TWI855418B - Threaded fastener made of a two-dimensional carbon-carbon composite material produced by laminating anisotropic non-woven fabrics - Google Patents

Abstract

The subject of the present invention is to provide a two-dimensional carbon/carbon composite screw part with high strength by improving the contribution of carbon fiber to the strength of the screw part, and to provide a two-dimensional carbon/carbon composite screw part that can relieve the thermal stress generated in the carbon/carbon composite screw part due to a large change in the ambient temperature of the screw part to prevent damage, and can relieve the looseness generated in the fastening part of the screw. The solution of the present invention is to make a screw part made of a two-dimensional carbon/carbon composite material made by laminating anisotropic non-woven fabrics using short-fiber carbon fibers, and to align the central axis direction of the screw part with the Y direction (the direction in which the short-fiber carbon fibers are less oriented) of the anisotropic two-dimensional carbon/carbon composite material.

Description

Two-dimensional carbon/carbon composite screw parts laminated with anisotropic non-woven fabric

The present invention relates to a screw part made of a two-dimensional carbon/carbon composite material laminated with anisotropic non-woven fabric.

Carbon/carbon composites (also called "C/C composites" or simply "C/C materials") are not only lightweight but also several times stronger and more elastic than conventional carbon materials or graphite materials. They also have excellent heat resistance, wear resistance, toughness, and thermal conductivity. Therefore, they are often used as nozzle materials for solid rockets, nose materials for ICBM missiles, and nose materials for aerospace aircraft and leading edges of wings.

Based on the excellent properties of carbon/carbon composite materials as mentioned above, they are used in brakes for aircraft, racing cars, Shinkansen vehicles, large and heavy vehicles, furnace internal structures of heat treatment furnaces, trays, heaters, product handling forks in semiconductor manufacturing furnaces or solar cell manufacturing furnaces, high-temperature fixtures for metal processing, etc., and their uses have been widely popularized in general industry.

Therefore, when carbon/carbon composite materials are widely used as general industrial materials, screw parts must be used when joining parts made of carbon/carbon composite materials to each other or when joining parts made of carbon/carbon composite materials to parts made of other materials.

Parts made of carbon/carbon composite materials have problems such as not being able to obtain sufficient strength or not being able to obtain sufficient durability due to the occurrence of high temperature creep even if screw parts made of heat-resistant steel are used in such high temperature environments. In order to tighten the parts together, screw parts made of carbon/carbon composite materials are used (see patent document 1).

The 2D (two-dimensional) carbon fiber reinforced carbon composite screw disclosed in Patent Document 1 is manufactured through the following steps (refer to paragraphs [0019] and [0020] of Patent Document 1).

(1) Phenolic resin is applied to a plain woven fabric of spun yarn or filament carbon fiber to make a prepreg, and the prepreg is cut into a specific size.

(2) Multiple sheets of the prepreg are laminated and formed into a thickness of 20 mm by hot pressing at 160°C.

(3) The formed body is heated to 800°C and subjected to sintering treatment (carbonization treatment).

(4) Then, asphalt impregnation and sintering are repeated several times, and heat treatment (graphitization treatment) is performed at 2000°C as the final heat treatment to obtain a flat plate of 2D carbon fiber reinforced carbon fiber composite material.

(5) Cutting and processing the entire screw bolt from the 2D carbon fiber reinforced carbon composite plate.

(6) At this time, cutting is performed in such a way that the central axis direction of the bolt is consistent with the direction of the warp or weft yarn of the plain woven fabric (refer to Figure 1 of Patent Document 1).

The 2D (two-dimensional) carbon fiber reinforced carbon composite screw manufactured through these steps is cut from a flat plate of 2D carbon fiber reinforced carbon composite laminated with carbon fiber plain woven fabric in such a way that the central axis direction of the bolt is consistent with the direction of the warp or weft yarn of the plain woven fabric. Therefore, it has the same mechanical properties such as strength and elastic modulus and thermal properties such as thermal expansion coefficient in the central axis direction of the bolt and in the direction perpendicular to the central axis direction of the bolt and parallel to the laminated surface of the plain woven fabric.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2001-289226

However, in screws made of two-dimensional carbon fiber reinforced carbon composite materials, the contribution of carbon fiber to the bending strength of the thread is insufficient, and there is a problem that the strength of the screw cannot be fully exerted as a bolt (screw part).

In addition, since the thermal expansion coefficient of carbon fiber in the fiber direction is generally negative, the thermal expansion coefficient of carbon/carbon composites is extremely small compared to the thermal expansion coefficients of graphite and heat-resistant steel. In addition, the thermal expansion coefficient of carbon/carbon composites is anisotropic according to the orientation ratio of carbon/carbon composite fibers, and the thermal expansion coefficient in the direction of high orientation ratio of carbon fiber has a lower value than the thermal expansion coefficient in the direction of low orientation ratio of carbon fiber.

