Screw member made of two-dimensional carbon / carbon composite material laminated with anisotropic nonwoven fabric

Abstract

Provided is a screw member made of a two-dimensional carbon / carbon composite material having high strength by increasing the contribution of carbon fibers to the strength of the screw member, and a screw member made of a two-dimensional carbon / carbon composite material capable of mitigating thermal stress generated in the screw member due to a large change in the atmospheric temperature in which the screw member is used, preventing breakage, and mitigating loosening in the fastening portion of the screw. The screw member is configured such that, in a screw member made of a two-dimensional carbon / carbon composite material in which an anisotropic nonwoven fabric using short fiber carbon fibers is laminated, orientation is performed in a manner in which the central axis direction of the screw member coincides with the Y direction of the two-dimensional carbon / carbon composite material having anisotropy (a direction in which the short fiber carbon fibers are oriented in small amounts).

Description

Technical Field

[0001] This invention relates to screw components made of two-dimensional carbon / carbon composite materials with anisotropic nonwoven fabrics laminated on them. Background Technology

[0002] Carbon / carbon composite materials (also known as "C / C composite materials" or simply "C / C materials") are several times stronger and have a higher elastic modulus than traditional carbon or graphite materials, while being lighter. They also have excellent heat resistance, wear resistance, toughness, and thermal conductivity. Therefore, they were originally used as nozzle materials for solid rockets, materials for the nose section of ICBMs and other missiles, or materials for the nose section and leading edge of wings of space shuttles.

[0003] Due to the excellent properties of carbon / carbon composite materials as described above, they have begun to be used in brakes for aircraft, racing cars, Shinkansen vehicles, and large heavy vehicles; furnace structural materials for heat treatment furnaces; trays; heaters; product handling forks in semiconductor manufacturing furnaces and solar cell manufacturing furnaces; and high-temperature fixtures for metal processing. Their applications are now widespread in general industrial uses.

[0004] Therefore, if carbon / carbon composite materials are widely used as general industrial materials, screw components are required when joining carbon / carbon composite components together or when joining carbon / carbon composite components with components made of other materials.

[0005] In high-temperature environments where components made of carbon / carbon composite materials are used, even screw components made of heat-resistant steel may not achieve sufficient strength or durability due to high-temperature creep. To fasten the components together, screw components made of carbon / carbon composite materials are used (see Patent Document 1).

[0006] The screw made of 2D (two-dimensional) carbon fiber reinforced carbon composite material disclosed in Patent Document 1 is manufactured by the following process (refer to paragraphs

[0019] and

[0020] of Patent Document 1).

[0007] (1) A prepreg is made by coating a plain weave fabric of carbon fiber yarn or filament with phenolic resin and then cutting the prepreg to the specified size.

[0008] (2) The prepreg is stacked in multiple layers and formed into a thickness of 20mm using a hot press at 160℃.

[0009] (3) Heat the molded body to 800°C and perform calcination (carbonization).

[0010] (4) Then, the asphalt impregnation and calcination were repeated multiple times, and the final heat treatment (graphitization treatment) was carried out at 2000℃ to obtain a flat plate of 2D carbon fiber reinforced carbon composite material.

[0011] (5) Machining full screw bolts from the flat plate of the 2D carbon fiber reinforced carbon composite material.

[0012] (6) At this point, the cutting process is performed with the direction of the warp or weft yarns of the plain weave fabric aligned with the direction of the central axis of the bolt (refer to Patent Document 1). Figure 1 ).

[0013] In screws made of 2D (two-dimensional) carbon fiber reinforced carbon composite material manufactured through such a process, since the bolt is cut from a flat plate of 2D carbon fiber reinforced carbon composite material in which the warp or weft yarns of the plain weave fabric are aligned with the central axis of the bolt, it has the same mechanical properties such as strength and elastic modulus and thermal properties such as coefficient of thermal expansion in the direction of the central axis of the bolt and in the direction perpendicular to the central axis of the bolt and parallel to the lamination surface of the plain weave fabric.

[0014] Existing technical documents

[0015] Patent documents

[0016] Patent Document 1: Japanese Patent Application Publication No. 2001-289226 Summary of the Invention

[0017] However, in the screws made of two-dimensional carbon fiber reinforced carbon composite materials as described above, there is a problem that the contribution of carbon fiber to the bending strength of the screw teeth is insufficient, and the strength of the bolt (screw component) cannot be fully utilized.

[0018] Furthermore, carbon fibers generally have a negative coefficient of thermal expansion along their fiber direction. Therefore, the coefficient of thermal expansion of carbon / carbon composites is very small compared to that of graphite, heat-resistant steel, and the like. Moreover, depending on the fiber orientation ratio, the coefficient of thermal expansion of carbon / carbon composites exhibits anisotropy, with the direction of higher fiber orientation having a lower coefficient of thermal expansion than the direction of lower fiber orientation.

