Ceramic core and method for producing the same

Abstract

The application relates to the technical field of precision casting, in particular to a ceramic core and a preparation method thereof, which comprises the following steps: A. obtaining a ceramic cold core after melting deposition 3D printing of a ceramic-based composite material; B. placing the ceramic cold core in a ceramic core mold, then injecting ceramic core slurry to perform injection molding, forming a ceramic core matrix, and obtaining a ceramic core blank body wrapped with the ceramic cold core; and C. obtaining the ceramic core after defatting and calcining of the ceramic core blank body. The ceramic core and the preparation method thereof have the advantages that the preparation flexibility of the ceramic core is improved under the premise of simplifying the preparation method, the problem that the ceramic core blank body is prone to depression is solved, and after the ceramic core is used for casting, the ceramic core can be easily cleaned up, so that the actual use requirement is met.

Description

Technical Field

[0001] This invention relates to the field of precision casting technology, and in particular to a ceramic core and its preparation method. Background Technology

[0002] Investment casting (also known as lost-wax casting) is a primary process for manufacturing high-temperature alloy precision castings with complex internal cavity structures, such as gas turbine guide vanes. In this process, the ceramic core, as a key component forming the complex flow channels and cooling channels inside the casting, directly affects the quality and performance of the final casting due to its dimensional accuracy and structural integrity.

[0003] The typical preparation process of ceramic cores is as follows: First, ceramic powder is mixed with an organic binder to prepare a ceramic core slurry; then, the ceramic core slurry is injected into a ceramic core mold using a hot-pressing method to form a ceramic green body with a predetermined shape; next, the organic binder in the green body is removed through a debinding process; finally, it is calcined at a high temperature to densify the ceramic core slurry, obtaining a ceramic core with certain strength and dimensional stability. However, when using the above method to prepare ceramic cores with a large thickness, the following problems exist during the cooling process after injection molding: there is a significant difference in heat conduction between the interior and surface of the thick-walled region. The interior of the thick-walled region dissipates heat slowly and cools lags behind, while the surface layer cools and solidifies first to form a relatively dense hardened layer, which strongly constrains the slurry that has not yet fully solidified inside; as the interior continues to cool and shrink, due to the restriction of the surface hardened layer, the internal shrinkage cannot be released freely, causing the thick-walled region to undergo inward collapse deformation, resulting in a depression on the surface of the final ceramic core.

[0004] To address the aforementioned issues, some existing technologies propose pre-forming holes or cavities in the ceramic core to reduce the accumulation of ceramic core slurry in thick-walled areas. This reduces the uneven shrinkage driving force caused by excessive ceramic material accumulation during the cooling process after injection molding. For example, existing technologies pre-place built-in structures to occupy specific spaces during the ceramic core molding process, reducing the amount of ceramic slurry filling during the molding stage, thereby reducing the uneven shrinkage driving force and minimizing shrinkage deformation. The cold core preparation method involves: first, preparing a one-piece cold core using a cold core mold; then, cutting off a portion of the cold core from the one-piece cold core and placing the remaining portion into the cold core mold at its corresponding structural position; finally, injecting hot-melt core slurry into the cold core mold for secondary filling and pressing to obtain a tenon-and-mortise joint cold core. However, this method involves numerous steps and a complex process, leading to problems such as complicated preparation methods. Furthermore, the shape of the cold core is still limited by the mold, resulting in low flexibility and difficulty in adapting to the personalized design requirements of different ceramic core structures.

[0005] In summary, existing thick ceramic cores suffer from drawbacks such as shrinkage deformation, complex preparation methods, and insufficient preparation flexibility. Summary of the Invention

[0006] The purpose of this invention is to provide a ceramic core and its preparation method, which helps to solve the problem of easy depression of ceramic core blanks while simplifying the preparation method. At the same time, the ceramic core is easy to disintegrate and clean after casting and use, so as to meet the actual use needs.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] A method for preparing a ceramic core includes the following steps:

[0009] A. A ceramic cold core is obtained by fused deposition modeling of ceramic matrix composites;

[0010] The raw materials of the ceramic-based composite material include ceramic powder, plastic matrix and plasticizer;

[0011] The raw materials of the plastic matrix, calculated by mass parts, include 40-50 parts of polylactic acid, 50-60 parts of polyethylene glycol, 3-5 parts of rod-shaped granules, 2-3 parts of stearic acid, and 2-3 parts of thermal initiator;

[0012] The rod-shaped particles consist of an inner layer and a coating layer from the inside out. The coating layer completely encloses the inner layer. The inner layer is made of organic fiber, and the coating layer is made of thermoplastic resin.

[0013] B. Place the ceramic cold core in the ceramic core mold, then inject the ceramic core slurry for injection molding to form a ceramic core matrix, and obtain a ceramic core blank encapsulating the ceramic cold core;

[0014] C. The ceramic core is obtained by degreasing and calcining the ceramic core blank;

[0015] The ceramic core is divided into an outer layer and an internal structure. The internal structure is formed by degreasing and calcining the ceramic cold core. The outer layer is formed by calcining the ceramic core matrix. The outer layer completely encloses the internal structure. The maximum thickness of the outer layer is ≥3cm, and the main body thickness of the ceramic cold core is ≥1cm.

[0016] The temperature profile for degreasing is as follows:

[0017] The time required to heat the room temperature to 100℃ is 1.5 to 2.5 hours.

[0018] The time required to raise the temperature from 100℃ to 120℃ is 1 to 1.5 hours.

[0019] The heating time from 120℃ to 180℃ is 2.5 to 3 hours.

[0020] The heating time from 180℃ to 280℃ is 1.5 to 2 hours.

[0021] It takes 2-3 hours to raise the temperature from 280℃ to 380℃.

[0022] The temperature rises from 380℃ to 450℃, taking 2–3 hours.

[0023] The heating time from 450°C to 650°C is 1 to 1.5 hours.

[0024] Keep warm at 650℃ for 0.4 to 0.6 hours.

[0025] Further, in step A, the preparation method of the rod-shaped particles is as follows: immerse the organic fiber in a nitric acid solution with a volume concentration of 5-15%, stir at room temperature for 1-3 hours to make the surface of the organic fiber have hydroxyl groups, then wash it repeatedly with deionized water until neutral and then dry it to obtain surface-activated organic fiber.

[0026] Surface-activated organic fibers are placed in a fluidized bed to suspend the organic fibers in a fluidized state, thus obtaining fluidized organic fibers.

[0027] Thermoplastic resin is heated to a molten state and pulse-sprayed onto the surface of fluidized organic fibers. After cooling and solidification, thermoplastic resin is coated onto the surface of the organic fibers to obtain rod-shaped particles.

[0028] In this case, the bed temperature of the fluidized bed is lower than the melting point of the thermoplastic resin.

[0029] Furthermore, the length of the rod-shaped particles is 150–500 μm, and the diameter is 30–50 μm;

[0030] The organic fibers have a length of 100–300 μm and a diameter of 15–30 μm.

[0031] Furthermore, in step A, the organic fiber includes either nylon fiber or polyester fiber;

[0032] The thermoplastic resin includes any one of polyethylene resin, polypropylene resin, polystyrene resin, and methyl methacrylate resin.

[0033] Further, in step A, the polyethylene glycol includes polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000;

[0034] The mixing ratio of polyethylene glycol 4000, polyethylene glycol 6000 and polyethylene glycol 8000, calculated by mass ratio, is 1:(2-3):(1-2).

