JP5277487B2 - Graphite elastic body and method for producing the same - Google Patents

Description

  The present invention is a graphite elastic suitable for use in various chemical synthesis devices, aerospace environment utilization devices, nuclear reactors, fusion reactors, high temperature furnaces such as heat treatments, sensors, differential thermal balances, chemical pumps, engine members, etc. The present invention relates to a body and a manufacturing method thereof.

  A metal spring has a large temperature dependence of the spring constant. Generally, a metal spring is commonly used at 200 ° C. or less, and its heat resistance is suddenly reduced to 600 ° C. Also, it has poor corrosion resistance against rust and chemicals. On the other hand, even with a ceramic spring, the heat resistance is limited to 1000 ° C., and the thermal shock resistance is poor. Since the specific gravity of both metal and ceramics is high, there are disadvantages such as an increase in the weight of the incorporated device. In order to compensate for the drawbacks of conventional springs, a carbon-based coil spring is proposed in which an organic linear body is formed into a spring shape and then carbonized (see, for example, Patent Document 1).

  This carbon-based coil spring is an organic material that can be carbonized, or an organic linear material in which carbon fibers, graphite whiskers, graphite powder, amorphous carbon powder, etc. are uniformly dispersed and reinforced in a complex orientation. After the body is formed in a coil shape, it is treated with a carbon precursor if necessary, and further heat-treated in an inert atmosphere for carbonization, and the entire surface of this carbon-based spring is covered with a metal according to the desired function. Formed. This carbon-based coil spring has excellent heat resistance and corrosion resistance even at high temperatures in the presence of oxygen, and is expected to have high strength and reliability.

Japanese Patent Laid-Open No. 6-144811

However, the conventional carbon-based coil spring described above has a drawback that a highly accurate spring cannot be obtained because it involves dimensional shrinkage in the process of carbonizing an organic linear body, and is manufactured by such a method. Since the carbon material is glassy carbon with high hardness, it was difficult to adjust the shape by post-processing. Although it is possible to produce a spring by processing a widely used isotropic graphite material into a predetermined shape such as a coil shape, the pores in the isotropic graphite material are generally flat and large. During use, cracks propagated from the ends of the flat pores, which easily led to breakage of the spring, and were not suitable as a material for a graphite spring.
The present invention has been made in view of the above circumstances, and provides a graphite elastic body that compensates for the disadvantages of the carbon material and does not break even when used repeatedly, and a method for manufacturing the same, and thus a metal spring cannot be used. The purpose is to achieve stable use and long life in the environment.

The above object of the present invention is achieved by the following configuration.
(1) It has a fine structure composed of a large number of graphite particles and pores. When the cross section is observed with a scanning electron microscope, the density of pores appearing in the cross section is 250 or more per 6000 μm ^2. A graphite elastic body characterized by being formed using a graphite material having a cross-sectional area of 5 μm ² or less and an average flatness of pores appearing in a cross-section of 0.55 or less.

  According to this graphite elastic body, fine graphite particles and pores are uniformly distributed, the strength and elastic modulus are increased, heat resistance, corrosion resistance and cutting workability are ensured, and dimensional accuracy is also increased.

(2) The graphite elastic body according to (1), wherein an outer peripheral portion of the cylindrical spring base material made of the graphite material is formed in a coil spring shape by being cut by a spiral cut-off groove about the axis.

  According to this graphite elastic body, it is possible to form a coil spring similar to a spirally wound rod having a square cross section. Moreover, in the case of a normal coil spring formed by winding a bar, the end (seat) that must be flattened can use the flat tube end of the cylindrical spring base material as it is, thus facilitating finishing. be able to. If the cylindrical spring base material is conical, a conical coil spring can be obtained in the same manner.

