Myth 1 of 8: Water is Obviously “Cheaper” than Solvents.
Regular city water alone won’t clean anything. It needs surfactants and detergents that lower surface tension and remove soils. These are consumed during cleaning and need replenishing. Higher temperatures are needed to activate cleaning chemistry, which is important for ensuring good wetting and evaporation after rinsing, but that consumes energy. Also, an aqueous cleaning system needs rinse and dry units.
In contrast, a solvent cleaning system uses significantly less energy for heating and drying. It occupies less space for an equivalent throughput and being less complex and needs less maintenance. Furthermore, the solvents are usually recovered and recycled. So, while a gallon of solvent cleaner may cost more than the same amount of aqueous cleaner, a solvent cleaning process has lower energy costs and consumes no water. The maintenance spend is lower and being smaller, the process may carry lower overheads.
Myth 2 of 8: Aqueous Systems Can’t Be Used in Critical Cleaning
First, let’s be clear that “critical cleaning” has a very specific meaning. It refers to the removal of sub-micron particles and non-volatile residues. It’s required when any surface contamination would yield adverse effects. While many processes and products might qualify, the term is used particularly with reference to medical devices.
Second, the statement is just wrong. Aqueous systems can be and are used in critical cleaning. However, surface tension – wetting – is a key consideration. The cleaner must penetrate every aspect of the part being cleaned. While solvents are inherently superior, with appropriate surfactants aqueous cleaners can perform as well. However, aqueous cleaners can leave a surface residue. This makes rinsing and drying critical steps in aqueous critical cleaning. But if the surface can be demonstrably clean, to agreed levels, on a consistent and repeatable basis, aqueous cleaners can be used.
Myth 3 of 8: Aqueous cleaning is always “safer” than solvent.
There’s a misapprehension that “Aqueous Cleaning” refers to cleaning with water. While water is involved, and under the right circumstances can be a solvent, in aqueous cleaning systems the water contains additives. These have several functions, such as lowering surface tension, creating chelation, (the drawing-out of metals,) modifying pH and saponification, (turning fats into salts of fats.) These additives, especially those strongly acidic or alkaline, can pose health hazards. Before assuming aqueous cleaning is safer, check the SDS to find out what’s being used.
Solvents also need a close look. Some release VOCs, especially during drying. Some give off strong or unpleasant odors, and some may be hazardous. There’s also the question of flammability: some are, and others aren’t. But it’s a generalization to say that aqueous is always safer than solvent.
Myth 4 of 8: Solvents are all BAD!
“Solvent” is an extremely broad term. Any substance that will dissolve another is, technically, a solvent, and that includes water. However, in popular parlance, “solvent” often refers to chemicals that will dissolve oil and grease. Examples include acetone, isopropanol, ethanol and butyl acetate. If these names appear familiar it’s because they are widely used and available. While odors and flammability can be a concern, providing usage recommendations are followed there is no reason to avoid them.
Some solvents used in the past, trichloroethylene is a prime example, are now known to be hazardous to health. Some VOC-releasing solvents also have hazards associated, Likewise, CFCs and HCFCs are bad for the environment and consequently are being phased out. But to say all solvents are bad is incorrect. The key is to read the SDS and understand what’s in it and the risks, if any.
Consider also the age of solvent cleaning equipment. Modern units are engineered to minimize and mitigate any release that may occur and so don’t have the emission problems of older cleaners.
Don’t overlook the hazards of some aqueous cleaners. Anything acidic or caustic could present health risks, so the same advice applies read the SDS. And one other point to consider: disposal. Aqueous cleaners need to be disposed of appropriately. Most can’t just be discharged down the drain.
Myth 5 of 8: Solvents will all be banned through government regulation.
It’s true that for some classes of solvents their use either has been or is in the process of being phased out. However, many others are still permitted, although in some cases there are regulations regarding aspects of usage like ventilation. In general, authorities like the EPA take the view that solvents used today will not be prohibited until equally effective and affordable, but more benign, versions emerge.
Some solvents used in the past have created environmental problems. Hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs) are two obvious examples. Use of these is governed by the Montreal and Kyoto protocols and they will disappear in due course. Likewise, solvents like trichloroethylene (TCE) are strictly regulated and again disappearing. Volatile organic compounds, (VOC’s) are problematic and regulations regarding their use may tighten in future. But a complete ban? Not until affordable alternatives become available. Learn more.
Myth 6 of 8: Solvent cleaning is always the most efficient process.
Solvents make very effective cleaners, in the right application. The key points to consider are, what is being cleaned, what is it being cleaned of, and what is it being cleaned for? Solvents are highly effective for dissolving oils and their low surface tension enables good penetration and evaporation. Solvent cleaning can often be a less expensive process than aqueous cleaning. In addition, solvents that dry quickly help keep work flowing through a factory while avoiding inventory build-up and the need for storage space.
However, aqueous cleaning solutions work by a combination of solubilization, saponification, emulsification and chelation. More simply, there are a wide range of dirt or soil types, such as triglycerides (fats) that are removed better by water-based processes. In addition, aqueous cleaning can tackle surface oxidation, like rust, tarnish and scale, that solvent cleaning will not remove.
Before committing to either solvent or aqueous cleaning, discuss your goals and objectives with specialists who understand the pros and cons of both. Their advice may surprise you!
Myth 7 of 8: Market is Dominated by Aqueous Cleaning
Compared to solvent cleaning, aqueous is still the newcomer, even though it has been in use for two decades. Use of aqueous cleaning is undoubtedly on the rise, but to say it dominates the market is just incorrect. Precision cleaning in particular, is a sector where solvent cleaning dominates.
The key, when choosing a cleaning method, is to take a holistic view and consider all aspects of the cleaning process. Do not just assume that because one is growing it’s the best approach for your business.
Myth 8 of 8: Cleaning is All About Picking a Chemistry
Chemistry is important for sure. The solvent or aqueous cleaner must be compatible with the soil or contamination you want to remove, but it’s more complicated than that. Consider also the material to be cleaned: some cleaners will damage some surfaces. Then there’s the degree of cleaning or cleanliness desired. Or to put this another way, why is the part or surface being cleaned?
Component geometry is another factor. With their lower surface tension solvents are generally more effective than aqueous cleaners in tight spaces and small holes. An added benefit is that they will dry faster too.
Solvent cleaning systems are, in general, less expensive to operate than aqueous processes, and occupy less space. As parts don’t need a lot of drying time after cleaning, solvent systems can work well in medium to high volume production environments where throughput is a consideration.
The bottom line is, yes chemistry matters, but many other factors determine the right cleaning process.
Take a holistic view before choosing a cleaning process.
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