Preparation method of high-strength carbon / carbon pressed plate with large-size carbon fiber three-dimensional structure

Abstract

The invention discloses a preparation method of a large-size carbon fiber three-dimensional structure high-strength carbon / carbon pressed plate, which comprises the following steps: step (1) design of a three-dimensional structure preform, including calculation of the size of carbon cloth required by the size of a carbon / carbon pressed plate, calculation of the number of layers of laid carbon cloth and calculation of the thickness of the plate preform; (2) manufacturing a carbon cloth three-dimensional structure prefabricated body; (3) carrying out resin hot press molding on the carbon fiber three-dimensional structure prefabricated body; and (4) a hot-pressing carbonization furnace is adopted, the pressed carbon fiber three-dimensional structure resin-based plate is subjected to carbonization treatment under the strong flat plate pressure, the carbon cloth flatly laid for multiple times is sewn into a carbon fiber plate prefabricated body of an integral three-dimensional structure through a specific sewing tool, and the characteristics of continuous carbon fibers are kept. The high-density carbon / carbon plate with high fiber content is obtained, the high-density carbon / carbon plate has good mechanical properties, and the breaking strength can reach 200 MPa or above.

Description

Technical Field

[0001] The present invention belongs to the field of carbon fiber three-dimensional structure pressed plates, and in particular relates to a method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure. Background Art

[0002] Carbon / carbon (C / C) composites, with their exceptional properties such as high strength, high-temperature resistance, wear resistance, and chemical stability, play an irreplaceable and important role in numerous fields, including aerospace, automotive braking, and high-temperature industries. With the continuous advancement and development of these fields, new requirements are being placed on the performance and dimensional specifications of C / C composites.

[0003] Currently, the traditional process for preparing carbon / carbon composites is primarily a gas-liquid combination method. This method involves densification through chemical vapor deposition followed by carbonization through liquid-phase impregnation, resulting in a carbon / carbon composite material of a certain density. While this method is well-suited for producing small-scale sheets, it does suffer from numerous drawbacks and deficiencies in the production of large-scale carbon / carbon sheets. During the preparation process, uneven internal stress distribution can easily lead to product deformation, severely impacting dimensional accuracy and quality stability. Furthermore, the gas-liquid combination method suffers from a long preparation cycle, low production efficiency, and relatively high costs.

[0004] Large-sized carbon / carbon sheets are usually made by a pressing process. Patent Publication No. CN116572564A describes a method for realizing a large-sized carbon / carbon composite material pressing process using a special device; Application No. CN202310791199.3 proposes a method for obtaining large-sized carbon / carbon composite materials by stacking laminated carbon fiber cloth in a vacuum bag film, evacuating the film and impregnating it with a resin impregnation liquid, hot-pressing and curing it into shape, and then carbonizing and high-temperature purification. Both of the above-mentioned two disclosed production process sheet methods have shortcomings. Patent Publication No. CN116572564A uses an ordinary needle-punched preform embryo and presses it with the help of a large-scale special tooling. On the one hand, the production operation is complicated by the tooling to prevent resin extrusion; on the other hand, due to the use of needle-punched sheets as preforms, the fiber strength is destroyed, and the mechanical properties of the obtained carbon / carbon sheets are limited. The laminated carbon cloth sheet proposed in application number CN202310791199.3 is formed by plying, pressing and curing. Large-sized carbon-carbon sheets are obtained by ordinary pressureless carbonization. The interlayer performance is insufficient and there is a serious risk of delamination. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure. The large-size carbon / carbon plate has a pure long fiber three-dimensional structure and good integrity. The prepared carbon / carbon composite material fully utilizes the characteristics of continuous fiber reinforcement and has excellent strength advantages.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows, comprising the following steps: 1. A method for preparing a high-strength carbon / carbon pressed sheet with a large-size carbon fiber three-dimensional structure, comprising the following steps: (1) Design of three-dimensional structural preforms, including calculation of carbon cloth size required for carbon / carbon pressed plate size, calculation of number of carbon cloth layers, calculation of plate preform density, and calculation of plate preform thickness (compression design).

