High-temperature-resistant ceramic coated sand for casting and preparation method thereof

Abstract

The present application relates to the technical field of coated sand for casting, in particular to a kind of high-temperature-resistant ceramsite coated sand for casting and a preparation method thereof, comprising the following processes: mixing ceramsite and iron red powder, heating to 300-400 DEG C;Placed in coated sand stirring machine, open stirring, when the system temperature drops to 120-140 DEG C, add resin, lubricant, graphite powder, stir until the system temperature drops to 50 DEG C, to obtain coated sand.The present application realizes the high-temperature-resistant property of the prepared coated sand by the high refractoriness and low thermal conductivity of high-alumina ceramsite, the high-temperature resistance and thermal conductivity of graphite powder, etc., and uses benzoxazine resin and polyurethane modified polyphenol resin as the resin system to improve the strength of the prepared coated sand under hot state and normal temperature, and to improve the collapsibility of the coated sand.

Description

Technical Field

[0001] This invention relates to the field of casting coated sand technology, specifically to a high-temperature resistant ceramic aggregate coated sand for casting and its preparation method. Background Technology

[0002] Coated sand is made by coating inorganic particles such as natural sand and sintered ceramsite with a solid resin. Due to its excellent flowability and filling properties, coated sand can produce castings with high precision and good surface quality. It is also widely used in the casting industry for producing cast steel and cast iron parts due to its minimal deformation and shrinkage when used as cores in high-pressure casting. Conventional coated sand uses phenolic resin for coating. While phenolic resin has excellent mechanical, heat-resistant, and flame-retardant properties, it also suffers from drawbacks similar to other thermosetting resins, such as poor toughness. Coated sand is prone to stress cracking at the interface, affecting its tensile strength, flexural strength, and thermal strength. Furthermore, the main aggregate in domestically produced high-temperature coated sand is high-silica sand, which has disadvantages such as large thermal expansion, large angular coefficient, and poor flowability, easily causing defects such as sand adhesion, veining, deformation, and cracking in castings. Therefore, we propose a high-temperature resistant ceramsite coated sand for casting and its preparation method. Summary of the Invention

[0003] The purpose of this invention is to provide a high-temperature resistant ceramic aggregate coated sand for casting and its preparation method, so as to solve the problems mentioned in the background art.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a high-temperature resistant ceramic aggregate coated sand for casting, comprising the following weight components: 100-150 parts ceramic aggregate, 1.5-5.0 parts resin, 0.5-1.0 parts graphite powder, 5-8 parts iron oxide red powder, and 0.10-0.50 parts lubricant.

[0005] Furthermore, the ceramsite is high-alumina sintered ceramsite sand, comprising the following weight components: 75-85% Al2O3, 12-20% SiO2, impurities Fe2O3 ≤ 3.0%, TiO2 ≤ 3.0%. The particle size of the ceramsite is 50-100 mesh.

[0006] In the coated sand material system, sintered ceramsite sand with high aluminum content is used. Its main component is Al2O3, which has high refractoriness, low thermal conductivity, and small thermal expansion. The content of impurities such as Fe2O3 and TiO2 is reduced to mitigate their negative impact on the refractoriness of the ceramsite.

[0007] Furthermore, the resin comprises the following components by weight: 80-90 parts benzoxazine resin, 10-20 parts polyurethane modified polyphenolic resin, 6-9 parts BT resin, 8-9 parts zinc chloride accelerator, and 3.2-3.6 parts silane coupling agent.

[0008] Furthermore, the silane coupling agent is KH550; the lubricant is calcium stearate.

[0009] Graphite powder: a mixture of flake graphite and earthy graphite in a mass ratio of 3:1, sourced from Qingdao Jinhai Graphite Products Co., Ltd., with a particle size of 140 mesh.

[0010] In the coated sand material system, flake graphite acts as a lubricant and provides high-temperature resistance, preventing agglomeration, improving the fluidity and release properties of the coated sand, and effectively preventing shelling during use. The addition of clay-like graphite provides good covering power for the ceramsite, reducing the amount of graphite powder and resin required, allowing the coated sand mold to maintain strength while exhibiting better collapsibility. Furthermore, the mixture of flake and clay-like graphite does not chemically react with the molten metal and is not wetted by metal or metal oxides, preventing graphite from carburizing the cast steel. Graphite powder has a strong cooling capacity for the molten metal, as well as strong heat absorption and thermal conductivity, accelerating heat conduction in the casting (liquid metal), speeding up its solidification, and reducing the penetration of molten metal into the coated sand mold.

