The part of the Electric locomotives that are in contact with the OHE is called “pantograph”. It is the part through which electricity flows into the locomotive transformer from the OHE.
In the panto-graph, the part that is in contact with the OHE is called the “shoe” or “pan”.A panto-graph may have two shoes (high-speed panto-graphs or DC panto-graphs) or a single shoe.
Each shoe is coated or fitted with thin slabs of graphite, the same graphite found in your pencils. Graphite is an excellent solid lubricant, and due to its extremely high melting point, it is used in surfaces that heat up extremely high, enough to vaporise conventional oil-based oils. Also, graphite is an excellent conductor of electricity.
Above, you can see the long thin black slabs of graphite on the shoes of panto-graph. These slabs are periodically replaced when they get weak. So this graphite lubricates the surfaces in contact, i.e. the OHE and panto-graph shoes now lowering the friction and heat generated. It also conducts the electricity to the panto-graph from the OHE owing to its conductive property.
The faivley/Stone India AM12, the most common pantograph used in Indian locomotives and EMUs.The faivley/Stone India dual shoe/pan pantograph used in DC locomotives and EMUs in India (no longer in operation)