[0019] When using screw components made of carbon / carbon composite materials in conjunction with components made of materials other than carbon / carbon composite materials, such as graphite or heat-resistant steel, in environments with drastic temperature changes and exposure to high temperatures, the following problems arise if the screw components made of two-dimensional carbon / carbon composite materials, as described above, are used for fastening: the difference between the coefficient of thermal expansion of materials such as graphite and heat-resistant steel and the coefficient of thermal expansion along the central axis of the screw components made of carbon / carbon composite materials is large. Due to the large changes in ambient temperature, excessive thermal stress acts on the screw components made of carbon / carbon composite materials, causing them to break or loosening at the fastening point of the screw.

[0020] Furthermore, since the screw components made of two-dimensional carbon / carbon composite materials, as described above, are made of plain weave fabric of spun or filament carbon fibers to manufacture 2D carbon fiber reinforced carbon composite materials, there is also the problem that the cost of the two-dimensional carbon / carbon composite materials themselves increases, resulting in a higher cost for the screw components made of two-dimensional carbon / carbon composite materials.

[0021] The present invention is made from the above-mentioned viewpoint, and its object is to provide a screw component made of two-dimensional carbon / carbon composite material that has high strength by increasing the contribution of carbon fiber to the strength of the screw component, and to provide a screw component made of two-dimensional carbon / carbon composite material that can mitigate thermal stress generated in the screw component made of carbon / carbon composite material due to large changes in ambient temperature when the screw component is used, thereby preventing breakage, and also mitigate loosening generated in the fastening part of the screw.

[0022] Furthermore, the objective of this invention is to provide screw components made of two-dimensional carbon / carbon composite materials having the above-mentioned characteristics at low cost.

[0023] To address the aforementioned issues, in the first aspect of the invention, the screw component is configured as follows: In a screw component made of a two-dimensional carbon / carbon composite material manufactured by laminating anisotropic nonwoven fabric using short-fiber carbon fibers, the direction in which a large number of short-fiber carbon fibers of the anisotropic nonwoven fabric are oriented is called the strong orientation direction, and the direction orthogonal to the strong orientation direction is called the weak orientation direction. The strong orientation directions of the anisotropic nonwoven fabric are aligned in one direction and laminated. When the strong orientation direction of the manufactured two-dimensional carbon / carbon composite material is defined as the X direction and the weak orientation direction of the two-dimensional carbon / carbon composite material is defined as the Y direction, the orientation is performed in such a way that the central axis direction of the screw component is consistent with the Y direction of the anisotropic two-dimensional carbon / carbon composite material.

[0024] Furthermore, in the second aspect of the invention, the screw component is configured such that, in the screw component of the first aspect of the invention, the ratio of the bending strength in the X direction to the bending strength in the Y direction of the anisotropic two-dimensional carbon / carbon composite material has the following condition:

[0025] [Bending strength in the X direction] / [Bending strength in the Y direction] > 1.5.

[0026] Furthermore, in the third aspect of the invention, the screw component is configured such that, in the screw component of the first or second aspect of the invention, the ratio of the tensile modulus of elasticity in the X direction to the tensile modulus of elasticity in the Y direction of the anisotropic two-dimensional carbon / carbon composite material has the following condition:

[0027] [Tension modulus in the X direction] / [Tension modulus in the Y direction] > 1.5.

[0028] Furthermore, in the fourth aspect of the invention, the screw component is configured such that, in any of the screw components of the first to third aspects of the invention, the ratio of the coefficient of thermal expansion in the X direction to the coefficient of thermal expansion in the Y direction of the anisotropic two-dimensional carbon / carbon composite material has the following condition:

[0029] [Coefficient of thermal expansion in the X direction] / [Coefficient of thermal expansion in the Y direction] < 0.8.

[0030] In this invention, screw components are manufactured from sheets made of two-dimensional carbon / carbon composite materials that are laminated with anisotropic nonwoven fabric containing short-fiber carbon fibers. Therefore, compared with screws made from sheets made of 2D carbon / carbon composite materials that are laminated with plain weave fabric containing spun or filament carbon fibers, screw components made of two-dimensional carbon / carbon composite materials can be provided at a lower cost.

[0031] Furthermore, in the screw component of the present invention, since the screw component is oriented in a manner that aligns with the Y direction (the direction of slight orientation of short fiber carbon fibers) of the anisotropic two-dimensional carbon / carbon composite material, the contribution of carbon fibers to the bending strength of the screw teeth can be increased, thereby improving the strength of the bolt (screw component).

[0032] Furthermore, in the screw component of the present invention, since the screw component is oriented such that the central axis direction is aligned with the Y direction (the direction of minor carbon fiber orientation) of the anisotropic two-dimensional carbon / carbon composite material, a two-dimensional carbon / carbon composite screw component can be provided that can mitigate thermal stress generated in the screw component made of carbon / carbon composite material due to large changes in ambient temperature, thus preventing breakage, and also mitigate loosening of the screw fastening portion. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the process of manufacturing anisotropic nonwoven fabrics by using short-fiber carbon fibers and intentionally changing the fiber orientation ratio according to the in-plane orientation of the nonwoven fabric.

[0034] Figure 2This is a flowchart illustrating the process of manufacturing two-dimensional carbon / carbon composite laminates using anisotropic nonwoven fabrics.

