Mechanical Behavior of Nozzle Guide Vane Bushing in Absence of Lubrication by Means of Novel Endurance Test Rig

Nowadays, Variable Guide Vanes such as Inlet Guide Vanes (IGVs) and Nozzle Guide Vane (NGVs) are key components in the design of axial expanders and gas turbines, which are now required to work with an ever-increasing flexibility due to the frequent shutdowns, start-ups and load changes to which they are subject. Such severe service conditions, due to the ever-increasing introduction of the renewable energies in the energy market, are particularly challenging for such components, which were already intrinsic complex in order to obtain higher availability performances. For this reason, a deeper understanding of the mechanical behavior of such components by means of experimental characterizations has become mandatory for the design process, especially when high loads are involved. Under such premises, the present work, starting from the recently presented novel design of an experimental test rig, aims at showing the results of a testing campaign performed on standard and coated bushing. The test article manufacturing technology selected for the campaign will be presented. Then results of static testing, aimed at measuring friction coefficients of the whole kinematic assembly, will be summarized both at room and operating temperature both for new and worn geometries. Also, the outcomes from accelerated endurance tests, lasting 200h and performed with peak temperature of 525°C in absence of lubrication, will be reported giving insights on the design of these kinematic couples. Inspections of analyzed specimens are also included in the postprocessing. These results are a key element for the improvement of the life prediction of these components enabling progressively more challenging operating conditions for the next generation of expanders.