Putai Sigma Purlin Roll Forming Machine for Long Spans
Sigma (Σ) section — a C purlin with the web folded back on itself
Web-stiffened rolls, 20–25 forming stations
Inline hydraulic punching for bolt holes and slots
Flying shear cut-off, length set on the control
Built on the same frame as our C Z purlin lineWhat a Sigma Purlin Actually Is
A sigma purlin is a cold-formed Σ section, a C shape with the web folded back on itself, so the section ends up with a stiffened web and two symmetrical flanges. The fold is not decoration. It moves steel away from the neutral axis, which raises the second moment of area for the same coil weight.
Buyers meet it in two places. Long-span roof purlins in industrial and agricultural buildings, where a C purlin would need a deeper section or a second row of supports. And floor cassettes, where the same weight advantage lets a shallower cassette carry the same load.
Our sigma purlin roll forming machine forms that section from galvanised coil, punches the connection holes inline and cuts to length without stopping the line.
What Changes on the Machine
The frame, the drive and the cut-off are shared with our C Z purlin roll forming machine platform. Three things are not shared.
The roll set. A sigma roll set cannot be swapped for a C or Z set on the same shafts, because the pass sequence differs in the middle of the line rather than at the edges. If you run both families, plan for two roll sets and a changeover, and ask us for the changeover time in writing before you order.
The web fold. The fold has to be formed step by step. A single heavy pass marks the coating and springs the flange, which shows up later as a purlin that will not sit flat. This is where the extra stations go.
The punch pattern. Sigma purlins usually need bolt holes on both flanges and, on some systems, slotted holes in the web fold itself. The punch station is built around your pattern and pitch, so it is fixed at order, not at installation.
From Coil to Bundled Purlin
The sequence below is standard on any purlin roll forming machine. The one unusual step is the web fold, and it is marked below.
Decoiler. Coil is loaded by crane or forklift and held on a mandrel. Capacity is set to the coil weight you actually buy, not to a catalogue maximum.
Leveling. Coil set is removed before forming. On 2.5 mm galvanised steel this unit is not optional — skip it and the purlins camber, which costs time on site.
Servo feed and punch. Length is measured on the material, and the punch station fires on that measurement. Bolt holes and slots are made before forming, so the pattern stays square to the section.
Forming. The section is built pass by pass. The web fold takes the extra stations described above.
Flying shear. The cut travels with the material, so the line does not stop for every length.
Run-out. Cut purlins drop onto a table and are bundled by hand, or stacked automatically if the line is ordered with a stacker.
Specifications
Sigma, C or Z: Which Section Fits the Job
FAQ
Q: Can one machine run sigma, C and Z?
A: No. Sigma needs its own roll set, and on our platform the roll set is not interchangeable with C or Z because the middle passes differ. One frame, separate roll sets, is the realistic arrangement.
Q: How many stations does a sigma line need?
A: Market machines run 20 to 25. The exact number follows your section depth and the fold radius, and it is fixed when the roller layout is drawn — not before. That count is what we quote for a sigma purlin roll forming machine, and it does not move after the drawing is signed.
Q: What thickness can it form?
A: 1-3mm. Market machines for this section run 1.5–3.0 mm in G350–G550, but the confirmed range for a sigma purlin roll forming machine has to come from our workshop, not from a competitor sheet.
Q: Is this the same as a C Z purlin machine?
A: Same frame and same cut-off, different tooling. If you already run our C Z purlin line, the spares and the control philosophy carry over; the roll set does not.
Tianjin Putai Technology