FKM-O-RINGSO-Rings are the most commonly used type of sealing in the world. These are endless rings with circular cross-section articles, characterized by two fundamental dimensions: inside diameter and thickness. They are regulated by the international norm ISO 3601, which decrees standard sizes for this kind of product and the related tolerances; from that it is also possible to infer and extrapolate tolerances of non-conventional-sized O-Rings. They have a high degree of the finish and can assure both axial and radial seal. O-Ring seals are already more than 100 years old and were first registered as gas sealing rings in a water-cock patent by Thomas Alva Edison in 1882. Other patents for the use of O-Rings were granted in North America in 1930. It was only with the discovery and development of synthetic rubber around 1930 that O-Rings began their successful growth. Elastomers behave like highly viscous fluids: pressure exerted on them is propagated to practically the same degree in all directions (Law of Hydrostatics, Blaise Pascal). The radial and axial forces generated by the gasket housing are reinforced by the pressure of the fluid to be retained. The total sealing force thus created, increases as the pressure of the fluid rises. In addition to their excellent sealing properties, O-Rings are simple to mould, easy to mount and maintain and do not require large housings. On the basis of the type of housing, another crucial point is the hardness: the lower is this value, the more the O-Rings adapt easily and better to the surface structure of the contact surfaces. Instead, the more the fluid pressure rises, the more it is necessary to have a smooth housing surface and use a compound with a higher degree of hardness. Most common hardnesses are 60, 70, 80 and 90 IRHD. Furthermore, as regards dynamic applications, the most used O-Rings have a hardness degree of 75 IRHD.

FKM sealings can be used for the most diverse applications, among which we can mention the contact with high temperature and aggressive fluids, like gasoline or engine oil. Polymers do not react to pressurisation: in other words, it is only compression that creates seal. For this reason, this type of compound has also good compression set properties: this feature regards a test under crushing at high temperature (around 150/200°C), which can give an idea of the part sealing capability under these hard conditions.