Silica-based ceramic material, foamed ceramic filter, manufacturing method and use

Abstract

The present invention relates to the field of casting technology, and provides a silica-based ceramic material, a foamed ceramic filter, a manufacturing method and uses thereof. The silica-based ceramic material provided by the present invention includes ceramic powder and auxiliary materials. The ceramic powder contains, by mass fraction, 40-80% silica, 8-30% aluminum oxide, and 8-30% silicon carbide. The auxiliary materials include an adhesive and a dispersant. The foamed ceramic filter manufactured from the silica-based ceramic material of the present invention has silica as the main component, has a wide source of silica, low cost, and the cost of the obtained silica-based foamed ceramic filter is significantly reduced compared to general silicon carbide and zirconia-based foamed ceramic filters in this field. In addition, the silica-based foamed ceramic filter provided by the present invention has excellent heat resistance, the maximum use temperature reaches 1600 °C, and fills the gap of foamed ceramic filters in the range of 1500-1600 °C.

Description

Technical Field

[0001] This application claims the priority of a Chinese patent application filed with the China National Intellectual Property Administration on May 10, 2023, with the application number CN202310517405.1 and the title of the invention "Silica-based Ceramic Material, Foamed Ceramic Filter, Manufacturing Method and Use", the entire content of which is incorporated herein by reference.

[0002] The present invention relates to the field of casting technology, and particularly to a silica-based ceramic material, a foamed ceramic filter, a manufacturing method and uses thereof.

Background Art

[0003] With the rapid development of the casting industry, the requirements for the performance and appearance of castings are becoming increasingly stringent. Non-metallic inclusions in castings are the most important factor causing casting defects, affecting the surface finish, mechanical and machining properties of castings, and leading to an increase in the rejection rate. Therefore, it is necessary to filter the inclusions in the molten metal before filling the mold.

[0004] At present, in the foundry industry, iron castings and steel castings generally filter molten metal using ceramic foam filters. The ceramic foam filter has a three-dimensional network structure, which can effectively remove inclusions in the molten metal, reduce turbulence, enable the molten metal to quickly and stably reach the filling flow rate, and improve the quality of the casting. Currently, the commonly used ceramic foam filters are silicon carbide-based ceramic foam filters or zirconia-based ceramic foam filters. The main raw materials used in these two types of ceramic foam filters are silicon carbide powder or zirconia powder, and the cost is high. Among them, the cost of the zirconia-based ceramic foam filter is higher (about 5 times that of the silicon carbide-based ceramic foam filter). The ceramic foam filter is a disposable consumable, which brings great economic pressure to users. In addition, the maximum operating temperature of the silicon carbide-based ceramic foam filter is 1500 °C, and the maximum operating temperature of the zirconia-based ceramic foam filter is 1700 °C. For some molten metals with a temperature of 1500-1600 °C, only the zirconia-based ceramic foam filter can be used for filtration. Currently, there is no ceramic foam filter in this field that can reach a maximum operating temperature of 1600 °C and has a low cost.

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of this, the present invention provides a silica-based ceramic material, a ceramic foam filter, a manufacturing method and uses thereof. The silica-based ceramic material provided by the present invention has silica as the main component, and the silica-based ceramic foam filter manufactured using it has a low cost, a maximum operating temperature reaching 1600 °C, and is suitable for molten metals with a filtration temperature of 1600 °C or lower.

Means for Solving the Problems

[0006] To achieve the above object of the present invention, the present invention provides the following technical solutions.

[0007] A silica-based ceramic material, comprising ceramic powder and auxiliary materials, The ceramic powder contains, by mass fraction, 40 - 80% silica, 8 - 30% aluminum oxide, and 8 - 30% silicon carbide. The auxiliary materials include an adhesive and a dispersant. The mass of the adhesive is 1 - 5% of the mass of the ceramic powder, and the mass of the dispersant is 0.5 - 1% of the mass of the ceramic powder.

[0008] Preferably, the aluminum oxide is α-aluminum oxide, the mesh number of the aluminum oxide is 200 mesh or more, and the purity is 98% or more. The mesh number of the silica is 1000 mesh or more, and the purity is 95% or more. The mesh number of the silicon carbide is 200 mesh or more, and the purity is 95% or more.

