A low-cost, fast-drying water-based casting coating and its preparation method

Abstract

The present invention provides a low-cost, fast self-drying water-based casting coating with fast self-drying speed, low production cost, low irritating odor, good brushability and leveling property and a preparation method thereof. The coating comprises a refractory base material, a binder, a dispersing suspending agent, an additive and water, wherein the binder adopts water-based polyvinyl butyral resin and fast-drying silica sol; the self-drying time of a coating with a thickness of 0.5 mm under conditions of low ambient humidity and good ventilation conditions does not exceed 60 minutes; even under conditions of an ambient temperature of 25°C and a relative humidity of up to 80%, the coating can basically achieve natural drying within 100 minutes, meeting the casting production requirements under high humidity climate conditions in the south. The present invention belongs to the technical field of casting coatings, and can replace alcohol-based coatings and ordinary drying-type water-based coatings for various casting production, effectively eliminating defects such as sand sticking, sand inclusions, and pores in castings, reducing production costs, and improving the production environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of high temperature coatings, and in particular relates to a low-cost, fast self-drying water-based casting coating and a preparation method thereof. Background Art

[0002] At present, the domestic sand casting industry widely uses alcohol-based coatings with methanol, ethanol and isopropanol as solvents. They ignite and burn immediately after application and have the characteristics of rapid curing. However, methanol is toxic and can harm the human visual nerves; and these alcohol solvents are Class A hazardous substances that are easily volatile, flammable and explosive; alcohol-based coatings have poor suspension stability and poor brushing effect; more toxic gases are generated during the pouring of molten metal, and the amount of gas generated is large, and castings are prone to pore defects. The above problems not only pollute the working environment, deteriorate production and transportation safety conditions and workers' health, but also affect the intrinsic quality of casting products.

[0003] Compared with alcohol-based paints, water-based paints with water as solvent are safe and reliable, easy to transport, cheap, clean and pollution-free, and have stable suspension and brushing performance. However, due to the generally low solid content of ordinary water-based paints, the water penetrates too deeply into the sand mold (core) after application, making it difficult to dry quickly and naturally. It needs to be placed in a heating furnace for a long time to dry, or baked with various flame spray guns. In addition, the dried coating easily absorbs moisture and reduces its strength during storage, resulting in a long production cycle, poor casting quality, and high energy consumption. At present, there are no mass-produced and standardized water-based paints that can dry quickly and naturally under normal atmospheric conditions in China.

[0004] The research and development team of the inventor of this application has disclosed a water-based self-drying / quick-drying sand casting coating in a Chinese patent with publication number CN103878302B, which uses room temperature self-crosslinking styrene acrylic emulsion as the main room temperature self-drying binder, and quick-drying silica sol as the main high-temperature binder. The self-drying time of a coating with a thickness of about 0.5 mm under general production conditions is 1.5h to 3.0h. The third embodiment discloses a water-based self-drying zirconium-containing composite silicate powder coating, which can be completely dried within 3.0 hours under the conditions of a coating thickness of about 0.8 mm, an ambient temperature of 33°C to 35°C, and a relative humidity of 54% to 60%, and can be completely dried within 2.0 hours under the conditions of a coating thickness of about 0.4 mm, an ambient temperature of 28°C to 30°C, and a relative humidity of 72% to 78%. The fourth embodiment discloses a water-based self-drying powder quartz coating, which can be completely dried within 2.5 hours (150 minutes) under the conditions of an ambient temperature of 32°C to 35°C and a relative humidity of 62% to 69% for a coating of about 0.5 mm in thickness. The dried coating has high strength, good moisture absorption resistance, and high-temperature explosion and cracking resistance grades of Grade I to Grade II, which basically meet the casting production requirements.

[0005] Based on the above coating component system of water-based self-drying / quick-drying sand casting coating, the research and development team of the inventor of the present application has further studied in recent years, improved the raw material requirements of the coating, optimized the production process, and increased the self-drying speed of the coating. A coating with a thickness of 0.5 mm can basically achieve natural drying in about 2 hours (120 minutes) under the conditions of ambient temperature of 25°C and relative humidity of 80% (see Feng Shengshan, Xie Shuzhong, Liu Chunjing, et al. Factors affecting the drying speed of water-based self-drying / quick-drying casting coatings [C]. Proceedings of the 2014 Guangdong Province Foundry and Die Casting Annual Conference; Feng Shengshan, Xie Shuzhong, Liu Chunjing, et al. Process performance of water-based self-drying / quick-drying casting coatings [C]. Proceedings of the 2014 China Foundry Week).

