Ultrasonic and ultrasonic cleaning

The human ear can only feel the oscillating frequency in the 20 Hz ~ 20 khz range of sound waves, the more than the human ear can feel the frequency of sound waves called ultrasound, ultrasound refers to the frequency is higher than 20 khz sound. Ultrasound is commonly used in medical treatment: one is to use a weaker ultrasound to input information, such as ultrasound diagnosis (b-ultrasound) , and the other is to use the energy generated by a stronger ultrasound to adjust the state or performance of raw materials, such as ultrasonic cleaning and ultrasonic atomization pulverization.

Ultrasonic cleaning does not use the ultrasonic wave directly to send to the surface of the object on the pollutants, but in the liquid immersion cleaning work-piece sent ultrasonic wave, so that the liquid produced ultrasonic vibration.

Ultrasonic cleaning machine is widely used in electronic components, semiconductor silicon wafers, circuit boards, electroplating parts, optical laser lenses, audio magnetic head, chemical fiber spinneret, printer ink-jet, medical equipment, glass containers, photographic equipment, communication equipment, gold and silver jewelry, precision machinery parts cleaning.

The advantages of ultrasonic cleaning are: faster cleaning speed, good cleaning quality, can clean the cavity and groove and other complex shapes of equipment and objects, and easy to use, in the disinfection supply room has been widely used.

The basic principle of ultrasonic cleaning

Ultrasonic cleaning mechanism is: the use of ultrasound generated in the liquid cavity in the release of energy when cracking to remove stains. According to the spread of sound energy by ultrasonic transducers, sound can produce pressure gradients, which also cause solution displacement to shrink and expand. When the pressure increases, the formation of cavitation bubbles (diameter about 50um ~ 500um) , that is, the so-called“Cavitation bubble.”. Because the pressure inside and outside the cavitation bubble is very different, when the cavitation bubble cracks, will form a local hydraulic shock wave (pressure up to hundreds of atmospheric pressure) . Under the influence of such pressure, all kinds of stains adhered to the surface of the object can be shed. In addition, under the influence of the ultrasonic field, the pulsation and agitation of the cleaning solution are intensified, and the dissolution and emulsification are accelerated, thus enhancing the cleaning.

The structure of ultrasonic cleaning machine

Ultrasonic cleaning equipment is mainly composed of three parts, ultrasonic power supply (ultrasonic frequency power source) , ultrasonic transducer and cleaning tank.

The ultrasonic frequency electric power source is the output device which converts the industrial electricity into the ultrasonic frequency electric power, and the ultrasonic transducer is the mechanical vibration which converts the ultrasonic frequency electric energy into the same frequency, the purpose of cleaning is realized by radiating the ultrasonic wave from the cleaning medium to the cleaning work piece, and the cleaning tank is a vessel for containing the cleaning solution and articles, the utility model can not be in the form of a single groove, but also can be in the form of a combination of multiple single grooves.

The main factors of ultrasonic cleaning

Ultrasonic frequency

The frequency of ultrasonic wave depends on the intensity of shock wave produced by cavitating bubble cracking.

The higher the frequency, the greater the sound intensity or power required to create holes in the liquid. When the ultrasonic frequency is low, it is easy to create holes, and under the premise of low frequency, there is a long time gap between the shrinking and thinning effect of the liquid, so that the bubble can grow to excessive size before collapsing, it is beneficial to the cleaning effect to increase the strength of collapse spatialization.

When water is used as the main ultrasonic solution, the physical cleaning force caused by cavitation effect is beneficial to the low frequency, and the ultrasonic wave of 20kHz-45kHz is usually used.

Output power density of ultrasound

The output power density of ultrasonic wave has an effect on the cleaning efficiency of ultrasonic wave. The basic parameter of ultrasonic cleaning is power, or more precisely, the power density of the surface of the object to be cleaned in the cleaning tank, which is directly related to the ultrasonic intensity, the sound intensity is also a key factor to influence the cavitation effect.

The effect of ultrasonic cleaning may not be completely proportional to“Power x cleaning time”. It is not hard to imagine that the cost of using a low-power ultrasonic cleaning machine for a long period of time will not have a very significant effect. If the power reaches the specified value, you can quickly remove the stains. If the power is too high, the cavitation strength will be greatly increased, and the cleaning effect will be improved, but it will cause the precise parts to form corrosion spots, and the cavitation at the bottom of the cleaning tank is obvious, and it is easy to be corroded by water spots, reduce the service life of ultrasonic cleaning machine. Too High A sound intensity can lead to too many cavitation bubbles, forming a natural barrier to sound waves, making it less easy to spread to all liquid space. In areas that avoid sound sources, the intensity of the sound wave weakens too quickly to form an effective cleaning.

The higher the output power density is, the better the hole function is, the better the cleaning effect is. For the equipment with obvious surface stain, complicated shape and deep blind hole, the higher output power density should be chosen. But the output power density is too large, long-term cleaning because of cavitation function corrosion. The frequency is 20.50 khz and the ultrasonic energy density is 2-3w/CM2. Under normal circumstances, the output power density of ultrasonic is set at 0.5-1w/CM2.

Temperature of cleaning

The cleaning temperature has a great influence on the cleaning effect. When the temperature rises, the number of holes increases, which is beneficial to the formation of holes. However, when the temperature is too high, the vapor pressure in the bubble increases, and the cavitation intensity also decreases. Therefore, it is necessary to maintain a sufficient temperature range, for oil stains, the use of water-based cleaning fluid at a relatively high temperature cleaning effect, usually set at 50 -60 C.

The amount of air in the solution

The air content in the solution should be reduced because of the bad influence of the propagation of ultrasonic wave and the strength of cavity when there is a big bubble in the solution. There are some ultrasonic cleaning equipment with degassing function, in cleaning before the first low-frequency vibration degassing, and then the power to the power level of conventional cleaning for ultrasonic cleaning.

Job Stress

When the solution pressure is large, it is difficult to form holes, so ultrasonic cleaning is basically carried out in open containers, sealed containers in the completion of the effect is relatively poor.

The location of the object being cleaned

The cleaning quality is best when the surface of the object is close to and facing the generator.

Acoustic characteristics of the cleaned object

Sound absorption of large objects such as rubber, cloth and other ultrasonic cleaning effect is not good, but strong reflection of the sound of materials such as metal materials, glass fiber reinforced plastic products cleaning effect is better.

Cleaning fluid selection

The interfacial tension and viscosity of the cleaning fluid have an important effect on the formation of the cavity. The larger the surface tension is, the greater the energy released from the collapse of the cavity, which is beneficial to ultrasonic cleaning.

The suitable cleaning range of ultrasonic cleaning

There are more and more reasons to harm the effect of ultrasonic cleaning, even if all the reasons are well controlled, ultrasonic cleaning has a good cleaning effect at the same time, it is possible to prevent cavitation corrosion of the equipment. It is unwise to carry out ultrasonic cleaning for a long time on the equipment, equipment and objects that can be cleaned by other cleaning methods. Therefore, it is necessary to choose whether to carry out ultrasonic cleaning according to the pollution and shape characteristics of the equipment.