O-Ring Materials Guide

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:

Buna-N/Nitrile

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®

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

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.

Ethylene Propylene

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.

Fluorocarbon (Viton®)

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

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. 

Hydrogenated Nitrile

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.

Silicone Rubber

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

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.

Polyurethane, Cast

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.

Polyurethane, Millable

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®

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

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.

Guide to O-Ring Selection

O-rings are elastomeric and donut-shaped gaskets designed to create fluid-tight seals between mated parts within a fluid system. Although simplistic in design and function, these components perform a critical role. When used correctly in fluid handling and processing systems, they ensure process liquids and gases remain inside the proper areas and potential contaminants stay outside of sensitive areas. Some of the typical industries that regularly make use of O-rings include transportation, medical, electronics, oil and gas, and food and beverage. 

The following article provides a comprehensive overview of O-rings—including their design considerations, types available, materials used, manufacturing processes, and industrial applications—to aid in proper selection. 

What Are O-Rings?

By technical definition, all O-rings can be considered gaskets, but not all gaskets can be regarded as O-rings. Although both create seals that prevent fluids from leaking in or out of the area between two mated components, there are critical differences in their design and performance. One of the primary distinctions between the two is the shape of flange they accommodate; gaskets require flanges with flat surfaces, while O-rings need ones with a channel or groove. For the latter, this design element helps avoid blowout in high-pressure environments in which other gaskets would likely fail.

When properly sized and compressed within the groove between two mated components, O-rings form tight seals that prevent the escape of gases and liquids. They are available in several variations to suit the needs of a wide range of applications.

Design Considerations for O-Rings

When choosing an O-ring for an application, the following design elements should be considered:

• Size and shape: the size and shape of an O-ring must suit the size and shape of the intended groove to ensure proper compression and sealing is achieved
• Material: the O-ring material must withstand the operating and environmental conditions of the application
• Static vs. dynamic: static O-rings are used for creating seals between stationary parts, while dynamic O-rings are used for moving parts

Types of O-Rings

As indicated above, many design factors affect the sealing performance of an O-ring. Some of the common types of O-rings available and their applications include:

• Round: O-rings with round cross-sections are extremely versatile and provide multi-directional sealing under minimal compressive force.
• Square: Square O-rings provide superior sealing capabilities, even in the presence of surface defects.
• Quad: Quad O-rings have a four-lobed design that allows for twice as much sealing power as round O-rings under relatively low compressive pressure.

Common O-Ring Materials

The type of material used to create an O-ring significantly influences its ability to perform reliably when used in the intended application. Typical elastomeric materials used in the construction of O-rings include:

• AFLAS®
• Buna/Nitrile
• Butyl
• Ethylene Propylene
• Fluorocarbon
• Fluorosilicone
• Hydrogenated Nitrile
• Kalrez®
• Neoprene
• Polyurethane
• PTFE
• Silicone

When selecting a material for an O-ring, there are several considerations to keep in mind, such as:

• Gland type and fill: The opening (gland) into which the O-ring is installed must allow for the appropriate level of compression and gland fill percentage to avoid O-ring failure.
• Stretch: The material should exhibit the appropriate amount of circumferential stretching to fit properly within the groove
• Compression squeeze: The material should maintain an appropriate level of compression squeeze (deformation) under the expected pressure level.
• Industry standards: Some industries require the use of materials that exhibit specific properties, such as food-grade or military-grade.

To learn more about selecting the right o-ring material for your application, read our o-ring materials guide.

How Are O-Rings Made?

The manufacturing technique used to create an O-ring largely depends on the material employed and the performance level required. The most common O-ring production methods include:

• Compression molding: The material is placed into and enclosed within an open heated mold cavity, compressing and shaping it into the O-ring shape.
• Transfer molding: The material is placed under intense pressure, forcing it into a mold cavity of the O-ring shape.
• Injection molding: The material is heated and injected into the cavity of a mold. Once cooled, it maintains the desired O-ring shape.
• Extrusion: The material is heated and forced through a die with an opening that forms it into the desired O-ring shape as it exits.

Applications of O-Rings

When selected and used properly, O-rings form fluid-tight seals in a wide range of equipment and systems, even when exposed to high-temperature and high-pressure conditions. Some examples of typical use cases include:

• Static axial systems: In static axial systems, the O-ring design should consider the pressure direction (inward or outward) as it affects the inner and outer groove diameters and widths required for optimal sealing.
• Reciprocating dynamic systems: In reciprocating hydraulic or pneumatic systems, the diameter of the O-ring depends on whether the O-ring is used for short stroke applications (smaller diameter preferred) or long-stroke applications (thicker cross sections preferred).
• Rotary systems: O-rings can function as reliable rotary shaft seals under the right conditions, but the correct O-ring compound for the application’s speed (feet per minute) must be selected.

