1. Types of Galvanizing

a) Hot-Dip Galvanizing (HDG)

• The steel is cleaned, fluxed, and immersed in a molten zinc bath (~450°C / 840°F).

• A metallurgical bond forms between the zinc and steel.

• Provides thick, durable protection, ideal for outdoor and heavy-duty applications.

b) Electrogalvanizing

• A thin zinc coating is applied using an electric current in a zinc electrolyte solution.

• Provides a smooth, uniform finish but is thinner than HDG.

• Used in automotive and appliance industries.

c) Galvannealing

• A combination of hot-dip galvanizing and annealing.

• Produces a matte finish with better paint adhesion.

• Common in automotive body panels.

d) Mechanical Galvanizing

• Zinc powder, glass beads, and chemicals are used to coat steel surfaces.

• Provides uniform coverage but is limited to small parts like fasteners.

e) Sherardizing (Vapor Galvanizing)

• Zinc powder is heated in a rotary drum with steel parts.

• Ideal for small components with complex shapes.

2. Advantages of Galvanizing

Corrosion Protection – Zinc coating protects steel from rust and oxidation.
Sacrificial Protection – Zinc corrodes first, protecting the underlying steel.
Durability – Can last 50+ years in some environments without maintenance.
Cost-Effective – Lower life-cycle costs compared to painting or coatings.
Low Maintenance – No need for frequent reapplication.
Environmentally Friendly – Zinc is naturally occurring and recyclable.

3. Galvanizing Process (Hot-Dip Galvanizing)

Step 1: Surface Preparation

• Degreasing: Removes oil and dirt.

• Pickling: Acid bath removes rust and scale.

• Fluxing: Prevents oxidation before dipping.

Step 2: Galvanizing (Zinc Bath)

• Steel is submerged in molten zinc at ~450°C.

• Zinc reacts with iron, forming a series of alloy layers.

Step 3: Cooling and Inspection

• The coated material is cooled in water or air.

• Thickness and adhesion are inspected for quality control.