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Rubber O-Rings
Industrial Applications of Rubber O-Rings
Most people have never heard of the o-ring before the Challenger disaster of 1986. Today, rubber o-rings have wide ranging applications and are found in equipment, devices and heavy machineries in practically every industry.
Some of the most common uses of the o-ring are found in industries such as:
Automotive manufacturing
Construction and heavy machineries
Food and drug manufacturing
Medical and pharmaceutical industries
Hydraulic and pneumatic applications
Aerospace and defense
Potable processing and distribution
Semiconductor manufacturing
The Mechanism of Sealing
The design of the rubber o-ring or its selection will have to take into account the mechanical mounting within which it is installed. When compressed, a calculated stress is applied to the o-ring against the contact surface of the mounting, and leakage is prevented so long as the contained fluid does not exert a pressure exceeding the stress at the contact point of the o-ring. The material of the rubber o-ring, which is highly incompressible, acts as a medium of transfer for the pressure of the contained fluid. An increase in pressure from the contained fluid correspondingly results in a rise in contact stress on the o-ring, thereby enabling the o-ring to maintain its sealing integrity even at high pressures.
Extrusion of rubber o-ring material through the mating components is a common mode of failure. Service conditions varies with each application, and material selection will have to take into consideration factors such as temperature extremes, chemical contact media, resistance to abrasion and wear, and pressure conditions in both static and dynamic environments. Material swelling is an indication of material compatibility with the contact fluid, and chemical attack can also cause brittle cracks and reduce the tensile properties of the material. Failure of rubber o-ring joint design can also be a simple matter of selecting the wrong o-ring size for a particular groove, or specifying an inappropriate material for a given application.
Description
FEP is a thermoplastic material with properties similar to PTFE. O-rings which are seamlessly coated with FEP have an elastic core made from FPM or VMQ and are used if very high thermal or chemical loads are present. The high chemical resistance of the coating protects the core against damage by the potentially aggressive medium.
FEP coated O-rings are used – similar to PTFE-rings – where the chemical resistance of the normal elastomer O-ring is no longer sufficient, but where a certain elasticity is needed. The elasticity is ensured by the inner ring and the chemical resistance is achieved by the seamless FEP coating.
Applications
FEP coated O-rings are perfectly suited for the chemical and petrochemical sector, medical technology, food sector, water and waste water technology and similar industrial applications. A typical application for FEP coated O-rings is the sealing of valve stems and as a secondary sealing element for slow switching and rotary movements.
Properties
· Very good chemical resistance against most liquids and chemicals
· Temperature range from approx. –60 °C to 200 °C [depending on inner ring material]
· No contamination of food, pharmaceutical or medical products
· Physiologically harmless, can be sterilised
· Sufficient elastic behaviour
· FEP O-rings can be replaced with standard O-ring seals without limitation
· No changes to the groove dimensions are necessary
· The O-rings are less flexible than elastomer O-rings due to the FEP coating. They can only be stretched minimally and have a lower elasticity or a higher permanent deformation
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