Pressing type ceramic core and preparation method thereof

Abstract

The invention relates to the field of precision casting, in particular to a pressing type ceramic core and a preparation method thereof. Comprising the following raw materials in parts by weight: 20-40 parts of zirconium silicate of 110-130 meshes, 50-70 parts of zirconium silicate of 300-350 meshes, 10-20 parts of zirconium silicate of 1000 meshes, 1-3 parts of calcium oxide, 0.5-2 parts of fibers, 3-6 parts of a composite organic additive, 4-8 parts of an inorganic binder and 1-5 parts of water. The composite organic additive comprises cellulose, a lubricant, a defoaming agent, a tackifier and a release agent; and the normal-temperature strength of the pressed ceramic core is not less than 8MPa, so that the problem that the surface quality of a casting is influenced due to high addition amount of an organic adhesive in an existing thermosetting forming pressing process is solved.

Description

Technical Field

[0001] This invention relates to the field of precision casting, and in particular to a pressed ceramic core and its preparation method. Background Technology

[0002] Ceramic cores are mainly used for forming complex cavities in precision casting. Currently, ceramic cores are generally prepared using a wax injection process, requiring debinding before high-temperature sintering. This results in long production cycles and high manufacturing costs. To improve production efficiency and core removal performance, thermosetting molding is currently used. This process eliminates the need for sintering and is easy to clean after casting, but surface quality is limited. In thermosetting molding, adhesives are needed to ensure the ceramic core's formation. To achieve sufficient room-temperature strength, a high content of adhesive is required. For example, patent document CN106977133B discloses a ceramic core, its preparation method, and its application. This invention uses an aqueous organic adhesive at a weight percentage of 5-15%. In subsequent applications, high-temperature molten metal exceeding 1000°C is required. At this temperature, the organic adhesive decomposes, generating a large amount of gas, which can easily form pores inside the metal casting, causing adverse effects and impacting the surface quality of the casting. Summary of the Invention

[0003] To address the aforementioned shortcomings, the present invention aims to propose a pressed ceramic core and its preparation method, thereby solving the problem that the excessive addition of organic adhesives in existing thermosetting pressing processes affects the surface quality of castings.

[0004] To achieve this objective, the present invention adopts the following technical solution: A pressed ceramic core, by weight, comprises the following raw materials: 20-40 parts of 110-130 mesh zirconium silicate, 50-70 parts of 300-350 mesh zirconium silicate, 10-20 parts of 1000 mesh zirconium silicate, 1-3 parts of calcium oxide, 0.5-2 parts of fiber, 3-6 parts of composite organic additives, 4-8 parts of inorganic binder, and 1-5 parts of water; The composite organic additive includes cellulose, lubricant, defoamer, thickener and release agent; The room temperature strength of the pressed ceramic core is not less than 8 MPa.

[0005] Preferably, the raw materials, calculated by weight, include the following: 20-40 parts of 120-mesh zirconium silicate, 50-70 parts of 325-mesh zirconium silicate, 10-20 parts of 1000-mesh zirconium silicate, 1-3 parts of calcium oxide, 0.5-2 parts of fiber, 3-5 parts of composite organic additives, 4-8 parts of inorganic binder, and 1-5 parts of water.

[0006] Preferably, the inorganic binder is silica sol.

[0007] Preferably, the fiber is a zirconium-containing refractory fiber.

[0008] A method for preparing a pressed ceramic core, used to prepare a pressed ceramic core as described in any one of the above claims, includes the following steps: S1. Weigh the required zirconium silicate, calcium oxide and fiber, add them to the mixer and mix them to obtain premixed ceramic powder; S2. Add the premixed ceramic powder to the kneader, add the composite organic additive, inorganic binder and water and stir and knead to obtain the kneaded mixture; S3. According to the mold requirements, add the corresponding weight of kneaded plastic mixture into the press cylinder, apply pressure to form, and obtain the core blank. S4. Keep the core blank warm and dry, and grind off the flash to obtain the pressed ceramic core.

[0009] Preferably, in step S3, the applied pressure is greater than 1.5 tons / cm². 3 .

[0010] Preferably, in step S4, the temperature for heat preservation and drying is 130-160℃, and the heat preservation time is 4 hours.

[0011] Preferably, in step S2, the mixing and kneading is performed in multiple kneading processes, with each kneading process lasting no less than 10 minutes.

