A method of manufacturing sand / polytetrafluoroethylene composites of arbitrary geometry

Abstract

The application discloses a manufacturing method of sand / polytetrafluoroethylene composite material with an arbitrary geometric configuration. First, raw sand is mixed with a curing agent to obtain a raw sand mixture. Then, through a 3D printing process, the raw sand mixture in a layer-by-layer state is bonded into a whole through a curing reaction of the adhesive to form a raw sand base with an arbitrary geometric configuration. Then, the raw sand base absorbs liquid components until the mass of the raw sand base no longer changes, thereby achieving absorption equilibrium. Finally, the sand mold is subjected to gradient constant temperature treatment, and then is reduced to room temperature to obtain the sand / polytetrafluoroethylene composite material with the arbitrary geometric configuration. The application provides a template for polytetrafluoroethylene forming through 3D printing of a raw sand base with a suitable hole structure, solves the problem of difficult forming of polytetrafluoroethylene-based complex components in combination with subsequent processing procedures, and due to the existence of the sand base, the hardness of the polytetrafluoroethylene-based components is significantly improved, the rigidity is enhanced, the creep resistance is improved, the wear resistance is better, and the dimensional stability is better.

Description

Technical Field

[0001] This invention relates to the field of composite material manufacturing, specifically to a method for manufacturing sand / polytetrafluoroethylene composite materials with arbitrary geometric configurations. Background Technology

[0002] 3D printing, also known as additive manufacturing, is a rapid prototyping technology. It's a technique that uses digital model files as a basis and employs bondable materials such as metals, polymers, and inorganic non-metallic materials to construct objects layer by layer. With the development of 3D printing technology and the improvement of equipment performance, fine sand can be layered and then a special adhesive can be sprayed according to the shape of the part's cross-section using a specially designed nozzle. This allows the sand to be bonded together. By repeatedly laying sand and selectively spraying adhesive, sand molds with complex geometries can be produced. Sand molds printed in this way are mostly used in the casting industry, greatly improving the problems of traditional casting processes being complex, lacking automation, and having low manufacturing precision, bringing benefits to 3D printing sand mold factories.

[0003] To avoid homogeneous competition, some 3D printing sand mold factories have begun exploring applications of 3D printed sand molds in decoration, art, architecture, outdoor, cultural and creative industries, as well as in the molding of special polymers, irregularly shaped plastic parts, and irregularly shaped refractory materials. However, the principle of 3D printing sand molds involves using an adhesive to bond and solidify sand particles layer by layer. After curing, the adhesive layer on the sand particle surface exhibits thermosetting properties, resulting in high rigidity but poor toughness. The unique molding process also leads to extremely high porosity in 3D printed sand molds, negatively impacting their strength. Furthermore, the printed sand molds exhibit mechanical anisotropy in the X, Y, and Z directions. Under these circumstances, 3D printed sand molds show deficiencies in strength and toughness when facing new applications. In addition, the natural hydrophilicity of sand makes 3D printed sand molds prone to absorbing moisture, especially outdoors or in high-humidity environments, where their strength deteriorates further due to moisture absorption. Therefore, the application of 3D printed sand molds in other fields is currently severely limited.

[0004] Polytetrafluoroethylene (PTFE) is a high-performance polymer with excellent high and low temperature resistance, chemical stability, electrical insulation, non-adhesion, weather resistance, non-flammability, and good lubricity. It has been widely used in chemical, petroleum, textile, electronics, medical, and machinery industries. However, PTFE also has several drawbacks: PTFE products have low hardness and poor creep resistance, requiring the addition of fillers to enhance their performance; their wear resistance is not ideal, and their rigidity is insufficient, necessitating the addition of wear-resistant materials for improvement; PTFE melt viscosity is high, preventing the use of molding methods similar to other thermoplastics, often requiring the production of semi-finished products through compression molding and extrusion, followed by finishing; PTFE has a relatively high coefficient of thermal expansion, and its linear expansion coefficient changes irregularly with temperature, resulting in significant thermal shrinkage and poor dimensional stability during processing. These drawbacks limit the application of PTFE. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to provide a method for manufacturing sand / polytetrafluoroethylene composite materials with arbitrary geometric configurations.

