JPH0380722B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing an isotropic carbon material, particularly to an improvement in a molding process. [Prior Art] Carbon materials are usually made by kneading main raw materials such as coke powder with a binder such as tar pitch, then molding using a die casting or extrusion press, and then molding this raw carbon material in a firing furnace.
Manufactured by a process of firing at 1000°C and further graphitizing at a high temperature of 2500°C or higher if necessary. In the above process, the main raw material used is generally in the form of acicular or flattened powder particles, and is molded using a unidirectional pressure means, resulting in anisotropy in the physical properties of the resulting carbon material. . This anisotropy causes problems such as displacement of thermal expansion and directional differences in electrical and mechanical properties, especially when applied to application members that are handled precisely at high temperatures. For this reason, recently, a process of isotropically molding a molding powder raw material with a small anisotropy ratio using a cold isostatic press (CIP: also referred to as a rubber press) has been put into practical use. In other words, in this method, a rubber case is filled with molding raw material made of finely pulverized secondary particles of a mixture of anisotropic coke powder and a binder, or raw coke with small anisotropy, and the molding material is poured from all directions through a liquid medium. Forming is performed by applying uniform hydrostatic pressure, and in addition to imparting a high degree of isotropy, a dense structure can be obtained, making it suitable for structural materials for nuclear reactors, electrodes for electric discharge machining, and crucibles for pulling semiconductor single crystals. It is also useful for manufacturing high-temperature precision parts such as heaters. [Problems to be Solved by the Invention] Although the above-described molding process is carried out at room temperature, the quality and properties of the molded product vary greatly depending on the season. According to the inventors' study of the actual situation, the quality of the molded product deteriorates only in the winter, especially when the molding powder is stored in a cold place and the temperature is below 10°C. It was found that the decrease in density and the dispersion phenomenon became remarkable. As a result of continued efforts by the inventors to clarify the situation, the inventors confirmed the fact that the quality of the molded product depends on the temperature state of the molding powder during molding, and that quality defects frequently occur when this temperature falls outside the range of 30 to 40°C. The present invention was developed based on the above knowledge, and its purpose is to always achieve high-quality isotropic molding when molding carbonaceous molding powder at a temperature of 10°C or less in winter using cold isostatic pressing. An object of the present invention is to provide a method for manufacturing carbon material. [Means for Solving the Problems] A method for producing an isotropic carbon material according to the present invention to achieve the above-mentioned object includes molding finely pulverized carbonaceous molding powder into a desired shape by cold isostatic pressing. In the method of later firing and graphitizing, before forming
Carbonaceous molding powder at a temperature of 10℃ or less is heated to 30~40℃.
The structure is characterized in that it is stored and temperature-controlled in a chamber or tank maintained at a temperature range of 30 to 40 degrees Celsius, and then molded using a molding rubber case whose temperature is regulated at 30 to 40 degrees Celsius. The carbonaceous molding powder targeted by the present invention is secondary particles obtained by pulverizing finely powdered petroleum coke or a mixture of pitch coke and tar pitch, or is self-sintering with an appropriate volatile content and has a small anisotropic ratio. Primary particles obtained by pulverizing raw coke at a temperature of 10°C or less. Therefore, preferably the maximum particle size is 500 μm or less, and the average particle size is 40 to 40 μm.
The target material is mainly carbonaceous molded powder that has been finely pulverized to a particle size of 80 μm and has been stored in storage at temperatures below 10 degrees Celsius during the winter. The carbonaceous molding powder is filled into a molding rubber case of the desired shape, and then molded using a cold isostatic pressure (CIP) press. At this time, the carbonaceous molded powder at a temperature of 10℃ or less is stored in a chamber or tank maintained at a temperature range of 30 to 40℃ during molding, and the powder temperature is adjusted in advance to within the above temperature range. , continued
An important requirement of the present invention is to fill a molding rubber case whose temperature is controlled at 30 to 40°C. Rubber cases for molding are subjected to a hydrostatic press after the occluded gas (mainly air) in the filled molding powder is degassed under reduced pressure and sealed. The molded body with an isotropic structure formed under the above temperature control conditions is packed into a firing furnace and fired at a temperature of approximately 1000°C, and if necessary, transferred to a graphitization furnace and graphitized at a temperature of 2500°C or higher. An isotropic carbon material is obtained by the chemical treatment. [Function] According to the present invention, the conditions for molding the carbonaceous molding powder by controlling the temperature to a specific temperature range of 30 to 40°C function to soften the binder part in the molding powder, and the molding process is performed to soften the binder part in the molding powder. Promotes powder flow and creates a state where it is easy to tighten. As a result, phenomena such as reduction and variation in compacted density that occur when compacting low-temperature carbonaceous compacted powder at a temperature of 10° C. or lower are effectively eliminated. On the other hand, it is also possible to effectively reduce molding defects such as corner chipping of molded bodies that occur under molding conditions exceeding 40°C. [Example] 70% by weight of petroleum coke fine powder (average particle size 20μm) and 30% by weight tar pitch were thoroughly kneaded in a kneading machine, and after cooling, the maximum particle size was 500μm or less and the average particle size was
It was finely pulverized into secondary particles of 60 μm to obtain carbonaceous molded powder. The above carbonaceous molding powder was heated at 5°C, 10°C, 30°C, and 40°C.
The mixture was stored and temperature-controlled in tanks maintained at each temperature level of 50°C and 50°C, and then filled into rubber cases adjusted to the corresponding temperatures. Next, the inside of the rubber case was evacuated to remove air and other gas components occluded in the molded powder. When the temperature was controlled at 5℃, the maximum degree of depressurization was 700mmHg in 20 minutes, but at a temperature of 10℃ or higher, the degree of depressurization reached 740mmHg within a short time of 10 minutes, indicating extremely effective degassing. . After the rubber case was sealed, it was placed in a cold isostatic press and pressurized isotropically with a hydrostatic pressure of 1000 kg/cm ² to obtain a green carbon molded body with a diameter of 30 mm and a length of 150 mm. The obtained raw carbon molded body at each temperature control stage
Table 1 shows the average apparent specific gravity, standard deviation, molding yield, and appearance of the 10 molded products.

