Ultrasonic cavitation and implosion provide a unique benefit in cleaning unmatched by other means. So much so that ultrasonic cleaning is often used as a benchmark to judge the effectiveness of other cleaning techniques.
The major factors in cleaning are Time, Temperature, Chemistry and Mechanical Effect or Motion (TTCM). There are other acronyms for these basics including WATCH (Water, Action, Time, Chemistry and Heat) and more, but in the end, they will virtually all include some mention of mechanical effect as was discussed in an earlier blog. And that’s where ultrasonic cavitation and implosion enter the picture. Wiping, brushing, spraying, turbulation, agitation and other means of introducing mechanical action may be necessary, appropriate and effective in cases of gross contamination and where cleaning requirements are less demanding. But in cases of critical cleaning applications and those where the surfaces to be cleaned are not readily accessible, ultrasonics often offers the best and sometimes the only solution.
Mechanics of Cleaning –
There are three basic cleaning scenarios.
- Removal of Soluble Contaminants
- Removal of Non-Soluble Contaminants
- Removal of mixed Soluble and Non-Soluble Contaminants
Although the mechanism of cavitation and implosion is the same in all of the above cases, the role it plays is slightly different for each.
Soluble contaminants can be either solid or liquid in nature. In order to remove them, it is necessary to continually renew the solvent/contaminant interface to prevent saturation of the solvent at the interface which prevents further progression of the dissolution process.
Once a saturated layer is created and is not removed, further dissolution is dependent on random molecular motion and may virtually stop depending on the viscosity and volatility of the components involved. Any means to create motion and speed interaction will benefit cleaning.
Liquid agitation, spray, brushing etc. are commonly employed means to do this. But each of these methods has limitations. Liquid agitation, for example, is only effective where a flow providing a exchange of liquid can be created. This not easily done in a deep blind hole. Spray, in order to be effective, must impinge directly on the surface being cleaned. Similarly brushing is only effective where the surface to be cleaned can be reached by a brush or other implement. The barrier layer effect also hinders the use of agitation and spray as do inevitable irregularities in the surface being cleaned not to mention enclosed or shielded areas of a part. Nearly all surfaces have irregularities on a microscopic scale with the ultimate being a sintered metal part.
Ultrasonic cavitation and implosion has the unique ability to not only disrupt the saturated layer between the cleaning solution and the contaminant to enhance further dissolution but also has the ability to reach into surface irregularities, blind holes and enclosed and surfaces hidden from other methods to provide thorough cleaning. As with any immersion cleaning process, the solvent will eventually become contaminated by the removed contaminant to the level that it has to be replaced to prevent re-deposition of dissolved contaminants.
Soluble contaminants are as stated above, only one classification of contaminants. Upcoming blogs will discuss insoluble and mixed contaminants and the benefits of ultrasonics in removing them as well.