Molly Ayala
The term galvanized refers to the process of applying a protective coating of zinc to the outer surface of a metal to prevent rust and corrosion. There are two main types of galvanization: electro-galvanization and hot-dip galvanization. Electro-galvanization is a form of zinc electroplating where a thin layer of zinc is electrically and chemically bonded to steel to protect against rust and corrosion. This process starts by submerging raw metal into an electrolytic solution of zinc and saline, which causes the zinc to chemically bond to the conductive steel. The resulting finish is smooth, drip-free, and shiny, making it ideal for architectural applications. However, it has a shorter lifespan compared to hot-dip galvanization, which is typically used for building materials that require durability and longevity.
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What You'll Learn
Electro galvanization is a form of zinc electroplating
The electroplated zinc coating consists of pure zinc that is tightly adherent to the steel. The coating is highly ductile, remaining intact even after severe deformation. The weight of the coating ranges up to 0.2 oz/ft² (60 g/m²), or thicknesses up to 0.36 mils (9.1 µm) per side. On wire, coating weights may reach up to 3 oz/ft² (915 g/m²). The coating of pure zinc is thinner than continuous sheet galvanizing, and there are no alloy layers, but it provides a smoother finish.
Electro galvanization is often used for coiled sheet steel, which is later formed into shapes such as corrugated sheets or welded into pipes and tubes. The finished coating is smooth, drip-free, and shiny, making it ideal for architectural applications or other uses where its aesthetic characteristics are valuable. However, once exposed to the elements, the finish can quickly deteriorate.
Electroplated zinc articles may receive a topcoat to further enhance corrosion protection and friction performance. The modern electrolytes used are both alkaline and acidic, containing sodium sulphate and sodium hydroxide (NaOH). They utilize proprietary brightening agents, with zinc being soluble as a cyanide complex Na2Zn(CN)4 and as a zincate Na2Zn(OH)4. Quality control of such electrolytes requires the regular analysis of Zn, NaOH and NaCN.
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The process involves submerging raw metal into an electrolytic solution
Electro-galvanization is a form of zinc electroplating that involves submerging raw metal into an electrolytic solution. This process protects the metal against rust and corrosion. The raw metal is fully immersed in a saline/zinc bath, with electricity used to move electrons from the zinc (anode) to the raw metal (cathode). The zinc chemically bonds to the raw metal, acting as a barrier layer to prevent corrosive substances from reaching the underlying metal.
The electrolytic solution is heated and stirred, aiding the conversion of the metal. The metal is then recovered via an electrolytic cell. The composition of the electrolyte solution depends on the type of metal being treated. For example, zinc-iron uses a different electrolyte solution to zinc-cobalt. The modern electrolytes used are both alkaline and acidic, containing sodium sulphate and sodium hydroxide.
The process of electro-galvanization can be compared to hot-dip galvanization. Both methods are used to protect the base metal from corrosion, but the price and corrosion-resistance characteristics can vary between the two methods. The layer formed by electro-galvanization is extremely thin, and therefore the life expectancy of the layer is less than that of hot-dipped material.
Electro-galvanization is a widely used process, with the electroplating of zinc first being invented in 1800. The process has continued to evolve to meet challenging corrosion protection, temperature, and wear resistance requirements.
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The finish is smooth, drip-free, and shiny
The finish of electro-galvanized steel is smooth, drip-free, and shiny. This finish is achieved through a process of electroplating, where steel is placed in an electrically charged solution of zinc and saline. The steel wires are fully immersed in a zinc bath, and electricity is used to move electrons from the zinc (anode) to bond them to the steel (cathode). This process results in a thin layer of zinc being electrically and chemically bonded to the steel, creating a barrier that protects against rust and corrosion.
The smooth and shiny finish of electro-galvanized steel is not only aesthetically pleasing but also functional. The drip-free characteristic of the finish ensures that the coating is uniform and consistent, providing optimal protection to the underlying steel. This finish is particularly valuable for architectural applications or other contexts where visual appeal is important.
