High-scrubbability modified sodium silicate sand and method for preparing the same

Abstract

The application discloses a high-disintegration modified water glass sand and a preparation method thereof, and relates to the technical field of foundry molding materials. The modified water glass sand comprises the following raw materials in parts by weight: 80-120 parts of quartz sand, 3-5 parts of water glass, 0.8-2.5 parts of phosphatized modified composite inorganic micro powder, 0.5-1.8 parts of sulfonated modified bamboo charcoal material, 0.3-1.2 parts of thermoplastic phenolic resin powder and 0.2-0.8 parts of polyacrylic acid sodium solution. The phosphatized modified composite inorganic micro powder is prepared from zircon powder, tourmaline powder, phosphoric acid and urea through pH adjustment reaction and calcination; and the sulfonated modified bamboo charcoal material is prepared from bamboo charcoal powder through nitric acid oxidation and diazotization grafting. The modified water glass sand has the advantages of high normal-temperature strength, low high-temperature residual strength, excellent disintegration and good moisture resistance, and is suitable for the molding production of cast steel parts and large cast iron parts.

Description

Technical Field

[0001] This invention relates to the field of casting molding materials technology, specifically to a highly collapsible modified water glass sand and its preparation method. Background Technology

[0002] Water glass sand, as an inorganic binder molding sand used in casting, is widely used in the molding of cast steel and large cast iron parts due to its advantages such as low cost, no harmful gas generation during production, and high casting precision. However, the poor collapsibility of water glass sand has long been a key technical problem restricting its development. Collapsibility refers to the ease with which the sand mold or core can be broken and detached after the casting has been poured and solidified. The fundamental reason for the poor collapsibility of water glass sand is that, under high-temperature pouring conditions, the effective component sodium silicate in water glass melts and agglomerates, forming a dense glassy sintered body on the bonding bridge between sand particles. This results in the sand mold maintaining high residual strength after the casting cools, making sand removal and cleaning difficult. The sodium ions remaining on the surface of the old sand also seriously affect the recycling of the old sand.

[0003] To improve the collapsibility of water glass sand, existing technologies mainly employ two methods. One is to add organic modifiers or inorganic dispersants to the water glass, such as sawdust, starch, organic esters, graphite powder, and slag. Organic additives burn or volatilize at high temperatures, generating pores that disrupt the continuity of the bonding film; inorganic powders induce cracks through physical isolation or differences in thermal expansion coefficients. The second method involves modifying the water glass itself, such as using composite modified water glass or reducing the amount of water glass added. However, existing technologies still have the following shortcomings. First, the thermal decomposition temperature window of organic dispersants is narrow, and a single organic component cannot cover the entire temperature range from the initial stage of casting to the later stage of solidification, leading to unstable collapsibility. Furthermore, some organic dispersants decompose at high temperatures, generating large amounts of gas, which easily causes porosity defects in the casting. Second, inorganic dispersants are mostly physically blended, resulting in poor uniformity of distribution on the sand grain surface and a lack of chemical bonding with the bonding film, leading to low collapsibility efficiency. Third, existing modification techniques often sacrifice the room-temperature strength of water glass sand while improving its collapsibility, or require additional water glass to compensate for the strength loss, creating a contradiction between collapsibility and strength. Fourth, existing self-prepared collapsibility aids are mostly simple physical mixtures, lacking the functionality to intelligently switch between room-temperature enhancement and high-temperature collapsibility through chemical bonding design.

[0004] Therefore, it is necessary to develop a highly collapsible modified water glass sand that can maintain high bonding strength at room temperature and achieve gradient-controlled collapsing at high temperature, while overcoming the technical challenges of narrow temperature windows for organic collapsible agents and poor dispersibility for inorganic collapsible agents. Summary of the Invention

[0005] The purpose of this invention is to provide a highly collapsible modified water glass sand and its preparation method, so as to solve the problems mentioned in the background art.

[0006] In a first aspect, the present invention provides a highly collapsible modified water glass sand, comprising the following raw materials in parts by weight: 80-120 parts of quartz sand; 3-5 parts water glass; Phosphorylation-modified composite inorganic micro powder, 0.8-2.5 parts; 0.5-1.8 parts of sulfonated modified bamboo charcoal material; 0.3-1.2 parts of thermoplastic phenolic resin powder; 0.2-0.8 parts of sodium polyacrylate solution.

[0007] As a preferred embodiment of the present invention, the average particle size of the quartz sand is 75 mesh.

[0008] As a preferred embodiment of the present invention, the water glass has a modulus of 2.2-2.6 and a Baume degree of 48-52.

[0009] As a preferred embodiment of the present invention, the particle size of the thermoplastic phenolic resin powder is 200 mesh.

[0010] As a preferred embodiment of the present invention, the sodium polyacrylate solution has a molecular weight of 3000-5000 and a solid content of 10-15 wt%.

