High-strength heat-resistant regenerated sand, its preparation method and application in cold box process

Abstract

The present invention relates to a high-strength and heat-resistant regenerated sand, a preparation method thereof, and an application in a cold-box process. The method comprises the following steps: crushing and screening old sand from a wet mold to obtain coarse-treated old sand; sequentially roasting, wet-purifying, and separating sand and water from the coarse-treated old sand to obtain dry sand; sequentially grinding and screening the dry sand, and then adding water glass for stirring and mixing to obtain modified sand; and rotating and curing the modified sand to obtain the high-strength and heat-resistant regenerated sand. The method involves multiple regeneration processes using thermal, wet, and mechanical methods, and then coating and modifying the surface of the regenerated sand to obtain modified regenerated sand with a smooth surface and excellent high-temperature resistance. The sand core prepared using the modified regenerated sand in the cold-box process has the advantages of high strength and a dense surface, thereby solving the problem of solid waste of old sand in foundries; saving non-renewable silica sand resources, and developing a resource recycling economy; and producing a high-quality regenerated sand that can prepare high-quality casting sand cores and improve the quality of castings.

Description

Technical Field

[0001] The invention belongs to the field of regenerated sand, and in particular relates to high-strength and heat-resistant regenerated sand, a preparation method thereof, and application in a cold box process. Background Art

[0002] Old casting sand is solid waste, and silica sand resources are non-renewable resources. Only a binder film remains on its surface, and the main physical and chemical properties and component structure have not changed. If it is scrapped as waste, it will be a waste of resources, which is a pity. Finally, casting is a basic process in manufacturing industries such as mechanical equipment. Casting technology determines the development speed and space of upper-level high-end manufacturing industries. Complex thin-walled castings generally use sand cores as inner cavity molds. However, more than 60% of complex thin-walled sand cores are made using the cold core box process. Therefore, providing high-quality casting sand and preparing high-quality casting sand cores are key parts of the development of my country's manufacturing industry.

[0003] The invention patent application number 202011445336.0 provides a high-collapse cold-box resin for cast aluminum engine cylinder blocks and its preparation method. Its purpose is to overcome the poor collapsibility and low room-temperature strength of existing resins, and also to address defects such as difficulty in sand removal and high casting scrap rates in the manufacturing process of cast aluminum engines. Component I is composed of phenyl ether phenolic resin, furfuryl alcohol, DBE, high-boiling point aromatic solvent S-150, hydrofluoric acid, and silane A1160; component II is composed of PM-200, urea-formaldehyde resin, high-boiling point aromatic solvent S-150, phosphorus oxychloride, and 3-isocyanate propyltriethoxysilane; and component III is the catalyst triethylamine. The main technical direction of this invention is to modify the resin used in cold core boxes to improve the strength of cold core box sand cores, but the resin synthesis process involves many chemical reactions, which can easily cause other unknown adverse effects; in addition, the binder system between sand particles is the main reason affecting the strength of the sand core, but this invention only considers the performance of the resin itself, and does not consider the compatibility with the sand particles, and its practicality is poor.

[0004] The invention patent application number 201610354785.1 provides a method for regenerating waste sand cores from cold core boxes for casting, comprising the following steps: (1) primary scrubbing; (2) treating the waste sand cores with a sodium citrate solution of 2% by mass, which is three times the weight of the waste sand cores, for 12 minutes, and then drying; (3) magnetic separation; (4) secondary scrubbing; (5) soaking the primary separated sand with a separator A, stirring, and removing suspended matter to obtain secondary treated sand; (6) soaking the secondary treated sand with a separator B, stirring, and removing suspended matter to obtain tertiary treated sand; (7) washing and drying the tertiary treated sand obtained in step (6) to obtain regenerated sand. However, after casting, the vast majority of the cold core box sand cores will flow into the wet model sand system, making it almost impossible to separate and regenerate them separately. The design of a separate regeneration method for waste sand cores from cold core boxes is too limited. In addition, the invention uses a lot of scrubbing, and the secondary polluted wastewater generated is difficult to treat, which limits the application prospects of this technology.

[0005] Patent application number 201910688569.4 discloses a novel cold-box sand casting method and its core-making process. This method addresses the technical issues of existing sand core-making methods, which fail to meet sintering resistance requirements, experience significant mold wear, and face the high price of chromite sand. However, this invention utilizes expensive ceramsite sand and roasted sand to produce high-quality cold-box sand cores, completely disregarding the recycling of used sand. This disregard for production costs and environmental friendliness significantly diminishes the technical significance of this invention.

