Experimental Investigation On Performance Of Grease For High-speed Railway Axleboxes Bearings

High-speed railway axleboxes bearings are lubricated by using lubricating grease.The reliability and life of axleboxes bearings are affected by the performance oflubricating grease. Due to nanoparticles exhibit excellent chemical and physicalproperties, the extreme pressure and antiwear performance of nano-grease can beimproved by using nanoparticles as additive. The lubricating state of high-speed railwayaxleboxes bearings can be significantly improved by using nano-grease as lubricantion.Nano-graese was synthetized in this dissertation, base grease and additive of which aredomestic grease for high-speed railway axleboxes bearings and WS₂and Si₃N₄nanoparticles. The experimental research of tribological performance of nano-greaseand lubricating mechanism of nanoparticles were carried out.Effects of ultrasonic power, ultrasonic frequency and water-tank temperature onhomodisperse of nanoparticles in base grease were investigated by using factorialexperiment. The perfect preparation process of nano-grease was determined. Effects ofWS₂and Si₃N₄nanoparticles on extreme pressure and antiwear and friction propertiesof nano-grease were investigated. The results showed that with the increasing ofnanoparticles additive, the PBvalue of grease increased first, and decresed later.Meanwhile the friction coefficient and wear scar diameter of ball decresed first, andincreased later, with the increasing of nanoparticles additive.Effects of the complex nanoparticles of WS₂and Si₃N₄on lubricating propertiesof nano-grease were investigated by using the double factors variance analysis. Theresults showed that effects of both nanoparticles on lubricating properties of nano-grease were marked, and the interaction of both nanoparticles is highly significant. Theoptimal lubricating properties of one of synthetic nano-greases is obtained, the PBvalue reach128kg, increasing by36.2%relative to base grease. The friction coefficientof nano-grease reduce to0.06512, reducing by21.2%relative to base grease, and the wear scar diameter of ball reduce to0.441mm, reducing by20.5%relative to the basegrease.The surface morphology and element distribution of ball were analyzed by theScanning Electron Microscope（SEM） and the Energy Dispersive Spectroscopy（EDS）. Itwas found that the lubricating mechanisms of WS₂nanoparticles were the self-repairperformance and the thin film lubrication performance, the lubricating mechanism ofSi₃N₄nanoparticles are the self-repair performance and the analogy-ball bearingperformance, the lubricating mechanism of the complex nanoparticles of WS₂and Si₃N₄is the synergism of the three performances.The optimal performance of nano-grease have been obtained through experimentalresearch in this dissertation, and the lubrication performance of the nano-grease meetthe EN12081standard. It apply to high-speed railway axleboxes bearings.This researchwill be scientific guiding significance for the development of grease with excellentlubrication performance.