Steel is a fascinating material. It can however be corroded by the elements and air contamination. Corrosion is responsible for more than 90 billion euros worth of damage every year in Germany alone. Hot-dip galvanizing protects steel from corrosion in an economical and environmentally-friendly manner and considerably increases its service life: corrosion protection lasts for decades.
Hot-dip galvanizing involves dipping steel into a zinc smelter ca. 450° C following the appropriate pre-treatment. Zinc and steel will then react with one another. An iron-zinc alloy will form on the surface of the steel. This indissoluble compound of zinc and steel creates a protection, which is clearly different from all other processes. Hot-dip galvanized surfaces are not just protected from wind and the weather but also optimally protected from mechanical exposure – for decades. Under normal conditions, hot-dip galvanizing will protect against corrosion for up to 50 years and generally more than 25 years in the case of higher exposure levels.
Hot dip galvanized pipe is molten matrix metal and the reaction of the iron alloy layer, so that the substrate and coating combination of both. Hot dip galvanized pipe is first pickled, the steel surface in order to remove iron oxide, after pickling, by mixing the aqueous solution tank for cleaning solution or ammonium chloride or zinc chloride, and then into hot-dip plating bath. Galvanized with coating uniformity, strong adhesion, long life and other advantages. Steel substrate occurs with molten bath complex physical, chemical reactions, the formation of corrosion-resistant zinc-iron alloy structure closely layer. Alloy layer and layer of pure zinc, steel base blend. Therefore it resistant to corrosion.
Hot dip galvanizing process:
Preparation – pickling – washing – solubilization – hot-dip zinc – Cooling – passive – cleaning – sorting – recheck – packaging – storage
When the temperature is too low, zinc was poor mobility, coating thickness and uneven, prone to sagging, poor visual quality; temperatures are high, good fluidity liquid zinc and zinc from the workpiece and easy solution to reduce the phenomenon of sagging and wrinkled skin happen, strong adhesion, coating thin, good appearance, high production efficiency; But the temperature is too high, the workpiece and zinc pot iron loss seriously, producing a large zinc slag, affecting dip zinc coating quality, large consumption of zinc, not even plating. At the same temperature, dip time is long, the coating thickness. Different temperatures, requiring the same thickness, the length of time required for the high temperature dip.
Hot-dip galvanizing (HDG), as referenced on this site, is the process of dipping fabricated steel into a kettle or vat containing molten zinc. The process is inherently simple which provides a distinct advantage over other corrosion protection methods. While the steel is in the kettle, the iron in the steel metallurgically reacts with the molten zinc to form a tightly-bonded alloy coating that provides superior corrosion protection to steel.
The information throughout this section on durability, longevity, cost, and sustainability applies only to the hot-dip galvanizing (commonly referred to as batch, general, or after-fabrication galvanizing). It is important to understand not all zinc coatings are created equally; thus, applying any of the information provided about hot-dip galvanizing to other zinc coatings is not accurate or recommended.
To understand the hot-dip galvanizing process and its evolution, it makes sense to start at the beginning, which dates all the way back to 79 AD.
Hot-dip galvanizing and cold galvanized the difference:
1. Galvanizing, also known as hot-dip galvanized, he is the ingot melted at high temperatures, a number of supplementary material in place, then dipped galvanized metal structure slot, the metal component on a layer of zinc coating . The advantages of hot-dip galvanizing corrosion of his ability, adhesion and hardness of zinc coating is better
“Cold plated” or “plating”, ie the zinc salt solution by electrolysis, to the plating on the coating, generally do not have heating, small amount of zinc, the wet environment is very easy to fall off.
2. Hot dip galvanized (galvanizing)
Hot-dip galvanizing is a chemical treatment, is the electrochemical reaction.
Cold galvanizing is the physical address, just brush the surface layer of zinc, the zinc layer is easy to fall off. Construction in the use of hot dip galvanizing.
Continuous hot dip galvanizing process: steel → heating → cooling to the temperature galvanized galvanized → cooling →
Cold galvanized zinc is only 10-50g/m2, its own corrosion resistance than hot dip galvanized a lot of difference. Galvanized by a relatively cheaper price.
Hot dip galvanized steel body is hot dip galvanized surface under the condition of its adhesion strong, not easy to fall off, although there hot dip galvanized pipe corrosion phenomenon, but in a very long period to meet technical, health requirements.
3. Technological differences
First of all, is the difference between process: hot-dip galvanizing is the workpiece degreasing, pickling, dipping, drying liquid immersion in molten zinc certain period of time, can be raised.
Also known as electro-galvanized cold galvanizing, is to use electrolysis devices work piece through the degreasing, pickling ingredients post into the zinc salt solution, and connect the anode electrolysis equipment; in place across parts of zinc plate connected to the electrolysis equipment positive, power on, use of current from the cathode to the anode of the directional movement of the workpiece will be deposited in a layer of zinc.
Zinc finished the difference: no cold galvanized hot-dip galvanizing delicate bright appearance, but the thickness of zinc coating of cold galvanizing aspects of hot-dip galvanizing is a few times. Galvanized corrosion resistance is also several times.
4. Environmental issues
Fewer emissions of some hot-dip galvanizing.
Galvanized pollutants are mainly artifacts of waste acid pickling.
Cold galvanized pollutants include parts of the waste acid pickling, electroplating waste, liquid waste such as passivation.
Cold galvanized the type and quantity of pollutants discharged are much more than hot dip galvanizing.
Hot-dip zinc standards: GB/T13912-92
Hot-dip galvanizing: hot dip galvanizing process is generally completed after Hemming, when the load is not less than 5mm thick flat steel, the galvanized zinc coating after the average weight of not less than 610 grams / square meter; when the load flat steel thickness less than 5mm, the galvanized zinc coating after the average weight of not less than 460 grams / square meter, and after galvanizing quality requirements should be consistent with the provisions GB/T13912