Thermal faceting affects only tin-based babbitt. Tin crystals are anisotropic, having different coefficients of thermal expansion in each crystal axis. Repeated thermal cycling results in faceting of the bearing surface due to a ratcheting process, which in severe cases may cause undulations in excess of 0.025 mm (0.001″). Rarely, cracks may form between the grains.
Addressing the Damage
In mild cases no action is required. In more severe cases, take steps to reduce the temperature cycling or change to another bearing material, such as AS40 (40% tin/aluminum).
Figure 1: Thermal ratcheting of whitemetal lining of pad due to thermal cycling through excessive temperature range in service
Figure 2: Faceting on a whitemetal pad due to thermal cycling