A kind of coated sand based on heat-resistant steel casting and its preparation process

Abstract

The invention provides coated sand based on heat-resistant steel casting and a preparation process thereof, belonging to the technical field of casting, and comprising the following steps: preparing modified nano barium yttrium tungsten oxide compounded with phenolic resin, mixing the surface-modified nano barium yttrium tungsten oxide with phenolic resin to obtain the modified nano barium yttrium tungsten oxide compounded with phenolic resin; preparing polybenzimidazole-modified UiO-66 compounded with silicone resin, dispersing UiO-66 in a polybenzimidazole solution, filtering and drying to obtain polybenzimidazole-modified UiO-66, and then mixing with silicone resin to obtain polybenzimidazole-modified UiO-66 compounded with silicone resin; adding silica sand, silane coupling agent-modified vanadium carbide, urotropine, calcium stearate, the modified nano barium yttrium tungsten oxide compounded with phenolic resin and the polybenzimidazole-modified UiO-66 compounded with silicone resin into a sand mixer for sand mixing, and performing three-layer coating and curing to obtain coated sand. The technical solution provided by the present invention achieves the purpose of high temperature resistance of coated sand.

Description

Technical Field

[0001] The invention relates to the technical field of casting, and in particular to coated sand based on heat-resistant steel casting and a preparation process thereof. Background Art

[0002] Coated sand is a modeling material for shell (core) precision casting. Through the casting process, the coated sand is made into a thin shell-shaped casting mold or core, which is used in the production of cast iron, cast steel, alloy cast iron, cast steel and non-ferrous metal castings. Since the German engineer invented coated sand in the 1940s, its preparation process has used phenolic resin as a binder and urotropine as a curing agent, which solved the problem of efficient and large-scale production of castings and enabled the rapid development of modern industry. The aggregate of coated sand is high-temperature resistant inorganic natural quartz sand or artificial sand, and the surface of the aggregate is coated with organic polymer resin. Since the coated sand contains urotropine curing agent, during the physical and chemical process of heating and curing of phenolic resin during core making, a large amount of harmful substances such as formaldehyde will be discharged into the working environment, seriously polluting the working environment and causing serious harm to the health of the operators.

[0003] At the same time, coated sand is prone to thermal deformation and reduced strength during high-temperature casting, resulting in more surface defects in castings, thermal cracking, sand sticking, etc., affecting the quality of castings. Traditional coated sand has insufficient antioxidant and wear resistance, and is prone to sand core breakage or surface oxidation damage during high-temperature metal pouring, making the surface of the casting uneven and rough.

[0004] During the casting process, gas is generated when the molten metal contacts the coated sand. The rapid increase in temperature will cause the sand core and sand mold to expand, and the pores in the coated sand will decrease. The gas cannot escape from the coated sand and can only be released through the unformed casting, which will cause a large number of pores in the casting product, greatly affecting the quality of the casting. Summary of the invention

[0005] In view of this, the present invention provides a coated sand based on heat-resistant steel casting and a preparation process thereof, so as to achieve the purpose of high temperature resistance of the coated sand.

[0006] The specific scheme of the present invention is as follows: a coated sand based on heat-resistant steel casting and a preparation process thereof, comprising the following steps:

[0007] Step S1: Preparation of modified nano-barium yttrium tungsten oxide compounded with phenolic resin material:

[0008] The nano-barium yttrium tungsten oxide modified by a silane coupling agent is mixed with a phenolic resin to obtain a modified nano-barium yttrium tungsten oxide compounded with a phenolic resin material;

[0009] Step S2: Preparation of polybenzimidazole-modified UiO-66 compounded with organic silicone resin material:

[0010] The UiO-66 and the polybenzimidazole solution are mixed evenly, filtered, and dried to obtain the polybenzimidazole-modified UiO-66, and then mixed evenly with the silicone resin to obtain the polybenzimidazole-modified UiO-66 composite silicone resin material;

[0011] Step S3: mixing and curing silica sand, silane coupling agent modified vanadium carbide, urotropine, calcium stearate, the modified nano barium yttrium tungsten oxide compounded with phenolic resin, and the polybenzimidazole modified UiO-66 compounded with organic silicone resin to obtain coated sand.

[0012] The present invention introduces modified nano-barium yttrium tungsten oxide. The modified nano-barium yttrium tungsten oxide has a high melting point and good antioxidant ability. It can form a dense protective film under high temperature environment to block oxygen, prevent oxidation of castings and coated sand, and avoid the formation of iron oxide and other substances on the surface of the castings that affect the smoothness of the casting surface. At the same time, the protective film can also prevent oxidative decomposition caused by contact between phenolic resin and oxygen, thereby improving the service life of coated sand. By using modified nano-barium yttrium tungsten oxide and compounding phenolic resin, the high temperature resistance of coated sand is effectively enhanced, and the occurrence of sand sticking and cracks in castings is reduced.

[0013] The present invention introduces polybenzimidazole-modified UiO-66 and composites with silicone resin. The silicone resin has a good thermal isolation effect, can improve the heat resistance of the coated sand, reduce heat conduction to the sand core of the sand mold, and avoid deformation of the coated sand. At the same time, the organic-inorganic hybrid structure formed by the curing of the resin has higher stability and can improve the mechanical strength of the coated sand.

