HOT - DIP GALVANIZING - PROCESS
For grease & oil removal from the surface of steel, It is immersed in acid based degreaser.
To clean the surface of carry over salts for effective acid cleaning.
The rust scale & mill scale are removed from the surface of the steel by passing it through 15 to 20% conc. HCL.
Steel is again rinsed to remove acid & iron salts.
Steel is then passed through heated zinc ammonium chloride solution to prevent oxidation & ensuring that the surface is prime before molten zinc immersion.
Oxide free steel is immersed in molten zinc at a temperature of 450-460 deg Celsius to form zinc–iron inter-metallic alloy. The period of dip depends on the mass to weight ration of steel item immersed.
The steel immersed in molten zinc is slowly withdrawn & quenched to ensure strong adhesion of zinc coating with the steel.
The steel is then chromate treated for providing passivation protection during transit or during storage of galvanised steels in humid conditions.