Elastomers

From the Greek word elastos – elastic, elastomers may be natural or synthetic materials (polymers), which have considerable elastic properties. Because they may also be moulded into shapes, which they retain, they qualify to be included in the category of plastics. Elastomers will tolerate repeated elongation and return to their original size and shape, in a similar way to natural rubber.

Some of the more common elastomers, to be found in the aerospace industry include:

• Buna ‘N’: It is also known as Nitrile and is a synthetic rubber, made (initially in Germany) by the polymerisation of butadeine and sodium (hence BuNa). It has excellent resistance to fuels and oils and is used for oil and fuel hoses, gaskets and seals. This material also has low ‘stiction’ properties when in contact with metal and is therefore, particularly suited to ‘moving-seal’ applications.
• Buna ‘S’: It is a relatively cheap material with a performance similar to natural rubber. It is often used for tyres and tubes, but its poor resistance to fuels/oils/cleaning fluids makes it unsuitable for seals.
• Fluoro-Elastomers: These have exceptional high-temperature properties and can be used at 250ºC. They are also solvent-resistant and are mainly used for high-temperature seals. These materials are expensive and has a common name as Viton.
• Neoprene: It has very good tensile properties and excellent elastic recovery qualities. It is also solvent-resistant and therefore, has a wide range of applications as fuel, hydraulic seals and gaskets. However, because of its special elastic recovery properties, it is also ideally suited to diaphragms and hydraulic seals.
• Poly-Sulphide Rubber: Although it possesses relatively poor physical properties, it has exceptionally high resistance to fuels and oils and is widely used for lining or sealing fuel tanks. It is also used for lightly stressed seals and hoses, which come into contact with fuels or oils. This compound is commonly known under the trade names of PRC or Thiokol.
• Silicone Rubber: It has very good high and low temperature properties (-80ºC to +200ºC). It is often used for seals, but is also used for the potting of electrical circuits, because of its ability to retain its rubbery state even at low temperatures.