Silicone vs. FKM

Silicone vs. FKM – What are the differences?

Silicone and FKM compete in many applications. This article examines the properties of silicone rubber and how it compares to fluororubber, an elastomer based on fluororubber (FKM).

Although silicone and fluororubber are quite similar in properties, the fluorine groups (trifluoropropyl) provide significant differences in chemical resistance and compatibility, resulting in a wider range of potential applications.

FKM properties

• -20° to 250° C temperature range
• excellent compression set
• excellent weathering resistance
• approx. 10 MPa tensile strength
• good abrasion resistance
• not compatible with: amines, oxygenated solvents, paint solvents
• compatible with: acids, alcohols, oxygenated solvents, alkalis, fuels and hydrocarbons, mineral oils
• good punchability

Silicone properties

• -50° to 230° C
• excellent compression set
• excellent weather resistance
• approx. 5 MPa tensile strength
• poor abrasion resistance
• not compatible with: Hydrocarbon fuels, alkalis and acids, steam above 121 °C, trichloroethylene, aromatic hydrocarbons.
• compatible with: oils, brake fluids, hot and cold water, salt water, high molecular weight chlorinated hydrocarbons, refractory hydraulic fluids, ozone
• good punchability

Comparison of silicone and FKM

Silicone and fluorocarbon have very similar temperature ranges, but silicone is generally better suited for low-temperature applications at -20°C. Hydrofluorocarbon is able to withstand higher temperatures at 250° C, although silicone with the addition of heat stabilizers and flame retardants can exceed this and offer temperature ratings up to 300° C, making it a solution for high temperature applications.

Both have very similar abrasion resistance (moderate to poor), which limits their ability to perform well in dynamic applications, and they have similar abilities to perform well in applications requiring long life due to their excellent resistance to pressure and weathering.

The tensile strength of fluororubber is higher than that of silicone at 10 MPa, making it an ideal potential selection for high force and high pressure applications.

In general, FKM’s chemical structure makes it an ideal material for applications requiring strong chemical compatibility with hydrocarbons, oils and fuel/petroleum.

Silicone is ideal for high temperature static sealing applications, but due to poor compatibility with oils and hydrocarbons, FKM is a better choice in such cases.

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