FKM seal

FKM seals, often also referred to as Viton seals, are sealing elements made from fluoroelastomer (fluororubber, FKM). The material is suitable for applications with increased requirements for temperature resistance and media resistance and is used in industry and plant engineering for demanding sealing tasks.

Properties of FKM seals

High chemical resistance:

FKM has a very high resistance to a wide range of aggressive media. These include acids, alkalis, oils, fuels and numerous solvents. FKM seals are therefore suitable for applications with permanent contact with chemically aggressive substances.

Temperature resistance:

FKM seals are designed for a broad temperature range. Typical service limits are between approximately −20 °C and +200 °C, depending on the respective compound. This makes them suitable for thermally highly loaded applications.

Weather and ozone resistance:

The material is resistant to UV radiation, ozone and changing weather influences. As a result, FKM seals can also be used in technically demanding outdoor applications.

Elasticity and mechanical stability:

FKM retains its elastic properties even under high thermal and chemical loads. At the same time, the material offers good mechanical strength for reliable and durable sealing.

Application areas of FKM seals

Chemical industry:

Use in reactors, pumps, valves and piping systems with contact with aggressive chemicals.

Automotive industry:

Use in fuel systems, engines and transmissions where high temperatures and media resistance are required.

Oil and gas industry:

Suitable for applications with hydrocarbons, high temperatures and increased pressure requirements, for example in production facilities and refineries.

Aerospace:

Use in systems with extreme ambient conditions as well as contact with fuels and hydraulic fluids.

Advantages of FKM seals

FKM seals combine high chemical resistance with excellent temperature and weather resistance. These properties ensure a long service life and reliable sealing function even under demanding operating conditions.

Difference from other sealing materials

Compared with EPDM seals or NBR seals, FKM offers significantly higher resistance to aggressive chemicals and high temperatures. EPDM and NBR are suitable for less demanding applications and offer economic advantages. Silicone also has good temperature resistance, but does not achieve the chemical resistance of FKM.

Limits and disadvantages of FKM seals

FKM seals are more cost-intensive than many other elastomers. At very low temperatures, the material can lose flexibility. In addition, the processing of FKM requires special manufacturing conditions due to its material properties. These factors should be taken into account when selecting the material.

In addition to seals, FKM is also available as FKM rubber sheet for technical applications.

Technical details and material variants for FKM seals

Material variants and their properties

Copolymers VDF/HFP (vinylidene fluoride / hexafluoropropylene):

This FKM variant offers a good combination of temperature resistance and flexibility.

• Temperature resistance: up to approx. 200 °C
• Higher flexibility at low temperatures compared with terpolymers
• Suitable for applications with moderate chemical requirements and increased low-temperature flexibility

Terpolymers VDF/HFP/TFE (vinylidene fluoride / hexafluoropropylene / tetrafluoroethylene):

Terpolymers have a higher fluorine content and therefore offer increased thermal and chemical resistance.

• Temperature resistance: up to 250 °C and above, depending on the compound
• Very high chemical resistance
• Suitable for applications with extreme temperatures and aggressive media

Crosslinking systems and their effects

Blocked diamines:

• Limited resistance to water vapour
• Suitable for dry applications without steam exposure

Bisphenolic crosslinking:

• Good chemical resistance and processability
• Limited resistance to certain fuels
• Suitable for versatile industrial applications

Peroxidic crosslinking:

• Very high resistance to steam and hydrolysis
• Suitable for humid environments, steam and hydraulic applications

Mechanical and physical properties

• Density: higher than EPDM or NBR seals
• Abrasion resistance: high, suitable for applications with friction
• Elongation at break: > 200 %
• Low compression set for a durable sealing effect

Temperature and chemical resistance

• Temperature range: approx. −20 °C to +200 °C
• Special FKM compounds up to over +250 °C
• Very high resistance to fuels, oils and hydrocarbons
• Resistant to many organic and inorganic acids and alkalis
• Resistant to most organic solvents

Limitations and special features

• Limited low-temperature flexibility at very low temperatures
• Not suitable for polar solvents, hot water, water vapour, ketones and esters
• Higher material costs compared with standard elastomers

Typical application areas

• Automotive industry: engines, transmissions, fuel systems
• Chemical industry: reactors, pumps, valves
• Oil and gas industry: refineries, production technology
• Aerospace: fuel and hydraulic systems

The selection of the suitable FKM material variant and the appropriate crosslinking system significantly influences the performance and service life of the seal in the respective application.

