A dry powdered sand mold coating for high-end casting and its use method

Abstract

The present invention relates to a dry powdered sand coating for high-end casting, which is obtained by mixing waste fly ash, high aluminum ore powder and composite additives with a particle size of more than 500 meshes according to a mass ratio of 2-4:8-12:1-2; the composite additive is obtained by mixing manganese ore powder, clinker, trishydroxymethylphosphine oxide and triethanolamine borate in a mass ratio of 8-10:2-4:0.1-0.4:0.5-1. The coating solves the technical problems such as casting sand sticking, casting sand holes, casting roughness, casting pores, and casting inclusions (slag) caused by the fact that traditional casting coatings are prone to chemical reaction with high-temperature molten metal, coating strength and refractoriness are poor.

Description

Technical Field

[0001] The present invention relates to the technical field of high-end casting, and in particular to a dry powdered sand mold coating for high-end casting and a method for using the same. Background Art

[0002] Lost foam casting (also known as full mold casting) is a new casting method in which paraffin wax or foam models with similar size and shape to the casting are bonded together to form a model cluster, coated with refractory paint and dried, and then buried in dry quartz sand (sand mold) for vibration molding. The mold is poured under negative pressure to vaporize and disappear, allowing the molten metal to occupy the position of the model, and then solidify and cool to form a casting.

[0003] During the casting process of high-end castings, a refractory coating is required on the surface of the sand mold (or wax pattern) to improve its fire resistance and chemical stability. Currently, water-based coatings are primarily used in my country. However, existing coatings still present the following technical challenges: 1. The coatings react chemically with the high-temperature molten metal, resulting in inclusions (slag) on ​​the casting surface, or the coatings can fall off during sand filling vibration, causing sand to stick to the casting. 2. The coatings are insufficiently strong and have poor refractoriness, which means they often cannot withstand the erosion of the high-temperature molten metal, causing the sand mold to be drawn into the casting, resulting in defects such as sand holes and air holes. Summary of the Invention

[0004] (1) Technical issues to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a dry powdered sand mold coating for high-end casting and a method for using the same, which solves the technical problems of traditional casting coatings easily reacting chemically with high-temperature molten metal, poor coating strength and refractoriness, etc., which lead to sand sticking to castings, sand holes in castings, rough castings, air holes in castings, and inclusions (slag) in castings.

[0006] (2) Technical solution

[0007] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] In a first aspect, the present invention provides a dry powdered sand mold coating for high-end casting, which is obtained by mixing waste fly ash with a particle size of 500 mesh or more, high-aluminum ore powder and a composite additive in a mass ratio of 2-4:8-12:1-2; the composite additive is obtained by mixing manganese ore powder, clinker, trishydroxymethylphosphine oxide and triethanolamine borate in a mass ratio of 8-10:2-4:0.1-0.4:0.5-1.

[0009] According to a preferred embodiment of the present invention, the mass content of Al2O3 in the high-aluminum ore powder is ≥90%.

[0010] According to a preferred embodiment of the present invention, the waste fly ash, high-aluminum ore powder and composite additives are mixed in a mass ratio of 3:10:1.

[0011] According to a preferred embodiment of the present invention, the composite additive is obtained by mixing manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 10:4:0.4:0.6.

[0012] According to a preferred embodiment of the present invention, each raw material is ground by a secondary ball mill and separated by an ultrafine air separator, and further homogenized and refined to a particle size of 15-20 μm, meeting the material requirements of dry powdered sand coating for high-end casting.

[0013] According to a preferred embodiment of the present invention, the manganese ore powder is a commercially available product. Preferably, the manganese ore powder contains 19%-21wt% manganese, 0.03%-0.07wt% phosphorus, 7-11wt% SiO2, 2.7-3.7wt% iron, and 0.05%-0.5wt% sulfur.

[0014] In a second aspect, the present invention provides a method for using a dry powdered sand mold coating for high-end casting, comprising the following steps:

[0015] S1. Grind the waste fly ash, high aluminum ore, and composite additive separately, mix them uniformly in a mass ratio of 8-10:2-4:0.1-0.4:0.5-1 to obtain a mixture with uniform chemical composition, and grind it to a size of 500 mesh or more; the composite additive is obtained by mixing manganese ore powder, clinker, trishydroxymethylphosphine oxide, and triethanolamine borate in a mass ratio of 8-10:2-4:0.1-0.4:0.5-1;

[0016] S2. Add the mixture to a blender and dry mix for 10-30 min. Then add a binder and water and wet mix for 20-40 min. Continue adding water and stirring to form a slurry. The binder is one or more of silica sol, white latex, coal tar, asphalt, rosin, phenolic resin, and ethyl silicate. The weight ratio of dry powder to binder is 1:1-3:1.