(3) An average of pores appearing in the cross section having a fine structure composed of a large number of graphite particles and pores, and the density of pores appearing in the cross section is 250 or more per 6000 μm ² when the cross section is observed with a scanning electron microscope. Forming a cylindrical spring base material using a graphite material having a cross-sectional area of 5 μm ² or less and an average flatness of pores appearing in the cross section of 0.55 or less;
A step of fitting a cylindrical body with an adhesive to the inner periphery of the cylindrical spring base material to obtain a workpiece;
A step of cutting the cylindrical spring base material in a spiral groove reaching the cylindrical body by rotating the workpiece relative to the axis while rotating the workpiece around the axis;
Heat-treating the parting grooved workpiece to decompose the adhesive, and removing the cylindrical body;
A method for producing a graphite elastic body, comprising:

  According to this method for manufacturing an elastic body made of graphite, the cylindrical body works as a reinforcing member for the cylindrical spring base material, the crushing strength of the cylindrical spring base material in the radial direction increases, and the spiral cut-off groove processing is performed in the cylinder. It becomes possible to form on the outer periphery of the spring base material.

The graphite elastic body according to the present invention has a fine structure composed of a large number of graphite particles and pores, and the density of pores appearing in the cross section when the cross section is observed with a scanning electron microscope is 250 per 6000 μm ^2. Since it is made of graphite material with an average cross-sectional area of pores appearing in the cross section of 5 μm ² or less and an average flatness of pores appearing in the cross-section of 0.55 or less, fine graphite particles and pores are uniformly distributed In addition, while having high strength and high elastic modulus, it has heat resistance, corrosion resistance and cutting workability, and can improve dimensional accuracy. As a result, the long-lived graphite that compensates for the shortcomings of carbon materials and can be used stably without being damaged even when used repeatedly in various chemical synthesis equipment, aerospace environment utilization equipment, nuclear reactors, fusion reactors, etc. An elastic body can be provided.

  According to the method for producing a graphite elastic body according to the present invention, a cylindrical spring base material is formed using the graphite material, and a cylindrical body made of a carbon material is formed on the inner periphery of the cylindrical spring base material with an adhesive. A workpiece is obtained by fitting, and the cylindrical spring base material is cut off by a spiral groove centering on the axis while rotating the work around the axis, and the work with the cut-off groove exceeds the decomposition temperature of the adhesive and is made of a graphite material. Since the cylindrical body is removed by heat treatment at an oxidation temperature or lower, the cylindrical body is used as a reinforcing member for the cylindrical spring base material, and the spiral parting groove processing is performed on the outer periphery without crushing the cylindrical spring base material radially inward. By applying to the part, a coil spring-like graphite elastic body can be obtained.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a graphite elastic body and a method for producing the same according to the present invention will be described with reference to the drawings.
In the case of a plate-like graphite elastic body, the graphite elastic body according to the present invention is a graphite elastic body that applies a load in the thickness direction. For example, a diaphragm used in a pressure sensor, a load cell, etc., a leaf spring, Furthermore, a spring etc. are mentioned. In the case of a linear graphite elastic body, it corresponds to an elastic body that applies a load in the thickness direction or the twist direction, and is not limited to a linear one, and includes a helical elastic body. For example, a coil spring, a spiral spring, etc. are mentioned.

FIG. 1 is a perspective view of a graphite elastic body according to the present invention.
Hereinafter, the form which made the graphite elastic body the coil spring 11 is demonstrated. The coil spring 11 is formed in a coil spring shape by cutting (cutting) an outer peripheral portion 13a of a cylindrical spring base material 13 made of a graphite material with a spiral cut-off groove 15 about an axis L. That is, the coil spring 11 is formed in a coil spring shape in which a bar having a square cross section is spirally wound. In the case of a normal coil spring formed by winding a rod, the end (seat) 13b that must be flattened can be used as it is in the coil spring 11, because the flat end 13b of the cylindrical spring base material 13 can be used as it is. Finishing can be facilitated. If the cylindrical spring base material 13 is conical, a conical coil spring can be obtained in the same manner.

