Fluoroelastomer (FKM)

FKM stands for fluoroelastomer, a family of synthetic rubbers designed for high-performance sealing applications. Best known under the trade name Viton® (originally developed by DuPont, now Chemours), FKM is valued for its exceptional resistance to heat, chemicals, oils, and fuels.

Unlike general-purpose rubbers such as Nitrile (NBR) or EPDM, FKM is a fluorinated polymer, which gives it superior durability and mechanical properties in aggressive environments. It performs reliably at elevated temperatures (typically up to +230°C) and maintains its sealing integrity when exposed to hydrocarbons, solvents, acids, and even ozone.

FKM rubber mouldings are commonly used in industries such as automotive, aerospace, chemical processing, oil and gas, and industrial manufacturing, where standard rubber compounds would degrade or fail under stress. Typical applications include rubber gaskets, FKM seals, and other custom components.

FKM is a high-performance rubber material known for its excellent chemical resistance, particularly to fuels, oils, and solvents. It also performs well at elevated temperatures, typically up to +230°C, making it ideal for demanding environments such as automotive, aerospace, and industrial applications. Its low compression set means it maintains its shape and sealing ability over time, and it offers strong resistance to ozone, UV, and weathering, contributing to long service life.

These qualities make FKM especially well-suited for high-integrity components like custom rubber seals, where long-term performance under stress is critical.

However, FKM also has some drawbacks. It is more expensive than general-purpose rubbers like NBR or EPDM, which may be a factor in cost-sensitive projects. Its low-temperature flexibility is limited, with standard grades becoming brittle below -20°C, although low-temp variants are available. Processing FKM can also be more complex, often requiring high moulding temperatures and post-curing. Additionally, it is not suitable for use with certain chemicals like ketones or some esters.

Here at Kea-Flex, we’ll help you choose the best material for your application. Whether you’re developing precision mouldings or specialised rubber products for extreme environments, we’ll guide you toward the most suitable solution based on your project’s unique requirements.

Viton® is a brand name for a type of fluoroelastomer (FKM), so while the terms are often used interchangeably, they are not exactly the same. Fluoroelastomer refers to the broader material category—a family of synthetic rubbers known for their excellent resistance to heat, chemicals, and oils.

Viton® was originally developed by DuPont (now produced by Chemours) and is one of the most recognised and widely used FKM materials. There are other FKM compounds available from different manufacturers, each with similar base characteristics but potentially varying in formulation or performance. So, while all Viton is FKM, not all FKM is Viton.

Yes, FKM is suitable for injection, compression, and transfer moulding. As a versatile fluoroelastomer, it can be processed using all the major rubber moulding techniques, depending on the part design, production volume, and performance requirements.

Injection moulding is often preferred for high-volume production and complex shapes, as it allows for precise control and fast cycle times. Compression moulding is commonly used for larger or simpler parts, and is ideal when working with high-viscosity FKM compounds. Transfer moulding provides a balance between the two, offering good detail and dimensional control with less waste than compression moulding.

That said, FKM requires careful temperature control and mould design due to its higher curing temperatures and specific shrinkage characteristics. In many cases, a post-curing process is recommended to improve chemical resistance and remove any residual volatiles from the moulded parts. Proper tooling, release agents, and cycle timing are essential to achieve consistent, high-quality results across all three moulding methods.

Yes, FKM does shrink during moulding, and this must be carefully considered during the design and toolmaking process. The typical shrinkage rate ranges from 1.5% to 2.5%, although this can vary depending on the specific FKM compound, the geometry of the part, and the moulding method used.

Factors such as curing temperature, mould pressure, and filler content can all influence the final dimensions of the moulded component. Because of this, precise tooling adjustments and allowances are necessary to ensure that the finished part meets the required tolerances.

In many cases, sample parts are produced and measured to fine-tune the mould before full production begins. Proper planning for shrinkage is essential when working with FKM to achieve accurate, high-quality results.

FKM compounds are typically available as either dipolymers or terpolymers, and the choice between them can affect performance depending on the application.

Dipolymers are made from two monomers, usually vinylidene fluoride (VDF) and hexafluoropropylene (HFP). These grades offer excellent resistance to oils, fuels, and chemicals, and provide good flexibility and mechanical strength. They’re commonly used in standard FKM applications where a balance of properties is needed.

Terpolymers, on the other hand, include a third monomer, typically tetrafluoroethylene (TFE), which improves the material’s chemical resistance and high-temperature stability. Terpolymers are often preferred for more aggressive environments, such as those involving oxidising chemicals or sustained high heat.

FKM (fluoroelastomer) is known for its strong and stable mechanical properties, particularly in demanding operating conditions. One of its key advantages is its high tensile strength, typically ranging from 7 to 12 MPa, depending on the specific compound and curing process. This allows FKM components to maintain their integrity under mechanical stress.

FKM also has a low compression set, meaning it retains its shape and sealing ability even after prolonged compression, making it ideal for static sealing applications like O-rings and gaskets. Its elongation at break generally falls between 150% and 300%, providing a good balance of flexibility and durability.

In addition, FKM offers excellent abrasion and wear resistance, along with good tear strength, although it is not as tear-resistant as some other elastomers. Its hardness typically ranges from 60 to 90 Shore A, allowing for varied applications across different industries.