A method for manufacturing hot-dip galvanized steel sheet without strip zinc dust and bright spot defects on the surface

Abstract

The invention relates to the technical field of hot galvanized steel sheet manufacturing, particularly to a manufacturing method for a hot galvanized steel sheet without strip zinc ash and bright spot defects on the surface. The method is characterized by: installing a condensation precipitation device outside a furnace nose to form negative pressure at a zinc pot side in the furnace nose, at the same time, heating a furnace nose side wall to raise the temperature to 450-550DEG C, making the zinc vapor over the zinc pot sucked away continuously and unable to accumulate on the side wall in the region, keeping the dew point of the nitrogen and hydrogen protective gases in the furnace nose in the range from -70DEG C to -20DEG C without additional humidification, cooling the zinc vapor in the condensation precipitation device, and precipitating and depositing zinc powder. Compared with the prior art, according to the method provided by the invention, the zinc vapor over the zinc pot is sucked away, and no zinc powder precipitates out, so that a high dew point method is no longer needed to inhibit the zinc vapor. Therefore, the strip zinc ash and bright spot defects are maximumly controlled.

Description

technical field [0001] The invention relates to the technical field of hot-dip galvanized steel sheet manufacturing, in particular to a method for manufacturing a hot-dip galvanized steel sheet without strip zinc dust and bright spot defects on the surface. Background technique [0002] In the manufacturing process of hot-dip galvanized sheets used for automotive exterior parts, since the steel strip must enter the hot-dip galvanizing pot through the connecting channel between the annealing furnace and the molten zinc tank (commonly known as "furnace nose"), the zinc liquid level in the furnace nose area The temperature is between 440°C and 480°C. The temperature of zinc vapor mixed with nitrogen and hydrogen protective gas inside the furnace nose is between 350°C and 500°C. Under the condition of only ordinary heat preservation, the temperature of the inner side wall of the furnace nose is only 150°C to 300 ℃, zinc vapor will precipitate on the side wall of the furnace nose...

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Problems solved by technology

[0003] In order to avoid strip zinc ash defects, the existing technology usually adopts two methods to deal with it: 1) Lift out the air knife and sinking roller regularly, hit the downflow trough with a sledgehammer, and use stainless steel pipe or rubber pipe to penetrate into the entire furnace nose area , into the compressed air to blow out the zinc ash, furnace ash, zinc slag and sundries in the furnace nose, and remove all the scum on the zinc liquid surface, so that the defects of zinc ash can be solved to a certain extent, but about a week 2) During production, spray humidified protective gas or pure nitrogen to the surface area of ​​the zinc liquid in the furnace nose, and pass the protective gas with a dew point of -60°C or nitrogen with a purity of 99.999% through the water tank to control the dew point temperature , the dew point temperature of the upper protective gas into the furnace is -60°C, and the water content is 0.001%; ​​while the lower protective gas dew point is controlled at -20°C after humidification, and the moisture content will rise to 0.1%. Oxidation produces a layer of Al on the surface of the furnace nose zinc liquid 2 o 3 and ZnO thin oxide film to prevent the escape of zinc vapor, which has received very good results, but excessive humidification will cause iron defects in strip steel

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