A coating for lost foam casting of alloy steel, its preparation method and application

Abstract

This invention provides a coating for lost foam casting of alloy steel, its preparation method, and its application. The coating comprises the following raw materials in parts by weight: 79-89 parts aggregate, 3-7 parts binder, 4-7 parts suspending agent, 1.5-3 parts surfactant, 1.5-2.5 parts defoamer, and 1-1.5 parts corrosion inhibitor. The aggregate, by weight percentage, comprises 78-82 wt% bauxite, 12-15 wt% mica, and 3-10 wt% quartz powder. The binder, by weight percentage, comprises 42-50 wt% anhydrous aluminum dihydrogen phosphate, 18-25 wt% silica, 12-17 wt% ethylene glycol, and 8-28 wt% magnesium oxide. The coating for lost foam casting of alloy steel of this invention maintains good suspension, high-temperature permeability, coating properties, high-temperature crack resistance, and peeling resistance. The casting surface is smooth and free of sand adhesion, and it emits few harmful gases during firing and can also absorb harmful gases generated by the combustion of the white foam.

Description

Technical Field

[0001] This invention relates to the field of lost foam coating technology, and in particular to a coating for lost foam casting of alloy steel, its preparation method and application. Background Technology

[0002] Lost foam casting, also known as vaporized foam casting or solid pattern casting, uses foamed plastic (EPS, STMMA, or EPMMA) polymer materials to replace the original wooden or metal molds. A pattern (white model) similar in size and shape to the casting is formed by bonding processed plastic sheets or foaming plastic beads. After being coated with a refractory coating (for strengthening, smoothing, and breathability) and dried, it is embedded in dry silica sand and subjected to three-dimensional vibration molding. The pattern is not removed after molding, thus creating a solid cavity with the pattern within the sand box. Molten metal is poured under negative pressure, causing the polymer model to vaporize and be extracted, then replaced by the liquid metal, cooled, and solidified to obtain the desired casting.

[0003] Compared with traditional casting methods such as sand casting, lost foam casting has a number of advantages:

[0004] (1) Lost foam casting has a high degree of design freedom. For parts with complex shapes, lost foam casting uses the method of making multiple mold pieces and then gluing them together to obtain the overall shape. Finally, the mold is cast to obtain the overall casting without the need for complex core molds and multi-part assembly, which greatly reduces the production cost and difficulty.

[0005] (2) Lost foam casting can achieve near-zero material utilization and material utilization rate can reach over 95%, while traditional casting technology usually has low material utilization and generates a large amount of waste. The castings produced by lost foam casting have high surface finish and dimensional accuracy, fewer internal defects, and reduce the workload of subsequent processing and cleaning.

[0006] (3) Lost foam casting can reduce or eliminate the manufacturing and maintenance costs of molds. At the same time, due to its one-time molding characteristics, it can shorten the production cycle and improve the production efficiency of enterprises.

[0007] (4) The casting material selection range is wide, and metal castings such as cast steel, cast iron and aluminum-magnesium alloy castings can be cast using the lost foam casting method.

[0008] Therefore, lost foam casting technology is widely used in industries such as automotive and aerospace. Due to these same characteristics, the coating layer on the white pattern in lost foam casting has a significant impact on the filling of the molten metal, the removal of decomposition products from the pattern, and the quality of the casting. The main function of the coating is actually to act as a mold during casting. It should have high refractoriness and chemical stability, certain room temperature strength and rigidity to prevent sand adhesion and mold collapse; high permeability to ensure timely removal of gaseous or liquid products generated by the thermal decomposition of the pattern; and high high-temperature strength and high-temperature crack resistance to prevent the coating from collapsing under the pressure of high-temperature fluid scouring and back pressure (high-temperature molten metal, vaporization products of the white pattern), preventing the coating from cracking and causing molten metal to seep into the molding sand, resulting in sand adhesion in the casting. To ensure the quality of the coating application, it should also have good suspension stability, good wettability and adsorption, and good coating adhesion and anti-dripping properties. Production experience indicates that 60% of the scrap in lost foam castings is attributed to the coating.

[0009] The quality of the coating is directly proportional to the quality of the final casting. Currently, commercially available lost foam casting coatings often contain environmentally unfriendly raw materials, especially common organic binders such as asphalt, coal tar, rosin, and phenolic resins. These raw materials, during sintering and high-temperature casting, undergo high-temperature decomposition, producing harmful VOCs such as benzene, toluene, styrene, and ethylbenzene. The commonly used surfactant OP-10 may also have adverse environmental impacts, particularly as it is difficult to degrade in water and poses a potential hazard to aquatic life. Summary of the Invention

[0010] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a coating for lost foam casting of alloy steel, its preparation method and application, to solve the problems of casting defects such as large amounts of harmful VOCs gases volatilized during casting and low high-temperature strength of coatings leading to mold collapse and sand adhesion.

[0011] To achieve the above and other related objectives, the present invention provides a coating for lost foam casting of alloy steel, characterized in that it comprises the following raw materials in parts by weight: 79-89 parts aggregate, 3-7 parts binder, 4-7 parts suspending agent, 1.5-3 parts surfactant, 1.5-2.5 parts defoamer, and 1-1.5 parts corrosion inhibitor;

[0012] The aggregate, by weight percentage, comprises 78-82 wt% bauxite, 12-15 wt% mica, and 3-10 wt% quartz powder;

[0013] The binder, by weight percentage, comprises 42-50 wt% anhydrous aluminum dihydrogen phosphate, 18-25 wt% silica, 12-17 wt% ethylene glycol, and 8-28 wt% magnesium oxide.

