Flexible heating device and preparation method of composite material

Abstract

The invention belongs to the field of composite material preparation. The invention provides a flexible heating device and a preparation method of a composite material. The flexible heating device comprises a plurality of heat-conducting fins with a heating function, a first heating metal wire is preset and distributed in each heat-conducting fin, and every two adjacent heat-conducting fins are connected through a second heating metal wire; the glass fiber wraps the surface of the second heating metal wire; and the temperature controller is connected with the heat conducting sheet. According to the flexible heating device disclosed by the embodiment of the invention, a simple and reliable thermal forming scene can be built, and the scene is not limited by gas heat transfer and equipment size, so that the manufacturing efficiency of a composite material is greatly improved.

Description

Technical Field

[0001] The present application relates to the technical field of composite material manufacturing, and in particular to a flexible heating device and a method for preparing a composite material. Background Art

[0002] High-performance resin-based composite materials are widely used in aerospace, rail transportation, automotive industry, electronics and electrical, construction and other fields due to their light weight, high strength, excellent designability and chemical corrosion resistance. The use of high-efficiency molding methods to manufacture large-size, high-quality composite components has gradually become an industry development trend.

[0003] Composite molding relies on the heat-driven curing or consolidation of resins. Improving the efficiency of heat transfer to composite preforms can significantly improve composite manufacturing efficiency. For molding processes using autoclaves, ovens, and presses, heat generated by electrical or dielectric heating must be transferred to the composite preform via a gas medium and the mold to complete the composite molding process. Subsequently, the heat within the composite preform is removed through the gas medium and the mold to complete the cooling process. Low gas heat transfer efficiency significantly reduces composite manufacturing efficiency.

[0004] For large-scale composite materials, molding is limited by the size of the equipment, which requires high investment and energy consumption, resulting in a waste of resources. Furthermore, current flexible heating modules generally suffer from low operating temperatures and insufficient strength.

[0005] It should be noted that the above content is not necessarily prior art, nor is it intended to limit the scope of patent protection of this application. Summary of the Invention

[0006] The embodiments of the present application provide a flexible heating device and a method for preparing a composite material to solve or alleviate the above-mentioned technical problems such as low gas heat transfer efficiency, limited equipment size, low operating temperature range, and low strength.

[0007] According to a first aspect of an embodiment of the present application, a flexible heating device is provided, comprising: a plurality of heat-conducting sheets with a heating function, each of the heat-conducting sheets having a preset first heating wire distributed therein, and two adjacent heat-conducting sheets being connected by a second heating wire; glass fiber, the glass fiber being wrapped around the surface of the second heating wire; and a thermostat, the thermostat being connected to the heat-conducting sheets.

[0008] The flexible heating device of the present embodiment enables a simple and reliable thermoforming scenario, unconstrained by gas heat transfer and equipment size limitations, significantly improving composite material manufacturing efficiency. Furthermore, the thermally conductive sheet in the flexible heating system is scratch-resistant and pressure-resistant, and can withstand long-term use at relatively high temperatures (e.g., above 200°C). Specifically, the first metal heating wire is encased in the thermally conductive sheet, and the second metal heating wire is encased in fiberglass. Both the fiberglass and the thermally conductive sheet offer excellent insulation properties, reducing direct exposure of the first and second metal heating wires and improving safety. During the heating and curing operation using this flexible heating device, heat is transferred directly from the thermally conductive sheet to the preform via auxiliary materials such as vacuum bagging, non-porous film, and adhesive felt. This overcomes the limitations of gas heat transfer in traditional ovens or autoclaves, resulting in high thermal conductivity. Furthermore, the flexible heating device is coated on the preform surface, allowing for the flexibility of adjusting the shape and size of the heating device to the desired part shape during the actual manufacturing process.

[0009] According to an embodiment of the present application, the thermal conductive sheet includes a mica sheet, an aluminum oxide sheet, an aluminum nitride sheet, a silicon boron nitride sheet or a composite sheet, wherein the surface of the composite sheet is covered with a coating, and the coating includes at least one of aluminum oxide, aluminum nitride, silicon nitride, and silicon boron nitride.

