| The development trend of high-speed railway passenger transport and heavy freight transport had put forward higher requirements for the braking system of railway locomotives.The high friction composite brake shoe was an important part of the railway locomotive braking system,and its performance was related to the safe operation of the train.The basic formula of brake-shoe materials was phenolic resin and nitrile rubber as binder,steel fiber,composite mineral fiber and sepiolite fiber as reinforcement,potassium feldspar,iron powder,barium sulfate,bauxite,graphite and other filler.The carbon fiber and graphene were added on the basis of the formula.Scanning electron microscopy and energy spectrum analysis,compression test,impact test,bending test,hardness test,and friction and wear test were used to study the effect of carbon fiber and graphene on the friction and wear properties and mechanical properties of high friction coefficient synthetic brake-shoe materials under different rotational speeds,temperatures and loads.The results of the research showed that when the content of carbon fiber was 2%and 4%,the carbon fiber was distributed evenly on the substrate,and the adhesion of inorganic filler,fiber and binder was better.When the content of carbon fiber was 6%and 8%,partial interlacing and agglomeration occurred.The content of carbon fiber was 2%-8%,with increasing the content of carbon fiber,the comprehensive mechanical properties of the materials increased at first and then decreased.The results showed when the content of carbon fiber was 4%,the brake-shoe materials obtained good mechanical properties.The content of carbon fiber was 4%,after adding 0.5%-2.0%graphene,as the content of graphene rose,the comprehensive mechanical properties of the materials increased at first and then decreased.When the content of graphene was 1.0%,the mechanical properties were better,the impact toughness was 11.725kJ/m~2,the compressive strength was54.6374MPa,the compression modulus was 1083.371MPa,the bending strength was20.67MPa,and Rockwell hardness was 87HRR.At the same rotational speed,when the content of carbon fiber was different,the friction coefficient and wear mass loss of the materials changed in different degrees.When the content of carbon fiber was 4%at 1000r/min,the friction coefficient was as high as 0.483,and the abrasion loss was as low as 3.2mg.When the content of carbon fiber was 4%,after adding 0.5%-2.0%graphene,with the increase of the content of graphene,the friction coefficient and wearing capacity of the materials were different.When the content of graphene was 1.0%at 1000r/min,the friction coefficient was the highest,which was 0.491,and the wear quantity was the smallest,which was 3.7mg.At the same temperature,with the increase of the content of carbon fiber,the results showed when the content of carbon fiber was 4%,the brake-shoe materials had good friction and wear resistance.When the content of carbon fiber was 4%,after adding 0.5%-2.0%graphene,the results showed as the content of graphene rose,the friction coefficient increased initially and then decreased;and the abrasion loss decreased first and then increased.When the content of graphene was 1.0%at 100℃,the friction coefficient was the largest,which was 0.457;and the minimum wear value was 5.8mg.At the same load,when the content of carbon fiber was different,the wear allowance of the materials was different.When the load was 30N,the abrasion value was up to 4.7mg when the materials were not added carbon fiber;and the wear loss was lower to 2.3mg when adding 4%carbon fiber.When the carbon fiber content was4%,with the addition of 0.5%-2.0%graphene,the results showed that the wear resistance of the materials was different when increasing the different content of graphene.When the content of graphene was 1.0%,the wear resistance was better.When the content of carbon fiber was 4%,the friction coefficient of the materials reached the maximum at 1000r/min and 100℃.The wear rate increased with the increase of the rotation speed,temperature and load.When the content of carbon fiber was 4%and the content of graphene was 1.0%,with increasing of the rotation speed,the friction coefficient of the materials first increased and then reduced;and the friction coefficient of the materials increased as the temperature went up;and the wear resistance decreased with the increase of the rotation speed,temperature and load.When the high friction composite brake-shoe materials were slightly worn,the scratches will be generated on the friction surface,and the friction surface had less surface films and the area was also small.The main form was dominated by abrasive wear.When the wear was severe,the friction surface was rough,produced a large number of surface films,and appeared peeling Layers,cracks and other phenomena.The wear patterns were mainly adhesive wear,abrasive wear and fatigue wear.In summary,on the basis of 15%binder,60%filler,8%steel fiber,3%composite mineral fiber and 14%sepiolite fiber,adding 4%carbon fiber and 1.0%graphene,the brake-shoe materials had good comprehensive properties. |
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