, high specific impulse, high specific power, high energy conversion efficiency, long operating times, adjustable thrust, and multiple starts. It holds broad application prospects in deep space exploration and weaponry. In recent years, my country's aerospace industry has flourished, with missions such as manned space flight, Mars exploration, and space station construction steadily underway, creating an urgent need for more advanced space propulsion technologies.
[0003] The core of nuclear thermal propulsion lies in the nuclear reactor. Researchers worldwide have long focused on updating and adapting nuclear fuel types. Nuclear thermal propulsion fuel elements differ from conventional pressurized water reactor (PWR) fuel elements in that their operating temperature can reach 2500K to 3000K. The fuel core power density must be at least 10 times that of PWR fuel, enabling the hydrogen to be heated to high temperatures in a shorter time. These elements lack an outer cladding, instead consisting of a protective coating covering the coolant channels. They operate under the flow of high-temperature hydrogen, requiring high resistance to hot hydrogen corrosion. Aiming to increase the core outlet temperature and reduce reactor weight and volume, four major core designs have been developed internationally: NERVA, CERMET, PBR, and CIS, each driving the development of different types of fuel elements. The CERMET core is a fast reactor design proposed by General Electric in the ROVER / NERVA program. The fuel is a solid solution of highly enriched UO2 and high-temperature refractory metals (such as tungsten, rhenium, and molybdenum). It possesses advantages such as high mechanical strength, a high melting point, good compatibility with hydrogen, and excellent structural stability, providing favorable conditions for long-term operation and multiple starts in nuclear thermal propulsion. Each fuel element has 331 working fluid flow channels, and the outer surface of the fuel element and the inner walls of the working fluid flow channels are coated with a tungsten-rhenium alloy to resist corrosion from high-temperature hydrogen. This design has excellent development prospects due to its superior performance.
[0004] However, due to the working principle of nuclear thermal propulsion fuel elements, no matter what type of core, there are strict requirements on its length. But no matter what type of core, its matrix phase has a high melting point and high hardness, making it difficult to prepare a longer core using traditional preparation methods. Summary of the Invention
[0005] In view of this, the present application is dedicated to providing a method for preparing a core block and a tool for preparing the core block, which solves the technical problem that the traditional preparation method is difficult to prepare longer core blocks by heating and docking two green blocks to be connected prepared by powder extrusion printing technology.
[0006] The first aspect of the present application provides a method for preparing a core block, which comprises: mixing a powder raw material and a binder, and obtaining a feed for powder extrusion printing after kneading and granulation, wherein the powder raw material is a metal material and / or a ceramic material; according to a three-dimensional slicing model, the screw system of the powder extrusion printing equipment extrude the feed in the barrel into a long filament by heating and rotating, and prints the green blank layer by layer on the printing panel according to a preset printing path; heating the side surfaces of two green blanks to be connected, and after the binder on the outer surface of the heated surface melts and has adhesiveness, aligning the two green blanks to be connected, and connecting the two green blanks to be connected together during the cooling process to obtain a green blank after the connection is completed; degreasing the green blank after the connection is completed to obtain a brown blank after degreasing; densifying and sintering the brown blank to obtain a core block after sintering.
[0007] In a specific embodiment of the present application, the side surfaces of two green sheets to be connected are heated, and after the adhesive on the outer surface of the heated surface melts and becomes adhesive, the two green sheets to be connected are aligned, and the two green sheets to be connected are connected together during the cooling process to obtain green sheets after the connection is completed, including: heating the side surfaces of the two green sheets to be connected by a clamp, and after the adhesive on the outer surface of the heated surface melts and becomes adhesive, the two green sheets to be connected are aligned by a clamp, and the two green sheets to be connected are connected together during the cooling process to obtain green sheets after the connection is completed.
[0008] In a specific embodiment of the present application, a powder raw material and a binder are mixed, and after internal mixing and granulation, a feed for powder extrusion printing is obtained, including: starting a mixer and a granulator, setting the internal mixing temperature and the granulation temperature, and adding the powder raw material into a preheated internal mixing chamber according to a preset ratio, wherein the powder raw material includes a base powder and a fuel phase powder; the binder is added into the internal mixing chamber at a mass ratio of 4:1 to 20:1 between the base powder and the binder, and the mixture is internally mixed at a set internal mixing speed. After being mixed evenly, the mixture is taken out, and the evenly mixed material is prepared as a feed for powder extrusion printing using a granulator.
[0009] In one embodiment of the present application, the mixing temperature ranges from 140°C to 220°C, and the granulation temperature ranges from 120°C to 180°C.
[0010] In a specific embodiment of the present application, the mixing speed range is 1 r / min to 40 r / min.
[0011] In a specific embodiment of the present application, the green body after connection is degreased to obtain a brown body after degreasing, including: degreasing the green body after connection is completed using an organic solvent; and thermally degreasing the green body after connection is completed to obtain a brown body.
[0012] In a specific embodiment of the present application, the temperature range of the heating surface is 120°C to 200°C.
[0013] In a specific embodiment of the present application, the heating time ranges from 10s to 20s.
[0014] According to a second aspect of the present application, there is provided a tool for preparing core blocks, which tool comprises a platform, a rotating shaft and two clamps. The platform is divided into a first part and a second part. The first part and the second part are connected by a rotating shaft so that at least one of the first part and the second part can rotate around the rotating shaft. The two clamps are respectively mounted on the first part and the second part, and are respectively used to fix and connect two green pieces to be connected. The tool has a switchable first mode and a second mode. In the first mode, the first part and the second part are in an unfolded state, and the bottom surfaces of the two clamps are in the same horizontal plane. In the second mode, the first part and the second part are in a folded state, and the two clamps are symmetrical along the platform.
[0015] In a specific embodiment of the present application, at least one of the first part and the second part is provided with a sliding mechanism, and at least one of the two clamps is slidable along the sliding mechanism.
[0016] The beneficial effect of the technical solution of the present application is that: by adopting powder extrusion printing technology to print the feed into a green body, and using powder extrusion printing to control and shape the feed, the integrated preparation of high-melting-point metal ceramics is realized, and the problem of difficulty in forming complex shapes in traditional molding processes is also improved. In addition, the green body prepared by powder extrusion printing technology is extremely convenient for connection. By heating the two green bodies to be connected and accurately aligning the heating surfaces of the two green bodies to be connected, the melting and viscosity characteristics of the adhesive at a lower temperature (such as within 200°C) are utilized to achieve the connection of the two green bodies to be connected, that is, the connection of high-melting-point materials is achieved at a lower temperature. Compared with the traditional connection process, the organizational structure of the connection is more consistent with the matrix structure, and the energy and material loss in the connection process are reduced. Moreover, it is conducive to the preparation of core blocks with a large aspect ratio, which can reduce the difficulty and cost of production. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 Shown is a schematic flow chart of a method for preparing a core block provided in one embodiment of the present application.
[0018] Figure 2Shown is a simplified schematic diagram of a process for preparing a pellet provided in another embodiment of the present application.
[0019] Figure 3 Shown is a schematic diagram of the three-dimensional structure of a tool for preparing core blocks provided in one embodiment of the present application.
[0020] Figure 4 Shown Figure 3 A schematic side view of a tool for pellet preparation is shown in a first mode.
[0021] Figure 5 Shown Figure 3 The figure shows a schematic diagram of the three-dimensional structure of the tooling for preparing core blocks in the second mode. DETAILED DESCRIPTION
[0022] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.
[0023] At least one embodiment of the present application provides a method for preparing a pellet, referring to Figure 1 and Figure 2 The preparation method of the core block includes the following steps.
[0024] S1: Mixing powder raw materials and binders, mixing and granulating to obtain feed for powder extrusion printing. The powder raw materials are metal materials and / or ceramic materials.
[0025] S2: Based on the 3D slice model, the screw system of the powder extrusion printing equipment extrudes the feed in the barrel into long filaments through heating and rotation, and prints the green body layer by layer on the printing panel according to the preset printing path.
[0026] It should be noted that the Powder Extrusion Printing (PEP) equipment uses PEP technology, which is a metal-ceramic indirect 3D printing (also known as three-dimensional printing) technology. The green body is a 3D printed part.
[0027] S3: heating the side surfaces of the two green sheets to be connected. After the adhesive on the outer surface of the heated surface is melted and has adhesive properties, aligning the two green sheets to be connected. During the cooling process, the two green sheets to be connected are connected together to obtain a green sheet after connection.
[0028] In some embodiments, the temperature of the heating surface is 120° C. to 200° C., and the heating time is 10 seconds to 20 seconds.
[0029] S4: Degreasing the green body after connection is completed to obtain a brown body.
[0030] S5: Densification sintering is performed on the brown blank to obtain a core block after sintering is completed.