[0010] According to an embodiment of the present application, the first heating wire and the second heating wire each independently include one of a nickel-chromium alloy, an iron-chromium-aluminum alloy, and a copper-nickel alloy.

[0011] According to an embodiment of the present application, the first metal heating wire is distributed in the thermal conductive sheet in a serpentine shape.

[0012] According to a second aspect of the embodiments of the present application, a method for preparing a composite material is provided, comprising the following steps: providing a mold; placing a composite material preform on the mold, wherein the surface of the mold in contact with the composite material preform is covered with a release layer; placing an insulating material on the side of the composite material preform away from the release layer, bagging the preform with a vacuum bag, and evacuating the preform with a vacuum pump; placing the flexible heating device described in the first aspect on the preform after evacuation, heating the preform to cure the composite material, and obtaining a composite material. The method of the present application can produce large-scale composite materials without the need for equipment investment; the method can be completed by simply placing multiple flexible heating devices on the surface of the preform, resulting in simple operation. Molding using the flexible heating device can achieve rapid temperature increases and decreases, and when cooling, the heating device can be directly removed from the surface of the workpiece, allowing it to cool naturally, thereby shortening the molding cycle. During molding, since the flexible heating device is directly placed on the preform surface, gas heat transfer is avoided, reducing heat energy loss during the molding process. The device can improve manufacturing efficiency and reduce energy consumption. The heating molding process does not involve a pressure vessel, thus providing a high safety factor.

[0013] According to an embodiment of the present application, the preform of the composite material includes a preform without matrix material or a preform containing matrix material.

[0014] According to an embodiment of the present application, the composite material preform is a preform that does not contain a matrix material, and the isolation material includes a release cloth and a guide net stacked in sequence, and the guide net is surrounded by a glue-absorbing felt, and the release cloth is in contact with the composite material preform.

[0015] According to an embodiment of the present application, the preform of the composite material is a preform containing a matrix material, and the isolation material includes a release cloth, a porous film, a glue-absorbing felt, a non-porous film and a breathable felt stacked in sequence, and the release cloth is in contact with the composite material preform.

[0016] According to an embodiment of the present application, the curing process includes a temperature rising stage and a temperature keeping stage.

[0017] According to an embodiment of the present application, the heating rate in the heating stage is 0.5~30℃ / min;.

[0018] According to an embodiment of the present application, the temperature of the insulation stage is 30~450°C, and the insulation time is 0.01~10h.

[0019] According to an embodiment of the present application, the length of the composite material is 0.1-30 m, and the width is 0.1-3 m. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the multiple drawings represent the same or similar components or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings only depict some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0021] Figure 1 is a schematic structural diagram of a flexible heating device provided in an embodiment of the present application; Figure 2 1 is a schematic diagram of the cross-sectional structure of the second heating wire wrapped with glass fiber provided in an embodiment of the present application; Figure 3 1 is a schematic structural diagram of a heat conducting sheet with a first heating wire embedded therein provided in an embodiment of the present application; Figure 4 This is a schematic diagram of the operation of forming a composite material using a material containing a matrix provided in an embodiment of the present application; Figure 5 This is a schematic diagram of the operation of forming a composite material using a perfusion process provided in an embodiment of the present application. Description of Reference Numerals 1: Heat conducting sheet; 2: First heating wire; 3: Second heating wire; 4: Glass fiber; 5: Temperature controller; 6: Sealing strip; 7: Composite material preform; 8: Perforated membrane; 9: Adhesive-absorbing felt; 10: Non-porous membrane; 11: Breathable felt; 12: Vacuum air nozzle; 13: Vacuum bag; 14: Flow guide net; 15: Resin pipe; 16: Mold; 17: Release material; 18: Flexible heating device. DETAILED DESCRIPTION

[0022] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. In the accompanying drawings, the sizes of layers, regions, and elements and their relative sizes may be exaggerated for clarity. The same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be understood as limiting the present application. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other unless there is a conflict.

