The cleaning process is the “recipe” for cleaning. Like any culinary recipe, it should clearly define the ingredients, times, temperatures and the method of application to be used for cleaning. Most cleaning consists of at least the three basic steps of washing, rinsing and drying.
The purpose of washing is to remove contaminants from the parts being cleaned and contain them in such a way that they are not re-deposited on the parts. Soluble contaminants generally go into solution with the washing chemistry while non-soluble contaminants are suspended in the cleaning solution to be swept away and removed by filtration or some other means. The washing process needs to be adequate to achieve the cleanliness required by the cleanliness specification.
- Chemistry and concentration
- Method of application (immersion, spray, ultrasonics, other). This should include other pertinent details such as spray pressure or volume, ultrasonic frequency, critical part positioning, agitation, rotation, etc.
The purpose of rinsing is to remove any residues remaining on the parts from cleaning. These may include residual cleaning chemistry and, in some cases, some remnant of the solubilized or suspended contaminant remaining on the parts from the cleaning process.
- Water quality. Tap, RO water or DI water, for example.
- Method of application (immersion, spay, ultrasonics, other). As in the case of cleaning, this should include other pertinent details such as spray pressure or volume, ultrasonic frequency, critical part positioning, agitation, rotation, etc.
Although not always required, drying is a critical part of many cleaning processes. In some cases, parts need to be absolutely dry while in others the removal of standing water is all that is required. This should be part of the cleaning specification.
- Air quality. Room air, filtered air, HEPA filtered air, other gasses, etc.
- Method of application (circulated air, radient, blow-off, vacuum, etc.)
The cleaning process is usually determined by small scale testing in-house or by a facility operated by a chemical or equipment supplier. If testing is performed by an outside entity, it is natural that those suppliers will submit reports that are biased toward the chemicals or equipment they supply. Proper analysis of these reports is critical but often difficult especially when the end user doesn’t have an experienced cleaning specialist on staff.
Here are a few questions to ask a chemical or equipment supplier regarding process recommendations –
- What is unique about the recommended chemical that makes it better suited than any other for this process? Were other options considered and tested? What were the results?
- If spray, immersion, ultrasonics or any other specific means of application is recommended, why was this method chosen? Can the chemistry be used with another method as well or must it be used only in the recommended way?
- Are there safety issues with using the selected chemistry? What is the life of the chemistry? What limits its life? Can it be replenished? What is required for disposal?
- Was the chemistry chosen for any properties other than cleaning? Rust or oxidation prevention, for example. Are there other considerations that should be taken into account?
- What is the cost?
Although not complete, the above list may be useful to those trying to define a cleaning process.
– FJF –