The Thickness Control Of Hot Dip Galvanized Coating And The Research Of Mn Steel Can Be Galvanized

With the rapid development of automobile industry, the quality requirement and variety for hot dip galvanized products is becoming increasing strict. Although some galvanized technologies has been relatively mature, there are a lot of problems in the production, including edge over galvanizing, coating thickness difference control and the galvanized ability of high strength Si-Mn steel. Now baffle has been employed to solve edge over galvanizing due to the edge pressure attenuation in the exhalation of air knife. In the aspect of coating thickness difference control, in order to avoid the failure of welding properties of hot dip galvanized products caused by coating, the coating is reduced on the welding surface. For the purpose of lightweight of automobile, higher strength of hot dip galvanized steel is needed. However, the alloy composition of high strength steel can impact on hot dip galvanizing.In this paper, simulation and experimental study had been conducted aiming at the above problems. The effect of baffle geometry and baffle swing on the coating uniformity was analyzed by means of simulation. Coating thickness and uniformity were calculated through thickness calculation model at the various bilateral air knife injection pressure. In the experiment, the galvanized ability of Mn steel was study. Moreover, the effects of Mn content and different annealing process on steel-based surface oxides were analyzed.In the simulation, the strip surface pressure for different baffle thickness and corner was computed via the Fluent module of Workbench. At the same time, fluctuations of coating thickness were calculated when baffle offsets by changing the position of the baffle. The simulation results show that when baffle thickness is 2 mm and corner is 90。, reducing edge over galvanizing is most effective. At the same time, the baffle migration simulation indicates that when baffle offsets, the strip edge pressure gradually decreases along migration direction. As the baffle continues offsetting, the inflection point of edge pressure will appear at the offset of 0.5 mm, and pressure can be improved. Nevertheless, strip surface pressure gradual augments with baffle offsetting along the reverse migration direction, and the strip edge pressure remains unchanged when the offset exceeds 0.6 mm. Each additional unilateral pressure 1KPa, the coating thickness decreased by about 1.8 μm. But when bilateral air knife injection pressure difference exceeds 2KPa, strip surface coating thickness sharply increases at the weak pressure side. Therefore, different injection pressure is employed to control the thickness difference, and air knife injection pressure differential should not exceed 2KPa. Annealing experiments of hot dip galvanized steel show that in the annealing process, Mn of steel substrate enriched on the steel substrate surface can form oxides. The number of surface oxides significantly increases with annealing temperature and annealing time.