Tin-lead and Tin-copper Alloys
Tin-lead & tin-copper alloys such as Babbitt metal have a low melting point that is ideal for use as solder, but these alloys also have ideal characteristics for plain bearings. Most importantly for bearings, the material should be hard and wear-resistant and have a low coefficient of friction. It must also be shock-resistant, tough and sufficiently ductile to allow for slight misalignment prior to running-in.
Pure metals are soft, tough and ductile with a high coefficient of friction. Intermetallic compounds are hard and wear-resistant but brittle. By themselves, these do not make ideal bearing materials.
Alloys consist of small particles of a hard compound embedded in the tough, ductile background of a solid solution. In service the latter can wear away slightly leaving the hard compound to carry the load. This wear also provides channels to allow in lubricant (oils). All bearing metals contain antimony (Sb) which forms hard cubic crystals.
| % Sn | % Sb | % Cu | % Pb | Applications |
|---|---|---|---|---|
| 93 | 3.5 | 3.5 | - | Light and medium IC engine big end bearings |
| 86 | 10.5 | 3.5 | - | Light and medium IC engine main bearings |
| 80 | 11 | 3.0 | 6 | General purpose heavy bearings (lead increases plasticity) |
| 60 | 10 | 28.5 | 1.5 | Heavy duty marine engine bearings, electrical machines |
| 40 | 10 | 1.5 | 48.5 | Low cost, general purpose, medium duty bearings |
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