Isostatic Pressinged Graphite Molds
Isostatic pressed graphite is a new type of carbon material. It began to be developed in the 1940s. The United States was the first country in the world to develop and produce isostatic pressed graphite, and products were marketed in the late 1950s. Isostatic pressed graphite has a series of excellent properties. It has excellent heat resistance, in an inert atmosphere, its mechanical strength increases with the increase of temperature, reaching the highest value at about 2500℃; Compared with ordinary graphite, isostatic pressed graphite has dense structure, good uniformity, low coefficient of thermal expansion, excellent thermal shock resistance, outstanding thermal and electrical conductivity, chemical resistance and homogeneity, and easy to process. Because of this series of excellent functions, isostatic graphite has been widely used in chemical, semiconductor, electrical, metallurgical, mechanical, nuclear and aerospace fields.
Isostatic molding is the key technology to ensure isotropic of isostatic graphite. The basic principle of isostatic pressure is PASCAL's law, which states that in a closed container filled with liquid, pressure applied at any point in the fluid must be transmitted to any part of the container with the same value. In the isostatic pressure process, pressure is transferred to the rubber mold through a liquid medium such as water, and the pressure is even in each direction. In this way, the powder is not oriented in the mold along the filling direction, but is compressed in an irregular arrangement. Thus, although graphite is anisotropic in its crystallographic properties, isostatic pressed graphite as a whole is isotropic.
The composition of isostatic graphite is roughly divided into three processes: feeding, pressurization and decompression. The powder is filled into a rubber mold and compacted by high-frequency electromagnetic oscillations to make it fine. After feeding, the mold is manually shaped and then sealed. At this time, the powder in the mold also contains a lot of air, which will affect the molding function and density of the product. Therefore, the sealing mold needs to be vacuumed to remove the air between the powder particles. In the production of some spherical products, the powder needs to be compressed into a ball, and then put into the isostatic pressure mold of the corresponding scale, such as Chengdu Carbon Co., Ltd. in the patent "a kind of coreless graphite data combination and pretreatment method", choose the first limited forming and then isostatic pressing molding molding process. After filling, the mold is transferred to a high-pressure vessel for pressure. The pressurization process needs to be carried out step by step. For example, the pressure is raised by 5MPa for a period of time, so that the remaining gas in the mold is partially discharged. At this time, the pressure in the high-pressure vessel is slightly decreased because the powder is compressed and the volume is shortened. Then the pressure is raised again to about 20MPa, and the volume of powder is shortened again after part of the gas is discharged. The pressure is then added to the desired working pressure, generally 100 to 200 mpa, and maintained at the selected high pressure for a period of time (20 to 60 minutes). The decompression process also needs to be slow because there is a small amount of air left in the powder, and the volume decreases significantly as the powder compacts. If the pressure drops precipitously, the compressed gas will expand rapidly, leading to cracks.
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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