Coating material for improving high temperature resistance of sand mold working surface and preparation method thereof

Abstract

The invention discloses a coating material for improving high temperature resistance of a sand mold working face and a preparation method of the coating material. The coating material comprises the following components in percentage by mass: 10-30% of modified light fibers, 10-30% of aluminum oxide hollow spheres, 40-60% of spherical aluminum oxide powder, 5-15% of desilicication zirconium micro powder, 5-10% of gelatinized starch and 3-15% of a binder, a water reducing agent accounting for 0.1-0.5% of the total mass of the components and a solvent accounting for 1-8 times of the total mass of the components are added; the modified light fiber is a chopped zirconia or alumina fiber with the surface coated with a porous aluminum-zirconium-based high-temperature-resistant ceramic material. The coating material has the advantages of excellent thermal shock resistance, low thermal conductivity and high adhesive strength, and can be used on a high-temperature contact surface of a sand mold with the casting temperature higher than 2000 DEG C, so that failure conditions such as cracking and stripping of the sand mold in the high-temperature casting process are effectively prevented, the service life of the sand mold in the casting process is remarkably prolonged, the casting quality is remarkably improved, and the production cost is reduced. The method is especially suitable for sand mold surface modification in the production process of casting high-zirconium refractory materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of refractory materials, and particularly relates to a coating material for improving the high-temperature performance of a sand mold working surface and a preparation method thereof. BACKGROUND

[0002] In the production process of fused cast high-zirconia refractory materials, the pouring process is a key process. This process requires pouring high-temperature melt with a temperature as high as 2000-2100 DEG C into a sand mold, and after annealing and cooling, a blank is finally formed. During the pouring process, the sand mold material directly withstands extreme service environments such as high temperature, high erosion, and high temperature difference, which causes the surface to easily crack, peel off and other failure conditions, and in severe cases, even causes the sand mold to be damaged, resulting in liquid leakage and high-temperature safety hazards.

[0003] Existing processes mostly strengthen the sand mold by increasing the thickness of the sand mold or using alumina surface sand, but as the size of the casting increases, the weight of the mold and the assembly difficulty increase sharply, which restricts the manufacture of large and complex structure blanks. At the same time, in order to balance the strength and permeability, the porosity of the sand mold is mostly controlled at 10%-25%, but this reduces the thermal shock resistance. The common preheating means of the mold cavity has limited effect and is easy to cause local cracking due to uneven heating distribution. Although coating a coating (such as alumina surface sand or various high-temperature inorganic coatings) on the surface of the sand mold can improve the short-time high-temperature performance of the surface, the existing coatings have a temperature resistance lower than the actual temperature of the fused casting, and are easy to fall off under high temperature or strong erosion, resulting in quality problems such as sand inclusion of the casting.

[0004] The disclosed patent CN115232524A discloses a water-based super-high-temperature-resistant coating, which is simple to operate but has a maximum use temperature of less than 1000 DEG C, which is difficult to apply to the actual pouring working condition of fused cast zirconia corundum. The disclosed patent CN101665364A discloses an inorganic bonding anti-molten slag coating, which performs well at 1400 DEG C, but generates a large amount of chrome spinel in situ at high temperature, which not only affects the structural integrity of the fused cast zirconia corundum casting, but also affects the appearance quality of the casting due to chromium ion pollution, and the invention does not mention whether the coating can help improve the high-temperature thermal performance of the sand mold at 2000 DEG C.

[0005] In summary, there is still a lack of a new sand mold surface modification material and its preparation process that can effectively adapt to the high-temperature forming process of fused cast zirconia corundum sand mold, significantly improve the high-temperature impact stability of the sand mold surface, and not affect the quality of the casting. Therefore, developing a sand mold surface modification technology with excellent high-temperature mechanical properties, heat shock resistance, and high-temperature fluid erosion resistance, and promoting the forming quality of fused cast zirconia corundum castings, has become a technical problem that the industry urgently needs to solve. SUMMARY

[0006] Based on the above technical problems, the present application provides a coating material for improving the high-temperature resistance of sand mold working surface and a preparation method thereof, which has the performance advantages of excellent thermal shock resistance, low thermal conductivity and high adhesion strength, can be used on the high-temperature contact surface of a sand mold with a casting temperature > 2000℃ or above, thereby effectively preventing the sand mold from cracking, peeling and other failure conditions during high-temperature casting, significantly improving the service life of the sand mold in the melting and casting process and the quality of the castings, and is particularly suitable for surface modification of sand molds in the production process of high-zircon refractory materials.

