JPH0288464A - Production of density and high strength carbon material and graphite electrode material for electric spark machining - Google Patents

Abstract

PURPOSE:To obtain a high density and high strength carbon material having regulable physical properties such as coefft. of thermal expansion without carrying out impregnation by adding less expensive aggregate than small spheres of carbonaceous mesophase to the spheres and graphitizing them. CONSTITUTION:Small spheres of carbonaceous mesophase are prepd. as starting material for a carbon material capable of being molded, calcined and graphitized without using a binder. 100 pts.wt. graphite powder and/or aggregate coke is mixed with 30-120 pts.wt. binder and this mixture is added to the small spheres of carbonaceous mesophase having self-sinterability by <=40wt.% of the total amt. They are molded, calcined and graphitized.

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention relates to a method for producing a high-density and high-strength carbon material that can be used as an electrode for electrical discharge machining, a jig, a crucible, or for nuclear power, and a method for producing a carbon material for electrical discharge machining. Regarding graphite electrode materials.

<Prior Art> Carbonaceous mesophase spherules are mesophase spherules that are generated in optically isotropic pitch when tar pitch and petroleum pitch are heat-treated at a temperature of 350°C to 500°C. It is well known that these small spheres are separated from the pitch matrix by a solvent fractionation method and serve as a raw material for isotropic, high-density, and high-strength graphite materials.

For example, according to Japanese Patent Publication No. 60-25364, by using a solvent with a slightly low extraction power for pitch such as benzene or oil in tar when separating small spheres with a solvent, part of the β component in pitch can be extracted. It has been shown that a raw material with excellent self-sintering properties can be obtained by allowing the particles to remain together with the small spheres and then calcining them at a temperature of 200 to 450°C in an inert atmosphere.

If the raw material obtained by this method is used, it can be molded, fired, and graphitized as it is, with a density of 1 to 8.
5 g/cm3 or more, bending strength is a o o kg/c
High-density, high-strength, and isotropic graphite material with a thickness of 1.5 m or more can be easily obtained.

<Problems to be Solved by the Invention> However, the carbonaceous mesophase spherules are not inherently a raw material with good crystallinity (graphitizability), and the variation in quality of the final graphite material is narrow. That is, once the density is determined, the strength, electrical resistivity, and coefficient of thermal expansion are necessarily determined, which has the disadvantage that individual control is difficult.

As a countermeasure for this problem, calcined coke with developed crystallites,
It is possible to adjust the quality by adding artificial graphite powder, natural graphite powder, etc. Furthermore, these raw materials are cheaper than the carbonaceous mesophase spherules. However, since these raw materials do not have self-sintering properties,
When added to the carbonaceous mesophase spherules, there is a drawback that the strength of the resulting graphite material decreases.

The present invention was made in view of the above-mentioned problems, and utilizes an aggregate that is cheaper than carbonaceous mesophase spherules, and has physical properties such as electrical resistivity and thermal expansion coefficient in a wide range. The purpose of the present invention is to provide a method for producing a high-density, high-strength carbon material that allows adjustment of carbon.

In addition, when graphite material made only of carbonaceous mesophase small spheres is used as an electrode for electrical discharge machining, it has the advantage of less electrode wear and faster machining speed compared to general-purpose electrode materials, but on the other hand, it has high hardness and machining The drawbacks were that it was difficult and expensive.

Furthermore, carbonaceous mesophase spherules are not inherently a raw material with good crystallinity, so once the density is determined, other properties such as electrical resistivity and hardness are determined, making individual control difficult.

As a countermeasure to this problem, we adjust the quality by adding artificial graphite powder, natural graphite powder, etc., which have excellent crystallinity and are cheaper than the mesophase mentioned above, and also add a binder to control strength, hardness, etc. It is possible to do so.

However, when the material manufactured by the above method is used as an electrode for electrical discharge machining, there is a drawback that micro protrusions are generated on the electrode surface due to non-uniformity inside the material, which significantly reduces machining accuracy. there were.

