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A History of Ultrasonic Cleaning

This mid-century technology is still fighting grime today


Today, ultrasonic technology is one of the most effective ways to clean thousands of items, ranging from consumer products, such as jewelry and optical lenses, to surgical instruments, industrial components, and electronic equipment.


Ultrasonic cleaning was discovered by accident in the 1930s when laboratory workers at RCA noticed a curious propagating wave action as they were applying liquid Freon to cool the inner workings of a radio. However, it wasn’t until the 1950s that ultrasonic technology was applied to cleaning tasks. Today, ultrasonic cleaning equipment ranges from inexpensive household jewelry cleaners to industrial baths used to clean hardware fittings to the applications of high-tech devices. These very different applications all employ the same basic process of controlled ultrasonic energy and clean countless types of precision components.



Ultrasonic Cleaning, Defined

Sound waves at frequencies above 20 kilohertz, which is the audible limit of human hearing, are termed ultrasonic. An ultrasonic bath consists of a tank, which holds water and a surfactant solution or another kind of liquid/solvent, and a transducer, which converts electrical energy to generate the sound waves. As the sound waves radiate through the liquid in the tank, they create rapidly alternating compression and rarefaction within the liquid, thereby leading to the creation of millions of microscopic bubbles. This process is called cavitation, a physics term that means “formation of cavities.” At high pressure, the bubbles grow until they reach a size where they can no longer support the weight and pressure of the liquid. This causes the bubbles to collapse, generating a tremendous surge of energy on a microscopic level. As these energetic bubbles implode in all directions, they create a highly effective scrubbing action that reaches every surface, nook, and cranny of the item submerged in the tank.


Ultrasonic cleaning is best suited for hard, nonabsorbent materials, like metals, plastics, glass, and ceramics, because the aggressive energy of all those exploding bubbles can damage softer materials. For more delicate parts and materials, the rigors of ultrasonic cleaning can be modified by applying a higher frequency that is gentler. In addition, the efficiency of the process can be enhanced by increasing temperature or adding a surfactant to reduce surface tension.


Mid-century Innovations

In 1946, Norman Branson left his job as a research engineer for General Electric to launch a small ultrasonic equipment company in the garage of his Danbury, Connecticut home. Although his first product, the “Audigage,” was an ultrasonic instrument for measuring the thickness of tank walls, Branson soon recognized how ultrasonic technology could be employed for cleaning—and how existing ultrasonic cleaning devices could be improved. He invented a simplified power supply, which made his devices more affordable and reliable. By the 1970s, Branson Ultrasonics, now an Emerson brand, was the largest manufacturer of ultrasonic cleaning equipment in the world.


Modern-day Advances

Around the turn of the 21st century, ultrasonic cleaning became more nuanced and precise, shifting from single-frequency cleaners to devices that could deliver “sweep frequency” that help prevent the creation of unwanted standing waves. Today’s manufacturers of ultrasonic cleaning equipment offer a wide range of frequencies that can be used throughout the vast number of diverse cleaning applications. Emerson’s offerings include 40, 80, 120, and 170 kHz.


The different frequency options are a result of researchers determining that each ultrasonic frequency is best suited to remove a range of particle sizes. For example, lower frequencies are ideal for removing larger particles, while higher frequencies are more effective at removing smaller particles. By introducing the option of a variety of frequencies into the same bath, a large range of particle sizes can be removed.


In addition to being fully programmable, many of today’s ultrasonic baths are completely self-adaptive and adjust to the changes in the load, tracking and maintaining the user-set delivered power.


Today, ultrasonic technology continues to advance, making ultrasonic cleaners easier to set up and operate, and less susceptible to user error. For example, many ultrasonic cleaning baths are fully programmable, allowing technicians to program and standardize cleaning settings. In addition to being fully programmable, many of today’s ultrasonic baths are completely self-adaptive and adjust to the changes in the load, tracking and maintaining the user-set delivered power. During the cleaning process, as changes begin to occur in the ultrasonic bath, such as the temperature or soil loading of the solution, the ultrasonic power will stay constant in the bath, which removes any variations in cleaning results as the condition of the solution in the bath changes during day-to-day operations.


Ultrasonic cleaning equipment manufacturers cater to precision cleaning requirements in the medical, aerospace, electronics and metal finishing market segments. A variety of configured systems, ranging from single CH and Flex Tanks to multi tank systems, offer customers the choice of selecting equipment that works best for their particular application.


By John Hurley, Regional Sales Manager, Precision Cleaning, Emerson