[0006] In recent years, some patents for water-based self-drying casting coatings have been disclosed in China, but they are mainly double-layer (double-component) models (such as Chinese invention CN104801661A discloses a method for preparing water-based coatings for casting hydraulic parts, and Chinese invention CN103223458A discloses a water-based self-drying casting coating and its preparation method and use method), in which one layer (component) contains a binder component, and the other layer (component) contains a curing agent component. After the second layer is applied, it reacts chemically with the first layer to cure the binder. Although the self-drying speed may be faster, the production, management and use process of the double-layer (double-component) model of water-based self-drying coatings are complicated, and one of the layers is still an alcohol-based coating, which is not a true water-based self-drying coating.

[0007] The above two-component (two-layer) water-based self-drying casting coating is difficult to be accepted by users, and the self-drying time of the single-component water-based self-drying casting coating is still relatively long, especially the self-drying curing speed of the coating under high humidity conditions needs to be improved, and the production cost of the coating is still relatively high due to the high production cost of the room temperature curing modified high molecular polymer emulsion binder used. In addition, the high molecular polymer emulsion binder and the latent curing agent (a volatile alkali solution) used to promote the curing of the high molecular polymer emulsion have a certain pungent odor, which has resulted in it not being widely promoted and applied in actual domestic casting production.

[0008] Therefore, it is imperative to further improve the self-drying curing speed and environmental protection performance of water-based self-drying sand casting coatings under the high humidity climate conditions in the south (especially to eliminate the irritating odor of the coatings) and reduce the production cost of the coatings. Summary of the invention

[0009] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a low-cost fast self-drying water-based casting coating with fast self-drying speed, low production cost, low irritating odor, good brushability and leveling properties and a preparation method thereof.

[0010] The technical solution adopted by the present invention is: the low-cost fast self-drying water-based casting coating includes a refractory base material, a binder, a dispersing suspending agent, an additive and water, the binder includes an aqueous polyvinyl butyral resin and a fast-drying silica sol, the aqueous polyvinyl butyral resin is used as a main binder for fast drying at room temperature, and the fast-drying silica sol is mainly used as a high-temperature binder.

[0011] The water-based polyvinyl butyral resin is formed by acetalization reaction between polyvinyl alcohol and n-butyraldehyde under the condition of hydrochloric acid as a catalyst. It is a milky white uniform liquid with a solid content of 8% to 20%, a viscosity of 200 mPa•s to 800 mPa•s at 20℃±1℃, and a density of 1.0 g / cm 3 ~1.1g / cm 3 , pH value is 7.0~9.0, and free formaldehyde content is ≤0.2%.

[0012] The specific preparation process of the waterborne polyvinyl butyral resin comprises the following steps:

[0013] Step S1.1, adding a proper amount of pure water to polyvinyl alcohol, stirring and heating to 80°C to 95°C to completely dissolve the polyvinyl alcohol, and obtaining a polyvinyl alcohol aqueous solution with a mass fraction of 10±2%; wherein the polyvinyl alcohol is preferably 17-88 type, with a degree of polymerization ≥1700 and a degree of alcoholysis ≥88%;

[0014] Step S1.2, when the temperature of the polyvinyl alcohol aqueous solution drops to 50°C to 55°C, slowly add n-butyraldehyde, the mass ratio of n-butyraldehyde to polyvinyl alcohol is 30% to 50%, and stir at the same time. When the temperature continues to drop to 8 to 18°C, add 0.4% to 0.5% hydrochloric acid by mass to the reaction system, adjust the pH to 5 to 6, reheat the solution, and slowly raise the temperature to 55°C to 65°C. Stir at a uniform speed to fully cause the acetal reaction. When the solution is slightly whitish, immediately add sodium hydroxide solution, adjust the pH to 8 to 9, and terminate the reaction; wherein the mass fraction of hydrochloric acid is preferably 50%, and the mass fraction of sodium hydroxide is preferably about 5%;

[0015] Step S1.3, adding an appropriate amount of melamine or hydrogen peroxide to the solution, so that it fully reacts with the residual free aldehyde in the solution that has not participated in the acetal reaction, controls the residual content of free aldehyde in the solution, and eliminates the residual irritating odor in the solution; the amount of melamine or hydrogen peroxide added is based on controlling the residual content of free aldehyde to ≤0.2%, providing a guarantee for achieving low odor of the coating.

