Ferrography
Ferrography is an oil analysis method that magnetically separates ferromagnetic and paramagnetic wear debris from a lubricant sample onto a glass slide over a magnetic field, enabling microscopic evaluation of particle size (10 μm to >1000 μm), shape, concentration, and composition to diagnose wear mechanisms and predict machinery failure.
In shop floor maintenance, ferrography involves draining a small oil sample down a ramp on a glass slide above a magnetic field, causing ferrous particles to precipitate by size. Analysts use optical microscopy to examine the ferrogram, identifying particle morphology (e.g., cutting, rolling, sliding) and heat-treating slides to reveal oxidation colors for metal identification. Results generate DL (large particles >5 μm) and DS (small particles) values for quantitative trend monitoring, enabling maintenance teams to shift from breakdown to proactive maintenance in CMMS systems. It is used for non-intrusive, on-line condition monitoring of aero-engines, mining equipment, and fluid-powered systems without teardown.
How does analytical ferrography differ from direct reading ferrography?
Direct reading (DR) provides quantitative DL/DS values via optical sensors; analytical ferrography combines quantitative data with qualitative microscopy to identify particle type, shape, and composition for root cause analysis.
Why is ferrography superior to atomic emission spectrometry for wear detection?
Spectrometry detects particles down to ~1 μm but misses larger, critical wear particles (>5–10 μm) that indicate active failure; ferrography captures the full 10–1000+ μm range where early fault signatures appear.
What wear contacts can ferrography identify?
It discriminates particles by morphology to identify four wear contacts: rolling, sliding, spinning, and impaction, linking them to specific component failures (e.g., bearing spalling vs. gear pitting).