A water-based coating for sand casting and preparation method thereof

Abstract

The present invention discloses a water-based coating for sand casting and a preparation method thereof, relating to the technical field of casting coatings. The preparation method comprises the following steps: first, adding refractory aggregate, a composite suspending agent, nano-alumina, and sodium lignin sulfonate to water and stirring uniformly to obtain a premix; then, adding sodium carboxymethyl cellulose to the premix and continuing stirring to obtain the water-based coating for sand casting. The coating prepared by the present invention exhibits excellent suspension and fire resistance properties.

Description

Technical Field

[0001] The invention relates to the technical field of casting coatings, in particular to a water-based coating for sand casting and a preparation method thereof. Background Art

[0002] In the sand casting industry, water-based coatings, as a key material, play a vital role in the quality and performance of castings. Using water as a solvent, water-based coatings offer significant advantages over traditional organic solvent-based coatings, such as environmental friendliness, safety, and low cost. Consequently, they are widely used in the modern foundry industry. However, practical applications of water-based coatings still face several challenges, with poor suspension being one of the most prominent.

[0003] Good suspension properties are crucial for ensuring stable performance and uniform coating of water-based coatings. During the sand casting process, the coating must be evenly applied to the sand mold surface, forming a dense protective film to prevent defects such as sand sticking and pinholes in the casting. If the coating's suspension properties are insufficient, solid particles (such as refractory aggregate) in the coating will easily settle quickly, resulting in an uneven coating composition. This not only affects the coating's application and causes inconsistent coating thickness on the sand mold surface, but can also cause localized degradation of the coating's performance, preventing it from effectively performing its protective function, ultimately reducing the quality and yield of the casting.

[0004] In order to improve the suspension properties of existing water-based coatings for sand casting, suspending agents are often added. Although traditional suspending agents, such as bentonite and attapulgite, have certain suspension capabilities, they are difficult to meet the growing demand for high-quality casting in practical applications due to the limitations of their own structure and performance. Taking attapulgite as an example, attapulgite is a clay mineral with a special crystal structure. Due to its unique fibrous morphology and large specific surface area, it has certain suspension properties in water-based systems and can slow down the sedimentation rate of particles in the coating to a certain extent. However, ordinary attapulgite has limited surface active sites and weak interactions with other components in the coating. Its suspension stability is still not ideal in complex casting environments and during long-term storage. Summary of the Invention

[0005] The present invention aims to provide a water-based coating for sand casting and a method for preparing the same, in order to solve the technical problem of poor suspension performance of water-based coatings for sand casting mentioned in the background art. The coating prepared by the present invention has good suspension performance and fire resistance.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A water-based coating for sand casting, characterized by comprising the following components in parts by weight:

[0008] 50-80 parts of refractory aggregate, 5-10 parts of composite suspending agent, 4-8 parts of nano alumina, 3-5 parts of sodium carboxymethyl cellulose, 0.5-1 part of sodium lignin sulfonate, and 60-100 parts of water.

[0009] Preferably, the refractory aggregate consists of zircon powder, kaolin and porous mullite.

[0010] In the technical solution of the present invention, the refractory aggregate consists of zircon powder, kaolin, and porous mullite. Zircon powder, with its high melting point, good chemical stability, and excellent thermal conductivity, prevents sand from sticking and facilitates uniform cooling of the casting. Kaolin, with its plasticity and adhesive properties, helps the coating adhere to the sand mold. Porous mullite, due to its porous structure, absorbs components and provides insulation, facilitating sequential solidification of the casting. A composite suspending agent evenly disperses solid particles, ensuring uniform and stable coating during storage and use, and facilitating uniform coating. Nanoalumina enhances wear resistance, improves fire resistance, and improves coating structure. Sodium carboxymethyl cellulose thickens, binds, and stabilizes the coating. Sodium lignin sulfonate disperses, improves air permeability, and provides corrosion inhibition. Water, as a solvent and carrier, is low-cost and environmentally friendly, imparting fluidity to the coating, which forms a coating upon drying. The synergistic effect of these components significantly improves the coating's suspension properties, fire resistance, wear resistance, coating performance, and air permeability, thereby enhancing casting quality and production efficiency.

[0011] Preferably, the mass ratio of the zircon powder, kaolin and porous mullite is 8:5:2.

