What is the hot dip galvanizing process and what is its use?
From the process of immersing the object, which has a chemically clean surface, a layer is formed on the melt due to the interaction between iron and zinc, which is called hot dip.
First, it takes shot plus or acid washing, and then it takes on an auxiliary coating to facilitate the interaction of iron with the melt, which is called flux lubricant. How to cool this sealed piece by normal cooling in air or immersion in hot water. At the surface of the part, the interaction occurs between zinc and iron, causing the adhesion strength of the layer to be high.
The life of the coating depends on two factors: thickness and environment.
Thickness: The value of these coatings mainly depends on their thickness and is not economically a thin and low value coating for special environments.
Environment: In industrial environments, the composition of gases in the atmosphere is such that the zinc coating does not have the resistance found in cleaner environments.
Suitable parts for galvanizing
Most iron or steel parts used in construction work can be heated galvanized. Stainless steel and alloy steels used for machine parts. These parts are usually not galvanized. Most of the parts that are normally galvanized are mild-steel or mild steels. Of course, the important factor is the type of surface. Steels may not be homogeneous and separation in them is effective. Shells formed during rolling – the remaining slaps are also effective. The presence of some silicon in steel above a certain level affects the interaction between molten zinc and iron.
Changes in the amount of carbon and to a lesser extent manganese also affect this. In mild steels where the percentage of the above values is small, this issue is not very important. But the reaction rate between zinc and iron increases when the percentage of silicon rises above 0.12%. In welded metals, the percentage of silicon in the welding points is usually higher than other points, and this is why the quality of zinc coating in these points is slightly different from other points. In the case of cast iron parts, it was previously thought that galvanizing these parts was difficult and required a lot of time to be galvanized. This is not true and they can also be galvanized if the surface of the cast iron parts is clean.
The best suitable combination for galvanizing cast iron parts
The best suitable composition for galvanizing cast iron parts is 3% silicon and 1% phosphorus. As the percentage of silicon increases from this amount, the reaction rate between cast iron and zinc decreases. With a lower percentage of silicon, the tendency to form dross increases. In addition, the thickness of the zinc coating increases greatly if a large immersion time is used. The same is true for low phosphorus. The presence of impurities, which is common in crude iron, causes problems in galvanizing. When washing with acid, the acid attack on these areas is more severe and after galvanizing, they cause a rough surface. Wrought iron is better cleaned by shot plus sanding, otherwise the stopping time of the acid should be increased to a minimum.