Hot Dip Galvanizing process
Hot dip galvanizing is a process by which a steel product is zinc coated by immersing it in a molten zinc kettle, obtaining protection against the corrosive action of oxidation.
Before being immersed into the molten zinc, the material must be pre-treated; the main phases are degreasing (to remove residual grease and oils from mechanical processing), pickling (to remove scale, calamine and rust) and fluxing (obtained in a solution of salts to crystallize the surface of the product before being immersed in the zinc kettle.
The surface preparation of the product is extremely important for the zinc to react with the steel.
When the steel product is in the zinc kettle, the ferrous component reacts with the molten zinc forming an extremely adherent alloy that guarantees high corrosion protection.
Why hot-dip galvanizing?
Any steel product must be protected from corrosion and the efficiency of the protective system is mainly based on its quality and duration.
The protection provided by hot-dip galvanizing is much superior to other solutions with zinc (electrolytic galvanizing, zinc-based spray, mechanical coatings, etc.), with a duration, based on the surrounding environment, which lasts several decades.
Moreover, the lower initial costs, durability, availability and versatility of zinc, combined with sustainability and aesthetics, distinguish zinc as the ideal solution to protect the steel product.
Duration of hot dip galvanizing
The UNI EN ISO 1461 standard requires a minimum thickness such as to guarantee a duration of many decades without any maintenance. With a corrosion rate of less than 1µm per year in most European countries, the thickness required by the standard guarantees an extremely long life for the product.
A famous example is the Brooklyn Bridge. In coastal marine areas, the wind effect is an abrasive factor to be considered during design. The tension cables of the bridge were hot-dip galvanized to ensure efficient protection against the erosive action of atmospheric agents, since its inauguration in 1883.
The economic convenience of hot dip galvanizing
By determining the efficiency on the basis of the quality and duration of the galvanizing, this latter highlights a considerable convenience especially when compared to painting.
In fact, the initial cost is already cheaper but the treatment significantly gains value over time because the protection is much longer and more effective, reducing if not eliminating maintenance costs.
Why spinning? What can be centrifuged?
In the hot-dip galvanizing process, the spinning ensures that small steel parts are cleaned in such a way that it is hardly necessary a fixing by the operators.
Centrifugal galvanizing is ideal for all the items that require thorough cleaning, such as threaded parts, plates, artifacts with holes or items that require coupling or assembly in general.
It is therefore the ideal protection process for all threaded items. It is good to know that when manufactured a screw or a tie rod must be turned to a smaller diameter in order to allow to screw it after the hot galvanizing to nuts with nominal diameter. You can also hot-dip galvanize a tie rod with a nominal diameter when considering to use oversized nuts to ensure coupling.
Conversely, according to the standard, the nut screw must be machined after hot dip galvanizing, because the thread do not allow to eliminate the zinc during spinning. Alternatively, the nut can be re-threaded after galvanizing, but it is strongly recommended to ask for advice before to do that.
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