Hot Dipped Galvanising

Hot Dip Galvanizing is one of the most cost-effective methods of coating steel, given its long protective life span.

Almost all Webforge products are available galvanised, either in-house or through fellow Valmont Company, Industrial Galvanizers. Webforge NZ has an in-house Galvanising facility in its Palmerston North plant. All Galvanizing is carried out to AS/NZL 4680.

Galvanizing is the practice of immersing oxide free iron or steel into molten zinc in order to form a zinc coating that is metallurgically bonded to the substrate's surface.

The zinc coating protects the surface against corrosion:

By shielding the base metal from the atmosphere, and Because it is more electronegative than iron or steel, the zinc provides cathodic or sacrificial protection

Even if the surface is scratched, exposing the base metal, the zinc is slowly consumed while the iron or steel remains protected from corrosion.

The hot dip galvanizing process is adaptable to coating nearly any product including tanks, sheets, strip, pipes and tubes, fittings, hardware, wire cloth, hollow ware, and structural assemblies.

Galvanizing consists of four fundamental steps:

  • Surface Preparation - cleaning and pickling to free the surface of dirt, grease, rust and scale
  • Prefluxing - to dissolve any oxide that may have formed on the substrate surface after pickling, and prevents further rust from forming
  • Galvanizing - clean, oxide free items are immersed in the molten zinc
  • Finishing 
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Good Design leads to Good Galvanizing

The design of fabricated product is critical in determining the surface quality of the finished product. Unless the pretreatment chemicals can penetrate to all surfaces of the item, the inaccessible surfaces will not be galvanized. 

Conversely, if the molten zinc cannot completely drain from the work, zinc puddles will freeze in pockets and cause problems.

During the initial stages of fabrication, designing with Galvanizing in mind will always result in higher quality outcome.

The main issues to be addressed in designing for Galvanizing to minimize defects are:

  1. The item needs to be suspended during Galvanizing. The provision of lifting lugs to eliminate touch marks from wire or chains is an example of design improving quality.

  2. The item needs to have adequate venting and drainage provisions to ensure the smooth flow of zinc into and out of the item.

  3. The dimensions of the item need to comfortably fit within the bath dimensions to allow adequate withdrawal angles. Double dipping of the item will frequently produce a better quality than single dipping an item that can barely be submerged in the bath.

Technical Information

For further information, please see the links below:

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