Wear of hardfaced valve spindles in highly loaded stationary lean-burn large bore gas engines

The technological evolution of more efficient natural gas-fuelled large bore engines aggravates the load situation within the engine and thus as well the tribological system valve spindle/seat ring. As a result of these changes, valve recession increases and component lifetime decreases, i.e. higher failure rates and more frequent service intervals. The tribological issues can be traced back to the cleaner combustion which demonstrably suppresses the formation of a protective layer on the sealing faces.
In this work, Stellite® and Tribaloy®-hardfaced valve spindles with different operating hours and from the same gas engine were analyzed in terms of quantitative wear, oxidation and microstructural alterations in the wear scar. The observed wear mechanisms are based on microstructure fatigue and delamination, depending on the microstructure of the hardfacing. The severely worn sealing interfaces show no tribofilm at all, whereas a protective oxide layer is observed on the surface of the Tribaloy® hardfacing that features low wear.
The second part of this work describes wear phenomena observed on specimens from laboratory experiments using a newly developed component test rig – the valve spindle tribometer. The authors describe their approach to investigate wear mechanisms by separated simulation of valve closure and peak combustion pressure depending on different key parameters such as valve closing velocity, temperature or atmosphere. From these preliminary results, probable wear mechanisms are derived and correlated with microstructural properties of the hardfacing alloys.