[0014] The porous structure of the UiO-66 metal-organic framework provides a channel for the gas, so that the gas generated by the coated sand when heated can be released from the channel provided, avoiding the gas from escaping from the molten casting, resulting in the problem of pores in the final molded casting. At the same time, the adsorption capacity of UiO-66 can also absorb part of the generated gas, further reducing the chance of gas bubbles forming on the surface of the casting and reducing the impact of gas on the casting.

[0015] Polybenzimidazole can be adsorbed on the surface of UiO-66 through hydrogen bonding and van der Waals forces, greatly improving the dispersibility of UiO-66 in silicone resin and ensuring that UiO-66 can be evenly dispersed. In addition, polybenzimidazole has extremely high thermal stability and is suitable for high temperature environments. It can provide protection for UiO-66, enhance its heat resistance, and ensure that UiO-66 can function stably. In addition, the nitrogen atoms and benzene ring structures contained in polybenzimidazole can form hydrogen bonds and π-π interactions with formaldehyde, and cooperate with the adsorption effect of UiO-66 to greatly improve the formaldehyde adsorption capacity, reduce the release of formaldehyde, and reduce the harm to the human body and the environment.

[0016] Optionally, in step S1: the method for preparing nano barium yttrium tungsten oxide modified by a silane coupling agent comprises the following steps:

[0017] The nano-barium yttrium tungsten oxide is added into anhydrous ethanol and dispersed evenly, and gamma-aminopropyltriethoxysilane is added and dispersed evenly, and the surface-modified nano-barium yttrium tungsten oxide is prepared by spray drying.

[0018] Nano-barium yttrium tungsten oxide is first physically mixed with γ-aminopropyltriethoxysilane, and then spray-dried to obtain efficient and uniform particle surface treatment of nano-barium yttrium tungsten oxide, which significantly improves the dispersibility of modified nano-barium yttrium tungsten oxide and ensures that nano-barium yttrium tungsten oxide can be evenly dispersed in phenolic resin.

[0019] Optionally, the ultrasonic dispersion time is 15-30 min; the stirring speed is 400-700 rpm, and the time is 1-3 h.

[0020] Optionally, the spray drying temperature is 140-160°C.

[0021] Optionally, in step S1: the method for preparing the silane coupling agent-modified nano-barium yttrium tungsten oxide compounded with phenolic resin material comprises the following steps:

[0022] The silane coupling agent-modified nano-barium yttrium tungsten oxide and the heated phenolic resin are subjected to high-shear emulsification stirring to obtain a modified nano-barium yttrium tungsten oxide compounded with a phenolic resin material.

[0023] Optionally, the heating temperature is 135-145°C; the high shear rate is 4700-5300rpm, the temperature is 60-70°C, and the time is 75-105min.

[0024] Optionally, the raw materials of the modified nano-barium yttrium tungsten oxide compounded with phenolic resin include: 0.08-0.1 parts of nano-barium yttrium tungsten oxide, 0.3-0.5 parts of γ-aminopropyltriethoxysilane, and 30-40 parts of phenolic resin.

[0025] Optionally, in step S2: adding polybenzimidazole powder to N-methylpyrrolidone solvent for ultrasonic dispersion, adding UiO-66 for ultrasonic dispersion again, heating and stirring to obtain polybenzimidazole-modified UiO-66.

[0026] Optionally, the ultrasonic dispersion time is 10-20 min; the second ultrasonic dispersion time is 20-40 min; the heating temperature is 60-80° C.; the stirring speed is 400-600 rpm, and the time is 7-10 h.

[0027] Optionally, the polybenzimidazole-modified UiO-66 and the heated silicone resin are subjected to high-shear emulsification stirring to obtain a polybenzimidazole-modified UiO-66 composite silicone resin material.

[0028] Optionally, the heating temperature of the silicone resin is 145-155°C; the high shear rate is 5300-5700rpm, the temperature is 70-80°C, and the time is 50-70min.

[0029] Optionally, the raw materials of the polybenzimidazole-modified UiO-66 compounded with silicone resin include: 4-6 parts of UiO-66, 0.2-0.4 parts of polybenzimidazole, and 20-30 parts of silicone resin.

[0030] Optionally, the preparation method of the silane coupling agent modified vanadium carbide comprises the following steps: adding vanadium carbide powder to anhydrous ethanol, ultrasonically dispersing for 25-40 minutes, adding γ-aminopropyltriethoxysilane, stirring at 600-800 rpm for 3-5 hours, filtering and drying to obtain silane coupling agent modified vanadium carbide.

[0031] Optionally, the raw materials for modifying vanadium carbide with a silane coupling agent include: 5-7 parts of vanadium carbide and 0.1-0.2 parts of γ-aminopropyltriethoxysilane.

[0032] Vanadium carbide can resist, absorb and disperse the concentrated stress caused by the inconsistent thermal expansion and contraction of coated sand through deformation, reduce the thermal stress concentration effect, and avoid uneven defects in castings. In addition, vanadium carbide has an extremely high melting point, hardness and wear resistance, which can effectively improve the overall high temperature resistance and wear resistance of coated sand.

