High-strength low-gas-forming heat-resistant precoated sand and preparation method thereof

Abstract

The invention relates to the technical field of precoated sand production, in particular to high-strength low-gas-forming heat-resistant precoated sand and a preparation method thereof. According to the method, second-time film covering is carried out on the basis of first-time film covering, specifically, 100 parts of crude sand are weighed, the crude sand is heated to 120-150 DEG C and then put into a sand mixer, and 1-3 parts of a binding agent, 0.1-0.5 part of a curing agent and 0.1-0.2 part of a lubricating agent are sequentially added for sand mixing; the second time of film covering is specifically conducted; cooling to 30-60 DEG C, then putting into the sand mixer again, adding 0.2-1.0 part of silica fume for mixing sand, and then adding 0.5-2.0 parts of sodium silicate for mixing sand to obtain the precoated sand. The precoated sand provided by the invention has the advantages of high strength, low gas evolution and good heat resistance, and can improve the qualification rate of castings of a foundry.

Description

Technical Field

[0001] The present invention relates to the technical field of coated sand production, and in particular to high-strength, low-gassing, heat-resistant coated sand and a preparation method thereof. Background Art

[0002] With the rapid development of industry and increasingly stringent environmental protection requirements, casting molding processes are constantly being upgraded and optimized. Compared with the traditional green sand process, the coated sand shell process has the advantages of better casting surface quality, higher casting qualification rate, and better factory environment. Therefore, the coated sand shell process for casting is gradually replacing the traditional green sand process.

[0003] The key performance characteristics of coated sand include strength and heat resistance. High strength ensures the integrity of the core during turnover, while heat resistance ensures its integrity during high-temperature casting. Currently, the primary method for improving strength is to increase the resin content, but this results in high sand core gassing, ultimately leading to porosity in the casting. The method for improving heat resistance is to add high-temperature resistant additives, but this disrupts the resin bond bridge, ultimately resulting in low core strength. Therefore, current coated sand technology struggles to combine the advantages of high strength, low gassing, and high-temperature resistance.

[0004] In view of the above, the present invention provides a high-strength, low-gas-emission, heat-resistant coated sand, which has the advantages of high strength, low gas evolution, and good heat resistance. Summary of the Invention

[0005] In response to the technical problems existing in the prior art, the present invention provides a high-strength, low-gassing, heat-resistant coated sand and a preparation method thereof. The coated sand has the advantages of high strength, low gassing and good heat resistance, and can improve the casting qualification rate of the foundry.

[0006] The technical method of the present invention to solve the above technical problems is as follows: S1. Weigh 100 parts of raw sand; S2, perform the first lamination: S201, heating the raw sand to 120-150°C and then putting it into the first sand mixer; S202, adding 1-3 parts of binder to mix sand; S203, adding 0.1-0.5 parts of curing agent to mix sand; S204, adding 0.1-0.2 parts of lubricant to the sand mix; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 30-60°C and then put into the second sand mixer; S302, add 0.2~1.0 parts of microsilica powder to mix sand; S303, adding 0.5-2.0 parts of sodium silicate to mix the sand to obtain coated sand; The sodium silicate / microsilica powder inorganic protective layer formed by the second coating covers the surface of the first coating.

[0007] On the basis of the above technical method, the present invention can also be improved as follows.

[0008] Preferably, in step S1, the raw sand is selected from Inner Mongolia scrubbing sand of 50 / 100 specification.

[0009] Preferably, in step S202, the binder is phenolic resin, and the binder phenolic resin is added to mix the sand, and the mixing time is 10 to 30 seconds.

[0010] Preferably, the phenolic resin has a softening point of 60-90° C. and a polymerization rate of 20-50 s.

[0011] Preferably, in step S203, the curing agent is methenamine, and the curing agent methenamine is added to mix the sand, and the mixing time is 30 to 50 seconds.

[0012] Preferably, in step S204, the lubricant is calcium stearate, and the lubricant calcium stearate is added to mix the sand, and the mixing time is 30 to 60 seconds.

[0013] Preferably, in the second coating: Step S301 , the material is cooled to 30-60° C. in a water mist cooling tank and then put into the sand mixer again.

[0014] Preferably, in step S302, microsilica powder is added to mix the sand, and the mixing time is 30 to 60 seconds.

[0015] Preferably, in step S303, sodium silicate is added to mix the sand, and the mixing time is 20 to 60 seconds to obtain coated sand.

[0016] The present invention also provides high-strength, low-gassing heat-resistant coated sand, which is prepared by the above method.