[0035] Figure 3 This diagram shows a two-dimensional carbon / carbon composite laminate made by laminating anisotropic nonwoven fabric using short-fiber carbon fibers, and a bolt (full-screw bolt) cut from it and processed by machining.

[0036] Figure 4 It means Figure 3 The cross-section perpendicular to the central axis of the bolt (all-screw bolt) made of a two-dimensional carbon / carbon composite material manufactured from laminated anisotropic nonwoven fabric is shown. Figure 5 The diagram shows the cross section B-B.

[0037] Figure 5 It means Figure 4 The diagram shows a cross-section A-A (the cross-section of the bolt along the central axis) of a bolt (all-screw bolt) made of a two-dimensional carbon / carbon composite material manufactured from laminated anisotropic nonwoven fabric.

[0038] Figure 6 This is a diagram showing the thermal stress strength test results of (all screw bolts). Detailed Implementation

[0039] Embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the embodiments of the present invention described herein are illustrative and are not intended to limit the invention.

[0040] First, the manufacturing process of the anisotropic nonwoven fabric using short-fiber carbon fibers used in this invention will be explained.

[0041] Figure 1 This is a flowchart illustrating the manufacturing process of the anisotropic nonwoven fabric using short-fiber carbon fibers used in this invention.

[0042] The manufacturing process of anisotropic nonwoven fabrics using short-fiber carbon fibers consists of the following steps:

[0043] Step 11 in manufacturing carbon fiber dispersion

[0044] • Step 12: The carbon fiber dispersion is flowed onto the mesh of a mesh conveyor to form a film.

[0045] Step 13: Drying the carbon fiber sheets.

[0046] Here, the carbon fiber dispersion contains an adhesive used to bond the carbon fibers after the carbon fiber sheets have been dried.

[0047] Step 11 of manufacturing the carbon fiber dispersion will be explained.

[0048] The carbon fiber used in this invention can be any of polyacrylonitrile (PAN) based or pitch-based fibers, and can also be any of flame-resistant yarn, carbonized yarn, or graphitized yarn. In this invention, the carbon fiber is in the form of short fibers, preferably with a length of 1 to 50 mm, more preferably 1 to 25 mm. However, the length of the carbon fiber is not limited to these values.

[0049] It should be noted that materials obtained by pre-mixing PAN-based short fibers and pitch-based short fibers in a specified ratio can be used, or flame-resistant yarns, carbonized yarns, and graphitized yarns can be used in combination.

[0050] For commercially available carbon fibers, in order to achieve good adhesion with the matrix resin when forming composite materials, surface oxidation treatments such as electrolytic surface treatment are applied to the carbon fiber surface. Alternatively, in order to bundle the carbon fibers into fiber bundles, sizing agents with functional groups such as epoxy, hydroxyl, acrylate, methacrylate, carboxyl, and carboxylic anhydride groups are attached to the carbon fiber surface.

[0051] The carbon fibers used in this invention can be subjected to surface treatments and sizing agents as described herein. Of course, carbon fibers without the effects of such surface treatments and sizing agents can also be used.

[0052] The adhesive used in this invention binds the short carbon fibers together in the nonwoven fabric stage, for example, at a weight ratio of 5 to 30% by weight in the nonwoven fabric stage.

[0053] As such adhesives, carboxymethyl cellulose (CMC), water-soluble polyacrylic acid resin, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, polyester, sodium alginate, dextrin, gelatin, polyvinyl alcohol, polyester, etc. can be used.

[0054] These binders decompose into carbonaceous material by heating to high temperatures (e.g., carbonization treatment above 400°C), but the carbonization yield of the binder is low. However, the generated carbonaceous material is evenly distributed around each of the split carbon fibers and binds the carbon fibers together, thus reliably maintaining the shape of the precursor even after the carbonization treatment.

[0055] In addition, during the carbonization process, most of the binder is vaporized and lost. Therefore, the carbonaceous material, which is the binder, exists in a porous state with many voids on the outer periphery of the carbon fiber.

[0056] In manufacturing carbon fiber dispersions, a dispersion consisting of open (short fiber) carbon fibers, a binder, and an organic solvent such as water or alcohol is added to a tank in a specified ratio and stirred to form a mixed solution in which the carbon fibers are uniformly dispersed. To ensure uniform dispersion of the carbon fibers in the mixed solution, an ultrasonic transducer can be installed on the tank wall to apply ultrasonic vibrations to the mixed solution.

[0057] In step 12, where the carbon fiber dispersion is fed onto the wire mesh of a wire conveyor to form a film, the mixed solution produced in step 11, which manufactures the carbon fiber dispersion, is pumped from a tank to a papermaking apparatus for papermaking processing. The papermaking apparatus can be a fourdrinier paper machine, a cylinder paper machine, a Yangqi paper machine, a double-wire paper machine, or other papermaking machines. Here, the papermaking process using a fourdrinier paper machine will be described.

[0058] In the papermaking process using a fourdrinier paper machine, a mixed solution in which carbon fibers are uniformly dispersed in a dispersion liquid is pressurized from a tank to the feed section. The feed section allows the mixed solution to flow onto the mesh of a wire conveyor, so that only the dispersion liquid falls through the mesh, thus forming a thin, uniform, and flat sheet on the upper surface of the mesh. Therefore, in step 12, a continuous sheet is typically formed in which (short fiber) carbon fibers are randomly oriented along the sheet surface and intertwined, and a mixture of binder and dispersion liquid exists around the carbon fibers. It should be noted that in this process, most of the dispersion liquid falls through the mesh due to gravity.

