Study On Tribological Properties Of Impregnated Graphite Pairing With Nitriding Steel

Mechanical seal has many advantages,such as good sealing performance,high reliability,long life and so on.It has been widely used in the aviation hydraulic plunger pump.The current aviation hydraulic piston pump is required to be able to work stably in high pressure,high speed,high temperature and high acceleration and other harsh conditions for a long time.So the hydraulic pump must have a reliable shaft seal to prevent the leakage of the hydraulic medium.Therefore,the selection of the friction material has become a key problem.It is of great theoretical value and engineering significance to investigation into friction and wear behaviors of impregnated graphite seal materials.In this paper,the friction and wear tests of the graphite and nitride steel(38CrMoAlA)pairs were carried out by pin-disk friction method by using the UMT-3 tester under the multi load dry grinding condition and the hydraulic oil lubrication condition.The mechanism of friction and wear is analyzed and explored,and the reasons for the difference in properties between different materials are revealed.Then we put forward some suggestions for the optimization of graphite materials.The study shows that the physical and mechanical properties of the metal impregnated graphite are generally better than resin impregnated graphite.The good structure is helpful to enhance the bearing capacity and wear resistance of the material.In coMParison,the transfer layer formed by resin impregnated graphite(K1)on the grinding pair is more complete and smooth,and has good lubrication effect.The friction coefficient is the lowest,but the stability of the transfer layer is generally poor,so the wear rate is high.The strength of the graphite transfer layer formed by the mixture of metal and graphite is high.So the impregnated metal graphite(D1,P3)have good wear resistance.The transfer layer formed by pure carbon graphite(Z1)is thicker and unstable,easily destroyed and solved,so its friction performance is poor.The proper increase of load can promote the formation of the transfer lubricating layer and reduce the friction coefficient.However,excessive load will cause damage to the graphite transfer layer,increasing the rate of desorption and exfoliating of the transfer layer,and resulting in the increase of wear rate.Continuous drip lubrication can ensure the friction surface is in a good fluid lubrication state,and the direct contact between the micro convex body and the graphite pin surface is avoided,so that the friction pairs exhibit good tribological properties.The friction pair is in the the starved lubrication state when it in the immersion lubrication condition,The friction coefficient is also periodic,and the wear rate of the graphite pin is larger.