A method for preparing a large-size ceramic core for titanium alloy casting

Abstract

The present invention provides a method for preparing a large-sized ceramic core for titanium alloy casting. The method comprises the following steps: designing a metal mold inner cavity structure by reverse modeling the target ceramic core, accurately controlling the wax coating thickness on the metal mold surface, providing a stable and precise mold inner cavity for subsequent ceramic core molding, ensuring the dimensional accuracy of the wax mold, and achieving a dimensional accuracy of CT3-CT6 for the prepared ceramic core; and facilitating wax dipping of the metal mold into blocks, cleaning the joint surfaces, controlling the heating temperature of the metal mold to 80-100°C, and demolding the mold after holding the mold for no less than 4 hours. This facilitates separation of the metal mold from the ceramic core, and compared with conventional high-temperature demolding methods that easily cause adhesion and mechanical demolding methods that easily cause breakage, this method achieves a demolding qualification rate of ≥98%. When preparing the ceramic core, specific slurries and sands are used for different layers, and the drying environments of each layer are different, making the ceramic core structure more stable and the surface defect rate ≤7%.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy casting, and in particular to a method for preparing a large-size ceramic core for titanium alloy casting. Background Art

[0002] The commonly used preparation technologies for ceramic cores are grouting molding, hot pressing molding and isostatic pressing, and each has the following characteristics: the grouting molding method uses a mold to grout the ceramic core, and after drying, demolding and sintering to obtain the finished ceramic core. It is suitable for the preparation of ceramic cores with simple structures, such as ceramic filter elements; the hot pressing molding method uses a mold for hot pressing and injection, and then cools and demolds, performs high-temperature dewaxing and sintering to obtain the finished ceramic core. It is suitable for small and medium-sized ceramic cores with medium complexity, such as aircraft engine turbine blades; the isostatic pressing method uses a rubber mold to perform high-pressure isostatic pressing, demolding, and sintering to obtain the finished ceramic core. It is suitable for the preparation of high-density and high-strength ceramic cores, such as high-temperature resistant furnaces.

[0003] The production of large-sized ceramic cores generally adopts the grouting molding method, that is, the reverse production of grouting in the wax mold of the open mold is the current mainstream process. However, the preparation of large-sized ceramic cores by this process has problems such as deformation of the wax mold and difficulty in ensuring dimensional accuracy. There are also public patents showing that ceramic cores are prepared by directly grouting and sanding multiple layers into the mold, but it is suitable for the preparation of ceramic cores with simple structures and no complex shapes. For large-sized ceramic cores, there are problems such as low demoulding efficiency, easy adhesion of the mold to the ceramic core in a high-temperature demoulding environment, easy damage to the ceramic core due to traditional mechanical demoulding, and short mold service life.

[0004] Chinese invention patent application publication number CN118237538A discloses a sand-ceramic composite mold for titanium or titanium alloy casting, as well as a casting method and application. This method requires the preparation of a metal mold, the molding of a wax mold with the metal mold, the preparation of a green ceramic core, and sintering to obtain a cooked ceramic core. Not only is the shrinkage process difficult to control, but the wax mold also suffers from shrinkage deformation and deformation due to its own weight, making removal difficult. Furthermore, the wax mold preparation requires a wax press, which limits the specifications of the wax mold and makes it unsuitable for large, complex castings. Summary of the Invention

[0005] In view of this, the present invention aims to propose a method for preparing large-size ceramic cores for titanium alloy casting to solve the problems of low demolding efficiency, adhesion between the metal mold and the ceramic core, and poor dimensional accuracy when preparing large-size ceramic cores in the existing technology.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for preparing a large-size ceramic core for titanium alloy casting comprises the following steps:

[0008] S1: Mold design, reverse modeling of the target ceramic core and design of the inner cavity structure of the metal mold;

[0009] S2: wax coating the inner cavity of the mold, wax-coating the metal mold in sections, lifting the wax control after evenly coated, and cooling the mold until no obvious wax drips, the cooling temperature is 10-18°C. After cooling, the surface of the metal mold is evenly coated with wax, and the wax layer thickness is 0.15-0.2mm;

