O-Ring Materials: Strengths, Limitations, and More
O-Ring Materials: Strengths, Limitations, and More
Named for their distinctive circular shape, O-rings are versatile elastomer gaskets that create a tight seal between two mechanical components. Although O-rings generally look alike and function similarly, subtle differences determine where a particular O-ring may be used. Material selection is a key consideration, as elastomers vary in their chemical and mechanical properties. This influences their performance in specific sealing tasks. Therefore, when purchasing O-rings, it's crucial to consider the specific needs and limitations of your application rather than opting for a one-size-fits-all solution.
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This guide explores common O-ring materials in detail, including their strengths, limitations, and typical applications. If you have questions after reviewing this material selection guide, feel free to contact our team at Arizona Sealing Devices or browse our O-ring selection.
O-Ring Materials: Strengths, Limitations, and Applications
At Arizona Sealing Devices, we work with various elastomers to produce O-rings. Below are the materials we most frequently use:
Buna-N/Nitrile
Nitrile is a synthetic rubber known for its excellent chemical resistance properties. Unlike other rubbers, nitrile resists fuels, oils, and many diluted acids and alkalines. This makes nitrile/Buna-N O-rings the best choice for automotive, aerospace, and marine fueling. Its high tensile strength and thermal resistance further enhance its use in these industries. However, nitrile should not be exposed to ethers, esters, ketones, or chlorinated hydrocarbons.
Aflas®
Aflas is another elastomer combining chemical, thermal, and electrical resistance properties, resisting acids, bases, and heat up to 446°F. It is popular in oil, aerospace, and general industrial environments. However, Aflas should not be used in direct contact with automotive fuels as it swells more than other elastomers.
Butyl
Butyl is ideal for vacuum-sealing, offering extremely low gas permeability. Its resistance to ozone, sunlight, and good shock-dampening capabilities make it a useful choice in hydraulic applications, particularly those utilizing synthetic lubricants. However, ethylene propylene has largely replaced butyl due to its superior durability.
Ethylene Propylene
Ethylene propylene is a modern alternative to butyl. It exhibits low gas permeability and outstanding heat, weather, and ozone resistance. These traits make it one of the most versatile elastomers for O-ring seals, often used in automotive cooling and brake systems and outdoor applications. However, it is susceptible to hydrocarbons.
Fluorocarbon (Viton®)
Fluorocarbon O-rings offer exceptional chemical and high-temperature resistance. They are highly durable and versatile, making them valuable in aircraft engines and automotive fuel systems. Nevertheless, fluorocarbon has limitations, including intolerance to low temperatures and certain chemicals like ketones, amines, low molecular weight esters, and ethers.
Fluorosilicone
Known for extreme-temperature stability, fluorosilicone is popular in aerospace and general-purpose O-ring applications, especially outdoors. Nevertheless, it is not suitable for dynamic sealing due to its low strength and limited abrasion resistance.
Hydrogenated Nitrile
Offering higher strength and chemical resistance, hydrogenated nitrile O-rings perform well in oil- and fuel-handling applications and general industrial use. However, like nitrile, hydrogenated nitrile should not be used with ethers, esters, ketones, and chlorinated hydrocarbons.
Silicone Rubber
Silicone rubber is known for medical-grade and FDA-compliant sealing applications. With its heat and cold resistance, it is suitable for extreme temperature static sealing. Its low abrasion resistance limits its use to static sealing applications.
Neoprene
Neoprene is an oil-resistant, weather-resistant, and ozone-resistant alternative to natural rubber, frequently used in the transportation industry and sealing refrigerators. However, neoprene is often more costly than nitrile, which offers similar properties at a lower price.
Polyurethane, Cast
Cast polyurethane stands out for its abrasion resistance, tensile strength, and shock absorption. It performs well in high-pressure hydraulic systems but should not be exposed to strong acids, bases, or brake fluids, limiting its use in some transportation applications.
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Polyurethane, Millable
Millable polyurethane is resistant to high-pressure hydraulic fluids, abrasion, oil, grease, cracking, and many chemicals. Though excellent under dynamic, heavy loads and outdoor use, it has a lower tensile strength compared to cast polyurethane and weakens at high temperatures.
Kalrez®
Kalrez offers exceptional chemical resistance, making it one of the best options for chemical processing, oil and gas, and semiconductor manufacturing. However, Kalrez O-rings may swell in certain solvents.
PTFE
PTFE O-rings are among the toughest, with an outstanding temperature range of -300°F to 450°F. However, PTFE is difficult to install due to its limited elastic memory and poor tear resistance, making it suitable only for static or slow dynamic loads.
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