Surface cleaning by ultrasound is referred to highly effective and efficient purification and cleaning processes. The advantages of this method are: the ability to quickly remove various types of pollution from the surface of the items; ability to clean parts of complex shape, with hard to reach cavities and channels; applicability of different detergents; possibility of carrying out the cleaning process at room temperature or moderate heating; ease of mechanisation and automation of the process.
Ultrasonic waves propagating in detergent solution from the radiation source, provide pressure on the surface of the item due cavitation phenomena. Cavitation is manifested in the fluid breaks under the action of the sound wave to form small bubbles (50-500 microns) filled with cleaning fluid vapors. Some bubbles collapse almost instantly (20-50 ms), creating a local pressure surges reaching the pressure of hundreds of atmospheres. Under the influence of this pressure the destruction of contaminants takes place. Another part of bubbles doesn’t collapse, and under the influence of intense pulsed ultrasound field and moves with the hydrodynamic flow, it contributes to the intensification of treatment.
Choosing the optimal procedure
Depending on the type of contamination (solid or liquid), and a kind of washing medium (solvent or alkali aqueous solution) cleaning mechanism is determined. Thus, the purification of solid contaminants in the aqueous environment pollution destroyed forces arising in the collapse of bubbles. When cleaning in a solvent or aqueous medium-soluble or viscous pollutants most important is the circulation of the fluid in which the major role is played by active pulsating bubbles. The main factors determining the cleaning process are: the frequency and intensity of ultrasonic vibrations, the properties and temperature of the cleaning liquid and the location of the parts to be cleaned in an ultrasonic field.
The frequency of the ultrasonic vibration determines the intensity of the collapse of cavitation bubbles. The lower the frequency, the greater the intensity of each separate act of collapsing, as at low frequency the bubble has more time to form and reaches a higher value. Furthermore, at low frequencies waves have a large penetration depth, which is particularly advantageous when cleaning complex parts having holes and chambers. Under the influence of low-frequency ultrasonic waves can have a vibrate effect on components themselves, which also contributes to cleaning.
However, at frequencies below 20 kHz, the sound becomes audible. The shrill sound of the whistle and the accompanying job ultrasonic devices on these frequencies is unpleasant for the human ear and has a painful impact. Based on the above assumptions, studies and technical expertise, the frequency of 20-25 kHz is the most appropriate for cleaning. This is the optimal number manufacturers are heading for – Hilsonic engineers, representing one of the most influential UK manufacturer of ultrasonic cleaner equipment, admits the numbers lie within the golden medium they are aiming at in designing and production.Read Article