Monitoring the degradation of a synthetic lubricant oil using infrared absorption, fluorescence emission and multivariate analysis: A feasibility study

The following describes a spectroscopic approach for achieving condition-ba se maintenance (CBM) through the monitoring of lubricant degradation in mac hinery. The approach uses infrared and fluorescence spectroscopy to monitor lubricant condition as a function of changing spectral variance. The use o f two different spectroscopies has been pursued because varying CBM require ments within the industrial and military communities can be mel with the co mplimentary advantages of each approach. Because the spectroscopic methods are inherently multivariate, the authors have also chosen to pursue a multi variate analysis of the data. The authors results show that multivariate in frared spectroscopy offers certain advantages over multivariate fluorescenc e spectroscopy and vice versa. It is shown that the two approaches fulfill different CBM requirements. This is an important and useful result because the CBM requirements for monitoring a given lubricant can vary greatly from one field application to the next. The authors have monitored a synthetic aircraft lubricant, Hatco Corporation (MIL-L-23699D), that is found in the rotary gearboxes of several military helicopters. The authors show that whe n used in conjunction with multivariate analysis techniques, such as PCA, t hat both infrared and fluorescence spectroscopy can provide an ideal means of monitoring the condition bf a lubricant as it degrades. The authors confirm that infrared absorption carl provide a means of monito ring the breakdown of the additive package, the decomposition of an ester f unctionality, and the production of a degradation breakdown product as a fu nction of degradation time. The authors also show that fluorescence emissio n can provide a rapid low-cost, easy-to-implement means of monitoring the " integrated" condition of a lubricant as a function of degradation time.