Soluble ceramic core using low-grade ball clay in-situ growing mullite whiskers

Abstract

The application discloses a soluble ceramic core for growing mullite whiskers in situ from low-grade ball clay, and raw materials of the soluble ceramic core include low-grade ball clay, sodium chloride and water.The method is as follows: the low-grade ball clay is dried, sieved, mixed with sodium chloride, sprayed and granulated with water, pressed into a mold, moved into a muffle furnace, heated to 300 DEG C at a rate of 5 DEG C / min, kept for 0.5 h, sintered from 300 DEG C to 725-775 DEG C at a rate of 3 DEG C / min for 1.0 h, then cooled to 100 DEG C and taken out, so as to obtain a soluble ceramic core for growing mullite whiskers in situ.The application has the advantages that the core is made by a pressing and sintering process, the process is simple, mullite whiskers are grown in situ in the ceramic core during the sintering process, the soluble ceramic core is reinforced and toughened, sodium chloride is used as a binder, there is no pollution, and the comprehensive performance is excellent.The bending strength of the soluble ceramic core is 7-15 MPa, the tensile strength is 2-6 MPa, the soluble ceramic core can be scattered at a water temperature of 90 DEG C, and the application provides a new technology for ceramic casting development.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic cores, in particular to a soluble ceramic core for ceramic casting. Background Art

[0002] With the development of the automotive industry, the demand for castings with complex internal cavities has gradually increased. Traditional organic resin sand cores have problems such as low strength, high gas emission, high environmental pollution, and poor collapsibility. The mold walls required for precision casting are very thin. During the molten metal casting process, due to their low strength, existing resin sand cores are difficult to withstand the erosion and corrosion of the molten metal, resulting in defects such as cracks and pores, which affect the quality of the casting. Currently, there are soluble or easily collapsible ceramic cores with advantages such as high temperature resistance and corrosion resistance. The internal fibrous structure makes the collapsed core easy to clean and can be used for casting molds with complex internal cavities. However, there is a relative lack of technology. The ceramic cores obtained by existing technologies generally have disadvantages such as high brittleness, low toughness, and easy fracture.

[0003] Fiber-reinforced ceramic matrix composites (CMCs) are materials in which fibers are added to a ceramic matrix to increase strength and toughness. They have been widely used in aerospace, transportation, and defense industries. The fibers used in fiber-reinforced ceramic matrix composites can be divided into continuous fibers, chopped fibers, and whiskers. There are two main methods for whisker-toughening ceramic composites: external whisker addition and in-situ whisker growth. The in-situ whisker growth method involves mixing ceramic powder with a whisker growth promoter and, under certain conditions, simultaneously producing a ceramic core containing whiskers. This patented method uses low-grade ball clay as a refractory material and sodium chloride as a growth promoter, then sintering to produce a ceramic composite containing mullite whiskers. Ball clay primarily consists of kaolinite and quartz. High-grade ball clay is characterized by a kaolin content exceeding 80% and a tailings content below 20%. High-grade ball clay is a high-quality refractory material. This type of ball clay offers advantages such as fine particle size, strong plasticity, excellent bonding properties, high dry strength, a wide firing range, high refractoriness, and resistance to corrosion by molten metals. It can be used as a ceramic raw material, but as a ceramic core, it is difficult to disintegrate after firing. Low-grade ball clay contains over 20% quartz, sometimes even as much as 40%. Low-grade ball clay often contains feldspar and other clay minerals, with a kaolinite content of less than 80%. Therefore, it cannot be used directly as a refractory raw material. However, as a ceramic core raw material, it offers good disintegration properties. Currently, low-grade ball clay is considered a "solid waste" from ball clay mining and is typically backfilled and digested. The tailings of low-grade ball clay are very fine (2-30μm) and have a varying particle size. As a ceramic core raw material, they not only facilitate sintering but also significantly enhance disintegration properties. Because low-grade ball clay contains a certain amount of kaolin, which provides a smooth surface for metal casting, low-grade ball clay is an excellent raw material for ceramic casting.

