| Grease is one of the key components of rolling bearings,which plays an important role in reducing friction and wear of rolling bearings and improving their life and reliability.With the progress of machining technology,machining accuracy is no longer the key problem restricting bearing life and reliability.Grease with high wear resistance and longevity is the key to further improve bearing performance.Furthermore,the environmental pollution caused by lubricating oil/grease is gaining attention from academic and industrial circles.Grease generally consists of 75%-80%base oil,20%-25%thickener and less than 1%additives.The preparation and selection of environmentally friendly base oils and thickeners,and the improvement of tribological properties of the original grease by green additives are the focus and hotspot of current research.In this paper,calcium sulfonate complex grease was prepared from green raw materials with poly-alpha-olefin oil oil as the base oil and calcium sulfonate compound soap as thickener.In order to further improve the tribological performance of the grease,nano-hexagonal boron nitride with potential to replace toxic additives was selected as the additive.The effect of nano-boron nitride on the tribological properties of calcium sulfonate complex grease was studied from the aspects of synergism and surface modification.The main research contents of this paper are:（1）The synergistic effect of nano-boron nitride and nano-Al2O3 on the tribology and vibration suppression of lubricating grease was studied.Hexagonal boron nitride and nano-Al2O3 were added into the complex calcium sulfonate grease with different mass ratios.The size morphology of the two nanoparticles and the internal structure of the grease thickener were observed by scanning electron microscopy.Through four ball test,studied the different quality than the tribological properties of nano-grease.For discussing their synergy mechanism in grease performance test,the scanning electron microscope observation of two kinds of nano-materials in the lubricant thickener structure distribution,the distribution of elements on worn surface of steel ball was analyzed by energy dispersive spectrometer（EDS）.The vibration signal of bearing was detected by BVT-1A bearing vibrometer,which was used to evaluate the vibration suppression performance of bearing mixed with nanomaterial grease with different mass proportions under the condition of limited lubricant supply.The model of the synergistic vibration reduction mechanism of two kinds of nanoparticles in oil film was established.In addition,the base oil spreading wetting experiment was carried out.The results show that nanoparticles can promote the backflow of base oil in the bearing raceway to improve the utilization rate of lubricating oil,so as to effectively suppress vibration.（2）In order to further enhance the tribological performance of nano-hexagonal boron nitride for complex calcium sulfonate grease,two methods were used to modify the surface of nano-boron nitride.Hydroxyl and tert-butyl oxygen groups were grafted on the surface of nano-hexagonal boron nitride by hydrothermal method in order to improve its agglomeration and poor oil solubility.The components were characterized by SEM,FTIR and Raman spectra.The tribological properties of nano-greases with different surface modification methods were evaluated by four-ball friction and wear experiments and dispersive experiments,and the antifriction mechanism of nano-hexagonal boron nitride after different modification was discussed by EDS analysis on the surface of steel balls.The experimental results show that the tribological properties of hydroxylated nano-hexagonal boron nitride as an additive are significantly improved,which is more conducive to reducing the agglomeration of nanoparticles and promoting the formation of a protective film at the frictional interface. |
PDF Full Text Request