Method for controlling thermal damage to the outer surface of the inner layer of a ceramic core during the injection of an aqueous core slurry in the preparation of a multilayer wall ceramic core

Abstract

The application discloses a method for controlling thermal damage of an inner layer core outer surface in a water-soluble core slurry injection process of a multilayer wall ceramic core, which integrates design of an inner layer core outer surface coating material, design of a wax paper position pasted on the inner layer core outer surface, design of a water-soluble core injection gate, and design of a water-soluble core injection process parameter, and comprises the following steps: preparing an inner layer core blank; uniformly coating a coating material on the outer surface of the inner layer core blank, and forming a protective layer after drying; pasting a wax paper on the outer surface of the inner layer core blank; preparing a water-soluble core blank; preparing an outer layer core blank; removing the water-soluble core blank and baking to obtain the multilayer wall ceramic core. The application solves the technical problems of the prior art, such as shear thermal damage, impact cracks and surface defects of the inner layer core outer surface in the water-soluble core slurry injection process, eliminates initial thermal damage from the source, and improves the preparation yield and structural stability of the multilayer wall ceramic core.

Description

Technical Field

[0001] This invention belongs to the field of ceramic core preparation technology, specifically relating to a method for controlling thermal damage to the outer surface of the inner core during the preparation of multi-layer ceramic cores by water-soluble core slurry injection. This control method is particularly suitable for the preparation of multi-layer ceramic cores used in high-end castings such as hollow turbine blades for aero-engines, heavy-duty gas turbine blades, and precision aerospace components. Background Technology

[0002] Multi-walled ceramic cores are core components in the fabrication of complex hollow precision castings, especially hollow blade castings with complex internal cooling structures. Their function is to form intricate cooling channels and irregularly shaped cavities within the casting. A multi-walled ceramic core typically consists of an inner core, a middle core (i.e., a water-soluble core), and an outer core. The inner and outer cores are retained structures, forming the main airflow channels and the outer walls of the cooling channels, respectively. The water-soluble core is removed after the outer core is formed through water dissolution, high-temperature ablation, or chemical corrosion, thus creating a complex and elongated cooling channel cavity between the inner and outer cores. This cooling channel cavity is a key technology for achieving efficient cooling of hollow blades.

[0003] Slurry injection molding technology has become the mainstream process for preparing multi-walled ceramic cores due to its significant advantages, such as high molding precision, strong adaptability to complex internal cavity structures, and suitability for mass production. However, during the high-pressure, high-speed injection filling process, the outer surface of the inner core is located within a narrow and enclosed multi-walled cavity. The water-soluble core slurry generates intense instantaneous shear heat and impact heat, accompanied by high-intensity mechanical erosion. This thermo-mechanical coupling effect easily induces a series of initial thermal damage defects on the outer surface of the inner core, including injection microcracks, surface delamination, local overheating, and morphological defects. More importantly, these initial thermal damage defects are not isolated but have obvious inheritance and expansion characteristics. They continue to amplify in subsequent processes such as green blank drying, high-temperature sintering, and high-temperature alloy liquid pouring, ultimately leading to serious problems such as ceramic core fracture, internal cavity blockage, and dimensional deviations in castings, significantly reducing the yield of ceramic cores and the production yield of castings. Therefore, effectively controlling the initiation of thermal damage on the outer surface of the inner core during the water-soluble core slurry injection molding process is the key to ensuring the quality of multilayer ceramic core preparation.

[0004] While existing technologies have attempted to address the aforementioned thermal damage problem through some control measures, these are mostly localized and singular approaches, lacking a systematic solution. Currently, they still suffer from the following major shortcomings: Firstly, in terms of gating design, there is a lack of strict quantitative control standards for the positional relationship and size design of the main gating and sub-gating. In practice, there is a general tendency to design gating sizes that are too large (which is believed to be beneficial for injection filling). However, excessively large gating will significantly increase the filling kinetic energy of the slurry, thereby exacerbating the thermal and mechanical shocks during the injection process and directly aggravating the thermal damage to the outer surface of the inner core.

[0005] Secondly, regarding surface protection, conventional protective silicone oils are unable to withstand the high-pressure erosion and instantaneous high temperatures during slurry injection. The coating is prone to peeling or thermal decomposition in the early stages of filling, thus losing its protective function on the outer surface of the inner core. Furthermore, although physical isolation methods such as applying wax paper are used, the lack of suitable application locations prevents precise protection of high-impact hotspots on the outer surface of the inner core, resulting in a high degree of randomness in the protective effect.

[0006] Third, in terms of injection process parameter design, most existing technologies do not precisely limit the injection flow rate, injection pressure, and holding time, which easily leads to pressure peaks and velocity mutations in the initial impact stage and the final pressurization stage of slurry filling, further increasing the probability of thermal damage to the outer surface of the inner core.

