Organic-inorganic hybrid heat-insulating coated sand and preparation method thereof

Abstract

The application discloses a kind of organic-inorganic hybrid heat insulation type coated sand and preparation method thereof, using diphenyl-benzimidazole modified phenolic resin as binder, hydrophobic modified nanometer silicon dioxide is introduced in the resin polymerization process, make it in situ uniform dispersion in resin matrix;Using the large number of discrete organic-inorganic heterogeneous interfaces constructed by nanoparticles and resin, phonon scattering and interface kapitza thermal resistance effect are generated, while maintaining the dense structure of resin matrix, effectively reduce thermal conductivity, and realize matrix dispersion reinforcement through rigid nano particles.The application does not need to be foamed and to be arranged, can be adapted to existing coated sand heat preparation process, give consideration to excellent high-temperature structural strength and heat insulation performance, effectively solve the technical problems of traditional coated sand poor heat insulation performance, strength and heat insulation performance mutual restriction.

Description

Technical Field

[0001] This invention belongs to the technical field of coated sand for casting, specifically relating to an organic-inorganic hybrid heat-insulating coated sand and its preparation method. Background Technology

[0002] In casting production, coated sand serves as a core molding material, and its thermal insulation performance and high-temperature strength directly affect the casting quality and production efficiency. Traditional coated sand often uses ordinary phenolic resin as a binder. While it possesses basic molding capabilities, it is prone to defects such as shrinkage cavities and porosity in castings due to high thermal conductivity and rapid heat transfer under high-temperature conditions. Furthermore, its insufficient high-temperature strength can easily lead to core collapse, making it difficult to meet the production requirements of complex and precision castings. To improve performance, existing technologies often employ single modification methods, such as adding inorganic thermal insulation fillers or optimizing the resin structure. However, these methods generally suffer from problems such as uneven filler dispersion and poor compatibility between resin and fillers, making it difficult to synergistically improve the thermal insulation and mechanical properties of coated sand. Simultaneously, some modified coated sands have drawbacks such as complex preparation processes, high costs, or insufficient environmental friendliness, limiting their industrial application. Therefore, developing an organic-inorganic hybrid heat-insulating coated sand that combines low thermal conductivity, high high-temperature compressive strength, and simple and cost-controllable preparation process to solve the technical bottleneck of traditional coated sand's difficulty in balancing heat insulation and strength has become a key issue that the foundry industry urgently needs to address. Summary of the Invention

[0003] To address the aforementioned issues, this invention proposes an organic-inorganic hybrid thermal insulation coated sand and its preparation method. This coated sand forms an organic-inorganic heterogeneous interface by in-situ independent dispersion of modified phenolic resin and hydrophobically modified nano-silica. It possesses both low room temperature thermal conductivity and excellent high-temperature compressive strength at 800℃, and exhibits good molding stability, collapse resistance, and environmental controllability. It can effectively solve the bottleneck of traditional coated sand in which thermal insulation and strength are difficult to improve simultaneously, thus meeting the production needs of complex precision castings.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: An organic-inorganic hybrid thermal insulation coated sand, wherein the coated sand is prepared from the following raw materials in parts by weight: 100 parts raw sand, 1.5-4.0 parts modified phenolic resin, 0.05-0.40 parts hydrophobically modified nano silica, 0.15-0.60 parts curing agent, and 0.05-0.20 parts lubricant; The amount of hydrophobic modified nano-silica added is 3-10 wt% of the mass of the modified phenolic resin, and the particle size is 20-50 nm.

[0005] Optionally, the raw sand is one or more of quartz sand, pearl sand and chromite sand, and the mesh size of the raw sand is 70-140 mesh.

[0006] Optionally, the hydrophobic surface modifier of the nano-silica is one or more of hexamethyldisilazane and dimethyldichlorosilane.

[0007] Optionally, the curing agent is hexamethylenetetramine; the lubricant is one or more of stearic acid, calcium stearate, and graphite.

