Abnormally low or high temperatures, or exposure to oil, fuels, UV, or ozone will challenge many gasket materials. Rather than struggle with one that can’t meet all the requirements, put Teflon® and Viton® at the top of your list.
These fluorocarbon-based materials excel in many regards, but they also have some important differences. This blog will explain what they do well, and where the differences are.
Teflon Overview
Teflon is the trade name for PTFE, which is the well-known non-stick, low friction material. For gasket and sealing applications, its important properties are:
- Temperature range: -328 to +500°F
- Yield strength: 2,973 psi
- Chemical resistance: Everything except fluorine-based compounds and the alkali metals (Li, Na and K)
- Resists attack by UV and ozone
In addition, it’s soft (typically Shore D of 60 – 80). However, it tends to lack compressibility, and will creep under load. Plus, its elastic recovery is quite poor.
Viton Overview
Viton is also a tradename, in this case for an elastomer more properly known as FKM. Important properties as a gasket material include:
- Temperature range: -40 to +570°F
- Yield strength: 1,711 psi
- Chemical resistance: Withstands attack by hydrocarbon oils and fuels, susceptible to strong acids, alkalies, and ketones
- Resists UV and ozone
Importantly for good sealing, the hardness of FKM is 85 Shore A or slightly softer than PTFE. It also has good compressibility and recovery.
Choosing Between PTFE and FKM
For many applications, FKM wins out due to better recovery from compression, (which is especially important in joints where the gap varies, either due to temperature changes or being opened up repeatedly).
However, for wider chemical resistance, and flexibility at very low temperatures, PTFE is the way to go. The caveat is that joints must not put too much load on the material because it will creep. That means going to flange designs with physical compression limiters.
Consult the Gasket Material Experts
At Hennig Gasket and Seals we think we’ve seen every type of gasket application. If you need advice on material selection, we’re happy to share our experience. Call 1-800-747-7661 or contact us.
