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Two Main Factors Affecting The Effect Of Ultrasonic Cleaning
Aug 08, 2018

The main mechanism of ultrasonic cleaning machine is the cavitation of ultrasonic waves generated by ultrasonic cleaning machine. The strength of ultrasonic cavitation is related to acoustic parameters, physical and chemical properties of cleaning fluid and environmental conditions. To obtain good cleaning effect, appropriate acoustics must be selected. Parameters and cleaning fluid.

1. Ultrasonic sound intensity or sound pressure selection

In the cleaning solution, the negative pressure occurs only when the amplitude of the alternating sound pressure exceeds the static pressure of the liquid, and the sound intensity in the ultrasonic cleaning tank is higher than the cavitation threshold to generate ultrasonic cavitation. For a typical liquid, the cavitation threshold is approximately 1/3 watt per square centimeter (the square of the 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 not the louder the better, the louder the sound. A large number of useless bubbles are generated, which increase the scattering attenuation and form a sound barrier. At the same time, the increase of the sound intensity also increases the nonlinear attenuation, which will weaken the cleaning effect away from the sound source. For some hard-to-clean dirt, such as oxides on metal surfaces, cleaning of dirt in the pores of chemical fiber spinnerets requires a higher sound intensity. At this time, the surface to be cleaned should be close to the sound source, and most of the time, the tank cleaner is not used. The rod-shaped focusing transducer is directly inserted into the cleaning liquid to be cleaned near the surface of the cleaning member.

2. Frequency selection

The ultrasonic cavitation threshold is closely related to the frequency of the ultrasound. 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, and at lower frequencies The liquid is subjected to compression and sparse action for a longer time interval. The bubble can grow to a larger size before collapse, and the cavitation intensity is increased, which is beneficial to the cleaning effect. At present, the operating frequency of the ultrasonic cleaning machine is roughly divided into three frequency bands according to the cleaning object; low frequency ultrasonic cleaning (20-50 KHz), high frequency ultrasonic cleaning (50-200 KHz) and megahertz ultrasonic cleaning (700 KHz-1 MHz or more). Low-frequency ultrasonic cleaning is suitable for applications where the surface of large parts or the surface of the dirt and cleaning parts is high. The low end of the frequency, high cavitation intensity, easy to corrode the surface of the cleaning part, is not suitable for cleaning parts with high surface finish, and the cavitation noise is large. At the frequency of about 40KHz, under the same sound intensity, the number of cavitation bubbles generated is more than the frequency of 20KHz, and the penetrating power is strong. It is better to clean the workpiece with complex surface shape or blind holes, and the cavitation noise is small. However, the cavitation intensity is low, suitable for cleaning dirt and the surface of the surface to be cleaned is weak, high-frequency ultrasonic cleaning is suitable for fine cleaning of computers and microelectronic components, such as magnetic disks, drives, heads, liquid crystal glass and Cleaning of flat displays, micro components and polished metal parts. These cleaning objects are required to be free of cavitation corrosion during the cleaning process. To be able to wash off micron dirt. Megahertz ultrasonic cleaning is suitable for cleaning integrated circuit chips, silicon wafers and film. It can remove micron and sub-micron dirt without any damage to the cleaning parts, because no cavitation occurs at this time. The ultrasonic cleaning mechanism is mainly the action of sound pressure gradient, particle velocity and sound flow, which is characterized by strong cleaning direction. The object to be cleaned is generally placed in a direction parallel to the sound beam.