The spec comparison table
An angle-iron flange is a separate L-section bar — formed into a ring for round duct, or a four-sided frame for rectangular duct — that is punched for bolts and then welded or riveted to the duct end. It is the heavy-gauge, service-removable alternative to a roll-formed TDF flange, and it needs its own set of machines. This table compares the six SBKJ machines that build a bolted angle-iron joint, from stock preparation through forming, punching and welding. Every value is taken from the model's own product page.
| Machine role |
Model |
Material / thickness |
Diameter or size range |
Angle-iron / flange spec |
Power |
Weight |
| Round flange former |
SBYFL-50 |
Carbon steel 2–4 mm; SS 2–3 mm |
From Φ250 mm |
20×30, 30×30, 30×40, 30×50 mm |
7.5 kW × 2 |
— |
| Round flange punch |
SBYFL-50-1 |
Carbon steel 2–4 mm; SS 2 mm |
Φ250–Φ1800 mm |
20×30, 30×30, 30×40, 30×50 mm |
7.5 kW |
1500 kg |
| Round flange welder |
SBYFLHJ-50 |
2–5 mm |
— |
— |
100 kW |
500 kg |
| Rectangular flange welder (4-gun) |
SB-FS1535L |
3.0–5.0 mm |
200×200 – 1500×3500 mm |
3#, 4#, 5# |
— |
3000 kg |
| Angle-iron punch / stock prep |
SBCK-50A |
5 mm Q235 (max punching) |
— |
∠30×30×3 – ∠50×50×5 mm |
11.8 kW |
— |
| Round-tube edge flanger |
SBSF-1525 |
Black steel 0.5–2 mm; SS 0.5–2.5 mm |
Φ100–Φ2000 mm |
Flanging width 75–152 mm |
2.5 kW |
520 kg |
Source: SBKJ Product Catalog 2026, manufacturer nameplate specifications, drawn from each model's product page. A dash (—) means the value is not published on that machine's page. The SBYFLHJ-50 welder and SBCK-50A punch list no machine weight on the welder page / no weight on the punch page respectively; the SBYFL-50 former page lists no weight, and the SB-FS1535L page lists no single drive-power figure (it uses a 220V mainframe plus a 380V welding supply). All units run 380V 3-phase 50Hz (60Hz on request) except where the page states otherwise. Bolted flange joints conform to EN 1505 / SMACNA duct construction.
The two flange families
Angle-iron flange machinery splits cleanly into a round line and a rectangular line, because the geometry of the joint is different.
Round bolted flange uses three machines in sequence. The SBYFL-50 Round Flange Forming Machine rolls angle-iron stock into a circular ring sized to the outside diameter of the spiral duct, working carbon steel 2–4 mm and stainless 2–3 mm from a minimum Φ250 mm. The SBYFL-50-1 Round Flange Punching Machine then punches the bolt holes, covering Φ250–Φ1800 mm at 1500 kg. Finally the SBYFLHJ-50 Round Flange Welding Machine — a high-power 100 kW unit — welds the finished ring to the duct end on 2–5 mm material. All three use the same 20×30 to 30×50 mm angle-iron range, so the ring, the punch pattern and the weld all match.
Rectangular bolted flange is a single-machine job. The SB-FS1535L Four-Gun Automatic Angle Iron Flange Welding Machine welds all four sides of a rectangular frame at once, handling welding sizes from 200×200 mm up to 1500×3500 mm in 3#, 4# and 5# angle iron at 3.0–5.0 mm thickness. At 3000 kg it is built for high-volume rectangular duct production where every section gets a bolted companion-angle frame.
Stock prep and the lighter alternative
Two more machines round out the angle-iron toolkit. The SBCK-50A Angle Iron Punching Machine is the upstream stock-prep station: it punches bolt holes and notches in L-section angle from ∠30×30×3 mm to ∠50×50×5 mm, with a maximum punching diameter of Φ15 in 5 mm Q235, running at 11.8 kW. It feeds the flange shop with ready-punched angle for hangers, support frames and bolt-through reinforcement.
The SBSF-1525 Round Tube Flanging Machine is the lighter-gauge alternative for round duct: instead of attaching a separate angle ring, it forms a flanged edge directly on the tube end. It works black steel 0.5–2 mm and stainless 0.5–2.5 mm across Φ100–Φ2000 mm at just 2.5 kW and 520 kg. For light commercial round duct that does not need a heavy bolted ring, an edge flange is faster and cheaper — the same trade-off, in round duct, that TDF represents for rectangular.
How to pick the right one
Two variables decide which angle-iron machines you need, in this order:
1. Round or rectangular duct. If you make round (spiral) duct and need bolted, service-removable joints, you need the round line — SBYFL-50 former, SBYFL-50-1 punch and SBYFLHJ-50 welder. If you make rectangular duct, the SB-FS1535L four-gun welder is the single machine that builds the frame. The SBCK-50A angle punch supports both by preparing the raw angle stock.
