4. Principle of ferrography

The test method is based on visual microscopic evaluation of particles extracted and deposited on a microscopic preparation called a ferrogram. It consists in assessing the wear mechanism by observing the shape, color and contours of these particles, and the effects of a magnetic field. Combined with other analytical tests, analytical ferrography helps determine the cause of a failure, and can thus contribute to failure prevention (and thus to preventive maintenance). It can be used to diagnose the type and severity of wear.

Ferrography, a technique successfully used to analyze lubricants or hydraulic fluids, was developed forty-three years ago by Foxboro Analytical. It involves 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 G. cm- ^...