Corrosion protection for shelters

For particularly durable protection, hot-dip galvanizing is combined with paint systems. When we talk about hot-dip galvanizing and subsequent coating, we refer to “duplex”.

However, there is a widespread misconception that “the thicker the layer structure, the greater the protective effect”. The protection times of the individual processes do not add up, but the corrosion protection achieved is actually significantly higher. Incidentally, the corrosion protection of the outer skin of our cars has been based on this basic principle since the mid-1980s. But how exactly does it work?

With duplex process against rust

Exposed to air and rain, untreated steel components would rust after a short time. Rust generally occurs when metals react with oxygen in the ambient air under the influence of water and form oxides and hydroxides on their surface. Salts dissolved in water accelerate this corrosion process, as can be observed particularly well on ships or ferrous components near the coast. To prevent the corrosion of iron and steel (base materials), the duplex process is used, in which the steel is coated with a protective layer (passivation). The steel is coated with a thin alloy layer of zinc to protect the metal underneath.

Through the fire

Hot-dip galvanizing is when steel is immersed in a liquid zinc melt. Depending on the suitability of the object to be galvanized, this is done either piece by piece (discontinuous hot-dip galvanizing) or in a continuous process (continuous hot-dip galvanizing or Sendzimir galvanizing). Piece galvanizing offers the advantage of seamless corrosion protection, which also covers cut edges and hollow profiles. In addition, double to triple the zinc coating thickness can be achieved here.

But here too, less is sometimes more: “The thicker the zinc coating, the better the corrosion protection”. Sounds logical, but leads to the protective layers flaking off and thus to the exact opposite:

Instead of providing particularly good protection, the corrosion process is unintentionally accelerated. The DIN EN ISO 1461 standard applies to batch galvanizing. Suppliers who work according to this standard refer to many years of practical experience, which prove a protection period of 50 years and more. Galvanized metal surfaces form so-called white rust under the influence of air and moisture, which can be prevented by further chemical passivation.

Brilliant appearance

Painting metal has two objectives: Paints offer (additional) corrosion protection and allow components to appear in a completely new light thanks to a variety of color options. Every painting process begins with thorough pre-cleaning of the material, as grease, oil and dirt particles hinder the application of paint. This can be done either with pre-treatment and cleaning agents or by using mechanical processes such as grinding, dry ice blasting, etc., which can be used to remove production-related impurities easily and in an environmentally friendly manner. The cleaned metal parts are then primed and coated with wet or powder paint. With highly developed wet paints, so-called high-solid paints, very good values can be achieved in terms of abrasion resistance and corrosion resistance. At the same time, the paint is applied with low emissions, which benefits the environment.

Thorough and environmentally friendly pre-cleaning with dry ice.

Hot-dip galvanizing in a zinc melt provides reliable corrosion protection, even for hollow profiles and on cut edges. Environmentally friendly high-solid lacquering and drying in a circulating air process with halogen radiators. State-of-the-art technologies ensure that the components are painted in an environmentally friendly and resource-saving manner. This completes the duplex process perfectly and guarantees the high durability of our bus shelters and bus shelters.