DESIGN VERSIONS
Design version of cable trays depends on the operating conditions of a cable way and on additional aesthetic requirements for cable way appearance. Cable way operating conditions are determined according to the climatic conditions of the region, cable way installation location indoors or outdoors, presence of corrosive environments and exposure to liquids.
Design versions of products are determined according to GOST 15150-69 Modifications for Different Climatic Regions. This regulatory document establishes the following classification of climatic versions and categories of products:
- PRODUCT VERSION OF COLD-ROLLED STEEL GALVANIZED USING SENDZIMIR PROCESS.
Steel sheets in the form of strips are treated in a liquid zinc bath after their preliminary preparation. As a result, a zinc coat is formed of the steel surface on both sides. Depending on the type of product, the zinc amount on both sides of a steel sheet may vary from 140 to 275 g/m2, which corresponds to a thickness of 10 to 20 µm.
Zinc coating provides both barrier and cathodic corrosion protection. Cathodic protection is of sacrificial type, as zinc sacrifices itself to protect steel on which it is applied.
The process will continue until the last zinc atom. Thus, the thicker zinc coating is, the higher product durability will be.
Cathodic protection will also appear in local spots where no coating is left. Therefore, though the integrity of zinc coating may be damaged during the product manufacturing process (cutting, punching, drilling, etc.), the cathodic nature of protection by galvanizing ensures corrosion resistance for metal thicknesses up to 2.0 mm.
Coating service life or durability means its destruction time until the base metal exposure. Corrosion failure is determined as a coating weight loss per a unit area, corrosion rate is determined as g/m2 per day or µm/year.
Products made of galvanized steel correspond to climatic versions UHL 2.5; UZ; UT 2.5.
- HOT-DIP GALVANIZING OF PRODUCTS BY DIPPING METHOD.
This type of coating is applied by product dipping into melted zinc at a temperature of 450 °C. During the hot-dip galvanizing (HDZ) process, a coating is formed on the steel surface with zinc/iron base and a top coat of pure zinc.
The dipping method allows us to produce a zinc coat of higher thickness of 45 µm and more (depending on the product steel thickness) as compared with the continuous cold galvanizing method. It is not recommended to use this method for galvanizing of thin-walled products with steel thickness of 0.7 to 1.0 mm, as this may result in deviations of geometrical parameters.
Hot-dip galvanizing is an expensive coating, but it allows increasing the product service life up to 25 years. Hot-dip galvanized products correspond to climatic versions UHL 1.5; UT 1.5; M.
- PRIMING. PAINT COATING.
Priming process consists in application of primer coating in one or more layers on a preliminary cleaned surface of a metal product. Priming provides for creation only of a barrier protection of products, thus the structures treated using this method are suitable mostly for indoor works, where high protection level is not required. Also, priming of products is a necessary stage prior to paint coating application to improve the metal adhesion properties. Priming may be applied both on cold-rolled and galvanized metal. However, it shall be noted that the priming coating integrity is often damaged during product transportation and installation. Thus, we recommend applying priming coating on galvanized metal.
Primed products generally correspond to climatic versions UZ; UHL3.
After cable way installation, paint coating must be applied. Paint coating ensures barrier corrosion protection of products and meeting aesthetic requirements. Durability of state-of-the-art weather-resistant paint coatings (in temperate climate) is approximately 7 to 10 years. Weakness of paint coating application is significant increase of cable way installation time as painting is applied after the installation of all structures.