[0016] The refractory base material is a room temperature processed refractory material or a natural refractory material that has not been subjected to high temperature calcination and electric melting treatment, including one or a combination of more than one of zircon powder, chromite powder, zirconium-containing composite silicate powder, powdered quartz, graphite powder and pyrophyllite powder.

[0017] The dispersing suspending agent is one or a combination of sodium-based rectorite powder, sodium-based bentonite powder, and sodium-based attapulgite powder. Rectorite powder has high refractoriness and low thermal shrinkage, bentonite powder has large water absorption expansion rate and good slurry stability, and attapulgite powder has good thixotropic anti-sagging properties. Each has its own advantages. When used in combination, the comprehensive performance of the coating is better, and the amount of water added to the coating can be reduced, which helps to increase the self-drying speed of the coating.

[0018] The particle size and distribution of the refractory base material are normally distributed between 25 μm and 110 μm in particle diameter.

[0019] The preferred solution is that the particle size and distribution of the refractory base material are normally distributed with an average particle size of 45 μm to 75 μm (i.e., 325 mesh to 200 mesh). At this time, the required moisture content of the coating is the lowest, the self-drying curing speed is the fastest, and the suspension, brushability and permeability of the coating are also taken into account. The coating has high density, strong crack resistance and strong resistance to metal liquid penetration.

[0020] The particle shape of the refractory base material is between obtuse and circular, and the angular coefficient is ≤1.45.

[0021] Preferably, the particle shape of the refractory base material is round or approximately round, and the angular coefficient is ≤1.30.

[0022] The quick-drying silica sol SiO 2 Content not less than 28%, Na 2 O content is not more than 0.5%, average particle size is not more than 15nm, pH value is 9.0-10.5, viscosity at 20℃±1℃ is not more than 10mPa•s, density is 1.10 g / cm 3 ~1.25g / cm 3 The smaller the particle size of the quick-drying silica sol, the greater the bonding force. The high-temperature strength of the coating can be ensured by using an average particle size of no more than 15 nm.

[0023] The additives include sintering stripping aid, water reducing agent, defoaming agent and preservative. Calculated based on 100 parts of the refractory base material, there are 1 to 3 parts of dispersing suspending agent, 2 to 10 parts of water-based polyvinyl butyral resin, 2 to 8 parts of quick-drying silica sol, 0 to 13 parts of sintering stripping aid, 0.2 to 1.5 parts of water reducing agent, 0.2 to 1.5 parts of defoaming agent, 0.1 to 0.5 parts of preservative and 28 to 60 parts of pure water. The numbers of parts recorded in the above scheme are all parts by mass.

[0024] The water reducer is one or a combination of polycarboxylic acid water reducer, lignin sulfonate water reducer, polycyclic aromatic salt water reducer and water-based resin sulfonate water reducer.

[0025] The defoaming agent is a non-ionic ether organic compound, and the preservative is a mixture of 5-chloro-2-methyl-4-isothiazoline-3-one, 2-methyl-4-isothiazoline-3-one, and 1,2-benzisothiazolin-3-one, wherein the mixing ratio of 5-chloro-2-methyl-4-isothiazoline-3-one, 2-methyl-4-isothiazoline-3-one, and 1,2-benzisothiazolin-3-one is 3:(1-3):(1-3).

[0026] The sintering and stripping aid is 0-8 parts of talc powder and 0-5 parts of ferric oxide powder, wherein the Fe 2 O 3 The content is not less than 75%, and the particle size is 10μm to 75μm. The coating used for cast steel does not need to add sintering stripping aids. Sintering stripping aids are added to the coating used for cast iron and non-ferrous metal castings to promote the coating to automatically peel off from the casting surface in pieces after the molten metal is poured and cooled.