[0006] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0007] In order to solve the problems existing in the prior art, the present invention provides a high-strength and heat-resistant regenerated sand, a preparation method thereof and an application in a cold box process.

[0008] The present invention provides a method for preparing high-strength heat-resistant regenerated sand, which comprises the following steps:

[0009] (1) Crushing and screening the wet mold old sand to obtain coarse treated old sand;

[0010] (2) roasting, wet-cleaning, and sand-water separation of the coarsely treated old sand to obtain dry sand;

[0011] (3) grinding and sieving the dried sand in sequence, and then adding water glass and stirring and mixing to obtain modified sand;

[0012] (4) The modified sand is subjected to a rotation curing treatment to obtain the high-strength and heat-resistant regenerated sand.

[0013] Preferably, in step (1), the particle size of the coarsely treated old sand is ≤12 mesh.

[0014] Preferably, in step (2), the coarsely treated used sand is first calcined at 500-1000° C. for 1-5 hours to obtain calcined sand; when the temperature of the calcined sand is cooled to ≤80° C., it is then put into a wet mixer together with water and acid solution and stirred at 120-720 r / min for 3-20 minutes to perform wet purification; after completion, the sand and water are separated by pressurization to obtain dry sand with a water content of 1-5wt.%.

[0015] Preferably, the weight ratio of the roasted sand to water is 1:0.5 to 1:3, and the weight ratio of the acid solution to water is 1 to 10:100; the acid solution is one or a combination of two or more of oxalic acid, hydrochloric acid, acetic acid, and sulfuric acid, and the pH of the acid solution is 1 to 3.

[0016] Preferably, in step (3), the dried sand is put into a grinder and ground at 360 to 1200 r / min for 1 to 5 min. After completion, 20-mesh and 140-mesh sieves are used for screening to remove particles larger than 20 mesh and particles smaller than 140 mesh, and the concentration is made ≥90%. Then, 0.2 to 1.0 wt.% of water glass by weight of the sand particles is added, and the mixture is stirred at a speed of 120 to 720 r / min for 20 to 50 s to obtain modified sand.

[0017] Preferably, the solid content of the water glass is 38-50 wt.%, the potassium oxide content is 10-13 wt.%, and the silicon dioxide content is 25-30 wt.%.

[0018] Preferably, in step (4), the modified sand is put into a rotary curing kiln and rotary cured for 3 to 10 hours at a curing temperature of 40 to 80° C. and a rotation speed of 10 to 60 r / min to obtain the high-strength and heat-resistant regenerated sand.

[0019] Based on the same technical concept, another solution of the present invention is to provide a high-strength and heat-resistant regenerated sand obtained by the above preparation method.

[0020] The present invention also provides an application of the high-strength and heat-resistant regenerated sand, which includes the step of using the high-strength and heat-resistant regenerated sand in the preparation of a cold box. The preparation method of the cold box includes the following steps:

[0021] (S1) taking the high-strength and heat-resistant regenerated sand, adding cold box resin component I and cold box resin component II, and mixing the sand for 10 to 60 seconds to obtain cold box sand;

[0022] (S2) blowing the cold box sand into the mold, wherein the sand injection pressure is 0.3-0.6 MPa and the exhaust time is 1-3 seconds;

[0023] (S3) using triethylamine for air blowing and curing for 30 to 300 seconds to form a sand core;

[0024] (S4) The sand core is cast and cleaned, and then flows into the green mold used sand system again for recycling.

[0025] Preferably, the weight ratio of the high-strength and heat-resistant regenerated sand, the cold box resin component I and the cold box resin component II is 100:0.3-2:0.3-2.

[0026] Among them, cold box resin component I: liquid phenolic resin, light yellow or brown liquid, viscosity ≤250mpa / s (25℃), density 1.05~1.15g / cm 3 (25℃).

[0027] Cold box resin component II: liquid polyisocyanate, brown liquid, viscosity ≤100mPa / s (25℃), density 1.05~1.20g / cm 3 (25℃).

[0028] To facilitate understanding of the present invention, the implementation principle of the present invention is described below:

[0029] (I) Used green sand is repeatedly recycled in the molding sand system. After being infiltrated by molten iron casting, its surface contains a large amount of clay, coal dust, organic resin, iron oxide, and magnetic sintering impurities. These substances have rough and sharp surfaces, which seriously weaken the resin coating effect. Calcination regeneration can embrittle the clay and ignite the coal dust and organic resin. In the wet process, acid is added to react with iron oxide and some magnetic sintering impurities to form salts, removing soluble impurities. Grinding removes embrittled clay, combustion ash, and salt, achieving a residual film removal rate of over 90% on the used sand surface.

