Leakage plating

There will be large or small black dot and block areas on the surface of galvanized steel strip. These black dot and block areas are not plated with zinc, with variable shapes and different sizes. In severe cases, flake appears on the upper and lower surfaces of the steel strip, which is called leakage plating or leakage steel. Serious point, block leakage and accompanied by zinc slag zinc particles is also called poor galvanizing. When the galvanized sample is subjected to mechanical bite or ball punching test, the surface of the zinc layer and the steel base are seriously separated, which is called the zinc layer falling off. It can also be seen directly on the production line that the zinc layer is partially separated from the steel base in a massive manner, and the zinc layer falls off, referred to as dezincification. Leakage plating is a defect that appears after galvanizing. Leakage plating or leakage steel has obvious black color and obvious color difference. The color difference is more serious when color coating, which affects the normal use of downstream customers. The surface of the steel strip is badly galvanized or the zinc layer falls off (dezincification) directly and cannot be used, and it is generally degraded.

Plating leakage is mainly caused by the following points,

1, the original plate in the library storage time is too long, the surface rust (raw steel plate rust seriously), in the annealing furnace can not be fully reduced;

2. There are defects on the surface of the original roll, such as pressing into the oxide scale, inclusions, etc;

3. The local oil stain of raw materials is too large, which is not cleaned in the cleaning section and furnace, or the oil stain accumulated by the pre-treatment degreasing groove roller system leaves periodic spots on the surface of the substrate;

4. The furnace nose ash at the furnace nose falls on the steel plate, and the galvanizing is not good (flake point leakage plating);

5. The dirt at the inlet seal is attached to the steel belt;

6. Resume production after shutdown for a long time. When the atmosphere in the furnace is not good, the surface of the steel strip cannot be fully reduced. For example, the protective gas is impure, the dew point is high, the hydrogen content is low, the annealing furnace leaks, water leakage or poor reduction conditions, and the unreduced oxides remain on the surface of the steel strip, which will cause leakage plating or zinc layer falling off;

Improper process control and poor operating conditions, such as high galvanizing temperature, long immersion time and improper control of aluminum content.

Leakage of plating prevention and treatment measures:

Balanced production to prevent steel strip inventory time is too long, generally not more than 20 days;

2. After the initial inspector of the Quality and Technology Department finds serious rust and other defects in the original plate, he shall timely feedback the purchasing department or the business department to contact and deal with them;

3. The production personnel shall strictly check the raw material substrate before boarding the machine, and the steel coil with serious corrosion of the raw material shall not be put on the machine for production. When producing steel coils with serious corrosion and oil pollution on the original plate, according to the actual situation, the steel coils on the machine that can be stripped must be stripped, and the coils that can be unrolled must be unrolled, and reported for feedback and waiting for treatment;

4, strengthen the pre-treatment cleaning capacity, increase the cleaning effect, once the surface of a variety of rollers found in the presence of dirt, should use special tools to clean, and periodic inspection and cleaning;

5, process control reduction annealing furnace furnace temperature and belt temperature, the steel plate annealing reduction;

6, regularly check the sealing of the annealing furnace, annealing furnace dew point, periodic cleaning furnace nose ash, strictly control the furnace nose into the protective gas purity, oxygen content and other factors affecting the atmosphere in the furnace, to prevent air leakage, water leakage and impure atmosphere;

7. The quality inspector on duty shall carefully check the surface quality of galvanized steel strip, timely feedback after finding plating leakage, find out the reason, and take measures to avoid more degraded products;

8. Strictly implement the operating procedures. When the annealing furnace changes, pay attention to adjusting the temperature, time, speed, ensuring the process, and balancing the production.