The graphite material used for the coil spring 11 has a fine structure composed of many graphite particles and pores. When the cross section of the graphite material was observed with a scanning microscope, pores appearing in cross-section, 6000 .mu.m ² per 250 or more, the average area of pores appearing on the cross-section is 5 [mu] m ² or less. In other words, the pores distributed in the graphite material are sufficiently small, and the number of pores present per unit volume of the graphite material is sufficiently large. For this reason, a smooth machined surface is obtained without dropping off in units of large particles during cutting. In addition, since there are no large pores and stress concentration is unlikely to occur, it is possible to provide a graphite material with little crack propagation even after repeated use.

  Moreover, when the cross section of the graphite material used for the graphite elastic body is observed with a scanning microscope, the average flatness of pores appearing in the cross section is 0.55 or less. The elastic modulus of the graphite material is increased with respect to the compressive strength by the blade during processing, and cutting waste generated during processing can be reduced. That is, the cutting resistance of the cutter is small and easy to process. Moreover, by setting the average flatness of the pores appearing in the cross section to 0.55 or less, the notch (cut) at the pore ends can be reduced, and a graphite material with less crack propagation can be provided.

The relationship between the pore shape of the graphite material as described above and its workability is presumed to be due to the following mechanism.
When the graphite material is cut, a compressive force acts in the traveling direction of the blade. At this time, cutting is performed when the strain energy stored as the blade advances exceeds the energy required for destruction. In order to obtain a smooth machined surface, it is necessary to work while producing fine cutting powder, and it is important that destruction occurs before storing large strain energy.
In order not to store large strain energy, it is important that the compressive strength is small and the elastic modulus is large, that is, the diameter of the particles to be cut has a positive correlation with the compressive strength / elastic modulus. From the above, it can be seen that a graphite material having a higher elastic modulus is advantageous under a predetermined compressive strength in order to obtain a machined surface with a small diameter of the particles to be cut (finely detailed).

Next, the relationship between the elastic modulus of the graphite material and the shape of the pores will be explained. Generally, the elastic modulus of the graphite material is expressed by the following Knudsen's empirical formula.
E (P) = E (0) exp (-bP)
(E (P): elastic modulus, P: porosity, b: empirical constant)
The empirical constant b strongly depends on the shape of the pores, and when the shape of the pores is spherical, the value is small, and the value rapidly increases as the flat spheroid changes to a cracked pore shape. Is known (“Introduction to New Carbon Materials”, edited by the Carbon Materials Society of Japan). Therefore, it can be seen that a graphite material having a round shape (small flatness) is advantageous for increasing the elastic modulus.
From the above, it is considered that the relationship between the pore shape of the graphite material and its workability is derived. That is, since the pore shape is round (that is, the average flatness of pores appearing in the observation cross section is 0.55 or less), the elastic modulus of the graphite material can be increased, so that a finely machined surface can be obtained. And a graphite material excellent in workability can be obtained.

Next, regarding the compressive strength, even if the pores are flat spheroids or cracked pores, the pores are crushed by applying a compressive load, so the shape of the pores does not have a great influence. It can be seen that the effect of porosity is greater on the compressive strength.
When the porosity is small, the compressive strength becomes too high to be cut, and the unevenness of the processed surface becomes large. When the porosity is high, the compressive strength can be reduced, but the graphite material becomes soft, and therefore, even if it is subjected to fine processing, it tends to be broken or broken. Moreover, it becomes easy to wear even in electric discharge machining.

There is a high correlation between the porosity and the bulk density of the graphite material. When the same raw material is used and the same graphitization treatment is performed, the same porosity density is obtained with the same porosity.
In the present invention, the starting material and the graphitization temperature are performed within a limited range, although there are components that mainly undergo pitch coke, and components that are directly carbonized and graphitized, starting from pitch. Therefore, the bulk density of the graphite material has a preferable range, and the value is 1.78 to 1.86 g / cm ³ , more preferably 1.82 to 1.85 g / cm ³ . The bulk density can be obtained by measuring volume and mass.

