Introduction to Ultrasonic Cleaning

Ultrasonic cleaning is based on the phenomenon known as cavitation. In an ultrasonic tank, cavities (or bubbles) are formed by piezoelectric transducers attached to the bottom or sides of a cleaning tank. The piezoelectric effect occurs in a certain group of crystalline solid materials, which have no center of symmetry. When these materials are mechanically stressed, they produce an electric charge, and when an electric field is applied across two poles, the dimensions change. By applying high frequency (20-80Khz) and high voltage, these elements expand and contract rapidly at a rate proportional to the frequency of the applied voltage. As a result of the contraction and expansion, the pressure inside the liquid changes from negative to positive with respect to atmospheric pressure. During the contraction, the pressure in the liquid is negative, allowing the cavities inside the liquid to grow in size, subsequently at the next phase of expansion the pressure in the liquid becomes positive, which causes the cavities to explode internally. The creation and the implosion of cavities causes an intense scrubbing action upon a submerged object. The size of the bubbles are microscopic, and can therefore penetrate the smallest cracks and holes to loosen the contaminants and remove them.
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All ultrasonic cleaners have three main components:
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	Ultrasonic generator or power supply that converts electrical energy from the wall (115VAC/60Hz) to high voltage and high frequency, which is then applied to ultrasonic transducers.
	Ultrasonic transducers convert high voltage and frequency to mechanical vibration.
	A cleaning tank that receives the mechanical energy and causes the cleaning media pressure to rise above and bellow the atmospheric pressure, thereby causing the formation and collapse of bubbles in the liquid. This process produces an intense scrubbing action that removes sediments from the submerged parts.

Ultrasonic cleaning equipment ranges from small bench-top units to larger capacity machines up to several thousand-gallon models. The smaller units are self-contained with a built-in power supply, and with the tank, heater and controls all within a single enclosure. The larger systems require the power supply to be a separate console, and the very large units may utilize immersible transducers which could then be mounted on the bottom or the side of the cleaning tank. . k6 o4 @6 e$ {! \& O/ X$ N
Effective application of the ultrasonic cleaning process requires a number of parameters, such as operating frequency, watts per gallon of liquid, transducer efficiency, cleaning tank design, and liquid temperature.
/ |0 t4 |2 x; {SonicWise has the experience and knowledge to design and manufacture the most efficient, rugged, and cost-effective ultrasonic cleaners for each application.

超声波清洗的原理

本文发表于：纳米科技世界论坛@nanost.net 作者：freeman3 点击550次

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本文地址：http://www.nanost.net/bbs/viewthread.php?tid=6878&fromuid=7411
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% C5 _0 c, t) k% G3 R @超声波清洗的原理，在理论要加以阐述是比较复杂的，里面牵涉许多因素和作用，可以体现超声波清洗作用的主要有以下三点。; F0 O. O- I/ k9 n; I9 G9 |2 z( T

( [4 X3 P8 }; @! v: @5 [ (1)空穴作用
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当强力的超声波辐射到液体中，清洗液以静压(一个标准气压)为中心进行变化，在压力到零气压以下时，溶解在液体中的氧会形成微小气泡核，进而产生无数近似 真空的微小空洞(空穴)。超声波的正压力时的微小空洞，在绝热压缩状态被挤碎，这个发生在挤碎瞬间的强力冲击波，可直接破坏污染物并使之分散在液中，形成 清洗机理。试验中这种强力的清洗作用，能在数十秒内对铝箔侵蚀成无数的小孔。
+ V, E/ T, U2 Q/ ^4 {- a 利用空穴作用的清洗，对去油污的效果比较好，通常在28KHZ~50KHZ的频率内进行机械另部件的清洗，清洗机的超声波强度大多设定在0．5~1w／cm2。
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(2)加速度+ R5 z: | ?* e) L3 z# J, l/ l7 n/ g

! [: Q3 f" C0 L9 c 清洗液体经超声波辐射，液体分子发生振动，这种振动加速度在28KHZ时是重力加速度的103倍，在950KHZ时将达到105倍，由这个强力加速度可以 对受污物的表面实行剥离清洗。然而，950KHZ的超声波不产生空穴，不适应去油污的清洗，只能在电子工业的半导体制造中，对亚微米粒子的污染进行清洗。$ `% G! J$ {% z; p/ J. h O
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(3)物理化学反应的促进作用
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" T% n6 E2 L. l6 b- z. S- G 由空穴作用使液体局部发生高温高压(1000气压，5500℃)，再经振动产生的搅拌，促使化学或物理作用的相乘，液体不断地乳化分散，进一步促进化学反应的速率。+ ]7 M. _) }; Z+ e/ U8 J

$ |' P @" P z: a清洗液深度的确定/ o' l% A: k7 ~
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液体中的超声波会因行波、回波的相互干扰及强合结果，将形成“驻波”现象，(见图1)。确定产生驻波的液体深度，能得到最好的超声波辐射效果。产生驻波的液体深度，可用下面公式计算。
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液深(λ/2)＝声速/频率÷2$ }* m5 {" n9 x

, s6 j% M. P9 x& Y- ~ 这个液体深度的正倍数数值，也是最适合的深度，例在20℃水温，28K1c时液深为27mm、54mm、81mm等等，38KHZ时液深为21mm、42mm、63mm等，但是，不同的液体、液温及超声振荡器，其驻波发生情况是不同的。