[0033] The vanadium carbide is modified by using γ-aminopropyl triethoxysilane coupling agent to ensure that the vanadium carbide can be evenly dispersed in the silica sand during the coating process, and the organic functional groups it carries can form covalent bonds with the phenolic hydroxyl or aldehyde groups carried by the inner layer of phenolic resin, thereby forming a cross-linked structure to better bond the coating layer. Vanadium carbide has excellent antioxidant properties at high temperatures and can form a protective oxide layer during the casting process, reducing the oxidation loss of the coated sand and allowing the coated sand to maintain a stable structure under high temperature conditions. At the same time, this oxide layer has high adhesion, and when combined with γ-aminopropyl triethoxysilane, it can form a good interface bond with the inner and outer layer coated resins, allowing the three-layer coating to be stably bonded to the silica sand surface.

[0034] Optionally, in step S3: the sand mixing and curing includes: adding silica sand to a sand mixer for the first sand mixing and heating; adding modified nano barium yttrium tungsten oxide compounded with phenolic resin and mixing for the second time; adding calcium stearate and mixing for the third time and cooling; adding urotropine and mixing for the fourth time and curing; adding silane coupling agent modified vanadium carbide and heating; adding polybenzimidazole modified UiO-66 compounded with organic silicone resin and mixing for the fifth time and cooling; adding urotropine and mixing for the sixth time; adding calcium stearate and mixing for the seventh time and curing to obtain coated sand.

[0035] The three-layer coating system superimposes the functions of different materials, making the coated sand show higher heat resistance, thermal conductivity, mechanical properties, etc. in high-temperature casting, providing a better molding environment for castings and greatly improving the quality of castings. At the same time, the overall performance of the coated sand is improved, the service life of the coated sand is extended, and the maintenance cost of the coated sand is reduced.

[0036] Optionally, the temperature of the first sand mixing is 160-180℃, and the mixing time is 10-15min; the temperature of the second sand mixing is 160-180℃, and the time is 10-15min; the temperature of the third sand mixing is 160-180℃, and the time is 5-10min; the temperature of the fourth sand mixing is 120-130℃, and the time is 5-10min; the temperature of the fifth sand mixing is 200-220℃, and the time is 10-20min; the temperature of the sixth sand mixing is 150-170℃, and the time is 5-10min; the temperature of the seventh sand mixing is 150-170℃, and the time is 15-20min.

[0037] To achieve the above objectives, the present invention also provides a coated sand prepared by the above-mentioned process for preparing coated sand based on heat-resistant steel casting.

[0038] Optionally, the coated sand includes the following components in parts by weight:

[0039] 900-1100 parts of silica sand, 20-30 parts of modified nano barium yttrium tungsten oxide compounded with phenolic resin, 10-20 parts of polybenzimidazole modified UiO-66 compounded with organic silicone resin, 3-5 parts of urotropine, 1-2 parts of calcium stearate, and 1-2 parts of silane coupling agent modified vanadium carbide.

[0040] The above technical solution of the present invention includes at least the following beneficial effects:

[0041] 1. The present invention introduces modified nano-barium yttrium tungsten oxide, and utilizes the high melting point and good antioxidant ability of modified nano-barium yttrium tungsten oxide to prevent oxidation of castings and coated sand. By using modified nano-barium yttrium tungsten oxide and compounding phenolic resin, the high temperature resistance and heat resistance of coated sand can be effectively enhanced, the heat dissipation rate of coated sand can be improved, the occurrence of sand sticking and cracks in castings can be reduced, and the quality of castings can be guaranteed.

[0042] 2. The present invention introduces polybenzimidazole to modify UiO-66, and utilizes the porous structure and adsorption capacity of the UiO-66 metal-organic framework to provide a gas channel and adsorb part of the gas to avoid the appearance of pores in the casting. Polybenzimidazole has extremely high thermal stability and can enhance the heat resistance of UiO-66. In addition, the nitrogen atoms and benzene ring structures contained in polybenzimidazole can form hydrogen bonds and π-π interactions with formaldehyde, and cooperate with the adsorption effect of UiO-66 to greatly enhance the formaldehyde adsorption capacity and reduce the harm to the human body and the environment.

[0043] 3. The present invention uses a three-layer coating method to prepare coated sand. The three-layer coating superimposes the functions of different materials to make the coated sand show better heat resistance, mechanical properties and air permeability in high-temperature casting, extend the service life of the coated sand, reduce the maintenance cost of the coated sand, and at the same time improve the quality of the casting molding environment and enhance the quality of the casting. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in combination with the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0045] In the following embodiments, nano barium yttrium tungsten oxide is prepared by grinding barium yttrium tungsten oxide to nanometer scale. The CAS number of barium yttrium tungsten oxide is 37265-86-4, which is purchased from Shanghai Hanhong Technology Co., Ltd. and is also called barium yttrium tungsten oxide.