[0007] The coating material for improving the high-temperature resistance of sand mold working surface comprises the following components in mass percentage: modified lightweight fiber 10-30%, alumina hollow sphere 10-30%, spherical alumina powder 40-60%, desiliconized zirconium micro powder 5-15%, gelatinized starch 5-10%, and binder 3-15%; in addition, 0.1-0.5% of water reducing agent of the total mass of the above components and 1-8 times of solvent of the total mass of the above components are added. The modified lightweight fiber is a chopped zirconia or alumina fiber coated with a porous aluminum-zirconium-based high-temperature-resistant ceramic material on the surface.

[0008] Preferably, the porous aluminum-zirconium-based high-temperature-resistant ceramic material comprises porous yttria-stabilized zirconia micro powder, alumina micro powder and aluminum sol. Preferably, the porous aluminum-zirconium-based high-temperature-resistant ceramic material comprises, in mass percentage, 40-70% of porous yttria-stabilized zirconia micro powder, 20-50% of alumina micro powder and 5-15% of aluminum sol. Preferably, the chopped zirconia fiber has a diameter of 10-15 μm, an average fiber length of 130-150 μm and a zirconia content in the fiber of ≥ 85%; and the chopped alumina fiber has a diameter of 8-10 μm, a length of 80-160 μm and an alumina content in the fiber of ≥ 97.5%. Preferably, the alumina micro powder comprises α-alumina micro powder and / or ρ-alumina micro powder.

[0009] Preferably, the modified lightweight fiber is prepared by the following method: The chopped zirconia or alumina fiber and a dispersing agent are added into an ethanol solution and uniformly mixed, and then dried to obtain pre-dispersed fiber; the porous aluminum-zirconium-based high-temperature-resistant ceramic material, a binding agent and a thickening agent are added into an ethanol solution and uniformly mixed to obtain a coating slurry; the pre-dispersed fiber is added into the coating slurry and uniformly mixed, and then dried to obtain the modified lightweight fiber. Preferably, the dispersing agent is sodium polyacrylate and polyvinylpyrrolidone; the amount of the sodium polyacrylate is 0.5-1.7% of the mass of the chopped zirconia or alumina fiber, and the amount of the polyvinylpyrrolidone is 0.9-2.5 wt% of the mass of the chopped zirconia or alumina fiber. Preferably, the binding agent is polyethylene glycol, the thickening agent is polyurethane thickening agent and glycerol; the amount of polyethylene glycol is 1.5-2% of the mass of the porous aluminum-zirconium-based refractory ceramic material, the amount of polyurethane thickening agent is 1.8-2.5% of the mass of the porous aluminum-zirconium-based refractory ceramic material, and the amount of glycerol is 3-5% of the mass of the porous aluminum-zirconium-based refractory ceramic material.

[0010] Preferably, the particle size distribution of the alumina hollow spheres includes: the proportion of alumina hollow spheres with a particle size of 150-200 μm is 20-30%, the proportion of alumina hollow spheres with a particle size of 100-150 μm is 10-50%, and the proportion of alumina hollow spheres with a particle size less than 100 μm is 10-80%. Preferably, the content of alumina in the alumina hollow spheres is ≥95%.

[0011] Preferably, the particle size distribution of the spherical alumina powder includes: the proportion of spherical alumina micropowder with a particle size of 30-90 μm is 5-20%, the proportion of spherical alumina micropowder with a particle size of 5-10 μm is 45-70%, and the proportion of spherical alumina micropowder with a particle size of 0.5-1 μm is 10-40%. Preferably, the content of alumina in the spherical alumina powder is ≥95%.

[0012] Preferably, the particle size of the desiliconized zirconium micropowder is 50-80 μm. Preferably, the content of zirconia in the desiliconized zirconium micropowder is ≥85%.

[0013] Preferably, the binder is at least one of aluminum sol, zirconium sol, titanium sol or silicon sol; the water reducing agent is at least one of sodium polyphosphate, sodium tripolyphosphate or sodium pyrophosphate; and the solvent is at least one of methanol, ethanol or water. Preferably, the binder is aluminum sol, and the solid content in the aluminum sol is 19-25%.

[0014] The application further provides a preparation method of the coating material for improving the high-temperature resistance of the working surface of the sand mold. S1, dry mixing alumina hollow spheres, spherical alumina powder, desiliconized zirconium micropowder and gelatinized starch to obtain a solid-phase mixture; S2, uniformly mixing modified lightweight fibers and a water reducing agent in a solvent to obtain a medium solution; S3, gradually adding the medium solution to the solid-phase mixture, uniformly mixing, adding a binder and uniformly mixing again to obtain the coating material.

[0015] Preferably, in step S1, the dry mixing speed is 400-600 rad / min, and the time is 10-15 min; in step S2, the uniform mixing stirring speed is 80-100 rad / min, and the time is 3-5 min; in step S3, the preliminary uniform mixing stirring speed is 600-1000 rad / min, and the time is 3-5 min.

[0016] The application also provides a use of the coating material prepared by the method. The coating material is applied to the surface of the sand mold with a thickness of 8-20 mm, and the coated sand mold is dried or placed at 250-360℃ for 100-150 min and then used.

