Backup rings can be made from a variety of materials, including polymers. In this article, we will look at PTFE and PEEK backup rings while at the same time reviewing some of the basics of backup rings.
Why Use Backup Rings?
Rubber o-rings are good, but when temperatures and pressures rise they have a bad habit of extruding into clearance between mating surfaces, which isn’t a good thing. In fact, extrusion failure is one of the main causes of o-ring failure. As the o-ring begins to extrude into the clearance gap, it will experience more and more damage until it is useless. This phenomenon is sometimes called nibbling, and when it occurs you will notice that the o-ring will have a ragged edge on the low-pressure side.
Extrusion failure is one of the main causes of o-ring failure.
Backup rings, also known as anti-extrusion rings, are used to keep o-rings from extruding into areas where they don’t belong. They are also used in conjunction with seals to either prevent damage to the seal or to control extrusion. Backup rings are made of an extrusion resistant, hard material. They fit between the o-ring (or seal) and the extrusion gap.
Where Should Backup Rings Be Used?
Backup rings are suggested for o-ring failures such as extrusion/nibbling (as we already discussed) and spiral failure (where cuts or splits spiral around the circumference of the o-ring). They should be used when temperatures or pressures are expected to reach a level that would cause the seal or o-ring to extrude. This could be continuous operating conditions or, as is quite common, pressure or
temperature spikes. Backup rings are also used when the design requires a large extrusion gap.
Note that when used with seals, backup rings are usually placed downstream of the seal gland.
Finally, backup rings can be used in both static and dynamic applications.
What Kinds of Materials Are Used for Backup Rings?
Two of the most common materials used for backup rings are PTFE and PEEK. Both PTFE and PEEK are far less likely to extrude than the elastomers used for seals and o-rings. This means they can retain their shape even in the presence of elevated temperatures, high pressures, and aggressive chemicals. This allows them to hold the o-ring or seal in place.
Both PEEK backup rings and PTFE backup rings are usually filled, meaning they have a filler material such as glass or carbon fiber added to increase their compressive strength and dimensional stability. Another benefit of using PEEK and PTFE for backup rings lies in their chemical resistivity, making them ideal for chemically aggressive environments. They also have low friction and relatively high continuous operating temperatures.
Conclusion
PTFE and PEEK are popular choices for backup rings because they are dimensionally stable, chemically resistant, have excellent compressive strength, and function well even at elevated temperatures and pressures. As an anti-extrusion device, they work extremely well with both o-rings and seals to prevent extrusion in situations that involve large clearances, high temperatures, and high pressures. If you are experiencing extrusion issues, don’t forget to consider a backup ring!
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