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 itsphysical 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 conductivity.
- 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.