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20-09-2008, 10:39 PM
Babbitt metal, also called white metal, is an alloy used to provide the bearing surface in a plain bearing. It was invented in 1839 by Isaac Babbitt in Taunton, Massachusetts, USA. The term is used today to describe a series of alloys used as a bearing metal. Babbit metal is characterized by its resistance to gall.
Common compositions for Babbitt alloys:
90% tin 10% copper
89% tin 7% antimony 4% copper
80% lead 15% antimony 5% tin
Originally used as a cast in place bulk bearing material, it is now more commonly used as a thin surface layer in a complex, multi metal structure.
Babbitt metal is soft and easily damaged, and seems at first sight an unlikely candidate for a bearing surface, but this appearance is deceptive. The structure of the alloy is made up of small hard crystals dispersed in a matrix of softer alloy. As the bearing wears the harder crystal is exposed, with the matrix eroding somewhat to provide a path for the lubricant between the high spots that provide the actual bearing surface.
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