[0004] Patent CN109574636A discloses a water-soluble ceramic core for investment casting of aluminum alloys and its preparation method. The core's base material is corundum powder, and the mineralizers are quartz powder, sodium chloride, and potassium chloride. The corundum powder accounts for 40-50%, the mineralizer 50-60%, and the plasticizers used are paraffin wax, beeswax, etc. This method involves pressing the plasticizer and pure corundum powder, followed by roasting, dewaxing, and final firing. However, this technique uses pure corundum powder, which is costly and produces a poor surface finish on the casting. Patent document CN114850412A discloses a hot-die casting water-soluble ceramic core for light alloy investment casting. It also uses raw materials such as fused corundum powder, potassium sulfate, plasticizer, lubricant, and surfactant in a weight ratio of 60-80:7.7-30:10-15:1-2:1-2. The ingredients include paraffin wax, beeswax, polyethylene, stearic acid, and oleic acid in a weight ratio of 90-95:2-4:2-4:1-2:1-2. Both patents use plasticizers such as paraffin wax or beeswax to improve the plasticity of the raw embryo. During the dewaxing and sintering process, the decomposition of organic matter inevitably pollutes the environment, and wax-based plasticization leads to stress concentration. During the degreasing process, the raw embryo is prone to defects such as collapse and deformation, as well as other weaknesses such as deformation. This patent uses low-grade ball clay as raw material, and takes advantage of its strong plasticity to press green bodies with higher strength without adding additional plasticizers. Therefore, this patent is different from the above patents in properties such as raw material source, plastic processing method, and green body reinforcement mechanism.

[0005] Patent CN102786295A discloses a method for preparing a soluble ceramic core, which uses fused alumina, zircon sand and sodium chloride particles as the main body, sodium chloride solution and polyethylene glycol as the binder, mixes and dries at low temperature, and obtains a water-soluble core ceramic core by high-temperature baking at 920°C. Patent CN105693254A discloses a water-soluble ceramic core material, which uses high-temperature resistant ceramic as the raw material, adds water-soluble inorganic salt and metal oxide, and adds at least one amorphous ceramic material. The mass fraction of water-soluble inorganic salt is 10%-50%, the mass fraction of water-soluble metal oxide is 2%-50%, the mass fraction of amorphous ceramic material is 0.1%-30%, and the balance is high-temperature resistant ceramic material. The green body is pre-fired at 800-1000°C for 2-5h, the water-soluble metal oxide is pre-fired at 800-1000°C for 1-5h, and the amorphous ceramic material is pre-fired at 500-800°C for 2-5h. After the final firing of the mixed material, the ceramic core is formed. One of the weaknesses of the above two patents is high energy consumption because the raw materials need to be pre-fired and the mixed material needs to be fired again. In addition, the above method does not consider the source of raw materials and the comprehensive utilization of "solid waste" resources, and the practical application is limited. This patent directly uses low-grade ball clay as raw material and sintered at a lower temperature, and the raw material does not need to be pre-fired, which can effectively utilize low-grade ball clay and promote resource utilization.

