Modified sodium silicate binder for casting sand mold and application

Abstract

The invention discloses a modified water glass binder for casting a sand mold and application, belongs to the technical field of casting, and aims at solving the technical problems that in the prior art, the use amount of a water glass binder is large, and the fluidity, compressive strength and collapsibility of the sand mold for casting need to be further improved. The water glass binder comprises the following components in parts by weight: 80-90 parts of activated water glass, 10-15 parts of a reinforcing agent, 8-12 parts of activated mica powder and 3-5 parts of polyethylene glycol, a sodium silicate solution is activated and then is matched with the reinforcing agent, the activated mica powder and the like, the use amount of the water glass binder is reduced, meanwhile, the fluidity of a casting sand mold is effectively improved, and the service life of the casting sand mold is prolonged. And the instant compressive strength, the 24-hour compressive strength and the collapsibility of the casting sand mold are also improved.

Description

Technical Field

[0001] The invention relates to the technical field of casting, and in particular to a modified water glass binder for casting sand molds and applications thereof. Background Art

[0002] Casting is an indispensable key process in the manufacturing industry and is widely used in the automotive, aerospace, energy equipment and other fields. With the advancement of industrial technology, the requirements for the precision, surface quality and performance of castings are increasing. Especially in the processing of high-precision sand molds, traditional binders can no longer meet the needs of modern casting technology. Water glass binder occupies an important position in the casting industry due to its environmental friendliness, low cost and good bonding properties.

[0003] For example, a Chinese invention patent with publication number CN102992786A discloses a method for preparing a silicate binder for casting. The method comprises spray-drying water glass with a modulus of 1.9 to 3.0 to obtain the silicate binder for casting. Alternatively, the water glass may be modified and the resulting modified water glass spray-dried to obtain the silicate binder for casting. The water glass or modified water glass is spray-dried. During the spray-drying process, the water glass is atomized and its moisture is carried away by a high-temperature air flow. The resulting silicate binder for casting is a hollow, fluffy solid powder with good quick-dissolving properties. Before use, the binder only needs to be dissolved in water to prepare a solution of the desired concentration. This method effectively circumvents the aging problem of traditional water glass binders, ensuring that the water glass is always in optimal use. The binder has good bonding properties, requires a low addition amount, and has good disintegration properties. This method is conducive to the recycling of old sand and reduces environmental pollution.

[0004] However, when processing high-precision casting sand molds, the viscosity of the traditional water glass binder is relatively high due to the self-aggregation of silicates in the binder. The solid powder or gel-like silicate binders in the prior art cannot effectively improve the fluidity of the sand mold, resulting in defects such as pores and sand inclusions in the sand mold when filling complex molds, which affects the surface quality and dimensional accuracy of the casting.

[0005] In addition, in order to overcome the problem of low 1h compressive strength and 24h compressive strength of sand mold specimens, the traditional water glass binder usually increases the dosage of water glass binder to more than 5%. However, at high temperatures, the metal oxides on the surface of the casting and the water glass sand mixture will undergo a chemical reaction to form silicates with a lower melting point. This silicate is prone to over-sintering. At the same time, the silicate easily penetrates into the gaps in the water glass sand mixture, wrapping the unmelted sand particles together, causing serious sand sticking. When cooled to room temperature, the strength of the sintered layer is too high and the sand mold has poor disintegration, resulting in difficulty in sand cleaning and increased subsequent processing costs. For high-precision castings, the sand cleaning process may even damage the casting surface.

[0006] In view of the technical defects in this aspect, a solution is now proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide a modified water glass binder for casting sand molds and its application, which is used to solve the technical problems in the prior art that the amount of water glass binder used is large and the fluidity, compressive strength and collapse performance of the casting sand mold need to be further improved.

[0008] The object of the present invention can be achieved by the following technical solution: a modified water glass binder for casting sand molds, comprising the following components in parts by weight: 80-90 parts of activated water glass, 10-15 parts of a reinforcing agent, 8-12 parts of activated mica powder, and 3-5 parts of polyethylene glycol;

[0009] The enhancer consists of dioctyl phthalate, modified starch, zinc phosphate and magnesium sulfate in a weight ratio of 8-10:6-7:4-5:2-3.