[0023] It should be understood that when an element or layer is referred to as being "on," "adjacent to," "connected to," or "coupled to" another element or layer, it can be directly on, adjacent to, connected to, or coupled to the other element or layer, or there can be intervening elements or layers. Conversely, when an element is referred to as being "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" another element or layer, there can be no intervening elements or layers. It should be understood that while the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are merely used to distinguish one element, component, region, layer, or portion from another. Thus, without departing from the teachings of the present application, a first element, component, region, layer, or portion discussed below may be referred to as a second element, component, region, layer, or portion. Furthermore, when a second element, component, region, layer, or portion is discussed, it does not necessarily indicate that the first element, component, region, layer, or portion is present in the present application.

[0024] In this application, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0025] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way are interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0026] In the present application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to an integer in the numerical interval, including the two endpoint integers of the numerical range, and each integer between the two endpoints, is equivalent to directly enumerating each integer. When multiple numerical ranges are provided to describe a feature or characteristic, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical range disclosed in this application should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows broadly including quantitative intervals such as percentage intervals, ratio intervals, and ratio intervals.

[0027] For molding processes using autoclaves, ovens, and presses, the heat generated by electric heating or dielectric heating must be transferred to the composite material preform through the gas medium and the mold to complete the composite material molding. Subsequently, the heat inside the composite material preform is removed through the gas medium and the mold to complete the cooling. The low gas heat transfer efficiency greatly reduces the manufacturing efficiency of the composite material. In addition, the flexible electric heating film is composed of two layers of polyimide film sandwiched between a metal heating circuit foil. The film is not strong enough and can be easily damaged by sharp tools and molds during preforming, causing the electric heating film to rupture and sever the internal circuit connection, which in turn causes the composite material to fail to mold due to uneven heat distribution. The base material used in the flexible heating module is silicone rubber pad, which to some extent solves the problem of insufficient strength of the flexible heating device. However, its operating temperature is below 200°C and is not suitable for composite materials with molding temperatures above 200°C, which has certain limitations.

[0028] Based on this, the present application proposes a flexible heating device. Figure 1The device includes a plurality of heat-conducting sheets 1, each of which is preset with a first heating wire 2, and two adjacent heat-conducting sheets 1 are connected by a second heating wire 3; a glass fiber 4, the glass fiber 4 is wrapped around the surface of the second heating wire 3; and a thermostat 5, the thermostat 5 is connected to the heat-conducting sheet 1.

[0029] The flexible heating device of the present embodiment enables a simple and reliable thermoforming scenario, unconstrained by gas heat transfer and equipment size limitations, significantly improving composite material manufacturing efficiency. Furthermore, the thermally conductive sheet in the flexible heating system is scratch-resistant and pressure-resistant, and can withstand long-term use at relatively high temperatures (e.g., above 200°C). Specifically, the first metal heating wire is encased in the thermally conductive sheet, and the second metal heating wire is encased in fiberglass. Both the fiberglass and the thermally conductive sheet offer excellent insulation properties, reducing direct exposure of the first and second metal heating wires and improving safety. During the heating and curing operation using this flexible heating device, heat is transferred directly from the thermally conductive sheet to the preform via auxiliary materials such as vacuum bagging, non-porous film, and adhesive felt. This overcomes the limitations of gas heat transfer in traditional ovens or autoclaves, resulting in high thermal conductivity. Furthermore, the flexible heating device is coated on the preform surface, allowing for the flexibility of adjusting the shape and size of the heating device to the desired part shape during the actual manufacturing process.

[0030] In some embodiments, reference Figure 2 , a schematic cross-sectional view of the second heating wire 3 being wrapped with glass fiber 4. This insulates the second heating wire.

[0031] In some embodiments, the thermally conductive sheet includes a mica sheet, an aluminum oxide sheet, an aluminum nitride sheet, a silicon boron nitride sheet, or a composite sheet. These thermally conductive sheets have good hardness and high-temperature resistance, which can further improve the flexible heating device's scratch resistance and heavy pressure resistance, as well as its high-temperature resistance, allowing it to be used at temperatures above 200°C.

[0032] Furthermore, the surface of the composite sheet is covered with a coating, and the coating includes at least one of aluminum oxide, aluminum nitride, silicon nitride, and silicon boron nitride.

