Galvanizing is a process used widely on a variety of metals to protect them from corrosion and abrasion. The process involves applying a thin coat of zinc to any base metal, the result is the Zinc acts as a shield against the environment. All the street signs and lamp posts that you pass while driving on the road are all Galvanized and therefore covered in a thin protective layer of zinc. You can tell Galvanized steel by it’s dull silver collar. This colouring is actually the outer layer of Zinc residing on the surface.
Why Galvanize Metals?
The primary reason for Galvanizing steel is to improve the corrosion resistant properties of the steel. The protective zinc coating helps the metal last longer than typical steel, especially when exposed to harsh weather conditions. Typical steel tends to oxidise and corrode faster. Galvanized steel is a very cost effective alternative to aluminium and stainless steel.
How Does Galvanized Steel Work?
Galvanizing can protect metals in a variety of ways. The first way that Galvanizing steel helps reduce corrosion is by providing a thin coat of zinc that prevents moisture, water and various other elements in the atmosphere from corroding the steel beneath. The zinc layer can be exposed by scratching the zinc layer off the surface. The result is the steel becomes susceptible to oxidisation and will wear down faster than the surrounding coated steel.
Galvanizing also protects the metals through a process called ‘galvanic corrosion’. This process happens when two metals with a different electrochemical structure are placed next to each other with an electrolyte present, salty ocean water being an obvious example. It will depend on the atomic structure, but one metal will be an anode whilst the other is a cathode. The anode corrodes quicker than it would by itself, and likewise the cathode corrodes slower than it normally would. Zinc tend to be the anode in this reaction. The result is that the zinc layer corrodes faster during galvanic corrosion whilst the steel corrodes much slower, elongating the lifespan of the actual steel.
Applications of Galvanized Steel
The extended lifespan of Galvanized steel makes it a perfect option for construction of mass infrastructure, due to the lower levels of maintenance required over it’s lifetime. Galvanized steel is also sustainable and recyclable.
– Using it in underwater environments, where there are varying changes in temperature;
– Just off the coast in seawater and marine environments;
– In mining underground in the presence of a soil-based environment;
– Any fixtures of placements where the steel comes into contact with other chemicals or building materials.
You can find Galvanized steel in air-conditioners, tubing, meter boxes, trailers and rendering mesh to name a few of it’s many applications.
Methods for Galvanizing Steel
There are a variety of ways to Galvanize steel. Below we will be mentioning the three most common methods for Galvanizing steel, and the benefits and drawbacks of each.
This method of Galvanizing requires dipping the base metal into a pool of molten liquid zinc. The base metal must be properly cleaned either mechanically, chemically or both. If not then the quality of the bonding between the zinc and the base metal will be compromised. Afterwards, a process of fluxing any remaining oxides is done. It is then placed into the zinc pool to form a metallurgical bond.
This system is highly economical and can be used with a variety of abnormal shapes. Unfortunately, the layer may be less even than other methods of Galvanizing.
Pre-Galvanizing involves rolling metal sheet through a cleaning process similar to the hot-dip galavanising method. After this rolling is complete, the metal will go through a pool of liquid zinc before being recoiled.
The benefits of this method, are that large coils can be quickly Galvanized with a more even coating. The only issue with this process is that when the metal is cut to shape, the edges remain unprotected.
Electro-Galvanizing is a unique process. Unlike Hot-Dip Galvanizing or Pre-Galvanizing, a liquid bath of zinc is not required. Instead this method uses electrical currents in an electrolyte solution to add zinc ions onto the base metal. The electrically reducing zinc ions are deposited onto a positively charged base metal. Electro-Galvanizing results in a very smooth even layer of zinc coating. In a similar way to pre Galvanizing, electro-Galvanizing is typically applied to large rolls of steel sheet.
The uniform coat that results from the electro-Galvanizing process makes it an ideal method for Galvanizing. However, the coating maybe thinner than either hot dipping or pre-Galvanizing. The result is reduced corrosion protection.