[0011] Iron oxide red powder: sourced from Shijiazhuang Changli Mineral Products Co., Ltd., with a particle size of 200 mesh;

[0012] The main component of iron oxide red powder is Fe2O3. In the coated sand material system, it mainly acts as a flux, reacting with SiO2 on the surface of ceramic particles at high temperatures to enhance the adhesion between coated sand particles and improve the strength of the sand mold made from the coated sand. After casting, it acts as an oxidant, reacting with FeO present in the liquid metal to generate Fe3O4, preventing FeO from reacting with SiO2 and causing adhesion between the sand mold and the casting. At the same time, iron oxide red powder can also react with CO to generate CO2, alleviating sand adhesion. Furthermore, it can inhibit the decomposition of resin at high temperatures, preventing the generated activated carbon from causing expansion and cracking of the sand mold and reducing the formation of veins.

[0013] A method for preparing high-temperature resistant ceramic aggregate coated sand for casting includes the following processes:

[0014] Mix ceramsite and iron oxide powder, and heat to 300-400℃; place in a coated sand mixer, start stirring, and when the system temperature drops to 120-140℃, add benzoxazine resin, polyurethane modified polyphenolic resin, BT resin and silane coupling agent, stir for 30-40s, add accelerator zinc chloride and stir for 60s; add lubricant and graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand.

[0015] Furthermore, when using a type of high-temperature resistant ceramic aggregate coated sand for casting, the molding temperature is 210–250°C and the molding time is 180–240 seconds.

[0016] Furthermore, the benzoxazine resin is sourced from Chengdu Keyi Polymer Technology Co., Ltd.

[0017] BT resin: Mix 120g of bisphenol A isocyanate and 40g of bismaleimide, heat to 120℃ to melt, and stir for 30 minutes to obtain the resin.

[0018] Furthermore, the polyurethane-modified polyphenolic resin is prepared by the following process:

[0019] (1) Preparation of polyphenoxyphosphazene:

[0020] Dissolve 50g of polydichlorophosphazene in 250mL of tetrahydrofuran, add it to sodium phenolate solution, heat to 35-85℃ and stir under reflux for 20-48h; cool to room temperature, evaporate the solvent under reduced pressure, wash with deionized water and n-heptane, and dry in a vacuum drying oven at 60℃ to obtain polyphenoxyphosphazene.

[0021] The polyphenylene phosphazene comprises the following components by weight: 50 parts polydichlorophosphazene, 13.0 to 26.0 parts sodium aminophenolate, and 64.9 to 73.0 parts sodium salt of 2,2′-diallyl bisphenol A;

[0022] The sodium phenolate solution contains: 13.0–26.0 g sodium aminophenolate, 64.9–73.0 g sodium salt of 2,2′-diallyl bisphenol A, and 250 mL tetrahydrofuran;

[0023] Sodium salt of 2,2′-diallylbisphenol A is prepared by the following process: 1.5 mol of 2,2′-diallylbisphenol A is mixed with 1.0 mol of sodium hydroxide, heated to 170°C under nitrogen atmosphere, and stirred at 100 rpm for 1 h; then heated to 220°C, vacuumed at -0.1 MPa for 2 h.

[0024] (2) Preparation of polyurethane prepolymer:

[0025] Polyether polyol was placed in a vacuum at 120℃ for 2 hours to dehydrate, then cooled to 50-60℃, and 1,6-hexylene diisocyanate was added. The mixture was reacted in a nitrogen atmosphere for 3-10 hours. Polyphenylene phosphazene was then added and reacted at 50-60℃ for 30-60 minutes to obtain a polyurethane prepolymer.

[0026] The polyurethane prepolymer comprises the following components by weight: 100 parts polyether polyol, 52.0 to 57.2 parts 1,6-hexylene diisocyanate, and 18 to 20 parts polyphenoxyphosphazene.

