Round duct comes as spiral-seamed tube wound from a narrow strip, or as pipe rolled from flat sheet and locked along its length. Elbows and square-to-round transitions are the main fittings that follow. EBR METAL builds a spiral duct forming machine for Ø100–1250 mm tube and two round duct fitting machines. One makes elbows, reducers and end caps, the other square-to-round transitions.
Spiral Duct and Round Duct Fitting Machines
Spiral Duct Machine
STF
PLC-controlled spiral tube former with automatic cut-off. Winds 137 mm strip into Ø100–1250 mm duct in 0.5–1.2 mm coated sheet and cuts each tube to a set length of 250–6000 mm. Tooling for 23 standard diameters comes with the machine. Own coil holder included.
Round Duct Elbow Machine
EMM
Makes elbows, reducers and end caps from Ø125 to Ø1250 mm, with an adapter set for Ø100–125 mm. Two stations, one for flange preparation and one for closing, let two operators work at the same time. Flange heights 5, 7.5 or 10 mm.
Rectangular to Round Converter
RRC
Forms off-set and center-line square-to-round transitions up to 750 mm long in 0.50–1.20 mm sheet. Compact and fully guarded, it needs little floor space and runs on 5 bar shop air.
Compare the Round Duct Making Machines
| Spiral Duct Machine (STF) | Round Duct Elbow Machine (EMM) | Rectangular to Round Converter (RRC) | |
|---|---|---|---|
| What it makes | Straight spiral-seamed round duct | Elbows, reducers and end caps | Off-set and center-line square-to-round transitions |
| Size range (mm) | Ø100–1250 (23 standard diameters, tooling included) | Ø125–1250, adapter set for Ø100–125 | Transitions up to 750 long |
| Sheet thickness (mm) | 0.5–1.2 coated, 0.4–0.7 chrome | 0.5–1.5 galvanized, 0.5–1.0 stainless | 0.50–1.20 |
| Strip width (mm) | 137 | — | — |
| Product length (mm) | 250–6000, cut automatically | — | — |
| Flange heights (mm) | — | 5 / 7.5 / 10 | — |
| Speed | 14 m/min at Ø100, 2.8 at Ø500, 1.4 at Ø1000, 1.2 at Ø1250 | Ø200 mm 90° four-segment elbow ≈ 2 min | — |
| Control | PLC touch screen | — | — |
| Power supply | 380 V / 3 Ph / 50–60 Hz | 380 V / 3 Ph / 50–60 Hz | 380 V / 3 Ph / 50 Hz |
| Compressed air | 6–8 bar, approx. 15 L/min | 6–8 bar (min. 6), approx. 9 L/min | 5 bar |
| Hydraulic oil (L) | 10 + 6 | 90 | — |
| Dimensions W × H × L (mm) | 1600 × 2400 × 3050 | 980 × 1100 × 2800 | 500 × 1000 × 1300 |
| Weight (kg) | 1950 | 850 | 60 |
Values come from each machine’s specification table. Sheet thickness capacities are given for ST37 (S235JR) mild steel.
How to Choose Round Duct Fitting Machines
Do you make straight round duct? Start with the Spiral Duct Machine. It winds coil strip into tube and cuts every piece to the length you set, producing the runs the fittings later connect. It comes in a banded type (two options) and a molded type.
Do you build elbows and other round fittings? Add the Round Duct Elbow Machine. It takes galvanized sheet up to 1.5 mm, thicker than the 1.2 mm limit of the spiral machine, and stainless up to 1.0 mm.
Does your system change from rectangular to round duct? The Rectangular to Round Converter forms those transitions. At 60 kg it moves easily around the shop.
Smaller batches or special sizes? Pipe rolled from flat sheet and closed with a longitudinal lock needs no spiral machine. See Spiral Seam or Longitudinal Seam below.
How a Spiral Duct Machine Works
- Coil feed. A coil of 137 mm strip sits on the machine’s own coil holder, which carries up to 750 kg. Because the holder is supplied with the STF, the 5-ton Decoiler of a rectangular duct line is not needed here.
- Forming and winding. The strip is formed and wound at an angle around the set diameter, and the edges of each turn lock together into a continuous spiral seam. Angle adjustment, greasing and loading are automatic. A volatile lubricating oil keeps the sheet free of stains.
- Cut-off. At the length set on the PLC touch screen, a high-speed cutting system cuts the tube with a burr-free edge.
