Study On The Tribological Performance And Wear Behaviours Of GF/PTFE Piston Ring Mating With Nitrided Cylinder Liner

The Stirling engine is a piston engine that can use most energy as a heat source(for example: biomass,fossil fuel,solar energy,etc.).It uses the heat source to heat the working fluid gas to expand it to push the piston to move and perform work.Based on the wide applicability of Stirling engine energy,the use of Stirling engine to convert heat energy into kinetic energy has attracted attention in many fields.Like other piston engines,the piston ring-cylinder liner of the Stirling engine is the key movement pair,and the quality of its seal has a vital impact on the performance of the whole machine.However,unlike internal combustion engines,the piston ring-cylinder liner of the Stirling engine works under dry friction conditions,and the self-lubricating glass fiber reinforced polytetrafluoroethylene composite material is often used as the piston ring material.In the actual machine,it is found that the wear matching between the piston ring and the cylinder liner is insufficient,and the piston ring wears a lot,which causes the sealing performance to decrease,and then the engine power decreases.Therefore,it is necessary to carry out the research on the friction and wear matching and related mechanism of the movement pair,so as to provide experimental and theoretical basis for improving the performance and forward design and manufacturing capacity of the piston ring and cylinder liner movement pair for Stirling engine.This article first studied the effect of surface nitriding process on the friction and wear performance of ion-nitrided stainless steel cylinder liner-glass fiber filled PTFE piston ring(GF/PTFE piston ring)pair;then used intermittent wear test to study GF/PTFE piston ring at different wear distances,the amount of wear when rubbing against duplex stainless steel nitrided cylinder liners and the change of the friction transfer film on the surface of the cylinder liner;finally,for the GF/PTFE piston ring-nitriding cylinder liner pair with excellent wear resistance,The effect of temperature on the friction and wear performance and wear mechanism of the pair is studied,and the results show that:1.Compared with the high temperature ion nitriding cylinder liner,the low temperature ion nitriding cylinder liner and the GF/PTFE piston ring have better tribological performance(low friction,low wear).Compared with the surface honing and polishing of the cylinder liner The tribological performance(low friction,low wear)when paired with GF/PTFE piston ring is better;the surface hardness of the cylinder liner has no direct effect on the wear of GF/PTFE piston ring and the friction of the friction pair;2.The wear change of GF/PTFE piston ring and nitrided cylinder liner can be divided into three stages: running-in period,transition period and steady-state wear period.During the running-in period,the wear rate of the piston ring drops rapidly,and the surface of the cylinder liner is polished to appear bright areas;in the transition period,the wear rate of the piston ring slowly decreases,and a strip-shaped transfer film appears on the surface of the cylinder liner;in the steady-state wear period,The wear rate of the piston ring stabilizes at a low wear rate with small fluctuations,and the strip transfer film on the surface of the cylinder liner is gradually connected into pieces;the friction transfer film on the surface of the high temperature ion nitriding and low temperature ion nitriding cylinder liner The different coverage area is one of the reasons affecting the friction and wear performance;3.At different temperatures,the friction coefficient of GF/PTFE piston ring and nitrided cylinder liner increases first and then becomes stable with the increase of the wear distance,but the wear rate and wear distance show an opposite trend.In addition,in the stable wear period,the friction coefficient and wear rate both increase with the increase of temperature.The wear evolution process of GF/PTFE piston ring can be summarized as: in the running-in stage,the direct contact between PTFE and the cylinder liner leads to a higher wear rate.After the top layer of PTFE is removed,the internal glass fibers begin to be exposed and become the main load-bearing phase,causing the wear rate to drop sharply.At lower temperatures,as the wear distance increases,the wear rate of GF/PTFE piston rings gradually stabilizes.As the temperature rises,the softening of the PTFE matrix leads to the shedding of glass fibers,which brings new wear behaviors,including: three-body abrasive wear,PTFE matrix flakes,scratches and renewal of the transfer film on the surface of the cylinder liner.Forming and filling of large-sized PTFE grooves.In the stable wear stage,the main wear behavior of the GF/PTFE piston ring surface at different times is different,but the wear behaviors are alternated with these types of wear behaviors,so the wear rate presents a dynamic and stable phenomenon,making the wear rate of the piston ring slightly fluctuation at 200 ℃.