A soluble ceramic core, preparation method and application

Abstract

The present invention relates to a soluble ceramic core, a preparation method and an application, belonging to the technical field related to rapid casting. The preparation method of the present invention comprises the following steps: (1) uniformly mixing ceramic powder and soluble salt, and printing a green body of the ceramic core by using a micro-droplet jet bonding forming process, and obtaining a ceramic core blank after curing, impregnation and drying; (2) putting the ceramic blank into a high-temperature sintering furnace for sintering, and obtaining a soluble ceramic core after cooling with the furnace. By uniformly mixing ceramic powder and soluble salt and preparing the soluble ceramic core by using the micro-droplet jet bonding forming process, the present invention has simple operation, high production efficiency and low cost, and is suitable for forming large and complex-structured ceramic cores. The ceramic core prepared by the present invention has good solubility and is very convenient to remove from the casting after casting is completed.

Description

Technical Field

[0001] The present invention belongs to the technical field related to additive manufacturing, and more specifically, relates to a soluble ceramic core, a preparation method and an application thereof. Background Art

[0002] With the rapid development of domestic fields such as aerospace and weaponry, new requirements have been put forward for the manufacturing technology of large and complex-shaped components, including unified structural functions, integral casting, thin walls, high precision, reliability, etc. Among them, some components have complex structures with large-sized cavity structures. The inner cavities of some castings have complex structures with fine or irregular pipelines, or the inner cavities cannot be dried and hardened through the shell hanging technology and are difficult to machine, such as impellers, oil return pipelines, air intake elbow pipes, etc. At this time, relying solely on precision casting shells cannot meet the casting requirements of complex castings, and it is necessary to cooperate with ceramic cores and shells to produce castings with complex inner cavities. However, traditional technologies for manufacturing ceramic cores, such as gel casting, injection molding, and hot pressing, generally have some disadvantages, including difficulty in manufacturing ceramic cores with complex geometric shapes, long preparation cycles, and difficulty in balancing the cost of mold design at low production volumes. Therefore, how to quickly prepare ceramic cores with complex structures and reduce production costs is an urgent problem to be solved currently.

[0003] Additive manufacturing technology refers to the process of slicing the 3D model of a part under the control of a computer and printing layer by layer to finally form a complete part. Applying additive manufacturing technology to the production process of ceramic shells can break through problems faced in traditional processes, such as long cycles, high costs, complex processes, and limitations, which is beneficial to the further development of various industries. Currently, the additive manufacturing technologies that can be used for the forming and preparation of ceramic shells mainly include: stereolithography (SLA) technology, selective laser sintering (SLS) technology, micro-droplet jet bonding (BJ) technology, and so on. Compared with SLA and SLS technologies, BJ technology for manufacturing ceramic cores has the comprehensive advantages of high efficiency, low cost, and excellent performance. First, the BJ technology uses an array of nozzles to spray materials, which belongs to surface forming, and its manufacturing efficiency is dozens to hundreds of times that of SLA and SLS. Secondly, the BJ technology belongs to bonding forming, without heat sources and thermal deformation, and has no stress and cracking problems during the manufacturing process, with broad application prospects.

[0004] To ensure the formation of a good cavity structure inside the casting, the ceramic core must have good chemical stability and high-temperature creep resistance. The commonly used ceramic core preparation materials are mainly SiO2 and Al2O3. In addition, materials such as ZrO2 and Y2O3 have also been gradually used in the preparation of ceramic cores in recent years. After the casting is successfully poured, the ceramic core needs to be removed from the casting to fully expose the internal cavity so that the function of the cavity can be fully exerted. However, it is difficult to remove the ceramic cores prepared from the above materials during the subsequent core removal process. Using strong alkali solution as the core removal medium and carrying out chemical corrosion reaction under high temperature and high pressure is the commonly used core removal method at present. However, this method has problems such as easy corrosion of the casting surface and unsatisfactory removal effect of complex curved cores. The core removal technology has become a major bottleneck restricting the use of ceramic cores. Therefore, it is urgent to develop a soluble ceramic core material and its preparation method to solve the problems existing in the above preparation technology and ceramic core materials and meet the needs of industrial production. Summary of the Invention

[0005] In view of the above defects or improvement requirements of the prior art, the present invention provides a soluble ceramic core based on micro-droplet jet bonding forming, its preparation method and application. A ceramic powder aggregate and a soluble salt dry binder are mixed as the ceramic core material. At high temperature, the ceramic aggregate and the molten salt are sintered together tightly. After cooling with the furnace, a soluble ceramic core is obtained. After pouring, the casting is placed in water. The salt in the ceramic core dissolves in water, and the ceramic core will collapse and can be easily separated from the casting. The operation is simple, greatly simplifying the subsequent core removal process and not causing damage to the casting itself.

