JPH04295060A - Production of heat resistant inorganic substance-carbon composite material - Google Patents

Abstract

PURPOSE:To produce a heat resistant inorg. substance-carbon composite material having high bending strength at a low cost. CONSTITUTION:Starting material contg. 1-60vol.% powder of one or more kinds of heat resistant inorg. substances selected among alumina, silicon carbide, silicon dioxide, boron carbide, silicon nitride, boron nitride, silicon and boron and 15-35vol.% pitch binder is mixed, press-molded at 480-600 deg.C and fired under ordinary pressure.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a nonferrous metal sintered carbon material with excellent heat resistance, friction resistance, oxidation resistance, etc. used in mechanical tools such as clutches and brakes of automobiles, etc. This invention relates to a method for producing a heat-resistant inorganic material/carbon composite material that has been dramatically improved.

0002

BACKGROUND OF THE INVENTION Various methods have been proposed so far for producing heat-resistant inorganic materials or carbon composite materials having excellent heat resistance, friction resistance, and oxidation resistance. For example, as a first method, JP-A-52-105917 discloses a method in which coke and boron carbide are sintered under pressure of 200 kg/cm 2 or more and at 2000° C. or more. In addition, as a second method, Japanese Patent Application Laid-Open No. 54-81315
The publication contains 25-60% by volume of boron carbide and 50-60% of free carbon.
5% by volume, bonded with thermosetting resin, density 1.
There is a disclosure of a method for producing a boron carbide/carbon composite with a weight of 4 to 1.8 g/cm3. In addition, as a third method, 100 parts by weight of mesophase small spheres produced by heat-treating pitch and 1 to 50 parts by weight of heat-resistant inorganic material particles (boron carbide B4C) are disclosed in JP-A-62-108767. There is a disclosure of a method of molding at room temperature and then firing. Furthermore, the fourth method relates to an improved method of the third method, and is
Japanese Patent No. 100063 discloses a method in which mesophase small spheres are pulverized into fine powder, pressure is reduced during firing, and artificial graphite is added as a sintering aid to increase strength.

0003

[Problems to be Solved by the Invention] However, in the case of the first method, it is necessary to perform pressure molding at an ultra-high temperature of 2000°C or higher, and this pressure and heat molding equipment is extremely expensive, making it uneconomical. It has problems such as. Moreover, the composite materials obtained by the second to fourth methods have a bending strength of at most 500
It was only possible to manufacture products with a weight of about kg/cm2, and it was not possible to expect a dramatic increase in strength.

Therefore, the main object of the present invention is to develop a heat-resistant inorganic material suitable as a friction-resistant, heat-resistant, and oxidation-resistant material.
The present invention provides a method for manufacturing carbon composite materials at a low cost with dramatically improved bending strength.

[0005]

[Means for Solving the Problems] The above-mentioned problem consists of powder of a heat-resistant inorganic substance of 1 to 60% by volume and a binder pitch of 15 to 60% by volume.
Mixing raw materials mainly containing 35% by volume, 480-60%
This can be solved by pressurizing and heating molding at a temperature of 0° C. or lower and then firing without applying pressure.

[0006]

[Operation] In the present invention, a binder pitch with a low volatile content that melts when heated is used as the binder. As a result, compared to the case where conventional mesophase small spheres or coke are used as a matrix, the fluidity of the pitch is good, so the adhesive force to the heat-resistant inorganic substance powder is improved, and the strength of the composite material is improved. As a binder pitch, a binder pitch with a high softening point and fluidity and low volatile content, which is obtained by heat treating coal tar pitch or petroleum pitch, is recommended in terms of adhesion to heat-resistant inorganic substances and carbonization yield. Preferably, and more specifically, those having a softening point of 230° C. or higher, a pour point of 350° C. or lower, and a volatile content of 25% or lower as measured with a Koka type flow tester manufactured by Shimadzu Corporation are preferable. Further, the amount added is 15 to 35% by volume. If it is less than 15% by volume, sufficient adhesive strength cannot be obtained and no increase in strength can be expected. Moreover, if it exceeds 35% by volume, the binder will be excessive, resulting in poor moldability and reduced strength.

In addition to the heat-resistant inorganic powder and binder pitch, it is also possible to add ceramic fibers such as carbon fibers and alumina fibers. The addition of the fibers can suppress cracking during molding and firing and improve the toughness of the product.

