Buna, otherwise known as Nitrile, Buna-N or NBR, is an incredibly versatile synthetic rubber. The unique properties of this material make Buna an ideal material for O-rings, vulcanized or spliced O-rings, gaskets, and other sealing applications for various industries.
Properties of Buna
Buna offers many unique properties; making it the sealing industry’s most commonly used material. It is a durable, versatile elastomer that’s typically black in color and resistant to various chemicals, including fuel, oil, diluted acids, alkaline, mineral, vegetable oils, and more. Buna is resistant to abrasion, has a low compression set, and has a high tensile strength ranging from 200 to 3000 psi with 300% elongation at break.
Buna is composed of the copolymer acrylonitrile and butadiene and can be formulated to withstand temperatures ranging from -85°F to 275°F. Its hardness durometer ranges from 40-90 and has a hardness rating of 70 Shore A. These features make Buna O-rings and gaskets commonly found in low temperature military equipment and off-road equipment.
Buna Sealing Device Compatibility
To determine if Buna is a right O-ring and gasket material for your intended application, it is important to know its compatibility with different chemicals and environments. Buna’s compatibility levels are as follows:
- Good to excellent. Oil resistance, dynamic resistance, set resistance, tensile strength
- Good. Abrasion resistance, cold resistance, heat resistance, impermeability
- Fair to good. Chemical resistance, water steam resistance
- Fair. Acid resistance, electrical properties, tear resistance, weather resistance
- Poor. Flame resistance, ozone resistance
Buna Sealing Device Applications
Buna’s unique properties and features make it the ideal material for sealing devices in many applications across a wide range of industries, including military, medical, automotive, and aerospace. Some common applications for Buna sealing devices include:
- Fuel tanks
- Gear boxes
- Military equipment
- General aerospace assemblies
Buna’s strong chemical resistance makes it suitable for applications where ordinary rubber cannot be used due to its reactivity with fuels and oils.
Buna O-Rings, Gaskets, and Other Sealing Devices from AZ Seal
Crafting your O-rings, gaskets, and other sealing devices from the correct material ensures that your equipment’s critical components are safe from damage caused by chemicals and extreme environments. Buna is a highly resistant and versatile synthetic rubber that offers many advantages over ordinary rubbers, making it the most commonly used sealing material for several applications across numerous industries.
AZ Seal is an ideal supplier of sealing device solutions using Buna as well as a wide variety of other materials to ensure that you have the best possible O-rings, gaskets, and other sealing devices for your specific application. To learn more about our products or to get started on your sealing solution, browse our catalog or contact our experts today.
Named for their standard circular shape, O-rings are versatile elastomer gaskets that form a tight seal between two mechanical components. However, while O-rings largely look alike and function similarly, there are actually key distinctions that determine where an O-ring may be used. Chief among these considerations is material selection. Despite their similar compositions, elastomers each have variations in their chemical and mechanical properties that influence how they perform at a given sealing task. When purchasing O-rings, it’s critical to consider your application’s needs and limitations rather than searching for a one-size-fits-all seal.
In this guide, we consider common O-ring materials in detail, including their strengths, limitations, and common applications. If you still have questions about after reviewing this material selection guide, we encourage you to contact our team at Arizona Sealing Devices, or browse our selection of O-rings.
O-Ring Materials: Strengths, Limitations, and Applications
At Arizona Sealing Devices, we work with a variety of elastomers to produce O-Rings. Here are the materials we use most frequently:
Among the most common elastomers used in O-ring manufacturing, Nitrile is a synthetic rubber unique for its chemical resistance properties. Whereas other rubbers often react with fuel and oil, nitrile is resistant to these substances, as well as many diluted acids and alkalines. As such, nitrile/Buna-N O-rings are the ideal choice for automotive, aerospace, and marine fueling. High tensile strength and thermal resistance enhance its utility in the aerospace and automotive industries. Despite its favorable chemical resistance characteristics, nitrile should not be exposed to ethers, esters, ketones, or chlorinated hydrocarbons.
Aflas is another elastomer that offers a combination of chemical, thermal, and electrical resistance properties, resisting acids, bases, and heat up to 446°F. Like nitrile, it is popular in oil, aerospace, and general industrial environments. However, Aflas should not be used in direct contact with automotive fuels because it swells more than comparable elastomers.
