A method for preparing water-soluble composite salt core based on hot melt extrusion 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 hot melt extrusion direct writing 3D printing technology. A water-soluble composite salt core material is composed of the following components: pre-treated water-soluble inorganic salt, binder and reinforcing agent, and in terms of mass percentage, pre-treated water-soluble inorganic salt: binder: reinforcing agent = 50%-70%: 20%-50%: 0%-10%. The water-soluble composite salt core prepared by the present invention can achieve rapid moldless forming, and by adjusting the proportion of each material in the slurry, the shrinkage rate, flexural strength, water solubility rate, moisture absorption rate and other properties of the water-soluble salt core can be comprehensively regulated. In addition, the raw materials used in the present invention are low in price, the equipment cost is low, the process is simple and green and environmentally friendly, which can promote the development of green manufacturing.

Description

Technical Field

[0001] 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 hot melt extrusion direct writing 3D printing technology. Background Art

[0002] With the rapid development of my country's aviation, aerospace, automotive manufacturing, and 5G communications sectors, demand for complex, thin-walled precision castings made of low-melting-point alloys such as aluminum and magnesium is increasing. These castings often have complex internal cavities, some of which are largely closed or have numerous elongated, curved channels of varying shapes. These complex internal structures require the use of prefabricated cores for casting, and the removal of the cores after the casting is formed. This creates high-quality precision castings, placing higher demands on the performance of the casting cores and their forming and cleaning methods.

[0003] Casting cores must have high room temperature strength and dimensional accuracy, good high temperature stability and air permeability, small gas emission, and excellent post-casting disintegration and cleaning properties; currently commonly used casting core materials such as resin sand cores, silica and alumina-based ceramic cores cannot meet the above performance requirements at the same time, and all require the use of mixed alkali method, alkali solution method, pressure de-coring method and hydrofluoric acid method to clean the residual cores in the inner cavity of the casting and the curved channels. It is very difficult to clean the residual cores in the nearly closed inner cavity of the casting. Among the above core cleaning methods, some will corrode the casting, some will produce toxic substances that pollute the environment, and some have complex de-coring processes and require special equipment (such as pressure de-coring method). Water-soluble salt core technology can solve the problem of cleaning casting core materials very well. After the casting is formed, the residual core can be quickly cleaned by dissolving it with water, which can save labor and improve the working environment.

[0004] At present, 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 forming. The melt casting method requires block forming and assembly through a mold, 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 a low water solubility rate. 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 of low-melting-point alloy castings such as aluminum (magnesium).

[0005] CN 104399865A discloses a water-soluble graphite composite salt core material, a graphite composite salt core, and a preparation method thereof, which are mainly used in aluminum piston internal cooling oil channel casting. The graphite composite salt core material includes 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 prepared by this method has high strength and low shrinkage, but the graphite powder and metal halide are easily mixed unevenly, resulting in stratification of the salt core, which affects the performance of the salt core.

[0006] CN 106670376A discloses a high-strength composite salt core for casting low-melting-point alloys. The components of its water-soluble salt core include water-soluble inorganic salts and reinforcing agents, wherein the inorganic salts include a 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 includes one or more of dalin sand, refractory mud powder, glass fiber powder, kaolin, quartz powder, bentonite, alumina powder, and high-alumina bauxite. The salt core is prepared by a melt casting method, and the prepared salt core has high strength and low moisture absorption rate. However, the low-melting-point salt determines the melting point of the entire salt core, so the salt core is only suitable for casting low-melting-point alloys and cannot meet the casting requirements of low-melting-point alloys such as aluminum (magnesium).

[0007] 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.

[0008] The preparation method of the above-mentioned water-soluble salt core includes 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 method of the salt core, and the search for a more complete preparation solution. Summary of the Invention

[0009] In response to the shortcomings of existing technologies and the need for improvement, the present invention provides a method for preparing water-soluble composite salt cores based on hot-melt extrusion 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 collaboratively controlling parameters such as the salt core material composition, heating temperature, extrusion direct writing 3D printing forming, and a step-by-step sintering process, complex structures such as irregularly shaped holes and runners can be directly formed as a whole, avoiding the precision errors caused by core assembly. This method has great 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.