[0030] (II) The sand grains are surface-modified using water glass and then placed in a curing kiln for constant-temperature dynamic curing, transforming the rough surface structure of the sand grains into a smooth one. The smooth surface structure of the sand grains is more conducive to cold-box resin coating, allowing for higher-strength sand cores with the same resin loading. This results in a high sand core yield rate and reduces the amount of cold-box resin added, thereby reducing sand core gas generation. This method is suitable for gas-sensitive aluminum alloy castings and achieves a high casting yield rate. Furthermore, the water glass layer vitrifies at high temperatures, forming a stable protective layer on the sand grain surface, resulting in excellent heat resistance.

[0031] (III) Since this type of regenerated cold box sand has high strength, the amount of resin added to the cold box can be reduced to reduce the gas emission of the sand core, and it is suitable for aluminum alloy castings that are sensitive to gas; since this type of regenerated cold box sand has excellent heat resistance, it is suitable for iron and steel castings with high casting temperatures.

[0032] The beneficial effects of the present invention are:

[0033] The method for preparing high-strength, heat-resistant regenerated sand described in the present invention uses green mold used sand as raw material, undergoes multiple regeneration processes using thermal, wet, and mechanical methods, and then coats the surface of the regenerated sand to obtain modified regenerated sand with a smooth surface and excellent high-temperature resistance. Sand cores prepared using this modified regenerated sand in a cold core box process exhibit advantages such as high strength and a dense surface. Finally, high-quality castings are obtained through casting and cleaning. This method solves the problem of used sand solid waste in foundries; conserves non-renewable silica sand resources and promotes a resource recycling economy; and produces high-quality regenerated sand that can be used to prepare high-quality casting sand cores and improve the quality of castings. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] This embodiment provides a method for preparing high-strength and heat-resistant regenerated sand, which comprises the following steps:

[0037] (1) Crushing and screening the wet mold old sand to obtain coarse treated old sand with a particle size of ≤12 mesh;

[0038] (2) calcining the coarsely treated used sand at 800° C. for 2 h to obtain calcined sand; when the calcined sand is cooled to 80° C., adding the calcined sand, water, and acid solution into a wet mixer and stirring at 360 rpm for 5 min to perform wet purification; after completion, pressurizing the sand and water to separate the sand and water to obtain dry sand with a water content of 3 wt.%; wherein the weight ratio of the calcined sand to water is 1:2, and the weight ratio of the acid solution to water is 5:100; the acid solution is hydrochloric acid, and the pH of the acid solution is 2;

[0039] (3) The dried sand was put into a grinder and ground at 360 r / min for 2 min. After grinding, 20-mesh and 140-mesh sieves were used to remove particles larger than 20 mesh and particles smaller than 140 mesh, and the concentration was adjusted to 92%. Water glass with a weight percentage of 0.5 wt.% of the weight of the sand was added, and the mixture was stirred at a speed of 360 r / min for 30 s to obtain modified sand. The water glass had a solid content of 38 wt.%, a potassium oxide content of 10 wt.%, and a silicon dioxide content of 25 wt.%.

[0040] (4) The modified sand is put into a rotary curing kiln and is rotary cured for 3 hours at a curing temperature of 40° C. and a rotation speed of 20 r / min to obtain the high-strength and heat-resistant regenerated sand.

[0041] This embodiment further provides an application of the high-strength and heat-resistant regenerated sand in a cold box process, wherein the application method comprises the following steps:

[0042] (S1) taking the high-strength and heat-resistant regenerated sand, adding cold box resin component I and cold box resin component II, and mixing the sand for 30 seconds to obtain cold box sand; wherein the weight ratio of the high-strength and heat-resistant regenerated sand, cold box resin component I and cold box resin component II is 100:0.5:0.5;

[0043] (S2) blowing the cold box sand into the mold, wherein the sand injection pressure is 0.6 MPa and the exhaust time is 2 seconds;

[0044] (S3) using triethylamine for air blowing and curing for 50 seconds to form a sand core;

[0045] (S4) The sand core is cast and cleaned, and then flows into the green mold used sand system again for recycling.