[0046] Example 1

[0047] Take 0.08 parts of nano-barium yttrium tungsten oxide and add it to 400 parts of anhydrous ethanol, ultrasonically disperse it for 20 minutes, add 0.5 parts of γ-aminopropyl triethoxysilane, stir it at 500rpm for 2 hours at room temperature to form a dispersion, atomize the dispersion into tiny droplets through the nozzle of the spray dryer, and quickly evaporate the solvent in a high-temperature airflow at 150℃ to form particles to obtain modified nano-barium yttrium tungsten oxide. Heat 35 parts of phenolic resin to 140℃ to reduce the viscosity, add modified nano-barium yttrium tungsten oxide, start the high-shear emulsifier and stir for 90 minutes, control the temperature at 145℃ and the speed at 5000rpm to ensure that the nano-barium yttrium tungsten oxide is completely dispersed, and obtain the modified nano-barium yttrium tungsten oxide compound phenolic resin material.

[0048] Take 5 parts of vanadium carbide powder and add it to 250 parts of anhydrous ethanol, ultrasonically disperse it for 30 minutes to ensure uniform dispersion, add 0.2 parts of γ-aminopropyltriethoxysilane to the solution, stir it at 700 rpm for 4 hours at room temperature, filter, wash, and dry to obtain silane coupling agent modified vanadium carbide.

[0049] Take 0.4 parts of polybenzimidazole powder, add it to 100 parts of N-methylpyrrolidone solvent, and ultrasonically disperse it for 20 minutes to form a polybenzimidazole solution. Add 5 parts of UiO-66 to the above solution, ultrasonically disperse it again for 30 minutes to ensure uniform dispersion, heat it to 70°C, and stir it at 500rpm for 8 hours, filter it with deionized water, wash it, and dry it to obtain polybenzimidazole-modified UiO-66. Heat 30 parts of silicone resin to 150°C, add polybenzimidazole-modified UiO-66, start the high shear emulsifier and stir it for 60 minutes, control the temperature at 75°C and the speed at 5500rpm to ensure complete dispersion, and obtain a polybenzimidazole-modified UiO-66 composite silicone resin material.

[0050] Take 1000 parts of silica sand, pour it into a sand mixer, mix it for 12 minutes for the first time, and heat it to 170°C; add 30 parts of modified nano barium yttrium tungsten oxide compounded phenolic resin for the first layer of coating, mix it for 10 minutes for the second time; add 1 part of calcium stearate, mix it for 5 minutes for the third time, and cool it to 120°C; add 2 parts of urotropine, mix it for 5 minutes for the fourth time, and realize the first stage of curing; then add 2 parts of silane coupling agent modified vanadium carbide for the second layer of coating, heat it to 210°C; add 20 parts of polybenzimidazole modified UiO-66 compounded organic silicone resin for the third layer of coating, mix it for 10 minutes for the fifth time, and cool it to 160°C; add 2 parts of urotropine, mix it for 5 minutes for the sixth time; finally add 1 part of calcium stearate, mix it for 15 minutes for the seventh time, realize the second stage of curing, and obtain coated sand.

[0051] Example 2

[0052] Take 0.09 parts of nano-barium yttrium tungsten oxide and add it to 450 parts of anhydrous ethanol, ultrasonically disperse it for 25 minutes, add 0.4 parts of γ-aminopropyl triethoxysilane, stir it at 600rpm for 3 hours at room temperature to form a dispersion, atomize the dispersion into tiny droplets through the nozzle of the spray dryer, and quickly evaporate the solvent in a high-temperature airflow of 155℃ to form particles to obtain modified nano-barium yttrium tungsten oxide. Heat 30 parts of phenolic resin to 65℃ to reduce the viscosity, add modified nano-barium yttrium tungsten oxide, start the high-shear emulsifier and stir for 100 minutes, control the temperature at 70℃ and the speed at 5200rpm to ensure that the nano-barium yttrium tungsten oxide is completely dispersed, and obtain modified nano-barium yttrium tungsten oxide compound phenolic resin.

[0053] Take 5 parts of vanadium carbide powder and add it to 250 parts of anhydrous ethanol, ultrasonically disperse it for 25 minutes to ensure uniform dispersion, add 0.15 parts of γ-aminopropyltriethoxysilane to the solution, stir it at 600 rpm for 3 hours at room temperature, filter, wash, and dry to obtain silane coupling agent modified vanadium carbide.

[0054] Take 0.2 parts of polybenzimidazole powder, add it to 100 parts of N-methylpyrrolidone solvent, and ultrasonically disperse it for 10 minutes to form a polybenzimidazole solution. Add 4 parts of UiO-66 to the above solution, ultrasonically disperse it again for 20 minutes to ensure uniform dispersion, heat it to 60°C, and stir it at 600rpm for 10 hours, filter it with deionized water, wash it, and dry it to obtain polybenzimidazole-modified UiO-66. Heat 20 parts of silicone resin to 75°C, add polybenzimidazole-modified UiO-66, start the high shear emulsifier and stir it for 70 minutes, control the temperature at 80°C and the speed at 5300rpm to ensure complete dispersion, and obtain polybenzimidazole-modified UiO-66 composite silicone resin.

