An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, forming a seal at the interface.
The O-ring may be used in static applications or in dynamic applications where there is relative motion between the parts and the O-ring. Dynamic examples include rotating pump shafts and hydraulic cylinder pistons. Static applications of O-rings may include fluid or gas sealing applications in which: (1) the O-ring is compressed resulting in zero clearance, (2) the O-ring material is vulcanized solid such that it is impermeable to the fluid or gas, and (3) the O-ring material is resistant to degradation by the fluid or gas. The wide range of potential liquids and gases that need to be sealed has necessitated the development of a wide range of materials.
O-rings are one of the most common seals used in machine design because they are inexpensive, easy to make, reliable and have simple mounting requirements. They have been tested to seal up to of pressure. The maximum recommended pressure of an O-ring seal depends on the seal hardness, material, cross-sectional diameter, and radial clearance.
O-rings can be produced by extrusion, injection molding, pressure molding or transfer molding.
The first patent for the O-ring is dated May 12, 1896, as a Swedish patent. J. O. Lundberg, the inventor of the O-ring, received the patent. The US patent for the O-ring was filed in 1937 by a then 72-year-old Danish-born machinist, Niels Christensen. In his previously filed application in 1933, resulting in Patent 2115383, he opens by saying, "This invention relates to new and useful improvements in hydraulic brakes and more particularly to an improved seal for the pistons of power conveying cylinders." He describes "a circular section ring ... made of solid rubber or rubber composition", and explains, "this sliding or partial rolling of the ring ...
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Cracks can be formed in many different elastomers by ozone attack, and the characteristic form of attack of vulnerable rubbers is known as ozone cracking. The problem was formerly very common, especially in tires, but is now rarely seen in those products owing to preventive measures. However, it does occur in many other safety-critical items such as fuel lines and rubber seals, such as gaskets and O-rings, where ozone attack is considered unlikely. Only a trace amount of the gas is needed to initiate cracking, and so these items can also succumb to the problem.
A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About 32 million metric tons of rubbers are produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubber, just like natural rubber, has many uses in the automotive industry for tires, door and window profiles, seals such as O-rings and gaskets, hoses, belts, matting, and flooring. They offer a different range of physical and chemical properties which can improve the reliability of a given product or application.
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