High-performance precoated sand and preparation method thereof

Abstract

The invention belongs to the technical field of casting materials, and discloses high-performance precoated sand and a preparation method thereof.According to the precoated sand, furfural modified bio-based phenolic resin serves as a main coating material, a condensation path is controlled through a synergistic reaction in combination with carboxyl functional groups, the content of free formaldehyde is effectively reduced, and the high-temperature film forming stability is improved. Meanwhile, a bifunctional grafted interfacial activator constructed by copolymerization of amino silane and an aniline compound is introduced, so that synergistic bonding between the resin and quartz sand is realized, and the interface bonding strength and coating compactness are improved. And nano SiO and flake graphite are used for compounding a lubricating filler, so that the oxidation resistance and the demolding effect of the lubricating filler are enhanced. The precoated sand has the advantages of being complete in forming, smooth in demolding, low in odor and high in high-temperature strength, and is suitable for application scenes with precision casting and high environmental protection requirements.

Description

Technical Field

[0001] This invention belongs to the field of casting materials technology, specifically relating to a high-performance coated sand and its preparation method. Background Technology

[0002] Coated sand is a functional molding material widely used in metal casting. It mainly consists of a sand matrix and a resin-based coating material. By forming a dense thermosetting resin film on the surface of the sand grains, it achieves excellent molding sand strength, thermal stability, and release properties. In actual casting processes, coated sand can be used to manufacture shell molds, shell cores, and castings with complex hollow structures. It offers advantages such as high molding accuracy, good dimensional stability, and high efficiency, making it particularly suitable for the production of high-precision cast iron, cast steel, and aluminum alloy castings.

[0003] However, traditional coated sand systems generally use phenolic resin as the coating resin, which easily generates high levels of free formaldehyde during high-temperature use, causing environmental pollution and casting defects such as inclusions and porosity. Simultaneously, the adhesion between the resin and sand particles is mostly physical adsorption or non-specific adhesion, resulting in insufficient interfacial bonding strength. This leads to easy coating peeling and cracking, affecting the thermal strength and demolding integrity of the sand core. Furthermore, some coated sands exhibit problems such as sintering and bonding at high temperatures, difficulty in demolding, strong odor, and poor reusability, making it difficult to meet the dual requirements of precision casting and environmentally friendly manufacturing. Existing technologies have attempted to improve these problems by adding inorganic fillers or reducing resin content, but defects such as uneven film formation, unstable interfaces, or decreased high-temperature performance still exist, making long-term stable application in complex castings difficult. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a high-performance coated sand and its preparation method. The method utilizes furfural-modified bio-based phenolic resin combined with a carboxyl group regulation system to significantly reduce the release of free formaldehyde. It also enhances the bonding strength between sand particles and resin through a grafted bifunctional interfacial activator and improves high-temperature oxidation resistance and demolding integrity with nano-lubricating fillers, thereby achieving a green, environmentally friendly, and high-performance casting coating material.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A high-performance coated sand comprises the following raw materials in parts by weight: 80-95 parts of modified bio-based phenolic resin, 3-8 parts of grafted bifunctional interfacial activator, 2-6 parts of nano-antioxidant lubricating filler, and 1000-1200 parts of quartz sand substrate.

[0007] More preferably, the preparation method of the modified bio-based phenolic resin specifically includes the following steps:

[0008] S101. Add phenolic monomers to a reaction vessel, slowly heat to 90-110°C with stirring, add furfural dropwise under constant temperature conditions, and simultaneously add catalyst to adjust the pH of the reaction solution to alkaline. Maintain the reaction for 1-2 hours to generate prepolymer.

[0009] S102. After the above condensation reaction has proceeded to the predetermined time, carboxymethyl melamine is added to the system, and the reaction continues for 0.5 to 1.5 hours under the same temperature conditions.

[0010] S103. After the reaction is complete, stop heating, cool to room temperature, and adjust the pH to neutral to weakly acidic to obtain the modified bio-based phenolic resin.

[0011] More preferably, the preparation method of the grafted bifunctional interfacial activator specifically includes the following steps:

[0012] S201. Grafting a surfactant with a bifunctional group to a reactive monomer (such as acrylates, amino acids or epoxy compounds);

[0013] S202. During the reaction, the temperature is adjusted and controlled at 50°C to 100°C, and the reaction time is 1 to 5 hours to achieve the best grafting efficiency and functional group ratio.

