Development of polytetrafluoroethylene composite lining for a hydrogenerator thrust pad application

Abstract

Babbitt is the usual lining material in the pads of hydrogenerator thrust bearings. During the start and stop of a hydroturbine, boundary lubrication dominates in the bearing and significant heating can occur in the contact. To avoid this problem, the rotor is normally jacked up. Another solution to the problem is polymer thrust pads with low friction. Such pads are extensively used in Russia and China. With these pads, jacking of the rotor is not necessary. Higher load-carrying capacity for these pads is also claimed. The present work describes the development of polytetrafluoroethylene (PTFE) composite pads for thrust pad application. In this approach, the composite is directly adhered to the steel backing unlike the present pad design where the pure PTFE is attached to the steel backing with bronze wire interface. The work involved material selection with a pin-on-disc machine followed by adhesive selection on the basis of bond strength tests under static and cyclic shear stresses. Finally the pads were evaluated in a scaled-down thrust bearing test rig for friction and wear behaviour. The results obtained show that bronze-filled PTFE lining directly adhering to steel backing is a successful replacement to babbitt.