Pros and Cons of Tank Bonded vs. Immersible Ultrasonic Transducers

Note – Before we start, there is a nomenclature conundrum when it comes to the term “ultrasonic transducer.”  Through convention, transducer elements, the individual devices that produce ultrasonic vibrations (much like an individual radio speaker), are commonly called “transducers.”  A number of transducer elements working in parallel constitute a transducer array but may be called a “transducer.”  A submerged housing containing a number of individual transducer elements is also commonly called a “transducer.”  The following makes an effort to differentiate these terms for clarity.

There are two basic ways to introduce ultrasonic energy into a cleaning tank.  The first is to bond individual ultrasonic transducer elements directly to the exterior of a stainless steel tank.  The second is by using submerged, liquid tight housings containing a number of transducer elements bonded internally and directed through the wall of the housing into the surrounding cleaning liquid.  Each approach has its benefits and drawbacks.

Attachment to Tank

The majority of ultrasonic cleaning tanks under 50 gallons capacity utilize transducer elements bonded to the exterior of the cleaning tank.  These may be attached to the bottom and/or to the side walls of the tank.  There are many arguments for this.

• Bonding to the tank utilizes tank surface that it already part of the tank structure thereby eliminating a secondary structure inside the tank to house the transducer elements.
• Bonding to the tank reduces the overall tank size as the extra tank volume required to accommodate submersible transducer housings is eliminated.
• Externally bonded transducer elements eliminate in-tank obstructions.  They are favored in precision and critical applications where system decontamination on a regular basis is of utmost importance.

A tank with transducer elements attached is usually less costly to build and therefore a less expensive option overall for smaller ultrasonic cleaning tanks.

On the negative side, with transducer elements bonded to the tank, the assembly becomes a unit.  Repair usually means replacing the entire tank and transducer array as transducer elements are permanently bonded and are not repairable in place.

Submersible (Immersible) Transducers

As tank size increases the argument turns in favor of submersible transducers which are often called “immersibles.”

 

• Bonding transducer elements usually involves considerable fixturing and often a controlled heating means, usually an oven.  When bonding directly to tanks, tank sizes may vary widely from installation to installation necessitating customized fixturing for each variation.  Larger tanks require larger heat capacity as the entire assembly must be accommodated.  Submersible transducers offer the opportunity to provide ultrasonic energy in a wide variety of tank sizes using a few standard modular submersible transducer configurations.
• Should it become necessary to replace ultrasonic transducers in a larger tank, submersible transducers are relatively easy to replace and usually without removing the tank from its location.  Most manufacturers stock a few standard submersible transducers which they can ship promptly.  In the case of transducer elements bonded to the exterior of a tank, replacement of the entire tank and attached transducers is often the only option.  This results in considerable expense and delay as the new tank is fabricated and placed in position.

Electrical connections to submersible ultrasonic transducers should be made using stainless steel tubing with welded fittings or with well-sealed bulkhead fittings.  Submerged threaded fittings are not acceptable.  Tank penetrations should be made above the liquid level in the tank if possible.  Although sometimes  unavoidable due to tank configuration, flexible hoses are not recommended for electrical connections in an ultrasonic environment.

 JF