Comparison and Control of Microbial Spoilage of Metal-Working Fluids and Associated Corrosion

The microbial environment in the metal-working fluid in a machine tool is complex, as the dissolved oxygen content, Eh, and temperature differ at different locations in the system. Thus different species of microorganisms flourish or decline at different points in the fluid depending on their individual needs and preferences. Experiments using simple shake flasks or stagnant flasks in the laboratory can produce misleading results. A recirculation apparatus is described that allows both aerobic and anaerobic microbial growth to occur. It can be monitored and manipulated (for example by reinoculation or the addition of biocides) over a long period. Metal swarf is added to the apparatus and its corrosion can be rated visually. The corrosiveness of the fluid can also be determined at intervals using the standard metal chip test.