FKM

Introduction to FKM Rubber

FKM rubber is a family of fluoroelastomers produced by copolymerizing vinylidene fluoride (VDF) with other monomers such as hexafluoropropylene (HFP), tetrafluoroethylene (TFE), or perfluoromethyl vinyl ether (PMVE). The fluorine content (typically 66-70%) gives it its unique properties. Developed in the 1950s for aerospace applications, FKM is cured via bisphenol or peroxide systems for heat resistance. Grades vary by monomer composition: Type 1 (VDF-HFP) for general use, Type 2 (VDF-HFP-TFE) for better chemical resistance, Type 3 (VDF-TFE-PMVE) for low-temperature flexibility, and specialty types like FFKM for ultra-high performance. It is compounded with fillers like carbon black, curing agents, and processing aids. FKM is expensive but offers unparalleled durability in harsh conditions.

 

Characteristics of FKM Rubber

FKM excels in environments where other rubbers fail, with properties tailored for extreme service. Here are its key characteristics:

  1. Mechanical Properties: FKM has good tensile strength (10-20 MPa), elongation at break (150-300%), and compression set resistance. It maintains flexibility and resilience under stress, with excellent vibration damping. However, it has lower tear strength than some rubbers and may require reinforcement for high-abrasion applications.
  2. Chemical Resistance: Outstanding resistance to hydrocarbons, fuels, oils, solvents, acids, and oxidizing chemicals due to its fluorinated structure. It withstands aggressive media like hot oils, aromatic hydrocarbons, and chlorinated solvents. However, it's vulnerable to polar solvents (e.g., ketones, esters), amines, and superheated steam unless specially formulated.
  3. Thermal Properties: Exceptional heat resistance, operating from -20°C to +250°C (or up to +300°C for short periods in some grades). Low-temperature grades can go down to -40°C without embrittlement. It has low thermal conductivity and resists thermal cycling well.
  4. Durability and Aging: Superior resistance to ozone, UV, weathering, and radiation. It exhibits minimal degradation in high-temperature aging and has low gas permeability, making it suitable for vacuum applications. Flame retardancy is inherent due to fluorine.
  5. Processing and Cost: Processed via compression, transfer, or injection molding, but requires specialized equipment due to its high viscosity and potential for scorching. It's one of the most expensive elastomers (5-10 times costlier than NBR), justified by its longevity and reduced maintenance in critical applications.
  6. Other Properties: Excellent electrical insulation, low outgassing in vacuum, and compatibility with biofuels and aggressive fluids. It can be vulcanized with peroxides for metal bonding or bisphenols for general use. Specific gravity is high (1.8-2.0), and it's available in FDA-compliant grades for food/pharma contact.

In formulations, FKM is rarely blended due to compatibility issues but can be compounded with metal oxides for acid acceptance or fillers for cost reduction.

 

Applications of FKM Rubber

FKM's premium properties make it essential in high-stakes industries where failure is not an option:

  1. Aerospace and Aviation: Used in O-rings, seals, gaskets, and fuel system components for jet engines, handling extreme temperatures and aviation fuels.
  2. Automotive Industry: In fuel injectors, turbocharger hoses, valve stem seals, and emission control systems, resisting biofuels, oils, and heat.
  3. Oil and Gas Sector: Critical for downhole seals, packers, and valves in drilling equipment exposed to sour gas (H2S), high pressures, and temperatures.
  4. Chemical Processing: Employed in pumps, valves, diaphragms, and lined pipes for handling corrosive chemicals and solvents.
  5. Semiconductor and Electronics: In plasma-resistant seals and O-rings for vacuum chambers and etching equipment due to low outgassing.
  6. Other Uses: Pharmaceutical equipment seals, food processing gaskets (FDA grades), and military applications like protective gear. Emerging in electric vehicles for battery seals exposed to coolants.

FKM production focuses on sustainability with recycling initiatives. It's a go-to material for reliability in extreme conditions, with global demand growing in energy and transportation sectors.