1. Main purpose

Hot-dip galvanized sheets are mainly used in industries such as automobiles, home appliances, construction, machinery, electronics, and light industry.

2. Classification of galvanizing in steel mills

There are two types of galvanized products manufactured by steel mills: electro-galvanized and hot-dip galvanized, and these two types are further subdivided. Electro-galvanized is divided into three types: single-sided, double-sided, and differential-thickness coatings from the thickness of the zinc layer. Hot-dip galvanizing does not have single-sided and differential thickness coatings, but hot-dip galvanizing is divided into galvanized and galvanized iron alloys, and electroplating does not have zinc-iron alloys. The electroplating coating on the coating type is extended to electro-galvanizing, electro-galvanizing-nickel, electro-tin, electro-chrome plating, and the extension of hot-dip galvanizing is more, including hot-dip galvanizing, zinc-iron, aluminum-zinc, zinc-aluminum, and zinc-aluminum-magnesium Wait.

3. Annealing method

There are two types of annealing methods for conventional cold-rolled coated products: continuous annealing and cover annealing.

4. Common steel types

Product categories: general commodity coil (CQ), deep-drawn hot-dip galvanized sheet (DQ), extra-deep-drawn hot-dip galvanized sheet (DDQ-EDDQ/SEDDQ), structural galvanized sheet (HSLA), bake-hardened hot-dip galvanized sheet Plate (BH), dual phase steel (DP), TRIP steel (phase transformation induced plasticity steel), etc., complex phase steel (CP), etc.

5. Defects of hot-dip galvanizing

Zinc layer peeling, scratches, passivation spots, zinc grains, thick edges, air knife streaks, air knife scratches, exposed steel, inclusions, mechanical damage, poor performance of the steel base, wavy edges, warping, unsuitable dimensions, pressure Printing, different thickness of zinc layer, roll printing, etc.

6. The main reason for the zinc layer falling off

The main reasons for the peeling off of the zinc layer are the reasons for the production of raw materials and the mismatch of processing. Due to surface oxidation, silicon compounds, NOF section oxidation atmosphere and protective gas dew point are too high, air-fuel ratio is unreasonable, hydrogen flow rate is low, furnace aerobic infiltration, the temperature of strip steel entering the pot is low, and the furnace temperature of NOF section is low. The grease evaporates endlessly, the aluminum content of the zinc pot is low, the unit speed is too fast, the reduction is insufficient, the residence time in the zinc solution is too short, and the coating is too thick. Processing mismatches include inconsistent bending radius, mold wear, scratches, too large or too small mold clearance, less stamping lubricating oil, long working hours of the mold without grinding and maintenance, etc.

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) Residual moisture on the surface of the strip steel;

(4) The passivation is not completely dried;

(5) Moisture or rain during transportation or storage;

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

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

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

8. The longest allowable storage time

If oiled, the packaging and storage are in place. Some products can be stored for more than one year, but it is best to use them for three months. If they are not oiled, the time is shorter to avoid oxidation caused by long-term storage. The specific storage time should be according to Execution standards corresponding to specific products.

9. Tolerance

The length tolerance is not allowed to have a negative value, and the maximum is not allowed to exceed +6mm. Regarding the tolerance, whether it is the length, width, or thickness tolerance, you can query it in the tolerance link in our applet.

10. Classification of spangles

Spangles are generally divided into large spangles, small spangles, and no spangles.

11. Protection principle of zinc layer

In a corrosive environment, zinc will corrode preferentially over steel, thereby protecting the steel base, and the zinc layer will form a certain protective film in terms of corrosion resistance to prevent excessive oxidation and delay the corrosion rate, and it can be painted with zinc during maintenance. Powder paint and other methods can prevent steel corrosion and ensure the safety properties of materials such as mechanical properties.

12. Passivation principle

The chromate passivation treatment of the galvanized sheet can form a passivation film. The trivalent chromium in the solution passivation group is difficult to dissolve in water, and its chemical properties are inactive, and it acts as a skeleton, while the hexavalent chromium is easily soluble in water. , can play the role of re-passivation 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 steam or humid air from directly corroding the galvanized sheet and play a protective role.

13. Methods of corrosion resistance

There are three ways to test the corrosion resistance of hot-dip galvanized sheets:

(1) Salt spray test; (2) Humidity test; (3) Erosion test.