Executive summary A slitter turns one master coil into a stack of narrow coils, and each slit coil has to stay together through stacking, storage and transport. Our automatic steel coil strapping machine sets each coil flat on a roller conveyor and feeds steel or PET strap through the coil eye, so the strap closes around the whole coil wall instead of only the outside. The PET eye strapper is specified for coils of 800–1,350 mm OD, 508–610 mm ID, 20–500 mm width and 100–2,500 kg, at about 12–15 s per strap. Below: the strapping cycle, steel against PET, cycle time, strap consumption and line integration.
Table of contents
- Why a slit coil needs a strap through the eye
- How the eye-strapping cycle runs
- Steel strap or PET strap
- What coil fits the PET eye strapper
- Cycle time on a slitting line
- Strap consumption per coil
- Line integration and coil protection
- Safety and standards
- Selection checklist
- Engineering FAQ
- Next step
- Related reading
- Sources
Why a slit coil needs a strap through the eye
A slit coil is a stack of narrow strip turns that is held together only by friction and its own weight. Set on edge, the coil rests on a narrow contact patch, and a thin slit strip can bend under that load. Lifted by the eye, the outer turns can telescope away from the stack.
A radial strap through the eye wraps the full coil wall — outside, faces and bore — so the turns stay packed while the coil is lifted, stacked and shipped. That is why eye strapping is the standard operation at the end of a slitting line, and why the strap has to follow the coil wall rather than a single outer diameter.
How the eye-strapping cycle runs
- The roller conveyor brings the slit coil flat, under the strapping frame, and stops it at the strap line.
- The strapping head above the table feeds the strap down through the coil eye and around the wall.
- The head tensions the strap to the set value, seals it and cuts it.
- The coil indexes to the next strap position, or the heads move to it, until the last strap is closed.
- The conveyor takes the strapped coil to a turning table, stacker or pallet.
Because the coil lies flat, the whole coil face is supported during the cycle. The heads sit above the table on both sides, so they can reach coils across the 20–500 mm width range without turning the coil over.
Steel strap or PET strap
The strapper is built around the strap you run. A steel head carries 31.75 mm steel strap and closes it with a seal, a punched joint or a TIG weld; a PET head carries 9–12 mm PET and seals it by friction weld. The head, strap path and sealing unit are matched to the material, so changing from steel to PET is a head configuration, not a setting on the control panel. The two materials also behave differently in transit.
| Point | Steel strap | PET strap |
|---|---|---|
| Static strength | Highest, for very heavy or sharp-edge coils | Moderate, up to about 2 t loads |
| Behaviour under shock | Rigid; can snap when the load moves | Elongates and recovers tension |
| Rust risk | Rusts in damp storage and sea freight | No rust marks on the coil |
| Joint | Seal, punched or TIG-welded joint | Friction weld or metal seal |
| Hot coils | The only option for coils still above about 200 °C | Not suitable |
A steel strap joint keeps roughly 70–75% of the strap breaking load with a seal, about 85% with a punched joint and about 90% with a TIG weld, so the head and the joint type belong in the same selection. On the steel head of our eye strapper the strap is 31.75 mm wide, 0.8 mm thick (recommended) and has a yield point of 900 MPa or greater. The head runs from a jumbo strap coil of OD under 840 mm, ID 406 mm, 190 mm height and about 430 kg, which keeps strap changes rare on a busy line. Steel strapping supplied to ASTM D3953 for rail use carries a minimum 6.5% elongation, which is what lets the strap follow the coil wall without cracking at the seal.
PET is the better fit for most slit coils that are packed dry and shipped by road or sea. PET strap on the eye strapper is 9–12 mm wide and 0.4–1.0 mm thick, applied at 100–1,000 N of tension, and it stretches slightly under impact and then recovers, so the coil stays tight without the rust and cut-edge risks of steel. Coils that are still hot, or coils with very sharp edges and heavy unit loads, stay on steel.
Two line conditions matter as much as strap price. Slitting lines often run oiled strip, and oil carried to the joint area can spoil a PET friction weld, so the strap path and the joint zone have to stay clean. Heavy burr on the slit edge cuts film and strap alike, and it is worth inspecting a coil before the strap type is fixed.
What coil fits the PET eye strapper
| Item | PET eye strapper |
|---|---|
| Coil OD | 800–1,350 mm |
| Coil ID | 508–610 mm |
| Coil width | 20–500 mm |
| Coil weight | 100–2,500 kg |
| Strap | PET, 9–12 mm wide, 0.4–1.0 mm thick |
| Strapping speed | about 12–15 s per strap |
| Strapping tension | 100–1,000 N |
| Air supply | 6–10 bar |
| Power | about 2.5 kW, 380 V, 50 Hz, 3-phase |
The line-level steel and PET heads share one specification envelope on our coil packing lines: strap material PET or cold-rolled medium-carbon steel in 19 mm or 32 mm widths, radial or circumferential strapping in typically 2–4 bands, and tension adjustable from 2,000 N to 22,200 N. That is the range a slitting line draws from when it straps 30 kg slit coils in the morning and 4 t coils in the afternoon. The gap between the PET head at 100–1,000 N and the line-level 2,000–22,200 N envelope is the practical difference between PET containment and the clamping force of a steel head.
