Galvanized iron sheet air ducts are core components of ventilation and air conditioning systems, and their manufacturing and installation quality directly affect system tightness, structural strength, and service life. To help engineering personnel systematically master key technologies, this article comprehensively sorts out the material selection, manufacturing processes, and installation standards of galvanized air ducts in accordance with the latest industry specifications.
 

 

The thickness of duct sheets must be strictly selected based on the system pressure level and duct dimensions:

- Low and medium pressure systems: When the long side dimension of the duct is ≤ 320mm, the thickness should be ≥ 0.5mm; 321–630mm requires ≥ 0.6mm; 631–1000mm requires ≥ 0.75mm; 1001–2000mm requires ≥ 1.0mm; and over 2000mm requires ≥ 1.2mm.

- High pressure systems: Thicker sheets are required, such as thickness ≥ 0.75mm for long side ≤ 630mm and ≥ 1.0mm for 631–1250mm.

The quality of the galvanized layer must meet standards, with zinc adhesion not less than 80g/m² under normal working conditions, and higher specifications should be adopted for corrosive environments.

 

1. Cutting and Seam Connection

Sheet cutting requires accurate size, and burrs must be removed after shearing. Joints should use seam connections (welding is prohibited). Common double-lock seams are suitable for high-pressure systems, while snap-lock seams are limited to medium and low-pressure systems. Seam operations must use wooden hammers to avoid damaging the galvanized layer.

 

2. Flange Manufacturing and Riveting

The inner diameter of angle steel flanges should be 2–3mm larger than the outer diameter of the duct. Bolt hole spacing is set according to system requirements: ≤150mm for air conditioning and supply/exhaust systems, ≤100mm for smoke control systems, with holes mandatory at the four corners. Ducts and flanges are riveted using galvanized rivets, with hydraulic riveting pliers recommended for construction; rivet spacing is consistent with bolt hole spacing.

 

3. Sealing and Reinforcement Treatment

Duct flange should be controlled at 6–9mm, tightly adhering to the flange and flat without warping. Overlapping corners should be flattened and tightly sealed with sealant. Flange gaskets are selected based on system type: 8501 sealant strips for ordinary ducts, and non-combustible materials (such as 9501 or asbestos boards) must be used for smoke control ducts, with gasket joints tongue-and-grooved without stacking.

Rectangular ducts with side length ≥630mm or insulated ducts with side length ≥800mm require reinforcement, commonly using angle steel reinforcement, beading, etc.

 

4. Manufacturing of Special Components

The angle of single-sided diameter reduction for reducers should be <30°, and double-sided reduction angle <60°. Elbows and tees should be made in a streamlined shape to reduce wind resistance and noise.

 

1. Support and Hanger Settings

For horizontal installation: When duct diameter or long side ≤400mm, bracket spacing ≤4m; >400mm requires ≤3m. Vertical installation spacing ≤4m, with at least 2 fixed points for a single straight duct. Supports and hangers must avoid air outlets and valves, with a distance ≥200mm from air outlets or connecting pipes.

 

2. System Safety Measures

When ducts pass through fireproof/explosion-proof walls, steel protection sleeves with thickness ≥1.6mm must be installed and sealed with non-combustible materials. For conveying flammable and explosive gases, anti-static grounding devices must be installed, and ducts must not pass through living areas. When the length of horizontal main ducts exceeds 20m, anti-sway fixed points should be installed.

 

3. Finished Product Protection and Repair

Manufacturing sites must be covered with wooden boards or construction carpets to protect the galvanized layer. Ducts should be stacked vertically to prevent deformation. Damaged galvanized layers during installation must be promptly treated with anti-corrosion measures (such as spraying epoxy zinc-rich paint).

 

4. Key Quality Acceptance

After installation, air ducts must undergo tightness testing, with air conditioning ducts using the light leakage detection method. Flange connections should have no gaps or exposed padding, with bolts in the same direction. Fireproof ducts and sealing materials must be non-combustible.