suspension solution should also be examined for evidence of contamination.
Contamination primarily comes from inspected components.
Oils, greases, sand, and dirt will be introduced to the system
through components. If the area is unusually dusty, the system
will pickup dust or other contaminates from the environment.
This examination is performed on the carrier
and particles collected for concentration testing. The graduated
portion of the tube is viewed under ultraviolet and white light
when fluorescent particles are being used, and under white light
when visible particles are being used. The magnetic particles
should be examined for foreign particles, such as dirt, paint
chips and other solids. Differences in color, layering or banding
within the settled particles would indicate contamination. Some
contamination is to be expected but if the foreign matter exceeds
30 percent of the settled solids, the solution should be replaced.
The liquid carrier portion of the solution
should also be inspected for contamination. Oil in a water bath
and water in a solvent bath are the primary concerns. If the solution
fluoresces brightly when fluorescent particles are being used,
this can be an indication that dye is being dislodged from the
particles by the mixing pump. While not technically contamination,
this condition should be further evaluated by allowing the collected
sample bath to set for 10 to 12 hours and viewed under ultraviolet
light. If a band that fluoresces brighter than the bulk of particles
is evident on top of the settled solids, the bath contains excessive
unattached fluorescent pigments and should be discarded.
Water Break Test
A daily water break check is required to evaluate the
surface wetting performance of water-based carriers. The water
break check simply involves flooding a clean surface similar to
those being inspected and observing the surface film. If a continuous
film forms over the entire surface, sufficient wetting agent is
present. If the film of suspension breaks (water break) exposing
the surface of the component, insufficient wetting agent is present
and the solution should be adjusted or replaced.