Ultrasonic agitation of cleaning solutions is just one of many tools that can be used to facilitate and enhance a cleaning process. High frequency vibrations are introduced into a bath of liquid cleaning solution by specially designed devices called transducers which are similar in concept to loudspeakers but designed to operate at much higher sound frequencies which are generally inaudible to the human ear. These transducers are powered by devices called ultrasonic generators which emit high frequency electrical signals.
High frequency vibrations in liquid produce a phenomenon known as cavitation. Cavitation is the formation of microscopic cavities within the cleaning liquid which, in turn, collapse in a process known as implosion. The implosion of cavitation bubbles is the driving force behind ultrasonic cleaning. The implosion or collapse of cavitation bubbles releases concentrated mechanical energy and high temperature impulses at the point of collapse which cause localized effects beneficial to the cleaning process.
Unlike brushing, spraying and other means of liquid agitation, ultrasonic agitation is able to penetrate deep into complex surface features to clean where other means can not. In fact, depending on the material and wall thickness, ultrasonic energy may be able to actually promote cleaning within a closed structure in areas totally inaccessible using other means. For all its capability, ultrasonic cleaning also has significant limitations. The effect is microscopic in nature and does not lend itself to removing thick layers of heavy contamination. Also, since it benefits from the presence of a hard surface to concentrate the effect of cavitation implosion, ultrasonic cleaning may not be effective in removing contaminants from soft or resilient materials such as rubber and soft plastics.
Ultrasonic cleaning is ideal for “precision cleaning” applications where contaminants consist of layers of material measuring no more than a few millimeters in thickness and particles from sub-micron up to several microns in size. In general, more delicate surfaces and contaminants consisting of smaller-sized particles are cleaned using higher frequency ultrasonic frequencies (>100kHz) while more robust surfaces and heavier contaminant loads utilize lower ultrasonic frequencies (25 to 100kHz). There is a lot more to know about ultrasonics.
As this blog develops, I will frequently be addressing other topics about and related to the application of ultrasonic energy to cleaning. Search category Ultrasonics.