Ultrasonic cleaning is based on cavitation, in which numerous bubbles are rapidly formed in the cleaning solution and rapidly imploded. The resulting impact peels off the dirt on the inner and outer surfaces of the workpiece immersed in the cleaning liquid. As the ultrasonic frequency increases, the number of bubbles increases and the blasting impact is weakened. Therefore, high-frequency ultrasound is particularly suitable for cleaning small particles without damaging the surface of the workpiece. Air bubbles are generated by applying high frequency (ultrasonic frequency), high intensity sound waves to a liquid. Therefore, any ultrasonic cleaning system must have three basic components: a tank for holding the cleaning fluid, a transducer for converting electrical energy into mechanical energy, and an ultrasonic generator for generating high-frequency electrical signals.
Transducer and generator
The most important part of the ultrasonic cleaning system is the transducer. There are two types of transducers, one is a magnetic transducer made of nickel or a nickel alloy; and the other is a piezoelectric transducer made of lead zirconate titanate or other ceramics. When a piezoelectric material is placed in an electric field of varying voltage, it deforms. This is called the "piezoelectric effect." Relatively speaking, magnetic transducers are made of materials that deform in a changing magnetic field.
Regardless of the transducer used, the most basic factor is the strength of the cavitation effect it produces. Ultrasound, like other sound waves, is a series of pressure points, a wave of alternating compression and expansion. If the sound energy is strong enough, the liquid is pushed away during the expansion phase of the wave, thereby generating bubbles; and during the compression phase of the wave, these bubbles burst or impinge instantaneously in the liquid, producing a very effective impact force, especially Suitable for cleaning. This process is called cavitation.
Theoretically, bursting cavitation bubbles produce pressures in excess of 10,000 psi and
If the ultrasonic energy is large enough, cavitation will occur throughout the cleaning fluid, so the ultrasonic waves can effectively clean tiny cracks and holes. Cavitation also promotes chemical reactions and accelerates the dissolution of the surface film. However, cavitation occurs only in the region when the liquid pressure in a region is lower than the gas pressure in the bubble, so that the ultrasonic amplitude generated by the transducer is sufficiently large to satisfy this condition. The minimum power required to generate cavitation is referred to as the cavitation critical point. Different liquids have different cavitation critical points, so the ultrasonic energy must exceed the critical point to achieve the cleaning effect. That is to say, cavitation bubbles can be generated only for energy exceeding the critical point for ultrasonic cleaning.
Importance of frequency
Noise is generated when the operating frequency is low (within the human hearing range). When the frequency is below 20 kHz , the working noise not only becomes very large, but may exceed the limits of safety noise as stipulated by occupational safety and health laws or other regulations. In high power applications requiring the removal of dirt regardless of the workpiece surface damage, the lower cleaning frequency is usually selected within a range from 20KHz to 30KHz is. Cleaning frequencies in this frequency range are often used to clean large, heavy-duty or high-density workpieces. 20KHz magnetic transducer and 25KHz piezoelectric transducer.
High frequencies are often used to clean smaller, more delicate parts or to remove tiny particles. High frequencies are also used in applications where damage is not allowed on the surface of the workpiece. The use of high frequencies improves cleaning performance in several ways. As the frequency increases, the number of cavitation bubbles increases linearly, producing more denser shock waves that allow them to enter smaller gaps. If the power remains the same, the cavitation bubbles become smaller and the energy released is correspondingly reduced, thus effectively reducing the damage to the surface of the workpiece. Another advantage of high frequencies is the reduced viscous boundary layer (Ponuri effect), allowing ultrasonic waves to "discover" very fine particles. This situation is similar to the pebbles at the bottom of the stream when the water level in the creek is lowered.
40kHz , 80kHz , 120kHz and 170kHz . When cleaning very small particles, a product with a frequency of 350KHz can be used . A MicroCoustics system for such applications has recently been introduced with a frequency of 400 kHz .Hydrolyzed Sponge White Powder
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