In demanding sealing applications such as engine bay and powertrain systems, aircraft fuel systems and chemical processing equipment, fluoroelastomers FKM remain the material of choice. Today, performance is defined not only by resistance to high temperature and aggressive media, but also by long-term sealing force retention, dimensional stability and controlled surface appearance throughout service life. In this context, the importance of filler selection is increasing, as it allows engineers to tailor both the mechanical and physical properties of seals and their colour and surface uniformity, particularly in applications where light or precisely colour-matched FKM compounds are required.
Carbon black remains a traditional benchmark as a reinforcing filler in elastomers, but its inherent black colour makes it unsuitable for light or accurately coloured FKM compounds. High-performance mineral fillers offer an alternative that enables bright, tintable compounds while allowing precise adjustment of mechanical and physical properties through controlled particle morphology and appropriately selected surface treatments. This opens the way to designing seals with the required profile of hardness, mechanical resistance and long-term stability, without the need to use carbon black as the main reinforcing component.
Comparative study in a standardized FKM system
In a comparative study, HPF The Mineral Engineers evaluated ten high-performance fillers in a standardized, peroxide-cured FKM matrix based on Viton GBL 600S. All compounds were developed using identical curing systems so that differences in final properties resulted solely from the type of filler and the applied surface modification. A compound containing carbon black N990 was used as the reference.
The study compared surface-treated, short-needled wollastonite from the Tremin 283 600 product series with kaolin fillers in two forms, hydrous kaolin (Chinafill KBE 1) and calcined kaolin (CALK 89/1.3). The test programme covered rheology and cure behaviour, mechanical properties and tear resistance, hardness and compression set, hot air ageing, as well as resistance to selected representative fluids such as jet engine oil and fuel.
At equal target hardness, compounds with mineral fillers produced light, tintable FKM materials with predictable processing behaviour and clear advantages over the carbon black system. Key benefits included lower compression set, high tear resistance and improved dimensional stability after thermal ageing and exposure to process fluids. High-performance mineral fillers thus demonstrated the potential to replace carbon black in applications where, in addition to achieving a specified hardness, the durability and appearance of seals are also critical.
Tremin 283 600 as a universal filler for FKM
Among the evaluated fillers, Tremin 283 600 showed the widest and most balanced performance window. Narrow Mooney viscosity and cure torque ranges support stable processing, while finished compounds combine low compression set with good strength and useful elongation. The use of different surface treatments enables targeted, precise tuning of the final properties of FKM composites to the requirements of a given application.
Kaolin fillers offer a property profile that complements wollastonite. Hydrous kaolin, depending on the applied surface treatment, allows the formulation of compounds oriented either towards high strength or high flexibility. Calcined kaolin, in turn, emphasises dimensional stability, low compression set and minimal swelling in aggressive media. The combination of different kaolin grades with short-needled wollastonite gives material designers wide possibilities to balance stiffness, flexibility and resistance to environmental influences in service.
Importance of filler selection in FKM seal design
The conclusions of the study indicate that high-performance mineral fillers can surpass carbon black in key parameters such as compression set, tear resistance and dimensional stability, while maintaining the same compound hardness. At the same time, they enable the use of light, design-flexible FKM compounds that can be colour-matched to construction or identification requirements in complex technical systems.
From a materials engineering perspective, high-performance mineral fillers represent a robust replacement solution for carbon black in demanding sealing applications where long-term stability of properties and control of external appearance are essential. Appropriate selection of filler type, particle geometry and surface modification makes it possible to optimise FKM compounds for operating conditions in engine compartments, aircraft fuel systems or chemical processing installations, where seals must maintain functionality and dimensional integrity despite prolonged exposure to high temperatures and aggressive media.
High-performance sealing applications made from FKM with mineral fillers
