Galvanized sheet trade necessary knowledge

1. Main purpose.

Hot galvanized sheet is mainly used in automobile, home appliances, construction, machinery, electronics, light industry and other industries.

2. Classification of galvanized steel plant.

There are two methods of galvanizing products shipped from steel mills: electric galvanizing and hot dip galvanizing, which are further subdivided. According to the different thickness of zinc layer, electrogalvanizing is divided into three categories: single-sided, double-sided and differential thickness coating. Hot-dip galvanizing has no single side and thickness of the coating, but hot-dip galvanizing is divided into galvanized and galvanized iron alloy, while electroplating has no zinc-iron alloy. From the type of coating, electroplating can be divided into electrogalvanizing, electrogalvanizing nickel, electroplating tin, electroplating chromium, etc. There are more extensions for hot dip galvanizing, including hot dip galvanizing, zinc iron, aluminum zinc, zinc aluminum and zinc aluminum magnesium. Wait a minute.

3. Annealing method.

Conventional annealing methods for cold rolled coating products include continuous annealing and cover annealing.

4. Common types of steel.

Product category: Ordinary commodity coil (CQ), deep drawing hot galvanized sheet (DQ), super deep drawing hot galvanized sheet (DDQ-EDDQ/SEDDQ), Structural galvanized sheet (HSLA), bake hardening hot galvanized sheet (BH), duplex steel (DP), TRIP steel (phase change induced plastic steel), composite phase steel (CP), etc.

5. Defects of hot dip galvanizing.

Zinc layer peeling, scratches, passivation spots, zinc particles, thick edges, air knife stripes, air knife scratches, exposed steel, inclusions, mechanical damage, poor basic steel properties, wavy edges, curved edges, inappropriate dimensions, embossing, inconsistent zinc layer thickness, roller printing, etc.

6. Main causes of zinc layer shedding.

The main causes of zinc spalling include raw material production and process mismatch. Raw materials include surface oxidation, silicon compounds, NOF oxidation atmosphere and protective gas dew point is too high, air fuel ratio is unreasonable, hydrogen flow rate is low, aerobic penetration in the furnace, strip steel into the pot temperature is low, NOF furnace temperature is low. The grease can not be completely evaporated, the zinc pot contains low aluminum, the unit speed is too fast, the reduction is insufficient, the residence time in the zinc liquid is too short, and the coating is too thick. Processing mismatches include inconsistent bending radius, mold wear and scratches, mold clearance is too large or too small, insufficient stamping oil, mold working time is too long without grinding and maintenance.

Comprehensive: Basic knowledge of galvanized sheet trading.

7. Causes of white rust and black spots.

The main causes of white rust are:.

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

(2) The surface is not oiled.

(3) There is residual moisture on the strip surface.

(4) The passivation layer is not completely dry.

(5) Exposure to moisture or rain during transportation or storage.

(6) The storage time of finished products is too long.

(7) Galvanized sheet and acid, alkali and other corrosive media contact or storage together.

White rust may evolve into black spots, but black spots are not necessarily caused by white rust alone, such as friction black spots.

Comprehensive: Basic knowledge of galvanized sheet trading.

8. The maximum allowed storage time.

If it's oiled, packing and storage are in place. Some products can be stored for more than a year, but it is best to use within three months. If not oiled, the time is shorter to avoid oxidation caused by long-term storage. The specific storage time should be carried out according to the execution standard of the specific product.

9. Tolerance.

The length tolerance is not allowed to have negative values, and the maximum tolerance is not allowed to exceed +6mm.

10. Zinc flower classification.

Zinc flowers are generally divided into large zinc flowers, small zinc flowers and zinc free flowers.

Comprehensive: Basic knowledge of galvanized sheet trading.

11. Protection principle of zinc layer.

In a corrosive environment, zinc corrodes preferentially over steel, thus protecting the steel matrix. In terms of corrosion resistance, the zinc layer will form a protective film to prevent excessive oxidation and slow down the corrosion rate. Zinc can be applied during maintenance. The corrosion of rebar is prevented by powder coating and other methods to ensure the mechanical properties and other safety properties of the material.

12. Passivation principle.

Passivation film can be formed by chromate passivation treatment of galvanized sheet. The trivalent chromium in the solution passivation group is insoluble in water, chemically inactive, and plays a skeleton role, while the hexavalent chromium is easily soluble in water, and can play a re-passivation role when the passivation film is scratched, and has the healing effect of the passivation film. Therefore, within a certain limit, the passivation film can prevent the direct corrosion of steam or humid air on the galvanized sheet and play a protective role.

13. Methods of corrosion resistance.

There are three test methods for the corrosion resistance of hot galvanized sheet:

(1) Salt spray test. (2) Moisture content test. (3) Erosion test.