Most of the carbon graphite materials (or products) in today’s market are formed by hot extrusion and molding (cold or hot). Isostatic pressing is a new molding method. With the method of isostatic pressing, it is designed according to the principle of equal pressure in each direction in liquid or gaseous medium. In the production, the powder to be pressed (or the initial pressing product) is put into soft plastic bag (such as rubber, aluminum skin or (Oil or emulsion) or gas (argon, nitrogen) .The cylinder is sealed, through the external pressure, compress the medium, so that the product (oil or emulsion) or gas (argon, nitrogen), after sealing, its Compressed to size.
Isostatic pressing machine is divided to three kinds: cold isostatic pressing (used at room temperature), temperature and isostatic pressing (medium temperature of 80 ~ 100 ℃, and hot isostatic pressing (medium temperature of 1000 ℃ above).
According to the information, the world’s first isostatic pressing machine is developed in Sweden in 1939. It is still the isostatic pressing machine’s exporting country. China’s first isostatic pressing machine of cold, hot isostatic is also imported from the country. The isostatic pressing machine was first used in the powder metallurgy (including carbide) and ceramic industries, and later used for the carbon graphite materials industry. The key component of the isostatic pressing machine is the cylinder, it can usually stand pressure of 200M
It is reported that some company has been able to manufacture machine with up to 1050M pressure.
In the former time, the cylinder block was overall casting, but now most of the machines are using steel wire pre-stress winding. With the large-scale product sizes, the cylinder diameter has been increased constantly.
Large-scale development .At present, some company has been able to mass production of 1 500 × 2 000mm of the isostatic pressing graphite .It is reported to the they will development size of 2 000mm diameter products. CFCCARBON Ltd has a big production ability, about 6,000 tons per year
In addition, there are many companies can produce isostatic graphite. in 1970’s China began manufacturing isostatic pressing machines of single-pressure 200M, with cylinder diameter of 200mm; in 1980’s, China has been able to mass production of diameter 500mm and 800mm of the isostatic pressing machine. it is able to produce the diameter of 1250mm, and is capable of producing a diameter of 1500mm isostatic pressing machine. CFCCARBON Ltd.’s high-purity graphite products factory has been able to mass production of `500 × 600mm isostatic pressing graphite and ready to continue large-scale development.
Development and Present Situation of Isostatic Pressing Technology at Home
The isostatic pressing machine is not only for pressing of products, but also for for asphalt impregnation device. the product and the asphalt are installed in the sealed metal aluminum skin, placed in the hot isostatic pressing machine, using the gas as medium, heating, pressing, until all the asphalt are carbonized. The products will get a max density of resin. This is because not only the asphalt can penetrate the entire pores of the product, but also there is no phenomenon of asphalt exudation during decompression of the bitumen after the decompression and during roasting, as in conventional equipment.
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