Full definition
FKM, commonly known as Viton, is a type of fluoroelastomer that is highly regarded for its exceptional sealing capabilities in industrial applications. This material is engineered to withstand a wide range of aggressive chemicals, making it invaluable in sectors such as automotive, aerospace, and oil and gas. FKM seals offer a premium combination of chemical resistance, heat resistance, and low compression set, which are crucial for maintaining effective sealing under demanding conditions. For instance, FKM O-rings can resist mineral oils and greases at temperatures up to 200°C, as well as various automotive and jet fuels, hydraulic fluids, and aromatic solvents such as toluene and xylene. This makes FKM an ideal choice for applications where exposure to harsh chemicals is inevitable.
The temperature range for FKM seals extends from -20°C to +200°C for continuous use, with specialized grades like GLT (Low Temperature) and GFLT (Fluoroelastomer) capable of functioning at temperatures as low as -40°C. A critical performance metric for these seals is their compression set, which is excellent under high temperatures — typically between 15% to 25% after a 70-hour exposure at 200°C. This characteristic ensures that the seals maintain their dimensional integrity and sealing force over time, which is essential for preventing leaks in critical applications.
In terms of hardness, FKM seals are generally specified within the 70-90 Shore A range, with 75A being the most common specification. The material is classified under ASTM D2000 as HK, which outlines its physical properties and performance metrics. Standard colors for FKM O-rings include brown (75A), black (90A high-temperature), and green (Viton GLT low-temperature), allowing for easy identification based on application requirements. However, it is important to note that while FKM exhibits outstanding chemical resistance, it has limitations, including poor resistance to hot water or steam, amines, ketones, and certain low-molecular-weight organic acids. Additionally, standard grades may show limited flexibility at lower temperatures, which can affect their performance in some environments. The cost of FKM O-rings is significantly higher than that of NBR (Nitrile Butadiene Rubber), typically ranging from $1 to $20 each depending on size. However, this investment is often justified by the dramatically longer service life and reliability in harsh chemical environments.