超聲波清洗機主要機理是超聲波清洗機產(chǎn)生的超聲波空化作用，超聲波空化強弱與聲學(xué)參數(shù)、清洗液物理化學(xué)性質(zhì)及環(huán)境條件有關(guān)，要獲得良好清洗效果必須選擇適當?shù)穆晫W(xué)參數(shù)和清洗液。

The main mechanism of ultrasonic cleaning machine is the cavitation effect generated by ultrasonic cleaning machine. The strength of ultrasonic cavitation is related to acoustic parameters, physical and chemical properties of cleaning solution, and environmental conditions. To achieve good cleaning effect, appropriate acoustic parameters and cleaning solution must be selected.

頻率選擇

Frequency selection

超聲空化閾值和超聲波的頻率有密切關(guān)系。頻率越高，空化閾越高，換句話說，頻率越高，在液體中要產(chǎn)生空化所需要的聲強或聲功率也越大；頻率低，空化容易產(chǎn)生，同時在低頻情況下，液體受到壓縮和稀疏作用有更長時間間隔。使氣泡在崩潰前能生長到較大的尺寸，增高空化強度，有利于清洗作用。目前超聲波清洗機的工作頻率根據(jù)清洗對象，大致分為三個頻段；低頻超聲清洗(20一50KHz)，高頻超聲清洗(50—200KHz)和兆赫超聲清洗(700KHz一1MHz以上)。低頻超聲清洗適用于大部件表面或者污物和清洗件表面結(jié)合強度高場合。

The threshold of ultrasonic cavitation is closely related to the frequency of ultrasound. The higher the frequency, the higher the cavitation threshold. In other words, the higher the frequency, the greater the sound intensity or power required to generate cavitation in the liquid; At low frequencies, cavitation is prone to occur, and at low frequencies, the liquid undergoes compression and sparsity with longer time intervals. Enabling bubbles to grow to a larger size before collapse, increasing cavitation intensity, is beneficial for cleaning. At present, the working frequency of ultrasonic cleaning machines is roughly divided into three frequency bands based on the cleaning object; Low frequency ultrasonic cleaning (20-50KHz), high-frequency ultrasonic cleaning (50-200KHz), and megahertz ultrasonic cleaning (700KHz to 1MHz or above). Low frequency ultrasonic cleaning is suitable for occasions with high bonding strength between the surface of large components or dirt and the surface of cleaning parts.

頻率低端，空化強度高，易腐蝕清洗件表面，不適宜清洗表面光潔度高的部件，而且空化噪聲大。40KHz左右的頻率，在相同聲強下，產(chǎn)生的空化泡數(shù)量比頻率為20KHz時多，穿透力較強，宜清洗表面形狀復(fù)雜或有盲孔的工件，空化噪聲較小。但空化強度較低，適合清洗污物與被清洗件表面結(jié)合力較弱場合，高頻超聲清洗適用于計算機、微電子元件的精細清洗，如磁盤、驅(qū)動器，讀寫頭，液晶玻璃及平面顯示器，微組件和拋光金屬件等的清洗。

Low frequency, high cavitation intensity, easy to corrode the surface of cleaned parts, not suitable for cleaning components with high surface smoothness, and high cavitation noise. At a frequency of around 40KHz, under the same sound intensity, more cavitation bubbles are generated than at a frequency of 20KHz, indicating strong penetration. It is recommended to clean workpieces with complex surface shapes or blind holes, as cavitation noise is relatively small. However, the cavitation intensity is relatively low, suitable for cleaning situations where the adhesion between dirt and the surface of the cleaned part is weak. High frequency ultrasonic cleaning is suitable for fine cleaning of computer and microelectronic components, such as disks, drives, read and write heads, LCD glass and flat displays, micro components, and polished metal parts.

這些清洗對象要求在清洗過程中不能受到空化腐蝕。要能洗掉微米級的污物。兆赫超聲清洗適用于集成電路芯片、硅片及簿膜等的清洗。能去除微米、亞微米級的污物而對清洗件沒有任何損傷，因為此時不產(chǎn)生空化作用，超聲波清洗機理主要是聲壓梯度、粒子速度和聲流的作用，特點是清洗方向性強，被清洗件一般置于與聲束平行的方向。

These cleaning objects are required to be free from cavitation corrosion during the cleaning process. To be able to wash away micrometer sized dirt. Megahertz ultrasonic cleaning is suitable for cleaning integrated circuit chips, silicon wafers, and thin films. It can remove micrometer and submicron scale dirt without any damage to the cleaned parts, as cavitation does not occur at this time. The ultrasonic cleaning mechanism mainly involves the effects of sound pressure gradient, particle velocity, and sound flow, characterized by strong cleaning directionality. The cleaned parts are generally placed in the direction parallel to the sound beam.

超聲波聲強或聲壓的選擇

Selection of ultrasonic intensity or pressure

在清洗液中只有交變聲壓幅值超過液體的靜壓力時才會出現(xiàn)負壓，在超聲清洗槽中的聲強要高于空化閾值才能產(chǎn)生超聲空化。對于一般液體，空化閾值約為每平方厘米1／3瓦(聲壓的千方正比于聲強)。聲強增加時，空化泡的大半徑與起始半徑比值增大，空化強度增大，即聲強愈高，空化愈強烈，有利于清洗作用。但不是聲功率越大越好，聲強過高。會產(chǎn)生大量無用氣泡，增加散射衰減，形成聲屏障，同時聲強增大也會增加非線性衰減，這樣都會削弱遠離聲源地方清洗效果。對于一些難清洗干凈的污物，例如金屬表面氧化物，化纖噴絲板孔中污物的清洗，則需要采用較高聲強。此時被清洗面應(yīng)貼近聲源，這時大多不采用槽式清洗器。而用棒狀聚焦式換能器直接插入清洗液靠近清洗件的表面進行清洗。

Negative pressure only occurs when the amplitude of the alternating sound pressure in the cleaning solution exceeds the static pressure of the liquid. In ultrasonic cleaning tanks, the sound intensity must be higher than the cavitation threshold to generate ultrasonic cavitation. For general liquids, the cavitation threshold is approximately 1/3 watt per square centimeter (the square root of sound pressure is directly proportional to sound intensity). When the sound intensity increases, the ratio of the large radius to the initial radius of the cavitation bubble increases, and the cavitation intensity increases. That is, the higher the sound intensity, the stronger the cavitation, which is conducive to the cleaning effect. But it's not that the higher the sound power, the better. The sound intensity is too high. A large number of useless bubbles will be generated, increasing scattering attenuation and forming a sound barrier. At the same time, an increase in sound intensity will also increase nonlinear attenuation, which will weaken the cleaning effect in areas far away from the sound source. For some difficult to clean dirt, such as metal surface oxides and dirt in the holes of chemical fiber spinnerets, high sound intensity is required for cleaning. At this time, the cleaned surface should be close to the sound source, and slot type washers are mostly not used. And use a rod shaped focusing transducer to directly insert the cleaning solution near the surface of the cleaning part for cleaning.