Analytical Ferrography is a technique for depositing and analysing wear particles contained in an oil or grease sample.
The sample is deposited onto a glass slide, with the particles trapped by strong magnets and the oil washed away with a suitable solvent. Both linear and rotary particle deposition systems exist. At STS preference is given to a rotary system, which has been developed at the company. It ensures good separation of particles over the three rings, with particles also being sorted by size with the larger particles settling out on the inner ring.
Once deposited the particles are analysed by a metallurgist, who is able to report on the relative quantities, types and sizes of particles present. A Particle Quantifier Index of the slide is also recorded. All of this is taken into account to produce a comprehensive report on the wear rate and situation.
You can find an example Ferrography Report here.