[0010] S3: mold assembly, cleaning the wax layer on the joint surface of the metal mold and joining the various blocks of the metal mold together;

[0011] S4: preparing a ceramic core, coating a high-viscosity surface layer slurry on the surface of the wax layer of the metal mold, then sprinkling surface sand on the surface of the high-viscosity surface layer slurry to form a surface layer after drying, then preparing a transition layer on the surface of the surface layer, the transition layer having the same preparation process as the surface layer, then coating a low-viscosity slurry on the surface of the transition layer, sprinkling bauxite sand on the surface of the low-viscosity slurry to form a reinforcement layer after drying, then coating a low-viscosity slurry on the surface of the reinforcement layer to form a sealing layer after drying;

[0012] S5: demoulding, heating the metal mold to a temperature of 80-100° C. for a holding time of not less than 4 hours, and then separating the metal mold from the ceramic core;

[0013] S6: calcining, heating at 5-8°C / min to 850-950°C, keeping warm for 120-240min, then heating at 10-15°C / min to 1050°C, keeping warm for 240-360min;

[0014] S7: Obtain a ceramic core green body.

[0015] This setting improves the dimensional accuracy of the wax mold, the demoulding qualification rate, and reduces the surface defect rate.

[0016] Furthermore, in step S2, before wax dipping, the metal mold is preheated at a temperature of 80-100°C for no less than 2 hours. During wax dipping, the surface temperature of the metal mold is no less than 65°C, and the wax dipping time is 3-5 seconds.

[0017] This process is suitable for batch operations of more than ten metal molds. It can realize simultaneous preheating and heat preservation of multiple metal molds, as well as rapid wax dipping and assembly line operations with high efficiency.

[0018] Furthermore, in step S2, the single metal mold is immersed in wax liquid at 80-100°C, and the insulation time in the wax liquid is not less than 180s.

[0019] This process is suitable for wax dipping of small quantities of single-piece metal molds. Its advantages are short process, high efficiency and low production cost.

[0020] Furthermore, in step S4, the high-viscosity surface layer slurry is prepared by using yttrium oxide powder of 200-400 mesh and neutral silica sol in a weight ratio of 2.5:1-5.5:1. The hanging viscosity of the high-viscosity surface layer slurry is 18-25, and the surface layer sand is zirconia sand of 40-100 mesh.

[0021] This setting can make the slurry have good bonding properties, ensuring that the yttrium oxide powder and neutral silica sol are fully mixed and tightly bonded together, while making the slurry firmly bonded to the metal mold wax layer and the surface sand, ensuring the stability of the ceramic core structure of each layer and avoiding problems such as delamination and falling off.

[0022] Furthermore, in step S4, the low-viscosity slurry is prepared by using 100-300 mesh bauxite powder and silica sol in a weight ratio of 5:1-7:1, the hanging viscosity of the low-viscosity slurry is 6-15, and the particle size of the bauxite sand is 30-60 mesh.

[0023] This arrangement enhances the bonding strength between the layers and ensures the stability of the overall structure of the ceramic core.

[0024] Furthermore, in step S4, the process preparation environment of the surface layer and the transition layer is the same, the temperature is 23±2°C, the humidity is 65~85%, and the drying time is not less than 4 hours; the process preparation environment of the reinforcement layer and the sealing layer is the same, the temperature is 23±2°C, the humidity is 45~55%, and the drying time is not less than 6 hours.

[0025] This setting can make the water in the high-viscosity surface slurry evaporate slowly and evenly, so that the yttrium oxide powder and the neutral silica sol can fully react and solidify, and tightly combine with the surface sand. The surface layer and transition layer formed have a uniform and dense structure, and can reduce defects such as pores and cracks, thereby improving the surface quality and bonding strength.

[0026] Relatively low humidity and long drying time are conducive to better solidification and shrinkage of bauxite powder and silica sol in low-viscosity slurry, enhancing the strength of the reinforcement layer and sealing layer. At the same time, it can make the bauxite sand and slurry fully bonded, improving the overall structural stability of the ceramic core.