[Table] From the results shown in the table, the examples of the present invention with temperature control stages of 30°C and 40°C have a high level of molding density with little structural variation and a molding yield of 100%. On the other hand, in the case of temperature control at 5℃, the molding density, degree of variation, and molding yield are all significantly deteriorated, and in the case of temperature control at 10℃, the molding yield is good, but the molding density decreases, and the variation also increases. It showed a tendency to increase. Further, when the temperature was adjusted to 50° C., although the molding density increased, the variation in molding density and the molding yield were significantly inferior to the examples of the present invention. Example 2 Each raw carbon molded body formed in Example 1 was placed in a firing furnace and fired at a temperature of 1000°C, and then transferred to a graphitization furnace and graphitized at a temperature of 3000°C. The physical properties of the isotropic carbon material thus produced are shown in the table.

〔Effect of the invention〕

As described above, according to the present invention, the seasonal factors that have been a problem in the past, especially the inconvenient phenomena during the molding process in winter, can be effectively eliminated, and it is possible to constantly produce high-quality isotropic carbon materials. can.
Moreover, since the gas components can be effectively degassed under reduced pressure within a short time, production efficiency is improved.

Claims (1)

[Claims] 1 In a method in which finely pulverized carbonaceous molded powder is molded into a desired shape by cold isostatic pressing, then fired and graphitized, the carbonaceous molded powder, which is in a state of 10°C or less before molding, is heated to a temperature of 30 to 40°C. Store in a room or tank maintained at a temperature range of 30 to 30 minutes.
A method for producing an isotropic carbon material, characterized by performing a molding process using a molding rubber case whose temperature is controlled to a temperature range of 40°C.