On the other hand, as the heat-resistant inorganic powder according to the present invention, one or a combination of two or more of alumina, silicon carbide, silicon dioxide, boron carbide, silicon nitride, boron nitride, silicon, and boron is used. The addition rate of this heat-resistant inorganic substance powder is 1 to 60% by volume.
It is said that If the addition rate is less than 1% by volume, the effect of improving oxidation resistance cannot be sufficiently exhibited. Furthermore, since it has a lower thermal conductivity than graphite or the like, if it exceeds 60% by volume, the thermal conductivity of the composite material will be low and the thermal shock resistance will deteriorate. In addition, if the particle size of the heat-resistant inorganic substance powder is too large, the strength of the composite material will decrease significantly, so the average particle size is preferably 20 μm.
m or less, more preferably 10 μm or less.

On the other hand, the purpose of pressure and heat molding is to suppress the density reduction due to foaming of the pitch, and pressurization only needs to be carried out in the temperature range where the pitch melts and solidifies. Pressure and heat molding is performed at a temperature of 600°C or less, and then high temperature firing is performed without pressure. In order for the pitch to solidify, a temperature of at least 480°C or higher, preferably 500°C or higher, is required. If the temperature exceeds 600°C, the shrinkage of the molded product will increase due to the shrinkage of the pitch, and the molded product will shrink under pressure restraint. This is not preferable because cracks are likely to occur.

[0010] The pressure molding in the present invention suppresses foaming of the pitch and densifies it rather than promoting sintering by pressure, so it is sufficient that the pressure molding is about several tens to several hundred kg/cm2 at most. , specifically preferably 20 kg/cm
2 or more, more preferably 60 kg/cm2 or more. Here, the temperature range to be pressurized does not need to be the entire range from room temperature to the maximum pressure heating temperature, but a part of the temperature range until the maximum temperature is reached, specifically 500 ° C where the pitch solidifies. Even by applying pressure in a similar temperature range, the strength and abrasion resistance of the product composite material are significantly improved compared to the case where pressure and heat molding is not performed.

[0011] The molded body obtained by pressurized and heated molding is then fired under non-pressurized conditions, and the atmosphere at the time of firing should not contain oxidizing gases in order to suppress the oxidation of carbon in the composite material. desirable. Specifically, it is desirable to carry out the process using an inert gas such as nitrogen or argon, a reducing gas such as hydrogen, or a vacuum atmosphere.

[0012] The heat-resistant inorganic material/carbon composite material produced by the above method has high strength and excellent wear resistance compared to conventional cold sintering methods and resin matrix methods. In addition, since the pressure and heat molding temperature only needs to be below 600°C, the pressure and heat molding equipment is much more expensive compared to conventional hot press molding, which heats and pressurizes to an extremely high temperature range of around 1600°C. It is inexpensive and economically advantageous.

[0013]

[Examples] Hereinafter, the effects of the present invention will be explained in detail based on examples. (Example 1) Aluminum oxide powder 45 with a nominal particle size of 5 μm
wt%, coal tar at 440°C under reduced pressure of 50 Torr
Softening point: 255°C, pour point: 310°C
, 20 wt% of high softening point pitch A with 21% volatile content and 35 wt% of coke powder B, which is obtained by carbonizing regular grade petroleum coke at 1000°C and pulverizing it to an average particle size of 10 μm, were used as raw materials to produce the heat resistance according to the present invention. An inorganic material/carbon composite was produced.

Specifically, 90g of aluminum oxide powder,
After weighing 40 g of high softening point pitch A and 70 g of petroleum coke, they were placed in a wide-mouth polyethylene bottle with an internal volume of 2 liters, and mixed by shaking vigorously for 5 minutes. It was placed in a stainless steel metal frame 5 with an inner diameter of 100 mm, and pressurized and heated.

The pressurized and heated molding apparatus presses and molds the molding material 6 with the upper and lower molds 3 and 4 that fit into the upper and lower openings of the metal frame 5, and also presses and molds the molding material 6 with the upper and lower molds 3 and 4 and the upper and lower press heads 1, By interposing the hot plates 7, 7 and their heat insulating materials 8, 8 between the two, it is possible to pressurize and heat at the same time.