The present invention was made in order to solve the above problems, and an object of the present invention is to provide an isotropic high-density, high-strength graphite material for electrical discharge machining electrodes that can adjust electrical resistivity, hardness, etc. over a wide range. It is said that

Means for Solving the Problems> In order to achieve the above objects, according to the present invention, graphite powder and/or aggregate coke and a binder are added to carbonaceous mesophase small spheres having self-sintering properties. Provided is a method for producing a high-density, high-strength carbon material, which is characterized by adding a mixture with a carbon material, followed by molding, firing, and graphitization.

The mixture contains graphite powder and/or aggregate coke 100
It is preferable that 30 to 120 parts by weight of a binder are mixed with the weight part, and that this mixture is added in a proportion of 40% by weight or less based on the total amount.

Further, it is preferable that the binder is a pitch containing a benzene-insoluble content of 40% by weight or more and less than 95% by weight.

The mixture may include graphite powder and/or aggregate coke.
It is preferable to add a mixture of 15 to 60 parts by weight of the pitches to 0 parts by weight in a ratio of 60% by weight or less based on the total amount.

In addition, carbonaceous mesophase small spheres having self-sintering properties, graphite powder and/or aggregate coke, and pitches,
Pitches are dry mixed without heating, then molded,
It is preferable to perform firing and graphitization treatment.

It is preferable that the pitches have a particle size of 10 μm or less.

Moreover, it is preferable that the particle size of the graphite powder and/or aggregate coke is 30 μm or less.

In the graphite electrode material for electrical discharge machining manufactured by the method of the present invention, the maximum particle diameter of carbonaceous mesophase small spheres is 30 μm.
In the following, it is preferable that the particle size of the graphite powder and/or aggregate coke is equal to or smaller than the maximum particle size of the carbonaceous mesophase spherules used.

The present invention will be explained in more detail below.

The carbonaceous mesophase spherules having self-sintering properties used in the present invention have a viscous component on the surface of the mesophase spherules with an average particle diameter of several to several tens of μm, as shown in Japanese Patent Publication No. 60-25364, for example. It is a raw material for carbon materials that can be molded, fired, and graphitized without using a binder to produce carbon materials. Also,
When the raw material for carbon material is individually molded, fired, and graphitized, the caking component is uniformly dispersed on the surface of the mesophase spherules, so the bulk density is 1.85 g/1, which is impossible when using a binder. cm' or more, especially bending strength of 800 kg/
A carbon material with a diameter of cm' or more can be easily obtained.

The present invention is characterized in that a mixture of graphite powder and/or aggregate coke and a binder is added to the small spheres.

The particle size of graphite powder and/or aggregate coke is 30μ
m or less, preferably 15 μm or less. 30
If it exceeds μm, the adhesive force with the mesophase spherules becomes weak, causing a decrease in strength.

In the electrode material for electric discharge machining, the maximum particle size of the small spheres is 3
The thickness is desirably 0 μm or less, preferably 15 μm or less. 3
If it exceeds 0 μm, the surface roughness of the workpiece after electrical discharge machining will be significantly reduced.

Physical properties such as electrical resistivity and hardness can be adjusted by adding a mixture of graphite powder and/or aggregate coke and a binder to the small spheres. By using graphite powder and/or aggregate coke with a maximum particle size smaller than a sphere, the inside of the graphite material becomes uniform, and when used as an electrode for electrical discharge machining, the discharge points are sufficiently dispersed to prevent microscopic protrusions on the electrode surface. Occurrence can be prevented.

Typical binders that can be used in the present invention include pitch, resins, and the like.

The mixing ratio of the graphite powder and/or aggregate coke and the binder depends on the particle size of the graphite powder and/or aggregate coke,
The addition ratio of the mixture and mesophase spherules varies, but based on 100 parts by weight of graphite powder and/or aggregate coke,
Preferably, 30 to 120 parts by weight of a binder are incorporated. If the binder is less than 30 parts by weight, graphite powder and/or
Or, the cohesive force between the coke aggregate and the spherulites is weak, resulting in a significant decrease in the strength of the graphite material obtained. When the amount of the binder exceeds 120 parts by weight, there are many components that gasify, and a large number of pores are generated in the sintered block, making it impossible to obtain high density and high strength.

Further, the addition ratio of the mixture to the mesophase spherules is preferably 40% by weight or less based on the total amount. Within this range, it can be added without reducing the original strength of the carbon material using the mesophase spherules.

