1. Choosing the right material
The determining factor in choosing a metal suitable for galvanizing is the silicon content, which should preferably be in the range of 0.15-0.21%. The thickness of the metal must also be taken into account, as the thickness of the zinc coating depends on it. We provide the minimum coating thickness according to the ISO standard.
2. Preparation of structures for galvanizing
Metal structures should preferably be prepared in accordance with the ISO 1090 standard, paying special attention to the quality of joints and post-treatment after welding.
New steel products are often coated with preservative oils or paint systems. In this case, the surface must be cleared before galvanizing. Paint is removed with abrasive blasting, while lubricating oils are removed chemically before galvanizing. Heavily rusted surfaces must also be cleared before galvanizing.
Attention must be paid to the correct choice of chemical aids:
Consequences of using an incorrect anti-spatter spray for galvanized products!
It is recommended to opt for a vegetable based anti-spatter:
3. Technological holes
Properly selected sizes and locations of technological holes play an important role in the quality of galvanizing, especially in hollow structures. If the holes need to be closed after galvanizing, we recommend using aluminium plugs.
Pictures showing the location of holes in the most popular/most common types of structures:
4. After galvanizing
The most common visual problems that do not affect corrosion protection after galvanizing include 'white rust' (zinc oxide), zinc runoff and acid runoff.
'White rust' is characteristic of fresh galvanized steel and manifests itself as whitish, unevenly shaped stains on the galvanized surface that wash off easily. These are zinc oxidation products that occur when fresh galvanized steel comes into contact with water and carbon dioxide. White spots should be rinsed with water or rubbed off with a fine abrasive. A freshly galvanized product should be placed in a dry, well-ventilated place.
Runoff on galvanized parts occurs when the parts are taken out of the bath and the zinc cools down rapidly. This is an unavoidable phenomenon that can be partially solved during the mechanical post-processing stage of galvanized parts.
If a product containing welded parts is treated with hydrochloric acid, the reaction products of hydrochloric acid remain under it. They are not completely removed during the galvanizing process and may appear after galvanizing in the form of brown, rusty runoff. This phenomenon is known as 'rust bleeding' and can be prevented by mechanically rubbing and rinsing the surface to be treated.
If you have any concerns or additional questions, please contact our managers!
It is important to keep in mind that the primary purpose of the galvanized coating is to protect against corrosion and that visual aesthetics are secondary (Section 6.1, ISO1461).