Galvanized sheet trade knowledge

1. the main use

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

2. steel galvanized classification

Steel factory galvanized products have two types of galvanizing, hot-dip galvanizing methods, and these two categories are subdivided, electric galvanizing from the thickness of the zinc layer is divided into single-sided, double-sided and differential thickness coating three categories, and hot-dip galvanizing is not single-sided and differential thickness coating, but hot-dip galvanizing is divided into galvanized and galvanized iron alloy, electroplating is not zinc iron alloy. The plating on the type of coating is extended to electrogalvanized, electrogalvanized nickel, electroplated tin, electroplated chromium, and the extension of hot galvanizing is more, including hot galvanizing, zinc iron, aluminum zinc, zinc aluminum, and zinc aluminum magnesium.

3. Annealing method

The annealing methods of conventional cold-rolled coated products are continuous annealing and mask annealing.

4. commonly used steel

Product categories: General 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 steel base performance, wave edges, bending, improper size, imprinting, improper zinc layer thickness, roll printing, etc.

6. the main reason for zinc layer shedding

The main causes of zinc layer shedding are raw material production and processing mismatch. Raw materials due to surface oxidation, silicon compounds, NOF oxidation atmosphere and protective gas dew point is too high, air fuel ratio is unreasonable, hydrogen flow is low, furnace oxygen infiltration, strip steel into the pot temperature is low, NOF furnace temperature is low, oil evaporation is not enough, zinc pot aluminum content is low, unit speed is too fast, insufficient reduction, zinc liquid residence time is too short, coating thickness. Processing mismatches include bending radius inconsistency, mold wear, scratching, mold clearance is too large or too small, stamping lubricating oil is less, mold working time is too long without grinding maintenance.

7. Causes of white rust and black spots

The main causes of white rust are:

(1) poor passivation, passivation film thickness is not enough or uneven;

(2) The surface is not oiled;

(3) residual moisture on the strip surface;

(4) passivation is not completely dried;

(5) Damp or rain during transportation or storage;

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

(7) 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 the black spots are not necessarily caused by white rust, such as rubbing black spots.

8. Maximum allowable storage time

If the oil is coated, the packaging and storage are in place, the storage time of some products can be more than 1 year, but it is best to use it for three months, and the time is shorter without oil, so as to avoid oxidation after storage for too long. The specific storage time should be implemented according to the corresponding standards for specific products.

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, generally divided into large zinc flowers, small zinc flowers, zinc flowers.

11. the protection principle of zinc layer

In a corrosive environment, zinc will be preferentially corroded than steel, thus protecting the steel base, and the zinc layer in corrosion resistance will be a certain protective film to prevent too fast oxidation, delay the corrosion rate, and can be painted in the maintenance of zinc powder paint and other ways to prevent corrosion of steel, to ensure the mechanical properties of the material and other safety properties.

12. passivation principle

The chromate passivation treatment of galvanized sheet can form a passivation film. The trivalent chromium in the solution passivation group is insoluble in water, and its chemical properties are not active, which plays a skeleton role, while the hexavalent chromium is easily soluble in water, which can play a re-passivation role when the passivation film is scratch, and has the healing effect of passivation film. Therefore, within a certain limit, the passivation film can prevent steam or humid air from directly eroding the galvanized sheet and play a protective role.

13. Method of corrosion resistance

There are three ways to test the corrosion resistance of hot galvanized sheet:

(1) salt spray test; (2) moisture test; (3) Erosion test.