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.
Modes of Failure
Extrusion: Extrusion can be the result of using a rubber o-ring
material that is too soft, and selecting a higher modulus elastomer may be
the solution. Other contributing factors include excessive clearances,
material degradation or using an incorrect size of o-ring.
Chemical Degradation: Failure is identified as swelling, cracking,
discoloration and blistering. Chemical degradation is often the result of
incompatibility of the elastomeric material with the contact chemical media.
Thermal Degradation: Radial cracks may be seen on the surface of the
o-ring that is exposed to the highest temperature. Cause may be due to
repeated temperature excursions and thermal properties of the material.
Selecting a seal with higher temperature compatibility may resolve this
problem.
Plasma Degradation: Seal displays discoloration with a powdery
surface deposition. Result of plasma incompatibility of seal material.
Perfluoroelastomer (FFKM) is the material of choice for applications in
plasma environments.
Abrasion and Wear: Flat surface is observed in an otherwise circular
rubber o-ring cross-section. The deformed surface is the result of abrasion
and wear on the contact surface of the seal, and is in a direction parallel
to the line of motion.
Compression Set: The o-ring or rubber seal exhibits a deformed flat
surface on its otherwise circular cross section, on the side that is in
direct contact with the mating surfaces. Caused by exceedingly high
compression, volume swell, excessive temperature as well as improperly cured
elastomers.
Contact our material specialists today for a free consultation.
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