Analysis Of Zinc Ripples And Vibration Of Steel Strip In Continuous Hot-dip Galvanizing Process

With the development of continuous hot-dip galvanization, the higher quality of steelstrip is required for car manufacturers. In the nowadays continuous hot-dip galvanizationprocess, the thickness of the coating is controlled by a gas jet through the air-knife. The airforces some of the molten zinc to return downwards into the bath.At first, we establish a two-dimensional numerical model of the flow of liquid zinc.The effect of process parameters such as the nozzle pressure, the height of nozzle slot andthe standoff distance on the coating thickness is analyzed with the numerical simulation ofair knife jet flow field and the simplified flow of liquid zinc.Secondly, the edge over coating may develop near the edge of the steel strip, and weanalyze the influence of the distance between the baffle and the steel strip on the flow filedof the strip edges. The distance between the baffle and the steel strip must be less than4mm. And the baffle is closer to the steel strip; the attenuation of flow field in the edge ofsteel strip is smaller. In addition, the influence of the moving speed of the strip tosplashing of liquid zinc is analyzed. The steel strip moves faster, it‘s more prone tosplashing of liquid zinc.For the undesired zinc ripples on the surface of steel strip, we adopt the large eddysimulation (LES) method to numerically solve for the3D unsteady turbulent jet flow field.And the liquid zinc flow model is utilized to numerically predict the coated zinc filmthickness. The effect of process parameters on the zinc ripples is analyzed as well. Theresults show that the nozzle pressure is larger or the height of nozzle slot is smaller or thestandoff distance is closer, the thickness of zinc film is more uniform.The influence of the turbulent jet flow on the steel strip is simplified as a harmonicforce at the impingement point, and the response of steel strip under the harmonic forcecan be obtained by commerce software. The nozzle pressure is smaller or the height ofnozzle slot is larger or the standoff distance is farther, the vibration of steel strip is moreserious.Combined with the advantages of the Coanda air-knife and the double air-knife, anovel Coanda double air-knife system is proposed. The results show that the Coandadouble air-knife system can obtain a thinner coating film, and prevent zinc rippleseffectively. The research results is very important for the improvement of efficiency and productquality in the hot-dip galvanized process.