Zinc’s good corrosion resistance is based on a protective film, a carbonate layer that forms on its surface. The service life of a zinc surface depends on the layer thickness. Long-term corrosion tests conducted in Finland and practical experience show that zinc corrodes in a rural setting by around 0.5 microns and in an urban setting by around 1 micron per year.
Uniform protection throughout
By submerging the steel into molten zinc, a uniform protective layer is obtained throughout. The zinc penetrates difficult-to-handle internal surfaces, tubes and other tight spots. The zinc coating is of uniform thickness throughout, even at the sharp points. Corners susceptible to knocks receive the enhanced protection of a paint coating.
Surface finishing in controlled conditions
Surface finishing of hot dip galvanized structures takes place entirely in dry and heated indoor premises to control process quality. During the process, items are not exposed to environmental conditions that might compromise the quality of surface finishing.
Surface finishing of a structure begins with shot-blast cleaning, as described in the SFS-EN ISO 12944-4 standard. Shot-blast cleaning removes from the surface zinc salts that form after galvanization as well as other impurities. Shot-blast cleaning is performed at low air pressure using a non-metallic cleaning abrasive whose grain size is optimized so that a sufficient surface coarseness is obtained to ensure paint adhesion. Blast cleaning takes place in uniform indoor conditions just prior painting to ensure that no corrosion products harmful to the protective paint compound remain on the cleaned surface.
Painting is performed with powder coat or two-component wet paints as per the customer’s order. During painting, painting chamber conditions are regulated according to the requirements of the paint products. Before painting, the structure is examined for possible surface imperfections and any such imperfections are removed before painting begins. During painting, the person performing the work measures the thickness of the paint layer and assesses paint consumption in relation to the area of the structure in question. The checking of the paint layer thickness ensures that the final product receives a layer thickness and sufficient protection to fulfill requirements
After application of the powder curing of takes place in a powder coating oven or, in the case of wet paints, in a painting chamber at an optimised temperature. During curing the paint film or films acquire the characteristics planned for surface finishing.
The products are checked visually and paint layer thickness and, if necessary, adhesion are measured.
After checking, the approved products are packed for delivery. The entire process is performed in the same premises and during the short surface-finishing process the structures are not exposed to varying environmental conditions, which ensures high quality end result.