Cause and Control of Zinc Ash on the Surface of Galvanized Aluminum Sheet

The appearance of zinc ash is that fine slag band forms strip or point inclusions along the longitudinal direction on the surface of galvanized aluminum plate, which is a slight defect, but the frequency of occurrence is higher than other slag defects.

The reason for its formation is that the zinc ash is produced by the scum on the zinc level at the furnace nose and the solid zinc slag condensed in the furnace nose cavity. The zinc slag falls on the surface of the strip steel and produces slight linear indentation along with the strip steel through the sink roll of the zinc pot, or the fine slag belt forms strip or point inclusions along the longitudinal direction on the surface of the galvanized aluminum plate, resulting in zinc ash defects.

The control measures are:

1. Optimizing nitrogen humidification system of furnace nose

The humidifying system can raise the dew point temperature and make the zinc vapor form a protective film on the surface of the zinc liquid to inhibit the continuous evaporation of the zinc liquid. If the dew point temperature is not properly controlled, excessive water vapor may cause defects. Therefore, the best dew point temperature of furnace nose should be determined in practice.

2. Cleaning of zinc slag in furnace nose

1) Make a special slag scoop and clean the scum in the furnace nose 2-3 times per shift.

2) The zinc slag adsorption and removal device in the furnace nose is added to blow the external hot air into the closed furnace nose through the fan.

3) Use the shutdown time to reduce the zinc pot, expose the zinc level at the furnace nose, and then manually remove the slag.

3. Temperature control of strip steel into boiler

1) The temperature of the strip steel entering the zinc pot shall be strictly controlled, because the temperature of the strip steel is more than 20 ℃ higher than the zinc liquid, which will not only increase the temperature of the zinc pot, but also lead to an increase in the amount of zinc slag.