A special steel sand for 3D printing metal casting and preparation method thereof

Abstract

The invention discloses a special steel sand for 3D printing metal casting and a preparation method thereof, which belongs to the technical field of steel sand processing and is used to solve the technical problems that the difference in thermal expansion coefficient between steel sand and standard sand in the prior art leads to poor dimensional stability of sand mold at high temperature and poor collapsibility of sand mold added with steel sand. The invention comprises the following steps: adding steel sand, anhydrous ethanol and KH-560 into a reactor and stirring, raising the temperature of the reactor to 50-55°C, and adding sodium hydroxide solution into the reactor. The invention optimizes the element composition and particle size distribution of the steel sand, performs surface modification on the steel sand, and then uses a mixed modification liquid to enhance the modified steel sand to prepare the special steel sand, so that the special steel sand is mixed with the standard sand to perform 3D printing of sand mold, which not only effectively enhances the room temperature compressive strength and dimensional stability of the sand mold, but also improves the collapsibility of the sand mold.

Description

Technical Field

[0001] The present invention relates to the technical field of steel sand processing, and in particular to special steel sand for 3D printing metal casting and a preparation method thereof. Background Art

[0002] With the rapid development of modern manufacturing industry, 3D printing technology, as an advanced manufacturing technology, has been widely used in many fields, especially in the field of metal casting. 3D printing technology, with its advantages of high precision, high efficiency and high flexibility, has brought revolutionary changes to the casting process. The casting sand mold 3D printing technology uses a special 3D printer to directly print out the sand mold required for casting, and then solidifies it through chemical or heat treatment, and removes the remaining waste parts. This technology not only shortens the production cycle and improves production efficiency, but also improves the dimensional accuracy and surface finish of the sand mold.

[0003] The prior art, a Chinese invention patent with publication number CN113695513A, discloses a water glass steel sand casting mold and a preparation method thereof, wherein the raw sand is steel sand, and the steel sand is bonded and shaped by water glass, and the preparation method of the water glass steel sand casting mold comprises the following steps: A, sand matching; B, model and sand box preparation; C, sand mixing; D, shaping; D, mold hardening; E, demolding, that is, the steel sand of the above casting mold has high heat storage and thermal conductivity, and enhances the quenching ability. The obtained casting has fine crystalline structure, dense texture, and excellent mechanical properties. The steel sand is recycled, which reduces the consumption of natural resources compared with mineral sand, and also avoids the generation of a large amount of solid waste sand.

[0004] The current sand mold 3D printing casting usually uses silica as the standard sand and water glass as the binder. The hardness of steel sand is much higher than that of silica standard sand. By adding steel sand to the standard sand, the hardness of the entire sand mold can be improved, so that the sand mold can better withstand the impact and pressure of the molten metal during the casting process, and reduce the casting defects caused by the deformation of the sand mold; however, the thermal conductivity of steel sand is high. When the casting is poured, the heat is transferred in the sand mold, and the thermal expansion coefficient between steel sand and standard sand is quite different, which makes it difficult for the sand mold to maintain the shape and size stability at high temperature. In addition, steel sand is not easy to break and fall off, resulting in poor collapsibility of the sand mold, and poor recycling performance of standard sand and steel sand.

[0005] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a special steel sand for 3D printing metal castings and a preparation method thereof, so as to solve the technical problems in the prior art that the difference in thermal expansion coefficient between steel sand and standard sand leads to poor dimensional stability of the sand mold at high temperature and poor collapsibility of the sand mold with steel sand added.

[0007] The purpose of the present invention can be achieved by the following technical solution: A method for preparing special steel sand for 3D printing metal casting, comprising the following steps:

[0008] S1. Add steel grit, anhydrous ethanol and KH-560 into a reactor and stir. The temperature of the reactor is raised to 50-55° C., sodium hydroxide solution is added into the reactor, and the mixture is stirred for 60-80 min. The modified steel grit is obtained by post-processing.

