Ultrasound boasts a multifactorial effect, so its application can significantly accelerate any of the cleaning methods and improve the quality of final results. Alternating pressure fluctuations of fluid particles and acoustic phenomena, the ‘sonic wind’, cavitation and ultrasonic capillary effect offer unparalleled efficiency.
The nature of the effect
The primary energy role is played by cavitation. During the collapse of the cavitation bubbles microstreams are formed and cumulative fluid velocity reaches a hundred meters per second, towards the surface to be cleaned. Under the influence of shock waves and high-speed microstreams an intensive film degradation of impurities (solid or liquid types) and its separation from the surface takes place. Cavitation provides intensive ultrasound emulsification of liquid and ultrasonic dispersion of separated solid contaminats.
Due to acoustic streaming is provided by removal of the boundary layer solution or destroyed under the influence of cavitation in the volume of fluid contamination. A particularly important role is played by acoustic streaming in removing soluble contaminants.
Cleaning efficiency increases when the surface to be treated to the emitter is reduced. However, placing the product to the emitter in less than 1-2 mm is impractical because at small gaps between the transmitter and the surface conditions remove contaminants from the boundary layer and decreases the activity of cavitation due to changes in the collapse scheme of cavitation bubbles.
The advantage of ultrasonic cleaning is not only an ability to achieve high-quality cleaning test surface from a wide variety of contaminants, but also to remove impurities from the capillary cavity defect. The most effective use of ultrasound is the mode that provides an emergence of ultrasonic capillary effect. The mode contributes to reagent capillaries filling to a greater depth and a greater rate. In addition, significantly accelerates the diffusion of dissolved gas to the mouth of the defect; dissolution of contaminants presents in the cavity of the defect; the diffusion of impurities to its mouth. As a result, accelerates the process of filling voids and defects in general and increases the depth of penetration of the working fluid in the blind capillary channels. The mode is supported in neoteric equipment, such as Hilsonic – a seasoned UK-based business, focusing its effort on studying ultrasound and producing an impressive line-up of ultrasonic cleaner devices.
The use of ultrasound for cleaning can significantly improve quality control. Thus discontinuities are cleaned to a sufficient depth not only in case of liquids, but also such contaminants sparingly as polishing paste. As a result, the number of identified traces close to the total number of defects is taken into account. The use as a detergent liquid water and aqueous solutions of glycerol and a dispersing agent for cleaning in an ultrasonic field is more effective than the use of solvents such as acetone or benzene. This is due to greater activity of acoustic cavitation in water and aqueous solutions than in acetone and petrol. The use of ultrasound allows solving the problem of replacing explosive, environmental hazards to more environment-friendly materials.