The purpose of the paper is to present findings on creating new pump-in and pump-out type of gas-lubricated grooved spool bearings. A gas-lubricated grooved spool bearing can generate a gas film bearing pressure with shaft rotation in either direction, and also support both an axial load and a radial load at the same time. So far, several studies on the gas-lubricated grooved spool bearings have been reported. However, such conventional studies investigated only one rotational direction. In previous researches the authors proposed a new idea for journal, thrust circular-disk, conical and spherical type bearings rotating both regular and reverse sides. As a result of such previous studies, proposed idea shows satisfactory properties as a bearing. In this paper, an optimal regular and reverse rotation-type gas-lubricated spool grooved bearing is developed referring to bearing parameters. Our approach utilized the narrow groove theory. Suitable combinations of parameters of thrust/journal bearing for spool bearing were shown by numerical analysis of bearing characteristics (the load carrying capacity, the stiffness, and the damping coefficient, etc). It is clarified that the present bearing is not inferior to the conventional bearing.
Hydrogenated amorphous carbon (a-C:H) films have been applied in many mechanical components because of their prominent mechanical and tribological properties. Since these properties of a-C:H films are deeply correlated with their microstructure, it is important to understand the microstructure of a-C:H films and then discuss the friction properties of a-C:H films in a microstructural point of view, to clarify the friction mechanism. In this study, the microstructure of a-C:H films was analyzed by Raman spectroscopy, and the friction tests were conducted using pin-on-disc type tribotester in the air. It was found that the frictional properties of a-C:H films depend on their microstructure, i.e., polymer-like carbon (PLC), diamond-like carbon (DLC) and graphite-like carbon (GLC) structures. The PLC and GLC-structured a-C:H films show lower friction coefficients compared to that of the DLC-structured film. Two different trends are observed in the relationship between the hardness and the friction coefficient with respect to the microstructure of a-C:H films. The chemistry of the friction interface is dependent on the microstructure of a-C:H films, which affects to the friction coefficient.
Conventionally, several reports on quantification of wear of current collecting materials have been published. The objectives of these reports were to predict the wear of current collecting materials in field. However, the measure to reduce the wear of current collecting materials has not been proposed yet. In this paper, the authors focus on wear mode transition phenomena to propose the wear reduction measure, and carry out an electric potential distribution analysis and a temperature distribution analysis. From the analysis results, it is found that the relationship between electric potential and temperature is formed parabolic curve, and the curve depends on only a contact voltage. Further, the authors propose a “wear mode map” which shows transition conditions between wear modes under electric flowing condition by formulating the parabolic curve. According the wear mode map, the authors identify the three dominant parameters of wear mode transition as a contact voltage, contact resistances include film resistance and melting points of current collecting materials.
Wear resistance is required for current collecting materials such as a contact wire and pantograph contact strip because lives of these materials are determined mainly by wear. Conventionally, contact wire and contact strip have been developed independently each other, and there is no concept to reduce wear of them by combining material properties. In this paper, the authors suggest a map which shows tendency of respective wear mode occurrence against any material combination by using a melting point and an electric resistivity. Based on the map, the authors select the wear specimens as nickel for imitation contact wire and iron-based sintered alloy for contact strip so that a melting wear mode of contact wire would not be occurred. As the result of wear test, the melting wear mode and large wear rate of contact wire could not be observed in any load condition as expected. Finally, the authors indicated the possibility of wear mode control for wear reduction measure by combining current collecting materials.