Galvanizing is the process of applying a zinc coating to the surface of steel or iron. It is currently the world’s most popular and cost-effective steel surface treatment process.
Galvanized metal can be used for building frameworks, ladders, metal benches, balconies, and fire escapes to ensure a longer lifespan and adequate corrosion and damage resistance.
This article will introduce everything you need to know about galvanizing. I hope you get some inspiration for your project after reading it.
What is Galvanizing?
Galvanizing, often known as galvanization, is the process of providing steel or iron with a protective zinc coating to prevent rusting. Several galvanizing types are available, but hot-dip galvanizing is the most commonly used.
Hot-dip galvanizing involves immersing iron or steel in a bath of molten zinc to form a coating of zinc-iron alloy and zinc metal resistant to corrosion. A metallurgical reaction occurs between the iron in the steel and the molten zinc. This reaction is a diffusion process, so the coating forms perpendicular to all surfaces creating a uniform thickness throughout the part.
Galvanizing Steps
The following are the steps in the galvanizing process:
- Cleaning the steel with a degreasing/caustic solution.
- After cleaning, the steel is pickled by lowering it into a vat of diluted hot sulfuric acid.
- Then put the steel into the flux solution (typically zinc-ammonium chloride).
- After the flux, the steel is immersed in a vat of molten zinc to galvanize it.
- Finally, the steel is inspected for consistency and completeness of coating.
The History of Galvanizing
The following will briefly introduce the development history of galvanizing so that you can have a further understanding of galvanizing.
79 AD – The records of zinc’s use in construction began, which could be regarded as the origin of galvanizing.
1742 – P.J. Malouin, a French scientist, presented a series of experiments involving coating iron with the molten zinc to the Royal Academy of Sciences. This is the first recorded history of galvanizing.
1772 – An Italian, Luigi Galvani, discovered the electrochemical process between metals while experimenting with frog legs.
1801 – Alessandro Volta advanced galvanizing research by discovering that the dissimilar metals’ contact will cause the flow of electrical current.
1829 – Michael Faraday discovered zinc’s sacrificial action during an experiment involving zinc, salt water, and nails.
1837 – Sorel in France obtained the first of many patents for a process of coating steel by immersing it in molten zinc after cleaning it.
1850 – The British galvanizing industry used 10,000 tons of zinc per year to produce galvanized steel.
1870 – The United States saw the opening of its first galvanizing plant. The steel was hand-dipped in the zinc bath at the time.
2000 – Improvements in metallurgy and furnace technology enhance the efficiency and sustainability of processes.
Today – Galvanizing is found in almost every primary application and industry where iron or steel is used.
What Metals Can Be Galvanized?
Iron and steel are the two most frequent types of galvanized metals. Additionally, other metals can also be galvanized. Generally, most ferrous metals can be galvanized, whereas most non-ferrous metals cannot.
You can use magnets to differentiate between ferrous and non-ferrous metals. Magnets will stick to ferrous metals but not non-ferrous metals.
The Importance of Galvanizing
Galvanizing is an effective solution for the cathodic protection of steel or iron from corrosion. It is an economical and durable surface treatment method. Let’s look specifically at the importance of galvanizing.
Complete Protection for Damaged Areas: Galvanized coatings will erode first than protected metal, giving cathodic or sacrificial security to areas of metal uncovered and damaged.
Complete Security: Galvanizing a metal gives it anti-corrosion properties. Every part of a galvanized product is protected, including breaks, sharp corners, and inaccessible areas.
The Simplicity of Investigation: The eye evaluates galvanized coatings promptly, and we can use basic non-destructive thickness testing techniques. If galvanized coatings are not damaged, the part is sound and continuous.
How Does Galvanizing Work?
Galvanizing protects the metal in a variety of ways. The two main types of protection are barrier protection and galvanic protection.
Barrier Protection
When applied to the surface, the zinc coating dries and hardens to form a protective zinc oxide layer impenetrable to air and moisture. Further corrosion is prevented since the underlying steel substrate cannot come into touch with external air or moisture.
Galvanic Protection
Galvanic protection is also referred to as cathodic protection. It sacrifices the zinc coating that acts as an anode to protect the underlying steel substrate that acts as a cathode. Galvanic protection is particularly advantageous when the protected steel is owing to cuts, scratches, dents, or coating damage.