[0008] Optionally, the preparation method of the organic-inorganic hybrid heat-insulating coated sand includes the following specific preparation steps: S1. Take nano-silica with a particle size of 20-50nm, add 5-15% of its mass of hydrophobic modifier, stir and modify at 80-120℃ for 1-3h, stirring speed is 300-500r / min, after modification, vacuum dry at 100-120℃ for 2-4h, pulverize and pass through a 200-mesh sieve to obtain hydrophobic modified nano-silica; S2. Phenol and formaldehyde are added as phenol monomers to the modified phenolic resin polymerization reactor. The molar ratio of phenol to formaldehyde is 1:1.1-1:1.5. Then an acidic catalyst is added, and the temperature is raised to 90-120℃ to initiate polymerization. When the viscosity of the system reaches 500-1000 mPa·s, the hydrophobic modified nano silica prepared in step S1 is slowly added. The temperature is kept constant at 90-120℃, and the mixture is stirred at 300-800 r / min for 2-5 h. After cooling to room temperature, the mixture is pulverized to obtain modified phenolic resin powder. S3. Add 70-140 mesh raw sand to the coating machine, preheat to 150-180℃ and keep warm for 5-10 minutes; then add modified phenolic resin powder and stir at 100-300 r / min for 3-8 minutes; then add curing agent and lubricant and continue stirring for 2-5 minutes; cool, crush, and sieve through a 70-140 mesh sieve to obtain the finished organic-inorganic hybrid heat-insulating coated sand.

[0009] Optionally, in step S2, the acidic catalyst used in the polymerization system is one or more of oxalic acid, p-toluenesulfonic acid, and hydrochloric acid, and the amount of catalyst used is 0.5-2.0% of the total mass of the resin monomers.

[0010] Optionally, in step S3, the moisture content of the raw sand is ≤0.2%; the material is cooled to room temperature of 25-35℃ before being crushed and screened.

[0011] The beneficial effects of this invention are as follows: The organic-inorganic hybrid insulating coated sand prepared by this invention has excellent thermal insulation performance, which can effectively reduce the probability of defects such as shrinkage cavities and porosity in castings. This invention constructs an organic-inorganic heterogeneous interface in situ within a polymerization system by combining modified phenolic resin and hydrophobically modified nano-silica, synergistically improving the room-temperature thermal insulation performance and high-temperature mechanical stability of the coated sand. Simultaneously, nano-silica can refine the microstructure of the matrix, fill internal pores, improve the compatibility between inorganic fillers and the resin matrix, and effectively inhibit nanoparticle aggregation. The formulation design of this invention is reasonable, the preparation process is simple and controllable, and the resulting coated sand exhibits excellent molding performance and high-temperature collapse performance, meeting the requirements for large-scale industrial production of complex precision castings. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0013] Example 1: An organic-inorganic hybrid thermal insulation coated sand of Example 1 is prepared from the following raw materials in parts by weight: 100 parts raw sand, 2.5 parts modified phenolic resin, 0.2 parts hydrophobically modified nano silica, 0.35 parts curing agent (urotropine), and 0.12 parts lubricant (calcium stearate). The preparation steps of hydrophobically modified nano-silica are as follows: S1. Take 35nm nano-silica powder and pre-dry it in an oven at 105℃ for 2 hours to remove surface adsorbed moisture. S2. Weigh 10% by mass of hexamethyldisilazane, a hydrophobic modifier for nano-silica; S3. Add nano-silica to a high-speed stirred reactor and stir at 400 r / min at room temperature. Slowly add hexamethyldisilazane. After the addition is complete, heat to 100℃ and stir for 2 hours to modify. S4. After modification, vacuum dry at 110℃ and -0.09MPa for 3 hours. S5. After cooling, pulverize and pass through a 200-mesh sieve to obtain hydrophobic modified nano-silica, and seal for later use.

[0014] The preparation steps of the modified phenolic resin are as follows: S1. Prepare the materials according to the molar ratio of phenol to formaldehyde of 1:1.3, and add 5% of 4,4'-biphenyldiol and 3% of 2-phenylbenzimidazole according to the total mass of phenolic monomers. S2. Add oxalic acid as an acidic catalyst, with an amount of 1.3% of the total mass of phenolic monomers, and then heat to 100℃ to carry out polycondensation reaction. S3. Monitor the viscosity of the system in real time during the reaction. When the viscosity reaches 800 mPa·s, slowly add the pre-prepared hydrophobic modified nano silica in the preset ratio, keep it at a constant temperature and stir for 2.5 h to make the hydrophobic modified nano silica uniformly dispersed and compounded in situ in the resin polymerization system. S4. After the reaction is complete, dehydration is carried out under reduced pressure at a temperature of 100℃ and a vacuum of -0.09MPa to remove residual water and free phenol and formaldehyde monomers from the system. S5. Cool to room temperature and discharge the material. After cooling and solidification, crush it and pass it through a 100-mesh sieve to obtain modified phenolic resin powder. Dry and seal it for later use.

