Archived Newsletters
Cleaning Basics - Degreasing
Ed Kanegsberg & Barbara Kanegsber
“Check out this website!” The message from a colleague indicated that he had spotted a new product for critical cleaning. Ah! A new product line of cleaning agents. A link! The siren song of the weblink along with the promise of new options for critical cleaning was a sure fire way to divert our attention.
What we found prompted us to get back to basics about the technique of degreasing. The new technology is indicated to be a “solvent for degreasingapplications,” a replacement for chlorinated degreasing solvents.
The product literature indicated that the solvent could be used in existing vapor degreasers but not in the vapor mode. Hmmm …. sounds like a recipe for Classic Pasta Primavera but one without garlic, basil, tomatoes, or olive oil. The result could be tasty, but we suspect it would be a different culinary experience.
Classic Degreasing
Let’s give you a brief overview of how vapor degreasing works. As the name implies, classically, critical cleaning in a vapor degreaser occurs when the part is in contact with solvent in the vapor phase. The part or component to be cleaned is suspended above the surface of a boiling tank of solvent, in a zone containing saturated solvent vapor. If the part has a temperature below the boiling point of the solvent, solvent will condense onto the part, much like the fogging of windows in a bathroom when a hot shower is running. The solvent then drips off the part back into the tank, carrying with it dissolved contaminants and dislodged particles. If the part has small holes or spaces, the vapor will condense in the holes and, if the solvent has a sufficiently low viscosity and surface tension, it will have sufficient wetting to penetrate and drain from the holes and spaces. The power of vapor degreasing is that you are cleaning with a penetrating, high purity, freshly distilled, liquid. In addition, the vapor degreasing solvent is self-rinsing.
Solvents for Vapor Degreasing Cleaning Systems
Why is the cleaning agent described on the website not suitable for classic vapor degreasing? The data sheet indicates that it has a very high boiling point, over 200 deg. C, so it could probably not be readily boiled in most current vapor degreasers. Also, It appears to have a viscosity higher than that of water, so it would not have the same wettability characteristics.
Most effective solvents for vapor degreasing have a moderate boiling point, low viscosity, low surface tension, a moderate to high solvency for soils of interest and evaporate or dry quickly. Water is not considered to be a vapor degreasing liquid because it does not meet any of these criteria. Most soils of interest are organic oil-like materials for which water has low solvency. An aqueous cleaning agent typically has many additives, including surfactants (1) to boost the solvency. However, these additives generally have boiling points much higher than that of water. Therefore, they do not become part of the vapor zone and would not contribute to cleaning of a part suspended above the surface.
Low viscosity and low surface tension are criteria that enable a liquid to easily penetrate into and out of small spaces and holes, to wet effectively (2). Part of the expected cleaning action of a vapor degreaser is the wettability of the solvent. You should be aware that this wettability is separate and distinct from solvency; many newer solvents that can be used in the vapor phase mode have low solubility for most industrial soils of interest.
Degreasing Agent
But the website we were referred to calls the new cleaning agent a “degreasing” agent. Is this incorrect? No, but it might be misleading. Degreasing is a general term for any cleaning agent that can be used to remove greasy or oil-like contaminants. These include aqueous based agents with surfactants and other additives as well as high boiling point bio-based solvents, in addition to those that would be suitable for vapor degreasing applications.
You might replace a cleaning agent suitable for use in a vapor degreaser with another type of degreaser but you lose the specific properties that make vapor degreasing so effective. These include a high-purity, penetrating, easily dried, very low-residue cleaning agent.
Dip Tank
Can you convert your vapor degreaser into a dip tank? Should you? Well, it depends on what you want to accomplish. If you are removing heavy oils from a non-complex part, if cleaning agent residue is not an issue, if you don’t need cleaning in the vapor zone, perhaps you can readily adapt the equipment to the new cleaning agent. In general, however, we find that for more productive manufacturing, it is better to select cleaning equipment that is designed for use with a particular cleaning agent.
In upcoming articles, we will explain more about cleaning techniques and about how to find the combination of cleaning agent and cleaning equipment that works best for your manufacturing facility.
References:
“The Physics of Cleaning—Part 7: Surfactants”; http://bfksolutions.com/Newsletter%20Archives/V7-Issue2/PhysicsCleaning7.html
“Physics of Cleaning Part 6”, http://bfksolutions.com/Newsletter%20Archives/V5-Issue3/Physics_of_Cleaning_Part_6.html
