A hollow beam of carbon fiber composite material and a method of manufacturing and use thereof

Abstract

The application relates to a hollow beam of carbon fiber composite material and a preparation method and application thereof, and belongs to the technical field of carbon fiber composite material beams. The preparation method comprises the following steps: S1, a core mold is prepared by using a foamed material, a cladding film is wrapped on the surface of the core mold, and a release agent is coated on the outer surface of the cladding film; S2, carbon fiber prepreg is laid on the outer surface of the cladding film according to the set layer number and direction, vacuumizing operation is conducted every time the set layer number is laid; S3, expansion foamed material is laid on the part prone to glue deficiency, and then outer layer prepreg is laid to obtain a preformed body; S4, compressed air is introduced between the core mold and the cladding film, the core mold is separated from the cladding film, and then the core mold is drawn out; and S5, the preformed body after the core mold is drawn out is placed in an external forming mold, heated and solidified, demolded, and a product of the hollow beam of carbon fiber composite material is obtained. Wrinkles caused by friction during the core drawing process are prevented by the cladding film, glue deficiency defects caused by the heating and solidification process are prevented by the expansion foamed material, and high mechanical properties are obtained.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber composite beam technology, specifically relating to a hollow carbon fiber composite beam, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Resin-based fiber-reinforced composite materials are increasingly used in rail transportation, aerospace, and wind turbine blades. They are crucial for reducing product weight and increasing efficiency, improving mechanical properties, reducing energy consumption, and lowering costs. In actual production, prepregs are often used as raw materials, and multiple layers of prepregs are cured into specific shapes.

[0004] Hollow beams offer advantages such as material savings, high structural stiffness, and minimal deformation. With the increasing use of composite materials, composite materials are now being used in load-bearing components of hollow beam structures as well. However, due to the complex stress conditions and high strength requirements of these load-bearing components, even minor surface quality defects can have an impact. Therefore, a more conservative approach needs to be taken regarding the surface quality of composite material products during production.

[0005] For integrally molded hollow beams of carbon fiber composites, it is necessary to avoid surface wrinkles or chaotic textures to prevent affecting the overall integrity of the product. For hollow beams of carbon fiber composites with variable cross-sections, corners and curved surfaces are common structural features; it is also important to avoid surface depressions at corners due to insufficient adhesive. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a hollow beam of carbon fiber composite material, its preparation method, and its application, thereby avoiding surface defects, improving forming quality, and ensuring the mechanical properties of the product during the preparation process.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, a method for preparing a hollow beam made of carbon fiber composite material includes the following steps: S1. Prepare a core mold using foam material, wrap the core mold surface with a covering film, and coat the outer surface of the covering film with a release agent. S2. According to the set number of layers and direction, lay carbon fiber prepreg on the outside of the coating film. After laying the set number of layers, perform a vacuuming operation. S3. Lay expanded foam material in areas prone to glue shortage, and then lay the outer layer of prepreg to obtain a preform. S4. Compressed air is introduced between the core mold and the covering film to separate the core mold from the covering film, and then the core mold is extracted. S5. Place the preform after removing the core mold into the external molding mold, heat and cure it, and then demold to obtain the hollow beam product of carbon fiber composite material.

[0008] Secondly, a hollow beam of carbon fiber composite material is prepared by the above-mentioned method for preparing hollow beams of carbon fiber composite material.

[0009] Thirdly, the application of the above-mentioned hollow beam of carbon fiber composite material and / or the method for preparing hollow beam of carbon fiber composite material includes: applications in rail transit vehicles and aerospace vehicles.

[0010] The beneficial effects of this invention are as follows: 1. The method for preparing hollow beams of carbon fiber composite materials provided by this invention is an integral molding technology. It prevents wrinkles caused by friction during the core-pulling process by using a coating film, and prevents defects such as insufficient adhesive during the heat curing process by using expanded foam material. Simultaneously, a vacuum operation is added during the laying process to remove the gas that causes wrinkles. The entire process ensures a wrinkle-free surface and no depressions on curved surfaces. When applied to hollow beams of variable cross-section carbon fiber composite materials, it effectively ensures that the product shape matches the design shape.

