FKM is a high-performance synthetic rubber material. This material belongs to a class of elastomers known as fluoroelastomers, which are specialized polymers developed for applications where standard rubber would degrade rapidly. FKM is primarily used in sealing applications, such as gaskets and O-rings, due to its exceptional resistance profile. The acronym FKM serves as the official designation for this material.
Defining FKM and Fluoroelastomers
FKM is defined chemically as a class of fluorocarbon-based synthetic rubbers, meaning its polymer structure incorporates a significant number of fluorine atoms. The presence of these fluorine atoms is the fundamental reason for the material’s superior performance characteristics. FKM is the American Society for Testing and Materials (ASTM) standard designation, defined under standard D1418, for this family of materials.
The chemical backbone of FKM is a fluorinated hydrocarbon polymer, with vinylidene fluoride (VDF) serving as the common monomer in all FKM types. Different monomers are copolymerized with VDF to create various grades. The high fluorine content, typically ranging from 62% to 70% by weight, creates extremely strong carbon-fluorine bonds that resist chemical attack and thermal breakdown.
“Viton” is a widely recognized brand name for a type of FKM material, originally developed by DuPont and now owned by Chemours. FKM is the generic, industry-standard term used by all manufacturers. While all materials sold under the Viton brand are FKM, not all FKM materials are Viton, though the terms are often used interchangeably in the marketplace.
Essential Performance Characteristics
FKM is selected for demanding applications due to its outstanding thermal stability, allowing it to maintain structural integrity under high heat. Most standard FKM compounds can withstand continuous service temperatures up to 200°C and tolerate intermittent exposure up to 260°C. This stability is directly linked to the high bond energy of the carbon-fluorine connections.
FKM also exhibits exceptional chemical compatibility, making it highly resistant to a broad spectrum of aggressive fluids that would typically cause other elastomers to swell or disintegrate. This includes resistance to petroleum-based oils, hydraulic fluids, and many solvents. The material’s unique structure prevents the absorption and subsequent swelling that occurs when conventional rubbers are exposed to these liquids.
This resistance extends to fuels, including gasoline and those containing alcohol, such as ethanol and biodiesel blends, which is a requirement for modern automotive systems. The polymer’s dense structure provides low permeability to gases and vapors. This property is highly valued in sealing applications where maintaining pressure or preventing leakage is paramount.
Another performance characteristic crucial for sealing is the material’s low compression set. Compression set refers to the permanent deformation that remains after an elastomer has been subjected to a constant compressive force over a period of time. FKM’s ability to return nearly to its original shape after prolonged compression ensures that seals and gaskets maintain their sealing force throughout their service life, even at elevated temperatures.
Standard Applications and Industry Use
FKM is the material of choice for components that must function reliably in demanding operating environments. Common finished products include O-rings, gaskets, shaft seals, and diaphragms, which are all used to prevent fluid or gas leakage between components. These seals are often found in machinery where high temperatures and exposure to corrosive substances are routine.
The automotive industry relies heavily on FKM, particularly in engine and fuel systems. FKM seals are utilized in fuel injectors, quick-connect fittings, and manifold gaskets to ensure longevity and prevent vapor emissions. The material’s resistance to chemically complex fuels like biodiesel is especially important for modern engine design.
In the aerospace sector, FKM is used in hydraulic and lubrication systems for aircraft, where seals must perform reliably across a wide temperature range and at high altitudes. The material’s stability under thermal cycling and resistance to specialized aviation fluids is a necessity for flight safety. FKM is also employed in the chemical processing and petroleum industries for pumps, valves, and analytical instruments that handle harsh acids, bases, and hydrocarbons.
Understanding FKM Grades and Types
FKM is a family of elastomers, with grades categorized primarily by their chemical composition and fluorine content. These variations are engineered to optimize the material for specific applications, often balancing chemical resistance against low-temperature flexibility. The standard types include Type 1 (dipolymers) and Type 2 (terpolymers).
Type 1 FKM represents the standard, general-purpose grade with a fluorine content around 66%. Type 2 FKM adds a third monomer, raising the fluorine content, typically to the 68% to 69% range. This significantly enhances resistance to chemical attack and high temperatures.
Increasing fluorine content to maximize chemical resistance can sometimes negatively affect the material’s flexibility at lower temperatures. To address this, specialized grades, such as those that include perfluoromethylvinylether (PMVE), are engineered to improve low-temperature performance while maintaining acceptable chemical resistance. Selecting the correct FKM grade involves a trade-off dictated by the specific environmental conditions of the application.