[0006] According to the first aspect of the present invention, a preparation method of a soluble ceramic core is provided, including the following steps:

[0007] (1) Uniformly mix the ceramic powder aggregate and the dry binder to form a mixed powder. Use the micro-droplet jet bonding forming process to make the mixed powder into a ceramic core green body, and then heat-cure, infiltrate and dry the ceramic core green body to obtain a ceramic core blank; the dry binder is a soluble salt;

[0008] (2) Sinter the ceramic core blank obtained in step (1), and the soluble ceramic core is obtained after cooling with the furnace.

[0009] Preferably, in step (1), the printing parameters in the micro-droplet jet bonding forming process are: printing layer height 0.05 mm - 0.20 mm, binder saturation 80% - 160%; the temperature of the heat curing is 180°C - 210°C, and the time is 3 h - 6 h.

[0010] Preferably, in step (1), the ceramic powder aggregate is one or a mixture of several of quartz, alumina, zirconia, and yttrium oxide; the dry binder is one or a mixture of several of chloride salts, sulfate salts, silicate salts, phosphate salts, and metaphosphate salts; the particle sizes of the ceramic powder aggregate and the dry binder are 325 mesh to 1000 mesh.

[0011] Preferably, in step (1), in the mixed powder, the mass fraction of the dry binder is 15% to 50%.

[0012] Preferably, in step (1), the impregnation liquid used for impregnation is an alcohol-based impregnation liquid, and the alcohol-based impregnation liquid is at least one of a nano-SiO2 alcohol-based dispersion, a nano-ZrO2 alcohol-based dispersion, or a nano-TiO2 alcohol-based dispersion. The impregnation time is 30 s to 3 min, and the impregnation method is atmospheric pressure impregnation or vacuum impregnation. When vacuum impregnation is used, the vacuum degree is 0 to 50 KPa, and the mass fraction is 10% to 40%; the impregnation liquid is used to penetrate into the pores of the ceramic core green body so that its shape can be kept intact during the sintering process and the collapse of the green body can be avoided.

[0013] Preferably, in step (2), the sintering is divided into two stages, which are sintering at 650 °C to 800 °C for 1 h to 3 h, and then sintering at 1100 °C to 1500 °C for 1 h to 3 h. The heating rate during the sintering process is 2 to 5 °C / min.

[0014] According to another aspect of the present invention, there is provided a soluble ceramic core prepared by the method described in any one of the above.

[0015] According to another aspect of the present invention, the present invention also provides an application of the above soluble ceramic core in precision casting.

[0016] Preferably, the soluble ceramic core cooperates with the mold shell and is used for the precision casting of cavity structure parts.

[0017] Preferably, after the casting is completed, the component is placed in water. The ceramic core reacts with water, cracks and disintegrates, and separates from the structural part to form a cavity structure part.

[0018] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0019] (1) The method of the present invention uses a mixture of ceramic powder aggregate and soluble salt dry binder as the ceramic core material. During the high-temperature sintering process, the ceramic aggregate and the molten salt are sintered tightly together. After cooling with the furnace, a soluble ceramic core is obtained. After casting, the casting is placed in water, and the salt in the ceramic core dissolves in water, causing the ceramic core to collapse and easily separate from the casting. Compared with ceramic cores prepared from materials such as pure SiO2, Al2O3, and Y2O3, the soluble ceramic core prepared by the present invention is more time-saving and labor-saving during demolding, is not prone to corrode the surface of the casting, has a more ideal removal effect when it is a complex curved core, is simpler in process operation, and greatly simplifies the later core removal process without causing damage to the casting itself. The preparation method of the present invention can solve the limitations of traditional processes in forming large and complex structure ceramic cores, shorten the production cycle, reduce production costs, and has great development potential.