[0055] Take 1100 parts of silica sand, pour it into a sand mixer, mix it for 10 minutes for the first time, and heat it to 165°C; add 20 parts of modified nano barium yttrium tungsten oxide compounded phenolic resin used for the first layer of coating, mix it for 10 minutes for the second time; add 1 part of calcium stearate, mix it for 8 minutes for the third time, and cool it to 125°C; add 2 parts of urotropine, mix it for 7 minutes for the fourth time, and realize the first stage of curing; then add 1.5 parts of silane coupling agent modified vanadium carbide used for the second layer of coating, heat it to 200°C; then add 15 parts of polybenzimidazole modified UiO-66 compounded organic silicone resin used for the third layer of coating, mix it for 15 minutes for the fifth time, and cool it to 150°C; add 1 part of urotropine, mix it for 10 minutes for the sixth time; finally, add 0.5 parts of calcium stearate, mix it for 20 minutes for the seventh time, realize the second stage of curing, and obtain coated sand.

[0056] Example 3

[0057] Take 0.1 parts of nano-barium yttrium tungsten oxide and add it to 500 parts of anhydrous ethanol, ultrasonically disperse it for 30 minutes, add 0.5 parts of γ-aminopropyl triethoxysilane, stir it at 700rpm for 2 hours at room temperature to form a dispersion, atomize the dispersion into tiny droplets through the nozzle of the spray dryer, and quickly evaporate the solvent in a high-temperature airflow at 160℃ to form particles to obtain modified nano-barium yttrium tungsten oxide. Heat 35 parts of phenolic resin to 65℃ to reduce the viscosity, add modified nano-barium yttrium tungsten oxide, start the high-shear emulsifier and stir for 105 minutes, control the temperature at 70℃ and the speed at 5300rpm to ensure that the nano-barium yttrium tungsten oxide is completely dispersed, and obtain modified nano-barium yttrium tungsten oxide compound phenolic resin.

[0058] Take 6 parts of vanadium carbide powder and add it to 300 parts of anhydrous ethanol, ultrasonically disperse it for 40 minutes to ensure uniform dispersion, add 0.1 parts of γ-aminopropyltriethoxysilane to the solution, stir it at 800 rpm for 3 hours at room temperature, filter and wash, and dry to obtain silane coupling agent modified vanadium carbide.

[0059] Take 0.3 parts of polybenzimidazole powder, add it to 100 parts of N-methylpyrrolidone solvent, and ultrasonically disperse it for 20 minutes to form a polybenzimidazole solution. Add 6 parts of UiO-66 to the above solution, ultrasonically disperse it again for 40 minutes to ensure uniform dispersion, heat it to 80°C, and stir it at 400rpm for 7 hours, filter it with deionized water, wash it, and dry it to obtain polybenzimidazole-modified UiO-66. Heat 25 parts of silicone resin to 65°C, add polybenzimidazole-modified UiO-66, start the high shear emulsifier and stir it for 50 minutes, control the temperature at 70°C and the speed at 5700rpm to ensure complete dispersion, and obtain polybenzimidazole-modified UiO-66 composite silicone resin.

[0060] Take 1100 parts of silica sand, pour it into a sand mixer, mix it for 15 minutes for the first time, and heat it to 180°C; add 25 parts of modified nano barium yttrium tungsten oxide compounded phenolic resin used for the first layer of coating, mix it for 15 minutes for the second time; add 1 part of calcium stearate, mix it for 10 minutes for the third time, and cool it to 120°C; add 3 parts of urotropine, mix it for 5 minutes for the fourth time, and realize the first stage of curing; then add 2 parts of silane coupling agent modified vanadium carbide used for the second layer of coating, heat it to 200°C; then add 15 parts of polybenzimidazole modified UiO-66 compounded organic silicone resin used for the third layer of coating, mix it for 15 minutes for the fifth time, and cool it to 160°C; add 2 parts of urotropine, mix it for 10 minutes for the sixth time; finally add 1 part of calcium stearate, mix it for 20 minutes for the seventh time, realize the second stage of curing, and obtain coated sand.

[0061] Example 4

[0062] Take 0.09 parts of nano-barium yttrium tungsten oxide and add it to 450 parts of anhydrous ethanol, ultrasonically disperse it for 30 minutes, add 0.3 parts of γ-aminopropyl triethoxysilane, stir it at 500rpm for 2 hours at room temperature to form a dispersion, atomize the dispersion into tiny droplets through the nozzle of the spray dryer, and quickly evaporate the solvent in a high-temperature airflow at 140℃ to form particles to obtain modified nano-barium yttrium tungsten oxide. Heat 35 parts of phenolic resin to 55℃ to reduce the viscosity, add modified nano-barium yttrium tungsten oxide, start the high-shear emulsifier and stir for 95 minutes, control the temperature at 65℃ and the speed at 4800rpm to ensure that the nano-barium yttrium tungsten oxide is completely dispersed to obtain modified nano-barium yttrium tungsten oxide compound phenolic resin.

[0063] Take 6 parts of vanadium carbide powder and add it to 300 parts of anhydrous ethanol, ultrasonically disperse it for 40 minutes to ensure uniform dispersion, add 0.15 parts of γ-aminopropyltriethoxysilane to the solution, stir it at 600 rpm for 5 hours at room temperature, filter, wash, and dry to obtain silane coupling agent modified vanadium carbide.