[0015] This embodiment describes a method for preparing an organic-inorganic hybrid heat-insulating coated sand, with the following specific preparation steps: S1. Select 100-mesh quartz sand. The moisture content of the raw sand is 0.15%, which meets the requirement of moisture content ≤0.2%. Put the weighed raw sand into the film coating machine. S2. Start the heating device of the film coating machine to raise the internal temperature of the film coating machine to 160℃ and keep it at a constant temperature for 8 minutes to preheat the raw sand and ensure that the sand particles are heated evenly. S3. After the heat preservation is completed, add the prepared modified phenolic resin powder into the coating machine, control the stirring speed to 200 r / min, and continue stirring for 5 min to make the modified phenolic resin powder melt and evenly coat the surface of the original sand particles. S4. Keep the stirring speed constant, add the curing agent hexamethylenetetramine and the lubricant calcium stearate into the coating machine in sequence, and continue stirring for 3 minutes to make the curing agent and lubricant evenly mixed and adhered to the surface of the coating sand. S5. Stop heating and cool the material to 30°C at a cooling rate of 8°C / min. Remove the cooled material and crush it. S6. The crushed material is screened using a 70-140 mesh screen. The material obtained through the screen is the finished organic-inorganic hybrid heat-insulating coated sand.

[0016] Example 2: An organic-inorganic hybrid thermal insulation coated sand of Example 2 is prepared from the following raw materials in parts by weight: 100 parts raw sand, 1.5 parts modified phenolic resin, 0.05 parts hydrophobic modified nano silica, 0.35 parts curing agent (urotropine), and 0.12 parts lubricant (calcium stearate). The preparation steps of the hydrophobic modified nano-silica and the modified phenolic resin are the same as in Example 1. The preparation method of the organic-inorganic hybrid heat-insulating coated sand in Example 2 is the same as that in Example 1.

[0017] Example 3: An organic-inorganic hybrid thermal insulation coated sand of Example 3 is prepared from the following raw materials in parts by weight: 100 parts raw sand, 4.0 parts modified phenolic resin, 0.4 parts hydrophobic modified nano silica, 0.35 parts curing agent (urotropine), and 0.12 parts lubricant (calcium stearate). The preparation steps of the hydrophobic modified nano-silica and the modified phenolic resin are the same as in Example 1. The preparation method of the organic-inorganic hybrid heat-insulating coated sand in Example 3 is the same as that in Example 1.

[0018] Comparative Example 1: The coated sand of Comparative Example 1 was prepared from the following raw materials in parts by weight: 100 parts raw sand, 2.5 parts modified phenolic resin, 0.35 parts curing agent (urotropine), 0.12 parts lubricant (calcium stearate). The preparation steps of the modified phenolic resin are the same as in Example 1; The preparation method of the coated sand in Comparative Example 1 is the same as that in Example 1, except that hydrophobic modified nano-silica is not added.

[0019] Comparative Example 2: The coated sand of Comparative Example 2 was prepared from the following parts by weight of raw materials: 100 parts raw sand, 2.5 parts ordinary phenolic resin, 0.2 parts hydrophobically modified nano silica, 0.35 parts curing agent (urotropine), and 0.12 parts lubricant (calcium stearate). The preparation steps of the hydrophobically modified nano-silica are the same as those in Example 1; The preparation method of the coated sand in Comparative Example 2 is the same as that in Example 1, except that the modified phenolic resin is replaced with ordinary phenolic resin.

[0020] Performance testing 1. Room temperature thermal conductivity test The room temperature thermal conductivity of the coated sand samples was tested using a hot-wire thermal conductivity tester. Before testing, the coated sand prepared in each example and comparative example was dried in a drying oven at 70°C to constant weight, cooled to room temperature, and then packed into a standard sample mold, compacted and leveled to ensure uniform filling and no obvious gaps inside. The filled sample was then placed stably on the test station of the thermal conductivity tester, and the test environment temperature was set to 25°C. After the instrument temperature stabilized, the test program was started. The hot-wire probe was used to sense the heat transfer rate of the sample, and the instrument automatically collected data and calculated the room temperature thermal conductivity of each group of coated sand. Each group of samples was tested in parallel three times, and the arithmetic mean was taken as the final test result.

