O-rings are donut-shaped rubber seals known for their circular cross-section. They can be employed in static or dynamic applications and are among machinery’s most widely used seals because they are simple to make, affordable, and reliable.
The majority of mechanical systems need seals. These components are essential to equipment operation because they prevent leakage when joining mechanisms together. A compressed seal called a gasket is used between two or more surfaces. This accessory goes hand in hand with different O-ring types in various sealing applications.
At Arizona Sealing Devices, we create O-rings using a range of elastomers for different applications.
What Are O-Rings and How Do They Work?
Niels Christensen, a 72-year-old machinist, submitted the first O-ring U.S. patent application. To develop a sealing technique, Niels performed several experiments before he concluded how effective rounded-shaped rubbers would work as seals.
Then, in 1936, he discovered that rubber rings placed in a groove that was one and a half times the minor radius of the ring produced the best seal for uses such as pistons and cylinders. After working through the application procedure for two years, he was given a patent in 1939.
Today, this circular elastic loop, known as an O-ring, serves as a seal in static and dynamic applications. Their primary function is to act as a seal between different types of constructions, including pipes, tubes, pistons, and cylinders.
O-rings are extremely flexible and come in various materials, depending on how they will be utilized. They stop the leaking of liquids or gases when positioned between two surfaces.
An O-ring employed as a static seal stays in place to control pressure or create a vacuum. They can move in either a rotational or reciprocating direction. The O-rings apply pressure inside a tube or pipe to create a seal — these are classified as self-energizing seals.
A range of production processes — including extrusion, compression molding, injection molding, transfer molding, and machining — are used to make O-rings. Depending on their use, they can be constructed from various materials, including silicone, polyurethane, neoprene, nitrile rubber, fluorocarbon, and other elastomers.
O-rings are normally round, although other shapes, such as squares and X-shapes, are employed for specific applications. Quality, quantity, cost, application temperature, sealing pressure, chemical compatibility, movement, action, lubrication, and other parameters are considered when designing an O-ring.
O-Ring Materials: Pros, Cons, and Applications
It’s crucial to select the appropriate O-ring material to guarantee proper performance. The kind of material to choose and its application depend on its chemical compatibility, temperature resistance, and other criteria.
Below are some of the industry’s most widely used O-ring materials, their advantages and disadvantages, and their various applications.
An elastomer made from the combination of chemical, thermal, and electrical resistance qualities is Aflas®. It can withstand acids, bases, and temperatures up to 446 °F. As a result, it is widely used in oil, aerospace, and other industrial settings, similar to nitrile.
However, Aflas® swells more than comparable elastomers. Hence, it shouldn’t be utilized in direct contact with vehicle fuels.
Nitrile is a synthetic rubber that is one of the most popular elastomers used in producing O-rings. It is resistant to many diluted acids and alkalis, unlike other rubbers that frequently react with fuel and oil. As a result, Nitrile/Buna-N O-rings are the best option for fueling in the automotive, aerospace, and marine industries.
Despite its good chemical resistance properties, nitrile should not be subjected to ethers, esters, ketones, or chlorinated hydrocarbons.
Butyl is the traditional material for vacuum sealing because it has a very low gas permeability. Other advantages include superior shock-dampening qualities, resistance to ozone and sunshine, and other properties. Butyl is also utilized in hydraulics applications — particularly synthetic lubricants — due to its shock-absorbing qualities and chemical resilience.
Cast polyurethane is distinguished for its tensile strength, shock absorption, and resistance to various substances — including ozone, oils, and greases. Cast polyurethane O-rings function admirably in wheels, other dynamic systems, and high-pressure hydraulic systems.
Despite the material’s ability to support enormous weights, polyurethane should not be subjected to potent acids, bases, or braking fluids. Thus, it has limited transportation applications.
Ethylene propylene, a newer substitute for butyl, has a low gas permeability and great heat, weather, and ozone resistance. As a result, it is one of the most flexible elastomers for O-ring seals. It is frequently utilized in vehicle cooling and brake systems and outdoors where weather resistance is an issue.
The main drawback of the material is its vulnerability to hydrocarbons.
Fluorocarbon O-rings are among the most robust and adaptable options, offering exceptional chemical and temperature resistance. Due to their resistance to swelling in high-octane and oxygenated fuels, they are particularly useful in aircraft engines and vehicle fuel handling systems. Additionally, they are more resistant to amine-based oil protectors.
The main drawback of fluorocarbon is its intolerance to low temperatures and a few substances, including ethers, ketone esters, amines, and low molecular weight esters.
Aerospace applications frequently use fluorosilicone, a saturated rubber with good extreme-temperature stability. Fluorosilicone is also growing in popularity for general-purpose O-rings, especially outdoor applications, due to its thermal and chemical-resistant qualities. However, due to its low strength and weak abrasion resistance, it is not a good option for dynamic sealing of any type.
Nitrile can be hydrogenated to produce a chemical structure that is more chemically saturated, stronger, and more resistant to chemicals. O-rings made of hydrogenated nitrile work well for handling oil and fuel and for general industrial use.
Like nitrile, hydrogenated nitrile has excellent thermal characteristics and seals between -85 °F and 350 °F. The same rules apply to hydrogenated nitrile as to regular nitrile when it comes to ethers, esters, ketones, and chlorinated hydrocarbons.
Kalrez® has excellent chemical resistance, and almost no industrial chemical will make it deteriorate. It is one of the greatest materials for chemical processing, oil and gas production, and semiconductor fabrication since it is almost as inert as Teflon. However, Kalrez® O-rings will swell in the presence of certain solvents.
High-pressure hydraulic fluids, abrasion, oil, grease, cracking, and various chemicals are all resistant to millable polyurethane. It performs admirably under dynamic, heavy loads, even when utilized outdoors, just like cast polyurethane. However, it has lesser tensile strength and weakens at high temperatures compared to cast polyurethane.
Natural rubber substitute neoprene is frequently used in transportation because it is ozone, weather, and grease resistant. Also able to withstand ammonia and Freon®, it is a strong option for sealing refrigerators. However, it is frequently more expensive than nitrile, which gives comparable qualities at a lower price when used as a generic O-ring material.
With an exceptional temperature range of -300 °F to 450 °F, PTFE produces some of the toughest O-rings available today. However, the downside is that PTFE has low tear resistance, very little elastic memory, and is challenging to install. Therefore, PTFE should only be used for static loads or slow dynamic loads due to its handicap when it comes to elasticity.
Silicone rubber is a good option for extreme temperature static sealing due to its temperature resistance. It is also very popular for medical-grade and FDA-compliant sealing applications.
Although its limited abrasion resistance restricts its utility to static sealing applications, silicone rubber also withstands weather, ozone, and acid exposure.
High-Quality Materials and O-Ring Manufacturing from Arizona Sealing Devices
Arizona Sealing Devices is an ISO 9001:2015/AS9120B certified company that offers a wide range of sealing products, from caps, gaskets, plugs, and seal kits. Our staff meticulously investigates each product to ensure it follows our quality standards and meets our customers’ requirements.
Contact us for a quote, our o-ring material guide, or more about our sealing services and products!