Spring-Energized Seals Jacketing Material
When selecting a jacketing material for a spring-energized seal, engineers look at the
- operating temperature,
- pressure (including whether or not it is static or cyclic),
- dynamic conditions,
- media involved,
- amount of seal squeeze,
- and the geometry involved.
In this article, we are going to look at some of the options out there for a polymer jacketing material.
Get even more information on Spring-Energized Seals from the following posts from Advanced EMC Technologies:
- Five Energizers for PTFE Spring-Energized Seals
- Polymer Labyrinth Seals -7 Questions and Answers You Should Know!
- Abradable Polymer Labyrinth Seals -5 Fascinating Facts about Modified PTFE
Polytetrafluoroethylene -PTFE, also known by its tradename Teflon, is probably the most popular choice for a spring-energized seal jacket. In its virgin state, it works well with low to medium static pressure up to 3,000 psi. It can also handle dynamic applications with minimum cycling. Due to its special properties and unbelievable low friction, it demonstrates reduced stick-slip. It also has the best chemical and corrosion resistance of any polymer. Virgin PTFE performs will in temperatures up to 350°F. Another benefit is that it is not subject to explosive decompression.
PTFE is available with a variety of fillers that can give it special characteristics for special applications. Molybdenum Disulfide (MSO2) Filled PTFE is used in medium to high static pressure systems, but is not well adapted to low pressure systems. The addition of MSO2 increases the hardness of the seal jacket and enables it to survive in environments with temperatures up to 400°F. Like virgin PTFE, it also has excellent chemical and corrosion resistance. Molybdenum Filled PTFE can handle extremely high pressures up to 40,000 psi, but is often limited to use with liquids at such high pressures because of its porosity.
Graphite Filled PTFE is yet another option. The addition of graphite increases the temperature range of PTFE to 500°F, and enables it to handle static pressures up to 3,000 psi. Graphite filled TFE retains the chemical and corrosion resistance of virgin PTFE. At high pressures, however, it exhibits porosity with gases. Its best applications seem to be those involving liquids and steam. PTFE can also be Carbon Filled, which is excellent for dynamic applications and high pressures up to 5,000 psi. The addition of carbon reduces creep and increases its coefficient of thermal conductivity.
Ryton is a trade name for PPS, or polyphenylene sulfide. Ryton Filled PTFE is used in medium pressure applications with high speed cycling. It can handle temperatures up to 575°F, and is recommended for use with shafts that have hardness greater than 60 Rockwell C.
UHMW Polyethylene, where UHMW stands for ultra-high molecular weight, is used as a spring-energized jacket material for temperatures ranging from -328°F to 180°F. This makes it ideal for cryogenic applications. It exhibits excellent toughness, a very high impact strength, and low friction. Its extreme abrasion resistance often makes it the first choice in situations involving abrasive media such as pain. Also available is a UHMW Hot which can operate at temperatures up 275° F.
PEEK is another polymer that is commonly used as jacket material. It is a popular choice because of its thermal stability over a wide range of temperatures. It exhibits low moisture absorption and has excellent chemical and corrosion resistance. It offers low smoke and toxic gas emission, too. One of its special characteristics is that it can stand continuous exposure to hot water and steam.
When used as a jacketing material, Hytrel is usually reserved for special environmental conditions and most often found in nuclear applications. Why? Its outstanding resistance to radiation. In addition, it works well under high pressure and its temperature range extends up to 304° F. It is also resistant to both dry heat and oil aging.
So Many Jacketing Material Choices
There are so many different choices available when choosing a jacket material for spring-energized seal. Whatever your application, chances are you can find just the right polymer to meet your needs.
Advanced EMC Technologies provides the most advanced choices in the marketplace customiziing for any design engineering needs. Get your copy of Advanced EMC High Performance Sealing Solutions Resource Guide.