Cold isostatic pressing

When we require complex shapes, we go for isostatic pressing. In this operation, pressure is applied from all sides uniformly with the help of a fluid. Thus, the problem of density variation, which could be there in dry pressing, can be avoided. The mold here should be flexible. When the pressing is carried out at room temperature, it is called cold isostatic pressing (CIP), and when carried out at high temperatures, it is called hot isostatic pressing (HIP). 

The wet bag process gives rise to a wide range of shapes and sizes. Tooling costs are low. The part size can be in the range of 150 mm to 2 m in diameter, and 460 mm to 3.7 m in height. However, the shape and dimensional control are poor. Because of this, green machining is needed. The cycle times are between 5 and 60 times. Hence, production rates are low. 

---

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). 

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. 

Cold-isostatic-pressing foUowed by vacuum sintering or HIP is also used to manufacture smaller intricate shapes. In this instance beryUium powder is loaded into shaped mbber bags and pressed isostaticaUy in a pressure chamber up to 410 MPa (60,000 psi). After the pressing operation the mbber bag is stripped from the part which is then vacuum sintered to about 99% of theoretical density at about 1200°C. If full theoretical density is required, the sintered part may be simply given a HIP cycle because there is no open porosity after vacuum sintering. In a similar manner, conventional axial cold-pressing... 

Cold isostatic pressing - [ADVANCEDCERAMICS - ELECTRONIC CERAMICS] (Vol 1)... 

The dried powder blend is pressed to desired shapes in hydraulic or mechanical presses. In special cases, a presintering followed by shaping to final form may be required. Large components and tools may require cold isostatic pressing followed by green forming. Rods and wires are formed by the extrusion process. 

Polycrystalline yttria-stabilized zirconia (YSZ-8) disks were prepared using 8 mol % Y203-doped zirconia powder (TOSOH zirconia, TZ-8Y, TOSOH Corp.). The powder was pressed uniaxially into disks which were cold isostatically pressed at 40,000 psi and then sintered at 1450°C for 4 h. Pt paste (Engelhard 6926) was painted on both faces of the YSZ-8 disks. Pt wires (0.0025 cm diam) were connected to the YSZ by using Pt meshes (150 X 150 mesh, 0.005 cm wire diam, Unique Wire Weaving Co., Inc.). 

All shaping methods (also called molding ) mentioned are well-known in the ceramic industry [244, 247], Selection criteria depend on economical and technical requirements. Simple shaped parts mainly produced by uniaxial pressing, cold isostatic pressing, casting and especially injection moulding are favoured for components with complex geometry [263]. 

The method has the advantage of avoiding interaction with die and punch materials and allows the sintering of complex shapes in controlled atmospheres. If the pieces concerned are small a large number can be processed in one operation so that the expense involved is moderate. As with cold isostatic pressing, the method avoids internal flaws and density variations due to the shearing action caused by die-wall friction. 

A new type of liquid-phase sintered SiC using yttria [1314-36-9J, Y20, as the oxide additive and submicrometer SiC powder for enhanced densification, produces a material which can be densified without the application of pressure (13). This material, sintered from cold isostatically pressed billets, appears to be comparable to silicon nitride in strength and fracture toughness. 

Cold Isostatic Pressing. In isostatic pressing, the powder is filled into flexible molds made of rubber or elastomers and subjected to hydrostatic pressure. The pressure is commonly in the range of 200 to 400 MPa. As a result of the uniform pressure, a much higher uniformity in density is achieved. Isostatic pressing has gained much... 

The milled powders were compacted in a metal die at a pressure of 100 MPa, then cold isostatic pressed at 200MPa. The size of the green compacts were 15 mm in diameter and 4 mm in height. 

Preformed metal oxide nanoparticles have also been used in the formation of inverse colloidal crystals [24-26]. Slurries of titania nanocrystals and the PS spheres are dropped onto a glass substrate and dried slowly (over 24 h) [24]. After pressing (cold isostatic press) the film is slowly heated to 520 °C to remove the PS and produce a titania matrix of >10 pmxlO mmx2-3 mm with ordered... 

Fig. 8.152 Photograph of an automated wet bag cold isostatic press (pressure chamber dimension 430 mm dia. 1,000 mm high, 200 MPa max. pressure) with mold washing and handling system (courtesy EPSI, Haverhill, MA, USA).

---