Viton
Viton is a brand of FKM, a synthetic rubber and fluoropolymer elastomer commonly used in seals, chemical-resistant gloves, and other molded or extruded goods. The name is a registered trademark of The Chemours Company previous Du Pont de Nemours and was introduced in 1957.
Viton fluoroelastomers are categorized under the ASTM D1418 and ISO 1629 designation of FKM. This class of elastomers is a family comprising copolymers of hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2), terpolymers of tetrafluoroethylene (TFE), vinylidene fluoride (VDF) and hexafluoropropylene (HFP) as well as perfluoromethylvinylether (PMVE) containing specialties. The fluorine content of the most common Viton grades varies between 66 and 70%.
While Viton can be sometimes distinguished from other types of rubber by its often green or brown colour, a more reliable test is its density of over 1800 kg/m3,[1] significantly higher than most types of rubber[2][3] (1010–1520 kg/m3).
Varieties
There are four families of viton polymers:
- A (dipolymers of VF2/HFP): general-purpose sealing, automotive and aerospace fuels and lubricants. Nominal polymer fluorine content: 66%.
- B (terpolymers of VF2/HFP/TFE): chemical process plant, power-utility seals and gaskets. Nominal polymer fluorine content: 68%.
- F (terpolymers of VF2/HFP/TFE): oxygenated automotive fuels, concentrated aqueous inorganic acids, water, steam. Nominal polymer fluorine content: 70%.
- Specialty types include GLT, GBLT, GFLT & Viton Extreme (copolymers of TFE/propylene and ethylene/TFE/PMVE): automotive, oil exploration, special sealing and ultra-harsh environments.
Applications
The performance of fluoroelastomers in aggressive chemicals depends on the nature of the base polymer and the compounding ingredients used for molding the final products (e.g. o-rings). This performance can vary significantly when end-users purchase Viton polymer containing rubber goods from different sources. Viton is generally compatible with hydrocarbons, but incompatible with ketones such as acetone and methyl ethyl ketone, ester solvents such as ethyl acetate, amines, and organic acids such as acetic acid. O-rings made of Viton are typically color-coded as black, but new gaskets, seals and O-rings should be green FKM or black FKM, but with a green mark on the outer edge.
Viton O-rings have been used safely for some time in SCUBA diving by divers using gas blends referred to as nitrox. Viton is used because it has a lower probability of catching fire, even with the increased percentages of oxygen found in nitrox. It is also less susceptible to decay under increased oxygen conditions.
Viton is used in after-market float valves ("needle and seats") for SU carburetors, for its fuel resistance and resiliency for sealing.
Viton o-rings are an upgrade to the original neoprene seals on Corvair pushrod tubes that deteriorated under the high heat produced by the engine, allowing oil leakage.
Viton tubing or Viton lined hoses are commonly recommended in automotive and other transportation fuel applications when high concentrations of biodiesel are required. Studies indicate that types B and F (FKM- GBL-S and FKM-GF-S) are more resistant to acidic biodiesel. (This is because biodiesel fuel is unstable and oxidizing.)
Viton o-rings are an alternative to Buna-N seals in BMW's automobile engine variable timing units, known as VANOS. In the VANOS, the Buna-N o-rings deteriorate. The Viton fluorocarbon o-rings have similar functional characteristics to Buna-N, but with much higher temperature and chemical resistance characteristics.
Viton/butyl gloves are highly impermeable to many strong organic solvents that would destroy or permeate commonly used gloves (such as those made with nitriles).
Precautions
At high temperatures or in a fire, fluoroelastomers decompose and may release hydrogen fluoride. Any residue must be handled using protective equipment.