[0006] Patent document CN106927798A discloses a water-soluble ceramic core and its preparation method. The raw materials are composed of 100-120 parts of fused corundum and 20-40 parts of inorganic salts (20-30 parts of sodium chloride, 5-75 parts of sodium carbonate, and 5-75 parts of potassium carbonate). The core is obtained by ball milling, pressing, and sintering at 720-750°C for 1-1.5 hours. Patent document CN110240471A discloses a water-soluble ceramic core and its preparation method. The raw materials are composed of 85-120 parts of quartz glass powder and 22-45 parts of a water-soluble inorganic salt, wherein the water-soluble inorganic salt is one or a combination of sodium carbonate and potassium carbonate. The raw materials are ground and mixed in proportion, then pressed into shape and demolded. The embryonic body is then calcined at 650-900°C for 0.5-1.5 hours to produce the water-soluble ceramic core. Both of the above patents do not incorporate plastic refractory clay, the plasticity of the green body is poor, and the surface of the finished product is rough, which is not conducive to precision casting. Patent document CN117383916A discloses a soluble ceramic core, preparation method and application. The method comprises uniformly mixing ceramic powder and soluble salt, and using a droplet jet bonding molding process to print out a ceramic core blank. After curing, infiltration and drying, a ceramic core blank is obtained. The ceramic blank is placed in a high-temperature sintering furnace for sintering, and the soluble ceramic core is obtained after cooling in the furnace. Patent document CN105777114A discloses a preparation method for a soluble ceramic core. The water-soluble ceramic core comprises the following ingredients in a mass ratio: 20%-60% sodium chloride powder and 40%-80% zircon powder, wherein the total mass fraction of sodium chloride powder and zircon powder is 100%, and the total weight fraction of ethyl silicate and plasticizer is 0.5%-1%, and the plasticizer is 15%-20%, wherein the plasticizer is 50% polyethylene glycol, 30% baking soda and 10% talc. The two aforementioned patents utilize press molding, dewaxing, or sintering to remove organic precursors. The high chemical content of these materials creates the dual challenges of high costs and environmental pollution. Patent CN107042309B discloses a water-soluble core component and its preparation method. The water-soluble ceramic core comprises 40-80% chloride salt, 10-30% carbonate, and 5-30% ceramic powder. The ceramic powder is one or a combination of alumina, zirconium oxide, and silica powder, and the carbonate is one or a combination of potassium carbonate and sodium carbonate. The ceramic core is produced by injection molding at a molding temperature of 155-180°C. After degreasing, the core is sintered at 450-550°C to obtain the water-soluble ceramic core. Patent CN107262661A discloses a high-temperature-resistant, high-strength water-soluble core and its preparation method. The water-soluble core comprises 75-95% water-soluble salt, 5-25% ceramic material, and 0-5% additives by weight.The water-soluble salts include any one or more of potassium sulfate, sodium sulfate, and magnesium sulfate; the ceramic materials include any one or more of aluminum nitride, titanium nitride, tantalum nitride, boron nitride, aluminum boron nitride, and silicon nitride; and the additives include any one or more of polyvinyl alcohol, polyvinyl pyrrolidone, and water glass. Therefore, the aforementioned patents still use aluminum-based or other transition metal refractory powders as the base material, which has poor plasticity, difficulty in molding, and a rough surface, making it unsuitable for precision casting. Furthermore, the decomposition of sulfates and other salts can form acid mist, causing pollution. A dissertation (Effect of Refractory Aggregate-Based Binders on the Performance of Water-Soluble Ceramic Cores, Lebao, 2022) used fused corundum powder and mullite powder as refractory aggregates and sodium chloride as a binder. The cores were prepared by press molding and the performance of the cores was studied at sintering temperatures of 775°C, 800°C, and 825°C. It was found that when the sodium chloride content was 20 wt.%, the core strength was higher at 800°C and 825°C. However, the ceramic cores produced by this method have defects such as high brittleness and easy cracking, poor impact resistance, and lack of fiber toughening measures. Therefore, the plasticity of the raw materials and finished products cannot meet the requirements of precision casting. This patent uses low-grade ball clay as raw material, which has both plastic clay and quartz sand particles, and adds sodium chloride as a binder and whisker additive to form mullite whiskers inside the ceramic core. These whiskers are an excellent type of high-temperature resistant material, which makes the prepared soluble ceramic core surface smooth and corrosion-resistant, with high strength and toughness, and the finished product has excellent thermal shock resistance.

