Zinc is most commonly used as an anti-corrosion agent, and galvanization (coating of iron or steel) is the most familiar form.

Zinc is more reactive than iron or steel and thus will attract almost all local oxidation until it completely corrodes away. A protective surface layer of oxide and carbonate ( Zn5(OH)6(CO3)2 ) forms as the zinc corrodes. This protection lasts even after the zinc layer is scratched but degrades through time as the zinc corrodes away.

The zinc is applied electrochemically or as molten zinc by hot-dip galvanizing or spraying. Galvanization is used on chain-link fencing, guard rails, suspension bridges, lightposts, metal roofs, heat exchangers, and car bodies.

The relative reactivity of zinc and its ability to attract oxidation to itself makes it an efficient sacrificial anode in cathodic protection (CP)

STC Exports and Maintains large quantities of special high grade zinc (HS code 7901).

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Zinc Durability

How Zinc Protects

Galvanized steel is one of the strongest construction materials in existence and has been used for centuries in the building of bridges, buildings, and other structures.
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Types of Products

Galvanized :

A pure zinc coating that is the standard continuous galvanized product typically used in building panels, steel framing, agricultural and automotive applications, as well as in numerous other functions. It has good surface finish and adhesion properties.

Electrogalvanized :

Generally a pure zinc coating, although alloys (e.g. Zn-Fe, Zn-Ni) are available. Coating thickness is typically lower than for a galvanized product. Provides an ultra-smooth finish which is desirable for surface critical parts such as automotive exterior body panels.

Continuous Galvanizing

In the continuous hot-dip galvanizing process, steel is fed through cleaning and annealing sections before entering a molten zinc bath at speeds up to 200 meters per minute (650 feet/minute). As the steel exits the molten zinc bath, gas “knives” wipe off the excess coating from the steel sheet to control coating thickness. The steel then undergoes a series of mechanical or chemical treatments. Depending on customer requirements, the coated steel can be passivated, oiled and recoiled, or cut to length and palletized before shipment to the fabricator. Continuously galvanized coatings are metallurgically bonded to the steel they protect. This ensures coating adhesion – critical for manufacturing processes that bend, stamp, roll or draw the steel into its final product shape.

Protecting steel against corrosion is the most important market for zinc, representing 60% of zinc use worldwide.

How Zinc Protects

One of zinc’s most exceptional qualities is its natural capacity to protect steel from corrosion. Damage caused by corrosion leads to costly and time consuming repairs and its estimated cost to all the world’s economies is $2.2 trillion USD ($2,200,000,000,000) annually. When left unprotected, steel will corrode in almost any environment

Barrier Protection

Zinc coatings provide a continuous, impervious metallic barrier that prevents moisture from contacting steel. Without direct moisture contact, there is no corrosion. However, since zinc gradually corrodes due to its much slower degradation in the presence of water and atmospheric pollutants in open air applications, barrier life is proportional to coating thickness. This subject has been researched for many years and the literature is well supplied with reports on zinc’s performance in different climates, with different alloy additions to the coating and at different coating thicknesses. Applying paint over zinc can also extend barrier longevity.

Cathodic Protection

Another outstanding protection mechanism is zinc’s remarkable ability to galvanically protect steel. When bare steel is exposed to moisture, such as at a cut edge or surface scratch, steel is protected by the sacrificial loss of zinc in the vicinity of the exposed steel. In the immediate presence of zinc, steel will not corrode until all the zinc has been sacrificed. This is particularly important for coated steel sheet since corrosion will continually undercut both aluminum or paint barrier coatings. The presence of zinc is the key to cathodic protection. All zinc-containing metallic coatings, including zinc-rich paints, share this beneficial characteristic.

General Galvanizing

General Galvanizing, also known as Hot Dip Galvanizing, After-Fabrication Galvanizing or Batch Galvanizing, refers to the galvanizing of fabricated or manufactured steel items. The fabricated steel article is cleaned and then dipped into a molten zinc bath, either on racks for small items or individually for large items.

Zinc coatings from this process are five to ten times thicker than continuously galvanized coatings and can offer long term outdoor protection in most environments. This resistance can vary from 20 years in an industrial site to over a century in a rural environment.

General galvanizing provides fabricated steel items with excellent protection against corrosion. The nature of the immersion process provides good edge protection and complete coverage of the outer surface area as well as inner protection of hollow parts. In general, a zinc coating of at least 60-70 μm is applied.

Because galvanizing requires no maintenance, the initial cost of a bridge, mass transit station, sign structure, etc. is the final cost, making hot-dip galvanized steel among the lowest life-cycle cost corrosion protection systems available.

Hot-dip galvanizing makes steel structures (handrail, guide rail, bridges, signs) safer. The galvanizing process applies zinc on difficult to reach corners and the inside of poles, box girders, towers, and handrail; places where corrosion usually begins on painted and unprotected steel.

The factory controlled galvanizing process is independent of weather. Steel can be coated with zinc 24/7/365 and galvanizers are in virtually all geographic areas of the world.

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