How do Ultrasonic Cleaners work?

When ultrasound moves through a liquid and hits against a solid object, it creates millions of tiny cavitation bubbles. Cavitation bubbles are tiny, vacuum-filled bubbles. Under the pressure of continuous vibration, these microscopic bubbles stretch and compress at a fast rate. Once they reach a certain size, according to the frequency and strength of the sound waves produced, the bubbles lose their structural integrity and collapse violently. When these implosions happen near a solid surface, the bubbles emit high-powered streams of plasma that collide with, agitate and remove foreign particles and substances from that surface.
Ultrasonic technology can be used to clean metals, plastics, glass, rubber, and ceramics. It effectively removes a wide variety of contaminants, even if present only in trace amounts, including dust, dirt, rust, oil, grease, soot, mould, carbon deposits, polishing compounds, wax, pigments, lime scale, bacteria, algae, fungus, fingerprints and biological soil.

What is "degassing", and why should it be done?

"Degassing" is the initial removal of gases present in the solution. Useful cavitation occurs after gasses have been removed from the cleaning solution, leaving a vacuum in the formed bubble. When the high pressure wave hits the bubble wall, the bubble collapses; it is the energy released by this collapse that will assist a detergent in breaking the bonds between parts and their soils.

Which frequency is best?

Generally there are two freqencies used, 28KHz and 40Khz.
28KHz is used with larger items, such as cleaning cast iron blocks used for injection molding, large steel cutting tools or large stainless steel plates. It works best when the grime is on the surface of the item and needs a little more aggression to remove it.
Most Ultrasonic Cleaners use 40KHz as the standard frequency. This produces mid-sized cavitation bubbles with a 40KHz transducer. This has enough power to shake contaminants loose but also penetrate closer to the substrate without causing damage. Typical uses of 40KHz ultrasonic cleaners include carburettor cleaning, removing oils and metal chips from general machine shop applications, soot removal from items damaged in fires, cleaning of ceramics used in the high technology fields, removal of biological contaminants from surgical tools, cleaning contaminants from printed circuit boards.

Why does the cleaning solution get hot?

The water in the cleaning bath will get hot even if you are not using the heating function. This is due to the cavitation caused by the ultrasonic action. This is normal and the longer you use the ultrasonic cleaner the hotter the water will get. If you are trying to keep the water below a certain temperature you can run the ultrasonic cleaner for a shorter amount of time.