Tribology Online Vol. 12(2017) No. 4

Ionic liquids have potential for use as novel high-performance lubricants because of their attractive characteristics such as low volatility, high-thermal stability, and oxidation stability. It is known that ionic liquids exhibit excellent lubricity for metals because of halogen constituents in their molecular structure. However, occurrence of corrosive damage on the contacting surfaces lubricated with the ionic liquids has also been reported. To prevent damage due to corrosion, it is necessary to use halogen-free ionic liquids whose lubricity may be inferior compared with that of halogen-containing ionic liquids. In this study, the lubricity of halogen-free ionic liquids 1-butyl-3-methylimidazolium dicyanamide ([BMIM][DCN]) and 1-butyl-3-methylimidazolium tricyanomethane ([BMIM][TCC]) was evaluated by using a reciprocating sliding friction and wear tester (SRV Optimol)) using an oscillating steel cylinder on H-free DLC disk test configuration under boundary lubrication conditions. The SRV test results showed that H-free DLC with [BMIM][TCC] at 50N exhibited superior lubricity than that with [BMIM][DCN] at the same load. In order to understand the observed, the worn surfaces of test specimens were analyzed by using Raman spectroscopy, the friction coefficient of the film by atomic force microscopy (AFM), and the chemical composition by time of flight secondary ion mass spectrometry (TOF-SIMS). From Raman spectroscopic analysis results, graphitization of the transfer films of both [BMIM][DCN] and [BMIM][TCC] did not occur. From AFM results, the topography of [BMIM][TCC] was smooth as compared with that of [BMIM][DCN]. Thus, it was considered that the surface roughness affected the lubricity. In addition, the tribofilm derived from [BMIM][TCC] also affected the lubricity because it showed low friction coefficient on the flat position. From ToF-SIMS results, it was considered that [BMIM][DCN] itself adsorbed on H-free DLC surface. On the other hand, [BMIM][TCC] is thermally decomposed by friction and generated isolated CN and covering the H-free DLC surface. The tribofilm formed by [BMIM][TCC] exhibited lower friction coefficient than that by [BMIM][DCN].

Lithium based grease formulations are the most common lubricants used in industry today. Sulfur containing additives play a key role in improving wear and friction performance of these greases. The current study is focused on developing an understanding of characteristics of chemical bonding between sulfur carriers (MoS₂, WS₂ , MoDTC and organo tungstate ) and the interacting surfaces and evaluates their effect as anti-wear and anti-friction agents. ASTM D2266 and spectrum loading tests with varying loads while keeping other tests parameters constant were performed on the grease blends to understand effects of cyclic loading on tribochemical degradation of sulfur carriers. Tribofilms formed on the wear surface were analyzed using surface characterization techniques like SEM, EDS and Stereo Optical Microscopes. Wear scar diameter (WSD) and coefficient of friction (COF) were reported for the tests performed. This research aims to gain better insight on the atomic coordination or oxidation states of sulfur atom in additives and their correlation with anti-wear and extreme pressure performance when blended in greases.

Engineering plastic materials like polyamide and polyacetal are widely used for worm wheels and other tribological elements under EHL conditions with grease; typical examples are found in electrical power steering systems and power window mechanisms. Low elastic modulus of those materials makes their contact pressure much lower than steel-to-steel contact, and EHL of those contacts is called “soft EHL”. The current concern of this technology is higher reliability and lower friction losses, which mean maintaining sufficient EHL film thickness and reducing traction in tribological terms. The present work tries to measure soft EHL film thickness and traction of oil and grease by an optical interferometry EHL system, in which a steel ball was made contact with a transparent polycarbonate disk having a similar elasticity as the above-cited engineering plastic materials. The results show that prediction is possible by using the analyses by Dong and Qian for the film thickness and by Muraki and Kimura for the traction coefficient.

This article aims to study the influence of slip on a hydromagnetic squeeze film in transversely rough porous narrow journal bearing. The Neuringer-Rosensweig model governs the fluid flow. The slip model of the Beavers and Joseph has been used. The stochastic modeling of Christensen and Tonder has been adopted for calculating the effect of transverse surface roughness. The pressure distribution is obtained by solving the concerned stochastically averaged Reynolds type equation. It is observed that the adverse effect of roughness gets compounded due to slip effect. Equally is the crucial role of eccentricity for the performance of a bearing system. The results confirm that slip has to be at minimum for any improvement in the performance. Besides, the absence of flow does not deter the system from supporting a good amount of load which does not happen in the case of a traditional lubricant.

Euler’s belt formula for a fixed circular drum is well known and is an important formula for mechanical engineers. However, there is little book in which belt equation for a drum of any contour is discussed precisely. This study was carried out to confirm the validity of the Euler’s belt formula applied to a drum of any contour. The calculated result was verified to ascertain whether it satisfied the static equilibrium equations of the force and moment. The results perfectly satisfied the static equilibrium equations of the force. As for an equilibrium of the moment, it was found in the case of a belt wrapped around an elliptical drum that the moment from the belt tension was equal to the integrated moment caused by frictional force and normal force along wrapped length. Normal force distribution under a belt on a cylindrical surface was evaluated experimentally by a pressure sensitive film which was found to correspond qualitatively to the theory. As an example, an equation to calculate the normal pressure and tension of a belt wrapped on an elliptical drum was derived.

It is well known that the surface roughness of metal substrates considerably influences the tribological properties of solid lubricants. In this study, the surfaces of metal substrates were modified by wet-blasting and polishing, and the lubrication performance of synthetic mica-organic intercalation compounds on these substrates was evaluated using an upsetting-ironing type tribometer. Wet-blasted substrates lubricated with synthetic mica exhibited the best anti-seizure ability, whereas a lubricated polished metal surface produced the worst results. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) revealed that concavities prepared by wet-blasting still remained on the ironed substrate surface, and the intercalated synthetic mica trapped in concavities was supplied to the flat areas as ironing advanced across the substrate surface. Furthermore, EDS and Fourier-transform infrared spectroscopy (FTIR) analysis showed that intercalated synthetic mica extended on the ironed surface while releasing organic compounds from its interlayer spaces. As the ironing process continued to progress, the initial concavities gradually became shallow, but they did not completely flatten. Therefore, a roughened surface is more advantageous for achieving improved lubricity due to the continuous supply of solid lubricant from concavities to the flattened areas where seizure is likely to take place.

The Japanese Society of Tribologists is pleased to announce that the Paper Award of Tribology Online 2016 was awarded to:

◊ “Flexible Control and Coupling of Adhesion and Friction of Gecko Setal Array during Sliding,” by Yu Tian, Dashuai Tao, Noshir Pesika, Jin Wan, Yonggang Meng, and Xiangjun Zhang, Vol. 10, No. 2 (2015) 106-114.

◊ “On the Magnitude of Load-Carrying Capacity of Textured Surfaces in Hydrodynamic Lubrication,” by Kazuyuki Yagi, Hajime Sato, and Joichi Sugimura, Vol. 10, No. 3 (2015) 232-245.

and

◊ “The Development to Control Simultaneously Viscosity and Separation Temperature of a Two Phase Lubricant for Practical Use,” by Kumiko Kamata, Yasushi Kawamura, Ryuji Maruyama, Eiji Nagatomi, and Hiroyuki Tazaki, Vol. 11, No. 1 (2016) 24-33.

The Award Medals were presented to the attended authors at the award ceremony by Dr. Shiro Nakano, the President of the Japanese Society of Tribologists, at the JAST Annual Meeting on 16th May, 2017. The medals were mailed to all 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.