A Study On The Low-speed Tribological Performance Of Port Plates In Axial Piston Pumps

Axial piston pumps are the core of power component in hydraulic system.They have many advantages,such as compact structure,high power density,easy to control variable,and so on.They are widely used in aerospace,engineering machinery,ship and marine engineering.The pair of port plates and cylinder barrels is one of the three friction pairs which are subjected to wear and failure in the axial piston pumps.Particularly under the low-speed conditions,a complete oil film can hardly be developed.Thus port plates are at the boundary lubrication,in which oil film is continuously formed and destroyed.The boundary lubrication condition directly affects the efficiency and start-up reliability.Therefore,it is crucial to study the lubrication characteristics and the friction and wear behaviors of port plates in axial piston pumps,which has important engineering and practical significance to further improve their efficiency,reliability and life.The surface morphology refers to the geometric features and properties of the surface of friction pair.Research shows that surface morphology plays an important effect on friction,wear and lubrication in mixed lubrication and other conditions.Selective laser melting is one of the typical additive manufacturing technology which can quickly form any structure of parts,providing an efficient way for the manufacture of complex structural products.Moreover,the technology can promote innovative product design,particularly for single,small batch production of hydraulic components to meet the future of individual hydraulic components.In this paper,a method of experimental research was used,simulating the working conditions of the port plates in axial piston pumps with some simplifications.The experiment is carried out on the oil-lubricated friction and wear test bench.The effects of surface morphology,SLM,working conditions and materials on the friction and wear characteristics of port plates were studied.The coefficient of friction,wear rate,temperature,microstructure,X-ray diffraction pattern and surface/cross-sectional morphology were used as the main evaluation indexes.The main results of this paper are as follows:1.The polished specimens have the lowest coefficient of friction and wear rate.Only a slight abrasive wear occurs during the test.Particles don't adhere to the upper specimens.A lot of small of brass particles are adhered to the fine grinding specimens,resulting in a high coefficient of friction.A large amount of particles accumulate on the surface of the coarse grinding specimens,which resulted in high wear rate,However,the coefficient of friction was lower because of the formation of micro-EHL in some local spots.A large number of particles are accumulated in the micro dimples of the textured surfaces,which have higher friction coefficient and wear rate.2.The microstructure of SLM samples is characterized by melting pools,pores and fine grains.After heat treatment,the melting pools disappear and the hardness increased.The heat treated SLM sample have slightly lower friction and wear than the TP samples when in contact with brass.When the SLM/TP 316L samples come in contact with hard material,the difference in friction and wear is noticeable.However,the heat-treated SLM TC4 had a lower friction coefficient and wear rate than TP TC4.The fine grain structure of SLM samples had a great influence on its tribological performance.The extent of plastic deformation and the formation of oxide layer positively prevents the crack formation and the material spalling.3.The coefficient of friction increases with increased speed to a maximum value(70 rpm)and then the coefficient of friction decreases with further increased speed.The temperature and wear increases with increased rotational speed.However,the wear rate does not change much.In addition,with the increase of rotating speed,the diameter of the spheroidized hole on the surface of the specimen becomes larger.Therefore,the oil storage capability and the reduction of wear debris caused abrasion starts to affect.Moreover,an oxide layer also appears,all of which are beneficial to friction reduction.