[0007] (2) Preparation of carbon cloth three-dimensional structure preform: a. Cut the carbon cloth according to the design size with a reserved margin. The carbon cloth can be unidirectional or plain weave. b. Lay the cut carbon cloth flat on the wooden board with EVA felt. Make sure the thickness of the carbon cloth reaches the designed value. Fix the four sides of the carbon cloth so that it fits the EVA felt as a whole. c. Using a positioning plate and a suturing needle to sew the flat carbon cloth. The needle has a handle with a cavity at the rear, a small hole at the needle tip, and a straight section with a suture thread channel. The suture thread passes through the straight section channel directly to the small hole at the needle tip, where it exits. Using the positioning plate, locate the first puncture point, lower the suturing needle through the carbon cloth layer, and insert the carbon fiber suture thread into the EVA interior. The high resilience of the EVA helps to clamp the carbon fiber suture thread. This way, one end of the carbon fiber suture thread is retained by the EVA, while the other end extends along the suture thread channel. As the suturing needle is raised, the carbon fiber suture thread extends outside the carbon cloth layer. Using the spacing designed for the positioning plate, locate the next puncture point, penetrate the carbon cloth layer, reach the interior of the EVA, and then withdraw the suturing needle. Repeat this process until the designed product size is fully covered and the flat carbon cloth layer is continuously penetrated by the suture thread, forming a monolithic carbon fiber three-dimensional preform with suture thread ends on the bottom surface.

[0008] d. The whole carbon fiber three-dimensional structure preform with sutures is pre-hardened in an oven. After hardening, the surface with the sutures is placed upwards and all the suture ends are cut off with scissors to obtain a whole carbon fiber three-dimensional structure preform with a clean surface.

[0009] (3) Resin hot pressing of carbon fiber three-dimensional structure preforms; the required amount of resin is calculated based on the density of the resin plate, and the resin is evenly applied to the stitched carbon fiber three-dimensional structure preform using a resin brush, and then transferred to a flat hot press to perform a temperature-raising curing process. After curing, a pressed carbon fiber three-dimensional structure resin-based plate with good flatness is obtained.

[0010] (4) A hot pressing carbonization furnace is used to complete the carbonization treatment of the pressed carbon fiber three-dimensional structure resin-based sheet under strong flat plate pressure to obtain a carbon / carbon pressed sheet blank. The carbon fiber three-dimensional structure resin-based sheet is carbonized under continuous high-intensity pressure. Unlike the traditional pressureless carbonization in a vacuum or inert atmosphere, the sheet thickness will not expand. Instead, due to the effect of high pressure, the sheet thickness will shrink. This makes it easier to obtain a higher density efficiency and a high-fiber content high-density carbon / carbon sheet with good mechanical properties.

[0011] (5) After carbonization, the carbon / carbon pressed sheet undergoes high temperature treatment to obtain a high-strength carbon / carbon pressed sheet with a flexural strength of more than 200 MPa.

[0012] 2. A method for preparing a high-strength carbon / carbon pressed sheet with a large-size carbon fiber three-dimensional structure. (2) Calculation of the required carbon cloth size and number of layers in step (1), as well as the density and thickness of the carbon fiber sheet preform, is as follows: Width of raw carbon cloth = width (or length) of carbon / carbon sheet blank to be produced + (20-50) mm; Thickness of sheet preform = expected thickness of carbon / carbon sheet blank / compression amount; Number of carbon cloth layers = thickness of sheet preform / thickness of single-layer carbon cloth under sewing conditions; Remark: Generally, the thickness of a single-layer carbon cloth weighing 360 grams is 0.3mm, the thickness of a carbon cloth weighing 420 grams is 0.35, and the thickness of a carbon cloth weighing 500 grams is 0.42mm.

[0013] The compression value is 0.55 when the board density is 0.6±0.05; the value is 0.65 when the board density is 0.7±0.05; This type of process is suitable for preparing large-scale plates. The length and width of the plate preform are generally greater than 1000mm; the conventional value is 1500-5000mm; 3. According to the method for preparing a large-scale carbon fiber three-dimensional structured high-strength carbon / carbon pressed sheet material as described in claim 1, the thickness of the EVA felt in step (2) b is not less than 10 mm, and is generally between 20 and 30 mm. The upper and lower layers of carbon cloth are cut so that all four sides are flush.

