Analysis on the Causes of Galvanized Steel Coil Damage

When we import galvanized steel coils, we are worried about damage during transportation. We study the damage of some steel coils. The main feature is that black spots or white spots appear on galvanized steel coils.

There are three types of galvanizing processes: electro-galvanizing, hot-dip galvanizing, and galvanizing. The more commonly used one is hot-dip galvanizing. The white spots on galvanized steel coils are generally formed by the oxidation of the galvanized layer, which is rust damage. The black spot defect is composed of densely gathered black spots and is in the form of flakes. There are many reasons for black spots on galvanized steel coils, such as:

1) The purity of zinc in the galvanized layer is not enough, and metal impurities form an electric corner on the zinc surface;

2) Black spots caused by passivation treatment. The content of impurities such as copper, iron and arsenic in the galvanized layer is relatively high, and after passivation treatment, black spots are formed;

3) The aluminum content in the galvanized layer is insufficient, resulting in gray-black spots of iron-zinc alloy without pure zinc layer on the surface of the galvanized sheet;

4) Abrasive black spots, caused during transportation and stacking.

Among them, during the transportation, the abrasion black spots are caused by the misalignment between the steel layers. During the transportation of the hot-dip galvanized coil, there are stress concentration parts between the steel coil and the fixed bracket and between the steel coils. Under the condition of a certain friction coefficient, when the stress exceeds the bonding force between the outer passivation film and the substrate, the outer layer will occur. The passivation film of the first layer is damaged, which leads to the exposure of the inner zinc layer. In the closed environment, the oxygen content is insufficient, which leads to the generation of under-oxidation products, which appear as black spots macroscopically.

Will the galvanized steel coil be affected by black spots or white spots due to the damage of the outer packaging during sea transportation?

The role of the galvanized layer of the galvanized steel coil is to prevent the internal steel coil from being corroded and rusted. In humid air, a dense basic zinc carbonate film will be formed on the surface of zinc, thereby preventing further oxidation of zinc and steel inside. Since zinc is easily soluble in acid and alkali, the corrosion resistance of zinc is poor in sulfur dioxide, hydrogen sulfide and marine gases, and the galvanized layer is easily corroded. Therefore, the damage of the outer packaging during the sea transportation will cause the galvanized layer to be directly exposed to the humid gas of the ocean, which will easily lead to the corrosion of the galvanized layer and further corrode the inner steel coil.

How to seal the galvanized steel coil?

The zinc steel coil should be wrapped with anti-rust paper first, then wrapped with plastic film, and the inner and outer buffer corner protectors should be installed, and then the inner peripheral guard should be installed. The standard is a direct layer of inner peripheral guard, but it is better to add another layer inside Then install the outer peripheral buffer guard plate, then install the outer peripheral guard plate and the end round guard plate, and then install the inner and outer metal corner guards, and finally tie it firmly with straps, both in the circumferential and radial directions. less than three.

All steel coils exported by Wanjuan will be packaged according to the requirements from a safety point of view to avoid damage during re-transportation. Order Galvanized Steel Coil for your project today.