[0033] In some embodiments, the first heating wire and the second heating wire each independently include one of a nickel-chromium alloy, an iron-chromium-aluminum alloy, and a copper-nickel alloy.

[0034] In some embodiments, reference Figure 3 The first metal heating wire 2 is distributed in the heat conducting plate 1 in a serpentine shape.

[0035] A second aspect of the embodiments of the present application provides a method for preparing a composite material, comprising the following steps: (1) providing a mold; (2) laying a composite material preform on the mold, wherein the surface of the mold in contact with the composite material preform is covered with a release layer; (3) laying an isolation material on the side of the composite material preform away from the release layer, and using a vacuum bag to make a bag and evacuate the bag; (4) placing the flexible heating device described in the first aspect on the vacuumed product, and heating the composite material preform to solidify the composite material preform, thereby obtaining a composite material.

[0036] The method of the present application can prepare large-sized composite materials without the need for equipment investment. It can be completed by simply laying multiple flexible heating devices on the surface of the preform, and the operation is simple. Using the flexible heating device for molding can achieve rapid temperature increase and decrease, and when cooling, the heating device can be directly peeled off from the surface of the workpiece to allow it to cool naturally, shortening the molding cycle. During molding, since the flexible heating device is directly laid on the surface of the preform, gas heat transfer is avoided, and heat energy loss during the molding process is reduced. The device can improve manufacturing efficiency and reduce energy consumption. The heating molding process does not involve a pressure vessel, and has a high safety factor.

[0037] According to an embodiment of the present application, step (1) provides a mold.

[0038] In some embodiments, mold customization is also included. During the mold customization process, the mold can be designed and manufactured according to the composite material's external structure.

[0039] Optionally, the material of the mold includes at least one of metal, plastic, composite material, glass, and wood.

[0040] In some embodiments, the method further includes processing the mold, wherein the processing method is to remove impurities on the mold cavity surface.

[0041] Furthermore, the mold release agent is evenly applied to the mold surface 2 to 3 times at intervals of 15 to 20 minutes, or a release cloth is covered on the mold surface.

[0042] According to an embodiment of the present application, in step (2), the composite material preform is laid on the mold, and the surface of the mold in contact with the composite material preform is covered with a release layer.

[0043] In some embodiments, the composite material preform includes a preform without a matrix material or a preform containing a matrix material.

[0044] Optionally, the reinforcing material is one or more of carbon fiber, aramid, glass fiber, ultra-high molecular weight polyethylene fiber, polypropylene fiber, polyamide fiber, polyphenylene sulfide fiber, polyetheretherketone fiber, and the reinforcing material is in the form of one or more of unidirectional fiber, woven fabric, knitted fabric, braided fabric, and non-woven fabric, and the weight of the reinforcing material is 5-600 g / m2 .

[0045] Optionally, the matrix material is one or more of epoxy resin, vinyl ester resin, unsaturated polyester resin, phenolic resin, bismaleimide resin, benzoxazine resin, polyimide resin, polyethylene resin, polypropylene resin, polyamide resin, polycarbonate resin, polyphenylene sulfide resin, polyetheretherketone resin, etc.; the weight of the matrix material is 30~800g / m 2 .

[0046] In some embodiments, the method further includes cutting a preform without a matrix material or a preform containing a matrix material: performing a shape design according to the shape of the composite product, and cutting the material without a matrix or the material containing a matrix; laying the cut material without a matrix or the material containing a matrix in a layering order to obtain a composite material preform.

[0047] According to an embodiment of the present application, in step (3), the isolation material is laid on the composite material preform material, and a vacuum bag is used for bagging and vacuuming.

[0048] In some embodiments, the composite material preform is a preform without matrix material, the isolation material includes a release cloth and a guide net stacked in sequence, the guide net is surrounded by adhesive felt, and the release cloth is in contact with the composite material preform.

[0049] In other embodiments, the composite material preform is a preform containing a matrix material, and the isolation materials are release cloth, porous film, adhesive-absorbing felt, non-porous film, and breathable felt in sequence.

[0050] The composite material preform is formed by: designing the shape according to the composite material product shape, cutting the material without a matrix or the material with a matrix, and then laying it in a layer-laying order.

