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Consequently, when the D
L
and D
S
numbers, under normal steady state wear, trend closer
together, this indicates larger particles have precipitated out and most of the particle
concentration present are small particles. In abnormal wear modes, except for corrosive wear,
large particle concentrations will increase. D
L
and D
S
data obtained can be processed in several
ways to easily identify abnormal wear modes. Most common methods are Severity of Wear
index, Cumulative Plots, Wear Particle Concentration (WPC) and Percentage Large Particle
(PLP).
Figure 8.1A Typical Large Particle Profile
Figure 8.1B Typical Small Particle Profile
If the Severity of Wear Index is plotted as a function of operating time, it will respond in a more
volatile manner than plotting either the D
L
or D
S
reading over time. Severity of Wear can be
calculated using the product of the indication of concentration and the indication of size
distribution.
indication of concentration = D
L
+ D
S
indication of size distribution = D
L
-D
S
Severity of Wear Index = (D
L
+ D
S
) (D
L
-D
S
) or D
L
(D
L
-D
S
)= D
L
2
-D
S
2
Another method, Cumulative Plots may be used where each new reading is added to the sum of
all of the previous readings resulting in a straight line, if the readings are the same and the
intervals in which they are plotted are the same (See Figure 8.2). A variation to this method uses
