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Ultrasonic Cleaning
超声清洗 (翻译 谭轶 2005年)
Ultrasonic cleaning is a good fit for a wide range of applications, from removing swarf and grinding and polishing residue to treating parts covered in oil, grease, or layers of paint. Ultrasonics can be used to clean miniature watch parts or to support the overhaul of jumbo jet engines. And from an industry perspective, the fields of electrotechnics, precision mechanics and light engineering, optics, metal processing, and medical equipment have proven particularly receptive to the ultrasonic concept.
So the impact of ultrasonic cleaning is clearly recognizable. But to truly understand the value of ultrasonics, one must understand how ultrasonic cleaners really work.
超声(波)清洗是工业领域一种广泛应用的新方法，可以去除工件表面的磨削，研磨，抛光后表面残留的碎屑，去除工件表面残留的油污，甚至可以去除油漆层。超声波清洗能够应用于从大到小的工业零件，大到波音 747 飞机的引擎大修，小到手表的部件制作，都有超声波清洗的用武之地，目前广泛应用超声波清洗的行业涉及电子，精密机械，照明工程，光学，冶金，医疗仪器设备等诸多领域。
超声波清洗对工业的推动和影响是显而易见的，要真正理解超声波的价值，我们需要进一步了解超声波的原理。
Ultrasonic Cleaning Explained
超声波清洗原理
The cleansing effect of ultrasound is the product of a phenomenon called cavitation. Billions of minute gas bubbles implode, causing shock waves that undermine dirt and blast it off a part's surface. One of the key advantages of this process is that it allows users to clean part surfaces that are completely inaccessible to a manual cleaning process.
超声波清洗的作用主要是一种叫做“空化效应”的现象造成的，每分钟数以十亿计的空泡（向内）爆裂，撞击到工件的表面，将工件表面的附着物剥离，分散开来。对于一些手工清洗难以达到的位置，（例如深孔，死角等）超声波清洗也可以有很好的清洗效果，这也是超声波清洗的一个优点。
Ultrasound frequencies generally range between 20 kilohertz and 50 kilohertz, depending on application requirements. Ultrasonic cleaning is typically performed at temperatures between 122 F and 176 F .
工业超声波清洗常用频率在 20 千赫到 50 千赫之间，常用清洗温度在 50 -80 ℃ 之间。
In an ultrasonic cleaning system, cavitation is produced by introducing sound waves into a cleaning liquid by means of a series of transducers mounted to a cleaning tank. The sound travels throughout the tank and creates waves of compression and expansion in the liquid. In the compression wave, the molecules of the cleaning liquid are compressed together tightly. Conversely, in the expansion wave, the molecules are pulled apart rapidly. The expansion is so dramatic that the molecules are ripped apart, creating microscopic bubbles. The bubbles contain a partial vacuum. As the pressure around the bubbles becomes greater, surrounding fluid rushes in and collapses the bubble. When this occurs, a jet of liquid is created, resulting in temperatures as high as 9,032 F (roughly the temperature of the surface of the sun). The extreme temperature, combined with the liquid jet's velocity, provides a very intense cleaning action. However, because the bubble expansion and collapse cycle is so short, the liquid surrounding the bubble quickly absorbs the heat, preventing the tank and cleaning liquid from becoming overly hot during the cleaning process.
在一个超声波清洗系统中,空化效应是由于一系列超声波换能器把声波导入清洗槽中的清洗液而产生.这个声波传遍整个清洗槽, 在液体中产生了波的压缩和扩张. 在压缩波时,清洗液中的分子被紧密的压缩在一起,相反,在扩张波时,分子被快速的拉开了. 扩张是那么戏剧性,以至于分子被裂开了,形成了精微的气泡. 气泡里是局部真空的. 当气泡周围的压力变大时,周围的液体就涌过来,并使气泡爆裂. 当这个发生时,就产生了液体的喷射,导致温度高达 9032华氏度 (约为太阳的温度).这个极高的温度,伴随着液体喷射的速度,产生了一个非常强烈的清洗作用.然而,因为气泡的扩张和爆裂周期是那么短暂,伴随在气泡外的液体迅速吸收了热量,从而在清洗过程中防止了清洗槽和清洗液过热.
Secrets to Ultrasonic Success
影响清洗效果的因素
There are seven major concerns related to successful ultrasonic cleaning:
有 7 个主要影响清洗效果的原因
1. Time （清洗时间）
2. Temperature （清洗液温度）
3. Chemistry （采用的清洗液）
4. Part Fixture Design （工件的设计外形）
5. Ultrasonic Output Frequency （超声波频率）
6. Watts Per Gallon （超声功率密度）
7. Loading （清洗装夹方式）
Time Cleaning times can vary tremendously in an ultrasonic process, depending largely on how dirty the part is and how clean is clean. A normal trial period is two to 10 minutes, since very few parts are sufficiently clean in a shorter period of time.
清洗时间是影响超声波清洗效果的一个主要因素，清洗时间取决于工件的污染程度以及清洁度要求，典型的清洗时间是 2-10 分钟，只有少数工件能够在很短的时间里面清洗干净。
Precleaning may be required to remove gross contamination or to chemically prepare the parts for a final clean. Some applications require more than one ultrasonic treatment to complete the required cleaning. Ultrasonic rinsing may also be required in some cases to more thoroughly remove wash chemicals.
实际操作中可能在精细清洗前需要一个预处理过程，一些工件需要一道以上的超声波清洗工序，在一些时候，需要布置超声波清水漂洗槽去除（前道工序）残留的清洗剂。
Temperature & Chemistry Temperature and chemistry are closely related. Generally, ultrasonic cleaning in an aqueous solution is optimized at 140 F . Some high pH solutions require higher temperatures. The chemical pH is a good place to start; but a thorough examination of chemistry is beyond the scope of this article.