[0010] A water-soluble composite salt core material, consisting of the following components:

[0011] The water-soluble inorganic salt, the binder and the reinforcing agent are pretreated, and the weight percentage is as follows: the pretreated water-soluble inorganic salt: the binder: the reinforcing agent = 50%-70%: 20%-50%: 0%-10%.

[0012] Furthermore, the pre-treated water-soluble inorganic salt is obtained by mixing a coating solution with an inorganic salt powder system, and the ratio of water-soluble inorganic salt to coating solution is 40%-60%: 40%-60% by mass percentage;

[0013] The inorganic salt powder system is at least two of sodium sulfate, potassium sulfate, sodium carbonate, potassium carbonate, calcium carbonate, sodium chloride, potassium chloride, magnesium chloride, calcium chloride or barium chloride;

[0014] The inorganic salt powder system has a melting point of 450-1200°C and a particle size of 500-3000 mesh;

[0015] The coating solution is prepared from polydimethylsiloxane and anhydrous ethanol.

[0016] Furthermore, the binder is one of carrageenan solution, starch solution, xanthan gum solution, sodium alginate solution, konjac gum solution, sodium carboxymethyl cellulose solution and agar solution, and the concentration of the binder is 0.1% to 15%.

[0017] Furthermore, 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 meshes.

[0018] A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology specifically comprises the following steps:

[0019] S1. 3D printing of the salt core blank: preparing a salt-based slurry, and 3D printing the salt-based slurry using a heatable direct-write 3D printing device at a temperature of 25°C to 220°C to obtain a salt core blank;

[0020] Wherein, the salt-based slurry is the above-mentioned water-soluble composite inorganic salt material or binder;

[0021] S2. Sintering of the water-soluble composite salt core: After the salt core green body is naturally dried, it is transferred to a high-temperature sintering furnace for sintering to obtain the water-soluble composite salt core.

[0022] Furthermore, in step S1, when the salt-based slurry is a water-soluble composite inorganic salt material, the preparation method of the salt-based slurry is:

[0023] The inorganic salt powder system is coated with a coating solution to obtain a pretreated water-soluble inorganic salt, the pretreated water-soluble inorganic salt and a reinforcing agent are mixed evenly in proportion to obtain a mixed powder, a binder is added to the mixed powder, and the mixture is heated and stirred to obtain a uniformly mixed salt-based slurry; in terms of mass percentage, the pretreated water-soluble inorganic salt: binder: reinforcing agent = 50%-70%: 20%-50%: 0%-10%.

[0024] Furthermore, in step S1, when the salt-based slurry is used as the binder, graphite powder is added to the binder, and the ratio by mass percentage is graphite powder: binder = 60%-70%: 30%-40%.

[0025] Furthermore, the binder in the salt-based slurry and the binder in the water-soluble composite inorganic salt material are both one of carrageenan solution, starch solution, xanthan gum solution, sodium alginate solution, konjac gum solution, sodium carboxymethyl cellulose solution and agar solution, and the concentration of the binder is 0.1% to 15%.

[0026] Furthermore, in step S2, the sintering is carried out by combining step-by-step sintering and liquid phase sintering, and the final sintering temperature is 450° C. to 1200° C.;

[0027] The specific sintering steps are as follows: first, heating 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, and then heating from 300°C to 360°C at a heating rate of 0.75°C / min, and keeping at 360°C for 60 minutes to remove the binder, dispersant and defoamer in the green body; then heating at a heating rate of 1-3°C / min, keeping at 5-30°C away from the final firing temperature for 30-60 minutes; then heating to the final firing temperature at a heating rate of 5°C / min, and keeping at this temperature for 10-30 minutes; then cooling to 5-30°C below the final firing temperature, and continuing to keep this temperature for 30-60 minutes; finally, cooling to room temperature with the furnace.

[0028] Furthermore, in step S2, the inner diameter of the printing needle is 0.61 mm to 3.8 mm, and the extrusion air pressure is 10 psi to 60 psi.

[0029] 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:

[0030] (1) Compared with the traditional method of preparing water-soluble salt cores, the advantage of hot melt extrusion 3D printing technology in preparing water-soluble salt cores is that it can quickly form parts without a mold, and the process is simple, the raw material cost is low, and the equipment requirements are low. It can achieve rapid and precise moldless forming of high-precision complex salt cores, obtain salt cores with complete structure, dense organization, and high precision, and solve the problem of difficult overall forming of complex salt cores.

