Study On Relationship Between Surface Roughness And Tribological Characteristics Of Carbon/Copper Counter-Pairs Under Electric Current Applied

Pantograph/catenary system belongs to important power transmission system of electric locomotive,and the pantograph strip/contact line is a typical rubbing pairs with electric current applied.The poor contact state of the rubbing pairs may lead to the off-line electric arc which may not only destroy or deteriorate the current-collection state but also can accelerate the wear of materials even endanger the operating security of locomotives.Many factors such as surface roughness, materials of counter-pairs, lubricating conditions,normal load, current density,sliding speed and so on have a great effect on generation of electric arc under current applied friction and wear. With the speed of train accelerated step by step,the frequency of electric arc off-line between pantograph/catenary system will be increased significantly, Accordingly the wear and erosion may produce different surface roughness of counter-pairs.Therefore, the study on the relationship between surface roughness and tribological characteristics of carbon/copper counter-pairs under electric current applied presented important significance.Adopting a ring-on-block contact configuration,the friction and wear tests of carbon/copper counter-pairs under different surface roughness and testing parameters have been carried out on a rubuilt CETR UMT-2 multifunctional friction and wear tester.And its influence on electric arc characteristic was investigated in detail. The main results have been obtained as follows:1) Effect of surface roughness:The real contact area decreased due to the existing of large size asperities of contact,which led to increasing of current desity and arc starting easily.So,the ablation by arc was the main reason of greatly fluctuating of friction coefficient and increasing of wear volume.With the decrease of surface,the frequency and strength of electric arc reduced,and also the wear decreased.2) The friction coefficient decreased with the increase of the normal force and gradually stabilized with or without electric current applied.The friction coefficient with current applied were higher that of without current applied,and the friction coefficient increased with the increase of the current. 3) The normal load is one of important factors of arc starting.Under a constant surface roughness,it existed a critical load for arc starting.Above the critical load,no visible arc can be generated.At the same time,the current-carrying friction system stabilized,and both the voltage and current were also invariable.The wear mechanism of the carbon material was main abrasive and adhesive wear.Beneath the critical load,the arc can be observed between the counter-pairs.Under this conditon,the voltage and temperature between the counter-pairs increased sharply,and the current decreased abruptly,which corresponded to the wear aggravated.The wear mechanism of carbon material changed to main abrasive wear,adhesive wear,arc ablation and material transfer.