When parts made of materials other than carbon/carbon composite materials, such as graphite or heat-resistant steel, are used in environments with drastic temperature changes and exposed to high temperatures and are combined with screw parts made of carbon/carbon composite materials, if they are fastened by two-dimensional carbon/carbon composite screw parts as described above, the thermal expansion coefficient of materials such as graphite or heat-resistant steel differs greatly from the thermal expansion coefficient of the carbon/carbon composite screw parts in the central axis direction. Due to the large change in ambient temperature, excessive thermal stress acts on the carbon/carbon composite screw parts, causing damage or loosening of the screw fastening part.

Furthermore, in the screw parts made of the two-dimensional carbon/carbon composite material as mentioned above, since the 2D carbon fiber reinforced carbon composite material is manufactured using a plain woven cloth of spun or filamentary carbon fibers, the cost of the two-dimensional carbon/carbon composite material itself is high, and as a result, the screw parts of the two-dimensional carbon/carbon composite material also have the problem of high cost.

The present invention is completed based on the above viewpoints, and its purpose is to provide a two-dimensional carbon/carbon composite screw part with high strength by improving the contribution of carbon fiber to the strength of the screw part, and to provide a two-dimensional carbon/carbon composite screw part that can relieve the thermal stress generated in the carbon/carbon composite screw part due to a large change in the ambient temperature of the screw part to prevent damage, and can relieve the looseness generated in the fastening part of the screw.

Furthermore, the subject of the present invention is to provide a screw part made of a two-dimensional carbon/carbon composite material having the above characteristics at a low cost.

In order to solve the above problems, the first aspect of the present invention is a screw component made of a two-dimensional carbon/carbon composite material by laminating anisotropic non-woven fabrics using short-fiber carbon fibers, and the screw component has the following structure: the direction in which the short-fiber carbon fibers of the anisotropic non-woven fabric are mostly oriented is called a strong orientation direction, and the direction orthogonal to the strong orientation direction is called a weak orientation direction, so that the strong orientation direction of the anisotropic non-woven fabric is aligned in one direction for lamination, and 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, and the central axis direction of the screw component is aligned with the Y direction of the anisotropic two-dimensional carbon/carbon composite material.

Furthermore, the invention of the second aspect is the screw component of the first aspect, which has the following structure: 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: [bending strength in the X direction]/[bending strength in the Y direction]>1.5.

Furthermore, the invention of the third aspect is a screw component of the first or second aspect, having the following structure: 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: [tensile modulus of elasticity in the X direction]/[tensile modulus of elasticity in the Y direction]>1.5.

Furthermore, the invention of the fourth aspect is a screw component according to any one of the first to third aspects, wherein the ratio of the thermal expansion coefficient in the X direction to the thermal expansion coefficient in the Y direction of the anisotropic two-dimensional carbon/carbon composite material satisfies the following condition: [thermal expansion coefficient in the X direction]/[thermal expansion coefficient in the Y direction]<0.8.

In the present invention, since the screw parts are manufactured from a two-dimensional carbon/carbon composite material sheet manufactured by laminating anisotropic non-woven fabric using short-fiber carbon fibers, compared with screws manufactured from a conventional 2D (two-dimensional) carbon/carbon composite material sheet laminated with a plain woven fabric of spun or filamentary carbon fibers, two-dimensional carbon/carbon composite material screw parts can be provided at a low cost.

In addition, in the screw component of the present invention, since the central axis direction of the screw component is aligned with the Y direction (the direction in which the short-fiber carbon fibers are less oriented) of the anisotropic two-dimensional carbon/carbon composite material, the contribution of the carbon fibers to the bending strength of the thread can be increased, and as a result, the strength of the bolt (screw component) can be increased.

Furthermore, in the screw component of the present invention, since the central axis direction of the screw component is aligned with the Y direction (the direction in which the carbon fibers are less aligned) of the anisotropic two-dimensional carbon/carbon composite material, it is possible to provide a screw component made of a two-dimensional carbon/carbon composite material that can relieve the thermal stress generated in the screw component made of the carbon/carbon composite material due to a large change in the ambient temperature in which the screw component is used, thereby preventing damage, and at the same time, can relieve the looseness generated in the fastening portion of the screw.

