Ultrasonic cleaners were originally used in industry in the 1950’s and have become a recognised method for the cleaning of small electronic parts, cables, rods, wires and detailed items which would be difficult to clean by any other method. Most hard, non-absorbent materials are suitable for ultrasonic cleaning, such as glass, plastic, aluminium and ceramic utilising chemically-optimised cleaning fluids. Traditionally this method is used in the marine, automotive, printing, medical, pharmaceutical and engineering industries.
A high tech ultrasonic cleaner works via sound waves introduced into a cleaning liquid by transducers mounted onto a cleaning tank. The sound travels throughout the ultrasonic cleaner’s tank creating oscillating waves of compression and expansion in the liquid. The expansion is so dramatic that molecules are ripped apart, creating microscopic cavitation bubbles, so small as to be invisible to the naked eye and existing for only a split second.
The combination of nanometre level force, highly localised and split-second heat, delivers precise and effective cleaning on surfaces of all types - delving into nooks and crannies normal cleaning cannot reach without damage or abrasion to the component.
The power of the bubble
The bubbles contain a partial vacuum whilst they exist. As the pressure around the bubbles becomes greater, the fluid around the bubble rushes in, collapsing the bubble very rapidly. Ultrasonics takes advantage of the associated phenomena to deliver ultra-precise cleaning capabilities. When the bubbles collapse, a jet of liquid is created that travels at an extremely high rate.
Localised temperature combined with the liquid jet's velocity, provides a very intense cleaning action in a tightly concentrated area that ultrasonic equipment can utilise. Because of the very short duration of the bubble expansion and collapse cycle, the liquid surrounding the bubble quickly absorbs any heat and the area cools rapidly. As a result, the tank and liquid only becomes warm and parts do not heat excessively from introduction to the ultrasonic washing equipment.
Cleaning Solution
It is the action of the cavitation that helps the cleaning solution do its job. The cleaning solution only contains ingredients designed to make ultrasonic cleaning more effective. For example, reduction of surface tension increases cavitation levels, so the solution often includes a good wetting agent. Aqueous cleaning solutions contain such wetting agents, alongside detergents and other components, and have a large influence on the cleaning process. The correct composition of the solution is dependent upon the item to be cleaned.
Solutions are mostly used warm, at about 50–65 °C (122–149 °F), however, in medical applications it is generally accepted that cleaning should be at temperatures below 38 °C (100 °F) to prevent protein coagulation.
Alongside water-based solutions for general purpose use, more extreme contaminants can be removed by chemical action supplied by a solvent solution; 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. Some machines are integrated with vapour degreasing machines using hydrocarbon cleaning fluids.