[0010] Furthermore, the preparation method of the activated water glass is as follows: placing the water glass in an electrolytic cell with a plurality of electrode sheets inserted therein, lowering the temperature of the electrolytic cell to 26-30° C., and performing pulse modification for 55-65 seconds to obtain the activated water glass.

[0011] The synthetic reaction mechanism of activated water glass is:

[0012] Na2SiO3 in water glass dissociates into Na⁺ and SiO3²⁻ in aqueous solution. During the pulse modification process, SiO3²⁻ migrates to the cathode under the action of the electric field and forms aluminosilicate complexes (such as Al2(SiO3)3) with Al³⁺ in the inter-electrode area, enhancing the adhesion and stability of water glass. The instantaneous high voltage of the pulse current destroys the network structure of polysilicate, increasing the ion concentration of SiO3²⁻ and HSiO3⁻, and causing rapid migration and rearrangement to form sodium silicate salt, thereby preparing low-condensation activated water glass.

[0013] Furthermore, the water glass is a sodium silicate solution with a modulus of 1.9-3.1 and a solid content of 40-45%. The electrode sheets are aluminum sheets, and the distance between two adjacent electrode sheets is 45-50 mm. During the pulse modification, the pulse voltage is 110 V and the pulse frequency is 50 Hz.

[0014] Furthermore, the preparation method of activated mica powder is as follows: mica powder, a modifier, and anhydrous ethanol are mixed, ultrasonically dispersed for 50-60 minutes, the temperature of the reaction system is increased to 50-60° C., sodium hydroxide solution is added to the reaction system, the reaction is kept warm for 60-80 minutes, and post-processed to obtain activated mica powder.

[0015] The synthetic reaction formula of activated mica powder is:

[0016]

[0017] Where: Mica powder particles; .

[0018] The synthetic reaction mechanism of activated mica powder is

[0019] During the reaction, the siloxane bonds in the modifier molecules are hydrolyzed under the catalysis of sodium hydroxide to form silanol groups that condense with the active sites on the surface of the mica powder particles to form grafted modifications, thereby preparing activated mica powder modified with D-arabitol.

[0020] Furthermore, the amount ratio of the mica powder, the modifier, the anhydrous ethanol and the sodium hydroxide solution is 7g:2.6-2.8g:80mL:10mL, the concentration of the sodium hydroxide solution is 3-5mol / L, and the particle size of the mica powder is 1-5μm. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, the mixture is filtered, the filter cake is washed with purified water until it is neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 65-75°C, and vacuum dried to constant weight to obtain activated mica powder.

[0021] Furthermore, the preparation method of the modifier is as follows: under an inert gas atmosphere, 1-amino-1-deoxy-D-arabitol and tetrahydrofuran are mixed and stirred until the system is dissolved, the temperature of the reaction system is increased to 40-50°C, isocyanatepropyltriethoxysilane is added to the reaction system, the reaction is kept warm for 60-80 minutes, and post-processed to obtain the modifier.

[0022] The synthetic reaction formula of the modifier is:

[0023]

[0024] The synthetic reaction mechanism of the modifier is:

[0025] During the reaction with isocyanate, the amino group has higher reactivity than the hydroxyl group. During the reaction, by controlling the dosage ratio of the reaction, the amino group on the 1-amino-1-deoxy-D-arabitol molecule and the isocyanate group on the isocyanatepropyltriethoxysilane molecule undergo a condensation reaction to form a modifier having D-arabitol-modified triethoxysilane.

[0026] Furthermore, the ratio of 1-amino-1-deoxy-D-arabitol to isocyanatepropyltriethoxysilane is 1 mol:1 mol, and the ratio of 1-amino-1-deoxy-D-arabitol to tetrahydrofuran is 1 g:7 mL. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is raised to 65° C., and low-boiling substances are distilled off under reduced pressure to obtain a modifier.

