Experimental Study On The Effect Of Laser Textured Oil-Collecting Surface On Non-Conformal Contact Lubrication Properties

The normal operation of mechanical equipment cannot be separated from good lubrication condition.Lubricants are often used in industry to form lubricating oil film to separate the surface of contact pair.However,mechanical parts operating under harsh conditions are often in the state of dry lubrication due to the difficulty in timely supply or insufficient supply of lubricants.The direct contact of friction pair aggravates the friction and wear,and endangers the safe operation of mechanical device.Improving lubrication efficiency and reducing friction are effective measures to ensure the normal operation of mechanical equipment and improve the service life.Due to the advantages of less environmental pollution and high resource utilization,the lubrication with limited oil supply has aroused widespread concern of tribology scholars in recent decades.Improving the lubricant utilization efficiency and ensuring the lubricant supply of contact pairs is the purpose of limited lubrication.The preparation of surface texture on the contact pair has been shown to be functional in improving the tribological properties of contact pair,which can play a role in improving the lubrication state under different lubrication conditions.On the other side,texture array on the surface of contact pair can also affect the surface wettability and promote the replenishment performance of the lubricant on surface.In this paper,the influence of surface texture on the point contact friction performance was studied.At the same time,the surface with oil gathering capacity was machined by combining low surface energy coating and micro-texture array.(1)Micro dimple texture with different parameters was machined on the surface of steel balls using a picosecond laser to explore the effect of micro dimple texture on the lubricating properties of point contact.The film thickness and film thickness profiles of lubricating oil film under different working conditions were measured.This showed that dimple affected the pressure distribution in the contact area,and in turn affected the local film thickness distribution.The phenomenon of local film thickness increasing occurred under pure sliding conditions between the dimple and outlet of the contact region,while film thickness reduction region formed from the dimple to the entrance of the contact area and both sides of the dimple edge.Velocity and applied load potentially affect the film thickness distribution as well.The film thickness increasing region became larger while the film reduction area became smaller with increasing sliding velocity.The increase in load results in a negative effect on the increase of film thickness.(2)A lubrication enhancement surface with oil capture capacity is prepared through the formation of stepped wettability gradient,which is generated between the antifingerprint coating(AFC)modified micropillar arrays(MA)on both sides of the central lipophilic lubricating track.The film thickness and shape of the oil pool on this machined surface under reciprocating motion were measured on a ball-on-disc test rig with limited oil supply.The effects of reciprocating frequency,width of lubricating track and load on the lubrication properties were investigated.Meanwhile,the lubricating properties of micro-pillar array surface without AFC modification and the surface only modified with AFC were compared.The results showed that the state of oil droplet on prepared AFCmodified micropillar array surface changes from Wenzel state to Cassie-Baxter state,thus it represents a stronger oleophobic property and the lubricant oil gets restrain in lubricating track.Compared with the other two oil gathering surfaces,the micro-pillar array surface has a better lubrication characteristic.Through increasing the replenishment speed of lubricants on both sides of lubricating track,the oil supply at the middle point of reciprocating stroke and two extreme points is obviously improved under the reciprocating motion,and the lubrication state gets improved with a higher film thickness.The measured central film thickness increased by up to 51.4 % compared with the smooth surface.Oil gathering capacity can be affected by the width of lubricating track in the experiments.It becomes strongest when the central track width is close to the Hertz contact region width.With the increase of the track width,the lubricant distribution on both sides of lubricant track becomes more dispersed,and the lubricating oil requires a longer reflux time,resulting in the weakening in the oil gathering capacity of micro-pillar array surface.The attached load has a significant effect on oil gathering capacity of this new surface.The increase in load enhances mechanical separation of lubricant and weakens the capillary reflux effect,resulting in the decrease of the oil gathering capacity and film thickness.(3)The AFC-modified micropillar arrays are prepared on the surface of steel block,and the reciprocating friction and wear experiments are carried out to explore the tribological properties under limited lubrication conditions and the effect of micropillar arrays on the improvement of friction properties under different working conditions.The results show that the surface with micropillar arrays can accelerate the replenishment speed of the lubricant and significantly decrease the friction coefficient.With the increase of reciprocating frequency,load and width of lipophilic track,the wear reduction capacity of surface with micropillar arrays decreases,which corresponds to the film thickness experimental results in Chapter 4.However,although the friction coefficients do not differ significantly,the textured samples can still effectively reduce the depth and width of the wear scar.