Katsumi Iwamoto

Influence of Manufacturing Error of Roundness for Characteristics of Cylindrical Journal Bearing

Influence of manufacturing error for characteristics of cylindrical journal bearing have been analyzed and evaluated. As a result, The manufacturing error of roundness on cylindrical journal bearings was found to affect the characteristics of the minimum oil film thickness, friction coefficient and non-dimensional stability threshold speed. Especially, the sensitivity of the non-dimensional stability threshold speed is larger than that of the minimum oil film thickness, friction coefficient. Therefore in the design of cylindrical journal bearings the manufacturing error of roundness is required to restrict to small value as far as possible.

Stress distribution of a coated film with an interlayer under elastohydrodynamic lubrication conditions

Abstract In recent years, there have been advances in techniques for improving sliding performance by using coated films possessing superior tribological properties to reduce failure of mechanical elements. Those techniques are often used under severe conditions, such as elastohydrodynamic lubrication (EHL). In this paper, to devise the optimum design of a coated film with an interlayer, the stresses generated in such a coated film are analysed by using a three-dimensional numerical analysis method, and the strength of the film is evaluated numerically. As a result, it is shown that, when the ratio of the modulus of elasticity of the coated film, Ec, to that of the substrate, Es, is 0.50, it is preferable that the thicknesses of the coated film and the interlayer be larger, and that the modulus of elasticity of the interlayer range from that of the coated film to that of the substrate. Furthermore, it is shown that in the case of Ec/Es=2.00, it is preferable to have a thicker interlayer irrespective of the values of the moduli of elasticity of the coated film and the interlayer.

Effective Shear Displacement on Lateral Adhesion Force of a Liquid Bridge Between Separated Plates

Adhesion force is among the most influencing factors in micro- and nano-mechanics. A liquid bridge between two bodies gives rise to the adhesion force, which usually acts as additional normal load. However, the adhesion force acts also in lateral. We measured the lateral adhesion force of a sheared liquid bridge between parallel plates. In addition, movement of contact lines is tracked by using an image processing technique, which allowed us to introduce an effective shear displacement. The lateral adhesion force has a linear relation with the effective shear displacement. It shows good agreement between experimental result and the analytical approach regarding changes of interfacial energy with simple rectangular shape of the liquid bridge. We further revealed that there is no contact line in pinned state even in the case with the very beginning of the sheared process. In this regard, however, the contact line on rougher surface is awkward in its movement. Therefore, the liquid bridge between two rougher surfaces has higher effective shear displacement, and it results in the higher lateral adhesion force.

Guideline of design on coated films with a gradient layer under elastohydrodynamic lubrication conditions

Abstract In recent years, there have been advances in techniques for improving sliding performance by using coated films possessing superior tribological properties to reduce failure of mechanical elements. Those techniques are often used under severe conditions, such as elastohydrodynamic lubrication (EHL). In this paper, to devise the optimum design of a coated film with a gradient layer, the stresses generated in such a coated film are analysed by using a three-dimensional numerical analysis method, and the strength of the film is evaluated numerically. As a result, it is shown that when the ratio of the modulus of elasticity of the coated film, Ec, to that of the substrate, Es, is 0.50, it is preferable to select the gradient layer in which the variation of modulus of elasticity decreases gradually approaching from the substrate to the coated film in the depth direction. Furthermore, it is shown that in the case of Ec/Es=2.00, it is preferable to select the gradient layer varying linearly the modulus of elasticity into the gradient layer.

Effects of Mobile and Bonded Molecules of Molecularly Thin Lubricant Film on the Vibrational Stability of a Sliding Ball

Lubrication by an extremely thin film has become very important in micromachines, magnetic recording disks, and so on. Molecularly thin perfluoropolyether (PFPE) films are considered a good lubricant for these micro devices. When the thickness of the PFPE film is thinned to several nanometers, it is possible to assume that the film consists of mobile and bonded molecules. In this paper, we investigated the role of these molecules from the viewpoint of the vibrational stability of the sliding ball with the disk surface. From experiments by the ball on disk type tribotester, it is found that both mobile and bonded molecules exist on the disk surface, the bouncing vibration of the sliding ball can be reduced wide load range. In the case where only mobile or only bonded molecules exists, there is little effect on the bouncing vibration.

Measurement method of physical properties of adsorbed layers

Lubrication by a molecularly thin film has become very important in micro machines, magnetic recording disks and so on. Molecularly thin film is considered a good lubricant for these micro devices. When, the thickness of the lubricant film is thinned to several nanometers, the tribological properties of the film become different from that of the bulk. Therefore it is important to know these properties. Quartz crystal microbalance (QCM) is common in thin film growth, where it is used for film thickness measurements. QCM allows one to evaluate the physical properties of viscous liquid layer on the quartz crystal surface. In this study, we investigated the effect of additives on the viscosity. When the additives formed the adsorbed layer on the quartz crystal, the decreases in the resonant frequency of the quartz crystal were observed. It is found that QCM can detect the properties of adsorbed layers.

Static Characteristics of Swing Pad Journal Bearings (Design Parameters)

Swing pad journal bearings consist of several segmented pads supported by curved laminates of rubber and metal. The pads swing and tilt because of the radial and circumferential deformation of rubber layer due to the hydrodynamic pressure in the oil film and also the frictional force. This type of bearing is expected to form a superior converging wedge in the oil film if the suitable values of design parameters is properly selected. Therefore, in the design of swing pad joural bearing, many parameters must be considered. The present paper evaluates such design papameters as the preload factor, the number of pad and pad configuration in simplified swing pad journal bearing whose pads are supported by a single layer of rubber. As the results, the swing pad bearing with lower preload factor and fewer number of pads is found to have superior performances. Furthermore, pad configuration and bearing temperature is found to affect the static characteristics in swing pad journal bearing.

Effects of Mobile and Chemically Bonded Molecules of Molecularly Thin Lubricant Film on the Vibrational Stability of a Sliding Ball

Lubrication by an extremely thin film has become very important in micro machines, magnetic recording disks and so on. Molecularly thin perfluoropolyether (PFPE) films are considered a good lubricant for these micro devices. When the thickness of the PFPE film is thinned to several nanometers, it is possible to assume that the film consists of mobile and chemically bonded molecules. In this paper, we investigated the role of these molecules from the viewpoint of the vibrational stability of the sliding ball with the disk surface. From experiments by the ball on disk type tribotester, it is found that chemically bonded molecules prevent direct contact between the slider and the disk surface. Furthermore, when mobile molecules exist on bonded molecules, the stability is improved in wide load range.Copyright