HVAC Duct Production Line: From Coil to Finished Duct

HVAC duct fabrication follows the same basic path in most shops. Coil sheet is unwound, straightened, stiffened, cut, locked, flanged and closed into a duct, while round duct takes its own route through a spiral tube former or a roll and a lock seamer. Below, each step is paired with the EBR METAL machine that handles it, so you can see a complete line before you plan your own. The exact order varies. It depends on the joint system you use, your duct sizes and how much of the work you want to automate.

Rectangular Duct Fabrication: The Main Line

Step 1. Load and Unwind the Coil

Galvanized coil is the usual starting material. It is specified by base thickness in millimeters plus its coating designation (for example under EN 10346 or ASTM A653). A gauge number alone leaves room for doubt. The coil sits on an decoiler (uncoiler) that feeds the line. The EBR METAL decoiler takes coils up to 5 tons and 1500 mm wide, and its brake stops the coil from unwinding when the line stops. If you change sheet thickness often, the Auto Duct Line with 3-Coil Selector holds three coils at once.

Step 2. Straighten the Sheet

Coil sheet keeps a curve from being wound. A straightener unit flattens it before it is cut. Every EBR auto duct line has one built in. Shops without an auto line can use a Cut-to-Length Line, which flattens the coil and cuts it into sheets of a set length and quantity.

Step 3. Add Stiffening Beads

Beads rolled into the sheet stiffen flat duct panels and reduce drumming. They do not replace the reinforcement that duct construction standards such as SMACNA or DW/144 call for. Each EBR auto duct line has two stiffening units. For sheets cut off-line, or in a shop without an auto line, the stand-alone Z Beading Machine and W Beading Machine do this job.

Step 4. Notch the Corners (Self-Flanged Duct)

For self-flanged duct, the corners of the blank are notched so the flanges and seams meet cleanly when the duct is folded. The notch shape depends on the joint system. The Auto Duct Line with Notching and the Auto Duct Line with Notching & Cleat Forming do this with a hydraulic notching unit.

Step 5. Cut to Length

The auto duct line cuts each blank to the programmed size. Off-line, the Cut-to-Length Line cuts coil into sheets, and hand-lever guillotine shears handle short straight cuts (see Hand Operated Machines).

Step 6. Form the Longitudinal Lock

The long seam of a rectangular duct is usually a mechanical lock such as the Pittsburgh lock or the snap lock. A Pittsburgh Lock Former rolls the female lock on one edge, and the Duct Flanging Machine forms the matching male edge. How well the duct holds air depends on seam type, seam quality and sealing together.

Step 7. Make the Transverse Connection

Duct sections are joined end to end in one of three common ways:

• Self-flanged (TDF-type) joints are roll-formed directly on the duct sheet. This suits automated lines. Machine: TDF Flange Forming Machine.
• Separate flange profiles are cut to length and attached to the duct. This suits larger and heavier duct. Machines: Flange Cutting Machine, then a spot welder joins them to the duct (we supply spot welding equipment with the line).
• Slip-and-drive joints use simple cleats and suit small, low-pressure duct.

No joint type has a built-in leakage class. Leakage is measured on the finished, assembled duct.

Step 8. Fold the Duct Body

A rectangular duct is made from one wrap-around blank, two L-shaped pieces or four flat panels. EBR auto duct lines can deliver flat sheet, an L-shape, a U-shape or a full square duct. For short runs and special parts, manual folding machines do the same job by hand (see Hand Operated Machines).

Step 9. Close the Seam

Once the duct is folded, the lock is closed by machine. The Duct Seam Closer closes the seams of square and rectangular duct, and the Pittsburgh Seam Closer closes Pittsburgh locks on straight duct and on elbows. On the Auto Duct Line with Notching & Cleat Forming, closing the lock can be part of the line itself.

Step 10. Corners, Sealing and Checks

Corners, gaskets and sealant come next. Joints, corners and gasket breaks are where duct most often leaks, so seal the joints with the same care you give the seam. Finally, the duct is checked for size and, where the job requires it, tested for leakage.

Hanging and Support Profiles

Installed duct hangs from profiles fixed to the building. The C Profile Roll Forming Machine makes C, U and L profiles for this, punches oval holes with hydraulic dies and cuts each piece to the length set on the PLC.

Round and Spiral Duct

Spiral duct fabrication. A narrow metal strip is wound into a tube with a continuous helical lock seam and cut to length as it comes off the machine. Because the seam runs in a helix, a spiral duct has no straight longitudinal seam. The EBR Spiral Duct Machine uses a 137 mm strip, makes Ø100–1250 mm tube from 0.5–1.2 mm sheet and cuts it automatically to lengths of 250–6000 mm. It comes with its own coil holder for coils up to 750 kg.

Round pipe rolled from sheet. Flat sheet is rolled into a cylinder on a slip roll (see Hand Operated Machines) and the longitudinal lock is closed on the Pipe Lock Seamer, which seams Ø150–1000 mm pipe with pneumatic pressure instead of a hammer.

Elbows. Round elbows are usually built from segments (gores) cut from a cylinder and joined. The Round Duct Elbow Machine flanges and closes the segment seams for Ø125–1250 mm elbows.

Fittings and Transitions

Fitting blanks such as transitions, offsets and tees are cut from flat sheet. The CNC Plasma Cutting Table cuts them along programmed paths, and the Plasma Sheet Feeder feeds sheet straight from the coil, so you are not tied to standard sheet sizes. Square-to-round transitions are formed on the Rectangular to Round Converter. Locks on fittings are made on the same lock former, flanging machine and Pittsburgh seam closer as straight duct.

Standards Your Customers May Ask About

A duct standard applies to the finished duct, which is built and tested for systems designed to that standard. Machines do not carry one. Buyers mention these most often:

• US: SMACNA HVAC Duct Construction Standards – Metal and Flexible (ANSI/SMACNA 006-2020) for construction, seams, joints, gauges and reinforcement. US leakage classes are numeric (ASHRAE 90.1).
• UK: BESA DW/144, Specification for Sheet Metal Ductwork: low, medium and high pressure classes up to 500, 1000 and 2000 Pa.
• Europe: EN 1505 and EN 1506 (dimensions), EN 1507 (strength and leakage, rectangular), EN 12237 (strength and leakage, circular). Leakage classes A to D, each three times tighter than the previous one. EN 16798-3 also uses ATC classes. A CEN draft (prEN 18289) is set to merge these standards, so check the edition named in your project specification.

Shop Utilities and Other Equipment

A line also needs stable power and compressed air. We can supply auxiliary equipment such as a voltage regulator, UPS, air compressor and air dryer with your machines.

Planning Your HVAC Duct Fabrication Line

Start from what you produce (rectangular, round or both), your joint system (Pittsburgh, snap lock, TDF, separate flange), your sheet thickness range and your daily output. A shop making mostly self-flanged rectangular duct will look at an auto duct line with notching, a lock former, a seam closer and a TDF flange machine. For a shop starting with round duct, the list is the spiral duct machine and the elbow machine. Send us your duct types, sheet range and production target, and we will suggest a setup and quote it as one package.

For a family-by-family overview of these machines and how to pick the ones your shop needs, read our guide Types of Duct Making Machines: A Buyer’s Overview.

Frequently Asked Questions