[0031] (2) In order to solve the problem that the bending strength and impact toughness of the existing salt core are difficult to improve 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.

[0032] (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.

[0033] (4) The salt-based slurry prepared with a heat-fusible binder does not require ball milling, and the green body can be transferred to a high-temperature sintering furnace for sintering in a short time after being formed, which shortens the production cycle to a certain extent.

[0034] (5) By adjusting the solid content of the slurry (by adjusting the mass proportion of the inorganic salt powder in the total slurry), the surface accuracy, bending strength and linear shrinkage of the salt core can be controlled. 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 regulated.

[0035] (6) 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

[0036] Figure 1 This is a flow chart of the preparation process of the water-soluble composite salt core of the present invention. DETAILED DESCRIPTION

[0037] 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.

[0038] The physical and chemical parameters of the sodium chloride powder used in the present invention are shown in Table 1:

[0039] Table 1

[0040]

[0041] The physical and chemical parameters of the sodium carbonate powder used in the present invention are shown in Table 2:

[0042] Table 2

[0043]

[0044] The physicochemical parameters of the potassium carbonate powder used in the present invention are shown in Table 3:

[0045] Table 3

[0046]

[0047] The physical and chemical parameters of the calcium carbonate powder used in the present invention are shown in Table 4:

[0048]

[0049] Table 4 The physicochemical parameters of the potassium chloride powder used in the present invention are shown in Table 5:

[0050] Table 5

[0051]

[0052] The physical and chemical parameters of the magnesium chloride powder used in the present invention are shown in Table 6:

[0053] Table 6

[0054]

[0055] The physical and chemical parameters of the calcium chloride powder used in the present invention are shown in Table 7:

[0056] Table 7

[0057]

[0058] The physical and chemical parameters of the barium chloride powder used in the present invention are shown in Table 8:

[0059] Table 8

[0060]

[0061] The physical and chemical parameters of the bauxite powder used in the present invention are shown in Table 9:

[0062] Table 9

[0063]

[0064]

[0065] The physical and chemical parameters of the glass fiber used in the present invention are shown in Table 10:

[0066] Table 10

[0067]

[0068] The physical and chemical parameters of the mullite powder used in the present invention are shown in Table 11:

[0069] Table 11

[0070]

[0071] The physical and chemical parameters of the sericite used in the present invention are shown in Table 12:

[0072] Table 12

[0073]

[0074] The present invention is to protect a water-soluble composite salt core material, which is composed of the following components:

[0075] The water-soluble inorganic salt, the binder and the reinforcing agent are pretreated, and the weight percentage is as follows: the pretreated water-soluble inorganic salt: the binder: the reinforcing agent = 50%-70%: 20%-50%: 0%-10%.

[0076] Wherein, pretreatment water-soluble inorganic salt is mixed with inorganic salt powder system by coating solution, and in mass percentage, water-soluble inorganic salt: coating solution=40%-60%:40%-60%, inorganic salt powder system is at least two of sodium sulfate, potassium sulfate, sodium carbonate, potassium carbonate, calcium carbonate, sodium chloride, potassium chloride, magnesium chloride, calcium chloride or barium chloride, the fusing point of inorganic salt powder system is 450-1200 ℃, and granularity is 500-3000 mesh; described coating solution is non-aqueous coating, is preferably organosilicon solution, and organosilicon solution is prepared by polydimethylsiloxane and dehydrated alcohol, and concentration is 50wt.%; described binding agent is one of carrageenan solution, starch solution, xanthan gum solution, sodium alginate solution, konjac gum solution, sodium carboxymethyl cellulose solution and agar solution, and the concentration of described binding agent is 0.1%~15%, and solvent is water. 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 meshes.

[0077] The present invention also protects a method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology, which specifically includes the following steps:

[0078] (1) Preparation of salt-based slurry

[0079] The salt-based slurry is the above-mentioned water-soluble composite inorganic salt material or binder, and:

[0080] When the salt-based slurry is the above-mentioned water-soluble composite inorganic salt material, the preparation method of the water-soluble composite inorganic salt material is:

[0081] Two or more inorganic salt powders are coated with a coating solution to produce a pretreated water-soluble inorganic salt. The pretreated water-soluble inorganic salt and a reinforcing agent are mixed in appropriate proportions to produce a mixed powder. The mixed powder is added to the binder solution in small amounts and repeatedly while heating and stirring to produce a uniformly mixed salt-based slurry. The preferred weight percentages of the components are as follows: 50%-70% pretreated water-soluble inorganic salt, 20%-50% binder, and 0%-10% reinforcing agent.

