Study of Gas Jet Impingement on the Blockage of the Air Wiping Nozzle During Galvanizing Processes

by Lee Tae Hyun

Publisher - POSCO

Category - General Novel

In The Continuous Galvanizing Process, Wiping Apparatus Controls The Coating Thickness Of Up-Rising Steel Strip Right After Hot-Dipping In The Zinc Pot. But Under The Certain Conditions, Droplets Of The Cut Molten Zinc And Micro Zinc Fume Cause The Nozzle Blockage Of Air Knife. Nozzle Blockage Disturbs The Wiping Gas Straightforward Outgoing, Making The Vortex And Turbulence At The Zinc Stuck Area Of The Nozzle. As A Result, Non-Uniformed Wiping Causes The Coating Thickness Difference; In Other Word, Color Difference. It Is Unavoidable To Have Long Stripe Until We Remove The Stuck Zinc In The Nozzle. Further, Not Only The Nozzle Blockage Of Air Knife, Zinc Powder Directly Stick On The Almost Solidified Zinc-Covered Strip Which Makes Dot Defects On The Surface. There Are Two Ways Of Preventing Those Defects. Firstly, We Need To Control The Jet-Going Direction And Turbulence Rate At The Critical Area; Wiping Zone. Second, It Is Necessary To Decrease The Zinc Drops Which Fall From The Strip Surface Minimizing Discontinuous Condition Such As Strip Vibration, C Or L-Curving, Drastic Decrease Or Increase The Wiping Pressure. Sometimes The Zinc Dust Goes Up To The Strip Surface Bouncing Off The Top Dross Of The Zinc Pot Surface. Based On The Results Obtained Cfd, There Were Many Actual Tests To Prevent The Nozzle Blockage And Direct Defects Of Zinc Dust.

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