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The main mechanism of the ultrasonic cleaning machine is the cavitation of the ultrasonic waves generated by the ultrasonic cleaning machine. The strength of the ultrasonic cavitation is related to the acoustic parameters, the physical and chemical properties of the cleaning liquid and the environmental conditions. To obtain a good cleaning effect, an appropriate acoustic parameters and cleaning fluids.

1. Selection of ultrasonic sound intensity or sound pressure

In the cleaning liquid, only when the amplitude of the alternating sound pressure exceeds the static pressure of the liquid will negative pressure appear. In the ultrasonic cleaning tank, the sound intensity must be higher than the cavitation threshold to generate ultrasonic cavitation. For general liquids, the cavitation threshold is about 1/3 watt per square centimeter (the thousand square of sound pressure is proportional to the sound intensity). When the sound intensity increases, the ratio of the maximum radius of the cavitation bubble to the initial radius increases, and the cavitation intensity increases, that is, the higher the sound intensity, the stronger the cavitation, which is beneficial to the cleaning effect. But it is not that the higher the sound power, the better, the sound intensity is too high. It will generate a lot of useless air bubbles, increase the scattering attenuation, and form a sound barrier. At the same time, the increase of the sound intensity will also increase the nonlinear attenuation, which will weaken the cleaning effect far away from the sound source. For some dirt that is difficult to clean, such as oxides on metal surfaces, and cleaning of dirt in the holes of chemical fiber spinnerets, a higher sound intensity is required. At this time, the surface to be cleaned should be close to the sound source, and most of the tank cleaners are not used at this time. The rod-shaped focusing transducer is directly inserted into the cleaning solution and close to the surface of the cleaning piece for cleaning.

2. Frequency selection

The ultrasonic cavitation threshold is closely related to the frequency of ultrasonic waves. The higher the frequency, the higher the cavitation threshold, in other words, the higher the frequency, the greater the sound intensity or sound power required to generate cavitation in the liquid; the lower the frequency, the easier cavitation occurs, and at low frequencies , the liquid is subjected to compression and thinning with a longer time interval. The bubbles can grow to a larger size before collapsing, and the cavitation strength is increased, which is beneficial to the cleaning effect. At present, the working frequency of ultrasonic cleaning machine is roughly divided into three frequency bands according to the cleaning object; low-frequency ultrasonic cleaning (20-50KHz), high-frequency ultrasonic cleaning (50-200KHz) and megahertz ultrasonic cleaning (700KHz-1MHz or more). Low-frequency ultrasonic cleaning is suitable for occasions where the surface of large parts or the surface of the dirt and the cleaning part has a high bonding strength. At the low end of the frequency, the cavitation intensity is high, and it is easy to corrode the surface of the cleaning part, which is not suitable for cleaning parts with high surface finish, and the cavitation noise is large. At a frequency of about 40KHz, under the same sound intensity, the number of cavitation bubbles generated is more than when the frequency is 20KHz, and the penetrating power is stronger. It is suitable to clean workpieces with complex surface shapes or blind holes, and the cavitation noise is small. However, the cavitation strength is low, and it is suitable for the occasions where the bonding force between the cleaning dirt and the surface of the cleaned part is weak. Cleaning of flat panel displays, micro-components and polished metal parts, etc. These cleaning objects require no cavitation corrosion during the cleaning process. To be able to wash off micron-sized dirt. Megahertz ultrasonic cleaning is suitable for cleaning integrated circuit chips, silicon wafers and thin films. It can remove micron and submicron dirt without any damage to the cleaning parts, because there is no cavitation at this time. The ultrasonic cleaning mechanism is mainly the effect of sound pressure gradient, particle velocity and sound flow, which is characterized by strong cleaning direction. , the cleaned parts are generally placed in the direction parallel to the sound beam.