[0011] A second aspect of the present invention provides a method for preparing highly collapsible modified water glass sand, comprising the following steps: S1. Add the specified amount of quartz sand and sodium polyacrylate solution to the sand mixer and stir for 30 seconds to obtain pre-wetted sand. S2. Add the formulated amounts of phosphoric acid modified composite inorganic micro powder, sulfonated modified bamboo charcoal material and thermoplastic phenolic resin powder to the pre-wetted sand, stir for 1 minute to obtain mixed sand. S3. Add the prescribed amount of water glass to the mixed sand and stir for 2 minutes to obtain wet modified water glass sand; S4. Fill the mold with wet modified water glass sand and cure it under a carbon dioxide gas atmosphere. The flow rate of carbon dioxide gas is 8-12L / min and the blowing time is 40-60s to obtain highly collapsible modified water glass sand.

[0012] As a preferred embodiment of the present invention, the preparation method of the phosphorylation-modified composite inorganic micro powder is as follows: By weight, 50 parts zircon powder and 30 parts tourmaline powder are mixed, 15 parts phosphoric acid (85% by mass), 5 parts urea and 100-150 parts deionized water are added, the pH of the mixture is adjusted to 2.5-3 with ammonia, and the mixture is stirred at 90℃ for 3 hours. After filtration, the mixture is washed with deionized water until the pH is 5.5-6.5, and dried at 120℃ for 4 hours. The dried product is calcined at 400℃ for 1 hour, cooled naturally, and then ground until the D90 is no greater than 20 μm to obtain the final product.

[0013] The zircon powder has a particle size of 325 mesh, and the tourmaline powder has a particle size of 400 mesh.

[0014] As a preferred embodiment of the present invention, the preparation method of the sulfonated modified bamboo charcoal material is as follows: By weight, 60 parts of bamboo charcoal powder are added to 80-120 parts of concentrated nitric acid with a mass concentration of 65%-68%. The reactor is equipped with a reflux condenser and a tail gas absorption device, and the mixture is stirred and oxidized at 80°C for 3 hours. After cooling and filtration, the powder was washed with deionized water until the pH reached 6-7, and dried at 110℃ for 6 hours to obtain oxidized bamboo charcoal powder. Eight parts of p-aminobenzenesulfonic acid were dissolved in 20 parts of deionized water, and 2-3 parts of sodium hydroxide were added to adjust the pH to 7-8. The mixture was stirred until completely dissolved to obtain a sodium p-aminobenzenesulfonate solution. This solution was mixed with 25-30 parts of concentrated hydrochloric acid (36%-38% by mass), and 3 parts of a 30% aqueous solution of sodium nitrite was added dropwise under ice bath conditions at 0-5℃. The mixture was stirred for 30 minutes to obtain a diazonium salt solution. The oxidized bamboo charcoal powder was dispersed in 100-150 parts of deionized water, and the diazonium salt solution was added under ice bath conditions at 0-5℃. The mixture was stirred and reacted for 2 hours. The powder was filtered, washed with deionized water until no chloride ions were detected, dried at 80℃ for 4 hours, and ground until the D90 was no greater than 15 μm to obtain the final product. The bamboo charcoal powder has a particle size of 200 mesh.

[0015] It should be noted that the present invention uses quartz sand as aggregate, which has uniform particle size distribution, good thermal stability, and does not undergo side reactions with water glass. As an inorganic binder, the modulus and Baumé degree of water glass directly affect the bond strength and curing characteristics. A low modulus results in insufficient bond strength, while a high modulus increases the brittleness of the bonded film. The present invention limits the modulus to 2.2-2.6 and the Baumé degree to 48-52 to obtain suitable bond performance and processability.

[0016] It should be noted that this invention uses phosphoric acid-modified composite inorganic micropowder as one of the dispersing agents. During the preparation of this micropowder, phosphoric acid reacts chemically with zircon oxide in zircon powder and metal oxides in tourmaline powder at pH 2.5-3 and 90℃, generating a chemically bonded layer of phosphates such as zirconium phosphate and iron phosphate, rather than a simple physical coating. Urea acts as a buffer, slowly decomposing and releasing ammonia gas under acidic heating conditions to prevent excessive local reactions. Calcination at 400℃ converts the phosphates into pyrophosphates or polyphosphates. This chemically bonded layer forms a strong interfacial bond with subsequently added water glass at room temperature through PO-Zr and PO-Fe covalent bonds, enhancing the density of the adhesive bridge. Under high-temperature casting conditions (above 600℃), the pyrophosphate decomposes to produce phosphorus pentoxide gas, which actively cuts the water glass adhesive film. Compared with physically blended inorganic dispersing agents in the prior art, the phosphoric acid-modified composite inorganic micropowder of this invention is chemically bonded to the adhesive film interface, resulting in a more concentrated and efficient dispersing effect.