[0007] In summary, a systematic method for controlling thermal damage that integrates gating system size design, surface protection technology, and injection process parameter control has not yet been established, severely restricting the large-scale production of multi-walled ceramic cores. Therefore, developing a method for controlling thermal damage to the outer surface of the inner core during the preparation of multi-walled ceramic cores using water-soluble core slurry injection is of great significance for overcoming the technological bottleneck in the preparation of ceramic cores for high-precision castings. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core by water-soluble core slurry injection. This method integrates the design of the coating material for the outer surface of the inner core, the design of the wax paper placement on the outer surface of the inner core, the design of the water-soluble core injection gating system, and the design of the water-soluble core injection process parameters. Specifically, it includes the following steps: Step 1: Use a hot press injection machine to inject the inner core slurry into the inner core mold for filling and die casting to obtain the inner core blank, and then trim the burrs on its outer surface. Step 2: Prepare the coating material according to the preset material ratio, and uniformly coat the coating material on the outer surface of the trimmed inner core blank. Then, dry the material to form a protective layer on the outer surface of the inner core blank. Step 3: According to the preset pasting position, paste wax paper onto the outer surface of the inner core blank that has formed a protective layer; Step 4: Place the inner core blank with the protective layer and wax paper attached into the water-soluble core mold. Use a hot press injection machine to inject the water-soluble core slurry into the water-soluble core mold according to the preset gating structure for filling and die casting to obtain the water-soluble core blank with the inner core blank inside. Then, trim the burrs on its surface. Step 5: Place the water-soluble core blank, which encloses the inner core blank, into the outer core mold. Use a hot press injection machine to inject the outer core slurry into the outer core mold for filling and die casting, to obtain the outer core blank, which encloses the water-soluble core blank and the inner core blank in sequence. Then, trim the burrs on its surface. Step 6: Soak the combination of inner core blank, water-soluble core blank and outer core blank in acidified water to remove the water-soluble core blank, clean it and dry it to make a multi-layer ceramic core blank. Step 7: Place the multi-layered ceramic core blank into a firing furnace for firing to produce a multi-layered ceramic core.

[0009] Preferably, in step one, the main die-casting parameters of the inner core blank are: injection flow rate 150-170 mL / s, die-casting temperature 70-80℃, die-casting pressure 3.5-4.5 MPa, and holding time 35-40 s.

[0010] In any of the above embodiments, preferably, in step two, the mass percentage of each substance in the coating material is as follows: 60-65 wt% phenyl hydroxy silicone oil, 18-22 wt% methyl hydrogen silicone oil, 5-8 wt% nano boron nitride, 1-4 wt% 2,6-di-tert-butyl-p-cresol, 2-6 wt% isopropanol, 1-4 wt% polyvinyl alcohol, and 1-4 wt% sodium dimethylbenzenesulfonate, with the sum of the contents of each substance being 100 wt%; the particle size of the nano boron nitride is 50-100 nm.

[0011] In any of the above embodiments, it is preferred that, in step two, the preparation method of the coating material includes the following steps in sequence: Step (1): Place the nano boron nitride in an oven for drying at a temperature of 110-130℃ for 2-3 hours. Step (2): Place the dried boron nitride nanoparticles into a mixer, then add 15-25 wt% phenyl hydroxy silicone oil and isopropanol and stir to mix. The stirring temperature is 40-50℃, the stirring speed is 500-800 rpm, and the stirring time is 40-60 min, so that the phenyl hydroxy silicone oil is adsorbed on the surface of the boron nitride nanoparticles to obtain a mixture. Step (3): Put the remaining phenyl hydroxy silicone oil and methyl hydrogen silicone oil into the reaction vessel and stir and mix them. The stirring temperature is 85-95℃, the stirring speed is 60-100rpm, and the stirring time is 30-40min to form a mixture. Step (4): Reduce the temperature of the reactor to 65-75℃, increase the stirring speed to 120-150rpm, and then slowly add polyvinyl alcohol and stir for 20-30min to make the polyvinyl alcohol evenly dispersed. Step (5): Keep the temperature and stirring speed of the reactor constant, add sodium dimethylbenzenesulfonate and stir for 10-20 minutes to reduce the interfacial energy of the system; Step (6): Keep the temperature of the reactor constant, slowly add the mixture obtained in step (1) into the reactor in 3-5 portions, and stir at a stirring speed of 1000-1200 rpm for 10-15 minutes after each addition, and finally stir at a stirring speed of 600-800 rpm for 15-20 minutes to make the mixture evenly dispersed. Step (7): Reduce the temperature of the reactor to 40-50℃, reduce the stirring speed to 60-80rpm, and then add 2,6-di-tert-butyl-p-cresol and stir for 20-30 minutes to obtain the coating material.

[0012] In any of the above schemes, it is preferred that, in step two, the drying temperature of the coating material is 50-60℃ and the drying time is 10-15 min; the thickness of the protective layer is 0.1-0.3 mm.

[0013] In any of the above embodiments, it is preferred that, in step three, the wax paper is pasted at a position corresponding to the injection direction when the water-soluble core slurry is injected into the water-soluble core mold, and the thickness of the wax paper is 0.2 mm.

[0014] In any of the above embodiments, it is preferred that, in step four, the gating structure includes a main gating, sub-gatings, and buffer gatings. The main gating is connected to the injection nozzle of the hot press injection machine. Several sub-gatings are provided on the side of the main gating near the water-soluble core mold. One end of each sub-gating is connected to the main gating and the other end is connected to the water-soluble core mold. Buffer gatings are provided on both sides of each sub-gating. One end of each buffer gating is connected to the sub-gating and the other end is connected to the water-soluble core mold.