[0082] When the salt-based slurry is used as the binder, graphite powder is added to the binder as a supporting material, and the mass percentage is graphite powder: binder = 60%-70%: 30%-40%.

[0083] (2) 3D printing of salt core blanks

[0084] While hot, the salt-based slurry is loaded into the extruder barrel of a heatable direct-write 3D printer. Temperature control, the extruder's trajectory, and the extrusion state are controlled by host computer slicing software. The salt-based slurry is deposited onto a substrate along a predetermined path to form a salt core blank. The extruder barrel's temperature is controlled within a range of 25°C to 220°C. After heating to the desired temperature until the material is completely molten (if heating is not required, the temperature can be set to 25°C). The blank is then printed by adjusting the printing parameters. For the direct-write process of the salt core blank, the preferred forming process parameters are as follows: a needle inner diameter of 0.61mm to 3.8mm, and an extrusion pressure of 10psi to 60psi. Heatable direct-write 3D printers are prior art. For example, the 3D printer described in Patent No. CN202311075788.8, entitled "Dual-Head Collaborative Direct-Write 3D Printing Device," can serve as a specific embodiment of the heatable direct-write 3D printer of the present invention.

[0085] (3) Sintering of water-soluble composite salt core

[0086] After 24 hours of natural drying, the salt core green body is transferred to a high-temperature sintering furnace for sintering. It is sintered at a higher temperature for a certain period of time to form better strength and other properties and to play the role of the reinforcing agent in enhancing the green body performance, thereby obtaining a high-strength water-soluble composite salt core.

[0087] The sintering conditions in step (3) are preferably as follows: a combination of step-by-step sintering and liquid phase sintering is used, and the final sintering temperature is 450°C to 1200°C. The specific sintering steps are: 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, and then heating from 300°C to 360°C at a heating rate of 0.75°C / min, and keeping at 360°C 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, keeping at 5-30°C above the final sintering temperature, and keeping at this temperature for 30-60 minutes; then heating to the final sintering temperature at a heating rate of 5°C / min, and keeping at this temperature for 10-30 minutes; then cooling to 5-30°C below the final sintering temperature, and keeping at this temperature for 30-60 minutes; finally cooling to room temperature with the furnace. The purpose of liquid phase sintering is to improve the bending strength of the salt core and avoid over-sintering.

[0088] In the present invention, by using a binder as a salt-based slurry and graphite powder as a supporting material, since graphite powder is easily burned out under sintering conditions of 500-600°C, a water-soluble salt core with a suspended structure can be prepared, which can be used in aluminum alloy components with complex internal structures and suspended channels.

[0089] It should be noted that Examples 1-8 all use a heatable direct-write 3D printing device, the computer-side control software is Simplify 3D slicing software, and the size of the printed body is 60 mm × 10 mm × 6 mm.

[0090] <Example 1>

[0091] The interfacial binding energy of NaCl(100) / Na2CO3(100) was obtained by first principle calculation to be 13.2 J / m 2 , a water-soluble composite salt core was prepared using NaCl-Na2CO3 as the matrix material.

[0092] A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology specifically comprises the following steps:

[0093] Sodium chloride (D50 = 10 μm) and sodium carbonate (D50 = 6.5 μm) are evenly mixed in a ratio of 30 mol% NaCl-70 mol% Na2CO3 to obtain an inorganic salt powder system; the inorganic salt powder system is coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt, wherein the mass ratio of the inorganic salt powder system to the organosilicon solution is 4:6.

[0094] Carrageenan and deionized water were used to prepare a binder solution with a mass fraction of 0.5% under heating conditions of 80°C.

[0095] 62 parts by mass of pretreated water-soluble inorganic salt and 10 parts by mass of bauxite powder were mixed evenly, and added in small amounts and multiple times to the heated and stirred carrageenan solution (28 parts by mass) until the pretreated water-soluble inorganic salt, bauxite powder and carrageenan solution were evenly mixed.