[0017] The beneficial effects of the present invention are: The present invention uses a secondary coating process to construct a sodium silicate bonding bridge and an inorganic protective layer on the surface of the sand grains. The sodium silicate bonding bridge significantly improves the strength of the coated sand. The sodium silicate / microsilica fume is non-flammable at high temperatures, improving strength while also maintaining the advantage of low gas evolution. The sodium silicate / microsilica fume forms an inorganic protective layer on the surface of the sand grains. During high-temperature casting of molten metal, the coating on the sand grains does not rapidly decompose, significantly improving high-temperature resistance. This invention achieves a breakthrough improvement in the performance of coated sand, resolving long-standing performance contradictions of coated sand, effectively reducing casting porosity defects, and significantly improving production efficiency and casting quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1This is a schematic flow chart of the method for preparing the high-strength, low-gassing, heat-resistant coated sand of the present invention; DETAILED DESCRIPTION The principles and features of the present invention are described below. The examples provided are intended to illustrate the present invention only and are not intended to limit the scope of the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0019] Example 1 This embodiment provides a high-strength, low-gassing, heat-resistant coated sand. The raw materials are prepared according to weight parts, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.5 part of microsilica powder, and 0.5 part of sodium silicate. The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.5 parts of microsilica powder and mix the sand for 50 seconds; S303, add 0.5 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0020] Example 2: The only difference between this example and Example 1 is that the amount of microsilica powder is 0.2 parts.

[0021] This embodiment provides a high-strength, low-gassing, heat-resistant coated sand. The raw materials are prepared according to weight parts, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.2 part of microsilica powder, and 0.5 part of sodium silicate. The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.2 parts of microsilica powder and mix the sand for 50 seconds; S303, add 0.5 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0022] Example 3: The only difference between this example and Example 1 is that the amount of microsilica powder is 0.9 parts.

[0023] This embodiment provides a high-strength, low-gassing, heat-resistant coated sand. The raw materials are prepared according to weight parts, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.9 part of microsilica powder, and 0.5 part of sodium silicate. The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.9 parts of microsilica powder and mix the sand for 50 seconds; S303, add 0.5 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0024] Example 4: The difference between this example and Example 1 is that the amount of sodium silicate is 1.0 part.

[0025] This embodiment provides a high-strength, low-gassing, heat-resistant coated sand. The raw materials are prepared according to weight parts, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.5 part of microsilica powder, and 1.0 part of sodium silicate. The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.5 parts of microsilica powder and mix the sand for 50 seconds; S303, add 1.0 part of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0026] Example 5: The difference between this example and Example 1 is that the amount of sodium silicate is 1.9 parts.

[0027] This embodiment provides a high-strength, low-gassing, heat-resistant coated sand. The raw materials are prepared according to weight parts, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.5 part of microsilica powder, and 1.9 parts of sodium silicate. The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.5 parts of microsilica powder and mix the sand for 50 seconds; S303, add 1.9 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0028] Example 6 This embodiment provides a high-strength, low-gassing, heat-resistant coated sand. The raw materials are prepared according to weight parts, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.3 part of microsilica powder, and 0.6 part of sodium silicate. The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.3 parts of microsilica powder and mix the sand for 50 seconds; S303, add 0.6 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0029] Comparative Example 1: The only difference between this comparative example and Example 1 is that the cooling process in step S301 is removed and no cooling is performed. Other implementation methods and conditions are the same as those in Example 1.

[0030] This comparative example provides a coated sand, wherein the raw materials are prepared according to parts by weight, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.5 part of microsilica powder, and 0.5 part of sodium silicate; The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, putting the mixed sand after the first coating into the second sand mixer; S302, add 0.5 parts of microsilica powder and mix the sand for 50 seconds; S303, adding 0.5 parts of sodium silicate and mixing the sand for 30 seconds to obtain coated sand; Comparative Example 2: The only difference between this comparative example and Example 1 is that step S302 is removed and microsilica powder is not added. Other implementation methods and conditions are the same as Example 1.

[0031] This comparative example provides a coated sand, wherein the raw materials are prepared according to parts by weight, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.5 part of microsilica powder, and 0.5 part of sodium silicate; The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.5 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0032] Comparative Example 3: The only difference between this comparative example and Example 1 is that step S303 is removed and sodium silicate is not added. Other implementation methods and conditions are the same as those in Example 1.

[0033] This comparative example provides a coated sand, wherein the raw materials are prepared according to parts by weight, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.5 part of microsilica powder, and 0.5 part of sodium silicate; The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.5 parts of microsilica powder and mix the sand for 50 seconds to obtain coated sand.

[0034] Comparative Example 4: The only difference between this comparative example and Example 1 is that the amount of microsilica powder is 0.1 parts.

[0035] This comparative example provides a coated sand, wherein the raw materials are prepared according to parts by weight, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.1 part of microsilica powder, and 0.5 part of sodium silicate; The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.1 parts of microsilica powder and mix the sand for 50 seconds; S303, add 0.5 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0036] Comparative Example 5: The only difference between this comparative example and Example 1 is that the amount of microsilica powder is 3 parts.