[0009] S2, adding calcium-based bentonite and ethanol solution to a high-speed disperser for dispersion, raising the temperature of the high-speed disperser to 45-50°C, stirring at this temperature for 20-30 minutes, adding additives to the high-speed disperser, stirring at this temperature for 30-50 minutes, lowering the temperature of the high-speed disperser to room temperature, adding powder and binder to the high-speed disperser, stirring at this temperature for 20-30 minutes, and obtaining a mixed modified liquid;

[0010] S3. Add modified steel sand and mixed modified liquid into the reactor, raise the temperature of the reactor to 50-55°C, stir for 60-80 minutes at room temperature, raise the temperature of the reactor to 70-80°C, pump the negative pressure of the reactor to 0.1MPa, keep warm and stir until the solvent evaporates completely, and obtain special steel sand.

[0011] The synthetic reaction mechanism of characteristic steel grit is:

[0012] The modified steel sand and the mixed modifying liquid are mixed in a certain proportion at room temperature so that the mixed modifying liquid is evenly covered on the surface of the steel sand. As the temperature of the reactor increases, the nano-aluminum silicate, nano-zirconium silicate and sodium silicate undergo hydrolysis and polycondensation reactions at high temperature to form a silicate network structure that is combined with the surface of the steel sand. At the same time, sodium tripolyphosphate and modified polyvinyl alcohol undergo cross-linking reactions at high temperatures to form a strong bonding layer, which promotes the silicate structure to be closely combined with the steel sand to prepare special steel sand.

[0013] Furthermore, in step S1, the amount ratio of the steel sand, anhydrous ethanol, KH-560 and sodium hydroxide solution is 5g:50mL:2g:10mL, the concentration of the sodium hydroxide solution is 0.2-0.4mol / L, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is lowered to room temperature, filtered, the filter cake is washed with purified water until it is neutral and then dried, and the filter cake is transferred to a drying oven at a temperature of 60-70°C and dried to constant weight to obtain modified steel sand.

[0014] Furthermore, the particle size of the steel sand is 0.1-0.7 mm, and the weight percentages of the steel sand components are: C, 0.8-1.2%, Si, 0.4-0.6%, Mn, 0.6-1.0%, Co, 0.8-1.0%, W, 1.4-1.6%, Cr, 0.6-0.8%, P<0.05%, S<0.03%, and the remainder is Fe and trace amounts of inevitable elements.

[0015] Furthermore, in step S2, the amount ratio of the calcium-based bentonite, ethanol solution, powder, binder and additive is 15-18g:80-100mL:10-15g:20-30g:1-2g, and the ethanol solution is a 45-55vol% ethanol aqueous solution.

[0016] Furthermore, the powder is composed of nano aluminum silicate, nano zirconium silicate and sodium silicate in a weight ratio of 2:1:4, the binder is composed of sodium tripolyphosphate and modified polyvinyl alcohol in a weight ratio of 3-5:7-9, the additive is composed of a dispersant, a defoamer, an antioxidant and an antistatic agent in a weight ratio of 3:2:1:1, the dispersant is a higher fatty acid salt, the defoamer is one or more of isooctyl alcohol, isopentanol and diisobutyl carbinol, the antioxidant is 2,6-di-tert-butyl-p-cresol, and the antistatic agent is sodium p-nonylphenoxypropyl sulfonate.

[0017] Furthermore, in step S3, the dosage ratio of the modified steel sand and the mixed modified liquid is 2g:3mL.

[0018] Furthermore, the preparation method of modified polyvinyl alcohol is: polyvinyl alcohol, allyltriethoxysilane, 7-octen-1-ol, N,N-dimethylformamide and initiator are added to a nitrogen-protected reactor and stirred, the temperature of the reactor is increased to 80-90°C, the reaction is carried out for 8-10 hours, and the modified polyvinyl alcohol is obtained by post-treatment.

[0019] The synthetic reaction formula of modified polyvinyl alcohol is:

[0020]

[0021] Where:

[0022] R:

[0023] The synthetic reaction principle of modified polyvinyl alcohol is:

[0024] Azobisisobutyronitrile was used as an initiator to attack the carbon-carbon double bonds in allyltriethoxysilane and 7-octen-1-ol, thereby initiating a free radical polymerization reaction between allyltriethoxysilane, 7-octen-1-ol and polyvinyl alcohol molecules, and introducing triethoxysilane and octanol segments into the polyvinyl alcohol molecular chain to prepare modified polyvinyl alcohol.

