A rapid drying composite ceramic powder for investment casting and a method of shell making thereof

Abstract

The present application relates to the technical field of ceramic powder, and particularly relates to a quick-drying composite ceramic powder for investment casting and a shell-making method thereof. The shell-making method of the quick-drying composite ceramic powder for investment casting comprises the following steps: preparing hydrophobic modified porous silica microspheres, preparing interface fusion enhancer, and making the composite ceramic powder. The hydrophobic modified porous silica microspheres are introduced to realize coating synergistic quick-drying, and stress cracks caused by uneven drying of a complex structure are fundamentally avoided; the bimodal distribution aggregate and the interface fusion enhancer synergistically act to build a high-strength composite shell; the quick-drying characteristic is matched with a forced drying process, the shell-making cycle is shortened by more than 60%, and energy consumption is reduced; the coating is evenly hung, the shell performance is excellent, the casting precision is high, defects are few, the comprehensive manufacturing cost is effectively controlled, and a reliable scheme is provided for large-scale production of high-end precision castings.

Description

Technical Field

[0001] This invention relates to the field of ceramic powder technology, specifically to a rapid-drying composite ceramic powder for investment casting and a method for preparing its shell. Background Technology

[0002] Investment casting, as an advanced precision casting process, is widely used in aerospace, high-end equipment manufacturing, medical devices, and other fields with stringent requirements for dimensional accuracy and surface quality, thanks to its unique advantage of producing precise, complex, and near-net-shape metal parts. One of the core steps in this process is the preparation of a high-strength, high-stability ceramic shell. As the only refractory intermediary structure connecting the wax model and the final metal casting, the ceramic shell plays a triple role in geometric replication, thermodynamic barrier, and structural support. Its performance directly determines the dimensional accuracy, surface finish, internal density, and even the overall service reliability of the casting, making it the "lifeline" of investment casting.

[0003] Currently, traditional shell-making processes in industrial production generally employ binders such as silica sol and ethyl silicate, mixed with refractory aggregates such as zircon powder, corundum powder, and mullite powder to formulate coatings. Ceramic shells are then prepared through layer-by-layer coating, sand application, and drying. Based on differences in binder systems, mainstream shells are mainly divided into silica sol shells, water glass shells, and composite shells. Silica sol shells, due to their high precision and high surface quality, have become the mainstream choice for high-end precision casting; however, this type of shell also suffers from slow drying speeds and long production cycles. Water glass shells are inexpensive but lack sufficient precision and strength, making them unsuitable for high-end applications. While composite shells can balance performance and cost, they still haven't solved the core challenge of manufacturing shells for complex structural components.

[0004] With the rapid development of high-end manufacturing, the demand for castings with extremely complex structures such as deep holes, narrow grooves, fine blades, and complex internal cavities, such as aero-engine turbine blades and high-end pumps and valves, is increasing. Traditional shell-making processes are gradually revealing many prominent technical bottlenecks when faced with such complex castings, which seriously restricts the large-scale application of investment casting technology in high-end fields. Specifically, this is manifested in the following three aspects:

[0005] Firstly, the drying process presents a significant challenge. During the coating process of complex castings, the coating tends to accumulate in deep holes and narrow grooves, and the drainage path is lengthy, resulting in extremely uneven drying rates across different parts of the shell. Often, the surface of the shell is dry and hardened while the interior remains moist. This difference in drying between the inside and outside creates enormous drying stress, which can easily lead to defects such as cracks, delamination, or even peeling during subsequent drying or firing, directly causing the casting to be scrapped. Even with auxiliary methods such as high-powered air drying, it is difficult to completely solve the problem of uneven drying within complex structures, and the hidden dangers caused by drying stress cannot be fundamentally eliminated.

[0006] Secondly, the bonding strength and integrity of the mold shell are insufficient. The ceramic powder used in traditional mold shell making has inherent limitations in particle size distribution, surface properties, and the wettability and bonding strength of the binder. When applied to complex curved surfaces and surfaces with fine structures, the coating is difficult to achieve uniform coverage, resulting in poor coating uniformity and weak interlayer bonding strength. Simultaneously, a "skinning" phenomenon easily occurs during the drying process, where a dense layer forms on the surface of the mold shell while the internal structure remains loose. This results in insufficient overall strength of the mold shell, making it unable to withstand the high-temperature thermal shock during subsequent dewaxing and firing processes, as well as the mechanical impact during molten metal pouring. This further exacerbates the risk of mold shell cracking and collapse, severely affecting the geometric stability and metallurgical quality of the casting.