[0015] In any of the above embodiments, preferably, in step four, the main gating system is cylindrical with a diameter of 5-8 mm; the sub-gating system is a flat trapezoid with a thickness of 1-2 mm, a height of 1.2 times the diameter of the main gating system, a long side length equal to the diameter of the main gating system, and a long side to short side length ratio of 1.6-2:1; the buffer gating system is cylindrical with a diameter equal to the thickness of the sub-gating system, and the included angle between the buffer gating system and the sub-gating system is 30-45°.

[0016] In any of the above schemes, the preferred method is that, in step four, the main die-casting parameters of the water-soluble core blank are: injection flow rate 10-15 mL / s, die-casting temperature 60-65℃, die-casting pressure 1-1.5 MPa, and holding time 15-30 s.

[0017] In any of the above schemes, the preferred method is that, in step five, the main die-casting parameters of the outer core blank are: injection flow rate 200-230 mL / s, die-casting temperature 70-80℃, die-casting pressure 6.5-7.5 MPa, and holding time 45-55 s.

[0018] In any of the above schemes, it is preferred that, in step six, the concentration of citric acid in the acidified water is 8-15 mg / L; first, a pressurized nozzle is used to clean the interlayer to further remove the residual water-soluble core in the interlayer, the water flow diameter does not exceed 2 mm, the pressure is 100-200 kPa, and then clean water is used to rinse the surface and interlayer of the multi-walled ceramic core blank; the drying temperature is 20-25℃, the wind speed is 3-5 m / s, and the drying time is 2-5 h.

[0019] In any of the above schemes, it is preferred that, in step seven, the firing temperature of the multi-walled ceramic core blank is 1150-1200℃ and the firing time is 5-8h.

[0020] The hot press, oven, mixer, reaction vessel, and calcining furnace used in this invention are all existing equipment, and there are no special requirements for their structure and model. The structures of the inner core mold, water-soluble core mold, and outer core mold can be designed according to the required core structure. The manufacturing process of each mold layer is a traditional process, with no special requirements for the process flow, process parameters, mold materials, or manufacturing equipment. The die-casting process of each core blank is also a traditional process, with no special requirements for the process flow, process parameters, or die-casting equipment. It is only necessary to ensure that key die-casting parameters such as injection flow rate, die-casting pressure, die-casting temperature, and holding time meet the requirements of this invention. The technical solution of this invention is applicable to various core slurries, and there are no special requirements for the material formulation and preparation process of each core slurry layer.

[0021] The present invention provides a method for controlling thermal damage to the outer surface of the inner core during the preparation of multi-walled ceramic cores using water-soluble core slurry injection, which has the following beneficial effects: (1) This invention solves the technical problems in the prior art where the outer surface of the inner core is prone to shear thermal damage, impact cracks, and surface defects during water-soluble core slurry injection molding. The control method of this invention integrates the design of the coating material of the outer surface of the inner core, the design of the wax paper placement on the outer surface of the inner core, the design of the water-soluble core injection gating system, and the design of the water-soluble core injection process parameters. It comprehensively suppresses the heat generation, heat conduction, and impact damage on the outer surface of the inner core during the water-soluble core slurry injection process, eliminates the initial thermal damage from the source, and improves the yield and structural stability of multi-layer ceramic cores.

[0022] (2) Before injecting the water-soluble core slurry, a special fine-diameter spray or brush tool is used to uniformly coat the outer surface of the inner core blank, covering it completely. After coating, the surface is dried to form a dense protective layer. This protective layer has strong adhesion and is resistant to high-temperature erosion. It can effectively isolate the instantaneous heat generated by the injection of the water-soluble core slurry from direct contact with the outer surface of the inner core, while reducing the friction coefficient between the slurry and the core substrate, reducing the generation of shear heat, and can be completely vaporized at high temperatures, leaving no residue contaminating the outer surface of the inner core.

[0023] (3) On the outer surface of the inner core blank, a 0.2mm thick wax paper is tightly adhered at a position corresponding to the injection direction when the water-soluble core slurry is injected into the water-soluble core mold. This wax paper is a high-temperature vaporization type wax paper. The wax paper must be adhered to ensure a smooth surface, free of bubbles and wrinkles. A segmented cutting and hot-pressing bonding process can be used to avoid the wax paper warping or falling off during the injection process. The wax paper can form a flexible buffer layer in the early stage of injection, absorbing the impact kinetic energy of the slurry, while blocking the instantaneous heat transfer. Moreover, the wax paper can be completely vaporized later, without affecting the dimensional accuracy and surface quality of the inner core blank.

[0024] (4) In view of the characteristics of large instantaneous thermal shock and obstructed heat dissipation in the inner cavity during water-soluble core slurry injection, the present invention has specially designed a water-soluble core injection gating structure. The design structure and size limitation can effectively reduce the amount of shear heat generated when the slurry passes through the gating, shorten the heat conduction path to the outer surface of the inner core, and at the same time reduce the impact cross-sectional area of ​​the slurry, reduce the mechanical erosion force, and block the path of thermal damage to the outer surface of the inner core from the source of structure and size, while ensuring the smooth filling of the water-soluble core slurry and avoiding material shortage in the inner cavity.