[0027] Furthermore, the preparation method of modified starch is:

[0028] The water-soluble starch and deionized water were stirred and mixed, the temperature of the reaction system was raised to 65-75°C, sodium hydroxide was added to the reaction system, and the reaction was kept warm for 60-80 minutes, 1-(oxirane-2-yl)ethane-1,2-diol was added to the reaction system, the temperature of the three-necked flask was raised to 85-95°C, and the mixture was stirred for 12-14 hours, and the modified starch was obtained by post-treatment.

[0029] The synthetic reaction mechanism of modified starch is:

[0030] During the reaction, water-soluble starch, under the action of heating and sodium hydroxide, destroys the hydrogen bonds in the starch molecules, making it easier to swell and disperse, while deprotonating the hydroxyl groups in the starch molecules to generate more reactive starch oxygen anions, providing active sites for subsequent grafting reactions. Then, 1-(oxirane-2-yl)ethane-1,2-diol reacts with the starch oxygen anions, and the starch oxygen anions attack the β-carbon atom of the propylene oxide derivative, forming an ether bond after ring-opening bonding. After the reaction is completed, hydrochloric acid is added dropwise to neutralize the system to pH = 7, terminating the side reaction under alkaline conditions and avoiding excessive depolymerization of starch. The small molecular impurities and unreacted raw materials in the reaction solution are then removed by dialysis to obtain a pure modified starch solution, which is then freeze-dried to obtain the modified starch.

[0031] Furthermore, the amount ratio of the water-soluble starch, deionized water, sodium hydroxide and 1-(oxirane-2-yl)ethane-1,2-diol is 10g:60mL:1g:2g, and the post-treatment includes: after the reaction is completed, the temperature of the three-necked flask is lowered to room temperature, hydrochloric acid is added dropwise to the three-necked flask, the pH of the system is adjusted to 7, the reaction solution is placed in a dialysis bag with a molecular weight cutoff of 8000-14000Da, and deionized water is used for dialysis until the liquid conductivity value in the dialysis bag is close to that of deionized water. The mixture in the dialysis bag is transferred to a freeze dryer at a temperature of -30°C, and freeze-dried to constant weight to obtain modified starch.

[0032] The present invention also proposes an application of a modified water glass binder for a foundry sand mold, and applies the modified water glass binder for a foundry sand mold to high-precision foundry sand mold processing.

[0033] The present invention has the following beneficial effects:

[0034] 1. The modified water glass binder for casting sand mold of the present invention modifies sodium silicate water glass by pulse modification, destroys the polysilicic acid network in the water glass, generates low polycondensation sodium silicate salt, reduces the viscosity of the water glass system, and the Al introduced into the aluminum electrode 3+ With SiO3 2-The formed aluminosilicate complex is dispersed in the form of nanoparticles, further reducing the viscous resistance of the binder, enhancing the lubricity between sand particles, and improving the fluidity of the casting sand. Moreover, the free SiO3²⁻ and HSiO3⁻ in the low-condensation activated water glass are more active, and react quickly with the hydroxyl groups on the surface of the sand particles to form initial silicon-oxygen bonds, accelerating the solidification of the casting sand mold. The aluminosilicate complex acts as a rigid skeleton, forming a micro-region reinforcement structure between the sand particles, providing early support. The aluminosilicate complex continuously reacts with the sodium ions in the water glass to form a more stable silicon-aluminum-sodium complex, strengthening the long-term cross-linking network, further improving the 24h compressive strength and making the sand mold structure more stable. The aluminosilicate complex decomposes into Al2O3 and SiO2 at high temperature, shrinks in volume and produces microcracks. The difference in thermal expansion coefficient of the silicate network with low condensation structure increases at high temperature, causing stress concentration, accelerating the disintegration of the skeleton, reducing the residual strength of the casting sand mold, and improving the collapsibility of the casting sand mold.