[0027] The method for preparing the low-cost, fast-drying water-based casting coating comprises the following steps:

[0028] Step S2.1, quantitatively weighing various raw materials;

[0029] Step S2.2, add a dispersing suspending agent and 1 to 3 times the amount of purified water to a wheel-rolling mixer, start the machine to stir and roll for more than 15 minutes, then transfer to a colloid mill and add an appropriate amount of purified water to cycle the process 2 to 3 times to obtain a dispersing suspending agent paste and discharge the material for later use;

[0030] Step S2.3, add the above-mentioned dispersing suspension paste into a double-shaft dual-speed stirring disperser, start the machine for stirring, and gradually add part of the purified water and various refractory base materials alternately, and continue stirring for more than 10 minutes;

[0031] Step S2.4, respectively add water-based polyvinyl butyral resin, quick-drying silica sol, sintering stripping aid, water reducing agent, defoaming agent, preservative and remaining purified water, and continue stirring for more than 10 minutes;

[0032] Step S2.5: discharging and packaging to obtain the low-cost, fast-drying water-based casting coating in slurry form.

[0033] Using a wheel-roll mixer instead of a common mixer to activate the dispersing suspending agent can significantly improve the activation effect and shorten the activation time, thereby reducing the amount of dispersing suspending agent added, thereby reducing the water consumption of the coating and increasing the self-drying speed of the coating. Using a double-shaft dual-speed stirring disperser instead of a common single-shaft high-speed mixer to prepare the coating can make the mixing more uniform, shorten the mixing time, and consume less electricity.

[0034] The beneficial effects of the present invention are:

[0035] (1) The coating of the present invention still has good brushability and leveling properties when the viscosity is as high as 25s to 40s (tested by using a Tu-6 viscosity cup at 20°C ± ℃);

[0036] (2) The required moisture content of the coating is reduced, and the solid content (non-volatile content) of the coating can reach up to 74%;

[0037] (3) Excellent suspension stability, with almost no precipitation after 2 hours of storage, and a suspension rate of more than 98% after 24 hours of storage;

[0038] (4) The coating has low irritating odor and can be easily applied under conditions of high viscosity, high solid content and low water consumption. It has low permeability to the sand mold (core) and has little adverse effect on the strength of the sand mold (core);

[0039] (5) The self-drying speed of the coating is significantly improved. The self-drying time of a coating with a thickness of 0.5 mm under normal production conditions is 1.0 h to 2.5 h (60 min to 150 min). If the ambient humidity is low and the ventilation conditions are good, the self-drying time of the coating can be shortened to less than 1.0 h (60 min). Even under the conditions of an ambient temperature of 25 ° C and a relative humidity of up to 80%, the coating can basically achieve natural drying within 1.75 h (100 min), meeting the casting production requirements under the high humidity climate conditions in the south.

[0040] (6) The coating can also be dried quickly on the surface by a blowtorch, coal gas, oxygen-acetylene gas or hot air (a coating with a thickness of 0.5 mm can be completely dried within 3 to 5 minutes under the action of hot air at 80°C ± 5°C);

[0041] (7) The dried coating has high strength and strong moisture absorption resistance. The high-temperature explosion and cracking resistance level is level I to level II, and the gas generation at 1000°C does not exceed 16 ml / g. Although the addition amount of water-based polyvinyl butyral is higher than that of room-temperature self-crosslinking styrene-acrylic emulsion, the solid content (non-volatile content) of water-based polyvinyl butyral is only about 1 / 4 of that of room-temperature self-crosslinking styrene-acrylic emulsion. The amount of pyrolysis gas generated by the non-volatile matter under the high temperature after the metal liquid is poured is significantly reduced.

[0042] (8) The production cost of the coating can be reduced to 1 / 2 to 3 / 4 of the original cost when using room temperature self-crosslinking styrene acrylic emulsion.

[0043] The invention can replace alcohol-based and common water-based zircon powder coatings, chromite powder coatings, zirconium-containing composite silicate powder coatings, corundum powder coatings, bauxite powder coatings, magnesia powder coatings, forsterite powder coatings, powdered quartz coatings, quartz powder coatings, graphite powder coatings and composite coatings thereof, and can be used for various cast steel, cast iron and non-ferrous metal castings produced by resin sand, water glass sand and clay sand processes. The coating has good sintering peeling property, and the workload of casting cleaning is significantly reduced. Defects such as sand sticking, sand inclusion, sand falling and pores in the castings are effectively prevented, and the surface of the castings is smooth and clean, which can fully meet the casting production requirements, especially the production requirements under high humidity conditions in the south, and achieve the purposes of saving energy consumption, improving environmental conditions and improving the quality of castings.

[0044] The invention can also be expanded to be applied to special casting coating technology fields such as lost foam casting coating, metal mold casting coating, and investment casting coating. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with the embodiments, and the parts recorded in the present invention are all parts by mass.