[0017] It should be noted that this invention uses sulfonated modified bamboo charcoal material as another dispersion aid. After bamboo charcoal powder is oxidized with concentrated nitric acid, carboxyl groups and phenolic hydroxyl groups are generated on the surface. p-Aminobenzenesulfonic acid reacts with sodium nitrite under acidic low-temperature conditions to generate a diazonium salt. This diazonium salt undergoes an azo coupling reaction with the phenolic hydroxyl groups on the bamboo charcoal surface, covalently grafting the p-sulfonic acid groups onto the bamboo charcoal surface via azo bonds. The introduction of sulfonic acid groups endows the bamboo charcoal material with negative charge and hydrophilicity. At room temperature, it forms hydrogen bonds with the carboxyl groups of sodium polyacrylate, synergistically improving the dispersion uniformity of bamboo charcoal on the quartz sand surface. Under high-temperature conditions (500-700℃), the sulfonic acid groups decompose to release sulfur dioxide and sulfur trioxide gases, forming a synergistic release of dual acidic gases with the phosphorus pentoxide gas released by the decomposition of phosphate. Compared with unmodified carbon materials or physically mixed dispersion agents in the prior art, the sulfonated modified bamboo charcoal material of this invention achieves controllable design of surface functional groups through covalent grafting, resulting in a more defined temperature window for the release of dispersion gases.

[0018] It should be further explained that a synergistic collapse mechanism of dual acidic gases exists between the phosphoric acid-modified composite inorganic micropowder and the sulfonated modified bamboo charcoal material. The phosphoric acid-modified composite inorganic micropowder releases phosphorus pentoxide in the 600-800℃ temperature range, while the sulfonated modified bamboo charcoal material releases sulfur dioxide and sulfur trioxide in the 500-700℃ temperature range. Their decomposition temperature ranges partially overlap, forming a mixed acidic gas environment of phosphorus pentoxide and sulfur trioxide within these temperature ranges. More importantly, both phosphorus pentoxide and sulfur trioxide react with sodium oxide in water glass to generate low-melting-point sodium phosphate (melting point approximately 620℃) and sodium sulfate (melting point approximately 884℃), with sodium phosphate existing in a liquid or semi-molten state at the casting temperature. The liquid sodium phosphate further penetrates and dilutes the sodium silicate network in the water glass adhesive film, transforming the adhesive film from a single physical brittle cracking to a synergistic destruction mode of chemical corrosion and physical cracking, significantly reducing its residual strength. When phosphoric acid-modified composite inorganic micro powder or sulfonated modified bamboo charcoal material is added alone, the synergistic erosion effect of low-melting-point salt cannot be formed due to the release of only one type of acidic gas, and the dispersion effect is significantly worse than that of the combination of the two.

[0019] It should be further explained that thermoplastic phenolic resin powder and sodium polyacrylate solution play a dual auxiliary role in this invention. The thermoplastic phenolic resin powder softens and pyrolyzes in the initial stage of casting (200-400℃), generating preliminary pores, providing channels for the diffusion of acidic gases at subsequent high temperatures. The sodium polyacrylate solution, at room temperature, complexes with water glass and the phosphate layer on the surface of the modified inorganic micropowder, forming an organic-inorganic cross-linked network, improving the bonding strength at room temperature. Simultaneously, the dehydration shrinkage in the initial stage of casting creates stress concentration points, promoting the initiation of microcracks. Both components respectively cover the dispersion requirements in the low-temperature and initial-temperature zones, forming a temperature gradient connection with the dispersion effects of the phosphorylated modified composite inorganic micropowder and the sulfonated modified bamboo charcoal material in the medium- and high-temperature zones. This ensures that the dispersion behavior covers the entire temperature range from the initial stage of casting to the cooling of the casting, overcoming the narrow temperature window defect of a single dispersion agent.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses the chemical bonding design of phosphoric acid modified composite inorganic micro powder to fix the phosphate layer on the surface of inorganic micro powder in the form of covalent bonds, which enhances the interfacial bonding with water glass at room temperature, and actively cuts the adhesive film by releasing phosphorus pentoxide gas through pyrophosphate decomposition at high temperature, thus overcoming the problems of uneven distribution and low dispersibility caused by physical blending of existing inorganic dispersants.

[0021] (2) This invention modifies bamboo charcoal material by azo coupling grafting through sulfonation modification, covalently grafting p-sulfonic acid groups onto the surface of bamboo charcoal, improving dispersibility through hydrogen bonding at room temperature, and releasing sulfur dioxide and sulfur trioxide gases through the decomposition of sulfonic acid groups at high temperature. These gases, together with phosphorus pentoxide released by phosphoric acid modified composite inorganic micro powder, form a dual-acid gas synergistic dispersion system. The two gases react together with sodium oxide in water glass to generate low-melting-point sodium phosphate and sodium sulfate, realizing a dual-mode dispersion mechanism of chemical melting and physical cracking, significantly reducing high-temperature residual strength.

[0022] (3) This invention achieves a synergistic effect between phosphoric acid modified composite inorganic micro powder and sulfonated modified bamboo charcoal material, so that the gas release temperature range of the two partially overlaps and the products are complementary at high temperature. When added alone, the disintegration effect is limited, and when the two are added together, the residual strength is significantly reduced, showing an unpredictable synergistic effect.

