Sand casting water-based paint and preparation method thereof

Abstract

The invention discloses a sand casting water-based coating and a preparation method thereof, and relates to the technical field of casting coatings. The preparation method of the sand casting water-based coating comprises the following steps: firstly, adding the refractory aggregate, the composite suspending agent, the nano aluminum oxide and the sodium lignin sulfonate into water, and uniformly stirring to obtain a premix; and then adding sodium carboxymethyl cellulose into the premix, and continuously stirring to obtain the sand casting water-based paint. The coating prepared by the invention has good suspension performance and fire resistance.

Description

Technical Field

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

[0002] In the field of sand casting, water-based coatings, as a key material, play a crucial role in the quality and performance of castings. Water-based coatings use water as a solvent and have significant advantages such as environmental protection, safety, and low cost compared to traditional organic solvent-based coatings. Therefore, they have been widely used in modern casting industries. However, currently, water-based coatings still face some problems that need to be solved urgently during actual application, and poor suspension is one of the most prominent problems.

[0003] Good suspension is a key factor in ensuring the stable performance and uniform coating of water-based coatings. During the sand casting process, the coating needs to be evenly coated on the surface of the sand mold to form a dense protective film to prevent defects such as sand sticking and sand holes in the casting. If the suspension of the coating is insufficient, the solid particles (such as refractory aggregates) in the coating are prone to sedimentation in a short time, resulting in uneven composition of the coating. This will not only affect the coating effect, making the coating thickness on the sand mold surface inconsistent, but also may cause a decrease in the local performance of the coating, unable to effectively play the protective role of the coating, and ultimately reducing the quality and yield of the casting.

[0004] To improve the suspension of existing water-based coatings for sand casting, the method of adding suspending agents is often used. Traditional suspending agents, such as bentonite and attapulgite, although having certain suspending ability, are difficult to meet the increasing high-quality casting requirements in actual applications due to the limitations of their own structures and properties. 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 suspending performance in the water-based system and can delay the sedimentation rate of particles in the coating to a certain extent. However, ordinary attapulgite has limited surface active sites and weak interaction with other components in the coating. In a complex casting environment and during long-term storage, its suspension stability is still not ideal. Summary of the Invention

[0005] The purpose of the present invention is to provide a water-based coating for sand casting and a preparation method thereof to solve the technical problem of poor suspension performance of the water-based coating for sand casting proposed in the above background technique. The coating prepared by the present invention has good suspension performance and refractory performance.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: A water-based coating for sand casting, characterized in that it comprises the following components by weight: 50 - 80 parts of refractory aggregate, 5 - 10 parts of composite suspending agent, 4 - 8 parts of nano-aluminum oxide, 3 - 5 parts of sodium carboxymethyl cellulose, 0.5 - 1 part of sodium lignosulfonate, 60 - 100 parts of water.

[0007] Preferably, the refractory aggregate is composed of zircon powder, kaolin and porous mullite.

[0008] In the technical solution of the present invention, the refractory aggregate is composed of zircon powder, kaolin and porous mullite. Zircon powder, with its high melting point, good chemical stability and good thermal conductivity, can prevent sand sticking and help the casting cool evenly. Kaolin has plasticity and adhesiveness, which helps the coating adhere to the sand mold. Porous mullite, due to its porous structure, can adsorb components and insulate heat, facilitating the sequential solidification of the casting. The composite suspending agent can evenly disperse solid particles, ensure the uniform stability during the storage and use of the coating, and help with uniform coating. Nano-aluminum oxide can enhance wear resistance, improve fire resistance and improve the coating structure. Sodium carboxymethyl cellulose plays a role in thickening, binding and stabilizing the coating. Sodium lignosulfonate has the functions of dispersion, improving air permeability and corrosion inhibition. Water, as a solvent and carrier, is low-cost and environmentally friendly, making the coating have fluidity and forming a coating after drying. The synergistic effect of each component significantly improves the suspension, fire resistance, wear resistance, coating performance and air permeability of the coating, etc., thereby improving the quality of the casting and production efficiency.

[0009] Preferably, the mass ratio of the zircon powder, kaolin and porous mullite is 8:5:2.

