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Dr. Dmitri Kopeliovich
Isostatic pressing is the powder compaction method involving applying pressure from multiple directions through a liquid or gaseous medium surrounding the compacted part.
Cold isostatic pressing (CIP) is conducted at room temperature.
A flexible (commonly polyurethane) mold immersed in a pressurized liquid medium (commonly water) is used in the cold isostatic pressing method (see the scheme below):
There are two types of cold isostatic pressing: wet bag and dry bag.
In the wet bag method the mold is removed and refilled after each pressure cycle. This method is suitable for compaction of large and complicated parts.
In the dry bag method the mold is an integral part of the vessel. The dry bag method is used for compaction of simpler and smaller parts.
The cold isostatic pressing (CIP) method has the following advantages as compared to the die cold pressing method:
Hot isostatic pressing (HIP) involves isostatic pressing conducted at increased temperature.
As a pressure medium a gas (Nitrogen or Argon) is used.
The work pressures, which are applied in the hot isostatic pressing method, are commonly between 15,000 psi to 44,000 psi (100 MPa to 300 MPa).
Hot isostatic method (HIP) combines pressing and sintering, causing consolidation of powder particles, healing voids and pores. The part shrinks and densifies, forming sound high strength structure.
Cans made of stainless steel, or mild steel are used in the method.
The method may be used without a mold. In this case the part is first compacted by cold isostatic pressing method, and then it is sintered in order to close the interconnecting porosity. The sintered (but still porous) part is then pressed isostatically at high temperature without any can (mold).
Titanium alloys, high speed steels, super-alloys, hard alloys and various ceramics are produced by the hot isostatic method (HIP).
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