[0014] S203. Unreacted raw materials and byproducts are removed by solvent extraction, centrifugation, and filtration to obtain purified grafted bifunctional interfacial activator.

[0015] More preferably, the nano-antioxidant lubricant filler is a composite filler formed by combining spherical nano-silica and flake graphite in a mass ratio of 2:1, wherein the spherical SiO2 particles have a diameter of 20–50 nm, and the graphite flakes have a diameter of D… 50 It is 1–2 μm.

[0016] A method for preparing high-performance coated sand includes the following steps:

[0017] S1. The dried quartz sand is put into a mixing device, and modified bio-based phenolic resin, grafted bifunctional interfacial activator and nano antioxidant lubricating filler are added in sequence under stirring conditions. The mixture is continuously mixed until a uniform coating is formed on the surface of the sand particles.

[0018] S2. The premixed sand is heated to gradually solidify the resin in the coating layer, forming a stable and dense coating structure.

[0019] S3. After the cured coated sand is naturally cooled to room temperature, it is sieved to remove particles that do not conform to the particle size range, thereby obtaining the high-performance coated sand.

[0020] More preferably, the mixing operation in step S1 is carried out after preheating the quartz sand, with the preheating temperature controlled at 120-180°C, to promote rapid wetting and coating of the resin on the surface of the sand particles.

[0021] More preferably, the order of adding the modified bio-based phenolic resin, the grafted bifunctional interfacial activator, and the nano-antioxidant lubricating filler in step S1 is as follows: first add the modified bio-based phenolic resin, then add the grafted bifunctional interfacial activator, and finally add the nano-antioxidant lubricating filler.

[0022] More preferably, the heating and curing process in step S2 includes a heating stage and a heat preservation stage. The heating rate in the heating stage is controlled at 3 to 10 °C / min, and the temperature in the heat preservation stage is maintained in the range of 150 to 250 °C.

[0023] More preferably, the screening operation in step S3 is carried out using a multi-stage screen combination with a screen particle size range of 30 to 70 mesh, to ensure that the particle size distribution of the final coated sand is stable and consistent.

[0024] The beneficial effects of this invention are:

[0025] This invention employs a modified bio-based phenolic resin system with furfural as the aldehyde source. This not only achieves partial substitution of petrochemical raw materials, effectively reducing environmental dependence, but also, through the introduction of carboxyl functional groups for structural regulation, enables the resin to form a more stable and dense three-dimensional cross-linked network during thermosetting. This significantly reduces the release of free formaldehyde, improves the problem of harmful gas emissions from traditional coated sand at high temperatures, and enhances its environmental performance. Simultaneously, this carboxyl modification also enhances the resin's polarity and chemical activity, enabling it to form a stronger adhesion bond during contact with sand particles, providing a foundation for subsequent interface structure construction.

[0026] Regarding interface enhancement, this invention introduces a grafted bifunctional interface activator. One end of the activator contains a structural group compatible with the resin system, while the other end has an active group that can physically adsorb or chemically bond with the surface of sand particles. This type of molecule forms a "molecular bridge" between the sand particles and the resin, achieving synergistic bonding of the interface layer and significantly improving the density and high-temperature stability of the coating layer. Simultaneously, a lubricating and antioxidant filler, composed of spherical nano-silica and flake graphite, not only effectively fills the tiny pores between the resin and sand particles, increasing the overall density of the coating layer, but also forms a thermally conductive shielding layer at high temperatures, buffering thermal stress and slowing down interface oxidation. Attached Figure Description

[0027] The invention will now be further described with reference to the accompanying drawings.

[0028] Figure 1This is a comparison chart of the compressive strength of the products of Examples 1-3 and Comparative Examples 1-2 at room temperature and high temperature. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] I. Preparation of Modified Bio-based Phenolic Resin

[0032] 470 g of phenol and 100 mL of deionized water were added to a four-necked reactor. Mechanical stirring was started and the temperature was raised to 95°C. While the phenol was being heated and stirred, 330 g of furfural was added dropwise, and simultaneously, 30% sodium hydroxide solution was slowly added until the pH of the reaction solution was adjusted to 8.5–9.0. The reaction was continued at a constant temperature with stirring for 1.5 hours. Maintaining the system temperature at 95°C, 20 g of carboxymethyl melamine was added to the reaction system, and the reaction was continued for 1 hour. After the reaction was completed, the system was allowed to cool naturally to below 40°C. The pH was adjusted to neutral (pH 7.0–7.5) using diluted hydrochloric acid. The mixture was filtered to remove impurities, yielding the modified bio-based phenolic resin.