[0009] Preferably, the adhesive includes one or more of silica sol, methyl cellulose, white latex, sodium carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, phenolic resin, and ethyl silicate. The dispersant includes sodium hexametaphosphate and / or sodium tripolyphosphate.

[0010] Preferably, the concentration of the silica sol is 30 - 50 wt%.

[0011] The present invention further provides a silica-based foamed ceramic filter manufactured from the silica-based ceramic material described in the above solution means.

[0012] Preferably, the crystal phase of silica in the silica-based foamed ceramic filter is one or more of β-quartz, α-quartz, γ-tridymite, β-tridymite, α-tridymite, β-cristobalite, α-cristobalite, and quartz glass.

[0013] Preferably, the open porosity of the silica-based foamed ceramic filter is 80 - 83%.

[0014] The present invention further provides a method for manufacturing the silica-based foamed ceramic filter described in the above solution means, comprising the steps of mixing ceramic powder, auxiliary materials and water to obtain a ceramic slurry, immersing a foaming matrix in the ceramic slurry, and then removing the excess slurry adsorbed on the foaming matrix to obtain a foamed impregnated substrate, and sequentially drying and sintering the foamed impregnated substrate to obtain the silica-based foamed ceramic filter as described in the above solution means.

[0015] Preferably, the amount of water used is 15-25% of the mass of the ceramic powder.

[0016] Preferably, the viscosity of the ceramic slurry is 20000-50000 mPa·s.

[0017] Preferably, the foaming matrix is a porous polyurethane foam.

[0018] Preferably, the number of pores of the porous polyurethane foam is 10-20 PPI, and the dimensions of the porous polyurethane foam are (75-100) mm×(75-100) mm×22 mm.

[0019] Preferably, the drying is oven drying or natural drying. The temperature of the oven drying is 100-120°C, the time is 60-90 min, and the time of the natural drying is 6-12 h.

[0020] Preferably, the sintering temperature is 1150-1300°C, and the heat preservation time is 2-4 h. The process of heating up to the sintering temperature is to heat up to the first temperature at the first heating rate, then heat up to the second temperature at the second heating rate, and then heat up to the sintering temperature at the third heating rate. The first heating rate is 70-90 °C / h, the first temperature is 500-550 °C, the second heating rate is 200-250 °C / h, the second temperature is 1000-1100 °C, and the third heating rate is 70-90 °C / h.

[0021] The present invention further provides the use of the silica-based foamed ceramic filter described in the above solution means or in the casting of the silica-based foamed ceramic filter manufactured by the manufacturing method described in the above solution means.

[0022] Preferably, the use temperature of the silica-based foamed ceramic filter is 1600 °C or lower.

[0023] The present invention provides a silica-based ceramic material, which includes ceramic powder and auxiliary materials. The ceramic powder includes, by mass fraction, 40-80% of silica, 8-30% of aluminum oxide, and 8-30% of silicon carbide. The auxiliary materials include an adhesive and a dispersant. The mass of the adhesive is 1-5% of the mass of the ceramic powder, and the mass of the dispersant is 0.5-1% of the mass of the ceramic powder. The silica-based ceramic material provided by the present invention has silica as the main component, a wide raw material supply source, low cost, and good high-temperature resistance.

[0024] The present invention further provides a silica-based foamed ceramic filter manufactured from the silica-based ceramic material described in the above solution means. The silica-based foamed ceramic filter provided by the present invention has silica as the main component, a wide source of silica, low cost, and the price is about 50% of silicon carbide powder. The cost of the obtained foamed ceramic filter is significantly reduced compared to general silicon carbide and zirconia-based foamed ceramic filters in this field. Moreover, the silica-based foamed ceramic filter provided by the present invention has good heat resistance, and the maximum use temperature reaches 1600 °C, filling the gap of foamed ceramic filters in the range of 1500 - 1600 °C. Additionally, the silica-based foamed ceramic filter provided by the present invention has good filtration performance and can effectively filter inclusions in molten metal.

