Ultrasonic Process

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Ultrasonic

Parameters
For an effective cavitation process should the amount of gas in the cleaning fluid be kept to a minimum. The added ultrasonic energy to the cleaning fluid will the gas (read oxygen) convert to gas bubbles and this keeps a minimum energy left to generate cavitation. It is therefore important to degas the liquid before a start is made with the cleaning, only then the cavitation process will be optimal.
The viscosity of the cleaning fluid must be kept to a minimum to generate optimal cavitation. Viscous liquids do not reciprocate quickly enough when generating cavitation and implosion.
For an effective cavitation process should the amount of gas in the cleaning fluid be kept to minimal? The addition ultrasonic energy to the cleaning fluid will the gas (oxygen) convert to gas bubbles and hence this keeps minimum energy left to generate cavitation. Therefore, It is important to degas the liquid before a start is made with the cleaning, only then the cavitation process will be optimal.
The ultrasonic power is directly related to the bath volume and mostly to the cleaning application and is expressed in Watts per liter. The intensity of cavitation is directly related to the ultrasonic power and choice of frequency.
Ultrasonic cavitation intensity is inversely proportional to the frequency related to the ultrasonic frequency. At a higher frequency, the intensity of the cavitation will decrease, where there is an increase in the number of cavitation bubbles. This is because the cavitation bubbles remains small with a minimal implosion force. In other words, the higher the frequency, the finer the "cleaning brush".

Ultrasonic

Cleaning Process

An ultrasonic cleaning device contains a tank made of stainless steel (figure 1 (1)), in which the cleaning liquid has to be filled. This can be water + cleaning agent. For better cleaning efficiency cleaning chemicals can be added to the bath. (2)

Ultrasonic transducers (3) are mounted at the bottom and sometimes also at the sides of the tank. These transducers convert an electrical alternating voltage in mechanical vibration, like a loudspeaker. An ultrasonic generator (4) produces
this alternating voltage, which has an operating frequency from about 20kHz to 40kHz normally used for cleaning purposes. Higher frequencies are used to support the subsequent rinsing. When the transducers are stimulated by the alternating voltage, the vibration spreads through the material of the tank into and in the fluid. Bubbles (5) which are in the fluid are brought to oscillation, so that their volume increases and decreases. When the intensity of the oscillation reaches a sufficient level these bubbles can implode. Then a so called Jetstream occurs, which removes by its stimulus the dust from a polluted surface like a micro brush

However, the bubbles in the ultrasonic bath are much smaller than shown in the video. To increase cleaning efficiency, most ultrasonic devices are equipped with a heater(6) to warm up the liquid.

Many ultrasonic devices also offer the option to select different frequency modes. “Sweep” is normally the standard model. Here the operation frequency sweeps a range of about +/- 1 kHz around a middle frequency. This causes the most common distribution of the bubbles in the tank. Another mode is “pulse”. Here the operating frequency switches very fast between two frequencies, which have a separation of about 1 kHz. The advantage is a higher cleaning efficiency. Older or simpler devices only have a fixed frequency.