2. Material gauge. The heavy bolted-flange machines run 2–5 mm material — well above the typical TDF range. The SBYFL-50 former tops out at carbon steel 4 mm, the SBYFLHJ-50 welder and SB-FS1535L reach 5 mm. If your round duct is light commercial (0.5–2 mm) and does not need a bolted ring, the SBSF-1525 edge flanger is the lighter, lower-power choice. Match the machine's thickness rating to the heaviest duct you actually run, not the lightest.
Angle iron vs TDF, in plain terms
Angle-iron (bolted) flange — a separate L-bar ring or frame, punched and welded to the duct, then bolted to the matching flange on site with a gasket between. It is robust, service-removable and the right choice for heavy industrial duct, high-pressure exhaust and round dust-collection duct. The cost is a second forming/punching/welding operation, which is why it needs the dedicated machines above.
TDF flange — roll-formed directly on the rectangular duct end, no separate part. Faster and cheaper per metre for light-to-mid commercial duct, but limited to thinner gauge. The dividing line is roughly 2 mm wall thickness and whether the joint needs to be bolt-through reinforced. For the full head-to-head, see TDF vs Angle Flange; for the TDF machine specs, see the TDF flange machine specs reference.
What this means for capital planning
A round angle-iron flange line is three machines, not one: the SBYFL-50 former (7.5 kW × 2), the SBYFL-50-1 punch (1500 kg, 7.5 kW) and the SBYFLHJ-50 welder (a 100 kW supply). Budget the floor space and the electrical supply for all three, plus the SBCK-50A angle punch (11.8 kW) if you also prepare your own hanger and reinforcement angle. The rectangular path is simpler — one SB-FS1535L at 3000 kg and 5300×2300×1400 mm — but its 100 kW-class welding load and dual-voltage supply (220V mainframe, 380V welding) need planning into the workshop layout. SBKJ provides a 2D workshop layout drawing with every quotation so the line is sized to the available floor and power before you commit. For the full electrical picture across the catalog, see the duct machine power & electrical requirements reference.
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FAQ
Which SBKJ machines make a round angle-iron flange versus a rectangular one?
Round bolted flanges are made on the round flange line: the SBYFL-50 rolls the angle-iron ring, the SBYFL-50-1 punches the bolt holes, and the SBYFLHJ-50 welds the flange to the duct. Rectangular bolted flanges are made on the SB-FS1535L four-gun automatic angle-iron flange welding machine, which welds four sides at once for rectangular frames from 200×200 mm up to 1500×3500 mm.
What material thickness can the angle-iron flange machines handle?
On the round line, the SBYFL-50 former handles carbon steel 2–4 mm and stainless steel 2–3 mm, the SBYFL-50-1 punch handles carbon steel 2–4 mm and stainless 2 mm, and the SBYFLHJ-50 welder handles 2–5 mm. The rectangular SB-FS1535L welds 3.0–5.0 mm material. The SBSF-1525 round-tube edge flanger works lighter gauge — black steel 0.5–2 mm and stainless 0.5–2.5 mm.
What rectangular frame sizes does the SB-FS1535L weld?
The SB-FS1535L four-gun automatic angle-iron flange welding machine handles rectangular welding sizes from 200×200 mm to 1500×3500 mm, using 3#, 4# and 5# angle iron at 3.0–5.0 mm thickness. The machine weighs 3000 kg with overall dimensions of 5300×2300×1400 mm.
What angle-iron sizes do the SBKJ flange machines use?
The round flange former (SBYFL-50) and punch (SBYFL-50-1) use 20×30, 30×30, 30×40 and 30×50 mm angle iron. The rectangular SB-FS1535L uses 3#, 4# and 5# angle iron. The SBCK-50A angle-iron punching machine processes L-section angle from ∠30×30×3 mm to ∠50×50×5 mm and punches up to Φ15 holes in 5 mm Q235.
When should I choose an angle-iron flange over TDF?
Angle-iron bolted flange suits heavy industrial duct above roughly 2 mm wall thickness, high-pressure process exhaust where reinforcement bars must bolt through the flange, service-removable joints, and round duct for dust collection, kitchen exhaust and material handling. The SBKJ angle-iron machines run 2–5 mm material — well above the typical TDF range — which is the practical dividing line between the two methods. See TDF vs Angle Flange for the full comparison.
What power supply do the angle-iron flange machines need?
Most run 380V 3-phase 50Hz (60Hz on request): the SBYFL-50 draws 7.5 kW × 2, the SBYFL-50-1 punch 7.5 kW, the SBCK-50A punch 11.8 kW and the SBSF-1525 flanger 2.5 kW. The SBYFLHJ-50 welder is a high-power 100 kW unit on 380V 3-phase. The SB-FS1535L uses a 220V/50Hz mainframe supply with a separate 380V/50Hz welding supply.