[0014] The present invention also provides a method for preparing the coating for lost foam casting of alloy steel as described above, comprising the following steps:

[0015] S1. Prepare sodium carboxymethyl cellulose suspension, sodium bentonite suspension, and sodium alginate suspension according to the ingredient ratio;

[0016] S2. Mix and grind the aggregate, anhydrous aluminum dihydrogen phosphate, silica and magnesium oxide according to the proportion of ingredients to obtain mixed abrasive.

[0017] S3. Mix the three suspensions in step S1 to obtain a mixed suspension. Add the surfactant, defoamer, preservative and ethylene glycol to the mixed suspension in batches. Add the resulting mixed suspension to the mixed abrasive obtained in step S2 in batches and mix evenly to obtain the coating for lost foam casting of the alloy steel.

[0018] The present invention also provides an application of the coating for lost foam casting of alloy steel as described above in the field of lost foam casting of alloy steel.

[0019] As described above, the coating, preparation method, and application of the lost foam casting material for alloy steel of the present invention have the following beneficial effects:

[0020] The coating for lost foam casting of alloy steel of this invention uses a high-temperature resistant and environmentally friendly binder, aluminum dihydrogen phosphate, and adds high-temperature resistant and environmentally friendly inorganic compounds, nano-sized silica and magnesium oxide, to increase adhesion strength. The surfactant is TO-9, which is more environmentally friendly, instead of OP-10. The environmentally friendly coating of this application can maintain its strength during firing, and at the same time maintains good suspension, high-temperature air permeability, coating properties, high-temperature crack resistance and peeling properties. The surface of the casting is smooth and free of sand. Detailed Implementation

[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0022] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0023] Furthermore, it should be understood that the one or more method steps mentioned in this invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated; moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of the invention.

[0024] The first aspect of this invention provides a coating for lost foam casting of alloy steel, comprising the following raw materials in parts by weight:

[0025] Aggregate 79-89 parts, 79-81 parts, 81-83 parts, 83-85 parts, 85-87 parts or 87-89 parts;

[0026] 3-7 parts, 3-4 parts, 4-5 parts, 5-6 parts, or 6-7 parts of adhesive;

[0027] Suspension agent 4-7 parts, 4-5 parts, 5-6 parts, or 6-7 parts;

[0028] Surfactant in amounts of 1.5–3 parts, 1.5–1.7 parts, 1.7–1.9 parts, 1.9–2.1 parts, 2.1–2.3 parts, 2.3–2.5 parts, 2.5–2.7 parts, 2.7–2.9 parts, or 2.9–3.0 parts;

[0029] Defoamer in the following amounts: 1.5–2.5 parts, 1.5–1.7 parts, 1.7–1.9 parts, 1.9–2.1 parts, 2.1–2.3 parts, or 2.3–2.5 parts;

[0030] Preservatives in amounts of 1-1.5 parts, 1-1.1 parts, 1.1-1.2 parts, 1.2-1.3 parts, 1.3-1.4 parts, or 1.4-1.5 parts;

[0031] The aggregate, by weight percentage, comprises 78-82 wt%, 78-79 wt%, 79-80 wt%, 80-81 wt%, or 80-82 wt% bauxite, 12-15 wt%, 12-13 wt%, 13-14 wt%, or 14-15 wt% mica, and 3-10 wt%, 3-4 wt%, 4-5 wt%, 5-6 wt%, 6-7 wt%, 7-8 wt%, 8-9 wt%, or 9-10 wt% quartz powder;

[0032] The binder, by weight percentage, comprises 42–50 wt%, 42–44 wt%, 44–46 wt%, 46–48 wt%, or 48–50 wt% anhydrous aluminum dihydrogen phosphate, 18–25 wt%, 18–20 wt%, 20–22 wt%, 22–24 wt%, or 24–25 wt% silica, 12–17 wt%, 12–13 wt%, 13–14 wt%, 14–15 wt%, 15–16 wt%, or 16–17 wt% ethylene glycol, and 8–28 wt%, 8–10 wt%, 10–14 wt%, 14–18 wt%, 18–20 wt%, 20–24 wt%, or 24–38 wt% magnesium oxide.

[0033] In some embodiments of the present invention, the suspending agent, by weight percentage, comprises 35-50 wt%, 35-40 wt%, 40-45 wt%, or 45-50 wt% sodium carboxymethyl cellulose, 45-50 wt%, 45-46 wt%, 46-47 wt%, 47-48 wt%, 48-49 wt%, or 49-50 wt% sodium bentonite, and 10-20 wt%, 10-12 wt%, 12-14 wt%, 14-16 wt%, 16-18 wt%, or 18-20 wt% sodium alginate.

[0034] In some embodiments of the present invention, the surfactant is isomeric tridecyl alcohol polyoxyethylene ether (TO-9).

[0035] In some embodiments of the present invention, the defoamer is n-octanol.

[0036] In some embodiments of the present invention, the preservative, by weight percentage, comprises 25-50 wt%, 25-30 wt%, 30-35 wt%, 35-40 wt%, 40-45 wt%, or 45-50 wt% potassium sorbate and 50-75 wt%, 50-55 wt%, 55-60 wt%, 60-65 wt%, 65-70 wt%, or 70-75 wt% chitosan.