[0033] II. Preparation of Grafted Bifunctional Interfacial Activators

[0034] 100 mL of anhydrous ethanol and 30 mL of deionized water were mixed and added to a three-necked flask. Stirring was started and the temperature was slowly increased to 60 °C. While stirring, 15 g of γ-aminopropyltriethoxysilane was added, and stirring continued until fully dissolved. Then, 10 g of aniline was added dropwise, and the reaction was maintained at 60 °C with stirring for 3 hours. During the reaction, the pH of the system was adjusted to 4.5–5.5 using glacial acetic acid. After the reaction was complete, the solution was placed in a rotary evaporator at 40 °C under reduced pressure to remove ethanol and water, yielding a viscous semi-solid product. The product was transferred to a vacuum drying oven and dried at 50 °C for 12 hours to obtain the grafted bifunctional interfacial activator.

[0035] III. Preparation of High-Performance Coated Sand

[0036] The high-performance coated sand contains the following raw materials in parts by weight: 80 parts modified bio-based phenolic resin, 3 parts grafted bifunctional interfacial activator, 2 parts nano-antioxidant lubricating filler, and 1000 parts quartz sand substrate.

[0037] The preparation steps of the high-performance coated sand are as follows:

[0038] S1. Place 1000 g of dry quartz sand in a preheating device, heat to 130℃, and maintain the temperature for 10 min to ensure the sand surface is thoroughly dehumidified. Transfer the preheated sand to a film-coated mixer and stir at 300 rpm. While stirring, add 80 g of modified bio-based phenolic resin, maintain the sand temperature at approximately 120℃, and continue stirring for 3 min to allow the resin to initially melt and coat the sand. Then add 3 g of grafted bifunctional interfacial activator and continue stirring for 2 min. Finally, add 2 g of nano-antioxidant lubricating filler and continue stirring for 2 min to ensure the filler is uniformly embedded in the resin layer.

[0039] S2. Heat the uniformly mixed coated sand to 150℃ and cure it at a heating rate of 3℃ / min. Then, keep it at 150℃ for 10 minutes to allow the phenolic resin to crosslink and set, the interface activator to fully react, and a dense film to be formed.

[0040] S3. Allow the cured coated sand to cool naturally to below 40°C, then sieve it using a 30-70 mesh combination sieve. Collect the coated sand with uniform particle size and complete surface coating after sieving, which is the high-performance coated sand.

[0041] Example 2

[0042] The preparation methods of the modified bio-based phenolic resin and the grafted bifunctional interfacial activator are the same as in Example 1.

[0043] The high-performance coated sand comprises the following raw materials in parts by weight: 95 parts modified bio-based phenolic resin, 8 parts grafted bifunctional interfacial activator, 6 parts nano-antioxidant lubricating filler, and 1200 parts quartz sand substrate.

[0044] The preparation steps of the high-performance coated sand are as follows:

[0045] S1. Place 1200 g of dried quartz sand in a stainless steel mixing device, preheat to 180°C under hot air circulation, maintain the temperature for 10 min, run the mixer at 350 rpm, add 95 g of modified bio-based phenolic resin, continue stirring for 3 min, then add 8 g of grafted bifunctional interfacial activator, continue stirring for 2 min, and finally slowly add 6 g of nano-antioxidant lubricating filler, stir for 2 min to ensure that the filler is fully embedded in the resin layer and dispersed evenly.

[0046] S2. Transfer the mixed coated sand to a high-temperature curing device, raise the temperature to 250°C at a rate of 10°C / min, and hold at that temperature for 15 min.

[0047] S3. Allow the high-temperature cured coated sand to cool naturally to room temperature, then sieve it using a 30-70 mesh combination sieve. Collect the coated sand with uniform particle size and complete surface coating after sieving, which is the high-performance coated sand.

[0048] Example 3

[0049] The preparation methods of the modified bio-based phenolic resin and the grafted bifunctional interfacial activator are the same as in Example 1.