[0017] In the application, the coating material essentially uses modified lightweight fibers as the key heat shock resistant structure. The addition of the fibers can effectively prevent the coating material from being peeled off and cracked due to thermal stress caused by rapid temperature change when the coating material is subjected to high temperature. When the coating material is in contact with high-temperature molten liquid with a temperature of 2000℃ or above, the matrix will be sintered in a short time. Due to the presence of sintering necks between the particles, the overall coating will shrink and crack. However, due to the mutual pulling between the fibers and the matrix in the coating, the cracking energy of the matrix is partially offset.

[0018] In the application, the addition of the modified lightweight fibers improves the heat shock resistance of the coating material. Although the existing technology also introduces fibers into the coating material, such as the environmentally friendly room temperature curing silicone high-temperature resistant coating and its preparation method disclosed in the published patent CN103409063A, the highest temperature resistance of the coating is only 900℃. Therefore, simply introducing refractory fibers cannot prepare a coating material that can improve the high-temperature performance of the sand mold plate. In fact, due to the special heating conditions (i.e., the pouring temperature directly reaches 2000℃ or above from room temperature), the thermal shock on the overall material is large, which can cause the cracking, delamination or deformation of the zirconia or alumina fibers, such as the grain and grain boundary thermal expansion difference (anisotropy) of the polycrystalline zirconia or alumina fibers, which causes the grain boundary cracks. Therefore, the chopped zirconia or alumina fibers are impregnated with a porous aluminum-zirconium-based high-temperature resistant ceramic material, which can form a lightweight refractory layer wrapped by porous zirconia on the surface of the fibers. This can effectively reduce the thermal shock of the fibers on the overall material, and also improve the high-temperature resistance of the fibers themselves.

[0019] In the application, the modified lightweight fiber is specifically based on chopped zirconia or alumina fiber as a matrix, and a porous aluminum-zirconium-based high-temperature-resistant ceramic material including porous yttrium-stabilized zirconia powder, alumina powder and the like is wrapped outside the fiber, thereby improving the high-temperature strength of the fiber; meanwhile, the fiber is dispersed (sodium polyacrylate and polyvinylpyrrolidone are dispersed in an ethanol medium) to significantly improve the dispersibility of the fiber and avoid agglomeration; then, a high-temperature stable composite material is coated on the surface of the fiber; and finally, the high-temperature stability and interfacial bonding performance of the fiber are significantly improved through ultrasonic mixing and high-temperature drying multi-step composite processes, and the high-temperature stability of the fiber is significantly improved, thereby significantly improving the thermal shock resistance of the coating material.

[0020] In the application, the aluminum oxide hollow sphere is used to improve the thermal shock resistance of the sand mold plate; since the thermal conductivity of the aluminum oxide material is low at high temperatures, the main matrix part of the coating is made of aluminum oxide raw material; in order to further slow down the speed of heat transfer, the aluminum oxide hollow microspheres are used, and after adjusting the particle size grading of different hollow spheres, a tight packing is formed between the aluminum oxide hollow spheres and the spherical alumina powder, thereby improving the overall density of the coating and the high-temperature molten liquid thermal shock and physical impact performance. Through comparative experiments, in the 2020 DEG C to room temperature thermal cycle test, when the coating thickness is 20 mm, the thermal cycle of the overall coated quartz sand sample can reach 3 times, and no cracking phenomenon occurs on the surface of the coating; the sample without coating appears cracking in the first cycle; after casting for 30 s in a 1980 DEG C temperature environment, the surface of the sand mold coated with the coating material does not appear to be eroded, and the coating thickness in the eroded area is reduced to 3 mm; the surface of the sand mold without coating appears a 15 cm deep sand erosion pit.

[0021] In the application, the aluminum sol and the like are used as the binder to avoid the gas generated by the high-temperature volatilization of the organic binder from entering the casting; since the surface temperature of the casting is high after casting, the organic binder in the traditional high-temperature coating will decompose and generate a large amount of gas at high temperatures; when the temperature in the cavity is high, the pressure in the cavity is high, and the gas will adhere to the surface of the melt; when the holding box is transferred or secondary casting is performed, the gas will enter the casting, resulting in a large number of pores in the casting and making the casting unusable; the binder of the application adopts inorganic bonding, effectively avoiding the source of the gas; in addition, the aluminum sol and the like will form secondary sintering at high temperatures, further enhancing the erosion resistance and coating bonding strength of the coating, and playing the role of a high-temperature binder.

[0022] In the application, in order to facilitate coating and rapid casting, solvent is used, the coating material has the characteristics of short curing time, and after short time drying in a low temperature drying kiln, the sand mold can be assembled, and the production efficiency of the mold is improved; in the application, the thick layer scraping coating + low temperature rapid drying surface covering mode can be used, and the process adaptability is strong, and the application process is simple and efficient, so the application process is simple and efficient.

[0023] In summary, the application improves the thermal shock resistance of the coating material by introducing modified lightweight fibers as the core skeleton, from the material internal structure organization level, improves the thermal shock resistance of the coating material, and improves the thermal shock resistance of the coating material. The protection and high temperature resistance of the coating material to the combination system of the inorganic aluminum sol binder, the coating can be used at a temperature of 2000 DEG C or above for a long time, maintains low thermal conductivity, high strength and excellent thermal shock stability, significantly prevents sand mold high temperature cracking and peeling, greatly improves the service life of the sand mold and the quality of the casting. At the same time, the coating improves the high temperature impact resistance and safe service performance of the sand plate, can effectively reduce the thickness of the sand plate during high temperature casting, and reduce the production cost. The coating material has the use performance of high temperature resistance, thermal shock resistance and high adhesion, compared with the prior art, the coating has no organic residue, has no effect on the surface quality of the casting, and can be applied to the high temperature casting sand mold lining with large size and complex structure, and effectively enhances the high temperature performance. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The SEM graph of the coating material described in embodiment 1 under different magnifications. DETAILED DESCRIPTION

[0025] In the following, the technical solutions are described in detail by specific embodiments, but it should be clear that these embodiments are used for illustration, but not to limit the scope of the application.

[0026] Embodiment 1 A coating material for improving the high temperature resistance of the working surface of the sand mold, comprising the following components: modified lightweight fiber 10%, alumina hollow sphere 10%, spherical alumina powder 60%, desiliconized zirconium powder 10%, paste starch 5%, aluminum sol 5%; plus 0.5% of the total mass of the above components of sodium polyphosphate and plus 3 times of the total mass of the above components of solvent ethanol aqueous solution (ethanol content is 75%); The modified lightweight fiber is a short-cut zirconia fiber coated with porous aluminum-zirconium-based high-temperature-resistant ceramic material, which is prepared by the following method: (1) according to the short cut zirconia fiber and ethanol aqueous solution weight ratio of 1:50 short cut zirconia fiber (diameter of 10-15 μm, average length of 130-150 μm, zirconia content ≥ 85%) is immersed in ethanol aqueous solution (ethanol content of 75%), then 0.6wt% of polyacrylic acid sodium and 2.5wt% of polyvinylpyrrolidone of the mass of the short cut zirconia fiber is added, and the immersion is stirred by a planetary mixer for a total of 200 min, stirring for 10 min every 40 min, the stirring speed is 80 rad / min, the immersed short cut zirconia fiber is placed in a drying room for drying, the drying temperature is 200℃, and the time is 300 min, to obtain a pre-dispersed fiber; (2) according to the porous aluminum zirconium-based high-temperature-resistant ceramic material and ethanol aqueous solution weight ratio of 1:1, the porous aluminum zirconium-based high-temperature-resistant ceramic material including 65wt% of porous yttria-stabilized zirconia powder (particle size of 1.5-3 μm, zirconia content ≥ 80%), 10wt% of ρ-alumina powder, 20wt% of α-alumina powder and 5wt% of aluminum sol is added into ethanol aqueous solution (ethanol content of 75%), then 1.5wt% of PEG-400, 1.8wt% of polyurethane thickener and 4wt% of glycerol of the mass of the porous aluminum zirconium-based high-temperature-resistant ceramic material is added, and the mixture is rapidly mixed and stirred in a planetary ball mill, the stirring speed is 1000 rad / min, and the stirring time is 25 min, to obtain a light coating slurry; (3) the pre-dispersed fiber is added into the light coating slurry, the obtained mixed slurry is placed in an ultrasonic vibrator for ultrasonic vibration treatment, the treatment time is 20 min, and the treated fiber is placed in a drying room for secondary drying, the drying temperature is 350℃, and the time is 120 min, to obtain the modified light fiber; The particle size distribution of the alumina hollow sphere includes: the proportion of the alumina hollow sphere with a particle size of 150 μm-200 μm is 20%, the proportion of the alumina hollow sphere with a particle size of 100 μm-150 μm is 10%, and the proportion of the alumina hollow sphere with a particle size less than 100 μm is 70%; the content of alumina component in the alumina hollow sphere is ≥ 95%; The particle size distribution of the spherical alumina powder includes: the proportion of the spherical alumina powder with a particle size of 30 μm-90 μm is 20%, the proportion of the spherical alumina powder with a particle size of 5 μm-10 μm is 60%, and the proportion of the spherical alumina powder with a particle size of 0.5 μm-1 μm is 20%; the content of alumina in the spherical alumina powder is ≥ 95%; The particle size of the desiliconized zirconium powder is 50-80 μm; the content of zirconia in the desiliconized zirconium powder is ≥ 85%; and the solid content in the aluminum sol is 22%.

