For slip rings in automotive alternators, a combination of graphite brush on copper ring is still almost exclusive. Materials from different grades of graphite material were paired with cooper and tested at different operating conditions (sliding speed, contact pressure, electric current). Influence of individual operating parameters on electrical and tribological properties of tested material combinations was analysed and connected with state of the art on slip ring field.
Because of some tribological and economical advantages, graphite/graphite material combinations indicate great potential for serial usage in automotive alternators and similar electrical devices. In this research, contact materials form different grades of graphite material were tested and mutually compared. Tests conducted at different operating conditions, thus influence of individual operating parameters on electrical and tribological behaviour of tested material combinations was analysed.
Different material combinations were tested on custom-made experimental stand. Based on tests results, and different special contact surfaces and contact film analyses the influence of contact surface electrical polarity on properties of contact film was investigated. The findings were compared with state of the art in this field.
Because of innovative axial design principle of slip-ring, the custom-made experimental stand was designed and made. It was designed in manner to simulate contact conditions as they are in real target application. The experimental stand enables in-situ measurement of tribological and electrical properties of sliding contact. In this paper, the experimental stand with its measuring equipment and its performances is presented in to detail. In addition, some test results are presented for reference.