[0035] Further, in step A, the molecular weight of the polylactic acid is 20,000 to 50,000.

[0036] Further, in step A, the raw materials of the ceramic matrix composite material, calculated by mass percentage, include 70-80% ceramic powder, 15-25% plastic matrix, and 5-10% plasticizer.

[0037] Furthermore, in step B, the ceramic core slurry includes ceramic powder;

[0038] According to the mass fractions, the raw materials of the ceramic powder in the ceramic core slurry and the ceramic powder in the ceramic matrix composite material both include 80-90 parts of fused silica powder, 5-10 parts of corundum powder and 10-15 parts of mullite powder.

[0039] Further, in step B, the ceramic core slurry includes a plasticizer, and calculated by mass parts, the ceramic core slurry includes 80-90 parts of ceramic powder and 10-20 parts of plasticizer;

[0040] The raw materials for the plasticizer in the ceramic core slurry and the plasticizer in the ceramic matrix composite both include paraffin wax, beeswax, and tributyl citrate.

[0041] A ceramic core is prepared using the above-described method for preparing ceramic cores.

[0042] The technical solution provided by this invention may include the following beneficial effects:

[0043] 1. This technology designs the raw material formulation so that the plastic matrix and plasticizer begin to decompose at 190–200℃, enter the first main decomposition stage at 220–240℃, and enter the second main decomposition stage at 300–450℃. By the end of the heat treatment at 650℃, the total decomposition rate can reach over 99%, and the plasticizer is almost completely decomposed into CO2 and H2O before the degreasing process is completed, leaving no solid residue. This decomposition window is highly matched with the degreasing process curve, ensuring that the organic components in the ceramic cold core have been basically vaporized and discharged when the degreasing is completed. This results in a porous structure in the ceramic cold core after degreasing, solving the problem of easy sinking of the ceramic core blank. At the same time, the ceramic core is easy to disintegrate and clean after casting and use, simplifying the preparation method of the ceramic core.

[0044] 2. This technical solution obtains ceramic cold cores by fused deposition modeling of ceramic matrix composites, which is a simple preparation method. At the same time, based on the digital manufacturing characteristics of 3D printing, there is no need to design and manufacture ceramic cold core molds separately for different ceramic core structures. Only the three-dimensional model needs to be adjusted to achieve rapid customization of the shape, size and internal pore structure of the ceramic cold core. It can flexibly adapt to the personalized design needs of various complex ceramic cores, significantly improving the flexibility of ceramic cold core and ceramic core preparation.

[0045] 3. This technical solution places the ceramic cold core in the thick-walled area of ​​the ceramic core mold. During the injection molding stage, the amount of ceramic slurry filling in this area is reduced by physically occupying the space. This reduces the internal cold shrinkage caused by excessive slurry accumulation in the thick-walled area from the source, and reduces the difference in cold shrinkage between the inside and outside. This means that even if the maximum thickness of the outer layer of the ceramic core is ≥3cm, shrinkage deformation can be reduced.

[0046] 4. As the main component of the rod-shaped particles, organic fibers can effectively constrain the relative displacement of ceramic powder particles, limit the overall shrinkage of the cold core, and make the dimensional changes of the cold core smaller and the shape more stable. The greater the stability of the cold core's dimensions, the more precise and reliable its physical positioning effect on the ceramic slurry in the thick-walled area of ​​the mold, and the more consistent the gap control between the cold core and the mold cavity. This reduces the spatial displacement caused by the shrinkage or deformation of the cold core itself, making the difference in cooling shrinkage between the inside and outside of the thick-walled area more controllable, and ultimately effectively suppressing the occurrence of shrinkage deformation. Attached Figure Description

[0047] Figure 1 This is a structural diagram of a ceramic cold core according to one embodiment of the present invention.

[0048] Figure 2 This is a structural diagram of a ceramic core mold according to one embodiment of the present invention.

[0049] Figure 3 This is a structural diagram of a ceramic core according to one embodiment of the present invention.

[0050] Figure 4 This is a physical image of a ceramic core mold according to one embodiment of the present invention.

[0051] Figure 5 This is a physical image of a ceramic core according to one embodiment of the present invention.

[0052] Among them: ceramic cold core 1; support foot 11; main body of ceramic cold core 12; ceramic core mold 2; inner cavity of ceramic core mold 21; ceramic core 3. Detailed Implementation

[0053] This technical solution provides a method for preparing a ceramic core, including the following steps:

[0054] A. A ceramic cold core is obtained by fused deposition modeling of ceramic matrix composites;

[0055] The raw materials of the ceramic-based composite material include ceramic powder, plastic matrix and plasticizer;

[0056] The raw materials of the plastic matrix, calculated by mass parts, include 40-50 parts of polylactic acid, 50-60 parts of polyethylene glycol, 3-5 parts of rod-shaped granules, 2-3 parts of stearic acid, and 2-3 parts of thermal initiator;

[0057] The rod-shaped particles consist of an inner layer and a coating layer from the inside out. The coating layer completely encloses the inner layer. The inner layer is made of organic fiber, and the coating layer is made of thermoplastic resin.

[0058] B. Place the ceramic cold core in the ceramic core mold, then inject the ceramic core slurry for injection molding to form a ceramic core matrix, and obtain a ceramic core blank encapsulating the ceramic cold core;

[0059] C. The ceramic core is obtained by degreasing and calcining the ceramic core blank;

[0060] The ceramic core is divided into an outer layer and an internal structure. The internal structure is formed by degreasing and calcining the ceramic cold core. The outer layer is formed by calcining the ceramic core matrix. The outer layer completely encloses the internal structure. The maximum thickness of the outer layer is ≥3cm, and the main body thickness of the ceramic cold core is ≥1cm.

[0061] The temperature profile for degreasing is as follows:

[0062] The time required to heat the room temperature to 100℃ is 1.5 to 2.5 hours.

[0063] The time required to raise the temperature from 100℃ to 120℃ is 1 to 1.5 hours.

[0064] The heating time from 120℃ to 180℃ is 2.5 to 3 hours.

[0065] The heating time from 180℃ to 280℃ is 1.5 to 2 hours.

[0066] It takes 2-3 hours to raise the temperature from 280℃ to 380℃.

[0067] The temperature rises from 380℃ to 450℃, taking 2–3 hours.

[0068] The heating time from 450°C to 650°C is 1 to 1.5 hours.

[0069] Keep warm at 650℃ for 0.4 to 0.6 hours.

[0070] To address the shortcomings of existing thick ceramic cores, such as shrinkage deformation, complex preparation methods, and insufficient preparation flexibility, this technical solution proposes a method for preparing ceramic cores. By designing the ceramic matrix composite material formulation and the ceramic core preparation method, this method can improve the preparation flexibility of thick ceramic cores and reduce shrinkage deformation while simplifying the preparation process, thus meeting practical application requirements.

[0071] Specifically, the raw materials for the plastic matrix include polylactic acid, polyethylene glycol, rod-shaped granules, stearic acid, and a thermal initiator. It should be noted that this technical solution, through the design of the plastic matrix raw materials, ensures a smooth and controllable overall gas generation rate of the ceramic cold core during the degreasing process. Simultaneously, after degreasing, the ceramic cold core forms a porous or mesh structure with pre-formed interconnected pores, providing direct exhaust channels for the decomposition gases. The ceramic core utilizes a conventional powder-embedded degreasing and sintering process, and the degreasing temperature profile has been optimized.

