FKM gaskets

FKM is the abbreviation for fluororubber compound, formerly also known as FPM. In order to differentiate between the terms, FKM is the international ISO designation for all fluoroelastomers, while FPM comprises the German DIN designation. This designation covers a whole group of different synthetic polymer blends whose common feature is the monomer VDF (vinylidene difluoride). The material belongs to the M-group of rubbers, which are characterized by a saturated carbon main chain. The fluororubber compound is sold under the trade names Tecnoflon®, Dai-El® and others. Viton® is one of the most important FKM brands and describes a brand name for flourelastomers, which was coined by the US company DuPont. The material (e.g. the quality of FKM 75 Shore) is of very high quality and has excellent properties, so that the material is considered an "all-round" elastomer. This is due to the combination of good heat and ozone resistance with resistance to a wide range of chemicals.

Available FKM materials at Rehm Dichtungen Ehlers GmbH

We have high-quality FKM qualities available in sheet and roll form.

CooperStandard

Other qualities

The properties of FKM as a sealing material

Depending on the fluororubber compound, the material has different properties for different defined applications. The most important types include the copolymers VDF and HFP (hexafluoropropylene) and terpolymers VDF, HFP and TFE (tetrafluoroethylene).

Terpolymers are more resistant to chemicals than copolymers due to their higher fluorine content and are also more resistant to high temperatures. Copolymers, on the other hand, have advantages in compression set and show higher flexibility at low temperatures. Flat gaskets made of FKM have a significantly higher density than other elastomers such as flat gaskets made of EPDM or NBR. Compared to other sealing materials, a greater mass is required to achieve the required volume. In this context, stretching with fillers and plasticisers is not practical, which means that the manufacturing process is considered to be significantly more complicated.

The functionality of the FKM is mainly determined by the cross-linking system used, of which there are three important ones. Cross-linking with blocked diamines does not make the material resistant to steam. If the gasket material is bisphenolically cross-linked, products made from the material are more reliable in processing, but less resistant to some fuels. Peroxide cross-linking makes the material well resistant to hydrolysis and steam. In summary, it can be said that above all the copolymers used and the cross-linking system used have an influence on the operating temperature range of FKM seals.

Regarding the physical properties of FKM, it can be said that due to the stable fluorine-carbon bonds, a high penetration resistance is achieved, whereby the material insulates well electrically. Furthermore, the sealing material is impermeable to gas and very abrasion-resistant.

In terms of mechanical properties, flat gaskets made of FKM are very resistant and show low impact elasticity. The elongation at break of this material is >200%. Another decisive advantage in terms of mechanical properties relates to the low compression set, which means that the material deforms only very slightly under the effect of pressure.

In terms of thermal properties, the material proves to be heat-resistant in the temperature range up to 200°C or 250°C. Thus, they are listed by us as heat-resistant flat gaskets under gasket materials for special requirements.

Due to the high fluorine content, which is approx. 65 to 70%, flat gaskets made of FKM are considered flame-retardant.

The advantages of FKM at a glance

In varying degrees, the different types are characterised by a number of advantages. The higher the fluorine content, the better the properties with simultaneously decreasing low-temperature flexibility. Fluororubber has good chemical and thermal resistance.

FKM is:

• Excellent resistance to:
  • Heat
  • Ozone, weathering and ageing
  • Light
  • Fuels, oils and flame-retardant pressure fluids HFD
  • organic solvents
• antistatic
• flame-retardant
• Very abrasion resistant

In addition, the material has a good insulating effect.

Not resistant are any FKMs in hot water, steam, in polar solvents, glycol-based brake fluids and in low-molecular organic acids. FPM, especially Viton®, is also incompatible with ketones and ester solutions. Likewise, seals made of FKM are not resistant to hydrogen fluoride, ammonium compounds and methanol. The low-temperature flexibility is moderate compared to other elastomers.

Differentiation of FKM gaskets from EPDM gasket material

Seals made of FKM and EPDM are characterised by their resistance to polar media. Furthermore, both materials are resistant to UV light, ozone and weathering. Both sealing materials also have good insulating properties. However, differences can be found in the temperature range, fuel resistance and resistance to hot and water vapour. While EPDM gaskets are temperature resistant in a temperature range between -30 and +100°C and are resistant to hot and water vapour, FKM gaskets have heat resistance up to 200°C or 250°C and fuel resistance.

If the use of flat gaskets made of NBR is ruled out due to high operating temperatures and complex chemical requirements, flat gaskets made of FKM can be considered as the suitable alternative.

The way to your flat gasket made of FKM

The FKM qualities available from us and stocked as standard are subjected to a quality control at the beginning of the goods receipt process. Following approval, the gasket material is stored in the form of rolls and sheets at the appropriate storage location. Only then can we guarantee a consistently high quality, also with regard to the respective sealing material.

FKM belongs to the group of sealing materials that can be processed in all our production processes. The selection of the most suitable production process for your flat gaskets made of this material depends on the number of pieces, the desired contour and the thickness of the respective material. On the selected process, the unprocessed roll or sheet material is then processed into your individual FKM flat gasket. In addition, it is possible to apply a self-adhesive film to the roll or sheet material in advance and then process it into your self-adhesive gaskets with the help of our manufacturing processes. Self-adhesive FKM gaskets serve exclusively as an assembly aid without changing the material properties. In addition to the production of flange and flat gaskets, we also offer unprocessed rolls or sheets as well as metre goods cut to size for your own further processing. Here, too, we offer the option of applying a self-adhesive finish to the material in advance.

After completion of the production and a renewed quality control, the flat or flange gaskets are packed and shipped to you.

Areas of application for FKM seals

The main areas of application include low-wear seals. They are mainly used in industries such as aerospace, the chemical industry or vacuum technology, but also in household appliances. Thanks to its resistance to fuels and oils, the material is also widely used in the petroleum industry. Especially in areas where there is permanent fuel contact. FKM flat seals, like the ones we cut for you, are used in the field of energy supply and in chemical plants.

We will be happy to answer whether the material is also suitable for your purposes. Please contact our customer service and let us advise you.

FAQ