Investigation of the Functional Mechanisms of PTFE Lip Seals

• Applicant: Professor Dr.-Ing. Werner Haas
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262224054

The common solution for sealing shafts in mechanical engineering is the radial lip seal made of elastomer. Since elastomeric radial lip seals relatively quickly reach their load limits, lip seals made of PTFE compounds are increasingly used in sealing technology. By utilizing PTFE (polytetrafluoroethylene) as sealing material the limitations of elastomers can be largely overcome. PTFE can withstand operating temperatures from -200°C to 250°C and has an almost universal chemical resistance. In addition to that PTFE has good dry running capabilities and a low coefficient of friction on technically relevant counter surfaces. For lip seals PTFE compounds (filled PTFE) are used to further improve the properties of PTFE.PTFE lip seals not only can replace elastomeric radial lip seals in critical sealing applications, but sometimes even may be used instead of relatively complex and expensive sealing systems such as mechanical seals. This allows the use of PTFE lip seals as universal seals in numerous cases which increases the operational reliability, improves the emergency operating features, eliminates the risk of fluid intolerance and reduces or even avoids downtime due to seal failures.Despite the enormous potential benefits for seal users through the availability of optimized PTFE lip seals, there is little progress by the seal manufacturers. This is mainly due to insufficient understanding of the functional mechanisms of PTFE lip seals. Without knowing the exact functional mechanisms a directed optimization is not possible. Therefore optimization can only be achieved through high experimental effort by trial and error.The aim of this research project is to resolve this drawback by conducting and publishing a comprehensive analysis of the static and dynamic functional mechanisms of PTFE lip seals.An important research method in this project is the numerical simulation of the flow processes in the sealing gap and sealing gap area. In particular the involved microscopic flow processes are considered because only thereby the elasto-hydrodynamic sealing gap is formed. Additionally the interaction of the macroscopic and the microscopic flow processes is studied. The findings from the simulations are validated and extended experimentally and are necessary for the derivation of the dynamic functional mechanisms of PTFE lip seals.Another important feature of this project is to study the interfacial effects in and around the sealing gap. These investigations are carried out experimentally and are primarily aimed at understanding the static functional mechanisms. Furthermore it is investigated whether interfacial effects have an impact on the dynamic functional mechanisms.

• DFG Programme: Research Grants