The ubiquitous silicone O ring is without doubt one of the most widely utilized sealing elements in use today and with good reason. Cheap, effective, and simple to use, the silicone O ring is a sealing industry standard with a multitude of potential applications. The silicone rubber compounds used in the manufacture of silicone O rings lend the finished products an impressive range of positive working characteristics such as excellent weathering, ozone, acid, and heat resistance. The material does, however, have a couple of weaknesses including poor tensile and shear strength and low impermeability characteristics. These negative points notwithstanding, silicone O rings are an appropriate choice of general purpose sealant when used within their design parameters.
There are a wide range of materials that go into producing O ring seals, each of which lends the products a specific set of beneficial characteristics. Silicone compounds are one of the materials used to produce a range of general purpose O rings with a good average strengths. Silicone rubbers are typically combinations of carbon, hydrogen, and oxygen in combination with a silicone base polymer. They exhibit excellent resistance to a number of environmental elements and are generally nonreactive and stable. Silicone O rings are also fairly cheap to produce, thereby making them attractive from a cost perspective.
On the upside, silicone O rings exhibit excellent weathering characteristics with outstanding ozone resistance. Resistance to heat exposure is also one of the strong points of silicone O ring seals; minimum and maximum working temperatures range between –120°F (-84°C) and 450°F (232°C) respectively. They are also able to hold their own in environments which feature chemical exposure including those with specific alkali and acid elements. The fact that silicone rubber compounds may be formulated to include inert fillers which have no negative impact on the performance of the end product also make silicone O rings some of the most cost effective options available.
The downside of silicone O ring use centers around their poor general mechanical performance. They do not stand up well to shear forces and as such are not suited to rotary closure applications. In addition, the silicone rubbers used in O rings do not possess high abrasion resistance or tensile strength values. Silicone O rings are also unsuited for applications featuring steam or oil exposure and are fairly permeable. They still provide excellent general purpose sealing options, however, and offer a viable alternative to more expensive PTFE, nitrile, and fluorocarbon varieties.