Modeling of Rigidly Mounted PTFE Face Seals Subject to Small Strain Harmonic Vibrations

PTFE and filled PTFE are used in sealing applications such as rotary valves, quarter-turn ball valves and pipeline gaskets, among others. Many times, these seals are designed to operate below their yield point such that plastic effects are negligible and viscoelastic effects dominate. This may lead to leakage since these devices are placed in service environments that are subjected to vibration. In seals made of viscoelastic materials, this vibration can lead to separation of the seal faces due to the delayed recovery of the material. In this paper, the isothermal viscoelastic dynamic response of a PTFE seal subjected to a harmonic input and static preload from an ideally rigid opposing face is examined. The model is a hybrid that combines the Golla–Hughes–McTavish finite element approach, a delayed recovery creep model and a penalty method contact model. Parameters for the models are taken from experimental data using a Dynamic Mechanical Analyzer test for pure PTFE material. Results for a simple application show face separation magnitude as a function of frequency and harmonic displacement amplitude. Results show that face separation occurs in PTFE seals even for small amplitude harmonic vibrations and that this is due to delayed recovery at low frequencies and to the viscoelastic damping at higher frequencies. A threshold of static preload is also found above which there is no separation and a leakage estimation is presented.