[0010] Preferably, the preparation method of the composite suspending agent includes the following steps: S1. Mix attapulgite with hydrochloric acid solution, heat and stir to react, then perform suction filtration, wash the filter cake with deionized water until the pH of the washing liquid is neutral, dry and grind to obtain acidified attapulgite; S2. Add acrylic acid to sodium hydroxide solution for neutralization reaction to obtain sodium acrylate solution, dilute with deionized water, then add potassium persulfate and sodium allylsulfonate, and under nitrogen protection, heat for free radical polymerization reaction. Dry and crush the reaction product to obtain modified sodium polyacrylate; S3. Mix acidified attapulgite with deionized water and stir to form a suspension, heat up, add modified sodium polyacrylate, keep the temperature for reaction, and after centrifugal separation, washing and drying, obtain intercalated modified attapulgite; S4. Add intercalated modified attapulgite to xanthan gum solution, heat and stir to react, and perform vacuum defoaming treatment to obtain the composite suspending agent.

[0011] In the technical solution of the present invention, attapulgite is first acidified. The hydrochloric acid solution undergoes a double decomposition reaction with the carbonate impurities in attapulgite, and at the same time, H + Through ion exchange, replace the interlayer Ca 2+ / Mg 2+ , more surface hydroxyl active sites are exposed. Then, the acidified attapulgite undergoes interlayer hydration swelling in water, and sodium polyacrylate is inserted into the interlayer through the hydrogen bond between the carboxylate group and the surface hydroxyl group of attapulgite. Finally, the pyruvate group in the xanthan gum molecule forms a coordination bond with the metal ions on the surface of attapulgite, and at the same time, its β-1,4 glycosidic bond backbone constructs a three-dimensional network structure through intermolecular forces. The entire modification process gradually constructs a composite suspending agent with a multi-level structure through the synergistic effect of multiple types of reactions such as acid-base reactions, intercalation compounding, and molecular self-assembly.

[0012] The composite suspending agent effectively prevents the settlement of each component 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 number of negative charges, generating an electrostatic repulsion effect with the refractory aggregate and nano-aluminum oxide particles in the coating. This charge repulsion effect keeps the solid particles in a dispersed state; Second, the -COO of sodium polyacrylate - combines with the interlayer cations of attapulgite, further increasing the negative charge density of the system (the ζ potential can reach more than -50 mV). Through the double-layer repulsion, the heterogeneous aggregation of the refractory aggregate is effectively prevented. The intercalated sodium polyacrylate forms an extended "molecular brush" structure between the attapulgite layers (the interlayer spacing expands to 1.5 - 1.7 nm), blocking the approach of particles through the volume exclusion effect, especially having a significant stabilizing effect on nano-aluminum oxide. Finally, the three-dimensional network structure constructed by xanthan gum wraps the solid particles, preventing settlement in the following ways: 1. The mechanical support of the network skeleton directly hinders the sinking of particles; 2. The thixotropic property of the network structure reduces the viscosity of the coating during construction shearing for easy brushing, and can quickly restore the network structure to lock the particles when at rest; 3. The hydrophilic groups in the network increase the viscosity of the medium through hydration, slowing down the sedimentation rate of the particles. Through the above actions, a "electrostatic stability - steric hindrance - network binding" composite stabilization mechanism is formed. This synergistic stabilization system can not only prevent the settlement of the relatively dense refractory aggregate, but also effectively stabilize fine particles such as nano-aluminum oxide, ensuring that each component of the coating remains evenly distributed for a long time, thus guaranteeing the performance consistency of the coating.

[0013] When the above-prepared composite suspending agent is added to the coating in the present invention, a further problem encountered is that the coating is prone to cracking under high-temperature conditions. To further solve this problem in the present invention, the sodium polyacrylate intercalated in attapulgite is replaced with a modified sodium polyacrylate loaded with sulfonic acid groups. After the modified sodium polyacrylate is intercalated in attapulgite, the interlayer spacing expands to 2.1 nm, forming a larger elastic buffer space, which 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 °C), the sulfonic acid group reacts with Al in the attapulgite 3+ to generate aluminum sulfonate , with a melting point > 1000 °C, this aluminosulfonate forms a stable ceramic network structure at high temperatures, which can not only maintain the structural integrity of the coating but also effectively inhibit crack propagation.

[0014] Preferably, in the step S1, the mass concentration of the hydrochloric acid solution is 5 - 10%.

