A method for preparing a water-soluble composite salt core based on slurry direct writing 3D printing technology

Abstract

The present invention belongs to the field of casting technology, and more specifically, relates to a method for preparing a water-soluble composite salt core based on slurry direct writing 3D printing technology. A water-soluble composite salt core material for low-melting-point alloy casting is composed of the following components: a pretreated water-soluble inorganic salt, a binder and an additive, wherein the pretreated water-soluble inorganic salt is obtained by mixing a coating solution with an inorganic salt powder, and in terms of mass percentage, the pretreated water-soluble inorganic salt: binder: additive = 60%-80%: 20%-30%: 0%-10%. Compared with the traditional method for preparing water-soluble salt cores, the water-soluble composite salt core material of the present invention has the advantage of slurry direct writing forming water-soluble salt cores in that parts can be quickly formed without a mold, and the process is simple, the raw material cost is low, and the equipment requirements are low. It can realize the moldless rapid and precise forming of high-precision complex salt cores, solving the problem of the difficulty in forming the complex salt core as a whole.

Description

Technical Field

[0001] The present invention belongs to the field of casting technology, and more specifically, relates to a method for preparing a high-strength water-soluble composite salt core by 3D printing of slurry for casting low-melting-point alloys such as aluminum (magnesium). Background Art

[0002] With the rapid development of my country's aviation, aerospace, automobile manufacturing and 5G communications, the demand for complex thin-walled precision castings of low-melting-point alloys such as aluminum (magnesium) is also increasing. Such castings often have complex internal cavity structures, some of which are basically closed or have many slender curved channels of different shapes.

[0003] Prefabricated cores are required to cast complex inner cavity structures, and the cores must be removed after the casting is formed. In order to form high-quality precision castings, higher requirements are placed on the performance of the casting cores and their forming and cleaning methods.

[0004] Casting cores must have high room-temperature strength and dimensional accuracy, good high-temperature stability and air permeability, low gas evolution, and excellent post-casting disintegration and cleanability. Currently commonly used casting core materials, such as resin sand cores, silica- and alumina-based ceramic cores, cannot simultaneously meet these performance requirements. They all require the use of mixed alkali methods, alkaline solution methods, pressure de-coring methods, and hydrofluoric acid methods to clean residual cores from the inner cavity of the casting and curved channels. Residual cores in nearly closed casting cavities are extremely difficult to clean. Some of the above core cleaning methods will corrode the casting, some will produce toxic substances that pollute the environment, and some (such as pressure de-coring) have complex de-coring processes and require specialized equipment. Water-soluble salt core technology can effectively solve the problem of cleaning casting core materials. After the casting is formed, the residual core can be quickly cleaned by dissolving it with water, saving labor and improving the working environment.

[0005] Currently, it is difficult to directly form this type of complex salt core as a whole. Traditional preparation processes include melt casting, pressing and sintering, and bonding. The melt casting method requires molds to be formed and assembled in pieces, which is a complex process and has low preparation efficiency. The pressing and sintering method has high preparation costs, a complex preparation process, and high equipment requirements. The salt cores prepared by the bonding forming method have low mechanical properties and low water solubility. Therefore, the water-soluble salt cores prepared by traditional processes are difficult to meet the requirements of die-casting production. The preparation of integrated, complex, and precise water-soluble salt cores has become a key problem in the manufacture of die-casting cavities for low-melting-point alloy castings such as aluminum (magnesium).

[0006] CN 104399865A discloses a water-soluble graphite composite salt core material, a graphite composite salt core, and a preparation method thereof, which are primarily used in aluminum piston internal coolant oil channel casting. The graphite composite salt core comprises a water-soluble metal halide (a single metal halide or a mixture of multiple metal halides) and graphite powder, and is prepared by a pressing and sintering method. The salt core produced by this method exhibits high strength and low shrinkage, but the graphite powder and metal halide are prone to uneven mixing, resulting in stratification of the salt core, which affects its performance.

[0007] CN 106670376A discloses a high-strength composite salt core for casting low-melting-point alloys. The water-soluble salt core comprises a water-soluble inorganic salt and a reinforcing agent, wherein the inorganic salt comprises one low-melting-point inorganic salt and one or more high-melting-point inorganic salts. The low-melting-point inorganic salts are potassium nitrate and sodium nitrate, and the high-melting-point inorganic salts are potassium chloride, potassium bromide, sodium chloride, and sodium bromide. The reinforcing agent comprises one or more of dalin sand, refractory clay powder, glass fiber powder, kaolin, quartz powder, bentonite, alumina powder, and high-alumina bauxite. The salt core is prepared using a melt-casting method, resulting in high strength and low moisture absorption. However, the low-melting-point salt determines the melting point of the entire salt core, making this salt core suitable only for casting low-melting-point alloys and unable to meet the casting requirements of low-melting-point alloys such as aluminum (magnesium).

[0008] CN 115815532A discloses a water-soluble salt core material, its preparation method, and its application. The water-soluble salt core comprises an inorganic salt and a binder, wherein the inorganic salt is a single salt with a high melting point, including one of sodium chloride, potassium chloride, sodium sulfate, or potassium sulfate; and the binder comprises two or more of an organic binder and an inorganic binder, one of which is bentonite. The salt core is prepared by extrusion molding. Although the preparation process is simple and can form water-soluble salt cores of complex shapes, salt cores composed of a single inorganic salt have lower strength than composite salt cores, and their mechanical properties need to be improved.