In the present invention, the number of pores appearing in the cross section, the average area, and the average flatness can be calculated by observing the graphite material with an electron microscope or the like. Specifically, first, the cut surface of the graphite material is processed by a CP (cross section polisher) method. It is obtained by observing with a FE-SEM after performing a flat milling process (45 °, 3 minutes) on the prepared cross section.
The analysis of the photographed image is binarized using image analysis software (Image J 1.37), and then the area of each void (pore appearing in the cross section) is calculated. Ellipse fitting is performed for each gap, and the flatness is calculated from the values of the major axis and minor axis.
The flatness is an ellipse (major axis-minor axis) / major axis fitted to a void (a pore appearing in a cross section).

  As described above, it is desirable to use SEM for the measurement of the number of pores appearing in the cross section, the average area, and the average flatness. Sufficient resolution is obtained to determine the shape of micron-order pores, and the particle part is gray at a single concentration, the pore part is black depending on the depth of the pore, black if it is deep, and if it is shallow Is displayed in white so that pores and particles can be clearly distinguished.

  For the measurement of the number of pores appearing in the cross section, the average area, and the average flatness, it is preferable to use a graphite material not filled with resin. This is because if the graphite material is filled with resin, the resin is sealed in the open pores present in the graphite material, and the correct number and shape of the pores cannot be determined.

The maximum pore diameter (major axis) is preferably 20 μm or less. When the maximum pore diameter is 20 μm or less, cracks develop along the pores at the time of cutting. Therefore, the fine pins break, and thin ribs cause cracks and holes.
The maximum pore diameter can also be measured from the cross section observed with the SEM as described above. The diameter of the pores obtained from the cross-sectional observation of the SEM is different from the diameters of the pores and graphite particles obtained with a mercury intrusion porosimeter or the like. The former measures the actual size, while the latter measures the diameter of the inlet portion of the continuous pores.

Next, a method for manufacturing the coil spring 11 will be described.
FIG. 2 is a block diagram showing an example of a lathe used for manufacturing the graphite elastic body shown in FIG. 1, and FIG. 3 shows the procedure for manufacturing the graphite elastic body shown in FIG. FIG.
To manufacture the coil spring 11, first, the cylindrical spring base material 13 shown in FIG. 3A made of a graphite material is formed. After adding carbonaceous fine powder to pitch and kneading the graphite material, heat treatment is performed and volatile content is adjusted while heat treatment at 400 to 500 ° C. to obtain a secondary material. Next, the obtained secondary raw material is pulverized while adjusting the particle size so as not to be excessively pulverized by a pulverizer having a function of removing fine powder having a small particle diameter, thereby obtaining a secondary raw material powder. Next, it is formed into a cylindrical shape by cold isostatic pressing (CIP molding), fired at about 1000 ° C. in a sintering furnace, and further graphitized at about 2500 ° C. in a graphitization furnace, and then a graphite material A cylindrical spring base material 13 is obtained.

  The pitch used is a coal-based or petroleum-based pitch, and may be a mixture thereof. Of these raw materials, it is desirable to use a coal-based pitch. In the case of coal-based pitch, optical anisotropy hardly develops (crystals hardly develop into needles), and a high-strength and highly elastic graphite material can be obtained.

The softening point of the pitch is desirably 50 ° C. or lower. When the temperature is 50 ° C. or higher, the viscosity at the time of kneading increases and the production becomes very difficult.
The carbonaceous fine powder used in the present invention is a core when the mesophase develops, and it is possible to use a carbonaceous powder such as carbon black, graphite fine powder, raw pitch coke fine powder, calcined pitch coke fine powder or the like. it can. The size of the fine powder is preferably 5 μm or less. This is because if a fine powder of 5 μm or more is used, it is difficult to control the particle size distribution when the secondary material obtained by kneading is pulverized, and the coarser side of the particle size distribution increases. The addition amount to the pitch is desirably 3 to 10% by weight. If the amount exceeds 10% by weight, the viscosity of the pitch will increase, making the production very difficult. When the amount is 3% by weight or less, the mosaic structure of coke cannot be sufficiently developed.