[0012] Preferably, the preparation method of the composite suspension comprises the following steps:

[0013] S1. Mixing attapulgite with hydrochloric acid solution, heating and stirring to react, then filtering, washing the filter cake with deionized water until the pH of the washing solution is neutral, drying and grinding to obtain acidified attapulgite;

[0014] S2, adding acrylic acid to a sodium hydroxide solution for neutralization reaction to obtain a sodium acrylate solution, adding deionized water to dilute it, then adding potassium persulfate and sodium allyl sulfonate, heating under nitrogen protection to carry out a free radical polymerization reaction, and drying and pulverizing the reaction product to obtain modified sodium polyacrylate;

[0015] S3, mixing the acidified attapulgite with deionized water to form a suspension, heating the suspension, adding modified sodium polyacrylate, and maintaining the suspension for reaction. The suspension is centrifuged, washed, and dried to obtain intercalated modified attapulgite.

[0016] S4. Adding the intercalated modified attapulgite into the xanthan gum solution, heating and stirring to react, and performing vacuum degassing treatment to obtain a composite suspension concentrate.

[0017] In the technical solution of the present invention, the attapulgite is first acidified, and the hydrochloric acid solution undergoes a double decomposition reaction with the carbonate impurities in the attapulgite. + Replacement of interlayer Ca by ion exchange 2+ / Mg 2+ , exposing more surface hydroxyl active sites. The acidified attapulgite then undergoes interlayer hydration and expansion in water, and sodium polyacrylate inserts into the interlayers through hydrogen bonding between carboxylate groups and hydroxyl groups on the attapulgite surface. Finally, the pyruvic acid groups in the xanthan gum molecules form coordination bonds with metal ions on the attapulgite surface, while its β-1,4 glycosidic backbone constructs a three-dimensional network structure through intermolecular forces. The entire modification process, through the synergistic effects of multiple reactions, including acid-base reactions, intercalation complexes, and molecular self-assembly, gradually constructs a composite suspension concentrate with a multi-level structure.

[0018] The composite suspending agent effectively prevents the sedimentation of various components in the coating system through a multi-level synergistic mechanism. Its stabilizing effect is mainly reflected in three aspects: first, the surface of the acidified modified attapulgite carries a large amount of negative charge, which produces electrostatic repulsion with the refractory aggregate and nano-alumina particles in the coating. This charge repulsion effect keeps the solid particles dispersed; second, the -COO - It combines with the cations between the attapulgite interlayers, further increasing the negative charge density of the system (zeta potential can reach over -50mV), effectively preventing heterogeneous aggregation of the refractory aggregate through double-layer repulsion. Intercalated sodium polyacrylate forms an extended "molecular brush" structure between the attapulgite interlayers (with interlayer spacing increased to 1.5-1.7nm), which blocks particles from approaching through volume exclusion, particularly effectively stabilizing nanoalumina. Finally, the three-dimensional network structure constructed by xanthan gum encapsulates the solid particles, preventing them from settling through the following methods: 1. The mechanical support of the network skeleton directly hinders particle sinking; 2. The thixotropic properties of the network structure reduce the viscosity of the coating during shearing, facilitating its application, while the network structure quickly recovers to lock the particles in place during static conditions; 3. The hydrophilic groups in the network increase the viscosity of the medium through hydration, slowing particle settling. Through the above effects, a composite stabilization mechanism of "electrostatic stabilization-steric hindrance-network restraint" is formed. This synergistic stabilization system can not only prevent the sedimentation of dense refractory aggregates, but also effectively stabilize fine particles such as nano-alumina, ensuring that the various components of the coating remain evenly distributed for a long time, thereby ensuring the performance consistency of the coating.

[0019] The present invention further encounters the problem of cracking the coating under high temperature conditions by adding the above-prepared composite suspension to the coating. To further solve this problem, the present invention replaces the sodium polyacrylate intercalated with attapulgite with modified sodium polyacrylate loaded with sulfonic acid groups. After the modified sodium polyacrylate is intercalated with attapulgite, the interlayer spacing is expanded to 2.1nm, forming a larger elastic buffer space that can absorb the thermal mismatch stress between the sand mold and the coating. In addition, after the intercalated modified sodium polyacrylate decomposes at high temperature (>500℃), the sulfonic acid groups react with the Al in the attapulgite. 3+ The reaction produces aluminum sulfonate , melting point>1000℃, the aluminum sulfonate forms a stable ceramic network structure at high temperature, which can not only maintain the structural integrity of the coating, but also effectively inhibit crack propagation.

[0020] Preferably, in step S1, the mass concentration of the hydrochloric acid solution is 5-10%.

[0021] Preferably, in step S2, the heating reaction temperature is 60° C., and the free radical polymerization reaction is carried out for 6 hours.