[0009] The preparation methods of the above-mentioned water-soluble salt cores include traditional preparation processes and emerging preparation processes. However, for water-soluble salt cores of low-melting-point alloy castings such as aluminum (magnesium) with slender and curved internal channels and complex spatial structures, how to achieve high-efficiency and high-quality simultaneous production requires further optimization of the material composition and preparation methods of the salt cores, and the search for a more complete preparation solution. Summary of the Invention

[0010] To address the shortcomings of existing technologies and address the need for improvement, this invention provides a method for preparing water-soluble composite salt cores using slurry direct writing 3D printing technology. This method is primarily used for castings of low-melting-point alloys such as aluminum (magnesium) with complex internal structures. By synergistically controlling parameters such as the salt core material composition, extrusion direct writing 3D printing, and a step-by-step sintering process, complex, irregularly shaped holes, flow channels, and other structures can be directly and integrally formed, avoiding the precision errors caused by core assembly. This method has promising application prospects in the development of complex core material systems and new products, and can be used for the rapid, moldless, and direct, integral forming of complex casting cores.

[0011] A water-soluble composite salt core material for low-melting-point alloy casting, comprising the following components:

[0012] Pre-treating water-soluble inorganic salts, binders and additives, wherein the pre-treated water-soluble inorganic salts are obtained by mixing a coating solution with inorganic salt powder, and the weight percentage of the pre-treated water-soluble inorganic salts: binder: additives = 60%-80%: 20%-30%: 0%-10%.

[0013] Furthermore, the mass percentage of the inorganic salt powder and the coating solution is 40%-60%:40%-60%.

[0014] Furthermore, the inorganic salt powder includes two or more of sodium sulfate, potassium sulfate, sodium carbonate, potassium carbonate, calcium carbonate, sodium chloride, potassium chloride, magnesium chloride, calcium chloride or barium chloride, and the melting point of the inorganic salt powder is 450-1200° C.;

[0015] The particle size of the inorganic salt powder is 500-3000 mesh;

[0016] The coating solution is prepared from polydimethylsiloxane and anhydrous ethanol.

[0017] Furthermore, the binder is one of polyvinyl alcohol aqueous solution, polyethylene glycol aqueous solution, polyacrylamide aqueous solution, methyl cellulose aqueous solution, epoxy resin aqueous solution, polyvinyl pyrrolidone-anhydrous ethanol solution, and polyacrylic acid-anhydrous ethanol, and the concentration of the binder solution is 1%~25%.

[0018] Furthermore, the additive is a mixture of an enhancer, a dispersant, and a defoamer, and the ratio by mass percentage is: enhancer: dispersant: defoamer = 97.5%-99.5%: 0.5%-1.5%: 0%-1%.

[0019] The reinforcing agent is one or more of bauxite powder, corundum powder, mullite powder, zirconium oxide powder, quartz powder, titanium oxide powder, sericite or glass fiber, and the particle size of the reinforcing agent is 300-1250 mesh;

[0020] The dispersant is one of ammonium polyacrylate or sodium dodecylbenzene sulfonate;

[0021] The defoaming agent is a silicone defoaming agent.

[0022] A method for preparing a water-soluble composite salt core by 3D printing of a slurry for low-melting-point alloy casting, specifically comprising the following steps:

[0023] S1. 3D printing of the salt core blank: preparing salt-based raw materials, grinding the salt-based raw materials sufficiently to obtain salt-based slurry, and using slurry direct writing equipment to 3D print the salt-based slurry to obtain the salt core blank;

[0024] Wherein, the salt-based raw material is the above-mentioned water-soluble composite salt core material or a mixture of a binder and a dispersant;

[0025] The inner diameter of the printing needle is 0.41mm~1.55mm, and the extrusion pressure is 5psi~50psi;

[0026] S2. Sintering of the water-soluble composite salt core: The salt core green body is subjected to natural drying, oven drying and sintering treatments in sequence to obtain the water-soluble composite salt core.

[0027] Furthermore, in step S1, when the salt-based raw material is a water-soluble composite salt core material, the preparation method of the salt-based slurry is:

[0028] The inorganic salt powder is coated with a coating solution to obtain a pretreated water-soluble inorganic salt, and the pretreated water-soluble inorganic salt, the binder solution and the additive are uniformly mixed to obtain a premixed solution, wherein the additive is a mixture of a reinforcing agent, a dispersant and a defoaming agent, and the mass percentage of each component is as follows:

[0029] Pretreatment water-soluble inorganic salt: binder: additive = 60%-80%: 20%-30%: 0%-10%.

[0030] Furthermore, in step S1, when the salt-based raw material is a mixture of a binder and a dispersant, graphite powder is added to the mixture, and the mass percentages of graphite powder, binder and dispersant are 70%-75%: 24%-29.5%: 0.5%-1%, and:

[0031] The dispersant is one of ammonium polyacrylate or sodium dodecylbenzene sulfonate;

[0032] The binder is one of polyvinyl alcohol aqueous solution, polyethylene glycol aqueous solution, polyacrylamide aqueous solution, methyl cellulose aqueous solution, epoxy resin aqueous solution, polyvinyl pyrrolidone-anhydrous ethanol solution, and polyacrylic acid-anhydrous ethanol.

[0033] Furthermore, the drying temperature condition is 40°C~90°C, and the drying time is 12h~24h; the sintering adopts a combination of step-by-step sintering and liquid phase sintering, and the final sintering temperature is 450~1200°C.

[0034] The water-soluble composite salt core is prepared by the above method.