  In the heat treatment of the raw material, the temperature and time are adjusted so that the volatile content measured by JIS8812 is 6 to 12% (more preferably 8 to 11%) to obtain a secondary raw material. When the volatile content is less than 6%, sufficient adhesion between the particles cannot be obtained, so that only a low-density graphite material can be obtained. In the case of 12% or more, the amount of hydrocarbon gas generated from the inside during firing is large, and it is easy to break, and the accumulated gas forms large pores.

The secondary raw material obtained by heat-treating the raw material is pulverized while controlling the particle size, and fine powder is removed from the obtained secondary raw material powder. The method of pulverization includes a method using a pulverizer equipped with an internal partial classifier, a method using a pulverizer plant equipped with a pulverizer and a precision airflow classifier, and a raw material crushed by the pulverizer separately with a precision airflow classifier. There is a method of adjusting the particle size.
The graphite material using the secondary raw material powder containing the fine powder is less likely to release the gas generated during firing and easily breaks. Furthermore, gas accumulates in the material and forms large pores.

The secondary raw material powder preferably has a median diameter (DP-50: 50% integrated diameter) of 5 to 10 μm as measured with a laser diffraction particle size measuring instrument. The pores that normally exist between particles are often pores with sharp edges and large flatness, and when the size of the particles is large, the size and shape of the pores have a synergistic effect and the elastic modulus decreases. growing. For this reason, when a median diameter is 10 micrometers or more, an elasticity modulus will fall large. Further, when the median diameter is 5 μm or less, the volatile matter generated from the compact of the secondary raw material powder during firing cannot be quickly discharged out of the raw material, and is easily broken. Furthermore, gas accumulates in the material and forms large pores.
Moreover, it is preferable that the secondary raw material powder has a particle size distribution range of 1 μm to 80 μm as measured with a laser diffraction particle size analyzer. If a raw material of 1 μm or less is included, the volatile matter generated from the molded body of the secondary raw material powder at the time of firing cannot be quickly discharged out of the raw material and is easily broken. Furthermore, gas accumulates in the material and forms large pores. When particles of 80 μm or more are contained, flat pores are easily formed near the outer periphery of the large particles and the interface between the large particles, the number of pores is reduced, and the average cross-sectional area is also reduced.

Next, as shown in FIG. 3B, the cylindrical spring base material 13 and the cylindrical body 17 are integrated by fitting a cylindrical body 17 on the inner periphery of the cylindrical spring base material 13 with an adhesive. Work W1 is obtained.
The adhesive is not particularly limited as long as it is thermally decomposed and volatilized. For example, α-cyanoacrylate (instant adhesive) or the like can be preferably used. If it is α-cyanoacrylate, it is depolymerized by heating to 2300 ° C. and decomposes into monomers. Further, since the oxidation start temperature of the graphite material is around 400 ° C., only the adhesive can be thermally decomposed without oxidizing the graphite material.

  Next, the lathe 19 shown in FIG. 2 is used to rotate the workpiece W1 around the axis while moving the cutter (bite) 21 in parallel with the axis L, and as shown in FIG. The spring base material 13 is cut through a spiral groove 23 reaching the cylindrical body 17 with the axis L as the center. That is, as in the case of threading the workpiece W1, the workpiece W1 is rotated about the spindle 25, and the tool 21 is brought into contact with the peripheral portion of the workpiece W1 from the tool rest 27 while the workpiece 21 is in contact with the peripheral portion of the workpiece W1. The blade 21 is moved along the guide shaft 31 parallel to the axis of the main shaft 25 in synchronization with the rotation of W1 to form the spiral groove 23. At this time, the cylindrical body 17 serves as a reinforcing member for the cylindrical spring base material 13, the crushing strength of the cylindrical spring base material 13 in the radial direction is increased, and the spiral cut-off groove processing is performed on the cylindrical spring base material 13. It can be formed on the outer peripheral portion 13a.

