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Ultrasonic Inspection: Bearings

Ultrasonic Testing

Ultrasonic technology provides the ability to monitor and determine the conditions of bearings including:

• Good Condition - A roller bearing that is in good condition and is properly lubricated normally produces a soft whirring sound with very few, if any, crackles.
• Under-Lubricated - Inadequate lubrication produces a very intense scraping or squeaking sound.
• Over-Lubricated - Too much lubrication can cause no sound at all
• Damaged - Flat spots, scratches, or nicks on a bearing cause a grating, scraping, or clicking noise referred to as crackles.

When testing bearings, it is ideal to use a solid probe and contact the housing of the bearing. This will allow maximum sensitivity and selectivity of the receiver. The CTRL UL101 ultrasound sensor will not detect any airborne ultrasound when a solid probe is attached and its sensitivity can be easily adjusted, thus eliminating background noise.

In some cases, the bearing housing cannot be reached safely and an acoustic attachment must be used. Both the Mini-Concentrator and PowerBeam 300 are ideal because of their narrow beam of reception. SoundCTRL can be used to record and analyze the ultrasonic signal from the UL101. Analysis and comparison to a baseline help determine the condition of the component. Over time, the bearing sound will grow in amplitude and crackles indicating wear. A sharp jump in either the RMS value or the crackle count will tell you it is time to replace the bearing.

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