[0011] 2. The hollow beam made of carbon fiber composite material provided by this invention has a high surface quality. By improving the surface quality, the integrity of the hollow beam is improved, thereby achieving high mechanical properties. It can effectively solve the problems of high density, high cost, poor corrosion resistance, poor wear resistance, and numerous weld points of metal materials in the current rail transit field. The manufacturing efficiency is increased by 50% compared with traditional methods, and the service life is increased by 2 to 3 times compared with traditional crossbeams. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0013] Figure 1 The diagram shows the structure of the hollow beam prepared in Example 1, where (a) is a three-dimensional perspective view of the hollow beam structure, (b) is a front view of the hollow beam structure, (c) is a top view of the hollow beam structure, and (d) is a side view of the hollow beam structure.

[0014] Figure 2 This is a schematic flowchart of the hollow beam preparation method in Example 1.

[0015] Figure 3 The temperature rise curve is shown for the curing process in Example 1. Detailed Implementation

[0016] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0017] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0018] A method for preparing a hollow beam made of carbon fiber composite material includes the following steps: S1. Prepare a core mold using foam material, wrap the core mold surface with a covering film, and coat the outer surface of the covering film with a release agent. S2. According to the set number of layers and direction, lay carbon fiber prepreg on the outside of the coating film. After laying the set number of layers, perform a vacuuming operation. S3. Lay expanded foam material in areas prone to glue shortage, and then lay the outer layer of prepreg to obtain a preform. S4. Compressed air is introduced between the core mold and the covering film to separate the core mold from the covering film, and then the core mold is extracted. S5. Place the preform after removing the core mold into the external molding mold, heat and cure it, and then demold to obtain the hollow beam product of carbon fiber composite material.

[0019] This invention prevents wrinkles caused by friction during the core-pulling process by using a coating film, and prevents defects such as insufficient adhesive during the heating and curing process by using expanded foam material. Simultaneously, a vacuum operation is added during the installation process to remove gases that cause wrinkles. The entire process ensures a wrinkle-free surface and no depressions on curved surfaces, effectively guaranteeing that the shape of curved corners matches the design shape, thus providing quality assurance for the production of variable cross-section hollow beams.

[0020] Optionally, the total number of layers can be 12 to 15, with a total thickness of 3.8 to 4.2 mm.

[0021] Optionally, the carbon fiber prepreg includes: carbon fiber unidirectional tape and twill prepreg, wherein the innermost and outermost carbon fiber prepregs are twill prepregs; preferably, the carbon fiber unidirectional tape is T300 carbon fiber unidirectional tape, and the twill prepreg is 3K twill carbon fiber prepreg.

[0022] Optionally, in S1, the shape of the core mold is the same as the cavity shape of the designed hollow beam.

[0023] Optionally, in S1, the nylon film is a thin nylon bag, which is placed over the mandrel and then laid on the surface. In S2, during vacuuming, a vacuum bag is wrapped around the outer surface of the laid material, and the vacuum bag is sealed with a sealing strip. The laid material and the mandrel are completely sealed in the vacuum bag, and then a vacuum is drawn. During the vacuuming process, the prepreg adheres tightly to the thin nylon bag on the surface of the mandrel due to its own adhesion and pressure. Therefore, the thin nylon bag is a general-purpose air bag, which is slightly larger than the mandrel.

[0024] Optionally, in S2, the prepreg is laid using a butt joint method to prevent unevenness on the surface.

[0025] Optionally, in S2, a vacuum operation is performed after every three layers of prepreg to remove the interlayer gas from the newly laid prepreg and prevent wrinkles from forming.

[0026] Optionally, in S2, the vacuuming operation is as follows: a perforated release film, a breathable felt, and a vacuum bag are wrapped around the outside of the laid prepreg, and a vacuuming operation is performed on a constant temperature heating table to remove the gas between the prepregs.

[0027] Optionally, in S2, the heating temperature of the constant temperature heating table is 40~50℃. At this temperature, the viscosity of the resin matrix of the prepreg decreases, but it does not reach the curing temperature. Therefore, air bubbles in the laying process can be extracted, making the laying tighter.

[0028] Optionally, in S2, vacuuming is performed once on each of the front and back sides during each vacuuming operation.

[0029] Optionally, in S3, the expanding foam material refers to: thermally expanding adhesive, which has stable properties at room temperature and can be cut, and has the function of slightly expanding and curing after heating. It can expand to a certain volume during the heating and curing process of S5, and is used to support the surface prepreg in areas prone to glue shortage, preventing surface collapse and glue shortage. The operation method is: before laying a layer of twill prepreg on the surface, apply a 2cm wide expanding foam material to the left and right rounded corners of the product. After final curing, due to the combined action of the air bag and the mold, the surface is flat and no repair is required.

[0030] Optionally, the thermally expanding adhesive is a self-expanding high-energy adhesive, preferably the HR-332 foam core material product from Xiamen Haor New Materials Co., Ltd.

