Aviation fuel is a low-viscosity liquid that produces only an extremely thin hydrodynamic film, too thin to provide adequate lubrication for traditional metallic bushings. In contrast, Metcar’s carbon-graphite material has no atomic attraction to a metallic shaft; the thin fuel film is sufficient to lubricate metallic shafts running in the carbon-graphite bushings.
Another advantage, carbon-graphite bushings are self-lubricating; they can run dry for short periods of time without catastrophic pump failure or significant wear, says the spokesperson.
In addition, Metcar carbon-graphite bushings are dimensionally stable, which permits the close bushing to shaft running clearances that are required in gear pump applications.
Finally, the new carbon-graphite bushings have a relatively low elastic modulus. While elastic enough that they can be press-fit into the metallic gear pump housing with no difficulty, after being properly press-fit, the Metcar bushings are pre-stressed in compression. They exhibit nearly the same coefficient of thermal expansion as the metallic gear pump housing material, assuring that the running clearance between the shafts and the bushings will remain the same throughout the entire operating temperature range of the pump.