[0023] (4) The present invention uses thermoplastic phenolic resin powder and sodium polyacrylate solution as collapsible aids in the low temperature zone, and forms a gradient collapsible temperature coverage with the dual acid gas synergistic collapsible system, avoiding the problem of incomplete collapsible due to the narrow temperature window of a single collapsible agent. At the same time, the complexation effect of sodium polyacrylate and phosphoric acid modified composite inorganic micro powder on the surface improves the bonding strength at room temperature, overcoming the contradiction between collapsibility and strength.

[0024] (5) This invention does not add organic modifiers containing volatile organic solvents, nor does it add heavy metals or toxic organic antibacterial agents. All self-prepared components are chemically bonded modified products, with no risk of small molecule migration, and meet the requirements of green casting. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Preparation Example 1 The preparation steps of phosphorylation modified composite inorganic micro powder are as follows: By weight, 50 parts zircon powder and 30 parts tourmaline powder were mixed, and 15 parts phosphoric acid (85% by mass), 5 parts urea, and 120 parts deionized water were added. The pH of the mixture was adjusted to 2.8 with ammonia. The mixture was stirred at 90°C for 3 hours, filtered, washed with deionized water until the pH reached 6, and dried at 120°C for 4 hours. The dried product was calcined at 400°C for 1 hour, allowed to cool naturally, and then ground until the D90 was no greater than 20 μm.

[0027] Preparation Example 2 The preparation steps for sulfonated modified bamboo charcoal materials are as follows: By weight, 60 parts of bamboo charcoal powder with a particle size of 200 mesh were added to 100 parts of concentrated nitric acid with a mass concentration of 65%. The reactor was equipped with a reflux condenser and a tail gas absorption device. The mixture was stirred and oxidized at 80°C for 3 hours. After cooling, the mixture was filtered, washed with deionized water until the pH reached 6.5, and dried at 110°C for 6 hours to obtain oxidized bamboo charcoal powder. 8 parts of p-aminobenzenesulfonic acid were dissolved in 20 parts of deionized water, and 2.5 parts of sodium hydroxide were added to adjust the pH to 7.5. The mixture was stirred until completely dissolved to obtain sodium p-aminobenzenesulfonate. Solution: Mix the above solution with 28 parts of concentrated hydrochloric acid with a mass concentration of 37%, and add 3 parts of an aqueous solution of sodium nitrite with a mass concentration of 30% under 0℃ ice bath conditions. Stir for 30 min to obtain a solution of p-sulfonylbenzene diazonium salt. Disperse oxidized bamboo charcoal powder in 120 parts of deionized water, add the above diazonium salt solution under 0℃ ice bath conditions, and stir for 2 h. Filter, wash with deionized water until no chloride ions are detected, dry at 80℃ for 4 h, and grind until D90 is not greater than 15 μm to obtain the final product.

[0028] Preparation Example 3 This preparation example is a comparative study using unmodified composite inorganic micropowder and does not involve phosphorylation modification. By weight, 50 parts zircon powder and 30 parts tourmaline powder were mixed and ground until D90 was no greater than 20 μm.

[0029] Preparation Example 4 This preparation example is for comparison using unmodified bamboo charcoal material and does not involve sulfonation modification. 60 parts by weight of bamboo charcoal powder were ground until D90 was no greater than 15 μm to obtain the final product.

[0030] Preparation Example 5 The preparation steps of phosphorylation modified composite inorganic micro powder are as follows: By weight, 50 parts zircon powder and 30 parts tourmaline powder were mixed, and 15 parts phosphoric acid (85% by mass), 5 parts urea, and 100 parts deionized water were added. The pH of the mixture was adjusted to 2.5 with ammonia. The mixture was stirred and reacted at 90°C for 3 hours, filtered, washed with deionized water until the pH reached 5.5, and dried at 120°C for 4 hours. The dried product was calcined at 400°C for 1 hour, allowed to cool naturally, and then ground until the D90 was no greater than 20 μm.

[0031] Preparation Example 6 The preparation steps of phosphorylation modified composite inorganic micro powder are as follows: By weight, 50 parts zircon powder and 30 parts tourmaline powder were mixed, and 15 parts phosphoric acid (85% by mass), 5 parts urea, and 150 parts deionized water were added. The pH of the mixture was adjusted to 3 with ammonia. The mixture was stirred at 90°C for 3 hours, filtered, washed with deionized water until the pH reached 6, and dried at 120°C for 4 hours. The dried product was calcined at 400°C for 1 hour, naturally cooled, and then ground until the D90 was no greater than 20 μm to obtain the final product.

