An ultrasonic cleaner is a cleaning device that uses ultrasound (usually from 15-400 kHz) and an appropriate cleaning solution to clean delicate items. The ultrasound is not effective without the cleaning solution; it enhances the effect of a solution appropriate for the item to be cleaned and the soiling.
They are often employed for cleaning of jewellery, lenses and other optical parts, coins, watches, dental and surgical instruments, fountain pens, industrial parts and electronic equipment. In everyday use such devices may be found in use in most jewelry workshops, watchmakers establishments, or in cellular phone repair workshops (where it could be used for cleaning a phone that has been exposed to enough moisture to hinder its operation).
In an ultrasonic cleaner, the object to be cleaned is placed in a chamber containing a suitable ultrasound conducting fluid (an aqueous or organic solvent, depending on the application). In aqueous cleaners, the chemical added is a surfactant which breaks down the surface tension of the water base. 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’ or ‘partial vacuum bubbles’ (cavitation). These bubbles collapse with enormous energy; temperatures of 10,000 K and pressures of 50,000 lbs per square inch have been reported; 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.
Transducers are usually piezoelectric material (e.g. lead zirconate titanate or barium titanate), and sometimes magnetostrictive (made of a material such as nickel or ferrite). 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 also used in many medical and dental techniques and industrial processes.
Water-based solutions are more limited in their ability to remove contaminants by chemical action alone than solvent solutions; e.g. for delicate parts covered with thick grease. The effort required to design an effective aqueous-cleaning system for a particular purpose is much greater than for a solvent system.
Flammable solutions should not be used, as they may be hazardous with the high local temperatures generated. Acids and bleaches should only be used if they will not react either with the item being cleaned or the cleaning tank. Solutions should be replenished when ther are noticeably spent.
To test for effectiveness, draw an "X" with an HB (normal) pencil across a wet frosted glass slide. Immerse it, and turn on. The "X" should start to fade immediately, and should be all gone within 10 seconds.To test for evenness of cleaning, take 3 pieces of aluminium foil of about 10×20 cm. Suspend the 3 pieces in the tank, one in the middle and the othe two near opposite edges. Run the ultrasonics for about 10 minutes. The 3 pieces should be about equally perforated and wrinkled.
If the item cleaned may be damaged by leaving it wet after rinsing, it can be warmed or centrifuged to hasten drying.
Devices for home and hobby use are readily available from about US$20 up as of January 2007.