[0035] In general, the water-soluble salt core material and preparation method of the present invention have the following main advantages compared with the prior art:

[0036] (1) Compared with the traditional method of preparing water-soluble salt cores, the advantage of slurry direct writing forming water-soluble salt cores is that parts can be quickly formed without molds, and the process is simple, the raw material cost is low, and the equipment requirements are low. It can achieve high-precision complex salt cores without molds, quickly and accurately forming, and obtain salt cores with complete structure, dense organization and high precision, thus solving the problem of difficult overall forming of complex salt cores.

[0037] (2) In order to solve the problem that it is difficult to improve the bending strength and impact toughness of the existing salt core at the same time, the multi-phase hybrid coupling of inorganic salt and reinforcing agent is used to simultaneously improve the bending strength and impact toughness of the composite salt core.

[0038] (3) After the inorganic salt powder is coated, a hydrophobic barrier is formed on the surface of the inorganic salt powder particles, which prevents the inorganic salt from dissolving when using a water-based binder, thereby expanding the selection range of the binder solution and having more environmental and cost advantages.

[0039] (4) By adjusting the direct writing forming parameters (filling rate, printing speed, needle inner diameter and filling line angle, etc.), the complete formability, surface quality, dimensional accuracy and strength of the blank can be coordinated and controlled.

[0040] (5) The sintering process adopts a combination of step-by-step sintering and liquid phase sintering. Step-by-step sintering can reduce cracks and deformation caused by sudden temperature changes by controlling the heating rate and holding time; liquid phase sintering helps to evenly distribute and better bond the particles, further optimize the microstructure of the material, improve the bending strength of the salt core, and avoid over-sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flow chart of the preparation process of the water-soluble composite salt core of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention clearer, the specific embodiments of the present invention are further described below in conjunction with specific examples and drawings. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this field or the product specifications are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0043] The physical and chemical parameters of the sodium chloride powder used in the present invention are shown in Table 1:

[0044] Table 1

[0045]

[0046] The physical and chemical parameters of the sodium carbonate powder used in the present invention are shown in Table 2:

[0047] Table 2

[0048]

[0049] The physical and chemical parameters of the magnesium chloride powder used in the present invention are shown in Table 3:

[0050] Table 3

[0051]

[0052] The physical and chemical parameters of the calcium chloride powder used in the present invention are shown in Table 4:

[0053] Table 4

[0054]

[0055] The physical and chemical parameters of the barium chloride powder used in the present invention are shown in Table 5:

[0056] Table 5

[0057]

[0058] The physicochemical parameters of the potassium chloride powder used in the present invention are shown in Table 6:

[0059] Table 6

[0060]

[0061] The present invention is to protect a water-soluble composite salt core material for low melting point alloy casting, which is composed of the following components:

[0062] Pre-treated water-soluble inorganic salts, binders and additives, wherein the pre-treated water-soluble inorganic salts are obtained by mixing a coating solution with an inorganic salt powder, and in terms of mass percentage, the pre-treated water-soluble inorganic salts: binder: additive = 60%-80%: 20%-30%: 0%-10%, and the inorganic salt powder: coating solution = 40%-60%: 40%-60%.

[0063] The inorganic salt powder includes two or more of sodium sulfate, potassium sulfate, sodium carbonate, potassium carbonate, calcium carbonate, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, or barium chloride, and the melting point of the composite inorganic salt multi-component system is 450-1200°C. The inorganic salt powder has a particle size of 500-3000 mesh. The coating solution is an organosilicon solution prepared from polydimethylsiloxane (PDMS) and anhydrous ethanol at a concentration of 50 wt.%. The binder is one of a polyvinyl alcohol aqueous solution, a polyethylene glycol aqueous solution, a polyacrylamide aqueous solution, a methylcellulose aqueous solution, an epoxy resin aqueous solution, a polyvinyl pyrrolidone-anhydrous ethanol solution, and a polyacrylic acid-anhydrous ethanol solution. The concentration of the binder solution is 1% to 25%.

[0064] The additive is a mixture of a reinforcing agent, a dispersant, and a defoaming agent. The reinforcing agent can increase the flexural strength and thermal stability of the salt core; the dispersant can prevent particle agglomeration in the slurry, improve deposition quality, and enhance the surface smoothness and forming accuracy of the salt core; the defoaming agent can eliminate bubbles in the slurry, preventing them from remaining in the formed structure during the slurry mixing and extrusion process, thereby improving the density and structural integrity of the salt core.

[0065] The reinforcing agent is one or more of bauxite powder, corundum powder, mullite powder, zirconium oxide powder, quartz powder, titanium oxide powder, sericite or glass fiber, and the particle size of the reinforcing agent is 300-1250 mesh;

[0066] The dispersant is one of ammonium polyacrylate or sodium dodecylbenzene sulfonate;

[0067] The defoaming agent is a silicone defoaming agent.

[0068] The water-soluble composite salt core material of the present invention is prepared by a slurry direct writing forming process, can have a complex and elongated structure, and can be quickly formed without a mold.

[0069] Another aspect of the present invention provides a method for preparing a high-strength water-soluble composite salt core based on slurry direct writing technology. The salt core is prepared by casting the above-mentioned water-soluble composite salt core material with a low-melting-point alloy such as aluminum (magnesium).

