Tribological And Rheological Properties Of Base Lubricant Esters

This research originated from the projects funded by State Key Laboratory of Mechanical Transmissions at Chongqing University,entitled "Typical Rolling and Sliding Contact Failure and Material Change Basis" and "Interface Mechanics Analysis and Research of Transmission Components." Mechanical transmissions involve numerous complex tribology and lubrication problems.Good lubrication could effectively reduce friction,wear,noise,and vibration,and prevent corrosion as well,but improper lubrication could lead to premature damage of transmission parts.Tribology research bears a great theoretical and engineering significance by means of exploring tribological properties of lubricants,understanding the film-forming ability of oils under a wide range of working conditions,and analyzing the relationship between lubricant rheological properties and lubrication states.This study focus on the tribological and rheological properties of nine base ester lubricants,their lubrication ability in terms of oil film thickness,friction,and rheological behaviors under different working conditions,and on the relationship between the physical-rheological properties of the esters and the characteristics of their molecular structures.The results of this study will help enrich the knowledge basis and methodology for the selection of industrial base esters and further development of new type of lubricants.The main research includes:1)Nine base ester samples were studied for their tensile and rotational rheology experimentally.The tensile forces of the samples were investigated to understand the behaviors of the ester molecules during stretching as a measure of their inter-molecular shear and integrity.Considering about their molecular structures,ester samples with the benzene ring structure can sustain greater tensile forces,those with branch structures show tensile force dependence on branches,and those with straight chain esters demonstrated relatively small tensile forces.Meanwhile,the influence of molecular structures outweigh their molecular weights.The tensile force measurement results were also correlated with the friction coefficients measured in a group of ball-on-disk tests;samples with higher tensile forces maintained smaller coefficients of friction and better tribological performance.Rotational rheological tests were conducted on various samples with an improved experimental method for better understand the rheological property of ester under extreme shear rate.2)Tribological experiments were carried out on the ester samples by using the TFM-150 elastohydrodynamic lubrication(EHL)instrument,for the understating of their lubrication ability under the influences of load,speed,and temperature,and the variation of friction coefficient with sliding-to-rolling ratio,as well as the effects of non-Newtonian fluid properties and the viscoelasticity on the friction.The film results under high speeds were analyzed by a linear fitting,and the results indicated that the ester with a smaller viscosity had a higher speed index.The relationship among viscosity,limiting shear stress,and maximum friction coefficient under various conditions were explored.An isothermal elasto-hydrodynamic lubrication(EHL)model in point contact was used to simulate the lubrication interfaces under the experimental conditions.3)The influences of trace water and anti-wear addictive on the tribological and rheological behaviors of the ester samples were studied.The results show that a certain content of water in ester samples tends to increase shear viscosity and film thickness at low-speed conditions;however,the film is not stable in the high-speed stage.The addition of the anti-wear addictive shows no obvious influence on the limiting shear stresses of the lubricants,but it helps decrease friction under certain conditions and reduce wear of the specimens under lubrication.