[0037] In this invention, aggregate is a major component of the coating and is directly related to defects such as sand adhesion, porosity, and slag inclusions in castings. The aggregate materials in this invention possess high refractoriness, high permeability, chemical stability, and do not wet or react with molten metal. They are also widely available, environmentally friendly, and inexpensive, thus reducing enterprise costs. Bauxite is chemically stable, heat-resistant, and does not readily react with metals or metal oxides, nor is it easily wetted by molten steel or other molten metals. Mica is chemically stable, heat-resistant, and corrosion-resistant; its layered internal structure provides good elasticity, and its addition to the coating improves the coating's high-temperature permeability, sintering strength, and suspension properties. Quartz sand is widely available and inexpensive; it undergoes a phase change at high temperatures, increasing in volume. Adding a small amount to the coating solution improves its permeability, and when combined with bauxite, it lowers the sintering temperature and promotes coating sintering.

[0038] In this invention, the main function of the binder is to bind the various powder components of the coating together, giving the coating strength, resisting the erosion of high-temperature molten metal, supporting the sand mold, and preventing the coating from peeling off or cracking. Aluminum dihydrogen phosphate is non-toxic and odorless, resistant to high temperatures, and has high high-temperature bonding strength, but it also has defects such as high sintering temperature and large film shrinkage, leading to deformation and cracking of the adhesive film. Nano-grade silica is a white, amorphous, semi-transparent solid colloidal nanoparticle, insoluble in water, with good permeability and dispersibility. In an aqueous solution, it undergoes a silanol condensation reaction to generate silane ether bonds, improving bonding strength and weakening the cracking tendency of the aluminum dihydrogen phosphate cured film. When combined with ethylene glycol, it undergoes a condensation reaction during sintering to generate a -SiO-O-SiO- glossy coating film, improving the coating's gloss and peelability. Ethylene glycol is a transparent, viscous liquid. As a commonly used chemical in the coating industry, ethylene glycol can significantly improve the dispersibility of solutes in solution, enhance the fluidity of the coating solution, and provide a certain moisturizing effect to prevent excessive shrinkage and cracking caused by excessively rapid drying of the coating. Magnesium oxide is a white, odorless, and non-toxic powder with extremely high temperature resistance. At room temperature, it can undergo a dehydration condensation crosslinking reaction with aluminum dihydrogen phosphate solution to produce a network of -O-Mg-O- bonds, thereby giving the coating a certain room / high temperature strength and reducing the thermosetting temperature of aluminum dihydrogen phosphate.

[0039] In this invention, the main function of the suspending agent is to uniformly suspend and disperse the powder particles in the carrier liquid, ensuring the formation of a uniform coating on the surface of the foam mold. Simultaneously, the suspending agent also imparts the required rheological properties to the coating. Sodium carboxymethyl cellulose is a white fibrous or powdery linear polymer compound; its aqueous solution is pale white or transparent colloidal and possesses certain suspension properties. Sodium-based bentonite, whose main component is montmorillonite, appears as a white powder with a fine, scaly, layered structure, similar to sodium carboxymethyl cellulose. Sodium carboxymethyl cellulose and sodium bentonite combine to form a stable network structure in aqueous solution and adsorb solid particles in the coating, preventing flocculation and settling of solid particles and improving the suspension of the coating solution. Sodium alginate is a byproduct of iodine and mannitol extraction from kelp or seaweed. It is a tasteless white or pale yellow powder and a natural polysaccharide that is highly soluble in water to form a gel. Sodium alginate aqueous solution can couple with bauxite. Aluminum ions coordinate with the carboxyl groups in sodium alginate. This coordination bond replaces the original sodium ions in the sodium alginate structure with aluminum ions, thereby forming a sodium alginate hydrogel with a three-dimensional network structure, which increases the overall suspension of the coating solution.

[0040] In this invention, the surfactant reduces the surface tension of the solvent, thereby enhancing the wettability of the water-based coating liquid on the surface of hydrophobic EPS or EPMMA foam molds and improving the coating's coatability. TO-9 is a low-biotoxicity, easily degradable nonionic surfactant, whose main component is isomeric tridecyl alcohol polyoxyethylene ether, with the chemical formula C... 13 H 27 O(CH2CH2O)9H is a colorless or pale yellow liquid. Compared with alkylphenol polyoxyethylene ether surfactants such as OP-10, it has similar emulsifying, wetting, and dispersing properties, but it has less biotoxicity and is more easily biodegraded.

[0041] In this invention, the defoamer, n-octanol, is a transparent, oily liquid with a citrus odor. During the mixing process of the coating production, air enters the carrier liquid and is difficult to expel, thus generating bubbles. When the coating is applied to the foam mold, the bubbles cannot break and flow down as surface defects during sintering. The defoamer can eliminate foam in time when it is generated, ensuring a smooth coating surface.

[0042] In this invention, the preservatives ensure that the coating can be preserved for a long time without the growth of microorganisms. In order to avoid the occurrence of drug resistance or screening effect, this invention uses two preservatives: potassium sorbate and chitosan. Potassium sorbate and chitosan are environmentally friendly preservatives.

[0043] In some embodiments of the present invention, the bauxite is 220-270 mesh, 220-230 mesh, 230-240 mesh, 240-250 mesh, 250-260 mesh or 260-270 mesh high-alumina bauxite, with an Al2O3 content >85%.

[0044] In some embodiments of the present invention, the mica is 250-270 mesh, 250-260 mesh, or 260-270 mesh.

