Tribology of journal bearings under environmentally adapted lubrication with shaft oscillation

Abstract: To make the hydro power application more environmentally adapted new EALs such as synthetic esters will replace the existing mineral oils. This study aims to exploit the EALs potential in boundary lubrication, especially in slow sliding journal bearings with shaft oscillation as those supporting the Kaplan turbine blades. In order to evaluate the performance of different lubricated environmentally adapted journal bearings a test rig was built. Many test rig parameters were set to simulate water turbine conditions. Tests were performed with different bearing and shaft materials and different lubricants suited for water turbine application, EALs, water with and the present used mineral oil reference. Additional lubricated tests in oscillating motion were conducted with a roller on disc and a pin on disc. All tests were performed with oscillating motion. The results showed that synthetic esters affect the contact material to a larger extent than the tested mineral oil. The synthetic esters were also sensitive to the selection of bearing and shaft material. Highly alloyed bronzes were more prone to corrosive wear. A coated shaft showed excellent performance with a low alloyed tin bronze. The comparison of self lubricated bearings with water lubrication to an EAL lubricated tin bronze on stainless steel showed large performance differences between the water lubricated materials. They showed both better and worse friction and wear results than the EAL lubricated tin bronze. The oscillating pin on disc can generate similar contact mechanisms as in a journal bearing. The most important conclusion of this work is that it is possible to find self lubricated journal bearings better suited for shaft oscillation than EAL lubricated bronze bearings in water turbine application. Water lubricated design of the bearings are the most environmentally adapted solution. EALs such as the tested synthetic esters have a promising future in the hydraulic systems controlling the turbines and can under certain boundary lubrication conditions with bronze show excellent performance.