[0012] The technical solution provided by this invention may include the following beneficial effects: This method uses 110-130 mesh zirconium silicate, 300-350 mesh zirconium silicate, and 1000 mesh zirconium silicate for particle size distribution, and uses a small amount of composite organic additives and inorganic binders. This reduces the gas generation of the ceramic core when casting high-temperature molten metal, ensures the surface quality of the casting, and obtains a pressed ceramic core with a room temperature strength of not less than 8MPa. The core is also easy to disintegrate and clean, meeting the requirements of precision casting. Detailed Implementation

[0013] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0014] To facilitate understanding of the present invention, a more complete description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0015] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0016] A pressed ceramic core, by weight, comprises the following raw materials: 20-40 parts of 110-130 mesh zirconium silicate, 50-70 parts of 300-350 mesh zirconium silicate, 10-20 parts of 1000 mesh zirconium silicate, 1-3 parts of calcium oxide, 0.5-2 parts of fiber, 3-6 parts of composite organic additives, 4-8 parts of inorganic binder, and 1-5 parts of water; The composite organic additive includes cellulose, lubricant, defoamer, thickener and release agent; The room temperature strength of the pressed ceramic core is not less than 8 MPa.

[0017] To address the problems existing in the prior art, this invention proposes a pressed ceramic core, comprising zirconium silicate, calcium oxide, fibers, composite organic additives, inorganic binders, and water. Zirconium silicate serves as the skeletal substrate of the pressed ceramic core. With a melting point exceeding 2500℃, zirconium silicate can withstand the scouring and erosion of high-temperature molten metal during casting, avoiding the thermal shock resistance issues or insufficient refractoriness of other refractory materials that may adhere to the molten metal, thus affecting the quality of precision casting products. The fibers form a three-dimensional interwoven network, increasing the core's strength. Furthermore, the composite organic additives and inorganic binders respectively provide the room-temperature strength and high-temperature strength of the pressed ceramic core, reducing the core breakage rate during preparation and improving its high-temperature strength during casting, thus meeting the requirements for the use of pressed ceramic cores.

[0018] Meanwhile, based on mass fractions, 3-6 parts of the composite organic additive effectively reduce gas generation during subsequent high-temperature molten metal casting, ensuring the surface quality of the metal casting. The selection of the composite organic additive is mainly based on the aforementioned zirconium silicate particle size distribution. The lubricant provides the necessary flow properties for molding, while cellulose primarily affects the room-temperature strength of the molded ceramic core. 4-8 parts of the inorganic binder mainly provide the high-temperature strength of the ceramic core, ensuring sufficient high-temperature strength when the ceramic core contacts the molten metal. However, ceramic cores are used to form complex cavities in precision castings, and they need to be disassembled and cleaned later. If too much inorganic binder is used, it will affect the collapsibility of the ceramic core during subsequent use. Therefore, 4-8 parts of inorganic binder are used, and zirconium silicate is particle size-graded. 20-40 parts of 110-130 mesh zirconium silicate, 50-70 parts of 300-350 mesh zirconium silicate, and 10-20 parts of 1000 mesh zirconium silicate are selected. The appropriate proportions of coarse, medium, and fine particles are used to form a good bulk density, thereby effectively reducing the use of composite organic additives. While reducing gas generation and obtaining better casting surface quality, it ensures that the room temperature strength of the pressed ceramic core is not less than 8 MPa, meeting the room temperature strength required for handling and casting. The use of 1000 mesh zirconium silicate powder increases the strength of the pressed ceramic core, avoids excessive cross-linking of the inorganic binder, and meets the requirements for collapsibility. The pressed ceramic core of this invention uses composite organic additives and inorganic binders to replace organic adhesives, and combines zirconium silicate for particle size distribution, which can achieve a room temperature strength of not less than 8MPa, effectively reducing gas generation during the casting process, ensuring casting quality, and having good collapsibility.

[0019] Specifically, in this composite organic additive, cellulose can improve adhesion, lubricant can reduce the interfacial tension between zirconium silicate particles, thickener can adjust the viscosity of the wet mixture formed by the mixing of various components, ensuring that the wet mixture can fill the complex cavity evenly, while defoamer can eliminate air bubbles, avoid the formation of pores inside the core, and ensure the quality of subsequent castings, and release agent ensures that the ceramic core can be completely removed from the mold after pressing. All components of this composite organic additive are organic compounds, which will also produce gas at high temperatures. However, because the amount of composite organic additive added is small, and with the particle size distribution of zirconium silicate and the use of inorganic binders, it can reduce gas generation while ensuring that the pressed ceramic core has high strength to meet the casting requirements.

[0020] Preferably, the composite organic additive can be selected as a functional low-gas-emission type to further reduce the gas generated by high-temperature decomposition during casting.

