Why High Frequencies May Not Solve Ultrasonic Cleaning Problems

We’re often asked about cleaning at higher frequencies, and often the assumption behind the question is a natural one: Higher is better. If high frequency sound waves are required in an ultrasonic cleaning process, shouldn’t moving to a higher range produce even better results? Not necessarily. High frequencies are not a silver bullet with ultrasonic cleaning. So let’s look at some reasons why they should or shouldn’t be used.

Cavitation

Ultrasonic cleaning uses a phenomenon called cavitation. Cavitation occurs when high frequency sound waves are introduced into a body of liquid causing millions of tiny bubbles to form. As these bubbles expand and contract they reach a threshold and collapse. This collapse creates high temperature, at a microscopic point with accompanying high velocity jet stream,   (upwards of 5000°C, 600 mph jet stream) to blast contaminants off the surface of the item being cleaned. No matter what frequency you’re using, the acoustic energy must be high enough to reach the threshold to create cavitation.

Therefore, especially for industrial applications, it’s crucial to ensure the ultrasonic generators and transducers are of top quality and deliver efficient acoustic energy for expected precision cleaning results. No matter how powerful the system or what frequency used, if a low percentage of the acoustic energy makes it to the liquid due to inefficient generators or transducers, the performance will be poor. Make sure you buy from a reputable company, one that focuses on designing, developing and manufacturing, and stands by its products with an excellent warranty on its generators and transducers.

You may need a lower frequency

As frequency increases, the cavitation bubble size decreases and becomes less aggressive. The result may be an inability to remove some soils. With 25kHz, the cavitation bubbles are much larger and very aggressive. This is better for more massive parts like engine blocks and dies with tenacious contaminants. But beware that it can damage the surface finish of the part if care is not taken. 25kHz should not be used for parts with a polished finish.

When are high frequencies needed?

Higher frequencies (68kHz to 170kHz) should be used on items that need especially gentle, sub-micron level cleaning. This includes delicate electronics and precision optics. These higher frequencies produce sub-micron sized cavitation bubbles that can navigate the tiniest cracks and crevasses. Higher frequencies are often used to clean pharmaceutical equipment, medical implants, titanium components, delicate electronics and precision optics.

The best all-around frequency

For most applications, 40kHz is the best choice because it has the best balance between power and cavitation bubble size. This is why it is used in over 90% of all industrial ultrasonic cleaning systems. 40kHz Cavitation bubbles are about one micron in size, small enough to get into tiny cracks and blind holes. It’s also powerful enough to remove stubborn contaminants yet gentle enough for all but the most fragile materials.

SIMULTANEOUS MULTI-FREQUENCY® delivers superior performance

Single stacked transducers produce a single frequency which produces a specifically sized cavitation bubble (one micron for 40kHz). Higher end cleaning applications, however, may require sub-micron level cleaning. Ultrasonic Power Corporation’s patented VIBRA-BAR® transducer technology produces SIMULTANEOUS MULTI-FREQUENCY®. With this design, two PZT (piezoelectric transducer) stacks are mounted in a specific pattern. The natural resonance is combined with the propagating energy from the two PZT stacks causing a complex resonance. The result is the base frequency (40kHz) and a range of frequencies from 40kHz to 90kHz. These higher frequencies are able to remove smaller particles than with just a single 40kHz frequency.

Ultrasonic Power Corporation’s SIMULTANEOUS MULTI-FREQUENCY® technology provides multiple frequencies from a single generator and transducer configuration. This is like having multiple frequency generators and transducers in a single package.

Challenges and solutions

No ultrasonic cleaner is worth investing in if it doesn’t deliver results. No matter what your unique cleaning situation, we’re ready to provide the ultrasonic cleaning results that fit your needs, so let’s begin finding a great solution to your cleaning challenges. We like to say “Our Technology, Your Solution”TM Talk with us soon.

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