[0027] Furthermore, in step S6, before firing, the micropores, cracks and local uneven defects on the surface of the ceramic core are checked, and the micropores, cracks and local uneven defects on the surface of the ceramic core are coated with a repair slurry, wherein the repair slurry is made of 200-400 mesh yttrium oxide powder and neutral silica sol in a weight ratio of 3.5:1 to 5.5:1, the hanging viscosity of the repair slurry is 22 to 28, and it is polished smooth after natural drying.

[0028] Inspecting and repairing micropores, cracks and local uneven defects can effectively improve the quality of the finished ceramic core and make the final product more in line with the requirements of use.

[0029] Furthermore, in step S1, the inner cavity structure of the metal mold is complementary to the outer shape of the target ceramic core, and the rest of the metal mold except the inner cavity structure is configured as a hollow structure to reduce the weight of the metal mold.

[0030] Setting the rest of the metal mold except the inner cavity structure as a hollow structure greatly reduces the weight of the mold without affecting the strength and performance of the mold. On the one hand, it reduces the amount of metal material used and reduces the manufacturing cost of the mold. On the other hand, the lighter mold is more convenient in transportation, installation and operation, which can improve production efficiency and reduce equipment energy consumption.

[0031] Compared with the prior art, the method for preparing large-size ceramic cores for titanium alloy casting according to the present invention has the following advantages:

[0032] 1) Dimensional accuracy is significantly improved;

[0033] 2) The demoulding qualification rate is greatly improved;

[0034] 3) The surface defect rate is significantly reduced. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. It should be noted that, unless there is a conflict, the features in the embodiments and embodiments of the present invention may be combined with each other.

[0036] Example 1

[0037] This embodiment provides a method for preparing a large-sized ceramic core for titanium alloy casting, comprising the following steps:

[0038] S1: Mold design, reverse modeling of the target ceramic core and design of the inner cavity structure of the metal mold;

[0039] S2: wax coating the inner cavity of the mold, wax-coating the metal mold in sections, lifting the wax control after evenly coated, and cooling the mold until no obvious wax drips, the cooling temperature is 10-18°C. After cooling, the surface of the metal mold is evenly coated with wax, and the wax layer thickness is 0.15-0.2mm;

[0040] S3: mold assembly, cleaning the wax layer on the joint surface of the metal mold and joining the various blocks of the metal mold together;

[0041] S4: preparing a ceramic core, coating a high-viscosity surface layer slurry on the surface of the wax layer of the metal mold, then sprinkling surface sand on the surface of the high-viscosity surface layer slurry to form a surface layer after drying, then preparing a transition layer on the surface of the surface layer, the transition layer having the same preparation process as the surface layer, then coating a low-viscosity slurry on the surface of the transition layer, sprinkling bauxite sand on the surface of the low-viscosity slurry to form a reinforcement layer after drying, then coating a low-viscosity slurry on the surface of the reinforcement layer to form a sealing layer after drying;

[0042] S5: demoulding, heating the metal mold to a temperature of 80-100° C. for a holding time of not less than 4 hours, and then separating the metal mold from the ceramic core;

[0043] S6: calcining, heating at 5-8°C / min to 850-950°C, keeping warm for 120-240min, then heating at 10-15°C / min to 1050°C, keeping warm for 240-360min;

[0044] S7: Obtain a ceramic core green body.

[0045] Specifically, by reverse modeling the target ceramic core and designing the inner cavity structure of the metal mold, the wax coating thickness on the metal mold surface is precisely controlled, providing a stable and precise mold cavity for subsequent ceramic core molding, ensuring the dimensional accuracy of the wax mold, and making the dimensional accuracy of the prepared ceramic core reach CT3-CT6, which is much higher than the CT10-CT12 of the traditional grouting molding method.

[0046] By wax-dipping the metal mold into blocks, cleaning the joint surfaces, controlling the heating temperature of the metal mold at 80-100℃, and keeping it warm for no less than 4 hours before demoulding, the metal mold and the ceramic core are easier to separate. Compared with traditional high-temperature demoulding that is prone to adhesion and mechanical demoulding that is prone to breakage, this method has a demoulding qualification rate of ≥98%, while the demoulding qualification rate of traditional grouting molding method is ≤62%.