[0020] (2) The present invention uses the preferably micro-droplet jet bonding forming process to prepare the ceramic core, which can solve the limitations of traditional processes in forming large and complex structure ceramic cores, shorten the production cycle, reduce production costs, and meet the production needs of the social market. Compared with SLA and SLS technologies, the preferably micro-droplet jet bonding forming process of the present invention belongs to surface forming, and its manufacturing efficiency is dozens to hundreds of times that of SLA and SLS. Secondly, there is no heat source and thermal deformation, and there are no stress and cracking problems during the manufacturing process, having broad application prospects.

[0021] (3) The preferably impregnation process of the present invention can enable the ceramic core blank to maintain its complete shape during the high-temperature sintering process, avoid the collapse of the blank, and ensure the sintering quality. Description of the Drawings

[0022] Figure 1 is a schematic flow chart of the preparation method of the soluble ceramic core of the present invention.

[0023] Figure 2 is a physical diagram of the ceramic core sample prepared in Example 1 of the present invention.

[0024] Figure 3 is the collapse diagram of the ceramic core sample prepared in Example 1 of the present invention at different times in water. Detailed Embodiments

[0025] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Such as Figure 1As shown in the figure, a preparation method of a soluble ceramic core based on micro-droplet jet bonding forming mainly includes the following steps:

[0027] (1) Mix the ceramic powder aggregate and the soluble salt dry binder evenly, put them into the powder cylinder, import the three-dimensional structure model of the ceramic core and adjust the printing parameters, and then print out the initial blank of the ceramic core;

[0028] (2) Put the printed initial blank together with the powder bed into the drying oven for heating and curing;

[0029] (3) Take out the cured blank from the powder bed, clean the powder thoroughly, carry out sol infiltration, and then put it into the drying oven for low-temperature drying;

[0030] (4) Sinter the ceramic core blank obtained in step (3), and the soluble ceramic core is obtained after cooling with the furnace.

[0031] Further, in step (1), the ceramic powder aggregate is one or a mixture of several of quartz, alumina, zirconia, yttrium oxide and other powders.

[0032] Further, in step (1), the soluble salt dry binder is one or a mixture of several of chloride salts, sulfate salts, silicate salts, phosphate salts, metaphosphate salts, etc.

[0033] Further, in step (1), in the mixed powder, the proportion of the soluble salt dry binder is 15% - 50%.

[0034] Further, in step (1), the particle sizes of the ceramic powder aggregate and the soluble salt dry binder are 325 mesh - 1000 mesh; the binder used in the micro-droplet jet bonding forming process is phenolic resin; the printing parameters are: printing layer height 0.05mm - 0.20mm, binder saturation 80% - 160%.

[0035] Further, in step (4), the sintering is divided into two stages, which are sintering at 650°C - 800°C for 1h - 3h, and then sintering at 1100°C - 1500°C for 1h - 3h, and the heating rate during the sintering process is 2 - 5°C / min.

[0036] Further, in step (2), the temperature of the heating and curing is 180°C - 210°C, and the time is 3h - 6h.

[0037] Further, in step (3), the infiltration liquid used for infiltration is an alcohol-based infiltration liquid, and the mass fraction is 10% - 40%; the infiltration liquid is used to penetrate into the pores of the ceramic core blank so that it can maintain its complete shape during high-temperature sintering and avoid the collapse of the blank.

[0038] Further, the impregnation liquid is at least one of a nano-SiO2 alcohol-based dispersion, a nano-ZrO2 alcohol-based dispersion, or a nano-TiO2 alcohol-based dispersion. The impregnation time is 30 s to 3 min, and the impregnation method is atmospheric pressure impregnation or vacuum impregnation. When vacuum impregnation is used, the vacuum degree is 0 to 50 KPa.

[0039] The present invention also provides a soluble ceramic core, which is prepared by using the preparation method of the soluble ceramic core as described above.

[0040] In actual additive manufacturing, the soluble ceramic core and the mold shell are cooperated with each other for precision casting of cavity structure parts. After the casting is completed, the structure part is placed in water. The ceramic core reacts with water, cracks and disintegrates, and separates from the structure part, and the structure part can obtain a cavity with the target shape.

[0041] The following further describes the present invention in detail with several specific embodiments.