[0051] According to an embodiment of the present application, in step (4), the flexible heating device described in the first aspect is placed on the vacuumed product to heat the composite material preform to solidify the composite material preform to obtain a composite material.

[0052] In some embodiments, a flexible heating device is wrapped around the surface of a preform with a vacuum bag and insulation material, the position of the heating device is adjusted according to the shape of the preform, and the device is fixed with glass fiber. Parameters of the flexible heating device are set to obtain a composite material.

[0053] In some embodiments, the curing process includes a temperature rise phase and a temperature hold phase.

[0054] Optionally, the heating rate in the heating stage is 0.5~30℃ / min, for example, 0.5℃ / min, 5℃ / min, 10℃ / min, 15℃ / min, 20℃ / min, 30℃ / min, etc.

[0055] Optionally, the temperature in the insulation stage is 30~450℃, for example, 30℃, 100℃, 300℃, 450℃, etc., and the insulation time is 0.01~10h, for example, 0.01h, 0.1h, 1h, 2h, 5h, 8h, 10h, etc.

[0056] In some embodiments, the method further includes demolding the solidified product, wherein the flexible heating device is disassembled during the demolding process, the vacuum bag and the isolation material are removed, and the composite material product is demolded.

[0057] In some embodiments, the length and width of the composite material are not particularly limited and can be set according to actual needs.

[0058] Optionally, the length is 0.1~30m, for example, 0.1m, 1m, 4m, 8m, 14m, 20m, 25m, 30m, etc.; the width is 0.1~3m, for example, 0.1m, 1m, 2m, 3m, etc.

[0059] In some embodiments, reference Figure 4 , provides an operation process of curing a preform containing a matrix material to form a composite material: after cleaning the surface of a mold 16, a sealing strip 6 is laid around the mold 16; a lower release material 17 is arranged on the upper surface of the mold 16, and a preform containing a matrix material is laid on the lower release material 17 according to the process requirements of the composite component to form a composite material preform 7 (a preform containing a matrix material), and the release material 17 is laid on the upper surface of the composite material preform 7 (a preform containing a matrix material), and the A suitable number of vacuum nozzles 12 are placed on the surface of the insulating materials, such as porous membrane 8, adhesive felt 9, non-porous membrane 10, and breathable felt 11. A vacuum bag 13 is placed tightly against the sealing strip 6. The air guide channel of the vacuum nozzle 12 should extend to the surface of the vacuum bag 13. Ensure that the sealing strip, mold 16, vacuum nozzle 12, and vacuum bag 13 are completely sealed to ensure overall airtightness. The vacuum bag 13 is then evacuated through the vacuum nozzle 12 using a vacuum pipe to compact the various layers of material in the vacuum bag 13. Finally, the flexible heating device 18 is placed on the surface of the vacuum bag 13, and the curing of the composite material is controlled by setting the parameters of the flexible heating device.

[0060] In some embodiments, reference Figure 5, an operation process for curing a preform without matrix material to form a composite material is provided: after cleaning the surface of a mold 16, a sealing strip 6 is laid around the mold 16; a lower demoulding material 17 is arranged on the upper surface of the mold 16, and a preform without matrix material is laid on the lower demoulding material 17 according to the process requirements of the composite component to form a composite material preform 7 (a preform without matrix material), and the demoulding material 17 is laid on the upper surface of the composite material preform 7 (the preform without matrix material), and a guide net 14 is laid thereon, and two or more resin pipes 15 are pre-buried; a vacuum bag 13 is tightly attached to the sealing strip 6, and it is noted that the sealing strip 6 and the mold 16, the resin pipe 15 and the vacuum bag 13 should be completely sealed to ensure the overall airtightness; and then a vacuum line is used to evacuate the vacuum bag 13 through one or more resin pipes 15 to compact the layers of material in the vacuum bag 13. Finally, the flexible heating device is laid on the surface of the vacuum bag 13, the temperature of the flexible heater is set to the resin infusion temperature, and the resin in the resin barrel is introduced into the composite material preform 7. After the infusion is completed, the stage temperature and insulation time of the flexible heating device temperature controller are set to complete the curing of the composite material.

