Part one of a special three part series on fluorine-based materials
Fluorocarbon compounds offer a remarkable blend of heat and fluids resistance.
Also referred to as fluoroelastomers, fluorocarbon compounds are thermoset elastomers containing fluorine. Fluorocarbons make excellent general-purpose seals thanks to their exceptional resistance to chemicals, oils, and temperature extremes (-15° F to +400° F). Specialty compounds can further extend the low temperature limit down to -22° F for dynamic seals and -40° F in static applications. Fluorocarbons typically have good compression set performance, low gas permeability, and resistance to ozone and sunlight. Over the last five decades, this remarkable combination of properties has prompted the use of fluorocarbon seals in a variety of demanding sectors. Though they were initially formulated for use in aerospace applications, fluorocarbons are now widely used in the automotive, appliance, fluid power, and chemical processing industries.
The original commercial fluorocarbon, Viton® A,
is the general-purpose type and is still the most widely used. It is
a copolymer of vinylidene fluoride (VF2) and hexafluoropropylene (HFP).
Generally composed of 66% fluorine, Viton A compounds offer excellent
resistance against many automotive and aviation fuels, as well as both
aliphatic and aromatic hydrocarbon process fluids and chemicals. Viton
A compounds are also resistant to engine lubricating oils, aqueous
fluids, steam, and mineral acids.
Viton B fluorocarbons are terpolymers combining tetrafluoroethylene (TFE) with VF2 and HFP. Depending on the exact formulation, the TFE partially replaces either the VF2 (which raises the fluorine level to approximately 68%) or the HFP (keeping the fluorine level steady at 66%). Viton B compounds offer better fluids resistance than the Viton A copolymers.
Viton GF fluorocarbons are tetrapolymers composed of TFE, VF2, HFP, and small amounts of a cure site monomer (Csm). Presence of the cure site monomer allows peroxide curing of the compound, which is normally 70% fluorine. As the most fluid resistant of the FKM types, Viton GF compounds offer improved resistance to water, steam, and acids.
Viton GFLT fluorocarbons are similar to Viton GF, except that perfluoromethylvinyl ether (PMVE) is used in place of HFP. The "LT" in Viton GFLT stands for "low temperature." The combination of VF2, PMVE, TFE, and a cure site monomer is designed to retain both the superior chemical resistance and high heat resistance of the G-series fluorocarbons. In addition, Viton GFLT compounds (typically 67% fluorine) offer the lowest swell and the best low temperature properties of the types discussed here. Viton GFLT can seal in a static situation down to approximately -40° F. A brittle point of -50° F can be achieved through careful compounding.
There are other fluorocarbon formulations in use, but hopefully this gave you a useful overview of some of the most common compounds. Please feel free to call us if you’d like to find out more about the benefits of fluorocarbon elastomers.
Viton® is a registered trademark of DuPont Dow Elastomers.