Flapper valve steel, Compressor, High efficiency, Fatigue, damping capacity
Due to the environmental, energy saving and economic requirements, development of very high efficient compressors is of great importance. Consequently, flapper valve material becomes a critical issue and a limiting factor for the development of compressor. This paper provides a discussion on the material selection of the flapper valve for the compressors with very high efficiency, based mainly on a basic research on the mechanisms of impact fatigue and a FEM simulation on the formation of stress concentration in the flapper valve during the impact process. Impact fatigue initiation is caused by the initial impact stress, but the fatigue crack propagation is caused by a wavy stress propagation. This causes the formation of secondary cracks at the stress concentration points where two stress waves have the same phase. The results indicate that the flapper valve materials for the very high efficient compressors should have both high impact fatigue strength for the initial stress, and high stress damping capacity to reduce the crack propagation rate. Most recent developed flapper valve steel, Sandvik Hiflex™, shows both higher impact fatigue strength and higher damping capacity comparing with other commercial flapper valve steels available. This flapper valve steel material has successfully been used in the newly developed high efficient compressors recently. Some case stories have been discussed.