[0096] Printing parameters were set in the host computer slicing software of a heated direct-write 3D printer: barrel heating temperature of 85°C, fill factor of 100%, print speed of 600 mm / min, and fill angle of 23° / -67° composite fill. A well-mixed salt-based slurry was loaded into the extruder barrel. A 0.61mm extruder tip was used for printing, with an extrusion pressure of 10 psi. The printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate and air-dried for 24 hours.

[0097] 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: first, heat from room temperature to 200°C at a heating rate of 1°C / min, then heat from 200°C to 300°C at a heating rate of 0.5°C / min, then heat from 300°C to 360°C at a heating rate of 0.75°C / min, and hold at 360°C 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 with the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0098] <Example 2>

[0099] The interfacial binding energy of NaCl(100) / K2CO3(011) was obtained by first principle calculation to be 1.04 J / m 2 , NaCl / K2CO3 was used as the matrix material to prepare the water-soluble composite salt core.

[0100] A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology specifically comprises the following steps:

[0101] Sodium chloride (D50 = 10 μm) and potassium carbonate (D50 = 5 μm) are evenly mixed in a ratio of 50 mol% NaCl-50 mol% K2CO3, and the inorganic salt powder system is coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt, wherein the mass ratio of the inorganic salt powder system to the organosilicon solution is 4:6.

[0102] A binder solution with a mass fraction of 10% was prepared by using starch and deionized water under a heating condition of 100°C.

[0103] 70 parts by mass of pretreated water-soluble inorganic salt and 5 parts by mass of glass fiber were mixed evenly, and added in small amounts and multiple times to the starch solution (25 parts by mass) that was being heated and stirred until the pretreated water-soluble inorganic salt, glass fiber and starch solution were evenly mixed.

[0104] Printing parameters were set in the host computer slicing software of a heatable direct-write 3D printer: barrel heating temperature of 90°C, fill factor of 100%, print speed of 600 mm / min, and a 45° / -45° composite fill angle. A well-mixed salt-based slurry was loaded into the extruder barrel. A 0.84mm extruder head was used for printing, with an extrusion 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 and air-dried for 24 hours.

[0105] 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: first, heat from room temperature to 200°C at a heating rate of 1°C / min, then heat from 200°C to 300°C at a heating rate of 0.5°C / min, then heat from 300°C to 360°C at a heating rate of 0.75°C / min, and hold at 360°C 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.

[0106] <Example 3>

[0107] 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.

[0108] A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology specifically comprises the following steps:

[0109] Sodium chloride (D50 = 10 μm) and calcium carbonate (D50 = 5 μm) are uniformly mixed in a ratio of 60 mol% NaCl-40 mol% CaCO3, and the mixed powder is coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt, wherein the mass ratio of the inorganic salt powder system to the organosilicon solution is 4:6.

[0110] Agar and deionized water were used to prepare a binder solution with a mass fraction of 1% under heating conditions of 80°C.

[0111] 66 parts by mass of pretreated water-soluble inorganic salt and 2 parts by mass of mullite powder were mixed evenly, and added in small amounts to the heated and stirred agar solution (32 parts by mass) until the pretreated water-soluble inorganic salt, mullite powder and agar solution were evenly mixed.

[0112] Printing parameters were set in the host computer slicing software of a heatable direct-write 3D printer: barrel heating temperature 80°C, fill factor 100%, print speed 600 mm / min, and a 0° / 90° composite fill angle. A well-mixed salt-based slurry was loaded into the extruder barrel. A 0.61mm extruder head was used for printing, with an extrusion 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 and air-dried 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: first, heat from room temperature to 200°C at a heating rate of 1°C / min, then heat from 200°C to 300°C at a heating rate of 0.5°C / min, then heat from 300°C to 360°C at a heating rate of 0.75°C / min, and hold at 360°C 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; finally, cool to room temperature in the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0114] <Example 4>

[0115] 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.

[0116] A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology specifically comprises the following steps:

[0117] Sodium chloride (D50 = 10 μm) and potassium chloride (D50 = 5 μm) are uniformly mixed in a ratio of 50 mol% NaCl to 50 mol% KCl, and the mixed powder is coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt, wherein the mass ratio of the inorganic salt powder system to the organosilicon solution is 4:6.

[0118] Konjac gum and deionized water were used to prepare a binder solution with a mass fraction of 5% under a heating condition of 90°C.