[0015] Preferably, in the step S2, the heating reaction temperature is 60 °C, and the free radical polymerization reaction is carried out for 6 h.

[0016] Preferably, the mass - to - volume ratio of sodium allylsulfonate to acrylic acid is 1 g / 2 - 5 mL.

[0017] In the technical solution of the present invention, to solve the problem of coating cracking, the present invention modifies sodium polyacrylate to load a sufficient amount of sulfonic acid groups on the sodium polyacrylate molecules. Through experiments, it is obtained that when the mass - to - volume ratio of sodium allylsulfonate to acrylic acid is greater than 1 g / 5 mL, the coating has good anti - cracking performance. The research team of the present invention unexpectedly found that as the sulfonic acid groups loaded on the sodium polyacrylate molecules continue to increase and reach a certain critical value, that is, when the mass - to - volume ratio of sodium allylsulfonate to acrylic acid is greater than 1 g / 2 mL, the porosity of the coating suddenly increases significantly, resulting in a significant decline in the densification performance of the coating. This may be because when an excessive amount of negatively charged sulfonic acid groups are loaded on the sodium polyacrylate, the potential of attapulgite is too low, the charge repulsion effect is too strong, and the repulsion force between particles is too large, making it difficult to form a dense coating. Therefore, the present invention strictly controls the mass - to - volume ratio of sodium allylsulfonate to acrylic acid within the range of 1 g / 2 - 5 mL.

[0018] Preferably, in the step S3, the mass ratio of acidified attapulgite to modified sodium polyacrylate is 1:0.2 - 0.6.

[0019] Preferably, in the step S4, the mass ratio of intercalated modified attapulgite to xanthan gum is 5:1 - 3.

[0020] A preparation method of a water - based coating for sand casting, comprising the following steps: First, add refractory aggregate, composite suspending agent, nano - alumina, and sodium lignosulfonate into water, stir evenly to obtain a premix; then add sodium carboxymethylcellulose to the premix and continue stirring to obtain the water - based coating for sand casting.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. Through the optimized ratio of zircon powder, kaolin, and porous mullite, anti - sticking of the casting, uniform cooling, and sequential solidification are achieved; 2. The "electrostatic - steric - network confinement" triple - stability mechanism of the composite suspending agent ensures the uniform dispersion of the coating, and nano - alumina further enhances the fire - resistance and wear - resistance of the coating; 3. Modify sodium polyacrylate with sulfonic acid groups to generate an aluminum sulfonate ceramic network at high temperatures, which not only absorbs thermal stress but also inhibits crack propagation. The strictly controlled sulfonic acid group loading balances the cracking of the coating and the porosity of the coating. Detailed implementation manners

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] Example 1 A water-based coating for sand casting comprises the following components by weight: Refractory aggregate (zirconium silicate powder, kaolin and porous mullite ratio = 8:5:2) 75 parts, composite suspending agent 9 parts, nano-aluminum oxide 7 parts, sodium carboxymethyl cellulose 4.5 parts, sodium lignosulfonate 0.8 parts, water 90 parts.

[0024] Preparation of the composite suspending agent: Step S1: Take 100 g of 200-mesh attapulgite and 200 mL of 8% hydrochloric acid solution and add them to a 500-mL three-necked flask. Stir at 300 rpm in a 60°C water bath for 2 hours to allow the hydrochloric acid to fully react with the carbonates and interlayer cations in the attapulgite. After the reaction is completed, filter with a Buchner funnel, and wash the filter cake with about 500 mL of deionized water repeatedly until the pH of the filtrate is 7 (detected with pH test paper). Then place the filter cake in an oven at 105°C and dry for 12 hours. Finally, grind it with a ball mill for 30 minutes and pass through a 200-mesh sieve to obtain acidified attapulgite.

[0025] Step S2: Slowly add 50 mL of acrylic acid to 10% NaOH solution in an 800-mL four-necked flask, control the pH = 8 to obtain a sodium acrylate solution. After diluting with 300 mL of deionized water, add 0.5 g of potassium persulfate and sodium allylsulfonate in turn. The mass-volume ratio of sodium allylsulfonate to acrylic acid is 1 g / 3 mL. Pass nitrogen (0.5 L / min) to remove oxygen, and stir and react at 200 rpm in a 60°C water bath for 6 hours to make the solution gradually polymerize and become viscous. After the reaction is completed, pour the product into a polytetrafluoroethylene mold, dry it in a vacuum drying oven at 80°C for 24 hours, crush it and pass through a 200-mesh sieve to obtain sulfonic acid group-modified sodium polyacrylate.