[0025] (5) The die-casting parameters of the water-soluble core slurry are precisely controlled, including injection flow rate, die-casting temperature, die-casting pressure, and holding time. By adjusting the injection flow rate, the slurry is prevented from being injected into the cavity too quickly, which would generate severe turbulence and excessive shear heat. This ensures that the slurry fills the multi-layered cavity at a stable flow rate, balancing the heat distribution in different areas of the cavity and preventing local overheating damage to the outer surface of the inner core caused by excessive local flow. By adjusting the die-casting pressure and holding time, the slurry can be ensured to fill the fine structure of the multi-layered cavity smoothly. At the same time, excessive injection pressure is avoided to prevent the slurry from being impacted and generating shear heat. This controls the mechanical and thermal impact of the slurry on the outer surface of the inner core from the source of the process parameters. Attached Figure Description

[0026] Figure 1 This is a plan view of a water-soluble core injection gating structure designed according to a preferred embodiment of the method for controlling thermal damage to the outer surface of the inner core during the preparation of multi-walled ceramic cores according to the present invention. Figure 2 for Figure 1 A schematic diagram of the sub-sprues in the water-soluble core injection gating structure designed in the embodiment shown; Figure 3 for Figure 1 Macroscopic morphology photograph of the outer surface of the inner layer core in the multilayer ceramic core prepared in the illustrated embodiment (no defects); Figure 4 Macroscopic morphology (burnt) of the outer surface of the inner layer of a multi-walled ceramic core prepared for comparison. Figure 5 Macroscopic morphology (cracks) of the outer surface of the inner core of a multi-walled ceramic core prepared for comparison. Figure 6 A macroscopic morphology photograph (layered) of the outer surface of the inner layer of a multilayered ceramic core prepared for comparison.

[0027] The diagram is labeled as follows: 1-Main runner, 2-Secondary runner, 3-Buffer runner, 4-Water-soluble core mold. Detailed Implementation

[0028] To further understand the invention, the following detailed description of the invention will be provided in conjunction with specific embodiments.

[0029] Example 1: According to a preferred embodiment of the method for controlling thermal damage to the outer surface of the inner core during the preparation of multi-walled ceramic cores, the method integrates the design of the coating material for the outer surface of the inner core, the design of the wax paper placement for the outer surface of the inner core, the design of the water-soluble core injection gating system, and the design of the water-soluble core injection process parameters. Specifically, it includes the following steps: Step 1: Use a hot press injection machine to inject the inner core slurry into the inner core mold for filling and die casting to obtain the inner core blank, and then trim the burrs on its outer surface. Step 2: Prepare the coating material according to the preset material ratio, and uniformly coat the coating material on the outer surface of the trimmed inner core blank. Then, dry the material to form a protective layer on the outer surface of the inner core blank. Step 3: According to the preset pasting position, paste wax paper onto the outer surface of the inner core blank that has formed a protective layer; Step 4: Place the inner core blank with the protective layer and wax paper attached into the water-soluble core mold. Use a hot press injection machine to inject the water-soluble core slurry into the water-soluble core mold according to the preset gating structure for filling and die casting to obtain the water-soluble core blank with the inner core blank inside. Then, trim the burrs on its surface. Step 5: Place the water-soluble core blank, which encloses the inner core blank, into the outer core mold. Use a hot press injection machine to inject the outer core slurry into the outer core mold for filling and die casting, to obtain the outer core blank, which encloses the water-soluble core blank and the inner core blank in sequence. Then, trim the burrs on its surface. Step 6: Soak the combination of inner core blank, water-soluble core blank and outer core blank in acidified water to remove the water-soluble core blank, clean it and dry it to make a multi-layer ceramic core blank. Step 7: Place the multi-layered ceramic core blank into a firing furnace for firing to produce a multi-layered ceramic core.

[0030] In step one, the main die-casting parameters of the inner core blank are: injection flow rate 160 mL / s, die-casting temperature 75℃, die-casting pressure 4 MPa, and holding time 38 s.

[0031] In step two, the mass percentage of each substance in the coating material is as follows: 62 wt% phenyl hydroxy silicone oil, 20 wt% methyl hydrogen silicone oil, 6 wt% nano boron nitride, 2 wt% 2,6-di-tert-butyl-p-cresol, 4 wt% isopropanol, 3 wt% polyvinyl alcohol, and 3 wt% sodium dimethylbenzenesulfonate; the particle size of the nano boron nitride is 75 nm.

[0032] The preparation method of the coating material includes the following steps in sequence: Step (1): Place the nano boron nitride in an oven for drying at 120°C for 2.5 hours. Step (2): Place the dried boron nitride nanoparticles into a mixer, then add 20wt% phenyl hydroxy silicone oil and isopropanol and stir to mix. The stirring temperature is 45℃, the stirring speed is 650rpm, and the stirring time is 50min, so that the phenyl hydroxy silicone oil is adsorbed on the surface of the boron nitride nanoparticles to obtain a mixture. Step (3): The remaining mass of phenyl hydroxy silicone oil and methyl hydrogen silicone oil are placed in the reaction vessel and stirred and mixed. The stirring temperature is 90℃, the stirring speed is 80rpm, and the stirring time is 35min to form a mixture. Step (4): Reduce the temperature of the reactor to 70°C, increase the stirring speed to 135 rpm, and then slowly add polyvinyl alcohol for stirring and mixing. The stirring time is 25 min to ensure that the polyvinyl alcohol is evenly dispersed. Step (5): Keep the temperature and stirring speed of the reactor constant, add sodium dimethylbenzenesulfonate and stir for 15 minutes to reduce the interfacial energy of the system. Step (6): Keep the temperature of the reactor constant, slowly add the mixture obtained in step (1) into the reactor in 4 portions, and stir at 1100 rpm for 12 minutes after each addition, and finally stir at 700 rpm for 18 minutes to make the mixture evenly dispersed. Step (7): Reduce the temperature of the reactor to 45°C, reduce the stirring speed to 70 rpm, and then add 2,6-di-tert-butyl-p-cresol and stir for 25 minutes to obtain the coating material.

