Isostatic Pressing

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The isostatic pressing process was pioneered in the mid-1950’s and has steadily grown from a research curiosity to a viable production tool. Many industries apply this technique for consolidation of powders or defect healing of castings. The process is used for a range of materials, including ceramics, metals, composites, plastics, and carbon.

Isostatic pressing applies a uniform, equal force over the entire product, regardless of shape or size. It thus offers unique benefits for ceramic and refractory applications. The ability to form product shapes to precise tolerances (reducing costly machining) has been a major driving force for its commercial development.

There are three basic types of isostatic pressing (Table 1). Cold isostatic pressing (CIP) is applied to consolidate ceramic or refractory powders loaded into elastomeric bags. Warm isostatic pressing (WIP) differs from CIP only in that shapes are pressed at warm temperature to about 100°C. Hot isostatic pressing (HIP) involves both temperature and pressure applied simultaneously to obtain fully dense parts (to 100% theoretical density), and is used mainly for engineered ceramics requiring optimum properties for high-performance applications.

Method	Advantages	Limitations	Cycle Time
Cold (room temperature)	Uniform green density	Slower than uniaxial pressing	5-30 min for wet bag
	Waxless, complex shapes	Parts may require post-machining	<1 min for dry bag
	Wet-bag: various shapes per cycle
	Dry-bag: automated, one part at a time
Warm (100°C)	Cost-effective for different shaped parts	Only suitable for specific applications	3-5 min
	Eliminates post sintering
Hot (2200°C)	Improves mechanical and physical properties	Cycle times can be slow	10-15h
	Near net shape
	Full density

Table 1: Comparison of Isostatic Pressing Methods

Isostatic presses are used for compressing pharmaceutical particles and raw material in to pre-determined shapes. The use of this pressurizing system ensures a uniform compaction pressure throughout the powder mass and a homogeneous density distribution in the final product. It is one of the most widely used pharmaceutical processing machines.

Working of Isostatic Press

Isostatic pressing is enabled to produce various types of materials from powder compacts by reducing the porosity of powder mixture. The powder mixture is compacted and encapsulated using isostatic pressure, by using pressure equally applied from all directions. Isostatic pressing confines the metal powder within a flexible membrane or hermetic container which acts as a pressure barrier between the powder and the pressurizing mediums, liquid or gas that surrounds it.

Advantages of Isostatic Press

• Powder is compacted with the same pressure in all directions, and, since no lubricant is needed, high and uniform density can be achieved.
• The process removes many of the constraints that limit the geometry of parts compacted unidirectionally in rigid dies.
• It is applicable to difficult-to-compact and expensive materials such as superalloys, titanium, tool steels, stainless steel, and beryllium, with material utilization that is highly efficient.

Application of Isostatic Press

Below is a list of some for the most common applications of the isostatic press.

• Pharmaceuticals
• Explosives
• Chemicals
• Food
• Nuclear fuel Ferrites

Figure 1: a) Cold isostatic press b) Hot isostatic press c) Warm isostatic press