[0021] Table 1. Test data of thermal conductivity at room temperature for different samples

[0022] The room temperature thermal conductivity of the coated sand in each embodiment was significantly lower than that of the comparative examples. Example 3 had the lowest thermal conductivity at only 0.22 W / (m·K), while Examples 1 and 2 had 0.24 W / (m·K) and 0.25 W / (m·K), respectively. In contrast, Comparative Example 1, without the addition of hydrophobically modified nano-silica, had a thermal conductivity as high as 0.35 W / (m·K), and Comparative Example 2, using ordinary phenolic resin, had a thermal conductivity of 0.32 W / (m·K). This indicates that the synergistic effect of the modified phenolic resin containing biphenyl and benzimidazole structures and the hydrophobically modified nano-silica effectively reduces the heat transfer efficiency of the coated sand. Furthermore, the thermal insulation performance shows an optimized trend with the increase of the amount of the core functional components, verifying the significant advantages of the formulation of this invention in improving thermal insulation performance.

[0023] 2. High-temperature compressive strength test The coated sand samples were tested using a high-temperature compressive strength tester. Before testing, the coated sand products of each embodiment and comparative example were pressed into cylindrical samples with a diameter of φ50mm×50mm using a standard mold. They were then dried in a 70℃ drying oven for 12 hours to fully remove adsorbed moisture from the inside and surface of the samples. After cooling to room temperature, they were placed in a high-temperature furnace and heated to 400℃ at a rate of 5℃ / min. The temperature was maintained for 30 minutes to ensure that the samples were fully heated and stabilized. The samples were then immediately transferred to the test platform of the high-temperature compressive strength tester, which had been preheated to 400℃. It was ensured that the center of the sample was aligned with the pressure head and that the force was uniform. Axial pressure was applied to the sample at a loading rate of 2mm / min until the sample broke. The maximum pressure value at which the sample broke was recorded. The high-temperature compressive strength at 400℃ (unit: MPa) was calculated according to the formula σ=F / S, where F is the maximum pressure value and S is the cross-sectional area of ​​the sample. Each group of samples was tested in parallel for 3 times, and the arithmetic mean was taken as the final test result.

[0024] Table 2. High-Temperature Compressive Strength Test Data for Different Samples

[0025] The high-temperature compressive strength at 400℃ of the example groups was superior to that of the comparative groups. Example 3 showed the best strength at 4.2 MPa, while Examples 1 and 2 showed strengths of 3.8 MPa and 3.5 MPa, respectively. In contrast, the high-temperature compressive strengths of Comparative Example 1 (without nanofillers) and Comparative Example 2 (ordinary phenolic resin) were only 2.5 MPa and 2.9 MPa, respectively. These results demonstrate that the special structure of the modified phenolic resin endows the coated sand with excellent high-temperature stability. The addition of hydrophobic modified nano-silica further enhances the structural load-bearing capacity at high temperatures. Furthermore, the amount of the core component is positively correlated with the high-temperature compressive strength. The formulation of this invention can effectively meet the requirements for high-temperature anti-collapse and anti-deformation properties of coated sand during casting.

[0026] 3. Tensile strength / bending strength test at room temperature The mechanical properties of the coated sand samples were tested at room temperature using a universal testing machine, in accordance with the method specified in JB / T 8583-2008 "Coated Sand for Foundry". Before testing, the coated sand samples of each example and comparative example were pressed into cylindrical samples with a diameter of φ30mm×60mm for tensile strength testing and cuboid samples with a diameter of 40mm×40mm×160mm for flexural strength testing using standard molds. Both types of samples were dried in a 70℃ drying oven for 12 hours to remove residual moisture and then cooled to 25℃ for later use. During the test, the tensile strength specimen is first clamped in the special tensile fixture of the testing machine, ensuring that the clamping is firm and the force axis is aligned. An axial tensile force is applied at a loading rate of 1 mm / min until the specimen breaks. The maximum tensile force value at the time of breakage is recorded. The room temperature tensile strength (unit: MPa) is calculated according to the formula σ=F / S, where F is the maximum tensile force value and S is the cross-sectional area of ​​the specimen. Replace the bending strength test fixture, place the cuboid specimen stably on the support, and apply vertical pressure at the mid-span of the specimen through the indenter at a loading rate of 2 mm / min until the specimen breaks. Record the maximum pressure value at the time of fracture. Calculate the room temperature bending strength according to the bending strength calculation formula (σ=3FL / (2bh2), where F is the maximum pressure, L is the support span, b is the specimen width, and h is the specimen height). For both types of performance tests, each group of specimens is tested in parallel 3 times, and the arithmetic mean is taken as the final test result (unit: MPa).