[0033] The drying temperature of the coating material is 55°C and the drying time is 12 minutes; the thickness of the protective layer is 0.2 mm.

[0034] In step three, the wax paper is pasted at a position corresponding to the injection direction when the water-soluble core slurry is injected into the water-soluble core mold, and the thickness of the wax paper is 0.2 mm.

[0035] In step four, such as Figures 1-2 As shown, the gating structure includes a main gating 1, sub-gating 2, and a buffer gating 3. The main gating 1 is connected to the injection nozzle of the hot press injection machine. Several sub-gating 2 are provided on the side of the main gating 1 near the water-soluble core mold 4. One end of each sub-gating 2 is connected to the main gating 1 and the other end is connected to the water-soluble core mold 4. Buffer gating 3 is provided on both sides of each sub-gating 2. One end of each buffer gating 3 is connected to the sub-gating 2 and the other end is connected to the water-soluble core mold 4.

[0036] The main gating system is cylindrical with a diameter of 6.5 mm; the sub-gating system is a flat trapezoid with a thickness of 1.5 mm and a height 1.2 times the diameter of the main gating system. The length of its long side is equal to the diameter of the main gating system, and the ratio of the length of its long side to the length of its short side is 1.8:1; the buffer gating system is cylindrical with a diameter equal to the thickness of the sub-gating system, and the angle between the buffer gating system and the sub-gating system is 38°.

[0037] The main die-casting parameters of the water-soluble core blank are: injection flow rate 12 mL / s, die-casting temperature 62℃, die-casting pressure 1.2 MPa, and holding time 22 s.

[0038] In step five, the main die-casting parameters of the outer core blank are: injection flow rate 215 mL / s, die-casting temperature 75℃, die-casting pressure 7 MPa, and holding time 50 s.

[0039] In step six, the concentration of citric acid in the acidified water is 12 mg / L; first, use a pressurized nozzle to clean the interlayer to further remove the residual water-soluble core in the interlayer, with a water flow diameter not exceeding 2 mm and a pressure of 150 kPa; then use clean water to rinse the surface and interlayer of the multi-walled ceramic core blank; the drying temperature is 22℃, the wind speed is 4 m / s, and the drying time is 3.5 h.

[0040] In step seven, the firing temperature of the multi-walled ceramic core blank is 1175℃ and the firing time is 6.5h.

[0041] In this embodiment, the structures of the inner core mold, water-soluble core mold, and outer core mold can be designed according to the required core structure. The manufacturing process of each mold layer is a traditional process, with no special requirements for the process flow, process parameters, mold materials, or manufacturing equipment. The die-casting process of each core blank is also a traditional process, with no special requirements for the process flow, process parameters, or die-casting equipment. It is only necessary to ensure that the key die-casting parameters such as injection flow rate, die-casting pressure, die-casting temperature, and holding time meet the requirements of this embodiment. The technical solution of this embodiment is applicable to various core slurries, and there are no special requirements for the material formulation and preparation process of each core slurry; existing technologies can be referenced.

[0042] This embodiment has the following beneficial effects: (1) It solves the technical problems in the prior art where the outer surface of the inner core is prone to shear heat damage, impact cracks, and surface defects during water-soluble core slurry injection molding. It comprehensively suppresses the heat generation, heat conduction, and impact damage of the outer surface of the inner core during water-soluble core slurry injection, eliminates the initial heat damage from the source, and improves the yield and structural stability of multi-layer ceramic cores. (2) The protective layer has strong adhesion and is resistant to high-temperature erosion, which can effectively isolate the instantaneous heat generated by the water-soluble core slurry injection from direct contact with the outer surface of the inner core. (3) The wax paper can form a flexible buffer layer in the early stage of injection, absorb the impact kinetic energy of the slurry, and block the instantaneous heat transfer. (4) A water-soluble core injection gating structure is designed, which can effectively reduce the amount of shear heat generated when the slurry passes through the gating, shorten the heat conduction path to the outer surface of the inner core, and block the occurrence path of heat damage on the outer surface of the inner core from the source of structure and size. (5) By adjusting the injection flow rate, the slurry is injected into the cavity too quickly, which will cause violent turbulence and excessive shear heat. This ensures that the slurry fills the multi-layer wall cavity at a stable flow rate, balances the heat distribution in each area of ​​the cavity, and prevents local overheating damage to the outer surface of the inner core caused by excessive local flow. By adjusting the die casting pressure and holding time, the slurry can be smoothly filled into the fine structure of the multi-layer wall cavity, while avoiding excessive injection pressure from aggravating the impact of the slurry and the generation of shear heat.