[0025] Furthermore, the amount ratio of polyvinyl alcohol, allyltriethoxysilane, 7-octen-1-ol, N,N-dimethylformamide and initiator is 7g:1g:3g:50mL:0.1g, the initiator is azobisisobutyronitrile, and the post-treatment includes: after the reaction is completed, distilling off N,N-dimethylformamide under reduced pressure to obtain modified polyvinyl alcohol.

[0026] The present invention also provides a special steel sand for 3D printing metal castings, wherein the special steel sand for 3D printing metal castings is processed according to a preparation method of special steel sand for 3D printing metal castings.

[0027] The present invention has the following beneficial effects:

[0028] 1. The preparation method of special steel sand for 3D printing metal casting mold of the present invention comprises the following steps: selecting steel sand, optimizing the element composition and particle size distribution of the steel sand, performing surface modification on the steel sand, and then using a mixed modification liquid to enhance the modified steel sand to prepare special steel sand; optimizing the metal element composition in the steel sand so that the thermal expansion coefficient of the steel sand matches that of the inorganic sand matrix, thereby reducing the volume change caused by thermal expansion and contraction; and the modified layer coated on the surface of the steel sand can form chemical bonds with the silicate molecules in the water glass, thereby enhancing the bonding force between the steel sand particles and the water glass sand matrix, thereby enhancing the strength of the sand mold; and the modified polyvinyl alcohol decomposes under high temperature, thereby reducing the bonding force between the sand mold particles and promoting the collapse of the sand mold.

[0029] 2. The preparation method of special steel sand for 3D printing metal casting molds of the present invention optimizes the element composition during the selection of steel sand. In the steel sand, metal elements such as iron, cobalt, tungsten, chromium, and manganese are the main components. These metal elements usually have a relatively low and relatively stable thermal expansion coefficient, which means that their volume or length changes when the temperature changes are relatively small and predictable, thereby reducing the thermal expansion coefficient of steel sand and standard sand, avoiding the size change of the sand mold when the temperature changes due to the difference in thermal expansion coefficient between steel sand and standard sand, and improving the dimensional stability of the sand mold. Nano-aluminum silicate and nano-zirconium silicate in the mixed modified liquid are used as inorganic powders, which have high thermal stability and can maintain the structure unchanged at high temperatures, thereby enhancing the overall high-temperature performance of the sample. In addition, inorganic powders such as nano-aluminum silicate and nano-zirconium silicate can also form a network structure with inorganic substances such as water glass to remain stable at high temperatures, and are not prone to expansion or contraction, thereby improving the dimensional stability of the sand mold.

[0030] 3. The preparation method of special steel sand for 3D printing metal casting of the present invention comprises the following steps: using polyvinyl alcohol as a base material, modifying it to prepare modified polyvinyl alcohol having a long carbon chain modified by triethoxysilane, combining it with sodium tripolyphosphate to prepare a binder, preparing a powder by combining nano-aluminum silicate, nano-zirconium silicate and sodium silicate, combining the binder, the powder and a calcium-based bentonite dispersion to prepare a mixed modified liquid, wherein the calcium-based bentonite is not prone to thermal decomposition or thermal expansion, and can maintain structural stability at high temperatures, and the calcium-based bentonite is a layered silicate mineral containing exchangeable cations between its layers. When the calcium-based bentonite is dispersed in an ethanol aqueous solution, its layered structure can adsorb and fix a large amount of water molecules to form a stable colloidal dispersion system, and the layered structure of the calcium-based bentonite can react with molecules such as modified polyvinyl alcohol and sodium tripolyphosphate in the binder. The binders interact with each other to form a tighter network structure, thereby enhancing the intermolecular interaction force within the binder and promoting the close bonding between the binder and the inorganic powder. In an aqueous ethanol solvent, the triethoxysilane in the binder is hydrolyzed into active silanol groups, which enable it to form chemical bonds with inorganic powders such as nano-aluminum silicate, nano-zirconium silicate, and calcium-based bentonite. The epoxy groups modified on the surface of the modified steel sand can undergo a ring-opening condensation reaction with the active hydroxyl groups under a high temperature environment to form chemical bonds, thereby forming special steel sand coated with multi-element inorganic powders bonded with the binder on the surface of the modified steel sand. The multiple phosphate ions contained in the sodium tripolyphosphate molecules in the binder can form hydrogen bonds or ionic bonds with inorganic substances such as silicate molecules, nano-aluminum silicate and nano-zirconium silicate, thereby enhancing the intermolecular interaction force inside the sand mold, thereby improving the room-temperature compressive strength of the material. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The polymerization degree of the polyvinyl alcohol used in the present invention is 500-800, and the alcoholysis degree is 87.0-89.0%.

