Page 285 - Root Cause Failure Analysis

Gearboxes or Reducers 273

component will induce misalignment in the gear set. The effect is identical to real
misalignment within the gearbox or between the gearbox and mated (i.e., driver and
driven) components.

Visual inspection of gears provides a positive means to isolate the potential root cause
of gear damage or failures. The wear pattern or deformation of gear teeth provide
clues as to the most likely forcing function or cause. The following sections discuss
the clues that can be obtained from visual inspection.

NORMAL WEAR
Figure 26-1 illustrates a gear that has a normal wear pattern. Note that the entire sur-
face of each tooth is uniformly smooth above and below the pitch line.

ABNORMAL WEAR
Figures 26-2 through 26-4 illustrate common abnormal wear patterns found in gear
sets. Each of these wear patterns suggests one or more potential failure modes for the
gearbox.

Abrasion

Abrasion creates unique wear patterns on the teeth. The pattern varies, depending on
the type of abrasion and its specific forcing function. Figure 262 illustrates severe
abrasive wear caused by particulates in the lubricating oil. Note the score marks that
run from the root to the tip of the gear teeth.

Figure 261 Normal wear pattern.