[0014] 4. A method for preparing a high-strength carbon / carbon pressed sheet with a large-size carbon fiber three-dimensional structure. ① The structure of the positioning plate 1 in step (2) c is as shown in the attached Figure 1 As shown, it is a ruler with positioning holes 11. The spacing between the positioning holes is the stitching spacing, which is selected according to the stitching density and is between 3-20mm.

[0015] ② The suture needle structure described in step (2) c, such as Figure 2 As shown, it is made of a 3mm diameter thin metal tube with one side of the tube wall ground off, and then sharpened to a point with a fine hole at the tip. The fine hole has a diameter of 1.5mm. The needle handle is made of wood. ③ The carbon fiber suture thread in step (2) c is 6k, 3k carbon fiber filament or a braided carbon rope with a diameter of 0.6-1mm, preferably a braided carbon rope with a diameter of 0.6-1mm.

[0016] ④ In step (2) c, the depth of the suture needle puncturing the EVA is not less than 10 mm and is between 15 and 20 mm.

[0017] 5. A method for preparing a high-strength carbon / carbon pressed sheet with a large-size carbon fiber three-dimensional structure. The hardening temperature of the integral carbon fiber three-dimensional structure preform with suture thread ends on the surface described in step (2) d is not less than 200°C.

[0018] 6. A method for preparing a large-size carbon fiber three-dimensional structure high-strength carbon / carbon pressed plate. ① The calculation formula for the resin amount in the resin hot pressing molding in step (3) is as follows: Coating resin mass kg = (designed pressed resin plate mass kg - carbon fiber 3D stitching fiber mass kg) / 0.6 / 0.8 Among them, the designed pressed resin board mass kg = designed pressed resin board volume * density, and the density is 1.4g / cm 3 ; ② In step (3), the thickness of the large-size carbon fiber three-dimensional structure high-strength carbon / carbon pressed plate is completed by placing a pad between the upper and lower pressing plates, and the designed thickness of the pressed plate = the thickness of the pad.

[0019] ③ The hot pressing process curve of the large-size carbon fiber three-dimensional structure high-strength carbon / carbon pressed plate in step (3) is as follows: RT-60℃±20℃,1±0.5h; 60℃±20℃, keep warm for 2±1h; 60℃~180℃±20℃, 20℃±10℃ / h; 180℃±20℃, keep warm for 2±1h; about 11h.

[0020] Hot press pressure curve: t / min P / MPa t / min P / MPa 0 0 20 3.5 1 1 22 3.5 3 1.5 25 4 5 1.5 27 4.5 7 2 30 5 8 2 35 5.5 10 3 40 7 12 3 42 9 15 3 45 11 / 9 17 3 The final pressure value depends on whether the pad is compacted by the upper and lower pressure plates.

[0021] 7. A method for preparing a high-strength carbon / carbon pressed sheet with a large-size carbon fiber three-dimensional structure. In step (4), a hot pressing carbonization furnace is used to complete the hot pressing carbonization. The carbon fiber hot pressing resin plate stack is placed flat directly under the hot pressing head. The head is pressurized to 8-10 MPa. The pressure is maintained and hot pressing and heating carbonization are started. The process curve is as follows: RT-180℃±20℃,1±0.5h; 180℃~350℃±20℃, 30℃±10℃ / h, about 6h; 350℃~650℃±20℃, 20℃±10℃ / h, about 15h; 650℃~900℃±20℃, 30℃±10℃ / h, about 8h; 900℃±50℃, keep warm for 3±1h; about 32h in total.

[0022] 8. A method for preparing a high-strength carbon / carbon pressed sheet with a large-size carbon fiber three-dimensional structure. The process parameters of the high temperature treatment in step (5) are as follows: RT-350℃±20℃,2±0.5h; 350℃~850℃±20℃, 100℃±10℃ / h, about 5h; 850℃~1500℃±20℃, 70℃±10℃ / h, about 9h; 1500℃~2000℃±20℃, 50℃±10℃ / h, about 10h; 2000℃±50℃, keep warm for 4±1h, about 28h in total.

[0023] The present invention has the following advantages: (1) Using carbon cloth (unidirectional cloth or plain cloth) as the base material to sew and prepare a three-dimensional continuous preform structure, it is easy to realize large-size carbon fiber preforms; (2) Pure continuous long carbon fiber three-dimensional structure, which can fully demonstrate the high strength of continuous carbon fiber; (3) Using hot pressing carbonization process, the thickness of carbon / carbon sheet material does not expand but shrinks under high temperature, which not only improves the densification efficiency, but also increases the fiber content of carbon / carbon sheet material, so as to obtain high-strength carbon / carbon sheet material products. (4) This method has low production cost, simple process, and is easy to promote and industrialize.