[0045] In some embodiments of the present invention, the quartz powder is 180-220 mesh, 180-190 mesh, 190-200 mesh, 200-210 mesh, or 210-220 mesh.

[0046] In some embodiments of the present invention, the silica is nano-sized silica.

[0047] In some embodiments of the present invention, the anhydrous aluminum dihydrogen phosphate, silica, magnesium oxide, sodium carboxymethyl cellulose, sodium bentonite, sodium alginate, potassium sorbate, and chitosan are all powders.

[0048] A second aspect of the present invention provides a method for preparing a coating for lost foam casting of alloy steel as described above, comprising the following steps:

[0049] S1. Prepare sodium carboxymethyl cellulose suspension, sodium bentonite suspension, and sodium alginate suspension according to the ingredient ratio;

[0050] S2. Mix and grind the aggregate, anhydrous aluminum dihydrogen phosphate, silica and magnesium oxide according to the proportion of ingredients to obtain mixed abrasive.

[0051] S3. Mix the three suspensions in step S1 to obtain a mixed suspension. Add the surfactant, defoamer, preservative and ethylene glycol to the mixed suspension in batches. Add the resulting mixed suspension to the mixed abrasive obtained in step S2 in batches and mix evenly to obtain the coating for lost foam casting of the alloy steel.

[0052] In some embodiments of the present invention, the concentration of the sodium carboxymethyl cellulose suspension in step S1 is 2-3 wt%. For example, it is 2-2.2 wt%, 2.2-2.4 wt%, 2.4-2.6 wt%, 2.6-2.8 wt%, or 2.8-3 wt%.

[0053] In some embodiments of the present invention, the concentration of the sodium-based bentonite suspension in step S1 is 1.5–2 wt%. For example, it is 1.5–1.6 wt%, 1.6–1.7 wt%, 1.7–1.8 wt%, 1.7–1.9 wt%, or 1.9–2 wt%.

[0054] In some embodiments of the present invention, the concentration of the sodium alginate suspension in step S1 is 1–1.5 wt%. For example, it is 1–1.1 wt%, 1.1–1.2 wt%, 1.2–1.3 wt%, 1.3–1.4 wt%, or 1.4–1.5 wt%.

[0055] In step S1, the solvents for the sodium carboxymethyl cellulose suspension, the sodium bentonite suspension, and the sodium alginate suspension are all deionized water.

[0056] The preparation of the sodium carboxymethyl cellulose suspension, the sodium bentonite suspension, and the sodium alginate suspension in step S1 specifically includes adding sodium carboxymethyl cellulose, sodium bentonite, and sodium alginate to deionized water, mixing them into slurries, and then soaking them. The soaking time is ≥20 hours, such as 21 hours, 22 hours, 23 hours, 24 hours, or ≥25 hours.

[0057] In some embodiments of the present invention, the bauxite, mica, and quartz powder in the aggregate described in step S2 are first kept at 200–230°C, 200–210°C, 210–220°C, or 220–230°C for at least 30 minutes before mixing, and then cooled in a dry environment before mixing and grinding. The treated aggregate has higher air permeability and adsorption capacity, and can form a more stable coating layer.

[0058] The heat preservation is carried out in a high-temperature sintering furnace.

[0059] In some embodiments of the present invention, the grinding in step S2 is carried out in a planetary ball mill, using zirconia grinding balls with a diameter of 1.4-1.6 mm, 1.4-1.5 mm, or 1.5-1.6 mm and a content of 90% or more, and grinding the mixed abrasive at a speed of 300-330 rpm, 300-310 rpm, 310-320 rpm, or 320-330 rpm for 3-4 hours, 3-3.5 hours, or 3.5-4 hours.

[0060] A third aspect of the present invention provides the application of the coating for lost foam casting of alloy steel as described above in the field of lost foam casting of alloy steel.

[0061] Example 1

[0062] A coating for lost foam casting of alloy steel is composed of the following raw materials in parts by weight as shown in Table 1:

[0063] Table 1

[0064]

[0065] A method for preparing a coating for lost foam casting of alloy steel, taking the above-mentioned parts by weight totaling 10 kg as an example, includes the following steps:

[0066] S1. Weigh 315g of sodium carboxymethyl cellulose, 315g of sodium bentonite powder, and 70g of sodium alginate. Add sufficient deionized water to each, and stir quickly with an electric stirrer to form a slurry. Soak for 24 hours to obtain 10.5kg of 3wt% sodium carboxymethyl cellulose suspension, 15.8kg of 2wt% sodium bentonite suspension, and 7kg of 1wt% sodium alginate suspension for later use.

[0067] S2. Add 6400g of bauxite, 1200g of mica, 400g of quartz powder, 315g of anhydrous aluminum dihydrogen phosphate powder, 175g of nano-grade silica powder and 105g of magnesium oxide powder to a planetary ball mill. Select zirconium oxide grinding balls with a diameter of 1.4-1.6mm and a content of over 90%. Set the speed to 300 rpm and grind the mixed abrasive for 4 hours. Before mixing, the bauxite, mica and quartz powder should be kept at 200℃ in a high-temperature sintering furnace for 30-40 minutes, and then cooled in a dry environment before being added to the planetary ball mill.

[0068] S3. Mix the three suspensions in step S1 and add 300g of TO-9, 200g of n-octanol, 50g of potassium sorbate, 50g of chitosan, and 105g of ethylene glycol to the mixture in small amounts several times. Add the resulting mixture to the abrasive mixture in step S2 in small amounts several times. Stir with an electric mixer for 1.5 hours to obtain the desired coating.