Butyl is the classic choice for vacuum-sealing, providing extremely low permeability to gases. Its other benefits include resistance to ozone and sunlight, as well as good shock-dampening capabilities. Due to its shock-absorbing properties and chemical resistance, butyl is also used in hydraulics applications—especially those that use synthetic lubricants. However, ethylene propylene has largely supplanted butyl due to its enhanced durability.
A modern alternative to butyl, ethylene propylene exhibits low gas permeability alongside excellent heat, weather, and ozone resistance. These characteristics make it one of the most versatile elastomers for O-ring seals. Ethylene propylene is often used outdoors where weather resistance is a concern, as well as in automotive cooling and brake systems. The material’s primary limitation is a susceptibility to hydrocarbons.
Offering outstanding chemical and high-temperature resistance, fluorocarbon O-rings are among the most durable and versatile available. They are particularly valuable in aircraft engines and automotive fuel handling systems because they resist swell in high-octane and oxygenated fuels. They also have improved resistance to amine-based oil protectants. Fluorocarbon’s primary limitation is an intolerance to low temperatures and certain chemicals, such as ketones, amines, low molecular weight esters, and ethers.
Fluorosilicone is a saturated rubber with excellent extreme-temperature stability, making it a popular material in aerospace applications. Having both thermal and chemical resistance properties, fluorosilicone is also becoming popular for general-purpose O-rings, especially for outdoor applications. However, fluorosilicone is not a good choice for dynamic sealing of any kind due to its low strength and limited abrasion-resistance.
Hydrogenating nitrile yields a more highly saturated chemical structure with correspondingly higher strength and chemical resistance. Hydrogenated nitrile O-rings perform well in oil- and fuel-handling applications, as well as general industrial use. Like nitrile, hydrogenated nitrile has excellent thermal properties, sealing at temperatures from -85°F to 350°F. Like standard nitrile, hydrogenated nitrile should not be used with ethers, esters, ketones, and chlorinated hydrocarbons.
Although silicone is well-known for medical-grade and FDA-compliant sealing applications, silicone rubber is also a solid choice for extreme temperature static sealing due to its heat and cold resistance. Silicone rubber also holds up to weather, ozone, and acid exposure, although its low abrasion resistance limits its utility to static sealing applications.
Neoprene is an oil-resistant, weather-resistant, and ozone-resistant alternative to natural rubber that finds frequent use in the transportation industry. Resistant to Freon® and ammonia, neoprene is also a good choice for sealing refrigerators. As general O-ring material, however, neoprene is often cost-prohibitive compared to nitrile, which offers similar properties at a lower cost.
Cast polyurethane stands out for its abrasion resistance, tensile strength, and shock absorption, though it also boasts resistance to many chemicals, including ozone, oils, and greases. Cast polyurethane O-rings offer excellent performance in high-pressure hydraulic systems, as well as in wheels and other dynamic systems. Polyurethane should not be exposed to strong acids, bases, or brake fluids, limiting some of its potential transportation applications despite the material’s capacity to carry heavy loads.
Millable polyurethane is resistant to high-pressure hydraulic fluids, abrasion, oil, grease, cracking, and many chemicals. Like cast polyurethane, it does well under dynamic, heavy loads, even when used outdoors. Compared to cast polyurethane, it has a lower tensile strength and weakens at high temperatures.
Kalrez features exceptional chemical resistance, and there’s virtually no industrial chemical that will cause it to degrade (although Kalrez O-rings will swell in the presence of certain solvents). Being nearly as inert as Teflon, Kalrez is one of the best options for chemical processing, oil and gas, and semiconductor manufacturing.
PTFE yields some of the toughest O-rings on the market with an outstanding temperature range of -300° to 450°F. The trade-off is that PTFE is difficult to install, having very limited elastic memory and poor tear resistance. The latter property also means that PTFE should be limited to static loads or slow dynamic loads.
Quality O-Rings from Arizona Sealing Devices
Without extensive experience in sealing, it can be difficult to determine which elastomer is right for a given project. The experts at Arizona Sealing can help.
Arizona Sealing Devices, Inc. has extensive experience with all of these elastomers, and we take pride in matching our clients to the materials that will suit them best over time. An O-ring supplier since 1989, we have since become an ISO 9001:2015-certified distributor of a broader range of sealing products, including caps, gaskets, plugs, and seal kits. We’ve also worked with satisfied customers from virtually every industry, developing a nuanced understanding of the practical limitations of different sealing applications. As a result, our clients return to us again and again for guidance and reliable elastomer products.
To learn more about Arizona Sealing’s personalized service and extensive product line, request a quote today.