Environment-friendly regenerated precoated sand and preparation method thereof

Abstract

The invention discloses environment-friendly regenerated precoated sand and a preparation method thereof, and belongs to the technical field of camshaft casting precoated sand. The environment-friendly regenerated precoated sand comprises the following components in percentage by mass: 94%-96% of regenerated quartz sand, 1.5%-2% of phenolic resin, 0.8%-1.2% of a curing agent, 0.1%-0.5% of a lubricating agent, 0.3%-0.5% of iron oxide powder, 0.1%-0.3% of silicon carbide, 0.3%-0.5% of a silane coupling agent and 0.5%-1% of water glass. The preparation method of the regenerated quartz sand comprises the following steps: crushing waste sand cores to obtain used sand with the particle size of 1-3mm; the used sand is heated; the heated old sand is rapidly cooled; the cooled used sand is roasted; and cooling to room temperature to obtain regenerated quartz sand. By the adoption of the environment-friendly regenerated precoated sand and the preparation method thereof, the problems that existing precoated sand is high in gas forming amount, low in strength, poor in high temperature resistance and difficult to recycle can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of camshaft casting coated sand, and particularly relates to an environmentally friendly recycled coated sand and a preparation method thereof. Background Art

[0002] Coated sand is an important material in the casting process. The main skeleton materials used in coated sand mainly include quartz sand, ceramsite sand, and perlite sand as the original sand. A thermoplastic phenolic resin is added to the original sand as a binder, and then a curing agent and a lubricant are added to form a resin layer on the surface of the original sand. Under heating conditions, the resin is cured under the action of the curing agent and bonded together by sand grains to form a sand mold. During the high-temperature casting process, the phenolic resin decomposes and generates gas. If the gas cannot overflow from the molten metal in time, it will remain on the surface or inside of the molten metal, forming defects such as shrinkage cavities or shrinkage porosity, affecting the quality of the casting. Especially during the casting process of cast iron camshafts, the casting temperature of cast iron camshafts reaches 1400 °C. Using less phenolic resin will result in low strength of the sand mold, serious sand sticking on the surface of the casting, and even collapse of the sand mold, affecting the forming quality of the casting. Adding more phenolic resin will result in a relatively large gas generation amount of the sand mold, easily forming hole defects on the casting, and also affecting the quality of the casting.

[0003] The existing patent CN202111658513.8 discloses a high-temperature resistant coated sand and a preparation method thereof. Using 90-96% high-silica recycled sand and 4-10% natural iron ore sand as aggregates, a phenolic resin modified with isopropyltriphenyl phosphate, combined with high-temperature resistant additives and graphite, is stirred, mixed, and reacted in a mixing device. The prepared coated sand has high strength and good thermal conductivity, can meet the needs of some heavier valve castings, and broadens the application field of coated sand. However, the gas evolution amount of this patent is relatively high.

[0004] The existing patent CN202210995462.6 discloses an environmentally friendly coated sand and its preparation method, including: silica sand, phenolic resin, curing agent hexamethylenetetramine, lubricant calcium stearate, and environmental protection agent; the environmental protection agent is polyacrylonitrile-based activated carbon fiber. The preparation method of the coated sand includes: (1) heating the silica sand to a predetermined temperature of 170°C - 200°C and adding it to the sand mixing bucket; (2) adding the phenolic resin into the sand mixing bucket and stirring evenly; (3) adding the hexamethylenetetramine aqueous solution into the sand mixer and stirring evenly to form a mixture; (4) when the temperature of the mixture drops to 120 - 130°C, adding the environmental protection agent into the sand mixing bucket and stirring evenly; (5) adding a coolant and stirring to reduce the sand temperature, so that the resin film becomes a solid resin film after cooling; (6) when the temperature of the mixture drops to 70 - 100°C, adding the lubricant calcium stearate powder and stirring evenly; (7) packaging. The above-mentioned coated sand absorbs harmful gases during low-temperature core making and absorbs the harmful gases released by phenolic resin during high-temperature casting, thereby achieving the purpose of reducing the gas evolution. However, the above patent adds polyacrylonitrile-based activated carbon fiber to the coated sand, resulting in poor high-temperature resistance and being not conducive to the recycling of the coated sand. Summary of the Invention

[0005] The purpose of the present invention is to provide an environmentally friendly recycled coated sand and its preparation method to solve the problems of high gas evolution, low strength, poor high-temperature resistance, and difficult recycling of the existing coated sand.