Brief Description of the Drawings

[0025]

Figure 1

Modes for Carrying Out the Invention

[0026] The present invention provides a silica-based ceramic material, which includes ceramic powder and auxiliary materials. The ceramic powder includes, by mass fraction, 40 - 80% silica, 8 - 30% aluminum oxide, and 8 - 30% silicon carbide. The auxiliary materials include an adhesive and a dispersant. The mass of the adhesive is 1 - 5% of the mass of the ceramic powder, and the mass of the dispersant is 0.5 - 1% of the mass of the ceramic powder.

[0027] Unless otherwise specified, all raw materials used in the present invention are commercially available products.

[0028] The silica-based ceramic material provided by the present invention includes ceramic powder and auxiliary materials, which will be described in detail below respectively.

[0029] The ceramic powder contains 40 to 80%, preferably 40 to 75% of silica by mass fraction. In the present invention, the mesh number of the silica is preferably 200 mesh or more (i.e., the particle size of the silica is 74 μm or less), and the purity is preferably 95% or more. In the present invention, there are no special requirements for the silica, and general silica powder in this field may be used. In the present invention, the silica mainly acts as a skeleton and is beneficial for improving the impact resistance of the foamed ceramic filter at high temperatures. In this field, in order to lower the sintering temperature and improve the sintering effect, silica is often added as a sintering aid to the silicon carbide-based foamed ceramic filter, but the addition amount is small. The present invention uses silica as the main raw material to provide a silica-based ceramic material. The foamed ceramic filter manufactured using the ceramic material of the present invention not only has good filtration performance and heat resistance, but also significantly reduces the cost.

[0030] The ceramic powder contains 8 to 30%, preferably 10 to 25% of aluminum oxide by mass fraction. In the present invention, the aluminum oxide is preferably α-aluminum oxide. The mesh number of the aluminum oxide is preferably 1000 mesh or more (i.e., the particle size of the aluminum oxide is 13 μm or less), and the purity is preferably 98% or more. The aluminum oxide acts as a matrix, which is beneficial for improving the sintering strength of the foamed ceramic filter and lowering the firing temperature of the product.

[0031] The ceramic powder contains 8 to 30%, preferably 10 to 20%, more preferably 10 to 15% of silicon carbide by mass fraction. In the present invention, the mesh number of the silicon carbide is preferably 1000 mesh or more (i.e., the particle size of the silicon carbide is 13 μm or less), and the purity is preferably 95% or more. The silicon carbide can improve the thermal conductivity of the foamed ceramic filter, lower the expansion coefficient, and further improve the thermal stability of the product.

[0032] In the present invention, it is preferable that the auxiliary material includes an adhesive and a dispersant. The mass of the adhesive is 1 to 5%, preferably 2 to 4%, of the mass of the ceramic powder. The mass of the dispersant is 0.5 to 1%, preferably 0.6 to 0.8%, of the mass of the ceramic powder.

[0033] In the present invention, it is preferable that the adhesive includes one or more of silica sol, methyl cellulose, white latex, sodium carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, phenol resin, and ethyl silicate. The concentration of the silica sol is preferably 30 to 50 wt%, more preferably 40 wt%. It is preferable that the dispersant includes sodium hexametaphosphate and / or sodium tripolyphosphate.

[0034] The present invention further provides a silica-based foamed ceramic filter manufactured from the silica-based ceramic material described in the above solution means. The crystal phase of silica in the silica-based foamed ceramic filter is preferably one or more of β-quartz, α-quartz, γ-tridymite, β-tridymite, α-tridymite, β-cristobalite, α-cristobalite, and quartz glass. The present invention strictly controls the blending ratio of the ceramic powder and the auxiliary material in the silica-based ceramic material. When silica is used as the main raw material, a foamed ceramic filter with good filtration performance and heat resistance can be obtained, meeting the requirements of molten metal filtration. In the present invention, the total porosity of the silica-based foamed ceramic filter is preferably 78 to 85%, and the open porosity is preferably 80 to 83%.