[0006] The technical solution of this invention to solve the aforementioned technical problem is to provide a method for manufacturing sand / polytetrafluoroethylene composite materials with arbitrary geometric configurations, characterized in that the method includes the following steps:

[0007] (1) Mix the raw sand and the curing agent evenly to obtain the raw sand mixture;

[0008] (2) Distribute the raw sand mixture into the sand-laying module of the 3D printer and introduce the adhesive into the nozzle of the 3D printer; during the process of laying the raw sand mixture layer by layer in the sand-laying module of the 3D printer, the nozzle of the 3D printer sprays the adhesive layer by layer according to the cross-sectional shape of each layer; under the action of the curing agent, the adhesive undergoes a curing reaction, bonding the raw sand mixture in the layered state into a whole, forming a raw sand matrix of arbitrary geometric configuration;

[0009] (3) Place the original sand matrix in the liquid component and let the original sand matrix absorb the liquid component until the mass of the original sand matrix no longer changes, thereby achieving absorption equilibrium and obtaining a sand mold of arbitrary geometric configuration;

[0010] The liquid component is composed of water, polytetrafluoroethylene emulsion and aluminum dihydrogen phosphate;

[0011] (4) The sand mold is subjected to gradient isothermal treatment and then cooled to room temperature to obtain sand / polytetrafluoroethylene composite material with arbitrary geometric configuration.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] (1) The present invention provides a template for the molding of polytetrafluoroethylene (PTFE) by using a sand matrix with a suitable arbitrary geometric configuration of hole structure formed by 3D printing. Combined with subsequent processing steps, the problem of difficult molding of complex PTFE components can be easily solved. At the same time, due to the presence of sand matrix, the hardness of PTFE components is significantly improved, rigidity is enhanced, creep resistance is improved, wear resistance is better, and dimensional stability is better, opening up new avenues for the preparation and application of complex PTFE components.

[0014] (2) Based on the wicking mechanism, this invention introduces polytetrafluoroethylene (PTFE) microparticles into the pores of the original sand matrix. Combined with subsequent gradient isothermal treatment, PTFE melts and adheres in the pores of the 3D printed sand mold to form a new skeleton, while the adhesive is completely decomposed. The rigidity of the sand mold caused by the curing products of the adhesive is no longer present. In addition, the toughness of the newly formed skeleton is outstanding. Therefore, the toughness of the 3D printed sand mold is optimized. Since the newly formed skeleton occupies the original pores, the problem of high porosity of the 3D printed sand mold is effectively solved. Furthermore, due to the formation of the new skeleton and the complete decomposition of the adhesive, the 3D printed sand mold no longer has mechanical anisotropy in the X, Y, and Z directions, and its strength is significantly improved. Since the newly formed PTFE skeleton has excellent hydrophobicity, the hydrophilicity problem of the 3D printed sand mold is completely solved, creating conditions for the application of 3D printed sand molds in other fields besides casting.

[0015] (3) In the printing process, the present invention can print original sand matrices with different pore sizes and porosities by controlling the size of sand particles and the frequency and resolution of adhesive spraying. The difference in pore size and porosity can be used to further control the amount and distribution of liquid components in the original sand matrix. By adjusting the composition of liquid components, the amount of polytetrafluoroethylene in the original sand matrix can be further controlled. Combined with subsequent gradient isothermal treatment, sand / polytetrafluoroethylene composite materials with controllable composition and different structures are finally prepared to meet the different requirements of composite material performance in different application fields. This can greatly promote the application range of sand / polytetrafluoroethylene composite materials with arbitrary geometric configuration.

[0016] (4) The liquid component prepared by the present invention can be stored stably for a long time without layering or precipitation. The liquid component can be uniformly introduced into the pores of the original sand matrix. The presence of multiple substances in the liquid component creates conditions for gradient constant temperature treatment. On the one hand, it is responsible for introducing PTFE component, and on the other hand, it contains high-temperature resistant adhesive. The high-temperature resistant adhesive is responsible for bonding the sand that tends to disperse due to adhesive decomposition during the subsequent segmented heating process, ensuring the integrity of the sand mold. Subsequently, based on the segmented heating and cooling process, the high-temperature resistant adhesive plays a role in evaporating liquid substances and avoiding the generation of bubbles, ensuring the strength of the sand mold, especially melting and bonding PTFE, forming an interpenetrating network with the sand, and molding it into a sand / PTFE composite material with arbitrary geometric configuration. Attached Figure Description

[0017] Figure 1 This is a tensile strength diagram of the original sand matrix with an eight-shaped block configuration in Embodiment 1 of the present invention;