[0006] To achieve the above purpose, the present invention provides an environmentally friendly recycled coated sand, including the following components in mass percentage: recycled quartz sand 94% - 96%, phenolic resin 1.5% - 2%, curing agent 0.8% - 1.2%, lubricant 0.1% - 0.5%, iron oxide powder 0.3% - 0.5%, silicon carbide 0.1% - 0.3%, silane coupling agent 0.3% - 0.5%, water glass 0.5% - 1%.

[0007] Preferably, the curing agent is a hexamethylenetetramine aqueous solution, and the solute mass percentage content of the hexamethylenetetramine aqueous solution is 40% - 50%.

[0008] Preferably, the lubricant is calcium stearate.

[0009] Preferably, the particle size of the iron oxide powder is 200 mesh - 500 mesh.

[0010] Preferably, the particle size of the silicon carbide is 1000 mesh - 1500 mesh.

[0011] The preparation method of the above-mentioned environmentally friendly recycled coated sand includes the following steps: S1. Prepare recycled quartz sand; weigh each raw material according to the raw material ratio; S2. Preheat the recycled quartz sand, add phenolic resin, sodium silicate, and silane coupling agent to the heated recycled quartz sand, and stir evenly. S3. Add curing agent, lubricant, iron oxide powder, and silicon carbide to the recycled quartz sand, and stir evenly. S4. After cooling to room temperature, obtain recycled coated sand.

[0012] Preferably, in S1, the preparation method of the recycled quartz sand includes the following steps: S11. Crush the waste sand core, then perform magnetic separation and screening to obtain used sand with a particle size of 1 mm - 3 mm. S12. Heat the used sand. S13. Put the heated used sand into cold water for rapid cooling. S14. Dry and screen the cooled used sand, and then perform roasting. S15. Cool the roasted used sand to room temperature to obtain recycled quartz sand.

[0013] Preferably, in S12, the heating temperature is 200°C - 400°C, and the heating time is 1 min - 3 min; in S13, the temperature of the cold water is not higher than 30°C.

[0014] Preferably, in S14, the roasting temperature is 600°C - 700°C, and the roasting time is 20 min - 40 min.

[0015] Preferably, in S2, the preheating temperature of the recycled quartz sand is 110°C - 130°C.

[0016] The advantages and positive effects of the environmentally friendly recycled coated sand and its preparation method of the present invention are as follows: 1. In the present invention, sodium silicate binder is added to the coated sand, reducing the usage amount of phenolic resin, which is beneficial to reducing the gas evolution. Phenolic resin and sodium silicate are connected through silane coupling agent, improving the connection strength of the coated sand. The gas generated by the thermal decomposition of phenolic resin acts on sodium silicate, which is beneficial to the collapsibility of the coated sand.

[0017] 2. In the present invention, ferric oxide and silicon carbide are added to the coated sand, which is beneficial to improving the cooling efficiency of the molten metal on the surface of the casting, reducing the erosion of the gas on the surface of the casting, and beneficial to improving the surface quality of the casting. Ferric oxide and silicon carbide adhere to the surface of the quartz sand, improving the surface wear resistance and strength of the quartz sand, enhancing the strength of the sand mold, and reducing the sand sticking phenomenon.

[0018] 3. Silicon carbide reacts with silane coupling agent, further improving the adhesion strength of iron oxide on the surface of the quartz sand.

[0019] 4. The present invention treats used sand by means of rapid heating and rapid cooling, which is conducive to the rupture and peeling of the surface film layer of the used sand under the action of stress. Then, heating is carried out to further remove the organic substances attached to the surface of the used sand, realizing the recycling and reuse of the used sand, and also being conducive to improving the strength of the recycled coated sand.