[0017] S3. Use a spray gun to spray the evenly mixed coating onto the surface of the sand mold;

[0018] S4. The paint is dried after being applied to the sand mold and is dried in a continuous low-temperature drying kiln.

[0019] According to a preferred embodiment of the present invention, the mass content of Al2O3 in the high-aluminum ore powder is ≥90%.

[0020] In S2, the slurry has a 24h suspension rate ≥95%, a conditional viscosity (6 mm) <12s, and a shear thinning index ≥7.5.

[0021] In S3, spraying is done with a spray gun. Compared with brushing, the coating thickness is more uniform, which improves work efficiency and lays a good foundation for high-end casting technology.

[0022] In S4, the paint is dried after being coated on the sand mold and is dried for 2-4 hours in a continuous low-temperature drying kiln equipped with good ventilation and drying equipment.

[0023] According to a preferred embodiment of the present invention, the waste fly ash, high-aluminum ore powder and composite additives are mixed in a mass ratio of 3:10:1.

[0024] According to a preferred embodiment of the present invention, the composite additive is obtained by mixing manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 10:4:0.4:0.6.

[0025] According to a preferred embodiment of the present invention, each raw material is ground by a secondary ball mill and separated by an ultrafine air separator, and further homogenized and refined to a particle size of 15-20 μm, meeting the material requirements of dry powdered sand coating for high-end casting.

[0026] Fly ash typically refers to the fine ash collected from the flue gases of coal-fired power plants. Fly ash is formed when coal enters a furnace at 1300-1500°C, undergoes suspended combustion, and then cools to form small spheres. It has a smooth surface and fine pores. Its main components are silicon dioxide, aluminum oxide, iron oxide, calcium oxide, magnesium oxide, and sulfur trioxide.

[0027] Manganese ore powder can improve the compressive strength of the coating. The main mineral component of refractory clinker is mullite (3Al2O3·2SiO2), which is a sintered mass of hard clay (such as bauxite or kaolin) calcined at high temperatures (1300-1500°C), then crushed and screened. Bauxite sand calcined with high-alumina bauxite has a refractoriness exceeding 1800°C when the Al2O3 mass fraction reaches 71.8%. Refractory clinker has low thermal expansion, stable volume at high temperatures, high refractoriness, and good slag resistance. It is less wettable by iron and its oxides than quartz.

[0028] Tris(hydroxymethyl)phosphine oxide (TMPO) is a catalyst and additive, fully miscible with water, exhibiting excellent heat stability, superior hydrolysis resistance, and non-toxicity. It is primarily used to accelerate coating cure and increase compressive strength. Triethanolamine borate itself exhibits excellent rust prevention, exceptional extreme-pressure lubrication for metals, and possesses a very high alkali reserve, making it a good pH stabilizer. It also promotes the activation of silica. Activated silica, in the presence of water, becomes a permeable, crystalline material that rapidly reacts with free calcium to form insoluble amorphous calcium silicate hydrate, which seals and plugs pores on the sand mold surface, smoothing the surface and reducing technical issues such as blisters, roughness, and porosity. The decomposition of organic matter, such as TMPO and binders, creates pores that impart excellent high-temperature breathability to the coating, reducing porosity and blisters and improving the surface quality of the casting.

[0029] (3) Beneficial effects

[0030] The beneficial effects of the present invention are:

[0031] The dry powdered sand mold coating for high-end casting of the present invention is improved on the basis of traditional casting coating. It can effectively prevent the oxidation of high-temperature molten metal, does not undergo chemical reaction during contact with sand molds and high-temperature molten metal, and can absorb dry powdered casting coating containing nitrogen, sulfur, carbon and other gases, thereby completely solving the problems of sand sticking to castings, sand holes in castings, rough castings, air holes in castings, and casting inclusion (slag) defects, with outstanding results.