[0064] Take 0.4 parts of polybenzimidazole powder, add it to 100 parts of N-methylpyrrolidone solvent, and ultrasonically disperse it for 15 minutes to form a polybenzimidazole solution. Add 6 parts of UiO-66 to the above solution, ultrasonically disperse it again for 20 minutes to ensure uniform dispersion, heat it to 75°C, and stir it at 400rpm for 9 hours, filter it with deionized water, wash it, and dry it to obtain polybenzimidazole-modified UiO-66. Heat 30 parts of silicone resin to 70°C, add polybenzimidazole-modified UiO-66, start the high shear emulsifier and stir it for 60 minutes, control the temperature at 75°C and the speed at 5500rpm to ensure complete dispersion, and obtain polybenzimidazole-modified UiO-66 composite silicone resin.

[0065] Take 900 parts of silica sand, pour it into a sand mixer, mix the sand for 10 minutes for the first time, and heat it to 160°C; add 20 parts of modified nano barium yttrium tungsten oxide compounded phenolic resin used for the first layer of coating, mix the sand for 10 minutes for the second time; add 0.5 parts of calcium stearate, mix the sand for 5 minutes for the third time, and cool it to 130°C; add 2 parts of urotropine, mix the sand for 10 minutes for the fourth time to achieve the first stage of curing; then add 1 part of silane coupling agent modified vanadium carbide used for the second layer of coating, heat it to 210°C; then add 20 parts of polybenzimidazole modified UiO-66 compounded organic silicone resin used for the third layer of coating, mix the sand for 20 minutes for the fifth time; cool it to 165°C, add 1 part of urotropine, mix the sand for 5 minutes for the sixth time; finally add 0.5 parts of calcium stearate, mix the sand for 15 minutes for the seventh time to achieve the second stage of curing, and obtain coated sand.

[0066] Example 5

[0067] Take 0.08 parts of nano-barium yttrium tungsten oxide and add it to 400 parts of anhydrous ethanol, ultrasonically disperse it for 15 minutes, add 0.4 parts of γ-aminopropyl triethoxysilane, stir it at 400rpm for 1 hour at room temperature to form a dispersion, atomize the dispersion into tiny droplets through the nozzle of the spray dryer, and quickly evaporate the solvent in a high-temperature airflow at 160℃ to form particles to obtain modified nano-barium yttrium tungsten oxide. Heat 40 parts of phenolic resin to 65℃ to reduce the viscosity, add modified nano-barium yttrium tungsten oxide, start the high-shear emulsifier and stir for 75 minutes, control the temperature at 60℃ and the speed at 4700rpm to ensure that the nano-barium yttrium tungsten oxide is completely dispersed, and obtain modified nano-barium yttrium tungsten oxide compound phenolic resin.

[0068] Take 7 parts of vanadium carbide powder and add it to 200 parts of anhydrous ethanol, ultrasonically disperse it for 30 minutes to ensure uniform dispersion, add 0.2 parts of γ-aminopropyltriethoxysilane to the solution, stir it at 700 rpm for 3 hours at room temperature, filter and wash, and dry to obtain silane coupling agent modified vanadium carbide.

[0069] Take 0.3 parts of polybenzimidazole powder, add it to 100 parts of N-methylpyrrolidone solvent, and ultrasonically disperse it for 20 minutes to form a polybenzimidazole solution. Add 4 parts of UiO-66 to the above solution, ultrasonically disperse it again for 40 minutes to ensure uniform dispersion, heat it to 60°C, and stir it at 600rpm for 10 hours, filter it with deionized water, wash it, and dry it to obtain polybenzimidazole-modified UiO-66. Heat 25 parts of silicone resin to 65°C, add polybenzimidazole-modified UiO-66, start the high shear emulsifier and stir it for 50 minutes, control the temperature at 70°C and the speed at 5400rpm to ensure complete dispersion, and obtain polybenzimidazole-modified UiO-66 compounded with silicone resin.

[0070] Take 1050 parts of silica sand, pour it into a sand mixer, mix it for 15 minutes for the first time, and heat it to 180°C; add 25 parts of modified nano barium yttrium tungsten oxide compounded phenolic resin used for the first layer of coating, mix it for 15 minutes for the second time; add 1 part of calcium stearate, mix it for 5 minutes for the third time, and cool it to 120°C; add 2 parts of urotropine, mix it for 10 minutes for the fourth time, and realize the first stage of curing; then add 2 parts of silane coupling agent modified vanadium carbide used for the second layer of coating, heat it to 220°C; then add 20 parts of polybenzimidazole modified UiO-66 compounded organic silicone resin used for the third layer of coating, mix it for 10 minutes for the fifth time, and cool it to 170°C; add 2 parts of urotropine, mix it for 7 minutes for the sixth time; finally, add 1 part of calcium stearate, mix it for 18 minutes for the seventh time, realize the second stage of curing, and obtain coated sand.