[0026] 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 under stirring at 300 rpm, and keep the temperature for reaction for 4 hours, so that sodium polyacrylate is inserted into the interlayer through the hydrogen bond action between the carboxylate group and the hydroxyl group on the surface of attapulgite. After the reaction is completed, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, wash with ethanol 3 times to remove unreacted polymers, and finally dry in vacuum at 60 °C for 12 hours to obtain intercalated modified attapulgite.

[0027] Step S4: Dissolve 25 g of xanthan gum in 500 mL of deionized water at 60 °C, and stir for 1 hour until completely dissolved. Add 50 g of intercalated modified attapulgite, homogenize with a high-speed shear emulsifier at 10000 rpm for 15 minutes, and then transfer to a 60 °C water bath and stir for 2 hours. Finally, place it in a vacuum degassing machine (0.1 MPa) for 30 minutes to remove air bubbles to obtain a composite suspending agent.

[0028] A preparation method of a water-based coating for sand casting, comprising the following steps: First, add refractory aggregate, composite suspending agent, nano-aluminum oxide and sodium lignosulfonate into water, and stir at 300 r / min for 50 minutes to mix evenly to obtain a premix; then add sodium carboxymethylcellulose to the premix, and continue to stir at 500 r / min for 30 minutes to obtain a water-based coating for sand casting.

[0029] Example 2 A water-based coating for sand casting, comprising the following components by weight: Refractory aggregate (the ratio of zircon powder, kaolin and porous mullite = 8:5:2) 60 parts, composite suspending agent 6 parts, nano-aluminum oxide 5 parts, sodium carboxymethylcellulose 3.5 parts, sodium lignosulfonate 0.6 parts, water 60 - 100 parts.

[0030] Preparation of the composite suspending agent: Step S1: Take 100 g of 200-mesh attapulgite and 200 mL of 6% hydrochloric acid solution and add them to a 500 mL three-necked flask, stir in a 60 °C water bath at 300 rpm for 2 hours to allow hydrochloric acid to fully react with the carbonate and interlayer cations in attapulgite. After the reaction is completed, filter with a Buchner funnel, wash the filter cake with about 500 mL of deionized water repeatedly until the pH of the filtrate is 7 (detected with pH test paper), then place the filter cake in an oven at 105 °C and dry for 12 hours, and finally grind with a ball mill for 30 minutes and pass through a 200-mesh sieve to obtain acidified attapulgite.

[0031] Step S2: Slowly add 50 mL of acrylic acid to 10% NaOH solution in an 800 mL four-necked flask, control the pH = 8 to obtain sodium acrylate solution. After diluting with 300 mL of deionized water, add 0.5 g of potassium persulfate and sodium allyl sulfonate in turn. The mass-volume ratio of sodium allyl sulfonate to acrylic acid is 1 g / 4 mL. Pass nitrogen (0.5 L / min) to remove oxygen, and stir and react in a 60 °C water bath at 200 rpm for 6 hours to make the solution gradually polymerize and become viscous. After the reaction is completed, pour the product into a polytetrafluoroethylene mold, dry it in a vacuum drying oven at 80 °C for 24 hours, crush it, and pass through a 200-mesh sieve to obtain sulfonic acid group-modified sodium polyacrylate.

[0032] 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 under stirring at 300 rpm, and keep the temperature for reaction for 4 hours to insert sodium polyacrylate into the interlayer through the hydrogen bond between the carboxylate group and the hydroxyl group on the surface of attapulgite. After the reaction is completed, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, wash with ethanol 3 times to remove unreacted polymers, and finally dry in a vacuum at 60 °C for 12 hours to obtain intercalation-modified attapulgite.

[0033] Step S4: Dissolve 15 g of xanthan gum in 500 mL of 60 °C deionized water, stir for 1 hour until completely dissolved. Add 50 g of intercalation-modified attapulgite, homogenize with a high-speed shear emulsifier at 10000 rpm for 15 minutes, and then transfer to a 60 °C water bath and stir for 2 hours. Finally, place it in a vacuum degassing machine (0.1 MPa) for 30 minutes to remove air bubbles to obtain a composite suspending agent.