1: Laminated body of anisotropic two-dimensional carbon/carbon composites

2: Screw parts (bolts, main screw bolts, nuts)

3: Spacers

4: Metal nuts or isotropic graphite nuts

11: Steps for making carbon fiber dispersion

12: The step of flowing the carbon fiber dispersion onto the net to form a film

13: Step of drying the carbon fiber sheet

21: Steps of laminating anisotropic nonwoven fabrics

22: Step of heating and pressing the anisotropic non-woven fabric layer combination to form a composite

23: The step of melting and impregnating asphalt or synthetic resin

24: The step of carbonizing the precursor impregnated with molten asphalt or molten resin

25: Steps for graphitizing carbon/carbon composite materials

[Figure 1] is a flow chart for explaining the process of manufacturing anisotropic nonwoven fabrics by using short-fiber carbon fibers and intentionally changing the fiber orientation ratio in the plane of the nonwoven fabric.

[Figure 2] is a flow chart for illustrating the process of manufacturing a two-dimensional carbon/carbon composite laminate using anisotropic nonwoven fabric.

[Figure 3] shows a laminate made of a two-dimensional carbon/carbon composite material produced by laminating anisotropic non-woven fabrics using short-fiber carbon fibers, and a bolt (full-thread bolt) cut out of the laminate by cutting.

[Figure 4] is a diagram showing a cross section perpendicular to the central axis of a bolt (full-thread bolt) made of a two-dimensional carbon/carbon composite material by laminating anisotropic non-woven fabrics as shown in Figure 3 (cross section B-B shown in Figure 5).

[Figure 5] shows the cross section A-A (cross section along the center axis of the bolt) of the two-dimensional carbon/carbon composite bolt (full-thread bolt) made by laminating anisotropic non-woven fabrics shown in Figure 4.

[Figure 6] is a diagram showing the thermal stress strength test conditions of (full-thread bolts).

The embodiments of the present invention are described based on the drawings. The embodiments of the present invention described here are examples of the present invention and are not limited to them.

First, the method for producing anisotropic nonwoven fabric using short-fiber carbon fibers used in the present invention is described.

FIG1 is a flow chart showing the manufacturing process of anisotropic nonwoven fabric using short-fiber carbon fibers used in the present invention.

The manufacturing process of anisotropic nonwoven fabric using short-staple carbon fibers consists of the following:

‧Process for manufacturing carbon fiber dispersion 11

‧Step 12 of flowing the carbon fiber dispersion onto the mesh of the mesh conveyor to form a film

‧Step 13 of drying the carbon fiber sheet

Here, the carbon fiber dispersion contains a binder that binds the carbon fibers together after the carbon fiber sheet is dried.

Step 11 of manufacturing carbon fiber dispersion is explained.

The carbon fiber used in the present invention can be any of polyacrylonitrile (PAN) and asphalt, and can also be any of flame-resistant yarn, carbonized yarn, and graphitized yarn. In the present invention, the carbon fiber is a short fiber, preferably with a length of 1 to 50 mm, and even better with a length of 1 to 25 mm. However, the length of the carbon fiber is not limited to the above.

In addition, PAN-based staple fibers and asphalt-based staple fibers mixed in a specific ratio may be used, and flame-resistant yarns, carbonized yarns, and graphitized yarns may be used in combination.

In general, commercially available carbon fibers are subjected to surface oxidation treatment such as electrolytic surface treatment in order to achieve good adhesion with the matrix resin when forming a composite material, or a sizing agent having functional groups such as epoxy, hydroxyl, acrylate, methacrylate, carboxyl, and carboxylic anhydride is attached to the surface of the carbon fibers in order to bundle the carbon fibers into fiber bundles.

The carbon fibers used in the present invention may also be subjected to the surface treatment or sizing agent described herein. Of course, carbon fibers from which the effects of such surface treatment and sizing agent have been removed may also be used.

The binder used in the present invention is used to bind the short carbon fibers to each other in the non-woven fabric stage, for example, the weight ratio in the non-woven fabric stage is 5 to 30 weight %.

As such binders, 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.

These binders are decomposed by heating at high temperatures (e.g., carbonization treatment at 400°C or above) to form carbonaceous materials, but the carbonization yield of the binder is low. However, since the generated carbonaceous material is evenly distributed around each carbon fiber after fiberization and the carbon fibers are bonded to each other, the shape of the precursor is indeed maintained in the stage after carbonization treatment.

In addition, during the carbonization process, since most of the binder will be vaporized and dissipated, the carbonaceous material of the carbonization product of the binder becomes a porous state with many cavities and exists on the periphery of the carbon fiber.

When manufacturing carbon fiber dispersion, the fiberized (short fiber) carbon fiber, binder, and dispersion made of water or alcohol and other organic solvents are put into a tank at a specific ratio and stirred to form a mixed solution in which the carbon fiber is evenly dispersed in the dispersion. In order to evenly disperse the carbon fiber in the mixed solution, an ultrasonic transducer can also be installed on the tank wall to apply ultrasonic vibration to the mixed solution.