[0050] The high-performance coated sand contains the following raw materials in parts by weight: 87.5 parts modified bio-based phenolic resin, 5.5 parts grafted bifunctional interfacial activator, 4 parts nano-antioxidant lubricating filler, and 1100 parts quartz sand substrate.

[0051] The preparation steps of the high-performance coated sand are as follows:

[0052] S1. Place 1100 g of quartz sand into a hot air drying oven and preheat at 150℃ for 10 minutes to remove surface moisture and improve coating efficiency. Transfer the preheated sand to a vertical mixer with heating function and set the stirring speed to 320 rpm. Add 87.5 g of modified bio-based phenolic resin, maintain the sand temperature in the range of 130~150℃, and continue stirring for 3 minutes. Then add 5.5 g of grafted bifunctional interfacial activator and continue stirring for 2 minutes. Finally, slowly add 4 g of nano-antioxidant lubricating filler and stir for 2 minutes. The filler is embedded in the molten resin and forms a three-dimensional composite structure.

[0053] S2. Transfer the mixed and coated sand into an electric constant temperature furnace, heat it to 200℃ at a heating rate of 5℃ / min, and keep it at that temperature for 12 minutes to cure.

[0054] S3. Allow the high-temperature cured coated sand to cool naturally to room temperature, then sieve it using a 30-70 mesh combination sieve. Collect the coated sand with uniform particle size and complete surface coating after sieving, which is the high-performance coated sand.

[0055] Comparative Example 1

[0056] The preparation method of the modified bio-based phenolic resin is the same as that in Example 1.

[0057] The high-performance coated sand contains the following raw materials in parts by weight: 87.5 parts modified bio-based phenolic resin, 4 parts nano-antioxidant lubricating filler, and 1100 parts quartz sand substrate.

[0058] The preparation steps of the high-performance coated sand are the same as those in Example 3, except that no grafted bifunctional interfacial activator is added.

[0059] Comparative Example 2

[0060] The preparation methods of the modified bio-based phenolic resin and the grafted bifunctional interfacial activator are the same as in Example 1.

[0061] The high-performance coated sand contains the following raw materials in parts by weight: 87.5 parts modified bio-based phenolic resin, 5.5 parts grafted bifunctional interfacial activator, 4 parts micron-sized talc powder, and 1100 parts quartz sand substrate.

[0062] The preparation steps of the high-performance coated sand are the same as in Example 3, except that the nano-antioxidant lubricating filler is replaced with micron-sized talc powder.

[0063] Performance testing

[0064] 1. Demolding integrity rate test

[0065] The coated sand obtained in Examples 1-3 and Comparative Examples 1-2 were used to prepare standard shell cores (50 mm × 50 mm × 10 mm) using the same process. The prepared shell cores were placed in a muffle furnace and heated to 800°C at a rate of 10°C / min, and held at that temperature for 15 minutes. After the holding period, the samples were immediately removed and placed on a platform at a constant temperature for natural cooling. After cooling to room temperature, the shell cores were demolded, and the presence of cracks, missing corners, surface peeling, or structural collapse was observed. Each group of samples was tested 10 times, and the number of successful complete demoldings was recorded. The demolding integrity rate was calculated, and the results are shown in Table 1 below.

[0066] Table 1 Demolding Integrity Rate

[0067] Group Demolding integrity rate (%) Example 1 88% Example 2 97% Example 3 95% Comparative Example 1 72% Comparative Example 2 78%

[0068] As shown in Table 1, the demolding integrity rates of Examples 1-3 were significantly better than those of Comparative Examples 1-2, especially Examples 2 and 3, which achieved demolding integrity rates of 97% and 95%, respectively. This is because the grafted bifunctional interfacial activator used in this invention constructs a strong interfacial layer between the resin and sand particles through chemical action, effectively preventing the coating layer from peeling off due to high-temperature stress. Simultaneously, the filler system formed by the composite of nano-sized spherical SiO2 and flake graphite is uniformly dispersed in the resin, forming a dual network of thermal conductivity and crack resistance, further enhancing the thermal stability and integrity of the coating layer. In contrast, Comparative Example 1 lacked an interfacial activator, resulting in insufficient interfacial adhesion and easy breakage during demolding; Comparative Example 2 used ordinary talc powder instead of nanofillers, making it difficult to form a dense synergistic structure, leading to uneven release of thermal stress and incomplete demolding.

