Simulation of temperature distribution in the oriented silicon steel coil in the heating stage of annealing process

Annular furnace is widely used for high temperature annealing of oriented silicon steel coils. The coils are placed under a cover in a protective atmosphere. The heating rate of the process must be strictly controlled to prevent magnetic property variations of the products. In this work, temperature distribution in the coil at the heating stage is simulated using finite method. Effects of fuel flux at burners on temperature distribution in the furnace are also analysed. Experiments are carried out to measure the parameters needed in simulations and to verify the simulation results. For a coil of 510 nun inside and 1710 nun outside diameters, the largest temperature difference in the coil is found to be as high as 438 degrees C, which occurs at about 8 h of heating. A total of 72 h is needed for the temperatures across the coil to reach a target level of 1170 degrees C. The temperature difference in the coil can be greatly reduced if NZ is replaced by Hy as protective atmosphere and the gap between sheet layers in the coil is reduced. Temperature distribution on the cover during heating is found to be rather uniform with the largest difference being within 30 degrees C.