[0046] Embodiment 1:

[0047] In this embodiment, the amount of the refractory base material is 100 parts, the dispersing suspending agent is 1.5 parts, the water-based polyvinyl butyral resin is 4.5 parts, the quick-drying silica sol is 3.5 parts, the sintering stripping aid is 5 parts, the water reducing agent is 0.5 parts, the defoaming agent is 0.2 parts, the preservative is 0.2 parts, and the purified water is 34 parts. Among them, the refractory base material is zirconium-containing composite silicate mineral powder, the dispersing suspending agent is sodium-based bentonite powder, the sintering stripping aid is talcum powder and ferric oxide powder (ratio is 3:2), the water reducing agent is a polycyclic aromatic salt water reducing agent, the defoaming agent is a non-ionic ether organic compound solution, and the preservative is a mixture of 5-chloro-2-methyl-4-isothiazoline-3-one (CMIT), 2-methyl-4-isothiazoline-3-one (MIT) and 1,2-benzisothiazolin-3-one (BIT) (ratio is 3:1:3). The above components are prepared into a coating according to the above coating preparation method.

[0048] The coating has better suspension stability, brushability and leveling properties than alcohol-based zircon powder composite coating (the coating has only slight brush marks), low irritating odor, fast self-drying speed, under the condition of ambient temperature of 34℃~36℃ and relative humidity of 56%~60%, the first layer of coating can be completely dried naturally in 50min~85min, the second layer of coating can be completely dried naturally in 30min~45min, the total self-drying time of two layers of coating is 80min~130min, and the self-drying time of coating with a thickness of 0.5mm is 65min~80min. 5min; the coating has high strength after drying and good moisture absorption resistance; it is used for the acid self-hardening furan resin sand process to produce thick-walled medium-sized injection molding machine head plate ductile iron castings. The gas emission of the mold during molten iron pouring is less than that when using alcohol-based coatings, and the gas emission time is shorter. When the castings are boxed after cooling, most of the coatings can be automatically peeled off in pieces. After shot blasting, the product logos of the castings are clear, and there are no sand sticking or pore defects on the surface. The surface quality is equivalent to that of castings produced with alcohol-based zircon powder composite coatings, but the coating use cost is significantly reduced, and the casting production safety is significantly improved.

[0049] Embodiment 2:

[0050] In this embodiment, the amount of the refractory base material is 100 parts, the dispersing suspending agent is 2 parts, the water-based polyvinyl butyral resin is 3 parts, the quick-drying silica sol is 4 parts, the sintering stripping aid is 0 parts, the water reducing agent is 0.5 parts, the defoaming agent is 0.5 parts, the preservative is 0.1 parts, and the purified water is 30 parts. Among them, the refractory base material is chromite powder, the dispersing suspending agent is sodium-based rectorite powder, the water reducing agent is a polycarboxylic acid water reducing agent, the defoaming agent is a non-ionic ether organic compound solution, and the preservative is a mixture of 5-chloro-2-methyl-4-isothiazoline-3-one (CMIT), 2-methyl-4-isothiazoline-3-one (MIT), and 1,2-benzisothiazolin-3-one (BIT) (the ratio is 3:2:2). The above components are prepared into a coating according to the above coating preparation method.

[0051] The coating is used for phenolic resin coated sand cores and is used in conjunction with clay wet sand mold technology to produce low alloy steel container corner fittings. Under ambient temperature of 25℃~30℃ and relative humidity of 60%~70%, when the heated and cured coated sand cores are demoulded and immediately transferred to the coating station for surface polishing, they are still hot, with a surface temperature of 60℃~70℃ (hot sand cores). At this time, the coating is applied, and the self-drying curing time of a single layer of coating (0.3 mm~0.4 mm thick) does not exceed 3 minutes; the coated hot sand cores are placed for a period of time until they cool to a surface temperature of about 30℃ (normal temperature sand cores) before coating, and the self-drying time of a single layer of coating is only 8~10 minutes, and the self-drying speed is very fast. The reasons are: the original sand particle size of the coated sand core is fine, the surface of the sand core is smooth, the pores between the sand particles are small, the coating thickness is thin, and the penetration depth of the coating aggregate is very small, but the capillary action of the pores between the sand particles is strong, the distance that water migrates to the inside of the sand core is long, it is easy to absorb water, and the water diffuses fully; the coated sand core after heating and curing, even if it is cooled to room temperature before coating, due to the small amount of residual water inside, the water in the coating not only evaporates outwards, but also quickly migrates and diffuses into the inside of the sand core, making the self-drying time of the coating significantly shorter than the self-drying time of the surface coating of self-hardening, air-hardening furan resin sand and water glass sand mold (core).