[0033] Example 1

[0034] This embodiment provides a method for preparing special steel sand for 3D printing metal casting, comprising the following steps:

[0035] S1. Select steel sand

[0036] The weight percentages of the steel sand components are: C, 0.8%, Si, 0.4%, Mn, 0.6%, Co, 0.8%, W, 1.4%, Cr, 0.6%, P, 0.04%, S, 0.03%, the remainder is Fe and trace amounts of inevitable elements, and the particle size of the steel sand is 0.1-0.7mm.

[0037] S2. Preparation of modified steel sand

[0038] Weigh: 50g of steel sand, 500mL of anhydrous ethanol, and 20g of KH-560, add them into a reactor and stir, raise the temperature of the reactor to 50°C, add 100mL of 0.2mol / L sodium hydroxide solution into the reactor, and stir for 60min. After the reaction is completed, lower the temperature of the reactor to room temperature, filter, wash the filter cake with purified water until it is neutral, and then drain, transfer the filter cake to a drying oven at 60°C and dry it to constant weight to obtain modified steel sand.

[0039] S3. Preparation of modified polyvinyl alcohol

[0040] Weigh: 70 g of polyvinyl alcohol, 10 g of allyltriethoxysilane, 30 g of 7-octen-1-ol, 500 mL of N,N-dimethylformamide and 1 g of azobisisobutyronitrile, add into a nitrogen-protected reactor and stir, raise the temperature of the reactor to 80°C, react for 8 hours, and after the reaction is completed, evaporate N,N-dimethylformamide under reduced pressure to obtain modified polyvinyl alcohol.

[0041] S4. Preparation of mixed modified liquid

[0042] Mix nano aluminum silicate, nano zirconium silicate and sodium silicate in a weight ratio of 2:1:4 to obtain a powder;

[0043] The sodium tripolyphosphate and modified polyvinyl alcohol are uniformly mixed in a weight ratio of 3:7 to obtain a binder;

[0044] Mixing sodium stearate, isooctyl alcohol, 2,6-di-tert-butyl-p-cresol and sodium p-nonylphenoxypropyl sulfonate in a weight ratio of 3:2:1:1 to obtain an additive;

[0045] Weigh: 150 g of calcium-based bentonite and 800 mL of 45 vol% ethanol aqueous solution, add them to a high-speed disperser, set the stirring speed to 800 r / min, increase the temperature of the high-speed disperser to 45°C, keep warm and stir for 20 minutes, add 10 g of additive to the high-speed disperser, keep warm and stir for 30 minutes, lower the temperature of the high-speed disperser to room temperature, add 100 g of powder and 200 g of binder to the high-speed disperser, keep warm and stir for 20 minutes, and obtain a mixed modified liquid.

[0046] S5. Preparation of special steel sand

[0047] The modified steel sand and the mixed modified liquid were added into the reactor at a dosage ratio of 2g:3mL, the temperature of the reactor was raised to 50°C, and the mixture was stirred at room temperature for 60min. The temperature of the reactor was raised to 70°C, the negative pressure of the reactor was evacuated to 0.1MPa, and the mixture was stirred at the temperature until the solvent was completely evaporated to obtain special steel sand.

[0048] Example 2

[0049] This embodiment provides a method for preparing special steel sand for 3D printing metal casting, comprising the following steps:

[0050] S1. Select steel sand

[0051] The weight percentages of the steel sand components are: C, 1.0%, Si, 0.5%, Mn, 0.8%, Co, 0.9%, W, 1.5%, Cr, 0.7%, P, 0.03%, S, 0.03%, the remainder is Fe and trace amounts of inevitable elements, and the particle size of the steel sand is 0.1-0.7mm.

