Zinc Ingots - SHG 99.9% Zn


14 Metre Zinc Hot Dip Tank


Technical Information

Zinc Coating: During the galvanising process, the zinc coating forms a metallurgical bond with the underlying steel. The molten zinc reacts with the surface of the steel to produce layers of zinc-iron alloys. The adherence of the coating is very high, typically between 20 – 30 M.P.A. The steel must be perfectly clean prior to dipping to avoid bare spots.

The inner layer, comprising a 75:25 zinc-iron alloy, is extremely hard and resistant to damage. The middle layer is a 90:10 zinc-iron alloy and the surface layer is pure unalloyed zinc and quite ductile. If the coating is physically damaged the galvanising will continue to provide cathodic protection to the exposed steel. Zinc corrodes very slowly but preferentially to the iron or steel, preventing the spread of corrosion from the exposed area. This is in contrast to other coatings that experience under-creep corrosion where there is a gap or pinhole in the coating.

The galvanised coating provides a uniform thickness of zinc on flat surfaces, and penetrates recesses to provide complete protection to potential corrosion spots. With painting, the coating thickness on the edges is less than on flat surfaces. This is in contrast with hot-dip galvanising, which provides full corner edge protection. These corners normally have 50% more zinc than the flat surfaces.

The thickness of the hot-dip galvanised coating is relative to the thickness of the steel profile that is to be galvanised. The zinc coating on a 3mm profile will be approximately 85-100 µm; thereafter the coating gets heavier according to the thickness of the steel profile, providing an extra-long lifetime. See table below:

Steel Profile ThicknessAverage Zinc Coating
 1.6mm – 2.0mm50 – 75 um 
 2.5mm – 3.5 mm75 – 100um 
 4.0mm – 6mm100 – 150um 
 7mm – 9mm150 – 200um 
 10mm – 12mm200 – 250um 
 12mm – 20mm250 – 300um 

Phoenix Galvanizing carries out work in accordance with the requirements of SABS SANS 121 SABS 1461 (certificate supplied on request). Customers undertaking work to this specification should be fully conversant with its contents, especially welding techniques and design for galvanising.

When steel that contains reactive levels of silicon and/or phosphorous is galvanised, the result is a dark, grey and heavy coating. Excessively thick coatings can be brittle. Customers should always order steel suitable for galvanising, preferably with a maximum silicon and phosphorous content of 0.3%.

Steel Profile: Generally, the thicker the profile of steel to be galvanised, the heavier the final coating of zinc on the steel surface will be. The reason for this is that the steel has to remain in the galvanising kettle for a longer time until the temperature of the steel reaches the temperature of the zinc. This has the effect of building up the zinc-iron alloy layers of the zinc coating and thereby increasing the final coating thickness.

Generally, steel less than 4mm is aluminium-killed steel and this tends to produce bright and shiny zinc coatings. Over 4mm, it is only by special order that customers will receive aluminium-killed steel. When aluminium-killed steel is used, coating thickness will be restricted to about 100 µm even on heavy sections and will always be aesthetically attractive.

On sections over 4mm, silicon-killed steel is normally used to make the thicker profiles. Silicon-killed steel is highly reactive with zinc and tends to produce heavier, darker grey coatings, which are less attractive but have a much higher corrosion resistance. Customers should always specify on their orders to steel suppliers that the steel should be suitable for hot-dip galvanising and on large orders even specify the limits of the silicon and phosphorous contents, i.e. phosphorous to be ideally less than 0.03mm and silicon to be less than 0.03mm (aluminium-killed steel) or in the range 0.15 to 0.30mm, which would be considered to be a controlled silicon-killed steel suitable for the galvanising process.

Hot Dip Galvanizers Association - Website