Carbon, Graphite, and Contacts

The "black art" of carbon and graphite technology is yielding to the science of materials and applications. This review represents the present state of this art; and since carbon, graphite, and contacts come together in so many different ways and in so many important ways, it is reasonable to discuss them in this context. From the developments in this field have come materials which have made possible such applications as electric arc steel furnaces, jet aircraft engines, high altitude aircraft, inexpensive appliances, aluminum reduction pots, electric machines, electric traction, and many other uses. The purpose is to discuss the fundamental physical processes involved in sliding conduction, friction, and the electric arc, and the roles that carbon and graphite play. To put this together, we will first discuss the pertinent properties of carbon (1), then the physical and chemical effects involved in contact drop, mechanics, friction, temperatures, the electric arc, commutation, and wear (2). The principles are similar for both electrical and mechanical sliding contacts, that is, for brushes and for seals and brakes, so all will be included. Furthermore, in a suitable application, all of the applicable phenomena must be coordinated and within practical operating limits. In most applications, many of\´the phenomena are interdependent in that they influence each other and are all influenced by the ambient conditions surrounding the ap- plication.