[0022] Preferably, the mass volume ratio of the sodium allyl sulfonate to acrylic acid is 1 g / 2-5 mL.

[0023] In the technical solution of the present invention, in order to solve the problem of coating cracking, the present invention is modified by polypropylene sodium so that a sufficient amount of sulfonic acid groups are loaded on the polypropylene sodium molecule. It is obtained by experiment that when the mass volume ratio of sodium allyl sulfonate and acrylic acid is greater than 1g / 5mL range, the coating has good anti-cracking performance. The present invention team unexpectedly found that as the sulfonic acid groups loaded on the polypropylene sodium molecule continue to increase and reach a certain critical value, that is, the mass volume ratio of sodium allyl sulfonate and acrylic acid is greater than 1g / 2mL, the porosity of the coating suddenly increases significantly, causing the compactness of the coating to decrease significantly. This may be because when an excessive amount of negatively charged sulfonic acid groups are loaded on polypropylene sodium, the potential of attapulgite is too low, the charge repulsion is too strong, and the repulsion between particles is too large, making it difficult to form a dense coating. Therefore, the present invention strictly controls the mass volume ratio of sodium allyl sulfonate and acrylic acid to be 1g / 2-5mL range.

[0024] Preferably, in step S3, the mass ratio of acidified attapulgite to modified sodium polyacrylate is 1:0.2-0.6.

[0025] Preferably, in step S4, the mass ratio of the intercalated modified attapulgite to the xanthan gum is 5:1-3.

[0026] A method for preparing a water-based coating for sand casting comprises the following steps:

[0027] First, refractory aggregate, composite suspending agent, nano-alumina and sodium lignin sulfonate are added into water and stirred evenly to obtain a premix; then, sodium carboxymethyl cellulose is added into the premix and stirred continuously to obtain a water-based coating for sand casting.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. Through the optimized ratio of zircon powder, kaolin and porous mullite, anti-sand adhesion, uniform cooling and sequential solidification of castings are achieved;

[0030] 2. The triple stabilization mechanism of the composite suspending agent, namely "electrostatics, steric hindrance, and network binding," ensures uniform dispersion of the coating, while nano-alumina further enhances the coating's fire resistance and wear resistance.

[0031] 3. Using sulfonic acid groups to modify sodium polyacrylate, an aluminum sulfonate ceramic network is formed at high temperatures, which absorbs thermal stress and inhibits crack propagation. Strictly controlled sulfonic acid group loading balances cracking and porosity of the coating. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the implementation regulations 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 any creative efforts are within the scope of protection of the present invention.

[0033] Example 1

[0034] A water-based coating for sand casting, comprising the following components in parts by weight:

[0035] 75 parts of refractory aggregate (ratio of zircon powder, kaolin and porous mullite = 8:5:2), 9 parts of composite suspending agent, 7 parts of nano alumina, 4.5 parts of sodium carboxymethyl cellulose, 0.8 parts of sodium lignin sulfonate, and 90 parts of water.

[0036] Preparation of composite suspension:

[0037] Step S1: 100 g of 200-mesh attapulgite and 200 mL of 8% hydrochloric acid solution were added to a 500-mL three-necked flask. The mixture was stirred at 300 rpm in a 60°C water bath for 2 hours to allow the hydrochloric acid to fully react with the carbonates and intercalated cations in the attapulgite. After the reaction was complete, the mixture was filtered using a Büchner funnel. The filter cake was repeatedly washed with approximately 500 mL of deionized water until the filtrate reached a pH of 7 (as determined by pH test paper). The filter cake was then dried in a 105°C oven for 12 hours. Finally, the mixture was ball milled for 30 minutes and passed through a 200-mesh sieve to obtain acidified attapulgite.

[0038] Step S2: In an 800mL four-necked flask, slowly add 50mL of acrylic acid dropwise to a 10% NaOH solution, controlling the pH to 8, to obtain a sodium acrylate solution. After dilution with 300mL of deionized water, 0.5g of potassium persulfate and sodium allyl sulfonate were added sequentially, with a mass-to-volume ratio of sodium allyl sulfonate to acrylic acid of 1g / 3mL. Nitrogen was introduced (0.5L / min) to remove oxygen. The mixture was stirred in a 60°C water bath at 200rpm for 6 hours, allowing the solution to gradually polymerize and become viscous. After the reaction, the product was poured into a polytetrafluoroethylene mold, dried in a vacuum drying oven at 80°C for 24 hours, crushed, and passed through a 200-mesh sieve to obtain sulfonic acid-modified sodium polyacrylate.

