HOT DIP GALVANIZING PROCESS
The hot dip galvanizing process starts by suspending steel articles and dipping them into a series of cleaning baths. Once cleaned, the steel is lowered at an angle into a bath of molten zinc. Immersing the steel on an angle allows air to escape from vented tubular shapes or pockets that may be within the design and permits the molten zinc to displace the air. The steel reacts with the molten zinc to form the galvanized coating. After being withdrawn from the zinc, the final step in most hot dip galvanizing processes is a quench to promote passivation of the zinc surface.
Inspecting galvanized steel is a simple process. Zinc will not adhere to or react with unclean steel; therefore, a visual inspection of the product provides a good assessment of the quality of the coating. The coating thickness is usually tested using a magnetic thickness gauge. The testing and sampling requirements are contained in the relevant local or International Standard for the product.
How Is Galvanized Steel Protected From Corrosion Damages?
The basic principle of galvanization is the galvanic protection of the parent steel part. Galvanic steel hinders corrosion progress with the help of the zinc coating. Hence, the passivation of the galvanic steel relies on the electrochemical relationship between steel and zinc. The elements in the world are ordered in an electrochemical array. This electrochemical array is decided by observing the reduction and oxidation abilities of the elements. In other words, the affinity of the elements against reduction and oxidation determines these elements’ positions in order.
The reactivity array of the elements against oxidation is called the EMF series. In the EMF series, each element’s potential difference against hydrogen is calculated, and these series are constructed. EMF series represents more noble metals at the top side and more active metals at the bottom side. In the middle of the series, half-noble elements are located (such as copper). The below figure represents the EMF series.
The elements at the down of the series are more active than those at the top, which means bottom-sided elements are more likely to corrode when compared with the top-sided ones. When a more noble metal is coupled with a more active metal, in other words, if one couples a top-sided element with a bottom-sided element, the corrosion rate of each element changes. The alteration of the corrosion rate causes adverse effects on noble and reactive elements. At the end of the coupling, the corrosion rate of the noble metal decreases, whereas the corrosion rate of active metal increases. Hence, when noble and active metals are coupled, noble metal becomes less likely to corrode. However, corrosion emerges on the active metal faster than the standard conditions (standard conditions means the array in the EMF series)
The fundamentals of galvanization can be explained by considering the EMF series and coupling conditions. Iron (actually, it’s steel, but as you know, steel is an iron-carbon alloy which at least contains 98% iron) is covered with zinc to hinder the possible corrosion damages. When iron is coated with zinc, iron and zinc are also coupled. Iron can be found at higher places than the zinc in the EMF series, so one can easily say that iron is nobler than zinc. Thus, coupling iron and zinc reduces the corrosion rate of iron (steel). Galvanized steel is protected from corrosion by lowering the corrosion rate itself. In brief, the zinc layer lowers the corrosion rate of steel and protects it. That’s why galvanized steel performs excellent performance in corrosive environments.
What Are The Benefits Of Galvanized Steel?
The wide range of application areas of galvanized steel can be counted as a piece of evidence for the benefits of the galvanized steel. The most popular benefits of galvanized steel can be exemplified as excellent corrosion protection, ease of surface modification, and excellent protection against mechanical injuries. Moreover, the cost-efficient features of the galvanizing process make them desirable for most vendors. The need for the galvanized steel for periodic maintenance is lesser than ordinary carbon steels, thanks to the zinc coating. Hence, long time cost efficiency of galvanized steel may be counted as a massive factor for material selection. The below diagram is constructed to show the essential advantages of galvanized steel. As mentioned before, the protective feature of the zinc coating and process quickness can be thought of as the major advantages of the galvanization process. The tough layer on the galvanized steel performs better resistivity against scratches and damages.
When the benefits of the galvanized steel are listed, some significant contributions of the zinc coating may be specified as below articles;
Lower first cost: When compared with the other surface coating processes, the cost-efficiency rate of the galvanizing process is notably higher than most of the coating operations. The cost-effective feature of galvanized steel made it a preferred material for engineering applications
Long life: The estimated lifetime of galvanized steel is determined as 50 years for rustic environments. Moreover, even in corrosive environments, galvanized steel can serve for 20 to 25 years. Thus, the long service life of galvanized steel generates a considerable advantage for most the industries
Tough coating: The iron-zinc multilayer of galvanized steel increases the strength of the steel surface. Therof, zinc coating develops the mechanical properties of the galvanized steel.
Total coating: The immersion process during the production of galvanized steel provides a full coating at every point on the steel’s surface. Hence, a continuous layer on the steel surface can be acquired. Even in hidden sections or in sharp corners, galvanization can be done entirely. This complete coating of the galvanized steel performs homogenous protection.
Shorter processing duration: Galvanized steel can be produced from raw material to end material in a couple of minutes. The quickness of the galvanized steel processing makes numerous products available in short times.