A method for molding a hollow profiled carbon fiber composite

Abstract

The application discloses a kind of hollow special-shaped carbon fiber composite material forming methods, including the chemical modification of original sand, and the modified sand is obtained;Then resin curing catalyst and water-soluble polymer are sequentially added, and coordination reaction is carried out, to obtain coated sand;Again, resin adhesive and coated sand are used as raw materials, and the sand core mold is prepared by pressing forming or 3D printing;Then the coating of barrier liquid resin infiltration is constructed for the surface of sand core mold, to obtain the sand core mold after coating;Finally, the sand core mold after coating is used as forming mold, and the carbon fiber composite material forming process is carried out;After the resin is cured, the forming mold is collapsed, the demolding process is completed, and the hollow special-shaped carbon fiber composite material is prepared.The application does not need to open mold, meets the subsequent processing strength requirement, significantly reduces the manufacturing difficulty of complex shape core mold, and realizes the separation of carbon fiber composite material and sand core film by collapsing, effectively solves the demolding problem of complex shape core mold.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of carbon fiber composite materials, in particular to a hollow special-shaped carbon fiber composite material forming method. BACKGROUND

[0002] Carbon fiber composite material is a kind of high-performance composite material with carbon fiber as reinforcing material and resin, metal and ceramic as matrix. It has excellent performance such as low density, high strength, high modulus, impact resistance, fatigue resistance, high temperature resistance and corrosion resistance. Carbon fiber composite material has been widely used in automobile, railway transportation, ocean and wind energy industries due to its high specific modulus and high specific strength. In the field of aerospace, carbon fiber composite material is widely used in the structure of the fuselage, which effectively reduces the weight and improves the performance. With the large application of carbon fiber composite material in the field of aerospace, many requirements for the shape of carbon fiber composite material such as hollow and special shape are put forward.

[0003] At present, the preparation methods of hollow special-shaped carbon fiber composite material parts mainly include hot press forming, winding forming, injection molding, pultrusion forming and stamping forming. These methods all need mold support, and the design and development of mold become the key. Factors such as mold material, structure and precision, process and economy need to be considered to ensure the size accuracy, surface finish and mechanical properties of the product, and at the same time reduce the production cost.

[0004] The current methods for preparing the core mold required for the hollow profiled carbon fiber composite material include hard plastic foaming method, soft plastic foaming method, low melting point alloy method, inflatable air bag method, etc. For the hard and soft plastic foaming method, the generation and diffusion of gas during the foaming process can affect the size accuracy and shape stability of the final core mold, making it difficult to ensure the molding of high-quality carbon fiber composite materials. For the low melting point alloy method, due to the flowability and solidification characteristics of the alloy during the melting process, local alloy accumulation or vacancies may occur, making it difficult to accurately control the shape and size of the product, ultimately affecting the quality and appearance of the carbon fiber composite material product. The precision of the inflatable air bag method is relatively limited, and the air bag will deform during the inflation process under the action of the mold, making it difficult to accurately control the shape and size, which has a greater impact on the molding precision and appearance quality of the carbon fiber composite material product. After using the hard plastic foaming method, soft plastic foaming method, low melting point alloy method, inflatable air bag method, etc. to form the core mold, a complex demolding mechanism or additional power and energy is usually required to complete the demolding process, which can easily cause serious damage to the carbon fiber composite material product during the demolding process, leading to an increase in product scrap rate and affecting the yield. At the same time, the hard plastic foaming method involves specific hard plastic resins and chemical foaming agents, etc. The recycling of these materials is relatively difficult, especially the hard plastic products after foaming treatment, which have complex structures, making it difficult to separate and recycle different components effectively. Moreover, some chemical foaming agents may pose potential environmental hazards and may pollute the environment. Soft foaming materials are difficult to separate and reprocess effectively due to their special physical properties, requiring special recycling equipment and complex process flow. Some chemical foaming agents may remain in the foamed product, affecting the environment. The low melting point alloy method uses low melting point alloy materials, which have certain recyclability, but the recycling of alloy materials usually requires specific equipment and high temperature conditions, making the recycling process complex and costly. The inflatable air bag method mainly relies on air bag materials such as rubber, nylon fabric composite rubber, etc. These materials have certain limitations in recycling, and rubber and other materials may be difficult to recycle and reuse due to aging, wear and tear, etc. after long-term use or disposal. Moreover, the air bag structure is complex, making it difficult to disassemble and separate different components.

[0005] The preparation and application defects of the above-mentioned core mold mainly focus on three aspects, namely the manufacturing difficulty of the complex shape core mold, the demolding difficulty of the complex shape core mold after the hollow special-shaped carbon fiber composite material is formed, and the recycling problem of the core mold material. First, in order to obtain a complex shape core mold, a special mold needs to be developed, and the difficulty and cost of developing a complex shape mold are extremely high: the core mold needs to bear a high impact force during the manufacturing process of the core mold by using the mold, so a material with high hardness and toughness needs to be selected for manufacturing; in order to ensure the machining precision and surface finish, strict quality control and detection of the raw material are also required; in addition, the design and manufacturing of the core mold need to consider the uniformity of the vibration frequency and amplitude in the manufacturing process to avoid quality problems caused by uneven stress, and the manufacturing difficulty limits the development and development of complex shape core mold. Secondly, the demolding of the complex shape core mold after the hollow special-shaped carbon fiber composite material is formed is also a big challenge. In the overall forming process of the hollow special-shaped carbon fiber composite material, the core mold made of low-melting-point alloy (for example, the patent document with publication number CN107599445A) is mostly used, and after solidification, the demolding is realized by melting. This process needs to accurately control the temperature and time to ensure the integrity of the composite material structure, and the production cost is extremely high. The shape and size of the carbon fiber composite material that can be formed are greatly limited. Finally, the core mold material is difficult to recycle and reuse, which not only wastes resources and is harmful to the environment, but also greatly increases the production cost.

[0006] 3D printing technology uses materials such as metal, plastic, ceramic, and sand that can be bonded to build three-dimensional objects through layer-by-layer accumulation. Using sand as the raw material for 3D printing greatly reduces the cost of mold production. Due to the intervention of computer-aided design, 3D printing technology has greater design freedom, making it possible to manufacture molds with complex geometric structures and internal space structures. However, the current adhesive system used in sand 3D printing is usually composed of resin and curing agent. The resin-bonded sand mold has high strength, and because the cured resin is not soluble in water, the conventional 3D printed sand mold cannot disintegrate when exposed to water, making it difficult to separate and remove the carbon fiber composite material and the sand core mold. Therefore, the application of 3D printed sand molds in the field of hollow special-shaped carbon fiber composite material forming is greatly limited.

[0007] Based on the above difficulties, how to use technical innovation in the aspects of raw sand, adhesive system, and coating, combined with 3D sand mold printing adhesive jetting technology, to design a demoldable sand core mold that can meet the subsequent processing strength requirements, is not bonded with carbon fiber composite material, and can quickly disintegrate, which is the key to the application of 3D printed sand molds in the field of hollow special-shaped carbon fiber composite material forming. SUMMARY

[0008] In view of the deficiencies of the prior art, the technical problem to be solved by the present application is to provide a molding method of hollow profiled carbon fiber composite material.