[0039] Step S3: Mix 50 g of acidified attapulgite with 300 mL of deionized water and ultrasonically disperse for 30 minutes (power 300 W) to form a stable suspension. Transfer the suspension to a 70°C water bath, and slowly add 25 g of modified sodium polyacrylate while stirring at 300 rpm. Incubate for 4 hours to allow the sodium polyacrylate to intercalate between the attapulgite layers through hydrogen bonding between the carboxylate groups and the hydroxyl groups on the attapulgite surface. After the reaction is complete, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and wash the mixture three times with ethanol to remove unreacted polymer. Finally, vacuum dry the mixture at 60°C for 12 hours to obtain the intercalated modified attapulgite.

[0040] Step S4: Dissolve 25g of xanthan gum in 500mL of 60°C deionized water and stir for 1 hour until completely dissolved. Add 50g of intercalated modified attapulgite and homogenize using a high-speed shear emulsifier at 10,000rpm for 15 minutes. Then, transfer to a 60°C water bath and stir for 2 hours. Finally, place in a vacuum degasser (0.1MPa) for 30 minutes to remove bubbles, yielding a composite suspension concentrate.

[0041] A method for preparing a water-based coating for sand casting comprises the following steps:

[0042] First, refractory aggregate, composite suspending agent, nano-alumina and sodium lignin sulfonate are added to water and stirred at 300 r / min for 50 minutes to mix them evenly to obtain a premix; then, sodium carboxymethyl cellulose is added to the premix and stirred at 500 r / min for 30 minutes to obtain a water-based coating for sand casting.

[0043] Example 2

[0044] A water-based coating for sand casting, comprising the following components in parts by weight:

[0045] 60 parts of refractory aggregate (ratio of zircon powder, kaolin and porous mullite = 8:5:2), 6 parts of composite suspending agent, 5 parts of nano alumina, 3.5 parts of sodium carboxymethyl cellulose, 0.6 parts of sodium lignin sulfonate, and 60-100 parts of water.

[0046] Preparation of composite suspension:

[0047] Step S1: 100 g of 200-mesh attapulgite and 200 mL of 6% hydrochloric acid solution were added to a 500-mL three-necked flask. The mixture was stirred at 300 rpm in a 60°C water bath for 2 hours to allow the hydrochloric acid to fully react with the carbonates and intercalated cations in the attapulgite. After the reaction was complete, the mixture was filtered using a Büchner funnel. The filter cake was repeatedly washed with approximately 500 mL of deionized water until the filtrate reached a pH of 7 (as determined by pH test paper). The filter cake was then dried in a 105°C oven for 12 hours. Finally, the mixture was ball milled for 30 minutes and passed through a 200-mesh sieve to obtain acidified attapulgite.

[0048] Step S2: In an 800mL four-necked flask, slowly add 50mL of acrylic acid dropwise to a 10% NaOH solution, controlling the pH to 8, to obtain a sodium acrylate solution. After dilution with 300mL of deionized water, 0.5g of potassium persulfate and sodium allyl sulfonate were added sequentially, with a mass-to-volume ratio of sodium allyl sulfonate to acrylic acid of 1g / 4mL. Nitrogen was introduced (0.5L / min) to remove oxygen. The mixture was stirred in a 60°C water bath at 200rpm for 6 hours, allowing the solution to gradually polymerize and become viscous. After the reaction, the product was poured into a polytetrafluoroethylene mold, dried in a vacuum drying oven at 80°C for 24 hours, crushed, and passed through a 200-mesh sieve to obtain sulfonic acid-modified sodium polyacrylate.

[0049] Step S3: Mix 50 g of acidified attapulgite with 300 mL of deionized water and ultrasonically disperse for 30 minutes (power 300 W) to form a stable suspension. Transfer the suspension to a 70°C water bath, and slowly add 15 g of modified sodium polyacrylate while stirring at 300 rpm. Incubate for 4 hours to allow the sodium polyacrylate to intercalate between the attapulgite layers through hydrogen bonding between the carboxylate groups and the hydroxyl groups on the attapulgite surface. After the reaction is complete, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and wash the mixture three times with ethanol to remove unreacted polymer. Finally, vacuum dry the mixture at 60°C for 12 hours to obtain the intercalated modified attapulgite.

[0050] Step S4: Dissolve 15g of xanthan gum in 500mL of 60°C deionized water and stir for 1 hour until completely dissolved. Add 50g of intercalated modified attapulgite and homogenize using a high-speed shear emulsifier at 10,000rpm for 15 minutes. Then, transfer to a 60°C water bath and stir for 2 hours. Finally, place in a vacuum degasser (0.1MPa) for 30 minutes to remove bubbles, yielding a composite suspension concentrate.

