An in-depth study of the serious problems caused by the proliferation of various microorganisms in the emulsions affecting the efficiency of the fluids and the working environment
Micro-organisms – or microbes – can be defined as living organisms visible only thanks to a microscope and their world is extremely varied: they are divided into unicellular organisms, which are less evolved and therefore more simple on a structural level, and multicellular. Bacteria and Fungi (intended as micromycetes) hold a main relevance into the world of Metalworking.
The biodegradation of emulsions
Water-Solubles used in Metalworking operations are typically formulated by adding a wide variety of chemicals to the mineral-oil base, such as fatty acid soaps, sulfonates, amides, amines, esters, nonionic surfactants called ethoxylated alcohols, Sulfur and Phosphorus based lubricating additives and other compounds.
Many of these substances are nutrients for microorganisms as sources of Carbon and other elements.
At the same time, there are other factors to act as contaminants: tramp oil from the machine tools affecting the processes, pollutants from both the processed materials and the surrounding environment and even the water used to prepare the emulsion itself.
These pollutants, in addition to being triggers for microorganism contamination, can provide them with additional nourishment.
Impact on Performances
The activity of microbes can affect the performance of the water-solubles in several ways:
- Surfactants and esters are degraded to acids causing foaming, mush generation and separation of the emulsion;
- The formation of acids leads to a pH drop, which in turn generates a major reduction in rustproofing power, thus causing corrosive phenomena on ferrous materials;
- The drop in pH also depletes the biostability of the product by accelerating the proliferation of microorganisms;
- Degradation of anti-wear lubricant additives and so-called EP (Extreme Pressure) additives decreases the cutting capabilities of the emulsion, resulting in decreased tool life and unacceptable surface finishes;
- Degradation of metal inhibitors can cause staining and residue on nonferrous materials (alloys of aluminum, copper etc…), thus making them unfit for trade.
Impact on Work Environment
Emulsions are never completely sterile and a minimum of microbial activity is always present, but when this reaches particularly significant levels, the first and most obvious sign is certainly the odor, such as can be found in plants on Monday mornings after two days of machinery inactivity.
The culprit of this bad smell is the metabolism of microbes, which generates substances such as acids and aldehydes. Among these by-products there is hydrogen sulfide, recognizable by the characteristic stench of rotten eggs. These gases accumulate during stops and are released from the emulsion when recirculation gets started again.
The presence of slime-like residues in the system or filters is also a clear indication of microbiological activity: these can be bacterial biofilms or fungi.
It’s important to remove tramp oil, when present, from the emulsion surface because, in addition to acting as a nutrient for microorganisms, it prevents oxygenation by promoting the activity of anaerobic bacteria.
Finally, it is necessary to remember the health risks from biodegradation, which include infections, reactions to toxins, and sensitization (or allergic reactions), risks that are significantly increased where there are wounds, such as cuts and abrasions, which have been improperly treated.
Conditions Monitoring
The most effective way to check for fungal or bacterial contamination is to treat a controlled culture medium (agar), with a few drops of the emulsion you want to test. The sample is stored in the laboratory in a controlled environment thus to promote the growth of clearly visible colonies.
Another simple method of analysis is the use of dip-slides, which is a ready-to-use culture medium. They contain agar on both sides and promote the growth of bacteria on one side and molds and yeasts on the other. The former are identifiable as red spots, the latter as white stains.
Note that the revealing the presence of anaerobic bacteria is more difficult because of the presence of oxygen but this does not mean that they are not there.