Since zinc is a highly reactive and electronegative metal, it will function as the anode and corrode first if adjacent steel is unprotected. Zinc will provide galvanic protection until the coating is completely depleted.
Types of Galvanizing
There are several different types of galvanizing with distinct characteristics and performance. The following will briefly describe various galvanizing types.
Hot-dip Galvanizing
Hot-dip galvanizing is one of the most prevalent galvanizing methods. Metal is immersed in a hot zinc bath at roughly 450 °C during hot-dip galvanization. Once removed from the bath, the zinc coating of the metal surface reacts with oxygen to generate zinc oxide and subsequently with carbon dioxide to form zinc carbonate. The metal must first be cleansed with a caustic solution and then pickled in an acidic solution before being galvanized. Zinc ammonium chloride can also be added to prevent the metal from prematurely oxidizing before galvanization.
Electro Galvanizing
Electro galvanizing does not entail immersing the material in a molten zinc vat. Instead, an electric current is passed through an electrolyte solution applied to the material, converting positively charged zinc ions to zinc metal. Reduced zinc ions are subsequently deposited on the positively charged material.
Galvannealing
Galvannealing is the outcome of combining hot-drip galvanizing and annealing. Before passing the coated metal through air knives to remove excess zinc, the hot-dip galvanizing process usually occurs. The metal is then temporarily heated in an annealing furnace at 500-565 °C, allowing the iron and zinc layers to diffuse into each other and form zinc-iron alloy layers. This method yields galvanized sheet metal resistant to welding and suitable for paint adhesion.
Pre-galvanizing
Pre-galvanizing involves rolling the metal sheet through a cleaning agent to rapidly prepare the material for galvanizing. The metal is then recoiled after passing through a pool of molten liquid zinc. The primary advantage of pre-galvanizing is that it enables the rapid galvanization of steel coils on a large scale and more uniformly.
Advantages of Galvanizing
The galvanizing metal is usually corrosion-resistant, tough, and long-lived. The following are some advantages of Galvanizing.
Time Saver
Galvanizing is a rapid and easy process. The galvanizing coating requires one dip to protect the metal. Other coatings must be painted or sprayed, which takes considerably longer. The drying time is further reduced because galvanizing only takes one day to set, whereas other coatings can take considerably longer.
Good Durability
Galvanized steel lasts considerably longer than other steel treatments. The steel will be protected by galvanized coating against corrosion; therefore, it will not be necessary to replace it in the future. Galvanized steel is assured to last for a long time.
Easy Maintenance
Galvanized steel does not require harsh chemicals to maintain or prevent corrosion. A cover already protects the steel. You just need a few wipe–downs per year to keep the steel looking good and running properly.
Easy Inspection Process
Galvanizing can form a continuous and sound covering. Any flaws in the metal underneath will be apparent, which can help us streamline the inspection process and make total fabrication faster.
Aesthetic Appeal
The coating’s matte-gray tone will fit its surroundings, so you won’t need to paint to make it seem nicer. The hue will not fade as the metal ages, so it will always be aesthetically beautiful. If you desire to alter the color, it may be powder-coated quickly for a seamless color change.
Cost Efficiency
Galvanizing has cost efficiency in the long term:
- The galvanizing streamlines the overall fabrication process and will save you money on labor hours.
- The products with galvanized coats are much less expensive than other metal preservation products.
- The coating has good longevity, helping you save money.
Applications of Galvanizing
High corrosion resistance makes galvanizing widely used in many industries, such as the construction, automotive, and telecommunication industry.
Construction Industry: Thousands of tons of galvanized construction steel are manufactured yearly to make structures such as building frameworks, fire escapes, street furniture, ladders, and balconies.
Automotive Industry: The anti-rust properties allow galvanized materials to be used as bodies on automobiles. Bumpers, frames, beams, and chassis can also be made from galvanized steel.
Telecommunication Industry: Rust protection is a desirable feature in the telecommunications industry since phone lines and electrical boxes are constantly exposed to the air. Galvanization helps to extend the life of such items.
The Differences Between Galvanized steel And Stainless Steel
There have been several debates on galvanized steel vs. stainless steel. However, both metal materials come with their unique advantages.
