Isostatic

Ewsuk K G 1986 Finai stage densification of aiumina during hot isostatic pressing PhD Thesis The Pennsyivania State University... 

Ewsuk K G and Messing G L 1986 A theoreticai and experimentai anaiysis of finai-stage densification of aiumina during hot isostatic pressing Hot IsostatIc Pressing Theories and Applications ed R J Schaefer and M Linzer (Materiais Park, OH ASM internationai) pp 23-33... 

Cold isostatic pressing Cold press molding Cold solvent cleaning Cold War... 

More complex shapes can be made by cold isostatic pressing (CIP). CIP uses deformable mbber molds of the required shape to contain the powder. The appHcation of isostatic pressure to the mold suspended in a pressure transfer media, such as oil, compacts the powder. CIP is not as easily automated as uniaxial pressing, but has found wide appHcation in the preparation of more complex shapes such as spark plug insulators (26). 

Isostatic Molding of Teflon TFE-Fluorocarbon Resins, preliminary information buUetia, E.I. du Pont de Nemours Co., Wilmington, Del., 1969. 

Other Industrial Applications. High pressures are used industrially for many other specialized appHcations. Apart from mechanical uses in which hydrauhc pressure is used to supply power or to generate Hquid jets for mining minerals or cutting metal sheets and fabrics, most of these other operations are batch processes. Eor example, metallurgical appHcations include isostatic compaction, hot isostatic compaction (HIP), and the hydrostatic extmsion of metals. Other appHcations such as the hydrothermal synthesis of quartz (see Silica, synthetic quartz crystals), or the synthesis of industrial diamonds involve changing the phase of a substance under pressure. In the case of the synthesis of diamonds, conditions of 6 GPa (870,000 psi) and 1500°C are used (see Carbon, diamond, synthetic). 

Probably the largest compound vessels built were two triple-wall vessels, each having a bore diameter of 782 mm and a length of 3048 mm designed for a pressure of 207 MPa (30,000 psi). These vessels were used by Union Carbide Co. for isostatic compaction unfortunately the first failed at the root of the internal thread of the outer component which was required to withstand the end load (40). A disadvantage of compound shrinkage is that, unless the vessel is sealed under open-end conditions, the end load on the closures has to be resisted by one of the components, which means that the axial stress in that component is high. 

With a batch process, such as hot isostatic compaction (HIP), heat exchange as used in a continuous reactor is not possible, and it is common practice to provide a furnace within the pressure vessel which is thermally insulated to ensure that the temperature of the vessel does not rise above 300°C. Most HIP operations involve gas pressures in the range 70—200 MPa (10—29,000 psi) and temperatures of 1250—2000°C, occasionally 2250°C (74). The pressure vessel may have a bore diameter from 27 to 1524 mm (75) and is nearly always provided with threaded closures sealed with O-rings made of elastomer provided the temperature is low enough. 

Quick Opening Devices. Breech block, tapered or interrupted thread, or pinned closures are often used when an end cover has to be removed quickly, as with some isostatic presses (126,136), or to enable the end cover to be removed easily after the vessel has been heated to high temperatures. 

P. J. James, ed.. Isostatic Pressing Technology, AppHed Science PubHshers, London, 1983, p. 214. 

In contrast to the cold isostatic pressing process, the hot process can readily employ powders having spherical or noninterlocking particles. The powder is simply poured in and vibration packed into a container of desired shape. The powder mass is then simultaneously compacted and bonded during the treatment. 

P/MForging. Even after conventional repressing of a P/M component, it is stiU difficult to increase density above 95%. However, hiU density in a P/M part improves its properties. Hot isostatic pressing in autoclaves works weU, especiaUy for titanium and superaUoy components, but the capital equipment is expensive and production rates are slow. 

---