"1. What is corrosion and how does galvanizing protect substrate (Steel, Aluminum) from corrosion:
Generally corrosion is an undesirable phenomenon which occurs in every material. It leads to loss of material when exposed to the environment. It can be controlled by applying/putting other active material coating or cover on the required material. Active materials are listed in EMF series. Often Zinc is used as an active material in the galvanizing process as it provides an impervious barrier between the substrate and corrosive elements in the atmosphere. It does not allow moisture and corrosive
chlorides and sulfides to attack the substrate. Zinc is more importantly anodic to most of the materials (steel, Aluminum etc), meaning it will corrode before the substrate until the zinc is entirely consumed.2. What is Hot-Dip Galvanizing (HDG):
Hot-Dip Galvanizing (HDG) is a process in which Zinc bonds to steel at the molecular level to produce a four-layer corrosion-resistant coating based on Fe-Zn content in each zone. The first three layers are zinc-iron alloy layers that are actually harder than the base steel. The fourth or top layer is pure zinc. In this process, the base steel is dipped in a tank having hot molten zinc at around 450 degrees Celsius. Hence it is called hot dipped galvanizing.3. Why is HDG superior to paint for corrosion protection:
Although the paint industry has made great improvements in paint systems HDG is still superior to paint for providing corrosion protection for decades and not just for years. That is why HDG is not just a coating of paint. HDG metallurgically bonds zinc to the steel. In addition to the metallurgical bond, HDG provides two other types of protection - Cathodic Protection and the Zinc Patina. Paint does not provide these extra protections. Though the paint is very easy to apply on the object with respect to HDG, for long term application HDG is being used currently.What are the major steps in the Hot Dip Galvanizing (HDG) process:
There are mainly three steps:
Cleaning and Fluxing – Generally, there is two type of cleaning done before fluxing the steel Caustic wash and Pickling (Acid wash). Steel is immersed in a caustic solution to remove organic material such as grease and dirt, followed by dipping in an acid bath (hydrochloric or sulfuric) to remove mill scale and rust. And finally lowered into a bath of flux (usually zinc ammonium chloride solution) that promotes zinc & steel reaction and retards further oxidation of the steel as steel will not react with zinc properly unless it is perfectly clean.
Galvanizing – The clean steel is lowered into a kettle containing 850 °F (455 °C) molten zinc where the steel and zinc metallurgically react to form three zinc-iron inter-metallic layers and one pure zinc layer.
Final inspection – the newly galvanized steel is sight-inspected (if it looks good, it is), followed up by measurement of coating thickness with a magnetic thickness gauge.
What types of products can be galvanized: Numerous different fabrications for a variety of applications are galvanized each year. Generally, we deal with Steel Wire of different diameter vary from 1.4mm to 4.00mm. We also meet with costumer’s requirement and the thickness specification. There is verity of product which can be galvanized such as structural Steel (angles, channels, wide-flange beams, I-beams, H-beams), grating, expanded metal, corrugated sheets, wire, cables, plate, castings, tubing, pipe, bolts & nuts.