In step 12 of making the carbon fiber dispersion flow to the mesh of the mesh conveyor to form a film, the mixed solution produced in the process 11 of producing the carbon fiber dispersion is sent from the tank press to the papermaking device for papermaking. As the papermaking device, a fourdrinier papermaking machine, a cylinder papermaking machine, a single-cylinder papermaking machine (Yankee machine), a double-line papermaking machine, and other papermaking machines can be used. Here, the papermaking process using the fourdrinier papermaking machine is explained as a premise.

In the papermaking process using a fourdrinier papermaking machine, a mixed solution in which carbon fibers are uniformly dispersed in a dispersion is pressed from a tank to the feed section. In the feed section, a thin, uniform, and flat sheet can be formed on the surface of the mesh because only the dispersion passes through the mesh of the mesh conveyor through which the mixed solution passes. Therefore, in step 12, the (short fiber) carbon fibers are randomly oriented along the sheet surface, entangled with each other, and a continuous sheet is formed in which a mixed solution of a binder and a dispersion exists around the carbon fibers. In this step, the dispersion falls through the mesh due to gravity, and most of it falls off.

Furthermore, after the carbon fiber dispersion flows onto the mesh of the mesh conveyor to form a film, the dispersion can be squeezed by compressing the continuous sheet containing the residual dispersion by various methods.

Next, the step 13 of drying the carbon fiber sheet is described. The continuous carbon fiber sheet formed by the step 12 of allowing the carbon fiber dispersion to flow onto the mesh of the mesh conveyor to form a film is not a state where the dispersion is completely removed, so the residual dispersion is removed by various methods. For example, the continuous carbon fiber sheet containing the wet dispersion can be pressed by a steam-heated iron cylinder to dry it.

After the above steps, a continuous sheet of (short fiber) carbon fiber is completed, but the conventional continuous sheet of carbon fiber obtained in this way is in a state where the (short fiber) carbon fibers are randomly oriented and entangled with each other, and a binder is arranged around the carbon fiber, and the continuous sheet-like carbon fiber nonwoven fabric has a specific adhesiveness due to the residual binder. After leaving the papermaking device, the continuous sheet-like carbon fiber nonwoven fabric produced in this way can be wound into a roll with release paper sandwiched therebetween, or cut into appropriate sizes to complete the carbon fiber nonwoven fabric.

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

The anisotropic nonwoven fabric used in the two-dimensional carbon/carbon composite material of the present invention is produced by adjusting the vertical falling speed _VL of the dispersion to the papermaking surface and the papermaking speed _VP in the step 12 of making a film on the mesh conveyor in the conventional carbon fiber nonwoven fabric manufacturing method, so that the short-fiber carbon fibers are more oriented in the papermaking direction. In this specification, the nonwoven fabric in which the carbon fibers are intentionally oriented more in a specific direction is called "anisotropic nonwoven fabric using carbon fibers" or simply "anisotropic nonwoven fabric".

In addition, in the thin sheet-shaped anisotropic non-woven fabric manufactured in this way, the direction in which the majority of the carbon fibers are oriented is called the "strong orientation direction", and the direction orthogonal to the "strong orientation direction" is called the "weak orientation direction".

In addition, the carbon fibers in the previously nearly isotropic carbon fiber nonwoven fabrics are arranged in a relatively large bend state in any direction. In contrast, the anisotropic nonwoven fabric using carbon fibers described here is a fabric in which most of the carbon fibers are oriented in a specific direction, that is, the carbon fibers oriented in the "strong orientation direction" are not greatly bent and are arranged in a nearly straight line.

Therefore, in the anisotropic nonwoven fabric described here, the carbon fiber nonwoven fabric has anisotropy due to the fiber orientation ratio, and the bending degree of the carbon fibers in the direction where the carbon fibers are mostly oriented is reduced, and the carbon fibers in the direction where the carbon fibers are mostly oriented are oriented in a state close to a straight line. When the anisotropic nonwoven fabric is used to manufacture a carbon/carbon composite material, the (tensile, bending) strength and (tensile, bending) elastic modulus characteristics of the carbon/carbon composite material in the direction where the carbon fibers are mostly oriented are greatly improved by the multiplication effect of (i) the effect caused by the majority orientation of the carbon fibers and (ii) the effect caused by the reduction of the bending degree of the carbon fibers.

Next, the manufacturing process of carbon/carbon composite materials using anisotropic nonwoven fabrics is described. Figure 2 shows a flow chart of the manufacturing process of carbon/carbon composite materials using carbon fiber anisotropic nonwoven fabrics.

First, in step 21 of laminating anisotropic nonwoven fabrics, the aforementioned carbon fiber nonwoven fabrics are cut into predetermined sizes, and a flat laminate of a predetermined shape is obtained by laminating the plurality of sheets.