[0027] Table 3. Test data of tensile strength / bending strength at room temperature for different samples.

[0028] The room temperature tensile and flexural strengths of the coated sand in the examples were significantly higher than those in the comparative examples. Example 3 showed a room temperature tensile strength of 4.5 MPa and a flexural strength of 7.2 MPa. Examples 1 and 2 also maintained relatively high levels of 3.9-4.2 MPa and 6.3-6.8 MPa, respectively. In contrast, the room temperature tensile strengths of Comparative Examples 1 and 2 were only 2.8-3.2 MPa and flexural strengths were 4.9-5.5 MPa. This indicates that the synergistic effect of the modified phenolic resin and the hydrophobically modified nano-silica not only improved the room temperature load-bearing capacity of the coated sand but also enhanced its tensile and flexural deformation resistance. Furthermore, the increased dosage of the core components further optimized the room temperature mechanical properties, ensuring that the coated sand is not easily damaged or collapsed during storage, molding, and transportation.

[0029] 4. Gas output test The gas generation of coated sand samples was tested using a water displacement gas generation analyzer. Before testing, undisturbed coated sand particles from each example and comparative example were dried in a 70℃ drying oven for 12 hours until constant weight. 5g of sample was accurately weighed and placed in a quartz crucible. The crucible was placed in the heating furnace of the gas generation analyzer. After sealing the instrument, distilled water was injected into the gas measuring tube and the instrument was adjusted to the zero mark. The heating furnace was set to a heating rate of 10℃ / min, and the temperature was raised to 900℃ and held for 10 minutes to simulate the gas generation of coated sand during casting. The gas generated by the heated sample pushed the distilled water in the gas measuring tube. The gas volume was read by the change in the scale of the gas measuring tube. After subtracting the blank test (the gas volume generated by the instrument when there was no sample), the gas generation of each group of coated sand was calculated (unit: mL / g). Each group of samples was tested in parallel three times, and the arithmetic mean was taken as the final test result.

[0030] Table 4. Gas Emission Test Data for Different Samples

[0031] The gas generation of the coated sand in each embodiment was lower than that of the comparative example. Example 2 had the lowest gas generation at 17.2 mL / g, while Examples 1 and 3 had 18.6 mL / g and 20.3 mL / g, respectively. In contrast, Comparative Examples 1 and 2 had gas generation as high as 24.5 mL / g and 22.8 mL / g, respectively. Although the gas generation in Example 3 increased slightly due to the increased resin content, it was still far lower than that of the comparative example. This indicates that the hydrophobic modified nano-silica has a significant inhibitory effect on the gas generation from the thermal decomposition of resin. The modified phenolic resin also has better thermal stability than ordinary phenolic resin. The formulation of this invention can effectively reduce the risk of porosity defects caused by excessive gas during casting, ensuring the quality of the casting.

[0032] 5. Collapse test The collapsibility of coated sand was tested using the high-temperature residual strength method. Before testing, the coated sand products of each example and comparative example were pressed into cylindrical specimens with a diameter of φ50mm×50mm using a standard mold. They were then dried in a 70℃ drying oven for 12 hours to remove moisture. After cooling to room temperature, they were placed in a high-temperature furnace and heated to 400℃ at a rate of 5℃ / min. The temperature was then held for 5 minutes to simulate the heating conditions of casting. The high-temperature furnace was then turned off, and the specimens were allowed to cool naturally to 25℃. After cooling, the specimens were removed, and an axial pressure was applied to the specimens using a universal testing machine at a loading rate of 2mm / min. The maximum pressure value at which the specimen broke was recorded. The residual compressive strength at room temperature (unit: MPa) was calculated based on the pressure and the force-bearing area of ​​the specimen. The lower the residual strength, the better the collapsibility. Each group of specimens was tested in parallel three times, and the arithmetic mean was taken as the final test result.