[0051] A method for preparing a water-based coating for sand casting comprises the following steps:

[0052] First, refractory aggregate, composite suspending agent, nano-alumina and sodium lignin sulfonate are added to water and stirred at 300 r / min for 50 minutes to mix them evenly to obtain a premix; then, sodium carboxymethyl cellulose is added to the premix and stirred at 500 r / min for 30 minutes to obtain a water-based coating for sand casting.

[0053] Example 3

[0054] A water-based coating for sand casting, comprising the following components in parts by weight:

[0055] Refractory aggregate (zircon powder, kaolin and porous mullite ratio = 8:5:2) 65 parts, composite suspending agent 7 parts, nano alumina 6 parts, sodium carboxymethyl cellulose 4 parts, sodium lignin sulfonate 0.7 parts, water 60-100 parts.

[0056] Preparation of composite suspension:

[0057] Step S1: 100 g of 200-mesh attapulgite and 200 mL of 8% hydrochloric acid solution were added to a 500-mL three-necked flask. The mixture was stirred at 300 rpm in a 60°C water bath for 2 hours to allow the hydrochloric acid to fully react with the carbonates and intercalated cations in the attapulgite. After the reaction was complete, the mixture was filtered using a Büchner funnel. The filter cake was repeatedly washed with approximately 500 mL of deionized water until the filtrate reached a pH of 7 (as determined by pH test paper). The filter cake was then dried in a 105°C oven for 12 hours. Finally, the mixture was ball milled for 30 minutes and passed through a 200-mesh sieve to obtain acidified attapulgite.

[0058] Step S2: In an 800mL four-necked flask, slowly add 50mL of acrylic acid dropwise to a 10% NaOH solution, controlling the pH to 8, to obtain a sodium acrylate solution. After dilution with 300mL of deionized water, 0.5g of potassium persulfate and sodium allyl sulfonate were added sequentially, with a mass-to-volume ratio of sodium allyl sulfonate to acrylic acid of 1g / 3.5mL. Nitrogen was introduced (0.5L / min) to remove oxygen. The mixture was stirred in a 60°C water bath at 200rpm for 6 hours, allowing the solution to gradually polymerize and become viscous. After the reaction, the product was poured into a polytetrafluoroethylene mold, dried in a vacuum drying oven at 80°C for 24 hours, crushed, and passed through a 200-mesh sieve to obtain sulfonic acid-modified sodium polyacrylate.

[0059] Step S3: Mix 50 g of acidified attapulgite with 300 mL of deionized water and ultrasonically disperse for 30 minutes (power 300 W) to form a stable suspension. Transfer the suspension to a 70°C water bath, and slowly add 20 g of modified sodium polyacrylate while stirring at 300 rpm. Incubate for 4 hours to allow the sodium polyacrylate to intercalate between the attapulgite layers through hydrogen bonding between the carboxylate groups and the hydroxyl groups on the attapulgite surface. After the reaction is complete, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and wash the mixture three times with ethanol to remove unreacted polymer. Finally, vacuum dry the mixture at 60°C for 12 hours to obtain the intercalated modified attapulgite.

[0060] Step S4: Dissolve 20g of xanthan gum in 500mL of 60°C deionized water and stir for 1 hour until completely dissolved. Add 50g of intercalated modified attapulgite and homogenize using a high-speed shear emulsifier at 10,000rpm for 15 minutes. Then, transfer to a 60°C water bath and stir for 2 hours. Finally, place in a vacuum degasser (0.1MPa) for 30 minutes to remove bubbles, yielding a composite suspension concentrate.

[0061] A method for preparing a water-based coating for sand casting comprises the following steps:

[0062] First, refractory aggregate, composite suspending agent, nano-alumina and sodium lignin sulfonate are added to water and stirred at 300 r / min for 50 minutes to mix them evenly to obtain a premix; then, sodium carboxymethyl cellulose is added to the premix and stirred at 500 r / min for 30 minutes to obtain a water-based coating for sand casting.

[0063] Example 4

[0064] A water-based coating for sand casting, comprising the following components in parts by weight:

[0065] 80 parts of refractory aggregate (ratio of zircon powder, kaolin and porous mullite = 8:5:2), 10 parts of composite suspending agent, 8 parts of nano alumina, 5 parts of sodium carboxymethyl cellulose, 1 part of sodium lignin sulfonate, and 100 parts of water.

