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altIn addition to the products manufactured by all its companies, NAGÉV group offers the hot-dip galvanizing services of NAGÉV Kft. and NAGÉV CINK Kft. Due to the process, the protection of new or properly prepared metal surfaces can be ensured at least for the time period of twenty years, but in case of products that are less exposed to extreme environmental conditions it is guaranteed for as much as 40-50 years.

The hot-dip galvanizing technology looks back on a history of nearly three centuries. During the past decades the process that has been previously available exclusively for the industry became available for all enterprises and the population too. Instead of manufacture-like methods and work performed in secret and dark workshops, today hot-dip technology is used in spacious and clean working environments in modern plants, taking care of environment protection.

During the hot-dip galvanizing process the properly cleaned steel surface (base metal) is dipped into liquid zinc (zinc bath). While in the zinc bath – due to the high temperature (between 445-455 °C) – zinc diffuses into the surface of the basic metal, forms an alloy with it, and is accumulated on its surface. The more time is spent in the zinc bath, the thicker zinc layer is created on the basic metal.

Factors with major influence on the quality of hot-dip galvanizing:

• Quality, chemical composition of the raw material of the structure to be dip galvanized

• The status of the surface subject to hot-dip galvanizing

• Technical preparation of the pieces subject to hot-dip galvanizing

The role of these three factors is summarized below. However, for more information we recommend that you download and read our Guideline on hot-dip galvanizing.

Selecting steel quality optimal for hot-dip galvanizing

altIn general, non-alloy carbon steels, slightly alloyed steels and cast irons are suitable for hot-dip galvanizing. Steels with high alloy and sulphur percentage are not suitable for this kind of metal coating. During dip galvanization the coatings created comply with the MSZ EN ISO 1461 standard. However, within the group of steels suitable for hot-dip galvanizing there are steel types that develop a sufficiently thin silver and shiny layer on their surface, while others form a thicker and grey layer. This phenomenon correlates primarily with the silica (Si) and phosphor (P) content of steels. See our Guideline for hot-dip galvanizing for more information on the composition of steel types and their suitability for dip galvanizing.

The status of the product surface subject to hot-dip galvanizing

Before shipping for hot-dip galvanizing, thick residues of fat, oil, non-water soluble paint, tar, slag from welding, silica spray, etc. on the surface of the pieces should be removed. These can be removed by using other surface cleaning methods (e.g. blast cleaning). Most dip galvanizing plants are not prepared to perform this task and it does not belong to their area of work either. However, rusty products in “commercial” status can be hot-dip galvanized after proper preparation performed at the galvanizing plant (fat removal, hydrochloric acid bath).

Preparation of the products subject to hot-dip galvanizing as part of the technology

altDuring the preliminary treatment, pieces are dipped into degreasing liquid, hydrochloric acid bath, then into liquid zinc at the temperature of 450 °C when performing hot-dip galvanizing. During the removal of the pieces all liquid residuals should be drained and no gases and no tar should be left inside the pieces, no “liquids bags” or “airbags” shall remain, since they result in a loss of material and quality problems. Therefore, drain and ventilation outlets of adequate size, number and position must be applied on structures subject to the treatment. Any liquid remaining in the closed spaces might suddenly convert into steam in the zinc bath, which might produce a pressure equal to hundreds of bars. A sudden explosion might destroy the structure itself; moreover, it is a source of accident risk for people working there. If the requirements on outlets are not met, then not only the airbags, the zinc and liquid residues will challenge the quality of the product, but the remaining and sticking tar as well. Due to the above reasons it is obvious that the existence of the outlets, their sizes and locations required in line with the technology play an important role.

See our Guideline for hot-dip galvanizing for more information on the need for preparation of pieces in line with the technology and the methods used.

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