[0007] Thirdly, the production cycle is lengthy and the production efficiency is low. In traditional shell-making processes, the natural drying time for each layer of coating can take several hours to tens of hours. However, complex structural castings often require more layers to ensure shell strength, resulting in a shell-making cycle that can last for days or even weeks, making it difficult to meet the demands of mass production and efficient delivery. To improve this situation, existing technologies have attempted to accelerate the drying speed by adding drying accelerators and adjusting the binder ratio. However, these methods often come at the cost of sacrificing key properties of the shell, such as room temperature strength and high-temperature thermal shock resistance. Other methods use finer powders to improve coating density and attempt to improve shell integrity. However, finer powders can exacerbate coating buildup, further increasing drying difficulty and the tendency for shell cracks to form, creating a technical dilemma of "sacrificing one aspect for another."

[0008] In summary, in the existing investment casting shell-making process, traditional ceramic powder materials cannot effectively address the core problems of slow drying speed, easy cracking, weak interlayer bonding, and poor shell integrity when making shells for complex castings, making it difficult to meet the production needs of castings with extremely complex structures.

[0009] Therefore, developing a new type of composite ceramic powder and its shell-making method that can dry quickly, blend perfectly with existing binder systems, effectively improve the bonding strength and integrity of the mold and shell, and is suitable for making shells with complex structures has become a technical problem that urgently needs to be solved in the current investment casting field. It has important practical significance and industrial value for promoting the development of investment casting technology towards higher precision, higher efficiency, and more complex structures. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a rapid-drying composite ceramic powder for investment casting and a method for preparing its shell.

[0011] This invention provides a rapidly drying composite ceramic powder for investment casting, characterized in that it comprises the following components by weight percentage:

[0012] Basic refractory aggregates: 70-90%;

[0013] Rapid moisture transport medium 5-20%;

[0014] Interface fusion enhancer 3-10%;

[0015] Auxiliary additives 0.5-5%;

[0016] The particle size of the basic refractory aggregate exhibits a bimodal distribution, with coarse powder accounting for 40-60% of the total basic refractory aggregate and fine powder accounting for 60-40% of the total basic refractory aggregate.

[0017] As a preferred aspect, the basic refractory aggregate is selected from one or more of zircon sand powder, calcined kaolin powder, fused silica powder, and corundum powder; the coarse powder has a particle size of 30-80 μm, and the fine powder has a particle size of 3-15 μm.

[0018] As a preferred aspect, the rapid water transport medium is a hydrophobically modified porous silica microsphere; wherein the average pore size of the porous silica microsphere is 5-50 nm and the specific surface area is ≥200 m² / g.

[0019] As a preferred aspect, the hydrophobically modified porous silica microspheres are specifically prepared by surface treatment of porous silica microspheres using a hydrophobic modifier.

[0020] As a preferred aspect, the hydrophobic modifier is one of hexamethyldisilazane or long-chain alkylsiloxane.

[0021] As a preferred aspect, the interface fusion enhancer is a nanoscale oxide powder surface-treated with a silane coupling agent; the particle size of the nanoscale oxide powder is 10-100 nm.

[0022] As a preferred aspect, the nano-sized oxide powder is selected from one or more of nano-silica, nano-alumina, and nano-zirconia; the silane coupling agent is one of γ-glycidoxypropyltrimethoxysilane and aminopropyltriethoxysilane.

[0023] As a preferred aspect, the auxiliary additive consists of cellulose ether and polyelectrolyte dispersant in a mass ratio of 2:3.

[0024] This invention also provides a method for preparing a shell from rapidly drying composite ceramic powder for investment casting, comprising the following steps:

[0025] Step 1: Mix the composite ceramic powder and binder at a powder-to-liquid ratio of (2.5-3.5):1, disperse them in a high-speed mixer, and prepare a casting coating.

[0026] Step 2: Immerse the investment casting mold into the casting coating, lift it up and let it drip evenly, then spread refractory sand on the fluidized bed;

[0027] Step 3: Place the coated module in a circulating drying environment with a temperature of 25-35℃, humidity of 40-60%, and wind speed of 2-5m / s for 1-3 hours;

[0028] Step 4: Then repeat steps 2 and 3 to achieve 5-9 shell layers. After that, perform steam dewaxing and high-temperature firing to obtain a ceramic shell for casting.