[0072] The initial heating process of degreasing, from room temperature to 180℃, is carried out in stages and slowly. This allows the plasticizers such as paraffin and beeswax in the ceramic core blank formed from the ceramic core slurry to be slowly heated to liquefaction, thus being adsorbed during the powder-burying and degreasing process, preventing vaporization and cracking of the blank. This process also creates an external channel for the degreasing and discharge of the ceramic cold core.

[0073] During the degreasing process in step C, polyethylene glycol in the plastic matrix melts and softens first at 80–100°C, increasing the mobility of its molecular chains. The thermal initiator decomposes at 120–150°C to generate free radicals, initiating the breakage of polylactic acid chains and reducing its decomposition temperature from 300–350°C to 220–250°C. The water vapor generated by the decomposition of polyethylene glycol at 200–250°C further promotes the hydrolysis of polylactic acid. Simultaneously, the thermoplastic resin coating in the rod-shaped particles gradually decomposes within the range of 300–450°C, and the organic fiber inner layer decomposes at 400–500°C. In addition, the plasticizer gradually decomposes within the range of 200–280°C. The decomposition products of both the rod-shaped particles and the plasticizer are small molecule gases, further increasing the gas escape channels of the system and forming a multi-stage synergistic effect with the decomposition of polyethylene glycol and polylactic acid. Stearic acid, as a compatibilizer, completely decomposes at 200–250°C, further participating in gas escape. The combined action of the aforementioned components, along with the controlled addition of each, ensures that the plastic matrix and plasticizer begin to decompose at 140–160°C, enter the first major decomposition stage at 180–240°C, and the second major decomposition stage at 300–450°C. By the end of the heat treatment at 650°C, the total decomposition rate reaches over 99%, with almost complete decomposition into CO2 and H2O before the degreasing process is finished, leaving no solid residue. This decomposition window closely matches the degreasing process curve, ensuring that the organic components in the ceramic cold core have been largely vaporized and discharged by the time degreasing is complete. This results in a porous structure in the ceramic cold core after degreasing, making it easy to disintegrate and clean, thus simplifying the preparation method of the ceramic core.

[0074] The degreasing process employs a 650℃ insulation platform, allowing sufficient time for gas to escape to the surface through the internal pores of the ceramic cold core and the interconnected pores gradually formed in the ceramic core matrix. Through the synergistic design of the materials and processes described above, the gas generation rate of the ceramic cold core is consistently lower than the gas permeation rate of the ceramic core matrix at this temperature. This effectively avoids defects such as internal pressure buildup, bubbling, or cracking caused by gas retention, ensuring that the ceramic core does not crack due to vaporization during the degreasing process.

[0075] Meanwhile, this technical solution obtains ceramic cold cores through fused deposition modeling (FDM) 3D printing of ceramic matrix composites, a simple preparation method. Furthermore, based on the digital manufacturing characteristics of 3D printing, there is no need to design and manufacture ceramic cold core molds separately for different ceramic core structures; only the 3D model needs to be adjusted to achieve rapid customization of the ceramic cold core's shape, size, and internal pore structure. This allows for flexible adaptation to the personalized design needs of various complex ceramic cores, significantly improving the flexibility of ceramic cold core and ceramic core preparation. It should be noted that the ceramic matrix composite is prepared by mixing the aforementioned ceramic powder, plastic matrix, and plasticizer in a mixer to obtain the feedstock, which is then extruded into printing consumables. The mixing and extrusion processes involved are existing technologies and will not be described in detail here.

[0076] Secondly, this technical solution reduces shrinkage deformation even when the maximum thickness of the outer layer of the ceramic core is ≥3cm through the following mechanism, the specific mechanism of which is as follows:

[0077] First, physical placement reduces slurry accumulation in thick-walled areas. By placing the ceramic cold core in the thick-walled area of ​​the ceramic core mold, the amount of ceramic slurry filling in this area is reduced during the injection molding stage. This reduces the internal cold shrinkage caused by excessive slurry accumulation in the thick-walled area from the source, thus mitigating the difference in cold shrinkage between the inside and outside.

[0078] Secondly, the rigid support of the ceramic cold core suppresses cooling shrinkage deformation. The ceramic cold core is a solid molded object at room temperature and has high room temperature strength. During the cooling process after injection molding, when the thick-walled area has not yet completely solidified, the ceramic cold core, as a rigid skeleton, is embedded in it, which can effectively resist the inward collapse force caused by internal cooling shrinkage, thereby suppressing the initiation of shrinkage deformation.

[0079] Third, as the main component of the rod-shaped particles, the organic fiber network can effectively constrain the relative displacement of ceramic powder particles, limit the overall shrinkage of the cold core, and make the dimensional changes of the cold core smaller and the shape more stable. The more precise and reliable the physical positioning effect of the cold core on the ceramic slurry in the thick-walled area of ​​the mold, the more consistent the gap control between the cold core and the mold cavity. This reduces the spatial displacement caused by the shrinkage or deformation of the cold core itself, making the difference in cooling shrinkage between the inside and outside of the thick-walled area more controllable, and ultimately effectively suppressing the occurrence of shrinkage deformation.

[0080] Fourth, after the plastic matrix and plasticizer in the ceramic cold core are completely decomposed during the degreasing stage, they form a porous or mesh structure. This not only provides a smooth channel for gas discharge, avoiding the accumulation of internal pressure in thick-walled areas due to poor gas exhaust, but also allows the porous structure to partially absorb shrinkage stress during sintering, effectively suppressing inward collapse caused by uneven shrinkage between the surface and interior, thereby significantly reducing shrinkage deformation.

[0081] Furthermore, during the injection molding process of ceramic core slurry, the slurry directly impacts the surface of the ceramic cold core under high injection pressure. Therefore, the ceramic cold core must possess sufficient strength to prevent cracking during injection molding, thereby obtaining a complete ceramic core preform. This technical solution achieves high strength in the ceramic cold core through the following mechanism:

[0082] First, the raw material for preparing ceramic cold cores, ceramic matrix composites, includes ceramic powder, plastic matrix and plasticizer. Adding ceramic powder can improve the strength and heat resistance of ceramic cold cores and reduce the risk of deformation during injection molding.

[0083] Secondly, due to their unique high aspect ratio morphology, the rod-shaped particles can form a three-dimensional overlapping network within the plastic matrix of the ceramic cold core. When the cold core is subjected to external loads, the rod-shaped particles can transfer and disperse local stress to the surrounding matrix through a bridging effect, avoiding stress concentration. Simultaneously, the rod-shaped particles, with organic fibers as the inner layer and thermoplastic resin as the outer layer, not only improve the uniformity of organic fiber dispersion in the plastic matrix, but also exhibit good compatibility with the plastic matrix, achieving chemical bonding or physical entanglement, enhancing interfacial bonding strength, and effectively hindering crack initiation and propagation. Furthermore, the inner organic fibers provide additional tensile strength. These synergistic effects enable the ceramic cold core to resist the impact pressure of the ceramic slurry and the tensile stress generated by cooling shrinkage during the injection molding stage, significantly improving the room temperature strength and crack resistance of the cold core, and further reducing the risk of deformation during injection molding.

[0084] Finally, this technical solution eliminates the need for additional adhesives to bond the ceramic powder and plastic matrix during fused deposition modeling (FDM) printing. This is because: the polylactic acid (PLA) in the plastic matrix, as a thermoplastic polymer, forms a continuous phase upon cooling, encapsulating and bonding the ceramic powder particles, providing room-temperature strength for FDM printing; the carboxyl groups of stearic acid bind to the surface of the ceramic powder, and the long-chain alkyl groups entangle with the PLA molecular chains, allowing stearic acid to act as a compatibilizer, achieving chemical bonding between the ceramic powder and PLA, thus compensating for the shortcomings of physical mixing; and the plasticizer ensures good melt flow during printing, indirectly guaranteeing the quality of interlayer bonding.

