Isostatic graphite blocks are a new type of graphite material developed in the 1960s. They have the advantages of large forming specifications, uniform material structure and high density, high strength, and isotropy (characteristics are independent of size, shape, and sampling direction). Therefore, isostatic graphite blocks are also known as "isotropic" graphite. Due to its excellent properties, it is closely related to advanced technology and defense technology today. It is an indispensable material for manufacturing single crystal silicon furnaces, metal continuous casting graphite crystallizers, and graphite electrodes for electrical discharge machining. It is also an excellent material for manufacturing rocket igniter, excitation electrode, nozzle and rudder, graphite nuclear reactor deceleration materials and reflection materials. At the same time, it cannot be replaced by other lower quality graphite products.
Special graphite materials are graphite with a carbon mass fraction greater than 99.99%, also known as "three high graphite" (high strength, high density, high purity), which belong to new carbon materials. According to different application fields or different process properties, they can be mainly divided into isostatic graphite blocks and molded graphite, which adopt different forming methods. Among them, when molded, the direction perpendicular to the pressure surface and the direction horizontal to the pressure surface bear different forces, resulting in different properties; therefore, molded graphite has the feature of "anisotropy." When isostatically pressed, the product is uniformly pressurized in all directions, and the volume density is relatively uniform. Therefore, isostatic graphite blocks have the feature of "isotropy."
Isostatic pressure refers to the state of simultaneously applying equal pressure to the sealed material in all directions. Isostatic pressing is to place the material to be pressed in a high-pressure container after sealing, and uniformly pressurize it from all directions using the properties of the incompressibility of the liquid medium and the uniform transmission of pressure. When the liquid medium is injected into the pressure container by the pressure pump, according to the principle of fluid mechanics, its pressure remains unchanged and uniformly transmitted in all directions. Therefore, the powder in the high-pressure container is uniformly and uniformly pressurized in all directions. The method of making the powder dense into a block is called isostatic pressing. Isostatic graphite block materials have the characteristic of isotropy, and the material's characteristics are independent of the size, shape, and sampling direction.
To a certain extent, isostatic pressing can overcome the disadvantage of uneven volume density of molded products, greatly reduce the probability of product cracking, and make the production of large-sized fine-structured products a reality. At the same time, the isostatic pressing process generally does not require adding lubricants to the powder, which reduces pollution to the product and simplifies the manufacturing process.