[0021] Preferably, the raw materials, calculated by weight, include the following: 20-40 parts of 120-mesh zirconium silicate, 50-70 parts of 325-mesh zirconium silicate, 10-20 parts of 1000-mesh zirconium silicate, 1-3 parts of calcium oxide, 0.5-2 parts of fiber, 3-5 parts of composite organic additives, 4-8 parts of inorganic binder, and 1-5 parts of water.

[0022] Specifically, by further limiting the mesh size of zirconium silicate, the particle packing density can be further improved under this optimized particle size distribution, ensuring that the room temperature strength of the resulting pressed ceramic core is not less than 8 MPa, and the mesh size matching can be controlled more precisely, reducing the fluctuation range between production batches.

[0023] Preferably, the inorganic binder is silica sol.

[0024] Specifically, water-based silica sol, as a high-temperature binder, can adjust the plasticity of the pressed mixture and improve the stamping performance, so that the ceramic core obtained after pressing has a good surface finish. The moisture contained in it is completely removed during drying in step S4. Subsequently, under the action of high temperature during casting, the nano-silica particles can combine with zirconium silicate to improve the high-temperature strength of the ceramic core and meet the surface quality requirements of precision castings.

[0025] Preferably, the fiber is a zirconium-containing refractory fiber.

[0026] Specifically, the fiber is a zirconium-containing refractory fiber, which enhances the strength of the ceramic core to meet the refractoriness requirements under high-temperature molten metal casting conditions.

[0027] A method for preparing a pressed ceramic core, used to prepare a pressed ceramic core as described in any one of the above claims, includes the following steps: S1. Weigh the required zirconium silicate, calcium oxide and fiber, add them to the mixer and mix them to obtain premixed ceramic powder; S2. Add the premixed ceramic powder to the kneader, add the composite organic additive, inorganic binder and water and stir and knead to obtain the kneaded mixture; S3. According to the mold requirements, add the corresponding weight of kneaded plastic mixture into the press cylinder, apply pressure to form, and obtain the core blank. S4. Keep the core blank warm and dry, and grind off the flash to obtain the pressed ceramic core.

[0028] Zirconium silicate of different mesh sizes in corresponding mass fractions, calcium oxide and fiber are mixed and stirred to obtain a relatively uniform premixed ceramic powder. Composite organic additives and inorganic binders are added to knead the premixed ceramic powder, which binds different particles together to meet the molding requirements. The water added in step S2 is used to adjust the dryness of the kneaded mixture.

[0029] According to the mold requirements, the required weight of kneaded mixture is added to the press cylinder, and pressure is applied to make the kneaded mixture fill the mold completely, resulting in a core blank with the required shape. The core blank is then kept warm and dried to obtain the corresponding pressed ceramic core, and the room temperature strength of the ceramic core is not less than 8MPa.

[0030] Preferably, in step S3, the applied pressure is greater than 1.5 tons / cm². 3 .

[0031] Specifically, under this applied pressure, it is possible to ensure that zirconium silicate particles of different sizes can achieve the required packing density, which, in combination with composite organic additives and inorganic binders, improves the strength of the core blank, which is beneficial to the progress of step S4, while ensuring the improvement of the room temperature strength requirements of the pressed ceramic core.

[0032] Preferably, in step S4, the temperature for heat preservation and drying is 130-160℃, and the heat preservation time is 4 hours.

[0033] Specifically, at this drying temperature, it is ensured that the moisture in the core blank is completely removed, while the cellulose is fully cured to obtain the required room temperature strength of the ceramic core.

[0034] Preferably, in step S2, the mixing and kneading is performed in multiple kneading processes, with each kneading process lasting no less than 10 minutes.

[0035] Specifically, multiple kneading processes ensure that the composite organic additives and inorganic binders of the liquid components can completely coat the premixed ceramic powder, resulting in a uniform distribution of each component in the kneaded mixture, forming a stable plastic body, and ensuring the integrity of the mold filling.

[0036] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0037] Example group Example 1 Calculated by weight parts: S1. Weigh 20 parts of 120-mesh zirconium silicate, 60 parts of 325-mesh zirconium silicate, 20 parts of 1000-mesh zirconium silicate, 3 parts of calcium oxide and 0.5 parts of zirconium-containing refractory fiber, add them to a mixer and mix for 1 hour to obtain premixed ceramic powder. S2. Add the premixed ceramic powder to the kneader, add 3 parts of composite organic additive, 5 parts of silica sol and 5 parts of water and stir and knead to obtain the kneaded mixture. The composite organic additive includes cellulose, lubricant, defoamer, thickener and release agent; S3. According to the mold requirements, add the appropriate weight of kneaded mixture into the press cylinder, applying a pressure greater than 1.5 tons / cm². 3 The pressure is used to form the core blank; S4. Dry the core blank at 150℃ for 4 hours, and grind off the flash to obtain a pressed ceramic core. The room temperature strength of the pressed ceramic core is 9MPa. Cast molten steel to form a casting, and use vibration shot blasting to physically clean the core. The surface of the casting is smooth with no obvious defects and no residual core debris.

