Preparation And Performance Of Friction Materials For Railway Brake Shoe Based On Inorganic Binder

With the rapid development of economy,the running speed of China’s railway locomotive is gradually increasing,the load is increasing,and the running condition of locomotive and rolling stock is becoming more and more difficult.The brake shoe friction material plays a vital role in the safety and reliability of railway locomotive and rolling stock braking.At present,synthetic brake shoe and wheel friction are mainly used in railway vehicles to realize tread braking.In the process of braking,the composite brake shoe is not resistant to high temperature.In the emergency braking,the friction coefficient often decreases sharply,which is easy to cause heat recession and wear rate increases sharply,causing major hidden danger to the safety of railway transportation.If the powder metallurgy materials or C/C composites with better performance are used,the operating cost will be increased a lot.Therefore,it is urgent for railway departments to develop and study a new friction material with stable friction performance,good heat decay resistance,simple preparation process and low cost.In this dissertation,it is analyzed that the root cause of heat decay in synthetic brake shoe is the poor high temperature resistance of resin binder.Therefore,the inorganic binder was prepared by alkali activation of slag and sodium silicate.Then,a new type of high temperature resistant inorganic binder based friction material for train brake shoe was prepared by hot pressing method by adding reinforcing material,filling material and friction modifier.The mechanical properties and friction properties of friction materials were studied by using AG-10 universal testing machine,constant speed friction testing machine,scanning electron microscope（SEM）and X-ray diffraction（XRD）.Through the combination of theory and experiment,the following conclusions are drawn.（1）The slag cementing material formed by the excitation of slag and sodium silicate is used as the inorganic binder matrix,and steel fiber is the performance-enhancing fiber.A dry pressing process is used to prepare an inorganic binder sample.When the ratio of slag to sodium silicate is 3.5:1,the compressive strength of the inorganic binder is 24.15 MPa,the flexural strength is 19.15 MPa,and the mechanical properties of the inorganic binder are the best.（2）The use of steel fiber as a reinforcing material can significantly improve the mechanical properties of the inorganic binder.The results show that when the content of steel fiber in the inorganic binder is 3%,the performance is the best,the compressive strength is 118.25 MPa,the flexural strength is 35.75 MPa,and the impact toughness is 0.35 J/cm².Compared with the performance of samples without steel fiber,the compressive strength,flexural strength and impact toughness are increased by 400%,95%and 130%,respectively.（3）Using the hot pressing production process,the inorganic binder-based friction material is prepared under the conditions of molding temperature of 140℃,molding pressure of 50MPa,holding time of 15 min,and curing time of 7 d.The performance is optimal.The friction and wear test is carried out by cyclic friction at 0～350℃.The friction coefficient is between0.37 and 0.45.There is no thermal decay phenomenon during the whole wear process.（4）When the content of graphite is 6%,the graphite added can form a continuous and dense film on the friction contact surface,which has a good lubricating effect,and the wear rate is from 3.74×10^-7 cm³/（N·M）is reduced to 0.56×10^-7 cm³/（N·m）,the friction coefficient is 0.42±0.01,and the friction material meets the requirements of TB T2403-2010 standard.