[0059] Alternatively, after the carbon fiber dispersion is fed onto the mesh of a mesh conveyor to form a film, the continuous sheet containing the residual dispersion can be compressed by various methods to further extrude the dispersion.

[0060] Next, step 13, which involves drying the carbon fiber sheets, will be explained. The continuous carbon fiber sheets formed after step 12, in which the carbon fiber dispersion is flowed onto the mesh of a mesh conveyor to form a film, are not completely free of the dispersion. Therefore, residual dispersion is removed using various methods. For example, the continuous carbon fiber sheets, moistened with the dispersion, can be dried by pressing them onto an iron cylinder heated with steam.

[0061] After the steps described above, a continuous sheet of (short fiber) carbon fibers is completed. However, the continuous sheet of carbon fibers obtained in this way is composed of (short fiber) carbon fibers randomly oriented and intertwined, with an adhesive disposed around the carbon fibers. The continuous sheet of carbon fiber nonwoven fabric has a specified adhesiveness due to the residual adhesive. After exiting the papermaking device, the continuous sheet of carbon fiber nonwoven fabric is wound into a roll or cut to an appropriate size as needed, with release paper sandwiched between the fibers, to complete the carbon fiber nonwoven fabric.

[0062] For conventional carbon fiber nonwoven fabrics manufactured in this way, since the short carbon fibers are randomly oriented in a two-dimensional plane (within the plane of the nonwoven fabric), the mechanical and thermal properties of the carbon fiber nonwoven fabric itself are originally isotropic and have no directionality within the plane of the nonwoven fabric. However, by controlling the manufacturing process of carbon fiber nonwoven fabric, the fiber orientation of the originally isotropic nonwoven fabric can be made anisotropic.

[0063] The anisotropic nonwoven fabric used in the two-dimensional carbon / carbon composite material of this invention is manufactured as follows: In step 12 of the conventional carbon fiber nonwoven fabric manufacturing method, where a carbon fiber dispersion is flowed onto the mesh of a mesh conveyor to form a film, the vertical falling speed V of the dispersion onto the papermaking surface is adjusted. L Papermaking speed V P This causes the carbon fibers of the short fibers to be biased towards the papermaking direction and thus oriented in large quantities. In this specification, the nonwoven fabric in which the carbon fibers are intentionally biased towards a specific direction and thus oriented in large quantities is referred to as "anisotropic nonwoven fabric using carbon fibers" or simply "anisotropic nonwoven fabric".

[0064] Furthermore, in sheet-like anisotropic nonwoven fabrics manufactured in this manner, the direction in which carbon fibers are biased towards a large number of orientations is called the "strong orientation direction," and the direction orthogonal to the "strong orientation direction" is called the "weak orientation direction."

[0065] It should be noted that in conventional nearly isotropic carbon fiber nonwovens, the carbon fibers are arranged in a highly curved state in any direction. In contrast, in anisotropic nonwovens using the carbon fibers described here, many carbon fibers that are oriented in a specific direction, i.e., carbon fibers oriented in the "strong orientation direction", are not highly curved and are arranged in a nearly straight state.

[0066] Therefore, in the anisotropic nonwoven fabric described here, the fiber orientation ratio of the carbon fiber nonwoven fabric is made anisotropic. As a result, the bending degree of the carbon fibers in the direction of the majority carbon fiber orientation is reduced, and the carbon fibers in the direction of the majority carbon fiber orientation are oriented in a near-straight state. Therefore, when carbon / carbon composite materials are manufactured using this anisotropic nonwoven fabric, due to the synergistic effect of (a) the effect of the majority carbon fiber orientation and (i) the effect of the reduced bending degree of the carbon fibers, the properties of the (tensile, bending) strength and (tensile, bending) elastic modulus of the carbon / carbon composite material in the direction of the majority carbon fiber orientation are greatly improved.

[0067] Next, the manufacturing process of carbon / carbon composite materials using anisotropic nonwoven fabric will be explained. Figure 2 This is a flowchart illustrating the manufacturing process of carbon / carbon composite materials using anisotropic nonwoven fabrics made from carbon fibers.

[0068] First, in step 21 of laminating anisotropic nonwoven fabric, the carbon fiber nonwoven fabric is cut into specified sizes and stacked in multiple layers to obtain a flat laminate of specified shape.

[0069] At this point, the carbon fibers of the anisotropic nonwoven fabric are aligned and stacked in one direction, in the direction in which they are predominantly oriented (i.e., the "strong orientation direction"), and then aligned and stacked in another direction, in the direction orthogonal to the direction in which they are predominantly oriented (i.e., the "weak orientation direction"), and then stacked in the other direction. Therefore, the "strong orientation direction" and the "weak orientation direction" also refer to two orthogonal directions along the stacking surface of the laminate.