[0035] The present invention further provides a method for manufacturing the silica-based foamed ceramic filter described in the above solution means, mixing ceramic powder, auxiliary material, and water to obtain a ceramic slurry; immersing a foam matrix in the ceramic slurry, and then removing the excess slurry adsorbed on the foam matrix to obtain a foamed dipped substrate; A method for manufacturing the silica-based foamed ceramic filter according to the above solution means, comprising the step of sequentially drying and sintering the foamed impregnated base material to obtain the silica-based foamed ceramic filter.

[0036] In the present invention, ceramic powder, auxiliary materials and water are mixed to obtain a ceramic slurry. In the present invention, the amount of water used is preferably 15% to 25% of the mass of the ceramic powder, more preferably 18% to 22%. The mixing is preferably carried out using a high-speed mixer. The viscosity of the ceramic slurry is preferably 20,000 to 50,000 mPa·s, more preferably 20,000 to 30,000 mPa·s or 40,000 to 50,000 mPa·s.

[0037] After obtaining the ceramic slurry in the present invention, a foaming matrix is immersed in the ceramic slurry, and then the excess slurry adsorbed on the foaming matrix is removed to obtain a foamed impregnated base material. In the present invention, the foaming matrix is preferably a porous polyurethane foam. The pore density of the porous polyurethane foam is preferably 10 to 20 PPI. The dimensions of the porous polyurethane foam are preferably (75 to 100) mm × (75 to 100) mm × 22 mm. In a specific embodiment of the present invention, in order to obtain a porous polyurethane foam that meets the dimensional requirements, the porous polyurethane foam further includes the steps of charging, slicing and punching before immersion. In the present invention, the temperature of the immersion is preferably room temperature, and the immersion time is preferably 1 to 3 minutes. The present invention has no special requirements for the specific operating conditions of the immersion. The porous polyurethane foam can be put into the ceramic slurry and immersed sufficiently. In the present invention, the method for removing the excess slurry adsorbed on the foaming matrix is preferably extrusion. The extrusion is preferably carried out using a roll press. The gap of the roll press is preferably 2 to 10 mm. The present invention controls the gap of the roll press to extrude about 60% of the slurry immersed in the foaming matrix to obtain a foamed impregnated base material.

[0038] In the present invention, after obtaining a foamed impregnated substrate, the foamed impregnated substrate is sequentially dried and sintered to obtain the silica-based foamed ceramic filter. In the present invention, the drying is preferably oven drying or natural drying. The temperature of the oven drying is preferably 100-120°C, more preferably 105-110°C. The drying time is preferably 60-90 min, more preferably 60-70 min. The natural drying time is preferably 6-12 h, more preferably 8-10 h.

[0039] In the present invention, the sintering temperature is preferably 1150-1300°C, more preferably 1200-1250°C. The heat preservation time of the sintering is preferably 2-4 h, more preferably 2.5-3.5 h. The process of heating up to the sintering temperature preferably includes heating up to a first temperature at a first heating rate, then heating up to a second temperature at a second heating rate, and then heating up to the sintering temperature at a third heating rate. The first heating rate is preferably 70-90°C / h, more preferably 75-85°C / h. The first temperature is preferably 500-550°C, more preferably 500-520°C. The second heating rate is preferably 200-250°C / h, more preferably 230-250°C / h. The second temperature is preferably 1000-1100°C, more preferably 1000-1050°C. The third heating rate is preferably 70-90°C / h, more preferably 75-85°C / h. The present invention preferably heats up in the above method, which is beneficial to uniformly heating the foamed impregnated substrate and improving the sintering effect. During the sintering process, the foamed matrix is decomposed by heat, and a foamed ceramic product, that is, the silica-based foamed ceramic filter of the present invention, remains. After the heat preservation is completed, the obtained product may be taken out after being cooled to 100°C together with the furnace.

[0040] The present invention further provides the use of the silica-based foamed ceramic filter described in the above solution means or the silica-based foamed ceramic filter produced by the production method described in the above solution means in casting. In the present invention, the silica-based foamed ceramic filter is used for filtering molten metal in the casting process, and the use temperature of the silica-based foamed ceramic filter is preferably 1600 °C or lower, more preferably 1500 to 1600 °C.

[0041] Hereinafter, with reference to the embodiments of the present invention, the technical solution means of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative labor belong to the technical scope of the present invention.

