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Captiva is aiming to utilise the properties of SMA shape memory alloy, an alloy that ‘remembers’ its shape and, with the application of heat, can be returned to that shape after being deformed.

When a shape memory alloy is in its martensitic form, it can be easily deformed to a new shape.

However, when the alloy is heated through its transformation temperatures, it reverts to austenite and recovers its previous shape with great force.

This process is known as shape memory.

The temperature at which the alloy remembers its high temperature form when heated can be adjusted by slight changes in alloy composition and through heat treatment.

In the nickel titanium alloys, for instance, it can be changed from above +100C to below -100C.

The shape-recovery process occurs over a range of just a few degrees and the start or finish of the transformation can be controlled to within a degree or two if necessary.

Many metallic O-ring seal designs utilise systems such as gas filling or internal springs to resist compression forces, while allowing deformation of the surface of the seal.

By harnessing the unique properties of shape-memory alloys to revert to its original shape, seals can be produced that are self-energising, without the need for external compressive loads to be applied.

By adjusting the transformation temperature the seals can be designed to operate only when system temperatures rise above critical limits, providing emergency seal integrity.

Captiva Sealing Consultants

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