Galvanizing is a form of surface finishing that protects steel particularly well against corrosion. Ordinary coatings, such as wet painting or powder coatings, protect the component by preventing rection with oxygen (oxidation). However, if the protective layer is damaged, corrossion occurs quickly at the damaged area.
In galvanizing, on the other hand, the protective layer consists of a thin layer of zinc, which in addition to protecting against oxygen, also has a decisive property. The zinc of the coating is less precious than the steel structure below. The zinc layer therefore acts as a so-called sacrificial anode. This means that the surrounding steel structure is protected from corrosion until the zinc layer is used up.
As a result, the steel structures are still protected from corrosion even in the event of defects such as scratches, cuts, holes or edges. In the case of major defects, however, rework should be carried out to prevent corrosion. one should nevertheless work to avoid corrosion. In addition, the corrosion protection should also be taken into account during subsequent processing and this should be taken into account in the installation situation and when selecting the connecting elements.
For further details on professional galvanizing and the handling of galvanized steel structures, please refer to the standards attached at the end of the text.
Processes for galvanizing steel structures
In hot-dip galvanizing, the steel structure or components are immersed in a bath of liquid zinc. The temperature of the zinc is about 450°C. The zinc layer thicknesses are between 50 and 150 micrometers. In continuous strip galvanizing plants, such as those used for galvanizing steel sheets or pipes, significantly smaller zinc layer thicknesses are also produced.
Cost of hot-dip galvanizing
Depending on the order volume, size and complexity of the components or steel constructions, the prices for hot-dip galvanizing start at approx. 0.20 €/kg. You will find suitable suppliers for hot-dip galvanizing from Central and Eastern Europe in our directory.
In electrogalvanizing, the components are not immersed in a zinc melt, but in an electrolyte bath. The steel construction or the components serve as cathode in electrogalvanizing. The anode is an electrode made of pure zinc. When a voltage is applied, a layer of zinc is deposited on the steel structure. The thickness of this zinc layer can be controlled by the duration of the process. However, the zinc layer does not become uniformly thick everywhere. As a general rule, this results in layer thicknesses of between 5 and 40 micrometers, which is considerably less than with hot-dip galvanizing. The corrosion protection by electrogalvanizing is therefore fundamentally worse than with hot-dip galvanizing, but the process also offers advantages:
Due to the low thickness of the zinc layer, the dimensional accuracy of the components is better than with hot-dip galvanizing. Threads, for example, do not have to be reworked after galvanizing. It can also be used for temperature-sensitive workpieces. To further improve corrosion protection, the components can also be chrome-plated or powder-coated.
Cost of electrogalvanizing
The cost of electrogalvanizing is much higher than for hot-dip galvanizing and starts at around 1€/kg. Suitable suppliers for electrogalvanizing can be found in our industry directory.
In spray galvanizing, zinc wire is melted and applied to the workpiece using compressed air as in painting. The coating thicknesses are similar to those of hot-dip galvanizing and lie between 80 and 150 micrometers. Spray galvanizing can also be used on components that are not suitable for hot-dip galvanizing.
The decisive disadvantages are that it cannot be used in cavities and that the amount of work involved is comparatively high. In addition, the components must be further coated or painted after zinc spraying. The labor costs are therefore a decisive factor in spray galvanizing.
Other galvanizing procedures
- Zinc lamelle coating – Zinc lamelle coating is suitable for screws and small parts in larger quantities.
- Mechanical galvanizing – Mechanical galvanizing is used for springs and fasteners.
- Diffusion galvanizing, also called sheradizing – Diffusion galvanizing is used for components with high temperature resistance.
Find suppliers for galvanized steel structures
Usually, the manufacturing companies for steel construction take over the order processing with the respective galvanizing shop. You can find suppliers for galvanized steel constructions without much effort via our intermediary service.
Galvanizing for handicraft or laboratory applications
Build your own electroplating plant
For handicraft supplies and for small parts such as jewellery, there are self-made kits for electrogalvanizing* for home use. These are usually used for silver plating or gilding, but with the appropriate electrolytes* and a suitable zinc anode* they are also suitable for galvanizing. In addition to electroplating baths, there are also simpler hand galvanizing devices*.
Zinc dust paint or liquid zinc
Zinc dust paint and liquid zinc* are simple ways to apply cathodic corrosion protection afterwards. It is a primer containing fine zinc particles. This zinc dust provides the anti-corrosion properties. They are available both for painting and as practical zinc sprays*.
Further literature on galvanizing steel:
DIN EN ISO 1461 – Zinc coated strains applied to steel by hot-dip galvanizing ( piece galvanizing) – Requirements
and testing – and related supplement 1
DIN EN ISO 14713 – Protection of iron and steel structures against corrosion – Zinc and aluminium coatings –
DIN EN 2063 – Thermal spraying – Metallic and other inorganic coatings – Zinc, aluminium and their alloys (ISO 2063:2005)
*the marked links are used for advertising purposes
Sources: Wikipedia, above standards