Influence of oil viscosity grade on thrust pad bearing operation

Abstract The effect of oil viscosity grade on the performance of tilting pad thrust bearings is examined in a wide range of shaft speeds and specific bearing loads. Data being discussed were obtained in tests carried out with 228 mm outer diameter (o.d.) and 267 mm o.d. bearings lubricated with ISO VG32 and ISO VG68 mineral oils in a fully flooded mode. In a low-speed range (below 40 m/s), the performance of the 228 mm bearing is analysed in terms of pad and collar temperatures, power loss and oil film thickness. Pad temperature and power loss are employed in the analyses of the 267 mm o.d. bearing operated at high sliding speeds of up to 115 m/s. The results show that there is a significant effect of oil viscosity grade on bearing main operating parameters. The substitution of ISO VG32 oil for ISO VG68 oil results in considerably reduced pad temperatures, lower power loss and thinner oil film thickness. However, no measurable difference in power loss was observed after the onset of turbulence. The influence of oil viscosity grade on pad temperature pattern is analysed. The thermal effect of oil viscosity grade on pad temperature pattern and power loss is also compared with the effect of offset pivot.