This study investigated oil film in contact portions formed by the dynamic loading of a push belt and pulley sheaves for automobile CVTs. Technical difficulties of direct oil film measurement came from the structure and movement of components in variator. We therefore employed an estimation method, which included the measurements of duochromatic interference of actual CVT belt elements, and thin film pressure sensors formed on a pulley sheave. Interferometry measurements showed that the film thickness, calculated by the formulae derived from the similarities between stable and transient Reynolds equations, indicated an accuracy of about 88%. This estimation approach was applied to an actual CVT variator under a typical operation mode. Crucial parameters regarding impulse contact were measured by the thin film sensor and sensor pressure showed peaks just after and immediately before contacts. Film thickness, which was estimated by the loading time and maximum pressure, indicated that the lubrication film had a thickness lower than the surface roughness of the components. That means the lubrication regime was in mixed or boundary, and the fact supports previous estimations by unit testing and chemical analysis of tribofilms.

The objective of the present work is to study theoretically, the steady-state performance of finite hydrodynamic porous journal bearings under micropolar lubrication. The fluid pressure in porous matrix follows Darcy’s equation. In the film zone, the modified Reynolds equation is developed considering micropolar lubrication theory. Both Darcy’s and modified Reynolds equations are solved using finite difference technique with successive over-relaxation method to obtain the steady-state film pressure. The steady-state performance characteristics are evaluated in terms of non-dimensional load carrying ability, friction force and friction parameter of a finite journal bearing for different values of micropolarity viz, l_m and N, and varying characteristics of porous bearing. The results show that the micropolar fluid is better than the Newtonian fluid when load carrying ability and friction parameters are concerned. The slip has a beneficial effect in terms of increase in load carrying ability and reduction in friction parameter approximately to 0.7, beyond which the advantage diminishes. l_m exhibits an optimal value around 10.0. In case of industrial machinery and home appliances which uses the porous bearings and where the lubricant either gets contaminated with micro-elements or dust, mixing of additives will return better results.

To determine the titanium adhesion inhibitory effect of organic solvents on the sliding surface between titanium (Ti) and ceramics, Ti disks were slid against silicon nitride (Si₃N₄) pins under dry conditions, in n-undecane, and in ethanol using a unidirectional pinon-disk machine. Ti disks were also slid against alumina (Al₂O₃) pins under dry condition and in ethanol. Contour measurement, microstructural observation and chemical analysis of the worn disk and pin surfaces were performed. Under dry conditions, the substances composed of Ti adhered to the whole of the wear scars of both the Si₃N₄ pin and Al₂O₃ pin. n-Undecane and ethanol inhibited the adhesion of Ti to the Si₃N₄ pin effectively. Tribochemical reaction products seemed to contribute to the wear of the Si₃N₄ pin/Ti disk pair in n-undecane and in ethanol. The amount of adhesion of Ti to the Al₂O₃ pin was less in ethanol than under dry conditions. Mechanical wear such as fracture and cutting seemed to be main wear mechanisms of the Al₂O₃ pin/Ti disk pair in ethanol. Wear of the Ti disk in ethanol was significantly affected by the surface roughness of the wear scar of the mating ceramic pin.

The diffusion of oxidized cobalt metal (CoOx) through a sputtered amorphous carbon film is investigated as a function of carbon film thickness and of temperature in dry air. A kinetic model is developed using the experimental data. The kinetic model is based on Fickian diffusion and includes modifications for carbon film porosity, tortuosity and for pore-clogging. The experimentally determined effective diffusion coefficient, D_eff, increases with increasing temperature and decreasing carbon film thickness. However, the bulk diffusion coefficient D is independent of carbon film thickness whilst strongly dependent on temperature. The diffusibility D_eff /D is thus a strong function of COC film thickness but is independent of temperature, indicative that the structure of the COC film is the significant determinant. An Arrhenius treatment yields an activation energy of 19 kcal/mol. The fitting parameters required to simulate the CoOx diffusion kinetics is tabulated. CoOx diffusion is modelled at 60°C as a function of carbon film thickness.

