What Are O Rings Made Of?

18 October 2019
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What Are O Rings Made Of?

There is no one simple answer to the question ‘what are O rings made of?’ because they can be made of a wide range of materials. Many O rings are made of elastomers. Elastomer is an umbrella term for a type of polymer that has elastic qualities. An elastomer can be made of natural or synthetic materials or a blend of both. It’s defining quality is that it can stretch and return to its original size. Elastomers are similar to rubber in that respect.

Elasticity is critical for O rings to function effectively. This quality ensures a snug fit that prevents any leakage of fluid or gas or any ingress. Therefore, O rings must be made of elastomers that retain their elasticity in specific environments. Some elastomers are designed for applications at extremely high temperatures while others are made to function in severe cold. Choosing an inappropriate elastomer for the application in question will cause the O ring seal to fail.

The materials the O ring is made of must also be resistant to whatever substances the seal must contain. Some applications expose an O ring to chemicals, and it is vital that the O ring used is of a material that won’t be damaged by the chemicals in use. This is another reason that choosing the wrong material can lead to O ring failure.

What Are the Most Common Materials that O Rings Are Made Of?
While O rings can be made of many different elastomers, some are widely used in a variety of applications.

 

  • - Nitrile Butadiene Rubber: Also known as NBR, this synthetic rubber copolymer provides superior resistance to chemicals, oils, and acids. It is puncture-resistant and functions at extremely low temperatures. NBR O rings are suitable for use petroleum products and are commonly used in hydraulics and pneumatics.
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  • - Silicone: This remarkably versatile materials can function well at both ends of the temperature spectrum, making it effective in aerospace and automotive applications as well as food processing and potable water.
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  • - Perfluoroelastomer: Offering the ultimate in chemical resistance, high-performance perfluoloelastomers (FFKM) also offer sustained sealing force in extremely high temperatures. This is a good choice for aerospace and automotive applications as well as chemical processing.
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  • - Fluorocarbon Elastomers: FPM and FKM are different names for the same material, which is also known by the brand name Viton. It is an incredibly versatile material, used in semiconductor manufacturing, aviation, food processing and pharmaceutical applications.
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  • - Ethylene Propylene: With exceptional resilience to sunlight, heat, steam, ozone and water, EPDM O rings are well-suited for food processing, pharmaceutical, dairy and braking systems. They should not be used for fuels.
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  • - Fluorinated Ethylene Propylene: A copolymer of hexafluoropropylene and tetrafluoroethylene, FEP is low friction and non-reactive. It is commonly used to encapsulate O rings.

Encapsulated O Rings
Encapsulated O rings: Sometimes an O ring needs a combination of qualities not found in one material. The solution can be an encapsulated O ring where the inner core is made of one type of polymer and it is then coated with a different type. This can achieve the right balance of elasticity and chemical resistance needed for some pharmaceutical, food, beverage and chemical processing applications.

This is not the definitive answer to the question ‘what are O rings made of?’, but these are some of the most widely used materials. Some specialist applications require O rings made of less common materials.

Some of the factors to consider in selecting an O ring are the temperature of the application, which liquids or gases it will be exposed to, and whether the application is static or has moving parts. If you have any questions about the best type of O ring for a specific application, our staff is here to help. We can advise you about the advantages of every type of O ring and help you make the right choice the longest and most effective seal.