[0052] This coating not only has a very low irritating odor and a high coating drying strength, but also has a good anti-sand sticking effect, reaching the performance level of alcohol-based zircon powder coatings. It can also basically eliminate casting cracks, pores and shrinkage defects, and can meet the high quality requirements of container corner fittings. At the same time, it significantly reduces the cost of coating use and improves the safety and environmental protection of casting production.

[0053] Embodiment three:

[0054] In this embodiment, based on 100 parts of the refractory base material, there are 2.4 parts of dispersing suspending agent, 6 parts of water-based polyvinyl butyral resin, 5 parts of quick-drying silica sol, 3 parts of sintering stripping aid, 0.8 parts of water reducing agent, 0.3 parts of defoaming agent, 0.2 parts of preservative, and 45-55 parts of purified water. The refractory base material is graphite powder and powdered quartz (ratio 3:7), the dispersing suspending agent is a compound of sodium bentonite powder and sodium rectorite powder (ratio 5:5), the sintering stripping aid is talcum powder and ferric oxide powder (ratio 2:1), the water reducer is a mixture of polycarboxylic acid water reducer and lignin sulfonate water reducer, the defoamer is a non-ionic ether organic compound solution, and the preservative is a mixture of 5-chloro-2-methyl-4-isothiazoline-3-one (CMIT), 2-methyl-4-isothiazoline-3-one (MIT), and 1,2-benzisothiazolin-3-one (BIT) (ratio 3:3:3). The above components are prepared according to the above coating preparation method to obtain the coating.

[0055] The coating has excellent suspension stability, brushability and leveling properties (the coating has almost no brush marks), and is mainly used for the production of various cast iron parts. When producing thick and large cast iron parts, the moisture content needs to be at the lower limit due to the large coating thickness requirement, while the moisture content is generally at the upper limit when producing thin and small cast iron parts; the coating with a thickness of about 0.5 mm takes 70 minutes to 100 minutes to dry completely naturally under the conditions of an ambient temperature of 25°C to 28°C and a relative humidity of 72% to 80%; if the ambient humidity is low and the ventilation conditions are good, the coating self-drying time can be shortened to less than 60 minutes; the strength of the coating after drying is very high and the moisture absorption resistance is good; when used for the acid self-hardening furan resin sand process to produce various cast iron parts, most of the coating can be automatically peeled off in pieces, and the castings have no sand adhesion and pore defects. Although the surface quality is comparable to that of cast iron parts produced with alcohol-based graphite powder composite coatings, there is basically no pungent odor of alcohol-based coatings at the production site, which also significantly reduces the cost of coating use and significantly improves the safety of casting production.

[0056] The above embodiments are merely implementation plans of the present invention provided to help understanding, and the scope of the present invention is not limited to the above contents.

[0057] It is particularly pointed out here that for ordinary technicians in this field, equivalent modifications, changes or improvements made to the present invention without departing from the principle of the present invention should all be included in the protection scope required by the claims.

Claims

1. A low-cost, fast-drying water-based casting coating, comprising a refractory base material, a binder, a dispersing suspending agent, an additive and water, characterized in that: The binder comprises water-based polyvinyl butyral resin and quick-drying silica sol, wherein the water-based polyvinyl butyral resin is used as a main binder that dries quickly at room temperature, and the quick-drying silica sol is used as a high-temperature binder; the water-based polyvinyl butyral resin is formed by acetalization reaction between polyvinyl alcohol and n-butyraldehyde under the condition of hydrochloric acid as a catalyst, and is a milky white uniform liquid with a solid content of 8% to 20%, a viscosity of 200 mPa•s to 800 mPa•s at 20℃±1℃, and a density of 1.0 g / cm 3 ~1.1g / cm 3 , pH value is 7.0-9.0, free aldehyde content ≤0.2%; The specific preparation process of the waterborne polyvinyl butyral resin comprises the following steps: Step S1.1, adding a proper amount of pure water to polyvinyl alcohol, stirring and heating to 80°C to 95°C to completely dissolve the polyvinyl alcohol, and obtaining a polyvinyl alcohol aqueous solution with a mass fraction of 10±2%; Step S1.2, when the temperature of the polyvinyl alcohol aqueous solution drops to 50°C to 55°C, slowly add n-butyraldehyde, the mass ratio of n-butyraldehyde to polyvinyl alcohol is 30% to 50%, and stir at the same time. When the temperature continues to drop to 8°C to 18°C, add 0.4% to 0.5% hydrochloric acid by mass of the reaction system, adjust the pH to 5 to 6, reheat the solution, and slowly raise the temperature to 55°C to 65°C. Stir at a uniform speed to fully cause the acetal reaction. When the solution is slightly whitish, immediately add sodium hydroxide solution, adjust the pH to 8 to 9, and terminate the reaction; Step S1.3, adding an appropriate amount of melamine or hydrogen peroxide to the solution to fully react with the residual free aldehyde in the solution that has not participated in the acetalization reaction, controlling the residual content of free aldehyde in the solution, and eliminating the residual irritating odor in the solution.