[0009] The technical scheme for solving the technical problem of the present application is to provide a molding method of hollow profiled carbon fiber composite material, characterized in that the method comprises the following steps:

[0010] Step 1, chemically modifying the original sand to arrange the chemical groups and structure on the surface of the original sand; then washing to remove impurities and unreacted substances on the surface, and drying to obtain modified sand;

[0011] Step 2, adding a resin curing catalyst solution to the modified sand, mixing uniformly to obtain modified sand containing the catalyst; then adding a water-soluble polymer, mixing uniformly to obtain a mixed system of the resin curing catalyst solution, the water-soluble polymer and the modified sand; then stirring and drying the mixed system to remove water and promote the coordination reaction to complete, at the same time, to improve the catalytic activity of the resin curing catalyst and coat the water-soluble polymer on the surface of the modified sand, to obtain coated sand with a core-shell structure of a core layer of modified sand and a shell layer of water-soluble polymer;

[0012] Step 3, using a resin-based adhesive and the coated sand of step 2 as raw materials, preparing a sand core mold by pressing or 3D printing;

[0013] Step 4, compounding a liquid permeation resistant coating on the outer surface of the sand core mold of step 3, and then compounding a resin matrix permeation and adhesion coating on the surface of the liquid permeation resistant coating, to improve the surface structure and roughness of the sand core mold, and to build a coating on the surface of the sand core mold to resist the penetration of liquid resin during the molding of the carbon fiber composite material, to obtain the sand core mold after coating;

[0014] Step 5, using the sand core mold after coating of step 4 as a molding mold for carbon fiber composite material, to perform the molding process of the carbon fiber composite material; after the resin is cured, using a solvent that can dissolve the water-soluble polymer of step 2 to collapse the molding mold, to complete the demolding process, and to obtain the hollow profiled carbon fiber composite material.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] (1) The present application optimizes the surface structure and groups of various sources of raw sand based on chemical modification, and builds a high-strength coating layer on the surface of various sources of raw sand based on the coordination between soluble metal salt and polymer and the interaction between polymer and various sources of raw sand surface structure and groups. The role of the above innovation is as follows: first, repairing the defects of various sources of raw sand surface, which serves to greatly improve the strength of sand core film, which is an important prerequisite for the application of sand core film; second, establishing a soluble shell layer, which serves to collapse the sand core film, which is a necessary condition for the application of sand core film as a hollow profiled carbon fiber composite forming mold; third, the coordination state of metal salt provides catalytic effect for the subsequent adhesive curing, which is the guarantee condition for the formation of sand core film by manual or 3D printing technology; fourth, the coated sand has low moisture regain, excellent fluidity and uniform particle size distribution, which provides support for the application in the sand laying system of industrial grade 3D sand mold printer.

[0017] (2) The present application designs a special adhesive, the viscosity and surface tension of which are matched with the requirements of the nozzle of industrial grade 3D sand mold printer, and the continuous and stable inkjet process can be completed through the nozzle system. After the sprayed adhesive contacts with the coated sand in the sand laying system, the coordination state of metal salt in the coating layer catalyzes the curing reaction of the adhesive, and the cured adhesive bonds the coated sand into an integral structure by point bonding. Based on the characteristics of the designed adhesive and the coated sand described above, the sand core film with various complex shapes can be obtained by using the characteristics of industrial grade 3D sand mold printer, which can accurately print various complex shaped sand molds, and can greatly provide special mold support for the molding of hollow profiled carbon fiber composite materials.

[0018] (3) The present application designs a special formula paint for the surface feature optimization of sand core mold. The surface of sand core mold is processed and optimized by coating layer superposition or composite coating, which fills the defects of sand core mold surface, gives the core mold a smoother surface, and effectively prevents the penetration of resin during the molding process of carbon fiber composite material, thereby preventing the adhesion of core mold and carbon fiber composite material, so that the prepared carbon fiber composite material has excellent surface finish. In addition, the excellent compressive and tensile strength of sand core mold effectively guarantees the high quality molding of carbon fiber composite material.

[0019] (4) The present application is more advanced in the demolding method of sand core mold. The coated sand shell layer in the core mold of the present application has excellent solubility. After the hollow profiled carbon fiber composite material is formed, based on the mechanism of "the skin does not exist, the hair will not be attached", dissolving the coated sand shell layer can destroy the bonding points constructed by the adhesive on the shell layer, so that the sand core mold completely collapses, thereby easily achieving the demolding goal. This demolding method is more simple and efficient, and effectively avoids the risk of damage to the finished product due to improper demolding operation.

[0020] (5) The technology involved in the present application has more time and economic advantages. On the one hand, the present application takes various source raw sand as a basic material, which has a wide source and low price. The chemical modification and film coating treatment significantly improve the performance of the raw material, but the chemical modifier and film coating agent are used in a very low amount and the cost is controllable, so the chemical modification and film coating treatment do not significantly affect the price of the raw material. On the other hand, the present application uses 3D printing technology to obtain a sandy core mold without opening an external mold, and the core mold with a predetermined shape can be directly obtained. The 3D printing technology provides high design flexibility, and the manufacturing goal of a complex shape sandy core mold can be easily achieved. The flexibility and convenience are better, the time and cost of traditional manufacturing mold opening are reduced, and the time and economic advantages are more prominent.

[0021] (6) The raw material of the present application also has advantages in recycling and environmental protection. After the carbon fiber composite material is formed, the collapsed sandy core mold can be directly used in the next cycle after simple drying and screening treatment, which greatly improves the recycling rate of the raw material and reduces the resource consumption and raw material procurement cost. From the perspective of environmental protection, the unique film-coated sand preparation and core mold forming process effectively avoids the large amount of waste, significantly reduces the environmental pressure, and uses water immersion or flushing to demold, avoiding the use and discharge of chemical solvents, greatly improving the environmental protection of the process. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is an electron micrograph of the raw sand of the present application example 1;

[0023] Figure 2 It is an electron micrograph of the modified sand of the present application example 1;

[0024] Figure 3 It is an electron micrograph of the film-coated sand of the present application example 1;

[0025] Figure 4 It is an XPS spectrum of the raw sand of the present application example 1;

[0026] Figure 5 It is an XPS spectrum of the modified sand of the present application example 1;

[0027] Figure 6 It is an XPS spectrum of the film-coated sand of the present application example 1;

[0028] Figure 7 It is an FTIR spectrum of the raw sand, the modified sand containing catalyst and the film-coated sand of the present application example 1;

[0029] Figure 8 It is a moisture regain graph of the raw sand, the modified sand and the film-coated sand of the present application example 1;

[0030] Figure 9Fig. 1 is a flowability chart of the raw sand and the coated sand of Example 1 of the present application, wherein a is the raw sand and b is the coated sand;

[0031] Figure 10 Fig. 2 is a particle size distribution chart of the raw sand of Example 1 of the present application;

[0032] Figure 11 Fig. 3 is a particle size distribution chart of the coated sand of Example 1 of the present application;

