IVD partner, explain the principle of ultrasonic cleaning today!
Ultrasonic cleaning is a very complicated process, here is only a brief introduction. The ultrasonic action includes the energy action of the ultrasonic wave itself, the energy action released when the cavity is destroyed, and the stirring and flowing action of the ultrasonic wave on the medium liquid.
1. The energy effect of ultrasound
Ultrasonic wave has very high energy. When it propagates in the media liquid, it transfers the energy to the media particle, and the media particle transfers the energy to the surface of the cleaning object and causes the dirt to dissociate and disperse. The sound wave is a longitudinal wave, that is, the vibration direction of the medium particle is consistent with the propagation direction of the wave. In the process of longitudinal wave propagation, the movement of medium particles causes the distribution of particles to be uneven, and regions with different densities appear. In the region where particle distribution is sparse, sound waves form negative sound pressure, and in densely distributed regions, sound waves form positive sound pressure, and form negative sound pressure and positive sound pressure alternately and continuously change. This change not only makes the media particles obtain a certain kinetic energy but also obtains a certain acceleration. The energy effect of high-frequency ultrasound is extremely huge. When the media particles with energy interact with the dirt particles, the energy is transferred to the dirt and causes their dissociation and dispersion.
2. The energy released when the hole is destroyed
Ultrasonic waves propagate in a medium in a straight line like ordinary sound waves. The speed of movement is related to the medium liquid, and the propagation speed is different in different medium liquids. The frequency of ultrasonic waves is higher than that of ordinary sound waves, so the wavelength is short and the energy is high.
Ultrasonic waves that advance in a straight line in the medium liquid will undergo transmission and reflection motions when they reach the interface with other substances. The degree of transmission and reflection is determined by the acoustic impedance of the material that constitutes the interface. The acoustic impedance is the ratio of the sound pressure on a given surface of the sound transmission medium to the particle velocity. Various sound transmission media have a fixed acoustic impedance rate. When the ultrasonic wave travels to the interface of two media with very different acoustic impedance rates, reflection mainly occurs, while transmission mainly occurs at the interface of two media with similar acoustic impedance rates. For example, when the ultrasonic wave travels to the water-air interface, because the air density is much smaller than that of water, the acoustic impedance rate is also far away, so the sound wave mainly reflects at this time; similarly, when the ultrasonic wave travels to the water-steel interface, due to the large difference in the acoustic impedance rate between the two media, the main reflection also occurs. When the ultrasonic wave travels to the water-plastic interface, the ultrasonic wave mainly transmits due to the similar acoustic impedance between the two media.
After the reflected ultrasonic wave is synthesized with the advancing ultrasonic wave, when the phase difference of each point remains stable, resonance occurs, and they are superimposed and strengthened at certain fixed positions, and the medium is prone to generate holes at these positions.
Since the ultrasonic wave propagates forward in the form of repeated alternating changes of positive pressure and negative pressure, tiny vacuum cavities are formed in the medium liquid during negative pressure. At this time, the gas dissolved in the medium liquid will quickly enter the cavity and form bubbles; while in the positive pressure stage, the cavity bubbles are adiabatically compressed and finally crushed. When the bubble bursts, a huge impact will be formed around the cavity, so that the liquid or solid near the cavity will be subjected to a high pressure of thousands of atmospheres. Release enormous energy. This phenomenon occurs intensely in the ultrasonic field in the low frequency range. When the holes explode suddenly, the dirt film on the surface of the object can be broken to achieve the purpose of decontamination.
When the ultrasonic frequency used is in the range of 28-100khz, several effects of ultrasonic waves exist. The huge pressure effect generated by the process of void disappearance is very prominent. When the ultrasonic frequency used is in the ultra-high frequency range, the effect of the ultrasonic wave is mainly its own huge energy effect, which does not generate cavities, but this huge energy has a great effect on the removal and cleaning of fine dirt.
In addition, ultrasonic waves not only help the medium liquid to dissolve dirt quickly, but also play a stirring role to make the medium liquid move, and the fresh medium liquid continuously acts on the dirt to accelerate the dissolution. Therefore, if the powerful impact force of ultrasonic waves is properly used, it can promote the dissociation of stubbornly attached dirt, and the situation of uneven cleaning power can be avoided. However, due to the possibility of damage to the cleaning object during the use of ultrasonic waves, it is not suitable to use ultrasonic cleaning when the cleaning object is very fragile.
3. Selection of washing medium
Ultrasonic cleaning is carried out with a certain liquid as the medium, and the selection of the medium is based on the principle that it can give full play to the effect of ultrasonic waves to achieve the purpose of decontamination. Since water is the liquid with the best cavitation effect, clear water is usually used as a medium, and the dosage is not very large, and it is not necessary to use spraying or stirring to make the water flow violently. However, due to the poor ability of clear water to disperse and dissociate oily dirt, surfactants or acid-base aqueous solutions are often used as the medium for ultrasonic cleaning.
Since the ability of various hydrophilic or lipophilic organic solvents to generate holes is worse than that of water, if these organic solvents are used as media, they can effectively remove dirt only by supplementing their ability to dissolve and disperse dirt. Moreover, organic solvents often have flammable, explosive and toxic problems, so water is usually used as a medium
4. Problems that should be paid attention to when using ultrasonic cleaning
Under certain conditions, ultrasonic cleaning can achieve better results, so the following issues need to be paid attention to.
1. Overcoming the inhomogeneity of hole generation
It has been mentioned that the cavitation is generated unevenly along the maximum sound pressure band. When the cleaning object is in a static state in the lotion, the unevenness of cleaning will be caused by the unevenness of the cavity. In order to overcome the occurrence of this phenomenon, the following methods are often used:
①Moving the cleaning object: When the cleaning object moves in the washing tank, the holes can act on the surface of the object more uniformly. The most common method is to rotate the cleaning object. When the object is located on the plane where the maximum sound pressure bands of the holes intersect vertically, the cleaning effect is more specific.
②Change the depth of the washing liquid: When the liquid level of the washing tank changes up and down, the position of the maximum sound pressure band of the cavity also changes accordingly, which can overcome the inhomogeneity.
③Formation of rectangular waveforms: several ultrasonic waves of different wavelengths are synthesized together, and the generated ultrasonic standing waves expand the range of the maximum sound pressure band, which can overcome inhomogeneity.
④Prevent the generation of resonance waves: If the liquid surface and the surface of the cleaning object are not perpendicular to each other, it can prevent the forced vibration and formation of resonance waves on the surface of the cleaning object. In this way, on the one hand, uneven cleaning can be reduced, and at the same time, damage to the cleaning object can be avoided.
2. Overcome the inhomogeneity of the effect caused by the reflection of ultrasonic waves
When the ultrasonic reflection occurs on the inner surface of the cleaning object, the inner surface of the metal pipe, the concave surface of the deep metal object, and the cleaning object container made of metal mesh, it will hinder the penetration of the ultrasonic wave and cause the uneven effect of the ultrasonic wave. This is a common problem in ultrasonic cleaning.
3. Damage to cleaning objects caused by cavitation:
Cavitation may damage the cleaning object and make the performance fragile.
In addition, when using ultrasonic waves to treat the blades of sharp knives and extremely thin metal sheets used in electronic machinery, damage due to cavitation often occurs, and the lower the frequency, the greater the strength of ultrasonic cavitation. Therefore, when using ultrasonic cleaning, the shape of the cleaning object and the nature of the material must be considered. Only by choosing an appropriate ultrasonic frequency and using an appropriate method can a good cleaning effect be achieved.