[0069] S4. Pack the obtained paint into buckets and store it at room temperature away from light.

[0070] Example 2

[0071] A coating for lost foam casting of alloy steel is composed of the following raw materials in parts by weight as shown in Table 2:

[0072] Table 2

[0073]

[0074]

[0075] A method for preparing a coating for lost foam casting of alloy steel, taking the above-mentioned parts by weight totaling 10 kg as an example, includes the following steps:

[0076] S1. Weigh 225g of sodium carboxymethyl cellulose, 225g of sodium bentonite powder and 50g of sodium alginate, add sufficient deionized water to each, stir quickly with an electric stirrer to form a slurry and soak for 24 hours to obtain 7.5kg of 3wt% sodium carboxymethyl cellulose suspension, 11.3kg of 2wt% sodium bentonite suspension and 5kg of 1wt% sodium alginate suspension for later use.

[0077] S2. Add 6800g of bauxite, 1300g of mica, 400g of quartz powder, 225g of anhydrous aluminum dihydrogen phosphate powder, 125g of nano-grade silica powder and 75g of magnesium oxide powder to a planetary ball mill. Select zirconium oxide grinding balls with a diameter of 1.4-1.6mm and a content of over 90%. Set the speed to 300 rpm and grind the mixed abrasive for 4 hours. Before mixing, the bauxite, mica and quartz powder should be kept at 200℃ in a high-temperature sintering furnace for 30-40 minutes, and then cooled in a dry environment before being added to the planetary ball mill.

[0078] S3. Mix the three suspensions in step S1 and add 200g of TO-9, 200g of n-octanol, 50g of potassium sorbate, 50g of chitosan, and 75g of ethylene glycol to the mixture in small amounts several times. Add the resulting mixture to the abrasive mixture in step S2 in small amounts several times. Stir with an electric mixer for 1.5 hours to obtain the desired coating.

[0079] S4. Pack the obtained paint into buckets and store it at room temperature away from light.

[0080] Example 3

[0081] A coating for lost foam casting of alloy steel is composed of the following raw materials in parts by weight as shown in Table 3:

[0082] Table 3

[0083]

[0084]

[0085] A method for preparing a coating for lost foam casting of alloy steel, taking the above-mentioned parts by weight totaling 10 kg as an example, includes the following steps:

[0086] S1. Weigh 180g of sodium carboxymethyl cellulose, 180g of sodium bentonite powder and 40g of sodium alginate, add sufficient deionized water, stir quickly with an electric stirrer to form a slurry and soak for 24 hours to obtain 6kg of 3wt% sodium carboxymethyl cellulose suspension, 9kg of 2wt% sodium bentonite suspension and 4kg of 1wt% sodium alginate suspension for later use.

[0087] S2. Add 7100g of bauxite, 1350g of mica, 450g of quartz powder, 135g of anhydrous aluminum dihydrogen phosphate powder, 75g of nano-grade silica powder and 45g of magnesium oxide powder to a planetary ball mill. Select zirconium oxide grinding balls with a diameter of 1.4-1.6mm and a content of more than 90%. Set the speed to 300 rpm and grind the mixed abrasive for 4 hours. Before mixing, the bauxite, mica and quartz powder should be kept at 200℃ in a high-temperature sintering furnace for 30-40 minutes, and then cooled in a dry environment before being added to the planetary ball mill.

[0088] S3. Mix the two suspensions in S1 and add 150g of TO-9, 150g of n-octanol, 50g of potassium sorbate, 50g of chitosan, and 45g of ethylene glycol to the mixture in small amounts several times. Add the resulting mixture to the abrasive in S2 in small amounts several times. Stir with an electric mixer for 1.5 hours to obtain the desired coating.

[0089] S4. Pack the obtained paint into buckets and store it at room temperature away from light.

[0090] Comparative Example 1

[0091] A coating for lost foam casting of alloy steel is composed of the following raw materials in parts by weight as shown in Table 4:

[0092] Table 4

[0093]

[0094] A method for preparing a coating for lost foam casting of alloy steel, taking the above-mentioned parts by weight totaling 10 kg as an example, includes the following steps:

[0095] S1. Weigh 315g of sodium carboxymethyl cellulose, 315g of sodium bentonite powder, and 70g of sodium alginate. Add sufficient deionized water to each, and stir quickly with an electric stirrer to form a slurry. Soak for 24 hours to obtain 10.5kg of 3wt% sodium carboxymethyl cellulose suspension, 15.8kg of 2wt% sodium bentonite suspension, and 7kg of 1wt% sodium alginate suspension for later use.

[0096] S2. Add 7530g of bauxite, 470g of quartz powder, 315g of anhydrous aluminum dihydrogen phosphate powder, 175g of nano-grade silica powder, and 105g of magnesium oxide powder to a planetary ball mill. Select zirconium oxide grinding balls with a diameter of 1.4-1.6mm and a content of over 90%. Grind the mixed abrasive at a speed of 300 rpm for 4 hours. Before mixing, the bauxite and quartz powder should be kept at 200℃ in a high-temperature sintering furnace for 30-40 minutes, and then cooled in a dry environment before being added to the planetary ball mill.

[0097] S3. Mix the three suspensions in step S1 and add 300g of TO-9, 200g of n-octanol, 50g of potassium sorbate, 50g of chitosan, and 105g of ethylene glycol to the mixture in small amounts several times. Add the resulting mixture to the abrasive mixture in step S2 in small amounts several times. Stir with an electric mixer for 1.5 hours to obtain the desired coating.