[0035] 2. The modified water glass binder for foundry sand molds of the present invention grafts hydrophilic D-arabitol modified groups on the surface of activated mica powder, allowing them to form hydrogen bonds with silicates in the water glass, thereby improving the dispersibility of the mica powder in the binder. The layered structure of the mica powder is fully exfoliated under ultrasonic dispersion and mechanical stirring to form nanoscale lamellae, reducing frictional resistance between sand particles and further improving the fluidity of the foundry sand. The D-arabitol modified groups on the surface of the activated mica powder form a hydrogen bond network with silicates, providing additional interfacial bonding force and enhancing the bonding strength between sand particles. The rigid lamellae structure of the mica powder serves as a skeletal support in the sand mold, dispersing stress and enhancing overall strength, further improving the compressive strength of the cast yarn. The D-arabitol modified groups in the activated mica powder decompose at high temperatures, generating gas and pores, which destroy the silicate skeleton. At the same time, the layered structure of the mica powder expands at high temperatures, causing microcracks, further weakening the strength of the foundry sand mold and reducing its residual strength.

[0036] 3. The modified water glass binder for casting sand molds of the present invention introduces a large number of hydrophilic hydroxyl groups and ether bonds into the modified starch, thereby enhancing its compatibility with water glass, promoting uniform dispersion, and forming a uniform colloidal solution. The introduction of ether bonds increases the flexibility of the molecular chain. The modified starch molecular chain is relatively long and can cooperate with the activated mica powder to form a certain lubricating layer between the sand particles, thereby reducing the friction between the sand particles, further promoting the flow of the casting sand, and improving the lubricity between the sand particles. In addition, the dioctyl phthalate in the reinforcing agent acts as a plasticizer to reduce the viscosity of the binder and improve the lubricity between the sand particles. The zinc phosphate / magnesium sulfate microparticles fill the gaps between the sand particles to reduce friction resistance. The hydroxyl groups in the modified starch combine with silicates through hydrogen bonds to quickly form a bonding network between the sand particles. The flexibility of the ether bonds enables the modified starch to form an elastic cross-linked structure between the sand particles, dispersing local stress and improving the strength of the casting sand mold. Zinc phosphate reacts with water glass to form a rigid phosphate network. Magnesium sulfate exchanges with Na⁺ in the water glass to form magnesium silicate, strengthening the cross-linked network and further improving the compressive strength of the casting sand mold. During the high-temperature treatment process, the starch carbonizes to form a porous structure, and the zinc phosphate / magnesium sulfate decomposes into metal oxides, causing volume shrinkage, weakening the sand mold skeleton, reducing the residual strength of the sand mold, and improving the collapse strength of the casting sand mold. DETAILED DESCRIPTION

[0037] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] In this application, water glass is a sodium silicate solution with a modulus of 1.9-3.1 and a solid content of 40-45%;

[0039] In this application, water-soluble starch was selected from Xinfeng Cellulose Factory in Hanzhuang, Dacheng County. The main component was modified potato starch with a density of 0.41-0.7 g / cm 3 , pH value is 5.3-6, viscosity is 282-1400, melting point is 247-260℃;

[0040] In the present application, the CAS number of 1-(oxiran-2-yl)ethane-1,2-diol is 17177-50-3.

[0041] Example 1

[0042] This embodiment provides a method for preparing a modified water glass binder for casting sand molds, comprising the following steps:

[0043] S1. Preparation of activated water glass

[0044] Aluminum sheets were used as electrodes and inserted into an electrolytic cell, with the spacing between two adjacent electrode sheets set to 45 mm. Then, water glass was added to the electrolytic cell, and the temperature of the electrolytic cell was lowered to 26°C. Several electrode sheets in the electrode cell were connected to a pulse current with a pulse voltage of 110 V and a pulse frequency of 50 Hz, and pulse modification was performed for 55 seconds to obtain activated water glass.