2. A low-cost, fast-drying water-based casting coating according to claim 1, characterized in that: The additives include sintering stripping aid, water reducing agent, defoaming agent and preservative. Calculated based on 100 parts of the refractory base material, the additives include 1 to 3 parts of dispersing suspending agent, 2 to 10 parts of water-based polyvinyl butyral resin, 2 to 8 parts of quick-drying silica sol, 0 to 13 parts of sintering stripping aid, 0.2 to 1.5 parts of water reducing agent, 0.2 to 1.5 parts of defoaming agent, 0.1 to 0.5 parts of preservative and 28 to 60 parts of purified water.

3. A low-cost, fast-drying water-based casting coating according to claim 1, characterized in that: The refractory base material is a room temperature processed refractory material or a natural refractory material that has not been subjected to high temperature calcination or electric melting treatment, including one or a combination of more than one of zircon powder, chromite powder, zirconium-containing composite silicate powder, powdered quartz, graphite powder and pyrophyllite powder; the dispersing suspending agent is one or a combination of more than one of sodium-based rectorite powder, sodium-based bentonite powder and sodium-based attapulgite powder.

4. A low-cost, fast-drying water-based casting coating according to claim 1, characterized in that: The particle size and distribution of the refractory base material are normally distributed between 25 μm and 110 μm in particle diameter.

5. A low-cost, fast-drying water-based casting coating according to claim 1, characterized in that: The particle shape of the refractory base material is between obtuse and circular, and the angular coefficient is ≤1.

45.

6. A low-cost, fast-drying water-based casting coating according to claim 2, characterized in that: The water reducer is one or a combination of polycarboxylic acid water reducer, lignin sulfonate water reducer, polycyclic aromatic salt water reducer and water-based resin sulfonate water reducer; the defoamer is a non-ionic ether organic compound; and the preservative is a mixture of 5-chloro-2-methyl-4-isothiazoline-3-one, 2-methyl-4-isothiazoline-3-one and 1,2-benzisothiazolin-3-one.

7. A low-cost, fast-drying water-based casting coating according to claim 2, characterized in that: The sintering stripping aid comprises 0-8 parts of talc powder and 0-5 parts of ferric oxide powder, wherein the Fe2O3 content of the ferric oxide powder is not less than 75%, and the particle size is 10 μm to 75 μm.

8. A method for preparing a low-cost, fast-drying water-based casting coating as claimed in claim 2, characterized in that: It includes the following steps: Step S2.1, quantitatively weighing various raw materials; Step S2.2, add dispersing suspending agent and 1 to 3 times amount of purified water into a wheel-rolling mixer, start the machine to stir and roll for more than 15 minutes, then transfer to a colloid mill and add appropriate amount of tap water to cycle the process 2 to 3 times to obtain a dispersing suspending agent paste and discharge the material for standby use; Step S2.3, add the above-mentioned dispersing suspension paste into a double-shaft dual-speed stirring disperser, start the machine for stirring, and gradually add part of the purified water and various refractory base materials alternately, and continue stirring for more than 10 minutes; Step S2.4, respectively add water-based polyvinyl butyral resin, quick-drying silica sol, sintering stripping aid, water reducing agent, defoaming agent, preservative and remaining purified water, and continue stirring for more than 10 minutes; Step S2.5: discharging and packaging to obtain the low-cost, fast-drying water-based casting coating in slurry form.