| With the increasing speed of the high-speed train,the braking system needs to consume more and more kinetic energy.Disc brake belonging to the basic braking device,the friction coefficient between brake pad and brake disc becomes a key parameter of selecting brake material.China has vast territory and a uneven climate.With the various high-speed rail lines going into service,high-speed train that is spread over the country has been able to take a day to reach destination and environmental conditions have become an unavoidable factor in the operation of high-speed trains.Moreover,due to the manufacturing and installation errors of the brake and brake disc,the local brake pressure on the brake sluice is far greater than the average brake pressure applied.Under these unconventional friction conditions,the friction coefficient of the brake material is the key to determine the quality of the brake material.Therefore,the study of the friction coefficient of the brake material under different environmental conditions can provide the basis for selecting the appropriate brake material.This paper uses pin-disc friction experimental setups to inspect the friction coefficients of three brake materials: the locomotive composite brake linings,350 km/h traction brake discs and locomotive powder metallurgy brake linings at special working conditions.Under the conditions of relative sliding speed(v=0.25m/s)and brake pressure in the range of0.53~0.98 MPa,the friction coefficient characteristics of the three brake materials are studied under different working conditions,such as dry friction,water spray and snows.The experimental results show that:(1)Under dry friction conditions,the friction coefficient of the three brake materials decreases as the brake pressure increases.In the experimental load range,the maximum friction coefficient of the three brake materials occurs at a brake pressure of 0.53 MP.(2)When the friction condition is wet,the friction coefficient of the three kinds of brake materials is obviously lower than that of the dry friction coefficient.In the experimental load range,the maximum friction coefficient of the three kinds of brake materials appears at the braking pressure of 0.98 MPa,the reason is that the thickness of the water film is affected with the increase of the braking pressure,and the proportion of the micro protrusion between the contact surfaces is large during the breaking process.(3)The friction coefficient recovery time and situation of three kinds of brake materials were observed by smearing snow on the surface of the friction disc.When the brake disc of locomotive composite material is applied in the condition of snow,the friction coefficient is unstable.The friction coefficient of 350 km/h motor vehicle brake disc is stable at 0.53 MPa and 0.98 MPa after the application of snow.The friction coefficient of locomotive powder metallurgy brake disc recovered slowly after applying snow.(4)The friction coefficient of the brake disc made of composite materials for locomotives is relatively stable under dry and wet conditions,and it is suitable for applications with high braking stability.The overall friction coefficient of locomotive powder metallurgy material is high,and the material is more sensitive to water existing.The coefficient of friction is lower under wet friction,and the coefficient of friction of 350 km/h motor vehicle brake disc is ranged between the other two materials. |
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