Designs and delivery forms of FKM seals

FKM seals are available in different designs to meet the respective technical requirements. In addition to standard dimensions, customised solutions are frequently used.

Standard seals

Standard FKM seals are manufactured in common dimensions and are suitable for series applications in mechanical and plant engineering. They are available at short notice and cover many typical use cases.

Custom-made FKM seals

For special geometries, particular installation situations or deviating material requirements, FKM seals are manufactured as cut pieces or moulded parts to drawing. This enables optimum adaptation to pressure, temperature and medium.

FKM as flat gasket and moulded part

FKM is used both for flat gaskets and for complex moulded parts. Flat gaskets are suitable for static sealing, while moulded parts reliably withstand dynamic loads as well.

As starting material, in addition to sealing rings, FKM rubber sheets are also available, from which individual seals can be manufactured.

Selection criteria for FKM seals

When selecting a suitable FKM seal, several technical factors should be taken into account:

• Service temperature and temperature peaks
• Contact media and chemical load
• Pressure conditions and mechanical stress
• Static or dynamic application
• Installation situation and tolerances

Careful coordination of these criteria ensures that the seal seals permanently and achieves a long service life.

Quality, standards and industrial requirements

FKM seals for industrial applications meet high quality requirements. Depending on the area of use, specific standards, material approvals or industry-specific specifications may be relevant.

For safety-relevant applications, the selection of tested qualities with documented material characteristics and consistent batch quality is recommended.

Advice and individual solutions

The selection of the suitable FKM seal depends strongly on the respective application. For complex requirements or special media, technical advice is recommended in order to optimally coordinate material variant, crosslinking system and geometry.

In addition to standard solutions, individual FKM seals can be realised as cut pieces or custom-made parts and enable precisely fitting solutions for demanding industrial applications.

Frequently asked questions about FKM seals

What are FKM seals?

FKM seals are made from fluororubber (FKM), a synthetic elastomer with high resistance to temperatures, chemicals and oils.

Where are FKM seals used?

FKM seals are used in technically demanding areas such as the chemical industry, automotive industry, oil and gas industry as well as in aerospace.

What advantages do FKM seals offer?

FKM seals offer very high chemical resistance, high temperature resistance, low ageing and a long service life.

How temperature-resistant are FKM seals?

Typical FKM seals are designed for temperatures from approximately −20 °C to +200 °C. Special compounds can withstand temperatures up to +250 °C or above.

What chemical resistance do FKM seals have?

FKM seals are resistant to oils, fuels, many solvents and numerous aggressive chemicals.

How is the size of an FKM seal determined?

The dimensions depend on the installation situation, the components to be joined as well as the pressure and temperature requirements of the application.

How are FKM seals maintained?

FKM seals should be kept clean and regularly checked for wear or damage in order to ensure a permanently reliable sealing effect.

How long do FKM seals last?

The service life is often several years and depends on temperature, pressure, media contact and mechanical stress.

Can FKM seals be used for food applications?

Standard FKM is generally not intended for food contact. For such applications, special, appropriately certified fluororubber qualities are available.

How are FKM seals installed?

FKM seals are inserted into the intended grooves or sealing surfaces and held in position by defined compression.

Are FKM seals UV-resistant?

FKM offers good resistance to UV radiation and is therefore also suitable for outdoor applications.

How do FKM seals differ from other sealing materials?

Compared with NBR or EPDM, FKM offers significantly higher temperature and chemical resistance and is suitable for technically more demanding applications.

How is the tightness of an FKM seal checked?

Tightness is checked by pressure tests, visual inspections or application-specific leakage testing procedures.

Can FKM seals be cut or adapted?

FKM seals can be manufactured as cut pieces or custom-made parts in order to be adapted exactly to the respective application.