[0033] Figure 12 Fig. 4 is the collapse test result of the coated sand core mold of Example 1 of the present application;

[0034] Figure 13 Fig. 5 is a physical photo of the product prepared in Example 1 of the present application, wherein a is the sand core mold, b is the sand core mold coated with the composite barrier liquid permeable coating, c is the coated sand core mold, and d is the hollow profiled carbon fiber composite material;

[0035] Figure 14 Fig. 6 is the surface roughness of the product prepared in Example 1 of the present application, wherein a is the outer surface of the sand core mold, b is the outer surface of the sand core mold coated with the composite barrier liquid permeable coating, c is the outer surface of the coated sand core mold, and d is the inner surface of the hollow carbon fiber composite material;

[0036] Figure 15 Fig. 7 is the test result of the coating barrier epoxy resin penetration and adhesion of Example 1 of the present application;

[0037] Figure 16 Fig. 8 is a printing process chart of the resin-based adhesive and the coated sand on the 3D printer of Example 4 of the present application, wherein a is the printing process, b is the contact condition of the adhesive and the coated sand sprayed out of the nozzle, and c is the sand mold after solidification molding;

[0038] Figure 17 Fig. 9 is an inkjet image of the resin-based adhesive in the nozzle of the 3D printer of Example 4 of the present application. DETAILED DESCRIPTION

[0039] The specific embodiments of the present application are given below. The specific embodiments are only used to further illustrate the present application and do not limit the protection scope of the present application.

[0040] The present application provides a molding method (referred to as method) of a hollow profiled carbon fiber composite material, characterized in that the method comprises the following steps:

[0041] Step 1, chemically modifying the raw sand to arrange the chemical groups and structures on the surface of the raw sand; then washing to remove the impurities and unreacted substances on the surface, and drying to remove the water, to obtain the modified sand;

[0042] Preferably, in step 1, the raw sand is raw sand of various sources, preferably silica sand; the particle size of the raw sand is 70-140 mesh.

[0043] Preferably, in step 1, the chemical modification is oxidation modification, surfactant modification or silane coupling agent modification.

[0044] Preferably, in step 1, the oxidation modification is specifically: the raw sand is immersed in a liquid oxidizing agent solution under stirring for oxidation modification.

[0045] The oxidation modification process is: the stirring speed is 50-100 r / min, the modification time is 6-12 h, and the modification temperature is room temperature (i.e. 20-35℃);

[0046] The liquid oxidizing agent solution is a mixture of liquid oxidizing agent and water, and the mass fraction is 5-50wt%; the mass of the liquid oxidizing agent is 5-50% of the mass of the raw sand.

[0047] The liquid oxidizing agent is at least one of hydrogen peroxide, concentrated nitric acid, dilute nitric acid, concentrated sulfuric acid, permanganic acid, dichromic acid, hypochlorous acid, chloric acid, chlorous acid, perchloric acid and nitrous acid.

[0048] Preferably, in step 1, the surfactant modification is specifically: the raw sand is immersed in a surfactant solution under stirring for surfactant modification.

[0049] The surfactant modification process is: the stirring speed is 50-100 r / min, the modification time is 6-12 h, and the modification temperature is room temperature.

[0050] The surfactant solution is a mixture of surfactant and water, and the mass fraction is 5-50wt%, and the mass of the surfactant is 3-10% of the mass of the raw sand.

[0051] The surfactant is at least one of cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium chloride (DTAC) and cetyltrimethylammonium chloride (CTAC).

[0052] Preferably, in step 1, the process of silane coupling agent modification is: water, ethanol and acid are prepared into a mixed solution; then the silane coupling agent is placed in the mixed solution for hydrolysis, and then the hydrolyzed silane coupling agent is added to the raw sand under stirring for silane coupling agent modification, so that the silane coupling agent reacts with the hydroxyl groups on the surface of the silica sand to form stable Si-O-Si bonds, hinder the agglomeration between the silica sand particles, and have better flowability and bulkiness in subsequent applications, thereby improving the strength of the sand mold.

[0053] The mass of water is 0.1-5% of the mass of the original sand, the mass of ethanol is 1-50% of the mass of the original sand, and the mass of acid is 0.1-10% of the mass of ethanol; the pH of the mixed solution is 3-4;

[0054] The acid is at least one of organic acid or inorganic acid, specifically at least one of acetic acid, oxalic acid, carbonic acid, hydrochloric acid and sulfuric acid;

[0055] The mass of the silane coupling agent is 0.1-5% of the mass of the original sand;

[0056] The silane coupling agent is at least one of 3-aminopropyl triethoxysilane (KH550), γ-glycidoxypropyl trimethoxysilane (KH560), γ-methacryloyloxypropyl trimethoxysilane (KH570), hexadecyl trimethoxysilane (A163), N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane (KH792) and N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxysilane (KH-602).

[0057] The temperature of hydrolysis is room temperature, and the time is 0.5-12h;

[0058] The modification process of the silane coupling agent is that the stirring speed is 15-200r / min, the modification time is 0.5-5h, the modification temperature is 80-150℃, and the stirring device is preferably a drum dryer with baffles.

[0059] Preferably, in step 1, water is used for washing; and the drying process is drying at 60-100℃ for 0.5-2h.

[0060] Step 2, the resin curing catalyst solution is added to the modified sand, and after mixing uniformly, the modified sand containing the catalyst is obtained; then the water-soluble polymer is added, and after mixing uniformly, the mixed system of the resin curing catalyst solution, the water-soluble polymer and the modified sand is obtained; then the mixed system is stirred and dried to remove water and promote the coordination reaction to complete, at the same time, the catalytic activity of the resin curing catalyst is improved, and the water-soluble polymer is coated on the surface of the modified sand by using the adsorption and coordination of the modified sand to the resin curing catalyst and the coordination between the resin curing catalyst and the water-soluble polymer, thereby obtaining the coated sand with core-shell structure whose shell layer is the water-soluble polymer and whose core layer is the modified sand (referred to as coated sand);

[0061] Preferably, in step 2, the mass fraction of the resin curing catalyst solution is 5-40wt%, and the mass of the resin curing catalyst solution is 0.1-5% of the mass of the modified sand.

[0062] The resin curing catalyst is at least one of aluminum chloride, copper chloride, iron chloride, zinc chloride, sulfuric acid, phosphoric acid, sulfonic acid, trichloroacetic acid, trifluoroacetic acid and oxalic acid.

[0063] Preferably, in step 2, the resin curing catalyst solution is mixed with the modified sand uniformly by stirring, and the stirring process is as follows: the stirring speed is 50-400 r / min, the time is 5-15 min, and the temperature is room temperature.

[0064] Preferably, in step 2, the mass of the water-soluble polymer is 0.1-3% of the mass of the modified sand.

[0065] The water-soluble polymer is at least one of polyethylene glycol powder, polyvinylpyrrolidone powder, and gum arabic powder.

[0066] Preferably, in step 2, the resin curing catalyst solution and the water-soluble polymer are mixed with the modified sand uniformly by stirring, and the stirring process is as follows: the stirring speed is 200-400 r / min, the time is 1-10 min, and the temperature is room temperature.