[0047] When preparing the ceramic core, specific slurry and sand are used for different layers, and the drying environment of each layer is different. This design can make the structure of the ceramic core more stable, with a surface defect rate of ≤7%, while the traditional method is ≥85%.

[0048] Preferably, in step S5, the metal mold is placed in a resistance furnace for heating, and after heat preservation, the metal mold is taken out, the fixed connecting pins of the metal mold are disassembled, and then the mold is separated from the ceramic core using an ejector mechanism.

[0049] As a preferred example of the present application, in step S2, before wax dipping, the metal mold is preheated at a temperature of 80 to 100°C for no less than 2 hours. During wax dipping, the surface temperature of the metal mold is no less than 65°C, and the wax dipping time is 3 to 5 seconds.

[0050] Specifically, preheating makes the temperature of the metal mold uniform, and the surface temperature is not lower than 65°C during wax dipping, which can enable the wax liquid to better infiltrate the mold surface. In this way, within a short period of 3-5 seconds of wax dipping, the wax liquid can be evenly adhered to the mold surface, and after cooling, a wax layer of uniform thickness is formed, which provides a stable foundation for the subsequent preparation of ceramic cores and helps to improve the dimensional accuracy and surface quality of ceramic cores. This process is suitable for batch operations of more than ten metal molds, and can realize simultaneous preheating and insulation of multiple metal molds, rapid wax dipping and assembly line operations, with high efficiency.

[0051] Preferably, the metal mold is placed in a resistance furnace for preheating.

[0052] As a preferred example of the present application, in step S2, the single metal mold is immersed in wax liquid at 80-100°C, and the insulation time in the wax liquid is not less than 180s.

[0053] Specifically, a wax liquid temperature of 80-100°C can make the wax liquid have good fluidity. A single mold is immersed in it and kept warm for more than 180 seconds, which can ensure that the wax liquid is evenly wrapped on the mold surface, forming a wax layer of uniform thickness, providing a guarantee for the subsequent preparation of high-precision ceramic cores. This process is suitable for wax dipping of small quantities of single metal molds. The advantages are short process, high efficiency and low production cost.

[0054] As a preferred example of the present application, in step S4, the high-viscosity surface layer slurry is prepared by using yttrium oxide powder of 200-400 mesh and neutral silica sol in a weight ratio of 2.5:1-5.5:1. The hanging viscosity of the high-viscosity surface layer slurry is 18-25, and the surface layer sand is zirconia sand of 40-100 mesh.

[0055] Specifically, the 200-400 mesh yttrium oxide powder has good high temperature resistance. During the titanium alloy casting process, it can withstand high temperature environments, ensure the structural stability of the ceramic core at high temperatures, and prevent the ceramic core from being deformed due to high temperatures during the casting process.

[0056] Neutral silica sol and yttrium oxide powder are prepared in a weight ratio of 2.5:1-5.5:1, which can make the slurry have good bonding properties. The viscosity of the high-viscosity surface slurry hanging piece is 18-25, which can ensure that the yttrium oxide powder and neutral silica sol are fully mixed and tightly bonded together. At the same time, the slurry is firmly combined with the metal mold wax layer and the surface sand, ensuring the stability of the ceramic core structure of each layer and avoiding problems such as delamination and falling off.

[0057] 40-100 mesh zirconia sand is used as the surface sand. The finer particle size can make the surface of the ceramic core smoother, reduce surface defects and improve surface quality.

[0058] Preferably, the surface sand can also be yttrium oxide sand with a mesh size of 40 to 100.

[0059] As a preferred example of the present application, in step S4, the low-viscosity slurry is prepared by using 100-300 mesh bauxite powder and silica sol in a weight ratio of 5:1-7:1. The hanging viscosity of the low-viscosity slurry is 6-15, and the particle size of the bauxite sand is 30-60 mesh.

[0060] Specifically, the low-viscosity slurry has a viscosity of 6-15 and good fluidity, which allows it to cover the surface of the transition layer more smoothly during coating. The 100-300 mesh bauxite powder and silica sol are formulated in a ratio of 5:1-7:1, which enables the slurry to better penetrate into the underlying structure, enhance the bonding force between the layers, and ensure the stability of the overall structure of the ceramic core.