[0052] S2. Preparation of modified steel sand

[0053] Weigh: 50g of steel sand, 500mL of anhydrous ethanol, and 20g of KH-560, add them into the reactor and stir, raise the temperature of the reactor to 53°C, add 100mL of 0.3mol / L sodium hydroxide solution into the reactor, and stir for 70min. After the reaction is completed, lower the temperature of the reactor to room temperature, filter, wash the filter cake with purified water until it is neutral, and then drain, transfer the filter cake to a drying oven at 65°C and dry it to constant weight to obtain modified steel sand.

[0054] S3. Preparation of modified polyvinyl alcohol

[0055] Weigh: 70 g of polyvinyl alcohol, 10 g of allyltriethoxysilane, 30 g of 7-octen-1-ol, 500 mL of N,N-dimethylformamide and 1 g of azobisisobutyronitrile, add into a nitrogen-protected reactor and stir, raise the temperature of the reactor to 85°C, react for 9 hours, and after the reaction is completed, evaporate N,N-dimethylformamide under reduced pressure to obtain modified polyvinyl alcohol.

[0056] S4. Preparation of mixed modified liquid

[0057] Mix nano aluminum silicate, nano zirconium silicate and sodium silicate in a weight ratio of 2:1:4 to obtain a powder;

[0058] The sodium tripolyphosphate and modified polyvinyl alcohol are uniformly mixed in a weight ratio of 4:8 to obtain a binder;

[0059] Zinc stearate, isoamyl alcohol, 2,6-di-tert-butyl-p-cresol and sodium p-nonylphenoxypropyl sulfonate are uniformly mixed in a weight ratio of 3:2:1:1 to obtain an additive;

[0060] Weigh: 165 g of calcium bentonite and 900 mL of 50 vol% ethanol aqueous solution are added to a high-speed disperser, the stirring speed is set to 900 r / min, the temperature of the high-speed disperser is increased to 47°C, and the mixture is stirred at this temperature for 25 min. 15 g of an additive is added to the high-speed disperser, and the mixture is stirred at this temperature for 40 min. The temperature of the high-speed disperser is lowered to room temperature, 125 g of a powder and 250 g of a binder are added to the high-speed disperser, and the mixture is stirred at this temperature for 25 min to obtain a mixed modified liquid.

[0061] S5. Preparation of special steel sand

[0062] The modified steel sand and the mixed modified liquid were added into the reactor at a ratio of 2g:3mL, the temperature of the reactor was raised to 53°C, and the mixture was stirred at room temperature for 70min. The temperature of the reactor was raised to 75°C, the negative pressure of the reactor was evacuated to 0.1MPa, and the mixture was stirred at the temperature until the solvent was completely evaporated to obtain special steel sand.

[0063] Example 3

[0064] This embodiment provides a method for preparing special steel sand for 3D printing metal casting, comprising the following steps:

[0065] S1. Select steel sand

[0066] The weight percentages of the steel sand components are: C, 1.2%, Si, 0.6%, Mn, 1.0%, Co, 1.0%, W, 1.6%, Cr, 0.8%, P, 0.02%, S, 0.01%, the remainder is Fe and trace amounts of inevitable elements, and the particle size of the steel sand is 0.1-0.7mm.

[0067] S2. Preparation of modified steel sand

[0068] Weigh: 50g of steel sand, 500mL of anhydrous ethanol, and 20g of KH-560, add them into the reactor and stir, raise the temperature of the reactor to 55°C, add 100mL of 0.4mol / L sodium hydroxide solution into the reactor, and stir for 80min. After the reaction is completed, lower the temperature of the reactor to room temperature, filter, wash the filter cake with purified water until it is neutral, and then drain, transfer the filter cake to a drying oven at 70°C and dry it to constant weight to obtain modified steel sand.

[0069] S3. Preparation of modified polyvinyl alcohol

[0070] Weigh: 70 g of polyvinyl alcohol, 10 g of allyltriethoxysilane, 30 g of 7-octen-1-ol, 500 mL of N,N-dimethylformamide and 1 g of azobisisobutyronitrile, add into a nitrogen-protected reactor and stir, raise the temperature of the reactor to 90°C, react for 10 hours, and after the reaction is completed, evaporate N,N-dimethylformamide under reduced pressure to obtain modified polyvinyl alcohol.

