Ultrasonic Cleaning: Theory and operating considerations

Theory and operating considerations By Joe Escobar In the arena of parts cleaning, ultrasonic cleaning is making inroads. Environmental impact consideration is leading many companies to look for greener cleaning methods, and...

When using ultrasonic cleaners, there are several issues to be aware of. One such operating consideration should be resonance.

Avoiding Resonance Damage

Manufacturers have strict time and frequency limits for cleaning their parts with ultrasonics. Sticking to these limits is essential to avoiding resonance damage. Although it may be tempting to leave a part in longer to get it cleaner, the effect that it can cause may be catastrophic. Be sure to follow all the manufacturer's recommended procedures when working with ultrasonic equipment.

With resonance being a critical issue, Pratt & Whitney Tool Support Services and Blackstone~NEY Ultrasonics have addressed the issue in the line of ultrasonic cleaners by randomly varying the frequency and amplitude of the ultrasound. Unlike other cleaners that vary the frequency in a small plus or minus range, this product actually changes the frequency in random steps. This provides the benefit of the part being subjected to randomly varying frequencies. It also prevents the part from getting excited into a resonant vibration that could cause damage.

Just about any object has frequencies at which it naturally vibrates known as resonance frequencies. This phenomenon is easily evident in a crystal glass. If you flick the glass with your finger, it will emit a clear tone as it vibrates. This is its resonant frequency. If an opera singer subjects the crystal glass to a note at its resonant frequency and at a high enough volume or amplitude, the glass will shatter.

The same theory affects parts that are cleaned using ultrasonics. The parts can be excited into resonance during the cleaning process. If they are allowed to remain in this state of resonance, damage can occur, especially in fragile components.

Use the proper equipment
The bottom line if you are considering using ultrasonic equipment for cleaning aircraft parts is to make sure the equipment is approved by the manufacturer. Although a bargain unit may seem harmless, it can cause damage to the part if improper frequencies are used. Even if it is an approved cleaner, be sure to closely monitor the cleaning times in order to prevent damage caused by resonance.

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