The influence of cell counts, cell size, EPS and microbial inclusions on the lubrication properties of microorganisms

Abstract

Metalworking fluids (MWF) play an essential role in many machining applications and can be classified e.g. according to DIN 51385 in non-water miscible- and water miscible metalworking fluids. Most of the several billion liters of the worldwide and annually consumed MWF are water-based and thus exposed to a microbial contamination, which leads to a deterioration of MWF compounds and therefore to a loss of quality and technical performance. To maintain the MWF quality, biocides are used to reduce the microbial load, regardless of their potential risk for health and environment. A further limitation poses the high consumption of raw materials (mainly mineral oils) for the production of MWF, with approximately 50,000 t of raw materials consumed annually in Germany. To overcome these limitations, the paradigm shift of using microorganisms as a lubricant in a manufacturing process is investigated in this paper. Preliminary investigations on a Brugger-tribotester indicated the great potential of microorganisms as replacement for conventional metalworking fluid components. Against this background, the approach presented here intends to investigate the influence of cell counts, cell size, extracellular polymeric substances and microbial storage products on the lubrication properties of selected microorganisms. The results of the tribological tests show, that some microorganism exhibit superior lubrication properties (up to 68 % higher) compared to a highly concentrated conventional metalworking fluid. Therefore, the potential of microorganisms to substitute conventional MWF components can be derived.