[0032] The dry powder sand mold coating for high-end casting of the present invention is applicable to various sand mold casting process fields such as self-hardening furan resin sand, alkaline phenolic resin sand, coated sand, cold core box resin sand, etc. The product is stored in dry powder form, is easy to store and has good stability. DETAILED DESCRIPTION

[0033] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below in conjunction with specific embodiments.

[0034] Example 1

[0035] This embodiment provides a dry powdered sand mold coating for high-end casting. The coating is prepared by mixing separately ground, sieved, and air-selected waste fly ash, high-aluminum ore powder, and a composite additive in a mass ratio of 3:10:1. The composite additive is prepared by mixing manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 10:4:0.4:0.6.

[0036] The high-alumina ore powder contains 93.6% Al2O3 by mass. The manganese ore powder is a commercially available product containing 21% manganese by weight, 0.06% phosphorus by weight, 7% SiO2 by weight, 2.7% iron by weight, and 0.1% sulfur by weight. The refractory clinker is bauxite sand calcined from high-alumina bauxite, with a refractoriness greater than 1800°C.

[0037] Usage: Add dry powdered paint into the mixer, dry mix for 20 minutes, then add 1.5 times the mass of white latex and a certain amount of water, wet mix for 40 minutes, continue to add water, stir and mix into slurry. When the slurry has a 24h suspension rate ≥95%, conditional viscosity (6mm) <12s, and shear dilution index ≥7.5, the requirements are met.

[0038] Use a spray gun to spray the evenly mixed paint onto the surface of the sand mold and dry it in a continuous low-temperature drying kiln equipped with good ventilation and drying equipment for 4 hours.

[0039] Example 2

[0040] This embodiment provides a dry powdered sand mold coating for high-end casting. The coating is prepared by mixing separately ground, sieved, and air-selected waste fly ash, high-aluminum ore powder, and a composite additive in a mass ratio of 4:12:2. The composite additive is prepared by mixing manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 8:2:0.2:0.5.

[0041] The high-alumina ore powder contains 93.6% Al2O3 by weight. The manganese ore powder contains 21% manganese by weight, 0.06% phosphorus by weight, 7% SiO2 by weight, 2.7% iron by weight, and 0.1% sulfur by weight. The refractory clinker is bauxite sand calcined from high-alumina bauxite, with a refractoriness greater than 1800°C.

[0042] Usage: Add the dry powdered coating to the blender and dry mix for 20 minutes. Then, add 1.5 times the weight of a 1:1 mixture of rosin and asphalt, and add a certain amount of water. Wet mix for 40 minutes. Continue adding water and stirring to form a slurry. When the slurry has a 24-hour suspension rate ≥95%, a conditional viscosity (6mm) <12s, and a shear thinning index ≥7.5, it meets the requirements. Use a spray gun to spray the evenly mixed coating onto the sand mold surface and dry it in a continuous low-temperature drying kiln equipped with good ventilation and drying equipment for 4 hours.

[0043] Example 3

[0044] This embodiment provides a dry powdered sand mold coating for high-end casting. The coating is prepared by mixing separately ground, sieved, and air-selected waste fly ash, high-aluminum ore powder, and a composite additive in a mass ratio of 3:9:1.5. The composite additive is prepared by mixing manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 9:3:0.4:0.6.

[0045] Among them, high aluminum ore powder, manganese ore powder, and refractory clinker are the same as those in Example 1.

[0046] Usage: Add dry powdered paint to a blender and dry mix for 20 minutes. Then add twice the mass of silica sol and a certain amount of water. Wet mix for 40 minutes. Continue adding water and stirring to form a slurry. When the slurry has a 24-hour suspension rate ≥95%, a conditional viscosity (6mm) <12s, and a shear thinning index ≥7.5, it meets the requirements. Use a spray gun to spray the evenly mixed paint onto the sand mold surface and dry it in a continuous low-temperature drying kiln equipped with good ventilation and drying equipment for 4 hours.

[0047] Example 4

[0048] This embodiment provides a dry powdered sand mold coating for high-end casting. The coating is prepared by mixing waste fly ash, which has been ground and sieved, and air-selected through a 500-mesh sieve, high-aluminum ore powder, and a composite additive in a mass ratio of 2:8:1. The composite additive is prepared by mixing manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 8:2:0.2:0.8.

[0049] Among them, high aluminum ore powder, manganese ore powder, and refractory clinker are the same as those in Example 1.

