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What is Galvanizing and why?

08-08-17
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What is Galvanizing and why?

Without protection, steel rusts due to atmospheric conditions and the degree of rust depends on the environment of the product.

 Galvanization is the process of applying a protective zinc coating to iron or steel in order to prevent rust and corrosion. The coating effectively becomes part of the steel as the zinc is bonded metallurgically to it.

 

Cleaning

Galvanizing can only occur if the steel’s surface is chemically clean. It is essential that it is free from dirt, grease and scale before the process can begin. The common practice is to degrease first then rinse in cold water to avoid contaminating the rest of the process.

The steel is then dipped in hydrochloric acid to remove any rust and mill scale. After further rinsing, the components will then commonly undergo a fluxing procedure by dipping in a flux solution. This removes the last traces of oxide and allows the molten zinc to wet the steel.

 

Galvanizing

 

When clean iron or steel is dipped into molten zinc (usually at around 450°C) a series of zinc-iron alloy layers are formed by a metallurgical reaction between it and the zinc. The initial rate of reaction is very rapid and the main thickness of coating is formed during this period. Subsequently, the reaction slows down and the thickness of the coating is not increased significantly even if left in the bath for a longer period of time.

The typical immersion time is about four or five minutes but it can be longer for heavy pieces that have high thermal inertia or where the zinc coating needs to penetrate internal spaces.

 

Post Treatment

 

Post galvanizing treatments can include air cooling or quenching in water. Conditions in the galvanizing plant such as air quality, temperature and humidity won’t affect the quality of the galvanized coating but are critically important for good quality painting. A paint or a powder coating can be applied for aesthetic reasons or for additional protection where the environment is extremely aggressive. Chemical coatings and other barrier systems might also be applied to minimise the occurrence of wet storage stain.

Galvanizing is a versatile process and products ranging in size from nuts and bolts to long structural sections can be treated this way. It is both economical and environment.

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