[0034] A preparation method of a water-based coating for sand casting, comprising the following steps: First, add refractory aggregate, composite suspending agent, nano-aluminum oxide and sodium lignosulfonate to water, stir at 300 r / min for 50 minutes to make them evenly mixed to obtain a premix; then add sodium carboxymethyl cellulose to the premix, and continue to stir at 500 r / min for 30 minutes to obtain a water-based coating for sand casting.

[0035] Example 3 A water-based coating for sand casting, comprising the following components by weight: Refractory aggregate (the ratio of zircon powder, kaolin and porous mullite = 8:5:2) 65 parts, composite suspending agent 7 parts, nano-aluminum oxide 6 parts, sodium carboxymethyl cellulose 4 parts, sodium lignosulfonate 0.7 parts, water 60 - 100 parts.

[0036] Preparation of the composite suspending agent: Step S1: Take 100 g of 200-mesh attapulgite clay and 200 mL of 8% hydrochloric acid solution and add them to a 500-mL three-necked flask. Stir at 300 rpm in a 60°C water bath for 2 hours to allow the hydrochloric acid to fully react with the carbonates and interlayer cations in the attapulgite clay. After the reaction is completed, filter with a Buchner funnel. Wash the filter cake repeatedly with about 500 mL of deionized water until the pH of the filtrate is 7 (detected with pH test paper). Then place the filter cake in an oven at 105°C and dry for 12 hours. Finally, grind with a ball mill for 30 minutes and pass through a 200-mesh sieve to obtain acidified attapulgite clay.

[0037] Step S2: Slowly add 50 mL of acrylic acid to 10% NaOH solution in an 800-mL four-necked flask, control the pH to 8 to obtain sodium acrylate solution. After adding 300 mL of deionized water for dilution, add 0.5 g of potassium persulfate and sodium allylsulfonate in sequence. The mass-volume ratio of sodium allylsulfonate to acrylic acid is 1 g / 3.5 mL. Pass nitrogen (0.5 L / min) to remove oxygen, and stir and react at 200 rpm in a 60°C water bath for 6 hours to make the solution gradually polymerize and become viscous. After the reaction is completed, pour the product into a polytetrafluoroethylene mold, dry in a vacuum drying oven at 80°C for 24 hours, crush and pass through a 200-mesh sieve to obtain sulfonic acid group-modified sodium polyacrylate.

[0038] Step S3: Mix 50 g of acidified attapulgite clay 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, and keep the temperature for reaction for 4 hours to allow sodium polyacrylate to insert into the interlayer through hydrogen bonding between the carboxylate group and the surface hydroxyl group of attapulgite clay. After the reaction is completed, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, wash with ethanol 3 times to remove unreacted polymers, and finally dry in a vacuum at 60°C for 12 hours to obtain intercalation-modified attapulgite clay.

[0039] Step S4: Dissolve 20 g of xanthan gum in 500 mL of deionized water at 60°C, and stir for 1 hour until completely dissolved. Add 50 g of intercalation-modified attapulgite clay, homogenize with a high-speed shear emulsifier at 10000 rpm for 15 minutes, then transfer to a 60°C water bath and stir for 2 hours. Finally, place it in a vacuum degassing machine (0.1 MPa) for 30 minutes to remove air bubbles to obtain a composite suspending agent.

[0040] A preparation method of a water-based coating for sand casting, comprising the following steps: First, add refractory aggregate, composite suspending agent, nano-aluminum oxide and sodium lignosulfonate to water, stir at 300 r / min for 50 minutes to make them evenly mixed to obtain a premix; then add sodium carboxymethylcellulose to the premix and continue to stir at 500 r / min for 30 minutes to obtain a water-based coating for sand casting.

[0041] Example 4 A water-based coating for sand casting, comprising the following components by weight: 80 parts of refractory aggregate (the ratio of zircon powder, kaolin and porous mullite = 8:5:2), 10 parts of composite suspending agent, 8 parts of nano-aluminum oxide, 5 parts of sodium carboxymethylcellulose, 1 part of sodium lignosulfonate, and 100 parts of water.