[0027] Polyether polyol: sourced from Shandong Lanxing Dongda Chemical Co., Ltd., hydroxyl value (KOH) 28.2 mg / g, viscosity at 25℃ 870 mPa·s, molecular weight 4000;

[0028] (3) Preparation of polyurethane-modified polyphenolic resin:

[0029] Phenoxy resin was dissolved in anhydrous tetrahydrofuran and then added to a polyurethane prepolymer for blending to obtain polyurethane-modified polyphenolic resin.

[0030] The mass ratio of phenolic resin to polyurethane prepolymer is (3-5):1;

[0031] The ratio of phenolic resin to anhydrous tetrahydrofuran is 100g:(300-500)mL;

[0032] Phenoxy resin: PKHH, sourced from Dongguan Haosheng Plastic Raw Materials Co., Ltd.;

[0033] In the above technical solution, a composite curing resin system for coated sand is established using benzoxazine resin and polyurethane-modified polyphenolic resin as the resin system and zinc chloride as the curing accelerator. This system enables the prepared sand mold to have superior strength at both hot and room temperatures, while also improving the collapsibility of the coated sand and achieving a comprehensive improvement in the performance of the coated sand.

[0034] First, a polyurethane prepolymer was prepared using polyether polyol, polyphenoxyphosphazene, and 1,6-hexylene diisocyanate. This prepolymer, as a component of the resin material, promotes the carbonization of the resin in a reducing atmosphere (casting interface atmosphere). Heating causes resin dehydration, and the carbonization reduces the bonding force between the ceramsite and the resin, thus improving the collapsibility of the coated sand. The isocyanate groups at the end of the prepolymer were then introduced into the polyphenol oxyresin system to prepare a polyurethane-modified polyphenol oxyresin. This process is milder and improves the toughness and temperature resistance of the polyphenol oxyresin, enhances the adhesion and wettability of the resin to the ceramsite surface, strengthens the interfacial strength between the resin and the ceramsite, reduces thermal cracking at high temperatures, and alleviates adhesion fracture. Finally, the prepolymer was mixed with benzoxazine resin, and the benzoxazine resin and polyurethane-modified polyphenol oxyresin were co-cured. The oxazine rings in the benzoxazine resin were cured at high temperatures. Ring-opening polymerization generates -OH groups, which copolymerize with isocyanates in polyurethane-modified polyphenolic resin. The polyurethane-modified polyphenolic resin has a large molecular weight and strong polarity; its ether bonds and hydroxyl groups can form hydrogen bonds with the phenolic hydroxyl groups in the benzoxazine resin, creating an island-like structure that improves the toughness of the coated sand and enhances the flexural strength of the molded sand. Due to its good flexibility, it is distributed within the cross-linked network of the cured benzoxazine resin, reducing the cross-linking density of the resin, decreasing thermal cracking, and improving the temperature resistance of the coated sand. BT resin, a thermosetting resin copolymerized from bismaleimide and cyanate, can reinforce the resin. It can also react with the allyl groups in the polyurethane-modified polyphenolic resin, increasing cross-linking points and forming triazine ring groups, further improving the heat resistance and mechanical properties of the coated sand.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] The present invention relates to a high-temperature resistant ceramsite coated sand for casting and its preparation method. By utilizing the high refractoriness and low thermal conductivity of high-alumina ceramsite and the high-temperature resistance and thermal conductivity of graphite powder, the high-temperature resistant properties of the coated sand are achieved. Furthermore, benzoxazine resin and polyurethane-modified polyphenolic resin are used as the resin system to achieve co-curing, thereby improving the strength of the coated sand at both hot and room temperatures and enhancing its collapsibility. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0038] Polyether polyol: sourced from Shandong Lanxing Dongda Chemical Co., Ltd., hydroxyl value (KOH) 28.2 mg / g, viscosity at 25℃ 870 mPa·s, molecular weight 4000;

[0039] Phenoxy resin: PKHH, sourced from Dongguan Haosheng Plastic Raw Materials Co., Ltd.;

[0040] Benzoxazine resin: sourced from Chengdu Keyi Polymer Technology Co., Ltd.;

[0041] Graphite powder: a mixture of flake graphite and earthy graphite in a mass ratio of 3:1, sourced from Qingdao Jinhai Graphite Products Co., Ltd., with a particle size of 140 mesh;

[0042] Iron oxide red powder: sourced from Shijiazhuang Changli Mineral Products Co., Ltd., with a particle size of 200 mesh.

