How a Spiral Duct Forming Machine Works
A spiral duct forming machine — usually called a spiral tubeformer — continuously rolls strip into a rigid round tube with a helical lock seam. Galvanized, stainless or colour-coated steel leaves the decoiler, passes through levelling rollers that remove coil memory, and is wrapped around a forming mandrel while the seam station rolls and crimps the interlocking profile. A flying saw cuts the continuous tube to length without stopping the line, and the finished tube is discharged onto the collection table.
The geometry does the structural work. Because the seam runs in a continuous helix, the tube gains stiffness from the spiral itself — a spiral duct of a given gauge is measurably stiffer than a comparable longitudinal-seam pipe of the same material — and the crimped seam delivers the leakage performance round systems are specified against. That combination is why spiral duct dominates commercial HVAC main runs, industrial dust collection and exhaust work.
Reference Specification: Band-Type Tubeformer
The specifications below are for the band-type build that most export catalogs list as the standard spiral duct forming machine. Mould-type, heavy-duty and plasma-cut builds differ mainly in diameter range and cutting method; treat every figure as build-dependent and confirm it on the quotation.
| Parameter | Band-Type Spiral Duct Forming Machine |
|---|---|
| Duct diameter | 80–1500 mm; the model family extends to 1600 mm and beyond |
| Strip thickness | 0.4–1.0 mm on the band-type build; the family is quoted to 1.2 mm, and heavy-duty builds to 1.5 mm |
| Strip width | 137 mm standard |
| Forming speed | 1–38 m/min, adjustable |
| Main motor | 5.5 kW |
| Cutting motor | 4 kW (flying saw) |
| Roll tooling | GCr15 bearing steel forming rollers, hardened |
| Drive | Spiral bevel gear reducer (low noise) |
| Decoiler | Mechanical expanding type, 1.5 t capacity, 480–610 mm inner diameter |
| Control | Inverter plus PLC; touchscreen on current builds |
| Pneumatic hydraulic station | 8 kgf/cm² |
| Footprint / weight | 3500×2800×2580 mm; about 2500 kg |
| Materials | Galvanized steel, stainless steel, colour-coated steel, aluminium |
| Certification / warranty | CE; warranty terms vary by build (1–2 years) — confirm at quotation |
Two numbers deserve attention when comparing quotes. The diameter range sets which jobs you can bid at all — 80–1500 mm covers essentially the whole commercial spiral order book, while a machine specified only to 1200 mm quietly excludes the large-diameter industrial work. The strip thickness ceiling sets your gauge flexibility: 1.0 mm is the band-type standard, and if you regularly run 1.2 mm at large diameters you are shopping in the heavy-duty class, where the frame and drive are built for it.
Band Type vs Mould Type vs Heavy-Duty Builds
The same tubeformer job is solved several ways in this equipment class, and the differences are mechanical, not cosmetic:
| Build | Forming principle | Diameter changeover | Choose it when |
|---|---|---|---|
| Band type (flexible) | Forming bands define the tube geometry; the mandrel stays in place | Quick — a setting adjustment, no mould swap | Your diameter mix varies day to day |
| Mould type | Fixed mould per diameter on a classic mandrel machine | Mould swap — minutes to an hour | You run long batches of one diameter |
| Heavy duty (PD-2000 class) | Reinforced frame and drive for thicker strip at large diameters | As per band or mould configuration | Large-diameter industrial duct is routine work |
| Plasma cut (PD-1600-PLASMA class) | Integrated plasma cutting instead of a saw | As per base machine | Cut-to-length accuracy and throughput dominate |
The band-type machine is the default choice for a general commercial shop because most shops run a diameter mix, not a single diameter. The mould-type machine wins on long runs of one diameter, where the changeover cost amortizes to nothing — but the moment the order book fragments into many diameters, mould changes eat the advantage. Heavy-duty builds carry a premium that is only justified when heavier gauge at large diameter is routine, and plasma cutting replaces a separate downstream operation rather than improving the forming itself.
Sizing the Machine to Your Diameter Mix
The classic sizing mistake is buying for the largest duct you have ever made instead of the mix you actually run — which buys idle capacity and floor space. Work through your last twelve months of orders: if most of your round duct falls between 100 and 1000 mm, a mid-range tubeformer is the right tool and the large-diameter machine is a cost you will carry for years.
Throughput arithmetic
Forming speed is quoted up to 38 m/min, but the honest planning number is output in finished ducts per hour. A 3 m tube at a realistic 10 m/min forming speed leaves the machine in under 20 seconds; with loading, seam start-up and discharge, one operator typically turns out 30–60 ducts per hour. Compare that with manual forming, where two or three workers manage a fraction of that — the payback case for the machine is labour, not speed for its own sake.