[0031] Optionally, in S4, after the coating film separates from the core mold, the core mold is extracted and the internal coating film is cleaned.

[0032] Optionally, in S5, the external forming mold is a double-sided mold, which can heat evenly and ensure forming quality.

[0033] Optionally, in S5, the heat curing process is as follows: heat up to 100 degrees Celsius at a rate of 2℃ / min, maintain the temperature for 30 minutes; heat up to 120 degrees Celsius at a rate of 1℃ / min, maintain the temperature for 30 minutes; heat up to 130 degrees Celsius at a rate of 1℃ / min, maintain the temperature for 300 minutes; and then cool naturally to room temperature.

[0034] Optionally, in S1, the shape of the core mold is the same as the cavity shape of the designed hollow beam; At this point, in S5, a low-temperature assembly method is required to place the preform into the outer mold.

[0035] Optionally, in S5, an air bag is placed in the internal cavity of the preform after the core mold is extracted, and the air inlet of the air bag reserved on the mold insert is connected. Then, the preform with the air bag is placed into the outer mold to support the preform internally during the molding and curing process. The inflatable bag needs to be airtight and is used to fill the internal cavity of the preform when inflated to provide support.

[0036] Optionally, the air bag is made of nylon and its shape is not strictly required. For example, it can be a straight cylindrical air bag that is bent and arranged in the internal cavity (e.g., arranged in a U-shape). During inflation, the U-shaped straight cylindrical air bag can automatically fill the internal cavity during the expansion process.

[0037] The method for preparing hollow beams of carbon fiber composite materials provided by this invention can prepare variable cross-section cavity beam structures.

[0038] Example 1 This embodiment provides a method for preparing hollow beams of carbon fiber composite materials, wherein the prepared hollow beams are as follows: Figure 1 As shown, Figure 1 (a) is a three-dimensional perspective view of the hollow beam structure; Figure 1 (b) Front view of the hollow beam structure; Figure 1 (c) Top view of the hollow beam structure; Figure 1 (d) Side view of the hollow beam structure. The hollow beam has cavities distributed along its length, and the cavities are open on the right side of the hollow beam. The cross-section of the cavities varies along the length, especially the left end of the cavity, which is semi-circular.

[0039] Specifically, the dimensions of the hollow beam are: length Width Height = (1720) 250 96); The internal cavity design dimensions are: length Width Height = (1712) 242 92), because the hollow beam is a variable cross-section structure with a rounded corner at one end, this dimension is only an approximate dimension.

[0040] like Figure 2 As shown, the preparation method includes the following steps: Core mold preparation: Core molds are prepared using foam materials; optionally, PVC foam materials are used to prepare core molds with the same shape as the designed product cavity using a carving machine. For longer core molds, a segmented preparation method is adopted, with adjacent segments connected and fixed with steel bars; and the joints on the surface are smoothed and rounded after being filled with putty powder.

[0041] Nylon film coating: A bag-shaped nylon coating film is made using a thin nylon film. The shape of the nylon coating film is the same as that of the mandrel. The nylon coating film is wrapped around the mandrel, and a release agent is applied to the outer surface of the nylon coating film.

[0042] Wrapping and Laying: Lay the cut T300 unidirectional tape and 3K twill prepreg on the nylon covering film surface outside the core mold from the inside out according to the order and angle in Table 1, using a butt joint method; after every three layers, use a perforated release film, breathable felt and vacuum bag to wrap the core mold and the surface layer from the inside out, and then vacuum on a constant temperature heating table, once on each side, to remove the interlayer gas that caused the wrinkles during the laying process; Preferably, the heating temperature of the constant temperature heating table is 40~50℃, which is used to reduce the viscosity of the resin in the prepreg without reaching the curing temperature. Under this condition, air bubbles embedded in the laying process can be extracted, making the laying tighter. During the vacuuming process, the vacuum degree is maintained at about -0.097Mpa for 15 minutes. Preferably, after vacuuming, the vacuum bag, breathable felt, and perforated release film on the surface are removed before continuing the installation.

[0043] After laying the foam materials in the order shown in Table 1 up to the 10th layer, the expanded foam material is then laid. The laying positions include corners and rounded corners. This is because during the subsequent heating and curing process, thermal expansion causes changes in mold pressure and linear dimensions. Also, due to the fluidity of the resin, corners and rounded corners are prone to defects such as missing corners, resulting in the product shape not matching the design shape. By filling these positions with expanded foam material in advance, effective support can be provided during the subsequent deformation process, correcting the shape changes caused by defects such as missing glue at corners and rounded corners.

