Effect of Mesophase particles on the Electrographite carbon brush tribology behavior under no-load condition

Abstract

Electrographite (EG) has partial electrical conductivity and is used as a current collector in direct current motors. EG is prepared from a suitable carbon source through a multi-step process to convert it to conductive carbon. In this work, EG was prepared with coal tar pitch (CTP) having different mesophase (MP) content (4, 8, 19, and 33%) and their characteristics were compared. The microstructural analysis of CTP indicated that increase in MP leads to increase in mesophase particle size. MP was found to have a significant impact on the physical and binding properties of CTP. X-ray diffraction studies showed EG to be a partially graphitized material with a degree of graphitization (DOG) ranging from 30% to 60%. Since coke-based materials graphitize more easily than lamp black, the DOG, crystal size, and d-spacing of coke-based material were higher. Graphitization in tube furnaces was better than induction and Acheson furnaces because of its concentrated heat in small size susceptor. The Design of Experiments (DOE) method with Face Centre Factorials was used to generate 14 different combinations of load (20 N,60 N, and 100 N) and velocity (1 m s−1, 3 m s−1, and 5 m s−1) for wear and COF analysis which were done on pin on disc apparatus. Response surface method (RSM) was used to investigate the relationship between wear, COF, and MP content. The CTP binder properties had a significant impact on wear. The COF decreased as the number of Brooks and Taylor structure MP particles increased. On the EG wear characteristics, adhesive wear was a more dominant factor than abrasive wear.