[0031] The technical solution provided in the embodiment of the present application prints the feed into a green body by using powder extrusion printing technology, and uses powder extrusion printing to control and shape the feed, thereby realizing the integrated preparation of high-melting-point metal ceramics, and also improving the problem of difficult complex shape molding in traditional molding processes. In addition, the green body prepared by powder extrusion printing technology is extremely convenient for connection. By heating the two green bodies to be connected and accurately aligning the heating surfaces of the two green bodies to be connected, the melting and viscosity characteristics of the adhesive at a lower temperature (such as within 200°C) are utilized to achieve the connection of the two green bodies to be connected, that is, the connection of high-melting-point materials is achieved at a lower temperature. Compared with the traditional connection process, the organizational structure of the connection is more consistent with the matrix structure, and the energy and material loss in the connection process are reduced. Moreover, it is conducive to the preparation of core blocks with a large aspect ratio, which can reduce the difficulty and cost of production.
[0032] In at least one embodiment of the present application, S3-1 is a specific implementation of the above-mentioned S3.
[0033] S3-1: The side surfaces of the two green sheets to be connected are heated by a fixture. After the adhesive on the outer surface of the heated surface is melted and has adhesive properties, the two green sheets to be connected are aligned by the fixture, and the two green sheets to be connected are connected together during the cooling process to obtain a green sheet after connection.
[0034] In the embodiment of the present application, the accuracy of the clamp is utilized to quickly and accurately align the heating surfaces of the two green pieces to be connected.
[0035] In at least one embodiment of the present application, S1-1 and S1-2 are a specific implementation of the above-mentioned S1.
[0036] S1-1: Start the internal mixer and granulator, set the internal mixer temperature and granulation temperature, and add the powder raw materials into the preheated internal mixer according to the preset ratio. The powder raw materials include base powder and fuel phase powder.
[0037] In some embodiments, the mass ratio of the matrix powder to the powder raw material is 30% to 70%.
[0038] The matrix powder is a metal material or a ceramic material. For example, the material of the matrix powder includes metal materials such as pure tungsten, tungsten alloy or molybdenum, and can also be a ceramic material such as silicon carbide and aluminum oxide.
[0039] The fuel phase powder is a metal material or a ceramic material. For example, the fuel phase powder or microspheres may be made of metal materials such as pure uranium, or ceramic materials such as uranium dioxide (UO2) or uranium nitride.
[0040] S1-2: Add the binder into the mixing chamber at a mass ratio of base powder to binder of 4:1 to 20:1, mix at the set mixing speed, take out after mixing evenly, and use a granulator to prepare the evenly mixed material into feed for powder extrusion printing.
[0041] In the above embodiment, the powder raw material and the binder are mixed and uniformly mixed in a mixing chamber, and the feed for powder extrusion printing is prepared using a granulator. In the embodiment of the present application, by adjusting the binder formula, the preparation method can be applied to a wider range of material systems.
[0042] In some embodiments, the mixing temperature ranges from 140° C. to 220° C., the granulation temperature ranges from 120° C. to 180° C., and the mixing speed ranges from 1 r / min to 40 r / min.
[0043] In at least one embodiment of the present application, S4-1 and S4-2 are a specific implementation of the above-mentioned S4.
[0044] S4-1: Degreasing the green body after connection is completed using an organic solvent.
[0045] S4-2: After the connection is completed, the green body is subjected to thermal degreasing to obtain a brown body.
[0046] In the embodiment of the present application, the soluble component wax of the binder in the green compact after connection is completed is removed by using an organic solvent, and the remaining binder in the green compact after connection is further removed by thermal degreasing.
[0047] At least one embodiment of the present application provides a tool for preparing a pellet, which is applicable to the method for preparing the pellet in the above embodiment. Figures 3 to 5, the tooling includes a platform, a rotating shaft and two clamps. The platform is divided into a first part and a second part. The first part and the second part are connected by a rotating shaft so that at least one of the first part and the second part can rotate around the rotating shaft. The two clamps are respectively mounted on the first part and the second part, and are respectively used to fix and connect the two green pieces to be connected. The tooling has a switchable first mode (i.e., mode A) and a second mode (i.e., mode B). In the first mode, the first part and the second part are in an unfolded state, and the bottom surfaces of the two clamps are in the same horizontal plane. In the second mode, the first part and the second part are in a folded state, and the two clamps are symmetrical along the platform.
[0048] It should be noted that a bearing may be provided in the rotating shaft, and the bearing may support the rotating shaft, reduce friction, and ensure smooth rotation of the rotating shaft.
