Treatment of high-altitude brushes by application of metallic halides

It has been found that the rapid wear of brushes under high-altitude conditions can be prevented by the treatment of the brushes with a suitable metallic halide. Carbon, electrographitic, and metal-graphite brush grades all respond to such treatments. A great many nondeliquescent metallic iodides, bromides, chlorides, and fluorides have been tested and found to prevent brush dusting on the heavy-duty electric units of aircraft. These treatments also have been applied with considerable success to earth-surface machines operating under severe commutating conditions. A mechanism by which this class of chemical compound may react to maintain a satisfactory low-friction film on a commutator is proposed.