4. Resistance Furnaces

Resistance furnaces are heating installations that use the heat generated by Joule effect in appropriate heating elements (resistors) located on the walls of the furnace chamber, and transmitted to the workpiece to be heated mainly by radiation and convection. The electrical energy transformed into heat in the resistors is used in part to raise the temperature of the charge and in part to heat the walls of the chamber and to compensate for the furnace heat losses. After a description of the different constructive types of furnaces (batch, continuous, for low, medium or high temperature, with protective atmosphere or in vacuum), heating cycle, criteria and materials for wall design and test methods of this type of furnace are analyzed. In the final paragraphs, we will describe the different types of resistors, characteristics of materials used for their construction and design criteria of resistors for classical radiation or convection furnaces. At the end, furnaces with high specific power resistors are briefly discussed, making also reference to the energy balance of this type of furnaces.