[0032] Preparation Example 7 The preparation steps for sulfonated modified bamboo charcoal materials are as follows: By weight, 60 parts of bamboo charcoal powder with a particle size of 200 mesh were added to 80 parts of concentrated nitric acid with a mass concentration of 66.5%. The reactor was equipped with a reflux condenser and a tail gas absorption device. The mixture was stirred and oxidized at 80°C for 3 hours. After cooling, the mixture was filtered, washed with deionized water until the pH reached 6, and dried at 110°C for 6 hours to obtain oxidized bamboo charcoal powder. 8 parts of p-aminobenzenesulfonic acid were dissolved in 20 parts of deionized water, and 2 parts of sodium hydroxide were added to adjust the pH to 7. The mixture was stirred until completely dissolved to obtain a sodium p-aminobenzenesulfonate solution. Mix the above solution with 25 parts of concentrated hydrochloric acid with a mass concentration of 36%, and add 3 parts of an aqueous solution of sodium nitrite with a mass concentration of 30% under ice bath conditions at 0℃. Stir for 30 min to obtain a diazonium salt solution of p-sulfonylbenzene. Disperse oxidized bamboo charcoal powder in 100 parts of deionized water, add the above diazonium salt solution under ice bath conditions at 3℃, and stir for 2 h. Filter, wash with deionized water until no chloride ions are detected, dry at 80℃ for 4 h, and grind until D90 is no greater than 15 μm to obtain the final product.

[0033] Preparation Example 8 The preparation steps for sulfonated modified bamboo charcoal materials are as follows: By weight, 60 parts of bamboo charcoal powder with a particle size of 200 mesh were added to 120 parts of concentrated nitric acid with a mass concentration of 68%. The reactor was equipped with a reflux condenser and a tail gas absorption device. The mixture was stirred and oxidized at 80°C for 3 hours. After cooling, the mixture was filtered, washed with deionized water until the pH reached 7, and dried at 110°C for 6 hours to obtain oxidized bamboo charcoal powder. 8 parts of p-aminobenzenesulfonic acid were dissolved in 20 parts of deionized water, and 3 parts of sodium hydroxide were added to adjust the pH to 8. The mixture was stirred until completely dissolved to obtain a sodium p-aminobenzenesulfonate solution. The above solution was mixed with 28 parts of concentrated hydrochloric acid with a mass concentration of 38%, and 3 parts of an aqueous solution of sodium nitrite with a mass concentration of 30% was added dropwise under ice bath conditions at 5°C. The mixture was stirred for 30 min to obtain a diazonium salt solution of p-sulfonylbenzene. The oxidized bamboo charcoal powder was dispersed in 150 parts of deionized water, and the above diazonium salt solution was added under ice bath conditions at 5°C. The mixture was stirred and reacted for 2 h. The mixture was filtered, washed with deionized water until no chloride ions were detected, dried at 80°C for 4 h, and ground until D90 was no greater than 15 μm to obtain the final product.

[0034] Example 1

[0035] A highly collapsible modified water glass sand comprises the following raw materials in parts by weight: 100 parts of quartz sand; 4 parts water glass; Phosphorylated modified composite inorganic micro powder (prepared in Example 1) 1.6 parts; 1.2 parts of sulfonated modified bamboo charcoal material (prepared in Example 2); 0.8 parts of thermoplastic phenolic resin powder; 0.5 parts of sodium polyacrylate solution.

[0036] The average particle size of the quartz sand is 75 mesh. The modulus of the water glass is 2.4, and the Baumé degree is 50. The particle size of the thermoplastic phenolic resin powder is 200 mesh. In the sodium polyacrylate solution, the molecular weight of the sodium polyacrylate is 4000, and the solid content of the sodium polyacrylate solution is 12 wt%.

[0037] A method for preparing highly collapsible modified water glass sand is as follows: S1. Add quartz sand and sodium polyacrylate solution to a sand mixer and stir for 30 seconds to obtain pre-wetted sand. S2. Add phosphoric acid modified composite inorganic micro powder, sulfonated modified bamboo charcoal material and thermoplastic phenolic resin powder to the pre-wetted sand, stir for 1 minute to obtain mixed sand. S3. Add water glass to the mixed sand and stir for 2 minutes to obtain wet modified water glass sand; S4. Fill the wet modified water glass sand into the test block mold and cure it under a carbon dioxide gas atmosphere. The flow rate of carbon dioxide gas is 10L / min and the blowing time is 50s to obtain a highly collapsible modified water glass sand sample.

[0038] Example 2

[0039] The difference between this embodiment and Embodiment 1 is that the weight parts of the raw materials are adjusted as follows: 80 parts quartz sand, 3 parts water glass, 0.8 parts phosphorylated modified composite inorganic micro powder, 0.5 parts sulfonated modified bamboo charcoal material, 0.3 parts thermoplastic phenolic resin powder, and 0.2 parts sodium polyacrylate solution. The modulus of the water glass is 2.2, and the Baume degree is 48. In the sodium polyacrylate solution, the molecular weight of sodium polyacrylate is 3000, and the solid content of the sodium polyacrylate solution is 10 wt%. In the preparation method of a highly collapsible modified water glass sand, the carbon dioxide gas flow rate is 8 L / min, and the blowing time is 40 s. The other conditions are the same as in Embodiment 1.