Strength – Because stainless steel contains chromium, it is stronger and more durable than galvanized steel.
Price– Unlike stainless steel, galvanized steel is less expensive and more readily available.
Life– Stainless steel has a longer life than galvanized steel since the zinc coating in galvanized steel can deplete owing to scratches or hard water salts.
Protective Shield – Stainless steel is protected against rust by its chromium content. In contrast, galvanized steel is protected from rust by a zinc coating.
Applications – Stainless steel is commonly used in manufacturing tools, buildings, monuments, sculptures, culinary utensils, skyscrapers, bridges, pipelines, automobiles, and machinery. Galvanized steel is applied to buildings and dwellings, framing and construction, ornamental fences, pipelines and fittings, washing machines, bolts, nuts, nails, dishwashers, etc.
The Differences Between Hot-dip Galvanizing And Electro galvanizing
The following will compare the differences between hot-dip galvanizing and electro galvanizing in terms of appearance, cost, corrosion resistance, and applications.
Appearance
First, let’s compare hot-dip galvanizing and electro galvanizing in appearance. Hot-dip galvanized products have a dull finish that can be streaky, contain drips, and is typically not applicable in architectural or aesthetic applications. The galvanic thickness can be inconsistent across hot dip galvanized products.
Electrogalvanized products, on the other hand, are more aesthetic with a clean, bright finish; they have uniforms and coating throughout.
Cost
In terms of cost, hot-dip galvanized products are more expensive because the process is more labor intensive and the resulting product is more durable.
Electrogalvanized products are less expensive, making them cost-effective for temporary and short-term applications. Regarding durability and corrosion resistance, hot-dip galvanized products are better than electro-galvanized products.
Corrosion Resistance
Hot-dip galvanized products offer a longer service life, and their zinc coating is 5 to 10 times thicker. The hot-dip galvanizing fuses zinc with the base metal and creates an alloy layer that is very hard and resistant to typical abrasions.
On the other hand, electro galvanizing produces a thin coating which, when damaged, will leave the base metal without much protection. Electrogalvanized products will corrode much faster when exposed to the elements.
Applications
Electrogalvanized products will corrode much faster when exposed to the elements. Hot-dip galvanized products are more suitable for applications involving exposure to natural elements or caustic environments.
On the other hand, electro-galvanized products can be used for applications with limited exposure to harsh or extreme environments. So they are more suitable for architectural or aesthetic applications. And because electro-galvanized products are cheaper, they can be a cost-effective alternative to hot-dip galvanized products for temporary or short-term applications.
Conclusion
Galvanizing is the process of applying a zinc coating on the surface of a metal (usually steel or iron). It is primarily employed as a protective measure to avoid corrosion to extend the service life of the protected metal component.
Galvanized materials are widely accessible as galvanized sheet metal for sheet metal fabrication processes such as bending and stamping. And it can be used for galvanized metal bars, tubes, and rods, which are excellent for CNC machining. When you require sheet metal material with one of the best rust protection, galvanized sheet metal is the ideal option.
LEADRP is a prototyping and low-volume manufacturing specialist with expertise in metal material selection. Please read about how we improve corrosion and rust resistance in parts with galvanization, or contact us for a free quote.
References
Galvanization – From Wikipedia
Galvanizing Process – From American Galvanizers Association
What is Galvanizing? – From American Galvanizers Association
Galvanized Steel: Types, Uses, Benefits. – From NMC
Hot-dip vs. Cold Galvanizing: What’s the Difference? – From Corrosionpedia
Everything You Need to Know About Galvanized Metal – From Schorr Metals
FAQ
The galvanizing process uses zinc instead of other metals because zinc oxidizes and experiences acid corrosion “sacrificially” to steel. That means that when zinc is in contact with steel, oxygen, and acids will attack the zinc rather than the steel beneath it.
The zinc coating of hot-dip galvanized steel will last in the harshest soil for 35 to 50 years and in less corrosive soil for 75 years or more. Although humidity affects corrosion, temperature itself has less of an impact.
In order to weld galvanized steel successfully, a skilled welder is required. Furthermore, to solve the coating issue, the zinc coating should be removed from the area where you are welding. The filler material can also be used on the zinc-coated portion of the welding area.
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