[0024] The present invention uses a three-dimensional continuous carbon fiber preform as a precursor of the carbon / carbon composite material and adopts a hot pressing carbonization process with high densification efficiency to achieve densification. The combination of the two can maximize the excellent strength characteristics of the continuous carbon fiber, and the prepared large-size carbon-carbon plate has very excellent mechanical properties.

[0025] The preform form of the continuous carbon fiber three-dimensional structure proposed by this method has the characteristics of good integrity, continuous and undamaged carbon fibers, etc. At the same time, with the help of hot pressing carbonization process, the expansion problem of the pressed plate during the carbonization process is solved. The forming process does not require the help of large-scale special tooling and is simple. The carbon / carbon plate achieved has a continuous carbon fiber three-dimensional structure with good integrity, high precision, and excellent mechanical properties. The flexural strength can be greater than 200MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural diagram of the positioning plate.

[0027] Figure 2 Schematic diagram of the structure of a suture needle. DETAILED DESCRIPTION

[0028] The present invention is further described below with reference to the accompanying drawings and embodiments, providing a clear and complete description of the technical solutions in the embodiments of the present invention. The embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention. Example 1

[0029] A method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure, characterized by comprising the following steps: Step (1) Design of the three-dimensional structure preform, including calculation of the carbon cloth size required for the carbon / carbon pressed plate size, calculation of the number of carbon cloth layers laid, and calculation of the plate preform thickness; Step (2) Preparation of carbon cloth three-dimensional structure preform: a. Cut the carbon cloth according to the design size with a reserved margin. The carbon cloth can be unidirectional or plain weave. b. Lay the cut carbon cloth flat on the wooden board with EVA felt. Make sure the thickness of the carbon cloth reaches the designed value. Fix the four sides of the carbon cloth so that it fits the EVA felt as a whole. c. Use the positioning plate 1 and the suture needle 2 to sew the flat carbon cloth; a needle handle 5 is provided at the rear of the suture needle 2, and the needle handle 5 has a cavity. The needle tip of the front end of the suture needle 2 is provided with a fine hole 4, and the straight rod section is provided with a suture thread channel 3. The carbon fiber suture thread passes through the suture thread channel 3 directly to the needle tip fine hole 4, and the carbon fiber suture thread passes through the fine hole 4.

[0030] Using the positioning plate, find the first puncture point, pierce the carbon cloth layer with the suture needle downwards, and insert the suture needle tip of the carbon fiber suture thread into the interior of the EVA. The high resilience of the EVA can be used to clamp the carbon fiber suture thread. In this way, one end of the carbon fiber suture thread is clamped by the EVA and retained in the EVA, and the other end extends along the suture thread channel. As the suture needle is lifted, the carbon fiber suture thread extends to the outside of the carbon cloth layer. Then, using the spacing designed by the positioning plate, find the next puncture position, and then puncture through the carbon cloth layer to reach the inside of the EVA. Then, pull out the suture needle, and repeat the same principle until the designed product size is fully covered, and the flat carbon cloth layer is continuously penetrated by the suture thread up and down, forming an integral carbon fiber three-dimensional structure preform with a suture thread head on the lower surface; d. The whole carbon fiber three-dimensional structure preform with sutures is pre-hardened in an oven. After hardening, the surface with the sutures is placed upwards and all the suture ends are cut off with scissors to obtain a whole carbon fiber three-dimensional structure preform with a clean surface.

[0031] Step (3) hot pressing the carbon fiber three-dimensional structure preform with resin; the required amount of resin is calculated based on the density of the resin plate, and the resin is evenly applied to the stitched carbon fiber three-dimensional structure preform using a resin brush, and then the preform is transferred to a flat hot press to perform a temperature-raising hot pressing curing process, and after curing, a pressed carbon fiber three-dimensional structure resin-based plate with good flatness is obtained.

