The bell-type annealing furnace manufactured by our company includes a furnace table, an inner cover, a heating cover, a cooling system, and a microcomputer with high-precision automatic control of the furnace temperature. The bell type annealing furnace is equipped with two furnace stands, two inner covers and a heating cover. One cooling hood and one furnace base are heating and warming and holding, while the other furnace base is in the process of cooling and discharging. The heating hood alternately heating two furnace bases can save energy consumption and achieve continuous production.
Annealing process of bell type annealing furnace:
The cold rolling strip annealing process system is mainly determined based on the chemical composition of the steel, the technical standards of the product, the size and coil weight of the strip. The process system must ensure that there is no adhesion between the coils in the production and that the surface does not oxidize.
A. Determination of heating rate The heating rate of steel is mainly determined by the thermal conductivity of the steel. The carbon content and alloy content in steel have a greater effect on heat conduction. If their content is high, the thermal conductivity is small, and the heating speed should be appropriately slower to avoid unevenness in structure and performance caused by excessive internal and external temperature differences. From room temperature to 400 ° C, the heating rate is generally unlimited. According to the principle of the crystallization process, the strip's internal structure does not change significantly from room temperature to 400 ° C. The elongated grains have just recovered during the rolling process and no recrystallization has yet formed. Therefore, the heating rate of the steel in this range The sooner the better. The strip is heated from 400 ° C to the holding temperature. The heating speed has a considerable impact on the performance and surface quality of the strip. Generally, it is recommended that the heating rate be 30 to 50 ° C / h. During the period when the strip is heated from 400 ° C to a temperature below 723 ° C, it is the recrystallization stage. Therefore, the heating rate must be controlled in this temperature range.
B. Determination of holding temperature and holding time The recrystallization temperature of steel is not a fixed temperature. It is related to the internal structure of the strip. The recrystallization temperature in actual production is selected according to the product in the range of 570 ~ 720 ° C. The holding temperature and holding time are mainly determined according to the product standards, technical conditions and the thickness of the steel type and strip. The holding time and temperature are also related to the coil weight and strip thickness. For large coils and thick steel plates, the holding temperature is high and the holding time is also long. For steel and thin gauge strips that are prone to interlayer adhesion defects, the heat preservation temperature can be appropriately lower and the heat preservation time can be shorter.
C. Bright annealing To make the strip steel without decarburization and oxidation, bright annealing must be performed. The key problem of annealed steel coils against oxidation is that the pressure in the protective cover must meet the process requirements. In addition, we must carefully do cold and hot blowing. The purpose of cold blowing and hot blowing is to use protective gas to drive away the air in the inner cover and the oil and gas moisture brought by the steel coil. The function of hot blowing is to remove the residual gas in the inner cover, and it is more important to remove all the harmful substances such as oil fume and water vapor produced by the emulsion brought by the coil, so as to avoid staining the surface of the steel plate. And reduce the surface quality of the steel plate.