This is one of the metallic coated products available along with other common products such as Electro-Zinc coated and Iron-Zinc coated steels. The feedstock for HDG is Cold Reduced coil which has been through the Tandem Mill but has not been annealed or temper rolled.

The process starts with the coil passing through either an electrolytic cleaning process or a cleaning furnace, and then an annealing furnace to soften the steel and bring it to a temperature ready to enter the bath of molten zinc, hence the term "hot-dipped".

Various coating weights or thicknesses can be achieved by jets of air delicately blowing the strip as it rises vertically out of the coating bath. This has the effect of wiping the surface so that the correct amount of zinc remains. The zinc coating then freezes as it passes through coolers and a quench tank before entering a Temper Mill and, in the most modern lines, a Tension Leveller. These units do the same job for HDG as similar units do for Cold Reduced coil, i.e. improve the shape of the strip and help control the ductility.

At the end of the process the surface is treated (or "passivated") with chemicals to help prevent storage rust problems. Prior to final coiling a very light oil film for further protection may be applied.

There are two different types of hot-dipped galvanised steels available, Structural and Forming and each of these come in a number of different grades, with differing properties. .

Structural Grades
...........................................................................................................................
S220GD, S250GD, S280GD, S320GD, S350GD, S550GD  
...........................................................................................................................

Forming Grades
...........................................................................................................................
DX51D, DX52D, DX53D, DX54D
...........................................................................................................................
All Structural and Forming Grades available with Galvanised coating weights to suit your requirements:
Z100, Z200, Z275, Z350, Z600, ZF100, ZF140

Surface Treatments including:
      C - Chemically Passivated
      O - Oiled

Surface Finishes available:
Standard Galvanised Coating: NA - Normal Spangle, MB - Smooth, MC - Extra Smooth
Iron Zinc Coated: RA - Regular, RB - Smooth, RC - Extra Smooth
.........................................................................................................................