Research On Tribological Performance Of Environmentally Friendly Water-based Lubricants

As the increasing of oil depletion, energy crisis, environmental pollution, water isexpected to replace oil to use in modern field of lubrication. Water-based lubricant hasbecome an important research direction in the tribology research，because of itsadvantages of low cost, convenient storage and transportation, not burning. However,the additives are always need to water-based lubricants to overcome their disadvantages,such as poor lubricity and corrosion resistance, Recently, more and more studies havefound that water soluble polymer, when added into water, not only can effectivelyimprove the viscosity of water by forming thick lubricating films, but also can stop thecontact between the metal in sliding contact by adsorption on the surface. Therefore thetribological properties of water-based lubricant could be effectively improved.On the other hand, with the rise of the ocean development in recent years, moreand more people get the attention of seawater environment material tribologyperformance. Sea water is a variety of the balanced salt solution. When the water-basedlubricants are used in sea water, inorganic salt ions is inevitable mixed with lubricants.Existing studies have found that inorganic salt ions, especially anion, can greatlyinfluence the solubility of water-soluble polymer in water and change the adsorption ofthe polymer in surface, which in the end affect its tribological properties. However, thetribological research of water soluble lubricant in presence of inorganic salt ions is notwell reported before.Therefore, in this thesis, we try to use common polysaccharide compounds innature (pullulan polysaccharides, pectin) and glycerol as water-soluble antifriction andantiwear additive. We systematically study anti-wear characteristics of water-basedlubricant under various lubrication conditions. At the same time, the effect of inorganicions on the tribological performance was investigated, and the friction mechanism wasanalyzed. The results are expected to provide some reference for environmental friendlywater-based lubricants. Experiment has made some progress and the results are as follows.（1） Pullulan polysaccharides (PU) not only can have a good anti-friction andanti-wear effect on bearing steel-45#steel friction pair, but also effective for bearingsteel-stainless steel. Adding PU to water improved the lubrication performance of thewater. The friction-reducing effect is better with the increasing of concentration of PU,In the process of friction effective boundary lubrication film is formed in contact area,thus greatly reduced the friction coefficient. The tribological performance of PU, inwater is obvious changed when anionic ions is added. Where F ions promotedlubricating property of pullulan polysaccharides, Cl ions have little effects. On thecontrary, NO3ions inhibited lubricating property of pullulan polysaccharides.Hofmeister series could explain how species of anionic to affect the lubricating propertyof pullulan polysaccharide aqueous solution.（2）Experiments found that the pectin (PE) in water solution has excellentlubrication performance on steel. In the process of friction, PE can adsorb on the surfacethrough the carboxyl to form lubrication layer, which reduces the friction. Frictioncoefficient decline with the increasing load. Salt ions have different effects on thetribological properties of pectin solution by influencing pectin’s adsorption on the steelsurface.(3) The tribological properties of the glycerol aqueous solution in steel-steelsteel-copper and steel-aluminum friction pairs are investigated. The experimental resultsshow that the glycerol solution can be used as effective lubricant for above three frictionpairs with different lubrication mechanism. In steel-steel contact, the lubrication layerformation in surface play an important role in reducing friction. In steel-copper contact,the presence of glycerol promotes the transfer of the copper to the steel surface.However, in steel-aluminum contact, because of high chemical reactive of aluminum,chemical wear is the main mechanism.In the end, three kinds of water-based lubricant are tested for improvement of water.Lubrication mechanism of aqueous solution is explored. The experimental results are expected to support for the further exploration of the environmentally friendlywater-based lubricants.