Teflon as a Gasketing Material

Teflon has certain unique characteristics which make it useful as gasketing material. It is immobile to all chemicals except molten alkali metals and fluorine at high temperatures and pressures. This i because Teflon has high heat resistance, low coefficient of friction and is non-adhesive. It is, moreover, capable of continuous service at temperatures from -90 to 500 F, without loss of efficiency. However, when heated to around 700 F, Teflon polymerizes into a solid that is in inflexible form. The other side to it is that Teflon is subject to cold flow under pressure and does not have the compressibility (without flow) and other properties necessary for satisfactory gasketing.

For proper gasketing, a gasketing material should have robust crack resistance. In addition, since solid polymerized Teflon gaskets permanently laterally deform under sustained high pressures, they cannot be re-used because of cold. When solid Teflon is used, for example, for packing around shafts in centrifugal pumps, the rubbing speed becomes a crucial factor. Frictional heat is developed at a slower rate in unlubricated Teflon packing than in other materials because of the low coefficient of friction of Teflon. However, the low thermal conductivity of Teflon slows down heat dissipation and due to its high coefficient of thermal expansion, it reduces clearance as the temperature rises. Therefore, it has been necessary to use means to provide space for expansion when using Teflon packing in high-speed applications.