[0098] S4. Pack the obtained paint into buckets and store it at room temperature away from light.

[0099] Comparative Example 2

[0100] A coating for lost foam casting of alloy steel is composed of the following raw materials in parts by weight as shown in Table 5:

[0101] Table 5

[0102]

[0103] A method for preparing a coating for lost foam casting of alloy steel, taking the above-mentioned parts by weight totaling 10 kg as an example, includes the following steps:

[0104] S1. Weigh 315g of sodium carboxymethyl cellulose, 315g of sodium bentonite powder, and 70g of sodium alginate. Add sufficient deionized water to each, and stir quickly with an electric stirrer to form a slurry. Soak for 24 hours to obtain 10.5kg of 3wt% sodium carboxymethyl cellulose suspension, 15.8kg of 2wt% sodium bentonite suspension, and 7kg of 1wt% sodium alginate suspension for later use.

[0105] S2. Add 6740g of bauxite, 1260g of mica, 315g of anhydrous aluminum dihydrogen phosphate powder, 175g of nano-grade silica powder, and 105g of magnesium oxide powder to a planetary ball mill. Select zirconium oxide grinding balls with a diameter of 1.4-1.6mm and a content of over 90%. Grind the mixed abrasive at a speed of 300 rpm for 4 hours. Before mixing, the bauxite and mica should be kept at 200℃ for 30-40 minutes in a high-temperature sintering furnace, and then cooled in a dry environment before being added to the planetary ball mill.

[0106] S3. Mix the three suspensions in step S1 and add 300g of TO-9, 200g of n-octanol, 50g of potassium sorbate, 50g of chitosan, and 105g of ethylene glycol to the mixture in small amounts several times. Add the resulting mixture to the abrasive mixture in step S2 in small amounts several times. Stir with an electric mixer for 1.5 hours to obtain the desired coating.

[0107] S4. Pack the obtained paint into buckets and store it at room temperature away from light.

[0108] Comparative Example 3

[0109] A coating for lost foam casting of alloy steel is composed of the following raw materials in parts by weight as shown in Table 6:

[0110] Table 6

[0111]

[0112] A method for preparing a coating for lost foam casting of alloy steel, taking the above-mentioned parts by weight totaling 10 kg as an example, includes the following steps:

[0113] S1. Weigh 315g of sodium carboxymethyl cellulose, 315g of sodium bentonite powder, and 70g of sodium alginate. Add sufficient deionized water to each, and stir quickly with an electric stirrer to form a slurry. Soak for 24 hours to obtain 10.5kg of 3wt% sodium carboxymethyl cellulose suspension, 15.8kg of 2wt% sodium bentonite suspension, and 7kg of 1wt% sodium alginate suspension for later use.

[0114] S2. Add 6400g of bauxite, 1200g of mica, 400g of quartz powder, 371g of anhydrous aluminum dihydrogen phosphate powder, and 206g of nano-grade silica to a planetary ball mill. Select zirconium oxide grinding balls with a diameter of 1.4-1.6mm and a content of over 90%. Set the speed to 300 rpm and grind the mixed abrasive for 4 hours. Before mixing, the bauxite, mica, and quartz powder should be kept at 200℃ in a high-temperature sintering furnace for 30-40 minutes, and then cooled in a dry environment before being added to the planetary ball mill.

[0115] S3. Mix the three suspensions in step S1 and add 300g of TO-9, 200g of n-octanol, 50g of potassium sorbate, 50g of chitosan, and 123g of ethylene glycol to the mixture in small amounts several times. Add the resulting mixture to the abrasive mixture in step S2 in small amounts several times. Stir with an electric mixer for 1.5 hours to obtain the desired coating.

[0116] S4. Pack the obtained paint into buckets and store it at room temperature away from light.

[0117] Comparative Example 4

[0118] A coating for lost foam casting of alloy steel is composed of the following raw materials in parts by weight as shown in Table 7:

[0119] Table 7

[0120]

[0121] A method for preparing a coating for lost foam casting of alloy steel, taking the above-mentioned parts by weight totaling 10 kg as an example, includes the following steps:

[0122] S1. Weigh 315g of sodium carboxymethyl cellulose, 315g of sodium bentonite powder, and 70g of sodium alginate. Add sufficient deionized water to each, and stir quickly with an electric stirrer to form a slurry. Soak for 24 hours to obtain 10.5kg of 3wt% sodium carboxymethyl cellulose suspension, 15.8kg of 2wt% sodium bentonite suspension, and 7kg of 1wt% sodium alginate suspension for later use.

[0123] S2. Add 6400g of bauxite, 1200g of mica, 400g of quartz powder, 420g of anhydrous aluminum dihydrogen phosphate powder and 140g of magnesium oxide powder to a planetary ball mill. Select zirconium oxide grinding balls with a diameter of 1.4-1.6mm and a content of more than 90%. Set the speed to 300 rpm and grind the mixed abrasive for 4 hours. Before mixing, the bauxite, mica and quartz powder should be kept at 200℃ in a high-temperature sintering furnace for 30-40 minutes, and then cooled in a dry environment before being added to the planetary ball mill.

[0124] S3. Mix the three suspensions in step S1 and add 300g of TO-9, 200g of n-octanol, 50g of potassium sorbate, 50g of chitosan, and 140g of ethylene glycol to the mixture in small amounts several times. Add the resulting mixture to the abrasive mixture in step S2 in small amounts several times. Stir with an electric mixer for 1.5 hours to obtain the desired coating.

