Isostatic Graphite
Isostatic graphite requires structurally isotropic raw materials, which need to be ground into finer powders. Cold isostatic pressing molding technology is required. The firing cycle is very long. In order to achieve the target density, multiple impregnation-roasting is required. cycle, the cycle of graphitization is also much longer than that of ordinary graphite.
It is precisely because of this series of excellent properties that isostatic graphite is widely used in the fields of metallurgy, chemistry, electrical, aerospace and atomic energy industries, and, with the development of science and technology, the application field is still expanding.
Forming
Different from ordinary extrusion molding and compression molding, isostatic graphite is formed by cold isostatic pressing technology. Fill the raw material compressed powder into the rubber mold, and make the compressed powder dense through high-frequency electromagnetic vibration, vacuumize after sealing, discharge the air between the powder particles, and put it into a high-pressure container filled with liquid media such as water or oil. Pressurize to 100-200 MPa and press into cylindrical or rectangular products.
According to Pascal's principle, the pressure is applied to the rubber mold through a liquid medium such as water, and the pressure in all directions is equal. In this way, the pressed powder particles are not oriented in the filling direction in the mold, but are compressed in an irregular arrangement. Therefore, although graphite is anisotropic in crystallographic properties, as a whole, isostatic graphite But isotropic. In addition to cylinders and rectangles, the formed products also have shapes such as cylinders and crucibles.
Isostatic pressing machine is mainly used in powder metallurgy industry. Due to the needs of high-end industries such as aerospace, nuclear industry, cemented carbide, and high-voltage electromagnetics, isostatic pressing technology has developed very fast, and has the ability to manufacture cold isostatic pressing machines with a working cylinder inner diameter of 3000mm, a height of 5000mm, and a maximum working pressure of 600MPa. . At present, the maximum size of the cold isostatic press used in the carbon industry to produce isostatic graphite is Φ2150mm×4700 mm, and the maximum working pressure is 180MPa.
The main application of isostatic graphite
Heater for Czochralski monocrystalline silicon thermal field and polycrystalline silicon ingot furnace
In the thermal field of Czochralski single crystal silicon, isostatic graphite components include crucibles, heaters, electrodes, heat insulation shielding plates, seed crystal holders, bases for rotating crucibles, various discs, heat reflection plates, etc. 30 kinds.
Among them, 80% of the isostatic graphite is used to make crucibles and heaters. In recent years, the diameter requirements for monocrystalline silicon rods have become larger and larger, and the production of 300 mm wafers has increasingly become the mainstream.
Correspondingly, the diameter of the heating zone of the single crystal furnace is mostly 800 mm. The diameter of the graphite crucible in the furnace reaches 860 mm in order to protect the quartz crucible placed therein. The diameter of the heater is about 960-1000 mm. The maximum reaches 1500 mm.
Since 2003, people's awareness of protecting the earth's living environment has gradually increased, and people are increasingly favoring natural energy that does not emit carbon dioxide. In this trend, the production of solar cells has increased rapidly.
In the manufacturing process of polysilicon wafers for solar cells, polysilicon fragments are first melted and cast into polysilicon square ingots. Among them, the heater of the ingot furnace needs to be made of isostatic graphite.
Atomic energy industry
In recent years, the global climate has warmed. Carbon dioxide from the use of fossil fuels is thought to be the main cause of the problem. In recent years, although the economic growth of developing countries has achieved world-renowned results, the problem of power shortage has deeply troubled these countries.
Under such circumstances, people's eyes have turned to atomic power generation, which has a much higher energy flow density than solar cells and wind power, and does not emit carbon dioxide and sulfur oxides.
At present, most of the nuclear reactors that have been put into use in the world are light water reactors. The working principle of this reactor type is to use the heat energy generated during nuclear cracking to vaporize cold water into water vapor at 300°C, and drive the turbine to generate electricity. However, due to the low temperature of the water reactor, the power generation efficiency of the light water reactor is not too high.
In contrast, high-temperature gas-cooled reactors do not have such problems. It uses inert gas (helium) as the coolant, not only the core outlet temperature can reach nearly 1000°C, the power generation efficiency is high, and it is also suitable for producing hydrogen.
It can be said that both power supply and environmental protection are correct. Graphite is suitable as the core material of this high-temperature gas-cooled reactor, because graphite not only resists high temperature, but also absorbs less neutrons and has good heat transfer.
Jiangsu High Industry on the research and development and production of high-performance polyurethane isostatic pressing molds. Through in-depth cooperation with many isostatic pressing equipment manufacturers and in-depth study of the industry, the developed isostatic pressing polyurethane mold series products have the characteristics of long service life, high precision, small deformation, easy demoulding, etc., and are widely used in ceramics, etc. Static pressing mould, cemented carbide isostatic pressing mould, rare earth permanent magnet material isostatic pressing mould, graphite isostatic pressing mould, etc.
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