Frequency and Power of the Ultrasonic Cleaner

- Mar 09, 2019-

The frequency and power of the ultrasonic cleaning machine along with the development of the industry, cleaning the workpiece by ultrasonic cleaning machine is more and more sophisticated, more and more is also high to the requirement of workpiece cleanness, so from the cleaning effect and economic considerations, how to correctly choose the frequency and power of the ultrasonic cleaning is critical, usually need to get the data from experiments.

There are two concepts: power and frequency. 

In ultrasonic precision cleaning, when a certain frequency of ultrasonic cleaning cannot reach the cleaning effect, if the impurity particles to be removed on the workpiece is large, it may be the ultrasonic power is insufficient, generally increase the ultrasonic power can solve the problem; On the contrary, if the impurity particles to be removed from the workpiece are very small, then no matter how much power is increased, it cannot meet the requirements of cleaning. The reason is: when the liquid flows through the workpiece surface, will form a layer of viscous film. At low frequencies, the viscous membrane of this layer is usually very thick, and small particles are buried inside. No matter what the power (intensity) of the ultrasonic wave is, cavitation bubbles cannot contact with small particles, so they cannot be completely removed. When the ultrasonic frequency increases, the thickness of the viscous film will decrease, and the cavitation bubble generated by the ultrasonic wave can contact with small particles and peel them from the workpiece surface. Therefore, the low-frequency ultrasonic cleaning effect of large particles of impurities is very good, but the effect of cleaning small particles of impurities is very poor. In contrast, high-frequency ultrasound is particularly effective in cleaning up small particles of impurities.

Ultrasonic frequency selection:

Generally speaking, the cleaning hardware, machinery, automobile and motorcycle, compressor and other industries use the cleaning machine of 28KHZ frequency. High frequency ultrasonic cleaning machine is suitable for fine cleaning of computer and microelectronic components. Megahertz ultrasonic cleaning is suitable for cleaning of integrated circuit chips, silicon wafers and wave films. It can remove dirt of micron and sub-micron level without any damage to the cleaning parts.For some precision cleaning (such as liquid crystal, semiconductor, etc.) applications, the use of traditional frequency not only cannot meet the requirements of cleaning, but also may cause damage to the workpiece. A typical example is the military electronic products, the industry has been expressly not allowed to use the traditional frequency (20~30KHz) ultrasonic cleaning machine. In fact, in some Europe and the United States, Japan and other developed countries, has been through the selection of high frequency cleaning machine (80KHz or above frequency, some have reached 200K or 400K) to solve this problem.

So why high frequency cleaning can avoid damage to the workpiece? Everyone knows that the basic principle of ultrasonic cleaning is based on the cavitation effect of liquid. In fact, the intensity of the toppling effect is directly related to the frequency. The higher the frequency is, the smaller the cavitation bubble will be and the weaker the cavitation intensity will be. For example, if the cavitation intensity at 25KHz is compared to that at 1, 40KHz, the cavitation intensity is 1/8. At 80KHz, the cavitation intensity drops to 0.02. So if the frequency is chosen correctly, the problem of ultrasonic damage to the workpiece does not exist.

Therefore, there is a close relationship between ultrasonic cavitation threshold and ultrasonic frequency. The higher the frequency is, the higher the cavitation valve is. In other words, at low frequencies, cavitation is more likely to occur, and at low frequencies, the compression and sparse effects on the liquid have a longer time interval, so that the bubbles can grow to a larger size before collapse, increasing the high-altitude intensity, which is conducive to the cleaning effect. So low frequency ultrasonic cleaning is suitable for large parts of the surface or dirt and cleaning parts of the surface of the high degree of integration. But it is easy to corrode the surface of cleaning parts, not suitable for cleaning parts with high surface finish, and cavitation noise. At a frequency of about 40 KHZ and with the same sound intensity, the number of cavitation bubbles is more than that at a frequency of 20KHZ, and the penetration is stronger. It is advisable to clean workpieces with complex surface shapes or blind holes, and the cavitation noise is small, but the cavitation intensity is low. It is suitable for the occasions where the surface adhesion between the dirt and the cleaned part is weak.

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