[0085] It should be noted that the thermal initiator can be dicumyl peroxide, and the specific type is not limited here.

[0086] It should be further explained that the ceramic cold core in this technical solution is actually located in the thick-walled region of the ceramic core. The ratio of the volume of the ceramic cold core to the volume of the ceramic core is closely related to factors such as the structure and thickness of the ceramic core. The ratio between the two can be adjusted according to actual needs to meet the actual application requirements, which will not be described here.

[0087] Preferably, in step A, the temperature of the fused deposition modeling 3D printing is 140–180°C, the nozzle diameter is 1–2 mm, and the speed is 15–45 mm / s.

[0088] A printing temperature of 140–180℃ is lower than the significant decomposition temperature (≥190℃) of thermal initiators (such as dicumyl peroxide), effectively preventing premature thermal degradation of the plastic matrix during printing while ensuring the melt flowability of the composite filament. A large-diameter nozzle of 0.6–1.2 mm effectively reduces the extrusion resistance of the ceramic matrix composite, preventing nozzle clogging. A medium-low printing speed of 15–45 mm / s provides sufficient interlayer bonding time for the molten material while avoiding uneven extrusion or interlayer misalignment caused by excessive speed. The combined application of these parameters ensures rapid molding of the ceramic cold core without a mold, resulting in a dense structure, precise dimensions, and reliable interlayer bonding, providing a stable support for the subsequent ceramic core injection molding stage.

[0089] Preferably, in step B, the injection temperature of the injection molding is 80-100°C, the injection pressure is 4-6 MPa, and the holding time is 5-35 s.

[0090] Preferably, in step A, the molecular weight of the polylactic acid is 10,000 to 30,000.

[0091] This technical solution controls the molecular weight of polylactic acid (PLA) within the range of 10,000 to 30,000. PLA features a short molecular chain, high end-group concentration, and low thermal decomposition barrier. With the synergistic effect of thermal initiators (such as diisopropylbenzene peroxide), PLA can be completely decomposed during degreasing. Simultaneously, PLA within this molecular weight range maintains sufficient mechanical strength at room temperature, meeting the requirements for 3D printing and the injection of ceramic slurry for mold support. Furthermore, the complete decomposition during degreasing leaves no carbide residue, ensuring the structural integrity of the ceramic cold core during the injection stage and guaranteeing complete vaporization and discharge before the end of degreasing. This avoids interference with subsequent sintering or the induction of impurity crystal defects in the casting due to incomplete decomposition.

[0092] Preferably, in step C, the calcination temperature is 1100–1300°C, and the calcination time is 60–120 min.

[0093] This technical solution limits the calcination temperature and time, ensuring that the calcination temperature range falls within the sintering activation range of fused silica, corundum powder, and mullite powder. This allows ceramic particles to effectively combine through diffusion and flow, achieving the required strength and high-temperature stability. Simultaneously, the shorter calcination time (60–120 min) prevents excessive grain growth or abnormal shrinkage due to prolonged holding time, keeping the difference in total shrinkage between the ceramic core matrix and the ceramic cold core within 0.5%, effectively preventing interface cracking. Furthermore, this calcination process ensures the stable preservation of the porous structure formed by the decomposition of the ceramic cold core during sintering. This provides a buffer space for shrinkage stress and prevents excessive pore closure due to prolonged high-temperature holding, thus avoiding loss of stress absorption capacity.

[0094] To further explain, in step A, the preparation method of the rod-shaped particles is as follows: the organic fiber is immersed in a nitric acid solution with a volume concentration of 5-15%, stirred at room temperature for 1-3 hours to make the surface of the organic fiber have hydroxyl groups, and then repeatedly washed with deionized water until neutral and dried to obtain surface-activated organic fiber.

[0095] Surface-activated organic fibers are placed in a fluidized bed to suspend the organic fibers in a fluidized state, thus obtaining fluidized organic fibers.

[0096] Thermoplastic resin is heated to a molten state and pulse-sprayed onto the surface of fluidized organic fibers. After cooling and solidification, thermoplastic resin is coated onto the surface of the organic fibers to obtain rod-shaped particles.

[0097] In this process, the bed temperature of the fluidized bed is lower than the melting point of the thermoplastic resin. The prepared rod-shaped particles and other raw materials of the plastic matrix are mixed evenly, and then the various raw materials of the ceramic matrix composite are mixed evenly to obtain the ceramic matrix composite.

[0098] This technical solution pre-activates the organic fibers by adding hydroxyl groups to their surface, thereby enhancing the interfacial bonding between the organic fibers and the thermoplastic resin. This improves the yield of rod-shaped particles with an inner layer and a coating layer.

[0099] Furthermore, the bed temperature of the fluidized bed is lower than the melting point of the thermoplastic resin, which helps to prevent the excessive flow of the thermoplastic resin from causing the organic fibers to stick together, and ensures that the rod-shaped particles exist in particulate form as much as possible.

[0100] To further explain, in step A, the length of the rod-shaped particles is 150–500 μm and the diameter is 30–50 μm;

[0101] The organic fibers have a length of 100–300 μm and a diameter of 15–30 μm.

[0102] In this technical solution, by further optimizing the length and diameter of the rod-shaped particles and organic fibers, it is beneficial to ensure that they can enhance the strength of the ceramic cold core and also ensure that they can be easily and completely decomposed during the degreasing process, so as to facilitate the formation of a porous structure.

[0103] To further clarify, in step A, the organic fiber includes either nylon fiber or polyester fiber;

[0104] The thermoplastic resin includes any one of polyethylene resin, polypropylene resin, polystyrene resin, and methyl methacrylate resin.

[0105] This technical solution, by limiting the types of organic fibers and thermoplastic resins, not only utilizes the good compatibility between thermoplastic resins and plastic matrices to enhance the compatibility and interfacial strength of other raw materials between rod-shaped particles and plastic matrices, but also benefits from the reinforcing and toughening effect of organic fibers to increase the strength of the ceramic cold core obtained by 3D printing.

[0106] To further explain, in step A, the polyethylene glycol includes polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000;

[0107] The mixing ratio of polyethylene glycol 4000, polyethylene glycol 6000 and polyethylene glycol 8000, calculated by mass ratio, is 1:(2-3):(1-2).

[0108] Different molecular weights of polyethylene glycol have different melting points (polyethylene glycol 4000 melting point is about 55-60℃, polyethylene glycol 6000 melting point is about 60-65℃, and polyethylene glycol 8000 melting point is about 65-70℃). By compounding polyethylene glycol 4000, polyethylene glycol 6000 and polyethylene glycol 8000, the ceramic cold core can gradually soften in the range of 50-80℃, rather than the sudden melting of a single molecular weight in a narrow temperature range, which would cause a sudden change in volume and stress concentration. This ensures a smooth transition of the ceramic cold core in the initial stage of degreasing and heating.

[0109] Furthermore, the thermal decomposition temperature of polyethylene glycol is positively correlated with its molecular weight. The compound system can extend the decomposition window from a narrow window formed by a single molecular weight to a wide window, thus broadening the decomposition temperature window. At the same time, the decomposition peaks of polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000 are staggered, avoiding instantaneous concentrated gas production. This makes the overall gas production rate of the ceramic cold core gradual and controllable, which is conducive to the orderly discharge of gas through the body pores and prevents internal pressure accumulation that could lead to bubbling or cracking.