[0038] Example 2 Calculated by weight parts: S1. Weigh 35 parts of 120-mesh zirconium silicate, 50 parts of 325-mesh zirconium silicate, 16 parts of 1000-mesh zirconium silicate, 2 parts of calcium oxide and 1.2 parts of zirconium-containing refractory fiber, add them to a mixer and mix for 1 hour to obtain premixed ceramic powder. S2. Add the premixed ceramic powder to the kneader, add 4 parts of composite organic additive, 7 parts of silica sol and 3 parts of water and stir and knead to obtain the kneaded mixture. The composite organic additive includes cellulose, lubricant, defoamer, thickener and release agent; S3. According to the mold requirements, add the appropriate weight of kneaded mixture into the press cylinder, applying a pressure greater than 1.5 tons / cm². 3 The pressure is used to form the core blank; S4. Dry the core blank at 150℃ for 4 hours, and grind off the flash to obtain a pressed ceramic core. The room temperature strength of the pressed ceramic core is 8.6MPa. Cast molten steel to form a casting, and use vibratory shot blasting to physically clean the core. The surface of the casting is smooth with no obvious defects and no residual core debris.

[0039] Example 3 Calculated by weight parts: S1. Weigh 40 parts of 120-mesh zirconium silicate, 70 parts of 325-mesh zirconium silicate, 10 parts of 1000-mesh zirconium silicate, 1 part of calcium oxide and 2 parts of zirconium-containing refractory fiber, add them to a mixer and mix for 1 hour to obtain premixed ceramic powder. S2. Add the premixed ceramic powder to the kneader, add 5 parts of composite organic additive, 8 parts of silica sol and 1 part of water and stir and knead to obtain the kneaded mixture. The composite organic additive includes cellulose, lubricant, defoamer, thickener and release agent; S3. According to the mold requirements, add the appropriate weight of kneaded mixture into the press cylinder, applying a pressure greater than 1.5 tons / cm². 3 The pressure is used to form the core blank; S4. Dry the core blank at 150℃ for 4 hours, and grind off the flash to obtain a pressed ceramic core. The room temperature strength of the pressed ceramic core is 8MPa. Cast molten steel to form a casting, and use vibration shot blasting to physically clean the core. The surface of the casting is smooth with no obvious defects and no residual core debris.

[0040] Comparative Example 1 Compared with Example 1, the difference in Comparative Example 1 is that, according to the mass fraction, the added zirconium silicate is 100 parts of 325-mesh zirconium silicate. The other raw materials and preparation methods are the same as in Example 1. A pressed ceramic core is obtained, which has a room temperature strength of 5 MPa. Molten steel is poured to form a casting, and the core is physically cleaned by vibration shot blasting. The inner cavity of the casting has obvious flash, and the core is locally damaged during wax injection. No core debris remains after the casting is cleaned.

[0041] Comparative Example 2 Compared with Example 1, the difference in Comparative Example 2 is that, according to the mass fractions, there are 50 parts of 120-mesh zirconium silicate, 50 parts of 325-mesh zirconium silicate, and 10 parts of 1000-mesh zirconium silicate. The remaining raw materials and preparation methods are the same as in Example 1. A pressed ceramic core is obtained, which has a room temperature strength of 6 MPa. Molten steel is poured to form a casting, and the core is physically cleaned by vibration shot blasting. The casting has local damage but no residual core debris.

[0042] Comparative Example 3 Compared with Example 1, the difference in Comparative Example 3 is that, according to the mass fraction, the added silica sol is 12 parts, while the remaining raw materials and preparation methods are the same as in Example 1, resulting in a pressed ceramic core with a room temperature strength of 10 MPa. Molten steel is poured to form a casting, and the core is physically cleaned by vibration shot blasting. The surface of the casting is smooth and without obvious defects. The pressed ceramic core has low collapsibility, and under the same cleaning operation as in Example 1, hard core blocks remain in the inner cavity of the casting.

[0043] Comparative Example 4 Compared with Example 1, the difference in Comparative Example 4 is that, according to the mass fraction, the added composite organic additive is 10 parts, while the other raw materials and preparation methods are the same as in Example 1. A pressed ceramic core is obtained, which has a room temperature strength of 9 MPa. Molten steel is poured to form a casting, and the core is physically cleaned by vibration shot blasting. A large number of pores appear on the surface of the casting, and the surface quality of the casting is poor.

