Hot-dip galvanizing defects
In the coating by the method of hot-dip galvanizing may occur surface defects that reduce the duration and reliability of the product corrosion protection. Some of these shortcomings are due to the specifics of the metal processing process. Surface imperfections can create a bare spot, in such places the thickness of the coating will be 0. Requirements of GOST do not allow the presence of such gaps on steel products that have undergone hot-dip galvanizing.
Surface defects may occur as a result of retention of the product by means of chains or wires, transportation required during galvanization. These defects can be avoided by proper suspension and movement of products during galvanizing. However, there are cases where the product can be suspended only in one way, and then to avoid the prints of restraints during galvanizing is not possible.
It should be noted that the appearance of damage to the surface during galvanizing is also possible after the impact of products on each other (the occurrence of chips). For this defect is characterized by a partial coating or zinc-free spots on galvanized steel, arising in the process of contact of one product with another. Most often this occurs on the same traverse, which adjoin the a lot of small parts that can be galvanizing. It should be borne in mind that when placing products in a galvanizing bath, a small distance between the products contributes to the contact of the products and as a result contributes to the appearance of defects. These disadvantages can be easily eliminated by increasing the horizontal and/or vertical spacing between the products.
The defect of the non-galvanized surface of different origin, which is below the permissible boundary values and correctly restored is not a reason for claims regarding the quality of galvanizing. Standards GOST 9.307-89 fix the size of the restored areas of uncovered areas on production. It should not be more than 2% of the total area of the product. In other words, products with areas of non-galvanizing, suitable for the above formulation should be repaired according to GOST.