When the working frequency is very low (within the range of human hearing), noise will be produced. When the frequency is lower than 20kHz, the working noise not only becomes very loud, but also may exceed the safety noise limit stipulated by relevant regulations. In the application that needs high power to remove dirt without considering the surface damage of workpiece, the lower cleaning frequency from 20kHz to 30kHz is usually selected. The cleaning frequency in this frequency range is often used to clean large, heavy parts or high-density materials.
Ultrasonic cleaning equipment manufacturers tell you: high frequency is usually used to clean smaller parts, or remove small particles. High frequency is also used in applications where the surface of the workpiece is not allowed to be damaged.
The use of high frequency can improve the cleaning performance from several aspects. With the increase of frequency, the number of cavitation bubbles increases linearly, resulting in more and more dense shock waves, which can enter into smaller gaps. If the power remains unchanged, the cavitation bubble becomes smaller, and the energy released is reduced accordingly, which effectively reduces the damage to the workpiece surface.
Another advantage of high frequency is that it reduces the viscous boundary layer (ponuri effect), which makes it possible for ultrasound to 'discover' fine particles. The frequency products commonly used in the market are 28kHz, 32kHz and 40KHz
The higher the ultrasonic power density is, the stronger the cavitation effect is, the faster the cleaning speed is, and the better the cleaning effect is. However, long-time and high-density cleaning is easy to cause cavitation corrosion on the surface of the cleaned object.
Generally speaking, the effect of ultrasonic is good at 50 ℃ - 85 ℃.