[0061] Below, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. It should be noted that these exemplary embodiments can be implemented in a variety of different forms and should not be construed as being limited to the embodiments described herein. The methods, reagents, and materials used in the examples are conventional methods, reagents, and materials in the art, unless otherwise stated. The raw materials in the examples can all be purchased from commercial sources.

[0062] The sources of the materials used in the examples are as follows: The medium-temperature epoxy resin adhesive is prepared by mixing LY1564 epoxy resin and 3487 curing agent in a mass ratio of 100:34.

[0063] High-temperature epoxy resin adhesive is prepared by mixing AM-8927A epoxy resin and AM-8927B curing agent in a mass ratio of 100:30.

[0064] Example 1: The 10 layers are 500mm×500mm×4mm in size and 400g / m2 in weight. 2SYT45S-12K carbon fiber unidirectional woven material without matrix material is sequentially laid on the surface of a glass mold coated with a release agent. Release cloth, guide mesh and other isolation materials and vacuum bags are then laid on the surface of the top preform without matrix material. Resin pipes are arranged at both ends, and a preform without matrix material is formed after vacuuming. A flexible heating device is placed on the surface of the vacuum bag and fixed with glass fiber yarn. A layer of glass fiber insulation material is then covered on the surface of the flexible heating device. After the temperature of the flexible heating device reaches the infusion temperature of 40°C and is kept at this temperature for 10 minutes, a medium-temperature epoxy resin glue is injected into the preform without matrix material. The temperature is increased to 80°C at a heating rate of 10°C / min and kept at this temperature for 3 hours to complete the resin curing. After curing is completed, the flexible heating device is disassembled, the vacuum bag and isolation materials are removed, and the composite material part is demolded.

[0065] Example 2: The 20 layers are 500mm×500mm×4mm in size and 200g / m 2 A T800H / QY9511 unidirectional material containing a bismaleimide matrix is ​​applied to the surface of a metal mold coated with a release agent at a 0° angle. A release cloth, a porous film, a wicking felt, a non-porous film, a breathable felt, and other insulating materials are then applied to the topmost layer of the matrix-containing unidirectional material, followed by a vacuum bag. After evacuation, a preform containing the matrix material is formed. A flexible heating device is placed on the surface of the vacuum bag, secured with glass fiber yarn, and covered with a layer of glass fiber insulation material. The heating rate of the flexible heating device is set at 20°C / min, and the composite material is formed according to a curing schedule of "125°C for 2h + 200°C for 5h." After curing, the flexible heating device is disassembled, the vacuum bag and insulating materials are removed, and the composite material is demolded to obtain the composite part.

[0066] Example 3: The gram weight is 380g / m 2 The T700SC / ST005 one-way material containing an epoxy matrix is ​​cut according to the results of the bogie side beam development, and laid on the surface of a metal mold coated with a release agent. The release cloth, porous film, adhesive felt, non-porous film, breathable felt and other isolation materials and vacuum bags are laid on the surface of the top one-way material containing the matrix in sequence, and a preform containing the matrix material is formed after vacuuming. The flexible heating device is placed on the surface of the vacuum bag, fixed with glass fiber yarn, and a layer of glass fiber insulation material is covered on the surface of the flexible heating device. The heating rate of the flexible heating device is set to 15℃ / min, and the bogie side beam is formed according to the curing system of "80℃ 1h+135℃ 2h". After curing is completed, the flexible heating device is disassembled, the vacuum bag and isolation material are removed, and the rough bogie side beam is demoulded to obtain the product. The total length of the product is 2.6m, the width is 15mm, and the maximum thickness is 80mm; Example 4: The weight is 500g / m 2 GX500-25K matrix-free carbon fiber twill woven material is cut according to the aircraft profiled beam development results and applied to a metal mold surface coated with a release agent. Release cloth, a flow guide net, and other insulating materials are then applied to the topmost preform surface, followed by a vacuum bag. Resin pipes are placed at both ends, and the preform is evacuated to form the matrix-free preform. A flexible heating device is placed on the vacuum bag surface, secured with glass fiber yarn, and covered with a layer of glass fiber insulation. After the flexible heating device reaches the infusion temperature of 25°C and maintains this temperature for 10 minutes, high-temperature epoxy resin is injected into the matrix-free preform. The heating rate of the flexible heating device is set at 15°C / min, and a curing schedule of "50°C for 6 hours followed by 100°C for 3 hours" is used to complete the rough aircraft profiled beam. The total length of the rough special-shaped beam is 8.9 meters.

