Assessing
the condition of rolling element bearings is arguably the single most important
job vibration analysts have. Unfortunately, the vibration symptoms generated
by a bearing going bad can vary greatly. However, bearings usually
undergo a fairly predictable series of symptoms as they deteriorate. Considering
the importance of the task and to enhance the analyst's chances of catching
a bad bearing, it is important to use all of the tools at your disposal.
These include:
-
Velocity or, preferably,
acceleration spectra that cover the frequency range between 30,000 and
120,000 cpm.
-
Enveloped spectra
such as ESP, gSE, HFD, etc. These spectra are sensitive to the impact energy
a developing bearing defect generates (a ball or roller striking a defect
is similar to a car hitting a pothole in the road - impact energy is created).
-
Time domain will
show the impacts better than the spectrum - especially on slow speed equipment.
Since most analysts
use velocity spectrums to analyze data, we will focus on the 'normal' progression
that occurs on velocity spectra. The advantage of using acceleration units
is that the specific frequencies in question show up more clearly (at higher
amplitudes relative to low-mid frequency range amplitudes). |