At this time, the alignment direction of the carbon fibers of the anisotropic nonwoven fabric, i.e., the "strong alignment direction", is aligned in one direction, and the direction of the alignment direction of the anisotropic nonwoven fabric, i.e., the "weak alignment direction", is aligned in another direction for lamination. Therefore, the "strong alignment direction" and the "weak alignment direction" refer to two directions orthogonal to the lamination surface of the laminate.

Next, step 22 of heating and pressing the anisotropic nonwoven fabric laminate is described. In step 22, the anisotropic nonwoven fabric laminate obtained in step 21 is heated and pressed to form a precursor (also called a "preform" or "mother body") of a carbon/carbon composite material.

In the step 22 of heating and pressing the anisotropic non-woven fabric laminate to form the anisotropic non-woven fabric, the organic binder contained in the anisotropic non-woven fabric is converted into an inorganic carbonaceous material in order to maintain the shape of the anisotropic non-woven fabric laminate.

When the flat laminate is heated and pressed to form a precursor of a carbon/carbon composite, the carbon fiber nonwoven fabric laminate is sandwiched between the hot pressing heating plates, and the laminate is heated by the heating plates and pressed to form.

Here, the heating temperature can be above 400°C. If heated to this temperature, the binder can be converted into a carbonaceous substance.

The precursor of the carbon/carbon composite material is in a state where the binder for binding the short carbon fibers is converted into a carbonaceous material, and the carbonaceous material binds and holds the individual carbon fibers, thereby maintaining the shape of the previously shaped flat plate.

In the heating step for forming the precursor of the carbon/carbon composite material, part of the binder vaporizes and disappears, and part of the binder remains as a carbonaceous substance, but the vaporized and disappeared part becomes pores, forming a porous material.

Next, step 23 of melting and impregnating asphalt or synthetic resin is explained. Step 23 is a process for filling carbon into the pores in the carbonaceous material and the micro spaces generated between carbon fibers by impregnating the precursor of the porous carbon/carbon composite material with asphalt or synthetic resin to form a dense matrix structure.

In step 23, first, heat and melt the powder or pellets of asphalt or synthetic resin placed in the container. The asphalt used here can be either coal tar asphalt or coal asphalt, and it is expected to be one with good impregnation and high carbonization yield. As the synthetic resin, it is expected to use a thermosetting resin such as phenol resin or furan resin, which has good impregnation and high carbonization yield, but is not limited to the resins exemplified here.

Secondly, the precursor of the carbon/carbon composite material is immersed in a container filled with molten asphalt or synthetic resin, so that the molten asphalt or molten resin is impregnated into the aforementioned pores or micro spaces.

At this time, the precursor of the carbon/carbon composite material can also be placed in a vacuum container, and the molten asphalt or molten resin can be impregnated by flowing the molten asphalt or molten resin into the vacuum container. After the precursor of the carbon/carbon composite material is impregnated in the molten asphalt or molten resin, external pressure can also be applied to force the molten asphalt or molten resin into the interior of the precursor.

The step 24 of carbonizing the pre-dried product impregnated with molten asphalt or molten resin is to heat the pre-dried product impregnated with molten asphalt or molten resin to about 800°C to 1500°C using a carbonization furnace, etc., to convert the impregnated asphalt or resin into carbon.

When the molten asphalt or molten resin impregnated in the precursor of the carbon/carbon composite material is carbonized, part of the molten asphalt or molten resin is converted into carbon, and part of it is vaporized and disappears, so new micropores are generated in the space impregnated with the molten asphalt or molten resin.

In order to fill the newly formed micropores with carbon, the step 23 of melting and impregnating the above-mentioned asphalt or synthetic resin and the step 24 of carbonizing the extrudate impregnated with the molten asphalt or molten resin may be repeated once or multiple times.

Through the above steps, a carbon/carbon composite material can be completed.

In step 25 of graphitizing the carbon/carbon composite material, the carbon fibers and matrix carbon of the carbon/carbon composite material can be converted into graphite with a highly crystalline structure by heating the carbon/carbon composite material to about 2000°C to 2800°C for graphitization as needed.

In the description so far, the anisotropic nonwoven fabric is described as being composed of short-fiber carbon fibers and a binder, but is not limited to this.

In step 11 of manufacturing the carbon fiber dispersion, non-softening petroleum and/or coal-based coke powder may be further added, or softening petroleum and/or coal-based binder asphalt powder and non-softening petroleum and/or coal-based coke powder may be added.

In this way, the non-softening petroleum and/or coal-based coke powder is dispersed and mixed in the binder of the anisotropic non-woven fabric, or the softening petroleum and/or coal-based binder asphalt powder and the non-softening petroleum and/or coal-based coke powder are dispersed and mixed in the binder of the anisotropic non-woven fabric.