[0050] Usage: Add the dry powdered coating to a blender and dry mix for 20 minutes. Then, add ethyl silicate (3 times its mass) and a certain amount of water. Wet mix for 40 minutes. Continue adding water and stirring to form a slurry. The slurry meets the requirements when its suspension rate is ≥95% after 24 hours, the conditional viscosity (6mm) is <12s, and the shear thinning index is ≥7.5. Use a spray gun to spray the evenly mixed coating onto the sand mold surface and dry it in a continuous low-temperature drying kiln equipped with good ventilation and drying equipment for 4 hours.

[0051] Example 5

[0052] This embodiment provides a dry powdered sand mold coating for high-end casting. The coating is prepared by mixing separately ground, sieved, and air-selected waste fly ash, high-aluminum ore powder, and a composite additive in a mass ratio of 4:10:1.5. The composite additive is prepared by mixing manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 8:2:0.2:0.8.

[0053] Among them, high aluminum ore powder, manganese ore powder, and refractory clinker are the same as those in Example 1.

[0054] Usage: Add the dry powdered coating to a blender and dry mix for 20 minutes. Then, add ethyl silicate (3 times its mass) and a certain amount of water. Wet mix for 40 minutes. Continue adding water and stirring to form a slurry. The slurry meets the requirements when its suspension rate is ≥95% after 24 hours, the conditional viscosity (6mm) is <12s, and the shear thinning index is ≥7.5. Use a spray gun to spray the evenly mixed coating onto the sand mold surface and dry it in a continuous low-temperature drying kiln equipped with good ventilation and drying equipment for 4 hours.

[0055] Example 6

[0056] This example is based on Example 1, but the composition of the composite additive is changed to: manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate are mixed in a mass ratio of 8:2:0.4:1. Other steps and conditions are the same as those in Example 1.

[0057] Example 7

[0058] This example is based on Example 1, but the composition of the composite additive is changed to: manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate are mixed in a mass ratio of 10:2:0.1:0.5. Other steps and conditions are the same as those in Example 1.

[0059] Example 8

[0060] This embodiment provides a dry powdered sand mold coating for high-end casting. The coating is prepared by mixing separately ground, sieved, and air-selected waste fly ash, high-aluminum ore powder, and a composite additive in a mass ratio of 3.5:11:1.5. The composite additive is prepared by mixing manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 9:3:0.3:1.

[0061] Among them, high aluminum ore powder, manganese ore powder, and refractory clinker are the same as those in Example 1.

[0062] Usage: Add the dry powdered coating to a blender and dry mix for 20 minutes. Then, add ethyl silicate (3 times its mass) and a certain amount of water. Wet mix for 40 minutes. Continue adding water and stirring to form a slurry. The slurry meets the requirements when its suspension rate is ≥95% after 24 hours, the conditional viscosity (6mm) is <12s, and the shear thinning index is ≥7.5. Use a spray gun to spray the evenly mixed coating onto the sand mold surface and dry it in a continuous low-temperature drying kiln equipped with good ventilation and drying equipment for 4 hours.

[0063] Comparative Example 1

[0064] This comparative example is based on Example 1, wherein the composite additive lacks manganese ore powder. Other steps and conditions are the same as those in Example 1.

[0065] Comparative Example 2

[0066] This comparative example is based on Example 1, wherein the composite additive lacks tris(hydroxymethyl)phosphine oxide. Other steps and conditions are the same as those in Example 1.

[0067] Comparative Example 3

[0068] This comparative example is based on Example 1, wherein the composite additive lacks triethanolamine borate. Other steps and conditions are the same as those in Example 1.

[0069] Comparative Example 4

[0070] This comparative example is based on Example 1, wherein the composite additive is composed of manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 3:2:0.5:0.5. Other steps and conditions are the same as those in Example 1.

[0071] Comparative Example 5

[0072] This comparative example is based on Example 1, wherein the composite additive is composed of manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 10:0.1:0.2:0.7. Other steps and conditions are the same as those in Example 1.

[0073] Comparative Example 6

[0074] This comparative example is based on Example 1, wherein the composite additive is composed of manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate salt mixed in a mass ratio of 8:1:1:2. Other steps and conditions are the same as those in Example 1.