[0043] Polydichlorophosphazene was prepared by the following process: 100g of hexachlorocyclotriphosphazene, 1g of aminosulfonic acid, 0.1g of calcium sulfate dihydrate, and 120mL of 1,2,4-trichlorobenzene were mixed, stirred and heated to 190℃, and then slowly heated to 208℃ for 6h; the mixture was then poured into n-heptane to precipitate and wash.

[0044] The ceramsite is a high-alumina sintered ceramsite sand, comprising the following weight components: 78% Al2O3, 17% SiO2, 2.2% Fe2O3, and 1.8% TiO2. The particle size of the ceramsite is 50-100 mesh.

[0045] Example 1

[0046] (1) Preparation of polyurethane-modified polyphenolic resin:

[0047] 1.1. Preparation of polyphenoxyphosphazene:

[0048] Dissolve 50g of polydichlorophosphazene in 250mL of tetrahydrofuran, add to sodium phenolate solution, heat to 35℃ and stir under reflux for 20h; cool to room temperature, evaporate solvent under reduced pressure, wash with deionized water and n-heptane, and dry in a vacuum drying oven at 60℃ to obtain polyphenoxyphosphazene; the sodium phenolate solution contains: 26.0g of aminophenol sodium, 64.9g of sodium salt of 2,2′-diallyl bisphenol A, and 250mL of tetrahydrofuran;

[0049] 1.2. Preparation of polyurethane prepolymer:

[0050] Take 100g of polyether polyol and dehydrate it under vacuum at 120℃ for 2h. Cool it down to 50℃ and add 52.0g of 1,6-hexylene diisocyanate. React in a nitrogen atmosphere for 3h. Add 18g of polyphenoxyphosphazene and react at 50℃ for 30min to obtain polyurethane prepolymer.

[0051] 1.3. Preparation of polyurethane-modified polyphenolic resin:

[0052] Dissolve 100g of phenolic resin in 300mL of anhydrous tetrahydrofuran, add 20g of polyurethane prepolymer and blend to obtain polyurethane modified polyphenolic resin.

[0053] (2) Preparation of coated sand:

[0054] Mix 1000g of ceramsite and 50g of iron oxide powder, and heat to 300℃. Place the mixture in a coated sand mixer and start stirring. When the system temperature drops to 120℃, add 12.1g of benzoxazine resin, 1.4g of polyurethane modified polyphenol oxy resin, 0.6g of BT resin, and 0.4g of silane coupling agent KH550. Stir for 30s, then add 1.1g of accelerator zinc chloride and stir for 60s. Add 1.0g of lubricant calcium stearate and 5g of graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand.

[0055] Example 2

[0056] (1) Preparation of polyurethane-modified polyphenolic resin:

[0057] 1.1. Preparation of polyphenoxyphosphazene:

[0058] Dissolve 50g of polydichlorophosphazene in 250mL of tetrahydrofuran, add to sodium phenolate solution, heat to 60℃ and reflux for 36h; cool to room temperature, evaporate solvent under reduced pressure, wash with deionized water and n-heptane, and dry in a vacuum drying oven at 60℃ to obtain polyphenoxyphosphazene; the sodium phenolate solution contains: 19.5g of aminophenol sodium, 69.0g of sodium salt of 2,2′-diallyl bisphenol A, and 250mL of tetrahydrofuran;

[0059] 1.2. Preparation of polyurethane prepolymer:

[0060] 100g of polyether polyol was placed in a vacuum at 120℃ for 2 hours to dehydrate, then cooled to 55℃. 54.6g of 1,6-hexylene diisocyanate was added, and the mixture was reacted in a nitrogen atmosphere for 6 hours. 19g of polyphenoxyphosphazene was added, and the mixture was reacted at 55℃ for 45 minutes to obtain a polyurethane prepolymer.

[0061] 1.3. Preparation of polyurethane-modified polyphenolic resin:

[0062] Dissolve 100g of phenolic resin in 400mL of anhydrous tetrahydrofuran, add 26g of polyurethane prepolymer and blend to obtain polyurethane-modified polyphenolic resin.