Thus, if anisotropic nonwoven fabrics containing binder asphalt powder, coke powder, etc. are used to manufacture carbon/carbon composites, most or all of the binder asphalt and coke powder will remain as carbon matrix in the carbon/carbon composite during the heat treatment step in the manufacturing process of the carbon/carbon composite, making it easier to increase the density of the carbon/carbon composite. As a result, the number of steps 23 of melting and impregnating asphalt or synthetic resin in the manufacturing process of the carbon/carbon composite can be reduced, or the step 23 can be omitted.

Next, a method for processing a screw component 2 from a laminate 1 made of a two-dimensional carbon/carbon composite material produced by laminating anisotropic non-woven fabrics using short-fiber carbon fibers is described.

In this manual, the so-called screw parts 2 are collectively referred to as bolts 2, main screw bolts 2, nuts 2, etc. Here, in addition to the main screw bolts 2, the processing methods thereof are also described as examples of screw parts 2.

FIG3 shows a laminate 1 made of a two-dimensional carbon/carbon composite material produced by laminating anisotropic non-woven fabrics using short-fiber carbon fibers, and a screw bolt 2 cut out of the laminate by cutting.

As described above, the two-dimensional carbon/carbon composite laminate 1 manufactured by the manufacturing process of the carbon/carbon composite using anisotropic non-woven fabric is formed by aligning the directionality of the anisotropic non-woven fabric and laminating it, so the completed laminate 1 also has the same directionality as the non-woven fabric.

The directionality of the laminate 1 made of the two-dimensional carbon/carbon composite material used in the present invention is defined as follows.

That is, the strong orientation direction of the anisotropic non-woven fabric is aligned and laminated in one direction, the direction corresponding to the strong orientation direction of the manufactured two-dimensional carbon/carbon composite is defined as the X direction, and the direction corresponding to the weak orientation direction of the two-dimensional carbon/carbon composite is defined as the Y direction.

From the laminate 1 made of a two-dimensional carbon/carbon composite material having two directions of "X direction" and "Y direction", the main screw bolt 2 is cut out in the direction shown in Figure 3. That is, the central axis of the main screw bolt 2 is consistent with the "Y direction" of the laminate 1 (refer to Figure 3), and the "X direction" is oriented in a direction perpendicular to the central axis of the bolt 2 (refer to Figure 3).

The material of the main screw bolt 2 is cut out from the laminate 1 made of the two-dimensional carbon/carbon composite material, and the method of processing it into the main screw bolt 2 is not particularly limited, and it can be manufactured by well-known mechanical processing such as a band saw, a milling machine, and a lathe.

FIG4 shows a cross section perpendicular to the central axis of the total screw bolt 2 manufactured in this way, and FIG5 shows a cross section A-A (a cross section along the central axis of the bolt) of the total screw bolt 2 shown in FIG4. The "X direction" and "Y direction" of the laminate 1 made of the two-dimensional carbon/carbon composite material are oriented in the direction shown in FIG3.

Generally, when the laminate 1 of the self-fiber reinforced composite material is manufactured into a bolt 2 by mechanical processing, the thread in the area P shown in FIG. 4 will support the axial load of the bolt 2, and this is also true for the main screw bolt 2 of the present invention.

Therefore, the screw component 2 of the present invention has the "X direction" (i.e., the direction in which the carbon fibers are more oriented) of the laminate 1 in the opposite region P. As a result, the contribution of the carbon fibers to the strength of the screw component 2 is increased, and the strength of the screw component 2 can be significantly improved.

[Implementation example]

The above-mentioned anisotropic non-woven fabric is used to make a flat carbon/carbon composite material. Using this material, M8 and M12 screw bolts 2 are cut and processed. Static load tests and thermal stress strength tests of bolts 2 are performed. The details of the production of two-dimensional (flat) carbon/carbon composite materials and the details of each test are as follows.

1. Production of flat carbon/carbon composite materials using (anisotropic) non-woven fabrics

In the embodiment, asphalt short-fiber carbon fibers are used to make anisotropic nonwoven fabrics with the carbon fibers oriented mostly in the papermaking direction. Therefore, the amount of carbon fibers oriented in the direction orthogonal to the papermaking direction is reduced accordingly. Therefore, the papermaking direction becomes the strong orientation direction of the anisotropic nonwoven fabric, and the direction orthogonal to the papermaking direction becomes the weak orientation direction.

In addition, the anisotropic non-woven fabric used here is only composed of carbon fibers and binders, and does not contain adhesive asphalt powder or coke powder.

