Although microbial growth in metalworking fluids can never be totally eliminated, its control is vital for maintaining an effective working fluid. The first step in controlling this unwanted proliferation is to recognize the means by which bacteria and fungi can enter the metalworking-fluid system.
The water used for concentrate dilution and fluid make-up is the primary source for entry of unwanted microorganisms into the system. While this water is usually treated, by ion exchange, reverse osmosis or other means, to remove chemical contamination in the form of dissolved chemicals and ions, it can still retain a significant microbial population. In fact, microbially-contaminated water-treatment resin beds can provide a constant source of re-inoculation to otherwise microbially-benign intake water. Moreover, contaminated coolant or make-up water, aerosolized by agitation, can carry bacteria and fungi through mist in the air from one work-area in an end-user’s plant to a totally different location in the building. Airborne microbial contamination can also result from outside the facility, by a plant ventilation system drawing in microbe-laden solids (dust) and/or liquids (water aerosols) along with fresh air. This can be especially problematic when the fluid-using plant is downwind of a brewery, bakery or cooling tower.
Another major factor in microbial contamination of use-diluted fluids is the adding of extraneous material, deliberately or otherwise, to coolant systems. The practice of tossing trash, such as rags, cigarette butts or partially-consumed food or drinks, into coolant-return sluices can be a major source of unwanted microbes. Sweeping chips and other trash off the floor into fluid-return trenches will also inoculate fluid systems with microorganisms. Replacing protective open-grate decking used to cover in-floor sluices with solid metal-plate covers can reduce the opportunity for swept-in contamination, but the undersides of these floor plates should be regularly checked for evidence of biofilm/biomass build-up which could re-inoculate the fluid being returned for cleanup and re-use. Additionally, workers can inadvertently track into the plant environment garden-soil or animal-waste residues which can find their way into returning fluids and bring a totally different spectrum of bacteria and fungi than that ordinarily expected in an industrial environment. Workers changing into plant-issued safety shoes and wearing plant coveralls can virtually eliminate this possibility.
Knowing what contamination sources to look for, and taking timely corrective action when they are discovered, can assist dramatically in reducing the microbial load of in-use metalworking fluids.
Alan Eachus is a member of the Metalworking Fluids Education & Training Subcommittee and is a consultant and subject matter expert on metalworking and metalworking fluids. You can reach him at firstname.lastname@example.org.
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