[0018] Figure 2 This is a tensile strength diagram of the figure-eight block-shaped sand / polytetrafluoroethylene composite material of Example 1 of the present invention;

[0019] Figure 3 A digital photograph of the composite material mold prepared in Example 1 of this invention;

[0020] Figure 4 A digital photograph of the gear prepared by the composite material mold in Embodiment 1 of the present invention;

[0021] Figure 5 A digital photograph of the spiral tube obtained by preparing the composite material mold in Example 1 of the present invention;

[0022] Figure 6 A digital photograph of the composite material water container prepared in Example 1 of the present invention;

[0023] Figure 7 A digital photograph of the composite material mold for plastic foaming prepared in Example 1 of the present invention. Detailed Implementation

[0024] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention and do not limit the scope of protection of the claims of this application.

[0025] This invention provides a method for manufacturing sand / polytetrafluoroethylene composite materials of arbitrary geometric configurations (hereinafter referred to as the method), characterized in that the method includes the following steps:

[0026] (1) Mix the raw sand and the curing agent thoroughly and evenly to obtain the raw sand mixture;

[0027] Preferably, in step (1), the raw sand and the curing agent are mixed by stirring at a speed of 100-400 r / min for 1-10 min;

[0028] Preferably, in step (1), the curing agent is mixed with the raw sand in the form of atomization so that the curing agent is more evenly dispersed in the raw sand and will not cause differences in the content of curing agent between raw sands;

[0029] Preferably, in step (1), the curing agent is at least one of a strong acid aqueous solution, a hexamethylenetetramine aqueous solution, a liquid organic acid ester, an ammonium chloride aqueous solution, an ammonium sulfate aqueous solution, an ammonium nitrate aqueous solution, or an ammonium phosphate aqueous solution;

[0030] The strong acid is at least one of phosphoric acid, sulfonic acid, or sulfuric acid; the liquid organic acid ester is at least one of propylene carbonate, triacetin, ethylene glycol diacetate, or dimethyl dicarboxylate.

[0031] Preferably, in step (1), the mass of the curing agent is 0.05 to 1.5% of the mass of the original sand, and the concentration of the curing agent is determined according to the selected curing temperature and curing time.

[0032] Preferably, in step (1), the particle size of the raw sand is 30 mesh to 500 mesh.

[0033] (2) Distribute the raw sand mixture into the sand-laying module of the 3D printer and introduce the adhesive into the nozzle of the 3D printer; during the process of laying the raw sand mixture layer by layer in the sand-laying module of the 3D printer, the nozzle of the 3D printer sprays the adhesive layer by layer according to the cross-sectional shape of each layer (that is: after laying a layer of raw sand mixture, spray the adhesive on the surface of the raw sand mixture layer, and then continue to lay a layer of raw sand mixture on it, and so on); under the action of the curing agent, the adhesive undergoes a curing reaction, bonding the raw sand mixture in the layered state into a whole, forming a raw sand matrix of arbitrary geometric configuration;

[0034] Preferably, in step (2), the adhesive is at least one of furan resin, phenolic resin or urea-formaldehyde resin; the mass of the adhesive is 0.5 to 5% of the mass of the original sand.

[0035] (3) Place the original sand matrix of arbitrary geometric configuration in the liquid component, so that the original sand matrix of arbitrary geometric configuration fully absorbs the liquid component until the mass of the original sand matrix no longer changes (i.e. the original sand matrix no longer absorbs the liquid component), thereby achieving absorption equilibrium and obtaining the sand mold of arbitrary geometric configuration.

[0036] Preferably, in step (3), the liquid component is composed of water, polytetrafluoroethylene emulsion and aluminum dihydrogen phosphate, wherein the water is 0-100 parts by weight (preferably 50-100 parts by weight, more preferably 70-100 parts by weight), the polytetrafluoroethylene emulsion is 20-100 parts by weight (preferably 30-100 parts by weight, more preferably 50-100 parts by weight), and the aluminum dihydrogen phosphate is 4-35 parts by weight (preferably 7-25 parts by weight, more preferably 10-25 parts by weight).

[0037] (4) The sand mold of arbitrary geometry is subjected to gradient isothermal treatment and then cooled to room temperature to obtain sand / polytetrafluoroethylene composite material of arbitrary geometry.