[0029] As a preferred aspect, the binder in step 1 is one of silica sol and ethyl silicate hydrolysate; the refractory sand spread in step 2 is one of zircon sand and mullite sand.

[0030] The present invention has the following advantages:

[0031] 1. This invention introduces hydrophobically modified porous silica microspheres as a rapid moisture transport medium. The internal nanopores can quickly adsorb free water in the coating through capillary action, while the hydrophobic surface prevents water from being retained in large quantities between the microspheres. This allows water to migrate quickly and uniformly to the coating surface for evaporation, achieving "synergistic fast drying" from the inside out. This fundamentally avoids stress cracks caused by uneven drying in complex structures.

[0032] 2. The bimodal aggregate used in this invention forms a densely packed structure, with fine powder filling the gaps between coarse powder, increasing the green density. Furthermore, the nano-oxides treated with silane coupling agents have one end bonded to the ceramic powder through chemical bonds, while the other end reacts chemically with the SiO2 network of silica sol or the organic binder components or undergoes strong hydrogen bonding, establishing a strong "bridge" between the powder and the binder matrix, greatly enhancing the interfacial bonding force. At the same time, the nanoparticles filling the spaces between micron-sized particles further improve the density and strength of the coating. Through the synergistic effect of the bimodal aggregate and the interfacial fusion enhancer, a high-strength composite shell is constructed.

[0033] 3. This invention precisely matches the rapid drying characteristics of the material with the forced drying process parameters. Under rapid drying conditions, compared to the traditional process where each layer needs to be naturally dried, the shell-making cycle is shortened. This not only significantly improves production efficiency and equipment turnover rate but also significantly reduces the energy consumption of constant temperature and humidity operation in the drying chamber, aligning with the development direction of green casting. Furthermore, the addition of auxiliary additives ensures that the ceramic powder has excellent suspension stability and dispersibility in the silica sol system. This results in the formulated coating having good flowability and dripping properties during application, forming a uniform thin layer even in the deep recesses of complex modules, avoiding sagging and accumulation. At the same time, the high powder-to-liquid ratio reduces the solvent content, further aiding rapid drying.

[0034] 4. The ceramic mold shell prepared by the method of the present invention has high surface smoothness, suitable air permeability, and good shell removal performance. The final cast metal casting has high dimensional accuracy and few surface defects. Due to the reduction of mold shell scrap rate, shortening of shell making cycle and reduction of energy consumption, the overall manufacturing cost is effectively controlled, providing a reliable technical solution for the large-scale production of high-end precision castings. Attached Figure Description

[0035] Figure 1 This is a flowchart of a shell-making method for rapidly drying composite ceramic powder used in investment casting, as described in an embodiment of the present invention. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0037] Example 1: A method for preparing a shell from rapidly drying composite ceramic powder for investment casting, referencing... Figure 1 ,include:

[0038] Composite ceramic powder formulation (by weight percentage):

[0039] Basic refractory aggregate (85%): Zircon sand powder is selected. Its particle size has a bimodal distribution, with coarse powder (D50: 50μm) accounting for 50% of the total aggregate and fine powder (D50: 8μm) accounting for 50% of the total aggregate; rapid moisture transport medium (10%): hydrophobic modified porous silica microspheres; interface fusion reinforcing agent (4%); auxiliary additives (1%).

[0040] Preparation of the above-mentioned hydrophobically modified porous silica microspheres:

[0041] Two parts by weight of porous silica microspheres with an average pore size of 20 nm and a specific surface area of ​​250 m² / g were placed in a vacuum drying oven at 120 °C and dried for 2 h. Then, the dried porous silica microspheres were dispersed in 100 parts by weight of anhydrous toluene and ultrasonically dispersed for 20 min to obtain a porous silica microsphere dispersion.

[0042] Hexamethyldisilazane was added to a porous silica microsphere dispersion at a mass ratio of 1:5. The mixture was then heated to 80°C and refluxed for 6 hours under nitrogen protection. After the reaction was completed, the mixture was centrifuged and washed three times alternately with anhydrous ethanol and acetone. Finally, it was dried in a vacuum drying oven at 60°C for 6 hours to obtain hydrophobically modified porous silica microspheres.

[0043] Preparation of the above-mentioned interface fusion enhancer:

[0044] Nano-silica with a particle size of 10 nm was placed in a vacuum drying oven and dried at 100 °C for 2 h. The dried nano-silica was then added to anhydrous ethanol to prepare a suspension with a mass fraction of 5%. The suspension was then stirred and dispersed at 5000 rpm for 15 min to obtain the nano-silica suspension.