[0110] Furthermore, due to the differences in decomposition rates, polyethylene glycols of different molecular weights can continuously and segmentally release water vapor within this temperature range, which promotes the hydrolysis and decomposition of polylactic acid for a longer period of time. This further reduces the main decomposition temperature of polylactic acid, which helps to ensure that the plastic matrix is ​​completely decomposed before the degreasing process is completed, so as to form a porous structure.

[0111] To further explain, in step A, the raw materials of the ceramic matrix composite material, calculated by mass percentage, include 70-80% ceramic powder, 15-25% plastic matrix, and 5-10% plasticizer.

[0112] This technical solution, by limiting the ceramic matrix composite material, not only helps to ensure the strength of the obtained ceramic cold core and prevents cracking during injection molding, thus obtaining a complete ceramic core blank, but also helps to ensure that the ceramic cold core obtained by using the ceramic matrix composite material forms a porous structure during the degreasing stage, reducing shrinkage deformation, and at the same time makes the ceramic core easy to disintegrate and clean after use.

[0113] To further explain, in step B, the ceramic core slurry includes ceramic powder;

[0114] According to the mass fractions, the raw materials of the ceramic powder in the ceramic core slurry and the ceramic powder in the ceramic matrix composite material both include 80-90 parts of fused silica powder, 5-10 parts of corundum powder and 10-15 parts of mullite powder.

[0115] Fused quartz powder, as the main matrix, imparts excellent alkali solubility to the core, ensuring rapid dissolution and removal under high-temperature, high-pressure alkaline core removal conditions. Mullite powder forms a needle-like whisker structure during sintering, significantly improving the high-temperature creep resistance and thermal stability of the ceramic core. Corundum powder, as a supplementary reinforcing phase, further refines the grains and enhances the room-temperature and high-temperature strength of the ceramic core, while its moderate alkali solubility does not significantly reduce the overall core removal rate. The synergy of these three components not only ensures sufficient high-temperature strength for the final calcined ceramic core during the casting stage but also achieves rapid and thorough alkali removal during the core removal stage.

[0116] Preferably, the D50 particle size of the ceramic powder in the ceramic matrix composite is 15-25 μm;

[0117] The ceramic powder in the ceramic core slurry has a D50 particle size of 10–15 μm.

[0118] This technical solution further limits the D50 particle size of ceramic powder in ceramic matrix composites and ceramic powder in ceramic core slurry, which helps to reduce the total shrinkage rate of ceramic core blanks and ceramic cold cores after calcination, and reduces the interfacial stress caused by the difference in shrinkage rate. This avoids interfacial cracking or overall deformation between ceramic cold cores and ceramic core matrix after injection, degreasing and calcination.

[0119] To further explain, in step B, the ceramic core slurry includes a plasticizer, and calculated by mass parts, the ceramic core slurry includes 80-90 parts of ceramic powder and 10-20 parts of plasticizer;

[0120] The raw materials for the plasticizer in the ceramic core slurry and the plasticizer in the ceramic matrix composite both include paraffin wax, beeswax, and tributyl citrate.

[0121] This technical solution facilitates the fused deposition modeling (FDM) 3D printing of ceramic cold cores by adding plasticizers such as paraffin wax and beeswax to the ceramic matrix composite material. The addition of plasticizers such as paraffin wax and beeswax to the ceramic core slurry facilitates the injection molding of the ceramic core.

[0122] Preferably, the plasticizers in the ceramic core slurry and the ceramic matrix composite material, calculated by mass parts, both contain 80-85 parts of paraffin wax, 15-20 parts of beeswax, and 5-10 parts of tributyl citrate.

[0123] To further explain, in step A, the interior of the ceramic cold core has a porous structure, and the outer wall of the ceramic cold core is a closed structure that prevents fluid from passing through.

[0124] This technical solution designs a porous structure inside the ceramic cold core, which not only reduces the amount of ceramic matrix composite material used, thereby reducing the amount of gas emitted, but also provides channels for gas emission, further reducing the risk of cracking of the ceramic cold core after degreasing.

[0125] A ceramic core is prepared using the above-described method for preparing ceramic cores.

[0126] This technical solution also proposes a method for preparing ceramic cores, which can improve the flexibility of ceramic core preparation and reduce shrinkage deformation while simplifying the preparation method, so as to meet the actual use requirements.

[0127] It should be noted that this technical solution can also be used to prepare castings, and the specific application method is as follows:

[0128] A ceramic core is placed into a wax mold, and wax is injected to form a wax model.

[0129] The wax mold is immersed in refractory slurry and sprinkled with refractory sand particles. After drying and curing, a ceramic mold shell is formed.

[0130] After the ceramic mold shell is steamed and fired in sequence, the wax mold in the ceramic mold shell is removed to obtain a hollow mold shell;

[0131] The alloy molten liquid at a temperature of 1600-1700℃ is poured into the hollow mold shell, and after solidification, it forms an intermediate part.

[0132] Remove the ceramic mold shell from the intermediate part to obtain the casting blank;

[0133] The casting blank is placed in an alkaline solution to cause a chemical reaction that dissolves the ceramic core, thereby removing the ceramic core and forming an internal cavity structure to obtain the casting.

[0134] This technical solution also proposes the application of ceramic cores in casting preparation. Since the ceramic cores in this technical solution have a porous internal structure, the amount of material to be removed is significantly reduced compared to solid ceramic cores. This not only increases the removal speed of the casting blank in alkaline solution, thereby improving the casting preparation efficiency, but also facilitates the complete dissolution and removal of the ceramic core, effectively avoiding internal cavity residue and improving the product yield.

[0135] Preferably, the alkaline solution is either a sodium hydroxide solution or a potassium hydroxide solution;

[0136] The alkaline solution has a temperature of 380–400°C, a pressure of 3.0–4.5 MPa, and a concentration of 0.1–0.5 mol / L.

[0137] It should be noted that the wax, refractory slurry and refractory sand used in this technical solution are all commonly used raw materials in the field, and the specific types are not limited or described here.

[0138] It should be noted that the alloy melt can be stainless steel melt, cobalt-based high-temperature alloy melt, or iron-based high-temperature alloy melt, etc., and the specific type is not limited here.

[0139] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0140] Example 1

[0141] A. A ceramic cold core 1 is obtained by fused deposition modeling of ceramic matrix composite material, such as... Figure 1 As shown;

[0142] Among them, the outer wall of the ceramic cold core 1 is provided with multiple support feet 11, so that the ceramic cold core 1 can be positioned in the inner cavity 21 of the ceramic core mold, so that the main body 12 of the ceramic cold core is suspended in the air, and the subsequent ceramic core slurry can wrap the ceramic cold core 1.

[0143] The fused deposition modeling (FDM) 3D printing temperature was 160℃, the nozzle diameter was 0.8mm, the layer thickness was 60% of the nozzle diameter, and the speed was 30mm / s.

[0144] Based on mass percentage, the raw materials of ceramic matrix composites consist of 75% ceramic powder, 20% plastic matrix, and 5% plasticizer.

[0145] According to the mass fraction, the raw materials of ceramic powder include 80 parts of fused silica powder, 8 parts of corundum powder and 10 parts of mullite powder.