[0043] Example 2: Another preferred embodiment of the method for controlling thermal damage to the outer surface of the inner core during the preparation of multi-walled ceramic cores according to the present invention is basically the same as that of Embodiment 1 in terms of control method, technical principle, and beneficial effects, except that: In step one, the main die-casting parameters of the inner core blank are: injection flow rate 150 mL / s, die-casting temperature 70℃, die-casting pressure 3.5 MPa, and holding time 35 s.

[0044] In step two, the proportions of each substance in the coating material are as follows: 60 wt% phenyl hydroxy silicone oil, 22 wt% methyl hydrogen silicone oil, 5 wt% nano boron nitride, 4 wt% 2,6-di-tert-butyl-p-cresol, 3 wt% isopropanol, 4 wt% polyvinyl alcohol, and 2 wt% sodium dimethylbenzenesulfonate; the particle size of the nano boron nitride is 50 nm.

[0045] The preparation method of the coating material includes the following main parameters: Step (1), the drying temperature of nano boron nitride is 110℃ and the drying time is 2h; Step (2), nano boron nitride is placed in a stirrer, and then 15wt% phenyl hydroxy silicone oil and isopropanol are added and stirred, the stirring temperature is 40℃, the stirring speed is 500rpm, and the stirring time is 40min to obtain a mixture; Step (3), the remaining mass of phenyl hydroxy silicone oil and methyl hydrogen silicone oil are placed in a reaction vessel and stirred, the stirring temperature is 85℃, the stirring speed is 60rpm, and the stirring time is 30min to form a mixture; Step (4), the temperature of the reaction vessel is reduced to 65℃, and the stirring speed is increased. Increase the temperature to 120 rpm, slowly add polyvinyl alcohol and stir for 20 min; Step (5), keep the reactor temperature and stirring speed constant, add sodium dimethylbenzenesulfonate and stir for 10 min; Step (6), keep the reactor temperature constant, slowly add the mixture in 3 portions, stir at 1000 rpm for 10 min after each addition, and finally stir at 600 rpm for 15 min; Step (7), reduce the reactor temperature to 40℃, reduce the stirring speed to 60 rpm, add 2,6-di-tert-butyl-p-cresol and stir for 20 min to obtain the coating material.

[0046] The drying temperature of the coating material is 50°C and the drying time is 10 min; the thickness of the protective layer is 0.1 mm.

[0047] In step three, the wax paper is pasted at a position corresponding to the injection direction when the water-soluble core slurry is injected into the water-soluble core mold, and the thickness of the wax paper is 0.2 mm.

[0048] In step four, the main gating system is cylindrical with a diameter of 5 mm; the sub-gating system is a flat trapezoid with a thickness of 1 mm and a height 1.2 times the diameter of the main gating system, the length of its long side is equal to the diameter of the main gating system, and the ratio of the length of its long side to the length of its short side is 1.6:1; the buffer gating system is cylindrical with a diameter equal to the thickness of the sub-gating system, and the angle between the buffer gating system and the sub-gating system is 30°.

[0049] The main die-casting parameters of the water-soluble core blank are: injection flow rate 10 mL / s, die-casting temperature 60℃, die-casting pressure 1 MPa, and holding time 15 s.

[0050] In step five, the main die-casting parameters of the outer core blank are: injection flow rate 200 mL / s, die-casting temperature 70℃, die-casting pressure 6.5 MPa, and holding time 45 s.

[0051] In step six, the concentration of citric acid in the acidified water is 8 mg / L; first, use a pressurized nozzle to clean the interlayer, with a water flow diameter not exceeding 2 mm and a pressure of 100 kPa; then use clean water to rinse the surface and interlayer of the multi-walled ceramic core blank; the drying temperature is 20℃, the wind speed is 3 m / s, and the drying time is 2 hours.

[0052] In step seven, the firing temperature of the multi-walled ceramic core blank is 1150℃ and the firing time is 5h.

[0053] Example 3: Another preferred embodiment of the method for controlling thermal damage to the outer surface of the inner core during the preparation of multi-walled ceramic cores according to the present invention is basically the same as that of Embodiment 1 in terms of control method, technical principle, and beneficial effects, except that: In step one, the main die-casting parameters of the inner core blank are: injection flow rate 170 mL / s, die-casting temperature 80℃, die-casting pressure 4.5 MPa, and holding time 40 s.

[0054] In step two, the proportions of each substance in the coating material are as follows: 64 wt% phenyl hydroxy silicone oil, 18 wt% methyl hydrogen silicone oil, 7 wt% nano boron nitride, 1 wt% 2,6-di-tert-butyl-p-cresol, 5 wt% isopropanol, 1 wt% polyvinyl alcohol, and 4 wt% sodium dimethylbenzenesulfonate; the particle size of the nano boron nitride is 100 nm.

