NEW LUBRICANTS FOR ROTATING ANODE X-RAY TUBE BEARINGS

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The project will develop new solid lubricant coatings for bearings that must operate at high rotational speed, high temperature, and under vacuum in rotating anode X-ray tubes for CT scanners and other medical and industrial applications. The lubricants will be applied by an ion- assisted process developed by Spire Corporation, in which an energetic ion beam both sputter-deposits the coating and concurrently bombards the deposited material. Ion bombardment initially modifies the substrate/coating interface to enhance adhesion, and continued bombardment during deposition densifies and homogenizes the microstructure for improved performance. The coating's composition can be far from phase-equilibrium, thus providing unique lubrication properties. In Phase I, we will identify and test promising coating materials based primarily on mixtures of silver and other ductile metals; a commercial manufacturer of X-ray tubes will test lubricated bearing balls in a rotating anode simulator, under realistic thermal-mechanical-vacuum conditions. Phase II would investigate a wider range of lubricant materials, processing parameters, and bearing components and initiate full-scale testing in actual X-ray tubes. PROPOSED COMMERCIAL APPLICATIONS: Bearing wear is the principal limitation on rotating anode X-ray tube lifetime in CT scanners and other X-ray equipment. New bearing lubricants could not only extend tube lifetime but also allow a major increase in X-ray intensity, along with proportional reduction of exposure time. An immediate commercial market exists for new solid lubricants for bearings in rotating anode X-ray tubes and in other precision machinery that operates in a vacuum environment.