However, it is important to note that despite its attractive finish, electro-galvanized steel has a shorter life expectancy compared to hot-dipped materials. Once exposed to the elements, the finish can deteriorate rather quickly. This is because the layer formed by electro galvanization is extremely thin, impacting its durability.
To address this limitation, a topcoat can be applied to enhance corrosion protection and improve friction performance. This additional layer further safeguards the steel and can be painted upon, providing a versatile surface. In some cases, a UV-resistant polymer is applied after electro-plating to prolong the life of the finish and maintain its smooth and shiny appearance.
Overall, the smooth, drip-free, and shiny finish of electro-galvanized steel is a result of the electroplating process, creating a protective barrier that also enhances the visual appeal of the material.
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The coating thickness is about 10 to 12 um
The process of electro-galvanization involves placing steel in an electrically charged solution of zinc and saline. This causes the zinc to chemically bond to the conductive steel, creating a protective layer that prevents corrosion and rust. The thickness of the zinc coating is crucial in determining the level of protection and durability of the galvanized product.
A thicker coating will generally provide longer-lasting protection. A coating thickness of about 10 to 12 micrometres (um) is considered suitable for providing "moderate" corrosion protection. This thickness range is often used for underhood automotive components, where protection from corrosion is essential.
The 10 to 12 um thickness falls within the range of 5 to 12 um, which offers twice the corrosion protection of a 3 to 5 um coating. This increased thickness provides enhanced durability and ensures that the galvanized product can withstand more extreme conditions.
However, it's important to note that the level of protection also depends on other factors, such as the chromate conversion coating and any additional topcoats applied. The type of electrolyte used, whether alkaline or acidic, and the presence of additives can also influence the performance of the coating.
To measure the thickness of the coating, specialized tools like coating thickness gauges are employed. These gauges can provide accurate readings of the zinc layer's thickness, helping to ensure that the galvanized product meets the required specifications and will provide the expected level of protection.
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Electro galvanization is used for easily replaceable products
Electro galvanization is a process of zinc electroplating where a thin layer of zinc is electrically and chemically bonded to steel to protect against rust and corrosion. The process involves fully immersing bare steel wires in a saline/zinc bath and using electricity to move electrons from the zinc (anode) to bond them to the steel (cathode). The zinc acts as a barrier layer, preventing corrosive substances from reaching the underlying steel or iron.
The process results in a smooth, drip-free, and shiny finish, making it ideal for architectural applications or other uses where aesthetics are important. However, the finish can quickly deteriorate when exposed to the elements. Electro galvanization is generally used for small objects such as screws, fasteners, and car parts, and it is a cost-effective process. It is also used for coiled sheet steel, which can later be formed into shapes such as corrugated sheets or welded into pipes and tubes.
The layer formed by electro galvanization is extremely thin, resulting in a lower life expectancy compared to hot-dipped materials. As such, electro galvanization is well-suited for easily replaceable products that are used indoors, away from extreme environments. The process is also commonly used for precision stamping and electronics due to its controlled and precise coating capabilities.
When choosing between electro-galvanized and hot-dipped galvanized products, it is important to consider the physical location and purpose of the item. For example, an ornamental item would not require the same level of protection as a structural item.
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Frequently asked questions
Galvanization is the process of applying a protective coating of zinc to iron or steel to prevent rusting and corrosion.
Electro galvanization is a form of zinc electro plating where a thin layer of zinc is electrically and chemically bonded to steel. This is done by submerging raw metal into an electrolytic solution.
Electro galvanization produces a uniform coating with a smooth, drip-free, and shiny finish. However, it has a very low life, ranging from several months to a few years. On the other hand, hot-dip galvanization offers a non-uniform coating with an unpleasant and dull finish, but has a much longer lifespan of 20-50 years.
Electro galvanization is commonly used for coiled sheet steel, which can then be formed into shapes such as corrugated sheets or welded into pipes and tubes. It is also used for easily replaceable products like outdoor furniture and gardening tools.
