Galvanizing


Excel provides comprehensive galvanising solutions to our clients. Since 2001, Excel has been successfully operating our own in-house Galvanising Plant at our works at Ajman.  Our Galvanising Plant works as a complement to our steel fabrication unit and tube mill.
This in-house plant is capable of Hot Dip Galvanising 50,000 tons of steel to BS EN 1461 standards, with an optimum output unit. Only the highest purity zinc is used as raw material. The Galvanising Plant is completely equipped for the entire pre-galvanising process, plus the post galvanising process. To provide the logistics it has been fitted with two electrical double girder cranes installed overhead. Our in-house design team provides our clients value-engineered solutions to modern-day engineering requirements.

Our state-of-the-art facility provides clients with high quality service and never comprises our commitments to sustainability, quality, and the environment. The entire plant has been housed in a specially constructed, purpose-built steel structure, designed in-house. Our vision for the Excel Galvanising Plant is that it will operate to meet the ever-increasing demand for galvanised structure materials for the extremely corrosive conditions in the Middle East.
 
Why Galvanise
 
Hot dip galvanising is an effective method to protect steel against corrosion. The initial cost for galvanising is low, and the corrosion protection life is very high. The life-time cost for galvanised steel is specifically advantageous in comparison with other corrosion protection systems.

Galvanised steel initially has a grey appearance, which harmonizes well with nature. If another colour is preferred, the galvanised surface can be painted. Painting further improves the corrosion protection of the galvanised steel.

Hot Dip Galvanising
Hot Dip Galvanising is so common in today’s engineering and financial world that many consider it a necessity. Galvanising is the electro-chemical process that enhances the innate properties of the steel material, protecting the steel from corrosion, which results in an extra long life. Hot Dip Galvanised steel is everywhere. It is used in steel construction materials, furniture and even aesthetic steel objects that are surround us in our daily lives. Hot Dip Galvanising is used frequently because it is a highly effective and cost efficient method to protect fabricated steel, structural steel, castings, or small parts from corrosion.
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The Process of Galvanising
Hot dip galvanising of steel requires that the steel first undergo rigorous preparation. The steel must be physically and chemically treated to remove any impurities before it is finally dipped into a kettle of molten zinc, at a temperature of around 450°C. When exposed to the air, pure zinc reacts with the oxygen to form zinc oxide, which further reacts with carbon dioxide to form zinc carbonate. Zinc carbonate is a dull grey, metallurgical alloy bonded coating that protects the steel from further corrosion, delivering a reinforced layer that protects the steel from corrosion.

Corrosion protection requirements can vary depending on the project specifications.  The most effective corrosion protection method for each project should be analysed based on several criteria.
  • durability
  • maintenance schedule
  • expected service life
  • initial cost
  • life-cycle costs
     
Hot-dip galvanised steel has superior durability, low initial and life-cycle costs, a long expected service life and a low-to-no maintenance schedule which makes it suitable for most applications.

Surface Preparation
Surface Preparation is a critical step in the application of any electro-chemical coating. In most instances, if a coating has failed before the end of the expected service life, it is due to incorrect or inadequate surface preparation.

The surface preparation step in the galvanising process has its own built-in means of quality control. Zinc simply will not react with a steel surface that is not perfectly clean. Any failures or inadequacies in surface preparation would be immediately apparent when the steel is withdrawn from the molten zinc. Any areas that have not been properly prepared remain uncoated. Immediate corrective action must be taken.

Surface preparation for galvanising typically consists of three steps: degreasing cleaning, acid pickling and fluxing.
  • Degreasing–A solution removes organic contaminants such as dirt, markings, grease and oil from the metal surface. Epoxies, vinyls, asphalt or welding slag must be removed before galvanising by grit-blasting, sandblasting or other mechanical means.
  • Pickling– Scale and rust are removed from the steel surface by “pickling” in a dilute solution of hydrochloric acid. The metal is then rinsed well to remove acid and iron salt.
  • Fluxing- The steel is immersed in liquid flux, which is usually a zinc ammonium chloride solution. This removes the oxides and prevents oxidation prior to dipping in the bath of molten zinc. The substrate item is individually dipped into a liquid flux bath, removed, allowed to dry, and only then is it galvanised.
Galvanising
After the exacting process of surface preparation is completed, the material to be galvanised is completely immersed in a bath that consists of a minimum 99.9% SHG pure molten zinc. Fabricated items are immersed in the bath long enough for them to reach the same temperature as the bath. The articles are withdrawn slowly from the galvanising bath and the excess zinc is drained off.

The chemical reactions continue after the articles are withdrawn from the bath for as long as they are close to the temperature of the bath. The articles are cooled in either water or ambient air immediately once they have been withdrawn from the bath. This results in the formation and structure of the chemically bonded, galvanised coating layer.

Inspection

The hot-dip galvanised coating quality is closely scrutinised after galvanising. 
Simple physical tests are performed to determine:
  • thickness
  • uniformity
  • adherence
  • appearance
Only the highest quality hot-dip galvanised coatings pass the Quality Control standards, here at Excel.