Material selection – FKM

FKM, also known generically as FPM, are a family of elastomers that can be defined as “fluorinated compounds“. Thanks to the presence of fluorine in the formulation, they are considered high-quality compounds, with generally excellent resistance to high temperatures and the attack of chemical substances.

Characteristics and fields of use of fluorinated materials

FKM can be used in standard formulations with temperatures between -20°C and +210°C, for short periods up to +230°C. Thanks to specific compounds and advanced formulations, the limit of use at low temperatures can be extended to -45°C/-50°C (always considered on the basis of TR10 – check out this post “Operating temperatures of O-Rings“).

They are resistant to ageing, ozone, UV rays, oxygen, fuels, many organic solvents and chemical substances. It also has excellent compatibility with mineral and synthetic hydraulic fluids and vegetable oils.

In the nuclear field, they can be defined as compatible with high-energy radiation.

The low gas permeability also makes FKM the main choice in high (or absolute) vacuum applications, guaranteeing excellent results in Outgassing tests.

Weak points and limitations of FKM use

FKM have poor resistance to hot water and steam (although there are specific formulations for these uses that improve their performance in this environment) as well as electrical insulation.

This type of compound is not compatible with polar solvents (MEK), some organic acids, some hydraulic fluids based on esters and methanol, ammonia and some amines.

FKM classification

As for all elastomers, the vulcanization process is activated by substances called “accelerators” (or simply vulcanizing agents) and in the case of the FKM family, you can have bisphenol compounds (the vulcanized agent is bisphenol), which guarantee better performance at high temperatures, or peroxidic compounds (with peroxide accelerator, more commonly called “perox”), which guarantee better resistance to vapours and hydrocarbons.

The basic polymers used to package the compounds can be:

Copolymers

• Fluorine content 65% / 66%
• Usually defined with the letter “A”
• They are among the most widely used polymers for general applications

Terpolymers

• Fluorine content 66.5% / 67%
• Usually defined with the letter “B”
• They offer better resistance to fluids and oils than copolymers

Tetrapolymers

• Fluorine content: 67% / 69%
• Usually defined with the letter “G”
• Even better resistance to fluids and oils. Good resistance even to vapour (Viton® GF type), for low-temperature applications (Viton® GLT type) or as a combination of the two (Viton® GFLT type)

The major manufacturers of fluorinated polymers are:

Chemours: Viton®

3MTM: DyneonTM

Solvay Solexis: Tecnocflon®

Daikin: Dai-ElTM

The ORINGONE offer for FKMs

The different application needs and some specific applications have led ORINGONE to develop a complete and varied range of fluorinated compounds. In addition to materials that can be defined as standard (copolymers) in various colours and hardnesses (from 60ShA to 90 ShA), the choice includes solutions for food and pharmaceutical applications with compounds certified according to FDA and 3-A Sanitary Standard, materials developed for the valve and Oil&Gas industry in general with NORSOK M-710 certified materials for Anti Explosive Decompression, as well as the entire family of tetrapolymers for low-temperature applications down to -50°C.

Find out more about the techniques and materials for producing O-Rings, read this article.