Galvanized wire is wire that has been coated by zinc to protect it from corrosion. However, the term “Galvanized Wire” does not give details on the process used in the galvanizing process. But why is this important? There are two ways of galvanizing iron/steel, either electro-galvanizing or hot-dip galvanizing. These two types of galvanizing processes give the metal wildly varying levels of corrosion resistance. While hot-dip galvanized iron/steel may last up to 25 years without rust in harsh environments, electro-galvanized wire would be corroded in months in similar conditions.
Galvanized wire has many applications. We will focus on the galvanized wire used for fencing which includes barbed wire and chain link. Since fencing is done outdoors, the type of galvanizing becomes a point we need to consider critically. We will consider each one in turn.
Electro-galvanizing is the process by which a thin layer of zinc is applied to the base metal using electricity. The bare steel wires are immersed in a saline/zinc bath and electricity is used to move electrons from the zinc (anode) and bond them to the steel (cathode). The resulting zinc coating is thin and soft meaning that it can be damaged easily during transportation or use leaving the base metal vulnerable to corrosion. If placed outdoors like in the case of fencing, it may come into contact with moisture, further reducing the life of the metal. For this reason, electro-plated wire is banned by the Kenya Bureau of Standards for use in wire products used for fencing according to the standard “KS 261-2019.”
Hot-dip galvanizing process
Hot-dip galvanizing is the process by which the wires are coated with a thick layer of zinc by dipping them in molten zinc. As the metal comes into contact with the hot molten zinc, a chemical reaction occurs in which an abrasion-resistant intermetallic layer of iron and zinc is formed on the surface of the metal followed by a coating of pure zinc. The intermetallic layer is a unique characteristic of the hot-dip galvanizing process. This intermetallic layer is harder than the base metal thereby protecting it from damage by abrasion.
The hot-dip galvanizing process protects the wire in two main ways. Like the electro-plating process, the zinc coating acts as a barrier between the steel and the external elements thereby reducing the rate of corrosion. The layer of zinc deposited in this case is 10 or more times thicker than in the electro-plating process, therefore, offering greater protection. The second way the hot-dip galvanizing process protects the base metal is that when a part of it is exposed, the zinc will corrode instead of the metal. This is referred to as cathodic protection which is only possible through the hot-dip galvanizing method.
The main material used in the manufacture of fencing products such as barbed wire and chain-link is galvanized wire. Zinc which is used in coating the wires is an expensive component in the manufacture of the galvanized wire costing as much as 300KES/KG in comparison to iron which costs 60KES/KG. This means that the main determinant in the cost of galvanized wire is the thickness of the zinc coating. The hot-dip process deposits much more zinc onto the metal surface making it considerably more expensive than electroplating. But as we have already seen, elelctro-plating produces a substandard material that is unsuitable for outdoor fencing purposes.
When purchasing galvanized wire or its products, there is no way to tell which process was used in the galvanization. This makes it easy for cheap imports of electro-plated wire to permeate the market. Much of this electro-galvanized wire is imported from Asian countries and is used to make fencing products against KEBS standards. They are then sold at significantly cheaper prices to unsuspecting buyers only to rust soon after installation.
As they say, cheap is expensive. To save on costs in the long run you must buy your galvanized products from a reputable brand.