A poorly
aligned machine can account for up to 30 percent of a machine’s
downtime. Not only is downtime expensive in terms of lost
production, but it also increases costs in the form of more
replacement parts, inventory, and energy consumption. Considering
the importance of the shaft alignment,
it is
interesting to note that a widespread understanding and use of tools
for detecting and diagnosing misalignment is still elusive. A survey
of the literature reveals that:
1.
Misalignment produces significant vibration levels.
2. A
machine can have parallel misalignment without exhibiting
significant 2X vibration levels.
3.
Misalignment is strongly influenced by machine speed
and coupling stiffness.
4. Softer
couplings are more forgiving, and tend to produce
less vibration.
5. Level
profiling of a single-point vibration spectrum for
a given operating condition does not provide a reliable indication
of machinery misalignment.
6.
Observation of spectra in several points & directions, at varying
speeds, may be needed to effectively diagnose misalignment.
Traditionally, vibration signatures (level profiling of singlepoint
vibration spectra), and orbit plots, have been used as the preferred
tools for detecting and diagnosing machinery misalignment. Although
these tools may be effective when used by an expert, ODS analysis
offers a simpler, more straightforward approach to detecting
misalignment. Misalignment is more easily characterized by a visual
as well as a numerical comparison of a machine’s ODS with its
baseline ODS, taken when the machine is properly aligned.
Figure 1: Accelerometers on Motor & Bearings
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