[0071] S4. Preparation of mixed modified liquid

[0072] Mix nano aluminum silicate, nano zirconium silicate and sodium silicate in a weight ratio of 2:1:4 to obtain a powder;

[0073] The sodium tripolyphosphate and modified polyvinyl alcohol are uniformly mixed in a weight ratio of 5:9 to obtain a binder;

[0074] Calcium stearate, diisobutyl carbinol, 2,6-di-tert-butyl-p-cresol and sodium p-nonylphenoxypropyl sulfonate are uniformly mixed in a weight ratio of 3:2:1:1 to obtain an additive;

[0075] Weigh: 180 g of calcium-based bentonite and 1000 mL of 55 vol% ethanol aqueous solution are added to a high-speed disperser, the stirring speed is set to 1000 r / min, the temperature of the high-speed disperser is increased to 50° C., and the mixture is stirred at this temperature for 30 min. 20 g of an additive is added to the high-speed disperser, and the mixture is stirred at this temperature for 50 min. The temperature of the high-speed disperser is lowered to room temperature, 150 g of a powder and 300 g of a binder are added to the high-speed disperser, and the mixture is stirred at this temperature for 30 min to obtain a mixed modified liquid.

[0076] S5. Preparation of special steel sand

[0077] Add modified steel sand and mixed modified liquid into the reactor at a ratio of 2g:3mL, raise the temperature of the reactor to 55°C, stir at room temperature for 80min, raise the temperature of the reactor to 80°C, evacuate the negative pressure of the reactor to 0.1MPa, and keep warm and stir until the solvent evaporates completely to obtain special steel sand.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 3 is that the steel sand used is of type SG14 and has a particle size of 0.1-0.7 mm.

[0080] Comparative Example 2

[0081] The difference between this comparative example and Example 3 is that step S2 is eliminated, and the modified steel sand in step S4 is replaced by the steel sand in step S1.

[0082] Comparative Example 3

[0083] The difference between this comparative example and Example 3 is that step S3 is eliminated, and the polyvinyl alcohol in step S2 is substituted for the modified polyvinyl alcohol in step S4.

[0084] Comparative Example 4

[0085] The difference between this comparative example and Example 3 is that no sodium tripolyphosphate is added to the binder in step S4.

[0086] Comparative Example 5

[0087] The difference between this comparative example and Example 3 is that no nano aluminum silicate is added to the powder in step S4.

[0088] Performance Test:

[0089] The special steel sand samples prepared in Examples 1-3 and Comparative Examples 1-5 were respectively mixed with 100-140 mesh 3D printing standard sand at a weight ratio of 1:4 to obtain mixed sand, and then the mixed sand and water glass were added to the sand mold 3D printing equipment, and printed layer by layer at a printing rate of 0.7 mm and a pressure of 1 g / m 2 The composite water glass is evenly sprayed on the top of each printed layer with a spraying amount of , to prepare a sand mold sample for metal casting;

[0090] Referring to the standard GB / T 43365-2023 "Test Method for Properties of Sand Molds for Additive Manufacturing Metal Castings", the room temperature compressive strength, high temperature compressive strength and high temperature expansion rate of the sand mold samples were tested. The specific test results are shown in Table 1 below.

[0091] Table 1-Performance test data of the sample

[0092]

[0093]

[0094] Data Analysis:

[0095] A comparative analysis of the data in Table 1 above shows that the special steel sand prepared in the present application is used to enhance the standard sand to prepare mixed sand, and then the mixed sand is combined with water glass to make the room temperature compressive strength of the sand mold reach 2.88 MPa, the high temperature compressive strength is reduced to 0.50 MPa, and the high temperature expansion rate is reduced to 0.29%. All performance data are better than those of the comparative example, indicating that the present invention optimizes the elemental composition and particle size distribution of the steel sand, performs surface modification on the steel sand, and then uses a mixed modification liquid to enhance the modified steel sand to prepare special steel sand, which is mixed with standard sand for 3D printing sand molds, which not only effectively enhances the room temperature compressive strength and dimensional stability of the sand mold, but also improves the collapsibility of the sand mold.

