A resistance furnace generates heat through the Joule effect when an electric current passes through a conductor.
The furnace uses electricity as the heat source, converting electrical energy into thermal energy via heating elements to heat metals inside the chamber. Compared with flame heating, resistance furnaces are more efficient, with thermal efficiency reaching 50–80%, easier temperature control, stable working conditions, and a long service life. They are suitable for applications requiring precise heating but consume relatively high power.
Types Based on Heat Transfer:
- Radiation resistance furnaces: Mainly heat via radiation; convection is minimal.
- Convection resistance furnaces: Heat mainly via convection, often called air-circulating resistance furnaces. Temperature usually stays below 650°C.
Types Based on Heating Method:
- Direct heating: Current passes directly through the material, causing rapid heating, ideal for forging billets or processes requiring fast heat-up. Direct heating furnaces can reach very high temperatures—for example, carbon materials in graphitization furnaces can exceed 2500°C. They are also used in vacuum resistance furnaces or furnaces with protective gas, commonly applied in powder metallurgy for sintering tungsten, tantalum, niobium, and other products.
- Indirect heating: The heating element heats the furnace chamber or protective medium, which then transfers heat to the material (not detailed in the original text).