[0061] The low-viscosity slurry formed by mixing 100-300 mesh bauxite powder with silica sol, combined with 30-60 mesh bauxite sand, can effectively improve the overall strength of the ceramic core after forming a reinforcement layer and a sealing layer, making it less likely to be damaged during subsequent processing and use.

[0062] As a preferred example of the present application, in step S4, the process preparation environment of the surface layer and the transition layer is the same, the temperature is 23±2°C, the humidity is 65~85%, and the drying time is not less than 4 hours; the process preparation environment of the reinforcement layer and the sealing layer is the same, the temperature is 23±2°C, the humidity is 45~55%, and the drying time is not less than 6 hours.

[0063] Specifically, this setting can make the water in the high-viscosity surface slurry evaporate slowly and evenly, so that the yttrium oxide powder can fully react and solidify with the neutral silica sol, and tightly combine with the surface sand. The surface layer and transition layer formed have a uniform and dense structure, and can reduce defects such as pores and cracks, thereby improving surface quality and bonding strength.

[0064] Relatively low humidity and long drying time are conducive to better solidification and shrinkage of bauxite powder and silica sol in low-viscosity slurry, enhancing the strength of the reinforcement layer and sealing layer. At the same time, it can make the bauxite sand and slurry fully bonded, improving the overall structural stability of the ceramic core.

[0065] As a preferred example of the present application, in step S6, before firing, the micropores, cracks and local uneven defects on the surface of the ceramic core are checked, and the micropores, cracks and local uneven defects on the surface of the ceramic core are coated with a repair slurry, wherein the repair slurry is made of 200-400 mesh yttrium oxide powder and neutral silica sol in a weight ratio of 3.5:1 to 5.5:1, the hanging sheet viscosity of the repair slurry is 22 to 28, and it is polished smooth after natural drying.

[0066] Specifically, inspecting and repairing micropores, cracks and local uneven defects can effectively improve the quality of the finished ceramic core and make the final product more in line with usage requirements.

[0067] The repair slurry is prepared with 200-400 mesh yttrium oxide powder and neutral silica sol at a ratio of 3.5:1-5.5:1, and the hanging viscosity is 22-28. This formula gives the repair slurry good filling and adhesion properties, can fully fill micropores and cracks, and tightly bond with the surface of the ceramic core, ensuring the strength and stability of the repaired area, making the repair effect long-lasting and reliable.

[0068] Preferably, the repair slurry is dipped into a brush and applied to the micropores, cracks and local uneven defects on the surface of the ceramic core.

[0069] Preferably, 400-800 mesh sandpaper is used for polishing.

[0070] As a preferred example of the present application, in step S1, the inner cavity structure of the metal mold is complementary to the outer shape of the target ceramic core, and the rest of the metal mold except the inner cavity structure is set as a hollow structure to reduce the weight of the metal mold.

[0071] Specifically, the inner cavity structure of the metal mold complements the target ceramic core shape, providing a precise mold cavity for the molding of the ceramic core. During the preparation process, it can ensure that the dimensions of each part of the ceramic core meet the design requirements, thereby improving the quality of the ceramic core.

[0072] Setting the rest of the metal mold except the inner cavity structure as a hollow structure greatly reduces the weight of the mold without affecting the strength and performance of the mold. On the one hand, it reduces the amount of metal material used and reduces the manufacturing cost of the mold. On the other hand, the lighter mold is more convenient in transportation, installation and operation, which can improve production efficiency and reduce equipment energy consumption.

[0073] The hollow structure increases the heat dissipation area of ​​the mold, which can enable the mold to dissipate heat or heat up more quickly during the processes of wax dipping, demolding, and heating. It helps to accurately control the temperature during the process, ensure that each process step is carried out according to the predetermined parameters, and improve the stability and reliability of the ceramic core preparation process.

[0074] Preferably, the metal mold is made of aluminum.

[0075] The traditional grouting molding method and the technical solution of Example 1 were used to produce large-size ceramic cores of Φ660*550 respectively. The differences in their technical effects are shown in the following table:

[0076] index Grouting molding method Example 1 Demolding qualification rate ≤62% ≥98% Dimensional accuracy CT10-CT12 CT3-CT6 Surface defect rate ≥85% ≤7%

[0077] In summary, the preparation method of large-size ceramic core for titanium alloy casting described in this application has the following advantages: 1) dimensional accuracy is significantly improved; 2) the demolding pass rate is greatly improved; 3) the surface defect rate is significantly reduced.