[0049] The platform can be a structure independent of the two fixtures, or a structure integrated with the two fixtures. For example, the first part can be an integrated structure with one fixture, and the second part can be an integrated structure with the other fixture.
[0050] The fixture in step S3 of the method for preparing a core block provided in an embodiment of the present application can be implemented using any fixture capable of fixing a green body, or can be implemented using a tool for preparing a core block provided in an embodiment of the present application.
[0051] For example, if a tool for core block preparation provided in an embodiment of the present application is used to perform the above S3, two clamps can be used to respectively fix and connect the two green billets to be connected, with the surfaces of the two green billets to be connected facing the rotating axis. The tool for core block preparation is switched to the second mode. In the second mode, the two green billets fixed on the tool are heated together with the tool. Then, the tool is switched to the first mode so that the heated surfaces of the two green billets are in contact and a certain force is applied. After cooling, the connection of the two green billets is completed.
[0052] In at least one embodiment of the present application, at least one of the first and second portions is provided with a sliding mechanism. At least one of the two clamps is slidable along the sliding mechanism. Thus, the sliding clamp ensures that the heated surfaces of the two green pieces are in full contact, thereby enhancing the connection stability between the two green pieces.
[0053] Below, in conjunction with specific embodiments, a method for preparing a pellet provided in an embodiment of the present application is described in detail. It should be noted that if the powder raw material includes fuel phase powder or microspheres, the feed can be a fuel feed, the green body can be a fuel green body, the brown body can be a fuel brown body, and the pellet can be a fuel pellet. If the powder raw material includes metal material and ceramic material, and the powder raw material includes fuel phase powder or microspheres, the feed can be a metal ceramic fuel feed, the green body can be a metal ceramic fuel green body, the brown body can be a metal ceramic fuel brown body, and the pellet can be a metal ceramic fuel.
[0054] Example 1:
[0055] The required materials are prepared into tungsten metal feedstock through mixing and granulation. The prepared tungsten metal feedstock is printed into the required finished product, i.e., green compact, by powder extrusion printing. The two green compacts to be connected are fixed with two clamps respectively so that their central axes are parallel to the bottom surface and the clamps of the clamps. The heating plate is then heated to 180°C, and the tooling for preparing the pellets is switched to the second mode. In the second mode, the same side of the two green compacts to be connected is heated so that the connection surface is heated and has adhesion. The tooling for preparing the pellets is then quickly adjusted to the first mode, and the bottom surface of the clamp is slid so that the two adhesive surfaces are tightly attached, so that the two metal ceramic fuel green compacts to be connected are connected. After the connection is completed, the metal green compacts are degreased and sintered to obtain densified tungsten metal, which is the required pellet. Finally, the obtained tungsten metal is prepared into a tensile sample, and the tensile strength is measured to be 1120MPa.
[0056] Example 2:
[0057] The required materials are prepared into 93W-Ni-Fe metal feed by mixing and granulating. The prepared tungsten alloy feed is printed into the required finished product by powder extrusion printing. The two green billets to be connected are fixed with two clamps respectively so that their central axes are parallel to the bottom surface of the clamp and the clamp. Then the heating plate is heated to 140°C, and the tooling for core block preparation is converted to the second mode. In the second mode, the same side of the two green billets to be connected is heated so that the connection surface is heated and has adhesion. It is then quickly adjusted to state A, and the bottom surface of the clamp is slid so that the two adhesive surfaces are tightly attached, so that the two green billets to be connected are connected. After the connection is completed, the alloy green billets are degreased and sintered to obtain a densified tungsten alloy, which is the required core block. Finally, the obtained tungsten alloy is prepared as a tensile sample, and the tensile strength is measured to be 731MPa.
[0058] Example 3:
[0059] The W-UO2 metal ceramic fuel feed is prepared from the required materials by mixing and granulation. The prepared W-UO2 feed is printed into the required finished product by powder extrusion printing. The two metal ceramic fuel green billets to be connected are fixed by two clamps respectively, so that the central axes of the two clamps are parallel to the bottom surface of the clamp and the clamp, and then the heating plate is heated to 170°C, and then the tooling for core block preparation provided in the embodiment of the present application is converted to the second mode. In the second mode, by heating the same side of the two metal ceramic fuel green billets to be connected, the connection surface is heated and has adhesion, and then the tooling for core block preparation is quickly adjusted to the first mode, and the bottom surface of the clamp is slid so that the two surfaces with adhesion are tightly attached, so that the two metal ceramic fuel green billets to be connected are connected. After the connection is completed, the alloy green billets are degreased and sintered to obtain densified W-UO2 metal ceramic fuel. The sample is cut along the vertical connection surface by wire cutting, and there are no obvious cracks under the metallographic microscope.