[0067] Preferably, in step 2, the drying process is as follows: the stirring speed is 15-200 r / min, the temperature is 40-120°C, and the time is 0.5-5 h, and the drying process is preferably carried out in a drum dryer equipped with baffles.

[0068] Preferably, in step 2, the addition amount of the resin curing catalyst solution and the water-soluble polymer is adjusted according to the specific requirements of the hardness, tensile strength, and collapse of the sand core film.

[0069] Preferably, in step 2, the resin curing catalyst solution is added in an atomized manner to make it more uniformly dispersed; and the water-soluble polymer is added in the form of powder to avoid caking during the subsequent drying process due to excessive moisture, and to make the coated sand easier to dry.

[0070] Step 3: using the resin-based adhesive and the coated sand of step 2 as raw materials, a sand core mold is prepared by pressing or 3D printing;

[0071] Preferably, in step 3, the specific steps for preparing the sand core mold by pressing are as follows: the resin-based adhesive is added to the coated sand while stirring, and then the coated sand mixed with the resin-based adhesive is uniformly filled into a mold for pressing; then the mold is placed in a hot box, and under the action of the coordination state resin curing catalyst in the coated sand, the resin-based adhesive undergoes a curing reaction to bond the coated sand into a whole, thereby obtaining the sand core mold.

[0072] The stirring process is as follows: the stirring speed is 50-400 r / min, the time is 5-15 min, and the temperature is room temperature.

[0073] The pressing process is as follows: the pressure is 0.01-15 MPa, and the pressing time is 2-10 min.

[0074] The temperature of the curing reaction is 40-120℃, and the time is 0.5-6h.

[0075] Preferably, in step 3, the specific steps for preparing the sand core by 3D printing are: distributing the coated sand into the sand laying module of the 3D printer, introducing the resin-based binder into the nozzle of the 3D printer, during the layer-by-layer sand laying process of the sand laying module, the nozzle sprays the resin-based binder according to the cross-sectional shape of the part layer by layer, under the action of the printer heating system, the coordination state resin curing catalyst in the coated sand promotes the curing reaction of the resin-based binder, and the coated sand on the cross section of the part is bonded into a whole, thereby preparing a sand core with a complex geometric configuration;

[0076] The process parameters of 3D printing are: the maximum forming size is 2500×1000×800mm, the printing speed is 27-32s / layer, the printing layer thickness is 0.2-0.5mm, and the printing layer number and printing time depend on the specific size of the sand core.

[0077] Preferably, in step 3, the mass of the resin-based binder is 0.8-5% of the mass of the coated sand.

[0078] Preferably, in step 3, the resin-based binder is composed of active reagents, viscosity regulators, surface tension regulators, defoaming agents and bacteriostatic agents; the active reagents are 60-100 parts by mass, the viscosity regulators are 1-10 parts by mass, the surface tension regulators are 0-1 parts by mass, the defoaming agents are 0.1-1 parts by mass, and the bacteriostatic agents are 0-1 parts by mass.

[0079] Preferably, in step 3, the active reagents are at least one of furfuryl alcohol, 5-hydroxymethyl furfuryl alcohol, 5-nitro furfuryl alcohol, furfural and furfuryl acid; the viscosity regulators are at least one of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, polyethyleneimine, phenolic resin and urea-formaldehyde resin; the surface tension regulators are at least one of silicone oil, sodium dodecyl sulfate and cetyltrimethylammonium bromide; the defoaming agents are at least one of silicone oil type defoaming agents, non-silicone oil type defoaming agents, polyether type defoaming agents and mineral oil type defoaming agents; and the bacteriostatic agents are at least one of sodium benzoate, benzoic acid, methyl paraben, propyl paraben, ascorbic acid and tea polyphenol.

[0080] Step 4: coating a barrier liquid permeable coating on the outer surface of the sand core prepared in step 3, and then coating a barrier resin matrix permeable and adhesive coating on the surface of the barrier liquid permeable coating, so as to improve the surface structure and roughness of the sand core, and at the same time, to build a coating on the surface of the sand core to prevent the liquid resin from penetrating during the molding of the carbon fiber composite material, thereby obtaining the sand core after coating (i.e., the sand core after coating the barrier liquid permeable coating and the barrier resin matrix permeable and adhesive coating);

[0081] Preferably, in step 4, the barrier liquid-permeable coating is formed by applying a barrier liquid-permeable coating material to the outer surface of the sand core mold and drying and curing it;

[0082] The barrier liquid-permeable coating material is prepared by dispersing ferric oxide particles in ethanol or a polyolefin solution; 5-20 parts by mass of ferric oxide particles, 20-100 parts by mass of ethanol or a polyolefin solution;

[0083] The ferric oxide particles have a particle size of 30-80 μm;

[0084] The polyolefin solution is prepared by dissolving a polyolefin in a mixed solvent of cyclohexane and ethanol; the polyolefin is 1-5 parts by mass, the cyclohexane is 50-100 parts by mass, and the ethanol is 0-100 parts by mass; the polyolefin is random polypropylene and / or polyolefin elastomer (POE);

[0085] The coating method is brush coating, dip coating, spray coating, shower coating, or roller coating; the drying temperature is 60-100°C, and the drying time is 10-30 min.

[0086] Preferably, in step 4, the barrier resin-permeable and adhesive coating is formed by applying a barrier resin-permeable and adhesive coating material to the outer surface of the barrier liquid-permeable coating and drying and curing it;

[0087] The barrier resin-permeable and adhesive coating material is a polyolefin solution or is prepared by dispersing nano-silica and polytetrafluoroethylene micro-powder in a polyolefin solution; the nano-silica is 1-5 parts by mass, the polytetrafluoroethylene micro-powder is 1-5 parts by mass, and the polyolefin solution is 80-150 parts by mass;

[0088] The nano-silica has a particle size of 5-30 nm, and the polytetrafluoroethylene micro-powder has a particle size of 1-5 μm;

[0089] The polyolefin solution is prepared by dissolving a polyolefin in a mixed solvent of cyclohexane and ethanol; the polyolefin is 1-5 parts by mass, the cyclohexane is 50-100 parts by mass, and the ethanol is 0-100 parts by mass; the polyolefin is random polypropylene and / or polyolefin elastomer (POE);

[0090] The coating method is brush coating, dip coating, spray coating, shower coating, or roller coating; the drying temperature is 40-100°C, and the drying time is 10-60 min.

[0091] Step 5: using the sand core mold coated in step 4 as a forming mold for carbon fiber composite materials, performing a carbon fiber composite material forming process; after the resin is cured, the mold is soaked or flushed with a solvent that can dissolve the water-soluble polymer of step 2, causing it to disintegrate and complete the demolding process, thereby obtaining a hollow special-shaped carbon fiber composite material.

[0092] Preferably, in step 5, the carbon fiber composite material forming process is winding forming, pultrusion forming, autoclave forming, vacuum bag forming or stamping forming.