[0069] 2. High-temperature thermal stability test method

[0070] Take 20 g each of the coated sand obtained in Examples 1-3 and Comparative Examples 1-2, place them in a high-temperature muffle furnace, and heat to 800°C at a rate of 10°C / min. Hold the temperature at this point for 15 minutes. After cooling to room temperature, weigh the residual mass and calculate the thermal weight loss rate. The results are shown in Table 2 below.

[0071] Table 2 High-Temperature Thermal Stability Test Results

[0072] Group Thermal weight loss rate (%) Description of apparent changes Example 1 6.2% No fusion, slight shrinkage Example 2 3.8% Stable structure, intact surface Example 3 4.1% Evenly coated and with intact morphology Comparative Example 1 10.5% Obvious delamination, charring, and edge curling Comparative Example 2 8.9% Localized sintering and uneven packing distribution

[0073] As shown in Table 2, the coated sand of the present invention exhibits significantly better structural retention and quality stability than the comparative samples at a casting temperature of 800℃. The thermal weight loss rates of Examples 2-3 are significantly lower than those of Comparative Examples 1-2, indicating that the modified bio-based phenolic resin forms a denser and more thermally stable coated network structure under the synergistic effect of the bifunctional interfacial activator and the nano-antioxidant lubricating filler. The combination of nano-SiO2 and flake graphite makes the resin less prone to decomposition or carbonization at high temperatures, thereby reducing mass loss and maintaining the integrity of the shell-core shape. In contrast, Comparative Example 1, lacking an interfacial activator, has weak bonding between the resin and sand particles, making it prone to delamination and coking at high temperatures; Comparative Example 2, due to its larger filler particle size, cannot form an effective nano-barrier layer, leading to localized sintering and structural damage.

[0074] 3. Free formaldehyde release test

[0075] Take 50 g each of the coated sand samples from Examples 1-3 and Comparative Examples 1-2, place them in a constant temperature drying oven at 180℃ and heat for 1 hour, collecting the released gas. The gas was determined according to the "Gas Analysis Method" in GB / T 17657-2013 standard, using a formaldehyde trapping solution to absorb the gas, followed by spectrophotometric analysis to calculate the free formaldehyde release. The results are shown in Table 3 below.

[0076] Table 3 Free formaldehyde release

[0077] Group Free formaldehyde release (%) Example 1 0.09% Example 2 0.06% Example 3 0.07% Comparative Example 1 0.21% Comparative Example 2 0.18%

[0078] As shown in Table 3, the free formaldehyde release of Examples 1-3 was all below 0.1%, significantly better than Comparative Examples 1 and 2. This result is mainly attributed to the use of furfural to replace part of the traditional formaldehyde as the aldehyde source and the introduction of carboxymethyl melamine for structural modification, which makes the decomposition of phenolic resin more stable at high temperatures and significantly reduces the formaldehyde release. Simultaneously, carboxyl modification also promotes the dense formation of the cross-linked network, effectively sealing potential free formaldehyde release channels. In contrast, Comparative Examples 1 and 2 did not employ a low-free formaldehyde design, resulting in significant decomposition reactions during heating at 180°C and the release of more formaldehyde gas.

[0079] 4. Compressive strength test

[0080] Standard cylindrical shell cores (Φ50 mm × height 50 mm) were prepared from the coated sand of Examples 1-3 and Comparative Examples 1-2. These cores were pressed into shape using a standard mold and cured by heat treatment at 200℃. Compressive strength tests were then conducted at room temperature (25℃) and high temperature (800℃). Room temperature compressive strength was determined by direct compression using a universal testing machine, while high temperature strength was measured using a high-temperature compressive strength testing device. Each sample was tested three times, and the average value was used for performance comparison. The results are shown in Table 4 below.

[0081] Table 4 Compressive strength test results

[0082] Group Compressive strength at room temperature (MPa) High-temperature compressive strength (MPa) Example 1 7.5 4.2 Example 2 9.1 5.7 Example 3 8.6 5.2 Comparative Example 1 5.2 2.8 Comparative Example 2 6.0 3.4

[0083] As shown in Table 4, Examples 1-3 exhibited excellent mechanical properties under both room temperature and high temperature conditions. Example 2, in particular, achieved a room temperature strength of 9.1 MPa and maintained 5.7 MPa at high temperature, significantly outperforming Comparative Examples 1 and 2. This performance improvement not only depends on the type of raw materials but also reflects the synergistic enhancement effect resulting from the coordinated proportions of the components. Especially under high temperature conditions, the degree of crosslinking of the modified phenolic resin, the distribution of the interface agent during curing, and the thermal shielding effect of the nanofiller all contribute to the overall structural stability of the sand core. In contrast, Comparative Examples 1 and 2 showed a significant decrease in strength at high temperatures, indicating that the lack of key structural factors led to a decrease in overall network stability, making thermally induced softening or cracking more likely.

