How to Change Over a Decoiler to a New Coil Size?
Coil size changes are the most repeated job on any coil line, and the one most often done from memory.
A changeover that is 95% right is worse than one that is obviously wrong, because the damage shows up two hundred parts later as edge marking or a loop that will not settle.
This is the sequence I would follow on a decoiler machine moving from one coil size to another, in the order the checks actually matter.
It assumes the decoiler and the uncoiler machine are already installed and aligned, and covers only what changes when the coil changes.
The specification questions behind these settings — capacity, mandrel type, control — are set out in the coil line guide library, and the machines themselves are listed in the product range.
Read the Coil Ticket Before You Touch the Machine
The ticket decides whether this is a two-minute job or a mandrel change. Read it standing still, before the crane moves.
Inner diameter. This is the check that stops the job. A 508 mm coil on a mandrel rated from 480 to 530 mm loads directly.
A 610 mm coil needs different segments or a different mandrel, and no amount of expansion pressure will close a 100 mm gap safely.
Weight against capacity. Compare the coil weight against the rated capacity at that outer diameter, not against the nameplate maximum.
A heavy coil at a large diameter loads the mandrel in bending, and the limit that matters is the mandrel's deflection, not its static rating.
Outer diameter. A larger coil raises the pay-off point and moves the first wrap further from the peeler. If the peeler arm has a fixed reach, a 1,500 mm coil and a 1,100 mm coil need different arm positions.
Eye direction. Coils stored eye-to-the-sky have to be rotated before loading. Load one the wrong way and the strip either pays off from the underside or has to be twisted through half a turn to reach the line.
Winding condition. A loose-wound coil behaves differently from a tight one. The outer wraps will drop before the mandrel has any tension on them, which is what the hold-down is for.
Position the Coil Car and Confirm the Eye Direction
The coil car does the alignment work, and every error it introduces is passed straight to the mandrel.
- Match the car height to the mandrel centre. A car 5 mm low forces the mandrel to lift the coil, and the segments scrape the inner wrap as they take the load.
- Centre the coil on the mandrel axis. Ten millimetres of offset means one segment contacts the bore first and the coil walks sideways as it expands.
- Confirm the pay-off direction. Match the coil eye to the direction the line takes the strip. A reversed coil has to be rotated on the car, not twisted downstream.
- Check the car track. Debris or a burr under a wheel throws the coil off centre before anyone notices. Sweep the track at every changeover, not every shift.
- Seat the coil against the back plate. Leave the car under the coil until the mandrel has taken the weight. Releasing early lets the coil drop onto the segments.
Expand the Mandrel Without Damaging the First Wrap
Expansion is a two-stage operation on every mandrel type, and collapsing it into one stage is where bore damage starts.
Stage one: light contact. Bring the segments out until they touch the bore, then stop. Confirm the coil is square against the back plate and the car has not shifted.
Check squareness. Measure the gap between the coil face and the back plate at four points a quarter-turn apart.
More than 2 mm of variation means the coil is cocked, and the strip will run to one edge from the first metre.
Stage two: full grip. Expand to the pressure that matches the coil weight and the maximum back tension on the line. Enough grip to stop the coil turning under load, no more.
Verify before you release the car. Try to turn the coil by hand. If it rotates, the mandrel is not gripping and the brake is about to do the work through friction alone.
On a loose-wound coil, keep the expansion pressure at the lower end of the range. Oversized segments bite into the inner wrap and start a telescope that runs outward through the whole coil.
Reset Brake Torque, Peeler and Hold-Down for the New Size
These three settings are all functions of coil diameter, which is why they cannot be left where the last coil ended.
Brake torque. Strip tension depends on torque divided by radius. Set the brake for the full coil and the tension climbs as the coil empties, which is the usual reason a coil pulls into the loop near its end.
Peeler arm. Set it for the new outer diameter so the first wrap is guided without being crushed. A peeler set for a 1,500 mm coil will rub the surface of an 1,100 mm coil.
Hold-down or snubber roll. Set the roll against the coil OD for the new diameter and the new strip width. It holds the loose outer wraps and stops the coil unwinding when the line stops.
Edge guides downstream. Reset for the new strip width with equal gaps on both sides. Unequal gaps turn a width change into a tracking problem.
Coil end. Look at the end of the strip before you start. A bent or kinked end will catch the peeler or jam the entry guide within the first revolution.
Where Changeover Errors Actually Show Up
None of these errors announce themselves at the machine. They surface later, downstream, and get blamed on the wrong equipment.
| Changeover step | What to verify | How to verify in under a minute | What skipping it costs you |
|---|---|---|---|
| Coil data against mandrel range | Inner diameter, weight at that outer diameter, coil width | Read the ticket against the mandrel rating plate | A blocked changeover, or segments forced into a bore they were not made for |
| Coil car height and centring | Car top matches mandrel centre; coil centred on the axis | Tape measure from the mandrel centre to the car surface, both sides | Bore scraping on loading, and a coil that walks as it expands |
| Squareness against the back plate | Gap at four points, a quarter-turn apart | Feeler gauge or a steel rule at four positions | Strip tracking to one edge for the whole coil, plus edge damage downstream |
| Mandrel grip | The coil cannot be turned by hand after expansion | Hand test with the car still under the coil | Slipping under tension, polished bore marks, and a brake doing work it cannot do |
| Brake torque for the new diameter | Torque set for the coil OD, not for the previous coil | Compare the setting against the chart for that coil weight | Tension climbing as the coil empties, and strip pulled into the loop near the end |
| Peeler, hold-down, edge guides | All three reset for the new diameter and width | Visual check against the new coil and a rule across the guides | Loose outer wraps, surface marking on the first metres, and tracking drift |
The pattern in that table is worth noticing. Every expensive error traces back to a check that takes under a minute and feels unnecessary because the last changeover worked.
With 370 people and a 45,000 m² plant behind the machines we build, the changeover procedure we hand over is deliberately short enough to be followed on a night shift.
How much does 5 mm of coil car misalignment cost?
It costs the inner wrap. A 5 mm height error makes the mandrel lift the coil, and the segments scrape the bore as they expand.
On a thin-wall coil that damage propagates for the first two or three wraps and shows up as a loose start on every subsequent pay-off.
How square does a coil have to sit on the mandrel, within 2 mm?
Keep the gap variation under 2 mm around the back plate. Beyond that the strip tracks to one side, and edge guides downstream can only hide it, not fix it.
How much does brake torque need to change as the coil empties?
Torque for a given strip tension falls in proportion to coil diameter. Going from a 1,500 mm coil to a 750 mm remnant halves the required torque.
A brake left at the full-coil setting doubles the tension by the end of the coil, which is enough to pull strip into the loop or stall the pay-off.
Should one mandrel cover a 508 mm coil and a 610 mm coil?
A single expanding mandrel typically covers a 60 to 80 mm band, for example 480 to 530 mm or 580 to 640 mm.
If your incoming coils span 508 mm and 610 mm, plan for interchangeable segments rather than assuming one mandrel will take both.
How long should a coil changeover take?
Twelve to twenty minutes for a like-for-like coil on a line where the coil car is already positioned, and thirty to forty-five minutes when the mandrel segments or the brake setting have to change.
Does a bigger coil always mean a longer changeover?
No, but it means more load on the mandrel and a longer reach for the peeler. Above roughly 8 tonnes, plan on a coil car with rotation and a mandrel rated for the bending load, not just the weight.
Where to go next
Changeover is the routine side of owning an uncoiler. The specification decisions that set what the machine can do at all — capacity, mandrel type and control — are set out in the guide library.
the coil line guide library