[0042] Preparation of the composite suspending agent: Step S1: Take 100 g of 200-mesh attapulgite and 200 mL of 10% hydrochloric acid solution and add them to a 500-mL three-necked flask. Stir at 300 rpm in a 60°C water bath for 2 hours to allow the hydrochloric acid to fully react with the carbonate and interlayer cations in the attapulgite. After the reaction is completed, filter with a Buchner funnel. Wash the filter cake repeatedly with about 500 mL of deionized water until the pH of the filtrate is 7 (detected with pH test paper). Then place the filter cake in an oven at 105°C and dry for 12 hours. Finally, grind it with a ball mill for 30 minutes and pass through a 200-mesh sieve to obtain acidified attapulgite.

[0043] Step S2: Slowly add 50 mL of acrylic acid to 10% NaOH solution in an 800-mL four-necked flask, control the pH = 8 to obtain sodium acrylate solution. After diluting with 300 mL of deionized water, add 0.5 g of potassium persulfate and sodium allylsulfonate in sequence. The mass-volume ratio of sodium allylsulfonate to acrylic acid is 1 g / 2 mL. Pass nitrogen (0.5 L / min) to remove oxygen, and stir and react at 200 rpm in a 60°C water bath for 6 hours to make the solution gradually polymerize and become viscous. After the reaction is completed, pour the product into a polytetrafluoroethylene mold, dry it in a vacuum drying oven at 80°C for 24 hours, crush it and pass through a 200-mesh sieve to obtain sulfonic acid group-modified sodium polyacrylate.

[0044] 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. Keep the temperature for 4 hours to allow sodium polyacrylate to insert into the interlayer through hydrogen bonding between the carboxylate group and the surface hydroxyl group of attapulgite. After the reaction is completed, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, wash with ethanol 3 times to remove unreacted polymers, and finally dry in a vacuum at 60°C for 12 hours to obtain intercalated modified attapulgite.

[0045] Step S4: Dissolve 30 g of xanthan gum in 500 mL of deionized water at 60°C, stir for 1 hour until completely dissolved. Add 50 g of intercalated modified attapulgite, homogenize with a high-speed shear emulsifier at 10000 rpm for 15 minutes, and then transfer to a 60°C water bath and stir for 2 hours. Finally, place it in a vacuum degassing machine (0.1 MPa) for 30 minutes to remove air bubbles to obtain the composite suspending agent.

[0046] A preparation method of a water-based coating for sand casting, comprising the following steps: First, refractory aggregate, composite suspending agent, nano-aluminum oxide and sodium lignosulfonate are added to water, and stirred at 300 r / min for 50 minutes to make them uniformly mixed, obtaining a premix; then sodium carboxymethyl cellulose is added to the premix, and stirring continues at 500 r / min for 30 minutes to obtain the water-based coating for sand casting.

[0047] Example 5 A water-based coating for sand casting, comprising the following components by weight: Refractory aggregate (zirconium silicate powder, kaolin and porous mullite ratio = 8:5:2) 50 parts, composite suspending agent 5 parts, nano-aluminum oxide 4 parts, sodium carboxymethyl cellulose 3 parts, sodium lignosulfonate 0.5 part, water 60 parts.

[0048] Preparation of the composite suspending agent: Step S1: Take 100 g of 200-mesh attapulgite and 200 mL of 5% hydrochloric acid solution and add them to a 500-mL three-necked flask. Stir at 300 rpm in a 60 °C water bath for 2 hours to allow the hydrochloric acid to fully react with the carbonate and interlayer cations in the attapulgite. After the reaction is completed, filter with a Buchner funnel, and wash the filter cake with about 500 mL of deionized water repeatedly until the pH of the filtrate is 7 (detected with pH test paper). Then place the filter cake in an oven at 105 °C and dry for 12 hours. Finally, grind with a ball mill for 30 minutes and pass through a 200-mesh sieve to obtain acidified attapulgite.

[0049] Step S2: Slowly add 50 mL of acrylic acid to 10% NaOH solution in an 800-mL four-necked flask, control the pH = 8 to obtain a sodium acrylate solution. After adding 300 mL of deionized water for dilution, 0.5 g of potassium persulfate and sodium allylsulfonate are added in sequence. The mass-volume ratio of sodium allylsulfonate to acrylic acid is 1 g / 5 mL. Pass nitrogen (0.5 L / min) to remove oxygen, and stir and react at 200 rpm in a 60 °C water bath for 6 hours to make the solution gradually polymerize and become viscous. After the reaction is completed, pour the product into a polytetrafluoroethylene mold, dry in a vacuum drying oven at 80 °C for 24 hours, pulverize and pass through a 200-mesh sieve to obtain sulfonic acid group-modified sodium polyacrylate.

