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, lm 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. lm 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, Deff, 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 Deff /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.