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Galvanizing

The Hot–Dip Galvanizing Process

Hot-Dip Galvanizing is a factory applied molten coating and as such the primary responsibility for surface preparation as well as coating application falls with the galvanizer.

There are three basic elements to the galvanizing process.

1.    Surface Preparation (Cleaning Cycle)
2.    Hot Dip Galvanizing
3.    Inspection (Quality Control)

 Hot Dip Galvanizing Process

 

 

 

 

 

 

 

 

 

Surface Preparation

Surface preparation is the most critical step in the galvanizing process. If the steel is not properly cleaned the zinc will not adhere to the steel.

The primary steps for surface preparation are:

1. Degreasing/Caustic Cleaning

2. Acid Pickling

3. Fluxing

 

Degreasing/Caustic Cleaning

The metal is first immersed into a heated alkali solution to remove organic contaminants such as dirt, oil, grease, shop oil and soluble markings from the metal surface.

Paint, epoxies, vinyl’s, asphalt or weld slag must be removed by grit blasting, sand blasting, or other mechanical means before galvanizing. Removal of these materials is the responsibility of the fabricator.

 

Acid Pickling

The metal is immersed into a diluted heated sulfuric acid solution to remove any mill scale and surface rust to provide a chemically clean metallic surface.

Surface preparation can also be accomplished using abrasive cleaning as an alternative to, or in conjunction with chemical cleaning.

 

Fluxing

In the last step the metal is immersed in a flux solution consisting of Zinc Ammonia Chloride (Dry Kettle Process). The flux removes oxides and prevents further oxides from forming on the surface of the metal prior to galvanizing, and promotes the metallurgical bonding of the zinc to the iron or steel items surface.

 

Galvanizing

In this step the material is completely immersed in a bath of 98% pure molten zinc. The bath temperature is maintained at about 850 degrees Fahrenheit. The material is immersed long enough to reach bath temperature at 850 degrees. The material then is slowly withdrawn and any excess zinc is removed by draining and wiping.

Standard Dimensions of our Kettle:

Length: 25’ 0”

Width: 3’ 9”

Depth: 8’ 6”

The bath chemistry is specified by the American Society of Testing and Materials in Selected Specification for Hot-Dip Galvanizing, Standard Specification for Zinc (Hot-Dip Galvanizing) Coatings on Iron and Steel Products A123/A 123M-02.

 

Inspection and Quality Control

The most important method of inspection for galvanized articles is visual and the coating thickness. A variety of simple physical and laboratory tests may be performed for:

1. Thickness
2. Uniformity of the Coating
3. Adherence of the Coating
4. Appearance

The primary objective of galvanizing is corrosion protection, which is far superior to painting.

 

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