Analysis And Optimization Of Tribological Properties Of Nano Copper Additive For Lubricating Grease

With the wide application of nanometer lubrication, the improvement of lubrication performances of lubricants base oil is becoming more and more intense. Nano copper powders have attracted much attention for unique physical and chemical properties, excellent extreme pressure characteristics, and repairing micro damage on the friction surface. The tribological properties of base oil can be effectively improved by adding nano copper powder. However, copper nano particles are formed easily to aggregate due to its surface energy and attraction, which affects seriously in their engineering application. Therefore, it is urgent to improve the dispersibility of nano coppers.In this paper, Nano copper powders were prepared by vacuum freeze-drying, the CUSO4·5H2O and NaH2PO2 were used as the precursor materials to improve their dispersion. The particles size and purity of the nano copper powders were characterized by transmission electron microscopy(TEM) and X-ray diffraction(XRD), respectively. The results show that the purity of nano copper powders prepared by freeze-drying is high; and its particles and shape were fine, and regular. The size of particles prepared by three freezing methods are 8-45nm, 4-25nm and 3-20nm, respectively.Then, homemade nano copper powders by freeze-drying were used as additive, we focus on the influence of nano copper powders on the tribological properties of liquid olefin and obtaining the optimum concentration. The results show that surface modification method was used to modify nano-copper powders. Compared to commercial nano-copper powders, the modified freeze-drying copper powders have better dispersion stability as lubricant additive, and the properties of that prepared by vacuum freezing are best, which can be stably dispersed in 18hours, and only 10% have settlement and stratification in 9 days. The lubricant containing 0.05% nano copper possessed the best lubrication performance, and the lubricating performance was gradually weakened with the increase of concentration. When the concentration reached 0.3%, it had the side effect on the lubricating performance.Considering the industrial application of nano copper powder, old oil was used as the base oil and the influence of the mileage on the performance of old oil improved by nano copper powder and copper formate was investigated. The results showed that copper formate could better improve the friction performance of old oil when it was used as additive. Compared with the old oil without additive, the average friction coefficient under different mileage is reduced by 46.7%,25.5% and 26.9%, respectively. And compared with lubricant using the same time, the average wear radius decreased by 61.21%,53.45% and 45.07%, respectively. While the friction performance of old lubricant using nano copper powder as additive haven’t been improved significantly, and it had no big difference with crude oil, which needs further study.Finally, the orthogonal experiment was used to optimize the design the process parameters of preparing nano copper by vacuum freeze-drying, and the optimum process was obtained from various factors. The results showed that stirring speed was 650 r/min, the surfactant was PVP or stearic acid, lyophilized thickness was 5mm, freezing methods was vacuum freeze-dried. Freezing modes has greater impact.The study on the friction performance of lubricant using nano copper powder prepared by freezing dry as additive will provide theoretical and experimental basis for nano copper additive being industrialized application.