Carbon Film Formation and Commutator Brush-Wear As Revealed by the Electron Microscope

Publisher Website
Google Scholar
Abstract
The faces of carbon or graphite brushes, polished by rubbing against a rotating copper disk and subsequently examined with the electron microscope by means of surface replicas, are found to consist of many tilted ``fingers,'' which are the projecting portions of the large and irregular graphite plates composing the brush. These graphite projections show a directional overlap, which is determined by the direction of motion of the disk, and when viewed stereoscopically they are found to be inclined at various angles up to nearly 90° with reference to the plane of the rotating base. They account for a previously observed ``directional memory'' of graphited surfaces and they show that such surfaces in general cannot be regarded as consisting simply of graphite plates oriented with the hexagonal planes flat and parallel to the plane of motion. The brush track on the rotating copper base is found to contain small islands of carbon deposited from the brush. These islands consist of large numbers of graphite wear‐fragments, which are individually of very small size in comparison with the projections of the brush face. These fragments are clearly derived from the projections by a tearing apart of their edges and are packed tightly and with random arrangement into the tool marks of the copper smoothing over the irregularities of the latter. It is not determined whether this ``carbon film'' of the brush track is continuous. The wear‐dust of unlubricated graphite is found to consist of particles which are very small in average size compared with those from which brushes are manufactured. The size of these wear‐fragments extends below the resolving power of the electron microscope, and this is consistent with recent data on similar particles of a size determined independently by adsorption measurements.

This publication has 3 references indexed in Scilit: