The main reasons for the falling off of the zinc layer of the galvanized sheet

We all know that the colors of color-coated galvanized sheets are various. The coloring problem of color-coated galvanized sheets and how to control the color difference are all problems that our manufacturers need to overcome, and they are also the key to ensuring product quality. The size of the zinc flowers on the substrate is different, and many small pits of different sizes are formed at the grain boundary, which will affect the color difference on the surface of the printing plate, especially the light color. It is better to choose a substrate without zinc flowers or small zinc flowers.

How to control the color difference of color galvanized sheet? Mainly, the production equipment uses natural gas to provide the oven temperature, so that the oven temperature is balanced and there is no temperature difference in time. The paint must be adjusted evenly before production. The stability of the paint film thickness has a great impact on the color difference of the color coated sheet. The adjustment of film thickness mainly includes: the adjustment of coating viscosity, the adjustment of the gap between the rubber roller and the coating roller of the roller coater, the change of the speed of the coating roller and the rubber roller, and the adjustment of the pressure of the coating roller and the steel support roller.

For the control of color-coated galvanized sheet, leakage coating is formed due to the swimming, deformation, oxidation and other factors of the substrate. Of course, controlling the color difference is a key factor to ensure the quality of the product, so it must be brought to the attention of every operator in order to more effectively ensure the availability of the product. Due to the uneven mixing of the paint or the high viscosity of the paint in different barrels, the paint extends from one side of the feed port to the return port in the material tray, showing the color difference band. In addition, when changing the color of the paint, the color contrast is large. Due to unclean cleaning, pollution forms color difference.

The main reasons for the shedding of the zinc layer:

Mainly include: falling off, scratches, passivation spots, zinc particles, thick edges, air knife stripes, air knife scratches, exposed steel, inclusions, mechanical damage, poor steel base performance, wavy edges, ladle bending, improper size, embossing, improper zinc layer thickness, roll printing,

The main reasons for the shedding of the zinc layer are: surface oxidation, silicon compounds, too dirty cold rolling emulsion, too high dew point of oxidation atmosphere and protective gas in the NOF section, unreasonable air-fuel ratio, low hydrogen flow, oxygen infiltration in the furnace, low temperature of strip steel entering the furnace, low furnace pressure in the RWP section, low air suction in the furnace door, low furnace temperature in the NOF section, endless oil evaporation, low aluminum content in the zinc furnace, too fast unit speed, insufficient reduction, zinc solution residence time is too short, coating is too thick.

The reasons for white rust and black spots are as follows: Black spots are formed by further oxidation of white rust. The main reasons for white rust are:

(1) Poor passivation, insufficient or uneven passivation film thickness;

(2) The surface of the strip steel is not coated with oil or residual water;

(3) There is moisture on the surface of the strip during coiling;

(4) The passivation is not completely dry;

(5) Wet or rainy during transportation or storage;

(6) The finished product is stored for too long;

(7) The galvanized sheet is in contact with or stored in corrosive media such as acid and alkali.