Ultrasonic Cavitation vs. Air in an Ultrasonic Cleaner

Sonic cleaning requires all surfaces to be wetted.
Sonic cleaning requires all surfaces to be wetted.

Ultrasonic cleaning procedures described in our posts nearly always call attention to the importance of degassing fresh cleaning solutions.  Degassing is the process of removing trapped air in liquids.  You can see this by letting a glass of water stand for awhile and note the bubbles that appear on the inside surface.  Trapped, entrained or dissolved, air inhibits cavitation, which is the implosion of micron-size vacuum bubbles that accomplish the cleaning.

Simply operating the equipment for a time, the length of which depends on the volume of cleaning solution, will drive off trapped air. The process can be hastened by a Degas mode on an ultrasonic cleaner. It does the job by switching on and off causing air bubbles to coalesce and allowing them rise to the surface and burst.

Removing Other Air in an Ultrasonic Cleaner

Air can be introduced into an ultrasonic cleaning solution when parts are immersed.  This most likely occurs with parts of complex design. Slots and blind holes are examples. Recesses and cups may also trap air bubbles.  However parts are configured operators should ensure the solution reaches all surfaces otherwise cavitation cleaning within those areas will not occur.

Sonic Cleaning Complex Parts

Operators should manage the cleaning cycle when sonic cleaning complex parts.  Here are some tips:

  • Place parts in the cleaning basket with holes in a horizontal position that fill as the basket is immersed in the cleaning tank.
  • Periodically agitate baskets if holes are on several surfaces. An alternative is to turn off the ultrasound and manually reposition parts while in the solution using gloves as the solution may be hot.  Do not reach into an operating bath.
  • If your shop frequently cleans large numbers of complex parts consider an Elma Flex system from Tovatech. It is available in several capacities and with precise ± 2 cm vertical oscillation that allows solutions to enter and flush out contaminants.  Rinse and drying stations are also available.
  • Tubes should be placed either vertically or on an angle in the cleaning solution to ensure they are filled. Cavitation action will penetrate thin walled tubing and remove interior contaminants.  Periodically raise and lower the tubes to replace the solution.
  • If a rinse cycle follows cleaning allow parts to drain into the cleaning tank to minimize dragging contaminants into the rinse tank. Agitation or repositioning may also apply for rinsing.

In summary, position is important when complex parts are placed in an ultrasonic cleaner.  Air trapped in blind holes and crevices blocks ultrasonic cavitation and must be replaced with cleaning solution.  Care should be taken to drain parts before they are placed in a rinse tank.

For more suggestions on cleaning complex parts please contact the scientists at Tovatech for help regarding equipment selection, processes and cleaning solution formulations. 

About Rachel Kohn

So how did an MIT Ph.D. end up selling refrigerators? When I figured out that a lot more scientists buy lab refrigerators than innovative leading-edge instruments. I hope that my many years of lab experience will help you find the right equipment for your work. Before co-founding Tovatech I worked in business development and project management at Smiths Detection, Photon-X, Cardinal Health, and Hoechst Celanese. And before that I spent 12 years as an R&D chemist at Hoechst Celanese and Aventis working on advanced drug delivery systems, polymer films and membranes, optical disks, and polysaccharides. Some day, eventually, I’ll make enough money to develop an innovative technology that will change the world. Read More