The versatility of O-rings makes them well-suited for use in a diverse set of industries, such as:

• Chemical processing
• Electronics
• Energy
• Fluid power
• Food and beverage
• Medical
• Oil and gas
• Transportation
• Water systems

O-Ring Seals from Arizona Sealing Devices

Founded in 1989, Arizona Sealing Devices is a distributor of high-quality standard and specialized sealing products. Equipped with over three decades of industry experience and an ever-expanding product selection, we can ensure that each O-ring variable (shape, size, material, etc.) and its compatibility with the operating system is carefully considered when choosing a sealing solution. 

We offer an extensive O-ring catalog, which encompasses a variety of material compounds and durometers, sizes (for inner, outer, and cross-sectional diameters), performance characteristics, and industry compliances (e.g., Mil-spec, food-grade, and metric). As an ISO 9001:2015 and AS9120B certified company, we guarantee the delivery of a quality and dependable product solution that meets all relevant regulatory requirements and satisfies your sealing needs. 

For additional information on O-rings or assistance choosing one for your unique application, contact us today.

How to Install O-Rings

O-rings are a vital tool for ensuring the effective operation of numerous vehicles, appliances, and other everyday items. Proper O-ring installation creates a strong seal, allowing the product to function efficiently without leakage.

What is an O-Ring?

While they may seem simple, O-rings actually serve an important purpose. This round, often rubber ring helps to prevent leaks and product failures. They do this by creating a seal between parts, which stops air and fluid from moving around within the final product. O-rings are generally designed to be installed within a groove and then compressed. They come in a variety of different materials, which can make material selection an important consideration.

How to Install an O-Ring

Due to their vital function, it’s important to know exactly how to install an O-ring without damaging it. The first step to proper installation is to choose an appropriate lubricant and use it to lightly coat your O-ring.

Once you have properly lubricated the O-ring, you should make sure to cover any sharp edges on the parts that may come into contact with the O-ring. This helps prevent the O-ring from being damaged during the installation process. It’s also important to be cognizant of how much you stretch the O-ring during installation—it should stretch no more than 50%, and any stretching should be performed uniformly rather than just one side.

After you have successfully slid the O-ring onto the shaft, the final step is to ensure that the seal is not twisted inside the groove. If installing a backup O-ring, make sure to do it on the low pressure side of the system so that the high pressure will push the O-ring against the backup rather than away from it.

Tips for O-Ring Installation

Here are some tips to ensure a successful O-ring installation: 

• Lubricate the threads. As the shaft consists of threading, it’s easy for the rubber seal to tear during installation. This can be avoided by covering the threads with masking tape and/or lubricant.
• Cover sharp corners. Jagged edges can cause tears in the O-ring — and even a tiny tear can effectively break the seal.
• Stretch the O-ring evenly. Minimizing stretching and ensuring that the O-ring is evenly stretched on all sides helps create a stronger final seal.
• Slide, don’t roll. During installation, make sure to never roll the O-ring down the shaft, as this can cause damage. Instead, lubricate the O-ring so that it can easily slide down the shaft.
• Assemble so that the female component has a radius around the corner. Placing the component’s lead inside the chamfer increases the safety of the O-ring.

Using O-Ring Lubricants

Choosing the appropriate lubricant is a vital step in the proper installation of an O-ring. There are many common types of lubricants, including:

• Petroleum distillates
• Soap and water
• Solvents
• Ester based lubricants

While there are many choices, however, they are not all created equal. Certain types of lubricant will actively damage the O-ring or cause safety issues. Solvents, for example, are not a particularly effective lubricant. They can be flammable, pose health risks, and contain high VOCs. 

Petroleum distillates are another common, but less than ideal choice, as they frequently cause rubber to dry out or swell. While soap and water may be safe, they are not especially effective. They may even reactivate when wet, which can significantly reduce the efficacy of the O-ring. 

The best choice for O-ring lubricant is almost always an ester based product. This type of lubrication is safe for workers and environmentally friendly. It also drastically reduces friction and offers effective temporary lubrication during the installation process.

Partner With the Qualified Sealing Experts

Although O-rings are a fairly simple tool, they serve a vital function in a myriad of products. Understanding the fundamentals of how to properly install an O-ring can ensure that your project will be successful.

At Arizona Sealing Devices, we’ve been specializing in high-quality sealing devices since 1989. Our team of experts is well-versed in helping clients find the best solution for their unique needs. To learn more about our offerings, contact us or request your quote today.