Furthermore, the amount of carbon fiber in the anisotropic nonwoven fabric was adjusted so that the carbon fiber content (volume content Vf) of the completed carbon/carbon composite material would be 40%.

In the manufacturing process of the two-dimensional carbon/carbon composite laminate 1, in the step 21 of laminating the anisotropic non-woven fabric, the strong orientation direction of the anisotropic non-woven fabric is aligned with the X direction of the laminate 1, and the weak orientation direction of the anisotropic non-woven fabric is aligned with the Y direction of the laminate 1. Therefore, most carbon fibers are aligned in the X direction of the laminate 1, and fewer carbon fibers are aligned in the Y direction of the laminate 1.

Furthermore, the step 23 of melting and impregnating the asphalt or synthetic resin and the step 24 of carbonization treatment are each performed only once. Furthermore, the step 25 of graphitization treatment is heat-treated at 2500°C.

From the five flat carbon/carbon composite materials prepared in the examples, test pieces were cut out and the flexural strength, tensile modulus and thermal expansion coefficient in the X and Y directions were measured. The results are shown in Table 1 (each measured value represents the average value of the measured values of the five flat plates). Table 1 also shows the flexural strength ratios σ _X /σ _Y , _EX /E _Y , and α _X /α _Y in the X and Y directions.

That is, the anisotropic two-dimensional carbon/carbon composite material produced in the embodiment has a bending strength ratio and a tensile elastic modulus ratio in the X direction and the Y direction of 2.50 times and 3.75 times respectively, which can achieve an anisotropy of more than 1.5 times, which is impossible to achieve using the two-dimensional carbon/carbon composite material using the conventional isotropic non-woven fabric.

In addition, the ratio of thermal expansion coefficients in the X direction to the Y direction is 0.74 times, which can achieve anisotropy of less than 0.8 times, which is impossible to achieve using conventional two-dimensional carbon/carbon composite materials using isotropic non-woven fabrics.

Next, the comparative example is explained. In the comparative example, in the stage of manufacturing the nonwoven fabric, the paper is made in a way that does not make the carbon fibers oriented in a specific direction. Therefore, in the plane of the nonwoven fabric, the short-fiber carbon fibers are roughly evenly dispersed and oriented, forming a nonwoven fabric with isotropic properties in the plane. Apart from this, the manufacturing steps of the nonwoven fabric of the comparative example and the embodiment are the same.

In addition, the manufacturing process of the flat carbon/carbon composite material is the same as the manufacturing process of the flat carbon/carbon composite material in the embodiment, except for laminating the isotropic non-woven fabric to form a laminate.

Specimens were cut out from 5 isotropic carbon/carbon composites prepared in the comparative example, and the flexural strength, tensile modulus and thermal expansion coefficient were measured. The results are shown in Table 2. (Each measured value represents the average value of the measured values of 5 flat plates).

2. Static load strength test of bolt 2 (total screw bolt)

In the embodiment, the bolt 2 (total screw bolt) is cut out by machining from the above-mentioned anisotropic two-dimensional carbon/carbon composite material so as to have the directionality as shown in FIG3. That is, the central axis direction of the total screw bolt 2 is aligned with the Y direction of the anisotropic two-dimensional carbon/carbon composite material. In the embodiment, the total screw bolt 2 of M8 and M12 sizes is manufactured.

In addition, for comparison with the embodiment, the total screw bolts 2 of Comparative Example 1 and Comparative Example 2 were prepared. In Comparative Example 1, the total screw bolts 2 were oriented in such a way that the central axis direction of the total screw bolts 2 was consistent with the X direction of the anisotropic two-dimensional carbon/carbon composite material, and the total screw bolts 2 of M8 and M12 sizes were cut out from the above-mentioned anisotropic two-dimensional carbon/carbon composite material by machining.

Furthermore, in Comparative Example 2, the isotropic two-dimensional carbon/carbon composite material of the above Comparative Example is machined to produce a total screw bolt 2 of M8 and M12 sizes.

Metal nuts 4 are installed at both ends of the M8 and M12 size total screw bolts 2 of the embodiment and comparative examples 1 and 2 manufactured here, and the metal nuts 4 are pulled away along the axis of the total screw bolt 2 to perform a static load strength test (tensile load test) on the total screw bolt 2. The results are shown in Table 3.

As can be understood from the results, the total screw bolt 2 of the embodiment (the bolt whose central axis direction is consistent with the Y direction of the anisotropic two-dimensional carbon/carbon composite (the weak orientation direction of the carbon fiber)) has superior screw strength compared with the total screw bolt 2 of the comparative example 1 (the bolt whose central axis direction is consistent with the X direction of the anisotropic two-dimensional carbon/carbon composite (the strong orientation direction of the carbon fiber)) or the total screw bolt 2 of the comparative example 2 (the bolt made of the isotropic two-dimensional carbon/carbon composite).

