- Principle of ultrasonic
- Commonly used cleaning process
- Cleaning technology application
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Principle of ultrasonic
The ultrasonic power, which is higher than 20KHz, is transferred into the cleaning liquid by converting the transducer into high frequency mechanical oscillation. Ultrasonic density in cleaning liquid and forward radiation, the liquid flow caused tens of thousands of tiny bubbles, the bubbles in the propagation of longitudinal ultrasonic waves in negative pressure zone formation, growth, and in the area of positive pressure (out), quickly closed the tiny bubble formation, growth, rapid closure is called cavitation. In the cavitation bubble in the closed form, instantaneous high pressure exceeds 1000 ATM, continuously produce instantaneous high pressure as a series of "explosion" continue to impact the surface of the object, the object surface and the cracks in the dirt off, so as to achieve the purpose of cleaning. This cavitation erosion is the basic principle of ultrasonic cleaning.
When ultrasonic waves propagate in the medium, the interaction between ultrasonic and medium will cause physical or chemical changes in the medium, resulting in a series of ultrasonic effects of mechanical, thermal, electromagnetic and chemical, including the following 4 kinds of effects.
(1) mechanical effect: the mechanical action of ultrasonic can contribute to the emulsification of the liquid, the liquefaction of the gel and the dispersion of the solid. When standing wave is formed in ultrasonic fluid medium, tiny particles suspended in fluid are condensed at wave nodes due to mechanical force, forming periodic accumulation in space. When ultrasonic waves propagate in piezoelectric materials and magnetostrictive materials, induced polarization and induced magnetization are caused by the mechanical action of ultrasound, namely magnetostrictive in dielectric physics.
(2) cavitation: a large number of small bubbles can be produced when ultrasonic acts on liquids. One reason is the local tension stress in the liquid and the negative pressure is formed. The decrease of pressure makes the original liquid gas supersaturated and escapes from the liquid and becomes a small bubble. Another reason is that the strong tensile stress "tearing" the liquid into a hole, called cavitation. An empty cavity is a liquid vapor or another gas that dissolves in a liquid, or even a vacuum. The small bubbles formed by cavitation will continue to move, grow or burst with the vibration of the surrounding medium. During the disillusionment, the liquid suddenly plunged into the bubble and produced high temperature, high pressure and shock wave. The internal friction accompanied by cavitation can form a charge and produce a luminescent phenomenon in the bubble. The technology of ultrasonic treatment in liquid is mostly related to cavitation.
(3) thermal effect: due to the high frequency and energy of the ultrasonic wave, it can produce significant heat effect when it is absorbed by the medium and produces vibration or friction. Chemical effect: the effect of ultrasound can induce or accelerate some chemical reactions. For example, pure distilled water by ultrasound processing to produce hydrogen peroxide; dissolved in water by ultrasound treatment with nitrogen after produce nitrite; dye solution by ultrasound treatment discoloration or fade after. The occurrence of these phenomena is always accompanied by cavitation. Ultrasound can also accelerate the hydrolysis, decomposition and polymerization of many chemical substances. Ultrasound has an obvious influence on the photochemical and electrochemical processes. After the ultrasonic treatment of various amino acids and other organic substances, the characteristic absorption band disappeared and showed a uniform general absorption. This indicates that the molecular structure is changed by cavitation. Ultrasonic cleaning effect and related parameters: A. cleaning medium: With ultrasonic cleaning, there are two kinds of cleaning agents: organic cleaning agent (chemical solvent) and water base cleaning agent. The cleaning medium is the chemical action, and the ultrasonic cleaning is the physical function, and the two functions are combined in order to clean the object fully and thoroughly. B. power density: The higher the power density of the ultrasonic wave, the stronger the cavitation effect, the faster the speed, the better the cleaning effect. For objects with high precision and high surface finish, a long high power density cleaning will produce "cavitation" corrosion on the surface of the object. C. ultrasonic frequency: The lower the ultrasonic frequency, the easier it is to produce cavitation in the liquid, and the stronger it is. High frequency, the ultrasonic direction is strong, suitable for fine object cleaning. D. cleaning environment: Generally speaking, the time and space effect of ultrasonic at 30 C ~40 is the best. The higher the temperature, the more significant the effect of the cleaning agent. When the ultrasonic cleaning is usually applied, the working temperature of 30 centigrade ~60 is used.