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Kokusai Electric Semiconductor Service Inc.

Ultrasonic cleaning guide

The cleaning effect is the greatest by combining 3 elements, that are chemical power, physical power and temperature like Figure 1, and it can perform the quality improvement, shortened time for cleaning, production efficiency improvement.
The ultrasonic cleaning of physical cleaning power is focused and explained here.

Fig. 1 Cleaning effect

Principle of the ultrasonic cleaning

The ultrasonic cleaning is thought that cavitations, straight current and acceleration generally act the cleaning object and can clean. In those, it explain about cavitations as example of single frequency ultrasonic here because the cleaning effect by cavitations is the biggest in low frequency ultrasonic.

What is Cavitation

Fig. 2 The sound pressure change in liquid by the time scale

  1. The water pressure (sound pressure) of the liquid changes when liquid is irradiated by ultrasonic wave.
  2. This sound pressure grows big than static pressure, and a expanding force acts when sound pressure became negative pressure (decompression), and the gas which cleaning fluid breaks off and can dissolve in cleaning fluid becomes a nucleus, and there is almost the cavity of the vacuum. This phenomenon is called cavitations.
  3. Because positive and negative pressure of the sound pressure are repeated in turn, and the cavity gradually grows up and it cannot endure compression of the positive pressure at last, and it is crushed instantly and becomes extinct, but a liquid molecule clashes at this time and produces by a big crash force.
  4. A dirt and garbage sticking the cleaning object are exfoliated by this crash force and can perform cleaning.

Selection of low frequency ultrasonic oscillation by cleaning usage.

By difference of oscillation mode and frequency, the strength of cavitations are different.
Choose oscillation mode and frequency by kind of materials and dirt (particle) of cleaning object.

The feature of each oscillation mode.

  • 26 kHz Single frequency
    Although there are much sound pressure irregularities to deep direction in liquid, it is suitable for mainly iron system metal cleaning because occurring cavitations are very strong.
  • 36 kHz SWEEP
    There are little sound pressure irregularities to deep direction in liquid and is suitable for uniform cleaning of aluminum-based metal, glass, ceramics, etc.

The feature of each oscillation mode.

Erosion outbreak situation of aluminum foil by difference of oscillation mode and frequency.

Erosion outbreak situation

  • The above photograph is situation that hole in aluminum foil was made by cavitations of ultrasonic wave.
  • Sound pressure is high at the area of hole and it shows that lot of cavitations occur.
The above photograph is data which was acquired in specific condition at our company. Therefore pay attention because the result may not become data similar to the above photograph even if it is performed erosion experiment of aluminum foil in use environment of client.

It is possible for uniform powerful cleaning without the irregularity with moving up and down of more than 1/2 wavelengths (approx. 30mm) by 26 kHz single frequency.