The forming tools are made of 2379 cold work tool steel for resistance to abrasion and pressure. Tooling for these 23 standard diameters is supplied with the machine and included in its price: Ø125, 150, 160, 200, 224, 250, 280, 300, 315, 350, 400, 450, 500, 560, 600, 630, 700, 710, 800, 900, 1000, 1125 and 1250 mm.
Banded or Molded Spiral Duct Machine
Both types wind the same spiral seam. The difference is how the strip is held to the diameter while it forms.
| Banded type | Molded type |
|---|---|
| A flexible steel band guides the strip into a circle. | A rigid forming head, or mould, shapes the strip. |
| To change diameter, a band of the right length is fitted and adjusted. | Each diameter has its own mould, for example one for Ø200 and another for Ø250. |
| Fewer large rigid formers are needed. | The diameter comes from the mould geometry. |
| Band setup and adjustment need care. | Changing diameter means changing the mould. |
How Gored Elbows Are Made
A round elbow is built from several short segments, called gores, each cut at an angle so that together they turn the airflow through the bend. Depending on the shop, the segments are cut on a plasma table such as our CNC Plasma Cutting Table or on a guillotine shear, then rolled on a slip roll (see Hand Operated Machines). The Round Duct Elbow Machine flanges and closes each joint after that.
Square-to-Round Transitions
A square-to-round transition joins a rectangular duct to a round one. In a center-line transition the round outlet sits on the center of the rectangle. An off-set transition shifts it toward one side, which helps where the two runs do not line up. Our catalogue states the Rectangular to Round Converter produces both types in half the time.
Spiral Seam or Longitudinal Seam?
Spiral-seamed duct is wound continuously from coil, and the spiral seam also stiffens the tube along its length. It suits long straight runs in standard diameters. For other work, round pipe can be rolled from flat sheet on EBR METAL’s slip roll machines, in manual (MR), manual with bench (SR) and motorized (MSR) versions with useful lengths from 600 to 2050 mm (see Hand Operated Machines). The pipe lock edge can be rolled on the Pittsburgh Lock Former, and the Pipe Lock Seamer (LSM 15) closes the longitudinal lock on pipe from Ø150 to Ø1000 mm. A 120 cm pipe takes about 3 seconds.
What Comes Before and After
The spiral duct machine runs from its own coil holder, and its tube goes on to the fittings. Where the round system meets rectangular duct from one of our Auto Duct Lines, the converter forms the transition. See the full sequence on the HVAC Duct Production Line page.
How the spiral seam is formed, what pressure it takes and how spiral duct compares with longitudinal-seam pipe is covered in our guide How Spiral Duct Is Made.
For gore counts, radius and sealing of round elbows, read our guide How Round Duct Elbows Are Made (Gore Elbows).
Frequently Asked Questions
Which machines do I need to make round duct and fittings?
A Spiral Duct Machine for the straight runs, a Round Duct Elbow Machine for elbows, reducers and end caps, and a Rectangular to Round Converter where round duct meets rectangular duct.
Is a spiral tube former the same as a spiral duct making machine?
Yes. Spiral Tube Former with Slitter (STF) is the catalogue name of our spiral duct machine. Its “slitter” is the automatic cut-off at the end of the machine, which cuts the finished tube to length. It does not slit coil.
Which diameters can the round duct machines make?
The spiral duct machine covers Ø100–1250 mm and comes with tooling for 23 standard diameters from Ø125 to Ø1250 mm, included in the machine price. The elbow machine works from Ø125 to Ø1250 mm, and an adapter set covers Ø100–125 mm. The converter is sized by transition length, up to 750 mm.
Which elbow angles and segment counts can the elbow machine make?
There is no fixed limit. The angle and the number of segments follow how you cut the gores, and the machine flanges and closes each joint. A Ø200 mm 90° four-segment elbow takes about 2 minutes.
How fast is the spiral duct machine?
It depends on the diameter. The machine runs at 14 m/min at Ø100, 2.8 m/min at Ø500, 1.4 m/min at Ø1000 and 1.2 m/min at Ø1250, for 0.5–1.2 mm sheet.
Do these machines need compressed air?
Yes, all three. The spiral duct machine needs 6–8 bar (approx. 15 L/min), the elbow machine 6–8 bar (approx. 9 L/min) and the converter 5 bar.
Can I make round pipe without a spiral duct machine?
Yes. Roll the sheet into a cylinder on a slip roll machine and close the longitudinal lock on the Pipe Lock Seamer.
What is the delivery time?
Many EBR METAL machines ship from stock. A machine built to order currently takes about 2–3 weeks, and the quotation confirms the date. Spare parts usually ship from stock.