[0020] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flowchart for preparing the recycled coated sand of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. In case of inconsistency, the meaning described in this specification or the meaning derived from the content recorded in this specification shall prevail. In addition, the terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application. For the purpose of accurately describing the technical content in this application and for accurately understanding the present invention, the following explanations or definitions of the terms used in this specification are given before describing the specific embodiments: The embodiments of the present invention will be described in detail below with reference to the drawings.

[0023] An environmentally friendly recycled coated sand comprises the following components by mass percentage: recycled quartz sand 94% - 96%, phenolic resin 1.5% - 2%, curing agent 0.8% - 1.2%, lubricant 0.1% - 0.5%, iron oxide powder 0.3% - 0.5%, silicon carbide 0.1% - 0.3%, silane coupling agent 0.3% - 0.5%, and sodium silicate 0.5% - 1%.

[0024] The curing agent is an aqueous solution of hexamethylenetetramine, and the solute mass percentage content of the aqueous solution of hexamethylenetetramine is 40% - 50%.

[0025] During the heating and molding process of the sand mold, hexamethylenetetramine reacts with the phenolic resin to form a three-dimensional network structure, realizing the curing of the resin and connecting the quartz sand together to form a sand mold. The silane coupling agent in the coated sand can promote the curing of the phenolic resin, enabling the phenolic resin to form a three-dimensional network structure faster, improving the curing efficiency of the phenolic resin, and also being conducive to improving the mechanical properties of the coated sand.

[0026] The lubricant is calcium stearate.

[0027] The particle size of the iron oxide powder is 200 mesh - 500 mesh.

[0028] Iron oxide powder adheres to the surface of quartz sand. Under high-temperature casting conditions, iron oxide powder reacts with quartz sand to form a dense protective layer on the surface of the sand mold that is resistant to high temperatures and erosion. It also improves the quality of the sand mold surface, prevents the sand mold from deforming or collapsing at high temperatures, and improves the casting quality of the casting. The dense protective layer formed on the surface of the sand mold can also reduce the overflow of gas generated by the thermal decomposition of phenolic resin, reduce gas generation, and improve the surface quality of the casting. The chilling effect of iron oxide powder on the molten metal can promote the cooling of the casting surface, reduce gas erosion, and improve the surface quality of the casting.

[0029] The particle size of silicon carbide is 1000 mesh to 1500 mesh.

[0030] Silicon carbide and iron oxide both adhere to the surface of quartz sand, forming a dense protective layer on the surface of quartz sand during the casting process. Small-sized silicon carbide fills between iron oxide particles, further improving the density of the surface protective layer. The gas generated by the decomposition of phenolic resin during the casting process acts on the protective layer, generating micro cracks on the inner surface of the protective layer, which is conducive to the collapse of the sand mold.

[0031] Silicon carbide has a high melting point (2700℃) and excellent thermal stability. Adding silicon carbide to coated sand can greatly improve its high temperature resistance and effectively resist the high temperature during the casting process. During the casting process of the cast iron camshaft, the casting temperature is above 1400℃. The casting temperature is relatively high. Ordinary coated sand is difficult to withstand such a high temperature, and it is easy to have problems such as sand mold deformation and collapse, which affects the casting quality of the camshaft. Adding silicon carbide to coated sand can improve the high temperature resistance of the coated sand, maintain the integrity of the sand mold, and ensure the dimensional accuracy and surface quality of the casting.

[0032] Silicon carbide itself has high hardness and strength. Adding it to coated sand can significantly enhance its mechanical properties, improve the compressive strength and wear resistance of the coated sand, and make the sand mold less likely to be damaged when subjected to impact and erosion by molten metal, thereby improving the casting quality of the casting.

[0033] The good thermal conductivity of silicon carbide can promote rapid heat dissipation in the sand mold during the casting process, help the metal liquid to solidify quickly, refine the grain structure, and improve the quality and performance of the casting. The rapidly solidified casting surface can also prevent the gas generated by the decomposition of the phenolic resin binder under high-temperature casting from eroding the casting, avoid the formation of pores on the casting surface, and improve the casting quality of the casting.

