Ultrasonic cleaning
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An ultrasonic cleaner, often colloquially referred to as a sonicator, 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 jewelery, 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). After conclusive studies, ultrasonic cleaning system proves to be more effective compared to other cleaning systems used in the medical field.[citation needed]
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[edit] Process Characteristics
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- Uses cavitation bubbles to penetrate blind holes, cracks, and recesses.
- Thoroughly removes tightly adhering or embedded particles from solid surfaces.
- Uses water or a mild solvent for cleaning medium.
- Can clean a wide range or workpiece shapes and sizes.
- May not require the part to be disassembled prior to cleaning.
Reference: Robert H. Todd, Dell K. Allen, and Leo Alting; Manufacturing Processes Reference Guide
[edit] Design and operating principle
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[citation needed]; 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.
[edit] Cleaning solution
Ultrasonic activity (cavitation) helps the solution to do its job; plain water would not normally be effective. The cleaning solution contains ingredients designed to make ultrasonic cleaning more effective. For example, reduction of surface tension increases cavitation levels, so the solution contains a good wetting agent (surfactant). Aqueous cleaning solutions contain detergents, wetting agents and other components, and have a large influence on the cleaning process. Correct composition of the solution is very dependent upon the item cleaned. Solutions are used warm, at about 50—65 °C (149 °F).
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.
[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. Ultrasonic waves can usually only be sent through a material at right angles to the material's surface (normal incidence). 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[citation needed].
Suitable materials for ultrasonic cleaning are stainless and mild steel, aluminium, copper, brass and other alloys, wood, plastics, rubber, and cloth.
Devices for home and hobby use are readily available from about US$20 up as of January 2007.