[0146] The raw materials for the plastic matrix, calculated by mass parts, include 40-50 parts of polylactic acid with a molecular weight of 20,000, 55 parts of polyethylene glycol, 4 parts of rod-shaped granules, 3 parts of stearic acid, and 2 parts of dicumyl peroxide; the polyethylene glycol includes polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000, and the mixing ratio of polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000 is 1:2:1, calculated by mass ratio.

[0147] The rod-shaped particles are 3μm long and 0.2μm in diameter. The rod-shaped particles consist of an inner layer and a coating layer from the inside out. The coating layer completely encloses the inner layer. The inner layer is made of polyester fiber, and the coating layer is made of methyl methacrylate resin.

[0148] The preparation method of rod-shaped particles is as follows: polyester fiber is immersed in a nitric acid solution with a volume concentration of 12%, stirred at room temperature for 2 hours to make the surface of polyester fiber have hydroxyl groups, and then repeatedly washed with deionized water until neutral and dried to obtain surface activated polyester fiber.

[0149] Surface-activated polyester fibers are placed in a fluidized bed at a temperature of 280℃ to make the polyester fibers in a suspended fluidized state, thus obtaining fluidized polyester fibers.

[0150] Methyl methacrylate resin is heated to a molten state and pulsed sprayed onto the surface of fluidized polyester fibers. After cooling and solidification, methyl methacrylate resin is formed on the surface of the organic fibers to obtain rod-shaped particles.

[0151] The raw materials for the plasticizer, calculated by weight, include 85 parts paraffin wax, 15 parts beeswax, and 10 parts tributyl citrate.

[0152] B. Place the ceramic cold core 1 into the ceramic core mold 2, as follows: Figure 2 and Figure 4 As shown, ceramic core slurry is then injected for injection molding to form a ceramic core matrix, resulting in a ceramic core blank encapsulating a ceramic cold core.

[0153] The injection temperature for injection molding is 100℃, the injection pressure is 5MPa, and the holding time is 20s.

[0154] According to the mass fractions, the ceramic core slurry includes 85 parts of ceramic powder and 15 parts of plasticizer;

[0155] According to the mass fraction, the raw materials of ceramic powder include 80 parts of fused silica powder, 8 parts of corundum powder and 10 parts of mullite powder.

[0156] The raw materials for the plasticizer, calculated by weight, include 85 parts paraffin wax, 15 parts beeswax, and 10 parts tributyl citrate.

[0157] C. After degreasing and calcining the ceramic core blank, ceramic core 3 is obtained, such as... Figure 3 and Figure 5 As shown;

[0158] The ceramic core is divided into an outer layer and an internal structure. The internal structure is formed by degreasing and calcining the ceramic cold core, while the outer layer is formed by calcining the ceramic core matrix. The outer layer completely encloses the internal structure. The maximum thickness of the outer layer is 10cm, and the thickness of the main body 12 of the ceramic cold core is 5cm.

[0159] The calcination temperature was 1100℃, and the calcination time was 100 min.

[0160] The temperature profile for defatting is as follows:

[0161] It takes 1.5 hours to heat the water from room temperature to 100°C.

[0162] It takes 1 hour to raise the temperature from 100℃ to 120℃.

[0163] It took 2.5 hours to heat the water from 120°C to 180°C.

[0164] It took 2 hours to raise the temperature from 180℃ to 280℃.

[0165] It took 2 hours to raise the temperature from 280℃ to 380℃.

[0166] It took 2 hours to raise the temperature from 380℃ to 450℃.

[0167] It took 1 hour to raise the temperature from 450°C to 650°C.

[0168] Keep warm at 650℃ for 0.5 hours.

[0169] The ceramic cold core 1 obtained in this embodiment 1 can maintain its shape during the injection molding process, so that a complete ceramic core 3 can be obtained through the above steps. The obtained ceramic core 3 is basically free from shrinkage deformation and cracking defects, and its flatness is within 0.1mm.

[0170] The ceramic core obtained in Example 1 was placed into a wax mold, and wax was injected to form a wax mold.

[0171] The wax mold is immersed in refractory slurry and sprinkled with refractory sand particles. After drying and curing, a ceramic mold shell is formed.

[0172] The ceramic mold shell is successively subjected to steam at 200°C and fired at 300°C to remove the wax mold in the ceramic mold shell, thus obtaining a hollow mold shell.

[0173] Stainless steel at 1600℃ is poured into a hollow mold shell and solidifies to form an intermediate part.

[0174] Remove the ceramic mold shell from the intermediate part to obtain the casting blank;

[0175] The casting blank is placed in a sodium hydroxide solution to cause a chemical reaction that dissolves the ceramic core, thereby removing the ceramic core and forming an internal cavity structure to obtain the casting. The sodium hydroxide solution is at a temperature of 380℃, a pressure of 3MPa, and a concentration of 0.5mol / L.

[0176] In this embodiment 1, the ceramic core was completely removed in 6 hours, and the yield of the casting was 95%.

[0177] Example 2

[0178] A. A ceramic cold core was obtained by fused deposition modeling of ceramic matrix composite material. The structure of the ceramic cold core was the same as that in Example 1.

[0179] The fused deposition modeling (FDM) 3D printing temperature was 140℃, the nozzle diameter was 1.2mm, the layer thickness was 80% of the nozzle diameter, and the speed was 45mm / s.

[0180] Based on mass percentage, the raw materials of ceramic matrix composites consist of 70% ceramic powder, 25% plastic matrix, and 5% plasticizer;

[0181] According to the mass fraction, the raw materials of ceramic powder include 90 parts of fused silica powder, 5 parts of corundum powder and 12 parts of mullite powder.

[0182] The raw materials for the plastic matrix, calculated by mass parts, include 40 parts of polylactic acid with a molecular weight of 10,000, 60 parts of polyethylene glycol, 5 parts of rod-shaped granules, 3 parts of stearic acid, and 2 parts of dicumyl peroxide; the polyethylene glycol includes polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000, and the mixing ratio of polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000 is 1:2:2, calculated by mass ratio.

[0183] The rod-shaped particles are 3μm long and 0.1μm in diameter. From the inside out, the rod-shaped particles consist of an inner layer and a wrapping layer. The wrapping layer completely wraps the inner layer. The inner layer is made of nylon fiber, and the wrapping layer is made of thermoplastic resin.

[0184] The preparation method of rod-shaped particles is as follows: Nylon fibers are immersed in a 10% nitric acid solution and stirred at room temperature for 1 to 3 hours to make the surface of the nylon fibers have hydroxyl groups. Then, they are repeatedly washed with deionized water until neutral and dried to obtain surface-activated nylon fibers.

[0185] Surface-activated nylon fibers are placed in a fluidized bed at 280°C to suspend the nylon fibers in a fluidized state, thus obtaining fluidized nylon fibers.

[0186] Polypropylene resin is heated to a molten state and pulse-sprayed onto the surface of fluidized nylon fibers. After cooling and solidification, polypropylene resin is coated onto the surface of the nylon fibers to obtain rod-shaped particles.

[0187] The raw materials for the plasticizer, calculated by weight, include 80 parts paraffin wax, 20 parts beeswax, and 10 parts tributyl citrate.

[0188] B. Place the ceramic cold core in the ceramic core mold, then inject the ceramic core slurry for injection molding to form a ceramic core matrix, and obtain a ceramic core blank encapsulating the ceramic cold core;

[0189] The injection temperature for injection molding is 80℃, the injection pressure is 4MPa, and the holding time is 30s.