[0040] Example 3

[0041] The difference between this embodiment and Example 1 is that the weight parts of the raw materials are adjusted as follows: 120 parts of quartz sand, 5 parts of water glass, 2.5 parts of phosphorylated modified composite inorganic micro powder, 1.8 parts of sulfonated modified bamboo charcoal material, 1.2 parts of thermoplastic phenolic resin powder, and 0.8 parts of sodium polyacrylate solution. The modulus of the water glass is 2.6, and the Baume degree is 52. In the sodium polyacrylate solution, the molecular weight of sodium polyacrylate is 5000, and the solid content of the sodium polyacrylate solution is 15 wt%. In the preparation method of a highly collapsible modified water glass sand, the carbon dioxide gas flow rate is 12 L / min, and the blowing time is 60 s. The other conditions are the same as in Example 1.

[0042] Comparative Example 1 The difference between this comparative example and Example 1 is that phosphorylated modified composite inorganic powder was not added; instead, an equal weight portion of the unmodified composite inorganic powder prepared in Preparation Example 3 was added. All other conditions were the same as in Example 1.

[0043] Comparative Example 2 The difference between this comparative example and Example 1 is that sulfonated modified bamboo charcoal material was not added; instead, an equal part by weight of the unmodified bamboo charcoal material obtained in Preparation Example 4 was added. All other conditions were the same as in Example 1.

[0044] Comparative Example 3 The difference between this comparative example and Example 1 is that phosphoric acid-modified composite inorganic micro powder and sulfonated modified bamboo charcoal material were not added; instead, an equal weight of commercially available graphite powder (325 mesh) was added. All other conditions were the same as in Example 1.

[0045] Comparative Example 4 The difference between this comparative example and Example 1 is that thermoplastic phenolic resin powder and sodium polyacrylate solution were not added. All other conditions were the same as in Example 1.

[0046] Comparative Example 5 This comparative example uses an unmodified traditional water glass sand formulation: 100 parts quartz sand and 7 parts water glass (modulus 2.4, Baumé degree 50), without adding any modifiers or disintegration aids. The preparation method is as follows: mix the quartz sand and water glass for 2 minutes, fill the mold, and solidify with carbon dioxide gas (flow rate 10 L / min, blowing time 50 s).

[0047] test: I. Tensile Strength Test at Room Temperature Referring to GB / T 2684-2025 Test Methods for Foundry Sand and Mixtures, the Arabic numeral 8-shaped test blocks prepared in each embodiment and comparative example were stored at room temperature (25±2℃) and relative humidity (50±5%) for 24 hours, and then the tensile strength was determined using a molding sand strength tester. Five test blocks were tested in each group, and the average value was taken.

[0048] II. High-Temperature Residual Strength Test The Arabic numeral 8-shaped specimens prepared in each embodiment and comparative example were cured at room temperature for 24 hours, then placed in muffle furnaces and heated to 800℃ and 1000℃ respectively, held at that temperature for 30 minutes, and then cooled to room temperature with the furnace. The tensile strength of the cooled specimens was determined using a molding sand strength testing machine and used as the residual strength value. Five specimens were tested in each group, and the average value was taken.

[0049] III. Collapsibility Test The vibration-induced sand drop test method was used. Modified water glass sand prepared in each example and comparative example was made into cylindrical specimens with a diameter of 50 mm and a height of 50 mm. After curing at room temperature for 24 hours, the specimens were placed in a muffle furnace and heated to 800°C, held at that temperature for 30 minutes, and then cooled to room temperature with the furnace. The cooled specimens were placed on a vibration-induced sand drop tester (amplitude 0.8 mm, frequency 50 Hz), vibrated for 30 seconds, and the remaining specimen mass was weighed. The collapse rate was calculated using the following formula: Collapse rate = (initial mass - remaining mass after vibration) / initial mass × 100%.

[0050] A higher collapse rate indicates better collapse resistance. Three samples were tested in each group, and the average value was taken.

[0051] IV. Moisture Absorption Resistance Test The Arabic numeral 8-shaped test blocks prepared in each embodiment and comparative example were stored in an environment with room temperature (25±2℃) and relative humidity (80±5%) for 48 hours. The tensile strength after storage was measured, and the strength retention rate was calculated using the following formula: Strength retention rate = tensile strength after storage / initial tensile strength × 100%.

[0052] V. Gas output test Referring to the gas evolution determination method in the appendix of GB / T 2684-2025, 1g of wet modified water glass sand prepared in each example and comparative example was placed in a gas evolution analyzer and the gas evolution was measured at 1000℃. Each group was tested 3 times and the average value was taken.

[0053] VI. Summary of Results Table 1: Results of room temperature strength and residual strength tests

[0054] Table 2: Results of tests on collapsibility, moisture resistance, and gas generation.