[0093] Preferably, in step 5, the vacuum bag forming is specifically: wrapping the carbon fiber prepreg neatly in the coated sandy core mold, wrapping the isolation film on the carbon fiber prepreg to prevent the carbon fiber prepreg from sticking to the vacuum bag; then placing the sandy core film wrapped with the carbon fiber prepreg and the isolation film in the vacuum bag, and laying a layer of air-permeable felt on it; then vacuumizing the vacuum bag to make it adhere to the carbon fiber prepreg, and pressing it, closing the valve of the vacuum bag, and placing it in a hot box, preheating at 40-80°C for 10-30 min, and then heat curing at 100-130°C for 1-2 h; then cooling to room temperature, taking out the sandy core film wrapped with the carbon fiber prepreg and the isolation film from the vacuum bag, tearing off the isolation film, and then soaking or flushing the forming mold with a solvent that can dissolve the water-soluble polymer of step 2 to make it collapse to complete the demolding process, thereby obtaining the hollow special-shaped carbon fiber composite material.

[0094] Preferably, in step 5, the carbon fiber prepreg is selected to be a unidirectional carbon fiber prepreg with a grammage of 100-300 g / m 2 and a thickness of 0.1-0.3 mm.

[0095] Preferably, in step 5, the solvent that can dissolve the water-soluble polymer of step 2 is at least one of water, ethanol, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide and dichloromethane, preferably water.

[0096] In the examples, the test methods are as follows: (1) observing the surface morphology on a Phenom XL desktop scanning electron microscope; (2) testing the content and change of elements by NEXSA X-ray photoelectron spectrometer; (3) analyzing the change of chemical bonds by Nicolet iS50 Fourier transform infrared spectrometer; (4) testing the moisture regain in a LHS-100SC constant temperature and humidity chamber; (5) determining the flowability based on the angle of repose method: forming a sand pile at a speed of 20 g per second from a height of 10 cm, and measuring the angle of repose θ; (6) analyzing the sand particle size and distribution by Mastersizer 3000 laser particle size analyzer; (7) detecting the viscosity of the adhesive on a MCR302 modular intelligent advanced rheometer; (8) analyzing the surface tension of the adhesive on a DSA30S full-automatic contact angle tester; (9) testing the surface roughness and line roughness of the product by OLS4100 laser confocal microscope Figure 14(10) The line roughness of the product is tested by using a laboratory TR220 surface roughness tester; (11) The printing forming of the binder and the coated sand is tested by using an Esun industrial-grade 3D printer; (12) The inkjet of the binder in the nozzle of the industrial-grade 3D printer is tested by using an Esun inkjet system.

[0097] Example 1:

[0098] Step 1, 70-140 mesh raw sand and hydrogen peroxide aqueous solution (mass fraction of 10wt%) with the same mass as the raw sand are added to the sand mixer, the hydrogen peroxide aqueous solution is completely immersed in the raw sand, stirring at room temperature at a speed of 100r / min, the stirring time is 4h, then repeatedly washed with water, after washing, placed in an oven at 100℃ for 2h to dry, so that it is completely dry, to obtain modified sand;

[0099] Step 2, the modified sand is added to the sand mixer, 0.5% of aluminum chloride solution (mass fraction of 31.2wt%) accounting for the mass of the modified sand is uniformly dispersed in the modified sand in the form of atomization at a stirring speed of 400r / min, the stirring time is 10min; then 0.375% of polyvinylpyrrolidone powder accounting for the mass of the modified sand is fully mixed with the modified sand containing the catalyst at a stirring speed of 400r / min, the stirring time is 10min; then the mixed system is transferred to a drum dryer equipped with a baffle, dried at 100℃ for 1h, to obtain coated sand;

[0100] Step 3, the coated sand is placed in the sand mixer, 2.5% of the resin-based binder (consisting of 97 parts by mass of furfuryl alcohol, 3 parts by mass of polyvinylpyrrolidone, and 0.2 parts by mass of silicone oil defoaming agent) accounting for the mass of the coated sand is added to the coated sand at a stirring speed of 400r / min, after stirring for 10min, it is taken out, the coated sand mixed with the resin-based binder is uniformly filled into the mold to press into a sand mold with a specific shape, and then placed in an oven at 80℃ for 4h to heat, so that the resin-based binder undergoes a curing reaction under the catalysis of aluminum chloride, and the coated sand is bonded into a sand core mold with a complex geometric configuration, and a corresponding eight-shaped block is made by using the method in the national standard GB 13022-91 for performance testing;

[0101] Step 4, a layer of liquid permeation resistant coating (consisting of 1 part by mass of ferric sesquioxide particles and 5 parts by mass of ethanol) is compounded on the surface of the sand core mold obtained in step 3, and dried and cured at 100℃ for 10min; then a layer of resin permeation and adhesion resistant coating (consisting of 3 parts by mass of POE dissolved in 97 parts by mass of cyclohexane) is compounded, and dried and cured at 100℃ for 1h, to obtain a sand core mold with a coating;

[0102] Step 5, using the sand core obtained in step 4 as a support mold, carbon fiber prepreg is neatly wrapped in the coated sand core, and a release film is wrapped on the carbon fiber prepreg to prevent the carbon fiber prepreg from sticking to the vacuum bag; then the sand core film wrapped with the carbon fiber prepreg and the release film is placed in a vacuum bag, and a layer of air-permeable felt is laid on it; then the vacuum bag is vacuumed to make it adhere to the carbon fiber prepreg, and pressure is applied to it, the valve of the vacuum bag is closed, and it is placed in a hot box, preheated at 80°C for 30 min, and then heat cured at 130°C for 1 h; then cool to room temperature, take out the sand core film wrapped with the carbon fiber prepreg and the release film from the vacuum bag, tear off the release film, and then use water to scatter the sand core film to complete the demolding process, and obtain a hollow special-shaped carbon fiber composite material with smooth surface.

[0103] From Figure 1 , 2 , 3 it can be seen that, compared with the original sand, the surface of the modified sand obtained in step 1 significantly reduces the argillaceous component, forming a rough surface structure conducive to film coating. Compared with the modified sand, the coated sand obtained in step 2 has a smoother surface, indicating that the coating layer can further optimize the surface structure of the original sand.

[0104] From Figure 4 , 5 , 6 it can be seen that, compared with the original sand, the number of hydroxyl groups on the surface of the modified sand obtained in step 1 significantly increases. The XPS spectrum of the coated sand obtained in step 2 shows the O1s peak of C=O in the polymer, proving the success of the coating.

[0105] From Figure 7 it can be seen that, compared with the modified sand containing the catalyst, the coated sand does not show the O-H absorption peak, while the coated sand shows the absorption peak of C=O in the polymer and the absorption peak of the polymer-metal ion coordination bond, further indicating the formation of the coating layer.

[0106] From Figure 8 it can be seen that, under the conditions of temperature 30°C and humidity 70%, the moisture regain of the coated sand does not have a large increase compared with the original sand and the modified sand.

[0107] From Figure 9 it can be seen that the angle of repose of the coated sand is close to that of the original sand and is very low, indicating that the coating does not affect the flowability of the sand.