[0042] Example 1

[0043] The preparation method of the soluble ceramic core provided in Example 1 of the present invention mainly includes the following steps:

[0044] S1, Mix 1000-mesh quartz and sodium chloride evenly, where the addition ratio of sodium chloride is 15%. The mixed powder is dried at 80 °C for 12 h, taken out, and the powder is sieved. The sieved mixed powder is spread evenly on the powder supply cylinder. The three-dimensional structure model of the ceramic core is imported into the computer, and the printing parameters of the 3D printer are adjusted. Subsequently, printing is started, and the nozzle, powder supply cylinder, and working cylinder operate according to the set program until the printing process ends. Among them, the printing parameters of the 3D printing device are: the printing layer height is 0.05 mm, and the binder saturation is 80%.

[0045] S2, After printing, the printed ceramic core blank and the powder bed are placed in a drying oven and heated and cured at 180 °C for 3 h. After cooling, the ceramic core blank is taken out of the powder bed, and the excess powder around it is cleaned. Subsequently, the ceramic core blank is immersed in a 10% nano-ZrO2 alcohol-based dispersion, taken out after impregnation at atmospheric pressure for 3 min, and then placed in a drying oven at 70 °C and dried for 6 h.

[0046] S3, The impregnated ceramic blank is placed in a crucible, completely filled with spherical alumina particles, and then placed in a muffle furnace for high-temperature sintering. Its sintering curve is sintered at 650 °C for 1 h, sintered at 1100 °C for 1 h, and the heating rate is 2 °C / min. Finally, it is cooled with the furnace to obtain a soluble ceramic core, as Figure 2 shown.

[0047] Example 2

[0048] The preparation method of the soluble ceramic core provided by Embodiment 2 of the present invention mainly includes the following steps:

[0049] S1. Mix alumina with 800 meshes and sodium sulfate evenly, wherein the addition ratio of sodium sulfate is 30%. Dry the mixed powder at 90 °C for 10 h, take it out and screen the powder. Spread the well-screened mixed powder on the powder supply cylinder, import the three-dimensional structure model of the ceramic core into the computer, and adjust the printing parameters of the 3D printer. Then start printing, and the nozzle, powder supply cylinder and working cylinder run according to the set program until the printing process ends. Among them, the printing parameters of the 3D printing device are: printing layer height 0.12 mm, binder saturation 120%.

[0050] S2. After printing, put the printed ceramic core blank and the powder bed into an oven and heat and cure at 200 °C for 5 h. After cooling, take out the ceramic core blank from the powder bed and clean the excess powder around it. Then, immerse the ceramic core blank in a 30% nano-SiO2 alcohol-based dispersion liquid, then put it into a vacuum impregnation device and impregnate it at a vacuum degree of 25 KPa for 2 min and then take it out, and then put it into an oven at 80 °C and dry it for 5 h.

[0051] S3. Put the impregnated ceramic blank into a crucible, completely bury it with spherical alumina particles, and then put it into a muffle furnace for high-temperature sintering. Its sintering curve is sintered at 700 °C for 1 h, sintered at 1300 °C for 1.5 h, and the heating rate is 3 °C / min for sintering. Finally, cool it with the furnace to obtain the soluble ceramic core.

[0052] Embodiment 3

[0053] The preparation method of the soluble ceramic core provided by Embodiment 3 of the present invention mainly includes the following steps:

[0054] S1. Mix zirconia with 325 meshes and tripotassium phosphate evenly, wherein the addition ratio of tripotassium phosphate is 50%. Dry the mixed powder at 100 °C for 12 h, take it out and screen the powder. Spread the well-screened mixed powder on the powder supply cylinder, import the three-dimensional structure model of the ceramic core into the computer, and adjust the printing parameters of the 3D printer. Then start printing, and the nozzle, powder supply cylinder and working cylinder run according to the set program until the printing process ends. Among them, the printing parameters of the 3D printing device are: printing layer height 0.20 mm, binder saturation 160%.

[0055] S2. After printing is completed, the printed ceramic core blank and the powder bed are placed in a drying oven and heated and cured at 210 °C for 6 h. After cooling, the ceramic core blank is taken out of the powder bed and the excess powder around it is cleaned up. Subsequently, the ceramic core blank is immersed in a 40% nano-TiO2 alcohol-based dispersion liquid, and then placed in a vacuum impregnation device and impregnated for 30 s under a vacuum degree of 50 KPa and then taken out, and then placed in a drying oven at 90 °C and dried for 6 h.

