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Improvement of coating surface by production process of galvanized steel coil

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Improvement of coating surface by production process of galvanized steel coil

The production process of galvanized steel coil improves the surface of the coating. The surface coating is thin and uniform, the surface is beautiful, and the tin layer is firmly attached, which can improve the product grade. Main solutions to improve the appearance of coating surface:

1. Measures to prevent wrinkling of zinc pot

 

When the steel coil is galvanized in the zinc pot, the zigzag flow pattern of "zinc pot fold" often appears on the coating surface. This is mainly due to the air knife flow and the irregular flow of zinc liquid in the coating, resulting in small vibration of the strip. By properly controlling the wiping pressure of the air knife, the distance from the nozzle to the steel and the height from the nozzle to the zinc level, the "zinc pot fold" pattern can be effectively prevented.

 

2. Measures to prevent the formation of zinc flower

 

In order to ensure the appearance of automobile coated steel plate, it is necessary to use the galvanized steel plate with the smallest zinc flower (extremely fine zinc flower pattern). The size of zinc flower increased with the increase of the mass concentration of lead and antimony in zinc solution, and decreased with the solidification speed of zinc coating. After the surface of conventional GI steel plate is corroded by cu2so4 aqueous solution, the size of zinc flower should be controlled, the lead content in zinc liquid should be reduced to the lower limit, and the cooling speed above the zinc pot should be controlled to produce small zinc flower steel plate. In addition, in the large-scale continuous hot-dip galvanizing production line, small zinc flowers can also be obtained by spraying water vapor or water air mixture on the liquid zinc layer.

3. Measures to prevent adhesion of zinc slag

 

1) control the content of aluminum and iron in zinc solution.

The effective aluminum content must be controlled to control the aluminum content in the zinc pot, and the iron content in the zinc solution must also be controlled so that the iron content in the zinc solution is less than 0.03% of the solubility of iron in the zinc solution.

2) temperature control of zinc solution.

When the temperature of zinc solution is in the range of 480 ~ 530 ℃, the iron loss will increase sharply. In addition, too high temperature will cause zinc and aluminum in zinc to oxidize and produce zinc slag. The temperature of zinc pot is generally controlled at 460 ± 3 ℃.

3) dredging slag.

In galvanizing production, the production of zinc slag is inevitable. The main component of the bottom slag is fezn7, and the main component of the scum is fe2al5. Generally speaking, the removal of bottom slag does not use the method of catching slag, but uses the chemical method to convert it into scum. Scum is usually fished out. Attention must be paid to the scum at the steel belt outlet of the zinc pot, because the scum here is easy to adhere to the steel belt surface.

4) adopt double zinc pot.

In order to avoid surface defects caused by dross adhering to the surface of strip steel, zinc pot can be installed on CGL unit, so that gallium plate and germanium plate can be produced with special zinc pot, and the amount of zinc slag generated after zinc liquid switching can be minimized. Germanium production can be carried out under stable zinc liquid conditions, which can reduce the number of zinc slag points attached to the surface of germanium plate, and can produce excellent appearance quality Different germanium plates.