[0070] Next, step 22, which involves heating and pressing anisotropic nonwoven fabric laminates, will be described. In step 22, a precursor (also referred to as a "preform" or "precursor") of a carbon / carbon composite material is formed by heating and pressing the anisotropic nonwoven fabric laminates obtained in step 21.

[0071] Step 22, which involves heating and pressing the anisotropic nonwoven fabric laminate, is performed to convert the organic binder material contained in the anisotropic nonwoven fabric into inorganic carbonaceous material while maintaining the shape of the anisotropic nonwoven fabric laminate.

[0072] In forming a precursor of carbon / carbon composite material by heating and pressing a flat laminate, the carbon fiber nonwoven fabric laminate is sandwiched between the hot plates of a hot press, and the laminate is heated and pressed using the heating plates.

[0073] Here, the heating temperature only needs to be above 400℃. If heated to this temperature, the adhesive material can be converted into a carbonaceous substance.

[0074] The precursor of the carbon / carbon composite material is a state in which the binder that binds the short fibers of carbon fibers is transformed into a carbonaceous material that binds and holds the individual carbon fibers together, thus maintaining the pre-shaped flat plate shape.

[0075] In the heating process used to form the precursor of carbon / carbon composite material, part of the binder vaporizes and disappears, part of the binder becomes carbonaceous material and remains, and the vaporized and disappeared part becomes pores, forming a porous material.

[0076] Next, step 23, which involves melting and impregnating the asphalt or synthetic resin, will be explained. Step 23 is performed to form a dense matrix structure by impregnating the porous carbon / carbon composite precursor with asphalt or synthetic resin, thereby filling the pores in the carbonaceous material and the microspaces created between the carbon fibers.

[0077] In step 23, the powder or fragments of asphalt or synthetic resin placed in the container are first heated to melt them. The asphalt used here can be any of coal tar pitch or coal pitch, preferably asphalt with good impregnation properties and high carbonization yield. As for the synthetic resin, thermosetting resins with good impregnation properties and high carbonization yield, such as phenolic resins or furan resins, are preferred, but are not limited to the resins exemplified here.

[0078] Next, the precursor of the carbon / carbon composite material is impregnated in a container containing molten bitumen or synthetic resin, so that the molten bitumen or molten resin is impregnated in the aforementioned pores or microspaces.

[0079] At this point, the carbon / carbon composite precursor can be placed in a vacuum container, and molten bitumen or molten resin can be poured into the vacuum container, thereby impregnating the molten bitumen or molten resin. Alternatively, after impregnating the carbon / carbon composite precursor in molten bitumen or molten resin, external pressure can be applied to force the molten bitumen or molten resin into the interior of the precursor.

[0080] In step 24, the precursor impregnated with molten asphalt or molten resin is carbonized. Using a carbonization furnace or the like, the carbon / carbon composite precursor impregnated with molten asphalt or molten resin is heated to about 800°C to 1500°C, converting the impregnated asphalt or resin into carbon.

[0081] When molten asphalt or molten resin impregnated with carbon / carbon composite precursors is carbonized, a portion of the molten asphalt or molten resin is converted into carbon, while a portion is vaporized and disappears, thus creating new micropores in the space impregnated with molten asphalt or molten resin.

[0082] In order to utilize carbon to fill the newly formed micropores, the above-mentioned steps 23 of melting and impregnating asphalt or synthetic resin and 24 of carbonizing the precursor impregnated with molten asphalt or molten resin can be performed again or repeated multiple times.

[0083] Carbon / carbon composite materials can be completed through the processes described above.

[0084] In step 25, which further graphitizes the carbon / carbon composite material, the completed carbon / carbon composite material is further heated to about 2000℃~2800℃ for graphitization treatment as needed, thereby converting the carbon in the fibers and matrix of the carbon / carbon composite material into graphite with a highly crystalline structure.

[0085] The description up to this point has stated that anisotropic nonwoven fabrics are composed of short-fiber carbon fibers and adhesives, but are not limited to this.

[0086] In step 11 of manufacturing the carbon fiber dispersion, petroleum and / or coal-based coke powder that does not have softening properties may be further added, or petroleum and / or coal-based binder pitch powder that has softening properties and petroleum and / or coal-based coke powder that does not have softening properties may be added.

[0087] Through this operation, the mixture becomes either a non-softening petroleum and / or coal-based coke powder dispersed and mixed in the binder of anisotropic nonwoven fabric, or a softening petroleum and / or coal-based binder pitch powder and a non-softening petroleum and / or coal-based coke powder dispersed and mixed in the binder of anisotropic nonwoven fabric.

[0088] Thus, if anisotropic nonwoven fabric containing binder asphalt powder, coke powder, etc., is used to manufacture carbon / carbon composite materials, then during the heat treatment process in the manufacturing process of carbon / carbon composite materials, most or all of the binder asphalt powder and coke powder remain as carbon matrix in the carbon / carbon composite material, making it easier to achieve high density in the carbon / carbon composite material. As a result, the number of times step 23, which involves melting and impregnating asphalt or synthetic resin, is performed in the manufacturing process of carbon / carbon composite materials can be reduced, or step 23 can be omitted.