[0042] Figure 1 is a process flowchart for manufacturing a silica-based foamed ceramic filter in an embodiment of the present invention. First, a porous polyurethane foam (i.e., a polyurethane sponge) is charged, sliced, punched, and formed. Next, it is immersed in a ceramic slurry, and then dried and fired. After the obtained product passes the inspection, it is packaged and stored in a warehouse.

[0043] Example 1 40 kg of commercially available silica with a purity of 95% and 200 mesh, 30 kg of α-aluminum oxide with a purity of 98% and 1000 mesh, 30 kg of silicon carbide with a purity of 95% and 1000 mesh, 15 kg of pure water, 5 kg of silica sol (concentration 40 wt%) and 1.0 kg of sodium hexametaphosphate were added, and uniformly stirred with a high-speed mixer to form a thixotropic slurry with a viscosity of 40000 mPa·s, that is, a ceramic slurry. A polyurethane foam with 10 PPI, 100×100×22 mm was immersed in the prepared ceramic slurry. After the slurry was sufficiently immersed, about 60% of the slurry was extruded with a roll press to obtain a foamed impregnated substrate. The obtained foamed impregnated substrate was dried at 110 °C for 1 h. Next, the substrate was put into a sintering furnace, heated to 500 °C at a heating rate of 90 °C / h, further heated to 1000 °C at a heating rate of 250 °C / h, then heated to 1150 °C at 90 °C / h and held for 2 h, and cooled to about 100 °C with the furnace and taken out, to obtain a silica-based foamed ceramic filter with a specification of 100×100×22 mm - 10 PPI. After detection, the open porosity of the silica-based foamed ceramic filter was 82%. When filtering molten steel at a temperature of 1527 °C using the silica-based foamed ceramic filter produced in Example 1, inclusions in the molten steel can be effectively filtered, the filtration efficiency reaches 95%, and 800 kg of the filtered molten steel will not be washed away. Even after filtering 800 kg of molten steel using the silica-based foamed ceramic filter produced in Example 1, the filter remains intact, indicating its good impact resistance. When filtering molten steel at a temperature of 1527 °C using a general silicon carbide-based foamed ceramic filter, the silicon carbide-based foamed ceramic filter was already crushed when filtering 500 kg of molten steel, indicating that it is difficult for a general silicon carbide-based foamed ceramic filter to achieve the filtration of molten metal at 1500 °C or higher. The silica-based foamed ceramic filter provided by the present invention not only has a low cost, but also has good high-temperature resistance and impact resistance, and is suitable for filtering molten metal at 1500 - 1600 °C.

[0044] Example 2 75 kg of commercially available silica with a purity of 98% and 325 mesh, 10 kg of α-aluminum oxide with a purity of 99% and 2000 mesh, 15 kg of silicon carbide with a purity of 96% and 3000 mesh, 18 kg of pure water, 3 kg of polyvinyl alcohol and 0.5 kg of sodium tripolyphosphate were added, and uniformly stirred with a high-speed mixer to obtain a thixotropic slurry with a viscosity of 30000 mPa·s, that is, a ceramic slurry. A 20 PPI 75×75×22 mm polyurethane foam was immersed in the prepared ceramic slurry. After sufficient immersion, it was roll-pressed to extrude about 60% of the slurry to obtain a foamed impregnated substrate. The obtained foamed impregnated substrate was naturally dried for 12 h. Then, the substrate was put into a sintering furnace, heated to 500 °C at a heating rate of 90 °C / h, further heated to 1000 °C at a heating rate of 250 °C / h, and then heated to 1250 °C at 90 °C / h and held for 2 h. After cooling to 100 °C together with the furnace and taken out, a silica-based foamed ceramic filter with a specification of 75×75×22 mm - 20 PPI was obtained. After detection, the open porosity of the silica-based foamed ceramic filter was 81%. When the molten steel at a temperature of 1600 °C was filtered using the silica-based foamed ceramic filter produced in Example 2, the inclusions in the molten steel could be effectively filtered, and the filtration efficiency reached 96%. 500 kg of the filtered molten steel was not washed away.

