Volume 8, Number 2     March/April 2000

Composite Coating Increases Bearing Life

Foil air bearings are self-acting, compliant surface bearings. When in operation, they support load on an air film. Benefits of foil air bearings include reduced cost, higher speed, lower weight, higher efficiency and greater accommodation for misalignment and distortion. During start-up and shutdown, however, sliding contact occurs between the shaft and foil surfaces, causing wear. A solid lubricant is therefore required for durable, long-term operation.

Previously, Teflon™ coatings were used to lubricate the bearings, but Teflon is limited to use in machinery that reaches no more than about 500 degrees Fahrenheit. A new high-temperature, composite coating developed at NASA’s Glenn Research Center increases the life of foil air bearings.

The family of coatings, called PS300, is a solid lubricant that provides low friction and wear to sliding mechanisms well above temperature limits of conventional lubricants. PS300 enables the use of foil bearings at temperatures never before achieved, allowing turbomachinery systems to operate at higher speeds and temperatures. Higher speeds and temperatures will yield breakthroughs in system performance. PS304, one of the coatings, successfully lubricated foil bearings at high loads for 100,000 start/stop cycles from 75 to 1,200 degrees Fahrenheit.

PS300 also efficiently solves many recurring industrial and aerospace lubrication problems. Operational problems involving high-temperature control valves at Glenn’s Advanced Subsonic Combustor Research Facility were alleviated with PS300. The coatings are also a key technology in enabling Glenn’s Oil-Free Turbomachinery Program. PS300 coating enables foil air to be applied to a wide range of turbomachinery applications because of its low raw materials and processing costs. For aircraft gas turbine engines, the coating allows operation at higher speeds and temperatures, while elimination of the conventional oil lubrication system cuts engine weight by 15 percent and reduces maintenance costs by 50 percent. According to Dr. Christopher DellaCorte, one of the inventors at Glenn, these propulsion benefits will have a dramatic, cascading effect on aircraft design, transportation cost and performance.

PS300 was originally developed to provide long-life lubrication of foil air bearings for oil-free turbomachinery. The successful demonstration of an oil-free turbocharger convinced NASA and industry to pursue the oil-free General Aviation Propulsion (GAP) engine project to demonstrate the world’s first oil-free aircraft engine.

The PS300 family of coatings satisfies critical high-temperature solid lubrication needs at costs low enough to make the technology practical for aerospace, government and commercial applications. The coatings are well-suited for industrial applications, including the automotive, trucking, power generation and power compressor industries. Successful field trials have been conducted, including the use of PS300 coatings as lubricants for steam control valves, automotive exhaust gas recirculation valves and large diesel engine wastegate systems.

"PS300 is a critical building block in the NASA Oil-Free Turbomachinery Program and is truly ‘starting a turbomachinery revolution,’" said DellaCorte.

For more information, contact Dr. Christopher DellaCorte at Glenn Research Center. 216-433-6056, Christopher.Dellacorte@grc.nasa.gov Please mention you read about it in Innovation.