O Rings and Oil Seals are mechanical gaskets shaped like a torus. They are an elastomer loop with a cross-section that is disc-shaped, intended to sit in a groove and compressed between two or more parts during assembly. This creates a seal at the interface.
The can be made use of in dynamic applications or in static applications. In dynamic applications, between the parts and the O-ring there exists a relative motion. Dynamic O Rings and Oil Seals examples contain hydraulic cylinder pistons and rotating pump shafts.
O Rings and Oil Seals are one of the most regularly used seals in machine design due to their many qualities. They are easy to make, inexpensive, reliable and have simple requirements for mounting. They have the ability to seal tens of megapascals pressure (thousands of psi).
An O-ring joint design, to be successful, needs a rigid mechanical mounting to apply a deformation to the O-ring that is predictable. This puts in a measured mechanical stress near the contacting surfaces of the O-ring. Leaking cannot occur provided that the fluid pressure being contained will not surpass the O-ring contact stress. Fortunately, the contained fluid pressure transfers across the o-ring material that is basically incompressible, and the stress of contact increases with rising pressure. Because of this, high pressure can be easily sealed with an O ring providing there is no mechanical failure. Extrusion through the mating parts is the most common failure.
The seal is planned to include a point contact between sealing faces and the O-ring. This enables a high stress locally, with ability to hold high pressure, with no yield stress exceeding of the O-ring body. The O-ring materials accommodate, because of its flexible nature, imperfections in the mounting parts. It is still important nevertheless to preserve good surface finish, especially at low temperatures of those mating parts where the seal rubber comes to its temperature of glass transition and turns increasingly crystalline. Especially in dynamic applications surface finish is also important. A surface that is too smooth will not allow the seal to be lubricated adequately by a fluid film and a surface finish that is too rough will abrade the surface of the o-ring.
Some of the Synthetic rubbers used in O rings and Oil Seals are Thermosets like Butadiene rubber, Butyl rubber, Chlorosulfonated polyethylene, Epichiorohydrin rubber, Ethylene propylene diene monomer, Ethylene propylene rubber, Fluoroelastomer, Nitrile rubber, Perfluoroelastomer, Polyacrylate rubber, Polychloroprene, Polyisoprene, Polysulfide rubber, Sanifluor, Silicone rubber, Styrene butadiene rubber.
Thermoplastics include, Thermoplastic elastomer styrenics, Thermoplastic polyolefin, Thermoplastic polyurethane polyester, Thermoplastic etheresterelastomers copolyesters, Thermoplastic polyamide Polyamides, Melt Processible Rubber, Thermoplastic Vulcanizate.