Machinery Lubrication India Jan Feb 14 10 | Page 25

systems, particularly along the pitchline
of gear teeth as well as in conditions
with too high of a load or speed and
excessive heat generation. For example,
the surface contact of gear teeth is a
combination of rolling and sliding
motion. This combined wear mode
region, along with the effects of
lubricant contaminants, can generate a
complex fusion of wear debris.

Severe Sliding Wear
A severe level of wear occurs in excessive
loads and high speeds between

fluid properties or heavy contamination
from water, acid, salt or bacteria. Heat
also plays a major role in corrosion.
Most lubricants have rust/corrosioninhibiting additives to combat the
effects of chemical wear.

Particle Morphology and
Topography
Since wear particles detach from
internal machine surfaces in a variable
manner, their morphology and
topography are unique. However, they
also fit certain patterns based on the
actions by which they become detached.

Platelet-shaped Particles

processes.

These two-dimensional particles are
generally flat with a rough perimeter.
Their thickness typically is about
one-tenth to one-thirtieth their lateral
dimension. They can be further
Striations indicate sliding motion

contacting surfaces. When surface
stresses are too great because of
increased load and/or speed on the
surface contact area, the area becomes
unstable and large particles break away,
further increasing the wear rate.

Chemical/Corrosive Wear
Corrosive wear is frequently labeled as
fretting corrosion, erosion, stress
fatigue, etc. These particles are often
too small to distinguish individually
and are usually the result of improper

noted that spherical particles are
frequently found as contaminants
rather than as wear debris. This type of
spherical-shaped contaminant likely
will be larger than 10 microns and often
is a byproduct of welding and grinding

Wire or Curl-shaped Particles
Typically long and skinny, these
particles may resemble a wire, splinter
or ribbon shape. While they can have
smooth sides and edges, they normally
will have a rougher appearance.
Another common characteristic is how
they are curled, which is similar to a
shaving curl in a wood-planing process.
For this reason, the particle may be
rough on one side and smooth on the
other. These types of particles have
been linked to cutting wear where one

described as having either a laminar or
wedge shape. One of the most common
ways platelet-shaped particles can
occur is by normal and tangential forces
through contacting asperities.

Spherical Particles
As their name implies, these particles
are fundamentally spherical. Normally
less than 10 microns, they appear in
small numbers and are sometimes
fused together. As wear debris, spherical
particles have been