[0045] S2. Preparation of activated mica powder

[0046] Weigh: 151.2 g of 1-amino-1-deoxy-D-arabinitol and 1058 mL of tetrahydrofuran are added to a nitrogen-protected three-necked flask and stirred until the system is dissolved. The temperature of the three-necked flask is raised to 40°C. 247.4 g of isocyanatepropyltriethoxysilane is added to the three-necked flask and the reaction is kept at this temperature for 60 minutes. The temperature of the three-necked flask is raised to 65°C, and low-boiling substances are evaporated under reduced pressure to obtain a modifier;

[0047] Weigh: 70 g of mica powder with a particle size of 1-5 μm, 26 g of a modifier, and 800 mL of anhydrous ethanol are added to a three-necked flask, ultrasonically dispersed for 50 minutes, the three-necked flask is fixed on an iron stand with a mechanical stirrer, the temperature of the three-necked flask is increased to 50° C., 100 mL of a 3 mol / L sodium hydroxide solution is added to the three-necked flask, and the reaction is kept warm for 60 minutes. The temperature of the three-necked flask is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral, and then dried, the filter cake is transferred to a drying oven at a temperature of 65° C., and vacuum dried to constant weight to obtain activated mica powder.

[0048] S3. Preparation of modified starch

[0049] Weigh: 50 g of water-soluble starch and 300 mL of deionized water are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 65° C., 10 g of sodium hydroxide is added to the three-necked flask, and the reaction is kept warm for 60 minutes. 20 g of 1-(oxirane-2-yl)ethane-1,2-diol is added to the three-necked flask, the temperature of the three-necked flask is raised to 85° C., and stirred for 12 hours. The temperature of the three-necked flask is lowered to room temperature, and hydrochloric acid is added dropwise to the three-necked flask to adjust the pH of the system to 7. The reaction solution is charged into a dialysis bag with a molecular weight cutoff of 8000 Da, and dialyzed with deionized water until the liquid conductivity value in the dialysis bag is close to that of deionized water. The mixture in the dialysis bag is transferred to a freeze dryer at a temperature of -30° C. and freeze-dried to constant weight to obtain modified starch.

[0050] S4. Preparation of enhancer

[0051] Dioctyl phthalate, modified starch, zinc phosphate, and magnesium sulfate are uniformly mixed in a weight ratio of 8:6:4:2 to obtain the reinforcing agent.

[0052] S5. Preparation of modified water glass binder

[0053] Weigh 80 parts of activated water glass, 10 parts of reinforcing agent, 8 parts of activated mica powder and 3 parts of polyethylene glycol 400 in parts by weight, add them into a beaker and mix, and perform ultrasonic dispersion for 40 minutes at room temperature to obtain a modified water glass binder.

[0054] Example 2

[0055] This embodiment provides a method for preparing a modified water glass binder for casting sand molds, comprising the following steps:

[0056] S1. Preparation of activated water glass

[0057] Aluminum sheets were used as electrodes and inserted into an electrolytic cell, with the spacing between two adjacent electrode sheets set to 47 mm. Then, water glass was added to the electrolytic cell, and the temperature of the electrolytic cell was lowered to 28°C. Several electrode sheets in the electrode cell were connected to a pulse current with a pulse voltage of 110 V and a pulse frequency of 50 Hz, and pulse modification was performed for 60 seconds to obtain activated water glass.

[0058] S2. Preparation of activated mica powder

[0059] Weigh: 151.2 g of 1-amino-1-deoxy-D-arabinitol and 1058 mL of tetrahydrofuran are added to a nitrogen-protected three-necked flask and stirred until the system is dissolved. The temperature of the three-necked flask is raised to 45°C. 247.4 g of isocyanatepropyltriethoxysilane is added to the three-necked flask and the reaction is kept warm for 70 minutes. The temperature of the three-necked flask is raised to 65°C, and low-boiling substances are evaporated under reduced pressure to obtain a modifier;

[0060] Weigh: 70 g of mica powder with a particle size of 1-5 μm, 27 g of a modifier, and 800 mL of anhydrous ethanol are added to a three-necked flask, ultrasonically dispersed for 55 minutes, the three-necked flask is fixed on an iron stand with a mechanical stirrer, the temperature of the three-necked flask is increased to 55° C., 100 mL of a 4 mol / L sodium hydroxide solution is added to the three-necked flask, and the reaction is kept warm for 70 minutes. The temperature of the three-necked flask is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral, and then dried, the filter cake is transferred to a drying oven at a temperature of 70° C., and vacuum dried to constant weight to obtain activated mica powder.