[0027] The preparation method of the coating material for improving the high-temperature resistance of the working surface of the sand mold specifically includes: (1) Dry mixing alumina hollow sphere, spherical alumina powder, desiliconized zirconium powder and gelatinized starch, dry mixing speed is 500 rad / min, dry mixing time is 15 min, to obtain solid phase mixture; (2) Adding modified lightweight fiber and sodium polyphosphate into ethanol aqueous solution, stirring and mixing by using planetary mixer, stirring speed is 100 rad / min, stirring time is 15 min, to obtain medium solution; (3) Gradually adding the medium solution into the solid phase mixture, stirring and mixing by using planetary mixer, stirring speed is 900 rad / min, stirring time is 3 min, then adding aluminum sol and stirring and mixing slowly, to obtain the coating material.

[0028] Example 2 A coating material for improving high temperature resistance of sand mold working surface, comprising the following components: modified lightweight fiber 20%, alumina hollow sphere 10%, spherical alumina powder 50%, desiliconized zirconium powder 10%, gelatinized starch 5%, aluminum sol 5%; additionally, 0.5% of total mass of the above components of sodium polyphosphate and 3 times of total mass of the above components of solvent ethanol aqueous solution (ethanol content is 75%) are added; The modified lightweight fiber is chopped zirconia fiber coated with porous aluminum-zirconium-based high-temperature-resistant ceramic material, and its specific preparation method is referred to Example 1; the selection of alumina hollow sphere, spherical alumina powder, desiliconized zirconium powder and aluminum sol is referred to Example 1; The preparation method of the coating material for improving high temperature resistance of sand mold working surface is also referred to Example 1.

[0029] Example 3 A coating material for improving high temperature resistance of sand mold working surface, comprising the following components: modified lightweight fiber 30%, alumina hollow sphere 10%, spherical alumina powder 40%, desiliconized zirconium powder 10%, gelatinized starch 5%, aluminum sol 5%; additionally, 0.5% of total mass of the above components of sodium polyphosphate and 3 times of total mass of the above components of solvent ethanol aqueous solution (ethanol content is 75%) are added; The modified lightweight fiber is chopped zirconia fiber coated with porous aluminum-zirconium-based high-temperature-resistant ceramic material, and its specific preparation method is referred to Example 1; the selection of alumina hollow sphere, spherical alumina powder, desiliconized zirconium powder and aluminum sol is referred to Example 1; The preparation method of the coating material for improving high temperature resistance of sand mold working surface is also referred to Example 1.

[0030] Example 4 A coating material for improving the high-temperature resistance of sand mold working surface, comprising the following components: modified lightweight fiber 10%, alumina hollow sphere 20%, spherical alumina powder 50%, desiliconized zirconium micro powder 10%, gelatinized starch 5%, and aluminum sol 5%; additionally, 0.5% of the total mass of the above components of sodium polyphosphate and 3 times the total mass of the above components of solvent ethanol aqueous solution (ethanol content 75%) are added; The modified lightweight fiber is a short-cut zirconia fiber coated with porous aluminum-zirconium-based high-temperature-resistant ceramic material, and its specific preparation method is referred to in Example 1; the selection of the alumina hollow sphere, spherical alumina powder, desiliconized zirconium micro powder, and aluminum sol is referred to in Example 1. The preparation method of the coating material for improving the high-temperature resistance of sand mold working surface is also referred to in Example 1.

[0031] Example 5 A coating material for improving the high-temperature resistance of sand mold working surface, comprising the following components: modified lightweight fiber 10%, alumina hollow sphere 30%, spherical alumina powder 40%, desiliconized zirconium micro powder 10%, gelatinized starch 5%, and aluminum sol 5%; additionally, 0.5% of the total mass of the above components of sodium polyphosphate and 3 times the total mass of the above components of solvent ethanol aqueous solution (ethanol content 75%) are added; The modified lightweight fiber is a short-cut zirconia fiber coated with porous aluminum-zirconium-based high-temperature-resistant ceramic material, and its specific preparation method is referred to in Example 1; the selection of the alumina hollow sphere, spherical alumina powder, desiliconized zirconium micro powder, and aluminum sol is referred to in Example 1. The preparation method of the coating material for improving the high-temperature resistance of sand mold working surface is also referred to in Example 1.