[0045] The above are only the preferred embodiments of the present invention. Those skilled in the art can make some improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be regarded as within the protection scope.

Claims

1. A silica-based ceramic material, comprising ceramic powder and auxiliary materials, wherein the ceramic powder contains, by mass fraction, 40-80% silica, 8-30% aluminum oxide, and 8-30% silicon carbide, the auxiliary materials include an adhesive and a dispersant, the mass of the adhesive is 1-5% of the mass of the ceramic powder, and the mass of the dispersant is 0.5-1% of the mass of the ceramic powder, characterized in that it is a silica-based ceramic material.

2. The aluminum oxide is α-aluminum oxide, the mesh number of the aluminum oxide is 200 mesh or more, and the purity is 98% or more, the mesh number of the silica is 1000 mesh or more, and the purity is 95% or more, the mesh number of the silicon carbide is 200 mesh or more, and the purity is 95% or more, characterized in that it is the silica-based ceramic material according to Claim 1.

3. The adhesive includes one or more of silica sol, methyl cellulose, white latex, sodium carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, phenolic resin, and ethyl silicate, and the dispersant includes sodium hexametaphosphate and / or sodium tripolyphosphate, characterized in that it is the silica-based ceramic material according to Claim 1.

4. The concentration of the silica sol is 30-50 wt%, characterized in that it is the silica-based ceramic material according to Claim 3.

5. A silica-based foamed ceramic filter, characterized in that it is manufactured from the silica-based ceramic material according to any one of Claims 1 to 4.

6. The crystal phase of silica in the silica-based foamed ceramic filter is one or more of β-quartz, α-quartz, γ-tridymite, β-tridymite, α-tridymite, β-cristobalite, α-cristobalite, and quartz glass, characterized in that it is the silica-based foamed ceramic filter according to Claim 5.

7. The open porosity of the silica-based foamed ceramic filter is 80-83%, characterized in that it is the silica-based foamed ceramic filter according to Claim 5.

8. Mixing ceramic powder, auxiliary materials and water to obtain a ceramic slurry; Soaking the foamed matrix in the ceramic slurry, and then removing the excess slurry adsorbed on the foamed matrix to obtain a foamed soaked substrate; Sequential drying and sintering of the foamed soaked substrate to obtain the silica-based foamed ceramic filter, characterized by including the steps of any one of claims 5 to 7. The manufacturing method of the silica-based foamed ceramic filter according to any one of claims 5 to 7.

9. The amount of water used is 15 to 25% of the mass of the ceramic powder, characterized by the manufacturing method according to claim 8.

10. The viscosity of the ceramic slurry is 20,000 to 50,000 mPa·s, characterized by the manufacturing method according to claim 8.

11. The foamed matrix is a porous polyurethane foam, characterized by the manufacturing method according to claim 8.

12. The pore number of the porous polyurethane foam is 10 to 20 PPI, and the dimensions of the porous polyurethane foam are (75 to 100) mm × (75 to 100) mm × 22 mm, characterized by the manufacturing method according to claim 8.

13. The drying is oven drying or natural drying. The temperature of the oven drying is 100 to 120 °C, the time is 60 to 90 min, and the time of the natural drying is 6 to 12 h, characterized by the manufacturing method according to claim 8.

14. The sintering temperature is 1150 to 1300 °C, and the heat preservation time is 2 to 4 h. The process of heating up to the sintering temperature is to heat up to the first temperature at the first heating rate, then heat up to the second temperature at the second heating rate, and then heat up to the sintering temperature at the third heating rate. The first heating rate is 70 to 90 °C / h, the first temperature is 500 to 550 °C, the second heating rate is 200 to 250 °C / h, the second temperature is 1000 to 1100 °C, and the third heating rate is 70 to 90 °C / h, characterized by the manufacturing method according to claim 8.

15. Use in the casting of the silica-based foamed ceramic filter according to any one of claims 5 to 7 or the silica-based foamed ceramic filter manufactured by the manufacturing method according to any one of claims 8 to 14.

16. The use temperature of the silica-based foamed ceramic filter is 1600 °C or lower, characterized by the use according to claim 15.

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