[0038] Preferably, in step (4), the gradient constant temperature treatment specifically involves: placing the sand mold at room temperature for 0–60 min (the purpose being to ensure that the liquid components on the surface of the sand mold can continue to penetrate into its interior), then sequentially treating it at a temperature of 60–100°C for 1–24 h (the purpose being to ensure that the liquid evaporates sufficiently to prevent blistering on the surface or inside of the sand mold due to liquid vaporization during subsequent heating treatment), treating it at a temperature of 100–200°C for 0.5–12 h (the purpose being to strengthen the adhesion strength of a certain substance in the liquid component to the sand particles), treating it at a temperature of 200–300°C for 0.25–6 h (the purpose being to further strengthen the adhesion strength of a certain substance in the liquid component to the sand particles, while triggering the thermal decomposition reaction of the adhesive), and treating it at a temperature of 300–400°C (preferably 365–400°C, more preferably 365–385°C) for 2–168 h (the purpose being to further strengthen the adhesion strength of a certain substance in the liquid component to the sand particles, promote the complete decomposition of the adhesive, and at the same time allow other substances in the liquid component to melt and adhere to each other).

[0039] Preferably, in step (4), the temperature is reduced to room temperature at a rate of 0.1 to 20 °C / min (the purpose is to provide sufficient time for certain substances in the liquid component to crystallize, to ensure the strength of the composite material, and at the same time maintain the dimensional stability of the composite material).

[0040] The sand mold obtained in step (2) of the comparative example and embodiment can be of any shape, wherein the sand mold used for testing mechanical properties and water contact angle is printed in the shape of a figure-eight block, and the figure-eight block sand mold is made in accordance with the provisions of national standard GB / T 2684-2009. In the test method, the mechanical properties of the figure-eight block sand mold are measured on an XQY-Ⅱ intelligent sand strength tester, and the water contact angle of the sand mold surface is measured on a DSA100 contact angle tester.

[0041] Example 1

[0042] (1) Add 100-200 mesh raw sand to a mixing tank. Then, under the precise metering of a metering pump, pump a strong acid aqueous solution with a mass concentration of 72%-73% into the mixing tank. Disperse the strong acid aqueous solution evenly in the raw sand at a stirring speed of 400 r / min for 5 min to obtain the raw sand mixture. The mass of the strong acid aqueous solution is 1.0% of the mass of the raw sand.

[0043] (2) The raw sand mixture is distributed into the sand-laying module of the 3D printer, and furan resin is introduced into the nozzle of the 3D printer. During the layer-by-layer sand-laying process of the sand-laying module of the 3D printer, the nozzle of the 3D printer sprays furan resin layer by layer according to the cross-sectional shape of each layer. Under the action of strong acid aqueous solution, the furan resin undergoes a curing reaction, bonding the raw sand mixture in layers into a whole, and obtaining a raw sand matrix with arbitrary geometric configuration. The mass of furan resin is 2.8% of the mass of raw sand.

[0044] (3) Place the original sand matrix of arbitrary geometric configuration in the liquid component, so that the original sand matrix of arbitrary geometric configuration fully absorbs the liquid component until the absorption equilibrium is reached, and obtain the sand mold of arbitrary geometric configuration; the liquid component consists of 0 parts by mass of water, 100 parts by mass of polytetrafluoroethylene emulsion and 8 parts by mass of aluminum dihydrogen phosphate.

[0045] (4) Place the sand mold of arbitrary geometry in a room temperature environment for 60 min, then treat it at 80℃ for 12 h, at 150℃ for 2 h, at 250℃ for 3 h, and at 380℃ for 48 h, and then cool it to room temperature at a rate of 0.25℃ / min to obtain the sand / polytetrafluoroethylene composite material of arbitrary geometry.

[0046] The test showed that the surface water contact angle of the original sand matrix obtained in step (2) was 0°, and the surface water contact angle of the sand / polytetrafluoroethylene composite material obtained in step (4) was close to 140°.

[0047] The original sand matrix obtained in step (2) is made into a herringbone block configuration according to the provisions of GB / T 2684-2009, and its tensile strength is 1.12 MPa. The composite material obtained in step (4) is made into a herringbone block configuration according to the provisions of GB / T 2684-2009, and its tensile strength is 4.68 MPa.