  If the workpiece W2 shown in FIG. 3 (d) in which the spiral groove 23 is formed is obtained, then the workpiece W2 with the parting groove is heat-treated at a temperature not lower than the decomposition temperature of the adhesive and not higher than the oxidation temperature of the graphite material. Then, the cylindrical body 17 is removed and the manufacture of the coil spring 11 shown in FIG.

Therefore, according to the coil spring 11 described above, it has a fine structure composed of a large number of graphite particles and pores, and when the cross section is observed with a scanning electron microscope, the density of pores appearing in the cross section is 250 per 6000 μm ^2. As described above, since the average cross-sectional area of pores appearing in the cross section is 5 μm ² or less and the average flatness of pores appearing in the cross section is 0.55 or less, fine graphite particles and pores are uniformly distributed. While having high strength and high elastic modulus, it has heat resistance, corrosion resistance and cutting workability, and can improve dimensional accuracy. As a result, it compensates for the shortcomings of carbon materials and does not break even when used repeatedly in various chemical synthesis equipment, aerospace environment utilization equipment, nuclear reactors, fusion reactors, etc. In addition, a long-life coil spring 11 that can be used stably can be provided.

  Further, according to the method of manufacturing the coil spring 11, the cylindrical spring base material 13 is formed using a graphite material, and the cylindrical body 17 made of a carbon material is fitted to the inner periphery of the cylindrical spring base material 13 with an adhesive. A workpiece W1 is obtained, and the cylindrical spring base material 13 is cut off by a spiral groove 23 centering on the axis L while rotating the workpiece W1 around the axis, and the workpiece W2 with the cut-off groove exceeds the decomposition temperature of the adhesive. In addition, since the cylindrical body 17 is removed by heat treatment at a temperature lower than the oxidation temperature of the graphite material, the cylindrical body 17 is used as a reinforcing member for the cylindrical spring base material 13 and the cylindrical spring base material 13 is not crushed radially inward. A helical spring cut-off groove is formed on the outer peripheral portion 13a to obtain a coil spring-like graphite elastic body.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to the following Example.

1. Production of graphite material (Examples 1-2)
After adding 5 parts by weight of calcined coke pulverized to an average of 2 μm to 95 parts by weight of a coal-based pitch with a softening point of 40 ° C., kneading, adjusting the volatile content while applying heat treatment at 415 ° C. The next raw material was obtained. Next, the mixture was pulverized by a pulverizer equipped with an inner classifier so as not to be excessively pulverized to obtain a secondary raw material powder. Next, after pressurizing at a pressure of 100 MPa with an isotropic isostatic press, firing was performed at a rate of temperature increase of about 5 ° C./hour up to 1000 ° C., and graphitization was performed at 2500 ° C.
Note that the secondary raw material powder obtained during the production did not contain powders of 1 μm or less and 80 μm or more in the particle size distribution measured with a laser diffraction particle size distribution meter.
Table 1 shows the characteristic values of the raw materials used, and Tables 2 and 3 show the characteristic values of the obtained graphite materials.

(Comparative Example 1)
A graphite material was produced in the same manner as in Examples 1 and 2 except that it was pulverized by a pulverizer having no inner partial classifier. In addition, the secondary raw material powder obtained during the production was not subjected to operations such as precision airflow classification, and the particle size distribution measured by a laser diffraction particle size distribution meter did not include powder of 80 μm or more. However, it contained 9.3% of powder of 1 μm or less.
Table 1 shows the characteristic values of the raw materials used, and Tables 2 and 3 show the characteristic values of the obtained graphite materials.

(Comparative Example 2)
After adding 65 parts by weight of calcined coke pulverized to an average of 14 μm to 35 parts by weight of a coal-based pitch having a softening point of 80 ° C., kneading, adjusting the volatile content while performing heat treatment at 250 ° C. The next raw material was obtained. Next, it was pulverized in a pulverization plant equipped with a pulverizer and a precision airflow classifier so as not to be excessively pulverized to obtain a secondary raw material powder. Next, after pressurizing at a pressure of 100 MPa with an isotropic isostatic press, firing was performed at a rate of temperature increase of about 5 ° C./hour up to 1000 ° C., and graphitization was performed at 2500 ° C.
In addition, the secondary raw material powder obtained in the middle of the production did not contain a powder of 1 μm or less in the particle size distribution measured with a laser diffraction particle size distribution meter, but contained about 3% of a powder of 80 μm or more. It was.