[0108] From Figure 10 , 11 it can be seen that the coated sand has the same particle size and distribution as the original sand, indicating that the coating process does not significantly change the particle size and distribution of the sand, providing convenience for subsequent application.

[0109] Under the bonding effect of the resin adhesive and the coating layer, the hardness of the eight-shaped block obtained in step 3 is 54.5HD and the tensile strength is 2.44MPa. The hardness and tensile strength of the sand mold are good, and the sand does not fall off. It is higher than the strength standard of the printed part and can be used for the support mold of carbon fiber composite materials. At the same time, the coating layer is water-soluble, and the sand mold can quickly collapse in water (such as Figure 12 The eight-shaped block obtained in step 3 has a moisture regain of 0.11% after being placed in an environment with a temperature of 28°C and a humidity of 60% for one day. After moisture regain, the tensile strength drops to 0.94 MPa. After drying, the strength can still be restored to the initial value.

[0110] Depend on Figure 14 It can be seen that the surface roughness of the sand core mold obtained in step 3 is 35.5 μm, and the surface roughness of the sand core mold after coating obtained in step 4 is reduced to 7.5 μm, the surface flatness and smoothness are improved, and the surface can block liquids such as epoxy resin (such as Figure 15 As shown in the figure, a is a sand core mold with only a liquid penetration barrier coating, b is a sand core mold after coating, and c is the adhesion between the surfaces of products a and b and the resin. It can be seen from Figure c that after the resin is cured, the cured resin on product b can be completely peeled off, while the cured resin on product a cannot be peeled off), which provides convenience for demolding carbon fiber composite special-shaped parts and ensuring the smooth surface of carbon fiber composite materials.

[0111] The surface roughness of the inner surface of the carbon fiber composite material obtained after demoulding reached 2.2 μm, and the tensile strength of the carbon fiber composite material was 78 MPa.

[0112] Example 2:

[0113] This embodiment is the same as Example 1, except that: in step 2, the polyvinyl pyrrolidone powder is replaced with polyethylene glycol (molecular weight 20,000) powder; in step 3, the resin adhesive is composed of 98 parts by mass of furfuryl alcohol, 2 parts by mass of polyethylene glycol (molecular weight 20,000), and 0.2 parts by mass of silicone oil defoamer.

[0114] The hardness of the splayed block obtained in step 3 was 44.0 HD and the tensile strength was 2.02 MPa. The moisture regain of the splayed block obtained in step 3 after one day in an environment with a temperature of 28°C and a humidity of 60% was 0.09%, and the tensile strength dropped to 0.65 MPa after moisture regain. This shows that changes in the type of coating polymer and the resin adhesive component will significantly affect the hardness and strength of the sandy core film, which in turn will affect the carbon fiber composite molding process. Despite this, the tensile strength of the carbon fiber composite still reached 77 MPa, indicating that the sandy core mold is suitable for carbon fiber composite molding.

[0115] Example 3:

[0116] The embodiment is the same as embodiment 1, the difference is only that in step 2, the polyvinylpyrrolidone powder is replaced by polyethylene glycol (molecular weight 2000) powder; in step 3, the composition of the resin-based adhesive is 98 parts by mass of furfuryl alcohol, 2 parts by mass of polyethylene glycol (molecular weight 2000), and 0.2 parts by mass of silicone oil defoaming agent.

[0117] The hardness of the eight-shaped block obtained in step 3 is 42.8 HD, and the tensile strength is 1.92 MPa. The moisture regain of the eight-shaped block obtained in step 3 is 0.13% after being placed in an environment with a temperature of 28°C and a humidity of 60% for one day, and the tensile strength decreases to 0.83 MPa after moisture regain. It can be seen that the change of the molecular weight of the coated polymer and the molecular weight of the components in the resin-based adhesive will significantly affect the hardness and strength of the sandy core film, and in turn will affect the molding process of the carbon fiber composite material. However, the tensile strength of the carbon fiber composite material still reaches 76 MPa, indicating that the sandy core mold is suitable for molding of carbon fiber composite materials.

[0118] Embodiment 4:

[0119] The embodiment is the same as embodiment 1, the difference is only that step 3 is: the coated sand is distributed into the 3D printer sand laying module, the resin-based adhesive (composed of 97 parts by mass of furfuryl alcohol, 3 parts by mass of polyvinylpyrrolidone, and 0.2 parts by mass of silicone oil defoaming agent) is introduced into the 3D printer nozzle, and during the layer-by-layer sand laying process of the 3D printer sand laying module, the 3D printer nozzle sprays the resin-based adhesive layer by layer according to the cross-sectional shape of the part. Under the action of the printer heating system, the aluminum chloride catalyzed resin-based adhesive undergoes a curing reaction, and the coated sand with a shell-core structure on the cross section of the part is bonded into a whole, and a sandy core mold with a complex geometric configuration is prepared.

[0120] The viscosity of the resin-based adhesive in step 3 is 10.8 mpa·s, and the surface tension is 36.8 mN / m, which meets the requirements of the industrial-grade 3D printer nozzle. From Figure 16 It can be seen that the coated sand is well laid, and after the adhesive contacts the coated sand, the coordination state of the aluminum chloride catalyzed adhesive in the coated layer undergoes a curing reaction, and the cured adhesive bonds the coated sand into a whole structure by point bonding. From Figure 17 It can be seen that the resin-based adhesive in step 3 has good inkjet performance in the actual printing process and is suitable for actual printing.

[0121] The hardness of the eight-shaped block obtained in step 3 is 45HD, and the tensile strength is 2.0 MPa. The moisture regain of the eight-shaped block obtained in step 3 is only 0.08% after being placed in an environment with a temperature of 28℃ and a humidity of 60% for one day, and the tensile strength decreases to 1.2 MPa after moisture regain. It can be seen that the adhesive designed in the application meets the printing requirements of the industrial-grade 3D printer, and the printed sand core film can be used for the molding of hollow special-shaped carbon fiber composites. The uniqueness of the 3D printing technology in molding complex sand core film can provide various mold supports for the molding of carbon fiber composites, and the one-time molding of complex carbon fiber composites can be realized.

[0122] Example 5:

[0123] The embodiment is the same as example 1, and the only difference is that in step 4, the composition of the liquid permeation blocking coating is 1 part by mass of iron trioxide particles and 5 parts by mass of polyolefin solution, and the composition of the resin permeation and adhesion blocking coating is 1 part by mass of nano-silicon dioxide, 2 parts by mass of polytetrafluoroethylene powder and 97 parts by mass of polyolefin solution.

[0124] The line roughness of the sand core mold after the coating obtained in step 4 is reduced from 3.5μm to 2.7μm, and the inner surface line roughness of the carbon fiber composite molded by the sand core film is reduced from 0.9μm in example 1 to 0.8μm. It can be seen that through the optimization of the coating system, a sand core film with a smoother surface can be obtained, and a high-quality carbon fiber composite product with a smoother surface can also be obtained.

[0125] Comparative example 1:

[0126] The only difference between the comparative example and example 1 is that the chemical modification of the raw sand is not performed in step 1.

