The banning of asbestos, a material suitable for a wide range of temperatures and pressures, has brought up new opportunities. This is why new non-asbestos gaskets have been manufactured, products that must be correctly chosen according to the working parameters. Even though they are more expensive than asbestos, they prove to be more advantageous on the long term. If chosen correctly, the non-asbestos sealing lasts more than asbestos products, thus avoiding long periods of time needed to replace the gaskets. Some of the main materials used for replacing asbestos:
Expanded graphite is used in high temperatures and has a very good level of chemical resistance. Its exfoliated shape consists of a series of “worms” fabricated from exfoliated material that mix together by compression in order to form the materials’ consistency. It can be manufactured without any binding material and has a good level of resistance to fluids – without changing the state of aggregation, and offers a much longer durability. It is softer and has a better compression than gaskets fabricated from a mixture of fibres, thus providing a higher degree of tightness.
PTFE is used especially in the food and pharmaceutical industries due to its chemical resistance properties. Its wide scale usage is limited because of its predisposition to dilatation. Sintered and expanded PTFE is used for many applications that require sealing. The majority of sintered PTFE is being replaced at the moment with the so-called by-axial or stabilized PTFE. This material is mechanically treated in order to ensure a supplementary capacity of the material towards expansion, relaxation and extrusion.
Compressed fibre materials are based upon production techniques that were first used for fibres fabricated from compressed asbestos, the so called IT Techniques (gumI asbesT). The gaskets manufactured from compressed fibre are tightened together using elastomers. This provides safety during cutting and flexibility in manoeuvrability and assembly. During its usage, especially above 100 C, the elastomer will become hard and start degrading. Even though this does not necessarily affect the integrity of the gasket at place, it can affect its ability to provide a reliable performance considering the temperature and pressure. Generally, good quality gaskets contain a small quantity of binding material. Today, aramide, carbon, glass, cellulose fibres replace the asbestos ones, whilst for the growth of density mineral ones.