Cycle time on a slitting line
Strapping time is the sum of the straps per coil, the time per strap and the transfer between positions. With the PET head at 12–15 s per strap and an illustrative 10 s transfer:
| Straps per coil | Strap time | Cycle with transfer | Coils per hour (ceiling) |
|---|---|---|---|
| 2 | 24–30 s | 34–40 s | 90–105 |
| 3 | 36–45 s | 46–55 s | 65–78 |
| 4 | 48–60 s | 58–70 s | 51–62 |
These figures are a ceiling, before strap-coil changes, coil turns and line stops. The 10 s transfer in the table covers the infeed and outfeed only. Each extra strap needs an intermediate index — a coil turn or a head move — so multi-strap cycles should budget that separately; on a four-strap coil it is typically 2–3 s per index, which we confirm against the coil and conveyor layout. The real check is the master coil: a master coil slit into 12 slit coils at four straps each needs 12 × 48–60 s, or roughly 10–12 minutes of strapping. Compare that with the slitter’s output per master coil and the strapper either keeps up or it does not; we size the head count and the conveyor buffer from that comparison. Where the mult count is high, the strapper can become the constraint, and the answer is usually an accumulation station ahead of the strapper, a second head, or a strap pattern that matches the transport risk instead of the maximum.
Strap consumption per coil
For a slit coil of 508 mm ID, 1,200 mm OD and 150 mm width, the coil wall is (1,200 − 508) ÷ 2 = 346 mm. One radial strap forms one closed loop around the coil wall cross-section: two side faces of 346 mm and the coil width across the outside and the bore, 2 × 150 mm, so its length is about 2 × (150 + 346) = 992 mm, or close to 1 m. Add 50–100 mm per loop for the joint and the tensioner feed, so four straps take about 4.2–4.4 m of strap per coil.
A 31.75 mm × 0.8 mm steel strap weighs 0.03175 × 0.0008 × 7,850 ≈ 0.2 kg/m, so a 430 kg strap coil holds about 2,150 m. At about 4.2–4.4 m per slit coil that is roughly 490–510 coils per strap coil. PET strap runs at a lower weight per metre, so the same coil count costs less strap weight, and the difference in strap price per coil is part of the proposal.
Line integration and coil protection
The strapper is one station in a line, not a stand-alone tool. We design it with the infeed and outfeed conveyors, a turning table for coils that need circumferential straps as well, and a stacker or pallet station after strapping. If the line needs a turnstile or downender after strapping, we check the coil OD and width against its arms in the same layout review, so the strapper and the handling equipment are sized together. Coils can be strapped with or without top, bottom, side or corner protection, and with VCI paper or film added before or after the strap.
For a slitting line, the usual sequence is: slit coil out of the slitter, turning or upending, edge protection, eye strapping, optional circumferential strapping and wrapping, then stacking and labelling. The strapper has to match the coil sizes of the whole sequence, not only the average coil, so we size it from the smallest and largest coil on the list.
Safety and standards
The strap line is a pinch and cut hazard, so the heads are guarded, the strap path is enclosed and the conveyor has emergency stops at the operator positions. For CE markets the risk assessment follows ISO 12100:2010, which sets the principles and methodology for machinery safety and risk reduction, and the general requirements for packaging machines come from EN 415-10:2014. Steel strap is specified to ASTM D3953, which covers flat steel strapping and seals for closing, reinforcing, bundling and palletizing loads. Which standards apply depends on the destination market and on the coil line around the strapper.
Selection checklist for a slit coil strapper
- Slit coil ID, OD, width and weight range, including the heaviest coil.
- Strap material (steel or PET), strap width and thickness, and joint type.
- Straps per coil, and whether circumferential straps are also needed.
- Slit coils per master coil and master coils per hour.
- Edge or corner protection, VCI paper or film, and labelling.
- Conveyor, turning table, stacker or pallet station after the strapper.
- Supply voltage, air supply and floor space for the line.
Engineering FAQ
Q: Can one machine run both steel and PET strap? A: Yes on one platform, with matched modular heads: a steel head and a PET head. The two materials cannot share one head, so the change is a head swap or a dedicated dual-station arrangement, not a control-panel setting. We confirm both configurations and the strap sizes in the proposal.
Q: How fast is the eye strapper? A: About 12–15 s per strap on the PET eye strapper. A four-strap coil therefore takes 48–60 s of strapping, before transfer time.
Q: How many straps does a slit coil need? A: Typically 2–4 radial straps, depending on coil weight, width and transport route. Heavy or long-route coils take more straps and often corner protection.
Q: How long does a strap coil last? A: About 490–510 slit coils for a 430 kg coil of 31.75 × 0.8 mm steel strap at four 4.2–4.4 m straps per coil. PET consumption is lower in weight per coil.
Q: Will the strap mark the coil surface? A: Tension is adjustable from 100 N on the PET head, and corner or edge protection is available where the surface is critical. The strap path is set so the strap follows the wall rather than digging into the edge.
Next step
Send your coil list with ID, OD, width, weight and the strap type you use to info@fhopepack.com. We reply with a strapper proposal that includes the head, strap plan, conveyors and the cycle-time check, and we confirm the layout against your slitting line before the order.
Related reading
- Slit coil eye strapping machine
- Automatic slitting coil PET strapping machine
- Automatic slitting coil packaging line with turntable stacker
- Steel coil strapping machinery
Sources
- PET eye strapper coil window, strap sizes, tension, speed, air and power: FHOPE product page, automatic slitting coil PET strapping machine.
- Steel strap size, thickness and yield point: FHOPE product page, slit coil eye strapping machine.
- Line-level strap material, band count and tension range: FHOPE product page, cold roll steel coil strapping and packing line.
- Steel strap elongation: Allstrap, 1.25 inch steel strapping, ASTM D3953.
- Joint efficiency by joint type: Itipack, the safest steel strapping joint worldwide.
- PET behaviour under impact and rust: ErgoPack, PP vs PET vs steel strapping.
- Standards: ISO 12100:2010, EN 415-10:2014, ASTM D3953.
