| Resumo : |
It is estimated that 43.87 million tons of lubricants will be consumed globally until 2022. Due to the growing demand of lubricants and the current dependence on mineral oil faced by the industrial sector, the development, manufacture, and use of new alternative oily bases for lubricants become strategic for the market. Therefore, bio-lubricants from vegetable-based oils (VOs) create a promising niche for the bio-economy. In addition, the application of bio-lubricants in industrial activities poses an eco-friendly, biodegradable, less toxic atmosphere and provides a lubricating film with higher tenacity which offers more stability on material surfaces than mineral-based oil. During the machining processes, the friction generated at the chip/cutting tool interface induces a significant increase of temperature, directly influencing the cutting tool's life and promoting the thermal expansion of the part, negatively influencing the tolerance limits required by the aircraft industry. Metalworking fluids (MWFs) are used to minimize the friction (lubrication property), dissipate the heat (cooling property) at a specific area (chip/cutting tool interface), facilitate the removal of material (chips), improve the finishing of the machined surface, decrease the cutting forces, reduce energy consumption and the cutting tool wear. The rich carbon composition of the emulsifiable MWFs provides an environment conducive to bacterial and fungal growth. The degradation of MWF affects quality and performance, making it unfit for use and reducing its life. For this reason, the MWFs have a high concentration of chemical biocides that are normally harmful to the environment and workers. According to the history scientific studies, what was clearly noticed was an increasing trend of researches on the use of renewable resources for the development of industrial products and more environment-friendly manufacturing processes. However, foster researches and investment in the development of alternative crops to produce bio-lubricants and natural biocides can guarantee greater power of choice. This thesis aims to propose essays to define these requirements to VOs to be used as bio-lubricants in machining processes on Al 7050 T7451 and Ti-6Al-4V alloys and as natural biocides. To reach this goal it was investigated 1) the influence of the fatty acid profile of VOs on the formation of the lubricating film by tribological tests, 2) the unsaturation number of the fatty acids in the lubricating performance applying in the machining processes, and 3) the VOs with biocidal potential for MWFs formulation. The results indicate that the technical performance of the VOs as lubricant changes according to the material surface. The increase in the unsaturation of the carbon chains promotes more resistance to movement between metal/metal contact, increasing to the coefficient of friction and cutting forces. However, it favors the reduction of the metal/metal contact, promoting less wear. The thermal stability of VOs may influence the lubricating film when it is under critical conditions. VOs have the potential to be used as natural biocides for microorganisms isolated from MWFs. |