| In order to satisfy the requirement of the stable and reliable output force of the switch machine,it's necessary to develop the friction materials used in the reducer and select the friction materials suitable for the working conditions of the switch machine,which is of great significance to improve the reliability and safety of the switch machine.In order to solve the problems of low friction stability and high friction rate of ZD6 switch machine friction belt in low temperature and high humidity environment,resin base friction material and powder metallurgy friction material were prepared by using molding method and powder metallurgy technology respectively.The mechanical properties,friction and wear properties and microstructure of the prepared friction materials were analyzed by universal mechanical testing machine,friction and wear testing machine,impact testing machine,hardness tester,scanning electron microscope(SEM)and energy dispersive spectrometer(EDS).The results indicate that:(1)The cashew shell oil modified phenolic resin(PF6224)based friction material has higher density,compression strength and impact strength,high stability of friction coefficient and low wear rate,and is a candidate material for the friction belt of ZD6 switch machine.(2)The friction coefficient of cashew shell oil modified phenolic resin based friction material in dry environment is between 0.28-0.39,the stability of friction coefficient is between 0.96-0.97,and the wear rate is1.0×10-7g·N-1·m-1.In wet environment its friction coefficient is between0.28-0.39,the stability of friction coefficient is between 0.97-0.98,and the wear rate is 1.5×10-7g·N-1·m-1.(3)The friction material with cashew shell oil modified phenolic resin as the matrix has shallow furrow in the braking process,no large area falling off phenomenon,and a smooth and uniform friction film is formed on the friction surface.The wear mechanism of the resin-based friction materials using PF6224 and NBR modified phenolic resin(F5170)is abrasive wear and slight fatigue wear.The wear mechanism of resin-based friction materials with boron modified phenolic resin(BPF),low polymerization rate unmodified phenolic resin(PF6816)and high polymerization rate unmodified phenolic resin(F2122)as matrix is abrasive wear and serious fatigue wear,and cracks and pits appear on the friction surface.(4)L9(34)orthogonal test table was used to conduct orthogonal test,and the preparation process of resin-based friction material was optimized by range analysis,it was found that among the three factors,pressing pressure has a great influence on the properties of resin-based friction material.When the pressing pressure is 250.0 kgf/cm2,the holding time is10 min,and the heat treatment temperature is 180?,the ZD6 switch machine resin-based friction material using PF6224 as the matrix has the best performance.(5)The properties of ZD6 switch machine powder metallurgy friction materials with different friction property regulators are good.Among them,the powder metallurgy friction material with artificial graphite as the friction property regulator has the highest compressive strength,impact strength and tensile strength,and the comprehensive performance is the best.The friction coefficient in dry environment is between 0.36-0.37,the stability of friction coefficient is between0.94-0.95,and the wear rate is 2.3×10-7g·N-1·m-1.In wet environment its friction coefficient is between 0.35-0.37,the stability of friction coefficient is between 0.93-0.94,and the wear rate is 2.2×10-7g·N-1·m-1.(6)A layer of graphite film will be formed on the friction surface of the powder metallurgy friction material with artificial graphite as the friction property regulator in the braking process,which can not only play a role in lubrication,but also play a role in filling cracks and pores on the surface of the friction material.It can also improve the friction and wear performance,reduce friction surface furrow marks.Its wear mechanism is abrasive wear.The friction surface of powder metallurgy friction materials with high carbon ferrochrome,carbon fiber powder,amorphous graphite and silicon carbide particles have obvious furrow marks and flake peeling phenomenon.The wear mechanism are abrasive wear and delamination wear.(7)When the pressing pressure is 5000 kgf/cm2,the bonding strength between the particles of ZD6 switch machine powder metallurgy friction material with artificial graphite as the friction property regulator is higher,while leaving a certain amount of porosity,so that the gas can be discharged smoothly during sintering,resulting in finer and more uniform grains,with the best performance.(8)The ZD6 switch machine resin-based friction belt and powder metallurgy friction belt developed in this experiment has stable forward and reverse friction currents in actual use conditions and has a smaller fluctuation than the existing friction belt,which proves that it has good friction coefficient stabilities and high practical value. |
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