What does hot-dip galvanizing mean?
It is a process which consists in producing a metallurgical bond between steel and zinc, in a factory, under carefully controlled conditions. Thus treated, steel acquires corrosion resistance due to a surprising molecular bond between the two metals and cathodic protection.
Pre-galvanizing metals inspection
We only galvanize after a prior thorough inspection of the materials to be processed. The inspection seeks to:
- 1. Determine if the design, welding, manufacturing methods, as well as the general state of the surfaces are suitable to undergo the galvanizing process;
- 2. Detect the presence of paint or other contaminants, requiring the use of additional cleaning steps, using sandblasting or chemical washing;
- 3. Create ventilation openings to facilitate the ventilation and drainage of hollow cavities;
- 4. Check if conditions may affect the galvanizing process other
Cleaning and degreasing
Then comes the surface preparation step, including:
- 1. Using an alkaline solution to degrease and remove oily residues and dirt;
- 2. Dipping in a sulfuric or hydrochloric acid solution to remove all traces of rust and calamine through stripping;
- 3. To increase the steel’s adhesive properties, it is dipped in a zinc ammonium chloride solution. This will also prevent oxidation of the steel prior to dipping in the molten zinc bath.
After the acid cleaning, the steel goes through a zinc ammonium chloride solution to protect it against oxidation before the galvanizing process, ensuring optimum fusion between the steel and the zinc.
- 1. After having completed all of the surface preparation steps, the steel is dipped in a bath of molten zinc, creating a metallurgical bond by fusing both metals.
- 2. Although it is at the heart of the process, the steel's dipping in the molten zinc is relatively short. Despite this, the steel-zinc metal alloy is optimal as soon as the steel's temperature reaches that of the liquid zinc or 416 degrees centigrade (780 F). As soon as the alloy layers are formed, the steel is gradually removed from the zinc bath, thus creating a uniform and pure surface.
- 1. As soon as it leaves the liquid zinc bath, the steel is dipped in water to facilitate quick handling.
- 2. Other substances may be present in the cooling solutions to facilitate partial passivation of the surfaces, to improve the coating’s life and protect against the onset of premature spots. In the case of steel used in reinforced concrete, chrome cooling is recommended because this process promotes compatibility with concrete mixes.
- 3. In some cases (design standards or end use of the product), dipping is not recommended. Cooling is then done in open air. These procedures are intended to prevent deformation and are also recommended when the surfaces will be painted after galvanizing.
International standards require a certain thickness of the galvanizing layer. Careful inspection will be performed to ensure that the standards are met. If necessary, a certificate will be issued.
Warning: for optimal efficiency and performance, the dipping baths, as well as the procedures and inspection equipment are regularly inspected.