4 Reasons: PTFE Rotary Shaft Seals for Low Friction High Speed Applications

PTFE rotary shaft seals are an excellent solution to high speed applications with surface speeds up to 30 m/s.  In this article, we are going to look at four reasons behind that continued popularity. 

Reason # 1 Low Friction

PTFE, also known as Polytetrafluoroethylene or by its trademarked name Teflon, has one of the lowest coefficient of friction of any solid known to mankind, even when in contact with metal.  It’s usually estimated at 0.05 to 0.10 for virginPTFE. Because of this extremely low friction, in many rotary applications there will be significantly less frictional drag when compared to options, such as conventional rubber shaft seals.

Reason # 2 Film Transfer

When PTFE rubs against a hard surface, it transfers a microscopic layer to that counter surface.  This contributes to its extremely low coefficient of friction.  Here’s how engineers and scientist describe the process:

1. The molecules on the contacting surface of PTFE are deformed due to applied forces acting at that surface.
2. The molecules begin to stretch along the direction of the sliding motion.
3. Because of the weak intermolecular forces, PTFE molecules are transferred to the counter surface in a film between 50 to 200 Angstroms thick.
4. As a result, PTFE is now sliding on PTFE instead of directly on the counter surface.

Reason # 3 Dry Running

Another awesome feature of PTFE is its ability to perform without additional lubrication.  PTFE is actually classified as a self-lubricating polymer.  It offers reduced stiction and breakout friction, which can be key for many rotary applications. 

Reason # 4 Chemical Resistivity

Another facet of PTFE that makes it popular as a shaft sealing material is its chemical resistivity.  The list of chemicals that can attack PTFE is short, and primarily consists of alkali metals, such as elemental sodium, and rare fluorinated solutions.  This chemical inertness is said to be a result of carbon-fluorine bonds in PTFE.

Another interesting facet of PTFE is its hydrophobic behavior, whereby it repels water and water-containing substances.  The hydrophobic behavior aids in its chemical inertness, and also makes it easier to keep clean.  This behavior due in part to the high electronegativity of fluorine.

CONCLUSION:

Of course, there are more reasons behind the popularity of PTFE for rotary shaft seals in high speed applications.  PTFE has an extended shelf life, can perform at both cryogenic and extremely high temperatures, and is known for its easy installation.  However, the main reasons are its low friction, film transfer, dry running, and chemical resistivity.

So, the next time you need a rotary sealing solution that involves high speeds and low friction, check out PTFE rotary shaft seals.  They might be just the solution you are looking for.

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