Benefits of vibration monitoring

Poor lubrication is responsible for one third of premature bearing failures. PHOTO: THINKSTOCK

Nothing does more for improving availability, reliability and longevity of plant equipment than proper lubrication.

Opinions abound as to what, exactly, proper lubrication means. Most would agree that the right amount of the right lube, in the right place, at the right time, for the right application, fits the bill. But how do you determine this?

One way is using the results of vibration monitoring.

“Vibration analysis appears to be the cheapest and one of the most effective methods for assessing machinery health, especially for rotating equipment,” said Andrew Jardine, the founder and principal of C-MORE, the Centre of Maintenance Optimization and Reliability Engineering based in Toronto, during a presentation to the Canadian Machinery and Vibration Analysis conference in Halifax.

And how it improves machinery lubrication was the subject of a technical presentation to the Society of Tribologists and Lubrication Engineers (STLE) in Hamilton.

Iraj Zarieh, a lubrication specialist and vibration analyst with VibeLube Inc. in Woodbridge, Ont., reminded his audience most rotating equipment runs with rolling bearings lubricated with grease, although oil is used for high-speed, high-load, high-temperature applications, requiring a special housing design. And more than one-third of all premature bearing failures are caused by poor lubrication practices that include: under- or over-greasing; poor quality lubricant, or lubricant unsuited for the application; poor storage and handling; and impurities.

Better monitoring

Traditional preventive maintenance can lead to over- or under-greasing, or no greasing at all. He recommended predictive maintenance as a better method to monitor lube condition and to adjust the intervals as well as the amounts of re-greasing.
Zarieh cited five useful tips for monitoring and identifying lubrication faults:

• infrared thermography
• listening with an accelerometer
• ultrasonic detection
• conventional vibration analysis
• vibration analysis with advanced signal processing using demodulation

Demodulation is a useful tool for detecting any type of low-frequency impacts in rotating parts, such as unbalance, looseness, rubbing or cracks in the outer race of a bearing. It also detects some electrical defects in non-variable speed electric motors, so-called bearing and gear “tones,” and lubrication deficiencies. But its main focus is on high-frequency vibration.
Using a high-pass filter, low-frequency data is eliminated and a data collector “zooms in” on the low-level, high-frequency vibration.

This means some peaks otherwise lost in the noise floor of a normal narrow band spectrum can be detected. But demodulation can’t be used on reciprocating engines or compressors, on motors with commutators, and on regular variable frequency drives.
Vibration is measured with a sensor attached to the machine housing. It registers bearing housing or shaft vibration relative to the bearing housing. Sensors must be properly mounted in the correct locations (follow the instruction manual) to get the best results.

Vibration data collectors analyze the measurements, then deliver time and spectrum analysis, and wave form. Vibrations can be harmonic, periodic, impulsive, pulsating or random.

The key take-away from Zarieh’s session is focused, purposeful and effective maintenance that includes vibration monitoring will lead to better lubrication practices while extending equipment life.