[0034] In addition to the phenolic resin binder, the binder also contains water glass binder, which can reduce the usage of the phenolic resin binder, reduce the gas production of the coated sand, and is beneficial to improving the surface quality of the casting.

[0035] A silane coupling agent is added to the recycled coated sand. The hydrolyzable groups in the silane coupling agent undergo hydrolysis reactions under the action of water to generate silanol groups, and the silanol groups undergo condensation reactions with the silanol groups ionized from sodium silicate. The amino groups in the silane coupling agent can undergo chemical reactions with the hydroxymethyl groups in the phenolic resin, improving the crosslinking density and performance of the phenolic resin. The silane coupling agent introduces organic groups into sodium silicate, increasing the compatibility and connection strength between sodium silicate and phenolic resin, and enhancing the connection strength between quartz sands. The active groups in the silane coupling agent can react with silicon carbide to form stable chemical bonds, improving the adhesion of silicon carbide on the surface of quartz sand.

[0036] During the casting process, the gas generated by the thermal decomposition of the phenolic resin acts on the high-strength crystals generated after the heating of sodium silicate. After the phenolic resin decomposes, there are many pores and stress on the crystals of sodium silicate, which is beneficial to the collapsibility of the coated sand.

[0037] As Figure 1 shown. The preparation method of the above environmentally friendly recycled coated sand includes the following steps: S1. Prepare recycled quartz sand; weigh each raw material according to the raw material ratio.

[0038] S2. Preheat the recycled quartz sand, and add phenolic resin, sodium silicate, and silane coupling agent to the preheated recycled quartz sand, and stir evenly. Stir evenly in the sand mixing cylinder, and the stirring time is 40S - 60S.

[0039] The preheating temperature of the recycled quartz sand is 110°C - 130°C. At the preheating temperature, the phenolic resin melts, and the phenolic resin and sodium silicate coat the surface of the recycled quartz sand.

[0040] S3. Add curing agent, lubricant, iron oxide powder, and silicon carbide to the recycled quartz sand, and stir evenly. The stirring time is 60S - 80S.

[0041] S4. After cooling to room temperature, obtain the recycled coated sand.

[0042] The preparation method of the recycled quartz sand includes the following steps: S11. Crush the waste sand core, and then perform magnetic separation and screening to obtain used sand with a particle size of 1mm - 3mm. Remove the impurities and iron impurities inside the coated sand through magnetic separation and screening.

[0043] S12. Heat the used sand.

[0044] The heating temperature is 200°C - 400°C, and the heating time is 1min - 3min.

[0045] S13. Put the heated used sand into cold water for rapid cooling.

[0046] The temperature of the cold water is not higher than 30°C.

[0047] The used sand is heated by a rapid heating method, so that the iron oxide, silicon carbide and sodium silicate adhering to the surface of the used sand form a high-hardness and dense substance during the pouring process, and the heat is unevenly distributed within a very short heating time, forming a large internal stress inside. Then it is quickly put into cold water for cooling. Due to the effect of thermal expansion and contraction, it undergoes brittle fracture under stress, causing it to peel off on the surface of the quartz sand, which is beneficial to the peeling of the inorganic substances on the surface of the quartz sand.

[0048] S14. Dry and screen the cooled used sand, and then perform roasting.

[0049] The roasting temperature is 600°C - 700°C, and the roasting time is 20 min - 40 min. Roasting the quartz sand further removes the organic substances adhering to the surface of the quartz sand, improves the surface smoothness of the quartz sand, is beneficial to the recycling and reuse of the quartz sand, and improves the quality of the regenerated coated sand.

[0050] S15. Cool the roasted used sand to room temperature to obtain regenerated quartz sand.

[0051] Example 1 An environmentally friendly regenerated coated sand includes the following components by mass percentage: regenerated quartz sand 95.8%, phenolic resin 1.5%, curing agent 1.0%, lubricant 0.2%, iron oxide powder 0.3%, silicon carbide 0.2%, silane coupling agent 0.3%, sodium silicate 0.7%.

[0052] The curing agent is an aqueous solution of hexamethylenetetramine, and the solute mass percentage content of the aqueous solution of hexamethylenetetramine is 40%.

[0053] The lubricant is calcium stearate.

