There are different galvanising processes which consist of dipping steel in a bath of molten zinc at +/- 455°C.
This process is not limited though to only depositing zinc over a surface. Indeed, a metallurgical diffusion reaction also takes place between zinc and iron, which metallurgically binds zinc to the base steel.
Several zinc-iron layers are formed whose zinc concentration increases as the distance to the coating surface shortens.
The specifications of this process are found in the EN ISO 1461 standard.
The different methods are:
- continuous or Sendzimir: continuous or Sendzimir galvanising process consists of applying a zinc coating over the surface of a metal strip when this is dipped at high speed in a bath of molten zinc. The metal strips, with thickness between 0.25mm and 6.3mm, are transformed into finite products after galvanising. The layer of zinc thus obtained is 15 – 30µm thick. Zinc-aluminium (Zn/Al) alloys can also be used in this process;
- discontinuous batch galvanising after manufacturing: process during which finished products are dipped for a rather short time in a bath of molten zinc. The thickness of the total layer is generally between 80 and 120µm. Standard for discontinuous hot-dip galvanising or batch galvanising: EN ISO 1461;
- centrifuge galvanising: only small parts, like bolts, nuts, threaded rods, etc., can be centrifuge hot-galvanised. After having been pre-treated, these parts are galvanised by batches in baskets or drums and are centrifuged when taken out of the bath, to remove the excess of zinc. The zinc layer obtained this way is thinner than in the case of discontinuous hot-dip galvanising. The minimum layer thickness is specified in the EN ISO 1461 standard. Products with threaded rods are separately standardised in EN ISO 10684.
ISO 2063 Standard