Why Galvanize
Hot dip galvanizing is a very effective method to protect steel against
corrosion. The initial costs for galvanizing is low, and protection life is
very high. The life time cost for galvanized steels is very advantageously in
comparison with other corrosion protection systems.
Galvanized steel has a grey appearance, which harmonize well with the nature.
If some other colour is preferred, it is possible to paint the galvanized
surface, which except the colour also further improves the already very good
corrosion protection of the galvanized steel.
HOT DIP GALVANISING timely necessity in engineering and financial world.
This is the process which will enhance the property of the steel material
resulting long life We are in constant contact with Hot Dip Galvanized steel
unconsciously from steel construction materials to aesthetic steel objects that
are surrounding our daily lives. It is a highly effective & cost efficient
method to protect fabricated steel, structural steel, castings, or small parts
from corrosion.
- Decreasing Bath Hard HCL
- Pickling HCL
- Rinsing Water
- Fluxing Ammonia and Zinc Chloride
- Hot plate
- Zinc batch
- Dychromizing
- Finishing & Fillin
Ø Tower parts – 86 Microns
Ø Bolt & Nuts - 45 Microns
Process of galvanizing
In the process of hot dip galvanizing steel under
goes rigorous preparation i.e physical and chemical treatment of the steel.
When sending steel through the Hot Dip Galvanising process, it undergoes work,
chemical treatment to remove impurities before finally dipping into a kettle of
molten zinc at a temperature of around 450°C. When exposed to the atmosphere,
pure zinc reacts with oxygen to form zinc oxide, which further reacts with
carbon dioxide to form zinc carbonate, a dull grey, fairly strong material that
stops further corrosion in many circumstances, to deliver a reinforced metallurgically
alloy bond that protects the steel from corrosion.
Depending upon the project requirement treatment of the steel is decided by
selecting the most effective corrosion protection system is important, and your
analysis of each method should include such things as the durability,
maintenance schedule, coating’s service life, and initial and life-cycle
costs.
Hot-dip galvanizing, with its superior durability, life-cycle cost, and
maintenance schedule make it suitable for most applications.
Surface Preparation is the most important step in the application
of any coating. In most instances where a coating fails before the end of its
expected service life, it is due to incorrect or inadequate surface
preparation.
The surface preparation step in the galvanizing process has its own built-in
means of quality control in that zinc simply will not react with a steel
surface that is not perfectly clean. Any failures or inadequacies in surface
preparation will be immediately apparent when the steel is withdrawn from the
molten zinc. Any areas that were not properly prepared will remain uncoated.
Immediate corrective action is taken.
Surface preparation for galvanizing typically consists of three steps:
degreasing cleaning, acid pickling and fluxing.
Degreasing– A solution often is used to remove organic contaminants
such as dirt, markings, grease and oil from the metal surface. Epoxies, vinyls,
asphalt or welding slag must be removed before galvanizing by grit-blasting,
sandblasting or other mechanical means.
Pickling – Scale and rust normally are removed from the steel
surface by pickling in a dilute solution of hydrochloric acid.
Rinsing - To remove acid and iron salt.
Fluxing - Steel is immersed in liquid flux (usually a zinc ammonium
chloride solution) to remove oxides and to prevent oxidation prior to dipping
into the bath of molten zinc. The item is separately dipped in a liquid flux
bath, removed, allowed to dry, and then galvanized.
Galvanizing In this step, the material is completely immersed in a
bath consisting of a minimum 99.9% SHG pure molten zinc. Fabricated items are
immersed in the bath long enough to reach bath temperature. The articles are
withdrawn slowly from the galvanizing bath and the excess zinc is removed by
draining.
The chemical reactions that result in the formation and structure of the
galvanized coating continue after the articles are withdrawn from the bath as
long as these articles are near the bath temperature. The articles are cooled
in either water or ambient air immediately after withdrawal from the
bath.
Inspection
The two properties of the hot-dip galvanized coating that are closely
scrutinized after galvanizing are coating thickness and coating appearance. A
simple physical tests may be performed to determine thickness, uniformity,
adherence and appearance