[0070] A method for preparing a water-soluble composite salt core by 3D printing of a slurry for low-melting-point alloy casting comprises the following steps:

[0071] (1) Preparation of salt-based slurry

[0072] The salt-based slurry of the present invention may be a mixture of the above-mentioned water-soluble composite salt core material or a binder and an additive;

[0073] When the salt-based slurry is a water-soluble composite salt core material, the preparation method of the salt-based slurry is:

[0074] The inorganic salt powder is coated with a coating solution to obtain a pretreated water-soluble inorganic salt. The pretreated water-soluble inorganic salt, binder solution, and additives are uniformly mixed to obtain a premixed solution, wherein the additives are a mixture of a reinforcing agent, a dispersant, and a defoaming agent, and the weight percentage of pretreated water-soluble inorganic salt: binder: additive is 60%-80%: 20%-30%: 0%-10%. The premixed solution is transferred to a ball milling jar and thoroughly milled in a planetary ball mill (the weight ratio of ball milling beads to salt base slurry is 1:5) at a speed of 180-300 rpm for 8-15 hours. After removal, a salt base slurry suitable for extrusion direct writing is obtained.

[0075] When the salt-based slurry is a mixture of a binder and a dispersant, the preparation method of the salt-based slurry is:

[0076] Graphite powder is added to the mixture, and the mass percentages of graphite powder, binder and dispersant are 70%-75%: 24%-29.5%: 0.5%-1% by mass.

[0077] (2) 3D printing of salt core blanks

[0078] The salt-based slurry is loaded into the extrusion barrel of the slurry direct writing machine. The extruder's trajectory and extrusion state are controlled by a computer program and a dispensing machine. The salt-based slurry is deposited on the substrate along a predetermined path to form a salt core blank. Methyl silicone oil is applied to the substrate surface to prevent cracking caused by rapid drying and to facilitate separation of the blank from the substrate.

[0079] (3) Sintering of water-soluble composite salt core

[0080] After 12 hours of natural drying, the salt core green body is transferred to a drying oven for drying. The oven drying temperature is 40℃~90℃ and the drying time is 12h~24h. The green body is then placed in a high-temperature sintering furnace for sintering. It is calcined at a higher temperature for a certain time to form better strength and other properties and to play the role of the additive in enhancing the green body performance, thereby obtaining a high-strength water-soluble composite salt core.

[0081] The sintering process of the present invention adopts a combination of distributed sintering and liquid phase sintering, with a final sintering temperature of 450-1200°C. The specific sintering steps are as follows: heating the green body to 360°C at a heating rate of 1-3°C / min, holding the temperature for 60 minutes to remove the binder and other organic matter in the green body; then heating at a heating rate of 1-3°C / min, holding the temperature at 5-30°C above the final sintering temperature for 30-60 minutes; then heating to the final sintering temperature at a heating rate of 5°C / min, holding the temperature for 10-30 minutes; then cooling to 5-30°C below the final sintering temperature, holding the temperature for 30-60 minutes; finally cooling to room temperature with the furnace. The purpose of using liquid phase sintering is to improve the bending strength of the salt core and avoid over-sintering.

[0082] The present invention discloses a method for preparing a water-soluble composite salt core by 3D printing using a slurry for direct writing of low-melting-point alloy casting. Graphite powder (burned out at 500-600°C) can be used as a supporting matrix material, and multiple extruder heads are used to 3D print a complex salt core. After high-temperature sintering, a suspended water-soluble composite salt core can be formed for use in aluminum alloy components with complex internal structures and suspended channels. The direct writing equipment is prior art, such as the 3D printing device described in Patent No. CN202311075788.8, entitled "A Dual-Head Collaborative Direct Writing 3D Printing Device," which can serve as a specific embodiment of the present invention's heatable direct writing 3D printing device.

[0083] It should be noted that Examples 1-8 all used direct writing equipment independently built by the inventor, the computer-side control software was Simplify 3D slicing software, and the size of the printed blank was 60 mm × 10 mm × 6 mm.

[0084] <Example 1>

[0085] The interfacial binding energy of NaCl (100) / Na2CO3 (100) was calculated to be 13.2 J / m by first principle. 2 , a water-soluble composite salt core was prepared using NaCl-Na2CO3 as the matrix material.

[0086] A method for preparing a water-soluble composite salt core by direct writing 3D printing of a slurry for low-melting-point alloy casting comprises the following steps:

[0087] A 10% polyvinyl alcohol (PVA) aqueous solution was prepared with deionized water. Sodium chloride (D50 = 10 μm) and sodium carbonate (D50 = 6.5 μm) were mixed in a ratio of 30 mol% NaCl to 70 mol% Na₂CO₃. The mixed powder was coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt. 66 parts by mass of the pretreated water-soluble inorganic salt, 34.4 parts by mass of the PVA aqueous solution, 0.5 parts by mass of ammonium polyacrylate, and 0.1 parts by mass of a defoamer were mixed and stirred in a container to obtain a premix. The premix was transferred to a ball mill, ball milling beads were added, and the mixture was milled in a spherical ball mill for 13 hours. A uniformly dispersed salt-based slurry was obtained after removal.

[0088] Printing parameters were set on the computer slicing software controlling the slurry direct writing machine: 100% infill, 600 mm / min print speed, and a 23° / -67° composite fill angle. The milled salt-based slurry was loaded into the extruder barrel, and a 0.51 mm extruder head was used for printing. The extrusion pressure was 5 psi, and the printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate, air-dried for 24 hours, and then transferred to a drying oven at 70°C for 24 hours.

[0089] The dried green body is sintered in a high-temperature sintering furnace. The sintering program is set on the control panel of the high-temperature sintering furnace: starting from room temperature, heat at a heating rate of 1°C / min to 360°C and hold for 60 minutes; then heat at a heating rate of 3°C / min to 600°C and hold for 60 minutes; then heat at a heating rate of 5°C / min to 620°C and hold for 30 minutes; then cool to 600°C and hold for 60 minutes; finally, cool to room temperature in the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0090] <Example 2>

[0091] The interfacial binding energy of NaCl(100) / K2CO3(011) was calculated to be 1.04 J / m by first principle. 2 , NaCl / K2CO3 was used as the matrix material to prepare the water-soluble composite salt core.