[0055] The preparation method of the coating material includes the following main parameters: Step (1), the drying temperature of nano boron nitride is 130℃ and the drying time is 3h; Step (2), nano boron nitride is placed in a stirrer, and then 25wt% phenyl hydroxy silicone oil and isopropanol are added and stirred, the stirring temperature is 50℃, the stirring speed is 800rpm, and the stirring time is 60min to obtain a mixture; Step (3), the remaining mass of phenyl hydroxy silicone oil and methyl hydrogen silicone oil are placed in a reaction vessel and stirred, the stirring temperature is 95℃, the stirring speed is 100rpm, and the stirring time is 40min to form a mixture; Step (4), the temperature of the reaction vessel is reduced to 75℃, and the stirring speed is reduced to 100rpm. Increase the stirring speed to 150 rpm, slowly add polyvinyl alcohol and stir for 30 min; Step (5), keep the reactor temperature and stirring speed constant, add sodium dimethylbenzenesulfonate and stir for 20 min; Step (6), keep the reactor temperature constant, slowly add the mixture in 5 portions, stir at 1200 rpm for 15 min after each addition, and finally stir at 800 rpm for 20 min; Step (7), reduce the reactor temperature to 50℃, reduce the stirring speed to 80 rpm, add 2,6-di-tert-butyl-p-cresol and stir for 30 min to obtain the coating material.

[0056] The drying temperature of the coating material is 60℃ and the drying time is 15min; the thickness of the protective layer is 0.3mm.

[0057] In step three, the wax paper is pasted at a position corresponding to the injection direction when the water-soluble core slurry is injected into the water-soluble core mold, and the thickness of the wax paper is 0.2 mm.

[0058] In step four, the main gating system is cylindrical with a diameter of 8 mm; the sub-gating system is a flat trapezoid with a thickness of 2 mm and a height 1.2 times the diameter of the main gating system, with its long side being equal to the diameter of the main gating system and the ratio of the long side to the short side being 2:1; the buffer gating system is cylindrical with a diameter equal to the thickness of the sub-gating system, and the angle between the buffer gating system and the sub-gating system is 45°.

[0059] The main die-casting parameters of the water-soluble core blank are: injection flow rate 15 mL / s, die-casting temperature 65℃, die-casting pressure 1.5 MPa, and holding time 30 s.

[0060] In step five, the main die-casting parameters of the outer core blank are: injection flow rate 230 mL / s, die-casting temperature 80℃, die-casting pressure 7.5 MPa, and holding time 55 s.

[0061] In step six, the concentration of citric acid in the acidified water is 15 mg / L; first, use a pressurized nozzle to clean the interlayer, with a water flow diameter not exceeding 2 mm and a pressure of 200 kPa; then use clean water to rinse the surface and interlayer of the multi-walled ceramic core blank; the drying temperature is 25℃, the wind speed is 5 m / s, and the drying time is 5 h.

[0062] In step seven, the firing temperature of the multi-walled ceramic core blank is 1200℃ and the firing time is 8h.

[0063] Comparative example: This comparative example uses a traditional water-soluble core slurry injection process. No buffer runner is included in the gating system. The main runner diameter is 8 mm, and the sub-runners are cylindrical with a diameter of 2 mm. The outer surface of the inner core is coated with a layer of ordinary silicone oil. Wax paper is also attached to the outer surface of the inner core at the position corresponding to the injection port of the sub-runner. The injection flow rate of the water-soluble core slurry is 25 mL / s, and the die-casting pressure is 2.5 MPa. Other process parameters of the comparative example are basically the same as in Example 1.

[0064] The multilayer ceramic cores prepared in the above embodiments and comparative examples were tested under the same testing conditions, environment, and equipment. The test results are shown in Table 1. The macroscopic morphology of the outer surface of the inner core in Example 1 is shown in Table 1. Figure 3 As shown, the macroscopic morphology of the outer surface of the inner core in the comparative example is as follows: Figures 4-6 As shown.

[0065] From Table 1 and Figures 3-6 Based on the test results, the outer surface of the inner core in the three embodiments showed no thermal damage defects and the dimensional deviation rate of the casting cavity was low. However, the outer surface of the inner core in the comparative embodiment showed multiple types of defects and the dimensional deviation rate of the casting cavity was high.

[0066] Special Note: The technical solution of this invention involves numerous parameters, and the synergistic effects between these parameters must be comprehensively considered to achieve the beneficial effects and significant progress of this invention. Furthermore, the value ranges of each parameter in the technical solution were obtained through extensive experimentation. For each parameter and the combinations thereof, the inventors have recorded a large amount of experimental data; however, due to space limitations, the specific experimental data is not disclosed here.

[0067] It will be readily understood by those skilled in the art that this invention includes any combination of the inventive description and specific embodiments outlined in the foregoing specification, as well as the various parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, not all of these combinations have been described in detail. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-layer ceramic core by injecting water-soluble core slurry, characterized in that, The control method integrates the design of the coating material for the outer surface of the inner core, the design of the wax paper placement on the outer surface of the inner core, the design of the water-soluble core injection gating system, and the design of the water-soluble core injection process parameters. Specifically, it includes the following steps: Step 1: Use a hot press injection machine to inject the inner core slurry into the inner core mold for filling and die casting to obtain the inner core blank, and then trim the burrs on its outer surface. Step 2: Prepare the coating material according to the preset material ratio, and uniformly coat the coating material on the outer surface of the trimmed inner core blank. Then, dry the material to form a protective layer on the outer surface of the inner core blank. Step 3: According to the preset pasting position, paste wax paper onto the outer surface of the inner core blank that has formed a protective layer; Step 4: Place the inner core blank with the protective layer and wax paper attached into the water-soluble core mold. Use a hot press injection machine to inject the water-soluble core slurry into the water-soluble core mold according to the preset gating structure for filling and die casting to obtain the water-soluble core blank with the inner core blank inside. Then, trim the burrs on its surface. Step 5: Place the water-soluble core blank, which encloses the inner core blank, into the outer core mold. Use a hot press injection machine to inject the outer core slurry into the outer core mold for filling and die casting, to obtain the outer core blank, which encloses the water-soluble core blank and the inner core blank in sequence. Then, trim the burrs on its surface. Step 6: Soak the combination of inner core blank, water-soluble core blank and outer core blank in acidified water to remove the water-soluble core blank, clean it and dry it to make a multi-layer ceramic core blank. Step 7: Place the multi-layered ceramic core blank into a firing furnace for firing to produce a multi-layered ceramic core.