[0063] (2) Preparation of coated sand:

[0064] Mix 1250g of ceramsite and 65g of iron oxide powder, and heat to 350℃. Place the mixture in a coated sand mixer and start stirring. When the system temperature drops to 130℃, add 24.7g of benzoxazine resin, 4.4g of polyurethane modified polyphenolic resin, 1.9g of BT resin, and 1.0g of silane coupling agent KH550. Stir for 35s, then add 2.4g of accelerator zinc chloride and stir for 60s. Add 3g of lubricant calcium stearate and 8g of graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand.

[0065] Example 3

[0066] (1) Preparation of polyurethane-modified polyphenolic resin:

[0067] 1.1. Preparation of polyphenoxyphosphazene:

[0068] Dissolve 50g of polydichlorophosphazene in 250mL of tetrahydrofuran, add to sodium phenolate solution, heat to 85℃ and reflux for 48h; cool to room temperature, evaporate solvent under reduced pressure, wash with deionized water and n-heptane, and dry in a vacuum drying oven at 60℃ to obtain polyphenoxyphosphazene; the sodium phenolate solution contains: 13.0g of aminophenol sodium, 73.0g of sodium salt of 2,2′-diallyl bisphenol A, and 250mL of tetrahydrofuran;

[0069] 1.2. Preparation of polyurethane prepolymer:

[0070] Take 100g of polyether polyol and dehydrate it under vacuum at 120℃ for 2h. Cool it down to 60℃ and add 57.2g of 1,6-hexylene diisocyanate. React in a nitrogen atmosphere for 10h. Add 20g of polyphenoxyphosphazene and react at 60℃ for 60min to obtain polyurethane prepolymer.

[0071] 1.3. Preparation of polyurethane-modified polyphenolic resin:

[0072] Dissolve 100g of phenolic resin in 500mL of anhydrous tetrahydrofuran, add 33g of polyurethane prepolymer and blend to obtain polyurethane-modified polyphenolic resin.

[0073] (2) Preparation of coated sand:

[0074] Mix 1500g of ceramsite and 80g of iron oxide powder, and heat to 400℃. Place the mixture in a coated sand mixer and start stirring. When the system temperature drops to 140℃, add 32.0g of benzoxazine resin, 8.9g of polyurethane modified polyphenol oxy resin, 3.5g of BT resin, and 1.6g of silane coupling agent KH550. Stir for 40s, then add 4.0g of accelerator zinc chloride and stir for 60s. Add 5g of lubricant calcium stearate and 10g of graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand.

[0075] Comparative Example 1

[0076] (1) Preparation of polyurethane-modified polyphenolic resin:

[0077] 1.1. Preparation of polyurethane prepolymer:

[0078] 100g of polyether polyol was placed in a vacuum at 120℃ for 2 hours to dehydrate, then cooled to 50℃. 52.0g of 1,6-hexylene diisocyanate was added, and the mixture was reacted in a nitrogen atmosphere for 3 hours. 2g of diethylamine was added, and the mixture was reacted at 50℃ for 30 minutes to obtain a polyurethane prepolymer.

[0079] 1.2. Preparation of polyurethane-modified polyphenolic resin:

[0080] Dissolve 100g of phenolic resin in 300mL of anhydrous tetrahydrofuran, add 20g of polyurethane prepolymer and blend to obtain polyurethane modified polyphenolic resin.

[0081] (2) Preparation of coated sand:

[0082] Mix 1000g of ceramsite and 50g of iron oxide powder, and heat to 300℃. Place the mixture in a coated sand mixer and start stirring. When the system temperature drops to 120℃, add 12.1g of benzoxazine resin, 1.4g of polyurethane modified polyphenol oxy resin, 0.6g of BT resin, and 0.4g of silane coupling agent KH550. Stir for 30s, then add 1.1g of accelerator zinc chloride and stir for 60s. Add 1.0g of lubricant calcium stearate and 5g of graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand.

[0083] Comparative Example 2

[0084] (1) Preparation of modified polyphenolic resin:

[0085] 100g of phenolic resin was dissolved in 300mL of anhydrous tetrahydrofuran. Under a nitrogen atmosphere, 7g of 1,6-hexylene diisocyanate was added and stirred for 3h to obtain modified polyphenolic resin.