[0092] A method for preparing a water-soluble composite salt core by direct writing 3D printing of a slurry for low-melting-point alloy casting comprises the following steps:

[0093] A 20% polyethylene glycol aqueous solution was prepared with deionized water. Sodium chloride (D50 = 10 μm) and potassium carbonate (D50 = 5 μm) were mixed in a ratio of 50 mol% NaCl to 50 mol% K2CO3. The mixed powder was coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt. 71 parts by mass of the mixed inorganic salt powder, 28.4 parts by mass of the polyethylene glycol aqueous solution, 0.5 parts by mass of ammonium polyacrylate, and 0.1 parts by mass of a defoamer were mixed and stirred in a container to obtain a premix. The premix was transferred to a ball mill, ball milling beads were added, and the mixture was milled in a spherical ball mill for 13 hours. A uniformly dispersed salt-based slurry was obtained after removal.

[0094] Printing parameters were set on the computer slicing software controlling the slurry direct writing machine: 100% infill, 600 mm / min print speed, and a 45° / -45° composite fill angle. The milled salt-based slurry was loaded into the extruder barrel, and a 0.61 mm extruder head was used for printing. The extrusion pressure was set to 10 psi, and the printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate, air-dried for 24 hours, and then transferred to a drying oven at 70°C for 24 hours.

[0095] The dried green body is sintered in a high-temperature sintering furnace. The sintering program is set on the control panel of the high-temperature sintering furnace: starting from room temperature, heat at a heating rate of 1°C / min to 360°C and hold for 60 minutes; then heat at a heating rate of 3°C / min to 620°C and hold for 60 minutes; then heat at a heating rate of 5°C / min to 640°C and hold for 30 minutes; then cool to 620°C and hold for 60 minutes; finally, cool to room temperature in the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0096] <Example 3>

[0097] The interfacial binding energy of NaCl(100) / CaCO3(010) was calculated to be 0.12 J / m by first principle. 2 , NaCl-CaCO3 was used as the matrix material to prepare the water-soluble composite salt core.

[0098] A method for preparing a water-soluble composite salt core by 3D printing of a slurry for low-melting-point alloy casting comprises the following steps:

[0099] A 2% methylcellulose aqueous solution was prepared with deionized water. Sodium chloride (D50 = 10 μm) and calcium carbonate (D50 = 5 μm) were mixed in a ratio of 60 mol% NaCl to 40 mol% CaCO₃. The mixed powder was coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt. The mass ratio of the inorganic salt powder system to the organosilicon solution was 4:6. 76 parts by mass of the pretreated water-soluble inorganic salt, 22.4 parts by mass of the methylcellulose aqueous solution, 1.5 parts by mass of ammonium polyacrylate, and 0.1 parts by mass of a defoamer were mixed and stirred in a container to obtain a premix. The premix was transferred to a ball mill, ball milling beads were added, and the mixture was milled in a spherical ball mill for 13 hours. A uniformly dispersed salt-based slurry was obtained after removal.

[0100] Printing parameters were set on the computer slicing software controlling the slurry direct writing machine: 100% infill, 600 mm / min print speed, and a 0° / 90° composite fill angle. The milled salt-based slurry was loaded into the extruder barrel, and a 0.41 mm extruder head was used for printing at a pressure of 20 psi. The printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate, air-dried for 24 hours, and then transferred to a drying oven at 70°C for 24 hours.

[0101] The dried green body is sintered in a high-temperature sintering furnace. The sintering program is set on the control panel of the high-temperature sintering furnace: starting from room temperature, heat at a heating rate of 1°C / min to 360°C and hold for 60 minutes; then heat at a heating rate of 3°C / min to 770°C and hold for 60 minutes; then heat at a heating rate of 5°C / min to 790°C and hold for 30 minutes; then cool to 770°C and hold for 60 minutes; and finally cool to room temperature in the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0102] <Example 4>

[0103] The interfacial binding energy of NaCl(100) / KCl(101) was calculated to be 0.05 J / m by first principle. 2 , a water-soluble composite salt core was prepared using NaCl-KCl as the matrix material.

[0104] A method for preparing a water-soluble composite salt core by 3D printing of a slurry for low-melting-point alloy casting comprises the following steps:

[0105] A 3% epoxy resin aqueous solution was prepared using deionized water. Sodium chloride (D50 = 10 μm) and potassium chloride (D50 = 5 μm) were mixed in a ratio of 50 mol% NaCl to 50 mol% KCl. The mixed powder was coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt. The mass ratio of the inorganic salt powder system to the organosilicon solution was 4:6. 73 parts by mass of the pretreated water-soluble inorganic salt, 25.9 parts by mass of the epoxy resin aqueous solution, 1 part by mass of ammonium polyacrylate, and 0.1 parts by mass of a defoamer were mixed and stirred in a container to obtain a premix. The premix was transferred to a ball mill, ball milling beads were added, and the mixture was milled in a spherical ball mill for 13 hours. A uniformly dispersed salt-based slurry was obtained after removal.

[0106] Printing parameters were set on the computer slicing software controlling the slurry direct writing machine: 100% fill rate, 600 mm / min print speed, and a 45° / -45° composite fill angle. The milled salt-based slurry was loaded into the extruder barrel, and a 0.51 mm extruder head was used for printing. The extrusion pressure was set to 15 psi, and the printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate, air-dried for 24 hours, and then transferred to a drying oven at 70°C for 24 hours.

