Powder painting is one of the most popular methods of surface treatment of materials, as it provides a high-quality coating for various types of metal surfaces, including galvanised sheet metal. It is an environmentally acceptable procedure used for the improvement of the aesthetic appearance and durability of materials, while ensuring good resistance to weathering, corrosion and abrasion.
 

What is powder painting?

It is the process of applying a powder coating onto metal surfaces using dry powders that are applied to metal materials using electrostatics. The powder is then set by heating, which causes the coatings to melt and form a solid, homogenous layer which covers the entire surface.
The procedure is very popular in industry and construction, as it provides high resistance to mechanical damage, corrosion and various chemical and temperature stresses. .
 

 
Powder painting of galvanised metal

Galvanised metal elements are coated with a thin layer of zinc which provides protection against corrosion. Although zinc provides excellent protection, powder painting is often used either for aesthetic reasons or for additional protection. However, the galvanised surface has specific properties that need to be taken into account in this procedure.

1. Surface preparation: Surface preparation is of key importance in the powder coating of galvanised metal elements. Zinc can contain oxide layers or impurities that affect the adhesion of the powder coating. This is why prior treatment is required, including cleaning the surface and removing oxides. Chemical (e.g. acid solutions) and mechanical treatment (mechanical sanding or “swipping” – sanding the surface with glass beads) are used, with the latter being more suitable and giving better long-term results.
2. Application of the coating: When the surface is ready, the powder is applied with electrostatics. The electrostatically charged powder coating is bonded to the metal surface. The metal is then heated in a furnace to a temperature of typically 180-200°C, which causes the coating to melt and harden to form a solid protective layer.
3. Quality of the coating: Powder painting gives a thicker and more uniform layer that provides better protection against abrasion and aggressive weather effects than other methods, e.g. liquid coatings.
    

Advantages of powder coating

• High resistance to corrosion: Powder coatings ensure excellent protection against corrosion, which is especially important with galvanised sheet metal, which is often exposed to damp or high-salt environments.
• Aesthetic appearance: Powder painting provides a wide range of colours and finishes (matt, gloss, texture) which can enhance the visual appearance of galvanised sheet metal products.
• Durability: Powder coatings are highly durable and resistant to impact, scratches and abrasion, which extends the life of galvanised sheet metal.
• Environmental friendliness: The powder coating procedure is environmentally friendly as the coatings do not contain organic solvents, which reduces the emission of harmful substances into the environment.
• Ease of maintenance: A powder coated surface is easy to clean and maintain, as it is resistant to dirt.
   

 
Shortcomings and challenges

• Weaker adhesion to untreated zinc: Zinc has a natural lubricity which can make the adhesion of the powder coating more difficult. This is why surface preparation is essential.
• Coating thickness limitations: Excessive coating thickness can lead to processing problems and possible bubbling or surface damage.
• Porosity of the zinc layer: The zinc layer is partially porous, trapping air in the pores, which starts to escape from the layer when the powder coating is heated/baked. Additionally, heating also leads to the formation of volatile components. To reach the surface, the derived components cut tiny channels through the dust layer, which remain open/visible even on the hardened surface. The problem is solved in two ways, either by specially adapted powder coatings which close the resulting channels after the expulsion of air, or by preheating the galvanised surface prior to painting. This reduces the amount of gaseous components in the layer, facilitating the hardening of the powder coating. The painting is then carried out on the cooled surface, the zinc layer is cooled and painted after preheating.
• Suitable for smaller metal elements: Certain paint shops can paint elements up to 10 m long, but most paint smaller elements around 4 m.
   

Using powder coated galvanised metal

Powder coating of galvanised metal is commonly used in various industries such as:

• Construction: In the manufacture of construction elements such as roofing, façade panels and protective fencing, where both aesthetic appearance and weather resistance are important.
• Automotive industry: In the manufacture of automotive parts exposed to moisture and aggressive chemicals.
• • Agriculture: In the manufacture of equipment exposed to corrosion due to contact with water or dust, such as storage, transport and agricultural tools.

Powder coating galvanised metal is an effective and durable solution to improve both the aesthetic appearance and the protection of the material. When the procedure is performed correctly and the right choice of materials, this process results in high resistance to corrosion, UV rays and mechanical damage, which means a longer service life and lower maintenance costs. Although the procedure is demanding, its benefits in many industries outweigh the initial investment. The KANSAI HELIOS Group offers a range of powder coatings suitable for indoor and/or outdoor applications.