[0084] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0085] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A high-performance coated sand, characterized in that, It contains the following raw materials in parts by weight: 80-95 parts modified bio-based phenolic resin, 3-8 parts grafted bifunctional interfacial activator, 2-6 parts nano-antioxidant lubricating filler, and 1000-1200 parts quartz sand substrate.

2. The high-performance coated sand according to claim 1, characterized in that, The preparation method of the modified bio-based phenolic resin specifically includes the following steps: S101. Add phenolic monomers to a reaction vessel, slowly heat to 90-110°C with stirring, add furfural dropwise under constant temperature conditions, and simultaneously add catalyst to adjust the pH of the reaction solution to alkaline. Maintain the reaction for 1-2 hours to generate prepolymer. S102. After the above condensation reaction has proceeded to the predetermined time, carboxymethyl melamine is added to the system, and the reaction continues for 0.5 to 1.5 hours under the same temperature conditions. S103. After the reaction is complete, stop heating, cool to room temperature, and adjust the pH to neutral to weakly acidic to obtain the modified bio-based phenolic resin.

3. The high-performance coated sand according to claim 1, characterized in that, The preparation method of the grafted bifunctional interfacial activator specifically includes the following steps: S201. Grafting a surfactant with a bifunctional group to a reactive monomer (such as acrylates, amino acids or epoxy compounds); S202. During the reaction, the temperature is adjusted and controlled at 50°C to 100°C, and the reaction time is 1 to 5 hours to achieve the best grafting efficiency and functional group ratio. S203. Unreacted raw materials and byproducts are removed by solvent extraction, centrifugation, and filtration to obtain purified grafted bifunctional interfacial activator.

4. The high-performance coated sand according to claim 1, characterized in that, The nano-antioxidant lubricating filler is a composite filler formed by combining spherical nano-silica and flake graphite in a mass ratio of 2:

1. The spherical SiO2 particles have a diameter of 20–50 nm, and the graphite flakes have a diameter of D… 50 It is 1–2 μm.

5. A method for preparing high-performance coated sand, wherein the high-performance coated sand is as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. The dried quartz sand is put into a mixing device, and modified bio-based phenolic resin, grafted bifunctional interfacial activator and nano antioxidant lubricating filler are added in sequence under stirring conditions. The mixture is continuously mixed until a uniform coating is formed on the surface of the sand particles. S2. The premixed sand is heated to gradually solidify the resin in the coating layer, forming a stable and dense coating structure. S3. After the cured coated sand is naturally cooled to room temperature, it is sieved to remove particles that do not conform to the particle size range, thereby obtaining the high-performance coated sand.

6. The method for preparing high-performance coated sand according to claim 5, characterized in that, The mixing operation in step S1 is carried out after preheating the quartz sand. The preheating temperature is controlled at 120-180℃ to promote the rapid wetting and coating of the resin on the surface of the sand particles.

7. The method for preparing high-performance coated sand according to claim 5, characterized in that, In step S1, the order of adding the modified bio-based phenolic resin, the grafted bifunctional interfacial activator, and the nano-antioxidant lubricating filler is as follows: first add the modified bio-based phenolic resin, then add the grafted bifunctional interfacial activator, and finally add the nano-antioxidant lubricating filler.

8. The method for preparing high-performance coated sand according to claim 5, characterized in that, The heating and curing process in step S2 includes a heating stage and a holding stage. The heating rate in the heating stage is controlled at 3 to 10 °C / min, and the temperature in the holding stage is maintained in the range of 150 to 250 °C.

9. The method for preparing high-performance coated sand according to claim 5, characterized in that, The screening operation in step S3 is carried out using a multi-stage screen combination with a screen particle size range of 30 to 70 mesh to ensure a stable and consistent particle size distribution of the final coated sand.

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