[0190] According to the mass fraction, the ceramic core slurry includes 80 parts of ceramic powder and 20 parts of plasticizer;

[0191] According to the mass fraction, the raw materials of ceramic powder include 90 parts of fused silica powder, 5 parts of corundum powder and 12 parts of mullite powder.

[0192] The raw materials for the plasticizer, calculated by weight, include 80 parts paraffin wax, 20 parts beeswax, and 10 parts tributyl citrate.

[0193] C. The ceramic core is obtained by degreasing and calcining the ceramic core blank;

[0194] The ceramic core consists of an outer layer and an internal structure. The internal structure is formed by degreasing and calcining the ceramic cold core. The outer layer is formed by calcining the ceramic core substrate and completely encloses the internal structure. The maximum thickness of the outer layer is 15cm, and the thickness of the main body of the ceramic cold core is 8cm.

[0195] The calcination temperature was 1200℃, and the calcination time was 80 min.

[0196] The temperature profile for defatting is as follows:

[0197] It takes 2.5 hours to heat the water from room temperature to 100°C.

[0198] It takes 1.5 hours to heat the water from 100℃ to 120℃.

[0199] It took 3 hours to raise the temperature from 120℃ to 180℃.

[0200] The temperature was raised from 180℃ to 280℃ in 1.5 hours.

[0201] It took 3 hours to raise the temperature from 280℃ to 380℃.

[0202] It took 2 hours to raise the temperature from 380℃ to 450℃.

[0203] It took 1.5 hours to heat the water from 450°C to 650°C.

[0204] Keep warm at 650℃ for 0.6 hours.

[0205] The ceramic cold core obtained in this embodiment 2 can maintain its shape during the injection molding process, so that a complete ceramic core can be obtained through the above steps. The obtained ceramic core is basically free from shrinkage deformation and cracking defects, and its flatness is within 0.1mm.

[0206] The ceramic core obtained in Example 2 was placed into a wax mold, and wax was injected to form a wax mold.

[0207] The wax mold is immersed in refractory slurry and sprinkled with refractory sand particles. After drying and curing, a ceramic mold shell is formed.

[0208] The ceramic mold shell is successively subjected to steam at 200°C and fired at 300°C to remove the wax mold in the ceramic mold shell, thus obtaining a hollow mold shell.

[0209] Stainless steel at 1600℃ is poured into a hollow mold shell and solidifies to form an intermediate part.

[0210] Remove the ceramic mold shell from the intermediate part to obtain the casting blank;

[0211] The casting blank is placed in a potassium hydroxide solution to cause a chemical reaction that dissolves the ceramic core, thereby removing the ceramic core and forming an internal cavity structure to obtain the casting. The potassium hydroxide solution is at a temperature of 400℃, a pressure of 4MPa, and a concentration of 0.5mol / L.

[0212] In this embodiment 2, the ceramic core was completely removed in 8 hours, and the yield of the casting was 94%.

[0213] Example 3

[0214] A. A ceramic cold core was obtained by fused deposition modeling of ceramic matrix composite material, and the structure was the same as that of the ceramic cold core in Example 1.

[0215] The fused deposition modeling (FDM) 3D printing temperature was 140℃, the nozzle diameter was 0.6mm, the layer thickness was 40% of the nozzle diameter, and the speed was 15mm / s.

[0216] Based on mass percentage, the raw materials of ceramic matrix composites consist of 80% ceramic powder, 15% plastic matrix, and 5% plasticizer.

[0217] According to the mass fractions, the raw materials of ceramic powder include 85 parts of fused silica powder, 5 parts of corundum powder and 10 parts of mullite powder.

[0218] Based on mass parts, the raw materials of the plastic matrix include 50 parts of polylactic acid with a molecular weight of 30,000, 60 parts of polyethylene glycol, 3 parts of rod-shaped granules, 3 parts of stearic acid, and 2 parts of dicumyl peroxide; the polyethylene glycol includes polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000, and based on mass ratio, the mixing ratio of polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000 is 1:3:2;

[0219] The rod-shaped particles are 2 μm long and 0.1 μm in diameter. The rod-shaped particles consist of an inner layer and a wrapping layer from the inside out. The wrapping layer completely wraps the inner layer. The inner layer is made of nylon fiber, and the wrapping layer is made of polyethylene resin.

[0220] The preparation method of rod-shaped particles is as follows: Nylon fibers are immersed in a 10% nitric acid solution and stirred at room temperature for 2 hours to make the surface of the nylon fibers have hydroxyl groups. Then, they are repeatedly washed with deionized water until neutral and dried to obtain surface-activated nylon fibers.

[0221] Surface-activated nylon fibers are placed in a fluidized bed at a bed temperature of 280℃ to make the nylon fibers in a suspended fluidized state, thus obtaining fluidized nylon fibers.

[0222] Polyethylene resin is heated to a molten state and pulse-sprayed onto the surface of fluidized nylon fibers. After cooling and solidification, polyethylene resin is coated onto the surface of the nylon fibers to obtain rod-shaped particles.

[0223] The raw materials for the plasticizer, calculated by weight, include 85 parts paraffin wax, 15 parts beeswax, and 5 parts tributyl citrate.

[0224] B. Place the ceramic cold core in the ceramic core mold, then inject the ceramic core slurry for injection molding to form a ceramic core matrix, and obtain a ceramic core blank encapsulating the ceramic cold core;

[0225] The injection temperature for injection molding is 100℃, the injection pressure is 6MPa, and the holding time is 15s.

[0226] According to the mass fractions, the ceramic core slurry includes 85 parts of ceramic powder and 15 parts of plasticizer;

[0227] According to the mass fractions, the raw materials of ceramic powder include 85 parts of fused silica powder, 5 parts of corundum powder and 10 parts of mullite powder.

[0228] The raw materials for the plasticizer, calculated by weight, include 85 parts paraffin wax, 15 parts beeswax, and 5 parts tributyl citrate.

[0229] C. The ceramic core is obtained by degreasing and calcining the ceramic core blank;

[0230] The ceramic core consists of an outer layer and an internal structure. The internal structure is formed by degreasing and calcining the ceramic cold core. The outer layer is formed by calcining the ceramic core substrate and completely encloses the internal structure. The maximum thickness of the outer layer is 3cm, and the thickness of the main body of the ceramic cold core is 1cm.

[0231] The calcination temperature was 1300℃, and the calcination time was 60 min.

[0232] The temperature profile for defatting is as follows:

[0233] It takes 2 hours to heat the temperature from room temperature to 100℃.

[0234] It takes 1.2 hours to heat the temperature from 100℃ to 120℃.

[0235] It took 2.8 hours to heat the temperature from 120℃ to 180℃.

[0236] The temperature was raised from 180℃ to 280℃ in 1.5 hours.

[0237] It took 3 hours to raise the temperature from 280℃ to 380℃.

[0238] It took 3 hours to raise the temperature from 380℃ to 450℃.

[0239] It took 1 hour to raise the temperature from 450°C to 650°C.

[0240] Keep warm at 650℃ for 0.4 hours.

[0241] The ceramic cold core obtained in this embodiment 3 can maintain its shape during the injection molding process, so that a complete ceramic core can be obtained through the above steps. The obtained ceramic core is basically free from shrinkage deformation and cracking defects, and its flatness is within 0.1mm.

[0242] The ceramic core obtained in Example 3 was placed into a wax mold, and wax was injected to form a wax mold.

[0243] The wax mold is immersed in refractory slurry and sprinkled with refractory sand particles. After drying and curing, a ceramic mold shell is formed.

