Carbon products of many types find commercial application with the largest quantities consisting of electrodes of various sizes and shapes. In manufacture, these carbon products and particular the electrodes are subjected to relatively high temperature heat treatment in order to provide the required mechanical strength and stability at high temperatures. The heat treatment also imparts the most desirable degree of electrical conductivity.
Most of these carbon products are baked in what are referred to as "carbon bake pits". These pits are formed with refractroy walls having channels and baffles through which the hot gases pass. The heat is conducted from the hot gases through the refractory walls to the carbon shapes which are embedded in green or calcined petroleum coke or a mixture of pulverized coke and silica sand. Some furnaces are electrically heated.
Whatever the heating system used, it is advantageous to provide insulation on top of the coke bed in the pit in order to reduce heat loss and fuel consumption and to ensure the proper temperature within the bed. Since the bed is formed by merely piling the coke over the carbon product to be heated, the surface of the bed is usually relatively uneven. For this reason, covers which are rigid have proved to be less than satisfactory.