[0046] Example 2

[0047] This embodiment provides a method for preparing high-strength and heat-resistant regenerated sand, which comprises the following steps:

[0048] (1) Crushing and screening the wet mold old sand to obtain coarse treated old sand with a particle size of ≤12 mesh;

[0049] (2) calcining the coarsely treated old sand at 500° C. for 5 h to obtain calcined sand; when the calcined sand is cooled to 75° C., adding the calcined sand, water, and acid solution into a wet mixer and stirring at 120 rpm for 20 min to perform wet purification; after completion, pressurizing the sand and water to separate the sand and water to obtain dry sand with a water content of 1 wt.%; wherein the weight ratio of the calcined sand to water is 1:0.5, and the weight ratio of the acid solution to water is 5:100; the acid solution is hydrochloric acid, and the pH of the acid solution is 1;

[0050] (3) The dried sand was put into a grinder and ground at 360 r / min for 5 min. After grinding, 20-mesh and 140-mesh sieves were used to remove particles larger than 20 mesh and particles smaller than 140 mesh, and the concentration was adjusted to 93%. Water glass with a weight percentage of 0.2 wt.% of the sand was added, and the mixture was stirred at a speed of 120 r / min for 50 s to obtain modified sand. The water glass had a solid content of 38 wt.%, a potassium oxide content of 10 wt.%, and a silicon dioxide content of 25 wt.%.

[0051] (4) The modified sand is put into a rotary curing kiln and is rotary cured for 10 hours at a curing temperature of 40° C. and a rotation speed of 10 r / min to obtain the high-strength and heat-resistant regenerated sand.

[0052] This embodiment further provides an application of the high-strength and heat-resistant regenerated sand in a cold box process, wherein the application method comprises the following steps:

[0053] (S1) taking the high-strength and heat-resistant regenerated sand, adding cold box resin component I and cold box resin component II, and mixing the sand for 10 seconds to obtain cold box sand; wherein the weight ratio of the high-strength and heat-resistant regenerated sand, cold box resin component I and cold box resin component II is 100:0.3:0.3;

[0054] (S2) blowing the cold box sand into the mold, wherein the sand injection pressure is 0.3 MPa and the exhaust time is 1 second;

[0055] (S3) using triethylamine for air blowing and curing for 30 seconds to form a sand core;

[0056] (S4) The sand core is cast and cleaned, and then flows into the green mold used sand system again for recycling.

[0057] Example 3

[0058] This embodiment provides a method for preparing high-strength and heat-resistant regenerated sand, which comprises the following steps:

[0059] (1) Crushing and screening the wet mold old sand to obtain coarse treated old sand with a particle size of ≤12 mesh;

[0060] (2) calcining the coarsely treated used sand at 1000° C. for 1 hour to obtain calcined sand; when the calcined sand is cooled to 70° C., adding the calcined sand, water, and acid solution into a wet mixer and stirring at 720 rpm for 3 minutes to perform wet purification; after completion, pressurizing the sand and water to separate the sand and water to obtain dry sand with a water content of 5 wt.%, wherein the weight ratio of the calcined sand to water is 1:3, and the weight ratio of the acid solution to water is 10:100; the acid solution is hydrochloric acid, and the pH value of the acid solution is 3;

[0061] (3) The dried sand was put into a grinder and ground at 1200 r / min for 1 min. After grinding, 20-mesh and 140-mesh sieves were used to remove particles larger than 20 mesh and particles smaller than 140 mesh, and the concentration was adjusted to 93%. Then, 1.0 wt.% of water glass was added to the sand particles, and the mixture was stirred at a speed of 720 r / min for 20 s to obtain modified sand. The water glass had a solid content of 50 wt.%, a potassium oxide content of 13 wt.%, and a silicon dioxide content of 30 wt.%.

[0062] (4) The modified sand is put into a rotary curing kiln and is rotary cured for 3 hours at a curing temperature of 80° C. and a rotation speed of 60 r / min to obtain the high-strength and heat-resistant regenerated sand.

[0063] This embodiment further provides an application of the high-strength and heat-resistant regenerated sand in a cold box process, wherein the application method comprises the following steps:

[0064] (S1) taking the high-strength and heat-resistant regenerated sand, adding cold box resin component I and cold box resin component II, and mixing the sand for 60 seconds to obtain cold box sand; wherein the weight ratio of the high-strength and heat-resistant regenerated sand, cold box resin component I and cold box resin component II is 100:2:2;

[0065] (S2) blowing the cold box sand into the mold, wherein the sand injection pressure is 0.6 MPa and the exhaust time is 1 s;

[0066] (S3) using triethylamine for air blowing and curing for 300 s to form a sand core;

[0067] (S4) The sand core is cast and cleaned, and then flows into the green mold used sand system again for recycling.

