One of the most important design decisions when selecting a bushing is choosing the right material to provide optimum performance. In this blog post, we will look at the five most popular polymer bushing materials PTFE, PEEK, Nylon, Ryton®, and UHMW PE and what they have to offer.
PTFE ($$$)
PTFE (often referred to by its trade name Teflon®) is frequently the material of choice for high speed, high temperature polymer bushing applications. It is excellent for high PV bearing applications, including surface speeds up to 5,900 ft/min (30 m/s). PTFE functions over a wide operating temperature range, from cryogenic temperatures to 550°F. It offers excellent chemical resistivity and extremely low friction and can even be used in dry running applications. Certain grades are FDA and USDA compliant, as well. The use of additives like fiberglass or graphite extend its strength, increase its dimensional stability, and further improve its wear properties.
PEEK ($$$$)
PEEK is another top contender for high speed, high temperature polymer bushing applications where higher loads are needed. (In fact, it offers higher load capacity than any other option.) Its maximum operating temperature is around 480°F. It has good chemical resistance, and excellent strength and wear properties. Like PTFE, there are various additives available that can further improve its performance.
Nylon ($$)
As a bushing material, Nylon provides strength, abrasion resistance, and good chemical resistance. In general, Nylon bushings are self-lubricating and non-galling with an operating temperature around 250°F. Chemically they are weak around strong acids, but perform very well in the presence of hydrocarbons and alcohols. Like PTFE and PEEK, Nylon can be strengthened through the use of additives. Note that Nylon does not perform well in cryogenic conditions.
Nylon 6 is not intended for high speed or high temperature applications. It also does not work well in situations where it will be exposed to moisture. Nylon 66, however, is a popular choice for replacing metal bearings. It has a higher maximum operating temperature than Nylon 6, and can be used to make injection molded bushings.
PPS ($$$)
PPS (sometimes better known by its tradename Ryton) is another popular alternative to both metal and ceramic bearings. It can handle continuous operating temperatures around 400°F and has a chemical resistance second only to PTFE. It experiences almost no creep and absorbs little to no moisture, making it very dimensionally stable. PPS can be reinforced with additives such as carbon and graphite. It is self-lubrication and wear resistant. PPS is often considered a lower-cost alternative to PEEK because of the similar temperature range and coefficient of friction.
UHMW PE ($$)
UHMW PE is known for its impact strength the highest of any polymer currently on the market and its toughness. It exhibits very little moisture absorption. UHMW PE also has a coefficient of friction so low that it is comparable to PTFE, and also exhibits hydrophobic and non-stick behavior comparable to PTFE. Its main limitation is its operating temperature, which is low compared to PTFE and PEEK.
Conclusion
In terms of limiting PV value, bearing grade PTFE and PEEK are the top choices followed by PPS and Nylon. For extremely high temperatures, again PTFE and PEEK rise to the top, followed by PPS. If the application does not involve high temperatures or high pressures, then UHMW PE and Nylon are excellent alternatives.
Interested in more information about polymer bushings? See these posts:
- Polymer Bushings Taking a Beating: Two Important Concepts Behind the Wear and Tear
- Factors That Influence Polymer Bushing Performance
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