[0107] The dried green body is sintered in a high-temperature sintering furnace. The sintering program is set on the control panel of the high-temperature sintering furnace: starting from room temperature, heat at a heating rate of 1°C / min to 360°C and hold for 60 minutes; then heat at a heating rate of 3°C / min to 660°C and hold for 60 minutes; then heat at a heating rate of 5°C / min to 680°C and hold for 30 minutes; then cool to 660°C and hold for 60 minutes; finally, cool to room temperature in the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0108] <Example 5>

[0109] The interfacial binding energy of NaCl(100) / Na2CO3(100) / MgCl2(100) was calculated to be 14.03 J / m by first principle calculation. 2 , a water-soluble composite salt core was prepared using NaCl-Na2CO3-MgCl2 as the matrix material.

[0110] A method for preparing a water-soluble composite salt core by 3D printing of a slurry for low-melting-point alloy casting comprises the following steps:

[0111] A 12.5% ​​polyvinylpyrrolidone solution was prepared in anhydrous ethanol. Sodium chloride (D50 = 10 μm), sodium carbonate (D50 = 6.5 μm), and magnesium chloride (D50 = 5 μm) were mixed in a ratio of 25 mol% NaCl, 58 mol% Na₂CO₃, and 17 mol% MgCl₂. The mixed powder was coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt. The mass ratio of the inorganic salt powder to the organosilicon solution was 5:5. 71 parts by mass of the pretreated water-soluble inorganic salt, 27.9 parts by mass of the polyvinylpyrrolidone solution, 1 part by mass of ammonium polyacrylate, and 0.1 part by mass of a defoamer were mixed and stirred in a container to obtain a premix. The premix was transferred to a ball mill, ball milling beads were added, and the mixture was milled in a spherical ball mill for 13 hours. A uniformly dispersed salt-based slurry was obtained after removal.

[0112] Printing parameters were set on the computer slicing software controlling the slurry direct writing machine: 100% fill rate, 600 mm / min print speed, and a 45° / -45° composite fill angle. The milled salt-based slurry was loaded into the extruder barrel, and a 0.61 mm extruder head was used for printing. The extrusion pressure was 40 psi, and the printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate, air-dried for 24 hours, and then transferred to a drying oven at 70°C for 24 hours.

[0113] The dried green body is sintered in a high-temperature sintering furnace. The sintering program is set on the control panel of the high-temperature sintering furnace: starting from room temperature, heat at a heating rate of 1°C / min to 360°C and hold for 60 minutes; then heat at a heating rate of 3°C / min to 420°C and hold for 60 minutes; then heat at a heating rate of 5°C / min to 450°C and hold for 30 minutes; then cool to 420°C and hold for 60 minutes; and finally cool to room temperature in the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0114] <Example 6>

[0115] The interfacial binding energy of NaCl(100) / Na2CO3(100) / CaCl2(110) was calculated to be 16.06 J / m by first principle. 2 , a water-soluble composite salt core was prepared using NaCl-Na2CO3-CaCl2 as the matrix material.

[0116] A method for preparing a water-soluble composite salt core by 3D printing of a slurry for low-melting-point alloy casting comprises the following steps:

[0117] A 12.5% ​​polyvinylpyrrolidone solution was prepared in anhydrous ethanol. Sodium chloride (D50 = 10 μm), sodium carbonate (D50 = 6.5 μm), and calcium chloride (D50 = 5 μm) were mixed uniformly in a ratio of 25 mol% NaCl, 58 mol% Na₂CO₃, and 17 mol% BaCl₂. The mixed powder was coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt. The mass ratio of the inorganic salt powder to the organosilicon solution was 5:5. 71 parts by mass of the pretreated water-soluble inorganic salt, 27.9 parts by mass of the polyvinylpyrrolidone solution, 1 part by mass of ammonium polyacrylate, and 0.1 part by mass of a defoamer were mixed and stirred in a container to obtain a premix. The premix was transferred to a ball mill, ball milling beads were added, and the mixture was milled in a spherical ball mill for 13 hours. A uniformly dispersed salt-based slurry was obtained after removal.

[0118] Printing parameters were set on the computer slicing software controlling the slurry direct writing machine: 100% fill rate, 600 mm / min print speed, and a 45° / -45° composite fill angle. The milled salt-based slurry was loaded into the extruder barrel, and a 0.84 mm extruder head was used for printing at a pressure of 40 psi. The printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate, air-dried for 24 hours, and then transferred to a drying oven at 70°C for 24 hours.

[0119] The dried green body is sintered in a high-temperature sintering furnace. The sintering program is set on the control panel of the high-temperature sintering furnace: starting from room temperature, heat at a heating rate of 1°C / min to 360°C and hold for 60 minutes; then heat at a heating rate of 3°C / min to 600°C and hold for 60 minutes; then heat at a heating rate of 5°C / min to 630°C and hold for 30 minutes; then cool to 600°C and hold for 60 minutes; finally, cool to room temperature in the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0120] <Example 7>

[0121] The interfacial binding energy of NaCl / Na2CO3 / BaCl2 was found to be 37 J / m by first principle calculations. 2 , a water-soluble composite salt core was prepared using NaCl-Na2CO3-BaCl2 as the matrix material.