[0068] Comparative Example:

[0069] Comparative Example 1: Compared with Example 1, Comparative Example 1 does not perform the roasting regeneration process, and other implementation methods and conditions are the same as Example 1.

[0070] Comparative Example 2: Compared with Example 1, Comparative Example 2 does not perform the wet purification process, and other implementation methods and conditions are the same as Example 1.

[0071] Comparative Example 3: Compared with Example 1, Comparative Example 3 does not perform the grinding and regeneration process of the grinder, and other implementation methods and conditions are the same as Example 1.

[0072] Comparative Example 4: Compared with Example 1, Comparative Example 4 does not perform the process of adding glass water (ie, does not perform the surface modification process), and other implementation methods and conditions are the same as Example 1.

[0073] Comparative Example 5: Compared with Example 1, Comparative Example 5 does not perform the curing process, and other implementation methods and conditions are the same as Example 1.

[0074] Comparative Example 6: Inner Mongolia scrubbing sand was used instead of the regenerated sand in Example 1, and the core making and casting were the same as in Example 1.

[0075] The various properties of Example 1 and Comparative Examples 1 to 6 are shown in Table 1, where:

[0076] Test method: Reference standard GB / T2684-2009.

[0077] Core making yield rate: Prepare 100 sand cores and calculate the qualified rate.

[0078] Casting yield rate: 100 castings are cast and the qualified rate is calculated.

[0079] Acid consumption value: This value represents the amount of alkaline material on the surface of the sand particles. The residual film on the surface of the used sand is alkaline, and the acid consumption value is used to measure the removal rate of residual material on the surface of the used sand. The higher the acid consumption value, the worse the used sand regeneration effect.

[0080] Conductivity: This represents the amount of soluble salts on the sand surface. Metal oxides in the residual film on the surface of used sand react with the wet process to form a large amount of soluble salts. Conductivity is used to measure the removal rate of residual substances on the used sand surface. The higher the conductivity, the worse the used sand regeneration effect.

[0081] Tensile strength indicates the strength of the sand core; high temperature resistance strength and high temperature resistance time both indicate the heat resistance of the sand core.

[0082] Table 1 Comparison of physical and chemical properties

[0083]

[0084]

[0085] Table 1 Comparison of physical and chemical properties (continued)

[0086] Group High temperature resistance time / s Core production yield / % Casting yield / % Example 1 201 96 98 Comparative Example 1 171 90 91 Comparative Example 2 169 89 90 Comparative Example 3 152 90 88 Comparative Example 4 109 86 89 Comparative Example 5 159 85 81 Comparative Example 6 131 93 89

[0087] From the data, we can see that:

[0088] Comparing the embodiment with comparative example 1, without performing the roasting regeneration process, the acid consumption value of the regenerated sand obtained increased by 102%, the electrical conductivity increased by 211%, the tensile strength decreased by 21%, the high temperature strength decreased by 26%, the high temperature resistance time decreased by 15%, the core making yield decreased by 6%, and the casting yield decreased by 7%.

[0089] Comparing the embodiment with comparative example 2, without performing the wet purification process, the acid consumption value of the regenerated sand obtained increased by 98%, the electrical conductivity increased by 246%, the tensile strength decreased by 25%, the high temperature strength decreased by 30%, the high temperature resistance time decreased by 16%, the core production yield decreased by 7%, and the casting yield decreased by 8%.

[0090] Comparing the embodiment with comparative example 3, without performing the grinding process, the acid consumption value of the regenerated sand obtained increased by 114%, the electrical conductivity increased by 507%, the tensile strength decreased by 37%, the high temperature strength decreased by 37%, the high temperature time decreased by 24%, the core making yield decreased by 6%, and the casting yield decreased by 10%.

[0091] Comparing the embodiment with comparative example 4, without surface modification, the acid consumption value of the regenerated sand obtained increased by 2%, the electrical conductivity increased by 7%, the tensile strength decreased by 12%, the high temperature strength decreased by 52%, the high temperature time decreased by 46%, the core production yield decreased by 10%, and the casting yield decreased by 9%.

