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Ultrasonic Cleaning with Corrosive Acidic Solutions

Quality ultrasonic cleaning tanks are fabricated of cavitation-resistant stainless steel and are compatible with a broad range of water based cleaning solutions.

But there are limitations to the types of aqueous chemistries that can be safely used when ultrasonic cleaning with acidic solutions.

Specifically, aqueous cleaning media with pH values in the acid range (pH <7) should never be used in the ultrasonic cleaner tank if fluoride, chloride or bromide ions will contact the stainless steel either from the cleaning formulation or from removed contaminants. Ultrasonic operation will cause these ions to destroy stainless steel tanks by crevice corrosion in a very short period of time.

Other Cleaning Chemistries to Avoid

Avoid high concentrations of, or high temperature ultrasonic operation of, certain other acidic or alkaline solutions such as but not necessarily limited to

  • Nitric acid
  • Hydrofluoric acid
  • Sulfuric acid
  • Potassium hydroxide
  • Formic acid
  • Hydrochloric acid

Examples of Corrosive Media

Potentially damaging chemicals can be released into the bath when removing fluoride, chloride or tetrafluoroborate-containing fluxing agents from soldered metal parts and electronic components; when using citric acid solution to decalcify medical equipment contaminated with physiological salt solution, and when ultrasonically rinsing items etched with hydrofluoric acid or ammonium bifluoride.

How to Protect your Ultrasonic Cleaner Tank

When cleaning with corrosive media such as those described above you must isolate the solution from stainless steel tank surfaces. This is accomplished by using an acid resistant plastic tub, the dimensions of which are less than the internal dimensions of the tank. It’s important too that the sides and bottom of the plastic tub do not contact the sides or the bottom of the stainless steel tank. The tub must accommodate the size of the parts being cleaned but also be large enough so that the rim of the tub rests on the rim of the tank.

Taking into account displacement caused by the plastic tub add the required amount of water to the ultrasonic cleaning tank along with a surfactant. Ideally the water/surfactant solution will not exceed the ultrasonic tank fill line when the plastic tub is in place. The tub should be immersed until its rim rests on the tank rim after the acid solution is added. Use the tank drain to bleed off excess water/surfactant solution as needed. This may be a trial-and-error exercise until you get your procedure established.

A Cycle for Cleaning with Acid

Before cleaning place the lid on the tub, turn on the ultrasonic cleaner, and activate the ultrasound to allow the solutions to mix and degas. Cavitation action created by the ultrasonic cleaner’s transducers passes through the water, through the plastic tub and into the cleaning solution. Cleaners such as the Elmasonic SH350EL have a degas mode that quickly drives off cavitation-inhibiting trapped air. Otherwise operate the ultrasound for 10-15 minutes or longer for larger tanks. Turn off the unit.

When you are ready to clean set the cleaning time and temperature. Elma SH-EL cleaners feature an auto-start function that will initiate cleaning action and start the timer when the set temperature is reached.

Carefully position parts in the solution, taking care that they do not contact each other. Place the lid on the tub to reduce evaporation and to help contain fumes, turn the unit on, activate the ultrasound and sweep function. The latter provides homogeneous distribution of cavitation energy throughout the cleaning bath.

At the end of the cycle inspect the parts. If satisfied, rinse them and allow them to drain.

Safety First

Protective measures also apply to staff working with acidic ultrasonic cleaning solutions. Observe safety warnings provided by cleaning solution manufacturers. They may include positioning the tank in a well ventilated area to draw off fumes and equipping personnel with required protective equipment. Plant safety personnel should post standard operating procedures both in the plant operations manual and at the cleaning location.

Remember to store acidic cleaning solutions in a safe place when not in use. Repeated use will diminish cleaning effectiveness, calling for replacement. Dispose of spent solutions in accordance with local regulations and flush the tub with fresh water.

Call the iUltrasonic cleaning professionals at 973-440-2191 for further information on cleaning with acidic solutions, to order plastic tub inserts, and for recommended acidic cleaning solution formulations to meet your requirements.


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