[0089] Next, the method for processing screw components 2 from a two-dimensional carbon / carbon composite material laminate 1 made of anisotropic nonwoven fabric using short-fiber carbon fibers will be described.

[0090] In this specification, screw component 2 is a general term for bolt 2, full screw bolt 2, nut 2, etc. Here, full screw bolt 2 is used as an example of screw component 2 and its processing method is described.

[0091] Figure 3 This diagram shows a two-dimensional carbon / carbon composite material laminate 1 made by laminating anisotropic nonwoven fabric using short-fiber carbon fibers, and a full-screw bolt 2 obtained by cutting and machining from it.

[0092] As described above, the two-dimensional carbon / carbon composite laminate 1, manufactured by using a manufacturing process of anisotropic nonwoven carbon / carbon composite material, is obtained by aligning the orientation of the anisotropic nonwoven material and stacking and molding it. Therefore, the laminate 1 formed also has the same orientation as the nonwoven material.

[0093] The orientation of the two-dimensional carbon / carbon composite material laminate 1 used in this invention is defined as follows.

[0094] That is, the strong orientation directions of the anisotropic nonwoven fabrics are aligned in one direction and stacked, the direction corresponding to the strong orientation direction of the manufactured two-dimensional carbon / carbon composite material is defined as the X direction, and the direction corresponding to the weak orientation direction of the two-dimensional carbon / carbon composite material is defined as the Y direction.

[0095] Laminate 1 made from such a two-dimensional carbon / carbon composite material with both "X" and "Y" directions Figure 3 The full-length bolt 2 is cut in the same direction as shown. That is, the central axis of the full-length bolt 2 is aligned with the "Y direction" of the laminate 1 (see reference). Figure 3 The orientation is in the "X direction" (refer to the direction perpendicular to the central axis of bolt 2). Figure 3 ).

[0096] There is no particular limitation on the method of cutting out the blank of the full screw bolt 2 from the laminate 1 made of two-dimensional carbon / carbon composite material and finishing it into the full screw bolt 2. It can be manufactured by well-known machining processes such as band saws, milling machines and lathes.

[0097] Figure 4 This is a diagram showing a cross-section perpendicular to the central axis of a fully threaded bolt 2 manufactured in this manner. Figure 5 It means Figure 4 The diagram shows the cross-section A-A (the section of the bolt along its central axis) of the all-screw bolt 2, and the "X direction" and "Y direction" of the two-dimensional carbon / carbon composite laminate 1 are shown in the figure. Figure 3 The indicated direction and orientation.

[0098] Typically, bolts 2 and the like are manufactured by machining a laminate 1 of fiber-reinforced composite materials. Figure 4 The axial load of the screw thread support bolt 2 in region P shown is the same as that in the all-screw bolt 2 of the present invention.

[0099] Furthermore, in the screw component 2 of the present invention, the "X direction" (i.e., the direction in which the carbon fibers are oriented in large quantities) of the laminate 1 exists in the opposing region P. As a result, the contribution of the carbon fibers to the strength of the screw component 2 can be increased, and the strength of the screw component 2 can be significantly improved.

[0100] Example

[0101] Flat carbon / carbon composite materials were fabricated using the aforementioned anisotropic nonwoven fabric. These materials were then used as blanks to machine M8 and M12 size full-screw bolts 2. Static load tests and thermal stress strength tests were conducted on the bolts 2. Details of the fabrication and testing of the two-dimensional (flat) carbon / carbon composite materials are as follows.

[0102] 1. Fabrication of flat carbon / carbon composite materials using (anisotropic) nonwoven fabric

[0103] In this embodiment, pitch-based short-fiber carbon fibers are used, and the carbon fibers are oriented in large quantities towards the paper-making direction to produce anisotropic nonwoven fabric. Therefore, the amount of carbon fibers oriented in the direction orthogonal to the paper-making direction is correspondingly reduced. Thus, the paper-making direction becomes the strongly oriented direction of the anisotropic nonwoven fabric, and the direction orthogonal to the paper-making direction becomes the weakly oriented direction.

[0104] In addition, the anisotropic nonwoven fabric used here is composed only of carbon fibers and adhesives, and does not contain adhesive asphalt powder or coke powder.

[0105] It should be noted that the amount of carbon fiber in the anisotropic nonwoven fabric was adjusted so that the carbon fiber content (volume content Vf) of the finished carbon / carbon composite was 40%.

[0106] In step 21 of the manufacturing process of the two-dimensional carbon / carbon composite laminate 1, the strong orientation direction of the anisotropic nonwoven fabric is aligned with the X direction of the laminate 1, and the weak orientation direction of the anisotropic nonwoven fabric is aligned with the Y direction of the laminate 1. Therefore, a large number of carbon fibers are oriented in the X direction of the laminate 1, and a small number of carbon fibers are oriented in the Y direction of the laminate 1.

[0107] Furthermore, step 23, which involves melting and impregnating the asphalt or synthetic resin, and step 24, which involves carbonization, are each performed only once. Additionally, in step 25, which involves graphitization, heat treatment is performed at 2500°C.