[0056] S3. The impregnated ceramic blank is placed in a crucible and completely filled with spherical alumina particles, and then it is placed in a muffle furnace for high-temperature sintering. Its sintering curve is sintered at 800 °C for 3 h, sintered at 1500 °C for 3 h, and the heating rate is 5 °C / min for sintering. Finally, it is cooled with the furnace to obtain a soluble ceramic core.

[0057] Application Example

[0058] With the continuous increase of the inlet gas temperature of the turbine engine, simply relying on improving the temperature-bearing capacity of materials and adopting heat insulation measures can no longer meet the service requirements. Therefore, improving the heat dissipation capacity of turbine blades through a complex air-cooled inner cavity structure has become the key to the manufacture of advanced engines, and ceramic cores are the core components for casting blades with complex air-cooled inner cavity structures. Taking the preparation of turbine blades as an example, first, a soluble turbine blade core is prepared according to the method in the above specific Embodiment 1. The core and the mold shell are properly matched and placed in a die-casting device. The molten titanium alloy liquid is poured into the gate above the mold shell with a crucible, and then pressurized to make the metal liquid fill the mold shell. After cooling, the castings after pouring are taken out and fully immersed in water. As Figure 3 shown, where Figure 3 (a) in Figure 3 (b) in Figure 3 (c) in Figure 3 are respectively the physical pictures of the castings soaked for 1 min, 2 min, and 3 min. After 5 min, the ceramic core is completely disintegrated. As

[0059] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a soluble ceramic core, characterized in that, It includes the following steps: (1) Uniformly mix ceramic powder aggregate with dry binder to form a mixed powder. Use the micro-droplet injection bonding forming process to make the mixed powder into a ceramic core green body, and then heat-cure, infiltrate, and dry the ceramic core green body to obtain a ceramic core blank; the dry binder is a soluble salt; in the mixed powder, the mass fraction of the dry binder is 15% - 50%; the infiltration liquid used for infiltration is an alcohol-based infiltration liquid, and the alcohol-based infiltration liquid is at least one of nano-SiO2 alcohol-based dispersion, nano-ZrO2 alcohol-based dispersion, or nano-TiO2 alcohol-based dispersion; the ceramic powder aggregate is one or a mixture of quartz, alumina, zirconia, and yttrium oxide; the dry binder is a mixture of one or more of chloride salts, sulfate salts, silicate salts, phosphate salts, and metaphosphate salts; (2) Sinter the ceramic core blank obtained in step (1), and the soluble ceramic core is obtained after cooling with the furnace; the sintering is divided into two stages, which are sintering at 650°C - 800°C for 1 h - 3 h, and then sintering at 1100°C - 1500°C for 1 h - 3 h. The heating rate during the sintering process is 2 - 5°C / min.

2. The preparation method according to claim 1, characterized in that, In step (1), the printing parameters in the micro-droplet injection bonding forming process are: printing layer height 0.05 mm - 0.20 mm, binder saturation 80% - 160%; the temperature for heat-curing is 180°C - 210°C, and the time is 3 h - 6 h.

3. The preparation method according to claim 1, characterized in that, In step (1), the particle sizes of the ceramic powder aggregate and the dry binder are 325 mesh - 1000 mesh.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step (1), the infiltration time is 30 s - 3 min, and the infiltration method is atmospheric pressure infiltration or vacuum infiltration. When it is vacuum infiltration, the vacuum degree is 0 - 50 KPa, and the mass fraction is 10% - 40%; the infiltration liquid is used to penetrate into the pores of the ceramic core blank so that it can maintain its complete shape during sintering and avoid the collapse of the blank.

5. A soluble ceramic core prepared by using the method according to any one of claims 1 - 4.

6. The application of the soluble ceramic core according to claim 5 in precision casting.

7. The application according to claim 6, wherein The soluble ceramic core cooperates with the mold shell and is used for the precision casting of cavity structure parts.

8. The application according to claim 6 or 7, characterized in that, After the poured component is put into water, the ceramic core reacts with water, cracks and disintegrates, and separates from the structural component to form a cavity structure part.

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