Galvanized Steel (GI/GP) Slitting & Cut to Length Lines
Galvanized steel's zinc coating is what the customer is paying for — and it is exactly what careless coil processing destroys. Flaking at slit edges, coating scratches from bare rolls, and white-rust staining from trapped moisture are the three classic GI processing failures.
Friend Engineering Works builds slitting lines and CTL lines configured for GI, GP and GC coils, used across India's roofing, ducting, purlin and panel industries. Our lines process galvanized coils from 0.10mm to 4mm with coating-safe contact surfaces and knife setups tuned for coated material.
Protecting the Zinc Coating During Processing
- Knife clearance set for coated material — wrong clearance causes zinc flaking and exposed steel at the slit edge
- Rubber or PU-covered feed and pinch rolls to avoid coating scratches
- Dry, covered strip path — trapped moisture between wraps causes white rust (wet storage stain)
- Correct recoiling tension — over-tension causes coating pickup between tight wraps on soft coatings
Typical GI Processing Applications in India
| Application | Typical Material | Equipment |
|---|---|---|
| Roofing sheets & color-coated lines | 0.3–0.8mm GI/PPGI | Slitting line + recoiler |
| HVAC ducting | 0.5–1.2mm GI | CTL line with leveler |
| Purlins (Z/C sections) | 1.5–3mm GI | Slitting line feeding roll formers |
| Cable trays & panels | 1–3mm GI/GP | CTL line + slitting line |
| Solar module mounting structures | 1.5–4mm GI/HDG | Slitting + CTL |
Line Specifications for Galvanized Coils
- Thickness range: 0.10mm – 4mm (heavier HDG structural strip as custom builds)
- Coil width: up to 2000mm
- Coil weight: up to 40 tonnes on hydraulic decoilers
- Slitting accuracy: ±0.1mm with burr-free, flake-free edges
Recommended Equipment
- Slitting Line — Friend Engineering Works slitting lines are designed to ensure the highest standards of quality and productivity while processing different materials.
- Cut to Length Line — We manufacture advanced Cut to Length Lines for uncoiling, straightening, gauging, cross-cutting to length, and stacking work.
- Decoiler Machine — Our decoiler machines are designed for efficient and safe uncoiling operations with heavy-duty construction.
Frequently Asked Questions
Does slitting damage the galvanized coating at the cut edge?
A correctly set slitter does not. Zinc is ductile and smears slightly over the cut edge, giving partial cathodic protection. Problems appear when knife clearance is wrong for the coating class — that causes flaking and burrs. Our slitter heads are set up and test-run for the specific GI grades you process.
What causes white rust on processed GI coils and how do I prevent it?
White rust (wet storage stain) forms when moisture is trapped between coil wraps. Prevention: recoil dry material with correct tension, store coils off the floor in ventilated areas, and avoid processing condensation-wet coils. The machine's role is uniform, tight recoiling so water cannot wick between wraps.
Can one line process both bare CR and galvanized coils?
Yes — GI and CR lines are mechanically similar, and many of our customers run both on the same line. The knife setup (clearance/overlap) should be adjusted per material, and contact rolls kept clean so zinc pickup does not mark subsequent CR coils.