Ultrasonic Cleaning: Frequency ranges and Applications

Now that you have read information on the UPC website, and our previous Blogs, you likely have a good feel for the basics about the technology behind precision ultrasonic cleaning.  There are many different aspects of the cleaning process that are application-specific and technically complicated, but for the purposes of this blog, let’s explore just one important aspect: frequency. High-frequency sound waves introduced into liquid to create cavitation, effectively scrub contaminants from the targeted parts in a cleaning tank.

A Closer Look at Cavitation

There are many technical papers written on the subject of cavitation, including some with respect to minimizing the adverse effects of cavitation in relation to propeller design.  Yet, at UPC, rather than finding ways to circumvent the adverse phenomenon, as those in the marine industry seek to do, we’re seeking to take advantage of cavitation by manipulating the amplitude and frequency of sound waves to make it work in useful ways, to promote precision ultrasonic cleaning.

Characteristics of the phenomenon of cavitation change as a result of the frequency at which the rarefaction and compression of the wave occurs.  The key concern is the size of the bubbles created – the lower the frequency, the larger the pressure waves. The larger the pressure waves, the larger the bubbles.  Larger bubbles create greater energy, and so bubble diameter size and ultrasonic frequency is an inverse relationship; the ultrasonic energy produced by cavitation (scrubbing) increases as frequency decreases.

One related point to consider is that while larger bubbles have higher energy output, they have less potential for cleaning penetration in small cracks, crevasses and blinds because of their size.  The frequency that is most often used as the ideal compromise between power and penetration for ultrasonic cleaning is 40kHz, which creates a cavitation bubble with a diameter of approximately 1 micron.  For industrial applications involving heavy mechanical equipment such as cleaning engine blocks, radiators, dies, and other metals where the finish isn’t a critical consideration, 25khz is often used – a lower frequency, a more powerful cleaning technique, but potentially destructive if used in the wrong parts cleaning applications.  Accordingly, for more delicate operations, such as precision optics, hard drive parts, and the like, 68kHz is another common frequency.  On the higher end of the spectrum, 170kHz is occasionally employed, often for pharmaceutical products, medical implants, and titanium components.

In our next blog, we will explore some other techniques that we employ (and have patented) for optimal application of much of the information we have covered here.  Be sure to check back here for our next blog – and in the interim, tweet @ultrasonicpower or visit our website to get in touch, – we would love to hear from you.