[0127] It is found that the hardness of the eight-shaped block obtained in steps 1 and 2 of the comparative example is 50.5HD, and the tensile strength is 2.3MPa, which is far lower than the performance of the eight-shaped block obtained in steps 1, 2 and 3 of example 1. The moisture regain of the eight-shaped block obtained in steps 1 and 2 of the comparative example is 0.15% after 24 hours, and the tensile strength of the eight-shaped block decreases to 0.6MPa after moisture regain, which is also lower than the performance of the eight-shaped block obtained in steps 1, 2 and 3 of example 1. It can be seen that chemical modification is extremely important for improving the performance of the sand mold, that is, the chemical modification step cannot be omitted.

[0128] Comparative example 2:

[0129] The only difference between the comparative example and example 1 is that no polyvinylpyrrolidone powder is added in step 2.

[0130] It is found that the sand core film is washed or soaked with tap water, and a certain external force is applied, and the sand core mold cannot collapse (such as Figure 12The hollow profiled carbon fiber composite material is demolded, which is a problem, and limits the molding. Therefore, the polymer coating is extremely important for the water collapse of the sandy core film and the subsequent demolding of the carbon fiber composite material, that is, the polymer coating step cannot be omitted. At the same time, the hardness of the dog leg block prepared by steps 1, 2 and 3 of the present comparative example is 41.5 HD, and the tensile strength is 1.8 MPa, which is far less than the performance of the dog leg block obtained by steps 1, 2 and 3 of the present comparative example 1 and the present example 1. Therefore, the polymer coating is also extremely beneficial to improving the strength of the sand mold, and the high-strength sandy core film brings great convenience to the subsequent carbon fiber molding operation.

[0131] Comparative Example 3:

[0132] The present comparative example is compared with the present example 1, and the only difference is that no barrier resin penetration and adhesion coating is used in step 4.

[0133] It is found that during the water collapse demolding process, the carbon fiber composite material is adhered to the surface of the sandy core mold, resulting in sand sticking to the inner surface of the hollow carbon fiber composite material, affecting the surface finish, and greatly reducing the quality of the finished product. Therefore, the barrier resin penetration and adhesion coating is extremely effective in preventing resin from penetrating during the molding process of the carbon fiber composite material, thereby assisting the water to achieve the goal of clean demolding, and at the same time, giving the carbon fiber composite material a smooth surface. Therefore, the barrier resin penetration and adhesion coating treatment step is also very important and cannot be omitted.

[0134] Comparative Example 4:

[0135] The present comparative example is compared with the present example 4, and the only difference is that the resin adhesive composition in step 2 is furfuryl alcohol.

[0136] It is found that when the resin adhesive is only furfuryl alcohol, since its viscosity is only 4.9 mpa·s, and its surface tension reaches 42 mN / m, it does not meet the requirements of the industrial 3D printer nozzle (viscosity of 6-12 mpa·s, surface tension of 25-40 mN / m). Therefore, the inkjet continuity is affected during printing, and there is a serious ink accumulation phenomenon, which greatly reduces the strength and precision of the printed product, and further affects the subsequent molding of the carbon fiber composite material. Therefore, the design of the adhesive system is extremely important to ensure the smooth progress of the 3D printing process.

[0137] The present application is not described in the prior art.

Claims

1. A method for forming a hollow special-shaped carbon fiber composite material, characterized in that: The method comprises the following steps: Step 1: Chemically modify the raw sand to arrange the chemical groups and structure on the surface of the raw sand; then wash to remove surface impurities and unreacted substances, and then dry to obtain modified sand; Chemical modification uses oxidation modification, surfactant modification or silane coupling agent modification; The oxidation modification specifically includes: immersing the raw sand in a liquid oxidant solution under stirring for oxidation modification; The liquid oxidant solution is a mixture of liquid oxidant and water, with a mass fraction of 5-50wt%; the mass of the liquid oxidant is 5-50% of the mass of the original sand; The liquid oxidant is at least one of hydrogen peroxide, concentrated nitric acid, dilute nitric acid, concentrated sulfuric acid, permanganic acid, dichromic acid, hypochlorous acid, chloric acid, chlorous acid, perchloric acid and nitrous acid; The surfactant modification is specifically as follows: the raw sand is immersed in a surfactant solution under stirring to carry out surfactant modification; The surfactant solution is a mixture of surfactant and water, with a mass fraction of 5-50wt%, and the mass of the surfactant accounts for 3-10% of the mass of the original sand; The surfactant is at least one of CTAB, DTAC and CTAC; The process of silane coupling agent modification is as follows: water, ethanol and acid are prepared into a mixed solution; the silane coupling agent is placed in the mixed solution for hydrolysis, and then the hydrolyzed silane coupling agent is added to the raw sand under stirring for silane coupling agent modification; The mass of water is 0.1-5% of the mass of the original sand, the mass of ethanol is 1-50% of the mass of the original sand, and the mass of acid is 0.1-10% of the mass of ethanol; the pH of the mixed solution is 3-4; The acid is at least one of acetic acid, oxalic acid, carbonic acid, hydrochloric acid and sulfuric acid; The mass of silane coupling agent is 0.1~5% of the mass of original sand; The silane coupling agent is at least one of KH550, KH560, KH570, A163, KH792 and KH-602; Step 2: adding the resin curing catalyst solution to the modified sand and mixing them evenly to obtain catalyst-containing modified sand; then adding the water-soluble polymer and mixing them evenly to obtain a mixed system of the resin curing catalyst solution, the water-soluble polymer and the modified sand; then drying the mixed system while stirring to remove moisture and promote the coordination reaction to be complete, while improving the catalytic activity of the resin curing catalyst, and coating the surface of the modified sand with the water-soluble polymer to obtain coated sand with a core-shell structure in which the shell layer is the water-soluble polymer and the core layer is the modified sand; Step 3: Using the resin adhesive and the coated sand from step 2 as raw materials, a sand core mold is prepared by compression molding or 3D printing; Step 4: Compounding a liquid penetration barrier coating on the outer surface of the sandy core mold in step 3, and then compounding a resin matrix penetration barrier and adhesion barrier coating on the surface of the liquid penetration barrier coating to improve the surface structure and roughness of the sandy core mold, and at the same time, constructing a coating on the surface of the sandy core mold to prevent liquid resin from penetrating during molding of the carbon fiber composite material, thereby obtaining a coated sandy core mold; Step 5: Use the coated sand core mold of step 4 as a forming mold for the carbon fiber composite material to carry out the carbon fiber composite material forming process; after the resin is solidified, use a solvent that can dissolve the water-soluble polymer of step 2 to collapse the forming mold, complete the demolding process, and obtain a hollow special-shaped carbon fiber composite material.

2. The method for forming a hollow special-shaped carbon fiber composite material according to claim 1, characterized in that: In step 1, the raw sand is from various sources; the particle size of the raw sand is 70-140 mesh; In step 1, washing is performed with water; and the drying process is: drying at 60-100° C. for 0.5-2 h.