[0078] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A method for preparing a large-size ceramic core for titanium alloy casting, characterized in that: The following steps are involved: S1: Mold design, reverse modeling of the target ceramic core and design of the inner cavity structure of the metal mold; S2: wax coating the inner cavity of the mold, wax-coating the metal mold in sections. Before wax coating, preheat the metal mold to 80-100°C for no less than 2 hours. During wax coating, the surface temperature of the metal mold is no less than 65°C. Wax coating is performed for 3-5 seconds. After wax coating is evenly applied, the mold is lifted up to control the wax. When no obvious wax drips, the mold is cooled to 10-18°C. After cooling, the surface of the metal mold is evenly coated with wax, and the wax layer is 0.15-0.2 mm thick. S3: mold assembly, cleaning the wax layer on the joint surface of the metal mold and joining the various blocks of the metal mold together; S4: preparing a ceramic core, coating a high-viscosity surface layer slurry on the surface of the wax layer of the metal mold, and then sprinkling surface sand on the surface of the high-viscosity surface layer slurry to form a surface layer after drying, and then preparing a transition layer on the surface of the surface layer, the transition layer and the surface layer having the same preparation process, the temperature being 23±2°C, the humidity being 65-85%, and the drying time being not less than 4 hours, and then coating a low-viscosity slurry on the surface of the transition layer, sprinkling bauxite sand on the surface of the low-viscosity slurry to form a reinforcement layer after drying, and then coating a low-viscosity slurry on the surface of the reinforcement layer to form a sealing layer after drying, the reinforcement layer and the sealing layer having the same process preparation environment, the temperature being 23±2°C, the humidity being 45-55%, and the drying time being not less than 6 hours; S5: demoulding, heating the metal mold to a temperature of 80-100° C. for a holding time of not less than 4 hours, and then separating the metal mold from the ceramic core; S6: calcining, heating at 5-8°C / min to 850-950°C, keeping warm for 120-240min, then heating at 10-15°C / min to 1050°C, keeping warm for 240-360min; S7: Obtain a ceramic core green body.

2. The method for preparing a large-size ceramic core for titanium alloy casting according to claim 1, characterized in that: In step S2, the single metal mold is immersed in wax liquid at 80-100°C, and the insulation time in the wax liquid is not less than 180s.

3. The method for preparing a large-size ceramic core for titanium alloy casting according to claim 1, characterized in that: In step S4, the high-viscosity surface layer slurry is prepared by using 200-400 mesh yttrium oxide powder and neutral silica sol in a weight ratio of 2.5:1-5.5:

1. The hanging viscosity of the high-viscosity surface layer slurry is 18-25, and the surface layer sand is 40-100 mesh zirconia sand.

4. The method for preparing a large-size ceramic core for titanium alloy casting according to claim 1, characterized in that: In step S4, the low-viscosity slurry is prepared by using 100-300 mesh bauxite powder and silica sol in a weight ratio of 5:1-7:

1. The hanging viscosity of the low-viscosity slurry is 6-15, and the particle size of the bauxite sand is 30-60 mesh.

5. The method for preparing a large-size ceramic core for titanium alloy casting according to claim 1, characterized in that: In step S6, before firing, the micropores, cracks and local uneven defects on the surface of the ceramic core are checked, and the micropores, cracks and local uneven defects on the surface of the ceramic core are coated with a repair slurry, wherein the repair slurry is prepared by using 200-400 mesh yttrium oxide powder and neutral silica sol in a weight ratio of 3.5:1 to 5.5:1, the hanging viscosity of the repair slurry is 22 to 28, and it is polished smooth after natural drying.

6. The method for preparing a large-sized ceramic core for titanium alloy casting according to claim 1, characterized in that: In step S1 , the inner cavity structure of the metal mold complements the outer shape of the target ceramic core, and the rest of the metal mold except the inner cavity structure is configured as a hollow structure.