Application Notes:
 

babbitt


is an alloy used to provide the bearing surface in a plain bearing. It was invented in 1839 by Isaac Babbitt in Taunton, MA. The term is used today to describe a series of alloys used as a bearing metal. Babbitt metal is characterized by its resistance to galling.  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. 

Common compositions for Babbitt alloys:

  • 90% tin (Sn) - 10% copper (Cu)
  • 89% tin (Sn) - 7% antimony (Sb) - 4% copper (Cu)
  • 80% lead (Pb) - 15% antimony (Sb) - 5% tin (Sn)

Babbitt metal is soft and easily damaged, and seems at first sight an unlikely candidate for a journal 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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