Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1449093
4 | January - February 2022 | www . machinerylubrication.com AS I SEE IT answers to those questions. The answers (particles) were briefly in the oil for sure, but they were quickly removed and now reside in the interstices of the filter. Over time, your filter becomes loaded with data, like a hard drive. But sadly, the filter is usually discarded, along with the data it's carrying. In contrast, a filter that's skillfully inspected and analyzed tells a story about the history of the machine and the oil. Yes, it is often more expensive than oil anal- ysis by itself. However, you can't analyze what isn't there. Go to where the data resides, not to where it used to be. Don't be a penny wise and a pound foolish. Many of the major labs that provide oil analysis services also provide used filter anal- ysis. Noria offers used filter testing as well. e report shown in figure 5 is an example of data that can be extracted from a filter as received by the lab for inspection and analysis. Visual Inspection of the Filter Make sure you're using a lab familiar with how to examine a used filter. ere are many subtleties requiring special knowledge and skills. ese relate to the filter media, the center tube (core), the seals, varnish (end caps and center tube), and adhesives. e complete filter needs to be examined, with findings included in the comments section of the report. Next, the filter should be dissected. e media pack will need to be cut away (or sheared) to allow the pleats to be spread open like an accordion. e condition of the pleat pack should be closely examined for structural and manufacturing integrity. Look for holes, breaks and sludge. e individual plies of the pleat pack can then be peeled away to allow the actual filter media to be examined (usually the center ply). Some filters have as many as six different plies. Many labs use light tables to look across the filter media for inconsistencies. A system should be used to characterize or grade the visual observations of the filter and media. For the filter in the through "signifi- cant concerns" were noted. A description of the nature of these concerns is provided in the table. e better labs will include annotated photos of the filter and media in the report. Wear Debris and Contamination Removing contamination is the primary function of the filter. Look for evidence that the filter is doing this job and the integrity of the media has not been compromised (cracks, ruptures, etc.). Particles can easily be removed from the filter media for both soft and hard analysis. One method is the particle resuspension method using an ultrasonic bath. Other labs backflush the filter or swatch of media to extract the particles for examination. Either method is suitable. e particles can then be examined visu- ally, similar to analytical ferrography. is can best be done by preparing a micropatch or ferrogram (or both). Contaminant and wear debris characterization can follow the meth- odology described in ASTM D7684. Photomicrographs of salient (meaningful) particles should always be included in the report. Ideally, these images are annotated or have a caption with descriptive information. Scanning electron microscopy (SEM) images are often provided by labs as well. Elemental analysis is important to better understand the composition of the particles. Examples of elemental data of particles extracted from a filter are seen on page two of the example report (Figure 5). e relative concentrations of metals help provide context about the type of particles and their origin. e data can be compared to previous filters to alert to changing conditions. Different methods can be used to analyze particles elementally. ese include Inductively Coupled Plasma (ICP), by acid digestion and x-ray fluorescence spectroscopy (XRF). SEM-ESD is another option. Varnish & Sludge Many filters will be loaded with soft contaminants. Various methods can be used Figure 3: Preparation of a micropatch Figure 4: Micropatch debris field using the resuspension method to remove particles from the filter for inspection and analysis.