[0054] The particle size of the iron oxide powder is 300 mesh.

[0055] The particle size of the silicon carbide is 1000 mesh.

[0056] The silane coupling agent is KH550.

[0057] The preparation method of the above-mentioned environmentally friendly regenerated coated sand includes the following steps: S1. Prepare regenerated quartz sand; weigh each raw material according to the raw material ratio.

[0058] S2. Preheat the regenerated quartz sand, add the phenolic resin, sodium silicate and silane coupling agent to the heated regenerated quartz sand, and stir evenly. Stir evenly in the sand mixing cylinder, and the stirring time is 50S.

[0059] The preheating temperature of the regenerated quartz sand is 110°C.

[0060] S3. Add the curing agent, lubricant, iron oxide powder, and silicon carbide into the recycled silica sand and stir evenly. The stirring time is 60S.

[0061] S4. After cooling to room temperature, the recycled coated sand is obtained.

[0062] The preparation method of the recycled silica sand includes the following steps: S11. Crush the waste sand core, then perform magnetic separation and screening to obtain used sand with a particle size of 1mm.

[0063] S12. Heat the used sand.

[0064] The heating temperature is 200°C and the heating time is 2 min.

[0065] S13. Put the heated used sand into cold water for rapid cooling.

[0066] The temperature of the cold water is 30°C.

[0067] S14. Dry and screen the cooled used sand, and then perform roasting.

[0068] The roasting temperature is 600°C and the roasting time is 30 min.

[0069] S15. Cool the roasted used sand to room temperature to obtain the recycled silica sand.

[0070] Example 2 An environmentally friendly recycled coated sand includes the following components by mass percentage: 95.1% recycled silica sand, 1.8% phenolic resin, 1.0% curing agent, 0.3% lubricant, 0.4% iron oxide powder, 0.2% silicon carbide, 0.4% silane coupling agent, and 0.8% sodium silicate.

[0071] The curing agent is an aqueous solution of hexamethylenetetramine, and the mass percentage of the solute in the aqueous solution of hexamethylenetetramine is 45%.

[0072] The lubricant is calcium stearate.

[0073] The particle size of the iron oxide powder is 300 mesh.

[0074] The particle size of the silicon carbide is 1200 mesh.

[0075] The silane coupling agent is KH550.

[0076] The preparation method of the above environmentally friendly recycled coated sand includes the following steps: S1. Prepare the recycled silica sand; weigh each raw material according to the raw material ratio.

[0077] S2. Preheat the recycled quartz sand, add phenolic resin, sodium silicate, and silane coupling agent to the heated recycled quartz sand, and stir evenly. Stir evenly in the sand mixer for 50S.

[0078] The preheating temperature of the recycled quartz sand is 120 °C.

[0079] S3. Add the curing agent, lubricant, iron oxide powder, and silicon carbide to the recycled quartz sand, and stir evenly. The stirring time is 70S.

[0080] After cooling to room temperature, recycled coated sand is obtained.

[0081] The preparation method of the recycled quartz sand includes the following steps: S11. Crush the waste sand core, then perform magnetic separation and screening to obtain used sand with a particle size of 2 mm.

[0082] S12. Heat the used sand.

[0083] The heating temperature is 300 °C, and the heating time is 2 min.

[0084] S13. Put the heated used sand into cold water for rapid cooling.

[0085] The temperature of the cold water is 25 °C.

[0086] S14. Dry and screen the cooled used sand, and then perform roasting.

[0087] The roasting temperature is 700 °C, and the roasting time is 20 min.

[0088] S15. Cool the roasted used sand to room temperature to obtain recycled quartz sand.

[0089] Example 3 An environmentally friendly recycled coated sand includes the following components by mass percentage: 95.5% recycled quartz sand, 1.6% phenolic resin, 1.0% curing agent, 0.3% lubricant, 0.5% iron oxide powder, 0.3% silicon carbide, 0.3% silane coupling agent, and 0.5% sodium silicate.

[0090] The curing agent is an aqueous solution of hexamethylenetetramine, and the solute mass percentage content of the aqueous solution of hexamethylenetetramine is 40%.

