According to the electric heating way, resistance furnace is divided into two directly heating and indirectly heating. An, thermocouple directly in the furnace, the current directly through the material, because of electric power concentrated in the material itself, so the material heat quickly, is suitable for the requirements of rapid heating process, such as forging billet heating. The resistance furnace can be heated to very high temperatures, the supplies graphitizing furnace carbon materials, for example, can put the material is heated to more than 2500 degrees. Thermocouple furnace can be done directly vacuum resistance furnace or protective gas resistance furnace, in powder metallurgy, commonly used in sintering tungsten, tantalum, niobium and other products. Second, the indirect heating type, the heat generated by the electric heating element, through the heat transfer temperature of the heating mode of components, referred to as indirect heating type, the characteristics of indirect heating is uniform heating, heating temperature, heating speed and furnace atmosphere is easy to control, but heating efficiency is low, the depth of the workpiece heating layer can't control. However, indirect heating type whether it is on purpose, or on the varieties are more widely used than direct heating, in addition to the special heat treatment to adopt direct heating type, general common type resistance furnace for indirect heating, indirect heating type resistance furnace according to the different structure, divided into box type resistance furnace, pit type resistance furnace, increasing vortex type resistance furnace, salt bath furnace, vacuum resistance furnace and electric resistance furnace, etc. , if again refining division, according to the use by as much as there are dozens of. According to the hot work way is different, divided into two categories, external heating and inner heating type. 1, external heating type refers to the electric heating element, the outside of the furnace chamber furnace chamber is a seal body, workpiece placed inside a sealed; Internal heating type refers to the electric heating element in a furnace cavity, artifacts and directly put in the furnace chamber. 2, the characteristics of the internal heating type is heat transfer speed, workpiece with electric heating element in an atmosphere environment, facilitate the temperature measurement and control, and hot parts is easy to maintain. External heating type is easy to make the furnace work under protective atmosphere, artifacts and electric heating element can be in different atmosphere environment, facilitate the isolation protection, heat transfer speed is relatively slow, but after the temperature is bigger, go against the workpiece temperature control, heating within the maintenance on hot parts is not convenient.