Performance Analysis of Environmentally Adaptable Grease in Large open gears

Abstract: Environmentally adaptable grease (EAG) lubricants are essential in applications with loss lubrication due to their biodegradable nature. This is because the lubricants could be expelled into the environment during usage in some applications e.g., marine and mining applications. However, although this type of grease is sustainable to use, it also needs to bridge the performance gap it has with the mineral-based grease counterpart.  In this thesis project, a tribological evaluation comparison between the performance of EAGs and traditional mineral-based greases in large open gears is carried out. A twin disc tribometer is used to mimic the contact mechanisms of the test gears while being lubricated automatically by the grease samples through a syringe pump. For the experiments, the material surface of all the discs in the tribometer setup is steel while the different grease samples are tested for each setup. Two of the grease samples; UPL 04123 (NLGI 1.5) and UPL 04124 (NLGI 0.5) are fully formulated EAGs, while the third is a popular commercial mineral-based grease currently used in large open gears in the mining industry. An investigation of the wear of the discs used in each grease test is carried out using optical interferometry and a Scanning electron microscope (SEM). The wear volumes and wear rates are then analysed and compared to evaluate the performance of the grease samples. The wear results from the tribological characterisation using the twin disc are validated with the ISO 14635-3 standard on the FZG back-to-back test rig. Also, chemical characterisation of the unused and used grease is carried out using the advanced ATR-FTIR method to evaluate additive depletion and lastly an SEM-EDS analysis to confirm the presence of tribofilm on the surfaces of the disc samples. In conclusion, it is found that there is a correlation between the consistency of the grease sample and wear prevention; where the commercial grease with the least consistency performs best, followed by the 0.5G and lastly the 1.5G. Also, there are clear indications in the wear rates of the actions of extreme pressure additives activation at high contact pressures between the discs. The inadequacies of the ATR-FTIR and SEM-EDS methods to evaluate additives and tribofilm respectively are also discussed.