Ultrasonic cleaning – method of cleaning the surface from solid and liquid contaminants is based on the excitation of ultrasonic frequency in the washing solution. The scientific basis for the creation and development of technology equipment ultrasonic cleaning laid in the field of acoustic cavitation conducted at the Acoustics Institute named after Academician Andreeva led by Professor Rosenberg.
Ultrasonic cleaning can replace manual labor, thereby speeding up the cleaning process, a high degree of surface smoothness virtually eliminate the use of inflammable and toxic solvents. Thus, according to Hilsonic statistics (the company is focusing its efforts on producing ultrasound equipment and ultrasonic cleaner models in particular) reports that despite the higher energy consumption and relatively high maintenance costs, its customers managed to cut down operational expenses by 18% on average.
Ultrasonic cleaning process provides its effect due to several phenomena that occur in the field of high intensity of ultrasound: acoustic cavitation, acoustic currents, radiation pressure and acoustic-capillary pressure.
Depending on the type of contamination, the predominant role is played by various purification processes. Thus, the destruction of contaminants occurs weakly interrelated, mainly under the influence of pulsating cavitation bubbles. On the edges of the film contamination pulsating bubbles, making intense vibrations, overcoming the cohesive forces of the film to the surface, penetrating the film and breaking it. Radiation pressure and acoustocapillary effect contribute to the penetration of cleaning solution in the micropores, bumps and blind channels. Acoustic flow is accelerated removal of dirt from the surface. If contamination is firmly connected to the surface, its elimination requires collapsing cavitation bubbles, creating a microshock impact to the surface.
To accomplish the desired ultrasonic cleaning efficiency it is necessary to choose the optimal values of the intensity of ultrasound and oscillation frequency. With increasing frequency cavitation bubbles reaches the final stage of the collapse, which reduces the effect of cavitation microshock. Excessive lowering of the frequency increases the level of airborne noise, and requires an increase in the size of the radiator. Therefore the majority of industrial plants make use of a range of 18-44 kHz.
An increased intensity of ultrasound beyond a certain limit leads to an increase of the amplitude values of the pressure and cavitation bubbles degenerate into a pulsating ones. At low intensities, weakly expressed cavitation and all secondary effects arising from the introduction of liquid ultrasonic vibrations determine the effectiveness of treatment. Work intensity interval equals 0.5-10 W/cm2.
The washing liquid
A major role in the cleaning process plays a properly selected composition of the washing liquid. It is necessary to take into account properties of the material items to be cleaned and the type of contamination. The cleaning fluid should be chemically reacting only with the surface contamination, but not with the material components to be cleaned. A significant impact on the course of development in detergent solutions play physico-chemical properties of the fluid. Increasing the vapor pressure inside the bubble cavitation decreases intensity sharply, so, for example, using the aqueous ultrasonic cleaning solutions is a more effective approach than using organic solvents.
The role of an ultrasonic bath
The bath may be of any volume, typically made mainly of stainless steel. The manufacturers can use both weldless, standard and special – welded-through approaches. For the treatment of articles in an acidic bath solution can be covered with a special protective coating, typically teflon. Electroacoustic transducers convert the energy into acoustic electric oscillations. For excitation of acoustic vibrations in an ultrasonic bath mainly magnetostrictive and piezoelectric transducers are used.