Rebar Machines for Tunnel Lining and Arc Reinforcement

Rebar Machines for Tunnel Lining and Arc Reinforcement

Tunnel lining reinforcement is not a straight-bar problem. Whether you are casting precast segmental rings, forming shotcrete shell reinforcement, or fabricating curved cage sections for mined tunnels, the rebar has to arrive at the face already bent to a controlled radius. A bar that is 15 mm out of radius on a 6 m segment ring will not fit the mould, and a bar that is 15 mm out on a 300 mm stirrup will not fit the cage. This article covers the machines that produce arc reinforcement, how radius accuracy is actually achieved, and what to specify when buying for tunnel work.

Why Arc Reinforcement Is a Different Buying Decision

Standard rebar benders index a bar to a fixed angle — 90°, 135°, 180°. Arc bending is continuous curvature: the bar is fed through or around a tooling set that imposes a radius, and the radius is a function of tooling geometry, roller spacing, and material springback. That means three things drive your purchase:

• Radius range and repeatability — the machine must hold the same radius across hundreds of identical bars, not just produce one acceptable sample.
• Bar diameter vs. radius ratio — bending a 32 mm bar to a tight radius is a different machine class than bending a 12 mm bar to a large sweep.
• Production volume — a segment factory producing 40 rings per week needs different throughput than a site fabricator making a few curved spacers per shift.

Arc Bending Machines: GWH50CG, GWH50CZN and the 36 mm CNC Class

For general tunnel and civil arc work, Gongda's GWH50CG and GWH50CZN arc bending machines handle bar up to 50 mm. These are the workhorses for large-radius sweeps — tunnel invert reinforcement, curved wall mats, and large-diameter ring sections. The CZN variant adds CNC control, which matters when you are running a family of radii and want to recall a setup rather than re-tool by hand.

For tighter, more precise work — smaller tunnel sections, curved stirrups, and radius-critical segment details — the SKDZWH-36 and GDWHWQ-36 CNC arc benders take bar up to 36 mm. The CNC control lets you store radius and length parameters per bar mark, which is the practical difference between a crew that hits tolerance and a crew that re-bends scrap.

Practical note: when specifying an arc bender, quote the minimum radius you need at your maximum bar diameter, not the other way around. Suppliers frequently quote maximum capacity at a generous radius. If your segment design calls for a 32 mm bar at a 1.2 m radius, confirm that specific combination in writing.

Bending Centers for Complex Segment Cages

Precast tunnel segment cages are rarely a single arc. They combine longitudinal bars, curved transverse bars, and closed links — often with double curvature. Two machines cover this:

• GDPMW-60 plane bending center — up to 60 mm, for heavy plane-curved reinforcement and large segment cage elements.
• GDLWZX-32 vertical bending center — up to 32 mm, for vertical-plane forming and three-dimensional cage geometry where the bar must be shaped in more than one plane.

For fabricators producing complete segment cages, pairing a plane bending center with a CNC stirrup bender is more efficient than trying to force all geometry through one machine. The GW25 single-head CNC stirrup bender (round steel up to 25 mm) handles the closed links and tight-radius elements, while the bending center handles the large sweeps.

Radius Accuracy: What Actually Controls It

Buyers often assume radius accuracy is a control-system feature. It is mostly mechanical and material:

• Tooling diameter — the mandrel or roller set defines the inside radius. Springback then adds to it. For a target outside radius, you need tooling sized for the actual yield behaviour of the steel you are running.
• Roller spacing and support — insufficient support lets the bar ovalise or flatten on large radii. This is where cheap arc benders fail on tunnel work.
• Material consistency — rebar from different mills, or HRB400 vs. HRB500, springs back differently. If your supplier changes, re-verify the first bars of each heat.
• Feed accuracy — for multi-radius bars, the length between tangent points must be indexed accurately, or the arc starts in the wrong place.

A workable acceptance test: bend ten bars to your tightest specified radius at your largest diameter, lay them on a template or against a segment mould, and measure gap. If the machine cannot hold that consistently, the control system is irrelevant.

Supporting Equipment for Tunnel Rebar Shops

Arc bending is one step. A tunnel reinforcement shop typically also needs:

• Cutting — GQ70A (up to 70 mm, 160-ton shear force) for heavy bar, or GQ50A (6–50 mm round / 6–36 mm ribbed) for general cutting.
• Straightening and cutting — YGT4-15A (4–15 mm, VFD-controlled) for coil-fed production of straight bar before bending.
• Shearing lines — GDQX-500 hydraulic rebar shearing production line for high-volume cut-to-length output.
• Thread rolling — HGS-40 (up to 40 mm) for mechanical couplers, common in segment connections where lap lengths are not feasible.
• Band saw — GD-350ZD (350 mm) for clean cutting of heavy sections and bundled bar.

Buying Checklist for Tunnel and Arc Work

• State your maximum bar diameter at minimum radius — this single figure eliminates most unsuitable machines.
• Confirm CNC radius recall if you run more than three or four radii in production.
• Ask for the tooling set included and the cost of additional mandrels and rollers.
• Verify voltage and control language for your site — export units are configured per destination.
• Check certification — EAC certification is available for Russian and CIS markets; confirm what your project requires before shipping.
• Request a video test on your actual bar size and radius before purchase. This is standard practice and the fastest way to validate a supplier.

Gongda machines are manufactured in Hefei, Anhui, with the factory rooted in the electromechanical works of Hefei University of Technology, and are exported to Russia, Spain, Latin America, the Middle East, Southeast Asia and Africa. For model selection on a specific tunnel radius and bar schedule, contact the export team on WhatsApp at +86 193 9277 7259 or by email at yuhua0095@gmail.com with your bar diameters, target radii and monthly volume.