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Isostatic pressing

A well-known production technique in the field of ceramics, this process consists in shaping simple form items by compacting powder in an isostatic as opposed to uniaxial manner.

The process
Ceramic powder is poured into a soft polymer mould (silicone, polyurethane) in the shape of the item.
The mould is sealed before being immersed in a liquid (oils, water+oil).
The liquid and thus the mould are then pressurised (150 to 500 Mpa)
At the heart of the container and of the liquid, the mould will be subjected to the same pressure on all its surface points thanks to the fluid, an isostatic pressure.
Once the cycle is over, the mould is taken out of the liquid and the piece is stripped.
There is no temperature increase during this shaping process.

This process only works with powders specially designed for cold pressing: pressing grain or atomised powder. Thanks to its organic content (<5%) the grain is poured evenly into the mould, lubricating the compression phase, giving good agglomeration and mechanical resistance of the compressed block. This organic fraction disappears when the powder is fritted.

A ceramic product is obtained by the high-temperature consolidation and densification of a granular structure.
This consolidation is accompanied by a shrinking of the granular structure (≈15 to 25% of the initial volume).
The shaping stage is always a critical one in the manufacture of ceramics :

  • It determines the mechanical and physical properties of the ceramic piece after fritting. During this stage, internal defects can occur (pores, cracks…) which will not disappear after firing.
  • It has an effect on the distortions incurred during the thermal treatment if the material produced has an uneven density.

Isostatic pressing guarantees the shaping of a component with homogeneous density and performance.
In order to guarantee the successful sequence of shaping and manufacturing operations, the choice of pressing powder is paramount.
Cerafast has selected the best suppliers of quality pressing grain so that reliability and performance can be guaranteed.

Cerafast makes standard use of automatic fixed-mould isostatic pressing; this technique is a variation of isostatic pressing which makes automatic the stages of mould-filling, pressing and stripping.

It is particularly adapted to the serial shaping of pipes and bars. It guarantees the repeatability of the pressing result in terms of:

  • Dimensions (diameter, length)
  • Geometric characteristics (concentricity, linearity)
  • Pressed density.