[0066] Preparation of composite suspension:

[0067] Step S1: 100 g of 200-mesh attapulgite and 200 mL of 10% hydrochloric acid solution were added to a 500-mL three-necked flask. The mixture was stirred at 300 rpm in a 60°C water bath for 2 hours to allow the hydrochloric acid to fully react with the carbonates and intercalated cations in the attapulgite. After the reaction was complete, the mixture was filtered using a Büchner funnel. The filter cake was repeatedly washed with approximately 500 mL of deionized water until the filtrate reached a pH of 7 (as determined by pH test paper). The filter cake was then dried in a 105°C oven for 12 hours. Finally, the mixture was ball milled for 30 minutes and passed through a 200-mesh sieve to obtain acidified attapulgite.

[0068] Step S2: In an 800mL four-necked flask, slowly add 50mL of acrylic acid dropwise to a 10% NaOH solution, controlling the pH to 8, to obtain a sodium acrylate solution. After dilution with 300mL of deionized water, 0.5g of potassium persulfate and sodium allyl sulfonate were added sequentially, with a mass-to-volume ratio of sodium allyl sulfonate to acrylic acid of 1g / 2mL. Nitrogen was introduced (0.5L / min) to remove oxygen. The mixture was stirred in a 60°C water bath at 200rpm for 6 hours, allowing the solution to gradually polymerize and become viscous. After the reaction, the product was poured into a polytetrafluoroethylene mold, dried in a vacuum drying oven at 80°C for 24 hours, crushed, and passed through a 200-mesh sieve to obtain sulfonic acid-modified sodium polyacrylate.

[0069] Step S3: Mix 50 g of acidified attapulgite with 300 mL of deionized water and ultrasonically disperse for 30 minutes (power 300 W) to form a stable suspension. Transfer the suspension to a 70°C water bath, and slowly add 30 g of modified sodium polyacrylate while stirring at 300 rpm. Incubate for 4 hours to allow the sodium polyacrylate to intercalate between the attapulgite layers through hydrogen bonding between the carboxylate groups and the hydroxyl groups on the attapulgite surface. After the reaction is complete, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and wash the mixture three times with ethanol to remove unreacted polymer. Finally, vacuum dry the mixture at 60°C for 12 hours to obtain the intercalated modified attapulgite.

[0070] Step S4: Dissolve 30g of xanthan gum in 500mL of 60°C deionized water and stir for 1 hour until completely dissolved. Add 50g of intercalated modified attapulgite and homogenize using a high-speed shear emulsifier at 10,000rpm for 15 minutes. Then, transfer to a 60°C water bath and stir for 2 hours. Finally, place in a vacuum degasser (0.1MPa) for 30 minutes to remove bubbles, yielding a composite suspension concentrate.

[0071] A method for preparing a water-based coating for sand casting comprises the following steps:

[0072] First, refractory aggregate, composite suspending agent, nano-alumina and sodium lignin sulfonate are added to water and stirred at 300 r / min for 50 minutes to mix them evenly to obtain a premix; then, sodium carboxymethyl cellulose is added to the premix and stirred at 500 r / min for 30 minutes to obtain a water-based coating for sand casting.

[0073] Example 5

[0074] A water-based coating for sand casting, comprising the following components in parts by weight:

[0075] 50 parts of refractory aggregate (ratio of zircon powder, kaolin and porous mullite = 8:5:2), 5 parts of composite suspending agent, 4 parts of nano alumina, 3 parts of sodium carboxymethyl cellulose, 0.5 parts of sodium lignin sulfonate, and 60 parts of water.

[0076] Preparation of composite suspension:

[0077] Step S1: 100 g of 200-mesh attapulgite and 200 mL of 5% hydrochloric acid solution were added to a 500-mL three-necked flask. The mixture was stirred at 300 rpm in a 60°C water bath for 2 hours to allow the hydrochloric acid to fully react with the carbonates and intercalated cations in the attapulgite. After the reaction was complete, the mixture was filtered using a Büchner funnel. The filter cake was repeatedly washed with approximately 500 mL of deionized water until the filtrate reached a pH of 7 (as determined by pH test paper). The filter cake was then dried in a 105°C oven for 12 hours. Finally, the mixture was ball milled for 30 minutes and passed through a 200-mesh sieve to obtain acidified attapulgite.

