Material analysis for a rotating inlet valve : Sliding contact in an oil-free super-critical steam environment

Sammanfattning: In this thesis, the aim is to study possible tribo-materials for a rotating inlet valve and to find a suitable material combination for the contact. The valve is part of a modern oil-free and high temperature steam engine. Systematic material selection together with tribological tests and wear analyses are performed. The metals Nitronic 60 and Stellite 6B are tested as self-mated metals, and run against graphite. None of these combinations are found suitable. However, the tests show carbon-based materials to be promising. After further study another carbon-based material, antimony impregnated mechanical carbon is selected as valve seat. For the mating part valve distributor, the material ZrO2-MgO is selected. This tribo-pair has shown friction and wear in the same interval as oil-lubrication. The friction and wear are 50% respectively 10% of the second best tribo-pair found in this thesis. The valve seat material is realizable if supported by a valve block of a Ni-resist cast iron with thermal expansion similar to the valve seat. Lastly a redesign of the valve distributor is suggested to comply with ceramic design guidelines.