Ultrasonic Bearing and Mechanical Inspection

Ultrasonic inspection of mechanical equipment with an Ultraprobe has many advantages.

 

Ultrasound inspection provides early warning of bearing failure, detects lack of lubrication, prevents over lubrication and can be used on all bearing speeds (high, medium and low). 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 test point. Basic inspection methods are extremely simple and require very little training. For those who require more sophistication, UE Systems offers training courses that range from one-day specialized classes to five-day certifiable courses.

 

Ultrasonic condition analysis is straightforward. Users of analog instruments can observe sound levels while simultaneously listening to the sound quality. Digital users have additional options such as viewing decibel levels, data logging, data analysis and trending through specialized software. More sophisticated digital instruments provide features for comprehensive mechanical or bearing condition monitoring programs including; data logging, software for trending, creation of alarm groups, sound sample recording, spectral analysis of sounds and software with customizable reporting formats that include graphs, charts and other relevant images.

 

How Ultrasound Bearing and Mechanical Inspection Works

Mechanical movements produce a wide spectrum of sound. One of the major contributors to excessive stress in machinery is friction. Ultrasound instruments detect friction. By focusing on a narrow band of high frequencies, the Ultraprobe detects subtle changes in amplitude and sound quality produced by operating equipment. It then heterodynes these normally undetectable sounds down into the audible range where they are heard through headphones and observed on a display panel for trending, comparison, and analysis.

 

It has been established that ultrasound 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. For those who utilize ultrasound spectral analysis, these conditions can often be observed through both FFT and time series analysis.

 

Typical ultrasound inspections include: bearings (it has proven to be very effective on low-speed bearings), pumps, motors, conveyors, gear & gear boxes, couplings, fans, compressors, robots….

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                         Bearing in a good condition                                            Bearing not in a good condition   

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Ultrasonic Bearing Inspection Method

There are three methods for ultrasonic bearing monitoring: comparative, historical and analytical. In order to note possible deviations that might indicate a possible failure condition or to establish a baseline for future surveys, compare similar bearings to each other for 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 received sound level so that the intensity or decibel level can be observed on the display panel. Then compare this base reading to other similar bearings, while listening for any sound quality anomalies.

 

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. High and low alarm levels can be set to note any bearings in need of corrective action. An 8 dB gain over a baseline with no change in sound quality will indicate a need to lubricate due to depleted lubricant. Levels, such as 16 dB or higher can signify a potential failed condition. The analytical approach can be integrated into the comparative or historical process. Sound anomalies can be recorded and analyzed through spectral analysis software. Some of the advanced instruments have on-board spectral analysis providing the ability to diagnosis issues while performing inspections out in the plant.

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