COA Oil & Grease Analyzer
Sweeping Flat Electrode Atomic Emission Spectrometry (SFE-AES) Method
A graphite flat electrode is used to hold oil or grease sample. The flat electrode is fixed on an XY sweeping wagon. Then spark starts on the flat electrode, strikes the sample on it, and produces optical emission signals. Meanwhile, the flat electrode is continually moving under the spark fireball until the sample is burned entirely. Spectrometric oil analysis of multi-elements is so realized. ASTM D8315 is a standard test method based on this technology.
This novel technology eliminates dependents of sample feeding system on the gravity and viscosity of samples, and thus leads to:
Advantages
1) Capturing large wear metal debris: the debris particles, no matter how large, “sit” on the wagon being sent into the fireball. In other words, the debris particles are no longer carried by oil itself. Thus, no matter whether the oil is thick or thin, large particles can always be fed into spark.
2) Because oil or grease sample is swept or scanned by a spark fireball, less populated large particles, if presenting on the flat electrode, can be illustrated by spectral signal surges.
3) Grease analysis: because sample “sits” on the wagon, and is fed into a spark gap by motion of the wagon, the viscosity of the sample is no longer a concern. Any kinds of lubricant, including grease, can be sent into a spark for testing. This eliminates tedious wet chemical methods to treat a grease sample for multi-elemental analysis.
4) Burned test sample is no longer recycled into its holder to be re-sparked during testing, as a problem encountered in RDE-AES oil analyzer.
Significance
Existence of large particles are the features of used oil. For wear metals, these particles, in size, are represented by those between 20 and 50 um in engine oil, 80 um or greater in gear-box oil and grease. In desert or windy areas, large sand and dust particles can enter in-service lubricant.
The concentrations contributed from large particles can be more sensitive to serious or catastrophic failure of industrial equipment than those from 10 um or less. In oil analysis, excluding these large particles significantly under-reports the concentrations of wear and contaminant elements. The corresponding results may not represent the actual state of in-service lubricant, as those obtained from ASTM D6595, D5185, and D7417. Graphite flat electrode method provides a quick and inexpensive way to report wear and contaminant elements in a comprehensive range of the size of particulates(high fidelity), and provides unique information in diagnostic method practiced in machine condition monitoring programs. As an extension, the measurement of the Concentration of Non-Suspendable Particles can be achieved (see Knowledge Base page).
Because SFE/AES results are truly relevant to the products of machine wear—particles, it expands the roles of elemental analysis for condition monitoring.
Expected Results
Wear metal and silicon dust results from this novel method may be much higher than those from ICP, RDE, and silver electrode based tester. This is well expected. While serving machinery, oil is in constant motion and disturbing, and makes large particles in suspension. SFE-AES results represent real wearing state of machinery, as well as true contamination of lubricants in operation.
Patented Method
The graphite flat electrode is actually the lower electrode of a spark gap. To eliminate cross-contamination caused by sparking electrodes, the graphite flat electrode is only used once and then discarded. The upper electrode is de-contaminated by an electrode sharpener. The whole system is somehow similar to traditional Rotating Disk Electrode (RDE) method, and thus named Sweeping Flat Electrode (SFE) method.
A US patent has been granted for the Sweeping Flat Electrode method.
The invention of SFE strikes almost all shortcomings of all types of traditional spark OES oil analyzers and is creating a new page for condition monitoring and lubricant analysis.