[0092] Comparing the embodiment with comparative example 5, without curing, the acid consumption value of the regenerated sand obtained increased by 2%, the electrical conductivity increased by 11%, the tensile strength decreased by 13%, the high temperature strength decreased by 33%, the high temperature time decreased by 21%, the core making yield decreased by 11%, and the casting yield decreased by 17%.

[0093] Comparing the embodiment with comparative example 6, using Inner Mongolia scrubbing sand instead of the regenerated sand in the embodiment, the acid consumption value decreased by 4%, the electrical conductivity decreased by 7%, the tensile strength decreased by 23%, the high temperature strength decreased by 26%, the high temperature time decreased by 35%, the core making yield decreased by 3%, and the casting yield decreased by 9%.

[0094] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing high-strength heat-resistant regenerated sand, characterized in that: The preparation method comprises the following steps: (1) Crushing and screening the wet mold old sand to obtain coarsely treated old sand; (2) roasting, wet-cleaning, and sand-water separation of the coarsely treated used sand in sequence to obtain dry sand, wherein the wet-cleaning is carried out by putting the roasted sand, water, and acid solution into a wet mixer; (3) grinding and sieving the dried sand in sequence, then adding water glass and stirring to obtain modified sand; (4) The modified sand is subjected to a rotation curing treatment to obtain the high-strength and heat-resistant regenerated sand.

2. The method for preparing high-strength heat-resistant regenerated sand according to claim 1, characterized in that: In step (1), the particle size of the coarsely treated old sand is ≤12 mesh.

3. The method for preparing high-strength heat-resistant regenerated sand according to claim 1, characterized in that: In step (2), the coarsely treated old sand is first roasted at 500-1000° C. for 1-5 hours to obtain roasted sand; when the temperature of the roasted sand is cooled to ≤80° C., it is put into a wet mixer together with water and acid solution, and stirred at 120-720 r / min for 3-20 minutes to perform wet purification; after completion, the sand and water are separated by pressurization to obtain dry sand with a water content of 1-5 wt.%.

4. The method for preparing high-strength heat-resistant regenerated sand according to claim 3, characterized in that: The weight ratio of the roasted sand to water is 1:0.5-1:3, and the weight ratio of the acid solution to water is 1-10:100; the acid solution is one or a combination of two or more of oxalic acid, hydrochloric acid, acetic acid, and sulfuric acid, and the pH of the acid solution is 1-3.

5. The method for preparing high-strength heat-resistant regenerated sand according to claim 1, characterized in that: In step (3), the dried sand is put into a grinder and ground at 360-1200 r / min for 1-5 min. After grinding, 20-mesh and 140-mesh sieves are used to remove particles larger than 20 mesh and particles smaller than 140 mesh, and the concentration is made ≥90%. Then, 0.2-1.0 wt.% of water glass by weight of the sand particles is added, and the mixture is stirred at a rotation speed of 120-720 r / min for 20-50 s to obtain modified sand.

6. The method for preparing high-strength and heat-resistant regenerated sand according to claim 5, characterized in that: The solid content of the water glass is 38-50 wt.%, the potassium oxide content is 10-13 wt.%, and the silicon dioxide content is 25-30 wt.%.

7. The method for preparing high-strength and heat-resistant regenerated sand according to claim 1, characterized in that: In step (4), the modified sand is put into a rotary curing kiln and rotary cured for 3 to 10 hours at a curing temperature of 40 to 80° C. and a rotation speed of 10 to 60 r / min to obtain the high-strength and heat-resistant regenerated sand.

8. High-strength and heat-resistant regenerated sand obtained by the preparation method according to any one of claims 1 to 7.

9. The use of the high-strength heat-resistant regenerated sand according to claim 8, characterized in that: The application includes the step of using the high-strength and heat-resistant regenerated sand in the preparation of a cold box. The preparation method of the cold box includes the following steps: (S1) taking the high-strength and heat-resistant regenerated sand, adding cold box resin component I and cold box resin component II, and mixing the sand for 10 to 60 seconds to obtain cold box sand; (S2) blowing the cold box sand into the mold, wherein the sand injection pressure is 0.3-0.6 MPa and the exhaust time is 1-3 seconds; (S3) using triethylamine for air-blow curing for 30 to 300 seconds to form a sand core; (S4) The sand core is cast and cleaned, and then flows into the green mold used sand system again for recycling.

10. The use according to claim 9, characterized in that The weight ratio of the high-strength and heat-resistant regenerated sand, the cold box resin component I and the cold box resin component II is 100:0.3~2:0.3~2.

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