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March - April 2015
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The categories of particle composition and how they appear on
a ferrogram have been defined as white nonferrous particles,
copper particles, Babbitt particles, contaminants (usually dirt or
silica), fibers and ferrous particles, including high-alloy steel,
low-alloy steel, dark metallic oxides, cast iron and red oxides (rust).
Refer to the related ASTM standard for a structured reporting and
databasing technique for interpreting particles presented on a
ferrogram or filtergram.
Besides the particle size and composition, the analysis of a ferro-
gram under a microscope can provide further benefits when the
particle's shape is taken into consideration. Whether the particle's
shape is spherical, spiral or laminar, or if the surface looks rough,
smooth or has clear striations will all indicate a unique wear mode.
In fact, there are several books dedicated to the study and charac-
terization of wear particle shapes and how they point to specific
wear modes.
Once the initial fault detection triggers an investigation, the
analytical approach requires using all available clues in order to
make a sound conclusion and determine if corrective action is
necessary. The results from particle counting, vibration analysis
and thermography can be used in conjunction with ferrous density
testing and elemental analysis to consider all possible causes and
effects of the initial trigger. When the type of information provided
by these strategies is not precise enough to point to a particle root
cause and location within a machine, more detailed analysis must
be employed. After all, the end game is to isolate the root cause,
and analytical ferrography is a proven method to bring evidence to
the root cause. Make sure your lab doesn't dismiss its value and fail
to perform this critical test.
About the Author
Bennett Fitch is a technical consultant with Noria Corporation. He
is a mechanical engineer who holds a Machine Lubricant Analyst (ML A)
Level III certification and a Machinery Lubrication Technician (MLT)
Level II certification through the International Council for Machinery
Lubrication (ICML). Contact Bennett at bfitch@noria.com.