[0032] Step (4) uses a hot pressing carbonization furnace to complete the carbonization treatment of the pressed carbon fiber three-dimensional structure resin-based sheet under strong flat plate pressure to obtain a carbon / carbon pressed sheet blank; the carbon fiber three-dimensional structure resin-based sheet is carbonized under continuous high-intensity pressure. Unlike the traditional pressureless carbonization under vacuum or inert atmosphere, the thickness of the sheet will not expand and change. Instead, due to the effect of high pressure, the thickness of the sheet will shrink, thereby making it easier to obtain a higher densification efficiency and a high-density carbon / carbon sheet with a higher fiber content, so that it has good mechanical properties; The carbonized carbon / carbon pressed sheet in step (5) is subjected to high temperature treatment to obtain a high-strength carbon / carbon pressed sheet with a flexural strength of more than 200 MPa. Example 2

[0033] A method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure comprises the following steps: Design of three-dimensional structural prefabricated bodies; Design plate size 2000*1500*15 The width of the carbon cloth is: length 2040 mm, width 1540 mm; Thickness of preform = 15 / 0.6 = 25mm Number of carbon cloth layers = 25 / 0.3 = 83 (estimated) (2) Preparation of carbon cloth three-dimensional structure preform: b. Lay the cut carbon cloth flat on a wooden board with 24mm thick EVA felt, until the thickness of the carbon cloth reaches 25mm. Fix the four edges of the carbon cloth so that it fits the EVA felt as a whole. c. Use the positioning plate and suture needle to sew the flat carbon cloth; Select a 0.8mm braided rope as the suture line; select a spacing of 8mm for the suture density; use the positioning plate to find the first puncture point, pierce the carbon cloth layer with the suture needle downwards, and insert the suture needle tip of the carbon fiber suture line into the interior of the EVA. The high resilience of the EVA can be used to clamp the carbon fiber suture line, so that one end of the carbon fiber suture line is clamped by the EVA and retained in the EVA, and the other end extends along the suture line channel. As the suture needle is lifted, the carbon fiber suture line extends to the outside of the carbon cloth layer. Then, use the spacing designed by the positioning plate to find the next puncture position, and then pierce through the carbon cloth layer to reach the inside of the EVA, and then lift the suture needle. The same principle is used, and this process is repeated until the designed product size is fully covered, and the flat carbon cloth layer is continuously penetrated by the suture line up and down, forming an integral carbon fiber three-dimensional structure preform with a suture line head on the lower surface.

[0034] d. The whole carbon fiber three-dimensional structure preform with sutures was pre-hardened in an oven at 200°C. The sutures were cut off with scissors to obtain a whole carbon fiber three-dimensional structure preform with a clean surface.

[0035] (3) Resin hot pressing molding of carbon fiber three-dimensional structure preforms; The mass of the resin to be applied is (63kg-41.25kg) / 0.6 / 0.8=45kg. Apply the required amount of resin evenly on the surface of the board. Transfer to the hot press and use the following process to hot press and solidify the shape: 3) The hot pressing process curve of the large-size carbon fiber three-dimensional structure high-strength carbon / carbon pressed plate is as follows: RT-60℃±20℃,1±0.5h; 60℃±20℃, keep warm for 2±1h; 60℃~180℃±20℃, 20℃±10℃ / h; 180℃±20℃, keep warm for 2±1h; about 11h.

[0036] Hot press pressure curve: t / min P / MPa t / min P / MPa 0 0 20 3.5 1 1 22 3.5 3 1.5 25 4 5 1.5 27 4.5 7 2 30 5 8 2 35 5.5 10 3 40 7 12 3 42 9 15 3 45 11 / 9 17 3 (4) Hot pressing carbonization: The following process is used Hot pressing carbonization is completed in a hot pressing carbonization furnace. The carbon fiber hot pressing resin plate stack is placed flat under the hot pressing head. The head is pressurized to 8-10MPa. The pressure is maintained and hot pressing and heating carbonization are started. The process curve is as follows: RT-180℃±20℃,1±0.5h; 180℃~350℃±20℃, 30℃±10℃ / h, about 6h; 350℃~650℃±20℃, 20℃±10℃ / h, about 15h; 650℃~900℃±20℃, 30℃±10℃ / h, about 8h; 900℃±50℃, keep warm for 3±1h; about 32h in total.

[0037] (5) The carbonized carbon / carbon pressed sheet undergoes a high temperature treatment at 2000°C to obtain a high-strength carbon / carbon pressed sheet with a flexural strength of more than 200 MPa.

[0038] High temperature treatment, its process parameters are as follows: RT-350℃±20℃,2±0.5h; 350℃~850℃±20℃, 100℃±10℃ / h, about 5h; 850℃~1500℃±20℃, 70℃±10℃ / h, about 9h; 1500℃~2000℃±20℃, 50℃±10℃ / h, about 10h; 2000℃±50℃, keep warm for 4±1h, about 28h in total.

[0039] The invention uses a specific stitching tool to stitch multiple layers of flat carbon cloth into a carbon fiber sheet preform with an integral three-dimensional structure, maintaining the characteristics of continuous carbon fibers. After hot pressing and curing, hot pressing and carbonization, and high-temperature graphitization treatment, a large-sized carbon / carbon pressed sheet with a continuous carbon fiber structure is obtained. The sheet has structural and process advantages, which enable it to obtain excellent mechanical properties. The reinforcing fibers of the sheet are all continuous carbon fibers, which can maximize the strength characteristics of carbon fibers. At the same time, the sheet production carbonization process adopts a hot pressing carbonization process, which is different from the traditional pressureless carbonization in a vacuum or inert atmosphere. The thickness of the carbon / carbon sheet will not expand and change during the hot pressing and carbonization process. Instead, the thickness will shrink due to the action of high pressure, making it easier to form a higher density efficiency and obtain a high-density carbon / carbon sheet with a higher fiber content. It has good mechanical properties and a flexural strength of more than 200MPa.

Claims

1. A method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure, characterized in that: The following steps are involved: Step (1) Design of the three-dimensional structure preform, including calculation of the carbon cloth size required for the carbon / carbon pressed plate size, calculation of the number of carbon cloth layers laid, and calculation of the plate preform thickness; Step (2) Preparation of carbon cloth three-dimensional structure preform: a. Cut the carbon cloth according to the design size with a reserved margin. The carbon cloth can be unidirectional or plain weave. b. Lay the cut carbon cloth flat on the wooden board with EVA felt. Make sure the thickness of the carbon cloth reaches the designed value. Fix the four sides of the carbon cloth so that it fits the EVA felt as a whole. c. Using a positioning plate (1) and a suturing needle (2) to sew the flat carbon cloth; a needle handle (5) is provided at the rear of the suturing needle (2), the needle handle (5) having a cavity, a fine hole (4) being provided at the tip of the needle at the front end of the suturing needle (2), a suturing thread channel (3) being provided at the straight rod section, a carbon fiber suturing thread passing through the suturing thread channel (3) directly reaching the fine hole (4) at the needle tip, and the carbon fiber suturing thread passing through the fine hole (4); Using the positioning plate, find the first puncture point, pierce the carbon cloth layer with the suture needle downwards, and insert the suture needle tip of the carbon fiber suture thread into the interior of the EVA. The high resilience of the EVA can be used to clamp the carbon fiber suture thread. In this way, one end of the carbon fiber suture thread is clamped by the EVA and retained in the EVA, and the other end extends along the suture thread channel. As the suture needle is lifted, the carbon fiber suture thread extends to the outside of the carbon cloth layer. Then, using the spacing designed by the positioning plate, find the next puncture position, and then puncture through the carbon cloth layer to reach the inside of the EVA. Then, pull out the suture needle, and repeat the same principle until the designed product size is fully covered, and the flat carbon cloth layer is continuously penetrated by the suture thread up and down, forming an integral carbon fiber three-dimensional structure preform with a suture thread head on the lower surface; d. The whole carbon fiber three-dimensional structure preform with sutures is pre-hardened in an oven. After hardening, the surface with the sutures is placed upwards and all the sutures are cut off with scissors to obtain a whole carbon fiber three-dimensional structure preform with a clean surface. Step (3) hot pressing the carbon fiber three-dimensional structure preform with resin; the required amount of resin is calculated based on the density of the resin plate, and the resin is evenly applied to the stitched carbon fiber three-dimensional structure preform using a resin brush, and then the preform is transferred to a flat hot press to perform a temperature-raising hot pressing curing process, and after curing, a pressed carbon fiber three-dimensional structure resin-based plate with good flatness is obtained; Step (4) uses a hot pressing carbonization furnace to complete the carbonization treatment of the pressed carbon fiber three-dimensional structure resin-based sheet under strong flat plate pressure to obtain a carbon / carbon pressed sheet blank; the carbon fiber three-dimensional structure resin-based sheet is carbonized under continuous high-intensity pressure. Unlike the traditional pressureless carbonization under vacuum or inert atmosphere, the thickness of the sheet will not expand and change. Instead, due to the effect of high pressure, the thickness of the sheet will shrink, thereby making it easier to obtain a higher densification efficiency and a high-density carbon / carbon sheet with a higher fiber content, so that it has good mechanical properties; The carbonized carbon / carbon pressed sheet in step (5) is subjected to high temperature treatment to obtain a high-strength carbon / carbon pressed sheet with a flexural strength of more than 200 MPa.

2. The method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure according to claim 1, characterized in that: The calculation method for the required carbon cloth size and number of layers in step (1), as well as the density and thickness of the carbon fiber sheet preform, is as follows: Width of raw carbon cloth = width (or length) of carbon / carbon sheet blank to be produced + (20-50) mm; Thickness of sheet preform = expected thickness of carbon / carbon sheet blank / compression amount; Number of carbon cloth layers = thickness of sheet preform / thickness of single-layer carbon cloth under sewing conditions; The thickness of a single layer of carbon cloth weighing 360 grams is 0.3mm, the thickness of a carbon cloth weighing 420 grams is 0.35, and the thickness of a carbon cloth weighing 500 grams is 0.42mm; The compression value is 0.55 when the board density is 0.6±0.05; the value is 0.65 when the board density is 0.7±0.05; This type of process is suitable for preparing large-size panels, with the length and width of the panel preform greater than 1000mm; the conventional value is 1500-5000mm.

3. The method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure according to claim 1, characterized in that: The thickness of the EVA felt in step (2) b is not less than 10 mm, and is preferably between 20 and 30 mm. The upper and lower layers of the carbon cloth are cut so that the four sides are flush.

4. The method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure according to claim 1, characterized in that: The positioning plate (1) in step (2) c is a ruler with positioning holes (11), and the spacing between the positioning holes (11) is the stitching spacing, which is selected according to the stitching density and is between 3-20 mm; The structure of the suture needle 2 in step (2) c is made of a thin metal tube with a diameter of 3 mm, with one side of the tube wall ground off, and a sharpened section. The needle tip has a fine hole (4) with a diameter of 1.5 mm; the needle handle 5 is made of wood; The carbon fiber suture thread in step (2) c is 6k, 3k carbon fiber filament or a braided carbon rope with a diameter of 0.6-1mm, preferably a braided carbon rope with a diameter of 0.6-1mm; In step (2) c, the depth of the suture needle puncturing the EVA is not less than 10 mm and is between 15 and 20 mm.

5. The method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure according to claim 1, characterized in that: The hardening temperature of the integral carbon fiber three-dimensional structure preform with suture thread ends on the surface in step (2) d is not less than 200°C.

6. The method for preparing a large-size carbon fiber three-dimensional structure high-strength carbon / carbon pressed plate according to claim 1, characterized in that: The calculation formula for the resin amount in the resin hot pressing molding in step (3) is as follows: The mass of the applied resin (kg) = (the mass of the designed pressed resin plate (kg) - the mass of the carbon fiber three-dimensional stitched part (kg)) / 0.6 / 0.8; where the mass of the designed pressed resin plate (kg) = the volume of the designed pressed resin plate * density, where the density is 1.4g / cm 3 ; The thickness of the large-size carbon fiber three-dimensional structure high-strength carbon / carbon pressed plate in step (3) is completed by placing a pad between the upper and lower pressing plates, and the designed thickness of the pressed plate = the thickness of the pad.

7. The method for preparing a high-strength carbon / carbon pressed plate with a large-size carbon fiber three-dimensional structure according to claim 1, characterized in that In step (4), a hot pressing carbonization furnace is used to complete the hot pressing carbonization. The carbon fiber hot pressing resin plate stack is placed flat directly under the hot pressing head. The head is pressurized to 8-10MPa, and the pressure is maintained to start hot pressing and heating carbonization.

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