[0048] The original sand matrix obtained in step (2) is made into a herringbone block configuration according to the provisions of national standard GB / T 2684-2009. Its tensile strength exhibits obvious anisotropy (e.g. Figure 1 As shown). The composite material obtained in step (4) is made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength no longer exhibits anisotropy (as shown). Figure 2 As shown in the figure, the introduction of polytetrafluoroethylene (PTFE) can significantly improve the hydrophobicity of the sand mold. Under the condition of curing furan resin decomposition, the synergistic effect of PTFE and aluminum dihydrogen phosphate can significantly improve the strength of the sand mold, both of which provide convenience for application.

[0049] The sand / polytetrafluoroethylene composite material prepared in Example 1 was used as a mold (e.g. Figure 3 Parts manufactured by molding, including gears (as shown). Figure 4 As shown), spiral tube (such as) Figure 5 (As shown).

[0050] The sand / polytetrafluoroethylene composite material prepared in Example 1 was used as a water container (e.g. Figure 6(As shown). During the 12-month testing period, the water container did not leak. When dropped from a height of 15 meters, the container landed intact. Repeated rubbing of the container surface did not result in any sand falling off. Even when both containers were placed upside down on the ground and an 85 kg adult stood on them, the containers did not break. This demonstrates that the prepared sand / PTFE composite material possesses excellent water resistance, toughness, wear resistance, and mechanical properties.

[0051] The sand / polytetrafluoroethylene composite material prepared in Example 1 was used as a plastic foaming mold (e.g. Figure 7 (As shown). During the plastic foaming process, the printed mold can withstand pressure. Due to the non-stick properties of polytetrafluoroethylene, the foam plastic can be easily demolded after molding, which brings convenience to the processing of foam plastics.

[0052] Comparative Example 1

[0053] The steps (1) to (3) are the same as those in Example 1, except that step (4) is not performed.

[0054] The sand molds with arbitrary geometric configurations obtained in step (3) were tested. The water contact angle of the original sand matrix obtained in step (2) was 0°, and the water contact angle of the sand molds with arbitrary geometric configurations obtained in step (3) was also close to 0°.

[0055] The original sand matrix obtained in step (2) is made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength is 1.12 MPa. The sand mold obtained in step (3) is made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength is 0.65 MPa. It can be seen that the treatment in step (3) does not affect the hydrophilicity of the sand mold, but due to the introduction of liquid components and the absence of the treatment in step (4), the strength of the sand mold will be negatively affected. Step (4) is also extremely necessary for the preparation of sand / polytetrafluoroethylene composite material.

[0056] Comparative Example 2

[0057] Compared to Example 1, the only difference is that the liquid component was not introduced into the original sand matrix, i.e., step (3) of Example 1 was not performed, and only steps (1), (2), and (4) of Example 4 were executed. Specifically:

[0058] (1) Add 100-200 mesh raw sand to a mixing tank. Then, under the precise metering of a metering pump, pump a strong acid aqueous solution with a mass concentration of 72%-73% into the mixing tank. Disperse the strong acid aqueous solution evenly in the raw sand at a stirring speed of 400 r / min for 5 min to obtain the raw sand mixture. The mass of the strong acid aqueous solution is 1.0% of the mass of the raw sand.

[0059] (2) The raw sand mixture is distributed into the sand-laying module of the 3D printer, and furan resin is introduced into the nozzle of the 3D printer. During the layer-by-layer sand-laying process of the sand-laying module of the 3D printer, the nozzle of the 3D printer sprays furan resin layer by layer according to the cross-sectional shape of each layer. Under the action of strong acid aqueous solution, the furan resin undergoes a curing reaction, bonding the raw sand mixture in layers into a whole, and obtaining a raw sand matrix with arbitrary geometric configuration. The mass of furan resin is 2.8% of the mass of raw sand.

[0060] (3) Place the sand mold of arbitrary geometry in a room temperature environment for 60 min, then treat it at 80℃ for 12 h, at 150℃ for 2 h, at 250℃ for 3 h, and at 380℃ for 48 h, and then cool it to room temperature at a rate of 0.25℃ / min to obtain the sand / polytetrafluoroethylene composite material of arbitrary geometry.

[0061] The results showed that the sand mold completely disintegrated due to the decomposition of the cured furan resin, rendering it unusable.

[0062] Example 2

[0063] The process is the same as in Example 1, except for step (3).

