Galvanized Steel (GI) Roll Forming Material Guide: Coil Sizes, Z275, Thickness & Applications

Galvanized Steel (GI) Roll Forming Material

1. Overview of Galvanized Steel in Roll Forming

Galvanized steel (GI – Galvanized Iron) is one of the most widely used materials in the roll forming industry due to its excellent corrosion resistance, durability, and cost-effectiveness. It is produced by coating steel with a layer of zinc, which protects the base metal from rust and environmental damage.

In roll forming, galvanized steel is commonly used for roofing sheets, wall cladding panels, purlins, structural components, and various construction profiles. The zinc coating acts as a sacrificial layer, meaning it corrodes before the steel underneath, significantly extending the lifespan of the product.

GI steel is typically manufactured from cold rolled steel substrate and then coated using a hot dip galvanizing process, ensuring a consistent and durable protective layer.

2. Material Composition & Structure

Galvanized steel consists of:

• Steel base (usually cold rolled steel)
• Zinc coating (Z coating)

Layer Structure:

1. Steel core
2. Zinc coating (both sides)

Coating Types:

• Z100 (light coating)
• Z180
• Z275 (most common)
• Z450
• Z600 (heavy-duty environments)

Surface Types:

• Regular spangle
• Minimized spangle
• Zero spangle

3. Available Coil Specifications

Thickness Range

• 0.3mm – 4.0mm

Coil Width

• 600mm – 1500mm

Coil Weight

• 3 tons – 15 tons

Coil ID / OD

• ID: 508mm / 610mm
• OD: up to 1600mm

Tolerance

• Tight thickness tolerance: ±0.02–0.04mm
• Excellent flatness for roll forming

4. Mechanical Properties

Typical values:

• Yield Strength: 250 – 550 MPa
• Tensile Strength: 350 – 700 MPa
• Elongation: 15% – 30%
• Hardness: 120 – 200 HB

Available grades:

• DX51D (standard forming grade)
• S320GD / S350GD (structural grades)

5. Coating Types

Zinc Coating (Z)

• Z100 → light protection
• Z180 → medium
• Z275 → industry standard
• Z450+ → heavy-duty / coastal

Coating Thickness

• 7–42 microns depending on coating weight

Lifespan

• Indoor: 20+ years
• Outdoor: 10–50 years depending on environment

Cost Level

• Medium (more than mild steel, less than aluminum or stainless)

6. Surface Finishes

• Regular spangle (visible zinc crystals)
• Minimized spangle
• Zero spangle (smooth finish)
• Matte finish
• Smooth surface for painting

7. Common Roll Forming Applications

Galvanized steel is used across almost all roll forming sectors:

• Roofing sheets (corrugated, trapezoidal, PBR, IBR)
• Wall cladding panels
• C and Z purlins
• Steel framing systems
• Gutters and downpipes
• Flashing and trim
• Fence panels and posts
• Cable trays and supports

8. Advantages of Galvanized Steel

• Excellent corrosion resistance
• Long lifespan
• Cost-effective compared to stainless or aluminum
• Widely available globally
• Suitable for outdoor applications
• Good balance of strength and formability

9. Disadvantages / Limitations

• Zinc coating can crack under tight forming
• Edge protection limited (cut edges exposed)
• Heavier than aluminum
• Not as corrosion resistant as stainless steel
• Surface can be damaged during forming

10. Roll Forming Machine Considerations

Roll Tooling

• Chrome plated rollers recommended
• Smooth surfaces to protect coating

Speed

• 15–60 m/min

Lubrication

• Usually not required
• Dry forming preferred

Cutting

• Hydraulic shear or flying cut-off
• Sharp blades to avoid burrs

Common Issues

• Zinc cracking in tight bends
• Surface scratching
• Coating damage from poor tooling

11. Common Problems in Production

• Coating peeling or cracking
• Oil canning in roofing panels
• Scratches from worn rollers
• White rust (improper storage)
• Uneven forming due to coil quality

12. Pricing Guide

Typical global pricing:

• Low: $700–$900 per ton
• Medium: $900–$1200 per ton
• High: $1200–$1600+ per ton

Factors affecting price:

• Zinc coating (Z275 vs Z450)
• Thickness
• Steel grade
• Country of origin
• Market conditions

13. Comparison with Other Materials

GI vs PPGI

• GI = raw zinc coated
• PPGI = painted version

GI vs Galvalume (PPGL)

• GI = better in some environments
• PPGL = better heat resistance

GI vs Aluminum

• GI = stronger and cheaper
• Aluminum = lighter and more corrosion resistant

14. Best Industries Using Galvanized Steel

• Construction and roofing
• Industrial buildings
• Agriculture
• Warehousing and logistics
• Infrastructure projects
• HVAC and ducting

15. How to Choose Galvanized Steel

Choose GI When:

• Corrosion resistance is required
• Outdoor use is expected
• Cost must be controlled
• Standard profiles are being produced

Avoid When:

• High-end architectural finish required
• Extreme corrosion environments (marine)

16. FAQ Section

What is galvanized steel used for in roll forming?

It is used for roofing, cladding, purlins, and structural profiles.

What does Z275 mean?

It refers to zinc coating weight (275 g/m²).

Is galvanized steel rust-proof?

It is corrosion resistant, but not completely rust-proof.

Can galvanized steel be painted?

Yes, it is often painted to create PPGI.

What thickness is common?

Typically 0.3mm to 2.0mm for roofing and cladding.

17. Machine Matcher Section

We supply roll forming machines for all material types including galvanized steel (GI).

• Custom-built machines to your profile
• New machines built to specification
• Global delivery available
• UK and USA technical support

Contact:
Machine Matcher
Sales & Technical Team

Quick Specs

Thickness
0.3–4.0mm

Yield Strength
250–550 MPa

Coil Width
600–1500mm

Coil ID
508 / 610mm