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Hot dip galvanizing - Process - detailed description of each stage

Hot-dip galvanizing process

The direct process of hot-dip galvanizing of metal includes 3 main stages:

  • Surface preparation;
  • Zinc-plating;
  • Control.

All these operations are important elements in the overall galvanizing of the metal.

Surface preparation

This is the most important operation before galvanizing. If the work is done poorly, the marriage will be made at the end of the process. On the dirty surface of the product zinc will not react with iron. All defects in the preparation of the metal will be visible when removing the metal. There are 3 main stages of the process:

  • Degreasing. In a hot solution of alkali metal is placed, where all impurities are removed: oil stains, dirt and grease. All mechanical obstacles must be removed by sandblasting or stripping.
  • Etching. The process takes place in acid baths, where it is possible to use other cleaning methods. The acid solution removes scale and oxidation from the metal surface.
  • Fluxing. This is the final process before the actual galvanizing. The product is immersed in a solution of zinc-ammonium chloride to create the necessary layer for the further formation of oxides on the metal surface. Also here are removed the remaining areas of the contaminated surface.

Hot-dip galvanizing process

Zinc-plating

In galvanizing operation, the product is immersed in a bath with 98% zinc heated to a temperature of 435 – 455 degrees Celsius. During the process, zinc interacts with iron to form an intermetallic bonded zinc – iron layer on top of which is a layer of pure zinc.

At the end, the product is removed from the bath. Excess zinc is drained.

The reaction of the metal and zinc will continue until the product temperature corresponds to the bath temperature. For cooling and drying, the galvanized metal is immersed in a passivation solution or water, can be positioned outdoors.

Control

Control of the process of galvanizing the metal, is simple. To do this, you need to visually inspect the product and identify flaws, if any. The necessary parameters can be determined by physical tests.

Galvanizing of metal is carried out according to GOST (9.307-89) of the Russian Federation. The standard includes the necessary parameters for galvanized metal.

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