[0032] Example 6 A coating material for improving the high-temperature resistance of sand mold working surface, comprising the following components: modified lightweight fiber 10%, alumina hollow sphere 10%, spherical alumina powder 60%, desiliconized zirconium micro powder 10%, gelatinized starch 5%, and aluminum sol 5%; additionally, 0.5% of the total mass of the above components of sodium polyphosphate and 3 times the total mass of the above components of solvent ethanol aqueous solution (ethanol content 75%) are added; The modified lightweight fiber is a short-cut zirconia fiber coated with porous aluminum-zirconium-based high-temperature-resistant ceramic material, and its specific preparation method is referred to in Example 1, except that short-cut alumina fiber (diameter 8-10 μm, average length 80-160 μm, alumina content ≥97.5%) is used instead of short-cut zirconia fiber; the selection of the alumina hollow sphere, spherical alumina powder, desiliconized zirconium micro powder, and aluminum sol is referred to in Example 1. The preparation method of the coating material for improving the high-temperature resistance of sand mold working surface is also referred to in Example 1.

[0033] Comparative Example 1 A coating material for improving the high-temperature resistance of sand mold working surface, comprising the following components: modified lightweight fiber 10%, alumina hollow sphere 5%, spherical alumina powder 60%, desiliconized zirconium micro powder 10%, gelatinized starch 5%, and aluminum sol 10%; additionally, 0.5% of the total mass of the above components of sodium polyphosphate and 3 times the total mass of the above components of solvent ethanol aqueous solution (ethanol content 75%) are added; The modified lightweight fiber is a chopped zirconia fiber coated with porous aluminum-zirconium-based high-temperature-resistant ceramic material, and its specific preparation method is referred to Example 1; the selection of the alumina hollow sphere, spherical alumina powder, desiliconized zirconium micro powder, and aluminum sol is referred to Example 1. The preparation method of the coating material for improving the high-temperature resistance of sand mold working surface is also referred to Example 1.

[0034] Comparative Example 2 A coating material for improving the high-temperature resistance of sand mold working surface, comprising the following components: modified lightweight fiber 10%, alumina hollow sphere 50%, spherical alumina powder 10%, desiliconized zirconium micro powder 10%, gelatinized starch 5%, and aluminum sol 15%; additionally, 0.5% of the total mass of the above components of sodium polyphosphate and 3 times the total mass of the above components of solvent ethanol aqueous solution (ethanol content 75%) are added; The modified lightweight fiber is a chopped zirconia fiber coated with porous aluminum-zirconium-based high-temperature-resistant ceramic material, and its specific preparation method is referred to Example 1; the selection of the alumina hollow sphere, spherical alumina powder, desiliconized zirconium micro powder, and aluminum sol is referred to Example 1. The preparation method of the coating material for improving the high-temperature resistance of sand mold working surface is also referred to Example 1.

[0035] Comparative Example 3 A coating material for improving the high-temperature resistance of sand mold working surface, comprising the following components: chopped zirconia fiber 10%, alumina hollow sphere 10%, spherical alumina powder 60%, desiliconized zirconium micro powder 10%, gelatinized starch 5%, and aluminum sol 5%; additionally, 0.5% of the total mass of the above components of sodium polyphosphate and 3 times the total mass of the above components of solvent ethanol aqueous solution (ethanol content 75%) are added; The chopped zirconia fiber has a diameter of 10-15 μm, an average length of 130-150 μm, and a zirconia content of ≥85%; the selection of the alumina hollow sphere, spherical alumina powder, desiliconized zirconium micro powder, and aluminum sol is referred to Example 1. The preparation method of the coating material for improving the high-temperature resistance of sand mold working surface is also referred to Example 1.

[0036] Comparative Example 4 A coating material for improving the high-temperature resistance of sand mold working surface, comprising the following components: modified lightweight fiber 10%, alumina hollow sphere 10%, spherical alumina powder 60%, desiliconized zirconium powder 10%, aluminum sol 5%, and gelatinized starch 5%; additionally, 0.5% of sodium polyphosphate based on the total mass of the above components and 3 times the solvent ethanol aqueous solution (ethanol content 75%) based on the total mass of the above components; The modified lightweight fiber is a chopped zirconia fiber coated with aluminum-based high-temperature-resistant ceramic material on the surface, and its specific preparation method is as follows: in step (2), aluminum-based high-temperature-resistant ceramic material including 32 wt% of p-alumina powder, 63 wt% of α-alumina powder, and 5 wt% of aluminum sol is added to the ethanol aqueous solution (ethanol content 75%); the selection of the alumina hollow sphere, spherical alumina powder, desiliconized zirconium powder, and aluminum sol is as described in Embodiment 1; The preparation method of the coating material for improving the high-temperature resistance of sand mold working surface is also as described in Embodiment 1.

