Ultrasonic wave is a kind of sound wave whose frequency is higher than 20000 Hz. It has good directivity, strong penetrability, and easy to obtain concentrated sound energy. It can be used for distance measurement, velocity measurement, ultrasonic cleaning machine, welding, gravel, sterilization and disinfection. It has many applications in medicine, military, industry and agriculture. Ultrasound is named because its lower frequency limit is approximately equal to the upper limit of human hearing.
How to calculate the frequency of ultrasonic wave, the sound velocity in solid is also different. After repeated measurement, it is found that the sound wave propagates in the solid in the form of longitudinal wave and transverse wave, and the wave velocity of these two kinds of waves is also different. For example, in stainless steel, the P-wave velocity is 5790 M / s and the S-wave velocity is 3100 M / s. The stainless steel is made into a rod with a longitudinal wave velocity of 5000 m / s.
In the cleaning of ultrasonic cleaning machine, the frequency of ultrasonic cleaning machine should be selected correctly. The frequency of ultrasonic cleaning machine is a decisive process parameter, because it has a direct impact on cavitation. The lower the frequency of ultrasonic cleaning machine is, the stronger the ultrasonic cavitation effect is, and the cleaning effect is ideal, but the noise is large. Therefore, the frequency of ultrasonic cleaning machine is about 20 kHz, which has strong cavitation effect and good cleaning effect.
For parts with higher surface finish and smaller diameter holes, the high frequency ultrasonic cleaner with shorter wavelength and more concentrated energy should be used. However, the high frequency ultrasonic vibration in the cleaning fluid attenuates greatly, the action distance is short, and the cavitation intensity is weak, so the cleaning efficiency is also low. In addition, due to the directionality of high frequency ultrasonic cleaning machine, some parts of the cleaned parts can not be cleaned.
When using ultrasonic cleaning machine without frequency tracking, it is necessary to adjust the frequency adjusting knob of ultrasonic cleaning machine generator frequently, so as to keep the frequency of output signal consistent with the natural frequency of transducer, so as to achieve the purpose of strongest cavitation effect and best cleaning effect.
Among metals, beryllium is a master of sound transmission. In the rod made of beryllium, the longitudinal wave velocity of sound wave reaches 12890 M / s, 38 times of atmospheric sound transmission. The longitudinal wave velocity in polyethylene rod is only 920 M / s, which is not as fast as that in water. Soft rubber is full of elasticity. The sound wave can't move in it. The speed is only 30-50 M / s, which is not as fast as the sound speed in the air! Wave speed divided by frequency equals wavelength.
When the ultrasonic wave acts on the liquid, the rupture of each bubble in the liquid will produce a shock wave with great energy, which is equivalent to hundreds of degrees of high temperature and thousands of atmospheres in an instant. This phenomenon is called "cavitation effect". Ultrasonic cleaning is to use the shock wave generated by the bubble breaking in the liquid to clean and wash the internal and external surface of the workpiece. The ultrasonic wave propagates in the liquid, which makes the liquid and the cleaning tank vibrate together under the ultrasonic frequency. When the liquid and the cleaning tank vibrate, they have their own natural frequency. This vibration frequency is the acoustic frequency, so people hear the buzz.