[0091] The lubricant is calcium stearate.

[0092] The particle size of the iron oxide powder is 500 mesh.

[0093] The particle size of the silicon carbide is 1500 mesh.

[0094] The silane coupling agent is KH550.

[0095] The preparation method of the above-mentioned environmentally friendly recycled coated sand comprises the following steps: S1. Prepare recycled quartz sand; weigh each raw material according to the raw material ratio.

[0096] S2. Preheat the recycled quartz sand, add phenolic resin, sodium silicate, and silane coupling agent to the heated recycled quartz sand, and stir evenly. Stir evenly in the sand mixing cylinder, and the stirring time is 50S.

[0097] The preheating temperature of the recycled quartz sand is 110°C.

[0098] S3. Add curing agent, lubricant, iron oxide powder, and silicon carbide to the recycled quartz sand, and stir evenly. The stirring time is 80S.

[0099] S4. After cooling to room temperature, obtain recycled coated sand.

[0100] The preparation method of the recycled quartz sand comprises the following steps: S11. Crush the waste sand core, then perform magnetic separation and screening to obtain used sand with a particle size of 3mm.

[0101] S12. Heat the used sand.

[0102] The heating temperature is 300°C, and the heating time is 3min.

[0103] S13. Put the heated used sand into cold water for rapid cooling.

[0104] The temperature of the cold water is 25°C.

[0105] S14. Dry and screen the cooled used sand, and then perform roasting.

[0106] The roasting temperature is 700°C, and the roasting time is 30min.

[0107] S15. Cool the roasted used sand to room temperature to obtain recycled quartz sand.

[0108] Example 4 An environmentally friendly recycled coated sand comprises the following components by mass percentage: 94.5% of recycled quartz sand, 1.9% of phenolic resin, 1.2% of curing agent, 0.5% of lubricant, 0.4% of iron oxide powder, 0.3% of silicon carbide, 0.3% of silane coupling agent, and 0.9% of sodium silicate.

[0109] The curing agent is an aqueous solution of hexamethylenetetramine, and the solute mass percentage content of the aqueous solution of hexamethylenetetramine is 50%.

[0110] The lubricant is calcium stearate.

[0111] The particle size of the iron oxide powder is 200 mesh.

[0112] The particle size of silicon carbide is 1500 mesh.

[0113] The silane coupling agent is KH550.

[0114] The preparation method of the above-mentioned environmentally friendly recycled coated sand includes the following steps: S1. Prepare recycled quartz sand; weigh each raw material according to the raw material ratio.

[0115] S2. Preheat the recycled quartz sand, add phenolic resin, water glass, and silane coupling agent to the heated recycled quartz sand, and stir evenly. Stir evenly in the sand mixing cylinder, and the stirring time is 60S.

[0116] The preheating temperature of the recycled quartz sand is 110°C.

[0117] S3. Add the curing agent, lubricant, iron oxide powder, and silicon carbide to the recycled quartz sand, and stir evenly. The stirring time is 80S.

[0118] S4. After cooling to room temperature, obtain the recycled coated sand.

[0119] The preparation method of the recycled quartz sand includes the following steps: S11. Crush the waste sand core, then perform magnetic separation and screening to obtain used sand with a particle size of 3mm.

[0120] S12. Heat the used sand.

[0121] The heating temperature is 300°C, and the heating time is 2min.

[0122] S13. Put the heated used sand into cold water for rapid cooling.

[0123] The temperature of the cold water is 25°C.

[0124] S14. Dry and screen the cooled used sand, and then perform roasting.

[0125] The roasting temperature is 700°C, and the roasting time is 20min.

[0126] S15. Cool the roasted used sand to room temperature to obtain recycled quartz sand.

[0127] Example 5 An environmentally friendly recycled coated sand, comprising the following components by mass percentage: 95.6% of recycled quartz sand, 1.6% of phenolic resin, 0.8% of curing agent, 0.1% of lubricant, 0.3% of iron oxide powder, 0.3% of silicon carbide, 0.5% of silane coupling agent, and 0.8% of water glass.

