Full definition
FKM rubber, commonly known as fluorocarbon or Viton, is a specialized class of synthetic rubber that is renowned for its exceptional chemical resistance and thermal stability. Comprising 64-70% fluorine by weight, FKM rubber is engineered to withstand a wide array of aggressive chemicals, including mineral oils, fuels, hydraulic fluids, and concentrated acids. This unique composition not only imparts superior resistance to many solvents that would degrade standard elastomers but also enhances its performance in high-temperature applications. Typical operational temperature ranges for FKM rubber span from -20°C to +200°C, with certain specialty grades capable of functioning at temperatures as low as -40°C. This makes it an ideal material for applications that encounter both extreme temperatures and harsh chemical environments.
In terms of mechanical properties, FKM rubber typically exhibits a hardness range between 60 to 90 Shore A, with tensile strengths varying from 10 to 17 MPa. One of its most significant advantages is its very low compression set at elevated temperatures, which allows it to maintain its shape and sealing capabilities over time. Additionally, FKM rubber possesses negligible gas permeability, making it suitable for applications where airtight seals are critical. It also displays inherent flame resistance, which adds to its utility in various industrial settings. The ASTM D2000 classification for FKM rubber is HK, indicating its suitability for demanding applications.
There are several types of FKM rubber categorized by their fluorine content. Type 1 (Viton A) contains approximately 66% fluorine and is the standard grade. Type 2 (Viton B) has a higher fluorine content of around 68%, offering better fuel resistance. Type 3 (Viton F) features the highest fluorine content, which translates to superior chemical resistance. Lastly, Type 4 (Viton Extreme/Aflas) is designed for base resistance and is made from TFE/propylene. Despite its numerous advantages, FKM rubber does have limitations; it shows poor resistance to low-molecular-weight esters, ketones, amines, hot water, and steam, along with reduced flexibility at low temperatures. Moreover, the high cost of FKM rubber, typically ranging from $20 to $80 per kilogram, can be a consideration in material selection. Its applications are diverse, including O-rings and seals in sectors such as oil and gas, chemical processing, automotive fuel systems, aerospace, semiconductor manufacturing, and pharmaceuticals.