A new metal protection technology implemented in new ShTV series CMO all-weather outdoor cabinets by cold galvanizing

12.05.2020

The most fearsome enemy for an outdoor all-weather cabinet is the environmental factors (solar radiation, snow and rain precipitation, flooding of the installation surface, increased dust and air pollution level) as well as the anti-icing agents. Therefore, for the outdoor cabinet, the resistance of metal to environmental conditions, corrosion and ageing are equally important along with the IP category and internal microclimate. Indeed, in some way or another, an all-weather cabinet is a part of urban landscape, where it is installed, and it should not turn into the rusty box but maintain its attractive appearance under any climatic conditions.

And since our company has set the aim to become an expert in manufacturing the outdoor all-weather solutions, we continuously experiment and test various production technologies, samples of metal and its protection methods in our laboratories.

Formerly, our products were coated as follows:

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Since the beginning of 2020, to improve the resistance of metal products subjected to weather impacts under different climatic conditions, we have developed the following process.

1. Surface preparation before coating

It comprises:

1.1. Degreasing + phosphatizing – it is the chemical method for pre-coating preparation.

Degreasing is necessary to remove any oils, dirt, metal oxides and graphite from the surface.

Phosphatizing is necessary to create an intermediate layer between the coating and the metal. This layer provides the additional protection of the metal surface against corrosion. The essence of the phosphatizing process consists in creating a layer of low-soluble iron phosphates on the protected layer surface. In addition, the iron phosphate layer ensures rigid adherence to organic coatings and improves the corrosion stability.

1.2. Primary and secondary washing.

Primary washing from the washing unit tank with cold water by pressure spraying. Preliminary washing to remove the residues of the reagent applied for phosphatizing (it is acidic).

Secondary washing from the washing unit tank with cold water by pressure spraying. Final washing of iron phosphates.

1.3. Washing the product surfaces with tap water by spaying – finishing product washing.

1.4. Product drying after phosphatizing

It is performed in the oven dryer at 120 °С.

2. Zinc coating

It is used to enhance the corrosion protection of the product surface. Epoxy zinc-rich primer with the Zn content up to 20% is used. It ensures high corrosion resistance under severe operating conditions. If the coating system has a penetrating damage, local corrosion may occur at this point, however it will not cause any effect on the coating adhesion in the adjacent surface, i.e. primer restricts the corrosion propagation area.

The primer is applied on the product in a chamber by powder spraying using the electrostatic precipitation method. After the powder paint is applied, the product is directed to the coating formation stage with the electroprecipitated primer. It comprises the primer layer melting, subsequent coating film formation, its hardening and cooling. Melting and polymerization are performed in a special furnace.

3. Applying finishing coating - polymer powder of the required size, gloss, structure

The polyether powder paint is used, which is applied in the spraying chamber on the already prepared primed product using the electrical precipitation method. After the powder paint is applied, the product is directed to the coating formation stage. It comprises the finishing polymer coating layer melting, subsequent film formation, its hardening and cooling. Melting and polymerization take place in a special furnace.

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The primer + polymer coating system ensures excellent protection of metal surface from corrosion. The protection efficiency depends on the surface properties, its preliminary preparation before coating, and the external coating applied. If the coating system has a penetrating damage, local corrosion may occur at this point, however it will not cause any effect on the coating adhesion in the adjacent surface. In case of coating damage, the primer + polymer coating system substantially restricts the corrosion propagation area.

We have tested different sample types of polymer coatings under GOST 9.401 Unified system of corrosion and ageing protection. Paint coatings. General requirements and methods of accelerated tests on resistance to the action of climatic factors. According to GOST 9.401 (it. 1.14 “the distance of corrosion propagation from the cut (Wd) is maximum 2 mm), all the samples have passed testing according to the B method. The best results were demonstrated by the samples primed with the epoxy zinc-rich primer both in terms of paint corrosion resistance and non-reduction of adhesion of the adjacent layer.

The new metal protection technology for CMO all-weather outdoor cabinets is implemented both in empty ShTV series wall-hanging and floor shells and in the manufacture of ready outdoor solutions of various configurations.


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