Machinery that operates at speeds below 600
rpm falls under the category of low-speed machines. These machines are
typically large and possess high rotating inertias, making them crucial
components of the production line. Although these machines are less prone to
breakdowns, they are considered critical, and their failure can result in
enormous production losses, significant downtime, and substantial replacement
costs. Historically, there has been limited interest in the condition monitoring of
these machines due to their infrequent failures.
The
parts of these machines that necessitate condition monitoring are primarily the
bearings and gears in motion. This article will cover modern and innovative
techniques for monitoring the condition of low-speed machinery, with a particular
emphasis on monitoring the condition of rolling element bearings.
Monitoring low-speed bearings present unique
challenges. In the case of high-speed bearings, vibration analysis,
thermography, and wear debris analysis are standard tools used in predictive
maintenance (PdM) programs. However, when it comes to low-speed bearings, these
conventional technologies are not effective until the speed is less than 250
rpm. Early bearing failure is a persistent issue in low-speed applications, and
the solution lies in using ultrasound.
Ultrasound
is an effective solution for monitoring slow-speed bearings, and the process is
simpler than one might expect. High-end ultrasound instruments possess a broad
sensitivity range and frequency tuning, which enables the acoustic quality of
the bearing to be heard, even at lower speeds. However, in extremely slow-speed
applications (typically below 25 rpm), there may be little or no ultrasonic
noise generated by the bearing. Therefore, it is crucial to analyze the recorded
ultrasound sound file using spectrum analysis software, focusing on the time
waveform for any anomalies. The presence of "crackling" or
"popping" sounds indicates the occurrence of a deformity. For bearing
speeds above 25 rpm, a baseline decibel level can be established, and the
associated decibel level readings can be trended over time.
Ultrasound
devices primarily function by converting high-frequency sound into audible
sound through heterodyning. An operator who understands the fundamentals of
bearing friction can differentiate between a healthy bearing producing a steady
and quiet signal and a faulty bearing causing an intermittent or repetitive
ringing or crackling sound. However, listening alone is insufficient. Reliable
measurements are necessary to establish a robust PdM program; otherwise, the
instrument is no more useful than a stethoscope. For instance, the UE Systems
Ultraprobe 15000 enables the user to listen to sound quality and compare
baseline information before saving the recording for upload to DMS software. Alarm
levels can be set, and data can be analyzed to determine the bearing's
condition.
In
summary, when monitoring slow-speed bearings, it is essential to rely on sound
quality and pattern. Using an ultrasonic instrument with sound recording
capabilities such as the Ultraprobe 15000 or OnTrak system is recommended to
facilitate data analysis. These tools can effectively manage the lifespan of
your bearings and significantly reduce the number of bearing failures caused by
improper lubrication. Once the sound is recorded, it can be analyzed using
sound spectrum analysis software. Maintenance professionals can then load the
file into the software and analyze it, providing valuable insights into when a
bearing needs lubrication or replacement if a failure is likely to occur.
View
product information:
https://www.uesystems.com/product/ultraprobe-15000/
https://www.uesystems.com/ontrak-smartlube/
By NTS
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