ASTM ENHANCEMENTS TO MICROSCOPIC PARTICLE IDENTIFICATION AND DOCUMENTATION

In 1982, Daniel Anderson published his influential book, "Wear Particle Atlas", which describes, sizes, and classifies particles found in oil.

The particles of greatest importance are wear metals, although other particles, such as fibers and foreign materials, are also identified.

Still widely referenced today, Wear Particle Atlas serves as a foundational reference for the various wear particle techniques currently being developed. This includes both microscopic and digital approaches.

Microscopic particle evaluation requires that particles are deposited onto a static surface and inspected with a microscope. Digital particle identification techniques measure pixels associated with the particles, which are dynamically measured as they flow past a detector array. The American Society for Testing and Materials (ASTM) is actively involved in developing standards to improve the value and utility of both approaches.

Microscopic Evaluation of Wear Particles

Using a microscope to inspect particles extracted from oil samples is a powerful and universally used advanced oil condition monitoring technique. As ASTM standardized this, it found that the classification and identification of particles were not uniformly applied by the end-user community.

As a result, ASTM D7684 was written to standardize the terminology and description of particle shapes, textures, and colors. ASTM D7670 (membrane filters) and D7690 (Ferrography) were written to support test methods that can be used to separate and deposit the particles from the oil onto patch or glass substrates for visual analysis.

While this technique is widely used, there are several problems with this long-standing and trusted method. Microscopic evaluation of particles requires a trained and experienced eye. Knowledge of both particle morphology and machine metallurgy is a requirement for properly executing microscopic particle evaluation.