[0078] Step S2: In an 800mL four-necked flask, slowly add 50mL of acrylic acid dropwise to a 10% NaOH solution, controlling the pH to 8, to obtain a sodium acrylate solution. After dilution with 300mL of deionized water, 0.5g of potassium persulfate and sodium allyl sulfonate were added sequentially, with a mass-to-volume ratio of sodium allyl sulfonate to acrylic acid of 1g / 5mL. Nitrogen was introduced (0.5L / min) to remove oxygen. The mixture was stirred in a 60°C water bath at 200rpm for 6 hours, allowing the solution to gradually polymerize and become viscous. After the reaction, the product was poured into a polytetrafluoroethylene mold, dried in a vacuum drying oven at 80°C for 24 hours, crushed, and passed through a 200-mesh sieve to obtain sulfonic acid-modified sodium polyacrylate.

[0079] Step S3: Mix 50 g of acidified attapulgite with 300 mL of deionized water and ultrasonically disperse for 30 minutes (power 300 W) to form a stable suspension. Transfer the suspension to a 70°C water bath, and slowly add 10 g of modified sodium polyacrylate while stirring at 300 rpm. Incubate for 4 hours to allow the sodium polyacrylate to intercalate between the attapulgite layers through hydrogen bonding between the carboxylate groups and the hydroxyl groups on the attapulgite surface. After the reaction is complete, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and wash the mixture three times with ethanol to remove unreacted polymer. Finally, vacuum dry the mixture at 60°C for 12 hours to obtain the intercalated modified attapulgite.

[0080] Step S4: Dissolve 10g of xanthan gum in 500mL of 60°C deionized water and stir for 1 hour until completely dissolved. Add 50g of intercalated modified attapulgite and homogenize using a high-speed shear emulsifier at 10,000rpm for 15 minutes. Then, transfer to a 60°C water bath and stir for 2 hours. Finally, place in a vacuum degasser (0.1MPa) for 30 minutes to remove bubbles, yielding a composite suspension concentrate.

[0081] A method for preparing a water-based coating for sand casting comprises the following steps:

[0082] First, refractory aggregate, composite suspending agent, nano-alumina and sodium lignin sulfonate are added to water and stirred at 300 r / min for 50 minutes to mix them evenly to obtain a premix; then, sodium carboxymethyl cellulose is added to the premix and stirred at 500 r / min for 30 minutes to obtain a water-based coating for sand casting.

[0083] Comparative Example 1

[0084] The difference between Comparative Example 1 and Example 1 is that the composite suspending agent is replaced by ordinary attapulgite, and the other steps are the same.

[0085] Comparative Example 2

[0086] The difference between Comparative Example 2 and Example 1 is that step S2 is omitted, and the modified sodium polyacrylate in step S3 is replaced by ordinary sodium polyacrylate (sodium polyacrylate does not carry sulfonic acid groups), and the remaining steps are the same.

[0087] Comparative Example 3

[0088] The difference between Comparative Example 3 and Example 5 is that in step S2, the mass volume ratio of sodium allyl sulfonate to acrylic acid is 1 g / 6 mL.

[0089] Comparative Example 4

[0090] The difference between Comparative Example 4 and Example 4 is that in step S2, the mass volume ratio of sodium allyl sulfonate to acrylic acid is 1 g / 1 mL.

[0091] Comparative Example 5

[0092] The difference between Comparative Example 5 and Example 4 is that in step S2, the mass volume ratio of sodium allyl sulfonate to acrylic acid is 1 g / 0.5 mL.

[0093] Performance testing:

[0094] 1. Paint suspension performance test:

[0095] The suspension test evaluates the ability of solid particles in a coating to remain dispersed and prevent sedimentation. To perform the test, carefully pour the prepared coating into a 100mL stoppered graduated cylinder until the mark is reached. The cylinder is then sealed to prevent external interference. The cylinder is then held in an upright position. Every hour, under stable, well-lit conditions, the sedimentation height of the solid particles in the coating is carefully observed and accurately recorded by looking straight ahead at the graduated cylinder scale. The sedimentation rate is calculated using the formula: sedimentation rate = (initial coating height - supernatant height after sedimentation at a certain point) / initial coating height × 100%. This formula reflects the ratio of the change in supernatant height due to sedimentation of solid particles in the coating over time to the initial coating height, thereby quantifying the coating's suspension performance. The results are shown in Table 1.