温度和清洗剂是两个紧密相关的因素。一般来说，使用水作为清洗剂，超声波作用范围最好在 60 ℃ ，一些 PH 较高的溶液需要更高的清洗温度。讨论化学药品的 PH 值是一个好的开始，但是深入的讨论化学知识不是这篇文章要涉及的内容。
In brief, the following should be considered the main components of aqueous ultrasonic cleaning chemistry:
简要的说，下面所列的是水基超声波清洗液的主要组成成分
A. Water (hard, soft, DI, or distilled) 水（硬水，软水，纯水，或者蒸馏水）
B. pH （酸，或者碱）
C. Surfactants （表面活性剂）
Wetting agents （润湿剂）
Dispersants （分散剂）
Emulsifiers （乳化剂）
Saponifiers （皂化剂）
D. Optional Ingredients （可选成分）
Sequestrants( 螯合剂 )
Inhibitors （抗化剂）
Buffering agents （缓冲剂）
Defoamers （消泡剂）
The chemical formulation must consider all of the above characteristics. Some chemicals designed for spray cleaning — or that include rust inhibitors — are not suitable for ultrasonic cleaning.
化学药剂的作用必须充分考虑上面的因素。一些为水射流清洗设计的化学药品，包括一些防锈剂，不适合用于超声波清洗作业中。
Part Fixture Design The procedure for ultrasonic cleaning is generally as follows: Put parts in basket and place basket through three or four process steps (i.e., ultrasonic wash, spray rinse (optional), immersion rinse, dry). Some parts loaded in baskets can mask or shadow from the radiated surface of the ultrasonic transducers. Most ultrasonic cleaning systems are designed for specific applications. Bottom-mounted transducers or side-mounted transducers are important considerations during the process design stage. Automated systems must specifically address the location of the transducers to ensure cleaning uniformity. Some parts require individual fixturing to separate the part for cleaning or subsequent processes. Some parts require slow rotating or vertical motion during the cleaning to ensure critical cleanliness.
工件的装夹设计
通常超声波清洗的程序是这样：把工件装入工艺料框，经过 3-4 个工序（例如：超声波清洗，喷淋漂洗（可选），浸泡漂洗，干燥），在清洗料框中，有时候超声波辐射会被工件遮挡住。
大多数超声波清洗设备都被设计为专门用途。
在设计阶段，要重点考虑超声波换能器的布置方式，可以采用底置，侧置。对于自动超声波清洗设备，必须准确的布置换能器以保证清洗效果的一致性。一些工件对超声波清洗和其他工序需要采取不同的装夹方式。一些工件需要在清洗过程中旋转或者微动以保证清洗效果。
Ultrasonic Output Frequency The majority of the ultrasonic cleaning that is done in industrial applications today uses 40 kHz as a base frequency. Lower frequencies, such as 20-25 kHz, are used for large masses of metal where ultrasonic erosion is of little consequence. The large mass dampens or absorbs a great amount of the ultrasonic cleaning power.
超声波输出频率 目前大多数工业清洗应用中把 40 千赫作为基础频率 , 较低的工作频率。例如 20-25 千赫 , 常用于超声波空化腐蚀少的金属，或者极大阻碍或吸收超声波传播的场合。
Watts Per Gallon In general, smaller parts require higher watts per gallon to achieve the desired level of cleanliness. Most industrial ultrasonic cleaning systems use watt density from 50 to 100 watts per gallon. However, tanks over 50 gallons usually require only about 20 watts per gallon because ultrasonic processes traditionally have shown diminishing returns in large tanks sizes.
功率密度（每加仑的瓦数）（ 1 加仑 = 3.8 升 ）
通常，小的工件需要较高的功率密度以达到要求的清洗效果。大多数工业清洗设备需要的功率密度在 50-100 瓦 / 加仑。不过，容积超过 50 加仑 的水槽，通常只需要大约 20 瓦 / 每加仑的功率密度，因为超声波系统水箱容积越大，通常需要的功率密度呈下降趋势。
( 在国内，我们常说的能量密度或者功率密度是指每平方厘米辐射面上面的声功率，一般工业清洗功率密度范围在 0.3 瓦 / 平方厘米 -1.0 瓦 / 平方厘米 )
Loading Loading of the parts to be cleaned must be considered when developing an ultrasonic cleaning process. A large dense mass, for example, prevents internal surfaces from being thoroughly cleaned (i.e., metal castings). A rule of thumb is that the load by weight should be less than the weight of half the water volume. So, for example, in five gallons (approximately 40 lbs .) of water, the maximum workload should be less than 20 lbs . In some cases, it is better to ultrasonically clean two smaller loads rather than one larger load.
工件的清洗载入方式，在清洗设备的设计阶段。必须充分考虑工件清洗时候的载入方式，一些较大的工件，内部比较难以清洗的工件（例如一些铸造件），一个原则是只能载入清洗液的一半重量的工件清洗，例如，在 5 加仑 的水中 ( 大约 40 磅 ) ，一次只能载入 20 磅 的工件清洗，在大多数案例中，分两次载入较少的工件清洗比一次载入较大的工件清洗效果要好得多。
Each of the factors outlined here must be considered when specifying an ultrasonic application to ensure a high level of cleaning success. Neglecting any single factor can have a negative impact on the overall cleaning process.
上面提到的相关因素，在设计一个高品质的超声波清洗系统式需要综合考虑，忽视了某一项可能会造成不必要的麻烦。
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