[0125] S4. Pack the obtained paint into buckets and store it at room temperature away from light.

[0126] The coatings prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 8 below.

[0127] The detection methods are as follows:

[0128] Suspension rate: Using the stoppered graduated cylinder sedimentation method, extract more than 100ml of paint, shake vigorously for more than 1 minute to mix the paint solution evenly, and then immediately transfer it to a stoppered graduated cylinder, filling the paint suspension in the stoppered graduated cylinder exactly to the 100ml mark; stopper the graduated cylinder tightly, shake vigorously again for more than 1 minute, let it stand on a vibration-free table for 4 hours, and read the volume of the precipitate (accurate to 1ml). Suspension rate = 1 - (volume / 100ml) * 100%, and take the average value of multiple measurements.

[0129] High-temperature air permeability: A 6cm diameter, 35-mesh circular sieve was immersed in the pre-prepared coating. After draining, the coating was neither dripping nor translucent. It was then placed in a drying oven at 50℃ for one hour. The sample prepared at room temperature was placed in a high-temperature box-type resistance furnace. When the furnace temperature reached 1200℃, the coating was held at this temperature for 10 minutes. After cooling, it was placed in a desiccator for later use. The air permeability was tested using a molding sand permeability tester. The sample was placed on a sample tube and tightened with bolts. The gaps in the sample tube were then sealed with Vaseline before measurement. Three sets of samples were prepared for each coating, and the average value was taken.

[0130] Coating properties: EPS foam is used to produce 100*100*20mm sheets. 3For the model, immerse the foam model completely in the paint at a uniform speed and then slowly remove it. Repeat this process twice to ensure that the paint is evenly applied to the model. Avoid placing it vertically in direct sunlight and observe whether the paint adheres well to the model. Based on experience, it is rated as excellent, good, or average. Excellent: The paint film adheres evenly to the surface without dripping; Good: The paint film surface has slight or localized dripping and uneven thickness, but it does not affect the overall appearance quality; Average: The paint film surface has obvious dripping and uneven thickness, which significantly affects the appearance quality.

[0131] High-temperature crack resistance: in 100*100mm 2 A coating of approximately 2 mm was applied to a smooth corundum ceramic surface. After the sample surface dried, it was placed in a preheated sintering furnace at 1200℃ and held for 10 minutes. The sample was then removed and the cracking of the coating surface was observed at high temperature, and four levels were determined: I. Smooth with no cracks or extremely fine cracks; II. Dendritic or network cracks with a crack width of less than 0.5 mm; III. Dendritic or network cracks with a crack width of 0.5 mm-1 mm; IV. Dendritic or network cracks with a crack width of more than 1 mm.

[0132] Peeling and casting surface quality: After the casting cools, clean the sand and remove the coating, and at the same time visually observe the coating peeling, whether the casting surface is smooth, whether there is sand adhering, and the shape of the peeled coating.

[0133]

[0134] As can be seen from Table 8 and Examples 1-3 above, as the proportion of aggregate increases, the proportion of binder and suspending agent decreases, which can improve air permeability but at the same time reduce the suspension rate, and has no significant effect on coating properties and high-temperature crack resistance.

[0135] Comparative Examples 1-4 were based on Example 1, but mica, quartz powder, magnesium oxide and silica were removed from the raw materials while keeping the proportions of the other components unchanged.

[0136] Comparative Example 1 removed mica from the aggregate while maintaining the ratio of bauxite to quartz powder. Compared to Example 1, Comparative Example 1 showed a significant decrease in suspension while high-temperature permeability remained largely unchanged, and a slight decrease in coatability. After sintering, Grade II cracks appeared, and sand adhesion was observed. This is because in Example 1, the flake-like particles of mica powder were arranged in parallel, overlapping, and layered within the coating film, forming a laminated structure that increased the density of the coating film, thereby improving its strength. Mica in casting coatings enhances both suspension and coatability. Furthermore, although the flake-like structure of mica can improve the hidden pores in the coating, the increased amount of quartz powder in Comparative Example 1 resulted in the phase transformation and thermal expansion of quartz during sintering offsetting the reduced permeability caused by the lack of mica.

[0137] Comparative Example 2 removed quartz powder from the aggregate while maintaining the ratio of bauxite to mica. The suspension properties of Comparative Example 2 showed little change, but the permeability decreased significantly. Coating properties and high-temperature crack resistance remained almost unchanged, but the coating did not peel off easily from the casting, and defects such as sand adhesion and porosity were present on the casting surface. Example 1 contained quartz powder. Quartz undergoes a solid-state phase transformation at approximately 560°C, with the dominant phase changing from the α phase to the more loosely latticeed β phase, significantly improving the permeability of the aggregate. Simultaneously, the alumina in the bauxite reacts with the silica in the quartz powder at high temperatures, forming a low-melting-point composite structure that promotes aggregate sintering. In Comparative Example 1, the removal of quartz powder severely reduced the permeability and sinterability of the aggregate. However, due to the increased mica content, the strength and crack resistance of the coating also improved. However, due to the reduced sinterability and permeability of the coating, it was difficult to peel off, and the casting... Surface defects such as sand adhesion and pores.