The mixing of this additive must be carried out as homogeneously as possible in order to prevent inhomogeneities within the resulting graphite material. When used as an electrode material for electrical discharge machining, if the mixture is uneven, the electrode will be worn out unevenly. An effective mixing method for this purpose is, for example, to use a rotary ball mill or the like for 1 to 5 hours.

Furthermore, since coke and the like have anisotropy, it is desirable to use cold isostatic pressure (CIP) molding when molding the mixture in order to prevent the development of anisotropy in the molded product. Molding pressure is 500 kg/c to develop strength.
m2 or more is desirable.

In addition, the binder that can be used in the present invention is preferably a pitch containing 40% by weight or more and less than 95% by weight of benzene-insoluble matter, and representative examples include coal-based and petroleum-based pitches. can. Benzene insoluble content is 40
In the case of pitches that are less than % by weight, it is difficult to pulverize them because of their large light content, and their residual carbon content is low, so they do not contribute to further increasing the density and strength of the carbon material.

If the benzene insoluble content exceeds 95% by weight, a homogeneous graphite material cannot be obtained. The reason is that 300 to 500
Pitch, which is a binder component, softens and melts in the carbonization reaction region at around ℃, wets the surface of aggregate coke, and at the same time reacts with the binder component present on the surface of mesophase spherules, producing benzene, which is necessary for developing strength as a carbon material. It is presumed that this is due to a lack of soluble content.

The blending ratio of graphite powder and/or aggregate coke and pitch as the binder varies depending on the particle size of graphite powder and/or aggregate coke and the addition ratio of these two raw materials and mesophase spherules. However, it is preferable to mix 15 to 60 parts by weight of pitches with respect to 100 parts by weight of graphite powder and/or aggregate coke. When the amount of pitches is less than 15 parts by weight, the caking force between the graphite powder and/or aggregate coke and the spherulites is weak, and the strength of the graphite material obtained is significantly reduced. When the amount of pitch exceeds 60 parts by weight, there are many components that gasify, and a large number of pores are generated in the sintered block, making it impossible to obtain high density and high strength.

Further, in this pitch, the addition ratio of the mixture to the mesophase spherules is preferably 60% by weight or less based on the total amount. Within this range, it can be added without reducing the original strength of the carbon material using the mesophase spherules.

The mixing of the additives must be carried out as homogeneously as possible to prevent inhomogeneities within the resulting graphite material. When used as an electrode material for electrical discharge machining, if the mixture is uneven, the electrode will be worn out unevenly.
An effective mixing method for this purpose is, for example, to use a rotary ball mill or the like for 1 to 5 hours.

Further, the mesophase small spheres, the graphite powder and/or the aggregate coke, and the pitch can be directly mixed at room temperature using, for example, a rotary ball mill.

In this dry mixing, the particle size of the graphite powder and/or aggregate coke is preferably 30 μm or less, preferably 10 μm or less. If it exceeds 30 μm, mixing with mesophase spherules and pitches will not be carried out sufficiently, and the quality of the graphite material will become non-uniform.

The particle size of pitches is preferably 10 μm or less. 10μ
If it exceeds m, mixing with the mesophase small spheres, graphite powder and/or aggregate coke will not be carried out sufficiently, and the quality of the graphite material will become non-uniform.

Furthermore, since coke and the like have anisotropy, it is desirable to use cold isostatic pressure (ARP) molding when molding the mixture in order to prevent the development of anisotropy in the molded product. Molding pressure is 500 kg/c to develop strength.
m' or more is desirable.

The mixture thus prepared becomes an isotropic, high-density, and high-strength carbon material by shaping, firing, and graphitizing as described above, even without impregnation.

<Example> The present invention will be specifically described below based on Examples.