[0044] It is evident that the pressed ceramic cores obtained in the example group all possess good room temperature strength, all not less than 8 MPa, meeting the requirements for daily handling and other tasks, and are not easily damaged. At the same time, through particle size distribution and the use of a small amount of composite organic additives, the formation of the casting can be ensured during high-temperature molten metal casting, preventing local defects in the casting due to insufficient strength, and ensuring the surface quality of the resulting castings. The addition of calcium oxide adjusts the collapsibility of the ceramic core. Among them, Example 1 has a higher proportion of fine powder, resulting in better surface quality and higher strength, while Example 3 has more coarse powder, resulting in lower strength, but the best collapsibility.

[0045] Compared with Example 1, Comparative Examples 1 and 2 did not perform particle size distribution on zirconium silicate. They used only single-mesh particles or the amount of zirconium silicate with different mesh sizes was not within the limits of this scheme, and thus could not achieve the required bulk density, thereby affecting the room temperature strength and consequently affecting the surface quality of the subsequent castings.

[0046] Compared with Example 1, Comparative Example 3 used too much silica sol. Although it can obtain a high room temperature strength pressed ceramic core, the excessive use of silica sol makes the structure of the cured ceramic core too dense. Under the same cleaning operation, hard core blocks will remain, requiring more time for mechanical cleaning, and the collapse resistance is poor.

[0047] Compared with Example 1, Comparative Example 4 used a higher content of composite organic additives, which decomposed at high temperature during the casting process and generated gas, affecting the surface quality of the casting.

[0048] In summary, this invention eliminates the need for prolonged sintering, shortens the production cycle, and yields a pressed ceramic core. Furthermore, the resulting pressed ceramic core exhibits a room temperature strength of no less than 8 MPa, meeting the requirements for daily transportation and high-temperature casting. Simultaneously, it effectively reduces gas generation, ensuring the quality of the formed casting meets the necessary specifications, and possesses good collapsibility, which is beneficial for production.

[0049] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A pressed ceramic core, characterized in that, The raw materials, calculated by weight, include the following: 20-40 parts of 110-130 mesh zirconium silicate, 50-70 parts of 300-350 mesh zirconium silicate, 10-20 parts of 1000 mesh zirconium silicate, 1-3 parts of calcium oxide, 0.5-2 parts of fiber, 3-6 parts of composite organic additives, 4-8 parts of inorganic binder, and 1-5 parts of water. The composite organic additive includes cellulose, lubricant, defoamer, thickener and release agent; The room temperature strength of the pressed ceramic core is not less than 8 MPa.

2. The pressed ceramic core according to claim 1, characterized in that, The raw materials, calculated by weight, include the following: 20-40 parts of 120-mesh zirconium silicate, 50-70 parts of 325-mesh zirconium silicate, 10-20 parts of 1000-mesh zirconium silicate, 1-3 parts of calcium oxide, 0.5-2 parts of fiber, 3-5 parts of composite organic additives, 4-8 parts of inorganic binder, and 1-5 parts of water.

3. A pressed ceramic core according to any one of claims 1-2, characterized in that: The inorganic binder is silica sol.

4. A pressed ceramic core according to any one of claims 1-2, characterized in that: The fiber is a zirconium-containing refractory fiber.

5. A method for preparing a pressed ceramic core, characterized in that, The method for preparing a pressed ceramic core according to any one of claims 1-5 includes the following steps: S1. Weigh the required zirconium silicate, calcium oxide and fiber, add them to the mixer and mix them to obtain premixed ceramic powder; S2. Add the premixed ceramic powder to the kneader, add the composite organic additive, inorganic binder and water and stir and knead to obtain the kneaded mixture; S3. According to the mold requirements, add the corresponding weight of kneaded plastic mixture into the press cylinder, apply pressure to form, and obtain the core blank. S4. Keep the core blank warm and dry, and grind off the flash to obtain the pressed ceramic core.

6. The method for preparing a pressed ceramic core according to claim 5, characterized in that: In step S3, the applied pressure is greater than 1.5 tons / cm². 3 .

7. The method for preparing a pressed ceramic core according to claim 5, characterized in that: In step S4, the temperature for heat preservation and drying is 130-160℃, and the heat preservation time is 4 hours.

8. The method for preparing a pressed ceramic core according to claim 5, characterized in that: In step S2, the mixing and kneading is done in multiple kneading sessions, with each kneading session lasting no less than 10 minutes.