Isostatic Pressing Transmission Medium

Using the pascal's principle to make isostatic pressing of powders, there are two main points in its forming:

a. the hydrostatic pressure or gas is equal to compressed stress at any point (i.e., isostatic pressure)
b. liquid or gas of internal powder by liquid, solid or gas, solid interface, if the pores of solid billet be connected with liquid or gas, it cannot compressed pores, so need to use the ompressed air tight bag package in order to suppress the solid.
Isostatic pressing transmission medium
There are three types of isostatic pressure media: liquid, solid and gas.
According to the characteristics of pressing transmission, liquid and gas can delivery pressure without loss., it called quasi-static, the pressure medium called quasi-static medium. Conversely, the transmission medium without this characteristic is called non quasi static medium. A solid medium is a non quasi-static medium.

1) Gas transmission medium
Generally use Ar, He, N2 and other gases.
Gases are easily compressed and even liquefied at high pressure. Therefore, under normal temperature, the gas transmission medium is applied to no more than 100MPa, or used in hot isostatic pressing. The following figure is the relationship between Ar density and pressure at room temperature.

2) Liquid transmission medium
Commonly used liquid  transmission medium has glycerin, water, mineral oil, butter and so on. Liquids also have compressibility, and they do not clot when the pressure is below 50MPa. At high pressure, the liquid may even solidify. When the water pressure exceeds 400MPa or the pressure of mineral oil exceeds about 600MPa, it will solidify. Therefore, the pressure at liquid isostatic pressing is usually less than 300MPa. For higher pressures, molten salts, glass melts, and various metal melts can also be used as pressure transmitting media, especially in hot isostatic pressing, where the maximum pressure is up to 1000MPA.

3) Solid pressure transfer medium
When the isostatic pressure exceeds 400MPA, usually use a solid of good elasticity or plasticity, such as rubber, plastic film, talcum powder, boron nitride powder, CR2O3 powder, zinc stearate as pressure medium; if the pressure continues to increase, to 1500MPA, available iron powder, nickel powder, talcum powder, etc. as the pressure transmitting medium
 

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