[0007] This invention utilizes low-grade ball clay resources, effectively reducing the "solid waste" of existing mines. This technology addresses the technical challenges of ceramic core strength, toughness, impact resistance, and cracking. Using low-grade ball clay with varying tailings contents as raw material, and sodium chloride as a whisker additive and binder, the ceramic core is calcined at a moderate temperature (<800°C). Mullite whiskers are generated in situ within the calcined ceramic core, enhancing the product's strength, toughness, and impact resistance. The product is also less prone to cracking during calcination, resulting in a high yield. Because the raw materials used in this technology contain plastic ball clay, the resulting product has a smooth surface, exceptionally high refractory and corrosion resistance, and is non-reactive with molten metal. Furthermore, the resulting sample exhibits high strength, high modulus, corrosion resistance, thermal vibration resistance, and mechanical impact resistance. The resulting core plate is immersed in water, dissolving the sodium chloride, resulting in excellent collapsibility and ensuring efficient mold collapse. Therefore, the ceramic core produced by this method can be precision cast and exhibits excellent overall performance. Summary of the Invention

[0008] The present invention utilizes low-grade ball clay to prepare ceramic cores, effectively digesting the "solid waste" of ball clay mines.

[0009] The present invention provides a soluble ceramic core using low-grade ball clay to in-situ grow mullite whiskers. Ultrafine quartz sand in the low-grade ball clay is calcined to form fibrous mullite whiskers, thereby improving the strength, toughness, heat resistance and mechanical impact resistance of the ceramic core.

[0010] The present invention provides a soluble ceramic core for in-situ growth of mullite whiskers using low-grade ball clay. The invention utilizes plastic ball clay without adding additional plasticizers, thus solving the pollution caused by the addition of paraffin wax, beeswax, etc. during the sintering process.

[0011] Technical solution:

[0012] In order to achieve the above technical requirements, the present invention provides a soluble ceramic core for in-situ growth of mullite whiskers using low-grade ball clay, which is achieved through the following technical solutions:

[0013] A soluble ceramic core for in-situ growth of mullite whiskers using low-grade ball clay is prepared from water and the following components: low-grade ball clay with different tailings contents and sodium chloride.

[0014] The present invention provides a soluble ceramic core for in-situ growth of mullite whiskers using low-grade ball clay. The raw materials mainly include low-grade ball clay with different quartz contents. The present invention has no other special restrictions on the source of the low-grade ball clay used.

[0015] The present invention also provides an in-situ grown mullite whisker soluble ceramic core and a preparation method thereof, comprising the following steps:

[0016] (1) Dry low-grade ball clay with different quartz contents in an oven at 110°C, then sieve for later use; remove non-mineral impurities such as branches, take 70-90% by mass of low-grade ball clay (of which quartz or tailings content is 40-70%), and mix with 10-30% by mass of sodium chloride and ball mill for 2-4 hours.

[0017] (2) The ball-milled ingredients are spray-granulated and 5-8% of the weight of the ingredients is added with water.

[0018] (3) Place the above ingredients in a closed, dark environment at room temperature for aging and let it stand for more than 24 hours to ensure that the water is evenly dispersed;

[0019] (4) Place the above ingredients into a mold, pound using a hydraulic press (450 kN, 5.0 min), take out, and dry at room temperature for 10.0-12.0 h to obtain a green body;

[0020] (5) After the green body is dried, the temperature is raised to 300°C at a rate of 5°C / min and kept at this temperature for 0.5h. Then the temperature is raised from 300°C to 725-775°C at a rate of 3°C / min and sintered for 1.0h. Finally, the temperature is lowered to about 100°C and taken out. Thus, a soluble ceramic core with mullite whiskers grown in situ using low-grade ball clay is obtained.

[0021] Positive effects of the present invention:

[0022] The present invention provides a soluble ceramic core using low-grade ball clay to in-situ grow mullite whiskers, which has the following positive effects:

[0023] 1. A soluble ceramic core using low-grade ball clay to in-situ grow mullite whiskers. By adding sodium chloride to react with the quartz in the low-grade ball clay, it can achieve medium-temperature sintering below 800°C. This saves energy while also in-situ growing mullite whiskers, significantly enhancing the strength, toughness, and impact resistance of the ceramic core.

