Ultrasonic cleaning

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Please improve this article if you can. (February 2007)

An ultrasonic cleaner

An ultrasonic cleaner is a cleaning device that uses ultrasound (usually from 15-400 kHz) to clean delicate items.

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).

1 Design
2 Uses
3 Suitable materials for ultrasonic cleaning
4 See also

[edit] Design

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 is built into the chamber, or may be lowered into the fluid. It is electronically activated to produce ultrasonic waves in the fluid. The main mechanism of cleaning action is by energy released from the creation and collapse of microscopic cavitation bubbles, which break up and lift off dirt and contaminants from the surface to be cleaned. The higher the frequency, the smaller the nodes between the cavitation points which allows for more precise cleaning. The bubbles created can be as hot as 10,000 degrees and 50,000 lbs per square inch, but are so small that cleaning and removal of dirt is the main result^{[citation needed]}.

[edit] Uses

Industrial ultrasonic cleaners are used in the automotive, sporting, printing, marine, medical, pharmaceutical, electroplating, disk drive components, engineering and weapons industries. Cleaners are also used to experimentally determine the elastic constants of many anisotropic materials. Traditionally, ultrasonic waves can only be sent through a material at angles normal to the materials surface. However, in water the angle of incidence for a longidunal wave can be set, inducing both longitudinal and transverse waves in the material. Then by measuring the time of flight for both waves, the elastic constants can be determined.

Devices for home and hobby use are readily available, and may cost as little as US$20, as of January 2007.

[edit] Suitable materials for ultrasonic cleaning

Ultrasonic transducers showing ~20 kHz and ~40 kHz stacks. The active elements (near the top) are two rings of lead zirconate titanate, which are bolted to an aluminium coupling horn.

Ultrasonic transducers work by rapidly changing size when excited by an electrical signal. This creates a compression wave in the liquid of the tank. These compression waves actually ‘tear’ the liquid apart, leaving behind a ‘void’ or ‘partial vacuum bubble’. When these ‘bubbles’ (and there are many millions of them in an active ultrasonic tank) collapse, they collapse with enormous energy. When sufficient energy is built up in the ‘bubble’ or cavitation, the cavitation collapses violently. The transducers are usually composed of piezoelectric material (e.g. lead zirconate-titanate or Barium Titanate), and occasionally are made of magnetostrictive material (e.g. nickel or ferrite). The often harsh chemicals traditionally used as cleaners in many industries can be reduced or eliminated with the introduction of ultrasonic technology. Ultrasonics are also used in many medical and dental techniques and industrial processes, as well as in industrial cleaning.