[0037] Comparative Example 5 A coating material for improving the high-temperature resistance of sand mold working surface, comprising the following components: modified lightweight fiber 10%, alumina hollow sphere 10%, spherical alumina powder 60%, desiliconized zirconium powder 10%, gelatinized starch 5%, and aluminum sol 5%; additionally, 0.5% of sodium polyphosphate based on the total mass of the above components and 3 times the solvent ethanol aqueous solution (ethanol content 75%) based on the total mass of the above components; The modified lightweight fiber is a chopped alumina fiber coated with porous zirconia-based high-temperature-resistant ceramic material on the surface, and its specific preparation method is as follows: in step (2), aluminum-zirconium-based high-temperature-resistant ceramic material including 95 wt% of porous yttria-stabilized zirconia powder (particle size 1.5-3 μm, zirconia content ≥80%) and 5 wt% of aluminum sol is added to the ethanol aqueous solution (ethanol content 75%); the selection of the alumina hollow sphere, spherical alumina powder, desiliconized zirconium powder, and aluminum sol is as described in Embodiment 1; The preparation method of the coating material for improving the high-temperature resistance of sand mold working surface is also as described in Embodiment 1.

[0038] Experimental test: The coating materials prepared in the examples and comparative examples are respectively applied to all surfaces of sand mold sample bricks and the inner cavities of the experimental sand mold molds of alumina; wherein the size of the sand mold sample bricks is 150 mm x 25 mm x 25 mm, the coating layer thickness is 12 mm, the sand mold sample bricks are completely immersed in a 2009 ℃ high-temperature alumina melt, after an immersion time of 20 s, they are quickly taken out and placed in room temperature for cooling until the coating layer on the surface of the test strip falls off, the cycle number is recorded, the bending strength of the test sample after the first immersion is measured, and the bending strength of the alumina sand mold test strip without the coating layer is 0.32 MPa when it is taken out after the first immersion, and the surface of the test strip has obvious thermal cracking.

[0039] Table 1 Performance test results of the coating materials obtained in the examples and comparative examples

[0040] As can be seen from the above table, when the surface of the alumina sand mold test strip is respectively coated with the coating materials in the examples or comparative examples, the bending strength of the test strip after the first immersion in the high-temperature melt and the cycle number of the test strip immersion are shown in the above table.

[0041] As can be seen from the above table, the test sample without the coating material treatment is broken after the first immersion in the high-temperature melt, and the bending strength of the test sample changes little, but the thermal cycle number of the test sample increases obviously with the increase of the modified lightweight fiber, indicating that the thermal shock resistance of the coating material is improved obviously with the increase of the modified lightweight fiber. Due to the sintering reaction of the external coating material caused by high temperature, the sand mold test strip is protected by the coating material and avoids thermal shock cracking, thereby improving the bending strength of the test strip. The network structure formed by the longitudinal and transverse intersection of the modified lightweight fiber in the coating material structure can effectively fix the matrix material around the fiber, so that the fiber material body can be ensured not to fail due to thermal shock even in the face of a sharply changing temperature field.

[0042] When the amount of the modified lightweight fiber is 10%, the bending strength and cycle number of the test sample increase first and then decrease with the increase of the amount of the alumina hollow spheres, but when the amount of the alumina hollow spheres exceeds the specified range, the matrix is cracked and falls off due to thermal shock after contacting the high-temperature melt, and the structure of the sand mold test strip is directly damaged due to thermal shock. When the amount of the alumina hollow spheres exceeds the specified range, the binder in the coating material cannot effectively bind the micro powder inside the matrix, resulting in a decrease in the bonding strength of the coating material and the falling off of the coating material.

[0043] When the fiber is also added, if the porous aluminum zirconium-based high-temperature-resistant ceramic material is not modified, the surface coating of the sample will be spalled and cracked after thermal shock cycle, which is due to the fact that the fiber framework is directly impacted by high temperature, causing thermal failure of the fiber structure. Or although the high-temperature-resistant ceramic material is also used for modification, the porous yttrium oxide stabilized zirconium oxide powder or the aluminum oxide powder is omitted, then in the process of high-temperature impact, the zirconium oxide will change due to phase change, and obvious volume change will occur, causing cracking failure of the fiber coating layer, and also affecting the integrity of the entire fiber structure.

[0044] The above merely describes the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and the inventive concept of the present application, should be covered within the protection scope of the present application, if the technical solution and the inventive concept of the present application are replaced or changed equivalently within the technical range disclosed by the present application.

Claims

1. A coating material for improving the high-temperature resistance of sand mold working surfaces, characterized in that, By mass percentage, it comprises the following components: 10-30% modified lightweight fiber, 10-30% hollow alumina spheres, 40-60% spherical alumina powder, 5-15% desilicationized zirconium micro powder, 5-10% gelatinized starch, and 3-15% binder; plus 0.1-0.5% water-reducing agent by mass of the above components and 1-8 times the mass of solvent by mass of the above components. The modified lightweight fiber is a short-cut zirconia or alumina fiber with a porous aluminum-zirconia-based high-temperature resistant ceramic material coated on its surface.

