Particle Science

Critical wear particle range

Particles in the 5–15 µm range cause the greatest proportion of abrasive wear in precision mechanical components because they match bearing clearances (5–25 µm), generating maximum contact between abrasive particle and component surface.

Particle size distribution

Industrial fluid contamination follows a size distribution weighted toward smaller particles — for every 5 µm particle, approximately 10× more 2 µm particles exist. ISO 4406 counts at ≥4 µm, ≥6 µm, and ≥14 µm to capture the critical wear range.

Particle morphology

Particle shape and surface texture reveal contamination source: angular silica particles indicate air intake breach; smooth metallic platelets indicate fatigue wear; ribbon-shaped particles indicate cutting wear; carbon agglomerates indicate oil thermal degradation.

ISO 4406 code interpretation

Each code increment doubles the particle count — ISO 17/15/12 contains approximately twice the particles per mL as ISO 16/14/11. Moving from ISO 19/17/14 (commodity) to ISO 16/14/11 (system approach) extends bearing life 3–5×.

Automatic particle counter (APC)

Instrument using light obscuration (ISO 11171) to count and size particles in fluid samples. APC must be calibrated against NIST-traceable reference particles. Sample bottles must be pre-cleaned to ISO 14/12/11 to avoid contaminating the sample.

Critical particle range

5–15 µm

Bearing clearance typical

5–25 µm

ISO 4406 count sizes[ISO 4406]

≥4, ≥6, ≥14 µm

Code increment = particle count change[ISO 4406]

×2 per code unit

Bearing life improvement ISO 16/14/11 vs 19/17/14

3–5×

APC sample bottle cleanliness[ISO 11171]

ISO 14/12/11 minimum