[0071] Example 6

[0072] Take 0.1 parts of nano-barium yttrium tungsten oxide and add it to 500 parts of anhydrous ethanol, ultrasonically disperse it for 25 minutes, add 0.3 parts of γ-aminopropyl triethoxysilane, stir it at 500rpm for 2 hours at room temperature to form a dispersion, atomize the dispersion into tiny droplets through the nozzle of the spray dryer, and quickly evaporate the solvent in a high-temperature airflow at 140℃ to form particles to obtain modified nano-barium yttrium tungsten oxide. Heat 40 parts of phenolic resin to 55℃ to reduce the viscosity, add modified nano-barium yttrium tungsten oxide, start the high-shear emulsifier and stir for 80 minutes, control the temperature at 65℃ and the speed at 4900rpm to ensure that the nano-barium yttrium tungsten oxide is completely dispersed to obtain modified nano-barium yttrium tungsten oxide compound phenolic resin.

[0073] Take 7 parts of vanadium carbide powder and add it to 200 parts of anhydrous ethanol, ultrasonically disperse it for 30 minutes to ensure uniform dispersion, add 0.15 parts of γ-aminopropyltriethoxysilane to the solution, stir it at 600 rpm for 4 hours at room temperature, filter and wash, and dry to obtain silane coupling agent modified vanadium carbide.

[0074] Take 0.2 parts of polybenzimidazole powder, add it to 100 parts of N-methylpyrrolidone solvent, and ultrasonically disperse it for 10 minutes to form a polybenzimidazole solution. Add 5 parts of UiO-66 to the above solution, ultrasonically disperse it again for 40 minutes to ensure uniform dispersion, heat it to 60°C, and stir it at 500rpm for 8 hours, filter it with deionized water, wash it, and dry it to obtain polybenzimidazole-modified UiO-66. Heat 20 parts of silicone resin to 70°C, add polybenzimidazole-modified UiO-66, start the high shear emulsifier and stir it for 60 minutes, control the temperature at 80°C and the speed at 5700rpm to ensure complete dispersion, and obtain polybenzimidazole-modified UiO-66 compounded with silicone resin.

[0075] Take 950 parts of silica sand and pour it into a sand mixer. Mix the sand for 12 minutes for the first time and heat it to 170°C. Add 30 parts of modified nano barium yttrium tungsten oxide compounded phenolic resin used for the first layer of coating and mix the sand for 15 minutes for the second time. Add 1 part of calcium stearate and mix the sand for 5 minutes for the third time and cool it to 125°C. Add 3 parts of urotropine and mix the sand for 5 minutes for the fourth time to achieve the first stage of curing. Then add 1.5 parts of silane coupling agent modified vanadium carbide used for the second layer of coating and heat it to 220°C. Then add 10 parts of polybenzimidazole modified UiO-66 compounded organic silicone resin used for the third layer of coating, mix the sand for 10 minutes for the fifth time and cool it to 160°C. Add 1 part of urotropine and mix the sand for 5 minutes for the sixth time. Finally, add 0.5 parts of calcium stearate and mix the sand for 20 minutes for the seventh time to achieve the second stage of curing to obtain coated sand.

[0076] The present invention also carries out comparative examples and related tests.

[0077] Comparative Example 1

[0078] The difference between Comparative Example 1 and Example 1 is that modified nano-barium yttrium tungsten oxide compounded with phenolic resin is not used, but phenolic resin is used instead of modified nano-barium yttrium tungsten oxide compounded with phenolic resin. The other compositions and preparation methods are the same as those in Example 1, and coated sand is prepared.

[0079] Comparative Example 2

[0080] The difference between Comparative Example 2 and Example 1 is that polybenzimidazole-modified UiO-66 compounded with silicone resin is not used, but silicone resin is used instead of polybenzimidazole-modified UiO-66 compounded with silicone resin. The other compositions and preparation methods are the same as those in Example 1, and coated sand is prepared.

[0081] Comparative Example 3

[0082] The difference between Comparative Example 3 and Example 1 is that the three-layer coating preparation method is not used, but the raw materials are added to the sand mixer at the same time to prepare coated sand. The other compositions and preparation methods are the same as those in Example 1, and coated sand is prepared.

[0083] Performance testing

[0084] The properties of the coated sands of Examples 1-6 and Comparative Examples 1-3 were tested according to the following standards.

[0085] Room temperature tensile strength, hot tensile strength, room temperature flexural strength, hot flexural strength and gas evolution were tested in accordance with JB / T8583-2008 standard; the reference standard for heat resistance test was JB / T 13037-2017, with heat resistance cracking time as the result; formaldehyde content test was carried out in accordance with GB / T16297-1996 standard; casting quality was tested based on whether the casting surface was smooth and whether pores appeared. The test results are shown in Table 1 below.

[0086] Table 1

[0087]

[0088] From the result data in Table 1, it can be clearly seen that the coated sand obtained in Examples 1-6 of the present invention has good performance and can be suitable for heat-resistant casting.

[0089] According to the comparison between Comparative Example 1 and Examples 1-6, it can be seen that the mechanical properties and heat resistance of the coated sand are significantly reduced due to the failure to use modified nano-barium yttrium tungsten oxide compounded with phenolic resin. It can be seen that modified nano-barium yttrium tungsten oxide compounded with phenolic resin can effectively improve the mechanical properties and heat resistance of the coated sand.

[0090] According to the comparison between Comparative Example 2 and Examples 1-6, it can be seen that the failure to use polybenzimidazole-modified UiO-66 compounded with organic silicone resin results in higher gas emission and formaldehyde content of the coated sand, and affects the quality of the casting, resulting in roughness and pores in the casting, indicating that polybenzimidazole-modified UiO-66 compounded with organic silicone resin has an impact on the air permeability and environmental protection performance of the coated sand.