2. The method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core according to claim 1, characterized in that, In step one, the main die-casting parameters of the inner core blank are: injection flow rate 150-170mL / s, die-casting temperature 70-80℃, die-casting pressure 3.5-4.5MPa, and holding time 35-40s.

3. The method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core according to claim 2, characterized in that, In step two, the mass percentage of each substance in the coating material is as follows: 60-65 wt% phenyl hydroxy silicone oil, 18-22 wt% methyl hydrogen silicone oil, 5-8 wt% nano boron nitride, 1-4 wt% 2,6-di-tert-butyl-p-cresol, 2-6 wt% isopropanol, 1-4 wt% polyvinyl alcohol, and 1-4 wt% sodium dimethylbenzenesulfonate, with a total content of 100 wt%; the particle size of the nano boron nitride is 50-100 nm.

4. The method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core according to claim 3, characterized in that, In step two, the preparation method of the coating material includes the following steps in sequence: Step (1): Place the nano boron nitride in an oven for drying at a temperature of 110-130℃ for 2-3 hours. Step (2): Place the dried boron nitride nanoparticles into a mixer, then add 15-25 wt% phenyl hydroxy silicone oil and isopropanol and stir to mix. The stirring temperature is 40-50℃, the stirring speed is 500-800 rpm, and the stirring time is 40-60 min, so that the phenyl hydroxy silicone oil is adsorbed on the surface of the boron nitride nanoparticles to obtain a mixture. Step (3): Put the remaining phenyl hydroxy silicone oil and methyl hydrogen silicone oil into the reaction vessel and stir and mix them. The stirring temperature is 85-95℃, the stirring speed is 60-100rpm, and the stirring time is 30-40min to form a mixture. Step (4): Reduce the temperature of the reactor to 65-75℃, increase the stirring speed to 120-150rpm, and then slowly add polyvinyl alcohol and stir for 20-30min to make the polyvinyl alcohol evenly dispersed. Step (5): Keep the temperature and stirring speed of the reactor constant, add sodium dimethylbenzenesulfonate and stir for 10-20 minutes to reduce the interfacial energy of the system; Step (6): Keep the temperature of the reactor constant, slowly add the mixture obtained in step (1) into the reactor in 3-5 portions, and stir at a stirring speed of 1000-1200 rpm for 10-15 minutes after each addition, and finally stir at a stirring speed of 600-800 rpm for 15-20 minutes to make the mixture evenly dispersed. Step (7): Reduce the temperature of the reactor to 40-50℃, reduce the stirring speed to 60-80rpm, and then add 2,6-di-tert-butyl-p-cresol and stir for 20-30 minutes to obtain the coating material.

5. The method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core according to claim 4, characterized in that, In step two, the drying temperature of the coating material is 50-60℃ and the drying time is 10-15 min; the thickness of the protective layer is 0.1-0.3 mm.

6. The method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core according to claim 5, characterized in that, In step three, the wax paper is pasted at a position corresponding to the injection direction when the water-soluble core slurry is injected into the water-soluble core mold, and the thickness of the wax paper is 0.2 mm.

7. The method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core according to claim 6, characterized in that, In step four, the gating structure includes a main gating system, sub-gating systems, and buffer gating systems. The main gating system is connected to the injection nozzle of the hot press injection machine. Several sub-gating systems are provided on the side of the main gating system near the water-soluble core mold. One end of each sub-gating system is connected to the main gating system and the other end is connected to the water-soluble core mold. Buffer gating systems are provided on both sides of each sub-gating system. One end of each buffer gating system is connected to the sub-gating system and the other end is connected to the water-soluble core mold.

8. The method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core according to claim 7, characterized in that, In step four, the main gating system is cylindrical with a diameter of 5-8 mm; the sub-gating system is a flat trapezoid with a thickness of 1-2 mm and a height 1.2 times the diameter of the main gating system, with its long side equal to the diameter of the main gating system and the ratio of the long side to the short side being 1.6-2:1; the buffer gating system is cylindrical with a diameter equal to the thickness of the sub-gating system, and the angle between the buffer gating system and the sub-gating system is 30-45°.

9. The method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core according to claim 8, characterized in that, In step four, the main die-casting parameters of the water-soluble core blank are: injection flow rate 10-15 mL / s, die-casting temperature 60-65℃, die-casting pressure 1-1.5 MPa, and holding time 15-30 s.

10. The method for controlling thermal damage to the outer surface of the inner core during the preparation of a multi-walled ceramic core according to claim 9, characterized in that, In step five, the main die-casting parameters of the outer core blank are: injection flow rate 200-230 mL / s, die-casting temperature 70-80℃, die-casting pressure 6.5-7.5 MPa, and holding time 45-55 s.

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