80kHz Ultrasonics / Evenly Distributed Cleaning Action for Lightly-bonded Contaminants

Late in 1992, Zenith demonstrated the ULTRAPROBE Ultrasonic Testing Instrument at the IMTS show at McCormick Center in Chicago, IL.  At this time, customers purchasing ultrasonic cleaning equipment were being told that the scrubbing action being produced in ultrasonic cleaners was completely evenly distributed, and that Standing Waves were overcome by the inclusion of Sweep Frequency Circuits which were added to the generators to sweep the output frequency to the transducers, thereby eliminating the gaps between standing waves.  They could not have been more incorrect. 

The ULTRAPROBE clearly indicated that standing waves are NOT eliminated by Sweep Frequency Circuits.  In fact, this circuit made NO VISIBLE CHANGE to the standing wave positions in an ultrasonic cleaning tank, and the same thing applies today.  No one in 1992 had ever seen a device such as this, or how ultrasonic cleaning action was distributed in an ultrasonic tank.  After all, other vendors claimed that standing waves did not exist.  Yet, every competitive system tested demonstrated the same standing waves regardless of the design of their Sweep Frequency Circuits.  Soon after the 1992 show, all major manufacturers of ultrasonic cleaning systems were offering frequencies above 40kHz, finally realizing the benefits of 80kHz that Zenith had promoted for decades.

All ultrasonic cleaning systems, regardless of manufacturer or frequency, produce a scrubbing action which is distributed as a series of an equidistant bands known as Standing Waves which begin at the transducer mounting location, which is typically the bottom of the tank.  The frequency of the ultrasonic cleaner will determine the distance between these bands of activity.  The higher the ultrasonic frequency, the closer these bands will be to one another, but the less powerful the activity will be at any one location.  High-frequency ultrasonic systems generally produce a very evenly distributed cleaning effect, but a less powerful one, while low-frequency ultrasonic systems produce a cleaning effect with large areas of inactivity, but the cleaning action is more powerful at standing wave locations.

The photograph at the right depicts Zenith's ULTRAPROBE Ultrasonic Testing Instrument, which visually displays the ultrasonic scrubbing action distribution in an 80kHz ultrasonic cleaning system.  This patented device is composed of a quartz test tube which is filled with a colored detergent mixture, and precious metal particles of a specific size.  When the tip of the instrument is inserted into an ultrasonic cleaning system, the metal particles migrate to areas of intense ultrasonic activity.  Note that there are light colored bands spaced roughly 1/4 inch apart in this instrument.  This is the scrubbing pattern that an 80 kHz ultrasonic system will produce.  As you can see, almost no areas of inactivity exist, and ultrasonic cleaning energy is very evenly distributed in this tank.

Although the 80kHz frequency produces a more evenly distributed cleaning effect, the scrubbing action that is produced is less powerful than lower frequencies, which can be positive or negative.  If parts being cleaned have contaminants which are highly bonded, the 80kHz frequency may not remove it from the parts without the use of a detergent or cleaning fluid which can loosen the bond of the contaminants to a level where existing scrubbing action can remove it.  In other words, cleaning fluid effectiveness becomes more important when removing highly-bonded contaminants in an 80kHz cleaning system

80kHz systems are perfect when the parts include a high level of detail, such as threaded areas, small holes, folded metals, or other similar features, and when the contaminants are lightly bonded.  These contaminants can include machining oils, coolants, lubricants, particles, metal chips, and similar contaminants.  However, with the proper cleaning agents, an 80kHz system can remove highly-bonded contaminants such as burned carbon, rust, and others.

80kHz ultrasonic systems are very quiet during operation since the frequency is well above the human hearing range.  The sound is composed of a gentle buzz that can barely be heard when the cover of the tank is closed.

80kHz ultrasonic cleaners are non-destructive to the ultrasonic cleaning tank.  Cavitational Tank Erosion, the slow deterioration of the cleaning tank at the transducer mounting locations, hardly exists at 80kHz, and systems have been operated for decades, every day, without a single tank failure. 

Here is an example of how frequency can make the difference between success and failure when cleaning fine detail in a part.  A recent customer had purchased 4 table-top ultrasonic cleaner through McMaster Carr with CROSSFIRE Multiple Frequency Ultrasonics operating at 25 and 40kHz.  The objective was to clean a hole the size of a human hair that was used to manufacture nylon strands.  The customer contacted Zenith directly after the system failed to clean successfully, and the recommendation was made to submit parts to Zenith for our Ultrasonic Testing Service.  Upon receipt of the parts, Zenith test-cleaned the items using a 40/80kHz CROSSFIRE system, and returned the samples for evaluation.  The higher-frequency system cleaned the item successfully, and all 4 systems were converted to 40/80kHz as a result. 

80kHz systems also have an improved ability to remove particles of a smaller size.  Testing which was performed a few years ago indicated that 40kHz ultrasonics performed better at removing particles larger than .7 microns in size, while 80kHz performed better at removing particles down to .2 microns and smaller.

Today, Zenith rarely delivers an ultrasonic system with all 80kHz ultrasonic components.  The customer typically purchased a CROSSFIRE 40/80kHz system for improved performance.  Although 80kHz alone could more-than-likely address the application, the CROSSFIRE option increases system capabilities, and is currently our best-selling equipment frequency.  By combining the 2 frequencies together, one does not sacrifice power for penetration, and the range of particles addressed by the system is greater than either frequency alone.

When to Use 80kHz Ultrasonic Cleaners:

  • When Cleaning Light-weight, Detailed Parts.
  • When Removing Lightly-bonded Contaminants.
  • When Lower Frequencies Fail to Clean a Part.
  • When Cleaning Thin Contaminant Layers.
  • Particles Being Removed are Possibly Sub-micron in Size.

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Zenith Ultrasonics
85 Oak St.
Norwood, NJ  07648-0412
800-432-SONIC (7664)