Preload Effects of a Guide Bearing on the Metal Temperature and the Shaft Vibration

Abstract

Segment type vertical guide bearings are widely used for vertical rotating machinery; nevertheless, bearing problems, such as excessive vibration and temperature rise, frequently take place in the actual rotating machine. The purpose of the present work is to investigate the influence of preload effects of a segment type vertical guide bearing on the bearing metal temperature and the shaft vibration, in a hydraulic pump-turbine. Investigations have been performed not only by in-situ measurement but also by theoretical analysis. A guide bearing consists of eight pads and runs bi-directionally. Both the shaft vibration and the bearing metal temperature are very high in the non-preloaded bearing but are slight in the preloaded bearing, comparatively. Bearing metal temperature is decreased by the increase of cooling effect of the lubricant due to the preload effect. Shaft vibration is also decreased by the increase of bearing stiffness. Theoretical analysis shows that the segment type vertical guide bearing has an optimum preload ratio at which the bearing stiffness reaches a maximum value while the bearing metal temperature is minimized. Furthermore, it is found that the characteristics of shaft vibration of a Francis type hydraulic pump-turbine highly depend on the generating power.