[0096] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing special steel sand for 3D printing metal casting, characterized in that: The following steps are involved: S1. Add steel grit, anhydrous ethanol and KH-560 into a reactor and stir. The temperature of the reactor is raised to 50-55° C., sodium hydroxide solution is added into the reactor, and the mixture is stirred for 60-80 min. The modified steel grit is obtained by post-processing. S2, adding calcium-based bentonite and ethanol solution to a high-speed disperser for dispersion, raising the temperature of the high-speed disperser to 45-50°C, stirring at this temperature for 20-30 minutes, adding additives to the high-speed disperser, stirring at this temperature for 30-50 minutes, lowering the temperature of the high-speed disperser to room temperature, adding powder and binder to the high-speed disperser, stirring at this temperature for 20-30 minutes, and obtaining a mixed modified liquid; S3. Add modified steel sand and mixed modified liquid into the reactor, raise the temperature of the reactor to 50-55°C, stir for 60-80 minutes at room temperature, raise the temperature of the reactor to 70-80°C, pump the negative pressure of the reactor to 0.1MPa, keep warm and stir until the solvent evaporates completely, and obtain special steel sand.

2. The method for preparing special steel sand for 3D printing metal casting according to claim 1, characterized in that: In step S1, the amount ratio of the steel sand, anhydrous ethanol, KH-560 and sodium hydroxide solution is 5g:50mL:2g:10mL, the concentration of the sodium hydroxide solution is 0.2-0.4mol / L, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is lowered to room temperature, filtered, the filter cake is washed with purified water until it is neutral and then dried, and the filter cake is transferred to a drying oven at a temperature of 60-70°C and dried to constant weight to obtain modified steel sand.

3. The method for preparing special steel sand for 3D printing metal casting according to claim 1, characterized in that: The particle size of the steel sand is 0.1-0.7 mm, and the weight percentages of the steel sand components are: C, 0.8-1.2%, Si, 0.4-0.6%, Mn, 0.6-1.0%, Co, 0.8-1.0%, W, 1.4-1.6%, Cr, 0.6-0.8%, P<0.05%, S<0.03%, and the remainder is Fe and trace amounts of inevitable elements.

4. The method for preparing special steel sand for 3D printing metal casting according to claim 1, characterized in that: In step S2, the amount ratio of the calcium-based bentonite, ethanol solution, powder, binder and additive is 15-18g:80-100mL:10-15g:20-30g:1-2g, and the ethanol solution is a 45-55vol% ethanol aqueous solution.

5. The method for preparing special steel sand for 3D printing metal casting according to claim 4, characterized in that: The powder is composed of nano aluminum silicate, nano zirconium silicate and sodium silicate in a weight ratio of 2:1:4; the binder is composed of sodium tripolyphosphate and modified polyvinyl alcohol in a weight ratio of 3-5:7-9; the additives are composed of a dispersant, a defoamer, an antioxidant and an antistatic agent in a weight ratio of 3:2:1:1; the dispersant is a higher fatty acid salt; the defoamer is one or more of isooctyl alcohol, isopentanol and diisobutyl carbinol; the antioxidant is 2,6-di-tert-butyl-p-cresol; and the antistatic agent is sodium p-nonylphenoxypropyl sulfonate.

6. The method for preparing special steel sand for 3D printing metal casting according to claim 1, characterized in that: In step S3, the usage ratio of the modified steel sand and the mixed modified liquid is 2g:3mL.

7. The method for preparing special steel sand for 3D printing metal casting according to claim 5, characterized in that: The preparation method of modified polyvinyl alcohol is as follows: polyvinyl alcohol, allyltriethoxysilane, 7-octen-1-ol, N,N-dimethylformamide and initiator are added into a nitrogen-protected reactor and stirred, the temperature of the reactor is increased to 80-90°C, the reaction is carried out for 8-10 hours, and the modified polyvinyl alcohol is obtained by post-treatment.

8. The method for preparing special steel sand for 3D printing metal casting according to claim 7, characterized in that: The amount ratio of polyvinyl alcohol, allyl triethoxysilane, 7-octen-1-ol, N,N-dimethylformamide and initiator is 7g:1g:3g:50mL:0.1g, the initiator is azobisisobutyronitrile, and the post-treatment includes: after the reaction is completed, N,N-dimethylformamide is evaporated under reduced pressure to obtain modified polyvinyl alcohol.

9. A special steel sand for 3D printing metal casting, characterized in that: The special steel sand for 3D printing metal castings is obtained by processing according to the preparation method of special steel sand for 3D printing metal castings according to any one of claims 1-8.

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