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Trending Bearing Wear with Ultrasonic Detection
Establish a Route-Based Method of
Data Collection
Today’s ultrasonic instruments
allow greater flexibility than instruments from only a few years
ago. Smaller, more powerful electronic components allow for complex
data storage and two-way communications with PC’s. Proper acoustic
vibration monitoring means establishing a route-based method of data
collection similar to that of your vibration routes. Establish
routes or groups of machines in a logical sequence and identify
asset names to each measurement point for storage, trending, and
time-based graphical representation of bearing condition.
Measured Value (dBmV) and its Correlation to Condition
At the outset, the goal is to
establish a baseline or normal operating range for each bearing to
be checked. Throughout the life of a bearing its ultrasonic level
should remain relatively constant (+/- 3 or 4 dBmV). As the
condition of the bearing changes, increases in acoustic energy due
to either lubrication breakdown or structural breakdown will be
observed. Increases correspond with an elevated reading (dBmV) on
the instrument. Trending acoustic energy with data logger software
allows the user to accurately predict when lubrication should be
applied to a bearing, and when the bearing itself is entering early
failure stages. Remember, trending acoustic vibration warns us of
the earliest signs of change in a bearing. Diligent use of the
information gathered results in better lubrication practices and
extended bearing life. The desired result is a much larger window
through which to schedule repairs and change outs.
To optimise ultrasonic inspection
techniques it is essential to listen to the bearings; not just read
the values on the display. Listening to the ultrasound of a bearing
provides significant qualitative information that correlates to the
measured values. A low, muffled smooth noise associated to stable
values indicates a normal functioning bearing. A strident
high-pitched noise indicates a lack of lubrication, an overload or a
rotation speed beyond spec of the bearing. A crackling noise
associated to unstable or high dB values indicates faults, wear or
loose metal particles in the lubricant. Ultrasonic detectors
provide an excellent quantitative measurement via the digital
display, but do not ignore the qualitative information provided by
the headphone output. |