[0037] This comparative example provides a coated sand, wherein the raw materials are prepared according to parts by weight, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 3 parts of microsilica powder, and 0.5 part of sodium silicate; The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 3 parts of microsilica powder and mix the sand for 50 seconds; S303, add 0.5 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0038] Comparative Example 6: The difference between this comparative example and Example 1 is only that 0.2 parts of sodium silicate is used.

[0039] This comparative example provides a high-strength, low-gassing, heat-resistant coated sand. The raw materials are prepared according to parts by weight, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.5 part of microsilica powder, and 0.2 part of sodium silicate. The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.5 parts of microsilica powder and mix the sand for 50 seconds; S303, add 0.2 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0040] Comparative Example 7: The difference between this comparative example and Example 1 is only 5 parts of sodium silicate.

[0041] This comparative example provides a high-strength, low-gassing, heat-resistant coated sand. The raw materials are prepared according to weight parts, including 50 / 100 Inner Mongolia scrubbing sand, 1.0 part of phenolic resin as a binder, 0.2 part of methenamine as a curing agent, 0.2 part of calcium stearate as a lubricant, 0.5 part of microsilica powder, and 5 parts of sodium silicate. The preparation process is as follows: S1. Raw sand: Take 50 / 100 Inner Mongolia scrubbing sand and make 100 portions; S2, perform the first lamination: S201, heating the scrubbing sand to 150° C. and then putting it into the first sand mixer; S202, adding 1.0 part of phenolic resin, mixing for 20 seconds, wherein the softening point of the phenolic resin is 80° C., and the polymerization speed is 30 seconds; S203, add 0.2 parts of urotropine curing agent, and mix the sand for 40 seconds; S204, add 0.2 parts of calcium stearate as lubricant, and mix the sand for 40 seconds; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 50°C and then put into the second sand mixer; S302, add 0.5 parts of microsilica powder and mix the sand for 50 seconds; S303, add 5 parts of sodium silicate and mix the sand for 30 seconds to obtain coated sand.

[0042] The coated sands prepared in the above Examples 1-6 and Comparative Examples 1-7 were tested respectively.

[0043] The test methods for tensile strength, high-temperature strength and gas evolution refer to the standard GB / T2684-2009. The high-temperature resistance time test method of coated sand is as follows: a prepared "I"-shaped sample is placed stably on a "concave"-shaped load table, placed in a high-temperature furnace at 1000°C, a constant pressure of 0.2MPa is applied to the sample, and its collapse time is measured. The test results are shown in Table 1.

[0044] Among them, 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.

[0045] The coated sands prepared in Examples 1-6 and Comparative Examples 1-7 were used to prepare sand cores and castings. The core production yield was calculated by preparing 100 sand cores and calculating the qualified rate; the casting production yield was calculated by preparing 100 castings and calculating the qualified rate. The test results are shown in Table 1.

[0046] Table 1 Performance test results of various coated sands:

[0047] This technical solution significantly improves the comprehensive performance of coated sand by optimizing the formula components and secondary coating process. The following is an explanation of the various influencing factors and technical effects combined with specific test data: The synergistic effect of microsilica fume and sodium silicate: When the addition amounts of microsilica fume and sodium silicate are within the range of (0.2-1.0 parts microsilica fume, 0.5-2.0 parts sodium silicate), the inorganic protective layer formed by the two at high temperatures effectively improves the heat resistance and structural stability of the sand core. Example 6 (0.3 parts microsilica fume, 0.6 parts sodium silicate) exhibited the best tensile strength, high-temperature resistance time, and yield, verifying the synergistic effect of this ratio.

[0048] The non-flammable properties of sodium silicate and microsilica significantly reduce the gas evolution of coated sand. While the gas evolution of Examples 1-6 remained stable at 11-13 mL, that of Comparative Examples 2 (no microsilica) and 3 (no sodium silicate) increased by 50% and 67%, respectively, confirming that the absence of either component exacerbates the release of organic resin pyrolysis gases. Specifically, microsilica forms an inert barrier at high temperatures, inhibiting gas release. In Example 3, increasing the amount of microsilica to 0.9 parts further reduced the gas evolution to 11 mL. Sodium silicate enhances interfacial bonding through silicon-oxygen bonds, improving sand core strength. Comparative Example 6 (0.2 parts sodium silicate) experienced a 70% drop in tensile strength and a 37% reduction in high-temperature endurance, demonstrating its irreplaceable bonding enhancement. The synergistic effect of the two components (0.2-1.0 parts microsilica, 0.5-2.0 parts sodium silicate) achieves a balance between strength and heat resistance.

