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Gregory Simmons (LTU)

Published: 13 May 2011

Synthetic lubricants and polymer composites for large full film journal bearings

The rapid build-up of variable renewable power sources such as wind and solar are leading to increased instability in the electrical grid. Many methods of controlling this instability have been proposed but existing hydroelectric power plants in many cases already been enlisted to fill the regulating power needs of industry and the population. Filling this regulating power role necessitates that a machine changes load state more often and experiences an increase in starts and stops. Likewise, the push for a less environmentally intrusive society has raised the importance of utilizing equipment with reduced impact.

This situation has created a host of opportunities to improve existing power plants and upgrade designs of new power plants to allow for reduced impact, better reliability, and increased efficiency. As one of the most critical and failure prone components of the power plant, the bearings hold great potential for improvements that together can reduce impact while increasing efficiency and reliability.

To accomplish these opportunities, this work investigates the potential of new, environmentally adapted, lubricants to improve power plant efficiency. It then continues by developing guidelines for power plant operators when considering changing lubricants. Finally, the potential of polymer faced bearings to improve plant reliability at start up is investigated.

A journal bearing test machine was constructed to investigate a number of new synthetic lubricants and polymer bearing materials. These tests found that a significant reduction in power loss could be accomplished without significantly affecting the bearing's minimum film thickness by changing from a traditional mineral oil based lubricant to a high viscosity index lubricant of much lower base viscosity grade.

Further experimental work led to the development of practical guidance for power plant operators contemplating a lubricant change. This technique focuses on the importance of maintaining equivalent viscosity in the minimum film thickness region after a lubricant change. Efficiency improvements can then be calculated by comparing the viscosity in the bulk of the bearing to that with the original lubricant.

Experimental work with polymer bearing facing materials demonstrated the dramatic reductions in break away friction that these materials can provide. A number of polymer composite materials were investigated for their friction characteristics at the moment of the start of sliding, finding that PTFE based materials were far superior to traditional Babbitt metal. The break away friction of PTFE materials was much lower than that of Babbitt and furthermore, the PTFE materials provided a much more stable friction than Babbitt through large variations in both pressure and oil bath temperature.

Finally, experimental work with a full scale polymer faced bearing provided insight into the function of polymer faced bearings as well as valuable lessons in the further development of these bearings and their monitoring systems.