O-rings are common seals used in many manufacturing industries. Because of their cost, simple production, easy installation and pressure resistance, they have found their way into a lot of common products, such as automobiles and engines. The aerospace industry has also put o-rings
to good use in many types of rockets.
O-rings function in so many applications because there is a diverse scope of material used in their fabrication. Many are made from rubber, or, more specifically, elastic polymers, or elastomers. These polymers are cured, often through vulcanization, resulting in a strong, durable and more elastic rubber. Different materials have different properties, though, with some being more elastic and others being more tear resistant, in addition to other qualities.
Because of the range of materials available, it can be difficult to determine which is appropriate for a project. While designers and contractors can help make a decision, there are many efficiencies and deficiencies that can guide or influence that decision as well.
Nitrile (Buna-N)
- Temperature range: Between -65 degrees Fahrenheit and 300 degrees Fahrenheit.
- Suited for: General purpose seals, such as petroleum oils, water and some hydraulic fluids. Buna-N is also resistant against tears and abrasive treatment.
- Deficiencies: Buna-N can have problems with automotive brake fluid, ketones, phosphate ester hydraulic fluids, and nitro and halogenated hydrocarbons. While it is ozone and weather resistant, this resistance is not infallible but can be supported through compounding.
- Applications: Nitrile functions well in applications that have limited temperature and resistance requirements.
Ethylene Propylene Rubber (EPR)
- Temperature range: Between -65 degrees Fahrenheit and 300 degrees Fahrenheit.
- Suited for: Skydrol, a hydraulic fluid, has a noxious smell and can irritate skin, and its corrosive properties can be damaging to equipment. EPR o-rings work well with Skydrol and other hydraulic fluids, as well as steam, water, silicone oils, brake fluids and alcohols.
- Deficiencies: Similar to nitrile, EPR is not perfect for a wide-range of applications due to wear and tear issues.
- Applications: The aerospace industry uses EPR o-rings in hydraulic pumps.
Fluorocarbon (Viton)
- Suited for: Fluorocarbon is an all around material that can handle a number of applications, especially diverse sealing jobs that involve movement. It is also suited for petroleum oils, silicone fluids and gases, acids and some halogenated hydrocarbons, like carbon tetrachloride.
- Deficiencies: Fluorocarbon is not recommended for Skydrol, amines, esters and ethers with low molecular weight and hot hydrofluoric acids.
- Applications: Fluorocarbon o-rings are very versatile, and features in many different automotive, appliance and chemical processing industries.
Neoprene
- Suited for: Neoprene can seal refrigerants in refrigeration and air conditioner units, as well as petroleum oils and mild acid resistance silicate ester lubricants.
- Deficiencies: Finished neoprene products are often compounded with lead-based agents, which can be hazardous to human health. Additionally, some people are allergic to basic neoprene. In a functional sense, it is not very resistant to petroleum lubricants and oxygen.
- Applications: Neoprene functions well in refrigeration units of air conditioning systems.
- Temperature range: Between -65 degrees Fahrenheit and 300 degrees Fahrenheit.
Polyurethane
- Temperature range: Between -65 degrees Fahrenheit and 212 degrees Fahrenheit.
- Suited for: Polyurethane features abrasion and extrusion resistance, as well as general toughness.
- Deficiencies: Applications requiring good compression and heat resistance would not be suitable for polyurethane.
- Applications: Polyurethane o-rings are often used for hydraulic fittings, cylinders and valves, pneumatic tools, and firearms.
Silicone
- Temperature range: Between -120 degrees Fahrenheit and 450 degrees Fahrenheit, although silicone o-rings have been shown to withstand -175 degrees Fahrenheit during short periods of exposure.
- Deficiencies: Silicone exhibits poor tear resistance, abrasion and tensile strength. Their poor abrasion resistance means they are better suited for static applications than dynamic. They do perform well with water, steam or petroleum fluids, either.
- Applications: High temperature fuel injection ports can use silicone o-rings.
- Temperature range: Between -100 degrees Fahrenheit and 500 degrees Fahrenheit.
- Suited for: Pure PTFE o-rings are very rigid and hard to apply, but PTFE encapsulated o-rings handle surface wear well, in addition to exhibiting corrosion and abrasion resistance, non-permeability, chemical inertness and low absorption.
- Deficiencies: Like silicone, PTFE is rigid and is better suited to static applications.
- Applications: Examples of PTFE o-ring use includes automotive steering devices and paint guns.
