Heat And Mass Transfer Model On High Temperature Annealing Process Of Silicon Steel In Annular Furnace And Study On The Distribution Of Magnetic Performance

As the main material of making electrical motor and transformer,the oriented silicon steel is the basic of equipment manufacturing.But the performance of products in mass production is not stable and uniform.It mainly because that the annealing atmosphere and temperature inside the coil can not be controlled correctly during high temperature annealing in annular furnace,the H2 O content between the layers of strips will increase significantly as the Mg(OH)2 in coating decomposing,it will break the structure of oxide layers at the surface of strip,causing an adverse impact on the magnetic performance and coating.The decrease of the magnetic performance of oriented silicon steel differs greatly as the temperature difference inside the coil.However,the temperature and atmosphere inside the coil are unknown throughout the annealing in annular furnace,the technological parameters could only be adjusted by experience.The accuracy is not precise enough for the manufacture of high performance oriented silicon steel.Hence,the complicated working condition and its impact on the quality of coil during high temperature annealing in annular furnace mast be analyzed completely.Therefor,the numerical model of high temperature annealing is built to analyze the annealing condition of coils.The model contains heat transfer simulation and mass transfer simulation.First,the heat transfer inside the annular furnace is simulated using Fluent,the result shows the temperature distribution of cover is uniform,its maximum difference is within 30?.Hence a simplified 2D model which only contains the region inside the cover is applied for instead.The model mainly consists of the coupled heat transfer between gas,cover and coil.The simulated result is verified through the test results in factory.There are 238 radiant surface in radiation model,the S2 S model in Fluent is applied to calculate the angle factors between the radiant surfaces above efficiently,the error is verified within 1.5‰.In mass transfer model,the Mg(OH)2decomposition rate formula is derived according to the result of TG analysis.Then themass transfer mechanism between the layers of coil and the distribution of vapour in protective atmosphere are analyzed.Finally the annealing temperature and atmosphere of coil during high temperature annealing in annular furnace could be simulated through the numerical model.For the application in factory,an efficient simulation software which could run on an average PC independently is developed based on the numerical model.The distribution features of the magnetic performance in coil is studied through experiment,and its relationship with the annealing condition is found out using the simulation software.The results show that the difference of annealing condition inside the coil is the greatest during the first soaking which takes about 20 h,the maximum difference of temperature within the coil is 438?,and it is still above 317? after the process optimization in simulation.The vapour content between the layers increases as the height declines,the maximum difference is above 90 vol%.The magnetic performance of coil decreases as the vapour content increases,a significant deterioration is more likely to appear near the bottom and the outer surface of coil.In order to reduce the H2 O content,speeding up the outflow of vapour at the bottom surface of coil is the best method.