can be found in two-(2) forms, either as a wear related particle or a contaminant related particle.  Wear related spheres  form as fatigue cracks in a loaded surface.  As the micro-cracks work through the surface and a spall begins to form, the spall will isolate, generating small (>5mm) spheres with oxidized surfaces.  Spheres are found in large concentrations and consistent sizes.  Spheres form in much of the same manner as having glue on your hands and rubbing your hands together. The result is little balls of material.

Equipment related spheres are tektites formed not specifically by a wear mechanism but by equipment related factors.  These factors include excessive aeration of lubricants in hydraulic systems.  Such aeration or restricted inlet flow to pumps cause fluid vacancies.  These vacancies or air bubbles then implode causing shocks which crack the surface in the load zone thus removing material.  Similar occurrence can be seen in cavitation of impellers in high speed operation.

Contaminant related spheres are typically the resultant tektites from such activities as welding, grinding, sand-blasting, mold dust, the result of combustion of coal or electrical shorts passing though the component.  Contaminant spheres are comparatively few in concentration and inconsistent in size.  Size can range from 6mm-12mm.

Regardless of the origin of these unique particle types, it is to be understood that these particles are hard and abrasive. The doughnut shaped appearance results form the way bi-chromatic light is reflected back to the observer.  The bright center returns a higher concetration of reflect light.  While progressing down the curved surface of the sphere returns less light directly back up to the observer.

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