Galvanized Steel: What It Is and How It’s Made

How Galvanized Steel Is Made: The Step-by-Step Process

The galvanizing process involves applying a protective layer of zinc to steel to prevent rust and corrosion. Various techniques are used depending on the desired outcome, each providing different levels of protection, finish, and application suitability. Here are the most common methods:

1. Hot-Dip Galvanizing

Hot-dip galvanizing is the most common and robust method of applying a zinc coating to steel. Here are the key steps in the hot-dip galvanizing process:

• Cleaning: The underlying metal is thoroughly cleaned with a caustic solution to remove dirt, oils, and other contaminants.
• Acid Treatment: The steel is then immersed in an acidic bath to remove mill scale (iron oxide flakes) from the surface, ensuring better adhesion for the zinc.
• Flux Application: A flux, such as ammonium chloride, is applied to the surface to facilitate better bonding between the zinc and the steel.
• Zinc Coating: The steel is submerged in a bath of molten zinc at approximately 840°F (450°C). This allows the zinc to bond to the surface, forming a strong, protective layer.
• Final Reaction: Once exposed to air, the zinc reacts with oxygen and carbon dioxide to form zinc oxide and zinc carbonate, which contribute to the corrosion-resistant shield on the steel.

The thickness of the zinc coating can be adjusted based on the intended use. For example, automotive parts often receive a thinner coating to allow for paint applications.

2. Electro-Galvanizing (Electroplating)

In electro-galvanizing, a thin layer of zinc is applied to the steel through an electroplating process, where an electrical current is used to deposit zinc onto the material’s surface. Here are the key steps:

• Preparation: The workpiece is cleaned in an alkaline solution to remove impurities.
• Electrolytic Bath: The metal is submerged in an electrolytic bath containing zinc salts, and an electric current is passed through the bath. This causes zinc to bond to the steel.
• Coating Formation: The process results in a uniform, thin galvanized coating with excellent adhesion to the material surface.

The process provides a smooth finish and is commonly used in applications that require fine details, such as automotive components or electrical enclosures.

3. Mechanical Plating (Peen Plating)

Mechanical plating is a unique process where zinc powder is applied to the steel surface through mechanical impact. It is ideal for small parts and components. Here’s how it works:

• Preparation: The steel parts are cleaned and placed in a rotating drum with zinc powder and glass beads.
• Impact Process: As the drum rotates, the steel parts are repeatedly struck by the glass beads, causing the zinc to bond to the surface.
• Finished Coating: The result is a zinc layer that provides a level of corrosion resistance, although it is not as thick or durable as hot-dip galvanizing.

This process is often used for small components such as fasteners and bolts, especially when a precise and uniform coating is required.

4. Sherardizing (Vapor Galvanizing)

Sherardizing, or vapor galvanizing, involves heating steel parts in a sealed container with zinc powder, which vaporizes and coats the steel. This method is best for small or irregularly shaped items. The steps are as follows:

• Zinc Powder Placement: Zinc powder is placed in a sealed drum along with the steel components.
• Heating: The drum is heated to high temperatures, causing the zinc powder to vaporize and bond with the steel.
• Coating Formation: The result is a uniform, thin zinc coating that provides corrosion resistance.

Sherardizing is suitable for parts that are too complex or small for other galvanizing methods.

5. Continuous Galvanizing

Continuous galvanizing is a highly efficient method for coating large quantities of steel, typically used in the production of steel strips or sheets. Here’s how the process works:

• Continuous Feeding: Steel coils or strips are continuously fed through a molten zinc bath in a controlled production line.
• Zinc Coating: The steel is submerged in the zinc bath, where it forms a strong protective layer.
• Cooling: The galvanized steel exits the bath and is cooled to form a durable coating.

This process is commonly used for high-volume production in industries like automotive manufacturing, where a consistent coating is required.

6. Zinc Spray Coating (Metallizing)

Zinc spray coating, also known as metallizing, involves spraying molten zinc onto the steel surface using a spray gun. This is typically used for on-site repairs or applications where large areas need to be coated. The steps include:

• Surface Preparation: The steel is cleaned and prepared for coating.
• Spraying: Molten zinc is sprayed onto the steel using a flame or electric arc.
• Coating Formation: The zinc bonds with the steel surface to form a protective coating.

Zinc spray coating is often used to repair damaged galvanized coatings or for areas that require localized protection.

Why Choose Galvanized Steel? Key Benefits and Advantages

Steel treated with zinc is known for its impressive corrosion resistance, durability, and cost-effectiveness. Below are some key reasons why it is favored across many industries:

Cost-Effectiveness

The process of galvanizing is much more affordable than using stainless steel. Existing steel parts can be treated with a protective zinc coating, thus extending the life of the materials and reducing the need for costly replacements. This makes it an ideal solution for industries that need to maintain high quality while managing costs.

Longevity

Materials coated with zinc can last up to 75 years, depending on environmental conditions. Its resistance to rust and corrosion reduces the need for maintenance, making it a long-term investment for industries such as construction and agriculture.

Reliable Protection

Even when the protective coating is damaged, the underlying steel remains shielded. The sacrificial nature of zinc means that it continues to protect the steel even in the event of wear or damage. Zinc’s ability to form new layers of protective compounds, such as zinc carbonate, ensures ongoing corrosion resistance.

Steel Types Suitable for Galvanizing

Galvanizing is a process where steel is coated with a protective layer of zinc to enhance its resistance to corrosion. Not all types of steel are ideal candidates for galvanizing, as the process depends on factors such as carbon content, alloy composition, and surface characteristics. Below is a summary of the steel types that are suitable for galvanizing, along with their key features.

Galvanized Steel vs. Boronizing: Which Treatment Is Right for You?

While both galvanizing and boronizing treatments improve the surface properties of steel, each serves distinct purposes:

• Galvanized Steel: Primarily provides a galvanized coating to guard against corrosion. Ideal for applications where rust resistance is a priority, such as in construction, automotive, and agriculture.
• Boronized Steel: Offers enhanced hardness, high-temperature stability, and superior mechanical properties. It is more suitable for industries with demanding performance requirements, such as aerospace or heavy machinery.

If corrosion resistance is your main concern, galvanized steel is the best choice. However, if your needs extend to enhanced performance under extreme conditions, consider exploring boronizing techniques like Borocoat®.

Real-World Uses of Galvanized Steel: Where It’s Most Effective

The unique properties of galvanized surfaces make them suitable for a variety of real-world applications across industries:

• Construction: Bridges, pipelines, structural beams, and roofing materials.
• Automotive: Exhaust systems, chassis, and parts requiring a protective coating.
• Agriculture: Fencing, silos, and equipment exposed to harsh weather conditions.
• Industrial Applications: Tools, machinery, and other equipment that are subjected to moisture-heavy environments.

Environmental Impact of Galvanized Steel

One of the most significant advantages of galvanized steel is its positive environmental impact:

• Recyclability: Both zinc and steel are highly recyclable, contributing to a reduction in waste and conserving natural resources.
• Durability: The extended lifespan of galvanized materials reduces the need for frequent replacements, which lowers the overall environmental footprint.
• Energy Efficiency: While the galvanizing process requires energy, the extended usability of galvanized surfaces offsets the initial energy investment. The protective coating also ensures that the workpiece remains in service for longer, reducing the need for new materials.

However, it’s important to consider the environmental footprint of zinc production, as the mining and refinement process can have an impact. Sustainability measures are continually being developed to mitigate these effects.