FKM vs. FFKM: Comparison of the sealing materials FKM and FFKM

Comparison of the sealing materials FKM and FFKM

Sealing materials play a critical role in numerous industries, from automotive to chemical. Two particularly important materials in this area are fluororubber (FKM) and perfluoroelastomer (FFKM). Both offer outstanding properties that make them ideal for special applications.

Properties of FKM

FKM, also known under the trade name Viton®, is a fluororubber that impresses with its high chemical resistance and thermal stability.

1. Chemical resistance:
   – FKM demonstrates excellent resistance to a wide range of chemicals including oils, fuels, acids and solvents. This property makes it ideal for use in the automotive and aerospace industries as well as chemical processing.
2. Thermal stability:
   – FKM can permanently withstand temperatures from -20°C to +200°C, making it suitable for applications with extreme temperature fluctuations.
3. Mechanical properties:
   – The material is characterized by high tensile strength and elasticity, which makes it durable and resistant to mechanical stress.
4. Weather resistance:
   – FKM is extremely resistant to weather influences, ozone and UV radiation, which makes it suitable for outdoor use.

Properties of FFKM

FFKM, also known by trade names such as Kalrez®, is a perfluoroelastomer known for its near-universal chemical resistance and extremely high thermal stability.

1. Chemical resistance:
   – FFKM offers outstanding resistance to almost all chemicals, including highly corrosive acids, bases, solvents and reactive gases. This property makes it a preferred material in the chemical and petrochemical industries.
2. Thermal stability:
   – FFKM can permanently withstand temperatures from -15°C to +327°C. It retains its elastic properties even at extremely high temperatures, making it ideal for high temperature applications.
3. Mechanical properties:
   – While FFKM has excellent chemical and thermal resistance, it is mechanically less robust than FKM. It has lower tensile strength and abrasion resistance.
4. Weather resistance:
   – FFKM also shows high resistance to weather influences, ozone and UV radiation, similar to FKM.

Advantages of FKM

1. Wide temperature range: FKM can be used in a wide temperature range from -45°C to 204°C.
2. Excellent chemical resistance: FKM offers excellent protection against a wide range of chemicals.
3. Excellent resistance to gas and liquid penetration: FKM shows excellent resistance to gas and liquid penetration.
4. Excellent weather and ozone resistance: FKM is very resistant to weather and ozone.
5. Inherently Higher Fire Resistance: Compared to non-fluorinated hydrocarbons, FKM is inherently more resistant to combustion.
6. High density and high quality feel: Some types of FKM are used in everyday items such as watches due to their high density and high quality feel.
7. Good mechanical properties: FKM improves sealing performance through good compression set properties.
8. Suitable for Explosive Decompression, CIP, SIP and FDA: FKM is suitable for use in applications requiring explosive decompression, cleaning (CIP), sterilization (SIP) and FDA requirements.

Disadvantages of FKM

1. Can swell significantly in fluorinated solvents: FKM can swell significantly in contact with fluorinated solvents.
2. Not suitable for use with molten or gaseous alkali metals: FKM should not be used in applications with molten or gaseous alkali metals.
3. Higher cost: FKM is more expensive than other non-fluorinated hydrocarbons.
4. Not as chemically resistant as FFKM: Although FKM offers excellent chemical resistance for most applications, it is not as resistant as FFKM.
5. Smaller temperature range than FFKM: FKM has a lower temperature range compared to FFKM, but still offers better temperature resistance than other elastomers.
6. Incorrect choice of FKM type can lead to rapid failure: Choosing the wrong FKM type for an application can lead to rapid seal failure.
7. Costly low temperature grades: FKM grades suitable for low temperatures are also quite expensive.

Advantages of FFKM

1. Wide temperature range: FFKM can be used in a wide temperature range from -55°C to 330°C.
2. Excellent chemical resistance: FFKM offers the best chemical resistance in its class, similar to PTFE.
3. Excellent resistance to gas and liquid penetration: FFKM shows excellent resistance to gas and liquid penetration.
4. Excellent weather and ozone resistance: FFKM is very resistant to weather and ozone.
5. Self-extinguishing and non-flammable in air: FFKM is self-extinguishing and non-flammable.
6. High density: FFKM has a high density.
7. Good mechanical properties: FFKM improves sealing performance through good compression set properties.
8. Suitable for Explosive Decompression, CIP, SIP and FDA: FFKM is suitable for use in applications requiring explosive decompression, cleaning (CIP), sterilization (SIP) and FDA requirements.

Disadvantages of FFKM

1. May swell significantly in fluorinated solvents: FFKM can swell significantly in contact with fluorinated solvents.
2. Not suitable for use with molten or gaseous alkali metals: FFKM should not be used in applications with molten or gaseous alkali metals.
3. Larger coefficient of thermal expansion: FFKM has a larger coefficient of thermal expansion than other elastomers, so the seal seat size may need to be adjusted.
4. High costs: FFKM is very expensive and is therefore usually only used when no other elastomer is suitable.

Fields of application

FKM applications

1. automotive industry:
   – FKM is often used in the automotive industry for seals in engines, fuel systems and transmissions where high resistance to oils and fuels is required.
2. Aerospace:
   – In the aerospace industry, FKM is used in seals for aircraft engines and hydraulic systems due to its thermal stability and chemical resistance.
3. Chemical processing:
   – FKM is suitable for seals in chemical processing plants where moderate chemical resistance and high temperature resistance are required.
4. Fuel cells:
   – In fuel cells, FKM is used because of its resistance to aggressive chemicals and high temperatures, particularly in the sealing of cell stacks and other critical components.

FFKM applications

1. Chemical and petrochemical industries:
   – FFKM is used in extremely corrosive environments, such as reactors, pumps and valves, where it must withstand a wide range of aggressive chemicals.
2. Semiconductor industry:
   – In semiconductor manufacturing, FFKM is used in process seals and gaskets for etching and cleaning processes because of its high purity and chemical resistance.
3. Oil and gas industry:
   – FFKM finds application in the oil and gas industry, particularly in well seals and valves exposed to extreme chemical and thermal conditions.
4. Electronics industry:
   – FFKM is used in the electronics industry where high chemical resistance and thermal stability are required, for example in seals for high-performance electronics.
5. Fuel cells:
   – FFKM is ideal for use in fuel cells because it meets the extreme chemical and thermal requirements. It is often used in the seals of cell stacks to ensure no leaks and maximize fuel cell efficiency.

cost and availability

- Cost:
– FKM is more cost-effective and therefore economically more advantageous for applications that do not place extreme demands on chemical resistance and thermal stability.
– FFKM is significantly more expensive, which is justified by its superior properties in demanding applications.

- Availability:
– Both materials are available in various forms such as O-rings, seals and customized parts, however FKM is more commonly available in the market due to its wider application.

FFKM offers greater versatility and outstanding performance in extreme chemical and thermal conditions. It is the material of choice for applications that require the highest performance and where cost is a secondary consideration.

FKM, on the other hand, offers many of the same benefits as FFKM, but at a lower cost. It is ideal for applications that require high chemical and thermal resistance but do not meet the extreme requirements of FFKM.

Both materials are suitable for demanding applications such as explosive decompression, CIP, SIP and FDA applications. The choice between FFKM and FKM ultimately depends on the specific requirements of your application and your budget.

Fuel cell technology in particular shows that FFKM optimally meets the requirements thanks to its outstanding performance at high temperatures and in aggressive chemical environments.