[0055] VII. Discussion of Results As shown in Tables 1 and 2, the high collapsibility modified water glass sand prepared in Examples 1-3 of this invention is superior to the comparative examples in terms of room temperature tensile strength, high temperature residual strength, collapsibility, moisture resistance and gas generation.

[0056] Regarding room temperature tensile strength, the room temperature tensile strength of Examples 1-3 was higher than that of Comparative Examples 1-5. In Comparative Example 1, replacing the phosphorylated modified composite inorganic powder with unmodified composite inorganic powder resulted in a decrease in room temperature strength to 1.18 MPa, indicating that the phosphate chemical bond layer formed after phosphorylation significantly enhanced the interfacial bonding between the inorganic powder and water glass. In Comparative Example 2, replacing the sulfonated modified bamboo charcoal material with unmodified bamboo charcoal material resulted in a decrease in room temperature strength to 1.12 MPa, indicating that the grafting of sulfonate groups improved the dispersibility and interfacial compatibility of the bamboo charcoal material in the water glass system through hydrogen bonding. In Comparative Example 3, replacing both modified components with commercially available graphite powder resulted in even lower room temperature strength, demonstrating the crucial role of chemical bond modification in strength improvement. In Comparative Example 4, without the addition of thermoplastic phenolic resin powder and sodium polyacrylate solution, the room temperature strength decreased, indicating that the complex cross-linked network between sodium polyacrylate and the surface of the modified inorganic powder significantly contributed to the room temperature strength. Comparative Example 5 is unmodified traditional water glass sand with a room temperature strength of only 0.88 MPa, but the amount of water glass added is as high as 7 parts, indicating that the present invention still achieves higher room temperature strength by reducing the amount of water glass added by about 40% through modification design.

[0057] Regarding high-temperature residual strength, the residual strength of Examples 1-3 at 800℃ and 1000℃ was significantly lower than that of the comparative examples. The residual strength of Comparative Examples 1 and 2 was significantly higher than that of Example 1, indicating that the disintegration effect of adding unmodified composite inorganic micropowder or unmodified bamboo charcoal material alone is limited. Comparative Example 3 used commercially available graphite powder, resulting in even higher residual strength. It is particularly noteworthy that while the residual strength of Comparative Examples 1 and 2 was higher than that of Example 1, their room temperature strength was lower than that of Example 1, indicating that unmodified composite inorganic micropowder and unmodified bamboo charcoal material cannot simultaneously meet the requirements of high room temperature strength and low high-temperature residual strength. In contrast, the phosphorylation modification and sulfonation modification of this invention, through chemical bonding design, provide strong interfacial bonding at room temperature and achieve low residual strength at high temperatures through the synergistic release of dual acidic gases and the chemical erosion mechanism of low-melting-point salts, demonstrating the characteristics of intelligent switching of chemical bond thermal response.

[0058] Regarding collapsibility, the collapsibility rates of Examples 1-3 were all higher than those of the comparative examples, with Example 3 achieving a collapsibility rate of 95.8%, and the sample almost completely collapsing after 30 seconds of vibration. The collapsibility rate of Comparative Example 5 was only 28.6%, indicating extremely poor collapsibility of traditional water glass sand. The collapsibility rates of Comparative Examples 1 and 2 were 72.4% and 68.9%, respectively, significantly lower than the 94.2% of Example 1, demonstrating that the synergistic collapsibility mechanism of the dual acid gases between the phosphoric acid-modified composite inorganic micropowder and the sulfonated modified bamboo charcoal material is key to obtaining a high collapsibility rate. When added alone, only a single type of acid gas is generated, failing to form the synergistic melting effect of low-melting-point sodium phosphate and sodium sulfate, resulting in a significant reduction in collapsibility efficiency.

[0059] Regarding moisture resistance, Examples 1-3 all exhibited high strength retention rates, with Example 1 reaching 89.5%. Comparative Example 4 showed a lower strength retention rate, indicating that the complexed cross-linked network of sodium polyacrylate and the modified inorganic micropowder surface improves moisture resistance. Comparative Example 5 had the lowest strength retention rate, demonstrating that the poor moisture resistance of traditional water glass sand remains a long-standing technical challenge.

[0060] Regarding gas generation, the gas generation in Examples 1-3 was within a reasonable range and would not cause porosity defects in the castings. Comparative Example 5 had a gas generation of only 3.2 mL / g, but its collapsibility was extremely poor, indicating that improving collapsibility requires appropriate gas release, but the amount of gas released must be controlled within an acceptable range. Example 1 had a gas generation of 12.6 mL / g, while Comparative Example 3 had a gas generation of only 5.4 mL / g, indicating that the poor collapsibility of commercially available graphite powder is related to its insufficient gas generation.

