The main components of box furnace are: furnace body, furnace, temperature controller, heating element and temperature measuring element.
The structure of box furnace is mainly composed of furnace frame, furnace shell, furnace lining, furnace door device, electric heating element and auxiliary device. The function of the furnace frame is to bear the load of the furnace lining and the workpiece. Usually, the section steel is welded into a frame, and the steel plate is wrapped. The function of furnace shell is to protect the furnace lining, strengthen the furnace structure and keep the furnace sealing. The steel plate is usually pasted on the steel frame and welded. The furnace frame and shell with reasonable design have enough strength. The small box type resistance furnace can be welded into furnace shell with thick steel plate without furnace frame. To a certain extent, it also plays a protective role.
The lining of box furnace is used to protect furnace temperature and reduce heat loss. A good lining material should not only have a certain degree of fire resistance, but also have less heat storage. The furnace lining is composed of refractory and thermal insulation materials. The refractory material is close to the electric heating element, and the insulation material is close to the shell. In order to reduce the heat loss, the lining of high-temperature box furnace adopts three-layer heat insulation design, and the inner layer adopts refractory materials, such as polycrystalline mullite fiberboard and zirconium containing fiberboard; the intermediate layer and outer layer adopt thermal insulation materials, such as high aluminum or standard ceramic fiber board, felt, fiber blanket, etc. The lining of medium temperature box furnace is made of lightweight refractory and thermal insulation materials such as high aluminum or aluminum silicate refractory fiber. Fiber blanket material is generally used in the layer near the furnace shell. Due to the low temperature of the low temperature box furnace, the material requirements of refractory layer and insulation layer are not high. The general aluminum silicate refractory fiber can meet the requirements. This can also play a more protective role on the furnace.
The furnace door device of box furnace includes furnace door and locking protection device. It is required that the furnace door device should be well sealed to reduce heat loss. The furnace door is generally made of cast iron or steel plate. The safety limit switch is installed on the furnace door opening device, which is connected with the heating control power supply. When the furnace door is opened, the control power supply is cut off to protect the safety of the operator. In order to observe the heating in the furnace chamber, an observation hole is usually designed in the center of the furnace door. It is convenient to monitor the work of box furnace.
Silicon carbide rod, molybdenum disilicide or metal alloy are often used as electric heating elements of box furnace. The heating temperature of SiC rod can reach 1350 ℃, which is installed on both sides of furnace chamber vertically or horizontally, and some furnaces are installed at the top and bottom of furnace chamber. Molybdenum disilicide can be up to 1600 ℃, but it becomes very brittle after heating, so it is usually embedded in the groove of refractory to prevent damage when loading and taking the workpiece. The installation length should be less than the length of the groove, and a certain space should be reserved at both ends. In contrast, metal alloy electric heating elements are more convenient in processing and installation box, and reasonable layout can also obtain better temperature uniformity. At present, metal or metal alloy electric heating elements are mostly used in box type resistance furnaces whose temperature is less than 1200 ℃. In the operation, we must pay attention to the correct operation method, which can also ensure the safety of the production workshop personnel.
The temperature of box furnace is measured by thermocouple. One thermocouple is used for small box furnace, and several thermocouples are used for large and medium box furnace, which are directly inserted into the furnace chamber to monitor the temperature at different points in the furnace chamber. In general, the thermocouple with nickel chromium nickel silicon (division number k) is used when the temperature is less than 1000 ℃, and Platinum Rhodium 10 platinum (division number s) is used when the temperature is greater than 1000 ℃.
The furnace structure of box furnace is these parts. In operation, as long as we understand its properties, and then operate according to the process requirements, we can ensure the normal use of box furnace in the production process.
On 2018-08-08 11:45:46
