Overview of ultrasonic cleaning principles
Overview of ultrasonic cleaning principles
The ultrasonic transducer radiates sound waves to the cleaning liquid contained in the tank through the wall of the groove, and the oil stain on the surface of the component immersed in the liquid is quickly peeled off due to the mechanical effect of ultrasonic cavitation. Ultrasonic cleaning is characterized by high speed, high quality and easy automation, especially for detailed cleaning with complex surface shapes. In some cases, it may be washed with water instead of oil or an organic solution. For parts that need to be cleaned with acid or alkali, ultrasonic cleaning can reduce the concentration of acid and alkali, thus reducing costs and improving working conditions. Ultrasonic cleaning has therefore been widely used in the electronics and instrumentation industries to clean semiconductor components, printed circuit boards and electrical vacuum parts, cleaning relays and bearings. Ultrasonic cleaning fluids are widely used in the mechanical industry, such as cleaning various components, such as watch parts, oil pump nozzle parts, large such as diesel engines, automotive parts, and entire missile components. In the optical and pharmaceutical industries, a variety of optical glass, vials and syringes can be cleaned and the like.
For some parts with high cleaning requirements, ultrasonic cleaning can achieve the required cleanliness. For example, integrated circuits, inertial navigation gyroscopes and aerospace bearings can be ultrasonically cleaned. In other cases where it is difficult to clean and is not conducive to human health, ultrasonic cleaning can be used and remote cleaning or automatic cleaning can be achieved. Ultrasonic cleaning is the most commonly used one in power ultrasound. The most important mechanism of action is ultrasonic cavitation. Microbubbles are present in the liquid and vibrate under the action of the sound field. When the sound pressure reaches a certain value, the bubbles rapidly grow and then close. When the bubble is closed, a shock wave is generated, and thousands of atmospheric pressures are generated around it, destroying the insoluble dirt. And let them disperse in the solution. The direct repeated impact of the vapor-type cavitation on the dirt, on the one hand, destroys the adsorption of the dirt and the surface of the object to be cleaned, and on the other hand, causes the fatigue of the dirt layer to break away. The vibration of the gas bubble can scrub the solid surface. Once the dirt layer is drilled, the bubble can also be drilled into the crack to vibrate and the dirt layer will fall off. Due to ultrasonic cavitation, the two liquids are rapidly dispersed at the interface to emulsify. When the solid particles are wrapped by the oil and adhere to the surface of the object to be cleaned, the oil is emulsified, and the solid particles are detached. Ultrasonic cavitation at the solid and liquid interface produces high-speed micro-radicals that remove or weaken boundary fouling, increase agitation, accelerate the dissolution of soluble contaminants, and enhance the cleaning of chemical cleaners.
As mentioned above, the mechanism of ultrasonic cleaning is mainly cavitation, so to achieve good cleaning results, it is necessary to select appropriate ultrasonic acoustic parameters and physical and chemical properties of the cleaning fluid. It is not that the higher the sound intensity, the better the cleaning effect. If the sound intensity is too high, a large amount of air bubbles will be generated, and a barrier will be formed on the surface of the sound source. The sound is not easily radiated to the entire liquid space, so the cleaning effect will be poor in places far away from the sound source. some. Everyone knows that the higher the ultrasonic frequency, the larger the cavitation threshold. That is to say, the ultrasonic cavitation requires a large sound intensity. Generally speaking, the cavitation effect is stronger at 10khz, but the cavitation noise is too large. Considering all aspects of cleaning effect and economic performance, the frequency is generally selected within the range of 20-40 khz, and the sound intensity is generally selected at 1-2 w/cm2. For some dirt that is difficult to clean, such as an oxide film on the metal surface, a higher sound intensity is used for cleaning.
When the temperature of the cleaning solution rises, the increase of the cavitation nucleus is advantageous for the ultrasonic cavitation, but when the temperature is too high, the increase of the vapor pressure in the bubble is unfavorable for the ultrasonic cavitation, and the temperature is also related to the cleaning liquid. Solubility-related, a suitable temperature for water is 60 ° C, and when selecting a cleaning solvent, a liquid having a large surface tension and a low viscosity is selected.
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