[0122] A method for preparing a water-soluble composite salt core by 3D printing of a slurry for low-melting-point alloy casting comprises the following steps:

[0123] A 12.5% ​​polyvinylpyrrolidone solution was prepared in anhydrous ethanol. Sodium chloride (D50 = 10 μm), sodium carbonate (D50 = 6.5 μm), and barium chloride (D50 = 5 μm) were mixed uniformly in a ratio of 25 mol% NaCl, 58 mol% Na₂CO₃, and 17 mol% BaCl₂. The mixed powder was coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt. The mass ratio of the inorganic salt powder to the organosilicon solution was 5:5. 68 parts by mass of the pretreated water-soluble inorganic salt, 30.9 parts by mass of the polyvinylpyrrolidone solution, 1 part by mass of ammonium polyacrylate, and 0.1 part by mass of a defoamer were mixed and stirred in a container to obtain a premix. The premix was transferred to a ball mill, ball milling beads were added, and the mixture was milled in a spherical ball mill for 13 hours. A uniformly dispersed salt-based slurry was obtained after removal.

[0124] Printing parameters were set on the computer slicing software controlling the slurry direct writing machine: 100% fill rate, 600 mm / min print speed, and a 45° / -45° composite fill angle. The milled salt-based slurry was loaded into the extruder barrel, and a 0.51 mm extruder head was used for printing at a pressure of 30 psi. The printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate, air-dried for 24 hours, and then transferred to a drying oven at 70°C for 24 hours.

[0125] The dried green body is sintered in a high-temperature sintering furnace. The sintering program is set on the control panel of the high-temperature sintering furnace: starting from room temperature, heat at a heating rate of 1°C / min to 360°C and hold for 60 minutes; then heat at a heating rate of 3°C / min to 600°C and hold for 60 minutes; then heat at a heating rate of 5°C / min to 630°C and hold for 30 minutes; then cool to 600°C and hold for 60 minutes; finally, cool to room temperature in the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0126] <Example 8>

[0127] The interfacial binding energy of NaCl / Na2CO3 / BaCl2 was found to be 37 J / m by first principle calculations. 2 , NaCl-Na2CO3-BaCl2 is used as the matrix material to prepare the water-soluble composite salt core, and graphite powder is used as the matrix material to prepare the supporting material of the water-soluble composite salt core.

[0128] A method for preparing a water-soluble composite salt core by direct writing 3D printing of a slurry for low-melting-point alloy casting comprises the following steps:

[0129] A 12.5% ​​polyvinylpyrrolidone solution was prepared in anhydrous ethanol. Sodium chloride (D50 = 10 μm), sodium carbonate (D50 = 6.5 μm), and barium chloride (D50 = 5 μm) were mixed uniformly in a ratio of 25 mol% NaCl, 58 mol% Na₂CO₃, and 17 mol% BaCl₂. The mixed powder was coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt. 68 parts by mass of the pretreated water-soluble inorganic salt, 30.9 parts by mass of the polyvinylpyrrolidone solution, 1 part by mass of ammonium polyacrylate, and 0.1 part by mass of a defoamer were mixed and stirred in a container to obtain a premixed solution. The premixed solution was transferred to a ball mill, ball milling beads were added, and the mixture was milled in a spherical ball mill for 13 hours. A uniformly dispersed salt-based slurry was obtained after removal.

[0130] Graphite powder (D50 = 5μm) was coated with an organosilicon solution to obtain pretreated graphite powder. The mass ratio of graphite powder to organosilicon solution was 6:4. 72 parts by mass of pretreated graphite powder, 26.9 parts by mass of polyvinyl pyrrolidone solution, 1 part by mass of ammonium polyacrylate, and 0.1 parts by mass of a defoamer were mixed and stirred in a container to obtain a premixed graphite slurry. The premixed graphite slurry was transferred to a ball mill, ball milling beads were added, and the slurry was milled in a spherical ball mill for 13 hours. After removal, a uniformly dispersed graphite-based slurry was obtained.

[0131] The printing parameters were set in the host computer slicing software of the dual-extruder 3D printing device: 100% infill, 600 mm / min print speed, and a 45° / -45° composite infill angle. The uniformly stirred salt-based slurry and graphite-based slurry were loaded into two extruder barrels, respectively. A 0.61 mm extruder was used for printing, and the extrusion pressure was 30 psi. The printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate, air-dried for 24 hours, and then transferred to a drying oven at 70°C for 24 hours.

[0132] The dried green body is sintered in a high-temperature sintering furnace. The sintering program is set on the control panel of the high-temperature sintering furnace: starting from room temperature, heat at a heating rate of 1°C / min to 360°C and hold for 60 minutes; then heat at a heating rate of 3°C / min to 600°C and hold for 60 minutes; then heat at a heating rate of 5°C / min to 630°C and hold for 30 minutes; then cool to 600°C and hold for 60 minutes; finally, cool to room temperature in the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0133] Comparative Example 1

[0134] Sodium chloride (D50 = 10 μm) and sodium carbonate (D50 = 6.5 μm) were mixed in a ratio of 30 mol% NaCl to 70 mol% Na2CO3 to obtain an inorganic salt powder system;

[0135] Prepare a 12.5% ​​polyvinyl pyrrolidone solution in anhydrous ethanol. Mix the inorganic salt powder system and the polyvinyl pyrrolidone solution in a mass ratio of 8:2 to obtain a mixed slurry. Slowly pour the mixed slurry into a mold, let it stand for a while, and after the slurry solidifies and forms, remove it from the mold to obtain a wet blank.

