Machinery Lubrication

Machinery Lubrication Jan Feb 2014

Machinery Lubrication magazine published by Noria Corporation

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28 January - February 2014 | By SuSAn BeneS, Fei weAr deBrIs ANAlysIs Alternatives traditional wear Particle Analysis M Figure 1. Sample preparation of oil samples for SEM/EDX analysis Figure 2. Sample setup Many of the methodologies existing today for oil testing provide only one key parameter of diagnostic information such as particle size or chemical composition. While a single param- eter can offer clues as to what is occurring in an engine or motor, more often than not it is inconclusive. Laboratories frequently recommend a battery of tests to obtain a more comprehensive diagnosis. This often leads to confusion as to how to interpret the data or even which method to request and how often. However, a new way of evaluating wear debris allows a complete diagnosis to be achieved with one test that can be performed by in-house maintenance technicians. SEM/EDX Historically, scanning electron microscopes (SEMs) have been viewed as manual imaging instruments that require qualified users in specialized environments. Recent advances in SEM tech- nology have provided more compact, easy-to-use instruments applicable to a more industrial setting. When combined with an energy dispersive X-ray (EDX) detector, the SEM has the ability to perform quick, quantitative composi- tional measurements. An SEM not only can measure and record the size and shape of a wear debris particle, but it can also determine the particle's elemental makeup, thereby combining the physical and chemical worlds of wear analysis into one. An automated SEM/EDX wear debris analysis system uses a single hardware control configuration for both the SEM and EDX components, making it more compact and robust for industrial wear debris applications. Simplifying the system even further, the instrument is set up to operate via pre-programmed recipes that allow the user to walk up to the system, load the samples, initiate the run and walk away, only to come back later to sample reports. All calibration and instrument operation is automated and does not require user management or monitoring. Utilizing back-scattered electrons (BSE) on an SEM enables the system to take advantage of the strong correlation of the average atomic number of the particles and the BSE signals. Hydrocarbons and other particle types with a low average atomic number tend to scatter fewer electrons than metallic particles and other particle types with a high average atomic number. Thus, in a BSE image, metallic particles look bright, while organics look dark. One of the main differences between SEM/EDX and tradi- tional methods is in its sample preparation. Figure 1 illustrates the sample preparation and analysis expectations of the SEM. Ultimately, a small portion of the oil sample is needed to prepare a representative sample on a filter membrane. Once loaded into the system, these analyzers move the beam across the full field through a sequential array of fairly coarse steps, constantly searching for a particle of interest and moving to the next field instead of capturing a high-resolution image of the frame. A particle is detected when the contrast intensity level of the particle exceeds the predefined threshold background set for each analysis activity. This particle-sizing sequence initiates a rotating 16-cord algo- to

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