Machinery Lubrication India Jan Feb 14 10 | Page 24

the ferrograms or filtergrams are then
studied using an optical microscope.
The main advantage of analytical
ferrography is its ability to determine
particle shapes, sizes and textures as
well as identify elements.

name suggests, particles are generated
from one surface gouging the other
surface, creating long, ribbon-like
chunks. This wear mode is often
compared to machining swarf from a
lathe but on a much smaller scale.

Ferrography utilizes either magnetism
or membrane filtration to collect
particles. ISO standards, such as ISO
16232, ASTM D7670 and D7690, are
used to properly prepare these samples
and analyze the particles’ visual
characteristics.
These
observed
characteristics shed light on where and
how these particles were generated.

Rolling Wear (Surface Fatigue)

Ferrograms
As an oil sample flows down a specially
designed glass slide called a ferrogram,
a magnet is positioned underneath to
trap the ferrous particles. The particles
tend to collect in strings along the

Non-ferrous particle
Ferrous particles
In this ferrogram, ferrous particles are
aligned along magnetic fields.

magnetic field. While many of the
non-ferrous particles will flow past and
not become trapped, some will be held
up by gravity or by contact with the
trapped ferrous particles. Both bottom
and top lighting can be used to help
characterize the particles’ critical
features.

Filtergrams
In contrast with ferrograms, filtergrams
do not have any bias toward ferrous
particles. As the oil sample is forced
through a filter membrane, any particles

Particles collect at random on a
filtergram.

greater than the pore size are randomly
trapped on the membrane surface.
However, bottom light transmission
during analysis is poor due to the
opaqueness of the filter membrane.

Rolling surface contact produces
surface fatigue. Particles generated
from surface fatigue tend to come in

Wear Modes
Rubbing (Break-In) Wear (Abrasive
Wear)

As the most common type of wear,
rubbing wear occurs whenever there is
surface sliding contact within a
machine. During initial surface contact,
this type of “break-in” wear should be
expected. It usually results in a
smoother,
low-wearing
surface.
Particles produced from rubbing wear
typically
have
a
platelet
(two-dimensional) morphology and
smooth topography.

the form of spalls, spherical or laminar
particles. The formation of pits and
spalls as a result of high load and a
low-contact surface area leads to the
shaping and sizing of these particles as
they are forced out of their original
setting. This type of wear typically
occurs with components of rolling
motion contact, such as in the case of
ball bearings.

Rolling and Sliding Wear Combined
(Surface Fatigue and Abrasive Wear)
This abnormal combination of wear

Cutting Wear (Abrasive Wear)
This abnormal wear is produced when
t w o
surfaces
penetrate
o n e
another.
As
its

22| January-February 2014 | www.machinerylubricationindia.com

modes is caused by fatigue and scuffing.
It is commonly associated with gear