[0064] Step (3) specifically involves placing the original sand matrix of arbitrary geometric configuration in the liquid component, allowing the original sand matrix of arbitrary geometric configuration to fully absorb the liquid component until absorption equilibrium is reached, thereby obtaining a sand mold of arbitrary geometric configuration; the liquid component consists of 21.1 parts by mass of water, 63.4 parts by mass of polytetrafluoroethylene emulsion and 9.3 parts by mass of aluminum dihydrogen phosphate;

[0065] The test showed that the surface water contact angle of the original sand matrix obtained in step (2) was 0°, and the surface water contact angle of the sand / polytetrafluoroethylene composite material obtained in step (4) was close to 134°.

[0066] The original sand matrix obtained in step (2) was made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength was 1.12 MPa. The composite material obtained in step (4) was made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength was 3.98 MPa. It can be seen that the introduction of polytetrafluoroethylene can significantly improve the hydrophobicity of the sand mold, and under the condition of curing furan resin decomposition, the synergistic effect of polytetrafluoroethylene and aluminum dihydrogen phosphate can significantly improve the strength of the sand mold.

[0067] Comparative Example 3

[0068] Compared with Example 2, the only difference is that the liquid component in step (3) does not contain aluminum dihydrogen phosphate. Step (3) specifically involves placing the original sand matrix of any geometric configuration in the liquid component, allowing the original sand matrix of any geometric configuration to fully absorb the liquid component until absorption equilibrium is reached; the liquid component consists of 100 parts by mass of water and 50 parts by mass of polytetrafluoroethylene emulsion.

[0069] The results showed that the furan resin, which was cured during the medium and high temperature treatment stages, decomposed, and the system did not contain aluminum dihydrogen phosphate. Furthermore, the polytetrafluoroethylene (PTFE) only melted during the high temperature treatment stage. Therefore, it could not effectively bind the sand that had disintegrated during the medium and high temperature treatment stages, causing the sand mold obtained in this comparative example to crumble upon contact. This demonstrates that the combination of aluminum dihydrogen phosphate and PTFE emulsion is essential for preparing sand / PTFE composite materials with arbitrary geometric configurations.

[0070] Example 3

[0071] The process is the same as in Example 1, except for step (3).

[0072] Step (3) specifically involves placing the original sand matrix of arbitrary geometric configuration in the liquid component, allowing the original sand matrix of arbitrary geometric configuration to fully absorb the liquid component until absorption equilibrium is reached, thereby obtaining a sand mold of arbitrary geometric configuration; the liquid component consists of 42.2 parts by mass of water, 42.3 parts by mass of polytetrafluoroethylene emulsion and 11.8 parts by mass of aluminum dihydrogen phosphate;

[0073] The test showed that the surface water contact angle of the original sand matrix obtained in step (2) was 0°, and the surface water contact angle of the sand / polytetrafluoroethylene composite material obtained in step (4) was close to 122°.

[0074] The original sand matrix obtained in step (2) was made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength was 1.12 MPa. The composite material obtained in step (4) was made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength was 3.36 MPa. It can be seen that the introduction of polytetrafluoroethylene can significantly improve the hydrophobicity of the sand mold, and under the condition of curing furan resin decomposition, the synergistic effect of polytetrafluoroethylene and aluminum dihydrogen phosphate can significantly improve the strength of the sand mold.

[0075] Comparative Example 4

[0076] Compared with Example 3, the only difference is that the liquid component in step (3) does not contain polytetrafluoroethylene emulsion. Step (3) specifically involves placing the original sand matrix of any geometric configuration into the liquid component, allowing the original sand matrix of any geometric configuration to fully absorb the liquid component until absorption equilibrium is reached; the liquid component consists of 100 parts by mass of water and 20 parts by mass of aluminum dihydrogen phosphate;

[0077] Tests showed that the surface water contact angle of the original sand matrix obtained in step (2) was 0°, while the surface water contact angle of the sand / polytetrafluoroethylene composite material obtained in step (4) was also close to 0°.

[0078] The original sand matrix obtained in step (2) was made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength was 1.12 MPa. The composite material obtained in step (4) was made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength was 1.38 MPa. It can be seen that the introduction of aluminum dihydrogen phosphate alone does not affect the hydrophilicity of the sand mold, but aluminum dihydrogen phosphate can act as a binder to ensure that the sand mold has sufficient strength under the condition of decomposition of cured furan resin.

