Steps to Fabricate Round HVAC Ducts

Steps to Fabricate Round HVAC Ducts

1. Material Preparation

• Material Selection: Choose galvanized steel, aluminum, or stainless steel sheets (common thickness: 0.5mm–1.2mm).

• Uncoiling & Flattening: Load the metal coil into a decoller machine and flatten it for cutting.

2. Cutting the Sheet

• Use a plasma cutter, shearing machine, or CNC cutting table to cut the sheet to required dimensions (width = duct circumference + seam allowance).

3. Forming the Cylinder

• For Straight Ducts:

• Bend the flat sheet into a cylinder using a roll forming machine or slip roll former.

• Overlap the edges by 10–15mm for seam locking.

• For Spiral Ducts:

• Feed the sheet into a spiral duct machine, which automatically rolls and locks the seam into a helical shape.

4. Seaming & Locking

• Straight Ducts: Secure the longitudinal seam with:

• Pittsburgh Lock (common for rectangular ducts adapted to round).

• Snap Lock or Button Punch for lighter gauges.

• Spiral Ducts: The machine self-locks the spiral seam via interlocking edges.

5. Joining Sections

• Couplings: Connect ducts using sleeve joints or flange systems (TDC/PDC flanges).

• Sealing: Apply mastic tape or aerogel sealant at joints to prevent air leakage.

6. Reinforcement (If Needed)

• Add external bead stiffeners or internal braces for ducts >500mm diameter to prevent collapse.

7. Quality Check

• Measure dimensions with a caliper or laser scanner.

• Test airflow resistance (if required) using a duct blaster.

8. Insulation (Optional)

• Wrap ducts with fiberglass or foam insulation (e.g., Armaflex) for thermal/acoustic control.

Key Tools Mentioned

• Spiral duct machine

• Roll forming machine

• Plasma cutter

• Pittsburgh lock former

• Duct blaster

Pro Tips

• Use AutoCAD or Revit for precise duct design before fabrication.

• For spiral ducts, maintain consistent machine speed to avoid seam deformation.