Match Ultrasonic Cleaner Frequency to Cleaning Task

Ultrasonic frequency is defined as sound waves above the range of hearing, nominally 20,000 cycles per second, or 20 kilohertz (KHz). The kHz designation – thousand cycles per second – derives from Heinrich Hertz (1857-1894), who discovered radio waves or radio frequency.

Ultrasonic frequency (or frequencies) is a key criterion when purchasing an ultrasonic cleaner for parts cleaning or for related sonicator bath applications.

Popular ultrasonic cleaner frequencies range from 35 kHz to 45 kHz with exceptions at both ends.

Ultrasonic Cleaning and Ultrasonic Frequency

The correct ultrasonic frequency yields superior results in terms of efficiency, thoroughness, and in certain cases avoiding damage to parts being cleaned.

Moreover, there are projects where more than one ultrasonic frequency is recommended, or when you are cleaning a variety of products calling for different ultrasonic frequencies.

Which leads into an explanation of how ultrasonic cleaners work. If you are familiar with this, feel free to skip to What Ultrasonic Frequency Should I Use?

A Brief on How Ultrasonic Cleaners Work

Understanding how ultrasonic cleaning works calls for an understanding of equipment components. At the basic, however, these units consist of: 

• Tanks to hold the cleaning solution. Tanks should be of stainless steel; their volume depends on the size of objects being cleaned.
• Ultrasonic transducers that create the cavitation (as explained below) are bonded to the bottom and/or sides of the tank.  Immersible transducers are also used.
• A generator to power the transducers
• Controls that range from a simple on-off switch to sophisticated microprocessors that govern cleaning time, sweep, pulse, degassing, temperature, ultrasonic frequency, ultrasonic power, auto safety shutoffs and other refinements. 

Ultrasonic cleaning equipment ranges from small tabletop units to huge, multi-gallon industrial cleaners.  The capacity of the cleaners has little or no bearing on the features they can offer.  Desired feature decisions are up to you, the purchaser, with help from experts at Tovatech: Elma’s exclusive master distributor in North America.

A good place to start is reviewing our post on parts cleaner specification tips and taking the time to view our learning center video on how ultrasonic cleaners work.

Another good source of info are the answers to ultrasonic cleaner frequently asked questions.

At the end of this post we offer points to consider beyond ultrasonic frequency when purchasing your ultrasonic cleaner.

The Role of Transducers in Ultrasonic Frequency

As noted above, ultrasonic transducers create the ultrasonic energy that creates cavitation that does the cleaning or sonicator bath activity.

There are two basic types of transducers: piezoelectric (a.k.a. electrostrictive) or magnetostrictive, but their function is the same. 

The ultrasonic cleaner generator provides electric current to the transducers, causing them to  vibrate at ultrasonic frequencies that in turn cause the bottom (and sides as the case can also be) of the tank to vibrate, sending sound waves through the ultrasonic cleaning solution.

This vibration forms the microscopic vacuum bubbles that implode, (not explode) on contact with items in the ultrasonic cleaner tank. This releases powerful jets of the cleaning solution that quickly and safely strip contaminants from all immersed surfaces.

The process is called ultrasonic cavitation. Ultrasonic frequency governs the cavitation bubble size, which directly affects the cleaning process.   

What Ultrasonic Frequency Should I Use?

In a sentence, the lower the ultrasonic frequency the larger the bubbles and the more vigorous the cleaning action – although the relative size of bubbles is not observable by the naked eye.

A low frequency such as 25 kHz produces (relatively) large cavitation bubbles that implode vigorously and therefore are favored for cleaning heavily soiled parts such as fabricated and cast metals or parts with coarse contaminants such as polishing pastes. 

The vast majority of cleaning operations can be performed with equipment operating at 37 to 45 kHz range. 

Complex and delicate surfaces should be cleaned at higher frequencies such as 80 kHz. The relatively smaller high-frequency bubbles release less energy upon implosion and are more numerous than those created at lower frequencies.  This means they clean more gently and are able to penetrate difficult-to-reach surfaces such as cracks, crevices and blind holes.

Higher frequencies are also recommended to avoid damaging highly polished surfaces of soft metals such as aluminum and silver.

Dual-frequency ultrasonic cleaners are a good choice if you clean a variety of products with differing characteristics.   

Matching Ultrasonic Cleaner Equipment to Ultrasonic Frequency

Here’s a representative guide to help you select Elmasonic ultrasonic cleaners delivering the right ultrasonic frequency for your cleaning tasks.  Please check the links for added details including multi-frequency options.

Points to Consider Beyond Ultrasonic Frequency

Ultrasonic “Noise”

While “ultrasonic” is defined as sound above the hearing range, ultrasonic cleaners, especially those operating a low frequencies, are not silent.

The noise emanates from vibrations in tank walls and products being cleaned, and relates to the ultrasonic frequency being used. For example, there is a significant difference in noise generation between a cleaner operating at 25 kHz and one operating at 80 kHz. 

You can reduce the impact of noise with hearing protectors and by options including sound deadening lids and noise protection boxes. 

Ultrasonic Cleaning Chemicals 

Cleaning solution chemistry is as important as ultrasonic frequency when it comes to getting the best results from your ultrasonic cleaner.

A good tutorial is our post on cleaning solutions for ultrasonic cleaning tasks.  It notes that most commonly used ultrasonic cleaning solutions fall into three categories: alkaline, acidic and neutral.  These are listed in ultrasonic cleaning chemistries.

These cleaning formulas are usually supplied as concentrates.  This means a little goes a long way.  When formulated with non-toxic biodegradable ingredients disposal concerns are eased.  Manufacturers provide dilution and cleaning temperature recommendations.

Because most ultrasonic cleaning solutions are water based there may be a concern about rusting when cleaning ferrous parts.  Rust inhibitors such as elma KS can be added to address this. 

Ultrasonic Cleaner Capacity

When purchasing an ultrasonic cleaner consider the size of the parts you are cleaning.

Most parts are placed in cleaning baskets, the dimensions of which are less than tank dimensions.

You’ll want to specify an ultrasonic cleaner tank size based on the corresponding basket size that will accommodate the parts to be cleaned.

Added to that, parts to be cleaned must be totally immersed in the cleaning solution. 

Because of this you must consider what is called the working depth of the cleaning solution. 

This is defined as the distance from the inside bottom surface of the basket to the surface of the liquid in a filled tank. 

If the working depth of the equipment you are considering is not provided or unclear from the specs, ask the manufacturer. 

Rather than go into more detail here, please check our post on selecting ultrasonic cleaner size.

In Conclusion

We hope this post is helpful when it comes to choosing the correct ultrasonic frequency for your cleaning challenges. You’ll find additional important information by viewing our informational video in our ultrasonic cleaning learning center. 

When it comes to selecting the right unit and ultrasonic frequency and other important specification details for your tasks please contact the experts at Tovatech: Elma’s exclusive master distributor in North America.