[0079] Example 4

[0080] The process is the same as in Example 1, except for step (3).

[0081] Step (3) specifically involves placing the original sand matrix of arbitrary geometric configuration in the liquid component, allowing the original sand matrix of arbitrary geometric configuration to fully absorb the liquid component until absorption equilibrium is reached, thereby obtaining a sand mold of arbitrary geometric configuration; the liquid component consists of 42.2 parts by mass of water, 21.1 parts by mass of polytetrafluoroethylene emulsion and 10.1 parts by mass of aluminum dihydrogen phosphate;

[0082] The test results showed that the surface water contact angle of the original sand matrix obtained in step (2) was 0°, and the surface water contact angle of the sand / polytetrafluoroethylene composite material obtained in step (4) was close to 115°.

[0083] The original sand matrix obtained in step (2) was made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength was 1.12 MPa. The composite material obtained in step (4) was made into a herringbone block configuration according to the national standard GB / T 2684-2009, and its tensile strength was 2.69 MPa. It can be seen that the introduction of polytetrafluoroethylene can significantly improve the hydrophobicity of the sand mold, and under the condition of curing furan resin decomposition, the synergistic effect of polytetrafluoroethylene and aluminum dihydrogen phosphate can significantly improve the strength of the sand mold.

[0084] Example 5

[0085] (1) Add 100-200 mesh raw sand to the sand mixing tank, and then pump the hexamethylenetetramine aqueous solution into the sand mixing tank under precise metering of the metering pump. Disperse the hexamethylenetetramine aqueous solution evenly in the raw sand at a stirring speed of 100 r / min for 10 min to obtain raw sand mixture; the mass of the hexamethylenetetramine aqueous solution is 0.1% of the mass of the raw sand.

[0086] (2) The raw sand mixture is distributed into the sand-laying module of the 3D printer, and phenolic resin is introduced into the nozzle of the 3D printer. During the layer-by-layer sand-laying process of the sand-laying module of the 3D printer, the nozzle of the 3D printer sprays phenolic resin layer by layer according to the cross-sectional shape of each layer. Under the action of hexamethylenetetramine aqueous solution, the phenolic resin undergoes a curing reaction, bonding the raw sand mixture in layers into a whole, and obtaining a raw sand matrix with arbitrary geometric configuration. The mass of phenolic resin is 5% of the mass of raw sand.

[0087] (3) Place the original sand matrix of arbitrary geometric configuration in the liquid component, so that the original sand matrix of arbitrary geometric configuration fully absorbs the liquid component until the absorption equilibrium is reached, and obtain the sand mold of arbitrary geometric configuration; the liquid component consists of 21.1 parts by mass of water, 63.4 parts by mass of polytetrafluoroethylene emulsion, and 9.3 parts by mass of aluminum dihydrogen phosphate;

[0088] (4) Place the sand mold of arbitrary geometry in a room temperature environment for 1 min, then treat it at 60℃ for 24 h, 100℃ for 12 h, 200℃ for 6 h, and 365℃ for 150 h, and then cool it to room temperature at a rate of 0.1℃ / min to obtain the sand / polytetrafluoroethylene composite material of arbitrary geometry.

[0089] Example 6

[0090] (1) Add 100-200 mesh raw sand to the sand mixing tank, and then pump ammonium chloride aqueous solution into the sand mixing tank under precise metering of the metering pump. Disperse the ammonium chloride aqueous solution evenly in the raw sand at a stirring speed of 250 r / min for 1 min to obtain raw sand mixture; the mass of ammonium chloride aqueous solution is 1.5% of the mass of raw sand.

[0091] (2) The raw sand mixture is distributed into the sand-laying module of the 3D printer, and urea-formaldehyde resin is introduced into the nozzle of the 3D printer. During the layer-by-layer sand-laying process of the sand-laying module of the 3D printer, the nozzle of the 3D printer sprays urea-formaldehyde resin layer by layer according to the cross-sectional shape of each layer. Under the action of ammonium chloride aqueous solution, the urea-formaldehyde resin undergoes a curing reaction, bonding the raw sand mixture in layers into a whole, and obtaining a raw sand matrix with arbitrary geometric configuration. The mass of urea-formaldehyde resin is 0.5% of the mass of raw sand.