[0067] Comparative Example 1: Comparative Example 1 is substantially the same as Example 1, except that after forming the preform without the matrix material, the preform and the mold are transferred to an oven for injection molding and forming. The oven is heated at a rate of 4°C / min.

[0068] Comparative Example 2: Comparative Example 2 is substantially the same as Example 2, except that after forming the preform containing the matrix material, the preform and the mold are transferred to an autoclave for curing. The autoclave has a heating rate of 5°C / min.

[0069] Comparative Example 3: Comparative Example 3 is substantially the same as Example 3, except that after forming the preform containing the matrix material, the preform and the mold are transferred to an autoclave for curing. The heating rate of the autoclave is 5°C / min.

[0070] Test Example 1: Molding Temperature Test During preforming, thermocouples were fixed to the mold surface near the periphery of the preform using pressure-sensitive tape. The temperatures at four test points were recorded in real time, and the average temperature of each test point during the constant temperature forming stage was calculated. The results are shown in Table 1. As can be seen from the table, when forming using the flexible heating device described in this patent technology, the mold surface temperature range is less than 2°C, which is comparable to the temperature control level of an autoclave and significantly higher than the temperature control level of an oven. This shows that the flexible heating device described in this patent technology has the advantage of uniform temperature field distribution.

[0071] Table 1 Mold surface temperature test results

[0072] Test Example 2: Molding Time Test A timer was used to record the molding time of Examples 1, 2, 3, 4 and Comparative Examples 1, 2, and 3. The timer was started synchronously when heating began. The test data is shown in Table 2. As can be seen from Table 2, the molding method described in this patent technology shortens the heating and curing time compared to traditional ovens and autoclaves. Since the flexible heating device can be manually removed after heating is completed, and the molding is cooled naturally or purged with cold air, the cooling time is also significantly shortened. This shows that the molding method described in this patent technology has the advantages of short molding time and high efficiency.

[0073] Table 2 Composite material molding time test results

[0074] In addition, the artificially removed flexible heating device can be used immediately to form a new round of composite materials, without occupying the heating equipment due to the cooling of the composite materials. In contrast, when using an oven or autoclave for molding, it is necessary to wait for the temperature to drop to a safe temperature before the equipment can be released and a new round of composite material molding can begin. This shows that the molding method described in this patented technology has high flexibility and high molding efficiency.

[0075] Test Example 3: Composite Material Bending Strength Test According to ASTM D7264, the flexural strength of the composite material was tested by three-point bending. The specimen size was 200 mm × 13 mm × 4 mm. During the bending test, the crossbeam displacement rate was kept at 1 mm / min and the span-to-thickness ratio was 32:1. The data of 5 specimens were tested and the average value was taken. The flexural strength of the composite material was calculated using formula (1): (1) Where, is the flexural strength of the composite material, MPa; is the maximum force measured, N; is the span, mm; and are the width and thickness of the spline, in mm.

[0076] Test Example 4: Composite Material Short Beam Shear Strength Test According to ASTM D2344, the short beam shear test was used to test the short beam shear strength of the composite material in the three-point bending mode. The spline size was 24 mm × 8 mm × 4 mm. When conducting the short beam shear test, the beam displacement rate was kept at 1 mm / min and the span-to-thickness ratio was 4:1. The data of 5 splines were tested and the average value was taken. The short beam shear strength of the composite material was calculated using formula (2): (2) Where, is the short beam shear strength, MPa.

[0077] Test Example 5: Composite Material Porosity Test An Olympus BX41M-LED metallographic microscope was used to measure the porosity of the composite material samples in Examples 1 and 2, as well as Comparative Examples 1 and 2. After grinding and polishing, the sample cross-sections were observed and photographed under a microscope. Grayscale analysis and porosity calculation were then performed on the cross-sectional photographs using Image J software.

