The power of an electric resistance furnace is determined based on the heat balance principle. Through heat balance calculations, the power of the furnace can be calculated relatively accurately. The required power of the furnace should include the furnace's heat storage, the heat required for workpiece heating, the heat required for workpiece heat preservation, the heat required for atmosphere decomposition, and heat losses. The furnace's heat storage is determined by the furnace's specifications, structure, main dimensions, lining thickness, and the thermal conductivity of the materials.
Generally speaking, the larger the furnace, the greater its heat storage, and vice versa. The heat required for workpiece heating and heat preservation is determined by the furnace's output, the nature and dimensions of the workpiece, the operating temperature, and the time. The higher the furnace's output, the greater its power, and vice versa. The heat required for atmosphere decomposition is determined by the nature of the atmosphere. Heat losses include heat dissipation from the feed inlet and discharge outlet, and radiation losses from other parts. Furnace power calculations can be performed using theoretical calculations based on the heat balance principle or empirical calculations.
The main parameters for the theoretical calculation method are output, temperature, and heating time.
There are three common empirical calculation methods: calculating power based on furnace volume and operating temperature; calculating power based on furnace surface area and operating temperature; or extrapolating power by analogy with the output of similar furnaces. Generally, power calculations are based on one primary method, verified and corrected using another or two methods. After determining the power, power allocation is performed according to the zoning of the resistance furnace, the type of heating element is selected, materials are chosen, and their parameters are calculated, including cold resistance, power supply voltage, wire diameter, and length. Specific material selection considers the material's oxidation resistance, high-temperature resistance, carburization resistance, processability, and surface load. Strip heating elements bear a slightly higher surface load than wire heating elements, potentially increasing it by up to 50%.
