1. After pickling, the quality and temperature of dissolving aid are generally about 60 ℃
2. Zinc pot temperature, zinc pot temperature is generally between 450-470 degrees is the best, but because zinc pot is very expensive, low temperature will extend the life of zinc pot, so manufacturers generally control at about 430 degrees. Low temperature
makes alloying worse.
3. The shorter the hot dip time, the longer the galvanizing time, the coarser and drier the surface, the more zinc content, and the lower the alloying.
4. Cooling, natural cooling is the best, but manufacturers generally
use water to quench, so as to meet the needs of production rhythm, and also make the surface finish high, but the alloying also stops.
From the perspective of engineering practice, usually the owners or coating suppliers will require sand sweeping
treatment. It is difficult for them to accept that the hot-dip galvanized coating is sprayed directly without any treatment. The reason is very simple, and the quality of subsequent coating can not be guaranteed without treatment.
For the old type
of hot-dip galvanizing surface, it is understandable to do sand sweeping treatment before painting, because dirt and oxidation will affect the adhesion. However, this surface treatment should not be done at the expense of the corrosion resistance of normal
zinc coating. For the new hot-dip galvanized coating surface, there is no such problem, so the surface treatment method does not need to use sand sweeping.
Chromate solution is usually used for passivation of hot-dip galvanized parts, which affects
the adhesion of subsequent coatings. For the components that need to be painted after hot galvanizing, it is better not to do passivation treatment.
In addition, before spraying, it is better to use non-metallic abrasive to sweep sand, which can
enhance the adhesion of subsequent coating.
It is worth noting that the pH value of the treatment solution is on the high side, and the adhesion will decrease with the strong alkalinity.