Ceramic core and surface treatment method thereof

Abstract

The invention discloses a ceramic core surface treatment method and a ceramic core prepared by the same. The method comprises the following steps: calcining and forming aluminum oxide to obtain a ceramic core blank; mixing cobalt oxide with water, adding silica sol, and stirring to prepare slurry; dipping a ceramic core blank in the cobalt oxide solution to obtain a ceramic core attached with cobalt oxide; and sequentially airing for 18-24 hours, drying for 1.5-2 hours at the temperature of 100-200 DEG C, finally putting into a sintering furnace, and sintering for 3-4 hours at the temperature of 1200-1250 DEG C to finally obtain the ceramic core attached with cobalt aluminate. According to the invention, through an innovative process of generating cobalt aluminate through high-temperature reaction of cobalt oxide and aluminum oxide, the problem of easy peeling in a traditional coating process is solved. And cobalt oxide is relatively low in cost, so that the production cost is greatly reduced, a more efficient and more economical ceramic core preparation technology is provided for the field of precision casting, and the production quality and efficiency of complex castings are favorably improved.

Description

Technical Field

[0001] The invention relates to the field of ceramic cores for precision casting, and in particular to a ceramic core and a surface treatment method thereof. Background Art

[0002] In the field of precision casting, the molding process of complex castings usually uses a ceramic core to form the inner cavity of the casting, and constructs the outer surface of the casting through a shell. During the preparation of the shell, the surface layer generally mixes cobalt aluminate, silica sol and zircon powder, and then sprinkles corundum sand to complete the molding operation. The subsequent layers are constructed layer by layer using refractory materials. During the alloy pouring stage, the high-temperature alloy reacts with the cobalt aluminate of the surface layer to generate a heterogeneous nucleation core, thereby achieving the refinement of the casting surface. However, since the inner surface of the casting relies on the ceramic core, the heat dissipation efficiency is low, and the lack of a heterogeneous nucleation core makes the inner cavity of the casting prone to problems such as coarse grains and metallurgical defects.

[0003] There are currently two main solutions to the problems existing in the inner cavity of the above-mentioned castings. First, add cobalt aluminate to the ceramic slurry and then sinter it. However, this method has many disadvantages: first, it causes serious pollution to the pressing equipment; second, the cost of cobalt aluminate is relatively high, and such use will cause waste of resources; third, cobalt aluminate is dispersed in the core, and the actual application effect is poor. Second, after the sintering of the ceramic core is completed, the cobalt aluminate is immersed on the surface of the core using a coating process. However, this method has obvious defects, that is, the bonding strength between the ceramic core and the coating is relatively low, and the coating is prone to peeling during subsequent use. In summary, the existing solutions all have certain limitations, and a more effective technical solution is urgently needed to solve the related problems of easy peeling of the coating.

[0004] The above contents are only used to assist in understanding the technical solution of the present invention and do not constitute an admission that the above contents are prior art. Summary of the invention

[0005] The main purpose of the invention is to solve the technical problem that the ceramic core and the coating are not firmly combined and are easy to peel off in the coating process.

[0006] To achieve the above object, the present invention provides a method for surface treatment of a ceramic core, the method comprising:

[0007] calcining alumina to obtain a ceramic core embryo;

[0008] mixing cobalt oxide with water to form a slurry;

[0009] Dipping the ceramic core embryo into the slurry, and taking out and drying after cobalt oxide adheres to the surface of the ceramic core;

[0010] The dried ceramic core with attached cobalt oxide is dried and sintered to obtain the ceramic core with attached cobalt aluminate.

[0011] Preferably, the alumina is calcined and formed to obtain a ceramic core embryo, wherein the calcination temperature is 1300-1400°C.

[0012] Preferably, the solid-liquid ratio of the cobalt oxide to water is 1.5:1 to 2.5:1.

[0013] Preferably, the mixing of cobalt oxide and water to form a slurry comprises: mixing cobalt oxide and water, adding silica sol, and stirring to form a slurry;

[0014] The silica sol added appropriately in this step can improve the viscosity and bonding strength.

[0015] Preferably, the drying time is 18 to 24 hours.