[0075] The casting sand coating performance tests of the above embodiments are as follows:

[0076] ① Room-Temperature Coating Surface Strength Test: First, use a precision balance to measure the sample mass m1. Then, place the prepared sample on a glass plate, which is tilted against the side of a sand container and secured at a 45° angle to the bottom. Then, drop jelly sand from a height of 1 meter. The sand falls onto the sample and rolls into the glass container. Once all the sand has fallen out of the container, use a precision balance to measure the sample mass m2 after flushing. The difference in mass before and after flushing, mΔ, is used as the surface strength of the coating. A smaller mΔ value indicates a higher surface strength.

[0077] ②Breathability at room temperature: cm 2 .(kPa.min) -1 The better the air permeability, the more conducive it is to obtaining a casting with no pores or sand holes on the surface.

[0078] ③ Carry out casting test: observe the inclusions (slag), sand sticking, sand holes, and air holes on the surface of the casting sample with the naked eye, and test the roughness Ra of the casting with AFM.

[0079] The properties of casting sand coating are as follows:

[0080]

[0081]

[0082] From the above sand coating performance test results, it can be seen that the dry powdered sand coating for high-end casting of the present invention can solve the problems of sand sticking to castings, sand holes in castings, rough castings, air holes in castings, and casting inclusion (slag) defects, and the effect is obvious.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dry powdered sand mold coating for high-end casting, characterized in that: The waste fly ash with a particle size of 500 mesh or more, high-aluminum ore powder and composite additives are mixed in a mass ratio of 2-4:8-12:1-2; The composite additive is prepared by mixing manganese ore powder, clinker, trishydroxymethylphosphine oxide, and triethanolamine borate in a mass ratio of 8-10:2-4:0.1-0.4:0.5-1; The mass content of Al2O3 in the high-aluminum ore powder is ≥90%; The manganese ore powder contains 19%-21wt% manganese, 0.03%-0.07wt% phosphorus, 7-11wt% SiO2, 2.7-3.7wt% iron, and 0.05%-0.5wt% sulfur.

2. The dry powdered sand coating according to claim 1, characterized in that: The waste fly ash, high-aluminum ore powder and composite additive are mixed in a mass ratio of 3:10:

1.

3. The dry powdered sand coating according to claim 1, characterized in that: The composite additive is prepared by mixing manganese ore powder, clinker, tris(hydroxymethyl)phosphine oxide, and triethanolamine borate in a mass ratio of 10:4:0.4:0.

6.

4. The dry powdered sand coating according to claim 1, characterized in that: Waste fly ash, high-alumina ore powder and composite additives are ground by a secondary ball mill and separated by an ultra-fine air separator, and further homogenized and refined to a particle size of 15-20 μm.

5. A method for using the dry powdered sand mold coating for high-end casting according to any one of claims 1 to 4, characterized in that: Including steps: S1, after grinding the waste fly ash, high aluminum ore, and composite additive respectively, mixing them in a mass ratio of 8-10:2-4:0.1-0.4:0.5-1 to obtain a mixture with uniform chemical composition, and crushing it to a size of more than 500 mesh; the composite additive is obtained by mixing manganese ore powder, clinker, trishydroxymethylphosphine oxide, and triethanolamine borate in a mass ratio of 8-10:2-4:0.1-0.4:0.5-1; S2, adding the mixture to a blender, dry mixing for 10-30 min, then adding a binder and water, wet mixing for 20-40 min, continuing to add water, continuing to stir, and mixing into a slurry; the binder is one or more of silica sol, white latex, coal tar, asphalt, rosin, phenolic resin, and ethyl silicate; the weight ratio of dry powder to binder is 1: 1-3: 1; S3. Use a spray gun to spray the evenly mixed coating onto the surface of the sand mold; S4. The paint is dried after being applied to the sand mold and is dried in a continuous low-temperature drying kiln.

6. The method of use according to claim 5, characterized in that: In S2, the slurry has a 24h suspension rate ≥ 95%, a 6mm viscosity < 12 s, and a shear thinning index ≥ 7.

5.

7. The method of use according to claim 5, characterized in that: The mass content of Al2O3 in the high-aluminum ore powder is ≥90%.

8. The method of use according to claim 5, characterized in that: The waste fly ash, high aluminum ore powder and composite additive are mixed in a mass ratio of 3:10:1; the composite additive is obtained by mixing manganese ore powder, clinker, trishydroxymethylphosphine oxide and triethanolamine borate in a mass ratio of 10:4:0.4:0.6.

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