[0044] Table 1

[0045] In Table 1, the number of layers is arranged in the order of application from the inside out of the surface of the coating film coated with release agent; in the material specifications, "3K twill" refers to: T300 3K carbon fiber twill prepreg; "C2000" refers to: 200g / m 2 The T300 3K carbon fiber unidirectional tape prepreg; "angle" refers to the angle between the length direction of the carbon fiber and the unidirectional tape prepreg; size refers to the size cut by the fabric cutter each time; thickness refers to the thickness of the prepreg laid each time; the different thicknesses of "C2000" are due to the fact that the 4th, 7th and 10th layers each include two layers, with the inner layer laid at 45° and the outer layer laid at -45°, resulting in a thickness that is twice that of the other layers.

[0046] After the expanded foam material is laid, the outermost layer of 3K twill carbon fiber prepreg is laid. Optionally, the laying direction of the outermost and innermost 3K twill prepreg is: the edge of the prepreg forms a 45° angle with the core mold extraction direction, avoiding perpendicularity to the core mold extraction direction, and preventing the edge from lifting or wrinkling when the mold is removed.

[0047] Pre-extraction: Compressed air is introduced between the core mold and the coating film to separate the core mold from the coating film.

[0048] Core pulling: Remove the core mold; clean the covering film inside the preform. The covering film can also be retained because the appearance requirements of the inner surface of this cavity are low. As long as the innermost prepreg is flat, the covering film can be left unremoved without affecting the molding. In the past, compressed air was used to blow the prepreg and the core mold apart for core pulling. However, the problem is that the unidirectional belt is prone to cracking when blown by compressed air, and wrinkles will appear after the air is turned off. Therefore, a covering film (nylon bag) with release agent needs to be placed on the core mold surface to prevent the core mold from being unable to be pulled out or to prevent wrinkles caused by the air blowing process, which will eventually lead to defects or messy textures on the product surface.

[0049] Meanwhile, mold cleaning: Clean the external molding mold and preheat it to 40~50℃. Apply release agent to the mold: Apply release agent to the surface of the external molding mold that contacts the preform, applying three coats with a 15-minute interval between each coat.

[0050] Bag making: Place an inflatable bag into the internal cavity of the preform after the core mold is removed. Arrange the straight cylindrical inflatable bag in a U-shape in the internal cavity and connect the two air inlets reserved on the mold insert. The U-shaped inflatable bag is made of nylon and the surface is not treated. Its main function is to inflate the preform during the molding process to exert an outward force on the inner wall of the preform, and combine it with the mold to exert an inward force on the preform, so as to ensure product quality.

[0051] Mold closing: The preform after the core mold is removed is placed into the outer mold of the mold, heated and cured, and then demolded to obtain the hollow beam product of carbon fiber composite material; Preferably, a low-temperature assembly method is adopted, which makes full use of the principle of thermal shrinkage and expansion of prepreg. The preform is placed in the outer mold of the mold, and the nylon air bag is still placed in the preform. The mold is closed while maintaining the appearance and structure of the preform.

[0052] Temperature curing: The temperature rise curve of its curing and molding process is as follows Figure 3 As shown, the first stage involves heating to 100 degrees Celsius at a rate of 2℃ / min and holding at that temperature for 30 minutes; the second stage involves heating to 120 degrees Celsius at a rate of 1℃ / min and holding for 30 minutes; the third stage involves heating to 130 degrees Celsius at a rate of 1℃ / min and holding for 300 minutes; and the fourth stage involves natural cooling to room temperature. Because a low-temperature assembly method is used, the preform expands during the heating process, generating outward pressure on the mold. Therefore, positive pressure is not required when using a double-sided mold. Demolding: After cooling to room temperature, open the double-sided mold, remove the internal product, and after demolding, perform post-processing and QC inspection to obtain the hollow beam product of carbon fiber composite material.

[0053] The method for preparing hollow beams of carbon fiber composite materials provided by this invention can be applied to cavity beam structures with variable cross-sections. It reduces the need for butt welding processes in cavity beam structures, enabling one-piece molding technology, improving the mechanical properties of the product, ensuring uniform surface texture, avoiding wrinkles, and solving defects at rounded corners. The one-piece molding process avoids the problems of high density, high cost, poor corrosion resistance, poor wear resistance, and numerous weld points associated with traditional metal materials. Manufacturing efficiency is increased by 50% compared to traditional methods, and service life is increased by 2 to 3 times compared to traditional beams. This ensures the strength of the carbon fiber beams.