Commissioning: getting diameter right from day one
A tubeformer produces a helix, and every diameter needs its own set-up. Shops that write settings down produce saleable tube from the first hour; shops that set by eye produce a morning of scrap. The discipline that matters:
- Level the frame in both axes and re-check after the first week — long frames settle.
- Set the helix angle from the diameter table first, then adjust for material springback.
- Measure diameter at three points along the tube; taper means the angle or the strip tension is unstable.
- Record helix angle, strip tension and speed for every diameter you run. This is the single highest-value habit on a tubeformer.
- Stabilise tension before touching the angle — most diameter drift is tension, not geometry.
- Cut a section and inspect the lock at the start of every new diameter; a seam that looks closed can still leak.
- Measure the first and last piece of every batch for length — length is a separate setting from diameter.
What the Tubeformer Does Not Do
The machine forms and cuts tube. Flanging the tube ends for bolted connections is a separate operation on a spiral duct flanger, and beading or other end detailing is downstream again. Budget the line, not the machine: decoiler, tubeformer, cutting, flanging and handling. The decoiler deserves specific attention — the 1.5 t mechanical expanding type with a 480–610 mm inner diameter covers standard export coils, but an oversized or undersized coil will not seat properly and tension problems follow for the life of the machine.
Factory Acceptance Checklist
Before the machine is crated, insist on a test run with your own material and check:
- Diameter accuracy. Measure formed tube at three points along the length at your two most common diameters; look for taper, not just average size.
- Seam quality. Cut a section and inspect the crimped lock for full engagement and consistent height.
- Length accuracy. Measure the first and last piece of a batch against the programmed length.
- Speed under load. Confirm the line holds rated speed with your heaviest in-spec gauge, not just light stock.
- Roll material. Ask for the GCr15 roller material and hardness figures on the test report.
- Control system. Run a diameter changeover yourself on the touchscreen; if it is not intuitive for you, it will not be for your operators.
- Decoiler fit. Confirm your coil dimensions against the expanding chuck range before shipment.
- Electrical. Nameplate voltage and phase against your supply; any change must be made at the factory.
- Leakage expectation. Ask for the seam leakage class the manufacturer claims, and how it is tested.
- Documentation. Manual, wiring diagram, PLC program backup, and video outgoing-inspection of your actual machine.
Common Faults: Symptom, Cause, Fix
| Symptom | Most likely cause | What to do |
|---|---|---|
| Diameter too large or too small | Helix angle set for a different diameter | Re-set the angle from the diameter table; run 3 m of scrap before measuring; then record the setting |
| Diameter drifts during a run | Strip tension unstable | Stabilise tension first; only adjust geometry if drift persists with stable tension |
| Seam leaks or looks open | Incomplete lock formation; poor strip edge condition | Inspect the lock on a cut section; check the strip edge for burrs; do not raise speed to close the seam |
| Tube surface marked or scored | Roll damage or debris in the forming head | Clean rolls with a brass brush, never steel; check the strip edge — this often starts after a slitter blade change |
| Cut length inconsistent | Length encoder or stop drifted | Check the length setting on the first and last piece of each batch and re-lock it; log for a week |
| Machine labours on heavier gauge | Material above the roll set specification | Verify thickness with a micrometer against the roll set spec; never force thicker material through |
FAQ
What materials can a spiral tubeformer run?
Galvanized steel is the standard; stainless, colour-coated steel and aluminium run with the correct roll set and surface handling. Strip thickness for the band-type build is 0.4–1.0 mm, with the family quoted to 1.2 mm and heavy-duty builds to 1.5 mm.
How long does a diameter changeover take?
On a band-type machine, a diameter change is a setting adjustment, not a mould swap — typically minutes once the settings are recorded. On mould-type machines, budget for the mould change itself.
What diameter range do I actually need?
Size for your order book mix, not your largest-ever duct. The commercial sweet spot for most shops is 100–1000 mm, well inside the standard 80–1500 mm range.
Does the machine cut to length?
Yes — a flying saw cuts the continuous tube without stopping production. Plasma-cut builds integrate cutting in line and are chosen when cut-to-length accuracy and throughput dominate.
Can one machine produce oval ducts?
Not directly. Oval and flat-oval duct is a separate operation — an ovalizer working on formed round tube, or a dedicated oval machine. Confirm at quotation if oval work is part of your mix.