3. The method for forming a hollow special-shaped carbon fiber composite material according to claim 2, characterized in that: In step 1, The oxidation modification process is: stirring speed is 50~100r / min, modification time is 6~12h, and modification temperature is room temperature; The surfactant modification process is as follows: stirring speed is 50-100 r / min, modification time is 6-12 h, and modification temperature is room temperature; The hydrolysis temperature is room temperature and the time is 0.5~12h; The modification process of silane coupling agent is: stirring speed is 15~200r / min, modification time is 0.5~5h, and modification temperature is 80~150℃.

4. The method for forming a hollow special-shaped carbon fiber composite material according to claim 1, characterized in that: In step 2, the mass fraction of the resin curing catalyst solution is 5-40wt%, and the mass of the resin curing catalyst solution is 0.1-5% of the mass of the modified sand; In step 2, the resin curing catalyst solution and the modified sand are mixed evenly by stirring, and the stirring process is: stirring speed is 50-400 r / min, time is 5-15 minutes, and temperature is room temperature; In step 2, the mass of the water-soluble polymer is 0.1-3% of the mass of the modified sand; In step 2, the resin curing catalyst solution, the water-soluble polymer and the modified sand are mixed uniformly by stirring, and the stirring process is: stirring speed is 200-400 r / min, time is 1-10 minutes, and temperature is room temperature; In step 2, the drying process while stirring is: stirring speed is 15-200 r / min, temperature is 40-120°C, and time is 0.5-5h; In step 2, the resin curing catalyst solution is added in an atomized manner to make it more evenly dispersed; the water-soluble polymer is added in powder form, which avoids agglomeration due to excessive moisture in the subsequent drying process and makes the coated sand easier to dry.

5. The method for forming a hollow special-shaped carbon fiber composite material according to claim 1 or 4, characterized in that: In step 2, the resin curing catalyst is at least one of aluminum chloride, cupric chloride, ferric chloride, zinc chloride, sulfuric acid, phosphoric acid, sulfonic acid, trichloroacetic acid, trifluoroacetic acid and oxalic acid; and the water-soluble polymer is at least one of polyethylene glycol, polyvinyl pyrrolidone and gum arabic.

6. The method for forming a hollow special-shaped carbon fiber composite material according to claim 1, characterized in that: In step 3, the specific steps of preparing the sand core mold by pressing and molding are: adding a resin adhesive to the coated sand while stirring, mixing evenly, and evenly filling the coated sand mixed with the resin adhesive into a mold for pressing and molding; then, under the action of a coordinated resin curing catalyst in the coated sand, the resin adhesive undergoes a curing reaction, bonding the coated sand into a whole, and obtaining a sand core mold; The stirring process is: stirring speed is 50~400r / min, time is 5~15min, and temperature is room temperature; The pressing process is: pressure of 0.01~15MPa, pressing time of 2~10min; The curing reaction temperature is 40~120℃ and the time is 0.5~6h; In step 3, the specific steps of preparing the sand core mold by 3D printing are: distributing the coated sand into the sand-laying module of the 3D printer, introducing the resin adhesive into the nozzle of the 3D printer, and during the sand-laying process of the sand-laying module, the nozzle sprays the resin adhesive layer by layer according to the cross-sectional shape of the part. Under the action of the printer's heating system, the coordinated resin curing catalyst in the coated sand promotes the resin adhesive to undergo a curing reaction, thereby bonding the coated sand on the cross-section of the part into a whole, thereby producing a sand core mold with a complex geometric configuration; The process parameters of 3D printing are: maximum molding size is 2500×1000×800mm, printing speed is 27~32s / layer, and printing layer thickness is 0.2~0.5mm.

7. The method for forming a hollow special-shaped carbon fiber composite material according to claim 1, characterized in that: In step 3, the mass of the resin adhesive is 0.8-5% of the mass of the coated sand; In step 3, the resin adhesive is composed of an active agent, a viscosity modifier, a surface tension modifier, a defoaming agent, and an antibacterial agent; the active agent is 60 to 100 parts by mass, the viscosity modifier is 1 to 10 parts by mass, the surface tension modifier is 0 to 1 part by mass, the defoaming agent is 0.1 to 1 part by mass, and the antibacterial agent is 0 to 1 part by mass; In step 3, the active agent is at least one of furfuryl alcohol, 5-hydroxymethylfurfuryl alcohol, 5-nitrofurfuryl alcohol, furfural and furoic acid; the viscosity modifier is at least one of polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol, polyethyleneimine, phenolic resin and urea-formaldehyde resin; the surface tension modifier is at least one of silicone oil, sodium lauryl sulfate and cetyltrimethylammonium bromide; the defoamer is at least one of silicone oil defoamer, non-silicone oil defoamer, polyether defoamer and mineral oil defoamer; and the antibacterial agent is at least one of sodium benzoate, benzoic acid, methyl parahydroxybenzoate, propyl parahydroxybenzoate, ascorbic acid and tea polyphenols.

8. The method for forming a hollow special-shaped carbon fiber composite material according to claim 1, characterized in that: In step 4, the liquid penetration barrier coating is formed by applying the liquid penetration barrier coating to the outer surface of the sand core mold and drying and curing it; The liquid penetration barrier coating is prepared by dispersing ferric oxide particles in an ethanol or polyolefin solution; the ferric oxide particles are 5 to 20 parts by mass and the ethanol or polyolefin solution is 20 to 100 parts by mass; The particle size of ferric oxide particles is 30~80μm; The polyolefin solution is prepared by dissolving polyolefin in a mixed solvent of cyclohexane and ethanol; wherein the polyolefin comprises 1 to 5 parts by mass, 50 to 100 parts by mass of cyclohexane, and 0 to 100 parts by mass of ethanol; the polyolefin is random polypropylene and / or a polyolefin elastomer; The coating method is brush coating, dipping, spraying, curtain coating or roller coating; the drying temperature is 60~100℃ and the drying time is 10~30min.

9. The method for forming a hollow special-shaped carbon fiber composite material according to claim 1, characterized in that: In step 4, the barrier resin penetration and adhesion coating is formed by applying the barrier resin penetration and adhesion coating to the outer surface of the barrier liquid penetration coating and drying and curing it; The resin penetration and adhesion barrier coating is made of polyolefin solution or nano-silicon dioxide and polytetrafluoroethylene powder dispersed in polyolefin solution; 1-5 parts by mass of nano-silicon dioxide, 1-5 parts by mass of polytetrafluoroethylene powder, and 80-150 parts by mass of polyolefin solution; The particle size of nano-silica is 5~30nm, and the particle size of polytetrafluoroethylene powder is 1~5μm; The polyolefin solution is prepared by dissolving polyolefin in a mixed solvent of cyclohexane and ethanol; wherein the polyolefin comprises 1 to 5 parts by mass, 50 to 100 parts by mass of cyclohexane, and 0 to 100 parts by mass of ethanol; the polyolefin is random polypropylene and / or a polyolefin elastomer; The coating method is brush coating, dipping, spraying, shower coating or roller coating; the drying temperature is 40~100℃, and the drying time is 10~60min.

10. The method for forming a hollow special-shaped carbon fiber composite material according to claim 1, characterized in that: In step 5, the solvent capable of dissolving the water-soluble polymer in step 2 is at least one of water, ethanol, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide and dichloromethane.

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