[0091] It can be seen from the comparison between Comparative Example 3 and Examples 1-6 that the overall performance of the coated sand is reduced due to the failure to adopt the three-layer coating preparation method. It can be seen that the three-layer coating preparation method has a great influence on the preparation of the coated sand.

[0092] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A preparation process of coated sand based on heat-resistant steel casting, characterized in that: The following steps are involved: Step S1: Preparation of modified nano-barium yttrium tungsten oxide compounded with phenolic resin material: The nano-barium yttrium tungsten oxide modified by a silane coupling agent is mixed with a phenolic resin to obtain a modified nano-barium yttrium tungsten oxide compounded with a phenolic resin material; Step S2: Preparation of polybenzimidazole-modified UiO-66 compounded with organic silicone resin material: The UiO-66 and the polybenzimidazole solution are mixed evenly, filtered, and dried to obtain the polybenzimidazole-modified UiO-66, and then mixed evenly with the silicone resin to obtain the polybenzimidazole-modified UiO-66 composite silicone resin material; Step S3: mixing and curing silica sand, silane coupling agent modified vanadium carbide, urotropine, calcium stearate, the modified nano barium yttrium tungsten oxide compounded with phenolic resin, and the polybenzimidazole modified UiO-66 compounded with organic silicone resin to obtain coated sand.

2. The process for preparing coated sand based on heat-resistant steel casting according to claim 1, characterized in that: In step S1: the preparation method of the silane coupling agent modified nano barium yttrium tungsten oxide comprises the following steps: The nano-barium yttrium tungsten oxide is added into anhydrous ethanol and dispersed evenly, and gamma-aminopropyltriethoxysilane is added and dispersed evenly, and the silane coupling agent-modified nano-barium yttrium tungsten oxide is prepared by a spray drying method.

3. The process for preparing coated sand based on heat-resistant steel casting according to claim 1, characterized in that: In step S1: the preparation method of the silane coupling agent modified nano barium yttrium tungsten oxide compounded with phenolic resin material comprises the following steps: The nano-barium yttrium tungsten oxide modified by a silane coupling agent and the phenolic resin heated to a molten state are subjected to high shear emulsification stirring to obtain a modified nano-barium yttrium tungsten oxide compounded with a phenolic resin material.

4. The process for preparing coated sand based on heat-resistant steel casting according to claim 2, characterized in that: The spray drying temperature is 140-160°C.

5. The process for preparing coated sand based on heat-resistant steel casting according to claim 1, characterized in that: In the step S2: adding polybenzimidazole powder to N-methylpyrrolidone solvent for ultrasonic dispersion, adding UiO-66 for ultrasonic dispersion again, heating and stirring to obtain polybenzimidazole-modified UiO-66.

6. The process for preparing coated sand based on heat-resistant steel casting according to claim 5, characterized in that: The polybenzimidazole-modified UiO-66 and the heated organic silicone resin are subjected to high shear emulsification stirring to obtain a polybenzimidazole-modified UiO-66 composite organic silicone resin material.

7. The process for preparing coated sand based on heat-resistant steel casting according to claim 1, characterized in that: The preparation method of silane coupling agent modified vanadium carbide comprises the following steps: adding vanadium carbide powder into anhydrous ethanol, ultrasonically dispersing for 25-40 minutes, adding γ-aminopropyltriethoxysilane, stirring at a speed of 600-800 rpm for 3-5 hours, filtering and drying to obtain silane coupling agent modified vanadium carbide.

8. The process for preparing coated sand based on heat-resistant steel casting according to claim 1, characterized in that: In the step S3, the sand mixing and curing includes: adding silica sand to a sand mixer for the first sand mixing and heating; adding modified nano barium yttrium tungsten oxide compounded with phenolic resin and mixing for the second sand mixing; adding calcium stearate and mixing for the third sand mixing and cooling; adding urotropine and mixing for the fourth sand mixing and curing; adding silane coupling agent modified vanadium carbide and heating; adding polybenzimidazole modified UiO-66 compounded with organic silicone resin and mixing for the fifth sand mixing and cooling; adding urotropine and mixing for the sixth sand mixing; adding calcium stearate and mixing for the seventh sand mixing and curing to obtain coated sand.

9. The process for preparing coated sand based on heat-resistant steel casting according to claim 8, characterized in that: The temperature of the first sand mixing is 160-180°C, and the sand mixing time is 10-15min; the temperature of the second sand mixing is 160-180°C, and the time is 10-15min; the temperature of the third sand mixing is 160-180°C, and the time is 5-10min; the temperature of the fourth sand mixing is 120-130°C, and the time is 5-10min; the temperature of the fifth sand mixing is 200-220°C, and the time is 10-20min; the temperature of the sixth sand mixing is 150-170°C, and the time is 5-10min; the temperature of the seventh sand mixing is 150-170°C, and the time is 15-20min.

10. A coated sand based on heat-resistant steel casting, characterized in that: The sand is prepared by using the process for preparing coated sand based on heat-resistant steel casting as described in any one of claims 1 to 8.

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