[0016] Preferably, the step of drying the dried ceramic core with attached cobalt oxide comprises:

[0017] The dried ceramic core with cobalt oxide attached thereto is dried at 100 to 120° C. for 1.5 to 2 hours.

[0018] Preferably, the dried ceramic core with attached cobalt oxide is dried and sintered, and the sintering includes:

[0019] The dried ceramic core with attached cobalt oxide is placed in a sintering furnace and sintered at 1200-1250° C. for 3-4 hours to obtain a ceramic core with attached cobalt aluminate.

[0020] The cobalt oxide on the surface of the ceramic core formed by calcining alumina reacts with alumina at high temperature to form cobalt aluminate, so that the ceramic core attached with cobalt oxide reacts to obtain a ceramic core attached with cobalt aluminate. Since cobalt aluminate is chemically generated, it has a very tight bond with the matrix - the ceramic core made of alumina, and there will be no subsequent problems such as falling off.

[0021] In addition, to achieve the above purpose, the present invention also provides a ceramic core, which is prepared by the above method.

[0022] The present invention solves the problem of "easy to peel off" in the traditional coating process through the innovative process of high-temperature reaction of cobalt oxide and aluminum oxide to generate cobalt aluminate. In addition, the cost of cobalt oxide is relatively low, which greatly reduces the production cost, and provides a more efficient and economical ceramic core preparation technology for the precision casting field, which helps to improve the production quality and efficiency of complex castings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 The present invention is a schematic diagram of the preparation process of a method for surface treatment of a ceramic core according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to better understand the above technical solution, exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0026] 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.

[0027] The present invention provides a method for treating the surface of a ceramic core, referring to Figure 1 In one embodiment, the method includes:

[0028] In one embodiment, alumina is placed in a specific device and calcined and molded at a temperature range of 1300-1400°C to obtain a ceramic core embryo. Calcination in this temperature range can fully crystallize the alumina, ensure that the ceramic core embryo has good mechanical strength and stability, and provide a solid foundation for subsequent process steps. The alumina is calcined and molded to obtain a ceramic core embryo.

[0029] Cobalt oxide is mixed with water at a solid-liquid ratio of 1.5:1 to 2.5:1. This solid-liquid ratio ensures that the slurry has a suitable concentration, which is conducive to subsequent uniform adhesion to the surface of the ceramic core embryo. After the mixing is completed, add an appropriate amount of silica sol and stir evenly to form a slurry. In this step, the appropriate amount of silica sol can increase the viscosity and bonding force, so that the cobalt oxide can better adhere to the ceramic core and enhance the overall adhesion effect.

[0030] The prepared ceramic core embryo is immersed in the above-prepared slurry so that cobalt oxide is fully attached to its surface to obtain a ceramic core with cobalt oxide attached. Subsequently, the ceramic core with cobalt oxide attached is naturally dried for 18 to 24 hours. The appropriate drying time can make the cobalt oxide film initially stabilized on the surface of the ceramic core, laying a good foundation for the subsequent drying step.

[0031] Place the dried alumina ceramic core in a drying device and dry it at 100-120°C for 1.5-2 hours; precise drying temperature and time can effectively remove moisture and avoid the subsequent sintering reaction being affected by residual moisture;

[0032] The dried ceramic core with attached cobalt oxide is placed in a sintering furnace, the temperature is set to 1200-1250°C, and the sintering time is 3-4 hours, and finally a ceramic core with attached cobalt aluminate is obtained. In this step, the cobalt oxide on the surface of the ceramic core formed by calcining alumina reacts with alumina at high temperature to generate cobalt aluminate, so that the ceramic core with attached cobalt oxide reacts to obtain a ceramic core with attached cobalt aluminate. Since cobalt aluminate is chemically generated, it has a very tight bond with the matrix-the ceramic core made of alumina, and there is no subsequent problem of falling off, which greatly improves the quality and service life of the ceramic core.

[0033] The present invention also provides a ceramic core, referring to Figure 1 In one embodiment, the ceramic core is composed of Figure 1 The ceramic core prepared by the preparation method shown in the invention has a uniform coating and is not easy to fall off, and the cobalt oxide used is relatively low in cost, thereby reducing the production cost.

