Lubrication science
Wear particle shapes: what the debris says about the damage
Quick answer
Rubbing, cutting, sliding, fatigue, corrosive and oxidation debris, and the machine problem behind each.
Why shape matters
A particle count says how much debris is in the oil. The shape, size, surface and colour of the particles say how it was made. Analytical ferrography collects particles with a magnet onto a slide and examines them under a microscope. Reading it is a skill, so treat it as a second opinion to confirm and diagnose, not a screening test.
Particle types
| Type | Look | Likely cause |
|---|---|---|
| Normal rubbing wear | Smooth, flat, silver-grey flakes, small | Normal wear-in and running |
| Cutting wear | Long, sharp, curled, thin, like wire or swarf | Abrasive contamination or misalignment cutting a surface |
| Severe sliding wear | Large, thick, scored or striated, often discoloured | Overload, lack of lubricant, high speed or temperature |
| Fatigue (spalling) wear | Chunky, laminar flakes with rounded edges | Rolling fatigue in bearings or gears |
| Corrosive wear | Reddish-brown corrosion pits and oxides | Water or acidic attack |
| Oxidation debris | Black, soot-like particles | Overheating and oil breakdown |
Severity guide
| Level | What you see | Action |
|---|---|---|
| Normal | Small, fine particles | Continue routine sampling |
| Caution | More particles, still mostly small | Monitor the trend and shorten the interval |
| Warning | High particle rate with large particles | Find the cause and fix it soon |
| Critical | Severe, large particles | Act at once and inspect the machine |
Ferrography and ICP together
- Elemental analysis (ICP) gives the amount of each metal, mostly for particles up to a few micrometres. It is good for trends.
- Ferrography gives particle size, shape and type. It is good for finding the cause.
- Use both: ICP to alarm, ferrography to explain.
Takeaway. Wear particles are the fingerprints of machine damage. Read them with the particle count, the elements and the trend, never alone.
Put it to work in the tool