3. Thermal stress strength test of bolt 2

Thermal stress strength test was conducted using the same total screw bolt 2 (anisotropic two-dimensional carbon/carbon composite bolt) of M8 and M12 sizes as the total screw bolt 2 of the embodiment used in the static load strength test of bolt 2 (total screw bolt) and the same total screw bolt 2 (isotropic two-dimensional carbon/carbon composite bolt) of M8 and M12 sizes as the total screw bolt 2 of comparative example 2.

The thermal stress strength test is carried out in the following order. First, as shown in Figure 6, the main screw bolt 2 is inserted into the through hole of the isotropic graphite spacer 3 with a through hole in the center, and the isotropic graphite nut 4 is screwed to the two ends of the main screw bolt 2. The isotropic graphite nut 4 is tightened with a certain torque to integrate the isotropic graphite spacer 3, the isotropic graphite nut 4 and the M8 or M12 size main screw bolt 2.

Secondly, in an inert gas environment, the integrated test piece was heated to 1200℃ and 2000℃. After that, the integrated test piece was cooled to room temperature, and the M8 and M12 size screw bolts 2 in the test piece were visually inspected for damage, and the thermal stress strength of the M8 and M12 size screw bolts 2 was evaluated.

Table 4 shows the results of the thermal stress strength test of the total screw bolt 2.

Assuming that the screw is assembled with an isotropic graphite spacer 3 having a thermal expansion coefficient one digit larger than that of the carbon/carbon composite, even when a large temperature difference (1200°C and 2000°C) is applied, in the embodiment (the bolt whose central axis direction is consistent with the Y direction (weak orientation direction of carbon fibers) of the anisotropic two-dimensional carbon/carbon composite), no damage or loosening of the screw due to thermal stress is observed.

On the other hand, in Comparative Example 2 (bolts made of isotropic two-dimensional carbon/carbon composite material), which was implemented under the same conditions as the total screw bolt 2 of Example, it was observed that all the screws were damaged due to thermal stress.

That is, the total screw bolt 2 of the embodiment has a better thermal stress strength than the total screw bolt 2 of the comparison example 2. It can be said that the total screw bolt 2 of the embodiment has a significant thermal stress relief effect.

This is considered to be the result of the multiplication effect of the axial thermal expansion coefficient of the total screw bolt 2 of the embodiment being larger than that of the total screw bolt 2 of the comparative example 2, having a value closer to the thermal expansion coefficient of the isotropic graphite spacer 3, and the axial tensile elastic modulus of the total screw bolt 2 being smaller than that of the total screw bolt 2 of the comparative example 2, making the thermal stress relief effect more significant.

1: Laminated body of anisotropic two-dimensional carbon/carbon composites

2: Screw parts (bolts, main screw bolts, nuts)

Claims (5)

A screw component is a screw component made of a two-dimensional carbon/carbon composite material by laminating anisotropic non-woven fabrics using short-fiber carbon fibers. The screw component is characterized in that the direction in which the short-fiber carbon fibers of the anisotropic non-woven fabric are more oriented is called a strong orientation direction, and the direction orthogonal to the strong orientation direction is called a weak orientation direction, so that the strong orientation direction of the anisotropic non-woven fabric is aligned in one direction for lamination, and 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, and the central axis direction of the screw component is aligned with the Y direction of the anisotropic two-dimensional carbon/carbon composite material. For example, the screw part of claim 1, wherein the ratio of the bending strength in the X direction to the bending strength in the Y direction of the aforementioned anisotropic two-dimensional carbon/carbon composite material meets the following conditions: [bending strength in the X direction]/[bending strength in the Y direction]>1.5. For a screw component as claimed in claim 1 or 2, the ratio of the tensile modulus of elasticity in the X direction to the tensile modulus of elasticity in the Y direction of the aforementioned anisotropic two-dimensional carbon/carbon composite material meets the following conditions: [tensile modulus of elasticity in the X direction]/[tensile modulus of elasticity in the Y direction]>1.5. For screw parts as claimed in claim 1 or 2, the ratio of the thermal expansion coefficient in the X direction to the thermal expansion coefficient in the Y direction of the aforementioned anisotropic two-dimensional carbon/carbon composite material meets the following conditions: [thermal expansion coefficient in the X direction]/[thermal expansion coefficient in the Y direction]<0.8. For example, the screw part of claim 3, wherein the ratio of the thermal expansion coefficient in the X direction to the thermal expansion coefficient in the Y direction of the aforementioned anisotropic two-dimensional carbon/carbon composite material meets the following condition: [thermal expansion coefficient in the X direction]/[thermal expansion coefficient in the Y direction]<0.8.

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