[0033] Table 5. Data on the Collapse Resistance Test of Different Samples

[0034] The residual compressive strength at room temperature in the example groups was significantly lower than that in the comparative examples. Example 2 showed the lowest residual strength at 1.2 MPa, while Examples 1 and 3 showed 1.5 MPa and 1.8 MPa, respectively. In contrast, Comparative Examples 1 and 2 exhibited residual strengths as high as 3.2 MPa and 2.8 MPa, respectively. Since lower residual strength indicates better collapsibility, this result confirms that the combination of modified phenolic resin and hydrophobically modified nano-silica in the formulation of this invention can effectively reduce the structural adhesion of the coated sand after high-temperature heating, making it easier to detach from the casting surface after cooling. Even though Example 3 showed a slight increase in residual strength due to the increased amount of core components, it still possessed excellent collapsibility performance, solving the problem of difficult sand removal with traditional coated sand and improving production efficiency.

[0035] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An organic-inorganic hybrid heat-insulating coated sand, characterized in that, The coated sand is prepared from the following raw materials in parts by weight: 100 parts raw sand, 1.5-4.0 parts modified phenolic resin, 0.05-0.40 parts hydrophobically modified nano silica, 0.15-0.60 parts curing agent, and 0.05-0.20 parts lubricant; The amount of hydrophobic modified nano-silica added is 3-10 wt% of the mass of the modified phenolic resin, and the particle size is 20-50 nm.

2. The organic-inorganic hybrid heat-insulating coated sand according to claim 1, characterized in that, The raw sand is one or more of quartz sand, pearl sand and chromite sand, and the mesh size of the raw sand is 70-140 mesh.

3. The organic-inorganic hybrid heat-insulating coated sand according to claim 1, characterized in that, The hydrophobic surface modifier of the nano-silica is one or more of hexamethyldisilazane and dimethyldichlorosilane.

4. The organic-inorganic hybrid heat-insulating coated sand according to claim 1, characterized in that, The curing agent is hexamethylenetetramine; the lubricant is one or more of stearic acid, calcium stearate, and graphite.

5. A method for preparing an organic-inorganic hybrid heat-insulating coated sand, used to prepare the organic-inorganic hybrid heat-insulating coated sand according to any one of claims 1-4, characterized in that, The specific preparation steps are as follows: S1. Take nano-silica with a particle size of 20-50nm, add 5-15% of its mass of hydrophobic modifier, stir and modify at 80-120℃ for 1-3h, stirring speed is 300-500r / min, after modification, vacuum dry at 100-120℃ for 2-4h, pulverize and pass through a 200-mesh sieve to obtain hydrophobic modified nano-silica; S2. Phenol and formaldehyde are added as phenol monomers to the modified phenolic resin polymerization reactor. The molar ratio of phenol to formaldehyde is 1:1.1-1:1.

5. Then an acidic catalyst is added, and the temperature is raised to 90-120℃ to initiate polymerization. When the viscosity of the system reaches 500-1000 mPa·s, the hydrophobic modified nano silica prepared in step S1 is slowly added. The temperature is kept constant at 90-120℃, and the mixture is stirred at 300-800 r / min for 2-5 h. After cooling to room temperature, the mixture is pulverized to obtain modified phenolic resin powder. S3. Add 70-140 mesh raw sand to the coating machine, preheat to 150-180℃ and keep warm for 5-10 minutes; then add modified phenolic resin powder and stir at 100-300 r / min for 3-8 minutes; then add curing agent and lubricant and continue stirring for 2-5 minutes; cool, crush, and sieve through a 70-140 mesh sieve to obtain the finished organic-inorganic hybrid heat-insulating coated sand.

6. The method for preparing an organic-inorganic hybrid heat-insulating coated sand according to claim 5, characterized in that, In step S2, the acidic catalyst used in the polymerization system is one or more of oxalic acid, p-toluenesulfonic acid and hydrochloric acid, and the amount of catalyst used is 0.5-2.0% of the total mass of the resin monomers.

7. The method for preparing an organic-inorganic hybrid heat-insulating coated sand according to claim 5, characterized in that, In step S3, the moisture content of the raw sand is ≤0.2%; the material is cooled to room temperature of 25-35℃ before being crushed and screened.

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