[0128] The curing agent is an aqueous solution of hexamethylenetetramine, and the mass percentage of the solute in the aqueous solution of hexamethylenetetramine is 40%.

[0129] The lubricant is calcium stearate.

[0130] The particle size of the iron oxide powder is 400 mesh.

[0131] The particle size of the silicon carbide is 1500 mesh.

[0132] The silane coupling agent is KH550.

[0133] The preparation method of the above environmentally friendly regenerated coated sand includes the following steps: S1. Prepare regenerated quartz sand; weigh each raw material according to the raw material ratio.

[0134] S2. Preheat the regenerated quartz sand, add phenolic resin, sodium silicate, and silane coupling agent to the heated regenerated quartz sand, and stir evenly. Stir evenly in the sand mixing cylinder, and the stirring time is 50S.

[0135] The preheating temperature of the regenerated quartz sand is 130 °C.

[0136] S3. Add the curing agent, lubricant, iron oxide powder, and silicon carbide to the regenerated quartz sand, and stir evenly. The stirring time is 60S.

[0137] S4. After cooling to room temperature, regenerated coated sand is obtained.

[0138] The preparation method of the regenerated quartz sand includes the following steps: S11. Crush the waste sand core, then perform magnetic separation and screening to obtain used sand with a particle size of 3 mm.

[0139] S12. Heat the used sand.

[0140] The heating temperature is 300 °C, and the heating time is 2 min.

[0141] S13. Put the heated used sand into cold water for rapid cooling.

[0142] The temperature of the cold water is 25 °C.

[0143] S14. Dry and screen the cooled used sand, and then perform roasting.

[0144] The roasting temperature is 700 °C, and the roasting time is 20 min.

[0145] S15. Cool the roasted used sand to room temperature to obtain regenerated quartz sand.

[0146] Comparative Example 1 An environmentally friendly recycled coated sand, comprising the following components by mass percentage: recycled quartz sand 95.1%, phenolic resin 1.8%, curing agent 1.0%, lubricant 0.3%, iron oxide powder 0.6%, silane coupling agent 0.4%, water glass 0.8%.

[0147] The difference between this comparative example and Example 2 is that: this comparative example does not contain silicon carbide, and the content of iron oxide powder is the sum of the masses of iron oxide powder and silicon carbide in Example 2.

[0148] Comparative Example 2 An environmentally friendly recycled coated sand, comprising the following components by mass percentage: recycled quartz sand 95.1%, phenolic resin 1.8%, curing agent 1.0%, lubricant 0.3%, silicon carbide 0.6%, silane coupling agent 0.4%, water glass 0.8%.

[0149] The difference between this comparative example and Example 2 is that: this comparative example does not contain iron oxide powder, and the content of silicon carbide is the sum of the masses of iron oxide powder and silicon carbide in Example 2.

[0150] Comparative Example 3 An environmentally friendly recycled coated sand, comprising the following components by mass percentage: recycled quartz sand 95.1%, phenolic resin 2.6%, curing agent 1.0%, lubricant 0.3%, iron oxide powder 0.4%, silicon carbide 0.2%, silane coupling agent 0.4%.

[0151] The difference between this comparative example and Example 2 is that: this comparative example does not contain water glass, and the content of phenolic resin is the sum of the masses of phenolic resin and water glass in Example 2.

[0152] Comparative Example 4 The preparation method of the recycled quartz sand comprises the following steps: S11. Crush the waste sand core, then perform magnetic separation and screening to obtain used sand with a particle size of 2 mm.

[0153] S12. Heat the used sand.

[0154] The heating temperature is 300 °C and the heating time is 2 min.

[0155] S13. Put the heated used sand into cold water for rapid cooling.

[0156] The temperature of the cold water is 25 °C.

[0157] S14. Dry and screen the cooled used sand to obtain recycled quartz sand.

[0158] The difference between this comparative example and Example 2 is that: the recycled quartz sand has not undergone a roasting process.

[0159] Comparative Example 5 The preparation method of recycled quartz sand comprises the following steps: S11. Crushing the waste sand core, then performing magnetic separation and screening to obtain used sand with a particle size of 2 mm.

