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Ferrography

Test equipment

Predict FM (Ferrogram Maker)

Ferroscope (Olympus bi-chromatic microscope, 100x, 500x, 1000x mag.) mounted with a digital camera

Hotplate with surface thermometer

Sample size

10ml (recommended), 3ml (minimum)

Standard

Astm D7690 (modified)

Unit

None (qualitative for ratings on wear severity levels which is based on concentration and size). Particle size reported in microns.

Test methodology

Analytical ferrography is the microscopic examination of the ferrous (iron) and other particles found in the oil sample.

FM Maker

Ferroscope

Hotplate with thermometer

An oil sample is let to flow over a specially treated slide at an angle above a strong magnet. The strong magnet will attract the ferrous particles, resulting in the deposition of ferrous particles onto the slide. Non-ferrous and contaminant particles, will be randomly deposited across the length of the slide, caught by the ferrous chains of particles.

The particles deposited neatly on a ferrogram is now ready to be analysed at the microscope.

The analyst is then able to visually inspect the present ferrous wear and deposited particles, aided by a Bi-chromatic (transmitted and reflected light), filters, polarizers, and magnifications of 100x, 500x, 1000x.

A digital camera attached to the microscope allows for capture of images of the particles.

Hotplate with surface Thermometer :

For heat treatment of the particles on the ferrogram, to 330 degree celcius for 90seconds.

Notes (application)

Ferrography (wear particle analysis) is a non-destructive,

optical technique to evaluate the size, shape, composition

and concentration of wear particles in oil or grease to

determine component wear condition.

Example :

  • Long curls of particles are indicative of abrasive wear, caused by hard contaminants.
  • Flat and pitted particles (as if rolled by a rolling pin) are indicative of rolling/laminar wear. Increased laminar wear together with small micro-spheres, points toward bearing fatigue wear mode.
  • Red ferrous oxide particles indicate rust and presence of water contamination.

There are various more particles that can be identified, giving an insight into the wear mechanism and wear severity of a system.

By using filters, polarizers, reflected and transmitted light, the particles can be better identified (ie. Metallic or non-metallic, etc)

A simple heat treatment allows for general metallurgy identification, especially for steel alloys. At 300c for 90s, low alloy steels change from a shiny gray-white to blue color.

Suitable for systems

Especially useful for Gearbox wear monitoring. Appropriate for every lubrication type (as long as a representative sampling location is available)

Also suitable for Grease samples.

Analytical ferrography needs to be complimented with a detailed system and component information, sampling point location and trending for a meaningful analysis.