[0024] 2. A soluble ceramic core that uses low-grade ball clay to in-situ grow mullite whiskers. By utilizing the plasticity of the low-grade ball clay, the high-temperature resistance and corrosion resistance of the mold are ensured, a smooth surface is obtained, and the precise dimensional requirements of the casting are guaranteed.

[0025] 3. A soluble ceramic core made of in-situ grown mullite whiskers using low-grade ball clay. The prepared ceramic core has good disintegration properties. When immersed in water at 90°C for 1.8-2 hours, the core can be de-cored and easily cleaned. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a ceramic core according to one embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram after collapse of one embodiment of the present invention.

[0028] Figure 3 This is a core fracture scan according to one embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described by way of examples below, which do not limit the present invention in any way. Without departing from the technical solution of the present invention, any modification or alteration of the present invention that can be easily implemented by a person skilled in the art will fall within the scope of the claims of the present invention.

[0030] Example 1:

[0031] The batch composition comprises 90% by weight of low-grade ball clay (of which the quartz content in the tailings is 40%) and 10% sodium chloride; 8% water is added; the mixture is fully and evenly mixed and dispersed, placed in a closed, light-proof environment at room temperature, and allowed to stand for more than 24 hours to ensure uniform moisture content; the mixture is taken out and evenly placed in a mold, pounded using a hydraulic press (450 kN, 5.0 min), taken out, and dried at room temperature for 10.0-12.0 h; the dried sample is placed in a muffle furnace and heated to 300°C at a rate of 5°C / min and maintained at that temperature for 0.5 h, then heated from 300°C to 725°C at a rate of 3°C / min and sintered for 1.0 h, then cooled to about 100°C and taken out.

[0032] Example 2:

[0033] The batch composition comprises 80% by weight of low-grade ball clay (of which the quartz content in the tailings is 60%) and 20% of sodium chloride; 7% of water is added; the mixture is fully and evenly mixed and dispersed, placed in a closed, light-proof environment at room temperature, and allowed to stand for more than 24 hours to ensure uniform moisture content; the mixture is taken out and evenly placed in a mold, pounded using a hydraulic press (450 kN, 5.0 min), taken out, and dried at room temperature for 10.0-12.0 h; the dried sample is placed in a muffle furnace and heated to 300°C at a rate of 5°C / min and maintained at that temperature for 0.5 h, then heated from 300°C to 725°C at a rate of 3°C / min and sintered for 1.0 h, then cooled to about 100°C and taken out.

[0034] Example 3:

[0035] The batch composition comprises 70% by weight of low-grade ball clay (of which the quartz content in the tailings is 50%) and 30% of sodium chloride; 6% of water is added; the mixture is fully and evenly mixed and dispersed, placed in a closed, light-proof environment at room temperature, and allowed to stand for more than 24 hours to ensure uniform moisture content; the mixture is taken out and evenly placed in a mold, pounded using a hydraulic press (450 kN, 5.0 min), taken out, and dried at room temperature for 10.0-12.0 h; the dried sample is placed in a muffle furnace and heated to 300°C at a rate of 5°C / min and maintained at that temperature for 0.5 h, then heated from 300°C to 725°C at a rate of 3°C / min and sintered for 1.0 h, then cooled to about 100°C and taken out.

[0036] Example 4:

[0037] The batch composition comprises 70% by weight of low-grade ball clay (of which the quartz content in the tailings is 55%) and 30% of sodium chloride; 5.5% of water is added; the mixture is fully and evenly mixed and dispersed, placed in a closed, light-proof environment at room temperature, and allowed to stand for more than 24 hours to ensure uniform moisture content; the mixture is taken out and evenly placed in a mold, pounded using a hydraulic press (450 kN, 5.0 min), taken out, and dried at room temperature for 10.0-12.0 h; the dried sample is placed in a muffle furnace and heated to 300°C at a rate of 5°C / min and maintained at that temperature for 0.5 h, then heated from 300°C to 725°C at a rate of 3°C / min and sintered for 1.0 h, then cooled to about 100°C and taken out.

