Why All Aqueous Cleaners Aren't The Same
Solvent-based cleaning systems are very effective at removing oils and greases. However, the EPA has determined solvents such as TCE, NPB, and PERC are "unreasonable risks to human health" as part of its ongoing TSCA review.
Parts cleaning operations have started converting to alternative cleaning technologies due to the latest EPA actions. Aqueous cleaning solutions have been in use for over three decades with proven efficacy equal to or better than solvents. Better yet, they are an environmental and worker-safe alternative.
Aqueous cleaners are water-based chemistries, as their name suggests. As a result, they are non-flammable and have less strict handling requirements as compared to halogenated solvents. Due to the various surfactant, inhibitor, and buffering technologies in these formulations, aqueous cleaning provides consistent and reliable results.
While all aqueous cleaning solutions share the same water base, not all necessarily work the same. This blog discusses the makeup of aqueous cleaners and how that affects their performance and price.
What is an aqueous cleaner?
Fan in Ultrasonic Cleaner Bath
Aqueous cleaning chemistries are diluted to between five and 25 percent concentration in water. Due to their high water concentration, these chemistries have minimal harmful vapor emissions and typically have far less stringent handling requirements than solvent-based degreasers.
The concentrated aqueous cleaning solution may contain any of the following, depending on the intended use by the cleaning solution manufacturer:
- Surfactants and detergents
- Anti-foaming agents
- PH buffers
- Chelating agents
The aqueous solution's pH is also essential to determine the types of soils the solution will remove. Neutral pH chemistry effectively removes water soluble and most hydrocarbon or synthetic oils. A high alkaline aqueous solution is better suited for removing salts, oxides, organic soils, grease, chips, and particulate held to the part surface by the oils. Finally, an acidic solution is necessary to remove scale, rust, or more stubborn oxidation.
Aqueous Cleaning Methods
Parts washers use aqueous cleaners in concert with a cleaning process that uses immersion or spray washing to remove the contaminant. Which method you choose depends on what you're trying to remove, where the contaminant is on the part surface, and the difficulty in removing the contaminant. For example, rust is much more difficult to remove than grease and would require a more aggressive cleaning process (and cleaning agent).
- Spray Cleaning: Spray washers use the mechanical energy of high-pressure water jets to remove contaminants from the part surface. This method works best for parts with smooth or relatively smooth surfaces, as cleaning effectiveness depends on how long the surface was directly exposed to the cleaning jet.
- Rotary Basket: Rotary basket systems utilize immersion, spray under immersion, and ultrasonics. This method is found where high volume, intricate parts cleaning requirements are in place.
- Immersion: The part is immersed in the cleaning solution for some time. Agitation achieved through fluid movement is typically necessary to dislodge soil from the part surface.
- Ultrasonic: Ultrasonic cleaning is a type of immersion that uses ultrasonic generators in the cleaning equipment tank to generate ultrasonic sound waves that produce bubbles on the surface of a part that violently forms and collapses. This process is highly effective in removing particulate and stubborn soils on more intricate parts where other cleaning methods may fail.
Other Factors that Affect Performance
While the chemistry of the parts cleaning solution is important, other factors affect performance and the result.
Higher temperatures may be necessary to allow the cleaning solution to remove more viscous contaminants. At higher temperatures, the chemical reactions within the solution occur faster, which cleans the part in less time. The higher temperature affects the viscosity of the soil, making it easier to remove. Temperatures can also be detrimental to the part, as the increased frequency of the chemical reactions can cause issues like etching or staining.
The part must be completely submerged or all parts evenly reached by the spray jets to get the best results. However, the part cannot spend an extended time in the cleaning process, or it may cause issues elsewhere on the line, such as material compatibility or a reduction in production output.
The cleaner must be appropriately used, effectively removing the contamination in the required amount of time while providing compatibility with the materials necessary. The concentration of the cleaner also will affect the tank/solution life by providing soil loading characteristics.
In the aerospace industry, all operating parameters such as cleaner, time, concentration and substrates allowed to be cleaned, are specified per the specification in place.
Cost vs. Process
Aqueous cleaners comparatively cost more to clean per part than solvent-based cleaning. There are a few reasons for this. While water is cheap, there is a much larger equipment outlay in an aqueous cleaning system. Cleaning also takes far longer, which increases overhead in the form of additional labor costs, energy requirements due to drying times, and building size since an aqueous cleaning system takes up more floor space.
Aqueous equipment manufacturers are aware of these issues. Machine footprints are shrinking as new technologies reduce cycle times, and vacuum drying reduces part drying times. As these manufacturers continue to innovate, the aqueous cleaning process costs will continue to fall.
However, despite claims to the contrary, aqueous cleaning can provide part cleanliness equivalent to that of solvent-based systems. While the higher cost is a significant disadvantage, depending on your process goals, the soils being removed, and other considerations – such as future EPA actions – adopting aqueous cleaning technology makes sense for a wide variety of applications.
How Brulin can help
Our specially formulated aqueous cleaners are developed for a broad range of applications. Our AquaVantage® 815GD used in immersion and ultrasonic cleaning is relied upon in many industries. AquaVantage® 1990 GD also boasts an unrivaled combination of cleanability, material compatibility, and recyclability for spray wash and rotary basket applications. No matter the cleaning need, Brulin has the right chemistry to meet your needs and operational objectives.