UC Merced

Lubricants in mechanical systems are currently being designed to have greater efficiency and longer run time between maintenances. In lubricated systems involving high heat processes and tight tolerances, one impediment to this goal is oil degradation which leads to the accumulation of a thin, hydrocarbon-based film, known as varnish. Varnish can have adverse effects on a system ranging from loss of efficiency to total shutdown and replacement of costly key parts. There are several ways to address varnish and its precursors within a system, but, in the event of severe accumulation, the method typically used is a high flow rate chemical flush. Although many chemical cleaners exist in the commercial market today, there is no standardized method of directly comparing the removal abilities of these fluids. In this study, we used our lab’s existing varnish removal test rig, which allows in situ imaging of the varnish removal process. The rig pairs real-time imaging with a post processing algorithm to measure varnish removal. Both quantitative and qualitative methods were used to evaluate not only the effectiveness of the cleaner fluids at removing the varnish layer, but also the mechanism by which each fluid removes varnish. The rig was used here to evaluate a set of 13 commercial cleaners. A wide range of removal capabilities was observed from the fluids included in the study, from barely any removal to nearly complete removal after 8 hours of testing. In the process of the research, we improved the testing methodology and approach for analysis of varnish removal. In addition, we designed a new test cell to accommodate more realistic test objects. This study demonstrates the importance of comprehensive characterization when selecting the appropriate chemical cleaner for a given system plagued by varnish accumulation.