Experimental Investigation Of Lubrication Replenishment Based On Different Directions Of Surface Motion

The present works focus on the experimental investigations into the inlet lubricant replenishment under different directions of surface motion.In practical engineering,mechanical parts are subjected to starvation due to insufficient replenishment of lubricants under high speed,high viscosity or limited lubricant supply conditions.Although starvation and replenishment issues have been extensively studied,some underlying replenishment mechanisms are still not explored,e.g.,the gyroscopic effect of the angular contact ball bearings and the meshing process of the hypoid and the helical gears.Under such conditions,the inlet conditions of lubricated contact are significantly different with those of traditional lubrication.Using a ball-on-disc optical apparatus,the replenishment behaviors of the lubricant and the evolution characteristics of the lubricant film were experimentally investigated under different angles between the surface velocities.The main contents cover:(1)Experimental observations of the lubricating properties of the base oil under the condition of different surface velocity directions.Under fully flooded and minimal oil supplying conditions,the effects of entrainment speed,surface velocity angle and base oil viscosity on inlet reservoir and lubricant film thickness were investigated.It was found that the film thickness decreased with the increase of the angle under the fully flooded.In the case of minimal oil supply conditions,once a surface angle was supposed,a remarkable inlet oil reservoir appeared and the film thickness rose consequently.(2)Experimental observations of the film evolutions of the composite lithium-based grease with same thickener but different base oil viscosities.The effects of entrainment speed,surface velocity angle and base oil viscosity on inlet oil reservoir and lubricant film thickness were compared.Two typical features of contacts were recognized: inlet oil reservoir formation and asymmetrical film shapes,which were different from traditional observations of grease lubrications.The film thickness and lubricating duration were significantly enhanced due to the presence of an inlet oil reservoir.The crossed lubrication tracks on two surfaces facilitated the lubricant replenishment,which was the main mechanism of inlet oil reservoir formation.(3)Experimental observations of the film evolutions of the composite lithium-based grease with the same base oil viscosity but different consistency.The effects of entrainment speed,surface velocity angle and consistency on the inlet oil reservoir and lubricant film thickness were compared.It was found that the optimum oil supply angles were 60° and 120°,which meant the lowest degree of starvation and the longest film thickness durations.The results showed that the higher the consistency of the grease,the higher thickness of the film,whilst starvations where prone to take place.(4)Experimental observations of the effects of the entrainment speed and the sliding speed on grease films.It was found that both the film shape and the inlet oil reservoirs were different the observations of former chapters.In the cases that the ball speeds were higher than those of the disc speeds,starvations were prone to occur.The starvation degree increased with the increase in the difference between the ball and the disk speed.Further research is required under such conditions.The present work confirms that angled surface motion is an efficient mechanism of lubricant replenishment.It is indicated that the limitations of traditional inlet boundary conditions in angle surface motions.The inlet supply conditions observed in this thesis should be considered in the starved contacts of hypoid and the helical gears.