[0092] (3) Place the original sand matrix of arbitrary geometric configuration in the liquid component, so that the original sand matrix of arbitrary geometric configuration fully absorbs the liquid component until the absorption equilibrium is reached, and obtain the sand mold of arbitrary geometric configuration; the liquid component consists of 42.2 parts by mass of water, 21.1 parts by mass of polytetrafluoroethylene emulsion, and 10.1 parts by mass of aluminum dihydrogen phosphate.

[0093] (4) Place the sand mold of arbitrary geometry in a room temperature environment for 30 min, then treat it at 100℃ for 2 h, 200℃ for 0.5 h, 300℃ for 0.25 h, and 400℃ for 2 h, and then cool it down to room temperature at a rate of 15℃ / min to obtain the sand / polytetrafluoroethylene composite material of arbitrary geometry.

[0094] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for manufacturing a sand / polytetrafluoroethylene composite material with arbitrary geometric configuration, characterized in that, The method includes the following steps: (1) Mix the raw sand and the curing agent evenly to obtain the raw sand mixture; (2) Distribute the raw sand mixture into the sand-laying module of the 3D printer and introduce the adhesive into the nozzle of the 3D printer; during the process of laying the raw sand mixture layer by layer in the sand-laying module of the 3D printer, the nozzle of the 3D printer sprays the adhesive layer by layer according to the cross-sectional shape of each layer; under the action of the curing agent, the adhesive undergoes a curing reaction, bonding the raw sand mixture in the layered state into a whole, forming a raw sand matrix with arbitrary geometric configuration; The adhesive is at least one of furan resin, phenolic resin or urea-formaldehyde resin; (3) Place the original sand matrix in the liquid component and let the original sand matrix absorb the liquid component until the mass of the original sand matrix no longer changes, thereby achieving absorption equilibrium and obtaining a sand mold with arbitrary geometric configuration; The liquid component is composed of 0-100 parts by weight of water, 20-100 parts by weight of polytetrafluoroethylene emulsion, and 4-35 parts by weight of aluminum dihydrogen phosphate. (4) The sand mold is subjected to gradient isothermal treatment and then cooled to room temperature to obtain sand / polytetrafluoroethylene composite material with arbitrary geometric configuration; The gradient isothermal treatment is as follows: place the sample in a room temperature environment for 0~60 min, then treat it sequentially at a temperature of 60~100℃ for 1~24 h, at a temperature of 100~200℃ for 0.5~12 h, at a temperature of 200~300℃ for 0.25~6 h, and at a temperature of 300~400℃ for 2~168 h.

2. The method for manufacturing sand / polytetrafluoroethylene composite material of arbitrary geometric configuration according to claim 1, characterized in that, In step (1), the raw sand and the curing agent are mixed by stirring at a speed of 100~400 r / min for 1~10 min.

3. The method for manufacturing sand / polytetrafluoroethylene composite material of arbitrary geometric configuration according to claim 1, characterized in that, In step (1), the curing agent is mixed with the raw sand in the form of atomization.

4. The method for manufacturing sand / polytetrafluoroethylene composite material of arbitrary geometric configuration according to claim 1, characterized in that, In step (1), the curing agent is at least one of the following: strong acid aqueous solution, hexamethylenetetramine aqueous solution, liquid organic acid ester, ammonium chloride aqueous solution, ammonium sulfate aqueous solution, ammonium nitrate aqueous solution, or ammonium phosphate aqueous solution.

5. The method for manufacturing sand / polytetrafluoroethylene composite material of arbitrary geometric configuration according to claim 4, characterized in that, In step (1), the strong acid is at least one of phosphoric acid, sulfonic acid or sulfuric acid; the liquid organic acid ester is at least one of propylene carbonate, triacetin, ethylene glycol diacetate or dimethyl dicarboxylate.

6. The method for manufacturing sand / polytetrafluoroethylene composite material of arbitrary geometric configuration according to claim 1, characterized in that, In step (1), the mass of the curing agent is 0.05 to 1.5% of the mass of the original sand; the particle size of the original sand is 30 mesh to 500 mesh.

7. The method for manufacturing sand / polytetrafluoroethylene composite material of arbitrary geometric configuration according to claim 1, characterized in that, In step (2), the mass of the adhesive is 0.5 to 5% of the mass of the original sand.

8. The method for manufacturing sand / polytetrafluoroethylene composite material of arbitrary geometric configuration according to claim 1, characterized in that, In step (4), the temperature is reduced to room temperature at a rate of 0.1~20℃ / min.

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