TINY BUBBLES

Ultrasonic parts cleaning is commonly used to streamline a variety of manufacturing and maintenance processes. This cleaning process is well known for improving quality, safety – and profits. Instead of the traditional method, where specially-outfitted personnel scrub and wash for hours on end and frequently miss hard-to-reach cracks and crevices, operators of this system can simply place parts to be cleaned in a tank of environmentally friendly, water-based cleaning soap, flip a switch and move on to other jobs.

An ultrasonic cleaning tank generates millions of microscopic bubbles per second, each containing vacuum pressure, that suck water and surface debris into themselves on contact with a hard surface. Since it cleans even the hardest to reach areas so efficiently, a growing number of manufacturers are adopting the tank. By following a few simple tips, even more benefits can be achieved from an ultrasonic parts cleaning process.

Get The Chemistry Right

Just as a computer needs to run the right software to achieve your objectives, the same is true in industrial parts cleaning. If the cleaning equipment is the "hardware" of parts cleaning, then the chemistry of the cleaning solution is the "software". To be effective, you've got to match the chemistry of the cleaning solution to the application.

Some companies stock about 40 chemistry-specific cleaning solutions because parts-cleaning applications can be chemistry-specific. For example, when cleaning off contaminants such as dirt, soil, oil, light grease, or carbon, you generally want a high pH, alkaline soap (acids have a low pH value). High pH, alkaline solutions can clean almost anything, but if pH goes too high, especially with softer metals such as aluminum, you can damage the part, so be careful.

Hard metals, like steel, stainless steel and titanium, can handle high pH values, but steel is more prone to rusting with water-based chemistries. This means steel or other ferrous metals require either a built-in rust inhibitor in the cleaning soap or a secondary rinse in a rust inhibitor. For water-damaged metals contaminated with rust or calcium deposits, you want to use a low pH, acidic cleaning soap. Acid removes the top layer of metal surface and can actually shine metal surfaces.

Some applications, such as electronics, require a neutral pH soap. This occurs, for instance, when you don't want to damage copper filaments or remove thin layers of metal. Neutral pH cleaning solutions are fine for parts with light surface contamination such as dust or light dirt particles. 

Get the Time and Temperature Right

Most industrial parts cleaning applications work best in the 135 deg F to 150 deg F range, where you achieve good microscopic cleaning energy. Going hotter may soften dirt and loosen its chemical bond faster, but it accelerates evaporation and can damage softer metals such as aluminum. Applications such as removing burnt-on carbon from surfaces require temperatures as high as 180 deg F. Some cleaning chemistries can break down above this range, so check with the manufacturer.

For critical applications, it may make sense to lower the temperature and leave parts in the cleaning solution longer, since time and temperature are inversely proportional. Delicate parts such as electronics, for instance, work best at temperatures below 150 deg F.

Get the Watt Density and Application Right

Ultrasonic watt density is a measure of how much ultrasonic power is available in a tank versus liquid volume. In general, lighter parts with less contamination need less power while bigger, heavier parts require more power since more energy is absorbed by the part.

"Cleaning light dust or oil doesn't require a lot of power, but cleaning baked on crystalline from an injection mold requires a lot more," states Frank Pedeflous, owner of Omegasonics (Simi Valley, CA). "Don't pay for more power than you need. But keep in mind that applying more power where appropriate can reduce cleaning time, since time and power are inversely related."

Typically, a watt density of 25 watts per gallon is fine for cleaning tanks larger than 30 to 40 gallons, according to Pedeflous. Smaller tanks, however, require higher watt density since there's less opportunity for ultrasonic energy to reflect off the sides of the tank.

Get the Output Frequency Right

Most industrial part cleaning applications are done at 40 kHz, or 40,000 cycles per second. This means the ultrasonic tank creates 40,000 microscopic cleaning bubbles per second per transducer. The 40 kHz rate is very effective at cleaning and maximizes equipment life expectancy.

For heavy items or items with heavy contamination, a lower 20 to 25 kHz output frequency is sometimes used since it produces a bigger, stronger-cleaning bubble (though fewer per second). When cleaning submicron debris (smaller than one micron) from parts, high frequencies of 68 kHz or 170 kHz are occasionally used, especially in medical or electronic applications.

Get the Right Process and Right Help

In choosing the right ultrasonic part cleaning process, there are other factors to consider. If filtration is needed for floating contaminants, an overflow wire can enable the skimming of contaminants that float to the surface. For suspended contaminants, you'd want to filter the entire bath. More complex parts cleaning might require multiple washes or a rinse.

While the basics of ultrasonic cleaning are simple, there's no question that getting the right guidance can help optimize a solution and minimize trial and error guessing. When this is the case, it makes sense to talk to a sales engineer who can help you pick the right equipment and process parameters for your application.

Whether looking to optimize an existing ultrasonic cleaning application or configure a new one, it's best to seek a reliable partner with engineering expertise and a successful track record.

Del Williams is a technical writer based in Torrance, California.

Frank Pedeflous, Omegasonics, 330 E Easy Street,  #A, Simi Valley, CA 93065-7523, 805-583-0875, [email protected], www.omegasonics.com