Effect Of Anti-wear And Friction-reducing Additives On The Friction And Wear Performance Of Lithium Greases

In the modern industrial production system,the problem of friction and wear becomes more and more prominent,so it is particularly important to reduce friction and wear.Lubricants improve the lubrication performance of grease,which is of great significance to save energy and improve machine efficiency.As a part of lithium lubricating grease,lubricating additives play a very important role in improving the antifriction and antiwear performance of lithium lubricating grease.In this thesis,nine types of lithium greases without additives,single types of anti-wear additives ZDDP,PB and friction modifiers BTA and Mo DDP,and compound types of additives ZDDP+BTA,PB+BTA and ZDDP+Mo DDP,PB+Mo DDP were systematically investigated to examine the effects of different types of additives on the friction reduction performance and anti-wear performance of lithium greases.The antifriction and antiwear mechanism of typical additives on lithium grease was studied.The friction reduction performance of the above nine types of lithium greases was investigated by using the SRV micro-vibration friction and wear tester.The friction surface morphology was characterized and analyzed using a super depth of field optical microscope and a three-dimensional optical profiler,and the anti-wear performance under different lubrication methods was compared.The anti-wear additive PB has good anti-wear performance and the friction modifier Mo DDP has good friction reduction performance.The two additives are compounded to obtain compound additive PB+Mo DDP,which has a good synergistic effect in lithium grease and can significantly improve the friction reduction and anti-wear performance of lithium grease,effectively eliminating the high friction phenomenon between the two friction surfaces during transient start,and make the lithium grease have excellent extreme pressure performance and strong ability to bear impact load.The friction reduction and anti-wear mechanism of typical additives,anti-wear additive PB,friction modifiers Mo DDP,compound additive PB+Mo DDP lithium greases were analyzed by X-ray photoelectron spectroscopy（XPS）.Under the action of friction heat,the active B atoms in PB particles infiltrate into the friction surface to form a lubricating film of boron compounds.The smaller the particle size of PB is,the easier it is to adsorb on the friction surface to form a more dense lubricating protective film,and improve the anti-wear performance of lithium grease.Under the action of friction heat,Mo DDP decomposes and reacts with the metal surface to form a chemical friction film composed of Mo S₂and phosphate.Phosphate film reduces direct contact between metals and has good wear resistance.The lamellar molybdenum disulfide is easy to cause the sliding of the two contact surfaces and has good antifriction properties.PB+Mo DDP combines the anti-wear performance of anti-wear additive PB and the friction modifier Mo DDP,with excellent synergistic effect,to improve the friction reduction and anti-wear performance of the lithium grease complex system.Rheology is the study of the elastic and viscous behavior of soft materials.Apparent viscosity represents the internal resistance to flow and is used to describe the internal friction of the lithium grease as it flows.The strain scan contains the relationship between the variation of the energy storage modulus and the loss modulus.The compound additive PB+Mo DDP has the best flow performance.