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Senin, 17 Mei 2010

ULTRASONIC BEARING & MECHANICAL INSPECTION

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DESCRIPTION

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.
Additional information regarding vibration data logging connection is available from the factory.
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