In situ observation of lubricant films formed with greases was performed with a micro Fourier transform infrared spectrometer (FT-IR) under elastohydrodynamic lubrication (EHL) conditions between a steel ball and a single-crystal silicon disk. Twelve mass percent of lithium stearate or aromatic-type urea compound were added as thickener to polyalphaolefin base oil. Peaks relating to CH, C=O and NH were monitored in the FT-IR analysis. The film thickness and the concentration of thickener were estimated from the absorbance of CH and the ratio of absorbance of C=O and CH. Two-dimensional distribution of the thickness and the concentration around EHL contact was obtained at a resolution of 50 μm. It was found that the concentration of thickener at EHL contact area was dependent on the type of thickener. Although the concentration of Li grease decreased at the EHL contact area, that of urea increased even at low entrainment speed. The thickener of urea grease was concentrated on the ball and the disk surfaces. The film thickness at EHL contact of each grease can be explained by the concentration of thickener at the contact. Lubricating characteristics of urea grease are discussed based on the concentration of thickener at the EHL contact.

Lubricants are very important consumables in all industries as failure in machine parts due to absence or wrong choice of lubricants carries enormous cost. The base oil used for the formulation of most lubricants is environmentally hostile mineral oil and 30% of lubricants consumed ends up in the ecosystem. However, mineral oil reserve is depleting and the environmental concern about the damaging impact of mineral oil is growing. The search for environment friendly substitutes to mineral oils as base oils in lubricants has become a frontier area of research in the lubricant industry. Vegetable oils are perceived to be alternatives to mineral oils for lubricant base oils due to certain inherent technical properties and their ability to be biodegradable. This paper is an overview of recent research on vegetable oils as base oil for lubricant production with focus on the prospects, challenges and efforts to overcome the challenges of using vegetable oils as base oil for the production of industrial lubricants. Compared to mineral oils, vegetable oils in general possess high flash point, high viscosity index, high lubricity, low evaporative loss, are renewable, and are environmentally friendly. Poor oxidative and hydrolytic stability, high cost, food versus energy debate, high temperature sensitivity of tribological behaviour and poor cold flow properties are reckoned to be the limitations of vegetable oils for their use as base oils for industrial lubricants. The current effort to overcome these limitations includes the use of non edible oils, additives, chemical modifications and thermal modifications. More research and legislation in favour of the use of vegetable oil lubricants is recommended.

This study investigated the effects of the electric potential of a surface on the lubricating capabilities of ionic liquids. The friction coefficient of 1-butyl-3-methylimidazolium iodide was unchanged by the electric potential of the surface because this ionic liquid has difficulty moving in a solution owing to its low conductivity. However, the friction coefficient, when lubricated with 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate and 1-butyl-3-methylimidazolium hexafluorophosphate, changed when the electric potential of the surface was varied. At -2.0 V, cations were adsorbed on the sliding surface. The alkyl chain of cations supported the load and achieved a low friction coefficient. However, at 2.0 V, anions were adsorbed on the sliding surface. Such ions cannot support the load, and thus reach a high friction coefficient.

Viscosity, density, pour point, flash point, and oxidation stability are some quality properties of engine oil. The entrance of any contamination into the engine oil can change its properties. In the present study the effect of calcite and silica sand dust particles on the quality of engine oil, namely, Sepahan Oil Production API, SC-CC, SAE 40, was investigated. The presence, amount, and particle size of silica and calcite in the engine oil were determined by X-ray diffraction (XRD), inductively coupled plasma spectroscopy (ICP), and energy dispersive X-ray spectroscopy (EDX), respectively. The concentrations of the silica and calcite particles (0, 1, 2, and 3 g/L) were used according to the dust conditions in the east of Isfahan, Iran. The quality of the oil was measured after 20 hours of the engine operation. The results showed viscosity, density, and the pour point of the engine oil were significantly (P<0.05) enhanced with the increase in the silica content, and its oxidation stability was decreased. However, no significant change was observed in the engine oil flash point. The calcite particles, except for the oil flash point, did not have any significant effects on the oil quality.