[0060] It should be noted that the combination of the various technical features in the embodiments of the present application is not limited to the combination described in the embodiments of the present application or the combination described in the specific embodiments. All technical features described in the present application can be freely combined or combined in any way unless there is a contradiction between them.
[0061] As used in this application and the claims, unless the context clearly indicates otherwise, the words "a," "an," and / or "the" are not intended to refer to the singular but may include the plural. Generally speaking, the term "comprising" only implies the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list. A method or apparatus may also include other steps or elements.
[0062] The terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the quantity of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features.
[0063] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.
Claims
1. A method for preparing a pellet, characterized in that: include: The powder raw material and the binder are mixed, and after banburying and granulation, a feed for powder extrusion printing is obtained, wherein the powder raw material is a metal material and / or a ceramic material; According to the 3D slice model, the screw system of the powder extrusion printing equipment extrudes the feed in the barrel into long filaments through heating and rotation, and prints the green blank layer by layer on the printing panel according to the preset printing path; The side surfaces of the two green sheets to be connected are heated, and after the adhesive on the outer surface of the heated surface is melted and has adhesiveness, the two green sheets to be connected are aligned, and the two green sheets to be connected are connected together during the cooling process to obtain a green sheet after connection; Degreasing the green billet after connection to obtain a brown billet; The brown blank is subjected to densification sintering, and a core block is obtained after the sintering is completed.
2. A method for preparing a pellet according to claim 1, characterized in that: The method comprises: heating the side surfaces of two green sheets to be connected, and after the adhesive on the outer surface of the heated surface is melted and has adhesiveness, aligning the two green sheets to be connected, and connecting the two green sheets to be connected together during the cooling process to obtain a green sheet after connection, comprising: The side surfaces of the two green sheets to be connected are heated by a clamp. After the adhesive on the outer surface of the heated surface is melted and has adhesiveness, the two green sheets to be connected are aligned by the clamp, and the two green sheets to be connected are connected together during the cooling process to obtain the green sheets after the connection is completed.
3. The method for preparing a pellet according to claim 1, characterized in that: The powder raw material and the binder are mixed, and after mixing and granulation, the feed material for powder extrusion printing is obtained, including: Start the internal mixer and granulator, set the internal mixing temperature and granulation temperature, add the powder raw materials into the preheated internal mixing chamber according to the preset ratio, the powder raw materials include base powder and fuel phase powder; add the binder into the internal mixing chamber at a mass ratio of base powder to binder of 4:1 to 20:1, mix at the set internal mixing speed, take out after mixing evenly, and use the granulator to prepare the evenly mixed material as feed for powder extrusion printing.
4. A method for preparing a pellet according to claim 3, characterized in that: The mixing temperature range is 140℃~220℃, and the granulation temperature range is 120℃~180℃.
5. A method for preparing a pellet according to claim 3, characterized in that: The mixing speed range is 1r / min~40r / min.
6. A method for preparing a pellet according to claim 1, characterized in that: The green blank after connection is degreased to obtain a brown blank, including: The green blank after connection is degreased by using an organic solvent; the green blank after connection is thermally degreased to obtain a brown blank.
7. A method for preparing a pellet according to any one of claims 1 to 6, characterized in that: The heating surface temperature range is 120℃~200℃.
8. A method for preparing a pellet according to any one of claims 1 to 6, characterized in that: The heating time ranges from 10s to 20s.
9. A tool for pellet preparation, characterized in that: Includes a platform, a rotating axis and two fixtures. The platform is divided into a first part and a second part, and the first part and the second part are connected by a rotation axis so that at least one of the first part and the second part can rotate around the rotation axis; The two clamps are respectively installed on the first part and the second part, and are respectively used to fix and connect two green blanks to be connected; The tooling has a switchable first mode and a second mode. In the first mode, the first part and the second part are in an unfolded state, and the bottom surfaces of the two clamps are in the same horizontal plane; in the second mode, the first part and the second part are in a folded state, and the two clamps are symmetrical along the platform.
10. A tool for pellet preparation according to claim 9, characterized in that: At least one of the first part and the second part is provided with a sliding mechanism, and at least one of the two clamps can slide along the sliding mechanism.