Medium-Speed Engine Bearings—Development Experience

After a brief history of the introduction of galvanically applied overlays to the surface of thin-walled half-bearings, the paper goes on to describe experiences in service engines. This shows that from the mid-1970s, overlay life could be sharply reduced due to a variety (or combination) of factors. These are described, the possible causes explained, and various palliatives investigated. The principle factor in the mid-1970s was the rapid rise in the use of lower quality heavy fuels initiated by escalating oil costs. The consequence of using these fuels was often rapid overlay loss, which in turn resulted in further problems, particularly: large areas of exposed nickel interlay, corrosion of the overlay, and/or corrosion of the base lining material. Four palliatives, elimination of the overlay, harder overlays, elimination of the interlayer, and modified surface topography are described and results of development testing and field service experience are presented.