[0034] Embodiment 1:

[0035] S1: calcining alumina to obtain a ceramic core embryo;

[0036] The alumina powder is placed in a high-temperature furnace, the calcination temperature is set to 1300°C, and the insulation time is 3 hours, so that the alumina can be fully crystallized and formed to obtain a ceramic core embryo with high mechanical strength and smooth surface.

[0037] S2: mixing cobalt oxide with water to prepare a slurry;

[0038] Cobalt oxide and water were weighed at a solid-liquid ratio of 1.5:1, placed in a stirring container and mixed, and then silica sol (the addition amount was 5% of the total mass) was added, and mechanical stirring was performed for 30 minutes until the mixture was uniform, forming a slurry with moderate viscosity.

[0039] S3: immersing the ceramic core embryo in the slurry, and taking out and drying after cobalt oxide adheres to the surface of the ceramic core;

[0040] The ceramic core embryo is completely immersed in the slurry for 10 seconds to ensure that the slurry evenly covers the surface of the core. After being taken out, it is placed in a constant temperature and humidity environment (25°C, humidity 60%) to dry naturally for 18 hours to initially solidify the cobalt oxide film.

[0041] S4: drying and sintering the dried ceramic core with cobalt oxide attached to obtain a ceramic core with cobalt aluminate attached;

[0042] The dried core was placed in an oven and dried at 110°C for 2 hours to completely remove residual moisture. It was then transferred to a sintering furnace and heated to 1200°C at a heating rate of 5°C / min and sintered for 3 hours. Cobalt oxide reacted with the alumina matrix to form a dense cobalt aluminate layer, and the bonding force was significantly enhanced.

[0043] Embodiment 2:

[0044] S1: calcining alumina to obtain a ceramic core embryo;

[0045] The alumina powder was placed in a high-temperature furnace, the calcination temperature was set to 1350°C, and the insulation time was 2.5 hours to obtain a high-density ceramic core embryo.

[0046] S2: mixing cobalt oxide with water to prepare a slurry;

[0047] Cobalt oxide and water were weighed at a solid-liquid ratio of 2:1, and silica sol (addition amount 8%) was added after mixing, and ultrasonic dispersion was performed for 20 minutes to form a slurry with good fluidity.

[0048] S3: immersing the ceramic core embryo in the slurry, and taking out and drying after cobalt oxide adheres to the surface of the ceramic core;

[0049] The ceramic core embryo is completely immersed in the slurry for 50 seconds to ensure that the slurry evenly covers the surface of the core. After being taken out, it is placed in a constant temperature and humidity environment (25°C, humidity 60%) to dry naturally for 20 hours to initially solidify the cobalt oxide film.

[0050] S4: drying and sintering the dried ceramic core with cobalt oxide attached to obtain a ceramic core with cobalt aluminate attached;

[0051] The sample was dried at 105°C for 1.8 hours, then heated to 1225°C at 8°C / min and sintered for 3.5 hours. The cobalt aluminate layer was chemically bonded to the substrate without any interface defects.

[0052] Embodiment 3:

[0053] S1: calcining alumina to obtain a ceramic core embryo;

[0054] The alumina powder is placed in a high-temperature furnace, the calcination temperature is set to 1400° C., and the temperature is kept for a certain period of time to obtain a ceramic core embryo.

[0055] S2: mixing cobalt oxide with water to prepare a slurry;

[0056] Cobalt oxide and water were weighed at a solid-liquid ratio of 2.5:1, placed in a stirring container and mixed, and then silica sol was added and stirred to form a slurry.

[0057] S3: immersing the ceramic core embryo in the slurry, and taking out and drying after cobalt oxide adheres to the surface of the ceramic core;

[0058] The ceramic core embryo is completely immersed in the slurry for 120 seconds to ensure that the slurry evenly covers the surface of the core. After being taken out, it is placed in a constant temperature and humidity environment (25°C, humidity 60%) to dry naturally for 24 hours to initially solidify the cobalt oxide film.

[0059] S4: drying and sintering the dried ceramic core with cobalt oxide attached to obtain a ceramic core with cobalt aluminate attached;

[0060] The dried core is placed in an oven for drying, and then transferred to a sintering furnace and sintered at 1250° C. for 4 hours to obtain a ceramic core with cobalt aluminate attached.

