In analytical ferrography, the solid debris suspended in a lubricant sample is separated. Solids are then passed across a bipolar magnetic field. A solvent wash cycle removes any lubricant remaining on the substrate, resulting in a ferrogram in which the particles are arranged by size and permanently attached to the slide for optical analysis using a biochromatic microscope. The particles are then examined and classified by size, shape, concentration and metallurgy. The information carried by the wear particles is valuable to help identify the wear mode and mechanism.
The analytical ferrography can be particularly effective in the detection of soft contaminants and the identification of their nature. It can be a powerful technique to identify machinery oil-related issues, root cause analysis, the morphology and the characteristics of insoluble particles, and the progressive mechanism of varnish formation. The ferrography test procedure is lengthy and requires a highly skilled analyst. However, the benefits can outweigh the costs. This analysis is the most recommended test if abnormal wear is observed.
Fourier transform infrared (FTIR) analysis is employed to measure organic molecular components, monitor the additive depletion and identify organic degradation by-products (oxidation). The particle count could also help monitor particle contamination. It should be noted that some particle counters are often not sensitive to small sizes of polar particles (less than 2 microns). The demulsibility of pump oil is usually a critical characteristic to evaluate, since it is affected by the presence of polar particles. The alteration of this property could be a signal of extreme particle contamination. P&S