[0038] Example 5:

[0039] The batch composition comprises 80% by weight of low-grade ball clay (of which the quartz content in the tailings is 65%) and 30% of sodium chloride; 7% of water is added; the mixture is fully and evenly mixed and dispersed, placed in a closed, light-proof environment at room temperature, and allowed to stand for more than 24 hours to ensure uniform moisture content; the mixture is taken out and evenly placed in a mold, pounded using a hydraulic press (450 kN, 5.0 min), taken out, and dried at room temperature for 10.0-12.0 h; the dried sample is placed in a muffle furnace and heated to 300°C at a rate of 5°C / min and maintained at that temperature for 0.5 h, then heated from 300°C to 750°C at a rate of 3°C / min and sintered for 1.0 h, then cooled to about 100°C and taken out.

[0040] Example 6:

[0041] The batch composition comprises 80% by weight of low-grade ball clay (of which the quartz content in the tailings is 70%) and 30% of sodium chloride; 7% of water is added; the mixture is fully and evenly mixed and dispersed, placed in a closed, light-proof environment at room temperature, and allowed to stand for more than 24 hours to ensure uniform moisture content; the mixture is taken out and evenly placed in a mold, pounded using a hydraulic press (450 kN, 5.0 min), taken out, and dried at room temperature for 10.0-12.0 h; the dried sample is placed in a muffle furnace and heated to 300°C at a rate of 5°C / min and maintained at that temperature for 0.5 h, then heated from 300°C to 775°C at a rate of 3°C / min and sintered for 1.0 h, then cooled to about 100°C and taken out.

[0042] Test example:

[0043] The performance of a soluble ceramic core prepared in Example 1-6 using low-grade ball clay for in-situ growth of mullite whiskers was tested. The test results are as follows:

[0044] Table 1 Ceramic core performance test

[0045]

[0046] As shown in Table 1, the performance of Examples 1 to 6 is as follows: bending strength ≥ 6 MPa, tensile strength ≥ 3 MPa, and all the examples can meet the enterprise standards.

Claims

1. A soluble ceramic core for in-situ growth of mullite whiskers using low-grade ball clay, characterized by: The soluble ceramic core comprises the following ingredients: 70-90% by mass of low-grade ball clay, 10-30% by mass of sodium chloride, and 5-8% by mass of water. The ball clay tailings in the low-grade ball clay account for 40-70% by mass.

2. The method for preparing a soluble ceramic core by in-situ growth of mullite whiskers using low-grade ball clay according to claim 1, wherein the specific implementation steps are: (1) Dry low-grade ball clay in an oven at 110°C and then sieve it for later use; take 70-90% by mass of low-grade ball clay, 40-70% by mass of quartz content in its tailings, take 10-30% by mass of sodium chloride, mix and ball mill for 2-4 hours; (2) spray granulating the above ball-milled ingredients, and adding 5-8% by weight of water to obtain a composite material; (3) Place the above composite material in a closed, dark environment at room temperature for aging for more than 24 hours to ensure that the water is evenly dispersed; (4) Place the product of step (3) into a mold, pound it with a hydraulic press, press it to 450 kN, and hold the pressure for 5.0 min to obtain a ceramic core with a certain size and properties, and then dry it at room temperature for 10.0-12.0 h for later use; (5) The dried sample was placed in a muffle furnace and heated to 300°C at a rate of 5°C / min and kept at this temperature for 0.5h. Then, the temperature was raised from 300°C to 725-775°C at a rate of 3°C / min, sintered for 1.0h, and then cooled to about 100°C and taken out to obtain a soluble ceramic core with in-situ growth of mullite whiskers using low-grade ball clay.

Images