2. The coating material for improving the high-temperature resistance of sand mold working surfaces according to claim 1, characterized in that, The porous aluminum-zirconium-based high-temperature resistant ceramic material includes porous yttrium-stabilized zirconia micro powder, alumina micro powder, and alumina sol. Preferably, the porous alumina-zirconium-based high-temperature resistant ceramic material comprises, by mass percentage: 40-70% porous yttrium-stabilized zirconia micro powder, 20-50% alumina micro powder, and 5-15% alumina sol; Preferably, the chopped zirconium oxide fibers have a diameter of 10-15 μm, an average fiber length of 130-150 μm, and a zirconium oxide content of ≥85%; the chopped alumina fibers have a diameter of 8-10 μm, a length of 80-160 μm, and an alumina content of ≥97.5%. Preferably, the alumina micro powder includes α-alumina micro powder and / or ρ-alumina micro powder.

3. The coating material for improving the high-temperature resistance of sand mold working surfaces according to claim 1 or 2, characterized in that, The modified lightweight fiber is prepared by the following method: Short-cut zirconia or alumina fibers and a dispersant are added to an ethanol solution, mixed evenly, and dried to obtain pre-dispersed fibers; porous alumina-zirconia-based high-temperature resistant ceramic material, binder, and thickener are added to an ethanol solution and mixed evenly to obtain a coating slurry; the pre-dispersed fibers are added to the coating slurry, mixed evenly, and dried to obtain the modified lightweight fibers. Preferably, the dispersant is sodium polyacrylate and polyvinylpyrrolidone; the amount of sodium polyacrylate is 0.5-1.7% of the mass of the chopped zirconia or alumina fibers, and the amount of polyvinylpyrrolidone is 0.9-2.5 wt% of the mass of the chopped zirconia or alumina fibers. Preferably, the binder is polyethylene glycol, and the thickener is a polyurethane thickener and glycerin; the amount of polyethylene glycol is 1.5-2% of the mass of the porous aluminum zirconium-based high-temperature resistant ceramic material, the amount of polyurethane thickener is 1.8-2.5% of the mass of the porous aluminum zirconium-based high-temperature resistant ceramic material, and the amount of glycerin is 3-5% of the mass of the porous aluminum zirconium-based high-temperature resistant ceramic material.

4. The coating material for improving the high-temperature resistance of sand mold working surfaces according to any one of claims 1-3, characterized in that, The particle size distribution of the alumina hollow spheres includes: 20-30% alumina hollow spheres with a particle size of 150μm-200μm, 10-50% alumina hollow spheres with a particle size of 100μm-150μm, and 10-80% alumina hollow spheres with a particle size of less than 100μm; Preferably, the alumina content in the hollow alumina spheres is ≥95%.

5. The coating material for improving the high-temperature resistance of sand mold working surfaces according to any one of claims 1-4, characterized in that, The particle size distribution of the spherical alumina powder includes: 5-20% spherical alumina micropowder with a particle size of 30μm-90μm, 45-70% spherical alumina micropowder with a particle size of 5μm-10μm, and 10-40% spherical alumina micropowder with a particle size of 0.5μm-1μm. Preferably, the alumina content in the spherical alumina powder is ≥95%.

6. The coating material for improving the high-temperature resistance of sand mold working surfaces according to any one of claims 1-5, characterized in that, The particle size of the desilicationized zirconium micropowder is 50-80 μm; Preferably, the zirconium oxide content in the desilication zirconium micro powder is ≥85%.

7. The coating material for improving the high-temperature resistance of sand mold working surfaces according to any one of claims 1-6, characterized in that, The binder is at least one of aluminum sol, zirconium sol, titanium sol, or silica sol; the water-reducing agent is at least one of sodium polyphosphate, sodium tripolyphosphate, or sodium pyrophosphate; and the solvent is at least one of methanol, ethanol, or water. Preferably, the binder is aluminum sol, and the solid content of the aluminum sol is 19-25%.

8. A method for preparing a coating material for improving the high-temperature resistance of a sand mold working surface as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. After dry mixing hollow alumina spheres, spherical alumina powder, desilicationized zirconium micro powder and gelatinized starch, a solid-phase mixture is obtained. S2. After mixing the modified lightweight fiber and water-reducing agent in the solvent, a medium solution is obtained. S3. The medium solution is gradually added to the solid mixture for initial mixing, and then the binder is added and mixed again to obtain the coating material.

9. The method for preparing the coating material for improving the high-temperature resistance of the sand mold working surface according to claim 8, characterized in that, In step S1, the dry mixing speed is 400-600 rad / min and the time is 10-15 min; In step S2, the mixing speed is 80-100 rad / min and the time is 3-5 min; in step S3, the initial mixing speed is 600-1000 rad / min and the time is 3-5 min.

10. The application of a coating material according to any one of claims 1-7 or a coating material prepared by the preparation method according to claim 8 or 9, characterized in that, include: Apply the coating material to the surface of the sand mold to a thickness of 8-20 mm. After coating, allow the sand mold to dry or let it stand at 250-360℃ for 100-150 minutes before use.

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