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, a fluororubber (FKM)-based elastomer.

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

FKM properties

• -20° to 250°C temperature range
• excellent compression set
• excellent weather resistance
• the. 10 MPa tensile strength
• good abrasion resistance
• not compatible with: amines, oxygen-containing 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
• the. 5 MPa tensile strength
• poor abrasion resistance
• incompatible with: hydrocarbon fuels, bases and acids, steam above 121°C, trichlorethylene, aromatic hydrocarbons.
• Compatible with: oils, brake fluids, hot and cold water, salt water, high molecular weight chlorinated hydrocarbons, fire resistant hydraulic fluid, ozone
• good punchability

Comparison silicone and FKM

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

Both have very similar abrasion resistance (fair to poor) which limits their performance in dynamic applications, and they have similar performances in long-life applications due to their excellent pressure and weather resistance.

Fluorocarbon rubber has a tensile strength of 10 MPa, higher than silicone, making it an ideal choice for high-force, high-pressure applications.

In general, the chemical structure of FKM makes it an ideal material for applications that require strong chemical compatibility with hydrocarbons, oils and fuels/petroleum.

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

The difference between FPM, FKM and Viton

In practice, the terms FPM, FKM and Viton very often lead to confusion and misinterpretation. All of these names are representative of a single raw material - fluororubber.

• FPM is the international abbreviation according to DIN ISO standard, while
• According to the American ASTM standard, FKM is the abbreviation for fluoroelastomers.
• Viton is the trademark of the company. DuPont performance elastomers.