Table 1 shows the characteristic values of the raw materials.

2. Characteristic Evaluation of Graphite Material The following items were measured, and the characteristics of the graphite material obtained above were evaluated.
(Number of pores appearing in the cross section, average area, average flatness)
The number of pores appearing in the cross section, the average area, and the average flatness were calculated according to the following procedure.
(A) Sample rough polishing The test piece prepared above was cut into a cylindrical shape having a thickness of about 5 mm, and both surfaces of the sample were subjected to leveling treatment on both sides of the sample using a GATAN jig MODEL 623 and SiC water resistant abrasive paper # 2400. did. Next, it was fixed to a brass sample stage.
(B) CP processing
CP machining was performed at an acceleration voltage of 6 kV using SM09010 manufactured by JEOL.
(C) Milling Ar milling treatment was performed using a flat milling device E-3200 manufactured by Hitachi High-Tech Co., Ltd. at an acceleration voltage of 5 kV, 0.5 mA, a sample inclination angle of 45 °, and a milling time of 3 minutes.
(D) FE-SEM Observation The sample prepared as described above was observed at an acceleration voltage of 2 kV using an ultra-high resolution field emission scanning electron microscope S-4800 manufactured by Hitachi High-Tech. FIGS. 4a to 4c show the graphite material of Example 1, FIGS. 5a to 5c show the graphite material of Example 2, FIGS. 6a to 6c show the graphite material of Comparative Example 1, and FIGS. 7a to 7c show the graphite material of Comparative Example 2. FIGS.
(E) Image Analysis Using the analysis software ImageJ1.37 manufactured by the National Institutes of Health, the SEM image obtained above was analyzed. The observation magnification at this time was 2000 times, and after performing the noise reduction processing, the binarization processing of the plane portion / void (pore) portion was performed. It should be noted that the analysis target of voids (pores) exceeds 0.2 μm, from which it can be determined whether or not the voids (pores).
Area measurement and optimal ellipse fitting are performed on the void (pore) part obtained by binarization with image analysis software (ImageJ) and the number is counted, and the cross section is obtained from the value obtained by the above processing. The number of appearing pores, average area, and average flatness were calculated.
(Compressive strength)
Measurements were performed according to JIS R7222.
(Elastic modulus)
Measurements were performed according to JIS R7222.

Table 2 shows the characteristic values of the graphite material.

3. Manufacture of coil springs The graphite materials of Examples and Comparative Examples are processed into a hollow cylindrical shape with a thickness of 2.5 mm to form a cylindrical spring base material 13 (FIG. 3A), and the inner circumference of the cylindrical spring base material 13 The cylindrical body 17 is bonded with α-cyanoacrylate to create a workpiece W1 in which the cylindrical spring base material 13 and the cylindrical body 17 are integrated (FIG. 3B), and the lathe 19 shown in FIG. Used, a spiral groove 23 having a width of 1 mm and a pitch of 2 mm is formed on the workpiece W1 (FIG. 3C), and the obtained workpiece W2 is heat-treated at 330 ° C. to extract the cylindrical body 17 (FIG. 3D). The coil spring 11 is completed (FIG. 3 (e)).