[0086] (2) Preparation of coated sand:

[0087] Mix 1000g of ceramsite and 50g of iron oxide powder, and heat to 300℃. Place the mixture in a coated sand mixer and start stirring. When the system temperature drops to 120℃, add 12.1g of benzoxazine resin, 1.4g of polyurethane modified polyphenol oxy resin, 0.6g of BT resin, and 0.4g of silane coupling agent KH550. Stir for 30s, then add 1.1g of accelerator zinc chloride and stir for 60s. Add 1.0g of lubricant calcium stearate and 5g of graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand.

[0088] Comparative Example 3

[0089] Mix 1000g of ceramsite and 50g of iron oxide powder, and heat to 300℃. Place the mixture in a coated sand mixer and start stirring. When the system temperature drops to 120℃, add 13.5g of benzoxazine resin, 0.6g of BT resin, and 0.4g of silane coupling agent KH550, and stir for 30s. Add 1.1g of accelerator zinc chloride and stir for 60s. Add 1.0g of lubricant calcium stearate and 5g of graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand.

[0090] Comparative Example 4

[0091] Mix 1000g of ceramsite and 50g of iron oxide powder, and heat to 300℃. Place the mixture in a coated sand mixer and start stirring. When the system temperature drops to 120℃, add 13.5g of phenolic resin (1391, sourced from Jinan Dahui Chemical Technology Co., Ltd.), 0.6g of BT resin, and 0.4g of silane coupling agent KH550. Stir for 30 seconds, then add 1.1g of accelerator zinc chloride and stir for 60 seconds. Add 1.0g of lubricant calcium stearate and 5g of graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand.

[0092] Comparative Example 5

[0093] Mix 1000g of ceramsite and 50g of iron oxide powder, and heat to 300℃. Place the mixture in a coated sand mixer and start stirring. When the system temperature drops to 120℃, add 13.5g of phenolic resin (1391, sourced from Jinan Dahui Chemical Technology Co., Ltd.) and 0.4g of silane coupling agent KH550, and stir for 30s. Add 1.1g of accelerator zinc chloride and stir for 60s. Add 1.0g of lubricant calcium stearate and 5g of graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand.

[0094] Comparative Example 6

[0095] Mix 1000g of ceramsite and heat to 300℃; place in a coated sand mixer and start stirring. When the system temperature drops to 120℃, add 13.5g of phenolic resin (1391, from Jinan Dahui Chemical Technology Co., Ltd.) and 0.4g of silane coupling agent KH550, stir for 30s, add 1.1g of accelerator zinc chloride and stir for 60s; add 1.0g of lubricant calcium stearate and stir until the system temperature drops to 50℃ to obtain coated sand.

[0096] experiment

[0097] The coated sand obtained in Examples 1-3 and Comparative Examples 1-6 was used to prepare "8"-shaped standard specimens. The molding temperature was 230℃ and the molding time was 210s. The hot tensile strength, room temperature tensile strength, and heat resistance time (refer to standards JB / T 8583—2008 and JB / T 13037—2017) were tested and the test results were recorded.

[0098] Collapse test: Wrap the sample in tin foil, place it in a muffle furnace at 500℃ for 10 min, remove it and cool it to room temperature, then sieve it on a 20-mesh sieve for 2 min. Calculate the mass change rate of the sample before and after the experiment, and record it as the collapse rate.

[0099] Hot tensile strength (MPa) Tensile strength at room temperature (MPa) Heat resistance time (s) Collapse rate (%) Example 1 1.90 5.51 251 78.0 Example 2 1.98 5.69 260 83.4 Example 3 2.03 5.82 267 87.4 Comparative Example 1 1.86 5.40 245 75.6 Comparative Example 2 1.78 5.27 240 74.8 Comparative Example 3 1.72 4.85 238 72.2 Comparative Example 4 1.67 4.60 225 68.7 Comparative Example 5 1.53 3.87 214 63.0 Comparative Example 6 1.45 3.60 195 60.5

[0100] Based on the data in the table above, the following conclusions can be clearly drawn:

[0101] The coated sand obtained in Examples 1-3 was compared with the coated sand obtained in Comparative Examples 1-6. The test results show that...

[0102] Compared with the comparative examples, the coated sand obtained in Examples 1-3 has higher hot tensile strength, room temperature tensile strength, heat resistance time and collapse rate data, which fully demonstrates that the present invention has achieved the improvement of the heat resistance, collapse and mechanical properties of the prepared coated sand.

[0103] Compared with Example 1, in Comparative Example 1, the component polyphenylene phosphazene was replaced with diethylamine; in Comparative Example 2, the modified polyphenol oxy resin was prepared from phenol oxy resin and 1,6-hexanediisocyanate; in Comparative Example 3, the polyurethane modified polyphenol oxy resin was replaced with an equal mass of benzoxazine resin; in Comparative Example 4, based on Comparative Example 3, the benzoxazine resin was replaced with phenolic resin; compared with Comparative Example 4, the component BT resin was removed in Comparative Example 5, and the components iron oxide red powder and graphite powder were removed in Comparative Example 6. The hot tensile strength, room temperature tensile strength, heat resistance time and collapse rate data deteriorated. It can be seen that the settings of the coating sand components and their preparation process in this application can promote the improvement of the heat resistance, collapse and mechanical properties of the coating sand.

[0104] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process method article or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process method article or apparatus.

[0105] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-temperature resistant ceramic aggregate coated sand for casting, characterized in that... The process includes the following: Mix ceramsite and iron oxide powder, and heat to 300-400℃; place in a coated sand mixer, turn on the mixer, and when the system temperature drops to 120-140℃, add resin, lubricant, and graphite powder, and stir until the system temperature drops to 50℃ to obtain coated sand; The resin comprises the following components by weight: 80-90 parts benzoxazine resin, 10-20 parts polyurethane modified polyphenolic resin, 6-9 parts BT resin, 8-9 parts zinc chloride accelerator, and 3.2-3.6 parts silane coupling agent; The polyurethane-modified polyphenolic resin is prepared by the following process: polyether polyol is placed in a vacuum for dehydration and then cooled, 1,6-hexanediisocyanate is added, and the reaction is carried out in a nitrogen atmosphere; then polyphenoxyphosphazene is added, and the reaction is carried out to obtain a polyurethane prepolymer; the phenolic resin is dissolved in anhydrous tetrahydrofuran, and the polyurethane prepolymer is added and blended to obtain the polyurethane-modified polyphenolic resin. The polyphenoxyphosphazene is prepared by the following process: polydichlorophosphazene is dissolved in tetrahydrofuran and added to a sodium phenolate solution containing sodium aminophenolate and sodium salt of 2,2'-diallylbisphenol A. The mixture is heated and stirred under reflux. After cooling to room temperature, the solvent is removed by vacuum evaporation. The mixture is washed with deionized water and n-heptane and then dried in a vacuum drying oven to obtain polyphenoxyphosphazene. The ceramsite is high-alumina sintered ceramsite sand, comprising 75~85wt% Al2O3 and 12~20wt% SiO2.

2. The method for preparing high-temperature resistant ceramic aggregate coated sand for casting according to claim 1, characterized in that... The coated sand comprises the following components by weight: 100-150 parts ceramsite, 1.5-5.0 parts resin, 0.5-1.0 parts graphite powder, 5-8 parts iron oxide red powder, and 0.10-0.50 parts lubricant.

3. The method for preparing high-temperature resistant ceramic aggregate coated sand for casting according to claim 1, characterized in that... The silane coupling agent is KH550; the lubricant is calcium stearate.

4. The method for preparing high-temperature resistant ceramic aggregate coated sand for casting according to claim 1, characterized in that... The polyphenylene phosphazene comprises the following components by weight: 50 parts polydichlorophosphazene, 13.0~26.0 parts sodium aminophenolate, and 64.9~73.0 parts sodium salt of 2,2'-diallyl bisphenol A.

5. The method for preparing high-temperature resistant ceramic aggregate coated sand for casting according to claim 1, characterized in that... The polyurethane prepolymer comprises the following components by weight: 100 parts polyether polyol, 52.0~57.2 parts 1,6-hexanediisocyanate, and 18~20 parts polyphenoxyphosphazene.

6. The method for preparing high-temperature resistant ceramic aggregate coated sand for casting according to claim 1, characterized in that... The BT resin is prepared by melt mixing of bisphenol A isocyanate and bismaleimide.

7. A casting high-temperature resistant ceramic particle coated sand prepared by the preparation method according to any one of claims 1-6.

8. The high-temperature resistant ceramic aggregate coated sand for casting according to claim 7, characterized in that: When in use, the molding temperature is 210~250℃ and the molding time is 180~240s.