[0136] The wet blank was placed in a drying oven and dried at 80°C for 12 hours to obtain a dry blank. The dry blank was then sintered in a step-by-step sintering process to obtain a sintered body. The specific sintering steps were as follows: first, heating from room temperature to 200°C at a heating rate of 1°C / min, then heating from 200°C to 300°C at a heating rate of 0.5°C / min, then heating from 300°C to 360°C at a heating rate of 0.75°C / min, and holding at 360°C for 60 minutes; then heating at a heating rate of 3°C / min to 600°C and holding for 60 minutes; then heating at a heating rate of 5°C / min to 620°C and holding for 30 minutes; then cooling to 600°C and holding for 60 minutes; and finally cooling to room temperature in the furnace. After sintering, the final water-soluble composite salt core product was obtained.

[0137] The performance tests of the water-soluble composite salt cores prepared in Examples 1-8 were performed, and the results are shown in Table 7:

[0138] Table 7 Experimental data of water-soluble composite salt core

[0139]

[0140] In summary, Examples 1-8 are water-soluble composite salt cores prepared by the present invention. Compared with the water-soluble composite salt core material prepared in Comparative Example 1, the water-soluble composite salt cores of Examples 1-8 have good bending strength, high surface quality, excellent water solubility rate and low moisture absorption rate, and have excellent comprehensive performance, which can meet the process requirements of precision casting of complex parts.

[0141] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A water-soluble composite salt core material for low melting point alloy casting, characterized in that: It is composed of the following components: Pre-treating water-soluble inorganic salts, binders and additives, wherein the pre-treated water-soluble inorganic salts are obtained by mixing a coating solution with inorganic salt powder, and the weight percentage of the pre-treated water-soluble inorganic salts: binder: additives = 60%-80%: 20%-30%: 0%-10%; The mass percentage of the inorganic salt powder and the coating solution is 40%-60%: 40%-60%; The inorganic salt powder includes two or more of sodium sulfate, potassium sulfate, sodium carbonate, potassium carbonate, calcium carbonate, sodium chloride, potassium chloride, magnesium chloride, calcium chloride or barium chloride, and the melting point of the inorganic salt powder is 450-1200° C.; The particle size of the inorganic salt powder is 500-3000 mesh; The coating solution is prepared from polydimethylsiloxane and anhydrous ethanol; The binder is one of polyvinyl alcohol aqueous solution, polyethylene glycol aqueous solution, polyacrylamide aqueous solution, methyl cellulose aqueous solution, epoxy resin aqueous solution, polyvinyl pyrrolidone-anhydrous ethanol solution, and polyacrylic acid-anhydrous ethanol; The additive is a mixture of an enhancer, a dispersant and a defoamer, and the ratio by mass percentage is as follows: enhancer: dispersant: defoamer = 97.5%-99.5%: 0.5%-1.5%: 0%-1%; The reinforcing agent is one or more of bauxite powder, corundum powder, mullite powder, zirconium oxide powder, quartz powder, titanium oxide powder, sericite or glass fiber; The dispersant is one of ammonium polyacrylate or sodium dodecylbenzene sulfonate; The defoaming agent is a silicone defoaming agent.

2. The water-soluble composite salt core material according to claim 1, wherein The concentration of the binder solution is 1% to 25%.

3. The water-soluble composite salt core material according to claim 1, wherein The particle size of the reinforcing agent is 300-1250 meshes.

4. A method for preparing a water-soluble composite salt core by direct writing 3D printing of a slurry for low melting point alloy casting, characterized in that: The specific steps include: S1. 3D printing of the salt core blank: preparing salt-based raw materials, grinding the salt-based raw materials sufficiently to obtain salt-based slurry, and using slurry direct writing equipment to 3D print the salt-based slurry to obtain the salt core blank; Wherein, the salt-based raw material is the water-soluble composite salt core material according to any one of claims 1 to 3; The inner diameter of the printing needle is 0.41mm~1.55mm, and the extrusion pressure is 5psi~50psi; S2. Sintering of the water-soluble composite salt core: The salt core green body is subjected to natural drying, oven drying and sintering treatments in sequence to obtain the water-soluble composite salt core.

5. The method according to claim 4, wherein In step S1, when the salt-based raw material is a water-soluble composite salt core material, the preparation method of the salt-based slurry is: The inorganic salt powder is coated with a coating solution to obtain a pretreated water-soluble inorganic salt, and the pretreated water-soluble inorganic salt, the binder solution and the additive are uniformly mixed to obtain a premixed solution, wherein the additive is a mixture of a reinforcing agent, a dispersant and a defoaming agent, and the mass percentage of each component is as follows: Pretreatment water-soluble inorganic salt: binder: additive = 60%-80%: 20%-30%: 0%-10%.

6. The method according to claim 5, wherein In step S1, it also includes using graphite powder as a matrix material to prepare a supporting material for the water-soluble composite salt core. The matrix material is a mixture of graphite powder, a binder and a dispersant. In the mixture, the mass percentages of graphite powder, binder and dispersant are 70%-75%: 24%-29.5%: 0.5%-1%, calculated by mass percentage.

7. The method according to claim 6, wherein and: The dispersant is one of ammonium polyacrylate or sodium dodecylbenzene sulfonate; The binder is one of polyvinyl alcohol aqueous solution, polyethylene glycol aqueous solution, polyacrylamide aqueous solution, methyl cellulose aqueous solution, epoxy resin aqueous solution, polyvinyl pyrrolidone-anhydrous ethanol solution, and polyacrylic acid-anhydrous ethanol.

8. The method according to claim 6, wherein In step S2, the drying temperature is 40°C to 90°C, and the drying time is 12 hours to 24 hours. The sintering is carried out by combining step-by-step sintering and liquid phase sintering, and the final sintering temperature is 450 to 1200°C.

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