[0045] Add silane coupling agent KH560 to an ethanol-water solution with an alcohol-water ratio of 9:1, then adjust the pH to 4.0 with glacial acetic acid, and stir for 30-60 minutes to hydrolyze and obtain the hydrolysate.

[0046] The hydrolysate was added to the nano-silica suspension, and the amount of silane coupling agent was 3% of the mass of nano-silica. Then, the mixture was heated to 70°C and refluxed under nitrogen protection with mechanical stirring for 2 hours. After the reaction was completed, the mixture was centrifuged at 8000 rpm for 10 minutes. The precipitate was washed three times with anhydrous ethanol. Finally, the washed product was placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain the interface fusion enhancer.

[0047] Shell preparation method for rapidly drying composite ceramic powder used in investment casting:

[0048] Step 1: Mix the above composite ceramic powder with silica sol at a powder-to-liquid ratio of 2.5:1, disperse in a high-speed mixer to prepare a casting coating;

[0049] Step 2: Immerse the investment casting mold into the casting coating, lift it up and let it drip evenly, then spread zircon sand in a fluidized bed;

[0050] Step 3: Place the coated module in a circulating drying environment with a temperature of 25℃, humidity of 40%, and wind speed of 2m / s for 1-3 hours;

[0051] Step 4: Then repeat steps 2 and 3 to make the number of shell layers reach 5. Then use conventional processes for steam dewaxing and high-temperature firing to obtain a ceramic shell for casting.

[0052] Example 2, a method for preparing a shell from rapidly drying composite ceramic powder for investment casting, see [link to example]. Figure 1 ,include:

[0053] Composite ceramic powder formulation (by weight percentage):

[0054] Basic refractory aggregate (88%): calcined kaolin powder. Its particle size has a bimodal distribution, with coarse powder (D50: 35μm) accounting for 45% of the total aggregate and fine powder (D50: 5μm) accounting for 55% of the total aggregate; rapid moisture transport medium (7%): hydrophobic modified porous silica microspheres; interface fusion enhancer (4.2%); auxiliary additives (0.8%).

[0055] Preparation of the above-mentioned hydrophobically modified porous silica microspheres:

[0056] Three parts by weight of porous silica microspheres with an average pore size of 10 nm and a specific surface area of ​​300 m² / g were placed in a vacuum drying oven at 120 °C and dried for 3 h. Then, the dried porous silica microspheres were dispersed in 120 parts by weight of anhydrous toluene and ultrasonically dispersed for 30 min to obtain a porous silica microsphere dispersion.

[0057] Hexamethyldisilazane was added to a porous silica microsphere dispersion at a mass ratio of 1:10 to the porous silica microspheres. The mixture was then heated to 110°C under nitrogen protection and refluxed for 12 hours. After the reaction was completed, the mixture was centrifuged and washed five times alternately with anhydrous ethanol and acetone. Finally, it was dried in a vacuum drying oven at 80°C for 8 hours to obtain hydrophobically modified porous silica microspheres.

[0058] Preparation of the above-mentioned interface fusion enhancer:

[0059] Zirconia nanoparticles with a particle size of 100 nm were placed in a vacuum drying oven and dried at 120 °C for 4 h. The dried zirconia nanoparticles were then added to anhydrous ethanol to prepare a suspension with a mass fraction of 15%. The suspension was then stirred and dispersed at 8000 rpm for 20 min to obtain the zirconia nanoparticle suspension.

[0060] The silane coupling agent KH550 was added to an ethanol-water solution with an alcohol-water ratio of 9:1, and then the pH was adjusted to 5.5 with glacial acetic acid. The solution was stirred and hydrolyzed for 60 min to obtain the hydrolysate.

[0061] The hydrolysate was added to the nano-zirconia suspension, and the amount of silane coupling agent was 5% of the mass of nano-zirconia. Then, the mixture was heated to 90°C and refluxed under nitrogen protection with mechanical stirring for 6 hours. After the reaction was completed, the mixture was centrifuged at 12000 rpm for 15 minutes. The precipitate was washed 5 times with anhydrous ethanol. Finally, the washed product was placed in a vacuum drying oven and dried at 80°C for 24 hours to obtain the interface fusion enhancer.

