ULTRASONIC BEARING & MECHANICAL
INSPECTIONS
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.
ULTRASONIC AND HOW IT 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.
ULTRASONIC INSPECTIONS CAN INCLUDE
GOOD BEARINGS
This is the FFT of a good bearing. Since there are no defects, the sound will be a smooth rushing sound. The spectral view will not show any harmonics or large peaks.
Sound of good bearings. Warning, audio may be loud.
BAD BEARINGS
This is a spectral view of a bad bearing. As a bearing enters the failure stage there is a rise in the decibel level of 12 – 16 dB over a baseline. This rise in amplitude is usually accompanied by a change in the sound quality.
Sound of bad bearings. Warning, audio may be loud.