Which Decoiler Drive Suits Your Coil Line?
A coil line was specified with a manual decoiler because the coils weighed 400 kg and the line ran at 12 metres a minute. It worked.
Two years later the same line was asked to run 900 kg coils at 22 metres a minute, and the operator was standing beside it with a hand on the brake lever.
The drive is the part of a decoiler that buyers most often undersize, because it is invisible in the quotation and it is not on the coil weight nameplate.
Manual, motorized and hydraulic drives all pay off strip. They differ in what happens to tension when the coil diameter changes, and that is where the decision lives.
The full capacity, type, mandrel and control chain is set out in the coil line guide library. The machine range is listed under our machines.
Which Job Is the Drive Actually Doing?
A decoiler drive is not there to pull strip. On most lines the equipment downstream pulls the strip, and the decoiler's job is to let it go at the right speed and under the right tension.
Three things follow from that. The drive has to hold back rather than push, it has to hold tension as the coil radius shrinks, and it has to stop without leaving slack in the strip.
Radius is what makes the job hard. A coil that starts at 1,250 mm outside diameter and runs down to 700 mm halves its radius, so the same torque produces roughly twice the tension at the tail.
A fixed brake cannot compensate for that. It applies the same friction at the start and the end of the coil, so tension falls through the run and the strip goes slack near the tail.
Everything that separates a manual stand from a hydraulic unit is a way of answering that one problem. Buyers who frame the decision this way usually stop comparing prices and start comparing control loops.
Four duties sit inside that single job, and each drive type handles them differently.
- Pay off at line speed. Strip has to leave the coil at the rate the line consumes it, or the loop either collapses or grows until it trips a sensor.
- Hold back tension. The drive resists the pull coming from downstream, which is what keeps the strip straight instead of overrunning into the line.
- Compensate for a falling radius. As the coil unwinds, torque has to rise to hold the same tension, and this is the duty that separates the three drive types most clearly.
- Stop without leaving slack. On an emergency stop the coil has to stay where it is, or the next start runs with a loose wrap and a shock load.
What Each Drive Gives the Line
Three drive types cover almost every decoiler sold, and each one buys a different thing.
| Drive type | What it gives the line | Where it costs you |
|---|---|---|
| Manual stand with a friction brake | Lowest purchase price, no power, no controls, nothing to maintain | Tension is set by hand and drifts through the coil. Changeover is a manual operation and the operator controls the tail by eye |
| Motorized with a variable-frequency drive | Speed matching to the line, controlled pay-off, repeatable changeover | Needs a loop or dancer to close the control loop, plus a brake for holding torque. Tension accuracy still falls as radius changes |
| Hydraulic motor with proportional control | Tension held roughly constant from full coil to core, high torque from a compact unit, fast mandrel expansion | Oil, filtration, cooling and leak management enter the maintenance budget, and the unit needs more floor space and a stiffer foundation |
The middle column is what the sales literature emphasises. The right-hand column is what the plant lives with for the next ten years.
A motorized unit with a load cell and closed-loop tension control narrows the gap to hydraulic considerably, and on strip under 2 mm it often closes it completely.
The distinction is worth checking rather than assuming.
Where Each Drive Stops Working
Every drive type has a band where it is the right answer, and the edges of those bands are worth stating plainly.
A manual stand runs out of road around 500 kg and 15 metres a minute. Below both figures it is genuinely the better buy. Above them the operator spends the shift adjusting a brake instead of running a line.
A motorized unit runs out of control range when the strip is thick. Holding tension within plus or minus 10 per cent over a 2:1 diameter change is achievable on 1.2 mm strip.
On 4 mm strip the torque needed at full coil is high enough that the same unit loses accuracy near the core.
A hydraulic unit runs out of justification when the plant cannot maintain it. Oil that is never sampled and filters that are never changed turn a constant-tension drive into an intermittent one.
A cooler that is never cleaned finishes the job over a slightly longer period.
All three run out of space on a heavy coil. Above roughly 10 tonnes the drive is no longer the constraint.
The foundation, the mandrel and the coil loading method are, and those are decided before the drive is chosen.
Two of those edges are softer than they look.
A manual stand with a well-maintained brake and a light coil runs for years without a complaint, and a hydraulic unit on a line that never exceeds 15 metres a minute is buying control the process never uses.
The edge that catches buyers is the speed one. Tension accuracy that looks adequate at 12 metres a minute can be visibly inadequate at 25, and the crossover is not marked anywhere on the machine or in the quotation.
How to Match the Drive to Coil Weight and Speed
Coil weight and line speed between them eliminate most of the options before any price is discussed.
| Coil weight band | Drive that usually fits | Where the choice gets expensive |
|---|---|---|
| Up to 500 kg | Manual stand with friction brake | Upgrading later means replacing the stand, because a manual frame has no provision for a motor mount |
| 500 kg to 3 t | Motorized with variable-frequency drive and a loop | Loop pit or dancer arm needs floor space, and retrofitting one into an existing line is a layout change |
| 3 t to 10 t | Motorized with closed-loop tension, or hydraulic | The load cell and control add cost that only pays back if tension actually matters to the part |
| Above 10 t | Hydraulic with a hydraulic mandrel | Foundation, coil car and crane capacity usually cost more than the drive itself |
Line speed sets a second constraint. Below about 15 metres a minute, tension variation matters less because there is time for the loop to absorb it.
Above 30 metres a minute, a slow tension response shows up as strip flutter at the entry of the line.
Strip thickness sets the third. Thin strip tolerates a light, slightly variable tension.
Thick strip needs tension that is both higher and steadier, which pushes the choice toward hydraulic or closed-loop motorized control.
What a Bigger Drive Cannot Fix
Upgrading the drive is a common first instinct when a coil line misbehaves. On four classes of problem it changes nothing.
Coil set and crossbow. Those are wound into the coil at the mill. The decoiler pays the strip off and cannot remove curvature, whatever drive it carries.
A slipping mandrel. If the coil turns on the mandrel under load, the drive is doing its job and the grip is not. Mandrel expansion, segment condition and coil inside diameter are the variables to check.
Misalignment between the decoiler and the line. A drive holds tension along the strip. It cannot correct an entry angle, and a line that is out of square will still track to one edge.
Coil quality at the tail. A deformed or telescoped inner wrap arrives as a handling problem. No drive setting recovers a coil that was damaged before it was loaded.
FANTY has been building coil handling equipment for twelve years, and the pattern in service calls is consistent.
Drive faults are usually found by checking the mandrel, the alignment and the coil before the control cabinet is opened.
Questions that come up before a decoiler drive is ordered.
At what coil weight does a manual decoiler stop being practical, 500 kg or 2 tonnes?
Around 500 kg, or whenever changeover takes more than about 15 minutes. Above both figures a powered drive usually pays for itself within a year.
How steady is tension over a 2:1 coil diameter change?
Roughly within plus or minus 10 per cent on a hydraulic uncoiler machine, against plus or minus 30 to 35 per cent for a fixed friction brake.
Does a motorized decoiler need a separate holding brake?
Usually yes. A variable-frequency drive controls speed well but holds little torque at zero speed, so a brake is needed to keep the coil from creeping during a stop.
Does a hydraulic decoiler need 30 per cent more floor space?
Roughly 30 to 50 per cent more once the power unit and cooler are counted. On a tight layout that difference can settle the drive choice before the budget does.
Where to go next
This article narrows one axis of the specification, the drive. Capacity, mandrel type and control method interact with it, and the full decision chain is set out in the decoiler guide.
our coil line knowledge base
