| Inspection of mechanical equipment with ultrasonic
instruments such as the Ultraprobe has many advantages. Ultrasound inspection
provides early warning of bearing failure, detects lack of lubrication,
prevents over lubrication and can be used on high as well as low speed
bearings. In addition, since ultrasound is a high frequency, short wave
signal, it is possible to filter out stray, confusing background noises
and focus on the specific item to be inspected. Basic inspection methods
are extremely simple and require very little training.
Ultrasonic condition analysis is straightforward. Users can observe
sound levels while simultaneously listening to sound quality and record
both sound and data for analysis through specialized software. Digital
instruments provide many possibilities for a comprehensive bearing condition
program including sound sample recording, data logging, trending, alarm
groups, sound (spectral) analysis and reporting.
How Ultrasound Bearing and Mechanical Inspection Works
Mechanical movements produce a wide spectrum of sound. By focusing
on a narrow band of high frequencies, the Ultraprobe detects subtle
changes in amplitude and sound quality. It then heterodynes these normally
undetectable sounds down into the audible range where they are observed
on a meter (for trending and comparison purposes) and heard through
headphones.
Based on research by NASA, it was established that ultrasonic monitoring
provides early warning of bearing failure. Various stages of bearing
failure have been established. An 8 dB gain over baseline indicates
pre-failure or lack of lubrication. A 12 dB increase establishes the
very beginning of the failure mode. A 16 dB gain indicates advanced
failure condition while a 35-50 dB gain warns of catastrophic failure.
Ultrasonic Bearing Inspection Method
There are two basic methods for ultrasonic bearing monitoring: comparative
and historical. In order to trouble shoot bearings or to establish a
baseline, it is necessary to compare similar bearings for potential
differences in amplitude and sound quality. To do this, make a permanent
reference point on a bearing housing or use the grease fitting, tune
to 30 kHz and adjust the sensitivity to read the intensity/decibel level
on the display panel. Then compare this base reading to other similar
bearings. An 8 dB gain over a baseline, with no change in sound quality
will indicate possible lubrication starvation. Levels, such as 12 dB
or higher can signify a potential failed condition. Once a series of
bearings have been tested, and a base line set, data is recorded and
then compared to future readings for historical trending and analysis.
Alarm levels can be set to note any bearings in need of corrective action.
Sound anomalies can be recorded for spectral analysis.
Ultrasonic inspection works extremely well with vibration technology.
In fact the two technologies complement each other and enhance any PDM,
(Predictive Maintenance) program.
Click
here to download the UE Bearing Inspection Guide (PDF).
Click here
to download the UE Mechanical Inspection Guide (PDF).
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