[0062] Shell preparation method for rapidly drying composite ceramic powder used in investment casting:

[0063] Step 1: Mix the above composite ceramic powder with silica sol at a powder-to-liquid ratio of 3.5:1, disperse in a high-speed mixer to prepare a casting coating;

[0064] Step 2: Immerse the investment mold assembly into the casting coating, lift it up and let it drip evenly, then spread mullite sand on the fluidized bed;

[0065] Step 3: Place the coated module in a circulating drying environment with a temperature of 35℃, humidity of 60%, and wind speed of 5m / s for 3 hours;

[0066] Step 4: Then repeat steps 2 and 3 to make the number of shell layers reach 9. Then use conventional processes for steam dewaxing and high-temperature firing to obtain a ceramic shell for casting.

[0067] Example 3, a method for preparing a shell from rapidly drying composite ceramic powder for investment casting, see [link to example]. Figure 1 ,include:

[0068] Composite ceramic powder formulation (by weight percentage):

[0069] Basic refractory aggregate (78%): composed of fused silica powder and corundum powder in a 1:1 weight ratio. Its particle size exhibits a bimodal distribution, with coarse powder (D50: 70μm) accounting for 60% of the total aggregate and fine powder (D50: 12μm) accounting for 40% of the total aggregate; rapid moisture transport medium (15%): hydrophobically modified porous silica microspheres; interface fusion enhancer (5%); auxiliary additives (2%).

[0070] Preparation of the above-mentioned hydrophobically modified porous silica microspheres:

[0071] 2.5 parts by weight of porous silica microspheres with an average pore size of 40 nm and a specific surface area of ​​220 m² / g were placed in a vacuum drying oven at 120 °C and dried for 2.5 h. Then, the dried porous silica microspheres were dispersed in 110 parts by weight of anhydrous toluene and ultrasonically dispersed for 25 min to obtain a porous silica microsphere dispersion.

[0072] Hexamethyldisilazane was added to a porous silica microsphere dispersion at a mass ratio of 1:7.5 to the porous silica microspheres. The mixture was then heated to 95°C and refluxed for 9 hours under nitrogen protection. After the reaction was completed, the mixture was centrifuged and washed four times alternately with anhydrous ethanol and acetone. Finally, it was dried in a vacuum drying oven at 70°C for 7 hours to obtain hydrophobically modified porous silica microspheres.

[0073] Preparation of the above-mentioned interface fusion enhancer:

[0074] Nano-alumina with a particle size of 50 nm was placed in a vacuum drying oven and dried at 110 °C for 3 h. The dried nano-alumina was then added to anhydrous ethanol to prepare a suspension with a mass fraction of 10%. The suspension was then stirred and dispersed at 6500 rpm for 17.5 min to obtain the nano-alumina suspension.

[0075] The silane coupling agent KH560 was added to an ethanol-water solution with an alcohol-water ratio of 9:1, and then the pH was adjusted to 4.75 with glacial acetic acid. The solution was stirred and hydrolyzed for 45 min to obtain the hydrolysate.

[0076] The hydrolysate was added to the nano-alumina suspension, and the amount of silane coupling agent was 4% of the mass of nano-alumina. Then, the mixture was heated to 80°C and refluxed under nitrogen protection with mechanical stirring for 4 hours. After the reaction was completed, the mixture was centrifuged at 10,000 rpm for 12.5 min. The precipitate was washed four times with anhydrous ethanol. Finally, the washed product was placed in a vacuum drying oven and dried at 70°C for 18 hours to obtain the interface fusion enhancer.

[0077] Shell preparation method for rapidly drying composite ceramic powder used in investment casting:

[0078] Step 1: Mix the above composite ceramic powder with silica sol at a powder-to-liquid ratio of 3:1, disperse in a high-speed mixer, and prepare a casting coating.

[0079] Step 2: Immerse the investment casting mold into the casting coating, lift it up and let it drip evenly, then spread zircon sand in a fluidized bed;

[0080] Step 3: Place the coated module in a circulating drying environment with a temperature of 30℃, humidity of 50%, and wind speed of 3.5m / s for 2 hours;

[0081] Step 4: Then repeat steps 2 and 3 to make the number of shell layers reach 7. Then use conventional processes for steam dewaxing and high-temperature firing to obtain a ceramic shell for casting.

[0082] Comparative Example 1 differs from Example 1 in that the rapid water transport medium in the composite ceramic powder formulation is replaced with an equal amount of porous silica microspheres, while the rest of the steps remain unchanged. This is referred to as Comparative Example 1.

