Prepainted zinc aluminium coated steel is the most common of the three current methods of galvanizing. However, there may still be many things you don't know about this method of galvanizing, such as the history of this method, the hot-dip galvanizing process or how to check the zinc coating is qualified. You will learn about these things with you in the article below.
What is hot dip galvanizing?
Prepainted zinc aluminium coated steel is the process of creating a protective layer on metal surfaces from oxidation and wear; thereby helping the metal to be more durable and have a longer service life.
Among 03 widely uses methods of galvanizing are hot-dip galvanizing, electrolytic galvanizing and cold galvanizing; Hot-dip galvanizing is the most common method.
To galvanize metal by hot-dip method, we dip the metal to galvanize into a bath of molten zinc solution. This method causes the outer layer of the metal to melt into an alloy with zinc.
This not only helps to evenly coat the zinc on the metal surface, but also makes it difficult for the zinc layer to peel off, helping to effectively protect the base metal surface.
Hot-dip galvanizing is one of the most common methods of galvanizing
The prepainted zinc aluminium coated steel began to appear in 1742, when the French chemist PJ Melouin presented the topic of protecting the surface of steel parts by dipping into a bath of molten zinc at the French Academy.
Following this topic, in 1836, another French chemist, Stanislas Sorel, was officially granted a patent for hot-dip galvanizing. He use sulfuric acid to remove dirt and oil from the metal surface, helping the zinc coating to better adhere to the metal, creating a stronger protective layer.
History of hot-dip galvanizing
In 1850, the Prepainted zinc aluminium coated steel was widely applied in the British iron and steel industry. In 1850 alone, the country's iron and steel industry uses about 10,000 tons of zinc to galvanize steel.
Since then, hot-dip galvanizing method has gradually become more popular and dominant compared to other plating methods.
The amount of zinc use has also increased several times, to 600,000 tons of zinc uses annually in North America alone, according to data provides by the American Galvanizers Association (AGA).
What are the steps in the hot-dip galvanizing process?
The process of prepainted zinc aluminium coated steel over time may vary slightly, but should ensure to comply with ASTM (or other equivalent standards such as CAN/CSA G164, ISO 1461) and include The basic steps are below:
After the metal surface has been cleaned, people proceed to dip the metal in a flux to completely remove the oxide layer that form on the metal surface. This process also helps to create a protective coating that prevents oxidation. The metal then dries in preparation for the plating process.
Avoid dipping for too long, causing the coating to be too thick, reducing adhesion and not aesthetically pleasing.
Clean metal surfaces before plating
Metal products, after being manufactured, may stick to a layer of oil as well as dust during storage and transportation. Since zinc does not 'stick' to unclean metal surfaces, surface cleaning is an extremely important preparatory step. Cleaning metal surfaces includes removing grease, removing old paint and removing other deposits.
Prepainted zinc aluminium coated steel method to remove grease; metal can soak in a degreasing bath or caustic soda solution to remove organic matter, dirt, and grease from the surface. After degreasing, the metal washes with water.
Metals can also soak in a dilute hydrochloric acid solution to remove oxides and other deposits. In addition, the use of electrolysis to remove carbon on the surface is also quite common.
Hot dip galvanizing prepainted zinc aluminium coated steel
The prepainted zinc aluminium coated steel method occurs when the temperature is between 454°C & 465°C. Fully immerse the surface-prepared and dried metal in the galvanizing bath. The molten zinc will wet the metal surface and a galvanizing reaction will occur, forming zinc alloy layers.
When the temperature in the galvanizing bath reaches the melting point (standard temperature is 454°C), the galvanizing reaction is complete.
During the prepainted zinc aluminium coated steel process; care should be taken to completely immerse the metal in the tank for an even coating. In addition, depending on the desired thickness of the galvanized layer, it is necessary to align the corresponding dipping time.
Cooling & Finished Product Inspection
Conduct metal cooling by overflowing water bath to make the finished product the most beautiful and glossy. Finally, observe the surface and check the thickness of the galvanized layer to make sure the finished product meets the requirements and meets the standards of ASTM, AS/NZS…
The prepainted zinc aluminium coated steel process allows full metal contact with the outer surface of the product, thereby ensuring optimum corrosion resistance. With products with complex structure, many details, the plating layer may be uneven.
The galvanizing layer formed after the galvanizing process will probably fill the thread pitches.
Hot dip galvanizing process
The hot-dip galvanizing process may vary from material to material, but it is important to ensure compliance with ASTM or other equivalent standards.
Further,, notes for hot-dip prepainted zinc aluminium coated steel process.
In order, for the finished product after galvanizing to meet the technical standards, it is necessary to ensure that the galvanizing process must take place according to the correct process and technique (in terms of time, temperature, amount of support solution moreover, the following points should be noted:
Application of hot-dip galvanizing
Prepainted zinc aluminium coated steel in general and hot-dip galvanizing in particular are widely applied in manufacturing industries today. Up to 600,000 tons of zinc consumes annually in North America to produce galvanized steel, of which 200,000 tons are for fabrication and 400,000 tons for continuous galvanizing.
Most of the industries that apply this prepainted zinc aluminium coated steel method use a large amount of iron and steel, but often rust due to oxidation under the influence of the environment. The applied hot-dip galvanizing methods help control corrosion better, prolonging the life of objects and works.
Street light poles galvanize by hot-dip galvanizing
Hot-dip prepainted zinc aluminium coated steel method widely applies in communication, transportation, automobile manufacturing, lighting industries...
As a popular galvanizing method, hot-dip galvanizing is a turning point in history. The effectiveness of this method contributes to improving the quality of life and has applies in many industries to this day.
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