[0061] S3. Preparation of modified starch

[0062] Weigh: 50 g of water-soluble starch and 300 mL of deionized water are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 70°C. 10 g of sodium hydroxide is added to the three-necked flask and the reaction is kept warm for 70 minutes. 20 g of 1-(oxirane-2-yl)ethane-1,2-diol is added to the three-necked flask. The temperature of the three-necked flask is raised to 90°C and stirred for 13 hours. The temperature of the three-necked flask is lowered to room temperature. Hydrochloric acid is added dropwise to the three-necked flask to adjust the pH of the system to 7. The reaction solution is charged into a dialysis bag with a molecular weight cutoff of 11,000 Da and dialyzed with deionized water until the liquid conductivity value in the dialysis bag is close to that of deionized water. The mixture in the dialysis bag is transferred to a freeze dryer at -30°C and freeze-dried to constant weight to obtain modified starch.

[0063] S4. Preparation of enhancer

[0064] Dioctyl phthalate, modified starch, zinc phosphate, and magnesium sulfate are uniformly mixed in a weight ratio of 9:6.5:4.5:2.3 to obtain the reinforcing agent.

[0065] S5. Preparation of modified water glass binder

[0066] Weigh 85 parts of activated water glass, 13 parts of reinforcing agent, 10 parts of activated mica powder and 4 parts of polyethylene glycol 400 in parts by weight, add them into a beaker and mix, and ultrasonically disperse them at room temperature for 50 minutes to obtain a modified water glass binder.

[0067] Example 3

[0068] This embodiment provides a method for preparing a modified water glass binder for casting sand molds, comprising the following steps:

[0069] S1. Preparation of activated water glass

[0070] Aluminum sheets were used as electrodes and inserted into an electrolytic cell, with the spacing between two adjacent electrode sheets set to 50 mm. Then, water glass was added into the electrolytic cell, and the temperature of the electrolytic cell was lowered to 30°C. Several electrode sheets in the electrode cell were connected to a pulse current with a pulse voltage of 110 V and a pulse frequency of 50 Hz, and pulse modification was performed for 65 seconds to obtain activated water glass.

[0071] S2. Preparation of activated mica powder

[0072] Weigh: 151.2 g of 1-amino-1-deoxy-D-arabinitol and 1058 mL of tetrahydrofuran are added to a nitrogen-protected three-necked flask and stirred until the system is dissolved. The temperature of the three-necked flask is raised to 50°C. 247.4 g of isocyanatepropyltriethoxysilane is added to the three-necked flask and the reaction is kept warm for 80 minutes. The temperature of the three-necked flask is raised to 65°C, and low-boiling substances are evaporated under reduced pressure to obtain a modifier;

[0073] Weigh: 70 g of mica powder with a particle size of 1-5 μm, 28 g of a modifier, and 800 mL of anhydrous ethanol are added to a three-necked flask, ultrasonically dispersed for 60 minutes, the three-necked flask is fixed on an iron stand with a mechanical stirrer, the temperature of the three-necked flask is increased to 60° C., 100 mL of a 5 mol / L sodium hydroxide solution is added to the three-necked flask, and the reaction is kept warm for 80 minutes. The temperature of the three-necked flask is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral, and then dried, the filter cake is transferred to a drying oven at a temperature of 75° C., and vacuum dried to constant weight to obtain activated mica powder.

[0074] S3. Preparation of modified starch

[0075] Weigh: 50 g of water-soluble starch and 300 mL of deionized water are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 75° C., 10 g of sodium hydroxide is added to the three-necked flask, and the reaction is kept warm for 80 minutes. 20 g of 1-(oxirane-2-yl)ethane-1,2-diol is added to the three-necked flask, the temperature of the three-necked flask is raised to 95° C., and stirred for 14 hours. The temperature of the three-necked flask is lowered to room temperature, and hydrochloric acid is added dropwise to the three-necked flask to adjust the pH of the system to 7. The reaction solution is charged into a dialysis bag with a molecular weight cutoff of 14,000 Da, and dialyzed with deionized water until the liquid conductivity value in the dialysis bag is close to that of deionized water. The mixture in the dialysis bag is transferred to a freeze dryer at a temperature of -30° C. and freeze-dried to constant weight to obtain modified starch.

