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In Situ Observation of EHL Films of Greases by Micro Infrared Spectroscopy

In situ observation of lubricant films formed with greases was carried out with a micro-FTIR under EHL conditions between a steel ball and a single crystal silicon disk. Lithium-stearate and aromatic-type urea compound were used as a thickener and 12 mass percent of the thickener was added in PAO. From the IR spectra, CH peak, C=O peak and NH peak were observed from Li-stearate grease and urea grease, respectively. 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 the resolution of 50 μm. It was found that the concentrate on of thickener at EHL contact region was dependent on thickener itself. Although the concentration of Li grease decreased at EHL contact region, 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 was discussed based on the concentration of thickener at EHL contact.