(Example 1) Raw needle coke (before calcination) with an average particle size of 5 μm 10
Pitch 60 with a softening point of 90°C (RB method, all softening points below are indicated by the RB method) (BI: 31 wt%) for 0 parts by weight
Parts by weight were blended, kneaded in a kneader at 130°C for 1 hour, allowed to cool, and then pulverized to obtain a mixture. In addition, tar pitch was heat-treated at 450°C to generate mesophase spherules, which were extracted and filtered using 6 times the volume of oil in tar.
Further, the mixture was calcined at 360° C. for 3 hours to obtain mesophase small spheres having self-sintering properties. For the mesophase spherules, each of the above mixtures was added in an amount of 10.20% of the total amount.
．． 30, 40, and 50% by weight were added in a rotary ball mill under a solvent of ethyl alcohol and mixed for 5 hours.
After filtration and drying, these were cold isostatically pressed (a r p) at a pressure of 1000 kg/cm' and then heated at 10°C.
The temperature was raised to too much °C at a temperature increase rate of /h and fired, and this was graphitized at a temperature of 2500 °C. The relationship between the addition ratio of these graphite material admixtures, bulk density and bending strength is shown in FIG. Graphite materials with an admixture content of 40% by weight or less have a bulk density of 1,85 g/cm' or more and a bending strength of 700 kg/cm' or more, achieving high density and strength. Graphite materials have a significant decrease in bulk density and bending strength.

(Comparative Example 1) Raw needle coke with an average particle size of 5 μm was added to mesophase small spheres having the same self-sintering properties as in Example 1 in an amount of 10 to 50% by weight based on the total amount, and mixed. It was molded, fired, and graphitized under the same conditions. The bending strength is shown in FIG. 2 in comparison with Example 1. It can be seen that the strength is significantly reduced compared to Example 1, in which pitch was blended into raw needle coke.

(Example 2) 2 pitches with a softening point of 90°C (BI: 31 wt%) were added to 100 parts by weight of calcined needle coke with an average particle size of 10 μm.
Blend in the range of 0 to 130 parts by weight and mix at 130°C to obtain a mixture, and form mesophase small spheres similar to Example 1.
The mixture was added in an amount of 20% by weight based on the total amount, and a graphite material was obtained in the same manner as in Example 1. The results of the bulk density are shown in Figure 3. Bulk density 1 when the blending ratio of pitch to 100 parts by weight of coke is in the range of 30 to 120 parts by weight,
A high density of 85 g/cn+" or more has been obtained.

(Example 3) A softening point of 107°C (B
100 parts by weight of pitch (I+33 wt%) was blended, kneaded in a kneader at 150 tons for 1 hour, allowed to cool, and then pulverized to obtain a mixture. These were added in an amount of 25% by weight based on the total amount to the same mesophase small spheres as in Example 1, and a graphite material was obtained in the same manner as in Example 1. The results are shown in FIG. It can be seen that when the average particle size is larger than 30 μm, the bending strength decreases significantly.

(Examples 4 to 5 and Comparative Example 2) Softening point 90 for each 100 parts by weight of calcined needle coke and quiche graphite with an average particle size of 5 μI
℃ (Br: 31 wt%) pitch 70 parts by weight is blended,
The mixture was kneaded in a kneader at 130°C for 1 hour, allowed to cool, and then ground to obtain a mixture. These were added in an amount of 20% by weight based on the total amount to the same mesophase small spheres as in Example 1, and graphite materials were obtained in the same manner as in Example 1 (Examples 4 and 5).

The results are shown in Table 1 together with Comparative Example 2 in which a graphite material was used without blending any admixtures. By mixing needle coke or quiche graphite with developed crystallites, the electrical resistivity and coefficient of thermal expansion are reduced.
Thus, the present invention is useful as a method for adjusting physical properties.

Table 1 (Note: The coefficient of thermal expansion is the value at 350 to 450°C) (Comparative Example 3) Tar pitch is heat treated at 450°C to generate mesophase spherules, which are extracted with 6 times the amount of oil in tar. , filtered, and further calcined at 360'e for 3 hours to obtain mesophase spherules having self-sintering properties with an average particle size of 15 μm and a maximum particle size of 30 μm. The above small spheres were cold isostatically pressed at 550 kg/cm' without adding any admixtures, and 10 tons
/h to raise the temperature to 1000℃ and bake, then 2500℃
Graphitized at ℃. Table 2 shows the physical properties of the graphite material obtained, and the electrode wear rate and machining speed when electrical discharge machining was performed under severe conditions of a machined surface of 10×IOI, a peak current of 16 A, a pulse width and a rest time of 24 μsec.