[0119] 67 parts by mass of pretreated water-soluble inorganic salt and 8 parts by mass of sericite were mixed evenly, and added in small amounts to the heated and stirred konjac gum solution (25 parts by mass) until the pretreated water-soluble inorganic salt, sericite and konjac gum solution were evenly mixed.

[0120] Printing parameters were set in the host computer slicing software of a heatable direct-write 3D printer: barrel heating temperature of 90°C, fill factor of 100%, print speed of 600 mm / min, and a 45° / -45° composite fill angle. A well-mixed salt-based slurry was loaded into the extruder barrel. A 0.84mm extruder head was used for printing, with an extrusion 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 and air-dried for 24 hours.

[0121] 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: first, heat from room temperature to 200°C at a heating rate of 1°C / min, then heat from 200°C to 300°C at a heating rate of 0.5°C / min, then heat from 300°C to 360°C at a heating rate of 0.75°C / min, and hold at 360°C 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.

[0122] <Example 5>

[0123] 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.

[0124] A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology specifically comprises the following steps:

[0125] Sodium chloride (D50 = 10 μm), sodium carbonate (D50 = 6.5 μm), and magnesium chloride (D50 = 5 μm) are uniformly mixed in a ratio of 25 mol% NaCl-58 mol% Na2CO3-17 mol% MgCl2, and the mixed powder is coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt, wherein the mass ratio of the inorganic salt powder system and the organosilicon solution is 5:5.

[0126] Carrageenan and deionized water were used to prepare a binder solution with a mass fraction of 0.5% under heating conditions of 80°C.

[0127] 68 parts by mass of pretreated water-soluble inorganic salt and 8 parts by mass of bauxite powder were mixed evenly, and added in small amounts and multiple times to the carrageenan solution (24 parts by mass) that was being heated and stirred until the pretreated water-soluble inorganic salt, bauxite powder and carrageenan solution were evenly mixed.

[0128] Printing parameters were set in the host computer slicing software for a heated direct-write 3D printer: barrel heating temperature of 80°C, fill factor of 100%, print speed of 600 mm / min, and a 45° / -45° composite fill angle. A well-mixed salt-based slurry was loaded into the extruder barrel. A 0.61mm extruder tip was used for printing, with an extrusion pressure of 50 psi. The printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate and air-dried for 24 hours.

[0129] 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: first, heat from room temperature to 200°C at a heating rate of 1°C / min, then heat from 200°C to 300°C at a heating rate of 0.5°C / min, then heat from 300°C to 360°C at a heating rate of 0.75°C / min, and hold at 360°C 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; finally, cool to room temperature with the furnace. After sintering, the final water-soluble composite salt core product is obtained.

[0130] <Example 6>

[0131] 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.

[0132] A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology specifically comprises the following steps:

[0133] Sodium chloride (D50 = 10 μm), sodium carbonate (D50 = 6.5 μm), and calcium chloride (D50 = 5 μm) are uniformly mixed in a ratio of 25 mol% NaCl-58 mol% Na2CO3-17 mol% BaCl2, and the mixed powder is coated with an organosilicon solution to obtain a pretreated water-soluble inorganic salt, wherein the mass ratio of the inorganic salt powder system and the organosilicon solution is 5:5.

[0134] Carrageenan and deionized water were used to prepare a binder solution with a mass fraction of 0.5% under heating conditions of 80°C.

[0135] 68 parts by mass of pretreated water-soluble inorganic salt and 8 parts by mass of bauxite powder were mixed evenly, and added in small amounts and multiple times to the carrageenan (24 parts by mass) that was being heated and stirred until the pretreated water-soluble inorganic salt, bauxite powder and carrageenan solution were evenly mixed.

[0136] Printing parameters were set in the host computer slicing software for a heated direct-write 3D printer: barrel heating temperature of 80°C, fill factor of 100%, print speed of 600 mm / min, and a 45° / -45° composite fill angle. A well-mixed salt-based slurry was loaded into the extruder barrel. A 0.61mm extruder tip was used for printing, with an extrusion pressure of 50 psi. The printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate and air-dried for 24 hours.

[0137] 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: first, heat from room temperature to 200°C at a heating rate of 1°C / min, then heat from 200°C to 300°C at a heating rate of 0.5°C / min, then heat from 300°C to 360°C at a heating rate of 0.75°C / min, and hold at 360°C 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.

