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Feature Focus: Effective Ultrasonic Parts Cleaning Requires the Right Soap Chemistry


Metal Finishing

Today, ultrasonic cleaning of parts is utilized in a dizzying array of applications. To that end, ultrasonic cleaning works best when paired with the appropriate soap for each application.

With ultrasonic equipment, cleaning is accomplished as energy is released by cavitation, the creation and collapse of microscopic bubbles formed at ultrasonic frequencies. The resultant shock waves break up and lift off dirt and other contaminants. However, the soap utilized can make or break the ultrasonic cleaning process. Pick the “wrong” soap and you could clean a part poorly, damage the underlying part, and even disrupt the cavitation process itself. Pick the right soap specifically designed for an application, and items such as smoke damage, scale, grease, oil or dirt simply melt away.

“No one soap detergent will work for everything,” said Frank Pedeflous, the owner of Omegasonics, based in Simi Valley, Calif. “If you use the wrong soap for cleaning you are going to waste a lot of time and energy, and you’re not going to get the results you want.”

Pedeflous ought to know. His company offers more than 38 pre-designed and pre-formulated detergents to fit just about any ultrasonic cleaning application. This ranges from Harrier Jump Jet fuel engine nozzles to decades-old paint on the Governor’s Mansion in New York State, to Jay Leno’s collection of some 90 antique cars.

Most of us just call these chemistries “soaps,” but Pedeflous points out that the cleaning agents painstakingly developed for industrial use include precise combinations of such diverse components as:

  • Surfactants to release grease from a substrate surface
  • Abrasive to rub or scour away accumulated dirt
  • Acids for removing mineral deposits
  • Caustics to attack unwanted organic compounds
  • Oxidizers to bleach and disinfect
  • Enzymes to break down proteins, fats, and carbohydrates
  • Chemicals to keep the newly-removed materials in suspension
  • pH modifiers to regulate various chemical activities
  • Foaming or anti-foaming agents, as needed
  • Viscosity modifiers
  • Aesthetic agents such as optical brighteners and fabric softeners
  • Corrosion inhibitors to protect cleaning equipment
  • Stabilizers and water softeners to keep the other ingredients working efficiently
  • Preservatives to increase longevity of other chemical ingredients

“Each ingredient,” Pedeflous notes, “performs a necessary role in the overall combination to produce a powerful cleaning agent optimized for specific applications.”

With a great many solvent-based chemistries recently outlawed, water-based detergents–which are inherently less expensive, less hazardous, and offer more disposal options–now do the same job in less time at a better cost. For example, trying to remove smoke and scale from items damaged by fire or marked by years of aging is extremely difficult with ordinary soap. Worse, it can damage the glass, rubber, plastic, or other substrate. But with a chemical cleaner designed and engineered specifically for those purposes,2 the results are far more satisfying.

In the same way, efforts to remove oil and dirt from metal parts will be more efficient, faster and cheaper with an alkaline or even a caustic chemistry. But again, selecting the right cleaning soap is key; otherwise, the underlying metal might be damaged or destroyed by the cleaning operation. “You want the right soap to clean the item without damaging the underlying part,” Pedeflous advises.

For instance, 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—particularly with softer metals such as aluminum and brass—you can damage the part.

Hard metals like steel, stainless steel and titanium can handle high pH values, but steel is more prone to rusting with water-based chemistries. Thus, 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, a low pH, acidic cleaning soap is ideal. Acid removes the top layer of metal surface and can actually shine metal surfaces.

Some applications, such as electronics, require a more neutral pH soap. This occurs, for instance, when you don’t want to damage copper traces 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.

While the pH of the cleaning chemistry is often critical, it’s not the only characteristic to consider. Other potential variables can be quite subtle. For example, many industrial customers need to clean solder flux from their products. Several soaps work very well against most types of solder flux, but one or two specialized fluxes require entirely different cleaning chemistries incorporating isopropyl alcohol.

Pedeflous adds that cleaning detergents should also be chosen with an eye on temperature. Generally, heat speeds up the cleaning process, but too much heat can be bad as well. For example, laptop computer cases often benefit from heated cleaning chemistry, but temperatures above 160° F will deform the plastic. The right chemistry for this application must work satisfactorily below that thermal ceiling. A different cleaning agent designed to remove ink residue from metal and rubber components, such as Anilox rollers, works great at temperatures up to 130°F. Any hotter, though, and the chemistry will breakdown.

When situations demand a faster production line, chemistries often need to be revised so they yield the desired cleaning results in less time. As Pedeflous notes: “The necessary change may be as simple as increasing the concentration of the cleaning agent, but sometimes it’s better to switch to a different type of soap.”

Other variables are equally important. Few customers realize the importance of selecting a cleaning detergent with the proper level of surfactants, for example, so the cleaning equipment will achieve proper cavitation. “The wrong cleaning chemistry will actually hinder the ultrasonic action” Pedeflous explains. “The chemistry must be selected not only to clean what needs to be cleaned, but to work properly in the ultrasonic tank.”

With the variety of variables at play, manufacturers using ultrasonic equipment should work with a supplier that can call on a wide range of experience to recommend a particular chemistry for each application. Pedeflous warns against using soaps designed for other non-ultrasonic cleaning systems or purchasing inexpensive knock-offs of the manufacturer’s recommended chemistry to save costs.

“Companies will think their ultrasonic equipment is not working properly, when, in fact, it is a direct result of a mistaken choice of the proper cleaning soap,” Pedeflous stated.

For more information, please contact Simi Valley, Calif.-based Omegasonics at (805) 583-0875 or visit www.omegasonics.com. You may also e-mail frankp@omegasonics.com.

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