[0076] S4. Preparation of enhancer

[0077] Dioctyl phthalate, modified starch, zinc phosphate, and magnesium sulfate are uniformly mixed in a weight ratio of 10:7:5:3 to obtain the enhancer.

[0078] S5. Preparation of modified water glass binder

[0079] Weigh 90 parts of activated water glass, 15 parts of reinforcing agent, 12 parts of activated mica powder and 5 parts of polyethylene glycol 400 in parts by weight, add them into a beaker and mix, and perform ultrasonic dispersion for 60 minutes at room temperature to obtain a modified water glass binder.

[0080] Comparative Example 1

[0081] The difference between this comparative example and Example 3 is that step S1 is eliminated, and the activated water glass in step S5 is replaced by the water glass in step S1.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 3 is that step S2 is eliminated, and the activated mica powder in step S5 is replaced by the mica powder in step S2.

[0084] Comparative Example 3

[0085] The difference between this comparative example and Example 3 is that step S3 is eliminated, and the modified starch in step S4 is replaced by the water-soluble starch in step S3.

[0086] Comparative Example 4

[0087] The difference between this comparative example and Example 3 is that zinc phosphate and magnesium sulfate are not added to the reinforcing agent in step S4.

[0088] Performance testing:

[0089] Using 70-mesh quartz sand as molding sand, the modified water glass binder prepared in Examples 1-3 and Comparative Examples 1-4 and the molding sand were uniformly mixed in a weight ratio of 3:100 to obtain multiple groups of molding sand;

[0090] The fluidity index of multiple groups of foundry sand samples was measured according to the standard GB / T 31057.3-2018 "Tests for physical properties of granular materials - Part 3: Measurement of fluidity index";

[0091] Referring to the standard GB / T 2684-2009 "Test methods for foundry sand and mixtures", multiple groups of foundry sand were prepared into casting specimens. The 1h compressive strength, 24h compressive strength and 800℃ residual strength of the multiple groups of casting specimens were tested. Among them, the 800℃ residual strength is the compressive residual strength of the sample after high-temperature treatment at 800℃. The specific test results are shown in Table 1 below.

[0092] Table 1-Performance test data of the sample

[0093]

[0094] Data Analysis:

[0095] The modified water glass binder prepared by the present invention is mixed with molding sand in a ratio of 3:100. The fluidity index of the prepared molding sand sample reaches 88. The 1h compressive strength of the casting sand mold prepared from the molding sand reaches 1.36 MPa, the 24h compressive strength reaches 4.41 MPa, and the 800°C residual strength reaches 0.27 MPa. All performance test data are better than those of the comparative example, indicating that the present invention not only effectively improves the fluidity of the molding sand by activating the sodium silicate solution and then cooperating with the reinforcing agent, activated mica powder, etc., but also improves the instant compressive strength, 24h compressive strength and collapsibility of the casting sand mold.

[0096] The above contents are merely examples and explanations of the structure of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

[0097] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these 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 any one or more embodiments or examples.

[0098] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A modified water glass binder for casting sand molds, characterized in that: The invention comprises the following components in parts by weight: 80-90 parts of activated water glass, 10-15 parts of a reinforcing agent, 8-12 parts of activated mica powder and 3-5 parts of polyethylene glycol; The enhancer consists of dioctyl phthalate, modified starch, zinc phosphate and magnesium sulfate in a weight ratio of 8-10:6-7:4-5:2-3.

2. The modified water glass binder for casting sand mold according to claim 1, wherein The preparation method of the activated water glass comprises the following steps: placing the water glass in an electrolytic cell plugged with a plurality of electrode sheets, lowering the temperature of the electrolytic cell to 26-30° C., and performing pulse modification for 55-65 seconds to obtain the activated water glass.

