5 Reasons Designers Specify DuPont™ Vespel® in Aerospace Applications

As new application requirements continue to push the limits of traditional materials, designers are increasingly turning to composites and highly engineered polymeric materials such as DuPont™ Vespel®. In addition to their unique performance characteristics, Vespel® parts and shapes carry a pedigree of success in aircraft and space applications extending more than 50 years.

Five popular benefits of Vespel® SP and SCP materials are as follows:

1. Broad Service Temperature Range

Vespel® polyimide materials are well-known for being situated near the top of the ubiquitous plastics pyramid because of their ability to maintain strength and stiffness at higher temperatures than other materials. However, Vespel® materials are also widely specified for use in cryogenic environments.

The continuous use temperature of Vespel® SP materials is commonly cited around 550 °F. While convenient, simplifying this performance metric to a single value can be a bit misleading. Unlike competitive thermoplastic materials such as Torlon® PAI or PEEK, Vespel® SP materials exhibit no observable glass transition temperature or abrupt softening point. Additionally, these Vespel® materials do not melt, which allow them to function at significantly elevated temperatures for shorter time periods.

For instance, according to a 2013 publication by the NASA Marshall Space Flight Center, Vespel® SP-211 (a graphite and PTFE-filled grade) “was selected as the top candidate seal material for use in the Oxidizer Turbine Bypass Valve (OTBV) on NASA’s Ares I Upper Stage J-2X engine” despite it being exposed to temperatures as high as 750 °F [1].

2. High PV Capabilities

In tribological systems, polymeric materials often offer several advantages, such as not requiring lubrication, being less abrasive on mating components, reducing noise and vibration, and being lighter weight.

DuPont™ Vespel® polyimide materials can provide these same benefits under pressure and velocity conditions significantly beyond the limitations of other plastics. To quantify this, Vespel® SP-21 thrust bearings have been found to survive PV conditions as high as 400,000 psi-ft/min [2].

Spline couplings, which connect metallic shafts in power transmission equipment, represent a demanding wear application in which Vespel® polyimide materials have been commonly specified since the 1970s. Prior to the use of Vespel®, metallic splines were found to exhibit accelerated wear upon misalignment, which can occur during regular use or even during installation or maintenance operations. Polymeric materials, including Vespel®, have been found to be able to better accommodate misalignment because of their ability to deform elastically in compression and redistribute loads more evenly, resulting in longer wear life and more consistent performance [3].

3. Vacuum Compatibility

There is no shortage of vacuum in space, so it stands to reason that certain space applications will require materials capable of performing under vacuum conditions.

Fortunately, DuPont™ Vespel® materials have been used successfully as replacements for ceramic seals and gaskets in ultra-high vacuum (UHV) environments for decades. As defined by the ASTM E595 standard developed by NASA, these materials exhibit low and acceptable levels of outgassing under vacuum enabling them for use in a variety of vacuum-related applications. Studies have also shown that Vespel® SP-1 helium (He) permeation levels at room temperature are roughly one-third those of PEEK [4].

For enhanced bearing and wear demands under vacuum, a molybdenum disulfide (MoS₂) filled grade (Vespel® SP-3) is available. Under vacuum conditions, other internal lubricants such as graphite can actually increase friction potentially leading to reduced wear life.

4. Oxygen Compatibility

Oxygen compatibility is a critical parameter in which failures can carry fatal consequences. In a study presented at the 4^th European Conference for Aerospace Sciences, the tendency for select polymeric materials to ignite when doused in liquid oxygen and struck with a hammer was examined. The author concluded “Impact tests clearly state that polyimide Vespel® SP-21 is compatible in liquid oxygen” [5].

Other organizations have reached similar conclusions. NASA found Vespel® SP-21 to meet the standards laid out in MSFC-SPEC-106B regarding its compatibility for use in liquid oxygen systems. Vespel® SP-21 has also been found compatible for service in oxygen environments by the Naval Air Engineering Center in accordance with Mil-V-5027C [6].

5. Radiation Resistance

Ionizing radiation from multiple sources can pose serious design challenges for components used in outer space. While polyaryletherketones (PAEKs) like PEEK are known to offer some of the best resistance to high frequency radiation among thermoplastics, polyimide materials including Vespel® and Kapton® (the DuPont trade name for thin gauge polyimide films) have long been used successfully in applications demanding resistance to various forms of space radiation.

A graphical representation of the resistance of polyimide and other popular engineering plastics to nuclear and space radiation excerpted from a NASA publication can be found below:

If you would like to explore how DuPont™ Vespel® parts and shapes might benefit your aerospace components, please contact Curbell Plastics at 1-800-553-0335 or ask one of our experts.

Curbell Plastics is the only authorized distributor of Authentic DuPont™ Vespel® polyimide shapes in the Western United States.