When performing pressure and heat molding using the pressure and heat molding apparatus, the temperature is raised from room temperature to 300°C at a temperature increase rate of 5°C/min under a press pressure of 1 kg/cm2.
℃ to 520℃ under a press pressure of 80 kg/cm2 at a rate of temperature increase of 5℃/Hr, held at that state for 1 hour, cooled to obtain a molded body, and this molded body was transformed into powder. It is packed in coke, heated to 1200° C. at a heating rate of 15° C./Hr in a nitrogen gas atmosphere, held for 4 hours, and then left to cool to carbonize. A test piece with dimensions of 10 mm x 10 mm x 60 mm was cut out from the heat-resistant inorganic material/carbon composite material obtained in this way,
Apparent density and bending strength (span 40 mm) tests were conducted. The test results are shown in Table 1.

[0017]

[Table 1]

As is clear from Table 1 above, known manufacturing methods (JP-A No. 54-81315, JP-A No. 1-1999)
100063), as mentioned above, at most 5
00kg/cm2, whereas in the case of the heat-resistant inorganic material/carbon composite material made by the method of the present invention, the weight is about 1200kg/cm2.
It was found that a bending strength of approximately g/cm2 can be ensured, and that the material has excellent strength.

(Example 2) As a heat-resistant inorganic substance, a reagent boron carbide powder with a nominal particle size of 10 μm or less, a boron content of 75 wt% or more, and a carbon content of 20 to 25 wt% and the high softening point used in Example 1 were used. A heat-resistant inorganic material/carbon composite material according to the present invention was manufactured using pitch A and coke powder B, which was also used in Example 1, as raw materials.

Specifically, after weighing 120 g of boron carbide powder, 50 g of high softening point pitch A, and 60 g of petroleum coke, they were placed in a plastic wide-mouth bottle with an internal volume of 2 liters, and mixed by shaking vigorously for 5 minutes. The raw material is transferred to a stainless steel metal frame 5 with an inner diameter of 100 mm in the pressurized and heated molding apparatus shown in FIG.
The material was then heated and pressure molded.

[0021] When performing pressure and heat molding using the pressure and heat molding apparatus, the temperature was raised from room temperature to 300°C at a temperature increase rate of 5°C/min under a press pressure of 1 kg/cm2, as in the example. , 80kg/cm2 from 300℃ to 520℃
The temperature was raised at a temperature increase rate of 5° C./Hr under a press pressure of 5° C./Hr, and this state was maintained for 1 hour, and then cooled to obtain a molded body. Then, this molded body was packed in coke powder and heated in a nitrogen gas atmosphere.
The temperature is raised to 1000°C at a heating rate of 5°C/Hr, held for 4 hours, and then left to cool to carbonize. Next, this carbonized molded body is
10°C in an argon stream using a 150mmφ graphitization furnace
The temperature is increased to 2000° C. at a heating rate of /min to graphitize. A test piece with dimensions of 10 mm x 10 mm x 60 mm was cut out from the heat-resistant inorganic substance/carbon composite material thus obtained, and an apparent density and bending strength (span 40 mm) test was conducted. The test results are shown in Table 2.

[0022]

[Table 2]

In the case of Example 2, a composite material having even higher bending strength than the heat-resistant inorganic material/carbon composite material shown in Example 1 could be obtained.

[0024]

[Effects of the Invention] As explained in detail above, the heat-resistant inorganic material/carbon composite material according to the present invention has excellent properties such as abrasion resistance and heat resistance of the carbon material, and is superior to conventional carbon materials. As a result, high bending strength and oxidation resistance can be obtained, so it exhibits excellent performance as a strength material and a wear-resistant material used under conditions such as an oxidizing gas atmosphere. In addition, since the heat molding is performed in an extremely low temperature range, the pressure and heat molding equipment is simple and inexpensive, and the economic effects brought about by this are also significant.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a pressure and heat molding apparatus used in Examples.

[Explanation of symbols]

1... Upper press head, 2... Lower press head, 3... Upper mold, 4... Lower mold, 5... Metal frame, 6... Molding material, 7... Hot plate, 8
…Insulation material

Claims (2)

[Claims] Claim 1: 1 to 60% by volume of a powder of a heat-resistant inorganic substance;
A heat-resistant inorganic substance/carbon composite material characterized by mixing raw materials mainly consisting of 15-35% by volume of binder pitch, pressurizing and heating molding at a temperature of 480-600°C or less, and then firing without pressure. manufacturing method. Claim 2: The heat-resistant inorganic substance is alumina, silicon carbide,
silicon dioxide, boron carbide, silicon nitride, boron nitride,
The method for producing a heat-resistant inorganic material/carbon composite material according to claim 1, wherein the material is one or a combination of two or more of silicon and boron.