The electrode wear rate shown here is the ratio of the length of the electrode wear to the depth at which the workpiece 5KD-11 is machined, and the processing speed is the weight processed per unit time.

(Examples 6 to 7) A softening point of 90° C. for 100 parts by weight of calcined needle coke pulverized to an average particle size of 4.5 μm and a maximum particle size of 13 μm.
(BI: 31 wt%) pitch was blended at a ratio of 70 parts by weight and 100 parts by weight, and heated at 130°C in a kneader, respectively.
The mixture was mixed for 1 hour, allowed to cool, and then ground to obtain a mixture (Examples 6 and 7, respectively).

To the mesophase small spheres obtained in Comparative Example 3, 20 parts by weight of the above mixture was added to the total amount, and wet-mixed for 5 hours in an ethyl alcohol solvent using a rotary ball mill. These raw materials were molded, fired, and graphitized in the same manner as in Comparative Example 3 to obtain a graphite material. The physical properties of these graphite materials are shown in Table 2. It had almost the same electrical discharge machining characteristics as graphite material made of mesophase small spheres alone.

(Comparative Example 4) Softening point 90°C (Bl: 3
65 parts by weight of pitch (1wt%) was blended and
A mixture was obtained by mixing at 30° C. for 1 hour, and 20rnifk parts of the above mixture was added to the total amount of the mesophase spherules obtained in Comparative Example 3. The mixture was wet-mixed in a rotary ball mill for 5 hours in an ethyl alcohol solvent. Mixed. Mixture Example 6
．． A graphite material was obtained by processing in the same manner as in 7. Table 2 shows the physical properties of this graphite material.

A high-density, high-strength graphite material was obtained in the same way as Comparative Example 3 and Example 6.7, but when used as an electrode for electrical discharge machining,
Fine protrusions were generated on the electrode surface, making it unsuitable as an electrode material for electrical discharge machining.

(Example 8) 100 graphite powders with an average particle size of 10 μm and a maximum particle size of 30 μm
85 parts by weight of pitch with a softening point of 110'C was blended with respect to the parts by weight, mixed with mesophase small spheres, molded, fired, and graphitized in the same manner as in Example 6.7 to obtain a graphite material. Table 2 shows the physical properties of the graphite material. Bending strength 800 kg
A material was obtained that had a high density of /cm2 or more, a hardness (Shore) of 69, which was lower than that of Comparative Example 3, and an electrode wear rate during electric discharge machining that was sufficiently practical.

(Comparative Example 5) Table 2 shows the physical properties of high-grade graphite materials A and B for electrical discharge machining and general-purpose graphite material C commercially available from various companies.

The graphite material according to the present invention had excellent characteristics in that the electrode consumption rate was equal to or lower than these commercially available materials.

(Comparative Examples 6 to 12) Tar pitch (quinoline solubility: 3 wt%, softening point: 8
0°C) was heat-treated at 450°C to generate mesophase spherules, which were extracted with tar oil (with a boiling point range of 150 to 230°C) at 6 times the temperature and filtered twice. The filtered residue was further calcined at 360°C for 3 hours in an inert atmosphere to obtain self-sintering particles with an average particle size of 15 μm and a maximum particle size of 30. Mesophase spherules of un were obtained.

On the other hand, a third pitch with a softening point of 100°C (BI: 25 wt%) was added to the calcined coke crushed to an average particle size of 5 μm.
Blend in the proportions shown in the table and mix in a kneader to 130%
The mixture was mixed for 1 hour at ℃, allowed to cool, and then ground to obtain a mixture.
Each of these mixtures and the above-mentioned small spheres were blended in the proportions shown in Table 3, wet-mixed for 5 hours in a rotating ball mill, filtered and dried, and then mixed at 900 kg/am.
Cold isostatic pressing was carried out, the temperature was raised to 1000°C at 10°C/h and fired, and then graphitized at 2500°C (Comparative Examples 6 to 6).
12). Table 3 shows the physical properties of each graphite material obtained. In addition, in Comparative Example 6, a graphite material was obtained without adding any admixture, and therefore omitting the wet mixing treatment.

(Examples 9 to 16) Bl: 60wt% high softening point pitch (R.

