2nd of December ,2022

FAQ about hot-dip galvanized sheet

1. What is the main application of hot-dip galvanized sheet?

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

2. What types of galvanizing methods are there in the world?

Answer: There are three methods of electro-galvanizing, hot-dip galvanizing and galvanizing.

3. What are the two types of hot-dip galvanizing according to the different annealing methods?

Answer: It can be divided into two types: in-line annealing and off-line annealing, which are also called shielding gas method and flux method.

4. What are the commonly used steel types for hot-dip galvanized sheets?

Answer: Product category: General commodity roll (CQ), structural galvanized sheet (HSLA), deep-drawing hot-dip galvanized sheet (DDQ), bake-hardened hot-dip galvanized sheet (BH), duplex steel (DP), TRIP steel (transformation induced plasticity steel), etc.

5. What types of galvanizing annealing furnaces are there?

Answer: There are three types: vertical annealing furnace, horizontal annealing furnace and vertical and horizontal annealing furnace.

6. How many cooling methods are usually used in cooling towers?

A: There are two types: air-cooled and water-cooled.

7. What are the main defects of hot-dip galvanizing?

Answer: Mainly include: shedding, scratches, passivation spots, zinc particles, thick edges, air knife streaks, air knife scratches, exposed steel, inclusions, mechanical damage, poor performance of steel base, wavy edges, ladle warps, dimensions Inconsistency, embossing, inconsistency in zinc layer thickness, roll printing, etc.

8. It is known: the production specification is 0.75×1050mm, and the coil weight is 5 tons. What is the length of the coil? (The specific gravity of galvanized sheet is 7.85g/cm3)

Solution: L=G/(h×b×p)=(5×1000)/(0.785×1.050×7.5)=808.816m

Answer: The strip steel coil is 808.816m long.

9. What are the main reasons for the peeling off of the zinc layer?

Answer: The main reasons for the peeling of the zinc layer are: surface oxidation, silicon compounds, too dirty cold-rolled emulsion, too high dew point of NOF section oxidation atmosphere and protective gas, unreasonable air-fuel ratio, low hydrogen flow rate, and aerobic infiltration of the furnace. The temperature of the strip steel entering the pot is low, the furnace pressure in the RWP section is low and the furnace door sucks air, the furnace temperature in the NOF section is low, the oil evaporates endlessly, the aluminum content in the zinc pot is low, the unit speed is too fast, the reduction is insufficient, and the zinc liquid The residence time in medium is too short and the coating is too thick.

10. What are the causes of white rust and black spots?

Answer: Black spots are formed by further oxidation of white rust. The main causes of white rust are:

Poor passivation, insufficient or uneven passivation film thickness; no oil on the surface or residual moisture on the strip surface; moisture on the strip surface during coiling; incomplete drying of passivation; damp or rain during transportation or storage ; The finished product is stored for too long; the galvanized sheet is in contact with or stored together with other corrosive media such as acid and alkali.

hot-dip galvanized sheet

11. How long is the maximum allowed storage time for finished products in the warehouse? Why?

Answer: It is allowed to be stored for three months to avoid oxidation caused by long-term storage.

12. What is the length tolerance of galvanized steel sheet?

Answer: The length tolerance is not allowed to have a negative value, and the maximum is not allowed to exceed +6mm.

13. What is big spangle? What is a small spangle?

Answer: Large spangles are normal spangles. Large spangles can be produced according to the normal production process. The diameter of the crystal nucleus is not less than 0.2mm; the diameter of the crystal nucleus is less than 0.2mm, which is called small spangles. Generally, this kind of spangles cannot be used. Recognizable by naked eyes.

14. What is the protection principle of the hot-dip galvanized layer?

Answer: Because zinc can form a film with good corrosion resistance on the surface in a corrosive environment. It not only protects the zinc layer itself, but also protects the steel base.

15. What is the principle of passivation of hot-dip galvanized sheet?

Answer: Chromate passivation treatment of galvanized sheet can form a passivation film, and its chemical reaction formula is as follows: Zn+H2GrO4-ZnGrO2=H2

The trivalent chromium in the solution passivation group is insoluble in water, chemically inactive, and acts as a skeleton, while the hexavalent chromium in it is easily soluble in water, and can play a role in repassivation when the passivation film is scratched. Has the healing effect of a passive film. Therefore, within a certain limit, the passivation film can prevent steam or humid air from directly corroding the galvanized sheet, and the zinc layer plays a protective role.

16. What are the methods for testing the corrosion resistance of hot-dip galvanized sheets?

Answer: There are three methods for testing the corrosion resistance of hot-dip galvanized sheets: salt spray test; humidity test; corrosion test.

17. Why is anti-rust treatment required for hot-dip galvanized products?

Answer: When the hot-dip galvanized sheet is in humid air, especially when the air contains acidic substances such as SiO2, CO2, NO2 and NO, the surface of the galvanized layer will soon form loose white rust. The main components of white rust are ZnO and Zn(OH)2. This kind of white rust not only affects the appearance, but also brings great difficulties to future use.

18. What are the causes of white rust?

Answer: The causes of white rust are: hot-dip galvanizing is put together with other corrosive media such as acid, alkali, and salt; the passivation film or anti-film is destroyed; the passivation or oiling effect is not good; the storage warehouse is not well ventilated, Moisture; galvanized sheets are watered during transportation; transported at low temperatures and stored at high temperatures, forming condensation.

19. How to calculate the coating thickness?

Answer: The coating thickness formula is: Dz=Gz (Sz*dz) where: Dz——coating thickness mm, Gz——coating weight g per square meter, Sz——coating area mm2, dz——proportion of zinc , the above formula can be simplified as: Dz=0.000139Gz

20. What are the causes of zinc particles?

Answer: The problem of the original plate is mainly the cleanliness of the original plate and the content of iron powder in the original plate; the temperature of the zinc liquid is too high, which makes the bottom dross float; the content of Al is too high, which affects the solubility of iron.

21. What is the significance of hot-dip galvanized sheet skinning?

Answer: With the continuous expansion of the use of hot-dip galvanized sheets, in the modern continuous hot-dip galvanizing line for strip steel, the following goals can be achieved by skinning the strip steel:

① Improve the straightness and flatness of the thin plate, and at the same time flatten the zinc particles on the surface to make the surface of the strip steel smooth, which is especially beneficial for deep drawing and other occasions with high precision in use in the future;

②The skinning roller used has been pre-shot blasted, so the surface of the skinned plate has a certain roughness. It can improve the adhesion of the coating and store a certain amount of grease, which is beneficial to the lubrication of the die during deep drawing;

③ For the galvanized plate that will be painted later, although the surface is controlled into small spangles, the small spangles can still be exposed through the paint layer. Therefore, for some galvanized sheets with high requirements, the surface of small spangles needs to be light-finished. This will give the galvanized sheet a more uniform silver-white appearance;

④Through skinning, the lower yield point can be reduced, so that the yield platform disappears or is not obvious, which can prevent the slip line from appearing in the subsequent stretching or deep drawing process, and improve the possibility of deep drawing.

send us a message