It is necessary to understand actual phenomena generated at the electric contacts to suggest the design concept for reducing wear of current collectors such as a contact wire and contact strip in an electric railway. However, rotating wear testing method like pin-on-disk which commonly used to evaluate the wear behavior cannot represent the wear modes of the current collector. In this paper newly linear wear testing method is introduced to represent the wear modes and the wear transition conditions between hard-drawn copper contact wire and iron-based sintered alloy contact strip. As a result, we found that the contact temperature which estimated from contact voltage is dependent on current and load, and then friction and wear properties at the current collectors under current condition are classified into three types by the maximum contact temperature.

To clarify the wear mechanism of current collecting materials such as a contact wire and a contact strip under electric current condition, it is necessary to clarify temperature distribution around the contact spot. However, the traditional method of estimating the maximum contact temperature such as the φ-θ theory cannot estimate the temperature distribution. In this paper, we newly proposed an electric field analysis model of hard-drawn copper and iron-based sintered alloy considering a degenerated layer such as an oxide film and wear debris. Then, we newly proposed the heat conduction equation applying the Wiedemann-Franz law, and analyzed temperature distribution in electrodes. As a result, we find that the relation between the maximum temperature and the contact voltage even in dissimilar electrodes are based on the φ-θ theory. The temperature distribution in electrode changes depending on whether or not degenerated layers exist, and the maximum temperatures of each electrode are not necessarily the same as those estimated by the φ-θ theory. Finally, we clarify the influence of the degenerated layer on the melting condition of electrodes, and explain the electric wear phenomena observed in the previous wear test.

We carried out wear tests with material combination of a hard-drawn copper contact wire and an iron-based sintered alloy contact strip by changing the apparent contact area with four steps to clarify the influence of the apparent contact area on wear properties under electric current flowing condition. And we focused on a film resistance such as an oxide film and a wear particle on the contact wire surface, and considered the relationship between wear depth and wear mode transition phenomena. Based on wear properties obtained from the wear test results and microscopic observations, we clarify the phenomena that the wear mode which maximizes the wear rate of contact wire will be changed depending on the apparent contact area, and that the wear depth determined by the apparent contact area and the load are important parameters for melting of contact wire. Finally, the possibility of suppressing the maximum wear of contact wire is suggested by decreasing the film resistance of contact wire with changing the apparent contact area.

The Japanese Society of Tribologists is pleased to announce that the Paper Award of Tribology Online 2018was awarded to:

◊ “Effect of Electric Field on Adhesion of Thermoplastic Resin against Steel Plate,” by Motoyuki Murashima, Noritsugu Umehara, Hiroyuki Kousaka, and Xingrui Deng, Tribology Online, Vol. 12, No. 2 (2017) 42-48.

and

◊ “Advanced Control of Frictional Properties on Paper Clutch Materials by a Combination of Friction Modifiers,” by Go Tatsumi, Shinji Hasegawa, and Yasushi Onumata, Tribology Online, Vol. 12, No. 3 (2017) 103-109.

Congratulations!The Award Medals were presented to the authors by Prof. Toshiaki Wakabayashi, the President of the Japanese Society of Tribologists, at the award ceremony in the JAST Annual Meeting on 20th May, 2019. The medals were mailed to the authors who were unable to attend the ceremony.

The Paper Award of Tribology Online is given annually to the author(s), either the JAST members or non-members, of the paper(s) judged as the best paper(s) published in Tribology Online (TROL) for the previous three years. All papers that appeared in TROL for the three years are reviewed by the JAST Awards Committee.