Many customers having purchased an ultrasonic cleaning system are disappointed when the parts they are cleaning are not consistently cleaned, especially inside detailed areas of the parts, or in blind holes and cavities!  In many of these instances, entrapped air in these locations has prevented effective ultrasonic cleaning of these areas.

Air entrapment is common when parts include several blind cavities or holes in different planes, when cleaning holes that are so small that liquid has difficulty filling it, and many other similar applications. 

Ultrasonic cavitation, the scrubbing action which is produced by the ultrasonic cleaning system, can ONLY produce effective scrubbing action in liquids.  As such, ultrasonic cleaning will not take place at all in areas of air entrapment.  Although air entrapment is a hurdle which must be overcome for many cleaning applications, equipment design can play a major role in the system's effectiveness when dealing with entrapped air.  For example, many of Zenith's system designs includes oscillation of parts during processing.  This oscillation will serve to flush cleaning and rinsing fluid into air entrapment areas, thereby filling and draining these areas  during processing.  This can largely overcome air entrapment issues on many part designs.

A common method for determining if parts will trap air is to place a load of parts into the intended basket or holding fixture, and lower the parts into a bath of water or cleaning fluid in an identical fashion as would normally take place during cleaning operations expected.  Once the parts are lowered, shake the basket or holding fixture while the parts are submerged, gently at first, then with increasing agitation.  If you see bubbles rising to the surface of the fluid as parts rotate or move around while submerged, the parts have trapped air at certain locations which will reduce or completely eliminate effective cleaning in these areas unless addressed.

The good news is that the ultrasonic cleaner will actually release most of the loosely-held air pockets from the parts the moment that the ultrasonic system is activated.  However, any air which is trapped too deeply to be released by minor agitation will not be released by ultrasonic activity.

Since one cannot change the design of the parts, the only solution is to rotate or agitate the parts after they are submerged to release any air which may be trapped.  Part oscillation operations do an excellent job of flushing out blind holes and cavities to get these areas clean.  In some cases, parts can be positioned so that blind holes or cavities fill and drain readily without trapping air.  This is achieved by positioning the blind hole in a horizontal plane so that it can fill and drain when submerged or lifted from the bath.  In fact, this is a standard practice not only to prevent air entrapment, but also to reduce drag-out of detergent from the cleaning tank into the rinsing tank which may create water spotting on parts being cleaned.

A more expensive alternative is the draw a vacuum above the liquid in the cleaning tank which will serve to release entrapped air.  However, although the cleaning fluid has entered the cavity, the liquid may not drain out of these areas when removed from the cleaning fluid, which creates a condition known as Detergent Drag-out.  Detergent will be transferred into the rinse tanks, which will contaminate the rinse water, and may prevent adequate cleaning results due to contaminated rinsewater. 

Your Zenith salesperson will be able to assist you in testing your product for air entrapment.

When Air Entrapment may be an Issue:

• Parts having Several Blind Holes or Cavities.
• Small-orifice Tubing or Holes which Prevents Water from Entering.
• Parts that are Stacked in Bulk May trap Air.

How to Prevent Air Entrapment Issues:

• Oscillate Parts during the Cleaning and Rinsing Processes.
• Rotate Parts to Release Entrapped Air.
• Detailed Areas are Not Cleaned Effectively.
• Systems do Not Last Long.

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Zenith Mfg. & Chemical Corp.
85 Oak St.
Norwood, NJ  07648-0412
800-432-SONIC (7664)
201-768-6999
sales@zenith-ultrasonics.com