[0138] Comparative Example 3 removed magnesium oxide from the adhesive while maintaining the same proportions of anhydrous aluminum dihydrogen phosphate, silica, and ethylene glycol. Comparative Example 4 removed silica from the adhesive while maintaining the same proportions of anhydrous aluminum dihydrogen phosphate, ethylene glycol, and magnesium oxide. Aluminum dihydrogen phosphate, as a new environmentally friendly high-temperature resistant adhesive, has a drawback: it is prone to severe shrinkage during sintering, resulting in a large film shrinkage rate and causing adhesive film deformation and cracking. The magnesium oxide added in this invention can partially react with aluminum dihydrogen phosphate at room temperature to form a three-dimensional network structure, thus initially curing and improving the adhesive film strength at high temperatures, reducing the tendency for deformation and cracking. The added silica has good dispersibility and can act as a nucleation point for aluminum dihydrogen phosphate crystals during sintering, helping crystal growth and promoting film formation. It also acts as a filler to compensate for the small cracks caused by shrinkage during aluminum dihydrogen phosphate film formation. Similar to magnesium oxide, both can improve the sintering performance of the adhesive. In contrast, in Comparative Examples 3 and 4, magnesium oxide and silica were removed respectively. During the drying and sintering of the coating, internal cracks were generated, which severely reduced the coating strength and crack resistance. In some areas, the coating even deformed and collapsed under the scouring of molten metal and the burning gas of the white film, resulting in surface defects such as unevenness and sand adhesion on the surface of the casting.

[0139] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0140] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A coating for lost foam casting of alloy steel, characterized in that, The raw materials include the following parts by weight: 79-89 parts aggregate, 3-7 parts binder, 4-7 parts suspending agent, 1.5-3 parts surfactant, 1.5-2.5 parts defoamer, and 1-1.5 parts preservative; The aggregate, by weight percentage, comprises 78-82 wt% bauxite, 12-15 wt% mica, and 3-10 wt% quartz powder; The binder, by weight percentage, comprises 42-50 wt% anhydrous aluminum dihydrogen phosphate, 18-25 wt% silica, 12-17 wt% ethylene glycol and 8-28 wt% magnesium oxide; The surfactant is isotridecyl alcohol polyoxyethylene ether; The defoamer is n-octanol; The preservative, by weight percentage, comprises 25-50 wt% potassium sorbate and 50-75 wt% chitosan.

2. The coating for lost foam casting of alloy steel according to claim 1, characterized in that, The suspending agent comprises, by weight percentage, 35-50 wt% sodium carboxymethyl cellulose, 45-50 wt% sodium bentonite and 10-20 wt% sodium alginate; And / or, the bauxite is 220-270 mesh high-alumina bauxite with an Al2O3 content > 85%; And / or, the mica is 250~270 mesh; And / or, the quartz powder is 180~220 mesh; And / or, the silica is nano-sized silica; And / or, the anhydrous aluminum dihydrogen phosphate, silica, and magnesium oxide are all powders.

3. The method for preparing the coating for lost foam casting of alloy steel according to any one of claims 1 to 2, characterized in that, Includes the following steps: S1. Prepare sodium carboxymethyl cellulose suspension, sodium bentonite suspension, and sodium alginate suspension according to the ingredient ratio; S2. Mix and grind the aggregate, anhydrous aluminum dihydrogen phosphate, silica and magnesium oxide according to the proportion of ingredients to obtain mixed abrasive. S3. Mix the three suspensions in step S1 to obtain a mixed suspension. Add the surfactant, defoamer, preservative and ethylene glycol to the mixed suspension in batches. Add the resulting mixed suspension to the mixed abrasive obtained in step S2 in batches and mix evenly to obtain the coating for lost foam casting of the alloy steel.

4. The method for preparing the coating for lost foam casting of alloy steel according to claim 3, characterized in that, The concentration of the sodium carboxymethyl cellulose suspension in step S1 is 2-3 wt%; And / or, the concentration of the sodium-based bentonite suspension in step S1 is 1.5~2wt%; And / or, the concentration of the sodium alginate suspension in step S1 is 1~1.5wt%.

5. The method for preparing the coating for lost foam casting of alloy steel according to claim 3, characterized in that, In step S1, the solvents for the sodium carboxymethyl cellulose suspension, the sodium bentonite suspension, and the sodium alginate suspension are all deionized water.

6. The method for preparing the coating for lost foam casting of alloy steel according to claim 5, characterized in that, The sodium carboxymethyl cellulose suspension, the sodium bentonite suspension, and the sodium alginate suspension mentioned in step S1 are obtained by adding sodium carboxymethyl cellulose, sodium bentonite, and sodium alginate to deionized water, mixing them into slurries, and then soaking them.

7. The method for preparing the coating for lost foam casting of alloy steel according to claim 3, characterized in that, Before mixing, the bauxite, mica and quartz powder in the aggregates mentioned in step S2 are kept at 200~230℃ for at least 30 minutes, and then cooled in a dry environment before mixing and grinding.

8. The method for preparing the coating for lost foam casting of alloy steel according to claim 7, characterized in that, The heat preservation is carried out in a high-temperature sintering furnace.

9. The method for preparing the coating for lost foam casting of alloy steel according to claim 3, characterized in that, The grinding described in step S2 is carried out in a planetary ball mill, using zirconia grinding balls with a diameter of 1.4~1.6mm and a content of more than 90%, and grinding the mixed abrasive at a speed of 300~330 rpm for 3~4 hours.

10. The application of the coating for lost foam casting of alloy steel according to any one of claims 1 to 2 in the field of lost foam casting of alloy steel.

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