4). Evaluation of Coil Spring Regarding the coil spring of the example (coil spring manufactured with the graphite material of Examples 1 and 2) and the coil spring of the comparative example (coil spring manufactured with the graphite material of Comparative Examples 1 and 2), The difference in appearance could not be confirmed with the naked eye. However, as can be seen from the cross-sectional photographs of the graphite materials shown in FIGS. 4a to c, FIGS. 5a to c, FIGS. 6a to c and FIGS. 7a to c, the graphite materials of the examples have round pores with relatively small sizes. Although the graphite material of the comparative example has a small number of round pores and a relatively large number of graphite materials in comparison with the coil spring produced in the example and the comparative example, while many of them are uniformly distributed The resistance to stress is greatly different from that of a coil spring made of graphite material. Specifically, the coil spring of the comparative example is chipped during compression from the natural length state to the most contracted state, and is broken only by repeating expansion and contraction several times. On the other hand, the coil spring of the example was not broken even when the expansion and contraction from the natural length state to the most contracted state was repeated, and was not damaged even after the expansion and contraction was repeated 1000 times.

1 is a perspective view of a graphite elastic body according to the present invention. It is a block diagram which shows an example of the lathe used for manufacture of the elastic body made from graphite shown in FIG. It is the schematic diagram which represented the procedure of manufacture of the graphite-made elastic body shown in FIG. 1 by (a)-(e). 2 is a cross-sectional SEM photograph of the graphite material produced in Example 1. 2 is a binarized image obtained by subjecting a cross-sectional SEM photograph of the graphite material produced in Example 1 to image processing. 3 is an elliptical fit diagram of a binarized image obtained by image processing of a cross-sectional SEM photograph of the graphite material produced in Example 1. FIG. 3 is a cross-sectional SEM photograph of the graphite material produced in Example 2. 4 is a binarized image obtained by image processing of a cross-sectional SEM photograph of the graphite material produced in Example 2. FIG. 4 is an elliptical fit diagram of a binarized image obtained by image processing of a cross-sectional SEM photograph of the graphite material produced in Example 2. FIG. 3 is a cross-sectional SEM photograph of the graphite material produced in Comparative Example 1. 3 is a binarized image obtained by image processing of a cross-sectional SEM photograph of the graphite material produced in Comparative Example 1. FIG. 4 is an elliptical fit diagram of a binarized image obtained by image processing of a cross-sectional SEM photograph of the graphite material produced in Comparative Example 1. 3 is a cross-sectional SEM photograph of the graphite material produced in Comparative Example 2. 4 is a binarized image obtained by image processing of a cross-sectional SEM photograph of the graphite material produced in Comparative Example 2. FIG. 6 is an elliptical fit diagram of a binarized image obtained by image processing of a cross-sectional SEM photograph of the graphite material produced in Comparative Example 2. FIG.

Explanation of symbols

11 Coil spring (graphite elastic body)
DESCRIPTION OF SYMBOLS 13 Cylindrical spring base material 13a Outer peripheral part 15 Spiral parting groove 17 Cylindrical body 21 Cutting tool 23 Spiral groove L Axis W1, W2 Workpiece

Claims (2)

It has a fine structure consisting of a large number of graphite particles and pores. When the cross section is observed with a scanning electron microscope, the density of pores appearing in the cross section is 250 or more per 6000 μm ² , and the average cross sectional area of the pores appearing in the cross section is 5 [mu] m ² or less, a black lead elastic body formed by using a graphite material having an average aspect ratio of the pores appearing in the cross section is 0.55 or less, the outer peripheral portion of the tubular spring base material made of the graphite material A graphite elastic body characterized by being formed in a coil spring shape by being cut by a spiral cut-off groove about an axis. It has a fine structure consisting of a large number of graphite particles and pores. When the cross section is observed with a scanning electron microscope, the density of pores appearing in the cross section is 250 or more per 6000 μm ² , and the average cross sectional area of the pores appearing in the cross section is Forming a cylindrical spring base material using a graphite material having an average flatness of pores appearing in a cross section of 5 μm ² or less and 0.55 or less;
A step of fitting a cylindrical body with an adhesive to the inner periphery of the cylindrical spring base material to obtain a workpiece;
A step of cutting the cylindrical spring base material in a spiral groove reaching the cylindrical body by rotating the workpiece relative to the axis while rotating the workpiece around the axis;
Heat-treating the parting grooved workpiece to decompose the adhesive, and removing the cylindrical body;
The method for producing a graphite elastic body according to claim 1 , comprising: