ferrography

Ferrography, or ferrographic analysis, is a diagnostic technique used to study wear debris and the condition of lubricants by isolating and examining ferromagnetic particles within oil or other fluids. The approach provides qualitative and semi-quantitative information about wear processes, contamination, and lubricant health.

The method relies on magnetic fields to attract and concentrate ferromagnetic particles onto a collector surface, where they form a deposit that can be visually and chemically analyzed. Particles are examined using optical microscopy, and can also be studied with scanning electron microscopy or spectroscopy to assess size distribution, shapes, and surface features. Based on particle morphology and concentration, wear mechanisms such as adhesive, abrasive, or fatigue wear, as well as contamination sources, can be inferred.

In practice, direct ferrography involves bringing a magnetic field into contact with a slide or filter so that particles are deposited in situ from the oil sample; indirect approaches collect particles on a substrate after filtration or separation for subsequent analysis. The results are typically semi-quantitative—indicating relative loading of wear particles—and qualitative in nature, aiding interpretation of lubricant condition and equipment performance. Ferrography is commonly applied to oil samples from engines, transmissions, gearboxes, hydraulic systems, and other machinery.

Applications include trouble-shooting lubrication problems, monitoring equipment health, guiding maintenance decisions, and understanding wear mechanisms. The technique is particularly useful for identifying ferromagnetic debris and assessing wear origins, but it does not detect non-magnetic debris; such wear requires complementary analytical methods. Proper interpretation relies on skilled analysis and consistent sampling and preparation.