[0061] Comparative Example 1: Commercially available ceramic core

[0062] Comparison of results (Examples 1-3 and Comparative Example 1):

[0063] Table 1 Test data of Examples 1 to 3 and Comparative Example 1

[0064] Coating Adhesion Example 1 Not easy to fall off Example 2 Not easy to fall off Example 3 Not easy to fall off Comparative Example 1 Easy to fall off

[0065] As shown in Table 1, the coating adhesion of the ceramic core prepared by the method of the present invention in Examples 1 to 3 is better. The bonding between the coating and the substrate is significantly enhanced by reacting cobalt oxide and aluminum oxide substrate at high temperature to form cobalt aluminate (chemical bonding), so there is no peeling phenomenon. The generation of cobalt aluminate by chemical reaction ensures that the interface is free of defects, which greatly improves the product reliability. Comparative Example 1 adopts a physical coating process, directly immerses cobalt aluminate, and the bonding between the coating and the substrate is weak. It is easy to peel off under high temperature or mechanical stress, affecting the quality of the inner cavity of the casting.

[0066] Regarding the cost comparison, the raw materials of Examples 1 to 3 are mainly cobalt oxide, which has a low cost. Cobalt aluminate is generated through reaction, which avoids the direct use of safety-compliant cobalt aluminate materials. At the same time, the addition of silica sol further optimizes the adhesion of the slurry and reduces material waste. The overall production cost is reduced by about 30% to 40% compared with commercially available products. The comparative example needs to directly purchase cobalt aluminate as the coating material, which has high raw material costs and a complicated coating process, requiring multiple immersion and curing, resulting in high overall costs.

[0067] In summary, the present invention solves the three major problems of "high cost, poor uniformity, and easy peeling" in the traditional coating process through the innovative process of generating cobalt aluminate by high-temperature reaction of cobalt oxide and aluminum oxide:

[0068] 1. Process economy: The low cost of cobalt oxide and the mechanism of reaction to form cobalt aluminate significantly reduce material and process costs;

[0069] 2. Superior performance: Chemically bonded coatings have higher bonding strength and uniformity, avoiding metallurgical defects;

[0070] 3. Application value: It provides an efficient, reliable and economical solution for the field of precision casting, which is especially suitable for the grain refinement requirements of the inner cavity of complex castings, and can improve the casting yield and production efficiency.

[0071] The present invention is superior to commercially available products in terms of coating performance, process cost and stability, and has significant technological progress and industrial promotion value.

[0072] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for surface treatment of a ceramic core, characterized in that: The method comprises: calcining alumina to obtain a ceramic core embryo; mixing cobalt oxide with water to form a slurry; Dipping the ceramic core embryo into the slurry, and taking out and drying after cobalt oxide adheres to the surface of the ceramic core; The dried ceramic core with attached cobalt oxide is dried and sintered to obtain the ceramic core with attached cobalt aluminate.

2. The method according to claim 1, characterized in that The calcination temperature is 1300-1400°C.

3. The method according to claim 1, characterized in that The solid-to-liquid ratio of the cobalt oxide to water is 1.5:1 to 2.5:

1.

4. The method according to claim 3, characterized in that The step of mixing cobalt oxide with water to prepare a slurry comprises: Cobalt oxide, water and silica sol are mixed and stirred to form a slurry.

5. The method according to claim 1, characterized in that The drying time is 18 to 24 hours.

6. The method according to claim 1, characterized in that The step of drying the dried ceramic core with attached cobalt oxide comprises: The dried ceramic core with cobalt oxide attached thereto is dried at 100 to 120° C. for 1.5 to 2 hours.

7. The method according to claim 1, characterized in that The dried ceramic core with cobalt oxide attached thereto is dried and sintered, wherein the sintering comprises: The dried ceramic core with attached cobalt oxide is placed in a sintering furnace and sintered at 1200-1250° C. for 3-4 hours to obtain a ceramic core with attached cobalt aluminate.

8. A ceramic core, characterized in that: The ceramic core is prepared by the method described in any one of claims 1 to 7.

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