>> Polytetrafluoroethylene (PTFE)
PTFE (polytetrafluoroethylene) is a synthetic, thermoplastic polymer which offers exceptional chemical resistance over a wide range of temperatures, and offers extremely low levels of friction.
PTFE lacks elasticity which prevents its use as an elastomeric-type sealing ring, however, it is commonly used for anti-extrusion as a back-up ring, and for non-stick requirements. Owing to its low friction and excellent chemical resistance, it is also commonly used for applications such as bearings, gears, rotary seals etc.
Non-filled (virgin) grades are stable up to +260°C and are quite flexible and resistant to breaking under tensile and compressive stresses. PTFE is also available with fillers added, to enhance its physical characteristics.
Typical fillers include:
- Glass fillers for improved deformation and wear.
- Inorganic fillers (e.g. calcium silicate, wollastonite) are used in a similar manner to glass fillers,
with reduced abrasiveness.
- Carbon-filled for considerable wear and deformation improvement, and increased thermal
- Graphite or molybdenum disulphide (MoS2) filled to lower the coefficient of friction.
- Bronze filled for excellent wear, deformation strength, thermal conductivity (reduced chemical resistance).
- Stainless steel fillers are used to increase wear resistance, and increased chemical resistance compared to bronze filled grades.
- Polyester filled for improved high temperature and wear resistance, for applications where running surfaces are non-hardened.
- Polyphenylenesulphide (PPS) filled for improved extrusion and deformation resistance.
- Polyimide (PI) fillers are used to increase wear and abrasion resistance, being polymeric, the abrasion of running surfaces is reduced.
- Combinations of some of the above are also often used to offer optimal performance in service.