PTFE (polytetrafluoroethylene, tradename Teflon) is a polymer material commonly used in sealing applications that offers unparalleled stability and sealing characteristics across an extremely wide range of temperatures, as shown in the table below.
In this article, we will discuss polymer sealing at the two temperature extremes: cryogenic and high temperature.
Cryogenic Applications
Cryogenic seals are used with super-cooled media, like liquid hydrogen or compressed natural gas, at temperatures below -238°F and down to -460°F (absolute zero). Cold temperatures like this are rough on a seal because at these temperatures most materials begin to exhibit highly brittle behavior and lubricants typically cannot be used because they will freeze. PTFE seals, however, can handle temperatures all the way down to -450°F and are capable of dry running because of their extremely low friction. PTFE cryogenic seals are used in industries like oil & gas, pharmaceuticals, and aerospace.
High Temperature Applications
PTFE seals work well at the other end of the spectrum, too. They can continue to function in extreme temperatures up to 600°F, and continuous operating temperatures up to 600°F. Note that a filler may be required to enable the PTFE to dissipate heat more quickly. It’s not uncommon to see PTFE seals in petroleum or steam applications where temperatures greatly exceed 200°F.
Spring-energized Seals
In order to retain sealing power under extreme temperatures, many engineers and designers go with spring-energized PTFE seals. The spring provides optimal sealing by forcing the lip of the seal against the mating surface and helps to account for dimensional changes as a result of temperature fluctuations.
Conclusion
PTFE is an ideal sealing material for both extremely high temperature applications and demanding cryogenic applications. It retains its key sealing properties stiffness, strength, dimensional stability (may require spring energizer), low friction, and chemical compatibility even in the most aggressive operating conditions.
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