Understanding Ultrasonic Cleaning

There are misconceptions and a lot of  misleading information relative to the principles of Ultrasonic Cleaning.  I hope the following will help to clarify some of these gray areas.

 

Comparing ultrasonic cleaners is not like comparing apples to apples.  Due to the fact that many sellers have little technical knowledge of the product they are selling, they offer invalid information on their product.

 

 

POWER OUTPUT

Generators are rated for RF power output.  In all cases, the generators are capable of the rated RF output but are detuned to extend the life of the generator, some as much as 20-25%. Question the supplier if an amp. probe or RF watt meter will verify their claims in field operation (even if these are not available to you).

 

TRANSDUCER BONDING

Some manufacturers claim they weld or braze their transducer for superior bond. The “superior bond” is not required with piezoelectric transducers.  Aircraft quality epoxy is more than sufficient and gives a superior mechanical to acoustical coupling.

SWEEP FREQUENCY

All ultrasonic cleaning systems have dead spots every half wave length. By sweeping the frequency the severity of the dead zone is lessened. This is a good feature to incorporate, but it does not eliminate the dead zone, as some claim.

In most cases a maximum sweep of only 1 to 2 KHz around the fundamental frequency exists due to the increased energy lost due to breaking and reversing the element movement.

 

TEMPERATURE VS.  ULTRASONIC POWER

Visualize a seesaw with temperature on one end and ultrasonic power on the other end. Most expect as temperature rises both chemical attack and ultrasonic power increase, but that is not true. As we increase temperature, most chemicals will get more aggressive up to their maximum temperature rating, but the ultrasonic cavitation implosion power will weaken.  The cooler the solution the more aggressive the ultrasonic (unless the solution is to cold for cavitation to initiate).

 

FREQUENCY
Most believe as the operating frequency increases the ultrasonic action gets more aggressive, just the opposite. As we lower the frequency the implosions gets more violent. When we introduce a level of power into the bath, the power doesn’t change but distributes differently. A high frequency (40 KHz) has a high count of implosion events for better distribution of the events where a low frequency (25 KHz) has fewer events but each event has  greater energy stored and released, the total power is the same but the egression of the implosion event differs.

Jim Hesson, founder of Hessonic Ultrasonics, has contributed a number of articles on the topic of ultrasonics.  For more in depth reading on ultrasonics for cleaning, you will  find a free book on his web site.

 

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