[0138] <Example 7>

[0139] 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.

[0140] A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology specifically comprises the following steps:

[0141] Sodium chloride (D50 = 10 μm), sodium carbonate (D50 = 6.5 μm), and barium chloride (D50 = 5 μm) were mixed in a ratio of 25 mol% NaCl to 58 mol% Na2CO3 to 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 system to the organosilicon solution was 5:5. A 0.5% binder solution was prepared using carrageenan and deionized water at 80°C. 68 parts by mass of the pretreated water-soluble inorganic salt and 8 parts by mass of bauxite powder were mixed and added in small amounts to the heated and stirred carrageenan solution (24 parts by mass) until the pretreated water-soluble inorganic salt, bauxite powder, and carrageenan solution were evenly mixed.

[0142] Printing parameters were set in the host computer slicing software for a heated direct-write 3D printer: barrel heating temperature of 80°C, fill factor of 100%, print speed of 600 mm / min, and a 45° / -45° composite fill angle. A well-mixed salt-based slurry was loaded into the extruder barrel. A 0.61mm extruder tip was used for printing, with an extrusion pressure of 50 psi. The printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate and air-dried for 24 hours.

[0143] 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: first, heat from room temperature to 200°C at a heating rate of 1°C / min, then heat from 200°C to 300°C at a heating rate of 0.5°C / min, then heat from 300°C to 360°C at a heating rate of 0.75°C / min, and hold at 360°C 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.

[0144] <Example 8>

[0145] 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.

[0146] A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology specifically comprises the following steps:

[0147] Sodium chloride (D50 = 10 μm), sodium carbonate (D50 = 6.5 μm), and barium chloride (D50 = 5 μm) were mixed in a ratio of 25 mol% NaCl to 58 mol% Na2CO3 to 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 system to the organosilicon solution was 5:5. A 0.5% binder solution was prepared using carrageenan and deionized water at 80°C. 68 parts by mass of the pretreated water-soluble inorganic salt and 8 parts by mass of bauxite powder were mixed and added in small amounts to the heated and stirred carrageenan solution (24 parts by mass) until the pretreated water-soluble inorganic salt, bauxite powder, and carrageenan solution were evenly mixed.

[0148] Graphite powder (D50 = 5 μm) was coated with an organosilicon solution to obtain pretreated graphite powder, with a mass ratio of 6:4 between the graphite powder and the organosilicon solution. A 0.5% binder solution was prepared using carrageenan and deionized water at 80°C. 72 parts by mass of the pretreated graphite powder were added to the heated and stirred carrageenan solution (28 parts by mass) in small, repeated additions until the pretreated graphite powder and carrageenan solution were evenly mixed.

[0149] Printing parameters were set in the host computer slicing software of a dual-extruder 3D printing device: barrel heating temperature of 80°C, fill factor of 100%, print speed of 600 mm / min, and a 45° / -45° composite fill angle. A uniformly stirred salt-based slurry and graphite-based slurry were loaded into the two extruder barrels, respectively. A 0.61mm extruder was used for printing, and the extrusion pressure was 50 psi. The printed body was deposited on a substrate pre-coated with dimethyl silicone oil. The body was removed from the substrate and air-dried for 24 hours.

[0150] 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: first, heat from room temperature to 200°C at a heating rate of 1°C / min, then heat from 200°C to 300°C at a heating rate of 0.5°C / min, then heat from 300°C to 360°C at a heating rate of 0.75°C / min, and hold at 360°C 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 with the furnace. After sintering, the final water-soluble composite salt core product with a suspended structure is obtained.

[0151] Comparative Example 1

[0152] Sodium chloride (D50 = 10 μm) and sodium carbonate (D50 = 6.5 μm) were uniformly mixed in a ratio of 30 mol% NaCl to 70 mol% Na2CO3 to obtain an inorganic salt powder system;

[0153] Prepare a 12.5% ​​polyvinyl pyrrolidone solution using 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.

[0154] 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.

[0155] The performance tests of the water-soluble composite salt cores prepared in Examples 1-8 were performed, and the results are shown in Table 13:

[0156]

[0157]

[0158] Table 13 Experimental data of water-soluble composite salt core

[0159] In summary, Examples 1-8 are water-soluble composite salt cores prepared by the present invention, which have excellent bending strength, high surface quality, good 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.