[0050] 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 under stirring at 300 rpm. Keep the temperature for reaction for 4 hours, so that sodium polyacrylate is intercalated into the layers through the hydrogen bond between the carboxylate group and the hydroxyl group on the surface of attapulgite. After the reaction is completed, centrifuge at 8000 rpm for 10 minutes, discard the supernatant, wash with ethanol three times to remove unreacted polymers, and finally dry in vacuum at 60 °C for 12 hours to obtain intercalated modified attapulgite.

[0051] Step S4: Dissolve 10 g of xanthan gum in 500 mL of deionized water at 60 °C, and stir for 1 hour until completely dissolved. Add 50 g of intercalated modified attapulgite, homogenize with a high-speed shear emulsifier at 10000 rpm for 15 minutes, and then transfer to a 60 °C water bath and stir for 2 hours. Finally, place it in a vacuum degassing machine (0.1 MPa) for 30 minutes to remove air bubbles, and obtain a composite suspending agent.

[0052] A preparation method of a water-based coating for sand casting, comprising the following steps: First, add refractory aggregate, composite suspending agent, nano-aluminum oxide and sodium lignosulfonate to water, and stir at 300 r / min for 50 minutes to make them evenly mixed to obtain a premix; then add sodium carboxymethylcellulose to the premix, and continue to stir at 500 r / min for 30 minutes to obtain a water-based coating for sand casting.

[0053] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the composite suspending agent is replaced with ordinary attapulgite, and the other steps are the same.

[0054] Comparative Example 2 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 with ordinary sodium polyacrylate (the sodium polyacrylate is not loaded with sulfonic acid groups), and the other steps are the same.

[0055] Comparative Example 3 The difference between Comparative Example 3 and Example 5 is that in step S2, the mass-volume ratio of allyl sulfonic acid sodium to acrylic acid is 1 g / 6 mL.

[0056] Comparative Example 4 The difference between Comparative Example 4 and Example 4 is that in step S2, the mass-volume ratio of allyl sulfonic acid sodium to acrylic acid is 1 g / 1 mL.

[0057] Comparative Example 5 The difference between Comparative Example 5 and Example 4 is that in step S2, the mass-volume ratio of allyl sulfonic acid sodium to acrylic acid is 1 g / 0.5 mL.

[0058] Performance Test: 1. Coating Suspension Performance Test: The suspension test is used to evaluate the ability of solid particles in the coating to remain dispersed and not settle. During the test, the prepared coating is carefully poured into a 100 mL stoppered graduated cylinder until it reaches the calibration line, and then the graduated cylinder is sealed immediately to avoid interference from external factors. The graduated cylinder is placed vertically and left standing. Every 1 hour, in an environment with sufficient and stable light, by looking straight at the calibration of the graduated cylinder, carefully observe and accurately record the sedimentation height of the solid particles in the coating. The sedimentation rate is calculated by the formula: sedimentation rate = (initial coating height - supernatant height after sedimentation at a certain time) / initial coating height × 100%. This formula reflects the proportional relationship between the change in the supernatant height caused by the sedimentation of solid particles in the coating over time and the initial coating height, thereby quantifying the suspension performance of the coating. The calculation results are shown in Table 1.

[0059] Table 1: 2. Coating Anti-Cracking and Fire Resistance Performance Test: The anti-cracking test is used to evaluate the ability of the coating to resist cracking under rapid temperature changes. First, place the sand mold test block coated with the coating into the heating equipment, heat it to 800 °C at a certain rate, and keep it at this temperature for 20 minutes to make the test block reach thermal equilibrium as a whole. Subsequently, quickly take out the test block from the heating equipment and cool it in normal temperature water. In a bright and non-reflective environment, carefully observe the cracking situation of the coating on the surface of the test block, and use a measuring tool with appropriate precision to measure and record the number of cracks and the maximum length of the cracks. The fewer the number of cracks and the shorter the maximum length of the cracks, the better the anti-cracking performance of the coating. The test results are shown in Table 2.

