Effect Of Several Additives On The Contact Fatigue Life Of Friction Pair Lubricated With Oil,Water

Today many different types of load carrying additives are used in lubricantformulations for friction and wear reducing, higher machine efficiency and prolongedlife. However, very few additives can be used to tackle fatigue problem as the usefullife of rolling elements is limited by contact fatigue and there is no sample solution.Fatigue is a surface phenomenon. Pulsating and alternating stresses will lead to afatigue of metal material fallowed by pitting. Although a limited work has beencarried out to assess the proneness of lubricants and additives to cause acceleratedrolling contact fatigue failure and the reports on the effect of most load-carryingadditives are often contradictory.In this study certain oiliness and antiwear agents used as antifatigue additivesboth in an oil and in water have been tested on a fixed speed rolling ball-on-rodmachine and a varied speed sliding ball-on-desk machine for their antifatigueeffectiveness. The preliminary results in rolling fatigue tests indicated that ZDDP andMoDTP as well as ethanolamine salts of fatty acids(ESFA) have beneficial effect onantifatigue performance of lubricating oil and water. The former has been found to beable to increase fatigue life of white oil significantly and the later is the most effectiveantifatigue agent in case of water-in-oil emulsion. Additive complex EMC-214containing ESFA, thioester and tricresyl phosphate(TCP) are less effective ascompared with ESFA and there is a continuous trend towards longer life withincreasing additive concentration over the range studied. Other additives studied ,including synthesized organic esters, NaDTC, sorbitan oleate(Span-80), TCP, aminesalt of dialkyldithiophosphate(T307), condensed compound of dialkyl dithiophosphate,formaldehyde and amine (T305), and dialkyl dithiocarbamate(T323) have adetrimental effect or little influence on the rolling fatigue life of what oil or water.Surface treatment technology allows improved functioning of machinecomponents with respects to friction, wear and fatigue resistance. Observation ofscanning electron micrographs of the worn ball surfaces obtained in a step loadingfriction test carried out on the sliding ball-on-desk machine reveals that the wearmechanisms in the ball-on-desk test are dominated by a contact fatigue denudation.Combination of two treatments i.e sulphidization of test specimens and application ofphosphorus additives in base oil are found to exhibit synergistic effects compared tothe performance of individual one. During the test the friction of MoDTP decreasesrapidly until it reaches a minimum value and is the most effective friction and wearreducing agent. The significant extension of fatigue life by using these antirust andfriction-reducing agents probably can be related to the combined effect on inhibitionof water corrosion and crack growth of fatigue in steel.