3. A modified water glass binder for casting sand mold according to claim 2, characterized in that, The water glass is a sodium silicate solution with a modulus of 1.9-3.1 and a solid content of 40-45%. The electrode sheets are aluminum sheets with a spacing of 45-50 mm between two adjacent electrode sheets. During the pulse modification, the pulse voltage is 110 V and the pulse frequency is 50 Hz.

4. The modified water glass binder for casting sand mold according to claim 1, wherein The preparation method of activated mica powder comprises the following steps: mixing mica powder, a modifier and anhydrous ethanol, performing ultrasonic dispersion for 50-60 minutes, raising the temperature of the reaction system to 50-60° C., adding sodium hydroxide solution to the reaction system, preserving the temperature for reaction for 60-80 minutes, and performing post-treatment to obtain the activated mica powder.

5. The modified water glass binder for casting sand mold according to claim 4, characterized in that: The mica powder, modifier, anhydrous ethanol and sodium hydroxide solution are used in a ratio of 7g:2.6-2.8g:80mL:10mL, the concentration of the sodium hydroxide solution is 3-5mol / L, and the particle size of the mica powder is 1-5μm. The post-treatment includes: after the reaction is completed, lowering the temperature of the reaction system to room temperature, filtering, washing the filter cake with purified water until it is neutral and then drying it, transferring the filter cake to a drying oven at a temperature of 65-75°C, and vacuum drying it to constant weight to obtain activated mica powder.

6. The modified water glass binder for casting sand mold according to claim 4, characterized in that: The preparation method of the modifier comprises the following steps: in an inert gas atmosphere, mixing 1-amino-1-deoxy-D-arabitol and tetrahydrofuran and stirring until the system is dissolved, raising the temperature of the reaction system to 40-50° C., adding isocyanatepropyltriethoxysilane to the reaction system, keeping the temperature for reaction for 60-80 minutes, and post-treating to obtain the modifier.

7. The modified water glass binder for casting sand mold according to claim 6, characterized in that: The ratio of 1-amino-1-deoxy-D-arabitol to isocyanatepropyltriethoxysilane is 1 mol:1 mol, and the ratio of 1-amino-1-deoxy-D-arabitol to tetrahydrofuran is 1 g:7 mL. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is raised to 65° C., and low-boiling substances are distilled off under reduced pressure to obtain a modifier.

8. The modified water glass binder for casting sand mold according to claim 1, characterized in that: The preparation method of modified starch is: The water-soluble starch and deionized water were stirred and mixed, the temperature of the reaction system was raised to 65-75°C, sodium hydroxide was added to the reaction system, and the reaction was kept warm for 60-80 minutes, 1-(oxirane-2-yl)ethane-1,2-diol was added to the reaction system, the temperature of the three-necked flask was raised to 85-95°C, and the mixture was stirred for 12-14 hours, and the modified starch was obtained by post-treatment.

9. The modified water glass binder for casting sand mold according to claim 8, characterized in that: The water-soluble starch, deionized water, sodium hydroxide, and 1-(oxirane-2-yl)ethane-1,2-diol are used in a ratio of 10 g:60 mL:1 g:2 g. The post-treatment comprises: after the reaction is completed, lowering the temperature of the three-necked flask to room temperature, dropwise adding hydrochloric acid to the three-necked flask to adjust the pH of the system to 7, placing the reaction solution into a dialysis bag with a molecular weight cutoff of 8000-14000 Da, dialyzing the solution with deionized water until the conductivity of the liquid in the dialysis bag is close to that of deionized water, transferring the mixture in the dialysis bag to a freeze dryer at a temperature of -30°C, and freeze-drying the mixture to a constant weight to obtain the modified starch.

10. An application of a modified water glass binder for casting sand molds, characterized in that: The modified water glass binder for casting sand molds according to any one of claims 1 to 9 is applied to high-precision casting sand mold processing.

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