Structural aspects of surfactant selection for the design of vegetable oil semi-synthetic metalworking fluids

The Role of Surfactant Structure on the Development of a Sustainable and Effective Cutting Fluid for Machining Titanium Alloys

In cutting operations of titanium alloys, most of the problems are related to the high consumption of cutting tools due to excessive wear. An improvement of metalworking fluid (MWF) technology would increase the productivity, sustainability, and quality of machining processes by lubricating and cooling. In this research article, the authors varied the surfactant’s charge, the hydrocarbon chain length, and the ethoxylation degree. Surfactants were dispersed at 1.2 mM in water and trimethylolpropane oleate to produce water-based MWF. Infrared reflection absorption spectroscopy and total organic carbon analysis were used to study the influence of surfactant structure on the film forming ability of the emulsion and performance was studied on Ti6Al4V using tapping torque test. The results showed that by changing the molecular structure of the surfactant, it is possible to vary the affinity between the ester and the substrate and reach an optimal combination, which improves the formation of a tribofilm. The mixture with anionic surfactants has good tribology performance, while non-ionic surfactants shorten the tool’s life. Moreover, the increase in the hydrocarbon chain length and the number of ethoxylations of surfactants promotes the adhesion of ester onto the metal surface, improving the lubricity properties of environmentally friendly MWF.

Comparison of life cycle emissions and energy consumption for environmentally adapted metalworking fluid systems

A number of environmentally adapted lubricants have been proposed in response to the environmental and health impacts of metalworking fluids (MWFs). The alternatives typically substitute petroleum with vegetable-based components and/or deliver minimum quantities of lubricant in gas rather than water, with the former strategy being more prevalent than the latter. A comparative life cycle assessment of water- and gas-based systems has shown that delivery of lubricants in air rather than water can reduce solid waste by 60%, water use by 90%, and aquatic toxicity by 80%, while virtually eliminating occupational health concerns. However, air-delivery of lubricants cannot be used for severe machining operations due to limitations of cooling and lubricant delivery. For such operations, lubricants delivered in supercritical carbon dioxide (scCO2) are effective while maintaining the health and environmental advantages of air-based systems. Although delivery conditions were found to significantly influence the environmental burdens of all fluids, energy consumption was relatively constant under expected operating conditions. Global warming potential (GWP) increased when delivering lubricants in gas rather than water though all classes of MWFs have low GWP compared with other factory operations. It is therefore concluded that the possibility of increased GWP when switching to gas-based MWFs is a reasonable tradeoff for definite and large reductions in aquatic toxicity, water use, solid waste, and occupational health risks.