[0244] The ceramic mold shell is successively subjected to steam at 200°C and fired at 300°C to remove the wax mold in the ceramic mold shell, thus obtaining a hollow mold shell.

[0245] Stainless steel at 1600℃ is poured into a hollow mold shell and solidifies to form an intermediate part.

[0246] Remove the ceramic mold shell from the intermediate part to obtain the casting blank;

[0247] The casting blank is placed in a potassium hydroxide solution to cause a chemical reaction that dissolves the ceramic core, thereby removing the ceramic core and forming an internal cavity structure to obtain the casting. The potassium hydroxide solution is at a temperature of 400℃, a pressure of 3.5MPa, and a concentration of 0.5mol / L.

[0248] In this embodiment 3, the ceramic core was completely removed in 5 hours, and the yield of the casting was 95%.

[0249] Comparative Example 1

[0250] The preparation method and raw materials of this comparative example are the same as those of Example 1. The difference is that this comparative example does not prepare a ceramic cold core, but uses it directly. That is, the preparation method of the ceramic core in Comparative Example 1 is as follows:

[0251] A. Inject the ceramic core slurry into the ceramic core mold for injection molding to obtain the ceramic core blank;

[0252] The injection temperature for injection molding is 100℃, the injection pressure is 5MPa, and the holding time is 20s.

[0253] According to the mass fractions, the ceramic core slurry includes 85 parts of ceramic powder and 15 parts of plasticizer;

[0254] According to the mass fractions, the raw materials for ceramic powder include 80 parts of fused silica powder, 10 parts of zircon powder and 10 parts of mullite powder;

[0255] The raw materials for the plasticizer, calculated by weight, include 85 parts paraffin wax, 15 parts beeswax, and 10 parts tributyl citrate.

[0256] B. After degreasing and calcining the ceramic core blank, a ceramic core with a maximum thickness of 10cm is obtained;

[0257] The calcination temperature was 1100℃, and the calcination time was 100 min.

[0258] The temperature profile for defatting is as follows:

[0259] It takes 1.5 hours to heat the water from room temperature to 100°C.

[0260] It takes 1 hour to raise the temperature from 100℃ to 120℃.

[0261] It took 2.5 hours to heat the water from 120°C to 180°C.

[0262] It took 2 hours to raise the temperature from 180℃ to 280℃.

[0263] It took 2 hours to raise the temperature from 280℃ to 380℃.

[0264] It took 2 hours to raise the temperature from 380℃ to 450℃.

[0265] It took 1 hour to raise the temperature from 450°C to 650°C.

[0266] Keep warm at 650℃ for 0.5 hours.

[0267] The ceramic core obtained in Comparative Example 1 exhibits significant shrinkage deformation and cracking defects, with a flatness greater than 0.3 mm.

[0268] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a ceramic core, characterized in that, Includes the following steps: A. A ceramic cold core is obtained by fused deposition modeling of ceramic matrix composites; The raw materials of the ceramic-based composite material include ceramic powder, plastic matrix and plasticizer; The raw materials of the plastic matrix, calculated by mass parts, include 40-50 parts of polylactic acid, 50-60 parts of polyethylene glycol, 3-5 parts of rod-shaped granules, 2-3 parts of stearic acid, and 2-3 parts of thermal initiator; The rod-shaped particles consist of an inner layer and a coating layer from the inside out. The coating layer completely encloses the inner layer. The inner layer is made of organic fiber, and the coating layer is made of thermoplastic resin. The preparation method of the rod-shaped particles is as follows: immerse organic fibers in a nitric acid solution with a volume concentration of 5-15%, stir at room temperature for 1-3 hours to make the surface of the organic fibers have hydroxyl groups, then wash repeatedly with deionized water until neutral and dry to obtain surface-activated organic fibers. Surface-activated organic fibers are placed in a fluidized bed to suspend the organic fibers in a fluidized state, thus obtaining fluidized organic fibers. Thermoplastic resin is heated to a molten state and pulsed sprayed onto the surface of fluidized organic fibers. After cooling and solidification, thermoplastic resin is coated onto the surface of the organic fibers to obtain rod-shaped particles. Among them, the bed temperature of the fluidized bed is lower than the melting point of the thermoplastic resin; B. Place the ceramic cold core in the ceramic core mold, then inject the ceramic core slurry for injection molding to form a ceramic core matrix, and obtain a ceramic core blank encapsulating the ceramic cold core; C. The ceramic core is obtained by degreasing and calcining the ceramic core blank; The ceramic core is divided into an outer layer and an internal structure. The internal structure is formed by degreasing and calcining the ceramic cold core. The outer layer is formed by calcining the ceramic core matrix. The outer layer completely encloses the internal structure. The maximum thickness of the outer layer is ≥3cm, and the main body thickness of the ceramic cold core is ≥1cm. The temperature profile for degreasing is as follows: The time required to heat the room temperature to 100℃ is 1.5 to 2.5 hours. The time required to raise the temperature from 100℃ to 120℃ is 1 to 1.5 hours. The heating time from 120℃ to 180℃ is 2.5 to 3 hours. The heating time from 180℃ to 280℃ is 1.5 to 2 hours. It takes 2-3 hours to raise the temperature from 280℃ to 380℃. The temperature rises from 380℃ to 450℃, taking 2–3 hours. The heating time from 450℃ to 650℃ is 1 to 1.5 hours. Keep warm at 650℃ for 0.4 to 0.6 hours.

2. The method for preparing a ceramic core according to claim 1, characterized in that, In step A, the length of the rod-shaped particles is 150–500 μm and the diameter is 30–50 μm; The organic fibers have a length of 100–300 μm and a diameter of 15–30 μm.

3. The method for preparing a ceramic core according to claim 1, characterized in that, In step A, the organic fiber includes either nylon fiber or polyester fiber; The thermoplastic resin includes any one of polyethylene resin, polypropylene resin, polystyrene resin, and methyl methacrylate resin.

4. The method for preparing a ceramic core according to claim 1, characterized in that, In step A, the polyethylene glycol includes polyethylene glycol 4000, polyethylene glycol 6000, and polyethylene glycol 8000; The mixing ratio of polyethylene glycol 4000, polyethylene glycol 6000 and polyethylene glycol 8000, calculated by mass ratio, is 1:(2-3):(1-2).

5. The method for preparing a ceramic core according to claim 1, characterized in that, In step A, the molecular weight of the polylactic acid is 20,000 to 50,000.

6. The method for preparing a ceramic core according to claim 1, characterized in that, In step A, the raw materials of the ceramic matrix composite material, calculated by mass percentage, include 70-80% ceramic powder, 15-25% plastic matrix, and 5-10% plasticizer.

7. The method for preparing a ceramic core according to claim 1, characterized in that, In step B, the ceramic core slurry includes ceramic powder; According to the mass fractions, the raw materials of the ceramic powder in the ceramic core slurry and the ceramic powder in the ceramic matrix composite material both include 80-90 parts of fused silica powder, 5-10 parts of corundum powder and 10-15 parts of mullite powder.

8. The method for preparing a ceramic core according to claim 7, characterized in that, In step B, the ceramic core slurry includes a plasticizer, and according to the mass parts, the ceramic core slurry includes 80-90 parts of ceramic powder and 10-20 parts of plasticizer; The raw materials for the plasticizer in the ceramic core slurry and the plasticizer in the ceramic matrix composite both include paraffin wax, beeswax, and tributyl citrate.

9. A ceramic core, characterized in that, It is prepared using the method for preparing the ceramic core according to any one of claims 1 to 8.

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