What is "Ultrasonics"?

Sound is a wave in air, with its tone or pitch determined by the frequency of such wave. Ultrasound is a sound wave with a frequency higher than human ear can detect, usually above 18 Kilohertz. The frequencies used for ultrasonic cleaning range from 20 KHz to over 100,000 KHz. The most commonly used frequencies for industrial cleaning are those between 20 KHz and 50KHz. Frequencies above 50KHz are more commonly used in small tabletop ultrasonic cleaners such as those found in jewelry stores and dental offices.

The Nature of Sound Waves

As a result of wave, any partical in a conducting medium is subjected to an pressure alternating from positive value, compression , to negative one, rarefaction. In non-elastic media such as water or most liquids, there is continuous transition as long as the amplitude of the wave is relatively low. As amplitude is increased, however, the magnitude of the negative pressure in the areas of rarefaction eventually becomes strong enough to cause the liquid to fracture. This phenomenon is known as cavitation. As the wave fronts pass, the cavitation "bubbles" oscillate under the influence of positive pressure, eventually growing to an unstable size. Finally implosions take place resulting from the violent collapse of the cavitation "bubbles" and shock waves radiate from the sites of the collapse. The collapse and implosion of myriad cavitation "bubbles" throughout an ultrasonically activated liquid result in the effect commonly associated with ultrasonics. It has been calculated that temperatures in excess of 10,000°F and pressures in excess of 10,000 PSI can be generated at the implosion sites of cavitation bubbles.

How Ultrasonics Benefit Cleaning

In most instances, cleaning requires that a contaminant, be dissolved (such as a soluble soil)or displaced (such as a non-soluble soil) or both dissolved and displaced (such as grease). The mechanical impact from ultrasonic wave can both speed up dissolution and displace particles. Similarly, it helps rinsing process. Residual cleaning chemicals are removed quickly and completely by ultrasonic rinsing. During a cleaning procedure when chemistry is applied, a saturated layer develops at the interface between the cleaning chemistry and the contaminant. It slows down cleaning action and eventually stops it when such layer fully covers the contaminant. In a traditional cleaning process, such layer must be manually removed or sprayed away. What if the area can not be reached?

Ultrasonic cavitation and implosion effectively destroy such saturated layer to keep reaction between fresh chemistry and the contaminant. This is especially powerful with irregular surfaces or internal passageways. Cavitation and implosion can displace and remove loosely held contaminants such as dust. Some contaminants are comprised of insoluble particles loosely attached and held in place by ionic or cohesive forces. Contaminations can also be more complex consisting of combination soils made up of both soluble and insoluble components. In both cases, micro-agitation of ultrasonics helps to speed both the dissolution and the displacement. Due to increased temperature and pressure, ultrasonic is found to enhance chemical reactions.

Ultrasonic cleaning are superior to other alternatives, including spray washing, brushing, turbulation, air agitation, and even electro-cleaning in many applications.