Ultrasonic cleaning

Ultrasonic cleaners are mostly used for the purification of small, complex and finely structured components. For example, use goldsmith, dental technicians, watchmakers and opticians ultrasonic cleaning baths for cleaning their products. Meanwhile, there are also larger, industrial ultrasonic cleaning systems, which are used for example in the automotive industry for cleaning surfaces prior to painting.

Construction

The system consists of a liquid-filled, possibly heated pan, one or more ultrasonic transducers or ultrasonic transmitters and a generator which supplies the transducer or transducers with high frequency electrical energy. Both directly outside on the walls and under the floor of the tub transducer systems can be flanged, but only if the material thickness of wall or floor is not too strong. In this construction, the ultrasound is then introduced directly into the liquid on the walls and / or floor. Another variant are called submersible transducers that are suspended in the fluid or mounted on racks in the basin. Finally, there is plate transducers, which are flanged to a corresponding opening in the pool wall.

The devices are usually manufactured in stainless embodiment. The arrangement and distribution of the acoustic transducer must be such that a uniformly strong, not static sound field is created. Some manufacturers therefore modulate the frequency to prevent standing waves. Is also a function of degassing of the cleaning liquid is not uncommon. Here, the power output of the device is pulsed to allow any gas bubbles to rise to the surface. The background is the poor training of cavitation bubbles in the presence of gas bubbles as they would swallow the performance. A good starting value for the sound power is about 10 W per liter of cleaning fluid. The sound generator require a minimum distance to a homogeneous sound field formed. The housing of the machine must be isolated from output acoustic oscillations. A touch of vibrating parts must be prevented.

Frequencies

Are commonly used frequencies from 20 kHz to 2 MHz. Low frequencies around 20 kHz produce bubbles of larger diameter with strong pressure shocks, in contrast, higher frequencies around 35 kHz are more suitable for intensive and gentle cleaning of surfaces. The current frequency is common for particles having a diameter greater than 1 micron as 200 kHz ("U.S. "). The frequency range above 400 kHz to 1-2 MHz in the literature as megasonic ("MS" ) referred. Here particles are optimally replaced with a diameter less than 1 micron.

The frequency required is determined by the smallest opening or structure that can be cleaned by the transducer. The wavelength in the water must be less than half the size of the opening diameter. Otherwise, the sound can not penetrate and the surface would be smooth and closed for the sound effect.

Application

The use of solvents, acids or alkalis substantially supports the cleaning effect of ultrasonic baths. However, also occur always on opposite effects. So if too dirty the wash solution is again an addition instead. There are no flammable liquids used as cleaning agents, as always, a heat input by the ultrasound into the liquid.

Ultrasonic baths are also used in sample preparation to disrupt biological substances in the analytical laboratory, so to fragment. One uses ultrasonic baths for cell disruption or per gram of tissue.