[0054] Meanwhile, this invention differs from conventional methods for forming cavity beam structures in the rail transit field: during the forming process, the external structure is adjusted through operations during the layup process. Its process offers advantages such as low cost, high efficiency, and mass production capability; and it easily ensures a complete appearance. Integrated molding effectively reduces the weight and cost of cavity beams, improves accuracy, and extends service life. Besides its application in rail transit, it can also be applied to aerospace vehicles, machinery manufacturing, and aircraft.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow beam of carbon fiber composite material, comprising the following steps: S1. Use foam material to prepare the core mold, wrap the core mold surface with a thin nylon bag as a covering film, and coat the outer surface of the covering film with a release agent. S2. According to the set number of layers and direction, lay carbon fiber prepreg on the outside of the covering film. After laying the set number of layers, perform a vacuuming operation. The vacuuming operation is as follows: cover the laid prepreg with a perforated release film, a breathable felt and a vacuum bag, and perform a vacuuming operation on a constant temperature heating table to remove the gas between the prepregs. The heating temperature of the constant temperature heating table is 40~50℃. In each vacuuming operation, vacuuming is performed once on both the front and back sides. S3. Lay expanded foam material on areas prone to adhesive shortage, then lay the outer layer of prepreg to obtain a preform; the expanded foam material refers to: thermally expandable adhesive, which has the function of being stable at room temperature and cut, and slightly expanding and curing after heating; S4. Pass compressed air between the core mold and the covering film to separate the core mold from the covering film and then extract the core mold; put a nylon air bag into the internal cavity of the preform after the core mold has been extracted, and connect the air inlet of the air bag reserved on the mold insert. S5. Place the preform after removing the core mold into the external molding mold, heat and cure it, and then demold to obtain the hollow beam product of carbon fiber composite material.

2. The method for preparing the hollow beam of carbon fiber composite material as described in claim 1, characterized in that, The total number of layers is 12-15, and the total thickness is 3.8-4.2mm; Carbon fiber prepregs include: unidirectional carbon fiber tape and twill prepregs, with the innermost and outermost carbon fiber prepregs being twill prepregs; The carbon fiber unidirectional tape is T300 carbon fiber unidirectional tape, and the twill prepreg is 3K twill carbon fiber prepreg.

3. The method for preparing the hollow beam of carbon fiber composite material as described in claim 1, characterized in that, In S1, the shape of the covering film is the same as that of the core mold; The shape of the core mold is the same as the shape of the cavity of the designed hollow beam; Using PVC foam material, a core mold with the same shape as the designed product cavity is prepared by a carving machine, and adjacent sections are connected and fixed with steel bars; and the surface seams are smoothed and rounded with putty powder.

4. The method for preparing the hollow beam of carbon fiber composite material as described in claim 1, characterized in that, In S2, the prepreg is laid using a butt joint method; After every three layers of prepreg are laid, a vacuum operation is performed to remove the interlayer gas from the newly laid prepreg. After vacuuming is complete, remove the vacuum bag, breathable felt, and perforated release film from the surface, and continue with the installation.

5. The method for preparing the hollow beam of carbon fiber composite material as described in claim 4, characterized in that, During the vacuuming process, the vacuum level was -0.097 MPa.

6. The method for preparing the hollow beam of carbon fiber composite material as described in claim 1, characterized in that, In S5, the external forming mold adopts a double-sided mold; The preform is placed into an external molding die using a low-temperature assembly method. The heating and curing process is as follows: heat up to 100 degrees Celsius at a rate of 2℃ / min, maintain the temperature for 30 minutes; heat up to 120 degrees Celsius at a rate of 1℃ / min, maintain the temperature for 30 minutes; heat up to 130 degrees Celsius at a rate of 1℃ / min, maintain the temperature for 300 minutes; and then allow the temperature to cool naturally to room temperature.

7. The method for preparing the hollow beam of carbon fiber composite material as described in claim 6, characterized in that, No positive pressure is applied during the use of double-sided molds.

8. A hollow beam of carbon fiber composite material prepared by a method for preparing a hollow beam of carbon fiber composite material as described in any one of claims 1-7.

9. A method for preparing a hollow beam of carbon fiber composite material as described in any one of claims 1-7 and / or an application of a hollow beam of carbon fiber composite material as described in claim 8, characterized in that, include: Applications in rail transportation vehicles and aerospace vehicles.

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