[0160] 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, characterized in that: It is composed of the following components: Pre-treating water-soluble inorganic salts, binders and reinforcing agents, and in terms of mass percentage, pre-treating water-soluble inorganic salts: binder: reinforcing agent = 50%-70%: 20%-50%: 0%-10%; The pre-treated water-soluble inorganic salt is obtained by mixing the coating solution with the inorganic salt powder system, and the mass percentage is: the inorganic salt powder system: the coating solution = 40%-60%: 40%-60%; The inorganic salt powder system is at least two of sodium sulfate, potassium sulfate, sodium carbonate, potassium carbonate, calcium carbonate, sodium chloride, potassium chloride, magnesium chloride, calcium chloride or barium chloride; The inorganic salt powder system has a melting point of 450-1200°C and a particle size of 500-3000 mesh; The coating solution is prepared from polydimethylsiloxane and anhydrous ethanol; The binder is one of carrageenan solution, starch solution, xanthan gum solution, sodium alginate solution, konjac gum solution, sodium carboxymethyl cellulose solution and agar solution; 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.

2. The water-soluble composite salt core material according to claim 1, wherein The concentration of the binder is 0.1% to 15%.

3. The water-soluble composite salt core material according to claim 1, wherein The particle size of the enhancer is 300~1250 mesh.

4. A method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology, characterized in that: The specific steps include: S1. 3D printing of the salt core blank: preparing a salt-based slurry, and 3D printing the salt-based slurry using a heatable direct-write 3D printing device at a temperature of 25°C to 220°C to obtain a salt core blank; Wherein, the salt-based slurry is the water-soluble composite salt core material according to any one of claims 1 to 3; S2. Sintering of the water-soluble composite salt core: After the salt core green body is naturally dried, it is transferred to a high-temperature sintering furnace for sintering to obtain the water-soluble composite salt core.

5. The method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology according to claim 4, characterized in that: In step S1, the preparation method of the salt-based slurry is: The inorganic salt powder system is coated with a coating solution to obtain a pretreated water-soluble inorganic salt, the pretreated water-soluble inorganic salt and the reinforcing agent are evenly mixed in proportion to obtain a mixed powder, and then a binder is added to the mixed powder, heated and stirred to obtain a uniformly mixed salt-based slurry; in terms of mass percentage, the pretreated water-soluble inorganic salt: binder: reinforcing agent = 50%-70%: 20%-50%: 0%-10%.

6. The method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology according to claim 5, characterized in that: In step S1, it also includes using graphite powder as a matrix material to prepare a support material for the water-soluble composite salt core. The matrix material is a mixture of a binder and graphite powder, and the mass percentage is graphite powder: binder = 60%-70%: 30%-40%.

7. The method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology according to claim 6, characterized in that: The binder in the salt-based slurry and the binder in the water-soluble composite inorganic salt material are both one of carrageenan solution, starch solution, xanthan gum solution, sodium alginate solution, konjac gum solution, sodium carboxymethyl cellulose solution and agar solution, and the concentration of the binder is 0.1%-15%.

8. The method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology according to claim 6, characterized in that: In step S2, the sintering is carried out by combining step-by-step sintering and liquid phase sintering, and the final sintering temperature is 450°C to 1200°C; The specific sintering steps are as follows: first, heat to 200°C at a heating rate of 1°C / min, then heat from 200°C to 300°C at a heating rate of 0.5°C / min, and then heat from 300°C to 360°C at a heating rate of 0.75°C / min, and keep at 360°C for 60 minutes to remove the binder, dispersant and defoamer in the green body; then heat at a heating rate of 1~3°C / min, and keep at 5~30°C away from the final firing temperature for 30min~60min; then heat to the final firing temperature at a heating rate of 5°C / min, and keep at this temperature for 10min~30min; then cool to 5~30°C below the final firing temperature, and continue to keep at this temperature for 30min~60min; finally, cool to room temperature with the furnace.

9. The method for preparing a water-soluble composite salt core based on hot melt extrusion direct writing 3D printing technology according to claim 6, characterized in that: In step S2 , the inner diameter of the printing needle is 0.61 mm to 3.8 mm, and the extrusion pressure is 10 psi to 60 psi.

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