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Ultrasonic cleaning is a process that uses ultrasound (usually from 20 to 40 kHz) to agitate a fluid, with a cleaning effect. Ultrasonic cleaners come in a variety of sizes, from small desktop units with an internal volume of less than , to large industrial units with volumes approaching 1,000 litres (260 US gal).
The principle of the ultrasonic cleaning machine is to convert the sound energy of the ultrasonic frequency source into mechanical vibration through the transducer. The vibration generated by the ultrasonic wave is transmitted to the cleaning liquid through the cleaning tank wall so that the micro-bubbles in the liquid in the tank can keep vibrating under the action of the sound wave, destroying and separating the dirty adsorption on the surface of the object.
Depending on the object being cleaned, the process can be very rapid, completely cleaning a soiled item in minutes. In other instances, cleaning can be slower, and exceed 30 minutes.Ellen Roberta and Raula Badavinac Dietz (2025). 9780766826601, Delmar Thomson Learning. . ISBN 9780766826601
Ultrasonic cleaners are used to clean many different types of objects, including industrial parts, jewellery, scientific samples, lenses and other optical parts, , dentistry and surgical instruments, , , , , , , firearm components, car , musical instruments, gramophone records , industrial machined parts, and electronic equipment, optical lenses, etc. They are used in many jewelry workshops, ' establishments, electronic repair workshops, and scientific labs.
It appears that ultrasonic cleaners developed as a natural evolution of several earlier inventions that used vibrations to agitate and mix substances, and thus there is no clear "inventor" of ultrasonic cleaning. , is the earliest patent on record that specifically uses the term "Ultrasonic cleaning" although earlier patents refer to the use of ultrasound for "intense agitation," "treatment" and "polishing," e.g. .
By the mid-1950s there were at least three ultrasonic cleaner manufacturers established in the United States and two in the United Kingdom; and by the 1970s ultrasonic cleaners were widely established for industrial and domestic use.
Objects must not be allowed to rest on the bottom of the device during the cleaning process, because that will prevent cavitation from taking place on the part of the object not in contact with solvent.
Transducers are usually Piezoelectricity (e.g. made with lead zirconate titanate (PZT), barium titanate, etc.), but are sometimes Magnetostriction. The often harsh chemicals used as cleaners in many industries are not needed, or used in much lower concentrations, with ultrasonic agitation. Ultrasonics are used for industrial cleaning and are also used in many medical and dental techniques and industrial processes.
Reduction of surface tension increases cavitation, so the solution usually contains a good wetting agent (surfactant). Aqueous cleaning solutions contain detergents, wetting agents and other components, which have a large influence on the cleaning process. The correct composition of the solution is very dependent upon the item cleaned. When working with metals, proteins, and greases, an alkaline detergent solution may be specifically recommended. Solutions are typically heated, often around , however, in medical applications, it is generally accepted that cleaning should be at temperatures below to prevent protein coagulation that can complicate cleaning.
Some ultrasonic cleaners are integrated with vapour degreasing machines using hydrocarbon cleaning fluids: Three tanks are used in a cascade. The lower tank containing dirty fluid is heated causing the fluid to evaporate. At the top of the machine there is a refrigeration coil. Fluid condenses on the coil and descends into the upper tank. The upper tank eventually overflows and relatively clean fluid runs into the work tank where the cleaning takes place. The purchase price is higher than simpler machines, but such machines may be more economical in the long run. The same fluid can be reused many times, minimising wastage and pollution.
Ultrasonic cleaning does not sterilize the objects being cleaned, because spores and viruses will remain on the objects after cleaning. In medical applications, sterilization normally follows ultrasonic cleaning as a separate step.
Industrial ultrasonic cleaners are used in the automotive, sporting, printing, marine, medical, pharmaceutical, electroplating, disk drive components, engineering and weapons industries.
Ultrasonic cleaning is used to remove contamination from industrial process equipment such as pipes and heat exchangers.
Design and operating principle
In an ultrasonic cleaner, the object to be cleaned is placed in a chamber containing a suitable solution (in an aqueous or organic solvent, depending on the application). In aqueous cleaners, (e.g., laundry detergent) are often added to permit dissolution of non-polar compounds such as oils and greases. An ultrasound generating transducer built into the chamber, or lowered into the fluid, produces ultrasonic waves in the fluid by changing size in concert with an electrical signal oscillating at ultrasonic frequency. This creates compression waves in the liquid of the tank which 'tear' the liquid apart, leaving behind many millions of microscopic 'voids'/'partial vacuum bubbles' (cavitation). These bubbles collapse with enormous energy; temperatures and pressures on the order of 5,000 K and 135 MPa are achieved; however, they are so small that they do no more than clean and remove surface dirt and contaminants. The higher the frequency, the smaller the nodes between the cavitation points, which allows for cleaning of more intricate detail.
Cleaning solution
In some circumstances, ultrasonic cleaners can be used with plain water, but in most cases, a cleaning agent is used. This solution is designed to maximise the effectiveness of ultrasonic cleaning. The primary solvent may be water or a hydrocarbon (historically, toxic solvents such as carbon tetrachloride and 1,1,1-Trichloroethane were used industrially, but have been phased out). There are several formulations, dependent on the item being cleaned and the type of contamination (e.g., degreasing of metal, cleaning of printed circuit boards, removing biological material, and so on).
Uses
Most hard, non-absorbent materials (metals, plastics, etc.) not chemically attacked by the cleaning fluid are suitable for ultrasonic cleaning. Ideal materials for ultrasonic cleaning include small electronic parts, cables, rods, wires, and detailed items, as well as objects made of glass, plastic, aluminium, or ceramic.Douglas Williams (1994). 9780788114519, United States Environmental Protection Agency. . ISBN 9780788114519
Louise, and Karen Simmers-Nartker, Sharon Simmers-Kobelak Simmers (2025). 9781418030216, Delmar Cengage Learning Academic Resource Center. . ISBN 9781418030216
Limitations
Ultrasonic cleaning is used widely to remove flux residue from soldered circuit boards. However, some electronic components, notably MEMS devices such as gyroscopes, and microphones can become damaged or destroyed by the high-intensity vibrations they are subjected to during cleaning. Piezoelectric buzzers can work in reverse and produce voltage, which may pose a danger to their drive circuits.
Safety
See also
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