[0049] The criticality of the secondary coating process: The secondary coating process (including the cooling step) used in the examples is crucial to performance improvement. Comparative Example 1 did not undergo cooling treatment, resulting in insufficient bonding of the coating layer, and the tensile strength and high-temperature resistance time were significantly inferior to those of the examples. This process forms a composite structure with sodium silicate as a bonding bridge and microsilica powder as a reinforcing skeleton on the surface of the sand particles through a staged coating process (the first coating is a resin-based bonding layer, and the secondary coating introduces sodium silicate and microsilica powder). In Examples 1-6, the process is combined with a cooling step (cooling to 50°C before the secondary coating) to ensure uniform coating of the inorganic material and avoid thermal damage caused by high-temperature residues. Comparative Example 1 did not undergo cooling, and the tensile strength decreased by about 25%, and the high-temperature resistance time was shortened by 20%, indicating that temperature control is the key to the densification of the bonding bridge.

[0050] Negative impact of component excess on performance: When the content of microsilica fume or sodium silicate exceeds the claimed range, performance deteriorates significantly. For example, in Comparative Example 4 (0.1 part microsilica fume), insufficient content leads to an incomplete protective layer and shortened high-temperature resistance. In Comparative Example 7 (5 parts sodium silicate), excessive content interferes with resin curing, resulting in increased gas generation and reduced yield. This demonstrates the necessity of the specified ranges (0.2-1.0 part microsilica fume, 0.5-2.0 part sodium silicate).

[0051] Comprehensive performance advantages: Compared with traditional processes (such as Comparative Examples 1-7), the coated sand in these examples exhibits approximately 30% to 50% higher tensile strength, 20% to 40% longer high-temperature endurance, and 15% to 30% lower gas generation. Furthermore, the core production and casting yield rates remain consistently high (reaching 100% in Example 6), demonstrating the reliability and applicability of this technical solution in industrial production.

[0052] Conclusion: This technical solution achieves a balance of high strength, low gassing, and excellent heat resistance through the synergistic ratio of microsilica fume and sodium silicate and an optimized secondary coating process. The formulation and process parameters of Example 6 represent the optimal implementation and can be widely used in the preparation of sand cores for complex castings, significantly improving casting quality and efficiency.

[0053] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing high-strength, low-gassing heat-resistant coated sand, characterized in that: The following steps are involved: S1. Weigh 100 parts of raw sand; S2, perform the first lamination: S201, heating the raw sand to 120-150°C and then putting it into the first sand mixer; S202, adding 1-3 parts of binder to mix sand; S203, adding 0.1-0.5 parts of curing agent to mix sand; S204, adding 0.1-0.2 parts of lubricant to the sand mix; S3, perform the second lamination: S301, after the first coating, the mixed sand is cooled to 30-60°C and then put into the second sand mixer; S302, add 0.2~1.0 parts of microsilica powder to mix sand; S303, adding 0.5-2.0 parts of sodium silicate to mix the sand to obtain coated sand; The sodium silicate / microsilica powder inorganic protective layer formed by the second coating covers the surface of the first coating.

2. The method for preparing high-strength, low-gassing, heat-resistant coated sand according to claim 1, characterized in that: In step S1, the raw sand is selected from Inner Mongolia scrubbing sand of 50 / 100 specification.

3. The high-strength, low-gas-generating, heat-resistant coated sand according to claim 1, characterized in that: In step S202, the binder is phenolic resin, and the binder phenolic resin is added to mix the sand, and the mixing time is 10 to 30 seconds.

4. The method for preparing high-strength, low-gassing, heat-resistant coated sand according to claim 3, characterized in that: The phenolic resin has a softening point of 60-90° C. and a polymerization speed of 20-50 s.

5. The method for preparing high-strength, low-gassing, heat-resistant coated sand according to claim 4, characterized in that, in step S203, the curing agent is methenamine, and the curing agent methenamine is added to mix the sand, and the mixing time is 30 to 50 seconds.

6. The method for preparing high-strength, low-gassing, heat-resistant coated sand according to claim 1, characterized in that: In step S204, the lubricant is calcium stearate, and the lubricant calcium stearate is added to mix the sand, and the mixing time is 30 to 60 seconds.

7. The method for preparing high-strength, low-gassing, heat-resistant coated sand according to claim 1, characterized in that: In the second coating process: Step S301, the product is cooled to 30-60°C in a water mist cooling tank and then put into the sand mixer again.

8. The method for preparing high-strength, low-gassing, heat-resistant coated sand according to claim 1, characterized in that: In the second coating: Step S302, microsilica powder is added to the sand mixing, and the sand mixing time is 30 to 60 seconds.

9. The method for preparing high-strength, low-gassing, heat-resistant coated sand according to claim 1, characterized in that: In the second coating: step S303, sodium silicate is added to mix the sand, and the mixing time is 20-60 seconds to obtain coated sand.

10. A high-strength, low-gassing, heat-resistant coated sand, characterized in that: The method according to any one of claims 1 to 9 is used for preparation.

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