[0078] The compressive strength, flexural strength, short beam shear strength, and porosity test results of the composite materials are shown in Table 3. The flexural strength and short beam shear strength of the composite materials in Examples 1 and 2 are comparable to those in Comparative Examples 1 and 2, indicating that products formed using the flexible heating device described in this patent technology can achieve performance comparable to products formed in an oven or autoclave. In terms of micro-defect control, the composite materials prepared using the molding method described in this patent technology are of excellent quality, with a void content of less than 2%.

[0079] Table 3 Mechanical properties and porosity test results of composite materials

[0080] It should also be noted that references to "some embodiments," "other embodiments," "embodiments," etc., in this application refer to specific features, structures, or characteristics described in conjunction with such embodiments as are included in at least one embodiment generally described in this application. The appearance of the same expression in multiple places in the specification does not necessarily refer to the same embodiment. Furthermore, when a specific feature, structure, or characteristic is described in conjunction with any embodiment, it is intended that the realization of such feature, structure, or characteristic in conjunction with other embodiments also falls within the scope of this application.

[0081] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0082] It should also be noted that the above are only preferred embodiments of the present application and do not limit the scope of patent protection of the present application. Any equivalent structure or equivalent process transformation made using the contents of the description and drawings of this application, or directly or indirectly applied in other related technical fields, are also included in the scope of patent protection of the present application.

Claims

1. A flexible heating device, characterized in that: include: A plurality of heat-conducting sheets with heating function, each of which is pre-distributed with a first heating metal wire, and two adjacent heat-conducting sheets are connected by a second heating metal wire; glass fiber, the glass fiber being wrapped around the surface of the second heating wire; A thermostat is connected to the heat conducting sheet.

2. The flexible heating device according to claim 1, characterized in that The thermal conductive sheet includes a mica sheet, an aluminum oxide sheet, an aluminum nitride sheet, a silicon boron nitride sheet or a composite sheet. The surface of the composite sheet is covered with a coating, and the coating includes at least one of aluminum oxide, aluminum nitride, silicon nitride, and silicon boron nitride.

3. The flexible heating device according to claim 1, characterized in that The first heating wire and the second heating wire each independently include at least one of nickel-chromium alloy, iron-chromium-aluminum alloy, and copper-nickel alloy.

4. The flexible heating device according to claim 1, characterized in that The first heating wire is distributed in the heat conducting sheet in a serpentine shape.

5. A method for preparing a composite material, characterized in that: The following steps are involved: Provide molds; Laying a composite material preform on the mold, wherein the surface of the mold in contact with the composite material preform is covered with a release layer; Laying the isolation material on the side of the composite material preform away from the release layer, and using a vacuum bag to make and evacuate the bag; The flexible heating device according to any one of claims 1 to 4 is placed on the vacuumed product, and heated to solidify the composite material preform to obtain a composite material.

6. The preparation method according to claim 5, characterized in that The composite material preform includes a preform without matrix material and a preform containing matrix material.

7. The preparation method according to claim 6, characterized in that The composite material preform is a preform that does not contain a matrix material. The isolation material comprises a demoulding cloth and a guide net which are stacked in sequence. The guide net is surrounded by a glue-absorbing felt. The demoulding cloth is in contact with the composite material preform.

8. The preparation method according to claim 6, characterized in that The composite material preform is a preform containing a matrix material, The isolation material comprises a release cloth, a porous film, a glue-absorbing felt, a non-porous film and a breathable felt which are stacked in sequence, and the release cloth is in contact with the composite material preform.

9. The preparation method according to claim 5, characterized in that The curing process satisfies at least one of the following conditions: Heating stage and heat preservation stage; The heating rate in the heating stage is 0.5-30°C / min; The temperature of the insulation stage is 30-450° C., and the insulation time is 0.01-10 hours.

10. The preparation method according to claim 5, characterized in that The composite material has a length of 0.1 to 30 m and a width of 0.1 to 3 m.

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