Formation Mechanism And Treatment Method Of C-warping Defect For Steel Strip In Hot Dip Galvanizing Continuous Annealing Process

With the large-scale upgrading of China’s manufacturing industry and the comprehensive promotion of the new policy of ’ carbon peak,carbon neutralization ’,the demand for high-quality hot-dip galvanized sheet is increasing.However,for the hot-dip galvanizing process,the C-warping defect of the steel strip leads to a serious out-of-tolerance problem of the coating thickness on the surface of the steel strip in the continuous annealing furnace after galvanizing,which directly restricts the improvement of the quality of the galvanized strip steel and causes great economic losses to the enterprise.Therefore,how to solve the problem of C-warping defect of steel strip in hot galvanizing continuous annealing process has become the focus of field research.In this paper,the hot galvanizing unit is taken as the object to study the formation mechanism and treatment method of C-warping defect of steel strip in hot galvanizing continuous annealing process.Firstly,the equipment and process characteristics of the hot galvanizing unit were fully considered,and the actual operation status of the unit was tracked.The defect morphology and harm of steel strip in hot galvanizing process were analyzed,and the process section of steel strip with C-warping defect was determined.The formation mechanism of steel strip with C-warping defect was studied,and the mechanical model of steel strip with C-warping defect mechanism was established.The prediction model of steel strip with C-warping defect was constructed by means of strip element method.Through model application and field verification,the error of prediction accuracy is within15 %,which meets the engineering requirements.Secondly,the working principle of the equipment in each process section of the continuous annealing furnace in the hot galvanizing process was analyzed,the surface temperature distribution form of the steel strip was set,the strip element subdivision method of steel strip and its conditions were given,and the main influencing factors of the steel strip C-warping were determined.In view of the indirect influence of tension on the C-warping defect of strip steel,considering the droop phenomenon between adjacent furnace rolls and the influence of transverse deformation of steel strip,the calculation formulas of steel strip droop and transverse strain variation were given.Aiming at the coupling of flame deflection,strip droop and other factors of open flame burner,the heat distribution coefficient of open flame burner was proposed,and the model of open flame burner affecting strip C-warping were established.According to the structural characteristics of the radiant tube,the model of the influence of the radiant tube on the surface temperature of the strip was constructed in different regions.Considering the combined action of genetic shape,strip droop of the upstream process section and fan pressure,the warpage inhibition rate and warpage control sensitivity were proposed as the indexes of strip warpage control,and the influence model of cooling process on strip C-warping was constructed by strip element method.Aiming at the problem of aggravating strip warping in the process of strip temperature compensation,the influence model of electric heating element state on C-warping defect was established.On this basis,the influence of these factors on the C-warping defect of steel strip was quantitatively analyzed with typical specifications.Thirdly,the corresponding treatment methods for the C-warping defect of steel strip were proposed from the aspects of steel strip tension,temperature of each process section and cooling fan,and the optimal setting model of steel strip tension with steel strip sag and transverse strain as constraints was established.In view of the multi-variable coupling and complex nonlinear characteristics of the continuous annealing furnace,the continuous annealing furnace was assumed to be a system,the outlet shape of the continuous annealing furnace was taken as the total optimization objective function,and the optimization sub-model of each process section was used to establish the comprehensive optimization setting model of the furnace temperature.The cooling fan was used to suppress the warping degree of the strip,and the optimization setting model of the cooling fan state was established,and the optimization process was given to form the C-warping defect treatment technology of the strip.Finally,the C208 hot-dip galvanizing line of an iron and steel enterprise was taking as the research object,the measurement experiments of galvanizing amount on strip surface and strip warping were carried out.At the same time,the C-warping defect treatment technology was applied to the line,and the effect was analyzed.The results show that the maximum warpage of typical specification strip steel at export decreases from 48.4mm to 14.5mm after optimization,and it is found that the shape closure rate of the unit has decreased by 13.5 % due to the C-warping defect after a year of stable operation of the unit,the unevenness of zinc plating on the surface of thick strip with thickness greater than 2.0 mm has decreased by 27.9 %,and the unevenness of zinc plating on the surface of thin strip with thickness less than 2.0 mm has decreased by24.1 %,which has created great economic benefits for the unit.