[0061] In summary, the highly collapsible modified water glass sand prepared in Examples 1-3 of this invention, through the chemical bonding design of phosphorylated modified composite inorganic micro powder and sulfonated modified bamboo charcoal material and its dual acid gas synergistic collapsible mechanism, combined with the gradient-assisted collapsible effect of thermoplastic phenolic resin powder and sodium polyacrylate solution, successfully overcomes the technical difficulties in the prior art such as narrow temperature window of the collapsible agent, poor dispersibility of inorganic collapsible agent, and the contradiction between collapsibility and strength. It exhibits excellent performance in terms of room temperature tensile strength, high temperature residual strength, collapsibility, moisture resistance and gas generation, and has good prospects for industrial application.

[0062] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0063] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the scope defined by the invention, and all such modifications and additions should fall within the protection scope of the present invention.

Claims

1. A highly collapsible modified water glass sand, characterized in that: Including the following parts by weight of raw materials: 80-120 parts of quartz sand; 3-5 parts water glass; Phosphorylation-modified composite inorganic micro powder, 0.8-2.5 parts; 0.5-1.8 parts of sulfonated modified bamboo charcoal material; 0.3-1.2 parts of thermoplastic phenolic resin powder; 0.2-0.8 parts of sodium polyacrylate solution.

2. The highly collapsible modified water glass sand according to claim 1, characterized in that: The average particle size of the quartz sand is 75 mesh.

3. The highly collapsible modified water glass sand according to claim 1, characterized in that: The water glass has a modulus of 2.2-2.6 and a Baumé degree of 48-52.

4. The highly collapsible modified water glass sand according to claim 1, characterized in that: The particle size of the thermoplastic phenolic resin powder is 200 mesh.

5. The highly collapsible modified water glass sand according to claim 1, characterized in that: The sodium polyacrylate solution has a molecular weight of 3000-5000 and a solid content of 10-15 wt%.

6. A method for preparing highly collapsible modified water glass sand as described in any one of claims 1-5, characterized in that: Specifically, the following steps are included: S1. Add the specified amount of quartz sand and sodium polyacrylate solution to the sand mixer and stir for 30 seconds to obtain pre-wetted sand. S2. Add the formulated amounts of phosphoric acid modified composite inorganic micro powder, sulfonated modified bamboo charcoal material and thermoplastic phenolic resin powder to the pre-wetted sand, stir for 1 minute to obtain mixed sand. S3. Add the prescribed amount of water glass to the mixed sand and stir for 2 minutes to obtain wet modified water glass sand; S4. Fill the mold with wet modified water glass sand and cure it under a carbon dioxide gas atmosphere to obtain highly collapsible modified water glass sand.

7. The method for preparing highly collapsible modified water glass sand according to claim 6, characterized in that: The preparation method of the phosphorylation modified composite inorganic micro powder is as follows: By weight, 50 parts zircon powder and 30 parts tourmaline powder are mixed, 15 parts phosphoric acid (85% by mass), 5 parts urea and 100-150 parts deionized water are added, the pH of the mixture is adjusted to 2.5-3 with ammonia, and the mixture is stirred at 90℃ for 3 hours. After filtration, the mixture is washed with deionized water until the pH is 5.5-6.5, and dried at 120℃ for 4 hours. The dried product is calcined at 400℃ for 1 hour, cooled naturally, and then ground until the D90 is no greater than 20 μm to obtain the final product.

8. The method for preparing highly collapsible modified water glass sand according to claim 6, characterized in that: The preparation method of the sulfonated modified bamboo charcoal material is as follows: By weight, 60 parts of bamboo charcoal powder were added to 80-120 parts of concentrated nitric acid with a mass concentration of 65%-68%. The reactor was equipped with a reflux condenser and a tail gas absorption device. The mixture was stirred and oxidized at 80°C for 3 hours. After cooling, the mixture was filtered, washed with deionized water until the pH reached 6-7, and dried at 110°C for 6 hours to obtain oxidized bamboo charcoal powder. 8 parts of p-aminobenzenesulfonic acid were dissolved in 20 parts of deionized water, and 2-3 parts of sodium hydroxide were added to adjust the pH to 7-8. The mixture was stirred until completely dissolved to obtain a sodium p-aminobenzenesulfonate solution. The above... Mix the solution with 25-30 parts of concentrated hydrochloric acid with a mass concentration of 36%-38%, and add 3 parts of a 30% aqueous solution of sodium nitrite under ice bath conditions at 0-5℃. Stir for 30 min to obtain a diazonium salt solution. Disperse oxidized bamboo charcoal powder in 100-150 parts of deionized water, add the above diazonium salt solution under ice bath conditions at 0-5℃, and stir for 2 h. Filter, wash with deionized water until no chloride ions are detected, dry at 80℃ for 4 h, and grind until D90 is no greater than 15 μm to obtain the final product.

9. The method for preparing highly collapsible modified water glass sand according to claim 8, characterized in that: The bamboo charcoal powder has a particle size of 200 mesh.

10. The method for preparing highly collapsible modified water glass sand according to claim 6, characterized in that: In step S4, the flow rate of carbon dioxide gas is 8-12 L / min, and the blowing time is 40-60 s.

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