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

Abstract

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.

Keywords

• grease
• thickener
• film thickness
• concentration
• ehl
• in situ
• ftir