Performances degradation of tilting-pad thrust bearings due to electrical pitting

Abstract

Electrical discharges in rotating machines may interest every kind of bearings, both roller, oil-film thrust or journal, when an electrical machine is installed in the shaft-line. The consequence of this phenomenon is a reduction of the performances of the bearing such as its load capacity, leading to possible failures of the bearing pads mainly due to overheating. In this paper, a case history of electro discharge machining of the thrust bearing of a small steam turbine is presented. A detailed model, able to take into account the effect of electrical pitting and loading capacity decreasing as a consequence of the damage of the Babbitt metal, is also proposed in the paper. Simulations show that the phenomenon causes the irreversible failure of the thrust bearing.