[0096] Table 1:

[0097]

[0098] 2. Coating crack resistance and fire resistance test:

[0099] The crack resistance test is used to evaluate a coating's ability to resist cracking when exposed to rapid temperature changes. First, a coated sand specimen is placed in a heating device, heated to 800°C at a constant rate, and held at this temperature for 20 minutes to allow the specimen to reach thermal equilibrium. The specimen is then quickly removed from the heating device and cooled in room-temperature water. Under bright, non-reflective conditions, the surface coating of the specimen is carefully observed for cracking. Using appropriately accurate measuring instruments, the number of cracks and the maximum crack length are measured and recorded. Fewer cracks and shorter maximum crack lengths indicate a better crack resistance. The test results are shown in Table 2.

[0100] The fire resistance test is used to check the stability of coatings in high temperature environments. First, prepare a sand mold test block with a size of 50mm×50mm×10mm, and apply the coating to be tested evenly and carefully on the surface of the test block to ensure that the coating thickness is consistent and there are no missing areas. Then, the coated test block is fully dried. Next, place the test block in a high-temperature furnace, set the heating program, and slowly heat it to 1500℃ at a rate of 10℃ / min. The temperature change must be controlled smoothly and precisely during the heating process. After reaching the target temperature, maintain the heat preservation time for 2 hours. During this period, continuously observe the state of the coating on the surface of the test block and record whether there is any obvious damage such as cracking or peeling. The test results are shown in Table 2.

[0101] Table 2:

[0102]

[0103] 3. Coating density performance test

[0104] The coating's density is tested using a scanning electron microscope (SEM) for microstructural analysis. During the test, a small sample is carefully removed from representative locations on the surface of a coated sand mold specimen using a cutting tool, ensuring the surface is flat and undamaged. The sample is then mounted on the SEM stage, and the microscope parameters are adjusted to obtain a clear microscopic image of the sample. Professional image analysis software is used to process and analyze the SEM image. The porosity of the coating is calculated by identifying and measuring the area and number of pores in the coating using the formula: Porosity = Total Pore Area / Total Coating Area × 100%. Lower porosity indicates a denser coating structure, and greater resistance to foreign matter intrusion and performance degradation. The calculated results are shown in Table 3.

[0105] Table 3:

[0106]

[0107] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. 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 water-based coating for sand casting, characterized in that: Comprise the following components by weight: 50-80 parts of refractory aggregate, 5-10 parts of composite suspending agent, 4-8 parts of nano-alumina, 3-5 parts of sodium carboxymethyl cellulose, 0.5-1 part of sodium lignin sulfonate, 60-100 parts of water; The preparation method of the composite suspension comprises the following steps: S1. Mixing attapulgite with hydrochloric acid solution, heating and stirring to react, then filtering, washing the filter cake with deionized water until the pH of the washing solution is neutral, drying and grinding to obtain acidified attapulgite; S2. Add acrylic acid to a sodium hydroxide solution for neutralization to obtain a sodium acrylate solution, add deionized water to dilute it, then add potassium persulfate and sodium allyl sulfonate, with the mass volume ratio of sodium allyl sulfonate to acrylic acid being 1 g / 2-5 mL. Under nitrogen protection, heat to 60° C. to carry out a free radical polymerization reaction for 6 hours. Dry and pulverize the reaction product to obtain modified sodium polyacrylate; S3, mixing the acidified attapulgite with deionized water to form a suspension, heating the suspension, adding modified sodium polyacrylate, and maintaining the suspension for reaction. The suspension is centrifuged, washed, and dried to obtain intercalated modified attapulgite. S4. Adding the intercalated modified attapulgite into the xanthan gum solution, heating and stirring to react, and performing vacuum degassing treatment to obtain a composite suspension concentrate.

2. A water-based paint for sand casting according to claim 1, characterized in that: The refractory aggregate consists of zircon powder, kaolin and porous mullite.

3. A water-based paint for sand casting according to claim 2, characterized in that: The mass ratio of the zircon powder, kaolin and porous mullite is 8:5:

2.

4. A water-based paint for sand casting according to claim 1, characterized in that: In step S1, the mass concentration of the hydrochloric acid solution is 5-10%.

5. A water-based paint for sand casting according to claim 1, characterized in that: In step S3, the mass ratio of acidified attapulgite to modified sodium polyacrylate is 1:0.2-0.

6.

6. A water-based paint for sand casting according to claim 1, characterized in that: In step S4, the mass ratio of the intercalated modified attapulgite to the xanthan gum is 5:1-3.

7. A method for preparing a water-based coating for sand casting according to any one of claims 1 to 6, characterized in that: The following steps are involved: First, refractory aggregate, composite suspending agent, nano-alumina and sodium lignin sulfonate are added into water and stirred evenly to obtain a premix; then, sodium carboxymethyl cellulose is added into the premix and stirred continuously to obtain a water-based coating for sand casting.

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