Study On Electrical Sliding Friction And Wear Properties Of Silver Matix Electrical Conductive Composites

In the electrical brush-rotor systems, currents pass between a brush and a rotor that slide against each other. Performance of an electrical brush is greatly affected by the combined effects of the current flow, the friction and wear, high temperature and chemical reaction. It is therefore desirable for brush to have as little electrical an thermal resistance as possible and high resistance to wear.The Ag-MoS₂ composites with MoS₂ content from 12wt% to 18wt% were fabricated by the means of powder metallurgy. Mechanical properties, physical properties and electrical friction and wear properties of the composites had been studied. The results showed, the density, bending strength, hardness and electrical conductibility of the composites decreased with the increase of the MoS₂ content, but the contact voltage drop increased with the increase of the MoS₂ content. The wear rate decreased with the increase of the content of MoS₂, a minimum is reached when the content of MoS₂ is 15wt% and then increased when the content of MoS₂ is further increased. The wear loss of the positive brush was larger than that of the negative brush due to the material transfer.The composition of the surface films of the Ag-MoS₂ composites were analyzed using XPS. The elemental C, O, Mo, S and Ag existed in the surface films after the electrical friction and wear. The surface films reduced the adhesive wear and improved the frictional and wear properties of the composites.The effects of adding carbon nanotubes or graphite to the Ag-MoS₂ composite on the friction and wear properties were studied. Carbon nanotubes increased the strength and reduced the over-thick lubricant film, and graphite improved the conductivity of the lubricant film. Thus both carbon nanotubes and graphite improved the electrical friction and wear properties of the composites, and the Ag-MoS₂-G-CNTs composites had the best general properties.The effect of sliding velocity and the current density on electrical friction and wear performance of the Ag-MoS₂-G-CNTs was studied. The experimental results showed that, with the sliding velocity increasing, both the contact resistance and the contact voltage increased because of the increase of the gap caused by the adhesive gas flow between the brush and the slipping ring. In the same process, the friction coefficient decreased with the increase of sliding velocity because of the lubrication of the gas, and the electrical wear rate decreased firstly and then increased with the increase of sliding velocity due to the chemical actions. With the increase of current density, the temperature of the frictional surface increased and the a-pot metal turned soft, so the contact area got larger, and the contact resistance decreased. Simultaneously, the hardness of composites decreased as current density increased, thus the wear rate of composites increased with the increase of current density.