Viton is a brand of FKM , a synthetic rubber and fluoro elastomer commonly used in seals , other chemically resistant gloves, and molded or extruded materials. The name is a registered trademark of the Chemours Company (formerly DuPont ) and was introduced in 1957.
Witton fluoroelastomers are classified under the designation ASTM D1418 and ISO 1629 FKM . This class of elastomers is a family comprising the copolymers of hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2), terpolymers of tetrafluoroethylene (TFE), vinylidene fluoride (VDF) and hexafluoropropylene as well as perfluoromethylvinylether (PMVE) (HFP) ) with specifications. The fluorine content of the most common Witton grades varies between 66 and 70%.
While Viton can sometimes be distinguished from other types of rubber by its often green or brown color, a more reliable test is its density .1800 kg/m 3 , [1] much higher than most types of rubber [2] [3] (1010–1520 kg/m3 ).
Varieties
There are four families of Viton polymers:
- A (depolymer of VF2/HFP): General purpose sealing, automotive and aerospace fuels and lubricants. Nominal polymer fluorine content: 66%.
- B (terpolymer of VF2/HFP/TFE): chemical process plants, electric-utility seals and gaskets. Nominal polymer fluorine content: 68%.
- F (terpolymer of VF2/HFP/TFE): oxygenated automotive fuel, concentrated aqueous inorganic acid, water, steam. Nominal polymer fluorine content: 70%.
- Specialty types include GLT, GBLT, GFLT and Viton Extreme (copolymers of TFE/Propylene and Ethylene/TFE/PMVE): automotive, oil exploration, special sealing and ultra-harsh environments.
Application
The performance of fluoroelastomers in aggressive chemicals depends on the nature of the base polymer and the compound ingredients used to mold the final products (such as O-rings ). This performance can vary significantly when end users purchase Viton Polymers containing rubber goods from different sources. Viton is generally compatible with hydrocarbons , but incompatible with ketones such as acetone and methyl ethyl ketone , esters such as solvents ethyl acetate , amines , and organic acids such as acetic acid, O-rings made from Viton are usually color-coded as black, but new gaskets, seals and O-rings must be green FKM or black FKM, but with a green marking on the outer edge.
Viton O-rings have been used safely in scuba diving for some time by divers using gas mixtures referred to as nitrox . Viton is used because it is less prone to fire even with the increased percentage of oxygen found in nitrox. It is also less susceptible to decay under increased oxygen conditions.
The after-market float valve (“needle and seats”) for SU carburetors uses Viton for its fuel resistance and flexibility for sealing.
Viton O-Rings are an upgrade of the original neoprene seals on Corvair pushrod tubes that have worn out under the high heat produced by the engine, causing oil leaks.
When higher concentrations of biodiesel are required, Viton tubing or Viton lined hoses are commonly recommended in automotive and other transportation fuel applications. 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.) [ citation needed ]
Viton O-rings are an alternative to Buna-N seals in BMW’s automobile engine variable timing units, known as Vanos . In Vanos, Buna-N O-rings are screwed. 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 impervious to many strong organic solvents that destroy or permeate commonly used gloves (such as those made from nitrile ) .
Precaution
At high temperatures or in a fire, fluoroelastomers decompose and may release hydrogen fluoride . Any residue should be handled using protective equipment.