[0083] Comparative Example 2 differs from Example 1 in that the interface fusion enhancer in the composite ceramic powder formula is replaced with an equal amount of nano-silica, while the rest of the steps remain unchanged. This is referred to as Comparative Example 2.

[0084] The ceramic shells prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to strength tests, and the results are shown in Table 1.

[0085] Three-point bending tests were conducted using a universal testing machine with a span of 40 mm and a loading speed of 1 mm / min. The maximum load at which the ceramic shell fractured was recorded, and the bending strength was calculated. The average value of three samples in each group was taken, and the appearance of the ceramic shell was observed. The test results are shown in Table 1.

[0086] Table 1. Performance test results of Examples 1-3 and Comparative Examples 1-2

[0087] Flexural strength (MPa) Appearance Example 1 19.4 The surface is smooth and free of visible cracks. Example 2 18.2 The surface is smooth and free of visible cracks. Example 3 18.7 The surface is smooth and free of visible cracks. Comparative Example 1 17.9 There are fine cracks on the surface Comparative Example 2 13.2 The surface is smooth and free of visible cracks.

[0088] As can be seen from the data in Table 1, in Comparative Example 1, due to the use of unmodified porous silica microspheres, moisture was difficult to drain quickly after entering the pores, resulting in localized drying delays and stress cracks. In Comparative Example 2, although nano-silica was used, no coupling treatment was performed, and its strength was far lower than that of the examples.

[0089] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A rapidly drying composite ceramic powder for investment casting, characterized in that, By weight percentage, it consists of the following components: Basic refractory aggregates: 70-90%; Rapid moisture transport medium 5-20%; Interface fusion enhancer 3-10%; Auxiliary additives 0.5-5%; The particle size of the basic refractory aggregate exhibits a bimodal distribution, with coarse powder accounting for 40-60% of the total basic refractory aggregate and fine powder accounting for 40-60% of the total basic refractory aggregate. The rapid water transport medium is a hydrophobically modified porous silica microsphere; wherein the average pore size of the porous silica microsphere is 5-50 nm and the specific surface area is ≥200 m² / g; The interface fusion enhancer is a nano-sized oxide powder surface-treated with a silane coupling agent; the particle size of the nano-sized oxide powder is 10-100 nm. The nano-sized oxide powder is selected from one or more of nano-silica, nano-alumina, and nano-zirconia; the silane coupling agent is one of γ-glycidoxypropyltrimethoxysilane and aminopropyltriethoxysilane. The auxiliary additives consist of cellulose ether and polyelectrolyte dispersant in a mass ratio of 2:3; The rapidly drying composite ceramic powder is used to prepare ceramic shells.

2. The rapidly drying composite ceramic powder for investment casting according to claim 1, characterized in that, The basic refractory aggregate is selected from one or more of zircon sand powder, calcined kaolin powder, fused silica powder, and corundum powder; the coarse powder has a particle size of 30-80μm, and the fine powder has a particle size of 3-15μm.

3. The rapidly drying composite ceramic powder for investment casting according to claim 1, characterized in that, The hydrophobically modified porous silica microspheres are specifically prepared by surface treatment of porous silica microspheres with a hydrophobic modifier.

4. The rapidly drying composite ceramic powder for investment casting according to claim 3, characterized in that, The hydrophobic modifier is one of hexamethyldisilazane or long-chain alkylsiloxane.

5. A shell-making method using the rapidly drying composite ceramic powder for investment casting as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Mix the composite ceramic powder and binder at a powder-to-liquid ratio of (2.5-3.5):1, disperse them in a high-speed mixer, and prepare a casting coating. Step 2: Immerse the investment casting mold into the casting coating, lift it up and let it drip evenly, then spread refractory sand on the fluidized bed; Step 3: Place the coated module in a circulating drying environment with a temperature of 25-35℃, humidity of 40-60%, and wind speed of 2-5m / s for 1-3 hours; Step 4: Then repeat steps 2 and 3 to achieve 5-9 shell layers. After that, perform steam dewaxing and high-temperature firing to obtain a ceramic shell for casting.

6. The shell-making method for rapidly drying composite ceramic powder for investment casting according to claim 5, characterized in that: The binder in step 1 is one of silica sol and ethyl silicate hydrolysate; the refractory sand spread in step 2 is one of zircon sand and mullite sand.

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