Ultrasonic Cleaning – Soluble Contaminants

In the blog entitled Get a Move On, I briefly discussed the importance of some form of mechanical action to assist cleaning.  This is true in both the case of soluble and insoluble contaminants.  In this blog I will dig a little deeper into the subject of the benefits of mechanical action in removing soluble contaminants with an emphasis on the role of ultrasonics.

Soluble contaminants, as we have discussed before, are liquid contaminants (oil, for example) that will mix with and be diluted by a solvent and solid contaminants (salts, for example) that can be dissolved by a solvent.

For the moment, let’s say that we have selected a suitable solvent for our contaminant and immerse a contaminanted part in a container of that solvent.  Without agitation, the solvent will start to do its job by mixing with and diluting or dissolving the contaminant it comes in contact with.  Soon, however, the solvent in contact with the contaminant becomes contaminated by or saturated with the contaminant.  Once this has happened, “cleaning” stops!  A good analogy can be found in any kitchen.  Everyone knows that you can put a dirty dish in water, even soapy water, but, even if left overnight, all traces of residue are not removed if you don’t add a little “elbow grease.”  Last night’s spagetti sauce may be softened by an overnight soak, but, unfortunately, it won’t be totally removed.  Getting the dish totally clean requires use of a sponge, dish rag, or whatever you use to wash dishes and, of course, completing the job requires a rinse.

Parts cleaning is not really any different than dish washing.  Once that saturated layer of solvent develops, the only way to further the cleaning process is to replace the saturated solvent with fresh solvent.  Parts cleaners do this using sprays, part agitation, turbulation, bubbling, brushing (occasionally) and other means of providing a mechanical assist.  The purpose of whatever mechanical means is used is to stir up the solvent so that spent solvent is replaced with fresh solvent.

Illustration showing solvent dissolving a contaminant.

Ultrasonic cavitation and implosion are very effective in stirring up solvent and contaminants on a micro-scale.  It is especially beneficial when the surfaces being cleaned have complex configurations as opposed to being flat.  The effects of ultrasonic cavitation and implosion penetrate wherever the solvent can penetrate.  Unlike many other means of adding mechanical agitation, ultrasonics is effective in removing contaminants from blind holes, the roots of threads and, since it is efficiently transmitted by many materials, is even able to clean enclosed or hidden areas of parts.

And yet, even though ultrasonic cleaning is very effective on a micro-scale, most cleaning applications require some macro-scale mechanical assist as well.  The surface of a thick layer of contaminant may be effectively penetrated by ultrasonic cavitation and implosion but eventually, the barrier layer exceeds the scope of the ultrasonic effect.  To further removal of such contaminants, ultrasonic cleaning systems benefit from part agitation and rotation as well as intermittent spraying and turbulation.

An upcoming blog will discuss how ultrasonics assists in the removal of insoluble contaminants from surfaces.

– FJF –