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Molybdenum Disulfide As a Lubricant in Rail Transit

The lubrication in the rail traffic is mainly for wheeltrack, moving parts in locmotives, motor cars and vehicles, and bow net. Molybdenum disulfide (MoS2) is a good lubricating material thanks to its frictional characteristics, physical and chemical properties. 

Since the advent of rail transit, the wear of rails and rims has become a concern. When the train passes the curve, due to the action of inertial force and centripetal force, the wheel flange and the rail side will roll and slide, causing severe wear on the rail side; and when passing through a straight track, the conicity between wheel tread and wheeltrack will cause hunting, resulting in wear between the wheel rim and the inner edge of the track inevitably.

By taking some measures, such as using high-strength steel, making wheel flange matching more reasonable, adjusting track parameters, and carrying out reasonable lubrication can effectively reduce wheeltrack wear. Among them, reasonable lubrication can not only reduce wear by 30% to 80%, save fuel by more than 2%, but also help the safe driving of the vehicle due to the reduction of the friction coefficient between the wheel flange and the rail side.

There are many ways of rail lubrication: artificial oiling trolleys, track pulley, ground rail lubricators, vehicle-mounted lubrication devices, etc. Lubricants used in the lubrication devices include three types: lubricating oil, grease and solid lubricating stick. 

MoS2 is a good solid lubricant. The low friction and easy cleavage are intrinsic to the material and a result of its crystal structure. Its formed solid lubricating film lubricates sacrificially by transferring lubricant between the two mating surfaces, which helps to reduce wear and coefficient of friction, and can withstand an average load of 108Pa or more to prevent the lubricating film from breaking and causing seizure. For example, the thickness of 2.5μm molybdenum disulfide film can withstand pressures above 2800MPa.

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