Tips on ultrasonic cleaning

Feb. 12, 2009
Ultrasonic parts cleaning commonly is used to streamline a variety of manufacturing and maintenance processes and is known for improving quality, safety and profits. Ultrasonic baths can optimize parts cleaning, safety, quality and ...

Ultrasonic parts cleaning commonly is used to streamline a variety of manufacturing and maintenance processes and is known for improving quality, safety and profits.

Ultrasonic baths can optimize parts cleaning, safety, quality and cost; a few tips can help you get the most out of an application.

Instead of personnel scrubbing and washing parts and, perhaps, missing hard-to-reach cracks and crevices, parts can be placed into a tank of water-based cleaning soap to be cleaned automatically.

The ultrasonic cleaning tank is designed to generate millions of microscopic bubbles per second, each containing vacuum pressure that suck water and surface debris into itself from hard surfaces. The process is designed to clean even the hardest to reach areas efficiently.

Here are several tips that will help you to get the greatest benefit from the ultrasonic parts cleaning process.

Get the Chemistry Right
You have to match the chemistry of the cleaning solution to the application. Some companies, such as Omegasonics, stock 40 chemistry-specific cleaning solutions because parts cleaning applications can be chemistry specific.

For example, when removing contaminants such as dirt, soil, oil, light grease, or carbon, a high pH, alkaline soap typically is required. 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, parts can be damaged.

Hard metals such as steel, stainless steel and titanium can handle high pH values, but steel is more prone to rusting with water-based chemistries, so 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 that are contaminated with rust or calcium deposits, a low pH, acidic cleaning soap may be required. Acid removes the top layer of metal surfaces and actually can shine metal surfaces.

Some applications, such as electronics parts, require neutral pH soap. Neutral pH cleaning solutions are called for when there is concern about damaging copper filaments or removing 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-degree to 150-degree F range. That temperature range provides good microscopic cleaning energy.

Higher heat may soften dirt and loosen its chemical bonds faster, but it also 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-degrees F.

The chemistries of some cleaning solutions can break down above this range, so the manufacturer’s specifications have to be followed.

For critical applications, lower temperatures may be called for that would require leaving parts in the cleaning solution for a longer period of time, because time and temperature are inversely proportional.

Delicate parts such as electronics, for instance, work best at temperatures below 150 degrees 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 larger, heavier parts require more power because 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. Don’t pay for more power than you need,” Frank Pedeflous, owner of Omegasonics, said.

However, applying more power where appropriate can reduce cleaning time, because time and power also are inversely related.

Typically, a watt density of 25 watts per gallon is correct for cleaning tanks as large as 40 gallons, Pedeflous said.

Smaller tanks, however, require higher watt density because there is 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.

That 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 that have heavy contamination, a frequency of 20 kHz to 25 kHz sometimes is used because it produces a bigger, stronger, cleaning bubble, but fewer bubbles per second.

When cleaning submicron debris — smaller than one micron — from parts, high frequencies of 68 kHz or 170 kHz occasionally are 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 weir can enable the skimming of contaminants that float to the surface.

For suspended contaminants, the entire bath may have to be filtered.

More complex parts cleaning might require multiple washes or a rinse.

While the basics of ultrasonic cleaning are simple, there is no question that getting the right guidance can help optimize a solution and minimize trial and error guessing. Anyone considering ultrasonic cleaning equipment should talk to a sales engineer who can help to pick the right equipment and process parameters for the 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.

This article was prepared by Omegasonics.

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