Table 4 shows the mesophase small spheres and calcined coke used in Comparative Examples 6 to 12. They were blended in different proportions and dry mixed for 5 hours using a rotary ball mill. These raw materials were molded, fired, and graphitized in the same manner as in Comparative Examples 6 to 12 to obtain graphite materials (Examples 9 to 16). Table 4 shows the physical properties of these graphite materials.

The production process can be extremely simplified because it can be directly mixed with mesophase small spheres in a dry process without creating a mixture of calcined coke and pitch. Moreover, a graphite material with higher density and higher strength can be obtained compared to the case where a pitch of less than 40 wt% of BI is used.

In addition, graphite material obtained from mesophase spherules (
A high-density, high-strength graphite material with lower electrical resistivity, lower hardness, and lower coefficient of thermal expansion than Comparative Example 6) can be obtained.

<Effects of the Invention> Since the present invention is configured as explained above,
A high-density, high-strength carbon material can be easily obtained without the need for an impregnation process, and is cheaper than when using only carbonaceous mesophase spherules, and has a wide range of electrical resistivity and thermal expansion properties. Adjustment of physical properties such as coefficients is possible. In particular, the present invention is industrially useful as it can be used as a high-grade carbon material for electrical discharge machining, machinery, nuclear power, and the like.

In addition, when pitches containing BI: 40 wt% or more and less than 95 wt% are used as a binder, dry mixing can be performed, and a high-density, high-strength carbon material can be produced in an extremely simple process.

FIG. 2 is a diagram showing the relationship between the proportion of the mixture or raw coke added to the mesophase spherules and the bending strength of the graphite material obtained.

FIG. 3 is a diagram showing the relationship between the blending ratio (parts by weight) of pitch to 100 parts by weight of calcined needle coke and the bulk density of the obtained graphite material.

FIG. 4 is a diagram showing the relationship between the average particle size of calcined needle coke and the bending strength of the graphite material obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the proportion of the mixture added to the mesophase microspheres and the bulk density and bending strength of the graphite material obtained. FIG, 1 FIG, 3 FIG, 2 FIG, 4

Claims (8)

[Claims] (1) Adding graphite powder and/or a mixture of aggregate coke and binder to carbonaceous mesophase small spheres having self-sintering properties, and then subjecting them to molding, firing, and graphitization treatment. A method for producing a characteristic high-density, high-strength carbon material. (2) The mixture is a mixture of 30 to 120 parts by weight of a binder to 100 parts by weight of graphite powder and/or aggregate coke, and this mixture is 40 to 120 parts by weight based on the total amount. 2. The method for producing a high-density, high-strength carbon material according to claim 1, wherein the carbon material is added in a proportion of not more than % by weight. (3) The binder has a benzene insoluble content of 40% by weight or more9
The method for producing a high-density, high-strength carbon material according to claim 1, which contains less than 5% by weight of pitches. (4) A claim in which the mixture is blended at a ratio of 15 to 60 parts by weight of the pitch to 100 parts by weight of graphite powder and/or aggregate coke, and is added at a ratio of 60% by weight or less to the total amount. Item 3. A method for producing a high-density and high-strength carbon material according to item 3. (5) Carbonaceous mesophase small spheres having self-sintering properties, graphite powder and/or aggregate coke, and pitches,
Pitches are dry mixed without heating, then molded,
The method for producing a high-density, high-strength carbon material according to claim 3 or 4, wherein the carbon material is subjected to firing and graphitization treatment. (6) The method for producing a high-density, high-strength carbon material according to any one of claims 3 to 5, wherein the pitch has a particle size of 10 μm or less. (7) The method for producing a high-density, high-strength carbon material according to any one of claims 1 to 6, wherein the graphite powder and/or aggregate coke has a particle size of 30 μm or less. (8) A graphite electrode material for electric discharge machining produced by the method according to any one of claims 1 to 7, wherein the carbonaceous mesophase small spheres have a maximum particle diameter of 30 μm or less, and are made of graphite powder and/or aggregate coke. A graphite electrode material for electric discharge machining, characterized in that the particle size is less than or equal to the maximum particle size of the carbonaceous mesophase small spheres used.