[0108] Test pieces were cut from the five flat carbon / carbon composite materials prepared in the examples, and the flexural strength, tensile modulus of elasticity, and coefficient of thermal expansion in the X and Y directions were measured. The results are shown in Table 1. (Each measured value represents the average of the measured values ​​of the five flat pieces.) It should be noted that Table 1 also shows the ratio of flexural strength in the X and Y directions σ. X / σ Y E X / E Y α X / α Y .

[0109] Table 1

[0110] Table 1. Properties of the anisotropic two-dimensional carbon / carbon composite materials of the embodiments.

[0111]

[0112] That is, in the anisotropic two-dimensional carbon / carbon composite material produced in the embodiment, the ratio of bending strength in the X direction to that in the Y direction and the ratio of tensile elastic modulus are 2.50 times and 3.75 times, respectively, achieving an anisotropy of more than 1.5 times that cannot be achieved using conventional isotropic nonwoven fabrics in two-dimensional carbon / carbon composite materials.

[0113] In addition, the ratio of the coefficient of thermal expansion in the X direction to that in the Y direction is 0.74, achieving an anisotropy of less than 0.8 times that cannot be achieved using conventional isotropic nonwoven fabrics in two-dimensional carbon / carbon composite materials.

[0114] Next, a comparative example will be described. In the comparative example, during the nonwoven fabric manufacturing stage, papermaking was performed with a large number of carbon fibers oriented without bias towards a particular direction. Therefore, within the plane of the nonwoven fabric, the short carbon fibers are almost evenly dispersed and oriented, resulting in a nonwoven fabric with isotropic properties within the plane. Apart from this, the manufacturing process of the nonwoven fabric in the comparative example is no different from that in the embodiment.

[0115] In addition, in the manufacturing process of the flat carbon / carbon composite material, isotropic nonwoven fabrics are laminated to form a laminate. Apart from this, there is no difference from the process of manufacturing the flat carbon / carbon composite material in the example.

[0116] Five isotropic carbon / carbon composite materials prepared in the comparative example were cut into test pieces, and their flexural strength, tensile modulus of elasticity, and coefficient of thermal expansion were measured. The results are shown in Table 2. (Each measured value represents the average of the values ​​measured from the five flat pieces.)

[0117] Table 2

[0118] Table 2 Properties of isotropic two-dimensional carbon / carbon composite materials of comparative examples

[0119] project Bending strength σ 190MPa Tensile modulus of elasticity E 40GPa coefficient of thermal expansion d <![CDATA[0.51x10 -6 1 / K]]>

[0120] 2. Static load strength test of bolt 2 (all-screw bolts)

[0121] In this embodiment, bolt 2 (a full-screw bolt) is machined from the aforementioned anisotropic two-dimensional carbon / carbon composite material to achieve the following properties: Figure 3 The orientation is shown. That is, the orientation is such that the central axis of the full screw bolt 2 is aligned with the Y direction of the anisotropic two-dimensional carbon / carbon composite material. In the embodiment, full screw bolts 2 of M8 and M12 sizes are manufactured.

[0122] In addition, for comparison with the embodiments, full-screw bolts 2 of Comparative Example 1 and Comparative Example 2 were manufactured. In Comparative Example 1, the full-screw bolt 2 was oriented such that the central axis direction of the full-screw bolt 2 was aligned with the X direction of the anisotropic two-dimensional carbon / carbon composite material, and full-screw bolts 2 of M8 and M12 sizes were machined from the anisotropic two-dimensional carbon / carbon composite material.

[0123] Furthermore, in Comparative Example 2, M8 and M12 size full screw bolts 2 were machined from the isotropic two-dimensional carbon / carbon composite material of the above-mentioned comparative example by machining.

[0124] Metal nuts 4 were installed at both ends of the M8 and M12 size full-screw bolts 2 prepared in the embodiments here, as well as Comparative Examples 1 and 2. The nuts 4 were stretched in a way that they were pulled apart along the axis of the full-screw bolt 2, and a static load strength test (tensile load test) was performed on the full-screw bolt 2. The results are shown in Table 3.

[0125] Table 3

[0126] Table 3 shows the static load strength test results of the all-screw bolt 2 in the examples and comparative examples.

[0127]

[0128] The results show that the all-screw bolt 2 of the embodiment (the bolt whose central axis is aligned with the Y direction (the weak orientation direction of the carbon fiber) of the anisotropic two-dimensional carbon / carbon composite material) has superior screw strength compared with the all-screw bolt 2 of Comparative Example 1 (the bolt whose central axis is aligned with the X direction (the strong orientation direction of the carbon fiber) of the anisotropic two-dimensional carbon / carbon composite material) and the all-screw bolt 2 of Comparative Example 2 (the bolt made of isotropic two-dimensional carbon / carbon composite material).

[0129] 3. Thermal stress strength test of bolt 2

[0130] The thermal stress strength test was conducted using the same M8 and M12 size full screw bolts (anisotropic two-dimensional carbon / carbon composite bolts) used in the static load strength test of bolt 2 (full screw bolts) as those used in the embodiment, and the same M8 and M12 size full screw bolts (isotropic two-dimensional carbon / carbon composite bolts) as those in Comparative Example 2.

[0131] The thermal stress strength test is conducted according to the following steps. First, as described below... Figure 6As shown, a full screw bolt 2 is inserted into the through hole of the isotropic graphite spacer 3 with a through hole in the center, and isotropic graphite nuts 4 are screwed onto both ends of the full screw bolt 2. The nuts are tightened with a constant torque, thereby integrating the isotropic graphite spacer 3, the nuts 4 and the M8 or M12 full screw bolt 2.

[0132] Next, the integrated test specimen was heated to 1200°C and 2000°C in an inert gas atmosphere, and then cooled to room temperature. The M8 and M12 size full screw bolts 2 in the test specimen were then visually inspected for damage, and the thermal stress strength of the M8 and M12 size full screw bolts 2 was evaluated.

[0133] The results of the thermal stress strength test of the all-screw bolt 2 are shown in Table 4.

[0134] Table 4

[0135] Table 4 Results of thermal stress strength test for all-screw bolt 2

[0136]

[0137] Assuming the assembly is combined with an isotropic graphite separator 3 having a coefficient of thermal expansion that is an order of magnitude larger than that of the carbon / carbon composite material, even when large temperature differences (1200°C and 2000°C) are applied, no damage to the screw or loosening of the screw due to thermal stress is observed in the all-screw bolt 2 of the embodiment (the bolt whose central axis is aligned with the Y-direction (weak orientation direction of the carbon fiber) of the anisotropic two-dimensional carbon / carbon composite material).

[0138] On the other hand, in the all-screw bolt 2 of Comparative Example 2 (a bolt made of isotropic two-dimensional carbon / carbon composite material) implemented under the same conditions as the all-screw bolt 2 of the embodiment, damage to the screw caused by thermal stress was observed in all of them.

[0139] That is, it can be said that the thermal stress strength of the all-screw bolt 2 in the embodiment is superior compared with that of the all-screw bolt 2 in Comparative Example 2, and the thermal stress mitigation effect is significant in the all-screw bolt 2 in the embodiment.

[0140] This is believed to be because the coefficient of thermal expansion in the axial direction of the all-screw bolt 2 in the embodiment is greater than that in the axial direction of the all-screw bolt 2 in Comparative Example 2, and has a value that is closer to the coefficient of thermal expansion of the isotropic graphite separator 3. Furthermore, the tensile modulus of elasticity in the axial direction of the all-screw bolt 2 is smaller than that in the axial direction of the all-screw bolt 2 in Comparative Example 2. As a result of these synergistic effects, the thermal stress mitigation effect becomes significant.

[0141] Symbol Explanation

[0142] 1. Laminates of anisotropic two-dimensional carbon / carbon composite materials

[0143] 2. Screw components (bolts, full screw bolts, nuts)

[0144] 3. Isolation components

[0145] 4 nuts

[0146] 11. Steps for manufacturing carbon fiber dispersion

[0147] 12. Step of flowing carbon fiber dispersion onto a wire mesh to form a film.

[0148] 13. Steps for drying carbon fiber sheets

[0149] 21. Steps for stacking anisotropic nonwoven fabrics

[0150] 22. Steps for heating and pressing anisotropic nonwoven fabric laminates

[0151] 23. The step of melting and impregnating asphalt or synthetic resin.

[0152] 24. Steps for carbonizing precursors impregnated with molten bitumen or molten resin.

[0153] 25. Steps for graphitizing carbon / carbon composite materials

Claims

1. A screw member, characterized by is a screw member made of a two-dimensional carbon / carbon composite material manufactured by laminating anisotropic nonwoven fabric in which short fiber carbon fibers are used, the direction in which the short fiber carbon fibers of the anisotropic nonwoven fabric are largely oriented is referred to as a strong orientation direction, and the direction orthogonal to the strong orientation direction is referred to as a weak orientation direction, when the strong orientation direction of the anisotropic nonwoven fabric is aligned in one direction and laminated, the strong orientation direction of the manufactured two-dimensional carbon / carbon composite material is defined as an X direction, and the weak orientation direction of the two-dimensional carbon / carbon composite material is defined as a Y direction, the screw member is oriented in a manner in which the central axis direction of the screw member coincides with the Y direction of the two-dimensional carbon / carbon composite material having anisotropy.

2. The screw member according to claim 1, wherein the ratio of the bending strength of the X direction to the bending strength of the Y direction of the two-dimensional carbon / carbon composite material having the anisotropy satisfies the following condition: [Bending strength of the X direction] / [Bending strength of the Y direction] > 1.

5.

3. The screw member according to claim 1, wherein the ratio of the tensile elastic modulus of the X direction to the tensile elastic modulus of the Y direction of the two-dimensional carbon / carbon composite material having the anisotropy satisfies the following condition: [Tensile elastic modulus of the X direction] / [Tensile elastic modulus of the Y direction] > 1.

5.

4. The screw member according to any one of claims 1 to 3, wherein the ratio of the thermal expansion coefficient of the X direction to the thermal expansion coefficient of the Y direction of the two-dimensional carbon / carbon composite material having the anisotropy satisfies the following condition: [Thermal expansion coefficient of the X direction] / [Thermal expansion coefficient of the Y direction] < 0.8.

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