What a Spiral Duct Flanger Actually Does
A spiral duct flanger is a finishing machine for round duct. It takes a length of spiral tube — straight off the tubeformer — and forms a Vanstone flange on the tube end: a stiffened, bolt-ready rim that lets the section couple to the next one with a gasket and bolts. No angle ring to weld, no rivet line, no beating the tube edge over a die by hand. One operator, one tube end at a time, and a connection that assembles on site without a welder.
The distinction that matters on the shop floor: a flanger forms the flange on the tube itself. It does not make the tube — that is the spiral tubeformer upstream. It does not close the seam — that is a seam locker on a different line. And it does not produce separate rings — that is a round flange forming line, a different product buyers confuse with this one. The flanger is the last station before fittings, and it is the one most often bought as an afterthought, then discovered to be the bottleneck because nobody sized it against the tubeformer's output.
The Machine at a Glance
Published figures for the Preda spiral duct flanger, with the practical meaning of each number in the right column.
| Parameter | Published figure | What it means on your floor |
|---|---|---|
| Duct diameter | 200–1200 mm (8–48 in.) | Covers commercial supply, exhaust and dust collection; above 1200 mm is custom territory |
| Material gauge | Galvanized up to 18 ga (≈1.2 mm) | Thinner for stainless and aluminum; gauge tooling is specified per material |
| Flange type | Vanstone / bead | Formed rim, bolt-ready — the standard for bolted flanged round duct joints |
| Motor power | 3 kW | Standard 380 V/3-ph; voltage conversion is a quotation item |
| Control | PLC with touchscreen | Settings per diameter and gauge; consistent results between shifts |
| Construction | Heavy-duty steel frame | Vibration-free operation; forming accuracy holds over years, not weeks |
| Certification / warranty | CE / 2 years | Ask for the CE file and the warranty terms in writing |
| Design | Patented machine | Not a generic bender — the forming head is the protected part |
| Indicative price | About USD 11,500 FOB | Build dependent — tooling count per diameter moves this materially |
How the Flange Is Formed
The machine forms the tube end in one pass through a diameter-specific forming head: the rim is rolled outward into a flange while a bead is set into the metal just below it. The bead is not decoration — it stiffens the rim so the flange holds round under bolt load, and it gives the gasket a defined seating line. Get the bead depth wrong and the joint either leaks or cracks the coating.
Roll forming, not spinning
Quality flangers roll-form the profile from the tube end inward with supported rollers; the tube never sees a point load. On lesser machines the flange is spun or beaten over a die, which works on 0.7 mm galvanized and fails on 1.2 mm — the rim waves and the holes will not line up. Ask which principle the machine uses before you compare prices.
Squareness comes from support, not from the head
A flange out of square with the tube axis will not bolt up, and the fault is almost always handling: a tube flanged while held in the air twists. Every serious flanger comes with tube supports and an end stop, and the acceptance test is a dry-fit on a mating flange — not a tape measure. A flange that measures right can still not bolt up.
Hole pattern is the fault that reaches site
Bolt holes are punched or drilled to the pattern of the mating flange. Two flangers can both produce "correct" flanges and still not match, because the pattern is a drawing, not a dimension. Verify the pattern against your drawing on the first piece of every diameter, every time — and if your pattern is unusual, send the drawing with the order.
Flanger, Ring Line or Seam Locker: Choosing the Right Machine
Buyers most often confuse the flanger with two other machines. The table separates them by output, not by price.
| Machine | Output | Unit of work | Choose it when |
|---|---|---|---|
| Spiral duct flanger (this machine) | Vanstone flange on the tube end | Per tube end, operator-paced | Your specification calls for bolted flanged joints on spiral duct |
| Round flange forming line YFL-40 | Separate angle or flat steel rings, 100–1600 mm, 5.5 kW, feed→form→weld→cut | Continuous from strip, cut to length | You want rings rather than a formed end flange — common on larger diameters |
| Hydraulic seam locker HF-1550 | Closed Pittsburgh seam on rectangular duct | Per duct panel | You run rectangular ductwork — a different line, not a substitute |
| Elbow machine (gorelocker) | Elbows and fittings | Per fitting | You make fittings as well as flanged tube ends — complementary |
Selection logic in one paragraph: if your round duct is joined with bolted flanges, you need an end flanger. If your joints are sleeved, taped or welded, you do not — spend the money on the tubeformer instead. If you build flanged rings as a product to sell, that is the ring line, a USD 18,000-class machine with welding integrated, not this one. And if your line already runs a tubeformer such as the PD-1200, the flanger is its natural partner — size them together.
Sizing: Match the Flanger to the Tubeformer
A flanger that cannot match the tubeformer's output silently becomes the constraint on the whole round duct line, and the mistake shows up months later. The arithmetic is short:
- Count ends, not ducts. Most tubes need two flanged ends. If your tubeformer produces 40 ducts/hour, the flanger must deliver 80 ends/hour — at both ends, including handling.