[0060] The fire resistance test is used to examine the stability of the coating in a high-temperature environment. First, prepare a sand mold test block with dimensions of 50 mm × 50 mm × 10 mm, evenly and carefully coat the coating to be tested on the surface of the test block, ensure that the coating thickness is consistent and there is no uncoated area, and then fully dry the coated test block. Then, place the test block into a high-temperature furnace, set the heating program, and slowly heat it to 1500 °C at a rate of 10 °C / min. The heating process should be stable and the temperature change should be accurately controlled. After reaching the target temperature, keep it for 2 hours of heat preservation time, and continuously observe the state of the coating on the surface of the test block during this period, and record whether obvious damage phenomena such as cracking and peeling occur. The test results are shown in Table 2.

[0061] Table 2: 3. Coating Densification Performance Test The coating density test was carried out by means of scanning electron microscopy (SEM) for microstructure analysis. During the test, first, representative different positions on the surface of the sand mold test block coated with the coating were selected, and small samples were carefully cut using cutting tools to ensure that the surface of the samples was flat and undamaged. The samples were fixed on the sample stage of the SEM, the microscope parameters were adjusted, and clear microscopic images of the samples were obtained. Using professional image analysis software, the SEM images were processed and analyzed. By identifying and measuring the area and quantity of pores in the coating, the porosity of the coating was calculated according to the formula: porosity = total pore area / total coating area × 100%. The lower the porosity, the denser the coating structure and the stronger the ability to resist the intrusion of external substances and prevent performance deterioration. The calculation results are shown in Table 3.

[0062] Table 3: Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A water-based coating for sand casting, characterized in that, Comprising the following components by weight parts: 50 - 80 parts of refractory aggregate, 5 - 10 parts of composite suspending agent, 4 - 8 parts of nano-aluminum oxide, 3 - 5 parts of sodium carboxymethyl cellulose, 0.5 - 1 part of sodium lignosulfonate, 60 - 100 parts of water.

2. The water-based coating for sand casting according to claim 1, wherein The refractory aggregate consists of zircon powder, kaolin and porous mullite.

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

2.

4. The water-based coating for sand casting according to claim 1, characterized in that, The preparation method of the composite suspending agent includes the following steps: S1. Mix attapulgite with hydrochloric acid solution, heat and stir for reaction, then carry out suction filtration, wash the filter cake with deionized water until the pH of the washing liquid is neutral, dry and grind to obtain acidified attapulgite; S2. Add acrylic acid to sodium hydroxide solution for neutralization reaction to obtain sodium acrylate solution, dilute with deionized water, then add potassium persulfate and sodium allylsulfonate, and under nitrogen protection, heat for free radical polymerization reaction, dry and crush the reaction product to obtain modified sodium polyacrylate; S3. Mix acidified attapulgite with deionized water and stir to form a suspension, heat up, add modified sodium polyacrylate, keep the temperature for reaction, and after centrifugal separation, washing and drying, obtain intercalated modified attapulgite; S4. Add intercalated modified attapulgite to xanthan gum solution, heat and stir for reaction, and carry out vacuum defoaming treatment to obtain the composite suspending agent.

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

6. The water-based coating for sand casting according to claim 4, characterized in that, In the step S2, the heating reaction temperature is 60 °C, and the free radical polymerization reaction is for 6 h.

7. The water-based coating for sand casting according to claim 6, wherein In the step S2, the mass volume ratio of sodium allylsulfonate to acrylic acid is 1 g / 2 - 5 mL.

8. A water-based coating for sand casting according to claim 4, characterized in that, In the step S3, the mass ratio of acidified attapulgite to modified sodium polyacrylate is 1:0.2 - 0.

6.

9. A water-based coating for sand casting according to claim 4, characterized in that, In the step S4, the mass ratio of intercalated modified attapulgite to xanthan gum is 5:1 - 3.

10. A preparation method of the water-based coating for sand casting according to any one of claims 1-9, characterized in that, Including the following steps: First, add the refractory aggregate, composite suspending agent, nano-aluminum oxide and sodium lignosulfonate to water, stir evenly to obtain a premix; then add sodium carboxymethyl cellulose to the premix and continue to stir to obtain a water-based coating for sand casting.

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