Norifumi Miyanaga

Development of Herringbon-Grooved Aerodynamic Journal Bearing Systems for Ultra-High-Speed Rotations

It is absolutely important for ultra-compact rotational machineries to achieve sable shaft rotation at ultra-high-speed. This paper discussed herringbone-grooved aerodynamic journal bearing systems developed for the purpose. In this system, the bearings are supported by rubber-O-rings for accurate and stable operations. To grasp the possibility for stabilization, two types of O-rings with different stiffness and damping properties under bearing supporting were tested in the experiment. As the results, the bearing system demonstrated the maximum rotational speed over 460,000 rpm without unstable phenomenon called whirl. However, the difference in rubber O-rings definitely affected the stability of the bearing system.

Effect of acid washing of SiC particles on dispersing and friction properties of Ni-P-SiC composite plating

This study investigated the effect of acidic solutions used in the washing process of SiC particles on the dispersibility of the particles in a nickel matrix. In addition, the friction behavior of the composite plating was investigated by sliding friction tests. As the results, by washing SiC particles with a HCl solution, the particles appeared in clumps and the rougher surface was created. On the other hand, by a HNO3 solution, the particles appeared with the homogeneous distribution, and thus the surface deposited was smoother. The Ni-P-SiC composite plating shows the lower friction force especially in the range of the slow sliding speed.

Investigations of Cylindrical and Conical Whirl Instabilities on Hydrodynamic Journal Bearings

Hydrodynamic journal bearings induced serious shaft vibrations called oil whirl. Since they often give severe damages to the mechanical systems, it is important to fully understand the phenomenon to avoid the occurrence by the proper bearing design. This study theoretically and experimentally investigated both cylindrical and conical whirl instabilities, which can be appeared in journal bearings, and their relation was discussed. As the result, the span length of the bearings had a significant effect on the vibration mode. The transitional state in which the cylindrical and conical whirl instabilities alternately appeared was observed.