- Convert the tubeformer's metres to tubes first. A 10 m/min line at 3 m average duct length is roughly 200 tubes/hour of forming capability; real output is operator-paced and lower. Measure your own line for two weeks before deciding.
- Tooling is diameter-specific. Run five diameters and you need tooling for five diameters staged at the machine. Walking to a store for tooling is the hidden cost that turns a fast machine into a slow line.
- If the gap is large, a second flanger is cheaper than the bottleneck. Two operator-paced stations at one diameter beat one station switching tooling all day.
Gauge, Tooling and Wear
The published limit is 18 ga galvanized, about 1.2 mm. Two practical consequences follow. First, stainless and heavy-gauge stock accelerate tooling wear sharply — if stainless is routine for you, keep a spare tooling set and confirm the material specification with a micrometer before every batch. Second, forming depth is a per-gauge setting: over-forming fractures the galvanising at the bend, and that cracked coating is exactly where corrosion starts in service. A flange that looks strong and fails early is a forming-depth problem, not a steel problem. Record the depth setting per gauge on a set-up card, and reduce it to the minimum that produces a bolt-ready flange.
Acceptance: Test This Before Final Payment
A flanger is accepted on joints, not on paint. Insist on the following at the factory FAT, or on your floor within the first week:
- Witnessed run at your gauge and your three most common diameters — not the salesman's demo stock.
- Dry-fit a mating flange at the machine on the first piece of every diameter; bolt holes must line up without force.
- Squareness check with the tube supported, on the first and last piece of three batches.
- Bead depth and flange height measured against the drawing; coating inspected for cracks at the bend.
- Tooling inventory against the diameter table you bought — count, size marking, condition on the bench.
- Throughput measurement — ends per hour over a two-hour run, compared with your tubeformer's output.
- Operator training on tooling change, depth setting and squareness checks, with the manual in your language.
- CE file, wiring diagrams, PLC backup and spares list delivered with the machine.
- Container loading photos before shipment, and the packing plan in the contract.
Faults: Symptom, Cause, Fix
Flange faults that survive to site are expensive, so diagnose at the machine with a mating flange in hand — never by measurement alone.
| Symptom | Most likely cause | What to do |
|---|---|---|
| Flange will not bolt up | Hole pattern misaligned, or flange out of square | Dry-fit a mating flange; check the pattern against the drawing; support the tube for every flange |
| Flange depth inconsistent | Tooling not seated, or the setting drifted | Re-seat the tooling; set depth from a test piece; check at the start of every diameter |
| Galvanising cracks at the bend | Forming depth too great | Reduce depth to the minimum bolt-ready value; record the setting per gauge |
| Flange out of square with the tube | Tube not supported during forming | Support the tube on a stand for every flange; check squareness on the first piece |
| Flanger cannot keep up with the tubeformer | Undersized for the line | Measure ends per hour against tubeformer output for two weeks; a second flanger may be cheaper than the bottleneck |
| Tooling wearing quickly | Material harder or thicker than specified | Confirm the material spec; keep a spare tooling set for stainless work |
FAQ
What materials can it flange?
Galvanized steel up to 18 ga is the published range; stainless and aluminum run at thinner gauges with the correct tooling and clean tube ends. Colour-coated stock is a quotation question — check coating adhesion at the bead.
How long does a diameter change take?
Plan on a tooling change plus a test piece: minutes when the tooling is staged at the machine, far longer when it is in a store. Budget a dry-fit and a squareness check before production restarts.
Can it make oval duct?
No. It flanges round tube ends. Flat-oval profile is produced downstream by an ovalizer that reshapes formed round duct.
What about warranty and support?
CE and a two-year warranty are published, with remote PLC diagnostics, free spare-part shipping in warranty and 24-hour response. Get the response commitment in writing, with a named contact.
Delivery and MOQ?
Single-machine orders are normal. Ask for the packing list, the tooling list and container loading photos before payment.
The Buying Checklist
- Joint type first — bolted flanges justify a flanger; sleeved or welded joints do not.
- Diameter mix — last 50 ducts by size, and the tooling count that mix implies.
- Gauge mix — micrometer-verified, including any stainless work and its tooling cost.
- Ends-per-hour math — against your tubeformer's measured output, not its brochure speed.
- Witnessed run — at your gauge, your diameters, with a dry-fit on a mating flange.
- Voltage — 380 V/3-ph standard; conversion is a factory option, quote it.
- After-sales — response time, spare-part pricing, remote diagnostics, training.
- Price context — the flanger sits near USD 11,500; the YFL-40 ring line near USD 18,000. Compare like with like.
Get the tooling list, the hole-pattern drawing and the witnessed dry-fit into the purchase contract, and the flanger stops being an afterthought and starts being the station that finishes your duct.