4. Principle of ferrography

The test method is based on a visual assessment under a microscope of particles extracted and deposited on a microscopic preparation called a ferrogram. It consists of evaluating the wear mechanism by observing the shape, color, and contours of these particles, as well as the effects of a magnetic field. Combined with other analytical tests, analytical ferrography can determine the cause of a failure and thus contribute to failure prevention (and therefore preventive maintenance). It allows a diagnosis to be made of the type of wear and its severity.

Ferrography, a technique successfully used for the analysis of lubricants or hydraulic fluids and developed more than fifty years ago by Foxboro Analytical, consists of fixing in a capillary tube (or on a glass plate) placed in an intense high-gradient magnetic field (of the order of 5·10 ^5...