Ultrasonic cleaning is a method of cleaning the surface of solids in washing liquids, in which ultrasonic vibrations are introduced into the liquid in one way or another. The use of ultrasound usually significantly speeds up the cleaning process and improves its quality. In addition, in many cases it is possible to replace flammable and toxic solvents with safer detergents without loss of cleaning quality.
Ultrasonic cleaning is used in many industries [1] , in the repair of machines and mechanisms, in jewelry and restoration, in medicine, in everyday life [2] , etc.
Cleaning occurs due to the combined action of various nonlinear effects that occur in a liquid under the influence of powerful ultrasonic vibrations. These effects are: cavitation , acoustic currents , sound pressure , sound capillary effect , of which cavitation plays a decisive role. Cavitation bubbles, pulsating and collapsing near contaminants, destroy them. This effect is known as cavitation erosion .
For ultrasonic cleaning, it is important to choose the right detergent solution so that it effectively dissolves or emulsifies contaminants, without possibly affecting the surface being cleaned. The latter circumstance is especially important, since ultrasound usually significantly accelerates the physicochemical processes in liquids, and an aggressive detergent can quickly damage the surface.
Ultrasonic cleaning should not be used when the cavitation resistance of the surface being cleaned is less than the resistance of contamination. For example, when removing stick-on films from aluminum parts, there is a high probability of destruction of the parts themselves.
Content
Pollution and its effects
From the point of view of ultrasonic cleaning, pollution differs in three ways:
- Cavitation resistance, that is, the ability to withstand micro-shock loads.
- The bond strength with the surface being cleaned, resistance to peeling.
- The degree of interaction with the washing liquid, that is, whether and how capable this liquid is to dissolve or emulsify contamination.
Cavitation-resistant contaminants lend themselves well to ultrasonic cleaning only if they are loosely bonded to the surface or interact with a washing solution. These are fatty contaminants that are well washed in slightly alkaline solutions. Coatings of varnish or paint, scale, oxide films are usually cavitation resistant and are well connected to the surface. For ultrasonic cleaning of such contaminants, fairly aggressive solutions are needed, because only the third of the listed signs can act here.
Cavitationally unstable contaminants (dust, porous organics, corrosion products) are relatively easily removed even without the use of special solutions.
Detergents
In ultrasonic cleaning, both plain water and aqueous solutions of detergents and organic solvents are used as a washing liquid. The choice of product is determined by the type of contamination and the properties of the surface being cleaned (see above).
Ultrasonic Cleaning Devices
For ultrasonic cleaning, you need a tank with a washing solution and a source of mechanical vibrations of the ultrasonic frequency, called an ultrasonic emitter . The surface of the ultrasonic transducer , the container body and even the part to be cleaned can act as a radiator. In the latter cases, the ultrasonic transducer is attached, respectively, to the housing or to the part.
An ultrasonic transducer converts the electrical vibrations supplied to it into mechanical vibrations of the same frequency. Most installations use frequencies from 18 to 44 kHz with oscillation intensities from 0.5 to 10 W / cm². The upper limit of the frequency range is due to the mechanism of formation and destruction of cavitation bubbles: at a very high frequency, the bubbles do not have time to slam, which reduces the micropack effect of cavitation.
Converters can be magnetostrictive or piezoceramic . The former are distinguished by their larger size and mass, significantly lower efficiency , but they allow to achieve high power, of the order of several kilowatts. Piezoceramic transducers are more compact, lighter, more economical, but their power, as a rule, is not so great - up to several hundred watts. Such power, however, is sufficient for the vast majority of applications, given that in large installations several emitters are used at once.
The most famous devices are ultrasonic baths , installations specially designed for ultrasonic cleaning. Converters in such bathtubs, as a rule, are either built into openings in the housing, or attached to the housing, making it a radiator, or placed inside as separate modules. Each method has its advantages and disadvantages.
Separate modules of ultrasonic transducers (emitters) can be integrated into production lines where fast and high-quality cleaning is required. So, for example, they act for the continuous cleaning of rolled metal and wire at different stages of their production and use.
Known converters made in the form of small hand tools for the accurate cleaning of complex surfaces.
See also
- Ultrasonic cavitation
Literature
- Ultrasound. Little Encyclopedia. Chap. ed. I.P. Golyamina. - M.: “Soviet Encyclopedia”, 1979, pages 242-247. ( book in DjVu format )
Notes
Links
- Natalya Buryakova. Ultrasound washing - myth or reality? // Magazine " Consumer ". - 2005. - No. 11 .