[0160] S12. Roasting the used sand at a roasting temperature of 700 °C for 20 min.

[0161] S13. Cooling the roasted used sand to room temperature to obtain recycled quartz sand.

[0162] The difference between this comparative example and Example 2 lies in that: the recycled quartz sand does not undergo the processes of rapid heating and rapid cooling.

[0163] The performance of the coated sand described in Examples 1-5 and Comparative Examples 1-5 is detected according to GB / T8583-2008 of the national standard, and the high-temperature resistance time of the coated sand at 1000 °C is tested. The detection results are shown in Table 1.

[0164] Table 1 Core performance of Examples 1-5 and Comparative Examples 1-5

[0165] In summary, the hot-state bending strength of the coated sand produced by using the recycled coated sand and the preparation method of the present invention is above 5.0 MPa, the normal-temperature bending strength is above 9.0 MPa, the normal-temperature tensile strength is above 5.0 MPa, and it has very good mechanical properties. The gas evolution amount is not higher than 14 ml / g, the gas evolution amount is low, which is beneficial to improving the casting quality of the casting. And the heat resistance time at 1000 °C is above 230 S, which can meet the casting requirements of high-temperature cast iron camshafts, and the linear expansion rate is lower than 1.45%, having very good thermal stability.

[0166] Therefore, by using the environmentally friendly recycled coated sand and its preparation method of the present invention, the problems of high gas evolution amount, low strength, poor high-temperature resistance performance and difficult recycling of the existing coated sand can be solved.

[0167] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An environmentally friendly regenerated coated sand, characterized by: It includes the following ingredients in percentage by mass: 94%-96% regenerated quartz sand, 1.5%-2% phenolic resin, 0.8%-1.2% curing agent, 0.1%-0.5% lubricant, 0.3%-0.5% iron oxide powder, 0.1%-0.3% silicon carbide, 0.3%-0.5% silane coupling agent, and 0.5%-1% water glass.

2. The environmentally friendly regenerated coated sand according to claim 1, characterized in that: The curing agent is a urotropine aqueous solution, and the solute mass percentage of the urotropine aqueous solution is 40%-50%.

3. The environmentally friendly regenerated coated sand according to claim 1, characterized in that: The lubricant is calcium stearate.

4. The environmentally friendly regenerated coated sand according to claim 1, characterized in that: The particle size of the iron oxide powder is 200-500 meshes.

5. The environmentally friendly regenerated coated sand according to claim 1, characterized in that: The particle size of the silicon carbide is 1000 mesh to 1500 mesh.

6. A method for preparing environmentally friendly regenerated coated sand according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Prepare regenerated quartz sand; weigh each raw material according to the raw material ratio; S2, preheating the regenerated quartz sand, adding phenolic resin, water glass and silane coupling agent to the heated regenerated quartz sand, and stirring evenly; S3, adding curing agent, lubricant, iron oxide powder and silicon carbide to the regenerated quartz sand and stirring evenly; S4. After cooling to room temperature, regenerated coated sand is obtained.

7. The method for preparing environmentally friendly regenerated coated sand according to claim 6, characterized in that: In S1, the preparation method of regenerated quartz sand comprises the following steps: S11, crushing the waste sand core, and then performing magnetic separation and screening to obtain waste sand with a particle size of 1mm-3mm; S12, heating the old sand; S13, putting the heated old sand into cold water for rapid cooling; S14, drying the cooled old sand, sieving it, and roasting it; S15, cooling the calcined old sand to room temperature to obtain regenerated quartz sand.

8. The method for preparing environmentally friendly regenerated coated sand according to claim 7, characterized in that: In the S12, the heating temperature is 200°C-400°C, and the heating time is 1 min-3 min; in the S13, the temperature of the cold water is not higher than 30°C.

9. The method for preparing environmentally friendly regenerated coated sand according to claim 7, characterized in that: In the S14, the calcination temperature is 600° C.-700° C., and the calcination time is 20 min-40 min.

10. The method for preparing environmentally friendly regenerated coated sand according to claim 6, characterized in that: In S2, the preheating temperature of the regenerated quartz sand is 110°C-130°C.

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